TM 9-8000 - CHG-1
TM 9-8000 - CHG-1
TM 9-8000 - CHG-1
com
TM 9-8000
TECHNICAL MANUAL
TM 9-8000 C1
CHANGE NO. 1
TM 9-8000, 25 October 1985, is changed as follows: 1. Remove old pages and insert new pages as indicated below. 2. New or changed material is indicated by a vertical bar in the margin of the page. Remove Pages 2-3 and 2-4 2-33 and 2-34 2-35 and 2-36 4-21 and 4-22 5-1 and 5-2 5-3 and 5-4 8-5 and 8-6 None 11-1 and 11-2 11-7 and 11-8 12-11 (12-12 Blank) 14-9 and 14-10 14-11 (14-12 Blank) 22-1 and 22-2 33-1 and 33-2 A-1 and A-2 A-3 and A-4 Insert Pages 2-3 and 2-4 2-33 and 2-34 2-35 and 2-36 4-21 and 4-22 5-1 and 5-2 5-3 and 5-4 8-5 and 8-6 8-6.1 (8-6.2 Blank) 11-1 and 11-2 11-7 and 11-8 12-11 (12-12 Blank) 14-9 and 14-10 14-11 (14-12 Blank) 22-1 and 22-2 33-1 and 33-2 A-1 and A-2 A-3 and A-4
File this change sheet in front of the publication for reference purposes.
TM 9-8000
By Order of the Secretary of the Army: CARLE.E. VUONO General, United States Army Chief of Staff
Official: WILLIAM J. MEEHAN II Brigadier General, United States Army The Adjutant General
Distribution: To be distributed in accordance with DA Form 12-37, Operator, Organizational, Direct and General Support Maintenance requirements for Carrier, Personnel, M113A1, Command Post, M577A1, Mortar, M06A1; Mortar, M125A1; Flame Thrower, M132A1; Gun, M741; Recovery Vehicle, XM1059. Also, to be distributed in accordance with DA Form 12-38, Operator, Organizational, Direct and General Support Maintenance requirements for Truck, Utility, -ton, 4x4, M151-sees.
TM 9-8000
HEADQUARTERS DEPARTMENT OF THE ARMY WASHINGTON, DC 25 October 1985 PRINCIPLES OF AUTOMOTIVE VEHICLES
REPORTING ERRORS AND RECOMMENDING IMPROVEMENTS You can help improve this manual. If you find any mistakes, or if you know of a way to improve the procedures, please let us know. Mail your letter, DA Form 2028 (Recommended Changes to Publications and Blank Forms), or DA Form 2028-2 located in the back of this manual directly to: Commander, US Army Tank-Automotive Command, ATTN: AMSTA-MB, Warren, MI 48397-5000. A reply will be sent to you.
TABLE OF CONTENTS
Page PART ONE CHAPTER 1 Section I. Section II. Section III. Section IV. Section V. Section VI. PART TWO CHAPTER 2. Section I. Section II. Section III. Section IV. Section V. Section VI. Section VII. CHAPTER 3. Section I. Section II. Section III. CHAPTER 4. Section I. Section II. Section III. Section IV. Section V. INTRODUCTION...................................................................................................... GENERAL INFORMATION ...................................................................................... Purpose of Manual ................................................................................................... Organization of the Manual ...................................................................................... History of Military Vehicles ....................................................................................... Characteristics of Military Vehicles........................................................................... Military Vehicle Categories....................................................................................... Classification of Vehicles.......................................................................................... ENGINES ................................................................................................................. PISTON ENGINE CHARACTERISTICS .................................................................. Engine Operation ..................................................................................................... Comparison of Engine Types ................................................................................... Classification of Piston Engines ............................................................................... Engine Measurements ............................................................................................. Timing....................................................................................................................... Engine Output .......................................................................................................... Engine Efficiency...................................................................................................... CONVENTIONAL ENGINE CONSTRUCTION ........................................................ Cylinder Blocks, Heads, and Crankcases ................ ................................................ Rotating and Reciprocating Parts............................................................................. Valves and Operating Mechanisms ......................................................................... GASOLINE FUEL SYSTEMS................................................................................... Components and Their Purposes ............................................................................ Principles of Carburetion .......................................................................................... Construction of the Basic Carburetor ....................................................................... Systems of the Carburetor ....................................................................................... Fuel Injection Systems for Gasoline Engines........................................................... 1-1 1-1 1-1 1-1 1-2 1-2 1-3 1-4 2-1 2-1 2-1 2-8 2-22 2-27 2-32 2-37 2-42 3-1 3-1 3-8 3-27 4-1 4-1 4-13 4-15 4-17 4-40
TM 9-8000 TABLE OF CONTENTS - CONTINUED Page Section VI. Section VII. Section VIII. CHAPTER 5. Section I. Section II. Section III. Section IV. Section V. Section VI. Section VII. Section VIII. Section IX. CHAPTER 6. Section I. Section II. CHAPTER 7. Section I. Section II. CHAPTER 8. Section I. Section II. Section III. Section IV. CHAPTER 9. Section I. Section II. Section III. CHAPTER 10. Section I. Section II. Section III. Section IV. Section V. Section VI. PART THREE CHAPTER 11. Section I. Section II. Section III. Section IV. Turbochargers and Supercharges ........................................................................... Governors................................................................................................................. Characteristics of Gasoline ...................................................................................... DIESEL FUEL SYSTEMS ........................................................................................ Characteristics of Diesel Fuels................................................................................. Combustion Chamber Design .................................................................................. Injection Systems ..................................................................................................... Fuel Supply Pumps .................................................................................................. Governors................................................................................................................. Timing Device........................................................................................................... Cold Weather Starting Aids ...................................................................................... Fuel Filters................................................................................................................ Engine Retarder System .......................................................................................... PROPANE FUEL SYSTEMS ................................................................................... Characteristics.......................................................................................................... Basic System............................................................................................................ EXHAUST AND EMISSION CONTROL SYSTEMS ................................................ Exhaust System ....................................................................................................... Emission Control System ......................................................................................... LUBRICATION SYSTEM ......................................................................................... Purpose .................................................................................................................... Engine Oils ............................................................................................................... Oil Pumps................................................................................................................. Types of Lubrication Systems .................................................................................. ENGINE COOLING SYSEMS .................................................................................. Cooling Essentials.................................................................................................... Liquid Cooling Systems............................................................................................ Air Cooling Systems ................................................................................................. GAS TURBINE ENGINES........................................................................................ Overview .................................................................................................................. Comparison to Piston Engine................................................................................... Basic Engine Structure............................................................................................. Fuel System ............................................................................................................. Lubrication System................................................................................................... Electrical System...................................................................................................... ELECTRICAL SYSTEMS AND RELATED UNITS................................................... BASIC PRINCIPLES OF ELECTRICITY.................................................................. Electricity .................................................................................................................. Semiconductor Devices ........................................................................................... Electrical Measurements .......................................................................................... Magnets.................................................................................................................... ii 4-45 4-48 4-52 5-1 5-1 5-3 5-8 5-28 5-30 5-33 5-35 5-37 5-39 6-1 6-1 6-1 7-1 7-1 7-2 8-1 8-1 8-2 8-5 8-12 9-1 9-1 9-1 9-11 10-1 10-1 10-4 10-6 10-15 10-16 10-18 11-1 11-1 11-1 11-4 11-10 11-13
TM 9-8000 TABLE OF CONTENTS - CONTINUED Page CHAPTER 12. Section I. Section II. Section III. Section IV. CHAPTER 13. Section I. Section II. Section III. CHAPTER 14. Section I. Section II. CHAPTER 15. Section I. Section II. Section III. CHAPTER 16. Section I. Section II. Section III. CHAPTER 17. Section I. Section II. Section III. Section IV. Section V. CHAPTER 18. Section I. Section II. PART FOUR CHAPTER 19. Section I. Section II. Section III. CHAPTER 20. Section I. Section II. Section III. BATTERIES ............................................................................................................. Construction ............................................................................................................. Principles of Operation ............................................................................................. Types of Batteries .................................................................................................... Military Applications.................................................................................................. CHARGING SYSTEMS............................................................................................ Principles of Operation ............................................................................................. DC Generator Principles .......................................................................................... AC Generator Systems ............................................................................................ STARTING SYSTEMS ............................................................................................. Electric Starting Motor .............................................................................................. Control Systems ....................................................................................................... IGNITION SYSTEMS ............................................................................................... Battery Ignition Systems........................................................................................... Magneto Ignition Systems ........................................................................................ Waterproofing Ignition Systems ............................................................................... LIGHTING SYSTEMS .............................................................................................. Motor Vehicle Lighting.............................................................................................. Blackout Lighting ...................................................................................................... Commercial Vehicle Lighting.................................................................................... INSTRUMENTS, GAGES, AND ACCESSORIES.................................................... Instrument Panel ...................................................................................................... Horns........................................................................................................................ Windshield Wipers ................................................................................................... Accessories .............................................................................................................. Automotive Wiring .................................................................................................... RADIO INTERFERENCE AND SUPPRESSION ..................................................... Interference .............................................................................................................. Suppression ............................................................................................................. POWER TRAINS ..................................................................................................... INTRODUCTION TO POWER TRAINS .................................................................. Purpose .................................................................................................................... Gears........................................................................................................................ Power Train Configurations...................................................................................... HYDRAULIC PRINCIPLES ...................................................................................... Principles.................................................................................................................. Oil Pumps................................................................................................................. Simple Hydraulic Jack .............................................................................................. iii 12-1 12-1 12-4 12-6 12-9 13-1 13-1 13-3 13-22 14-1 14-1 14-8 15-1 15-1 15-18 15-24 16-1 16-1 16-11 16-12 17-1 17-1 17-18 17-20 17-21 17-26 18-1 18-1 18-3 19-1 19-1 19-1 19-3 19-14 20-1 20-1 20-3 20-6
TM 9-8000 TABLE OF CONTENTS - CONTINUED Page CHAPTER 21. Section I. Section II. Section III. CHAPTER 22. Section I. Section II. Section III. Section IV. Section V. CHAPTER 23. Section I. Section II. Section Ill. Section IV. CHAPTER 24. Section I. Section II. CHAPTER 25. Section I. Section II. CHAPTER 26. Section I. Section II. Section III. CHAPTER 27. Section I. Section II. Section III. Section IV. CHAPTER 28. Section I. Section II. Section III. CLUTCHES, FLUID COUPLINGS, AND TORQUE CONVERTERS ....................... Clutches ................................................................................................................... Fluid Couplings......................................................................................................... Torque Converters ................................................................................................... CONVENTIONAL TRANSMISSIONS ...................................................................... Purposes .................................................................................................................. Basic Types.............................................................................................................. Sliding Gear Transmission ....................................................................................... Constant Mesh Transmission................................................................................... Gearshift Linkage ..................................................................................................... AUTOMATIC TRANSMISSIONS ............................................................................. General Operation.................................................................................................... Drive Train Mechanisms .......................................................................................... Drive Train Arrangements ........................................................................................ Hydraulic System...................................................................................................... CROSS-DRIVE TRANSMISSION ............................................................................ Function.................................................................................................................... Construction and Operation ..................................................................................... X1100 SERIES CROSS-DRIVE TRANSMISSION .................................................. Function.................................................................................................................... Construction and Operation ..................................................................................... AUXILIARY TRANSMISSIONS, SUBTRANSMISSIONS, AND OVERDRIVES....................................................................................................... Auxiliary Transmissions............................................................................................ Subtransmissions ..................................................................................................... Overdrives ................................................................................................................ TRANSFER ASSEMBLIES ...................................................................................... Purpose .................................................................................................................... Conventional Transfer Assemblies .......................................................................... Differential-Type Transfer Assemblies ..................................................................... Positive Traction Transfer Case ............................................................................... PROPELLER SHAFTS, SLIP JOINTS, AND UNIVERSAL JOINTS ........................ Propeller Shafts and Slip Joints ............................................................................... Conventional Universal Joints .................................................................................. Constant Velocity Joints ........................................................................................... iv 21-1 21-1 21-12 21-14 22-1 22-1 22-1 22-1 22-6 22-9 23-1 23-1 23-2 23-6 23-12 24-1 24-1 24-1 25-1 25-1 25-1
26-1 26-1 26-2 26-3 27-1 27-1 27-2 27-4 27-6 28-1 28-1 28-2 28-5
TM 9-8000 TABLE OF CONTENTS - CONTINUED Page CHAPTER 29. Section I. Section II. Section III. Section IV. Section V. PART FIVE CHAPTER 30. Section I. Section II. Section III. Section IV. Section V. Section VI. Section VII. CHAPTER 31. Section I. Section II. Section III. Section IV. CHAPTER 32. Section I. Section II. Section III. Section IV. Section V. Section VI. CHAPTER 33. Section I. Section II. Section III. Section IV. Section V. Section VI. CHAPTER 34. Section I. Section II. Section III. Section IV. Section V. Section VI. Section VII. Section VIII. DIFFERENTIALS, FINAL DRIVES, AND DRIVING AXLES .................................... Conventional Differentials ........................................................................................ No-Spin Differentials ................................................................................................ Final Drives and Driving Axles ................................................................................. Controlled Differential............................................................................................... Wheel Vehicle Performance .................................................................................... CHASSIS COMPONENTS....................................................................................... SUSPENSION SYSTEMS IN WHEELED VEHICLES ............................................. Overview .................................................................................................................. Solid Axle Suspension Systems ............................................................................... Independent Axle Suspension Systems................................................................... Heavy Vehicle Suspension....................................................................................... Air-Over-Hydraulic Suspension ................................................................................ Shock Absorbers ...................................................................................................... Auxiliary Units........................................................................................................... SUSPENSION SYSTEMS IN TRACKED VEHICLES.............................................. Principal Parts .......................................................................................................... Configurations .......................................................................................................... Suspension Lockout System .................................................................................... Spade System .......................................................................................................... WHEELS, TIRES, AND TRACKS ............................................................................ Wheel Center Section .............................................................................................. Wheel Rims .............................................................................................................. Bead Locks and Bead Clips ..................................................................................... Tires ......................................................................................................................... Tubes ....................................................................................................................... Tracks ...................................................................................................................... STEERING SYSTEMS AND WHEEL ALINEMENT................................................. Steering Systems ..................................................................................................... Steering Gears ......................................................................................................... Power Steering - Hydraulic Type.............................................................................. Air Steering............................................................................................................... Four-Wheel Driving and Steering ............................................................................. Wheel Alinement Principles ..................................................................................... BRAKING SYSTEMS ............................................................................................... Principles of Braking................................................................................................. Drum Brake Mechanisms ......................................................................................... Disk Brake Mechanisms........................................................................................... Auxiliary Brake Mechanisms .................................................................................... Mechanical Brake System........................................................................................ Hydraulic Brake System ........................................................................................... Power Braking Systems ........................................................................................... Airbrake System ....................................................................................................... 29-1 29-1 29-3 29-8 29-22 29-24 30-1 30-1 30-1 30-3 30-6 30-9 30-12 30-14 30-16 31-1 31-1 31-5 31-5 31-7 32-1 32-1 32-2 32-4 32-5 32-9 32-13 33-1 33-1 33-6 33-8 33-13 33-15 33-17 34-1 34-1 34-4 34-11 34-18 34-21 34-23 34-29 34-33
TM 9-8000 TABLE OF CONTENTS - CONTINUED Page Section IX. Section X. Section XI. PART SIX CHAPTER 35. Section I. Section II. CHAPTER 36. Section I. Section II. Section III. Section IV. Section V. Section VI. Section VII. CHAPTER 37. Section I. Section II. CHAPTER 38. Section I. Section II. Section III. Section IV. APPENDIX INDEX Air-Over-Hydraulic Brake System ............................................................................ Vacuum-Over-Hydraulic Brake System ................................................................... Electric Brake System .............................................................................................. HULLS, BODIES, AND FRAMES............................................................................. VEHICLE STRUCTURE........................................................................................... Wheeled Vehicles .................................................................................................... Tracked Vehicles...................................................................................................... ACCESSORIES ....................................................................................................... Power Takeoff .......................................................................................................... Winches ................................................................................................................... Tire Inflation System................................................................................................. Gasoline and Water Tankers ................................................................................... Dump Truck Mechanisms ........................................................................................ Wrecker Truck Equipment ....................................................................................... Underwater Ventilating System ................................................................................ PRINCIPLES OF REFRIGERATION ....................................................................... General..................................................................................................................... System Components ................................................................................................ TRAILERS AND SEMITRAILERS............................................................................ Semitrailers .............................................................................................................. Three-Quarter Trailers ............................................................................................. Full Trailer ................................................................................................................ Matching Towing Vehicle to Trailer .......................................................................... DEFINITION OF TERMS ......................................................................................... ................................................................................................................................. LIST OF ILLUSTRATIONS Figure Page 2-1. 2-2. 2-3. 2-4. 2-5. 2-6. 2-7. 2-8. 2-9. 2-10. 2-11. 2-12. 2-13. Piston Engine Principles........................................................................................................ Piston Engine Operation ....................................................................................................... Piston and Crankshaft ........................................................................................................... Piston to Crankshaft Relationship ......................................................................................... Intake and Exhaust Ports ...................................................................................................... Intake and Exhaust Valves.................................................................................................... Piston Positions..................................................................................................................... Four-Stroke Cycle Operation................................................................................................. Valve Train Operation ........................................................................................................... Timing Gears......................................................................................................................... Flywheel ................................................................................................................................ Internal Combustion Engine Versus External Combustion Engine ....................................... Two-Stroke Cycle Engine...................................................................................................... vi 2-1 2-2 2-2 2-3 2-3 2-3 2-4 2-5 2-6 2-7 2-7 2-8 2-8 34-40 34-41 34-43 35-1 35-1 35-1 35-4 36-1 36-1 36-4 36-5 36-6 36-9 36-12 36-15 37-1 37-1 37-4 38-1 38-1 38-4 38-5 38-8 A-1 Index 1
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure 2-14. 2-15. 2-16. 2-17. 2-18. 2-19. 2-20. 2-21. 2-22. 2-23. 2-24. 2-25. 2-26. 2-27. 2-28. 2-29. 2-30. 2-31. 2-32. 2-33. 2-34. 2-35. 2-36. 2-37. 2-38. 2-39. 2-40. 2-41. 2-42. 2-43. 2-44. 2-45. 2-46. 2-47. 2-48. 2-49. 2-50. 2-51. 2-52. 2-53. 2-54. 2-55. 2-56. The Two-Stroke Cycle........................................................................................................... The Four-Stroke Cycle Diesel ............................................................................................... Comparison of Diesel and Gasoline Engine Compression Strokes ...................................... Comparison of Diesel and Gasoline Engine Intake Strokes ................................................. Comparison of Gasoline and Diesel Engine Regulation of Power ........................................ Four-Stroke Cycle Diesel ...................................................................................................... Multifuel Engine..................................................................................................................... The Two-Stroke Cycle Diesel Engine.................................................................................... The Two-Stroke Diesel Cycle................................................................................................ Comparison of Two- and Four-Stroke Cycle Diesel Power Stroke Lengths ................................................................................................................... Measuring Crankshaft Rotation............................................................................................. Typical Multiple-Cylinder Configurations ............................................................................... Power Delivery in One-, Four-, Six-, and Eight-Cylinder Engines .............................................................................................................................. The Rotary Engine................................................................................................................. The Rotary Engine Cycle....................................................................................................... Speed Relationship of Rotor to Eccentric Shaft .................................................................... Two-Rotor Configuration ....................................................................................................... Typical Air-Cooled Arrangement ........................................................................................... Typical Liquid-Cooled Arrangement ...................................................................................... Typical Flathead Cylinder Head ............................................................................................ T-Head Engine ...................................................................................................................... L-Head Engine ...................................................................................................................... Typical Overhead Valve Cylinder Head................................................................................. I-Head Engine ....................................................................................................................... Single Overhead Camshaft Configurations ........................................................................... Double Overhead Camshaft Configurations ......................................................................... F-Head Engine ...................................................................................................................... Typical Cylinder Arrangements ............................................................................................. Bore, Stroke, and Displacement ........................................................................................... Illustrating the Weight of Air .................................................................................................. Atmospheric Pressure at Sea Level ...................................................................................... Vacuum in the Cylinder ......................................................................................................... Demonstrating Volumetric Efficiency .................................................................................... Fresh Air Intake System ........................................................................................................ Port Design Consideration .................................................................................................... Compression Ratio................................................................................................................ Increasing Compression Ratio .............................................................................................. Ignition Timing ....................................................................................................................... Effect of Increasing Ignition Timing ....................................................................................... Opening and Closing Points of the Valve.............................................................................. Valve Opening Duration ........................................................................................................ Valve Timing Diagram Showing Valve Overlap..................................................................... Crankshaft Rotational Periods of Imperceptible Piston Movement .......................................................................................................................... vii Page 2-9 2-10 2-11 2-12 2-12 2-13 2-14 2-15 2-16 2-17 2-18 2-18 2-19 2-20 2-21 2-21 2-22 2-22 2-23 2-23 2-23 2-24 2-24 2-24 2-25 2-25 2-26 2-26 2-27 2-28 2-29 2-29 2-30 2-31 2-31 2-32 2-32 2-33 2-33 2-34 2-35 2-36 2-36
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure 2-57. 2-58. 2-59. 2-60. 2-61. 2-62. 2-63. 2-64. 2-65. 2-66. 3-1. 3-2. 3-3. 3-4. 3-5. 3-6. 3-7. 3-8. 3-9. 3-10. 3-11. 3-12. 3-13. 3-14. 3-15. 3-16. 3-17. 3-18. 3-19. 3-20. 3-21. 3-22. 3-23. 3-24. 3-25. 3-26. 3-27. 3-28. 3-29. 3-30. 3-31. 3-32. 3-33. 3-34. 3-35. 3-36. 3-37. One Foot Pound of Work ...................................................................................................... Forms of Energy.................................................................................................................... Horsepower ........................................................................................................................... Torque Effect......................................................................................................................... Prony Brake........................................................................................................................... Dynamometers ...................................................................................................................... Conversion of Torque to Work .............................................................................................. Torque Output Versus Speed................................................................................................ Torque-Horsepower-Speed Relationship .............................................................................. Pulley System with a 90-Percent Efficiency .......................................................................... Liquid-Cooled Cylinder Block ................................................................................................ Requirements of a Cylinder................................................................................................... Cylinder Sleeves.................................................................................................................... Engine Crankcase ................................................................................................................. Typical Cylinder Head Installation ......................................................................................... Combustion Chamber ........................................................................................................... Valves and Ports ................................................................................................................... Cylinder Head Cooling........................................................................................................... Cylinder Head Sealing........................................................................................................... Air-Cooled Cylinder ............................................................................................................... Air-Cooled Crankcase ........................................................................................................... Piston .................................................................................................................................... Controlling Piston Expansion ................................................................................................ Cam-Ground Piston............................................................................................................... Full- and Partial-Skirted Pistons ............................................................................................ Piston Structure..................................................................................................................... Purpose of Piston Rings........................................................................................................ Piston Ring Types and Description ....................................................................................... Configurations of Piston Rings .............................................................................................. Types of Compression Rings ................................................................................................ Operation of Compression Rings .......................................................................................... Heat Dam .............................................................................................................................. Ring Gap ............................................................................................................................... Ring Gap Variations .............................................................................................................. Staggered Ring Gaps............................................................................................................ Top Ring Groove Insert ......................................................................................................... Oil Control Rings ................................................................................................................... Piston Ring Expanders.......................................................................................................... Piston Ring Wear-In .............................................................................................................. Piston Pin .............................................................................................................................. Piston Pin Construction ......................................................................................................... Piston Pin Configurations ...................................................................................................... Connecting Rod Constructions.............................................................................................. Crankshaft Construction........................................................................................................ Crankshaft Throw Arrangements .......................................................................................... Crankshaft Counterweights ................................................................................................... Vibration Damper .................................................................................................................. viii Page 2-37 2-38 2-38 2-39 2-39 2-40 2-41 2-41 2-41 2-42 3-1 3-2 3-3 3-4 3-4 3-5 3-5 3-6 3-6 3-7 3-7 3-8 3-9 3-9 3-10 3-10 3-11 3-12 3-12 3-13 3-14 3-15 3-15 3-15 3-15 3-16 3-16 3-17 3-17 3-18 3-18 3-19 3-19 3-20 3-21 3-22 3-23
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure 3-38. 3-39. 3-40. 3-41. 3-42. 3-43. 3-44. 3-45. 3-46. 3-47. 3-48. 3-49. 3-50. 3-51. 3-52. 3-53. 3-54. 3-55. 3-56. 3-57. 3-58. 3-59. 3-60. 4-1. 4-2. 4-3. 4-4. 4-5. 4-6. 4-7. 4-8. 4-9. 4-10. 4-11. 4-12. 4-13. 4-14. 4-15. 4-16. 4-17. 4-18. 4-19. 4-20. 4-21. 4-22. 4-23. Crankshaft Lubrication Passages ......................................................................................... Crankshaft Bearings.............................................................................................................. Typical Insert Bearing Installation.......................................................................................... Bearing Materials .................................................................................................................. Bearing Requirements........................................................................................................... Connecting Rod Lubrication .................................................................................................. Crankshaft Main Bearings ..................................................................................................... Flywheel ................................................................................................................................ Valve Configurations ............................................................................................................. Exhaust Valve Configurations ............................................................................................... Valve Seats ........................................................................................................................... Valve Guides ......................................................................................................................... Valve Springs, Retainers, and Seals..................................................................................... Valve Rotators....................................................................................................................... Camshaft Support ................................................................................................................. Driving the Camshaft............................................................................................................. Auxiliary Camshaft Functions................................................................................................ Mechanical Tappets .............................................................................................................. Hydraulic Tappets ................................................................................................................. Tappet-to-Cam Lobe Relationship ........................................................................................ Push Rod............................................................................................................................... Rocker Arms ......................................................................................................................... Examples of Adjusting Valve Clearance ............................................................................... Common Fuel Tank Locations .............................................................................................. Typical Removable Fuel Tank Construction ......................................................................... Typical Fuel Cell Installation.................................................................................................. Bladder-Type Fuel Cell.......................................................................................................... Typical Fuel Filter Locations.................................................................................................. Fuel Filter Operation.............................................................................................................. Fuel Filter Configurations ...................................................................................................... Fuel Filter Element Configurations ........................................................................................ Mechanical Nonpositive Pump .............................................................................................. Mechanical Positive Pump Installation .................................................................................. Double Action Pump.............................................................................................................. Bellows-Type Electric Fuel Pump.......................................................................................... Vane-Type Electric Pump...................................................................................................... Typical Intake Manifold.......................................................................................................... Ram Induction Manifold......................................................................................................... Exhaust-Heated Intake Manifold ........................................................................................... Water-Heated Intake Manifold .............................................................................................. Air Filter ................................................................................................................................. Wet-Type Air Filter ................................................................................................................ Dry-Type Air Filter ................................................................................................................. Example of Atomization......................................................................................................... Venturi Effect......................................................................................................................... Secondary Venturi................................................................................................................. ix Page 3-23 3-24 3-24 3-25 3-25 3-25 3-26 3-26 3-27 3-28 3-28 3-29 3-29 3-30 3-30 3-31 3-31 3-32 3-33 3-33 3-34 3-34 3-35 4-1 4-2 4-2 4-3 4-3 4-3 4-4 4-5 4-6 4-7 4-7 4-8 4-8 4-9 4-10 4-10 4-11 4-12 4-12 4-13 4-14 4-14 4-15
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure 4-24. 4-25. 4-26. 4-27. 4-28. 4-29. 4-30. 4-31. 4-32. 4-33. 4-34. 4-35. 4-36. 4-37. 4-38. 4-39. 4-40. 4-41. 4-42. 4-43. 4-44. 4-45. 4-46. 4-47. 4-48. 4-49. 4-50. 4-51. 4-52. 4-53. 4-54. 4-55. 4-56. 4-57. 4-58. 4-59. 4-60. 4-61. 4-62. 4-63. 4-64. 4-65. 4-66. 4-67. 4-68. 4-69. 4-70. 4-71. 4-72. 4-73. Air-Fuel Ratio Demonstration ................................................................................................ Throttle Valve ........................................................................................................................ Float Circuit ........................................................................................................................... Controlling Fuel Bowl Pressure ............................................................................................. Main Jet................................................................................................................................. Idle and Low-Speed Systems................................................................................................ High-Speed Systems............................................................................................................. Vacuum Power Jet ................................................................................................................ Vacuum-Operated Metering Rod .......................................................................................... Mechanically Operated Metering Rod ................................................................................... Acclerator Pump Circuit......................................................................................................... Diaphragm Accelerator Pump ............................................................................................... Duration Spring ..................................................................................................................... Choke Valve Operation ......................................................................................................... Manual Choke System .......................................................................................................... Automatic Choke System ...................................................................................................... Electric Choke ....................................................................................................................... Engine Coolant Heated Choke.............................................................................................. Well-Type Exhaust Heated Choke ........................................................................................ Exhaust Heat-Tube Type Choke ........................................................................................... Choke Vacuum Piston........................................................................................................... Choke Piston Integral with Choke Housing ........................................................................... Remote Chock Pulloff ........................................................................................................... Two-Stage Choke Pulloff....................................................................................................... Fast Idle Cam Operation ....................................................................................................... Chock Unloader..................................................................................................................... Two-Barrel Carburetor with Fixed Linkage............................................................................ Mechanical Progressive Linkage Operation.......................................................................... Vacuum Progressive Linkage Operation............................................................................... Secondary Air Valve Operation ............................................................................................. Typical Four-Barrel Carburetor.............................................................................................. Updraft, Downdraft, and Sidedraft Carburetors..................................................................... Primer System....................................................................................................................... Degasser System .................................................................................................................. Hot Idel Compensator ........................................................................................................... Throttle Return Dashpot ........................................................................................................ Antidiesel/Air-Conditioning Solenoid Operation..................................................................... Idle Solenoid System Operation............................................................................................ Heated Air Intake System Operation..................................................................................... Mechanical-Timed Injection .................................................................................................. Electronic-Timed Injection ..................................................................................................... Continuous Injection.............................................................................................................. Throttle Body Injection........................................................................................................... Turbocharger......................................................................................................................... Centrifugal Supercharger ...................................................................................................... Rootes Supercharger ............................................................................................................ Vane-Type Supercharger ...................................................................................................... Pressure Box......................................................................................................................... Centrifugal Governor ............................................................................................................. Velocity-Vacuum Governor - Type I ...................................................................................... x Page 4-15 4-15 4-16 4-16 4-17 4-18 4-19 4-19 4-20 4-20 4-21 4-22 4-23 4-24 4-24 4-25 4-25 4-26 4-26 4-27 4-27 4-27 4-28 4-28 4-29 4-29 4-30 4-31 4-32 4-33 4-33 4-34 4-34 4-35 4-36 4-36 4-37 4-38 4-39 4-41 4-42 4-43 4-44 4-46 4-47 4-47 4-47 4-48 4-49 4-50
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure 4-74. 4-75. 4-76. 4-77. 4-78. 5-1. 5-2. 5-3. 5-4. 5-5. 5-6. 5-7. 5-8. 5-9. 5-10. 5-11. 5-12. 5-13. 5-14. 5-15. 5-16. 5-17. 5-18. 5-19. 5-20. 5-21. 5-22. 5-23. 5-24. 5-25. 5-26. 5-27. 5-28. 5-29. 5-30. 5-31. 6-1. 7-1. 7-2. 7-3. 7-4. 7-5. 7-6. 7-7. 7-8. 7-9. 7-10. Velocity-Vacuum Governor - Type II ..................................................................................... Centrifugal-Vacuum Governor .............................................................................................. Normal Combustion .............................................................................................................. Detonation ............................................................................................................................. Preignition.............................................................................................................................. Fuel Density Compensator.................................................................................................... Open Combustion Chamber ................................................................................................. Precombustion Chamber ...................................................................................................... Turbulence Chamber ............................................................................................................ Spherical Chamber................................................................................................................ General System Operation.................................................................................................... Multiple Unit Injection Pump.................................................................................................. Multiple Unit Injector.............................................................................................................. Injector Nozzles..................................................................................................................... Wobble Plate injection Pump ................................................................................................ Distributor Injection System................................................................................................... Fuel Metering System ........................................................................................................... Distributor-Type Unit Injectors............................................................................................... Unit Injection System............................................................................................................. Unit Injector Operation .......................................................................................................... Pressure-Timed Injection System ......................................................................................... Pressure-Timed Gear Pump ................................................................................................. Pressure-Timed Delivery Injector Operation ......................................................................... PSB Distributor Injection System .......................................................................................... PSB Injection Pump .............................................................................................................. PSB Injection Pump Operation.............................................................................................. Plunger-Type Supply Pump................................................................................................... Mechanical (Centrifugal) Governor ....................................................................................... Vacuum-Operated Governor ................................................................................................. Timing Device........................................................................................................................ Timing Device Operation....................................................................................................... Manifold Flame Heater System ............................................................................................. Ether Injection System .......................................................................................................... Primary Fuel Filter ................................................................................................................. Secondary Fuel Filter ............................................................................................................ Jacobs Engine Brake ............................................................................................................ Liquefied Petroleum Gas System.......................................................................................... Typical Exhaust System ........................................................................................................ Exhaust Manifold................................................................................................................... Manifold Heat Control Valve.................................................................................................. Muffler ................................................................................................................................... Vehicle Emissions ................................................................................................................. Draft Tube System ................................................................................................................ PCV System .......................................................................................................................... Catalytic Converter................................................................................................................ Air Pump System................................................................................................................... Naturally Aspirated System ................................................................................................... xi Page 4-51 4-52 4-53 4-54 4-55 5-3 5-4 5-5 5-5 5-6 5-9 5-10 5-11 5-13 5-15 5-17 5-18 5-18 5-19 5-20 5-22 5-23 5-24 5-25 5-26 5-27 5-29 5-31 5-32 5-33 5-34 5-36 5-37 5-38 5-39 5-40 6-1 7-1 7-2 7-3 7-4 7-4 7-5 7-6 7-8 7-10 7-11
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure 7-11. 7-12. 8-1. 8-2. 8-3. 8-4. 8-5. 8-6. 8-7. 8-8. 8-9. 8-10. 8-11. 8-12. 8-13. 8-14. 8-15. 8-16. 8-17. 9-1. 9-2. 9-3. 9-4. 9-5. 9-6. 9-7. 9-8. 9-9. 9-10. 9-11. 9-12. 9-13. 10-1. 10-2. 10-3. 10-4. 10-5. 10-6. 10-7. 10-8. 10-9. 10-10. 10-11. 10-12. 10-13. 10-14. EGR System.......................................................................................................................... Fuel Evaporation System ...................................................................................................... Typical Engine Lubrication System ....................................................................................... How Oil Lubricates ................................................................................................................ Sources of Oil Contamination................................................................................................ Rotor-Type Oil Pump............................................................................................................. Gear-Type Oil Pump ............................................................................................................. Oil Pickup and Strainer.......................................................................................................... Oil Filters ............................................................................................................................... Oil Filtering Mediums............................................................................................................. Filter System Configurations ................................................................................................. Oil Temperature Regulator.................................................................................................... Oil Cooler .............................................................................................................................. Oil Level Indicator.................................................................................................................. Oil Pressure Regulator .......................................................................................................... Splash-Type Lubrication System........................................................................................... Combination Splash and Force-Feed Lubrication System.................................................... Force-Feed Lubrication System ............................................................................................ Full Force-Feed Lubrication System ..................................................................................... Liquid-Cooled System ........................................................................................................... Engine Radiator Construction ............................................................................................... Water Pump Construction ..................................................................................................... Viscous Fan Clutch ............................................................................................................... Electrically Motorized Fan ..................................................................................................... Variable Pitch Fan ................................................................................................................. Bellows-Type Thermostat...................................................................................................... Pellet-Type Thermostat ......................................................................................................... Coolant Bypass ..................................................................................................................... Pressure Cap ........................................................................................................................ Expansion Tank..................................................................................................................... Closed Cooling System ......................................................................................................... Air Cooling System................................................................................................................ Early Examples of Gas Turbine Engines............................................................................... Theory of Gas Turbine Engine .............................................................................................. Comparison of Piston Engine to Turbine Engine .................................................................. The Otto Cycle ...................................................................................................................... The Brayton Cycle................................................................................................................. Air Inlet Section ..................................................................................................................... Axial Compressor .................................................................................................................. Centrifugal Compressor ........................................................................................................ Combustion Chamber ........................................................................................................... Typical Recouperator ............................................................................................................ Recouperator Plate Detail ..................................................................................................... Radial InflowTurbine.............................................................................................................. Axial Flow Design.................................................................................................................. Impulse Turbine..................................................................................................................... xii Page 7-12 7-14 8-1 8-3 8-4 8-6 8-6 8-7 8-8 8-9 8-10 8-11 8-11 8-11 8-12 8-12 8-13 8-13 8-14 9-2 9-3 9-4 9-5 9-5 9-6 9-7 9-8 9-9 9-10 9-10 9-11 9-12 10-1 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 10-12 10-13 10-13
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure 10-15. 10-16. 10-17. 10-18. 10-19. 10-20. 10-21. 10-22. 10-23. 11-1. 11-2. 11-3. 11-4. 11-5. 11-6. 11-7. 11-8. 11-9. 11-10. 11-11. 11-12. 11-13. 11-14. 11-15. 11-16. 11-17. 11-18. 11-19. 11-20. 11-21. 11-22. 12-1. 12-2. 12-3. 12-4. 12-5. 12-6. 12-7. 12-8. 13-1. 13-2. 13-3. 13-4. 13-5. 13-6. 13-7. Reaction Turbine ................................................................................................................... Impulse-Reaction Turbine Blade ........................................................................................... Turbine Construction ............................................................................................................. Gas Turbine Fuel Pumps ...................................................................................................... Fuel Injection Nozzles ........................................................................................................... Typical Oil Storage Tank ....................................................................................................... Typical Fuel-Oil Cooler.......................................................................................................... Typical Ignition System.......................................................................................................... Typical Electric Starter .......................................................................................................... Composition of Matter ........................................................................................................... Composition of Electricity ...................................................................................................... Conductors and Insulators .................................................................................................... Covalent Bonding of Silicon................................................................................................... Phosphorus-Doped Silicon.................................................................................................... Boron-Doped Silicon ............................................................................................................. Hole Movement Theory ......................................................................................................... Diode Operation .................................................................................................................... Zener Diode Operation.......................................................................................................... Transistor Configurations ...................................................................................................... Transistor Operation.............................................................................................................. Basic Electrical Circuit........................................................................................................... Typical Automotive Circuit..................................................................................................... Circuit Configurations ............................................................................................................ Magnetic Lines of Force ........................................................................................................ Bar and Horseshoe Magnet .................................................................................................. Effects Between Magnetic Poles........................................................................................... Electromagnetism ................................................................................................................. Electromagnetism in a Wire Loop ......................................................................................... Electromagnetism in a Wire Coil ........................................................................................... Left-Handed Rule .................................................................................................................. Electromagnetic Induction ..................................................................................................... Cross Section of a Typical Storage Battery........................................................................... Plate Construction ................................................................................................................. Cell Group Construction ........................................................................................................ Battery Cell Elements............................................................................................................ Battery Container Construction ............................................................................................. Battery Discharge/Charge Cycle ........................................................................................... Comparison of Discharge Characteristics ............................................................................. Battery Installation Configurations......................................................................................... Simple Single-Loop Generator .............................................................................................. Multiple-Loop Generator........................................................................................................ AC and DC Flow.................................................................................................................... Field Winding Configurations ................................................................................................ Shunt-Wound Generator ....................................................................................................... Shunt-Wound Generator Operation ...................................................................................... Generator Drive Systems ...................................................................................................... xiii Page 10-13 10-14 10-14 10-15 10-16 10-17 10-18 10-19 10-19 11-1 11-3 11-3 11-5 11-5 11-6 11-6 11-7 11-8 11-8 11-9 11-11 11-12 11-13 11-14 11-14 11-14 11-15 11-15 11-16 11-16 11-17 12-1 12-2 12-2 12-3 12-4 12-5 12-9 12-11 13-2 13-2 13-3 13-4 13-5 13-5 13-6
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure 13-8. 13-9. 13-10. 13-11. 13-12. 13-13. 13-14. 13-15. 13-16. 13-17. 13-18. 13-19. 13-20. 13-21. 13-22. 13-23. 13-24. 13-25. 13-26. 13-27. 13-28. 13-29. 13-30. 13-31. 13-32. 13-33. 13-34. 13-35. 13-36. 13-37. 13-38. 13-39. 14-1. 14-2. 14-3. 14-4. 14-5. 14-6. 14-7. 14-8. 14-9. 14-10. 14-11. 14-12. 14-13. 14-14. Cutout Relay.......................................................................................................................... Reverse-Series Field............................................................................................................. Vibrating Point Voltage Regulator ......................................................................................... Vibrating Point Regulator Circuit ........................................................................................... Carbon-Pile Regulator and Circuit......................................................................................... Third-Brush Regulation ......................................................................................................... Light Switch Control of a Third-Brush Generator .................................................................. Step-Voltage Control of a Third-Brush Generator................................................................. Thermostatic Control of a Third-Brush Generator................................................................. Split-Series Field Regulation ................................................................................................. Main and Auxiliary Generators .............................................................................................. Paralleling Relays.................................................................................................................. Carbon-Pile Regulation of Generators .................................................................................. Typical Alternator................................................................................................................... Diode Arrangement in Rectifier Bridge.................................................................................. Comparison for Outputs of AC and DC Generators.............................................................. Simple AC Generator ............................................................................................................ Rotor Construction ................................................................................................................ Stator Construction................................................................................................................ Rotor-to-Stator Relationship.................................................................................................. Wound-Pole Alternator .......................................................................................................... Lundell Alternator .................................................................................................................. Lundell Inductor..................................................................................................................... Inductor Alternator................................................................................................................. Brushless-Rotating Rectifier.................................................................................................. Generator Cooling ................................................................................................................. AC and DC Regulator Comparison ....................................................................................... Vibrating Point Regulating Circuit.......................................................................................... Transistorized Voltage Regulator .......................................................................................... Solid-State Regulator Circuit ................................................................................................. Fuel Pressure Field Switch Circuit ........................................................................................ Field Relay and Warning Light Circuit ................................................................................... Simple DC Motor ................................................................................................................... Automotive Starting Motor..................................................................................................... Typical Starting Motor............................................................................................................ Field Winding Configurations ................................................................................................ Starter Drives ........................................................................................................................ Gear Reduction Starter ......................................................................................................... Overrunning Clutch ............................................................................................................... Pedal Shift Starter ................................................................................................................. Solenoid Shift Starter ............................................................................................................ Bendix Starter Drive .............................................................................................................. Key and Pushbutton Control Circuits..................................................................................... Vacuum Lockout Switch Control Circuit ................................................................................ Generator Lockout Relay ...................................................................................................... Oil Pressure Lockout Circuit.................................................................................................. xiv Page 13-7 13-8 13-9 13-11 13-12 13-13 13-15 13-16 13-17 13-17 13-19 13-21 13-22 13-23 13-24 13-25 13-25 13-26 13-26 13-27 13-27 13-28 13-29 13-30 13-31 13-32 13-33 13-34 13-35 13-36 13-36 13-37 14-1 14-2 14-3 14-4 14-4 14-5 14-5 14-6 14-7 14-8 14-9 14-9 14-10 14-11
TM 9-8000
LIST OF ILLUSTRATIONS - CONTINUED Figure 15-1. 15-2. 15-3. 15-4. 15-5. 15-6. 15-7. 15-8. 15-9. 15-10. 15-11. 15-12. 15-13. 15-14. 15-15. 15-16. 15-17. 15-18. 15-19. 15-20. 15-21. 15-22. 15-23. 15-24. 15-25. 16-1. 16-2. 16-3. 16-4. 16-5. 16-6. 16-7. 16-8. 16-9. 16-10. 16-11. 16-12. 16-13. 16-14. 16-15. 16-16. 16-17. 16-18. 16-19. 16-20. 16-21. 16-22. 16-23. Principles of Self-Induction.................................................................................................... Capacitor Action .................................................................................................................... Typical Automotive Ignition System....................................................................................... Ignition Switch and Positions................................................................................................. Ignition Coil Construction ...................................................................................................... Ignition Distributor ................................................................................................................. Typical Spark Plug Construction and Heat Range Descriptions ........................................... Resistor Spark Plugs............................................................................................................. Booster Gap Spark Plugs.............................................................. ........................................ Ballast Resistor ..................................................................................................................... Secondary Cable Construction.............................................................................................. Parallel-Connected Multiple Contacts ................................................................................... Alternately Actuated Multiple Contacts.................................................................................. Dual-Circuit Contact Points ................................................................................................... Twin-Ignition System ............................................................................................................. Transistorized Point Ignition .................................................................................................. Solid-State Ignition System ................................................................................................... Capacitive-Discharge Ignition System................................................................................... Vacuum Timing Controls ....................................................................................................... Centrifugal Timing Controls................................................................................................... Computerized Timing Control System................................................................................... Typical Magneto System ....................................................................................................... Magneto Generator ............................................................................................................... Magneto Control System....................................................................................................... Waterproof Ignition System ................................................................................................... Typical Automotive Lighting Circuit ....................................................................................... Lamp Construction and Configurations ................................................................................. Focused Light Beam Construction ........................................................................................ Automotive Headlamp Pattern .............................................................................................. Automotive Headlamp Configurations................................................................................... Sealed-Beam Headlamp Construction .................................................................................. Instrument-Mounted Headlamp Switch ................................................................................. Turn Signal Lever-Mounted Headlamp Switch...................................................................... Blackout Light/Headlamp Switch........................................................................................... Floor-Mounted Dimmer Switch.............................................................................................. Turn Signal Lever-Mounted Dimmer Switch ......................................................................... Overload Breakers ................................................................................................................ Demonstration of Circuit Breaker Operation ......................................................................... Demonstration of Fuse Operation ......................................................................................... Blackout Driving Light............................................................................................................ Blackout Stop and Marker Light ............................................................................................ Military Composite Light ........................................................................................................ Typical Turn Signal Switch .................................................................................................... Typical Turn, Signal Wiring Diagram.................................................................................... Turn Signal Flasher ............................................................................................................... Typical Backup Light System ................................................................................................ Stoplight Switch Configurations............................................................................................. Typical Stoplight System ....................................................................................................... xv Page 15-2 15-3 15-4 15-5 15-5 15-6 15-7 15-7 15-7 15-8 15-8 15-9 15-10 15-11 15-12 15-13 15-14 15-15 15-16 15-17 15-18 15-19 15-20 15-22 15-25 16-1 16-2 16-3 16-5 16-6 16-6 16-7 16-8 16-9 16-10 16-10 16-10 16-10 16-11 16-11 16-12 16-12 16-13 16-13 16-14 16-14 16-15 16-15
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure 17-1. 17-2. 17-3. 17-4. 17-5. 17-6. 17-7. 17-8. 17-9. 17-10. 17-11. 17-12. 17-13. 17-14. 17-15. 17-16. 17-17. 17-18. 17-19. 17-20. 17-21. 17-22. 17-23. 17-24. 17-25. 17-26. 17-27. 17-28. 17-29. 17-30. 17-31. 17-32. 17-33. 17-34. 17-35. 17-36. 17-37. 18-1. 18-2. 18-3. 19-1. 19-2. 19-3. 19-4. 19-5. 19-6. 19-7. 19-8. Typical Instrument Panel....................................................................................................... Ammeter Operation ............................................................................................................... Voltmeter Operation .............................................................................................................. Low-Voltage Warning Lamp .................................................................................................. No-Charge Indicator Lamp .................................................................................................... Thermostatic Fuel Gage: Self-Regulating ............................................................................. Thermostatic Fuel Gage: Eternally Regulated ...................................................................... Thermostatic Fuel Gage: Differential Type ........................................................................... Magnetic Fuel Gage .............................................................................................................. Types of Sending Units for Pressure Gages ......................................................................... Mechanical Pressure Gages ................................................................................................. Oil Pressure Warning Lamp .................................................................................................. Types of Temperature Gage Sending Units.......................................................................... Mechanical Temperature Gage............................................................................................. Temperature Warning Lights ................................................................................................ Mechanical Speedometer Installation ................................................................................... Mechanical Speedometer Operation..................................................................................... Odometer Operation.............................................................................................................. Mechanical Tachometer and Engine Hours Gage ................................................................ Electric Speedometer and Tachometer Operation................................................................ Tachograph ........................................................................................................................... Vacuum Gage Readings ....................................................................................................... Electric Horn, Vibrator Type .................................................................................................. Horn Circuit Using a Relay .................................................................................................... Air Horns ............................................................................................................................... Electric Wipers ...................................................................................................................... Wiper Arm and Blade ............................................................................................................ Auxiliary Power Receptacle................................................................................................... Typical Heating Ventilation and Air-Conditioning System ..................................................... Typical Heater Core .............................................................................................................. Cable-Operated Mode Doors ................................................................................................ Vacuum-Operated Mode Doors ............................................................................................ Wiring Harnesses .................................................................................................................. Harness Bindings .................................................................................................................. Wire Identification.................................................................................................................. Electrical Terminals ............................................................................................................... Wire Receptacles and Connectors........................................................................................ Typical Ignition System.......................................................................................................... Radio Interference Suppression Filters and Cable Shielding................................................ Examples of Bonding ............................................................................................................ Power Takeoff ....................................................................................................................... Power Takeoff Driving Winch ................................................................................................ Mechanical Advantage .......................................................................................................... Internal and External Gears .................................................................................................. Types of Gears...................................................................................................................... Planetary Gear System ......................................................................................................... Laws of Planetary Gearing .................................................................................................... Typical Locations of Antifriction Bearings.............................................................................. xvi Page 17-1 17-2 17-2 17-3 17-3 17-4 17-5 17-6 17-7 17-8 17-9 17-9 17-9 17-11 17-11 17-12 17-13 17-14 17-14 17-15 17-15 17-17 17-18 17-19 17-19 17-20 17-21 17-22 17-23 17-24 17-24 17-25 17-26 17-27 17-28 17-29 17-30 18-2 18-4 18-5 19-2 19-3 19-4 19-5 19-5 19-6 19-7 19-8
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure Page 19-9. 19-10. 19-11. 19-12. 19-13. 19-14. 19-15. 19-16. 19-17. 19-18. 19-19. 19-20. 19-21. 20-1. 20-2. 20-3. 20-4. 20-5. 20-6. 20-7. 20-8. 21-1. 21-2. 21-3. 21-4. 21-5. 21-6. 21-7. 21-8. 21-9. 21-10. 21-11. 21-12. 21-13. 21-14. 21-15. 21-16. 21-17. 21-18. 21-19. 22-1. 22-2. 22-3. 22-4. 22-5. 22-6. Typical Ball Bearings............................................................................................................. Typical Roller Bearings.......................................................................................................... Typical Tapered Roller Bearings ........................................................................................... Typical Needle Bearings........................................................................................................ Typical Sealed Bearings........................................................................................................ Synthetic Rubber Oil Seals.................................................................................................... Wick Seals ............................................................................................................................ Typical Gaskets..................................................................................................................... Typical Front-Wheel Drive Configuration .............................................................................. Typical Rear-Wheel Drive Configurations ............................................................................. Typical Four-Wheel Drive Power Transmission .................................................................... Typical Six-Wheel Drive Power Transmission ...................................................................... Typical Eight-Wheel Drive Vehicle ........................................................................................ Compressibility of Gases and Liquids ................................................................................... Pascals Law.......................................................................................................................... Mechanical Advantage .......................................................................................................... Gear-Type Pumps ................................................................................................................. Rotary Pumps........................................................................................................................ Vane Type ............................................................................................................................. Internal-External Gear Pump................................................................................................. Simple Hydraulic Jack ........................................................................................................... Components of Typical Clutch .............................................................................................. Clutch-Drive Plate with Flexible Center................................................................................. Single, Large Coil Spring Clutch............................................................................................ Cross-Sectional View of Large Coil Spring Clutch ................................................................ Diaphragm Spring Clutch Operation ..................................................................................... Diaphragm Spring Clutch - Disassembled View ................................................................... Clutch Activation.................................................................................................................... Mechanical Operating Systems............................................................................................. Hydraulic Operating Systems................................................................................................ Single Dry Plate Clutch.......................................................................................................... Clutch Disk with Two Driven Disks........................................................................................ Multiple-Disk Clutch............................................................................................................... Semicentrifugal Clutch - Cross-Sectional View ..................................................................... Fluid Coupling - Disassembled View..................................................................................... Fluid Coupling - Schematic View........................................................................................... Torque Converter - Partial Cutaway View ............................................................................. Torque Converter Cutaway so Curvature of Vanes and Oil Flow is Visible .................................................................................................................... Primary and Secondary Stators Showing Freewheeling Rotors............................................ Torque Converter with Lockup Clutch ................................................................................... Transmission Shifting Mechanism and Control Lever........................................................... Transmission Gears in Neutral Position ................................................................................ Transmission Gears in Low Position ..................................................................................... Transmission Gears in Intermediate Position ....................................................................... Transmission Gears in High Position .................................................................................... Transmission Gears in Reverse Position .............................................................................. xvii 19-9 19-9 19-10 19-11 19-11 19-12 19-13 19-14 19-15 19-15 19-16 19-16 19-17 20-1 20-2 20-3 20-3 20-4 20-5 20-5 20-7 21-1 21-2 21-3 21-4 21-5 21-6 21-6 21-7 21-8 21-9 21-10 21-11 21-12 21-13 21-14 21-15 21-16 21-17 21-18 22-2 22-3 22-4 22-4 22-5 22-5
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure 22-7. 22-8. 22-9. 22-10. 22-11. 23-1. 23-2. 23-3. 23-4. 23-5. 23-6. 23-7. 23-8. 23-9. 23-10. 23-11. 23-12. 23-13. 23-14. 23-15. 23-16. 23-17. 23-18. 23-19. 23-20. 23-21. 23-22. 23-23. 23-24. 23-25. 23-26. Constant Mesh Transmission Assembly ............................................................................... Main Shaft Assembly............................................................................................................. Synchronizers........................................................................................................................ Synchromesh Transmission .................................................................................................. Gearshift Linkage .................................................................................................................. Automatic Transmission Cross-Sectional View..................................................................... Multiple-Disk Clutch............................................................................................................... Multiple-Disk Clutch Operation.............................................................................................. Brake Band............................................................................................................................ Brake Band Operation........................................................................................................... Overrunning Clutches............................................................................................................ Typical Two-Speed Automatic Transmission Utilizing Compound Planetary Drive Train ......................................................................................................... Compound Planetary Drive Train Operation ......................................................................... Simpson Drive Train Operation ............................................................................................. Typical Hydraulic Supply System .......................................................................................... Typical Transmission Hydraulic Pump .................................................................................. Typical Torque Converter Feed Circuit ................................................................................. Typical Range Control Circuit................................................................................................ Manual Valve Operation........................................................................................................ Operation of the Governor..................................................................................................... Typical Governor Pressure Versus Speed ............................................................................ Shift Valve ............................................................................................................................. Transmission Hydraulic System in Neutral............................................................................ Transmission Hydraulic System In Low (L) Range ............................................................... Transmission Hydraulic System In Reverse (R) ................................................................... Transmission Hydraulic System In Drive (D) - Low Range ................................................... Transmission Hydraulic System In Drive(D) - Direct Range ................................................. Transmission Hydraulic System In Drive (D) - Forced Downshift Range................................................................................................................ Operation of the Accumulator ............................................................................................... Transmission Modulator ........................................................................................................ Hydraulic Schematic of a Typical Three-Speed Automatic Transmission...................................................................................................................... Cross-Drive Transmission - Right Front View ....................................................................... Cross-Drive Transmission - Disassembled into Main Subassemblies ...................................................................................................................... Torque Converter Construction and Principles of Operation ................................................ Power Flow through Cross-Drive Transmission In Low Range............................................. Power Flow through Cross-Drive Transmission in High Range ............................................ Power Flow through Cross-Drive Transmission in Reverse Range ...................................... Power Flow through Cross-Drive Transmission during Left Steering In Neutral Range..................................................................................................... Power Flow through Cross-Drive Transmission during Right Steering In Neutral Range..................................................................................................... Power Flow through Cross-Drive Transmission during Left Steering In Low Range.......................................................................................................... xviii Page 22-7 22-8 22-8 22-9 22-10 23-1 23-2 23-3 23-4 23-5 23-5 23-6 23-7 23-9 23-12 23-13 23-15 23-17 23-18 23-19 23-20 23-20 23-21 23-22 23-23 23-25 23-26 23-27 23-28 23-29 23-30 24-2 24-3 24-4 24-5 24-7 24-9 24-11 24-14 24-17
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure 24-10. 24-11. 25-1. 25-2. 25-3. 25-4. 25-5. 25-6. 25-7. 25-8. 25-9. 25-10. 25-11. 25-12. 25-13. 25-14. 25-15. 26-1. 26-2. 26-3. 26-4. 26-5. 26-6. 26-7. 27-1. 27-2. 27-3. 27-4. 27-5. 27-6. 27-7. 27-8. Range Control Valve and Steering Control Valve Schematic Diagram.............................................................................................................................. Brake - Schematic View ........................................................................................................ X1100 Transmission - External View .................................................................................... Xl100 Transmission - Internal View....................................................................................... Lockup Torque Converter ..................................................................................................... Power Flow through X1100 Transmission in Neutral ............................................................ Power Flow through X1100 Transmission in First Range ..................................................... Power Flow through X1100 Transmission in Second .......................................................... Power Flow through X1100 Transmission in Third Range.................................................... Power Flow through X1100 Transmission in Fourth Range.................................................. Power Flow through X1100 Transmission in Reverse 1 Range............................................ Power Flow through X1100 Transmission in Reverse 2 Range............................................ Hydrostatic Steer Unit-Zero Steer ......................................................................................... Hydraulic Diagram for X1100 Transmission-Zero Steer ....................................................... Hydrostatic Steer Unit in Left-Steer Position ......................................................................... Hydrostatic Steer Unit in Right-Steer Position....................................................................... Final Drive Assembly............................................................................................................. Typical Location of Auxiliary Transmission ........................................................................... Auxiliary Transmission - Sectional View................................................................................ Automatic Subtransmission................................................................................................... Overdrive Unit ....................................................................................................................... Overdrive In Locked-Out Position ......................................................................................... Overdrive in Engaged Position.............................................................................................. Typical Overdrive Control Circuit........................................................................................... Typical Driveline Arrangement with Transfer Assembly........................................................ Typical Conventional Transfer Assembly for 6 x 6 Vehicles ................................................. Typical Conventional Transfer Assembly Using Chain Drive for Front Axle...................................................................................................................... Power Flow In Transfer Assembly......................................................................................... Differential-Type Transfer Assembly ..................................................................................... Transfer Assembly Sprag Unit .............................................................................................. Positive Traction Transfer Case Operation ........................................................................... Air-Control Diagram of Transmission and Transfer Assembly Using an Air-Controlled Double-Sprag Unit ....................................................................... Typical Propeller Shaft and Slip Joint.................................................................................... Typical Universal Joint........................................................................................................... Speed Fluctuations Caused by Conventional Universal Joints............................................. Various Conventional Universal Joints.................................................................................. Rzeppa Constant Velocity Joint............................................................................................. Bendix-Weiss Constant Velocity Joint................................................................................... Tracta Constant Velocity Joint............................................................................................... Double Cross and Roller Constant Velocity Joint.................................................................. xix Page
24-20 24-21 25-2 25-3 25-3 25-4 25-5 25-6 25-7 25-8 25-9 25-10 25-10 25-11 25-12 25-12 25-13 26-1 26-2 26-2 26-3 26-4 26-6 26-7 27-1 27-2 27-3 27-3 27-5 27-7 27-8 27-9 28-1 28-2 28-3 28-4 28-6 28-7 28-8 28-9
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure 29-1. 29-2. 29-3. 29-4. 29-5. 29-6. 29-7. 29-8. 29-9. 29-10. 29-11. 29-12. 29-13. 29-14. 29-15. 29-16. 29-17. 29-18. 29-19. 29-20. 29-21. 29-22. 30-1. 30-2. 30-3. 30-4. 30-5. 30-6. 30-7. 30-8. 30-9. 30-10. 30-11. 30-12. 30-13. 30-14. 30-15. 30-16. 30-17. 30-18. 30-19. 30-20. 30-21. 30-22. 30-23. 30-24. Differential Operation ............................................................................................................ Conventional Differential ........................................................................... ............................ Comparison of Conventional and High-Traction Differential Gears ................................................................................................................................. Sprag-Type No-Spin Differential ........................................................................................... Silent-Type No-Spin Differential ............................................................................................ Multiple Plate Clutch No-Spin Differential ............................................................................. Cone Clutch-Type No-Spin Differential ................................................................................. Gear Drive Configurations..................................................................................................... Worm Gear Drive .................................................................................................................. Hypoid Gear Drive................................................................................................................. Axle Configurations ............................................................................................................... Independent Live Axle Suspension ....................................................................................... Double-Reduction Drive Axle ................................................................................................ Dual-Ratio Drive Axle ............................................................................................................ Double-Reduction Dual-Ratio Drive Axle .............................................................................. Gear Carrier with Power Divided........................................................................................... Front Live Axle Assembly and Four-Wheel Drive Installation ............................................... Helical Gear Drive for Steerable Wheels .............................................................................. Tandem Axles with Individual Propeller Shafts ..................................................................... Tandem Axles with Power Divider......................................................................................... Controlled Differential............................................................................................................ Controlled Differential with Final Drive .................................................................................. Leaf Springs .......................................................................................................................... Coil Springs ........................................................................................................................... Torsion Bar............................................................................................................................ Hotchkiss Drive ..................................................................................................................... Torque Tube Drive ................................................................................................................ Torque Arm Drive .................................................................................................................. Coil Spring and Control Rod Drive ........................................................................................ Dead Front Axle .................................................................................................................... Freewheeling Independent Suspension ................................................................................ Driven Parallel Wishbone Coil Spring Front Suspension ...................................................... Driven Parallel Wishbone Torsion Bar Suspension .............................................................. Swinging-Arm Independent Rear Suspension ...................................................................... MacPherson Strut Suspension.............................................................................................. Auxiliary Spring Suspension.................................................................................................. Variable Load Spring Arrangement ....................................................................................... Bogie Axle Configuration....................................................................................................... Air Compressor ..................................................................................................................... Pressure Regulator Valve ..................................................................................................... Height Control Valve.............................................................................................................. Air Shock Absorber ............................................................................................................... Single-Acting Cam-Operated Shock Absorber...................................................................... Vane-Type Shock Absorbers ................................................................................................ Direct-Acting Shock Absorber ............................................................................................... Pusher Axle and Controls...................................................................................................... xx Page 29-1 29-2 29-3 29-4 29-5 29-6 29-7 29-8 29-9 29-10 29-11 29-12 29-13 29-14 29-15 29-16 29-18 29-19 29-20 29-21 29-22 29-23 30-1 30-2 30-3 30-3 30-4 30-4 30-5 30-6 30-7 30-7 30-8 30-8 30-9 30-10 30-11 30-11 30-12 30-13 30-13 30-13 30-15 30-15 30-16 30-17
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure 31-1. 31-2. 31-3. 31-4. 31-5. 31-6. 32-1. 32-2. 32-3. 32-4. 32-5. 32-6. 32-7. 32-8. 32-9. 32-10. 32-11. 32-12. 32-13. 32-14. 32-15. 32-16. 32-17. 32-18. 32-19. 32-20. 32-21. 32-22. 32-23. 32-24. 32-25. 32-26. 32-27. 32-28. 32-29. 32-30. 32-31. 32-32. 33-1. 33-2. 33-3. 33-4. 33-5. 33-6. 33-7. 33-8. 33-9. 33-10. The Volute Spring.................................................................................................................. Torsion Bar Spring Used in Tracked Vehicles ...................................................................... Road Wheels......................................................................................................................... Idler Wheel Operation ........................................................................................................... Hydromechanical Lockout System ........................................................................................ The Spade System................................................................................................................ Disk Wheel ............................................................................................................................ Cast Aluminum Wheel........................................................................................................... Wire Wheel ........................................................................................................................... Drop Center Rim ................................................................................................................... Semidrop Center Rim............................................................................................................ Safety Rim............................................................................................................................. Split Rims .............................................................................................................................. Bead Locks............................................................................................................................ Bead Clips ............................................................................................................................. Radial Tire Construction........................................................................................................ Bias-Ply Tire Construction..................................................................................................... Solid Tire Construction .......................................................................................................... Directional Mud and Snow Tread .......................................................................................... Nondirectional Mud and Snow Tread .................................................................................... Cross-Country Tread............................................................................................................. Regular Treads...................................................................................................................... Rock Service Tread............................................................................................................... Earthmover Tread ................................................................................................................. Standard Tube....................................................................................................................... Combat Tubes....................................................................................................................... Bullet-Resisting Tube ............................................................................................................ Tube Flaps ............................................................................................................................ Cured-On Rubber-Covered Valve ......................................................................................... All-Metal-Stem Cured-On Valve ............................................................................................ Cured-In Valve ...................................................................................................................... Spud-Mounted Valve............................................................................................................. Snap-In Tubeless Tire Valve ................................................................................................. Valve Cores........................................................................................................................... Valve Caps ............................................................................................................................ Sectional Band Tracks .......................................................................................................... Double-Pin Tracks................................................................................................................. Single-Pin Tracks .................................................................................................................. Ackerman Steering System................................................................................................... Fifth-Wheel Steering ............................................................................................................. Solid Axle Suspension........................................................................................................... Center Steering Linkage........................................................................................................ Parallelogram Steering Linkage ............................................................................................ Rack and Pinion Steering Linkage ........................................................................................ Worm and Sector Steering Gear ........................................................................................... Worm and Roller Steering Gear ............................................................................................ Cam and Lever Steering Gear .............................................................................................. Worm and Nut Steering Gear................................................................................................ xxi Page 31-2 31-2 31-3 31-4 31-6 31-7 32-1 32-1 32-1 32-2 32-2 32-3 32-3 32-4 32-5 32-5 32-6 32-6 32-7 32-7 32-7 32-8 32-8 32-8 32-9 32-9 32-10 32-10 32-10 32-11 32-11 32-11 32-12 32-12 32-12 32-13 32-14 32-15 33-1 33-2 33-3 33-4 33-4 33-5 33-6 33-6 33-7 33-7
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure 33-11. 33-12. 33-13. 33-14. 33-15. 33-16. 33-17. 33-18. 33-19. 33-20. 33-21. 33-22. 33-23. 33-24. 33-25. 34-1. 34-2. 34-3. 34-4. 34-5. 34-6. 34-7. 34-8. 34-9. 34-10. 34-11. 34-12. 34-13. 34-14. 34-15. 34-16. 34-17. 34-18. 34-19. 34-20. 34-21. 34-22. 34-23. 34-24. 34-25. 34-26. 34-27. 34-28. 34-29. 34-30. 34-31. 34-32. 34-33. 34-34. Rack and Pinion Steering Gear............................................................................................. Typical Power Steering Pump ............................................................................................... Control Valve......................................................................................................................... Power Steering Gearbox ....................................................................................................... Hydraulic Cylinder ................................................................................................................. Configurations of Power Steering Systems........................................................................... Air Steering............................................................................................................................ Axle End Construction for Four-Wheel Drive ........................................................................ Four-Wheel Steering ............................................................................................................. Steering Geometry, Illustrating Toe-Out................................................................................ Caster Angle.......................................................................................................................... Camber Angle ....................................................................................................................... Kingpin Inclination ................................................................................................................. Toe-in .................................................................................................................................... Tracking................................................................................................................................. Development of Friction and Heat......................................................................................... Braking Requirements........................................................................................................... Total Vehicle Stopping Distance of an Average Vehicle ....................................................... Action During Wheel Rolling and Skidding............................................................................ Internal Expanding and External Contracting Brakes............................................................ Brakeshoes and Brake Lining ............................................................................................... Brakedrum Construction ....................................................................................................... Self-Energizing and Servo Action.......................................................................................... Drum Brake Configurations ................................................................................................... Self-Adjusting Mechanisms ................................................................................................... Disk Brake Assembly ............................................................................................................ Floating Caliper ..................................................................................................................... Fixed Multipiston Calipers ..................................................................................................... Self-Energizing Disk Brakes.................................................................................................. Contracting Transmission Brake ........................................................................................... Disk Transmission Brake ...................................................................................................... Parking Brake Configurations ............................................................................................... Mechanical Brake System..................................................................................................... Principles of the Hydraulic System........................................................................................ Diagram of Hydraulic Brake System ..................................................................................... Master Cylinder and Components......................................................................................... Wheel Cylinder Configurations.............................................................................................. Brake Lines ........................................................................................................................... Power Booster and Operation ............................................................................................... Tandem-Type Booster........................................................................................................... Piston-Type Booster.............................................................................................................. Bellows-Type Booster............................................................................................................ Brake-Pedal Booster ............................................................................................................. Hydraulic-Power Booster....................................................................................................... Pneumatic Principle............................................................................................................... Typical Airbrake System........................................................................................................ Typical Air Compressor, Two-Cylinder.................................................................................. Typical Air Compressor, Three-Cylinder ............................................................................... Governor ............................................................................................................................... xxii Page 33-8 33-9 33-10 33-11 33-12 33-13 33-14 33-16 33-16 33-17 33-18 33-19 33-19 33-20 33-21 34-1 34-1 34-2 34-3 34-4 34-5 34-6 34-8 34-9 34-10 34-12 34-14 34-15 34-17 34-18 34-19 34-20 34-22 34-24 34-25 34-26 34-27 34-28 34-30 34-31 34-31 34-32 34-32 34-33 34-33 34-34 34-35 34-36 34-37
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure 34-35. 34-36. 34-37. 34-38. 34-39. 34-40. 34-41. 34-42. 34-43. 35-1. 35-2. 35-3. 35-4. 35-5. 36-1. 36-2. 36-3. 36-4. 36-5. 36-6. 36-7. 36-8. 36-9. 36-10. 36-11. 36-12. 36-13. 36-14. 36-15. 36-16. 36-17. 36-18. 36-19. 36-20. 36-21. 36-22. 36-23. 37-1. 37-2. 37-3. 37-4. 37-5. 37-6. 37-7. 37-8. Airbrake Valve ....................................................................................................................... Brake Chamber ..................................................................................................................... Quick Release Valve ............................................................................................................. Relay Valve ........................................................................................................................... Slack Adjuster - Partial Cutaway View .................................................................................. Air-Over-Hydraulic Brake System ......................................................................................... Vacuum-Over-Hydraulic Brake System - Released .............................................................. Vacuum-Over-Hydraulic Brake System - Applied ................................................................. Electric Brake System ........................................................................................................... Separate Frame and Body .................................................................................................... Integrated Frame and Body................................................................................................... Truck Frame (Ladder) ........................................................................................................... Typical Tank Hull................................................................................................................... Unarmored Hulls ................................................................................................................... Winch and Power Takeoff Installation ................................................................................... Single-Speed, Single-Gear Power Takeoff ........................................................................... Single-Speed, Single-Gear Power Takeoff Installation ......................................................... Auxiliary Transmission Power Takeoff Driving Winch........................................................... Typical Positions of Transfer and Power Takeoff Control Levers for Two-Speed Transfer Assembly with Power Takeoff ......................................... Jaw-Clutch Worm-Gear Winch ............................................................................................. Location of Central Tire-Pressure Control System Components .......................................... 2 1/2-Ton 6 x 6 Gasoline Tank Truck .................................................................................... 2000-Gallon Tank Semitrailer ............................................................................................... Location of Portable Pump and Hose in Tank Semitrailer .................................................... Portable Pump....................................................................................................................... Dump Truck - Side View ....................................................................................................... Dump Body - Raised ............................................................................................................. Endgate Opened for Dump ................................................................................................... Dump Body Control Lever (Drivers Seat Removed)............................................................. Control Linkage Between Control Lever, Control Box, and Power Takeoff .................................................................................................................... Crane Assembly on Wrecking Truck ..................................................................................... Crane A-Frame...................................................................................................................... Main Drive Chain and Associated Parts................................................................................ Tank Prepared for Deepwater Fording.................................................................................. Ventilation System for Deepwater Fording............................................................................ Crankcase Breather for Fording ............................................................................................ Air Cleaner and Connections for Deepwater Fording............................................................ Effects of Ambient Temperature on Closed Systems ........................................................... Refrigeration Cycle................................................................................................................ Receiver and Components.................................................................................................... Expansion Valve and Expansion Tube.................................................................................. Typical Evaporator................................................................................................................. Thermostatic Switch .............................................................................................................. Hot Gas Bypass Valve........................................................................................................... Suction Throttling Valve ........................................................................................................ xxiii Page 34-37 34-38 34-38 34-39 34-39 34-40 34-42 34-43 34-44 35-1 35-2 35-3 35-5 35-5 36-1 36-2 36-3 36-3 36-4 36-5 36-6 36-7 36-7 36-8 36-8 36-9 36-10 36-10 36-11 36-12 36-13 36-13 36-14 36-16 36-17 36-18 36-18 37-1 37-3 37-4 37-5 37-6 37-7 37-7 37-8
TM 9-8000 LIST OF ILLUSTRATIONS - CONTINUED Figure 37-9. 37-10. 37-11. 37-12. 37-13. 37-14. 37-15. 38-1. 38-2. 38-3. 38-4. 38-5. 38-6. 38-7. 38-8. 38-9. Pilot-Operated Absolute (POA) Valve ................................................................................... Compressor Components ..................................................................................................... Compressor Superheat Switch.............................................................................................. Two-Cylinder Axial Compressor............................................................................................ Four-Cylinder Radial Compressor......................................................................................... Six-Cylinder Axial Compressor.............................................................................................. Condenser............................................................................................................................. Typical Semitrailer Chassis ................................................................................................... Truck Tractor and Semitrailer Connections .......................................................................... Kingpin and Plate .................................................................................................................. Fifth Wheel ............................................................................................................................ Landing Gear......................................................................................................................... Typical Three-Quarter Trailers .............................................................................................. Typical Full-Trailer Chassis ................................................................................................... Trailer Converter Dolly........................................................................................................... Tow Vehicle for Three-Quarter and Full Trailer..................................................................... Page 37-9 37-10 37-11 37-12 37-13 37-14 37-15 38-1 38-2 38-2 38-3 38-4 38-5 38-6 38-7 38-7
LIST OF TABLES Table 12-1. 37-1. Lead-Acid Vs Nickel-Cadmium Batteries .............................................................................. Refrigerant-12 Pressure-Temperature Relationship ............................................................. xxiv Page 12-8 37-2
TM 9-8000 PART ONE INTRODUCTION CHAPTER 1 GENERAL INFORMATION Section I. PURPOSE OF MANUAL 1-1. Usage. The manual is to be used to provide basic descriptive information to the field and to service and troop schools concerning the automotive vehicle and how it works. It also contains information that makes it a convenient reference manual. The information contained within will be of particular interest to the following: vehicles, these subjects have been omitted. The flow of power is traced from its development in the engine to its final outlet at the wheels, with the units discussed in the order in which they contribute to the power flow. Diesel and gasoline engines, except for their fuel systems, are explained together, as are radial and in-line engines. After the flow of power is traced to the wheels, those chassis components, sometimes referred to as running gear (i.e., steering system, brakes, wheels and tracks, and frames), are explained; then hulls and bodies; and finally such miscellaneous items as special equipment and trailers. 1-3. Emphasis. Wheeled vehicles have been emphasized for two reasons: first, the majority of tracked vehicles employ special adaptation with the same fundamental principles of wheeled vehicles; second, instruction will be facilitated by the reference to wheeled vehicles because most parts are more accessible and more visible than on tracked vehicles. Again, to aid instruction, the military vehicle has been correlated with commercial vehicles that may be familiar to the student.
Section II. ORGANIZATION OF THE MANUAL 1-4. General. Many different methods are used to group vehicle units and assemblies. The method employed in this text has been chosen because it more readily lends itself to a logical and simplified development of the material to be presented. 1-5. Engine. The basic engine (gasoline, diesel, and gas turbine) is discussed later in the manual with all of its supporting systems, such as cooling, lubrication, ignition, fuel, and exhaust. 1-6. Electrical System and Related Units. The electrical system includes all lighting systems and electrically operated accessory systems. 1-7. Power Train. The power train includes all components and systems that are used to get the power from the engine to the driving wheels. 1-8. Chassis Components. The chassis com ponents (also known as running gear) include the suspension, brakes, steering, wheels, tires, and tracks. 1-9. Bodies, Hulls, and Frames. Bodies, frames, and hulls include the various body frame configurations, hull designs, trailer configurations, truck body configurations, and accessory systems(including refrigeration).
1-1
TM 9-8000
1-10. Terminology. The terminology part of the manual will describe those terms used in the text that
Section III. HISTORY OF MILITARY VEHICLES 1-11. Pre-World War II. In 1912, four commercial trucks were purchased by the US Army for experimental purposes. Thus, motor vehicles were introduced as a means of transporting military personnel, supplies, and equipment. By 1916, when a punitive expedition was sent against the Mexican bandits, interest had been stimulated to the point that a nonstandard fleet of trucks was assembled at the Mexican border and used in the campaign. At that time, it was discovered that commercial transportation did not meet military requirements on operations over rough terrain or in the vital requirements of maintenance and repair. This discovery brought about the standardized designs of operating equipment and a variety of modifications to meet military requirements. As a result, a majority of the thousands of vehicles used in World War I were standardized and possessed a moderate degree of interchangeability. Trench warfare caused the development of an automotive vehicle used only for combat purposes; thus the tank was developed. American design and experimentation were carried on in the period between the two World Wars to develop a fleet of military wheeled vehicles that were entirely standardized and had a high degree of interchangeability. Under the program, industry began to produce vehicles with both front-and rear-wheel drives, a feature required of a military vehicle for successful operation over any terrain but found only in special commercial equipment. After German tanks and combat vehicles proved so successful against the Polish, French, and British armies in 1939 and 1940, American tank development was increased. The United States equaled, and in some instances surpassed, the Axis powers in the race to develop superior combat vehicles and was able to use overwhelming quantities of automotive materiel against them to help bring about their defeat. 1.12. Post-World War II. Since World War II, the United States has continually pressed its research and development program for more and better vehicles. Foreign commitments have forced the United States to rapidly update its military equipment to meet particular countries soil and climatic conditions, including adapting to temperatures from - 70F (-57C) to +125F (+52C), rough and hilly terrain, sand, mud, snow, and swamps. It is difficult to visualize the many and varied requirements that must be incorporated in each tactical and combat vehicle, whether it be wheeled or tracked. The development of our military vehicles is parallel with the history of our country. Sudden involvement usually results in crash programs to revise and modify existing materiel; however, during peacetime and when the time element is not critical, the trend is toward a partial or completely new concept of a vehicle (or system) for a designated purpose. Whatever the case may be, certain elements must be taken into consideration. One is product improvement, which usually comes about by a gradual change, with the modification of a single component, whether it be a bolt or a gear in a transmission. Closely associated with this is reliability, the ability to meet certain requirements as specified with a minimum of maintenance. Many tactical requirements of military vehicles are closely related, and to meet these ends, families of vehicles have dominated the scene. Generally speaking, this means a specific chassis and power train, with or without modification, is used with added equipment to produce a cargo truck, wrecker, or tank truck. In addition to satisfying these requirements, a high degree of interchangeability of repair parts is achieved. This is one form of standardization of designs. Additional aspects that must be considered for development of today's vehicles include newer techniques in maintenance, the introduction of advanced metals for lightweight construction, air transportability, and capability to ford a body of water.
Section IV CHARACTERISTICS OF MILITARY VEHICLES 1-13. General. Military vehicles incorporate all forms of wheeled and tracked vehicles including the full range of body types found in commercial vehicles. However, there are also bodies and equipment that are unique to military operations. They include all types of trucks, tractors, truck
1-2
TM 9-8000 tractors, personnel carriers, tanks, self-propelled guns, motorized and mechanized special purpose equipment, trailers, vans, and special purpose towed vehicles. The principal distinction between these vehicles and their commercial counterparts is that military vehicles are specifically designed for military purposes. This includes combat operations and the transportation of cargo, personnel, or equipment; towing other vehicles or equipment; and operations, both cross country and over roads, in close support of combat vehicles and troops. They are designed and constructed to endure the rigors of the military environment and to continue to operate at, or above, a prescribed minimum performance level in this environment. They have excellent cross-country performance capabilities over all types of terrain where tactical or combat operations can be conducted. This Includes snow and ice, rocky terrain, swamps, and desert sands. In order to negotiate water barriers with a minimum of preparation, all sensitive equipment is either permanently water-proofed to prevent damage by Immersion, or designed to function underwater. 1-14. Features. Some of the features and characteristics that are standard on military vehicles are:
a. 24-volt, fully waterproofed, fungus-proofed electrical systems that are fully suppressed to prevent Interference to electronic equipment. b. Engines capable of operating while submerged in either fresh water or sea water. c. Oversized capacities.
air, oil, and fuel fully
filtering
d. Oversized generator capacity. e. Oversized engine oil and cooling capacities. f. Engines that are less critical of the fuel they require and have a lower specific weight (pound per horsepower). g. Reliability over an extremely wide temperature range. h. Provisions for operating during blackout conditions. i. j.
All-wheel drive on wheeled vehicles. Improved ease of servicing and maintenance.
Section V. MILITARY VEHICLE CATEGORIES 1-15. Administrative Vehicles. Administrative vehicles comprise the standard commercially available vehicles commonly used at camps, posts, stations, and various US Government Installations for routine administrative duties. These vehicles have a minimum of modifications to adapt them to military service. In some instances, no modification whatsoever Is made. 1-16. Tactical Vehicles. Tactical vehicles generally are defined as vehicles that have been designed and manufactured specifically to meet the severe requirements Imposed by combat and tactical operations In the field. Whereas combat vehicles are defined as vehicles designed to perform specific functions In combat, tactical vehicles are designed specifically to support the tactical play of the operation. Military tactics Is that branch of the military that deals with the arranging, positioning, and maneuvering of the forces In or near contact with the enemy; also, the maneuvering and positioning of materiel and supplies in support of the forces in contact. Because the main purpose of tactical vehicles is to give direct support to the combat vehicles, they are required to have the same high quality of mobility as do combat vehicles; and like combat vehicles, they are designed to exacting military characteristics to survive and perform satisfactorily In the military environment. The majority of wheeled vehicles fall into the tactical rather than the combat vehicle category. 1-17. Combat Vehicles. Combat vehicles are defined as land or amphibious vehicles, with or without armor or armament, designed for specific functions In combat or battle. The later Installation of armor or armament onto other than combat vehicles does not alter their original classification. They may be wheeled or tracked but In all cases they are designed to have a high degree of mobility In off-road operations. Some typical
1-3
TM 9-8000 combat vehicles are tanks, self-propelled artillery, missile launchers, and armored cars. The majority of combat vehicles at the present time are tracked vehicles, but this is not a requirement of this classification. Due to their missions, combat vehicles usually are equipped with both armor and armament; however, certain antitank vehicles are unarmored and depend upon their decreased silhouette and increased speed and maneuverability for protection. A continuing demand for greater firepower and mobility has resulted in an increasing use of lightweight armor on vehicle bodies and hulls. The reduction in vehicle weight enables some vehicles that would otherwise be too heavy to take part in airborne operations; it also improves their amphibious capabilities. Weight reduction in the newer types of combat vehicles is largely due to extensive use of aluminum in their construction, including aluminum armor.
Section VI. CLASSIFICATION OF VEHICLES 1-18. General. The term vehicle, as used in the Army, includes all wheeled and tracked equipment, all chassis powered by a self-contained power unit, and trailers and semitrailers towed by vehicles. (See para 1-13 for characteristics.) 1-19. Classification According to Design.
d. Trailers. Trailers are vehicles designed to be towed and are provided with a drawbar or tongue for attachment to a coupling mounted on the towing vehicle. e. Semitrailers. Semitrailers are vehicles designed to be towed and are supported in part by a prime mover (towing vehicle) through a fifth wheel or similar coupling.
1-20. Classification by Ground Contact. Under this general classification, vehicles may be further subclassified into wheeled and tracked vehicles.
a. General Transport Vehicles. General transport vehicles are motor vehicles designed to be used interchangeably for movement of personnel and cargo and used to satisfy general automotive transport needs without modification to the chassis. The 2 1/2-ton, 6 x 6 cargo truck is an example of a general transport vehicle. b. Special Equipment Vehicles. Special equipment vehicles are general transport vehicles that have had some minor modifications such as a special body or special equipment mounted thereon. The ordnance shop truck (ordnance maintenance truck, 2 1/2-ton, 6 x 6) is in this class because a special body to house shop equipment has been mounted on the chassis of a general transport vehicle, 2 112-ton, 6 x 6. c. Special Purpose Vehicles. Special purpose vehicles are motor vehicles designed and intended for a specialized requirement for which no general transport vehicle chassis can be adapted. This category includes items that are specified from time to time by agencies other than the Army Materiel Command. That agency, however, retains the responsibility for the basic components of the vehicle. All tractors, regardless of size or intended purpose, are classified as special purpose vehicles.
a. Wheeled vehicles may be classified by the number of wheels and the number of driving wheels. Where such data as 4 x 4, 6 x 6, 8 x 8, etc, appear in vehicular nomenclature, the first figure indicates total number of wheels and the second figure indicates number of driving wheels.
Vehicle has four wheels 4x4 It should be noted that all six-wheel vehicles have three axles; that is, wheels are considered a unit whether they are single (one tire) or dual (two tires). b. Tracked vehicles are so called because the tracks serve the purpose of providing a supporting platform of relatively large area under the road or suspension wheels of the vehicles. Vehicle has four driving wheels
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PART TWO ENGINES CHAPTER 2 PISTON ENGINE CHARACTERISTICS Section I. ENGINE OPERATION 2-1. Introduction. 2-2. Reciprocating Motion to Rotary Motion. The force of the piston acting in a downward motion is of little value if it is to turn the wheels of the vehicle. In order to utilize this straight line or reciprocating motion, it must be transformed into rotary motion. This is made possible through the use of a crankshaft. The crankshaft, as the name implies, is a shaft connected to the driving wheels of a vehicle through the drive train on one end. On the other end of the shaft is a crank with a crankpin offset from the shafts center. Figure 2-3 illustrates how the piston and the crankshaft are connected through the connecting rod and the crankpin. Figure 2-4 illustrates how reciprocating motion of the piston is changed to rotating motion of the crankshaft. 2-3. Intake and Exhaust. If the engine is going to operate, the fuel and air mixture must be fed into the combustion chamber. The burnt gases also must be exhausted after the fuel is burned. To accomplish this, there is a passage to the combustion chamber called the intake port and a passage from the combustion chamber to the exhaust
a. Because the most widely used piston engine is the four-stroke cycle type, it will be used as the example for section I, Engine Operation and as the basis for comparison in section II, Comparison of Engine Types. b. The operation of the piston engine can best be understood by comparing it to a simple cannon. In A, figure 2-1 a cannon barrel, charge of gunpowder, and a cannonball are illustrated. In B, figure 2-1 the gunpowder is ignited. The gunpowder burns very rapidly and as it burns there is a rapid expansion of the resulting gases. This rapid expansion causes a tremendous increase in pressure that forces the cannonball from the barrel.
In A, figure 2-2 the cannon barrel has been replaced by a cylinder and a combustion chamber. The cannonball has been replaced by a piston. A mixture of vaporized fuel and air has replaced the gunpowder. In B, figure 2-2 the gasoline is ignited. This time, the resulting force acts to push the piston downward.
TM 9-8000
TA233310 2-2
TM 9-8000
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2-5. Intake Stroke (A, Fig. 2-8). The Intake stroke begins at top dead center. As the piston moves down, the intake valve opens. The downward movement of the piston creates a vacuum in the cylinder. The vacuum causes a fuel and air mixture to be drawn through the intake port Into the combustion chamber. As the piston reaches bottom dead center, the Intake valve closes. 2-6. Compression Stroke (B, Fig. 2-8). The compression stroke begins with the piston at bottom dead center. Both the intake and the exhaust valves remain closed. As the piston moves toward top dead center, the amount of space in the upper cylinder gets smaller. The fuel and air mixture is compressed and the potential energy in the fuel is concentrated. The compression stroke ends when the piston reaches top dead center. 2-7. Power Stroke (C, Fig. 2-8). As the piston reaches top dead center, ending the compression stroke, the spark plug (para 15-3) ignites the compressed fuel and air mixture. Because both valves are closed, the force of the resulting explosion pushes the piston down, giving a powerful driving thrust to the crankshaft. The power stroke ends as the piston reaches bottom dead center. 2-8. Exhaust Stroke (D, Fig. 2-8). As the piston reaches bottom dead center, ending the
power stroke, the exhaust valve opens, beginning the exhaust stroke. As the piston moves upward toward top dead center, it pushes the burnt gases from the fuel and air mixture out of the combustion chamber through the exhaust port. As the piston reaches top dead center, ending the exhaust stroke, the exhaust valve closes. As the exhaust valve closes, the intake valve opens to begin the Intake stroke in the next cycle. 2-9. Valve Train. It is obvious in paragraphs 2-5 thru 28 that it is very important to operate the valves in a timed sequence. If the exhaust valve opened In the middle of the intake stroke, the piston would draw burnt gases into the combustion chamber with a fresh mixture of fuel and air. As the piston continued to the power stroke, there would be nothing in the combustion chamber that would burn. The engine is fitted with a valve train to operate the valves. A simplified valve train is illustrated in A, figure 2-9. The camshaft is made to rotate with the crankshaft through the timing gears. The raised piece on the camshaft is called a cam lobe. As illustrated in view B, the valve spring Is designed to hold the valve closed. The cam lobe contacts the bottom of the lifter as it rotates with the camshaft, as shown in view C. As
Change 1 2-4
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the cam lobe pushes up on the lifter, it will in turn push the valve open against the pressure of the spring. In view D, the cam lobe has passed the center of the lifter bottom. As it rotates away from the lifter, the valve spring pulls the valve closed. By proper positioning of the cam lobes on the camshaft, a sequence can be established for the intake and exhaust valves. It is demonstrated in paragraphs 2-5 thru 2-8 that the intake valve and the exhaust valve must each open once for every operating cycle. As explained in paragraph 2-4, the crankshaft must make two complete revolutions to complete one operating cycle. Using these two facts, a camshaft speed must be exactly one-half the speed of the crankshaft. To accomplish this, the timing gears are made so that the crankshaft gear has exactly one-half as many teeth as the camshaft gear, as shown in figure 2-10. The timing marks are used to put the camshaft and the crankshaft in the proper position to each other. 2-10. Engine Accessory Systems.
b. Ignition System. The ignition system (chapter 15) ignites the fuel and air mixture in the combustion chamber at the precise moment needed to make the engine run. c. Cooling System. The cooling system (chapter 9) removes the excess heat from the engine that is generated from combustion. d. Lubrication System. The lubrication system (chapter 8) provides a constant supply of oil to the engine to lubricate and cool the moving parts. e. Flywheel (Fig. 2-11). As discussed in paragraphs 2-5 thru 2-8, for every two revolutions that the crankshaft makes, it only receives one power stroke lasting for only one-half of one revolution of the crankshaft. This means that the engine must coast through one and one-half crankshaft revolutions in every operating cycle. This would cause the engine to produce very erratic power output. To solve this problem, a flywheel is added to the end of the crankshaft. The flywheel, which is very heavy, will absorb the violent thrust of the power stroke. It will then release the energy back to the crankshaft so that the engine will run smoothly.
a. Fuel System. The fuel system (chapter 4) supplies the engine with a properly proportioned fuel and air mixture. It also regulates the amount of the mixture to the engine to control engine speed and power output.
TM 9-8000 Section II. COMPARISON OF ENGINE TYPES 2-11. Internal Combustion Engine Versus External Combustion Engine.
a. Internal Combustion Engine (A, Fig. 2-12). An internal combustion engine is any engine in which the fuel is burned within it. A four-stroke cycle engine is an internal combustion engine because the combustion chamber is located within the engine as shown in figure 2-12. b. External Combustion Engine (B, Fig. 2-12). An external combustion engine is an engine in which the fuel is burned outside of the engine. A steam engine is a perfect example. The fuel is burned in an outside boiler, where it makes steam. The steam is piped to the engine to make it run.
2-12. Four-Stroke Cycle Versus Two-Stroke Cycle. The engine described in section I is a four-stroke cycle engine. There is another form of gasoline piston engine that has no valve mechanisms and completes one operating cycle for every revolution of the crankshaft. It is called a two-stroke cycle engine and is illustrated in figure 2-13. Instead of placing intake and exhaust ports In the combustion chamber, they are placed in the
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downward stroke is also an intake and an exhaust stroke. As the piston moves from bottom dead center back to top dead center, it is going through a compression stroke.
center, the spark plug ignites the fuel and air mixture, beginning the downward power stroke again.
a. Downward Stroke (A, Fig. 2-14). The piston begins the power stroke at top dead center. As the exploding fuel and air mixture pushes the piston downward, it first covers the inlet port. This seals the crankcase. As the piston continues downward, it pressurizes the sealed crankcase, which contains a vaporized fuel and air mixture. As the piston continues to bottom dead center, it uncovers the intake and the exhaust ports. The pressure built up in the crankcase forces the fuel and air mixture into the cylinder through the intake port. The top of the piston is shaped to divert the mixture upward and away from the exhaust port. As the mixture enters the cylinder, it displaces and pushes the burnt gases out through the exhaust port. b. Upward Stroke (B, Fig. 2-14). As the piston moves upward, it covers the intake and exhaust ports. This seals the upper cylinder so that the upward movement of the piston compresses the fuel and air mixture. At the same time, the upward movement of the piston creates a suction in the crankcase so that as the inlet port is uncovered, a mixture of fuel and air is drawn into the crankcase. As the piston reaches top dead
c. The Fuel and Lubrication System. The fuel and air mixture must first pass through the crankcase before it gets to the combustion chamber. For this reason, the fuel and air mixture must also provide lubrication for the rotating and reciprocating parts. This is accomplished by mixing a small percentage of oil with the fuel. The oil, mixed with the fuel and air mixture, enters the crankcase in a vapor that constantly coats the moving parts. d. Power Output. It may seem like a two-stroke cycle engine will put out twice as much power as a comparable four-stroke cycle engine because there are twice as many power strokes. However, this is not the case. Because the force of the fuel and air mixture entering the cylinder must be relied upon to get rid of the burnt gases in the cylinder from the last power stroke, there is a certain amount of dilution of it. The mixing of the intake mixture with exhaust gases reduces its potential power output. Also, with the inlet and exhaust ports opened together, a certain amount of the fuel and air mixture is lost. There is also a much shorter period that the inlet port is open. This reduces the amount of power from each powerstroke.
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e. Advantage and Usage. The two-stroke cycle engine is used almost exclusively in very small equipment. It is lightweight and able to run at very high speeds due to the absence of a mechanical valve train.
2-13. Gasoline Engine Versus Diesel Engine.
a. General. In many respects, the four- stroke cycle gasoline engine and the four-stroke cycle diesel engine are very similar. They both follow an operating cycle that consists of intake, compression, power, and exhaust strokes. They also share in the same system for intake and exhaust valves. The component parts of a diesel engine are shown in figure 2-15. The main differences between gasoline engines and diesel engines follow.
(1) The fuel and air mixture is ignited by the heat generated by the compression stroke in a diesel engine versus the use of a spark ignition system on a gasoline engine. The diesel engine needs no ignition system. For this reason, the gasoline engine is referred to as a spark ignition engine and a diesel engine is referred to as a compression ignition engine.
(2) The fuel and air mixture is compressed to about one-twentieth of its original volume in a diesel engine. In contrast, the fuel and air mixture in a gasoline engine is compressed to about one- eighth of its original volume. The diesel engine must compress the mixture this tightly to generate enough heat to ignite the fuel and air mixture. The contrast between the two engines is shown in figure2-16. (3) The gasoline engine mixes the fuel and air before it reaches the combustion chamber. A diesel engine takes in only air through the intake port. Fuel is put into the combustion chamber directly through an injection system. The air and fuel then mix in the combustion chamber. This is illustrated in figure 2-17. (4) The engine speed and the power output of a diesel engine are controlled by the quantity of fuel admitted to the combustion chamber. The amount of air is constant. This contrasts with the gasoline engine where the speed and power output are regulated by limiting the air entering the engine. This is illustrated in figure 2-18.
b. Operation.
(1) Intake (A, Fig. 2-19). The piston is at top dead center at the beginning of the intake stroke. As the piston moves downward, the intake valve opens. The downward movement of the piston draws air into the cylinder. As the piston reaches bottom dead center, the intake valve closes. The intake stroke ends here. (2) Compression (B, Fig. 2-19). The piston is at bottom dead center at the beginning of the compression stroke. The piston moves up- ward, compressing the air. As the piston reaches top dead center, the compression stroke ends. (3) Power (C, Fig. 2-19). The piston begins the power stroke at top dead center. Air is compressed in the upper cylinder at this time to as much as 500 psi (3448 kPa). The tremendous pressure in the upper cylinder brings the temper- ature of the compressed air to approximately 10000F (5380C). The power stroke begins with the injection of a fuel charge into the engine. The heat of compression ignites the fuel as it is injected. The expanding force of the burning gases pushes the piston downward, providing power to the crankshaft. The power generated in a
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diesel engine is continuous throughout the power stroke. This contrasts with a gasoline engine, which has a power stroke with rapid combustion in the beginning and little or no combustion at the end. (4) Exhaust (D, Fig. 2-19). As the piston reaches bottom dead center on the power stroke, the power stroke ends and the exhaust stroke begins. The exhaust valve opens and the piston pushes the burnt gases out through the exhaust
port. As the piston reaches top dead center, the exhaust valve closes and the intake valve opens. The engine is now ready to begin another operating cycle.
c. Advantages.
(1) The diesel engine is much more efficient than a gasoline engine. This is due to the much tighter compression of the fuel and air mixture. The diesel engine produces tremendous
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TM 9-8000 low-speed power, and gets much more fuel mileage than the gasoline counterpart. This makes the engine very suitable for large trucks. (2) The diesel engine requires no ignition tuneups because there is no ignition system. (3) Because diesel fuel is of an oily consistency and less volatile than gasoline, it is not as likely to explode in a collision. d. Disadvantages. (1) The diesel engine must be made very heavy to have enough strength to deal with the tighter compression of the fuel and air mixture. (2) The diesel engine is very noisy. (3) fumes. (4) Because diesel fuel is not very volatile, it is difficult to start a diesel engine in cold weather. Diesel fuel creates a large amount of (5) A diesel engine operates well only in lowspeed ranges in relation to gasoline engines. This creates problems when using them in passenger cars that require a wide-speed range.
e. Usage. Diesel engines are widely used in all types of heavy trucks, trains, and boats. In recent years, more attention has been focused on using diesels in passenger cars. f. Multifuel Engine (Fig. 2-20). The multifuel engine is basically a four-stroke cycle diesel engine with the capability of operating on a wide variety of fuel oils without adjustment or modification (chapter 5, section I). The fuel injection system is equipped with a device called a fuel density compensator. Its job is to vary the amount of fuel to keep the power output constant regard- less of the fuel being used. The fuel system for the multifuel engine is described in detail in chapter 5, section I. The multifuel engine uses a spherical combustion chamber to aid in thorough mixing, complete combustion, and minimizing knocks. The spherical combustion chamber is covered in chapter 5, section II.
TM 9-8000 2-14. Two-Stroke Cycle Diesel (Fig. 2-21). regulated by controlling the quantity of fuel injected into the combustion chamber. (6) Unlike any of the other engine types, the two-stroke cycle diesel engine must have a supercharger to force the intake air into the upper cylinder. The most common type used is the rootes. Principles of supercharging are covered in chapter 4, section VI.
a. General. The two-stroke cycle diesel is a hybrid engine sharing operating principles of both a two-stroke cycle gasoline engine and a four-stroke cycle diesel engine. The major features of the engine are as follows.
(1) It completes an operating cycle every two piston strokes or every crankshaft revolution. Like a twostroke cycle gasoline engine, it gives a power stroke every time the piston moves downward. (2) It is a compression ignition engine, making it a true diesel engine. (3) It utilizes an exhaust valve on top of the combustion chamber as in a four-stroke cycle diesel engine. Intake ports are cut into the cylinder wall as in a two-stroke cycle gasoline engine. (4) It mixes its fuel and air in the combustion chamber as in a four-stroke cycle diesel engine. The air enters through the intake ports and the fuel is injected into the combustion chamber by the fuel injection system. (5) The air supply to the engine is constant while the speed and power output of the engine is
b. Operation(Fig. 2-22).
(1) Scavenging. Scavenging begins with the piston at bottom dead center. The intake ports are uncovered in the cylinder wall and the exhaust valve opens. Air is forced into the upper cylinder by the supercharger. As the air is forced in, the burnt gases from the previous operating cycle are forced out. (2) Compression. As the piston moves toward top dead center, it covers the intake ports. The exhaust valve closes at this point. This seals the upper cylinder. As the piston continues upward, the air in the cylinder is tightly compressed. As in the four-stroke cycle diesel, a tremendous amount of heat is generated by the compression. (3) Power. As the piston reaches top dead center, the compression stroke ends. Fuel is injected at this point. The intense heat of compression causes the fuel to ignite. The burning fuel pushes the piston down, giving power to the crankshaft. The power stroke ends when the piston gets down to the point where the intake ports are uncovered. At about this point, the exhaust valve opens and scavenging begins again. c. Advantages. The two-stroke cycle diesel engine has all of the advantages that a four-stroke cycle engine has over a gasoline engine plus the following: (1) Because it is a two-stroke cycle engine, it will run smoother than its four-stroke cycle counterpart. This is because there is a power stroke generated for every crankshaft revolution. (2) The two-stroke cycle diesel has a less complicated valve train because it does not use intake valves.
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d. Disadvantages.
(1) The two-stroke cycle engine must use a supercharger to force in the intake air and push
out the burnt exhaust gases. This is because the movement of the piston is not such that it will accomplish this naturally. The supercharger uses engine power to run it.
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TM 9-8000 (2) The two-stroke cycle diesel uses either two or four exhaust valves per cylinder, which complicates the valve mechanism. (3) As with the two-stroke cycle gasoline engine, the diesel counterpart will not produce twice as much power as a four-stroke cycle engine even though it produces twice as many power strokes. By studying figure 2-23, it can be seen that the power strokes are only a portion of the downstroke of the piston in a twostroke cycle diesel. In a four-stroke cycle diesel, the power stroke lasts from top dead center to bottom dead center. measured. Section I demonstrated that each piston stroke is one-half of a crankshaft revolution. This is expressed as 180 degrees of crank-shaft rotation. We also can recall that there are two complete crankshaft revolutions for every four-stroke operating cycle. This is expressed as 720 degrees of crankshaft rotation.
e. Usage. The two-stroke cycle diesel is used in most of the same applications as the four-stroke cycle diesel.
2-15. Multicylinder Engine Versus SingleCylinder Engine.
a. General. The rotation of a crankshaft is measured by breaking up one revolution into 360 equal parts. Each part is called a degree. The standard starting point is with the piston at top dead center. Figure 2-24 illustrates how this is
b. Power Overlap. In a simple four-stroke cycle engine, the power stroke produces a driving force that rotates the crankshaft. This means that out of a 720degree operating cycle, there are only 180 degrees when the crankshaft actually receives any driving force. In reality, the power stroke is actually even shorter. This is due to the fact that engineers have found that an engine will run better if the exhaust valve is set to begin opening approximately four-fifths of the way through the power stroke. This reduces the power stroke still further, to approximately 145 degrees (para 2-7). When the engine runs, it has to rely on power that is stored in the flywheel from the power stroke to push it through the 575 degrees remaining in the operating cycle. A much smoother running engine can be made by making it a multicylinder engine. A multicylinder engine
Figure 2-23 . Comparison of Two-and Four-Stroke cycle Diesel Power Stroke Lengths.
2-17
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SIX-CYLINDER ENGINE
FOUR-CYLINDER ENGINE
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Figure 2-26. Power Delivery in One-, Four-, Six-, and Eight-Cylinder Engines
ders. An eight-cylinder engine has an even larger 55degree power overlap. It becomes very obvious from figure 2-26 that the more cylinders that an engine has, the smoother the power delivery will be. . Power Increase. It also is obvious that the most practical way to increase the power output of an engine is to make a lot of small cylinders instead of one big one. A multicylinder engine is not only smoother but more reliable also. This is because each piston weighs less than a comparable size single-cylinder engine. The constant changing of direction of the piston causes more bearing wear if the piston is excessively heavy Also, the single-cylinder engine is not as smooth, which will decrease not only the life of the engine, but also the equipment that it is operating. 2-16. Piston Engine Versus Rotary Engine.
a. General. A relatively new configuration of the gasoline engine, called the rotary, has reached the automotive scene within the past 25 years. Its operating cycle is exactly the same as the piston engine, consisting of intake, compression, power, and exhaust operating phases. But rather than having reciprocating pistons rotating a crankshaft, it uses a triangular-shaped rotor that rotates around Inside of a specially shaped housing. The basic rotary engine is illustrated in figure 2-27. As the rotor moves around the inside of the housing, it also rotates an offcenter or eccentric shaft through an internal gear. The housing has intake and exhaust ports cast into the housing in strategically located points.
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c. Advantages. If the eccentric shaft receives one power stroke for each eccentric shaft revolution, then the rotor is equivalent to a two-piston, four-stroke cycle engine. As a result, the engine is a much more compact unit. The absence of the reciprocating parts and the absence of the valve train serve to help the engine attain higher speeds safely, giving it more flexibility in usage. The absence of these parts also serves to make this engine smoother than its piston engine counterpart. d. Disadvantages. A large percentage of the combustion area is exposed to the intake charge because of the rotary engine design. This large surface area, when wetted with fuel during intake and ignited at the beginning of the power stroke, produces dirty combustion. While rubbing against the housing, the seals on each corner of the triangular-shaped rotor are subjected to high rotational speeds. This results in rapid seal wear and is of a major concern to manufacturers. The many irregular curves in the design make the machining processes of the rotary engine difficult. The rotary engine also is hard to modify for development purposes. The rotary engine has not had a major impact on automotive engine development. Lack of research and development have kept it from realizing its full potential.
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e. Usage. Rotary engines are in use in passenger automobiles and small equipment such as snowmobiles. The engines usually are made in a two-rotor configuration as shown in figure 2-30. A two-rotor design is equivalent to a four-cylinder, four-stroke cycle piston engine.
a. Air Cooled. Engines that use air as a cooling medium generally are used in aircraft and small equipment such as motorcycles, snowmobiles, and gasoline power equipment. The air-cooled engine usually is identified by removable cylinders with cooling fins covering the outside surfaces. A typical air-cooled engine is shown in figure 2-31.
b. Liquid Cooled. Engines that use liquid as a cooling medium are used in the majority of
a. Valves in the Cylinder Block. These engines are known as flathead engines. This is due to the fact that the cylinder head is shaped like a flat slab. A typical flathead engine cylinder head is shown in figure 2-33. The cylinder heads only functions are to complete the combustion chamber and to hold and locate the spark plug. Flathead engines are virtually obsolete in all current automotive applications. The configuration of valve trains that were used in flathead engines are as follows.
(1) T-Head (Fig. 2-34). The intake and the exhaust valves were located on opposite sides of the cylinder, each requiring their own cam-shaft. The T-head engine got its name from the imaginary letter formed by the piston and the valve heads
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TM 9-8000 (2) L-Head (Fig. 2-35). The intake and the exhaust valves were both located on the same side of the piston and cylinder. The L-head engine was a much simpler design than the T-head because it required only one camshaft. The L-head engine got its name from the imaginary letter formed by the piston and the valve heads. b. Valves in the Cylinder Head. These engines come in two groups. The first group have their camshafts located in their cylinder blocks. These engines are known as the overhead valve (ohv) engines. The second group have their camshafts located in their cylinder heads. These engines are known as the overhead camshaft (ohc) engines. A typical ohv cylinder head is shown in figure 2-36. The configurations of valve trains for engines with the valves in the head are as follows. (1) I-Head (Fig. 2-37). This configuration has its camshaft located in the cylinder block. The camshaft operates the valves through the lifter, push rod, and rocker arm. The I-head gets its name from the letter formed by the piston and the valve. Although this configuration is the most popular for current gasoline and diesel engines, it Is rapidly being superseded by overhead camshaft configurations in passenger cars. (2) Single Overhead Camshaft (Fig. 2-38). This configuration has its camshaft located in the cylinder head. When the single overhead camshaft configuration is used, the intake and the exhaust valves are both operated from a common camshaft. The valve train may be arranged to operate the valves directly through the lifters as shown in view A. The valve train also may be arranged to operate the valves through rocker
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Figure 2-38. Single Overhead Camshaft Configurations (3) Double Overhead Camshaft (Fig. 2-39). This configuration has its camshafts located in the cylinder head. When the double overhead camshaft is used, the intake and the exhaust valves each operate from a separate camshaft. Each camshaft operates the valves directly through the lifters. This configuration, though cumbersome, provides the most engine performance and is used mostly in more expensive automotive applications. c. F-Head Engines (Fig. 2-40). The F-head engine is a combination of the two valve arrangement groups. In this engine, the intake valves are of the overhead type, located in the cylinder head. The exhaust valves, however, are located in the cylinder block. The engine gets its name by the Imaginary letter F formed by the cylinder and the valve heads. This configuration usually is not used In current automotive design. 2-19. Classification by Cylinder Arrangement. Multicylinder engines are classified by cylinder arrangement. Each cylinder arrangement has its own advantages. The most common arrangements are shown in figure 2-41. a. In line (A, Fig. 2-41). This is a very common arrangement in automotive and truck applications alike. It is commonly built in four- and sixcylinder configurations. Until approximately 30 years ago, it was common to build an in-line engine with eight cylinders. As the cars became shorter and wider, the inline eight-cylinder engine was replaced by the Varrangement.
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b. V-Type (B, Fig. 2-41). This is also a very common arrangement in automotive and truck applications. The cylinders usually are arranged at 90 degrees to each other with opposing cylinders sharing a common crankpin. The V-type engine, in the eightcylinder configuration, has replaced the in-line eightcylinder engine in automotive applications for two reasons.
(1) The V-type engine is much shorter, making it more suitable for modern body styles. (2) The V-type engine has a much shorter crankshaft that is less subject to torsional vibration (para 3-9). This makes the V-type engine smoother than the in-line engine. For exactly the same reasons as above, the V-type engine is replacing the in-line engine in sixcylinder configurations. A V-type engine in a six-cylinder configuration is suitable for front-wheel drive compact cars where the engine is mounted transversely (sideways).
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TM 9-8000 c. Horizontal Opposed (C, Fig. 2-41). Less common than the in-line and the V-type, this engine is designed to fit in compartments where height is a consideration. The cylinders are arranged at 180 degrees to each other with opposing cylinders sharing a common crankshaft journal. This engine arrangement almost always is used for air-cooled configurations, although at least one auto manufacturer is using a horizontal- ly opposed, water-cooled engine in their product. d. Radial (D, Fig. 2-41). The radial engine has cylinders placed in a circle around the crankshaft. The crankshaft has only one throw, with one of the pistons connected to this throw by a master rod. The connecting rods from the other pistons are fastened to the crankshaft through this master rod. This engine is almost exclusively an aircraft engine and is of little interest when studying automotive technology.
Section IV. ENGINE MEASUREMENTS 2-20. Bore and Stroke (Fig. 2-42). Area of cylinder bore = 0.785xdiameter = 0.785D Area of cylinder bore = 0.785x4 = 0.785x16 =12.56 Area of cylinder bore = 12.56 sq in.(81 .02 sq cm). b. stroke. Multiply the area of the cylinder bore by the
a. Bore. The bore is the diameter of the cylinder. b. Stroke. The stroke is the distance that the piston travels as it moves from top dead center to bottom dead center.
2-21. Piston Displacement (Fig. 2-42). Piston displacement is the volume of space that the piston displaces as it moves from top dead center to bottom dead center. The piston displacement is used to express engine size. To find the displacement of an eightcylinder engine with a bore of 4 in. (10.16 cm) and a stroke of 3 in. (7.62 cm), do the following. a. Find the area of the cylinder bore. To find the area of the cylinder bore, use the formula:
12.56sqin.x3in. = 37.68cu in.(617.37cc) This is the piston displacement for one cylinder. c. Multiply the displacement of one cylinder by he number of cylinders that the engine has.
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37.68cuin.x8cylinders = 301.44 cu in.(4938.96 cc) The displacement of the engine would be expressed as 301 cu in. in the English system. To express the displacement of the engine in the metric system, convert the cubic centimeter figure to liters. This is done by dividing the cubic centimeters by 1000. This Is because 1 liter = 1000 cc. 4938.96 = 4.938961iters 1000 The displacement of the engine would be expressed as 4.9 liters in the metric system. 2-22. Vacuum In Cylinder on Intake Stroke. a. The Atmosphere. The earth Is surrounded by an ocean of air that Is known as the atmosphere. Because it Is colorless and odorless, people are not always aware of it. However, the atmosphere does have weight. Figure 2-43 illustrates a theoretical setup for measuring the weight of air. Note the platform balance with a box on each side. One box appears to be an empty container, but it is really full of air. The other box is sealed and all of the air has been removed. This box will contain nothing; this Is known as a vacuum. Both boxes are exactly 1 cu ft in size. With both boxes on the platform balance, the box containing the air Is heavier than the box that Is a vacuum. After placing 1 114 oz (35.4 g) of weight on the side of the balance that holds the box with the vacuum, note that both sides of the platform balance will be equal in weight. This demonstration, of course, would be very difficult to really do, but it clearly illustrates that air weighs approximately 1 114 oz (35.4 g) per cubic ft.
b. Atmospheric Pressure (Fig. 2-44). Elevation is always referred to in relation to the level of the oceans. This is known as sea level. Because the atmosphere extends for many miles above the earth, the weight of all of this air creates a large force on the earths surface. In fact, the weight of the air creates a pressure of approximately 14.7 psi (101.3 kPa) on all things at sea level. As the elevation Increases, this atmospheric pressure progressively decreases. c. Vacuum in the Cylinder (Fig. 2-45). When the piston moves downward on the intake stroke, it may appear that it is sucking the mixture into the cylinder. Actually, what is really happening is that by the piston moving downward, it is making a larger space in the cylinder that contains nothing (a vacuum). The atmospheric pressure outside the cylinder will then push its way in through the Intake port, filling the cylinder.
2-23. Volumetric Efficiency.
a. General. Volumetric efficiency Is a way of measuring an engines ability to take In, or aspirate, Its intake mixture. As the piston moves down on the intake stroke, atmospheric pressure will push the Intake mixture Into the cylinder. Under ideal conditions, the volume of mixture that enters the engine for each intake stroke would be exactly equal to the displacement of the cylinder. This Is rarely the case In a real-life situation for the following reasons:
(1) The Intake stroke happens so quickly that the mixture cannot get into the cylinder fast enough to fill it to its full capacity. For this reason an engine generally will have a higher volumetric efficiency at lower speeds than it will at higher speeds. (2) As the mixture passes through the engine on its way to the cylinder, it picks up heat. As the mixture heats up, it becomes less dense. This means that less mixture actually enters the cylinder. (3) Sharp bends, obstructions, and rough surfaces on the walls of the Intake ports will slow down the Intake mixture, decreasing volumetric efficiency. b. Measuring Volumetric Efficiency. efficiency Is expressed as a ratio of the Volumetric
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amount of mixture that enters the cylinders on the intake stroke to the amount of mixture that the cylinders could actually hold. Figure 2-46 demonstrates a typical engine with a volumetric efficiency of 80 percent. As the piston moves from top to bottom dead center, the cylinder volume increases by 100 cu in., yet only 80 cu in. of air enters the cylinder.
changes include reshaping ports to smooth out bends, reshaping the back of the valve heads, or polishing the inside of the ports.
(3) By altering the time that the valves open or how far they open, volumetric efficiency can be improved.
c. Increasing Volumetric Efficiency. Any increase in volumetric efficiency will increase engine performance. Volumetric efficiency may be increased by doing the following.
(1) Keep the intake mixture cool (fig. 2-47). By ducting intake air from outside of the engine compartment and keeping the fuel cool, the intake mixture can be kept cooler. The cooler the mixture is, the higher the volumetric efficiency will be. This is because a cool mixture is denser or more tightly packed.
(4) By supercharging and turbocharging, the volumetric efficiency figure can be brought to over 100 percent. Principles of supercharging and turbocharging are covered in detail in chapter4.
2-24.
a. General. The compression ratio is the method that is used universally to measure how tightly the mixture is squeezed during the compression stroke. b. Measuring Compression Ratio. The compression ratio is found by measuring the volume that the mixture occupies when the piston is at bottom dead center, and dividing it by the volume that the mixture occupies when the piston is at top dead center. The following example illustrates this concept: For a given engine, the volume of the space occupied by the mixture is 80 cu in. when the piston is at bottom dead center. As the piston moves to top dead center, the mixture is squeezed into an area with a volume of 10 cu in. To calculate the compression ratio, do the following:
(1) Divide the volume at bottom dead center by the volume at top dead center. 80cu in. 10cu in. =8
(2) Modify the intake passages (fig. 2-48). Any changes to the intake passages that make it easier for the mixture to flow through will cause an increase in volumetric efficiency. Other
(2) Put the quotient into the form of a ratio. Compression ratio = 8:1 This simply means that the mixture is compressed to one-eighth of its original volume. TA233338
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Figure 2-47. Fresh Air Intake System c. Effect of Compression Ratio. As the compression ratio is increased, the mixture is squeezed into a tighter space. This means that there is a higher initial pressure at the start of the power stroke and that the burning gases have further to expand. For these reasons, any increase in compression ratio will effect an increase in engine power output. Passenger car engines that are modified for competition usually receive a boost in compression ratio by installing
pistons with domes, or by shaving material off of the surface of the cylinder head as shown in figure 2-50. Both of these actions will serve to reduce the volume of the combustion chamber, raising the compression ratio. The limiting factor when increasing compression ratio is finding a fuel that will not ignite itself from the heat of compression, causing detonation. Detonation is covered in detail in paragraph 4-40.
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a. General. Ignition timing refers to the timing of the spark at the spark plug gap in relation to the position of the piston.
2-32
B Measuring Ignition Timing (Fig. 2-51). The standard way to express the time when the ignition spark occurs is by citing the respective crankshaft position in degrees. This position is expressed in terms that use top dead center for the TA233340
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TM 9-8000 however, this Is not the case. Even though the compressed mixture burns very quickly, it does take a certain amount of time for the pressure to rise in the combustion chamber. Because of this time lag, it is desirable to have the spark occur before the piston reaches top dead center. This way there is time for the pressure In the combustion chamber to rise to its maximum as the piston reaches top dead center. This, In turn, allows the piston to get the maximum push from the combustion. If the spark occurs too late into the power stroke, very little of the push from the combustion is utilized. This Is because the piston already will be moving away by the time the gases start expanding from the combustion. This will reduce greatly the amount of pressure that Is exerted on the piston and much power would be lost. The limiting factor to timing advance is that It can cause detonation. Detonation is covered in detail In paragraph 440. for the pressure to build in the combustion chamber. There are timing advance mechanisms built into most Ignition systems. They will be discussed in detail in paragraph 15-8. 2-26. Valve Timing.
a. General. Valve timing is a system developed for measuring In relation to the crankshaft position (in degrees), the points when the valves open, how long they stay open, and when they close. Valve timing is probably the single most important factor in tailoring an engine for specific needs. By altering valve timing, an engine can be made to produce its maximum power in a variety of, speed ranges. The following factors together make up a valve operating sequence. b. Opening and Closing Point. The opening and closing points are the positions of the crankshaft (in degrees) when the valve Just begins opening and just finishes closing. Typical opening and closing points are illustrated in figure 2-53. Note the Intake valve opening 28 degrees before top dead center and closing at 71 degrees after bottom dead center.
d. Ignition Timing and Engine Speed. It is desirable to have Ignition progressively advance as engine speed increases. This Is because there Is less time for the pressure to build In the combustion chamber as the speed increases. By making the spark happen earlier (as much as 30 degrees btdc) at high speeds, there Is more time
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c. Duration. Duration Is the amount of crankshaft rotation (in degrees) that a given valve will remain open. In figure 2-54, a typical intake valve cycle is illustrated. The duration that it remains open is a total of 279 degrees. d. Valve Overlap. Valve overlap is a period in the four-stroke cycle when the intake valve opens before the exhaust valve closes. Typical valve overlap is Illustrated In figure 2-55. The intake valve Is opening 28 degrees before top dead center for the beginning of the intake stroke. The exhaust valve Is remaining open for 45 degrees after top dead center and into the intake stroke. This gives a valve overlap of 73 degrees. a. Valve Timing Considerations. Throughout the crankshaft revolution, the speed of the piston changes. From a stop at the bottom of the stroke, the piston will reach its maximum speed halfway through the stroke and gradually slow to a stop as It reaches the end of the stroke. The piston will behave exactly the same on the downstroke. There are two periods of crankshaft rotation In which there Is almost no perceptible movement of the piston. One of these periods begins at approximately 15 to 20 degrees before top dead center and ends at approximately 15 to 20 degrees after top dead center. The other pedod
begins at approximately 15 to 20 degrees before bottom dead center and ends at approximately 15 to 20 degrees after bottom dead center. These two positions are illustrated in figure 2-56. These two periods of crankshaft rotation are utilized when establishing a valve timing sequence as follows. (1)During the period that occurs at top dead center, valve overlap is introduced to increase volumetric efficiency. By opening the intake valve before the exhaust valve Is closed, the intake mixture is pulled in by the momentum of the exiting exhaust gas. The intake mixture coming In also helps to sweep or scavenge the cylinder of exhaust gases. Because the overlap occurs during one of the periods of little piston movement, there Is no problem with exhaust being pushed Into the Intake port or exhaust gas being pulled into the cylinder through the exhaust port by the piston. (2) During the period that occurs at bottom dead center, the pressure remaining In the cylinder at the end of the power stroke Is utilized by opening the exhaust valve early. When the exhaust valve opens, the pressure In the cylinder starts pushing the exhaust gas out of the cylinder.
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TM 9-8000 Section VI. ENGINE OUTPUT 2-27. Work (Fig. 2-57). Work is the movement of a body against an opposing force. Work is measured in units of foot pounds (Newton meters). One foot pound of work is the equivalent of lifting a 1-lb. weight 1 ft. When sliding something horizontally, work is measured by the force required to move the object multiplied by the distance that it is moved. Note that work is always the force exerted over a distance. Also note that if there is no movement of the object, then there is no work accomplished, no matter how much force is applied. 2-28. Energy(Fig. 2-58). energy of the auto back into heat energy. Friction is covered in detail in paragraph 34-1. When all of this kinetic energy is transformed into heat energy, the auto will be stopped. The heat energy will then dissipate into the air. It is very easy to see that work was accomplished when the automobile was set into motion. it may not be as easy to see that work was also accomplished to stop the automobile. Because stopping requires applying a force over a distance, it also fits the definition of work. 2-29. Power (Fig. 2-59). Power is the rate of work. Engines are rated by the amount of work that they can do in 1 minute. The unit of measure for rating engines is called horsepower. The horsepower unit was developed about the time that steam engines were being developed. Through testing, it was found that the average horse could lift a 200-lb. weight to a height of 165 ft in 1 minute. The equivalent of one horsepower can be reached by multiplying 165 ft by 200 lb. (work formula) for a total of 33,000 ft lb. per minute. 2-30. Torque Effect (Fig. 2-60) . Torque is a force that, when applied, tends to result in the twisting of the object rather than its physical movement. When measuring torque, the force that Is applied must be multiplied by the distance from the axis of the object. Because the force in pounds (Newtons) is multiplied by distance In feet (meters), torque is expressed in terms of pound feet (Newton meters). When applying torque to an object, the force and the distance from the axis will be dependent on each other. For example, if a 100-ft lb. torque is applied to a nut, a 100-lb. force would be applied if the wrench were 1-ft long. If a 2-ft-long wrench were used, a 50-lb. force is all that would be necessary. 2-31. Prony Brake. (Fig. 2-61). The prony brake is a device that measures the actual usable horsepower of an engine. It is used very little today, but is understood very easily. This makes it very useful for learning the concept of horsepower-measuring devices. The device consists of a flywheel that is surrounded by a large braking device. An arm is attached to this braking device with its other end exerting pressure on a scale. In operation, the engine is .attached to, and drives, the flywheel. The TA233345 2-37
a. General. Energy is the ability to do work. Energy takes many forms, such as heat, light, sound, stored energy (potential), or an object in motion (kinetic energy). b. Energy at Work. Energy performs work by changing from one form into another. To illustrate this, consider the operation of an automobile. From start to finish, it will do the following.
(1) When it is sitting still and not running, it has potential energy stored in the gasoline. (2) To set it into motion, the gasoline is burned, changing its potential energy into heat energy. The autos engine then transforms the heat energy from the burning gasoline into kinetic energy by forcing the car into motion. (3) The action of stopping the auto is accomplished by the brakes. By the action of friction, the brakes will transform the kinetic
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Dynamometer(Fig. 2-62).
a. General The modern method for checking engine power output is by using a dynamometer. The dynamometer can be used to check the output of the engine at the crankshaft or the horsepower of the engine can be measured at the driving wheels of the automobile by using a chassis dynamometer. b. Types of Dynamometers. The dynamometer, like the prony brake, loads an engine down to a given rpm and measures the torque that it produces at that given speed. There are two basic typesof dynamometers.
(1) One type of dynamometer-uses a large electrical generator to which the engine is attached. The engine brake horsepower then can be calculated by converting the electrical power generated into horsepower readings. (2) Another type of dynamometer uses a water brake to absorb engine power and calculate brake horsepower. TA233346
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Figure 2-60. Torque Effect. c. Converting Torque to Work (Fig. 2-63). The amount of work that is accomplished when a torque is given can be calculated if the amount of movement in complete revolutions also is given. (Remember, there is no work accomplished unless there is movement.)
For example: a 100-ft lb. torque is applied to a shaft to rotate it six times. How much work is accomplished? Work can be found with the following formula: 6.28 x number of rotations x torque, therefore: 6.28 x6x 100ft lb. = 3,768ft lb.
d. Engine Torque (Fig. 2-64). The engine exerts torque to drive the automobile. The amount of torque produced by the engine generally will increase with speed within the engines operational range. As the speed increases beyond the operational range, the engine torque will fall off. This is because of decreases in volumetric efficiency at excessive speed.
2-33. Torque-Horsepower-Speed (RPM) Relationship. Figure 2-65 shows the relationship between speed, torque, and horsepower for a given engine. As illustrated in figure 2-65, horsepower will continue to increase with speed even after torque begins to fall off. The reason that this happens is because horsepower is dependent on speed and torque. The horsepower will
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2-34. Rated Speed. The rated speed as indicated in figure 2-65 is the speed at which the governor in a military vehicle is set. The rated speed usually is just under the maximum horsepower speed. Operation over the rated speed, causes disproportionate engine wear and excessive fuel consumption. 2-35. Gross and Net Horsepower. The gross horsepower of an engine is the amount of power the engine delivers without any accessories or a muffler. Net horsepower is the horsepower left to propel the automobile after the requirements of all of the accessories have been deducted from the gross horsepower. 2-36. Indicated Horsepower. Indicated horsepower is the power developed inside of the engine based on the pressure developed in the cylinders. It is always much higher than the brake horsepower because it does not consider friction or the inertia of the reciprocating masses within the engine.
Figure 2-63. Conversion of Torque to Work. b. Torque can be substituted into the formula because it is equal to the length of the arm times the scale reading. This yields:
6.28 x torque x engine rpm 33,000 c. This can be simplified further by dividing the 33,000 constant by the 6.28 constant. This provides a formula that shows a direct torquehorsepower-speed relationship:
Figure 2-65. Torque-Horsepower-Speed Relationship TA233349 Figure 2-64. Torque Output Versus Speed.
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Section VII. ENGINE EFFICIENCY 2-37. Frictional Losses (Fig. 2-66). Efficiency is the relationship between results obtained and the effort required to obtain those results. Efficiency Is expressed as follows: Efficiency = output Input within the pulley system. The engine also is subject to many power losses. The two categories of losses are thermal and mechanical. The overall efficiency of an engine will be calculated in the next three paragraphs. 2-38. Thermal Efficiency. Thermal efficiency Is the relationship between actual heat energy stored within the fuel and the power produced In the engine (indicated horsepower). The thermal efficiency figure Indicates how much of the potential energy contained in the fuel actually Is used by the engine to produce power and how much energy is lost through heat. There Is an extremely large amount of energy from the fuel that is lost through heat In an internal combustion engine. This unused heat that is produced while the engine Is producing power Is of no value to the engine and must be removed from It, a. The heat Is dissipated in the following ways. (1) The cooling system removes heat from the engine to control engine operating temperature. (2) A major portion of the heat produced by the engine exits through the exhaust system. (3) The engine radiates a portion of the heat to the atmosphere. 4) A portion of this waste heat may be channeled to the passenger compartment to heat it. (5) The lubricating oil in the engine removes a portion of the waste heat.
System efficiency can be calculated using this formula. For example, if a 90-lb. box was lifted with a rope and pulley, it would require a force of 100 lb. Therefore: Efficiency = output Input x100 =
= 90 percent.
The above results simply mean that only 90 percent of the total effort used for lifting the box actually went to that task. The remainder, or 10
b. In addition to energy lost through wasted heat, there are the following inherent losses in the piston engine.
(1) Much energy is consumed when the piston must compress the mixture on the compression stroke. (2) Energy from the gasoline is consumed to pull the Intake mixture Into the cylinder. TA233350
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(3) Energy from the gasoline Is consumed to push the exhaust gases out of the cylinder. c. The combination of all of the factors in a piston engine that use and waste energy leaves the average engine approximately 20 to 25 percent thermally efficient. To calculate the thermal efficiency, the potential energy In the gasoline and the indicated horsepower must be expressed In a common unit of measure. Both of these factors may be converted to British thermal units (Btu). The conversion factors are:
2-39. Mechanical Efficiency. Mechanical efficiency within the engine is the relationship between the actual power produced in the engine (Indicated horsepower) and the actual power delivered at the crankshaft (brake or shaft horsepower). The actual power at the crankshaft Is always less than the power produced within the engine. This is due to the following:
a. Frictional losses between the many moving parts. b. In four-stroke cycle engines, a great deal of horsepower Is used to drive the valve train. Mechanical efficiency Is calculated by dividing the brake or shaft horsepower by the Indicated horsepower. For example: When checked on a dynamometer, the engine with the Indicated horsepower of 90, referred to In paragraph 2-38, produces a brake horsepower of 85. To calculate the mechanical efficiency, do the following:
brake horsepower Mechanical efficiency = x indicated horsepower 100 = 85 90 =94percent.
For example: A given engine delivers 90 Indicated horsepower for a period of 1 hour, and in that time consumes 50 lb. (7 1/2 gal.) of gasoline. Given this data, the thermal efficiency of the engine can be calculated by doing the following: (1) Calculate how many Btus of work are performed by 1 hp In 1 hour by doing the following: 33,000 ft lb. per minute x 60 minutes 1 hphr = 778 ft lb. per Btu (2) Calculate the Btus of work output for 90 hp hr using the Information from (1) by doing the following: 2445 Btus x 90 = 22,050 Btus. (3) Calculate how many Btus were inputted bydolng the following: 18,800 Btus x 50 lb. = 940,000 Btus input per hour. (4) Calculate the thermal efficiency by doing the following: = 2445 Btu.
2-40. Overall Efficiency. In paragraphs 2-38 and 2-39, the thermal and mechanical losses of the engine were calculated. Use the following procedure to calculate the overall efficiency of the engine. The overall efficiency Is the relationship between the power Input and the true output of the engine (brake or shaft horsepower). The input will be expressed, as in paragraph 2-38, in Btus. The power output also must be converted to Btus. Begin by using the information calculated in paragraph 2-38b: Total power lnput = 940,000 Btus per hour. 1 hp hr = 2,445 Btus. 2-43
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The overall efficiency then is calculated by using the following procedures. a. Calculate the work output in Btus for 85 horsepower-hours by doing the following: 85hpx2445Btus = 207,825 Btus.
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CHAPTER 3 CONVENTIONAL ENGINE CONSTRUCTION Section I. 3-1. CYLINDER BLOCKS, HEADS, AND CRANKCASES contains the crankcase, cylinders, coolant passages, and, in the case of flathead engines, the valve seats, ports, and guides.
a. General (Fig. 3-1). The cylinder, or the engine block, is the basic foundation of virtually all liquid-cooled engines. The block is a solid casting made of cast iron or aluminum that
b. Construction. The cylinder block is a onepiece casting that is usually an iron alloy containing nickel and molybdenum. This is the best overall material for cylinder blocks. It provides excellent wearing qualities, low material and production costs, and it only changes dimensions minimally when heated. Another material that is used for cylinder blocks, although not extensively, is aluminum. Aluminum is used whenever weight is a consideration. It is not as practical to use for the following reasons:
(1) iron. (2) Aluminum is not as strong as cast iron. Aluminum is more expensive than cast
(3) Due to the softness of aluminum, it cannot be used on any surface of the block that is subject to wear. This necessitates the pressing, or casting, of steel sleeves into the cylinder bores. Threaded holes must be deeper, which introduces extra design considerations. All of these things increase production costs. (4) Aluminum has a much higher expansion rate than iron when heated. This creates problems with maintaining tolerances.
c. Cylinders (Fig. 3-2). The cylinders are bored right into the block. A good cylinder must be round, not varying in diameter by more than approximately 0.0005 in. (0.012 mm). The diameter of the cylinder also must be uniform for its entire length. d. Cylinder Sleeves (Fig. 3-3). Cylinder sleeves or liners commonly are used to provide a wearing surface other than the cylinder block for the pistons to ride against. This is important for the following reasons:
(1) Alloys of steel can be used that will wear longer than the surfaces of the cylinder block. TA233351
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(2) Providing a flange at the top of the block that locks the sleeve in place when the cylinder head is bolted into place. This is more desirable than a friction fit, because it locks the sleeve tightly. (3) Casting the sleeve into the cylinder wall. This is a popular means of securing the sleeve in an aluminum block. Whatever method is used to secure the sleeve, it is very important that the sleeve fits tightly. This is important so that the sleeve may transfer its heat effectively to the water jackets.
e. Crankcase (Fig. 3-4). The crankcase is the part of the cylinder block that supports and encloses the crankshaft. It is also where the engines lubricating oil is stored. The upper part of the crankcase usually is part of the cylinder block, while the lower part is removable. This removable lower part usually is called an oil pan, and is made of cast aluminum or pressed steel. f. Cooling and Lubrication (Fig. 3-1). The cylinder block also provides the foundation for the cooling and the lubrication systems. It provides the mountings for the pumps, and has the coolant and lubrication passages cast into it.
3-2.Cylinder Heads.
a. General (Fig. 3-5). The cylinder head is a separate one-piece casting that bolts to the top of the cylinders on an air-cooled engine, or to the top of the cylinder block on a liquid-cooled engine. b. Construction.
(1) The cylinder heads on liquid-cooled engines have been made almost exclusively from cast iron until recent years. Due to weight considerations that have become more Important, a large percentage of cylinder heads now are being made from aluminum. (2) The cylinder heads on air-cooled engines are made almost exclusively from aluminum. This is due to the fact that aluminum will conduct heat approximately three times as fast as cast iron. This is a critical consideration with air cooling. TA233352
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c. Combustion Chambers (Fig. 3-6). The cylinder head seals the end of the cylinder. This serves to provide a combustion chamber for the ignition of the mixture and to hold the expansive forces of the burning gases so that they may act on the piston. There is a threaded hole to position the spark plug in the combustion chamber on gasoline engines. On diesel engines there is a similar arrangement to position the fuel injector. d. Valves and Ports (Fig. 3-7). The cylinder head on overhead valve configurations supports the valves and has the ports cast into it. The cylinder head on overhead camshaft configurations also supports the camshaft. e. Cooling.
(1) Cylinder heads on air-cooled configurations (A, fig. 3-8) have fins cast into their outer surfaces. (2) Cylinder heads on liquid-cooled configurations (B, fig. 3-8) have passages for coolant flow cast into them.
f.
Sealing.
(1) Cylinder heads on air-cooled configurations (A, fig. 3-9) are sealed to the tops of the cylinders by soft metal rings. The lubrication system usually feeds oil to the heads through the push rods.
(2) Cylinder heads on liquid-cooled configurations (B, fig. 3-9) are sealed to the cylinder block by the head gasket. The head gasket usually is made of two sheets of soft steel that sandwich a layer of asbestos. Steel rings are used to line the cylinder openings. They are to hold the tremendous pressures created on the power stroke. Holes are cut in the gasket to mate the coolant and lubrication feed holes between the cylinder block and the cylinder head. 3-3. Cylinders - Air-Cooled Engines (Fig. 3-10). The cylinders on air-cooled engines are separate from the crankcase. They usually are made of forged steel. This material is most suitable for cylinders because of its excellent wearing qualities, and its ability to withstand the high temperatures that air-cooled cylinders do obtain. The cylinders have rows of deep fins cast into them to dissipate engine heat. The cylinders TA233354
3-4
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a. General (Fig. 3-11). The crankcase is the basic foundation of all air-cooled engines. It is made as a one- or two-piece casting that supports the crankshaft, provides the mounting surface for the cylinders and the oil pump, and has the lubrication passages cast into it.
b. Construction (Fig. 3-11). Crankcases in air-cooled engines are made of aluminum because it has the ability to dissipate large quantities of heat. There is usually a removable lower half to the crankcase that holds the reservoir of lubricating oil. It commonly is referred to as the oil pan. On air-cooled engines, the oil pan usually is cast aluminum. Its surface is covered with fins. The oil pan on an air-cooled engine plays a key role in the removal of waste heat from the engine through its lubricating oil.
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TM 9-8000 Section II. ROTATING AND RECIPROCATING PARTS 3-5. Piston. reason, it has been found that aluminum is the best material for piston construction. It has a very high strength-to-weight ratio. In addition to being lightweight, aluminum is an excellent conductor of heat and is machined easily. Pistons also are manufactured from cast iron. Cast iron also is an excellent material for pistons in lowspeed engines. It is not suitable for high speeds because it is a very heavy material.
a. General (Fig. 3-12). The piston is the part of the engine that receives the energy from the combustion and transmits it to the crankshaft. b. Requirements (Fig. 3-12). The piston must withstand incredible punishment under severe temperature extremes. The following are examples of conditions that a piston must withstand at normal highway speeds.
(1) As the piston moves from the top of the cylinder to the bottom (or vice versa), it accelerates from a stop to a speed of approximately 50 mph (80 km/h) at midpoint, and then decelerates to a stop again. It does this approximately 80 times per second. (2) The piston is subjected to pressures on its head in excess of 1000 psi (6895 kPa). (3) The piston head is subjected to temperatures well over 600F (3160C).
d. Controlling Expansion (Fig. 3-13). Pistons must have features built into them to help them control expansion. Without these features, pistons would fit loosely in the cylinders when cold, and then bind in the cylinders as they warm up. This is a problem with aluminum, because it expands so much. To control expansion, pistons may be designed with the following features:
(1) It is obvious that the crown of the piston will get hotter than the rest of the piston. To prevent it from expanding to a larger size than the rest of the piston, it is machined to a diameter that is approximately 0.03 to 0.04 in. (0.762 to 1.016 mm) smaller than the skirt area. (2) One of the ways to control expansion in the skirt area is to cut a slot up the side of the skirt. As a split-skirt piston warms up, the split will merely close up, thereby keeping the skirt from expanding outward and binding the piston in the cylinder. (3) Another variation of the split-skirt piston is the T-slot piston. The T-slot piston is similar to the split-skirt piston with the addition of a horizontal slot that retards heat transfer from the piston head to the piston skirt. (4) Some aluminum pistons have steel braces cast into them to control expansion.
c. Construction Materials. When designing pistons, weight is a major consideration. This is because of the tremendous inertial forces created by the rapid change in piston direction. For this
e. Cam Grinding (Fig. 3-14). By making the piston egg-shaped, it will be able to fit the cylinder better throughout its operational temperature range. A piston of this configuration is called a cam-ground piston. Cam-ground pistons are machined so that their diameter is smaller parallel to the piston pin axis than it is perpendicular to it. When the piston is cold, it will be big enough TA233358 Figure 3-12. Piston
3-8
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f. Partial-Skirted (Slipper-Skirt) Pistons (Fig. 3-15). The purpose of the piston skirt is to keep the piston from rocking in the cylinder. The slipper-skirt piston has large portions of its skirt removed in the non thrust areas. Removal of the skirt in these areas serves the following purposes:
g. Strength and-Structure (Fig. 3-16). When designing a piston, weight and strength are both
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h. Coatings. Pistons that are made from aluminum usually are treated on their outer surfaces to aid in engine break-in and increase
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c. Configurations. Piston rings are arranged on the pistons in three basic configurations. They are:
(1) The three-ring piston (A, fig. 3-19) that has two compression rings from the top, followed by one oil control ring. This is the most common piston ring configuration.
b. Description (Fig. 3-18). Piston rings are secured on the pistons by fitting Into grooves. They are split to allow for installation and expansion, and they exert an outward pressure on the cylinder wall when installed. They fit into grooves that are cut into the piston, and are allowed to float freely in these grooves. A properly formed piston ring, working in a cylinder that is within limits for roundness and size, will exert an even pressure and a solid contact with the cylinder wall around its entire circumference. There are two basic classifications of piston rings. (1) The Compression Ring. The compression ring seals the force of the exploding mixture into the combustion chamber.
(2) The Oil Control Ring. The oil control ring keeps the engines lubricating oil from getting Into the combustion chamber. 3-11
(2) The four-ring piston (B, fig. 3-19) that has three compression rings from the top, followed by one oil control ring. This configuration is common in diesel engines because they are more prone to blowby. This is due to the much higher pressures generated during the power stroke. (3) The four-ring piston (C, fig. 3-19) that has two compression rings from the top, followed by two oil control rings. The bottom oil control ring may be located above or below the piston pin. This is not a very common configuration in current engine design. TA233361
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d. Compression Ring. As stated in paragraph 3-6b, the purpose of the compression ring is to hold the pressure from the power stroke in the combustion chamber. There are many different cross sectional shapes of piston rings available (fig. 3-20).
The various shapes of rings all serve to preload the ring so that its lower edge presses against the cylinder wall. As shown in figure 3-21, this serves the following functions:
(1) The pressure from the power stroke will force the upper edge of the ring into contact with the cylinder wall, forming a good seal. (2) As the piston moves downward, the lower edge of the ring scrapes, from the cylinder walls, any oil that manages to work past the oil control rings. (3) On the compression and the exhaust strokes, the ring will glide over the oil, increasing its life.
e. Heat Dam (Fig. 3-22). There is an additional groove cut in the piston just above the top ring groove. The purpose of it is to divert some of the intense heat that is absorbed by the piston head away from the top ring. The groove Is called a heat dam. f. Ring Gap. The split in the piston ring is necessary for:
(1) Installing the ring on the piston.
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(2) The top compression ring is exposed directly to the high pressures of the compression stroke. To remedy the potential problem of premature top ring groove wear, some aluminum pistons are fitted with an insert in the top ring groove. The insert usually is made from nickel iron. Because of the better wear qualities, the ring groove will last longer than if the ring fit directly against the aluminum.
i. Oil Control Rings (Fig. 3-27). The oil control rings serve to control the lubrication of the cylinder walls. They do this by scraping the excess oil from the cylinder walls on the downstroke. The oil then is forced through slots in the piston ring and the piston ring groove. The oil then drains back into the crankcase. The rings are made in many different configurations that can be one-piece units or multipiece assemblies. Regardless of the configuration, all oil control rings work basically in the same way. j. Piston Ring Expanders (Fig. 3-28). Expander devices are used in some applications. These devices fit behind the piston ring and force it to fit tighter to the cylinder wall. They are particularly useful in engines where a high degree of cylinder wall wear exists. k. Piston Ring Wear-in (Fig. 3-29). When piston rings are new, a period of running is necessary to wear the piston rings a small amount so that they will conform perfectly to the cylinder walls. To make the job of wearing in the piston rings more effective and quicker, the following procedures are performed.
(1) The cylinder walls are surfaced with a tool called a hone. The hone leaves fine scratches in the cylinder walls. The piston rings are made with grooves in their faces. The grooved faces of the piston rings rubbing against the roughened cylinder walls serve to accelerate ring wear during the initial stages, and speed wear-in. As the surfaces wear smooth, the rings will be worn in. (2) Extreme pressure may be applied to high spots on the piston rings during the wear-in period. This can cause the piston rings to TA233363
The gap must be such that there is enough space so that the ends do not come together as the ring heats up. This would cause the ring to break. This is illustrated in figure 3-23. There are a few variations of ring gap joints (fig. 3-24). Two cycle engines usually have pins in their ring grooves to keep the gap from turning. This is important because the ring would break if the ends were allowed to snap into the inlet or the exhaust ports.
g. Second Compression Ring (Fig. 3-25). The primary reason for using a second compression ring is to hold back any blowby that may have occurred at the top ring. A significant amount of the total blowby at the top ring will be from the ring gap. For this reason, the top and the second compression rings are assembled to the piston with their gaps 60 degrees offset with the first ring gaps. h. Top Ring Groove Insert (Fig. 3-26). The top ring groove is very vulnerable to wear for the following reasons:
(1) It is close to the piston head, subjecting it to intense heat.
3-13
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TM 9-8000 to provide the desired wearing qualities. At the same time, the piston pin must not be brittle. To satisfy the overall requirements of a piston pin, it was found that
c.
a casehardened steel pin is best. Casehardening is a process that hardens the surface of the steel to any desired depth. The pin is also made hollow to reduce the overall weight of the reciprocating mass.
c. Configurations. The following are the bushing. Figure 3-26. Top Ring Groove Insert.
3-7. Piston Pins. (2) A semifloating pin (B, fig. 3-32) is locked to the connecting rod by a screw or friction. The pin pivots freely in the piston pin bosses. (3) The full-floating piston pins (C, fig. 3-32) pivot freely in the connecting rod and the piston pin bosses. The outer ends of the piston pins are fitted with lockrings to keep the pin from sliding out and contacting the cylinder walls.
a. General (Fig. 3-30). The piston pin serves to connect the piston to the connecting rod. It passes through the pin bosses in the piston and the upper end of the connecting rod. b. Construction (Fig. 3-31). A piston pin must be hard
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3-9. Crankshaft.
a. General (Fig. 3-34). The crankshaft is the part of the engine that transforms the reciprocating motion of the pistons to rotating motion. b. Construction (Fig. 3-34). Crankshafts are made from forged or cast steel. The forged steel unit is the stronger of the two. It usually is reserved for commercial and military use. The cast unit is used primarily in light and regular duty gasoline engines. After the rough forging or casting is produced, it becomes a finished product by going through the following steps:
(1)All surfaces are rough machined. (2)All holes are located and drilled.
Connecting Rods.
a. General (Fig. 3-33). The connecting rods connect the pistons to the crankshaft. They must be extremely strong to transmit the thrust of the pistons to the crankshaft, and to withstand the Inertial forces of the directional changes of the pistons. b. Construction (Fig. 3-33). The connecting rods are normally in the form of an I-beam. This design gives the highest overall strength and lowest weight. They usually are made of forged steel, but may be made of aluminum in small engines. The upper end attaches to the piston pin, which connects it to the piston. The lower end is attached to the crankshaft. The lower bearing hole in the connecting rod is split so that it may be clamped to the crankshaft. Because the lower end has much greater movement than the upper, the hole is much larger. This provides much greater bearing surface. Figure 3-29. Piston Ring Wear-In.
3-17
TM 9-8000 operation. For the various engine configurations, typical throws are arranged as follows: (1) In-line four-cylinder engines have throws one and four offset 180 degrees from throws two and three. (2) V-type engines have two cylinders operating off of each throw. The two end throws are on one plane offset 180 degrees apart. The two center throws are on another common plane. They are also offset 180 degrees apart. The two planes are offset 90 degrees from each other. (3) In-line six-cylinder engines have their throws arranged on three planes. There are two throws on each plane that are in line with each other. The three planes are arranged 120 degrees apart. (4) V-type 12-cylinder engines have throw arrangements like the in-line six-cylinder engines. The difference is that each throw accepts two-engine cylinders.
Figure 3-30. Piston Pin. (3) The crankshaft, with the exception of the bearing journals, is plated with a light coating of copper.
(4) The bearing journals are case- hardened. (5) The bearing journals are ground to size. (6) Threads are cut into necessary bolt holes.
(5) V-type six-cylinder engines have three throws at 120-degree intervals. Each throw accepts two-engine cylinders.
d. Crankshaft Vibration. A crankshaft is very prone to vibration because of its shape, extreme weight, and the tremendous forces acting on it. The following are three basic areas that are of concern when considering vibration in crankshaft design.
(1) Vibration Due to Imbalance (Fig. 3-36). An inherent problem with a crankshaft is
c. Throw Arrangements (Fig. 3-35). The arrangement of the throws on the crankshaft determines the firing order of the engine. The position of the throws for each cylinder arrangement is paramount to the overall smoothness of
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(2) Vibration Due to Deflection. The crankshaft will have a tendency to bend slightly when subjected to the tremendous thrust from the piston. This deflection of the rotating member will cause a vibration. This vibration is minimized by
(3) Torsional Vibration (Fig. 3-37). Torsional vibration occurs when the crankshaft twists because of the power stroke thrusts. It Is particularly noticeable on engines with long crankshafts, such as In-line engines. It is a major reason why in-line, eight-cylinder engines are no longer produced. The vibration is caused by the cylin- ders furthest from the crankshaft output. As these cylinders apply thrust to the crankshaft, it twists, and as the thrust decreases, the crankshaft unwinds. The twisting and unwinding of the crankshaft produces a vibration. The use of a
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c. Materials (Fig. 3-41). Most bearings begin with a steel backing to give them rigidity. The lining then is applied to the steel backing. The lining usually consists of an alloy of copper, tin, and lead. The lining also may be made of babbit. Babbit is a popular bearing material that is an alloy consisting of copper, tin, and antimony. The lining thickness usually ranges from 0.002 to0.005 in. (0.051 to 0.127 mm). The bearing then is coated with either aluminum or tin to a thickness of approximately 0.001 in. (0.025 mm). d. Bearing Requirements (Fig. 3-42). Bearings must be able to support the crankshaft rotation and deliver powerstroke thrusts under the most adverse conditions. A good bearing must have the following qualities.
(1) Strength. Engine bearings are constantly subjected to tremendous forces from the thrust of the power strokes. The bearings must be able to withstand these loads without spreading out or cracking. (2) Corrosion. The bearing must be resistant to moisture and acids that always are present in the crankcase. TA233370
e. Lubrication (Fig. 3-38). The crankshaft has internal drilled passages to supply lubrication to its bearings.
3-10. Crankshaft Bearings.
a. General (Fig. 3-39). The crankshaft is supported in the crankcase and rotates in the main bearings. The connecting rods are sup- ported on the crankshaft by the rod bearings. b. Construction (Fig. 3-40). Crankshaft bearings are made as precision inserts. They simply slip into place in the upper and lower halves
3-20
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TM 9-8000 f. Crankshaft Main Bearings (Fig. 3-44). The upper halves of the main bearings fit right into the crankcase, and the lower halves fit into the caps that hold the crankshaft in place. The main bearings have holes drilled in their upper halves through which a supply of oil is fed to them. The crankshaft has holes drilled in the journals that receive oil from the main bearings to feed the rod bearings. It is a common practice to cut a groove In the center of the main bearing Inserts. This supplies a more constant supply of oil to the connecting rod bearings. One of the main bear- Ings also serves as a thrust bearing. This controls back and forth movement of the crankshaft. This thrust bearing Is characterized by side flanges. 3-11. Flywheel(Fig.3-45).
Figure 3-36. Crankshaft Counterweights. (3) Antiscuffing. The bearing surface should be able to absorb enough oil to keep It from scuffing during startup, or any other time when It must run momentarily without an oil supply.
(4) Embedabillty. The surface of the bearing must be soft enough to allow particles of foreign matter to embed themselves and prevent damage of the shaft journal. (5) Conformability. The bearing must be able to conform or fit itself to the surface of the crankshaft Journal. (6) Conductivity. The bearings must be able to conduct heat to the connecting rod so that they will not overheat.
a. General. The flywheel stores energy from the power strokes, and smoothly delivers it to the drive train of the vehicle. It mounts on the end of the crankshaft, between the engine and the transmission. b. Manual Transmission. When the vehicle Is equipped with a manual transmission, the fly- wheel serves to mount the clutch. c. Automatic Transmission. When the vehicle Is equipped with an automatic transmission, the flywheel serves to support the front of the torque converter. On some configurations, the flywheel is combined with the torque converter. d. Starter Ring Gear. The outer edge of the flywheel Is lined with gear teeth. They are to engage the drive gear on the starter motor. e. Construction. The flywheel on large, low- speed engines usually Is made of cast iron. This Is desirable due to the heavy weight of the cast Iron, which helps the engine maintain a steady speed. Small, high-speed engines usually use a forged steel or forged aluminum flywheel for the following reasons.
(1) The cast iron is too heavy, giving it too much inertia to allow the speed variations necessary on small engines. (2) Cast iron, because of its weight, will pull itself apart at high speeds due to centrifugal force. TA233372
(7) Resistance to Heat. The bearing must be able to maintain all of these characteristics throughout its entire operating temperature range. e. Connecting Rod Lubrication (Fig. 3-43). The connecting rod bearings fit into the lower end of the connecting rod. They are fed a constant supply of oil through a hole In the crankshaft Journal. A hole In the upper bearing half feeds a passage In the connecting rod to provide oil to the piston pin.
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3-24
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3-26
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a. General (Fig. 3-46). Each cylinder in a four-stroke cycle engine must have one intake and one exhaust valve. The valves that are commonly used are of the poppet design. The word poppet is derived from the popping action of the valve. Poppet-type valves are made in the following three basic shapes: the mushroom, semitulip, and tulip. The valve shape that is used in a given engine is dependent upon the requirements and combustion chamber shape. b. Construction. Construction and design considerations are very different between intake and exhaust valves. The difference is based on their temperature operating ranges. Intake valves are kept cool by the incoming Intake mixture. Exhaust valves are subject to intense heat from the burnt gases that pass by it. The temperature of the exhaust valve can be in excess of 13000F (704.40C). Intake valves are made of a nickel chromium alloy. Exhaust valves are made of a silichrome alloy. In certain heavy-duty water- cooled and most aircooled engines, the exhaust valves are hollowed out and filled partially with metallic sodium (B, fig. 3-47). The sodium, which liquefies at operating temperatures, splashes between the valve head, where it picks up heat, and the valve stem, where the heat is transferred to the valve guide. Some exhaust valves use a special hard facing process (A, fig. 3-47) that keeps the face of the valve from taking on the shape of the valve seat at high temperatures.
c. Valve Seats (Fig. 3-48). valve seats are very important, as they must match the face of the valve head to form a perfect seal. The seats are made so that they are concentric with the valve guides; that is, the surface of the seat is an equal distance from the center of the guide all around. There are two common angles that are used when machining the valve seat; they are 30 and 45 degrees. The face of the valve is usually ground with a one-half to a 1-degree difference to help the parts seat quickly. In some cases, a small portion of the valve seat has an additional 15- degree angle ground into it to narrow the contact area of the valve face and seat. By reducing the contact area, the pressure between the mating parts is increased, thereby forming a better seal. The valve seats can be either part of the cylinder head or separate inserts. Valve seat inserts generally are held into the head by an interference fit.
The head is heated in an oven to a uniform high temperature and the seat insert is shrunk by cooling it in dry ice. While the two parts are at opposite temperature extremes, the seat insert is pressed into place.
d. Valve Guides (Fig. 3-49). The valve guides are the parts that support the valves in the head. They are machined to a fit of a few thousandths of an inch clearance with the valve stem. This close clearance is important for the following reasons:
(1) It keeps the lubricating oil from getting
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Integrally with the head, or they may be removable. Removable valve guides usually are press fit into the head.
e. Valve Springs, Retainers, and Seals (Fig. 3-50). The valve assembly is completed
by the spring, retainer, and seal. Before the spring and the retainer fit into place, a seal is placed over the valve stem. The seal acts like an umbrella to keep the valve operating mechanism oil from running down the valve stem and into the combustion chamber. The spring, which keeps the valve in a normally closed position, is held in place by the retainer. The retainer locks onto the valve stem with two wedged-shaped parts that are called valve keepers.
f. Valve Rotators. It Is common in heavy-duty applications to use mechanisms that make the exhaust valves rotate. The purpose is to keep carbon from building up between the valve face and seat, which could hold the valve partially open, causing it to burn. The release-type rotator (A, fig. 3-51) releases the spring tension from the valve while open. The valve then will rotate from engine vibration. The positive rotator (B, fig. 3-51) is a two-piece valve retainer with a
REMOVABLE VALVE SEAT
TIM 9-8000 tappets or the lifters are the connecting link between the camshaft and the valve mechanism.
b. Camshaft Construction. Camshafts usually are made from cast or forged steel. The surfaces of the lobes are hardened for long life. c. Camshaft Support (Fig. 3-52). The cam-shaft is supported, and rotates, in a series of bearings along its length. The bearings usually are pressed into their mountings and made of the same basic construction as crankshaft bearings. In some cases, when the engine is constructed of aluminum, the camshaft is supported directly in its mountings and no bearings are used. The thrust, or the back and forth movement, usually is taken up by the thrust plate, which bolts to the front of the engine block. Any forward thrust loads are then taken up by the front camshaft bearing journal. The drive gear or sprocket then is bolted to the front of the camshaft. Its rear surface rides against the thrust plate to take up any rearward thrust. d. Driving the Camshaft. The following are the three basic configurations for driving the cam-shaft. (1) Gear Drive (A, Fig. 3-53). A gear on the crankshaft meshes directly with another gear on the camshaft. The gear on the crankshaft usually is made of steel, while the gear on the camshaft may be steel for heavy-duty applications, or it may be made of aluminum or pressed fiber when quiet operation is a major consideration. The gears are helical in design (para 19-4). Helical gears are used because they are stronger, and they also tend to push the camshaft rearward during operation to help control thrust. (2) Chain Drive (B, Fig. 3-53). Sprockets on the camshaft and the crankshaft are linked by a continuous chain. The sprocket on the crankshaft usually is made of steel, while the sprocket on the camshaft may be steel for heavy-duty applications. When quiet operation is a major consideration, an aluminum sprocket with a nylon covering on the teeth is used. There are two common types of timing chains. One is a silent link-type chain that is used in standard and light-duty applications. The other is the roller-link chain, which is used in heavy-duty applications. The TA233379
a. General. The camshaft provides for the opening and closing of the engine valves. The
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(3) Belt Drive (C, Fig. 3-53). Sprockets on the crankshaft and the camshaft are linked by a continuous neoprene belt. The belt has square-shaped Internal teeth that mesh with teeth on the sprockets. The timing belt is reinforced with nylon or fiberglass to give It strength and prevent stretching. This drive configuration Is limited to overhead camshaft engines.
e. Timing Belt and Chain Tensioners (Fig. 3-53). Most engines with chain-driven and all engines with beltdriven camshafts employ a tensioner. The tensioner pushes against the belt or chain to keep It tight. This serves to keep It from
f.
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h. Tappets. Tappets (or lifters) are used to link the camshaft to the valve mechanism. The bottom surface Is hardened and machined to be compatible with the surface of the camshaft lobe. The following are the two basic lifter classifications: (1)Mechanical Tappets (Fig. 3-55). Mechanical (or solid) lifters are simply barrel-shaped pieces of metal. When used In flathead engines, they have an adjusting screw mechanism to set the clearance between the tappets and the valve stems. Mechanical tappets may also come with a wider bottom surface. These are called mushroom tappets. Another variation Is the roller tappet, which has a roller contacting the camshaft. They are used mostly In heavy-duty applications to reduce component wear. (2)Hydraulic Tappets (Fig. 3-56). The hydraulic tappet Is very popular In overhead valve engines. It uses oil under pressure to automatIcally maintain zero clearance In the valve mechanism. The lifter body, which contacts the camshaft lobe, Is hollow. Inside the lifter body, there Is a plunger that operates the valve mechanism. Injecting oil into the cavity under the TA233381
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i. Camshaft-to-Tappet Relationship (Fig.3-57). The face of the tappet and the lobe of the camshaft are designed so that the tappet will be made to rotate during operation. The cam lobe is machined with a slight taper that mates with a crowned lifter face. The camshaft lobe does not meet the tappet in the center of its face. Using this
a. General. The valves in overhead valve and overhead camshaft engines use additional components to link the camshaft to the valves. Overhead valve engines use push rods and rocker arms. Overhead camshaft engines use various configurations of rocker arms. b. Push Rods (Fig. 3-58). Push rods usually are constructed of hollow steel. Most air-cooled engines use the push rods to supply lubricant to the upper valve mechanism. c. Rocker Arms (Fig. 3-59). Rocker arms are manufactured of steel, aluminum, or cast iron. The most common for current use are the stamped steel variety. They are lightweight, strong, and cheap to manufacture. They usually pivot on a stud and ball, though some engines use a shaft arrangement. Cast iron rockers are used TA233382
3-32
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d. Adjusting Clearance (Fig. 3-60). The provision for adjusting valve clearance on solid-
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clearance is adjusted by putting selective shims between the cam lobe and the lifter. Various thicknesses of the shims are used to obtain the desired clearances.
TM 9-8000
TM 9-8000 CHAPTER 4 GASOLINE FUEL SYSTEMS Section I. COMPONENTS AND THEIR PURPOSES
4-1. Fuel Tanks.
a. Purpose. The fuel tank is for storage of gasoline in liquid form. b.Location (Fig. 4-1). The location of the fuel tank is dependent on utilizing an area that is protected from flying debris, shielded from collision damage, and one that is not subject to bottoming. A fuel tank can be located just about anywhere in the vehicle that meets these requirements. c. Construction. Fuel tanks take many forms in military vehicles such as those described below.
(1)The removable fuel tank (fig. 4-2) is most commonly used in wheeled vehicles. The most common material for fuel tanks is thin sheet metal that is coated with a lead-tin alloy to prevent corrosion. Because corrosion is of major concern, fiberglass and a variety of molded plastics are also popular for the manufacture of fuel tanks. The walls of the tank are manufactured with ridges
to give them strength. Internal baffles are in-stalled in the tank to prevent the fuel from sloshing and to increase overall strength. Some tanks are made with a double wall with a layer of latex rubber in between. The purpose of the wall is to make the tank self-sealing. (2)The fuel cell (fig. 4-3) is a compartment that is integral with the body or the hull of the vehicle. Fuel cells can be located anywhere that there is an empty space. They are used in vehicles that require large fuel storage capacity. A fuel cell can take advantage of hollow areas of the vehicle where use of a removable fuel tank would be impractical. Fuel cells are suited particularly for combat situations because they may be located in areas that provide a maximum of shielding. (3)The bladder-type fuel cell (fig. 4-4) is much the same as a fuel cell, except for the addition of a flexible liner. The liner serves to seal the cell much like an inner tube seals a tire.
d. Filler Pipe (Fig. 4-2). A pipe is provided for filling the tank or cell that is designed to prevent
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e. Fuel Outlet (Fig. 4-2). The outlet pipe is located approximately In. (1.27 cm) above the bottom of the fuel tank or cell. This location Is ideal to allow sediment to fall to the bottom of the tank or cell without it being drawn into the fuel system. f. Fuel Gage Provision (Fig. 4-2). A provision usually is made to install a fuel gage. This provision usually is In the form of a flanged hole. g. Drainplug (Fig. 4-2). A threaded drain-plug usually is provided at the bottom of the tank for draining and cleaning.
4-2. Fuel Filters.
A. Purpose. The fuel filter traps foreign material that may be present in the fuel and preventing it from entering the carburetor or sensitive fuel Injection components. b. Location (Fig. 4-5). There Is at least one fuel filter used in the fuel system. A fuel filter can be located in any accessible place along the fuel delivery line. Filters also can be located inside fuel tanks, carburetors, and fuel pumps.
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(2) In-line Filter Elements that Fit In the Carburetor Inlet or Inside the Fuel Tank on the
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Outlet (B, Fig. 4-7). These filters are replaceable at intervals and contain no sediment bowls. (3) Glass Bowl Filter with Replaceable Element (C, Fig. 4-7). The sediment bowl must be washed out whenever the element is replaced. Some fuel pumps have a glass bowl-type gas filter built in. e. Element Configurations (Fig. 4-8). Filter elements are made from ceramic, treated paper, sintered bronze, or metal screen. There is one filter element that differs from the others. It consists of a pile of laminated disks that are spaced 0.0003 in. (0.0076 mm) apart. As the gasoline passes between the disks, foreign matter is blocked out.
4-3. Fuel Pumps.
b. General The mechanical-type fuel pump generally is the most popular for gasoline engine applications. It usually is more than adequate and is much cheaper than an electric pump. The electric pump is more desirable though, for the following reasons.
(1) The electric pump will supply fuel to the engine immediately when the ignition key is turned on. The engine must be turning with the starter for a mechanical pump to operate. (2) The pump, by design, will operate more efficiently if it pushes the fuel rather than pulling it. An electric pump can be mounted close to the tank, or in the tank, to take advantage of this characteristic. (3) The electric pump can be mounted away from heat to reduce the possibility of vapor lock (para4-37). c. Mechanical, Nonpositive Type (Fig. 4-9). This is currently the most popular configuration of an automotive fuel pump. Operation is as follows:
a. Purpose. The fuel pump delivers gasoline from the fuel tank to the engine. Early automotive equipment utilized gravity to feed gasoline to the engine. This Is no longer practical because it limits the location of the fuel tank to positions that are above the engine.
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(4) As the rocker arm pulls the diaphragm down, the inlet check valve is unseated and fuel is drawn into the pump chamber. The outlet check valve seals the outlet passage. (5) As the diaphragm spring pushes the diaphragm back up, the inlet check valve seals the inlet and the fuel in the pump chamber is pushed through the unseated outlet check valve and through the pump outlet. (6) The action is repeated each time the rocker arm operates the diaphragm. (7) Pressure will build in the fuel line and the pump chamber as the fuel pump fills the carburetor bowl. As the pressure rises to the desired level in the pump chamber, it will hold the diaphragm down against the pressure of the diaphragm spring. The rocker arm will move up and down in the slotted pull rod. There will be no pumping action until the fuel line pressure again drops below the desired level. In this way, the
d. Mechanical, Positive Type (Fig. 4-10). The positive-type mechanical pump operates in the same manner as the nonpositive type. The difference is that the diaphragm pull rod is solidly linked to the rocker arm. The pump, therefore, will not regulate fuel line pressure. When this type of pump is used, a separate fuel pressure regulation device must be used that will bypass excess fuel back to the fuel tank.
e. Double Action Fuel Pump (Fig. 4-11). Vehicles that use vacuum-operated windshield wipers often will utilize a supply pump that is built Into the fuel pump. The pump serves to operate the windshield wipers during periods of high engine load when manifold vacuum is low (para 17-14). The pump operates from the same TA233390
4-5
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the armature down and repeat the pumping process. (1) As electric current is fed to the pump, the electromagnetic coil pulls the armature down, expanding the bellows. (2) The expansion of the bellows causes fuel to be drawn In through the inlet valve. (3) As the bellows are fully expanded, a pair of contact points are open, switching off the electromagnet. (4) The return spring pushes the armature back up, contracting the bellows. This action pushes the fuel out of the pump through the outlet valve. (5) The contact points are closed as the bellows are fully contracted. This causes the electromagnet to pull (6) The pump will stop when the fuel pressure is high enough to hold the bellows expanded against the return spring. The operating pressure of the pump Is determined by the return spring pressure.
g. Electric, Vane-Type (Fig. 4-13). The 48 vane-type electric fuel pump operates by the same principles as the pump described in paragraph 20-6. It is driven by an electric motor.
4-4. Fuel Tank Ventilation Systems.
a. Purpose. The fuel tank needs a ventilation system to keep the pressure within it equal to
4-8
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atmospheric pressure. This is important for the following reasons: (1) Air must be allowed to enter the tank as the fuel is pumped out. Without ventilation of the tank, the pressure in the tank would drop to the point where the fuel pump would not be able to draw any more fuel from it. In some cases, the higher pressure around the outside of the tank could cause it to collapse. (2) Temperature changes cause the fuel in the tank to expand and contract. Absence of a ventilation system could cause excessive or insufficient fuel line pressure.
(1) Deliver the mixture to the cylinders in equal quantities and proportions. This is important for smooth engine performance. The lengths of the passages should be as near to equal as possible to distribute the mixture equally. (2) Help to keep the vaporized mixture from condensing before it reaches the combustion chamber. Because the ideal mixture should be vaporized completely as it enters the combustion chamber, this is very important. To reduce the condensing of the mixture, the manifold passages should be designed with smooth walls and a minimum of bends that collect fuel. Smooth flowing intake manifold passages also increase volumetric efficiency (para 2-23). (3) Aid in the vaporization of the mixture. To do this, the intake manifold should provide a controlled system of heating (para 7-3). This system of heating must heat the mixture enough to aid in vaporization without heating to the point of significantly reducing volumetric efficiency (para 2-23).
(2) By providing a line to the fuel tank that vents the fuel tank at a point that is high enough to prevent water from entering during fording operations. (3) Vehicles that are subject to emission control regulations have fuel tank ventilation systems that work in conjunction with the evaporation control system. This system is discussed in paragraph 7-5. 45. Intake Manifold.
b. Ram Induction (Fig. 4-15). Intake manifolds can be designed to provide optimum performance for a given engine speed range by varying the length of the passages. The inertia of the moving intake mixture will cause it to bounce back and forth in the manifold passage from the end of one intake stroke to the beginning of the next intake stroke. If the passage is the proper length so that the next intake stroke is just beginning as the mixture is rebounding, the inertia of the rnixture will cause it to ram itself into the cylinder. This will increase the volumetric efficiency of the engine In the designated speed range. It should be noted that the ram manifold
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will serve no useful purpose outside of its designated speed range. c. Heating the Mixture. As stated in paragraph 45a(3), providing controlled heat for the In coming mixture Is very Important for good performance. The heating of the mixture may be accomplished by doing one or both of the following: (1) Directing a portion of the exhaust through a passage In the intake manifold (fig.4-16). The heat from the exhaust will transfer and heat the mixture. The amount of exhaust that Is diverted Into the Intake manifold heat passage Is
controlled by the manifold heat control valve. operation is covered In paragraph 7-3.
Its
(2) Directing the engine coolant, which Is laden with engine heat, through the intake manifold on Its way to the radiator (fig. 4-17). 4-6. Air Filters. a. Purpose (Fig. 4-18). The air filter fits over the engine air Intake to filter out any foreign matter. Any foreign matter that enters the Intake will act as an abrasive between the cylinder walls and the pistons, greatly shortening engine life. The two types of filters currently In use are the wet and dry type. b. Wet Type (Fig. 4-19). The wet-type, or the oil bath, air filter consists of the main body, the filter element that is made of woven copper gauze, and the cover. Operation is as follows: The incoming air enters between the cover and the main body. It is pulled down to the bottom of the main body, where it must make a 180-degree turn as it passes over the oil reservoir. As the air passes over the oil reservoir, most of the particles will not be able to make the turn, they will hit the oil and be trapped. As the air continues upward and passes through the filter element, the smaller particles that bypassed the oil will be trapped. The air keeps the filter element soaked with oil by creating a fine spray as it passes the reservoir. The air then makes another 180-degree turn and enters the carburetor. TA233396 4-10
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c. Dry Type (Fig. 4-20). The dry-type air filter passes the Incoming air through a filtering medium before it enters the engine. The filtering medium consists of oil-soaked copper mesh or replaceable pleated paper, the latter being the most common.
4-7. Carburetor. The carburetor will be discussed, system by system, In paragraphs 4-13 thru 4-24. It serves the following basic functions:
a. The carburetor mixes fuel and air Into the correct proportions for the most efficient use by the engine. The carburetor also must constantly vary the mixture proportions to meet the engines needs as Its speed and load requirements vary. b. The carburetor regulates engine speed and power output. c. The carburetor atomizes the fuel as it mixes it with the air (para 4-9e).
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4-8. Composition of Air. Air is composed of various gases, mostly nitrogen and oxygen (78 percent nitrogen and 21 percent oxygen by volume). These gases, as are all substances, are made of tiny particles called molecules. In the air surrounding the earth, as In all gases, the molecules are able to move quite freely in relation to each other. The molecules of air are attracted to the earth by gravity, creating the atmosphere (para 222a). The weight of the air molecules creates atmospheric pressure (para 2-22b). 4-9. Evaporation. Evaporation is the changing of a liquid to a vapor. The molecules of the liquid, not being closely tied together, are constantly moving about among themselves. Any molecule that moves upward with sufficient speed will jump out of the liquid and into the air. This process will cause the liquid to evaporate over a period of time. The rate of evaporation is dependent on the following:
c. Closed Chamber. As evaporation takes place in a closed container, the space above the liquid will reach a point of saturation. When this happens, every molecule of liquid that enters the air will cause another airborne molecule of liquid to fall back. d. Volatility. The term volatility refers to how fast a liquid vaporizes. Some liquids vaporize easily at room temperature. Alcohol, for instance, vaporizes more easily than water. A highly volatile liquid is one that is considered to evaporate easily. e. Atomization (Fig. 4-21). Atomization is the process of breaking up a liquid into tiny globules or droplets. When a liquid is atomized, the droplets are all exposed individually to the air. For this reason, atomization greatly increases evaporation by increasing the exposed surface area of the liquid.
4-10. Venturi Effect (Fig. 4-22). Venturi effect is used by the carburetor to mix gasoline with air. The basic carburetor has an hourglass-shaped tube called a throat. The most constricted part of the throat is called the venturi. A tube called a discharge nozzle Is positioned in the venturi. The discharge nozzle is connected to a reservoir of gasoline called the float bowl. The negative pressure that exists in the combustion chamber because of the downward intake stroke of the piston causes atmospheric pressure to create an airflow through the carburetor throat. This airflow must Increase temporarily in speed as it passes through the venturi, due to its decreased size. TA233398 4-13
a. Temperature. The rate of movement of the molecules Increases with temperature. Because of this, the amount of molecules leaving the liquid for a given time will increase as the temperature Increases. b. Atmospheric Pressure. As atmospheric pressure Increases, the amount of air molecules present over the liquid also increases. The Increased presence of air molecules will slow the rate of evaporation. This is because the molecules of liquid will have more air molecules to collide with. In many cases, they will fall back into the liquid after collision.
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Section III CONSTRUCTION OF THE BASIC CARBURETOR 4-13. Throttle Valve (Fig. 4-25). The throttle valve is used to regulate the speed and power output of the engine. It is controlled by the accelerator pedal, and usually consists of a flat, round plate that tilts with the throttle shaft. As the accelerator pedal is fully depressed, the throttle valve is moved from a position of completely restricting the throat to being completely open. The idle stop screw is used to keep the throttle valve open slightly so that the engine may run at a regulated idle speed with no foot pressure on the accelerator. This screw may be turned in or out to regulate engine idle speed. 4-14. Float Circuit.
a. Purpose. The float circuit maintains a steady working supply of gasoline at a constant level in the carburetor. This is very critical to proper engine performance. An excessively high float level will cause fuel to flow too freely from the discharge tube, causing an overly rich mixture; whereas an excessively low float level will cause an overly lean mixture.
4-3,
b. Operation (Fig. 4-26). As explained in paragraph the fuel pump delivers gasoline to
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c. Venting (Fig. 4-27). The pressure in the float bowl must be regulated to assure the proper delivery of fuel and purging of vapors. The following systems and devices are added to the float circuit system to provide for these needs. (1) Balance Tube. Due to the restriction imposed by the air filter and changing air velocities because of varying engine speeds, the air pressure in the air horn is usually lower than atmospheric pressure. The pressure in the float bowl must equal that of the air horn in order for the carburetor to provide fuel delivery. A tube called a balance tube is run between the air horn and the float bowl to accomplish this task.
it
(2) Idle Vent. Because gasoline Is highly volatile, can create overly rich mixtures during
TM 9-8000 long periods of engine idle. This is because the fuel begins to evaporate in the float bowl and the vapors get into the air horn through the balance tube. The solution to this problem is to have an outside vent for the float bowl that is opened whenever the enigine is idling. The idle vent is activated by linkage from the throttle valve. The idle vent system on later vehicles may be part of the emission control system (para 7-11).
Section IV. SYSTEMS OF THE CARBURETOR 4-15. General. The two operating systems of the carburetor each contain two circuits that give them the flexibility to operate throughout the entire engine speed range. Both of these systems obtain gasoline from the float bowl through the main jet (fig. 4-28). The main jet is a precisely sized opening that helps govern the amount of fuel used. The main jet usually is replaceable and is available in a variety of sizes. Carburetors can be tailored to meet various needs by varying jet sizes. In addition to the above, the carburetor must provide other systems to compensate for temperature change and for quick changes in throttle position. 4-16. Idle and Low-Speed System. idle. As the throttle begins to open, the effectiveness of the idle circuit falls off gradually as the low-speed circuit takes over. The transition between the two circuits is a smooth one. Operation from engine idle through lowspeed range is as follows: (1) The throttle valve is almost closed at engine idle. This creates a high vacuum in the area of the carburetor under the throttle valve. This high vacuum causes atmospheric pressure to push gasoline through the idle port from the float bowl. The gasoline mixes with the air that is drawn in around the throttle valve. The mixture then is drawn into the engine. (2) As the throttle valve is opened, the vacuum under it begins to fall off, causing less gasoline to be drawn from the idle port. As more air flows through the throat, the gasoline will begin flowing through the low speed or off-idle discharge port, which is usually in the shape of a rectangular slot or a series of two or three holes. During the low-speed system operation, there is still not enough airflow through the throat for the discharge nozzle to work.
a. Purpose. The idle and low-speed system provides the proper air-fuel mixture when the engine is at idle and during periods of small throttle opening. During these periods, there is not enough air flowing through the throat to make the discharge nozzle work. b. Operation (Fig. 4-29). The idle and the low-speed portions of the system are really separate circuits in operation. The idle circuit sustains the engine at an
TM 9-8000
Figure 4-29. Idle and Low-Speed Systems. c. Idle Mixture Screw (Fig. 4-29). A needle- shaped screw Is used in the carburetor to regulate the Idle port opening. The air-fuel ratio of the Idle system can be adjusted by turning the screw In or out. d. Air Bleeds (Fig. 4-29). Air bleeds also are used in the idle and low-speed circuits to help atomize the fuel. e. Passage to Float Bowl (Fig. 4-29). The passage that supplies the Idle and low-speed circuits must at some point be higher than the level of the gasoline In the float bowl. If this passage went straight to the Idle and low-speed ports, the float bowl would be able to drain through them.
4-17. High-Speed and High-Speed Enrichment Circuits. discharge nozzle, where It mixes with the air In the venturi. Opening the throttle valve and accelerating engine speed Increases the airflow in the venturi, which causes a proportional increase in the amount of gasoline from the discharge nozzle. The high-speed enrichment system Increases the fuel flow to the discharge nozzle by either Increasing the main jet opening or providing a second supply of fuel from the float bowl. There are three basic high-speed enrichment systems that are covered In para- graphs 4-17c, d, and e.
a. Purpose. The high-speed circuit supplies the fuel-air mixture to the engine during medium to full throttle valve opening. The high-speed circuit gradually will take over from the low-speed circuit as the throttle Is depressed. The carburetor Is designed to provide approximately a 15:1 to 17:1 air-fuel ratio under normal steady speed conditions. The high-speed enrichment circuit will enrich the mixture to approximately 11:1 to 12:1 if a heavy demand is placed on the engine. b. Operation (Fig. 4-30). The high-speed circuit takes Its gasoline from the float bowl through the main jet. The gasoline is fed through a passageway to the
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c. Power Jet (Flg. 4-31). The power Jet system Includes a Jet that Is opened by a vacuum- operated piston. The Jet provides an extra supply of fuel to the discharge nozzle from the float bowl. When the throttle valve Is not opened wide, there will be high manifold vacuum because the carburetor throat is restricted. This high manifold vacuum Is used to hold the vacuum piston against its spring. When the piston is up, the spring in the power jet will hold it closed. The throttle valve is opened when extra power is demanded, causing a drop in manifold vacuum. As manifold vacuum drops, the spring on the vacuum piston pushes the piston down, which in turn pushes the power valve open. The power jet sometimes is referred to as the economizer and the vacuum piston is referred to as the step-up or power piston. d. Vacuum-Operated Metering Rod (Fig. 4-32). The vacuum-operated metering rod uses a rod with a diameter that gets progressively TA233403
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e. Mechanically Operated Metering Rod (Fig 4-33). The mechanically operated metering rod works the
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a. Purpose. When the throttle valve Is suddenly opened, there is a corresponding sudden increase In the speed of the airflow through the carburetor. Because the air is lighter than the gasoline, it will accelerate quicker, causing a very lean mixture to reach the engine for a brief period. This would result in a severe lag In engine performance if not for the accelerator pump circuit. its job is to inject a measured charge of gasoline into the carburetor throat whenever the throttle valve is opened. b. Operation. (Fig. 4-34). The accelerator pump circuit consists of a pump that is operated by linkage directly from the throttle valve. There are passageways that connect the pump to the float bowl and pump discharge nozzle. There are two check valves in the system to control the direction of gasoline flow. Operation is as follows:
(1) The pump piston Is pushed down In the pump chamber as the throttle valve is opened, forcing gasoline through the outlet passageway. (2) At the same moment, the inlet check ball will seat keeping gasoline from being pumped back into the float bowl. (3) The discharge check needle will be forced off its seat, allowing gasoline to pass to the pump discharge nozzle, where it will be discharged into the throttle of the carburetor. (4) The pump piston Is raised in the pump chamber when the throttle valve Is closed, causing the discharge check needle to seat, blocking the outlet
TM 9-8000 (5) At the same moment, the inlet check ball is pulled off its seat and gasoline is pulled into the pump chamber from the float bowl (6) The pump chamber is filled with gasoline and ready to discharge whenever the throttle valve Is opened.
c. Diaphragm Pump (Fig. 4-35). The diaphragmtype pump system works just like the piston type with the exception of the pump design, which is a flat rubber diaphragm. By flexing this diaphragm, a pressure differential is created that results In pump action.
d. Controlling pump discharge (Fig. 4-36). The linkage between the accelerator pumpa6-hd the throttle cannot be solid. If it were, the pump would act as a damper, not allowing the throttle to be opened and closed readily. The linkage usually activates the pump through a slotted shaft or some- thing similar. When the throttle is closed, the pump Is held by its linkage. When the throttle is opened, the pump is activated by being pushed down by a spring that is called a duration spring. The tension of the duration spring controls the length of time that the injection of fuel lasts. The spring is calibrated to specific applications. Too much spring pressure will cause fuel to be discharged too quickly, resulting in reduced fuel economy. Too little spring pressure will cause fuel to be discharged too slowly, resulting In engine hesitation.
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a. Purpose. When the engine is cold, the gasoline tends to condense into large drops in the manifold rather than vaporizing. By supplying a richer mixture (8:1 to 9:1), there will be enough vapor to assure complete combustion. The carburetor is fitted with a choke system to provide this richer mixture. The choke system provides a very rich mixture to start the cold engine. It then gradually makes the mixture less rich as the engine reaches operating temperature. b. Operation (Fig. 4-37). The choke system consists of a flat plate that restricts the throat above the venturi but is located below the balance tube so that it has no affect on the pressure In the float bowl. This plate is called a choke valve, and, like the throttle valve, is mounted on a shaft to tilt it opened or closed. c. Manual Choke System (Fig. 4-38). The manually operated choke used to be the most popular way of controlling the choke valve. Due to emission regulations, the possible danger In use with catalytic converters (para 7-8), and technological advances in automatic choke systems, manual choke systems are little used today. The choke valve is operated by a flexible cable that extends into the drivers compartment. As the control is pulled out, the choke valve will be
closed so that the engine can be started. As the control is pushed back in, the position of the choke valve is adjusted to provide the proper mixture. The following are two features that are incorporated into manual choke systems to reduce the possibility of engine flooding by automatically admitting air into the engine: (1) A spring-loaded poppet valve that is automatically pulled open by the force of the engine intake strokes. (2) A choke valve that is pivoted off center on its shaft. This will create a pressure differential between the two sides of the choke valve when it is subjected to the engine intake, causing it to be pulled open against the force of spring-loaded linkage.
d. Automatic Choke System (Fig. 4-39). The automatic choke control system is centered around a thermostatic coil spring. The spring exerts pressure to hold the choke valve closed. Heat is applied to the coil after the engine Is started. The heat causes the coil to expand, allowing the choke to open. e. Providing Automatic Choke Heat. The four methods of providing controlled heat to the automatic choke thermostatic spring are: TA233408
4-23
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Figure 4-37. Choke Valve Operation. (1) Electricity (Fig. 4-40). A large portion of the vehicles currently produced use an electric coil to heat the thermostatic coil. The heating coil is switched on with the ignition switch. Some systems employ a control unit that prevents power from reaching the electric coil until the engine compartment reaches a desired temperature. (2) Engine Coolant (Fig. 4-41). Another method of heating the thermostatic coil is to circulate engine coolant through a passage in the thermostat housing. (3) Intake Manifold Crossover (Fig. 4-42). One of the most popular methods of providing choke heat, until recent years, is to utilize exhaust heat. The most popular way of doing this Is to mount the choke mechanism containing the thermostatic coil in a molded well on the intake manifold over the crossover passage. The choke mechanism then operates the choke valve through linkage. (4) Exhaust Manifold (Fig. 4-43). This system has the choke mechanism mounted on the carburetor in a sealed housing. The choke housing Is connected to a tube that runs through the exhaust manifold. This tube
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(1) Choke Piston (Fig. 4-44). The choke piston is integral with the carburetor, as is the passage that supplies vacuum to it. The vacuum passage is situated on the side of the piston cylinder so that it will only pull the choke valve open the desired amount before the piston will cover the vacuum passage. This will block the passage, keeping the piston from moving any further.
The
f. Regulating Choke Valve Opening. As with the manual choke system, a device must be incorporated that will open the choke a measured
(2) Choke Piston Integral with Choke Housing. choke piston system also may be
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(3) Remote Choke Pulloff (Flg. 4-46). The remote choke pulloff is the most common con- figuration In current automotive design. It Is made from either metal or plastic and uses a rubber diaphragm that pulls the choke open through linkage. The linkage is
(4) Two-Stage Choke Pulloff (Fig. 4-47). A variation of the choke pulloff Is the two-stage choke pulloff that has a spring-loaded telescoping pull rod. The choke valve, in the beginning, will be pulled open only partially. As the thermostatic coil heats and relaxes, it will be overcome by the pressure of the spring on the telescoping pull rod and choke valve will
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Figure 4-44. Choke Vacuum Piston. Figure 4-45. Choke Piston Integral with Choke Housing.
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h. Choke Unloader (Fig. 4-49). If for some reason the engine should flood when it is cold, a device is needed to open the choke so that air may be admitted to correct the condition. The device that accomplishes this is the choke unloader. The choke unloader usually consists of a projection from the fast idle cam that interacts with the throttle linkage. The operation is as follows:
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d. Progressive Throttle Linkage. Progressive throttle linkage is set up to open one throttle valve or one set of throttle valves at the beginning of the linkage travel and begin to open the second throttle valve or set
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e. Progressive Linkage Configurations. A carburetor equipped with progressive linkage is designed so that the accelerator pedal directly operates the primary throttle valve(s). There are two ways in which the secondary throttle valve(s) are operated.
(1) Mechanically operated secondary throttle valve(s) (fig. 4-51) are actuated by linkage from the primary throttle valve(s). The linkage is designed so that it will not be actuated until the primary throttle valve(s) are approximately two-thirds open. The operating arm on the primary throttle shaft is made to be approximately three times as long as the arm on the secondary throttle shaft so that the secondary throttle valve(s) will open all the way during the final third of primary throttle valve opening. The operating arm on the secondary throttle shaft operates through a spring so that it will not interfere with the primary throttle operation when the choke lockout is engaged. (2) Vacuum-operated secondary throttle valve(s) (fig. 4-52) are actuated by a vacuum diaphragm TA233415
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f. Secondary Air Valve (Fig. 4-53). Carburetors equipped with mechanically operated secondary throttle valves are subject to engine hesitation if the throttle suddenly is opened all the way at low engine speeds for the following reasons:
(1) The opening of primary and secondary
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Figure 4-52. Vacuum Progressive Linkage Operation. g. Four-Barrel Carburetor (Fig. 4-54). The fourbarrel or four-venturi carburetor consists of two primary venturis on a fixed throttle shaft that are progressively linked to two secondary venturis that are also on a fixed throttle shaft. The four- barrel carburetor is popular for the V-8 engine configurations for the following reasons:
(1) The intake manifold may be divided to separate consecutive cylinders (para 4-20c). (2) The carburetor better serves the engine throughout the entire load and speed range. 4-21. Updraft, Downdraft, and Sidedraft Carburetion. Carburetors may be built so that the airflow in the throat is downward, upward, or sideways, asshowninfigure4-55. 422. Primer System (Fig. 4-56). Some gasoline engines are fitted with a primer system to aid cold starting. The primer system consists of a hand pump that forces gasoline through a line to inject it at strategic locations along the intake manifold. The system is not used very much in modern equipment. 4-23. Degasser System (Fig. 4-57). The degasser system Is designed to shut off the supply of fuel to the idle circuit whenever there is high manifold vacuum such as periods of deceleration preventing large amounts of fuel from being drawn into the engine through the idle port. The degasser consists of a needle valve, a spring that holds the needle valve open, and a TA233417 4-32
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vacuum diaphragm that operates the needle valve through a fulcrum. The diaphragm is operated by a manifold vacuum. During periods of normal engine idle, the manifold vacuum is not high enough to operate the diaphragm and the needle valve remains open. During periods of decelera- tion, the manifold vacuum is high enough to cause the diaphragm to close the needle valve, shutting off the idle system. The needle valve also can be closed by pushing a button on the instrument panel that will energize a solenoid, closing the needle valve. The purpose of this manual actuation device is to clear the idle circuit and manifold of unburned gases before the engine is turned off. 4-24. Accessory Systems. There are numerous devices that are used on carburetors to improve drivability and economy. Their application varies from vehicle to vehicle. The following subparagraphs list the most popular of these devices.
temperature increases, opening the valve. This will in turn admit air under the throttle valve compensating for the overly rich mixture.
b. Throttle Return Dashpot (Fig. 4-59). The throttle return dashpot acts as a damper to keep the throttle from closing too quickly when the accelerator pedal is suddenly released. This is important to prevent stalling on cars equipped with automatic transmissions. The throttle lever contacts the dashpot rod just before the throttle valves close. This will, in turn, push in on the dia phragm. The diaphragm slows the closing of the throttle because it must exhaust the air from the chamber through a tiny venthole. When the throttle opens again, the dashpot spring pushes the diaphragm back into operating position, drawing air into the chamber. c. Antidiesel Solenoid (Fig. 4-60). The anti- diesel solenoid controls the throttle opening at engine idle to prevent dieseling. Engine dieseling is a condition that causes the engine to continue running after the ignition switch is turned off. It is a particular problem with newer emission con- trolled vehicles due to higher operating temperatures, higher idle speeds, leaner fuel mixtures, and lower octane gasoline (para 4-40). The solenoid is energized when the ignition switch is turned on, causing the plunger to open the throttle to idle speed position. The plunger length is adjustable so that the idle speed can be adjusted. When the ignition switch is turned off, the solenoid is deenergized and the throttle closes tightly, cutting off the air-fuel mixture. This will keep the engine from dieseling.
a. Hot Idle Compensator (Fig. 4-58). The hot idle compensator is a thermostatically controlled valve that helps to prevent engine stalling when idling In very hot weather. Long periods of engine idle cause an excessive amount of vaporization of gasoline in the float bowl. These vapors will find their way into the carburetor throat and cause an overly rich mixture. The hot idle compensator consists of a bimetallic strip of metal operating a valve that controls an air passage that ends under the throttle valve. The bimetallic strip, which consists of two pieces of dissimilar metal with different expansion rates, will curl upwards as the
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d. Air-conditioning Solenoid (Fig. 4-60). The airconditioning solenoid is used on some engines to boost engine idle speed whenever the air-conditioner compressor is running. This compensates for the load placed on the engine, thus preventing stalling. Its operation is similar to the Antidiesel solenoid described in the preceding subparagraph. e. Idle Solenoid System (Flg. 4-61). The idle solenoid system serves the same purposes as the degasser system described in paragraph 4-23. The system uses a solenoid whose operation is similar to the ones used in the two preceding subparagraphs. The solenoid operates a needle valve that opens and closes the carburetor idle port. The needle valve is in a normally closed position. The solenoid is activated when the ignition switch is turned on, opening the needle valve. The purpose of shutting off the idle system with the engine is to help eliminate engine
dieseling (para 4-40). A sensing switch is located in the intake manifold to shut off the idle system whenever manifold vacuum is excessively high, to prevent excess amounts of fuel from being sucked in through the idle port during deceleration.
f. Heated Air Intake System (Fig. 4-62). Most later model vehicles are fitted with a heated air intake system to provide the best performance in all temperatures with leaner fuel mixtures. The heated air intake system uses a damper door in the air filter snorkel to select either cold fresh air intake or heated air that is ducted from a heat stove on the exhaust manifold. The damper door is moved by a diaphragm that operates by manifold vacuum. The position of the damper door is determined by a temperature sensor. The system will keep the temperature of the intake air at about 1000 to 1150F (37.80 to 46.1C). Operation is as follows: TA233422
Figure 4-60. 4-37
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(1) When Inlet air temperature is below 1000F (37.80C), the temperature sensor will allow full vacuum to flow to the operating diaphragm, pulling the damper door to the heated air position. (2) When the Inlet air Is over 115F (46.10C), the temperature sensor will bleed manifold vacuum off Into the atmosphere. This will cause the diaphragm spring to push the damper door Into the unheated fresh air position.
(3) The temperature sensor will at times also bleed off only a portion of vacuum, causing the damper door to remain between the hot and cold position. This will regulate the temperature by providing a blend of hot and cold air. (4) At any time the engine Is heavily accelerated, the manifold vacuum will drop and the damper door will move to the fresh air Intake position.
TM 9-8000
FOR GASOLINE ENGINES 4-25. General. Fuel injection systems are an increasingly popular alternative to the carburetor for providing an air-fuel mixture. They inject, under pressure, a measured amount of fuel into the Intake air, usually at a point near the intake valve. Fuel injection systems provide the following advantages. (1) Fuel delivery can be measured with extreme accuracy, giving the potential for improved fuel economy and performance. (2) Because the fuel is injected at the intake port of each cylinder, fuel distribution will be much better and fuel condensing in the manifold will not be a problem. (3) There is no venturi to restrict the air Intake, making it easier to keep volumetric efficiency high (para 2-23). (4) The fuel injector, working under pressure, can atomize the fuel much finer than the carburetor, resulting In improved fuel vaporization. There are three basic configurations of gasoline fuel Injection: timed, continuous, and throttle body. 4-26. Timed Fuel Injection Systems. the engine camshaft. It is always in the same rotational relationship with the camshaft so that it can be timed to feed the fuel at just the right moment to the injectors. There is one injector for each cylinder. Each injector contains a spring loaded valve that is opened by fuel pressure injecting fuel into the intake at a point just before the intake valve. The throttle valve regulates engine speed and power output by regulating manifold vacuum, which in turn regulates the amount of fuel supplied to the injectors by the metering unit.
a. General. Timed fuel Injection systems for gasoline engines inject a measured amount of fuel in timed bursts that are synchronized to the Intake strokes of the engine. Timed injection is the most precise form of fuel injection but it is also the most complex. There are two basic forms of timed fuel injection: mechanical and electronic. The operation of the two are very different and will be covered separately In the two following subparagraphs. b. Mechanical-Timed Injection (Fig. 4-63). The mechanical-timed injection system uses a high-pressure pump that draws fuel from the gas tank and delivers it to the metering unit. A pressure relief valve is installed between the fuel pump and the metering unit to regulate fuel line pressure by bleeding off excess fuel back to the gas tank. The metering unit is a pump that is driven by
4-40
c. Electronic-Timed Fuel Injection (Fig. 4-64). The operation of electronic-timed fuel injection is somewhat different than the mechanical-timed system described in the previous subparagraph. In an electronic system, all of the fuel injectors are connected in parallel to a common fuel line that is fed by a high-pressure pump from the gas tank. A fuel pressure regulator also is installed in line with the injectors to keep fuel pressure constant by diverting excess fuel back to the gas tank. Each injector contains a solenoid valve and is normally In a closed position. With a pressurized supply of fuel behind it, each injector will operate individually whenever an electric current is applied to its solenoid valve. By sending electric current impulses to the injectors in a sequence timed to coincide with the needs of the engine, the system will supply gasoline to the engine as it should. The system is fitted with an electronic computer to serve this function and the function of providing the proper amount of fuel. The computer receives a signal from the ignition distributor to establish the timing sequence. The engine is fitted with a variety of sensors and switches that gather information such as:
(1) Intake air temperature (2) Engine speed (3) Manifold vacuum (4) Engine coolant temperature
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TM 9-8000 to the mixture control unit by the fuel pump. The fuel pressure regulator maintains fuel line pressure by sending excess fuel back to the gas tank. The mixture control unit regulates the amount of fuel that is sent to the injectors based on the amount of airflow through the intake and the engine temperature. The mixture control unit on mechanical systems will be operated by the airflow sensing plate and the warm-up regulator. This information on electronic systems will be fed into a computer that will, in turn, regulate the fuel injection rate. The accelerator pedal will regulate the rate of airflow through the intake by opening and closing the throttle valve. A cold-start injector is installed in the intake to provide a richer mixture during engine startup and warmup. It is actuated by electric current from the thermal sensor whenever the temperature of the coolant is below a certain level. The cold-start injector works in conjunction with the auxiliary air valve. Its function is to speed up the engine idle during warm-up. actuated by the thermal sensor. It also is
4-28. Throttle Body Injection (Fig. 4-66). Throttle body injection is a form of continuous injection that uses one or two injectors delivering gasoline to the engine from one central point in the intake manifold. Though throttle body injection does not provide the precise fuel distribution of the direct port injection described in the previous paragraph, it is much cheaper to produce, yet provides a much higher degree of precision fuel metering than a carburetor. The throttle body injection unit is usually an integral one, containing all of the major system components, in most cases. The unit mounts on the intake manifold in the same manner as a carburetor. Airflow sensors and electronic computers usually are mounted in the air cleaner body.
TM 9-8000 Section VI. TURBOCHARGERS AND SUPERCHARGERS 4-29. General. Turbocharging or supercharging is a method of increasing engine volumetric efficiency (para 2-23) by forcing the air-fuel mixture into the intake rather than merely allowing the pistons to draw it in naturally. Supercharging and turbocharging in some cases will push volumetric efficiencies over 100 percent. Engines must be modified to operate properly in some cases, because the extra air-fuel mixture will cause higher compression pressures, resulting in detonation (para 440c). 4-30. Turbochargers (Fig. 4-67). A turbocharger uses the force of the engine exhaust stream to force the air-fuel mixture into the engine. It consists of a housing containing two chambers. One chamber contains a turbine that is spun as hot exhaust gases are directed against it. The turbine shaft drives an impeller that is located in the other chamber. The spinning impeller draws an air-fuel mixture from the carburetor and forces it into the engine. Because the volume of exhaust gases increases with engine load and speed, the turbocharger speed will increase proportionally, keeping the manifold pressure boost fairly uniform. A device known as a waste gate is installed on turbocharged engines to control manifold pressure. It is a valve that, when open, allows engine exhaust to bypass the turbocharger turbine, effectively reducing intake pressure. The wastegate valve is operated by a diaphragm that is operated by manifold pressure. The diaphragm will open the waste-gate valve whenever manifold pressure reaches the desired maximum. 4-31. Superchargers. draws air into its center and throws it off at its rim. The air then is pushed along the inside of the circular housing. The diameter of the housing gradually increases to the outlet where the air is pushed out. The air from the outlet then is routed to the carburetor via a pressure box (para 4-31e).
c. Rootes Supercharger (Fig. 4-69). The rootes supercharger is of the positive displacement type, and consists of two rotors inside a housing. As the rotors are driven by the engine, air is trapped between them and the housing. It then is carried to the outlet where it is discharged. The rotors and the housing in this type of supercharger must maintain very tight clearances and therefore are very sensitive to dirt. d. Vane Supercharger (Fig. 4-70). The vane supercharger operates the same way as the vane oil pump described in paragraph 20-6. It is a positive displacement-type supercharger that usually is belt driven by the engine. The air output of the vane supercharger usually is routed to the carburetor via a pressure box (para 4-31e). e. Pressure Box (Fig. 4-71). A large percentage of superchargers are situated so that they force air into the carburetor throat rather than drawing the mixture from the bottom of the carburetor. This creates a problem because it will cause pressure in the venturi that is higher than atmospheric. This, in turn, will cause air to be blown into the discharge nozzle rather than fuel being drawn out. The solution is to enclose the carburetor in a sealed pressure box. The outlet of the supercharger then pressurizes the pressure box, providing the necessary boost. A relief valve usually is provided on the box to prevent pressure in the box from exceeding a desired limit.
a. General. Superchargers are engine driven air pumps that force the air-fuel mixture into the engine. They are made in three basic configurations: centrifugal, rootes, and vane. b. Centrifugal Supercharger (Fig. 4-68). The centrifugal supercharger has an impeller equipped with curved vanes. As the impeller is driven by the engine, it
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a. Velocity-Vacuum Governor - Type I. The first type of centrifugal-vacuum governor (fig. 4-73) uses a spring that tends to pull the throttle toward the open position. The spring is attached on one end to a vacuum piston through an adjusting screw. The other end of the spring is attached to the throttle shaft through a lever. There is also a damper piston connected to this lever. Operation is as follows:
(1) As engine speed increases to the governed maximum, the speed of the mixture forces the throttle valve toward the closed position against the force of the governor spring. 4-49
TM 9-8000
Figure 4-73. Velocity-Vacuum Governor-Type I. b. Velocity-Vacuum Governor - Type II. The second type of velocity-vacuum governor (fig. 4-74) also uses a spring to pull the throttle valve toward the open position. One end of the spring is attached to the carburetor housing through an adjusting screw. The other end of the spring is attached to the throttle shaft through a flywheel that is attached to the end of the shaft. A compensator spring is located so that it operates with the throttle shaft during periods of small throttle openlng. Operation is as follows:
(1) As engine speed increases to the governed maximum, the speed of the mixture forces the throttle valve toward the closed position against the force of the governor spring. (2) The flywheel, by inertial force, prevents fluctuation of the throttle valve that would occur due to pulsation of the intake mixture caused by the time between, or the overlapping of, the intake strokes. (3) During periods of light loads, the engine can reach Its maximum governed speed with a relatively small throttle opening. This could cause the intake mixture to close the throttle valve too much, causing 4-50 excessive speed reduction. To prevent this, an extra compensator spring is fitted to offer additional resistance to throttle valve closing during periods of small throttle opening. (4) By loosening or tightening the engine speed adjusting screw, the maximum engine speed can be adjusted. The screw accomplishes this by changing the tension of the governor spring. 4-35. Centrifugal-Vacuum Governor (Fig. 4-75). A centrifugal-vacuum governor consists of two units that work together to regulate maximum engine speed. One is the centrifugal unit that is mounted under the Ignition distributor. The other is the vacuum unit that is mounted under the carburetor.
a. Centrifugal Unit. The centrifugal unit is driven by the engine at the Ignition distributor drive. Its purpose is to control the vacuum unit based on engine speed. Operation is as follows: TA233433
TM 9-8000
b. Vacuum Unit. The vacuum unit is basically a diaphragm with a rod connecting It to the throttle valve shaft. When pressure is equal above and below the diaphragm, the governor spring pulls the diaphragm rod into a nongoverning position. When pressure drops under the diaphragm, as dictated by the governor valve, atmospheric pressure will push the diaphragm down against the force of the governor spring, causing the diaphragm rod to pull the throttle valves toward the closed position. This effectively will limit engine speed.
TA233434 4-51
TM 9-8000
a. Starting Ability. To provide satisfactory cold weather performance and starting, the choke system causes a very rich mixture to be delivered to the engine. Gasoline that is not volatile enough will cause excessive amounts of TA233435
TM 9-8000 raw unvaporized fuel to be introduced to the combustion chambers. Because unvaporized fuel does not burn, it is wasted. This reduces fuel economy and causes a condition known as crankcase dilution.
b. Crankcase Dilution. Crankcase dilution occurs when the fuel that is not vaporized leaks past the piston rings and seeps into the crankcase. The unvaporized fuel then dilutes the engine oil, reducing its lubricating qualities. A certain amount of crankcase dilution occurs in all engines during warm-up. It is not considered harmful in normal quantities because it vaporizes out of the oil as the engine warms up. The vapors then are purged by the crankcase ventilation system (para 7-7). c. Vapor Lock. Vapor lock is one of the difficulties experienced in hot weather when using highly volatile fuels. When fuel has a tendency to vaporize at normal atmospheric temperature, it may form so much vapor in the fuel line that the action of the fuel pump will cause a pulsation of the fuel vapor rather than normal fuel flow. Heat Insulating materials or baffles are often placed between the exhaust pipe and fuel line to help avoid vapor lock. Hot-weather grades of gasoline are blended from lower volatility fuels to lessen the tendency toward vapor lock. d. Fuel Distribution. When the fuel is not distributed evenly to all cylinders, the engine will run unevenly and power output will decrease. To ensure good distribution, the fuel must be vaporized completely and mixed with air in the manifold before entering the combustion chamber.
4-38. Purity. Petroleum contains many Impurities that must be removed during the refining process before gasoline suitable for automotive use is produced. At one time, considerable corrosion was caused by the sulfur inherent in petroleum products, but modern refining processes have made it almost negligible. Another problem was the tendency for the hydrocarbons in the gasoline to oxidize into a sticky gum when exposed to air, which resulted in clogged carburetor passages, stuck valves, and other operational difficulties. Chemicals that control gumming are now added to gasoline. Dirt, grease, water, and various chemicals also must be removed to make gasoline an acceptable fuel. 4-39. Deicing Agents. Moisture in gasoline tends to freeze in cold weather, causing clogged fuel lines and carburetor idle ports. Deicing agents are added to gasoline that mix with the moisture and act as an antifreeze to prevent freezing. 4-40. Antiknock Quality. 4-53
a. Combustion. To understand what is meant by antiknock quality, first review the process of combustion. When any substance burns, it actually is uniting in rapid chemical reaction with oxygen (one of the constituents of air). During this process, the molecules of the substance and oxygen are set into very rapid motion and heat is produced. In the combustion chamber of an engine cylinder, the gasoline vapor and oxygen in the air are ignited and burn. They combine, and the molecules begin to move about very rapidly as the high temperatures of combustion are reached. The molecules, therefore, bombard the combustion chamber walls and the piston head with a shower of fast moving molecules. It is actually this bombardment that registers the heavy push on the piston and forces it downward on the power stroke. b. Combustion Process. The normal combustion process in the combustion chamber (fig. 4-76) goes through three stages when producing power. They are as follows: (1) Formation of Nucleus of Flame. As soon as a spark jumps the gap of the spark plug electrode, a small ball of blue flame develops in the gap. This ball is the first stage, or nucleus, of the flame. It enlarges with relative slowness and,
TM 9-8000 during its growth, there is no measurable pressure created by heat. (2) Hatching Out. As the nucleus enlarges, it develops into the hatching out stage. The nucleus is torn apart so that it sends fingers of flame into the mixture in the combustion chamber. This causes enough heat to give just a slight rise in the temperature and pressure In the entire air-fuel mixture. Consequently, a lag still exists in the attempt to raise pressure in the entire cylinder. (3) Propagation. It is during the third, or propagation, stage that effective burning occurs. The flame now burns in a front that sweeps across the combustion chamber, burning rapidly and causing great heat with an accompanying rise in pressure. This pressure causes the piston to move downward. The burning during normal combustion is progressive. It increases gradually during the first two stages, but during the third stage, the flame is extremely strong as it sweeps through the combustion chamber. further compressed and are heated to high temperatures. Under certain conditions, the extreme heating of the unburned part of the mixture may cause it to Ignite spontaneously and explode. This rapid, uncontrolled burning in the final stage of combustion is called detonation. It is caused by the rapidly burning flame front compressing the unburned part of the mixture to the point of self-ignition. This secondary wave front collides with the normal wave front, making an audible knock or ping. It is an uncontrolled explosion, causing the unconfined gases in the combustion chamber to rap against the cylinder head walls. Detonation may harm an engine or hinder its performance in several ways. In extreme cases, pistons have been shattered, rings broken, or heads cracked. Detonation also may cause overheating, excessive bearing wear, loss of power, and high fuel consumption.
d.
Octane Rating.
c. Detonation (Fig. 4-77). If detonation takes place, it will happen during the third stage of combustion. The first two stages are normal, but In the propagation stage, the flame sweeps from the area around the spark plug toward the walls of the combustion chamber. Parts of the chamber that the flame has passed contain inert gases, but the section not yet touched by the flame contains highly compressed, heated combustible gases. As the flame races through the combustion chamber, the unburned gases ahead of it are
(1) The ability of a fuel to resist detonation is measured by its octane rating. The octane rating of a fuel is determined by matching it against mixtures of normal heptane and iso-octane in a test engine under specified test conditions until a pure mixture of hydrocarbons is found that gives the same degree of knocking in the engine as the gasoline being tested. The octane number of the gasoline then is specified as the percent of the isooctane In the matching iso-octane, normal heptane mixture. For example, a gasoline rating of 75 octane is equivalent in its knocking characteristics to a mixture of 75 percent iso-octane and 25 percent normal heptane. Thus, by definition, normal heptane has an octane rating of 0 and isooctane has an octane of 100. (2) The tendency of a fuel to detonate varies in different engines and in the same engines under different operating conditions. The octane number has nothing to do with starting qualities, potential energy, volatility, or other major characteristics. Engines are designed to operate within a certain octane range. Performance is improved with the use of higher octane fuels within that operational range. Engine performance will not be improved if a gasoline with an octane rating higher than the operational range is provided. (3) Tetraethyl lead is the most popular of the compounds added to gasoline to raise its octane rating. The introduction of catalytic conTA233437 4-54
TM 9-8000 verters, however, has created a need for a higher octane lead-free gasoline that is produced by more careful refining processes and numerous substitutes for lead. Lead-free gasolines to date, however, do not have the antiknock qualities of leaded ones. Modern automotive engines made for use with lead-free gasoline, therefore, must be designed for lower octane ratings.
4-55/(4-56 blank)
TM 9-8000 CHAPTER 5 DIESEL FUEL SYSTEMS Section I. CHARACTERISTICS OF DIESEL FUELS 5-1. General. Fuels used in modern high-speed diesel engines are derived from the middle distillate fraction of crude oil. The middle distillates span the boiling range between gasoline and heavy residual oil, and typically include kerosene, jet fuel (aviation kerosene), diesel fuel, and burner fuel (home heating oil). Although large, slow-speed diesel engines used in stationary and marine applications will burn almost any grade of heavy oil, the smaller, high-speed diesel engines used in most military equipment require middle distillate diesel fuels. These fuels must meet exacting specification requirements to ensure proper engine performance. 5-2. Cleanliness and Stability. Cleanliness is an important characteristic of diesel fuel because the extremely close fit of the injector parts can be damaged by particles. Dirt or sand particles in the fuel cause scoring of the injector parts, leading to poor performance or seizure. Moisture in the fuel can also damage or cause seizure of injector parts when corrosion occurs. Fuel stability is its capacity to resist chemical change caused by oxidation and heat. Good oxidation stability means that the fuel can be stored for long periods without formation of gum or sludge. Good thermal stability prevents the formation of carbon in hot parts such as fuel injectors or turbine nozzles. Carbon deposits disrupt the spray patterns and cause inefficient combustion. 5-3. Viscosity. The viscosity of a fluid is an indication of its resistance to flow. What this means is that a fluid with a high viscosity is heavier than a fluid with a low viscosity. The viscosity of diesel fuel must be low enough to flow freely at its lowest operational temperature, yet high enough to provide lubrication to the moving parts of the finely machined injectors. The fuel must also be sufficiently viscous so that leakage at the pump plungers and dribbling at the injectors will not occur. Viscosity also will determine the size of the fuel droplets, which, in turn, govern the atomization and penetration qualities of the fuel injector spray. 5-4. Ignition Quality. The ignition quality of a fuel is its ability to ignite spontaneously under the conditions existing in the engine cylinder. The spontaneous-ignition point of a diesel fuel is a function of the pressure, temperature, and time. Because it is difficult to reproduce the operating conditions of the fuel artificially outside the engine cylinder, a diesel engine operating under controlled conditions is used to determine the ignition quality of diesel fuel. The yardstick that is used to measure the ignition quality of a diesel fuel is the cetane-number scale. The cetane number of a fuel is obtained by comparing it to the operation of a reference fuel. The reference fuel is a mixture of alpha-methylnaphthalene, which has virtually no spontaneous-ignition qualities, and pure cetane, which has what are considered to be perfect spontaneous-ignition qualities. The percentage of cetane is increased gradually in the reference fuel until the fuel matches the spontaneous-ignition qualities of the fuel being tested. The cetane number then is established for the fuel being tested based on the percentage of cetane present in the reference mixture. 5-5. Knocking. Diesel engines have a tendency to produce a knock that is noticeable particularly during times when the engine is under a light load. This knocking occurs due to a condition known as Ignition delay or ignition lag. When the power stroke begins, the first molecules of fuel injected into the combustion chamber first must vaporize and superheat before ignition occurs. During this period, a quantity of unburned fuel builds up in the combustion chamber. When ignition occurs, the pressure increase causes the built-up fuel to Ignite instantly. This causes a disproportionate increase in pressure, creating a distinct and audible knock. Increasing the compression ratio of a diesel engine will decrease ignition lag and the tendency to knock. This contrasts with a gasoline engine, whose tendency to knock will Increase with an Increase in compression ratio. Knocking in diesel engines is affected by factors other than compression ratio, such as the type of combustion chamber, airflow within the chamber, Injector nozzle type, air and fuel temperature, and the cetane number of the fuel.
Change 1 5-1
TM 9-8000 5-6. Multifuel Engine Authorized Fuels. Multifuel engines are four-stroke cycle diesel engines that will operate satisfactorily on a wide variety of fuels. The fuels are grouped accordingly: regulated to a constant 20 psi regardless of engine speed and load range.
a. Primary and Alternate I Fuels. These fuels will operate the multifuel engine with no additives. b. Alternate II Fuels. These fuels generally require the addition of diesel fuel to operate the multifuel engine. c. Emergency Fuels. These fuels will operate the multifuel engine with the addition of diesel fuel. Extended use of fuels from this group will cause eventual fouling of fuel Injection components. It should be noted that there are no adjustments necessary to the engine when changing from one fuel to another.
5.7. Fuel Density Compensator (Fig. 5.1). The multifuel engine operates on a variety of fuels that have. a broad range of viscosities and heat values. These variations In the fuels affect engine output. Because it is unacceptable for the power output of the engine to vary with fuel changes, the multifuel engine is fitted with a device known as a fuel density compensator. The fuel density compensator is a device that serves to vary the quantity of fuel Injected to the engine by regulating the full load stop of the fuel pump (para 4-3). The characteristics of the fuels show that their heat values decrease almost Inversely proportional to their viscosities. The fuel density compensator uses viscosity as the Indicator for regulating fuel flow. Its operation is as follows: a. The fuel supply enters the compensator through the fuel pressure regulator, where the supply pressure is
b. The pressure regulated fuel then passes through a series of two orifices. The two orifices, by offering greatly different resistances to flow, form a system that is sensitive to viscosity changes.
(1) The first orifice is annular, formed by the clearance between the servo piston and its cylinder. This orifice is sensitive to viscosity. (2) The second orifice is formed by an adjustable needle valve, and, unlike the first, it is not viscosity sensitive. (3) After the fuel passes through the two orifices It leaves the compensator through an outlet port. From here the fuel passes back to the pump. c. The higher the viscosity of the fuel, the more trouble that It will have passing through the first orifice. Because of this, the fuel pressure under the servo piston will rise proportionally with viscosity. Because the second orifice is not viscosity sensitive, the pressure over the servo piston will remain fairly constant. This will cause a pressure differential that Increases proportionally with viscosity, that in turn will cause the piston to seek a position In Its bore that becomes higher as viscosity increases.
d. The upward movement of the servo piston will move a wedge-shaped moveable plate, which will decrease fuel delivery. A lower viscosity fuel will cause the piston to move downward, causing the pump to Increase fuel delivery.
Change 1 5-2
TM 9-8000
Change 1 5-3
TM 9-8000 5-9. Open Chamber (Fig. 5-2). The open chamber is the simplest form of chamber. It is suitable only for slow-speed, four-stroke cycle engines, but is used widely in two-stroke cycle diesel engines. In the open chamber, the fuel is injected directly into the space at the top of the cylinder. The combustion space, formed by the top of the piston and the cylinder head, usually is shaped to provide a swirling action of the air as the piston comes up on the compression stroke. There are no special pockets, cells, or passages to aid the mixing of the fuel and air. This type of chamber requires a higher injection pressure and a greater degree of fuel atomization than is required by other combustion chambers to obtain an acceptable level of fuel mixing. This chamber design is very susceptible to ignition lag. 5-10. Precombustion Chamber (Fig. 5-3). The precombustion chamber is an auxiliary chamber at the top of the cylinder. It is connected to the main combustion chamber by a restricted throat or passage. The precombustion chamber conditions the fuel for final combustion in the cylinder. A hollowed-out portion of the piston top causes turbulence in the main combustion chamber as the fuel enters from the precombustion chamber to aid in mixing with air. The following steps occur during the combustion process:
a. During the compression stroke of the engine, air is forced into the precompression chamber and, because the air compressed, it is hot. At the beginning of injection, the precombustion chamber contains a definite volume of air. b. As the injection begins, combustion begins in the precombustion chamber. The burning of the fuel combined with the restricted passage to the main combustion chamber creates a tremendous amount of pressure in the precombustion chamber. The pressure and the initial combustion cause a superheated fuel charge to enter the main combustion chamber at a tremendous velocity.
c. The entering mixture hits the hollowed-out piston top, creating turbulence in the chamber to ensure complete mixing of the fuel charge with the air. This mixing ensures even and complete combustion. This chamber design will provide satisfactory performance with low fuel injector pressures and coarse spray patterns because a large amount of vaporization takes place in the combustion chamber. This chamber also is not very susceptible to ignition lag, making it more suitable for high-speed applications. 5-11. Turbulence Chamber (Fig. 5-4). The turbulence chamber is similar in appearance to the precombustion chamber, but its function is different. There is very little clearance between the top of the piston and the head, so that a high percentage of the air between the piston and the cylinder head is forced into the turbulence chamber during the compression stroke. The chamber usually is spherical, and the opening through which the air must pass becomes smaller as the piston reaches the top of the stroke, thereby increasing the velocity of the air in the chamber. This turbulence speed is approximately 50 times crankshaft speed. The fuel injection is timed to occur when the turbulence in the chamber is the greatest. This ensures a thorough mixing of the fuel and the air, with the result that the greater part of combustion takes place in the turbulence chamber itself. The pressure created by the expansion of the burning gases is the force that drives the piston downward on the power stroke. 5-12. Spherical Combustion Chamber (Fig. 5-5). The spherical combustion chamber is TA233440
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a. As the air enters the combustion chamber, a swirl effect is introduced to it by the shape of the intake port (A, fig. 5-5).
TM 9-8000
TM 9-8000
b. During the compression stroke, the swirling motion of the air continues as the temperature in the chamber increases (B, fig. 5-5).
c. As the fuel is injected, approximately 95 percent of it is deposited on the head of the piston and the remainder mixes with the air in the spherical combustion 5-7
chamber (C, fig. 5-5). d. As combustion begins, the main portion of the fuel is swept off of the piston head by the high velocity swirl that was created by the intake and the compression strokes. As the fuel is swept off of the head, it burns through the power stroke, maintaining even combustion and eliminating detonation (D and E, fig. 5-5).
TM 9-8000
atomization. (3) To control the start, rate, and duration of the injection. 5-14. Multiple Unit Injection.
a. Methods. There are two methods of injecting fuel into a compression-ignition engine. One method is air Injection. This method uses a blast of air to force a measured charge of fuel into the combustion chamber. The other method is solid injection, where direct mechanical pressure is placed on the fuel itself to force it into the combustion chamber. This chapter only will cover solid injection systems because air injection virtually is unused in automotive applications. b. Fuel Atomization and Penetration. The fuel spray entering the combustion chamber must conform to the chambers shape so that the fuel particles will be well distributed and thoroughly mixed with the air. The shape of the spray is determined by the degree of atomization and penetration produced by the orifice through which the fuel enters the chamber. Atomization (para 4-9e) is the term used to indicate the size of the droplets the fuel is broken down into. Penetration is the distance from the orifice that the fuel droplets attain at a given phase of the injection period. The dominant factors that control penetration are the length of the nozzle orifice, the diameter of the orifice outlet, the viscosity of the fuel, and the injection pressure of the fuel. Increasing the ratio of the length of the orifice to its diameter will increase penetration and decrease atomization. Decreasing this ratio will have an opposite effect. Because penetration and atomization are opposed mutually and both are important, a compromise is necessary if uniform fuel distribution is to be obtained. The amount of fuel pressure for injection is dependent on the pressure of the air in the combustion chamber, and the amount of turbulence in the combustion space. c. Function of the Injection System. It is Impossible to cover the operation and construction of the many types of modern injection systems in this text. However, the operation of the more common systems will be discussed. If the three basic functions of diesel fuel injection are kept in mind while studying the operation of the systems, it will be easier to understand how they work. The three basic functions are:
(1) To meter the fuel accurately. (2) To distribute the fuel equally to all of the cylinders at a high enough pressure to ensure 5-8
a. General System Operation (Fig. 5-6). The basic system consists of a fuel supply pump, fuel filter, multiple unit injection pump, and one injector for each cylinder. The operation of the system is as follows:
(1) The fuel supply pump and the fuel filter provide a low-pressure supply of fuel to the multiple unit injection pump. Pressure usually is regulated to approximately 15 psi (103.4 kPa). (2) The multiple unit injection pump contains an individual injection pump for each engine cylinder. Fuel is delivered to the injectors at each cylinder from the multiple unit injection pump in a timed sequence and a regulated amount based on accelerator pedal position and engine speed. (3) The injectors receive fuel charges from their respective injection pumps and spray it into the combustion chambers in a spray pattern that is tailored to provide the best overall performance for their particular application.
TM 9-8000
TM 9-8000
TM 9-8000 the volume of fuel injected to the cylinders to be varied by changing the effective length of the pump stroke (the length of the pump stroke that occurs before the spill port is uncovered by the bypass helix). The rack extends down the whole row of Injection pumps so that they are all operated simultaneously. The end result is that the Injection pumps can be moved from full to no-fuel delivery by moving the rack back and forth. The movement of the rack is controlled by the governor (para5-24). (5) When the plunger begins Its pump stroke It covers both ports. When this happens, the pressure exerted on the fuel causes the spring-loaded delivery valve to lift off of Its seat, thereby permitting fuel to discharge Into the tubing that leads to the spray nozzle. At the Instant that the bypass helix uncovers the spill port, the fuel begins to bypass. This causes the pressure In the pump cavity to drop. The high pressure in the delivery line combined with spring pressure causes the delivery valve to close. When the delivery valve closes, It prevents fuel from the line from draining back Into the pump, which could cause the system to lose its prime. As the delivery valve seats, It also serves to reduce pressure In the delivery line. The delivery valve has an accurately lapped displacement piston Incorporated Into It to accomplish pressure relief. The pressure is relieved in the line by the Increase In volume as the delivery valve seats.
c. Fuel Injectors (Fig. 5-8). For proper engine performance, the fuel must be Injected Into the combustion space In a definite spray pattern. This is accomplished by the fuel Injector.
(1) The fuel enters the nozzle holder body through the high-pressure Inlet. It then passes
TM 9-8000 down to the pressure chamber above the valve seat. (2) At the moment that the pressure developed by the injection pump exceeds the force exerted by the pressure adjusting spring, the nozzle valve will be lifted off of its seat, resulting in the injection of fuel into the cylinder. The valve usually requires a fuel pressure of 1000 to 4000 psi (6895 to 27580 kPa) to open, depending on the engine combustion chamber requirements. (3) A controlled seepage exists between the lapped surfaces of the nozzle valve and its body to provide for lubrication. The leakage or overflow passes around the spindle and into the pressure adjusting spring chamber. From here, the fuel leaves the injector through the overflow outlet and finally to the overflow lines, which lead back to the low-pressure fuel supply. nozzle orifice. At the beginning of the injection period, only a small quantity of fuel is injected into the chamber because the straight section of the pintle is in the nozzle orifice. The volume of the fuel spray then increases progressively as the pintle is lifted higher, because the straight section leaves the nozzle orifice and the tapered tip of the pintie in the orifice provides a larger opening for the flow of fuel. (3) Another type of throttling nozzle has its pintle flush with the nozzle-body tip for no-fuel delivery and extended through the body for maximum fuel delivery. In this type, fuel under high pressure from the injection pump acts on the seat area of the pintle, forcing it outward against a preloaded spring. This spring, through its action on a spring hanger, also returns the pintle to its seat, sealing the nozzle against further injections or dribble when the line pressure is relieved at the pump. When the pintle moves outward due to fuel pressure, an increasingly larger orifice area is opened around the flow angle of the pintle. (4) The hole nozzles have no pintle but basically are similar in construction to the pintle type. They have one or more spray orifices that are straight, round passages through the tip of the nozzle body beneath the valve seat. The spray from each orifice is relatively dense and compact, and the general spray pattern is determined by the number and the arrangement of the holes. As many as 18 holes are provided in larger nozzles, and the diameter of these drilled orifices may be as small as 0.006 in. (0.152 mm). The spray pattern may not be symmetrical, as in the case of the multifuel engine, where the spray pattern is off to one side so as to deposit the fuel properly in the spherical combustion chamber (para 5-12). The size of the holes determines the degree of atomization attained. The smaller the holes, the greater the atomization; but if the hole is too small, it will be impossible to get enough fuel into the chamber during the short time allowed for injection. If the hole is too large, there will be an overrich mixture near the nozzle tip and a lean mixture at a distance from it. Using multiple holes in the Injector tips usually overcomes both difficulties because the holes can be drilled small enough to provide proper atomization and a sufficient number can be provided to allow the proper amount of fuel to enter during the injection period.
d. Injector Nozzles (Fig. 5-9). Because of the widely differing requirements in the shapes of the fuel spray for various chamber designs and the wide range of engine power demands, there is a large variety of injector nozzles in use. The spray nozzles are put into two basic groups: pintle nozzles and hole nozzles. Pintle nozzles generally are used in engines having precombustion or turbulence chambers, whereas the hole nozzles generally are used in open chamber engines.
(1) In pintle nozzles, the nozzle valve carries an extension at its lower end in the form of a pin (pintle), which protrudes through the hole in the nozzle bottom. This requires the injected fuel to pass through an annular orifice, producing a hollow, cone-shaped spray, the nominal included angle of which may be from 0 to 60 degrees, depending on the combustion chamber requirement. The projection of the pintle through the nozzle orifice includes a self-cleaning effect, discouraging the accumulation of carbon at this point. (2) A specific type of pintle nozzle that is used extensively in small bore high-speed diesel engines is the throttling nozzle. It differs from the standard pintle nozzle in that the pintle projects from the nozzle for a much greater distance, and the orifice in the bottom of the nozzle body is much longer. The outstanding feature of the throttling nozzle is its control of the rate at which fuel is injected into the combustion chamber. When no fuel is being injected, the pintle extends through the 5-12
TM 9-8000
TM 9-8000
5-15.
a. General System Operation. The wobble plate pump system basically is the same as the multiple unit injection system (para. 5-14). The difference in the system lies in the injection pump. In a wobble plate pump, all of the pump plungers are actuated by a single wobble plate instead of a camshaft that has a separate cam for each pump plunger. Also, the metering of the fuel is accomplished by a single axially located rotary valve in the wobble plate unit, whereas the rotary movement of the individual plungers controls the amount of fuel in the multiple unit injection pump. b. Wobble Plate Pump Principles. A plate is mounted on a shaft and set at an angle to it so that as the shaft rotates, the plate moves laterally in relation to any given point on either side of it. The pump derives its name from the fact that the plate appears to wobble back and forth as it rotates. The end of the push rod is placed in a guide plate that lays against the wobble plate. The push rod is held in a bore in the pump body so that is can move only In a direction parallel to the wobble plate shaft. The rotation of the wobble plate then causes the guide plate to wobble, thus moving the push rod back and forth. The push rod is connected to the pump plunger so that movement to the left actuates the pump on its delivery stroke and a spring returns it on the suction stroke. c. The Wobble Plate Injection Pump. As stated previously, the wobble plate injection pump contains an individual plunger-type pump for each cylinder. The pump plungers are spaced equally about the wobble plate. As the wobble plate rotates, it will actuate all of the individual Injection pumps. At any given time during rotation, half of the plungers will be moving on their delivery stroke while the other half will be on their return stroke.
(1) The rotary metering valve is driven by the same shaft that drives the wobble plate. The rotary valve consists of a lapped cylindrical shaft that is fitted closely in a barrel to prevent fuel from escaping at its ends. Fuel is admitted to the barrel at the center of the valve, which contains a spool like reduction In diameter. This reduction in diameter acts as a fuel reservoir. (2) The reduced portion of the valve is in the 5-14
shape of a band broken by a triangular land that is the same diameter as the ends of the valve. The reservoir created by the reduced portion of the valve is connected to each pump cavity by individual ports so that the pump cavities may be supplied with fuel. This reservoir receives a constant supply of low-pressure fuel from the delivery pump. As with the multiple unit injection system, delivery pump pressure is regulated to approximately 15 psi (103.43 kPa). (3) The triangular land serves to consecutively block each pump delivery port as it rotates. The triangular land is situated so that it will block each pump delivery port at the same time that the wobble plate is moving the respective pump plunger at the maximum speed through its delivery stroke. Fuel is delivered to the fuel injector as long as the delivery port is blocked. (4) The rotational relationship of the rotary valve and the wobble plate causes each pump to deliver a fuel charge to its respective injector in turn as the pump rotates. The pumps in the Injection unit are connected to the fuel injectors to coincide with the firing order of the engine. The pump is gear driven by the engine at a speed of exactly one-half that of the crankshaft. The end result will be the injection of fuel to each cylinder at the beginning of each power stroke. (5) To obtain zero delivery, the valve is moved endwise to a position where the delivery ports are never blocked by the triangular land. When this occurs, the movement of the pump plungers merely causes the fuel to move back and forth in the delivery ports. This results in zero delivery to the injectors due to insufficient pressure to open the spring-loaded delivery valves. (6) To cause the pump to deliver fuel, the rotary valve is moved endwise so that the triangular land begins to block the delivery ports. Due to the triangular shape of the land, further endwise movement of the rotary valve will in- crease the time that the port is blocked, increasing fuel delivery. The end result is that fuel delivery can be controlled by the endwise movement of the rotary valve. Endwise movement of the rotary valve is accomplished by the control lever. The position of the control lever is determined by the governor (para 5-24).
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TM 9-8000
5-16.
a. General System Operation (Fig. 5-11). The distributor injection system used in automotive diesel engines is classed as a low-pressure system in that pumping, metering, and distribution operations take place at low pressure. The high pressure required for Injection is built up by the injector at each cylinder. A suction pump lifts fuel from the tank and delivers it to the float chamber. From here a second low-pressure pump delivers the fuel to the distributor. Fuel passes through the distributor to the metering pump, where it is divided into measured charges. The fuel charges then are delivered back to the distributor, where they are sent to the injectors in the proper sequence. The measured charges then are sprayed into the engine cylinders at the proper time and under high pressure by the fuel injectors. b. Distributor. The distributor consists of a rotating disk and a stationary cover to which the fuel lines to the individual injectors are connected. The disk and the cover have a series of holes that, when properly indexed, form passages from the fuel supply pump to the metering pump. The disk is timed so that this occurs when the metering plunger Is moving down on its suction stroke, thus permitting the metering pump to be filled with oil. As the disk continues to rotate, it lines up with the correct discharge hole in the cover just as the metering plunger begins its delivery stroke, forcing the fuel into the proper injector line. As it continues to rotate, the disk works in the same timed sequence in conjunction with the metering pump to feed fuel to the remaining cylinders. The rotating disk turns at one-half crankshaft speed because power strokes occur every other crankshaft revolution in a four-stroke cycle diesel engine. c. Metering Unit (Fig. 5-12). The metering unit is a closely fitted reciprocating pump, obtaining its motion through a link from the plunger lever. The plunger lever is operated by a vertical lever, controlled in turn by an eccentric rocker lever running directly off a cam on the fuel pump main shaft. The position of the vertical lever in the eccentric of the rocker lever determines the travel of the plunger lever and, in turn, the travel of the metering pump plunger. As the pump plunger starts upward on its controlled stroke, it pushes fuel to the injector through passages formed by the rotating distributor disk. The stroke of the metering plunger, which determines the amount of fuel going to each
5-16
injector, is varied by changing the position of the plunger lever between the stop pins in the cam rocker lever. The position of the plunger lever is adjusted by the governor (para 5-25) through the control lever.
d. Injectors (Fig. 5-13). The injector consists of a forged body with a properly fitted plunger. This plunger is forced down against spring action by the engine camshaft through a rocker arm and push rod. There is a fuel cup mounted on the end of the body combined with a hole-type nozzle (para 5-14).
(1) The fuel metering pump forces a precisely measured fuel charge into the cup on the intake stroke of the engine. The quantity of the fuel charge is based on the speed and load requirements of the engine. The operation of this system depends on the injector delivery line being full of fuel. Then it will naturally follow that any fuel added by the fuel metering pump will discharge an equal amount of fuel at the other end of the line into the injector. (2) The fuel lies in the cup during the compression stroke of the engine, and the compressed air is forced through the small spray holes in the cup. The fuel in the tip of the cup is exposed to the intense heat of compression. The turbulence caused by the air rushing in through the holes in the nozzle tip serves to break the fuel charge into droplets. (3) A few degrees before top dead center, at the beginning of the power stroke, the injector plunger is forced down, causing the fuel charge to be sprayed out of the cup, through the nozzle holes, and into the combustion chamber. The downward movement of the injector plunger is spread out through the entire power stroke. (4) There is a small check valve located in the inlet passage of the injector body. Its purpose is to allow fuel to enter the injector cup but block high combustion chamber pressure from blowing air into injector delivery lines. 5-17. Unit Injection System (Fig. 5-14).
a. Overall System Operation. The unit injection system operates in the same manner as the
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c. Injector Units (Fig. 5-15). Unit Injectors combine the Injection pump, the fuel valves, and the nozzle In a single housing. These units provide a complete and Independent Injection system for each cylinder. The units are mounted TA233450
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(5) For metering purposes, a recess with an upper helix and a lower helix or a straight cutoff is machined into the lower end of the plunger. The relation of this upper helix and lower cutoff to the two ports changes with the rotation of the plunger. As the plunger moves downward, the fuel in the high-pressure cylinder or bushing is first displaced through the ports back into the supply chamber until the lower edge of the plunger closes the lower port. The remaining oil is then forced upward through the center passage in the plunger into the recess between the upper helix and the lower cutoff, from which it can flow back into the supply chamber until the helix closes the upper port. The rotation of the plunger, by movement of the rack, changes the position of the helix in relation to the ports. This will advance or retard the closing of the ports and the beginning and ending of the injection period. This will result in a regulation of the volume of the fuel charge that is injected into the cylinder. (6) When the control rack is pulled out completely, the upper port is not closed by the helix until after the lower port is uncovered. This means that all the fuel in the high-pressure cylinder bypasses back to the fuel supply and no fuel is injected into the combustion chamber. (7) When the control rack is pushed in fully, the upper port is closed shortly after the lower port has been covered, thus producing a full effective stroke and maximum injection. (8) From the no-delivery to the full-delivery positions of the control rack, the contour of the helix advances the closing of the ports and the beginning of injection. (9) On the downward travel of the plunger, the metered amount of fuel is forced through the center passage of the valve assembly, through the check valve, and against the spray tip valve. When sufficient fuel pressure is built up, the spray tip valve is forced off of its seat and fuel is discharged through the hole-type injector nozzle (para 5-14). The check valve prevents air leakage from the combustion chamber into the fuel system in the event that the spray tip valve does not seat properly. (10) On the return upward movement of the plunger, the high-pressure cylinder is again filled with oil through the ports. The constant circulation of fuel through the injectors back through the return helps to 5-21
maintain an even operating temperature in the injector, which would otherwise tend to run very hot due to extreme pressures. Constant circulation also helps to remove all traces of air from the system. The amount of fuel circulated through the injector is in excess of maximum needs, thus ensuring sufficient fuel for all conditions. 5-18. Pressure-Timed (PT) Injection System.
a. Overall System Operation (Fig. 5-16). The pressure-timed injection system has a metering system that is based on the principle that the volume of liquid flow is proportional to the fluid pressure, the time allowed to flow, and the size of the passage the liquid flows through. The operation of the system is as follows:
(1) A fuel tank with a vented filler cap stores the fuel supply. (2) Fuel is supplied from the tank to the pressure-timed gear (PTG) pump through the delivery line. An in-line filter is placed in series in the line to trap foreign matter and moisture. (3) A return line from the PTG pump to the fuel tank is provided to bleed off excess fuel so that operating pressures can be regulated. (4) The PTG pump (para 5-18b) delivers controlled amounts of fuel to the pressure-timed delivery (PTD) injectors. (5) Delivery of fuel to the PTD injectors is through a common-rail type delivery line.
(6) A common-rail type return line connects the PTD injectors to the fuel tank so that excess fuel may be diverted back to the fuel tank.
b. PTG Injection Pump (Fig. 5-17). The PTG pump is driven directly by the engine at a one-to- one speed ratio. The pump contains four main components. These four components and their respective operations are as follows:
(1) The gear-type pump (para 5-23) draws fuel from the supply tanks and forces it through the pump filter screen to the governor. It is driven by the pump main shaft and picks up and delivers fuel
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(1) Metering (A, Fig. 5-18). This phase begins with the plunger just beginning to move downward and the engine is on the beginning of the compression stroke. The fuel is trapped in the cup, the check ball stops the fuel from flowing backwards, and the fuel begins to be pressurized. The excess fuel flows around the lower annular ring, up the barrel, and is trapped there.
(2) Prelnjection (B, Fig. 5-18). The plunger is almost all the way down, the engine is TA233453
c. PTD Injectors. A PTD injector is provided at each engine cylinder to spray the fuel into the combustion chambers. PTD injectors are of the unit type, operated by an engine-based camshaft. Fuel flows from a connection at the top of the fuel pump
5-23
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almost at the end of the compression stroke, and the fuel is being pressurized by the plunger.
(3) Injection (C, Fig. 5-18). The plunger is almost all the way down, the fuel is injected out the eight orifices, and the engine is on the very end of the compression stroke.
(4) Purging (D, Fig. 5-18). The plunger is all the way down, injection is finished, and the fuel is flowing into the injector, around the lower annular groove, up a drilled passageway in the barrel, around the upper annular groove, and out through the fuel drain. The cylinder is on the power stroke. During the exhaust stroke, the plunger moves up and waits to begin the cycle all over again. 5-19. PSB Distributor lnjection System.
described in paragraph 5-16, uses a pump that sends measured charges of fuel to each injector at a properly timed interval. The difference in the PSB system is that the charges of fuel are sent directly from the pump at the high pressure that is necessary for injection. This eliminates the need for unit-type injectors and the associated linkage and camshafts, making the system less cumbersome. The injectors are of the same basic design as the ones used in the multiple unit injection system (para 5-14). The nozzles usually are of the hole type (para 5-14).
b. The PSB Injector Pump. The PSB injection pump (Fig. 5-20) is compact and self-contained, housing all components of the injectors. Operation is shown in figure 5-21.
(1) The PSB pump contains a plunger-type pump that creates the high-pressure fuel charges for the injectors. The pump is driven by a camshaft
a. Overall System Operation (Fig. 5-19). The PSB distributor system, like the distributor system
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1. SLIDING GEAR 2. TIMING DEVICE SPRING 3. TIMING DEVICE HUB 4. TIMING POINTER 5. TIMING COVER 8. TAPPET ROLLER PIN 7. TAPPET GUIDE S. SPRING LOWER SEAT 9. PLUNGER LOCK 10. PLUNGER INNER SPRING 11. SPRING UPPER SEAT 12. PLUNGER GUIDE 13. DRIVE GEAR RETAINER 14. PLUNGER DRIVE GEAR 15. GEAR THRUST WASHER 16. PLUNGER SLEEVE 17. HYDRAULIC HEAD 18. PLUNGER BORE SCREW 19. FUEL PLUNGER 20. FUEL DELIVERY VALVE 21. DELIVERY VALVE SCREW 22. PLUNGER BUTTON
23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43.
STOP PLATE SMOKE LIMIT CAM GOVERNOR COVER GOVERNOR END CAP GOVERNOR INNER SPRING GOVERNOR OUTER SPRING GOVERNOR HOUSING GOVERNOR WEIGHT SLIDING SLEEVE FRICTION DRIVE SPIDER CAMSHAFT BUSHING-TYPE BEARING TAPPET ROLLER CAMSHAFT CAMSHAFT BALL BEARING INJECTION PUMP HOUSING TIMING DEVICE HOUSING END PLAY SPACER SLIDING GEAR SPACER SPIDER THRUST PLATE WEIGHT AND SPIDER ASSEMBLY OUTER PLUNGER SPRING
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that is contained within the PSB unit. Fuel is delivered to the PSB pump from the fuel tank by the fuel delivery pump at a regulated pressure of approximately 20 psi (137.9 kPa). The low pressure fuel supply enters the pump chamber through the inlet port when the plunger is retracted fully. As the plunger begins its delivery stroke, the fuel inlet passage is blocked, trapping fuel in the pump chamber. The delivery stroke of the plunger then pushes the charge of fuel out of the chamber through the delivery passage. The high-pressure fuel charge then unseats the delivery valve, allowing it to flow into the distribution chamber. (2) The pump plunger has a spool like recess in its diameter about halfway down its sides that, in conjunction with the pump cylinder, forms the distribution chamber. A slot is cut into the plunger at the top of the distribution chamber. As it reciprocates, the plunger also is rotated through a quill gear. As it rotates, the slot lines up with equally spaced passages around the inside of the plunger bore. Each passage is connected to a fuel injector. The reciprocating and rotating motion are timed so that the plunger will go through a delivery stroke as the slot lines up with each injector passage. This enables the PSB injector pump to deliver a fuel charge to each consecutive injector every time the plunger makes one complete revolution. (3) The PSB pump is geared to the engine so that the camshaft rotates at crankshaft speed. The cam contains half as many lobes as the engine has cylinders (there would be three cam lobes if the engine had six cylinders). The pump plunger is geared to rotate at onehalf of camshaft speed. This arrangement allows the PSB pump to deliver a charge of fuel to each injector for every
to
the
(4) A hole called a spill port is drilled through the lower portion of the pump plunger. The spill port is connected to the pump chamber by another drilled passage. The spill port is covered by a plunger sleeve whose position is adjusted by the control lever through an eccentrically mounted pin. (5) The movement of the control lever controls the up and down position of the plunger sleeve. The position of the control lever is determined by the governor (para 5-25). When the sleeve is in its extreme downward position, the spill port is immediately uncovered as the plunger begins its delivery stroke. This causes all of the pressure from the pump chamber to bleed off to the pump return. In this position, there will be no fuel delivery to the injectors. (6) When the plunger sleeve is in the extreme upward position, the spill port is covered until the plunger almost reaches the end of the delivery stroke. This position will deliver maximum fuel to the injectors. As the plunger moves upward, the pressure developed in the pump chamber unseats the delivery valve. Fuel flows into the distribution chamber and is sent to whatever injector is scheduled to receive it by the slot in the plunger. (7) The amount of fuel delivered by each injection charge will increase proportionately as the plunger sleeve is moved from its extreme downward to its extreme upward position. The higher the plunger sleeve, the longer the effective pump stroke (plunger movement before the spill port is uncovered).
Section IV. FUEL SUPPLY PUMPS 5-20. General. Fuel injection pumps must be supplied with fuel under pressure for the following reasons: a. The injection pumps lack the suction ability to draw fuel from the tank by themselves. c. Without a supply pump, the system would lose its prime whenever the pump is in the no- delivery mode. The supply pumps in use generally are of the positive displacement type with a performance that is independent of any reasonable variations in viscosity, pressure, or temperature of the fuel. In a majority of the equipment, the fuel supply pump is built into the injection pump unit. This cuts down on fuel tubing and the complexity of the
b. It is important to supply fuel to the injection pump In excess so that fuel may be used to cool and lubricate the system before bypassing it back to the tank.
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equipment, and allows the supply pump to share the same engine power takeoff as the injection pump. 5-21. Vane-Type Supply Pump. The basic overall operation of the vane-type supply pump is the same as the vane-type oil pump (para 20-6) 5-22. Plunger-Type Supply Pump (Fig. 5-22).
b. Operation.
(1) The plunger follows the camshaft by the force of its plunger spring. As the follower comes off the high point of the cam lobe, the plunger moves toward the retracted position. This plunger movement creates a suction in the pump chamber, causing fuel to enter through the inlet valve.
a. This type of pump always is mounted on the Injection pump, where it is driven by the injection pump camshaft. It is a variable-stroke, self regulating pump
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(2) As the cam lobe comes around again, It forces the plunger upward. This forces the fuel out of the chamber through the outlet valve and the Injection pump. (3) The cam follower drives the plunger through a spring. The spring Is calibrated so that it will flex rather than drive the plunger when the pressure In
the pump chamber reaches the desired maximum. This effectively regulates pump pressure. 5-23. Gear-Type Supply Pump. The basic overall operation of the gear-type supply pump Is the same as the gear-type oil pump (para 20-4).
Section V. GOVERNORS 5-24. General. All diesel engines require governors to prevent overspeeding of the engines under light loads. Automotive diesel engines also demand control of idling speed. Any of the governors provide a variable-speed control that, In addition to controlling minimum and maximum speeds, will maintain any intermediate speed desired by the operator. Engine speed in a diesel Is controlled by the amount of fuel injected. The Injection, therefore, is designed to supply the maximum amount of fuel that will enable it to operate at full load while reaching a predetermined maximum speed (rpm). If, however, the maximum fuel charge were supplied to the cylinders while the engine was operating under a partial or unloaded condition, the result would be overspeeding and certain failure. Thus, it can be seen that the governor must control the amount of fuel injected in order to control the engine speed. 5-25. Actuation. Governors may be actuated through the movement of centrifugal flyweights or by the airpressure differential produced by a governor valve and venturi assembly. The centrifugal flyweight type may incorporate a mechanical linkage system to control the injection pump, or it may include a hydraulic system to transmit the action of the weights to the pump. On engines where the rate of acceleration must be high, the governorcontrolling weights must be small to obtain the required rapid response from the governor. The problem is that the smaller flyweights will not exert enough force to control the injection pump properly. When this is the case, the flyweights will be used to control a hydraulic relay valve, which, in turn, will control the Injection pump through a servo piston. 5-26. Mechanical (Fig. 5-23). (Centrifugal) Governors counterbalanced by springs. When the speed of the engine increases, the weights fly outward, pulling with them suitable linkage to change the setting of the pump control rod. The governor linkage is connected to the injection pump in such a manner that the spring moves the control mechanism toward the full-fuel position. The outward movement of the governor fly-weights, through the sliding governor sleeve, will move the pump control rod toward the no-fuel position against the force of the governor spring.
b. With this type of governor, the operator controls the tension of the governor spring to control the quantity of fuel rather than operating the fuel control rod directly. The fuel delivery control system of the injection pump is connected to the governor yoke in such a manner that any movement of the yoke will affect directly the quantity of the fuel injected. The spring tension is controlled by the operating lever, the movement of which is determined by the position of the foot throttle. The travel of the operating lever is limited by the idle and maximumspeed screws. When the weights are fully collapsed (engine stopped), the spring moves the sliding sleeve and yoke so that the fuel injection pump is in the full-fuel position. When the weights are fully extended, the sliding sleeve and the yoke move to the rear and decrease the amount of fuel delivered. c. If the load on the engine is decreased, the engine tends to accelerate. However, when the engine does accelerate, the increased centrifugal force causes the governor flyweights to move outward, resulting in the movement of the fuel control rod through the governor sleeve toward the no-fuel position. This will cause an equilibrium to develop between the flyweights and the governor spring. The movement of the operating lever varies the spring tension. This will cause a change in the point of equilibrium between the
a. The operation of the mechanical governor is based on the centrifugal force of rotating weights 5-30
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d. To accelerate the vehicle with a given load, the foot throttle Is depressed, which in turn increases the governor spring tension. The increase in tension causes the governor sleeve to move the control rod through the yoke toward the full-fuel position. As engine speed increases, the flyweights will move outward until they reach the point of equilibrium with the governor spring. At this point, engine speed will stabilize.
5-27. Vacuum Governors (Fig. 5-24).
b. When the engine is running, the pressure In the sealed chamber is reduced below the atmospheric pressure existing in the other chamber. TA233459
a. The vacuum governor operates by utilizing the pressure drop created by the velocity of the air passing 5-31
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d. For any position of the governor valve between idling and full load of the engine, the diaphragm finds its relative position. Because any movement of the diaphragm also is transmitted to the control rod, the amount of fuel delivery definitely is controlled at all speeds. The diaphragm is moved in the direction of less fuel delivery as the pressure drop between the chambers is increased. The spring will move the control rod in the direction of greater fuel delivery as the pressure drop is decreased.
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Section VI. 5-28.General. Alarge percentage of fuel Injection pumps have timing devices incorporated in them. Varying the time when fuel injection begins will improve diesel engine performance and fuel economy for the same reasons that varying spark timing will improve the performance of a gasoline engine(para2-25). 5-29. Description (Fig. 5-25).
bore in the housing guides and supports the spider assembly. A timing opening with cover Is located in the top of the housing and is used to observe the position of the timing pointer in relation to the timing mark on the timing device hub during injection pump timing procedures.
a. The timing device usually consists of an aluminum casting with mounting flanges at both ends. A
b. The timing device hub, with external left hand helical splines for engaging the internal helical splines of the sliding gear, has a tapered
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bore and keyway. The hub Is secured to the camshaft extension by a woodruff key, nut, and setscrew. The hub usually Is counterbored to receive the timing device springs. The springs oppose the flyweight forces of the weight and spider assembly. c, The weight and spider assembly has external right-hand helical splines to mesh with the Internal helical splines of the sliding gear. The spllned end is machined to receive the end play spacer. Three flyweights are pinned to a flange adjacent to the spilnes. The weight and spider thrust plate located between the flange and the timing device housing carries the back thrust of the flyweights and prevents housing wear.
both the weight and spider assembly and the timing device hub. Correct assembly of the spline train is ensured by a wide land on both the hub and weight and the spider assembly. The sliding gear has a missing tooth on each set of Internal splines to receive the wide lands. Three arms extend from the outer surface of the sliding gear to provide seats for the three timing device springs. The force on these springs Is controlled by a sliding gear spacer. 5-30. Operation (Fig. 5-26).
d. The sliding gear has Internal left-hand helical splines at one end and Internal right-hand helical splines at the other end and meshes with the external splines of
a. As the engine rotates the weight and spider assembly, centrifugal force opens the flyweights from their collapsed position against the force of the three timing device springs.
TM 9-8000
b. As the flyweights swing out, the sliding gear is forced toward the timing device hub.
c. The longitudinal movement of the sliding gear on
its helical spline causes a slight change in the rotational relationship in the injection pump to the engine, causing injection to begin slightly earlier in the power stroke.
Section VII. COLD WEATHER STARTING AIDS 5-31. Purpose. Diesel engines are very difficult to start In cold weather. This Is due mainly to the low volatility of the fuel. The two most popular methods of assisting a diesel engine in starting are: the Instrument panel. (3) The Intake manifold flame heater system has a filter to remove Impurities from the fuel before it reaches the nozzle. (4) Two fuel solenoid valves are used In the flame heater system. The valves are energized (open) whenever the flame heater system is activated. The valves ensure that fuel Is delivered only when the system Is operating. They stop fuel flow the Instant that the engine, or heater system, is shutdown. 5-33. Ether Injection System (Fig. 5-28).
a. Preheating the Induction air In the Intake manifold so that adequate vaporization will take place for combustlon. b. Injecting a fuel Into the engine that remains volatile enough In cold weather to initiate combustion.
5-32. 5.27). Intake Manifold Flame Heater System (Fig.
a. General. Engines are equipped with a flametype manifold heater for heating the induction air during cold weather starting and warm-up operations. b. Operation. The flame heater assembly is composed of a housing, spark plug, flow control nozzle, and two solenoid control valves. The spark plug Is energized by the flame heater Ignition unit. The nozzle sprays fuel under pressure Into the Intake manifold elbow assembly. The fuel vapor is Ignited by the spark plug and burns In the Intake manifold, heating the air before it enters the combustion chambers.
(1) Because this system uses fuel from the fuel tank of the vehicle, its components must be compatible with all approved fuels when the system Is used with a multifuel engine. (2) The flame fuel pump assembly Is a rotary type, driven by an enclosed electric motor. The fuel pump receives fuel from the vehicle fuel tank through the vehicles supply pump and delivers It to the spray nozzle. The pump Is energized by an ON-OFF switch located on 5-35
a. General. The ether Injection system assists In the cold weather starting of a diesel engine by Injecting ether Into the Intake manifold. Ether, which is very volatile, will vaporize readily In cold weather, Initiating combustion. b. Operation. A pressurized canister containing ether Is fitted to the engine. The flow of ether from the canister to the spray nozzle Is controlled by a solenoid valve that closes when it is de-energlzed. This solenoid Is controlled by a push-button switch on the Instrument panel.
(1) When the switch Is pushed, the solenoid is energized. This opens the ether canister. Pressure from the canister pushes ether through a connecting tube to the nozzle, where it discharges Into the Intake. (2) The system contains a coolant temperature sensor that will keep the system from functioning when coolant temperature is above 50F(100C).
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a. Primary Filters (Fig. 5-29). Metal filters are used as primary filters because the fine particles that will pass through them are not injurious to the supply pump. The filter element is usually of the metal disk type, as described in paragraph 4-2. Solids larger than 0.005 in. (0.127 mm) remain outside the metal disks, while the larger foreign matter and the majority of the water settles to the bottom of the bowl. From here, the foreign matter can be removed through a drain plug. A ball relief valve in the filter cover enables the oil to bypass the filter element if the disks become clogged. b. Secondary Filters (Fig. 5-30). Fabric filters, because of their greater filtering qualities, are used principally as main filters for protecting the fuel injection pump. Many of the filters In use are similar to the lubricating oil filters described in paragraph 8-13. The bag-type filter also is used. The filtering medium is a large bag of close, evenly woven, lintless, acid-resisting textile material. Maximum benefit is derived from the bags large area by keeping the sides of the TA233464
5-37
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TA233465 5-38
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housing. The cavity contains a rotor that is connected to the turbine output shaft. Stationary reaction vanes are mounted on both sides of the rotor. When the transmission fluid fills the cavity, it churns against the reaction vanes and slows down the rotor. The retarding efforts then are transmitted to the drive line to slow down the vehicle. The retarder will continue to operate as long as the retarder pedal is depressed. The rotational energy is transformed into heat energy and absorbed by the transmission fluid. If the retarder is operated continuously, the fluid temperature can rise faster than it can be cooled. Once this happens and the fluid temperature approaches a predetermined level, a warning light on the instrument panel indicates that the retarder operation should be discontinued until the fluid cools down and the warning light goes out. When the retarder pedal is released, the retarder valve closes and the fluid in the cavity automatically discharges and permits the rotor to turn without drag.
5-40. Jacobs Engine Brake. The Jacobs engine brake (Fig. 5-31) consists of a slave piston mounted over the exhaust valve. The system operates by opening the exhaust valve near the top of the compression stroke. This releases the compressed cylinder charge into the exhaust system. This blowdown of compressed air into the exhaust system prevents the return of energy from the piston on the expansion stroke. The result is an energy loss because the work done in compressing the charge is not returned to the usable energy. The system Is operated by a three position switch that allows the driver to select the degree of braking required. The three-position switch is set to allow braking on two, four, or all cylinders. This enables the driver to predetermine how much braking will be needed to properly slowdown the vehicle.
TM 9-8000
CHAPTER 6 PROPANE FUEL SYSTEMS Section I. CHARACTERISTICS tanks also are filled between 80 and 90 percent of capacity to allow for thermal expansion. These pressurized fuel tanks eliminate the need for a fuel pump. LPG burns at a slower rate than gasoline, which results in smoother operation because of prolonged power impulses. Being a gas, LPG minimizes crankcase dilution and prolongs engine life.
6-1. Liquefied Petroleum Gas. Liquefied petroleum gas, or LPG, is used for fuel on some vehicles. This fuel remains a liquid under pressure and vaporizes when it comes in contact with the atmosphere. LPG fuel is stored in heavy steel tanks mounted on the vehicle. To keep the mixture liquefied, these tanks are pressurized between 20 and 175 psi (137.9 and 1206.6 kPa). The
Section II. BASIC SYSTEM 6-2. Operation. A typical LPG system is illustrated in figure 6-1. In this system, liquid fuel exits the storage tank by a tube mounted inside the supply tank. The tube is configured so that it is immersed in the liquid fuel at all times. The fuel then is routed to the first regulator. This regulator reduces pressure to 4 to 15 psi (27.58 to 103.42 kPa). The liquid fuel exits the regulator as half vapor and half liquid. The vapor and liquid combination then Is heated, causing it to become all vapor. The second regulator reduces the pressure of the gas to atmospheric pressure. The gas then enters a carburetor or mixing valve and then enters the cylinders.
TM 9-8000 CHAPTER 7 EXHAUSTAND EMISSION CONTROL SYSTEMS Section I. EXHAUST SYSTEM 7-1. Purpose (Fig. 7-1). The waste products of combustion are carried from the engine to the rear of the vehicle by the exhaust system, where they are expelled to the atmosphere. The exhaust system also serves to dampen engine noise. 7-2. Exhaust Manifold (Fig. 7-2). The exhaust manifold connects all of the engine cylinders to the exhaust system. It usually Is made of cast Iron. If the exhaust manifold Is formed properly, It can create a scavenging action that will cause all of the cylinders to help each other get rid of exhaust gases. Back pressure (the force that the pistons must exert to push out the exhaust gases) can be reduced by making the manifold with smooth walls and without sharp bends. All of these factors are taken into consideration when the exhaust manifold is designed and the best possible manifold is manufactured to fit into the confines of the engine compartment. 7-3. Manifold Heat Control Valve (Fig. 7-3). A valve Is placed In the exhaust manifold on some gasoline engines to deflect exhaust gases toward a hot spot In the Intake manifold until the engine reaches operating temperature. This valve, whose purpose Is described in paragraph 4-5, is a flat metal plate that is the same shape as the opening that it controls. It pivots on a shaft and is operated by a thermostatic coil spring. The spring pulls the valve closed against a counterweight before warmup. The spring expands as the engine warms up and the counterweight pulls the valve open: 7-4. Muffler (Fig. 7-4). a. The muffler reduces the acoustic pressure of exhaust gases to discharge them to the atmosphere with a minimum of noise. The muffler usually is located at a point about midway in the vehicle with the exhaust pipe between it and the exhaust manifold and the tailpipe leading from it to the rear of the vehicle. b. The inlet and the outlet of the muffler usually are slightly larger than their connecting pipes so that It may hook up by slipping over them. The muffler then Is secured to the exhaust pipe and the tailpipe by clamps.
TM 9-8000
Section II. EMISSION CONTROL SYSTEMS 7-5. Purpose (Fig. 7-5). When the fuel is burned In the combustion chamber, the ideal situation would be to have the fuel combine completely with the oxygen from the intake air. The carbon would then combine to form carbon dioxide (COI, the hydrogen would combine to form water (H20), and the nitrogen that is present In the intake air would stand alone. The only other product present in the exhaust would be any oxygen from the intake air that was not used in the burning of the fuel. In a real life situation however, this is not what happens. The fuel never combines completely with the oxygen and undesirable exhaust emissions are created as a result. The major pollutants are: a. Carbon Monoxide (CO). Carbon monoxide is formed as a result of insufficient oxygen in the combustion mixture and combustion chamber temperatures that are too low. Carbon monoxide Is a colorless, odorless gas that is poisonous TA233470 7-2
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TA233471 7-3
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TA233473 7-5
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crankcase of blowby fumes. The fumes are then aspirated back into the engine where they are reburned. (1) A hose is tapped into the crankcase at a point that is well above the engine oil level. The other end of the hose is tapped into the intake manifold or the base of the carburetor. It should be noted that if the hose is tapped into the carburetor base, it will be in a location that is between the throttle valves and the intake manifold so that it will receive manifold vacuum. (2) An inlet breather is installed on the crankcase in a location that is well above the level of the engine oil. The inlet breather also is located strategically to ensure complete purging of the crankcase by fresh air. (3) The areas of the crankcase where the vacuum hose and the inlet breather are tapped have baffles to keep the motor oil from leaving the crankcase. (4) A flow control valve is installed in the line that connects the crankcase to the manifold vacuum. It is called a positive crankcase ventilation (PCV) valve and serves to avoid the air-fuel mixture by doing the following: (a) Any period of large throttle opening will be accompanied by heavy engine loads. Crankcase blowby will be at its maximum during heavy engine loads. The PCV valve will react to the small amount of manifold vacuum that also is present during heavy engine loading by opening fully through the force of its control valve spring. In this way, the system provides maximum effectiveness during maximum blowby periods. (b) Any period of small throttle opening will be accompanied by small engine loads, high manifold vacuum, and a minimum amount of crankcase blowby. During these periods, the high manifold vacuum will pull the PCV valve to its position of minimum opening. This is Important to prevent an excessively lean air-fuel mixture. (c) In the event of engine backfire (flame traveling back through the intake manifold), the reverse pressure will push the rear shoulder of the control valve against the
valve body. This will seal the crankcase from the backfire, which could otherwise cause an explosion. (5) The positive crankcase ventilation system can be the open or the closed type. (a) The open type has an inlet breather that is open to the atmosphere. When this system is used, it is possible for a portion of the crankcase blowby to escape through the breather whenever the engine is under a sustained heavy load. This is unacceptable on later automotive equipment and, as a result, the system is no longer used. (b) The closed type has a sealed breather that is connected to the air filter by a hose. Any blowby gases that escape from the breather when this system is used will be aspirated into the carburetor and burned. This Is the system that is currently used. 7-8. Catalytic Converters (Fig. 7-8). a. Purpose. As stated in paragraph 7-5, it is virtually impossible to keep carbon monoxide and hydrocarbon emissions at acceptable levels by controlling them in the cylinder without shortening engine life considerably. It has been found that the most practical method of controlling these emissions is outside of the engine in a device called a catalytic converter. The catalytic converter is a device that is similar in appearance to a muffler. It is positioned in the exhaust system, usually between the engine and the muffler. As the engine exhaust passes through the converter, carbon monoxide and hydrocarbons are oxidized (combined with oxygen), changing them to carbon dioxide and water. b. Construction and Operation. The catalytic converter contains a material (usually platinum or palladium) that acts as a catalyst. A catalyst is something that causes a reaction between two substances without actually getting involved. In the case of the catalytic converter, oxygen is joined chemically with carbon monoxide and hydrocarbons in the presence of its catalyst. (1) The oxidation process that occurs within the catalytic converter generates a
7-7
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TM 9-8000 c. Special Considerations. Vehicles equipped with catalytic converters require special considerations and generally are made to work in conjunction with other emission systems. (1) The use of gasoline containing lead is destructive to a catalytic converter. in use, the lead will coat the catalyst as the exhaust passes through the converter. This will halt catalytic converter operation completely. (2) The use of gasoline with a high sulphur content will cause considerable amounts of sulphur dioxide to be produced in the converter and emitted to the atmosphere. (3) A heat shield must be installed between the converter and the vehicle floor because the converter can, at times, produces enough heat to ignite the interior floor covering. A heat shield also is installed under the converter to minimize the possibility of igniting objects such as grass and leaves. This is of particular importance to military vehicles during cross-country operation. (4) An overly rich air-fuel mixture is disastrous to a catalytic converter. Excessive carbon monoxide and hydrocarbons result in such a high rate of oxidation in the converter that it can overheat to the point where its outer shell actually can melt. Because of this, the engine always must be kept in the proper state of tune. (5) An adequate amount of oxygen must be present in the exhaust stream for the catalytic converter to operate. Therefore, a supporting system such as an air injection system (para 7-9) usually is placed on catalytic converter equipped engines to dilute the exhaust stream with fresh air. 7-9. Air Injection Systems. a. Purpose. Air injection systems mix fresh air with the vehicle exhaust. There are two purposes for air injection systems: (1) The exhaust gases still are burning as they are pushed out of the combustion chamber through the exhaust valve. The burning will be prolonged and intensified by injecting fresh air into the exhaust manifolds at each exhaust port. This more complete burning will reduce carbon monoxide and hydrocarbon emissions greatly. (2) Air injection is vital to ensure an adequate supply of oxygen in the exhaust stream on vehicles equipped with catalytic converters. b. Air Pump System (Fig. 7-9), The air pump system uses an engine-driven pump to force air into the exhaust. (1) The pump usually is a vane-type pump that operates exactly like the vane-type oil pump (para 20-6). The pump is driven by a belt. A relief valve is built into the pump to prevent it from building too much pressure. (2) The air from the pump is directed through rubber hoses to the air manifold. The air manifold distributes the air to each exhaust port. The point where the air is fed in may be located at the exhaust manifold or directly into the cylinder head at the exhaust port. The air is fed in through nozzles called injection tubes. (3) A check valve is installed between the air manifold and the air pump feed hose to prevent hot exhaust from feeding back to the pump. (4) Whenever the throttle is closed suddenly, a temporary overrich air-fuel mixture will result. The rich mixture will leave the engine with a large percentage of it unburned. When an engine is equipped with an air pump, the rich mixture will flare up and explode as it enters the exhaust and contacts the injected fresh air, resulting in a backfire condition. To correct this situation, an antibackfire valve is installed in series in the air pump feed hose. The antibackfire valve prevents the overrich mixture from occurring by injecting a short burst of air into the intake manifold whenever the throttle is released, thus preventing a backfire. Some models use a diverter valve. The diverter valve eliminates backfiring temporarily by diverting the air pump delivery to the atmosphere whenever the throttle is released suddenly, allowing the rich mixture to pass through. c. Naturally Aspirated System (Fig. 7-10). The naturally aspirated system uses the negative pulses of the exhaust system to draw
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TM 9-8000 (1) The crossover passage in the intake manifold is used as the source of exhaust gas for the system. A vacuum-operated EGR valve controls the passage of exhaust gas to the engine intake. Exhaust gas recirculation will occur whenever vacuum is applied to the valve. (2) The EGR valve should not be operational before the engine reaches operating temperature. If it were, it would cause extreme drivability problems. Also, there is no reason for exhaust gas recirculation before warmup because virtually no oxides of nitrogen are manufactured. The EGR valve also will not operate during periods of heavy engine loading because it would hinder performance. (3) There are two different methods of supplying vacuum to the EGR valve.
(a) One system uses a vacuum port into the carburetor throat located just above the throttle plate. As the throttle begins to open, vacuum will begin to be applied to the port and operate the EGR valve. The valve will continue to operate fully until approximately half throttle is reached. As the throttle is open past the halfway point, exhaust gas recirculation gradually will diminish to zero as the throttle approaches the fully opened position. (b) Another system uses a vacuum port that Is directly in the carburetor venturi. This will provide vacuum for the EGR valve whenever the engine Is running at high speed. The problem with using venturi vacuum is that it is not strong enough to operate the EGR valve. To make the system feasible, manifold vacuum is used to operate the EGR valve through a vacuum amplifier. The vacuum amplifier switches the manifold vacuum supply onto the EGR valve whenever venturi vacuum Is applied to its signal port. At times of large engine loading (wide throttle opening), manifold vacuum will be weak, producing the desired condition of no exhaust gas recirculation. (4) A switch that uses coolant temperature as an Indicator is used to block vacuum to the EGR valve before the engine reaches operating temperature. This valve is used with all systems.
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TM 9-8000 7-11. Fuel Evaporation Control System (Fig. 7-12). a. Purpose. Gasoline evaporation is a major source of hydrocarbon emissions in automotive equipment. Gasoline, because it is very volatile, evaporates In the fuel tank and the carburetor float bowl. The vaporized fuel must be vented. On uncontrolled vehicles, fuel vapor is vented to the atmosphere through the gas cap and the idle vent (para 4-14). The discharge of these vapors to the atmosphere no longer is acceptable on automotive vehicles. As a result, all currently produced vehicles are equipped with a fuel evaporation control system. b. Construction and Operation. The fuel evaporation control system Is integrated to control fuel tank and carburetor evaporation together. (1) A charcoal-filled canister Is used to store gasoline vapors. The fuel tank and the idle vent are connected to the canister. Any evaporation that occurs during periods of vehicle shutdown is collected in the canister and stored in the charcoal. (2) A purge line connects the canister to the carburetor through a vacuum port. The port is tapped into the carburetor throat just above the throttle valve. (3) The bottom of the charcoal canister is open. The opening is covered by a fiberglass filter. (4) Fuel vapors that are stored in the canister are purged as the throttle is open after the engine is started. The vacuum at the purge line causes fresh air to enter through the bottom of the canister. The filter keeps foreign matter from entering the canister. As the air passes through the charcoal it removes the stored fuel vapors. The vapors then are drawn into the carburetor through the purge line, where they are reburned. (5) The fuel cap is a pressure-vacuum type. Air can be drawn into the tank to occupy the space left by the gasoline as it is burned. However, it will not allow any fumes to pass out of the tank through it. (6) A valve is installed in series in the vent line to the fuel tank. It will prevent gasoline from passing from the tank to the canister in the event of overfill or vehicle rollover.
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TM 9-8000 CHAPTER 8 LUBRICATION SYSTEM Section I. PURPOSE 8-1. General (Fig. 8-1). The lubrication system In an automotive engine supplies a constant supply of oil to all moving parts. This constant supply of fresh oil is important to minimize wear, flush bearing surfaces clean, and remove the localized heat that develops between moving parts as a result of friction. In addition, the oil that is supplied to the cylinder walls helps the piston rings make a good seal to reduce blowby (para3-6). 8-2. Oil as a Lubricant. The primary function of engine oil is to reduce friction between moving parts (lubricate). Friction, in addition to wasting
TM 9-8000 engine power, creates destructive heat and rapid wear of parts. The greater the friction present between moving parts, the greater the energy required to overcome that friction. The Increase In energy adds to the amount of heat generated, causing moving parts that are deprived of oil to melt, fuse, and seize after a very short period of engine operation. The effectiveness of a modern lubrication system makes possible the use of friction-type bearings (para 19-7) In an engine. Friction between the pistons and the cylinder walls Is severe, making effective lubrication of this area Imperative. Lubrication of the connecting rod and main bearings is crucial because of the heavy loads that are placed on them. There are many other less critical engine parts that also need a constant supply of oil, such as the camshaft, valve stems, rocker arms, and timing chains. 8-3. Oil as a Coolant. Engine oil circulated throughout the engine also serves to remove heat from the friction points. The oil circulates through the engine and drains to the sump. The heat picked up by the oil while It Is circulated Is removed by an airflow around the outside of the sump. In some Instances where the sump Is not exposed to a flow of air, It Is necessary to add an oil cooling unit that transfers the heat from the oil to the engine cooling system.
Section II. ENGINE OILS 8-4. General. Mineral oil Is used in most internal combustion engines. Engine oils generally are classified according to their performance qualilties and their thickness. a. How Oil Lubricates (Fig. 8-2). (1) Every moving part of the engine is designed to have a specific clearance between it and its bearing. As oil is fed to the bearing it forms a film, preventing the rotating part from actually touching the bearing. (2) As the part rotates, the film of oil acts as a series of rollers. Because the moving parts do not actually touch each other, friction Is reduced greatly. (3) It is Important that sufficient clearance be allowed between the part and the bearing. Otherwise the film might be too thin. This would allow contact between the parts, causing the bearing to wear or burn up. (4) It also is Important that the clearance not be too large between rotating parts and their bearings. This Is true particularly with heavily loaded bearings like those found on the connecting rods. The heavy loads could then cause the oil film to be squeezed out, resulting In bearing failure. b. Oil Contamination (Fig. 8-3). Oil does not wear out but it does become contaminated. When foreign matter enters through the air Intake, some of it will pass by the piston rings and enter the crankcase. This dirt, combined with foreign matter entering through the crankcase breather pipe, mixes with the oil, and when forced into the bearings, greatly accelerates wear. Water, one of the products of combustion, will seep by the piston rings as steam and condense In the crankcase. The water In the crankcase then will emulsify with the oil to form a thick sludge. Products of fuel combustion will mix with the oil as they enter the crankcase through blowby (para 3-6). The oil, when mixed with the contaminants, loses its lubricating qualities and becomes acidic. Engine oil must be changed periodically to prevent contaminated oil from allowing excessive wear and causing etching of bearings. Oil contamination is controlled In the following ways. (1) Control engine temperature; a hotter running engine burns its fuel more completely and evaporates the water produced within it before any appreciable oil contamination occurs. (2) The use of oil filters removes particulate matter from the oil before it reaches the bearings, minimizing wear. (3) An adequate crankcase ventilation system will purge the crankcase of blowby fumes effectively before a large amount of contaminants can mix with the oil. (4) The use of air intake filters trap foreign material and keep it from entering the engine. c. Oil Dilution (Fig. 8-3). Engine oil thins out when mixed with gasoline, causing a dramatic
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TM 9-8000 after 1980. The SF oil is designed to meet the demands of the small, high-revving engines that are popular due to the trend toward downsizing of vehicles. An SF oil can be used In all automotive vehicles. API service ratings have related military specifications designations. (7) CA. Meets all automotive manufactures requirements for gasoline and naturally aspirated diesel engines operated on low sulfur fuel. Widely used during the 1940s and 1950s. (8) CB. Meets all automotive manufactures requirements for gasoline and naturally aspirated diesel engines operated on high sulfur fuel, introduced in 1949. (9) CC. Meets all automotive manufactures requirements for lightly supercharged diesel and heavy duty gasoline engines, introduced in 1961. (10) CD. Meets all automotive manufactures requirements for moderately supercharged diesel engines, introduced in 1955. 8-6. VISCOSITY AND VISCOSITY MEASUREMENTS. a. General. The viscoity of an oil refers to its resistance to flow. When oil is hot, it will flow more rapidly than when it is cold. In cold weather, therefore, oil should be thin (low viscosity) to permit to retain its film strength. The ambient temperature in which a vehicle operates determines feather an engine oil of high or low viscosity should be used. If, for example, too thin an oil were used in hot weather, consumption would be high because It would leak past the piston rings easily. The lubricating film would not be heavy enough to take up bearing clearances or prevent bearing scuffing. In cold weather, heavy oil would not give adequate lubrication because its flow would be sluggish; some parts might not receive oil at all. b. Viscosity Measurement. Oils are graded according to their viscosity by a series Society of Automotive Engineers (SAE) numbers. The viscosity of the oil will increase progressively with the SEA number. An SAE 4 oil would be very light (low viscosity) and SAE 90 oil would be very heavy (viscosity). The viscosity of the oil used in gasoline engines generally ranges from SAE 5 (arctic use) to SAE 60 (desert use). It should be noted that the SAE number of the oil has nothing to do with the quality of the oil. The viscoity number of the oil is determined by heating the oil to a predetermined temperature and allowing it to flow through a precisely sized orifice while measuring the rate of flow. The faster an oil flows, the lower the viscosity. The testing device is called a viscosimeter. Any oil that meets SAE low temperature requirements will be followed by the letter W. An example would be SAE 10W. 8-7. Multiweight Oils. Multiweight oils are manufactured to be used In most climates because they meet the requirements of a light oil in cold temperatures and of a heavy oil in hot temperatures. Their viscosity rating will contain two numbers. An example of this would be 10W-30. An oil with a viscosity rating of 10W-30 would be as thin as a 10Wweight oil at 0 f(-17.7 c). 8-8. Detergent Oils. Detergent oils contain additives that help keep the engine clean by preventing the formation of sludge and gum. All SE and SF oils are detergent oils.
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TM 9-8000 SECTION III. OIL PUMPS 8-9. General. Oil pumps are mounted either inside or outside of the crankcase, depending on the design of the engine. They usually are mounted so that they can be driven by a worm or spiral gear directly from the camshaft. Oil pumps generally are of the gear or the rotor type. 8-10. Rotor-Type Oil Pump (Fig. 8-4). Refer to paragraph 5-21 for the operation of a gear-type oil pump. 8-11. Gear-Type Oil Pump (Fig. 8-5). Refer to paragraph 5-23 for the operation of a gear-type oil pump. 8-12. Oil Strainer and Pickup (Fig. 8-6). Most manufacture of in-line and V-type engines place at least one oil strainer or screen in the lubrication system. The screen usually Is a fine mesh bronze screen that is located in the oil pump on the end of the oil pickup tube. The oil pickup tube then is threaded directly into the pump inlet or may attach to the pump by a bolted flange. A fixed-type strainer, like the one described, is located so that a constant supply of oil will be assured. Some automotive engines use a pickup that is hinged from the oil pump. The pickup is designed to float on top of the oil, thus preventing sediment from being drawn into the oiling system. 8-13. Oil Filters. a. General (Fig. 8-7). The oil filter removes most of the Impurities that have been picked up by the oil as it is circulated through the engine.
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Figure 8-13. Oil Pressure Regulator Section IV. TYPES OF LUBRICATION SYSTEMS
8-17. Splash System (Fig. 8-14). The splash lubrication system no longer is used in automotive engines, though it is used in small equipment engines. In a splash lubrication system, dippers on the connecting rods enter the oil in the crankcase with each crankshaft revolution, thus splashing the oil. As the oil is thrown upward, it finds its way into the various engine parts. A passage Is drilled In each connecting rod from the dipper to the bearing to ensure lubrication. This system Is too uncertain for modern automotive applications. One reason is that the level of oil in the crankcase will vary greatly the amount of lubrication received by the engine; a high level results in excess lubrication and oil consumption and a slightly low level results In inadequate lubrication. 8-18. Combination Splash and Force-Feed System (Fig. 8-15). In the combination system, oil is delivered to some parts by means of splash and to other parts through oil passages, under pressure from a pump In the crankcase. The main and the camshaft bearings are usually the items that are force fed while the connecting rods are fitted with dippers that supply oil to the rest of the engine by splash. Some configurations utilize small troughs under each connecting rod that are kept full by small nozzles that deliver oil under pressure from the oil pump. These cil nozzles deliver an increasingly heavy stream as speed increases. At very high speeds these oil streams are powerful enough to strike the dippers directly. This causes a much heavier splash so that adequate lubrication of the pistons and the connecting rod bearings is provided at higher speeds. If a combination system is used on an overhead valve engine, the upper valve train is lubricated by pressure from the oil pump. 8-19. Force-Feed Lubrication System (Fig. 8-16). A somewhat more complete pressurization of lubrication is achieved in the force-feed lubrication system. Oil is forced by the oil pump
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TM 9-8000 on to lubricate the pistons and walls by squirting out through strategically drilled holes. This lubrication system is used in virtually all engines that are equipped with semifloating piston pins (para3-7). 8-20. Full Force-Feed Lubrication System (Fig. 8-17). In the full force-feed lubrication system, all of the bearings mentioned In paragraph 8-18 are lubricated by oil under pressure. This includes main bearings, rod bearings, camshaft bearings, and the complete valve mechanism. In addition, the full force-feed lubrication system provides lubrication under pressure to the pistons and the piston pins. This is accomplished by holes drilled the length of the connecting rod, creating an oil passage from the connecting rod bearing to the piston pin bearing. This passage not only feeds the piston pin bearings, but also provides lubrication for the pistons and cylinder walls. This lubrication system is used in virtually all current automotive engines that are equipped with fullfloating piston pins (para 3-7).
9-1. Need for Cooling. All internal combustion engines are equipped with some type of cooling system because of the high temperatures they generate during operation. High temperatures are necessary to generate the high gas pressures that act on the head of the piston. Power cannot be produced efficiently without high temperatures. However, it is not possible to use all of the heat of combustion without harmful results. The temperature in the combustion chamber during the burning of the fuel is well above the melting point of iron. Therefore, if nothing is done to cool the engine during operation, valves will burn and warp, lubricating oil will break down, and bearings and pistons will overheat, resulting in engine seizure. 9-2. Cooling Mediums. a. Liquid. Liquid is the most popular coolant in automotive use. A liquid cooling system provides the most positive cooling and is best for maintaining an even engine temperature. b. Air. Air cooling is most practical for small
vehicles and equipment because no radiator or hoses are required. Air cooling generally will not be used wherever water cooling is practical. This is because aircooled engines do not run at even temperatures and require extensive use of aluminum to dissipate heat. c. Other Sources of Engine Cooling. There are other sources of heat dissipation for the engine in addition to the cooling system. (1) The exhaust system dissipates as much, if not more, heat than the cooling system, although that is not its purpose. (2) The engine oil, as stated in paragraph 81, removes heat from the engine and dissipates it to the air from the sump. (3) The fuel provides some engine cooling through vaporization. (4) A measurable amount of heat is dissipated to the air through radiation from the engine.
Section II. LIQUID COOLING SYSTEMS 9-3. Flow of Coolant (Fig. 9-1). A simple liquid-cooled cooling system consists of a radiator, coolant pump, piping, fan, thermostat, and a system of jackets and passages in the cylinder head and cylinder block through which the coolant circulates. Some engines are equipped with a water distribution tube inside the cooling passages that directs additional coolant to the points where the temperatures are highest. Cooling of the engine parts is accomplished by keeping the coolant circulating and in contact with the metal surfaces to be cooled. The pump draws the coolant from the bottom of the radiator, forces it through the jackets and passages, and ejects it into the upper tank on the top of the radiator. The coolant then passes through a set of tubes to the bottom of the radiator from which the cooling cycle begins again. The radiator is situated in front of a fan that is driven either by the water pump or an electric motor. The fan ensures an airflow through the radiator at times when there is no vehicle motion. It should be noted that the downward flow of coolant through the radiator creates what is known as a thermosiphon action. This simply means that as the coolant is heated in the jackets of the engine, it expands. As it expands, it becomes less dense and therefore lighter. This causes it to flow out of the top outlet of the engine and into the top tank of the radiator. As the coolant is cooled in the radiator, it again becomes more dense and heavier. This causes the coolant to settle to the bottom tank of the radiator. The heating in the engine and the cooling in the radiator therefore creates a natural circulation that aids the water pump. The earliest automotive vehicles relied on thermosiphon action and used no water pump. 9-4. Engine WaterJackets (Fig. 9-1). a. The water passages in the cylinder block and cylinder head form the engine water jacket. In
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TM 9-8000 methyl alcohol, and ethyl alcohol. Ethyl and methyl alcohol provide adequate protection as an antifreeze when used in sufficient quantities. The main objection to these liquids, however, is that they evaporate below the operating temperature of modern automotive engines, making them impractical. Glycerin offers the same degree of protection as alcohol, but does not evaporate in use because of its high boiling point. Ethylene glycol (antifreeze compound) has an extremely high boiling point, does not evaporate in use, is noncorrosive, has no odor, and gives complete protection against freezing in normal use. Ethylene glycol gives a maximum protection against freezing to - 65F ( - 53.8C) when it is mixed to a solution of 60 percent with 40 percent water. If the proportions of ethylene glycol are raised in the solution, it will result in a higher freezing point for the solution, consequently giving less protection. If a 100percent solution of ethylene glycol were used, its freezing point would not be much below that of water. Other antifreeze solutions, however, do not show this increase of freezing point with increasing concentration. Two good examples are methyl alcohol, which freezes at -144F (-97.8C) and ethyl alcohol, which freezes at 174F (-114.3C). b. Corrosion Resistance. The cooling system must be free of rust and scale in order to maintain its efficiency. The use of inhibitors or rust preventatives will reduce or prevent corrosion and the formation of scale. Inhibitors are not cleaners and therefore will not remove rust and scale that have already accumulated. Most commercially available antifreeze solutions contain inhibitors. If water alone is used as a coolant, an inhibitor should be added. 9-6. Radiators (Fig. 9-2). Radiators for automotive vehicles using liquid cooling systems consist of two tanks with a heat exchanging core between them. The upper tank contains an outside pipe called an inlet. The filler neck generally is placed on the top of the upper tank; attached to this filler neck is an outlet to the overflow pipe. The lower tank also contains an outside pipe that serves as the radiator's outlet. Operation of the radiator is as follows.
a.
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and, through the use of an internal baffle, distributes it across the top of the core.
b. The core is made up of numerous rows of small vertical tubes that connect the upper and lower radiator tanks. Sandwiched between the rows of tubes are thin sheet metal fins. As the coolant passes through the tubes to the lower tank the fins conduct the heat away from it and dissipate this heat into the atmosphere. The dissipation of the heat from the fins is aided by directing a constant airflow between the tubes and over the fins. c. The lower tank collects the coolant from the core and discharges it to the engine through the outlet pipe d. The overflow pipe provides an opening from the radiator for escape of coolant or steam if pressure in the system exceeds the regulated maximum. This will prevent rupture of cooling system components. Some radiators are designed with their tanks on the sides in a vertical position. They are connected by a core that contains horizontal tubes. This radiator configuration is called a crossflow radiator and operates in the same manner as the conventional vertical flow radiator, though it should be noted that there is no thermosiphon effect (para 9-3) with a cross flow radiator.
9-7. Water Pump (Fig. 9-3). All modern cooling systems have water pumps to circulate the coolant. The pump, usually located on the front side of the engine block, receives coolant from the lower tank and force sit through the water jacket into the upper radiator tank. The pump is a centrifugal type and has an impeller with blades that force coolant outward as the impeller rotates. It usually is driven by the engine crankshaft through a Vbelt. Advantages of a centrifugal pump as a water pump are that it is inexpensive, circulates great quantities of coolant for its size, and is not clogged by small amounts of foreign matter. Another advantage is that a centrifugal pump permits a limited amount of thermosiphon action after the engine is shut down to help prevent boil over. The pump housing usually is cast from iron or aluminum. The impeller can be made from iron, aluminum, or plastic. It rides on a shaft that is supported in the housing on a sealed double row ball bearing. The pump shaft also has a spring-
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(1) The bellows type (fig. 9-7), which consists of a flexible metal bellows attached to a valve. The bellows, which is sealed and expandable, is filled with a highly volatile liquid such as ether. The bellows chamber is contracted when the coolant is cold, holding the valve closed. The liquid in the bellows vaporizes as the coolant is heated, causing the bellows to expand.
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closed, sealing the system. The larger of these two valves is the pressure valve and the smaller is the vacuum valve. The pressure valve acts as a safety valve that will vent any pressure over the rated maximum through the overflow pipe. The vacuum valve allows air to enter the system as the engine cools down. This is to prevent atmospheric pressure from collapsing the hoses. 9-11. Expansion Tank (Fig. 9-11). Some vehicles use an expansion tank in their cooling systems. The expansion tank is mounted in series with the upper radiator hose. It is used to supply extra room for coolant expansion and generally takes the place of the upper radiator tank. The radiator pressure cap and the overflow line also are mounted on the expansion tank. 9-12. Closed Cooling System (Fig. 9-12). a. Purpose. The purpose of a closed cooling system is twofold. First, the system is designed to maintain a completely full radiator at all times. This will increase the efficiency of the system by allowing a maximum amount of coolant in the system during all operating conditions. Second, during an overheating condition, the closed cooling system prevents coolant loss through the overflow line by collecting it in the recovery tank. b. Operation. As the temperature of the cooling system rises, the pressure also will rise. This will open the pressure valve in the pressure cap, causing coolant to exit through the overflow tube, thus venting excess pressure. An open-type cooling system will empty coolant onto the road, causing a low coolant level after the temperature returns to normal. When a closed cooling system is used, the overflow line is connected to the bottom of a coolant recovery tank to catch and hold any expelled coolant. As the temperature of the coolant drops, the corresponding drop in pressure causes atmospheric pressure to push the coolant in the recovery tank back into the cooling system through the open vacuum valve in the pressure cap.
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b. The primary means of removing heat from an aircooled engine is by dissipation to the air. The duct work and the cooling fans cause a constant flow of air over and around the cylinders and cylinder heads. The finned design of these components add a tremendous amount of surface area to them so that they are able to dissipate an adequate amount of heat.
9-11 TM 9-8000
TA233502 9-12
10-1. History of the Turbine Engine. There are two types of engines that provide most of our power today: the gas turbine (the older of the two) and the piston engine. The basic idea of the gas turbine is over 2,000 years old. The principle of the gas turbine was used to obtain continuous turning of the spit for roasting meat over an open fire. Turbine blades were placed in the chimney to be turned by the rising hot gases. The bladecarrying shaft was connected through gearing to the spit to obtain a very slow rotary motion. Modern science and engineering has made
possible the advent and use of this principle. For centuries man has devoted himself to the task of harnessing energy for the betterment of mankind. Ever since mans first use of fire in the early ages, it has been his desire to put energy to work in more efficient ways and means. The following three examples are early applications of turbine engines. a. Aeolipile (Fig. 10-1). The first reaction engine known to be used to perform work was built in approximately 150 BC by Hero of Alexandria,
TM 9-8000 and was called an Aeolipile. It consisted essentially of a boiler, suspended over a fire, from which two tubes led to a closed vessel in the shape of a sphere, into which steam under pressure was introduced. When the steam escaped from two bent tubes mounted opposite one another on the surface of the sphere, the tubes became jet nozzles. A force was created at the nozzles that caused the sphere to rotate around an axis. b. Brancas Stamping Mill (Fig. 10-1). A further application of the gas turbine propulsion principle, utilizing what was probably the first actual impulse turbine, was the invention of a stamping mill built in 1629 by Giovanni Branca, an Italian engineer. The turbine was driven by steam generated in a boiler. The jet of steam from a nozzle in this boiler impinged on the blades of a horizontally mounted turbine wheel which, through an arrangement of gearing, caused the mill to operate. c. Newtons Steam Wagon (Fig. 10-1). In 1687, Sir Isaac Newton formulated the laws of motion and employed the basic principle used by Hero. The wagon consisted essentially of a large boiler mounted on four wheels. Steam generated by a fire built below the boiler was allowed to escape through a nozzle facing rearward. The speed of the vehicle was controlled by a steam cock located in the nozzle. The steam wagon demonstrates Newtons Third Law of Motion: For every action, there is always an equal and opposite reaction. 10-2. Introduction. Gas turbines are internal combustion engines. They generate power by compressing a gas (air) that has been pumped into a suitable chamber, adding heat energy (by burning fuel), and expanding and expelling the heated gas through a nozzle using rotating machinery that carries out the process in a steady flow. The gas that operates the turbine is the product of the combustion that takes place when a suitable fuel is mixed and burned with the air passing through the engine. The gas turbine represents one of mans more ingenious means of harnessing energy. With the use of a few pounds of heat-resistant metal, properly shaped, and in the presence of pressurized combustion gases, well supplied with heat, the gas turbine is capable of harnessing probably more mechanical shaft energy than any other manmade device of equal size and weight. 10-3. Theory of Operation. In order to master the theory of operation behind the gas turbine engine, four basic principles must be under- stood: mass, pressure, accelerated mass, and conversion of energy. Each is discussed below. a. Mass. All turboshaft engines attain their high rotational torque output, or power, from energy transferred to the turbines by the accelerated air mass within the engine. Figure 10-2 illustrates this concept. Within container 1 there are a certain amount of air molecules; the exact amount is referred to as mass. This air mass is one of the key components required to drive the turbine in the mass acceleration principle. b. Pressure. A second component required in the acceleration principle is pressure, or driving force. To attain this pressure, container 2 (fig. 10-2) is heated and the molecules contained within expand and exert pressure equally in all directions. c. Accelerated Mass. An accelerated mass is obtained by funneling the pressurized gas down a narrow passageway (container 3). It is this convergency or narrowing down of the nozzle area that causes the molecules to accelerate and produce the velocity energy required to perform the rotational mechanical work. d. Conversion of Energy. The high-velocity gases possess a large amount of kinetic energy. This energy due to motion now must be converted to mechanical energy, which can be accomplished by adding a turbine wheel to container 4 (fig. 10-2). The first force, as seen in the illustration, is the impact or push of the highvelocity gases exiting the nozzle and hitting the turbine wheel. The second force, which is a reaction force, is generated by the high-velocity gases exiting the turbine wheel in the opposite direction of rotation.
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TM 9-8000 Section II. COMPARISON TO PISTON ENGINE exhaust event. Figure 10-3 illustrates the comparison of events between the four-stroke cycle piston-type engine and the gas turbine. 10-5. Otto Cycle Versus Brayton Cycle. a. Otto Cycle. Both the piston engine and the gas turbine operate on cycles that can be represented graphically. Figure 10-4 illustrates the pressure volume relationship for both the Otto-cycle engine and the Brayton-cycle engine. The Otto-cycle engine pressure/ volume relationship is as follows: The intake stroke is represented by line 1-2. As this event occurs, the piston is moving downward, increasing the volume in the cylinder. At the close of the intake valve, a slight pressure differential occurs, due to pumping losses. This results in a small vacuum in the cylinder at the start of the compression stroke. Line 2-3 illustrates the compression
10-4. Cycle Characteristics and Variations. The fourstroke cycle piston-type engine is designed to perform four events: intake, compression, power, and exhaust. One cycle (four events) is completed as the crankshaft rotates twice for a total of 720 degrees (fig. 10-3). Each event is completed within 180 degrees of crank- shaft rotation and is called a stroke. Gas turbine engine operation consists of four events that are essentially the same as the reciprocating engine. Air is first drawn through the air inlet section that relates to the intake event. It then passes through the compressor section, relating to the compression event. The air then enters the combustor, mixes with fuel, and is ignited. As the airfuel mixture burns, the pressure increase is directed through the turbines that extract work from the flowing gases which relates to the power event. Passing through the turbines, the used gases are exhausted to the atmosphere, relating to the
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Section III. BASIC ENGINE STRUCTURE 10-8. Air Inlet Section. The air inlet section (fig. 10-6) serves to furnish a uniform and steady airflow to the face of the compressor. Inlet sections may be equipped with or without inlet guide vanes. Inlet guide vanes serve to direct the air into the first stage of the compressor. 10-9. Compressors. The compressor is designed to provide the combustion chamber with a maximum amount of high-pressure air that is heated and expanded through the turbines. The amount of energy released from the heated airmass is proportional directly to the mass of air consumed. This is the major reason why the compressor is one of the most important components in the gas turbine. A poorly designed compressor will not provide the combustion chamber with the proper amount of high-pressure air, and will result in a lack of power. Modern compressors are able to achieve compression ratios of approximately 15:1 and efficiencies approaching 90 percent. Two common types of compressors are discussed below. a. Axial. The axial compressor performs the compression process in a straight line parallel to the axis of the engine. The axial compressor is composed of rotating members called rotors and stationary members called stators. A row of rotors and stators is called a stage. The axial compressor is composed of a series of stages (fig. 10-7). During operation the air is arrested in the first stage of compression and is turned by a set of stator vanes, picked up by a set of rotor blades, TA233507
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TM 9-8000 Section IV. FUEL SYSTEM 10-14. Requirements. The fuel system is designed to provide the engine with the proper amount of fuel under all operating conditions. The fuel systems incorporated on gas turbine engines range from simple valves to complex microprocessor control assemblies. The fuel control system can receive inputs from one or two sources on some models, while other systems monitor multiple engine variables. Basically, these fuel systems are categorized into either a hydro-mechanical or electronic group. 10-15. Fuel Pumps. Fuel pumps are used to pressurize the fuel prior to injection into the combustion chamber. Gear pumps (para 20-4) generally are used to generate the fluid pressure required for operation. Some pumps are designed as a two-stage configuration.in this design an impeller is used for the first-stage pressure increase. The fuel then is routed to a heat exchanger to cool the pressurized fuel. A gear pump then is used for the final pressure increase. A pressure relief valve also is used to limit the amount of pressure the pump develops at high speed (fig. 10-18). 10-16. Fuel Nozzles. Fuel nozzles are used to induce fuel into the combustion chamber. They are designed to produce an accurately shaped spray pattern and maintain combustion during varying engine operating conditions. injection nozzles generally are either the single or dual spray pattern design (fig. 10-19). The single nozzle provides one spray pattern of fuel under all conditions (fig. 10-19). The dual nozzle is designed to provide a single spray pattern at low
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Section V. LUBRICATION SYSTEM 10-17. Requirements. The lubrication system is designed to clean, cool, and lubricate the internal components of the engine. While each lubrication system is designed for a particular engine, certain components are common on most systems. A wide variety of operating temperatures makes the design of the lubrication system even more difficult. Gas turbine engines operate in vehicles that can be exposed to temperatures as low as -60F (-51.1C), as well as internal temperatures as high as 400F (204.4C). One severe problem experienced with gas turbine engines occurs as the engine is stopped. A large amount of heat, stored in the turbine, then is transferred to the bearings. This phenomenon raises the temperature of the bearing much higher than that encountered during operation. The temperature of the lubricating oil, which is now stagnant around the bearing, also is greatly increased. Care must be taken in selecting an oil that will not break down under these severe conditions. 10-18. Lubrication Oils. Lubricating oils used in gas turbine engines must possess certain performance factors. Oils must resist foaming and provide a steady stream of oil to bearings. This ensures proper lubrication and cooling under all operating conditions. Mineral oil and synthetic oils commonly are used for lubricating purposes in turbine engines, as discussed below. a. Mineral Oils. Mineral oils generally are used in smaller, low-power engines and where temperatures do not reach extremes. These oils generally are not used because they are incapable of providing satisfactory performance at both very low and very high operating temperatures. They have been known to be extremely thick at low TA233517
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b. Synthetic Oils. Synthetic oils are commonly used as the lubrication medium. They are treated with the proper compounds to allow them to withstand extreme operating conditions. More information on synthetic oils can be found in chapter 8.
10-19. Lubrication System Components. The construction and operation of components common to most gas turbine engines is discussed below.
c. Scavenger Pumps. These pumps are used to collect oil that has passed through the components to be lubricated. The pumps then pressurize the oil to force it to the next stage in the lubrication system. Both gear and rotor pumps generally are used for scavenging operations. d. Filters. Oil filters are used to help remove impurities from the oil. They are serviced at regular intervals. Three basic types of oil filters are used in turbine engines: screen, screen disk, and cartridge. The screen and screen-disk type filters are cleaned and reused while the cartridge type is removed and replaced by a new one. e. Oil Coolers. Oil coolers are designed to transfer unwanted heat from lubricating oil to another medium, usually fuel or a passing air stream. The fuel-oil cooler uses a high volume of fuel with respect to oil passing through the cooler to transfer unwanted heat from the oil to fuel. A typical fuel-oil cooler is illustrated in figure 1021. The air-oil cooler is the same type as the one discussed in paragraph 8-14.
a. Oil Tanks. Oil tanks are used for onboard storage of oil for the lubrication system. They usually are made of welded sheet aluminum or steel. Cooling fins sometimes are used to provide additional heat transfer through the sides of the tank. Oil tanks sometimes are pressurized to ensure a constant supply of oil to the pressure pump. A typical oil tank with dipstick is shown in figure 10-20. b. Pressure Pumps. Both gear-and rotor-type pumps are used to generate fluid pressure for
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PART THREE ELECTRICAL SYSTEMS AND RELATED UNITS CHAPTER 11 BASIC PRINCIPLES OF ELECTRICITY Section I. ELECTRICITY 11-1. Composition of Matter. that it is made up of those same basic particles having positive and negative electrical charges as discussed above.
a. To understand electricity, first study matter, the name for all material substances. Everything (solids, liquids, and gases) is made up of tiny particles known as atoms. These atoms combine in small groups of two or more to form molecules. Air is made up of molecules. These molecules are made up of atoms, and these toms can be further subdivided. When atoms are divided, smaller particles are created, some of which have positive and others, negative electrical charges. Atoms of different materials are discussed below. b. There are over 100 different basic materials in the universe. These basic materials are called elements. Iron is one element; copper, aluminum, oxygen, hydrogen, and mercury are other elements. An element gets its name from the fact that it cannot be broken down easily into simpler (or more elemental) substances. In other words, more than 100 basic elements are the building materials from which the universe is made. If any one of these elements is studied closely, it is obvious
c. The basic particles that make up all the elements, and thus all the universe, are called protons, electrons, and neutrons. A proton is a basic particle having a single positive charge; a group of protons produces a positive electrical charge. An electron is a basic particle having a single negative charge; therefore, a group of electrons produces a negative electrical charge. A neutron is a basic particle having no charge; a group of neutrons, therefore, would have no charge. d. Examine the construction of atoms of the various elements, starting with the simplest of all, hydrogen. The atom of hydrogen consists of one proton, around which is circling one electron (fig. 11-1). There is an attraction between the two particles, because negative and positive electrical charges always attract each other.
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Opposing the attraction between the two particles, and thus preventing the electron from moving into the proton, is the centrifugal force on the electron caused by its circular path around the proton. This is the same sort of balance achieved if a ball tied to a string was whirled in a circle in the air. The centrifugal force exerted tries to move the ball out of its circular path, and is balanced by the string (the attractive force). If the string should break, the centrifugal force would cause the ball to fly away. Actually, this is what happens at times with atoms. The attractive force between the electron and proton sometimes is not great enough to hold the electron in its circular path, and the electron gets away.
a. When there are more than two electrons in an atom, they will move about the nucleus in different size orbits. These orbits are referred to as shells. The innermost shells of the atom contain electrons that are not easily freed and are referred to as bound electrons. The outermost shell will contain what is referred to as free electrons. These free electrons differ from bound electrons in that they can be moved readily from their orbit. b. If a point that has an excess of electrons (negative) is connected to a point that has a shortage of electrons (positive), a flow of electrons (electrical current) will flow through the connector (conductor) until an equal electric charge exists between the two points.
11-3. Electron Theory of Electricity (Fig. 11-2). A charge of electricity is formed when numerous electrons break free of their atoms and gather in one area. When the electrons begin to move in one direction (as along a wire, for example), the effect is a flow of electricity or an electric current. Actually, electric generators and batteries could be called electron pumps, because they remove electrons from one part of an electric circuit and concentrate them in another part of the circuit. For example, a generator takes electrons away from the positive terminal and concentrates them at the negative terminal. Because the electrons repel each other (like electrical charges repel), the electrons push out through the circuit and flow to the positive terminal (unlike electrical charges attract). Thus, we can see that an electric current is actually a flow of electrons from negative to positive. This is just the reverse of the old idea of current flow. Before scientists understood what electric current was, they assumed that the current flowed from positive to negative. However, their studies showed that this was wrong, because they learned that the current is electron movement from negative (concentration of electrons) to positive (lack of electrons). 11-4. Conductors and insulators (Fig. 11-3).
e. A slightly more complex atom is shown in figure 11-1. This is an atom of helium. Notice that there are now two protons in the center and that two electrons are circling around the center. Because there is an additional proton in the center, or nucleus, of the atom, an electron must be added so as to keep the atom in electrical balance. Notice also that there are two additional particles in the nucleus; these are called neutrons. Neutrons are necessary in order to overcome the tendency of the two protons to move apart from each other. For, just as unlike electrical charges attract, so do like electrical charges repel. Electrons repel electrons. Protons repel protons, except when neutrons are present. Though neutrons have no electrical charge, they do have the ability to cancel out the repelling forces between protons in an atomic nucleus and thus hold the nucleus together. f. A still more complex atom is shown in figure 1-1. This is an atom of lithium, a light, soft metal. Note that a third proton has been added to the nucleus and that a third electron is now circling around the nucleus. There also are two additional neutrons in the nucleus; these are needed to hold the three protons together. The atoms of other elements can be seen in a similar manner. As the atomic scale Increases in complexity, protons and neutrons are added one by one to the nucleus, and electrons to the outer circles. After lithium comes beryllium with four protons and five neutrons, boron with five protons and five neutrons, carbon with six and six, nitrogen with seven and seven, oxygen with eight and eight, and so on. In each of these, there are normally the same number of electrons circling the nucleus as there are protons in the nucleus.
a. General. Any material that will allow electric current to flow through it is an electrical
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b. Conductors (A, Fig. 11-3). Whenever there are less than four electrons in the outer orbits of the atoms of a substance, these electrons will tend to be free. This will cause the substance to permit free motion of electrons, making it a conductor. Electrical energy is transferred through conductors by means of the movement of free electrons that migrate from atom to atom within the conductor. Each electron moves a short distance to the neighboring atom, where it replaces one or more electrons by forcing
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them out of their orbits. The replaced electrons repeat this process in nearby atoms until the movement is transmitted throughout the entire length of the conductor, thus creating a current flow. Copper is an example of a good conductor because it only has one free electron. This electron is not held very strongly in its orbit and can get away from the nucleus very easily. Silver is a better conductor of electricity but it is too expensive to be used in any great quantity. Because of this, copper is the conductor used most widely in automotive applications.
c. Insulators (B, Fig. 11-3). Whenever there are more than four electrons in the outer orbits of the atoms of a substance, these electrons will tend to be bound, causing restriction of free electron movement, making it an insulator. Common insulating substances in automotive applications are rubber, plastic, Bakelite, varnish, and fiberboard.
Section II. SEMICONDUCTOR DEVICES 11-5. Fundamental Principles. electrons in its outer shell), will yield one free electron per molecule, thus making the material an electrical conductor. The process of adding impurities to a semiconductor is called doping. Any semiconductor material that is doped to yield free electrons is called Ntype material. (3) When boron, which has three electrons in its outer ring, is used to dope the silicon crystal, the resultant covalent bonding yields seven electrons in the outer shell. This leaves an opening for another electron and is illustrated in figure 11-6. This space is called a hole and can be considered a positive charge just as the extra electrons that exist in N-type semiconductor material are considered a negative charge. Materials that have holes in their outermost electron shells are called positive or P-type materials. In order to understand the behavior of P-type semiconductors, it is necessary to look upon the hole as a positive current carrier, just as the free electron in N-type semiconductors are considered negative current carriers. Just as electrons move through N-type semiconductors, holes move from atom-to-atom in P-type semiconductors. Movement of holes through P-type semiconductors, however, is from the positive terminal to the negative terminal. For this reason, any circuit analysis of solidstate circuitry is done on the basis of positive to negative (conventional) current flow.
a. Description. Paragraph 11-4 explains that any substance whose atoms contain less than four electrons in their outermost orbits is classified as an electrical conductor. It also is explained that any substance whose atoms contain more than four electrons in their outermost orbits is classified as an electrical insulator. A special case exists, however, when a substance contains four electrons in the outermost orbits of its atoms. This type of substance is known as a semiconductor and is the basis for all modern electronic equipment. The most popular of all semiconductors is silicon. b. Characteristics of Semiconductors. in its pure state, silicon is neither a good conductor or insulator. But by processing silicon in the following ways, its conductive or insulative properties can be adjusted to suit just about any need.
(1) When a number of silicon atoms are jammed together in crystalline (glasslike) form, they form a covalent (sharing) bond. Therefore, the electrons in the outer ring of one silicon atom join with the outer ring electrons of other silicon atoms, resulting in a sharing of outer ring electrons between all of the atoms. It can be seen in figure 11-4 that covalent sharing gives each atom eight electrons in its outer orbit, making the orbit complete. This makes the material an insulator because it contains more than four electrons in its outer orbit. (2) When certain materials such as phosphorus are added to the silicon crystal in highly controlled amounts the resultant mixture becomes a conductor (fig. 11-5). This is because phosphorus, which has five electrons in forming a covalent bond with silicon (which has four 11-4
c. Hole Movement Theory (Fig. 11-7). When a source voltage, such as a battery, is connected to N-type material, an electric current will flow through it. The current flow in the N-type semiconductor consists of the movement of free
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a. Purpose. A diode is a device that will allow current to pass through itself in only one direction. A diode can be thought of as an electrical checkvalve. b. Construction. A diode is made by joining N-type material and P-type material together. The negative electrical terminal is located at the N-type material and the positive terminal is located on the P-type material. c. Operation. When a diode is placed in a circuit, the N-material is connected to the
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a. General (Fig. 11-10). Transistors, as they apply to automotive applications, are switching devices. They can switch large amounts of electric current on and off using relatively small amounts of electric current. Because transistors operate electronically, they last much longer than the relays they replace. This is because they have no contact points to burn. The major automotive applications of transistors are for electronic ignition systems and voltage regulators. b. PNP Transistors (Fig. 11-11). The PNP transistor is the most common configuration in automotive applications. It is manufactured by sandwiching an N-type semiconductor element between two P-type semiconductor elements. A positive charge is applied to one of the P-type elements. This element is called the emitter. The other P-type element connects to the electrical
c. NPN Transistors (Fig. 11-11). The NPN transistor is similar to the PNP transistor. The difference is that it is used in the negative side of the circuit. As the name NPN implies, the makeup of this transistor is two elements of N-type material (collector and emitter) with an element of P-type material (base) sandwiched in between. The NPN transistor will allow a high-current negative charge to flow from the collector to the emitterwhenever a relatively low current positive charge is applied to the base.
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a. Amperes. Current flow, or electron flow, is measured in amperes. While it is normally considered that one ampere is a rather small current of electricity (approximately what a 100-watt light bulb would draw), it is actually a tremendous flow of electrons. More than 6 billion billion electrons a second are required to make up one ampere. b. Voltage. Electrons are caused to flow by a difference in electron balance in a circuit; that is, when there are more electrons in one part of a circuit than in another, the electrons move from the area where they are concentrated to the area where they are lacking. This difference in electron concentration is called potential difference, or voltage. The higher the voltage goes, the greater the electron imbalance becomes. The greater this electron imbalance, the harder the push on the electrons (more electrons repelling each other) and the greater the current of electrons in the circuit. When there are many electrons concentrated at the negative terminal of a generator (with a corresponding lack of electrons at the positive terminal), there is a much stronger repelling force on the electrons and, consequently, many more electrons moving in the wire. This is exactly the same as saying that the higher the voltage, the more electric current will flow in a circuit, all other things, such as resistance (para 11-10), being equal.
11-10. Resistance.
c. Some elements can lose electrons more readily than other elements. Copper loses electrons easily, so there are always many free electrons in a copper wire. Other elements, such as iron, do not lose their electrons quite as easily, so there are fewer free electrons in an iron wire (comparing it to a copper wire of the same size). Thus, with fewer free electrons, fewer electrons can push through an iron wire; that is, the iron wire has more resistance than the copper wire. d. A small wire (in thickness or cross-sectional area) offers more resistance than a large wire. in the small wire, there are fewer free electrons (because fewer atoms), and thus fewer electrons can push through. e. Most metals show an increase in resistance with an increase in temperature, while most nonmetals show a decrease in resistance with an increase in temperature. For example, glass (a nonmetal) is an excellent insulator at room temperature but is a very poor insulator when heated to red heat.
11-11. Ohms Law.
a. The general statements about voltage, amperage, and ohms (para 11-9 and 11-10) can all be related in a statement known as ohms law, so named for the scientist Georg Simon Ohm who first stated the relationship. This law says that voltage is equal to amperage times ohms. Or, it can be stated as the mathematical formula:
E=IxR
a. Even though a copper wire will conduct electricity with relative ease, it still offers resistance to electron flow. This resistance is caused by the energy necessary to break the outer shell electrons free, and the collisions between the atoms of the conductor and the free electrons. It takes force (or voltage) to overcome the resistance encountered by the flowing electrons. This resistance is expressed in units called ohms. The resistance of a conductor varies with its length, crosssectional area, composition, and temperature. b. A long wire offers more resistance than a short wire of the same cross-sectional area. The electrons have farther to travel.
where E is volts, I is current in amperes, and R is resistance in ohms. For the purpose of solving problems, the ohms law formula can be expressed three ways: (1) To find voltage: E = IR (2) To find amperage: l = E/R (3) To find ohms: R = E/I
b. This formula is a valuable one to remember because it makes understandable many of the things that happen in an electric circuit. For instance, if the voltage remains constant, the
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a. General (Fig. 11-12). A very basic circuit consists of a power source, a unit to be operated, and a wire to connect the two together. if the unit to be operated is to be controlled, a switch will be included in the circuit also. b. Automotive Circuits (Fig. 11-13). The body and chassis in an automobile are made of steel. This feature is utilized to eliminate one of the wires from all of the automobiles circuits. By attaching one of the battery terminals to the body and chassis, any electrical component can be connected by hooking up one side, by wire, to the car battery and the other side to the body. The practice of connecting one side of the battery to the automobile body is called grounding. Virtually all current automotive manufacturers ground the negative side of the battery. This is referred to as an electrical system with a negative ground. Vehicles with a positive ground are very uncommon at the present time. c. Series Circuits (A, Fig. 11-14). A series circuit consists of two or more resistance units (electrically operated components) that are connected together in an end-to-end manner so that any current flow in the circuit is dependent on a complete path through all of the units. The following characteristics of series circuits are important:
c. A great majority of electrical troubles on automotive vehicles result from increased resistance in circuits due to bad connections, deteriorated wiring, dirty or burned contacts in switches, or other such problems. With any of these conditions, the resistance of the circuit goes up and the ampere flow through that circuit goes down. Bad contact points in the ignition circuit will reduce current flow in the circuit and cause weak sparks at the spark plugs. This will result in engine missing and loss of power. d. If the resistance stays the same but the voltage increases, the amperage also increases. This is a condition that might occur if a generator voltage regulator became defective. In such a case, there would be nothing to hold the generator voltage within limits, and the voltage might increase excessively. This would force excessive amounts of current through various circuits and cause serious damage. If too much current went through the light bulb filaments, for example, the filaments would overheat and burn out. Also, other electrical devices probably would be damaged. e. On the other hand, if the voltage is reduced, the amount of current flowing in a circuit will also be reduced if the resistance stays the same. For example, with a run-down battery, battery voltage will drop excessively with a heavy discharge. When trying to start an engine with a run-down battery, the voltage will drop very low. This voltage is so low that it cannot push enough current through the starter for effective starting of the engine.
11-12. Circuit Configurations.
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HEADLIGHT 7. DIMMER SWITCH BATTERIES 8. BLACKOUT DRIVE LIGHT BLACKOUT AND SERVICE TAILLIGHT 9. BLACKOUT SERVICE LIGHT TRAILER RECEPTACLE 10. INSTRUMENT CLUSTER BLACKOUT TAILLIGHT, SERVICE TAILLIGHT, 11. HORN BUTTON AND SERVICE STOPLIGHT 12. HORN 6. LIGHT SWITCH Figure 11-13. Typical Automotive Circuit. (1) Any break in the circuit (such as a burnedout light bulb) will render the entire circuit inoperative. (2) The current (amperage) will be constant throughout the circuit. (3) The total resistance of the circuit is equal to the sum of the individual resistances. (4) The total voltage of the circuit is equal to the sum of the individual voltage drops across each component. operated components) connected in separate branches. In a parallel circuit, each component receives full voltage from the source. The following characteristics of parallel circuits are important. (1) The total resistance of the circuit will always be less than the resistance of any individual component. (2) The disconnection or burning out of any individual component in the circuit will not affect the operation of the others. (3) The current will divide itself among the circuit branches according to the resistances of
d. Parallel Circuits (B, Fig. 11-14). A parallel circuit consists of two or more resistance units (electrically
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(2) The total circuit resistance will be equal to the sum of the total parallel circuit resistance plus the individual resistances of the series circuit components. (3) Current flow through the total parallel circuit will be equal to the current flow through any individual series circuit component. (4) The disconnection or the burning out of any of the series components will completely disable the entire circuit, whereas a failure of any of the parallel circuit components will leave the balance of the circuit still functioning.
e. Series-Parallel Circuit (C, Fig. 11-14). The series-parallel circuit is a combination of the two configurations. There must be at least three resistance units to have a series-parallel circuit. The following characteristics of series-parallel circuits are important.
(1) The total circuit voltage will be equal to the sum of the total parallel circuit voltage drop plus the voltage drops of the individual series circuit components. .
Section IV. MAGNETS 11-13. Magnetic Field. filings would become arranged in curved lines (fig. 1115). These curved lines, extending from the two poles of the magnet (north and south), follow the magnetic lines of force surrounding the magnet. Scientists have formulated the following rules for these lines of force. (1) The lines of force (outside the magnet) pass from the north to the south pole of the magnet. (2) The lines of force act somewhat as rubberbands and try to shorten to a minimum length.
a. General. It was stated in paragraph 11-9 that electric current is a flow of electrons and that the imbalance of electrons in a circuit (that causes electrons to flow) is called voltage. Magnets will be studied to learn what causes a generator to concentrate electrons at the negative terminal and take them away from the positive terminal. b. Magnetic Lines of Force. If iron filings were sprinkled on a piece of glass on top of a bar, magnet, the
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Figure 11-15. (3) The lines of force repel each other along along their entire length and try to push each other apart. (4) The rubberband characteristic opposes the push-apart characteristic. (5) The lines of force never cross each other. (6) The magnetic lines of force, taken together, are referred to as the magnetic field of the magnet.
c. Bar and Horseshoe Magnets. The magnetic fields of a bar and of a horseshoe magnet are shown in figure 11-16. In each, note how the lines of force curve and pass from the north to the south pole. d. Effects Between Magnetic Poles (Fig. 11-17). When two unlike magnetic poles are brought together, they attract. But when like magnetic poles are brought together, they repel. These actions can be explained in terms of the rubberband and the push-apart characteristics. When unlike poles are brought close to each other, the magnetic lines of force pass from the north to the south poles. They try to shorten (like rubberbands), and, therefor try to pull the two poles together. On the other hand, if like poles are brought
a. An electric current (flow of electrons) always produces a magnetic field. In the wire
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shown in figure 11-18, current flow causes lines of force to circle the wire. It is thought that these lines of force result from the movement of the electrons along the wire. As they move, the electrons send out the lines of force. When many electrons move, there are many lines of force (the magnetic field is strong). Few electrons in motion means a weak magnetic field or few lines of force.
b. Electron movement as the basis of magnetism in bar and horseshoe magnets can be explained by assuming that the atoms of iron are so lined up in the magnets that the electrons are circling in the same direction. With the electrons moving in the same direction, their individual magnetic lines of force add to produce the magnetic field. c. The magnetic field produced by current flowing in a single loop of wire is shown in figure 11-19. The magnetic lines of force circle the wire, but here they must follow the curve of the wire. If two loops are made in the conductor, the lines of force will circle the two loops. In the area
d. When many loops of wire are formed into a coil as shown in figure 11-20, the lines of force of all loops combine into a pattern that resembles greatly the magnetic field surrounding a bar magnet. A coil of this type is known as an electromagnet or a solenoid. However, electromagnets can be in many shapes. The field coils of generators and starters, the primary winding in an ignition coil, the coils in electric gages, even the windings in a starter armature, can be considered to be electromagnets. All of these produce magnetism by electrical means, as discussed in paragraph 11-15. e. The north pole of an electromagnet can be determined, if the direction of current flow (from negative to positive) is known, by use of the left- handed rule (fig. 11-21). The left hand is held around the coil with the fingers pointing in the direction of current flow. The thumb will point to the north pole of the electromagnet. This rule is based on current, or electron, flow from negative to positive Figure 11-18. Electromagnetism.
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a. Current can be induced to flow in a conductor if it is moved through a magnetic field. In figure 11-22 the wire is moved downward through the magnetic field between the two magnetic poles. As it moves downward, cutting lines of force, current is induced in it. The reason for this is that the lines of force resist cutting, and tend to wrap around the wire as shown. With lines of force wrapping around the wire, current is induced. The wire movement through the magnetic field produces a magnetic whirl around the wire, which pushes the electrons along the wire. Figure 11-20. Electromagnetism in a Wire Coil. f. The left-handed rule also can be used to determine the direction that lines of force circle a wirecarrying current if the direction of current is known. This is done by circling the wire with the left hand with the thumb pointing in the direction of current flow (negative to positive). The fingers will then point in the direction that the magnetic field circles the wire. g. The strength of an electromagnet can be increased greatly by wrapping the loops of wire around an iron core. The iron core passes the lines of force with much greater ease than air. b. If the wire is held stationary and the magnetic field is moved, the effect is the same; that is, current will be induced in the wire. All that is required is that there be relative movement between the two so that lines of force are cut by the wire. It is this cutting and whirling, or wrapping, of the lines of force around the wire that produces the current movement in the wire. c. The magnetic field can be moved by moving the magnet or, if it is a magnetic field from an electromagnet, it can be moved by starting and stopping the current flow in the electromagnet. Suppose an electromagnet such as the one shown in figure 11-20 has a wire held close to it. When the electromagnet is connected to a battery, current will start to flow through it. This current, as it starts to flow, builds up a magnetic field. In other words, a magnetic field forms because of the current flow. This magnetic field might be considered as expanding (like a balloon, in a sense) and moving out from the electromagnet. As it moves outward, its lines of force will cut through the wire held close to the electromagnet. This wire, therefore, will have current induced in it. The current will result from the lines of force cutting across the wire. If the electromagnet is
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d. Thus it can be seen that current can be induced in the wire by three methods: the wire can be moved through the stationary magnetic field; the wire can be held stationary and the magnet can be moved so the field is carried past the wire; or the wire and electromagnet both can be held stationary and the current turned on and off to cause the magnetic field buildup and collapse, so the magnetic field moves one way or the other across the wire.
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TM 9-8000 CHAPTER 12 BATERIES Section I. CONSTRUCTION 12-1. General. The storage battery provides electrical energy through chemical reactions. When a generator in the electrical system of a motor vehicle produces more electrical energy than required for ignition and for operating electrical accessories, the surplus (under certain conditions) passes through the battery to reverse the chemical reaction. This is known as charging the battery. When the generator is not producing the necessary electrical energy, the battery, through chemical reaction, can supply the energy required in the electrical system of the vehicle. The battery then is said to be discharging. The most common battery for automotive use is the lead-acid battery. 12-2. Component Parts. The storage battery, as used for starting, lighting, and ignition purposes, consists of three or more cells, depending on the voltage desired. A battery of three cells (2 volts each) connected in series is a 6-volt battery, and one of six cells connected in series is a 12volt battery. figure 12-1. Typical battery construction is shown in
a. Plates.
(1) Each cell consists of a hard rubber jar or compartment into which two kinds of lead plates, known as positive and negative, are placed. These plates are insulated from each other by suitable separators and are submerged in a sulfuric acid solution. (2) The backbone of both the positive and negative plates is a grid made of stiff lead alloy casting. The grid, usually composed of vertical and horizontal crossmembers, is designed carefully to give the plates mechanical strength and, at the same time, to provide adequate conductivity for the electric current created by the chemical action. The active material, composed chiefly of
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lead oxides, is applied to the grids in paste form, then allowed to dry and harden like cement. Part of a grid is shown in figure 12-2 with a cross section showing the active material in place. The plates are then put through an electrochemical process that converts the hardened active material of the positive plates into brown lead peroxide, and that of the negative plates into gray, spongy, metallic lead. This process is known as forming the plates.
b. Groups. After the plates have been formed, they are built into positive and negative groups. The plates of each group are permanently joined by melting a portion of the lug on each plate to form a solid weld with a connecting post strap. The heat necessary for this process, termed lead burning, is produced by a gas flame or an electric arc. The connecting post strap to which the plate lugs are burned contains a cylindrical terminal that forms the outside connection for the cell. The negative group of plates has one more plate than the positive group to provide a negative plate on both sides of all positive plates. These groups are shown in figure 12-3. c. Separators. To prevent the plates from touching and causing a short circuit, sheets of insulating material (microporous rubber, fibrous glass, or plasticimpregnated material), called separators, are inserted between the plates. These separators (fig. 12-4) are thin and porous so the electrolyte will flow easily between the plates. One side of the separator (that is placed
d. Elements. The assembly of a positive and negative group, together with the separators, is called an element (fig. 12-4). Because storage battery plates are more or less of standard size, the number of plates in an element is, roughly, a measure of the battery capacity. The distance between the plates of an assembled element is, approximately one-eighth inch.
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f. Container.
(1) A battery container is a receptacle for the cells that make up the battery. It is made of hard rubber or a polypropylene plastic, which is resistant to acid and mechanical shock. Most motor vehicle batteries are assembled in one-piece containers (fig. 125) with three or six
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g. Cover. After all of the elements have been fitted into the case, they are connected together in series by burning lead cell connectors across the terminals. The battery top then is sealed with a hard rubber cover that provides openings for the two battery posts and a vent plug for each cell. The vent plugs allow gas to escape and prevent the electrolyte from splashing outside the battery. The battery is filled through the vent plug openings.
a. Chemical Action. To charge the cell, an external source of direct current must be connected to the battery terminals. The chemical reaction is reversed then and returns the positive
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and negative plates and the electrolyte to their original condition. When all the sulfate on the plates has been returned to the electrolyte to form sulfuric acid, the cell is recharged fully and ready to be used for the next discharge. Charging should be started before both plates have become sulfated entirely. The chemical process in the cell during discharge and charge is shown in figure 12-6.
capacity ratings according to the ampere-hours obtained from the battery under certain working conditions. The capacity of a battery is the number of amperes delivered, multiplied by the number of hours the battery is capable of delivering this current. One of the inherent characteristics of a storage battery is that its ampere-hour capacity depends upon the rate of discharge. A battery will give more ampere-hours at a long, low, or intermittent discharge rate than at a short, high, or continuous discharge rate. This is because the voltage drops faster at higher rates. Like other chemical processes, the battery is less efficient in cold weather than in hot weather. At 0F (-18C), a battery has only approximately 40 percent of the full cranking capacity available at 80F (27C). In an emergency, little, if any, permanent harm will result if the battery is discharged at a very high rate, provided it is promptly recharged. The battery is likely to deteriorate if left in a discharged condition.
b. Electrical Action. A storage battery can be charged by direct current only. If only alternating current is available, a motor-generator set or a rectifier must be used to convert it into direct current. In charging, the positive wire of the charging circuit must always be connected to the positive (+) terminal of the battery and the negative wire to the negative (-) terminal. The electrolyte in each cell must be brought to the proper level by the addition of pure water before the battery is charged. c. Capacity. All batteries are given normal
Section III. TYPES OF BATTERIES 12-6. Deep-Cycle Battery. Deep-cycle batteries are units that are designed to be subjected to heavy discharge loads for long periods of time. They also must be able to take high-rate charging. The batteries used in forklifts (or any electric vehicles) are nickel cadmium or lead acid. Because the initial cost of nickel-cadmium batteries are approximately 35 times that of lead acid, they are used only when their cost can be justified in terms of their extremely long cycle life. Lead-acid batteries come in four basic varieties: be able to sustain high discharge rates for relatively long periods of time. At the same time, they must have a high specific power output and be relatively lightweight. The golf cart battery has thicker plates than the SLI battery and can withstand about 200 to 400 deep cycles.
c. Semi-Industrial Battery. The semi-industrial battery has thicker plates and is larger and heavier than the golf cart battery. It can withstand about 500 to 1,000 deep cycles through its life. d. Industrial Battery. The industrial battery is used mainly as a source of power in electric industrial vehicles, where cycle life and total power output are important. In some cases industrial batteries will use tubular plates instead of the standard pasted plates. This design can withstand as much as 2,000 deep cycles during its life though it exhibits a low power density, resulting in a very large, heavy battery.
12-7. Nickel-Cadmium Batteries.
a. SLI Battery. The SLI (starting, lighting, and ignition) battery is designed to deliver high power outputs for relatively short periods of time. Because of its thin plate design, it has less energy available than a deep cycle battery and will have a life limited to less than 100 deep discharge cycles. It is suited to automotive usage because it is lightweight and has a higher specific power output (power-per-pound) than deep cycle batteries. In normal automotive usage, the life of an SLI battery may exceed 5,000 shallow cycles (starting an engine and recharging would be considered a shallow cycle). b. Golf Cart Battery. The golf cart battery must
a. General. The nickel-cadmium, alkaline battery has been receiving serious consideration
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and extensive testing for tank-automotive applications. This battery employs nickel and cadmium compounds as the active material and potassium hydroxide as electrolyte. There are actually two basic types of nickelcadmium batteries. These are distinguished by the method used to construct the plates. One is called a pocket plate and the other a sintered-plate design. In addition, the nickel-cadmium battery is produced with both vented cells and completely sealed cells. The vented sintered-plate, nickel-cadmium battery is the one most often used in military applications because it offers high discharge rates at wider temperature ranges. For this reason, the discussion of the nickel-cadmium battery will be confined largely to the sintered-plate version. The basic difference between the pocket and sintered plate is that, in the pocket type, the active material of the plates is encased within perforated steel pockets, while the sintered type has the active material contained in a sintered structure surrounding the grid. Although the sintered method is more expensive per ampere-hour than the pocket plate type, superior performance at high rates and reduced capacity loss at low temperatures qualify it as the logical choice for military applications.
the trivalent nickel hydroxide Ni(OH)3 is converted to the divalent hydroxide Ni(OH)2 at the positive plate with the reverse process occurring during charging. The negative plate consists of metallic cadmium when fully charged. This is converted to the hydroxide during discharge and back to metallic cadmium during charging.
c. Features.
(1) The low internal resistance of the sintered-plate battery makes it ideal for service requiring long battery life and high current drains over a wide temperature range. (2) The sintered-plate construction of the positive and negative electrode allows plates to be constructed as thin as 0.02 inch. This allows more plates to be installed in a given size cell with less space between plates. The internal resistance of the sinteredplate cell is thus about one-half that of a pocket plate type. (3) The specific gravity of the potassium hydroxide electrolyte does not change during charge or discharge. This is because the electrolyte does not enter into the chemical reaction between the positive and negative electrodes, as does sulfuric acid in the lead acid battery. For this reason, specific gravity readings of the nickel-cadmium electrolyte are not an indication of the state-of-charge. The open circuit voltage of a charged nickel-cadmium cell is about 1.3 volts, and the average and final discharge voltages at normal rates of discharge are about 1.2 and 1.1 volts, respectively. (4) The fact that the electrolyte serves virtually as a conductor offers several advantages. One is that very little gassing occurs on charging, except when overcharged, and none on -discharge. Therefore, little water is lost. Another is that the rate of self-discharge is very low. Thus, the battery may be left standing on open circuit for periods up to a year and still retain as much as 70 percent of its original charge. Still another advantage of the nickel-cadmium battery is that it will accept a charge at a temperature as low as -40F, by virtue of self-heating. At temperatures below -40F, however, the electrolyte forms a slush that does slow down chemical reactions. 12-7
b. Construction.
(1) The sintered plate consists of three components. One is the metal grid that acts as the current collector. This grid is constructed either of pure nickel, a woven screen of nickel-plated steel, expanded metal, or perforated sheet. The second component is a fine nickel powder that is sintered on the grid and has a porosity of approximately 80 percent. The third component is the active material that is impregnated in the pores of the sintered powder. A nickel salt is used for the active material in the positive plate, and a cadmium salt for the negative. (2) Once the plates are constructed, they are formed into cell elements similar to the lead-acid battery. The plates are isolated from one another with nyloncellophane type separators and placed into a container usually of high-impact plastic. (3) The positive plate of the nickel-cadmium battery is made up of Ni(OH)3 and Ni(OH)2 whereas the negative consists of Cd and Cd(OH)2. During discharge,
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(5) The last two characteristics in table 12-1 point out possibly the most and least desirable features of the nickel-cadmium battery; that is, the desirable feature of cranking ability at low temperature, and the undesirable initial acquisition cost. The latter indicates an initial cost of approximately 35 times that of the leadacid battery. Whether this added cost can be justified by longer life and better performance is up to the electrical designer to evaluate in that particular application. In addition, the manufacture of nickel-cadmium batteries requires critical materials during war time.
battery now used for commercial application. This battery is a completely sealed unit that requires no maintenance. The major difference between this battery and conventional design is the absence of antimony in the lead grids.
d. Performance Characteristics. A discharge performance comparison between the nickel-cadmium battery and the lead-acid battery is shown in figure 12-7. This figure shows discharge characteristics of fully charged 34 ampere-hour, 24-volt, lead-acid and nickelcadmium batteries discharged at the 1-hour rate of 30 amperes. This figure illustrates an important characteristic of the nickel-cadmium battery, that is, its ability to maintain a nearly constant voltage until approximately 90 percent of the capacity is delivered. This feature, combined with its recharge capability at low temperatures, makes the nickel-cadmium battery a prime candidate for heavy-duty applications.
12-8. Maintenance-Free Battery.
b. Features. Because lead alone is not rigid enough to hold its form in use, antimony usually is added to stiffen conventional battery plates. As a result of the added antimony, the conventional battery uses an excessive amount of water during the charge and discharge cycles. In the maintenance-free battery, the designers replaced the antimony with a calcium additive to strengthen the plates. This design effort resulted in a battery with very little water loss over its lifetime. Another advantage of the sealed battery is that the battery posts do not become corroded as a result of acid leakage. However, batteries filled and sealed at the factory would become a charging problem in the military system due to wet storage. Because of shipping delay and distances involved, and long-term storage require-ments, a battery seldom is used within the first year after its production.
12-9. Other Storage Batteries.
a. General. Another development that could be applied to military vehicles is the maintenance-free
a. General. Although the lead-acid and the nickelcadmium storage batteries have received the most attention, several other battery types deserve a brief description. These are: nickel iron, nickel zinc, silver zinc, and silver cadmium.
Table 12-1. Lead-Acid Vs Nickel-Cadmium Batteries. Lead-Acid Battery weight, lb Number of cells Voltage A-hr capacity (5-A rate) Cranking ability at -40F minimum time, at 300-A rate Initial acquisition cost (current Government catalog) 12-8 70 6 12 100 Nickel Cadium 70 10 12 70
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Figure 12-7. Comparison of Discharge Characteristics. b. Nickel Iron. This is a battery of rugged construction, used for many years for heavy cycling service to provide reliable, long-life service in applications such as electric industrial trucks and railway cars. The battery may have limited use in certain tankautomotive applications. Charging problems occur due to high over voltage and performance is poor at low temperatures. c. Nickel Zinc. This battery has received attention only in recent years. It is still in the development stage. Problems to be overcome are low nickel plate capacity, separator deterioration, and poor zinc cycle life. With added improvements it could become competitive with silver-zinc types in many applications. d. Silver Zinc. This battery is the best high-rate have an exceptionally long cycle life. These shortcomings are expected to be improved in the near future. e. Silver Cadmium. This battery has similar construction to the silver zinc, but has lower cell voltage and more moderate discharge rate. It is similar in cost to the silver zinc, but better in cycle service due to its cadmium electrode. This battery, as well as the silver zinc, presently is used for space satellite applications, and possibly could have future use in tank-automotive applications.
12-10. Battery Installation Considerations. The design of a battery installation will vary with the type of vehicle. There are, however, certain design features that can be applied to all vehicles used in a tank-automotive application.
a. The battery always should be mounted in a location that is clean and protected from accumulations of mud, dust, and excess moisture.
Protection from the elements is beneficial not only to the operation of the battery itself, but can be the means to prevent unforeseen accidents. For example, if saltwater comes in contact with the positive plates of a damaged lead-acid battery, it will produce chlorine gas. Proper design will avoid the possibility of such an occurrence. Also, provisions for periodic cleaning of the battery installation always should be made.
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b. The battery should be mounted to facilitate maintenance and provide ready access to the batteries without the need for removing other components. All access plates should be hinged and employ quickrelease fasteners when feasible. Allow for adequate clearance so that maintenance personnel wearing arctic clothing can gain access for removal and replacement. Allow enough overhead room to provide for easy, accurate testing and servicing of the batteries. c. Battery boxes should be designed to protect the vehicle and crew from gases produced during battery charging. These gases are oxygen and hydrogen, which constitute a highly explosive mixture. Thus, adequate ventilation must be provided to allow all gas to escape. This ventilation also is necessary to limit temperature rise in hot climates.
12-11. Battery Installation Configurations (Fig. 12-8).
(2) Additional batteries may be required to meet heavy current demands of certain military vehicles.
b. Two 12-Volt Batteries in Series. The connection of two 12-volt batteries in series will add their voltages together to deliver 24 volts. It should be noted that the amount of current output, however, will remain the same as for one battery. c. Four 12-Volt Batteries in Series-Parallel. By taking two pairs of 12-volt batteries connected in series (24 volts for each pair) and connecting them in parallel with each other, a battery pack of 24 volts will result, with twice the current output of each individual battery. This battery configuration is used to meet the demands of heavy-duty use and to provide extra power for cold weather cranking. d. Six 12-Volt Batteries in Series-Parallel. This configuration consists of three pairs of 12-volt seriesconnected batteries in parallel with each other. This configuration will provide 24 volts with three times the current capacity of each individual battery at 24 volts and is used in extreme heavy-duty applications.
a. General. Current tank-automotive vehicles always use more than one battery. There are two reasons for this:
(1) Because the standard batteries are 12 volts, two batteries are required to meet the 24-volt requirement of military vehicles.
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13-1. General. The generator is a machine in which the principle of electromagnetic induction is used to convert mechanical energy into electrical energy. The generator restores the current used in cranking the engine to the battery. It also supplies, up to the limit of its capacity, current to carry the electrical load of the lights, ignition, radio, and horn. A generator and a motor are basically the same in construction and use the same electrical principles; however, their operation is opposite. In the generator, mechanical motion is converted into electrical energy. In the motor, electrical energy is converted into mechanical motion. 13-2. Simple Single-Loop Generator. a. Induced Current. If a single loop of wire is rotated in the magnetic field between a north and a south pole, there will be an electrical pressure produced in the two sides of the loop. The voltage and current produced will relate to the direction of the magnetic field and the direction of rotation. If each end of the loop is connected to a metal segment of a commutator on which brushes rest (fig. 13-1), this electrical pressure will cause a current to flow through any external circuit that may be connected across the two brushes. b. Commutation. If the loop is rotated through a complete revolution (fig. 13-1), sides 1 and 2 will cut magnetic lines of force in first one direction and then in the other. This will produce current in each side of the loop, first in one direction and then in the other. That is, in side 1, current will flow in one direction when it is passing the north pole and in the other direction when it is passing the south pole. However, because the commutator segments also rotate with the loop, the current always will leave the right-hand brush (4) and enter the left-hand brush (3). The directions of current produced in each side of the loop can be determined by use of the left-handed rule, described in paragraph 1114. 13-3. Multiple-Loop Generator. The advantages of a multiple-loop generator are explained below.
a. More Current Induced. In the simple, single-loop generator (fig. 13-1), the current produced in each side of the loop reaches a maximum when the sides are cutting the lines of force in a perpendicular direction. This is the position in which the loop is shown. As the loop moves away from this position, it cuts fewer and fewer lines of force and less and less current is produced. By the time the loop has turned 90 degrees from the position shown, the sides are moving parallel to the lines of force and are cutting no lines, therefore no current is being produced. The current produced from the single loop is shown in graph form in figure 13-1. Many loops, or turns, of wire are required in the conductor in order for the generator to produce an appreciable amount and even flow of current. The rotating member that contains the wire loops and the commutator is called an armature. Figure 13-2 shows an armature in place in a generator. Note that many turns are used in the armature windings. b. Smoother Current Flow. The windings are assembled in a soft iron core because iron is more permeable than other substances that could be used. The windings are connected to each other and to the commutator segments in such a way that the current impulses overlap and produce a smooth flow of current. This could be compared to the overlapping of power impulses in an 8- or 12-cylinderenglne.
13-4. Generator Speed. In order for the generator to provide rated output, it must be operated at sufficient speed. Because military vehicles spend a large amount of time at engine idle, it is important to note that during these periods the generator may be required to supply full rated current on a large portion thereof. Therefore, the requirement for establishing the speed at which full rated output must be delivered is the controlling factor for optimizing the size of the generator. As a general rule, engines have a speed ratio between four and five to one from idle to maximum speed; that is, the typical engine idles at 650 rpm and has a maximum speed of 3,000 rpm. Typical
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TM 9-8000 generator speeds can be two to four times engine rpm. 13-5. Field Intensity. The magnetic lines of force that are created by the generator field are critical to the generators output. The more lines of force that there are for the armature to cut, the more output the generator will produce. Generator field coils are designed to produce the most intense field that is possible. The key factors that affect field intensity are: a. The number of wire turns in the coil.
a. General. There are two basic forms of electrical current flow: Direct current (dc) and alternating current(ac). b. Alternating Current. Alternating current forces electrons from one terminal to the other and then back again (the direction of current flow alternates). A graph of the voltage versus time for alternating current is shown in figure 13-3. It can be seen that the value of the voltage rises in the positive direction, reaches a peak, falls in the negative direction, reaches a negative peak, and then rises to zero. This is a constantly repeating cycle. Generators normally produce alternating current. c. Direct Current. Direct current flow forces electrons from the negative terminal to the positive terminal (current flow is always in one direction or direct). Direct current voltage versus time is shown in figure 13-3. d. Compatibility. An automotive electrical system, due to the need for a storage battery that
Section II. DC GENERATOR PRINCIPLES 13-7. Field Winding Configurations (Fig. 13-4). The purpose of the field windings is to create the lines of force electromagnetically that induce a current flow in the armature. The field winding usually is connected in parallel with the armature winding (that is, across the brushes). This is called shunt-field winding. The shunt-field winding usually is connected only at one end to the brushes. The other end of the field winding then is made to pass through a voltage regulation circuit (para 13-13). In this manner, the output of the generator is controlled. Depending on the TA233543 13-3
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a. A-Type Field Circuit. The A-type field circuit shunts one end of the field winding to the negative generator brush and controls output through the regulation circuitry to the positive (battery) connection. b. B-Type Field Circuit. The B-type field circuit shunts one end of the field winding to the positive generator brush and controls output through the regulation circuitry to the negative (ground) connection.
13-8. Shunt-Wound Generator (Fig. 13-5).
a.General. Most motor vehicle generators are shunt wound, with an outside means of regulating the voltage output. Approximately 8 to 12 percent of the total current generated by the armature is shunted (sent) through the field coils for producing the magnetic field. b. Components. The generator essentially consists of an armature, a field frame, field coils, and a commutator with brushes to establish electrical contact with the rotating element. The magnetic field of the generator usually is produced by electromagnets or poles magnetized by current flowing through the field coils. Soft iron pole pieces (or pole shoes) are contained in the
c. Field Frames. In the two-pole type frame, the magnetic circuit flows directly across the armature, while in the four-pole type each magnetic circuit flows through only a part of the armature core. Therefore, the armature must be constructed in accordance with the number of field poles because current is generated when the coil, winding on the armature, moves across each magnetic circuit. d Brushes and Commutator. The current is collected from the armature coils by the brushes (usually made of carbon) that make rubbing contact with a commutator. The commutator consists of a series of insulated copper segments mounted on one end of the armature, each segment connecting to one or more armature coils. The armature coils are connected to the external circuit (battery, lights, or ignition) through the commutator and brushes. Current induced in the armature coils thus is able to flow to the external circuit. e. Principle of Operation. In figure 13-6, assume that the magnetic field flows from the north pole piece (N) to the south pole piece (S), as indicated by the arrows. When the armature is TA233544
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the magnetism remaining in the pole pieces after the field-magnetizing current has stopped. If there is no residual magnetism in the pole pieces, there will be no initial output of the generator, and it will not build up voltage to push current. If the pole pieces lose residual magnetism through long storage, or by being newly rebuilt, subjected to extreme heat or cold, dropped, vibrated, or struck by a sharp blow, it can be restored by passing direct current through the field winding in the proper direction. If current is passed through the field windings in the reverse direction, the generator will be polarized in reverse. This reverse polarity will cause the generator to discharge the batteries instead of charging them, and also could cause damage to some of the vehicle accessories. Several conditions are necessary for the generator to build up a voltage. Two of the most important requirements are that the pole pieces have residual magnetism as a foundation on which to build, and that the current in each field coil be in a direction around the pole that it will produce magnetism to assist, and not oppose, the residual magnetism. If the field current opposes it, the voltage built up will not be higher than that produced by the residual magnetism.
g. Construction. The armature core is made of sheets of iron insulated from each other so that the magnetic field will not induce eddy currents in the core. Eddy currents are currents that are induced within the core by the constant variation in the lines of force. Making the armature core in one piece would allow eddy currents to become large enough to create a counter-voltage, which would result in a large portion of the generators output to be converted to heat. The armature core is wound with coils of copper wire and mounted on a shaft with a commutator on one end. Field coils are made of many coils of fine wire arranged for shunt connection. The field frame, usually two or four poles with brushes, brush holders, and end housings with bearings, completes the essential parts of the generator. h. Generator Drives (Fig. 13-7). The method of mounting and driving the generator depends to a large extent on the construction and design of the engine. It usually is mounted on the side of the engine and driven by belts or
TM 9-8000
b. Construction. The circuit breaker consists of two windings: a shunt winding and a series winding. These are assembled on a single core, above which is placed an armature. The shunt winding consists of many turns of fine wire, and is connected across the generator. The series winding consists of a few turns of heavy wire designed to carry full generator output, and is connected to the charging circuit. The armature operates a moving contact point that is positioned above a stationary matching point. Common practice is to place the cutout relay inside the voltage regulator. c. Operation. When the generator is not operating, the armature is held away from the winding core by spring tension, and the points are separated. As soon as the generator begins
13-7
TM 9-8000 engine make it necessary to regulate the output of the generator to prevent excessive current or voltage overload. On the average motor vehicle, a charging current in excess of 12 to 15 amperes may be harmful to a fully charged battery if continued too long. With the increased use of electrical accessories, generators have been increased in output until they are capable of producing far more than 15 amperes. Some heavy-duty generators, for example, may produce as much as 150 amperes. 13-12. Reverse-Series Field Generator (Fig. 13-9). The reverse-series field generator is self-regulating. the simplest methods, used on special applications, is the use of a reverse-series field for differential action. A shunt field is connected across the brushes to produce the magnetizing action. Charging current going through the reverse-series field, however, has a demagnetizing action so that, as the current increases, it tends to restrict the rise of current above a reasonable value.
a. Operation. Because the output of the generator depends on the number of conductors in the armature, their speed of rotation, and the strength of the magnetic field in which they rotate, varying the strength of this field is the only convenient method of regulation. One of
b. Disadvantages. This type of differentially wound generator has disadvantages that limit its use on motor vehicles without some additional external regulator. If a break should occur in the charging circuit (except during normal circuit breaker operation), destroying generator regulation by the series field, the voltage will become excessive. This usually results in damage to the field and armature winding and to the voltage winding of the circuit breaker. Therefore, such generators usually have some form of external voltage regulation.
13-13. Vibrating Point Regulator.
a. Current Regulation.
(1) The vibrating regulator (fig. 13-10) can be used to regulate the current or the voltage, depending on how the regulator coil is connected. A circuit diagram of a typical vibrating regulator used for limiting the current from the generator is shown in figure 13-11. The regulator consists of a soft iron core, a heavy winding or current coil around the core, a set of regulator contact points normally held closed by spring tension, and a resistance unit connected across the two regulator contact points. (2) As the generator output increases, the current regulator prevents the current output of the generator from exceeding its rated maximum. It does this by cutting a resistance intermittently in and out of the shuntfield circuit as the regulator contact points open and close, due to the varying magnetic pull of the core. The resistance is connected in the shunt-field circuit, but normally is short circuited by the regulator contacts when they are closed. One of these is mounted on a soft iron contact armature, to which the spring for holding the points in contact is attached. The TA233548
TM 9-8000
TM 9-8000 armature, which then decreases the charging current. When the current decreases to a predetermined amount, the current coil does not magnetize the core sufficiently to overcome the pull of the spring, which then closes the contacts. With the contacts closed, the resistance unit is once more short circuited and the full field strength is restored, causing the charging current to increase again. The regulator will continue to repeat this cycle. Under operating conditions, the armature vibrates rapidly enough to keep the generator output constant. As a result, the generator will never produce more than the predetermined rate (for example, 40 amperes), no matter how high the speed of the car. This will be true regardless of the connected electrical load. (3) This method of generator regulation is termed current regulation, because the current output of the generator is used for regulation. It is very important, therefore, that no breaks occur in the charging circuit after the generator reaches a voltage that will operate the circuit breaker. If a break does occur, no current will flow through the current coil to operate the vibrating points and, due to lack of regulation, the generator will build up an excessive voltage at high speeds. A voltage regulator is used to prevent excessive voltage. (4) The charging rate of the generator can be adjusted easily in all electrical systems controlled by a vibrating regulator. To increase the maximum charging rate, the spring tension on the vibrating armature should be increased slightly. To decrease the maximum charging rate, the spring tension should be decreased. Care must be taken that the generator output does not exceed the value for which it was designed. current does not flow through the regulator winding. The winding on the core consists of a voltage coil of fine wire. The two ends of the voltage coil are connected across the generator brushes and in parallel with the battery instead of in series with it. The iron core, regulator points, and resistance unit, however, are practically the same; the only important exception is that the voltage regulator resistance is considerably higher than that used with the current regulator. (2) The current flowing in the regulator coil and resultant magnetic pull of the core on the contact armature depend on the voltage developed by the generator. For an example of regulator operation, assume that the regulator is adjusted to operate at 12.8 volts. With increasing generator speed, the voltage tends to rise above 12.8 volts. However, if this value is exceeded by a small amount, the increased magnetic pull of the core on the contact armature due to the current flowing in the voltage coil will overcome the spring tension and pull the armature toward the core. This action will open the contacts and insert a resistance in the generator field circuit. This added resistance decreases the current in the field winding, and the voltage developed by the armature drops below 12.8 volts. (3) When the voltage drops, the pull of the spring on the regulator armature overcomes the magnetic pull of the core and closes the contacts. This short-circuits the resistance unit and allows the field current to increase. The cycle of operation is repeated rapidly, preventing the generator voltage from rising above that for which the regulator is set. The regulator on most late-type military equipment will prevent the generator from building up an excessive voltage if a break occurs in the charging circuit. But this is not true on standard passenger cars and light-duty equipment. In these, if a break occurs in the voltage regulator circuit, regulation of the generator may be lost and at high speeds an excessive charging rate will result. (4) It is obvious that increasing the tension of the regulator spring will increase the output voltage of the generator. Under no circumstances should the regulator spring tension be increased in an attempt to have the generator charge at a higher rate at lower speeds. The generator cannot begin to charge until the circuit breaker closes. The closing of the circuit breaker 13-10
b. Voltage Regulation. (1) A circuit diagram of a typical vibrating voltage regulator is shown in figure 13-11. Although the construction of this relay does not differ materially from that of the current regulator, the principle of operation is somewhat different. With this regulator, the voltage output of the generator is used for automatic regulation. By comparing both circuits, it will be seen that the principal difference in the two regulators is in the winding of the controlling coil and its connections. In the voltage regulator, the charging
TM 9-8000
TM 9-8000
is independent of the action of the regulator. Increasing the tension of the regulator springs so that the generator will develop an excessive voltage will send excessive current to the battery, overcharging it. It also will cause the generator to overheat, possibly burning it out.
c. Charging Rate.
(1) Current Regulator. With the vibrating current regulator, the maximum possible charging current remains constant for any one setting of the regulator, regardless of the condition of the battery. To vary this maximum generator output, the spring tension of the regulator must be adjusted. The setting must never exceed the rated maximum of the generator. (2) Voltage Regulator.
(a) The main advantage of the voltage regulator is that the output of the generator is controlled to a great extent by the amount of charge in the battery. When the generator reaches a speed at which it develops the regulated voltage, there will be no further increase in voltage with increasing speed. The voltage will be maintained constant at all loads and at all higher speeds. (b) During the time the generator is connected to the battery, the difference in voltage between the two is the voltage available for sending current into the battery. In a discharged battery, the difference in voltage between the generator and the battery will be relatively great, so that a comparatively high charging current will pass from the generator to the battery. As the charge continues, the voltage of the battery increases, so that the difference in voltage between the generator and the battery is diminishing continually. With a fully charged battery, the voltage is equal nearly to that of the generator so that the difference between the two is very slight. As this slight difference in voltage is all that is available for sending current into the battery, the charging current will be small. The charging current, therefore, is variable and depends upon the charge in the battery. In practice, the charging current with the constant voltage regulator varies from a maximum of 25 to 35 amperes for a discharged battery to a minimum of 4 to 6 amperes for a fully charged battery.
a. General. In the vibrating-contact type regulator, a set of contacts open and close to insert and remove a resistance in and from the generator field circuit. This, in effect, inserts a variable resistance into the field circuit that controls the generator. When only a small output is required, the voltage regulator maintains the resistance in the field circuit most of the time. When output requirements increase, the resistance is in the field a smaller part of the time. This same variable-resistance effect can be achieved by a carbon-pile regulator. b. Construction. The carbon-pile regulator consists essentially of a stack of carbon disks held together by spring pressure. The spring pressure is applied by an armature. The resistance through the carbon pile is relatively small with full spring pressure applied. But with less pressure, the resistance increases. The carbon pile is connected to the generator field circuit so that its resistance is in series with the field. With full pressure applied, there is no regulation and generator output can increase to a high value. To
TM 9-8000 limit current output to a safe value, or to provide voltage regulation, the armature pressure can be adjusted to vary the resistance. The rheostat is connected to the shunt-winding circuit of the voltage regulator. Its purpose is to permit adjustment of the voltage regulator setting. When all resistance in the rheostat is cut out (by turning the knob), the full generator voltage is imposed in the shunt winding. But when some of the rheostat resistance is cut in, less than full generator voltage is imposed on the shunt winding (part of it being in the rheostat). In the latter case, generator voltage must go higher before voltage regulation commences. Thus, accurate setting of the regulator can be made. 13-15. Third-Brush Regulation (Fig. 13-13). Third-brush regulation is much simpler in operation and less expensive to manufacture than other methods of control. However, it can be used only for relatively small and specialized applications. Generators with this type of control have an extra brush called the third brush, located between the two main brushes.
c. Current Regulation. To limit current, or to provide current regulation, the carbon-pile regulator has a heavy winding through which all current from the generator must pass. This winding produces a magnetic pull as current asses through it, which opposes the armature spring pressure. When the output reaches the value for which the generator is rated, the magnetic pull overcomes the spring pressure sufficiently to reduce the pressure on the carbon disks and thereby increase the resistance of the pile. This increased resistance, which is in the generator field circuit, prevents any further increase of output. d. Voltage Regulation. A winding is incorporated in the carbon-pile voltage regulator to regulate voltage. This shunt winding is connected across the generator so that generator voltage is forced on it. When this voltage reaches the value for which the regulator is set, the winding produces enough magnetic pull on the armature to reduce the armature spring pressure. This causes the resistance of the voltage-regulator carbon pile to increase. The increased resistance, which is in the generator field circuit, prevents any further generator voltage increase and thereby reduces generator output.
a. Arrangement. Arrangement of a typical two-pole, third-brush generator is shown in figure 3-13. One end of the shunt-field winding is connected to the third brush, the other end is grounded. Only a part of the total voltage generated is supplied to the field by the third brush. b. Operation.
(1) When the generator is running at a low speed and little or no current is flowing in the
TM 9-8000 armature winding, the magnetic field produced by the field windings is approximately straight through the armature from one pole piece to the other. The voltage generated by each armature coil is then practically uniform during the time the coil is under the pole pieces. (2) As the generator speed and current increase, the armature winding acts like a solenoid coil to produce a cross-magnetic field. The magnetic whirl around the armature winding distorts the magnetic field produced by the shunt-field windings so that the magnetism is not distributed equally under the pole pieces. With this distortion of the magnetic field, the armature coils no longer generate a uniform voltage while passing under the different parts of the pole. Although the voltage across the main brushes remains nearly the same, a greater proportion of this voltage is generated by the coils between the positive brush and the third brush than was generated between them when little current was flowing through the armature winding. This is due to the distortion of the magnetic field, which crowds more magnetic lines of force between the positive and the third brush. (3) The coils that connect the commutator between the negative and the third brush are in the region of the weakened field and generate a lower proportion of the voltage. The result is a dropping off of the voltage between the negative and third brushes, which is applied to the shunt-field winding, thereby weakening the field strength. As the field strength decreases with increased generator current, the result will be an automatic regulation of the current output. the field winding will depend upon the number of armature coils spanned by the brushes that collect the field current. Thus, moving the third brush in the direction of the armature rotation increases the average current delivered to the shunt-field winding and, consequently, the output of the generator. Moving the brush against the direction of armature rotation decreases the output. When this brush is moved, care should be taken to see that it makes perfect contact with the commutator. (3) Because the third-brush generator depends upon the current flowing through the armature winding to produce the field distortion necessary for regulation, it is obvious that it is current-regulated internally (as distinct from external current regulation). Therefore, it must have a complete circuit available through the battery at all times. Otherwise, regulation would be destroyed and excessive field currents would burn out the generator windings. The generator terminals must be grounded in case the third- brush generator is disconnected from the battery. 13-16. Control of Third-Brush Generator. A fuse is sometimes provided in the field circuit to guard against the possibility of the third-brush generator burning up. When used, it is placed either in the generator end plate or in the regulator control unit. If the battery becomes disconnected, there is a rise in voltage at the generator. This, in turn, sends an abnormally heavy current through the field winding and this field current burns out the fuse. As soon as the fuse is blown, the field circuit is open and no current can flow through it. The generator then merely turns, producing practically no voltage, and does no harm. The third-brush generator provides current regulation only and does not take battery voltage into consideration. In fact, a fully charged battery that has a high voltage actually will get more current from a thirdbrush generator than a battery that is completely discharged, because the high voltage holds up the voltage at the generator, makes the field stronger, and causes the generator output to increase. This, combined with the varying demands of radio sets and other currentconsuming devices, necessitates more accurate regulation than a third-brush generator alone can give.
c. Output.
(1) One of the outstanding characteristics of generators with third-brush regulation is that the output of the generator increases gradually up to an intermediate speed. After this, due to obvious field distortion, the output falls off as the speed continues to increase. At high generator speeds, the output is approximately onehalf its maximum value. (2) In practically all generators that have third-brush regulation, provision is made for changing the output to suit the conditions under which the generator is operated. This can be done by moving the position of the third brush on the commutator. The average voltage applied to
a. Switch Control. Practically all systems of regulation provide a means for inserting a resistance in series with the third-brush field.
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TM 9-8000 A simple way of accomplishing this is shown in figure 1314. A resistance is mounted on the back of the lighting switch and connected in series with the field. When the lights are off, the generator output current is limited by the resistance in the field circuit. When the lights are turned on, the resistance is shorted so that the generator delivers full current to take care of the additional lighting circuit load. This is just a two-step arbitrary system of regulation, however, that will not meet the varied load requirements of normal vehicle operation. through the fine winding on the control unit to pull the contact points apart. When this happens, the resistance across the contacts is connected in series with the field winding to lower the field strength and, consequently, to reduce the generator voltage and the current output. When the voltage is lowered sufficiently, spring tension will close the contact points and the higher charging rate will be restored. (3) When there is sufficient electrical load (such as lights, radio, or heater) to require a higher generator output, the contact points will close, because the load will lower the generator voltage and the generator will produce maximum output for the selected position of the third brush and the speed at which it is driven.
b. Step-Voltage Control.
(1) The purpose of step-voltage control is to increase or decrease the output of a third- brush generator in accordance with the requirements of the battery and the connected electrical load. It is really a two-stage regulator in which the change from one output to the other is controlled by the generator voltage. The generator voltage is control led then by battery voltage. (2) A step-voltage control unit is shown in figure 13-15. A fine-winding voltage coil, connected to the generator armature terminal so that it receives the armature voltage, is the controlling element. Contacts are connected in series with the field terminal and have a resistance unit connected across them. When the battery is fully charged, its voltage raises the generator to such a value that sufficient magnetizing current flows
c. Vibrating Regulator Control. A vibrating regulator (para 13-13) also can be used with a third-brush generator. Such a regulator is controlled by a voltage coil that operates vibrating contacts. When the battery is discharged, there is insufficient voltage to operate the regulator. The generator output is controlled then only by the third brush. As the battery becomes charged, the voltage of the system will increase and more current will be forced through the regulator coil. The regulator points then begin to vibrate, connecting a resistance in the generator field circuit and cutting down the output to a fairly constant value.
TM 9-8000
d. Thermostatic Control.
(1) Another type of control for the third-brush generator uses a thermostat blade to control the field strength. If the generator is set to give the greatest possible current to take care of demands during the winter, the battery would be in a constant state of overcharge in warm weather and soon be ruined. The thermostat blade automatically takes care of the changing current demands under different conditions. (2) The control consists of a bimetal thermostat blade made of a strip of spring brass welded to a strip of nickel steel. The blade warps or bends when heated, due to the greater expansion of the brass side. The blade is set so that a contact on its end is held firmly against a fixed contact at low temperatures. When the temperature rises to approximately 1600 to 1650F, the blade bends and separates the contacts. (3) The thermostat is connected in the third-brush field circuit (fig. 13-16) so that the full field current passes through the thermostat contacts when closed, permitting full current from the generator. After the engine has been run 13-16
long enough for the high charging rate to heat the generator, the thermostat contacts open (due to the bending of the thermostat blade), causing a resistance unit across the contacts to be connected in series with the third-brush field and thereby reducing the current output. The charging rate is reduced approximately 30 percent when the thermostat contacts are opened. (4) The chief advantages of thermostatic control are that it gives a large battery-charging rate in cold weather when the efficiency of the battery is lower than in warm weather, and also a larger charging rate when the vehicle is being driven intermittently and the demands on the battery are greater because of frequent use of the starter. This control also prevents the generator and battery from overheating in summer by reducing the charging rate when the temperature rises. 13-17. Split-Series Field Generators (Fig. 13-17 a. Generator regulation sometimes is accomplished by means of a split-series field. A generator with this method of regulation combines third-brush, reversedseries (differential), and cumulative-compound principles. TA233554
TM 9-8000
The series-field winding is divided so that the generator output is changed according to the load.
This weakens the total field strength, keeping the generator output down for the delivery of a reasonable charging rate. c. When the lighting switch is closed, the entire lighting current flows through section 1 of the series field in the same direction as the shunt
b. With lights off, no current flows through one part of the series field (1, fig. 13-17). The current going to the battery flows through the remainder of the series field (2, fig. 13-17) in the opposite direction to the shunt-field current.
TM 9-8000 field. The strength of the field is thereby increased, giving a higher generator output to take care of the lighting load. generator. Where two generators are working in a Single set of batteries and a single electrical System, the problem of paralleling exists. That is, the two generators must be connected in parallel. Unless special provision is made, trouble may result if two generators are parallel. The reason for this is that one generator may attempt to carry most or all of the load while the other generator might use current or act like a motor. The problem is further complicated if one of the generators varies in speed (as the unit on the power plant might). b. System Description. To provide effective paralleling, each of the voltage regulators contains an additional paralleling winding. These windings become connected to each other through two paralleling relays when both generators are operating. With this condition, the paralleling windings can increase the voltage and thus the output) of the generator that is producing more than its share. Therefore, the two generators can be kept in step. 13-19. Generator System - Main and Auxiliary Generators.
d. If the lights are turned on before the generator circuit breaker closes, the entire lighting current is supplied by the battery. This current then flows through all of the series field, instead of through section 1 only, in the same direction as the shunt field, making the total field strength still greater. This will build up the generator voltage to close the circuit breaker. The entire current output of the generator that passes through the circuit breaker flows to the center tap of the series field, where it divides. Part of the current then flows in one direction through to the battery and the remainder flows to the lights.
e. As soon as the circuit breaker closes, the generator begins to pick up the lighting load. This lessens the drain on the battery and thereby reduces the current flowing through section 2 of the series field. When the generator output just equals the lighting current, the current in section 2 is zero and, as the generator output increases further, current begins to flow in the reverse direction through section 2 to the battery. This tends to weaken the field built up by the shunt winding and section 1 of the series winding. By obtaining the proper relationship between the shunt winding and the two sections of the series winding, results quite similar to those obtained from voltage regulation are secured, and the battery is kept in a charged condition. f. The charging rate of the split-series field generator may be adjusted by shifting the third brush as in the regular third-brush generator. In some generators of this type, separate coils are used for the two sections of the series field. In others, the two sections are combined into one coil. Generators of this type do not have standard connections and must not be confused with the ordinary third-brush generator. Neither terminal should be grounded under any circumstances. 13-18. Paralleling Generators.
a. General. A wiring circuit of a combat vehicle using a main and auxiliary generator is shown in figure 13-18 in schematic form. This system uses two generators, two carbon-pile regulators, plus various relays and switches. The following chart identifies the circuits in figure 13-18.
CIRCUIT 1 2 7 10 61 62 65 81 421 422 459 459B 478A 478M 506 508 CIRCUIT NAME Main Generator Feed Main Gen Positive Line Battery Ground Instrument Panel Feed Auxiliary Generator Field Aux Gen Positive Line Auxiliary Engine Starter Battery - Positive Line Aux Eng Fuel Cutoff Valve Aux Eng Magneto Ground Master Relay Control Master Relay Feed Aux Gen Equalizing Main Gen Equalizing Main Gen Warning Light Aux Gen Warning Light
a. General. Some military vehicles have two separate power plants, each with its own generator and regulator working into a common set of batteries. Certain combat vehicles have a single power plant, but they also carry an auxiliary
13-18
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TM 9-8000
b. Generator. The generator is a shunt generator with a maximum output of 150 amperes, and is used with a 24-volt battery set. The generator contains an additional field winding of a few turns of very heavy wire through which the entire generator output passes. This is a series winding. It is wound so that its magnetic field opposes the magnetic field from the shunt windings. This acts as a current-limiting device because the higher the output, the greater the opposition from the serieswinding magnetic field. When the output reaches the rated maximum, the series-winding field is so strong that it effectively prevents any further increase in output. More increases would strengthen the series-winding field, thus further opposing the shunt- winding field and causing a decreased total field and, consequently, a drop-off of output. This series-field winding in the generator also plays an important part in the operation of the regulators and certain relays in the control system (para c and d, below). c. Pilot Relay. There is a pilot relay for each generator. Because both operate the same, the one used with the main generator will be discussed. It contains a shunt winding that is connected across the main generator terminals. In addition, it has two sets of contacts: an upper set and a lower set. The upper set is used in conjunction with the paralleling system, so consider the lower set first. This lower set is open when the generator is not operating. But when the generator begins to run and its voltage increases sufficiently to charge the battery, then the lower set closes. The shunt winding in the relay produces this action because, with sufficient voltage, it has a strong enough magnetic pull to pull down the relay armature and close the lower contacts. When the lower contacts close, this causes the differential-voltage-and-reverse-current relay to operate. d. Differential-Voltage-and-Reverse-Current Relay.
(1) Closing. When the pilot relay closes its points, one of the windings in the differential- voltage-and-reversecurrent relay becomes connected between the insulated battery terminal and the installed generator terminal. If the generator voltage is greater than the battery voltage, the difference (or differential) between the two causes current to flow in the winding
(which is called the differential-voltage winding). As this current flows, a magnetic field is produced that pulls the relay armature down and causes relay contacts to close. When the relay contacts close, the line-switch winding is connected across the generator so that it closes, thereby directly connecting the generator to the battery. (2) Opening. With the relay and line switch closed so the generator charges the battery, current flows through the battery and back to the generator by means of ground wire and the series winding in the generator field. Because the current is flowing through the series winding, there is a voltage difference between the two ends of this winding. This voltage varies with the rate of current. With a high generator output, a high current is flowing and the voltage across the series winding is greater. This voltage is applied to the differentialvoltage-and-reverse-current relay. When the generator is charging and the relay is closed, this voltage is imposed across a second winding in the relay (the reverse-current winding) in such a direction as to help the differential-voltage winding hold the relay contacts closed. But when the generator voltage falls below the battery voltage, the battery begins to discharge through the generator. In other words, the current reverses. This means that the current in the series-field winding, and thus the voltage across the series-field winding, also reverses. The resultant reverse voltage, which is applied to the reverse-current winding, causes the magnetic field of this winding to reverse. This winding then no longer helps the differential-voltage winding, but opposes it. As a result, the total magnetic field is so weakened that the relay armature is pulled up by its spring tension and the contacts open. This then opens the line switch winding circuit so the line switch opens. This disconnects the generator from the battery.
e. Line Switch. The line switch is a simple magnetic switch. When its winding is electrically energized, it pulls the armature down so the switch is closed. When the winding is disconnected, the spring pressure under the armature moves the armature up so the switch opens. f. Paralleling Relays.
(1) Connections. In operation, the contacts of the paralleling relays are connected in 13-20
TM 9-8000 series with the paralleling windings in the two voltage regulators and to the two series-field windings in the two generators. Whenever a generator begins to charge, the armature on the pilot relay moves from the upper to the lower position, opening the upper and closing the lower contacts. When the upper contacts are closed (meaning that the generator is not charging), the paralleling relay winding is shorted through them and no paralleling relay action can take place. But when the pilot relay opens these upper contacts and closes the lower contacts, the winding of the paralleling relay becomes connected across the generator. Now, generator voltage can energize the winding and cause the paralleling relay to close its contacts. Only one paralleling relay will be actuated if only one generator is operating. This means that no paralleling can take place. But when both generators are operating so that both paralleling relays are in action, then the contacts of the relays, the paralleling windings in the regulators, and the series-field windings in the generator are all in series. (2) Operation. When all are in series, current will flow in the circuit if one generator is putting out more current than the other. To understand how this might be, refer to figure 13-19, which is a simplified sketch of the generator series-field windings and the regular paralleling windings connected in series. The paralleling relay contacts are not shown here because they are closed and are therefore a part of the circuit. Suppose that the main generator is putting out more current than the auxiliary generator. This means that more current flows through the series-field winding of the main generator than through the series-field winding of the auxiliary generator. Under these conditions, there will be a greater voltage across the main generator seriesfield winding. This means that current will flow from this winding, through the paralleling windings, and the auxiliary generator series-field winding. The current flow through the paralleling windings in the regulators helps the regulating winding in one regulator and opposes the regulating winding in the other. it helps in the main generator regulator; this means that the spring pressure on the carbon-pile armature is lightened further so that the carbon-pile resistance increases, cutting down the main generator output. On the other hand, the paralleling winding in the auxiliary generator regulator opposes the regulating winding. This means that the spring pressure on the carbon-pile armature is increased. Carbon-pile resistance is reduced and the auxiliary generator output goes up.
(3) Paralleling. With paralleling, if one generator tries to produce more output than the other, its output is cut down immediately while the output of the low generator is increased. The action is entirely automatic once the system has been adjusted correctly. In order to achieve adjustment, the voltages of the two carbon-pile regulators must first be set, then the voltages perfectly balanced by means of the no-load voltage-adjusting potentiometer, or pot. Finally, the two paralleling rheostats must be adjusted. All these adjustments must be made by authorized personnel and according to instructions supplied in the applicable technical manual. g. Regulators. The carbon-pile regulators, one for each generator, operate on generator voltage (para 1316). A simplified sketch of one carbon-pile regulator circuit is shown in figure 13-20 (paralleling winding not shown). Some special features of this circuit will be of interest. The carbon pile is connected between the insulated generator brush and the generator shunt field. The regulator winding is connected across the generator brushes so that full generator voltage is imposed on it. It therefore regulates on generator voltage as explained in paragraph 13-16. There is a voltage-adjusting rheostat connected in series with the winding so that voltage adjustment can be made. In addition, the circuit goes to ground through an adjustable resistor called a potentiometer. The potentiometer permits accurate balancing of the two voltage regulator settings. TA233560
13-21
TM 9-8000
b. Rectifier Bridge (Fig. 13-22). The ac generator produces alternating current at its output. As stated in paragraph 13-6, this is unacceptable for an automotive electrical system. The ac generator is fitted with a rectifier bridge to convert the output to dc. If the two output wires of a basic ac circuit are each fitted with a silicon diode (para 11-5), the alternating cur- rent can be Section III.13-20.General.Most of the military vehicles are now given one direction and thus be changed to direct current. To change current direction, use diodes that equipped with an ac charging system. The reason for allow current flow toward the alternator on one wire changing to the ac system is that an alternator is capable (positive) and away from the alternator on the other wire of producing a higher voltage at idle speed, whereas a dc (negative). Because most automotive alternators have generator produces very little voltage at idle speed. three outputs (three-phase stator), the rectifier bridge will Many of the military vehicles are equipped with radios, consist of six diodes (three positive and three negative). firing devices, and other high-current-drawing equipment. The diodes will be connected so that they combine the When this equipment is in operation and the vehicles three ac outputs of the alternator into one dc output. engine is at a low rpm, a dc generator will not produce the required current and voltage to keep the batteries charged and supply the current required to operate the 13-22. Comparison to a DC Generator. accessories properly. a. Advantages. 13-21. The Basic Alternator. (1) The ac generator is configured opposite to the dc generator. The current is produced in the stator, which a. Construction (Fig. 13-21). The alternator is does not rotate. This compares with the dc generator composed of the same basic parts as a dc generator. that produces current from its armature, which must There is a field that is called a rotor and a generating transmit its output through brushes. This means that the part known as the stator. The purpose of the alternator brushes must be very large and, therefore, will wear out is to produce more power and operate over a wider speed range than that of a generator. Because of this, TA233558 the construction of the functional parts is different. The stator is the section in which the current is induced. It is made of a slotted laminated ring with the conductors placed in the slots. The current generated in the windings is transferred to the rest of the system through three stationary terminals. 13-22
TM 9-8000
c. Comparison of Output Characteristics. It can be seen from figure 13-23 that the dc generator has a much narrower speed-producing range than the ac generator. The initial startup is at a much higher rpm, which is undesirable for vehicles that operate mostly in low-speed rang-s. As high speeds are reached, the dc generator output will fall below its rated output largely due to the brushes bouncing on the commutator segments, causing poor commutation.
13-23. The Automotive Alternator.
b. Disadvantages.
(1) The ac generator requires electronic rectification through the use of silicon diodes. Modern rectifier bridges, though extremely durable under normal conditions, are extremely sensitive to accidental polarity reversal. This can result from jump starting, battery charging, and battery installation.
a. The Basic Alternator. A basic alternator would consist of one winding or loop in the stator and a single pair of poles in the rotor (fig. 13-24). When the rotor of this machine is turned through 360 degrees, it will induce a single cycle of ac just as the simple generator armature did. b. Rotor Design (Fig. 13-25). The rotor is designed with two pole pieces that sandwich the TA233560
13-23
TM 9-8000
TM 9-8000
TM 9-8000
d.
Rotor-to-Stator
Relationship
(Fig.
13-27).
a. Wound-Pole Alternator. Figure 13-28 illustrates the configuration of a typical wound- pole alternator with rotating field. Alternate
TM 9-8000 temperature, high-altitude, or high-speed applications. Brush arc is an explosion hazard; fuel or oil cannot be used safely as a coolant. The rotor winding is hard to cool and is relatively unreliable in high-speed or roughdrive applications that cause stress on rotor windings and insulation. The wound-pole alternator has an extensive history of development, but is best suited for low- speed applications in a limited range of environments.
b. Lundell Alternator. The Lundell rotor, as shown in figure 13-29, develops a field by placing the excitation windings around the axis of the rotor shaft, resulting in each end of the shaft assuming a polarity. Coupled to each end are interspaced fingers forming opposite polarities that provide an alternating field when rotated. Field excitation is achieved through slipring conduction. The following are advantages of the Lundell rotor. This rotor has a simple rotor winding construction and stationary output current windings. The disadvantages of the Lundell rotor are windage (air resistance) losses and the use of sliprings and brushes. c. Lundell Inductor. This generator type differs from the previously described Lundell type, in
TM 9-8000 attached to each end of the rotor. The segment varies the reluctance in the magnetic circuit as it rotates. As a result, the fixed stator poles experience a variation in magnetic strength or coupling and produce a resulting output voltage in the stator coils. In contrast to other types of generators, the iron does not experience a flux reversal. Consequently, there is only a 50-percent utilization of the iron in the stator. Figure 13-31 illustrates typical construction of the inductor alternator. The advantages of an inductor alternator are easier winding construction for field and stator coils; simplified cooling; it is brushless; and it has an integral solid rotor without windings that permits high-speed operation. The disadvantages of an inductor alternator are that it has less than 50 percent use of iron, resulting in a heavier unit and the increased total air gap in the magnetic circuit requires more excitation. e. Brushless-Rotating Rectifier. Another means for eliminating brushes and sliprlngs is found in the rotating rectifier type of alternator. The machine consists of five main functional elements. These include a statormounted exciter field, the exciter armature, a main rotating field, the main output stator windings, and the output rectifier assembly. The exciter field induces alternating current in the rotating armature and the output is rectified and directly coupled to the rotating main field, which excites the stator-mounted output windings. With this arrangement, a small amount of exciter field excitation can be amplified in the exciter stage to supply a high level of main field current. A diagram of elements is shown in figure 13-32, along with a cross section through the alternator. The advantages of the brushless rotating rectifier are that it is brushless and a low exciter field current permits a low-level regulator. However, the disadvantages of the brushless-rotating rectifier are that a wound rotor limits top speed, multiple windings contribute to complexity and cost, a large number of heat-producing rotating elements increases cooling requirements, and a large magnetic circuit limits response. 13-25. Cooling Generators. The common methods used for cooling generators use heat transfer by airflow or oil circulation. Each has its particular application based on their advantages and disadvantages. TA233564
d. Inductor Alternator. An inductor alternator employs a fixed, non-rotating field coil that induces excitation in the central portion of the rotor as if it were a solenoid. Each end of the rotor assumes a polarity. A multilobed segment is
13-28
TM 9-8000
Figure 13-30. Lundell Inductor. a. Air Cooling (A, Fig. 13-33). In tank-automotive applications, air cooling Is the most common method. The usual arrangement consists of a fan that forces air through the alternator to cool the rotor, stator, and rectifier. The major advantage of air cooling Is that the generator and cooling are self-contained, drawing air from the environment. However, fan power requirements can become excessive at high speeds because fan designs usually are structured to provide sufficient cooling at the lowest speed corresponding to rated output. Fan power at high speeds then appears as a severe reduction in generator efficiency. Another factor is that, unless it is filtered, cooling air can deliver
abrasive particles, water, or other substances to the generator interior. Furthermore, rotor and stator design must permit unrestricted passage of air through the generator. This can be accomplished by designing passages through the rotor and stator. However, roughness in the surface of the rotor contributes to windage losses, further affecting unit efficiency.
b. Oil Cooling (B, Fig. 13-33). 0il cooling features a transfer of alternator heat into the circulating oil flow, followed by cooling of the hot oil in a heat exchanger. The oil supply can be part of the driving power system
TA233565 13-29
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TA233566 13-30
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TM 9-8000
13-32
TM 9-8000 13-26. AC Generator Regulation. The regulation of ac generator output, though just as important as the regulation of dc generator output, is much simpler for the following reasons: the force of a spring. The upper and lower contacts always maintain the same distance from each other. The upper contact is shunted directly to the ground. The lower contact connects to battery voltage as does the operating coil. A resistor is connected from the battery to the field connection.
a. The ac generator, because of its rectifier bridge, will not allow current to backflow into it during shutdown. This eliminates the need for a cutout relay. b. An ac generator will limit its current automatically by regulating the voltage. A current regulator, therefore, is not needed in the voltage regulator.
Because a cutout relay and a current regulator are not necessary, an ac generator voltage regulator contains only a voltage regulation element. A typical singleelement voltage regulator for an ac generator is shown in figure 13-34. For comparison, a typical three-element voltage regulator for a dc generator is also shown. 13-27. Vibrating Point Regulator.
b. Operation (Fig. 13-35). The lower contact normally is connected to the center contact because of spring tension. As the magnetic coil is energized, the movement of the upper and lower contacts will disconnect the center and lower contacts. As they move further, the upper contact will become connected to the center contact. The following describes the operation:
(1) As the operation begins, the center contact is connected to the lower contact, sending full battery voltage to the field winding. This will cause the alternator to produce full output. (2) As the alternator raises system voltage, the force exerted by the magnetic coil increases. This causes the upper and lower contacts to move, which in turn breaks the connection between the center and lower contacts. The field then receives reduced voltage from the resistor, causing a corresponding reduction in alternator output. The resulting lower system voltage decreases magnetic coil force, allowing the lower and center points to come together again. This is a
a. Description (Fig. 13-35). The vibrating point voltage regulator is a single-element unit that limits system voltage. The element consists of a double set of contact points that are operated by a magnetic coil. The center contact is stationary and connected directly to the generator field. The upper and lower contact points are pulled downward by the magnetic coil against
TM 9-8000
TA233570 13-34
TM 9-8000
a. Fuel Pressure Field Switch (Fig. 13-38). The fuel pressure field switch is a device that is used on high output alternators to prevent the alternator from placing a load on the engine until it is running by opening the alternator field circuit until the fuel pressure reaches the normal operational range. b. Field Relay. The field relay is used in two basic applications:
TA233571 13-35
TM 9-8000
Figure 13-37. & Figure 13-38. Fuel Pressure Field Switch Circuit
13-36
TM 9-8000
TM 9-8000 CHAPTER 14 STARTING SYSTEMS Section I. ELECTRIC STARTING MOTOR 14-1. General. Any internal combustion engine must be cranked manually to start it running on its own. Early automotive vehicles were started by the driver through the use of a handcrank. A system of cranking the engine with an electric motor was developed as automotive technology progressed. The modern electric starting system has reduced the task of starting an internal combustion engine to the turn of a key or the pushing of a button. 14-2. Simple DC Motor. a. Construction. An electric motor is constructed essentially the same as a generator. If the brushes of the simple generator are connected to a battery and current is permitted to flow through the loop of wire (1, fig. 14-1), the loop of wire will rotate in the direction indicated by the arrow. This rotation is due to the repulsion between the field magnetism and the magnetic whirl set up around the loop of wire by the current (2, fig. 14-1).
b. Operation. The repulsion is caused by all the magnetic lines of force tending to flow around the conductor in the same direction. This distorts and crowds the magnetic lines on one side of the conductor more than on the other, which results in a repulsion of the conductor (3, fig. 14-1). In other words, the rubberband characteristic of the lines of force (that is, when they try to shorten to a minimum length) causes the lines to exert a push on the conductor. If the magnetic field is reversed, with the direction of current unchanged, the magnetic lines of force will crowd to the other side of the conductor, and it will be repelled in the opposite direction (4, fig. 14-1). The same action would result if the current, instead of the magnetism, were reversed. Thus, in figure 14-1, owing to the current flowing in reverse directions
TM 9-8000 in the two sides A and B of the loop, and the consequent field distortion (2, fig. 14-1), A will be repulsed upward and B downward, and the loop will rotate in a clockwise direction. 14-3. Automotive Starting Motor. armature rotation. They are constructed of heavy copper wire that is usually rectangular in cross section. An insulating material is placed within the windings to insulate the coils from each other. The coils then are insulated on the outside by either wrapping them in paper or sealing them in rubber. The field coils are secured to the field frame by the pole shoes. The pole shoes serve as a core for the field coils to increase permeability.
a. General (Fig. 14-2). In use, the motor armature has many armature coils equally spaced around the entire circumference of the armature. Each of these coils carries current and consequently exerts a force to rotate the armature as it passes the pole pieces. The switching of the armature coils to the brushes is handled by a segmented commutation. The result is a comparatively high turning power (or torque) that is sufficient to crank the engine if it is applied through suitable gear reductions. b. Construction. A cutaway view of a typical automotive starter is shown in figure 14-3. The basic motor consists of the following parts.
(1) Armature. The armature contains multiple loops of heavy copper. These coils pass through a laminated core of iron to increase the permeability of the armature. The commutator segments are made of heavy copper bars that are set into mica or epoxy resins. The armature rotates on bronze bushings. (2) Field Coils. The field coils electromagnetically create the magnetic field that cause
c. Field Circuit Configurations. Field circuits will vary according to the application of the starter. The following are the most popular.
(1) Two Windings: Parallel (A, fig. 14-4). The wiring of two field coils in parallel will increase their field strength because they each receive full voltage. Note that two additional pole shoes are used. Though they have no windings, their presence will strengthen further the magnetic field. (2) Four Windings: Series-Parallel (B, Fig. 144). The wiring of four field coils in a series-parallel combination will create a much stronger magnetic field than the two field coil configuration described above. (3) Four Windings: Series (C, Fig. 14-4). The wiring of four field coils in series will provide a large amount of low-speed starting torque, which is a very necessary characteristic of an automotive starting motor. An undesirable characteristic of series-wound motors is that they will build up excessive speed if allowed to run free to the point where they will destroy themselves. (4) Six Windings: Series-Parallel (D, Fig. 14-4). Three pairs of series-wound field windings provide the magnetic field for a heavy-duty starter. This configuration uses six brushes. (5) Three Windings: Two Series, One Shunt (E, Fig . 14-4). The use of one field coil that is shunted to ground with a series-wound motor will control motor speed. The shunt coil, because it is not affected by speed, will draw a steady, heavy current, effectively limiting speed. 14-4. Starter Motor Drives.
a. General (Fig. 14-5). The starter may drive the engine through a pinion or by a dog clutch attached to the starter armature shaft. The shaft is brought together
TA233575 14-2
TM 9-8000
b. Gear Reduction Starters (Fig. 14-6). The gear reduction obtained through the flywheel gear with a single reduction is usually approximately 11:1 or 12:1 (sometimes it is as high as 16:1); that is, the speed of the starter armature is 11 or 12 times that of the flywheel. The pinion gear on the armature shaft meshes directly with the gear teeth on the flywheel. In some instances, however, a double reduction is used, in which case
c. Overrunning Clutch (Fig. 14-7). Power can be transmitted through the overrunning clutch in one direction only, which prevents the engine from driving the starter. The shell and sleeve assembly of the clutch is driven by the starter armature shaft. The inner portion, or rotor, is connected to the pinion, which meshes with the teeth on the engine flywheel. Steel rollers are located in wedge-shaped spaces between the rotor and the shell. Springs and plungers normally hold the rollers in position within the wedge spaces. When the starter armature shaft turns, the rollers are jammed between the wedge-shaped surfaces, causing both the inner and the outer members to rotate as a unit and
TA233576 14-3
TM 9-8000
TM 9-8000
d. Pedal Shift (Fig. 14-8). With this type of starting mechanism, the starter pinion is meshed when the driver presses the starter pedal. When the yoke lever is moved by the action of the driver in stepping on the starter pedal, the pinion gear is shifted into mesh with
e. Solenoid Shift (Fig. 14-9). Shifting the overrunning clutch pinion gear in mesh with the flywheel gear is made automatic on a good proportion of modern vehicles by the use of a solenoid.
TM 9-8000
f. Bendix Starter Drive (Flg. 14-10). The Bendix drive is a starting mechanism that seldom is used on modern vehicles. This automatic screw pinion shift mechanism is built in two distinct styles: the inboard type, in which the pinion shifts toward the starter to engage the flywheel, and the outboard type, in which the pinion shifts away from the starter. The same general construction is used in both types. A sleeve having screw threads (usually a triple thread), with stops at each end to limit the lengthwise travel of the pinion, is mounted on the extended armature shaft. The pinion gear, which is unbalanced by a weight on one side, has corresponding internal threads for mounting on this sleeve. The sleeve is connected to the starter armature shaft through a special drive spring attached to a collar pinned to the armature shaft.
TA233579 14-6
TM 9-8000
(a) It is simple in construction. (b) The mechanism is automatic in operation, requiring no action by the operator other than pressing the starter switch. (c) It gives high starting speed, because the starter is permitted to pick up speed before the load is applied. (d) The engine is given a high cranking torque immediately, thus requiring little cranking and minimizing the demand on the battery.
(3) Disadvantages. The chief disadvantages are listed below. (a) The quick impulse given to the pinion is likely to cause nicking or breaking of the teeth when TA233580 14-7
TM 9-8000 the pinion does not mesh properly on first contact with the flywheel teeth.
(b) Breakage or nonfunctioning of the pinion latch will cause the pinion to drift toward the flywheel teeth, which is likely to cause damage if the engine is running. (c) All of the starter torque is transmitted through the drive spring, which puts it under considerable strain.
Section II. CONTROL SYSTEMS 14-5. Key and Pushbutton Switch Control Circuits (Fig. 14-11). One method of controlling the solenoid shift is by a pushbutton on the instrument panel. Pushing the button closes the control circuit so that current can be supplied to the solenoid coil. Current practice, however, is to eliminate a separate pushbutton switch by incorporating a start position into the key switch. A relay frequently is used in the control circuit to supply current to the solenoid coils. Only a low-current control circuit to the instrument panel pushbutton Is then necessary. The relay will close the circuit through the solenoid coil, which carries a larger current. 14-6. Vacuum Lockout Switch Control Circuit (Fig. 14-12). The vacuum lockout switch is incorporated on some vehicles to prevent the starter from accidentally being engaged after the engine is running. The switch has a diaphragm that is actuated by manifold vacuum after the engine starts. The movement of the diaphragm opens the switch, disabling the starter solenoid circuit. 14-7. Generator Lockout Relay (Fig. 14-13). A generator lockout relay sometimes is used to prevent the starter from accidentally being engaged on a running engine. The relay is actuated by the stator terminal on the alternator to open the starter solenoid circuit as the engine runs and the alternator begins producing current. 14-8. Oil Pressure Lockout Circuit (Fig. 14-14). The oil pressure lockout circuit is used on some models to prevent accidental starter engagement to a running engine. As the engine starts, the lockout switch is turned on by the engine oil pressure. The lockout switch will, in turn, actuate a relay that opens the starter solenoid circuit.
TA233581 14-8
TM 9-8000
TM 9-8000
TM 9-8000
TM 9-8000 CHAPTER 15 IGNITION SYSTEMS Section I. BATTERY IGNITION SYSTEMS 15-1. Function. Ignition of the fuel-air mixture in the engine cylinder may be accomplished by either of two methods: heat of compression, as in diesel engines; or electric spark, as in gasoline engines. Spark ignition may be subdivided into two classes: battery and magneto. These two systems are essentially the same. With either, the fundamental job is to step up low voltage to a much higher value, and to deliver the high voltage to the spark plugs with the proper timing. The high voltage is capable of pushing current through the high resistance set up by the pressure in the combustion chamber and across from one spark plug electrode to the other. The hot spark created ignites the fuel-air mixture. This section pertains to battery ignition, its theory and operation. Paragraphs 15-9 thru 15-15 describe magneto ignition. 15-2. Operating Principles. (4) The effect of the countervoltage is to prevent an immediate magnetic buildup. That is, the countervoltage slows down the rate at which the current flow can increase and the magnetic field can expand and strengthen. The increase of the magnetic field produces the countervoltage; this countervoltage opposes further increases of current flow. However, the external voltage is stronger and therefore continues to increase the strength of the current until it reaches the value determined by the resistance of the circuit, including the electromagnet. (5) Actually, in most electromagnets, the countervoltage effect slows buildup time only a very small fraction of a second. But with electromagnets of many hundreds or thousands of turns, it does take time for buildup to occur. In the ignition system, if buildup time took too long, the high-voltage sparks would not be produced fast enough and high engine speed could not be attained. However, the ignition coil can function with adequate speed for normal ignition even at high speed. (6) Not only does the countervoltage appear during buildup, it also occurs during magnetic collapse. That is, when the electromagnet is disconnected from the voltage source so that mined by use of the left-handed rule, imagining the expanding lines of force from the first loop cutting across the second loop. Note that the lines of force cut across the second loop in a direction that will induce an opposing current. (3) It would be more correct to say that an opposing voltage is induced. The voltage must come first, then the current. That is, there first must be an electron concentration and an electron shortage in a circuit for current (or electrons) to flow. With this electron imbalance (or this voltage) in existence, there will be an electric current. The opposing or countervoltage that is self-induced by the expanding lines of force is opposite in direction to the voltage from the external source that is forcing current through the loops of the electromagnet.
a. Self-Induction(Fig. 15-1).
(1) The principle of electromagnetic induction has been described in paragraph 11-15. When a wire is moved through a magnetic field, or a magnetic field is moved past a wire, the wire will have current induced in it. The magnetic field can be moved past the wire mechanically, or it can be made to move (if it is from an electromagnet) by turning the current on and off. This action causes the magnetic field to build up and collapse. Any wire held in this magnetic field will have current induced in it. (2) The turns of wire in the electromagnet itself will have current induced in them by the moving magnetic field. For example, figure 15-1 shows two loops, or turns, of an electromagnet. When current first starts to flow, it enters the first loop and a magnetic field begins to build up along with the increase of current. The magnetic field consists of circular lines of force surrounding the wire, and the lines of force move outward and cut through the adjacent loops. These lines of force produce a current in the adjacent loops as they cut through. It is important to note that the induced currents oppose the original currents. This can be deter-
15-1
TM 9-8000
TA233585 15-2
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TA233586 15-3
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and collapse as the contacts are closed and opened is obvious. For example, when the contacts are closed, a magnetic field builds up. This magnetic field moves across the second (or secondary) winding when it builds up. This induces a voltage in the secondary winding so that a current flows through it and through the lamp. If the lamp is of the right size, it will light up momentarily because the magnetic field does not take long to build up. (2) When the contacts are opened, the magnetic field collapses and again moves across the secondary winding, inducing a voltage that causes the lamp to flash momentarily. (3) With a capacitor (fig. 15-2), the lamp would be brighter as the contacts opened. The reason for this is that the capacitor speeds up the magnetic collapse. The lines move faster across the secondary winding in collapsing because of the capacitor effect. Fastermoving lines mean a higher voltage and more current, which, in turn, means a brighter light. 15-3. Ignition System.
illustration are the means of opening and closing the contacts and the means of distributing the induced highvoltage surges from the secondary to the spark plugs in the various cylinders. An actual diagram of an ignition is shown in figure 15-3. Note the functions of the various components in the system.
b. Battery. The battery and generator furnish the source of voltage and current for the ignition system. The battery is required when first starting, but, after the vehicle starts moving, the generator takes up the ignition load. c. Ignition Switch (Fig. 15-4). The ignition switch enables the driver to turn the ignition on for starting and running the engine and to turn it off to stop the engine. Most modern configurations of ignition switches incorporate four positions that serve the following functions.
(1) Off. The off position shuts off the electrical system. Certain systems such as the headlights usually are not wired through the ignition switch and will continue to operate. (2) Accessory. The accessory position turns on the power to the entire vehicle electrical system with the exception of the ignition system.
a. General. Figure 15-3 shows most of the essentials of an ignition system. Not shown in the
TM 9-8000
TM 9-8000
f. Spark Plugs (Fig. 15-7). The spark plug consists of a porcelain insulator in which there is an insulated electrode supported by a metal shell with a grounded electrode. Several types of spark plugs have been used. They have the simple purpose of supplying a fixed gap in the cylinder
TM 9-8000
Figure 15-7. Typical Spark Plug Construction and Heat Range Descriptions
(3) Some spark plugs Incorporate an auxiliary (booster) gap In the top terminal. This gap allows the coil to build a higher voltage and reduce misfiring, especially when spark plugs are dirty or fouled. A booster gap spark plug is shown In figure 15-9.
g. Ballast Resistors (Fig. 15-10). A ballast resistor is used between the ignition switch and the points. It effectively will control primary Ignition voltage to prevent premature burning of the points. It contains a resistor element inside of a ceramic casing. The resistor element is made of a special material that increases
TM 9-8000
period. Full voltage would cause the points to burn. (2) At high engine speeds the points open and close quickly. The short duration of point closure tends to cool the ballast resistor. This causes a decrease in resistance, which, in turn, increases the voltage to the points. This is desirable because of the short coil saturation period at high speeds.
h. Secondary (Spark Plug) Cables (Fig. 15-11). The secondary ignition cables carry the high-voltage electric current to the spark plugs.
(1) An ignition cable in its simplest form consists of a solid or stranded conductor of steel or copper that is surrounded by a heavy insulation of neoprene, hypalon, or silicon rubber. The design of the insulating material is important because of the high-voltage electric current. A poorly designed insulating material will leak electric current through it, causing spark plug misfire. This is true particularly in damp weather or when the insulation is subjected to high engine compartment temperatures. (2) The secondary cable in its simplest form usually is inadequate for modern applications because the high voltage creates radio signals that interfere with TV and radio reception. The most common alternative is TVRS secondary cable. Rather than a conventional insulated wire, the TVRS cable is made of a fiberglass or linen stranding that is filled with carbon. The
TM 9-8000
insulation usually has a braided structure of rayon molded Into it to increase strength. TVRS cable has a very high resistance value that effectively eliminates radio interference, but is very susceptible to conductor breakage if not handled carefully. (3) An alternative to TVRS cable is shielded solid conductor cable. This type of cable is a solid conductor encased by a layer of insulation. The cable is then encased in a metallic shielding and an outer layer of insulation. This type of secondary cable, though very expensive, is very strong and widely used in military vehicles. 15 4.Multiple Contact Distributors.
connected in parallel but made to operate progressively. That is, they are so set with respect to the cam lobes that one arm opens its contacts slightly before the other. The circuit actually is not broken until the second set of contacts open. Both sets of contacts are open for a shorter period of time than they are in simultaneous operation. This allows the ignition coil a slightly longer period of time in which to buildup. The breakers are arranged for progressive parallel operation.
a. General. Distributors may have more than one set of contacts. Some distributors use two sets in parallel for longer contact closing and higher magnetic strength of the coil. Others may use two sets for alternate firing of cylinders. Still others have two sets for dual ignition or for operation of two semi-independent ignition systems. b. Parallel Operation (Fig. 15-12). To counteract the bounce, or chatter, of the breaker arm and to prevent overload of the contact points, two breakers can be connected in parallel and adjusted to open at the same time. If one pair of contacts has a tendency to bounce open at high speed, it is likely that the other pair will not bounce at exactly the same instant. Therefore, the circuit will be closed more positively than it would be with only one pair of contacts. The breaker arms also can be
c. Alternate Operation (Fig. 15-13). This is another arrangement that increases the time of contact and allows better magnetization of the coil. The two pairs of contacts still operate electrically in parallel, but use a cam with only half as many lobes as there are cylinders to be fired. The breakers are so arranged around the cam that one pair of contacts will close almost immediately after the other pair has opened. Thus, the two sets of breaker contacts almost overlap each others movements so there is no waste of time. Shortly after one pair of contacts opens the circuit, the other pair closes it, so the coil can start to build up at once in preparation for the next spark. One set of contacts operates for half the cylinders and the other set for the other half. d. Dual-Circuit Operation (Fig. 15-14).
(1) Another breaker arrangement, very similar in appearance to the one used for alternate operation, is used with two separate coils for firing a large number of
TM 9-8000
breaker contact points. Two-circuit operation particularly is adaptable to V-type engines, with each set of contacts taking care of one bank of cylinders. Because each set of breaker contacts is independent of the other electrically, the breakers require synchronizing for proper operation. On some V-type engines, the two breaker arms open at Irregular Intervals, and therefore the manufacturers specifications should be checked before any attempt is made to adjust the contact points.
e. Dual (Twin) Ignition (Fig. 15-15). Practically all automobiles have single Ignition (one spark plug in each cylinder), although dual ignition has been used to advantage. No particular new theory is Involved in producing and delivering current to the spark plugs In dual Ignition. The principal difference is the use of two sparks to fire the fuel charge at two separated points within the same cylinder. If two sparks are delivered at widely separated points at the same Instant, the fuel charge will start to burn from two points and meet in the center, thus securing more rapid and complete combustion. The firing of two spark plugs in each cylinder from one current source is sometimes called twin Ignition. The dual Is provided with two coils and two breaker arms operating on two circuits to supply sparks to two sets of spark plugs. To obtain the full advantage of dual ignition, the breaker contacts must be synchronized to fire two sparks simultaneously In each cylinder. The rotor segments then will deliver sparks to two opposite terminals In the distributor head, which are connected on two spark plugs within the same cylinder. Each rotor segment fires alternate terminals around the head; one segment firing the spark plugs on the right side of the cylinders and the other segment firing the spark plugs on the left side of the cylinders.
15-5. Transistorized Point Ignition (Fig. 15-16).
a. General. The transistorized point Ignition system operates much the same way as the conventional Ignition system. The difference Is the addition of a transistor to carry coil current. The purpose of this Ignition system is to lengthen the life of the contact points, which are traditionally the most troublesome component of the Ignition system.
TA233593
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Figure 15-14. Dual-Circuit Contact Points. b. Operation. The contact points handle the switching of the coil current (about 4 or 5 amperes) In the conventional ignition system. Despite the use of a condenser, there is a large amount of arcing that occurs between the points when they open and close. This arcing causes the points to burn and require regular replacement. By adding a transistor amplifier circuit to the Ignition system, operation will be as follows:
(1) The transistor will handle the switching of the coil current electronically. There is no degradation to electronic components when they operate, providing they are operating within their limits. (2) The contact points In the system handle the signal to the base of the transistor that Initiates the switching of coil current. Because the switching current is so low (about 0.5 ampere) very little arcing occurs at the points, greatly extending their life. (3) The points In a transistorized system have such a long life that the major concern with them is the TA233594 15-11
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a. General. The recent rise of electronic ignition systems is due to the superiority of electronic ignition over conventional ignition systems in several major areas. These systems totally remove one area of maintenance from the ignition system, that of the ignition (contact) points. Also, because the electronic ignition system produces a higher voltage than the conventional system, the electronic ignition system usually can fire a fouled spark plug. In the area of high performance, the electronic ignition system is far superior in that its voltage does not deteriorate as quickly at high engine speeds as the conventional ignition system. Because the electronic ignition system does not contain ignition points that wear, ignition performance does not deteriorate with mileage. b. Description. The electronic ignition system differs from that of a conventional ignition system in that it consists of a special pulse sending distributor, an electronic control unit, a two-element ballast resistor, and a special Ignition coil. Also, the ignition breaker points and capacitor used in the conventional ignition systems have been replaced by a gear like piece called a reluctor
c. Operation.
(1) The ignition primary circuit is connected from the battery, through the ignition switch, through the primary side of the ignition coil, to the control unit where it is grounded. The secondary circuit is the same as in the conventional ignition system. The magnetic pulse distributor also is connected to the control unit. (2) As the distributor shaft rotates, the distributor reluctor turns past the pickup unit, and each of the eight teeth (on an eight-cylinder engine) on the reluctor pass near the pickup unit once during each distributor revolution. As the reluctor teeth move close to the pickup unit, voltage is Induced into the pickup unit. That is, as a tooth on the reluctor passes the pickup coil, magnetic lines of force flow from the permanent magnet, through the pole piece, and through the reluctor back to the magnet. Voltage is induced in the windings as these magnetic lines of force pass
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can be made to handle higher voltages without harmful effects, whereas ignition points cannot. The quicker switching time of this system allows longer coil primary circuit buildup and longer induction time when the primary circuit collapses. This increased time allows the primary circuit to build up more current and the secondary circuit to discharge more current. The higher secondary current produces a hotter spark at the spark plug, which allows the engine to operate more efficiently. 15-7. Capacitive-Discharge Ignition (Fig. 15-18) . The capacitive-discharge system offers several advantages over the other systems. This system is similar to full transistor-magnetic control, except that certain components have been added to the primary circuit. These are the power converter, capacitor, and the resistor or silicon controlled rectifier (SCR). The power converter has an output voltage of 250 to 300 volts. This voltage is used to charge the capacitor with the the resistor In its off condition. When the the resistor gate (1) receives a signal from the pulse generator, the circuit from the anode (2) to the cathode (3) is closed, and the capacitor immediately discharges at a high rate through the primary. A high secondary voltage can be reached about 100 times faster with the capacitivedischarge system than with the inductive systems. This decreases spark plug fouling, materially Increasing potential spark plug life. Another advantage is that it uses less current than either the conventional system or the other solid-state systems. This means less demand on the battery during starts and a potentially longer
a. General. Spark advances are required so that the spark will occur in the combustion chamber at the proper time in the compression stroke. At high speed, the spark must appear earlier so the fuel-air mixture will have ample time to burn and give up its energy to the piston. At part throttle, when the fuel-air mixture is less highly compressed, a spark advance is required to ignite the slower-burning mixture in ample time for it to burn and deliver its power. Centrifugal and vacuum advance mechanisms produce these advances. b. Vacuum Control (Fig. 15-19). The vacuum advance mechanism makes use of a vacuum chamber connected to the intake manifold and a vacuum diaphragm linked to the breaker plate assembly. The breaker plate is supported so it can turn back and forth a few degrees. When there is a wide-open throttle and little or no vacuum in the intake manifold, a full measure of fuel-air mixture is entering the cylinders and no spark advance beyond the centrifugal advance is needed. But when the throttle is closed partially, part of the fuel-air mixture is throttled off and the mixture entering the cylinders is less highly compressed. For satisfactory combustion, the spark must be advanced further beyond the advance produced by the centrifugal mechanism. To secure this additional advance, the vacuum line
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c. Centrifugal Control (Fig. 15-20). The centrifugal advance mechanism is located in the distributor housing and consists essentially of a pair of weights mounted on pins on a weight base and linked by weight springs to the advance cam. When Idling, the springs hold the advance cam in a no-advance position. As speed increases, the centrifugal force on the weight causes them to move out. This action forces the toggles on the weights to move against the advance cam so the cam is pushed ahead against the spring tension. As the advance cam turns ahead, the breaker cam lobes open
15-16
d. Computerized Control (Fig. 15-21). The trend in modern automotive design is to use a computer to control ignition advance. Electronic ignition is very adaptable to computer control because the amplifier circuit can be integrated right into the computer module. With this arrangement the ignition timing is regulated within the module by electronically regulating the signal from the distributor pickup to the amplifier. This is the job of the computer. The computer establishes the proper ignition timing based on signals it receives from various sensors on the engine. The sensors provide information such as engine speed, throttle position, coolant temperature, ambient temperature, and manifold vacuum. The computer is able to change ignition timing many hundreds of times per second in contrast to mechanical devices that are slow to react to the engines needs. Because of this, a computer- controlled system of spark advance will allow the engine to be more responsive while running on leaner fuel mixtures. This will result in a cleaner running, more economical engine.
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a. Ignition of the fuel-air mixture in the combustion chamber of the gasoline engine requires an electric spark. The electric spark can be produced In two ways: by magneto Ignition or by battery Ignition. The magneto is a compact combination of generator, Ignition coil, and distributor. It requires no battery. Voltage is Induced
b. The problem In magneto Ignition is to generate a spark of sufficient voltage to Ignite the fuel-air mixture Instantly and to synchronize the spark with the engine cycle so that maximum power will be realized from the combustion. The fundamental units are listed below:
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(2) A transforming device to Increase the voltage of the electricity developed. (3) An Interrupting device to determine the proper timing of the electrical impulses. (4) A distributor to direct the electrical impulses In the proper order to the different cylinders. (5) A spark gap In each cylinder In the engine.
(6) The proper wiring and switches to bring these units together to form the Ignition system. c. The first four units are contained within the magneto. The spark plug supplies the fifth unit, wiring and switches make up the sixth unit. The same four fundamental units that make up the magneto also can be classified broadly as just two parts: a generator and a transformer. The generator provides a means of Inducing low voltage In a primary circuit. The transformer changes the low voltage of the primary circuit to the high voltage In a secondary circuit so that 15-19
d. The magneto ignition system generally is reliable, requires little maintenance, and does not have a battery to run down or wear out. Its principal disadvantage is that it turns so slowly during the cranking of the engine that a hot spark Is not produced. Therefore, a supplementary high-voltage source must be provided. This may be a booster magneto or a hightension coil to which primary current is supplied by a battery. In some magnetos, an Impulse starter is provided that produces high armature speeds at engine cranking speeds to provide a hot spark.
15-10. Source of Electrical Energy (Fig. 15-23). In studying the magneto, It should be understood that three things are necessary to Induce voltage: an electrical conductor, a magnetic field, and relative motion between the field and the conductor. In the magneto, a permanent magnet supplies the magnetic field, a wire coil is the conductor, and the engine TA233602
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a. Breaker Points. The interrupting device, which breaks the primary circuit when the high voltage spark is desired, is a set of breaker points. One end of the primary winding is connected to a ground; the other to the insulated breaker point. When the points are closed, the circuit is completed through them to a ground; when open, the circuit is broken. Lobes on a cam actuate the breaker points, Interrupting the primary circuit and timing the Induction of maximum voltage in the secondary circuit. The cam Is mounted on either the armature or rotating magnet. b. Capacitor. When the breaker points are opened, the current then flowing in the primary circuit tends to arc across the points due to self induction. This reduces the speed with which the circuit is broken and the magnetic field collapses. This action is controlled by inserting a capacitor In parallel with the breaker points. When the primary circuit is broken, the capacitor receives the surge of current and then, on discharging, reverses the normal flow of current. The capacitor thus hastens the collapse of the magnetic field around the primary winding and Increases the amount of voltage induced.
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15-13. Distributor.
a. The magneto distribution operates much the same as the battery ignition distributor (para 15-3). The distributor rotor, which directs the electrical impulses in proper order to the cylinders, usually is driven through suitable gearing, at one-half crankshaft speed. This ratio ensures that each cylinder will be fired during the cycles of the engine. The cam is much larger than those used in battery ignition distributors and contains the contact spring and cam electrode that, together, serve the same purpose as the rotor segment in a battery ignition distributor. That is, the cam electrode connects the hightension center electrode (connected to secondary of coil) to each of the outer distributor electrodes in turn. These outer electrodes are connected by high-tension leads to the spark plugs. b. One end of the secondary winding is connected to the primary. The other end terminates at the hightension insert, which is a piece of metal extending through the Bakelite case covering the coil. The hightension voltage developed in the secondary coil passes through the insert to a contactor such as the high-tension contact spring in the magneto cover. From there, it goes to the center electrode and then, internally, through the distributor rotor to the outer electrodes. The rotor is timed so that the cam electrode will line up with the center electrodes to which spark plug leads are connected, at the proper time for igniting the fuel-air charges in the cylinders. c. The spark plug assembly provides a gap where a surge of high voltage may cause a spark to ignite the fuel-air mixture. One spark plug electrode is connected to the high-tension cables from the distributor blocks; the other is fastened to a ground. Most air-cooled engines have two spark plugs for each cylinder and two separate magnetos for the ignition system. The second spark plug ensures better combustion and is added insurance against ignition failure. d. The high-tension wires that conduct the current from the distributor blocks to the spark plugs are commonly called the ignition harness. As a magneto ignition system transmits a form of high-frequency current, radiations emanating from it during operation will interfere with radio reception if the Ignition system is
15-21
not shielded. This shielding is a metal covering of woven construction that surrounds the wires. Plain metallic shields cover the distributor blocks and booster coil. The shielding is grounded to the engine so that it can pick up the undesirable radiations from the magneto and carry them directly to a ground. The radiations are thus prevented from reaching the vehicles radio aerial and interfering with reception. 15-14. Booster Coil. Magneto speed during cranking is not high enough to develop a hot spark. An external source of high-tension current for starting is provided, either by a booster magneto or by a high-tension coil, with the primary current being supplied by a battery. The coil method is most common. Current from the booster coil, which operates just like the coil in the battery ignition system, is conducted to the booster electrode of the magneto. This connects the booster coil with the magneto primary coil when the contacts open, thereby causing a current surge through the primary (from the booster coil), which produces a rapid change of magnetic field strength in the primary. This action Induces in the secondary a high-voltage surge sufficiently strong to fire the plugs. 15-15. Magneto Switches(Fig. 15-24).
a. Because the magneto is self-energizing, it cannot be turned off by disconnecting it from some external source of energy as in the battery ignition system. Instead, the magneto coil must be grounded. Because one end of the magneto coil is grounded already, grounding the other (or breaker point) end effectively will prevent the magneto from producing highvoltage surges. This is accomplished by means of a grounding switch on the vehicle instrument panel. When the switch is turned off, contacts in the switch are closed and the magneto coil is grounded through them. The magneto, booster, and main-engine starter switches all are located together in the same housing. The main magneto switch actually has four positions because, in the application shown, four magnetos are used (fig. 1524). The four positions are OFF (all magnetos grounded), A (two of the magnetos that fire the plugs in the accessory ends of cylinders are ungrounded and operative), F (the two magnetos that fire the plugs in the flywheel ends of the cylinders are ungrounded and operative), and BOTH (all four magnetos are operative).
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Figure 15-24. Magneto Control System. (Part A) b. The magneto switch is mounted in the same housing with the booster and the main-engine starter switch. This places the switches that must be operated for starting together. The starter switch, when operated, closes a relay that, in turn, brings the starter Into operation. At the same time that the starter switch is operated, the booster switch also must be operated.
This switch, just next to the starter switch, connects the booster coil to the circuit when closed. Both the starter switch and the booster switch are spring loaded and so placed that their levers must be brought down and pivoted toward each other for closing. Thus, both can be closed by the thumb and fingers of one hand. If the TA233604 15-22
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Section III. WATERPROOFING IGNITION SYSTEMS 15-16. General. Because many vehicles must operate under very wet conditions and must be able to ford fairly deep waters, it is necessary to waterproof the ignition system. The system must be so watertight that, even though the components are immersed, they can continue to function normally and will not suffer any damage. 15-17. Description (Fig. 15-25). The distributor and ignition coil are sealed in a common housing and enclosed by a common cover. This application also has a means of ventilating the distributor, thus preventing the condensation of water and the formation of harmful chemicals. Otherwise, such chemicals might form due to the arcing that takes place between the rotor segment 15-24 and the cap inserts at the outer high-tension terminals. The ventilation is accomplished by connecting two tubes to the distributor: one leading to the air cleaner (from which clean air can be obtained) and the other to the intake manifold. The intake manifold vacuum causes air to pass through the distributor from the air cleaner, thus keeping the distributor well ventilated. The various leads in the ignition system are enclosed in a watertight conduit. This conduit prevents moisture from getting to the leads with resultant insulation deterioration. The conduit also prevents shorting or grounding caused by presence of water.
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16-1. General (Fig. 16-1). The history of motor vehicle lighting parallels the history of the lighting of houses and buildings, with oil lamps and gas lamps having been used In the early motor vehicles. With the development of a satisfactory electrical system, electric lighting has become the standard means of lighting motor vehicles. The lighting system found on most modern motor vehicles consists of the following:
g. Wires and control switches to connect these lights and lamps to the current source.
16-2. Lamps.
a. Two headlights for Illuminating the road ahead of the vehicle. b. Two parking, or side, lights for Indicating the location of the vehicle when parked.
c. Taillights to light the rear license plate and to show a red light to the rear.
a. General Description (Fig. 16-2). Small gasfilled Incandescent lamps with tungsten filaments are used on motor vehicles. The filaments supply the light when sufficient current Is flowing through them. The lamps are designed to operate at low voltage, such as 6, 12, or 24 volts. b. Construction (Fig. 16-2). Most lamps are provided with a single contact for each filament within the lamp, the current through each filament being completed to the shell of the lamp base. A double filament lamp with the single-contact construction is shown in figure 162. Two contacts are provided on the lamp base, each being connected with one of the filaments. The return from both filaments is to the lamp base shell, which is grounded through the lamp socket. Thus, there are two separate circuits with two contacts on the base, each of which might properly be termed a single contact, for a grounded circuit. Because the volt-
d. Instrument Instruments.
panel
lights
to
Illuminate
the
e. Body lights, such as dome and step lights, to light the Interior of the vehicle. f. Special lights, such as spotlights, signal lights, blackout lights, and stop and backing lights.
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c. Size (Fig. 16-2). Lamps range in size from the small one-half candlepower instrument panel lamps to the large 50 or more candlepower driving lamps. d. Current Requirements. The 2-candle power lamp consumes 0.21 ampere at 12 volts. The 4candlepower lamp consumes 0.22 ampere at 12 volts. A lamp similar to the one shown in figure 16-5, having two filaments, one of 32 candlepower and the other of 21 candlepower, will draw 1.3 and 1.8 amperes. One reason for the rapid discharge of storage batteries in winter is the increased number of hours that lamps are used. There is a direct relation between the total current
16-2
a. Use of Reflector. A lamp bulb is mounted within a reflector so that the light can be gathered and directed In a confined beam. The best light beam from a lamp is obtained by the use of a parabolic or bowl-shaped reflector, which is the type In general use. There is a focal point near the rear of the parabolic reflector at which the light rays from the lamp are picked up by the polished surface of the reflector and directed In parallel lines to give a beam with a circular cross section. Any other position of the lamp will not give as limited a beam, but will tend to scatter the light.
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b. Use of Prismatic Lens. The light beam is distributed over the road by means of a prismatic lens. The effect of a prismatic lens fitted to a parabolic reflector is shown in figure 16-3. The lens bends the paralleled rays from the reflector so that the light is distributed over the road. The vertical flutes of the lens spread the light rays so that the beam is flattened, with the edges thrown out toward the side of the highway. c. Combinations of Beams. Many combinations of light beams are possible. One combination of headlight beams that has been used commonly is shown in figure 16-4. The beam from the right headlight is projected high to the right side of the road and low to the left side, and the beam from the left headlight is projected high to the left side and low to the right side. Portions of the beam are deflected lower than other portions because of the design of the lens. When the right and left beams are not the same, the lenses for right and left headlights are not interchangeable. These beams combine to give a nearly symmetrical beam for driving. With some headlights, the left light illuminates the right side of the road, while the right light illuminates the left side of the road. Both lights together give a symmetrical beam.
16-4. Headlights.
(1) A superior headlight that has been adopted is the sealed-beam headlamp unit. Not only does it provide far better and more powerful illumination than previous lamps, but it maintains its initial brilliancy with only a slight loss throughout its life. This is because the lens is permanently sealed to the reflector, barring moisture (which corrodes the reflector) and preventing, the entrance of dust and dirt. (2) When a filament burns out, the whole unit must be replaced. However, it has a greater filament life than other types of lamps and requires no maintenance to keep it in good condition. (3) The sealed-beam headlamp unit is made in two types: one with a silver-plated metal reflector and the other with an aluminum-surfaced glass reflector. The metal type contains a conventional double-filament lamp that is sealed in the unit mechanically, whereas the glass type is its own lamp because the lens and reflector are fused together, forming a gas tight unit with the filaments sealed into the reflector. (4) Two filaments are provided in the sealedbeam headlight lamp unit: one provides an upper beam for country driving, and the other gives a downward beam for passing or city driving. With the upper beam in use, current sealed-beam lamp units provide 50 percent more light than previous 32-candlepower lamps, and also distribute the light more effectively. The upper beam filament requires 40 to 45 watts, and the depressed beam filament requires 30 to 35 watts, which is more current than that required by the 32-candlepower lamps. Directing the headlight to the roadway is the only adjustment required on sealed-beam headlamps. (5) The sealed-beam headlamp is mounted with long self-locking screws and springs. The screws serve to aim the headlamps, depending on their position. 16-5. Road Illumination (Fig. 16-4). Modern development has brought about a radical change in what is considered good road illumination. The high-intensity beam of light has given way to the principle of more illumination and lower general intensity. The 32-
a. General(Fig. 16-5).
(1) In headlights of the older type, means are provided for focusing and directing the light. Focusing means bringing the filament of the lamp to the focal point of the reflector; aiming means pointing or directing the light properly. (2) Later developments brought into general use a 2-filament lamp having its position fixed with respect to its mounting socket at the rear of the reflector so that the filaments remain fixed at the proper focus (fig. 16-5). It is necessary only to direct the light to Improve the lighting of the roadway. (3) The most common headlamp configuration in modern automotive use is the sealed beam.
16-4
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a. Cause of Glare. Any light source is said to produce glare if it reduces the clarity of vision of anyone looking toward it. Practically speaking, the blinding or dazzling effect of light is not due to the brilliancy of the light but to the lack of illumination in the immediate vicinity through which the rays are projected. The headlight, for example, that produces glare on a dark road at night would not produce glare on a well-lighted street, and in the day tirne with the sun shining, it would hardly be noticed. If the strong light rays can be kept below the eye level, the nuisance of glare will be eliminated. b. Elimination. Many tests have been conducted by the Society of Automotive Engineers and by manufacturers to eliminate headlight glare as much as possible and still have enough light for safe driving. Two beams are specified to meet these requirements: Figure 16-6. Sealed-Beam Headlamp Construction.
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an upper beam to provide enough light in front of the vehicle while driving, and a depressed beam to avoid dangerous glare under normal conditions of passing. The driver is responsible for selecting the proper beam. The maximum and minimum intensity at important points of both beams are definitely specified and can be checked with the light intensity or foot- candle meter. 16-7. Headlamp Control Systems. Two headlamp controls usually are provided: one to turn them on and off, and the other to select between the upper and the depressed beams.
of the instrument lamps. The rheostat is controlled by turning the knob. (2) The current trend in the design of headlight switches integrate them with the turn signal switch (fig. 16-8). The switch usually is controlled by a knob at the end of the turn signal lever. The turning of the knob to the first on position turns on the tail, park, and instrument lamps. Moving it to the second position also will turn on the headlights. With this switch configuration, the intensity of the instrument lamps usually is controlled by a separate rheostat that is mounted on the Instrument panel. (3) Military vehicles that are used in tactical situations are equipped with a headlight switch that is integrated with the blackout lighting switch (fig. 16-9). An important feature of this switch is that it reduces the possibility of accidentally turning on the lights in a blackout. With the main switch off, no lights are on. It can be turned to the left, without operating the mechanical switch, to get blackout marker lights (including blackout taillights and stop lights), and black-
a. Control Switch. The control switch is usually a master-type switch controlling the head, tail, parking, and instrument lights.
(1) One type of headlight switch is a push pull type that mounts on the instrument panel (fig. 16-7). When the switch is pulled outward it will have two on positions. The first on position will turn on the tail and parking lights. Pulling the switch out to the second on position will turn on the headlights in addition to the lights turned on at the first on position. This type of switch also has a control rheostat built into it to control the intensity
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16-11). The operator selects the desired headlamp beam by moving the lever towards the front or rear. If this dimmer switch configuration is used with a headlamp switch that Is also Integrated in the turn signal lever, then the two switches and the turn signal switch usually are serviced as one unit. 16-8. Overload Breakers. Besides limiting the current by current regulation, the battery and wiring should be protected against excessive loads that might occur due to shorts or grounds in the wiring system. This protection may be secured by a current-limiting circuit breaker or a single fuse. The location of an overload breaker In the electrical system is shown in figure 16-12.
b. Dimmer Switch. The dimmer switch is used to control solely the selection of headlamp beams. The main consideration in locating the headlamp switch is the ease of finding it by the driver without diverting attention from vehicle operation.
(1) One of the most common locations for the dimmer switch is on the floor to the left of all of the control pedals (fig. 16-10). This switch configuration uses a single metallic button that alternately selects between headlamp beams each time it is depressed. (2) Currently, the most popular dimmer switch configuration is Integrated In then turn signal lever (fig.
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b. Fuse (Fig. 16-14). A common method of protection is to use a fuse In the lighting circuit.
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a. The blackout driving light (fig. 16-15) is designed to provide a white light of 25 to 50 candlepower at a distance of 10 feet directly in front of the lamp. The lamp is shielded so that the top of the light beam is directed not less than 2 degrees below the horizon. The beam distribution on a level road at 100 feet from the lamp is 30 feet wide on a properly designed light. b. The blackout stoplight, marker light (fig. 16-16), and taillight are designed to be visible at a horizontal distance of 800 feet and not visible beyond 1200 feet. The lights also must be invisible from the air above 400 feet with the vehicle on upgrades and downgrades of 20 percent. The horizontal beam cutoff for the lights is 60 degrees right and left of the beam centerline at 100 feet. c. The composite light (fig. 16-17) is currently the standard lighting unit that is used on the rear of tactical military vehicles. The composite light combines service stop, tail, and turn signals with blackout stop and tail lighting.
16-11. Controls and Lockouts. Blackout lighting control switches are designed to prevent the service lighting from being turned on accidentally. Their operation is described in paragraph 16-7a (3). 16-12. Infrared Lighting. Infrared (ir) lighting provides vision to troops at night, like blackout lighting. Unlike 16-11
a. Active System. The active system uses a light source combined with a red lens to emit light in the near ir range. The emitted light is reflected back from the illuminated object and focused in an image-converter tube. The tube converts an image formed in one wavelength of radiation into an image in a visible wavelength for viewing. The tube contains both the sensor and display in one unit. The ir lighting system employed on present
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b. Passive System. A passive ir system cannot be detected or disabled by methods that are effective against active systems. Furthermore, most natural objects radiate In the ir region, making a passive system very attractive. There are basically two types of passive ir systems: light intensification, and far-infrared.
(1) Light intensification systems are expected to eventually replace the present active ir systems for tank-automotive applications. In the light intensification system, images formed by the ambient light from starlight or moonlight are intensified by Image convertertype tubes. The Image converter tubes have a high detective photo-cathode sensitivity in the visible
Section III. COMMERCIAL VEHICLE LIGHTING 16-13. Turn Signal System. to be shut off automatically after the turn is completed by the action of the canceling cam.
a. General. Vehicles that operate on any public roads in the United States must be equipped with turn signals that indicate a left or right turn by providing a flashing light signal at the front and rear of the vehicle. b. Control Switch (Fig. 16-18). The turn signal switch is located on the steering column. It is designed
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TM 9-8000 switch. When the turn signal switch is turned off, it must pass stoplight current to the rear lamps. As a left or right turn signal is selected, the stoplight circuit is opened and the turn signal circuit is closed to the respective rear lamp. Also note that when this circuit is used, the front and instrument lamps must be on a separate switch circuit.
d. Flasher Unit (Fig. 16-20). The turn signal flasher unit creates the flashing of the turn signal lamps. It consists basically of a bimetallic strip (two dissimilar metals bonded together) wrapped in a wire coil. The bimetallic strip serves as one of the contact points.
(1) When the turn signals are actuated, current flows into the flasher, first through the heating coil to the bimetallic strip, then through the contact points and out of the flasher, where the circuit will be completed through the turn signal lamps. (2) The current flowing through the heating coil will heat the bimetallic strip, causing its dissimilar metals to expand at different rates. This
Figure 16-18. Typical Turn Signal Switch (2) A common design for a turn signal system is to use the same rear lamps for both the stop and turn signals. This complicates the design of the switch somewhat. Note that the stoplight circuit must pass through the turn signal
a. General. The backup lamp system provides a warning to pedestrians and visibility to the rear whenever the vehicle is shifted to reverse. A typical backup light system is shown in figure 16-21. b. Switch Configurations. The most common backup light switch configurations are:
(1) The backup light switch may be mounted on the transmission and operated by the shift linkage. (2) The backup light switch may be mounted on the steering column and operated by the gearshift linkage. (3) The transmission or gearshift mounted backup light switch on many automatic transmissionequipped vehicles is combined with the neutral safety switch.
a. General. All vehicles that are used on public highways must be equipped with a stoplight system. The stoplight system consists of one or two red lamps on the rear of the vehicle that light up whenever the brake is applied. Typical stoplight wiring circuits are shown in figure 16-22. It should be noted that some stoplight circuits are integrated in the turn signal circuit. These circuits are described in paragraph 16-13. b. Stoplight Switch Configurations (Fig. 16-23). Some models have stoplight switches that are actuated mechanically by the brake
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c. Parking Lights.
(1) The smaller lights used for parking sometimes are located immediately above or below the main headlights. (2) Side lights sometimes serve as parking lights, in which case, a separate housing is used. (3) A smaller lamp, located within the main headlight and above the main headlight lamp, frequently has been used to provide a parking light. A 4- or 6candlepower lamp, or smaller, is used for a parking light.
a. Instrument Lights. Ordinarily, indirect lighting is used for the instrument lamps, which light whenever the lighting switch is in any of the ON positions. Many cars are equipped with an instrument panel lamp switch so that the instrument panel lamps can be turned off when desired. b. Dome Lights. Practically all closed motor vehicles make use of dome or tonneau lights. These ordinarily are controlled by means of a switch on the body post near each door.
17-1. Purpose (Fig. 17-1). The instrument panel usually is placed so that the Instruments may be read easily by the driver. They inform the driver of the approximate speed, engine temperature, oil pressure, rate of charge or discharge of the battery, amount of fuel in the fuel tank, distance traveled, and the time. Certain controls frequently are mounted on the Instrument board, such as the throttle, choke, starter, heater, and windshield wiper. 17-2. Battery Condition Gages. One of the Instruments that almost always Is included on an Instrument panel is a battery condition gage. It is a very Important indicator because, if interpreted properly, it can be used to troubleshoot or prevent breakdowns. The following are the three basic configurations of battery condition gages.
a magnetic effect that deflects the ammeter needle in proportion to the amount of current. This coil is matched to the maximum current output of the generator and this varies with different applications. Some model wheeled vehicles have replaced the ammeter with a battery generator indicator that does not give a calibrated reading, but shows ranges by colors or bands.
a. Ammeter (Fig. 17-2). The ammeter is used to indicate the amount of current flowing to and from the battery. It does not give an indication of total generator output because other units in the electrical system, besides the battery, are sup- plied by the generator. If it shows a 10-ampere discharge, it indicates that a 100 ampere-hour battery would be discharged in 10 hours; that is, 10 amperes flowing for 10 hours. Current flowing from the storage battery to the starting motor is never sent through the ammeter, because the great quantities used (200 to 600 amperes) cannot be measured on an instrument of such limited capacity. In the typical ammeter, all the current flowing to and from the battery, except for starting, actually is sent through a coil to produce
b. Voltmeter (Fig. 17-3). Voltmeters are gaining popularity as an Instrument panel battery condition Indicator. This is because the electrical system voltage is a more accurate indication of the condition of the electrical system than the amperage and is easier to interpret by the operator. During vehicle operation, the voltage indicated on the voltmeter is considered to be normal in a range of 13.2 to 14.5 volts for a 12-volt electrical system. As long as the system voltage remains in this range, the operator can assume that no problem exists. This contrasts with an ammeter, which gives the operator no Indication of problems such as an improperly calibrated voltage regulator, which could allow the battery to be drained by regulating system voltage to a level that is below normal. c. Indicator Lamp. The indicator lamp has gained increasing popularity as an electrical system condition gage over the years. Although it does not provide as detailed an analysis of electrical system condition as a gage, it usually is considered more useful to the average vehicle operator. This Is because it is highly visible when a malfunction occurs, whereas a gage usually Is
TM 9-8000 directly from the alternator stator through the stator terminal. When the ignition switch is closed, before the engine is started, current flows through the resistor and the indicator lamp to the alternator field, causing the indicator lamp to light. After the engine is started, the alternator begins to produce current, energizing the field relay coil from the stator. The relay coil pulls the relay points closed, shunting the alternator field directly to the battery. This results in a zero potential across the indicator lamp, causing it to go out. 17-3. Fuel Gages. Most fuel gages are operated electrically and are composed of two units: the gage, mounted on the instrument panel; and the sending unit, mounted on the fuel tank. The ignition switch is included in the fuel gage circuit so that the electrical fuel gage operates only when the ignition switch is on. Operation of the electrical gage depends on either coil action or thermostatic action.
Figure 17-2. Ammeter Operation ignored because the average vehicle operator does not know how to Interpret its readings. The Indicator lamp can be utilized in two different ways to indicate an electrical system malfunction. (1) Low-Voltage Warning (Fig. 17-4). The indicator lamp can be set up to warn the operator whenever the electrical system voltage has dropped below the normal operational range. The lamp is operated by a calibrated relay that opens the circuit to it whenever electrical system voltage is in the normal range (13.2 to 14.5 volts for a 12-volt system). Whenever the voltage falls below the normal range, the magnetic field becomes insufficient to overcome the force of the relay spring, which pulls the contact points closed. This closes the circuit to the indicator lamp. (2) No-Charge Indicator (Fig. 17-5). The indicator lamp also can be set up to indicate whenever the alternator is not producing current. The circuitry that operates a no-charge indicator lamp usually is incorporated in the voltage regulator. The voltage regulator that is used on a vehicle equipped with a nocharge indicator lamp contains a second element called a field relay. The field relay has two contact points. One contact point is connected to battery voltage through the ignition switch. The other point also is connected the same way, except for the inclusion of a series-parallel arrangement of the no- charge indicator light and a resistor. The resistor value Is matched with the resistance of the indicator lamp so that their parallel arrangement will produce a zero-voltage drop. When the field relay Is open, alternator field current is supplied through the resistor-indicator light combination. The magnetic coil of the field relay is energized
a. Thermostatic Fuel Gage: Self-Regulating (Fig. 176). This gage configuration consists of an instrument panel gage and an electromechanical sending unit that is located inside of the fuel tank. The instrument panel gage contains an electrically heated bimetallic strip that is linked to a pointer. A bimetallic strip consists of two dissimilar metals that, when heated, expand at different rates, causing it to deflect or bend. In the case of the instrument panel fuel gage, the deflection of the bimetallic strip will result in the movement of the pointer, causing the gage to give
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a reading. The sending unit consists of a hinged arm with a float on the end of it. The movement of the arm controls a grounded point that makes contact with another point that is attached to an electrically heated bimetallic strip. The heating coils in the tank unit and the gage are connected to each other in series. Operation is as follows. (1) When the fuel tank is empty, the float lays on the bottom. In this position, the arm- operated cam exerts no pressure on the grounded contact. When the Ignition is switched on, current flows from the ground, through the heating coil in the sending unit, through the heating coil in the instrument panel gage, and to the battery. The heating of the bimetallic strip in the sending unit causes it to deflect, opening the contact points. The opening of the points will allow the bimetallic strip to cool and return to its original position, again closing the points. The cycle of opening and closing the points will continue, supplying current pulses to the heating element in the fuel gage. The length of the pulses from the sending unit when the tank is empty will only heat the gage bimetallic strip enough to cause deflection that will move the pointer to the empty position on the gage face.
(2) When the fuel tank contains fuel, the float will raise the arm, causing the cam to push the grounded contact tighter against the bimetallic strip contact. This will cause an increase in the amount of heat required to open the contact points in the sending unit. The result will be longer current pulses to the instrument panel gage, causing higher gage readings. The gage reading will increase proportionally with the float level in the fuel tank. (3) The tank unit will compensate for variations in electrical system voltage automatically. High voltage will increase heating, causing the points to cycle faster and if the voltage is lower, heating will decrease, causing slower point cycling. (4) Because the gage pointer is moved by the heating and cooling of the bimetallic strip, the gage reading will not react to sudden fuel level changes caused by fuel sloshing. This will prevent erratic operation. b. Thermostatic Fuel Gage: Externally Regulated (Fig. 17-7). The externally regulated thermostatic fuel gage uses an Instrument panel
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gage whose operation is the same as the gage used with the self-regulating system described ir paragraph 17-3a. The differences in the system are the use of a variable resistance fuel tank sending unit and an external voltagelimiting device. The sending unit controls the gage through the use of a rheostat. A rheostat is a wire wound resistance unit whose value varies with it effective length. The effective length of the rheostat is controlled in the sending unit by sliding brush that is operated by the float arm. The power supply to the gage is kept constant through the use of a voltage limiter. The voltage limiter consists of a set of contact points that arc controlled by an electrically heated bimetallic arm. (1) When the fuel tank is empty, the float lays on the bottom. The float arm will position the contact brush so that the full length of the rheostat resistor will be utilized. The resulting high resistance will drop voltage to the gage sufficiently so that the pointer will rise only to empty. (2) As the fuel level rises in the tank, the float will raise the float arm, which, in turn, will move the contact brush on the rheostat resistor. As the float arm moves upward, the resistance will decrease proportionally, resulting in a proportional voltage increase to the gage. The gage readings will increase proportionally, resulting in accurate readings of the fuel level in the tank. (3) The voltage limiter effectively will en- sure a constant supply of current regulated to the equivalent of 5 volts, to provide accurate gage readings regardless of electrical system voltage variations.
c. Thermostatic Fuel Gage: Differential Type (Fig. 17-8). The differential-type fuel gage system uses an instrument panel gage whose operating principles are much the same as the thermostatic gage described In paragraph 17-3a. The differential-type thermostatic gage, however, uses two electrically heated bimetallic strips that share equally in operating and support- ing the gage pointer. The pointer position is obtained by dividing the available voltage between the two strips (differential). The tank unit is a rheostat type whose operating principles are much the same as the tank unit described in paragraph 17-3b. The tank unit in this system, however, contains a wire-wound resistor that is connected between two external terminals. Each one of the external terminals connects to one of the instrument panel gage bimetallic strips. The float arm moves a grounded brush that raises resistance progressively to one terminal, while lowering the resistance to the other. This causes the voltage division and resulting heat differential to the gage strips that formulate the gage readings. Two additional bimetallic strips are provid- ed for temperature compensation. In addition, one of these blades operates contact points to limit voltage to approximately 5 volts. (1) When the tank is half full, the float arm positions the contact brush midway of the rheostat. This causes equal resistance values to each sending unit circuit, resulting in equal heating of the gage bimetallic strips, causing the gage to read one-half. (2) Fuel levels above or below half will cause the tank unit to divide the voltage to the gage bimetallic strips in the correct proportions to
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create correct gage readings. An example would be a one-quarter full fuel tank. At this level, the tank unit would divide the voltage so that 75 percent of the current would flow through the right-side strip and 25 percent would flow through the left-side strip. This would produce a one- quarter gage reading.
poles on the gage pointer will be positioned midway between the coils. When the armature is in this position, the pointer will indicate a full reading. (3) Variations in electrical system voltage will affect both magnetic coils equally and, therefore, will not upset the differential created between them. Because of this, the magnetic gage is self-regulating and requires no voltage- limiting devices. (4) The magnetic gage is very sensitive to road shock and sudden changes in voltage such as those caused by the fuel sloshing in the tank. Because of this, the armature of the instrument panel gage will be fitted with a damping device or a flywheel. 17-4. Pressure Gages.
d. Magnetic Fuel Gage (Fig. 17-9). The basic instrument panel gage consists of a pointer that is mounted on an armature. Depending on the gage design, the armature may contain either one or two poles. The gage is motivated by a magnetic field that is created by two separate magnetic coils that are contained within the gage. One of these coils is connected directly to the battery, producing a constant magnetic field. The other coil produces a variable field whose strength is determined by a rheostat-type tank unit whose operation is the same as the one described in paragraph 17-3b. The coils usually are placed 90 degrees apart.
(1) When the tank is empty, the tank unit creates a very high resistance. This causes the variable magnetic coil to produce almost no magnetic field. Therefore the armature poles on the gage pointer will be attracted to the constant magnetic coil. The pointer will point to empty when the armature is in this position. (2) When the tank is full, the tank unit will create resistance. Therefore, the armature
a. Usage. Pressure gages are used widely in automotive applications to keep track of things such as engine oil pressure, fuel line pressure, air brake system pressure, and the pressures of the hydraulic systems in special purpose vehicles. Depending on the equipment, a mechanical or an electric pressure gage may be utilized. b. Electric Gage (Fig. 17-10). The instrument panel gage may be of the thermostatic type described in paragraph 17-3a, or of the magnetic type described in paragraph 17-3d. The sending
no
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unit that Is used with each gage type varies as follows: (1) The sending unit that Is used with the thermostatic gage utilizes a flexible diaphragm that moves a grounded contact. The contact that mates with the grounded contact Is attached to a heated bimetallic strip. The flexing of the diaphragm, which Is done with pressure changes, varies the point tension. The different positions of the diaphragm produce gage readings In the same manner as the different positions of the float arm of the tank sender In paragraph 17-3a. (2) The sending unit that Is used with the magnetic-type gage also translates pressure Into the flexing of a diaphragm. In the case of the magnetic gage sending unit however, the diaphragm operates a rheostat. The flexing of the diaphragm In the pressure sender produces the same results as does the movement of the float arm In the tank sender described In paragraph 17-3d. This type of sender also can be used with a thermostatic-type gage If a voltage-limiting de- vice like the one used In paragraph 17-3b also Is used.
tube, it will tend to straighten out. As it straightens, the attached gage pointer will move, giving a reading
d. Indicator Lamp (Fig. 17-12). The oil pressure warning light Is used In place of a gage on many vehicles. The warning light, although not an accurate indicator, Is valuable because of Its high visibility in the event of a low oil pressure condition. Because an engine can fail or be damaged permanently in less than a minute of operation without oil pressure, the warning light often Is used as a backup for a gage to attract Instant attention to a malfunction. The warning light receives battery power through the ignition switch. The circuit to ground is completed through the engine sender switch. The sender switch consists of a pressure-sensitive diaphragm that operates a set of contact points. The contact points are calibrated to turn on the warning light whenever the engine oil pressure drops below approximately 15 psi (103.4 kPa), depending on the equipment.
17-5. Temperature Gages(Fig. 17-13).
c. Mechanical Gages (Flg. 17-11). The mechanical pressure gage uses a thin tube to carry an actual pressure sample directly to the gage. The gage basically consists of a hollow, flexible C-shaped tube called a bourden tube. As fluid or air pressure Is applied to the bourden
17-8
a. Usage. The temperature gage Is a very Important indicator In automotive equipment. The most common use Is to Indicate engine, transmission, and differential oil temperatures and engine coolant temperatures. Depending on the type of equipment, the gage may be electric or mechanical. TA233627
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b. Electric Gage (Fig. 17-13). The instrument panel gage may be the thermostatic-type described in paragraph 17-3a, or the magnetic type described in paragraph 17-3d. The sending unit that is used with each gage type varies as follows:
(1) The sending unit that is used with the thermostatic gage usually contains two bimetallic strips, each of which has a contact point. One bimetallic strip is heated electrically. The other bimetallic strip bends to increase the tension of the contact points. The different positions of the bimetallic strip will create gage readings in the same manner that the different float arm positions of the tank sender will in paragraph 17-3a. (2) The sending unit that is used with the magnetic gage contains a device called a thermistor. A thermistor is an electronic device whose resistance decreases proportionally as its temperature increases. This type of sending unit also can be used with a thermostatic gage if a voltage-limiting device like the one described in paragraph 17-3b also is used.
operated by the bending of a bimetallic strip that is calibrated to turn on the warning light at approximately 2300F (1100C). Some models also utilize a cold indication light that will indicate to the driver that the engine has not yet reached operating temperature. The light usually is green in color, whereas the hot indication is red. The sending unit for this application has an extra terminal. Internally, the sender has an extra contact. The bimetallic strip simply completes the circuit to the cold light until engine temperature reaches approximately 1500F (65.60C). The strip then will open the cold light circuit. As long as the temperature of the engine Is normal, the bimetal- lic strip will remain between the contacts for the cold and hot indicator lights. 17-6. Speedometers and Tachometers.
c. Mechanical Gage (Fig. 17-14). The gage unit contains a bourdon tube and operates by the same principles as the mechanical oil pressure gage described in paragraph 17-4c. The motivating force of the mechanical temperature gage is a permanently attached capillary tube that connects the gage to a bulb fitted in the engine water jacket. The bulb contains a liquid such as ether, whose vapor pressure is proportional to its temperature. As the temperature increases, the ether boils and expands. The vapor pressure acts on the gage through the capillary tube to produce temperature readings. d. Indicator Lights (Fig. 17-15). The tem- perature warning light is used on many vehicles in place of a gage. The indicator light, although not as detailed as a gage, Is valuable because of its high visibility in the event of an overheat condition. Because an engine can become damaged permanently or destroyed by operating for short periods while overheated, warning lights often are used as a backup for temperature gages to attract Instant attention to a malfunction. The warning light receives battery power through the ignition switch. The circuit to ground is completed through the engine sender switch. The sender switch contains a set of contact points that are
a. Usage. Speedometers and tachometers are used in virtually all types of automotive equipment. Speedometers are used to indicate vehicle speed in miles per hour or kilometers per hour. The speedometer in most cases also contains an odometer. An odometer is a device that keeps a permanent record of the amount of mileage that a vehicle has been used. Some speedometers also contain a trip odometer that can be reset to zero at anytime so that individual trips can be measured. The odometer is calibrated to measure distance In miles or kilometers, depending on the application. A tachometer is a device that is used to measure engine speed in revolutions per minute (rpm). The tachometer also may contain a device known as an engine-hours gage. The engine- hours gage usually is Installed on equipment that uses no odometer to keep a record of engine use. b. Mechanical Speedometers and Odometers. The speedometer and odometer (fig. 17-16) usually are combined into a single unit that is driven by a flexible shaft.
(1) The flexible shaft consists of a flexible outer casing that is made of steel or plastic and an inner drive core that is made of wire-wound spring steel. Both ends of the core are molded square so that they can fit into the driving member at one end and the driven member at the other end and be able to transmit torque. (2) The flexible shaft, better known as a speedometer cable, usually is driven by gears from the transmission output shaft. When the
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TM 9-8000 gears are selected to drive the speedometer, it is Important that the drive axle gear ratio and the diameter of the tires on the drive wheels be taken Into consideration so that the speedometer will be driven at the proper speed. (3) The speedometer (fig. 17-17) consists of a permanent magnet that is rotated by the speedometer cable. Surrounding the rotating magnet is a metal cup that Is attached to the speedometer Indicating needle. The revolving magnetic field exerts a pull on the cup, causing it to tend to rotate. The rotation of the cup Is countered by a calibrated hairspring. The influence of the hair spring and rotating magnetic field on the cup produce accurate speed readings by the needle that is attached to the cup. (4) The odometer (fig. 17-18) is driven by a series of gears that originate at a spiral gear on the Input shaft. The odometer consists of a series of drums with digits printed on their outer circumference that range from zero to nine. The drums are geared to each other so that each time the one furthest to the right makes one revolution, it will cause the one to its immediate left to advance one digit. The second to the right then will advance the drum to its immediate left one digit for every revolution that it makes. This sequence continues to the left through the entire series of drums. The odometer usually contains six digits to record 99,999.9 miles or kilometers. Models with trip odometers usually do not record tenths on the total odometer and therefore will contain five digits. When the odometer reaches its highest value, it will reset to zero automatically. Most new automobiles incorporate a small dye pad in the odometer to color the drum of its highest digit to indicate that total vehicle mileage is in excess of the odometers capability. (5) The trip odometer also is driven by a series of gears from the input shaft. It usually contains four digits to record 999.9 miles or kilometers before resetting itself to zero. The trip odometer is connected to an external knob and can be reset to zero by the vehicle operator.
c. Mechanical Tachometers and Engine Hours mechanical tachometer Gage (Fig. 17-19). A operates exactly the same as the mechanical speedometer described in paragraph 17-6b. The main difference is that it is driven by the engine and is calibrated to measure engine speed. The engine-hours gage is incorporated in the tachometer in most cases. Its purpose is to keep a record of operating time. It measures in hours to the nearest tenth. d. Electric Speedometer and Tachometer (Fig. 1720). The electric speedometer or tachometer utilizes a mechanically driven permanent magnet generator to supply power to a small electric motor. The electric motor then is used to rotate the input shaft of a mechanical speedometer or tachometer whose operation is the same as the one described in paragraph 17-6b. The voltage from the generator will increase proportionally with speed and the motor speed will likewise Increase proportionally with voltage, enabling the gages to indicate speed. The signal generator for the speedometer usually is driven by the transmission output shaft through gears. The signal generator for the tachometer usually is driven by the distributor through a power takeoff on gasoline engines. When the tachometer is used with a diesel engine, a special power takeoff provision is made, usually on the camshaft drive. e. Electronic Speedometers and Tachometers. Electronic speedometers and tachometers are selfcontained units that use an electric signal from the engine or transmission as an indicator to formulate a reading. They differ from the electric units described in paragraph 17-6d that use the generated signal as the driving force. TA233631
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The gage unit usually Is transistorized and will supply information through either a magnetic analog (dial) or a light emitting diode (LED) digital gage display. The gage unit derives its Input signal in the following ways: (1) An electronic tachometer can obtain a pulse signal from the. ignition distributor that switches the coil on and off. This Is the most popular signal source for a tachometer that is used on a gasoline engine. The pulse speed at this point will change proportionally with engine speed. (2) A tachometer that is used with a diesel engine can use the alternating current generated at the stator terminal of the ac generator as a signal. The frequency of the ac current will change proportionally with engine speed. (3) An electronic speedometer derives its signal from a magnetic pickup coil that has its field Interrupted by a rotating pole piece. The signal
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TM 9-8000 (45.05 km/h), and then stopped and idled for E minutes. The vehicle then was moved out again accelerated to approximately 45 mph (72., km/h) and did stop-and-go driving for about 3: minutes, accelerating from 0 to 45 mph (72., km/h) three times and traveling about 15 miles (24.13 km). At 8:11 am it stopped, after having traveled approximately 15 miles (24.13 km). I idled for about 48 minutes and then was shut down at 9 am. 17-8. Vacuum Gage (Fig. 17-22). A vacuum gage measures the difference in pressure between the Intake manifold and the atmosphere in Inches of mercury (InHg). The unit of measure Is derived from applying a vacuum to the top end of a 17-16 tube whose bottom end is dipped in mercury. The reading then is obtained by measuring how far in inches the mercury rises In the tube. A vacuum gage Is very useful for:
a. Engine Diagnosis. A vacuum gage can locate things such as valve malfunctions, manifold vacuum leaks, or improperly adjusted ignition timing. b. Driving for Maximum Efficiency. Because intake manifold vacuum decreases proportionally with engine load increases, the vacuum gage can be used as a driving aid to attain maximum fuel economy and engine life.
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17-9. Principles of Operation (Fig. 17-23). The most common type of horn is the vibrator type, in which the general principle of operation is the same as that of a vibrating coil. A vibrating diaphragm is operated by the coil that also operates the contacts that break the circuit. Magnetism from the coil pulls the diaphragm toward it when the contacts are closed. The contacts then are pulled open by the coil, reducing the magnetism and allowing the diaphragm to return to its normal position. When the contacts are closed again, a new surge of current induces magnetism in the coil and starts a second movement of the diaphragm. This cycle is repeat- ed rapidly. The vibrations of the diaphragm within an air column produce the note of the horn. Tone and volume adjustments are made by loosening the adjusting locknut and turning the adjusting nut. This very sensitive adjustment controls the current consumed by the horn. Increasing the current increases the volume. However, too much current will make the horn sputter and may lock the diaphragm. 17-10. Dual Horns. In dual horns, one horn with a low pitch is blended with another horn with a high pitch. These horns, although operated electrically, produce a sound closely resembling that of
an air horn. The sound frequency of the low-pitch horn is controlled by a long air column and the high-pitch horn sound frequency is controlled by a short air column. The air column is formed by the projector and a spiral passage cast into the base of the horn. 17-11. Controls (Fig. 17-24). The current draw of a horn is very high, therefore, usually it is operated by a relay. The control switch usually is mounted on the steering wheel and may be controlled by a button or a horn ring.
a. The horn receives electric current through the ignition switch and the relay contact points. The relay contact points normally are open, keeping the horn from operating. b. The relay contact points are closed when- ever the magnetic coil is energized. The magnetic coil receives positive battery current from the ignition switch. The horn switch completes the circuit to ground.
17-12. Air Horns (Fig. 17-25). The air horn is a trumpet like device that operates from compressed air. Air horns usually are used on vehicles that are equipped with airbrakes because they can operate from the vehicles compressed
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TM 9-8000 air system. Air horns also may have their own compressed air system. The air horn is controlled by an air valve. 17-13. Backup Alarms. Large vehicles some- times utilize an air or electric horn at the rear that Section III. WINDSHIELD WIPES 17-14. Vacuum Wipers. Vacuum-operated windshield wipers utilize the negative pressure that Is present in the engines intake manifold as a vacuum source to operate the windshield wiper motor. Because the pressure in the intake manifold varies with engine loading, the speed of the wipers varies greatly with engine loading to the extent that the windshield wipers actually will stop when the engine is loaded heavily, such as when the vehicle Is climbing a hill. Some vehicles utilize an auxiliary vacuum pump to help alleviate this problem. This pump usually is built into the engines fuel pump (para 4-3). The windshield wiper motor transmits its power to the transmission linkage in the form of reciprocating motion. The transmission for a vacuum system utilizes a pulley and cable system to link the motor to the windshield wiper arms and blades. Because of the erratic operation of the vacuum wiper system, it has been replaced almost completely by the electric wiper system in modern automotive applications. 17-15. Electric Wipers (Fig. 17-26). Electric windshield wipers are the most popular type for use on modern automotive equipment. Electric windshield wipers operate at a constant, easily controlled speed, making them much more desirable than their vacuum counterparts. One of the drawbacks to using electric windshield wipers in early automotive equipment was the heavy electric current requirements that their motor is actuated when the transmission is shifted to reverse. The purpose of this is to warn pedestrians when the vehicle is backing up.
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placed on the vehicles 6-volt electrical system. This problem was solved as 12-volt electrical systems became standard. The electric wiper motor, through a worm gear, drives a shaft that is connected to a crank. The circular motion of this crank is transformed into reciprocating motion by the wiper transmission to operate the wiper arms. In addition to the control switch that is used to control the windshield wipers, a separate, mech- anically operated park switch also is Incorporated into the motor. The purpose of this switch is to provide power to the wiper motor long enough to return the wiper arms and blades to a retracted position whenever they are switched off by the operator. 17-16.Air-Operated Wipers. Air-operated
windshield wipers are used almost exclusively on heavy vehicles that are equipped with a compressed air supply system to operate the wiper motor. Air-operated wiper motors directly produce the reciprocating motion that is required to operate the wiper arms. Because of this, they often are mounted In a position that allows a wiper arm to be connected directly to them. 17-17. Wiper Arm and Blade (Fig. 17-27). The wiper arm fits onto a splined shaft on the wiper transmission and is spring loaded to press the blade against the windshield. The blade is a flexible rubber squeeze-type device. It is spring steel backed and is suspended from the arm by a mechanism that is designed to maintain total contact with the windshield throughout the stroke.
Section IV. ACCESSORIES 17-18. Auxiliary Power Receptacle (Fig. 17-28). The auxiliary power receptacle usually is installed at the rightrear corner of the cab body, near the vehicle batteries. The receptacle has two insulated prongs, each connected by cable to one battery terminal. This means that the receptacle is wired in parallel with the battery. It is used to facilitate charging of the batteries from an external source or the connecting of additional electrical power from an external source to operate electrical components on the vehicle. The receptacle greatly simplifies these proceTA233638
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TM 9-8000 b. Heater Core (Fig. 17-30). The heater core is a component that transfers heat from the engine coolant to the passenger compartment. Its construction is similar to a radiator (para 9-6), except that it is on a much smaller scale. The heater core fits into the heater unit and is connected to the engines cooling system by two hoses called heater hoses. The connection to the engines coolant passages is made at strategic points that will cause the engines water pump to force a constant supply of engine-heated coolant through the heater core. The heater core feed line is fitted with a control valve that can be controlled by the operator. The purpose of the valve is to open, restrict, or shut off the coolant flow through the heater core to control the heater temperature. The temperature control valve can be either cable operated, or it can be operated by a vacuumactuated diaphragm that receives its vacuum supply from the engine.
c. Mode Door (Fig. 17-29). The mode door selects the heater units mode of operation. As the door is moved through its full travel, air is ducted through the heat, vent, or defrost outlets. d. Fresh-Air Door (Fig. 17-29). The fresh- air door selects either a fresh-air or interior-air (recirculate) intake for the heater unit. e. Door Controls. The heater control doors can be controlled two different ways:
(1) Cable Operated (Fig. 17-31). The doors can be operated by cable from the instrument panel. Cable-operated doors usually have the advantage of crossover operation. This means that the fresh-air door, for example, can be positioned halfway between the fresh air and recirculate intakes, allowing a blend of fresh and recirculated air. (2) Vacuum Operated (Fig. 17-32). The doors can be operated by actuators that are powered by a vacuum supply from the engine. This vacuum supply is routed to the actuators by rubber hoses that first pass through control valves in the instrument panel. The control valves usually are built into a master control switch that is controlled by the operator. The advantage to this control system is that it is much easier to route the rubber supply hoses in the tight confines of the instrument panel area than it is to route control cables that will bind if kinked. TA233639
a. General (Fig. 17-29). The heater, defroster, and ventilation mechanisms usually are combined into one unit to make up a complete system. The unit, which is called a heater unit, consists of a chambered box containing a heater core (para 17-19b) and control doors to allow the operator to select the desired mode of operation. The outside of the box contains openings for:
(1) Outside air intake, so that fresh air can be drawn into the vehicle. (2) Interior air intake, so that air can be recirculated. (3) Defroster outlets, so that forced air can be provided to clear the windshield. (4) Heater outlets, so that heated air can be provided, usually at floor level. (5) Ventilation outlets so that air can be forced into the passenger compartment at instrument panel level. An electric blower motor also is combined with this unit to provide air movement.
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TM 9-8000 conjunction with a multiple element resistor, provides the circuitry to make these motor selections possible. 17-20. Auxiliary Heaters.
a. Engine Compartment Heaters. The engine compartment, particularly in vehicles equipped for arctic operation, contain one or more auxiliary heating devices. The most common devices are:
(1) Water Jacket Heater. The water jacket heater Is an electric resistance-type heater that operates usually from an external 110-volt power supply. The heating unit usually Is installed in place of one of the cylinder block core hole plugs. (2) Engine Oil Heater. The engine oil heater Is also an electric reslstance-type heater that operates from an external 110-volt power supply. The engine oil heater Is a bayonet-type device that fits In the engine in place of the dipstick.
Figure 17-30. Typical Heater Core f. Blower Motor. The blower motor Is a simple electric motor that drives a circular fan. This circular fan commonly Is referred to as a squirrel cage. The controls of the blower usually Include a three- or four-position switch providing various speed choices to the operator. The switch, In (3) Blanket Heaters. Engine compartment components also can be heated by blanket-type electric heaters. These devices are used to heat the battery or can be used to cover the engine, retarding engine cool down after operation.
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Figure 17-32. Vacuum-Operated Mode Doors b. Interior Heaters. Auxiliary heaters also are used to heat the vehicles interior compartments. There are two basic types.
(1) Self-contained. These usually are pro- pane or butane space heaters. For portable shelters, an electric-type space heater will be used. This type of heater requires an external power supply. (2) Supplemental Hot Water Heaters. These heaters contain a fan motor and a heater core (para 1719). They are connected to the englnes cooling system and operate by the same principles as the vehicles main heater.
17-25
17-21. General.
a. Electrical power and control signals must be delivered to electrical devices reliably and safely so that the electrical system functions are not impaired or converted to hazards. This goal is accomplished through careful circuit design, prudent component selection, and practical equipment location. b. The list of common equipment used to fulfill power distribution requirements in military vehicles includes single-conductor cable, multiconductor cable, bus bars, terminal blocks, terminals, and connectors. In order to facilitate the successful application of such equipment, guidelines for the design of main power distribution circuits, conductor selection and routing practices, wiring and cable assembly requirements, human factors, environmental considerations, circuit protection requirements, and circuit identification techniques are discussed in this section. Included are the general power distribution considerations necessary for effecting good performance, economy, and safety in a vehicle electrical system design.
17-22. Wiring Harnesses.
subassembly that will interconnect specific elec- trical components and/or equipment. There are two basic types of wiring assemblies: (1) Cable Assembly. The cable assembly consists of a stranded conductor with insulation or a combination of insulated conductors enclosed in a covering or jacket from end to end. Terminating connections seal around the outer jacket so that the inner conductors are isolated completely from the environment experienced by the outer jacket. Cable assemblies may have two or more ends. (2) Wiring Harness. Wiring harness assemblies contain two or more individual conductors laid parallel or twisted together and wrapped with binding materials such as tape, lacing cord, and wiring ties. The binding materials do not isolate the conductors from the environment completely, and conductor terminations may or may not be sealed. Wiring harnesses also may have two or more ends.
b. Wiring Harness Bindings. Several methods are employed to bind the wire bundles together in wiring harness assemblies. Each method has an intended or preferred application in military vehicles.
a. General (Fig. 17-33). Wiring assemblies consist of wires and cables of definitely pre- scribed length, assembled together to form a
Figure 17-33
17-26
TM 9-8000 (1) Tape Binding (A, Fig. 17-34). This binding is intended for vehicle interior wiring applications where wires are unprotected, and an additional measure of snag protection and abrasion resistance is required. Cables are bound together with one-half overlapping turns of tape. Tape, Type EF-9, Black, MIL-I-5126, has demonstrated suitable low-temperature flexibility (-100F cold bend) in the military environment. (2) Spaced Bindings (B, Fig. 17-34). This binding is intended for vehicle interior wiring in protected locations, or in junction and control box applications. Cables are bound together with one-half overlapping turns of tape in spaced intervals. Tape should form 2- to 2.25-in. Wrap lengths spaced at 8- to 12-in. intervals. (3) Spaced Bindings - Heat-Shrinkable Tubing (C, Fig. 17-34). One alternative method for spaced binding uses sleeving in lieu of tape. A heat-shrinkable modified neoprene rubber sleeving, MIL-I-23053/11, has demonstrated suitable low-temperature flexibility (55C brittleness) in the military environment and the cables are bound together with 0.75- to 1.25-in. lengths of the heat-shrinkable sleeving spaced at 8- to 12-in. intervals (4) Spaced Bindings - Cable Ties (D, Fig. 1734). Another alternative spaced-binding method uses wire ties or straps. Cable straps, adjustable, selfclinching, MS3367-1, MS3367-3, MS3367-4, or MS33675 are suitable for this application. Cables are bound together with straps spaced at 8- to 12-in. intervals. (5) Laced Bindings (E, Fig. 17-34). Lacing is intended for wiring used in junction and control box applications. Lacing cord in accordance with MIL-T43435, Size 3, Type I, Finish B, Waxed, Color Optional, has performed satisfactorily in the military environment. (6) High-Temperature Bindings (F, Fig. 1734). This binding method is intended for harnesses used on engines, transmissions, or other systems where additional protection against high temperature is required. Cables are covered, or bound together with insulating sleeving. Sleeving ends and junctions are bound to cables with one-half overlapping turns of tape. Tape endings must overlap fully. Insulating sleeving, electrical, Class 200, Type C, Category C or D, MIL-I-3190, has demonstra-
TM 9-8000 ted suitable high-temperature and humidity resistance in these applications. Tape 19207-10886484 has demonstrated adhesive qualities that withstand steam cleaning and the oily, high-temperature environment associated with vehicle power packs. 17-23. Wiring Harness Identification (Fig. 17-35). Wires in an electrical system should be identified by a number, color, or code to facilitate tracing circuits during assembly, troubleshooting, or rewiring operations. This identification should appear on wiring schematics and diagrams and whenever practical on the individual wire. The assigned identification for a continuous electrical connection should be retained on a schematic diagram until the circuit characteristic is altered by a switching point or active component. An extension of this system involves the use of suffix letters on wiring diagrams and wiring assemblies to identify the segments of wires between terminals and connector contacts. The use of suffix letters is advantageous when it is necessary to identify several individual wires of a common circuit that are bound in the same harness. Tank-automotive electrical circuits have been identified over the years with unique numbers for specific circuits, based on the premise that maintenance personnel would become familiar with wire numbers for these circuits and this familiarity would facilitate their ability to service a variety of vehicles. Furthermore, common standard automotive electrical components in the supply system such as headlight, taillight, and stoplight switch assemblies are marked with these standard wire numbers. Therefore, these numbers should be used to the maximum extent practical for the identification of circuits in future military vehicle electrical systems. There are several practical methods used to apply wire identification characters on wiring assemblies. Four of the commonly employed methods are:
a. Lettering may be hot stamped per MIL-M-81531, with 0.05-in. minimum height type, directly on the wire or cable insulation using white letters on dark backgrounds or black letters on light backgrounds. b. Lettering may be hot stamped per MIL-M-81531, with 0.05-in. minimum height type, on MIL-1-23053/2 heat-shrinkable sleeving, length and diameter as required, assembled over the wire insulation. c. Lettering may be indented or embossed with 0.093-in. minimum height type on band, marker blank, MS39020, style and length as required, in accordance with MIL-STD-130. Of these, the metal marker bands with indented or embossed characters are the most durable and they remain legible even if painted over.
17-24. Wire Terminal Ends.
a. General (Fig. 17-36). Wire lug terminals are divided into two major classes: the solder type; and the solderless type, which also are called the pressure or crimp type. The solder type has a cup in which the wire is held by solder permanently, whereas the solderless type is connected to the wire by special tools that deform the barrel of the terminal and exert pressure on the wire to form a strong mechanical bond and electrical connection. Solderless-type terminals gradually have replaced solder-type terminals in military equipment. b. Solderless Terminals (Fig. 17-36). Solderless terminals come in a variety of designs. Some of the more common recommended terminals are the ring-tongue, rectangular-tongue, and flag types. One of the major sources of trouble when a terminal is connected to a wire has always been the breakage of the wire near its junction with the terminal. Wire failures have been decreased by adding a sleeve to the basic terminal. The inside diameter of the sleeve is slightly larger than the outside diameter of the wire insulation. In the crimping operation, when the
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c. Solder-Type Terminals (Fig. 17-36). Solder-type terminals come in most of the configurations. Although they are considered to make more positive, permanent connections, they are not used as widely as solderless connectors because of the difficulty involved with installing them.
a. General. Connectors have evolved to facilitate the coupling and uncoupling of electrical equipment for replacement or service. The typical connectors used on military vehicles permit the elements of a system to be fabricated and serviced as individual assemblies or components so that the final system configuration is built and maintained more easily. The interconnection generally is accomplished using multiconductor or singleconductor cable assemblies or wiring harnesses, which permit convenient placement of the system components. Connectors and receptacles also are attached directly to individual components to permit the easy removal of items that are connected to mating parts without the use of interconnecting cables (circuit boards and relays). A compatible connection system consists of a plug assembly, a mating receptacle assembly, and the wires or cables leading to them. Connector assemblies exist in a variety of configurations, each of which is intended for a particular environmental and/or mounting condition.
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Figure 17-37. Wire Receptacles and Connectors b. Types. Plugs and receptacles are available with either pin- or socket-type contacts, that is, with either male or female contacts. The placement of one in preference to the other is based on a general rule prescribing that sockets (female) are used on the power side of a connection. This arrangement is intended to prevent accidental shorting of the power side of the connection, which could injure personnel or damage equipment. Connectors are designed specifically for high- or low-voltage applications. The various connector receptacles that are available for vehicle usage are classified as in-line or cable, box, wall, or bulkhead types.
(1) The In-line type has no means of supporting itself, is used on a cable end, and is joined to a mating element that also is cable connected. These in-line receptacles permit the Interconnection of power distribution systems using two or more cable or harness assemblies to facilitate maintenance. (2) The difference between box- and wallmounted receptacles is related to the environmental protection of the conductor connections. The boxmounted style has exposed conductor connections, and is intended to be mounted on a box or component that is sealed and thereby provides the conductor connections with protection from the environment. A wall-mounted receptacle is intended to be mounted on an exposed or unprotected enclosure; therefore, the connections to the conductors are sealed. (3) The bulkhead receptacle penetrate a panel while maintaining a seal compartments established by the panel. feature of the bulkhead receptacle is that connection on both sides is used to between the The unique it allows the
TA233647 17-30
TM 9-8000 of the panel to be removed easily. This is a significant difference from box- or wall-mounted receptacles, which have only one easily removable connection. (4) There is also a variety of connector plug assemblies used on vehicles, and the primary physical difference between them is the backshell configuration. This backshell is used to direct the connecting wire or cable either axially or in angles up to 90 degrees from the axis of the connector, as well as to provide a water seal and strain relief for the cable or wire. c. Requirements. (1) Electrical connectors must be capable of withstanding the effects of the military environment. Protection against damage due to temperature extremes, water, oil, and physical abuse is mandatory. (2) It is good practice to provide one or more spare contacts in the connector pair more than the actual number required for the circuits to carry. Then, any increase in circuits necessitated by functions added later will not require the use of another connector. It is advisable to keep the number of contacts per connector down to a number that can be mated and separated without excessive force. Where a large number of circuits must be handled, it may be advisable to use more than one connector pair. Every effort should be made to choose connectors that will allow signal and power leads to be bundled separately. (3) The current to be passed through each contact must be determined. The contact size then can be established with a safety factor sufficient to provide safe operation under conditions of temporary overload. Another important safety factor is mechanical strength. In many applications, size 12 contacts are used, even though the current may be less than 100 mA because the mechanical strength of the size 12 contact is needed. (4) Great care should be exercised in the selection of connectors to make certain that they will meet mechanical strains placed upon them in application. On vehicles, connector housings are used as personnel steps if they happen to be in the right location, and it is not an uncommon sight to see military equipment lifted or carried by one or more of its connectors even though connectors or thin housings are not intended for these purposes. (5) The selected connector must have the means to prevent incorrect mating built into it. This may be effected through dissimilar-size guide pins, a nonsymmetrical arrangement of contact barriers, or the design of the connector shell housing. Contact pins should never be used for alinement or polarization.
17-31/(17-32 blank)
TM 9-8000 CHAPTER 18 RADIO INTERFERENCE AND SUPPRESSION Section I. INTERFERENCE 18-1. Automotive Radio. Although the supply and maintenance of radio equipment is a responsibility of the Signal Corps, its use by motor vehicle units for coordinating convoy movements in isolated areas must be considered. Transmitting and receiving equipment of this type depends upon the electrical system of the vehicle in which it is installed for its source of power. such sparks will disclose the location of the vehicle to sensitive electrical detectors. Because the units of the electrical equipment are connected by a wire or a series of wires, as in an automotive ignition system, the wiring acts as an antenna to transmit the interference created by the spark into the air. The captive effect of the wires and the spark-producing unit causes the radiated energy to affect a wide band of frequencies on a radio receiver, with pronounced effects on certain frequencies. 18-2. Ignition Noises. a. Cause. When distributor breaker points are opened and closed by operation of the engine, the ignition coil produces a high-voltage current that flows across the gap in the spark plug to cause ignition. The sparks at the plugs and those at the breaker points cause violent surges of current to flow in all wires of the circuit (fig. 18-1). A magnetic field builds up around each wire and collapses with each make and break of the circuit. The rapidity with which these changes in the magnetic field are repeated is determined by the engine speed.
a. Installation. Installation of these units varies in different types and makes of equipment. In general, units of radio equipment should be mounted on brackets, panels, or metal members that are attached to the body or frame by welding or riveting. All paints, lacquers, or primers should be removed from all mounting surfaces that come in direct contact with the equipment, and the surfaces should be tinned in order to ensure the best possible ground. The units should be located so that all switches or controls are within easy access of the operator. All flexible control cables should be free of sharp bends. So far as possible, installation or removal of this type of equipment should be done by specialists of the Signal Corps who are trained in this type of work. b. Power Requirements. Radio units require from 4 to 5 amperes for receivers and 12 to 16 amperes for large units and transmitters. In many instances, it will be found necessary to equip the vehicle with a larger generator with a regulator device to supply the additional current. All power leads from the vehicle electrical system should be of sufficient size to meet the current requirements and should be equipped with fuses or other overload protection devices. All leads should be as short as possible. High-voltage direct current sometimes is necessary, in which case a motor generator is required. c. Interference. Any sparks created by the operation of electrical equipment (such as spark plugs, circuit breakers, coils, generators, regulators, magnetos, or distributor assemblies), by loose or dirty connections, or by chafing of metal to metal, may cause interference with radio reception of nearby radio receivers. In addition,
b. Recognition. The resultant noise in the receiver from breaker points, distributors, or spark plugs is recognized by clicking sounds that vary in rapidity and intensity with the speed of the engine.
18-3. Generator Noises.
a. Causes. With the generator in operation, there is some sparking between the brushes and commutator segments. Generators in good mechanical condition may exhibit some sparking, but this usually is not severe enough to cause radio interference. This type of sparking is increased by any of the mechanical defects listed below.
(1) Brushes do not fit commutator. (2) Brushes are worn more than one-half their original length.
18-1
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(3) Brush spring tension is incorrect. (4) commutator. Oil or carbon particles collect around
ence can be recognized by a roaring or whining noise that varies in pitch with the speed of the engine. 18-4. Body Noises.
(5) Commutator is worn out-of-round. (6) capacity. (7) grooved. (8) There is high insulation between segments of commutator. Commutator segments are burned or Generator is loaded in excess of rated
b. Recognition. Sparking between the brushes and commutator segments may cause interference in nearby radio sets. This type of interfer-
a. Causes. Body noises are produced by loose screws and bolts that allow various parts of the body to chafe against each other. This chafing produces static discharges that are a source of interference to radio receivers. Static charges caused by friction and induced charges from wiring on the vehicles are collected by the vehicle body. These charges are retained by poorly grounded sections of the body until they build up to a sufficient value to jump to any well-grounded part of the vehicle. Each discharge causes a spark of sufficient intensity to create interference in a radio receiver. These effects are produced only when the vehicle is in motion, or for a very short period after the vehicle is stopped.
TM 9-8000
b. Recognition. Looseness in the hood, brackets, and bolts can cause considerable noise in a receiver. This type of disturbance is intermittent, varies in value, and can be detected
by a frying or snapping sound. It can be detected only when the vehicle is in motion; or, when moving the loose parts, it can be recognized by a scratching sound in a receiver.
Section II. SUPPRESSION 18-5. Description of Suppression Methods. Various methods are used to suppress radio interference caused by a vehicle. These methods include resistorsuppressors, capacitors, filters, bonding, and shielding. Application of one of these methods usually is sufficient to suppress the interference from any one source adequately. However, in some instances, it may be necessary to use a combination of these methods to obtain the desired amount of suppression. and the capacitor wire is connected to the terminal. A capacitor allows the interfering voltage to pass freely to ground (frame and body of vehicle), and at the same time prevents any loss of the useful direct current. Thus, the surges are conducted away from the wiring and cannot cause interference.
a. Resistor-Suppressors. A resistor-suppressor consists of a short carbon rod of high resistance, protected by a plastic cover. Resistor-suppresssors are connected in the high-tension wires at the spark plugs and distributor to reduce the intensity of surges and thus reduce interference from these sources. The resistance of the suppressors is high enough to control the surges but not high enough to affect the operation of the engine in any way. Some special-purpose spark plugs have a built-in resistor (para 15-3). b. Capacitors. These are units of metal foils separated by paper insulation and protected by a metal case. The case is filled with an impregnating compound to keep the moisture out. A wire connected to one side of the capacitor is provided for connection to a circuit. The other side of the capacitor is connected internally to the case. Surges created in the wiring by sparks at the generator brushes, regulator, and gage contacts are not as strong as those produced by the high-tension ignition circuit because the voltage is low, but they are strong enough to cause interference in a radio set. Resistorsuppressors cannot be used in these circuits because their resistance would reduce the low-voltage current too much. However, capacitors, because of their inherent capacitance, may be used to dissipate these surges. They are attached to the circuit as near as possible to the point at which the spark occurs. The case of the capacitor is mounted on the metal frame of the unit causing interference,
c. Filters. An assembly made of a closely wound coil of heavy wire and one or more capacitors mounted in a metal container is called a filter (fig. 18-2). The capacitors act in the same manner described in paragraph b above, and the coil of wire acts to block the interfering voltage from getting farther in the circuit. Filters are used In some generator, regulator, and lowtension ignition circuits. d. Bonding (Fig. 18-3). This term is applied to the method of electrically connecting individual metal sections to each other and to the frame or hull of the vehicle. Such bonding is necessary to provide an easy path for grounding static charges. Bonding is accomplished by internal-external toothed lockwashers, and by bond straps. The better the connection between metal parts, the greater is the effect in preventing interfering waves from being thrown off to affect radio reception. e. Shielding. This term is applied to the method of covering all wiring carrying interfering voltages or surges with a metal shield (fig. 18-2). Woven metal conduit is used where flexibility is required, while solid conduit is used elsewhere. Units causing interference, such as the spark plugs, ignition coil, distributor, and regulator, ate enclosed in metal boxes. This shielding does not reduce the intensity of the interfering surges, but prevents their radiation. While such shielding is effective in preventing the radiation of interfering waves, filters and capacitors are necessary to eliminate any interfering surges that would otherwise travel on the wires and affect the radio set through the power supply. Such filters and condensers are enclosed in metal
18-3
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(e)
frame.
(a) From hood to firewall. (b) From hood top panel to hood side
panel.
(c) From overhead valve covers to firewall. (d) From engine block to frame.
(a)
screws.
TM 9-8000
(c) At gage sending unit. (d) Under head of radiator grille mounting
screws.
side of the supply line. The complete shielding system is used on most tanks having radial engines and on some armored cars. In tanks, all wiring is enclosed in flexible metal conduit or solid metal conduit. Very little bonding is necessary with this system. In most cases, only the engine is bonded to the support or hull. Control devices consisting of metal rods or tubing extending from crew compartment to engine compartment may be bonded at the points they enter the crew compartment. (1) Usually one filter is used, enclosed in a shielding box. It always is mounted close to the regulator and the battery. (2) Capacitors are used on the electrical devices in the turret. They will be found at the brushes of the traversing motor, generator, and in the circuits of the stabilizer control switchbox. In armored scout cars and gun motor carriages that have the completely shielded system, all high-tension, primary ignition, and charging circuit wiring is shielded with flexible metal conduit, which is grounded every 2 feet with clips and internal-external tooth washers. The distributor, ignition coil, and regulator are shielded. (3) Filters may or may not be used. If one is used, it will be mounted close to the regulator on the firewall. (4) A capacitor is mounted on the generator. (5) Usually, the only bond is the one from engine to frame. Both sides of the engine are bonded.
(e) Under head of fender mounting screws. (f) Under head of any bolt or screw securing a separate section of metal that will help form a shield in the vicinity of the engine compartment. b. Transport Vehicles - Completely Shielded Suppression System. A few vehicles have a completely shielded system of suppressing, and in such cases, usually only one filter is used. It is mounted in a metal box close to the regulator (it may be on the cab side of the firewall). A capacitor will be found mounted on the generator, in a round metal shielding case. In most cases, the only bond is between the engine and the frame. c. Tanks and Armored Cars. The resistorsuppressor system used on tanks with in-line engines, and on most armored cars, is basically the same as that used on transport vehicles described above. Usually, there will be fewer bonds and toothed lockwashers and more capacitors. Less bonds and washers are needed because of the heavy, bolted, or welded construction of the hull or body. Resistor-suppressors, filters, and capacitors are used in the same circuits as in the transport vehicles. More capacitors will be used to bypass the interfering surges from such accessories as auto-pulse fuel pump, electric gages, windshield wipers, traversing motors, auxiliary generators, and similiar items. The capacitors always are mounted close to the device causing interference, with the lead connected to the hot
18-6
TM 9-8000 PART FOUR POWER TRAINS CHAPTER 19 INTRODUCTION TO POWER TRAINS Section I. PURPOSE 19-1. Providing Power to Propel Vehicle. One important function of the power train is to transmit the power of the engine to the wheels. In a simple situation, a set of gears or a chain could perform this task, but automotive vehicles usually are not designed for such simple operating conditions. They are designed to have great pulling power, move at high speeds, travel in reverse as well as forward, and operate on rough ground as well as on smooth roads. To meet these widely varying demands, a number of units have been added. These include clutches, transmissions, auxiliary transmissions, transfer cases, propeller shafts, universal joints, final drives, differentials, live axles, devices for resisting drive torques and thrust, and the bearings used therein. 19-2. Providing Power to Operate Accessories (Power Takeoff). The power train also is designed to direct power to the accessories. These branches from the main flow of power are known as power takeoffs. They may be connected to the transmission, auxiliary transmission, or transfer case. The simplest type of transmission power takeoff is the single-gear, singlespeed type shown in figure 19-1. This unit is bolted over an opening provided for that purpose at the side of the transmission case. This opening is closed by a cover plate when no power takeoff is used. The opening in the transmission case and the power takeoff gear meshes with a gear on the transmission countershaft. As shown in figure 19-1, the gear slides on the splined main shaft, off which the power is taken. The shifter shaft, controlled by a lever in the drivers cab, slides the gear in and out of mesh with the countershaft gear. Because it is driven by the countershaft, the power takeoff shaft rotates in the same direction as the engine crankshaft. Transmission power takeoffs are available in several different designs: a single-speed, two-gear model in which the rotation of the power takeoff shaft is opposite to that of the engine; a model having a single speed forward and reverse; and a model having two speeds forward and one reverse. Several different mountings also are available. The same types of power takeoffs also are applied to auxiliary transmissions. Figure 19-2 shows a winch driven off of an auxiliary transmission. Power sometimes is taken off a transfer case. The transfer case drive shaft, which is connected to the transmission, extends through the case, and the power takeoff shaft is engaged to it by a dog clutch. This transfer case has two speeds and a neutral position. It is necessary to put the transfer case sliding gear in the neutral position if the vehicle is to be stationary while the power takeoff is in use. If the power takeoff is needed while the vehicle is in motion, the transfer case may be shifted either into high or low range. With this arrangement, the power takeoff will work on any speed of the transmission. When the power takeoff clutch is engaged, the winch capstan operates; but the winch drum does not rotate until the winch clutch is engaged. The several types of power takeoffs have been described as operating winches, but their uses for operating various kinds of hoists, pumps, and other auxiliary power-driven machinery are essentially the same.
19-1
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a. Torque Ratio. Torque has been defined as a twisting, or turning, effort. When one gear drives the other, it turns the other by the application of torque. The torque ratio between two meshing gears varies with the mechanical advantage, that is, with the gear ratio of the driving to the driven gear. When a small gear drives a larger gear, for example, the speed is reduced but the torque delivered by the larger gear is increased. Thus, when a 12-tooth gear drives a 24-tooth gear, torque is doubled; that is, the torque of the large
TA233652 19-3
TM 9-8000 torque increase (or torque multiplication) may be much greater than 12:1. transmitted through the system. If a large resistance must be overcome, the torque multiplication also must be high. If this factor is not correct, the driving system can be overloaded. On the other hand, if a small resistance is to be overcome, the driving system might not be used to its fullest capabilities, therefore producing an inefficient system.
b. Mechanical Advantage. The use of a lever to move heavy objects is well known. When a box is too heavy to be lifted by hand, a crowbar or lever can be used to lift it, as shown in figure 19-3. With the lever placed as shown, only half as much force is required on the lever to raise the box. Suppose that a lifting force of 200 pounds is required to raise the end of the box. With the lever arranged as shown, only a 100-pound downward push is needed on the lever. The farther out on the lever the hand is put (away from the pivoting point, or fulcrum), the less downward push is required. But also, the farther the hand must move to raise the box. The mechanical advantage of the lever is the ratio between the two distances from the fulcrum. In the example shown, the mechanical advantage is 2:1. c. Mechanical Advantage in Gears. A rough comparison between mechanical advantage in levers and mechanical advantage in gears can be made. Such a comparison is shown at the bottom of figure 19-3. One end of the lever moves twice as far as the other. When two gears are meshed and one gear has twice as many teeth as the other, the smaller gear will rotate twice for each revolution of the larger gear. In other words, the mechanical advantage between the two gears would be 1:2 when the larger gear drove the smaller gear. If the smaller gear drove the larger gear, the mechanical advantage would be 2:1 because the smaller gear would have to exert half the force for twice the distance. d. Mechanical Efficiency. The mechanical efficiency of a system is dependent upon gear ratios and the amount of power that must be
e. Internal and External Gears. Gears are basically of two types: internal and external. Internal gears are shaped cylindrically with teeth machined on the inside. External gears usually are circular with teeth around the outside of the gear. An example of both gears is shown in figure 19-4.
19-4. Types of Gears. There are many types and designs of gears and gear systems. Some of the most popular gears found in the automotive vehicle are discussed below. a. Spur. Spur gears (fig. 19-5) are the most common type of gear. The teeth are machined perpendicular to the axis of rotation. Because these gears mesh only one tooth at a time, they are not capable of absorbing great amounts of torque. They generally are noisy during operation and are used to change direction and/or speed.
b. Helical. Helical gears (fig. 19-5) have teeth machined at an angle to their centerline of rotation. This characteristic enables the gear to engage more than one tooth at a time. This type of gear, therefore, is stronger and able to transmit more torque than spur gears. Because of the angle cut of the gear, two meshing gears tend to move apart during use. This reaction therefore requires the use of a thrust washer or tapered bearing when using helical gears. Helical gears
c. Herringbone. Herringbone gears (fig. 19-5) can be formed by attaching two helical gears in such a way that their teeth meet in a V-formation. The Vconfiguration cancels the side thrust created by each helical gearset. As herringbone gears mesh, more than one tooth is engaged at a time. This feature allows the gear to transmit large amounts of torque and operate quietly. d. Bevel. Bevel gears (fig. 19-5) generally are used to change direction. Their teeth are machined at angles to the drive centerline to correspond with the angle of input and output shafts. Bevel gears, like spur gears, engage one
TM 9-8000 tooth at a time; therefore, they are not able to transmit large amounts of torque and are noisy during operation. and also revolve around the sun. In the planetary gear system, the planet gears are assembled on shafts in a planet carrier or cage. Arrangements can be made to put power into any of the three rotating members and, at the same time, hold other members so that the gear ratio through the system can be increased or decreased. In addition, by the proper arrangement of turning and holding, the system can reverse rotation. 19-6. Six Basic Laws of Planetary Gearing. The chart in figure 19-7 shows the six conditions that can result in the planetary gear system from turning or holding the various members. For example, the column under Condition 1 shows that holding the sun gear while turning the pinion cage causes the internal gear to turn faster than the pinion cage. When the pinion cage is turned, the pinions must move around the sun gear because they are meshed with the sun gear. The pinions also are meshed with the internal gear, and, as they move around the sun gear and also rotate on their shafts, they force the internal gear to rotate. The rotation might be said to come from two sources: the rotation of the pinions on their shafts; and the rotary motion of the pinions as they are carried around by the pinion cage. The other conditions listed in the chart (fig. 19-7) are not all used in automotive power trains, but they should be studied for a full understanding of the action of the planetary gear system. If the sun gear is held and the internal gear turned, then the pinion cage will turn, but more slowly than the internal gear. If the sun gear is turned and the internal gear held, the pinion cage will turn more slowly than the sun gear. On the other hand, if the internal gear is turned and the pinion cage held, the sun gear will turn faster than the internal gear, but in a reverse direction. The fifth condition results if the internal gear is held and the pinion cage turned; this causes the sun gear to turn faster than the pinion cage. The sixth condition is a common one because, by its use, reverse and gear reduction can be accomplished at the same time. The sun gear is turned while the pinion cage is held. This causes the internal gear to turn more slowly than the sun gear and in a reverse direction. 19-7. Sliding Surface Bearings (Friction). Essentially, a bearing is a support for a load. In automotive applications, bearings support moving parts, most of which are rotating parts. Not
e. Worm. Worm gears (fig. 19-5) basically are two different types of gears designed to mesh at right angles to each other. One gear is shaped similar to a helical gear, while the other is straight with teeth machined in a spiral form around the exterior of the shaft. Worm gears only can be driven by the rotating action of the long, spiral-shaped gear. The spiral-shaped gear also must have a means of absorbing thrust, because the rotating action of this gear causes it to move lengthwise during operation. This configuration produces great gear reduction and quiet operation.
19-5. Planetary Gear Systems. The planetary gear system (fig. 19-6) consists of three rotating members: the internal gear (or ring gear); the sun gear; and the planet pinion set, consisting of the planet pinions and the planetpinion carrier, or cage. The reason the system is called a planetary gear system is that the planet gears rotate and at the same time revolve around the sun gear, just as the planets in our solar system rotate
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a. Sleeve-Type Bearings. These include bearings for rotating parts and for parts that merely slide over each other without turning. Most of the bearings of the mechanisms described in this section are for rotating parts. However, two examples of bearings for parts that do not rotate relative to each other are the shifter shafts in transmissions, which merely slide endwise in holes in the case, and the slip joints of propeller shafts.
The simplest type of sliding surface bearing applied to a rotating part is one in which an accurately finished shaft, or journal, rotates in an accurately finished hole without any bushing, the two being separated by an oil film. Such bearings may be used for differential pinions; the holes are in the rotating pinions, which turn on the stationary differential spider or cross pin. Such bearings usually are known as plain bearings and are used only for low speeds or light duty or both. Probably the next simplest plain bearing, also of the sliding-surface type, is the bushing that is replaceable when worn. A bushing is usually of bronze or similar relatively soft material and is pressed into a hole and reamed to fit, forming a lining in which a journal rotates. Plain bushings are suitable for radial loads only. Bronze bushings formerly were used to a considerable extent in automotive power transmission systems but have been superseded by antifriction bearings
b. Thrust Washers. A thrust washer is a form of friction bearing designed to limit lateral movement. These washers generally are placed between moving parts or one moving part and a stationary member. They generally are not designed to absorb thrust constantly, as overheating can occur. Thrust washers generally are made of bronze or hardened steel.
19-8. Ball and Roller Bearings (Antifriction). These bearings are used throughout automotive power transmission systems. The usual locations of antifriction bearings in a truck chassis are shown in figure 19-8. They are known as antifriction bearings, because friction in them is eliminated because they depend upon rolling contact rather than sliding contacts. Ball bearings often are referred to as having point contact between balls and raceways; in the same sense, roller bearings are said to have line contact between rollers and races. These are merely descriptive terms, however, because the elastic deformation occurring under load results in substantial areas of contact in either type. The starting friction of ball and roller bearings is but slightly greater than their running friction, an important advantage in machinery that is required to start frequently under load. They also can sustain high overloads for short periods without failure. Ordinarily, a ball or roller bearing does not fail suddenly, but gives warning by a gradual decrease in smoothness of running; whereas, the plain bearing is subject to an accelerated type of failure that often results in TA233656 19-7
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b. Roller. As in the case of ball bearings, the details of construction of roller bearings vary considerably for different applications. Like ball bearings, they are designed for radial, thrust, and combined loads. Roller bearings, which have greater contact area than ball bearings, are used for heavy-duty applications.
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TM 9-8000 solid inner and outer races, with solid outer race and no inner race, and with a split outer race and no inner race. c. Tapered Roller. Tapered roller bearings (fig. 1911) are used extensively in automotive power transmission systems, especially for the more heavily loaded rotating members. The rolling members and raceways of the tapered roller bearings are constructed on the elements of a cone, so that lines that coincide with the contacting surfaces of rollers and races all meet at a common point on the axis of the bearing as shown at the bottom of figure 19-11. True rolling contact is thus obtained. The essential parts are an inner race or cone, an outer race or cup, tapered rollers, and a cage or roller retainer. These bearings are suitable for heavy duty, and can withstand radial loads and thrust loads in one direction or a combination of both. Such bearings also are available with double and quadruple rows of tapered rollers. Flat thrust bearings having tapered rollers, suitable for thrust loads only, also are available. d. Needle Bearings. Needle bearings (fig. 19-12) (or quill bearings, as they sometimes are called) are cylindrical roller bearings in which the diameter of the roller is not over one-eighth the roller length. Separate outer and inner races may be used, or the inner race may be the shaft and the outer race integral with the housing. No spacing cage is used ordinarily; the rollers merely are constrained against endwise movement. Needle bearings are suitable for radial loads only. These bearings are used where a high load-carrying capacity is required in a small space. Needle bearings are used in many universal joints. 19-9. Bearing Lubrication. A basic requirement of ball and roller bearing lubrication is to protect the highly finished surfaces from corrosion. The supporting surfaces of the cage, or retainer, essentially are plain bearings and require an oil film. A small quantity of oil or grease will lubricate a bearing if it is distributed evenly. An excess quantity of lubricant is undesirable because it will cause the bearing to heat and will aggravate leakage from the bearing housing. Operating temperature is the controlling factor in selecting the proper grade of lubricant. Load, speed, and weather conditions directly affect this temperature, as does the particular type of bearing and the shaft enclosures. The antifriction bearings in automotive power transmission systems are not lubricated as separate units but as parts of assemblies such as
TM 9-8000 19-11. Oil Seals. Oil seals used in the automotive assembly are designed to prevent leakage be- tween rotating and nonrotating members. Two basic types of oil seals are used on todays vehicles. Each Is discussed below. a. Synthetic Rubber Seals. The synthetic rubber oil seal (fig. 19-14) is the most common type of oil seal. It is composed of a metal case used to retain its shape and maintain rigidity. A rubber element Is bonded to the case, providing the sealing lip or lips that rub against the rotating shaft. Different types of oil seal designs are illustrated in figure 19-14. A coil spring, some- times called a garter spring, also is used to hold the rubber element around the shaft with a con- trolled amount of force. This allows the seal to conform to minor shaft runout. Some synthetic rubber seals fit into bores mounted around the shaft. This type Is generally a split design and does not require a metal case or garter spring. Some oil seals rely on pressure to aid In sealing. Figure 19-14 illustrates the effects of pressure on lip seals. Internal pressure developed during operation forces the sealing lips tighter against the rotating shaft (fig. 19-14). This type of seal only will operate effectively against fluid pressure from one direction. Leather also is used as a lip seal. In this configuration, the seal Inside diameter is smaller than the shaft (fig. 19-14). As the shaft is Installed, the seal bows outward to form a lip seal. b. Wick Seals (Fig. 19-15). The wick seal made of graphite-impregnated asbestos wicking sometimes Is used to control oil leakage. This seal conforms to the recess In which it Is Installed. When using this type of seal, a knurled finish is used on the rotating shaft. The oil Is contained between the knurls and seal, which rub together. As the shaft rotates, the oil is driven back by the propeller effect of the seal and knurl finish. An oil slinger sometimes Is used with wick seals (fig. 19-15). The oil slinger is a raised washerlike area on the shaft. As oil meets the slinger, it is propelled outward by centrifugal force. A catch trough then Is used to collect the oil and return it to the sump. 19-12. Gaskets (Fig. 19-16). Gaskets, other- wise known as static seals, are used to form pressure-tight Joints between stationary members. They usually are made of a deformable material In the shape of a sheet or ring, which
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a. Power generally is delivered in a straight line. The majority of front-wheel drive vehicles use a transversely mounted engine. This feature eliminates the power from being driven through different angles at the drive axles. b. The front-wheel drive configuration has fewer moving parts. This helps reduce friction and increase engine life.
These features help make the front-wheel drive configuration one of the most popular designs on modern vehicles. 19-14. Rear-Wheel Drive. The rear-wheel drive configuration applies the driving force to the rear
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20-1. Liquids Versus Gases (Fig. 20-1). One major factor that influences the compressibility of liquids and gases Is their molecular bonding. Liquids have molecules moving freely around them, but not separating. Gases have molecules that are more active and tend to separate readily. Because both liquids and gases are compressed
separately, their molecules act differently. Liquids have molecules that travel very short distances with almost no space between them. Attempting to compress the liquids yields almost no change In the space between molecules. Therefore, the volume also remains constant. This is the major reason why liquids are not compressed
TM 9-8000 readily. Gases, on the other hand, react differently when compressed. As a gas is compressed, the space between molecules is decreased, therefore allowing the volume to be decreased. As a result, the molecules are forced to travel shorter distances and interact more violently. This increased molecular interaction results in the generation of heat while compressing a gas. 20-2. Pascals Law. Pascals law states that in an enclosed system, fluid pressure developed by an external source acts evenly and in all directions without changing magnitude in the system. This principle is the basis for many systems in automotive vehicles. For example, brake, lubrication, and fuel systems are all dependent on Pascals law. Figure 20-2 illustrates Pascals law; note that the initial force of 50 psi (344.8 kPa) is distributed evenly throughout the system. 20-3. Mechanical Advantage in Hydraulic Systems. Hydraulic systems possess a definite amount of mechanical advantage. Comparisons can be made between a simple lever arrangement and a basic hydraulic system. Figure 20-3 illustrates how a lever and hydraulic system can be used to perform the same task. In this figure, both systems increase mechanical advantage, therefore making it easier to move the object. In A, figure 20-3, a long solid rod, with the fulcrum placed close to the object, is used to develop the mechanical advantage. In B, figure 20-3, a large-diameter piston is used to develop the force to move the object. In each system, certain factors must be forfeited to obtain this mechanical advantage. Each is listed below.
a. In the lever system, the rod must be pushed through a great arc to obtain a small movement with an increased force on the opposite end of the rod. b. The hydraulic system requires the use of a large amount of fluid under the piston to raise the object slightly. This is illustrated in detail in paragraph 20-8.
These are two of the most important factors that must be considered when developing mechanical advantage.
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Section II. 20-4. Gear Type oil pumps are shown in figure 20-4. In this type, a primary gear, driven by an external member, drives a companion gear. Oil is forced into the pump cavity, around each gear, and out the other side into the oil passages. The pressure is derived from the action of the meshed gear teeth, which prevent oil from passing between the gears, and forces it around the outside of each gear instead. The oil pump Incorporates a pressure relief valve, which is a spring- loaded ball that rises when the desired
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wedging action of the oil as it is forced toward the outlet port by the vane. 20-7. Internal-External Gear Type. The internalexternal gear pump is composed of a large internal gear, driven by an external gear offset from center. The space between the two gears is occupied by a filler block (fig. 20-7). As the small gear rotates, it meshes with, and drives, the larger gear. As the gears disengage and come in contact with the filler block, a differential in pressure is developed, causing oil to enter the pump. It then is transported past the filler block in the teeth of both gears. Because the gear teeth begin to mesh again and more oil is carried by the gears, pressure rises in the outlet chamber and exits through the outlet port. TA233670
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TM 9-8000 c. As the oil is forced into cylinder B, it will push piston Section III.20-8.Construction.A simple hydraulic jack is B upward, lifting the load through the ram. constructed using four basic components; each is discussed below. d. Piston B will rise each time the jack handle is moved up and down. a. Reservoir. The reservoir (fig. 20-8) is a storage location for the liquid medium. As the piston height is 20-10. Mechanical Advantage in the Jack. Because the increased, fluid is transferred from the reservoir to the hydraulic jack is capable of lifting heavy loads with cylinder under piston B. The lowering of the piston relatively small amounts of physical force, the jack is displaces the fluid back to the reservoir. known to have mechanical advantage. The mechanical b. Hand Pump. The hand pump (fig. 20-8) is a smalladvantage of the hydraulic jack is obtained from the following areas: diameter piston and cylinder combination used to generate fluid pressure to raise the large piston. a. The mechanical advantage from the jack handle, which is in reality a lever (para 20-3). The hydraulic jack c. Lifting Cylinder. The lifting cylinder (fig. 20-8) is shown in figure 20-8 has a distance of 10 inches from the composed of a large-bore piston and cylinder, which end of the jack handle to the piston and a distance of 1 receives fluid pressure from the hand pump. The fluid inch from the piston to the fulcrum. The mechanical pressure acts on the bottom of the large piston to raise it. advantage of the lever is equal to: The increased area of the piston allows heavy loads to be moved with relatively small pressure applied to the 10 + 1 = 10. jack handle.
d. Check Valves. Two check valves (fig. 20-8) are placed in the system, one before the small piston, and one after. The check valves control the flow of the fluid to raise and lower the ram.
20-9. Operation (Fig. 20-8). a. As the jack handle is pulled upward, piston A rises in cylinder A, pulling in oil from the reservoir through check valve 1.
b. The mechanical advantage in the hydraulic system, which is equal to the quotient of the areas of the lift piston divided by the pump piston, is equal to:
10 + 1 = 10. The total mechanical advantage of the jack then is calculated by multiplying the two mechanical advantages in a and b above as follows: 10X10 = 100.
b. As the jack handle is lowered, piston A forces oil from cylinder A through check valve 2 and into cylinder B.
It is thus seen that the hydraulic jack shown in figure 20-8 produces a total mechanical advantage of 100.
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TM 9-8000 CHAPTER 21 CLUTCHES, FLUID COUPLINGS, AND TORQUE CONVERTERS Section I. CLUTCHES
a. General. Automotive clutches depend on friction for their operation, whether it be solid friction as in the conventional clutch, or fluid friction and inertia as utilized in the fluid coupling and torque converter. The fluid coupling serves the same purpose as the conventional clutch, but the difference in the principle of operation makes It necessary to discuss the two mechanisms separately. Therefore, the first part of this chapter will be concerned with conventional clutches; fluid couplings and torque converters will be discussed in paragraphs 21-5 thru 21-9. b. Purpose. A clutch in an automotive vehicle provides a means of connecting and disconnecting the engine from the power transmission system. Because the internal combustion engine does not develop a high starting torque, it must be disconnected from the power train and allowed to operate without load until it develops enough torque to overcome the inertia of the vehicle when starting from rest. The application of the engine power to the load must be gradual, to provide smooth engagement and to lessen the shock on the driving parts. After engagement, the clutch must transmit all the engine power to the transmission without slipping. Further, It is desirable to disconnect the engine from the power train during the time the gears In the transmission are being shifted from one gear ratio to another.
c. Operation. The transmission of power through the clutch Is accomplished by bringing one or more rotating drive members secured to the crankshaft into gradual contact with one or more driven members secured to the unit being driven. These members are either stationary or rotating at different speeds. Contact is established and maintained by strong spring pressure controlled by the driver through the clutch pedal and suitable linkage. As spring pressure increases, the friction increases; therefore, when the pressure Is light, the comparatively small amount of friction between the members permits a great deal of slippage. As the spring pressure Increases, less slippage occurs until, when the full spring pressure is applied, the speed of the driving and driven members is the same. All slipping has stopped and there is, in effect, a direct connection between the driving and driven parts.
21-2. Clutch Elements. The principal parts of a clutch are the driving members, attached to the engine and turning with it; the driven members, attached to the transmission and turning with it; and the operating members, which include the spring or springs and the linkage required to apply and release the pressure that holds the driving and driven members In contact with each other. Figure 21-1 shows a clutch cutaway so operating members can he seen.
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a. Driving Members. The driving members of a clutch usually consist of two cast-iron plates or flat surfaces machined and ground to a smooth finish. Cast iron is recommended because it contains enough graphite to provide some lubrication when the driving member is slipping during engagement. One of these surfaces usually is the rear face of the engine flywheel, and the other is a heavy, flat ring with one side machined and surfaced. This part is known as the pressure plate. It is fitted into a steel cover, which also contains some of the operating members, and is bolted to the flywheel. b. Driven Members.
(1) The driven member is a disk with a splined hub that is free to slide lengthwise along the splines of the clutch shaft. These same splines also transmit torque from the disk to the clutch shaft. (The driven member sometimes is referred to as the clutch plate, but the word disk will be used here to denote the driven member and thus differentiate between this part and the clutch pressure plate.) The clutch disk usually is made of spring steel in the shape of a single flat disk of a number of flat segments. Suitable frictional facings are attached to each side of the disk by means of copper rivets. These facings must be heat resistant because friction produces heat. The most commonly used facings are made of cotton and asbestos fibers woven or molded together and impregnated with resins or similar binding agents. Very often, copper wires are woven or pressed into the material to give it additional strength. (2) In order to make clutch engagement as smooth as possible and eliminate chatter, several methods have been used to give a little flexibility to the driven disk. One type of disk is dished, so that the inner and outer edges of the friction facing make contact with the driving members first, and the rest of the facing makes contact gradually as the spring pressure increases and the disk is flattened out. In another type, the steel segments attached to the splined hub are twisted slightly, which also causes the facings to make gradual contact as the disk flattens out. (3) The driven member of the clutch (fig. 21-2) usually is provided with a flexible center to
c. Operating Members. The driving and driven members are held in contact by spring pressure. This pressure may be exerted by a single, large coil spring as shown in figures 21-3 and 21-4; a number of small helical springs located circumferentially around the outer portion of the pressure plate as shown in figure 21-1; or a one-piece conical or diaphragm spring as TA233674
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b. Mechanical _ Operating System (Fig. 21-8). The mechanical clutch operating system Is the most common. One type of system uses mechanical rod-type linkage while another type uses a flexible cable.
a. General (Fig. 21-7). The automotive clutch, through spring pressure, normally is In
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c. Hydraulic Operating System (Fig. 21-9). The hydraulic clutch operating system moves the fork by hydraulic pressure. Movement of the pedal creates pressure in the master cylinder, which actuates the slave cylinder. The slave cylinder then moves the clutch fork.
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214. Types of Clutches. a. General. Automotive clutches may be classified according to the number of plates or disks used. The single-plate clutch contains one driven disk operating between the flywheel and the pressure plate (fig. 21-10). The flywheel is not considered to be a plate, even though it acts as one of the driving surfaces. A double-plate clutch Is substantially the same except that another driven disk and an immediate driving plate (fig. 21-11) are added. A clutch having more than three driven disks (fig. 21-12) is referred to as a multiple-disk clutch. A further classification based on whether or not oil is supplied to the friction surfaces provides a positive method of
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other type would Impose a severe shock on the engine and power train when starting a heavy load.
b. Single Dry Plate (Fig. 21-10). The transmission Is driven by a single friction plate that is sandwiched between the flywheel and an Iron pressure plate. When the clutch Is engaged fully, the driven disk Is clamped firmly between the flywheel and the pressure plate by the pressure of the springs. When the operator disengages the clutch by depressing the pedal, the release yoke or fork Is moved on Its pivot, and pressure Is applied to the release bearing sleeve, or collar, containing the release bearing. The rotating race of the release bearing presses against the clutch release levers and moves them on their pivot pins. The outer ends of the release levers, which are fastened to the cover, move the pressure plate to the rear, compressing the clutch springs and allowing the driving members to rotate Independently of the driven member. The release yoke moves only on Its pivot, which is fastened to the flywheel housing by means of a bracket or a transverse shaft. All parts of the clutch, except the release bearing and collar, rotate with the
flywheel when the clutch Is engaged. When the clutch is disengaged, the release bearing rotates with the flywheel, but the driven disk and the clutch shaft come to rest. c. Diaphragm Clutch. In some clutches, a diaphragm Is used Instead of coil springs. It is a conical piece of spring steel punched as shown in figure 21-5 to give it greater flexibility. The diaphragm Is positioned between the cover and the pressure plate so that the diaphragm spring Is nearly flat when the clutch Is In the engaged position. The action of this type of spring Is similar to that of the bottom of an ordinary oil can (fig. 21-5). The pressure of the outer rim of the spring on the pressure plate Increases until It reaches the flat position and decreases as this position Is passed. The outer rim of the diaphragm Is secured to the pressure plate and Is pivoted on rings approximately 1 Inch from the outer edge so that the application of pressure at the Inner section will cause the outer rim to move away from the flywheel and draw the pressure plate away from the clutch disk, releasing or disengaging the clutch. When the pressure is released from the inner section, the oil can action of the diaphragm TA233680
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causes the Inner section to move out, and the movement of the outer rim forces the pressure plate against the clutch disk, thus engaging the clutch.
d. Multlple-Dlsk Clutch. Typical multiple-disk clutches are shown In figures 21-11 and 21-12. Disks ranging In numbers from 2 to 10 (and often as many as 11 driving and 10 driven disks for heavy vehicles) are used. The driving disks have lugs similar to gear teeth around their outside edges. These mesh with Internal splines In the clutch case, which Is bolted to and rotates with the flywheel. The driven disks are carried on parallel pins, which are solidly set In the clutch spider. This construction permits movement of all the disks and the pressure plate in order to provide clearance between them. When the clutch is engaged, the spring moves the pressure plate
forward, holding all the disks together firmly. This causes the clutch spider to revolve and turn the clutch shaft to which it Is keyed. In multiple-disk clutches, the facings usually are attached to the driving disks. This reduces the weight of the driven disks and, consequently, their tendency to continue spinning after the clutch is released. Because of the considerable number of disks Involved, the pressure plate has to move farther to separate the disks completely than It does In clutches having fewer driving and driven members. There Is, therefore, less mechanical advantage on the clutch pedal and a greater foot pressure Is required to depress it. e. In a wet-type clutch, the disks and the entire internal assembly run In an oil bath. The operation of this type of clutch Is similar to that of the dry type, except that the friction surfaces are TA233681
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made of different materials and the gradual engagement between the driving and driven members is caused by pressing the oil from friction increases.
f. Helical Spring (Semi-centrifugal). Many passenger car clutches are of the semi-centrifugal type shown in figure 21-13, in which the pressure
21-10
between the plates is increased as the speed of between the disks. As the oil is eliminated, the clutch increases. This is accomplished by means of centrifugal weights built into the outer ends of the release levers so that the outward pull of centrifugal force is transformed into pressure on the plate. This construction permits the use of relatively light clutch springs, thus facilitating the depression of the clutch pedal for gear shifting.
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Section II. 21-5. Principles.The fluid coupling (fig. 21-14) is 21-6. Operation. used either with a conventional clutch and transmission or as a part of an automatic transmission, in which case, a. Coupled Phase. The fluid coupling consists of an it may replace the clutch. The principle of this type of impeller, or driving torus, driven by the engine and a drive is illustrated by the action of two electric fans facing turbine, or driven torus, mounted on the driven shaft. each other, one with the power connected and the other These parts are shown In figure 21-14 and depicted with the power disconnected. As the speed of the powerschematically in figure 21-15. There is no metallic driven fan is increased, the flow of air transmits power to connection between the two torus members. The the motionless fan and it begins to rotate. The freeassembly is kept filled with oil under control of a relief running fan gains speed until It Is rotating almost as valve, by means of high-capacity pumps. When the rapidly as the power-driven fan. The same action takes crank-shaft and impeller rotate, the oil Is thrown by place In the fluid coupling except that oil, instead of air, centrifugal force from the center to the outside edge of transmits the power. the impeller between the vanes. This increases the velocity of the oil and increases its TA233684
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b. Uncoupled Phase. When the engine is Idling, the energy supplied to the oil is not enough members.
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Section III. 21-7.Principles. In some respects,the torque converter is like the fluid coupling. It has driving and driven members with vanes. Oil is passed from the driving to the driven member when the coupling Is In operation, thereby transmitting driving force to the driven member. However, in the torque converter, the vanes are curved and additional rotatable members provide the means
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tween the driving and the driven shafts. It actually can take the place of the conventional transmission because, with it, there is no need for gearshifting; the vehicle can be accelerated from a standing stop to high speed with the torque converter providing, in effect, the varying gear ratios. In actual practice, the torque converter is used with a gear system (including planetary gears) to provide a high range (for normal operation), a low range (for steep hills, or pulling out of mud), reverse, and neutral. There also may be a parking position at which the gear system is locked. 21-8. Operation.
a. All torque converters have a driven member (called the turbine) and a driving member (called the pump). In addition, they have one or more other rotatable members (or elements) placed between the pump and the turbine that have the purpose of changing the direction of oil flow under high-torque-multiplication operation. Figures 2116 and 21-17 show torque converters in sectional and cutaway views. b. The primary action of the torque converter results from the action of the pump in passing oil at an angle into the blades of the turbine (fig. 21-16). The oil pushes against the faces of the turbine vanes, thereby tending to cause the turbine to rotate in the same direction as the pump. If the pump is rotating much more rapidly than the turbine, the oil enters the turbine and pushes against the turbine vanes with great force. As the oil passes around through the turbine (fig. 21-17), it imparts force against the turbine vanes, all along the vanes. But it does not give up all of its force of motion to the turbine vanes. It still has considerable energy, even though passing through the turbine has reversed its direction of motion as shown in figure 21-17. If this reversed direction of motion were not changed, the oil would reenter the pump in a direction opposing pump rotation. It would act as a brake on the pump, tending to slow it down. Considerable engine power would be consumed in overcoming this action. However, the additional members in the torque converter again change the direction of the oil before it reenters the pump, thereby avoiding loss of power. As can be seen in figure 21-18, the curved blades of the added members
21-15
TM 9-8000 turbine Is rotating at very slow speed with the pump rotating at high speed, the torque at the output shaft (attached to turbine) may be several times the torque at the input shaft (attached to the engine).
d. In actual operation, the secondary stator and primary stator are stationary when there is a great difference between pump and turbine speed. At the same time, the secondary pump Is overrunning, or running faster than, the primary pump; the secondary pump does not enter into the converter action at all at this time. The secondary pump Is mounted on a freewheeling or overrunning clutch very similar to the overrunning clutch used in automotive starters (para 23-7). The freewheeling clutch permits the secondary pump to run freely in one direction, but, when it attempts to slow down below shaft speed, it locks on the shaft because the rollers jam between the race and notches in the hub as shown in figure 21-18. However, when the turbine is stopped or turning slowly and the pump is turning rapidly, the direction of oil flow is as shown by the arrows in figure 21-17. As it moves to the secondary pump, it strikes the back sides of the secondary pump vanes, pushing the secondary pump ahead so that it overruns. Under this condition, the secondary pump vanes simply are moving out of the way of the oil. The secondary pump enters the action only when the pump and turbine are turning at about the same speeds, as described below.
e. When the turbine speed Increases due to the application of the torque, so that it turns at more nearly the same speed as the pump, the oil leaves the turbine vanes with less of the reverse direction of motion mentioned above. Consequently, it begins to strike the back sides of the secondary stator vanes so the secondary stator now begins to overrun on its overrunning clutch. It Is no longer needed, and therefore, In effect, it moves out of the way by overrunning or freewheeling.
Figure 21-17. Torque Converter Cutaway so Curvature of Vanes and Oil Flow is Visible.
where it picks up more energy of motion, and then back into the turbine again, that produces the torque multiplication. Each time the oil passes from the pump to the turbine, it gives a push to the turbine. The oil still has energy of motion after it leaves the turbine and is reversed in direction by the stators and secondary pump. When it comes around to the turbine again, it gives more of this push to the turbine. Repeated applications of this push Increases the total push so that, when the 21-16
f. When turbine speed increases to nearly pump speed, as when cruising at steady speed along the highway, the oil leaves the turbine vanes with very little reverse direction of motion. The primary stator also begins to overrun because the oil begins to strike the back sides of its vanes. At the same time, the oil begins to strike the front TA233688
TM 9-8000
h. Because torque converters vary consider- ably In design, the amount of torque multiplication they can achieve also varies. Practical limits seem to be 5:1. Many torque converters provide satisfactory operation with a much lower torque multiplication (some passenger car units provide less than 2.5:1).
i. Many torque converters have oil coolers. Because the oil is subjected to violent agitation and motion, it becomes hot. The oil cooler acts much like the radiator in liquid-cooling systems. As oil passes through the radiator, it gives up heat and emerges at a lower temperature. 21-9. Lockup Torque Converter (Fig. 21-19). Even at normal highway speeds, there is a certain amount of slippage In the torque converter. Some vehicles have a frictional lockup clutch incorporated in their torque converters to eliminate this TA233689
21-17
TM 9-8000
slippage. The principal purpose of the lockup feature Is Increased gas mileage. Another benefit, however, is increased transmission life through the elimination of the heat caused by torque converter slippage. The lockup unit consists of a friction disk that locks the turbine to the
torque converter housing. The friction disk is operated by a hydraulic piston whose pressure is controlled by the automatic transmission control system. The lockup feature usually is designed to operate in high gear at speeds over 35 mph (56 km/h).
21-18
TM 94000
CHAPTER 22
22-1. Change Vehicle Direction. One major purpose of the transmission is to provide the operator with the option of maneuvering the vehicle in either the forward or reverse direction. This is a basic requirement of all automotive vehicles. Almost all vehicles have multiple forward gear ratios, but in most cases, only one ratio is provided for reverse.
22-2. Provide Gear Ratio Selection. Another major function of the transmission is to provide the operator with a selection of gear ratios between engine and wheels so that the vehicle can operate at best efficiency under a variety of driving conditions and loads.
Section II. BASIC TYPES 22-3. Sliding Gear. The sliding-gear type Is known as the conventional transmission. There are two types of sliding-gear transmissions. One Is the progressive, in which the arrangement is such that it is necessary to pass one gear through another In definite order. Thus, In a three-speed progressive transmission, it is Impossible to shift from low to high without going through second. The us of this system Is limited almost entirely to motorcycles. The other sliding-gear type Is known as selective. In this system, the operator can select any ratio without going through intermediate stages. Sliding-gear transmissions use spur gears for easy engagement; consequently, the transmission usually Is noisy when operating in the Intermediate speeds. 22-4. Constant Mesh. The conventional sliding-gear transmission has been superseded, particularly on passenger vehicles, by systems In which the gears always are In mesh with their mates, and selection is made by sliding components In and out of connection. Two of the most common of these systems are the constant-mesh and the synchromesh, which have additional features to prevent clashing of gears.
Section III. SLIDING GEAR TRANSMISSION 22-5. Construction. Conventional transmissions have the following fundamental components: the case, which houses the gears and shafts; the control cover, which houses the shifter mechanism; and the various shafts and gears. Three-speed selective transmissions have three shafts. They are, In the order of the flow of power, the Input shaft, countershaft, and main shaft. The function of the three shafts, together with the gears that connect them, Is discussed in detail below. mediate stages. Sliding-gear transmissions use mesh with the external teeth on the rear of the main drive gear when the gear Is shifted forward into the direct-drive position. The first-and-reverse speed main shaft gear can be shifted forward to mesh with the countershaft first-speed gear or rearward to mesh with the reverse idler gear. The countershaft reverse gear usually is In constant mesh with the reverse Idler gear. In some transmissions, the reverse Idler gear is shifted to mesh with the countershaft reverse gear at the same time that the first-and-reverse speed main shaft gear Is shifted to mesh with the reverse idler gear.
a. Gears. The transmission second-and- third and first-and-reverse speed main shaft gears have grooved hub extensions, Into which the shift forks are fitted that slide them back and forth on the main shaft splines. Thus, the second-and-third speed main shaft gear can be shifted rearward to mesh with the countershaft second-speed gear. The second-and-third speed main shaft gear also has internal teeth that
b. Shafts and Bearings. The Input shaft has an Integral main drive gear and rotates with the clutch driven plate or disks; that is, the shaft rotates all the time the clutch is engaged and the engine Is running. The main drive gear Is In constant mesh with the countershaft drive gear. Because all the gears in the countershaft cluster
22-1
TM 9-8000 are either made Integral or keyed on, they also rotate at the time the clutch is engaged. The transmission main shaft Is held in line with the Input shaft by a pilot bearing at its front end, which allows It to rotate or come to rest independently of the Input shaft. The main shaft, countershaft, and Input shafts, with their respective gears, are mounted on anti-friction bearings (para 19-8) in the transmission case. c. Shift Rails and Forks. Shift rails and forks are provided to move the gears when the control lever Is moved by the driver to change speeds. 22-6. Shifting. The three-speed selective transmission described above Is operated by a control lever assembled to, and extending from, the control housing (fig. 22-1). The lever has a ball fulcrum fitting into a socket In the housing. It Is kept from rotating by a setscrew entering a slot In the side of the ball fulcrum but Is free to move backward, forward, and sidewise. The end of the lever below the ball fulcrum engages both slots, but there Is an Interlock device (usually a ball or pin engaging notches in each shifter shaft) that permits one shifter shaft to move at a time, but not both. This prevents two speeds being engaged at once. When the control lever handle Is pressed to the left, the slot In the first-and-reverse shifter shaft Is engaged and the fork can be moved backward or forward. After the first-and-reverse shifter shaft has been returned to the neutral position, the control lever can be pressed to the right and the second-and-third shifter shaft and fork can be moved forward or backward. The shifter shafts are held In the different speeds and the neutral position by spring-loaded balls or poppets engaging notches In the shifter shafts. 22-7. Power Flow. The following paragraphs describe the power flow of the sliding gear transmission.
TM 9-8000
a. Neutral. The gears are shown in the neutral position in figure 22-2. The input shaft drives the countershaft through the main drive gear and countershaft drive gear. None of the countershaft gears are in mesh with the main shaft sliding gears, however, so the main shaft is not driven. When the gears are in this position, there is no connection between the engine and the driving wheels, so the vehicle remains stationary while the engine is running. The path of transmitted power is shown by the arrows. b. Low Speed. When the gears are in first-speed position, the first-and-reverse speed main shaft gear is shifted forward to mesh with and be driven by the countershaft first-speed gear (fig. 22-3). The countershaft rotates at about 0.7 crankshaft speed. There is a further speed reduction between the countershaft first-speed gear (driving) and the first-and-reverse main shaft gear (driven) of approximately 1.5. There-fore, the crankshaft rotates 1.5 x 1.5, or 2.25 times for each turn of the propeller shaft, thus Increasing the torque on the output shaft by 2.25:1. c. Intermediate Speed. The second-speed position is shown in figure 22-4. In passing from
first to second speed, both sliding gears have been shifted rearward; the first-and-reverse speed main shaft gear has been shifted out of engagement into the neutral position and the second-and-third speed main shaft gear has been shifted into mesh with the countershaft second-speed gear. The input shaft, through its integral main drive gear, is now driving the countershaft through the countershaft drive gear (as is the case in all speeds), and the counter-shaft is driving the main shaft through the countershaft second-speed gear and the second-and-third speed main shaft gear as shown by the arrows (fig. 22-4). Because the countershaft second-speed gear and the secondand-third speed main shaft gear are the same size, their gear ratio is 1:1. This means that the main shaft rotates at the same speed as the countershaft; that is, the engine crankshaft makes about 1.5 revolutions to one of the propeller shaft. d. High Speed. The third-speed, or direct-drive, position of the gears is shown in figure 22-5. In passing from second speed to third speed, the second-and-third speed main shaft gear has been shifted forward, causing the Internal teeth in this gear to engage the external
TM 9-8000
teeth on the main drive gear. A device of this kind, with internal teeth on one member that mesh or engage with external teeth on another member, Is often called a dog clutch, or clutch gear. It makes a direct connection between the input shaft and main shaft as shown by the arrows (fig. 22-5).
e. Reverse. The reverse position of the gears is shown in figure 22-6. To better illustrate the reverse idler gear, the parts have been turned
TM 9-8000
TM 9-8000 Section IV. CONSTANT MESH TRANSMISSION 22-8. Construction. The basic components of the constant mesh transmission are similar to the sliding gear transmission discussed in paragraph 22-5. However, major differences in designs are discussed in the following text. prevent it from moving endwise relative to the gear until the latter has reached the end of its travel. The driven members are the main drive gear and second-speed main shaft gear, each of which has external cones and external teeth machined on its sides to engage the internal cones of the sliding gear and the internal teeth of the sliding sleeve. The synchromesh clutch is shown disengaged and engaged in figure 22-9. The synchromesh clutch operates as follows. When the transmission control lever is moved by the driver to the third-speed or direct-drive position, the shift-fork moves the sliding gear and sliding sleeve forward as a unit until the internal cone on the sliding gear engages the external cone on the main drive gear. This action brings the two gears to the same speed and stops endwise travel of the sliding gear. The sliding sleeve then slides over the balls and silently engages the external teeth on the main drive gear, locking the main drive gear and transmission main shaft together as shown in figure 229. When the transmission control lever is shifted to the second-speed position, the sliding gear and sleeve move rearward and the same action takes place, locking the transmission main shaft to the second-speed main shaft gear. The synchromesh clutch is not applied to first speed or to reverse. First speed is engaged by an ordinary dog clutch when constant mesh is employed, or by a sliding gear; reverse always is engaged by means of a sliding gear. Figure 22-10 shows a synchromesh transmission in cross section that uses constant-mesh helical gears for the three forward speeds and a sliding spur gear for reverse. 22-6
a. Gears. In this type of transmission (fig.22-7), certain countershaft gears are constantly in mesh with gears on the main shaft. The meshing gears on the main shaft are fixed so they cannot move endwise, but they are supported on roller bearings so they can rotate independently of the main shaft. For example, the main shaft assembly of the transmission shown in figure 22-7 is illustrated in figure 22-8 in disassembled view. Note that the main shaft third-speed gear (4) is supported on the shaft by bearing rollers (5). Note also that this gear has internal teeth that match external teeth on the main shaft third-and-fourth-speed clutch gear (1). Usually, helical gears are used in this type of transmission. The first-reverse-and-second gear (10) is a sliding type and, therefore, is a spur gear. b. Synchronizers. The construction of a typical synchromesh clutch is shown in figure 22-9. The driving member consists of a sliding gear splined to the transmission main shaft with bronze internal cones on each side. It is surrounded by a sliding sleeve having internal teeth that are meshed with the external teeth of the sliding gear. The sliding sleeve is grooved around the outside to receive the shift fork. Six spring loaded balls in radially drilled holes in the gear fit into an internal groove in the sliding sleeve and
TM 9-8000
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22-8
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TM 9-8000 CHAPTER 23 AUTOMATIC TRANSMISSIONS Section I. GENERAL OPERATION 23-1. Description (Fig. 23-1). The automatic transmission, like the conventional transmission, is designed to match the load requirements of the vehicle to the power and speed range of the engine. The automatic transmission, however does this automatically depending on throttle position, vehicle speed, and the position of the shift control lever. Automatic transmissions are built in models that have two, three, or foul forward speeds and in some that are equipped with overdrive. Operator control is limited to the selection of the gear range by moving a control lever. 23-2. Coupling (Fig. 23-1). The automatic transmission is coupled to the engine through a torque converter (para 21-7). The torque converter is used with an automatic transmission, mainly because it does not have to be manually disengaged by the operator each time the vehicle is stopped. Because the automatic transmission shifts without any interruption of engine torque application, the cushioning effect of the fluid coupling within the torque converter also is desirable. 23-3. Shifting. Because the automatic transmission shifts gear ratios independent of the operator, it must do so without the operator releasing the throttle. The automatic transmission does this by utilizing planetary gearsets whose elements are locked and released in various combinations that produce the required forward and reverse gear ratios. The locking of the planetary gearset elements is done through the use of hydraulically actuated multiple-disk
TM 9-8000 clutches and brake bands. The hydraulic pressure that actuates these locking devices is controlled by the valve body. The valve body can be thought of as a hydraulic computer that receives signals that indicate vehicle speed, throttle position, and gearshift lever position. Based on this information, the valve body sends hydraulic pressure to the correct locking devices to produce the required gear ratios. 23-4. Operator Controls. The only operator control for an automatic transmission is the gearshift lever although the accelerator pedal also can be considered an operator control because it forces the transmission to shift to a lower ratio when it is fully depressed .
Section II. DRIVE TRAIN MECHIANISMS b. Construction (Fig. 23-2). The multiple-disk clutch is comprised of the following components: a. General (Fig. 23-2). The multiple-disk (1) Disks and Plates. The active clutch, in most cases, is used to transmit torque by components of the multiple-disk clutch are the disks and locking elements of the planetary gearsets to rotating the plates. The disks are made of steel and are faced members within the transmission. in some cases, the with a friction material. They usually have teeth cut into multiple-disk clutch also is used to lock a planetary their inner circumference to positively key them to the gearset element to the transmission case so that it can clutch hub. The plates are act as a reactionary member. 23-5. Multiple-Disk Clutch.
TM 9-8000 made of steel with no facing. They usually have teeth cut into their outer circumference to positively key them inside of a clutch drum or to the inside of the transmission case. By alternately stacking the disks and plates, they are locked together or released by simply squeezing them. (2) Clutch Drum and Hub. The clutch drum holds the stack of disks and plates, and usually is attached to the planetary gearset element that is being driven. The clutch hub usually attaches to the driving member and fits inside of the clutch disks and plates. (3) Pressure Plate. The pressure plates are thick clutch plates that are placed on either end of the stack. Their purpose is to distribute the application pressure equally on the surfaces of the clutch disks and plates. (4) Clutch Piston. The clutch piston uses hydraulic pressure to apply the clutch. Hydraulic pressure usually is supplied to the clutch piston through the center of the rotating member. (5) Clutch Piston Seals. The clutch piston seals serve to prevent the leakage of hydraulic pressure around the inner and the outer circumferences of clutch piston. (6) Clutch Springs. The clutch springs ensure rapid release of the clutch when hydraulic pressure to the clutch piston is released. The clutch springs may be in the form of several coil springs equally spaced around the piston or one large coil spring that fits in the center of the clutch drum. Some models use a diaphragm-type (Belleville) clutch spring.
c. Operation(Fig. 23-3).
(1) Released. When the clutch is released, there is no hydraulic pressure on the clutch piston and the clutch disks and plates are free to rotate within each other. The result is that the clutch hub rotates freely and does not drive the clutch drum. (2) Applied. When the clutch is applied, hydraulic pressure is applied to the clutch piston which, in turn, applies pressure to the clutch disks and plates, causing them to lock together. The result is that the clutch hub drives the clutch drum through the clutch. 23-6. Brake Band.
a. General (Fig. 23-4). The brake band is used to lock a planetary gearset element to the
TM 9-8000
b. Construction (Fig. 23-5). The brake band is comprised of the following elements:
(1) Band. The brake band is a circular piece of spring steel that is rectangular in cross section. its inside circumference is lined with a friction material. The brake band has bosses on each end so that it can be held and compressed. (2) Drum. The drum fits inside of the band and attaches to the planetary gearset element that is to be locked by the band. Its outer circumference is machined smoothly to interact with the friction surface of the band. By pulling the open ends of the band together, the rotation of the drum stops. (3) Anchor. The anchor firmly attaches one end of the brake band to the transmission case. A provision for adjusting the clearance between the band and the drum usually is provided on the anchor. (4) Servo. The servo uses hydraulic pressure to squeeze the band around the drum. The servo piston is acted on by hydraulic pressure from the valve body that is fed through an internal passage through the case. The servo piston has a 23-4
c. Operation (Fig. 23-5). (1) Released. When the brake band is released, there is no hydraulic pressure applied to the servo and the drum is free to rotate within the band.
(2) Applied. When the brake band is applied, hydraulic pressure is applied to the servo which, in turn, tightens the band around the drum. The result is that the drum is locked in a stationary position, causing an output change from the planetary gearset. 23-7. Overrunning (One-Way) Clutch (Fig. 23-8). The overrunning clutch is used in certain automatic transmissions to lock a planetary gearset element to the transmission case so that it can act as a reactionary member. The operation of the overrunning clutch is the same as that of the one used in the torque converter (para 21-7), and it can be of the sprag or roller type. There is no control system necessary for this mechanism. TA233702
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TM 9-8000 23-8. General. Automatic transmissions are built with two, three, and four forward speeds and, therefore, utilize many variations of drive train arrangements. The following paragraphs describe the two most popular arrangements: the compound planetary drive train and the simpson drive train. 23-9. Compound Planetary Drive Train. (1) Neutral. When the gearshift lever is placed in neutral, the clutch and brake bands are released. Because of this there is no reactionary member in the planetary gearset to provide positive drive. Therefore, no torque is transmitted to the output shaft as all of the planetary gearset elements are free to spin around their axes. earlier two-speed drive trains that utilized two separate planetary gearsets.
b. Operation (Fig. 23-8). The compound planetary drive train provides two forward speeds, reverse, and neutral. Power flow in the different gear ranges are as follows:
a. General (Fig. 23-7). This arrangement combines two multiple-disk clutches and one brake band with a compound planetary gearset. The compound planetary gearset is really two gearsets that are integrated together through the use of long and short pinions. Because of the compactness of this unit, it has all but superseded
Figure 23-7. Typical Two-Speed Automatic Transmission Utilizing Compound Planetary Drive Train.
23-6
TM 9-8000
TM 9-8000 (2) Low. When the gearshift lever is placed in low, the direct and reverse clutches are released and the low brake band is applied, locking the low sun gear. Power flow through the drive train is as follows:
(a) From the input sun gear to the long planetary pinions. (b) From the long planetary pinions to the short planetary pinions. (c) The locked sun gear then provides a reaction point so that the planetary pinions and carrier can walk around it, rotating the output shaft.
The result is a speed reduction ratio from the input shaft to the output shaft of about 1.8:1. The low- gear power flow also is used when the gearshift lever is in the drive position before the vehicle attains sufficient speed for the transmission to shift to direct drive. (3) Direct Drive. When the gearshift lever is placed in drive, the transmission is in low gear until the vehicle reaches a speed sufficient to allow the transmission to automatically shift to direct drive. The shift to direct drive releases the low brake band and applies the direct clutch, locking the low sun gear to the input shaft. The reverse clutch remains released. Power flow through the drive train is as follows:
(c) Because the input and low sun gears are both locked, the planetary pinions are locked and unable to rotate. This forces the planetary carrier and the attached output shaft to rotate at a 1:1 ratio with the input shaft. (4) Reverse. When the gearshift lever is placed in reverse, the low brake band and the direct clutch are released. The reverse clutch is applied, locking the internal gear of the planetary gearset. Power flow through the drive train is as follows: (a) From the input sun gear to the long planetary pinions. (b) From the long planetary pinions to the short planetary pinions. (c) The short planetary pinions walk around the inside of the locked internal gear, rotating the planetary carrier and the attached output shaft in the opposite direction of the input shaft. The speed reduction ratio of the input to the output shafts is approximately 1.8:1.
23-10. Simpson Drive Train.
(a) From the input sun gear to the long planetary pinions. (b) From the long planetary pinions to the short planetary pinions.
a. General (Fig. 23-9). This arrangement combines two multiple-disk clutches, two brake bands, an overrunning clutch, and two planetary gearsets operating on a common sun gear. The simpson drive train is the standard for virtually all three-speed automatic transmissions that are currently produced. b. Operation (Fig. 23-9). The simpson drive train provides three forward speeds, reverse, and neutral. Power flow is outlined by the following chart and accompanying text.
KICKDOWN BAND LOW-REVERSE BAND OVERRUNNING CLUTCH
RANGE
GEAR
FRONT CLUTCH
REAR CLUTCH
2-drive 1-low
off off on on on on on on
23-8
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TM 9-8000 (1) Neutral When the gearshift lever is placed in neutral, the clutch and brake bands are released. The input shaft rotates freely and no torque is transmitted to the output shaft. (2) Drive-Low. When the gearshift lever is placed in drive, the automatic transmission will be in low gear when the vehicle is in a speed range of zero to approximately eight miles per hour. In drive-low the rear clutch is engaged, locking the input shaft to the internal gear of the front planetary gearset. Power flow through the drive train is as follows:
(c) Because the sungear is locked, it acts as a reactionary member. This causes the planetary pinions to walk around it and rotate the front planetary carrier, which drives the attached output shaft.
(4) Direct Drive. When the gearshift lever is in drive and vehicle speed is above approximately 25 miles per hour, the automatic transmission normally is in direct drive. In direct drive, both the front and rear clutches are applied, which ultimately results in the locking of the internal gear to the internal gear in the front planetary gearset. This results in the planetary gears being locked and the whole planetary gearset and the attached output shaft rotating at a 1:1 speed ratio with the input shaft. (5) Low. When the gearshift lever is placed low, the power flow through the drive train is identical to that of drive-low described above. The only difference is the use of the rear brake band rather than the overrunning clutch to lock the carrier of the rear planetary gearset. Because the rear brake band prevents the element from rotating in either direction, the drive train is able to provide engine braking during vehicle deceleration with the transmission in low. This contrasts with drive-low, which allows the vehicle to freewheel during deceleration due to the one-way locking of the overrunning clutch. (6) Reverse. When the gearshift lever is in reverse, the front clutch is applied, locking the sun gear to the input shaft. The rear brake band also is applied, holding the carrier of the rear planetary gearset stationary. Power flow through the drive train is as follows:
(a) From the input shaft to the internal gear of the front planetary gearset. (b) From the internal gear to the pinions of the front planetary gearset. (c) Because the front planetary carrier is locked to the output shaft, it cannot rotate backwards and therefore acts as a reactionary member. This causes the planetary pinions to drive the sun gear. (d) The sun gear, which is common to both planetary gearsets, then drives the rear planetary pinions. (e) The rear planetary carrier, which is locked to the transmission case by the over- running clutch, serves as a reactionary member. The rear planetary pinions, therefore, drive the rear planetary internal gear and the attached output shaft at a speed reduction ratio of approximately 2.45:1.
(3) Drive-Second. When the gearshift lever is in drive and the vehicle is between approximately 8 to 20 miles per hour, the transmission normally will be in second gear. In second gear the rear clutch is applied, locking the input shaft to the internal gear of the front planetary gearset. The front brake band also is engaged, locking the sun gear stationary. Power flow through the drive train is as follows:
(a) From the input shaft to the internal gear of the front planetary gearset. (b) From the internal gear to the pinions of the front planetary gearset.
23-11
(c) Because the rear planetary carrier is held stationary, it acts as a reactionary member. The rear planetary pinions, therefore, drive the internal gear of the rear planetary gearset and the attached output shaft in reverse rotation to the input shaft at a speed reduction ratio of approximately 2.2:1.
TM 9-8000 Section IV. SYSTEM HYDRAULIC 23-11. Purposes. The hydraulic system serves four basic purposes:
d. The hydraulic system provides a constant fresh supply of oil to all critical wearing surfaces of the transmission.
23-12. Supply System (Fig. 23-10). The supply system provides a clean pressure-regulated supply of oil for the hydraulic system of the automatic transmission. Early automatic transmissions used a combination of an engine-driven pump that worked in conjunction with an output shaft-driven pump. This configuration no longer is used and, therefore, will not be covered. The operation and construction of a typical system is described below.
a. The planetary holding devices (clutches and brake bands) are all actuated by hydraulic pressure from the hydraulic slave circuits. b. The shifting pattern of the transmission is controlled by the hydraulic system. This is done by switching hydraulic pressure to programmed combinations of the planetary holding devices based on vehicle speed and engine load indicators. c. The hydraulic system circulates the oil through a remote cooler to remove excess heat that is generated in the transmission and torque converter.
a. Hydraulic Pump (Fig. 23-11). The typical hydraulic pump is usually a standard-type internalexternal rotor-type pump (para
TM 9-8000
c. Regulator Valve. The regulator valve controls the pressure of the hydraulic pump so that the hydraulic system of the transmission receives a constant working pressure. The pressure supply received by the hydraulic system is called line pressure. The basic regulator valve is shown in figure 23-10.
(1) Pump pressure is fed to the hydraulic system through the spool valve. The spool is held to the right by a calibrated spring. In this position, the spool closes the port that allows pump pressure to be fed back to the pump suction line. (2) After the pump pressure leaves the spool valve, a portion of it is fed back to the end of the spool valve, opposite to the spring. This pump
d. Modulation of the Regulator Valve (Fig. 23,10). After the pump pressure passes through the regulator valve, it becomes regulated line pressure. In operation, however, automatic transmissions need more than one set line pressure. To accomplish this, additional signals are fed to the regulator to modulate the line pressure for specific purposes. The following
TA233708 23-13
TM 9-8000 considerations are the most common in the modulation of line pressure: (1) Under normal conditions the regulator valve functions in an unmodulated mode as described in paragraph 23-12d. The normal line pressure is sufficient to operate the transmission and still maintain a smooth shifting quality. (2) During periods of heavy acceleration, additional line pressure is required to hold the clutches and brake bands tight enough to transmit the increased engine torque. This is particularly important during the initial application of the elements during shift changes to minimize slip- page during engagement, which would cause burning and premature wear of friction facings. (3) Operation in reverse places additional torque requirements on the clutch or brake band that holds the element of the planetary gearset. For this reason, the line pressure is increased at least twofold during operation in reverse. (4) Any condition that causes a drop below line pressure will cause the regulator valve to temporarily cut off the oil supply to the torque converter. A common occurrence of this condition is the shifting to reverse, which temporarily increases the requirements placed on the pump while the engine is idling and the pump is turning slowly. Modulation of the line pressure is a fairly simple matter. Pressure signals are fed back into the regulator valve to assist the spring. The result is that the line pressure must increase to overcome the higher pressure before the suction feedback port is uncovered. The feedback signals come from the manual valve and the throttle modulation system. 23-13. Converter Feed Circuit (Fig. 23-12). (2) The majority of the heat generated within the transmission originates in the torque converter. It is therefore logical that the oil, after it circulates through the torque converter, should pass directly to the cooler. This arrangement effectively isolates the transmission from this major heat source. (3) One of the major reasons for lubrication within the transmission is to cool the localized areas where heat is generated between moving parts. For this reason, the lubrication of the transmission is handled by the oil after it is passed through the cooler.
b. Oil Supply. The supply of oil for the converter feed circuit passes through the regulator valve (para 2312c). The regulator valve will cut off this oil supply if line pressure drops below an operating minimum. Under normal circumstances, however, the oil pressure cutoff will last no more than a few seconds and will not affect transmission operation. During periods of engine shutdown, the regulator valve also prevents the torque converter from draining back to the oil sump. This condition otherwise would require the pump to refill the converter at each engine restart, creating an unacceptable delay in operation. c. Regulation of Circuit Oil Pressure. The regulator valve supplies the converter feed circuit at regulated line pressure. The converter feed circuit, however, requires a constant pressure that is independent of transmission operating modes and generally lower than line pressure. The converter control valve controls the pressure for the converter feed circuit. The converter control valve is a balance-type spool valve whose operating principles are much like that of the regulator valve (para 23-12c). When operating pressure is low, the calibrated spring pushes the spool to the left, opening the delivery port. As pressure reaches the desired level, the spool is forced to the right, blocking the delivery port. A metered orifice is usually provided between the torque converter and the cooler to control the volume of oil flow through the system. d. Oil Flow Through the Torque Converter. Oil flow through the converter, in most cases, is as follows:
23-14
a. General The torque converter supply, cooling, and lubrication tasks are all handled by the converter feed circuit of the hydraulic system. This integration is a logical one for the following reasons:
(1) All phases of this circuit will function within approximately the same operating pressure range.
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e. Cooler. The cooler is a heat exchanger that is located remotely from the transmission. The following are the most popular configurations:
TM 9-8000 tubing arranged in rows. The rows of tubing pass through a series of fins. As the oil passes through the tubing, its latent heat is transferred to the air via conduction through the fins. This type of cooler usually is located in front of the engine radiator where it is subjected to airflow. This condition is important for its efficient operation. for an automatic shift from first to second gear, but blocks an automatic shift from second to third gear. (2) Vehicle Speed Versus Engine Loading. The shifting of the automatic transmission is controlled by two pressure signals that are indicators of speed and engine loading. These signals, as will be described later in this para- graph, work against each other to produce a shifting sequence. The center of all shift control is the valve body. This unit, which can be thought of as a hydraulic computer, receives information from the indicators described above. Based on this information, the valve body switches line pressure to the proper planetary holding elements to produce the required gear range. As the information changes, the valve body changes its line pressure outputs accordingly. For the sake of simplicity, a two- speed transmission will be used to explain the operation of all of the typical components. A hypothetical, automatic transmission hydraulic system will be constructed in this paragraph . It must be stressed that this hypothetical system by no means contains all of the devices necessary in a real transmission. It is useful for the sake of learning, because it clearly illustrates how the decision and the action of shifting is initiated. b. Manual Valve. The manual valve is the device that selects the desired shift program through the position of the gearshift lever. A manual valve is basically a multiport spool valve that switches line pressure to selected passages as it is moved through its operating positions. A hypothetical manual valve for a two-speed transmission is illustrated in figure 23-14 in all of its operating positions.
f. Lubrication. After the oil is passed through the oil cooler, it is piped through internal passages in the transmission case to the rear section of the transmission where it provides lubrication for components such as the planetary gearsets and the output shaft bearings. The oil then drains back to the sump. (At this time, it should be noted that the oil sump also dissipates heat from the transmission oil and is considered to be a source of transmission cooling.)
23-14. Range Control System (Fig. 23-13).
a. General. The range control system provides automatic or operator-controlled shifting of the transmission. The shifting of the transmission is controlled by the following two indicators:
(1) Manual Selection. The position of the gearshift lever selected by the operator chooses the desired shifting program. The selections available to the operator of a typical two-speed unit are:
(a) Neutral (N). In neutral (N), the engine freewheels, providing no driving force to the vehicle. (b) Drive (D). in drive (D), the transmission provides automatic shifting through the lowto high-gear ranges. (c) Drive-Low (L). in drive-low (L), the transmission is locked in the low range and no automatic shifting occurs. (d) Reverse (R). Reverse (R) reverses the direction of engine torque to drive wheels, and the vehicle is driven backwards. (e) Park (P). Park (P) is the same as neutral except that the drive wheels are locked by a positive latching device within the transmission.
The three-speed transmission has all of the above selections plus drive second. This position allows 23-16
c. Governor. The governor modulates line pressure to produce a signal that is an indication of vehicle speed. This signal is used by the valve body to formulate gear-range selections for the transmission. The governor uses a spool valve that is operated by centrifugally operated weights. The weights are rotated by the output shaft of the transmission because it is solidly linked to the drive wheels and, therefore, consistently provides a true indication of vehicle speed. As the weights rotate they are acted on by centrifugal force which tends to pull them outward from the axis of rotation. The weights are pulled
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TM 9-8000 inward by specially calibrated springs that allow the weights to move from a fully retracted to a fully extended position within a desired output shaft speed range. The spool valve is in a position where all line pressure is blocked when the governor weights are fully retracted. As the weights move outward, the spool valve gradually opens the line pressure port to the governor pressure port. The result is an approximate linear speed and governor pressure increase. A hypothetical governor is illustrated in figure 23-15. A graph showing the typical relationship between governor pressure and speed is shown in figure 23-16. gear position. This is how a forced downshift (passing gear) is initiated. A hypothetical shift valve is illustrated in figure 23-17.
e. Operation. The following subparagraphs describe the operation of a hypothetical hydraulic system for a two-speed automatic transmission in all of its modes of operation. It must be noted that a reverse band rather than a reverse clutch is used in the hypothetical transmission. The reason for this is to allow a wider variety of holding elements to be illustrated.
(1) When the shift lever is placed in neutral (N) (fig. 23-18), line pressure is blocked at the manual valve and none of the frictional elements are applied. (2) When the shift lever is placed in drivelow (L) (fig. 23-19), the manual valve delivers line pressure directly to the low band. The compound planetary gear train (para 23-9) then is in low gear. (3) When the gearshift lever is placed in reverse (R) (fig. 23-20), the manual valve delivers line pressure directly to the reverse band. The compound planetary gear train (para 23-9) then is in low near.
d. Shift Valve. The shift valve is a simple balance-type spool valve that selects between low and high gear when the manual valve is in the drive (D) position. Governor pressure acts on the spool valve in one direction, trying to push the spool towards the highgear position. At the same time, spring pressure modulated by the position of the accelerator pedal tries to push the spool toward the low-gear position. The decision of the shift valve is dependent on which pressure is greater: governor or throttle. The shift valve also contains a device known as a throttle plug. At full throttle the throttle plug makes physical contact with the shift valve spool, forcing it into the low-
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TM 9-8000 (4) When the gearshift lever is placed in drive (D) (fig. 23-21), the manual valve delivers line pressure directly to the low band and to the governor. Because the vehicle is not moving, the governor does not supply pressure to the shift valve and the compound planetary gear train (para 23-9) remains in low gear. (5) As the vehicle begins to move with the gearshift lever in drive, the transmission is in low gear, providing the engine with the necessary mechanical advantage to accelerate the vehicle to speed. As the vehicle speed increases, the governor pressure rises proportionately. When vehicle speed reaches a point where the governor pressure on one side of the shift valve spool can overcome the throttle spring pressure on the other side of the shift valve spool, the spool moves to the direct or high-gear position (fig. 23-22). As the valve spool moves, the shift valve begins to deliver line pressure to apply the direct clutch and release the low band. The low band, so that it can be released while it is still under apply pressure, uses a double-acting servo. The double-acting servo can be released by applying pressure under the piston. The diameters of the piston and the bore of the double-acting servo are stepped so that the pressure under the piston will act on a greater surface area and therefore overcome apply pressure. The application of the direct clutch and the release of the low band place the compound planetary gear train (para 23-9) in high gear or direct drive. The pressure exerted by throttle spring against the shift valve spool increases proportionately as the accelerator is depressed. This in turn will proportionately raise the vehicle speed at which automatic upshifts occur. (6) If a situation arises when quick acceleration is needed, the operator can initiate a forced downshift by pushing the accelerator to the floor (fig. 23-23). This action causes the throttle plug to contact the shift valve spool, forcing it into the low-gear position. This action cuts off line pressure to the direct clutch and the release side of the low-band servo, causing the direct clutch to release as the low band applies. This places the compound planetary gear train (para 23-9) in low gear.
f. Auxiliary Devices. The hypothetical hydraulic system illustrated above is a good learning tool; however, to actually function, many more devices are necessary. The following devices are necessary in addition to the basic operation of the hydraulic system:
(1) Devices called accumulators (fig. 2324) are connected into the pressure supply lines of selected planetary gearset holding elements. An accumulator is a spring-loaded piston that causes line pressure to build gradually when the element is applied. This gives a cushioning effect to its application, resulting in smoother shifting of the transmission. (2) Valves are installed to prevent the transmission from being shifted into reverse during forward movement and to prevent a forced downshift above a predetermined speed. (3) A modulator (fig. 23-25) is used in some automatic transmissions in place of throttle linkage. The modulator is a diaphragm device that uses engine manifold vacuum to indicate engine load to the shift valve. To get an idea of how complicated the hydraulic system really is, a schematic view of an actual hydraulic system is shown in figure 23-26.
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Figure 23-23. Transmission Hydraulic System in Drive (D)- Forced Downshift Range
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24-1. General. Several models of cross-drive transmissions are in use, differing in some details from each other. All, however, operate in a similar manner. This type of transmission is a combination transmission and steering unit for use on tracked vehicles. 24-2. Functions. The cross-drive transmission provides hydraulic drive through a torque converter and contains the planetary gearing, steer-
ing mechanism, braking mechanism, and hydraulically operated clutches. The brakes are foot operated. The forward- and reverse-speed ranges and the steering are selected and hydraulically controlled from the drivers compartment. The transmission mounts crosswise in the vehicle and drives the two tracks through two flanges: the right output shaft flange and the left output shaft flange (right and left facing toward the front of the vehicle).
24-3. General. There are several models of cross-drive transmissions. In general, this discussion will apply to all models of cross-drive transmissions except for the X1100-3B unit, which is covered in chapter 25. Reference should be made to the applicable technical manual whenever a detailed study of a particular crossdrive transmission is made. Figure 24-1 shows an external view of a cross-drive transmission, while figure 24-2 shows the main subassemblies in the transmission. 24-4. Torque Converter. The torque converter is a four-element (or four-member) converter similar to units described in paragraph 21-7. Note the location of the converter units in figure 24-3. The converter contains a pump and turbine plus two stators mounted on the converter ground sleeve by freewheeling clutches. Converter action is shown in figure 24-3. The pump drives the turbine through the medium of oil as described in paragraph 21-8. The stators reverse the direction of oil flow into a helping direction as it comes off the turbine vanes. Action is described below. a. In the first converter phase (A, fig. 24-3), the stators are locked and the oil flow direction is reversed by the action of the two stators. The oil passes from the pump vanes, circulates through the turbine, two stators, and back to the pump. b. In the second converter phase (B, fig. 24-3), the turbine has picked up speed and there is less torque multiplication. The oil leaves the 24-1
turbine vanes at less of an angle and it begins to strike the back faces of the first stator vanes. The first stator thus begins to free wheel. In effect, it is simply moving out of the way. The second stator, however, still is needed to change the direction of oil flow. c. In the coupling phase (C, fig. 24-3), the turbine and pump are revolving at nearly the same speed. The assembly acts like a fluid coupling. Both stators free wheel. Details of torque converter operation are found in paragraph 21-7. d. The converter contains a lockup clutch that engages automatically when the transmission speed reaches a certain value. As this happens, the pump and turbine are locked together and rotate as a single unit. Power, therefore, is transmitted mechanically through the converter and no speed reduction or torque multiplication occurs. 24-5. Planetary Gearing In Gear Ranges. a. General. The cross-drive transmission contains four planetary gear systems: the low- range planetary, the reverse-range planetary, and the two output planetaries. The low- and reverse-range planetaries are located in the right housing of the transmission (fig. 242). At each end of the cross-drive shaft is an output planetary that drives the output flanges. All the planetaries are similar, having four planet pinions and the usual sun gear and internal gear (also called ring
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Figure 24-4. Power Flow through Cross-Drive Transmission in Low Range. (Part A)
together so they turn as a unit and no hydraulic torque conversion occurs. Direct mechanical drive is delivered from the transmission input shaft, through the high-range clutch, to the transmission output. The power path is the same as that shown in figure 24-5, the only difference being that there is no speed reduction or torque Increase in the torque converter. d. Reverse Range. When the driver places the range control valve in reverse, oil pressure is directed to the reverse-range clutch, causing it to engage. The reverserange clutch hub and reverse-range planet carrier are held stationary. This causes the reverse-range planet pinions to rotate in the direction shown in figure 24-6 as they are driven by the reverse-range sun gear. The reverse-range planet pinions, in turn, drive the reverse-range ring gear. Because the reverse-range ring gear is bolted to the right output ring gear (through the low-range planet carrier), the right output ring gear rotates. The crossdrive shaft, being splined to both the right output ring gear and the left output ring gear, carries the rotary motion to the left output ring gear so that both ring gears drive through their respective output planetary systems to drive the two output flanges. Note that the direction of rotation is reversed as compared to the two forward driving ranges (low and high) shown in TA233726
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figure 24-5. This reversal results because the reverserange clutch holds the reverse-range planet carrier stationary as shown In figure 24-6. 24-6. Steering. a. General. Steering Is accomplished through the two steer clutches, the steer differential, and the gearing to the output planetary sun gears. Driving power Is carried to the two steer clutches at all times by the gearing on the converter turbine output shaft. However, when neither of the steer clutches Is engaged and the vehicle Is moving straight ahead or straight reverse (both output flanges turning at the same
24-8 speed and In same direction), no power Is passing through the steering system. But when one of the steer clutches Is engaged, power Is carried through the steering system, and this causes the two sun gears In the two output planetaries to turn In opposite directions. As they turn In opposite directions, they provide opposing rotary motion to the output planetaries. b. Left Steer In Neutral Range. Steering can be accomplished with the transmission In neutral; that Is, with, ,"o power passing through the cross-drive shaft to the output planetaries. With this condition, the low-, high, and reverse- range clutches are disengaged. No driving power TA233727 24-6
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Figure 24.5 Power Flow through Cross-Drive Transmission in High Range. (Part A)
Is being transmitted to the output ring gears. When the left steering valve Is actuated by the driver for left steer, oil pressure Is Introduced Into the left-steer-clutch piston, causing the left- steer clutch to engage. The clutch receives pressure proportional to the amount of steer applied, so that any variation from light to hard left steering will result. With the left-steer clutch engaged, the drive Is from the turbine output shaft, through the leftsteer clutch to the rear differential bevel gear. This bevel gear then drives the two engaged bevel gears in opposite directions, as shown In figure 24-7. These driven bevel gears, therefore, drive the two output sun gears In opposite directions. The output ring gears cannot turn In opposite directions because they are both splined to the cross-drive shaft. The
output ring gears remain stationary and the two sun gears cause the planet pinions to rotate and move around the ring gears, thereby rotating the planet carriers. The right planet carrier rotates In a forward direction and the left planet carrier rotates In the reverse direction, as shown. This causes the right output flange to rotate In a forward direction and the left output flange to rotate Inthe reverse direction. Under the conditions described, which produce left steering, the vehicle pivots to the left. c. Right Steer In Neutral Range. For right steer In neutral range, the low-, high-, and reverse-range clutches are disengaged and no driving power Is being transmitted to the output ring gears. These are the same conditions as TA233728
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Figure 24-5. Power Flow through Cross-Drive Transmission in High Range (Part B)
when a left steer in neutral range is being made. When the right steering valve is actuated by the driver for right steer, oil pressure is introduced into the right-steer-clutch piston, thereby causing the right-steer-clutch to engage as indicated in figure 24-8. As with left steering, the clutch receives pressure proportional to the amount of steering applied so that any variation from light to hard right steering will result. With the right-steer clutch engaged, the drive is from the turbine output shaft, through the right-steer clutch to the differential front bevel gear. This bevel gear then drives the two engaged bevel gears in opposite directions as shown in figure 248. Notice that these two bevel gears are turning in directions that are the reverse of those shown in figure
The two bevel gears drive the two output sun gears in opposite directions as shown, causing the right output flange to rotate in a reverse direction and the left output flange to rotate in a forward direction so that the vehicle pivots to the right. d. Left Steer In Low Range. In low range, the output ring gears are driving the output planet carriers forward so that both output flanges are rotating in a forward direction. When the left steering valve is actuated by the driver for left steering, oil pressure is directed to the leftsteer-clutch piston, engaging the left-steer clutch (fig. 24-9). The clutch receives pressure proportional to the amount of steer applied. When the left-steer clutch engages, driving power Is TA233729 24-8
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slowed down and the left output speeded up, the vehicle steers to the right. f. Right and Left Steer In High Range. Right steer and left steer In high range are identical to right steer and left steer in low range, except that the transmission Is In high range (fig. 24-5). g. Right and Left Steer In Reverse Range. Right steer and left steer In reverse range are identical to right steer and left steer in low range or in high range, except that the transmission is in reverse range (fig. 24-6). 24-7. Hydraulic System. a. General. The hydraulic system and the 24-10
lubrication system use the same oil, operating from a common oil reservoir in the transmission. The oil also circulates through a cooling radiator and helps prevent excessive temperatures in the transmission. The radiator has separate cores for each. Actually, there are two separate radiators, one on each side of the engine, In the application shown. Each has separate cores for engine and transmission oil. The hydraulic system uses two separate valve systems for range and steering control. b. Range Control Valve (Fig. 24-10). The range control valve consists essentially of a cylinder with a series of ports and a cylindrical valve that can be shifted into various positions by operation of the control lever In the driving TA233731
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Figure 24-7. Power Flow through Cross-Drive Transmission during Left Steering in Neutral Range
compartment. When the valve Is shifted, various ports are uncovered so that oil pressure Is admitted, through the oil lines, to the different clutches. Oil pressure cannot be directed to more than one clutch at a time. In neutral, oil pressure Is cut off from the low-range clutch, highrange clutch, and reverse-range clutch so that there is no drive to the output ring gears. However, steering In neutral range can be accomplished by operation of the steering valves as described below . c. Low Range (Fig. 24-10). When the range- control valve is shifted to low range, oil pressure is admitted to the low-range clutch (through line 18). Oil pressure Is cut off from the other range clutches. The low-range clutch engages and the
power flow through the transmission Is as shown In figure 24-4. Note that the low-range line also is connected to a low-range accumulator (through line 19). The accumulator Is a spring-loaded piston In a cylinder. The piston moves to compress the spring as oil pressure Is admitted into the low-range clutch line. This provides a cushioning effect and softens the engagement of the low-range clutch, thereby preventing a sudden and jolting shift. d. High Range (Fig. 24-10). When the rangecontrol valve is shifted to high range, oil pressure is admitted to the high-range clutch (through line 17). Oil pressure is cut off from the other range clutches. The high-range clutch therefore engages, and the power flow through the transmission is as shown in figure 24-5. TA233732
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Figure 24-7 Power Flow through Cross-Drive Transmission during Left Steering in Neutral Range
e. Reverse Range (Fig. 24-10). When the rangecontrol valve is shifted to reverse range, oil pressure is admitted to the reverse-range clutch (through line 20). Oil pressure is cut off from the other range clutches. The reverse- range clutch therefore engages, and the power flow through the transmission is as shown in figure 24-6. f. Steering Valves (Fig. 24-10). The right- and leftsteering valves (1 and 2) are operated by linkage from the drivers compartment. These valves are modulatingtype valves, which means they are not simple open-orclosed valves but can be opened to admit more or less oil pressure to the steer clutches. The driver can vary the
oil pressure to the steer clutches by varying the amount of pressure applied to the steering control. This, in turn, varies the amount of steering obtained. When a left steer is applied to the control, the left-steering valve admits oil pressure to the left-steer clutch to produce a left steer; the power flow through the transmission steering system being as shown in figures 24-7 and 24-9. When a right steer is applied to the control by the driver, the rightsteering valve admits oil pressure to the right-steer clutch to produce a right steer. g. g. Pressure Regulating Valves (Fig. 24-10). The range control valve body also contains TA233733 24-12
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Figure 24-7. Power Flow through Cross Drive Transmission during Left Steering in Neutral Range (Part C)
various pressure regulating valves. Main pressure from the oil pump is admitted to the valve body through line (15). The main-pressure regulator valve (16) prevents excessive pressure while the main-pressure relief valve (14) opens to permit excessive oil to flow back to the oil reservoir. Oil pressure to the converter is regulated by valve (6) while oil pressure to the lubrication system is regulated by valve (7). Valve (11) is a cooler bypass valve that bypasses oil from the lubrication system and is not needed to maintain pressure. Valve (3) is a steeringoverspeed safety valve that prevents excessive pressure to the steer clutches that would result in rapid steering. 24-8. Braking. Each of the two output planetary systems 24-13 includes a friction disk brake assembly (fig. 24-11). Each assembly consists of six internally splined disks splined to the output planet carrier and five externally splined disks splined to the brake anchor. The brake anchor is bolted to the transmission end plate and, there- fore, is stationary. Inside the brake anchor is a brake-apply camstationary ring. Next to the stationary ring is a brakeapply cam-rotating ring. A single brake pedal in the drivers compartment applies both brakes at the same time. When a brake is applied, mechanical linkage causes the brake-apply shaft to rotate. This causes the TA233734
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Figure 24-8. Power Flow through Cross-Drive Transmission during Right Steering in Neutral Range
brake-apply cam-rotating ring to rotate a few degrees, forcing the 12 brake-apply balls to roll up grooved ramps. Because these ramps are located between the two cam rings, the balls force the two rings apart. The stationary ring, being fastened to the anchor plate, cannot move, so the rotating ring must move. This movement cornpresses the disk pack through the brake-apply ring, thereby applying the brake. The same action takes place on both assemblies. When the brakes are released, the brake-apply mechanism rotates the rotating ring back to Its original position so the pressure on the disk pack is relieved
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Figure 24-8. Power Flow through Cross-Drive Transmission during Right Steering in Neutral Range (Part B)
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Figure 24-8 Power Flow through Cross-Drive Transmission during Right Steering in Neutral Range (Part C)
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Figure 24-9. Power Flow through Cross-Drive Transmission during Left Steering in Low Range (Part A)
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Figure 24-9. Power Flow through Cross-Drive Transmission during Left Steering in Low Range
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Figure 24-9. Power Flow through Cross-Drive Transmission during Left Steering in Low Range (Part C)
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Figure 24-10. Range Control Valve and Steering Control Valve Schematic Diagram
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25-1.General. The X1100-3B, a cross-drive transmission, features a hydraulic torque converter combined with a series of planetary gear packages for propulsion, a hydrostatic pump and motor unit with combining planetaries for differential steering control, and Integral power- assisted brakes. Different Input modules are used with the respective engine to Increase versatility. 25-2. Function. The X1100-3B transmission provides hydraulic drive through a locking torque
converter. The transmission offers four forward speeds and two reverse speeds with fully automatic shifting and converter lockup in all modes. All controls to the transmission are initiated by the driver, Including the brake system, which is operated by a foot pedal. The transmission provides a hydrostatic steering system and integral hydraulic brakes.
25-3. General. There are several models of cross-drive transmissions. This discussion will limit itself to the X1100-3B unit; all other models are covered in chapter 24. Figure 25-1 shows an external view of the X1100-3B cross-drive transmission, while figure 25-2 illustrates the b. main subassemblies In the transmission. c. 25-4. Torque Converter. The torque converter used In the X1100-3B is a three-element assembly including a pump, stator, and turbine. The pump assembly Is the Input element and Is driven by the engine. The converter turbine Is the output element and Is splined to the turbine shaft assembly. The stator Is the reaction (torque multiplying) element. A lockup clutch is used in the torque converter. It serves to provide a direct drive from the engine to the transmission. Both converter phase and lockup phase are Illustrated In figure 25-3. Details of torque converter operation are found in paragraph 21-7. 25-5. Planetary Gearing In Gear Ranges. . d. e.
b. Neutral. There are no clutches applied in neutral; therefore, torque produced in the converter Is not transmitted beyond the range Input gear and forward clutch housing. Figure 25-4 illustrates the power flow In the neutral position. c. First Range. In the first range, the forward and first clutches are applied. The first clutch application anchors the rear planetary ring gear against rotation. The forward clutch application locks the range Input gear and main shaft together to rotate as a unit. The rear sun gear Is splined to the main shaft and rotates with it and, In turn, rotates the rear planetary pinions. The pinions are part of the carrier assembly that Is splined to the range output gear. With the ring gear held stationary by the applied first clutch and rear sun gear rotating the pinions, the rear planetary carrier must rotate within the ring gear and drive the range output gear. Figure 25-5 illustrates the power flow In first range. d. Second Range. As the selector is placed in the second range, the forward and second clutches are applied. The second clutch application anchors the carrier of the front planetary assembly against rotation. The forward clutch application locks the range input gear and main shaft together to rotate as a unit. The rear sun gear Is splined to both the rotating main shaft and the center ring gear, and all three parts rotate at one input speed. With the carrier of the front planetary assembly anchored against rotation (by second-clutch application), the rotating
General. The range planetary pack consists of hydraulically applied clutches and planetary gearing which provide the four forward speeds and two reverse speeds. The range pack consists of five clutches and three planetary gear sets. All forward and reverse ranges are engaged by applying two clutches at a time In various combinations. Range shifts are accom- plished by changing the application of a single clutch.
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center ring gear rotates the center sun gear via the planetary pinions. This sun gear is splined to the sun gear shaft assembly to which the front sun gear also is splined. The rotating front sun gear rotates the front carrier pinions whose carrier is anchored against rotating by the applied second clutch. In turn, the rotating front carrier pinions rotate the front ring gear, which, along with the center carrier, is splined, via the front ring gear and rear carrier assembly, to the range output gear. Figure 25-6 illustrates the power flow through the X1100 transmission in second range. e. Third Range. In this configuration the forward and third clutches are applied. The third clutch application anchors the sun gear shaft against rotation, which, in turn, prevents the center sun gear (splined to rear of shaft) from rotating. The forward clutch application locks the range input gear and main shaft together to rotate as a unit. The rear sun gear is splined to both the main shaft and the center ring gear and rotates at range input speed. With the center sun gear
25-2 stationary and the center ring gear rotating, the ring gear drives the center planetary carrier pinions. This rotates the center planetary carrier at a speed reduction. This carrier (and also the rear planetary carrier) is splined to the front ring gear and rotates with it as a unit. The rear carrier is splined to the range output gear which rotates with the rear carrier at the same speed as the center planetary carrier. Figure 25-7 illustrates the power flow in third range. f. Fourth Range. In this configuration the forward and fourth clutches are applied. With the clutches applied, the transmission main shaft and the sun gear shaft are locked together and rotate as a unit at range Input speed. With the center and rear sun gears rotating at the same speed (locked together), and their carriers splined to the front ring gear, all components rotate at range input speed. The transmission range output gear is splined to the rear carrier and gives a range output ratio of 1.00:1. The fourth range power flow is illustrated in figure 25-8. TA233743
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TM 9-8000 CHAPTER 26 AUXILIARY TRANSMISSIONS, SUBTRANSMISSIONS, AND OVERDRIVES Section I. AUXILIARY TRANSMISSIONS 26-1. Purpose. An auxiliary transmission (fig. 26-1) is used to compound the number of gear ratios that are available from the main transmission. It usually is a separate two-speed transmission that mounts in series between the transmission and the driving axle by utilizing two propeller shafts. By providing two speeds, the auxiliary transmission effectively will double the number of gear ratios available from the main transmission. Vehicles equipped with auxiliary transmissions generally are more versatile than vehicles without them because a low-speed range is available for pulling power and a high-speed (direct-drive) range is available for highway usage. 26-2. Operation (Fig. 26-2). The auxiliary transmission is controlled by a lever in the drivers compartment. The gear ratios usually are selected in the box by a sliding dog clutch. The gear ratios of the auxiliary transmission must be selected while the vehicle is not in motion.
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compartment. The manual subtransmission is used in conjunction with a manual or an automatic transmission. b. Automatic. The automatic subtransmission is used by some manufacturers, not as an auxiliary transmission, but as a unit that becomes an integral part of the main transmission. In this configuration, a basic light-vehicle type automatic transmission design is integrated with a subtransmlsslon. The resulting transmission
provides four forward gear ratios and sufficient strength for heavy-duty use. In this case, the subtransmission uses a planetary gearset with hydraulically actuated holding elements whose operating principles are much the same as the drive train of an automatic transmission (para 23-5). The shifting of the subtransmlssion is integrated into the control system of the main transmission and shifting is programmed so that both transmissions function as one.
Section III. OVERDRIVES 26-5. Purpose. A transmission overdrive (fig. 26-4) provides a gear ratio less than 1:1. It reduces engine wear by requiring less revolutions of the engine for a given mileage than required if direct drive is used, and reduces gasoline consumption by providing a more suitable gear ratio for high speeds on level roads. When In operation, the overdrive reduces the engine rear-axle gear ratio by approximately 30 percent. A freewheeling device usually Is Incorporated in the overdrive, which also helps to save gasoline. The overdrive usually Is a separate unit bolted to the rear of the transmission case. In some transmissions, an overdrive is obtained by the gear ratios provided in the transmission. 26-6. Configurations. The overdrive unit sometimes Is Installed in the vehicle as an integral part of the transmission, much like a subtransmission (para 26-4). In other applications, the overdrive unit is located between the transmission and the driving axle, In series with the drive shaft. The configuration Is similar to an auxiliary transmission (para 26-1).
TM 9-8000 26-7. Unit Construction (Fig. 26-5). The basic overdrive unit is a planetary gear-overrunning clutch combination. This combination is necessary in an overdrive unit because the unit must be able to shift while the vehicle is moving. This contrasts with the sliding gears or dog clutches that are used In auxiliary and subtransmissions that can be operated only while the vehicle is not moving. The two factors that control the overdrive modes of operation are: a. The sun gear is locked to or released from the pinion gear cage. This is accomplished by a mechanical linkage from the operators controls that, through a fork and collar, slide the sun gear in or out of mesh with the gear teeth cut into the pinion carrier. b. The sun gear is held stationary or allowed to rotate freely. This Is accomplished by a solenoidoperated pawl that engages a notched plate that is attached to the sun gear. The solenoid is actuated by an electrical control system (para 26-9). Various combinations of the above factors are used to produce the three modes of operation that will be discussed in the next paragraph. 26-8. Operation. The overdrive unit is semi-automatic in operation. When a minimum speed is reached (usually about 25 miles per hour) the overdrive unit automatically will engage if the driver releases the accelerator pedal momentarily. A control lever also is provided that locks out the overdrive unit mechanically. The modes of operation are: a. Locked Out (Fig. 26-5). The locked-out mode of the overdrive is used whenever the use of overdrive is not desired. The locked-out mode is selected by the operator through the movement of an instrument panel mounted lever. The movement of this lever slides the sun gear into mesh with the internal gear teeth in the pinion carrier, resulting in the two members locking together. The locking of the sun gear to the pinion carrier
TM 9-8000 results in the entire planetary gearset rotating as a solid unit. b. Overdrive (Fig. 26-6). When the operator desires overdrive, the control lever is moved to the overdrive position. This lever movement slides the sun gear out of mesh with the pinion carrier, allowing the planetary gearset to operate. The control system of the overdrive unit will semiautomatically select between the two following modes of operation: (1) At speeds below approximately 30 mph, the solenoid pawl is disengaged. This combination results in all planetary gearset members being free to rotate. The result will be direct drive through the roller clutch when engine torque is applied. When the accelerator is released, the roller clutch will retract and the vehicle will freewheel. (2) At speeds above approximately 30 mph (48 kmlh), the solenoid is energized and the pawl tries to engage the sun gear plate. The pawl will be blocked by the bulk ring, however, until the engine power flow is interrupted (the operator momentarily releases the accelerator). As the accelerator is released, the sun gear, which is being driven by the pinions, slows down and reverses direction as the overdrive unit begins to freewheel. This reversal of the sun gear causes it to pull back the bulk ring, allowing the pawl to engage the sun gear plate, locking the sun gear. The locking of the sun gear results in the planetary gearset causing the overdrive effect. 26-9. Overdrive Control System. a. General (Fig. 26-7). The overdrive unit is semiautomatically operated by an electrical control system that is influenced by vehicle speed, throttle position, and the position of the lockout control lever. The following components make up this system: (1) Solenoid. The solenoid, when energized, operates the sun gear locking pawl. Inside the solenoid are two electromagnetic coils: the pull-in and the hold-in coils. The pull-in coil initially actuates the sun gear locking pawl. To do this, the pull-in coil must be very powerful and, therefore, will use a lot of electic current. Because of this, the pull-in contacts are situated to deenergize the pull-in coil when the solenoid is actuated fully. The hold-in coil, which is somewhat lighter, then is utilized to hold the solenoid in the fully actuated position for the duration of overdrive operation. (2) Solenoid Relay. The solenoid relay provides power to the solenoid whenever a signal current is applied to it from the signal circuit. (3) Governor. The governor is a centrifugaltype switch that completes the single circuit to the solenoid relay whenever the vehicle reaches approximately 30 mph (48 kml/h). (4) Rail Switch. The rail switch interrupts the signal circuit whenever the overdrive unit is locked out, preventing engagement. (5) Throttle Switch. The throttle switch interrupts the signal circuit whenever the accelerator is pressed to the floor, allowing the operator extra power. The throttle switch, in conjunction with the ground-out contacts, also will disable the engine temporarily. This interruption of engine power is necessary to allow the locking pawl to disengage from the sun gear wheel. The process of disengaging the overdrive unit by the action of the throttle switch takes only a fraction of a second. b. Reverse Lockout. The linkage of the overdrive lockout mechanism is integrated with the transmission so that the lockout is engaged whenever the transmission is shifted to reverse. This arrangement is necessary because the roller clutch will not drive the vehicle in reverse.
26-5
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TM 9-8000
TM 9-8000 CHAPTER 27 TRANSFER ASSEMBLIES Section I. PURPOSE 27-1. Divided Engine Torque (Fig. 27-1). Transfer assemblies are used in off-road vehicles to divide engine torque between the front and rear driving axles. The transfer case also allows the front driving axle to be disengaged, which is necessary to prevent undue driveline-component wear during highway use. Another purpose of the transfer case is to move the propeller shaft for the front driving axle off to the side so that it can clear the engine. This arrangement is necessary to allow adequate ground clearance and to allow the body of the vehicle to remain at a practical height from the ground. 27-2. High- and Low-Gear Range. The transfer assembly also provides a high and low final drive gear range in the same manner as an auxiliary transmission. In most cases the shifting of the gear ranges is accomplished through a sliding dog clutch and shifting must be done while the vehicle is not moving.
TM 9-8000 Section II. 27-3. General (Fig. 27.2 ). The conventional transfer case provides full-time torque to the rear axle. Torque transmittal to the front axle is selected by the operator through linkage to a floor-mounted lever. Torque transmittal within the transfer case usually is through gears. Some light-duty applications utilize a chain within the case to transmit torque to the front driving axle. Transfer cases that are used in some 6 x 6 vehicles have a separate provision for each driving axle and a provision for the front driving axle. 27-4. Typical Operation (Fig. 27-4). a. High Range. When driving both the front and rear axles in the high range (1:1), the external teeth of the sliding gear (splined to the
1. 2. 3. 4. 5. 6. 7.
MAINSHAFT CONSTANT MESH GEAR MAINSHAFT SLIDING GEAR MAINSHAFT REAR AXLE (REAR UNIT) DRIVE GEAR REAR AXLE (REAR UNIT) DRIVE GEAR ASSEMBLY IDLER SHAFT CONSTANT MESH GEAR IDLER SHAFT
DRIVE SHAFT CONSTANT MESH GEAR REAR AXLE (FRONT UNIT) DRIVE SHAFT DRIVE SHAFT CONSTANT MESH GEAR FRONT AXLE DRIVE SHAFT DRIVE SHAFT SLIDING GEAR IDLER SHAFT LOW SPEED GEAR IDLER SHAFT CONSTANT MESH GEAR
TM 9-8000
transmission main shaft) are in mesh with the internal teeth of the constant mesh gear mounted on this shaft. Likewise, the external teeth of the front-axle sliding gear are in mesh with internal teeth on the constant-mesh gear or the sliding clutches are engaged. Disengagement of the drive to the front axle is accomplished by shifting the sliding gear on the frontaxle main shaft out of mesh with the constant-mesh gear, permitting the latter to roll free on the shaft, or sliding the clutches out of mesh. b. Low Range. When using the low range in the transfer assembly, the sliding gear on the transmission main shaft is disengaged from the constant-mesh gear and engaged with the idler gear on the idler shaft. This reduces the speed by having the sliding gear mesh with the larger idler gear. The shifting linkage on some vehicles is arranged so that shifting into the low range is possible only when the drive to the front axle is engaged. This prevents the driver from applying maximum torque to the rear drive only, which might cause damage.
Figure 27-3. Typical Conventional Transfer Assembly Using Chain Drive for Front Axle.
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TA233764 27-4
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1. 2. 3. 4. 5. 6. 7. 8.
ADAPTER INPUT DRIVE GEAR PILOT BEARINGS RANGE SELECTOR SLIDING CLUTCH RANGE SELECTOR HOUSING LOW-SPEED GEAR BUSHING LOW-SPEED GEAR THRUST WASHER AND LOCATING PIN GASKET, RANGE SELECTOR HOUSING TO INTERMEDIATE HOUSING 9. INPUT BEARING RETAINER 10. INPUT BEARING 11. INPUT BEARING RETAINING RING (LARGE) 12. INPUT BEARING RETAINING RING (SMALL) 13. THRUSTWASHER, LOCATING PIN, LUBRICATING WASHER AND RETAINING RING 14. INTERMEDIATE (CHAIN) HOUSING 15. DRIVE SHAFT SPROCKET 16. GASKET, INTERMEDIATE HOUSING TO DIFFERENTIAL HOUSING 17. SLIDING LOCK CLUTCH 18. DIFFERENTIAL HOUSING 19. REAR OUTPUT FRONT BEARING 20. O-RING, DIFFERENTIAL HOUSING TO REAR OUTPUT SHAFT HOUSING 21. VENT
22. OIL SEAL, REAR OUTPUT FRONT BEARING 23. OIL SEAL, VENT 24. OIL PUMP 25. SPEEDOMETER DRIVE GEAR 26. REAR OUTPUT REAR BEARING 27. REAR OUTPUT SHAFT HOUSING 28. REAR OUTPUT SHAFT 29. WASHER, REAR OUTPUT 30. NUT, REAR OUTPUT 31. RUBBER WASHER, REAR OUTPUT 32. REAR OUTPUT YOKE 33. OIL SEAL, REAR OUTPUT BEARING 34. SHIM PACK 35. INPUT SHAFT O-RING SEAL 36. INPUT SHAFT ROLLER BEARINGS 37. DIFFERENTIAL CARRIER ASSEMBLY 38. SPRING CUPWASHER 39. LOCKOUT CLUTCH SPRING 40. REAR RETAINING RING, DRIVE SHAFT SPROCKET 41. FRONT RETAINING RING, DRIVE SHAFT SPROCKET 42. FRONT OUTPUT REAR BEARING COVER 43. FRONT OUTPUT REAR BEARING 44. FRONT OUTPUT DRIVE SPROCKET 45. GASKET, FRONT OUTPUT REAR BEARING COVER
46. MAGNET 47. DRIVE CHAIN 48. GASKET, FRONT OUTPUT BEA, ING RETAINER 49. FRONT OUTPUT BEARING OUTER RETAINING RING 50. FRONT OUTPUT BEARING 51. FRONT OUTPUT SHAFT SEAL 52. FRONT OUTPUT BEARING RETAINER 53. RUBBER SPLINE SEAL 54. WASHER, FRONT OUTPUT 55. NUT, FRONT OUTPUT 56. FRONT OUTPUT YOKE 57. COUNTERGEAR 58. COUNTERGEAR SPACERS AND BEARINGS 59. COUNTERGEAR SHAFT 60. COUNTERGEARTHRUSTWASHER 61. GASKET, ADAPTER TO SELECTOR HOUSING 62. GASKET, INPUT BEARING RETAINER 63. INPUT BEARING OUTER RING 64. INPUT GEAR BEARING 65. INPUT GEAR SEALS 66. INPUT BEARING RETAINING RING 67. INPUT GEAR 68. INPUT GEAR BEARING RETAINER
TA233765
TM 9-8000 Section IV. POSITIVE TRACTION TRANSFER CASE 27-7. Purpose. Some transfer assemblies contain an overrunning sprag unit (or units) on the front output shaft. On these units, the transfer is designed to drive the front axle slightly slower than the rear axle. During normal operation, when both front and rear wheels turn at the same speed, only the rear wheels drive the vehicle. However, if the rear wheels should lose traction and begin to slip, they tend to turn faster than the front wheels. As this happens, the sprag unit automatically engages so that the front wheels also drive the vehicle. The sprag unit simply provides an automatic means of engaging the front wheels in drive whenever additional tractive effort is required. There are two types of spragunit-equipped transfers: a single-sprag-unit transfer and a double-sprag-unit transfer. Essentially, both types work in the same manner. 27-8. Sprag-Unlt Construction and Operation. a. Transfer Assembly. The transfer assembly is very similar to that described in section II, the basic difference being that a sprag unit has been substituted for the hand-operated sliding clutch on the front output shaft. The sprag unit acts as an overrunning clutch, permitting the front wheels to turn freely at the same speed as the rear wheels, but locking up to drive the front wheels when the rear wheels tend to turn faster than the front wheels (as when the rear wheels lose traction and slip). b. Sprag. A sprag (fig. 27-6) is a steel block shaped to act as a wedge in the complete assembly. In the sprag unit under discussion, there are 42 sprags assembled into an outer race and held in place by two energizing springs (fig. 27-6). The springs fit into the notches in the ends of the sprags and hold them in position. The outer race is in the driven gear on the front output shaft. The inner race is on the front output shaft itself. 27-9. Single-SpragUnit(Fig.27-7). a. Forward. During normal operation, when front and rear wheels of the vehicle are turning at the same speed, the outer race of the sprag unit (in the driven gear) turns a little slower than the inner race (on the front output shaft). This prevents the sprags from wedging between the races. No lockup occurs and the front wheels turn freely; they are not driven. However, if the rear wheels should lose traction and tend to turn faster than the front wheels, the outer race tends to turn faster than the inner race. When this happens, the sprags wedge or jam between the two races and the races turn as a unit to provide driving power to the front wheels. Just as soon as the rear wheels regain traction so that they slow down to frontwheel speed, the outer race slows down in relation to the inner race and the sprag unit releases. b. Reverse. In reverse, it is necessary to lock out the single-sprag unit, because rotation is reversed, and this means that no driving can be achieved through the sprag units at all. Lockout is accomplished through a linkage to the transmission that shifts a reverse-shift collar in the transfer. As the reverse-shift collar is shifted, internal splines in the collar mesh with external splines on the reverse-shift driven gear and on the front output driven gear so there is a solid drive around the sprag unit. 27-10. Double-Sprag Unit. a. Sprag Unit Operation. The double-sprag unit operates the same way as the slngle-sprag unit in forward speeds. In reverse, however, the difference between the two units becomes apparent. In the doublesprag unit, a second sprag unit has been included that comes into operation only in reverse. When the shift is made to reverse, the forward sprag unit is locked out, almost exactly as described in paragraph 27-9 for the single-sprag unit. However, the reverse sprag unit comes into operation. The front wheels drive in reverse when the rear wheels lose traction, and tend to revolve faster than the front wheels. The shift from one sprag unit to the other is accomplished by a linkage to the transmission that shifts a reverse-shift collar in the transfer. As the reverse-shift collar is shifted, internal splines in the collar unmesh from the external splines on the outer race of one sprag unit and mesh with the external splines on the other sprag unit.
27-6
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TA233766 27-7
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Figure 27-8. Air-Control diagram of Transmission and Transfer Assembly using an Air-Controlled Double-Sprag Unit
27-9
TM 9-8000 and causes engagement of the forward sprag unit. When the transmission is shifted into reverse, the air cylinder control valve admits air to the opposite side of the piston, causing engagement of the reverse sprag unit. When the forward sprag unit is engaged, the front wheels will freewheel or turn only in a forward direction. Likewise, if the reverse sprag unit is engaged, the front wheels cannot be turned in a forward direction. Also, if a vehicle with air pressure in the system is parked with the transmission shift lever in neutral position, it cannot be pushed backward until the transmission shift lever is shifted to reverse.
27-10
TM 9-8000
CHAPTER 28 PROPELLER SHAFTS, SLIP JOINTS, AND UNIVERSAL JOINTS Section I. PROPELLER SHAFTS AND SLIP JOINTS 28-1. Propeller Shafts (Fig. 28-1). power to the wheels.
a. Purpose. The power, having been transmitted through an angle by means of a universal Joint, is next carried along the power train by a device known as a propeller, or drive, shaft. Propeller shaft is the most commonly used term; however, either may be used. In amphibious vehicles, both terms are used: propeller shaft, to indicate the device that transmits power to the propeller; and drive shaft, to Indicate that which transmits
b. Construction. Propeller shafts may be solid or tubular. The torsional stress In a shaft varies from zero at the axis to a maximum at the outside. Because the center of the shaft resists only a small portion of the load, hollow shafts are used wherever practicable. A solid shaft is somewhat stronger than a hollow shaft of the same diameter,
TM 9-8000
but a hollow shaft is much stronger than a solid shaft of the same weight. 28-2. Slip Joints(Fig. 28-1).
shaft.
a. Purpose. Because flexing of the springs causes the axle housing to move forward and backward, some provision must be made to allow the propeller shaft to contract and expand. A device known as a slip joint provides the necessary telescopic action for the propeller
b. Construction. A slip joint consists of a male and female spline, a grease seal, and a lubrication fitting. The male spline is an integral part of the propeller shaft and the female portion is fixed to the universal joint directly behind the transmission or transfer case. As the axle housing moves forward and backward, the slip joint gives freedom of movement in a horizontal direction and yet is capable of transmitting rotary motion.
Section II. CONVENTIONAL UNIVERSAL JOINTS 28-3. Purpose (Fig. 28-2). A universal joint is a flexible coupling between two shafts that permits one shaft to drive another at an angle to it. It is flexible in the sense that it will permit power to be transmitted while the angle between the shaft is being varied continually. A simple universal joint is composed of three fundamental units consisting of one journal and two yokes. The two yokes are set at right angles to each other, and their open ends are joined by the journal. This construction permits each yoke to pivot on the axis of the journal and also permits the transmission of the rotary motion from one yoke to the other. As a result, the universal joint can transmit the power from the engine through the shaft to the drive axle, even though the engine is mounted rigidly in the frame at a higher level than the axle, which is constantly moving up and down in relation to the frame. 28-4. Characteristics of Operation (Fig. 28-3). A peculiarity of the conventional universal joint is that it causes a driven shaft to rotate at a variable speed in respect to the driving shaft. It has been found that there is a cyclic variation, in the form of an acceleration and a deceleration of the speed, twice during each revolution. The extent of such fluctuation depends on the amount of angularity, roughly about 7 percent for an angle of 15 degrees, and about 30 percent for an angle of 30 degrees. This fact is shown graphically in figure 28-3, where the variations of the angular velocity during one revolution of a shaft driven through a conventional universal joint are plotted. The driving shaft is running at a constant velocity of 1,000 rpm, and the angle between the shafts is 30 degrees. Sketches of the universal joint positions at the minimum and maximum velocity fluctuation points are placed above the corresponding portions of the curve to enable the reader to correlate the curve with the action of the universal joint yoke and journal. a. In a quarter of a revolution, the speed of the driven shaft varies from a minimum of 866 to a maximum of 1,155 rpm. The speed of the driven shaft equals that of the driving shaft at four points during the revolution; that is, 45, 135, 225, and 315 degrees, where the curve intersects the constant velocity (dotted) line. The extent of each fluctuation depends on the size of the angle between the shafts; the greater the angle, the greater the variation in the speed of the two shafts.
b. This variation of velocity cannot be eliminated with a simple universal joint, but its effect can be minimized by using two universal joints, one at each end of the shaft. If only one joint is used between the transmission and the rear axle, the acceleration and deceleration caused by the joint is resisted on one end by the engine and on the other end by the inertia of the vehicle. The combined action of these two forces produces great stress on all parts of the power train and, in addition, results in a nonuniform force being applied to the wheels. When two universal joints TA233770 Figure 28-2. Typical Universal Joint.
28-2
TM 9-8000
b. Ball and Trunnion. Two universal joints of the ball-and-trunnion type are used in an application, one on each end of the propeller shaft. This type of joint is shown in C, figure 28-4. There is a trunnion pin through the end of the propeller shaft. The pin is fitted with balls that ride in grooves in the flanged body. The balls are assembled on bearings so they can rotate with little friction. Compensated springs at each end of TA233771
a. Journal-Type Universal Joint. There are several variations of this type of universal joint, two of
28-3
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TM 9-8000
the propeller shaft hold it in a centered position. Variations in length are permitted by the longitudinal movement of the balls in the body grooves, and angular
displacement is allowed by outward movement of the balls on the trunnion pins. This type of universal joint is recognized easily by the flexible dust boot that covers it.
Section III. CONSTANT VELOCITY JOINTS 28-6. Characteristics of Operation. driving engagement will, at all times, bisect the angle between the driving and the driven shaft. 28-7. Types.
a. The speed fluctuations caused by the conventional universal joints described in paragraph 28-5 do not cause much difficulty in automotive propeller shafts where they have to drive through small angles only. In front-wheel drives where the wheels are cramped up to 30 degrees in steering, velocity fluctuations present a serious problem. Conventional universal joints would cause hard steering, slippage, and tire wear each time the vehicle turned the corner. Constant-velocity universal joints, which eliminate the pulsations, are used exclusively to connect the front axle shaft to the driving wheels.
b. The conventional universal joint produces velocity fluctuations because the journal connecting the two yokes does not allow free movement other than a pivoting action. Velocity fluctuations occur because the journal tilts back and forth (wobbles) as the joint rotates. This tilting movement is translated into rotary movement and, when the journal tilts toward the output shaft, it adds to the speed of the output; and when the journal tilts away from the output shaft, it subtracts from the speed and the output shaft rotates slower than the input shaft. The only time that the speeds of the two shafts are equal is when the journal lies in the plane that bisects the angle between the two shafts. As stated in paragraph 28-5, this occurs only four times during each revolution.
c. It can be seen that a universal joint transmitting constant velocity must be designed to permit the point of driving contact between the two halves of the coupling to remain in a plane that bisects the angle between the two shafts. If this is accomplished, some arrangements must be made for the points of the driving contact to move laterally as the joint rotates. Keeping this in mind, it will be easier to understand the principles of constantvelocity joints that are in universal use today. Three types used in Army vehicles are: Rzeppa, Bendix-Weiss, and Tracta. These types are discussed separately to show that, in all, a plane passed through the points of the 28-5
a. Rzeppa (Fig. 28-5). The Rzeppa joint is a ballbearing type in which the balls furnish the only points of driving contact between the two halves of the coupling. The details of the component parts, adapted for use in a front driving axle, are shown In figure 28-5. The inner race (driving member) is splined to the inner axle shaft; the outer race (driven member) is a spherical housing that is an integral part of the outer shaft; the ball cage is fitted between the two races. The close spherical fit between the three main members supports the inner shaft whenever it is required to slide in the inner race, relieving the balls of any duty other than the transmission of power. The movement of the six balls is controlled by the cage. The cage positions the balls in a plane at right angles to the two shafts when the shafts are in the same line. A pilot pin, located in the outer shaft, moves the pilot and the cage by a simple leverage in such a manner that the angular movement of the cage and the balls is one-half the angular movement of the driven shaft. When the driven shaft is moved 20 degrees, the cage and the balls move 10 degrees. As a result, the balls of the constant-velocity universal joint are positioned from the top view, to bisect the angle formed. b. Bendix-Weiss (Fig. 28-6). The Bendix-Weiss joint also uses balls that furnish points of driving contact, but its construction differs from that of the Rzeppa in that the balls are a tight fit between the two halves of the coupling and no cage is used. The center ball rotates on a pin inserted in the outer race, and serves as a locking medium for the four other balls. The driving contact remains on the plane that bisects the angle between the two shafts, but it is the rolling friction between the four balls and the universal
TM 9-8000
TM 9-8000
1. 2. 3. 4. 5. 6.
HUBCAP DRIVE FLANGE SCREW FRONT WHEEL BEARING CUP WHEEL BEARING SPINDLE BRAKE DRUM WHEEL BRAKE CYLINDER
7. BRAKE LOCKING PLATE 8. KINGPIN BEARING CUP 9. KINGPIN 10. OIL SEAL 11. BENDIX-WEISS UNIVERSAL JOINT 12. WHEEL SPINDLE BEARING THRUST WASHER
KINGPIN LOCKPIN WHEEL BEARING SPINDLE BEARING BRAKE SHOE ANCHOR PIN HUB OIL SEAL HUB BOLT NUT FRONT WHEEL BEARING CONE
TM 9-8000
and the plane in which the balls lie will be reduced to 80 degrees, fulfilling the requirement that the balls must lie In the plane that bisects the angle of drive.
c. Tracta Joint (Fig. 28-7). The Tracta universal joint is the simplest to Install and service. It is, in effect, one universal joint within another, with points of driving contact on the outer portions of the Joint. This universal Joint consists of four main parts: a forked driving shaft, a forked driven shaft, a female (or slotted) Joint, and a male (or spigot) Joint. The complete Inner Joint, consisting of the female Joint and the male Joint, floats between the forks; movement between the Individual halves of the Inner Joint is permitted In a direction perpendicular to that permitted by the slotted forks, by the action of the spigot moving In the slot. With this arrangement, the points of driving contact are allowed to move as the universal joint rotates, thereby
remaining in a plane that bisects the angle between the two shafts. The fork ends subtend an angle greater than 180 degrees so as to be self-locking once the joint is assembled to the inner parts of the joint. A flat surface is milled on the cylindrical section of the joint to permit the Joint to be Inserted in place.
d. Double Cross and Roller (Flg. 28-8). The double cross and roller Joint uses two cross and roller Joints in tandem to form a single joint. The joints are linked through a centering yoke that works In conjunction with specially designed, spring-loaded centering ball. The components are contained within the center coupling yoke. As the shaft rotates, the action of the centering ball and yoke act to maintain an equally divided drive angle between the connected shafts, resulting In a constant drive velocity.
TM 9-8000
TM 9-8000
CHAPTER 29 DIFFERENTIALS, FINAL DRIVES, AND DRIVING AXLES Section I. CONVENTIONAL DIFFERENTIALS 29-1. Purposes (Fig. 29-1). bevel drive pinion rotates the bevel drive ring gear and the differential case to which the final drive gear is bolted. The axle shafts are splined to the differential side gears. Were it not for the differential pinions, each wheel, with its respective axle shaft and side gear, would rotate freely with respect to the differential case and bevel drive gear.
a. Transmit Torque to Axles. One of the purposes of the differential is to transmit engine torque to the drive axles. The drive axles usually are on a rotational axis that is 90 degrees different than the rotational axis of the propeller shaft. b. Divide Engine Torque. Another purpose of the differential is to divide engine torque between the driving wheels so that they are free to rotate simultaneously at varying speeds. This is important particularly if the vehicle is not moving in a straight line.
29-2. Principles of Operation (Fig. 29-2). The
a. Straight Ahead. When both wheels are rotating at the same speed, as they do on a smooth, straight road, the differential pinions do not rotate around their own axis but serve only to
TM 9-8000
b. Turns. When the wheels rotate at different speeds, as they do when making a turn, the slowing down of the inner wheel decreases the rotation of its axle shaft and differential side gear with respect to the differential drive ring gear and the differential case. The case forces the differential pinions to rotate along the inner differential side gear, advancing the opposite side gear an equivalent amount with respect to the differential case. The outer wheel thus turns at a higher speed than the inner wheel. If the differential drive ring gear makes four revolutions while the inner wheel is making one, the outer wheel will rotate seven times.
29-3. High-Traction Differential Gears (Fig. 29-3). A fault in the conventional differential is that if one driving wheel loses traction and spins, the other wheel, which has more traction, remains stationary and does not drive the vehicle. In order to overcome this, several devices have been employed from time to time. One device is the hand-controlled differential lock. This is a dog clutch, controlled by a hand lever, that clutches one 29-2
TM 9-8000
Section II. NO-SPIN DIFFERENTIALS 29-4. Purpose. To provide a means of improving tractive effort at the driving wheels when one wheel tends to slip from loss of traction, It is necessary that the differential prevent actual slippage and supply torque to the driving wheels only to the extent that the wheels can utilize the torque without slipping. The no-spin differential does this by using various types of clutches between the driving axles. 29-5. Sprag-Type No-Spln Differential (Fig. 294). The sprag-type no-spin differential does not contain pinion gears and side gears as does the conventional differential. Instead, it consists essentially of a spider attached to the differential drive ring gear through four trunnlons, plus two driven clutch members with side teeth that are indexed by spring pressure with side teeth In the spider. Two side members are splined to the wheel axles and, In turn, are splined into the driven clutch members. clutch member remains fully engaged with the spider clutch teeth. The spider clutch teeth (the driving teeth) drive the right (inside) wheel at differential drive ring gear speed. The left wheel (outside) covers a greater distance and must turn faster than differential drive ring gear speed. The differential must permit this action because, as the left wheel begins to turn faster, the leftdriven clutch member also turns faster than differential drive ring gear and spider speed. As the left-driven clutch member begins to turn faster, the cam lobes or ramps on its edge ride up on the cam lobes on the center cam. This action pushes the left-driven clutch member away from the spider so the clutch teeth disengage. As the crest of the ramp is passed, spring pressure forces the teeth of the driven clutch member back Into full engagement with the teeth on the spider. But the action is repeated as long as the left wheel turns more rapidly than the right wheel. Full drive is applied to the right wheel; no drive is applied to the left wheel. But as soon as the vehicle completes the turn and the left wheel slows down to right wheel speed, driving power is applied equally to TA233779
a. Operation in Turning. The center spider is held in place by a snap ring that center cam to rotate but does not permit laterally. When making a right turn, the
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both. For a left turn, the action is similar except that full drive is applied to the left wheel; the right wheel turns more rapidly than the left wheel.
b. Tractive Effort. With this differential, one wheel cannot spin because of loss of tractive effort and thereby deprives the other wheel of driving effort. For example, one wheel is on ice and the other wheel is on dry pavement. The wheel on ice is assumed to have no traction. However, the wheel on dry pavement will pull to the limit of its tractional resistance at the pavement. The wheel on ice cannot spin because wheel speed is governed by the speed of the wheel applying tractive effort.
29-6. Silent-Type No-Spin Differential (Fig. 295). In the silent-type no-spin differential, the construction is very similar to the unit described above. However, the center cam has wider teeth to carry the two sets of cams in each driven clutch member. One set is fixed, the other is able to rotate in one direction or the other a few degrees with respect to the fixed set. The rotatable or holdout cam ring is slotted, and a key in the spider fits this slot to limit the independent rotation of the cam. The key also limits the rotation of the center cam. In operation, when one wheel is turning faster than the other (as in rounding a turn), the faster-turning splined side member and driven clutch member cause the ramps on the center cam and driven clutch member cam to push the driven clutch member away from the spider. This action is similar to that described above for the
other no-spin differential. The teeth are separated so that no driving can take place. In this unit, however, the teeth do not index repeatedly because the rotatable cam, left slightly behind, prevents this. The ramps on the rotatable cam are halfway between the ramps on the fixed cam of the driven clutch member. The staggered ramps will not permit teeth engagement. As soon as the turn is completed, the driven clutch member slows down to spider speed, the ramps realign, and teeth engagement takes place. Where a vehicle has a tandem driving axle unit or multiple axles, a no-spin differential may be placed in the transfer case between the output shafts to the driving axles. The differential prevents loss of tractive effort from slippage or tractive loss of one set of wheels. Also, it tends to balance torque and prevents interaxle trapped torque, which reduces total tractive effort. 29-7. Clutch-Type No-Spin Differential.
a. General. The clutch-type no-spin differential uses friction clutches to lock the axles together whenever one drive wheel experiences uncontrolled slippage. The clutch configurations that are used commonly are the cone or the multiple plate type. b. Multiple Plate Clutch Type (Fig. 29-6). This type of no-spin differential uses four side gear pinions on two shafts that are at right angles to each other. The shafts, which are V-shaped on
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their ends, engage similar V-shaped slots In the differential case. Each side gear is backed by a series of multiple disk clutches. Operation is as follows:
situated between the side gears to wedge the clutches into the case. In a straight-ahead (1) Straight Ahead. position, the axle shafts will turn at the same speed, and operation virtually will be the same as a conventional differential. (2) Around Comers. Around a corner, the Inner drive wheel must slow down. The unequal speed between the side gears will cause the side gear pinions to walk around the side gears. This walking will cause the outer axle shaft to rotate faster than the differential case. Because the cones have spiral grooves cut Into their clutch surfaces, the Inner cone clutch will draw Itself Into the case and lock tight and the outer cone clutch will back itself out of the case and allow the outer drive axle to freewheel. The end result is the majority of the engine torque being sent to the Inner drive wheel.
Ahead (A, Fig. 29-6). (1) Stralght Whenever the differential case attempts to rotate the side gears through the side gear pinions and shafts, the shafts will slide up their V-shaped ramps and exert outward pressure. This outward pressure will tend to lock the side gears to the differential case through the clutches.
(2) Around Corners (B, Fig. 29-6). As the vehicle turns a corner, the Inner drive wheel must slow down. The unequal speed between the side gears will cause the side gear pinions to walk around the side gears. This walking will cause the outer axle shaft to rotate faster than the differential case, allowing the pinion shaft on that side to slide down Its ramp. This releases the outer clutches, causing the differential to act like a conventional unit.
(3) Slippage of One Wheel. If one wheel loses traction, all engine torque will be transferred
c. Cone Clutch Type (Flg. 29-7). The cone clutch no-spin differential uses two spirally grooved cones that fit into the housing. These cones fit behind the side gears and are splined to the axle shafts. Coil springs are
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immediately to the opposite wheel via the cone clutches. (4) Slippage of One Wheel in Reverse. Because the spiral grooves that are cut into the cone clutches are directional, the cone clutch no-spin differential will not work in reverse because the cone clutches will unscrew themselves from the case, causing the no-spin feature to be inoperative. Section III. 29-8. Overview. 29-9. Gear Drives.
b. The gear ratio of the bevel gear final drive is found by dividing the number of teeth on the bevel drive gear by the number of teeth on the pinion. For a worm gear, it is found by dividing the number of teeth on the worm gear by the number of threads on the worm. In the case of chain drives, the sprockets are considered gears, and the number of teeth on the driven sprocket is divided by the number of teeth on the driving sprocket.
a. A final drive is that part of a power transmission system between the propeller shaft and the differential. Its function is to change the direction of the power transmitted by the propeller shaft through 90 degrees to the driving axles. At the same time, it provides a fixed reduction between the speed of the propeller shaft and the axle driving the wheels. In passenger cars, this speed reduction varies from about 3:1 to 5:1. In trucks, it varies from about 5:1 to 11:1.
a. General (Fig. 298). All the final drives in general use are geared. The most common of these consists of a pair of bevel gears; that is, a drive pinion connected to the propeller shaft and a bevel drive gear attached to the differential case on the driving axle. These bevel gears may be spur, spiral-bevel, or hypoid. Spur gears have straight teeth, while spiral-bevel and hypoid
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gears have curved teeth. Spur gears are used very little for this purpose because they are noisy. Spiral-bevel gears are used most often. Hypoid gears are used in several passenger cars and in light trucks because they permit the bevel drive pinion to be placed below the center of the bevel drive gear, thereby lowering the propeller shaft to give more body clearance. This gear also operates more quietly. Worm gears are used extensively in trucks because they allow a large speed reduction. These consist of helical worm, similar to screws, and meshing teeth gears. The worms have single, double, triple, or quadruple threads. These type gears are shown in figure 29-8. Internal gear drives were once popular and still are used in rare instances. They permit a large speed reduction like the double chain drive, which they resemble. A jackshaft is driven by the propeller shaft through bevel gears and the differential as it is in the double-chain drive, except that the jackshaft is mounted on the dead rear axle and parallel to it. Spur pinions keyed on the ends of the jackshaft drive internal gears attached to the wheels. The first gear reduction takes place in the bevel pinion and differential drive ring gear and the second in the internal gears.
b. Worm (Fig. 29-9). The worm gear rear axle is used in some trucks because it allows a large speed reduction. The threads on the worm are similar to screw threads and may be single, double, triple, or quadruple. The worm meshes with a worm gear having helical teeth cut in its outside circumference. The worm may be compared to a screw and the worm gear to a nut. As the worm rotates, it pulls the worm gear around. The worm usually is made of steel and the worm gear of bronze. The driving worm may be mounted at either the top or the bottom of the worm gear. But, usually it is necessary to place the worm at the top in order to allow sufficient road clearance under the rear axle housing. The rear worm bearing must be very strong and rugged because it takes the entire thrust reaction from driving the worm gear. If play develops in the worm because of wear, this bearing also must withstand repeated impact. When the vehicle is operated in reverse, or when the road wheels are driving the mechanism, the front bearing resists these forces. Sometimes a worm of hourglass form is used in the worm gear as it provides more tooth bearing surface and, consequently, less stress in the teeth.
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c. Hypoid (Fig. 29-10). Hypoid gearing has come into rather extensive use recently, mainly for passenger cars. A portion of a hypoid rear axle is shown in figure 29-10. This rear axle is almost the same as the spiralbevel gear rear axle, except that the drive pinion and bevel drive gear are cut with a somewhat different tooth form, which permits the drive pinion to mesh with the bevel drive gear below the center of the latter. This construction allows the propeller shaft to be lowered and sometimes makes a shaft tunnel in the floor of the rear compartment of the vehicle unnecessary. Due to their design, hypoid gears operate under extremely high tooth pressure and require a special hypoid lubricant.
29-10. Live Axle Configurations.
axle shafts are supported in the housing by roller bearings at the center and outer ends. The rear wheels are keyed on tapers at the outer ends of the axle shafts and held by castle nuts and cotter pins. In addition to turning the wheels, the rotating axle shafts carry the entire weight of the rear of the vehicle on their outer ends. All stresses caused by turning corners, skidding, or by wobbling wheels are taken by the axle shafts. The differential side gears are keyed on the inner ends of the axle shafts, which carry the weight of the differential case. The stresses created by the operation of the differential are taken by the axle shafts. Side thrust on the axle shafts is taken care of by the roller bearings, and ball bearings are provided at each side of the differential case to take care of end thrust. This type of rear axle is obsolete now.
a. General. A live axle is one that supports part of the weight of a vehicle and also drives the wheels connected to it. The term is applied to the entire assembly, which consists of a housing containing a bevel drive pinion, bevel drive gear differential and axle shafts together with their bearings, and sometimes additional mechanisms. The term live axle is opposed to the term dead axle. A dead axle is one that carries part of the weight of a vehicle but does not drive the wheels. The wheels rotate on the ends of the dead axle. The usual front axle of a passenger car is a dead axle and the rear axle is a live axle. In four wheel drive vehicles, both front and rear axles are live axles, and in six-wheel drive vehicles all three axles are live axles. b. Plain (A, Fig. 29-11). The plain, or nonfloating, rear axle was one of the first used. In it, the
c. Semifloating (B, Fig. 29-11). The semi-floating rear axle is used on most passenger and light commercial vehicles. The principal difference between it and the plain live axle is In the manner of supporting the differential assembly. In the plain live axle, the differential case Is carried on the Inner ends of the axle shafts. In the semifloating axle, it is carried by bearings mounted in the differential carrier. The axle shafts are splined to the differential side gears. This relieves the axle shafts of the weight of the differential and the stresses caused by its operation that are taken by the axle housing. The Inner
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d. Three-Quarter Floatlng (C, Fig. 29-11). The three-quarter floating rear axle is used on a few passenger cars. The Inner ends of the axle shafts sometimes are secured with nuts and the axle shafts cannot be withdrawn without removing the differential cover. In other designs, the axle shaft can be withdrawn after the nuts holding the hub flange have been removed. The wheels, however, are supported by bearings on the outer )ends of the axle tubes. The housing, Instead of the axle shafts, carries the weight of
29-11
e. Full Floating (D, Fig. 29-11). The full-floating rear axle is used on most heavy trucks. It is the same as the three-quarter floating axle, except that each wheel is carried on the end of the axle tube on two ball or roller bearings and the axle shafts are not connected rigidly to the wheels. Each wheel is driven through a dog clutch, through a spline clutch, or through a flange on the end of the axle shaft that is bolted to the outside of the wheel hub. The latter construction is used frequently but is not truly full floating, because there is a rather rigid connection between the axle shaft and the wheel hub. With the true full-floating axle, the axle shaft transmits only the turning TA233787
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effort or torque. The stresses caused by turning, skidding, and wobbling of the wheels are taken entirely by the axle housing through the wheel bearings. The axle shafts can be removed and replaced without removing the wheel or disturbing the differential. Most military all-wheel drive trucks have full-floating axles.
runs on roller bearings at each end; these also are mounted in the differential carrier. The spur pinion drives a spur gear that is bolted to the differential case. The usual design is the full-floating axle configuration (para 29-10e).
f. Independent Suspension (Fig. 29-12). Live axles that are made to work with independent suspension usually are arranged so that the differential carrier is fixed to the chassis. The axles then are connected to it through constant velocity joints (para 286) so that the wheels are free to travel with the suspension. g. Double Reduction (Fig. 29-13). Double reduction rear axles often are used for heavy-duty trucks. The first gear reduction is obtained through a spiral-bevel pinion and gear as in the common single-reduction rear axles. The bevel pinion runs in brackets mounted on the differential carrier in two roller bearings. The bevel gear is mounted rigidly on a jackshaft with a spur pinion that
h. Dual Ratio (Fig. 29-14). Dual-ratio, or twospeed, rear axles sometimes are used on trucks and passenger cars. They contain two different gear ratios that can be selected at will by the driver, usually by a manual-control lever. A dual-ratio rear axle serves the same purpose as the auxiliary transmission described previously. Like the latter, it doubles the number of gear ratios available for driving the vehicle under the various load and road conditions. This type of rear axle is shown in a cross-sectional view in figure 29-14. It is driven by the conventional spiral-bevel pinion and differential drive ring gear, but a planetary gear train is placed between the differential drive ring gear and differential case. The internal gear of the planetary train is bolted rigidly to the bevel drive gear. A ring on which the planetary gears are pivoted is bolted to the differential case. A
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i. Double Reduction, Dual Ratio (Fig. 29-15). Double-reduction, dual-ratio rear axles also are sometimes used in heavy-duty motor vehicles. Rear axles of this type combine the features of the doublereduction and dual-ratio axles in one unit. A spiral-bevel pinion drives a TA233789
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k.
/. Interwheel DIfferential. One of the latest developments In front-wheel drives is dual wheels having an Interwheel differential that makes them easily steerable. Each wheel is equipped with Its own brake. Vertical steering knuckle pivots are used. The differential is of the spur gear type, the pinions having a tooth form that gives It the same action as the hightraction differential described In paragraph 29-3. When
29-15
(1) The forward rear axle is of the full-floating, double-reduction type having a spiral-bevel pinion and gear for the first reduction, and a spur pinion and gear for the second reduction. The spiral-bevel pinion is driven through a power divider, which also drives the rearward rear axle through a shaft that passes through the pinion of TA233791
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the forward rear axle, and is attached to the forward end of the interaxle drive shaft. (2) The power divider is attached to the forward end of the gear carrier, which is mounted on the upper side of the axle housing. Both forward and rear axles are driven from the forward drive flange through the power divider by means of a driving cage carrying two parallel rows of radial wedges or plungers engaging at their outer ends with internal (female) cams on a cage that drives the bevel pinion of the forward rear axle. At their inner ends, the plungers engage with external (male) cams on the interaxle drive shaft, which drives the bevel pinion of the rear axle. Due to the wedging action between the cams and the plungers, they rotate together with no relative movement, unless running condition require a differential action. (3) Whenever either the forward or the rear pair of wheels tends to run ahead of the other pair, due to slippage or uneven road surfaces, there is a relative movement of the external and internal cams, which is permitted by the sliding of the radial plungers in the driving cage. This restricted movement provides a differential action that divides the driving effort to the two pairs of wheels to provide the maximum tractive effort. The wheel spindles are pressed into the axle housing, and the brake assemblies are carried by integral flanges. The underslung springs, which tie the two rear axle housings together in parallel relation, are attached by means of rubber shock insulators set in sockets on the bottom of the housing, and retained by caps. (4) A ball-joint torque rod, between the top of the gear carrier housing and a chassis frame crossmember, takes the torque conveyed to the axle assembly by the driving and braking.
As in the case of rear live axles, the axle housings usually are built up, but they may be pressed steel for light vehicles and single-piece castings for heavy-duty vehicles. The split-type housing frequently is used. The principal difference between front live axles and rear axles is that in front-wheel drives, provision must be made for steering. In rear driving axles, the axle shafts are connected directly to the wheels. Because the front wheels must turn on the steering knuckle pivots, they usually are driven by the axle shafts through universal joints (para 28-7) concentric with the steering knuckle pivots. Figure 29-17 shows the housings of the steering knuckle pivots and constant-velocity universal joints, as well as the tie rod, brakedrums, hub flanges, and wheel mounting studs for a typical front live axle assembly. (2) A type of front-wheel drive that drives the front wheels through gearing and permits them to steer without the use of a universal joint is shown in figure 2918. It has been used to a very limited extent. A spiralbevel pinion keyed to the end of the axle shaft drives the lower half of a double bevel gear on the lower end of the steering knuckle pivot. The top half of the double gear meshes with a fourth gear that is integral with the wheel hub. The gear and hub turn on the steering knuckle. When the wheels are cramped, the bevel gear on the wheel hub rotates around the bevel gear on the steering knuckle pivot. (3) Constant-velocity universal joints, used with front-wheel drives to avoid strain on the steering mechanism, are discussed in chapter 28.
m. FourRear-WheelDrives.
(1) Motor vehicles that carry extremely heavy loads often are equipped with four rear wheels in order to increase traction and to avoid excessive weight on the rear tires; that is, the weight of the load is divided among twice as many tires as when only one rear axle is used. Dual wheels generally are used with this arrangement; therefore, the weight of the rear of the vehicle and load is divided among eight tires instead of four. (2) Different spring suspensions are used, but the bogie is most general. A bogie consists of two axles joined by a trunnion axle. The trunnion
I.
(1) In four- or six-wheel drives, the front wheels are driven through a driving axle assembly very similar to a rear axle. It may be of the single or double-reduction type. Figure 29-17 shows a usual arrangement of transfer assembly, propeller shafts, universal joints, driving axles, and springs for a four- or six-wheel drive vehicle. Front-wheel drives ordinarily are Hotchkiss drives with the front springs pivoted at the rear and shackled at the front. Axles are of the full-floating type. 29-17
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Figure 29-17. Front Live Axle Assembly and Four-Wheel Drive Installation.
29-18
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Section IV. CONTROLLED DIFFERENTIAL 29-11. Purpose. The controlled differential is used in tracked vehicles for: (a) Transmitting engine torque to the tracks. (b) Steering of the vehicle through the controlled use of side-to-side braking. 29-12. Construction (Fig. 29-21 and 29-22). The controlled differential is, in reality, two different assemblies having left and right units joined by the differential carrier. Each side consists of a brakedrum, a sun gear, three external pinions, three internal pinions, and one compensating gear. 29-13. Operation (Fig. 29-21 and 29-22). When the vehicle is moving straight ahead, the entire differential assembly turns as a unit and transmits equal power and speed to each track through the final drive. When the left brake band is applied to the brakedrum, the left compensating gear is retarded and rotates slower than the differential carrier, while the right compensating gear is speeded up and rotates faster than the differential carrier. As each compensating shaft is splined to each compensating gear, the final analysis will result in the left track revolving slower than the right track, causing the vehicle to turn to the left. Exactly the reverse procedure takes place if the right brake is applied.
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1. OIL MANIFOLD 2. RIGHT COMPENSATING CASE COVER 3. 4. 5. 6. COMPENSATING CASE LEFT COMPENSATING CASE COVER SMALL PINION BEARING DIFFERENTIAL FINAL DRIVE SHAFT GEAR
13. STEERING BRAKEDRUM 14. STEERING BRAKEDRUM FLANGE LARGE PINION BEARING 15. COMPENSATING CASE COVER EXTERNAL GEAR BEARING OIL SCREEN 16. FINAL DRIVE SHAFT BEARING STEERING BRAKESHOE 17. DIFFERENTIAL FINAL DRIVE SHAFT
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Section V. WHEEL VEHICLE PERFORMANCE 29-14. General. There are many different aspects of vehicle performance. Miles per gallon of fuel, miles per hour in first, second, or other gear ratio, and the amount of weight a vehicle can carry are all commonly considered factors. Other factors of equal importance include tractive factor, grade ability, and drawbar pull. These three factors refer to less-known performance aspects that should be considered further. 29-15. Performance Factors. 79 x 36.7 x 0.85 factor of the 1/4-ton, 4 x 4 truck at maximum gear reduction and unloaded. Unloaded, the vehicle weighs 2,625 pounds. The engine torque is 79 ft lb. The gear reduction in the transmission in low gear is 2.798:1; in the transfer in low range, 2.43:1; and in the differentials, 5.38:1. Total gear reduction is 36.7:1, in low range, low gear. Tire radius is 1.25 feet, unloaded; and slightly less, loaded. However, use the figure 1.25 feet for ease of figuring. Substituting all this data in the formula gives:
a. Tractive Factor.
(1) Tractive factor refers to the pushing effort the wheels can make against the ground as a result of the application of torque to them through the power train from the engine. Actually, the tractive factor is given in pounds-of-push for each pound of vehicle weight. Tractive factor can be determined by the following formula: ET x R x 0.85 Tractive factor = GW x TLR where ET and R = = Engine torque from dynamometer tests, with at least distributor water pump operating (ft lb). Gear ratio at reduction under consideration. Efficiency of power transmission (arbitrarily chosen as an average value). Gross vehicle weight (lb). Tire loaded radius (ft).
= 0.75.
(3) This figure means the tires can exert a push against the ground of 0.75 pound for every pound of vehicle weight. If the tires do not slip, the vehicle can be pushed forward 0.75 pound for every pound of vehicle weight.
b. Grade Ability.
(1) Grade ability refers to how steep a grade the vehicle can climb. Grade, itself, is referred to in percent: a 10-percent grade, or a 26-percent grade, for example. A 1-percent grade rises 1 foot in every 100 feet. A 26percent grade rises 26 feet in every 100 feet. If the tractive factor is known, the grade ability can be easily figured by use of the formula: Grade ability = (Tractive factor - 0.015) x 100 where 0.015 equals rolling resistance per pound of vehicle weight (arbitrarily chosen as an average value). (2) Figure the maximum grade ability of the 1/4-ton, 4 x 4 truck for which calculated the tractive factor (maximum) was 0.75. Substituting in the formula would give: Grade ability = (0.75 - 0.015)x 100 = 0.735 or 73.5 percent. (3) The truck, unloaded and in low range, low gear, could go up a 73.5-percent grade; that is a grade that rises 73.5 feet every 100 feet. it can be seen that the grade ability of a vehicle will vary with the load and the gear ratio. It will decrease as
0.85 =
GW TLR
= =
(2) Figure the tractive factor of a 114-ton, 4 x 4 utility truck. This can be determined in any gear, and with the truck loaded or unloaded. The tractive factor will increase with increased gear ratio, and will decrease as the vehicle is loaded. Generally, the tractive factor is figured with maximum payload because this gives an indication of the vehicle performance under the most adverse conditions. However, calculate the tractive 29-24
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c. Drawbar Pull.
(1) The drawbar pull is an indication of how much the vehicle can pull on a trailer attached to it. Drawbar pull can be calculated if the tractive factor and weight on powered wheels are known by use of the following formula: Drawbar pull = Tractive factor x weight on powered wheels. (2) In the vehicle under discussion (1/4-ton, 4 x 4 truck), it was determined that the maximum tractive factor was 0.75 with a vehicle weight of 2,625 pounds. Because all wheels are powered, multiplying these two figures together gives the drawbar pull, or 0.75 x 2,625 pounds equals 1,970 pounds. That is, the vehicle can
produce a maximum drawbar pull of 1,970 pounds (provided, of course, that no wheels slip). Note that, if the vehicle itself is loaded, it will tend to increase the drawbar pull; however, at the same time, loading the vehicle reduces the tractive factor. If, for example, a 1,000-pound load were added to the vehicle, giving a gross weight of 3,625 pounds, the tractive factor would drop to approximately 0.55. This, times 3,625 pounds, gives a maximum drawbar pull of approximately 1,970 pounds. For a vehicle having all-wheel drive, the drawbar pull is a constant, regardless of the weight carried by the vehicle. Note that the term maximum has been used here; this means that the vehicle could supply this amount of pull. However, in actual performance, the vehicle is not required to supply this amount of drawbar pull. The applicable technical manual for any vehicle specifies the maximum trailer load to be attached. The 1/4-ton, 4 x 4 truck under analysis, for example, has a maximum limit of 2,000 pounds trailer load on the highway (1,500 pounds cross country).
29-25/(29-26 blank)
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PART FIVE CHASSIS COMPONENTS CHAPTER 30 SUSPENSION SYSTEMS IN WHEELED VEHICLES Section I. OVERVIEW 30-1. Purpose. The suspension systems main purpose is to support the weight of the vehicle. Military vehicles, which are often very heavy and must be able to cross all types of terrain, depend heavily on their suspension systems. In wheeled vehicles, the suspension must not only be effective over a wide range of speed and land conditions, but also must allow for steering geometry and changes in terrain. In tracked vehicles, such as a tank, the suspension system must support the vehicle so that the immense weight will not sink down, even in soft ground. The suspension system also must absorb bumps and jolts. 30-2. Spring Configurations.
a. Leaf Springs. Leaf springs usually are semielliptical in shape and are made of high quality alloy steel. There are two types of leaf springs. The single leaf spring, or monoleaf (A, fig. 30-1), is a single layer spring that is thick in the center and tapers down at each end.
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Single leaf springs generally are used on lighter suspension systems that do not have to carry great loads. A multileaf spring (B, fig. 30-1) is made up of a single leaf with additional leaves attached to it using spring clamps. The additional leaves make the spring stiffer, allowing it to carry greater loads. As a multileaf spring operates, there is a friction generated between the leaves, causing it to have a dampening quality. These types of springs may not require the use of a shock absorber in some applications. The multileaf spring uses a frictional material laminated between the leaves to reduce wear and eliminate any squeaks that might develop. To keep the leaves equally spaced lengthwise, the multileaf spring uses a center bolt. The center bolt rigidly holds the leaves together in the middle of the spring, pre- venting the leaves from moving off center. Leaf springs are attached to the vehicle using a bracket usually mounted rigidly to the frame in the front, and a shackle in the rear, which allows the spring to expand and contract without binding as it moves through its arc.
springs, are frictionless and require the use of a shock absorber to dampen vibrations. Their cylindrical shape requires less space to operate in. Pads sometimes are used between the spring and chassis to eliminate transferring vibrations to the body. Coil springs are not able to absorb any torque when employed in the suspension system. Therefore, control arms and stabilizers are required to maintain the proper geometry between the body and suspension system (fig. 30-2).
b. Coil Springs. These springs usually are made of round spring steel wound into a coil (fig. 30-2). Because of their simplicity, they are less costly to manufacture and also have the widest application. Spring stiffness is changed on coil springs by toughening them. Coil springs, like torsion bars and volute (or spiral-shaped)
c. Torsion Bars. The torsion bar consists of a steel rod usually made of spring steel. It is treated with heat or pressure to make it elastic, so it will retain its original shape after being twisted. Torsion bars, like coil springs, are frictionless and require the use of shock absorbers. The torsion bar is serrated on each end and is attached to the torsion bar anchor at one end and to the suspension system at the other (fig. 30-3). Torsion bars are marked to indicate proper installation by an arrow stamped into the metal. It is essential that they be installed properly because they are designed to take stress in one direction only. The elasticity of the rod is utilized and as long as the elastic limit is not exceeded, the torque resistance will return the suspension to its normal position in the same manner as a spring arrangement.
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a. The Hotchkiss drive is the conventional front and rear live axle suspension that once was used exclusively in American military vehicles. In this drive, a propeller
TM 9-8000 poor riding qualities, thereby limiting vehicle mobility. However, this drive system is in extensive use because of simplicity, low cost, and ruggedness. An advantage of the Hotchkiss drive is that the flexible connection between axle and frame throws less strain on the driving mechanism than do other types. When sudden loads are applied, as in suddenly engaging the clutch, the axle housing can rock around the drive shaft slightly, which cushions the shock transmitted through the driving mechanism and reduces the load between the teeth of the final driving mechanism. The suspension springs are shackled at both ends. In a torque tube drive, both the torque reaction and the driving thrust are resisted by the torque tube. Because the suspension springs do not resist the torque reaction and drive thrust, they can be made more flexible and give better riding qualities than a Hotchkiss drive. In a torque tube drive, the driving thrust is applied to the frame at the engine mounting or at a frame crossmember. In a torque rod or Hotchkiss drive, the force is applied at the suspension springs. The torque tube drive seldom is used in contemporary designs.
b. The torque tube drive, while not common on heavy military vehicles, is used on a limited number of passenger and light commercial vehicles. In this type of drive, the propeller shaft (drive shaft) is housed in a steel tube called the torque tube (fig. 30-5). The rear end of the torque tube is bolted rigidly to the rear axle housing by means of a flange. Its front end is connected to the transmission or a frame crossmember by means of a ball-and-socket joint. One universal Joint is used in the propeller shaft and is located at the ball-and-socket Joint of the torque tube. A slip Joint is placed in the propeller shaft to take up end play arising when the driven axle moves up and down. A center bearing generally is used to support the drive shaft in the torque tube.
Two suspension system radius rods are used to connect the outboard ends of the axle housing with the transmission end of the torque tube. This will keep the axle housing alined at right angles to the torque tube.
c. The torque arm drive rarely is used. It consists of a solid or tubular arm, rigidly connected to the driving axle housing at its rear end and to a frame crossmember, through a ball-and-socket Joint or spring bracket, at its front end (fig. 30-6). An open propeller shaft is used on a torque arm drive. The torque arm drive is similar to the torque tube drive. The main difference is that it uses an open propeller shaft running parallel to the torque arm, instead of a drive shaft housed within a torque tube. d. Coil Spring and Control Rod Drive. This type of live axle suspension commonly is used in modern vehicles. In this configuration (fig. 30-7), the coil springs are placed between the axle housing and the frame. Their sole purpose is to support the weight of the vehicle. All torque reaction due to accelerating and braking and all
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e. Dead Front Axle. The dead front axle (fig. 30-8) supports the vehicle weight and resists the torsional
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TA233804 30-6
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Figure 30-10. Driven Parallel Wishbone Coil Spring Front Suspension. 30-7
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universal joints are necessary in the power shafts of this design, because the swinging-arm pivot axis is out of line with the power shaft. The pivot axis, however, does pass through the inboard universal joint to minimize the relative sliding motion of the splined coupling. 30-8. MacPherson Struts. The MacPherson suspension system uses a tubular strut, which houses the shock absorber mechanism and links the wheel and body together (fig. 30-13). The strut usually is surrounded by a coil spring attached to the top of the strut, which is mounted to the body. The lower half of the spring is mounted by a flange that is attached to the bottom half of the strut, which is mounted to the spindle or control arm. There are also other types of configurations in which the spring is mounted next to the strut; this type makes replacement of the strut relatively easy. 30-9. Comparison. The development of the independent suspensions came about mostly to reduce the unsprung mass, thereby improving the handling and traction of high-speed road cars. However, the demand for greater speed and mobility for military vehicles warrants the use of independent suspension on such vehicles. In addition to the improved performance associated with reduced unsprung mass, the use of independent suspensions increases the speed and mobility of the military vehicle by reducing front end vibration (wheel shimmy and axle tramp), permitting the use of softer suspension springs, providing more ground clearance, and permitting more optimum wheel spacing. The disadvantages of independent suspensions for military vehicles are primarily those of cost and
Section IV. HEAVY VEHICLE SUSPENSION 30-10. Springs. Several configurations of spring suspension have been used for vehicles that carry widely varying loads, to provide the necessary variable load rate. if the secondary spring is secured to the frame. From that point on, the two springs carry the load jointly and their load ratings are added. This allows the vehicle to carry heavy loads without deflecting the mainsprings.
a. Auxiliary springs, often called secondary springs (fig. 30-14), commonly are used in addition to the mainspring to accomplish this purpose. When the load on the spring reaches a certain amount, the deflection of the mainspring brings the free ends of the secondary spring against bearing plates on the frame, or on the axle
30-9
b. Another method of suspension that also provides a spring with variable load rating is shown in figure 3015. The spring is made with flat ends that bear against curved bearing plates.
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energy of the road shock, rather than just one end. Thus, the effect of road shocks is cut in half. When only one axle is deflected up or down from its normal loaded position, the trunnion axle and the vehicle frame are
raised or lowered half this amount. In this manner, bogie axles reduce by half the impact or shock not only to the vehicle, but also to the road.
Section V. AIR-OVER-HYDRAULIC SUSPENSION 30-13. Purpose. The air-over-hydraulic suspension system is designed to keep the body level under different loading conditions. When the vehicle weight is increased, either by adding cargo or passengers, the body will become lower to the ground. The leveling system then will sense a low condition and allow pressure to increase in the special shock absorbers, raising the body with respect to the ground. When the weight is removed, the system will allow air pressure to bleed from the air shock absorbers, restoring the vehicle to its normal riding height. 30-14. Components of Air-Over-Hydraulic Suspension. the intake valve is opened by the linkage, allowing pressure to increase in the shock absorber. This, in turn, raises the vehicle to its normal position. As soon as the vehicle is level, the intake valve closes and a steady pressure is maintained in the shocks. When weight is removed from the vehicle, the linkage opens the exhaust valve and pressure is released in the shocks, restoring the vehicle to a normal riding position. The linkage also is dampened through the use of a fluid to prevent the control valve from reacting to bumps and changes in road conditions.
a. Air Compressor. The air compressor (fig. 3017) is commonly a vacuum-operated two-stage unit requiring no lubrication. The sliding distributor valve directs intake manifold vacuum alternately to the right or left side of the diaphragm, moving it from side to side. When the diaphragm, which is connected to a double piston, moves to the right, it allows air to enter the first stage chamber. At the end of the stroke, the check valve on that chamber closes, and the distributor valve diverts the vacuum to the opposite side of the diaphragm. As the piston then moves to the left, the air in the first stage moves through the air passage in the center of the piston to the second stage chamber. At the end of that stroke, the check valve on the air passage closes and, as the piston moves to the right again, the check valve on the second stage cylinder opens, allowing the compressed air to enter the air reservoir tank. As pressure in the reservoir tank builds up to a predetermined amount, it puts an equal force on the second stage piston and the pumping action stops. b. Pressure Regulator Valve. This component (fig. 30-18) regulates the air pressure to the height control valve to a predetermined amount, regardless of the pressure in the reservoir. The valve is nonadjustable and must be replaced if proper pressure is not maintained.
c. Height Control Valve. This valve (fig. 30-19) is attached to the frame of the vehicle, and linkage is used to attach the valve to the suspension system. When the frame moves downward because of additional weight, 30-12
1. VACUUM LINE 2. DIAPHRAGM 3. PISTON 4. CHECK VALVE 5. FIRST-STAGE HOUSING 6. CHECK VALVE 7. SECOND-STAGE END OF PISTON
8. AIR PASSAGE 9. SECOND-STAGE CYLINDER 10. CHECK VALVE 11. SECOND-STAGE HOUSING 12. AIR RESERVOIR TANK 13. SLIDING DISTRIBUTOR VALVE 14. ARM
Figure
30-17. Air
Compressor.
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Section VI. SHOCK ABSORBERS 30-16. Purpose. The primary function of the shock absorber is to regulate the suspension spring rebound so that the primary vibrations are damped out, thereby permitting greater vehicle speeds and mobility. These benefits are achieved by virtue of reduced bouncing and pitching of the body or hull and reduced variations of the traction with the terrain. Additional benefits derived from the use of shock absorbers are: improved ride quality, reduction of wheel dance, prevention of excessive sidesway, reduction of wheel shimmy, and general improvement of the desirable vehicle traveling qualities, collectively termed roadability. 30-17. Classification of Shock Absorbers. 30-18. Types of Shock Absorbers. the spring is being extended from the position to which it was compressed by the vertical impact. There is some disadvantage in this arrangement when the moving vehicle hits a hole. The spring extends so that the ground-contacting elements can maintain good contact with the ground. The high damping force exerted by the shock absorber interferes with this action, resulting in a downward acceleration of the vehicle body. This is an acceptable condition, because the downward acceleration of the sprung mass cannot exceed the acceleration of gravity because no other downward force is acting on the sprung mass.
a. Single Acting. Shock absorbers are of two general classes: single acting and double acting. Those that check only spring rebound are termed single acting. They are so designed, or attached to the suspension system in such a manner, that the damping force is not generated during spring deflection. Their main disadvantage is that they provide damping only part of the time, imposing the requirement of stiffer springs in the system. Also, a slight preload on the suspension spring is experienced due to the shock absorber return spring. This has a tendency to stiffen the suspension spring out of proportion for mild terrain irregularities. b. Double Acting. Those shock absorbers that provide damping during spring deflection as well as during rebound are termed double acting. They permit the use of softer suspension springs and allow optimum damping in both directions. In most cases, the damping force developed by the double-acting shock absorber during spring compression is much lower than is developed during rebound. This is desirable because a high damping force during spring compression would have the same effect on impact isolation as would a very stiff spring; that is, it would transmit the shock to the vehicle body, causing it to displace vertically. It is desirable not to interfere with the impact-isolating properties of the spring during its compression stroke, because there is no upper limit to the amount of acceleration that the vehicle body can experience when the ground-contacting elements pass over a vertical obstacle at high speed. For this reason, the larger damping force is exerted during rebound; that is, when
30-14
a. Single Acting, Cam Operated. A typical singleacting, cam-operated shock absorber is shown in figure 30-21. When the sprung and unsprung masses of the suspension system move toward each other, the shock absorber arm rotates counterclockwise, moving the cam to the right, thereby permitting the piston spring to move the piston to the right. This causes the intake valve in the piston to open, allowing oil to flow from the reservoir into the increasing cylinder volume. Because the piston motion and oil flow are caused by the piston spring, the shock absorber has little effect upon the spring action of the vehicle. During rebound, the cam moves to the left, forcing the piston to the left against the oil in the cylinder. The intake valve closes, and the oil in the cylinder is forced out through the relief valve. The restricted passage of the oil through the relief valve orifice is the primary factor in generating the damping force during rebound. b. Vane Type. The housing of the vane-type shock absorber, shown in figure 30-22, is divided into two working chambers by stationary partitions, each of which contains a check valve. The central shaft is connected to the unsprung mass through the arm and link, and has a pair of vanes attached to it that extend into each working chamber. As the suspension spring is compressed, the central shaft rotates, and the vanes develop a pressure in the chamber that causes oil to flow unrestricted through the opened check
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c. Direct Acting. The direct-acting shock absorber (fig. 30-23) consists of an inner cylinder filled with a special shock absorber oil, divided into an upper and lower chamber by a double-acting piston. The shock absorber is mounted by studs and rubber bushings inserted through the eye on each end so that it is acted directly upon by spring action. The piston push rod, therefore, is forced up and down within the inner cylinder. A reservoir that contains an ample supply of oil surrounds the inner cylinder and is joined to it by a reservoir check valve. When the vehicle spring is compressed, the piston is forced down, and some of the oil below the piston is forced through compression valves (only one is illustrated in figure 30-23) inside the piston to the upper chamber. These valves operate only on the downstroke. Because the push rod moves into the cylinder on the downstroke, some of the oil in the lower chamber is forced through the check valve at the bottom of the cylinder into the reservoir.
When the vehicle spring rebounds, the piston is moved up, and oil from the upper chamber is forced into the lower chamber through spring-loaded rebound valves inside the piston. These valves control the rebound of the vehicle spring.
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Section VII. AUXILIARY UNITS 30.19. Torque Arms. When power and brake effort are applied, there is a tendency for the entire axle and spring assembly to rotate. To prevent this, strengthening arms are added to the axles. These are known as torque arms, torque rods, and torque tubes. The function of these three is the same, the major difference being that the torque tubes connect with the power train, whereas the other two connect with the frame of the vehicle. Parallel torque arms (fig. 30-6), used between axles in bogie suspensions, ensure correct spacing and alinement of the axles, prevent transfer of weight from one axle to the other (or the tendency of one axle to dig in more than the other), and help to avoid uneven tire wear and Jumping axle when brakes are applied. 30-20. Swaybars. A vehicle tends to roll outward when turning, particularly at high speeds. To prevent this roll, swaybars or stabilizers (fig. 30-9) are used. The swaybar consists of a bar of alloy steel mounted across the chassis and secured to the frame through rubber bushings with arms on each end connected to the axle or TA233813 30-16
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independent suspension arms. When one side of the vehicle rises faster than the other, the twist set up on the swaybar reacts on the axle or independent suspension arms, tending to keep the frame level. If both sides rise equally, no twist is set up in the swaybar. 30-21. Pusher Axle. The pusher axle (fig. 30-24) is a nondriving axle. It is used in Conjunction with the standard suspension to increase the load-bearing capabilities of larger vehicles. The axle is raised and lowered by the operator using controls located inside the cab.
It is operated by varying air pressure in air suspension bags, mounted between the axle and the frame. The air bags serve to lower the pusher axle, force the axle against the road, and distribute loads evenly between wheels. Because of a lack of inherent dampening capabilities, shock absorbers also are used with the pusher axle. The shock absorbers stabilize fluctuations in the air bags caused by road surface characteristics. Air cylinders are used to raise the axle, and chains are used to secure the axle in a stowed position when not in use.
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CHAPTER 31 SUSPENSION SYSTEMS IN TRACKED VEHICLES Section I. PRINCIPAL PARTS 31-1. Springs. wheels also have been developed, thus aiding in the reduction of the vehicles weight. Solid rubber tires are laminated to the road wheels to absorb the shocks as the vehicle moves. This also serves to quiet the interaction between the road wheel and track. There is also a space between the road wheel that provides a channel in which the track center guides travel. The center guides aline the track and serve to keep it on the vehicle. 31-3. Idler Wheels and Track Support Rollers. Idler wheels, mounted on an arm assembly, are installed at the front of the vehicle (fig. 31-4). These assemblies are linked to the front road wheel support arms by track adjusting link assemblies. As the front road wheel support arm is moved upward by a bump or obstruction, the track adjusting link assembly swings the compensating idler arm towards the front to take up the slack in the track. The track adjusting link assembly may be lengthened or shortened to adjust the amount of track tension. The track support rollers hold up the returning track and prevent excessive sag. They may be rubber coated to reduce noise and help minimize vibration. The number of track support rollers that is used on a vehicle depends upon the type and length of track to be supported.
a. Volute. The volute spring (fig. 31-1) consists of a wide strip of steel, tapered both in width and in thickness, wound to form a distorted spiral. Each coil overlaps the adjacent coil, with the widest and thickest part having the greatest diameter. The spring usually is wound so that adjacent coils rub, thereby producing frictional forces that tend to damp out oscillations. As the spring is compressed, its resistance increases because the heavier coils are brought into play. This characteristic protects the spring from overload. This type of spring is desirable when heavy loads must be supported, and space limitations prohibit the use of conventional springs. b. Torsion Bars. The torsion bar spring used in tracked vehicles (fig. 31-2) has the same characteristics as the automotive type discussed in paragraph 30-2c. When the spring is employed in the tracked vehicle, it must support a greater weight, and usually is made thicker and longer than the automotive type.
31-2. Road Wheels. The tracked vehicle rolls on the bottom of its tracks by means of road wheels (fig. 31-3). For the most part, road wheels are steel disk type and of riveted or welded construction. Forged aluminum road 31-1
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Section II. CONFIGURATIONS 31-4. Torsion Bar Suspension. The torsion bars generally are mounted inside the vehicle and extend completely across the width of the hull. Because of this configuration, the springs are protected from damage such as road hazards and, to some extent, land mines. Road wheels are mounted to crankshaped arms connected to the hull through antifriction bearing mountings, which relieve the springs of all except the torsional loads (fig. 31-2). One end of a torsion bar is splined to the pivoting axle of each suspension arm. The other end of the bar is secured rigidly to the opposite side of the hull. The means of securing the stationary end of the torsion bar are well suited to applying mechanisms for varying the spring preload, thereby providing a means for adjusting the freestanding position of the vehicle to best suit the operating conditions. Angular displacement of the suspension arm is resisted by the torsional spring force of the bar. Because the arms operate in sealed antifriction bearings, and because of the lack of friction in the spring, little natural damping of the spring system is available. This condition makes the use of shock absorbers essential to minimize bouncing and pitching of the vehicle. 31-5. Horizontal Volute Spring Suspension. In the horizontal volute spring suspension (fig. 31-1) the spring is located between bellcranklike suspension arms. When a load is applied to the bogie wheels, the suspension arms pivot upward, transmitting the force directly to the spring, thereby compressing it. Vertical displacement of only one road wheel changes the spring load, thereby changing the load on the other wheel. The balance of forces in the suspension mechanism results in a wheel motion that is a combination rocking motion and vertical deflection. 31-6. Suspension Snubbers. Volute suspension snubbers are mounted on brackets bolted to the hull above each road wheel position (fig. 31-3). The volute springs serve to cushion road wheel arm bottoming shock loads. Inboard stub spindles on the support arms contact the springs near the upper limit of the support arm travel. A double volute spring is used for the front road wheel arm, and a single volute spring at the other road wheel arm positions. 31-7. Shock Absorbers. Suspension systems in tracked vehicles employ either direct-acting, cam and lever, or double-acting shock absorbers, which are discussed in chapter 30, section VI.
31-8. Purpose. The basic function of a suspension lockout system is to bypass the suspension system and attempt to lock the vehicle to the ground. When the system is used in combat vehicles, it allows large guns to be fired from relatively light vehicles because the recoil is transmitted directly to the ground with minimum carriage movement. Suspension lockout systems also are used on lifting vehicles. When the system is activated on such vehicles, it allows the operator to maneuver large objects without the suspension compressing and possibly tipping over the vehicle. 31-9. Hydraulic Lockout System.
designed to combine lockout, damping, and bump-stop functions for each road wheel arm. (2) Damping is controlled through a three-way valve mounted in the drivers compartment. (3) Control pressure is supplied from a hydraulic accumulator, through the three-way valve and a reducing valve to a common line, which supplies all of the lockout cylinders. (4) To lock the cylinder, control pressure is applied to the spool, depressing the spring until the spool land closes the right-hand ports in the rod, trapping the fluid in both ends of the cylinder.
a. Operating Principles.
(1) This unit uses a hydraulic cylinder
31-5
b. Construction. The construction of the system is that of a double-rod-end cylinder with passages into the valve region in the rod from
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opposite sides of the piston. In the open position, the valve spool is preloaded by the spring against a hollow sleeve stop. 31-10. Hydromechanical Lockout System.
a. Operating Principles. The hydromechanical lockout system (fig. 31-5) is a suspension-damping device that incorporates a suspension lockout. Basically, the damping device is a frictional damper (disk brake) to which a hydraulic actuating cylinder is added. The hydraulic-actuating cylinder or brain box supplies and controls the pressure to the frictional damper where the energy absorption takes place. As the road wheel moves up or down, the brain box develops pressure through the use of a piston rod, which is connected to the road wheel arm through linkage. The pressure developed is routed to the frictional damper. which forces the stators and rotors together, creating a
TM 9-8000 Section IV. SPADE SYSTEM 31-11. Construction and Operation. The spade system (fig. 31-6) is another form of anchoring the vehicle to the ground while a projectile is being fired. The spade system usually is mounted in the rear of the vehicle and transmits the force due to the recoil of the gun during firing into the ground. The spade is shaped like a bulldozer blade and has projections on the bottom to penetrate hard soil.
TM 9-8000 CHAPTER 32 WHEELS, TIRES, AND TRACKS Section I. WHEEL CENTER SECTION 32-1. Disk Wheels. The center disk of a wheel (fig. 321) may be a solid plate or of a slotted steel construction. In both cases, the disk is welded or riveted to the rim, and the wheels are demountable at the hub. The disk is dished to bring the point of ground contact under the large wheel bearing, and to permit the mounting of dual wheels. Modern passenger cars almost exclusively use the steel-disk type wheel. 32-2. Pressed and Cast Spoked Wheels. On light vehicles, the wheel center section and rim are connected by spokes and the wheels are demountable at the hub. For heavier trucks, the spokes are integrated with the center section and a demountable rim is used. Another form of cast wheel (fig. 32-2), sometimes called a mag wheel, is a one-piece design made of lightweight alloys. These types of wheels are very popular on modern automobiles and are made in many sizes and styles. Great care must be taken when mounting and demounting tires on these rims, because the wheel assemblies are soft and brittle, which causes them to crack easily. 32-3. Wire Wheels. This type of wheel consists of a pressed-steel hub and rim connected by welded spokes (fig. 32-3). This design allows greater amounts of air to flow past the brake assemblies, therefore keeping them cool and minimizing brake fade. Wire wheels, however, are hard to clean, require the use of full-circle antiskid chains only, and are not adapted for use with dual wheels.
TM 9-8000 Section II. WHEEL RIMS 32-4. Drop Center. The drop center rim (fig. 32-4) is made . n one piece and is fastened to the wheel permanently. Its important feature is a well that permits the mounting and demounting of tires. Bead seats are tapered to match a corresponding taper on the beads of the tire. Drop center rims are used generally on smaller vehicles, such as 114-ton 4 x 4 trucks. 32-5. Semidrop Center. The semidrop center rim (fig. 32-5) is also fastened permanently to the wheel. This rim has a shallow-well, tapered-head seat to fit the taper of the beads of the tire. It also has a demountable flange or side ring, which fits into a gutter on the outside edge of the rim, holding the tire in place. This type of rim is standard equipment on 3/4-ton 4 x 4 trucks. 32-6. Safety. Safety rims (fig. 32-6) are similar to drop center rims. The major difference is that safety rims have a slight hump at the edge of the bead ledge that holds the bead in place when the tires go flat. These rims currently are used on many passenger cars and light trucks. 32-7. Split. A split rim (fig. 32-7) is a rim that has a removable bead seat on one side of the rim. The seat is split to allow for its removal so tires can be changed. Some bead seats also require the use of a lockring to retain the seat. These rims are found usually on large vehicles.
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TM 9-8000 Section III. BEAD LOCKS AND BEAD CLIPS 32-8. Bead Locks. A metal device called a bead lock (fig. 32-8) fits between the beads of the tire so that pressure can be applied by tightening the rim flanges against the outside of the bead. The bead lock is slightly wider than the space between the tire beads when mounted on the rim. Thus, a compression fit is obtained that locks the beads in place so they will not slip on the rim and will hold the tire in position. This is necessary in combat to support the load when operating tires without air pressure. 32-9. Bead Clips. Bead clips (fig. 32-9) are used instead of bead locks on certain sizes of tires. Bead clips are used in multiples; five to six clips are spaced equally on each bead of the tire.
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TM 9-8000 32-12. Types of Treads. a. Mud and Snow(MS) Tread. (1) Directional. The directional mud an( snow tread (fig. 32-13) is of a V-design with large spaces between the lugs. The spaces between the lugs are kept free from snow because of tire rotation and flexing, therefore improving traction. A directional tire may be mounted on the rim only one way and will deliver traction in one direction only. The point of the V-design must contact the ground first when traction is required A directional tread also may be called a traction tread. (2) Nondirectional. The nondirectional mud and snow tread design (fig. 32-14) also has large spaces between the lugs. The lugs are placed perpendicular to the centerline of the tire This design provides good traction in both directions. b. Cross-Country Tread. The cross-country tread (fig. 32-15) is the same as the mud and snow tread, except that the cross-country tread has rounded shoulders. c. Regular Tread. Regular tread (fig. 32-16 consists of small spaces between tread patterns This allows for a quiet ride and safe operation or wet and dry roads. This tread commonly is used on modern highwayoperated tires. d. Rock Service Tread. Rock service tread (fig. 32-17) is characterized by narrow voids between lugs so that loose rock cannot be caught and tear the tread lugs loose from the tire body
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TM 9-8000 Section V. TUBES 32-14. Types of Tubes. a. Standard. Standard tubes (fig. 32-19) are circular rubber containers that fit inside the tire and hold the air that supports the vehicle. Though it is strong enough to stand only a few pounds of air pressure when not confined, the tube bears extremely high pressures when enclosed in a tire and wheel assembly. Because the tube is made of comparatively soft rubber to fulfill its function, it is easily chafed, pinched, punctured, or otherwise damaged. Standard tubes generally are made of butyl, a synthetic rubber that has air-retention properties superior to natural rubber. Standard tubes are made of one layer of rubber molded in the shape of a doughnut. They are used regularly for standard tires. b. Combat. Combat tubes (fig. 32-20) are constructed the same as standard tubes except that they are smaller than standard tubes with the same size markings. Because the inside cross section of combat tires is smaller, combat tubes only will be used with combat tires. However, in the event that combat tubes are not available, it is permissible to use the next size smaller standard tube. c. Bullet Resisting. Bullet-resisting tubes (fig. 3221) are of a heavy, thick construction that automatically seals bullet punctures. Bullet-resisting tubes are identified by their extra weight and thickness and generally have green-painted valve stems. 32-15. Tube Flaps. Tube flaps (fig. 32-22) usually are constructed of a strip of semihard rubber with tapered ends that form a circle. Flaps are required in tube-type tires that are used on flat-base rims. They protect the tube from being pinched between the tire bead and the rim and from irregularities on the base of the rim. 32-16. Types of Valves. a. Cured-On Valve. (1) Rubber-Covered Valve. Cured-on valve stems (fig. 32-23) have a rubber base that is vulcanized on the outer surface of the tube and cannot be removed unless it is cut off for replacement. The rubber-covered stem is bendable when the stem is longer than 3 inches. (2) All-Metal-Stem Cured-On Valve. This valve (fig. 32-24) is mounted to the tube the same way as the rubber-covered valve, but this type uses a nonbendable, all metal stem. b. Cured-On Large-Bore Valve. Cured-on largebore valve stems generally are used on tubes for very large tires such as for earthmovers. The large bore permits rapid inflation and deflation of tubes. Except for size, they are similar to the cured-on valve described above. c. Cured-In Valve. Cured-in valve stems (fig. 3225) are similar to cured-on valve stems except that the rubber base is inverted and vulcanized to the inner surface of the tube. The rubber base also may be vulcanized directly to the rubber body of the tube.
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TM 9-8000 Section VI. TRACKS 32-19. Track Characteristics. The track is a circular flat-band assembly that is mounted under the road wheels and driven by sprockets in the rear of the vehicle. The track is designed to distribute the weight of the vehicle over a large area so that the vehicle will not sink on soft surfaces. The assembly also is able to bridge large gaps in terrain that would render a wheeled vehicle immobile. 32-20. Sectional Band Tracks. Sectional band tracks (fig. 32-30) are designed so that sections of this type track are replaced when worn or damaged, rather than replacing the whole track assembly. In this design, parallel cable reinforced bands are clamped between the cover plates and track bars by means of through bolts and self-locking nuts. Each track section is made to a convenient length for ease of handling and is connected to adjacent sections by connector plates. The joint is made between the track bars. However, some designs provide for the joint to be made at the track bar. 32-21. Pin Connected Tracks. a. Double-Pin Tracks. Double-pin tracks (fig. 3231) consist of a pair of track blocks assembled onto two rubber-bushed pins. The b. Detachable Center Guide. The detachable center guide (fig. 32-31) serves the same function as the integral center guide but is detachable from the shoe. blocks are linked together by the end connectors, which engage the track pins. The end connectors are secured to the pins by means of wedges and wedge nuts. b. Single-Pin Tracks. Except for the single-pin arrangement, the general design features are similar to the double-pin track links. Component nomenclature is somewhat different in that the single-pin track (fig. 3232) has no blocks. The basic metal and rubber structure is called the body. The addition of the bushings completes the link, which is comparable to the link of the double-pin track. The link, pin, nuts, and washers make up the shoe assembly. 32-22. Shoe Types. a. Integral Center Guide. An integral center or track guide (fig. 32-32) is cast into the track shoe itself. It engages the road wheel so that the alinement of the track is maintained and also absorbs lateral forces caused by steering and side slope conditions.
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32-23. Pad Types a. Integral Rubber Pad. Integral rubber pads frequently are placed on the ground-engaging surface of the track to cushion the interaction of the track with the ground and improve traction on hard surfaces. The integral rubber pad is vulcan-
Ized permanently or cemented to the track shoe assembly, and when worn out, must be replaced as a unit. b. Detachable Rubber Pad. This type of pad (fig. 32-32) serves the same purpose as the integral pad but is detachable from the shoe.
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TM 9-8000 CHAPTER 33 STEERING SYSTEMS AND WHEEL ALINEMENT Section I. STEERING SYSTEMS 33-1. Steering Methods. a. Ackerman System. The ackerman system (fig. 33-1) is used exclusively on passenger cars and many wheeled military vehicles. Correct ackerman steering during a turn requires that each wheel turn around a point located on an extension of the rear axle centerline. The steering arms are bent slightly toward each other so that their centerlines, if extended, would intersect in front of the rear axle. With the ackerman system, as the vehicle is making a turn, the inside wheel will turn sharper than the outer wheel, therefore allowing all the wheels to travel around a common point. b. Fifth Wheel. Fifth-wheel steering (fig. 33-2) is accomplished by pivoting an entire axle around a central point. The wheels of each axle maintain their initial position with respect to each other and the interconnecting axle during a turn. This type of steering commonly is applied to towed vehicles because of the mechanical difficulties of controlled steering and because greater under-body clearance is required for fifth-wheel steering systems. 33-2. Solid Axle Steering Linkage. The steering linkage on vehicles with a solid front suspension (fig. 333) only needs to deal with the relative motion between the front axle and frame. For this reason the steering linkage is fairly simple and easily designed. a. The common solid axle suspension utilizes a drag link to connect the pitman arm to the steering linkage. The drag link is made in a tubular or rod form and is provided with springs to cushion shocks and prevent transmission of the shocks to the steering gear. A housing is provided on one end of the drag link to receive the ball end of the pitman arm. Ball sockets, coil springs, spring seats, and a screw plug secured by a cotter pin are inserted in this housing to hold the pitman arm ball. Sometimes the slot in which the pitman arm is inserted extends the entire length of the
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Change 1 33-2
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TM 9-8000 discussed in paragraph 33-2d but are constructed slightly different. The tie rod ends have a cast housing incorporating a threaded shaft in the design. The tie rods provide a swivel connection to both steering arms and both connections to the centerlink. 4) Adjusting Sleeves. The inner and outer tie rods are connected by adjusting sleeves. These are tubular in design and threaded over the inner and outer tie rods. The adjusting sleeves provide a location for toe adjustment. Clamps and clamp bolts are used to secure the sleeves. Some manufacturers require the clamps be placed in a certain position in relation to the tie rod top or front surface to prevent interference with other parts. c. Rack and Pinion Steering Linkage (Fig. 33-6). The rack and pinion steering linkage is the simplest form of steering linkage. A ball socket joint, which has a hollow threaded shaft, is generally used to connect the tie rod assembly to the rack and pinion steering gear. The threaded end of the socket assembly accepts the tie rod and allows for toe adjustment. Clamps also are used to secure the tie rod and socket joint. This type of steering linkage is found on many smaller cars.
TM 9-8000 Section II. 33-4.Worm andSectorType.In the worm and sector larger at one position than another and therefore the road wheels are turned faster at certain positions than at steering gear (fig. 33-7) the pitman arm shaft carries a others. At the center or straight ahead position, the gear that meshes with the worm on the steering gear steering gear ratio is high, giving more steering control. shaft. Generally, only a sector of a gear is used because However, as the wheels are cramped or turned to the it turns through an arc of approximately 70 degrees. The side, the ratio decreases so that the action is much more steering wheel turns the worm on the lower end of the rapid. This design is very helpful for parking or for steering gear shaft, which rotates the sector and the maneuvering the vehicle. pitman arm through the use of the shaft. The worm is assembled between tapered roller bearings that take 33-6. Cam and Lever Type. A cam and lever steering both thrust and load. An adjusting nut or plug is provided gear in which the worm is known as a cam, is shown in for adjusting the end play of the worm. Some means of figure 33-9. The pitman arm shaft carries a lever on the adjusting the end play of the cross-shaft also is provided. inner end. This lever carries a stud that engages with the cam. The stud may be integral or mounted on roller 33-5. Worm and Roller Type. The worm and roller bearings. Roller bearings reduce friction and allow easier steering gear (fig. 33-8) is quite similar to the worm and steering. As the steering wheel is turned, the stud moves sector type except that a roller is supported by ball or up and down on the cam and carries the lever with it to roller bearings within the sector mounted on the pitman rotate the pitman arm shaft. The pitch of the cam is not arm shaft. These bearings assist in reducing sliding constant, therefore the lever moves more rapidly as it friction between the worm and sector. As the steering nears either end of the cam. Maximum leverage occurs wheel turns the worm, the roller turns with it but forces at the straight ahead position when the stud engages the the sector and the pitman arm shaft to rotate. The fine pitch section of the cam. This makes the initial hourglass form of worm, which tapers from both ends to turning of the wheels easier. Therefore, a variable ratio the center, affords better contact between the worm and is obtained with cam and lever steering. A twin lever roller at all positions. It provides a variable ratio to permit provided with two studs (fig. 33-9) is used on a design for faster and more efficient steering. Variable ratio means heavier vehicles that the ratio is
Figure 33-7. Worm and Sector Steering Gear Figure 33-8. Worm and Roller Steering Gear
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33.13. Purpose. Heavy vehicles are difficult to steer because large loads on the tires tend to increase their turning resistance. This problem cannot be overcome satisfactorily by using a steering gear with a very high reduction ratio because it would require numerous revolutions of the steering wheel to turn the vehicle wheels; therefore, some form of power steering to aid the driver In steering the heavier vehicles is required. Air steering Is a desirable method of power steering, because the heavier vehicles on which it
would be used usually have an airbraking system from which the air pressure can be obtained. If there is no airbraking system, an air compressor and reservoir are required to obtain the necessary air pressure. 3314. Components. Air steering control consists primarily of three major units: a combination of levers mounted on the steering gear pitman arm shaft; two control valves; and an air cylinder containing a doubleacting piston (fig. 33-17). TA233846
33-13
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TM 9-8000 The control valves are mounted directly on the air cylinder, each valve controlling one side of the cylinder. The air pressure delivered from the air line to the cylinder is proportional to the force applied on the top of the valve piston plunger by the control rod. The valves are actuated by a rocker arm so that air Is delivered to one side of the cylinder at a time. These valves are adjusted so that the air can be exhausted from both sides of the cylinder simultaneously, but air pressure can be delivered to only one side at a time (fig. 33-17) 33-15. Operation. a. Neutral. In the neutral position the force on the steering wheel is removed, the steering wheel position remains constant, and the control link- age shifts and shuts off the air supply to the air cylinder. When this happens, the air cylinder remains pressurized In that position and holds the steering linkage steady until the steering wheel is turned again. b. Right and Left Turns. If the steering wheel is turned in one direction, the steering linkage shifts one way and the control valves allow one side of the cylinder to exhaust while pressurizing the opposite side. The piston rod then extends or retracts, providing the power steering assist to the linkage.
Section V. FOUR-WHEEL DRIVING AND STEERING 33-16. Construction. a. Four-Wheel Drive. A construction in which all four wheels of the vehicle drive, is used on many military vehicles. A typical construction for a wheel that drives and steers is illustrated in figure 33-18. A universal joint is used at the end of the axle shaft so that the wheel will be free to pivot at the end of the axle, as well as be driven through the axle. The end of the axle housing encloses this universal joint and is provided with vertical trunnion pins that act as a steering knuckle pivot. The wheels, mounted on steering knuckles attached to these trunnion pivots, are free to turn around the pivots at the same time they are driven through universal joints on the inner axle shaft. Steering knuckle arms are mounted on the steering knuckles so that the wheels can be turned around the trunnion steering pivots by the steering linkage. b. Four-Wheel Steering. All four wheels can be steered from the steering wheel by connecting the steering linkage of these wheels to the pitman arm (fig. 33-19). The rear wheels are connected together by knuckle arms and a tie rod. Because the rear wheels must be turned in the opposite direction to the front wheels to travel in the same arcs around the center of rotation, the drag links to the front and rear wheel steering linkage cannot be connected directly to the steering gear arm. The drag link to the front wheels must move forward while the drag link to the rear wheels moves rearward, and vice versa. To accomplish this, an intermediate steering gear arm is pivoted on the frame side member near the middle of the vehicle. The drag links are connected to opposite ends of this arm so that, as it Is turned by direct connection to the pinion arm (by means of an intermediate drag link), the front and rear drag links are moved in opposite directions.
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33-17. Steering Geometry/Toe-Out. The front end assembly of the modern motor vehicle requires careful design and adjustment because each front wheel is pivoted separately on a steering knuckle. Because of this construction, the front wheels are not in the same radius line (drawn from the center of rotation (fig. 33-20)) when a vehicle is making a turn. Because each wheel should be at right angles to its radius line, it is necessary for the front wheels to assume a toed-out position when rounding curves. If they do not, the tires slip, which causes excessive tire wear. The inner wheel (the one closer to the center of rotation) turns more than the outer wheel, so it will travel in a smaller radius. This difference in the turning ratios of the two wheels is called toe-out. It is usually specified as the number of degrees over 20 that the inner wheel is turned when the outer wheel is turned 20 degrees. Toe-out on turns may be checked but there is no provision made for its adjustment. The steering linkage must be examined carefully for bent or defective parts if this angle is not within the manufacturers specifications. 33-18. Caster. Caster is the angle (fig. 33-21),
measured in degrees, that the steering knuckle pivots are tilted forward or backward from the vertical axis when viewed from the side. Caster tends to keep the front wheels pointed straight ahead, making it easier to return the wheels to a straight ahead position after a turn has been made. The principle is the same as that used in tilting the front fork of a bicycle, which makes it possible to ride the bicycle without firmly holding the handlebars. Part of the effort applied for turning castered wheels out of the straight ahead position slightly raises the front end of the vehicle upward. Consequently, when the steering gear is released, the weight of the vehicle forces the front end down and straightens the wheels. Caster is designated as positive for backward tilt and negative for forward tilt of the steering knuckle pivots viewed from the side. Caster may be obtained on a solid axle suspension by inserting a thin wedge or shim between the axle and the spring. The axle can be made so that the supports for the steering knuckle pivots are tilted vertically. In parallel arm suspension, caster is obtained by mounting the steering knuckle support in the control arms so that it is tilted to the desired amount. If the axis of the steering knuckle pivot is
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extended, It must strike the ground ahead or behind the point where the tire meets the ground. The caster varies from about 1/2 to 3 degrees. 33-19. Camber. Wheel camber (fig. 33-22) Is the angle made by the wheel with the vertical axis when It is In the straight ahead position. Positive cambered wheels are closer together at the bottom than they are at the top. For many years, front-wheel camber as great as 3 degrees has been used. For driving on crowned roads, this camber permitted better roiling contact by bringing the wheel perpendicular to the road and made steering easier. In recent years, the construction of graded roads and the use of low-pressure fires has led to a decrease In camber. If the vehicle were run on a flat road and had no lost motion at the 33-18
bearings, zero camber would be ideal; but It Is not practical to build front axles with zero camber because of the possible accumulation of bearing clearances and the slight deflection of the axle under the vehicle load. Therefore, a camber of about 1 degree Is recommended at present. Excessive camber causes continual slippage of the tire on the road, because each wheel tries to follow a path away from that traveled by the vehicle. This is due to the fact that a cambered wheel tends to roll like a cone because Its axis Is not horizontal. 33-20. Kingpin Inclination. King pin, or pivot, Inclination (fig. 33-23) is the amount In degrees that the steering knuckle pivots are tilted sideways toward the center of the vehicle. Inclination of the TA233850
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34-1. Braking Action. Braking action is the use of a controlled force to accomplish the three basic tasks of reducing speed, stopping, and holding an object in a stationary position. Braking action usually is accomplished by rubbing two surfaces together that cause friction and heat (fig. 34-1). Friction is the resistance to relative motion between two surfaces in contact. The mechanical energy of reaction then is transformed into hear energy. Heat energy is an unwanted product of friction and must be dissipated to the surrounding environment as efficiently as possible. Automotive vehicles use this rubbing action to develop the friction required for braking. Braking action also may be accomplished by establishing a rubbing contact with the roadway, as is done by some trolleys, which apply a braking surface to the rails. 34.2. Braking Requirements. It is known that to increase a vehicles speed requires an increase in the power output of the engine. It also is true, although not so apparent, than an increase in speed requires an increase in the braking action required to bring a vehicle to a stop (fig. 34-2). A
moving vehicle, just as any other moving body, has what is known as kinetic energy. Kinetic energy is the energy an object possesses due to its relative motion and may 2 be expressed as (mass) x (velocity) . This kinetic energy, which increases with the square of the speed, must be overcome by braking action. If the speed of a vehicle is doubled, its kinetic energy is increased fourfold; four times as much energy, therefore, must be overcome by the braking action. Brakes must not only be capable of stopping a vehicle, but must stop it in as short a distance as possible. Because brakes are expected to decelerate a vehicle at a faster rate than the engine can accelerate it, they must be able to control a greater power than that developed by the engine. This is the reason that well-designed, powerful brakes have to be used to control the modern high-speed motor vehicle. It is possible to accelerate an average passenger car with an 80-hp engine from a standing start to 80 mph in about 36 seconds. By applying the full force of the brakes, such a vehicle can be decelerated from 80 mph to a full stop in about 4.5 seconds. The time required to decelerate to a sop is one-eighth the time required to accelerate from a standing
TM 9-8000 start, therefore the brakes harness eight times the power developed by the engine. Thus, about 640 (8 x 80) hp has to be spent by the friction surfaces of the brakes of an average passenger car to bring it to a stop from 80 mph in 4.5 seconds. 34-3. Vehicle Stopping Distance. Driver reaction time is the time frame between the instant the driver decides that the brakes should be applied and the moment the brake system is activated. During the time that the driver is thinking of applying the brakes and moving his or her foot to do so, the vehicle will move a certain distance, depending on its speed. After the brakes are applied, the vehicle will travel an additional distance before it is brought to a stop. Total stopping distance of a vehicle is the total of the distance covered during the drivers reaction time and the distance during which brakes are applied before the vehicle stops. Figure 34-3 illustrates the total stopping distance required at various vehicle speeds, assuming an average reaction time of 3/4 second and that good brakes are applied under most favorable road conditions. 34-4. Factors Affecting Retardation. The amount of retardation obtained by the braking system of a vehicle is affected by several factors. For wheel brakes used on motor vehicles, these factors are: a. Pressure exerted on braking surfaces (rotating and non-rotating members). b. Weight carried on wheel. c. Overall radius of wheel (distance from center of wheel to outer tread of tire). d. Radius of brake drum or rotor (rotating member). e. Coefficient of friction between braking surfaces. f. Coefficient of friction between tire and road. When the radius of the wheel or weight of the vehicle is increased, the pressure required on braking surfaces also will be increased for a fixed amount of retardation. These factors are independent of the design of the braking system and generally are a fixed value. However, limitations of these factors, particularly the weight of the vehicle to be carried by the wheels, must be considered when designing a braking system. If the radius of the brakedrum or coefficient of friction between the braking surfaces is in- creased, less pressure will be required to obtain the same degree of retardation. The best results are obtained when these factors are correlated within the limits permitted by the design of the braking system. The coefficient of friction between tire and road determines maximum retardation obtained by the application of brakes. 34-5. Maximum Retardation Point. When brakes are applied, the wheel either will roll or skid, depending on relative values of coefficients of friction between braking surfaces and between tire and road. Heavy jamming of the braking
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surfaces together will tend to increase the friction to such a degree that the wheel will lock. When this happens, braking action is caused by friction between tire and road, which heats and wears the tire. Maximum retardation is reached when friction between the brake surfaces is such that the wheel is about to lock. At this point, friction between the brake surfaces is almost the same as that between tire and road. This is the maximum amount of friction that can be used in retarding motion of the vehicle. Friction encountered between tire and road is the limiting factor of braking. Should friction between braking surfaces go beyond this, the braking surfaces will
lock and the wheel will skid. The action produced when a wheel rolls and when it skids is shown in figure 34-4. When a wheel rolls along a road, there is no relative motion at the point that the tire makes contact with the road because the wheel rolls with the road surface, but when a wheel skids, there is relative motion at the point of contact because the wheel is not rotating while moving over the road surface. When a wheel skids, friction is reduced, which decreases the braking effect. Nevertheless, brakes are de- signed so that the vehicle operator is able to lock the wheels if he or she applies enough force on the foot pedal.
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34-6. Rotating and Nonrotating Units. There are many types of brake system designs In use on modern automotive vehicles. Regardless of the design, all systems require the use of a rotating and nonrotating unit. Each of these units houses one of the braking surfaces, which, when forced together, produce the friction required for braking action. The rotating unit on many motor vehicle wheel brakes consists of a drum that is secured to and driven by the wheel. The nonrotat- Ing unit consists of the brakeshoes and linkage required to apply the shoes to the drum. Brakes may be of the internal expanding or external contracting type (fig. 34-5), depending on how the stationary surface is forced against the rotating surface. 34-7. Construction. a. Brakeshoes. Brakeshoes (fig. 34-6) are used to support, strengthen, and move the brake lining. Because the brake lining material Is soft and brittle, it Is necessary to add a supportive foundation to the lining so it will not collapse and break during use. The brakeshoes also serve to attach the brake lining to a stationary member, usually the backing plate, so the braking action may be accomplished. Brakeshoes are made of malleable Iron, cast steel, drop-forged steel, pressed steel, or cast aluminum. Pressed steel
commonly is used because it is cheaper to produce In large quantities. Steel shoes expand at about the same rate as the drum when heat Is generated by brake application, thereby maintaining the clearance between the brakedrum and brakeshoe under most conditions. The brake lining Is riveted or bonded to the face of the brakeshoe and makes contact with the Inner surface of the brakedrum. Semitubular brass rivets sometimes are used to attach the brake lining to the brakeshoe. The brass rivets are chosen over other types because brass does not score the drums excessively if the lining should be neglected and worn past the point of replacement. Aluminum rivets are not used because they may corrode due to moisture. The brake lining also may be bonded directly to the brakeshoe. In this process, a special cement Is used to adhere the lining to the brakeshoe. After application, the shoe Is baked at a predetermined temperature to ensure proper setting of the cement. In some brake assemblies, the lining Is not fastened to either the shoe or the drum, but floats between them and Is held by a lining retainer on one side and the brake shield on the other. b. Brake Lining. Variation in brake design and operating conditions make it necessary to have different types of brake linings. Brake linings come In woven and molded form (fig. 34-6). The
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mate with a lip on the backing plate that provides the rotating seal to help keep water and dirt from entering the brake assembly. Brakedrums may be made of pressed steel, cast iron, a combination of the two metals, or aluminum. Cast iron drums dissipate the heat generated by friction faster than steel drums and have a higher coefficient of friction with any particular brake lining. However, cast iron drums of sufficient strength are heavier than steel drums. To provide lightweight and sufficient strength, centrifuse brakedrums (fig. 34-7), made of steel with a cast iron liner for the braking surface, are used. A solid cast iron drum of the same total thickness as the centrifuse drum would be too weak, while one of sufficient strength would be too heavy for the average passenger car. Aluminum brakedrums are constructed similar to the centrifuse drums. They consist of an aluminum casting with a cast Iron liner for a braking surface. This design allows heat to be transferred to the surrounding atmosphere more readily and also reduces weight. Cooling fins or ribs (fig. 34-7) also are added to most brakedrums. The fins or ribs increase the surface area of the outside portion of the brakedrum, allowing the heat to be transferred to the atmosphere more readily, thereby keeping the drum cooler and helping to
minimize brake fade. For good braking action, the drum should be perfectly round and have a uniform surface. Brakedrums become out-of- round from pressure exerted by brakeshoes and from heat developed by application of the brakes. The brakedrum surface becomes scored when it is worn by braking action. When the surface is scored or the drum is out-of- round, it may be necessary to machine the brakedrum until it is smooth and true again. Care must be taken not to exceed the maximum allowable diameter according to manufacturers specifications. If this caution is ignored, the drum can be distorted easily due to overheating, and result in brake failure. Each drum is stamped with the maximum diameter information and, if exceeded, it should be discarded and replaced with a new one. 34-8. Hydraulic Actuation. The hydraulically operated service brake uses fluid pressure to operate a hydraulic cylinder, which in turn operates the brakeshoes. The fluid pressure is generated by a hydraulic system whose operation is discussed in paragraph 34-23. 349. Pneumatic Actuation. The pneumatically actuated service brake uses a controlled, compressed air supply from the air system as de-
TM 9-8000 scribed in section VI. The brakes are actuated by a rotating cam, which is connected to a camshaft and in turn operates by the air system. 34-10. Operation. Brake systems, as discussed in paragraph 34-6, require a rotating and non- rotating member. In the drum brake assembly, whether hydraulically or pneumatically actuated, the drum provides the rotating member and the brakeshoe the stationary member. The primary function in the drum brake assembly is to force the brakeshoes against the rotating drum to provide the braking action. Most drum brake assemblies use what is called self-energizing action. This self-energizing action is produced as the brake- shoe engages the rotating brake-drum. As the brake actuating mechanism forces the shoes outward (A, fig. 34-8), the top of the brakeshoe tends to stick or wedge to the rotating brakedrum and rotate with it. This effect on brakeshoes greatly reduces the amount of effort required to achieve a given amount of retardation. If two brakeshoes were linked together, as shown in B, figure 34-8, application of the brakes would produce a self-energizing effect and also a servo effect. The servo effect is a result of the primary shoe, or shoe towards the front of the vehicle, attempting to rotate with the brakedrum. Due to the fact that both shoes are linked together, the rotating force of the primary shoe applies the secondary shoe. This effect is termed servo action (B, fig. 34-8). In the forward position, the anchor point for both brakeshoes is at the heel of the secondary shoe. As the vehicle changes direction, the toe of the primary shoe becomes the anchor point, and the direction of selfenergizing and servo action changes (C, fig. 34-8). The most popular configurations of the drum brake assembly are discussed below. a. Single Anchor, Self-Energizing Servo Action. In this configuration (A, fig. 34-9) both brakeshoes are selfenergizing in both forward and reverse directions. The shoes are self- centering and provide servo action during brake application. This system is provided with one anchor pin, which is rigidly mounted to the backing plate and is nonadjustable. Both the forward and reverse brake torque is transmitted to the backing plate through the anchor pin. One brake cylinder with dual pistons is used in this configuration. This system is used on many modern vehicles. b. Single Anchor, Self-Centering. In this configuration (B, fig. 34-9), only the primary brakeshoe is selfenergizing in the forward direction and therefore provides the majority of the brake force. This system is selfcentering, in that the lower shoe anchor does not fix the position of the brakeshoes in relation to the drum. The shoes are allowed to move up and down as needed. Some configurations provide eccentric cams for front to rear brakeshoe adjustments. One brake cylinder is provided in this system. c. Double Anchor, Single Cylinder. In this arrangement (C, fig. 34-9), each brakeshoe is anchored at the bottom by rotating eccentric- shaped anchor pins. Only the primary shoe is self-energizing, and the system does not develop servo action. Spring clips are used at the middle of the shoe to hold the shoes against the backing plate. Brakeshoes are adjusted manually by rotating the anchor pins. One wheel brake cylinder is provided in this arrangement. d. Double Anchor, Double Cylinder. In this system (D, fig. 34-9) the brakeshoes are provided with an anchor at each heel. The anchors are eccentric-shaped to allow for adjustment and centering. Each shoe has a single piston cylinder mounted at the toe of the brakeshoe, which allows both shoes to be self-energizing in the forward direction only. Eccentrics mounted in the middle of the shoe also allow for brake adjustment. 34-11. Disadvantages. The drum brake assembly, although well suited for the wheeled vehicle, has some disadvantages. One problem that might occur during heavy braking is what is known as brake fade. During panic stops or repeated harsh stops, brake lining and brakedrums develop large amounts of heat that reduce the coefficient of friction between brakeshoe and drum. This reduction in friction greatly decreases the vehi- cles stopping ability, and in most cases, additional pressure directed on the brake pedal will not increase the vehicles stopping performance. The enclosed design of the drum brake assembly does not allow for cooling air to enter the brake assembly and therefore heat developed during braking must be dissipated through the brake- drum and backing plate. As brakes heat up because of repeated application, cooling air flowing past the drum and backing plates is limited. This condition causes the radius of the
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(2) The primary shoe self-energizes, and, through servo action, applies the secondary shoe. (3) The heel of the secondary shoe is lodged against the anchor pin.
(4) The movement of the primary shoe tightens the cable by shifting the cable guide out- ward and in the direction of rotation. (5) The cable then moves the adjusting lever upward. If enough shoe-to-drum clearance TA233862 34-10
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is available, the adjusting lever will engage the next tooth on the star wheel. The brakeshoes re- tract and the cable slackens as the brakes are released. The return spring then helps force the adjusting lever downward, which rotates the star wheel and therefore expands the brakeshoes. In the reverse direction, the toe of the primary shoe is forced against the anchor and the secondary shoe moves around to tighten the adjusting cable. The adjusting process then is completed. b. Link Type. The link-type self-adjusting system (B, fig. 34-10) uses solid linkage rods to connect the adjusting lever to the stationary anchor point. The adjuster is operated by the two linkage rods connected together by a bell crank, which pivots on the secondary brakeshoe. One rod attaches to the anchor point and the bell- crank, while the other rod connects the bell crank and the adjusting lever. In this configuration, the selfadjuster works only in the reverse direction. As the vehicle is backing up and the brakes are applied, the adjusting process Is as follows: (1) The secondary shoe moves away from the anchor because of the self-energizing action.
(2) The pivot point of the bell crank is moved in the direction of rotation. (3) The lever moves up on the star wheel through the connection of the linkage. If enough clearance Is available between the brakeshoes and drum, the lever will engage an- other tooth on the star wheel. As the brakes are released, the shoes retract and the return spring helps force the adjusting lever down, therefore rotating the star wheel and expanding the adjusting screw to remove excess shoe-to-drum clearance. c. Lever Type. The lever-type self-adjusting system (C, fig. 34-10) is similar to the link type, In that it operates in the reverse direction only. While the link-type system uses linkage rods to perform the self-adjusting process, the lever type uses a stamped metal lever to engage the star wheel and an actuating link to connect to the anchor pin. The adjusting process is the same as the link-type system.
34-13. General. The disk brake system (fig. 34-11) is another form of brake system used in many modern vehicles. Like the drum system, the disk brake system is operated hydraulically and has rotating and nonrotating components. Disk brakes can be used on all four wheels or they can be mounted on the front wheels and used in conjunction with drum brakes, which are mounted in the rear. These configurations are very popular because the disk system is a very efficient brake system, it stays cool due to its open design, and is less prone to brake fade. The rotating member is in the form of a heavy roundshaped disk. The disk or rotor Is attached to the wheel assembly and may be a solid or vented construc- tion. The disk may be an Integral part of the hub or detachable from the hub by the use of bolts. The clamp assembly or caliper is the stationary member in the system and usually is mounted to the spindle or splash shield to provide support. The caliper is fitted with one or more pistons that are actuated hydraulically by the fluid pressure developed in the brake system. Brake pads are designed to fit into the caliper and provide the
frictional surface for the rotor to engage during braking. a. Operating Principles. The disk brake, like the drum brake assembly, is operated by pressurized hydraulic fluid. The fluid, which is routed to the calipers through steel lines and flexible high-pressure hoses, develops its pressure in the master cylinder. Once the brake pedal is depressed, fluid enters the caliper and begins to force the piston(s) outward. This outward movement forces the brake pads against the moving rotor. Once this point is reached, the braking action begins. The greater the fluid pressure exerted on the piston(s) from the master cylinder, the tighter the brake pads will be forced against the rotor. This increase in pressure also will cause an increase in braking effect. As the pedal is released, pressure diminishes and the force on the brake pads is reduced. This allows the rotor to turn more easily. Some calipers allow the brake pads to rub lightly against the rotor at all times in the released position. Another design uses the rolling action of the piston seal to
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maintain a clearance of approximately 0.005 Inch (fig. 34-11) when the brakes are released. b. Comparison to Drum Brakes. Both the disk and drum brake assemblies used on modern vehicles are well-designed systems. Each system exhibits certain Inherent advantages and disadvantages. The most Important points of Interest are discussed below. One major factor that must be discussed In automotive brakes, as well as all other brake systems, is the systems ability to dissipate heat. As discussed In paragraph 34-1, the byproduct of friction is heat. Because most brake systems use this concept to develop braking force, It Is highly desirable for brake systems to dissipate heat as rapidly and efficiently as possible. The disk brake assembly, because of Its open design, has the ability to dissipate heat faster than the drum brake. This feature makes the disk brake assembly less prone to brake fade due to a buildup of excess heat. The disk assembly also may have additional heat transfer qualities due to the use of a ventilated rotor. This type of rotor (fig. 34-11) has built-in air passages between friction surfaces to aid in cooling. While the drum brake assembly requires an Initial shoeto-drum clearance adjustment and perodic checks, the disk brake assembly Is self- adjusting and maintains proper adjustment at all times. The disk assembly automatically compensates for lining wear by allowing the piston In the caliper to move outward, thereby taking up excess clearance between pads and rotor (fig. 34-11). The disk system is fairly simplistic In comparison to the drum system. Due to this design, and its lack of moving parts and springs, the disk assembly Is less likely to malfunction. Overhauling the disk brake assembly Is faster because of Its simplistic design.. It also Is safer due to the fact that the disk brake assembly Is open and asbestos dust from linings Is less apt to be caught In the brake assembly. Like brakedrums, rotors may be machined if excessive scoring Is present. Rotors also are stamped with a minimum thickness dimension (fig. 34-11), which should not be exceeded. The drum brake assembly requires the drum be removed for lining Inspection, while some disk pads have a built-in lining wear Indicator (fig. 34-11) that produces an audible highpitch squeal when linings are worn excessively. This harsh squeal Is a result of the linings wearing to a point, allowing a metal Indicator to
rub against the rotor as the wheel turns. Because of its small frictional area, and lack of self- energizing and servo effect, the disk brake assembly requires the use of an auxiliary power booster to develop enough hydraulic. pressure for satisfactory braking. 34-14. Floating Caliper. The floating caliper (fig. 34-12) is designed to move laterally on its mount. This movement allows the caliper to maintain a centered position with respect to the rotor. This design also permits the braking force to be applied equally to both sides of the rotor. The floating caliper usually Is a onepiece solid construction and uses a single piston to develop the braking force. This type of caliper operates by pressurized hydraulic fluid like all other hydraulic calipers. The fluid under pressure first enters the piston cavity and begins to force the piston outward. As this happens, the brake pad meets the rotor. Additional pressure then forces the caliper assembly to move In the opposite direction of the piston, thereby forcing the brake pad on the opposite side of the piston to engage the rotor. As pressure Is built up behind the piston, it then forces the brake pads tighter against the rotor to develop additional braking force. 34-15. Fixed Caliper. The fixed caliper (fig. 34-13) is mounted rigidly to the spindle or splash shield. In this design, the caliper usually is made In two pieces and has either two, three, or four pistons In use. The pistons, which may be made of cast iron, aluminum, or plastic, are provided with seals and dust boots and fit snugly In bores machined In the caliper. The centering action of the fixed caliper Is accomplished by the pistons as they move In their bores. If the lining should wear unevenly on one side of the caliper, the excess clearance would be taken up by the piston simply by moving further out In its bore. As the brakes are applied, the fluid pressure enters the caliper on one side and Is routed to the other through an Internal passageway or an external tube con- nected to the opposite half of the caliper. As pressure Is Increased, the pistons force the brake pads against the rotors evenly and therefore maintain an equal amount of pressure on both sides of the rotor. As discussed above, the fixed calipers use a multlplston design (fig. 34-13) to provide the braking force. The fixed calipers may be designed
34-13
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to use two, three, or four pistons. The dual piston design provides a slight margin of safety over a single-piston floating caliper. In the even of a piston seizing in the caliper, the single-piston caliper would be rendered useless, while the dual-piston design would still have one working[ piston to restore some braking ability. The three and four-piston design provides for the use of larger brake lining. The brake force developec may now be spread over a larger area of the brake pad. 34-16. Self-Energizing Disk Brakes. There are two designs of the self-energizing disk brake system. Each one is discussed separately in the following text. a. Rotating Plate Type. This type of self energizing disk brake assembly (fig. 34-14 consists of a pair of pressure plates or flat ring, faced on one side with a brake lining an( assembled In a brake housing attached to the wheel. Six steel balls are positioned in a series
arrangement in ramps between the two plates so that, when one plate is turned a few degrees, the balls ride up on the ramps and move the plates away from each other. This outward movement forces the plates into contact with the inner faces of the brake housing for braking action. The action is partially self-energizing because the plate that turns in the direction of motion tends to rotate further as it comes in contact with the inner face of the rotating brake housing. The frictional contact between the two tends to carry the outer plate around and produces a self-energizing action. b. Wedge-Type Disk Brake. The basic wedge design of a self-energizing disk brake is illustrated in figure 3414. The self-energizing effect is accomplished by means of a wedge-shaped disk brake pad. The friction force between pad and rotor tends to force the pad into the wedge- shaped piston, producing a self-energizing effect.
34-16
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TM 9-8000
Section IV. 34-17.ContractingTransmissionBrake.The contracting transmission brake generally is mounted between the output shaft of the transmission or transfer case (fig. 34-15). The rotating drum is splined or bolted to the transmission or transfer main shaft. The brake is designed for either forward or backward motion of the vehicle. For this reason, one end of the brake band is anchored just opposite that at which the operating force is applied. As the brakes are applied, the halves of the brake band wrap against the drum, preventing rotation in either direction. The mechanism for operating this brake usually is a simple bellcrank arrangement connected to a handbrake lever by a flexible cable. A spring disengages the brake band lining when the actu- ating force is released. The contracting transmission brake usually is not used in modern vehicles. 34-18. Disk Transmission Brake.The disk transmission brake (fig.34-16)usually is mounted on the rear of the transmission or transfer case, or on a cross member of the frame. The rotating member of the brake consists of a specially designed steel disk splined or bolted to the transmission output shaft. This disk has two faces that act as the rotating braking surface. Passages are arranged so that a large volume of air cools the braking surface when the disk is rotating. The shoes are supported on swinging brackets and are clamped against the disk faces
by means of a cam lever arrangement. A spring removes the shoes from the disk faces when the hand or foot lever is released. 34-19. Parking Brake. The parking brake usually is operated by an auxiliary foot pedal or hand lever located in the driver compartment. This brake mechanism is designed to keep the vehicle stationary when the operator is not present. There are different systems used for the disk and drum brake assemblies; each is discussed below. a. Disk Type. The disk brake system uses two basic types of parking brake systems (fig. 34-17). One system incorporates an integral parking brake mechanism in the caliper assembly. This system uses an actuator screw, operated by a lever and the parking brake cable, to apply the brake pads. As the parking brake is applied, the actuator screw is rotated, which forces the piston assembly and inner brake pad outward to meet the rotor. Further application shifts the caliper assembly and applies the outer brake pad. Another parking brake system used with disk brake systems uses two small internally expanding brakeshoes (fig. 34-17). The shoes are expanded against the internal section of the brake disk by an actuating lever operated by the parking brake cable. b. Drum Brake Type. The drum brake system uses one basic parking brake assembly (fig. 34-17). This configuration uses a parking brake lever that is activated by a flexible cable routed to both rear wheels. As the parking brake is applied, the parking brake lever pivots on the top of the secondary brakeshoe. This action allows the parking brake strut to move forward and apply the primary shoe. Further application now pivots the parking brake lever on the parking brake strut, thereby forcing the secondary shoe against the brakedrum. 34-20. Advantages and Disadvantages of Transmission Brakes. Transmission and transfer assembly brakes theoretically are more efficient than wheel brakes because the braking effort is multiplied by the final drive ratio, and their braking action is equalized perfectly through the differential. However, they put a severe strain on the power transmission system, and they are not TA233867
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TM 9-8000 positive In performance for they do not prevent the action of the differential assembly from taking place. Therefore, in some conditions, the vehicle may move while the brake is applied.
Section V. MECHANICAL BRAKE SYSTEM 34-21. Means of Actuation. The energy supplied by the operators foot in pushing down on the brake pedal is transferred to the brake mechanism on the wheels by various means. A mechanical hookup has been used since the earliest motor vehicles, but hydraulic pressure is used most extensively at the present time. Mechanically operated braking systems are obsolete on todays automobiles, but these systems may be used for a portion of the braking systems in many vehicles. 34-22. Hookup.
a. Cross-Shaft. In a mechanical braking system, the force applied to the pedal is transmitted to the brakes by means of rods and cables. The mechanical linkage may be arranged in various ways, but its operation Is essentially the same. In order to have all the wheel brakes applied uniformly, a cross-shaft is provided near the center of the vehicle frame, on which the levers connected to the rods and cables leading to the wheel brakes are mounted. The brake pedal also is connected to a lever on the cross-shaft (fig. 34-18). When the pedal Is depressed, the cross-shaft (fig. 34-18) is turned so that levers on the top of the shaft are turned backward and those on the bottom of the shaft forward. By connecting the front brake rods to the levers on the top of the shaft, and the rear brake rods to the levers on the bottom of the shaft, all the brake rods are pulled together and the four wheel brakes are applied at the same time. The usual practice In mechanical systems has been to link the hand brake to the foot brake so that both operate the same braking units. With such an arrangement, the hand brake linkage Incorporates an overrunning slot in the hand brake pull rod where It is connected to a lever on the cross-shaft. This allows the pedal linkage to operate without Interference from the hand lever. Both controls may be operated Independently by also Incorporating an overrunning slot In the foot brake linkage.
34-21
b. Two Cross-Shafts. In some mechanical brake arrangements, two cross-shafts (fig. 34-18) are provided, so that the hand brake is applied to the shoes In the rear wheels only. The front and rear cross-shafts are connected together by an interconnecting rod Joined to a lever on each shaft. An overrunning slot must be provided on the interconnecting rod (fig. 34-18) and the hand brake pull rod if the rear wheel brakes only are to be applied by the brake hand lever. Some braking systems Incorporate additional shoes on the rear wheels for the hand brake, in which case the hand brake has its own cross-shaft and hookup, and is In no way connected with the foot or service brakes. c. Front Wheel Control. The hookup of the brake rods to the front wheels must be designed to allow the wheels to turn without locking In any position. If the front wheels lock, steering is destroyed. One means of controlling the front wheels is the use of the brake rod attached to a camshaft, with a small universal joint above the steering knuckle pivot. A more popular and satisfactory method employs a flexible steel cable connecting the end of the brake rod to the brake camshaft lever (fig. 34-18). Because of the flexibility of the cable and its sheath, motion of the wheel does not affect tension on the cable. Flexible steel cables also may be used advantageously on the rear wheels because of the vibration of the wheels when traveling over the road. On some braking systems, the pressure on the wheel brakes is distributed evenly by various types of equalizers. Equalizers are designed to take up all the slack In the hookup to each brake so that all brakes will be applied at the same time. This prevents the possibility of too much pressure being applied to any one brake, which would lock that wheel and probably make the vehicle skid. One of the main reasons why the mechanical braking system has been supplanted Is the difficulty of maintaining equal pressure on all brakes.
TM 9-8000
34-23. Principles of the Hydraulic System. In hydraulic braking systems, the pressure applied at the brake pedal is transmitted to the brake mechanism by a liquid. To understand how pressure is transmitted by a hydraulic braking system, it is necessary to understand the fundamentals and principles of hydraulics. Hydraulics is the study of liquids in motion, or the pressure exerted by liquids conveyed in pipes or conduits. One well-known hydraulic principle is that liquids cannot be compressed under ordinary pressures. This may be demonstrated by placing a weight on top of a piston fitted to a jar (A, fig. 34-19). The force of the weight does not change the level of the liquid, therefore, it does not diminish the volume or compress the liquid. Another well-known hydraulic principle is Pascals law (para 20-2), which states that force exerted at any point upon a confined liquid is distributed equally through the liquid in all directions. That is, if a total force of 20 pounds, including piston and weight, is placed upon liquid in a jar, and if the piston in the jar has an area of 5 square inches, the unit hydraulic pressure is increased by 20/5, or 4 psi. This is illustrated in B, figure 34-19. A gage inserted at any point in the jar will indicate the same pressure of 4 psi, because the liquid transmits the pressure equally throughout the jar. Use of these hydraulic principles may be illustrated by interconnecting two jars, of the same diameter, containing liquid (C, fig. 34-19). If a force is exerted on a piston in one jar, as in the left jar in C, figure 34-19, a piston placed in the other jar will receive the same amount of force, due to the transmission of pressure by the liquid. When the areas of the two pistons are equal, moving one piston produces identical movement in the other piston because the liquid is not compressible and therefore maintains the same volume. By connecting one jar with another jar that has twice the diameter and therefore four times the area of the first jar (D, fig. 34-19), the results are somewhat different, although the same basic facts apply. When a force is exerted on the piston in the small jar, the piston in the large jar will receive four times as much force because the hydraulic pressure acts on four times the area.
Because the liquid will always occupy the same volume, the large piston will move one-fourth as far as the small piston. Thus, a mechanical advantage is obtained very similar to that obtained from a simple lever. With four jars, all of the same diameter, connected to a central jar (E, fig. 34-19), an approximation of the action in four-wheel brakes is obtained. A force exerted on the piston in the central jar will be transmitted to each of the other jars so that the piston in each will receive an identical force but will move only one-fourth as far as the central piston. If the four jars have a larger diameter than the central jar, the total pressure on each of the four pistons is greater than that applied to the central one, and each of the four pistons moves less than one-fourth as far as the central piston. Hydraulic brake systems operate in such a manner. 34-24. Operation. In a hydraulic brake system, the force is applied to a piston in a master cylinder that corresponds to the central jar (fig. 34-20). The brake pedal operates the piston by linkage. Each wheel brake is provided with a cylinder fitted with opposed pistons connected to the brake shoes. The brake pedal, when depressed, moves the piston within the master cylinder, forcing the brake liquid or fluid from the master cylinder through tubing and flexible hose into the four wheel cylinders. A diagram of a hydraulic brake system is shown in figure 34-20. The brake fluid enters each of the wheel cylinders between opposed pistons, making the pistons move the brake shoes outward against the brake-drum. As pressure on the pedal is increased, greater hydraulic pressure is built up within the wheel cylinders and, consequently, greater force is exerted against the ends of the shoes. When pressure on the pedal is released, retracting springs on the brake shoes return the wheel cylinder pistons to their release position, forcing the brake fluid back through the flexible hose and tubing to the master cylinder.
34-23
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b. Check Valve. A combination inlet and outlet check valve (fig. 34-21) is in the head of the master cylinder, held in place by the piston return spring. The check valve consists of a rubber valve cup In a steel valve case. This assembly rests on a rubber valve seat that fits in the end of the cylinder. In some designs, the check valve consists of a spring-operated outlet valve seated on a valve cage, rather than a rubber-cup outlet valve. The principle of operation is the same. The piston return spring normally holds the valve cage against the rubber valve seat to seal the brake fluid in the brake line.
c. Dual Master Cylinder. The dual master cylinder (fig. 34-21) contains two brake circuits that are separated hydraulically. The individual brake systems may be designed to divide the system front to rear, diagonally, or in various other fashions. If a brake fluid leak develops in one circuit, the other circuit still provides emergency stopping capability. As the brake pedal Is depressed under normal operating conditions, it forces the primary piston forward to cover the primary compensating port. At this time, the primary chamber is sealed and direct hydraulic pressure is transmitted to the secondary piston. As the brake pedal continues to travel, the secondary piston covers the compensating port. Further application of the brake pedal develops the pressure required to apply the brake components. Should a leak develop in the primary circuit, the brake system would not be rendered useless. During the application of the brakes, the primary piston would continue to move forward, unable to build pressure due to the malfunction. Approximately halfway through its maximum stroke, the primary piston contacts the secondary piston. Further application of the brake would force the secondary piston forward to develop pressure In the secondary system, which would allow for braking action to take place In two wheels. Should the secondary circuit fail, braking for the other two wheels would still be available. The primary piston would move forward and cover the primary compensating port as before. Because of the rupture in the secondary circuit, the secondary or floating piston would be moved to its extreme stop by the force of the return spring. Further application of the brake would develop enough pressure in the primary circuit to apply the brakes connected to this circuit, therefore allowing the vehicle to maintain some stopping ability. TA233872
a. Piston. The piston (fig. 34-21) is a long, spool-like member with a rubber secondary cup seal at the outer end and a rubber primary cup that acts against the brake liquid just ahead of the Inner end. This primary cup is kept against the end of the piston by a return spring. A steel stop disk, held in the outer end of the cylinder by a retainer spring, acts as a piston stop. A rubber boot covers the piston end of the master cylinder to prevent dust and other foreign matter from entering it. This boot is vented to prevent air from being compressed within it.
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TM 9-8000 34-26. Wheel Cylinder. The wheel cylinder (A, fig. 3422) changes hydraulic pressure to the mechanical force that pushes the brake shoes against the drums. The wheel cylinder housing is a casting mounted on the brake backing plate. Inside the cylinder are two pistons that are moved in opposite directions by hydraulic pressure and which, at the same time, push the shoes against the drum. The pistons or piston stems are connected directly to the shoes. Rubber piston cups fit tightly in the cylinder bore against each piston to prevent the escape of brake liquid. There Is a light spring between the cups to keep them in position against the pistons. The open ends of the cylinder are fitted with rubber boots to keep out foreign matter. Brake fluid enters the cylinder
TM 9-8000 from the brake line connection between the pistons. At the top of the cylinder, between the pistons, Is a bleeder hole through which air is released when the system is filled with brake fluid. A stepped wheel cylinder (B, fig. 34-22) is used to compensate for faster rate of wear on the front shoe than on the rear shoe, due to selfenergizing action. By using a larger piston for the rear shoe, the shoe receives more pressure to offset the selfenergizing action on the front shoe. This requires a stepped wheel cylinder with two bore sizes. If it is desired that both shoes be independently self-energizing, especially on the front wheels, it Is necessary to have two wheel cylinders, one for each shoe. Each cylinder has a single piston (C, fig. 34-22), and is mounted on the opposite side of the brake backing plate from the other cylinder. Such an arrangement is shown In figure 34-9. 3427. Hill Holder. The hill holder provides greater ease of vehicular control on hills and in traffic. The device Is connected to the clutch pedal and keeps the brakes applied as long as the clutch pedal Is depressed when the car is on an upgrade, even after the brake pedal Is released. The driver then Is able to use his or her right foot for the accelerator pedal. 34-28. Brake Lines. The brake lines transmit fluid under pressure from the master cylinder to the wheel cylinders. High-quality double thick steel tubing (fig. 34-23) is used where no flexing is involved. The tubing also is copper plated and coated with lead to prevent rust and corrosion. Due to the relative movement of the suspension, a high-pressure hose (fig. 34-23) is used to transmit fluid to each front wheel brake assembly and to the components on the rear axle(s). Mounting brackets also are used where flex hoses connect to solid hoses. The mounting brackets help hold the assemblies secure and reduce vibration, which may cause metal fatigue. 34-29. Brake Fluid. Hydraulic brake fluid is the liquid medium In the brake system used to transmit fluid motion and pressure to the wheel brake components. The hydraulic brake fluid used in todays modern vehicles must have some important properties; the most important are discussed below. The fluid must remain a liquid during all operating temperatures. The boiling point of the
a. Standard Fluid. Standard brake fluid is composed chiefly of equal parts of alcohol and caster oil. This combination of fluids worked well under normal conditions but boiled easily and became a vapor under heavy-duty application. Standard fluid also tends to separate into components when exposed to low temperatures. The Increasing requirements of brake fluid led to the development of silicone brake fluid b. Silicone Brake Fluid. After 40 years of research and development, a brake fluid that was acceptable under extreme operating conditions was developed. This fluid achieved low water pickup and good corrosion protection. The fluid also provides good lubrication qualities and rubber compatibility. Silicone brake fluid has been used in all military vehicles since the end of 1982. TA233875
34-28
TM 9-8000 and holds the pressure constant regardless of Increases In supply pressure to the valve. In- creases In brake fluid requirement in the closed- off brake line due to heat expansion or contraction are adjusted automatically by the valve through a brief reopening of the valve to supply pressure. Once the pressure adjustment Is completed, the valve automatically closes off the brake line with the limited pressure.
34-30. Proportioning Valve. Due to the lack of selfenergizing and servo effect, disk brakes operate at higher line pressures than drum brakes. For this reason, a proportioning valve Is used. The proportioning valve Is designed to limit the amount of pressure routed to the rear brakes when a combination of disk brakes and drum brakes are used on a vehicle. By limiting pressure to the rear wheels, the chances of rear wheel lockup are reduced during a hard stop. 34-31. Limiting Valve. The limiting valve closes off one brake line at a certain brake line pressure
34-32. Construction. Power braking systems are designed to reduce the effort required to depress the brake pedal when stopping or holding a vehicle stationary. Most power brake systems use the difference in pressure between intake manifold vacuum and atmospheric pressure to develop the additional force required to decrease brake pedal pressure. When a vehicle Is powered by a diesel engine, the absence of intake manifold vacuum requires the use of an auxiliary vacuum pump. This type of pump usually Is driven by the engine or by an electric motor. The vacuum power booster may be classified into two basic categories: vacuum suspended and atmospheric suspended (A, fig. 34-24). The vacuum-suspended power booster utilizes Intake manifold vacuum that acts on both sides of the diaphragm in the released position. When the brakes are applied, one side of the diaphragm is vented to atmosphere. This causes the diaphragm to move in the direction of the lowest pressure. This movement develops a force that is directed on the push rod of the master cylinder to aid in reducing brake pedal pressure. The atmospheric-suspended booster allows atmospheric pressure to act on the diaphragm in the released position. When the brakes are applied, the side of the diaphragm toward the master cylinder is subjected to controlled vacuum, therefore moving the diaphragm in that direction, which assists in applying the brakes. The power brake unit functions during three phases of braking application: brakes released, brakes being applied, and brakes holding. A typical vacuum-suspended power brake unit (B, fig. 34-24) will be used to describe these operations. 34-29
a. Released Position (C, Fig. 34-24). With the brakes fully released, and engine operating, the rod and plunger return spring moves the valve operating rod and valve plunger to the right. As this happens, the right end of the valve plunger Is pressed against the face of the poppet valve, which in turn, closes off the atmospheric port. With the vacuum port opened, vacuum Is directed to both sides of the diaphragm and the return spring holds the diaphragm away from the master cylinder In the released position. b. Applied Position (D, Fig. 34-24). As the brake pedal is depressed, the valve operating rod moves to the left, which causes the valve plunger to move left also. The valve return spring then Is compressed as the plunger moves and the poppet valve then comes in contact with the vacuum port seat. As this happens, the vacuum port to the right side of the diaphragm closes. Continued application of the brake pedal causes the atmospheric port to open by the valve rod forcing the valve plunger away from the poppet. As this happens, atmospheric air pressure rushes into the control vacuum chamber and applies pressure to the hydraulic push rod. c. Holding Position (E, Fig. 34-24). As the driver stops depressing the brake pedal, the plunger also will stop moving. The reaction of the brake fluid transmitted through the reaction disk now will shift the valve plunger slightly to the right, which shuts off the atmospheric port. As this position is held, both sides of the diaphragm contain unchanging amounts of pressure, which
TM 9-8000
TM 9-8000 exerts a steady amount of pressure on the master cylinder piston. 34-33. Tandem Booster. The tandem booster (fig. 3425) makes use of dual diaphragm plates to increase the apply pressure to the master cylinder piston assembly. This is used for heavy-duty application on some larger vehicles. 34-34. Piston Booster. The piston-type booster (fig. 3426) uses a sliding piston assembly fitted to the outer shell of the booster. The piston is provided with seals to assist in airtight operation. 34-35. Bellows Booster. The bellows-type booster (fig. 34-27) works by an expanding and contracting bellows. The booster usually is mounted above the brake pedal pivot point and acts against the brake pedal itself, rather than the master cylinder. 34-36. Brake-Pedal Booster. The brake-pedal booster (fig. 34-28) is configured the same way
TM 9-8000
34-37. Hydraulic-Power Booster. The hydraulic-power booster, also called a hydroboost (fig. 34-29), Is operated by hydraulic pressure developed by the power steering pump. Should the power steering pump become Inoperative, an auxiliary electric pump then is used for backup and safety reasons. The hydraulic booster Is attached directly to the master cylinder and is actuated by the brake pedal. The hydroboost system has an accumulator built into the system The accumulator, which is spring loaded and can also contain pressurized gas, is filled with fluid, and pressurized whenever the brakes are applied. Should the power steering system fail because of a lack of fluid or a broken belt, the accumulator will retain enough fluid and pressure for about three brake applications. TA233878
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34-38. Pneumatic Principle. Unlike liquids, gases are compressed easily. If a gas, such as air, Is continued and a force applied to it, it is compressed and has less volume. Such a force can be exerted by placing a weight on a piston that fits into a container. The air that originally filled the entire container is pressed into only a portion of the container, due to the force of the weight upon it (fig. 34-30). The pressure of the compressed air, resulting from the force exerted upon it by the weight, will be distributed equally in all directions just as it is in a liquid. Compressed air under pressure may be stored conveniently and made available for the power application of brakes. a. Essential Action. An air pump or compressor driven by the engine Is used to compress air and force it into a reservoir, where it is forced under pressure and made available for operating the brakes. Air under pressure in the reservoir is released to the brake lines by an air valve operated by the brake pedal. This released air goes to brake chambers (located close to the wheel brakes), which contain a flexible diaphragm. Against this diaphragm is a plate that is connected directly to the mechanism on the wheel brakes by linkage. The force of the compressed air admitted to the chamber causes the diaphragm to move the plate and operate the brake shoes through the linkage. Considerable force Is available for
as 100 psi. All brakes on a vehicle, and on a trailer when one Is used, are operated together by means of special regulating valves.
b. Fundamental Units. A diagram of a typical airbrake braking, because operating air pressure can be as high system used on a motor vehicle is shown in figure 34-31. The fundamental units and their functions are described in paragraph 34-39.
TM 9-8000
a. Air Compressor. Air compressors usually are single-acting reciprocating units, either self-lubricated or lubricated from the vehicle engine lubricating system. Both water-cooled and air-cooled cylinder heads are used. Compressors having a displacement of approximately 7 cfm have two cylinders (fig. 34-32), while those with a displacement of 12 cfm have three cylinders (fig. 34-33).
The air compressors operate continuously while the engine is running, but the actual compression of air is controlled by the governor. With a partial vacuum created on the piston downstroke, intake ports are uncovered near the bottom of the stroke. Intake ports are covered as the piston starts its upstroke. Air in the cylinder is
b. Unloader. When the reservoir air pressure reaches the maximum setting of the governor, air under pressure is allowed by the governor to pass into a cavity below an unloading diaphragm in the cylinder head. This air pressure lifts one end of the unloading lever, which pivots on its pin and forces the unloading valves off their seats. With the unloading valves off their seats, the unloading cavity forms a passage between the cylinders above the pistons. Air then passes back and forth through the cavity between the cylinders and compression is stopped. A drop in air pressure below the minimum setting of the governor causes TA233880
34-34
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c. Governor. The governor maintains the air pressure in the reservoir between the desired maximum and minimum values, by controlling the compressor unloading mechanism. The Bourdon gage principle of a curved metal tube that tends to straighten under internal pressure is utilized. Air under pressure from the reservoir always is present below the lower valve and in the tube. As air pressure increases, the load of the tube (fig. 3434) on the lower valve is relieved, because the
34-35
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Figure 34-33. Typical Air Compressor, Three-Cylinder. d. Airbrake valve. The airbrake valve lever Is connected to the brake pedal. Movement of the lever controls the operation of the Inlet and exhaust valves (fig. 34-35) that control the air under pressure delivered to or released from the brake chambers. As the brake pedal is de- pressed, the brake valve lever moves toward its applied position. The plunger and regulating spring are forced down, applying mechanical force on the diaphragm. The exhaust valve spring Is weaker than the Intake valve spring, so the exhaust valve is forced downward onto its seat before the Intake valve Is opened. When the intake valve opens, air from the reservoir Is allowed to flow through the brake valve to the brake chambers to apply the brakes. When the air pressure below the diaphragm overcomes the mechanical
34-36 force exerted on top of the diaphragm, the diaphragm lifts sufficiently to close the intake valve and maintain the system in the holding position. Further depression of the pedal puts additional mechanical force on the diaphragm, thereby allowing further brake application. If the driver releases the brake pedal, reducing the mechanical force on the diaphragm, the Inlet valve remains closed, while the exhaust valve opens to allow the air under pressure to be exhausted from the brake chambers to release the brakes.
e. Brake Chamber. The brake chamber (fig. 34-36) converts the energy of the compressed air Into mechanical force to operate the brakes. Air TA233882
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under pressure enters the brake chamber behind the diaphragm and forces the push rod out against the return spring force. Because the yoke on the end of the push rod is connected to the slack
adjuster, this movement rotates the slack adjuster, brake camshaft, and cam to apply the brakes.
TM 9-8000
through the port to the cavity above the diaphragm (fig. 34-38). Because this cavity is comparatively small, it is subject to quick changes in air pressure, causing the valve to react quickly. Operation of the valve is similar to that of the quick release valve. Air pressure from the brake valve forces the diaphragm down to close the exhaust port beneath the diaphragm outer edge. Further air pressure depresses the center of the diaphragm, opening the supply valve, and compressed air flows into the cavity below the diaphragm and into the brake chambers. As soon as the air pressure above the diaphragm is equalized by the brake chamber air pressure, the diaphragm is raised to the holding position, closing the supply valve and keeping the exhaust port closed. When the air pressure above the diaphragm is reduced by the operator releasing the brake pedal, the brake chamber air pressure lifts the diaphragm, opening the exhaust port and exhausting the compressed air pressure from the brake chamber.
h. Slack Adjuster. Slack adjusters (fig. 34-39) function as adjustable levers and provide a means of adjusting the brakes to compensate for wear of linings. During brake operation, the entire slack adjuster rotates with the brake camshaft, which is connected to the slack adjuster through the splined central hole. For brake adjustment, the worm moves the gear, changing the position of the lever arm with respect to the camshaft.
g. Relay Valve. The relay valve (fig. 34-38) is controlled by the brake valve, and speeds up application and release of the rear wheel brakes for long wheel-base vehicles. It reacts quickly to slight changes in air pressure from the brake valve. When the brake pedal is operated, air under pressure from the brake valve is delivered
34-38
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TM 9-8000 Section IX. 34-40.Construction. The air-over-hydraulic brake 34-41. Operation. The air-hydraulic cylinder (fig. 34-40) system is shown in figure 34-40. Air pressure is supplied consists of an air cylinder and a hydraulic cylinder in by a compressor and stored in reservoirs, as with the tandem, each fitted with a piston with a common piston airbrake system. The master cylinder is similar to the rod between. The air piston is of greater diameter than master cylinders used in hydraulic brakes. Also, the the hydraulic piston. This difference in areas of the two wheel brake cylinders and wheel brake construction are pistons gives a resultant hydraulic pressure much very similar to that used in hydraulic brakes. The greater than the air pressure admitted to the air cylinder. essential difference between the straight hydraulic brake Automatic valves, actuated by fluid pressure from master system and the air-over-hydraulic brake system lies in cylinder, control the air admitted to the air cylinder. Thus, the air-hydraulic cylinder. This cylinder consists of three the fluid pressure in brake lines is always in a direct ratio essentials: a large-diameter air piston; a small-diameter to foot pressure on brake pedal. An air line from an airhydraulic piston in tandem with it, both on the same rod; hydraulic cylinder leads to a trailer coupling at the rear of and a set of valves controlled by hydraulic pressure from vehicle. the master cylinder for admitting air into the air-cylinder section of the air-hydraulic cylinder. Valve action varies with the amount of brake pedal pressure, as mentioned in paragraph 34-39d. When heavy brake pedal pressure Is applied by the
TM 9-8000 driver for hard braking, the hydraulic pressure in he master cylinder (which operates the valves) causes greater valve movement, and therefore, he valves admit more air pressure into the air- hydraulic cylinder. This higher air pressure . causes a stronger braking action. With only a light brake pedal pressure, the valves admit less air pressure into the air-hydraulic cylinder and the braking action is lighter
34-42. Construction. Hydrovac is the trade name for a one-unit, vacuum-power braking system. It combines a hydraulically actuated control valve, a tandem piston vacuum- power cylinder, and a hydraulic slave cylinder into one assembly. It is connected hydraulically to both the master cylinder and the wheel brakes, eliminating the need for mechanical connections with the brake pedal and linkage. The vacuum-power cylinder Is divided into four compartments by the front and rear pistons and the center plate. The vacuum source Is connect ed directly to the compartment between the center plate and rear piston. The vacuum Is connected from this compartment, by means of the vacuum line, to the relay or control valve. From the control valve, the vacuum Is connected to the front compartment by a passage In the valve body. 34-43. Operation. In the released position (fig. 34-41), with the control valve diaphragm plate and the vacuum valve seat held down by the valve spring to keep the vacuum valve open and the atmospheric valve closed, the vacuum is connected through the vacuum valve and atmospheric control line to the compartment between the center plate and front piston and, through the ports in the hollow piston rod, to the rear compartment. Vacuum , therefore, is present In all four compartments in the released position and both pistons remain inoperative. The piston return spring holds the pistons In the OFF position. The push rod, in the released position, maintains the bypass (check) valve off its seat, permitting a direct hydraulic connection from the master cylinder, through the hydraulic slave cylinder, to the wheel cylinders. With this construction, foot pedal pressure can be applied to the wheel cylinders for braking action, should vacuum or Hydrovac failure make the power cylinder Inoperative. The relay valve diaphragm has vacuum on both sides and Is held in the OFF position by the valve spring. When the vacuum In the Hydrovac is the same as, or greater than, the 34-41
source vacuum, the poppet valve in the vacuum check valves rests on its seat and, in the event of engine failure or rapid acceleration, traps the vacuum in the Hydrovac system in readiness for brake application. As the foot pedal is de- pressed, fluid is forced from the master cylinder through the open bypass (check) valve to the slave cylinder and on to the wheel cylinders. The fluid also is forced through the drilled bypass passage to the relay valve hydraulic piston, which is forced outward against the pressure of the valve spring, gradually forcing the diaphragm plate and vacuum valve seat toward the applied position. The movement of the diaphragm first closes the vacuum valve against Its seat, sealing off the vacuum from the atmospheric control line. After the vacuum valve Is seated, further motion of the diaphragm causes the atmospheric valve to leave Its seat, permitting air from the air cleaner to enter the atmospheric control line, then to the compartment between the center plate and front piston and, through the hollow piston rod, to the rear compartment (fig. 3442). With the vacuum still present on the front sides of both pistons, and atmospheric pressure on the rear sides of both pistons, the pistons are caused to move toward the slave cylinder by the difference in pressure, Movement of the pistons and push rod toward the slave cylinder first closes the bypass (check) valve, and causes the slave-cylinder piston to move outward, forcing fluid under high pressure into the wheel cylinders to apply the brakes. The foot pedal pressure, acting through the mastercylinder, also acts against the slavecylinder piston, assisting the vacuum pistons and push rod. The pressure at the wheel cylinders (that is, the total braking effort) is the sum of the output of the vacuum pistons In the Hydrovac and of the foot pedal pressure at the master cylinder. Release of foot pedal pressure allows the valve spring In the relay or control valve to return the atmospheric and vacuum valves to the released position by removing the fluid pressure from below the relay valve hydraulic piston. The atmosphere Is exhausted from the rear sides of both pistons,
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making them inoperative and allowing the piston return spring to move the pistons to the released position. When the foot pedal movement stops at some intermediate point between the released and fully applied position, the pistons will move toward the lap position so that the fluid pressure under the relay-valve hydraulic piston will be reduced the necessary amount to allow the 34-42
diaphragm to drop and close both the atmospheric and vacuum valves in the control valve. Thereafter, the slightest foot pedal movement, either toward the released or the applied position, will result in the opening of either the vacuum or the atmospheric valve, and will release partially or apply further the brakes.
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Section XI. 34-44. Construction. T he electric brake system, which operates from the storage battery or the electrical system, is quite simple. Wiring replaces the rods, cables, and tubings used in other types of brakes. The controller can be mounted at any convenient place in the drivers compartment. It usually is attached to the steering column. A bronze lever (fig. 34-43) within the controller, connected by linkage to the brake pedal, acts as a rheostat switch. The controller is provided with electrical terminals to connect it in the electric brake circuit. As the brake pedal is
depressed, the bronze lever comes in successive contact with leaves of varying lengths and completes the electric circuit from the battery to an electromagnet in the brake. Electric current is supplied to the electromagnet, the amount depending on the number of leaves contacted by the bronze lever. When the brake is fully depressed, all the leaves are in contact with the bronze lever and the maximum amount of current flows to the brake. TA233888
34-43
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34-45. Operation. The armature assembly revolves with the brakedrum and is kept in constant contact with the electromagnet by means of flat springs. When the brake pedal is depressed, the current flows from the controller to the brake and through a coil of copper wire in the magnet, setting up a magnetic field and causing the magnet to attract the armature. The farther the foot pedal is depressed, the greater the amount of current is that reaches the magnet and the tighter the magnet clings to the armature. This attraction of the magnet to the armature causes the magnet, which can revolve within a limited arc, to start turning with the armature. As the magnet turns, it engages a cam lever, which In turn expands the brake band evenly against the brakedrum in the conventional way. When the current is cut off by removing pressure from the brake pedal, the magnet in each brake Is
demagnetized and remains stationary. The brake return springs release the brake bands from contact with the brakedrums. The principle of the electric brake permits use of a selfadjusting feature to compensate for lining wear. As the brake band wears, the electromagnet moves a little farther to drive the brake lining against the surface of the drum. An automatic stop on the brake band prevents the rivets from coming into contact with the drum after excessive wear, eliminating danger of scoring of the drum. If the vehicle Is standing still and the current is turned on, there is no action of the brakes. If the wheel revolves in the slightest degree, however, the brake is operated.
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PART SIX HULLS, BODIES, AND FRAMES CHAPTER 35 VEHICLE STRUCTURE Section I. WHEELED VEHICLES -
35-1. Separate Frame and Body. The separate frame and body type of vehicle construction (fig. 35-1) is the most common technique used when producing most fullsized automobiles and cargo vehicles. In this type of construction, the chassis frame and the vehicle body are made separately and each is a complete unit by itself. The chassis frame is designed to support the weight of the body and absorb all of the loads imposed by the terrain, suspension system, powerplant, drive train, and steering system while the body merely contains and, in some cases, protects the cargo. The body generally is bolted to the frame at a few points to allow for flexure of the frame and to distribute the loads to the intended load-carrying members. With this type of construction, the body structure only needs to be strong and rigid enough to contain the weight of the cargo and resist any dynamic loads associated with cargo handling and cargo movement during vehicle operation and to absorb shocks and vibrations transferred
from the frame. In some cases, particularly under severe operating conditions, the body structure may be subjected to some torsional loads that are not absorbed completely by the frame; however, this is not common. This explanation basically applies to heavy trucks and not to passenger automobiles. In a typical passenger automobile, the frame supplies approximately 37 percent of the torsional rigidity and approximately 34 percent of the bending rigidity; the balance is supplied by the body structure. The following are the most important advantages of the separate body and frame construction. a. Ease of mounting and dismounting of body structure.
b. Versatility; various body types can be adapted readily to standard truck chassis.
c. Strong, rugged designs are achieved easily, although at a penalty to vehicle weight.
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d. Isolation of noise generated by drive line components from crew and passenger compartments through the use of rubber mounts between frame and body structures.
e. Simplistic design that yields a relatively Inexpensive and easy manufacturing process. The separate body and frame has many advantages, as listed above, but along with this design, other criteria must be considered. The vehicle silhouette and cargo floor are higher. Weight is Increased. This configuration also is inherently less desirable for amphibious vehicles, because it is less effective in developing maximum buoyancy for minimum weight. 35-2. Integrated Frame and Body (Monocoque). The integral frame and body type of construction (fig. 35-2), also referred to as unitized construction, combines the frame and body Into a single, one-piece structure by welding components together, by forming or casting the entire structure as one piece, or by a combination of these techniques. Merely welding a conventional body to a conventional
chassis frame, however, does not constitute an integral frame and body construction. In a truly integrated structure, the entire frame-body unit is treated as a loadcarrying member that reacts to all the loads experienced by the vehicle-road loads as well as cargo loads. Integral-type bodies for wheeled vehicles are fabricated by welding preformed metal panels together. The panels are preformed in various load bearing shapes that are located and oriented so as to result in a uniformly stressed structure. Some portions of the integrated structure resemble frame-like parts, while others resemble body-like panels. This should not be surprising, because the structure must perform the functions of both of these elements. The following are some of the advantages and disadvantages of the integral frame and body type of construction, when compared to the separate frame and body concept. a. Substantial weight reduction, which Is possible when using a well-designed unitized body.
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trucks, the frames are simple, rugged, and of channel iron construction. The side rails usually are parallel to each other at standardized SAE widths to permit the mounting of stock transmissions, transfer assemblies, rear axles, and similar components. Trucks that are to be used as prime movers have an additional reinforcement of the side rails and rear crossmembers to compensate for the added towing stresses. 35-4. Brackets and Hangers. Frame members serve as supports to which springs, independent suspensions, radiators, or transmissions may be attached. Additional brackets, out-riggers, engine supports, and horns are added for the mounting of running boards, longitudinal springs, bumpers, engines, towing hooks, shock absorbers, gas tanks, and spare tires.
f. Difficulties encountered when different body types are mounted on a basic chassis.
35-3. Truck Frame (Ladder). Trucks of up to 1-ton capacity have frames whose rear sections resemble a ladder. This type of frame (fig. 35-3) allows for different types of truck beds or enclosures to be attached to the frame. For larger
35-5. Armored Hulls of Tanks. The tank hull is the strongest and heaviest hull used on any vehicle. It must be fabricated to withstand ballistic shocks from highvelocity kinetic energy-type projectiles, the blast effects of high-explosive rounds and mines, and the penetrating effects of chemical energy rounds, and be rigid enough to provide a stable firing platform for the primary weapon system and fire control equipment. In addition, it must provide sufficient space in its interior to house the propulsion system, an adequate fuel supply, working space for the crew, and stowage space for ammunition and necessary supplies and equipment. The hull also must be small and light enough to have a reasonable degree of maneuverability and to be able to pass over and through standard traffic lanes, bridges, and overpasses. Tank hulls of the type shown in figure 35-4 are one-piece castings of armor steel with a welded floor of rolled armor plate. They contain a drivers compartment in the front portion, a crew compartment at the center, and a compartment for the engine and transmission at the rear. The crew compartment is separated from the engine compartment by a steel bulkhead that is welded in place and serves as a firewall between the two compartments. Access doors and plates in this bulkhead provide access to the accessory end of the engine. 35-6. Unarmored Hulls and Self-Propelled Guns. There are, in general, two types of unarmored selfpropelled guns. The first type, such as the M56, 90-mm self-propelled gun (fig. 35-5), is unarmored in order to achieve the weight restriction imposed by phase I airborne operations. These weapon systems provide close support and antitank capabilities to airborne operations. Although these vehicles are subjected to direct enemy fire, they rely on their speed and agility for their safety. As the airborne weight limitations are relaxed, due to improved aircraft, it is probable that future
airborne assault weapons will be armored lightly. This type of vehicle hull will be required to have swimming capabilities as well as the capability to withstand the weapon firing loads. The second type of unarmored self-propelled guns is large-caliber weapon systems employed primarily for counterbattery fire, the destruction of field works and reinforced concrete, interdiction fire, and to demoralize the enemy. This class of vehicles includes the 175-mm (fig. 35-5) and 8-inch howitzers. These vehicles do not require extensive armor, because they normally are employed far enough behind the battleline to encounter only long-range predicted fire weapon attacks. Furthermore, because the weapon weight for this type of vehicle Is large, the addition of armor would degrade their mobility seriously. The prime hull design consideration for this type of vehicle is the weapon firing reaction load. 35-7. Wheeled Amphibian Hulls. Wheeled amphibious vehicles have both a hull and a frame. Designed to provide buoyancy necessary for flotation, the basic hull assembly is of all-steel, watertight, welded construction, with reinforcements to add to its rigidity. It is built to accept the chassis frame and powerplant. The frame, similar to a conventional truck frame, is installed inside and is bolted to the hull. The powerplant and power train are supported by the frame. The running gear, underneath the hull, is attached to both the hull and frame. 35-8. Tracked Amphibian Hulls. The hull of tracked landing vehicles is defined as the framework of the vehicle, together with all inside and outside plating but exclusive of equipment. It is the main, or central, section that runs from front to rear; it consists of the cab, cargo compartment, and engine room. Technically, a part of the hull are the pontons that are welded to each side of it. Engines, controls, armament, and driving assemblies are housed in, or mounted on, the main hull.
35-4
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TM 9-8000 CHAPTER 36 ACCESSORIES Section I. POWER TAKEOFF 36-1. Purpose. A power takeoff Is an attachment for connecting the engine to power-driven auxiliary machinery when its use Is required. It is attached to the transmission, auxiliary transmission, or transfer case. A power takeoff installed at the left side of a transmission Is shown in figure 36-1. It is used to drive a winch, located at the front of the truck, through a universal joint and propeller shaft. 36-2. Construction. The simplest type of transmission power takeoff is the single-gear, singlespeed type shown in figures 36-2 and 36-3. This unit is bolted over an opening provided for the purpose at the side of the transmission case. This opening is closed by a cover plate when no power takeoff is used. The opening in the transmission case and the power takeoff gear meshes with a gear on the transmission countershaft. As shown in figure 36-2, the gear slides on the splined main shaft, off which the power is taken. The shifter shaft, controlled by a lever in the drivers cab, slides the gear in and out of mesh with the countershaft gear. Since it is driven by the countershaft, the power takeoff shaft rotates in the same direction as the engine crankshaft. 36-3. Main Transmission Power Takeoffs. Transmission power takeoffs are available in several different designs: a single-speed, twogear model in which the rotation of the power takeoff shaft is opposite to that of the engine; a model having a single speed forward and reverse; and a model having two speeds forward and one reverse. Several different mountings also are available. 38-4. Auxiliary Transmission Power Takeoffs. The same types of power takeoffs also are applied to auxiliary transmissions. Figure 36-4 shows a winch driven off an auxiliary transmission.
TM 9-8000
Figure 36-2. 36-5. Transfer Case Power Takeoff . Power sometimes is taken off a transfer case. The transfer case drive shaft, which is connected to the transmission, extends through the case, and the power takeoff shaft is engaged to it by a dog clutch. This transfer case has two speeds and a neutral position. It is necessary to put the transfer case sliding gear in the neutral position if the vehicle is to be stationary while the power takeoff is in use. If the power takeoff is needed while the vehicle is in motion, the transfer case may be shifted either into high or low range. With this arrangement, the power takeoff will work on any
speed of the transmission. The positions of all the cab control levers of one model of vehicle are shown in figure 36-5 as they are placed on the instruction plate in the cab. When the power takeoff clutch is engaged, the winch capstan operates; but the winch drum does not rotate until the winch clutch is engaged. 36-6. Usage. The several types of power takeoffs have been described as operating winches, but their uses for operating various kinds of hoists, pumps, and other auxiliary power-driven machinery are essentially the same .
36-2 TA233895
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Figure 36-5. Typical Positions of Transfer and Power takeoff Control Levers for Two-Speed Transfer Assembly with Power Takeoff.
Section II. WINCHES 36-7. Purpose. Using its winch and some type of rigging, a vehicle can pull itself or another vehicle through such obstacles as very muddy or very rough terrains. This is the primary reason for providing winches on standard military vehicles. The winch in this case is powered by the engine of the vehicle through a power takeoff from the transmission. Field expedients may utilize the winch for such devices as simple cranes in a field shop. However, on special equipment and vehicles, winches are furnished for special purposes such as powering the crane of a wrecker. Some of these latter winches are powered by separate gasoline engines. 36-8. Mounting . Generally, the winch is mounted behind the front bumper and is secured to the front crossmember of the frame or between the two side frame rails. It may be mounted behind the cab. The tandem winch assembly, for example, consists of a front (upper) and rear (lower) winch that is secured to a mounting assembly fastened to the chassis frame at the rear of the cab. 36-4 36-9. Operation. The typical front-mounted winch is a Jaw-clutch worm-gear type. The winch consists of a worm and shaft which drives a worm gear that is keyed to a shaft (fig. 36-6). A bushed drum is mounted on the worm-gear shaft which is controlled by a sliding clutch. The wormshaft is driven by a drive shaft connected to a power takeoff unit mounted on the transmission. The hand-operated sliding clutch is keyed to the worm-gear shaft outside of the winch drum, and must be engaged with the jaws on the side of the winch drum when the winch is to be operated. Disengagement of the sliding clutch permits the drum to turn on the worm-gear shaft. Two brakes are provided to control the winch drum. The wormshaft brake prevents the winch drum from rotating under load, when the power takeoff is disengaged. The shifter bracket brake prevents the drum overrunning the cable when the cable is being unreeled. A shearpin on the worm drive shaft prevents damage from overloading. The power takeoff is controlled by a shift lever located in the drivers compartment.
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Section III. TIRE INFLATION SYSTEM 36-11. Purpose. Amphibious trucks are equipped with a central tire-pressure control system, by means of which the tires may be inflated or deflated to meet various conditions encountered by the vehicle. When operating on sand, the tires are deflated to obtain adequate flotation; to travel on a hard surface, the tires are inflated. 36-12. Construction. Location of each component of the system is shown in figure 36-7. A two cylinder, water-cooled, self-lubricated pump with a capacity of 9 cfm is mounted in the front compartment and driven directly by the engine crankshaft. This maintains pressure in the air tank. It is controlled by a governor that stops the pump when maximum allowable pressure is attained and automatically starts the pump when pressure in the tank drops below a prescribed limit. Air pressure is piped from the tank to the inflation and deflation control valves assembly. When the control valve lever is placed in the INFLATE position, air passes through the valve to the air line manifold and valves, then to each tire, and through individual air lines and tire inflating devices. A safety valve is located in the system. The tire-inflating device, or hub device, is mounted on each wheel hub. It is an airtight rotary joint that provides a connection between the air supply line and the tire. The inner part rotates with the wheel hub while the outer part is held stationary by a swivel-ended strut attached to the hull. TA233898 36-5
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TM 9-8000 Section V. DUMP TRUCK MECHANISMS 36-17. General. Dump trucks (fig. 36-12) have a steel body that pivots at the rear. The dump body pivots on two hinge pins when it is raised by a hydraulic hoist cylinder mounted on a transverse base shaft. The pressure developed in the hydraulic hoist cylinder by the operation of a special pump causes the dump body to move up into the position shown in figure 36-13. Since the hydraulic cylinder is double acting, it also is used to hold or lower the dump body. The endgate (fig. 36-14) normally is pivoted at the top, and is secured in this position by lockpins through endgate upper latches. Lower latches hold the endgate closed until they are released by the hand lever on the front left corner of the body. The endgate is released for dumping in this manner, and the extent that it opens is controlled by adjustment of the chains in the locking slots (fig. 36-14). 36-18. Body Control Box. A dump body control lever in the rear and at the left of the drivers seat operates a shift control lever connected by linkage to a control box. Figure 36-15 shows the control lever, while figure 36-16 shows the linkage between the control lever, the control box, and the power takeoff. The body control box contains two cams that move as the control lever is moved; this causes the dump body to raise, hold, or lower, according to the control lever position. 36-19. Dump Body Control Lever (Fig. 36-15). The dump body control lever, located in the cab, has four positions. In position A, the body is down and the power takeoff is disengaged. When the control lever is moved to position B, the forward arm in the control box is engaged and the shift linkage engages the power takeoff. To raise the body, the control lever is moved forward past position C to position D. The lift can be stopped and the body held in any position by returning the control lever to position C. With the lever at position B or D, the body is automatically checked at either the up or down position at the limit of travel. 36-20. Control Valve and Pump. When the power takeoff is engaged, the pump is driven. It can now deliver hydraulic fluid to the hydraulic cylinder, _provided the control valve is properly positioned. The control valve is linked to the control lever (fig. 36-15). When the control lever is moved to position D, the control valve directs the hydraulic
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Figure 36-16. Control Linkage Between Control Lever, Control Box, and Power Takeoff.
Section VI. WRECKER TRUCK EQUIPMENT 36-22. General. Wrecking trucks (fig. 36-17) include front and rear winches and a crane assembly. Winches are described in paragraph 36-7. The crane assembly consists of a combination of units, all mounted on the crane A-frame (fig. 36-18). The units include the boom, boom pivot and controls, topping pivot, boom winch and controls, crane winch, crane winch drive and controls, crane winch transmission, and center propeller shaft with connecting parts. All of these units are essential to the operation of the crane. There are other units mounted on the A-frame which are not part of the crane, including the rear winch, rear winch drive, rear winch transmission, and front winch jaw clutch. 36-23. Operation. The various mechanisms incorporated in the crane are driven by the engine through a center propeller shaft. The main drive chain (fig. 36-19) carries the driving power from the propeller shaft to the hoist gearcase, boom gearcase, and swinger gearcase input sprocket. Each gearcase has its own control lever and control system. With these controls, the boom may be raised or lowered, it may be pivoted, and the crane winch can be made to rotate in one direction or the other in order to raise or lower the load.
TA233905 36-12
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a. Combat and transport vehicles, if expected to ford deep water or operate in surf landings, must be specially prepared or equipped to go through such an operation and be used immediately. This means that the vehicle must be able to go through fording or landing operations and continue to operate in a normal condition; that is, the special preparations must not reduce the operative effectiveness of the vehicle. b. Late-type ordnance transport vehicles are specially designed and built for fording and landing operations without modifications. Necessary waterproofing and engine-accessory ventilating systems are already installed on such vehicles. All breathing mechanisms on the vehicles are connected to the carburetor air cleaner and secure air through it. Most important is the engine, which requires large amounts of air for operation. But in addition, the carburetor float chamber, brake master cylinder, fuel tank, transmission and transfer, ignition distributor, and the crankcase ventilator are all vented through the air cleaner. For normal fording operations where a specified depth will not be exceeded (for example, 30 inches on the 1/4-ton 4x4 utility truck M151), no special preparations are required. For deepwater fording, special air intake and exhaust extension tubes must be installed. These raise the height of the intake and exhaust so that deeper water can be forded. All instruments, switches, starter, generator, regulator, battery vents, ignition filter, distributor, and ignition cables are waterproofed, because they will be immersed during fording operations. c. With tanks and tanklike vehicles, the problems of waterproofing and engine ventilation are different from transport vehicles. With tanks, the hull itself must be made waterproof so the individual engine components do not require special treatment or venting. On this type of vehicle, all normal or abnormal openings (cracks, seams, and holes) must be sealed tightly so that no water can enter when the tank is immersed. Examples of normal openings that must be sealed include filled caps, machinegun mounts, and hull ventilators. These generally are sealed by use of nonhygroscopic tape and sealing compounds. Examples of abnormal openings that must be sealed include holes (missing bolts, etc) and cracks or seams in the hull. These can be sealed by first caulking the larger holes with rags, and then covering all openings with sealing
36-15
compound. In addition, special gun shield covers are used to prevent entrance of water around the shield. Special air intake and air exhaust stacks (fig. 36-20) must be installed, and sealing boots placed on machinegun ports in the hull. 36-25. Applications.
a. Operation of a transport vehicle under water is made possible by the sealing, at time of manufacture, of all parts or assemblies that are affected immediately by the entrance of water. Watertight housings are provided for such parts as the instruments, switches, starter, generator, regulator, and distributor. b. A series of ventilating tubes (fig. 36-21) are required to provide venting of various accessories, as described below.
(1) The carburetor float chamber is vented to the air horn by an internal passage and is extended to the air cleaner tube by an external tube (6). (2) The brake master cylinder is vented through the tube (5) that extends up between the foot pedals to the dash elbow (4), mounted on the dash, and the dash elbow to the dash tee tube (3) to the dash tee (15), and the air cleaner to the dash tee tube (14) to the air cleaner. (3) The fuel tank is vented through the gasoline tank to the air cleaner vent tube (2) which connects to the air cleaner. (4) The transmission and transfer are vented through the transfer to the dash tee vent tube (13) connected to the top of the transfer to the air cleaner through the dash tee (15) and the air cleaner to the dash tee tube (14). (5) Positive circulation of air through the distributor housing is ensured by connecting the distributor to the vacuum line tube (11) and the distributor to the air cleaner tube (12). One tube (11) from the air cleaner provides an air intake for
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c. A special type of air cleaner (fig. 36-23), mounted on the engine side of the dash panel, is used with underwater ventilating systems. The air
36-16
d. It is extremely important, in any fording operation, to observe the procedures outlined in the applicable technical manual. These procedures specify the maximum depth of water to be forded by normal and by deepwater fording, the speed at which the vehicle should be driven (3 to 4 mph), and the correct transmission gear ratio (low or low-low).
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1 - WINDSHIELD WIPER TO AIR CLEANER VENTTUBE 2 - GASOLINE TANK TO AIR CLEANER VENT TUBE 3 - DASH ELBOW TO DASH TEE TUBE 4 - DASH ELBOW 5 - MASTER CYLINDER TO DASH ELBOW VENTTUBE 6 - CARBURETOR TO AIR CLEANER VENT TUBE
7 - CRANKCASE VENTILATION VALVES B- VACUUM LINE TEE 9 - CRANKCASE VENTILATION OUTLET TUBE 10 - CRANKCASE VENTILATION INLET TUBE 11 - DISTRIBUTOR TO VACUUM LINE TUBE 12 - DISTRIBUTOR TO AIR CLEANER TUBE 13 - TRANSFER TO DASH TEE VENT TUBE 14 - AIR CLEANER TO DASH TEE TUBE 15 - DASH TEE TA233909 Figure 36-21. Ventilation System for Deepwater Fording. 36-17
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TM 9-8000 CHAPTER 37 PRINCIPLES OF REFRIGERATION Section I. GENERAL 37-1. Ambient Temperature. The temperature of the air surrounding an object is referred to as ambient temperature. As ambient temperature increases, it causes the molecules to interact more violently and increase their length of travel. This results in an increase in physical size. If this principle were applied to a closed system, the result would be an increase in pressure. The opposite happens when the ambient temperature is lowered. The interaction of molecules is less violent and their length of travel is reduced, which results in a decrease in closed system pressure. Figure 37-1 shows the effects of ambient temperature on a closed system. 37-2. Gases Used in Refrigeration. With the exception of changes in state, gases used in refrigeration are recycled much like engine coolant. Different pressures and temperatures cause the gas to change state from liquid to gas and back to a liquid again. The boiling point of the refrigerant changes with system pressure. High pressure raises the boiling point and low pressure reduces it. These gases also provide good heat transfer qualities and do not deteriorate system components. There are two gases used in the refrigeration process: Refrigerant- 12 and Refrigerant-22. Extreme caution should be used if they are handled. Refrigerant-12, otherwise known as R-12, Freon-12, or F-12, boils at -21.70F (-29.80C) when at sea level. Because of this low boiling point and its ability to pass through the system endlessly, R-12 is an ideal refrigerant. If the R-12 is pressurized enough, the boiling point would be moved well above the temperatures endured on the hottest day. Table 37-1 indicates the pressure of Refrigerant-12 at various temperatures. For instance, a drum of Refrigerant at a temperature of 800F (26.60C) will have a pressure of 84.1 psi (579.9 kPa). If it is heated to 1250F (51.60C), the pressure will increase to 167.5 psi (1154.9 kPa). It also can be used conversely to determine the temperature at which Refrigarent-12 boils under various
TM 9-8000
e. As the low-pressure refrigerant moves through the coils in the evaporator, it absorbs heat from the airstream, therefore producing a cooling effect. f. As the refrigerant nears the end of the coils in the evaporator, greater amounts of heat are absorbed. This causes the low-pressure liquid refrigerant to boil and change to a gas as it exits the evaporator. g. The refrigerant then enters the compressor. The pumping action of the compressor increases refrigerant pressure, which also causes a rise in temperature. h. The high-pressure, high-temperature gas then enters the condenser, where heat is removed by an outside ambient airstream moving over the coils. This causes the gas to condense and return to a liquid form again. i. The high-pressure liquid refrigerant now enters the receiver again to begin another cycle. This continuous cycle, along with the dehumidifying and filtering effect, produce a comfortable atmosphere on hot days
37-2
b. The refrigerant then is routed to the expansion valve through high-pressure lines and hoses. c. The expansion valve then reduces refrigerant pressure to the evaporator by allowing a controlled amount of liquid refrigerant to enter it. d. A stream of air is passed over the coils in the evaporator as refrigerant enters.
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TM 9-8000 Section II. SYSTEM COMPONENTS 37-4. Receiver. The receiver (fig. 37-3), otherwise known as a filter-drier or accumulator-drier, is a cylindrical-shaped metal tank. The tank is hollow with an inlet to the top of the hollow cylinder. The outlet port has a tube attached to it that extends to the bottom of the receiver. This tube assures that only liquid refrigerant will exit the receiver, because any gas entering will tend to float above the liquid.
c. Relief Valve. Some systems utilize a relief valve mounted near the top of the receiver. This valve is designed to open when system pressure exceeds approximately 450 to 500 psi. As the relief valve opens, it vents refrigerant into the atmosphere. As soon as excess pressure is released, the valve closes again so the system will not be evacuated completely. d. Sight Glass. A sight glass is a small, round, glass-covered hole, sometimes mounted on the outlet side of the receiver near the top. This observation hole is a visual aid used in helping to determine the condition and amount of refrigerant in the system. If bubbles or foam are observed in the sight glass while the system is operating (above 700F (210C)), it may indicate the system is low on refrigerant. Some systems have a
a. Filter. The filter is mounted inside the receiver on the end of the outlet pipe. This filter removes any impurities from the refrigerant by straining it. b. Desiccant. A special desiccant or drying agent also is located inside the receiver. This agent removes any moisture from the system.
TM 9-8000 moisture-sensitive element built into the sight glass. If excessive moisture is present, the element turns pink. If the system moisture content is within limits, the element remains blue. pressure exerted on the diaphragm from the thermal bulb. Operation of the valve is as follows. (1) High-pressure liquid refrigerant flows into the valve and is stopped at the needle seat. (2) If the evaporator is warm, pressure is developed in the thermal bulb and transferred to the diaphragm through the capillary tube. (3) The diaphragm overcomes the pressure developed in the equalizer tube and valve spring pressure, causing it to move downward. (4) This movement forces the valve actuating pin downward to open the valve.
37-5. Refrigerant Expansion Systems. The refrigerant expansion systems are designed to regulate the amount of refrigerant entering the evaporator and also reduce its pressure.
a. Expansion Valve. One type of expansion system used on modern vehicles is the expansion valve (A, fig. 37-4). The valve action is controlled by the valve spring, suction manifold, and
TM 9-8000 As the refrigerant flows, it cools the evaporator and therefore reduces pressure in the thermal bulb. This allows the valve to close and stop refrigerant from flowing into the evaporator. By carefully metering the amount of refrigerant with the expansion valve, the evaporator cooling efficiency is increased greatly. drivers compartment. It is a continuous tube looped back and forth through many cooling fins firmly attached to the tube. The evaporator dehumidifies the air by passing an airstream over the cool fins. As this happens, the moisture condenses on the fins and drips down to collect and exit under the vehicle. Dust and dirt also are collected on the moist fins and drain with the moisture. The temperature of the evaporator must be kept above 320F. Should the temperature fall below 320F, moisture condensing on the evaporator would freeze, preventing air from passing through the fins. A typical evaporator is shown in figure 37-5. There basically are three methods of regulating evaporator temperature; each is discussed below.
b. Expansion Tube. The expansion tube (B, fig. 37-4) provides the same functions as the expansion valve. A calibrated orifice is built into the expansion tube. The tube retards the refrigerant flow through the orifice to provide the metered amount of refrigerant to the evaporator. The tube also has a fine screen built in for additional filtration.
37-6. Evaporator. The evaporator is designed to absorb heat from the airstream directed into the
a. Thermostatic Switch. This system (fig. 37-6) uses an electrically operated switch to
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b. Hot Gas Bypass Valve. The hot gas bypass valve was used on some older models to control evaporator icing (fig. 37-7). The valve is mounted on the outlet side of the evaporator. The high-pressure gas from the compressor Joins with the low-pressure gas exiting the evaporator. These two gases mix, causing a pressure increase. The boiling point also increases, resulting in a loss of cooling efficiency. This, in turn, causes the evaporator temperature to increase, thus eliminating freezeup. The compressor is designed to run constantly (when it is activated) in the hot gas bypass valve system. c. Suction Throttling Valve. The suction throttling valve (fig. 37-8) is used now in place of the hot gas bypass valve system. It is placed in line with the outlet of the evaporator. This system is designed to limit the amount of low-pressure vapor entering the compressor. The suction throttling valve operates as follows:
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d. Pilot-Operated Absolute Suction Throttling Valve. The Pilot-Operated Absolute (POA) valve (fig. 37-9) is able to maintain the proper minimum evaporator pressure regardless of
TA233917 37-8
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a. Two-Cylinder Axial. The two-cylinder axial compressor (fig. 37-12) has two reciprocating pistons fitted into cylinders. A special valve plate, operated by differential pressures, is used to control gas flow. b. Four-Cylinder Radial. The four-cylinder radial compressor (fig. 37-13) positions four pistons at right angles to each other. The pistons are driven by a central shaft connected to the engine by the electric clutch assembly and V-belt. The radial compressors compact design is very popular on todays vehicles.
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c. Six-Cylinder Axial Compressor. This design uses three double-ended pistons driven by a wobble plate (fig. 37-14). The three cylinders effectively produce a six-cylinder compressor. As the shaft rotates, the wobble plate displaces the pistons perpendicular to the shaft. Piston drive balls are used to cut down friction between the wobble plate and pistons. Piston rings also are used to aid In sealing.
37-8. Condenser. The condenser (fig. 37-15) is designed to remove heat from the compressed refrigerant, returning it to a liquid state. Condensers generally are made from a continuous tube looped back and forth through rigidly mounted cooling fins. They are
made of aluminum and can encounter pressures of approximately 150 to 300 pslg, and temperatures ranging from 1200 to 2000F (480 to 930C). The condenser usually is mounted in front of the radiator and subjected to a steady stream of cooling air. 37-9. Refrigeration 011. Refrigeration oil provides lubrication for the compressor. Each system has a certain amount of refrigeration oil (usually approximately 6 to 10 oz (177 to 296 mL)) added to the system Initially. If the system stays sealed, the oil will not break down or need to be changed. Refrigeration oil is highly refined and must be free of moisture.
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CHAPTER 38 TRAILERS AND SEMITRAILERS Section I. SEMITRAILERS 38-1. General Description. A typical semitrailer chassis (fig. 38-1) consists mainly of a frame, spring suspension, axle, fifth-wheel connection, and a landing gear. It resembles the conventional truck chassis in that its frame is made of two pressed-steel side members with several crossmembers and has laminated leaf spring suspension. The wheels and tires are interchangeable with those of the tractor used for hauling the trailer. Figure 38-1 illustrates a semitrailer chassis with tandem axles for carrying heavy trailer loads. Early semitrailer frames were built of straight side members, which meant that the rear of a level trailer body had to be at a considerable height above the ground to clear the rear wheels of the tractor. Such a high frame is not acceptable because it heightens the center of gravity, making it easier to overturn the trailer. A kickup (fig. 38-1) in the semitrailer frame permits a lower center of gravity without reducing the necessary clearance space above the rear wheels of the motor vehicle. Crossmembers are located where the greatest strains occur to the trailer frame. They may be tubular, channel, or box-shaped, with gusset plates riveted or welded to the side members to make a rigid, strong frame. Another type of semitrailer with a variable wheelbase is the pole trailer used for transporting long or irregularly shaped goods, such as poles, pipes, or structural members. In this case, the pole, or boom, forms the trailer frame. The pole is attached to a turntable mounted on the tractor in much the same manner as a fifth wheel. The trailer axle unit is attached by adjustable clamps to the other end of the pole. A truck tractor used to haul a semitrailer must be a special design. Its wheelbase is shorter than that of a standard truck, and the engine and transmission units are designed to produce the necessary power for pulling a loaded semitrailer. Truck tractors may be designed with the cab over the engine, or may be of conventional truck design, with either single or dual rear axles. The flexible hose connecting the brake system of the tractor to the trailer is shown clearly at the rear of the tractor cab (fig. 38-2). 38-2. Kingpin and Plate. A heavy steel plate assembly (fig. 38-3), known as the upper fifth-wheel plate, is attached securely to the underside of the front end of the semitrailer frame. This plate serves as the bearing, or front end, support of the semitrailer when it is coupled to a tractor. The front edge of the plate is turned up approximately 45 degrees to form a skid that slides on the lower fifth-wheel plate (mounted on the truck tractor) when the semitrailer is being hitched to the truck tractor. In the center of the upper fifth-wheel plate
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a. Full Trailer. Full trailers may be classified as nonreversible, reversible, and converted semitrailers. A nonreversible full trailer can be towed and steered from one end only. Its frame is supported by front and rear two-wheel trucks that consist of a square frame made of channel sections containing the spring hangers. The rear truck is bolted to the trailer frame and forms an Integral part of the chassis. A lower fifth-wheel ring mounted on top of the front truck fits together with an upper fifth-wheel ring attached underneath the front end of the trailer frame. The front truck, therefore, turns around the fifth wheel, which allows the trailer to be steered. A towing tongue is pivoted to the front truck, and the other end contains a lunette that connects with the pintle hook of the towing vehicle. The trailer chassis Illustrated In figure 38-7 is equipped with electrical and airbrake connections, which are hooked up to the towing vehicle. A safety chain is provided to prevent the trailer from running away if the pintle hook connection should break loose.
A reversible full trailer may be towed or steered from either end. It is similar to the nonreversible trailer In construction and appearance, except that both front and rear trucks are mounted by fifth wheels. The towing tongue is detachable and may be used with either truck. Both trucks are provided with locks so that one may be prevented from turning when the other is connected to the towing ends, thus Increasing the operating flexibility of the trailer.
the fifth wheel on a dolly (fig. 38-8) and using the dolly In place of a tractor as the semitrailer front end support. This combination is known as a converted semitrailer. The dolly is a short two-wheel trailer chassis with a standard lower fifth wheel mounted on its frame. The front end of its frame is tapered to receive a bracket that contains a lunette for towing the trailer by a pintle assembly. A retractable landing gear supports the front end of the dolly when not in use. The open hooks on either side at the front end of the frame are used for Joining the towing vehicle and the trailer with safety chains. The rear-end view of a heavy-duty vehicle (fig. 38-9), used for towing three-quarter and full trailers, Illustrates the pintle assembly. The rear bumpers protect the frame of the vehicle and guide the trailer lunette (towing hook) into the pintle assembly during the trailer coupling operation. The electric brake lead of the trailer is plugged Into the electric brake connection, shown with the cover open. The airbrake connections enable the airbraking system of the towing vehicle to be Joined to that of the trailer when the trailer is equipped with alrbrakes. The alrbrake connection is shown with Its cap removed, as It would appear when ready for coupling. 38-10. Drawbar and Lunette. The drawbar and lunette used on full trailers are similar to those used on threequarter trailers described In paragraphs 38-6 and 38-7.
b. Semitrailer Converted to a Full Trailer. A semitrailer may be converted to a full trailer by mounting
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38-11. Matching Brake and Electrical Systems. Matching a towing vehicle and a trailer means more than coupling them. The brake and electrical systems must match. Furthermore, the trailer load must not exceed the performance of the towing vehicle. 38-12. Matching Electrical Systems. The towing vehicle and trailer electrical systems must be of the same voltage. If the towing vehicle has a 6-volt system, the trailer must have a 6-volt system. Likewise, if one has a 12-volt system, the other must have a 12-volt system. Connecting 6-volt lights into a 12-volt system will cause them to burn out as soon as they are turned on. On the other hand, 12-volt lights connected to a 6volt source will give little or no light. 38-13. Matching Brake Systems. The brake systems 38-8
also must match. If the towing vehicle has an airpressure brake system, the trailer must also have an airpressure brake system. Like-wise, if the towing vehicle has a vacuum-type or an electric braking system, the trailer must have a matching braking system. 38-14. Matching Load and Performance. To avoid overloading the towing vehicle, excessive loads must not be hitched to it. The trailer load must not be above that which the towing vehicle was designed to pull. The technical manual of the towing vehicle usually has the maximum trailer load listed in the tabulated data section. If it does not, the drawbar pull can be calculated as explained in paragraph 29-15c.
TM 9-8000
APPENDIX DEFINITION OF TERMS ABDC. After bottom dead center. AC. Alternating current, or current that reverses Its direction at regular Intervals. Accelerating Pump. A device in the carburetor that supplies an additional amount of fuel, temporarily enriching the fuel-air mixture when the throttle is suddenly opened. Acceleration. The process of increasing velocity. Average rate of change of increasing velocity, usually in feet per second. Accelerator. Pedal and linkage used to control engine speed. Accumulator. A container used In an air conditioning system to filter and remove moisture. Accumulator Piston. A unit In the automatic transmission used to apply the brake band quickly and smoothly. Ackerman Steering. The steering system design that permits the front wheels to round a turn without sideslip by turning the Inner wheel in more than the outer wheel. Air Bleed. A passage in the carburetor through which air can seep or bleed into fuel moving through a fuel passage. Airbrakes. Vehicle brakes actuated by air pressure. Air Cleaner. A device, mounted on the carburetor or connected to the carburetor, through which air must pass before entering the carburetor air horn. A filtering device In the air cleaner removes dust and dirt particles from the air. Air Conditioning. A system designed to provide control over air temperature, movement, and humidity. Air-Cooled Engine. An engine cooled by air circulating between cylinders and around cylinder head as opposed to the liquid-cooled engine cooled by a liquid passing Amphibious Vehicle. A vehicle with a hull that permits it to float in water, and tracks or wheels that permit It to travel on land. Angle of Approach. The maximum angle of an incline onto which a vehicle can move from a horizontal plane without interference; as, for Instance, from front bumpers. Angle of Departure. The maximum angle of an Incline from which a vehicle can move onto a horizontal plane without Interference; as, for Instance, from rear bumpers. through jackets surrounding the cylinders. Air Filter. A filter through which air passes, and which removes dust and dirt particles from the air. Air filters are placed in passages through which air must pass, as in crankcase breather, air cleaner, etc. Air-Fuel Ratio. The ratio between the volume of air and the volume of fuel used to establish the combustion mixture. Air Horn. That part of the air passage In the carburetor that is on the atmospheric side of the venturi. The choke valve is located in the air horn. Air-Pac Brakes. vacuum. A type of braking system using a
Alloy. A mixture of two or more materials. Alternator. A device similar to a generator but which produces ac current. Ambient Temperature. The temperature environment surrounding an object. of the
Ammeter. An electric meter that measures current, In amperes, in an electric circuit. Ampere. Unit of electric-current-flow measurement. The current that will flow through a 1-ohm resistance when 1 volt is Impressed across the resistance.
Change 1 A-1
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DEFINITION OF TERMS-CONTINUED Antifreeze. A substance added to the coolant system In a liquid-cooled engine to prevent freezing. Antifriction Bearing. A bearing of the type that supports the imposed load on rolling surfaces (balls, rollers, needles), minimizing friction. Antiknock. Refers to substances that are added to automotive fuel to decrease the tendency to knock when fuel-air mixture is compressed and Ignited In the engine cylinder. Armature. The rotating assembly in a direct current generator or motor. Also, the iron piece In certain electrical apparatus that completes a magnetic, and in many cases, an electric, circuit. Asbestos. burning. A fibrous material that resists heat and Axial. In a direction parallel to the axis. Axial movement is movement parallel to the axis. Axis. A centerline. The line about which something rotates or about which something is evenly divided. Axle. A cross support on a vehicle on which supporting wheel, or wheels, turn. There are two general types: live axles that also transmit power to the wheels, and dead axles that transmit no power. Backfiring. Preexplosion of fuel-air mixture so that explosion passes back around the opened Intake valve and flashes back through the intake manifold. Backlash. The backward rotation of a driven gear that is permitted by clearance between meshing teeth of two gears. Back Pressure. The resistance of gases to flow through a system. Baffle. A plate or shield to divert the flow of liquid or gas. Ballast. A resistor that changes voltage In direct proportion to heat of wire. Ball Bearing. A type of bearing that contains steel balls that roll between inner and outer races. Battery. A device consisting of two or more cells for converting chemical energy into electrical energy. Battery Capacity. Rating of a batterys current output. Automatic Choke. A choke that operates automatically in accordance with certain engine conditions, usually temperature and intake manifold vacuum (also electrically controlled). Automatic Leveling Control. A system designed to maintain proper riding height, regardless of changes In vehicle load. Automatic Transmission. A transmission that reduces or eliminates the necessity of hand shifting of gears to secure different gear ratios in the transmission. A-2 Battery Charging. The process of supplying a battery with a flow of electric current to produce chemical actions in the battery; these actions reactivate the chemicals in the battery so they can produce electrical energy again. Battery, Maintenance-Free. A battery that does not require addition of water during its normal life. Battery Rating. A standardized measurement of a batterys ability to deliver electrical power under certain conditions.
ATDC. After top dead center. Atmosphere. The mass of air that surrounds the earth. Atmospheric Pressure. The weight of the atmosphere per unit area. Atom. The smallest particle, or part, of an element, composed of electrons and protons and also of neutrons (with the exception of hydrogen). Atomization. The spraying of a liquid through a nozzle so that the liquid is broken into tiny globules or particles.
BBDC. Before bottom dead center. BDC. Bottom dead center; the position of the piston when it reaches the lower limit of travel In the cylinder. Bead. The circular wire-reinforced section of a tire that Joins with the wheel rim. Bearing. A part In which a Journal pivot, or pin, turns or revolves. A part on or In which another part slides. Bendix Drive. A type of drive used in a starter that provides automatic coupling with the engine flywheel for cranking and automatic uncoupling when the engine starts. Bevel Gear. One of a pair of meshing gears whose working surfaces are inclined to the centerlines of the driving and driven shafts. Bezel. A device used to attach a glass face to an instrument. Blackout Lights. A lamp Installed on a vehicle for use during blackouts, which can be seen from the air only at very close range. Block. See Cylinder Block. Blowby. Leakage of the compressed fuel-air mixture or burned gases from combustion, passing piston and rings, and into the crankcase. Blower. A mechanical device for compressing and delivering air to engine at higher than atmospheric pressure. Body. The assembly of sheet metal sections, framework, doors, windows, etc, which provides an enclosure for passengers or carriage space for freight. Bogie. A suspension unit consisting of tandem axles jointed by a single cross support (trunnion axle) that also acts as a vertical pivot for the entire unit. Boiling Point. The temperature at which a liquid boils.
Bond. To bind together. Bore. The diameter of an engine cylinder hole. Also, the diameter of any hole; as, for example, the hole into which a bushing is fitted. Boss. An extension or strengthened section, such as the projections within a piston which supports the piston pin. Bottled Gas. A gas that remains a liquid when confined In a tank under pressure. Bound Electrons. Electrons located in the Inner orbits around the nucleus of an atom. Bourdon Tube. A hollow circular-shaped tube used as the pressure-sensing element in some gages. Brake Anchor. A steel pin-shaped stud, rigidly mounted to the backing plate, upon which the brakeshoe either is attached or rests against. Brake Backing Plate. A rigid steel plate upon which certain brake components are attached. Brake Band. A flexible band, usually of metal with an Inner lining of brake fabric, that is tightened on a drum to slow or stop drum rotation. Brake, Disk-Type. A braking network consisting of a rotating disk that is restrained during application by stationary brake pads mounted on both sides of the disk. Brakedrum. A metal drum mounted on a car wheel or other rotating members; brakeshoes or brake band, mechanically forced against it, cause it to slow or stop. Brake Fade. A reduction in the coefficient of friction between retarding members as a result of excessive heat buildup. Brake Fluid. A compounded fluid used in hydraulic braking system; it transmits hydraulic force from the brake master cylinder to the wheel cylinder. Brake Horsepower. The power actually delivered by the engine that is available for driving the vehicle.
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Brake Hose. A tubular hose used to transmit fluid pressure when a flexible joint is required. Brake Line. A rigid tube used to carry brake fluid. Brake Lining. A special woven fabric material with which brakeshoes or brake bands are lined: it withstands high temperatures and pressures. Breaker Points. An adjustable cam-operated switch Inside the distributor used to trigger the coil. Brakes. The mechanism that slows or stops a vehicle or mechanism when a pedal or other control is operated. Also called the brake system. Brakeshoes. The curved metal part, faced with brake lining, that is forced against the brakedrum to produce braking or retarding action. Brake System. The system on a vehicle that slows or stops it as a pedal or lever is operated. Bronze. An alloy consisting essentially of copper and tin. Brushes. The carbon or carbon and metal parts in a motor or generator that contact the rotating armature commutator or rings. BTDC. Before top dead center. Bushing. A sleeve placed in a bore to serve as a bearing surface. Bypass. A separate passage that permits a liquid, gas, or electric current to take a path other than that normally used. Cab. Separate drivers compartment provided on trucks. Caliper. A disk brake component used to house the piston(s) and brake pads. Cam. A moving part of an irregular form designed to move or alter the motion of another part.
Camber. To curve or bend; the amount in Inches or degrees that the front wheels of an automotive vehicle are tilted from a true vertical at the top. Cam-Ground. A process by which the piston is ground slightly eggshaped and, when heated, becomes round. Camshaft. valves. A shaft with cam lobes used to operate
Capacitance. That property of a circuit that tends to Increase the amount of current flowing in a circuit for a given voltage or to delete In its entirety. Capacitor (Condenser). A device for inserting the property of capacitance into a circuit; two or more conductors separated by a dielectric. Carbon Monoxide. A colorless, odorless, tasteless, deadly gas found in engine exhaust. This gas is formed by Incomplete burning of hydrocarbons. Carbon-Pile Regulator. A type of regulator for regulating or controlling voltage or amperage in a circuit, which makes use of a stack, or pile, or carbon disks. Carburetor. The device In a fuel system that mixes fuel and air and delivers the combustible mixture to the Intake manifold. Caster. The amount in degrees that the steering knuckle pivots are tilted forward or backward from a true vertical. Casting. Pouring metal Into a mold to form an object. Catalytic Converter. A device used on some exhaust systems to reduce harmful emissions. Cell. A combination of electrodes and an electrolyte that converts chemical energy into electrical energy; two or more cells connected together form a battery. Center Link. Also referred to as a relay rod used to transmit motion from pitman arm to tie rods. Center Steering Linkage. A steering system configuration using two tie rods connected to steering arms and to a central idler arm; the idler arm pivots on the frame on one end and is connected to the drag link on the other. A-4
TM 9-8000 DEFINITION OF TERMS-CONTINUED Centrifugal Advance. The mechanism in an ignition distributor by which the spark is advanced or retarded as the engine speed varies. Centrifugal Force. The force acting on a rotating body, which tends to move its parts outward and away from the center of rotation. CFM. Cubic feet per minute. Charge Indicator. The device on a vehicle that indicates, by a needle, whether or not the battery is receiving a charge from the generator. Charging Rate. The rate of flow, in amperes, of electric current flowing through a battery while it is being charged. Chassis. An assembly of mechanisms, attached to a frame, that make up the major operating part of an automotive vehicle (less body). Choke. A device in the carburetor that chokes off, or reduces, the flow of air into the intake manifold; this produces a partial vacuum in the intake manifold and a consequent richer fuel-air mixture. Choke Stove. A device used to draw heat from around the exhaust manifold into the carburetor during engine warmup. CID. Cubic inch displacement. Circuit. A closed path or combination of paths through which passage of the medium (electric current, air, liquid, etc) is possible. Circuit Breaker. In electric circuits, a mechanism designed to break or open the circuit when certain conditions exist; especially the device in automotive circuits that opens the circuit between the generator and battery to prevent overcharging of the battery. (One of the three units comprising a generator regulator.) Clearance. A given amount of space between two parts. Clockwise. The direction of movement, usually rotary, which is the same as movement of hands on the face of a clock. Compression Stroke. The piston stroke from bottom dead center to top dead center during which both valves are closed and the gases in the cylinder are compressed. Compensating Port. A small hole in the brake master cylinder to permit fluid to return to the reservoir. Compression. The act of pressing into a smaller space or reducing in size or volume by pressure. Compression Ratio. The ratio between the volume n the cylinder with the piston at bottom dead center and with the piston at top dead center. Compression Rings. The upper rings on a piston; the rings designed to hold the compression in the cylinder and prevent blowby. Coil Spring. A type of spring made of an elastic metal such as steel, formed into a wire or bar and wound into a coil. Combat Vehicle. A type of vehicle, usually armored, for use in armed combat. Combustion. A chemical action, or burning; in an engine, the burning of a fuel-air mixture in the combustion chamber. Combustion Chamber. The space at the top of the cylinder and in the head in which combustion of the fuelair mixture takes place. Commutation. The process of converting alternating current that flows in the armature windings of direct current generators into direct current. Commutator. That part of rotating machinery that makes electrical contact with the brushes and connects the armature windings with the external circuit. Clutch. The mechanism in an automotive vehicle, located in the power train, that connects the engine to, or disconnects the engine from, the remainder of the power train. Coil. In electrical circuits, turns of wire, usually on a core and enclosed in a case, through which electric current passes.
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TM 9-8000
DEFINITION OF TERMS-CONTINUED Compressor. A device used to Increase pressure. Concentric. Having a common center, as circles or spheres, one within the other. Condense. To transform a vapor into a liquid. Condenser. 1. See Capacitor. 2. A unit used in refrigeration systems that removes heat of compression from a gas to return It to a liquid state. Conductor. A material through which electricity will flow readily. Connecting Rod. Linkage between the crankshaft and piston, usually attached to the piston by a piston pin and to the crank journal on the crankshaft by a split bearing and bearing cap. Control Rack. A toothed rod inside mechanical Injection pumps that rotates the pump plunger to control the quantity of Injected fuel. Coolant. The liquid that circulates In an engine cooling system that reduces heat generated by the engine. Cooling Fan. The fan In the engine cooling system that provides a forced circulation of air through the radiator or around the engine cylinders so that cooling is affected. Cooling Fins. The thin metal projections on the aircooled engine cylinder and head that greatly Increases the heat-radiating surfaces and helps provide cooling of engine cylinder. Cooling System. A system that reduces heat generated by the engine and thereby prevents engine overheating; Includes, In liquid-cooled engine, engine water Jackets, radiator, and water pump. Core. An Iron mass, generally the central portion of a coil or electromagnet or armature around which the wire is coiled. Counterbalance. A weight attached to a moving part so it will be in balance. Counterclockwise. The direction of movement, usually rotary, which is opposite in direction to movement of hands on the face of a clock. Cowl. The front portion of the vehicle body or cab that partially encloses the dash panel and forms the windshield frame. Crank. A device for converting reciprocating motion Into rotary motion, and vice versa. Crankcase. The lower part of the engine in which the crankshaft rotates. In automotive practice, the upper part is the lower section of the cylinder block, while the lower section is the oil pan. Crankcase Breather. The opening or tube that allows air to enter the crankcase and thus permits crankcase ventilation. Crankcase Dilution. Dilution of the lubricating oil In the oil pan by liquid gasoline seeping down the cylinder walls past the piston rings. Crankcase Ventilation. The circulation of air through the crankcase, which removes water and other vapors, thereby preventing the formation of water sludge and other unwanted substances. Cranking Motor. See Starter. Crankshaft. The main rotating member or shaft of the engine, with cranks to which the connecting rods are attached. Cross-Drive Transmission. A special type of transmission used In tanks and other heavy vehicles that combines the actions of a transmission with torque converter, steering system, and differential. Current Regulator. A magnetic-controlled relay by which the field circuit of the generator is made and broken very rapidly to secure even current output from the generator and to prevent generator overload from excessive output. (One of the three units comprising a generator regulator.) Cutout Relay. 1. See Circuit Breaker. 2. An automatic magnetic switch attached to the generator to cut out generator circuit and prevent overcharging of battery. A-6
TM 9-8000 DEFINITION OF TERMS-CONTINUED Cycle. A series of events with a start and finish during which a definite train of events takes place. In the engine, the four piston strokes (or two piston strokes on two-stroke cycle engine) that complete the working process and produce power. Cylinder. A tubular-shaped structure. In the engine, the tubular opening In which the piston moves up and down. Cylinder Block. That part of an engine to which, and In which, other engine parts and accessories are attached or assembled. Cylinder Head. The part of the engine that encloses the cylinder bores; contains water jackets (on liquid-cooled engines) and valves (on I-head engines). Cylinder Sleeve. A pipe-shaped removable Insert used as the cylinder wall on some engines. Damper. A device for reducing the motion or oscillations of moving parts, air, or liquid. Dash Panel. The partition that separates the drivers compartment from the engine compartment. Sometimes called firewall. Dashpot. A unit used to slow down movement or arrest vibrations or oscillations of a moving part. DC. Direct current, or current that flows in one direction only. Dead Axle. An axle that simply supports and does not turn or deliver power to the wheel or rotating member. Deceleration. The process of slowing down; opposite of acceleration. Degasser. A device used In connection with carburetors for shutting off the flow of fuel during deceleration so that gases from Incomplete combustion during deceleration are prevented. Desiccant. moisture. A substance used to absorb and retain DOHC. Double overhead camshaft. Detonation. In the engine, excessively rapid burning of the compressed fuel-air mixture so that knocking results. Diaphragm. A flexible membrane, usually made of fabric and rubber in automotive components, clamped at the edges and usually spring-loaded; used in fuel pump, vacuum pump, distributor, etc. Diesel Engine. An engine using the diesel cycle of operation; air alone is compressed and diesel fuel is Injected at the end of the compression stroke. Heat of compression produces Ignition. Dieseling. A condition In which an engine continues to run after the Ignition is turned off. Also referred to as engine run-on. Differential. A mechanism between axles that permits one axle to turn at a different speed than the other and, at the same time, transmits power from the driving shaft to the axles. Differential Winding. In electrical machinery, a winding that is wound In a reverse direction or different direction than the main operating windings. The differential winding acts to modify or change the action of the machine under certain conditions. Diode. A device that permits current flow In one direction and resists flow in the other. Disk Brake. A braking network that uses a rotating disk called a rotor and stationary brake pads such that when forced together perform a retarding action. Disk Wheel. A wheel constructed of stamped steel. Displacement. The total amount of air or liquid an object consumes while moving from one location to another. Distribution Tubes. Tubes In the cooling system used to direct coolant flow to vital areas. Distributor. See Ignition Distributor.
A-7
TM 9-8000 DEFINITION OF TERMS-CONTINUED Dolly. A two-wheel trailer coupled to a semitrailer to support and steer its front end when it is converted into a full trailer. Drag Link. An intermediate link in the steering system between the pitman arm and an intermediate arm, or drag-link arm. Drive Shaft. A shaft used to transmit rotary motion. Drop Center Rim. A rim in which the center section is closer to the center of the rim than the two outer edges. Drop Forged. A part that has been formed by heating until red hot and pounding with a hammer. Dry Sleeve. A cylinder sleeve that is supported its entire length by the block; coolant does not contact the sleeve in this configuration. Dry Sump. An oiling system that uses a scavenger pump to collect oil and transfer it to an auxiliary container or sump. Dual Ignition. An ignition system using two spark plugs for each cylinder so that a dual spark effect takes place, driving each power stroke. Dual-Ratio Axles. An axle in a truck that contains a mechanism for changing driving ratio of the wheels to either high or low ratio. Two-speed differential. Dynamometer. A device for measuring the power output of an engine. Eccentric. Offcenter. Eddy Currents. Currents that are induced in an iron core and circulate in the core. Efficiency. The ratio between the effect produced and the power expended to produce the effect. Electric Brakes. A brake system that uses electric current for energizatlon. Electrical System. In the automotive vehicle, the system that electrically cranks the engine for starting, furnishes A-8 high-voltage sparks to the engine cylinders to fire compressed fuel-air charges, lights the lights, and operates heater motor, radio, etc. Consists, in part, of starter, wiring, battery, generator, generator regulator, Ignition distributor, and ignition coil. Electricity. A form of energy that involves the movement of electrons from one place to another, or the gathering of electrons in one area. Electrode. Either terminal of an electric source; either conductor by which the current enters and leaves an electrolyte. Electrolyte. The liquid in a battery or other electrochemical device, in which the conduction of electricity is accompanied by chemical decomposition. Electromagnet. A temporary magnet constructed by winding a number of turns of insulated wire into a coil or around an iron core; it is energized by a flow of electric current through the coil. Electron. A negative-charged particle that is a basic constituent of matter and electricity. Movement of electrons is an electric current. Electron Theory. A theory stating that electron flow is from one area to another. EMF. Electromotive force. Emissions. Products of automotive engine combustion that are released into the atmosphere. Energy. The capacity for performing work. Engine. An assembly that burns fuel to produce power; sometimes referred to as the powerplant. Ethylene Glycol. A solution added to antifreeze to help prevent freezing. Evaporation. The action that takes place when a liquid changes to a vapor or gas. Evaporator. A unit in an air conditioning system used to absorb heat from a passing airstream.
TM 9-8000
DEFINITION OF TERMS-CONTINUED Exhaust Manifold. That part of the engine that provides a series of passages through which burned gases from the engine cylinders may flow to the muffler. Exhaust Stroke. The piston stroke from bottom dead center to top dead center during which the exhaust valve is opened so that burned gases are forced from the engine cylinder. Exhaust Valve. The valve that opens to allow the burned gases to escape from the cylinder during the exhaust stroke. Expansion Tank. A tank separate from the radiator used to compensate for expansion and contraction of engine coolant. Expansion Valve. A unit used on some air conditioning systems to control flow and reduce pressure of the refrigerant. Fan. See Cooling Fan. Ferrous Metal. A metal that contains iron or steel. F-Head. A type of engine with valves arranged to form an F; one valve is in the head, the other in the cylinder block. Field. In a generator or electric motor, the area in which a magnetic flow occurs. Field Coil. A coil of wire, wound around an iron core, that produces the magnetic field in a generator or motor when current passes through it. Field Frame. The frame in a generator or motor Into which the field coils are assembled. Field Winding. See Field Coil. Fifth Wheel. The flat, round, heavy steel plates (upper and lower) together with a kingpin for coupling semitrailer to truck tractor. The lower plate is mounted on the truck tractor, the upper on the semitrailer. Filament. A fine wire inside a light bulb that emits light A-9 when current passes through it. Filter. A device through which gas or liquid is passed; dirt, dust, and other impurities are removed by the separating action. Final Drive. That part of the power train on tractors, truck tractor tanks, and tank like vehicles that carries the driving power to the wheels or sprockets to produce the vehicle motion as they turn. Firewall. The partition between the engine compartment and drivers compartment. Firing Order. The order in which respective cylinders deliver their power strokes. Flashpoint. The temperature at which an oil will ignite and burn. Float. In the carburetor, the metal shell that is suspended by the fuel in the float bowl and controls a needle valve that regulates the fuel level in the bowl. Float Bowl. A section in the carburetor used as a reservoir for gasoline and in which the float is placed. Float Circuit. In the carburetor, the circuit that controls entry of fuel and fuel level in the float bowl. Float Level. The height of fuel in the carburetor as set by the float. Fluid Coupling. A coupling in the power train that connects between the engine and other power train members through a fluid. Flux. Lines of magnetic force moving through a magnetic field. Flywheel. The rotating metal wheel, attached to the crankshaft, that helps level out the power surges from the power strokes and also serves as part of the clutch and engine-cranking system. Foot Pound. A unit of work done in raising 1 pound avoirdupois against the force of gravity to the height of 1 foot.
TM 9-8000 DEFINITION OF TERMS-CONTINUED Force. The action that one body may exert upon another to change its motion or shape. Four-Stroke-Cycle Engine. An engine that requires four piston strokes (intake, compression, power, exhaust) to make the complete cycle of events in the engine cylinder. Frame. An assembly of metal structural parts and channel sections that support the engine and body and that is supported by the vehicle wheels. Free Electrons. Electrons in outer orbits of an atom that are easily moved out of orbit. Freon-12. A gas used in air conditioning and refrigeration systems. Frequency. The number of vibrations, cycles, or changes in direction in a unit of time. Friction. The resistance to motion between two bodies in contact with each other. Friction Bearing. A bearing having no moving parts. The shaft that rotates simply rubs against or rides on a thin film of oil between the bearing and shaft. Fuel. The substance that is burned to produce heat and create motion of the piston on the power stroke in an engine. Fuel Filter. A device placed in the fuel line of the fuel system to remove dirt and other harmful solids. Fuel Gage. An indicating device in the fuel system that indicates the amount of fuel in the fuel tank. Fuel Injection. A fuel delivery system that sprays fuel either directly into cylinders or into the intake manifold just ahead of the cylinders. Fuel Line. The tube or tubes connecting the fuel tank and the carburetor and through which the fuel passes. Fuel Passage. Drilled holes in the carburetor body and tubes through which fuel passes from the float bowl to A-10 the fuel nozzles. Fuel Pump. The mechanism in the fuel system that transfers fuel from the fuel tank to the carburetor. Fuel Tank. The storage tank for fuel on the vehicle. Fulcrum. The support, as a wedge-shaped piece or a hinge, about which a lever turns. Full-Floating Axle. An axle that is designed only to deliver power to the wheel. Vehicle weight and wheel retaining are accomplished by other members. Full Trailer. An independent and fully contained vehicle without motive power. Fuse. A circuit-protecting device that makes use of a substance that has a low melting point. The substance melts if an overload occurs, thus protecting other devices in the system. Fusible Link. A length of special wire inserted in a circuit to protect against excessive current draw. Gasket. A flat strip, usually of cork or metal, or both, placed between two surfaces to provide a tight seal between them. Gasoline. A hydrocarbon, obtained from petroleum, that is suitable as an internal combustion engine fuel. Gear Ratio. The relative speeds at which two gears turn; the proportional rate of rotation. Gears. Mechanical devices to transmit power or turning effort, from one shaft to another; more specifically, gears that contain teeth that engage or mesh upon turning. Gearshift. A mechanism by which the gears in a transmission system are engaged. Generator. In the electrical system, the device that changes mechanical energy to electrical energy for lighting lights, charging the battery, etc.
TM 9-8000 DEFINITION OF TERMS-CONTINUED Generator Regulator. In the electrical system, the unit that is composed of the current regulator voltage regulator, and circuit breaker relay. Glow Plug. A device placed in some diesel engines that glows when activated to aid in starting. Governor. A mechanism that controls speed or other variable. Specifically, speed governors used on automotive vehicles to prevent excessive engine speed by controlling actions in the carburetor. Grid. A lead screen or plate to which battery plate material is attached. Ground. Connection of an electrical unit to the engine or frame to return the current to its source. Gusset Plate. A plate at the joint of a frame structure of steel to strengthen the joint. Half Track. A vehicle using tracks Instead of wheels at the rear. Handbrake. A brake operated by hand. Also referred to as the parking brake. Headlight. Lights at the front of the vehicle designed to Illuminate the road ahead when the vehicle is traveling forward. Heat. A form of energy. Heat Crossover. A passage from one exhaust manifold under carburetor to the other manifold to provide heat to the base of carburetor during warmup. Heat Exchanger. A device used to cool or heat by transferring heat from one object to another. Heat Stove. A metal shroud around the exhaust manifold or intake manifold that supplies the carburetor with warm air when needed. Helical. In the shape of a helix, which is the shape of a screw thread or coil spring. Hemispherical Combustion Chamber. A round domeA-11 shaped combustion chamber with valves placed on opposite sides of a centrally located spark plug. Herringbone Gears. Gears having teeth machined in a V-configuration. High-Speed Circuit. In the carburetor, the passages through which fuel flows when the throttle valve is fully opened. High Tension. Another term for high voltage. In the electrical system, refers to the ignition secondary circuit since this circuit produces high-voltage surges to cause sparking at the spark plugs. Hill Holder. A device that automatically prevents the vehicle from rolling backwards down a hill when the vehicle is brought to a stop. Horn. An electrical signaling device on the vehicle. Horsepower. A measure of a definite amount of power; 550 foot pound per second. Hotchkiss Drive. A type of rear live axle suspension In which the springs serve as torque members. Hull. In a tank, the protective shell that encloses the vehicle components and occupants. Hydraulic Brakes. A braking system that uses a fluid to transmit hydraulic pressure from a master cylinder to wheel cylinders, which then cause brakeshoe movement and braking action. Hydraulic Steering. A steering system that uses a fluid to produce an assisting hydraulic pressure on the steering linkage, thus reducing the steering effort on the part of the driver. Hydraulic Traversing Mechanism. A turret traversing system that makes use of hydraulic pressure to furnish the motive power to traverse the turret. Hydraulic Valve Tappet. A valve tappet that, by means of hydraulic pressure, maintains zero valve clearance so that valve noise is reduced.
TM 9-8000
DEFINITION OF TERMS-CONTINUED Hydrocarbon. A mixture of hydrogen and carbon found in vehicle emissions. Hydromatic. A type of automatic transmission containing a fluid coupling and automatic controls for shifting from one gear ratio to another. Hydrometer. A device to determine the specific gravity of a liquid. This indicates the freezing point of the coolant in a cooling system or, as another example, the state of charge of a battery. Hydrovac Brakes. A type of braking system using vacuum to assist in brake operation. The vacuum action reduces the effort required from the driver to operate the vehicle brakes. Hypoid Gearing. A type of gearing configuration in which the pinion gear meshes with the ring gear below the centerline of the ring gear. Idle. The engine speed when the accelerator pedal is fully released; generally assumed to mean when the engine is doing no work. Idle Circuit. The circuit in the carburetor through which fuel is fed when the engine is idling. Idler Arm. A steering component designed to support one end of the center link. Idler Gear. A gear placed between a driving and a driven gear to make them rotate in the same direction. It does not affect the gear ratio. Idling Adjustment. The adjustment made on the carburetor to alter the fuel-air mixture ratio or engine speed on idle. Ignition. The action of setting fire to; in the engine, the initiating of the combustion process In the engine cylinders. Ignition Advance. Refers to the spark advance produced by the distributor in accordance with engine speed and intake manifold vacuum. Ignition Coil. The component of the ignition system that acts as a transformer and steps up battery voltage to many thousand volts; the high voltage then produces a A-12 spark at the spark plug gap. Ignition Distributor. The component of the ignition system that closes and opens the circuit between the battery and ignition coil, and distributes the resultant high-voltage surges from the coil to the proper spark plugs. Ignition Switch. The switch in the ignition system that can be operated to open or close the ignition primary circuit. Ignition Timing. Refers to the timing of the spark at the spark plug as related to the piston position in the engine cylinder. I-Head. head. A type of engine with valves in the cylinder
Impeller. The rotor of a centrifugal pump that causes the fuel-air in an engine to be thrown into a diffuser chamber to effect thorough mixing and good distribution. Independent Suspension. A type of suspension system designed to spring each wheel separately, therefore allowing each wheel to move independently from the other. Indicated Horsepower. A measurement of engine power based on power actually developed in the engine cylinders. Induction. The action or process of producing voltage by the relative motion of a magnetic field and a conductor. Inhibitor. A substance added to a liquid to prevent unwanted actions. Injector. The mechanism, including nozzle, that injects fuel into the engine combustion chamber on diesel engines. In-Line Engine. An engine in which all engine cylinders are in a single row, or line. Insert. A form of screw thread insert to be placed In a tapped hole into which a screw or bolt will be screwed. The Insert protects the part into which the hole was tapped, preventing enlargement due to repeated removal and replacement of the bolt.
TM 9-8000 DEFINITION OF TERMS-CONTINUED Insulation. A substance that stops movement of electricity (electrical insulation) or heat (heat insulation). Insulator. A substance (usually of glass or porcelain) that will not conduct electricity. Intake Manifold. That component of the engine that provides a series of passages from the carburetor to the engine cylinders through which fuel-air mixture can flow. Intake Stroke. The piston stroke from top dead center to bottom dead center during which the intake valve is open and the cylinder receives a charge of fuel-air mixture. Intake Valve. The valve in the engine that is opened during the intake stroke to permit the entrance of fuel-air mixture into the cylinder. Integral. Whole; completeness. entire; lacking nothing of fifth-wheel assembly. Kingpin Inclination. The number of degrees that the kingpin, which supports the front wheel, is tilted from the vertical. Knock. In the engine, a rapping or hammering noise resulting from excessively rapid burning or detonation of the compressed fuel-air mixture. Knuckle. A joint or parts carrying a hinge pin that permit one part to swing about or move in relation to another. Laminated. Made up of thin sheets, leaves, or plates. Laminated Leaf Spring. A spring made up of leaves of graduated size. Landing Gear. A retractable support under the front end of a semitrailer to hold it up when it is uncoupled from the truck tractor. Lands. Piston metal between ring grooves. Leaf Spring. A suspension component made up of one or several layers of flat spring steel. Lean Mixture. A fuel-air mixture that has a high proportion of air and a low proportion of fuel. Lever. A rigid bar or beam of any shape capable of turning about one point, called the fulcrum; used for transmitting or changing force or motion. Leverage. The mechanical advantage obtained by use of lever; also an arrangement or combination of levers L-Head. block. A type of engine with valves in the cylinder
Interference. In radio, any signal received that overrides or prevents normal reception of the desired signal. In mechanical practice, anything that causes mismating of parts so they cannot be normally assembled. Internal Combustion Engine. An engine in which the fuel is burned inside the engine, as opposed to an external combustion engine where the fuel is burned outside the engine, such as a steam engine. Internal Gear. A gear in which the teeth point inward rather than outward as with a standard spur gear. Ion. An electrically charged atom produced by an electrical field. Jackshaft. An intermediate driving shaft. Jet. A metered opening in an air or fuel passage to control the flow of fuel or air. Journal. That part of a shaft that rotates in a bearing. Kingpin. The pin by which a stud axle is articulated to an axle beam or steering head; also the enmeshing pin in a A-13
Light. In the electric circuit, an electrical device that includes a wire in a gas-filled bulb that glows brightly when current passes through it; often called a lamp. Lighting Switch. In the electrical circuit, a switch that turns light on or off.
TM 9-8000 DEFINITION OF TERMS-CONTINUED LPG. Liquefied petroleum gas. Lubrication. The process of supplying a coating of oil between moving surfaces to prevent actual contact between them. The oil film permits relative movement with little frictional resistance. Lunette. An eye that hooks into a pintle assembly to tow vehicles. MacPherson Strut. A front end suspension system In which the wheel assembly is attached to a long telescopic strut. Magnet. Any body that has the ability to attract Iron. Magnetic Clutch. An electric clutch that engages and disengages the air conditioning compressor. Magnetic Field. The space around a magnet that the magnetic lines of force permeate. Magnetic Flux. The total amount of magnetic Induction across or through a given surface. Magnetic Pole. Focus of magnetic lines of force entering or emanating from magnet. Magnetism. The property exhibited by certain substances and produced by electron (or electric current) motion, which results in the attraction of Iron. Magneto. A device that generates voltage surges, transforms them to high-voltage surges, and distributes them to the engine cylinder spark plugs. Main Bearing. In the engine, the bearings that support the crankshaft. Manifold. See Intake Manifold or Exhaust Manifold. Master Cylinder. In the hydraulic braking system, the liquid-filled cylinder in which hydraulic pressure is A-14 Meshing. The mating or engaging of the teeth of two gears. Metering Rod. A small rod, having a varied diameter, operated within a Jet to vary the flow of fuel through the Jet. Modulator. A pressure control or adjusting valve used In hydraulic systems of automatic transmissions. Molecule. The smallest particle into which a chemical compound can be divided. Motor. A device for converting electrical energy into mechanical energy. Muffler. In the exhaust system, a device through which the exhaust gases must pass; In the muffler, the exhaust sounds are greatly reduced. Mutual Induction. Induction associated with more than one circuit, as two coils, one of which induces current In the other as the current in the first changes. Needle Bearing. An antifriction roller-type bearing in which the rollers have a very narrow diameter In relation to their length, developed by depression of the brake pedal, Master Rod. In a radial engine, the rod to which all other connecting rods are attached or articulated. Matter. Anything that has weight and occupies space. Mechanical Efficiency. In an engine, the ratio between brake horsepower and Indicated horsepower. Mechanism. A system of parts or appliances that acts as a working agency to achieve a desired result. Member. Any essential part of a machine or structure.
TM 9-8000 DEFINITION OF TERMS-CONTINUED Needle Valve. The type of valve with a rod- shaped, needle-pointed valve body that works into a valve seat so shaped that the needle point fits into it and closes the passage; the needle valve in the carburetor float circuit is an example. Negative. A term designating the point of lower potential when the potential difference between two points is considered. Negative Terminal. The terminal from which electrons depart when a circuit is completed from this terminal to the positive terminal of generator or battery. Neutron. atom. A neutral-charge particle forming part of an
Oil Control Rings. The lower rings on the piston that are designed to prevent excessive amounts of oil from working up Into the combustion chamber. Oil Cooler. A special cooling radiator through which hot oil passes. Air also passes through separate passages in the radiator, providing cooling of the oil. Oil Gage. An Indicating device that indicates the pressure of the oil in the lubrication system. Also, a bayonet-type rod to measure oil In the crankcase. Oil Gallery. A pipe or drilled passageway in the engine used to transport oil from one area to another. Oil Pan. The lower part of the crankcase in which a reservoir of oil is maintained. Oil Pump. The pump that transfers oil from the oil pan to the various moving parts in the engine that require lubrication. Oil Ring. Normally the bottom piston ring used to scrape excess oil off the cylinder wall. Oil Slinger. A device mounted to a revolving shaft such that any oil passing that point will be thrown outward where It will return to the point of origin. Oil Strainer. A strainer placed at the Inlet end of the oil pump to strain out dirt and other particles, preventing these from getting Into moving engine parts. One-Way Clutch. A device used to lock a shaft In one direction while permitting rotation In the other. Otto Cycle. The four-stroke cycle composed of Intake, compression, power, and exhaust strokes. Overflow Tank. A special tank In the cooling system (a surge tank) for hot or dry country to permit expansion and contraction of engine coolant without loss. Overhead Valve. A valve mounted In the head above the combustion chamber, Valve In I-head engine.
Nonferrous Metals. All metals containing very little or no iron. North Pole. The pole of a magnet from which the lines of force are assumed to emanate. No-Spin Differential. A special type of differential that prevents the spinning of one of the driving wheels even If it is resting on smooth Ice. Nozzle. An orifice or opening In a carburetor through which fuel feeds Into the passing air-stream on Its way to the Intake manifold. Octane Rating. engine fuel. A measure of the antiknock value of
Odometer. The part of the speedometer that measures, accumulatively, the number of vehicle miles traveled. Ohm. A measure of electrical resistance. A conductor of 1-ohm resistance will allow a flow of 1 ampere of current when 1 volt is Imposed on it. Ohmmeter. A device for measuring ohms resistance of a circuit or electrical machine. Oil. A liquid lubricant derived from petroleum and used In machinery to provide lubrication between moving parts. Also, fuel used In diesel engines. A-15
Overload Breaker. In an electrical circuit, a device that breaks or opens a circuit if it is overloaded by a short, ground, use of too much equipment, etc.
Overrunning Clutch. A type of drive mechanism used in a starter that transmits cranking effort but overruns freely when the engine tries to drive starter. Also, a special clutch used in several mechanism that permits a rotating member to turn freely under some conditions but not under other conditions. Parabolic Reflector. A reflector that sends all reflected light originating at the focal point outward in parallel rays. Parallel Circuit. The electrical circuit formed when two or more electrical devices have like terminals connected together (positive to positive and negative to negative) so that each may operate independently of the other. Parallelogram Steering Linkage. A steering configuration using two short tie rods connected to steering arms and to a long center link. The link is connected to the pitman arm on one end and the idler arm on the other. Parking Brake. See Handbrake. Payload. The amount of weight that can be carried by a vehicle. PCOJ. Positive crankcase ventilation; a system designed to prevent crankcase vapors from being discharged into the atmosphere. Period. cycle. The time required for the completion of one
another shaft or rotating part. Ping. A metallic rattling sound produced in the combustion chamber resulting from air-fuel mixture exploding rather than burning evenly. Pinion. The smaller of two mating or meshing gears. Pintle Assembly. A swivel-type assembly used to engage with a lunette for towing trailers. Piston. In an engine, the cylindrical part that moves up and down in the cylinder. Piston Boss. pinhole. An enlarged area around the piston
Piston Displacement. The volume displaced by the piston as it moves from the bottom to the top of the cylinder in one complete stroke. Piston Head. A portion of the piston above the top ring. Piston Lands. A portion of the piston between the ring grooves. Piston Pin. The cylindrical or tubular metal pin that attaches the piston to the connecting rod; also called wrist pin. Piston Ring. One of the rings fitted into grooves in the piston. There are two types: compression rings and oil control rings. Piston Rod. See Connecting Rod. Pitman Arm. The arm that is a part of the steering gear; it is connected by linkage to the wheel steering knuckle. Pivot Inclination. See Kingpin Inclination. Planetary Gears. Set of gears that includes a central spur gear, called the sun gear, around which revolves one or more meshing planetary gears. An internal gear, meshed with the planetary gears, completes the set. Plies. Layers of rubber-impregnated fabric that make up the body of the tire.
Permanent Magnet. A piece of steel or alloy in which molecules are so aligned that the piece continues to exhibit magnetism without application of external influence. Phase. That portion of a whole period that has elapsed since the activity in question passed through zero position in a positive direction. Pickup Coil. A device used in electronic-type distributors that sends electrical pulses to a control unit. Pilot. A short plug at the end of a shaft to align it with A-16
TM 9-8000
DEFINITION OF TERMS - CONTINUED Poppet. A spring-loaded ball engaging a notch. A ball latch. Positive. A term designating the point of higher potential when the potential difference between two points is considered. Potential. A characteristic of a point in an electric field or circuit indicated by the work necessary to bring a unit positive charge from infinity; the degree of electrification as compared to some standard (the earth, for example). Potential Difference. The arithmetical difference between two electrical potentials; same as electromotive force, electrical pressure, or voltage. Power. The rate of doing work. Power Booster. A device that increases brake pedal force on master cylinder during stops. Power Divider. A mechanism placed between dual rear axles to apportion driving effort between the two pairs of wheels to provide the maximum tractive effort. Powerplant. The engine or power-producing mechanism on the vehicle. Power Steering. Vehicle steering by use of hydraulic pressure to multiply the drivers steering effort so as to improve ease of steering. Power Stroke. The piston stroke from top dead center to bottom dead center during which the fuel-air mixture burns and forces the piston down so the engine produces power. Power Takeoff. An attachment for connecting the engine to power-driven auxiliary machinery when its use is required. Preignition. Premature ignition of the fuel-air mixture being compressed in the cylinder on the compression stroke. Primary Brakeshoe. The brakeshoe installed facing the front of the vehicle; usually a self-energizing shoe. Primary Circuit. Low-voltage part of ignition system. Propane. A petroleum product, sometimes referred to as LP gas, useful as engine fuel. Propeller Shaft. The driving shaft in the power train that carries engine power from the transmission to the differential; also, the shaft that turns the propeller in amphibian vehicles. Proportioning Valve. A valve in the brake system that prevents rear wheels from locking during harsh stops. Proton. A basic particle of matter having a positive electrical charge, normally associated with the nucleus of the atom. PSI. Pounds per square inch; a measure of force per unit area. PTO. Power takeoff; a location on the transmission or transfer case from which an operating shaft from another unit can be driven. Pulsation Damper. A unit used to smooth fuel pulsations from fuel pump to carburetor. Pump. A device that transfers gas or liquid from one place to another. Race. The inner or outer ring that provides a contact surface for balls or rollers to ride on. Rack and Pinion Steering. A steering network using a pinion gear mounted on the end of the A-17 Primary Winding. Low-voltage winding in ignition coil. Primer. An auxiliary fuel pump operated by hand to feed additional fuel into the engine to produce a richer mixture for starting. Prismatic Lens. A lens with parallel grooves or flutes that deflect and distribute light rays. Progressive Linkage. Carburetor linkage designed to open throttle valves. Primary throttle valves are first opened and, at a certain throttle position, secondary valves begin to open. Prony Brake. A device using a friction brake to measure horsepower.
TM 9-8000
DEFINITION OF TERMS - CONTINUED steering shaft. The pinion engages a long rack and is connected to the steering arms via tie rods. Radial. Pertaining to the radius of a circle. Radial Engine. An engine with each cylinder located on the radius of a circle and with all cylinders disposed around a common crankshaft. Radial Tire. A tire having plies parallel and at right angles to tread pattern. Radiator. A device in the cooling system that removes heat from the coolant passing through it, permitting coolant to remove heat from the engine. Radius. Distance from the center of a circle or from center of rotation. Rectifier. An electrical device that changes alternating current to direct current. Refrigerant-12. A refrigeration gas commonly used in automotive air conditioning systems. Regulator. A device used to control output of the charging system. Relay. In the electrical system, a device that opens or closes a second circuit in response to voltage or amperage changes in a controlling circuit. Residual Magnetism. The magnetism retained by a material after all magnetizing forces have been removed. Resistance. The opposition offered by a substance or body to the passage through it of an electric current. Resistor. In an electrical system, a device made of resistance wire, carbon, or other resisting material, that has a definite value of resistance and serves a definite purpose in the system by virtue of that resistance. Rheostat. A resistor for regulating the current by means of variable resistance. A-18 Rim. That part of a vehicle wheel on which the tire is mounted. Ring Gear. A gear in the form of a ring such as the ring gear on a flywheel or differential. Rock Position. The piston and connecting rod position (top or bottom dead center) at which the crank can rock or rotate a few degrees without appreciable movement of the piston. Rocker Arm. A device used to direct upward motion of push rod into downward motion to open the valve. Used in overhead valve installations. Rod. See Connecting Rod. Rod Cap. The lower detachable part of the connecting rod that can be taken off by removing bolts or nuts so the rod can be detached from the crankshaft. Roller Bearing. A type of bearing with rollers positioned between two races. Rotary Engine. A piston engine in which the crankshaft is fixed and cylinders rotate around the crankshaft. Rotor. A part that revolves in a stationary part; especially the rotating member of an electrical mechanism. RPM. Revolutions per minute; a measure of rotational speed. SAE. Society of Automotive Engineers. SAE Horsepower. A measurement based upon the number of cylinders and the cylinder diameter. Scavenging. A cleaning or blowing out action in reference to exhaust gas.
TM 9-8000 DEFINITION OF TERMS - CONTINUED Sealed Beam. A special type of headlight in which the reflector and lens are sealed together to enclose and protect the filaments. Sealed Bearing. A bearing that has been lubricated and sealed during manufacturing and cannot be lubricated during service. Seat. The surface upon which another part rests. Secondary Brakeshoe. facing rear of car. A brakeshoe that is installed bearing cap for example, to adjust bearing clearance. Shimmy. Abnormal sidewise vibration, particularly of the front wheels. Shock Absorber. A device placed at a vehicle wheel to regulate spring rebound and compression. Short Circuit. In electrical circuits, an abnormal connection that permits current to take a short path or circuit, thus bypassing important parts of the normal circuit. Shroud. Forward subassembly of a body or cab containing dash, cowl, and instrument panel. Also, a hood placed around a fan to improve fan action. Shunt. Parallel connections, in a portion of an electrical circuit. Sidewall. bead. The section of tire between the tread and
Secondary Wires. The wire from the coil to the distributor central tower and the spark plug wires. Self-Energizing. A brakeshoe that develops a wedging action to assist in development of brake force. Self-Induction. A property of a circuit that causes it to magnetically affect voltage and current in the circuit. Semielliptical Spring. A series of leaf springs starting with the longest on top and a number of progressively shorter springs attached below. Semitrailer. A type of trailer supported at the rear by attached wheels and at the front by the truck tractor; the truck tractor can be coupled and uncoupled by means of fifth wheel. Separator. In the storage battery, the wood, rubber, or glass mat strip used as insulator to hold the battery plates apart. Series Circuit. The electrical circuit formed when two or more electrical devices have unlike terminals connected together (positive to negative) so that the same current must flow through all. Servo Action. Brakeshoes configured such that the primary brakeshoe assists in applying the secondary shoe. Shackle. A swinging support that permits a leaf spring to vary in length as it is deflected. Shim. A strip of copper or similar material, used under a A-19
Sight Glass. A glass window in an air conditioning system used for detection of moisture or bubbles. Slip Joint. In the power train, a variable-length connection that permits the propeller shaft to change effective length. Sodium Valve. A valve that has been filled with sodium to increase heat transfer. SOHC. Single overhead camshaft. Solenoid. A coil of wire that exhibits magnetic properties when electric current passes through it. Solid Axle. A single beam configuration that connects two wheels. South Pole. The pole of the magnet into which it is assumed the magnetic lines of force pass. Spark Plug. The assembly that includes a pair of electrodes which has the purpose of providing a spark gap in the engine cylinder.
TM 9-8000 DEFINITION OF TERMS - CONTINUED Specific Gravity. The ratio of the weight of a substance to weight of an equal volume of chemically pure water at 39.2F (4C). Speed. Rate of motion. Speedometer. An indicating device, usually connected to the transmission, that indicates the speed of motion of the vehicle. Spider. In planetary gearsets, the frame, or part, on which the planetary gears are mounted. Spiral Bevel Gear. A bevel gear having curved teeth. Spline. A slot or groove cut in a shaft or bore; a splined shaft onto which a hub, wheel, etc, with matching splines in its bore is assembled so the two must engage and turn together. Spool Valve. A hydraulic control valve housing piston(s) connected by a central rod. Sprag Unit. A form of overrunning clutch; power can be transmitted through it in one direction but not in the other. Springs. Flexible or elastic members that support the weight of a vehicle. Spur Gear. A gear with radial teeth parallel to the axis. Starter. In the electrical system, the motor that cranks the engine to get it started. Starter Solenoid. An electric relay used to deliver electrical power to the starting motor. Starting System. The electrical system, including the starter battery, cables, switch, and controls, that has the job of starting the engine. Static Electricity. Accumulated electrical charges, usually considered to be those produced by friction. Stator. A part of the torque converter that stands still as torque is being multiplied, then rotates as the turbine approaches impeller speed. A-20
Steering Gear. That part of the steering system, located at the lower end of the steering shaft, that carries the rotary motion of the steering wheel to the vehicle wheels for steering. Steering Geometry. The difference in angles between the two front wheels and the car frame during turns; the inside wheel turns more sharply than the other wheel turns since it must travel on an arc of a smaller radius. Also called toe-out during turns. Steering Linkage. Linkage between steering gear and vehicle wheels. Steering System. The system of gears and linkage in the vehicle that permits the driver to turn the wheels for changing the direction of vehicle movement. Stoplight. A red light illuminated upon application of the brake cable. Storage Battery. A lead-acid electrochemical device that changes chemical energy into electric energy. The action is reversible; electric energy supplied to the battery stores chemical energy. Stroke. The movement, or the distance of the movement, in either direction, of the piston travel in an engine. Sulfation. A crystalline formation of lead sulfate on storage battery plates. Sun Gear. In a planetary gear system, the central gear. Supercharger. A device used in connection with engine fuel-air systems to supply more air at greater pressure to the engine, thereby increasing volumetric efficiency. Superheat Switch. A switch used to disengage the compressor during an overheating or loss of oil condition. Suppression. In the electrical system, the elimination of stray electromagnetic waves due to action of ignition, generator, etc, so that they cannot be detected by radio.
TM 9-8000 DEFINITION OF TERMS - CONTINUED Suspension. The system of springs, etc, supporting the upper part of a vehicle on its axles or wheels. Swaybar. A connecting bar placed between wheel supports, parallel to the axles, that prevents excessive vehicle roll or sway on turns. Switch. In the electrical system, a device used to open or complete an electrical circuit. Synchromesh. A name designating a certain type of transmission that has the virtue of permitting gear-ratio shifts without gear clashing. Synchronize. To make two or more events or operations occur at the same time. Tachometer. minute. A device for measuring revolutions per Thermistor. temperature. Thermostat. temperature. A resistor whose value varies with TDC. Top dead center; the position of the piston when it reaches the upper limit of travel in the cylinder. Teflon. A plastic with excellent self-lubricating (slippery) bearing properties. Temper. To effect a change in hardness and strength of steel through heating and cooling. Temperature Gage. An indicating device in the cooling system that indicates the temperature of the coolant and gives warning if excessive engine temperatures develop. Tension. A stress caused by a pulling force. Thermal Efficiency. The ratio between the power output and the energy in the fuel burned to produce the output.
Tactical Vehicle. A vehicle designated primarily to meet field requirements in direct connection with combat, tactical operations, and the training of troops for combat. Taillight. Lights, usually red or amber, attached to rear of vehicle, that are used as markers. Tailpipe. The exhaust piping running from muffler to rear of vehicle. Tandem Axles. Two axles, one placed directly in front of the other. Tank Sending Unit. A device in the fuel tank that provides indication of fuel level for instrument panel gage. Taper. To make gradually smaller toward one end; a gradual reduction in size in a given direction. Tapered Roller Bearing (Antifriction). A bearing utilizing series of tapered, hardened steel rollers operating between an outer and inner hardened steel race. Tappet. A screw used to adjust clearance between valve stem and lifter or rocker arm.
Thermostatic Switch. A switch that is turned on or off by temperature change. Third-Brush Generator. An auxiliary brush that regulates the current output of the generator by increasing or decreasing the field coil current. Three-Quarter Trailer. Trailers, usually two-wheeled, used for light loads. The load is practically balanced on the trailer suspension, although some of the load is thrust on the truck tractor connection. Throttle. A mechanism in the fuel system that permits the driver to vary the amount of fuel-air mixture entering the engine and thus control the engine speed. Throttle Valve Plate. The disk in the lower part of the carburetor air horn that can be tilted to pass more or less fuel-air mixture to the engine. Thrust. A force tending to push a body out of alinement. A force exerted endwise through a member upon another member. A-21
TM 9-8000 DEFINITION OF TERMS - CONTINUED Thrust Bearing. A bearing that is designed to resist axial (sideway) forces of a rotating member. Tie Rod. A rod connection in the steering system between wheels. TIG. Tungsten inert gas; gas tungsten arc welding. Timed Fuel Injection. Fuel injection system that injects fuel on an individual cylinder basis and in sequence with the cylinders intake stroke. Timing. Refers to ignition or valve timing and pertains to the relation between the actions of the ignition or valve mechanism and piston position in the cylinder. Timing Belt. A flexible toothed belt that, through sprockets, drives the engine camshaft. Timing Chain. A link- or roller-type continuous chain that, through sprockets, drives the engine camshaft. Timing Gears. A pair of helical gears that drive the engine camshaft. Timing Marks. A pair of reference points that are used to obtain correct timing of the valves or ignition distributor of the engine. Tire. The rubber and fabric part that is assembled on the wheel rim and filled with compressed air (pneumatic type). Toe-In. A measurement in inches that is obtained by measuring the distances between the front tires at the forward and rearward edges and taking the difference between the two dimensions. The measurements are taken with the wheels in the straight ahead position. Toe-Out. The normal condition that occurs with ackerman steering as the front wheels are turned. Because the inner wheel must turn sharper than the outer, the wheels are further apart at the forward edge (toe) than the rearward edge. Tolerance. The amount of variation permitted from an exact size or measurement; the actual amount from smallest acceptable dimension to largest acceptable dimension. A-22
Torque. A twisting or turning effort. Torque is the product, of force times the distance, from the center of rotation at which it is exerted. Torque Converter. A special form of fluid coupling in which torque may be increased (at expense of speed). Torque Multiplication. A term that refers to engine torque increase that occurs within a torque converter. Torque Rod. An arm or rod used to ensure accurate alinement of an axle with the frame and to relieve springs of driving and braking stresses. Torque-Tube Drive. The type of rear-end arrangement that includes a hollow tube that encloses the propeller shaft and also takes up stresses produced by braking and driving. Torque Wrench. A special wrench with a dial that indicates the amount of torque in feet pound being applied to a bolt or nut. Torsion Bar. A bar-shaped spring that is anchored on one end and operates by offering resistance as torque is applied at its other end. Torsional Vibration. Vibration in a rotary direction; a portion of a rotating shaft that repeatedly moves ahead, or lags behind, while the remainder of the shaft is exhibiting torsional vibration. Torus. Rotating member of fluid coupling. Track. 1. The endless tread on which a tank rides. 2. The measurement between the center of the treads of the tires on an axle. Tracked Vehicle. A vehicle that uses tracks instead of wheels for mobility. Traction. The force exerted in drawing a body along a plane as when a truck tractor pulls a semitrailer, Tractlve Effort. The pushing effort the driving wheels can make against the ground, which is the
TM 9-8000 DEFINITION OF TERMS - CONTINUED same as the forward thrust or push of the axles against the vehicle. Tractor. A motor vehicle (wheeled or tracked) especially designed to tow trailers. Trailer. A vehicle without motive power towed by a motor vehicle, designed primarily for cargo carrying. Transfer. The auxiliary assembly for applying power to both forward and rear propeller shafts, and to front wheels as well as rear wheels. Transfer Case. A gearbox, driven by transmission, that will provide driving force to both front and rear propeller shafts on four-wheel drive vehicle. Transmission. The device in the power train that provides different gear ratios between the engine and driving wheels, as well as reverse. Transmission Brake. A brake placed at the rear of the transmission, usually used for parking. Tread. The design on the road-contacting surface of a tire that provides improved frictional contact. Trip Odometer. An auxiliary odometer that may be reset to zero at option of driver. Used for keeping track of mileage on trips up to 1000 miles. Truck Tractor. A motor vehicle especially designed to tow semitrailers. Trunnion. Either of two opposite pivots or cylindrical projections from the sides of a part assembly, supported by bearings, to provide a means of swiveling or turning the part or assembly. Trunnion Axle. A supporting axle that carries a load with other axles attached to it. Its use as a part of a bogie permits independent wheel action in a vertical plane and within designed limits. Turbine. A mechanism containing a rotor with curved blades; the rotor is driven by the impact of a liquid or gas against the curved blades. Turbine Engine. An engine that uses the expansive force of burning gases to spin a turbine. Turbocharger. An exhaust-driven compressor that forces fuel and air mixture into the engine. Turning Radius. The diameter of the circle made by a vehicle during operation with front wheels turned fully in either direction. Turret Traversing Mechanism. A mechanism for rotating a tank turret on a horizontal plane. Two-Stroke-Cycle Engine. An internal combustion engine requiring but two piston strokes to complete the cycle of events that produce power. Understeer. A vehicle handling characteristic that causes a vehicle to turn less sharply than the operator intends it to. Unit Body. A car body that has enough inherent rigidity to act as a frame also. Universal Joint. A device that transmits power through an angle. Unsprung Weight. Weight of a vehicle that is not supported by springs. Updraft Carburetor. A carburetor in which air passes through it in an upward direction. Vacuum. A space entirely devoid of matter. Vacuum Advance. The mechanism on an ignition distributor that advances the spark in accordance with vacuum in the intake manifold. Vacuum Brakes. Vehicle brakes that are actuated by vacuum under the control of the driver. Vacuum Pump. A pump, used in a vacuum brake system (for example), that produces a vacuum in a designated chamber. Vacuum Switch. In the starting system, an electric switch that is actuated by vacuum to open the starting system control circuit as the engine starts, producing a vacuum in the intake manifold. Valve. A mechanism that can be opened or closed to allow or stop the flow of a liquid, gas, or vapor from one place to another. A-23
TM 9-8000 DEFINITION OF TERMS - CONTINUED Valve Seat. The surface, normally curved, against which the valve operating face comes to rest, to provide a seal against leakage of liquid gas, or vapor. Valve Seat Insert. A metal ring inserted into the valve seat; made of special metal that can withstand operating temperature satisfactorily. Valve Spring. The compression-type spring that closes the valve when the valve-operating cam assumes a closed-valve position. Valve Tappet. The part that rides on the valve operating cam and transmits motion from the cam to the valve stem or push rod. Valve Timing. Refers to the timing of valve closing and opening in relation to piston position in the cylinder. Valve Train. The train of moving parts to the valve that causes valve movement. Vapor Lock. A condition in the fuel system in which gasoline has vaporized, as in the fuel line, so that fuel delivery to the carburetor is blocked or retarded. Velocity. The rate of motion or speed at any instant, usually measured in miles per hour or feet per second or minute. Venturi. In the carburetor, the restriction in the air horn that produces the vacuum responsible for the movement of fuel into the passing airstream. Vibration. An unceasing back and forth movement over the same path; often with reference to the rapid succession of motions of parts of an elastic body. Vibration Damper. A weighted device that is attached to the engine crankshaft at the end opposite its power output. Its purpose is to absorb engine vibration. Viscosity. A measure of an oils ability to flow at a determined temperature. Volatility. A measurement of the ease with which a liquid turns to vapor. A-24
Volt. A unit of potential, potential difference, or electrical pressure. Voltage Regulator. A device used in connection with a generator to keep the voltage constant and to prevent it from exceeding a predetermined maximum. (One of the three units comprising a generator regulator.) Volumetric Efficiency. The ratio between the amount of fuel-air mixture that actually enters an engine cylinder and the amount that could enter under ideal conditions. Volute Springs. Helical coil springs made from flat steel tapered both in width and thickness. V-Type Engine. An engine with two banks of cylinders set at an angle to each other in the shape of a V. Wander. To ramble or move without control from a fixed course, as the front wheels of a vehicle. Water Jacket. A jacket that surrounds cylinders and cylinder head, through which coolant flows. Water Manifold. A manifold used to distribute coolant to several points in the cylinder block or cylinder head. Water Pump. In the cooling system, the pump that circulates coolant between the engine water jackets and the radiator. Wheel Alinement. The mechanics of keeping all the parts of the steering system in correct relation with each other. Wheel Brake. A brake that operates at the wheel, usually on a brakedrum attached to the wheel. Wheel Cylinder. In hydraulic braking systems, the hydraulic cylinder that operates the brakeshoes when hydraulic pressure is applied in the cylinder. Winch. A mechanism actuating a drum upon which a cable is cooled, so that when a rotating power is applied to the drum, a powerful pull is produced.
TM 9-8000 DEFINITION OF TERMS - CONTINUED Wobble Plate. That part of a special type of pump (wobble pump) that drives plungers back and forth as it rotates to produce pumping action. It is a disk, or plate, set at an angle on a rotating shaft. Work. The result of a force acting against opposition to produce motion. It is measured in terms of the product of the force and the distance it acts. Worm Gear. A gear having concave, helical teeth that mesh with the threads of a worm; also called a worm wheel.
A-25/(A-26 blank)
TM 9-8000 INDEX Para Administrative vehicles...................................................... Airbrake system: Airbrake valve .............................................................. Air compressor ............................................................. Brake chamber............................................................. Governor ...................................................................... Pneumatic principle...................................................... Quick release valve...................................................... Relay valve................................................................... Slack adjuster .............................................................. Unloader....................................................................... Air cooling systems: Classification ................................................................ Principle ....................................................................... Air filters ............................................................................ Air-fuel ratio ....................................................................... Air horns ............................................................................ Air Injection systems ......................................................... Air-operated windshield wipers ......................................... Air-over-hydraulic brake system: Construction ................................................................. Operation ..................................................................... Air-over-hydraulic suspension system: Air compressor ............................................................. Air shock absorbers ..................................................... Height control valve...................................................... Pressure regulator valve .............................................. Purpose........................................................................ Air steering: Components................................................................. Operation ..................................................................... Purpose........................................................................ Alarm, backup ................................................................... Alternating current generator............................................. Alternators: Automatic ..................................................................... Basic ............................................................................ Brushless-rotating rectifier ........................................... Inductor ........................................................................ Lundell inductor............................................................ Lundell type.................................................................. Wound pole .................................................................. Ammeter............................................................................ Amperage.......................................................................... Antifreeze .......................................................................... Antiknock quality ............................................................... Atmosphere ....................................................................... Atmospheric pressure ....................................................... 1-15 34-39d 34-39a 34-39e 34-39c 34-38 34-39f 34-39g 34-39h 34-39b 2-17 9-13 4-6 4-12 17-12 7-9 17-16 34-40 34-41 Automatic transmission: Drive train arrangements ..................................... Drive train mechanisms ....................................... General operation ................................................ Hydraulic system.................................................. Auxiliary generator .................................................... Auxiliary heaters........................................................ Auxiliary power receptacle ........................................ Auxiliary transmission: Operation ............................................................. Purpose................................................................ Axles: Bogie.................................................................... Live ...................................................................... Pusher.................................................................. Backup alarm ............................................................ Backup light system .................................................. Ball bearing ............................................................... Ballast resistor........................................................... Bars, torsion: Automotive ........................................................... Tracked vehicle.................................................... Batteries: Charge ................................................................. Charging systems ................................................ Component parts ................................................. Deep cycle ........................................................... Discharge............................................................. Ignition systems ................................................... Installation............................................................ Maintenance-free ................................................. Nickel cadmium ................................................... Principles of operation ......................................... Storage batteries.................................................. Bead clip ................................................................... Bead lock .................................................................. Bearing lubrication .................................................... Bearings: Ball ....................................................................... Crankshaft ........................................................... Needle.................................................................. Roller.................................................................... Sealed.................................................................. Sleeve type .......................................................... Sliding surface ..................................................... Tapered roller....................................................... Bellows booster......................................................... Bendix starter drive ................................................... Blackout lighting ........................................................ Para
23-8 23-5 23-1 23-11 13-19 17-20 17-18 26-2 26-1 30-12 29-10 30-21 17-13 16-14 19-8a 15-3g 30-2c 31-1b 12-5 13-1 12-2 12-6 12-4 15-3 12-10 12-8 12-7 15-2 12-9 32-9 32-8 19-9 19-8a 3-10 19-8d 19-8b 19-10 19-7a 19-7 19-8c 34-35 14-4f 16-9
30-14a 30-15 30-14c 30-14b 30-13 33-14 33-15 33-13 17-13 13-20, 13-26 13-23 13-21 13-24e 13-24d 13-24c 13-24b 13-24a 17-2a 11-9a 9-5a 4-40 2-22a 2-22b
INDEX - 1
TM 9-8000
INDEX - CONTINUED Para Bogie axles .................................................... Booster coil, magneto ignition ....................... Boosters: Bellows.................................................... Brake pedal............................................. Hydraulic power ...................................... Piston ...................................................... Tandem................................................... Brake: Action ...................................................... Boosters.................................................. Contracting transmission ........................ Disk ......................................................... Disk transmission.................................... Drum ...................................................... Fixed caloper .......................................... Floating caliper........................................ Fluid ........................................................ Hill holder ................................................ Hydraulic ................................................. Limiting valve .......................................... Lines ....................................................... Lining ...................................................... Master cylinder........................................ Operation ................................................ Parking.................................................... Pedal booster.......................................... Pneumatic ............................................... Power...................................................... Proportioning valve ................................. Requirements.......................................... Retardation ............................................. Retardation point..................................... Rotating and nonrotating units ................ Self-energizing ........................................ Shoes...................................................... Vehicle stopping distance ....................... Wheel cylinder ........................................ Brake systems: Air............................................................ Air-over-hydraulic.................................... Electric .................................................... Hydraulic operation ................................. Hydraulic, principles................................ Mechanical.............................................. Power...................................................... Vacuum-over-hydraulic ........................... Brayton cycle ................................................. 30-12 15-14 34-35 34-36 34-37 34-34 34-33 34-1 34-33 34-17 34-13 34-18 34-7c 34-15 34-14 34-29 34-27 34-8, 34-23 34-31 34-28 34-7b 34-25 34-10 34-19 34-36 34-9 34-32 34-30 34-2 34-4 34-5 34-6 34-16 34-7a 34-3 34-26 34-38 34-40 34-44 34-24 34-23 34-21 34-32 34-42 105b Camber .......................................................... Camshaft........................................................ Functions ................................................. Tappets.................................................... Timing belt ............................................... Captive-discharge ignition.............................. Carbon-pile regulator ..................................... Carburetion: Composition of air.................................... Downdraft ................................................ Evaporization........................................... Multiple venturi......................................... Updraft..................................................... Venturi effect ........................................... Carburetor systems: Accelerator pump circuit .......................... Accessory systems.................................. Choke system.......................................... Degasser system..................................... Float circuit .............................................. High-speed enrichment ........................... Idle and low-speed system ...................... Primer system.......................................... Throttle valve ........................................... Caster............................................................. Catalytic converters........................................ Centrifugal governors..................................... Centrifugal-vacuum governors ....................... Charging systems .......................................... Choke system ................................................ Circuit breaker................................................ Circuit configurations: Automotive............................................... Parallel..................................................... Series ...................................................... Series-parallel.......................................... Classification of engines: Cooling..................................................... Cylinder arrangements ............................ Design ..................................................... Valve arrangements ................................ Clutch: Diaphragm ............................................... Elements.................................................. Helical spring ........................................... Multiple disk............................................. Operating system .................................... Overrunning............................................. Principles ................................................. INDEX - 2 Para 33-19 3-13 3-13g 3-13h 3-13e 15-7 13-14 4-8 4-21 4-9 4-20 4-21 4-10 4-18 4-24 4-19 4-23 4-14 4-17 4-16 4-22 4-13 33-18 7-8 4-33 4-35 13-1 4-19 13-10 11-12b 11-12d 11-12c 11-12e 2-17 2-19 1-19 2-18 21-4c 21-2 21-4f 21-4d 21-3 23-7 21-1
TM 9-8000
INDEX - CONTINUED
Para Clutch - Continued Single dry plate ....................................... Wet ......................................................... Coil springs.................................................... Combat vehicles ............................................ Combustion chamber design, diesel: Open chamber ........................................ Precombustion chamber ......................... Spherical chamber .................................. Turbulence chamber ............................... Combustion, continuous................................ Commercial vehicle lighting........................... Compression brake ....................................... Compression ratio: Effect of increasing ................................. Measuring ............................................... Compression stroke ...................................... Compressors ................................................. Conductors .................................................... Connecting rods ............................................ Constant mesh transmission: Construction............................................ Gears ...................................................... Synchronizers ......................................... Contracting transmission............................... Control systems: Generator lockout relay........................... Key and pushbutton switch ..................... Oil pressure lockout ................................ Vacuum lockout switch ........................... Controlled differential..................................... Conventional differential................................ Converter, catalytic........................................ Cooling generator .......................................... Cooling systems: Air............................................................ Antifreeze................................................ Closed cooling ........................................ Coolants.................................................. Corrosion resistance ............................... Engine water jackets............................... Expansion tank ....................................... Fan and shrouding .................................. Liquid ...................................................... Radiator pressure cap............................. Radiators................................................. Thermostats ............................................ Water pump ............................................ Cooling systems, classification: Air ............................................................ Liquid ....................................................... Crankcase: Air-cooled engine..................................... Dilution..................................................... Ventilation controls .................................. Crankshaft: Bearings .................................................. Lubrication ............................................... Throw arrangements ............................... Vibration................................................... Cross-drive transmission: Braking .................................................... Construction ............................................ Functions ................................................. Hydraulic system ..................................... Operation................................................. Planetary gearing..................................... Steering ................................................... Torque converter ..................................... Cutout relay.................................................... Cylinder: Air-cooled engines................................... Blocks ...................................................... Heads ...................................................... Deicing agents ............................................... Diesel vs gasoline engine: General.................................................... Operation................................................. Diesel fuels: Cleanliness .............................................. Ignition quality.......................................... Knocking.................................................. Viscosity................................................... Diesel fuel systems: Cold weather starting aids ....................... Combustion chamber design................... Engine retarder........................................ Fuel filters ................................................ Governors................................................ Injection ................................................... Timing devices......................................... Differential, controlled: Construction ............................................ Operation................................................. Purpose ................................................... INDEX-3
Para
21-4b 21-4e 30-2b 1-17 5-9 5-10 5-12 5-11 10-6 16-13 5-38 2-24c 2-24b 2-6 10-9 11-4b 3-8 22-8 22-8a 22-8b 34-17 14-7 14-5 14-8 14-6 29-11 29-1 7-8 13-25 9-13 9-5a 9-12 9-5 9-5b 9-4 9-11 9-8 9-3 9-10 9-6 9-9 9-7
2-17a 2-17b 3-4 4-37b 7-7 3-10 3-9e 3-9c 3-9d 24-8 24-3 24-2 24-7 24-3 24-5 24-6 24-4 13-10 3-3 3-1 3-2 4-39 2-13a 2-13b 5-2 5-4 5-5 5-3 5-31 5-8 5-37 5-34 5-24 5-13 5-28 29-12 29-13 29-11
TM 9-8000
INDEX - CONTINUED
Para Differential, conventional: High-traction gears.................................. Principles of operation ............................ Purpose................................................... Differential, interwheel................................... Differential, no-spin: Clutch type ............................................. . Purpose................................................... Silent type ............................................... Sprag type............................................... Differential-voltage-and-reversecurrent-relay ............................................... Diodes ........................................................... Direct current generator ................................ Direct current motor....................................... Disk brakes.................................................... Disk transmission .......................................... Distributor, magneto ...................................... Distributor, multiple contact ........................... Distributor-type system, diesel engine......................................................... Dome lights ................................................... Drawbar ......................................................... Drawbar pull .................................................. Drives: Eight wheel.............................................. Final ........................................................ Four wheel .............................................. Front wheel ............................................. Rear wheel.............................................. Six wheel....................... .......................... Drive train arrangements: Compound planetary............................... Simpson .................................................. Drive train mechanisms: Automatic transmission........................... Brake band.............................................. Multiple-disk clutch.................................. Overrunning clutch.................................. Dual horn ....................................................... Dump truck mechanisms: Body control box ..................................... Control lever............................................ Control valve and pump .......................... General ................................................... Hydraulic cylinder.................................... Dynamometer ................................................
Para Efficiencies of engines: Mechanical .............................................. 2-39 Overall ..................................................... 2-40 Thermal ................................................... 2-38 Eight-wheel drive............................................ 19-17 Electric brake system: Construction ............................................ 34-44 Operation................................................. 34-45 Electric windshield wipers .............................. 17-15 Electrical system: Amperage ................................................ 11-9a Batteries .................................................. 12-1 Battery ignition ........................................15-2 Carbon-pile regulator............................... 13-14 Circuit breaker ......................................... 13-10 Circuit configurations ............................... 11-12 Conductors .............................................. 11-4b Cutout relay ............................................. 13-10 Diodes ..................................................... 11-6 Electricity, composition ............................ 11-2 Electromagnetic induction ....................... 11-15 Electromagnetism.................................... 11-14 Electron theory......................................... 11-3 Fuse......................................................... 16-8b Ignition ..................................................... 10-21 Insulators ................................................. 11-4c Lighting system........................................ 16-1 Magnetic field .......................................... 11-13 Magneto................................................... 15-9 Matter, composition ................................. 11-1 Motor, direct current ................................ 14-2 Ohms law................................................ 11-11 Resistance............................................... 11-10 Semiconductor devices ........................... 11-5 Solid-state voltage regulator.................... 13-29 Starter, motor drives ................................ 14-4 Starting .................................................... 10-22 Step voltage control................................. 13-16b Transistorized point regulator .................. 13-28 Transistors............................................... 11-8 Third-brush regulator ............................... 13-16 Vibrating point regulator........................... 13-13, 13-27 Voltage..................................................... 11-9b Zener diodes............................................ 11-7 Electromagnetic Induction.............................. 11-15 Electromagnetism .......................................... 11-14 INDEX-4
29-3 29-2 29-1 29-10j 29-7 29-4 29-6 29-5 13-19d 11-6 13-7 14-2 34-13 34-18 15-13 15-4 5-16 16-16b 38-6 29-15c 19-17 29-8 19-15 19-13 19-14 19-16 23-9 23-10 23-8 23-6 23-5 23-7 17-10 36-18 36-19 36-20 36-17 36-21 2-32
TM 9-8000
INDEX - CONTINUED Para Emission control system................................ Energy ........................................................... Engine: Classifications ......................................... Compression ratio................................... Connecting rods...................................... Crankcase............................................... Crankshaft .............................................. Cylinder block ......................................... Cylinder head.......................................... Efficiency................................................. Exhaust manifold .................................... Exhaust stroke .................. ...................... Exhaust valve.......................... .............. F-head..................................................... Flywheel.................................................. Horizontal opposed ................................. Ignition timing.......................................... I-head...................................................... In-line ...................................................... Intake manifold ....................................... L-head..................................................... Measurements ........................................ Oils........................... ............................... Operation ...................... .......................... Radial...................................................... T-head..................................................... Valve-operating mechanisms ................. V-type...................................................... Water jackets .......................................... Ether injection system ................................... Evaporation, fuel............................................ Exhaust: Manifold ....................... ........................... Port .......................... ............................... Stroke...................................................... Valve ....................................................... Exhaust emissions, control of........................ Exhaust gas recirculation system.................. Expansion tank .............................................. 7-5 2-28 2-17 2-24 3-8 3-1e 3-9 3-1 3-2 2-38 7-2 2-8 2-3 218c 2-10e, 3-11 2-19c 2-25 2-18a 2-19a 4-5 2-18a 2-20 8-4 2-1 2-19d 2-18a 3-14 2-19b 4-39 5-33 7-11 7-2 2-3 2-8 2-3 7-6 7-10 9-11 Fixed caliper................................................... Floating caliper............................................... Fluid, brake .................................................... Fluid couplings: Operation................................................. Principles ................................................. Flywheel ......................................................... Force-feed system ......................................... Four-stroke cycle operation............................ Four-wheel drive ............................................ Four-wheel driving and steering..................... Frame and body, tracked vehicle................... Frame and body, wheeled vehicle: Brackets and hangers.............................. Integrated (monocoque) .......................... Separate .................................................. Trucks (ladder) ........................................ Front-wheel drive ........................................... Para 34-15 34-14 34-29 21-6 21-5 2-10e, 3-11 8-19 2-5, 2-6 19-15 33-16 35-5 35-4 35-2 35-1 35-3 19-13
Fan ................................................................ Field intensity .......................................... Field winding configurations .......................... Fifth wheel ..................................................... Filters, air....................................................... Final drive ......................................................
Gages: Fuel.......................................................... 17-3 Oil pressure ............................................. 17-4 Temperature ............................................ 17-5 Gaskets .......................................................... 19-12 Gasoline: Antiknock quality...................................... 4-40 Crankcase dilution ................................... 4-37b Deicing agents......................................... 4-39 Fuel distribution ....................................... 4-37d Origin ....................................................... 4-36 Purity........................................................ 4-38 Starting ability ........................................4-37a Vapor lock................................................ 4-37c Volatility ................................................... 4-37 Gasoline and water tankers: Considerations......................................... 36-16 General.................................................... 36-13 Semitrailer ............................................... 36-14 Tank truck................................................ 36-15 Gasoline engine: Continuous fuel injection systems ................................................... 4-27 Timed fuel injection systems ................... 4-26 Gas turbine engine: Air inlet section ........................................ 10-8 Brayton cycle ........................................... 10-5b INDEX-5
TM 9-8000
INDEX - CONTINUED Para Gas turbine engine - Continued Combustion chamber .............................. Compressors .......................................... Continuous combustion .......................... Cycle characteristics ............................... Electrical system ..................................... Exhaust ................................................... Fuel system............................................. History..................................................... Introduction ............................................. Lubrication system .................................. Operation ................................................ Otto cycle ............................ .................... Recouperator .......................................... Thermal comparison ............................... Turbines .................................................. Gear drives .................................................... Gear reduction starter ................................... Gears: Bevel.............................................................. External................................................... Helical ..................................................... Herringbone ............................................ Internal .................................................... Mechanical advantage ............................ Mechanical efficiency.............................. Spur ........................................................ Steering................................................... Torque ratio............................................. Worm ...................................................... Gearshift linkage: Mechanical.............................................. General transport vehicles ...................... Generators: Alternating current................................... Cooling.................................................... Direct current .......................................... Field winding ........................................... Generator speed ..................................... Main and auxiliary system....................... Multiple loop............................................ Paralleling ............................................... Regulation............................................... Reverse-series field ................................ Shunt wound ........................................... Simple single loop................................... Split-series field....................................... Third-brush, control................................. Third-brush regulation............................. Para
10-10 10-9 10-6 10-4 10-20 10-13 10-14 10-1 10-2 10-17 10-3 10-5a 10-11 10-7 10-12 29-9 14-4b 19-4d 19-3e 19-4b 19-4c 19-3e 19-3b 19-3d 19-4a 33-3 19-3a 19-4e 22-9 1-19a 13-20, 13-26 13-25 13-7 13-7 13-4 13-19 13-3 13-18 13-11 13-12 13-8 13-2 13-17 13-16 13-15
Generator lockout relay.................................. Generator speed ............................................ Glare elimination ............................................ Governors, diesel engines: Actuation.................................................. Mechanical (centrifugal) .......................... Vacuum ................................................... Governors, gasoline engines: Centrifugal ............................................... Centrifugal-vacuum ................................. Velocity-vacuum ...................................... Grade ability ................................................... Ground contact............................................... Headlamp control system .............................. Headlights ...................................................... Heater ............................................................ Height control valve........................................ Hill holder, brake ............................................ History of military vehicles: Post-World War II .................................... Pre-World War 11 ................................... Horizontal opposed engine ............................ Horns: Air ............................................................ Backup alarm........................................... Controls ................................................... Dual ......................................................... Operation................................................. Horsepower: Dynamometer .......................................... Gross and net .......................................... Indicated .................................................. Hulls: Amphibious trucks ................................... Armored tanks ......................................... Tracked vehicles...................................... Unarmored and self-propelled guns......................................................... Hydraulic brake system: Brake fluid................................................ Brake lines............................................... Hill holder................................................. Limiting valve........................................... Master cylinder ........................................ Operation................................................. Principles ................................................. Proportioning valve.................................. Wheel cylinder ......................................... INDEX-6
14-7 13-4 16-6 5-25 5-26 5-27 4-33 4-35 4-34 29-15b 1-20 16-7 16-4 17-19 30-14c 34-27 1-12 1-11 2-19c 17-12 17-13 17-11 17-10 17-9 2-32 2-35 2-36 35-7 35-5 35-8 35-6 34-29 34-28 34-27 34-31 34-25 34-24 34-23 34-30 34-26
TM 9-8000
INDEX - CONTINUED
Para Hydraulic jack, simple: Construction............................................ Mechanical advantage ............................ Operation ................................................ Hydraulic power booster................................ Hydraulic principles: Liquid versus gas .................................... Mechanical advantage ............................ Pascals law ............................................ Hydraulic system, automatic transmission: Converter feed circuit.............................. Hydraulic pump ....................................... Modulation .............................................. Oil sump and filter ................................... Purpose................................................... Range control system ............................. Regulator valve ....................................... Supply system......................................... Ignition: Battery..................................................... Timing ..................................................... Ignition system, gas turbine engine ..................................................... Ignition systems, magneto: Booster coil ............................................. Distributor................................................ Electrical energy...................................... General ................................................... Interrupting device .................................. Switches.................................................. Transforming device ............................... Ignition systems, waterproofing..................... Ignition timing devices ................................... I-head engine................................................. Independent axle suspension system: Driven...................................................... Freewheeling .......................................... Infrared lighting: Active system.......................................... Injection systems, diesel: Passive system ....................................... Distributor type........................................ Ether ....................................................... Fuel ......................................................... Multiple unit............................................. Pressure-timed ....................................... PSB distributor ........................................ Injection systems, diesel - Continued Unit .......................................................... Wobble plate pump ................................. In-line engines................................................ Instrument lights............................................. Instruments: Ammeter .................................................. Fuel gage................................................. Indicator lamp .......................................... Panel........................................................ Pressure gage ......................................... Speedometer ........................................... Tachometer ............................................. Temperature gage ................................... Voltmeter ................................................. Insulators........................................................ Intake: Manifold ................................................... Port .......................................................... Stroke ...................................................... Valve........................................................ Intake manifold flame heater system......................................................... Interference, radio .......................................... Internal combustion engine ............................ Interrupting device.......................................... Interwheel differential ..................................... Jacobs engine brake ...................................... Key and pushbutton switch control circuit........................................................... Kingpin and plate ........................................... Kingpin inclination .......................................... Knocking, diesel engine ................................. Lamps ............................................................ Landing gear .................................................. Leaf springs.................................................... L-head engines .............................................. Light beams.................................................... Lighting system: Backup..................................................... Beams ..................................................... Blackout................................................... Commercial vehicle ................................. Glare elimination...................................... Headlamp control .................................... INDEX-7
Para
5-17 5-15 2-19a 16-16a 17-2a 17-3 17-2c 17-1 17-4 17-6 17-6 17-5 17-2b 11-4c 4-5 2-3 2-5 2-3 5-32 18-2 2-11a 15-12 29-10j 5-40
15-3 2-25 10-21 15-14 15-13 15-10 15-9 15-12 15-15 15-11 15-16 15-8 2-18a 30-7 30-6 16-12a 16-12b 5-16 5-33 5-13 5-14 5-18 5-19
14-5 38-2 33-20 5-5 16-2 38-4, 38-8 30-2a 2-18a 16-3 16-14 16-3 16-9 16-13 16-6 16-7
TM 9-8000
INDEX - CONTINUED Para Lighting system - Continued Headlights ............................................... Infrared.................................................... Lamps ..................................................... Overload breakers .................................. Road illumination .................................... Lights: Backup .................................................... Blackout .................................................. Dome ...................................................... Head ....................................................... Infrared.................................................... Instrument ............................................... Parking........................ ............................ Stop......................................................... Turn signal .............................................. Lines, brake ................................................... Lining, brake .................................................. Live axles: Front wheel ............................................. Independent suspension......................... Rear, dual ratio ....................................... Rear, double reduction............................ Rear, double reduction, dual ratio...................................................... Rear, full floating ..................................... Rear, plain............................................... Rear, semifloating.................... ............... Rear, three-quarter floating..................... Liquefied petroleum gas ................................ Liquid cooling systems: Coolants............................ ...................... Engine water jacket............... .................. Expansion tank ....................................... Fan and shrouding .................................. Radiator .................................................. Radiator pressure cap............................. Thermostat.............................................. Water pump ............................................ Lubrication system: API rating system.................................... Bearing.................................................... Components............................................ Crankshaft .............................................. Detergent oils.......................................... Engine oils .............................................. Force-feed system ............... ................... Full force-feed system ............................ Multiweight oils........................................ Para
16-4 16-12 16-2 16-8 16-5 16-14 16-9 16-16b 16-4 16-12 16-16a 16-16c 16-15 16-13 34-28 34-7b 29-10I 29-10f 29-10h 29-10g 29-10i 29-10e 29-10b 29-10c 29-10d 6-1 9-5 9-4 9-11 9-8 9-6 9-10 9-9 9-7 8-5 19-9 10-19 3-9e 8-8 8-4 8-19 8-20 8-7
Lubrication system - Continued Oil as a lubricant...................................... Oil coolers................................................ Oil filters................................................... Oil level indicator ..................................... Oil pumps ................................................ Oil strainer ............................................... Pressure regulator ................................... Splash and force-feed system ................. Splash system ......................................... Viscosity................................................... Lunette ........................................................... Muffler ............................................................ Magnetic field ................................................. Magneto ignition systems: Booster coil.............................................. Distributor ................................................ Electrical energy ...................................... Switches .................................................. Main generator ............................................... Main generator system................................... Maintenance-free battery ............................... Manifold: Exhaust.................................................... Intake....................................................... Manifold heat control valve ............................ Master cylinder............................................... Matching towing vehicle to trailer: Brake system........................................... Electrical system...................................... Load and performance ............................ Matter, composition........................................ Mechanical brake system: Hookup .................................................... Means of actuation .................................. Mechanical (centrifugal) governors .................................................... Military vehicles, features ....................................................... Motors: Automotive starting.................................. Direct current ........................................... Multifuel engines: Authorized fuels....................................... Fuel density compensator ....................... Multiple-loop generator .................................. INDEX-8
8-2, 10-18 8-14 8-13 8-15 8-9 8-12 8-16 8-18 8-17 8-6 38-7 7-4 11-13 15-14 15-13 15-10 15-15 13-19 13-19 12-8 7-2 4-5 7-3 34-25 38-13 38-12 38-14 11-1 34-22 34-21 5-26 1-14 14-3 14-2 5-6 5-7 13-3
TM 9-8000
INDEX - CONTINUED Para Needle bearing .............................................. No-spin differential ........................................ 19-8d 29-4 Pascals law.................................................... Pedal shift ...................................................... Performance factors....................................... Petroleum gas, liquefied................................. Piston: Booster .................................................... Pins.......................................................... Rings ....................................................... Piston engine operation ................................. Piston rings: Compression ........................................... Oil control ................................................ Pistons ........................................................... Planetary ........................................................ Six basic laws .......................................... Plate and kingpin............................................ Power: Horsepower ............................................. Power braking system.................................... Power divider ................................................. Power steering, hydraulic: Components ............................................ Configurations ......................................... Operation................................................. Purpose ................................................... Power stroke .................................................. Power takeoff: Auxiliary ................................................... Construction ............................................ Purpose ................................................... Transfer case .......................................... Transmission ........................................... Usage ...................................................... Power trains: Bearings .................................................. Gears, principles...................................... Gears, types ............................................ Purpose ................................................... Track vehicles.......................................... Power trains, wheeled vehicles: Differential ............................................... Drive, front wheel..................................... Final drive ................................................ Propeller shaft ......................................... Slip joints ................................................. Transfer assembly ................................... Universal joints ........................................ Precombustion chamber ................................ INDEX-9 Para 20-2 14-4d 29-15 6-1 34-35 3-7 3-6 2-1 3-6b 3-6b 3-5 19-5 19-6 38-2 2-29 34-32 29-10k 33-10 33-12 33-11 33-9 2-7 36-4 36-2 36-1 36-5 36-3 36-6 19-7, 19-8 19-3 19-4 19-1 19-18 29-1 19-13 29-8 28-1 28-2 27-1 28-3 5-10
Ohms law...................................................... Oil: Coolant.................................................... Coolers.................................................... Detergent ................................................ Engine........................ ............................. Filters ......................... ............................. Level indicator.............. ........................... Lubricant ................................................. Multiweight .............................................. Strainer ................................................... Oil pressure gage .......................................... Oil pressure lockout circuit ............................ Oil pumps: Gear ........................................................ Internal-external gear.............................. Rotary...................................................... Vane........................................................ Oil seals: Synthetic rubber...................................... Wick ........................................................ Operation, engine: Compression stroke ................................ Exhaust stroke ........................................ Intake stroke ........................................... Power stroke ........................................... Otto cycle....................................................... Overdrive: Configurations....................... .................. Control system ........................................ Operation ................................................ Purpose................................................... Unit construction ..................................... Overload breakers: Circuit breaker......................................... Fuse ........................................................ Overrunning clutch ........................................
11-11 8-3 8-14 8-8 8-4 8-13 8-15 8-2 8-7 8-12 17-4 14-8 20-4 20-7 20-5 20-6 19-11a 19-11b 2-6 2-8 2-5 2-7 10-5a 26-6 26-9 26-8 26-5 26-7 16-8a 16-8b 23-7, 14-4c
Panel, instrument .......................................... Parallel circuits .............................................. Paralleling generators.................................... Parking brake ................................................ Parking lights .................................................
TM 9-8000
INDEX - CONTINUED Para Pressure regulator ......................................... Pressure regulator valve................................ Pressure-timed injection system, diesel engine........................................... Pumps, diesel engines: Gear type ................................................ Plunger type.................... ........................ Vane type................................................ Prony brake ................................................... Propane fuel system: Liquefied petroleum gas.......................... Operation ................................................ Propeller shafts: Construction............................................ Purpose................................................... PSB distributor injection system, diesel engine .............................................. Pusher axles.................................................. 8-16 30-14b 5-18 5-23 5-22 5-21 2-31 6-1 6-2 28-1b 28-1a 5-19 30-21 Refrigeration - Continued Cycle........................................................ Evaporator................... ............................ Expansion system ................................... Gases ...................................................... Oil ............................................................ Receiver .................................................. Regulation generator...................................... Regulator: Carbon-pile .............................................. Solid-state voltage ................................... Third-brush .............................................. Transistorized point ................................. Vibrating point.......................................... Resistance ..................................................... Resistor, ballast.............................................. Retarder system: Brake ....................................................... Compression brake ................................. Hydraulic.................................................. Jacobs engine brake ............................... Purpose ................................................... Reverse-series field generator ....................... Road illumination............................................ Rods, connecting ........................................... Roller bearings ............................................... Sealed beam .................................................. Sealed bearing ............................................... Self-energizing brakes ................................... Semiconductor devices .................................. Semitrailers: Converted to full ............................................. Description............................................... Fifth wheel ............................................... Kingpin and plate..................................... Landing gear............................................ Series circuits................................................. Series-parallel circuits .................................... Shifting, automatic transmission .................... Shock absorbers: Air ............................................................ Direct acting............................................. Double acting........................................... Purpose ................................................... Single acting ............................................ Single acting, cam operated .................... Vane type................................................. INDEX-10 Para
37-3 37-6 37-5 37-2 37-9 37-4 13-11 13-14 13-29 13-16 13-28 13-13, 13-27 11-10 15-3g 34-4 5-38 5-39 5-40 5-37 13-12 16-5 3-8 19-8b 16-4b 19-10 34-16 11-5 38-9b 1-19e, 38-1 38-3 38-2 38-4 11-12c 11-12e 23-3 30-15 30-18c 30-17b 30-16 30-17a 30-18a 30-18b
Radial engine................................................. 2-19d Radiator pressure cap ................................... 9-10 Radiators ....................................................... 9-6 Radio, automotive: Installation............................................... 18-1a Interference............................................. 18-1c Power requirements................................ 18-1b Suppression of interference .................... 18-5 Radio Interference: Body noises............................................. 18-4 Generator noises .................................... 18-3 Ignition noises ......................................... 18-2 Rated speed .................................................. 2-34 Ratio, air-fuel ....................... .......................... 4-12 Ratio, compression ......................................2-24 Rear axles: Rear, dual ratio ....................................... 29-10h Rear, double reduction............................ 29-10g Rear, double reduction, dual ratio...................................................... 29-10i Rear, full floating ..................................... 29-10e Rear, plain............................................... 29-10b Rear, semifloating ................................... 29-10c Rear, three-quarter floating..................... 29-10d Rear-wheel drive ........................................... 19-14 Recirculating system exhaust gas................. 7-10 Recouperator................................................. 10-11 Refrigeration: Ambient temperature .............................. 37-1 Compressor ............................................ 37-7 Condensor .............................................. 37-8
TM 9-8000
INDEX - CONTINUED
Para Shoes, brake ................................................. Shunt-wound generator................................. Simple single-loop generator......................... Simpson drive train........................................ Six-wheel drive .............................................. Sleeve-type bearing....................................... Sliding gear transmission: Construction............................................ Gears ...................................................... Power flow .............................................. Shifting .................................................... Shift rails and forks ................................. Shafts and bearings ................................ Sliding surface bearing.................................. Slip joints ....................................................... Solenoid shift ................................................. Solid-state ignition ......................................... Solid-state voltage regulator.......................... Spark plugs ................................................... Special equipment vehicles........................... Special purpose vehicles............................... Speedometer ................................................. Spherical chamber ........................................ Splash and force-feed lubrication system........................................................ Splash lubricating system.............................. Split-series-field generator ............................ Spring, coil..................................................... Starter motor drives....................................... Starting aids, cold weather ............................ Starting motor ................................................ Starting system.............................................. Step voltage control....................................... Steering gears: Cam and lever......................................... Rack and pinion ...................................... Worm and nut ......................................... Worm and roller ...................................... Worm and sector .................................... Steering systems: Ackerman................................................ Air............................................................ Fifth wheel...................... ......................... Four wheel .............................................. Geometry....................................................... Hydraulic........................................................ Independent suspension linkage................... 34-7a 13-8 13-2 23-10 19-16 19-7a 22-5 22-5a 22-7 22-6 22-5c 22-5b 19-7 28-2 14-4e 15-6 13-29 15-3f 1-19b 1-19c 17-6 5-12 8-18 8-17 13-17 30-2b 14-4 5-31 14-3 10-22, 14-1 13-16b 33-6 33-8 33-7 33-5 33-4 33-1a 33-13 33-1b 33-16 33-17 24-7 33-3 Steering systems - Continued Power....................................................... Solid axle steering linkage....................... Steering gears ......................................... Toe-out .................................................... Steering through cross-drive transmission................................................ Stoplight system............................................. Storage batteries............................................ Subtransmission: Automatic................................................. Manual..................................................... Purpose ................................................... Superchargers................................................ Suppression, radio: Applications ............................................. Bonding.................................................... Capacitors ............................................... Filters....................................................... Resistor-suppressors .............................. Shielding.................................................. Suspension systems, tracked vehicles: Horizontal valve spring suspension .............................................. Hydraulic lockout system......................... Hydromechanical lockout system ............ Idler wheels and rollers............................ Road wheels............................................ Shock absorbers...................................... Spade system.......................................... Springs .................................................... Suspension lockout system ..................... Suspension snubbers .............................. Torsion bar suspension ........................... Suspension systems, wheeled vehicles: Air-over-hydraulic..................................... Axles........................................................ Bogie axles .............................................. Heavy vehicle .......................................... Independent axle ..................................... Live axle................................................... MacPherson ............................................ Purpose ................................................... Solid axle ................................................. Spring configurations............................... Swaybars........................................................ Switch, headlamp control ............................... Synthetic rubber oil seal................................. INDEX-11
Para
33-9 33-2 33-4 33-17 24-6 16-15 12-9 26-4b 26-4a 26-3 4-31 18-6 18-5d 18-5b 18-5c 18-5a 18-5e
31-5 31-9 31-10 31-3 31-2 31-7 31-11 31-1 31-8 31-6 31-4 30-13 30-11 30-12 30-10 30-5 30-4 30-8 30-1 30-3 30-2 30-20 16-7a 19-11a
TM 9-8000
INDEX - CONTINUED Para Torque converters: Cross-drive transmission ......................... Lockup ..................................................... Operation................................................. Principles ................................................. Torque-horsepower-speed (RPM) relationship.................................................. Torque ratio gear............................................ Torsion bars: Automotive............................................... Tracked vehicles...................................... Tracking ......................................................... Tracks: Characteristics......................................... Pad types................................................. Pin connected.......................................... Sectional band......................................... Shoe types............................................... Tractive factor ................................................ Trailers: Full ........................................................... Landing gear............................................ Semi ........................................................ Tank......................................................... Three-quarter........................................... Trailer matching to towing vehicle .................................................. Transfer assemblies: Conventional............................................ Differential type........................................ Divided engine torque.............................. Double-sprag unit .................................... High- and low-gear range ........................ Positive traction ....................................... Single-sprag unit...................................... Sprag unit ................................................ Typical operation ..................................... Transforming device ...................................... Transistorized point ignition ........................... Transistorized point regulator......................... Transistors ..................................................... Transmissions: Automatic................................................. Auxiliary ................................................... Constant mesh ........................................ Cross-drive .............................................. Sliding gear.............................................. Subtransmlssions .................................... X1100 series cross-drive ......................... INDEX-12 Para
Tachograph operation ................................... Tachometer ................................................... Tactical vehicles ............................................ Tandem booster ............................................ Tapered roller bearing ................................... Temperature gage......................................... T-head engine ............................................... Thermostat .................................................... Third-brush generator, control....................... Third-brush regulation ................................... Three-quarter trailers: Description .............................................. Drawbar .................................................. Landing gear ........................................... Lunette .................................................... Throttle body injection ................................... Timing: Belt.......................................................... Ignition .................................................... Valve ....................................................... Timing device ................................................ Timed fuel injection systems: Electronic ................................................ Mechanical.............................................. Tire inflation system: Construction............................................ Purpose................................................... Tires: Assembly ................................................ Bus.......................................................... Combat ................................................... Earthmover ............................................. Grader..................................................... Identification............................................ Ozone-resistant rubber ........................... Passenger............................................... Rock-service ........................................... Runflat..................................................... Tactical.................................................... Treads..................................................... Truck ....................................................... Tube flaps ............................................... Tubes, types ........................................... Valves ..................................................... Toe-in ............................................................ Toe-out .......................................................... Torque ........................................................... Torque arms ..................................................
17-7 17-6 1-16 34-33 19-8c 17-5 2-18a 9-9 13-16 13-15 38-5 38-6 38-8 38-7 4-28 3-13e 2-25 2-26 5-28 4-26c 4-26b 36-12 36-11 32-10 32-11c 32-11b 32-11f 32-11g 32-18 32-13 32-11d 32-11e 32-11h 32-11a 32-12 32-11c 32-15 32-14 32-16 33-21 33-17 2-30 30-19
24-4 21-9 21-8 21-7 2-33 19-3a 30-2c 31-1b 33-22 32-19 32-23 32-21 32-20 32-22 29-15a 38-9 38-4 38-1 36-15 38-5 38-12 27-3 27-5 27-1 27-10 27-2 27-7 27-9 27-8 27-4 15-11 15-5 13-28 11-8 23-1 26-1 22-8 24-1 22-5 26-3 25-1
TM 9-8000
INDEX - CONTINUED Para Treads, tire: Cross country.......................................... Desert ..................................................... Earthmover ............................................. Mud and snow......................................... Regular ................................................... Rock service ........................................... Traction ................................................... Tubes: Bullet resisting......................................... Combat ................................................... Identification............................................ Standard ................................................. Tube flaps ............................................... Turbines ........................................................ Turbochargers ............................................... Turbulence chamber ..................................... Turn signal system ........................................ Two-stroke cycle engine, diesel .................... Valves - Continued Clamp-in tubeless tire.............................. Core......................................................... Cured-in................................................... Cured-on.................................................. Cured-on large bore ................................ Exhaust.................................................... Guides ..................................................... Height control .......................................... Intake....................................................... Large bore tubeless tire........................... Operating mechanism ............................. Pressure regulator ................................... Quick release........................................... Relay........................................................ Rotators ................................................... Seats ....................................................... Snap-in tubeless tire................................ Springs, retainers, and seals ................... Spud mounted ......................................... Tappet ..................................................... Timing...................................................... Valve timing.................................................... Valve train ...................................................... Vapor lock ...................................................... Vehicle stopping distance .............................. Velocity-vacuum governor.............................. Ventilation control, crankcase ........................ Ventilation system, fuel tank .......................... Venturi effect .................................................. Vibrating point regulator ................................. Viscosity ......................................................... Voltage ........................................................... Voltmeter........................................................ Volumetric efficiency ...................................... V-type engine ................................................. Water Jackets ................................................ Waterproofed generators ............................... Waterproofed ignition systems....................... Water pump ................................................... Wheel alinement: Camber.................................................... Caster ...................................................... Kingpin inclination.................................... Steering geometry ................................... Toe-in ...................................................... Toe-out .................................................... INDEX-13 Para
32-12b 32-12g 32-12e 32-12a 32-12c 32-12d 32-12f 32-14c 32-14b 32-18 32-14a 32-15 10-12 4-30 5-11 16-13 2-14
Underwater ventilating system: Applications............................................. Purpose................................................... Unit injection system, diesel engine......................................................... Universal joints: Ball and trunnion ..................................... Bendix-Weiss .......................................... Constant velocity..................................... Double cross and roller ........................... Journal type............................................. Operation ................................................ Purpose................................................... Rzeppa.................................................... Tracta...................................................... Vacuum gage ................................................ Vacuum governors ........................................ Vacuum lockout switch.................................. Vacuum-over-hydraulic brake system: Construction............................................ Operation ................................................ Vacuum windshield wipers ............................ Valves: Airbrake................................................... Cap ......................................................... Clamp-in double bent..............................
36-25 36-24 5-17 28-5b 28-7b 28-6 28-7d 28-5a 28-4 28-3 28-7a 28-7c 17-8 5-27 14-6
32-16f 32-17a 32-16c 32-16a 32-16b 2-3 3-12d 30-14c 2-3 32-16g 3-14 30-14b 34-39f 34-39h 3-12f 3-12c 32-16e 3-12e 32-16d 3-13h 2-26 2-26 2-9 4-37c 34-3 4-34 7-7 4-4 4-10 13-13, 13-27 8-6 11-9b 17-2b 2-23 2-19b 9-4 13-9 15-6 9-7 33-19 33-18 33-20 33-17 33-21 33-17
TM 9-8000
INDEX - CONTINUED Para Wheel center section: Disk ......................................................... Pressed and cast spoked ....................... Wire ........................................................ Wheel cylinder ............................................... Wheeled vehicles: Drawbar pull............................................ Grade ability............................................ Performance factors ............................... Power trains ............................................ Suspension system................................. Wheel rims: Drop center ............................................. Safety...................................................... Semidrop center...................................... Split ......................................................... Wick seals............................................... Winches: Level wind ............................................... Mounting ................................................. Operation ................................................ Purpose................................................... Windshield wipers: Air operated ............................................ Arm and blade......................................... Electric .................................................... Vacuum................................................... Wiring, automotive: Connectors .............................................. Harnesses ............................................... Harness identification .............................. Terminal ends.......................................... Wobble plate pump, diesel engine................. Wrecker truck equipment: General.................................................... Operation................................................. Para
32-1 32-2 32-3 35-26 29-15c 29-15b 29-15 19-1 30-1 32-4 32-6 32-5 32-7 19-11b 36-10 36-8 36-9 36-7 17-16 17-17 17-15 17-14
X1100 series cross-drive transmission: Control pumps ......................................... Final drive....................................................... Function................................................... General.................................................... Planetary gearing..................................... Servo sleeve............................................ Servo valve.............................................. Steering ................................................... Stroke limiter valve .................................. Supercharge check valves ...................... Torque converter .....................................
25-7b 25-8 25-2 25-1 25-5 25-7c 25-7d 25-6 25-7e 25-7a 25-4
11-7
M 9-8000
Official:
MILDRED E. HEDBERG Brigadier General United States Army The Adjutant General
Distribution: To be distributed in accordance with DA Form 12-37, Operator, Organizational, Direct and General Support Maintenance requirements for Carrier, Personnel, M113A1, Command Post, M577A1, Mortar, M106A1; Mortar, M125A1; Flame Thrower, M132A1; Gun, M741; Recovery Vehicle, XM1059. Also, to be distributed in accordance with DA Form 12-38, Operator, Organizational, Direct and General Support Maintenance requirements for Truck, Utility, 1/4-ton, 4x4, M151-series.
TM 9-8000
TM 9-8000
TM 9-8000
PIN: 010403-001