WOLKITE UNIVERSITY

College of Engineering and Technology

Department of Mechanical Engineering

Project title: Design of Transmisssion system for GMC SIrra 1500

Submitted by:

NAME ID

1. FETIYA WABELLA YEASUFE………………..ENGR/360/09

2. AMAR ADEM ……………………………………ENGR/097/09
3. KALID MUSTAFA………………………………ENGR/491/09

Submitted to Mr. YONATAN .T (Msc)

Summation date may,2021 G.C

 ACKNOWLEDGMENT
First we would like to give an Enormous thanks to the Almighty God who gives us patient,
courage and wisdom to finish this project. We express our sincere gratitude to our teacher MR.
YONATAN for giving us the opportunity to work on this project and for his guidance and
encouragement without which this work could have not been completed. Last but not least, we
would like to thank our friends who were always besides out and played a great role in
completion of our work.

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 Contents
ACKNOWLEDGMENT..............................................................................................................................i
CHAPTER ONE........................................................................................................................................1
1.1 Introduction.......................................................................................................................................1
1.1.1 Types of Transmission................................................................................................................4
1.1.2 Components of Transmission.....................................................................................................4
1.1.3 Classification of Transmission....................................................................................................6
1.1.4 Necessity of gear box in an automobile....................................................................................16
1.1.5. Function of a gear box.............................................................................................................16
1.2 Objective..........................................................................................................................................17
1.2.1 General objective......................................................................................................................17
1.2.2 Specific objective......................................................................................................................17
1.3 Methodology Analytical methodology.............................................................................................17
CHAPTER TWO.....................................................................................................................................18
2.1 Detail design for gear box............................................................................................................18
2.1.1 Specifications for GMC sierra 1500 medium truck..................................................................18
2.1.2 Selected transmission type.......................................................................................................19
2.1.3 Maximum engine power...........................................................................................................20
2.1.4 Transmission ratio ranges.........................................................................................................21
2.1.5 Central distance........................................................................................................................21
2.1.6 Gear parameter selection......................................................................................................21
2.1.7 Gear modulus........................................................................................................................21
2.1.8 Designing for each speed gear..................................................................................................23
2.1.9 The formula of helical gear.......................................................................................................24
2.1.10 The formula of spur gear........................................................................................................25
2.1.11 The size of transmission shaft.................................................................................................25
CHAPTER 3............................................................................................................................................27
3.1 Result and conclusion........................................................................................................................27
REFERENCES........................................................................................................................................29
APPENDIX..............................................................................................................................................30
 LIST OF FIGURES
FIGURE 1 SPUR GEAR...................................................................................................................................6
FIGURE 2 HELICAL GEAR..............................................................................................................................7
FIGURE 3 BEVEL GEAR.................................................................................................................................8
FIGURE 4 MITTER GEAR................................................................................................................................9
FIGURE 5 HYPOID GEAR.............................................................................................................................10
FIGURE 6 STRAIGHT GEAR..........................................................................................................................10
FIGURE 7 SLIDING MESH GEARBOX............................................................................................................14
FIGURE 8 CONSTANT MESH........................................................................................................................15
FIGURE 9 TRANSMISSION............................................................................................................................16
FIGURE 10 FREE HAND SKETCHES FOR GEARBOX.......................................................................................19
FIGURE 11 FREE HAND SKETCH FOR GEAR ARRANGEMENT........................................................................23
FIGURE 12 VON MISES STRESS ANALYSIS...................................................................................................27
FIGURE 13 DISPLACMENT ANALYSIS.........................................................................................................28
FIGURE 14 STRAIN ANALYSIS....................................................................................................................28
FIGURE 15 SPUR GEAR 2D DRAWING..........................................................................................................30
FIGURE 16 MAIN SHAFT 2D........................................................................................................................30
FIGURE 17 L-SPUR GEAR 2D......................................................................................................................31
FIGURE 18 IDLE SHAFT...............................................................................................................................31
FIGURE 19 HUB 2D....................................................................................................................................32
FIGURE 20 DRIVE SHAFT 2D.......................................................................................................................32
FIGURE 21 DOG CLUTCH 2D.......................................................................................................................33
FIGURE 22 EXPLODED SIDE VIEW...............................................................................................................33
FIGURE 23 ASSEMBLED RIGHT VIEW..........................................................................................................34
FIGURE 24 EXPLODED TOP VIEW................................................................................................................34
FIGURE 25 EXPLODED TOP VIEW 2.............................................................................................................35
 List of Table

TABLE 1 RESULT OF TRANSMISSION DESIGNING........................................................................................26

 CHAPTER ONE
1.1 Introduction
A transmission is a machine in a power transmission system, which provides controlled
application of power. Often the term 5-speed transmission refers simply to the gearbox, that
uses gears and gear trains to provide speed and torque conversions from a rotating power source
to another device.

The term transmission properly refers to the whole drive train, including clutch, gearbox, prop

shaft (for rear-wheel drive vehicles), differential, and final drive shafts. The most common use is
in motor vehicles, where the transmission adapts the output of the internal combustion engine to
the drive wheels. Such engines need to operate at a relatively high rotational speed, which is
inappropriate for starting, stopping, and slower travel. The transmission reduces the higher
engine speed to the slower wheel speed, increasing torque in the process. Transmissions are also
used on pedal bicycles, fixed machines, and where different rotational speeds and torques are
adapted.

Often, a transmission has multiple gear ratios (or simply "gears") with the ability to switch
between them as the speed varies. This switching may be done manually (by the operator) or
automatically (by a control unit). Directional (forward and reverse) control may also be
provided. Single-ratio transmissions also exist, which simply change the speed and torque (and
sometimes direction) of motor output. [1]

Modern automated manual transmissions (AMT) have their roots and origins in older clutch less
manual transmissions that began to appear on mass-production automobiles in the early-1930s
and 1940s, prior to the introduction of hydraulic automatic transmissions. These systems were
designed to reduce the amount of clutch or gear shifter usage required by the driver. These
devices were intended to reduce the difficulty of operating conventional unsynchronized manual
transmissions ("crash gearboxes") that were commonly used at the time, especially in stop-start
driving. An early example of this transmission was introduced with the Hudson Commodore in
1942, called Drive-Master. This unit was an early semi-automatic transmission, based on the
design of a conventional manual transmission, which used a servo-controlled vacuum-operated
clutch system, with three different gear shifting modes, at the touch of a button; manual shifting

1
and manual clutch operation (fully-manual), manual shifting with automated clutch operation
(semi-automatic), and automatic shifting with automatic clutch operation (fully-automatic).
Another early example of this transmission system was introduced in the 1955 Citroën DS,
which used a 4-speed BVH transmission. This semi-automatic transmission used an automated
clutch, which was actuated using hydraulics. Gear selection also used hydraulics; however, the
gear ratio needs to be manually selected by the driver. This system was nicknamed Citro-
Matic in the U.S. [2]

In motor vehicles, the transmission generally is connected to the engine crankshaft via a flywheel

or clutch or fluid coupling, partly because internal combustion engines cannot run below a
particular speed. The output of the transmission is transmitted via the driveshaft to one or
more differentials, which drive the wheels. While a differential may also provide gear reduction,
its primary purpose is to permit the wheels at either end of an axle to rotate at different speeds
(essential to avoid wheel slippage on turns) as it changes the direction of rotation. Conventional
gear/belt transmissions are not the only mechanism for speed/torque adaptation. Alternative
mechanisms include torque converters and power transformation (e.g. diesel-electric
transmission and hydraulic drive system). Hybrid configurations also exist. Automatic
transmissions use a valve body to shift gears using fluid pressures in response to engine RPM,
speed, and throttle input.[1]

The function of any transmission is transferring engine power to the driveshaft and rear wheels
(or axle half shafts and front wheels in a front-wheel-drive vehicle). Gears inside the
transmission change the vehicle's drive-wheel speed and torque in relation to engine speed and
torque. Lower (numerically higher) gear ratios serve as torque multipliers and help the engine to
develop enough power to accelerate from a standstill.

Initially, power and torque from the engine comes into the front of the transmission and rotates
the main drive gear (or input shaft), which meshes with the cluster or counter shaft gear -- a
series of gears forged into one piece that resembles a cluster of gears. The cluster-gear assembly
rotates any time the clutch is engaged to a running engine, whether or not the transmission is in
gear or in neutral.

2
All modern transmissions are of the constant-mesh type, which still uses a similar gear
arrangement as the sliding-gear type. However, all the main shaft gears are in constant mesh with
the cluster gears. This is possible because the gears on the main shaft are not splined to the shaft,
but are free to rotate on it. With a constant-mesh gearbox, the main drive gear, cluster gear and
all the main shaft gears are always turning, even when the transmission is in neutral.

Alongside each gear on the main shaft is a dog clutch, with a hub that's positively splined to the
shaft and an outer ring that can slide over against each gear. Both the main shaft gear and the
ring of the dog clutch have a row of teeth. Moving the shift linkage moves the dog clutch against
the adjacent main shaft gear, causing the teeth to interlock and solidly lock the gear to the main
shaft. [3]

Specifically, in order to ensure good transmission performance, it should meet the following
requirements.

1) Choose the correct gear shift number and transmission gear ratios, and make the optimal
matching of engine parameters to ensure that the car has good power and economy.

2) Set neutral to ensure the car engine and the transmission can separate for a long time.

3) Set reverses, so that the car can travel backwards.

4) Set the power output apparatus.

5) Shift quickly, labor-saving, easily.

6) Reliable. During driving, the transmission cannot out-of-mesh, random mesh.

7) Transmission should have a high efficiency.

8) Transmission should be simple, smooth, no noise.

3
There are 6 ways to improve automatic transmission performance and reliability. These are
servicing the transmission, changing driving habits, driving with lower gears when loaded,
maintaining engine performance, having proper alignment of tires, and having the correct tire
size. [4]

1.1.1 Types of Transmission

Automatic Transmission (AT)

This is a transmission that uses a torque converter, planetary gear set and clutches or bands to shift
through a vehicle's forward gears automatically. Some automatics allow the driver a limited amount of
manual control over the vehicle (aside from choosing a forward, reverse or neutral mode) -- for example
allowing the driver to control up shifts and downshifts by utilizing buttons or paddles on the steering
wheel or the gear selector. Common names for such transmissions are "shiftable automatic," "Tiptronic"
and "autostick."

Manual Transmission (MT)

With a manual transmission, the driver selects all gears manually using both a movable gear selector and
a driver-operated clutch. This type of transmission is also known as a "stick shift" or a "standard"
transmission.

Automated Manual Transmission (AM)

Like a manual transmission, an automated manual also employs a mechanical clutch; however, the action
of the clutch is not controlled by the driver via the clutch pedal but rather is automated using electronic,
pneumatic or hydraulic controls. Sometimes referred to as a "Direct Shift Gearbox" ("DSG") or a
"Sequential Manual Gearbox" ("SMG"), this transmission allows for either fully automatic forward gear
shifts or manual shifts through the gear selector or through buttons or paddles on the steering wheel.

Continuously Variable Transmission (CVT)

This transmission has a continuously variable drive ratio (as opposed to conventionally stepped gear
ratios) and uses belts, pulleys and sensors rather than gears to maintain a steady acceleration curve with
no pauses for gear changes. [5]

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1.1.2 Components of Transmission
The transmission system consists of the following components:

1. Countershaft:

A countershaft is a shaft that connects with the clutch shaft directly. It contains the gear which connects it
to the clutch shaft as well as the main shaft. It may be run at the engine speed or at lower than engine
speed according to gear ratio.

2. Main shaft:

It is the shaft that runs at the vehicle speed. It carries power from the countershaft by use of gears
and according to the gear ratio, it runs at a different speed and torque compares to the
countershaft. One end of this shaft is connected with the universal shaft.

3. Gears:

Gears are used to transmit the power from one shaft to another. They are the most useful
component of the gearbox because the variation is the torque of the countershaft and the main
shaft is depends on the gear ratio. The gear ratio is the ratio of the driven gear teeth to the driving
gear teeth. If the gear ratio is large than one, the main shaft revolves at a lower speed than the
countershaft and the torque of the main shaft is higher than the countershaft. On the other hand,
if the gear ratio is less than one, than the main shaft revolves at a higher speed than the
countershaft and the torque of the main shaft is lower than the countershaft. A small car gearbox
contains a four-speed gear ratio and one reverse gear

4. Bearings:

Whenever the rotary motion encounters, bearings are required to support the revolving part and
reduce the friction. In the gearbox, both the counter and main shaft are supported by the bearing.
[6]

5
1.1.3 Classification of Transmission

 Based on gear

1- Spur Gears

Spur gears are used to transmit power between two parallel shafts. The teeth on these gears are
cut straight and are parallel to the shafts to which they are attached. [8]

Figure 1 spur gear

Characteristics:

•Simplest and most economical type of gear to manufacture.

•Speed ratios of up to 8 (in extreme cases up to 20) for one step (single reduction) design; up to
45 for two step design; and up to 200 for three-step design.

Limitations:

•Not suitable when a direction change between the two shafts is required.

•Produce noise because the contact occurs over the full face width of the mating teeth
instantaneously.

6
2- Helical Gears

Helical gears resemble spur gears, but the teeth are cut at an angle rather than parallel to the shaft
axis like on spur gears. The angle that the helical gear tooth is on is referred to as the helix angle.
The angle of helix depends upon the condition of the shaft design and relative position of the
shafts. To ensure that the gears run smoothly, the helix angle should be such that one end of the
gear tooth remains in contact until the opposite end of the following gear tooth has found a
contact. For parallel shafts, the helix angle should not exceed 20 degrees to avoid excessive end
thrust.[8]

Figure 2 helical gear

Characteristics:

The longer teeth cause helical gears to have the following differences from spur gears of the
same size:

•Tooth strength is greater because the teeth are longer than the teeth of spur gear of equivalent
pitch diameter.

•Can carry higher loads than can spur gears because of greater surface contact on the teeth.

•Can be used to connect parallel shafts as well as non-parallel, non-intersecting shafts.

•Quieter even at higher speed and are durable.

7
Limitations:

•Gears in mesh produce thrust forces in the axial directions.

• Expensive compared to spur gears.

3-Bevel Gears

A bevel gear is shaped like a section of a cone and primarily used to transfer power between
intersecting shafts at right angles. The teeth of a bevel gear may be straight or spiral. Straight
gear is preferred for peripheral speeds up to 1000 feet per minute; above that they tend to be
noisy.

Figure 3 bevel gear

Characteristics:

•Designed for the efficient transmission of power and motion between intersecting shafts. A
good example of bevel gears is seen as the main mechanism for a hand drill. As the handle of the
drill is turned in a vertical direction, the bevel gears change the rotation of the chuck to a
horizontal rotation.

•Permit a minor adjustment during assembly and allow for some displacement due to deflection
under operating loads without concentrating the load on the end of the tooth.

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4- Mitter Gears

Mitter gears are identical to bevel gears with the exception that both gears always have the same
number of teeth.

Figure 4 mitter gear

Characteristics:

•They provide a steady ratio; other characteristics are similar to bevel gears.

•They are used as important parts of conveyors, elevators and kilns.

Limitations

•Gear ration is always 1 to 1 and therefore not used when an application calls for a change of
speed.

5-Hypoid Gears

Hypoid gears are a modification of the spiral bevel gear with the axis offset. The distinguishing
feature of hypoid gears is that the shafts of the pinion and ring gear may continue past each
other, never having their axis intersecting.

9
 Figure 5 Hypoid gear

The major advantages of the hypoid gear design are that the pinion diameter is increased, and it
is stronger than a corresponding bevel gear pinion. The increased diameter size of the pinion
permits the use of comparatively high gear ratios and is extremely useful for non-intersecting
shaft requirements such as automotive applications where the offset permits lowering of the
drive shaft.

6- Racks (Straight Gears)

The rack is a bar with a profile of the gear of infinite diameter, and when used with a meshing
pinion, enables the rotary to linear movement or vice versa.

Figure 6 straight gear

Characteristics:

•Racks with machined ends can be joined together to make any desired length.

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•The most well-known application of a rack is the rack and pinion steering system used on many
cars in the past. The steering wheel of a car rotates the gear that engages the rack. The rack slides
right or left, when the gear turns, depending on the way we turn the wheel. Windshield wipers in
cars are powered by a rack and pinion mechanism.

7-Herringbone (double helical) gears

Herringbone, also known as double helical gears, is used for transmitting power between two
parallel shafts. Double helical gearing offers low noise and vibration along with zero net axial
thrust. [8]

Characteristics:

•Conduct power and motion between non-intersecting, parallel axis that may or may not have
center groove with each group making two opposite helices. Action is equal in force and friction
on both gears and all bearings, and free from any axial force.

•Offer reduced pulsation due to which they are highly used for specialized extrusion and
polymerization. The most common application is in heavy machinery and power transmission.

•Applications include high capacity reduction drives like that of cement mills and crushers.

Limitations:

•Manufacturing difficulty makes them costlier.

•Noise level of double helical gears averaged about 4dB higher than otherwise similar single
helical gears. The phenomenon is due to the axial shuttling which occurs as the double helical
pinion moves to balance out the net thrust loading.

 Based on position of shaft axes:

Gears may be classified according to the relative position of the axes of revolution. The axes
may be:

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1. Parallel shafts where the angle between driving and driven shaft is 0 degree. Examples
include spur gears, single and double helical gears.

2. Intersecting shafts where there is some angle between driving and driven shaft. Examples
include bevel and miter gear.

3. Non-intersecting and non-parallel shafts where the shafts are not coplanar. Examples
include the hypoid and worm gear.

 Based on peripheral velocity:

Gears can be classified as:

1. Low velocity type, if their peripheral velocity lies in the range of 1 to 3 m/sec.

2. Medium velocity type, if their peripheral velocity lies in the range of 3 to 15 m/sec.

3. High velocity type, if their peripheral velocity exceeds 15 m/sec.

 Based on teeth position:

Gears are classified as straight, inclined and curved.

1. Straight gear teeth are those where the teeth axis is parallel to the shaft axis.

2. Inclined gear teeth are those where the teeth axis is at some angle.

3. Curve gear teeth are curved on the rim’s surface.

 Based on Arrangement of gears

1- Progressive type gear box

Usually these gearboxes are used in motor cycles. In these gearboxes the gears pass through the
intervening speeds while shifting from one speed to another. There is a neutral position between
two positions. These gearboxes are a combination of sliding and constant mesh gear boxes. The
various gearspeeds are obtained by sliding the dog clutch or gear to the required position. [9]

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2- Epicyclic (or) planetary type gear box

The epicylic or planetary type transmission uses no sliding dog’s or gears to engage but different
gear speeds are obtained by merely tightening brake-bands on the gear drums, which simplify
gear changing. A planetary gear set consists of ring gear or annular wheel, sun gear and planet
gears with carrier. In order to obtain different speeds any one of these three units can be held
from rotation by means of brake bands.[9]

3- Selective type gear box

It is the transmission in which any speed may be selected from the neutral position. In this type
of transmission neutral position has to be obtained before selecting any forward or reverse gear.
Some selective type gearboxes are,

 Constant mesh gearbox with positive dog clutch.

 Constant mesh gearbox with synchromesh device.

 Sliding mesh gearbox.

Sliding mesh gearbox

It is the simplest and oldest type of gearbox.

 The clutch gear is rigidly fixed to the clutch shaft.

 The clutch gear always remains connected to the drive gear of countershaft.

 The other lay shaft gears are also rigidly fixed with it.

 Two gears are mounted on the main shaft and can be sliding by shifter yoke when shifter
is operated.

 One gear is second speed gear and the other is the first and reverse speed gears. All gears
used are spur gears.

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  A reverse idler gear is mounted on another shaft and always remains connected to reverse
gear of counter shaft.

Figure 7 sliding mesh gearbox

First gear

By operating gearshift lever, the larger gear on main shaft is made to slide and mesh with first
gear of countershaft. The main shaft turns in the same direction as clutch shaft in the ratio of 3:1.

Second gear

By operating gear shift lever, the smaller gear on the main shaft is made to slide and mesh with
second gear of counter shaft. A gear reduction of approximately 2:1 is obtained.

Top gear

By operating gearshift lever, the combined second speed gear and top speed gear is force d
axially against clutch shaft gear. External teeth on clutch gear mesh with internal teeth on top
gear and the gear ratio is 1:1.

Reverse gear

By operating gearshift lever, the larger gear of main shaft is meshed with reverse idler gear. The
reverse idler gear is always on the mesh with counter shaft reverse gear. Interposing the idler

14
gear, between reverse and main shaft gear, the main shaft turns in a direction opposite to clutch
shaft.

Neutral gear

When engine is running and the clutch is engaged, clutch shaft gear drives the drive gear of the
lay shaft and thus lay shaft also rotates. But the main shaft remains stationary as no gears in main
shaft are engaged with lay shaft gears.

 Constant Mesh Gearbox

Figure 8 constant mesh

In this type of gearbox, all the gears of the main shaft are in constant mesh with corresponding
gears of the countershaft. The gears on the main shaft which are bushed are free to rotate. The
dog clutches are provided on main shaft. The gears on the lay shaft are, however, fixed. When
the left Dog clutch is slid to the left by means of the selector mechanism, its teeth are engaged
with those on the clutch gear and we get the direct gear. The same dog clutch, however, when
slid to right makes contact with the second gear and second gear is obtained. Similarly
movement of the right dog clutch to the left results in low gear and towards right in reverse gear.
Usually the helical gears are used inconstant mesh gearbox for smooth and noiseless operation.
[9]

 Synchromesh Gearbox

15
This type of gearbox is similar to the constant mesh type gearbox. Instead of using dog clutches
here synchronizers are used. The modern carsuse helical gears and synchromesh devices in
gearboxes, that synchronize the rotation of gears that are about to be meshed. [9]

 Synchronizers

This type of gearbox is similar to the constant mesh type in that all the gears on the main shaft
are in constant mesh with the corresponding gear son the lay shaft. The gears on the lay shaft are
fixed to it while those on the main shaft are free to rotate on the same. Its working is also similar
to the constant mesh type, but in the former there is one definite improvement over the latter.
This is the provision of synchromesh device which avoids the necessity of double-declutching.
The parts that ultimately are to be engaged are first brought into frictional contact, which
equalizes their speed, after which these may be engaged smoothly. [9]

1.1.4 Necessity of gear box in an automobile

The gearbox is necessary in the transmission system to maintain engine speed at the most
economical value under all conditions of vehicle movement. An ideal gearbox would provide an
infinite range of gear ratios, so that the engine speed should be kept at or near that, the maximum
power is developed whatever the speed of the vehicle.[9]

1.1.5. Function of a gear box

1. Torque ratio between the engine and wheels to be varied for rapid acceleration and for
climbing gradients.

2. It provides means of reversal of vehicle motion.

3. Transmission can be disconnected from engine by neutral position of gearbox.

16
 Figure 9 transmission

1.2 Objective

1.2.1 General objective

The main aim of this project is to design gearbox for medium size truck of GMC.

1.2.2 Specific objective

The specific objective of this project : -

 To describe about gearbox

 To perform the detail analysis about gearbox for GMC sierra 1500 medium size truck.
 To check analysis by using software like solid work.
 To discuss the result and compare the analysis and simulations

1.3 Methodology Analytical methodology

 Literature survey
Books, journals, previous research works to know: basic concepts of transmission, properties
that have been considered during material selection is viewed
 Analytical methodology
The next thing is the detail design of the system which gives us the overall information about
strength, efficiency, dimension and durability of the product.
 Software modeling
It is used to model the parts and assembly of the machine. In this method Simulation and 3d
model of Gearbox is made using solidwork 2018 edition.

17
 CHAPTER TWO

2.1 Detail design for gear box

2.1.1 Specifications for GMC sierra 1500 medium truck
Transmission description – automatic

Number of transmission speed – 8

First gear ratio – 4.56

Second gear ratio – 2.97

Third gear ratio – 2.08

Fourth gear ratio – 1.69

Fifth gear ratio -1.27

Sixth gear ratio – 1.00

Seventh gear ratio – 0.85

Eighth ear ratio – 0.65

Reverse gear ratio – 3.81

Final drive axel ratio NA

Transfer case model magna

18
Maximum torque @RPM 348@1500

Weight 7000 pound

Maximum speed 90.7 miles per hour or 40.6 m/s

Engine position four wheel drive

Tire type – front 255/70R17

Rear 255/70R17

Vehicle overall length – 231.75inch

Vehicle overall width – 81.24inch

Vehicle overall height – 75.63inch

Drive train efficiency =95%

Automatic driveline efficiency =85%

Rolling friction resistance coefficient =0.02

2.1.2 Selected transmission type

Figure 10 Free hand sketches for gearbox

19
Transmission shaft

 Multi speed transmission shaft

 Fixed shaft type
 Lay shaft transmission
 First gear and reverse gear are spur gears
 Second and eighth gear are helical gears

Synchronizer

 Form of reveres selection with idle gear between lay shaft and output shaft
 Inertia type synchronizer
 Snap ring the transmission and part location
 Gear box shell
 Integral type gear box shell
 Automobile control mechanism

Shaft lever

Fork shaft

Pin type fork shaft

2.1.3 Maximum engine power

Pe max- Maximum engine power

Io-final drive ratio

 Automotive driveline efficiency，

K -stress concentration factor, for spur gear

z - Number of gear teeth

σ- Gear bending stress

20
 1.2∗60
Tmax=
2 πN

1.2∗2 π 1500
471.8 Nmm=
1.2∗60

P=61.727 KW

A=B∗H=3.96 m2

2.1.4 Transmission ratio ranges

ig 1 4.56
=
ig 8 0.65

ig 1 ig 2 ig 3 ig 4 ig 5 ig 6 ig 7
= = = = = =
ig 2 ig 3 ig 4 ig 5 ig 6 ig 7 ig 8

4.56 2.97 2.08 1.69 1.27 1 0.87

= = = = = =
2.97 2.08 1.69 1.27 1 0.87 0.65

1.54 ≥ 1.43≥ 1.23 ≥1.33 ≥ 1.27 ≥1.177 ≥ 1.3

io=4.56 ,ign=0.65 , igR=3.82

so 5 ≤ig 1≤ 6.7 we select as specified for vehicle 4.76( Liu , 1996 , pp .175−176)

Reverse gear ratio igR and reverse transmission ratio smaller than first speed gear transmission
ratio so it selected igr=3.82 according to the experience (Liu, 1996, p. 174)

2.1.5 Central distance

A=Ka √ T 1 max

T 1 max=Tmax∗ig 1∗driveline efficiency =1828.7 Nm

A=220.2mm 2

2.1.6 Gear parameter selection

Transmissions use a helical gear and spur we need to determine the modulus gear pressure angle,
helical angle, tooth width and other parameters.

21
2.1.7 Gear modulus
Spur gear modulus

3
2T 1 KδKf
m= √
πKcZYσw

Helical gear modulus

2 T 1 Kδcosβ
mn=
√
3

πZKcKeYσw

On the basis of the nation standards, helical gear modulus mn=3. Spur gear module
m=4syncronizer gear is involutes tooth profile, medium size truck m=2-3.5, so it selects
m=3(Liu, 1996, p.178)

Pressure angle

The pressure angle is small the contact ratio is big it has smooth transmission and low noise
when the pressure angle is big it can improve the bending strength of the gear contact strength
and the surface contact strength. The china standard stipulates the pressure angle is 20◦. in the
same transmission lower speed gear has large pressure angle and higher speed gear has small
pressure angle, the joint pressure angle between the synchronizer and clutch is 20◦,25◦,30◦ its
generally 20◦.

Helical angle

The selection of helical gear is depending on the meshing performance, influence of the strength
and balance of axial force. When the helical angle value is increase the overlap coefficient of
gear meshing is increasing. The transmission has smooth running and low noise. But if the
helical angle is too big, it can make the axial force too large enough adverse to the bearing work
and reduce the transmission efficiency. Experiments show that when β>30 gear bending strength
fell sharply, and the intensity of the contact is still rising. For medium truck the helical angle
value of the transmission is generally 10-30

22
Tooth width

b=Ke∗Mn

Spur gear width: b1=(4.4-7)*4=17.6-28

Helical gear width: b2=(7-8.6)*3=21-25.8

So based on the data all teeth are selected 25mm.

2.1.8 Designing for each speed gear

Figure 11 Free hand sketch for gear arrangement

1. Determination fifth speed gear constant mesh gear teeth

The whole number of teeth Zh=2A/m. the smaller first speed spur gear teeth are 13 to 17

Z 2 i∗Z 18
= =1.27 … … . ( 1 )
Z1 Z 17

mn ( Z 1+ Z 2 )
A= … … …( 2)
2cosβ

By rearranged the above two equations Z17=44 and Z18=65

2. Determination of the eighth speed gear teeth

Z 2 i∗Z 16
= =1.27 … … . (3 )
Z1 Z 15

23
 mn ( Z 15+Z 16 )
A= … … …(4 )
2 cosβ

By rearranging the above two equations Z15=60 and Z16=44

By using the same method can be calculated

The seventh speed gear teeth Z14=55 and Z13=55

The ninth speed gear teeth Z12=36 and Z11=68

The third speed gear teeth Z10=36 and Z9=68

The first speed gear teeth Z8=34 and Z7=70

The second speed gear teeth Z6=71 and Z5=33

The sixth speed gear teeth Z4=30 and Z3=73

The fourth speed gear teeth Z2=30 and Z1=73

3. Determination for reverse gear

The reverse idler gear teeth Z20=23 and the modulus m=4. When seeking Z21 and Z19 the
center distance must be 100mm

2A
Z=
m

Z 2 iRZ 21
=
Z1 Z 19

So we get the result Z21=44 and Z19=55

The distance between the idler shaft and the output shaft

A 1=0.5∗m ( Z 19+ Z 20 )

2.1.9 The formula of helical gear

Z∗mn
Pitch diameter d=
cosβ

24
Addendum: ha=fo∗mn

Duodenum: hf =( fo +C ) mn

Tooth height: h=( hf +C ) mn

Tip diameter: da=d +2 ha

Root diameter df =d−2 hf

Z-teeth Qty

2.1.10 The formula of spur gear

Pitch diameter: d=Z∗m

Addendum: ha=fo∗m

Duodenum: hf =( fo +C ) mn

Tooth height: h=( 2 fo +C ) mn

Tip diameter: da=d +2 ha

Root diameter: df =d−2 hf

2.1.11 The size of transmission shaft

1. The outer shaft and lay shaft maximum diameter can be based on the center distance
D= ( 0.45−0.6 ) A so we chose the second shaft and the intermediate shaft maximum size
and the other sizes are depend on the gear size.
2. The length of the shaft is depending on the length the gear also needs to consider the
actual installation requirements.

25
 Table 1 Result of transmission designing

Gear Main shaft Lay shaft Main shaft Gear Width of

outer hole diameter gear
diameter diameter for lay
shaft
First 260 100 45 40 25
Second 250 110 50 40 25
Third 240 220 45 40 25
Fourth 100 260 50 40 25
Fifth 110 250 40 60 25
Sixth 250 110 50 40 25
Seventh 143 217 40 60 25
Eighth 160 200 40 60 25
Nine 180 180 40 60 25
Reveres 100 200 40 60 25

26
 CHAPTER 3
3.1 Result and conclusion
This project mainly focused on designing of gearbox for GMC sierra 1500 medium size truck
based on the specification on of vehicle. Parts of gear box like gears, shafts, bearings forks and
synchronizers of parameter is done depending up on the known engine power. The calculated
detail design and simulation result shows the result is precise to the analysis done by solid work
in every part of their parameters and stress simulation. The applied load is 15KN. In the detail
design there are different calculation made for different parts. To check whether the design is
safe or not simulation is performed using solid work 2018. Below there are different figures
which shows von mises ,strain and displacement analysis is made for the main shaft The
maximum stress developed is less than that of the material young’s modulus so the design is
safe.

Figure 12 Von mises stress analysis

27
Figure 13 Displacment Analysis

Figure 14 Strain Analysis

28
 REFERENCES
[1]-https://en.wikipedia.org/wiki/Transmission_(mechanics)(accessed on 25 may at 4:03 PM)

[2]- https://en.wikipedia.org/wiki/Automatic_transmission(accessed on 25 may at 4:10 PM)

[3]- https://www.edmunds.com/car-technology/manual-transmission-basics.html(accessed on 25
may at 4:11 PM)

[4]- https://www.autoblog.com/2016/11/18/how-to-improve-automatic-transmission-
performance-and-reliabilit/(accessed on 25 may at 4:15 PM)

[5]-https://help.edmunds.com/hc/en-us/articles/206102597-What-are-the-different-types-of-
transmissions-(accessed on 25 may at 4:23 PM)

[6]- https://innovationdiscoveries.space/what-are-the-main-components-of-the-gear-box/
(accessed on 26 may at 2:03 PM)

[7]-https://gearmotions.com/helical-gears-vs-spur-gears (accessed on 26 may at 1:03 PM)

[8]- https://www.cedengineering.com/userfiles/Basic Fundamentals of Gear Drives R1.pdf

(accessed on 26 may at 2:10 PM)

[9]- http://fmcet.in/AUTO/AT6501_uw.pdf (accessed on 26 may at 2:03 PM)

29
 APPENDIX

Figure 15 spur gear 2D drawing

Figure 16 main shaft 2D

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Figure 17 L-spur gear 2D

Figure 18 idle shaft

31
 Figure 19 hub 2D

Figure 20 drive shaft 2D

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 Figure 21 dog clutch 2D

Figure 22 exploded Side view

33
Figure 23 assembled Right view

Figure 24 exploded Top view

34
Figure 25 Exploded top view 2

35