Entoto polytechnic college

Chapter 2
GENERAL OVERVIEW OF AUTOMOTIVE SYSTEMS
Automobile engineering is the one of the stream of mechanical engineering. It deals with the
various types of automobiles, their mechanism of transmission systems and its applications.
Automobiles are the different types of vehicles used for transportation of passengers, goods,
etc. Basically all the types of vehicles works on the principle of internal combustion processes
or some times the engines are called as internal combustion engines. Different types of fuels
are burnt inside the cylinder at higher temperature to get the transmission motion in the
vehicles. Most of the automobiles are internal combustion engines vehicles only. Therefore,
every mechanical and automobile engineers should have the knowledge of automobile
engineering its mechanism and its various applications.
COMPONENTS OF THE AUTOMOBILE
The automobile can be considered to consist of five basic components :
1. The Engine or Power Plant : It is source of power.
2. The Frame and Chasis : It supports the engine, wheels, body, braking system, steering,
etc.
3. The transmission which transmits power from the engine to the car wheels. It consists
of clutch, transmission, shaft, axles and differential.
4. The body.
5. Accessories including light, air conditioner/hearer, stereo, wiper, etc

FUNCTIONS OF MAJOR COMPONENTS OF AN AUTOMOBILE

1. Engine or Power Plant

The engine is the power plant of the vehicle. In general, internal combustion engine with petrol
or diesel fuel is used to run a vehicle. An engine may be either a two-stroke engine or a four-
stroke engine.
An engine consists of a cylinder, piston, valves, valve operating mechanism, carburetor (or
MPFI in modern cars), fan, fuel feed pump and oil pump, etc. Besides this, an engine requires
ignition system for burning fuel in the engine cylinder.
2. Transmission System (Clutch and Gear Box)
Clutch
The purpose of the clutch is to allow the driver to couple or decouple the engine and
transmission. When clutch is in engaged position, the engine power flows to the transmission
through it (clutch). When gears are to be changed while vehicle is running, the clutch permits
temporary decoupling of engine and wheels so that gears can be shifted. In a scooter, the clutch
is operated by hand where as in a car the clutch is operated by foot. It is necessary to interrupt
the flow of power before gears are changed. Without a clutch, it will by very difficult.
Gear Box

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Gear box contain gearing arrangement to get different speeds. Gears are used to get more than
one speed ratios. When both mating gears have same number of teeth, both will rotate at same
number speed. But when one gear has less teeth than other, the gear with less number of teeth
will rotate faster than larger gear. In a typical car, there may be six gears including one reverse
gear. First gear gives low speed but high torque. Higher gears give progressively increasing
speeds. Gears are engaged and disengaged by a shift lever.
The power developed by the engine is transferred to the wheels by transmission system.
Transmission system must do three jobs :
1. It must provide varying gear ratios. Number of gear ratios are equal to number of gears
in a vehicle.
2. It must provide a reverse gear for moving vehicle in reverse direction.
3. It must provide a neutral or disconnecting arrangement so that the engine can be
uncoupled from the wheels of the vehicle. In a conventional transmission system, there
is a clutch, a manually operated transmission (gear box), a propeller shaft and a
differential or final drive.
3. Chasis and Frame
The chasis is formed by the frame with the frame side members and cross members. The frame
is usually made of box, tubular and channel members that are welded or riveted together. In
addition to this, it comprises of the springs with the axles and wheels, the steering system and
the brakes, the fuel tank, the exhaust system, the radiator, the battery and other accessories.
Along with this the frame supports the body.
4. Final Drive
Final drive is the last stage in transferring power from engine to wheels. It reduces the speed
of the propeller shaft (drive shaft) to that of wheels. It also turns the drive of the propeller shaft
by an angle of 90o to drive the wheels.
The propeller shaft has a small bevel pinion which meshes with crown wheel. The crown wheel
gives rotary motion to rear axles. The size of crown wheel in bigger than that of bevel pinion,
therefore, the speed of rear axles (or crown wheel) in lower than the speed of pinion. Final
drive is of two types, i.e. chain type and gear type.
5. Braking System
Brakes are used to slow down or stop the vehicle. Hydraulic brakes are generally used in
automobiles, where brakes are applied by pressure on a fluid. Mechanical brakes are also used
in some vehicles. These brakes are operated by means of leavers, linkages, pedals, cams, etc.
Hand brake or parking brake is usually a mechanical brake. These are used for parking the
vehicles on sloppy surfaces and also in case of emergency.
6. Steering System
In front wheels can be turned to left and right by steering system so that the vehicle can be
steered. The steering wheel is placed in front of driver. It is mechanically linked to the wheels
to provide the steering control. The primary function of the steering system is to provide
angular motion to front wheels so that vehicle can negotiate a turn. It also provides directional

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stability to vehicle when the vehicle moves ahead in straight line. Now-a-days, many vehicles
are equipped with power steering which uses pressure of a fluid to reduce steering effort. When
driver turns the steering wheel, a hydraulic mechanism comes into play to provide most of the
effort needed to turn the wheel.
7. Suspension System
Suspension system of an automobile separates the wheel and axle assembly of the automobile
from its body. Main function of the suspension system is to isolate the body of the vehicle from
shocks and vibrations generated due to irregularities on the surface of roads. Shock absorbers
are provided in the vehicles for this purpose. It is in the form of spring and damper. The
suspension system is provided both on front end and rear end of the vehicle.
A suspension system also maintains the stability of the vehicle in pitching or rolling when
vehicle is in motion.
ENGINE CLASSIFICATIONS
Today’s automotive engines can be classified in several ways depending on the following
design
features:
■ Operational cycles. Most technicians will generally come in contact with only four-stroke
engines. However, a few older cars have used and some cars in the future will use a two-stroke
engine.
■ Number of cylinders. Current engine designs include 3-, 4-, 5-, 6-, 8-, 10-, and 12-cylinder
engines.
■ Cylinder arrangement. An engine can be flat (opposed), inline, or V-type. Other more
complicated designs have also been used.
■ Valve train type. Engine valve trains can be either the overhead camshaft (OHC) type or the
cam shaft in-block overhead valve (OHV) type. Some engines separate camshafts for the intake
and exhaust valves. These are based on the OHC design and are called double overhead
camshaft (DOHC) engines. V-type DOHC engines have four camshafts—two on each side.
■ Ignition type. There are two types of ignition systems: spark and compression. Gasoline
engines use a spark ignition system. In a spark ignition system, the air-fuel mixture is ignited
by an electrical spark. Diesel engines, or compression ignition engines, have no spark plugs. A
diesel engine relies on the heat generated as air is compressed to ignite the air-fuel mixture for
the power stroke.
■ Cooling systems. There are both air-cooled and liquid-cooled engines in use. Nearly all of
today’s engines have liquid-cooling systems.
■ Fuel type. Several types of fuel currently used in automobile engines include gasoline, natural
gas, methanol, diesel, and propane. The most commonly used is gasoline although new fuels
are being tested.

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CLASSIFICATION OF VEHICLES
Based on Operational cycles
1. Four-Stroke Gasoline Engine
When the action of the valves and the spark plug is properly timed to the movement of the
piston, the combustion cycle takes place in four strokes of the piston: the intake stroke, the
compression stroke, the power stroke, and the exhaust stroke. The camshaft is driven by the
crankshaft through gears, or sprockets, and a cogged belt, or timing chain. The camshaft turns
at half the crankshaft speed and rotates one complete turn during each complete four-stroke
cycle.
Four-Stroke Cycle A stroke is the full travel of the piston either up or down in a cylinder’s
bore. The reciprocal movement of the piston during the four strokes is converted to a rotary
motion by the crankshaft. It takes two full revolutions of the crankshaft to complete the four-
stroke cycle. One full revolution of the crankshaft is equal to 360 degrees of rotation; therefore,
it takes 720 degrees to complete the four-stroke cycle. During one piston stroke, the crankshaft
rotates 180 degrees.
2. Two-Stroke Gasoline Engine
In the past, several imported vehicles have used two stroke engines. As the name implies, this
engine requires only two strokes of the piston to complete all four operations: intake,
compression, power, and exhaust.
Based on Source of energy
1. Gasoline engine
A vehicle driven by the power generated by internal combustion engine using a gasoline fuel.
Gasoline engine produces high power in any speed range.
2. Diesel engine
A vehicle driven by the power generated by internal combustion engine using diesel fuel.
Diesel engine produces large torque and consumes less fuel.
3. Battery
A vehicle driven by electric motors powered by series of automotive batteries. The first
developed electric car is the Baker produced in 1902. Vehicles could also be farther classified
according to how they work using battery and weather engine is also present on not.
Based on Construction and combustion
The following are the classifications of vehicles according to the types of engine constructions
and combustion.

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1. External combustion engine
In a steam engine, fuel is burnt outside the cylinders and power is generated by the expansion
of another liquid or gas heated by combustion or burning.
2. Internal combustion engine
Fuel is burned inside the cylinder ,power generated by the fuel is then expand to provide
mechanical energy. Internal combustion engines can be farther classified as follow
1. Reciprocating engine
An engine that produces its power by the internal burning of fuel inside the cylinders. The
created combustion or pressure pushes the piston down and crankshaft mechanism force to
move up the piston in a cycle.
The reciprocating movement of the pistons converted into rotary motion by the crankshaft. It
can be either gasoline or diesel engine depending on the fuel used

Based on Engine Configurations

Depending on the vehicle, either an inline, V-type, slant, or opposed cylinder design can be
used. The most popular designs are inline and V-type engine.
1. Inline Engine
In the inline engine design , the cylinders are all placed in a single row. There is one crankshaft
and one cylinder head for all of the cylinders. The block is cast so that all cylinders are located
in an upright position.
2. V-Type Engine
The V-type engine design has two rows of cylinders located 60 to 90 degrees away from each
other. A V-type engine uses one crankshaft, which is connected to the pistons on both sides of
the V. This type of engine has two cylinder heads, one over each row of cylinders.
3. W-type
the W-type engine. These engines are basically two V-type engines joined together at the
crankshaft. This design makes the engine more compact. They are commonly found in late-
model Volkswagens.
4. Slant Cylinder
Slant Cylinder Engine Another way of arranging the cylinders is in a slant configuration. This
arrangement is much like an inline engine, except the entire block has been placed at a slant.
The slant engine was designed to reduce the distance from the top to the bottom of the engine.
Vehicles using the slant engine can be designed more aerodynamically.
5. Opposed Cylinder
Opposed Cylinder Engine In this design, two rows of cylinders are located opposite the
crankshaft . These engines have a common crankshaft and a cylinder head on each bank of

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cylinders. Porsches and Subarus use this style of engine, commonly called a boxer engine.
Boxer engines have a low center of gravity and tend to run smoothly during all operating
conditions.

6. Radial
Radial type: in this arrangement, the engine pistons are positioned in a circular plane around a
central crankshaft.

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Based on Engine mounting position
The following are classifications of vehicles according to engine mounting and drive train
components positions:
 Front engine, Front wheeI drive (FF)
FF vehicIe has no propeller shaft that provides spacious interiors and comfortable ride.
 Front engine, Rear wheeI drive (FR)
FR vehicIe is well balanced that provides the best control and driving stability.
 Rear engine, Rear wheeI drive (RR)
RR vehicIe has an engine mounted at the rear that drives the rear wheels.

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Based on Applications
The following are the classifications of vehicles according to its applications.
 Passenger vehicles
Designed to mainly transport small number of passengers and carry light luggages.
 CommerciaI vehicIe
Designed for commercial purposes to carry cargo or transport group of passengers.
 Bus
Designed to transport group of passengers and carry their luggages.
 Truck
Designed to carry heavy and large cargos.
 SpeciaI purpose vehicIe
Designed and manufactured for its special purpose and particular applications.
Based on Purpose
 Passenger vehicles: These vehicles carry passengers. e.g: Buses, Cars, passenger
trains.
 Goods vehicles: These vehicles carry goods from one place to another place. e.g:
Goods lorry, Goods carrier.
 Special Purpose: These vehicles include Ambulance, Fire engines, Army Vehicles
Based on Load Capacity:
 Light duty vehicle: Small motor vehicles. eg: Car, jeep, Scooter, motorcycle
 Heavy duty vehicle: large and bulky motor vehicles. e.g: Bus, Truck, Tractor
Based on number of wheels and axles
 Two wheeler : motorcycles, scooters
 Three-wheelers : Tempo, auto-rickshaws
 Four wheeler : car, Jeep, Bus, truck
 Six-wheelers : Buses and trucks have six tires out of which four are carried on the rear
wheels for additional reaction.

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Body styIe and shape
The body is the part of vehicle that carries people or luggage. The following are the common
types of body styles.
 Sedan
Most common passenger car which is designed for the comfort of driver and passenger with
rows of seats in the front and back.
 Coupe
Sporty look with 2 seats for the driver and passenger that emphasizes style and performance
The roof is smaller and height of the vehicle is lower.
 Hatchback or Liftback
Similar to coupe in which the passenger and luggage areas are open to one another. Rear door
and window can be lifted up or opened like hatch of a ship.
 Hardtop
Sedan without window frames (no door sash) and center pillars. The back and front windows
open up as one that offers wide or good views. The style with center pillars without sash is
called the “pillared hardtop”.
 ConvertibIe
Passenger sedan or coupe that can be driven with its roof in up or down condition.
 Pickup
Compact truck with engine compartment extends in front of the driver’s seat.
 Wagon and van
It has integrated passengers and luggages space. Wagon mainly carries group of passengers.
Van mainly carries light luggages.
 Limousine
Long passenger vehicle with a partition between the driver and passenger cabins to provide
privacy on the occupants of the rear seats.

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