UNIT I

VEHICLE STRUCTURE AND ENGINES

Types of automobiles, vehicle construction and different layouts, chassis, frame and body,
vehicle aerodynamics (various resistances and moments involved), IC engines –components-
functions and materials, variable valve timing (VVT).
 Automobile engineering is an applied science that includes elements of Mechanical
engineering, Electrical engineering, Electronic Engineering, Software Engineering and Safety
engineering as applied to the design, manufacture and operation of automobiles, buses and
trucks and their respective engineering subsystems.
The word automobile comes, via the French automobile, from the Ancient Greek word
(autos, "self") and the Latin mobiles ("movable"); meaning a vehicle that moves itself, rather than
being pulled or pushed by a separate animal or another vehicle. The alternative name car is
believed to originate from the Latin word carrus or carrum ("wheeled vehicle)
What is an Automobile?
The automobile is a self-propelled vehicle that travels on land. It usually has four wheels.
An engine provides the power to move the vehicle. As the name implies, it is a mobile or moving
power unit on road. Self- propelled means unit which contains its own power source, necessary
for moving, within itself .As a vehicle, it is used for transportation of passenger and goods.
Introduction
Transportation has become unavoidable for the social and economic development of
mankind. Men animals and various goods are transported from one place to another by different
modes of transport.
1. Water transport such as ships, boats, hovercrafts.
2. Air transport such as aero planes, helicopters.
3. Space transport such as space crafts.
4. Land transport such as railways, roadways.
Road transport is most popular mode of traveling and transportation and accounts for
nearly 70% of all modes of transport available.
Motor vehicle is a self-propelling unit which carries the passengers or goods and ply on
the road surface. The motor vehicle or automobile or auto vehicle is driven by an internal
combustion engine or a prime mover operated by combustion of a fuel or electricity or a battery.
There is a wide range of automobiles designed for specific duty. The two-wheeler
mopeds, scooters, motor-cycle are used by individuals, four-wheeler cars and jeeps are family
vehicles, vans (minibus) and buses serve the society by transporting people, trucks are required
for carrying goods, tractors are field vehicles, bulldozers are used in construction work and gun-
carriage is involved in military operations. The automobile has created a new revolution in the
history of mankind. The modern age is called “auto age” as the impact of the society has been
very profound.
HISTORY OF AUTOMOBILE DEVELOPMENT
The history of automobile development and growth is very fascinating. It runs together
with the history of development of engines. This can studied as under.
1.2.1. European Development
The awn of automobile history dates back to 1770 when a Frenchman, Nicholas Carnot,
built the first road vehicle propelled by its own power. The French artillery officer built a three-
wheeler steam tractor for handling a canon. It could work for 15 minutes only and attained a
sped of about 2.5 mph.
The automobile or the car as we now today evolved from the horse-drawn carriage, and
perhaps the 19th century tricycle; but as the years went by it gradually lost its likeness to any of
its progenitors. The saga of the car really began as recently as 1860, when Jean Etienne Lenoir, a
Belgian inventor, built the first practicable gas engine. Etienne’s engine was fed on a mixture of
coal gas and air and no compression meant that it was not efficient.
The next significant development came in 1876 when Count Nikolous Otto, a German
engineer, successfully applied the four- stroke principle which enabled the charge to be
compressed with significantly better performance. At about the same time petrol came to
substitute the coal gas. During the 1880’s Germany was the hub of automobile development with
Gottlieb Daimler and Carl Benz at the helms of affairs. They were building their cars for sale in
1886. The engine was placed in the front of the chassis, hooked up to a sliding gear transmission,
brake pedal, clutch and acceleration were incorporated.
By the turn of the century, designers began increasing the number of the cylinder and a
prototype in-line 6-cylinder engine appeared in 1902. The design improvement awakened the
public to the next six years, production and sale of these vehicles became a business.
The early 1920’s saw the beginning of a period of gradual change and refinement in
automobile design. The spark ignition engine was the power plant of motor vehicle and kicked
out steam and electrical rivals. Water-cooled engine were almost certain. The engine were
located in the front of the chassis. The poppet valve was used in every engine design. Major
improvements have been made in every car feature. The main design requirements emphasized
on production of reliable vehicles to function at all times under all condition which would be
increasingly comfortable to ride in and easy to operate.
1.2.2. American Development
When Europe was struggling to make his vehicle run, came the period, in which the
development of mass-production methods permitting lower prices played a dominant role in
America. In 1908 Ford started off his Model T with an initial run of 2,000 vehicles, an output
unheard of at that time. Ever since, the correlation of design and production efficiency has
influenced the trend of modern vehicle construction and popularized the use of automobiles. The
life of tyres has been increased, independent front-wheel suspension has been introduced; four-
wheel hydraulic brakes have been incorporated, the higher compression ralios and availability of
new materials have helped to enhance power-weight ratio.
Substantial progress has been made after the second world war in every car feature such as
reliability and safety, ease and comfort, economy of operation, pleasing appearance. Safety and
exhaust emission were the additional features. Research and development continue to produce
computer controlled vehicles powered with nuclear engines and fuel cells.
1.2.3. Indian Development
At the end of 1900, the cars arrived in India and were used by Britishers and Kings of
states. In pre-Independent India, cars were imported and it was only in 1946, Hindustan Motors
was set up in Calcutta. It was followed by Premier Automobiles in 1947 to produce cars and
Mahindra and Mahindra in 1949 to produce jeeps in Bombay. Standard Motors was established
in Madras in 1950. The industrial giant, Tata introduced a plant for the manufacture was started
in India with foreign collaborations and as such could not contribute much to improve the design
and manufacture of new cars.
The production of all the cars was far below the nation’s demand. Maruti Udyog Limited
was emphasized in 1982 in collaboration with Suzuki of Japan to manufacture small cars. It has
helped to automobiles the country. New models have been introduced by various companies in
recent years which have the latest features and machines available for all income group of the
country’s population.
Requirements of an Automobile
The following requirements must be fulfilled for an automobile.
1. It should develop power by itself.
 2. The rate of power development must be easily controlled.
3. There should be an arrangement to transmit developed power to wheels.
4. An arrangement must exist to continue and discontinue power flow to wheels.
5. It should be possible to control or vary the torque.
6. The driving thrust should successfully be carried in the vehicle.
7. It must have a directional control.
8. An arrangement must exist to stop the vehicle while it is running.
All above requirements are fultilled by the following arrangements.
1. The power is developed by the engine.
2. The rate of power development is controlled by an accelerometer.
3. The power developed by the engine is transmitted to wheels by transmission system.
4. The gear box is provided for varying or changing the torque.
5. The driving thrust is carried to the chassis frame through the suspension system.
6. Directional control is maintained through the steering.
7. The moving vehicle is stopped by means of brakes.

Types of Automobiles
Automobile can be classified with respect to different purpose. A general classification of the
automobile is show in figure.
(i) With respect to the purpose:
a) Passenger vehicles - Car, bus, jeep, scooter mopeds & motor cycle
b) Goods carriers - Trucks & Lorries
(ii) Weight of the vehicle:
a) Heavy weight vehicles – Buses, Truck & Trailors
b) Light weight – Cars, Jeep
c) Medium weight – Minibus & Station wagon
(iii) With respect to the fuel used:
a) Petrol vehicle – Scooters, Cars, Motor cycle
b) Diesel vehicle – Buses, Trucks
c) Gas vehicles – Coal gas LPG CNG
d) Electric vehicle – Heavy cranes, Battery truck, cars & fork lifters
 e) Solar vehicle.
(iv) With respect to body style:
a) Closed cars – Sedan cars, Saloon cars, SUV
b) Open cars – Sports cars & Convertible cars.
c) Special style – Estate care, Station wagon
(v) With respect to capacity:
a) Heavy transport vehicles
b) Light transport vehicles
(vi) With respect to the number of wheels:
a) Two wheelers
b) Three wheelers
c) Four wheelers
d) Six wheelers
(vii) With respect to the drive of the vehicle:
a) Single wheel drive
b) Two wheel drive
c) Four wheel drive
d) Six wheel drive
(viii) With respect to the side of drive sheet:
a) Left hand drive – Most of the American, European and UAE vehicles
b) Right hand drive – Indian vehicles
(ix) With respect to the side of power drive:
a) Front wheel drive
b) Rear wheel drive
c) Four wheel drive
(x) With respect to transmission:
a) Conventional type – ordinary gear box is fitted – Most of Indian
b) vehicles
c) Semi – automatic type – Combined manual and automatic gear box
d) Fully automatic
(xi) With respect to their construction:
 a) Single unit vehicles
b) Articulated vehicles
c) Heavy tractor vehicles
(xii) With respect to motion:
a) Reciprocating piston engines
b) Rotary – Wankel engine
c) Gas turbine
(xiii) With respect to the suspension:
a) Conventional type – leaf springs
b) Independent – coil spring, Torsion bar, Pneumatic.
(xiv) With respect to engine capacity:
a) 50CC
b) 100CC
c) 150CC
d) 200CC
(xv) With respect to combination of number of wheels and axles:
a) 4 x 2
b) 4 x 4
c) 6 x 4

VEHICLE CONSTRUCTION
The automobile consists of two main parts
1. Chassis
2. Body
A vehicle arrangement without body is called chassis.
Various components and systems of the chassis are
1. The power system,
Power units are clutch, gearbox transmission, differential, Rear axle shaft, universal joint
&propeller shaft etc …
2. Running system
Running systems consists brakes, wheels, frame, suspension and steering system
3. Electrical system.
Electrical system consists of starting circuit, charging circuit, ignition circuit lighting and horn
circuit.
2. Body
The purpose of the body is to provide accommodation to the driver and the passenger and to
protect them against adverse conditions.

Frame
It is rigid structure that forms a Skelton to hold all the major units together. The engine is
mounted in the front of the frame and is connected to the clutch and transmission to form a
compact power assembly. The unit is fastened to the frame through rubber-cushioned motor
mounts to lessen the transfer of engine vibration. The transmission is connected to the final-
drive gears through the propeller shaft and universal joints. The final-drive gears and differential
to the rear wheels revolve inside the rear-axle housing.
Wheels and Tyres
The wheels and tyres assemblies support the frame and the units mounted on it through
front and rear suspension systems.
Suspension System
The suspension system is made up of springs, shock absorbers and linkage so as to allow
the wheels and tyres to follow the road roughness without excessively raising the frame and
transmitting shock.
Steering System
Some parts of the steering system (steering gear) are bolted to the frame and some
(steering column) connected to the body.
Fuel System
The fuel tank is fastened to the rear of the frame and is connected to the fuel pump
through metal tubes. The exhaust pipe and muffler conducts the poisonous gases from the
engine to the rear of the vehicle.
Electrical System
It consists of a battery, starting motor, generator and controls along with engine ignition
system (ignition coil, distributor, spark plugs and wires).
Brake System
The complete brake system is incorporated in the chassis. The brake pedal controls a
master cylinder which is connected to brakes on each wheel by oil lines.
Cooling System
A radiator is mounted on the chassis which is connected to the engine by rubber hoses to
allow cooling water or coolant to circulate between radiator and engine. Fan, water pump and
fan belt are other parts of the cooling system.
Auxiliaries
Lights, instruments, accessories, etc. are connected to the chassis and are furnished with
electrical energy from battery and generator.

COMPONENTS OF AN AUTOMOBILE
The main components of an automobile are:
 1. The basic structure.
2. The engine.
3. The transmission system.
4. The auxiliaries.
5. The controls.
6. The superstructure.
The items, 1 to 5 constitute automobile chassis.
The Basic Structure
It consists of the frame, the suspension system, axles, wheels and tyres. It provides
support for other items of automobile.
1. Frame
There are two distinct forms of construction in common use:
1. The conventional pressed steel frame to which all the mechanical units are attached and
on which the body is superimposed.
2. The integral or frameless construction, in which the body structure combines the
functions of body and frame.
The frameless construction is possible only in the case of closed car, since the roof, screen
pillars and rear panel are essentially load-taking parts of the structure.
The frameless construction has the following advantages over the conventional framed
construction:
 Reduced weight and saving in fuel consumption.
 Low manufacturing cost.
 During collision, the body absorbs the shock due to impact and providing safety to the
passengers.
 Lower body position and increased stability of the automobile.
These advantages are accompanied by the following disadvantages also:
 Reduction of strength and durability.
 Economical only if frameless construction is adopted in mass production.
  Increased cost of repairs in case of damage to body during accidents.
 Topless cars are difficult to design with the frameless construction.
2. Suspension System
The suspension system connects the body of the vehicle with the wheels and restricts
direct impact of wheels to the chassis and body.
3. Axles
The front and rear axles are beams supported at the ends and subject to the following loads :
1. The vertical load at the spring centers due to the weight of the vehicle.
2. A fore and aft load at the wheel centre due to driving or banking effort.
3. The torque reactions due to drive or brakes.
4. A side thrust at the radius of the tyre due to centrifugal force when rounding a
curve.
There are three types of live rear axles.
a) Fully floating type.
b) Three-quarter floating type.
c) Semi-floating type
4. Wheels
Wire-spoked wheels have been used mainly on sports cars on account of their light
weight and quickness in changing the wheel. However, the pressed steel wheel has displaced
these for all ordinary purposes. Such a wheel consists of a central flanged disc pressed into a
rolled section rim and retained in position by welding. Light alloy wheels are currently used in
case of luxury and sports cars and are called ‘formula wheels’.
The Power Plant
The power plant (engine) provides power for propulsion of the vehicle. The power plant
generally consists of an internal combustion engine which may be either a spart-ignition, or
compression-ignition type.
The gas-turbines have also been used successfully in certain cars, though the cost has been a
disadvantage in spite of their better performance compared to I.C. engines.
The Transmission System
The transmission system consists of a clutch, a gear box (also called transmission) giving
three, four or even five different ratios of torque output to torque input, a propeller shaft to
transmit the torque output from the gear box to the rear axle and a differential gear to distribute
the final torque equally between the driving wheels. The various components are:
Clutch: Its purpose is to enable the driver to disconnect the drive from the road wheels
instantaneously and to engage to the road wheels gradually while moving the vehicle from rest.

FIG 1.2 Layout of Complete Transmission System of An Automobile

The main transmission (1) is fitted with a transfer case (2) at its back. The transfer case
(2) is an auxiliary transmission, connected to front differential (3) through a front drive
(propeller) shaft (4) and to rear differential (6) through a rear drive shaft (5). By shifting to
gears in the transfer case by a selector lever (A) the engine power is divided and transmitted to
both front and rear differentials. High speed in transfer case provides a direct drive i.e. 1:1 ratio
and low speed provides a ratio of 2:1.These ratios help to drive the vehicle on rugged terrain,
upgradients muddy and sandy roads without spinning of wheels.
Gear box (transmission):
The gear box or the transmission provides the necessary leverage variation between the
engine and road wheels.
Bevel pinion and crown wheel: They turn the drive round through 90o and also provide a
permanent reduction in speed. The permanent reduction is necessitated because of the fact that
speed of the engine has to be maintained at optimum level at all times, yet a minimum value of
torque has to be made available at the road wheels.
Universal joints:
They provide for the relative movement between the engine and the driving wheels due
to flexing of road springs.
Differential:
While taking turns, the driving wheels must turn at different speeds. This is done with the
help of differential.

TYPES OF DRIVES OF AUTOMOBILES (Layouts of Car)

Some of the important drives of automobiles may be classified as follows:
1. Front engine - Rear wheel drive
 2. Rear engine - Rear wheel drive
3. Front engine - Front wheel drive
4. Four wheel drive
1. Front Engine - Rear Wheel Drive
In this layout a front mounted engine-clutch-gear box unit drives a beam type rear axle
suspended on leaf sprints through a propeller shaft with two universal joints. With the help of
coil sprints, the front wheels are independently sprung. As shown in Fig. 1.4 this layout is one of
the oldest layout which remained unchanged for many years. some of the advantages provided
by this system are :
a) Balanced weight distribution between the front and the rear wheels.
b) Easy front wheel steering.
c) Behind the rear seats, large luggage space is available.
d) Accessibility to various components like engine, gearbox and rear axle is better in
comparison to other layouts. The control linkages-accelerator, choke, clutch and
gearbox are short and simple.
e) Full benefits of the natural air stream created by vehicle’s movement is taken by
the forward radiator resulting in reduced power losses from a large fan.
f) Small length of the propeller shaft permits the angularity of the universal joints to
be small and easily provided by simple types.
By mounting the rear wheel drive assembly on the body unit and using universally jointed
shafts to independently steer rear wheels as shown in Fig. 1.5, the layout design can be modified
and improved. It provides number of benefits like improved handling, comfort and rear wheel
grip as well as reduced unspring weight.
2. Rear engine-Rear wheel drive
This arrangement eliminates the necessity for a propeller shaft when the engine is
mounted adjacent to the driven wheels. The engine-clutch-gear box-final drive form a single unit
in this layout. As shown in Fig. 1.6, to reduce the ‘overhang’ distance between the wheel centres
and the front of the engine, the final drive is generally placed between the clutch and the gear
box. In comparison to front wheel drive it has a simpler drive shaft layout. Further, the weight of
rear engine on the driving wheels provides excellent tranction and grip especially on steep hills
as well as when accelerating. Inspire of the low proportion of the vehicle weight transferring to
the front wheels, very effective rear wheel braking is possible. Due to the absence of the
propeller shaft the obstructed floor space is reduced. The front of the vehicle can, therefore, be
designed for good visibility and smooth air flow. the exhaust gases, fumes, engine heat and
noises are also carried away from the passengers. It results in compact layout and short car.
 The layout also has got certain disadvantages like restricted luggage space due to narrow
front compartment which houses the fuel tank also. Natural air cooling is not possible, it requires
a powerful fan. The floor is further obstructed due to long linkage required for the engine, clutch
and the gear box controls. The rearward concentration of weight causes the vehicle to be more
affected by side winds at high speeds. this makes the vehicle unstable resulting in over steering
and turning very sharply into a curve. This necessitates the steering correction in the opposite
direction.
3. Front engine-front wheel drive.
This layout provides optimum body-luggage space and a flat floor line resulting in a
transverse longitudinal engine position. This drive pulling the car along provides good grip and
good road holding on curves due to major weight at the front. The chances of skidding especially
on slippery surfaces are very much reduced. Good road adhesion is provided by the large
proportion of the vehicle weight acting on the driven wheels. when the vehicle is to be ‘steered
in’ to the curve, it provides ‘under steer’ characteristics always preferred by drivers.
The combination of steered and driven wheels with short drive shafts provides the main
disadvantage. This requires special universal joints and a more complicated assembly. to prevent
the rear wheels from skidding under heavy braking, the ‘reduced’ weight at the rear usually
necessitates special arrangement.
4. Front wheel steering Rear wheel drive
 Access to the engine is very easy.
 Slowing down of the water circulation causing cooling troubles can be avoided and
long hose connections can be saved due to situating of the radiator in the main air
stream.
 This arrangement helps minimize the linkage between the clutch, gear box and
engine.
 The angularity of the propeller shaft is kept to minimum and there is no need of
joints due to the shaft length.
Rear Engine-Rear Wheel Drive
Advantages
 Better road adhesion preferably on steep hills and while accelerating with increased
weight on the driving wheels.
 Generally a proportional part of weight of the car is transferred to the front wheels while
braking. Therefore, due to the firm road surface contact maintained by rear engine car
results in assistance to stopping of the vehicle.
 In this arrangement, front wheels are only for steering purposes.
 The necessity of the propeller shaft is altogether eliminated due to the combination of
engine, gear box and final drive. This also requires only one common oil sump.
 Good visibility and stream lining is provided by proper design of vehicle front.
 The passengers are kept away from inconveniences like noise, heat and fumes.
Disadvantages
 At high speed, the increased weight at the rear end makes the vehicle unstable.
 To control the engine, clutch and gear box, long linkages are required.
 The width of the car at the front gets reduced for accommodating the movement of the
steering wheels resulting in reduction of size of the luggage compartment for given length
and with of the car.
 The wheels get turned too sharply into the curve due to tendency of over-steering. This
necessitates the turning of the steering wheels in the opposite direction to make
correction by the driver.
 Efficient cooling becomes very difficult to obtain due to screening of the engine by the
vehicle body.
Front Engine - Front Wheel Drive
Advantages
 As compared to rear wheel driven car, there is a faster and safer traveling due to good
road holding on curves.
 Good road adhesion is obtained due to a large part of the vehicle’s weight being carried
on the driving wheels under normal conditions.
  Under-steer conditions generally preferred by many drivers are promoted by this type of
drive. The car comes back to closer radius if the throttle is released. This makes the
steering wheel to run more in the direction of turn to make it a better condition.
 A lower flat floor lines is provided due to dispensing with the propeller shaft resulting in
lowering of centre of gravity.
 The engine, clutch, gear box and final drive are combined similar to the rear engine car.
This provides a more comfortable drive due to final drive spring.
Disadvantages
 Due to the weight of the vehicle moving to the rear, the weight on the driving wheels is
reduced on steep gradients as well as while accelerating.
 The tractive effort which is most needed on steep gradients and during accelerating is
reduced.
 This disadvantage becomes more serious on slippery gradients.
 Under these conditions certain modifications in modern designs have been made to
ensure provision of sufficient traction.
5. Four-wheels drive
To increase maneuverability of the vehicle required to travel on rough unconstructed
roads and tracks another arrangement known as four-wheel drive is provided. due to all the four
wheels getting driven, whole of the weight of the vehicle is available for traction. But this
advantage is not worth the additional cost on good road surfaces. The system is provided in
jeeps which are known as 4 X 4 wheel drive vehicles.
6. Left hand and Right and drives
In different countries, the automobiles are driven on different sides of the road, In United
Kingdom and all the countries, which were once colonies of the British Rule. The vehicles are
driven on the left hand side of the road. In all other countries of the world, normally vehicles are
driven on the right hand side of the road. For better driving control, the vehicle drivers must be
nearer to one another while passing or crossing. Similarly for safety consideration, the drivers
must be in the centre of the road while driving. Therefore, two types of vehicles are
manufactured.
 (a) Left hand drive: The steering is fitted on the left hand side of the automobile and
such vehicles are convenient to drive in countries following right hand drive rules, e.g. U.S.A.,
Russia, European countries.
(b) Right hand drive: The steering is fitted on the right hand side of the automobile and
such vehicles are convenient to drive in countries following left hand drive rules, e.g. U.K., India,
and Pakistan. However, though rare, left hand cars also driven in such countries.

LAYOUT OF CHASSIS
The main parts of and automobile are mounted on the chassis. The layout of these
components on the chassis are different in different types of vehicles, i.e., cars, jeeps, trucks,
buses, etc. The main difference in the layout of this chassis is the position of the engine.
1 Layout of chassis of a four wheel driven automobile is shown in Fig.

 Propeller shaft
 Universal joint
 Differential
 Springs
The following main components of the Chassis are
 Front axle
 Rear axle
 Battery
 Wheels
  Frame
 Suspension system
 Steering system
 Braking system
 Internal combustion engines
 Clutch
 Gear box
Classification of Chassis:
According to the fitting of engine:
(a) Full-forward
(b) Semi-forward
(c) Bus chassis
(d) Engine at back
(e) Engine at centre
In full-forward chassis, the engine is fitted outside the driver cabin or seat. Example: Cars
and Mahindra jeeps.
In semi-forward chassis, a half portion of the engine is exactly in the driver's cabin
whereas the remaining half is at the front side but it is outside the driver's cabin. Example: Tata
SE series of vehicles.
In bus chassis, the total engine is fitted in the driver cabin. It provides the increased floor
area in the vehicle. The driver seat is just above the front wheel. Example: Busses and trucks.
In most of the vehicles, the engine is fitted at the front portion of chassis. The drive is only
given to front wheels. Example: Matador vehicles. In some vehicles, the engine is fitted at the
back portion of the chassis. Example: Volkswagen cars, Leyland bus of England. In some vehicles,
the engine may be fitted at the centre of the chassis. Example: Royal tiger world master buses of
Delhi transport
2. According to the number of wheels fitted in the vehicles and the number of driving
wheels:
(a) 4 x 2 drive chassis - It has four wheels out of which 2 are driving wheels
(b) 4 x 4 drive chassis - It has four wheels and all of them are driving wheels
(c) 6 x 2 drive chassis - It has six wheels out of which 2 are driving wheels
 (d) 6 x 4 drive chassis - It has six wheels out of which 4 are driving wheels.

LAYOUT OF CHASSIS
Above figure shows the front and top views of layout of the typical chassis. In this layout,
the engine location is at the front end of the vehicle. The engine is connected to the gearbox
through clutch. The drive of the engine can be connected or disconnected from the gearbox by
using clutch assembly. The clutch pedal provided at the vicinity of the driver facilitates to engage
or disengage the clutch with gearbox whenever required.
From gearbox, power is transmitted to the differential through a propeller shaft and
univeral joint and dinally to the wheels via rear axles. The radiator is placed at the front of the
engine.
Components and Drive Systems in Chassis
1. Frame:
Frame is the foundation for carrying the engine and body of the vehicle. It also carries
steering, power train ete. by means of springs, axles, rubber pads etc. The frames are nade of box,
tubular, channel or U-shaped section, welded or riveted together. In order to ike them rigid to
withstand shocks, blow twists and vibration mats, cross-bracing or cross members are used.
When the engine, wheels, power trains, brackets and steering systems are fitted on the
frame, the assembly is known as chassis. Frame bends upward in a shape at the rear to provide a
space for rear springs. It is tapered at the front to provide the space for turning front wheels
when steered.
2. Suspension systems:
Suspension systems are used in vehicles
 to insulate the wheel and axles from the frame
 in order to avoid the transmission of road effects to passengers while
travelling on uneven road
 to provide a comfortable ride to passengers and
 to avoid additional stresses in the motor car frame.
3. Steering system:
 The function of a steering system is to enable the driver to accurately control the
direction taken by the vehicle under all operating conditions. The system must be light and easy
to operate, free from shock and vibration as direct as possible. The steering system also helps to
convert the rotary motion of the driver's steering wheel into the angular turning of the front
wheels as well as to multiply the driver's effort with the leverage or mechanical advantage of
turning wheels.
4. Braking system:
The most vital factor in running and controlling the modern vehicle is the braking system.
In order to bring the moving motor vehicle to rest or slow down in a shortest possible time, the
energy of motion possessed by the vehicle must be converted into some other forms of energy.
Brake is a friction device for converting the power of momentum or kinetic energy of the moving
vehicle into heat.
5. Internal combustion engines:
In internal combustion engines, the combustion takes place within the engine unlike
steam engines which work using steam which has externally been raised in a boiler. In all
Internal Combustion (IC) engines, the air is supplied along with a measured quantity of fuel. This
fuel burns within the engine and it produces a high pressure and high temperature gas,
6. Clutch:
It is a friction type uncoupling device. It consists of a single steel disc faced with suitable
friction material. It is clamped between two surfaces directly disengaging the clutch, the two
surfaces are positively separated by pressing the clutch pedal The main function of the clutch is
to take up the drive smoothly from the engine and to release or disengage whenever desired. The
disengagement of clutch is required while changing the gear or bringing the vehicle to rest.
7. Gear box:
It consists of various types of gears which are constantly in mesh. The gear change takes
place by sliding the dogs. The main function of the gear-box is to provide the necessary variation
to the torque applied by the engine to the road wheel according to the operating conditions. The
necessary variations are provided due to the presence of different gear ratio among various
meshing gears.

8. Propeller shaft:
 The function is to transmit power from the rear end of the gear-box to the final reduction
gear in the axle. The vertical movement of the rear axle relative to the frame is also
accommodated. It is an ordinary Hooke's joint. The small and limited angular displacement in the
rubber joints is advantageous in damping out torsional vibrations.
9. Universal joint:
Due to the flexibility of road springs, the rear axle is constantly moving up and down. The
propeller shaft fitted to the rear axle must also be free to move up and down. To permit the
turning of the propeller shaft, this movement takes place and universal joints are fitted at cach of
its ends. Therefore, the relative movement between engine and driving wheel is maintained by
the universal joint.
10. Differential:
The differential gear carries power from propeller shaft to rear wheel axles. It helps two
rear wheels to turn at different speeds when rounding a curve. The outer wheel must over-run
than the inner wheels when taking a turn. The differential gear also ensures that the final output
torque is equally distributed between two wheels without any consideration of their relative
speeds.
11. Springs:
Springs are fitted between frame and wheel to prevent the upward movement of the
frame along with up and down movement of the wheel. Spring is a reservoir of energy which is
stored in steel springs by bending them or by twining them. When the spring resumes to its
normal state, this energy is released
12. Front axle:
It is used for steering front wheels carried on stub axles swiveling upon kingpin's axle
extremities. Steering arms and track rod link, two stub axles are together used for swiveling
them by a steering wheel about kingpins. The steering wheel linked to one of the stub axle by a
shaft, a gear box and suitable linkage are operated by the driver's hand wheel. An axle in which
one-piece beam is used to support the vehicle through springs (axle and spring arrangement)
was previously used. Now, an arrangement known as independent front suspension replaces the
axle and spring arrangement. Under the control of springs, wheels are free to rise and fall
independently in the vertical direction to each other.
13. Rear axle:
 Rear axle or driving axle is a tube such as shaft enclosing driving shafts with suitable
bearings for rotating the wheels. It is used for fixing the rear wheels. It is enlarged at the centre
for enclosing the final drive gears used for providing main speed reduction between engine and
driving wheels. The change of direction from the line of a propeller shaft to the transverse line of
the axle shafts is also provided by the rear axle.
When going round a curve, the inner wheel has to travel for a smaller distance in
comparison to the outer wheel. But both the rear wheel would rotate at the same speed if they
are connected by a shaft. This rotation of both wheels would result the slipping of one or both of
them on the road surface causing excessive tyre wear as well as severe twisting loads on the
shaft. Moreover, two wheels of exact diameter can only turn at the same speed without slip on
the straight road. Each wheel is provided with its own separate half-shaft connected by a
differential gear and meeting at the centre of the axle. Therefore, when going round a curve, the
wheels are free to rotate at different speeds although they are provided with equal drive by the
differential gear.
For preventing the transmission of shock from uneven road surfaces to the vehicle,
springs are used to support the vehicle on the axle. In order to allow the vertical movements of
wheels relative to the frame as well as to allow the parts of the shaft to operate at different angle,
final drive gears and the differential gear are used. These gears are mounted in a casting
attached to the frame with independent sprung wheels attached by means of shafts through
devices called universal joints.
14. Battery:
In reality, the battery is the heart of the electrical system of a motor vehicle. It supplies
current to the cranking motor and ignition system. The function of the battery is to store
electrical energy which can be used whenever required. Battery may be called nerve- centre of
the whole installation because it supplies electrical energy for operating all electrical devices and
other units except the charging device. It also supplies the electricity for operating the various
electrical devices when the vehicle is not operating or running slowly and generator speed is
insufficient to meet the full load requirements.

15. Wheels:
 The wheels are fitted below the chassis to support the load of the vehicle and passengers.
They are fitted with hollow rubber tyres filled with air in rubber tubes under sufficient pressure
necessary for carrying the load. The shocks caused by road irregularities are absorbed by them.
By fitting springs between wheels and vehicle to allow the vertical movement of the wheels in
relation to vehicle, a greater part of unevenness of road surfaces is taken care of.

Characteristics of a Good Chassis

For a good chassis design and its good performances, it must have the following
characteristics,
1. Fast pickup 9. Power accessibility
2. Strength 10. Economy of operation
3. Safety 11. Low centre of gravity
4. Durability 12. Stability
5. Dependability 13. Load clearance
6. Ease of control 14. Braking ability
7. Quietness 15. Good springing
8. Speed 16. Simplicity of lubrication
 FRAMES
Frame is the main part of a chassis. It is the backbone of the vehicle. All other parts of the
chassis are mounted on the frame. It is a rigid structure which forms a skeleton to hold all major
parts together. At the front end of the frame, the engine is mounted. The engine in turn is
connected to clutch and transmission unit to form a complete power assembly. The frame is
supported by wheel and tyre assembly. Some parts of the steering system are connected to the
frame and remaining to the body. The fuel tank is fastened to the rear end of the frame.
Functions or Importance of Frame
1. To form a base for mounting engine and transmission systems.
2. To withstand the engine and transmission thrust and torque stresses as well as
accelerating and braking torque.
3. To carry the load of passengers and goods in the body.
4. To accommodate a suspension system.
5. To carry other parts of the vehicle.
6. To resist the effect of centrifugal forces when cornering a curve.
7. To withstand bending and twisting stresses due to the fluctuating or rear and front axles.
8. To support the load of the body, engine, gear box, battery, fuel tank etc.
Requirements of a Good Frame
It must be strong, light and designed to withstand the shock blows, twists, vibrations and
other strains to which it is subjected to road conditions.
It should also resist the distorting force such as
 weight of the components and passengers causing a sagging effect due to bending action.
 horizontal forces provided by road irregularities.
 upward twisting forces caused by road shocks.
Frame Construction
In order to provide good resistance to bending and torsional effect, the frame sections are
made of proper forms. A typical passenger car frame is shown in Figure. There are three
common types of frame sections as
 Channel.
 Tubular
 Box
Types of Frames:
There are three types of chassis frame construction as follows:
 Conventional frame construction
 Semi-integral frame construction
 Integral or Frameless construction
1. Conventional frame construction

This type of frame is also called as non-load carrying frame. This frame is shown in
Figure. The loads on the vehicle are transferred to the suspension by this type of frame. The
frame supports the various parts of the vehicle such as the engine, power transmission elements
and car body. The total frame is mounted on the wheel axle by means of springs.

The body of the vehicle is made of flexible materials such as wood and mounted on the
frame by using rubber mountings in between body and frame. This arrangement makes the body
completely isolated from the frame deflection. It is mostly used in heavy vehicles such as trucks.
For commercial vehicles with relatively low volume production, it has advantages of
strong chassis of small proportional weight sufficient to carry the considerable pay loads,
localized accident damage which is easy to repair in comparison to the integral chassis. Further,
both long and short wheel base version of the same vehicle can be produced.
The cross-sections of the frame are usually channel, tubular or box type. Figure shows a
dismantled view of conventional chassis frame and body construction.

2. Semi-integral frame construction:

 In this type of frame, the rubber body mountings are replaced by relatively stiff
mountings. This arrangement transfers a part of the frame load to the body structure also. This
type of frame is mainly used in European cars and American cars. But this construction is heavy
in nature as compared to the conventional type.

3. Integral frame construction or Frameless construction:

This type of construction is also called as chassis less, unitary or monocock construction.
This is now-a-days used in passenger cars. This construction provides a stiff light construction
particularly is no separate frame. All the assembly units are attached to the body.

In this design, heavy side members of the frame are eliminated and cross members are
combined with the floor of the body. The body of the vehicle gives a mounting for engine,
transmission, suspension and other mechanical units and components. This type of construction
is led to much reduction of weight which is important in design consideration.
Structure of this type includes a floor structure
having side members, cross members, floor and other
components. They are welded together as one
assembly. The surfaces are having ribbed portion to
increase strength and rigidity. For carrying the engine
and front suspension, a sub-frame is also attached to
the front of the body shell. The floor and side panel
surfaces have pressed grooves to increase stiffness.
 In this type of construction, the stresses are evenly distributed throughout the structure.
A strong structure with good torsional rigidity and resistance in bending are provided by this
construction.
The structure is also free from shakes on rough roads which cause an increased Life of
door locks, hinges and many other small parts along with a reduced body rattle.
Very low carbon (0.1%) steel with good ductility is required for manufacturing the panels
by pressing. The structural members are required to be stiffened by forming thin steel sheet into
intricate sections by spot welding due to low strength of this material. Entire body is immersed
in a rust protective solution to increase corrosion resistance and rusting resistance.
In order to avoid the objectionable drumming sound from panel due to vibration, a sound
damping material should be packed on inside of the panel.

Frame materials:
The various steels used for conventional pressed frame are as follows.
1. Aluminium allow (ALPAX)
2. Mild steel sheet
3. Carbon steel sheet
4. Nickel alloy steel sheet.
The composition of sheet nickel alloy steel is given as follows.
Carbon – 0.25 to 0.35%
Manganese - 0.35 to 0.75%
Silicon - 0.30% (Max.)
Nickel - 3%
Phosphorus - 0.05% (Max.)
Sulphur - 0.5% (Max.)
 VEHICLE BODY

The basic form of a modern autumeible body is older horse driver carriage. They have a
single seat type body construction which provides less safety to the passenger from weather.
Larger and more stylish bodies were developed and manufactured with passage of time to
provide increased space, safety or protection to the passengers.
Body is the super-structure for all velticies. It may either be constructed, separately and
bolted to the chassis or manufactured integral with the chassis (e. Frameless construction) Both
the chassis and the body make the complete vehicle.
A body consists of windows and dours, engine cover, roof, luggage cover etc. The
electrical system in the body is connected to the chassis electrical units so that the battery and
the generator alternator can furnish the required electrical energy to the system.

Importance of Vehicle Body Design

1. Weight of the body is 40% of total weight of the car and 60 to 70% of total weight of
buses. Therefore, the reduction in body weight is important.
2. If the weight of the body is reduced, it will also improve the fuel economy (Le
mileage).
3. The body of the vehicle determines its aerodynamic characteristics. Better
aerodynamic structure leads to fuel economy at high speed and stability in cross
winds. The positive pressure at the front of the vehicle should be minimized and it
should be deflected smoothly to prevent the creation of eddies.
4. The body is also important for aesthetic and ergonomics consideration. It should give
a pleasant appeal and style for the customer.

Requirements of Vehicle Body

The vehicle body should fulfill the following requirements.
1. Stresses induced in the body should be distributed evenly to all portions.
2. Weight of the body should be as minimum as possible.
3. It should be able to cope with impact loads of reasonable magnitude
 4. It must be strong enough to withstand all types of forces acting on the vehicle. The
forces are including the weight of the a car, inertia, luggage, braking and cornering
forces.
5. It should have reasonable fatigue life.
6. It must provide adequate space for both passengers and the luggage.
7. It should have minimum number of components.
8. It must have sufficient torsional stiffness i.e., ability to resist the twisting stresses
produced by irregular road surface.
9. It should have good access to the engine and suspension elements.
10. It must ensure a quite ride, easy entry and exit.
11. It should create minimum vibration during running.
12. The shape of the body should be minimum drag.
13. It is easy to manufacture as well as cheap in cost.
14. It should be designed in such a way that passengers and luggage are protected
from bad weather.
15. It should give appeal finish in shape and colour.

Types of Vehicle Body

For different types of auto-vehicles, passenger space and overall dimensions vary. Various
types of bodies for different vehicles can be listed as below.
1. Car
2. Truck - Straight truck or Punjab body
3. Truck-half body type
4. Truck-platform type
5. Tractor, Tractor with articulated trailer
6. Tanker
7. Dumper truck
8. Delivery van
9. Pick-up
10. Jeep
11. Buses and Mini-buses
 12. Three wheelrs

Figure: Different types of bodies fro different vehicles

The car bodies have a great resistance to wind. For high-speed vehicles, a special
attention is given to streamline the body. The streamlining is the process for shaping the body to
reduce air resistance. It is mainly used for racing cars.
 Straight truck vehicle bodies are constructed into two parts. One is driver cabin and one is
goods carriage. Goods carriage is a closed type with particular standard height. These vehicles
are used to carry goods which are affected by weather conditions. Examples Vegetables, sugar,
rice, sea foods etc.
Truck half body is having a driver cabin as usual but the goods carriage has open at the
top. It is used to carry various goods which are not affected by weather, Trock platform type has
also a separate driver cabin. Its goods carriage is a platform type. It usually carries goods such as
iron billets, barrels, concrete slabs ete,
Tractor consists of small length body in addition to driven cabin. Usually, an articulated
trailer is attached to the rear end of the trailer. This trailer has various cabins. Figure 1.23 shows
different types of bodies normally designed for different vehicles. It may be an open type or a
closed type depending on the purpose of use. It is used to carry passenger cars, mopeds, motor
cycles etc. Most of these vehicles have six wheels.
Tanker is the vehicle which consists of a tank to carry fluids of various natures. The tank
may be welded or bolted to the chassis frame behind the driver cabin. The tank has an opening at
the top to pour fluid and a drain cock at the bottom to drain the fluid.
Dumper truck has heavy goods carrying panel with open top in the rear side. The rear
side can be tilted up and down by hydraulic cylinders. It is used to carry brick, stones, marbles
etc.

Body Construction and its Components

The main purpose of designing the car body is for containing and protection of the engine
and accessories as well as the passenger. To fulfill above requirements, the vehicle body has
various components which are grouped under the following three groups.
(a) Structure: All load carrying elements are defined as structure.
(b) Finish: This group includes all unstressed units such as bonnet, boot, lid, bumper etc.
(c) Equipment: This group includes various parts such as rim, seats, doors, window etc.
The various components of car body are: body, sheets, pillar-less frame, front and rear
doors, front panel, roof panel, floor panel with engine beams, wheel arches, bonnet, wind screen
pillar, wind screen, front and rear window, front and rear bumper, cowl assembly, front and rear
seats, luggage space as a continuation of passenger compartment, folding roof with windup
windows, sliding roof and folded flat windscreen, hood etc.

All steel sections of bodies are stamped out by dies separately and welded to other
sections for forming the steel bodies. The body of the car is made up of many sheet metal panels.
Each panel is so designed to give enough strength and rigidity to the assembled unit. At critical
locations of the body, the reinforcing members are incorporated at proper interspaces.

The main skeleton of a car body has two types of panels: 1. Outer panel. 2. Inner panel.
The outside panels provide the shape of the car body whereas the inner panels reinforce the
shell of the body. The various curved shapes are given to outer panels to provide the strength to
panels. The inner panels provide mounting locations for various trim panels and connecting
assemblies. These two panels are welded together to pillars and rails so as to form the skeleton
of the car body.

Materials for Body Construction:

The materials used for construction of various parts of the body are steel, wood, plastics,
toughened glass and aluminium. In earlier days, wooden bodies were used for construction. But
now-a-days, steel is mainly used for body construction because of low cost and easy to
manufacture. Wooden bodies require a separate steel chassis frame to carry the load. The body
structure was heavy. Further, wooden bodies are flexed considerably and hence, they have
shorter life. Initial cost is also high. Therefore, these bodies become obsolescence now-a-days.
Sheet metal is widely used for body construction. It has high stiffness which results
negligible non-flexing and hence, it has longer life. Its initial cost is also less. Aluminium has also
been used by some manufactures because of its good formability, light in weight and more
resistance to corrosion qualities. But, its main disadvantage is lesser stiffness and rigidity.
Phun day, plastic bodies are popular, Thermoplastics are quite often used for many
componems such as boot covers, grills etc, whereas thermosetting plastics are mainly used for
body shells. The most widely used thermosetting plastic is glass fibre reinforced resin This
material can be moulded to any shape easily. The resulting structure is of light weight. The latest
type of plastics used for body construction is carbon fibre reinforced plastics. It is stronger than
steel and also weightless but the cost is very high.
Wind screen and window panels are made by toughened glass. As already meritioned in
the previous section, it has a special property when broken. It does not form sharp edges or
pieces. All broken pieces are in the form of rounded granules which do not cause injury. There
are two different types of safety glasses, namely, laminated safety glass and tempered safety
glass. Laminated safety glass consists of two layers of glass bonded together with the help of
another inner layer of vinyl transparent plastic under heat and pressure. When this glass is
shattered by impact, the centre layer of plastic holds the broken pieces of glass together and
thus, it is not allowing them to fly. These glasses are generally used for windscreen of the vehicle.
The tempered safety glans is made from a single piece of case- hardened or heat-treated glass.
Initially, it is cut to the required shape and then heat-treated until it becomes soft. Then it is
blasted with cold air to the outer surface to create tension between inner soft and outer ard
surface. Thus, it becomes five times harder than ordinary glass. These glasses are used for side or
rear windows