VEHICLE STRUCTURE AND ENGINES
TYPES OF AUTOMOBILES:
Automobiles can be classified with respect to different purposes which are as follows:
(i) With respect to the purpose:
(a) Passenger vehicles. Examples: Car, Bus, Jeep, Scooter,
Mopeds, Motor cycle.
(b) Goods carriers. Examples: Trucks, Lorry’s.
(ii) With respect to the fuel used
(a) Petrol vehicles
(b) Diesel vehicles
(c) Gas vehicles
(d) Electric vehicle
(e) Solar vehicle
(iii) With respect to capacity:
(a) Heavy Transport vehicle or Heavy Motor vehicles.
Example: Bus, Lorries, Trucks, Tractors.
(b) Light transport vehicle or light motor vehicles.
Example: Car, Scooter, Mopeds, Motor cycles, Jeeps.
(iv) With respect to the number of wheels:
(a) Two wheelers. Examples: Scooters, Mopeds.
(b) Four wheelers. Examples: Car, Jeep, Buses, Trucks,
(c) Three wheelers. Examples: Auto, Tempos
(d) Six wheelers. Example: Heavy trucks.
(v) With respect to tile drive of the vehicle:
(a) Single wheel drive vehicles.
(b) Two wheel drive vehicles.
(c) Four wheel drive vehicles
(d) Six wheel drive vehicles.
(vi) With respect to the side of drive:
(b) Left hand drive. Example: Most of the American, UAE vehicles.
(C) Right hand drive. Example: Most of the Indian vehicles.
(vii} With respect to transmission:
(b) Conventional. Example: Most of Indian vehicles.
(c) Semi-automatic. Example: Most of British vehicles.
(d) Automatic. Examples: American vehicles.
(viii) With respect to their construction:
(a) Single unit vehicles.
(b) Articulated vehicles and tractors.
A general classification of the automobiles is shown schematically
in Figure 1.2.
1. Before invention of automobile, the most common type of vehicle used in our country was
bullock cart. Now-a-days, we are also using bullock cart in rural areas. It is better to understand
the construction of bullock cart before discussing with automobile. Figure 1.3 shows the bullock
2. A bullock cart consists of the following main parts:
Frame (ii) Wheels and axle (iii) Yoke (iv) Body or superstructure and platform.
3. These parts can be divided into the following two main portions.
Machine portion (ii) Carriage portion
4. Machine portion consists of a frame in which wheels are attached through the axle. A yoke is
fixed at the front of the frame through which the cart is pulled by bullocks.
5. The carriage portion consists of platform and body which is mounted over the frames. The
platform consists of two long beam connected by cross members. The load or goods to be carried
by this portion and the total load are borne by the frame.
6. The basic construction of automobile is similar to that of a cart. An automobile also consists of
machine portion and carriage portion similar to a cart. The difference between a cart and an
automobile being that cart is a simple vehicle whereas automobile is a self-propelled vehicle.
A vehicle consists of engine to drive the vehicle. In addition to that, an automobile also consists
of power transmission systems such as clutch,
gear box, propeller shaft, universal joints,
7. Automobile is also provided with steering for
directional control, acceleration for speed control
and brakes for stopping purposes. The speed of
the cart is very slow as compared to the
automobile. Due to this fact, the automobile is
subjected to more shocks which in turn put more
strains on the frame. Therefore, the automobile is
needed robust frame and shock absorbers to bear
all stresses and strains.
8. The axle is not directly fitted with the frame in the automobile. It is suspended with the frame
through strong springs. In order to arrest shocks and save the passengers from jerks and jolts due
to rough road condition, shock absorbers are provided.
9. Figure 1.4 shows the layout of a car. It consists of an engine which is located at the front of the
vehicles followed by transmission systems. The radiator is located in front of the engine.
10. Various other parts of the vehicle shown in the Figure 1.4 are generator, starter, steering, clutch,
rear axle, differential, universal joint, wheel, tyres, body, lamp etc
11. The power developed by the engine is transmitted to the rear wheel through clutch, gearbox,
propeller shaft, universal joint, and, differential. Lamps are provided with the automobile so that
these could be driven safely during night hours. Horn is provided for making warning sound to
the other road users.
12. The body or superstructure is built upto fulfill the requirements or trends of the passenger. Brake
is provided to the vehicle to stop or slow down the speed whenever required. Fuel tank is
provided to store the required amount of fuel. Radiator is provided for cooling the engine and
related parts of the vehicle.
To construct any automobile, chassis is the basic requirement. Chassis is a French term and was initially
used to denote the frame or main structure of a vehicle. It is now extensively used in complex vehicles
except the body. A vehicle without body is called a chassis. Main Components of Chassis
2. Front suspension
3. Steering mechanism
4. Engine, clutch and gear box
6. Propeller shaft
8. Rear and front springs and shock absorber
9. Differential unit
10. Universal joint
11. Brakes and braking systems
12. Storage battery
13. Fuel tank
14. Electrical systems
Layout of Chassis:
Figure 1.5 shows the layout of the chassis. It shows that
the engine is located at the front end of the vehicle. It is
connected to the gearbox through clutch. The drive of the
engine can be connected or disconnected from the gearbox by
the driver with the help of clutch pedal.
From the gearbox, the power is transmitted to the differential
through propeller shaft and universal joint and finally to the
wheels via rear axles. Radiator is placed in front of the
Classification of Chassis:
The chassis can be classified on the following basis:
1. According to the fining of engine:
(a) Full-forward (b) Semi-forward
(c) Bus chassis (d) Engine at back
(e) Engine at centre
a) In full-forward chassis, the engine is fitted outside
the driver cabin or seat. Example: Cars, Mahindra
b) In semi-forward chassis, a half portion of the engine
is exactly in the driver's cabin whereas the other half
is in front but outside the driver's cabin.
Example: Tata SE series of vehicles.
c) In bus chassis, 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, Trucks. In most of the vehicles, the engine is
fitted in front portion of the chassis. The drive is given
to front wheels only. Example: Matador vehicles.
d) In some vehicles, the engine is fitted in the back
portion of the chassis. Example: Volkswagen cars,
Leyland bus of England.
e) 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 tile number of wheels fitted in the vehicles and tile 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
Characteristics of Good Chassis:
For good chassis design and its good performances, it must have the following characteristics:
1. Fast pickup
6. Ease of control
9. Power accessibility
10. Economy of operation
11. Low centre of gravity
13. Load clearance
14. Braking ability
15. Good springing
16.Simplicity of lubrication
The frame is the main part of the chassis. It is the backbone of the vehicle. All other parts of the
chassis are mounted on the frame. It is the rigid structure that forms a skeleton to hold all the major parts
together. At the front end of the frame, the engine is mounted. The engine inturn is connected to the clutch
and transmission unit to form a complete power assembly. The frame is supported by the wheel and tyre
assembly. Some part of the steering system is connected to the frame and remaining to the body. The fuel
tank is fastened to the rear end of the frame.
Functions of the Frame
1. To form the base for mounting engine and transmission systems.
2. To withstand the engine and transmission thrust and torque stresses as well as accelerating and
3. To accommodate suspension system.
4. To carry the other parts of the vehicle and its passengers.
5. To resist the effect of centrifugal forces when cornering a curve.
6. To withstand bending and twisting stresses due to the fluctuating or rear and front axle.
Requirements of Good Frame:
It must be strong, light and designed in such a way that it may withstand the shock blows, twists,
vibrations and other strains to which it is subjected to the road conditions.
It should also resist the distorting force such as:
a) Weight of the components and passengers causing a sagging effect due to bending action.
b) Horizontal forces provided by road irregularities.
c) Upward twisting forces caused by road shocks to provide a torsional effect.
1. In order to provide a good resistance to bending and
torsional effect, the frame sections are made of proper
forms. A typical passenger car frame is shown in
Figure 1.7. There are three common types of frame
sections i.e., channel, tubular and box. These are
made from cold rolled open earth steel or heat-treated
2. Channel section provides good resistance to bending
but it is poor in torsion while tubular section provides
good resistance to torsion and poor resistance to
bending. The box sections are comparatively resistant
to bending and torsion. These sections are shown in
3. The frame is narrow at the front end because of short
turning radius of front wheels. It is widening out at
the rear end to provide a bigger space for body.
4. The rear and front of the frame are curved upward to
accommodate the movement of the axle due to
springing and also kept the chassis height as low.
It also avoids impact due to the rear axle
bouncing. Figure1.9 shows the simplified diagram
of the frame. It consists of two longitudinal or side
members of channel section.
5. The side members are braced by a number of
cross members of channel or tubular section. In
conventional design, the cross members are at
right angles to side members as shown in Figure
1.9. Several modern chassis frame have cross
members that cross in the form of 'X' between
the side members as shown in Figure 1.10. The
brackets are provided to connect the springs and
support running boards. If necessary, more
brackets are provided to support the engine, gear
6. The engine, clutch and gearbox are bolted
together to form one rigid assembly. It is
mounted usually on the front end of the frame
by means of rubber pads to withstand engine
Load on Chassis Frame
A chassis frame is subjected to the following loads:
1. Loads of short duration:
When the vehicle is crossing a broken patch of road, it is acted upon by heavy and suddenly applied
loads of short duration. This load results in longitudinal torsion.
2. Combined loads of moment any duration:
These loads occur while negotiating curve, applying brakes and striking a pot hole.
3. Inertia loads:
These loads are applied on the vehicle due to application of brake for short period. This load tends to
bend the side members 10 the vertical plane.
4. Impact loads:
These loads are applied during collision of vehicle with another object. It results in a general collapse.
5. Load due to road camber:
Load due to road camber, side wind, and cornering force while taking a turn. It results in lateral
bending of side members.
6. Load due to wheel impact:
Load due to wheel impact with road obstacles may cause that particular wheel to remain obstructed
while the other wheel tends to move forward. It will tend to distort the frame to parallelogram shape.
7. Static loads:
Loads due to chassis parts such as engine, steering, gearbox, fuel tank, body etc. are constantly acting
on the frame.
The load of the vehicle which is loaded beyond the specified design load is known as overloads.
Materials for Frame:
The various steels used for conventional pressed frame are mild steel sheet, carbon steel sheet and
nickel alloy steel sheet. The composition of sheet nickel alloy steel is given as follows:
Carbon -0.25 to 0.35%
Silicon- 0.30% (Maximum)
Manganese -0.35 to 0.75%
Types of Frame
There are three types of chassis frame construction as follows.
I. Conventional frame construction
2. Semi-integral frame construction
3. Integral or Frameless construction
1. Conventional frame construction:
1. This type of frame is also called as non-load carrying frame. This frame is shown in Figure 1.7.
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.
2. 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.
3. 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 1.11 shows a
dismantled view of conventional chassis frame and body
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:
1. This type of construction is also called as chassis less,
unitary or monocoque construction. This is now-a-days
used in passenger cars. This construction provides a stiff
light construction particularly suitable for mass-produced
vehicles. In this type of construction, there 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
2. 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.
3. 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.
4. 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. Figures 1.12, 1.13, 1.14and 1.15 are
shown in different types of integral construction car and bus.
1. The basic form of the modern automobile body is older horse driver carriage. They have single
seat type body construction which provides very little 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 from weather.
2. Body is the super-structure for all vehicles. It may either be constructed separately and bolted to
the chassis or manufactured integral with the chassis (i.e. Frameless construction). The chassis
and the body make the complete vehicle.
3. A body consists of windows and doors, 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 about 40% of total weight of the car and about 60 to 70% of total weight of
buses. Therefore, reduction in body weight is important.
2. If we reduce the weight of the body it will also improve the fuel economy· (i.e. mileage).
3. The body of the vehicle determines its aerodynamic characteristics. Better aerodynamic structure
leads to fuel economy at high speeds and stability in cross winds. The positive pressure on 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 pleasant
appeal and style for the customer.
Requirements of the Vehicle Body:
The vehicle body should fulfill the following requirements.
1. It must be strong enough to withstand all types of forces acting on the vehicle. The forces are
including the weight of the car, inertia, luggage, braking and cornering forces.
2. Stresses induced in the body should be distributed evenly to all portions.
3. Weight of the body should be as minimum as possible.
4. It should be able to cope with impact loads of reasonable magnitude.
5. It should have reasonable fatigue life.
6. It must provide adequate space for both the passenger 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 such that the air drag is minimum
13. It is easy to manufacture as well as cheap in cost.
14. It should be designed in such a way that the passengers and the luggage are protected from
15. It should give peel 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
1. Car 2. Straight truck 3. Truck - half body type
4. Truck-platform type 5. Tractor
6. Tractor with articulated trailer 7. Tanker
8. Dumper truck 9. Delivery van
10. Station wagon 11. Pick-up 12. Jeep 13. Buses
14. Mini-buses 15. Three wheeler (i.e., Auto)
1. The salient features of the car body are four doors,
pillerless frame, two front seats with two extra seats at
back, partition between driver and passengers, luggage
space as a continuation of passenger compartment, folding
roof with windup windows, sliding roof and folded flat
windscreen. The car bodies have great resistance to wind.
2. For high-speed vehicles, 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.
3. Straight truck vehicle bodies are constructed into two
parts. One is driver cabin and other goods carriage. Goods
carriage is closed type with particular standard height.
These vehicles are used to carry the goods which are
affected by the weather conditions. Example: Vegetables,
sugar, rice, sea foods etc.
4. Truck half body is having 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. Truck platform type has also a separate driver
cabin. Its goods carriage is platform type. It usually carries goods such as Iron billets, barrels,
concrete slabs etc.
5. Tractor consists of very 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 1.16 shows
the above types of vehicle body arrangement. It may be open type or 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.
6. 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 fluids and a drain cock at the bottom to drain the fluid.
7. 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. For other
types, figure itself illustrates the type of body construction and its intended purpose.
Body construction and its components:
1. 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 the 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.
2. The various components of car body are body, sheets, front and rear doors, front panel, roof
panel, floor panel with engine beams, wheel arches, bonnet, wind screen piller, wind screen front
and rear window, front and rear bumper, cowl assembly, seats, hood etc. These components are
schematically shown in Figure1.17.
3. All steel sections of bodies are stamped out by dies separately and welded to other sections for
forming all 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 the critical locations
of the body, the reinforcing members are
incorporated at proper interspaces.
4. The main skeleton of the 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 the panels. The inner panels
provide mounting locations for the various trim
panels and connecting assemblies. These two panels
are welded together and to the pillars and rails so as
to form the skeleton of the car body. Initially, the
floor of the car body is assembled and then pillars,
rails and panels are welded in order to form the
complete car body. The floor is made up of 3 pressed steel panels such as front, centre and rear
5. Each unit is so designed that it gives a lower profile
and the car accommodates more passengers. In order
to give additional strength, rigidity and prevent
excessive vibration, metal strips have been welded
at different places of the floor panel. Then rear
wheel houses inner panels and rocker panels are
welded to the floor. The wheel house panel is
welded to the floor in such a way that it gives
sufficient clearance for the up and down movement
of the wheels while running a car on the road. The
box shaped rocker panels which are fixed to the
sides of the floor provides added strength to the
floor panel. The cowl assembly or the front portion of
the car is made up of many smaller panel stampings
of steel sheet metal as shown in Figure 1.20. The
wind-shield opening frame accommodates the front
glass which is curved in shape in many cars.
6. The top outer cowl panel is sometimes vented to allow
the fresh air to enter into the car. The dashboard panel
accommodates different warning and indicating devices
required to operate the car. The instrument panel is
usually welded to the cowl but in some design, it is also
bolted to the cowl. The pillars on the sides of the cowl
are used for fastening the front door hinges and cowl
side panels. The fire wall of the cowl assembly is the
sheet metal panel which separates the front passenger
space from the engine space. This wall is insulated in
such a way that the engine heat and noise are prevented
from entering into the passenger space. Usually, the
cowl assembly is welded to the rocker panel and floor
7. The Centre pillar supports the rear doors and hinges. It
also supports the sticker plates of the front doors. The
roof rails and centre pillars are usually of box section. It
gives maximum strength to the body. Drip mountings
are added to the side rails of the roof panel. The drip
mountings are U shaped channel. It is used to catch and
direct the water of the roof to the back of the car during
raining. The roof panel is welded to the top side rails.
The rear window and front windshield frames are
attached to the roof panel by spot welding.
8. The rear quarter panels are welded to the rear wheel
house panel, the floor panel and the rear of the rocker
panel. The trunk lid provides cover for the trunk
compartment. It is attached to the body with the help of
hinges as shown in Figure 1.24. In order to prevent the
water and dust to enter into the compartment, a rubber
weather strip is provided. Locking arrangement is also
provided for the rear compartment.
9. Engine compartment is formed by assembling different
sheet metal panels. This assembly covers the front wheels
and therefore it prevents the dirt, mud, snow etc. being
thrown off by the front tyres on the engine and the body of
the car. The radiator support is provided to support the
radiator by means of bolt. A stone shield is bolted to the
radiator support and the fenders. It prevents stricking of
small flying stones on to the radiator grills and radiator and
thus it avoids their damage. The two tenders which cover
the front wheels are connected by the radiator support.
10. The arrangement of engine hood is shown in Figure 1.25. It is
constructed in the same manner as the trunk lid. It has inner and
outer panels. The inner panel acts as the reinforcement to the
engine hood. It provides mounting locations for the hood lock
and hinges. The outer panel gives the shape to the body. The
hood is attached to the car body by means of hinges.
11. One of the most important components inside the car body is a
seat. The seats of the car are of various types such as folding
back, bucket or rigid. The seats of the present day cars are
generally of the bucket type. The seats are mounted on rails
which make them adjustable. The back can also be tilted in the
convenient position and they are also provided with head rest
for safety in case of accident.
12. Present day cars use four doors, two in front and two in rear.
The front doors are hinged on front pillars whereas rear doors
are hinged on centre pillars. Each door is provided with a check arm consisting' of an articulated
plate secured on pillar and sliding into a slot in door. The
rubber weather strips are bonded with a special compound
around the doors.
13. Each the door consists of door handle, window, window glass
regulator crank, arm rest, drop glass panel as shown in Figure
1.27. In modern cars, five doors are provided. Fifth door is used
as a trunk lid here. The glasses used in cars, buses and trucks
are specially designed in such a way that it does not form sharp
edges when broken.
14. But in ordinary glass, used for house window will form sharp
edges when it is broken. The special glass used in automobiles
prevents the passenger seriously injured in case of any accident.
15. Bumpers are provided at the front and rear end of the car. These are used to protect the front end
and rear end of the car from damage in case of the light collisions. They are manufactured by
heavy gauge steel sheet. It is of channel section with the open side turned inwards. It is bolted or
riveted to the ends of the longitudinal members of the car frame or front body rails.
Materials for body construction:
1. The materials used for construction of various parts of the body are steel, wood, plastics,
toughened glass; aluminium. In earlier days, wooden bodies were used for construction. But nowa-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 short 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 in negligible non-flexing and hence
a 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.
2. Present day, plastic bodies are popular. Thermoplastics are quite often used for many components
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
weightless. But the cost is very high.
3. Wind screen and window panels are made by toughened glass. As already mentioned in the
previous section, it has a special property when broken, it does not form sharp edges or pieces.
All the broken pieces are in the form of rounded granules which do not cause injury.
4. There are two different types of safety glasses, namely, laminated safety glass ad 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 thus not
allowing them to fly. These glasses are generally used for windscreen of the vehicle. The
tempered safety glass is made from a single piece of casehardened 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 hard surface. Thus, it
becomes five times harder than ordinary glass. When it breaks, it will form granular particles
which will not cause injury. These glasses are used to side or rear windows.
RESISTANCES TO VEHICLE MOTION:
A moving vehicle has to overcome the following resistances:
1. Air resistance:
It is the resistance offered by air to the vehicle motion. It depends upon the following factors:
(1) Size of vehicle
(4) Wind velocity
2. Gradient resistances:
It is the component of the vehicle's weight which is parallel to the plane of the road.
This component remains constant but independent of the vehicle's speed.
3. Miscellaneous resistance:
Other resistances such as rolling resistances depend upon the following parameters:
(1) Road characteristics (2) Tyre characteristics
(3) Vehicle weight
(4) Vehicle speed.
AERODYNAMICS OF AUTOMOBILE BODY:
Aero means air, dynamics means motion. Aerodynamics is, therefore, the behaviour of air in motion
relative to the vehicle body. The body design pertaining to shape and size of the vehicle must hav
acceptable aerodynamic characteristics. The following are various forces acting on the vehicle:
(i) Drag force (Fx):
1. Force of air drag is acting in the direction of vehicle motion with the wind acting along the
longitudinal direction axis. This force is also called air resistance.
2. This offers resistance to the motion of the vehicle. The various factors, such as profile drag (57%
of total vehicle), induced drag (8%), and skin friction (10%), interference drag (15%) and cooling
and ventilation system drag (10%) affects the total drag. The total aerodynamic drag can be
calculated by using the equation.
Cx- drag coefficient
ρ- Density of air
V - Velocity of air
A - Projected area of the vehicle viewed from front.
3. The profile of the body should be carefully selected to avoid. The drag force stream lines of air
flow around the body should be continuous and separation of the boundary layer should be
avoided. Skin friction drag can be reduced by using very smooth and well-polished body.
Avoiding excessive projections such as door handles, mirrors, aerials helps in reducing drag.
(ii) Lift force (Fz):
1. Aerodynamic lift force is the vertical component of the resultant force caused by the pressure
distribution on the body. Lift force can be calculated by using the equation
CZ - drag coefficient
ρ - Density of air.
2. The aerodynamic lift will tend to reduce the pressure between the tyres and the ground which
causes loss of steering on the front axle and loss of traction on the rear axle.
(iii) Cross wind force (Fy):
Cross wind force is acting in the lateral direction, on the side of the vehicle. This is formed by the
asymmetric flow f air around the vehicle body. These forces are acting at the centre of pressure instead of
centre of gravity and hence cause moments as follows:
(i) Pitching moment (My) which caused by the drag
force Fx or lift force F, about Y axis. This moment
makes the rear wheels lift off the ground and further
reduces the available traction.
(ii) Yawing moment (Mz) which is caused by the cross
wind force Fy about Z axis.
(iii) Rolling moment (My) which is caused by the cross
wind force Fy about Z.
Figure 1.28 shows the forces and moment acting on the
Need For a Gearbox:
1. When a vehicle is running, various resistances oppose it. In order to keep the vehicles moving at a
uniform speed, a driving force or tractive effort is equal to the sum of all the opposing forces. If
the tractive effort increases the total opposing resistance, the excess tractive effort will accelerate
the vehicle. If the tractive effort is less than the total resistances, the excess of the resistances will
lower down the speed of the vehicle.
2. When a vehicle starts to move from the rest, it will need more force or high torque at the time of
starting and also for hill climbing, accelerating or carrying heavy loads due to various opposing
resistances. It is done for obtaining uniform speed and driving force or tractive force. These two
forces should be exactly equal to the sum of opposing forces. It can be achieved by running the
engine at high speed and wheels at low speeds. After starting the vehicle, it is moving due to
momentum gained by the weight of vehicle.
3. The same force or torque need not require to keep the vehicle in moving. So, the speed of the
road wheels has to be progressively increased when the vehicle gains speed gradually. The
gearbox is mainly provided for high torque at the time of starting, hill climbing, acceleration and
pulling a load. It can be achieved by a set of gears which are enclosed in a gearbox and gear
Purposes of the gearbox:
1. It helps the engine to be disconnected from the driving wheels.
2. It helps the running engine to be connected to the driving wheel smoothly and without shock.
3. It provides the leverage between the engine and the driving wheels to be varied.
4. It helps to reduce the engine speed in the ratio of 4:1 in case of passenger cars and in a greater ratio
in case of Lorries.
5. It helps the turning of the drive round through 90°.
6. It helps the driving wheels to be driven at different speeds.
7. It gives the relative movement between the engine and the driving wheels due to flexing of the
1. An engine is a prime mover. It is used to convert the heat energy obtained from fuel into useful
mechanical work. It is heart of the automobile. It is one of the important and biggest units in the
automobile. If it fails to work, the vehicle is dead.
2. Automobile engines are classified in many different ways. All automotive engines are of the
internal combustion type. The Internal Combustion Engine (I.C. engine) is a heat engine that
converts chemical energy in a fuel into mechanical energy. Chemical energy of a fuel is first
converted into thermal energy by means of combustion or oxidation with air inside the engine.
This thermal energy is again converted into useful work through mechanical mechanism of the
engine. Most of the I.C. engines are reciprocating engines having pistons that reciprocate back
and forth in cylinders internally within the engine.
I.C. engines are classified on the basis of:
(i) Type of ignition:
a. Spark Ignition engines (S.I. engines)
b. Compression Ignition engines (C.I. engines)
(ii) Cycle of operation (Thermodynamics cycle):
a. Otto cycle engine
b. Diesel cycle engine
c. Dual cycle engine
(iii) Engine cycle per stroke:
a. Four stroke cycle
b. Two stroke cycle
(iv) Types of fuel used:
a. Petrol engine b. Diesel engine c. Gas engine
(v) Method of cooling:
a. Air-cooled engines
b. Water-cooled engines.
(vi) Number of cylinders:
a. Single cylinder engine
c. Three cylinder engine
e. Six cylinder engine
g. Twelve cylinder engine
b. Two cylinder engine
d. Four cylinder engine
f. Eight cylinder engine
h. sixteen cylinder engine
(vii) Valve location:
a. Square engine b. L-head engine c. I-head engine d. F-head engine e. T-head engine.
(viii)Arrangement of cylinders:
a. Vertical engine b. Horizontal engine
e. Opposed cylinder engine
(ix) Speed of the engine:
a. Low speed engine
c. Radial engine
d. V-engine engine
b. Medium speed engine c. High speed engine
(x) Types of lubrication system:
a. Wet sump lubrication system
b. Dry sump lubrication system
(xi) Method of governing:
a. Quantity governing b. Quality governing
(xii) Field of application:
a. Automobile, truck, bus
e. Aircraft engine.
c. Hit and Miss governing
b. Locomotive engine c. Stationary engine d. Marine engine
Classification based on number of cylinders:
(i) Single Cylinder Engine:
1. It has only one cylinder. A single cylinder engines are generally used in light motor vehicles such
as mopeds, motor cycles, and scooters. Maximum size of the cylinder is restricted to 250-300cc.
Although a single cylinder engine seems to be the most popular choice due to fewer parts to
manufacture and maintain, yet the disadvantages are more than advantages.
2. Since, it requires heavy construction for more power due to higher unbalanced forces. Also
weight increases at a greater rate in comparison to the power providing a lower power to weight
ratio. A single cylinder engine may be two stroke or four stroke cycle engine.
(ii) Multi cylinder engines:
1. Multi cylinder engine has two, three, four, six, eight, twelve or sixteen cylinders which are
arranged in many different ways. As compared to single cylinder engine, the unbalanced forces
due to reciprocating parts are much lesser as the number of cylinders increases. Also more power
can be developed with less weight to power ratio.
2. Two cylinder engines have two cylinders which are arranged in V-type, Inline or opposed manner.
The range of size of the twin cylinder engine varies from 500 to 1000cc for heavy vehicles while
and for three wheelers it varies from 600 to 800cc for small cars. The two cylinder engines are
used in Fiat (101model) having 500cc.
3. Three cylinder engines are confined to only two strokes. They produce power impulse every 1200
of crank rotation indicating that the torque produced is comparatively smooth. In case of three
cylinder two stroke engines, three power strokes in one revolution of the crankshaft with firing
interval of 1200 take place.
4. Four cylinder engines have become increasingly popular in recent years. A basic reason is the
trend towards small, lightweight, fuel efficient cars. A 180° crankshaft arrangement is always
used. The balance of the four cylinder engines is not as good as the balance of the opposed twocylinder engines. But the torque is much more uniform. In these engines, two pairs of four
cylinders are moving in the opposite direction. The pairs move up and down together with each
cylinder being on a different stroke. In case of four cylinder four stroke engines, four power
strokes in two revolutions of the crankshaft with firing interval of 1800 are produced. The four
cylinders of this engine may be arranged inline, opposed, square four and Vee four resulting the
engines to be called as such, i.e. inline, opposed square four, and Vee four cylinder engines.
5. Some five cylinder automotive engines are being built. Mercedes produces a five-cylinder diesel
engine. Volkswagen has a five cylinder inline spark-ignition engine for a front-drive car.
6. Six-cylinder engines give a better dynamic balance and a more uniform torque than four-cylinder
engines. Most of the high powered as well as modern cars of the moderate powers are employing
the six cylinder engines. Though expensive and complicated these engines have much smoother,
more flexible and quiter running. It requires only a light flywheel due to the lower ratio of
maximum to mean torque. Six-cylinder engines are generally in-line engines built with 120°
crankshafts. Some of the important six-cylinder engines are Triumph, Vitesse, Jaguar car, B.M.C.
Morris, Austin, Chevrolet Corvoir engine etc.
7. The eight-cylinder engines have many advantages over six cylinder engines. They provide more
uniform torque and better acceleration while the balance is not very good. Eight cylinders can be
arranged in one long line or in two rows of four cylinders each inclined to one another. V-8
engines are almost universally in use. The Rolls Royce and Daimler car manufacturers are
producing different V-8 model engines. Three big manufactures of car i.e., Ford, Chrysler and
General Motors are employing V-8 engine as standard engines.
8. Twelve and sixteen-cylinder engines have been used in buses,
trucks and industrial plants. The cylinders are mostly of V-type.
Sometimes, they are in three banks of W-type or four bank of Xtype. Some of the passenger cars made with twelve-cylinder
engine are the Ferrari, the Jaguar and the Maserati.
Classification based on arrangement of cylinders:
1. The cylinders can be arranged in several ways such as vertical, horizontal, inline, V-type, flat or
pancake, radial. Single cylinder engines can be arranged in either vertical or horizontal as shown
in Figure l.29. Two cylinder engines can be arranged in three
ways, namely, inline vertical, opposed cylinder and V-type. In
inline engine, the cylinders are arranged in side-by-side, one row
and parallel to each other as shown in Figure l.30 (a). The
cylinders are generally placed in vertical.
2. In V-type engines (Figure 1.30 (b), the cylinders are arranged in
two rows. The two rows are set at an angle of 60° or 90° to each
3. This arrangement is more compact and economical than inline
type. In opposed cylinder arrangement, the two cylinders are
arranged horizontally opposite to each other. The piston and
connecting rod movements are identical. The crankshaft and
cam shafts are positioned between the two cylinders as shown in
4. In Three cylinder engines, cylinders are arranged vertically in
line with the crankpins arranged at 120° intervals around the
shaft. The crank case serves as intake and pre-compression
chamber. The crank case is divided into three compartments.
Each sealed off section of the crank case is provided to one of
the cylinders. Figure 1.31 Shows three cylinder inline four
stroke cycle engine.
5. In four cylinder engine, the cylinders may be arranged inline,
opposed, square four or flat 4 and V-four manner. In inline four
cylinder engines, piston 1 and 4 are always moving in pair
opposite to the direction of piston pair 2 and 3 as shown in
Figure 1.32. In this arrangement, firing interval is regular. Since,
this engine is similar to two, two-cylinder engines arranged end
to end, the overall balance is very good due to the two rocking
couples by neutralizing each other, the engine is not completely
balanced and a secondary vibration is produced. This can be
reduced by using light weight pistons and connecting rods.
6. In opposed four cylinder engines, the cylinders are arranged
horizontally in pairs on each side of a flat four crankshaft. Here,
the engine balance is superior to that of the inline engine. In this
engine, one power stroke is occurred in every 1800 of crankshaft
rotation. The torque is also smooth.
7. In V-type engines, the cylinders are arranged in two rows. The
two rows are set at an angle of 600 or 900 to each other. This
arrangement is more compact and economical than inline type.
In opposed cylinder arrangement, the two cylinders are arranged
horizontally opposite to each other. The piston and connecting
rod movements are identical. The crankshaft and cam shafts are
positioned between the two cylinders as shown in Figure 1.33
8. In Three cylinder engines, cylinders are arranged vertically
inline with the crankpins arranged at 1200 intervals around the shaft. The crank case serves as
intake and pre-compression chamber. The crank case is
divided into three compartments. Each sealed off section of the
crank case is provided to one of the cylinders. Figure 1.34
shows three cylinder inline four stroke cycle engine.
9. In four cylinder engine, the cylinders may be arranged inline,
opposed, square four or flat 4 and V-four manner. In inline
four cylinder engines, piston 1 and 4 are always moving in pair
opposite to the direction of piston pair 2 and 3 as shown in
Figure 1.35. In this arrangement, firing interval is regular.
Since, this engine is similar to two, two-cylinder engines
arranged end to end, the overall balance is very good due to
the two rocking couples by neutralizing each other.
10. In opposed four cylinder engines, the cylinders are arranged
horizontally in pairs on each side of a flat four crankshaft.
Here, the engine balance is superior to that of the inline
engine. In this engine, one power stroke is occurred in every
180° of crankshaft rotation. The torque is also smooth. In Vtype engines, the cylinders are arranged in two rows. The two
rows are set at an angle of 60°or 90° to each other. This
arrangement is more compact and economical than inline type.
In opposed cylinder arrangement, the two cylinders are
arranged horizontally opposite to each other. The piston and
connecting rod movements are identical arrangement is found
in air cooled Volkswagen and water cooled Jewett's Javelin.
11. V-four engines have cylinders arranged in two rows of two
cylinders each. The two rows are set at an angle (preferably 60°) to each other. It is similar to two
cylinder V engines having a common crank shaft. The engine has a firing order of 1, 3, 4, and 2
with firing interval of
180°. This engine is balanced by using
a balance shaft
that runs in a
direction opposite to
12. The general arrangement of cylinders is shown in Figure 1.37. Six cylinder engines are generally
inline engines built with 120° crank shaft. The arrangement M crank shaft is as shown in Figure
1.38. This arrangement is such that the crank throws of cylinders 1 and 6, 2 and 5, and 3 and 4 are
in the same revolution of the crankshaft. The possible firing order for good distributions of fuel is
1-5-3-6-2-4 and 1-4-2-6-3-5.
13. Six cylinder V-engines are very important engines which are built to have a bank of three
cylinders set at an angle or at V to each other. Same crank pin is used to attach connecting rods
from opposing cylinders in two banks. The arrangement of
cylinders in V-6 engine is shown in Figure 1.39. Opposed sixcylinder engines are also available. The arrangement of cylinders
is in same manner as that of four cylinder opposed engine. Three
cylinders are placed in each side of the two rows but opposite to
14. Eight cylinder inline engines provide a long engine with long
and expensive crank and camshaft. The interval of explosions of
this engine is 90°. The crank throws for different pairs of
cylinders are in the same radial plane such as cylinders 1 and 8,
cylinders 2 and 7, 3 and 6, and 4 and 5.
15. The firing order is 1-6-2-5-8-3-7-4 or 1-8-2-6-4-5- 3-7. The disadvantages of this engine are long
and expensive crankshaft, and its liability to torsional oscillation of the crankshaft. Eight cylinder
V-8engines employing two banks of four cylinders each at right angles have replaced the inline
eight-cylinder models in most of the higher power automobiles. The angel between the cylinder
rows in V-8 engine is kept usually 90°. These engines can operate smoothly and silently.
Advantages of V-8 engines over inline engines:
The main advantages of V-8 engines are summarized as follows:
1. It is the shortest of all the eight-cylinder engines other than radial engines. It is also lighter and
more rigid engine. The shorter engine provides more space for passenger on small wheel base.
2. It provides relatively a simple valve gear arranged both for the side valve or overhead valve type
engine enabling a single crankshaft to be located above the crank shaft for 90° angle arrangement
of the two cylinder banks.
3. It permits the use of intake manifolding that assures relatively even distribution of air-fuel
mixture to all cylinders since all cylinders are relatively close together.
4. Good engine balance can be obtained by suitable choice of crankshaft angles. Very good balance
would be resulted, if the two outer cranks at 900 to the parallel inner pairs and in the same plane
5. It is not affected by similar torsional vibrations as the in-line type.
6. Since, the carburetor and other parts are rested between the two rows of cylinders, it permits
lowering of the engine load line and thus a lower car profile.
7. Instead of an eight-throw as inline type, only a four throw crankshaft is used. In this case, same
crank pin is used for operating two connecting rods from opposite cylinders. This arrangement
provides even firing intervals between the cylinders.
Twelve cylinder engines were originally designed for aeroplanes. But certain cars such as Rolls Royse,
Daimler and Lincoln Zephyer are also used these engines. These engines consist of two sets of six
cylinder inline engines with each forming a bank V-inclined at 60° or 75°. They have common crankshaft
and camshaft with six sets of forked and plain connecting rods. The Italian Ferrari is the only car which is
being manufactured with a twelve-cylinder engine.
Sixteen-cylinder engines having two sets of straight light cylinders inclined at an angle of V have been
used in Cadillac cars. These engine have been perfectly balanced with top gear performance. The
cylinders arranged in two banks of eight cylinders each are inclined at 135°.
Radial engines are mostly used in aircraft.
1. These engines are air cooled and have cylinders arranged in a star form about the crankshaft axis.
The cylinders are radiating from a common centre similar to the spokes of the wheel. A common
crankpin is employed for all the connecting rods. To get uniform firing intervals, the cylinders
are odd in number such as 5, 7, 9 etc. These engines are compact with low weight per
horsepower and accessibility, simplicity of the single throw crank shaft and single cam ring for
operating the valves. But, they are not used in motor vehicles due to more frontal area and more
complicated exhaust pipe system.
Classification based on arrangement of valve:
(i) Square engine:
1. Engine which has same bore and stroke is called a square engine. Usually engines that have a
borezstroke ratio of 0.95 to 1.04 are referred as square engines.
2. A piston engine is oversquare or shortsroke if its cylinders have a greater bore than stroke. Since
a shorter stroke means less friction and ·less stress on the crankshaft. An oversquare engine is
generally more reliable, wears less, and can be run at a higher speed. In oversquare engines
power does not suffer, but low-speed torque does to some degree, since torque is relative to crank
throw. An Oversquare engine cannot have as high a compression ratio as a similar engine with a
lower bore/stroke ratio, and using -the same octane fuel. This causes the oversquare engine to
have poorer fuel economy, and somewhat poorer exhaust emissions. Engines can be modified by
being "destroked", shortening the stroke to increase maximum rpms and top-end horsepower, at
the expense of low-end torque.
3. Oversquare engines are lighter and shorter than similar undersquare engines along the direction
of piston travel, but they are wider in directions perpendicular to piston travel. As the length is
not a large problem, these engine types are highly favored by many manufacturers because of
their power and compact size.
4. A piston engine is undersquare or shortstroke if its cylinders have a smaller bore than stroke.
Since a longer stroke usually means greater friction, more stress on the crankshaft, and a smaller
bore means smaller valves which restricts gaseous exchange. An undersquare engine usually has
a lower redline than an oversquare one, but it may generate more low-end torque. In addition, a
long stroke or undersquare engine can have a higher compression ratio with the same octane fuel
compared to a similar displacement engine with a higher bore/stroke ratio. This also equals better
fuel economy and somewhat better emissions. An undersquare engine does not overheat as easily
as similar oversquare engine. Engines can be modified with a "stroker" crankshaft, which
increases an engine’s stroke from stock, increasing torque. Undersquare engines typically are
shorter in length, heavier, and taller than equivalent oversquare ones, which is one of the reasons
why this type of engine is not generally used.
(ii) L-head engine:
In this arrangement, all the valves are arranged in one line (except in case of V-8 engine) with the
intake and exhaust valves are arranged side by side. The combustion chamber and the cylinder are
arranged in the form of inverted 'L'. All valves can be operated by a single crankshaft. Figure 1.42 shows
1. One cam shaft is only required.
2. Height is reduced.
3. As the valves are arranged in one line, the removal of the cylinder
is quite easy for servicing.
4. It is more dependable.
1. More space for combustion chamber is required.
2. Knocking tendency is more than T-head engine.
3. Location of spark plug is difficult.
4. High compression ratio is not possible.
(iii) I-head engine:
In these engines, the cylinder head carries the valve. It is also called as
overhead valve engine. In case of inline engines, the valves are arranged in a
single row while the valves may be arranged in a single row or double row
in each bank in case of V-engines. All the valves are actuated by a single
1. A single camshaft actuates all valves.
2. Clearance volume is less. Hence, compression ratio can be increased
3. The spark plug can be located at centre.
4. Smooth operation can be obtained.
I. More valve mechanism parts are involved.
2. The cylinder head requires more cooling.
3. It is more complicated design.
4. The size of the inlet and exhaust valve is limited.
(iv) T-head engine:
It has the inlet valve on one side and the exhaust valve on the other side of
the cylinder. Thus, two earn shafts are required to operate them. The
combustion chamber and the cylinder form a letter '1". Generally, small
engines are made with T-head arrangement.
1. Unequal temperature occurs in the cylinder.
2. More power is wasted in operating two camshafts.
3. Cost and weight are more.
(v) F-head engine:
In this arrangement, inlet valves are located in the cylinder head and exhaust valves by the sides of
cylinders. These engines being combination of L-head and I-head engineers are known as F-head
engines. Both inlet and exhaust sets are driven from the same camshaft.
I. More turbulence is possible.
2. More speed is possible.
I. More space is required for the combustion chamber.
2. Location of spark plug is difficult.
3. Design of combustion chamber is difficult.
Classification based on methods of cooling:
(i) Air-cooled engines:
In these engines, the cylinders are usually mounted separately. They have
metal fins which provide a large surface area. This permits the engine heat
to be carried away from the cylinders. Air-cooled engines have shrouds which direct the airflow around
the cylinders for cooling. Air-cooling is generally provided in small one cylinder or two cylinder engines
such as mopeds, motor cycles, and scooters. Some of the earlier car models were air-cooled. Example:
(ii) Water Cooled engines:
Most of the present day engines are water cooled. These engines use a liquid i.e. water to take heat from
the engine. These engines have water jackets around the cylinders and combustion chambers. The water is
passed through all parts of the engine and takes away the heat from it and passed through the radiator for
cooling. In the radiator, water is cooled by passing air around the fined tube.
This engine was introduced by Felix Wankel in 1954. The engine works on ordinary Otto cycle. It is a
rotary combustion engine. The piston in this engine undergoes rotary motion. This engine has been
developed by Dr. Walter Froede of Germany for installation in NSU motor vehicles. This engine was
installed in two seater NSU spider sports car for the first time. Several automobile manufacturers in
various countries have obtained licenses and started the manufacture of Wankel rotary engine.
The engine rotor has three lobes. The rotor rotates in an eccentric pattern. The lobes are in contact with
the oval housing to form a tight seal. This seal compares with the seal formed by the piston rings against
the cylinder wall in a reciprocating engine. The rotor is mounted on the crankshaft through external and
internal gears. The rotor lobes A, Band C seal are placed tightly against the side of oval housing as shown
in Figure 1.46 (a). The rotor also has overshaped recesses which are shown as dashed lines. The oval
chamber not only revolves about its own centre but also a .circular path around the output shaft.
This engine has inlet and exhaust parts. The housing is surrounded by water jackets for cooling. When the
engine runs, the four cycles of operation will also take place around the rotor simultaneously. The
working of engine and its action during one complete rotation of the rotor are shown in Figure 1.46.
1. Intake process:
In Figure 1.46 (a), lobe A has passed the intake port, and the air fuel mixture is starting to enter (1). As the
rotor moves the space between lobes A and C will increase (2) as shown in Figure 1.46(b). This motion
produces vacuum, which causes the air fuel
mixture to enter. The air fuel mixture continues to
enter as the space between lobes A and Care
continued to increase in (3) of Figure 1.46 (c).
The lobe C starts to move past the intake port as
shown in Figure 1.46 (d). Further movement of
rotor carries lobe C past the intake port. So, the
air fuel mixture is sealed between lobes A and (C)
2. Compression process:
To understand this process, let us go back to
Figure 1.46 (a) again. Here the air fuel mixture
has been trapped between lobes and A and B at
(5). Further rotation of the rotor decreases the
space between lobes A and B at (6). By that time,
the rotor reaches the position shown in Figure
1.46 (c) and the space (7) is at a minimum. This
position is same as the TDC position of the piston
on the compression stroke in the reciprocating engine. Now, the spark plug fires and ignites the
3. Power or Expansion process:
Pressure exerted on the side of the rotor when the combustion takes place and this forces the rotor to
move around. This process is same as the power stroke of the reciprocating engine. The high pressure of
the burnt mixture in (8) forces the rotor around to position (9) again. Expansion continues to rotate the
rotor until the leading lobe passes through the exhaust port.
4. Exhaust process:
Then the burnt gases are exhausted from between the lobes as shown by (11) and (12) in Figure 1.46 (c)
and (d). As the rotor continues to rotate, the space between the lobes decreases and gases are exhausted.
This process is same as the exhaust stroke of the piston in the reciprocating engine. After this process, the
leading lobe passes the intake port, and the whole cycle is repeated. Note that, there are three lobes and
three spaces between the lobes. This means that there are three complete cycles of intake, compression,
power and exhaust going on at the same time. Thus, there are three power cycles for each revolution of
the rotor. The engine is delivering power almost continuously.
Wankel engine can have more than one rotor also. Units with a maximum of four rotors have been
produced. But most common has been the twin rotor Mazda engine.
1. Simple and cheaper in construction because of no more parts such as connecting rod, crank shaft, valve
2. Smaller in size, lighter in weight and more compact for the same output of reciprocating engine.
3. There is no balancing problem.
4. It produces more power per kg weight of engine.
5. Volumetric efficiency is very high.
6. Running cost is less.
1. Fuel consumption is more at low speed.
2. At lower speeds, the torque produced is less.
3. Frequent spark plug changes are required because of
ignition troubles are experienced with ordinary coil
4. Braking effect of the engine is far less.
5. The main problem in this engine is of sealing between
the rotor lobes, the rotor sides and the walls of the oval
6. Cylinder distortion may occur due to the close location
of inlet and exhaust ports.
1. Figure 1.47 shows the construction details of an
I.e. engine (Four stroke petrol engines). The main
components of a four stroke cycle engine are
cylinder, piston, connecting rod, piston rings,
cam shaft, crank shaft, crank case, inlet and
outlet valves, spark plug, cylinder head, push
rod, gudgeon or piston pin, rocker arm, cam
follower, valve spring, big end bearing, inlet port etc.
2. The piston reciprocates inside the cylinder. Piston rings are inserted in the circumferential
grooves of the piston. The cylinder and cylinder head are bolted together. The reciprocating
motion of the piston is converted into rotary motion of the crankshaft by means of a connecting
rod and crank. The small end of the connecting rod is connected to the piston by a gudgeon pin or
piston pin. The big end of the connecting rod is connected to the crank pin. Crank pin is a bearing
surface and it is rigidly fixed to the crankshaft. The crankshaft is mounted on the main bearing.
The main bearings are housed in the crankcase.
3. Camshaft is driven by the camshaft through timing gears. The camshaft actuates the inlet and
outlet valves. The valve springs are provided to bring back the valves in the closed position. The
oil sump containing lubricating oil is provided at the bottom of the crankcase. Lubricating oil is
circulated to the various parts of the engine from the oil sump. A spark plug is provided in petrol
engines to ignite the air fuel mixture in the engine cylinder. An injector is provided in diesel
engines to inject the fuel into hot compressed air during power stroke.
COMPONENTS OF I.C. ENGINE:
The following is a list of major components found in most of the reciprocating I.C. engines:
1. Cylinder block:
It is the main body of an engine which contains cylinders. The piston reciprocates inside the cylinder to
develop power. The cylinders are accurately finished to accommodate
pistons. The cylinder block also houses crank, crankshaft, piston and other
engine parts. During combustion, high pressure and temperature will be
developed inside the cylinder. Therefore, it should be made of material
which can resist high temperature and pressure.
It is made of grey cast iron or aluminium with steel sleeves. In water
cooled engines, the cylinder block is provided with water jackets for
circulation of cooling water as shown in Figure 1.48.
2. Cylinder head:
The cylinder head is bolted at the top of the cylinder block. It houses the
inlet and exhaust valves through which the charge is taken inside of the
cylinder and burnt gases are exhausted to the atmosphere from the
cylinder. It also contains spark plug hole or injector hole and cooling water jacket. The materials used for
cylinder heads are cast iron, aluminum alloy etc.
3. Crank case:
It may be cast integral with the cylinder block. Sometimes, it is cast separately and bolted to the cylinder
block. It supports crankshaft and camshaft with the help of bearings. Sometimes, the bottom of crankcase
may be used as oil sump. It is made of cast iron, aluminum alloys or alloy steels.
4. Oil sump or oil pair:
Oil sump is fitted at the bottom of crankcase by using gasket. It
contains lubricating oil. A drain plug is provided to the oil sump to
drain out the oil. It is made of pressed steel sheet.
5. Cylinder liners:
Inside the cylinder, the piston constantly is moving up and down
which cause will wear of cylinder. When the cylinder diameter is
increased beyond certain limit, we may have to discard the entire
cylinder block which is costly. To avoid earlier cylinder wear, a
separate liner which is in the form of sleeve is inserted into the
cylinder bore. Here, the wear will take place in the liner only which can be replaced easily when worn
out. There are two types of liners:
1. Wet liner: The liners are surrounded by cooling water as shown in Figure 1.49. It provides wearresisting surface for the piston to reciprocate. It also acts as a seal for the water jacket.
2. Dry liner: Dry liners have metal-to-metal contact with the cylinder block. They are not directly in
touch with cooling water. Linear material should withstand abrasive wear and corrosive wear. Chromium
plated mild steel tubes are used as liners.
It is a cylindrical shaped mass that reciprocates inside the cylinder.
The piston serves the following purposes:
It acts as a movable gas tight seal to keep the gases inside the
It transmits the force of explosion in the cylinder to the crankshaft
through connecting rod.
The top of the piston is called as crown and sides are called as
skirt. It has grooves to hold piston rings and oil ring. It is opened
at the bottom end and closed at the top. Sometimes, T-slots are
provided in the skirt to allow expansion.
Piston is made of cast iron, Aluminium alloy, chrome-Nickel
alloy, nickel-iron alloy and cast steel. They are manufactured
by casting or forging method.
7. Connecting rod:
It is used to connect the piston and crankshaft with the help of
bearing. It is usually steel forging of circular, rectangular, I, T
or H cross-section. Its small end is connected with the piston
by the piston pin and its big end is connected to the crank by
the crank pin. It has a passage for the transfer for lubricating
oil from the big end bearing to small end bearing.
The connecting rod must withstand heavy thrust. Hence, it must
have great strength and rigidity. They are generally made of
plain carbon steel, Aluminium alloy, and nickel alloy steels.
8. Piston rings:
They are used to maintain air tight sealing between piston and
cylinder to prevent gas leakages. Piston rings are fitted in the
grooves which are provided for them in the top portion of the
piston skirt. Two types of piston rings are used in a piston.
a) Compression rings:
These rings provide an effective seal for the high pressure gases
inside the cylinder. Each piston is provided with at least two
b) Oil rings:
These rings wipe off the excess oil from the cylinder walls. It
also returns this excess oil to the oil sump through the slots
provided in the rings. The materials used for piston rings are
cast iron, alloy cast iron containing silicon and manganese,
alloy steels etc. Piston rings are generally coated with chromium
9. Crank shaft:
It is used to convert reciprocating motion of the piston
into rotary motion. Big end of the connecting rod is
connected to crank shaft. It can be single crank type for
single cylinder engines and multiple crank type for multi
cylinder engine. The crankshaft is held in position by the
main bearings. There are minimum two bearings provided
to support the crankshaft. Figure 1.53 shows the cranks
shaft of a four-cylinder in-line engine. The counter
weights are provided to keep the system in perfect
balance. Crankshaft gear, vibration damper and fan belt pulley are connected to the front end of the
crankshaft. Flywheel is mounted at the rear end of the crankshaft. The material of the crankshaft should
be strong enough to resist heavy impact force of the piston. They are made from a hot billet steel, carbon
steel, nickel-chromium and other heat treated alloy steels.
The flywheel is heavy and perfectly balanced wheel usually connected to the rear end of the crankshaft.
Flywheel serves as an energy reservoir. It stores energy during power stroke and releases during other
strokes. Thus, it gives a constant output torque. It is usually made of cast iron or cast steel.
11. Cam Shaft:
It is used to convert rotary motion of the camshaft into
linear motion of the follower or lifter. Thus, it operates
the inlet and exhaust valves through rocker arms. It has
so many cams as the number of valves in an engine. An
additional cam is also provided to drive the fuel pump.
The camshaft rotates inside the plain bearings. It is
driven by crankshaft through chain or gear train. It is
rotated at half of the speed of the crankshaft. Figure
1.55 shows a tappet valve. Normally, valve contains
head (angular face ground 30° to 45°), face, stem and
spring retainer lock groove. The head of the inlet valve
is bigger than the head of the exhaust valve.
Inlet valve is made of plain nickel, nickel-chrome or chrome
molybdenum. The exhaust valve is subjected to more heat. Hence,
should be made of high heat resistance material such as siliconchrome steel, high speed steel, cobalt-chrome steel and tungsten
The valves are actuated by cams mounted on a cam shaft. Different
types of valve operating mechanisms are
(i) Side valve mechanism
(ii) Overhead valve mechanism
(iii) Overhead inlet and side exhaust valve mechanisms.
(i) Side valve mechanism:
This mechanism is shown in Figure 1.56. The cam mounted on the camshaft operates the valve tappet
during its rotation. The valve tappet is pushed up. The valve tappet pushes the valve from its sheet against
the spring force. Thus, the valve is opened, when the cam is not in action, the valve returns back to its seat
by the valve spring and spring retainer.
(ii) Over head valve mechanism:
Figure 1.57 shows overhead valve mechanism. Here, the valves are located in the cylinder head.
When the cam rotates, the valve lifter will push the push rod upwards. Push rod moves the rocker arm.
Since the rocker arm is pivoted at its centre, it pushes the valve off its seat against the spring force. Thus,
the valve is opened. When the cam is not in action, the valve returns back to its seat by the valve spring
and spring retainer.
(iii) Overhead inlet and side exhaust valve mechanism:
In this system, inlet valve is located in the cylinder head whereas the exhaust valve is located in the
cylinder block. The inlet valve is actuated by overhead valve mechanism. The exhaust valve is actuated
by side valve mechanism.