Automobile stands for vehicle which can move
Self propelled vehicles…
Automobile differ from aeronautical and marine.
Power is produced by….transmitted….
Requirements of an automobile:
1.It should develop power by itself.
2. Power control.
3. Power should be transmit to wheels.
4. Continue and discontinue power flow to
5. Torque should be control.
6. Directional control.
7.Should stop vehicle while it is running.
1. Single unit vehicles.
2. Articulated vehicles.
3. Heavy tractor vehicles.
Types of automobiles:
1. With respect to purpose.
2. Weight of the vehicle.
3. Fuel used.
4. With respect to no of wheels.
5. Drive of the vehicle.
6. With respect to transmission.
7. Engine capacity.
Different layout of a car
1) Front engine:
• Clutch, gearbox and final drive
• Independent rear suspension system.
• Tail heavy.
• Handling will be difficult due to high speed.
• Large amount of space.
• Increase load will provide better grip on road.
• Used in sports car.
• Location of engine provide excellent weight
• Good handling and maximum traction from
• Disadvantage in traditional cars.
• Two seat.
• Road holding is improved in wet and slippery
• Passenger and cargo spaces are good because
no need of transmission shaft.
• Good road adhesion is obtained.
• Lower flat floor line is provided.
• Provide more comfortable.
• Acceleration is affected because the load
transfer to rear of the vehicle.
• Complicated drive shafts are needed for CV
• Special universal joints and more complicated
assembly required due to short distance of
• Possible for skidding under heavy brake.
• Reasonably balanced weight distribution
between front and rear.
• A large luggage space is available.
• Control linkages such as coke, clutch and gear
box are short and simple.
• Cooling by wind.
• Noise and vibration by universal joint and
• Propeller shaft operation need floor tunnel
• When stuck in mud, tends to plough into
• Short line drive.
• Improved traction in rear wheels.
• Effective rear wheel braking.
• Absence of drive shaft give more floor space.
• Front of the vehicle can be designed for good
• This drive arrangement results a compact car.
• Vehicle affected by side winds at high speed.
• Difficult to accommodate the liquid cooling.
• Difficult to fix fuel tank in a safe zone.
• Space for luggage is reduced.
• Natural air cooling is not possible.
• Steering is difficult in slippery conditions.
• Increased traction.
• Wear of tyres and other components are
• Easily recover when it struck in mud.
Increase weight, cost, fuel consumption,
Difficult to accommodate ABS.
Major components of engine are:
• Cylinder, Cylinder liner and cylinder head
• Crank case and oil pan
• Piston and piston rings
• Connecting rod
• Crank shaft and flywheel
• Valves and valve mechanism
• Lubrication system
• Cooling system
Circular shaped container within which piston
travels in reciprocating motion.
Combustion takes place.
Has to withstand high temperature and pressure
Inside the cylinder a replaceable liner is inserted
which is known as cylinder liners.
1. Dry liner
Liner directly inserted into cylinder block. Cooling
water not in contact with the dry liner.
2. Wet liner
Cooling water is in direct contact with the outer
surface of the liner
Part is mounted on the cylinder is called cylinder
It contain inlet and exhaust ports and valve sets.
SI-engine, threaded hole for spark plug
CI-engine, hole for fuel injector
• Main active part, has to close fit with the
• Movement of the piston changes the volume
in the cylinder and provide combustion space
• Moves only inside the cylinder in a
reciprocating motion & produces the power
for the engine
• Circular rings fitted in the circumferential
grooves of the piston.
• Special alloy steel-to retain elastic properties
at high temperature.
• Upper ring-compression ring-tight gas seal
• Lower ring-oil ring- remove oil from the
• The connecting rod is the connecting link
between the piston and the crank shaft.
• By oscillating movement of the connecting rod
reciprocating motion of piston converted into
rotary motion of crank shaft.
• It converts reciprocating motion of the piston
into rotary motion.
• All other working parts are directly or
indirectly connected coupled to it.
Purpose: To store energy necessary to keep the
engine crankshaft running during idle periods.
• Not necessary to receive to receive power
Cam and Camshaft
• Camshaft contain cam depend upon no of
cylinder (cylinder x 2) or (Valves=cam)
• Used to open or close the valve
• ½ N of crank used to operating the valve
Valves and valve mechanism
Valves-gate for opening and closing the inlet and outlet in
Poppet and mushroom valve
Two type: 1. side valve mechanism
2. over head valve mechanism
Side valve mechanism:
Mainly depend upon poppet adjustment, valve
opening affected by lifting the valve of their seat
Over head mechanism:
Two additional parts: push rod and rocker arm
Valve mounted over the head of the engine
Crank case & Oil sump
• Crank case serves as a base of the engine.
Cover called crank case sump is fixed on to the
bottom of the crank case.
• The sump protects the engine from below.
Resistance to vehicle motion
• Involves the basic principles of newton’s
• Acceleration of an object is proportional to
the net force exerted on it.
• Several forces acting on the vehicle and the
net force acting on it governs the motion of
• Propulsion unit helps the vehicle to overcome
the resisting force due to gravity, air and tire
• Acceleration of vehicle depends on
– The power by propulsion unit
– Road condition
– Aerodynamics of the vehicle
Resistance can be categorized as
– Air resistance
– Gradient resistance
– Rolling resistance
– Inertia force
I. Air resistance
Vehicle traveling in air at particular speed
encounters a force resisting. This is known as
Aerodynamic drag depends upon:.,
Size of the vehicle
Shape of the vehicle
Speed of the vehicle
II. Gradient Resistance
When vehicle goes in slope, its weights produces a
components of force that is always directed
Slope - ϴ
W has two components
One is perpendicular to
road surface W cos ϴ
Other one is along to
road surface W sin ϴ
III. Rolling resistance
When vehicle rolls tyres in contact with the road
surface, it will make friction.
Rolling resistance is the sum of the following
Resistance from tyre deformation
Resistance due to tyre slip angle
Resistance due to bearing friction and
Road rolling resistance
IV. Inertia force
In addition to the driving resistance inertia forces
occur during acceleration and braking.
Total mass of the vehicle & inertia mass are the
factors influencing the resistance to acceleration.
Moment of inertia of the drive elements of engine,
clutch, gearbox, drive shaft including all the road
wheels are reduced to the driving axle
Aerodynamics of automobile body
Aerodynamic is the behaviour of air in motion
relative to the vehicle body.
Various aerodynamic forces acting
I. Drag force
II. Lift force
III. Cross wind force
• Drag force is mainly known as air resistance
CD – Drag coefficient
ρ – density of air
V – velocity of air
A – Projected area of the vehicle viewed from
• Forward motion of the vehicle pushes air in
front of it.
• This results in high air pressure in front of the
vehicle, and creates a zone of low air pressure.
• High pressure zone in the front of the vehicle
oppose its movement.
• Skin friction:., difference in speed b/w two air
molecules produces friction
• Avoiding excessive projections like door
handles, mirrors aerials help in reducing drag
Aerodynamic lift force is the vertical component
of the resultant force caused by the pressure
distribution on the body.
Aerodynamic lift will tend to reduce the
pressure b/w tyres and ground
Cross wind force
Cross wind force is acting in the lateral direction
on the side of vehicle.
These forces acting at the centre of pressure
instead of center of gravity, they cause various
Pitching moment (My):
Caused by the drag force or lift force about
Y axis. This moment makes the rear wheels lift
off from the ground
Yawing moment (Mz):
Caused by the cross wind force Fy about Z
Rolling moment (Mx)
Caused by cross wind force about X axis
To construct any automobile, chassis is the
A vehicle without body is called chassis,.
Main components of chassis:
Engine, clutch and gear box
Propeller shaft, Wheels, Differential unit
Universal unit, Brakes
Battery, fuel tank, electrical system and silencer.
Classification of chassis:
1) Full forward.
3) Bus chassis.
4) Engine at back.
5) Engine at centre.
Components in chassis:
• Foundation to carry engine and body of vehicle.
• Frames made by tubular, channel and U shaped
• Frame into chassis.
• Bends upward in shape at rear and tapered at the
• Insulate the wheel and axles from the frame.
• Provide comfortable ride to passengers.
• Avoid the transmission of road effect to
3) Steering system:
• Used to accurately control the direction of a
• Must be light and easy to operate.
• Rotary motion into angular turning.
4) Braking system:
• It bring the vehicle into rest or slow down.
• Energy conversion.
5) IC engine:
• Friction type uncoupling device.
• Single steel disc faced with suitable friction
• Take up the drive from engine and release
7) Gear box:
• Contain various types of gears which are
constantly in mesh.
• Gear changes takes place by sliding the dogs.
• Function- To provide the variation to the
torque applied by the engine to rear wheels.
8) Propeller shaft:
• Transmit power from the rear end of gear box
to the final reduction gear.
• Hooke’s joint- small and limited angular
displacement in rubber joints.
• Carries power from propeller shaft to rear
• Different speed in rear wheels while in curve.
• It ensure the final output torque is equally
distributed to rear wheels.
10) Universal joint:
• Rear axle moves up and down by road
• Permit turning of propeller shaft.
• Fitted between frame and wheel to prevent
moment of frame along with up and down
moment of wheels.
• Spring is a reservoir of energy..stored by bending
and release when it will resumes into its normal
12) Front axle:
• It used for steering front wheels about kingpin’s
• Steering arms and track rod link, two stub axles
13) Rear axle:
• Rear axle is a tube such as shaft enclosing
driving shaft with suitable bearings.
• It enlarged at centre for final gear drive.
• Change of direction from the line of propeller
shaft to the axle shaft.
• Suspension system.
• Frame is the main part of chassis. All other
parts of chassis mounted on the frame.
• At the front end engine is mounted. Frame is
supported by wheel and tyre assembly.
• Some parts of steering system connected with
frame and remaining to the body.
Importance of frame:
• To form base for mounting engine and transmission
• Should withstand the engine and transmission thrust and
• Carry load.
• Accommodate suspension and other parts.
Requirements of a good frame:
• Must be strong, light.
• Withstand the blows, twists, vibrations and strains.
• Frame sections are more important to make a
Three frame sections 1) Channel
•Semi integral frame
1. Conventional frame:
• Known as non load carrying frame.
• Loads on the vehicle transferred to
• Total frame mounted on the wheel axle by
means of springs.
• Rubber mountings between body and frame,
this makes the body completely isolated from
• Mainly used in heavy trucks.
• Has advantages of strong chassis of less
• Easy to repair in comparison to the integral
• Cross section of frame usually channel,
tubular or box type
2.Semi integral frame:
• In the semi integral type, the body mounts are
made of stiff material.
• The body structure has now become semi
• Some of the load transferred to the body
• The semi integral type permits case of styling
changes and eliminate road noise when
proper insulation are used.
• Called as chassis-less.
• Used in passenger cars, suitable for mass
• No separate frame, all assembly units are
attached to the body.
• Heavy side members are eliminated and cross
members are combined with floor.
• Body of the vehicle give space for mounting
engine, suspension and other units.
• Much weight reduction.
Defects in frame:
Defects in frames and body generally occur
due to the impact on rough road and impact with
other objects or vehicle. The following kind of
defects may occur:,
1. Misalignment in horizontal and vertical frame.
2. Twisting of main frame and sub-frame.
3. Buckled main frame and sub-frame.
4. Bent side members
5. Broken or loose gusset plates and rivets.
Frame repair and alignment:
Although the chassis frame is strong enough, it
does not require any care. But if the vehicle is
carelessly driven on rough road or if it is heavily load,
some defects occur in the frame.
1. Loose rivets:
Due to rough driving and heavy loads, the chassis
rivets become loose. So the frame members also
becomes loose and creates noise.
While replacing the loose rivets,
1. Rivet head is cut by drill or gas torch not by chisel.
2. If the hole size is increased, then the oversize rivet
is used for tight fit.
3. Before fitting the new rivet, the hole is carefully
4. The new rivet is properly heated and fitted by a
5. The loose rivet should be welded or it should be
Cracks may also occur in the chassis frame. Chalk
solution is made in water and pasted it on the frame where
the crack is suspected. Holes are drilled one on each side of
the crack if the arrangement for repairing is not available.
If the frame bends due to the accident, it is adjusted by
heating the deflected member and straightening by a jack.
Classification based on number of cylinders:
1. Single cylinder engine:
• Has one cylinder, mostly used in light motor
vehicle. Maximum cylinder size 250-300cc.
• Popular due to few parts to manufacture and
• Requires heavy construction for more power.
Reason for using single cylinder in two wheelers:
i) Compact in size
ii) Power developed is enough to carry two
iii) Vehicle In lighter weight, so it give high
2. Multi cylinder engines:
Multi cylinder engine has two, three, four, six,
eight cylinders which arranged in many ways.
Reason for using multi cylinder:
i) Multi cylinder engine develops more power
required to propel the commercial vehicle.
ii) Vibration is less due to balancing of the crank.
iii) Swept volume of the engine is high and also surface
volume ratio is increased. It results a greater power
output and better cooling.
iv) Diesel engine normally run at higher compression
ratio of 18:1. At this high compression ratio, the
thermal efficiency is high.
Classification based on arrangement of cylinders:
• horizontal engine- push forward the vehicle.
• Fuel economy is high.
• Crankcase cannot used for storing lubrication
• There will be excessive wear at the lower side
of the piston and cylinder liner. The weight of
the piston is carried by the cylinder liner.
• Consumption of lubricating oil is more.
• The size range varies from 500-1000 cc for
twin cylinder engine.
• In v-type engine cylinders are arranged 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
cylinders are arranged horizontally opposite to
• Cylinders are arranged
vertically in-line with the
crankpins arranged at 120˚
intervals around the shaft.
• It only confined with two
• The crankcase is divided
into three compartments.
• Each sealed off section of
the crank case is provided
to one of the cylinders.
Four cylinder engine:
• Four cylinder engines are widely used in small,
lightweight and fuel efficient cars.
• 180˚ crankshaft arrangement is always used.
• Balancing of four cylinder engine is not good,
but the torque is much uniform
• Piston 1 and 2 moving in
opposite to the direction of
piston 2 and 3.
Four cylinder inline engine
• In opposed four cylinder engines, the cylinders
are arranged horizontally in pairs on each side
of a flat four crankshaft.
• In this engine, one power stroke is occurred in
every 180˚ of crankshaft rotation.
• This arrangement is called as flat four.
• V four engine have cylinders arranged in two
rows of two cylinders each.
• Two rows are set at an angle 60˚ each other.
• Firing order is 1,3,4,2
• Most of the modern and high powered cars
are employing with six cylinder engine.
• Generally inline engine built with 120˚ crank
• Possible firing order is 1-5-3-6-2-4- and
• Six cylinder V-engines are very important
engine which are built to have a bank of three
cylinders at v to each other.
• Opposed six cylinder engine are also available.
The cylinders are placed in each side of two
rows but they are opposite to each other.
• Eight cylinder engine have many advantages over
six cylinder engines. It provide a long engine and
expensive crank and camshaft.
• The interval of explosions of this engine is 90˚.
• Twelve cylinder engine. 60˚ - 75˚.
• Radial engine…
• Firing order- odd.
• Not used in motor
vehicles due to more
Body is the super structure for all vehicles.
Either be constructed separately and bolted to
the chassis or manufactured integral with the
chassis (Frameless construction).
Importance of vehicle body design
• Body contribute 40% of total W in car, 60% in
buses, so reduction in body weight is
• Body weight have the impact on fuel economy
• Positive pressure on the front of the vehicle
should be minimized, and it should be
• Main consumer appeal of style should also be
Requirements of vehicle body:
1. It must be strong enough to withstand all types of
forces acting on the vehicle.
2. Stresses induced in the body should be distributed
evenly to all portions.
3. Weight of the vehicle should be minimum.
4. It must provide space for passengers and luggage.
5. It should have good access to the engine and
6. It should create minimum vibration during running.
7. Easy to manufacture and minimum cost.
8. Minimum drag, good shape and colour.
Components of vehicle body
• Structure- All load carrying elements are
defined as the body structure.
• Finish- The finished group includes all
unstressed units such as bonnet, lid, bumper.
• Equipment- Equipment group includes seats,
heating system and doors.
• All steel sections are made by dies separately
and welded to other sections for forming the
• Each panel is designed to give enough
• Car body have two types of panels.
1. Outer panel (shape)
2. Inner panel (Reinforce)
• Inner panels provide mounting locations for
various trim panels and connecting assemblies
• Initially the floor of the car body is assembled
and then pillars, rails and panels are welded.
• Floor made by 3 parts,: front, centre and rear
• Box shaped rocker panels are fixed to sides of
• Centre pillar supports the rear doors and
hinges of front door. It support the roof rails.
• Roof rails and centre pillars are usually in box
section, it give maximum strength to body.
• Roof panel is welded to the top side rails.
• Rear window and front windshield frames are attached to
the roof panel by spot welding.
• Engine compartment is formed by assembling different
sheet metal panels.
• Radiator support is provided to support the radiator by
means of bolts.
• Engine hood is manufactured as like truck lid.
• It has inner and outer panels.
• Inner panel acts as the reinforcement to the engine
hood, it provide mounting locations for the hood lock
• Outer panel gives the shape of the body, hood is
attached to the car body by means of hinges
• Seat – folding back and bucket. Rails
• Front doors are hinged on front pillars, rear
doors are hinged with center pillar.
• Rubber weather strips are bonded around doors.
• Special glass used in auto to prevents the
passenger in case of any accident. Does not
make sharp edges when broken.
• Bumpers are provided at the front and rear end
to protect the vehicle from light impact.
• Materials for body construction.
• Wind screen and window panels are made by hard
• Laminated safety glass and tempered glass.
• In laminated safety glass two layers of glass bonded
together with the help of another inner layer of vinyl
transparent plastic under heat and pressure.
• The tempered safety glass is made from a single piece
of heat treated glass.
• It cut to the required shape and then heat treated until
it becomes soft.
• Then it is treated with cold air to the outer surface.
• It becomes five times harder than ordinary glass.
• Used for side or rear windows.
Air fuel mixture from carburettor Air is only from atom
Spark plug is required Fuel injector
Compression ratio varies from 6 to 8 Compression ratio 12 to 18
Operated by Otto or constant volume cycle Operated by diesel or constant pressure
Starting is easy due to low compression ratio Starting is little difficult
Running cost is high Running cost is low
Initial cost is low Initial cost is high
Maintenance cost is less because of few
Maintenance cost is more because of
more number of parts.
Thermal efficiency is low Thermal efficiency is considerably high
Used for high speed application Used for low speed operations
Comparison of SI Engine and CI Engine
Comparison of two stroke and four stroke engines:
Two stroke / advantages Four stroke / disadvantages
A cycle is completed in 2 strokes
or one revolution of the crank
A cycle is completed in 4 strokes.
For the same power developed
the two stroke engine is much
For the same power developed
the four stroke engine is bulky,
Turning moment is more
uniform,: lighter flywheel.
Turning moment is not uniform,:
Contain ports are operated by
Contain valve which is operated
by separate mechanism
Initial cost is low-less
Initial cost is high-complicated
Mechanical efficiency is more. Mechanical efficiency is low.
Two stroke/ disadvantages Four stroke/ advantages
Thermal efficiency is low Thermal efficiency is high
Volumetric efficiency is low Volumetric efficiency is high
Greater cooling and lubrication are
Lesser cooling and lubrication are
Overall efficiency is less Overall efficiency is more
Greater rate of wear and tear Lesser rate of wear and tear
It is used in light vehicles only Used in heavy vehicles
Exhaust is noisier Exhaust is more uniform and hence
Specific fuel consumption is more
because of escaping with exhaust gases
Specific fuel consumption is less because
of separate exhaust stroke.
Less compression ratio More compression ratio
Valve timing diagram-four stroke cycle SI engine
IVO -- Inlet valve open
IVC – Inlet valve close
IS – Ignition start
EVO – Exhaust valve open
EVC – Exhaust valve close
TDC – Top dead center
BDC – Bottom dead center
Theoretical valve timing diagram:
Inlet and exhaust
valves open and close
at both dead centers,
all processes are
sharply completed at
TDC or BDC
• Inlet valve opens 10-30°
• Air fuel mixture is sucked
into the cylinder till the
inlet valve closed.
• IVC at 30-40° after BDC.
• Spark produced 20-40°
• EVO 30-60°before BDC.
• EVC 8-20°after TDC.
• Valve overlap period.
Valve timing diagram for a four stroke CI engine:
• IVO 10-25° before TDC.
• IVC 25-50°after BDC.
• FIS 5 to 10° before TDC.
• FIC 25° after TDC.
• EVO 30 to 50° before BDC.
• EVC 10 to 15° after TDC.
• Overlap period.