UNIT- I VEHICLE STRUCTURE AND

ENGINES
CONTENTS:

Types of automobiles,
Vehicle construction and different layouts,
Chassis, frame and body,
Vehicle aerodynamics (various resistances and moments involved),
Ic engines components, functions and materials,
Variable valve timing (vvt).

What is Automobile?
Self propelled vehicle (A vehicle producing power within itself for its propulsion).
It is used for the transportation of passengers and goods from one place to another on
the road or ground.
Brief history of Automobiles:
Germany-Birth place-The list of German automobile pioneers Otto, Carl Benz, Rudolf
diesel, etc.,
Captain Nicholas Cugnot- French Engineer-Father of Automobiles
Leading manufacturer of motor vehicles in the world as follows:
USA- Ford, Chrysler
UK-Rolls Royce, Daimler
Japan- Toyota, Nissan, Honda, Suzuki, Mitsubishi
Germany- BMW, Volkswagen, Audi, Skoda, Mercedes-Benz, Porsche
Italy-Fiat
Sweden- Volvo
France- Renault
India-Tata motors, Mahindra&Mahindra, Hindustan motors,
South Korea- Hyundai

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 Basic components (Parts):
The power plant (Engine) - Source of power
The chassis - Supports the engine and body
The transmission system -Transmit the power from engine to the drive wheels
Body - Super structure for all vehicles.
The auxiliaries - Electrical equipment

Now we are enter into the syllabus wise notes which is given
below.

Types of Automobiles:
Automobiles can be classified with respect to different purposes. A general
classification of the automobiles is shown in fig.

(i) With respect to purpose

(a) Passenger vehicles
(Ex): Car, bus, jeep, motor cycles,
(b) Goods carriers
(Ex): Trucks, Lorries
(ii) With respect to weight of the vehicle
(a) Light weight vehicles
(Ex): Cars, Jeeps
(b) Medium weight vehicles
(Ex): Minibus, station wagon
(c) Heavy weight vehicles
(Ex): Buses, Trucks, Trailers

(iii) With respect to fuel used

(a) Petrol vehicles
(Ex): Scooters, Cars, Motor cycles,
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 (b) Diesel Vehicles
(Ex): Buses, Trucks, etc.,
(c) Gas vehicles
(Ex): LPG, CNG vehicles
(d) Electric vehicles
(Ex): Heavy cranes, battery used cars, forklifts, etc.,
(e) Solar vehicles

(iv) With respect to number of wheels

(a) Two wheelers
(Ex): Scooters, Mopeds
(b) Three wheelers
(Ex): Auto, Tempos
(c) Four wheelers
(Ex): Car, Jeep, Bus, Truck
(d) Six wheelers
(Ex): Heavy trucks

(v) With respect to the side of drivers seat:

(a) Left hand drive

(Ex): Most of the American, European, UAE vehicles
(b) Right hand drive
(Ex): Most of the Indian Vehicles

(vi) With respect to transmission

(a) Conventional type:
In this type, ordinary gear box is fitted.
(Ex): Most of Indian vehicles

(b) Semi automatic type:

A combination of manual and some automatic gear box is fitted.
(Ex): Most of British vehicles

(c) Fully automatic type:

In this type, vehicles are equipped with full automatic transmission system by
using epicyclical gears and torque converters.
(Ex): American and European vehicles

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(vii) With respect to engine capacity
The capacity of the engine is expressed in swept volume of the cylinder
which is normally expressed in cubic centimeter (CC).
(Ex): TVS XL- 50CC, Bajaj Discover, TVS Sport, Splendor-100CC, Hero
Xtreme-150 CC, Maruti Suzuki Alto 800,

(viii) With respect to construction

(a) Single unit vehicles.
(b) Articulated vehicles and heavy tractor vehicles.
Chassis:
To construct any automobile, chassis is the basic requirement.
A vehicle without body is called chassis. (A carrying unit)
Back bone of the vehicle
The components of the vehicle such as power plant, transmission system, axles,
wheels and tyres, suspension, controlling systems such as braking, steering etc.,
Electrical system parts are mounted on the chassis frame.
It is the main mounting of all components including the body. So it is called
carrying unit.
Main components of chassis:
Frame
Front suspension
Steering mechanism
Engine, clutch and gearbox
Radiator
Propeller shaft
Wheels
Rear and front springs & Shock absorbers
Differential unit
Universal joint
Braking systems
Storage battery
Fuel tank
Electrical system
Silencer
Characteristics Of Good Chassis:
Fast pickup
Strength
Safety
Durability
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 Dependability
Ease of control
Quietness
Speed
Power accessibility
Economy of operation
Low centre of gravity
Stability
Load clearance
Braking ability
Good springing
Simplicity of lubrication
Layout of Chassis:

In this layout, the engine location is at the front end of the vehicle.

The drive of the engine can be connected or disconnected for the gear box by using
clutch assembly.

The clutch pedal provided at the vicinity of the driver facilitates to engage or
disengage the clutch with gearbox whenever required.

From gearbox, power is transmitted to the differential through a propeller shaft and
universal joints and finally to the wheels via rear axles.

The radiator is placed at the front side of an engine.

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Components and drive systems in chassis:
Frame:
Frame is the foundation for carrying the engine and body of the vehicle.
The frames are made of box, tubular, channel or U-shaped section, welded or
riveted together.

Suspension System:
To insulate the wheel and axles from the frame in order to avoid the transmission of
road effects to passengers while travelling on uneven road.
To provide comfortable ride to passengers.
To avoid additional stresses in the motor car frame.

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Steering System:
Enable the driver to accurately control the direction taken by the vehicle under all
operating conditions.
The system must be light and easy to operate, free from shock and vibration as
direct as possible.
The steering system also helps to convert the rotary motion of the drivers steering
wheel into the angular turning of the front wheels as well as to multiply the drivers
effort with the leverage or mechanical advantage of turning wheels.

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Braking system:
A brake is a mechanical friction device that inhibits motion, slowing or stopping a
moving object (vehicle) or preventing its motion.
The most vital factor in running and controlling the modern vehicle.
Most brakes commonly use friction between two surfaces which can be pressed
together to convert the kinetic energy of the moving vehicle into heat.
Frame:
Main part of a chassis.
It is a rigid structure which forms a skeleton to hold all major parts together.
A vehicle frame is a high strength structure used to support all other parts of the
vehicle.
Main functions (Importance) of Frame:
To support the chassis components and the body.
To withstand static and dynamic loads without distortion
To resist the effect of centrifugal forces when cornering a curve.
To carry the load of passengers and goods in the body.
To accommodate suspension system.

Types of frames:
Tubular Section
Excellent resistance to torsion.
Resistance increases as diameter is increased.
Other frame sections:
Hat section (Not commonly used due to weakness)
Double channel or I section (Good resistance to both bending and torsion)
Channel section (Excellent resistance to bending. Resistance increases as depth of
section is increased)
Box section (Good resistance to both bending and torsion)

Materials for frame:

Carbon 0.25-0.35%
Manganese 0.35-0.75%
Silicon 0.30 % maximum
Nickel 3%
Phosphorous 0.05% maximum
Sulphur 0.5% maximum

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Frame Construction
In order to provide good resistance to bending and torsional effect, the frame
sections are made of proper forms.
There are three common types of frame sections such as channel, tubular and box
sections.
They are made from steel or heat treated alloy steel.
Types of frame construction:
Conventional frame construction
Semi-integral frame construction
Integral or frameless construction
Conventional frame construction:
Also called non load carrying frame.
The loads on the vehicle are transferred to the suspension by this type of frame.
The body of the vehicle is made of flexible materials such as wood and mounted on
the frame by using rubber mountings between body and frame.
Mostly used in cars.

Semi integral frame construction:

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

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Integral or frameless construction:
Also called chassis less, unitary or monologue construction.
Used in Passenger cars.
It provides stiff light construction which is suitable for mass produced vehicles.
All assembly parts are attached to the body.
Heavy side members are eliminated and cross members are combined with the floor
of the body.
This type of construction is led to much reduction of weight.
All the members are welded together and form a single assembly.
Here, the stresses are evenly distributed throughout the structure.

Components Of An I.C Engines:

An engine is a device that converts thermal energy into mechanical work. The
thermal energy is produced by the combustion of air fuel mixture inside the cylinder by
means of a spark produced by the spark plug. Since it uses thermal energy it is called as
thermal engines. It is a source of power for many applications.

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Cylinder:
It is the part of the engine in which the conversion of thermal energy to mechanical
work takes place. The piston reciprocates inside the cylinder.
Since energy conversion takes place inside the cylinder it must withstand high
pressure and temperature.

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 It must be able to resist wear and tear and must dissipate heat. So material selection
is an import ant consideration. Ordinary cast iron is used in light duty engines but in
heavy duty engines alloy steels are used.
The cylinders are provided with liners so that they can be replaced when worn out.
Liners are made of nickel chrome iron.

Cylinder head:
The cylinder head closes one side of the cylinder. They are usually cast as a single
piece and are bolted to the top of the cylinder.
Between the cylinder and the cylinder head, gasket is provided Gasket is provided
in order to act as sealing (to prevent gases escaping during the expansion stroke)
and also to reduce shock.

Piston and piston rings:

Piston is the main part of the engine. The main function of the piston is to compress
the charge and to transmit the gas force to the connecting rod during the power
stroke.
Piston rings are circumferential rings that are provided in the piston grooves.
The piston rings are not fully circular; there is a clearance (Ring gap) between the
two ends.
This is provided because during the expansion stroke piston rings expand.

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There are two types of piston rings
Compression rings
Oil scraper rings

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 The upper rings are the compression rings.
They help in sealing and preventing the gas from leaking past the piston into the
casing.
The lower rings are the oil scraper rings.
They are provided to remove the oil film from the cylinder walls

Connecting rod:
The connecting rod connects the piston and the crankshaft.
The piston is connected to the connecting rod by means of gudgeon pin.
It converts the reciprocating motion into rotary motion.
The upper end of the connecting rod is called small head that is connected to the
piston and the lower end is called big end.

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Crankshaft:
It is steel forged and smooth finished. Both the ends of the crankshaft are supported in the
bearings.
One end is provided with the flywheel. The crankshaft is provided with counter weights for
balancing.

Cam and camshaft:

The main function of the camshaft is to open and close the valves at the appropriate time.
The cam is operated by means of gear arrangement driven by the flywheel.
The cam converts rotary motion into linear motion that operates the rocker arm. The motion of the
rocker arm operates the valves.
Sometimes two camshafts are provided to operate inlet valve and exhaust valve separately.

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Valves:
Valves play a major role in allowing the air fuel mixture into the cylinder (inlet valve)
for combustion and also releasing the exhaust gases from the cylinder after combustion
(outlet valve).

Manifolds:
There are two types of manifolds
Inlet manifold:
It is a pipe like structure that connects the carburetor with the inlet valves.
The air fuel mixture from the carburetor passes through the inlet manifold to the
inlet valves.

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Exhaust manifold
This pipe like structure connects the outlet valve to the atmosphere. The exhaust gas
from the cylinder passes through the exhaust manifold into the atmosphere.
Valve and Port Timing Diagrams
Valve timing Diagram
A valve timing diagram is a representation of the positions of the crank when the
various operations as inlet valve opening, closing, exhaust valve opening and
closing and also the beginning and end of various strokes.
The valves cannot open and close abruptly; it requires a finite period of time for its
operation so a time advance is given for proper functioning. The timing of the
valves is controlled by cam settings.
Valve timing for 4 stroke petrol (Spark Ignition) engine:
Now let us see the various position of the crank when the inlet and exhaust valves
during the various processes. Inlet valve opening: The valve timing is different for
low speed and high speed.
The inlet valve opens before the piston reaches the TDC during the exhaust stroke.
This is to ensure that the fresh charge enters the cylinder as soon the piston as soon
as the piston starts to move down.
Actual valve timing diagram for actual valve timing diagram for low high speed 4
stroke SI engine speed 4 stroke SI engine

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Inlet valve closing:
The closing of the inlet valve takes place during the start of compression stroke (i.e.
when the piston move from BDC to TDC after finishing suction stroke and the
starting of compression stroke).
I f the inlet valve is allowed to close exactly at BDC then less charge than the
capacity enters during the suction stroke so the inlet valve closing degrees after the
crank reaches the BDC position-25is delayed to 20 during slow speed and 40-
50degrees after the crank reaches the BDC position during high speed.
Exhaust valve opening:
The exhaust valve opens at the end of expansion stroke. The exhaust valve opening
is done before the piston reaches the BDC so as to provide more time for all the
burnt gases to escape.
The opening of the exhaust valve is necessary because if there are some burnt up
gases left in the cylinder it may affect the cylinder walls and the degrees before
BDC forspark plug. So the exhaust valve is opened 30-35 slow speed and 45-
50degrees before BDC for high speed.

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Exhaust valve closing:
The exhaust valve closing is also important to let out all the burnt gases. The time
between the exhaust valve opening and the exhaust valve closing determines the
amount of burnt gases that escapes.
Usually the exhaust valve is closed after the piston reaches the TDC position. An-
108 important phenomenon in the valve timing diagram is the angle of overlap.
The angle of overlap is the angle for which both the inlet valve and the exhaust
valves remains opened. Thus it can be seen that from the diagram the angle of
overlap during slow speed is 5+8=13.
The crank position at which ignition occurs is also indicated in the valve before
TDC-40timing diagram. The ignition is provided 38 during compression.

Variable valve timing: (VVT)

In internal combustion engines, variable valve timing (VVT) is the process of
altering the timing of a valve lift event, and is often used to improve performance, fuel
economy or emissions. It is increasingly being used in combination with variable valve lift
systems. There are many ways in which this can be achieved, ranging from mechanical
devices to electro-hydraulic and camless systems. Increasingly strict emissions regulations
are causing [citation needed] many automotive manufacturers to use VVT systems.

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Vehicle aerodynamics
Automotive aerodynamics is the study of the aerodynamics of road vehicles. Its
main goals are reducing drag and wind noise, minimizing noise emission, and preventing
undesired lift forces and other causes of instability at high speeds. Air is also considered a
fluid in this case. For some classes of racing vehicles, it may also be important to
produce down force to improve traction and thus cornering abilities.
Aerodynamics is the study of forces and the resulting motion of objects through the
air. Studying the motion of air around an object allows us to measure the forces of lift,
which allows an aircraft to overcome gravity, and drag, which is the resistance an aircraft
feels as it moves through the air.
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1) Aerodynamic drag:.

Aerodynamic means the behavior of the air motion relative to the car body.
Aerodynamic drag is also called as air resistance.
Air drag force acts in the direction of vehicle motion.
The total aerodynamic drag of a vehicle include many factors such as profile drag
(57%), induced drag (8%), skin friction (10%), interference drag (15%) and cooling
and ventilation drag (10%).

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 Stream line of air flow around the vehicle should be continuous and separation of
the boundary layer with its attendant vertices should be avoided. Skin drag
coefficient should be decrease by smooth and well-polished of body surface.
The accessories such as mirror, door handle aerials and badges which project
outward from normal surface of body produce interference drag and projection
below the vehicle such as axle, propeller shaft, tow bar also contribute interference
drag hence such projection should be avoided.

(2) Aerodynamic lift:

It is the vertical component of the resultant force caused by the pressure distribution
on the vehicle body.
The aerodynamic lift and pitching moment are undesirable effects. The
aerodynamic lift tends to reduce the pressure between the tyre and the ground. This
causes the loss of steering on the front axle and loss of traction on the rear axle.
Pitching causes rear wheel lift off the ground and reduces available traction. It is the
rocking chair or rotating action about the transverse axis through the vehicle
parallel to ground. Due to pitching, the front suspension moves out of phase with
the rear resulting in rocking effect in a vehicle.

(3) Side force:

The imbalance of the wheel due to centrifugal force acts on the vehicle during
turning which produces a side thrust.
To sustain that force, the plane of the wheel makes some angle with the direction of
motion of the vehicle. This is achieved by the direction of tyre which is flexible.
The angle form during taking turn to sustain the side thrust is known as slip angle
and the force produce to counter acts the side thrust is called as cornering force.

(4) Yawing movement (Bouncing):

It is vertical movement of the complete body .When complete body of vehicle goes
up and down which is known as bounce or bouncing. Depending upon the
movement of front end or rear end the bounce is known as front end bounce or rear
end bounce.

(5) Rolling movement:

It is the movement of a vehicle about its longitudinal axis produced due to

centrifugal force act during cornering.
The retarding and cornering forces are applied at road levels but the centre of
gravity of a vehicle is at a certain height. During cornering, a turning couple is
produced about the longitudinal axis of the vehicle owing to centrifugal force acting
at centre of gravity and forces acting at the point of contact of road and tyre patch.
This results in a motion known as rolling.
A combination of rolling and pitching is called diagonal pitch.
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