autokriti 7.0
TRANSCRIPT
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OUR V S ON
The prime objective of SAEINDIA NIT Kurukshetra Collegiate club is
to provide a platform to the budding engineers and help them to
practically apply the theoretical knowledge; to bring dynamism in their
vision and thinking; to find solutions to the existing problems by
encouraging collaboration between the minds of future engineers and
with pioneers of the industry.
The idea, vision and objectivity of the club and its working can be
uniformly summarized under the club motto
I gni te to Achieve.
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Index
1. Introduction to
Automotive.4
1.1Automotive.4
1.2
Automobile.4
1.3Components of an automobile.. .............4
2. Basic terminology..5
2.1 Vehicle axis system...5
2.2 Some common terms used in automobiles........................5
3. Chassis..6
3.1 Types of chassis...6
4. Aerodynamic
fundamentals....8
4.1 Introduction..84.2 Aerodynamic forces.....8
5. Engine..9
5.1 Introduction.....9
5.2 External and internal combustion engines.......................9
5.3 Classification of engines..........9
5.4(a) Petrol engine...11
5.4(b)Diesel engine...............................................................................................................11
5.5 Fuel injection..18
5.6 Turbochargers and superchargers...............20
5.7 Petrol engine v/s Diesel engine...............23
6. Transmission...24
6.1 Clutch..24
6.2 Types of clutches.24
6.3 Gear Ratio25
6.4 Types of transmission......25
6.5 Differential...31
6.6 Types of driveline.... .. 33
7.Electronics in cars............................................................................................................................. 35
7.1 Engine........................................................................................................................... 35
7.2 Transmission............................................................................................................ ...... 36
7.3 Chassis electronics....................................................................................................... . 36
7.4 Active Safety............................................................................................................... ... 37
7.5 Driver Assistance............................................................................................................37
7.6Passenger comfort........................................................................................................... 37
8. Suspension system........ 38
8.1 Objectives of suspension system....... 388.2 Fundamental concepts.....38
8.3 Type of suspension......................................................................................................... 40
8.4 Magnetic suspension........................................................................................................43
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8.5 Hydro-pneumatic suspension..........................................................................................43
8.6 Motion ratio.....................................................................................................................43
8.7Modern suspension trends...............................................................................................44
9 Steering system.......................45
9.1 Fundamental........................45
9.2 Steering behaviour.......46
9.3 Type of steering system.......47
9.4 Steering geometry............................................................................................................47
9.5 Steering ratio..................................................................................................................48
9.6 Power steering.................................................................................................................48
10
Wheel......50
10.1 Tyre type...........50
10.2 Tyre properties..50
10.3 Tyre size notation..5110.4 The wheel assembly..52
11
Brakes..53
11.1 Introduction53
11.2 Brake fade..53
11.3 Types of brakes..53
11.4 Methods to reducebrake fade............54
11.5 Types of calipers........55
11.6 Hydraulic brakes....56
11.7 Inboard brakes...............................................................................................................56
11.8 Brake biasing.................................................................................................................56
11.9 Proportioning valve.......................................................................56
11.10 Anti-lock braking system........................57
11.11 Types of brake fluid57
# Common abbreviations..58
# Appendix60
# Test Yourself.60
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1. INTRODUCTION TO AUTOMOTIVE
1.1 Automotive:It is a branch of engineering dealing with automobiles or anything automatically in
motion. Automotive engineering includes:
1.
Mechanical Engineering
2.
Vehicle Dynamics
3. Engine design
4.
Drive train Engineering
1.2 Automobile:The word automobile comes, via the French automobile, from the Ancient Greek
word (auts,self) and the Latin mobilis (movable); meaning a vehicle that moves itself. A
passengers and goods. Each of these vehicles is operated by engine which consumes gasoline (petrol),
diesel, natural or LPG gas etc.
The first practical automobile with a petrol engine was built by Karl Benz in1885 in Mannheim, Germany.
Benz was granted a patent for his automobile. After that the automobile became a primary mode of
transportation for all countries. In 1806, Francois Issac de Rivaz of Switzerland invented an internal
combustion engine that used a mixture of hydrogen and oxygen for fuel. Further developments led to the
introduction of modern gasoline or petrol fuelled internal combustion engine in 1885.
1.3 COMPONENTS OF AN AUTOMOBILE
The main units of an automobile
are:
The super structure or chassis
The power plant or engine
Transmission system or power
train
Steering system
Suspension system
Brakes
Wheels
Electrical system
Figure 1 -Various components of an automobile
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2. BASIC TERMINOLOGY
2.1Vehicle axes system
2.1.1 Longitudinal axis:The line passing
through the front and rear roll centre of the vehicle
(vehicle rolls about this line) represented as X-
axis.
2.1.2 Lateral axis:Axis about which vehicle
pitches, represented by Y axis.
2.1.3 Vehicle axis:Axis about which vehicle
experiences yaw movement.
2.2 Some common terms used
in automobiles:
2.2.1 Wheel base:Wheel base is the
longitudinal distance measured between contact
patches of front to rear wheel.
2.2.2 Track width:The lateral distance
between the contact patches of left and right wheel
is track width of vehicle.
2.2.3 Turning radius:It is actually a
misnomer as it is the diameter of the circle of the
outside wheels that a car turns through while
turning at full lock.
2.2.4 Indicated Power:Indicated power is the
power actually developed by the engine cylinder.
2.2.4 Brake horse power (bhp): BHP is the
power available at the crankshaft.
Figure 2Axes of motion of a vehicle
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3. CHASSIS
3.1 Type of chassis
3.1.1 Ladder Chassis
Indicated by its name, looks like a ladder - two
longitudinal rails interconnected by several lateral
and cross braces. The longitude members are the
main stress bearing members. They deal with the
Fig.3 Ladder chassis
load and also the longitudinal forces caused by
acceleration and braking. The lateral and crossmembers provide resistance to lateral forces
produced during cornering and further increase
torsional rigidity.
3.1.2 Tubular Space FrameAs ladder chassis is not strong enough, motor
racing engineers developed a 3 dimensional
design - Tubular space frame. Tubular space
frame chassis employs dozens of circular-sectiontubes, a square section can also be used for easier
connection to the body panels, though circular
section provides the maximum strength.
Figure 4Tubular frame chassis of a formula
SAE carThese tubes are welded together and form a very
complex structure. For higher strength required by
high performance sports cars, tubular space frame
chassis usually incorporate a strong structure
under both doors hence result in difficult access to
the cabin.
3.1.3 Monocoque frame chassis
Monocoque is a one-piece structure which definesthe overall shape of the car. While ladder, tubular
space frame and backbone chassis provides only
the stress members and need to build the body
around them, monocoque chassis is already
incorporated with the body in a single piece. It is
actually made by welding several pieces together.
The floor-pan, which is the largest piece, and
other pieces are pressed by big stamping
machines. They are spot welded together by robotarms.
Figure 5Monocoque chassis of Lamborghini
Aventedor
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3.1.4 ULSAB Monocoque chassis
(Ultra-Light Steel Auto Body)Pressing sheet metal to make chassis creates
inhomogeneous thickness at the edges hence to
maintain minimum thickness designers have to
choose a thicker sheet metal. By the Hydro form
technique thin steel tubes are used. The steel tubes
are placed in a die which defines the desired
shape, then fluid at very high pressure will be
pumped into the tubes, which expands the latter to
the inner surface of die. The thickness of steel
tube remains uniform which results in lighter
design.
3.1.5 Backbone frame chassisA strong tubular backbone (usually in rectangular
section) connects the front and rear axle and
provides nearly all the mechanical strength. Inside
which there is space for the drive shaft in case of
front-engine, rear-wheel drive layout. The whole
drive-train, engine and suspensions are connected
to both ends of the backbone. The body is built on
the backbone, usually made of glass-fibre. It is
strong enough for smaller sports cars but not up to
the job for high-end ones.
Figure 6Backbone chassis
3.1.6 Aluminium space frame
chassisIt consists of extruded aluminium sections;
vacuum die cast components and aluminium
sheets of different thicknesses. They all are made
of high-strength aluminium alloy. At the highly
stressed corners and joints, extruded sections are
connected by complex aluminium die casting. It is
very complex and production cost is far higher
than steel monocoque.
3.1.7 Carbon fiber monocoqueThe carbon fiber called Kevlar offers highestrigidity-to-weight ratio. Kevlar can be found in the
body panels of many exotic cars, although most of
them simultaneously use other kinds of carbon-
fiber in even larger amount.
Carbon-fiber panels are made by growing carbon-
fiber sheets on either side of an aluminium foil,
the foil, which defines the shape of the panel, is
stacked with several layers of carbon fiber sheetsimpregnated with resin, then cooked in a big oven
for 3 hours at 120C and 90 psi pressure. After
that, the carbon fiber layers will be melted and
form a uniform, rigid body panel.
Figure 7Carbon fiber chassis of a super sports
car
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4. AERODYNAMIC FUNDAMENTALS
4.1 INTRODUCTION
Following section covers different types of
aerodynamic forces deployed in a vehicle.
4.2 AERODYNAMIC FORCES
It plays a major role in high performance cars
through its contribution to Road load.
The force due to friction of air interacts with the
moving vehicles and causes drag, lift (or
downward), momentum role, pitch, yaw and noise
hence decreases fuel economy, handling etc.
The fluid flow follows Bernoullis equation for
automotive aerodynamics.
P (static) +P (dynamic) =P (total)
4.2.1 Side force: The lateral wind component
will impose a side force on the vehicle, attempting
to change the direction of travel. In case of a
strong cross wind the side force is greater than the
drag force, such that the angle of overall windforce is much greater than the relative wind angle.
4.2.2 DRAG: It is the largest and most
important aerodynamic force encountered by a
passenger car at normal highway speed. More than
65% of drag arises from the body (fore-body,
after-body, under body and skin friction. After
body is the measure contributor of drag as it
contains a separation zone. Slope angle of
15degree consistently reduces drag.
DA=(V2)CDA
CD=Aerodynamic drag co-efficient
A=Front area of vehicle
=Air density
(v2) is the dynamic pressure of the air. The
drag properties of a car are characterised by the
Figure 8 - Drag forces with (upper) and
without (lower) spoiler
4.2.3 Lift
The pressure difference between the top and the
bottom of the vehicle causes a lift force. These
forces are significant as they influences driving
stability and handling through reduced control
forces available at tires. Front lift that reduces
steering controllability is reduced by deploying a
front bumper spoiler and by rear ward inclination
of front surface. The lift at the rear of the vehicle
which reduces traction and stability is variable
with vehicle design. This lift can be reduced by
spoilers etc.
Figure 9Uplift produced due to airflow
value of product of co-efficient of drag and frontarea of the vehicle.
Modifications in TATA NANO have shown a
drag reduction of 14.28% at a speed of 60 km/h
with the drag coefficient reduced to 0.336 from
0.392, thereby reducing the fuel consumption
allotted to external body by an amount of
approximately 14.28%, which means, there is a
saving of 2.14L of petrol for every full tank
refill.
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5. ENGINE
5.1 INTRODUCTION
Engine is a machine designed to convert chemical
energy of the fuel into useful mechanical motion.
5.2 EXTERNAL & INTERNAL
COMBUSTION ENGINES:
5.2a EXTERNAL COMBUSTION
ENGINES:
A Steam engine is an external combustion engine
in which heat is supplied to the working fluid
from fuel burned outside the engine. The water
turns to steam in a boiler and expands greatly in
volume, and can be used to generate mechanical
power, usually via pistons or turbines.
5.2b INTERNALCOMBUSTION
ENGINES:
An internal combustion engine is also a heat
engine that burns fuel containing chemical energy
to get heat energy and then converts this heat
energy into mechanical energy.
5.3 CLASSIFICATION OF
ENGINES:
5.3.1 ON THE BASIS OF BASICENGINE DESIGN:
Rotary Engine
Reciprocating Engine
5.3.1a Rotary Engines
In order to reduce engine components and produce
more compact engine and to reduce losses caused
by alternating movements in traditional engine, an
engine with rotary pistons was invented which is
called Wankel engine. But now it is not used
because of its sealing and leakage problem.
Figure 10A 4-stroke wankel engine
5.3.1b Reciprocating Engine
A Reciprocating engine also known as a piston
engine is a heat engine that uses one or more
reciprocating pistons to convert pressure on piston
into a rotating motion. Reciprocating engines have
different layouts or cylinder configurations such
as straight, V, H, W, U, X etc. V configuration is
mostly used.
Figure11 Various configurations of an engine
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5.3.2 On the basis of working cycle
5.3.2a Two stroke engine
In 2-stroke engines intake and exhaust valves are
replaced by openings in the lower portion of the
cylinder wall. During the latter part of the power
stroke, the piston uncovers first the exhaust port,
allowing the exhaust gases to be partiallyexpelled, and then the intake port allowing the
fresh air-fuel mixture to rush in and drive most of
the remaining exhaust gases out of the cylinder.
The mixture is then compressed as the piston
moves upwards during the compression stroke and
is subsequently ignited by a spark plug.
5.3.2b Four stroke engine
In four stroke engines the piston reciprocates fourtimes in the cylinder. Since the 4-stroke engine
produces two rotations of the crankshaft while 2-
stroke engine produces single rotation each time
the fuel is burnt, the efficiency of 4-stroke engines
is greater than 2-stroke engines. As their name
implies, operation of 4-stroke engine have four
basic steps. The four strokes are as follows:
a) Suction or intake stroke:
Initially when engine is started piston moves
downwards towards bottom of the cylinder which
creates low pressure at top. Due to this intake
valve opens and the fuel mixture containing petrol
vapours and air are sucked in by the cylinder.
Carburetor now decides in what ratio
gasoline/petrol and air should be mixed.
b) Compression stroke:
After this the inlet valve gets closed. The piston
now moves towards the top of cylinder and
compresses the fuel mixture to one tenth of its
initial volume. The temperature and pressure
inside the cylinder increases due to compression
caused.
c)Power stroke:
During this stroke the inlet and exhaust valve
remains closed. As the piston reaches near topposition spark plug produces an electric spark.
Combustion is started by an ignition system that
fires a high voltage spark. The spark produced
causes explosion of fuel. The hot gases expand
and force the piston to move downwards. The
piston is linked to the piston rod and the piston rod
to the crank shaft.
d)Exhaust stroke:
In this stroke the exhaust valve remains open at
the start. The piston is forced to move upwards
because of the momentum gained. This forces
gases to move through the exhaust valve into the
atmosphere. Now the exhaust valve closes and the
intake valve opens. After this the four strokes of
the engine are repeated again and again.
Figure 12
Working cycle of a 4-stroke engine
5.3.3 ON THE BASIS OF
IGNITION:
5.3.3a SPARK IGNITION
In SI engines, the burning of the fuel occurs by a
spark generated by a spark plug located in the
cylinder head of engine. Due to this fact they are
called SI engines. These are called petrol or
gasoline engines because petrol is used in these
engines.
W16 configuration is used in
BUGATTI VEYRON.
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5.3.3b COMPRESSION IGNITION
In CI engines, the burning of the fuel occursbecause of the high pressure exerted on the fuel.
The fuel is compressed to high pressures. Thus the
temperature of the fuel increases and it starts
burning, hence these engines are called CI
engines.
COMPARISON OF CI AND SI ENGINES
The CI engine has the following advantages over
the SI engine.
1. Reliability of the CI engine is much higher than
that of the SI engine. This is because in case of the
failure of the battery, ignition or carburetor
system, the SI engine cannot operate, whereas theCI engine, with a separate fuel injector for each
cylinder, has less risk of failure.
2. The distribution of fuel to each cylinder is
uniform as each of them has a separate injector,
whereas in the SI engine the distribution of fuel
mixture is not uniform, owing to the design of the
single carburetor and the intake manifold.
3. Since the servicing period of the fuel injectionsystem of CI engine is longer, its maintenance
cost is less than that of the SI engine.
4. The expansion ratio of the CI engine is higher
than that of the SI engine; therefore, the heat loss
to the cylinder walls is less in the CI engine than
that of the SI engine.Consequently, the cooling
system of the CI engine can be of smaller
dimensions.
5. The torque characteristics of the CI engine are
more uniform which results in better top gear
performance.
6. The CI engine can be switched over from part
load to full load soon after starting from cold,
whereas the SI engine requires warming up.
7. The fuel (diesel) for the CI engine is cheaper
than the fuel (petrol) for SI engine.
8. The fire risk in the CI engine is minimised due
to the absence of the ignition system.
9. On part load, the specific fuel consumption of
the CI engine is low.
Why are Diesel engines still popular?
The first, the ecological regulations are
kept in foreign countries and the owners of
ecology-friendly autos have discounts on
assurance and other taxes.
Secondly, on condition of quality oil
fueling and maintenance on the regular base diesel
engine can operate up to half-million kilometers
without capital repair. And that is the sure gain.
The third, the turbo-supercharging diesel
engine can surely play the role of fire-starter.
Many car manufacturers follow that way.
5.4(a) PETROL ENGINE
Petrol Engine was introduced by the German
engineers Gottlieb Daimler and Karl Benz in
1885. It is considered as one of biggest
achievement in the automotive field. It uses petrol
called as gasoline in USA as a fuel. Within the
engine burning of fuel mixed with air causes hotgases to expand against parts of the engine and
force them to move. So petrol engines are called
internal-combustion engines. Petrol engines are
compact and light in weight for the power they
produce.
5.4(b)Diesel engine
The diesel engine(also known as a compression-
ignitionor 'CI' engine) is aninternal combustion
engine in which ignition of thefuel that has been
injected into thecombustion chamber is initiated by
Compression ratio of TATA INDICA is
22:1
Compression ratio of TATA NANO is 10.3
https://en.wikipedia.org/wiki/Internal_combustion_enginehttps://en.wikipedia.org/wiki/Internal_combustion_enginehttps://en.wikipedia.org/wiki/Combustionhttps://en.wikipedia.org/wiki/Diesel_fuelhttps://en.wikipedia.org/wiki/Combustion_chamberhttps://en.wikipedia.org/wiki/Combustion_chamberhttps://en.wikipedia.org/wiki/Diesel_fuelhttps://en.wikipedia.org/wiki/Combustionhttps://en.wikipedia.org/wiki/Internal_combustion_enginehttps://en.wikipedia.org/wiki/Internal_combustion_engine -
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the high temperature which a gas achieves when
greatly compressed (adiabatic compression).
The diesel engine has the highestthermal
efficiency (engine efficiency) of any
practicalinternal orexternal combustion engine due
to its very highcompression ratio andinherentleanburn which enables heat dissipation by
the excess air.
Basic Engine Parts
5.4.1 Cylinder head
The cylinder head is a casting bolted to the top of
the cylinder block, injector location holes, form
the
Figure 13Cylinder head of a 4 cylinder engine
upper face of combustion chamber. The coolant
passages, cavities, intake and exhaust ports, and
the spark plug are also located within the head
casting. The cylinder head is detachable for easy
access to the valves and piston tops and to
facilitate machining of the cylinder bore,
combustion chamber and valve ports.
5.4.2 Cylinder block
The cylinder block is the portion of the engine
between the cylinder head and sump. All the
engine parts are mounted on it or in it and this
holds the parts in alignment. Large diameters
holes in the block castings from the cylinder bores
required to guide the pistons. Both spark-ignition
and compression-ignition cylinder blocks are
similar but later blocks are relatively heavier andstronger to withstand high compression ratios and
internal pressure.
Figure 14Cylinder block of a 4 cylinder
engine
Within the cylinder, combustion process produces
rapid and periodic rises in temperature and
pressure. These induce circumferential and
mechanical properties such as strength, toughness,
hardness, and corrosion and wear resistance.
5.4.3 Crank case and Crank shaft
The crankcase supports the individual main
journals and bearings of the crankshaft and also
TATA NANO has 624cc, 2-
cylinder engine which gives
32.5bhp power @5500 rpm and
45Nm torque@3500rpm
TATA INDICA has 1405cc,4
cylinder engine which gives 84bhp
power @6000 rpm,
120Nm Torque @3500 rpm
https://en.wikipedia.org/wiki/Adiabatic_compressionhttps://en.wikipedia.org/wiki/Thermal_efficiencyhttps://en.wikipedia.org/wiki/Thermal_efficiencyhttps://en.wikipedia.org/wiki/Engine_efficiencyhttps://en.wikipedia.org/wiki/Internal_combustionhttps://en.wikipedia.org/wiki/External_combustionhttps://en.wikipedia.org/wiki/External_combustionhttps://en.wikipedia.org/wiki/Compression_ratiohttps://en.wikipedia.org/wiki/Lean_mixturehttps://en.wikipedia.org/wiki/Lean_mixturehttps://en.wikipedia.org/wiki/Compression_ratiohttps://en.wikipedia.org/wiki/External_combustionhttps://en.wikipedia.org/wiki/Internal_combustionhttps://en.wikipedia.org/wiki/Engine_efficiencyhttps://en.wikipedia.org/wiki/Thermal_efficiencyhttps://en.wikipedia.org/wiki/Thermal_efficiencyhttps://en.wikipedia.org/wiki/Adiabatic_compression -
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maintains the alignment of the journal axes of
rotation as they are subjected to rotary and
Figure 15Crank shaft of a 4 cylinder engine
reciprocating inertia forces and the periodic torque
impulses. The crankshaft, which is one of a series
of links between pistons and the drive wheels, is a
one piece art located in the bottom end of theengine that harnesses the huge forces produced by
the explosions in the combustion chamber. The
front end of the crankshaft, known as the snout,
turns the sprocket, or timing gear, to drive the
camshaft, pulley that runs a belt connected to the
alternator, fan, water pump and power steering.
The other end of the crankshaft is connected to the
flywheel, which is toothed, allowing the starter
motor to rotate the crankshaft.
FUNCTION
When the fuel is ignited in the combustion
chamber in presence of highly compressed air, the
resulting explosions forces the pistons downward
with tremendous force. The function of the
crankshaft is to change the up-down motion of the
pistons to a rotating motion. This is accomplished
by having the connecting rods (which are attachd
to the pistons) connect to the crankshaft in an
offset manner, so that as they go up and down
their angle changes.
5.4.4 Cam shaft
Its job is to open and close the valves at just the
right time during engine rotation, so that
maximum power and efficient cleanout of exhaust
can be obtained. The camshaft drives thedistributor to electrically synchronize spark
ignition. Camshafts do their work through
eccentric lobes that
Figure 16Camshaft of a 4 cylinder engine
actuate the components of the valve train. The
camshaft itself is forged from one piece of steel,
on which the lobes are ground. On single camshaft
engines there are twice as many lobes as there are
cylinders, plus a lobe for fuel pump actuation and
a drive gear for the distributor. The camshaft
operates cam followers that in turn operate the rest
of the valve train.
Dual overhead camshaft(DOHC):The
main benefit of dual overhead cams is that they
allow an engine to have four valves per cylinder.
Each camshaft operates two of the valves, one
camshaft handles the intake valves, and onehandles the exhaust valves. It is now used in high
performance cars.
5.4.5 Rocker shafts and rocker arm
assembly
Rocker arm assembly consists of rocker
arm,rocker shaft and springs. Rocker arm comes
in contact with the valves as directed by the
rotation of the camshaft.
Rocker shaft
Rocker shaft provides a rigid pivot support for the
rocker arms. These shafts are machined from
hollow steel tubing. These are mounted and
clamped on cast-iron or aluminium alloy
pedestals, which are generally fitted between each
pair of rocker-arms. For lubrication purpose radial
Single Overhead Camshaft is used in
both TATA Nano and TATA Indica
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holes are drilled through rocker-shaft to align with
each rocker arm, and both end of the shaft are
plungged to prevent the oil leakage. One of the
support pedestals normally incorporates a vertical
drilled hole to supply the oil from the camshft to
the hollow rocker shaft. This hole matches with acorresponding radial hole in the shaft. When
reassembling the rockers and shaft, these twoholes
must align, to restore oil supply to the shaft.
Figure 17A rocker shaft
After machining, the shaft is case-hardened to
withstand the rubbing action.
Rocker-arm
A rocker-arm rockes or oscillates about its pivot
and relays the push rod up-and-down movement
to the stem of the poppet valve. Therefore this arm
acts as a rocking beam.
Figure 18A rocker arm assembly
5.4.6 Piston
The automotive engine piston converts the
combustion pressure to a force on the crankshaft.
The piston starts, accelerates and stops twice in
each crankshaft revolution. This reciprocatingaction of the piston produces large inertial forces.
The inertial force depends on the piston and less
inertia permits higher engine operating speeds.
During operation of the piston, a temperature
gradient of about 150 k from the head of the
piston to its bottom is experienced. Also it has to
support piston sealing rings. Therefore, design of
a piston is based on a compromise between
strength, weight and thermal expansion control.
Functions of a piston in brief are:
It must form a sliding gas and oil tight seal
within the cylinder.
It must transmit thegas load to the small end of
the connecting rod.
It generally acts as a bearing for the gudgeon pin.
Figure 19Piston & its parts
Figure 20Piston & its Gudgeon pin
The gudgeon-pin(piston pin) connects the pistonand connecting rod. It is supported in holes bored
in the piston at right angles to the piston axis
atabout mid height position, and the centre portion
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of the gudgeon pin passes through the connecting
rod small-end eye. This hinged joint transfers
directly the gas thrust from the pistons to the
connecting rod and allows the rod to pivot relative
to the cylinder axis with an oscillating motion.
Connecting rod
The connecting rod joins the piston to the
crankshaft and transfers piston reciprocating force
to crankshaft rotation. The small end of the
connecting rod reciprocates and the large end
follows the crank pin rotational pattern. For this
movement, the connecting rod should be as light
as possible. Each connecting rod is fastened to the
piston pins and to the crank pin(journal) of thecrank shaft by a plain split bearing.
5.4.7 Push Rod
A push rod is a straight stem with a roller ball at
each end. Some push rods are fabricated in one
piece, while others are fabricated in three pieces
that include the stem with welded roller balls at
each end. The engine will not start or run without
push rods.
FunctionThe roller ball at the lower end of the push rod
rides on the lobes of the camshaft. The upper ball
seats into a recessed cup on the underside of a
rocker arm. As the offset lobe of the cam contacts
the lower ball, the push rod is forced up and lifts
the rocker arm. This action opens an intake or
exhaust valve in the cylinder head of the engine.
As the cam turns farther, the push rod drops back
to its original starting point. This relaxes pressure
on the rocker arm and the valve closes.
Figure 21Valve train with pushrods
5.4.8 Valve train and Valve timings
The valve train consists of valves, rockerarms,
pushrods, lifters, and the camshafts. Valve train
opening/closing and duration, as well as the
geometry of the valve train, controls the amount
of air and fuel entering the combustion chamber at
any given point in time. Timing for open/close
duration is controlled by the camshaft that is
syncronized to the crankshaft by a chain or belt.
Valve trains are built in several configurations,
each of which vary slightly in layout but still
perform the task of opening and closing the
valves at the time necessary for proper operation
of the engine. These layouts are differentiated by
the location of the camshaft within the engine:
Overhead Camshaft:The camshaft (or
camshafts, depending on the design) is located
above the valves within the cylinder head, and
operates either indirectly or directly on the valves.
Cam-in-block:the camshaft is located within
the engine block, and operates directly on the
valves, or indirectly via pushrods and rocker arms.
Because they often require pushrods they are often
calledpushrod engines.
Cam less:this layout uses no camshafts at all.Technologies such as Solenoids are used to
individually actuate the valves.
DID YOU KNOW?
Only about 15% of chemical energy gets
converted to useful kinetic energy of the
vehicle.
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Intake and Exhaust Valves
Now-a-days, this is located in the cylinder head on
all the engines. Among the commonly used
sleeve, rotary and poppet type valves, the poppet
vave is most common because this offers
readonable weight, good strength and good
heattransfer characteristics.
Figure 22Intake and exhaust valve
The poppet valve also has great flow
characteristics and provides a good means to
direct fluid flow into the combustion chamber.
The stem of the valve usually rides up and down a
provision incorporated into the head itself that ismachined called a valve guide.To see how valve timing works in a 4-stroke
engine cycle, lets show piston motion as a circle.
In the simple cycle, each stroke is shown as a
semi-circle. Theoretically speaking the intake
valve opens at top dead centre, and closes at
bottom dead centre and the exhaust valve opens at
bottom dead centre, and closes at top dead centre
before the new air fuel mixture enters the cylinder.In practice, however, the intake valve usually
opens earlier than top dead centre, and stays open
a little past bottom dead centre. The exhaust valve
opens a little before bottom dead centre and stays
open a little past top dead centre.
This make valve opens 16 before the piston
reaches top dead centre and it closes 55 after
bottom dead centre.
The exhaust valve opens 55 before bottom
dead centre and stays open until 16 past top
dead centre. This gives exhaust gases more
time to leave.
By the time the piston is at 55 before BDC on
the power stroke, combustion pressures have
dropped considerably and little power is lost
by letting the exhaust gases have more time to
exit.
When an intake valve opens before TDC andthe exhaust valve opens before BDC, it is
called lead.
When an intake valve closes after BDC and
the exhaust valve closes after TDC, it is called
lag.
On the exhaust stroke, the intake and exhaust
valve are open at the same time for few
degrees around TDC. This is called valve
overlap.
VVT (Variable Valve Timing)
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 frommechanical devices to electro-hydraulic and cam
less systems. Two-stroke engines use a power
valve system to get similar results to VVT.
5.4.9 Sump or oil panThe sump is attached to the bottom of the cylinder
block underneath the crankcase. The functions of
the sump are:
To store the engines lubrication oil forcirculation within the lubrication system.
DID YOU KNOW?
The Free Valve concept by Koenigsegg offers
the unique ability to have independent
control of the intake and exhaust valve can
be independently programmed.The system
has a verified fuel consumption reduction of
12-17 percent.
http://en.wikipedia.org/wiki/Internal_combustion_enginehttp://en.wikipedia.org/wiki/Poppet_valvehttp://en.wikipedia.org/wiki/Camlesshttp://en.wikipedia.org/wiki/Camlesshttp://en.wikipedia.org/wiki/Two-stroke_cyclehttp://en.wikipedia.org/wiki/Two-stroke_power_valve_systemhttp://en.wikipedia.org/wiki/Two-stroke_power_valve_systemhttp://en.wikipedia.org/wiki/Two-stroke_power_valve_systemhttp://en.wikipedia.org/wiki/Two-stroke_power_valve_systemhttp://en.wikipedia.org/wiki/Two-stroke_cyclehttp://en.wikipedia.org/wiki/Camlesshttp://en.wikipedia.org/wiki/Camlesshttp://en.wikipedia.org/wiki/Poppet_valvehttp://en.wikipedia.org/wiki/Internal_combustion_engine -
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To collect the oil draining from the sides of
the crankcase walls and if ejected directly
from the journal bearings.
To provide a centralized storage area for any
contaminants like liquid fuel, water,
combustion products blown past the pistonring, and worn metal particles.
To provide a short recovery period for the hot
churned up and possibly aerated oil before it is
re-circulated in the lubrication system.
Figure 23Oil sump of an engine
The sump generally has a shallow downward
slope at one end, which changes into a relatively
deep but narrow-walled reservoir at the other end.The incoming oil flows towards the deep end,
where it submerges the pick-up pipe and strainer
of the lubricating system. A drain plug is located
at the lowest level in the sump for easy drainage
of used oil.
5.4.10 FlywheelIn a combustion engine, & especially in one with
one or two cylinders, energy is imparted to thecrankshaft intermittently, & in order to keep it
Figure 24Flywheel of an engine
rotating at a fairly uniform speed under a
substantially constant load, it is necessary to
provide it with a flywheel. A flywheel is an
inertial energy-storage device. It absorbs
mechanical energy and serves as a reservoir,
storing energy during the period when the supplyof energy is more than the requirement and
releases it during the period when the requirement
of energy is more than the supply.
Functions and Operation
The main function of a fly wheel is to smoothen
out variations in the speed of a shaft caused by
torque fluctuations. If the source of the driving
torque or load torque is fluctuating in nature, thena flywheel is usually called for. Many machines
have load patterns that cause the torque time
function to vary over the cycle. Internal
combustion engines with one or two cylinders are
a typical example. Piston compressors, punch
presses, rock crushers etc. are the other systems
that have fly wheel. Flywheel absorbs mechanical
energy by increasing its angular velocity and
delivers the stored energy by decreasing itsvelocity.
5.4.11 Spark PlugsAll spark plugs share the same basic design and
construction. The high voltage from your vehicle's
high-tension electrical system is fed into the
terminal at the top of the spark plug. It travels
down through the core of the plug and arrives at
Figure 25
Spark plug of a petrol engine
the centre electrode at the bottom where it jumps
to the ground electrode creating a spark. The crush
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washer is designed to be crushed by tightening the
spark plug down when it's screwed into the
cylinder head, and as such, it helps keep the screw
threads under tension to stop the spark plug from
shaking loose or backing out. The insulator
basically keeps the high-tension charge away fromthe cylinder head so that the spark plug doesn't
ground before it gets a chance to generate the
spark. This type of plug is known asaprojected nosetype plug, because the tip extends
below the bottom of the spark plug itself. The
other main type of spark plug has the centre
electrode recessed into the plug itself and merely
grounds to the collar at the bottom. The advantage
of the projected nose type is that the spark is better
exposed to the fuel-air mixture.
5.4.12 CarburetorA carburetor is basically a shaped tube. The shape
of the tube is designed to swirl the incoming air
and generate a vacuum in a section called the
venturi pipe (or just the venturi). In the side of the
venturi is a fuel jet which is basically a tiny hole
connected to the float chamber via a pipe. It has a
miniscule hole in the end of it which determines
the flow of fuel through it. The fuel is pulled
through the jet by the vacuum created in the
venturi. At the bottom of the tube is a throttle
plate or throttle butterfly which is basically a flat
circular plate that pivots along its centre line. It is
connected mechanically to the accelerator pedal or
twist-grip throttle via the throttle cable. The more
you push on the accelerator or twist open the
throttle, the more the throttle butterfly opens. Thisallows more air in which creates more vacuum,
which draws more fuel through the fuel jet and
gives a larger fuel-air charge to the cylinder,
resulting in acceleration.When the throttle is
closed, the throttle butterfly in the carburetor is
also closed. This means the engine is trying to
suck fuel-air mix and generating a
vacuum behind the butterfly valve so the regular
fuel jet won't work. To allow the engine to idlewithout shutting off completely, a second fuel jet
known as the idle valve is screwed into the venturi
downwind of the throttle butterfly. This allows
just enough fuel to get into the cylinders to keep
the engine ticking over.
Figure 26Cut through diagram of a
Carburetor
5.5 FUEL INJECTION
INTRODUCTIONFuel injection is a system for admittingfuel into
aninternal combustion engine.It has become the
primary fuel delivery system used inautomotive
engines,having replacedcarburetors during the
1980s and 1990s.Edward Butler, from Erith, Kent,
and Henri Tenting, from Paris, were the first two
men to develop a fuel injection system for theinternal combustion engine in 1883 and 1891,
respectively.
The primary difference between carburetors
and fuel injection is that fuel injection atomizes
the fuel by forcibly pumping it through a small
nozzle under high pressure, while a carburetor
relies on suction created by intake air accelerated
through a Venturi tube to draw the fuel into the
airstream.
Figure 27 - cut through diagram of a typical
fuel injector
http://en.wikipedia.org/wiki/Fuelhttp://en.wikipedia.org/wiki/Internal_combustion_enginehttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Enginehttp://en.wikipedia.org/wiki/Carburetorhttp://en.wikipedia.org/wiki/Atomizer_nozzlehttp://en.wikipedia.org/wiki/Suctionhttp://en.wikipedia.org/wiki/Venturi_tubehttp://en.wikipedia.org/wiki/Venturi_tubehttp://en.wikipedia.org/wiki/Suctionhttp://en.wikipedia.org/wiki/Atomizer_nozzlehttp://en.wikipedia.org/wiki/Carburetorhttp://en.wikipedia.org/wiki/Enginehttp://en.wikipedia.org/wiki/Automobilehttp://en.wikipedia.org/wiki/Internal_combustion_enginehttp://en.wikipedia.org/wiki/Fuel -
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WORKING:
The Fuel Injection System as the name suggests is
mainly consists of an Injector, a valve with a small
nozzle at the extreme end which is responsible to
supply the fuel to the combustion chamber with
force resulting the atomization of the fuel, thisforce is generated from the fuel pump which is
generally placed inside the fuel tank, the atomized
fuel is easier to burn when combined with the
radical oxygen molecules of the air intake creating
an optimum fuel and air ratio hence resulting into
increased fuel efficiency with remarkably cleaner
emission. When the injector is energized, an
electromagnet moves a plunger that opens the
valve, allowing the pressured fuel to squirt out
through a tiny nozzle. The nozzle is designed to
atomize the fuel as fine a mist as possible so that it
can burn easily.
TYPES OF FUEL INJECTION
1.Single-Point, Central Fuel Injection or
Throttle Body Injection (TBI)
Single-point simply replaces the carburetor with
one or two fuel-injector nozzles in the throttle
body, which is the throat of the engines air intake
manifold. The system injects fuel into the throttle
body (a wet system), so fuel can condense and
cling to the walls of the intake system.
2. Multi-Point Fuel Injection (MPFI)
Multi-point fuel injection devotes a separate
injector nozzle to each cylinder, right outside its
intake port, which is why the system is sometimes
called Port injection. The injector sprays gasoline
into the air inside the intake manifold. The
gasoline mixes with the air in a reasonably
uniform manner. This mixture of gasoline and air
then passes through the intake valve and enters
into the cylinder.
The main advantage is that MPFI meters fuel
more precisely than do TBI designs, better
achieving the desired air/fuel ratio and improving
all related aspects. Also, it virtually eliminates thepossibility that fuel will condense or collect in the
intake manifold.
3. Direct Injection
In Direct injection fuel is directly injected into the
combustion chamber. It suffers from an
extraordinarily high back-pressure due to its
placement, as well as other severe disadvantages.
Because of the exposure of the injector tips to the
combustion process, carbon build-ups easily clog
the injector tips.
Figure 28a) Single point fuel in jection b)
Mul ti poin t fuel injection c) Dir ect in jection
4. Programmed Fuel Injection (Pgm-FI)
The PGM-FI system precisely controls fuel
injection to match engine requirements, reducing
emissions and increasing driveability. The electric
fuel pump supplies fuel to the pressure regulator.
The fuel injectors are electric solenoid valves
which open and close according to signalsreceived from the Electronic Control Unit (ECU).
The ECU has sensors which measure the
temperatures of the engine, coolant, oil, and
outside air as well as pressure sensors to monitor
oil and barometric pressure. Based on these
readings and the location of the throttle, the ECU
calculates how much oxygen and fuel should be
mixed for optimal and efficient performance. The
ECU receives input from various sensors todetermine engine operating conditions. This
allows the ECU to determine the correct amount
of fuel to be injected by its pre-set program.
MPFI is used in TATA NANO
& Indirect Injection in used in
TATA INDICA
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5. Gasoline direct injection system
GDI engine operate with lean mixture and
unthrottled at part loads, this operation provide
significant improvements in fuel economy. At full
load, as the GDI engine operates with
homogeneous charge and stoichiometric or
slightly rich mixture, this engine gives a betterpower output. In GDI engine, fuel is injected into
cylinder before spark plug ignites at low and
medium loads. At this condition, Air/Fuel (A/F)
ratio in cylinder vary, that is, mixture in front of
spark plug is rich, in other places is lean. In all
cylinder A/F ratio is lean and A/F ratio can access
until 40/1. In homogeneous operation, fuel starts
injecting into cylinder at intake stroke at full
loads. The fuel, which is injected in the intake
stoke, evaporates in the cylinder. The evaporation
of the fuel cools the intake charge. The coolingeffect permits higher compression ratios and
increasing of the volumetric efficiency and thus
higher torque is obtained.
6.Indirect Injection System
An indirect injection diesel engine delivers fuel
into a chamber off thecombustion chamber,called
a pre combustion chamber or ante-chamber, where
combustion begins and then spreads into the main
combustion chamber, assisted
byturbulence created in the chamber.
This system allows for a smoother, quieter
running engine, and because combustion is
assisted by turbulence,injectorpressures can be
lower, about 100 bar (10 MPa; 1,500 psi), using a
single orifice tapered jet injector. Mechanical
injection systems allowed high-speed running
suitable for road vehicles (typically up to speeds
of around 4,000rpm). The pre-chamber had thedisadvantage of increasing heat loss to the
engine's cooling system, and restricting the
combustion burn, which reduces the efficiency by
510%.[51]Indirect injection engines are cheaper
to build and it is easier to produce smooth, quiet-
running vehicles with a simple mechanical
system. In road-going vehicles most prefer the
greater efficiency and better controlled emission
levels of direct injection. Indirect injection diesels
can still be found in the many ATV diesel
applications.
Fig.29 Indirect Injection System
5.6 TURBOCHARGER & SUPERCHARGER
5.6.1 TURBOCHARGER
A turbo can significantly boost an engine's
horsepower without significantly increasing its
weight, which is the huge benefit that makes
turbos so popular. Turbochargers are a type of
forced induction system. They compress the air
flowing into the engine. The advantage of
compressing the air is that it lets the engine
squeeze more air into a cylinder, and more air
means that more fuel can be added. Therefore, you
get more power from each explosion in each
cylinder. A turbocharged engine produces more
power overall than the same engine without the
charging. This can significantly improve the
power-to-weight ratio for the engine.
In order to achieve this boost, the turbocharger
uses the exhaust flow from the engine to spin a
turbine, which in turn spins an air pump. The
turbine in the turbocharger spins at speeds of up to
150,000 rpm - that's about 30 times faster than
most car engines can go. And since it is hooked up
to the exhaust, the temperatures in the turbine are
also very high.
https://en.wikipedia.org/wiki/Combustion_chamberhttps://en.wikipedia.org/wiki/Turbulencehttps://en.wikipedia.org/wiki/Injectorhttps://en.wikipedia.org/wiki/Rpmhttps://en.wikipedia.org/wiki/Diesel_engine#cite_note-51https://en.wikipedia.org/wiki/Diesel_engine#cite_note-51https://en.wikipedia.org/wiki/Diesel_engine#cite_note-51https://en.wikipedia.org/wiki/Diesel_engine#cite_note-51https://en.wikipedia.org/wiki/Rpmhttps://en.wikipedia.org/wiki/Injectorhttps://en.wikipedia.org/wiki/Turbulencehttps://en.wikipedia.org/wiki/Combustion_chamber -
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Figure 30Turbocharger plumbing in a car
Turbochargers allow an engine to burn more fuel
and air by packing more into the existing
cylinders. The typical boost provided by a
turbocharger is 6 to 8 pounds per square inch(psi). Since normal atmospheric pressure is 14.7
psi at sea level, you can see that you are getting
about 50 percent more air into the engine.
Therefore, you would expect to get 50 percent
more power. It's not perfectly efficient, so you
might get a 30 to 40percent improvement instead.
Working
A turbocharger is made up of two main sections:
the turbine and the compressor. The turbine
consists of the turbine wheel and the turbine
housing. It is the job of the turbine housing to
guide the exhaust gas into the turbine wheel. The
energy from the exhaust gas turns the turbine
wheel, and the gas then exits the turbine housing
through an exhaust outlet area.
The compressor also consists of two parts: the
compressor wheel and the compressor housing.
The compressors mode of action is opposite that
of the turbine. The compressor wheel is attached
to the turbine by a forged steel shaft, and as the
turbine turns the compressor wheel, the high-
velocity spinning draws in air and compresses it.
The compressor housing then converts the high-
velocity, low-pressure air stream into a high-pressure, low-velocity air stream through a
process called diffusion. The compressed air is
pushed into the engine, allowing the engine to
burn more fuel to produce more power.
Figure 31Inside a turbocharger
One of the main problems with turbochargers is
that they do not provide an immediate power
boost when you step on the gas. One way to
decrease turbo lag is to reduce the inertia of the
rotating parts, mainly by reducing their weight.
This allows the turbine and compressor to
accelerate quickly, and start providing boost
earlier. One sure way to reduce the inertia of the
turbine and compressor is to make the
turbocharger smaller.A small turbocharger will provide boost more
quickly and at lower engine speeds, but may not
be able to provide much boost at higher engine
speeds.
Some turbochargers use ball bearings instead of
fluid bearings to support the turbine shaft. They
are super-precise bearings made of advanced
materials to handle the speeds and temperatures of
the turbocharger. They allow the turbine shaft to
spin with less friction than the fluid bearings used
in most turbochargers. They also allow a slightly
smaller, lighter shaft to be used. This helps the
turbocharger accelerate more quickly, further
reducing turbo lag.
Ceramic turbine bladesare lighter than the steel
blades used in most turbochargers. This allows the
turbine to spin up to speed faster, which reduces
turbo lag.
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5.6.2 Supercharger
A supercharger is a great way to achieve forced
air induction. A supercharger is any device that
pressurizes the air intake to above atmospheric
pressure. Both superchargers and turbochargers do
this. In fact, the term "turbocharger" is a shortened
version of "turbo-supercharger," its official name.
The difference between the two devices is their
source of energy. Turbochargers are powered by
the mass-flow of exhaust gases driving a turbine.
Superchargers are powered mechanically by belt-
or chain-drive from the engine's crankshaft.
Working
Getting more fuel into the charge would make for
a more powerful explosion. But you can't simply
pump more fuel into the engine because an exact
amount of oxygen is required to burn a given
amount of fuel. This chemically correct mixture --
14 parts air to one part fuel -- is essential for an
engine to operate efficiently. The bottom line: To
put in more fuel, you have to put in more air.
That's the job of the supercharger. Superchargers
increase intake by compressing air above
atmospheric pressure, without creating a vacuum.
This forces more air into the engine, providing a
boost. With the additional air in the boost, more
fuel can be added to the charge, and the power of
the engine is increased. In high-altitude situations,
where engine performance deteriorates because
the air has low density and pressure, a
supercharger delivers higher-pressure air to the
engine so it can operate optimally. Unlike
turbochargers, which use the exhaust gases to
power the compressor, superchargers draw their
power directly from the crankshaft. Most are
driven by a belt, which wraps around a pulley that
is connected to a drive gear. The drive gear, in
turn, rotates the compressor gear. To pressurize
the air, a supercharger must spin rapidly -- more
rapidly than the engine itself. Making the drive
gear larger than the compressor gear causes the
compressor to spin faster.
Figure 32Cut through diagram of a
supercharger
As the air is compressed, it gets hotter, whichmeans that it loses its density and cannot expand
as much during the explosion. This means that it
can't create as much power when it's ignited by the
spark plug. For a supercharger to work at peak
efficiency, the compressed air exiting the
discharge unit must be cooled before it enters the
intake manifold.
5.6.3 Intercooler
When air is compressed, it heats up; and when air
heats up, it expands. So some of the pressure
increase from a turbocharger is the result of
heating the air before it goes into the engine, the
goal is to get more air molecules into the cylinder,
not necessarily more air pressure.
Fig.33 Intercooler
An intercooler or charge air cooler is an additional
component that looks something like radiator,
except air passes through the inside as well as the
outside of the intercooler. The intake air passes
through sealed passageways inside the cooler,
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while cooler air from outside is blown across fins
by engine cooling fan. The intercooler further
increases the power of the engine by cooling thepressurized air coming out of the compressor
before it goes into the engine. This means that if
the turbocharger is operating at a boost of 7 psi,
the intercooled system will put in 7 psi of cooler
air, which is denser and contains more air
molecules than warmer air.
5.7 PETROL ENGINE v/s
DIESEL ENGINE
5.7.1 EXPANSION STROKE
1. In petrol engine, the air and fuel mixture is
ignited using a spark plug and burns expanding
and forcing the piston down.
2. In diesel engine, fuel is injected at a high
pressure into the hot, compressed air in the
cylinder, causing it to burn and force the piston
down. No spark is required.
5.7.2 LIFE
Petrol destroys lubrication and burns the engine
whereas diesel doesnt. so a diesel engine would
last longer than a petrol engine.
5.7.3 WEIGHT
Petrol engines are lighter than diesel engines.
5.7.4 LOAD CARRYING CAPACITY
Diesel engine would pull heavy loads easily than a
petrol engine. Though the pick-up of a petrol
engine would be much more than of a diesel
engine. The diesel engine would be steady and
carry heavier loads to longer distances.
5.7.5 FUEL EFFICIENCY
Diesel engines have better fuel efficiency as
compared to petrol due to the fact that they havehigher compression ratio.
Sr.no. Diesel engine petrol engine
1 It has got no carburetor, ignition coil and sparkplug.
It has got carburetor, ignition coil & spark plug.
2 Its compression ratio varies from 14:1 to 22:1 Its compression ratio varies from 5:1 to 8:1.
3 It uses diesel oil as fuel. It uses petrol (gasoline) or power kerosine as fuel.4 Only air is sucked in cylinder in suction stroke. Mixture of fuel and air is sucked in the cylinder in
suction stroke.
5 It has got fuel injection pump and injector. It has got no fuel injection pump and injector, insteadit has got carburetor and ignition coil.
6 Fuel is injected in combustion chamber where
burning of fuel takes places due to heat ofcompression.
Air fuel mixture is compressed in the combustion
chamber when it is ignited by an electric spark.
7 Thermal efficiency varies from 32 to 38%. Thermal efficiency varies from 25 to 32%.
8 Engine weight per horse-power is high. Engine weight per horsepower is comparatively low.
9 Operating cost is low. Operating cost is high.
10 Torque produced is even. Torque produced is less even.
No intercooler is used in tata indica
DID YOU KNOW?
Superchargers can spin at speeds as high as
50,000 to 65,000 RPM,Which is more than
Engines RPM
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6.TRANSMISSION
6.1 CLUTCH
A clutch is a mechanical device that engages and
disengages the powertransmission,especially fromdriving shaft to driven shaft. The clutch is what
enables you to change gears, and sit at traffic lights
without stopping the engine. The clutch is
composed of three basic elements; the flywheel, the
pressure plate and the clutch plate(s). The flywheel
is attached to the end of the main crank and the
clutch plates are attached to the gearbox lay shaft
using a spline.
Figure 34
Components of a diaphragm springclutch
In the diagram here, the clutch cover is bolted to
the flywheel so it turns with the flywheel. The
diaphragm springs are connected to the inside of
the clutch cover with a bolt/pivot arrangement that
allows them to pivot about the attachment bolt. The
ends of the diaphragm springs are hooked under the
lip of the pressure plate. So as the engine turns, the
flywheel, clutch cover, diaphragm springs and
pressure plate are all spinning together.
The clutch pedal is connected either mechanically
or hydraulically to a fork mechanism which loops
around the throw-out bearing. When you press on
the clutch, the fork pushes on the throw-out bearing
and it slides along the lay shaft putting pressure on
the innermost edges of the diaphragm springs.
These in turn pivot on their pivot points against the
inside of the clutch cover, pulling the pressure plateaway from the back of the clutch plates. This
release of pressure allows the clutch plates to
disengage from the flywheel. The flywheel keeps
spinning on the end of the engine crank but it no
longer drives the gearbox because the clutch plates
aren't pressed up against it.As you start to release
the clutch pedal, pressure is released on the throw-out bearing and the diaphragm springs begin to
push the pressure plate back against the back of the
clutch plates, in turn pushing them against the
flywheel again. Springs inside the clutch plate
absorb the initial shock of the clutch touching the
flywheel and as you take your foot off the clutch
pedal completely, the clutch is firmly pressed
against it. The friction material on the clutch plate
is what grips the back of the flywheel and causes
the input shaft of the gearbox to spin at the same
speed.
6.2 Types of Clutches
6.2.1 Multi-plate clutches
Adding plates to a clutch unit to form a multi-plate
clutch will increase its torque capacity, without
increasing spring strength or clutch diameter. This
clutch assembly has more than two friction discs, with
friction material riveted to both sides of each. An
internally-splined hub on each disc mates with the
splines on the transmission input shaft. A cast-iron
separator plate fits between each disc. The separator
plate locates on driving pins on the flywheel.
Figure 35Components of a Multi-plate clutch
This friction unit is between the flywheel and the
pressure plate when the pressure plate assembly is
bolted to the flywheel. The pressure plate spring
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then provides a frictional clamping force on each
mating surface.
6.2.2 Wet & Dry Clutches
A wet clutch is immersed in a cooling lubricatingfluid that also keeps surfaces clean and provides
smoother performance and longer life. Wet
clutches; however, tend to lose some energy to the
liquid. Since the surfaces of a wet clutch can be
slippery (as with a motorcycle clutch bathed in
engine oil), stacking multiple clutch discs can
compensate for the lowercoefficient of friction and
so eliminate slippage under power when fully
engaged. A dry clutch, as the name implies, is not
bathed in liquid and should be, literally, dry.
6.2.3 Centrifugal Clutch
A centrifugal clutch is aclutch that usescentrifugal
force to connect two concentric shafts, with the
driving shaft nested inside the driven shaft. The
input of the clutch is connected to the engine
crankshaft while the output may drive a shaft. As
engine rpm increase, weighted arms in the clutchswing outward and force the clutch to engage. The
most common types have friction pads or shoes
radially mounted that engage the inside of the rim
of housing.
Figure 36Parts of a Centrifugal clutch
On the centre shaft there are an assorted number of
extension springs, which connect to a clutch shoe.When the central shaft spins fast enough, the
springs extend causing the clutch shoes to engage
the friction face.
6.3 Gear ratio
Gear ratio is defined as the ratio of the speed of
the input shaft to that of the output shaft. It is
calculated as the ratio of the number of teeth on
the output gear to the number on the input gear.For example, imagine an input gear with 10
teeth, a secondary gear with 20 teeth and a final
gear with 30 teeth. From the input gear to the
secondary gear, the ratio is 20/10 = 2:1. From
the second gear to the final gear, the ratio is
30/20 = 1.5:1. The total gear ratio for this
system is (2*1.5):1, or 3:1. i.e. to turn the
output gear once, the input gear has to turn
three times. This also neatly shows how you
can do the calculation and misses the middle
gear ratios - ultimately you need the ratio of
input to output. In this example, the final output
is 30 and the original input is 10. 30/10 = 3/1 =
3:1.
Figure 37Figure depicting gear ratios
6.4 Types of Transmission
6.4.1 Manual Transmission
6.4.1a Constant Mesh type Gearbox
You can see the helical gears meshing with each
other. The lower shaft in this image is called the
layshaft - it's the one connected to the clutch - the
one driven directly by the engine. The output shaft
is the upper shaft in this image. Well look at theoutput shaft. You can see 5 helical gears and 3 sets
of selector forks. At the most basic level that tells
you this is a 5-speed box (note that my example has
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no reverse gear). With the clutch engaged, the
layshaft is alwaysturning. All the
Figure 38A constant mesh gearbox
helical gears on the layshaft are permanently
attached to it so they all turn at the same rate. They
mesh with a series of gears on the output shaft that
are mounted on sliprings.Therefore they actually
spin aroundthe output shaft without turning it.
Look closely at the selector forks; you'll see they
are slipped around a series of collars with teeth on
the inside. Those are the dog gears and the teeth are
the dog teeth. The dog gears are mounted to the
output shaft on a splined section which allows themto slide back and forth. When you move the gear
stick, a series of mechanical pushrod connections
move the various selector forks, sliding the dog
gears back and forth.Observing the close-up of the
area between third and fourth gear, when the
gearstick is moved to select fourth gear, the
selector fork slides backwards. This slides the dog
gear backwards on the splined shaft and the dog
teeth engage with the teeth on the front of thehelical fourth gear.
Fig. 39 Gear selection in a constant mesh
gearbox
This locks it to the dog gear which itself is locked
to the output shaft with the splines. When the
clutch is let out and the engine drives the layshaft,
all the gears turn as before but now the second
helical gear is locked to the output shaft and it is -
fourth gear.
6.4.1b Reverse Gear
Reverse gear is normally an extension of
everything you've learned above but with one extra
gear involved. Typically, there will be three gears
that mesh together at one point in the gearbox
instead of the customary two. There will be a gear
each on the layshaft and output shaft, but there will
be a small gear in between them called the idlergear. The inclusion of this extra mini gear
Figure 40Idler gear being used to reverse
direction of motion
causes the last helical gear on the output shaft to
spin in the opposite direction to all the others. The
principle of engaging reverse is the same as for any
other gear - a dog gear is slid into place with a
selector fork. Because the reverse gear is spinning
in the opposite direction, when you let the clutch
out, the gearbox output shaft spins the other way -
in reverse. The image here shows the same gearbox
as above modified to have a reverse gear.
6.4.1c Synchromesh gearbox
A synchro is a device that allows the dog gear to
come to a speed matching the helical gear before
the dog teeth attempt to engage. In this way, you
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don't need to 'blip' the throttle and double-clutch to
change gears because the synchro does the job of
matching the speeds of the various gearbox
components for you. To the left is a colour-coded
cutaway part of my example gearbox. The green
cone-shaped area is the syncho collar. It's attachedto the red dog gear and slides with it.
Figure 41Cone shaped synchro collars
As it approaches the helical gear, it makes friction
contact with the conical hole. The more contact it
makes, the more the speed of the output shaft and
free-spinning helical gear are equalised before the
teeth engage. If the car is moving, the output shaft
is always turning (because ultimately it is
connected to the wheels). The layshaft
is usually connected to the engine, but it is free-
spinning once the clutch has been operated.
Because the gears are meshed all the time, the
synchro brings the layshaft to the right speed for
the dog gear to mesh. This means that the layshaft
is now spinning at a different speed to the engine,
but that's OK because the clutch gently equalises
the speed of the engine and the layshaft, either
bringing the engine to the same speed as the
layshaft or vice versa depending on engine torque
and vehicle speed.
6.4.2 Continuously Variable
Transmission
Unlike traditional automatic transmissions,continuously variable transmissions don't have a
gearbox with a set number of gears, which means
they don't have interlocking toothed wheels. The
most common type of CVT operates on an
ingenious pulley system that allows an infinite
variability between highest and lowest gears with
no discrete steps or shifts. Most CVTs only have
three basic components: A high-power metal or
rubber belt, A variable-input "driving" pulley, Anoutput "driven" pulley
CVTs also have various microprocessors and
sensors, but the three components described above
are the key elements that enable the technology to
work. The variable-diameter pulleys are the heart
of a CVT. Each pulley is made of two 20-degree
cones facing each other. A belt rides in the groove
between the two cones. When the two cones of the
pulley are far apart (when the diameter increases),the belt rides lower in the groove, and the radius of
the belt loop going around the pulley gets smaller.
When the cones are close together (when the
diameter decreases), the belt rides higher in the
groove, and the radius of the belt loop going
around the pulley gets larger.
Figure 42CVT at low and high speeds
CVTs may use hydraulic pressure, centrifugal force
or spring tension to create the force necessary to
adjust the pulley halves. One of the pulleys, known
as the drive pulley (or driving pulley), is connected
to the crankshaft of the engine. The driving pulley
is also called the input pulley or variator because
it's where the energy from the engine enters the
transmission. The second pulley is called the driven
pulley because the first pulley is turning it. As an
output pulley, the driven pulley transfers energy to
the driveshaft. When one pulley increases itsradius, the other decreases its radius to keep the
belt tight. As the two pulleys change their radii
relative to one another, they create an infinite
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number of gear ratios -- from low to high and
everything in between. For example, when the
pitch radius is small on the driving pulley and large
on the driven pulley, then the rotational speed of
the driven pulley decreases, resulting in a lower
gear. When the pitch radius is large on the drivingpulley and small on the driven pulley, then the
rotational speed of the driven pulley increases,
resulting in a higher gear. CVT has an infinite
number of gears that it can run through at any time,
at any engine or vehicle speed.
When you roll off the throttle, the centrifugal force
is reduced and the spring loaded rollers drop back,
allowing the front pulley to open slightly, which
allows the belt to ride lower within the spring-
loaded, sliding halves of the pulley, which in turn
allows the rear pulley to close up and lower the
gearing.
6.4.3 Automatic Transmission
Automatic transmission is totally different from
manual transmission. There is no clutch pedal and
no gear shifter in an automatic transmission car.
Once you put the transmission into drive,
everything else is automatic. Automatic
Transmission uses a torque converter instead of a
clutch. The key difference between a manual and
an automatic transmission is that the manualtransmission locks and unlocks different sets
ofgears to the output shaft to achieve the various
gear ratios. While in an automatic transmission, the
same set of gears produces all of the different gear
ratios. The planetary gearset is the device that
makes this possible in an automatic transmission.
Any planetary gearset has three main components:
The sun gear, the planet gears and the planet
gears' carrier, the ring gear.Each of these three components can be the input,
the output or can be held stationary. Choosing
which piece plays which role determines the gear
ratio for the gearset. We can get lots of different
gear ratios out of this gearset.
Input Output Stationary CalculationGear
Ratio
Sun (S)Planet
Carrier (C)Ring (R) 1 + R/S 3.4:1
PlanetCarrier (C)
Ring (R) Sun (S) 1 / (1 + S/R) 0.71:1
Sun (S) Ring (R)Planet
Carrier (C)-R/S -2.4:1
Figure 43 Sun and Planet gears arrangement
in an automatic transmission
Also, locking any two of the three components
together will lock up the whole device at a 1:1 gear
reduction. Notice that the first gear ratio listed
above is a reduction -- the output speed is slower
than the input speed. The second is an overdrive --
the output speed is faster than the input speed. The
last is a reduction again, but the output direction is
reversed. There are several other ratios that can be
gotten out of this planetary gear set, but these are
the ones that are relevant to automatic
transmission.
But in the Compound Planetary Gearset there aretwo sun gears and two sets of intermeshing planet
gears. It has one ring gear that is always the output
of the transmission. It looks like a single planetary
gearset but actually behaves like two planetary
gearsets combined. In this system we can now have
four forward gear ratios and one reverse gear. In
the arrangement shown we have two sets of planet
gears that are arranged as inner and outer planets
and the inner one are shorter and only engage the
smaller sun gear and the outer planet gears. And
then the outer planet gear in turn rotates the larger
sun gear at the bottom and the outermost ring gear.
TATA NANO has Synchromesh on all
forward gears, Sliding mesh on reverse
gear with overdrive on 4th gear. It has 4-
speed manual transmission
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Hydraulic automatic transmissions
The predominant form of automatic transmission
ishydraulically operated; using afluid coupling or
torque converter, and a set ofplanetary gearsets to
provide a range of gear ratios.Fluid couplings and
torque converters are fluid-filled units installed
between the engines crankshaft and the
transmission. They consist of two sets of blades.
One set of blades is driven by the engine, and the
other set of blades is connected to the
transmissions input shaft. The blade setconnected
to the engine is called the impeller, and the blade
set connected to the input shaft is called the
turbine. See Figure 1-13. A hydraulic pump in the
transmission forces fluid into the converter. Insidethe converter, the fluid is spun by the impeller
blades. As the fluid is thrown from the impeller
blades, it strikes the turbine blades. See Figure 1-
14. Power is transmitted from the impeller to the
turbine through the fluid. When the vehicle is
stopped, the fluid from the impeller continues to
strike the turbine, but the fluid allows enough
slippage between the impeller and the turbine to
prevent engine stalling.
Hydraulic automatic transmissions consist of three
major components:
1.Torque Converter
F lu id coupli ngs and torque converters are fluid-
filledunits installed between theenginescrankshaft and the transmission. They consist of
two sets of blades. One set of blades is driven by
the engine, and the other set of blades is connected
to the transmissions input shaft. The blade set
connected to the engine is called the impeller, and
the blade set connected to the input shaft is called
the turbine. A hydraulic pump in the transmission
forces fluid into the converter. Inside the converter,
the fluid is spun by the impeller blades. As the
fluid is thrown from the impeller blades, it strikes
the turbine blades.
When the impellar is driven by the engine
crankshaft, the fluid around the impellar rotates in
the same direction.as impellar speed increases
,centrifugal force causes the fluid to flow outward
from the center of the impellar.as speed increases
further,fluid is forced out away from the impellar
towards the turbine.The fluid strikes the vanes of
turbine causing it to rotate in the same direction as
the impellar.
After the fluid dissipates its energy against the
vanes of the turbine,it flows inward along the vanes
of the turbine. When it reaches the interior of the
turbine,the turbines curved inner surface directs the
fluid at the vanes of the stator.Fluid strikes the
curved vane of the stator causing the one way
clutch to lick the stator and redirect the fluid at the
impellar vanes in the direction of the engine
rotation, increasing engine torque.
As the impellar and turbine approach the same
speed, fluid strikes the back of the stator
vanes,releasing the one way clutch and allows the
stator to freewheel.Unless the stator
freewheels,being mounted to the transmission
body,fluid will strike the vanes of the stator and
limit engine rpm and upper engine performance.
Fig.44 Torque converter
2. Planetary gear train
It Consists ofplanetary gear sets as well as clutches
and bands. These are the mechanical systems that
provide the variousgear ratios,altering the speed of
rotation of the output shaft depending on which
planetary gears are locked.
To effect gear changes, one of two types of clutches
or bands are used to hold a particular member of the
planetary gearset motionless, while allowing anothermember to rotate, thereby transmitting torque and
producing gear reductions or overdrive ratios. These
clutches are actuated by the valve body (see below),
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their sequence controlled by the transmission's
internal programming. Principally, a type of device
known as asprag or roller clutch is used for routine
upshifts/downshifts.
3. Hydraulic controls uses specialtransmission
fluid sent under pressure by anoil pump to control
various clutches and bands modifying the speed of
the output depending on the cars running condition.
Dual Clutch Transmission (DCT)
A dual-clutch transmission offers the function of
two manual gearboxes in one. A dual-clutch
gearbox uses two clutches, but has no clutch pedal.
Sophisticated electronics and hydraulics control the
clutches, just as they do in a standard automatictransmission. In a DCT, however, the clutches
operate independently. One clutch controls the odd
gears, while the other controls the even gears.
Using this arrangement, gears can be changed
without interrupting the power flow from the
engine to the transmission. A two-part transmission
shaft is at the heart of a DCT. Unlike a
conventional manual gearbox, which houses all of
its gears on a single input shaft, the DCT splits up
odd and even gears on two input shafts. The outer
shaft is hollowed out, making room for an inner
shaft, which is nested inside. The outer hollow
shaft feeds second, fourth and sixth gears, while the
inner shaft feeds first, third and fifth.
Figure45Basic arrangement of a 6-speed dual
clutch transmission
The diagram shows this arrangement for a typical
6-speed DCT. Notice that one clutch controlssecond, fourth and sixth gears, while another
independent clutch controls first, third and fifth
gears. That's the trick that allows lightning-fast
gear changes and keeps power delivery constant. A
standard manual transmis