Mechanical Engineer

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CORPORATE H.R. TATA MOTORS LIMITED 1

CONTENTS

INTRODUCTION TO TATA MOTORS ............................................................................. 4

AUTOMOBILES ............................................................................................................... 9

MAJOR SUB SYSTEMS OF AN AUTOMOBILE ..........................................................9

INTERNAL COMBUSTION ENGINE ..........................................................................10

PARTS OF AN INTERNAL COMBUSTION ENGINE .................................................10

FOUR STROKE CYCLE (PETROL ENGINES) ..........................................................11

DIESEL ENGINES ......................................................................................................13

DIESEL CYCLE ..........................................................................................................13

ENGINE BLOCK .........................................................................................................14

CYLINDERS................................................................................................................14

ENGINE CONFIGURATION .......................................................................................15

ENGINE CAPACITY ...................................................................................................15

PISTON.......................................................................................................................16

POPPET VALVES.......................................................................................................16

CAM SHAFT ...............................................................................................................17

CRANK SHAFT...........................................................................................................17

POWER TRAIN .............................................................................................................. 19

MANUAL TRANSMISSION.........................................................................................19

AUTOMATIC TRANSMISSION...................................................................................20

GEARS........................................................................................................................20

CLUTCH......................................................................................................................20

DIFFERENTIAL...........................................................................................................21

DRIVE SHAFT / PROPELLER SHAFT.......................................................................23

FRONT WHEEL DRIVE..............................................................................................23

REAR WHEEL DRIVE ................................................................................................24

FUEL SUPPLY SYSTEM ............................................................................................... 27

FUEL PUMP................................................................................................................27

FUEL INJECTION IN A PETROL ENGINE.................................................................27

CARBURETOR...........................................................................................................27

FUEL INJECTION IN DIESEL ENGINE......................................................................28

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FUEL INJECTOR........................................................................................................28

TURBOCHARGER......................................................................................................29

VALVES ......................................................................................................................29

IGNITION SYSTEM ........................................................................................................ 31

BATTERY OPERATED IGNITION..............................................................................31

SPARK IGNITION.......................................................................................................32

COMPRESSION IGNITION ........................................................................................32

SPARK PLUG .............................................................................................................32

ALTERNATOR............................................................................................................33

BATTERY....................................................................................................................33

EXHAUST SYSTEM ...................................................................................................34

PARTS OF AN EXHAUST SYSTEM ..........................................................................34

MANIFOLD..................................................................................................................34

CATALYTIC CONVERTOR ........................................................................................35

EXHAUST PIPE..........................................................................................................35

SILENCER OR MUFFLER.........................................................................................36

COOLING SYSTEM ....................................................................................................... 38

RADIATOR..................................................................................................................38

INTERCOOLER ..........................................................................................................38

BRAKING SYSTEM ....................................................................................................... 40

BRAKE PEDAL ...........................................................................................................40

BRAKES......................................................................................................................40

1) DRUM BRAKES......................................................................................................40

2) DISC BRAKES........................................................................................................40

3) HYDRAULIC BRAKES............................................................................................40

HYDRAULIC BRAKES................................................................................................40

BUILD ............................................................................................................................. 42

CHASIS.......................................................................................................................42

MONOCOQUE............................................................................................................42

AXLE...........................................................................................................................42

SUSPENSION.............................................................................................................43

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STEERING..................................................................................................................43

GLOSSARY.................................................................................................................... 45

CAR BODY STYLES...................................................................................................45

TECH SPEAK .............................................................................................................48

LIST OF SOME USEFUL LINKS.................................................................................... 66

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INTRODUCTION TO TATA MOTORS

COMPANY Tata Motors is India’s largest automobile company. It is the leader by far in commercial

vehicles in each segment, and the second largest in the passenger car market with

winning products in the compact, midsize car and utility vehicle segments. The company

is the world’s fifth largest medium and heavy commercial vehicle manufacturer and the

world's second largest medium and heavy bus manufacturer.

Established in 1945, Tata Motors’ presence indeed cuts across the length and breadth of

India. Over 3 million Tata vehicles ply on Indian roads, since the first rolled out in 1954.

The company’s manufacturing base is spread across Jamshedpur, Pune and Lucknow,

supported by a nation-wide dealership, sales, services and spare parts network

comprising about 1,200 touch points. The company also has a strong auto finance

operation, Tata Motor Finance.

At the core of the company’s approach to doing business is the Tata Business

Excellence Model. Incorporating sound business principles, like customer satisfaction,

quality, attention to detail, conservation of resources and protection of the environment,

this model shapes the way Tata Motors designs, manufactures and markets its products.

PRODUCTS

The company’s main product lines are:

• Passenger Cars: the compact car, Indica, launched in 1998, the mid size, Indigo,

launched in 2002, and the Indigo Marina, launched in 2004 in both petrol and

diesel versions.

• Utility Vehicles: the Tata Sumo launched in 1994, the Tata Safari launched in

1998 and their variants

• Small Commercial Vehicles: the company created a new segment in 2005 by

launching the Tata Ace, India’s first indigenously developed mini-truck.

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• Light Commercial Vehicles: which include pickups, trucks and buses ranging

from 2T GVW to 7.5T GVW

• Medium and Heavy Commercial Vehicles: which include trucks, buses, dumpers

and multi- axled vehicles from 9T GVW to 40T GVW. Through Tata Daewoo

Commercial Vehicle Company Limited. It now offers a range of high horsepower

trucks ranging from 220 HP to 400 HP in dump truck, tractor-trailers, mixers and

cargo applications.

Adopting the principle of Kaizen or continuous learning, the company is constantly

improving its standards. The versatile yet simple 5S approach to process

improvement - sort, straighten, simplify and standardize in a self-disciplined manner-

is a way of life at Tata Motors.

These principles help optimize various operations of the company and conserve

precious resources. By working closely with vendors and partners, at the design and

manufacturing stages, the company ensures that they too follow the same principles.

INTERNATIONAL BUSINESS

Tata Motors, the first company from India’s engineering sector to be listed in the New

York Stock Exchange (September 2004), has also emerged as an international

automotive company. While currently about 18% of its revenues are from international

business, the company’s objective is to expand its international business, both through

organic and inorganic growth routes.

Over the years, the company has received more than 50 awards from the Government

of India for its exports initiatives. In 2004, it acquired the Daewoo Commercial Vehicle

Company, Korea’s second largest truck maker. The rechristened Tata Daewoo

Commercial Vehicle Company has already begun to launch new products. In 2005, Tata

Motors acquired a 21% stake in Hispano Carrocera, a reputed Spanish bus and coach

manufacturer, with an option to acquire the remaining stake as well. Hispano’s presence

is being expanded in other markets.

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These acquisitions will further extend Tata Motors’ international footprint, established

through exports since 1961. The company’s commercial and passenger vehicles are

already being marketed in several countries in Europe, Africa, the Middle East, South

East Asia, South Asia and Australia. It has assembly operations in Malaysia, Kenya,

Bangladesh, Ukraine, Russia, Spain and Senegal.

SUBSIDIARIES

Through its subsidiaries, the company is engaged in engineering and automotive

solutions, construction equipment manufacturing, automotive vehicle components

manufacturing and supply chain activities, machine tools and factory automation

solutions, high-precision tooling and plastic and electronic components for automotive

and computer applications, and automotive retailing and service operations.

RESEARCH & DEVELOPMENT

The foundation of the company’s growth over the last 50 years is a deep understanding

of economic stimuli and customer needs, and the ability to translate them into customer-

desired offerings through leading edge R&D. The company’s Engineering Research

Centre (ERC), in Pune which has 1400 scientists and engineers, was established in

1966. Tata Daewoo Commercial Vehicle Company and Hispano Carrocera also have

R&D establishments at Gunsan in Korea and Zaragoza in Spain. These three facilities

together enable the company to share and access knowledge and technology for

designing and developing world-class products. Besides product development, R&D also

focuses on environment-friendly technologies in emissions and alternative fuels.

The ERC has enabled pioneering technologies and products. It was Tata Motors, which

developed the first indigenously developed Light Commercial Vehicle, India’s first Sports

Utility Vehicle and, in 1998, the Tata Indica, India’s first fully indigenous passenger car.

Within two years of launch, Tata Indica became India’s largest selling car in its segment.

The pace of new product development has quickened through an organization-wide

structured New Product Introduction (NPI) process. The process with its formal structure

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for introducing new vehicles in the market, brings in greater discipline in project

execution. For example, the NPI process helped Tata Motors create a new segment by

launching the Tata Ace, India’s first mini-truck. The years to come will see the

introduction of several other innovative vehicles, all rooted in emerging customer needs.

The ERC in Pune, among whose facilities are India’s only certified crash-test facility

and hemi-anechoic chamber for testing of noise and vibration has received several

awards from the Government of India. Some of the more prominent amongst them are

the National Award for Research and Development Efforts in Industry in the Mechanical

Engineering Industries sector in 1999, the National Award for Successful

Commercialisation of Indigenous Technology by an Industrial Concern in 2000, and the

CSIR Diamond Jubilee Technology Award in 2004.

CORPORATE SOCIAL RESPONSIBILITY

True to the tradition of the Tata Group, Tata Motors is committed in letter and spirit to

Corporate Social Responsibility. It is a signatory to the United Nations Global Compact,

and is engaged in community and social initiatives on human rights, labour and

environment standards in compliance with the principles of the Global Compact.

Tata Motors has led the automobile industry’s anti-pollution efforts through a series of

initiatives in effluents and emission control. The company introduced emission-friendly

engines in its products in India even before such norms were made statutory. It ensures

that its products are environmentally sound by reducing hazardous materials in vehicle

components, developing extended life lubricants, fluids and using ozone-friendly

refrigerants. The company uses some of the world's most advanced equipment for

emission check and control.

Tata Motors undertakes soil and water conservation programmes and extensive tree

plantation drives. The company is committed to restoring and preserving environmental

balance, by reducing waste and pollutants, conserving resources and recycling

materials.

Simultaneously, it also plays an active role in community development, serving rural

communities adjacent to its manufacturing locations in Jamshedpur, Pune and Lucknow.

Among them are cooperative societies, such as the Tata Motors Grihini Udyog. This

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society provides inputs on skill development to women. The women work for four hours

per day, in activities ranging from preparing spices and condiments to cable harness and

electronic items. The society has provided employment to nearly 1200 women. Tata

Motors also focuses on improving the health of rural communities through women

trained as village health workers. They are trained in basic diagnostic skills and first aid,

and are at the forefront of all development initiatives. Through this initiative, the women

gain financial independence which in turn improves their social stature and makes them

change agents in their community.

These continuing initiatives received national recognition from the Institute of Directors

and the World Environment Foundation in 2004, when the company was awarded the

‘Golden Peacock Award’ for Corporate Social Responsibility.

With principles and practices, which others want to emulate, Tata Motors today is

recognized as among the most respected countries in India. With the foundation of its

rich heritage, it is today is etching a refulgent future across the world.

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AUTOMOBILES

An automobile is a wheeled vehicle that carries its own motor. Different types of

automobiles include cars, buses, trucks, vans, and motorcycles, with cars being the

most popular. The term is derived from Greek 'autos' (self) and Latin 'movére' (move),

referring to the fact that it 'moves by itself'. Earlier terms for automobile include

'horseless carriage' and 'motor car'. As of 2005 there are 600 million cars worldwide

(0.074 per capita).

MAJOR SUB SYSTEMS OF AN AUTOMOBILE The major subsystems of an automobile are

1) engine

2) transmission

3) fuel supply system

4) fuel ignition system

5) exhaust system

6) cooling system

7) braking system

8) build

The following chapters describe each system with all major components and working in

brief.

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ENGINES An engine is something that produces

some effect from a given input.

Automotive production down the ages

has required a wide range of energy-

conversion systems. These include

electric, steam, solar, turbine, rotary,

and different types of piston-type

internal combustion engines. The

gasoline internal combustion engine,

operating on a four-stroke Otto cycle, has traditionally been the most successful for

automobiles, while diesel engines are widely used for trucks and buses. Karl Benz led in

the development of new engines. The internal combustion engine was originally selected

for the automobile due to its flexibility over a wide range of speeds. Also, the power

developed for a given weight engine was reasonable; it could be produced by

economical mass-production methods; and it used a readily available, moderately priced

fuel- petrol.

INTERNAL COMBUSTION ENGINE The internal combustion engine is a

heat engine in which the burning of a

fuel occurs in a confined space called a

combustion chamber. This creates

gases of high temperature and

pressure, which are permitted to

expand. The defining feature of an

internal combustion engine is that useful

work is performed by the expanding hot

gases acting directly to cause movement, for example by acting on pistons, rotors, or

even by pressing on and moving the entire engine itself.

PARTS OF AN INTERNAL COMBUSTION ENGINE The parts of an engine vary depending on the engine's type. For a four-stroke engine,

key parts of the engine include the crankshaft (purple), one or more camshafts (red and

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blue) and valves. For a two-stroke engine, there may

simply be an exhaust outlet and fuel inlet instead of a

valve system. In both types of engines, there are one or

more cylinders (grey and green) and for each cylinder in

a petrol engine there is a spark plug (darker-grey), a

piston (yellow) and a crank (purple). A single sweep of

the cylinder by the piston in an upward or downward

motion is known as a stroke and the downward stroke

that occurs directly after the air-fuel mix in the cylinder is

ignited is known as a power stroke. The various parts of

an engine are discussed later.

FOUR STROKE CYCLE (PETROL ENGINES)

The four-stroke cycle (or Otto cycle) of an internal combustion engine is the cycle most

commonly used for automotive and industrial purposes today (cars and trucks,

generators, etc). The Otto cycle is characterized by four strokes, or straight movements

alternately, back and forth, of a piston inside a cylinder:

• Intake stroke

• Compression stroke

• Combustion stroke

• Exhaust stroke

Intake Stroke- During the intake stroke, the piston moves downward, drawing a fresh

charge of vaporized fuel/air mixture. The illustrated engine features a 'poppet' intake

valve which is drawn open by the vacuum produced by the intake stroke. Some early

engines worked this way, however most modern engines incorporate an extra cam/lifter

arrangement as seen on the exhaust valve. The exhaust valve is held shut by a spring

(not illustrated here).

Compression Stroke- As the piston rises the poppet valve is forced shut by the

increased cylinder pressure. Flywheel momentum drives the piston upward,

compressing the fuel/air mixture.

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Power Stroke. At the top of the compression stroke the spark plug fires, igniting the

compressed fuel. As the fuel burns it expands, driving the piston downward

Intake Stroke Compression Stroke Power Stroke Exhaust Stroke

Exhaust Stroke. At the bottom of the power stroke, the exhaust valve is opened by the

cam/lifter mechanism. The upward stroke of the piston drives the exhausted fuel out of

the cylinder.

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DIESEL ENGINES The diesel engine is a type of internal combustion engine;

more specifically, it is a compression ignition engine, in

which the fuel is ignited by being suddenly exposed to the

high temperature and pressure of a compressed gas,

rather than by a separate source of ignition, such as a

spark plug, as is the case in the petrol engine. This is

known as the diesel cycle, after German engineer Rudolf

Diesel In a diesel engine, instead of the air fuel mixture as

in petrol engines, only air is sucked in and the fuel is injected into the cylinder in the

power stroke.

DIESEL CYCLE When a gas is compressed, its temperature rises; a diesel engine uses this property to

ignite the fuel.

INTAKE STROKE: Air is drawn into the cylinder of a diesel engine

COMPRESSION STROKE: Air taken in the previous stroke is compressed by the rising

piston at a much higher compression ratio than for a spark-ignition engine, up to 25:1.

The air temperature reaches 700–900 °C, or 1300–1650 °F.

POWER STROKE: At the top of the piston stroke, diesel fuel is injected into the

combustion chamber at high pressure, through an atomizing nozzle, mixing with the hot,

high-pressure air. The resulting mixture ignites and burns very rapidly. This contained

combustion causes the gas in the chamber to heat up rapidly, which increases its

pressure, which in turn forces the piston downwards. The connecting rod transmits this

motion to the crankshaft, which is forced to turn, delivering rotary power at the output

end of the crankshaft.

EXHAUST STROKE: Scavenging (pushing the exhausted gas-charge out of the

cylinder, and drawing in a fresh draught of air) of the engine is done either by ports or

valves.

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To fully realize the capabilities of a diesel engine, use of a turbocharger to compress the

intake air is necessary; use of an aftercooler/intercooler to cool the intake air after

compression by the turbocharger further increases efficiency

ENGINE BLOCK The cylinder block is a machined casting (or sometimes an

assembly of modules) containing cylindrically bored holes for

the pistons of a multi-cylinder reciprocating internal

combustion engine, or for a similarly constructed device such

as a pump. It is a complicated part at the heart of an engine,

with adaptations to attach the cylinder head, crankcase,

engine mounts, drive housing and engine ancillaries, with

passages for coolants and lubricant

CYLINDERS

Internal combustion engines can contain any number

of cylinders with numbers between one and twelve

being common; though as many as 30 have been

used. Having more cylinders in an engine yields two

potential benefits:

First: the engine can have a larger displacement with

smaller individual reciprocating masses (that is, the

mass of each piston can be less) thus making a smoother running engine (since the

engine tends to vibrate as a result of the pistons moving up and down).

Second: with a greater displacement and more pistons, more fuel can be combusted

and there can be more combustion events (that is, more power strokes) in a given period

of time, meaning that such an engine can generate more torque than a similar engine

with fewer cylinders.

The down side to having more pistons is that, over all, the engine will tend to weigh more

and tend to generate more internal friction as the greater number of pistons rub against

the inside of their cylinders. This tends to decrease fuel efficiency and rob the engine of

some of its power. For high performance petrol engines using current materials and

technology (such as the engines found in modern automobiles), there seems to be a

break point around 10 or 12 cylinders, after which addition of cylinders becomes an

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overall detriment to performance and efficiency, although exceptions such as the W-16

engine from Volkswagen exist.

ENGINE CONFIGURATION

Engine configuration is an engineering

term for the layout of the major

components of an internal combustion

engine. These components include

cylinders, pistons, crankshaft or

crankshafts and camshaft or camshafts.

Common configurations include the

straight or inline configuration, the more

compact V configuration and the wider but

smoother flat or boxer configuration.

Aircraft engines can also adopt a radial configuration which allows more effective

cooling. More unusual configurations, such as "H", "U", "X", or "W" have also been used.

ENGINE CAPACITY An engine's capacity is the displacement or swept volume by the pistons of the engine. It

is generally measured in litres or cubic inches for larger engines and cubic centimetres

(abbreviated to cc's) for smaller engines. Engines with greater capacities are usually

more powerful and provide greater torque at lower rpms but also consume more fuel.

Apart from designing an engine with more cylinders, there are two ways to increase an

engine's capacity. The first is to lengthen the stroke and the second is to increase the

piston's diameter. In either case, it may be necessary to make further adjustments to the

fuel intake of the engine to ensure optimal performance.

An engine's quoted capacity can be more a matter of marketing than of engineering. The

Morris Minor 1000, the Morris 1100, and the Austin-Healey Sprite Mark II all had engines

of the same stroke and bore according to their specifications, and were from the same

maker. However the engine capacities were quoted as 1000cc, 1100cc and 1098cc

respectively in the sales literature and on the vehicle badges.

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PISTON In general, a piston is a sliding plug that fits closely inside the

bore of a cylinder. Its purpose is either to change the volume

enclosed by the cylinder, or to exert a force on a fluid inside the

cylinder. Most pistons fitted in a cylinder have piston rings.

Usually there are two spring-compression rings that act as a

seal between the piston and the cylinder wall, and one or more

oil control rings below the compression rings. As the piston

moves inside the cylinder, it transforms the energy from the

expansion of a burning gas (usually a mixture of petrol or diesel

and air) into mechanical power (in the form of a reciprocating

linear motion). From there the power is conveyed through a

connecting rod to a crankshaft, which transforms it into a rotary

motion, which usually drives a gearbox through a clutch.

POPPET VALVES Four-stroke engines, of either spark ignition or compression

ignition varieties, use poppet valves to allow air (or an

air/fuel mixture) into the cylinder and exhaust gases out.

A poppet valve is a valve consisting of a hole, usually round

or oval, and a tapered plug, usually a

disk shape on the end of a shaft also

called a valve stem. The shaft guides the plug portion by sliding

through a valve guide. The stem is used to push down on the valve

and open it, with a spring generally used to close it when the stem is

not being pushed on. The engine normally operates the valves by

pushing on the stems with cams and cam followers. The shape and

position of the cam determines the valve lift and when and how

quickly (or slowly) the valve is opened. The cams are normally

placed on a fixed camshaft which is then geared to the crankshaft,

running at half crankshaft speed in a four-stroke engine.

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CAM SHAFT The camshaft is an apparatus used in

piston engines to operate valves. It

consists of a cylindrical rod running the

length of the cylinder bank with a

number of oblong lobes or cams

protruding from it, one for each valve.

The cams force the valves open by

pressing on the valve, or on some

intermediate mechanism, as they rotate.

The relationship between the rotation of the camshaft and the rotation of the crankshaft

is of critical importance. Since the valves control the flow of fuel intake and exhaust, they

must be opened and closed at the appropriate time during the stroke of the piston.

CRANK SHAFT The crankshaft, sometimes casually

abbreviated to crank, is that part of an

engine which translates reciprocating linear

piston motion into rotation. It typically

connects to a flywheel, to reduce the

pulsation characteristic of the four-stroke

cycle. The figure shows the arrangement of

crank shaft ( red ), pistons ( grey ) ,

cylinders ( blue ) and flywheel ( dark grey ).

The crankshaft has a linear axis about which it rotates, typically with several bearing

journals riding on replaceable bearings held in the engine block, the main bearings. In

addition, to convert the reciprocating motion into

rotation, the crankshaft has "crank throws" or

"crank pins", additional bearing surfaces whose

axis is offset from that of the crank, to which the

"big ends" of the connecting rods from each

cylinder attach. The distance of the axis of the

crank throws from the axis of the crankshaft

determines the piston stroke measurement, and thus engine displacement.

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POWER TRAIN An auto's drivetrain or powertrain

consists of all the components that

generate power and deliver it to

the road surface. Besides the

engine it includes the

transmission, driveshaft,

differentials, and the final drive

(drive wheels, caterpillar track,

propeller, etc). Sometimes

"powertrain" is used to refer to

simply the engine and transmission, including the other components only if they are

integral to the transmission. A vehicle's driveline consists of the parts of the drivetrain

excluding the engine and transmission. It is the portion of a vehicle, after the

transmission, that changes depending on whether a vehicle is front wheel drive, four

wheel drive, or rear wheel drive.

Engines typically operate over a range of 600 to about 6000 revolutions per minute

(though this varies from design to design and is typically less for diesel engines), while

the car's wheels rotate between 0 rpm and around 2500 rpm. Furthermore, the engine

provides its highest torque outputs approximately in the middle of its range, while often

the greatest torque is required when the vehicle is moving from rest or travelling slowly.

Therefore, a system that transforms the engine's output so that it can supply high torque

at low speeds, but also operate at highway speeds with the motor still operating within its

limits, is required. Transmissions perform this transformation.

Manual transmission Manual transmissions come in two basic types: a

simple unsynchronized system where gears are

spinning freely and must be synchronized by the

operator to avoid noisy and damaging "gear clash",

and synchronized systems that will automatically

"mesh" while changing gears.. They are cheaper,

lighter, usually give better performance and fuel

efficiency

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Automatic transmission Automatic transmission employs hydraulics to select

gears, depending on pressure exerted by fluid within the

transmission assembly. Rather than using a clutch to

engage the transmission, a torque converter is put in

between the engine and transmission. It is possible for

the driver to control the number of gears in use or select

reverse, though precise control of which gear is in use is

usually not possible. Automatic transmissions are easy

to use.

GEARS A gear is a toothed wheel designed to transmit

torque to another gear or toothed component.

The teeth (or cogs) of a gear are shaped to

minimize wear, vibration and noise, and to

maximize the efficiency of power transmission.

The larger gear is known as a wheel and the

smaller as a pinion. This is the principle of the

automobile transmission, allowing selection between various mechanical advantages.

Gear Ratio : A gear ratio occurs when 1 gear drives another gear. For example, lets

take two different size gears, one with 40 teeth and the other with 20. The one with 20

teeth will make two revolutions compared to one revolution performed by the gear with

40 teeth. This setup would create a gear ratio of 2:1. The driven gear (40 teeth) turns 1/2

the speed of the drive gear (20 teeth) but multiplies the torque by 2. The higher the ratio,

4:1 for example, the more torque will be created, but the slower the output speed.

CLUTCH A clutch is a mechanism for transmitting rotation, which can be engaged and

disengaged. In everyday use, the term clutch refers to a subcomponent of motor vehicle

engine's transmission designed to allow engagement or disengagement of the engine to

the gearbox or whatever apparatus is being driven.

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There are many different vehicle clutch designs, but

most are based on one or more friction discs, pressed

tightly together or against a flywheel using springs. The

spring pressure is released when the clutch pedal is

depressed thus either pushing or pulling the diaphragm

of the pressure plate, depending on type, and the

friction plate is released and allowed to rotate freely. A

wet clutch is immersed in a cooling lubricating fluid,

which also keeps the surfaces clean and gives

improved performance and longer life. Clutch Disc

A dry clutch, as the name implies, uses no fluid. No pressure on the pedal means that

the clutch plates are engaged (driving), while depressing the pedal will disengage the

clutch plates, allowing the driver to shift gears. A manual transmission contains cogs for

selecting gears. These cogs have matching teeth, called dog teeth, which means that

the rotation speeds of the two parts have to match for engagement. This speed matching

is achieved by a secondary clutch called a synchromesh, a device that uses frictional

contact to bring the two parts to the same speed, and a locking mechanism called a

blocker ring to prevent engagement of the teeth (full movement of the shift lever into

gear) until the speeds are synchronized.

DIFFERENTIAL In an automobile and other four-

wheeled vehicles, a differential is a

device, usually consisting of gears, for

allowing each of the driving wheels to

rotate at different speeds, while

supplying equal torque to each of

them.

The following description of a

differential applies to a "traditional"

rear-wheel-drive car or truck: Power is supplied from the engine, via the gearbox, to a

propeller shaft (U.S. term: driveshaft), which runs to the rear axle. A pinion gear (shown

in green in the diagrams) at the end of the propeller shaft is encased within the

differential itself, and it engages with the large ring gear (British term: crownwheel),

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shown in the diagrams. The ring gear is attached to a carrier, which holds a set of small

planetary gears. The three planetary gears are set up in such a way that the two outer

gears (the side gears), can rotate in opposite directions relative to each other. The pair

of side gears drive the axle shafts to each of the wheels. The entire carrier rotates in the

same direction as the ring gear, but within that motion, the side gears can counter-rotate

relative to each other.

Input torque is applied to the ring gear, which

turns the entire carrier (all blue), providing

torque to both side gears (red and yellow),

which in turn may drive the left and right

wheels. If the resistance at both wheels is

equal, the pinion gear (green) does not rotate,

and both wheels turn at the same rate.

If the left side gear (red) encounters resistance,

the pinion gear (green) rotates about the left

side gear, in turn applying extra rotation to the

right side gear (yellow ).

Thus, for example, if the car is making a turn to the right, the main ring gear may make

10 full revolutions, and during that time, the left wheel will speed up because it has

further to travel, and the right wheel will slow down correspondingly, as it has less

distance to travel. The side gears will turn in opposite directions relative to each other

by, say, 2 full turns, resulting in the left wheel making 12 revolutions, and the right wheel

making 8 revolutions. When the vehicle is travelling in a straight line, there will be almost

no movement of the planetary system of gears, other than the minute movements

necessary to compensate for slight differences in wheel diameter, undulations in the

road (which make for a longer or shorter wheel path) etc.

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DRIVE SHAFT / PROPELLER SHAFT

A driveshaft or driving shaft or Cardan shaft is a

mechanical device for transferring power from

the engine or motor to the point where useful

work is applied. Most engines or motors deliver

power as torque through rotary motion: this is

extracted from the linear motion of pistons in a

reciprocating engine; water driving a water wheel; or forced air or water in a turbine.

Driveshafts are carriers of torque: they are subject to torsion and shear stress, which

represents the difference between the input force and the load. They thus need to be

strong enough to bear the stress, without imposing too great an additional inertia by

virtue of the weight of the shaft.

FRONT WHEEL DRIVE In automobile design, an FF, or Front-engine, Front wheel drive, layout places both the

engine and driven wheels at the front of the vehicle. This layout is typically chosen for its

compact packaging - that is, it takes up very little space, allowing the rest of the vehicle

to be designed more flexibly.

Advantages of front wheel drive

• Interior space: Since the powertrain is a single unit contained in the engine

compartment of the vehicle, there is no need to devote interior space for a

driveshaft tunnel or rear differential, increasing the volume available for

passengers and cargo.

• Cost: Fewer components overall

• Weight: Fewer components mean lower weight

• Fuel economy: Lower weight means better petrol mileage

• Improved drivetrain efficiency: the direct connection between engine and

transaxle reduce the mass and mechanical inertia of the drivetrain compared to a

rear-wheel drive vehicle with a similar engine and transmission, allowing greater

fuel economy.

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• Assembly efficiency: the powertrain can be often be assembled and installed as

a unit, which allows more efficient production.

• Slippery-surface traction: placing the mass of the drivetrain over the driven

wheels improves traction on wet, snowy, or icy surfaces.

• Predictable handling characteristics

• Front wheel drive wears down the front tires first so you don't have to switch tires

to get the best tires in the rear.

Disadvantages of front wheel drive

• Lack of weight shifting will limit the acceleration of a front wheel drive vehicle. In

a rear wheel drive car the weight shifts back during acceleration giving more

traction to the driving wheels. The fact that this does not happen in a front wheel

car is the main reason why nearly all racing cars are rear wheel drive. However,

since front wheel cars have the weight of the engine over the driving wheels the

problem only applies in extreme conditions.

• In some towing situations front wheel drive cars can be at a traction

disadvantage since there will be less weight on the driving wheels. Because of

this, the weight that the vehicle is rated to safely tow is likely to be less than that

of a rear wheel drive or four wheel drive vehicle of the same size and power.

• The driveshafts may limit the amount by which the front wheels can turn, thus it

may increase the turning circle of a front wheel drive car compared to a rear

wheel drive one with the same wheelbase.

REAR WHEEL DRIVE In Automobile design, an RR, or Rear-engine, Rear wheel drive, layout places both the

engine and drive wheels at the rear of the vehicle. This layout is typically chosen for a

combination of several reasons. For optimal handling and to eliminate the phenomenon

known as torque steer, the wheels which propel the car should not be the same ones

that steer it. For optimum traction, the engine should be nearest to the driven wheels

since the engine is typically the densest/heaviest component of the car.

Advantages

• Better handling in dry conditions - accelerating force is applied to the rear

wheels, on which the down force increases, due to load transfer in acceleration,

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making the rear tires better able to take simultaneous acceleration and curving

than the front tires.

• Less costly and easier maintenance - Rear wheel drive is mechanically simpler

and typically does not involve packing as many parts into as small a space as

does front wheel drive, thus requiring less disassembly or specialized tools in

order to replace parts.

• Even weight distribution - The division of weight between the front and rear

wheels has a significant impact on a car's handling, and it is much easier to get a

50/50 weight distribution in a rear wheel drive car than in a front wheel drive car,

as more of the engine can lie between the front and rear wheels (in the case of a

mid engine layout, the entire engine), and the transmission is moved much

farther back.

• Towing - Rear wheel drive puts the wheels which are pulling the load closer to

the point where a trailer articulates, helping steering, especially for large loads.

• Weight transfer during acceleration. (During heavy acceleration, the front end

rises, and more weight is placed on the rear, or driving wheels).

• Drifting - Drifting is a controlled skid, where the rear wheels break free from the

pavement as they spin, allowing the rear end of the car to move freely left and

right. This is of course easier to do on slippery surfaces. Severe damage and

wear to tires and mechanical components can result from drifting on dry asphalt.

Disadvantages

• More difficult to master - While the handling characteristics of rear-wheel drive

may be useful or fun in the hands of some drivers, for others, having the rear

wheels move about is unintuitive and dangerous.

• Decreased interior space - This isn't an issue in a vehicle with a ladder frame like

a pickup truck, where the space used by the drive line is unusable for

passengers or cargo.

• Increased weight - The components of your typical rear wheel drive vehicle's

power train may be less complex, but there are more of them. The driveshaft

adds weight. The transmission is probably heavier.

• More difficult handling on low grip surfaces (wet road, ice, snow, gravel...) as the

car is pushed rather than pulled. It can also lead to accidents in light rain. The

decline in popularity of rear wheel drive cars can be attributed to these factors.

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FUEL SUPPLY SYSTEM

Fuel Injection is a method or system for metering fuel into an internal combustion

engine. The fuel is then burned in air to produce heat, which in turn is converted to

mechanical work by the engine. In modern automotive applications, fuel injection is

typically only one of several important tasks performed by an engine management

system. An engine's air/fuel ratio must be accurately controlled under all operating

conditions to achieve the desired engine performance, emissions, driveability and fuel

economy

FUEL PUMP

A fuel pump is an essential component

on a car or other internal combustion

engined device. Fuel has to be pumped

from the fuel tank to the engine and

delivered under low pressure to the

carburetor or under high pressure to the

fuel injection system. Some fuel injected

engines have two fuel pumps for this

purpose: one low pressure/high volume supply pump in the tank and one high

pressure/low volume pump on or near the engine.

FUEL INJECTION IN A PETROL ENGINE CARBURETOR The carburetor is a device which mixes air

and fuel for an internal-combustion engine. A

carburetor basically consists of an open pipe,

the carburetor’s "throat" or "barrel", through

which the air passes into the inlet manifold of

the engine. The pipe is in the form of a venturi

— it narrows in section and then widens

again, causing the airflow to increase in

speed in the narrowest part. Below the venturi

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is a butterfly valve or throttle. This valve controls the flow of air through the carburetor

throat and thus the quantity of air/fuel mixture the system will deliver, thereby regulating

engine power and speed. The throttle is connected, usually through a cable or a

mechanical linkage to the accelerator pedal on a car. Fuel is introduced into the air

stream through small holes at the narrowest part of the venturi.

FUEL INJECTION IN DIESEL ENGINE FUEL INJECTOR

The fuel injector acts as the fuel-dispensing nozzle. It

injects liquid fuel directly into the engine's air stream. In

almost all cases this requires an external pump. The

pump and injector are only two of several components in

a complete fuel injection system. Both mechanical and

electronic injection systems can be used in either direct

or indirect injection configurations

TYPES OF INJECTION METHODS 1) Direct Injection

2) Indirect injection

DIRECT INJECTION In direct injection, the fuel is injected straightaway into the cylinder. Modern diesel

engines make use of one of the following direct injection methods:

Distributor pump direct injection The first incarnations of direct injection diesels used a rotary pump much like indirect

injection diesels, however the injectors were mounted in the top of the combustion

chamber rather than in a separate pre-combustion chamber.

Common rail direct injection In older diesel engines, a distributor-type injection pump, regulated by the engine,

supplies bursts of fuel to injectors which are simply nozzles through which the diesel is

sprayed into the engine's combustion chamber.

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Unit direct injection This also injects fuel directly into the cylinder of the engine. However, in this system the

injector and the pump are combined into one unit positioned over each cylinder. Each

cylinder thus has its own pump, feeding its own injector, which prevents pressure

fluctuations and allows more consistent injection to be achieved.

INDIRECT INJECTION An indirect injection diesel engine delivers fuel into a chamber off the combustion

chamber, called a prechamber, where combustion begins and then spreads into the

main combustion chamber, assisted by turbulence created in the chamber. This system

allows smoother, quieter running, and because combustion is assisted by turbulence,

injector pressures can be lower, which in the days of mechanical injection systems

allowed high-speed running suitable for road vehicles (typically up to speed of around

4,000 rpm).

TURBOCHARGER A turbocharger is an exhaust gas-driven

compressor used to increase the power output of

an internal-combustion engine by increasing the

mass of oxygen entering the engine. A key

advantage of turbochargers is that they offer a

considerable increase in engine power with only a

slight increase in weight.

VALVES Four-stroke engines, of either spark ignition or compression ignition varieties, use

poppet valves to allow air (or an air/fuel mixture) into the cylinder and exhaust gases out.

Very early engines used alternative valve types such as slide valves, but these proved

less satisfactory, especially for high-speed engines.

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IGNITION SYSTEM The ignition system of an internal-combustion engine is an important part of the overall

engine system that provides for the timely burning of the fuel mixture within the engine.

All conventional petrol (petrol) engines require an ignition system. The ignition system is

usually switched on/off through a lock switch, operated with a key or code patch.

BATTERY OPERATED IGNITION The battery operated ignition system uses an ignition coil (a type of autotransformer) to

step the voltage up to the needs of the ignition, and a distributor to route the ensuing

pulse to the correct spark plug at the correct time.

TYPES OF IGNITION SYSTEMS : 1) Mechanically timed ignition

2) Electronic Ignition

MECHANICALLY TIMED IGNITION Most four-stroke engines have used a mechanically timed

electrical ignition system. The heart of the system is the

distributor which contains a rotating cam running off the

engine's drive, a set of breaker points, a condenser, a rotor

and a distributor cap. External to the distributor is the

ignition coil, the spark plugs, and wires linking the spark

plugs and ignition coil to the distributor. The power source

is a lead-acid battery, kept charged by the car's electrical

system, which generates electricity using a dynamo or alternator.

ELECTRONIC IGNITION The disadvantage of the mechanical system is the use of

breaker points to interrupt the low voltage high current

through the primary winding of the coil; the points are

subject to mechanical wear where they ride the cam to

open and shut, as well as oxidation and burning at the

contact surfaces from the constant sparking. They require

regular adjustment to compensate for wear, and the

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opening of the contact breakers, which is responsible for spark timing, is subject to

mechanical variations. In addition, the spark voltage is also dependent on contact

effectiveness, and poor sparking can lead to lower engine efficiency. Electronic ignition

(EI) solves these problems. The lack of moving parts compared with the mechanical

system leads to greater reliability and longer service intervals.

SPARK IGNITION The term spark-ignition is normally used to refer to internal

combustion engines where the fuel-air mixture is ignited with a

spark. The term contrasts with compression-ignition engines,

where the heat from compression alone ignites the mixture.

Spark-ignition engines can be either two-stroke or four-stroke,

and are commonly referred to as "petrol engines" in US English

and "petrol engines" in British English.

COMPRESSION IGNITION Unlike the spark ignition where the air fuel mixture injected into the cylinder in the intake

stroke is ignited by an electric spark using a spark plug, the compression ignition works

on the principle of thermodynamic laws of compression, whereby the air which is forced

into the cylinder is compressed to great extent suddenly in the compression stroke which

leads to the sudden rise in temperatures inside the cylinder. At this moment fuel in the

form of very fine spray is injected into the cylinder by a fuel injector. The high

temperatures in combustion chamber lead to instantaneous burning of the fuel ( power

stroke ). Thus there is no need of an electric spark and the engine utilizes the high

temperatures of compressed air to ignite the fuel. Such type of ignition is utilized in

diesel engines and therefore they are also called compression engines.

SPARK PLUG A spark plug (sometimes in British English, a

sparking plug) is an electrical device that fits into

the cylinder head of internal combustion engines (

PETROL ENGINES ) and ignites compressed

aerosol petrol by means of an electric spark. Spark plugs have an insulated center

electrode which is connected by a heavily insulated wire to an ignition coil or magneto

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circuit on the outside, forming, with a grounded terminal on the base of the plug, a spark

gap inside the cylinder.

ALTERNATOR

An alternator is an electromechanical device that

converts mechanical energy to alternating current

electrical energy. Alternators are used in

automobiles to charge the battery and to power all

the car's electric systems when its engine is

running. Modern automotive alternators have a

voltage regulator built into them.

BATTERY A automobile battery is a type of electric battery that

supplies electric energy to the starter motor and the ignition

system of a vehicle’s engine. The term is also used for the

main power source of an electric vehicle. They are usually

lead-acid batteries that provide a nominal 12-volt potential

difference by serially connecting six cells that each produce

about 2 to 2.1 volts.

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EXHAUST SYSTEM An exhaust system conveys burnt gases from an internal combustion engine and

typically includes a collection of pipes. In the most basic sense, the exhaust system just

vents waste gases from the engine. Depending on the overall system design, the

exhaust gas may flow through a turbocharger to increase engine power, a catalytic

converter to reduce air pollution, and a muffler to reduce noise.

PARTS OF AN EXHAUST SYSTEM MANIFOLD

In most production engines, the manifold is an

assembly designed to collect the exhaust gas from

multiple cylinders and combine those flows into a

single pipe. A header is another name for a

manifold, but which specifically refers to an

enhanced manifold that has been designed for

performance. Headers are generally circular steel

tubing with bends and folds calculated to make the paths from each cylinder's exhaust

port to the common outlet all of equal length, and joined at narrow angles to encourage

pressure waves to flow through the outlet, and not back in the direction of the other

cylinders.

HEADER BACK Header-back (or header back) refers to the portion of the exhaust system from the outlet

of the header or manifold to the final vent to open air— everything from the header back.

TIP The end of the final length of exhaust pipe where it vents

to open air, generally the only visible part, often ends

with just a straight or angled cut, but may include a fancy

tip. The tip is usually chromed, and is often of larger pipe

than the rest of the exhaust system. This produces a

final reduction in pressure, as well as prevents rusting of

the tips, and can be used to enhance the appearance of

the car.

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CATALYTIC CONVERTOR

A catalytic converter is a device used to reduce the toxicity

of emissions from an internal combustion engine. Catalytic

converters are used on spark ignition (petrol; liquefied

petroleum gas (LPG); compressed natural gas (CNG))

engines; and compression ignition (diesel) engines. The

reasons for use on each type of engine are different. For

spark ignition engines the most commonly used catalytic

converter is the three-way converter. A three-way catalytic

converter has three simultaneous tasks:

• Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → O2 + N2

• Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2

• Oxidation of unburnt non-methane hydrocarbons (HC) to carbon dioxide and

water: CxHy + nO2 → xCO2 + mH2O

For compression ignition (i.e., Diesel) engines, the most commonly used catalytic

converter is the diesel oxidation catalyst. The catalyst uses excess O2 (oxygen) in the

exhaust gas stream to oxidize CO (Carbon Monoxide) to CO2 (Carbon Dioxide) and HC

(hydrocarbons) to H2O (water) and CO2. A two-way catalytic converter has two

simultaneous tasks:

• Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2

• Oxidation of unburnt non-methane hydrocarbons (unburnt and partially-burnt

fuel) to carbon dioxide and water: CxHy + O2 → xCO2 + mH2O

EXHAUST PIPE An exhaust pipe is usually tubing used to guide waste exhaust gases away from a

controlled combustion inside an engine. An exhaust pipe must be carefully designed to

carry toxic and/or noxious gases away from the users of the machine. Also, the exhaust

gases from most types of machine are very hot; the pipe must be heat-resistant, and it

must not pass through or near any combustible materials.

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SILENCER or MUFFLER A muffler or silencer is a device for reducing the amount of noise emitted by an internal

combustion engine. Engine exhaust blows out through the muffler. Mufflers are typically

installed along the exhaust pipe of the engine. They usually contain a series of baffles to

absorb sound, although the majority of the noise reduction is not through absorption but

through destructive interference in the muffler itself. The muffler accomplishes this with a

resonating chamber, which is specifically designed such that opposite sound waves are

likely to collide, canceling each other out. They are a common piece of equipment on

automobiles, usually slung under the rear of a car. Catalytic converters also often have a

muffling effect.

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COOLING SYSTEM In the process of combustion and friction between the various moving parts of the engine

substantial amounts of heat is generated which needs to be dissipated in order to

maintain safe temperatures for engine and various systems to work properly. Broadly

speaking , the an automobile may be either air cooled or water cooled.

In case of an air cooled engine, the engine is mounted such that air passes through it

when the automobile is in motion. The passing over of air over the engine block ensures

it cooling.. However this type of cooling is effective only for smaller engines like those

used in scooters or motorbikes. Bigger engines generally are water cooled. In this

system water is circulated through a water jacket in the engine block with an aid of a

pump. The water while it passes through the engine block carries with it the heat of

combustion. This heat is then dissipated through a radiator placed in front of the vehicle.

RADIATOR In automobiles with an internal combustion engine, a

radiator is connected to channels running through the

engine and cylinder head, through which is pumped a

liquid. This liquid is typically a mixture of water with

ethylene glycol (a.k.a. antifreeze).

The fluid moves in a closed system from the radiator to

the engine, where it conducts heat away from the engine

parts and carries the heat primarily to the radiator. The

radiator is typically mounted behind the vehicle's grille,

with cold air driven through the radiator to cool the radiator, the fluid inside, and

therefore the engine. Between the engine and the radiator lies the thermostat, a

temperature operated valve. It remains closed, restricting coolant flow, until the engine

reaches the thermostat's activation temperature. This arrangement allows the engine

temperature to be maintained in the ideal operating range.

INTERCOOLER An intercooler is a device used on turbocharged and supercharged internal combustion

engines to improve the volumetric efficiency and increase the amount of charge in the

engine, thereby increasing power.. Modern automobile designs are technically

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aftercoolers because they appear most often

at the very end of the chain, but this name is

no longer used.

Turbochargers and superchargers compress

incoming air, causing it to become heated.

Since hot air is less dense than cooler air at

the same pressure, the total charge delivered

to the cylinders is higher than non-

compressed air, but still less than it could be. By cooling the charge after compression,

even more charge can be delivered, increasing power. Additionally, intercoolers help to

increase the total amount of boost possible without causing engine knocking.

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BRAKING SYSTEM The barking system in an automobile is used to retard the vehicle in order to either come

to a stop or control the speed. The main components of the braking system are the

brake pedal and brakes which may be of three types discussed below.

BRAKE PEDAL The brake pedal is a simple lever. It is attached at one point

to the framework of the automobile, a rod extends from a

point along its length to the master cylinder, and the pedal is

at the end of the lever.

BRAKES The three types of brakes

being used commonly

1) drum brakes

2) disc brakes

3) hydraulic brakes

DRUM BRAKES A drum brake is a brake in which the friction is caused by a set of

shoes or pads that press against the inner surface of a rotating drum. The drum is

connected to a rotating wheel. (Below-left)

DISC BRAKE: The disc brake is a device for slowing or stopping the rotation of a wheel.

A brake disc, usually made of cast iron or ceramic, is connected to the wheel or the axle.

To stop the wheel, friction material in the form of brake pads (mounted in a device called

a brake caliper) is forced mechanically, hydraulically or pneumatically against both sides

of the disc. (bottom-right)

HYDRAULIC BRAKES The hydraulic brake is an arrangement of braking mechanism which uses hydraulic fluid,

typically some type of light-viscosity petroleum oil, to transfer pressure from the

controlling unit, which is usually near the operator of the vehicle, to the actual brake

mechanism, which is usually at or near the wheel of the vehicle.

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BUILD CHASIS

A chassis (plural: "chassis") consists

of a framework which supports an

object, analogous to an animal's

skeleton. In the case of a motor

vehicle, the term chassis means the

frame plus the "running gear" like

engine, transmission, driveshaft,

differential, and suspension. A body

(sometimes referred to as

"coachwork"), which is usually not necessary for integrity of the structure, is built on the

chassis to complete the vehicle.

Monocoque Monocoque (French for "single shell") or

unibody is a construction technique that uses

the external skin of an object to support some

or most of the load on the structure.

AXLE An axle is a central shaft for a rotating wheel or gear. Axles are an important structural

component of a wheeled vehicle. The axles maintain the position of the wheels relative

to each other and to the vehicle body. Since for most

vehicles the wheels are the only part touching the

ground, the axles must bear the weight of the vehicle

plus any cargo, and also any acceleration forces

between the vehicle and the ground.

DRIVE AXLES

An axle that is driven by the engine is called a drive axle. Modern front wheel drive cars

typically combine the transmission and front axle into a single unit called a transaxle.

The drive axle is a split axle with a differential and universal joints between the two half

axles. Each half axle connects to the wheel by use of a constant velocity (CV) joint which

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allows the wheel assembly to move freely vertically as well as to pivot when making

turns. In rear wheel drive cars and trucks, the engine turns a driveshaft which transmits

rotational force to a drive axle at the rear of the vehicle. The drive axle may be a live

axle, but modern automobiles generally use a split axle with a differential. Some simple

vehicle designs, such as go-karts, may have a single drive wheel. The drive axle is a

split axle with only one of the two shafts driven by the engine.

SUSPENSION Suspension is the term given to the system of

springs, shock absorbers and linkages that

connects a vehicle to its wheels. Suspension

systems serve a dual purpose - contributing to the

car's handling and braking for good active safety

and driving pleasure, and keeping vehicle

occupants comfortable and reasonably well

isolated from road noise, bumps, and vibrations.

STEERING Steering is the term applied to the collection of components,

linkages, etc. which allow for a car or other vehicle to follow a

course determined by its driver. The most conventional steering

arrangement is to turn the front wheels using a hand–operated

steering wheel which is positioned in front of the driver, via the

steering column, which may contain universal joints to allow it to

deviate somewhat from a straight line.

Power Steering

Power steering aims to make steering less strenuous for the driver. There are two types

of power steering systems—hydraulic and electric/electronic. There is also a hydraulic-

electric hybrid system possible.

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8

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GLOSSARY

Following is the list of the important terms that are used commonly in the automobile

industry. The aim of this glossary is to simplify the jargon and help understand the

various technical terms better.

CAR BODY STYLES

Cars can come in a large variety of different body styles. Some are still in production,

while others are of historical interest only. These styles are largely (though not

completely) independent of a car's classification in terms of price, size and intended

broad market; the same car model might be available in multiple body styles. Please

note that while each body style has a historical and technical definition, in common

usage such definitions are often blurred. Over time, the common usage of each term

evolves. For example, people often call 4-passenger sport coupes a 'sports car', while

purists will insist that a sports car by definition is limited to two-place vehicles.

CABRIO COACH OR SEMI-CONVERTIBLE : A car that has a retractable textile cover

for what amounts to a large sunroof.

CONVERTIBLE : A body style with a removable or retractable roof and rear window. CABRIOLET : Another term for a convertible

COUPÉ (UK/EU) OR COUPE (US) : A 2-door, 2- or 4-seat car with a fixed roof. Its doors

are longer than those of a sedan, and the rear passenger area smaller. In cases where

the rear seats are very small and not intended for regular use it is called a 2+2.

COUPÉ CONVERTIBLE : A type of convertible with a rigid roof (as opposed to a fabric

or vinyl roof) that retracts into the lower bodywork.

CROSSOVER SUV (OR XUV) :A type of Sport Utility Vehicle (SUV) which is based on

a car platform rather than truck chassis. This also refers to a vehicle which is marketed

as neither an SUV, a minivan nor a wagon, but combines design elements of those

types.

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ESTATE CAR : A British English term for what North Americans call a station wagon.

FASTBACK : A design where the roof slopes at a smooth angle to the tail of the car, but

the rear window does not open as a separate door.

HARDTOP : A style of automobile roof. Originally referred to a removable solid roof on a

convertible; later, also a fixed-roof car whose doors have no fixed window frames, which

is designed to resemble such a convertible. A pillarless hardtop (the most common kind)

is completely open on the sides with the windows down.

HATCHBACK : Identified by a rear door including the back window that opens vertically

to access a storage area not separated from the rest of the passenger compartment.

May be 2 or 4 door and 2 or 4 seat, but generally called in British English 3 door, 5 door.

LIMOUSINE : By definition, a chauffeur-driven car with a (normally glass-windowed)

division between the front seats and the rear. In German, the term simply means a

sedan.

MINIVAN : A boxy wagon-type of car usually containing three or four rows of seats, with

a capacity of six or more passengers. Often with extra luggage space also. As opposed

to the larger van, the minivan was developed primarily as a passenger vehicle, though is

more van-like than a station wagon. In Britain, these are generally referred to as People

carriers.

MPV : Multi-purpose vehicle, a large car or small bus designed to be used on and off-

road and easily convertible to facilitate loading of goods from facilitating carrying people.

NOTCHBACK : A cross between the smooth fastback and angled sedan look. It is a

sedan type with a separate trunk compartment.

PICKUP TRUCK AKA PICK-UP : Small or medium sized truck. Not based on a

passenger car, but of similar size. This light commercial vehicle features a separate

cabin and rear load area (separate cargo bed).

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ROADSTER : Originally a two-seat open car with minimal weather protection — no top

was provided, neither any side glass. In some cases an optional hard or soft top might

be offered, along with side curtains, but there was no side glass. In modern usage, the

term is often used mean simply a convertible two-seat sports car, similarly to spyder.

SALOON : The British English term for a sedan.

SEDAN : A car seating four or more with a fixed roof that is full-height up to the rear

window. Normally a 4 door; 2 door is rarer in the US but they do occur (more so

historically). This is the most common body style. In the U.S., this term has been used to

denote a car with fixed window frames, as opposed to the hardtop style where the sash,

if any, winds down with the glass. As hardtops have become rarer, this distinction is no

longer so important.

SPORT UTILITY VEHICLE (SUV) : Derivative of off-road or four-wheel drive vehicles

but with car-like levels of interior comfort and drivability. Also sometimes called a "soft-

roader".

STATION WAGON : A car with an full-height body all the way to the rear; the load-

carrying space created is accessed via a rear door or doors.

T-TOP : A derivative of the Targa top, called a T-bar roof, this fixed-roof design has two

removable panels and retains a central narrow roof section along the front to back axis

of the car (e.g. Toyota MR2 Mk 1.)

TARGA TOP : A semi-convertible style used on some sports cars, featuring a fully

removable hard top roof panel which leaves the A and B pillars in place on the car body.

VAN : In North America 'van' refers to a truck-based commercial vehicle of the wagon

style, whether used for passenger or commercial use. Usually a van has no windows at

the side rear (panel van), although for passenger use, side windows are included. In

other parts of the world, 'van' denotes a passenger-based wagon with no rear side

windows.

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NON-ENGLISH TERMS Some non-English language terms are familiar from their use on imported vehicles in

English-speaking nations even though the terms have not been adopted into English.

• Barchetta : Italian term for a roadster. The name means, roughly, "small boat".

• Berlina : Italian term for a sedan.

• Berline : French term for a sedan.

• Berlinetta : Italian term for a sport coupé.

• Break : French term for a station wagon.

• Jeep : German and Greek term for a sport utility vehicle. Not to be confused with

the english-language jeep, which originated from the WWII 'GP' (general

purpose) military vehicle.

• Turismo : Spanish term for a sedan. Literally means tourism, used mostly in

Latin American countries.

TECH SPEAK

This component compiles the list of various technical terms with a brief write up on each

to help understand the mechanics of an automobile better.

AutomaticTransmission A transmission that shifts its own

gears according to the prevailing

speed, load, and road condition. Also

called automatic gearbox. Operation

can be electrical or hydraulic.

The transmission transfers the

engine's power from the crankshaft to

the driveshaft (which, in turn, sends it

on to one or more axles and the

driving wheels). An automatic

transmission does this using a torque

converter rather than a manually

operated clutch. A torque converter uses hydraulic pressure to engage and disengage

the transmission gears from the engine.

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Benefit: An automatic transmission allows the driver more comfort and ease of use than

a manual transmission, particularly in urban and stop-and-go driving situations.

Anti-roll bar : A torsion bar bent in the form of an elongated letter U, installed so that

the ends are attached to the lower suspension arms and the centre portion is held by

bushes on a transverse chassis/body member. This leaves the ends free to move up

and down with the wheels, but if one wheel moves upwards while the other moves

downwards, during cornering for example, the bar goes into torsion and restricts the

amount of chassis/body roll.

A-/B-/C-/D-pillar : The A-pillar is the roof support next to the windscreen and the pillar

behind the front door is the B-pillar. The C-pillar can be either the rear roof support or, in

the case of five-door station wagons, SUVs and MPVs, the pillar behind the rear side

door. The rear roof support on these vehicles then becomes the D-pillar.

Aspect ratio : The ratio between the height and width of a tyre, expressed as a

percentage. The height is measured from the tyre seat diameter on the rim to the crown

of the tyre. Modern tyres have aspect ratios as low as 35 per cent, whereas older tyres

may have aspect ratios of over 80 per cent.

Axle Ratio: The number of times the driveshaft revolves to turn the axle one revolution.

For example, a 4:1 axle ratio means the drive shaft turns 4 times for every one time the

tire turns. This ratio multiplies the torque applied to the wheels.

BDC (Bottom Dead Centre) : The instant when the piston is at the lowest point in its

rotational cycle.

Beam axle : A rigid beam that connects two wheels together.

Bending moment : If a force acts in such a way that it may cause a material to bend,

then the force multiplied by the perpendicular distance to the axis about which the

bending could take place is called the bending moment. The formula is identical to that

used to calculate a torque.

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BMEP (Brake Mean Effective Pressure): This is the average pressure acting on the

piston during one complete working cycle, as calculated from the power determined at

the flywheel with a dynamometer, or engine brake. It is a useful measure of engine

development, since a higher value would mean a more modern engine.

Boost pressure: The pressure, above atmospheric, delivered by a supercharger or

turbocharger.

Break-over angle (ridge angle): If the biggest ridge a vehicle can drive over is

idealized as an equal-legged triangle, then the top angle of the triangle is called the

break-over angle by some authorities, whereas others quote one of the bottom angles.

Bulkhead : The partition between the engine compartment or boot and the interior.

Bore and Stroke: These are two separate measurements of the area of the combustion

process in an individual cylinder. The bore is the diameter of the cylinder and the stroke

is the total distance the piston travels within the cylinder from top to bottom. The area of

the cylinder, multiplied by the stroke, times the number of cylinders, equals the engine's

total displacement.

Brake Horsepower (BHP): The measure of an engine's horsepower without the loss in

power caused by the inefficiencies in the accessories and drivetrain.

Cam : lobe-shaped portion of the camshaft that actuates the valve mechanism

Camshaft : A shaft in the engine used to operate the intake and exhaust valves. It is

driven from the crankshaft by gears, belts or chains and opens and closes the valves as

it rotates. The camshaft is located in the engine block in a pushrod overhead-valve

(OHV) engine where the cam lobes operate pushrods that, in turn, operate the

valvetrain. A camshaft located in the top of the cylinder head is referred to as an

overhead camshaft. There can be either one (single overhead camshaft or SOHC) or

two (dual overhead camshaft or DOHC) camshafts per row of cylinders

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CAD (Computer Aided Design): The ability of a computer to calculate fast, and show

the results in graphical form, is utilised to create software packages that enable

designers to study the properties of a particular design quickly and accurately. The final

design is often combined with CAM (computer aided manufacturing), written as CAD-

CAM.

Camber: An outward tilt of the front wheel at the top, as seen from the front

central locking can activate the locking and unlocking from a small unit on the key fob

away from the car, either by infra-red or radio waves. Some systems unlock all the doors

at the same time, but modern systems are often selective, i.e. they first unlock only the

driver's door, and then the others and the boot.

Cargo Weight Rating : Includes payload rating minus the weight of all occupants at a

weight of approximately 180 lbs. a person. What you need to know: Vehicles that

operate above the Payload rating are a potential safety hazard because the engine,

frame, suspension, brakes and tires are not designed for weight above the rating the

manufacturer has set.

Centre of mass: The point at which the earth's gravitational force can be assumed to

act on a car, for any calculations where the mass distribution is not important. It is

sometimes called the centre of gravity.

Cetane number: The ignition quality of a diesel fuel is measured in terms of a cetane

number, which is a measure of its ability to self-ignite. In this sense, it is opposite to the

octane numbers that are used to evaluate petrol, because petrol is designed not to self-

ignite.

Chassis: The basic framework that supports the body, engine, drivetrain and

suspension in older cars, and still does in heavy trucks. Modern cars have unit-

construction (or Monocoque) bodywork.

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CKD (Completely Knocked Down) : Vehicles assembled away from the parent factory

are referred to as CKD units, because the components are sent out in CKD packs.

These packs may contain sub-assemblies as well as loose parts.

Chassis [Pronunciation: chassie] : The structural elements of a vehicle. A unibody

chassis includes everything but bolted-on body panels. If a vehicle has a separate

frame, the term chassis refers to the frame.

Clearance volume : This is the space between the top of the piston at TDC and the

walls of the combustion chamber. It is also known as the combustion chamber space.

Coil spring. A spring shaped as a coil.

Cross ply : A tyre constructed so that the strengthening plies inside the casing run at

various angles from one side to the other across the tread area.

CV joint: The letters CV denote a constant velocity joint, i.e. one that can transmit

torque at an angle from one shaft to another without any speed variation. The need for

such a joint arose because a Hooke's joint transmits a speed variation, the amount of

which is dependent upon the angle between the shafts

Cubic Centimeter (CC ) : The combustion chamber is the engine area where

compression and combustion take place. As the piston moves up and down, the size of

the combustion chamber changes. It has some maximum volume as well as a minimum

volume. The difference between the maximum and minimum is called the displacement

and is measured in liters or CCs (Cubic Centimeters, where 1,000 cubic centimeters

equals a liter). For any engine, this is the theoretical volume of air displaced by one

piston as it moves from TDC ( Top Dead Centre ) to BDC ( Bottom Dead Centre),

multiplied by the number of cylinders. It can be calculated by multiplying the piston area

by the stroke length and the number of cylinders.

Generally, the displacement tells you something about how much power an engine can

produce. A cylinder that displaces half a liter can hold twice as much fuel/air mixture as a

cylinder that displaces a quarter of a liter, and therefore you would expect about twice as

much power from the larger cylinder (if everything else is equal). So a 2.0 liter engine is

roughly half as powerful as a 4.0 liter engine.

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Cylinder Head : The top part of the engine that attaches to the cylinder block. It seals

the cylinders and includes the upper part of the combustion chamber as well as the

valve train (including camshafts). All Toyota vehicles are equipped with a cross-flow

cylinder head design that provides the straightest possible path for the air-fuel mixture.

By allowing this mixture to flow smoothly, the engine can perform more efficiently,

resulting in improved power and economy.

Differential, Limited-Slip Differential (LSD) : Limited Slip Differential (LSD) prevents

all of the torque from being directed to the rear slipping wheel. The LSD also helps

achieve excellent driving stability and acceleration response. During acceleration, the

LSD ensures that the torque is split between the two rear wheels

DOHC : DOHC stands for double overhead cam. A DOHC engine has two camshafts

per cylinder head, so inline engines have two cams, but V engines have four. Usually,

double overhead cams are used on engines with four or more valves per cylinder -- a

single camshaft simply cannot fit enough cam lobes to actuate all of those valves. Of the

two cams, one drives the intake valves and the other operates the exhaust valve. In a

single overhead cam engine (SOHC), one cam has enough lobes to drive both the

intake and exhaust valves. DOHC is also known as "twin overhead camshafts."

The main reason to use double overhead cams is to allow for more intake and exhaust

valves. More valves means that intake and exhaust gases can flow more freely because

there are more openings for them to flow through. This increases the power of the

engine.

Dry Disc Clutch : In a car, you need a clutch because the engine spins all the time and

the car wheels don't. In order for a car to stop without killing the engine, the wheels need

to be disconnected from the engine somehow. The clutch allows us to smoothly engage

a spinning engine to a non-spinning transmission by controlling the slippage between

them. To understand how a clutch works, it helps to know a little bit about friction. A

clutch with only one plate is a dry clutch.

Dry weight : The weight of a vehicle without any fluids.

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Dynamometer (dyno): A device that is capable of applying a load to an engine, and

measuring the torque output, from which the power can be calculated if the engine

revolutions are known. Efficiency : There are many different types of efficiency, but they all attempt to measure

how much wastage is inherent in a process. The usual form of the formula is: output

divided by input times 100 to give a percentage. For example, the volumetric efficiency

of an engine is the amount of air actually inhaled in a certain time divided by the

theoretical amount, as given by the displacement, times 100.

Another example is the overall efficiency of an engine, which is the energy equivalent of

the torque at the flywheel divided by the total energy in the fuel delivered to the

combustion chamber

Ergonomics. The study of the relationship between people and their working

environment. Thus, for example, if the interior layout of a car is such that all the controls

fall easily to hand it, is called an ergonomically efficient design. Four-by-Two (4X2) : Used to describe a vehicle with two-wheel drive. The first figure is

the number of wheels, and the second is the number of powered wheels. Another term

for two-wheel drive.

Four-by-Four (4X4) : Used to

describe a vehicle with four-wheel

drive. The first figure is the number

of wheels, and the second is the

number of powered wheels. Four

Wheel Drive (4WD) transfers engine

power to all four wheels. 4WD

systems usually lack a center

differential that allows use in dry

conditions. 4WD provides superior

traction compared with front or rear-

wheel drive.

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Four Wheel Drive (4WD) - Part time : A part time four wheel drive system operates in

two wheel drive mode until you choose to engage four wheel drive for off road or other

adverse driving conditions.

Four Wheel Drive (4WD) – Permanent : Permanent four wheel drive sends torque to all

four wheels on a continuous basis. There is no option for two wheel drive but the driver

can usually choose a high or low mode depending on the driving conditions

Front-Engine/Front-Wheel Drive : Sometimes abbreviated "FF" or "FWD," this refers to

a vehicle with the engine in front of the passenger compartment driving the front wheels.

This layout is efficient in terms of packaging, providing more room for passengers and

cargo by combining the entire drivetrain in one unit and eliminating the need for a

driveshaft tunnel. Benefit: By placing the weight of the engine over the drive wheels,

traction is also improved in certain situations.

Front-Engine/Rear-Wheel Drive : Abbreviated "FR" or "RWD," this is a layout in which

the engine is in front of the passenger compartment and drives the rear wheels through

a driveshaft that connects to the rear axle. Benefit: This provides benefits in weight

distribution for improved handling in sports and luxury cars. It is also used in trucks to

enhance load-carrying and towing ability; since the load-carrying area of the vehicle is

over the driving wheels, traction is improved

Gear Ratio : A gear ratio occurs when 1 gear drives another gear. For example, lets

take two different size gears, one with 40 teeth and the other with 20. The one with 20

teeth will make two revolutions compared to one revolution performed by the gear with

40 teeth. This setup would create a gear ratio of 2:1. The driven gear (40 teeth) turns 1/2

the speed of the drive gear (20 teeth) but multiplies the torque by 2. The higher the ratio,

4:1 for example, the more torque will be created, but the slower the output speed.

Glow plug : A special plug, fitted to diesel engines, which carries a heater element,

necessary for cold starting because compression alone does not supply enough heat to

initiate combustion.

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Gross Axle Weight Rating (GAWR) : The maximum amount of weight that can be

supported by each axle, as designated by the manufacturer. What you need to know:

The total load on each axle must not exceed its GAWR

Gross Combined Weight (GCW) : The total weight of a vehicle, including all its cargo,

plus the weight of a trailer and its entire contents.

Gross Combined Weight Rating (GCWR) : The maximum allowable weight of the

GCW as specified by the manufacturer. Exceeding this limit compromises safety. What

you need to know: Vehicles that operate above the GCWR are a potential safety hazard

because the engine, frame, suspension, brakes and tires are not designed for weight

above the rating the manufacturer has set.

Gross Vehicle Weight (GVW) : Maximum legal weight at which a vehicle can be

operated. The total weight of a vehicle with driver and passengers, cargo, fuel, coolant,

any dealer or after-market installed accessories, and tongue weight if towing.

Gross Vehicle Weight Rating (GVWR) : It is the maximum permissible total weight of

the vehicle that may not be exceeded, as designated by the manufacturer. GVWR is

identified on the manufacturer's label, which is usually located on the driver's door or

door jam. What you need to know: Vehicles that operate above the GVWR are a

potential safety hazard because the engine, frame, suspension, brakes and tires are not

designed for weight above the rating the manufacturer has set.

Ground Clearance: The distance between the lowest point on the vehicle and the

ground. This number is particularly useful for 4-wheel-drive trucks and sport utility

vehicles, which are more likely to encounter obstacles.

Homogeneous Charge Compression Ignition, or HCCI: It is a form of internal

combustion in which well mixed fuel and oxidizer (typically air) are compressed to the

point of auto-ignition. As in other forms of combustion, this exothermic reaction releases

chemical energy into a sensible form that can be translated by an engine into work and

heat.

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HCCI has characteristics from each of the two most popular forms of combustion used in

IC engines: homogeneous charge spark ignition (petrol engines) and stratified charge

compression ignition (diesel engines). As in homogeneous charge spark ignition, the fuel

and oxidizer are mixed together. However, rather than using an electric discharge to

ignite a portion of the mixture, the concentration and temperature of the mixture are

raised by compression until the entire mixture reacts simultaneously.

Horse Power : A measurement of the engine's ability to perform work.. In metric terms,

it is the ability to raise 250 kilograms a distance of 30 centimeters in one second. It is

also equal to 745.7 watts. In fps ( foot-pound-second ) unit one horsepower is defined as

the ability to lift 33,000 pounds one foot in one minute. To find horsepower, the total rate

of work in foot pounds accomplished is divided by 33,000. If a machine was lifting 100

pounds 660 feet per minute, its total rate of work would be 66,000 foot pounds per

minute. Divide this by 33,000 foot pounds per minute to arrive at 2 horsepower

The measurement of mechanical power, or the work needed to carry a weight over a

given distance in a specified period of time. The base measurement is 100 pounds

carried 330 feet per minute.

Independent Suspension : Suspension in which each wheel is sprung individually so

that any disturbance on the wheel has no effect on the opposite wheel. This compares to

a "rigid" or "solid" axle where the wheels are connected and a disturbance at one end

affects the other. Independent suspensions can apply to the front, rear or all four wheels.

Joule. This is the metric unit of work or energy, and is equal to a Newton-meter.

Kerb Weight : The weight of an empty vehicle, without cargo and driver and

passengers, but including maximum amounts of fuel, oil, coolant and standard

equipment, including the spare tire and tools.

Knock. Irregular combustion may cause knocking, which can sometimes be heard, but

the so-called high speed knock cannot be heard by human ears.

Leaf Spring : A number of slightly curved, flexible steel plates of varying lengths,

mounted one atop the other. The plates are attached at the ends to the underbody. The

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curved shape of the plates allows them to flex and absorb bumps. Made of spring steel

or various composite materials that deflects by bending when forces act upon it . Leaf

springs are used primarily in suspensions. The ends are attached to the chassis, and the

middle is fixed to the axle. Also called semi-elliptic springs.

Live axle. An axle that transmits power, either because it is hollow and carries a

driveshaft, or because it is the driveshaft, as is the case with front-wheel drive.

Mag wheels. Although the name implies wheels made from magnesium, almost all are

made from cast aluminum.

Overdrive : A final drive ratio of less than 1:1. This allows the engine to operate at lower

rpm during highway driving, requiring less fuel and reducing engine noise.

OHV (OverHead Valve). This term describes any engine that has all its valves in the

cylinder head. The valves may be operated by pushrods or an overhead camshaft. In the

latter case, however, the head is rather referred to as a single

overhead camshaft (SOHC), or double overhead camshaft (DOHC).

Overhead Cam (OHC) : This is when the camshaft is located in the cylinder head, rather

than in the engine block (see Camshaft). This design eliminates the need for pushrods

and lifters, reducing weight and improving engine responsiveness and efficiency. The

advantages tend to increase at high rpm.

Oversteer. When a car corners, each tyre develops a different slip angle. If the average

of the rear slip angles is greater than the average of the front slip angles, then the car

seems to require less steering input than it would if it was rolling slowly around the same

corner. This condition is called oversteer. Also see understeer.

Pascal. The metric unit of pressure and stress is the Pascal (Pa). It is defined to be a

force of one Newton distributed over one square metre. It is so small that a unit 1 000

times bigger, the kilopascal (kPa), is used for most purposes. Tyre pressures are

measured in kPa where 100 kPa = one Bar. The latter is not a recommended

metric unit.

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Payload : The maximum amount of weight, including driver and passengers, that can be

carried in the truck's bed and cabin. Basically, the payload is the GVWR minus the Curb

Weight.

Piston speed. The average piston speed, given by double the stroke length in metres

times engine revs per second, is an important measure of an engine's state of

development. This follows because both stroke length and r/min are factors that help to

determine the inertial loads in an engine. Modern engines have values between 15 and

18 m/s, and GP engines are pushing towards 25 m/s.

Platform. This could mean the basic steel pressing onto which the rest of the body

panels are welded. It also sometimes refers to the basic pressing plus the

suspension, wheels and even the engine. The various manufacturers do not agree as to

exactly what constitutes a platform. It is sometimes also called a floorpan, and this name

could also apply to both of the above meanings

Power. Power is the rate of doing work (i.e. the work done divided by the time taken).

The modern unit is the watt, defined so that one watt = one joule per second. The

Imperial unit is the horsepower (= 746 watts), while the old German unit is the PS (= 736

watts).

The perception of power in the public's mind is complicated by the various power ratings

that have been used by governments to tax motorists. None of these was related to the

real output as measured on a test bench, or dynamometer. Britain used an RAC

horsepower rating that only took the bore into account, and France had an even more

weird CV rating. This resulted in an engine developing 30 kW being called a 14 HP in

Britain and an 11CV in France!

Power Steering : A steering system assisted by hydraulic or vacuum pressure from a

pump. This reduces steering effort. Power steering is essential to make large, heavy

vehicles manageable. Small vehicles often do not require power steering.

Benefit: Power steering multiplies the driver's steering force and lessens the amount of

steering input required to turn the wheels.

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Power-to-Weight Ratio : The horsepower rating of an engine divided by the vehicle's

curb weight. The resulting number is the number of pounds of vehicle per horsepower.

With other factors being equal, the fewer pounds per horsepower the higher the

performance. For example, a vehicle with a ratio of 1:15 (one horsepower to 15 pounds

of curb weight) should accelerate much more quickly than one with a ratio of 1:30.

Powertrain (Drivetrain) : A name given to the components that create power and send

it to the driving wheels, including the engine, transmission, driveshaft, differential and

axle(s).

Revolutions per minute (rpm) : RPM indicates how many times the engine crankshaft

rotates per minute. If the engine is running at 4,000 RPM, the valves are opening and

closing 2,000 times every minute, or 33 times every second

Rack and pinion : Torque can be converted to linear force by a

rack and pinion. The pinion is a spur gear, and meshes with a

toothed bar or rod that can be thought of as a sector gear with an

infinitely large radius of curvature. Such a mechanism is used in

automobiles to convert the rotation of the steering wheel into the

left-to-right motion of the tie rod(s). Rack and Pinion Steering : A steering system having a pinion gear at the lower end of

the steering column that engages a rack or a toothed rod that connects to the wheel

steering arms. The ends of the rack are linked to the steered wheels with tie rods. When

the gear is rotated by the steering shaft, it moves the rack from side to side: turning the

wheels. The steering wheel is connected to a pinion gear that meshes with a rack, or

linear gear. As the pinion rotates, the rack moves side to side, this moves the steering

linkage, causing the wheels to pivot left or right.

Radial ply : A tyre constructed so that the strengthening plies inside the casing run

radially (i.e. at right angles to the tyre centerline) from one side to the other side across

the tread area.

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Radian: The angular measure favored by scientists and engineers, because it simplifies

the mathematical calculations. An angle of 90 degrees is equivalent to ¼/2 radians, and

this can be used as a conversion factor to convert from degrees to radians. Pi (¼) is the

circumference of a circle divided by its diameter, i.e. 3,142.

Reed valve: Some two-stroke engines improve intake-mixture control by having a

number of flat plates, called reeds, at the intake port in the crankcase. They open and

close, depending on pressure differences, to introduce some measure

of timing into the mixture inhalation process.

Rigid Axle : A simple non-independent suspension, consisting of a rigid transverse

member with wheel hubs solidly bolted to it. The axle can be attached to the body by leaf

springs, or by a combination of suspension arms and links.

Roll angle: The angle, measured from the vertical, that a car's body adopts when

cornering.

Roll centre: The centre about which body roll takes place during cornering. The position

of this centre is determined by the suspension geometry.

Slip angle. The flexibility of a tyre causes the longitudinal centreline of any wheel to

deviate from the path followed by the contact patch centreline, as soon as the steering

wheel is turned from the straight-ahead position. The angle between the wheel

centreline and the contact patch centeline is called the slip angle, and each wheel will

normally run at a different angle, because its value depends on a number of factors.

These include suspension geometry, tyre construction, tyre pressure and cornering

speed. The difference between the average front and rear slip angles will determine

whether a car oversteers or understeers.

SOHC (Single Overhead Cam): An engine whose valves are driven by a single

camshaft in the cylinder head.

Speed rating: The speed rating of a tyre is the maximum safe speed that a tyre can

sustain, not continuously, but for a reasonable period of time, without weakening. The

rating is usually denoted by a letter of the alphabet shown on the side of the tyre. It is

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important to note that the rating only applies to a new tyre in good condition, but not to

retreads.

Spoiler: A specially shaped wing or body panel that is bolted to the front or rear of a

vehicle, sometimes to improve the local airflow, and sometimes just as a styling

statement.

Steering Ratio : The ratio of the gearing within a steering system, such as the rack to

the pinion or the interfacing and worm gear to the recirculating-ball and nut. A smaller

ratio (such as 4:1, compared to 6:1) means that the front wheels turn more tightly in

response to steering input, a condition normally associated with sporty vehicles. A larger

ratio means that the steering responds more subtly.

Suspension The assembly of springs, shock absorbers, torsion

bars, joints, arms, etc., that cushions the shock of

bumps on the road and serves to keep the wheels

in constant contact with the road, thereby improving

control and traction.

Synchromesh. A set of specially shaped rings inside the gearbox that offer frictional

surfaces to the rotating gears, against which the various gears can be forced to slow

down their rotation, to make gear-changing easier.

TDC (Top Dead Centre). This refers to the instant when the piston is at the highest

point in its rotational cycle.

Torque : Is a force that tends to rotate or turn things. For example, you generate torque

anytime you apply a force using a wrench. When you use a wrench, you apply a force on

the handle. This force creates a torque on a nut, which tends to turn the nut. To calculate

the torque, you just multiply the force by the distance from the centre. In the case of the

nut, if the wrench is a meter long, and you put 200 Newtons of force on it, you are

generating 200 Newton-meter of torque. If you use a two meter long wrench you only

need 100 Newtons of force on it to generate the same torque. So by lengthening the

wrench, you have multiplied the torque (same as a lever). In an engine, torque is the

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twisting motion at the crankshaft in foot-pounds. What you need to know: Torque gets it

going, and horsepower keeps it going

It is thus a measure of the twisting force. Torque is measured in lb.-ft. (pound-foot) or

N-m (Newton-meters). The RPM at which the engine produces maximum torque is

important. For instance, if Engine A produces 200 N-m @ 3000 RPM, and Engine B

supplies 200 N-m @ 5000 RPM, then Engine A will accelerate better at low speeds.

Engine B will accelerate better at high speeds.

Torsion Bar : A type of spring that twists as it is compressed or stretched. Torsion bar

springs are simple and rugged, used in the suspension system.

Torsion Bar Spring : A basically straight bar fastened to the frame at one end and to

the control arm of the suspension at the other end. The bar acts as a spring as it resists

twisting when the wheel moves up and down. Benefit: The advantages are relatively low

weight, no wear and maintenance and, in some vehicles, packaging advantages.

Torsion Bar suspension : Long rods of spring steel which take the place of springs.

One end of the bar is anchored and the other arm (attached to the suspension) is free to

twist. The bars' resistance to twisting causes springing action.

Torsion Beam Suspension : Also called a Twist Beam Suspension, this is a rigid axle

design. The cross member acts as a torsion bar to resist twisting of the suspension

arms. The result is increased roll rigidity and a very small positive camber angle during

cornering. Benefit: The compact design offers good space utilization and lower weight

than most other rigid axle designs.

Torque converter: A fluid coupling, filled with oil, consisting of three members with

vanes shaped in such a way that it can multiply the engine torque by a factor of up to

three while coupling the engine to the transmission.

Understeer: When a car corners, each tyre develops a different slip angle. If the

average of the front slip angles is greater than the average of the rear slip angles, then

the car seems to require more steering input than it would if it was rolling slowly around

the same corner. This condition is called understeer. See also oversteer.

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Valve lag: This is the crankshaft rotation angle at which a valve closes after TDC or

BDC.

Valve lead : This is the crankshaft rotation angle at which a valve opens before TDC or

BDC.

Valve timing diagram: This a diagram that shows the crankshaft rotation angles at

which the intake and exhaust valves open and close, during one complete cycle of

events.

Viscosity: The resistance of a fluid to flow is called its viscosity, commonly, if

incorrectly, known as its thickness. The SAE number of an oil is an indication of its

viscosity, with a higher number indicating a more viscous oil. Most liquids (but not all;

see viscous coupling) become less viscous as they are heated up.

Valve Train : The system that operates intake and exhaust valves, consisting of

camshaft, valves and springs, lifters, pushrods and rocker arms.

Variable Valve Timing (VVT) : What it is: Variable Valve Timing allows the point at

which an engine's valves open and close to change with operating conditions - such as

engine speed and throttle position. in addition to changing the valve timing with respect

to the crankshaft, some systems also change the duration the valve is open and the

extent to which it opens. Varying these parameters allows the engine to operate more

efficiently at all engine speeds while maintaining drivability.

How it works: Traditionally, camshafts open and close intake and exhaust valves at fixed

points in the engine cycle regardless of engine speed or throttle position. Variable Valve

Timing can employ several mechanisms to change valve opening and closing. it can

affect either the intake valves and/or the exhaust valves, depending on the design.

Some methods include advancing or retarding the cams or valves or activating additional

camshafts or rocker arms. Customer benefit: Improved power, fuel economy and

emissions (depending on the system).

Watt : The metric unit of power. It is the energy, or work done, in Newton-meters

divided by the time taken in seconds.

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Weight Distribution : Expressed as two numbers, one front and one rear, this figure

represents the percentage of weight resting on the front and rear axles. Benefit: A more

even weight distribution aids in handling, and is important to the service life of many

components, including axles, springs, bearings and tires.

Wheel Size (e.g. 15 X 7) : Wheel size is defined by the diameter and width of the wheel.

A 15 X 7 wheel has a 15-inch diameter and a 7-inch width

Wheelbase: The distance from the center of the front wheel to the center of the rear

wheel as viewed from the side of the vehicle. A longer wheelbase generally contributes

to a smoother ride, while a shorter wheelbase results in a tighter turning radius

Wishbone Suspension (Double Wishbone Suspension): An independent suspension

that uses curved members (wishbones) to control suspension travel. A wishbone

suspension offers good axle control, and limits undesirable suspension.

Yaw: One of the three rotations that a car is capable of executing. Rotation about the

vertical (also called polar) axis through the centre of mass of a vehicle is called yaw. The

other rotations are: ROLL, which occurs around a horizontal longitudinal axis through

the centre mass; PITCH, which occurs around a horizontal transverse axis through the

centre mass.

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LIST OF SOME USEFUL LINKS

Following is the list of some useful links that provide valuable information on cars such

as classification & types of cars, glossary to technical terms etc. There is also a link

which in provides animated working diagrams of engine cycles.

http://www.keveney.com – This site hosts animated engine cycles namely Otto cycle and

diesel cycles in addition to other engines as well.

http://auto.howstuffworks.com – the automobile section of the How Stuff Works portal.

This site features information on various types of engines, parts and their working, fuels

etc with well labeled diagrams as well as animated drawings.

http://www.cars.com – a very informative portal on cars

http://www.sonirodban.com/tiger.html - link having comprehensive glossary of

automobile terms.

http://www.cartoday.com/content/car_magazine/booklets/techno_terms/index.asp -

another useful link for automobile tech speak

http://www.siamindia.com/ - homepage of the Society of Indian Automobile

Manufacturers.

http://www.tata.com/0_products_services/companies_industries/automotive/commercial

_vehicles.htm - page hosted by the TATA Motors limited homepage showcasing the

TATA portfolio.

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Mechanical Engineer

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