Automobile Engineering: Unit - II

Cooling, Lubrication and electrical

systems, Transmission systems, need
for clutch types of clutches with their
mechanical details.
 Automobile Engineering: Unit - II
• Engine Cooling: Introduction
• Lot of heat is produced during the combustion of air-
fuel mixture inside the engine cylinder. The
temperature inside the cylinder may be as high as
2500oC. Such a high temperature will break the
lubricating film between the moving parts, weld the
moving parts or may cause any mechanical breakage
of the engine parts. Hence this temperature must be
reduced by some means to such a value, about 200oC
- 250oC, at this temperature the engine work
efficiently.
 Automobile Engineering: Unit - II
• Too much cooling would, however, lower thermal efficiency
of the engine. Thus, the purpose of the cooling system is to
keep the engine at its most efficient operating temperature
at all engine speeds and all driving conditions.
• About 15% of the total heat produced is utilised for useful
work at the crankshaft. Remaining amount of heat is
absorbed in friction, removed by exhaust gases and taken
by cooling system. The cooling system is designed to
remove above 30 to 35% of heat produced in the engine
cylinder. When the combustion takes place, the cylinder
walls, cylinder head, piston and valves are heated.
 Automobile Engineering: Unit - II
• Cooling beyond permissible limits decreases the overall
efficiency due to the following reasons:
1. Thermal efficiency is decreased due to more loss of
heat to the cylinder walls.
2. The vaporization of fuel is less, it decreases
combustion efficiency.
3. Viscosity of lubricant increases at low
temperature, it increases friction.
Although various metals are used for the construction of
cylinder and piston, but for better engine cooling, aluminium
alloy is the best for various reasons:
 Automobile Engineering: Unit - II
• 1. Aluminium is a much better heat conductor than
cast iron or steel. For the same temperature difference, it
will conduct about three times the quantity of heat,
while copper is better still and will conduct six times the
quantity of heat.
• 2. Aluminiuun alloys enable the use of higher
compression ratio, facilitate better cooling and lighter the
engine weight, because aluminium has only one third of
the density of cast iron.
• 3. Concerning strength properties, a suitable aluminium
alloy containing 9 to 12% copper, has tensile strength
equivalent to that of cast iron
 Automobile Engineering: Unit - II
• 2 PROPERTIES OF AN EFFICIENT COOLING
SYSTEM
• 1. An efficient cooling system removes 30 to 35%
of the heat generated in the combustion
chamber. Too much removal of the heat
decreases thermal efficiency of the engine.
• 2. It removes heat at a fast rate when the engine
is hot and at a slow rate when the engine is
started until the engine reaches at its normal
operating temperature.
 Automobile Engineering: Unit - II
• 3. METHODS OF COOLING
• Then are following four methods of engine
cooling
• 1. Air cooling. 2. Water cooling.
• 3. Liquid cooling. 4. Steam cooling.
• Most automatic engines use air cooling and water
cooling methods. Liquid cooling and steam
cooling methods are rarely used in actual
practice.
 Automobile Engineering: Unit - II
• 4. AIR COOLING
• In this method of cooling, the heat is dissipated directly to the
air after being conducted through the cylinder walls. Fins and
flanges on the outer surfaces of the cylinders and heads serve to
increase the area exposed to the cooling air, and so raise the rate
of cooling. The amount of heat dissipated depends upon the
following factors:
1. Surface area of metal into contact with air. 2. Rate
of air flow
3. Temperature difference between the heated surface and
the air.
4. Conductivity of the metal
 Automobile Engineering: Unit - II
• 5. ADVANTAGES OF AIR COOLED ENGINES
• 1. Lighter in weight due to absence of radiator, cooling
jackets and coolant.
• 2. No topping up the cooling system.
• 3. No leaks to guard against.
• 4. Antifreeze not required.
• 5. Engine warm up faster than with water cooled designs.
• 6. Can be operated in cold climates where water may
freeze.
• 7. Can be used in areas where their is scarcity of cooling water.
 Automobile Engineering: Unit - II
• DISADVANTAGES:
• 1. Less efficient cooling, because the co –
efficient of heat transfer for air is less than that for
water.
• 2. Not easy to maintain even cooling all around
the cylinder, distortion of the cylinder may take place.
• 3. More noisy operation.
• 4. Limited use in motor cycles, and scooters
where the cylinders are exposed to air stream.
 Automobile Engineering: Unit - II
• Cylinder with Fins The surface area
over the cylinder is increased by
means of fins. These fins are either
cast as integral part of the cylinder
Sometimes particularly in aero
engines, fins are machined from the
forged cylinder blanks.
• As a rule the fins are usually made of
about the cylinder wall thickness at
their roots, tapering down to about
one half the root thicknesses. The
length of the fin varies from one –
quarter to one – third of the cylinder
diameter. The distance between the
two fin centers is one – quarter to
one – third of their length of the fin.
 Automobile Engineering: Unit - II
• 8. FAN COOLING
• Fan cooling is used in larger air cooled engines,
particularly on cars. A fan, having two or four
blades is driven either at engine speed or twice
the engine speed, and the air-flow is directed
on the cylinder heads. The cooling depends
chiefly upon the engine speed and not upon the
forward speed of the car. The fan usually absorb
about I H.P. for every 15 to 20 H. P. output.
 Automobile Engineering: Unit - II
• 9. MODERN AIR-COOLED ENGINES
• At present, air cooling is used on engines in
scooters, motor-cycles, aero planes, combat tanks,
small stationary installations and in one model of
an American rear-engine car. In Germany, air
cooling is used in some petrol and C. 1. engines
including 2, 4 and 8 cylinder models A good
example ol De modem air-cooled type is the Krupp
four-cylinder opposed compression ignition engine.
This has a cooling fan fitted at the front end, and is
driven by engine.
 Automobile Engineering: Unit - II
• 10. WATER COOLING
• In this method of cooling, water is circulated through
water jackets around each of the combustion chambers,
cylinders, valve seat and valve stems. The circulating
water, when passes through the engine jackets in the
block and cylinder heat, takes heat of the combustion.
When it passes through the radiator, it is cooled by air
drawn through the radiator by a fan and by air flow
developed by the forward motion of the vehicle. Afar
passing through the radiator, the water again goes in the
engine jackets.
 Automobile Engineering: Unit - II
• 1. Thermo siphon system: In this
circulation of water is obtained
due to the difference in densities
of hot and cold regions of the
cooling water. There is no pump
to circulate the water. The hot
water from the engine jacket
being lighter, rises up in the horse
pipe and goes in the radiator
from the top side. It is cooled
there and hence goes down at
the bottom side of the radiator.
From where it goes again in the
engine jackets. The system is
quite simple and cheap, but the
cooling is rather slow.
•
 Automobile Engineering: Unit - II
• 2. Pump circulation System:
In this system of water
cooling, the circulation of
water is obtained by a pump.
The pump is driven by means
of a V-belt from a pulley on
the engine crank shaft the
system is more elective. The
circulation of water becomes
faster as the engine speed
increases. Then is no
necessity of maintaining the
water upto a correct level.
Automobile Engineering: Unit - II
 Automobile Engineering: Unit - II
• 12. COMPONENTS OF THE WATER COOLING
METHODS:
• 1. Radiator 2. Thermostat
3. Pump 4. Fan
5. Water Jackets
 Automobile Engineering: Unit - II
• 13. RADIATOR
• Radiator is a device for having a large amount of
cooling surface to the large amount of air so that the
water circulating through it is cooled efficiently. It
consists of upper tank and lower tank and between
them a core. The upper tank is connected to the
water outlet or outlets from engine jacket by a hose
pipe, and the lower tank is connected to the jackets
inlet through the water pump. The core is a radiating
element, which cools the water.
Automobile Engineering:Types of Radiator
Cores
 Automobile Engineering: Unit - II
• There are two basic types of radiator cores-tubular type and
cellular type. In tubular type core the upper and lower tanks
are connected by a series of tubes through which water
passes. Fins are placed around the tubes to improve heat
transfer. Air passes around the outside of the tubes, between
the fins, absorbing heat from the water in passing. In cellular
type core, air passes through the tubes and the water flows
in the spaces between them. The core is composed of a large
number of individual air cells which an surrounded by water.
Because of its appearance the cellular type usually is known
as a honeycomb radiator, especially when the cells infront are
hexagonal in the form..
 Automobile Engineering: Unit - II
• Radiators are also classified according to the
direction of the water flow through them. In some,
the water flows from top to bottom—down flow
type radiators. In other, the water flows
horizontally from an input tank on one side to
another tank on the other side—cross flow type
radiator.
• Radiators are usually made of copper and brass
because of their high heat conductivity. The various
sections of the radiator are almost completely
joined together by soldering.
 Automobile Engineering: Unit - II
• THERMOSTAT
• A thermostat valve is used in the water
cooling system to regulate the
circulation of water in system to
maintain the normal working
temperature of the engine parts during
the different operating conditions. The
thermostat valve automatically works in
the cooling system. When the engine is
stared from cold, the thermostat valve
prevents the flow of water from engine
to radiator so that the engine readily
reaches to its normal working
temperature, after which it
automatically comes into action.
Generally the thermostat valve does
not permit the water below 70oC.
 Automobile Engineering: Unit - II
• Two types of thermostats are
used in automobile vehicles.
Bellows type and Pellet type. All
thermostats work on the same
general principle--a heat unit
operating a valve.
• the bellows type thermostat,
shown in Fig. 6, the heat unit
consists of a closed bellows filled
with a volatile liquid under
reduced pressure. When the
bellows is heated, the liquid
vaporized and creates enough
pressure to expand the bellows.
 Automobile Engineering: Unit - II
• In pellet thermostat, shown
in Fig. 7, the heat unit
consist of a sealed in wax
pallet, which expands on
heating and contracts on
cooling. The pellet is
connected by piston and
flange to a valve so that on
expansion of the pellet it
opens the valve. When the
pellet contracts on cooling,
a coil spring closes the
valve.
 Automobile Engineering: Unit - II
• WATER PUMP
• A pump is used in the water cooling
system to increase the velocity of the
circulating water. Impeller type pump
is mounted at the front end of the
cylinder block between the block and
the radiator. The pump consists of a
housing with inlet and outlet, and an
impeller. The impeller if a flat plate
mounted on the pump shaft with a
series of flat or curved blades or
vanes. When the impeller rotates, the
water between the blades is thrown
outwards by centrifugal force, and is
forced through the pump outlet and
into the bottom of the radiator, and
the water from the radiator is drawn
into the pump to replace the water
forced through the outlet.
 Automobile Engineering: Unit - II
• The pump is driven by a belt to the drive pulley
mounted on the front end of the engine
crankshaft. The impeller shalt is supported on
one or more beatings. A seal prevents water
from leaking out around the bearing. The pack
less type pump is used in modem engine. The
packing gland type pump is found only in older
models.
 Automobile Engineering: Unit - II
• FAN

• A fan is mounted behind the radiator on the water pump shaft. It is

driven by the same belt that drives the pump and the generator.
The purpose of the fan is to draw air through the radiator. When the
vehicle is going at high speed, the natural draft of air passing
through the radiator is sufficient for cooling, but when the engine is
going at low speed, or upside a hill, the natural draft is certainly
insufficient to produce the desired cooling effect. Here the fan
serves the purpose.
• The fan requires a little power and usually runs at a speed greater
than that of the crankshaft. Many engines use a variable speed fan
drive which reduced fan speed to conserve horse power at high
engine speed and also when cooling requirements are low.
 Automobile Engineering: Unit - II
• WATER JACKET
• Water jackets are cast into the
cylinder block and heads. Jackets
are simply the passages through
which water circulates around the
cylinders. Valve ports and seats,
combustion chambers and any
other hot parts that require
cooling. The heat of combustion is
conducted through the metal walls
to the water in the jackets which
removes the excess heat as it
circulates through them. Fig. 9
shows water jackets in L = head
engine.
 Automobile Engineering: Unit - II
• LIQUID COOLING
• In this method of cooling, instead of water, other
liquids having higher boiling points are used for
cooling. Glycerin (boiling point 290oC) and
ethylene glycol (boiling point 195oC) are examples
of such liquids. Due to their higher boiling point
these liquids have increased capacity to carry
heat, and hence the weight of coolant and
radiator is decreased.
•
 Automobile Engineering: Unit - II
• STEAM COOLING
• In this method of cooling, steam is
used for cooling. The cooling system
consists of the same
• components as those for water
cooling, except the radiator. The
radiator is in the form of condenser in
this system. The circulation of water
is made by a pump. The water in the
cylinder jackets is converted into
steam, which flows out at the top of
the engine block and goes to the
bottom of the radiator. (Fig.10). the
steam is condensed in the radiator
and the water thus formed is again
circulated by the pump.
 Automobile Engineering: Unit - II
• CLOSED SYSTEM
• In closed type water cooling system, the circulation of
water is closed in the system under pressure, not opened
to atmospheric pressure. The boiling point of the water
or the coolant is raised by keeping it under pressure in
the closed cooling system. A pressure relief valve is
provided in the system to prevent pressure from
becoming excessive and causing leaks in the system.
Whenever the pressure exceeds a predetermined value,
the relief valve opens to the atmosphere and the excess
of pressure is released.
 Automobile Engineering: Unit - II
• CLOSED SYSTEM
 Automobile Engineering: Unit - II
• ANTI-FREEZE MIXTURES
• When the water freezes in the engine cooling system, the resulting
expanding force is often sufficient to crack the cylinder block, pipes
and the radiator. This occurs when the car is parked in unheated
areas where temperatures below freezing point (0oC). To prevent
freezing, anti-freeze mixtures or solutions are added in cooling
water. The most commonly used anti-freeze materials are as
follows:
• 1. Wood Alcohol 2. Denatured Alcohol
• 3. Glycerin 4. Ethylene Glycol
• 5. Propylene Glycol 6. Mixture of Alcohol and
Glycerin
 Automobile Engineering: Unit - II
• A good anti-freeze material should have the following
requirements:
• 1. It should mix readily with water.
• 2. It should prevent freezing of the mixture at lowest temperature
encountered.
• 3 . It should circulate freely in the cooling system.
• 4. It should not damage cooling system by corrosive action.
• 5. It should not lose its anti-freezing property after extended use.
• 6. It should be reasonably cheap.
• 7. It should not waste by vaporization.
• 8. It should not deposit any foreign matter in the water jackets or in
the radiator.
 Automobile Engineering: Unit - II
• Lubrication: is essentially required in motor vehicle maintenance. To supply lubricating oil between the
moving parts is simply termed as lubrication.
• 2. OBJECTS OF LUBRICATION
• 1. To reduce friction between the moving parts.
• 2. To reduce wear of the moving parts.
• 3. To act as a cooling medium for removing heat.
• 4. To keep the engine parts clean, especially piston rings and ring grooves, oil ways and filters.
• 5. To absorb shocks between beatings and other engine parts thus reducing engine noises and extending
engine life.
• 6. To form a good seal between piston rings and cylinder walls
• 7. To prevent deposition of carbon, soot and lacquer.
• 8. To absorb and carry away harmful substances resulting from incomplete combustion.
• 9. To prevent metallic components from corrosive attack by the acid formed during the combustion
process.
• 10. To resist oxidation which causes sludge and lacquers.
 Automobile Engineering: Unit - II
LUBRICATING SYSTEMS
In motor vehicles, there are two separate systems of lubrication:
1. Engine Lubrication System
2. Chassis Lubrication system
• The engine lubrication system may be either pressure type or splash
type systems are used. Only equipment outside the engine, such as
starter, generators, water pump and distributors, are separately
lubricated.
• This system circulates the oil from a common reservoir or sump to the
main bearings connecting rod bearings, wrist pins, camshaft bearings
and cams, cylinder wails, valves and timing drive. All modem American
passenger cars and trucks use the pressure system in which oil is
forced under pressure by a geared pump to the various rotating and
reciprocating parts.
 Automobile Engineering: Unit - II
• FUNCTIONS OF LUBRICATING OIL
• There are five important functions of the lubricating oil in
an automotive engine
• 1. To minimize friction and wear.
• 2. To cool by carrying away heat.
• 3. To seal the pistons and thus preventing escape of
gases in the cylinders with consequent loss of power
• 4. To cushion the parts against vibration and impact.
• 5. To clean the parts as it lubricated them, carrying away
impurities.
 Automobile Engineering: Unit - II
• The magnitude of the retarding frictional force mainly
depends upon the following three factors:
• 1 Nature of the surface: Friction is low when
surface are smooth and highly polished. Rough surface
produce high frictional forces.
• 2 Pressure which forces the surface together:
Friction is low when pressure is low. High pressure
produces high frictional forces.
• 3 Kind of material: Friction is low when material is
hard. Soft materials produce high frictional forces.
 Automobile Engineering: Unit - II
• HYDRODYNAMIC THEORY OF LUBRICATION

• When the shaft rotates in a bearing it

takes an eccentric position in the bearing,
This is due to the loading of the journals
W and the direction of rotation. The oil
film is maintained by the wegding action
as the oil is toned into the wedge at the
bottom by the pressure generated when
the oil is carried from the wide space A
and forced into the narrow space B at the
bottom by rotating journal to which the oil
adheres. This is called the hydrodynamic
theory of lubrication. From the above
theory it is clear that the oil film is
maintained, only when the journal is in
motion. When the journal comes to rest
the oil film is squeezed out.
•
 Automobile Engineering: Unit - II
• 6. PROPERTIES OF LUBRICANTS
• An engine lubricating oil must have certain properties for its
satisfactory function, as follows :
• 1. viscosity. 2. Flash point. 3. Fire
point.
• 4.Cloud point 5. Pour point. 6. Oiliness.
• 7. Corrosion. 8. Colour. 9. Dilution.
• 10. Emulsification. 11. Physical stability. 12. Chemical
stability. 13. Sulphur content 14. Specific gravity.

• 15. Neutralization number.

• 16. Adhesiveness. 17. Film strength. 18.
Cleanliness.
 Automobile Engineering: Unit - II
• 1. Vlscosity. Viscosity is a measure of the resistance to flow or
internal friction of an oil. The viscosity of an oil is usually
specified as the time in seconds that it takes for a given
amount of the oil to flow by gravity through a standard sized
orifice at a given temperature. Viscosity is inversely
proportional to temperature. It decreases as the temperature
rises and increases as it falls. The viscosity is measured by
viscometer. There are many types of viscometers, as follows:
• (a) Saybolt Universal Viscosimeter. (b) Redwood
Viscosimeter.
• (c) Engler viscosimeter. (d) Barbey viscosimeter.
• The unit of viscosity is given as "seconds say bolts" or seconds
Redwood" etc. viscosity. For example, if an oil has a viscosity
of 50 at 210oF, it means that 50 seconds were required for the
 Automobile Engineering: Unit - II
• 2. Flash point: The flash point has been defined as the lowest
temperature at which the lubricating oil will flash when a
small flame is passed across its surface. When the oil is
heated, it leaches a temperature at which, if a small flame is
brought near it, a flash spreads across the oil. It happens due
to the volatilization of the light particles in the oil.
• 3. Fire point the lowest temperature at which the oil will
burn continuously is called the fire point. The fire point also
must be high in a lubricating oil, so that the oil does not burn
in service.
• 4. Cloud point. The oil changes from liquid state to solid state
when subjected to low temperatures. In some cases the oil
starts solidifying which makes it to appear cloudy. The
temperature at which this takes place is called the cloud
 Automobile Engineering: Unit - II
• 5. Pour point. The pour point of an oil is indication of its
ability to move at low temperatures. This property must be
considered because of its effect on starting an engine in cold
weather and on free circulation of oil through exterior feed
pipes when pressure is not applied.
• 6. Oiliness. It is the characteristic property of an oil. An oil is
said to be oil when it has oiliness. This property is highly
desirable in helping the lubricant to adhere to the cylinder
walls.
• 7. Corrosion. Corrosion has been defined as the destruction
of a solid body by chemical or electro chemical action which
starts unintentionally from its outer surface. A lubricant
should not corrode the working parts and it must sustain its
properties even in the presence of foreign matter and
 Automobile Engineering: Unit - II
• 8. Colour. Colour of a lubricating oil is not of so much
importance for its property expect as a lest for checking the
uniformity of any given grade or brand of oil.
• 9. Dilution. During the combustion petrol vapour may escape
past the piston rings if the rings are worn or broken.
Considerable amount of such hens mixed with the crankcase
oil and dilutes it, thus affecting its lubricating property.
Crankcase ventilation is however, adopted to escape the
petrol fumes.
• 10. Emulsification. A lubricating oil, when mixed with water is
emulsified and loses its lubricating property. The
emulsification number is an index of the tendency of an oil to
emulsify with water.
 Automobile Engineering: Unit - II
• 11. Physical stability. A lubricating oil must be stable
physically at the lower and the highest temperatures between
which the oil is to be used. At the lowest temperature there
should not be any separation of solids, and at the highest
temperature it should not vaporize beyond a certain limit.
• 12. Chemical stability. A lubricating oil should also be stable
chemically. There should not be any tendency for oxide
formation. The oxidation products, being sticky, clog the
working parts, cause the faulty piston rings and valve action.
The oil should also not decompose at high temperatures to
form carbon which makes spark plug and valves faulty to
function.
 Automobile Engineering: Unit - II
• 13. Sulphur content if sulphur is present in considerable
amount in the lubricating oil it promotes corrosion. The
corrosion test shows the amount of sulphur content. The scale
used is the one recommended by Americal Petroleum
Institute and the result is called the API gravity.
• 15. Neutralization number. An oil may contain impurities that
are not removed while refining. It may contain alkaline or acid
products. The neutralization number test is a simple
procedure to determine acidity or alkalinity of an oil. It is
the weight in milligrams of potassium hydroxide required to
neutralize the acid content of one gram of oil
• 16. Adhesiveness. It is the property of lubricating oil due to
which the oil particles stick with the metal surfaces.
•
 Automobile Engineering: Unit - II
• 17. Film strength. It is the property of a lubricating oil due to
which the oil retains thin film between the two surfaces even
at high speed and load. The film does not break and the two
surfaces do not come in direct contact. Adhesiveness and film
strength cause the lubricant to enter the metal pores
and cling to the surfaces of the bearings and journals keeping
them wet when the journals are at rest and preventing metal
to metal contact until the film of lubricant is built-up
• 18. Cleanliness. A lubricating oil must be clean. It should not
contain dust and dirt particles. These impurities may either be
filtered out or removed with the change of oil at periodic
intervals. Further, the oil must contain agents, called
detergents which remove the impurities from the engine
parts during oil, circulation.
 Automobile Engineering: Unit - II
• 7. ADDITIVES IN OIL Any mineral oil, by itself, does
not have all the properties as described in the
previous articles. To give the desired properties,
certain additives are mixed in the oil during the
manufacturing process. These additives are as
follows: 1. Viscosity-index improved.
• 2. Rust inhibitors. 3. Pour-point depressants.
• 4. Oxidation inhibitors. 5. Corrosion inhibitors.
• 6. Foam inhibitors. 7. Detergent-dispersants.
• 8. Extreme-pressure agents.
 Automobile Engineering: Unit - II
• 8. SAE Numbers
• The Society of Automotive Engineers (SAE) rates oil viscosity
in two different way, for winter and for other than winter.
Winter grade oils are tested at 0o and 210oF. There are three
grades, SAE 5 W. SAE 10 W and SAE 20 W, the 'W ' indicating
winter grade. For other than winter use, the grades are SAE
20, SAE 30, SAE 40 and SAE 50, all without the 'W ' suffix.
Some oil have multiple ratings, which means they are
equivalent, in viscosity, to several single rating oils. For
example SAE 10 W 30 W oil is comparable to SAE 10 W, SAE 20
W and SAE 30 oils.
 Automobile Engineering: Unit - II
• TYPES OF LUBRICANTS
• The lubricants are of three types :
• 1. Solid lubricants: graphite, mica, soap stone or steatite.
• 2. Semi-solid lubricants: grease.
• 3. Liquid lubricants: mineral oil, vegetable oil, animal oil, etc.
• Graphite and Mica are examples of solid lubricants. Graphite
has low co efficient of friction and is stable at high
temperature. Semi solid lubricants such as grease, are used in
chassis lubrication. Grease is widely used in automobiles at
places where retention of liquid lubricants is difficult and
where high temperatures are encountered, like in axles.
 Automobile Engineering: Unit - II
• 1. Calcium-based grease are fairly water proof and are useful
for water pumps, chassis and wheel beatings
• 2. Sodium-based creases are able to withstand moderably
high temperatures and tend to absorb water, which reduces
rusting problem
• 3. Aluminium based greases have good staying – properties
when combined with a chemical, but not suitable for high
temperature. They an used on exposed chains, transmissions,
chassis and flame fittings.
• 4. Lithium - based greased. One type of lithium based
creases can do all the jobs, and sometimes called
multipurpose grease. It is used in wheel bearings, chassis
fittings, Erase cups, universal joints and water pumps
 Automobile Engineering: Unit - II
• Lubricating oils are classified according to their source: as
animal, vegetable, mineral.
• Animal oils are obtained from the animal fats such as Lard
and Fish, Whale, Tallow, etc. They are not suitable for
automotive engine lubrication because they are oxidized
easily and become gummy after some use.
• Vegetable oils are obtained from linseed, rope seed, Hazel
nut, palm olive, caster, etc. These oil also are not suitable for
automotive engine lubrication because they are oxidized
easily and become gummy after some use.
• Mineral oils are obtained from petroleum and chiefly contains
hydrocarbons. Mineral oils are almost entirely used for
lubricating automotive engines, because they have good
lubricating properties. They are cheap and more plentiful than
 Automobile Engineering: Unit - II
• Application:
• 1. Very heavy pressure and slow speed: Graphite, soapstone.
2. Heavy pressure and high speed: Palm oil, rape oil, castor oil,
medium mineral oils.
3. Heavy pressure and slow speed: Grease, palm oil, lard oil,
tallow oil.
4. Light pressure and high speed: Sperm oil olive oil, light
mineral oils.
5. Ordinary machinery: Rape oil, lard oil, tallow oil, heavy
mineral oils.
6. Steam cylinders: Lard oil, tallow oil, tape oil, heavy mineral
oils.
7. Clock and watches: Hezel - nut oil, neat's foot oil, olive oil,
sperm oil, light mineral oils.
 Automobile Engineering: Unit - II
• LUBRICATING PARTS
• The engine parts which are to be lubricated an
as follows :
• 1. Main crankshaft bearings.
• 2. Big end bearings.
• 3. Small end bearings. 4. Cam shaft
bearings
• 5. Piston rings and cylinder walls.
• 6. Timing gears. 7. Valve mechanism.
 Automobile Engineering: Unit - II
• LUBRICATING SYSTEMS
• The different systems for lubricating the
automobile engine are as follows :
• 1. Petroil system. 2. Splash system.
• 3. Pressure system. 4. Semi-pressure
system.
• 5. Dry sump system.
 Automobile Engineering: Unit - II
• LUBRICATING SYSTEMS
• The different systems for lubricating the
automobile engine are as follows :
• 1. Petroil system. 2. Splash system.
• 3. Pressure system. 4. Semi-pressure
system.
• 5. Dry sump system.
 Automobile Engineering: Unit - II
• LUBRICATING SYSTEMS: Splash system:
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• LUBRICATING SYSTEMS: Pressure system:
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• LUBRICATING SYSTEMS: Pressure system:
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• 4. Semi - pressure system: It is the
combination of splash system and pressure
system. Some parts are lubricated by splash
system and some pars by pressure system.
• 5. Dry sump system: The system in which the
lubricating oil is not kept in the oil sump is
known as dry sump system. In this system, the
oil is carried in a separate tank from where it
is fed to the engine.
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• Dry sump system:
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• OIL PUMP is generally located inside the
crankcase below the oil level. The function of
the oil pump is to supply oil under pressure to
the various engine parts to be lubricated. The
different types of the oil Pumps used for
engine lubrication an as follows:
• 1. Gear pump 2. Rotor pump.
• 3. Plunger pump 4. Vane pump.
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• Gear pump. There is very little Clearance between the gear teeth and
housing. One gear is attached to a shaft which is driven through suitable
gears from the camshaft or crank shaft of the engine. The other gear is
free to revolve on its own bearing. When the pump is in action, the oil is
driven between the gear teeth from the inlet side, carried around
between the gears and pump housing, and forced out the outlet side. The
pressure and quantity of the supplied by the pump depend upon the
speed of the gears.
• This type of pump is almost universally used in the automotive engine,
due to its simplicity in construction. It can deliver oil at a pressure of about
2 – 4 kg/cm2. A pressure relief valve is also provided in many oil pumps to
relief the excessive pressure due to high engine speeds or clogged oil
lines.
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Gear pump with pressure relief valve:
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• Rotor Pump: • Plunger Pump:
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Vane pump:
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• Electrical systems: Introduction
• Internal combustion engines are not self-starting and need to be rotated at a
certain minimum speed in order for the engine to commence running by the
fuel supply. This is the function of the starting motor. The starting motor is
direct current motor which cranks the engine for starting. It is series wound
and designed to operate on large currents at low voltages it must be capable
of exerting a very high torque when starting and at low speeds. The armatures
and fields are built with thick wire to keep the resistance low and to enable
them to carry large currents without overheating. The faster it turns, the less
current it draws, the slower, it tums, the more torque it develops. A motor
used in passenger car draws about 60 amperes. When running at no load,
about 600 amperes when cranking the engine slowly. Compression ignition
engines may use a 12 volts starting motor to provide the power to rotate the
crankshaft. The torque produced is 1 to 2 kg - m. The motor is powerful
enough to tum the engine at a speed such that the carburettor supplies proper
air-fuel mixture for starting.
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• Although the mechanical construction of motor
is very similar to generator, their functions are
entirely different. Whereas function of the
generator is to generate voltage when
conductors are moved through a magnetic field,
the function of the motor is to develop a torque
or twisting effort when the current is passed
through the conductors held in a field. The
generator is shunt wound but the starting
motor is series wound.
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• 2. MOTOR PRINCIPLE:
• In a generator the mechanical energy is converted into
electrical energy, in a motor the electrical energy is
converted into mechanical energy. If a current from an
outside source is applied to the terminal of a generator,
the armature would revolve, and the generator will act
as a motor. The working of a motor is based on the
simple principle that when a current carrying conductor
is placed in a magnetic field, a mechanical force is
experienced by a conductor, the direction of the force is
given by Fleming’s right hand rule.
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• DRIVE ARRANGEMENT
• The starting motor is linked to the engine flywheel through a
set of gears. A pinion gear is attached to the starter armature
which drives a ring gear attached to the flywheel. The
arrangement is so made that the two gears engage to crank
the engine until it starts and then disengage automatically
when the engine is running. The gear ratio is about 15:1. The
armature rotates 15 times to cause the flywheel to rotate
once. Thus the cranking motor requires only one fifteen as
much power as would an electric motor directly coupled to
the crank. The armature may revolve at about 2000 to 3000
rpm when the cranking motor is operated and hence the
flywheel will rotate as high as 200 rpm.
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• When the engine starts, its speed may increase to
about 3000 rpm. If the pinion is still in mesh with the
flywheel, it will evolve the armature at about 4500
rpm, which is a very high speed. At this exceed, the
centrifugal force would cause the conductors and
commutator segments to be thrown out of armature
damaging the motor. Hence the pinion must be
disengaged from the flywheel, after the engine has
started. The automatic engagement and
disengagement of the motor with the engine
flywheel is obtained with the help of drive
arrangement.
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• Bendix drive:
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• Bendix drive:
• When the starting motor is at rest the pinion gear is not engaged with the
flywheel. When the starting motor is switched on, the armature begins to
rotate. This causes the sleeve to rotate also, because the sleeve is fastened to
the armature shaft through a spring. The pinion, because of its inertia of rest
and its unbalanced weight, turns very little, but it moves forward on the
evolving bolt, until it engages with the teeth of the flywheel. The slight turning
of the pinion gear helps to engage it properly with the flywheel. When the
pinion gear strikes with the collar, it begins to turn with the sleeve, causing
flywheel to run with it. When the flywheel turns, the crankshaft also tums and
the engine start. The spring between the armature shaft and the threaded
sleeve takes the shock of the start.
• After the engine has started, the pinion gear is turned by the engine much
faster than whenrotated by the starting motor. This causes the pinion gear to
turn back on the threaded sleeve, making it disengaged with the flywheel.
 Automobile Engineering: Unit - II
STARTING MOTOR SWITCHES: Magnetic Switch
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Manual Switch:
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• IGNITION SYSTEM: INTRODUCTION
• The spank ignition engines require some device to ignite
the compressed air-fuel mixture inside tile cylinder at the
end of the compression stroke. Ignition system serves
this purpose. It is a part of electrical system which carries
the electrical current to spark plug which gives park to
ignite the air-fuel mixture at the correct time. The
ignition system consists of a battery, switch ignition
distributor, ignition coil, spark plugs and necessary
wiring. Some systems use transistors to reduce the load
on the distributor contact points.
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REQUIREMENTS OF AN IGNITION SYSTEM
The ignition system supplies high voltage surges of current (as
high as 30,000 volts) to the spark plug. These surges produce the
electric sparks at the spark plug gap that ignite or set fire to the
compressed air-fuel mixture in the combustion chamber. The
sparking must take place at the collect time at the end of the
compression stroke in every cycle of operation. At high speed or
during part throttle operation, the spark is advanced so that it
occurs somewhat earlier in the cycle, the mixture thus has
sufficient time to bum and deliver its power. The ignition system
should function efficiently at the maximum and minimum speeds
of the engine. It should be easy to maintain, light and compact. It
should not cause any interference
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TYPES OF AN IGNITION SYSTEM: Battery ignition
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MAGNETO IGNITION SYSTEM:
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• IGNITION COIL (or Induction Coil): The ignition
coil is simply a transformer to step up the
voltage in the ignition system. It consists of a
soft iron core, primacy winding and secondary
winding. The primacy winding consists of 200 -
300 tums of thick wire (20 SWG) and the
secondary winding 15,000 - 20,000 turns of fine
wire (40 SWG). The core is formed by
lamination of soft iron. The ignition coils may be
of two types :
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• Core type ignition coil:
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• Can type ignition coil:
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Contact Breaker:
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DISTRIBUTOR:
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• FIRING ORDER
• The order or sequence in which the firing takes place in different
cylinders of a multi-cylinder engine is called the firing order. In
spark ignition engine, the high tension leads from the distributor
are connected to the spark plugs at the different cylinders
according to the firing order. A proper firing order reduces
engine vibrations, maintains engine balancing and secures an
even flow of power. The firing order differs from engine to
engine. Probable firing order, for different engines are as follows:
• 3 - cylinder engine: 1 – 2 – 3
• 4 - cylinder in line engine : 1 – 3 – 4 – 2, 1 – 2 – 4 – 3
• 6 - cylinder in line engine (cranks in 3 pairs): 1 – 5 – 3 – 6 – 2 –
4; 1 – 4 – 2 – 6 – 3 – 5; 1 – 3 – 2 – 6 – 4 – 5; 1 – 2 – 4 – 6 – 5 – 3
 Automobile Engineering: Unit - II
IGNITION ADVANCE MECHANISMS:
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Spark Plugs:
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• Some spark plugs are provided with a built in resistor, which forms part of
the center electrode. The resistor serves two purposes:
• 1. It reduces radio and television interference from the ignition
system.
• 2. It reduces spark plug electrode erosion caused by excessively
long sparking
• Spark plug gap. The gap between the center electrode and the ground
electrode is called the spark plug gap. This gap is adjusted to
recommended specifications by bending the ground electrode. It varies
from 0.4 mm to 1.0 mm. It is measured with a feeler gauge. The electrical
resistance of the spark plug depends upon the nature and compression of
the fuel mixture and also upon the gap. Too large or too small gap reduces
the efficiency of the entire ignition system, which in tum causes losses in
engine power and operating efficiency.
 Automobile Engineering: Unit - II
Checking of spark plug gap:
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• LIGHTING AND WIRING
• INTRODUCTION
• Lights are used in modem vehicles for various
purposes. The main lights are:
• 1. Head lights. 2. Parking lights.
• 3 . Direction-signal lights. 4. Blinker lights
• 5. Stop lights. 6. Back-up lights.
• 7. Taillights. 8 . Interior lights.
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• Wiring circuit of a typical passenger car lighting system:
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• Transmission systems: INTRODUCTION
• The power developed inside the engine cylinder is utilized to
turn the wheels so that the motor vehicle can move on the
road. The circular motion of the crankshaft is transmitted to
the rear wheels. It is transmitted through the clutch, gear
box, universal joints, propeller shaft or drive shaft,
differential and axles extending to the wheels. The
application of engine power to the driving wheels through
all these parts is called power transmission. The power
transmission system is usually the same on all modem
passenger cars and trucks, but its arrangement may vary
according to the method of drive and type of the transmission
units.
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• CLUTCH AND ITS FUNCTION
• Clutch is a device used in the transmission system of a motor vehicle to
engage and disengage the engine to the transmission. Thus, the clutch
is located between the engine and the transmission. When the clutch
is engaged, the power flows from the engine to the rear wheels
through the transmission system and the vehicle moves. When the
clutch is disengaged, the power is not transmitted to the rear wheels
and the vehicle stops while the engine is still running. The clutch is
disengaged when starting the engine, when shifting the gears, when
stopping the vehicle and when idling the engine. The clutch is
engaged only when the vehicle is to move and is kept engaged when
the vehicle is moving the clutch also permits the gradual taking up of
the load.
•
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• 3. PRINCIPLES OF OPERATION
• The clutch works on the principles of friction. When two friction surfaces
are brought in contact with each other and pressed they are united due to
the friction between them. If now one is revolved, the other Will also
revolve. The friction between the two surfaces depends upon the area of
the surfaces, pressure applied upon the and coefficient of friction of the
surface materials. The two surfaces can be separated and brought into
contact when required. One surface is considered as driving member
and the other as driven member. The driving member is kept rotating.
When the driven member is brought in contact with the driving member,
it also starts rotating. When the driven member is separated from the
driving member it does not revolve. This is the principle on which a clutch
operates
•
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• REQUIREMENTS OF A CLUTCH
• l. Torque transmission: The clutch should be able to transmit maximum torque of the engine.
• 2. Gradual engagement: The clutch should engage gradually to avoid sudden jerks.
• 3. Heat dissipation: The clutch should be able to dissipate large amount of heat which is
generated
• 4. Dynamic balancing: The clutch should be dynamically balanced.
• 5. Vibration damping: The clutch should have suitable mechanism to damp vibrations and
to eliminate noise produced during the power transmission.
• 6. Size: The clutch should be as small as possible in size so that it will occupy minimum space.
• 7. Free pedal play: The clutch should have free pedal play in order to reduce elective
clamping load
• 8. Easy in operation: The clutch should be easy to operate requiring as little exertion as
possible
• 9. Lightness: The driven member of the clutch should be made as light as possible
•
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• MAIN PARTS OF A CLUTCH
• The main parts of a clutch are divided into
three groups :
• 1. Driving members.
• 2. Driven members.
• 3. Operating members.
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• Major parts of Single Plate Clutch:
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• Clutch Plate:
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• TYPES OF FRICTION MATERIALS:
• 1. Millboard type: Millboard type faction materials mainly include asbestos sheets
heated with different type of impregnants.
• 2. Moulded type: friction materials are made from a matrix of asbestos fibre and
starch or any other suitable binding materials. They are then heated to a certain
temperance for moulding in dies under pressure. They are also made into
sheets which: are rolled, passed and backed till they are extremely hard and dense.
Metallic wires are also sometimes inserted to improve wearing qualities.
• 3. Woven type: Woven type facing materials are made by impregnating a cloth
with certain binders or by wearing threads of brass or copper wires covered with
long fibre asbestos and cotton. The woven sheets heated with a binding solution
are baked and rolled. The woven type friction materials are further classified into
two types:
• laminated type and solid woven type. Laminated type friction materials prepared
by holding one layer over the other with a binder between them. In the solid
woven type, the cloth is woven just to the required thickness.
 Automobile Engineering: Unit - II
• The most common friction materials are as
follows:
• 1. Leather: Co-efficient of friction 0.27.
• 2. Cork: Co-efficient of faction 0.32.
• 3. Fabric: Co-efficient of friction 0.40.
• 4. Asbestos: Co-efficient of friction 0.20
• 5. Reybestos and Ferodo. Co-efficient of friction
0.20.
• They an almost universally used for clutch lining.
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• PROPERTIES OF GOOD CLUTCH LINING
• 1. Good wearing properties.
• 2. High co-efficient of friction.
• 3. High resistance to heat.
• 4. Good binder in it.
• 5. Cheap and easy to manufacture.
 Automobile Engineering: Unit - II
• Different types of clutches an as follows:
• 1. Friction clutch :
• (a) Single plate clutch.
• (b) Multi plate clutch :
(i) Wet (ii) Dry
• (c) Cone clutch.
• (i) External. (ii) Internal.
• 2. Centrifugal clutch.
• 3. Semi- Centrifugal clutch.
 Automobile Engineering: Unit - II
• Different types of clutches:
• 4. Conical spring clutch or Diaphragm clutch :
• (a) Tapered finger type. (b) Crown spring
type.
• 5. Positive clutch - Dog and spline clutch.
• 6. Hydraulic clutch.
• 7. Electro-magnetic clutch.
• 8. Vacuum clutch.
• 9. Over running clutch or free – wheel unit
 Automobile Engineering: Unit - II
• SINGLE CLUTCH PLATE:
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MULTIPLATE CLUTCH:
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Plates with inner and outer spines of multi plate clutch:
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CONE CLUTCH:
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• Forces on a Cone Clutch • If α = Semi Cone
Angle
• P = Axial Force
• Q = Normal Force
• Then Q =
which is greater than P
 Centrifugal Clutch
• It consists of weights A pivoted at
B. When the engine speed
increases the weights fly off due
to the centrifugal force, operating
the bell crank levers, which press
the plate C. The movement of the
plate C passes the spring E, which
ultimately presses the clutch
plate D on the flywheel against
the spring G. This makes the
clutch engaged. The spring G
keeps the clutch disengaged at
low speeds at about 500 rpm.
The stop H limits the movement
of the weights due to the
centrifugal force.
 Automobile Engineering: Unit - II
SEMI-CENTRIFUGAL CLUTCH:
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SEMI-CENTRIFUGAL CLUTCH:
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DIAPHRAGM CLUTCH:
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DOG AND SPLINE CLUTCH:
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ELECTROMAGNETIC CLUTCH :
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VACUUM CLUTCH
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HYDRAULIC CLUTCH :
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• Derivation of single disc or
plate clutch.
• Consider an elementary ring
of radius r thickness dr and
axial thrust W, as shown in
figure ,
• Let, T = Torque transmitted,
• P = Intensity of axial pr
with which the contact
surfaces an held together,
ri and r2 = External and internal
radii of friction forces, and µ =
Coefficient of friction
 Automobile Engineering: Unit - II
• We know that area of contact surface or friction surface = 2
π r dr
• Normal Or Axial forces on the ring,
• δw = Pressure Area = P 2 π r dr
• And the frictional force on the ring acting tangentially at
radius r
• Fr = µ . δw = µ. P 2 π r dr.
• Frictional Torque Tr = Fr r = µ. P 2 π r dr. r
= 2 π µ. P r2 dr.

• Now considering the following two cases:

• 1. Uniform Pressure 2. Uniform Wear
 Automobile Engineering: Unit - II
• 1. Uniform Pressure: When the pressure is uniformly
distributed over the entire area of the friction face, then the
intensity of pressure,
• P= ………………… (i)
• Frictional torque on the elementary ring of radius r and
thickness dr
• Tr = 2 π µ. P r2 dr.
• By integrating this equation within the limits from r2 to r1 we get
the total frictional torque,
• Total frictional torque acting on the friction surface or on the
clutch
• T = = 2 π µ. P
 Automobile Engineering: Unit - II
• Substituting the value of P from equation (i)
• T=2πµ
• = µW=µWR
• Where R = Mean radius of friction
surface, =
 Automobile Engineering: Unit - II
• Taking Uniform Wear Case:
• Let P be the normal intensity of pressure at a
distance r from the axis of the clutch. Since the intensity
of the pressure varies inversely with the distance,
therefore.
• P r = C (a Constant)
• ……. (i)
• Total force on the friction surface,
• W = = = 2 = Or
• C=
 Automobile Engineering: Unit - II
• We know that the frictional torque acting on the ring.
• Tr = 2 π µ. P r2 dr = 2 π µ. r2 dr = 2 π µ. C r dr
• Total frictional torque on the friction surface
• T= =2
• = =
• =
• = W = WR
• Where R = Mean radius of the friction
surface =
 Automobile Engineering: Unit - II
• Multiple Disc Clutch:
• Let n1 = number of discs on the driving shaft,
• n2 = number of discs on the driven shaft
• Number of pair of contact surfaces, n = n1 + n2 – 1
• Total frictional torque acting on the friction surfaces or
the clutch
• T=n WR
• R= [For Uniform pressure]
• = [For Uniform Wear]