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The functions of pistons are to transmit the force of explosion to the crankshaft, to form a seal so that the
high pressure gases in the combustion chamber do not escape into the crankcase as to serve as a guide and
bearing for small end of the connecting rod.
The top of the piston is called “piston crown” or head and the bottom part is called “skirt”. Towards the top
of the piston few grooves are cut to house the piston rings. The bands left between the rings are called “lands”,
these lands support the rings against gas pressure and guide them in the cylinder liner. The material used
earlier was cast iron, which is now replaced by Aluminium alloy containing Silicon. Cast iron has high specific
weight,so heavy inertia force act on the engine while piston reverse its direction at dead centers. Aluminium
alloy is three times lighter than cast iron and thermal conductivity is high. Aluminium alloy is not strong as Cast
iron and unequal co-efficient of expansion for Aluminium.

Connecting rod

The function of connecting rod is to convert the reciprocating motion of the piston into rotary motion of
crankshaft. A combination of axial and bending stresses act on the connecting rod while in operation. Axial
stress due to cylinder gas pressure and inertia force arising on account of reciprocating motion, where as
bending stress are caused due to centrifugal effects.
The main cross section of the con rod is an “I” section. The “I” section is made to blend smoothly into
the two rod ends. The small end of the rod has either a solid eye or a split eye that holds the piston pin. The
big end works on the crank pin and is always split. In some con rod, a small drilled hole is provided between
two ends for carrying lub oil from big end to small end for lubrication of piston pin and piston. The con rod is
generally made by drop forging of steel or duralumin. Now for small and certain medium engines, the con rods
are made of cast from malleable or spheroidal graphite cast iron.

Crankshaft It is the component

smits to clutch and subsequently to the wheels. Crankshaft assembly includes crankshaft, bearings, fly
wheel, vibration damper and gear train. Crank shaft consists of main journal, crankpin, crank web, counter
weight and oil holes. Main journals are supported in main or journal bearings in the crank case, which forms
the axis for rotation of crankshaft. The number of journal bearing is generally one more than the number of
cylinders. Crank pins are the journals for the con rod big end bearing and are supported by the crank webs.
Oil holes are drilled from the main journals to the crank pins through crank web to provide lubrication of big
end bearings. Counter weights are provided on crank shaft as an integral or detachable part, to avoid distortion
and bending of crankshaft because of the centrifugal force acting at each crankpin due to rotation of both the
crankshaft as well as the big end of the connecting rod tend to bend and distort when the engine is running. A
thrust bearing is provided near the fly wheel end to catch the thrust developed by acceleration / deceleration,
clutch release forces, gear drives, auxiliary drives etc. Timing gear, vibration damper and auxiliary pump drives
are mounted at the front end or free end of crankshaft. Fly wheel is mounted at the drive end or rear end. Fly
wheels are made of cast iron alloys or rolled steel.
Crankshafts are generally of two types:- one piece and built up. One piece construction is generally used
for automobile crank shaft.
Crankshaft must be adequately strong, tough, hard and should posses high fatigue strength. The material
used earlier was forged steel, now SAE 1045 & 3140, chrome- vanadium & chrome- molybdenum steels. SAE
1045 contains 0.6 to 0.9 % manganese. SAE 3140 contains 1 to 1.4 % Nickel, 0.5 to 0.75% Chromium and 0.7
to 0.9 % manganese. SG CI is now commonly used which has high strength ductility and toughness.
1.11 Crank Pin
A crankpin or crank journal is the part of a shaft or axle that rests on bearings. In a reciprocating engine,
the crankpin is the part of a crankshaft where the lower end of a connecting rod attaches. In a multi-cylinder
engine, a crankpin can serve one or many cylinders, for example:
In a in-line or opposed engine, each crankpin normally serves just one cylinder. In a V engine, each
crankpin may serves one or two cylinders, depending on the design. In a radial engine, each crankpin serves
an entire row of cylinders.
1.12 Camshaft
A shaft with cams for operating poppet valves and fuel pump. Cam shaft provides a means of actuating the
opening and closing intervals of the inlet and exhaust valves. It also provides a drive for the ignition distributor
and mechanical fuel pump.
Camshaft is forged from alloy steel or cast from hardenable cast iron.
1.13 Valves
To admit air fuel mixture in the engine cylinder and to force the exhaust gases out at correct timings,
valve is provided.
Engine valve may be broadly divided into three categories. They are Poppet valves, Rotary valves and
Sleeve valves.
Poppet valves
Poppet valves are universally used in automobiles. It consists of head, stem, face, margin, tip and
spring retaining grooves. The two valves used in an automobile are inlet and exhaust valves.
Because of the high operating temperature the exhaust valve should have following material
a. High strength and hardness to resist tensile load and stem wear.
b. High fatigue and creep resistance.
c. Corrosion resistant.
d. Least coefficient of thermal expansion
e. High thermal conductivity for better heat dissipation
Inlet & exhaust valves
Materials used
For inlet valve :- Sili- chrome (Carbon 0.4 %, Nickel 0.5 %, Manganese 0.5 %, 3.5 % Silicon and 8%
Chromium. For exhaust valve :- Molybdenum is added additionally along with the above composition. Now
Austenite steel of grade 21-12 is used. It contains Carbon 0.25 %, Manganese 1.5%, Silicon 1%, Nickel 12%,
Chromium 21 %.
Another improved grade is Austenite steel grade 21-4N, contains Carbon 0.5%, Manganese 9%,
Silicon 0.25%, Nickel 4%, Chromium 21 % and Nitrogen 4%.
 The valve seats are faced very accurately and of the same angle to which the valve face ground.
Valve seat inserts are simply rings made of alloy steel consists of Chromium, silicon, cobalt or tungsten.
Sleeve valves
Sleeve valves are cylindrical in shape. They surround the piston and actually form the working
cylinder. The advantages are simplicity in construction, silent in operation because there are no valve cams /
tappets / valves etc. Mean time between decarbonisation of valves increases by 5 times. Reduced tendency
to detonate. The biggest disadvantage is excessive lub oil consumption because of larger area of lubrication
requirement for the sleeve surface.
Rotary valves
The valve is rotary. The disc type rotary valve consists of a rotating disc with a port. These ports
communicate with inlet and exhaust valve manifold alternately during rotation. The main advantage is noise
free operation. The main disadvantage is pressure sealing and lubrication.
1.14 Fly wheel
A fly wheel is an inertial energy storage device. It absorbs mechanical energy and serves as a
reservoir, storing energy during the period when the supply of energy is more than the requirement and
releases it during the period when the requirement is more than the supply.
To smoothen out variations in the speed of a shaft caused by torque fluctuations. If the source of the
driving torque or load torque is fluctuating in nature, then a flywheel is usually called for. Many machines have
load patterns that causes the torque time fluctuation to vary over the cycle. ICE with one or two cylinders are
a typical example. Flywheel absorbs mechanical energy by increasing its angular velocity and delivers the
stored energy by decreasing its velocity.
Size of fly wheel
Design parameters- Size of the flywheel directly depends upon the acceptable changes in speed.
Speed fluctuation- The change in the shaft speed during a cycle is called the speed fluctuation and is
equal to ɷmax – ɷmin.
Common uses of a flywheel
Smoothing the power output of an energy source. For example, flywheels are used in reciprocating engines
because the active torque from the individual pistons is intermittent.
 Energy storage systems
 Delivering energy at rates beyond the ability of an energy source.
 Controlling the orientation of a mechanical system, gyroscope and reaction wheel
 Flywheels are typically made of steel and rotate on conventional bearings.
Stresses in fly wheel rim
The following types of stresses are induced in the rim of a flywheel:
-Tensile stress due to centrifugal force.
-Tensile bending stress caused by the restraint of the arms.
-The shrinkage stresses due to unequal rate of cooling of casting. These stresses may be very high but
there is no easy method of determining it. This stress is taken care of by a factor of safety.
1.15 Hub & arms
In automotive suspension, a steering knuckle is that part which contains the wheel hub or spindle, and
attaches to the suspension and steering components. It is also called as steering knuckle, spindle or hub, as
well. The wheel and tire assembly attach to the hub where the wheel rotates while being held in a stable plane
of motion by the knuckle /suspension assembly.
A device that mixes petrol and air in correct proportion and supply to combustion chamber in appropriate
quantity. Petrol dust formed in the carburetor is based on the same principle as used in the insecticide sprayer.
1.16Petrol Injections
The main drawback of using a carburetor in a multi cylinder engine is that it becomes difficult for a single
carburetor to ensure supply of uniform mixture quality in each cylinders. Use of multi carburetor leads to
difficulty in matching the operation of carburetor during running. The solution to this is “petrol injection” .
1.17 Types of petrol injections
(a) According to duration & timing of fuel injection:-
(i) Continuous type,In this the fuel is being injected continuously all the time engine is running.
(ii) Intermittent type, the injector nozzles are opened only for the time period required.
(iii) Sequential, fuel is injected only at the exact moment when it will be most useful. A separate control
system is required for this.
(b)According to the number of injectors:-
(i) Single point injection,It consists of a single injector for the entire engine, mounted above the throttle
butterfly valve, similar to the conventional carburetor. The mixture passes to the inlet manifold &
supplies each cylinder.
(ii) Multi point (multi port) injection, In this system there is a separate injector for each cylinder
mounted in the inlet port. In this injector may spray directly into the combustion chamber (DMPI).
1.19 Advantages of petrol injections
a. Volumetric efficiency is increased because the restriction imposed by the carburetor venturi is
b. A very high quality of fuel distribution therefore higher compression ratio can be obtained.
c. Less fuel consumption
d. Fuel injection equipment is more precise than carburetor.
e. Reduced exhaust pollution because of better compression ratio.
1.18Disadvantages of petrol injections
a.Initial cost is high
b. Relatively complicated mechanism
c.Increased maintenance
1.19Common rail direct fuel injection
It is a direct fuel injection system for diesel engines.On diesel engines, it features a high-pressure (over
100 bar or 10 MPa or 1,500 psi) fuel rail feeding individual solenoid valves, as opposed to a low-pressure fuel
pump feeding unit injectors (or pump nozzles). Third-generation common rail diesels now feature piezoelectric
injectors for increased precision, with fuel pressures up to 2,500 bar (250 MPa; 36,000 psi).
In petrol engines, it is used in Gasoline direct injection (GDI) engine technology.
Modern common rail systems, whilst working on the same principle, are governed by an engine control
unit (ECU) which opens each injector electrically rather than mechanically.
The common rail system is suitable for all types of road cars with diesel engines, ranging from city cars
(such as the Fiat Panda) to executive cars (such as the Audi A8). The main suppliers of modern common rail
systems are Robert Bosch.
1.20Supercharging systems
A naturally aspirated engine is an internal combustion engine in which air intake depends solely on
atmospheric pressure and does not rely on forced induction through a turbocharger or a supercharger. Many
sports cars specifically use naturally aspirated engines to avoid turbo lag.
A supercharger is an air compressor that increases the pressure or density of air supplied to an internal
combustion engine. This gives each intake cycle of the engine more oxygen, letting it burn more fuel and do
more work, thus increasing power. Power for the supercharger can be provided mechanically by means of a
belt, gear, shaft, or chain connected to the engine’s crankshaft. Common usage restricts the term
supercharger to mechanically driven units; when power is instead provided by a turbine powered by exhaust
gas, a supercharger is known as a turbocharger or just a turbo – or in the past a turbo supercharger.
1.21 Turbo lag
It’s the time taken by the turbocharger to respond to change in speed or load. The speed of the turbine
depends on the temperature of the exhaust gas, so increase and decrease in temperature changes the speed
of the turbine, but it take some time for the turbine to reach appropriate rotational speed to cope with the
change in load or speed. This delay is known as turbo lag.
1.22 Hybrid Cars
Safety features
The vehicles are equipped with sophisticated transmissions, regenerative braking and multiple
controllers combined with numerous sensors to provide functionality and a driving experience only slightly
different from a conventionally powered vehicle.
Operating Safety
In order to achieve a user-experience similar to what drivers are accustomed, hybrid/electric vehicles
must respond to driver inputs in a predictable and reliable manner. Computers control the combustion engine,
electric motor, and multiple driver aids, including traction and stability control. The sophisticated systems
commonly include several computer processors and many sensors. Failure of these systems can result in
unexpected and unreliable vehicle performance that may cause a crash.
Battery charging occurs during regenerative braking or during recharging for a “plug in” type hybrid vehicle.
The recharging is computer controlled to prevent over charging and overheating that can cause an electric
shock hazard or fire.
Computer Controlled Transmission
A sophisticated computer controlled transmission is required to combine power from the combustion
engine and the electric motor. The power split may range from electric only, a combination of electric and
combustion engine, or solely combustion engine. Failure of proper power delivery can result in unwanted or
inadequate acceleration and may cause a crash.
The battery state of charge and operating temperature are continuously monitored. Excessive temperatures
can lead to vehicle fires. Short circuits can lead to vehicle fire even after the vehicle is shut off.
The brakes may incorporate regenerative braking that recovers and stores electric energy. This may
include the use of the electric motor as a generator in combination with conventional hydraulic brakes in order
to slow the vehicle. The combining of the two systems is achieved with a sophisticated computer controlled
system. Improper operation may cause inadequate braking and result in a crash.
Hybrid/electric vehicle must be designed and manufactured with additional crash safety features to
protect the high energy battery pack and high voltage power electric circuits and components. Damage to
these systems can cause electric shock and dangerous chemical exposure to occupants and emergency
Post Crash Safety
First responders must be trained to properly handle a damaged hybrid/electric vehicle. Vehicles are
generally equipped with a master switch to de energize or isolate high voltage circuits that would pose a risk to
emergency personnel.
Vehicle storage after a crash must be in an isolated location away from other vehicles and structures. For
example, a damaged vehicle may have a slow coolant leak that can eventually cause a short circuit in the high
voltage battery pack resulting in a vehicle fire.
1.23 Formula 1 Car
A Formula One car is a single-seat, open cockpit, open-wheel racing car with substantial front and rear
wings, and an engine positioned behind the driver, intended to be used in competition at Formula One racing
events. The regulations governing the cars are unique to the championship. The Formula One regulations
specify that cars must be constructed by the racing teams themselves, though the design and manufacture can
be outsourced.
Formula One currently uses 1.6 litre four-stroke turbocharged 90 degree V6 reciprocating engines.
The power a Formula One engine produces is generated by operating at a very high rotational speed, up to
15,000 revolutions per minute (rpm). This contrasts with road car engines of a similar size which typically
operate at less than 6,000 rpm. The basic configuration of a naturally aspirated Formula One engine had not
been greatly modified since the 1967 and the mean effective pressure had stayed at around 14 bar MEP. Until
the mid-1980s Formula One engines were limited to around 12,000 rpm due to the traditional metal valve
springs used to close the valves. The speed required to operate the engine valves at a higher rpm called for
ever stiffer springs, which increased the power loss to drive the camshaft and the valves to the point where the
loss nearly offset the power gain through the increase in rpm. They were replaced by pneumatic valve
springs introduced by Renault, which inherently have a rising rate (progressive rate) that allowed them to have
extremely high spring rate at larger valve strokes without much increasing the driving power requirements at
smaller strokes, thus lowering the overall power loss. Since the 1990s, all Formula One engine manufacturers
used pneumatic valve springs with the pressurised air allowing engines to reach speeds of over 20,000 rpm.
Formula One cars use short stroke engines. To operate at high engine speeds, the stroke must be
relatively short to prevent catastrophic failure, usually from the connecting rod, which is under very large
stresses at these speeds. Having a short stroke means a relatively large bore is required to reach a 1.6
litre displacement. This results in a less efficient combustion stroke, especially at lower rpm. The stroke of a
Formula One engine is approximately 39.7 mm (1.56 in), less than half the 98.0 mm (3.86 in) bore diameter,
what is known as an over-square configuration.
In addition to the use of pneumatic valve springs a Formula One engine’s high rpm output has been
made possible due to advances in metallurgy and design, allowing lighter pistons and connecting rods to
withstand the accelerations necessary to attain such high speeds. Improved design also allows narrower
connecting rod ends and so narrower main bearings. This permits higher rpm with less bearing-damaging heat
build-up. For each stroke, the piston goes from a virtual stop to almost twice the mean speed (approximately
40 m/s), then back to zero. This occurs once for each of the four strokes in the cycle: one Intake (down), one
Compression (up), one Power (ignition-down), one Exhaust (up).
Transmission technology
Formula One cars use semi-automatic sequential gearboxes, with regulations stating that 8 forward
gears (increased from 7 from the 2014 season onwards) and 1 reverse gear must be used, with rear-wheel
drive. The gearbox is constructed of carbon titanium, as heat dissipation is a critical issue, the driver initiates
gear changes using paddles mounted on the back of the steering wheel and electro-hydraulics perform the
actual change as well as throttle control. Clutch control is also performed electro-hydraulically, except to and
from a standstill, when the driver operates the clutch using a lever mounted on the back of the steering wheel.
A modern F1 clutch is a multi-plate carbon design with a diameter of less than 100 mm (3.9 in), weighing less
than 1 kg (2.2 lb) and handling around 720 hp (540 kW). As of the 2009 race season, all teams are using
seamless shift transmissions, which allow almost instantaneous changing of gears with minimum loss of drive.
Shift times for Formula One cars are in the region of 0.05 seconds. In order to keep costs low in Formula One,
gearboxes must last five consecutive events and since 2015, gearbox ratios will be fixed for each season (for
2014 they could be changed only once). Changing a gearbox before the allowed time will cause a penalty of
five places drop on the starting grid for the first event that the new gearbox is used.
Brakes of F1 car
Disc brakes consist of a rotor and caliper at each wheel. Carbon composite rotors are used instead of
steel or cast iron because of their superior frictional, thermal, and anti-warping properties, as well as significant
weight savings. These brakes are designed and manufactured to work in extreme temperatures, up to 1,000
degrees Celsius (1800 °F). The driver can control brake force distribution fore and aft to compensate for
changes in track conditions or fuel load. Regulations specify this control must be mechanical, not electronic,
thus it is typically operated by a lever inside the cockpit as opposed to a control on the steering wheel.
An average F1 car can decelerate from 100 to 0 km/h (62 to 0 mph) in about 15 meters (48 ft),
compared with a 2009 BMW M3, which needs 31 meters (102 ft). When braking from higher speeds,
aerodynamic down force enables tremendous deceleration. An F1 car can brake from 200 km/h (124 mph) to a
complete stop in just 2.9 seconds, using only 65 metres (213 ft)
Module II
2.1 Clutch fundamentals
Clutches are designed to engage and disengage the transmission system from the engine when a vehicle is
being driven away from a standstill and when the gearbox gear changes are necessary. The gradual increase
in the transfer of engine torque to the transmission must be smooth. Once the vehicle is in motion, separation
and take-up of the drive for gear selection must be carried out rapidly without any fierceness, snatch or shock.
2.2 Driven plate inertia
To enable the clutch to be operated effectively, the driven plate must be as light as possible so that when
the clutch is disengaged, it will have the minimum of spin, i.e. very little flywheel effect. Spin prevention is of
the utmost importance if the various pairs of dog teeth of the gearbox gears, be they constant mesh or
synchromesh, are to align in the shortest time without causing excessive pressure, wear and noise between
the initial chamfer of the dog teeth during the engagement phase.
Smoothness of clutch engagement may be achieved by building into the driven plate some sort of
cushioning device, which will be discussed later in the chapter, whilst rapid slowing down of the driven plate is
obtained by keeping the diameter, centre of gravity and weight of the driven plate to the minimum for a given
torque carrying capacity.
2.3 Driven plate transmitted torque capacity
The torque capacity of a friction clutch can be raised by increasing the coefficient of friction of the rubbing
materials, the diameter and/or the spring thrust sandwiching the driven plate. The friction lining materials now
available limit the coefficient of friction to something of the order of 0.35. There are materials which have
higher coefficient of friction values, but these tend to be unstable and to snatch during take-up. Increasing the
diameter of the driven plate unfortunately raises its inertia, its tendency to continue spinning when the driven
plate is freed while the clutch is in the disengaged position, and there is also a limit to the clamping pressure to
which the friction lining material may be subjected if it is to maintain its friction properties over a long period of
2.4 Driven plate wear
Lining life is also improved by increasing the number of pairs of rubbing surfaces because wear is directly
related to the energy dissipation per unit area of contact surface. Ideally, by doubling the surface area as in a
twin plate clutch, the energy input per unit lining area will be halved for a given slip time which would result in a
50% decrease in facing wear. In practice, however, this rarely occurs as the wear rate is also greatly
influenced by the peak surface rubbing temperature and the intermediate plate of a twin plate clutch operates
at a higher working temperature than either the flywheel or pressure plate which can be more effectively
cooled. Thus in a twin plate clutch, half the energy generated whilst slipping must be absorbed by the
intermediate plate and only a quarter each by the flywheel and pressure plate. This is usually borne out by the
appearance of the intermediate plate and its corresponding lining faces showing evidence of high
temperatures and increased wear compared to the linings facing the flywheel and pressure plate.
Nevertheless, multiplate clutches do have a life expectancy which is more or less related to the number of
pairs of friction faces for a given diameter of clutch.
For heavy duty applications such as those required for large trucks, twin driven plates are used, while for
high performance cars where very rapid gear changes are necessary and large amounts of power are to be
developed, small diameter multiplate clutches are preferred
2.5 Clutch friction materials
Clutch friction linings or buttons are subjected to severe rubbing and generation of heat for relatively short
periods. Therefore it is desirable that they have a combination of these properties,
a) Relatively high coefficient of friction under operating conditions
b) capability of maintaining friction properties over its working life
c) relatively high energy absorption capacity for short periods
d) capability of withstanding high pressure plate compressive loads
e) capability of withstanding bursts of centrifugal force when gear changing
f) adequate shear strength to transmit engine torque
g) high level of cyclic working endurance without the deterioration in friction properties
h) good compatibility with cast iron facings over the normal operating temperature range
i) a high degree of interface contamination tolerance without affecting its friction take-up and grip
(a) Asbestos-based linings – Generally, clutch driven plate asbestos-based linings are of the woven variety.
These woven linings are made from asbestos fibre spun around lengths of brass or zinc wire to make lengths
of threads which are both heat resistant and strong. The normal highest working temperature below which
these asbestos linings will operate satisfactorily giving uniform coefficient of friction between 0.32 and 0.38
and a reasonable life span is about 260 ○C.
(b) Asbestos substitute friction material – The DuPont Company has developed a friction material derived from
aromatic polyamide fibres belonging to the nylon family of polymers and it has been given the trade name
Hevlar aramid.
(c) Metallic friction materials
Metallic and semi-metallic facings have been only moderately successful. The metallic linings are
normally made from either sintered iron or copper- based sintered bronze and the semi-metallic facings from
a mixture of organic and metallic materials. Metallic lining materials are made from a powder produced by
crushing metal or alloy pieces into many small particles. They are then compressed and heated in moulds
until sufficient adhesion and densification takes place. This process is referred to as zintering. The metallic
rings are then ground flat and are then riveted back to back onto the driven plate.
(d) Ceramettallic Friction Materials- Cerametallic button friction facings are becoming increasingly popular
for heavy duty clutches. Instead of a full annular shaped lining, as with organic (asbestos or substitute)
friction materials, four or six cerametallic trapezoidal-shaped buttons are evenly spaced on both sides
around the driven plate. The cerametallic material is made from a powder consisting mainly of ceramic and
copper. It is compressed into buttons and heated so that the copper melts and flows around each particle
of solid ceramic. After solidification, the copper forms a strong metal-ceramic interface bond. These buttons
are then riveted to the clutch driven plate and then finally ground flat.
2.6 Angular driven plate cushioning and torsional damping
Axial driven plate friction lining cushioning
The driven plate consists of a central splined hub. Mounted on this hub is a thin steel disc which in
turn supports, by means of a ring of rivets, both halves of the annular friction linings.
Axial cushioning between the friction lining faces may be achieved by forming a series of evenly spaced ‘T’
slots around the outer rim of the disc. This then divides the rim into a number of segments (Arcuate). A
horseshoe shape is further punched out of each segment. The central portion or blade of each horseshoe is
given a permanent set to one side and consecutive segments have opposite sets so that every second segment
is riveted to the same friction lining. The alternative set of these central blades formed by the horseshoe punchout
spreads the two half friction linings apart. An improved version uses separately attached, very thin spring steel
segments (borglite) positioned end-on around a slightly thicker disc plate. These segments are provided with a
wavy ‘set’ so as to distance the two half annular friction linings.
Torsional damping of driven plate
Crankshaft torsional vibration – Engine crankshafts are subjected to torsional wind-up and vibration at
certain speeds due to the power impulses. Superimposed onto some steady mean rotational speed of the
crankshaft will be additional fluctuating torques which will accelerate and decelerate the crankshaft,
particularly at the front pulley end and to a lesser extent the rear flywheel end . If the flywheel end of the
crankshaft were allowed to twist in one direction and then the other while rotating at certain critical speeds, the
oscillating angular movements would take up the backlash between meshing gear teeth in the transmission
system. Consequently, the teeth of the driving gears would be moving between the drive (pressure side) and nondrive
tooth profiles of the driven gears. This would result in repeated shock loads imposed on the gear teeth, wear,
and noise in the form of gear clatter. To overcome the effects of crankshaft torsional vibrations a torsion
damping device is normally incorporated within the driven plate hub assembly
2.7 Pull type diaphragm clutch
In this type of diaphragm clutch, the major components of the pressure plate assembly are a cast iron pressure
plate, a spring steel diaphragm disc and a low carbon steel cover pressing. To actuate the clutch release, the
diaphragm is made to pivot between a pivot ring positioned inside the rear of the cover and a raised
circumferential ridge formed on the back of the pressure plate. The diaphragm disc is divided into fingers caused
by radial slits originating from the central hole. These fingers act both as leaf springs to provide the pressure plate
thrust and as release levers to disengage the driven plate from the drive members.
When the driven and pressure plates are bolted to the flywheel, the diaphragm is distorted into a dished disc
which therefore applies an axial thrust between the pressure plate and the cover pressing. This clutch design
reverses the normal method of operation by pulling the diaphragm spring outwards to release the driven plate
instead of pushing it.
The pull type clutch allows a larger pressure plate and diaphragm spring to be used for a given diameter of
clutch. Advantages of this design over a similar push type clutch include lower pedal loads, higher torque
capacity, improved take-up and increased durability. This clutch layout allows the ratio of the diaphragm
finger release travel to pressure plate movement to be reduced.
Pull type diaphragm clutch
2.8 Multiplate diaphragm clutch
Multi plate diaphragm clutches basically consist of drive and driven plate members. The drive plates
are restrained from rotating independently by interlocking lugs and slots which permit axial movement, but not
relative rotational spin, whilst the driven plates are attached and supported by internally splined hubs to
corresponding splines formed on the gearbox spigot shaft.
The diaphragm spring is in the form of a dished annular disc. The inner portion of the disc is radially
slotted, the outer ends being enlarged with a circular hole to prevent stress concentration when the spring is
distorted during disengagement. These radial slots divide the disc into a number of release levers (fingers).
The diaphragm spring is located in position with a shouldered pivot post which is riveted to the cover
pressing. These rivets also hold a pair of fulcrum rings in position which are situated either side of the
diaphragm. As the friction linings wear, the spring diaphragm will become more dished and subsequently will
initially exert a larger axial clamping load. It is only when the linings are very worn, so that the distance
between the cover pressing and pressure plate become excessive, that the axial thrust will begin to decline.
2.9 Multi plate hydraulically operated automatic transmission clutches
Automatic transmissions use multiplate clutches in addition to band brakes extensively with epicyclic
compound gear trains to lock different stages of the gearing or gear carriers together, thereby providing a
combination of gear ratios.
These clutches are comprised of a pack of annular discs or plates, alternative plates being internally and
externally circumferentially grooved to matchup with the input and output splined drive members respectively.
When these plates are squeezed together, torque will be transmitted from the input to the output members by
way of these splines and grooves and the friction torque generated between pairs of rubbing surfaces. These
steel plates are faced with either resinated paper linings or with sintered bronze linings, depending whether
moderate or large torques are to be transmitted. Because the whole gear cluster assembly will be submerged
in fluid, these linings are designed to operate wet (in fluid). These clutches are hydraulically operated by servo
pistons either directly or indirectly through a lever disc spring to multiplate, the clamping load which also acts
as a piston return spring. In this example of multiplate clutch utilization hydraulic fluid is supplied under
pressure through radial and axial passages drilled in the out- put shaft. To transmit pressurized fluid from one
member to another where there is relative angular movement between components, the output shaft has
machined grooves on either side of all the radial supply passages. Square sectioned

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