FRICTION

CLUTCHES
-
A BRIEF
DESCRIPTION
First Technical Report

ABSTRACT
Clutches are useful in devices that have two rotating shafts. In these devices,
one shaft is typically attached to a motor or other power unit (the driving
member), and the other shaft (the driven member) provides output power for
work to be done. In a drill, for instance, one shaft is driven by a motor, and
the other drives a drill chuck. The clutch connects the two shafts so that they
can either be locked together and spin at the same speed (engaged), or be
decoupled and spin at different speeds (disengaged).

Friction clutches Page 1

 Content
A.NOMENCLATURE………………………………………………………………………..6
B.LIST OF FIGURES……………………………………………………………………….7
1. CHAPTER 1
INTRODUCTION
1.1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
...8
2.CHAPTER 2
HISTORY
2.1 HISTORY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
... 9
3. CHAPTER 3

CLUTCH CONSTRUCTION

3.1 CLUTCH
CONSTRUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.2 CLUTCH OR DRIVEN PLATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. 16

3.3 PLATE TO HUB

CONNECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.4 FRICTION FACING OR PADS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. 18

4. CHAPTER 4
DESIGN OF CLUTCH
4.1 CLUTCH DETAILS
DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.2 FRICTIONAL CONTACT AXIAL OR DISC CLUTCHES . . . . . . . . . . . . . . . . . . . .
. . . . 21
4.3 METHOD OF
ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

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Friction clutches
4.4 UNIFORM PRESSURE AND
WEAR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4.5 ELEMENTARY ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . 21
4.6 UNIFORM WEAR CONDITION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . 23

5. CHAPTER 5
OPERATION OF CLUTCH
5.1 OPERATION OF
CLUTCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
6.CHAPTER 6

TYPES OF CLUTCH

6.1 SINGLE PLATE

CLUTCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

6.2 MULTI PLATE

CLUTCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

6.3 CONE CLUTCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . 29

6.4 CENTRIFUGAL
CLUTCH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

7.CHAPTER 7
MAJOR TYPES OF CLUTCHES BY APPLICATION

7.1 VEHICULAR [GENERAL] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . 33

7.2
MOTORCYCLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 34

7.3 AUTOMOBILES NON-

POWERTRAIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

8. CHAPTER 8

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Friction clutches
8.1
SUMMARY……………………………………………………………………………………35

X. APPENDIX A
BASIC CONCEPTS IN FRICTION…………………………………………………………
36

Y. ACKNOWLEDGEMENT

NOMENCLATURE
1.kPa – kilopascal
2.ºC – degree centigrade
3. - coeffiecient of friction
4. - area of object
5. - newton
6. - normal force
7. – frictional force
8. pi = 3.142
9. – torque
10. Rw - constant wear rate
11. P – constant pressure
12. V – sliding velocity
13. - angular velocity
14. Pmax - maximum pressure
15. Fa – axial force

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Friction clutches
 16. Rm – mean radius

LIST OF FIGURES
FIG. 1.1 CLUTCH IN AUTOMOBILE

FIG. 2.1 TRANSMISSION BELT CLUTCH FROM THE BENZ

FIG. 2.2 PROFESSOR HELE-SHAW FROM ENGLAND WAS THE FIRST TO

EXPERIMENT
WITH MULTI-PLATE CLUTCHES. MULTI-PLATE DRY CLUTCH WITH RIVETED
LINING.

FIG. 2.3 INITIAL DESIGN OF THE COIL SPRING CLUTCH WITH CLUTCH SPRINGS
PERPENDICULAR TO THE CENTRAL AXIS.

FIG. 2.3 DE DION AND BOUTON WERETHE FIRST TO RECORGANISE THAT

SINGLE PLATE CLUTCHES WOULD BE THE WAY OF THE FUTURE.

FIG. 3.1 CLUTCH CONSTRUCTION.

FIG. 3.2 CLUTCH PLATE.

FIG. 4.1 BASIC CLUTCH STRUCTURE.

FIG. 6.1 SINGLE PLATE CLUTCH.

FIG. 6.2 MULTI PLATE CLUTCH.

FIG. 6.3 CONE CLUTCH IN DIFFERENTIALS.

FIG. 6.4 CONE CLUTCH.

FIG. 6.5 CENTRIFUGAL CLUTCH.

CHAPTER 1
1.1 INTRODUCTION
A Clutch is a machine member used to connect the driving shaft to a driven
shaft, so that the driven shaft may be started or stopped at will, without

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Friction clutches
stopping the driving shaft. A clutch thus provides an interruptible connection
between two rotating shafts
Clutches allow a high inertia load to be stated with a small power. A
popularly known application of clutch is in automotive vehicles where it is
used to connect the engine and the gear box. Here the clutch enables to
crank and start the engine disengaging the transmission Disengage the
transmission and change the gear to alter the torque on the wheels. Clutches
are also used extensively in production machinery of all types. It is a
mechanical device, by convention understood to be rotating, which provides
driving force to another mechanism when required, typically by connecting
the driven mechanism to the driving mechanism. Clutches and brakes are
similar; if the driven member of a clutch is fixed to the mechanism frame, it
serves as a brake.
Clutches are useful in devices that have two rotating shafts. In these devices,
one shaft is typically attached to a motor or other power unit (the driving
member), and the other shaft (the driven member) provides output power for
work to be done. In a drill, for instance, one shaft is driven by a motor, and
the other drives a drill chuck. The clutch connects the two shafts so that they
can either be locked together and spin at the same speed (engaged), or be
decoupled and spin at different speeds (disengaged).

Clutch in automobile

CHAPTER 2
2.1 HISTORY

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Friction clutches
Transmission belt clutch from the Benz

In the course of over 100 years of automotive history, nearly all components
have undergone enormous technological developments.
Reliability,production costs and service-friendlinessas well as, more recently,
environmental safety, have been and continue to be the criteria
demanding new and better solutions from automotive engineers. The basic
designs are usually known early on, but only the availability of new
materials and processing procedures makes their realisation feasible.It was
not until the end of the first decade of this century that the internal
combustion engine surpassed the competing steam and electricity-based
automotive drive concepts on a large scale. In 1902, a petrol-engined vehicle
for the first time broke the overall speed record; up to then, electric and
steampowered vehicles had set the standards, and proponents of the three
drive concepts continued to compete for the absolute speed record
throughout the first decade.Steam and electric drives have a decisive
advantage over “motorised vehicles with liquid
fuels”, as they used to be called. Thanks to the Almost ideal torque band,
they required neither clutches nor transmissions, and thus wereeasier to
operate, had fewer malfunctions and were easier to service. As an internal
combustion engine only delivers its output at engine speed, there must be a
division between engine and transmission. The speed-dependent drive
principle of the petrol engine necessitates a mechanical aid for starting, as
sufficient output (torque) is only available aftercertain engine speeds have
been attained. Besides the function of a starting clutch, however, that of a

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Friction clutches
dividing clutch is equally important,for it allows load-free gear changing
while driving. Because of the complexity of the related problems, many
smaller vehicles in the early years of automotive design did not have a
starting clutch; the motor car had to be pushed into motion.The operating
principles of the first clutches originated in the mechanised factories of early
modern industry. By analogy with the transmission belts used there, flat
leather belts were now introduced into motor cars. When tensioned by a
roller, the belt transmitted the drive
output of the engine’s belt pulley to the drive gears, and when loosened, it
slipped through –i. e. disengaged. As this procedure caused the leather belts
to wear out fast, a new tactic was adopted of installing an idler pulley of the
sam size beside the drive belt pulley. By moving lever, the transmission belt
could be guided

from the idler pulley on to the drive pulley.The motor car patented by Benz in
1886, which Bertha Benz used to make the first long-distancejourney in the
history of motor vehicles –
from Mannheim to Pforzheim – already operated according to this clutch
concept. The disadvantages of a belt drive, such as low efficiency, high
susceptibility to wear and inadequaterunning characteristics especially pedal
tensioned the spring band, which then coiled itself (self-reinforcing) more and
more firmly around the drum, driving t HE transmission shaft – and engaging
the clutch. The compression of the springs required only slight force and
effected a gentle engagement of the clutch. At about the same time that the
Daimler corporation were developing their spring bandclutch, Professor Hele-
Shaw from England was already experimenting with a multi-plate clutch that
can be regarded as the forerunnerof today’s conventional single-disc dry
clutch. Multi-plate clutches, named “Weston clutches” after the first large-

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Friction clutches
scale producer, had a decisive advantage over the cone friction clutch: much
greater friction surface area with a lower space requirement and constant
engagement. In the case of the multi-plate clutch, the flywheel is connected
to a drum-shaped housing that has grooves on the inside corresponding to
the shape of the outer edge of the plate, allowing it to turn with the
crankshaft or flywheel and at the same time to move longitudinally. An
identical number of discs with matching inner recesses are centred on a hub
connected to the clutch shaft. The discs can move longitudinally along the
clutch shaft on the hub. During installation, inner and outer clutch plates are
alternately combined to form a plate packet, so that a driving and a driven
disc always follow one another. The plate pairs formed in this fashion,
originally with a bronze disc always turning against a steel one, were pressed
together by a pressure plate under the force of a clutch spring. In this way,
all clutch plates were constantly engaged. This gradual increase of frictional
effect enabled the multi-plate clutch to engage very gently. As the spring
pressure eased off, the plates disengaged again, in part supported by the
spring-loaded strips bent out from the plane of the plate. By varying the
number of plate pairs,
a basic clutch type could be adjusted to eachengine output.Multi-plate
clutches operated either immersed
in oil/petroleum or dry, in which case, however,special, riveted friction linings
were used.The greatest drawback of the multi-plate clutch was certainly the
drag effect, especially in the oil bath, causing only partial disengagement,
and thus making gear changing difficult. By 1904, De Dion & Bouton had
introduced the single-plate clutch principle, which because of the initially
inadequate materials only came into widespread use in the US during the
1920s largely on demand from the supply industry,

. Professor Hele-Shaw from England was the first to experiment

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Friction clutches
with multi-plate clutches. Multi-plate dry clutch with riveted lining

who towards the end of that decade granted licences to European

manufacturers. Within a few years, the single-plate had superseded cone and
multi-plate clutches. While De Dion & Bouton still lubricated the friction
surfaces of their multi-plate clutches with graphite, clutch technology greatly
advanced with the advent of Ferodo-asbestos linings, which were used from
about 1920 to the present day, when they were replaced by asbestos-free
linings. The advantages of the single-plate dry clutch were clear: the low
mass of the clutch plate allowed it to come to rest more quickly when
released, making shifting much easier – farewell to transmission
brakes. The initial design of the single-plate dry clutch was relatively
complicated. The clutch housing was flanged onto the flywheel, and the
clutch cover screwed into the housing. This cover held lug levers which were
pressed inwards by springs and which transmitted pressure from an
intermediate disc via the friction plate and hence the power transmission
from the flywheel The friction disc was connected to the connecting or
transmission shaft by a driver The clutch was engaged and disengaged by a
slip-ring disc that moved a cone back and forth The sides of the cone
accordingly actuated the spring-pressured lug levers, which stressed or
released, i. e. engaged/disengaged, the intermediate The coil spring clutch,
in which the clamping disc. As the cone rotated about the slip-ring disc at
rest, lubrication was required at regular intervals load is produced by coil
springs, was able to gain acceptance. At first, experiments were made with
centrally arranged springs, but clutch housing entered large-scale production
only the version with several smaller coil or clutch springs distributed along
the outer edge of the The levers compress the coil springs via a release
bearing that moves freely on the clutch shaft, releasing the pressure plate
and thus disengaging. The clamping load could be varied by using different
spring packages but had the crucial disadvantage that, as the engine speed
increased, the coil springs located outside on the pressure plate were
pressed further outwards against the spring housings by centrifugal force.
The friction arising between the spring and the housing
+then caused the clamp load characteristics to change. As the engine speed
increased, the clutch became progressively heavier. In addition to this, the
bearings for the release levers were constantly under strain, making them
susceptible to wear, and the spring housings especially when gear changing
at high engine speeds, quickly wore through.

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Friction clutches
Initial design of the coil spring clutch with clutch springs
perpendicular to the central axis.

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Friction clutches
. De Dion & Bouton were the first to recognise that singleplate
clutches would be the way of the future

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Friction clutches
CHAPTER 3
3.1 Clutch Construction
Two basic types of clutch are the coil-spring clutch and the diaphragm-spring
clutch. The difference between them is in the type of spring used. The coil
spring clutch shown in left Fig 3.2.6 uses coil springs as pressure springs
(only two pressure spring is shown). The clutch shown in right uses a
diaphragm spring. The coil-spring clutch has a series of coil springs set in a
circle.

Clutch construction

At high rotational speeds, problems can arise with multi coil spring clutches
owing to the effects of centrifugal forces both on the spring themselves and
the lever of the release mechanism.
These problems are obviated when diaphragm type springs are used, and a
number of other advantages are also experienced

Machine Design I
Indian Institute of Technology Madras
3.2 Clutch or Driven Plate
More complex arrangements are used on the driven or clutch plate to
facilitate smooth function of the clutch
The friction disc, more generally known as the clutch plate, is shown partly
cut away in Fig. It consists of a hub and a plate, with facings attached to the
plate.

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Friction clutches
Clutch plate

.
First to ensure that the drive is taken up progressively, the centre plate, on which
the friction facings are mounted, consists of a series of cushion springs which is
crimped radially so that as the clamping force is applied to the facings the crimping
is progressively squeezed flat, enabling gradual transfer of the force .On the
release of the clamping force, the plate springs back to its original position crimped
(wavy) state.

3.3 Plate to hub Connection

Secondly the plate and its hub are entirely separate components, the drive being
transmitted from one to the other through coil springs interposed between them.
These springs are carried within rectangular holes or slots in the hub and plate and
arranged with their axes aligned appropriately for transmitting the drive. These
dampening springs are heavy coil springs set in a circle around the hub. The hub is
driven through these springs. They help to smooth out the torsional vibration (the
power pulses from the engine) so that the power flow to the transmission is smooth.
In a simple design all the springs may be identical, but in more sophisticated
designs the are arranged in pairs located diametrically opposite, each pair having a
different rate and different end clearances so that their role is progressive providing
increasing spring rate to cater to wider torsional damping
The clutch plate is assembled on a splined shaft that carries the rotary motion to
the transmission. This shaft is called the clutch shaft, or transmission input shaft.
This shaft is connected to the gear box or forms a part of the gear box.

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Friction clutches
3.4 Friction Facings or Pads
It is the friction pads or facings which actually transmit the power from the
fly wheel to hub in the clutch plate and from there to the out put shaft. There
are

. grooves in both sides of the friction-disc facings. These grooves prevent the
facings from sticking to the flywheel face and pressure plate when the clutch is
disengaged. The grooves break any vacuum that might form and cause the facings
to stick to the flywheel or pressure plate. The facings on many friction discs are
made of cotton and asbestos fibers woven or molded together and impregnated
with resins or other binding agents. In many friction discs, copper wires are woven
or pressed into the facings to give them added strength. However, asbestos is being
replaced with other materials in many clutches. Some friction discs have ceramic-
metallic facings.
Such discs are widely used in multiple plate clutches
The minimize the wear problems, all the plates will be enclosed in a covered
chamber and immersed in an oil medium
Such clutches are called wet clutches

The properties of the frictional lining are important factors in the design of the clutches.
Typical characteristics of some widely used friction linings are given in the table
TABLE
PROPERTIES OF
COMMON CLUTCH
/BRAKE LINING

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Friction clutches
 MATERIALS
Friction material DYNAMIC MAXIMUM MAXIMUM
against steel or COEFFIECIENT OF PRESSURE TEMPERATURE
o
cl FRICTION kPa C
DRY IN OIL
Molded 0.25-0.45 0.06-0.09
Woven 0.25-0.45 0.08-0.10
Sintered metal 0.15-0.45 0.05-0.08 1030-2070
Cast iron of 0.15-0.25 0.03-0.06 690-720
hard steel

CHAPT
ER 4
CLUTC
H
DESIGN
4.1 CLUTCH
DESIGN
DETAILS
Two inertia’s and traveling at the respective angular velocities ωIand I1 1 and
ω2, and one of which may be zero, are to be brought to the same speed by
engaging. Slippage occurs because the two elements are running at different
speeds and energy is dissipated during actuation, resulting in temperature

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Friction clutches
To design analyze the performance of these devices, a knowledge on the following
are required.
1. The torque transmitted
2. The actuating force.
3. The energy loss
4. The temperature rise
4.2 FRICTION CLUTCHES
As in brakes a wide range of clutches are in use wherein they vary in their are in use
their working principle as well the method of actuation and application of normal
forces. The discussion here will be limited to mechanical type friction. clutches or
more specifically to the plate or disc clutches also known as axial clutches

4.2 Frictional Contact axial or Disc Clutches

An axial clutch is one in which the mating frictional members are moved in a
direction parallel to the shaft. A typical clutch is illustrated in the figure
below. It consist of a driving disc connected to the drive shaft and a driven
disc co9nnected to the driven shaft. A friction plate is attached to one of the
members. Actuating spring keeps both the members in contact and
power/motion is transmitted from one member to the other. When the power
of motion is to be interrupted the driven disc is moved axially creating a gap
between the members as shown in the figure.

4.3 METHOD OF ANALYSIS

The torque that can be transmitted by a clutch is a function of its geometry
and the magnitude of the actuating force applied as well the condition of
contact prevailing between the members. The applied force can keep the
members together with a uniform pressure all over its contact area and the
consequent analysis is based on uniform pressure condition.

4.4 Uniform Pressure and wear

However as the time progresses some wear takes place between the
contacting members and this may alter or vary the contact pressure
appropriately and uniform pressure condition may no longer prevail. Hence
the analysis here is based on uniform wear condition

4.5 Elementary Analysis

Assuming uniform pressure and considering an elemental area dA

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Friction clutches
 dA = 2Π.r dr

The normal force on this elemental area is

dN=π 2.r.dr.p

The frictional force dF on this area is therefore

dF =f.π.2.r.dr.p

Now the torque that can be transmitted by this elemental are is equal to the
frictional force times the moment arm about the axis that is the radius ‘r’
i.e.
T = dF. r = f.dN. r = f.p.A.r
= f.p.2.π.r. dr .r

The total torque that could be transmitted is obtained by integrating this

equation between the limits of inner radius ri to the outer radius ro
ro
T= ∫2 π pf r2 dr =2/3 π pf (ro3 - ri3)
ri
Integrating the normal force between the same limits we get the actuating
force that need to be applied to transmit this torque.
ro
Fa= ∫2 π pf r dr = π pf (ro2 - ri2)
ri

Equation 1 and 2 can be combined together to give equation for the torque

T =f.Fa .2/3.(ro3 - ri3)/ (ro2 - ri2)

4.6 Uniform Wear Condition

According to some established theories the wear in a mechanical system is
proportional to the ‘PV’ factor where P refers the contact pressure and V the
sliding velocity. Based on this for the case of a plate clutch we can state
The constant-wear rate Rw is assumed to be proportional to the product of
pressure p and velocity V.
Rw= pV= constant
And the velocity at any point on the face of the clutch is
V=r.ω
Combining these equation, assuming a constant angular velocity ω
pr = constant = K

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Friction clutches
The largest pressure pmax must then occur at the smallest radius ri ,
K=pmax .ri
Hence pressure at any point in the contact region
p=pmax .ri / r

In the previous equations substituting this value for the pressure term p and
integrating between the limits as done earlier we get the equation for the
torque transmitted and the actuating force to be applied.
I.e The axial force Fa is found by substituting for p=pmax .ri / r for p

and integrating equation dN=2πpr dr

ro
F= ∫2 π p r dr
ri
ro
Fa= ∫2 π (pmax .ri / r) r dr = 2π pmax .ri (ro - ri)
ri

Similarly the Torque

ro
Fa= ∫2 π pmax .ri r f dr = f π pmax .ri f (ro2 - ri2)
ri

Substituting the values of actuating force Fa

The equation can be given as
T= f.Fa. (ro + ri) / 2

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Friction clutches
CHAPTER 5
Operation Of Clutch
5.1 Operation Of Clutch
When the driver releases the clutch pedal, power can flow through the
clutch. Springs in the clutch force the pressure plate against the friction disc.
This action clamps the friction disk tightly between the flywheel and the
pressure plate. Now, the pressure plate and friction disc rotate with the
flywheel.
As both side surfaces of the clutch plate is used for transmitting the torque, a
term ‘N’ is added to include the number of surfaces used for transmitting the
torque
By rearranging the terms the equations can be modified and a more general
form of the equation can be written as
T= N.f. Fa.Rm
T is the torque (Nm).
N is the number of frictional discs in contact.
f is the coefficient of friction
Fa is the actuating force (N).
Rm is the mean or equivalent radius (m). Note that N = n1 + n2 -1
28Where n1= number of driving discs
n2 = number of driven discs
Values of the actuating force F and the mean radius for the two conditions of
analysis

CHAPTER 6
TYPES OF CLUTCH

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Friction clutches
6.1SINGLE PLATE CLUTCH

Single plate clutch

This is shown in the above diagram. The

operation is as follows:
The flywheel A is bolted to to a flange on the drive shaft axially along the
driven shaft D to which it is splined. It B. The plate C is fixed to a boss which
is free to slide axially along the driven shaft D to which it is splined. It
therefore rotates with shaft D. Two rings G of special friction material are
riveted or bonded to A and E or alternatively to plate C.The presser plate E
is bushed internally so that it revolves freely on the driven shaft D. It is
integral with the withdrawl sleeve F. A number of springs are arranged
around the clutch ( Shown as S) so as to press the two friction surfaces
together.
The Clutch operates by moving the withdrawl sleeve to the right. This
compresses the Springs S are removes the pressure between the friction
surfaces. Hence it is possible to start of stop the driven shaft at will.Most
light vehicles use a single-plate clutch to transmit torque from the engine to
the transmission input shaft. The flywheel is the clutch driving member. The
clutch unit is mounted on the flywheel’s machined rear face, so that the unit
rotates with the flywheel. The clutch unit consists of - a friction-type disc,
with 2 friction facings and a central splined hub. - a pressure plate assembly,
consisting of a pressed steel cover, a pressure plate with a machined flat
face, and a segmented diaphragm spring. And a release bearing and

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Friction clutches
operating fork. The friction disc is sandwiched between the machined
surfaces of the flywheel and the pressure plate when the pressure plate is
bolted to the outer edge of the flywheel face. The clamping force on the
friction facings is provided by the diaphragm spring. Unloaded, it is a dished
shape. As the pressure plate cover tightens, it pivots on its fulcrum rings,
and flattens out to exert a force on the pressure plate, and the facings.The
transmission input shaft passes through the center of the pressure plate. Its
parallel splines engage with the internal splines of the central hub, on the
friction disc. With engine rotation, torque can now be transmitted from the
flywheel, through the friction disc, to the central hub, and to the
transmission. When the clutch pedal is depressed, the movement is
transferred through the operating mechanism, to the operating fork and the
release bearing. The release bearing moves forward and pushes the center
of the diaphragm spring towards the flywheel. The diaphragm pivots on its
fulcrum rings causing the outer edge to move in the opposite direction and
act on the pressure-plate retraction clips. The pressure plate disengages, and
drive is no longer transmitted. Releasing the pedal allows the diaphragm to
re-apply its clamping force and engage the clutch, and drive is restore

6.2. MULTI PLATE CLUTCHAdding plates to a clutch unit to form a multi-

plate clutch will increase its torque capacity, without increasing spring
strength or clutch diameter. This clutch assembly has two friction discs, with
friction material riveted to both sides of each. An internally-splined hub on
each disc mates with the splines on the transmission input shaft. A cast-iron
separator plate fits between each disc. The separator plate locates on driving
pins on the flywheel. This friction unit is between the flywheel and the
pressure plate when the pressure plate assembly is bolted to the flywheel.
The pressure plate spring then provides a frictional clamping force on each
mating surface. Torque is transmitted from the flywheel through the friction
facings to the transmission input shaft. When the clutch pedal is depressed
the release bearing acts on the pressure plate diaphragm and moves the
pressure plate away from the flywheel.This releases the clamping force on
the facings and separator plate and allows each clutch driving member to
rotate freely without turning the transmission input shaft. When the pedal is
released, the spring tension forces the pressure plate, discs and separator
against the flywheel, clamping all components together.

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Multi plate clutch

6.3.CONE CLUTCH

Cone clutch
From Wikipedia, the free encyclopedia
1. Cones: female cone , male cone
2. Shaft: male cone is sliding on splines
3. Friction material: usually on female cone, here on male cone
4. Spring: brings the male cone back after using the clutch control
5. Clutch control: separating both cones by pressing
6. Rotating direction: both direction of the axis are possible
A cone clutch serves the same purpose as a disk or plate clutch. However, instead
of mating two spinning disks, the cone clutch uses two conical surfaces to transmit
torque by friction.
The cone clutch transfers a higher torque than plate or disk clutches of the same
size due to the wedging action and increased surface area. Cone clutches are
generally now only used in low peripheral speed applications although they were
once common in automobiles and other combustion engine transmissions.
They are usually now confined to very specialist transmissions in racing, rallying, or
in extreme off-road vehicles, although they are common in power boats. This is

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because the clutch does not have to be pushed in all the way and the gears will be
changed quicker. Small cone clutches are used in synchronizer mechanisms in
manual transmissions.

CONE CLUTCH IN DIFFERENTIALS

CONE CLUTCH

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6.4. CENTRIFUGAL CLUTCH
A centrifugal clutch is a clutch that uses centrifugal force to connect two
concentric shafts, with the driving shaft nested inside the driven shaft.
The input of the clutch is connected to the engine crankshaft while the output may
drive a shaft, chain, or belt. As engine RPM increases, weighted arms in the clutch
swing outward and force the clutch to engage. The most common types have
friction pads or shoes radially mounted that engage the inside of the rim of a
housing. On the center shaft there are an assorted number of extension springs,
which connect to a clutch shoe. When the center shaft spins fast enough, the
springs extend causing the clutch shoes to engage the friction face. It can be
compared to a drum brake in reverse. This type can be found on most home built
karts, lawn and garden equipment, fuel-powered model cars and low power
chainsaws. Another type used in racing karts has friction and clutch disks stacked
together like a motorcycle clutch. The weighted arms force these disks together and
engage the clutch.
When the engine reaches a certain RPM, the clutch activates, working almost like a
continuously variable transmission. As the load increases the rpm drops,
disengaging the clutch, letting the rpm rise again and reengaging the clutch. If
tuned properly, the clutch will tend to keep the engine at or near the torque peak of
the engine. This results in a fair bit of waste heat, but over a broad range of speeds
it is much more useful than a direct drive in many applications.
Centrifugal clutches are often used in mopeds, underbones, lawnmowers, go-karts,
chainsaws, and mini bikes to
• keep the internal combustion engine from stalling when the blade is
stopped abruptly; and,
• disengage loads when starting and idling.
Thomas Fogarty, who also invented the balloon catheter, is credited with inventing
a centrifugal clutch in the 1940s, only three months after a Canadian boy named
Andrew Wilson drew up the first recognized design.[1] That being said, automobiles
were being manufactured with centrifugal clutches as early as 1936.[2]

CENTRIFUGAL CLUTCH

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CHAPTER 7

Major Types of Clutches by Application

7.1 Vehicular (General)

There are different designs of vehicle clutch but most are based on one or more
friction discs pressed tightly together or against a flywheel using springs. The
friction material varies in composition depending on many considerations such as
whether the clutch is "dry" or "wet". Friction discs once contained asbestos but this
has been largely eliminated. Clutches found in heavy duty applications such as
trucks and competition cars use ceramic clutches that have a greatly increased
friction coefficient. However, these have a "grabby" action generally considered
unsuitable for passenger cars. 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. However, raising the engine speed too high while
engaging the clutch will cause excessive clutch plate wear. Engaging the clutch
abruptly when the engine is turning at high speed causes a harsh, jerky start. This
kind of start is necessary and desirable in drag racing and other competitions,
where speed is more important than comfort.In a modern car with a manual
transmission the clutch is operated by the left-most pedal using a hydraulic or cable
connection from the pedal to the clutch mechanism. On older cars the clutch might
be operated by a mechanical linkage. Even though the clutch may physically be
located very close to the pedal, such remote means of actuation are necessary to
eliminate the effect of vibrations and slight engine movement, engine mountings
being flexible by design. With a rigid mechanical linkage, smooth engagement
would be near-impossible because engine movement inevitably occurs as the drive
is "taken up." No pressure on the pedal means that the clutch plates are engaged
(driving), while pressing the pedal disengages the clutch plates, allowing the driver
to shift gears or coast.

7.2 Motorcycles
Motorcycles typically employ a wet clutch with the clutch riding in the same oil as
the transmission. These clutches are usually made up of a stack of alternating plain
steel and friction plates. Some of the plates have lugs on its inner diameter locking
it to the engine crankshaft, while the other plates have lugs on the outer diameter
that lock it to a basket which turns the transmission input shaft. The plates are
forced together by a set of coil springs or a diaphragm spring plate when the clutch
is engaged.
On most motorcycles the clutch is operated by the clutch lever located
on the left handlebar. No pressure on the lever means that the clutch
plates are engaged (driving), while pulling the lever back towards the
rider will disengage the clutch plates through cable or hydraulic
actuation, allowing the rider to shift gears or coast.
Racing motorcycles often use slipper clutches to eliminate the effects
of engine braking which, being applied only to the rear wheel, can lead
to instability.

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7.3 Automobile Non-powertrain
There are other clutches found in a car. For example, a belt-driven engine cooling
fan may have a clutch that is heat-activated. The driving and driven members are
separated by a silicone-based fluid and a valve controlled by a bimetallic spring.
When the temperature is low, the spring winds and closes the valve, which allows
the fan to spin at about 20% to 30% of the shaft speed. As the temperature of the
spring rises, it unwinds and opens the valve, allowing fluid past the valve which
allows the fan to spin at about 60% to 90% of shaft speed.

CHAPTER 8
8.1 SUMMARY
A Clutch is a machine member used to connect the driving shaft to a driven
shaft, so that the driven shaft may be started or stopped at will, without
stopping the driving shaft. A clutch thus provides an interruptible connection
between two rotating shafts
Clutches allow a high inertia load to be stated with a small power. A
popularly known application of clutch is in automotive vehicles where it is
used to connect the engine and the gear box. Here the clutch enables to
crank and start the engine disengaging the transmission Disengage the
transmission and change the gear to alter the torque on the wheels. Clutches
are also used extensively in production machinery of all types. It is a
mechanical device, by convention understood to be rotating, which provides
driving force to another mechanism when required, typically by connecting
the driven mechanism to the driving mechanism. Clutches and brakes are
similar; if the driven member of a clutch is fixed to the mechanism frame, it
serves as a brake.
Clutches are useful in devices that have two rotating shafts. In these devices,
one shaft is typically attached to a motor or other power unit (the driving
member), and the other shaft (the driven member) provides output power for
work to be done. In a drill, for instance, one shaft is driven by a motor, and
the other drives a drill chuck. The clutch connects the two shafts so that they
can either be locked together and spin at the same speed (engaged), or be
decoupled and spin at different speeds (disengaged).

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APPENDIX –A
BASIC CONCEPTS OF FRICTION
Friction is the force resisting the relative motion of solid surfaces, fluid
layers,and/or material elements sliding against each other. It may be thought
of as the opposite of "slipperiness".
There are several types of friction:
• Dry friction resists relative lateral motion of two solid surfaces in
contact. Dry friction is subdivided into static friction between non-
moving surfaces, and kinetic friction between moving surfaces.
• Fluid friction describes the friction between layers within a viscous
fluid that are moving relative to each other.[1][2]
• Lubricated friction is a case of fluid friction where a fluid separates
two solid surfaces.[3][4][5]
• Skin friction is a component of drag, the force resisting the motion of
a solid body through a fluid.
• Internal friction is the force resisting motion between the elements
making up a solid material while it undergoes deformation.
When surfaces in contact move relative to each other, the friction between
the two surfaces converts kinetic energy into heat. This property can have
dramatic consequences, as illustrated by the use of friction between pieces
of wood to start a fire.
Another important consequence of many types of friction can be wear, which
may lead to performance degradation and/or damage to components.
Friction is a component of the science of tribology.
Friction is not a fundamental force but occurs because of the electromagnetic
forces between charged particles which constitute the surfaces in contact.
Because of the complexity of these interactions friction cannot be calculated
from first principles, but instead must be found empirically.
Basic properties
Basic properties of friction have been described as laws:
• Amontons' 1st Law: The force of friction is directly proportional to
the applied load.
• Amontons' 2nd Law: The force of friction is independent of the
apparent area of contact.
• Coulomb's Law of Friction: Kinetic friction is independent of the
sliding velocity.
Amontons' 2nd Law is an idealization assuming perfectly rigid and inelastic
materials. For example, wider tires on cars provide more traction than narrow
tires for a given vehicle mass because of surface deformation of the tire.
Dry friction
Dry friction resists relative lateral motion of two solid surfaces in contact. The
two regimes of dry friction are static friction between non-moving surfaces,

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and kinetic friction (sometimes called sliding friction or dynamic friction)
between moving surfaces.
Coulomb friction, named after Charles-Augustin de Coulomb, is an
approximate model used to calculate the force of dry friction. It is governed
by the equation:
where
• is the force exerted by friction (in the case of equality, the maximum
possible magnitude of this force).
• is the coefficient of friction, which is an empirical property of the
contacting materials,
• is the normal force exerted between the surfaces.
The Coulomb friction may take any value from zero up to , and the direction
of the frictional force against a surface is opposite to the motion that surface
would experience in the absence of friction. Thus, in the static case, the
frictional force is exactly what it must be in order to prevent motion between
the surfaces; it balances the net force tending to cause such motion. In this
case, rather than providing an estimate of the actual frictional force, the
Coulomb approximation provides a threshold value for this force, above
which motion would commence. This maximum force is known as traction.
The force of friction is always exerted in a direction that opposes movement
(for kinetic friction) or potential movement (for static friction) between the
two surfaces. For example, a curling stone sliding along the ice experiences a
kinetic force slowing it down. For an example of potential movement, the
drive wheels of an accelerating car experience a frictional force pointing
forward; if they did not, the wheels would spin, and the rubber would slide
backwards along the pavement. Note that it is not the direction of movement
of the vehicle they oppose, it is the direction of (potential) sliding between
tire and road.
In the case of kinetic friction, the direction of the friction force may or may
not match the direction of motion: a block sliding atop a table with rectilinear
motion is subject to friction directed along the line of motion; an automobile
making a turn is subject to friction acting perpendicular to the line of motion
(in which case it is said to be 'normal' to it). The direction of the static friction
force can be visualized as directly opposed to the force that would otherwise
cause motion, were it not for the static friction preventing motion. In this
case, the friction force exactly cancels the applied force, so the net force
given by the vector sum, equals zero. It is important to note that in all cases,
Newton's first law of motion holds.
The normal force
Block on a ramp (top) and corresponding free body diagram of just the
block (bottom).
Main article: Normal force
The normal force is defined as the net force compressing two parallel
surfaces together; and its direction is perpendicular to the surfaces. In the

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simple case of a mass resting on a horizontal surface, the only component of
the normal force is the force due to gravity, where . In this case, the
magnitude of the friction force is the product of the mass of the object, the
acceleration due to gravity, and the coefficient of friction. However, the
coefficient of friction is not a function of mass or volume; it depends only on
the material. For instance, a large aluminum block has the same coefficient
of friction as a small aluminum block. However, the magnitude of the friction
force itself depends on the normal force, and hence the mass of the block.
If an object is on a level surface and the force tending to cause it to slide is
horizontal, the normal force between the object and the surface is just its
weight, which is equal to its mass multiplied by the acceleration due to
earth's gravity, g. If the object is on a tilted surface such as an inclined
plane, the normal force is less, because less of the force of gravity is
perpendicular to the face of the plane. Therefore, the normal force, and
ultimately the frictional force, is determined using vector analysis, usually via
a free body diagram. Depending on the situation, the calculation of the
normal force may include forces other than gravity.
Coefficient of friction
The 'coefficient of friction' (COF), also known as a 'frictional coefficient' or
'friction coefficient' and symbolized by the Greek letter µ, is a dimensionless
scalar value which describes the ratio of the force of friction between two
bodies and the force pressing them together. The coefficient of friction
depends on the materials used; for example, ice on steel has a low
coefficient of friction, while rubber on pavement has a high coefficient of
friction. Coefficients of friction range from near zero to greater than one –
under good conditions, a tire on concrete may have a coefficient of friction of
1.7.
For surfaces at rest relative to each other , where is the coefficient of static
friction. This is usually larger than its kinetic counterpart.
For surfaces in relative motion , where is the coefficient of kinetic friction.
The Coulomb friction is equal to , and the frictional force on each surface is
exerted in the direction opposite to its motion relative to the other surface.
The coefficient of friction is an empirical measurement – it has to be
measured experimentally, and cannot be found through calculations.
Rougher surfaces tend to have higher effective values. Both static and
kinetic coefficients of friction depend on the pair of surfaces in contact; for a
given pair of surfaces, the coefficient of static friction is usually larger than
that of kinetic friction; in some sets the two coefficients are equal, such as
teflon-on-teflon.
Most dry materials in combination have friction coefficient values between
0.3 and 0.6. Values outside this range are rarer, but teflon, for example, can
have a coefficient as low as 0.04. A value of zero would mean no friction at
all, an elusive property – even magnetic levitation vehicles have drag.
Rubber in contact with other surfaces can yield friction coefficients from 1 to
2. Occasionally it is maintained that µ is always < 1, but this is not true.

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While in most relevant applications µ < 1, a value above 1 merely implies
that the force required to slide an object along the surface is greater than the
normal force of the surface on the object. For example, silicone rubber or
acrylic rubber-coated surfaces have a coefficient of friction that can be
substantially larger than 1.

REFERENCES
BOOKS
1. Crouse W.H., ‘Automotive Mechanics’, Tata McGraw Hill
Publishing Company.
2. Joseph Heitner, ‘Automotive Mechanics’, C.B.S.Publisher and
Distributors.
3. Narang G.B.S., ‘Automobile Engineering’, S.Chand and
Company Ltd
4. Newton, Steeds & Garrett, ‘Motor vehicle’, ‘The English
language book society
5. Singh Kripal, ‘Automobile Engineering’, Vol.II., New Chand
Jain.
6. A.W.Judge, ‘Automotive systems’, Volume 1 to 8.
7. Harbans Singh Reyat, ‘The Automobile’
8. A Book of Car.

INTERNET REFERENCES
1. HOWSTUFFWORKS.COM
2. GOOGLE LINKS
3. AUTOMOBILE ENGINEERING.COM

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