Clutches are useful in devices with two rotating
shafts. In these devices, one of the shafts is
typically driven by a motor or pulley, and the other
shaft is driving another device. In a drill, for
instance, one shaft is driven by a motor and the
other is driving a drill chuck. The clutch connects
the two shafts so that they can either be locked
together and spin at the same speed, or be
decoupled and spin at different speeds.
• In a car, you need a clutch because the engine
spins all the time and the car wheels don't. In
order for a car to stop without killing the engine,
the wheels need to be disconnected from the
engine somehow. The clutch allows us to
smoothly engage a spinning engine to a non-
spinning transmission by controlling the slippage
between them. To understand how a clutch
works, it helps to know a little bit about friction.
• A clutch is a mechanical device that provides for
the transmission of power (and therefore usually
motion) from one component (the driving
member) to another (the driven member) when
engaged, but can be disengaged.
• Clutches are used whenever the transmission of
power or motion must be controlled either in
amount or over time (e.g., electric screwdrivers
limit how much torque is transmitted through use
of a clutch; clutches control whether automobiles
transmit engine power to the wheels).
• In the simplest application, clutches connect and
disconnect two rotating shafts (drive
shafts or line shafts). In these devices, one shaft
is typically attached to a motor or other power
unit (the driving member) while the other shaft
(the driven member) provides output power for
work. While typically the motions involved are
rotary, linear clutches are also possible
• Clutch is used to engage or disengage the
engine to the transmission or gear box.
• When the clutch is in engaged position, the
engine power or rotary motion of engine
crankshaft is transmitted to gear box and then to
When clutch is disengaged, the engine power
does not reach to gear box (and to wheels)
although engine is running.
Clutch is also used to allow shifting or changing
of gears when vehicle is running. For shifting
gears, clutch is first disengaged then gear is
shifted and then clutch is engaged. Clutch has to
be disengaged to stop the vehicle and also at the
time of idling.
• It operates on the principle of friction. When two
surfaces are brought in contact and are held
against each other due to friction between them,
they can be used to transmit power. If one is
rotated, then other also rotates. One surface is
connected to engine and other to the
transmission system of automobile. Thus, clutch
is nothing but a combination of two friction
• It consists of
• (a) a driving member,
• (b) a driven member, and
• (c) an operating member.
• Driving member has a flywheel which is mounted on the
engine crankshaft. A disc is bolted to flywheel which is known
as pressure plate or driving disc.
• The driven member is a disc called clutch plate. This plate can
slide freely to and fro on the clutch shaft.
• The operating member consists of a pedal or lever which can
be pressed to disengaged the driving and driven plate.
Some types of clutches used in vehicles are given below :
• (a) Friction Clutch : It may be (i) single plate clutch, (ii)
multi-plate clutch, or (iii) cone clutch. Multi-plate clutch
can be either wet or dry. A wet clutch is operated in an oil
batch whereas a dry clutch does not use oil.
(b) Centrifugal clutch.
(c) Semi-centrifugal clutch.
(d) Hydraulic clutch.
(e) Positive clutch.
(f) Vacuum clutch.
(g) Electromagnetic clutch.
• The vast majority of clutches ultimately rely on
frictional forces for their operation. The purpose
of friction clutches is to connect a moving
member to another that is moving at a different
speed or stationary, often to synchronize the
speeds, and/or to transmit power. Usually, as
little slippage (difference in speeds) as possible
between the two members is desired.
I. single plate clutch
II. multi-plate clutch or (iii) cone clutch. Multi-plate
clutch can be either wet or dry. A wet clutch is
operated in an oil batch whereas a dry clutch
does not use oil.
• A single plate is commonly used in cars and light
vehicles. It has only one clutch plate which is
mounted on the splines of the clutch shaft. A
flywheel is mounted on the crankshaft of the
engine. A pressure plate is connected to the
flywheel through the bolts and clutch springs. It is
free to slide on the clutch shaft with the
movement of clutch pedal. When clutch is in
engaged position, the clutch plate remains
gripped between flywheel and pressure plate.
Friction linings are provided on both the sides of
clutch plate. On one side clutch plate is in touch
with flywheel and on other side with pressure
• plate. Due to friction on both sides, the clutch
plate revolves with engine flywheel. Therefore,
clutch transmits engine power to clutch shaft.
Clutch shaft is connected to transmission (or
gear box) of automobile. Thus, clutch transmits
power from engine to transmission system which
intern rotates wheels of engine.
• When the clutch plate is to be disengaged, the
clutch pedal is pressed. Because of this pressure
plate moves back and clutch plate is disengaged
from flywheel. Thus, clutch shaft stops rotating
even if engine flywheel is rotating. In this
position, power does not reach the wheels and
• Working: The diagram shows the pressure plate
back by the release levers against the
springs; so that the friction lining on the clutch
are free of wheel rotates without driving the
plate and hence the shaft.
• When the pressure of the thrust race is released
compression springs are free to move the
• The pressure plate moves to the left, sliding the
plate on its splined hub, along the driven shaft
the friction touches the flywheel .
• The compression springs now cause the lining to
be gripped between the pressure plate and the
and pressure plate causes the clutch plate to
tuning the driven shaft.
• A multiple plate clutch is a type of clutch
system where multiple driven and drive plates
are used in order to make up for torque loss due
to slippage. This slippage is usually caused by a
fluid that the plates are immersed in for cooling,
cleaning and lubrication. This type of clutch
system is commonly referred to as a wet clutch
system. The type of arrangement is what is
found in the automatic transmission in your car.
This clutch system allows gears to be shifted up
and/or down, without interrupting the power flow
through the transmission, by lifting the
• A multi-plate clutch has more than one driven
plate. Although this type of clutch has been
widely used on cars up to about 1930, the
several advantages of the single-plate clutch,
specifically its ability to completely disengage the
drive has caused a very rare use of a multi-plate
unit as a main transmission clutch installed
between the engine and gear box. However, a
multi-plate type of clutch finds a use in automatic
gearboxes. In these gearboxes, a number of
clutches hold the various gear elements, and as
the clutch diameter in these units is limited, a
multi-plate clutch is suitable.
• Multi-plate clutch consists of more than one
clutch plates contrary to single plate clutch which
consists of only one plate. Friction surfaces are
made in case of multi-plate clutch. Due to
increased number of friction surfaces, a multi-
plate clutch can transmit large torque. Therefore,
it is used in racing cars and heavy motor vehicles
witch have high engine power. The clutch plates
are alternatively fitted with engine shaft and the
shaft of gear box. He plates are firmly held by the
force of coil springs and they assembled in a
• One plate slides in the grooves on the flywheel
and the next plate slides on spines provided on
pressure plate. Thus, each alternate plate slides
in grooves on the flywheel and the other on
splines of pressure plate. If we take two
consecutive plates, then one has inner and other
has outer splines.
• When the clutch pedal is pressed, the pressure
plate moves back against the force of coil spring,
hen the clutch plates are disengaged and engine
flywheel and gear box are decoupled. However,
when clutch pedal is not pressed the clutch
remain in engaged position and the power can
be transmitted from engine flywheel to the gear
• The main purpose for a wet multi-plate clutch is
increased power transmission capability in a
compact size. As a side effect, multi-plate wet
clutches generally have very good progressive
engagement “feel”. This is why they are used as
crane hoist clutches, tracked vehicle steering
clutches, and heavy machine tool drives, apart
• Wet clutches are designed for moderate slipping,
partly due to the cooling effect of the oil, and
partly due to the hydrodynamic effects present
preventing shoe contact. Properly maintained, a
wet clutch should last many times longer than a
dry single-plate clutch under similar service
• Illustrates the layout of a multi-plate spring type
clutch, fitted on early motor cars. A cover, bolted
to the flywheel, engages by means of slots with a
series of lugs on the outer plates. These steel
plates may be plain or fitted with cork or friction
material inserts and act on inner plates, splined
to a hub. Thrust springs push the plates together
to form a drive.
• For the clutch disengagement, the end plate is
withdrawn to compress the springs and release
the other plates. In this arrangement it is difficult
to ensure the disengagement of all plates. To
overcome this problem the plates are either
dished or fitted with small springs to push the
Generally wet type clutch is used in automatic
gearboxes, and is operated by a piston governed
by hydraulic pressure. Sintered bronze plates of
partially fusing powdered bronze or compressed
paper are used in many designs. The porous
surface of this plate traps the oil, to provide long
life and smooth operation.
• These clutches basically have drive and driven
plates. The drive plates are not allowed to rotate
independently by using interlocking lugs and
slots, which do not permit relative rotational spin,
but axial movement. The driven plates are
mounted on the internally splined hubs, which
splines on the gearbox spigot shaft (Fig. 24.17).
A dished annular disc forms the diaphragm
spring, the inner portion of which is radially
slotted and the outer ends are enlarged with a
circular hole to prevent stress concentration
during disengagement. These radial slots divide
the disc into number of release levers
• During operation, due to engagement and
disengagement of the clutch, the diaphragm
cone angle changes continuously as wear
occurs. In order to accommodate the change, the
diaphragm pivots and rolls about the fulcrum
rings. During engagement of the clutch the
diaphragm bears against the outer ring, and
during disengagement the reaction load is taken
by the inner ring. As the friction linings wear, the
spring diaphragm becomes more dished so that
a larger axial clamping load is applied initially. As
the linings wear increases, the distance between
the cover pressing and pressure plate become
excessive, so that the axial thrust begins to