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7/31/2019 Auto Module 01
1/13
Clutch Automobile Engineering Prof. Pradeepkumar Suryawanshi
DON BOSCO INSTITUTE OF TECHNOLOGY, MUMBAI
Department of Mechanical EngineeringAutomobile Engineering (B.E. Sem- VIII)
Module 01
CLUTCH1.1 Clutch:A clutch is a device used to transmit the rotary
motion of one shaft to another when desired. Theaxes of the two shafts are coincident. It can also
be described as a machine member used to
connect a driving shaft to a driven shaft so thatthe driven shaft may be started or stopped at will,
without stopping the driving shaft. Thus it is an
interruptible connection between two shafts.
1.2 Requirements of Clutch:
i) Torque Transmission: The clutch should
be able to transmit maximum torque of
engine under all working conditions. It is
usually designed to transmit 125 to 150 percent of maximum engine torque.
ii) Gradual Engagement: The clutch shouldpositively take the drive gradually without the
occurrence of sudden jerks.
iii) Heat Dissipation: During clutch operation
large amount of heat is generated. The
rubbing surfaces should have sufficient area
and mass to absorb the heat generated. Theproper design of clutch should ensure proper
ventilation or cooling for adequate dissipation
of heat.
Clutch temperature is the major factor limiting
the clutch capacity. This requires that theclutch facing must maintain a reasonable
coefficient of friction with mating surfaces
under all working conditions. Moreover the
friction material should not crush at hightemperatures and clamping loads.
iv) Dynamic balancing: The clutch should bebalanced dynamically particularly in high
speed clutches.
v) Vibration Damping: Suitable mechanism
should be incorporated within the clutch toeliminate noise produced in the transmission.
vi) Size: The size of the clutch must besmallest possible so that it should occupy
minimum amount of space.
vii) Inertia: The clutch rotating parts should
have minimum inertia. Otherwise when theclutch is disengaged for gear changing, theclutch plate will keep on spinning, causing
hard shifting and gear clashing in spite of
synchronizer.
viii) Clutch free pedal play: To reduce
effective clamping load on the carbon thrust
bearing and wear thereof, sufficient Clutchfree pedal play must be provided in the clutch.
ix) Ease of operation: For higher torquetransmission the operation of disengaging the
clutch must not be tiresome to the driver.
1.3 Classification of Clutches:
Clutches can be classified as follows:
Positive Clutches:a) Square Jaw Clutch
b) Spiral Jaw Clutch
Friction Clutches:a) Single Plate Clutch
b) Diaphragm spring type singleplate clutch
c) Multiplate Clutch
d) Cone clutch
e) Semi-centrifugal Clutchf) Centrifugal Clutch
g) Wet Clutch
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Clutch Automobile Engineering Prof. Pradeepkumar Suryawanshi
Fluid Flywheel
1.4 Positive Clutches:
The positive clutches are used when a positive
drive is required. This type of clutch is designed
to transmit torque without slip. It is the simplestof all shaft connectors, sliding on a keyed shaft
section or a splined portion and operating with ashift lever on a collar element. The simplest type
of a positive clutch is a jaw or claw clutch. The
jaw clutch permits one shaft to drive another
through a direct contact of interlocking jaws. Itconsists of two halves one of which is
permanently fastened to the driving shaft by a
sunk key. The other half of a clutch is movableand it is free to slide axially on the driven shaft,
but it is prevented from turning relatively to itsshaft by means of feather key. The jaws of theclutch may be of square type or spiral type as
shown in Fig. 1.1
Fig. 1.1 Positive clutches. (a) Square-jaw clutch. (b)
Spiral-jaw clutch.
Fig. 1.2 Square-jaw clutch.
A square jaw type is used where engagement and
disengagement in motion and under load is notnecessary. This type of clutch will transmit power
in either direction of rotation. The spiral jaws may
be left-hand or right-hand, because power
transmitted by them is in one direction only. Thistype of clutch is occasionally used where the
clutch must be engaged and disengaged while inmotion. Engagement speed should be limited to
10 rpm for a square-jaw clutch and 150 rpm for a
spiral-jaw clutch. If disengagement under load isrequired, the jaws should be finish-machined and
lubricated. The use of jaw clutches are frequently
applied to sprocket wheels, gears and pulleys. In
such a case the non-sliding part is made integralwith the hub. Fig 1.3 shows the photographic
views of square and spiral jaw clutches.
Fig 1.3 Photographic views of square and spiral jaw
clutches
1.5 Principle of Friction Clutches:
The principle of friction clutch may be explainedby means ofFig.1.4
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Clutch Automobile Engineering Prof. Pradeepkumar Suryawanshi
Fig.1.4 Principle of Friction Clutches
Let disc C keyed to shaft A, rotates at some
speed, say N rpm. Initially when clutch is not
engaged shaft B and disc D keyed to it arestationary. Now apply some axial force W to the
disc D so that it comes in contact with disc C. As
soon as the contact is made the force of friction
between C and D will come into play andconsequently the disc D will start rotating. The
speed of D depends upon friction force present,
which in turn, is proportional to the force Wapplied. If W is increased gradually, the speed of
D will be increased consequently till the stage
comes when the speed of D becomes equal to thespeed of C. Then the clutch is said to be fully
engaged.
1.6 Single Plate Clutch:
A single disc or plate clutch shown in Fig.1.5consists of a clutch plate C whose both sides are
faced with a friction material G.
Fig.1.5 Single disc or plate clutch
It is mounted on a hub which is free to move
axially along the splines of the driven shaft D andis held between the flywheel A and the pressure
plate E. The pressure plate is mounted inside the
clutch body which is bolted to the flywheel. Both
the pressure plate and flywheel rotate with engine
crankshaft or the driving shaft. The pressure platepushes the clutch plate towards the flywheel by a
set of coil springs S. The springs are arrangedcircumferentially which provide axial force to
keep the clutch in engaged position. The three
levers known as release levers or fingers arecarried on pivots suspended from the case of the
body as shown in Fig 1.6. These are arranged in
such a manner that the pressure plate moves away
from the flywheel by the inward movement of athrust bearing. A pedal is provided to pull the
pressure plate against the spring force whenever itis required to be disengaged. Ordinarily clutchremains in engaged position.
Fig.1.6 Single disc or plate clutch with linkage
When the clutch pedal is pressed down, its
linkage forces the thrust release bearing to movein towards the flywheel and pressing the longerends of the lever inward. The levers are forced to
turn on their suspended pivot and the pressure
plate moves away from the flywheel by the knife
edges, thereby comprising the clutch springs asshown in Fig 1.6 a).
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Clutch Automobile Engineering Prof. Pradeepkumar Suryawanshi
Fig 1.6 a) Operation of the release levers
With the movement of the pressure plate, the
friction plate is released and clutch is disengaged.On the other hand, when the foot is taken off from
the clutch pedal, the thrust bearing is moved back
by the levers. This allows the springs to extendand thus the pressure plate pushes the clutch plate
back towards the flywheel.
The axial pressure exerted by the spring providesa frictional force in the circumferential direction
when the relative motion between driving and
driven members tends to take place. If the torquedue to this frictional force exceeds the torque to
be transmitted, then no slipping takes place and
power is transmitted from the driving shaft to thedriven shaft.
Fig 1.7 shows exploded photographic view and
Fig 1.8 shows cut away section of clutchassembly of single plate clutch.
Fig 1.7 Exploded photographic view of single plate clutch
Fig 1.8 Cut away section of clutch assembly of single plate
clutch
Advantages:
1. As compared to cone clutch, the pedalmovement is less in this case which leads to easier
gear changing.
2. It is more reliable compared to cone
Clutch.
Disadvantages:
As compared to cone clutch, the springshave to be stiffer and this means greater force
required to be applied by the driver while
disengaging.
1.7 Diaphragm spring type single plate clutch:
The construction of this type of clutch is similarto the single plate type of clutch described above
except that here diaphragm springs (also knownas Belleville springs) are used instead of theordinary coil springs. In the free condition, the
diaphragm spring is of conical form, but when
assembled, it is constrained to an approximately
flat condition because of which it exerts a loadupon the pressure plate. A diaphragm spring type
clutch is shown in Fig 1.9 and Fig 1.10 shows a
diaphragm spring in free condition.
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Clutch Automobile Engineering Prof. Pradeepkumar Suryawanshi
Fig 1.9 A diaphragm spring type clutch
Fig 1.10 A diaphragm spring in free condition
Advantages:
This type of clutch has now virtually
superseded the earlier coil spring design in many
countries in clutch sizes ranging upto 270 mm indiameter. However in case of heavy vehicles, the
coil spring type clutches are still being used,
because of the difficulty to provide sufficientclamping force by a single diaphragm spring. The
diaphragm spring offers following distinct
advantages.1. It is more compact means of storing
energy. Thus compact design results in
smaller clutch housing.
2. As the diaphragm spring iscomparatively less affected by the
centrifugal forces, it can withstand higher
rotational speed. On the other hand, thecoil springs have tendency to distort in the
transverse direction at higher speeds.
3. In case of coil springs, load-deflectioncurve is linear. Therefore with the wear of
the clutch facing the springs have less
deflection due to which they would apply
less force against the clutch plate. On the
other hand, in case of diaphragm spring
the load-deflection curve is not linear (Fig
1.11).
Fig 1.11 Load- Deflection curve
Therefore in this case as the clutch facing
wears, force on the plate gradually
increases, which means that even in wornout condition, the spring force is not less
than its value in case of new clutch.
Further it is also seen from Fig 1.12 thatthe load-deflection curve depends upon
the ratios h/t, where h is the free dishheight and tis the thickness of the spring.
Therefore in this case with suitable design,the load-deflection curve can be improved
to give lower release loads.
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Clutch Automobile Engineering Prof. Pradeepkumar Suryawanshi
Fig 1.12 Effect ofh/ton Load- Deflection curve
4. The diaphragm acts as both clampingspring and release levers. Therefore many
extra parts like struts, eye bolts, levers,
etc. are eliminated in the diaphragm springbecause of which the loss of efficiency
due to friction wear of these parts also
does not occur, which results inelimination of squeaks and rattles.
Fig 1.13 Cut away section of clutch assembly of single
plate clutch (Diaphragm spring type)
Fig 1.13 shows cut away section of clutch
assembly and Fig 1.14 shows explodedphotographic view of Diaphragm spring type
single plate clutch
Fig 1.14 Exploded photographic view of single plate clutch
(Diaphragm spring type)
1.8 Design of Single plate Clutch:
Consider two friction surfaces maintained in
contact by an axial thrust W as shown in Fig1.15(a). Let,
T = Toque Transmitted by clutch p = Intensity of pressure with which the
contact surfaces are held togetherr2 = ri = Inner radius of the friction surface
r1 = ro= Inner radius of the friction
surface
= Coefficient of frictionConsider an elementary ring of radius r and
thickness dr as shown in Fig 1.15(b).
We know that,
Area of the contact surface or friction surface,
dA = 2r.dr
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Clutch Automobile Engineering Prof. Pradeepkumar Suryawanshi
Fig 1.15 Forces on a single plate clutch
Normal or axial force on the ring,
dW = Pressure x Area = p . 2r.dr (i)
The friction force acting on the ring tangentiallyat radius r,Fr= . dW = . p . 2r.dr
Hence Friction torque acting on the ring,
Tr= r. Fr = . p . 2r2.dr (1)
Friction torque of a clutch is usually calculated on
the basis of two assumptions. Each assumption
leads to a different value of torque. In one case itis assumed that the intensity of pressure on the
contact surface or friction surface is constant
whereas in the second case, it is uniform wearing
of the contact surface or friction surface.
i) Considering uniform pressure:
Under this assumption, pressure is assumed to beuniform over the surface area and the intensity of
pressure is given by,
( )(2)
areasectional-Cross
ForceAxial
22
io rr
Wp
pressure
=
=
Equation (2) can be obtained by integrating
equation (i) within the limits from ri to ro.The total friction torque can be found by
integrating equation (1) within the limits from ri to
ro.
The total friction torque acting on the frictionsurface or on the clutch,
Substituting expression for p from equation (2),
( )
=3
.233
22
io
io
rr
rr
WT
)3(3
222
33
RWrr
rrWT
io
io =
=
SurfacFrictionofRadiusMean3
222
33
=
=
io
io
rr
rrR
Where
ii) Considering uniform axial wear:
For uniform wear over an area, the intensity ofpressure should vary inversely proportional to the
elementary areas, i.e. it should decrease with
increase in the elementary area and vice-versa.This can be illustrated by drawing a line with a
chalk. In doing so a little quantity of chalk is worn
from the stick. Now if it is desired that the chalk
is worn by the same amount, but the length of theline is doubled, the pressure on the chalk has to be
reduced to half that in the previous case.
Therefore for uniform wear, product of thepressure applied and the distance traveled must be
constant. For uniform wear of the surface, let
)4(CConstant
r2r2
rradiiatarearradiiatarea
width)(equalrandrradiiatsurfacetheofwidth
ratsurfacesobetween twpressureNormal
ratsurfacesobetween twpressureNormal
oi
oi
oi
o
i
==
==
==
==
pr
rprp
bpbp
pp
b
p
p
ooii
oi
oi
o
i
Thus in case of uniform wear of the two surfaces,
product of the normal pressure and thecorresponding radius must be constant. This
means the pressure is less where the radius is
more and vice-versa. Pressure on an elemental
area at radius r can be found as given below.
BE Mech Sem-VIII/Auto Engg/Module:01 Page 7
=
=.=
3.2
3.22p..
33
32
io
r
r
r
r
rrpT
rpdrrT
o
i
o
i
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Clutch Automobile Engineering Prof. Pradeepkumar Suryawanshi
Fig 1.16 Multi-plate Clutch
Fig 1.17 Multi-plate Clutch (Inner and outer plates)
Design of a multiplate clutch:
The total friction torque acting on the friction
surface or on the clutch is given by,
surfacesfrictionofpairsofNumberWhere
)8(
==
n
RWnT
1. If N is the total number of friction plates inthe multiplate clutch, then 1= Nn
2. If 1n is the number of plates on the
driving shaft and 2n is the number of
plates on the driven shaft, then
121 += nnn
1.10 Cone Clutch:
Fig 1.18 Cone clutch
Fig 1.18 shows simplified diagram of the cone
clutch. It was extensively used in automobiles, butnow-a-days it has been completely replaced by
the plate clutch. It consists of only one pair of
friction surface which is in the form of cones. In
the engaged position the male cone is fully insidethe female cone so that the friction surfaces are in
complete contact. This is done by means of
springs which keep the male cone pressed all thetime.
Advantages:
The only advantage of cone clutch is that the
normal force acting on the contact surfaces is
larger than the axial force as compared to thesingle plate clutch in which the normal force
acting on the contact surfaces is equal to the axial
force.
Disadvantages:
The cone clutch is practically obsolete because of
certain inherent disadvantages.1. If the angle of cone is made
smaller that 200 the male cone tends to
bind or join in the female cone and itbecomes difficult to disengage the clutch.
2. A small amount of wear on the cone surface
results in considerable amount of axialmovement of the male cone for which it is
difficult to allow.
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Clutch Automobile Engineering Prof. Pradeepkumar Suryawanshi
1.11 Design of Cone Clutch:
Consider a pair of friction surfaces of a coneclutch maintained in contact by an axial thrust W
as shown in Fig 1.19(2). Let
T = Toque Transmitted by clutch
p = Intensity of pressure with whichthe
conical contact surfaces are held togetherri = Inner radius of the friction
surface
ro= Inner radius of the friction surface = Coefficient of friction
= Semi-angle of the cone or the
angle of the friction surface with the axis of
the clutchb = Width of the friction surface
(alsoknown as face width or cone face)
Consider an elementary ring of radius r and
thickness dr as shown in Fig 1.19(1).
Let dlis the length of ring of the friction surface,
such that
sin
cosdr
ecdrdl ==
We know that,
Area of the contact surface or friction surface, dA
= 2r. dl=
sin
r2 dr
Fig 1.19 Forces on Friction surface of Cone Clutch
Normal force on the ring,
dP = Pressure x Area = p . dA=
sin
r2dr
p
Axial force on the ring,
)9(2
sin
sin
2sin
drprdW
drprdPdW
=
==
The friction force acting on the ring tangentiallyat radius r,
Fr = . dP = .
sin
r2dr
p
Hence Friction torque acting on the ring,
Tr = r. Fr= . )10(sin
r2 2
drp
i) Considering uniform pressure:The total axial force can be found by integrating
equation (9) within the limits from ri to ro.
( ) 11(2
22
force,axialTotal
222
io
r
r
r
r
rrpr
pdrprW
o
i
o
i
=
=.=
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Clutch Automobile Engineering Prof. Pradeepkumar Suryawanshi
Equation (11) shows that the total axial force is
independent of the cone angle.
The total friction torque can be found by
integrating equation (10) within the limits from rito ro.
The total friction torque acting on the frictionsurface or on the clutch,
Substituting expression forp from equation (11),
( )3 3
2 2
3 3
2 2
2 .sin 3
2(12)
3 sin
o i
o i
o i
o i
r rWTr r
r rWT W R
r r
=
= =
3 3
2 2
2Mean Radius of Friction Surface
3
o i
o i
Where
r rR
r r
= =
ii) Considering uniform axial wear:
We know that,
dr2r.dr2r
C=r.dr2.p=dW = C
[ ] ( )
( ))13(
2
222
force,axialTotal
io
io
r
r
r
r
rr
WC
rrCrCdrCW oi
o
i
=
==.=
We know that the friction torque acting on the
ring,
Tr = r. Fr =
sin
r2 2dr
p =
sin
r2dr
C
The total friction torque acting on the frictionsurface or on the clutch,
Substituting expression for C from equation (13),
( )
( )
( )SurfaceFrictionofRadiusMean
sin2
)14(sin2
22.
sin
2 22
=+
=
=+
=
=
io
io
io
io
rrR
Where
RWrrW
T
rr
rr
WT
Equation (14) gives the more conservative results
as compared to equation (12) and hence can besafely used for design of cone clutch.
1.12 Centrifugal Clutch:
The centrifugal clutches are usually incorporated
in motor pulleys. It consists of a number of shoeson the inside of pulley as shown in Fig 1.20
Fig 1.20 Centrifugal Clutch
The outer surfaces of the shoes are covered with a
friction material. These shoes, which can move
radially in guides, are held against the boss ofspider on the driving shaft by means of springs.
The springs exert a radially inward force which is
assumed constant. When rotating, under the
action of centrifugal force, the shoes are movedradially outwards. The magnitude of this
centrifugal force depends upon the speed at which
the shoe is rotating. When centrifugal force isequal to the spring force, the shoe is just floating.
BE Mech Sem-VIII/Auto Engg/Module:01 Page 11
=
=.=
2sin
.2
2sin
.2
sinC2
22
2
io
r
r
r
r
rrCT
rCdrrT
o
i
o
i
=
=.=
3sin
.2
3sin
.2
sin2p..
33
32
io
r
r
r
r
rrpT
rpdrrT
o
i
o
i
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Clutch Automobile Engineering Prof. Pradeepkumar Suryawanshi
Therefore net outward radial force (i.e. centrifugal
force) with which the shoe presses against the rimat the running speed,
rmrmrmPPP sco222
16
7
16
9 ===
The friction force acting tangentially on each
shoe,
)( scor PPPF ==
The friction torque acting on each shoe,
RPPRPRFT scorr === )(
And the total friction torque transmitted,
)15()( RPPnT
RPnRnFnTT
sc
orr
=
===
The mass of the shoe can be evaluated fromequation (15).
ii) Size of the shoes:
Let,
l= Contact length of the shoe
b = Width f the shoeR = Radius of the shoe when it
presses
against the pulley rim (same as theinside radius of the pulley)
= Angle subtended by the shoe
at thecentre of spider in rad
p = Intensity of pressure exerted
on theshoe (In order to ensure
reasonable
life, it may be taken as 0.1N/mm2)
Now, Rl=Area of contact o the shoe, lbA =The force with which the shoe presses against the
rim= p . plbA =
Since the force with which the shoe presses
against the rim at the running speed is
sco PPP = ,
Therefore
)16(sc PPplb =
The width of the shoe can be obtained fromequation (16).
iii) Dimensions of the springs:
We have discussed above that the load on thespring is given by,
17(16
9
4
3 22
2
1 rmrmrmPs =
==
By using the load value from eqn (17), the
dimensions of spring may be obtained as usual.
References:
1) Theory of Machines by S S Rattan, Tata
McGraw Hill Education Pvt ltd.2) Automobile Engineering Vol. 1 by Kirpal
Singh, Standard Publishers Distributors.
3) Theory of Machines by R S Khurmi, S
Chand Technical4) Design of Machine Elements by V B
Bhandari, Tata McGraw Hill Education
Pvt ltd.5) http://books.google.com
6) http://www.google.co.in/imghp?
hl=en&tab=wi
BE Mech Sem-VIII/Auto Engg/Module:01 Page 13
http://books.google.com/http://www.google.co.in/imghp?hl=en&tab=wihttp://www.google.co.in/imghp?hl=en&tab=wihttp://books.google.com/http://www.google.co.in/imghp?hl=en&tab=wihttp://www.google.co.in/imghp?hl=en&tab=wi