Friction Clutches
A clutch enables two co-axial shafts to be
engaged or disengaged while at rest or in
relative motion.
Types of Friction Clutches
1. Disc or plate clutches
2. Cone clutches
3. Centrifugal clutches
Flat-plate friction clutches
Friction
plate
springs
W
Driving
shaft
T
Pressure
plates
Single-plate Friction Clutch
W (axial thrust)
T
Driven
shaft
Friction
lining
(Disengaged position)
Flat-plate friction clutches
Friction plate
W
Driving
shaft
T
Pressure
plates
Single-plate Friction Clutch
springs
W (axial
thrust)
T
Driven
shaft
Friction
lining
(Engaged position)
Flat-plate friction clutches
An example is the clutch found in most
automobiles.
Clutch plate or friction plate
Torsional
springs
Splined boss
(hub)
Friction
lining
Pressure plate and housing
Clutch
housing
Diaphragm
spring
Pressure
plate
Multi plate clutches
In a multi plate clutch, the torque is
transmitted by friction between several pairs
of co-axial annular driving faces maintained
in contact by an axial thrust.
Both sides of each plate are lined with friction
material, so that a single-plate clutch has two
pairs of driving faces in contact.
Multi plate clutches
n = no. of pairs of driving faces.
Then, for a plate clutch, the maximum
torque transmitted is
T  n  Wr m
Multi plate clutch
Pressure plates
1
2 3 4 5 6
driven
driver
No. of driving
pairs n = 6
Friction plates
Exercise Problems
Problem 15
A car engine has its rated output of 12 kW. The
maximum torque developed is 100 N-m. The clutch
used is of single plate type having two active surfaces.
The axial pressure is not to exceed 85 kN/m2. The
external diameter of the friction plate is 1.25 times
the internal diameter. Determine the dimensions
of the friction plate and the axial force exerted by the
springs. Coefficient of friction = 0.3
[Ans. 129.5 mm ; 103.6 mm ; 1433 N]
Problem 16
A single plate clutch (both sides effective) is
required to transmit 26.5 kW at 1600 r.p.m.
The outer diameter of the plate is limited to
300 mm and intensity of pressure between
the plates is not to exceed 68.5 kN/m2.
Assuming uniform wear and a coefficient of
friction 0.3, show that the inner diameter of
the plates is approximately 90 mm.
Problem 17
A multi plate clutch has three pairs of contact
surfaces. The outer and inner radii of the
contact surfaces are 100 mm and 50 mm
respectively. The maximum axial spring force
is limited to 1 kN. If the coefficient of friction is
0.35 and assuming uniform wear, find the
power transmitted by the clutch at1500 r.p.m.
[Ans. 12.37 kW]
Problems
A multi-plate clutch is to transmit 12kW at
1500rev/min. The inner and outer radii for the
plates are to be 50mm and 100mm respectively.
The maximum axial spring force is restricted to
1kN. Calculate the necessary number of pairs of
surfaces if =0.35 assuming constant wear. What
will be the necessary axial force?
(Answer, 3; 970N)
Cone clutch
α = semi-apex angle of
the cone
α
Only one pair of driving
surfaces is possible, n =1
w
Driven
shaft
Driving
shaft
Friction
lining
The maximum torque transmitted =
T = μWrm cosecα
Centrifugal clutch
ω
F=mrω2
P
Driven
shaft
ω
Driving
shaft
Friction lining
Total friction torque , T = nµR(F-P)