A clutch enables two co-axial shafts to be engaged or disengaged while at rest or in relative motion.

Friction Clutches

Types of Friction Clutches

1. Disc or plate clutches2. Cone clutches3. Centrifugal clutches

T

TW (axial thrust)W

Friction plate

Friction lining Pressure

plates

springs

Single-plate Friction Clutch (Disengaged position)

Driving shaft

Driven shaft

Flat-plate friction clutches

Single-plate Friction Clutch (Engaged position)

T

TW (axial thrust)

WFriction plate

Friction lining

Pressure plates

springs

Driving shaft

Driven shaft

Flat-plate friction clutches

An example is the clutch found in most automobiles.

Flat-plate friction clutches

Torsional springs

Splined boss (hub)

Friction lining

Clutch plate or friction plate

Pressure plate

Diaphragm spring

Clutch housing

Pressure plate and housing

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

mWrnT

Multi plate clutches

No. of driving pairs n = 6

driver driven

Pressure plates

Friction plates

21 43 65

Multi plate clutch

Exercise Problems

Problem 15A car engine has its rated output of 12 kW. The

maximum torque developed is 100 N-m. The clutchused 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 dimensionsof 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)

Driving shaft

Driven shaft

Friction lining

α

The maximum torque transmitted =

α = semi-apex angle of the cone

Only one pair of driving surfaces is possible, n =1

Cone clutch

T = μWrm cosecα

w

Centrifugal clutch

Driving shaft

Driven shaft

Friction lining

Total friction torque , T = nµR(F-P)

F=mrω2

ω

ω

P

R