Friction Clutches A clutch enables two coaxial shafts

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

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 k. W. 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 k. N/m 2. 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 k. W 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 k. N/m 2. 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 k. N. If the coefficient of friction is 0. 35 and assuming uniform wear, find the power transmitted by the clutch at 1500 r. p. m. [Ans. 12. 37 k. W]

Problems A multi-plate clutch is to transmit 12 k. W at 1500 rev/min. The inner and outer radii for the plates are to be 50 mm and 100 mm respectively. The maximum axial spring force is restricted to 1 k. N. Calculate the necessary number of pairs of surfaces if =0. 35 assuming constant wear. What will be the necessary axial force? (Answer, 3; 970 N)

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

F=mrω2 Centrifugal clutch ω Driving shaft R Friction lining Total friction torque , P Driven shaft T = nµR(F-P) ω