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 Disc or plate clutches Cone clutches Centrifugal clutches

Single-plate Friction Clutch (Disengaged position) Flat-plate friction clutches Friction plate springs W Driven shaft W (axial thrust) Driving shaft T T Friction lining Pressure plates Single-plate Friction Clutch (Disengaged position)

Single-plate Friction Clutch (Engaged position) Flat-plate friction clutches T W (axial thrust) W Friction plate Friction lining Pressure plates springs Driving shaft Driven shaft Single-plate Friction Clutch (Engaged position)

Flat-plate friction clutches An example is the clutch found in most automobiles.

Clutch plate or friction plate Torsional springs Friction lining Splined boss (hub)

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 driver driven No. of driving pairs n = 6 Pressure plates Friction plates 2 1 4 3 6 5 No. of driving pairs n = 6

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 w T = μWrm cosecα Only one pair of driving surfaces is possible, n =1 α w Driving shaft Driven shaft Friction lining The maximum torque transmitted = T = μWrm cosecα

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