1. Unit -V CAMS, CLUTCHES AND BRAKES Presented By Dr. C. Saravana Murthi Asst. Professor Dept. of Mechanical Engg. United Institute of Technology

2. Contents About the Transmission system Definition of Clutch Classification of clutches Positive Contact Clutches Outline of Single Plate Clutch Mechanical Model of Single plate Torque Transmitting Capacity Problems

3. The mechanism that transmits the power developed by the engine of automobile to the driving wheels is called the TRANSMISSION SYSTEM. Transmission System in Automobile

4. Introduction Define Clutch The clutch is a mechanical device, which is used to connect or disconnect the source of power from the remaining parts of the power transmission system at the will of the operator.

5. Classification of Clutches

6. Two halves carrying projections or halves One half is fixed and the other can move along the axis Jaws of moving half enter into socket of mating half Eg. Square jaw, spiral jaw Advantages No slip and positive engagement No heat during engagement/disengagement Drawbacks Engagement only when stationary or rotate at very low speed High speed engagement results in shocks Positive Contact Clutches

8. Consists of two flanges, one rigidly keyed to driving shaft and one connected to driven shaft with splines Actuating force is given by spring. Power transmission between driving and driven flange is through friction. Fork inserted on the collar of the driven flange for axial movement of driven flange. Outline of Single Plate Clutch

9. Friction Clutch: Single plate

10. Video - Friction Clutch: Single plate

11. Video - Friction Clutch: Multi plate Clutch

12. Friction Clutch: Single plate Advantages Smooth engagement Slip only during engagement Acts as safety device

13. Design Considerations for Single plate Design Considerations Selection of type of clutch Selection of friction material of contact surfaces Designing for sufficient torque capacity Smooth engagement/disengagement Provision for holding contact surface without any external assistance Low weight of rotating parts to reduce inertia forces Provision for taking or compensating wear Provision for carrying away the heat generated

14. Mechanical Model Two inertia’s I 1 and I 2 traveling at the respective angular velocities ω I and ω 2 and one of which may be zero, are to be brought to the same speed by engaging. Slippage occurs because the two elements are running at different speeds and energy is dissipated during actuation, resulting in temperature rise. Mechanical Model of Single plate

15. D : Outer diameter of friction disc (mm) : Do d : Inner diameter of friction disc (mm) : Di p : Intensity of pressure at radius r (N/mm2) : p P : Operating axial force (N) : Fap Mt : Torque transmitted (N-mm) : T μ : Friction coefficient : μ r : radius of the element dr from the centre of the disc : r Single plate clutch - Torque transmitting capacity

17. Conclusions Uniform pressure theory applicable for new friction lining Uniform wear theory applicable for worn-out friction lining Friction radius for new clutch is slightly greater than worn-out clutches Torque transmitting capacity of new clutch slightly higher Major life of friction lining comes under uniform wear criterion Logical and safer to use uniform wear theory in design of clutches

18. Factors Considered for design Service factor: To compensate for the starting torque Location of clutch: Low torque capacity requirement Coefficient of friction

19. Problem – 1 - Single plate clutch Determine the maximum, minimum and average pressure in a plate clutch when the axial force is 4 kN. The inside radius of the contact surface is 50 mm and the outside radius is 100 mm. Solution: Solution. Given : W = 4 kN = 4000 N ; r 2 = 50 mm ; r 1 = 100 mm Maximum pressure Let P max = Maximum pressure. Since the intensity of pressure is maximum at the inner radius (r 2 ), therefore P max × r 2 = C or C = 50 P max We also know that total force on the contact surface (W), 4000 = 2 C (r 1 – r 2 ) = 2 × 50 P max (100 – 50) = 15 710 P max P max = 4000 / 15 710 P max = 0.2546 N/mm 2

22. Problem – 2 - Single plate clutch A single plate clutch, effective on both sides, is required to transmit 25 kW at 3000 r.p.m. Determine the outer and inner diameters of frictional surface if the coefficient of friction is 0.255, ratio of diameters is 1.25 and the maximum pressure is not to exceed 0.1 N/mm 2. Also, determine the axial thrust to be provided by springs. Assume the theory of uniform wear.

24. ∴ Outer diameter of frictional surface, d 1 = 2 r 1 = 2 × 120 = 240 mm Inner diameter of frictional surface, d 2 = 2 r 2 = 2 × 96 = 192 mm Axial thrust to be provided by springs, W = 2π C (r 1 – r 2 ) = 2π × 0.1 r 2 (1.25 r 2 – r 2 ) = 0.157 (r2)2 = 0.157 (96)2 = 1447 N Result (i)Outer diameter of frictional surface, d 1 = 240 mm (ii)Inner diameter of frictional surface, d 2 = 192 mm (iii)Axial thrust to be provided by springs, W = 1447 N

25. A multiple disc clutch has five plates having four pairs of active friction surfaces. If the intensity of pressure is not to exceed 0.127 N/mm 2, find the power transmitted at 500 r.p.m. The outer and inner radii of friction surfaces are 125 mm and 75 mm respectively. Assume uniform wear and take coefficient of friction = 0.3. Problem – 3 - Multi plate clutch Solution: Given : n1 + n2 = 5 ; n = 4 ; p = 0.127 N/mm 2 ; N = 500 r.p.m. ; r 1 = 125 mm ; r 2 = 75 mm ; μ = 0.3 For uniform wear, p. r = C (a constant). Since the intensity of pressure is maximum at the inner radius (r 2 ), therefore, p.r 2 = C C = 0.127 × 75 = 9.525 N/mm Axial force required to engage the clutch, W = 2 πC (r 1 – r 2 ) = 2π × 9.525 (125 – 75) W = 2993 N