Friction Clutch

Introduction

The power is transmitted by friction surfaces between driver and driven shaft. The frictional contact is made by engaging two discs having friction surface made of metal, woven, or ceramic material. The engagement of two friction surface is made by helical compressive spring.

The friction-clutch design, besides allowing for the main requirements (minimum clutch weight, simplicity, of construction, high reliability, and others), should ensure the following:

• Reliable transfer of engine torque to the transmission in all service conditions.
• Smooth starting of the automobile from rest and complete engagement of the clutch.
• Proper disengagement, i.e. complete disconnection of the engine form the transmission with guaranteed clearance between friction surfaces.
• Minimum moment of inertia of driven elements of the clutch, which permits smoother shifting of gears and reduces the wear of the friction surfaces in the synchronizer.
• Necessary heat rejection from friction surfaces.
• Safeguards the transmission against dynamic loads.
• Convenience and ease of control, which are estimated by the effort to be applied to the pedal and pedal movement on disengaging the clutch.

Clutch Frictional Material

Clutch friction linings are subjected to severe rubbing so that generation of heat in relatively short periods takes place. Therefore, the lining material should have a combination of the following properties to withstand the operating conditions.

• Relatively high coefficient of friction under entire operating conditions.
• Maintenance of friction properties during entire working life.
• Relatively high energy absorption for short periods.
• Withstanding high pressure plate compressive loads.
• Withstanding high impacts of centrifugal force during gear changing.
• Adequate shear strength to transmit engine torque.
• High level of endurance in cyclic working without effecting friction properties.
• Good compatibility with cast iron facings over the entire range of operating tempera­ture.
• A high degree of tolerance against interface contamination without affecting its friction take-up and grip characteristics.