Temperatures Reached in Friction Clutch Transmissions

Expressions are given to determine the torque capacity of a clutch and the rate at which heat is dissipated by dry friction during a single clutch engagement, together with equations to enable calculation of the rubbing-path temperatures as well as temperatures at various depths inside the contacting bodies during the slipping period. It is shown how the maximum friction surface temperature varies with the thickness of the pressure plate and for design purposes a rapid method of calculating temperatures is given when the slipping time is known. Some curves showing the agreement between temperatures determined theoretically and measured experimentally inside a clutch facing during continuous slipping are given. The temperatures attained after regular repeated clutch engagements are considered when cooling is by convection alone and a method of calculation is outlined, when in addition to convection losses radiation losses need to be taken into account. A formula is given to enable the area of the rubbing path to be calculated if the temperature is not to exceed a specified value. In an appendix the temperatures are calculated when the torque linearly decreases with slipping speed and a comparison is made with the case when the torques are assumed to be constant.