Clutch Parameter Effects on Torque and Friction Stability

Approximation formulas are presented for the time response of the film thickness and torque in a wet clutch. The approximation formulas show the effects of various clutch parameters on the film thickness, the hydrodynamic torque and the asperity torque. Clutch parameters affecting the film thickness and torque include friction material characteristics, lubricant properties, the geometry of the clutch plates and the time-dependent apply pressure. The approximation formulas are obtained from heuristic curve fits of previously published and validated models. It is also shown that a positive gradient (dT_f/dω_slip > 0) of the friction torque, T_f, with respect to slip speed, ω_slip, promotes friction stability. This stability gradient is obtained analytically using the approximation formulas so that the effects of the clutch parameters on friction stability are also shown. These formulas can help hardware designers, friction material developers, lubricant formulators and control calibrators improve the torque capacity and friction stability of clutches for diverse operating conditions.