ATF Effects on Friction Stability in Slip-Controlled Torque Converter Clutches

A model of an automotive powertrain equipped with a slip-controlled torque converter clutch (TCC) is presented that incorporates the clutch control system and the friction-related properties of the automatic transmission fluid (ATF) and clutch friction material. Prior research has established that stability of a slip-controlled TCC is enhanced by maintaining a positive slope of the coefficient of friction, μ, with respect to sliding speed, v. The model presented here agrees with this result, but suggests that it is neither a necessary nor sufficient condition guaranteeing stability. The model indicates that other factors affecting stability at the equilibrium sliding speed include the magnitude of μ, the engine speed, the engine torque-speed slope, the ATF pressure, and the time constants of the clutch control system. This model will aid in the development of future wet clutch systems with improved friction stability performance.