Abstract: The temperature change of automatic transmission fluid(ATF) will change its viscosity, which will not simply affect the lubrication and contact statuses of friction components but the clutch dynamic response. Thus, the influence of ATF temperature on the friction torque characteristics should be granted a much higher priority. A coupled numerical multi-physics model is proposed with the fluid lubricating, asperity contact, dynamic response and heat conduction taken into account. Based on the heat exchange characteristics of the clutch and ATF, the lumped parameter method is employed to obtain the clutch average temperature rise. Finally, the clutch bench test is carried out to verify the developed numerical model. The results show that the variation of friction torque can be divided into three stages during the clutch engagement process, namely, the preparation stage A, the slow change stage B and the exponential growth stage C. Notably, the ATF temperature mainly affects the variation of friction torque at stage B. At the early stage B, the higher the ATF temperature is, the smaller the viscous torque is, and the larger the contact torque is. Subsequently, the increase of ATF temperature slows down the decrease of viscous torque and promotes the increase of contact torque, thus contributing to the increase of the growth rate of friction torque. In order to ensure the clutch friction stability at stage B, the optimal ATF temperature range is 80-100℃.

Key words: Cu-based wet clutch, friction torque, ATF temperature, lumped parameter method