润滑油温度对铜基湿式离合器摩擦转矩的影响

润滑油的温度变化会改变自身黏度,从而影响摩擦元件的润滑和接触状态,对离合器的动力响应产生显著影响,因此需要研究润滑油温度对湿式离合器摩擦转矩特性的影响。考虑离合器的流体润滑、粗糙接触、动力响应和热量传导,建立一个多物理场耦合的热力学模型;根据润滑油与离合器之间的换热特性,采用集总参数法得到离合器的平均温升。离合器台架试验验证所建立数值模型的准确性。结果表明在离合器的接合过程中,摩擦转矩的变化可分为三个阶段,即接合准备阶段A、缓慢变化阶段B和指数增长阶段C。润滑油温度主要影响阶段B的摩擦转矩。在阶段B早期,润滑油温度越高,黏性转矩越小,接触转矩越大。随后,润滑油温度的升高减缓黏性转矩的下降趋势,促进接触转矩的增加,从而促进摩擦转矩增长率的增加。为了保证离合器在阶段B的摩擦稳定性,最佳的润滑油温度范围为80~100℃。

Influence of the Temperature of Lubricating Oil on the Friction Torque of Cu-based Wet Clutch

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℃.