初始制动时预测湿式制动器热对流特性的积分方法

湿式制动器对重型车辆安全具有关键影响,以湿式制动器摩擦副间隙的冷却液压油(Automotive transmission fluid,ATF)为研究对象,考虑车辆初始制动阶段流体的黏性摩擦和层流流动特征,利用积分方法建立了摩擦副流体的非稳态能量方程,并获得了能同时满足轴向和径向边界条件的三维温度和热流密度显式解析表达式,通过简化动量方程和多项式分布假设也获得了径向速度和压力的理论解,与以往试验对比表明,压力和温度解析解与试验结果具有较好的一致性,理论模型有望推广用于液黏离合器等其他HVD装置的ATF速度场、温度场和热流密度场的理论预测。

Integration Method of Thermal Convection Characteristics Prediction for Unsteady Laminar Flows during Initial Braking Stage of Wet Brakes

A wet brake has a crucial influence on the safety of heavy-duty vehicles. A theoretical thermal analysis is conducted on the automotive transmission fluid (ATF) within a wet brake for initial braking stage. The energy equation of ATF is formulated using the integration method for unsteady laminar flows. An analytical model assuming the polynomial distribution pattern is developed to approximate the temperature rise due to the hydroviscous friction and relative motion between the separator disks and friction disks of the wet brake. The closed-form analytical solutions of three-dimensional (3D) temperature and heat fluxes of convective heat transfer are obtained,respectively,which can satisfy all the boundary conditions for both radial and axial directions. The theoretical expressions of the radial velocity and pressure of ATF are also proposed based on the simplified Navier-Stokes equation. Finally,the temperature rises and pressure predicted by the analytical models are validated by comparing with the previous experimental data. The analytical methods of 3D velocity,temperature and heat flux proposed might have the potentials to be extended to predict those of HVD (hydroviscous drive) devices such as hydroviscous clutches,dynamometers,and so on.