车用空载湿式离合器高速碰撞摩擦特性及带排转矩分析

Rub-impact Characteristics and Drag Torque at High Circumferential Velocities in No-load Multi-plate Wet Clutch for Vehicles

试验发现高速空载工况下湿式离合器易出现摩擦片和钢片之间的碰撞摩擦(简称碰摩),由此引起离合器带排转矩的急剧增大,高速带排对传动装置的效率和可靠性会造成重大影响,因此建立可靠的摩擦副碰摩模型用来探究高速带排的演变规律十分有必要。采用小扰动法获得间隙流场的刚度和阻尼,积分得到流体力;分析摩擦片与钢片碰摩过程中的弹性变形和能量损失,构建摩擦副的碰撞接触力和摩擦力方程;在此基础上,考虑流体力、碰撞力、摩擦力以及对偶摩擦片与钢片之间的运动耦合,建立多摩擦副流体与固体耦合碰摩动力学模型,利用4阶龙格-库塔法求解,研究摩擦副非线性运动的分岔和混沌特征。结果表明:当摩擦副未发生碰摩时,摩擦片和钢片运动稳定,呈现周期性运动规律;当摩擦副发生碰摩时,在轴向碰摩力作用下,摩擦片和钢片运动失稳,呈现混沌运动状态;随着润滑油流量的增大,摩擦副发生碰摩的临界转速提高,但是摩擦副的碰摩频率也会提高,导致带排转矩增大。

It is found in experiments that the rub-impact between friction plate and steel plate is easy to appear in the high-speed no-load wet clutch,which results in the sharp increase in drag torque.The high-speed drag torque has significant negative influence on the efficiency and reliability of transmissions.So it is necessary to establish a reliable rub-impact model of friction pair to explore the change law of high-speed drag torque.The fluid stiffness and damping are derived to obtain the fluid forces by small perturbation method.The elastic deformations and energy loss in the process of rub-impact between friction plate and steel plate are analyzed to establish the rubbing function of friction pairs.On this basis,the fluid force,rub-impact force,friction,and coupling motion between the friction plate and steel plate in three degrees of freedom are taken into consideration to establish a fluid-solid coupling rub-impact dynamic model for multi-plate wet clutch,which is solved by fourth-order Runge-Kutta method.Then the bifurcation and chaos characteristics of non-linear motion of friction pairs are analyzed.The research results indicate that,when the friction pair does not contact,the friction/steel plates move stably and show periodic movement rule;when the friction pair impacts,the friction/steel plates lose stability and show chaotic motion under the action of axial rub-impact force;and with the increase in the flow rate of lubricating oil,the critical rub-impact speed of friction pair climbs,but the rub-impact frequency also grows,resulting in the increase in the drag torque.