活塞销轴承混合润滑特性研究

Analysis of the Performance of Piston Pin Bearing in Mixed Lubrication

基于弹流润滑理论、平均流量模型及微凸峰接触理论,对发动机活塞销轴承的混合润滑进行了研究。首先,将活塞销孔轴承与活塞销及连杆小头轴承作为一个系统,利用四阶的龙格库塔方法求解了活塞销在流体润滑状态下的转动速度。结果表明:采用此方法得到的活塞销转动速度变化规律与采用谱分析方法所得到的结果十分接近。其次,数值求解了考虑弹性变形时油膜压力分布和微凸峰接触压力的分布,考察了不同发动机转速对活塞销轴承最小膜厚比和摩擦力大小的影响。结果表明:活塞销轴承从发动机工作循环压缩冲程后半段到排气冲程的前半段时间内,处于混合润滑状态;随着发动机从低转速到高转速的过程中,活塞销轴承所受的摩擦力开始逐渐减小,当发动机的转速增加到某一临界转速后,活塞销轴承所受的摩擦力反而明显增加;在考虑活塞销轴承的弹性变形之后,接触压力的分布沿轴向发生了变化,且呈现中间小两边大的形态,与实际发动机活塞销轴承的破坏规律相符。

Based on the EHL theory, the average flow model and the asperity contact theory, the study is presented for mixed lubrication of piston pin bearing. Firstly, the piston pin boss bearing, the piston pin and the connecting rod small end bearings were taken as a whole system, and the fourth-order Runge-Kutta method was used to solve the rotation speed of the piston pin operating in hydrodynamic lubrication. Good agreement is obtained among the results when the spectral technique was used. Secondly, the oil film pressure distribution and the asperity contact pressure distribution were numerically solved when elastic deformation was taken into consideration, and the effect of engine speed on the minimum film thickness ratio and friction distribution was analyzed. The results showed that piston pin bearing was operating under mixed lubrication condition from the latter period of the compression stroke to the first period of the exhaust stroke of engine cycle. Friction of piston pin bearing decreases during the process while the engine speed is up to a critical value, and friction increases obviously when engine speed is over the critical value. Once elastic deformation is taken into the consideration, the contacting pressure distribution will be changed in axial direction, with the pattern of small pressure value in the middle and large value at the ends. This shows the same failure behavior of piston pin bearing.