船用柴油机凸轮动态摩擦学分析及型线优化设计

Marine Diesel Engine Cam Dynamic Tribological Analysis and Profile Optimization Design

柴油机配气凸轮工作环境较为恶劣,工作过程中配合界面间载荷、速度及曲率半径等工况周期性变化,导致润滑接触条件苛刻,磨损情况恶劣。以某船用柴油机配气凸轮机构典型工况为算例,针对凸轮-挺柱常见的磨损问题,研究凸轮-挺柱动态接触特性;采用余弦-等速段和高次五项式对凸轮型线进行优化设计,并对凸轮-挺柱副动态接触及弹流润滑状态进行数值分析。结果表明:原凸轮磨损的原因是凸轮-挺柱副在运动周期内动态接触应力出现明显波动,最大值超过许用应力值;经型线优化设计后,凸轮-挺柱动态接触应力降到许用值以下,改善了动态接触特性,凸轮型线具有较好的润滑特性,运行过程中可保持较稳定的油膜润滑状态;凸轮转速和接触载荷的改变会直接影响凸轮-挺柱的润滑状态,尤其是随凸轮转速增大,润滑膜厚增大,压力减小,润滑接触状态明显改善。

The working environment of the diesel valve cam is relatively harsh,during the working process,the working conditions such as the load,speed and radius of curvature between the interfaces change periodically,resulting in harsh lubrication contact conditions and poor wear.The typical working condition of the valve cam mechanism of a marine diesel engine was taken as an example,for the common wear problems of the cam-tappet,the cosine-constant speed section and high-order pentathine were used to optimize the design of the cam profile,the dynamic contact and elastohydrodynamic lubrication of cam-tappet pair were analyzed.The results show that the reason for the wear of the original cam is that the dynamic contact stress fluctuates significantly during the movement period of the cam-tappet pair,and the maximum value exceeds the allowable stress value.After the optimized design of the profile,the dynamic contact stress of the cam-tappet is reduced below the allowable value,which improve the dynamic contact characteristics.The cam profile has good lubrication characteristics and can maintain a stable oil film lubrication state during operation.The change of cam speed and contact load will directly affect the lubrication state of cam-tappet,especially with the increase of cam speed,the lubrication film thickness is increased,the pressure is decreased and the lubrication contact state is improved.