Research On The Influence Of Cam Wear On Dynamic Performance Of Valve Trains

A valve train is the gas exchange mechanism in an internal combustion engine,and its performance has an important influence on the performance of the internal combustion engine.With the increasing high demands of the internal combustion engine,power and speed of a diesel engine are becoming higher and higher r,which results in a worse contact between the cam and the tappet,and thus the phenomenon of cam wear becomes more and more serious.Wear of cam will lead to the change of cam profile,which will affect the accuracy of the motion,and have a great influence on a valve train’s performance.In this paper,as the cam-tappet pair of the valve-train in one diesel engine is concerned,the wear of the cam is calculated by the principles and methods of elastic-hydrodynamic lubrication(EHL)and friction,and the changes of the valve train’s dynamic performance before and after cam wear were analyzed.The main research work is as follows:1).Multi-body dynamics method was used to simulate and evaluate the dynamic performance of the valve train of one diesel engine.2).Based on the EHL theory,the lubricant oil thickness between the cam and tappet contact points were calculated.According to the minimum oil film thickness and the surface roughness,the lubrication condition of different points on the cam has been judged.3).According to the relationship between the wear coefficient and the minimum oil film thickness,the wear coefficient of the cam has been obtained.Based on the quasi-static method and the Archard’s wear equation,the wear of the cam was calculated and the cam profile after wear was obtained by the dynamic wear calculation program developed in this paper.The effects of the engine speed on the wear are also discussed.4).Based on the kinematics and dynamics simulation,the valve train’s dynamic performance under different wear was calculated,and the valve’s displacement,velocity,acceleration,time-area value,cam’s ample factor were analyzed.The variation of the contact force,the entrainment velocity and the minimum oil film thickness of the cam-tappet pair were also analyzed.The wear trend was also analyzed and the wear life was predicted as well.The results show that the valve’s time-area value and ample factor are reduced because of the cam wear,which will reduce the charging coefficient significantly of the engine.