Mixed lubrication analysis of cam/tappet interface on the direct acting type valvetrain system

This paper reports on the mixed lubrication characteristics between the cam and the tappet contact surface of direct acting type valve train systems. First, the dynamic characteristics are solved by using the lumped mass meth od to determine the load conditions at the contact point. Then, the minimum oil film thickness is calculated with consideration of elastohydrodynamic line contact theory and the friction force is obtained by using the mixed l ubrication model which separates the hydrodynamic and the boundary friction . Finally, the average surface temperatures are calculated by using the fla sh temperature theory. The results show that, there are some peaks in the f riction force due to the asperity contact friction, and flash temperature a t the position of minimum oil film thickness. It is thought that there is a relationship between the surface temperature and cam surface wear, and the refore, the analysis on the worn cam profile has been performed.