A tribological study of roller follower valve trains. Part 1: A theoretical study with a numerical lubrication model considering possible sliding

摘要

In this paper, a lubrication model for roller follower valve trains considering possible sliding of the roller on the cam surface has been developed. Based upon this model, an end pivoted roller follower valve train was studied focusing upon itstribological performance. Theoretical studies showed that during most of one cam cycle, the roller rotated with the same surface velocity as that of the cam relative to the contact point. At high camshaft rotational frequencies, however, sliding may takeplace on the cam flanks where the acceleration of the surface of the cam is the highest. Compared with fixed-pad follower valve trains, the tribological performance of roller follower valve trains is significantly enhanced by the thicker lubricant film at the cam/roller contact. The power loss at the cam/roller interface was also calculated based on the elastohydrodynamic lubrication theory and it was found that this power loss was very low, the friction loss reduction being due to the essentially rollingmotion between the cam and the follower.