Paper XX(i) Mixed lubrication of a cam and flat faced follower

Abstract

Considerable attention has been focussed upon the mechanical power losses in internal combustion engines in recent years. Broadly speaking these may be of the order of 15% of the fuel energy. Most of these losses can be attributed to the friction associated with the lubricated machine elements in the engine, namely piston ring assembly, bearings and valve train components. Development of the understanding of the operational characteristics of dynamically loaded engine bearings and piston rings is more advanced than that of the valve train, particularly the cam and follower. The work described in the present paper represents part of a continuing study of cam and follower lubrication characteristics. It is widely thought that the cam and follower contact operates with a degree of surface interaction for virtually the whole of its cycle. As an initial step towards the understanding of surface topography influences, a rigid surface model for the mixed lubrication of a cam and follower is developed in this paper. Results are presented to demonstrate the effect of surface roughness and its distribution upon nominal film thickness, the load carried by the asperities and power loss. The proportion of the total load carried by the asperities and the proportion of power loss associated with asperity contact are detailed. The influence of lubricant viscosity and camshaft speed upon nominal film thickness during the cycle are also discussed.