Elastohydrodynamic Lubrication and Wear of Cams Bearing Against Cylindrical Tappets

This paper offers a theoretical treatment of the lubrication of a cam bearing against a cylindrical reciprocating tappet. The tappet lift, velocity and acceleration are specified as a function of camshaft angle, and the effect of variations in the curvature of the cylindrical face of the tappet is explored, the cam form being modified to maintain a constant tappet lift curve. A certain tappet curvature minimises the Hertzian pressure on the cam nose, but affords very poor lubrication conditions. To avoid high wear it is therefore necessary to purchase better lubrication at the sacrifice of higher Hertzian stresses.