Examination of the Axial Shape of the Automotive Valvetrain Cam for Engine Friction Reduction

Abstract

Friction tests were conducted with a direct-acting automotive valvetrain to evaluate the effect of the axial cross-sectional shape of the cam on friction using various cam shapes from concave to convex. The results revealed that friction levels could be understood as a function of the contact ratio between the cam and mating valve lifter regardless of the cam cross-sectional shape. A flat shape with a high contact ratio was found to have the lowest level of friction. Compared to a convex-shaped cam of the same height, a concave cam tended to show higher friction because of the lower contact ratio with the valve lifter. The results of finite element method (FEM) calculations also showed that the higher contact pressure of concave cams in the contact area was a factor that caused greater friction.