A Study of the Effects of Ceramic Tappet Shim Surface Roughness on the Friction Characteristics in the Valve Train System

摘要

A Si_3N_4 tappet shim was developed in a direct OHC engine for the friction reduction of valve train system that contributes significantly to the engine friction in real driving condition. For commercializing Si_3N_4 tappet shim, it is important to reduce the machining cost. Therefore we analytically and experiemntally figure out the optimum condition. Using ceramic tappet shims machined with different surface roughness, the effects of roughness on the friction loss were analyzed in view of the lubrication behavior. In this experiment needle bearings were installed in the camshaft journal bearing in order to concentrate on the friction behavior in sliding cam/tappet contacts. Friction loss quickly drops at a certain roughness and its value remains constant despite further smoothing.