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

세라믹 태핏심 표면 거칠기에 따른 엔진 밸브트레인계의 마찰 특성에 관한 연구

A $Si_3N_4$ tappet shim was devdoped 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 experimentally 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. From this results it is shown that the friction torque of valve train system quickly drops at a certain surface roughness of ceramic tappet shim and its value remains constant despite further smoothing.