The analysis of friction in the bearing of rocker arms

Rocker arms are important parts in many valve train systems of combustion engines. They are responsible for translating the profile of the camshaft into motion for opening and closing the inlet and outlet valves. The design, materials and lash adjuster elements for existing rocker arms were discussed. The modified rocker arm bearing was designed for the investigated Benzer 50cc four-stroke engine. The modification for the analysed engine includes the change of bearing for both inlet and outlet rocker arms. The original rocker arm bearing is of the slide type and mates with the axis fixed via the pin to the cylinder head. The modified bearing can be of the needle roller or the slide type and include two bearings mating with the axis, to which the rocker arm is fixed. The aim of the presented study was to obtain the courses of pressure in cylinder against the crankshaft angle, which was needed to calculate the loading force of rocker arm bearing and then friction torque therein. The models of valve train assembly and of the bearing operating under boundary friction were elaborated. Resulted values of the friction torque in rocker arm bearing for different operating conditions of engine were presented in the paper.