The analysis of the dynamic contact stresses occurring in the valve-camshaft system of the internal combustion engine

摘要

The work analyzes the dynamic contact stresses, taking into the consideration shear stress occurring between the cam and the follower in the valve-camshaft system of a high speed engine. After calculating the dynamic and friction forces as the function of the rotational speed of an engine, the method of calculating contact stresses is presented. The results of calculations are also presented as a function of angle of rotation of the camshaft. In the dynamic model the effect of the rebound phenomenon on the instantaneous increase of Hertzian stresses was considered. The places of the potential damage of the surfaces of the cams are listed. The results of the analysis are presented as a function of the angle of rotation of the camshaft for the varying speeds of an engine. The maximum permissible speed of an engine was determined, above which the allowable contact stresses are exceeded. At the end of this paper the proposal of changing the cam shape of the camshaft is presented, so that to allow the increase in the maximum allowable rotational speed of an engine. This can be done without increasing the stiffness of springs, which allows us to maintain the same (not increased) contact stresses at the increased rotational speed of an engine.