Elastic dynamics modelling and analysis for a valve train including oil film stiffness and dry contact stiffness

An elastic dynamics model for a valve train including combined stiffness of oil film and dry contact between a cam and a tappet, is proposed. Multi-directional elastic deformations of the valve train are solved by discretizing slender components into Rayleigh beam and bar elements. The oil film stiffness is determined by non-Newtonian elastohydrodynamic lubrication in the line contact, whereas the dry contact stiffness is achieved by using finite element contact analysis. A numerical solution for the dynamic model is developed and verified by conducting a dynamic stress experiment. The influences of rotation speed on the oil film stiffness and contact force between the cam and the tappet are discussed, and the combined effects of rotation speed and oil film stiffness on a dynamic transmission error of the valve train are analyzed. Results show that the oil film stiffness decreases when the cam rotation speed increases within a certain range, whereas the sharp increased contact force may enlarge the oil film stiffness when the speed exceeds a critical value. The oil film stiffness variation slight influences the contact force, but such variation significantly affects the dynamic transmission error.