Investigating the effects of coating on cam/tappet thermal elastohydrodynamic lubrication through numerical simulation has great significance in the design of coated cam/tappet conjunctions. This paper presents a numerical model for the prediction of the thermal elastohydrodynamic lubrication of a coated cam/tappet and the results of a study of the effects of coating parameters on cam/tappet lubrication performance. In the model, the Reynolds equation is solved by the damped Newton method to obtain the pressure distribution, and energy equations are used to obtain the temperature distribution. The total elastic deformation is calculated by the finite element method. The effects of the coating's mechanical properties on pressure and temperature were found to be significant, as were the effects of the coating's thermal properties on temperature. These effects were found to increase with increasing coating thickness. A soft coating with low thermal inertia has the greatest ability to reduce friction loss, and the higher the inlet temperature is, the lower the friction loss is. The influence of coating of both the cam and tappet on friction loss is greater than the effect of coating of the tappet only, which is greater than the effect of coating of the cam only.

Purpose This paper aims to investigate the lubrication performance of cam/tappet contact during start up. Especially, the thermal insulation effects of coating on the lubrication performance during cold start up process and warm start up process are studied. Design/methodology/approach A numerical model for the analysis of thermal elastohydrodynamic lubrication of coated cam/tappet contact is presented. In this model, the Reynolds equation and the energy equations are discretized by the finite difference method and solved jointly. Findings During start up, the contact force at cam nose-to-tappet contact decreases with increasing time, while the absolute entrainment velocity has the upward trend. The minimum film thickness, maximum average temperature and friction power loss increase with increasing time, while the coefficient of friction decreases during start up. Because of the thermal insulation effect, the coating can significantly increase the degree of temperature rise. Compared with the uncoated case, the coated cam/tappet results in a lower friction power loss. Generally, the friction power loss in the cold start up process is much higher than that in the warm start up process. Originality/value By this study, the lubrication performance and the kinematics and the dynamics of the cam/tappet during start up process are investigated. Meanwhile, the thermal insulation effect of coating is also illustrated. The difference of lubrication performance between cold start up process and warm start up process is analyzed. The results and thermal elastohydrodynamic lubrication method presented in this study can be a guidance in the design of the coated cam/tappet.