Research On The Contact Stress Of The Cam-tappet Friction Pair And Coating Experiment

In order to improve the reliability and lifetime of the timing valve system of thehigh-power engine, the contact stress of the cam-tappet friction pair is calculated andanalyzed in this paper.With the elasticity of the transmission chain of the timing valve system, the moving ofthe air valve is not according to the outline of the cam. The elastic deformation also makesthe contact force of the cam-tappet pair greater. The displacement, speed and accelerationof the air valve, as well as the contact force and stress can be calculated by the single-massdynamic model. And the finite element method (FEM)is also used in analyzing the contactstress. The results show that the dynamic model is more closing the reality than the stiffnessmodel. But the trends of them are similar. According to the simulation result, thedistribution of the contact stress is different from the description of the Hertz contact theory.The max value of simulation contact stress is larger than that calculated by Hertz formula.Adding coating in the friction surface of the parts can reduce the wear effectively.High velocity oxygen fuel (HVOF) technique is used to build the WC-12Co wear-resistingcoating; atmospheric plasma spraying (APS) and laser cladding technique are used toprepare Fe-based composite wear-resisting coating; magnetron sputtering technique is usedto make DLC anti-friction coating; bonding methord is used to prepare MoS2-basedanti-friction coating. The wear properties of wear-resistant and anti-friction compositecoating were tested using MRH-3high-speed ring block wear testing machine. The resultshows that the friction pair of ring with WC-12Co wear-resisting coating and block withFe-based composite wear-resisting coating can make a lower coefficient of friction. Andcoefficient of friction can be reduced by the MoS2-based anti-friction coatings. But it isinstable.