Study On Wear Of Cam In Mixed Lubrication

The relative sliding velocity of the friction surfaces and the contact loads between the cam and tappet of a valve train increase with the increase of power and speed of diesel engines, which result in increasingly worsening working conditions and more serious wear of cam and tappet. In this thesis, as the cam-tappet pair of the valve train in a diesel engine is concerned, using the principles and methods of elastic-hydrodynamic lubrication(EHL) and wear, the wear of the cam is calculated. The main research work is as follows:1).The lubricant oil thickness at different points of on the cam are simulated by the EHL theory. Therefore, the lubrication conditions of various points on the cam can be determined by the result of film thickness and the surface roughness.2). A calculation method of wear coefficient in mixed lubrication is presented according to the lubricating oil film thickness and the roughness distribution of cam surface.3).The wear coefficient of cam material is measured through the test in which the cam tappet material pairing are wearing in boundary lubrication.4). According to the relationship between the wear coefficient and the minimum film thickness, the wear of the cam is simulated based on ARCHARD’s wear equation, and the wear whether run-in is considered or not is compared. The effects of the engine speed, the valve spring preload, and the valve spring stiffness on the wear are also discussed. As the engine speed increases, the wear of the cam decreases due to the increased lubricant oil thickness. With the increase of the valve spring preload and the valve spring stiffness, the wear of the cam also increases due to the bigger contact load and the thinner lubricant oil film.