Experimental Study On Lubrication Film Of Eccentric Ball-disk Contact Pairs

The lubrication of cam-tappet pairs in the valve train of internal combustion engines plays an important role in theirs service life.Thus,a lot of work has been carried out to analyze the lubrication in contact pairs by researchers at home and abroad.Cam-follower pairs are difficult to simulate numerically because of the unconstant curvature radius,speed,load,as well as the large sliding-roll ratio experienced by the film.In the mean time the measurement of lubrication films is also hard work.In this dissertation,a custom-made optical elastohydrodymanic lubrication measurement system,aimed at an eccentric ball-disk contact,which is a particular cam-follower mechanism,has been developed and the characteristics of transient lubricant film in this contact pair were studied,and it is expected that the present studies can provide some fundamentals for measurement of lubrication film of common cam-tappet contact pairs.Meanwhile,the lubricant replenishment are explored to promote lubrication of cam-follower contact under the condition of limited oil supply.The main work includes:(1)The design and construction of an optical eccentric ball-disc contact-testing system have been completed.Loading unit,friction measurement unit,electronic control box and transmission unit based on rocker arm swing were deigned and assembled.(2)Experimental measurement of lubrication films has been carried out for the eccentric ball-disc contact.The influences have been investigated of rotational speeds,initial preloading loads,eccentricity and lubricant viscosity with stationary disc.(3)Lubricant replenishment by stepped wettability has been proposed and shown to have significant effects on lubricant reflow and film building.Stepped wettability was achieved by modification of surface energy of the contact surfaces,and the distribution of oil bath and the film thickness in the contact zone were studied with different rotational speeds and oil supplies.(4)Using numerical calculation the EHL of eccentric ball-disc contact was simulated and the related EHL behaviors have been studied.Some experimental results were analyzed.