The Effects of a Stationary Surface Pocket on EHL Line Contact Start-Up

Abstract

In this paper, the start-up process of line contact elastohydrodynamic lubrication with a stationary central surface pocket is studied. The solution of the pressure profile and film thickness distribution in the contact area is achieved by using a mixed lubricated-solid contact model. The mass balance of pocket lubricant flow is enforced by using a simple algorithm which adjusts the pocket cavitation boundary. With the surface pocket in the center of contact, the Hertzian contact area is divided into two micro-EHL contacts: the inlet micro-EHL contact and the outlet micro-EHL contact. The amount of lubricant trapped inside the pocket determines the overall start-up behavior. If the lubricant trapped is less than a critical amount, the two micro-EHL contact would be in start-up condition in serial: the lubricant film builds up in the inlet micro-EHL contact area first and then the lubricant film builds up in the outlet micro-EHL contact after the inlet lubricant flow fills the pocket. The start-up time in this case is longer than the start-up time for smooth surface start-up. If the lubricant trapped is more than the critical amount, the two micro-EHL contact would be in start-up condition in parallel: a lubricant film builds up in the inlet micro-EHL contact and at the same time a lubricant film builds up in the outlet micro-EHL contact. The start-up time in this case is much smaller than that of the smooth surface start-up. Compared with the smooth surface start-up condition, because the solid contact vanishes faster, there would be less frictional heat generated in the contact area and thus the surface temperature rise during the start-up process would be much smaller. These effects could prove beneficial in applications with frequent start and stop or oscillating running conditions, in which direct solid to solid contact occurs at the start (restart) of motion.