The transition between fully flooded and starved regimes in EHL

Abstract

Lubricant starvation of the contact can occur in high-speed oil or grease lubricated bearings resulting in reduced elastohydrodynamic (EHL) film thickness (Lubricat. Sci. 11 (1999) 227). To achieve optimum bearing performance and component life, it is obviously desirable to be able to predict when starvation will occur and the resulting level of surface protection. For both oils and greases, the transition between fully flooded and starved behaviour is determined by lubricant loss and replenishment of the track (ASME Trans. J. Tribol. 120 (1998) 126; Cann PME, Chevalier F, Lubrecht AA. Track depletion and replenishment in a grease lubricated point contact: a quantitative analysis. Proceedings of the 23rd Leeds–Lyon Symposium on Tribology. 1996. p. 405–14). The current paper develops a criterion for the fully flooded and starved transition of an oil-lubricated contact based on four primary factors controlling lubrication level; these are volume of oil, contact dimensions, oil viscosity and speed. Experiments have been carried out using an optical EHL device to investigate the effect of each of these parameters on starvation. The results show how the boundary between the fully flooded and the starved regime and the film thickness in the starved regime depend on these parameters. A single dimensionless parameter (SD), based on replenishment local to the contact, has been established between the operating parameters and the transition from the fully flooded to starved regime. In this paper, the starvation criterion has been developed for an oil-lubricated contact with a fixed volume of oil present. The next stage is to extend the analysis to grease and the prediction of lubrication failure in bearings.