Surface Feature Effects in Starved Circular EHL Contacts

Computation of the EHL film thickness of micro-pitted surfaces for starved elastohydro-dynamic conjunctions has been performed. Transient calculations have shown that pits filled with lubricant release part of their content in the inlet zone as they enter the EHL contact. Initially, a fraction of this released oil remains in the inlet region and produces an upstream shift of the meniscus. The remainder of the oil is entrained and builds up the film thickness at the trailing edge of the pit. With time, the fraction of oil in the inlet also becomes entrained and the meniscus slowly returns to its equilibrium position. The time interval during which the film thickness is enhanced thus becomes prolonged and may persist even after the pit has left the contact. Computations carried out with several pits have shown that this process is not disturbed. The beneficial increase of film thickness is lost if the contact becomes fully flooded. Experimentally, the advantage of making small recesses in bearing surfaces has been shown before. This paper now reveals the lubrication mechanisms involved, allowing improvements in the design of surface features in EHL contacts.