EFFECTS OF LUBRICANT COMPRESSIBILITY ON THE FILM THICKNESS IN EHL LINE AND CIRCULAR CONTACTS

As a first step towards generalized (non-closed-form coefficients in R eynolds' equation) lubricant behaviour, this paper describes the incor poration of the Jacobson and Vinet density pressure equation in a mult ilevel solver for the pressure and the film thickness in an EHL contac t. However, the use of this model is also of interest on its own accou nt, as compression experiments (Jacobson and Vinet, Ramesh) have indic ated limitations to the applicability of the widely used Dowson and Hi gginson equation. In this paper, results of the isothermal steady-stat e line and circular contact are presented and compared with results ob tained assuming an incompressible lubricant and with results employing lubricant compressibility according to the Dowson and Higginson equat ion. The observed phenomena are traced back to Reynolds' equation, and it is shown that the reduction of the central film thickness due to c ompressibility can be predicted easily, regardless of the type of dens ity pressure equation used. In addition it is shown that, using the Ja cobson and Vinet equation, the minimum film thickness in a line contac t, beyond a certain load, may occur in the centre of the contact, inst ead of at the exit. This phenomenon is analysed theoretically, and it is shown to be very unlikely to occur in the circular-contact problem.