Modelling Non-Steady EHL with Focus on Lubricant Density

Abstract

A pressure increase has an effect on several physical and rheological properties such as, e.g., viscosity and density in an ehl contact. Results from dynamic dilatometry measurements, using a split-Hopkinson bar test rig, and the Roeland viscosity-pressure relation have been introduced into the governing equations for EHL pressure and oil film thickness. 5P4E shows a relatively stiffer behaviour than given by the conventionally used Dowson-Higginson equation whereas PAO shows a weaker behaviour. This difference results in different pressure and film thickness profiles. The stiffer 5P4E gives a slightly higher first pressure maximum and a considerably higher pressure spike approaching that of an incompressible fluid. The corresponding central film thickness is higher for 5P4E whereas the minimum film thickness is more or less the same in the two cases. The difference in pressure profiles leads to different von Mieses sub-surface stress mainly just below the surface at the location of the pressure spike.