Thermal elastohydrodynamic lubrication characteristics of couple stress fluids in rolling/sliding line contacts

Abstract

Abstract

A mathematical model is developed to analyse the effect of polymer additives on thermal elastohydrodynamic lubrication (EHL) behaviour under heavily-loaded rolling/sliding line contacts. The lubricant is assumed to be couple stress fluid and a non-dimensional couple stress parameter represents the molecular length of the additives. The Reynolds and mean temperature equations for the couple stress fluid (CSF) are derived using the rheological relationship presented by Stokes. The thermal EHL characteristics computed for polymer modified oils are found to have a strong dependence on the couple stress parameter. Polymer additives are shown to cause a significant increase in fluid-film thickness along with a noteworthy reduction in the coefficient of friction without any rise in fluid pressure. In addition, the polymer additives are found to cause a minimization of the thermal reduction in the fluid-film thickness as a well as decrease in fluid temperature, particularly under low speed-high load conditions, where fluid films are quite thin. These improvements are desirable in situations involving continuously varying slide to roll ratios, e.g. in gears.