Modelling of Film Thickness and Traction in a Variable Ratio Traction Drive Rig

The paper describes the application of a full non-Newtonian, thermal elastohydrodynamic lubrication (EHL) model for the prediction of film thickness and viscous traction force in a special high speed rolling traction rig. The primary objective of the work was to identify a suitable lubricant rheological model that would describe the behavior of practical EHL traction drive contacts over their operating range. Experiments were carried out on a special rolling contact rig at temperatures of 60, 90 and 120°C and contact loads giving maximum Hertzian pressures of 1, 2 and 3 GPa. Entrainment speeds of up to 18 m/s were investigated. Corresponding modelling work was carried out using lubricant physical properties obtained for the traction fluid Santotrac 50. Viscosity data for this lubricant were available from the work of Bair and Winer, but a degree of extrapolation was required to this data to cover the range of the experiments. In view of the crucial importance of viscosity/pressure behavior in the prediction of traction attention was therefore focused upon the lower contact loads for which reliable viscosity/pressure data are available. A best-fit exercise was then carried out to establish an appropriate rheological model to account for shear thinning of the lubricant. Different non-Newtonian relationships were investigated including those of Johnson and Tevaarwerk, Bair and Winer, and a model which combined the features of both of these. The most encouraging agreement between experiment and theory over the range of temperatures and speeds considered was obtained with the Johnson and Tevaarwerk (Eyring) model.