On the mechanisms of the reduction in EHL traction at low temperature

Various experiments have revealed a dramatic traction reduction in elastohydrodynamic lubrication (EHL) contacts under subambient temperatures or with fluids of high viscosity and high pressure-viscosity coefficients. This paper conducts a systematic theoretical analysis to identify and analyze the mechanisms of this reduction. A thermal EHL model is used for the analysis that is capable of capturing many possible effects, including a thermally induced cross-film shear localization within the EHL film. The analysis is carried out for a wide range of ambient viscosity and pressure-viscosity coefficients. The results and analysis suggest that the thermal effects are responsible for the dramatic reduction of the EHL traction. Two thermal effects become particularly pronounced with high viscosity and high pressure-viscosity coefficients. One is the lubricant re-circulation induced inlet shear that generates and accumulates heat in a prolonged inlet region and significantly increases the film temperature in the region of high pressure. The other is the thermally induced cross-film shear localization that generates high temperature in a small central layer of the EHL film.