On the Mechanisms of the Reduction in EHL Traction at Low Temperature

Abstract

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.

Modeling and Analysis of the Meshing Losses of Involute Spur Gears in High-Speed and High-Load Conditions

“…Furthermore, recent research has revealed the development of thermally induced shear localization across the EHL film under certain conditions [21,22]. The shear localization can dramatically reduce the EHL traction and may also reverse the trend of traction behavior with temperature as shown in Willermet et al [23], Webster et al [24] and Chang et al [21]. Therefore, Eq.…”

“…Because the lubricant viscosity is exponentially related to temperature, it can be very difficult to devise a close-form formula to calculate thermal EHL traction with consistent quality under various speed-andload conditions, as shown in Dama and Chang [18]. Furthermore, recent research has revealed the development of thermally induced shear localization across the EHL film under certain conditions [21,22]. The shear localization can dramatically reduce the EHL traction and may also reverse the trend of traction behavior with temperature as shown in Willermet et al [23], Webster et al [24] and Chang et al [21].…”

The influence of the slide-to-roll ratio on the friction coefficient and film thickness of EHD point contacts under steady state and transient conditions

“…14 at ue=0.15 m/s, as well as the local increase in the central film thickness for S=-1.8 shown in Fig.15, indicate the first stages in the development of a dimple. Besides, the local increase in the central film thickness might also reduce the effect of shearing [17]. The measurement of the temperature directly inside the contact was unfortunately not possible in this study.…”

Effects of thermally induced inhomogeneous shear and surface thermal boundary conditions on the shear stress in sliding elastohydrodynamic contacts

“…It leads to a number of unusual EHL behaviours including generation of sizeable dimples in the central EHL region 1,2 and dramatic reduction of EHL traction. [3][4][5] Chang carries out a parametric analysis, which suggests that the shear localisation is largely characterised by a single dimensionless parameter: 6…”