Abstract
An analytical friction model is presented, predicting the coefficient of friction in elastohydrodynamic (EHD) contacts. Three fully formulated SAE 75W-90 axle lubricants are examined. The effect of inlet shear heating (ISH) and starvation is accounted for in the developed friction model. The film thickness and the predicted friction are compared with experimental measurements obtained through optical interferometry and use of a mini traction machine. The results indicate the significant contribution of ISH and starvation on both the film thickness and coefficient of friction. A strong interaction between those two phenomena is also demonstrated, along with their individual and combined contribution on the EHD friction.
Highlights
The elastohydrodynamic (EHD) regime of lubrication is the most frequently encountered in non-conforming lubricated conjunctions such as in meshing gears, rolling element bearings and cam–follower contacts [1, 2]
A typical EHD contact comprises three distinct regions: (1) the inlet region, where the lubricant is entrained into the contact and rapid buildup of pressure occurs; (2) the central contact region, where the lubricant film acts like a glassy solid with high viscosity and an almost uniform film thickness; and (3) the outlet region, where a sharp negative pressure gradient leads to lubricant film rupture and cavitation
The current study presents a methodology for prediction of coefficient of friction and the lubricant film thickness for highly loaded EHD contacts with medium-to-high lubricant shear, similar to the conditions experienced in automotive differential hypoid gears
Summary
Rb Radius of the ball ðmÞ Rcf Conductive thermal resistance through the lubricant film ðK=WÞ. Re Effective contact radius of curvature along the direction of entraining motion ðmÞ. Rfi Conductive thermal resistance of the moving heat source of surface i ðK=WÞ rh Radius of the circular Hertzian contact footprint ðmÞ. Effective contact radius of curvature along the side-leakage (lateral) direction ðmÞ.
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