Superlubricity in EHL Contacts with Water-Containing Gear Fluids

Abstract

Fluid friction in elastohydrodynamically lubricated (EHL) contacts depends strongly on the lubricant considered. Synthetic oils can have significantly lower fluid friction than mineral oils. Water-containing fluids have the potential to significantly reduce fluid friction further. The aim of this study is to investigate the film formation and frictional behavior of highly-loaded EHL contacts with water-containing fluids. Comparisons are made with mineral and polyalphaolefin oils. Measurements at an optical EHL tribometer show good lubricant film formation of the considered water-containing gear fluids. Measurements at a twin-disk test rig show coefficients of friction smaller than 0.01, which is referred to as superlubricity, for all considered operating conditions.

Bearing Power Losses with Water-Containing Gear Fluids

“…This is commonly referred to as superlubricity (Hirano et al [15]). In addition, the film thickness measured at an EHL tribometer in [14] demonstrated a good lubricant film formation of water-containing gear fluids. A pressure-viscosity coefficient of approximately 6 1/GPa was derived.…”

“…Recent investigations by the authors have shown that water-containing gear fluids can strongly reduce friction in elastohydrodynamically lubricated (EHL) contacts. Experimental investigations conducted by Yilmaz et al [14] at a twin-disk test rig show measured coefficients of friction smaller than 0.01 for a wide range of operating conditions. This is commonly referred to as superlubricity (Hirano et al [15]).…”

“…The oil sump in the test housing was cooled and heated to control the oil sump temperature of ϑ Oil = 75 • C. All experiments were conducted with an oil filling level 30 mm below the shaft axes. The considered lubricants were the same as those used in the studies [14,16] of the authors. Therefore, the following description is mainly based on these studies.…”

Minimizing gear friction with water-containing gear fluids

“…The considered lubricants were the same as used in preliminary basic study of the authors (Yilmaz et al [24]). Three water-containing gear fluids were compared with conventional gear oils.…”

“…In a study preliminary to the present study, the authors investigated the film formation and frictional behavior of highly-loaded EHL contacts with water-containing gear fluids in fluid film lubrication regime (Yilmaz et al [24]). Measurements at the optical EHL tribometer showed good lubricant film formation of the considered water-containing gear fluids due to their high pressure-viscosity coefficient and density.…”