Influence of Lubricant Properties on ARKL Temperature Rise and Transmission Efficiency

Abstract

It has been suggested in the literature that the ability of a lubricant to produce low “end of test temperature” (EOTT) in the achsialrillenkugellager (ARKL)—that is, axial groove ball bearing—thrust bearing test is an indicator of its likely efficiency in vehicle transmissions. Based on this, the current study has used regression analysis to correlate the ARKL EOTT with a range of physical and friction properties of a set of 26 lubricants. The latter have been selected to span a wide variety of base oil and additives types. It has been found that the most important lubricant property in determining ARKL EOTT is the elastohydrodynamic (EHD) friction or traction coefficient at low slide–roll ratio. Lubricants with low EHD friction were found to give low EOTT. Two lubricant properties of secondary importance have been identified. One is the lubricant viscosity index (VI), where a high VI contributes to high EOTT. The second is the heat transfer capability of the fluid, where a high capability was found to correlate with lower EOTT.

The findings help clarify how low EOTT in the ARKL test can be achieved via lubricant composition. If the correlation between ARKL and transmissions that has been suggested in the literature is valid, then these findings are transferable to the design of high efficiency transmission lubricants.

KEY WORDS:

• Transmission Lubricant
• Efficiency
• Friction
• Elastohydrodynamic Lubrication

ACKNOWLEDGEMENTS

The authors thank Evonik RohMax and SK Lubricants for assistance in lubricant design and supply and for carrying out some of the tests described in this article. They also thank Gearing Scientific Ltd. (Ashwell, UK) for carrying out the thermal conductivity and specific heat measurements on the test lubricants.

Review led by Fabrice Ville