Evaluation of the frictional properties of transmission lubricants

Mineral, semi synthetic, or synthetic oils show a very different frictional behavior. In the EHL regime, friction is dominated by the base oil, in the mixed and boundary lubrication regime by the additive system. No load losses are related to the operating viscosity. Therefore, power loss and efficiency of a gearbox strongly depend on the lubricant. An efficiency test on the FZG back-to-back gear test rig was developed for the evaluation of the frictional properties of lubricants. The test method consisted of operating conditions with regimes in the range of boundary, mixed, and EHL. The standard straight mineral control oil FVA3 was used. Using a gear test rig ascertained a reliable transfer of the results to transmissions in practice. From the results of the efficiency test, a calculation method for the mean coefficient of gear friction at boundary, mixed and EHL for any type of lubricant and additive system could be derived and transferred to arbitrary gearboxes in practice. This is an abstract of a paper presented at the Technische Akademie Esslingen 14th International Colloquium Tribology (Stuttgart/Ostfildern, Germany 1/13-15/2004).