Influence of water on the tribological properties of zinc dialkyl-dithiophosphate and over-based calcium sulphonate additives in wet clutch contacts

• Simplified model lubricants are investigated for water contamination.
• The water–surfactant interaction reduces the possibility of water–ZDDP interactions.
• Water affects more rapidly in commercial ATF due to the complex additives system.
• Friction deterioration continues even after external water removal from ATF.
• The significance of contamination history during ATF condition monitoring is revealed.

Usually the wet clutch lubricant properties vary with different formulations of base oil types and additives. The aim of this paper was to evaluate the effect of water on the performance of additives in ATF. Simplified lubricants, ZDDP and over-based Ca-sulfonates detergent additives in an API Group I mineral base oil, were employed to compare with the commercial fully-formulated automatic transmission fluid (DEXRON®VI) during water-contamination. A full-scale wet clutch test rig was used to evaluate the frictional response due to water contamination of the lubricants. Fourier Transform Infrared Spectroscopy was utilized to evaluate the variation in the solubility of these polar organic additives in the water phase and Karl-Fischer titration was utilized to evaluate the post-test water content for different formulations.