Friction Modelling in Boundary Lubrication Considering the Effect of MoDTC and ZDDP in Engine Oils

Abstract

A predictive friction model has been developed in boundary lubrication conditions to understand the sensitivity of the model to molybdenum dithiocarbamate (MoDTC), a friction modifying additive and zinc dialkyldithiophosphate (ZDDP), an antiwear additive in engine oil. Controlled experiments were performed on a block-on-ring tribometer to record the friction performance of the tribofilms produced by ZDDP and MoDTC additives under conditions representative of boundary lubrication conditions in the cam and follower interface. A statistical approach was used to develop an empirical friction model. The boundary lubrication friction model considers ZDDP and MoDTC additive concentration in an ester-containing polyalphaolefin (PAO) base oil, temperature and sliding speed as the factors affecting friction. The friction significantly depends on ZDDP, MoDTC, speed and temperature; showing a ZDDP/MoDTC synergetic effect on reducing friction. The results show good agreement between the measured and the predicted friction values, with a high correlation coefficient.

Keywords

• friction model
• boundary lubrication
• tribofilm
• modtc
• zddp