Friction Reduction in Lubricated Components Through Engine Oil Formulation

Improvement of engine fuel efficiency through the use of low friction engine oils is a major task in engine lubrication research. This friction reduction can be achieved by improving the rheological characteristics and elastohydrodynamic (EHD) properties of engine oils, and by controlling boundary chemical interactions between oil-based additives and lubricated components in the engine. In order to achieve minimal frictional power loss under all lubrication regimes, engine tribological systems must be designed to effectively use advanced lubricant technology, material and surface modifications. This paper presents results of cooperative research addressing opportunities for minimizing friction through extension of hydrodynamic lubrication regime in lubricated components using various formulation approaches.

A set of experimental oils has been evaluated using laboratory test rigs that simulate hydrodynamic, EHD, mixed and boundary lubrication. Results indicate that SAE 5W-20 oils formulated to future expected ILSAC GF-3 specifications can offer significant reductions in friction relative to conventional 5W-30 oils. These improvements in performance can be achieved in all lubrication conditions and under both moderate and high contact pressures. In hydrodynamic and EHD conditions, the SAE 5W-20 oils used in this study offer reduced viscous losses, while in mixed lubrication, these oils exhibit reduced limiting traction coefficients, which result in lower frictional power loss. While the presence of Mo-based friction reducing additives effectively reduces friction in mixed lubrication, similar performance can be achieved through the use of other additives. However, Mo-based additives offer definite advantage in reducing friction under predominantly boundary lubrication conditions.