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The friction reducing potential of low viscosity engine oils in bearings has been investigated using a journal bearing test rig. Friction was measured on both the journal and bearing of a production connecting rod and compared to results from a simple analytical model over a range of speeds and loads. Hydrodynamic lubrication conditions existed over most test conditions, but mixed lubrication conditions were shown to exist at low speeds in heavily loaded journal bearings. Results indicate significant friction reduction through the use of low viscosity oils under hydrodynamic lubrication conditions. In mixed lubrication conditions, oils with friction reducing additives exhibit lower friction than those without such additives. These findings suggest the possibility that a low viscosity oil with effective friction reducing additives can extend low friction benefits over the entire range of operation of engine bearings.

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.

Lubrication conditions in journal bearings lubricated with low friction engine oils have been investigated using two complementary experimental techniques. Load supporting capacity under conditions ranging from fully flooded to mixed lubrication was measured for several candidate oils using a bench test that simulates the dynamic motion of a journal bearing at fixed, measurable eccentricities. The performance of these oils was also assessed using a bearing test rig in which journal friction is measured under typical engine conditions of speed, load and temperature. Significant mixed lubrication conditions were shown to exist at low speeds in heavily loaded journal bearings. Under such conditions, oil with friction reducing additives exhibit higher load supporting capacity, distinct separation of moving parts, and reduced friction relative to oils without such additives.