Surface and Engine Oil Effects on Journal Bearing 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. Increase in load supporting capacity is also possible through reduced clearances and improved surface finish on the journals and bearings. These actions have the causal effect of extending the transition from hydrodynamic to mixed lubrication to lower speeds and higher loads, resulting in lower friction, and reduced potential for wear.