Main Bearing Friction and Thermal Interaction During the Early Seconds of Cold Engine Operation

Motoring tests have been carried out on an unloaded crankshaft to examine friction levels and the influence of local thermal conditions in and around the main bearings, at speeds covering the range of 200–1000 rev/min and from initial temperatures down to −20°C. The temperatures of the bearing oil film and the adjacent metal are strongly coupled. This directly influences the variation of friction with time during the early seconds of running. The possibility of lowering friction during this period by reducing the strength of the thermal coupling has been investigated. Heat conduction through the bearing shells can be reduced by raising the contact resistance at the rear surface of the shells, raising oil film temperature, and hence, reducing local oil viscosity. Experimental data and model predictions illustrate that a significant reduction in bearing friction can be achieved.