General Friction Considerations for Engine Design

Reductions in engine friction can improve engine thermal efficiency and thereby reduce vehicle fuel consumption. Lubrication regimes encountered in the engine range from high-friction boundary-lubricated contacts where the coefficient of friction may be as high as 0.2 to low-friction hydrodynamic contacts where the coefficient of friction could be as low as 0.001. The particular design technique used to minimize friction depends on the regime in which the contact is operating. For boundary lubricated contacts, such as the cam-lifter or the oil-control rings, the most effective technique is to reduce the normal load acting on the contact. For hydrodynamically lubricated contacts, such as the journal bearings or the piston skirt, a reduction in the area of the contact is effective.