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Properties of engine bearings were investigated with different bearing materials and different HTHS viscosity oils by means of both an engine test and a rig test. The rig test well simulated the bearing wear which occurred in the engine test. Lead-bronze bearings with lead-tin-indium overlay gave the least amount of wear in operating under high speed and heavy load conditions even with low HTHS viscosity oil. Aluminum bearings without overlay gave good wear resistance in the case of no seizure occurrence. The wear amount of bearings were well correlated with HTHS viscosity, not with kinematic viscosity.

A newly developed bearing is a lead-free aluminum alloy bearing with low frictional layer which consists of molybdenum disulfide in thicknesses of sub-micron levels on the bearing surface without required binders such as resin. The new bearing had a 50% lower static friction coefficient compared to the conventional aluminum alloy bearing, and exhibited comparable anti-seizure property and fatigue strength to the conventional bearing by evaluation of rig tests. These rig tests verified that the new bearing showed excellent frictional reduction properties. This paper describes details and performances of this newly developed bearing.

Resin-based overlays as lead-free bearing materials for automobile engines are experimentally studied using tribology testing apparatus and an engine bench test rig. A resin overlay newly proposed is composed of Polybenzimidazole (PBI) as the base resin and solid lubricant Molybdenum disulfide (MoS2) as an additive. PBI has high temperature performance and good adhesion and physical strength under higher temperatures. Consequently, a PBI-based overlay has good sliding properties in terms of wear resistance and fatigue resistance. The resin overlay shows applicability to automobile engine bearings which are used under high loads.

Recent automotive engines for high performance vehicles have been designed for higher speeds and outputs. Not only the combustion load but also the inertia force applied on the connecting rod has been increasing. Automotive engines have also become compact and lighter in weight for needs of lower fuel consumption. For these reasons, the rigidity of the connecting rod has been reduced in comparison with the increasing inertia force. As a result, fretting damage may occur between two surfaces of the connecting rod big end bore and the bearing outer surface, causing breakage of the connecting rod itself. Countermeasures for fretting such as a tighter bearing fit ( interference ) and higher rigidity of the connecting rod big end are generally adopted. But the details for these countermeasures can not be easily predicted at the design stage. Rather they are obtained only by durability tests on the actual engines.