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Emission control and other restrictions prescribed in the EU's recent EUROIV regulations require automobile manufacturers to decrease NOX and PM (Particulate Matter) in exhaust emissions. Diesel engines in recent years tend to have higher cylinder pressure in pursuit of higher performance and meeting emission regulations. At the same time, under the ELV (End-of-Life Vehicles) regulation, use of lead, which is an environmental pollutant, in automobile parts has become increasingly difficult in recent years. Accordingly, we have developed lead-free overlay for tri-metal copper bearings for applications of highly specific load. We chose a dual-layer structure, bismuth and silver overlay. This type of structure can create fatigue resistance without compromising the two advantages of lead overlay: conformability and anti-seizure property.

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.