Recent automotive engine developments have made great progress in protecting the global environment and in meeting exhaust gas regulations and fuel economy regulations. As a result, engine bearings tend to be used under severe conditions such as higher specific load onto the bearings and with low viscosity of lubricating oil. Aluminum alloy bearings are widely adopted as main bearings and connecting rod bearings in gasoline and diesel engines for passenger cars, and generally Al-Sn-Si alloy bearings without an additional overlay are used. Although these Al-Sn-Si alloy bearings have good anti-seizure properties and excellent running-in-properties, their material strength under high temperature conditions is not sufficient because of the low melting point of Sn phase contained in the alloy, and they could potentially result in damage to the bearing as seizure and fatigue under these conditions.
In such cases, Cu-Pb-Sn alloy bearings with lead-based overlay are usually applied. On the other hand Al-Zn-Si alloy bearings with bismuth overlay are also becoming to be applied from the view point of superior corrosion resistance and lower cost. This means that there is a strong demand for an aluminum bearing alloy which may be able to replace copper alloy bearings.
Based on the above background, a further higher strength Al-Zn-Si alloy bearings combined with a polymer overlay has been developed. This paper describes the bearing performance and other details of this newly developed material that have been verified through the research work on this material and the bearing rig and engine bench tests.