Abstract
Keywords - Engine bearing, Aluminum alloy, Fatigue, Wear, Silicon particle
Abstract
Engine bearings have been kept on developing to satisfy such recent engine requirements as longer life, lower fuel consumption by direct injection and higher cylinder pressure, and protection of global environment by adoption of frequent start-stop operation.
Al-Sn-Si alloy bearings are widely adopted as main bearing and con-rod bearing in gasoline and compact diesel engines. They have such better characteristics as possibility with no overlay due to its conformability of tin, excellent corrosion resistance, reasonable prices and lower contents of lead as one of the hazardous substances for the environment, than conventional copper lead alloy bearings with lead based alloy overlay.
However, there are two issues for Al-Sn-Si alloy bearing in the engine, which offer two types of bearings with respective characteristics. Firstly, fatigue may occur on the bearing alloy under severe condition such as in diesel engines. A new bearing with no lead have been developed by applying solid solution treatment of bimetal, consequently concluded to have the higher fatigue strength, with usual property on Al-Sn-Si alloy bearings. Secondarily, wear of the bearing alloy may extraordinarily increase in an engine operated under frequent start-stop condition. Addition of Si to aluminum alloy bearing has been worked since 1980s. Si, which is dispersed in the form of hard particles, works for decrease burrs on the surface of crankshaft made of cast iron, to lap adhesive metals onto the crankshaft surface and to minimize the wear of the bearing alloy. Wear can be effectively restricted by existence of larger size of Si particles compared with conventional size in the aluminum bearing alloy. However, enlargement of Si particles may both improve anti-wear property and decrease fatigue strength at the same time.
In order to resolve this issue, a bearing has been developed with enhanced wear resistance while maintaining the fatigue strength. This has been achieved by controlling distribution of the size for the Si particles included in the Al-Sn-Si bearing alloy in addition to the enlargement, based on the results of the investigation. A new bearing with no lead have been concluded to have the higher wear resistance, with usual property on Al-Sn-Si alloy bearings. Two types of newly developed Al-Sn-Si alloy bearings were verified to have the superior performance in actual engines respectively.