Search Results

Recently, a lead-free Al-Sn-Si alloy bearing with metallic overlay has started to be used for a portion of automotive engines. This bearing has good anti-seizure and excellent running-in properties, and is an environmentally friendly alternative to the current copper-lead alloy with lead based overlay in accordance with the ELV regulation for the removal of lead from bearings. But automotive engines have been required to exhibit higher performance in order to enhance their commercial power, which tends to require the engine bearing to perform under higher temperature due to higher specific load on the bearing and higher rotational speed of the crankshaft. It is clear that the current lead-free aluminum alloy bearing is not satisfactory with respect to fatigue strength in some cases, and requires higher strength under the higher temperature conditions.

Foreign particles remaining in an engine cause bearing trouble on rare occasions. It is required to promptly and effectively discharge foreign particles from the bearing clearance space to improve reliability of the engine. In this paper, the bearing configuration of at the parting line between upper and lower bearings which are capable of discharging foreign particles are experimentally studied. Tests were conducted for fundamental visualization of oil flow and particles. As a result, the behavior of the particles in the bearing clearance space and the effects of the bearing configurations were well demonstrated. In the bench test using an actual engine, the bearing configuration with grooves at the parting line of the bearing demonstrated the effectiveness to prevent bearing damage caused by foreign particles. The influence of the bearing configurations on oil flow rate was confirmed not to increase the flow rate.

There has been a requirement for automotive bearings materials to be free of the toxic material lead, in accordance with ELV regulations and from the perspective of environmental problems. Currently, bismuth is used as a replacement for lead in copper alloy based main journal bearings and connecting rod bearings for automotive engines. In recent years, there has been changing to lead-free materials for truck engine bearings. Compared with automotive engines, lots of contaminations in the oil and local contact between the shaft and bearings can occur in truck engines. The ability to tolerate contamination and local contact is therefore required for truck engine bearings. In this development, we find that the addition of 8 mass% bismuth and 1.5 mass% molybdenum carbide particles into copper-tin alloy is effective for improving the ability which allow the contamination and local contacts. The development of above mentioned lead-free copper alloy bearing material is described here.