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The number of vehicles with engines using idling stop systems and hybrid systems to improve fuel consumption has recently been increasing. However, with such systems the frequent starts and stops of the engine, where the oil film between the bearings and shaft is squeezed out and direct contact between the components is more likely, can result in increased wear of the engine bearings, particularly in the main bearing. Bearings with resin overlays have been shown to display superior resistance to wear from such start-stop cycles. Moreover, cast iron shafts without quenching treatment have also been used in engines for cost reduction. Because the cast shaft has low hardness and unstable surface graphite after abrasive finishing, increase in the wear amount cannot be suppressed by conventional resin overlay in comparison with steel shaft. Therefore, the resin overlay with improved wear resistance achieved by adding hard particles was developed.

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.