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To meet the requirement for higher performance engine bearings, the microgrooved bearings, that is the plain bearings with shallow circumferential grooves, have been developed. Recently, the performance of microgrooved bearings obtained experimentally have reported1)2). The authors calculated the bearing performance of the microgrooved bearings by elastohydrodynamic lubrication theory. In this paper, the authors described thecalculation method and the performance of the microgrooved bearings obtained theoretically.

The purpose of this study is to analyze con-rod bearing lubrication under reduced oil supply rate conditions. An engine was modified to measure the oil supply rate to a con-rod big-end bearing. Then the effects of the oil supply rate on bearing temperatures and the contact between a journal and a bearing were investigated in order to analyze lubrication characteristics. The bearing temperatures increased in accordance with reduced oil supply rate. On the other hand, the contact frequency hardly changed under almost all conditions, but steeply increased near one-third of the standard oil supply rate at the highest speed of 5000 rpm in the experiments. The results show that the reduced oil supply rate decreases the cooling effect but the hydrodynamic lubrication was sufficiently achieved except the above-mentioned severe condition.

Temperature distributions on the surface of a connecting rod big end bearing were measured to understand the margin to the allowable limiting temperature. The results show that the temperature difference between the bearing surface and the feed oil is independent of the engine load but quadratically increased with the engine speed, and that the bearing surface temperature on the rod side is higher than those on the cap side, and that the high temperature regions appeared near the edges on the rod side of the bearing under high speed operations. The results were analyzed by the observation of rubbing traces on the bearing surface and the EHD lubrication theory.

Oil consumption mechanism was analyzed by measuring the radial movement of the upper side rail in a three piece type oil ring, together with the piston movement. Ultra-miniature inductive displacement sensors were designed to measure the oil ring movement and fitted on the upper side rail with a part of the 3rd land cut out. The clearance between the side rail and the cylinder wall was measured under various operating conditions. The results showed that the radial movement of the oil ring was affected by the piston movement, which results in the possibility of degrading the oil control ability for the cylinder wall because the oil ring temporarily moves with the piston. Accordingly, the designs to improve the piston movement or to be less affected by the movement proved to be an important factor for the reduction of the oil consumption.