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Recent automotive engines for high performance vehicles have been designed for higher speeds and outputs. Not only the combustion load but also the inertia force applied on the connecting rod has been increasing. Automotive engines have also become compact and lighter in weight for needs of lower fuel consumption. For these reasons, the rigidity of the connecting rod has been reduced in comparison with the increasing inertia force. As a result, fretting damage may occur between two surfaces of the connecting rod big end bore and the bearing outer surface, causing breakage of the connecting rod itself. Countermeasures for fretting such as a tighter bearing fit ( interference ) and higher rigidity of the connecting rod big end are generally adopted. But the details for these countermeasures can not be easily predicted at the design stage. Rather they are obtained only by durability tests on the actual engines.

This study focuses on the oil flow, supplied from the oil hole in plain bearings; the oil flow in bearings that were statically loaded was measured precisely using a test rig. In the case that oil was supplied through an oil hole, experimental results showed that the bearing oil flow depended largely on the circumferential angle of the oil feed hole in relation to the loading direction. When compared with the results of conventional theoretical analysis, it became obvious that the conventional analysis method could not make an exact prediction. The authors have assumed that such difference would come from the oil film extent. Using a transparent bearing so that the behavior of the oil film within the bearing clearance could be visible, the oil film extent for different circumferential positions of the oil feed hole were observed. The bearing oil flow was calculated based on the actually measured oil film extent. The calculated result was compared with the experimental one.