A Study of Oil Film Pressure Distribution on Connecting Rods Big Ends

As a result of demands for friction reduction and other performance requirements, there has been a trend towards reductions of bearing width and increases in load. Thus, high performance predictions are required to determine bearing feasibility limits. Measurement of oil film distribution is essential to judging bearing feasibility. Therefore, a thin film sensor was developed to enable highly accurate oil film pressure measurements in small bearings used in passenger vehicles. The sensor has a particularly smooth surface, making measurement possible with little effect on the lubrication conditions of sliding parts. For this research, the sensor was formed on the shaft so that oil film pressure distribution could be measured around the total periphery of the bearings. Three-dimensional oil film distribution measurements were conducted by the detection of multiple points on the sensor. Using this sensor, oil film pressure distribution was measured under different connecting rod big end rigidities, and the corresponding changes were analyzed. As a result, it was possible to verify that differences in rigidity caused differences in oil film pressure distribution. Oil film pressure shows one peak in the direction of the load in the case of a rigid connecting rod, whereas the pressure is dispersed and the direction of the peak does not match that of the load in the case of an elastic connecting rod. Elastohydrodynamic (EHD) calculations, which incorporate the rigidity of the bearings and housing, were performed using the same conditions as the measurements. Calculation results and measurement results corresponded well. In this way, the validity of both measurements and calculations was verified.