Oil Film Thickness in Engine Main Bearings: Comparison Between Calculation and Experiment by Total Capacitance Method

The minimum oil film thicknesses (MOFT) in the crankshaft main bearings of a 1.5 liter, L-4, gasoline engine are measured and calculated to study the dynamically loaded engine bearing. The MOFT are measured simultaneously at each of the five main bearings using the total capacitance method(TCM). To improve the reliability of the TCM, a reasonable determination method of bearing clearance is introduced and the effects of bearing cavitation and aeration on the test results are analyzed. Also the crankshaft is grounded by means of a slip ring instead of the friction contact method to improve the test precision. The calculation is based on the model of statically determinate beam, short bearing approximation and Mobility method From the comparison between the measured and calculated MOFT curves, it is found that a qualitative similarity exists between them, but in all cases, measured MOFT are smaller than that of calculated The crankshaft vibration and the imbalance of the load distribution between the engine bearings have important influence upon the MOFT curve. So. it is found that the calculation result from the model of the statically determinate beam has a limitation in predicting bearing performance.