1998-10-19

Determination of Bearing Oil Film Thickness (BOFT) for Various Engine Oils in an Automotive Gasoline Engine Using Capacitance Measurements and Analytical Predictions 982661

Minimum bearing oil film thickness (MBOFT) was measured in both a main and a connecting-rod bearing of a production V-6 engine using the total capacitance method (TCM). MBOFT was measured at 1500 rpm and at three different engine loads (64, 128, and 192 Nm). The oil sump temperature was controlled at 100°C. Five engine oils were tested (SAE grades 5W-20, 20W-20, 5W-30, 10W-30, and 20W-50) with emphasis given to the SAE 5W-30 and 10W-30 oils. MBOFT was also calculated using a computer code.The absolute minimum of the MBOFT (MBOFTmin, closest approach between the journal and the bearing) increased with increasing values of a Sommerfeld parameter (viscosity/load) and this dependence was similar in both the main and the connecting-rod bearings. But, for the main bearing the MBOFTmin values showed a higher dependence on the Sommerfeld parameter than those for the connecting-rod bearing. Similar results were obtained with the theoretical calculations of the MBOFT_min values.The experimental data indicated a 10 percent higher MBOFTmin for the SAE 10W-30 oil than for the SAE 5W-30 oil in both bearings. This difference was smaller in the theoretical calculations, about 4 percent for the main and 2 percent for the connecting-rod bearing. Uncertainties in the prediction of the oil viscosity at the high temperatures and pressures of the bearing may have been responsible for this difference.

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