Comparison between Theoretical Calculations and Oil Film Thickness Measurements Using the Total Capacitance Method for Crankshaft Bearings in a Firing Engine

Abstract

Comparisons were made between theoretical calculations and experimental measurements for minimum bearing oil film thickness (MBOFT) in main and connecting rod bearings of a typical automotive V6 engine running at 1500 rpm under three load conditions (64, 128, and 192 Nm.). Data for five oils (SAE grades 5W–20, 20W–20, 5W–30, 10W–30, and 20W–50) were obtained for the main bearing and for two oils (SAE 5W–30 and 10W–30) for the connecting-rod bearing. The theoretical calculations were done using the FLARE computer code while the measurements were made using the total capacitance method (TCM). Considering the complexities involved in a firing engine, overall, reasonably good agreement between theory and experiment was observed, especially for the absolute minimum of the MBOFT (MBOFTmin). The experimental data showed higher dependence on the Sommerfeld number than that of the theoretical calculations for the main bearing. The shapes of the MBOFT vs. crank angle curves were also similar between theoretical predictions and experimental measurements, although there were differences as well. Several causes of discrepancy affecting both the calculations and the measurements were investigated. Bearing non-circularity, cavitation, and crankshaft flexibility and dynamics were identified to be the main causes of the discrepancy. A novel approach based on analysis was developed for estimating the error in the based on analysis was developed for estimating the error in the oil film thickness measurements using TCM due to cavitation and bearing non-circularity, including the presence of holes and grooves. Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999