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The constant engine development requirements of increased durability with lower cost, size and power loss need innovations in technology from designers and manufacturers of critical components such an engine bearings. A detailed experimental program has shown that a connecting rod bearing with “end-relief” grooves can give surprising and unexpected benefits in reducing bearing temperature. Bearing shells with “end-relief” resulted in an effective bearing width reduced by 6mm or 30%, yet still gave benefits in temperature reduction. The depth of the “end-relief” was too large for any hydrodynamic oil film to generate pressure to support the applied load.

This paper reports on attempts to correlate measured oil flow rates for a big-end connecting rod bearing with those predicted by theory. The oil flow measurements were made on a 2.0 litre naturally aspirated gasoline engine. The theoretical predictions were made using an elastohydrodynamic model of the bearing system. This model used a finite difference solution technique, which incorporated a lubricant mass conservation algorithm. The measured bearing bore shape was used to give precise clearance data. Measured bearing temperature was used to calculate the effective operating viscosity. Locally refined mesh densities were used in the region of the relief bearing to improve accuracy. The correlation between experimental measurements and theoretical predictions has proved excellent, except at very high speed when theory tends to over-estimate the measured oil flow.

This paper details part of an on-going experimental program to map the operating characteristics of crankshaft bearings. Data from fired engines is essential to validate computer models and enhance understanding of these critical components in the engine system. Oil flow data is particularly valuable when used in conjunction with temperature data, especially at conditions close to the maximum rated engine speed where oil “starvation” effects can be significant. The results from a 2 litre gasoline engine detailing the oil flow, pressure and temperature show that the most challenging areas of bearing performance are at conditions close to the maximum rated engine speed.