Prediction of Crank Pin Journal Temperature Based on the Oil Flow Rate

Improving the durability and reliability of crankshaft bearings has become an important issue for automotive engines recently because of conflicting demands for lower fuel consumption and higher power output. This study focused on the connecting rod big-end bearing which is subjected to harsher operating conditions on account of these requirements. It is known that the crank pin journal temperature is an indicator of big-end bearing seizure. Having a simple method for predicting the crank pin journal temperature with the required accuracy at the design stage is indispensable to efficient engine development.

In this study, analyses were first conducted to determine the oil flow rate at the big-end bearing which is a major determinant of the crank pin journal temperature. A bearing oil flow rate analysis was conducted by using the bearing oil film thickness found by an elastohydrodynamic lubrication (EHL) analysis and the crank pin oil hole outlet pressure found by an oil hole pressure analysis, and the bearing oil flow rate was predicted. In addition, the influence of various bearing specifications, such as the oil hole position and bearing clearance, on the oil flow rate was ascertained.

An analysis was then conducted to predict the crank pin journal temperature using the oil flow rate and friction loss found by the oil flow rate analysis and EHL analysis. On that basis, a simple method was devised for predicting how much the crank pin journal temperature of a modified bearing specification would change in relation to the baseline specification. That method was then used to examine the effect of each bearing specification on the amount of change in the crank pin journal temperature.