Predicting Boundary Friction of Aging Limited Slip Differentials

Abstract

The prediction of friction is a challenge for scientists and engineers in a wide variety of applications in industry today. One such an application is the limited slip differential. The friction characteristics of the wet clutch are central to the performance of the limited slip differential system. Frictional changes with aging of the limited slip differential affect both the torque transfer accuracy and the tendencies to vibrations and noise generation due to stick-slip or shudder. Therefore, the objective of this work is to establish a method to predict the frictional changes of aging limited slip differential systems. In this study, a number of experiments were performed to establish a method to predict the changes in boundary friction with time due to aging. Accelerated aging was performed for different sets of operating conditions. Results from the tests were used to establish and verify a model to predict friction increase in limited slip differentials. The method assumes that frictional changes with aging are caused by decreased concentrations of friction modifying additives. The decrease in concentration was assumed to depend on the lubricant bulk temperature according to the Arrhenius equation. The model agreed well with tests performed at operating conditions close to the real operating conditions of the limited slip differential. The developed method can be implemented in a vehicle where it can be used to compensate for frictional changes and to indicate when service should be made.