SAE International Thermal Mapping of an Automotive Rear Drive Axle 2011-01-0718

In recent years, there has been a sustained effort by the automotive OEMs and suppliers to improve the vehicle driveline efficiency. This has been in response to customer demands for greater vehicle fuel economy and increasingly stringent government regulations. The automotive rear axle is one of the major sources of power loss in the driveline, and hence represents an area where power loss improvements can have a significant impact on overall vehicle fuel economy. Both the friction induced mechanical losses and the spin losses vary significantly with the operating temperature of the lubricant. Also, the preloads in the bearings can vary due to temperature fluctuations. The temperatures of the lubricant, the gear tooth contacting surfaces, and the bearing contact surfaces are critical to the overall axle performance in terms of power losses, fatigue life, and wear. It is therefore important to understand the temperature variations in an automotive rear axle as a function of operating loads and speeds. However, quantitative understanding of the axle thermal behavior is limited and published information is sparse. This study attempts to bridge this gap. In this paper, an automotive rear drive axle is used to investigate the thermal behavior and power losses under a range of speed and load conditions developed from a typical EPA fuel economy driving cycle. The test axle is instrumented with thermocouples at various critical locations on the rotating and stationary components. A wireless telemetry system was used to extract the temperature readings of those rotating thermocouples. The axle tests were run on a dynamometer with simulated wind cooling and the tests were run till the lubricant reached steady state conditions. Findings from these tests will be discussed in this paper.