Evaluations of Vibrations in a Wet Clutch

Abstract: BorgWarner Powerdrive Systems is constantly developing the performance of wet clutches used in passenger car all-wheel drive systems. The Haldex limited slip coupling, LSC, is the trade name of the all-wheel drive system sold and developed by BorgWarner Powerdrive Systems. In a primary front-wheel driven vehicle, the Haldex LSC can transfer torque to the rear axle based on sensor input with full electronic control and can thus work seamlessly together with other systems such as traction and stability control. In the design of such an all-wheel drive system; it is critical to avoid issues with drive line vibrations as well as the accompanying noise generation. This is a complex issue and even though the goal is to avoid these problems, they may still occur to a certain degree. BorgWarner now wants to investigate whether changes in the friction disc quality may affect the occurrence of vibrations. The friction disc quality could e.g. be described in terms of variations in height, material composition, material porosity and Young's modulus with the variations distributed around the circumferential of the friction disc. This study is however limited to investigate if a difference in height could be the cause of drive line vibrations. The goal is to determine if there is a correlation between a shifting thickness around the circumferential of the friction disc and the occurrence of vibrations. With the help from RISE Sicomp and their 3D-scanner it was possible to determine the difference in height around the circumference of the disc. The discs was scanned and then analyzed with the help of GOM-software. When the height was measured around the disc they were exposed to a run-in, this with the use of an LSC test rig. This way it is possible to see how the friction characteristics changes while it is being used and to later see if the height difference has changed. All this to see the correlation between the difference in height around the disc and the friction characteristics. A micro tomography scanner at LTU was used to section through the disc. It uses x-ray and makes it possible to look at sections all through the disc to see if there is a difference in the strucure of certain areas. If one pillow is more porous then another one. Based solely on the tomography test it is hard explaining the difference in Young’s modulus, the result showed little to none difference between different areas of the disc. With the help from 3D-scanning it has been shown that there is in fact a height difference. That difference becomes smaller with time when used, this due to the wearing of the highest area being greater than that of a lower area. The run-in seems to always have a positive result on the disc. Friction measurements during run-in showed that also a disc with small differences in height could display unfavorable friction characteristics. This would imply that the height difference matters but is not the only contributing factor to vibrations. Even though the difference in thickness of the friction disc has shown to contribute to vibrations, there are still factors that remains unclear. If the height would have been the only factor the friction measurements would support this more than what the actual case is. The other factors need further examination.