Testing of a wet plate clutch system for anti-shudder performance

The wet clutch system ( WCS ) is a complex combination of friction plates, separator plates and lubricant. The basic function of the WCS is to transfer torque under various operating conditions such as slipping, shifting, start/launch and/or torque converter clutch operation. During these conditions the slope of the coefficient of friction versus slip speed ( µ-V ) curve must be positive to prevent shudder of the WCS. A test procedure is needed to evaluate the WCS over a durability duty cycle to monitor the µ-V curve slope and shudder potential. The clutch plates and fluid must be tested together and remain together during the test to evaluate as a WCS. The objective of this paper is to describe this new test procedure which builds on the basics of the SAE J2964 - Low Speed Continuous Slip µ-PVT test procedure but a duty cycle is added to age the WCS. The test includes measurement of the µ-V slope at several intervals during the test ( before break in, after break in, and after each 12 hour aging segment of testing ). The aging segments are run at a specified continuous slip speed and constant power while the lubricant temperature is controlled and the plate interface temperatures are measured. The dµ/dV is calculated to show the slope of the µ-V curve at the different intervals and graphed to show when the slope changes from positive to negative. A negative dµ/dV slope can indicate a potential for shudder in the WCS. This new procedure can be used to compare friction materials performance with different lubricant chemistry by comparing the resulting dµ/dV change over time. It can also assess groove pattern designs, separator plate surface finish and plate materials effect on the dµ/dV slope.