Investigation of the Drag Losses of Wet Clutches at Dip Lubrication

Wet running multi-plate clutches and brakes are important components of modern automotive and industrial powertrains. In the open stage, drag losses occur due to fluid shearing. This can subsequently lead to a perceptible reduction in the overall drivetrain efficiency. Injection or dip lubrication is used, depending on the application and the requirements. For the former a deep fundamental understanding already exists, whereas up until now the latter has not been extensively investigated. This contribution gives a detailed insight into the experimental research of the drag losses of wet running multi-plate clutches at dip lubrication. In a base study, the flow conditions and origins of the drag torque generation were investigated. Built on this, the effects of operating and geometry parameters, such as oil viscosity and level, clearance, groove design, plate size and number of gaps on the drag loss characteristic, were determined based on full factorial testing. The paper further explains the set-up of the LK-4 drag loss test rig used. An important outcome of this contribution is the development of a systematic testing procedure to accurately acquire the drag torque. Through the demonstration of the repeatability of the test results, it was in fact confirmed that the scientific outcomes are not expected to alter over time. Moreover, the developed evaluation methodology is described in detail. This research investigates a wide size range of friction and steel plates of serial production parts from automotive and industrial applications, in order to not only characterize the phenomenon and the trends for a specific dimension, but also to compare the behavior within different sizes. In this study we found that in most cases the parameters number of gaps, clearance, oil temperature, groove design and oil level have a significant effect on the drag loss characteristic.