Thierry Janssens

Engagement behavior of degrading wet friction clutches

This paper presents modeling, simulation and experimental validation of the friction material degradation effects on the dynamic engagement behavior of a wet friction clutch system. The clutch system is modeled as a 3 DOF lumped-mass-spring-damper incorporating an extension of the Generalized Maxwell Slip (GMS) friction model. The effects of the dynamic sliding velocity (relative velocity between the input and output shafts) and changing normal load are taken into account in the friction model. As the degradation progresses, the Stribeck-function parameters and the tangential contact stiffness change, so affecting the friction characteristics. These parameters are then used in the simulations to investigate their effects on the engagement behavior of the clutch. The simulation results show that the sliding velocity profile and the post-lockup torsional vibration response change. Furthermore, in order to verify and validate the simulation results, the experimental data obtained from accelerated lifetime tests, carried out on two different paper-based wet friction clutches using a fully instrumented SAE#2 test setup, are analyzed and discussed. The experimental results show qualitative agreement with the simulation results.

Friction Behavior of a Wet Clutch Subjected to Accelerated Degradation

This study aims at experimentally investigating the sliding friction characteristics of a wet clutch during its lifetime. More precisely, the objective is to understand how the Stribeck and the frictional lag (i.e, sliding hysteresis) parameters evolve as the clutch degradation progresses. For this purpose, a novel test procedure has been proposed and a set of experiments has been carried out on a fully assembled (commercial) clutch using a modified SAE#2 test setup. Furthermore, a systematic methodology for the Stribeck and the frictional lag parameters identification is developed. Regardless of the applied pressure, it appears that the first three identified Stribeck parameters tend to decrease with the progression of the degradation, while the last parameter tends to increase. In regard to the frictional lag parameter, the trend shows pressure dependency.

Theoretical and Experimental Contact Stiffness Characterisation of Nominally Flat Surfaces

In this study the tangential contact stiffness between two elastic bodies having nominally flat surfaces with different material combinations is investigated. The tangential contact stiffness between these two elastic bodies is first calculated based on the Greenwood-Williamson-McCool contact theory. Then, the tangential contact stiffness is determined by experimental investigation on a tribometer under the effect of different values of normal load and tangential displacement amplitude. The tangential contact stiffnesses obtained from the experimental data show a good agreement with the theoretical results, where the trends are similar and they are in the same order of magnitude.