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. 1. Introduction Adhesive wear and thermal degradation are the main aging sources of clutch friction materials, which are unavoidably present when clutches are in operation. The dominance of these aging sources is determined by many factors, such as the used friction material, oil, and operational condition, Regarding the sliding friction, the characteristics can be classified into two categories, namely, the stationary friction characteristic and the dynamic friction characteristic [1, 2]. As discussed in the literature, the stationary friction characteristic is typified by the Stribeck curve while the dynamic one is typified by the frictional lag. To the authors' knowledge, how the Stribeck curve and the frictional lag evolve with the progression of the friction material degradation is not fully understood yet. No articles have been found in the open literature that address this issue. This study aims at experimentally investigating the typical sliding friction characteristics of a wet friction clutch during its lifetime. More precisely, the objective of the study is to understand how the Stribeck and the frictional lag (i.e., sliding hysteresis) parameters evolve as the degradation progresses. A profound understanding of the evolution of the Stribeck parameters and the sliding hysteresis loop during clutch lifetime may allow to model the evolution of the clutch friction characteristics during the lifetime. This model can then be integrated to a clutch model such that simulations of the dynamic engagement behavior of the clutch with the progression of the friction material degradation is possible. Eventually, the gained knowledge can lead to the derivation of physical features, which are useful for