Effects of Additives Adsorbed to Wet Clutch Disks on Their Tribological Performance Found in a Comparative Investigation

Tribolayer build-up was investigated on wet clutch steel disks with experiments in three different test levels of the tribological verification chain via X-ray photoelectron spectroscopy. A new characteristic value of the tribolayers was developed, i.e., the lateral elemental distribution uniformity. This value together with the parameters of additive elemental concentration as well as the thickness and the vertical composition of the layers were the basis for the subsequent correlation of the tribolayer properties with the tribological performance of clutch systems from different tests. One important finding was a non-zero threshold concentration of the additive elements calcium and phosphorous below which the clutch performance was unsatisfactory, even with a uniformly covered disk, concluding that the presence of some slightly higher additive element concentration seemed to stabilize the clutch performance. The importance of representative investigation area selection was demonstrated.