Surface Chemical Characterization of Steel Clutch Plate in Atf

Automatic transmission fluids (ATF) were tested using a new type disc-on-disc simulation tribo-test-rig Wazau triometer with the aim of studying the tribofilm formation on the steel surfaces during the engagement of wet friction clutches. XPS, SIMS, SEM and EDX were used to investigate the chemical composition of this tribofilm. The result confirms that there exist tribochemical reactions between ATF additives and steel rubbing surfaces. P/Ca/O element ratio of the tribofilm is consistent, which has never been reported before in the tribological field of clutch discs. All the results suggest that the chemical composition of this tribofilm is calcium phosphate. Since calcium phosphate ceramics have excellent mechanical and tribological properties, the friction characteristics of wet clutches must have been changed.