Measurement and Characterization of “Resonance Friction” at High Sliding Speeds in a Model Automotive Wet Clutch

Abstract

The friction forces between various lubricated ''friction materials'' and sapphire disks were measured using a new ''high-speed'' rotating disk attachment to the surface forces apparatus (SFA). Two different clutch lubricants and two different friction materials were tested at sliding speeds and normal loads from 5 to 25 m/s, and 0.2 to 1 N (nominal pressures *1 MPa), respectively. The results show that ''resonance friction''-characterized by large amplitude oscillatory (i.e., sinusoidal) vibrations, also known as shudder or chatter-dominates dynamical considerations at high sliding speed, replacing the smooth sliding or low-amplitude stick-slip that is characteristic of low speed/low load sliding. The characteristic (rotational) speeds or frequencies at which resonance friction occurs depend only on the coupled/uncoupled mechanical resonance frequencies of the loading and friction-sensing mechanisms. In contrast, the intensity of and time to enter/ exit shudder depends strongly on the lubricating oil and, to a lesser extent, on the friction material. Physical-chemical analyses of the friction materials before and after testing showed that the samples undergo primarily structural rather than chemical changes. Our results provide new fundamental insights into the resonance friction phenomenon and suggest means for its control.

Taking into account the universal dependence of the viscosity of a boundary lubricant on temperature and strain rate to describe stop-start experiments

“…OF VISCOSITY Viscous stresses σ v that appear in the lubricant layer depend on strain rate [22,27], (10) where η eff is the effective viscosity.…”

“…To ensure stable functioning of mechanisms, researchers perform numerous experi ments on studying the discontinuous mode [3,4,7,8] using atomic force microscopy (AFM) [9] and surface force apparatus (SFA) [4]. Using SFA, the authors of [4,7] were able to investigate the properties of the molecules pressed between two atomically smooth mica surfaces, as well as "resonance friction" was studied at a shear velocity of 5-25 m/s [10].…”