HIGH-FREQUENCY VIBRATIONS IN THE CONTACT OF BRAKE SYSTEMS

Abstract

The processes and interactions that occur due to friction in the brake are still not fully understood today. In particular, the processes in the boundary layer have been shown to be responsible for a variation in the coefficient of friction and the associated wear. Dynamic contact structures in the boundary layer are made responsible for this behaviour. Vibration analyses on brake systems usually concentrate on operating vibrations analyses of the brake system components. In order to gain an understanding of the cause of such phenomena and oscillations, it is necessary to understand the mechanism of origin in the contact area. Therefore, highly specialized tribotesters have been developed at the Institute for Dynamics and Vibration to investigate the dynamic processes through experiments and simulative investigations. It can be shown that ultrasonic frequencies are generated in the friction boundary layer. These ultrasonic frequencies could not only be found in pin-on-disc testers, but also in complete vehicle brake systems. It was possible to identify that the vibration signatures between 20 and 80 kHz depend on a whole series of different influencing variables and have no dependence on the testing machine. In connection with the friction theories, it is an open question whether these oscillations can be made responsible as a kind of trigger pulse for the squealing of 1 to 20 kHz. In addition, it is a problem that the parking sensors installed in the vehicle work on an ultrasonic basis in the same frequency range and can therefore lead to failure due to these frequencies.