The present paper presents a complex measuring system which is used for principle research on brake squeal. The aim is to create a measuring system in order to investigate the excitation mechanisms in detail. To achieve this, a complete vehicle axle is mounted on a test rig and equipped with different measuring devices. The purpose is to measure forces and accelerations as close as possible to the contact area of brake disc and pad. This leads to the development of a sensing element which measures the acting friction force. Through optimal design this sensor can measure with a high resolution. As a result, it is possible to measure the static friction force and a superposed vibration of this force, which only occurs during a squeal event.
Furthermore, eddy current sensors are used for contact-free measurement of the relative displacement of the brake pad to the brake calliper. Triaxial acceleration sensors are mounted in the disc vents to determine the operating deflection shapes of the brake disc. A rotary encoder measures the rotating speed and allows the determination of the rotary angle of the brake disc. This is necessary in order to correlate the brake disc and brake pad signals.
The focus of this work is the result of a series of measurements performed with the previous described measuring system. Since several research teams are focussed on the influence of ultrasonic vibrations on friction, also measurements with high sampling frequency (200 kHz) are performed. As a consequence, ultrasonic oscillations can be investigated.
Moreover, sensitivity analyses are performed, which means that only one parameter of the brake setup changes and thus, the direct influence of this parameter on the resulting squealing is determined. The influences of different environmental conditions as well as several brake pads are tested. In addition, the brake system is tested both with and without shims and finally, even the shape of the brake pad is changed.
This paper covers different measuring methods and sensors which are implemented on a test rig. It presents some interesting measurements which are analysed in detail and suitable counter-measures for the investigated system are discussed. Nevertheless, it has to be noted that the findings are only valid for the investigated brake system. For general statements a measurement series with different brake systems would be necessary.
Wallner, Daniel*, Halder, Clemens, Meister, Markus - Graz University of Technology