Brake Squeal-Modeling and Experimental Investigation Using a Work Criterion

Squealing automotive brakes are usually not accepted by customers. However, squealing is an omnipresent phenomenon in disc brakes at least in certain operation states. During the development process of new brakes, engineers succeed more or less in covering this phenomenon with tools like using shims, modifying the structure or varying the mounted pads. In 2002 Popp et al. [1] described the pre-conditions for positive work of the friction forces (i.e. excitation of squeal) based on a very simple model. The essential point in this model is a phase shift between the in-plane movement of the pad and the friction force. In [2] it was shown that it is possible to suppress actively brake squeal using this approach. Active pads with integrated piezoceramics were used as actuators. The authors of the present paper use multi body brake models for the investigation of the origin of the excitation mechanism by observing the work per period of the friction forces and comparing the results with the classic stability analysis. A measurement technique based on these theoretical investigations is developed for detecting parameter regions (e.g. for the brake pressure and corresponding squealing frequencies) which are suspicious for squeal. Considering two models of the brake, phase shifts between signals and measuring the work of the nonconservative forces are considered with respect to the question of detecting the tendency to squeal. Based on these theoretical results measurement procedures are developed and tested at test rigs at TU Berlin and TU Darmstadt. The results of this procedure coincide with results of state of the art experimental investigations but can be performed much faster. This new procedure yields even more significant results than the ones described in [2].