The effect of squeal in a disk brake system is initiated by an instability due to friction forces leading to self-excited vibrations. To determine critical operation states of an existing brake system it is common to use standard procedures like SAE tests. These procedures usually are very time consuming. Faster alternative approaches were considered in (1, 2) based on the investigation of vibration shapes due to their character with respect to self-excitation. The work of the friction force - as the origin of brake squeal - can be either positive or negative resulting in excitation or damping of vibrations. Based on a simple model the contribution of the friction force towards instability or stability may be determined by measuring the acceleration signals from a few selected points on the brake. This is useful for detecting parameter regions (e.g. for the brake pressure or temperature) which are suspicious for squeal and the corresponding squealing frequencies. It is possible to use this method with different kinds of excitation (e.g. by integrated piezoceramics) or even just with ambient excitation resulting from the regular operation of the test rig. These current procedures were tested at TU Berlin and at Audi in Ingolstadt. Such methods seem to be a good tool for engineers in development departments to give a rapid reflection on the usefulness of countermeasures.
Gödecker, Holger; Hochlenert, Daniel; von Wagner, Utz; - TU Berlin Kruse, Sebastian; - Audi AG