Vehicle brakes often suffer from noise and vibration; at high frequencies called "squeal", at lower frequencies "judder" or "moan". These noises arise from vibration of the brake disc and mechanism, caused by unsteady friction forces at the rubbing interface between disc and brake pads. This project is part of a research programme organised by Bosch, to increase understanding of brake noise and to provide tools for the design of quieter brakes.

 

The only frictionally-excited oscillator which is well understood is the vibration of a violin string excited by bowing. Work in Cambridge over the last 20 years has shed considerable light on this problem. It is intended to apply this experience to the related problem of brake vibration. The major task is to explore the mechanisms by which brake vibration can be caused. In the literature of the subject several different mechanisms have been proposed, some analogous to the excitation of a bowed string and others rather different. We intend to review these mechanisms and classify the characteristic "signatures" of each. Examination of experimental results on brake systems and on idealised laboratory test rigs may then show correlations with some of these signatures. This would give valuable clues as to which aspects of the brake system are most important for particular types of noise generation, which in turn would allow rational design modifications to be made to ameliorate the problem.

This work complements other research projects sponsored by Bosch, in which the focus is more on developing full computational models of realistic braking systems. Such models are necessary, but they will inevitably be complex and contain many parameters. By studying simpler models in more depth, we hope to provide (i) test cases for validation of the fuller models, and (ii) physical insights to guide the use of such models in design optimisation.