An Assumed Modes Method Approach to Disc Brake Squeal Analysis

Disc brake squeal is a widespread cause for discomfort. The purpose of the work is to gain insight into the disc brake squeal problem and to investigate the mechanisms that generate instabilities that leads to audible noise. This paper presents a mathematical model for high frequency disc brake noise. Information of the flexible properties of the components is used to generate a small yet appropriate model. By using the technique of “Assumed Modes Method”, a model incorporating the flexible properties of a continuous disc can be accomplished resulting in only a limited number of degrees of freedom. Knowledge of the modal properties of disc and pads are used to select assumed modes for the model components. The basic concept of mode coupling is the starting point: Two orthogonal modes are present in a disc at the same frequency owing to it's rotational symmetry. When the pad-disc contact is established, this external disturbance causes the pairs of modes to split-up and they will coexist at different frequencies. Non-conservative effects, such as the friction forces, will tend to couple the two modes, and when they eventually re-appear at the same frequency they are able to exchange energy in a way that leads to an unstable behavior of the brake system. The model can explain the inherent resistance against squeal as well as the mechanisms that break this resistance. The analysis shows that the assumed modes method can be used to achieve a model with a smaller number of degrees of freedom and hence is suitable for parameter studies that can help in finding ways to suppress squeal in disc brake systems.