Brake squeal as dynamic instability: an experimental investiation

This paper presents an experimental analysis performed on a simplified brake apparatus. In past years a common approach for squeal prediction was the complex eigenvalues analysis. The squeal phenomenon is treated like a dynamic instability: when two modes of the brake system couple at the same frequency, one of them becomes unstable, leading to increasing vibration. The presented experimental analysis is focused on correlating squeal characteristics with the dynamic behavior of the system. The experimental modal identification of the setup is performed and different squeal conditions and frequencies are reproduced and analyzed. Squeal events are correlated with the modal behavior of the system as a function of the main parameters. A clear distinction between squeal events involving the dynamics of the pad and squeal events involving the dynamics of the caliper is performed. The effect of the adding of damping is also investigated on the squeal phenomenon. Two opposite roles of the modal damping are described: a large modal damping can either prevent the rise of squeal instabilities or enlarge the squeal propensity of the brake apparatus. The robustness of the obtained squeal events permits a further analysis on the triggering mechanism of the squeal instability during braking.