A Study of Disc Brake High Frequency Squeals and Disc In-Plane/Out-of-Plane Modes

As an effort to solve high frequency brake squeals, increasing attentions have been placed on the relationship of the in-plane (IP) and the out-of-plane (OP) modes of a disc brake. However, there exists wide confusions between the frequency lineup and the mode coupling that largely hinders the efforts on correct solutions for brake squeals.

This paper investigates the relationship between disc brake IP-OP modes interaction and brake squeal by both analytical and experimental approaches. It starts with a systematic discussion and categorization of the modal patterns of a typical disc brake rotor. Then, the relationship between IP-OP mode and high frequency squeal is evaluated by means of disc mode indicating function (DMIF) testing and dynamometer testing for three rotor designs. At last, comprehensive correlation study is performed for 19 different front and rear brake systems from the results of 60 dynamometer noise tests.

It has been found that the frequency lineup between disc IP and OP modes will not lead to coupled modes. It has also been found that the disc IP circumferential modes show excellent correlation with high frequency brake squeals and the disc OP modes are totally irrelevant to these squeals. As a result, this paper proposes the concept of disc IPC vibration-friction interaction induced squeal mechanism, and points out that the velocity dependency of friction coefficient at high frequency between the rotor and the pad is the root cause of brake squeals.