Yao Liang, Hiroshi Yamamura, Yutaka Nakano, Noriyuki Shirasuna
Disc brake squeal refers to the high-frequency noise caused by self-excited vibration induced by the friction force between discs and pads. It has received considerable attention over decades, as customers have come to increasingly demand less noise, vibration and harshness of vehicles. The vibration of the disc, which is considered to be one of the main sources triggering squeal, is classified as either inplane (IP) or out-of-plane (OP). Substantial effort has been made to investigate and mitigate the squeal induced by the OP vibration of the disc. Meanwhile, there is still no effective remedy for the squeal related to the disc IP vibration, despite numerous investigations have been made to suppress it. Consequently, this paper focuses on the disc IP vibration related squeal. A squeal experiment which is developed for measuring and recording squeal signals is introduced. The squeal signals include acoustic signals of squeal and acceleration signals of main components in a disc brake system. Furthermore, natural frequencies of the main brake components are confirmed using experimental modal analysis. General time-frequency-energy characteristics of the squeal signals are first presented by using results of basic Fourier transform-based signal processing methods. Subsequently, more detailed frequency and energy features of those non-stationary and nonlinear squeal signals are illustrated based on decomposition results of the ensemble empirical mode decomposition and the Hilbert transform. The resultant figures indicate that the recorded high-frequency squeal is mainly caused by the disc IP circumference vibration. Furthermore, it is inferred that the lower frequency component (with higher energy), which becomes the predominant component of the squeal phenomenon, is induced by the higher frequency component (with lower energy generated) firstly.
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