Influence of physical parameters and operating conditions for structural integrity of mechanical system subjected to squeal noise
Résumé
This work proposes to study the effects of physical parameters and loading conditions on both dynamic and acoustic responses of a brake system subjected to squeal. A simplified brake system model composed of a disc and a pad is investigated. The friction interface is modeled by introducing linear and non-linear stiffnesses at several local nodes to model contact. The classical Coulomb law is applied to model friction and the friction coefficient is assumed to be constant. A stability analysis of this system is performed with respect to the friction coefficient and the hydraulic brake pressure. The system presents up to four instabilities and the focus is on a single instability case with a fundamental frequency of 930 Hz. For this case, self-excited vibrations are investigated for two loading conditions: static and ramp loadings. Time responses for these cases are significantly different: the amplitude of the case with ramp loading is 130 times higher than the amplitude of the static load case. Spectrum analysis are performed by the Continuous Wavelet Transform and the response associated with the static load is composed of the fundamental frequency and its harmonic components. Time response with the progressive load is composed of two fundamental frequencies, their harmonic components and linear combinations which are not expected according to the stability analysis. Noise emissions for these two loading conditions present significantly different features in terms of level and directivity. It is noted that levels in the near field are about 127 dB for the static load and 193 dB for the progressive load. Moreover, the directivity patterns in the near and far fields are composed of lobes for the static load and circular wave front lines for the ramp loading.
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