Time-Frequency Analysis of Disc Brake Squeal in a Brake Experiment

Automotive brake squeal has become a challenging issue to reduce traffic noise and improve the vehicle quality. Since the generation mechanism of brake squeal is extremely complex, involving multiple disciplines such as nonlinear dynamics, contact mechanics, tribology and acoustics, it is still not well understood. The brake bench experiment is an important method to investigate the evolution of squeal and the transient nonlinear dynamic behavior of brake system, because of the difficulties in modeling the nonlinear time-varying system parameters in braking, such as friction coefficient, contact stiffness and damping in brake pads, for analytical and numerical method. Here a laboratory experiment is constructed to simulate vehicle disc brake squeal. The rotation speed, brake pressure, torque, temperature and sound pressure are measure during the braking process with squeal events. The variations of friction coefficient versus temperature and brake pressure are investigated respectively. It is obtained that the friction coefficient increases with the increasing temperature and brake pressure. The evolution of brake squeal and its transient dynamic behavior are analyzed and discussed through three time-frequency analysis methods including STFT, CWT and HHT. The results demonstrate that the squeal signal is composed of several frequency components and may be dominated by one or two components with high energy which are related to the vibration modes of physical brake parts. The instantaneous frequencies of IMFs vibrate substantially with time induced by the nonlinear friction and contact between the disc and pad pairs.