Sound Source Identification of In-Plane Squeal of Disc Brakes Using Array Microphones and Its Verification by Acoustic Simulation

As the vehicle electrification progresses and the demand for acoustic comfort increases, the NVH performance of brakes becomes more important theme. In-plane squeal of disc brake is one of phenomena that is difficult to countermeasure. In this study, we used array microphones to search for sound sources of in-plane squeal in order to elucidate the mechanism. The Microphones were set in the out-of-plane direction and the lateral direction of a disc in brake components on a full-sized dynamometer. In the vibration mode in which in-plane stretch vibration was dominant, the sparse and dense parts showed high sound pressure. 3D laser vibrometer was used to check displacements of the disc, and the result indicated a possibility that the sparse and dense parts could vibrate in the out-of-plane direction and generate the sound. Then, complex eigenvalue analysis (CEA) and acoustic simulation were conducted to validate the experimental results. Firstly, frequency of instability mode occurred in CEA was almost the same as that of the actual brake squeal and the mode was identified as in-plane squeal mode. Secondary, acoustic simulation resulted that areas near the sparse and dense parts in a disc had high sound pressure as similar to the sound source identified by array microphones. Finally, parametric studies of friction material property showed correlation between the CEA results and the sound pressure distribution obtained by acoustic simulation.