Modification of Strain Distribution on Contact Surface of Shoe to Reduce Low Frequency Squeals for Brake Disc with Small Holes

The purpose of this study is to propose an effective model to estimate the excitation force accompanied with stick-slip between shoe and disc, considering the strain distribution on contact surface of the shoe, and then to propose an effective concept to design the brake which reduced the brake squeal under practical use. In order to investigate the influence of configuration of the hole, three types of discs were prepared in which the size of holes was different. The SPL (Sound Pressure Level) and the frequency of squeal for three types of discs were measured when the brake squeal was observed at conditions of low sliding speed. The change of stability of the brake shoe passing on hole was analyzed by 2-D simplified brake system model. In order to investigate how the strain distribution of the shoe affected on the excitation force caused by stick-slip, FE (Finite-element) and FDTD (Finite-difference time-domain) analysis were utilized to simulate the elastic wave propagation in the shoe under braking. Test result showed that the SPL of the brake squeal was reduced at significant peak of SPL around 700Hz when the disc had large diameter holes on the frictional surface. The stability analysis also showed that the stable region was extended when large hole was opened on the disc. The excitation force estimated by FE and FDTD model of the shoe was reduced when the diameter holes was increased. These results indicated that the excitation force at brake squeal was prevented by the modification of strain distribution. Such discussion was experimentally confirmed by the bench test with modified shoes which had concentrated strain distribution. This paper proposed an effective concept to prevent the squeal of the brake disc for motorcycles.