Creep groan is a phenomenon in which the brake is released while the vehicle is stopped, stick-slip occurs friction surface and vibration sound of 10-300Hz is generated. Improving this phenomenon is an important issue for the quietness and comfort of automobiles. Numerous studies have been conducted on the mechanism of creep groan generation, and it has been reported that the oscillation force is a stick-slip phenomenon at the friction interface. However, it was rare to directly measure the friction phenomenon during creep groan and evaluate the relationship with vibration. Acoustic emission (AE) is a phenomenon in which strain energy stored inside a material is released. AE sensing can be used to elucidate the friction phenomenon. In this study, the AE signals of the brake pads where creep groan is occurring under the condition that the brake is released on the slope were measured. Then, it was confirmed that the brake parts are shaken every time a slip caught as an AE occurs. It was found that there is a good correlation between the AE signal amplitude and the acceleration vibration of the rotor. Based on the frequency of AE signals, creep groan was found to be resulting from a combination of long-period slip and short-period stick-slip. In addition, from the in situ observation of the friction interface between the brake pad and rotor materials and the frequency analysis of AE signal waveforms, it was confirmed that the main cause of vibration was strain energy release accompanied by deformation and fracture of the friction surface.

Mr. Hajime Toyoda, Member, Resonac Corporation; Dr. Alan Hase, Associate Professor, Saitama Institute of Technology; Mr. Manabu Ono, Manager, Resonac Corporation; Mr. Shinichi Arai, Head of Application R&D 2nd group, Resonac Corporation; Mr. Yusuke Yazawa, Member, Resonac Corporation; Mr. Yasuhiro Hara, Member, JAPAN BRAKE INDUSTRIAL CO., LTD.