Analysis of Stick-slip Phenomenon During Creep Groan Using Acoustic Emission Sensing

When the brakes are released and the vehicle starts, the brakes and suspensions vibrate and the car body resonates at 10 to 300 Hz, which is called brake creep groan. This low-frequency noise is more likely to occur in high-humidity environments. As vehicles become quieter with the introduction of EVs, improving this low-frequency noise has become an important issue. It is known that the excitation force is the stick-slip between the brake rotor and pads, but there are few studies that directly analyze stick-slip occurring in a vehicle. Acoustic emission (AE) is a phenomenon in which strain energy stored inside a material is released as elastic stress waves, and AE sensing can be used to elucidate the friction phenomena. In this study, the AE sensing is used to analyze changes in the stick-slip occurrence interval and generated energy when creep groan occurs. As a result, it was confirmed that the AE signal increased with high humidity. Furthermore, the friction phenomena during creep groan and their changes with humidity were also analyzed by frequency analysis of the AE signal waveforms, in-situ observations of the friction interface and their digital image correlation (DIC), ultimately determining the cause of creep groan.