Characterization of the High Frequency Squeal on a Laboratory Brake Set-up

This paper presents an experimental investigation on high-frequency brake squeal noise conducted on an appropriately designed experimental rig, called laboratory brake. Brake squeal is one of the major issues in the design process of an automotive brake and the development of a robust procedure for a “squeal-free” design is still under investigation. The high-frequency squeal is the most frequent noise generated by automotive brakes and is characterized by a wavelength of the “squealing mode” comparable to the length of the brake pad. The proposed “laboratory brake” is a good compromise between simple test rigs, such as the beam-on-disc, and the experimental setups that use real brakes. The beam-on-disc setup is a useful tool to understand the mechanism leading to the instability, but it does not simulate appropriately a real brake. On the other hand, real brakes are too complex for fundamental investigation and for efficient modeling. The experimental analysis shows a strong correlation between the length of the pad, the dynamic behavior of the system, and the squealing deformed shape. Moreover, depending on the length of the pad compared with the wavelength of the disc mode, three different kind of squeal instability may occur during experiments: the sine mode squeal, the cosine mode squeal and the rotating squeal. The latter is characterized by nodal diameters rotating during a squeal cycle. A linear reduced model, able to reproduce the dynamic behavior of the experimental setup, is used to predict the squeal occurrence. However, such linear model is not able to predict the rotating squeal characteristic that seems to be caused by nonlinear interactions due to the contact between the disc and the caliper.