Brake squeal has been analyzed by finite elements for some time. Among several methods, complex eigenvalue analysis is proving useful in the design process. It requires hardware verification and it falls into a simulation process. However, it is fast and it can provide guidance for resolving engineering problems. There are successes as well as frustrations in implementing this analysis tool. Its capability, robustness and reliability are closely examined in many companies.
Generally, the low frequency squealing mechanism is a rotor axial direction mode that couples the pads, rotor, and other components; while higher frequency squeal mainly exhibits a rotor tangential mode. Design modifications such as selection of rotor design, insulator, chamfer, and lining materials are aimed specifically to cure these noise-generating mechanisms. In GM, complex eigenvalue analysis is used for brake noise analysis and noise reduction. Finite element models are validated with component modal testing. Also dynamometer and vehicle test results are compared with finite element results. From several vehicle level brake noise analyses, our experience shows that complex mode shapes are capable of depicting the noise generating mechanisms, and the complex eigenvalues are able to depict the noise frequencies.
Production brake squeal models using complex root analysis can be stabilized by an optimization procedure that is available in MSC/Nastran V2001. Since there are many closely spaced modes in a brake squeal model, a design change to stabilize roots in a frequency range is a very difficult task. However, with an optimization procedure the stabilization can be automatically achieved.
After identifying noise generating mechanisms and creating representative analysis model, several brake corners were analyzed for brake noise performance in the case studies. Figures showing the analysis results are included. Possible countermeasures were suggested, and the results showed improved noise performance.