Computer aided engineering prediction of brake noise: modeling of brake shims

Brake shims, applied to brake pads, are used for suppressing high frequency noise in disc brake units. Also called brake insulators, they do this mainly by adding more damping to the system in the brake pad area. This reduces the likelihood of the energy transfer between the components which would cause modal coupling. Finite element analysis (FEA), as a simulation and analysis technique, is widely used in the industry to perform squeal analysis as a part of the virtual development of new brake units. However, in most computer aided engineering (CAE) simulations of brake noise, shims are modeled as thin sheets of steel or are not modeled at all. This introduces some inaccuracy because the damping effect and flexibility of the rubber and adhesive material are ignored. Such inaccuracy in predicting system behavior, in the virtual design stage, means the analyst may not be able to locate the right frequencies of any occurring instability in order to decide on a noise fix. Also, the over-prediction of instabilities by complex eigenvalue analysis (CEA) adds to the inaccuracy of the process. This paper introduces a simplified CAE model for the brake shim, which when implemented in brake system modeling helps in highlighting the actual frequencies at which instability occurs in the system by taking into account the correct level of damping in the system in the virtual design stage. The method is confirmed by correlating the analysis predictions with the noise performance of a brake unit in dynamometer tests.