Analysis of disc brake squeal using the finite element method
The problem o f disc brake squeal has been examined by developing a finite element model of the coupled pad-disc system , conducting complex eigenvalue analysis and associating unstable modes with potential squeal problem areas. A key issue in this process is the representation of the contact pressure distribution at the frictional interface between the disc and the pad. Non-linear contact analysis using the finite element model of the pad revealed that contact is only partial at the pad-disc interface and that the contact pressure distribution depends on the friction coefficient, Young’s modulus of the friction material and the way the applied pressure is distributed on the pad backplate. A new method is proposed in which interface contact stiffness is related to brake line pressure using a statistical approach based on the measured surface properties of the interface. Complex eigenvalue analysis of the coupled pad-disc system has shown that unstable modes exist within different ranges of contact stiffness thereby providing an explanation of the effect of varying line pressure on squeal. The two most unstable modes from the analysis show good correlation with experimental squeal results. The coupled model is then used for parametric studies the results of which indicate that high coefficient of friction and uniform contact pressure distribution increase instability whilst a trailing edge biased pressure distribution and a high support stiffness at the pad backplate reduce it. Limiting the disc symmetry by introducing equispaced slots was shown to be effective in reducing instabilities involving diametral modes of the disc with the same order of symmetry only Other modes were stabilised by increasing the rigidity of the pad. The overall results suggest that either the pad or the disc can be mainly responsible for the instability depending on the mode thus unifying the different approaches to disc brake squeal and enabling the most appropriate component to be targeted for squeal abatement purposes.