The influence of disc geometry on the centre of pressure and squeal propensity for an automotive disc brake

In recent experimental work it has been observed that position of the centre of pressure (CoP) at the brake pad/disc contact area has influence on the onset of brake squeal. Also, preliminary studies have shown that variation of the brake disc top-hat geometry has some impact on the number or shift of unstable modes of vibration. In this paper, a reduced isothermal Abaqus finite element model of a four-piston opposed brake assembly is used to show how structural modifications of disc geometry influence the CoP position and whether some correlation between unstable modes of vibration and CoP position can be found. A number of disc model variants have been developed reflecting changes of a disc top-hat height parameter. For all model variants, the first step of the simulation includes determination of the pressure distribution at the pad/disc interface and evaluation of the CoP position, while in the following step, a complex eigenvalue analysis is performed to investigate possible unstable modes of vibration. To facilitate post-processing, the simulation results including the pressure distribution map at the brake pad/disc interface, CoP position and complex eigenvalues are imported to a new Matlab program CalBrakes. This technique of linking Matlab to Abaqus is explained in this paper to give suggestions how to effectively speed up the evaluation process for running a large number of finite element models. An initial analysis of pressure distribution has shown that a certain shift of the CoP position for different variants of the disc top-hat structure exists. It is interesting that the higher the top-hat height parameter, the more significant the difference between the inboard and outboard CoP position is established. A subsequent complex eigenvalue analysis has shown that there is not a noticeable change of number and frequency instability values for discs with different top-hat height parameters. Ongoing work is aimed at identifying other geometric features of the disc that may impact on both CoP and squeal propensity.