Abstract
Brake squeal is one of the main NVH challenges in the brake development of passenger cars. The conflict of goals in the development process and the late testability lead to the need of a deeper basic understanding of the squeal phenomenon and definition of design rules. On the other hand, brake squeal is still a very interesting field of research also for the universities because of its combination of different fundamentals, such as friction and stability behaviour of systems with local nonlinearities.
Major nonlinearities of the brake system are the joints, especially the contact area formed by the oscillating brake pad and the caliper. The state-of-the-art calculation method, which still is the complex eigenvalue analysis, linearizes these joints, hence neglecting its nonlinear influence in the stability analysis. Vehicle and bench experiments show that special driving manoeuvres like parking, where the brake pad often leaves the steady state, are likely causing brake squeal. The system in these manoeuvres sometimes behaves opposed to the linearized stability analysis, indicating a limit cycle beyond the Hopf point. Therefore, these states must be investigated more closely.
This paper investigates the nonlinear influence of the pad caliper joint in a fixed brake caliper, also called abutment. Bench tests with pressure foils at the abutment of the brake caliper and mode shape analysis were done and a simple FE model for a transient simulation is proposed. It is shown that the joint activity varies with driving manoeuvres, leading to different stability behaviours and limit cycle amplitudes.
KEYWORDS brake squeal, transient analysis, nonlinear joint, stability analysis, FEM