We present numerical methods for model reduction in the numerical simulation of disk brake squeal. Automotive disk brake squeal is a high frequency noise phenomenon based on self excited vibrations. Our method is based on a variation of the proper orthogonal decomposition method and involves the solution of a large scale, parametric eigenvalue problem. Several important challenges arise, some of which can be traced back to the finite element modeling stage. Compared to the current industrial standard our new approach is more accurate in vibration prediction and achieves a better reduction in model size. This comes at the price of an increased computational cost, but it still gives useful results when the classical modal reduction method fails to do so. We illustrate the results with several numerical experiments, some from real industrial models, some from simpler academic models. These results indicate where improvements of the current black box industrial codes are advisable.

There are several low frequency vibration phenomena which can be observed in automotive disk brakes. Creep groan is one of them provoking noise and structural vibrations of the car. In contrast to other vibration phenomena like brake squeal, creep groan is caused by the stick-slip-effect. A fundamental investigation of creep groan is proposed in this paper theoretically and experimentally with respect to parameter regions of the occurrence. Creep groan limit cycles are observed while performing experiments in a test rig with an idealized brake. A nonlinear model using the bristle friction law is set up in order to simulate the limit cycle of creep groan. As a result, the system shows three regions of qualitatively different behavior depending on the brake pressure and driving speed, i.e. a region with a stable equilibrium solution and a stable limit cycle, a region with only a stable equilibrium solution, and a region with only a stable limit cycle. The limit cycle can be interpreted as creep groan while the equilibrium solution is the desired vibration-free case. These three regions and the bifurcation behavior are demonstrated by the corresponding map. The experimental results are analyzed and compared with the simulation results showing good agreement. The bifurcation behavior and the corresponding map with three different regions are also confirmed by the experimental results. At the end, a similar map with the three regions is also measured at a test rig with a complete real brake.

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Brake noise, especially brake squeal, has been a subject of intensive research both in industry and academia for several decades. Nevertheless, the state of the art simulations does not provide a predictive tool, and extensive experimental investigations are still necessary to find an appropriate design. Actual investigations focus on the consideration of nonlinearities which are in fact essential for this phenomenon. Unfortunately, by far not all relevant effects caused by nonlinearities are known. One of these nonlinear effects that the actual research focuses on is the limit cycle behavior representing squeal. In contrast to this, the actual paper considers the influence of the equilibrium position established while applying the brake pressure. The elements of the brake, namely, the carrier, caliper and pad, are highly nonlinear and elastically coupled and allow for multiple equilibrium positions depending e.g. on the initial conditions and transient application of the brake pressure while the frictional contact between the pads and the disk may excite small amplitude self-excited vibrations around this equilibrium, i.e. squeal. The current paper establishes a method and corresponding setup, to measure the position engaged by the brake components using an optical 3D-measuring system. Subsequently, it is demonstrated that in fact different equilibrium positions can be engaged for the same operation parameters and that the engaged position can be decisive for the occurrence of squeal. In fact, certain positions result in squeal while others do not for the same operation parameters. Taking this effect into consideration may have significant consequences for the design of brakes as well as simulation and experimental investigation of brake squeal.

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