Structural optimization of an asymmetric automotive brake disc with cooling channels to avoid squeal

Abstract

Brake squeal is still a major issue in the automotive industry due to comfort complaints of passengers and resulting high warranty costs. Many measures to avoid squeal have been discussed in the engineering community reaching from purely passive measures like the increase of damping, e.g. by the application of shims, to the active or semiactive suppression of squeal. While active measures can be effective but are elaborate and therefore more expensive, passive measure are less complex in most cases. This leads to the necessity to develop passive, economic and robust measures to avoid squeal. Asymmetry of the brake rotor has been proposed to achieve this goal and the resulting split of all double eigenfrequencies of the brake rotor has lately been shown to stabilize the system. Thus, a structural optimization of an automotive brake disc with cooling channels is presented in this paper with the objective to split all eigenfrequencies of the brake rotor in a certain frequency range by introducing asymmetry to the cooling channels. Constraints of the optimization are balance constraints, to guarantee a balanced operation for all rotor speeds, and minimal and maximal distance constraints of the cooling ribs, due to cooling and material strength requirements. First, a modeling approach of the brake disc with cooling channels is shortly presented which helps to avoid remeshing during the structural optimization. The introduced optimization problem is known to be highly nonlinear, nonconvex and with many local optima to be expected. Therefore, two approaches for the solution of the problem are chosen. The first, a deterministic one, is a Sequential Quadratic Programming (SQP) approach efficiently targeting local optima. In order to increase the possibility to find the global optimum, a set of randomly distributed starting configurations is chosen, leading to satisfying results. The other, a heuristic approach, uses a Genetic Algorithm (GA) directly aiming for the global optimum. The GA also delivers very satisfying results, nevertheless, the best solution has been found with the SQP approach. In order to validate the basic idea that a defined separation of eigenfrequencies helps to avoid squeal, modal analysis and squeal tests have been performed with a simplified disc with radial holes. The conducted experiments strongly support the theoretical findings and demonstrate the superior squeal behavior of the optimized disc.