Today the development tools for brake systems can generally be divided into three categories: simulation, dynamometer testing and vehicle testing. Despite the significance of dynamometer testing in the NVH-development there still is a lack of procedures to detect the robustness of a brake system with respect to brake squeal. While system's robustness is influenced by sensitivities to tolerances and changing system properties over time, these influences are not taken into account during dynamometer tests because in general only one system of one specification is tested at a time. This may result in discrepancies between dynamometer test and customers' feedback concerning noise occurrence.
This work examines new characterization methods for friction induced vibration. Based on the findings in , the work of the friction force in the spectral range of squeal can be used to characterize the stability of friction systems. A further approach is to identify and to evaluate the alteration of the modal damping of considered eigenfrequencies in the environment of instabilities. For the investigation of both approaches an external excitation is useful. Hence, this work introduces and compares different methods to excite a friction brake in the frequency range of squeal to develop a procedure characterizing a system's robustness in future work.
The concepts examined during this study include an electrodynamic-shaker, a brake-piston equipped with a piezoactuator, a piezoelectric hydraulic module and an electromagnetic excitation. The comparison of these concepts is based on frequency response functions. These are detected by actuating the system with the named concepts and measuring its response via accelerometers. Major evaluation criterions are the maximum excitation in the considered frequency range, possible locations of excitation suitable for a stimulation of all squeal relevant mode shapes, usability for different brake concepts and reproducibility of results.
The presented results contain the comparison of frequency response functions for different excitation concepts, the maximum reached system's excitations for the different concepts and the reproducibility of experiments results. The analysis is performed with a simplified brake system containing disc, pads and caliper mounted in a auxiliary frame. Based on these results the work concludes with the suitability of the different concepts for the excitation of brake systems in order to use them for robustness studies in future work.
Philippe, Stegmann, Sebastian Kruse, Klaus Augsburg - Audi AG, Ilmenau University of Technology