As vigorous acoustic radiations involving serious environmental pollution and customer complaints, squeal in disc brake systems engages multiphysics and multiscales problematics that are highly investigated. Recently, experimental as well as numerical results established that the impact of contact localizations at pads/disc friction interfaces on squeal behavior seemed significant to study these emissions. These studies involved modifications at macroscopic and mesoscopic scales, respectively obtained by varying geometries with classically used industrial pad shapes to act on load bearing area; and friction material to adapt tribological circuit. In this research project, NVH experimental aspects are of interest, the purpose being to improve tribological mechanisms knowledge generating instability, and identify key parameters to introduce into multiscale simulations. The analysis is focused on the associations between solicitation parameters and squeal appearances, characterized by their frequencies and occurrences ratios. Macroscopic influent parameters are namely investigated, remembering that meso –and microscopic- scales also have an impact on squeal behavior. In this purpose, a full scale disc brake system is provided by Hitachi Astemo, and baseline configurations are tested on a dynamometer bench with a specifically designed NVH squeal matrix. An enriched instrumentation through in-operando thermal surface tracking allows to access to supplementary solicitation informations. Namely, it becomes conceivable to follow the assumed macroscopic contact area during and throughout brakings, as well as lining material thermal excitation level, under different specific brake operational conditions, depending on rotational speed, pressure, or initial braking temperature. Finite element simulations of the full system authorize to appreciate initial braking states, that are compared to the obtained experimental macroscopic localizations. In addition, post-mortem surfaces analyses, such as photographs and topographical measurements, are precious means regarding the understanding of involved mechanisms at mesoscopic scale. An apparent correlation is established between operational parameters and squeal characteristics, through tests involving variations of input specifications. Explanations are finally enriched via Complex Eigenvalue Analysis simulations, where the implementation of the previously identified key parameters is discussed. Particularly, brake system response seems highly dependent on pressure and initial brake temperature. Furthermore, the different experimentally studied pad shapes highlight the potential influence of the assumed macroscopic contact distribution difference, that could be linked to the change in vibratory response, implicitly created by shape modification.
Mr. Nicolas Strubel, PhD Student, Engineer, Hitachi Astemo; Mr. Philippe Dufrénoy, PhD, Professor, LaMcube, University of Lille, Polytech Lille; Mr. Jean-François Brunel, PhD, LaMcube, University of Lille, Polytech Lille; Mr. Thierry Chancelier, Physical Laboratory Manager, Hitachi Astemo; Mr. Saïd Hamdi, Testing engineer, Hitachi Astemo; Mr. Sylvain Thouviot, PhD, Simulation manager, Hitachi Astemo; Mr. Yassine Waddad, PhD, Simulation engineer, Hitachi Astemo