The current rapid evolution of automotive vehicles is pushing brake disc designers to evolve their design for reasons of performance, weight reduction, etc. Low-frequency vibration issues (cold and hot judder) are re-emerging that need to be considered for multi-criteria design optimization. Even if this problem has been solved in the past, the origin of these low frequency vibrations has always been controversial. Thus, even if it is known that these vibrations are caused by hot or cold residual deformations of the disc and that it is possible to attenuate them by acting on some key parameters, such as the out-of-plane deformation amplitude of the disc, the origin of these localizations is still debated, without predictive modelling. The objective of this work is to consider the origin of these low frequency vibrations, i.e., the associated thermal localization mechanisms and to propose a quantitative approach to the resulting out-of-plane deformations. Firstly, a classification of the hot spot mechanisms was carried out, showing that different physical explanations are possible, and depend on the brake geometry and the level of stresses applied. The study then focused on ventilated discs with a study of the influence of the disc design (2 geometries considered). The results show that this design is influential, which is a known result, but also that the complete design of the brake and in particular the choice of the brake pad. This is shown through thermomechanical modelling of the brake system, which provides quantitative deformation information. It is thus shown that the vibration arises from the thermal localizations associated with the out-of-plane deformations which are themselves dependent on the radial localizations (hot bands). This was made possible by considering the evolution of the disc/pad contact pressure during the transient braking situation. The simulation results have been confronted to experiments with successful judder measurements to validate the modelling and to propose solutions for vibration mitigation. This modelling is integrated into the multi-criteria methodology for defining disc brakes. The interest of predictive modelling is also to identify the key influencing parameters.
University of Lille: Ing. Maxime Cathelineau, Dr. Jean-François Brunel, Dr. Philippe Dufrénoy; Stellantis: Ing. Dounia Fassi Fihri, Ing. Pierre-Gilles Belon