Detection, Classification and Objective Rating of Creep Groan Phenomena in Brake NVH Development

Groaning brakes are unpleasant, for passengers and passers-by. Even after many years of research, the characteristic low-frequency, stick-slip-induced brake creep groan is still a problem in terms of customer feedback and quality perception of passenger cars. Groan-free braking is certainly possible, whether through active measures such as piezo-based smoothing of the friction curve, or through passive measures such as the optimization of the friction characteristics by means of pad formulation or disc coating. However, this technically optimal goal is rarely achieved. The reasons for this are high costs for active systems or design conflicts within the numerous requirements placed on the friction materials. Hence, compromises have to be made and a certain “amount” of brake creep groan has to be allowed. How to quantify this “amount” resp. the annoyance due to creep groan noise is the content of the present work: essential aspects of testing, detection, classification and last but not least the objective rating itself are shown. The results of this work form the basis for a modern NVH development process, which is able to precisely quantify the annoyance of brake creep groan and therefore enables an effective and efficient reduction of creep groan noise and vibration.