Braking Systems Creep Groan Noise: Detection and Evaluation

“Creep groan” is a braking systems noise that is observed when a vehicle is starting to move from a stopped condition with brake pressure applied. Motion takes place when brake pressure is reduced while a motive force, such as an idling engine through an automatic transmission, or gravity due to the vehicle being on a slope, is present. The vibration causing the sound is commonly thought to result from friction force variation in stick-slip mode. Detection and evaluation of “creep groan” noise has been a challenge for NVH test groups. First, this sound typically is not purely tonal like the more common brake squeal, although ultimately it may produce a tonal subjective impression. In this work the authors study different methods that may be applied to “creep groan” detection and evaluation. A method for pre-filtering time-data signals to enhance detectability of “creep groan” events is documented, and methods for evaluating and quantifying this noise related to its time-varying behavior, subjective impression and annoyance are also presented.