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“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.

This paper will survey different noise matrices used in the brake industry to evaluate brake noise performance on dynamometers. Results that show temperature dependence, temperature history, braking power as well as brake pressure and initial velocity will be presented. Statistical analysis of both dynamometer and road test cycles will be presented. The results will emphasize how different cycles cover the space of pressure, initial temperature, initial speed, and stop brake power. Recommendations for controlling the different parameters will be given.