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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 presents results of experimental investigation into the creep groan problem of disc brakes when used on rear axles of cars and light trucks. Improvements in test procedures and data analysis leads to clearly defined limit cycles in the motion of brake components. The limit cycles are related to both brake design and axle resonances. Creep groan frequency and signature are shown to depend on the choice of friction material. Simple monotonic friction models are shown to be limited in their capability of describing creep groan motion.