Analysis of Disk Brake Creep Groan Vibrations at Automobile Chassis Front Corner Level Using High-Speed Recordings and Digital Image Processing

Automobile brake creep groan denotes self-excited vibro-acoustic effects during a cross-fade of moderate brake pressures with slow vehicle velocities near standstill. Friction-induced creep groan phenomena are perceived inside and outside a passenger car. The mainly emphasized structure-borne low-frequency range extends up to about 400 Hz. Although creep groan is technically harmless, it attracts increasing attention in customer-focused assessments of comfort, reliability and safety. In view of this acute product quality problem, effective countermeasures must be developed based on a holistic understanding. The present work supports this challenging task by means of unique experimental investigations. These relate to an exemplary MacPherson type front axle setup including floating caliper disk brake system. Realistic creep groan vibrations are provoked and sustained via a drum-driven chassis corner test rig. Two representative manifestations at similar brake pressures and drum velocities are analyzed in particular. Apart from conventional caliper acceleration and disk rotation measurements, a low-cost high-speed camera is pointed to the friction system. It vividly reveals mechanisms which are invisible to the human eye. A processing strategy for the picture series is created. It enables object tracking and stick-slip recognition. Results obtained thereby correlate with the analyzed sensor data. The basic creep groan frequency is around 22 or 87 Hz here. Both periodic non-linear vibrations rely on macroscopic stick-slip transitions of the friction pair which interact with characteristic inherent resonances of different chassis corner components. Eventually, this case study proofs that the adopted non-contact method is helpful to better comprehend creep groan phenomena.