Avoiding creep groan: Investigation on active suppression of stick-slip limit cycle vibrations in an automotive disk brake via piezoceramic actuators

Creep groan in automotive disk brakes is a prevalent low frequency vibration phenomenon. It may occur when a car accelerates slowly from standstill with slightly operating brake as it might be the case for cars with automatic transmission or at slopes. The origin of creep groan is friction-induced vibrations from the pad-disk contact in the brake resulting in stick-slip limit cycles. These stick-slip limit cycles may excite comprehensive structural vibrations in the car leading to structure-borne sound and passengers' discomfort. The investigations in the present paper focus on the origin of this phenomenon - by considering set-ups concentrating on the pad-disk contact - and the possibility of suppressing the stick-slip limit cycle vibrations by excitation with piezoceramic actuators. Therefore, two test set-ups are investigated. The simpler one just uses disk, brake pads and caliper from an industrial brake, while carrier and suspension are replaced. The other one considers a complete brake including serial carrier and suspension. Low frequency stick-slip limit cycles could be observed in both test set-ups and a corresponding nonlinear model including the bristle friction law is developed for both systems. By integrating piezoceramic staple actuators in the system, external high frequency oscillations can be applied. The stick-slip limit cycle vibrations can be eliminated by providing harmonic high-frequency in-plane or out-of-plane vibrations, where plane means with respect to the disk. This effect can be explained in the model by the corresponding influence of the excitation on the static friction coefficient. The results from the simpler set-up are successfully transferred to the set-up with the complete brake including suspension. Additionally, this active technique is shown to be able to prevent the stick-slip vibrations even from occurring.