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Characterisation of Brake Creep Groan Vibrations
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on June 03, 2020 by SAE International in United States
Event: 11th International Styrian Noise, Vibration & Harshness Congress: The European Automotive Noise Conference
Creep Groan is an impulsive brake noise at very low velocities of the vehicle. Generally, stick-slip between brake disc and brake pads is assumed as the most dominating vibration mechanism of creep groan. This contribution will show by sophisticated measurement techniques, that stick-slip and speed dependent friction is an important trigger of this annoying vehicle noise. However, the overall vibration is much more complex than common stick-slip vibration models. It turns out, that in typical brake systems of passenger vehicles creep groan occurs around 15-20 Hz and 70-90 Hz. The mechanism at 15-20 Hz is an impulsive noise. Transitions between stick and slip phases trigger complex nonlinear vibrations of the complete brake and suspension system. At 70-90 Hz, the vibrations show a more harmonic-like behaviour, caused primarily by speed-dependent friction characteristics. Flexibilities in the suspension bushings, elastic deformations of suspension parts, wheel and tyre support the growth of instable self excited vibrations. In practical vehicle operation, the range of 70-90 Hz is the most relevant one. In many cases, the 15-20 Hz vibrations are not detected, because high brake pressures are required for this phenomena. This leads frequently to inappropriate model reductions, focusing on just one of the possible vibration states. The physical nature of the instable vibration system is incompletely addressed. Transient dynamic Finite Element simulations of the suspensions systems allow to study this phenomena. Full-scale models of the complete suspension system - consisting of wheel, brake, link arms and bushings - show the existence and properties of the bifurcating vibration states. Reduced stripped-of-models are not able to distinguish between the “hard” and “soft” creep groan characteristics.