Friction-induced vibration in disk brake systems

Friction forces are known to induce rotor whirling and stator torsional oscillations in disk brake mechanical systems that are potentially damaging to the brake system. This dissertation presents a detailed analysis of the dynamic behavior of a single rotor/stator disk brake system. We consider the dynamics of the stator, the rotor, and the combined rotor/stator system. First, a non-rotational mathematical model is constructed with the purpose of showing that friction induced vibration can occur in the stator without assuming stick-slip rotor/stator contact or a friction coefficient that decreases with increasing slipping velocity. Self-induced vibrations are analyzed via the application of the method of multiple scales. The stability boundaries of the primary, super-harmonic, and subharmonic resonance are determined.; Rotational effects are investigated by considering three mathematical brake models. The first two models describe a spinning rotor engaging a rigid stator. The third has a spinning rotor engaging a stator with torsional flexibility. Again, a constant friction coefficient is assumed. The stability of steady whirl solutions for the mathematical models are determined as a function of the system parameters. It is determined that only forward whirl modes are stable and under some circumstances no stable steady whirl modes exist. It is shown that unsteady rotor whirl can be an important excitation source of stator torsional oscillations and that the settling time to no-slip decreases as the ratio of the stator to rotor stiffness increases.; Experimental rotor whirl speed and stator squeal frequency results are presented that agree with the analytical predictions of the rotational models. That is the experimental results show the same trends predicted in the analytical models. It was discovered analytically and verified experimentally that for high stiffness ratios there exists whirl modes of the rotor that have a very high whirl speed at a low spin speed which can result in component damage. Additionally, it was found that a time increasing brake line hydraulic pressure results in a violent ramping up of the rotor whirl speed.