Structural modifications for squeal noise reduction

Brake squeal is an example of noise caused by vibrations induced by friction forces that can lead to a dynamic instability. The onset of squeal is due to the lock-in phenomenon, i.e. the instability occurring when two modes of the system coalesce and one becomes unstable. The sensitivity of the onset of instabilities with respect to the system parameters is due to the high modal density and to the large uncertainties on the dynamics of the single brake. This makes impossible the design of a 'squeal-free' brake apparatus. This paper suggests an innovative approach to avoid the growth of squeal vibrations, by exploiting the introduction of lumped structural modifications in the disc. The modification rotates with the disc while the disc modes are fixed in space. Depending on the relative position between the concentrated modification and the nodes of the disc modes, the natural frequencies of the disc shift back and forward. This expedient allows to change continuously the lock-in conditions between the system modes that are involved in squeal. The vibrations due to the lock-in between the pair of modes have not enough time to increase because of the repetitive look-out and they can be reduced until they completely disappear.