On the transient dynamics of a multi-degree-of-freedom friction oscillator: a new mechanism for disc brake noise

In this paper, we examine the dynamics of a simple model for a braking process. The 4 dof model is designed to capture some of the dynamics of a set of brake pads halting a rotor. We find from our model that the motion of the system transverse to the direction of braking experiences a sharp change in excitation when the slip velocity in the braking direction is low. This change results in a complicated vibration which occurs at low slip speeds. In addition, there is often no correlation between the frequencies of the resulting vibration and the natural frequencies of system in the absence of friction. Based on the results from our numerical investigations we are able to propose a new mechanism for disc brake squeal. This mechanism is similar to previously proposed mechanisms in that we view squeal as a friction-induced phenomenon. However, in contrast to the majority of these mechanisms, we are able to encompass the transient, dissipative nature of a braking process.