Self-sustained oscillations of a magnetic track brake frame

Magnetic track brakes (MTBs) are additional brake systems for railway vehicles used in low-adhesion and emergency conditions. In particular, the frame of this brake may exhibit self-sustained vibrations. To study the underlying mechanisms of these oscillations, a nonlinear mathematical model of the MTB is derived that consists of two submodels: a mathematical model of the mechanical subsystem and a model of the coupled electro-magnetic subsystem. Mechanical vibrations of the brake-frame are described by four degrees of freedom. Nonlinear dry friction, which is observed between the rail and the frame, is accounted for in the mechanical model. The coupled electromagnetic subsystem is modelled by a lumped parameter approach, describing the oscillating magnetic fluxes due to the mechanical motion of each electromagnet. The self-sustained vibrations are studied numerically for different vehicle velocities. The Neimark-Sacker bifurcation is observed. As a result of this bifurcation, the self-sustained quasi-periodic vibrations are originated. The stick-slip motions of the frame are observed, caused by the dry friction between the rail and the magnet.