I. Introduction
Improving transportation safety and efficiency in freight trains requires continuous monitoring by on board sensors, which need energy supply for measuring and for transmitting information [1]-[3]. The lack of electricity in freight cars can be overcome by resorting to alternative energy sources. A very promising solution is represented by railcar suspensions, where usually vibrations energy is dissipated through oil shock absorbers or frictional dampers [4]. Among the different solutions for regenerative suspensions proposed in the literature, a very efficient regenerative system for railcar suspensions, based on a bidirectional moving rack, a Mechanical Motion Rectifier (MMR) gearbox and an electromagnetic generator, is introduced and discussed in [5].