Active control of railway vehicles to avoid hunting instability

The paper deals with the application of active control to increase the operating speed of high speed trains by avoiding the occurrence of hunting instability. To this end, an innovative controlled electro-mechanic damper was designed to substitute traditional yaw dampers currently in use. The main components of this system are a brushless motor, with gear and spindle, used to apply a longitudinal force between the carbody and the bogie of the vehicle, and a velocity transducer used to measure the yaw vibrations of the bogie. The electric motor is controlled in order to apply a force to the bogie opposite to its yawing velocity, thereby maximising the amount of energy dissipation. In order to compare the performances of this new device to those of traditional oil dampers, a prototype was built and tested in a laboratory test rig reproducing the yawing behavior of an unstable bogie. A mathematical model of the active system was then defined and validated by comparison with the measurements performed on the test rig. Finally, the model of the electro-mechanic damper was interfaced to a model of the railway vehicle, thereby allowing to estimate the increase of operating speed corresponding to the use of the proposed device.