Theoretical and experimental analyses on stabilization of hunting motion by utilizing the traction motor as a passive gyroscopic damper

The wheelset on a railway vehicle experiences the problem of hunting motion, the onset of which occurs when travelling above the associated critical speed. This is known as a flutter-type self-excited oscillation resulting from non-conservative contact forces acting between the wheels and rails. Traditional methods for preventing hunting motion while running on a straight rail include using bolsters, yaw dampers, or stiffer supports. However, these methods decrease the running performance on a curved rail. To enhance the running performance on both straight and curved rails, we propose using a gyroscopic damper. Until now, a gyroscopic damper has been theoretically and experimentally shown to increase the critical speed for hunting motion. This control method does not need state feedback control, but is not a passive control method, because the gyroscope is rotated by an additional actuator provided separately from the traction motor. In practice, the weight increase from the additional actuator has been a problem in applying this control method. In this study, using the traction motor itself as a passive gyroscopic damper, a new stabilization control mechanism is proposed that eliminates the need for an additional actuator to rotate the gyroscope. An analytical model of a single railway vehicle wheelset was introduced at a scale corresponding to the experimental equipment. From the eigenvalue analysis, it was found that the critical speed increased with an increase in the rotor speed of the gyroscopic damper. Experiments were conducted using a simple apparatus consisting of a roller rig and a two-degree-of-freedom wheelset with a gyroscopic damper that has a mechanism equivalent to what is proposed. The results experimentally validate the proposed passive gyroscopic damper for the stabilization of hunting motion.