Keywords: stabilization, railway vehicle, hunting motion, gyroscopic damper, scale model, experiment.

A railway wheelset experiences the problem of hunting motion above a critical speed, which is known as a flutter-type, self-excited oscillation arising from a non-conservative contact force acting between the wheels and rails. Traditional methods to prevent the hunting motion are utilization of bolsters and yaw-dampers, or improving the support stiffness. There is also the proposed stabilization control method for the flutter-type, self-excited oscillation that occurs in a bridge deck by the utilization of a gyroscopic damper. In this study, a stabilization control method for the hunting motion is proposed by a gyroscopic damper in a way that is similar to the stabilization method for the bridge deck. The wheel of a railway vehicle generally has a tread angle to make the running performance on the curved rails smoother. A large tread angle makes the running performance on the curved rails better, while producing hunting motion even at a low speeds. In order to improve the running performance on straight and curved rails, the utilization of a gyroscopic damper was proposed.

The gyroscopic damper is fitted to the box on the front wheelset, as the axis of rotation of the rotor of the gyroscopic damper corresponds to the running direction of the wheelset. This structure results in the stability of the hunting motion by the coupling of the yawing motions of the wheelset, and the rolling motion of the internal gimbal. The disturbance torque decreases with the increasing inclination of the inner gimbal. Restoring the mechanism of the internal gimbal is needed to continue the stabilization of the wheelsets hunting motion. Providing a spring between the inner gimbal and external gimbal is useful in situations where the vehicle is driving straight. On the other hand, the use of springs is difficult due to the centrifugal force. The spring functions can be implemented using the actuator. However, reliability is desired. This study examines a passive recovery mechanism using a pendulum structure attached to the inner gimbal.

The validity of the proposed method is theoretically and experimentally confirmed for the increase of the critical speed of the hunting motion on straight and curved rails. The dimensionless equations of motion are derived by using the representative length and the representative time. Eigenvalue analysis is performed in the neighbourhood of the equilibrium point. The results show that critical speed has been increased by the rotation of the gyro. The effect of the gyroscopic damper is experimentally investigated by using a 1/10 scale experimental vehicle set-up and experimental track layout. The results show critical speed has been increased by the rotation of the gyro.

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