This paper is aimed to show the feasibility for improving the ride quality of railway vehicles with semiactive secondary suspension systems using magnetorheological (MR) dampers. A nine degree-of-freedom railway vehicle model, which includes a car body, two trucks and four wheelsets, is proposed to cope with vertical, pitch and roll motions of the car body and trucks. The governing equations of the railway vehicle suspension systems integrated with MR dampers are developed. To illustrate the feasibility and effectiveness of the controlled MR dampers on railway vehicle suspension systems, the LQG control law using the acceleration feedback is adopted as the system controller, in which the state variables are estimated from the measurable accelerations with the Kalman estimator. In order to make the MR dampers track the optimal damping forces, a damper controller to command the voltage to the current drivers for the MR dampers is proposed. The acceleration responses of the car body of the train vehicle with semiactive secondary suspension system integrated with MR dampers are evaluated under random and periodical track irregularities. This semiactive controlled system is also compared to the conventional passive suspension system using viscous dampers without MR dampers, and the secondary suspension system integrated with MR dampers in passive on and passive off modes. The simulation results show that the vibration control of the train suspension system with semiactive controlled MR dampers is feasible and effective.

In this article, an MR valve possessing simultaneously annular fluid flow resistance channels and radial fluid flow resistance channels is designed, and its structure and working principle are described. In addition, a mathematical model for the MR valve with both annular and radial flow paths is developed and the simulation is carried out to evaluate the newly developed MR valve. The simulation results based on the proposed model indicate that the efficiency of the MR valve with circular disk-type fluid resistance channels is superior to that with annular fluid resistance channels under the same magnetic flux density and outer radius of the valve. Furthermore, the results also show that the efficiency of the MR valve can be improved significantly with two types of fluid flow resistance gaps, viz. annular fluid flow resistance gaps and circular disk-type fluid flow resistance gaps simultaneously.

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It is challenging to control the damping forces of magnetorheological (MR) fluid dampers because of the strong nonlinearity between the damping force of an MR fluid damper and the velocity across the damper, and the semiactive relationship between the damping force and the applied voltage/current. Hence, the desired damping force ought to be generated by an MR fluid damper cannot be commanded directly, only the command voltage applied to the current driver for the MR damper can be directly controlled. In this article, the configuration of a semiactive control system with MR fluid dampers is discussed and a damper controller based on signum function for MR fluid dampers is proposed. The damper controller is used to generate and adjust the command voltage to track the desired damping force determined by the system controller based on the desired and the actual damping forces. Two key factors for controlling the damping force of an MR fluid damper through a damper controller are considered in this article: (1) tracking ability of the controlled damping force to the desired damping force, and (2) energy requirement for the MR fluid damper. The characteristics of the controlled damping force and its corresponding command voltage are analyzed and compared with the Heaviside function damper controller. The simulation results show that the signum function controller outperforms the Heaviside function controller for better damping tracking ability while requiring less energy for the MR damper.