Secondary yaw control to improve curving vs. stability trade-off for a railway vehicle

Active primary/secondary suspensions have been proposed to solve the trade-off between curving and stability in railway vehicles. One concept is known as secondary yaw control (SYC), which consists of applying a controllable yaw torque between the carbody and the two bogies. This has been studied in the past mainly to enhance the vehicle's curving ability, but this paper extends the idea by examining the implications of designing a bogie with soft yaw stiffness between the bogie frame and the wheelsets and using SYC to provide active stabilisation. To this aim, a state feedback control law is designed according to the LQR technique. The paper presents the general concept of the active suspension control to be investigated and the specific control strategies applied. Then the effectiveness of the proposed actuation concept is investigated by means of numerical simulations performed on mathematical models of the passive and actively controlled vehicles implemented in a fully nonlinear multi-body simulator.