Active secondary yaw control to improve curving behaviour of a railway vehicle

Active primary / secondary suspensions have been proposed as a means to solve the trade-off between curving and stability which represents a key problem in the design of modern railway vehicles. In particular, one concept proposed for active control of the vehicle’s running behaviour is known as Secondary Yaw Control (SYC) and consists of applying a controllable yaw torque between the carbody and the two bogies. This concept has been studied in the past mainly to enhance the vehicle’s curving ability. 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 and LQG techniques. The paper presents the general concept of active suspension control investigated and the 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. Comparisons are performed and benefits assessed between the actively controlled vehicle and the passive one in terms of: non-linear stability in straight track running; and safety and wear in curves.