Analysis on the mechanism of active control of yaw damper on modes and time-delay stability of vehicle systems

To explore how active suspension improves the motion stability of vehicle systems, root locus analysis was used to study the effects of active control strategies and yaw damper parameters on the modal characteristics of vehicle systems. First, a 7-degree-of-freedom lateral simplified dynamic model of the vehicle system was established, considering the lateral and yaw DOFs of the wheelset and frame as well as the nonlinear wheel-rail creep relationship. Then, the Jacobian matrix of the system was theoretically derived; the variation of each motion mode trajectory with active control parameters was expounded based on eigenvalue and modal changes to summarize the system’s motion stability characteristics, with time-domain signal analysis for supplementary explanation. The results show that rational active control parameters can increase the damping ratio of each system mode and thus the critical speed to 352 m/s, and the improvement rate reaches 118.63%. However, active control with certain feedback parameters, while suppressing lateral mode instability, may accelerate the instability of the yaw mode, complicate the system’s frequency structure after instability and further worsen the limit cycle behavior. When the value of parameter Pv1 is above 40000 N·s/m, and the absolute value of parameter Pv2 is above 160000 N·s/rad, active control will have a significant adverse impact on the system. Furthermore, the role of condition numbers in determining the critical speed of time-delay systems was analyzed, and the condition number method was applied to railway vehicle systems for calculating the critical speed under time-delay conditions, result shows that at a time delay of 40 ms, the improvement effect drops to 18.63% and 16.15%, therefore, it is necessary to use time delay compensation to suppress time delay. This study provides theoretical support for the optimal design and engineering application of active suspension parameters.