Influence of low-frequency yaw damper dynamic stiffness on carbody hunting instability of high-speed freight wagons

With increasing operational speeds, high-speed freight wagons rely on yaw dampers to enhance vehicle stability. However, improper vehicle-damper parameter matching can induce severe low-frequency carbody hunting instability. This study investigates the specific impact of yaw damper low-frequency dynamic stiffness, governed by damping valve orifice variations, on this instability. To elucidate this mechanism, a physics-based yaw damper model was developed, incorporating internal structural parameters and pressure–flow characteristics of the hydraulic components. After experimental validation, this model was co-simulated with a high-speed freight wagon MBS model to systematically examine stability evolution under varying low-frequency damper dynamic stiffness configurations. Simulation results demonstrate that excessively low-frequency stiffness induces divergent limit cycles, markedly reduces the nonlinear critical speed, and amplifies low-frequency lateral oscillations. Furthermore, quantitative analysis using the RMS of lateral acceleration and Continuous Comfort Index confirms that such stiffness levels cause these indicators to exceed acceptable thresholds, increasing the risk of cargo damage. This study highlights the sensitivity of carbody hunting stability to the yaw damper’s low-frequency stiffness and offers theoretical guidance for damper design and optimisation in high-speed freight wagons.