The aim of this study is to decrease vertical vibration of rolling stock. This paper reports a newly developed air suspension system including a variable coefficient damper that proved fine damping performance in vibration tests. The results show that:
1. When sky-hook control algorithm is applied to the variable coefficient damper, the response of air suspension system to sine wave excitation reduced approximately by half around the resonant frequency. In the range over the resonant frequency, the response of the system with sky-hook control is as good as that without control.
2. Combination of air throttle and this system decreases the damping performance at frequencies higher than the resonant frequency. When an air throttle is used, it is recommended to reduce minimum damping force of the variable coefficient damper.