An air suspension system including variable coefficient dampers is introduced to suppress vertical vibration of railway vehicle. Bouncing, pitching and bending modes of vibration can be suppressed independently by using the semi-active sky-hook control algorithm. Some excitation tests on a rolling stock testing plant show that this alogorithm effectively suppresses each modes of vibration simultaneously with the dampers expanding and contracting to some extent. Running tests prove that the power spectrum density (PSD) of carbody acceleration is reduced around each eigen frequency of the natural mode of vibration and the riding comfort level (LT) is improved as compared with the case where passive air suspensions are installed.

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