Theoretical and experimental analysis of dynamic characteristics of a two-tube air spring with auxiliary reservoir

Air springs are widely used in new energy vehicles, rail systems, and vibration isolation applications. This paper presents a novel two-tube air spring with an auxiliary reservoir (TASAR), which incorporates unilateral valves for flow control during both stretching and compression strokes. Unlike the conventional one-tube air spring with auxiliary reservoir (OASAR), TASAR allows independent regulation of stiffness and damping for different strokes, thus enhancing vibration isolation performance. The dynamic model of TASAR is developed based on the air state equation, continuity equation, and fluid mechanics, considering the nonlinear characteristics of the rubber bladder and the coupling effects between gas and solid. An equivalent mechanical model, representing stiffness and damping in a series–parallel connection, is also proposed. Critical parameters in the model are identified through experiments, with the relative error in estimating dynamic stiffness and damping coefficient under harmonic excitation found to be less than 15%. Simulation results indicate that TASAR has lower dynamic stiffness and higher stretching damping in the medium frequency range (2–10 Hz), compared to OASAR, achieved by adjusting the diameter and length of the stretching tube, which improves comfort.