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This paper addresses the problem of ride height tracking for an electronically-controlled active air suspension (AAS) system in the presence of parametric uncertainties and unmodeled dynamics. A mathematical model of a quarter vehicle with AAS system is first built on the basis of thermodynamics to describe the dynamic characteristics. Then, by employing the backstepping technique, a novel height tracking controller is proposed in order to guarantee that 1) the ride height of a vehicle can converge on a neighborhood of the desired height, achieving global uniform ultimate boundedness (GUUB); 2) the controller is robust to the parametric uncertainties by designing parameter estimators and introducing some conservativeness in the control law to dominate the unmodeled dynamics. Moreover, a group of smooth projectors is used to ensure all estimates remain within predefined corresponding bounds. To validate the efficiency and performance of the proposed strategy, the simulation and experimental results are presented and analyzed, showing that the proposed control strategy is superior to the PID controller and the recently proposed hybrid model predictive controller. INDEX TERMS Active air suspension, pneumatic system, automobile height control, robust control, parameter estimation.

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This paper focuses on a ride comfort based suspension (RCS) system using an optimal stiffness-determination method. The proposed RCS system is composed of a variable hydraulic damper with gas chamber (VHDGC) and an air spring. In this work, the detailed structure, modeling process and parameter sensitivity of the proposed VHDGC are presented. Moreover, the mathematical relationship between the proposed damper and the air spring is considered. Numerical results reveal that the ride comfort of the proposed RCS system can be greatly improved as compared with the passive suspension. In addition, the overall performance of the RCS system is also guaranteed. In sum, the proposed RCS system is a promising solution in improving the ride comfort of the vehicle.