Active Pneumatic Suspension - Modeling, Control and Hardware-in-the-Loop Simulations

It is assumed that autonomous driving is the key technology for our future transportation system. However, studies have shown that the incidence of kinetosis, i.e. motion sickness, is significantly higher in autonomous driving cars than in conventional vehicles. Since especially vertical dynamic oscillations (heave) in the frequency range from 0.1 Hz to approx. 1 Hz are perceived as particularly disturbing, active spring-damper systems can provide a remedy. The active air spring, which we develop at the Institute for Fluid Systems at TU Darmstadt, is such a system. It combines the advantages of an air spring (level control, load independent body natural frequency, etc.), which result from the separation of the functions "load carrying" and "energy storing", with those of an active system. The actuating force is generated by adjusting the load-carrying (pressure-effective) area of the air spring during operation with an edge frequency of more than 5 Hz. This is realized by adjusting the air spring rolling piston diameter with four radially adjustable segments. For this purpose, a compact hydraulic linear actuator was developed which is integrated into the air spring piston. In this article, we describe the concept of the active air spring and introduce the functional prototype. Thereafter, the general optimal vertical dynamic design of an active system is discussed using the example of a quarter car model and the influence of system variables such as actuating force and actuating frequency is addressed. In the next step, a simple modeling of the overall system is carried out with regard to the H-2-optimal controller design and the suitability of the actuator concept for use in an active chassis as well as the robustness of the controller is shown exemplarily. In order to optimally tune the system to reduce oscillations that cause kinetosis and decrease driving comfort, frequency-specific weighting filters in accordance with VDI Guideline 2057 are used for the control design. Finally, the functional performance of the active air spring is demonstrated in hardware-in-the-loop experiments in which the functional prototype is coupled with a virtual quarter vehicle in a real-time simulation environment.