The focus of my internship lay on improving a controller that was deployed in an Active Hydro–Pneumatic suspension (AHP). This is a relatively new suspension design with the particularity that it works without the classical mechanical parts of a suspension, such as steel springs and dampers.
Instead a hydraulic system is used, which consists, roughly speaking, of a plunger cylinder, a flow resistance, a hydro–pneumatic capacitor and a strong hydraulic pump together with a fast response servo valve.
At the heart of each AHP suspension strut, there is a force controller, which is responsible for tracking a certain desired force (calculated by other, higher level or “outer loop” controllers). The current controller, which is of the PI–type, does not allow for sufficient performance in the context of its application, and it was my task, to come up with a “better” one.
In the bigger picture, our test vehicle “PEGaSOS” is part of the CEmACS project, an interesting public project spread across and funded by several institutions, such as Research & Technology (Germany), the Hamilton Institute at NUI Maynooth (Ireland), Lund University (Sweden), Glasgow University (Scotland) and SINTEF (Norway).
Among many other things, one aspect of the project is developing a test vehicle that can be used as a simulator for the dynamics of other (and potentially not, or not–yet–existing) vehicles. Using steer–by–wire, four–wheel–steering and the AHP suspension, PEGaSOS will allow to realistically imitate the handling characteristics and driving feeling of another vehicle that is given only by its specific vehicle dynamics (reference) model.
Authors: Florian Knorn