Philipp Albrecht-Zagar,
"Contributions to model reduction and actuation of hydraulic valves"
, 2024
Original Titel:
Contributions to model reduction and actuation of hydraulic valves
Sprache des Titels:
Englisch
Original Kurzfassung:
This dissertation is a cumulative work divided into two parts. The first part addresses scientific questions concerning the model reduction of hydraulic systems. Two different methods are discussed, which can be used to reduce a mathematical model in a consistent way. On the one hand, the well-known method of singular perturbation theory is applied to obtain different representations of a system. On the other hand, it is shown how the theory of switched systems can be applied to hydraulic feedback circuits to obtain reduced expressions that approximate the behavior of the system accurately enough. This approach is applied to the model of an electrohydraulic actuator that uses counterbalance valves to compensate the rod volume of the differential cylinder. It is shown that the newly developed method and the resulting reduced mathematical model can systematically account for non-linear effects such as end stops of the valve's poppet. Furthermore, a much simpler system consisting of a pressure relief valve and an oil volume is analyzed in order to compare the proposed so-called "sliding mode method" with the results of a conventional reduction using singular perturbation theory.
Part II presents scientific findings on hydraulic valve actuation based on a novel piezoelectric valve concept. In an introduction, the use of piezoelectric materials is briefly explained and contrasted with conventional electromagnetic actuators. Two concepts of a miniaturizable piezo valve are presented, both using a buckling beam as a displacement amplification element for a piezo stack. The buckling beam as an actuator element for valves, as well as important aspects that strongly influence the function of the actuator (e.g. bearing friction) are discussed and the practicability of introduced mathematical models is substantiated with measurements. For the investigation of the two valve concepts, prototypes were designed and suitable analytical models were derived. Measurements showed that flow forces in particular have a major impact on the functionality of the prototypes. Critical parameters that influence the miniaturizability of the valve are explained and an outlook is given on possible follow-up work with regard to the scalability of the valve concept.
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