FPMC 2022 BATH/ASME Symposium on Fluid Power and Motion Control
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The key element of hydraulic switched inertance control systems is the switching valve. Off the shelf valves do not have sufficient performance in terms of dynamical response, characterized by the switching time and the durable switching frequency, necessary for a compact design of the system. In the published work two concept classes of switching valves have been considered so far: fast switching solenoid valves and rotary valves, driven by an electrical motor. Both concepts have pros and cons. The solenoids of of conventional on-off valves dominate the valve costs and for the strongly increased performance level of fast valves needed in switched inertance control the costs are even higher, the more so because of the costs of the power electronic devices needed for a proper control. Rotary valves typically require a second actuator in addition to the rotary drive and a sophisticated valve design, all together leading to high costs too and, furthermore, to a bulky embodiment. For a practical realization of inertance hydraulics simple and cheap components which are composed of proven hydraulic design concepts are necessary. This paper investigates a concept based on a conventional, hydraulically piloted 2-2 way on-off valve. The pilot system uses as input the desired output pressure of the buck converter in form of a pressure signal and an RC filtered feedback of the actual pressure. These pressures act via small plunger cylinders in opposite direction on the on-off valve. These plungers feature a jumping active hydraulic area for a robust feedback. The valve performs close to rectangular oscillations, the frequency of which is mainly determined by the characteristic time of the RC filter. The concept is studied by a simple analytical model to obtain its basic operating characteristics and by a detailed numerical model to analyse the role of parasitic effects on system performance.