Digital hydraulics is an ongoing trend that offers many interesting advantages and possibilities. Digital refers to that the system output is discrete, e.g. using an on/off valve with only discrete values or a finite amount of flow steps available. The advantages mentioned when compared to analogue systems are better performance, robust and fault tolerant, and amplitude independent bandwidth. On the other side noise and pressure pulsations must be handled, the physical size can be a problem, and the system requires complicated control. When considering control of linear motion, there are mainly two branches, controlling the flow with several parallel connected on/off valves, which generates discrete output flow values, or switching valves, which in theory can generate any mean output flow. The latter only requires one valve for each flow path but the demand for fast valves is very high, while the former requires many valves but avoids high frequent switching. With the introduction of a multi-chamber cylinder, secondary control is now also possible for linear motion. This paper is a first step in the investigation of the system applied to an excavator arm. The cylinder has four chambers, each with different area. Three pressure lines are used and a valve-pack of 27 on/off valves. The valve-pack connects the three pressure lines with each chamber generating 81 available force steps. The scope has been to start out with relative simple control of the velocity of the cylinder. To handle unnecessary switching of valves, different penalty strategies were tested. The results are promising where relatively smooth control could be achieved at the same time challenges with the system were identified. Next step is to investigate the force transients due to different capacitance in all four chambers as well as mode control for better accuracy. Energy potential compared to original system remains to investigate as well.
In recent years much research has been done in the area of variable-valve actuation in order to improve the eYciency of combustion engines. Currently, a number of diVerent concepts for variable-valve actuation are under development or at a prototype stage. Hydraulic actuation has been an obvious candidate, but the lack of suYciently fast switching valves with appropriate owrates has been the major shortcoming. Design of such highly dynamic systems requires accurate models of the actual included components.In this paper a model of a fast 2/2 switching valve is presented, where both the magnetic path as well as the spool assembly are modelled. The model presented here is primarily aimed at system simulations; therefore it has to be kept simple with the number of parameters low.Some of the parameters are often hard to obtain, especially when it comes to magnetic material properties. In this study, an optimization strategy has been utilized in order to parameterize the model against measured data. However, even for major deviations from the operational point used for the model adaptation, the model predicts the valve response suYciently accurately.
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