This paper presents an analysis of the potential for engine speed reduction in hydraulic equipment, taking into account not only the minimum engine speed required to meet the current flow demand, but also the minimum speed capable of accelerating the engine to meet increased flow demand in the near future. This is a predictive task, as it requires an estimate of the operator's intention to increase flow demand. We present an analysis of the potential for engine speed reduction using a work cycle from a 40 ton excavator loading a truck, which results in a potential 33% reduction in the mean engine speed with no reduction in useful work rate. We also present two new engine speed control algorithms to perform this predictive task. These controllers are easy to tune and require only a small amount of information about the plant and work cycle. A simulation study is performed that demonstrates the controller's performance and studies the effect of tuning parameters.
Hydraulic linear actuators dominate in high power applications but are much less common in low power (<100 W) systems. One reason for this is the cost: electric actuators in this power range generally exhibit lower performance but are also much less expensive than hydraulic systems. However, in recent years, some miniature hydraulic components have been mass produced, driving down prices. This paper presents the application of these low-cost components, together with a novel very low-cost 3D-printed valve to create an electrohydrostatic actuator. Capable of very high power and force density, this system is competitive on cost with lower-performing electric actuators. This paper presents models for the system’s performance, as well as experimental validation data.
Switched inertance converters use digital valves to exploit the inertia of a flow in order to trade flow for pressure or vice versa. These components can be used to efficiently match load and supply pressures, avoiding the energy wasted by using resistive valves. While theoretical switched inertance converters can be highly efficient, practical implementations suffer from a number of energy losses. One of these losses is the valve switching loss: the energy wasted due to the flow experiencing a pressure drop across the partially open valve as the digital valve shifts from one position to the other. This paper quantifies the effect of this loss on the valve’s overall performance. Two novel strategies for mitigating this effect are introduced: a shaped inertance tube design and positioning of the tank-flow valve along the length of the inertance tube.
This paper presents an improved method of time-domain modeling of pressure wave propagation through liquid media in rigid tapered pipes. The method is based on the transmission line model (TLM), which uses linear transfer functions and delays to calculate the pressures and/or flows at the pipe inlet and outlet. This method is computationally efficient and allows for variable rate simulation. The proposed form of the model differs from previous TLM models in the literature, allowing it to accurately model both low and high frequency characteristics.
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