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Generally, the valve controlled electro-hydraulic systems are able to achieve high motion tracking precision, but suffer from large amount of throttling losses. As an alternative, although the direct pump controlled systems are highly energy efficient, it is far more complicated to attain high tracking precision. In order to achieve both objectives of high precision tracking performance and high energy efficiency, a kind of novel pump and valve combined electro-hydraulic system is developed in this paper. The basic working principles are that the pump supplies the majority amount of flow driving the actuator in a highly efficient way, while the valves are involved to ensure the tracking precision. The controller with four parts is designed to handle the challenges from not only the common nonlinear properties of the hydraulic system, but also the additional flexibilities brought by the hardware combination. Two sets of comparative experiments are conducted to show the advantages of the proposed method by tracking both slow and fast motion reference trajectories. The results indicate that the proposed system is able to realize the same high level of tracking precision as the valve control method, but consumes about 35%-47% less of energy.
Lyu et al. (Wed,) studied this question.