Efforts to save energy have been made in a number of fields due to a shortage of energy resources, such as oil, and a need to protect the earth’s environment. In the field of hydraulics, energy saving pump units are very important because of the energy they consume. At present, a variable displacement-type hydraulic pump units (VD pump unit) and inverter control-type pump units (INV pump unit) are widely used. In this paper, the authors propose using an intermittently operated pump unit coupled with an accumulator (ACC pump unit). First, the electric power consumption, pump output pressure, rotation speed, and efficiency of three types pump units are measured when the same work is done using a modeled machine tool. Next, the load is abstracted to clarify the general characteristics of intermittent work, and the electric power consumption and efficiency of each pump unit are measured. Finally, the static characteristics of each pump unit are measured, and it is verified that the ACC pump unit saves the most energy.

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