As a result of a shortage of energy resources such as oil and the need to protect the earth’s environment, energy saving efforts have been made in a number of fields. In the case of hydraulic equipment, energy saving in pump units is key because this unit is the major consumer of energy.
Up to the present, variable-displacement hydraulic pump units (VD pump units) and inverter-control hydraulic pump units (INV pump units) have been widely employed. Here the authors propose the use of an intermittently operated hydraulic pump unit coupled with an accumulator (ACC pump unit) . In a previous report, the superiority of the ACC pump unit was demonstrated through an experiment using a modeled machine tool and a simplified load model. In this report, we compare electric power consumption, pump output pressure, rotation speed and efficiency of the VD pump unit, INV pump unit and ACC pump unit when hydraulic fluid is supplied to the load at a fixed flow rate. In addition, the effects of the accumulator volume and the pressure ratio between the upper and lower limits on efficiency and the ON-OFF switching period of the ACC pump unit are determined.

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A highly accurate unified computation of transient response in pipelines is desirable in order to improve pneumatic components. This paper deals with a high resolution simulation of transient response in laminar pipe flow by solving the governing equations directly. The authors employed a TVD scheme for computation of its stable and less diffusive properties. To apply this scheme, the governing equations must be described for a conservative system. The time-dependent friction loss in laminar pipe flow, which had only been discussed for a non-conservative system, was therefore transformed into a conservative system and solved with the Chakravarthy-Osher TVD scheme. Computations for a pneumatic pipeline with several pipe diameters were performed. The computations for the developed method were compared with the standard CIP method, and showed higher resolution, more stable computation and shorter computation time than the CIP method. The developed method can be easily applied to turbulent or high-amplitude pipe flow by simply changing the friction term.

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Hydraulic systems feature compact, high-output power and rapid response. However, when air bubbles are mixed into the hydraulic oil, they lower the efficiency of hydraulic systems and contribute to instrument malfunctions. Therefore, it is important to eliminate these bubbles from the oil. Our project team has been developing an active bubble elimination device termed a bubble eliminator, which removes air bubbles using a swirl flow. The shape of the device affects the removal performance, so the choice of shape parameters is key to improved performance of the device. The purpose of this study is to optimize the shape parameters of the bubble eliminator. We focus particularly on the optimal diameter of the vent port. In order to determine this parameter, flow behaviors in the bubble eliminator are investigated in the laboratory with transparent bubble eliminators and numerical analysis of the experimental conditions. The validity of numerical simulation is verified by comparing its results with flow patterns obtained from image photos of an experimental flow visualization. Numerical analysis is carried out under fixed conditions, and an optimal diameter for the vent port is determined.

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