This paper describes the design and performance of an electrohydraulic position control system which is basically composed of a solenoid valve, a hydraulic actuator and a microprocessor. Selflearnings trategiesw ere used to take advantage of a simple On-Off control which is the most suitable for a minimum time control, and to achieve more accurate positioning than a conventional PWM control without instability. This was done by developing acontrol algorithm for the microprocessor which always automatically adjusts the length of control pulse to the optimum value in accordance with the error regardless of changes in the operating condition and physical differences between components. Tests carried out in the laboratory indicate that a positional accuracies of about 10 μm and response speed up to about 5 Hz could be achieved by the present system, even though the solenoid valve had a switchings peed similar to those commerciallya vailable.
One of the authors developed an electrohydraulic fuel injection timing control system for diesel engines on the basis of the present system, which has already been put to practical use.

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Recently, a new instantaneous flowrate measurement system making use of cylindrical chokes has been proposed and developed by the authors. The newly developed instantaneous flowmeter has been already shown to respond to changes in the flowrate at high frequencies above 200Hz in comparison with the LDV instantaneous flowmeter.
In this report, the instantaneous flowmeter making use of cylindrical chokes is compared with the gear-motor-type flowmeter.
The results of the frequency response test indicated that the gain of the flowrate of the gearmotor-type flowmeter relative to the flowrate of the cylindrical choke flowmeter was nearly unity up to 100 Hz and the phase lag of the flowrate of the gear-motor-type flowmeter relative to the flowrate of the cylindrical choke flowmeter became 90 degrees at 120 Hz. It was also found that the pressure difference between both ports of gear-motor-type flowmeter increases in proportiont o the frequency of the flowrate variation in a high frequency region of more than 10 Hz.
It can be explained that the delay of the gear-motor-type flowmeter in the high frequency region is mainly attributed to a first-orderd elay consisting of the inertia of gears and internal leakage of the gear motor.
It was shown that the instantaneous flowmeter utilizing cylindrical chokes can be made use of for dynamic testing and monitoring in the area of the oil hydraulic systems.

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A conventional valve-controlled servo system is usually powered by a constant pressure power source where the pressure is set by a relief valve. In this kind of power source, the power loss becomes maximum when the actuator is stopping at a certain position.
In this study, a new type of energy-saving power source is proposed. In this power source, the speed of the induction motor to drive the fixed displacement pump is controlled by an inverter in order to adjust the delivery of this pump and to control the system pressure without making use of the relief valve.
The power efficiency of the energy-saving power source with the inverter is investigated. The methods of pressure feedback control and programmed control using the microcomputer are discussed and the results have been experimentally verified.

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