Making use of a direct drive servovalve's driving current, which is in proportion to the driving force, and the spool displacement obtained from a built-in LVDT, it is possible to get the state variables such as flow force, flow rate and load pressure for the purpose of valve control without attaching other transducers on the servovalve. In this paper, experiments were carried out using different loads. With PWM driving, no hysteresis appeared regardless of the flow rate. Because of the flow force compensation on the spool of the valve used in the experiment, an empirical equation was used for calculation of the flow rates from the measured flow forces. Under different loads, the calculated flow rates were in consistence with the measured ones. Then, load pressures were obtained from the calculated flow rates, with the discharge coefficients acquired using empirical equations. The calculated load pressures were in good agreement with the measured results.

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To investigate the effect of working fluid in solenoids on dynamic characteristics of proportional control valves for improving the valve responses, as an example under one of most severe conditions, dynamic characteristics of a proportional control valve with damping chokes are experimentally investigated. Damping chokes are usually used to improve the stability of spool position control, however, the effect on the dynamic characteristics has not yet been sufficiently clarified. For example, it is known that the dynamic characteristics are changed by the tank line back pressure when high water content fluid is used. The phenomena thought to be caused by cavitation bubbles, however, has not yet been clarified.
In this paper, firstly, the dynamic characteristics of a proportional control valve equipped with additional damping chokes are experimentally investigated. Secondly, a mathematical model describing the nonlinear dynamic characteristics is derived and verified by computer simulation. Finally, a robust control method using a disturbance observer is applied to improve the characteristics and the performance is subsequently examined with computer simulations and experiments.

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A high pressure electro-hydraulic 2 port valve, 6mm in diameter with a 0.4mm stroke, was developed for a cyclic pressure test of diesel fuel pipes. The valve compensates steady-state flow force and reduces leaks from both the valve seat and lands to as low as possible for controlling 200MPa diesel fuel. This paper describes the valve design, test results of flow force compensation and of the relation between leak and Hertzian pressure at the valve seat, leaking from the clearance of the lands. It is applied to the cyclic pressure test of a pipe, 560mm in length and 1.59mm in bore.

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The sound power radiated from a hydraulic fluid power pump under real operating conditions is investigated using FEM analysis so as to develop a computer simulation program for reducing the pump audible noise level by the vibration control technique. A variable-displacement, swash-plate type of axial piston pump, is examined as the test pump. The author's devised a new method replacing the real moving exciting force with the virtual stationary forces applied on the three node points of the FEM model, which enables one to analyze the forced vibration of pump structure with the FEM, is used for the estimation of air-vibration power level on the entire surface of the pump structure. The measurements of the sound radiation power are also taken by the sound intensity method based on the ISO 9614 in order to investigate the appropriateness and industrial availability of the present FEM analysis. The value of the sound radiation efficiency necessary for the estimation of sound power by the FEM is experimentally determined by comparing the air-vibration power predicted from the measured vibration acceleration at 190 points on the pump's surface with the measured sound radiation power.
The harmonic amplitudes of sound radiation power estimated by the FEM analysis agrees well with the measured values with an accuracy sufficient for practical usage for its complex structure for almost all harmonics up to around 3 kHz except the frequency ranges around some resonances and anti-resonances. It is also shown that the effects of improvement of valve-plate design on the noise reduction can be predicted by the proposed FEM simulation analysis within an accuracy of around 3dB in an over-all RMS of sound power.

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