An oil hydraulic pilot relief valve has been empirically investigated to fully understand its static performance. Constriction components which dominate the flow in the valves have been individually examined in detail, revealing that the static relation between the pressure drop, flow rate and opening area for a constriction can be represented, not by the traditional hydraulic orifice equation which has always been used for the purpose but by a new one including an additional pressure loss proportional to the flow rate and the fluid viscosity and inversely proportional to the square of the opening area. The new characteristic equation has proved to consistently predict the experimental findings in which the rise in oil temperature results in an increase in the piston displacement, but causes little changes as regards regulated pressure. It has also turned out that, contrary to conventional preconception, the fluid force exerted on a poppet is negligible. On the other hand, that regarding a piston can be influential and works to increase the pilot flow.

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The purpose of this study is to find a faster and more convenient method for simulating a transient response of viscoelastic transmission lines. Another objective of this study is to formulate and evaluate rational polynomial approximations for an exact model for viscoelastic transmission lines. If an approximation by rational polynomials is carried out using precision accuracy, we can adopt conventional methods of numerical integration for ordinary differential equations, and thus, we obtain a faster and more convenient method for simulation. It could be confirmed that the results of simulation agreed well with the experimental results, and thus, the usefulness of the proposed method could be verified.

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The more efficiency regarding the hydrodynamic torque converter is an important because of the role it plays as the automatic transmission in fuel consumption and power train performance.
As for the stator which is in charge of torquing up, it is necessary to clarify the flow through the stator for the optimization of the hydrofoil.
In this study, a circular flow apparatus for visualization was used for detailed measurements of the flow around the stator blade.
By making bubbles the tracer and visualizing the water flow, separation, separated region and velocity distribution could be clarified by LDV measurements. Concerning separation and separated region, the difference between the two kinds of typical stator blades used for the torque converter was studied.

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Regarding electrical power sources, the switching regulator is widely used because the efficiency exceeds that of other types such as the regulator using an analog circuit. A pneumatic pressure servo system directly operated by switching valves is expected to have a higher efficient and compact pressure regulator, instead of the diaphragm type pressure regulator, though there is a ripple in the output pressure fundamentally. The ripple is not improved sufficiently because when the operating threshold level of switching valves is set to its extreme to reduce the ripple, unexpected switching occurs caused by noise which is included in the output pressure.
In this report, the mechanism of the appearance of the unexpected switching action is analyzed, and as a result, it is shown that the principal cause of this problem is the resonance occurring in the pressure vessel and the detected pressure crosses the threshold level incorrectly having a detrimental influence on the resonance. The frequency of resonance can be supposed easily and it is convenient in designing a noise filter to its reduction. From this viewpoint, the digital FIR or IIR filter is introduced to overcome this problem and the effect on the reduction of ripple and the performance are determined by the use of experiments. Furthermore, the proper design of the filter for this system is discussed and shown.

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