A slipper in piston pumps and motors is modeled as a bearing system combined with spherical and thrust hydrostatic bearings. The tribological characteristics of the bearing in fluid film lubrication are examined theoretically in an unsteady state. The equations of the load-carrying capacity, recess pressure, leakage flow rate, frictional torque and power loss with a capillary or orifice restrictor are formulated. The motion of the hydrostatic slipper is simulated numerically with a time-lag condition of loads. The effects of the operating conditions and the bearing geometry on the dynamic characteristics are discussed. In conclusion, the time-lag between the supply pressure and load affects notably changes in the clearance and rotational speed. The preceding change in load causes larger clearance during the low pressure period. A decrease in bulk modulus or an increase in the recess volume yields obvious changes in the clearance. As the supply pressure increases, the clearance changes largely and the mean power loss increases substantially.

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The aim of our study is to suppress cavitation near the flange of an actual poppet valve by changing the shape of the flange. The experimental flow visualization technique and numerical flow analysis using the vortex method and boundary element method are employed to achieve the purpose. In the flow visualization, cavitation phenomenon near the flange is observed using an industrial fiber scope inside an actual balanced piston type relief valve which is used in oil hydraulic systems. On the other hand, in the flow analysis, the two dimensional vortex method and boundary element method are applied to estimate cavitation near the flange. Ten types of poppets are designed by changing the shape of the flange, which is expected to influence the jet flow issuing from the orifice. In conclusion, the physical region of cavitation and the cavitation region of the Reynolds number-cavitation number plane are small for an optimal poppet geometry obtained in the present study.

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This paper presents development research of a silencer called “multi degree of freedom type Helmholtz resonator”. It was newly developed and its attenuation characteristics (transmission loss and insertion loss) were investigated theoretically and experimentally. Unlike a conventional Helmholtz resonator, this device has a feature that it is possible to adjust freely the resonance modes to desired resonance modes, i.e., the desired resonance frequencies and mode shapes, with a single closed-end cylindrical tube configuration. The present resonator was devised in order to attenuate the successive several harmonics of fixed discrete-frequency pressure pulsation such as those generated by a fixed speed hydraulic pump. A successful mathematical means (optimum design method) of sizing the desired variables so that the plural resonance frequencies coincide with the desired ones is outlined. Calculated (designed) attenuation characteristics of the present resonators, which are designed under three kinds of constraint conditions, i.e., constraint condition of transmission loss, amplitude of pressure pulsation after silencer insertion and insertion loss at the desired objective resonance frequencies, all agree well with experimental results.

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Brake mounted pneumatic cylinders are used for the purpose of transferring machinery for many industries because of their low cost and their cleanliness. It is important to improve the positioning accuracy of pneumatic cylinder for matching to the demand of every industry. Therefore many researchers have studied learning algorithms to improve accuracy and to estimate the overrun error by changing the operating time of the valves. However some trials are needed to learn the characteristics, and load change is not taken into account at all. In this paper a new learning algorithm based on the braking model is introduced and is confirmed to realize not only high learning speed but quick adaptation to load change as well. It is found through various field tests that good positioning has been achieved and that this method is practical and effective.

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