The efficiency of a swashplate type axial piston motor is studied to improve its performance during starting and low-speed operation. The lubrication of hydrostatic slipper bearings, considered as one of the important problems, is greatly influenced by the friction characteristics of the ball joint. It deeply depends on understanding of this friction characteristics to elucidate lubrication and behavior of hydrostatic slipper bearings.
In this report, we made an attempt to formulate a new measuring method using a strain gage to eliminate the effects of particular friction of apparatus, and to measure thrust force of the ball joint and friction moment at the same time. The effects of friction characteristics of the ball joint on swashplate angle, supply pressure and rotation speed are experimentally cleared. Further, an improvement by using the slipper with forced lubrication holes is examined.

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Lubrication between the piston and cylinder of a swashplate type axial piston pump or motor affects performance greatly. It is desirable to make fluid lubrication condition in this sliding parts so that to decrease friction and abrasion. Understanding the lubrication condition between the piston and cylinder is very important to make optimal fluid lubrication in wide operating ranges.
In this report, degree of metal contact or separation based on fluid film between the piston and cylinder is observed by measuring separation voltage (contact electric resistance) under a constant voltage applied across the piston and cylinder. Further, effects of each operating condition and radial clearance between the piston and cylinder is examined by evaluating lubrication condition using data processing by a personal computer.

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This paper describes an adaptive speed control scheme for a pneumatic servo system which is composed of an axial piston motor and an electro-pneumatic proportional valve. The features of the adaptive control scheme are that it is applicable to non-minimum phase systems and that its structure is as simple as the MRAC.
Experiments of the adaptive speed control were carried out for several conditions, and their results were compared with those of the conventional PI-D control. From the experimental results summarized below, the effectiveness of the proposed scheme was confirmed :
(1) Three sampling periods (T_s=36, 71, 106msec) were tested, and the stability of the adaptive control system was confirmed for each Ts even through the identified plant model was non-minimum phase. The steady state error was not influenced by T_s, and its maximum value (±1.0rpm) was smaller than that of PI-D control (±2-±2.5rpm) for a reference speed larger than 300rpm.
(2) The second order reference model was used to specify the wave-form of the step response, and good tracking performance was obtained for several damping coefficients and natural frequencies. The distortion of the step response for large amplitude inputs was much smaller than that of PI-D control.
(3) A sudden change of the load torque or supplied air pressure was applied to the control system as a disturbance. The speed fluctuation was much the same as that of PI-D control.

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We have proposed a remote instantaneous flowrate measurement method, a quasi-remote instantaneous flowrate measurement method and an instantaneous flowrate measurement method by using pressure measurements at two separated points along the pipeline for estimating unsteady flowrate through an arbitrary cross section of the pipeline in hydraulic control systems. In these approaches, unsteady flowrate can be accurately estimated by using the distributed parameter models of the hydraulic pipeline with considering unsteady velocity distribution over the cross section of the pipeline. Under unsteady laminar oil flow conditions, the excellent agreement of estimated and measured flowrate waveforms by a cylindrical choke type instantaneous flowmeter is obtained.
Because these approaches make use of the distributed parameter models for estimating unsteady flowrate, the spatial resolution along the axial direction of the pipeline has an outstanding ability. The accuracy and dynamic response of the estimated unsteady flowrate depend on the values of the parameters used such as the length of the pipeline, kinematic viscosity of the oil, sonic velocity inside the oil-filled pipeline, radius of the pipeline; therefore, it is possible that such variations would cause the estimation errors of unsteady flowrate measurement due to parameter changes accompanied by varying an operating conditions.
The paper describes the estimation errors of unsteady flowrate measurement due to parameter changes in quasi-remote instantaneous flowrate measurement method and instantaneous flowrate measurement method using pressure measurements at two separated points along the pipeline. By introducing error performance index, the influence of parameter changes on the accuracy and dynamic response of the estimated unsteady flowrate are evaluated. Of the four parameters, the variations of the length of the pipeline and sonic velocity produce large errors in the estimated unsteady flowrate during transient periods. The kinematic viscosity is relatively insensitive in the estimated unsteady flowrate.

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