In this paper, analyses of transient responses for hydraulic line systems including viscoelastic pipe are made by using an approximate calculating method due to frequency response.
The transfer functions of test lines were first derived by using a transfer matrix of the transmission line.In this transfer matrix, the viscoelastic characteristics of the pipe material and frequency dependent unsteady friction were taken into consideration.
The numerical results using the frequency transfer functions are compared with the strict solution obtained by applying the characteristics method or the experimental results. Also, the comparisons of the CPU time between the numerical methods using the frequency transfer function and the characteristics method (high-speed computing method) are made by using a personal computer. These results confirmed that the approximate calculating method due to frequency response is useful for analyzing the transient response of hydraulic line systems including viscoelastic pipe.

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In this paper, the control characteristics of a positioning accuracy improvement of hydraulic cylinders using a microcomputer are reported in the case of using a directional control valve and proportional-type flow-control valve. According to the experimental results, the positioning time has a tendency to become short when the load was added against the forward direction in method (1) and (2) among the three methods. Next, it became clear that the best suited return length of control method (3) positioned by correcting the error is three times the first overshoot ΔL.And, the positioning movement of the hydraulic cylinder has been simulated in the positioning accuracy and expression for calculating a limit value of the positioning accuracy has been proposed.

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In this paper, a method to analyze the characteristics of fluid films between a spherical valve plate and a cylinder block of axial piston machines is derived. Since the radius of the spherical surface is much larger than the pitch circle radius of valve plate ports, emphasis is put to clarify the difference between spherical valve plates and traditional plane valve plates. The characteristics discussed are the load carrying capacity and the film coefficients of both elasticity and damping. As a result, it is shown that the spherical valve plate is slightly superior to the plane valve plate.

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