A hydraulic power steering system uses a hydro-mechanical bilateral servo mechanism to assist the driver in applying steering input commands to the vehicle. A violent self-excited vibration accompanied with sound, known as "judder", can occur during rapid steering maneuvers. It is explained explicitly using the present simulation model that the self-excited vibration is caused by the interaction of the hydraulic and mechanical (structural) dynamics of the vehicle. It is demonstrated that the main factors inducing the self-excited vibration are the response delay of wave propagation in the supply line, which can be represented decisively by the phase lag of frequency response characteristics of hydraulic impedance of the supply line at the servo valve end, as well as the sensitivity of the servo valve. Some specific analytical results that reveal the interaction of the hydraulic/mechanical dynamics are examined and compared with the experimental results performed on the bench test apparatus. Analytical results agree well with the test results. It is also explained that even if the system is dynamically unstable in substance the self-excited vibration can not occur owing to the coulomb friction acting on the rack bar, not when the vibration is excited over some threshold value. The proposed numerical simulation technique will be found to be very useful in searching the optimum parameters for steering design.

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Measurement and monitoring of air consumption in pneumatic elements are very important as countermeasures to environmental problems. However, it has been very difficult to measure the unsteady air flow and air consumption of such elements, with high degree of speed or accuracy. In this paper, we developed an air consumption measuring system for pneumatic elements, using an isothermal chamber and a laminar flow meter. We then evaluated the characteristics of the measuring system components and presented the design specifications of the developed measuring system. Moreover, we examined the frequency response and the transient response of this system. Finally, we practically tested the device to measure the air consumption of a pneumatic air tool. As a result, we confirmed the high usefulness.

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This paper studied the robust position control of cylinder using hydraulic transformer connected to constant pressure system. Based on the nominal model derived from mathematical model, the feedback type two-degree-of-freedom controller is designed and implemented. From simulation and experimental results, the disturbances including nonlinear friction torque, leakage flow and load force can be compensated and the good positioning accuracy is obtained. It shows that the proposed controller is effective.

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This study concerns the development and fundamental characteristic analysis of a novel proportional poppet type water hydraulic valve. In this study, we developed a novel proportional poppet type water hydraulic valve which uses leakage from the clearance between the main poppet and sleeve as initial flow to stabilize the initial operation of main poppet by taking advantage of characteristics of water that has low viscosity and thereby leaks easily. The experiment verified that the relation between the main flow rate and pilot flow rate of the developed valve is linear and that the developed valve is suitable for the PWM control. Furthermore, it is also demonstrated that a decline in control chamber pressure that follows the change of pilot flow is caused by the occurrence of cavitation around the main poppet, and that fundamental characteristics of the developed valve remain unaffected by this event.

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