The primary purpose of this study is to develop an actively controlled suspension for automobiles or railway cars. To improve the riding quality, since pretty low frequency vibrations have to be attenuated, the very low natural frequency of a suspension is required. This has been usually accomplished by using an air spring. When an actuator is mounted to control this suspension, it is preferable for the actuator to have as low stiffness as an air spring. A pneumatic actuator is most suitable for such applications.
In this study, an active suspension is constructed using a pneumatic servo comprising a pneumatic cylinder and electro-pneumatic proportional pressure control valves. Some control schemes are examined to find the effective control method to improve the vibration control performance. As a result of comparing some types of feedback control, it was proven that the relative displacement feedback control with a negative feedback gain is most effective to attenuate the vibration, and in which the control performance is most insensitive to the operating delay of the pneumatic servo system. Further, an optimal regulator is applied to this suspension, and a modeling procedure of the suspension and a suitable performance index necessary to design the control system are clarified.
Through this study, it is indicated that a pneumatic servo can be available to an active suspension, and of which performance may be additionally improved by compensating for the operating delay of the control valves.

View full abstract

A fluidic sonic oscillator is used as a pulse generator, temperature sensor and flow meter. We proposed an oscillator in which the intermediate position of the loop on the sonic oscillator is open to air. The authors call this oscillator control loop open-type oscillator. We think that it is interesting to study oscillatory phenomena of this oscillator and it is important to pursue possibilities as an oscillator.
In this paper, the oscillation frequency of this control loop open-type oscillator is investigated theoretically and experimentally. We think this oscillator has the same phenomena as the sonic oscillator of which pressure variation at the intermediate position of a loop was nearly zero. However it did not oscillate if there were restrictors at output conduits on the oscillator. At first, we propose a mathematical model. The mathematical model for the oscillator is derived distributed parameter elements model and lumped parameter elements model in accordance with compressibility of the fluid in the control loop.
Next, we analyzed it using digital simulation methods and describing function methods. Theoretical results were confirmed by the experimental ones.
The results obtained can be summarized as follows.
1) We proposed a mathematical model for the control loop open-type oscillator and analyzed it. The results agreed well with experimental results.
2) This oscillator is useful as a pulse generator, temperature sensor and flow meter similar to the sonic oscillator.

View full abstract

The problem in the study assigned was improvement of the 'Swashplate Type Axial Piston Motor', especially its starting and low-speed performance. The aim of this report is to provide technical data to help explain these problem points and increase overall efficiency. The lubrication of some sliding parts, which used hydrostatic bearings, was considered an important problem.
It is thought that leakage characteristics of the hydrostatic slipper bearing produces a large effect on this motor's characteristics. The static balance problem of the hydrostatic slipper bearing during the starting condition is considered. The theoretical formulae for friction of the sliding parts, slipper's tilt to swashplate and piston's tilt to cylinder bore were considered with a simulation being carried out.
The results obtained are as follows :
(1) At a swashplate angle of 15°, the slipper was balanced to the swashplate statically in a tilting condition, but when the swashplate was 0°, it was balanced in a parallel condition.
(2) While loading and unloading, the leakage showed hysteresis at a swashplate angle15°, but this was not shown when the swashplate angle was 0°.
(3) At a swashplate angle of 15°, the leakage increased as the piston's thrust-out length increased, but was constant at a swashplate angle of 0°.

View full abstract