Primarily in use at present is the nozzle flapper type servo valve providing with a torque motor.
It is not in all cases appropriate for construction machines requiring large flow, owing to small control flow of the nozzle flapper.
To deal with this situation, the linear motor servo valve using a magnet for a proportional solenoid has been developed.
By driving metering spool directly by a linear motor, neutral leak is kept small and control flow increases.
This valve operates independently of supply pressure fluctuation, i.e, pressure compensating characteristics.
For large stroke of the linear motor, the orifice diameter is large, thus greatly lessening the possibility of contamination failure of the valve.
Frequency response of the main spool is as much as 70Hz.
This valve is thus shown suitable for construction machines.
The servo valve was applied to the excavator vibro cylinder and the results indicated good controllability and high endurance.

抄録全体を表示

Load-sensing concept and general control scheme are not new and they have been widely used for many industrial hydraulic systems, including hydraulic excavators.
However, when applied to hydraulic excavators, many technical problems still remain to be resolved. For example, vibration due to the load sensing servo loop, acceleration control of the inertia load and maneuverability of simultaneous multi-operation of the actuators, are some of the main problems that need a solution.
We have constructed a simulator model of a hydraulic excavator which incorporates all control components, that is, engine-pump speed sensing circuitry, L. S on-off regulator, 6 pressure compensated valves and 6 actuators combinations, namely, boom, arm, bucket cylinders and swing, and travel hydraulic motors.
The most difficult problem regarding load sensing is how to overcome instability due to low damping of the load-sensing dynamics.
The second most difficult problem is how to obtain smooth operation during inertia load. Of course, there are other many important problems to solve for the realization of load sensing shovel, but the above two are extremely important for an actual system.
We studied these problems by simulating the detailed behavior of the load-sensing hydraulic system, with good results being obtained.
By combining the above-mentioned simulator study, we could develop an electronically controlled load-sensing hydraulic excavator, which is a first in this area.

抄録全体を表示

This paper describes a new method for the model reference I-PD controller using neural networks. I-PD controllers are being widely used because of their excellent performance. However, an effective method for determining I-PD gains has yet to be developed. In this paper, we have come up with an auto-tuning method for the I-PD controller using neural networks. This method deals with coupling coefficients of the networks as I-PD gains of the I-PD controller. The coupling coefficients are adjusted using a back-propagation algorithm so as to minimize the error between the controlled object and reference model outputs. The experiments conducted show that this method is effective in controlling the position of pneumatic cylinder.

抄録全体を表示

On the occasion of the brake, if we apply the same pressure to front and rear wheels, the rear wheels lock before the front wheels. This is owing to the change in the load of the front and the rear wheels with the deceleration. To avoid this situation, “Pressure proportioning valve” is installed in vehicles to decrease the brake pressure on the rear wheels.
Ever increasing demand for a vehicle improvement has led to smoother passenger riding comfort. Even slight noise is no longer permitted. Many countermeasures for this purpose have been applied on a case by case basis without knowing the reasons of the noise generation.
This paper discusses the mechanism and characteristics of the noise generated from the hydraulic components of the brake system. The following conclusions were made based on the results of this study;
(1) Auditory noise from the hydraulics of the brake system on the occasion of the brake and the release is generated by lateral vibration of the poppet valve which regulate the brake pressure.
(2) By the vibration of the poppet valve, there occurs the pressure pulsation. The pressure pulsation stimulates the pipe wall. Owing to the stimulation by the pressure pulsation, the components of the natural frequencies of the pipe wall are emphasized and the auditory noise is emitted to the surroundings.
(3) Additional countermeasures for noise reduction are proposed.

抄録全体を表示

To clarify unsteady cavitation mechanism of orifices, which are widely used in fluid power systems, some experiments about two shapes of orifices were carried out under sinusoidal and stepwise flows.
Cavitation was mainly detected by pressure ripples at the outlet side of the orifice, and also a TV camera was used to observe the cavitation clouds. For the case of sinusoidal flows, the effects of average flow rate, amplitude and frequency to the inception and desinence of cavitation or cavitation choking were mainly shown along with the number of cavitations.
Finally, cavitation characteristics of a orifice are compared with those of a long orifice already reported.

抄録全体を表示