Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Patent
1993-04-27
1994-08-02
Look, Edward K.
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
60452, 60484, 91446, 91448, 91461, F16D 3102, F15B 1108
Patent
active
053334493
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Field of the Invention
The present invention relates to a valve apparatus for use in a hydraulic drive system of construction machines such as hydraulic excavators, and more particularly to a valve apparatus used when an optional hydraulic actuator is attached to a hydraulic drive system of load sensing type.
2. Background Art
Recently, in hydraulic drive systems for construction machines such as hydraulic excavators, for example, from the standpoint of economy, many machines have adopted load sensing control by which a delivery pressure of a hydraulic pump is controlled to be held higher by a fixed value than the highest one of the load pressures of plural hydraulic actuators. On the other side, in consideration of versatility of work to be carried out, such an arrangement has been adopted that an optional hydraulic actuator such as a crasher is detachably attached to the end of a front.
As disclosed in JP, A, 60-11706, for example, a hydraulic drive system of load sensing type uses, as a directional control valve for controlling a flow of hydraulic fluid supplied from a hydraulic pump to a hydraulic actuator, a directional control valve of closed center type that is blocked at the center in its neutral position and has a load pressure detecting function. On the other hand, a hydraulic drive system provided with a directional control valve of open center type that is kept fluid-communicated at the center in its neutral position, has been known for many years and has become widespread. At the present time, it is not said that the directional control valve of closed center type for use in the hydraulic drive system of load sensing type is so common as the directional control valve of open center type.
Meanwhile, the hydraulic drive system of load sensing type includes a pressure compensating valve which holds constant a differential pressure across a flow control portion of the directional control valve for the purpose of maintaining a plurality of actuators independently of one another when those actuators are driven at the same time. A single valve apparatus having both a flow control function and a pressure compensating function has so far been described in "Practical Oil Hydraulic Pocketbook (1986)", pp. 190-191, Hydraulic Industries Association of Japan (Incorporated Body) and "Oil Hydraulic Power And Its Industrial Applications", pp. 246, 249 and 250, Walter Ernst, 1960, McGraw-Hill Book Company, Inc., for example. That valve apparatus has an inlet chamber and an outlet chamber; a flow control valve portion comprising a passage communicating between the inlet chamber and the outlet chamber, a spool disposed between the communicating passage and the outlet chamber and having an opening, the extent which is changed when displaced, and a manually operable adjuster held abutted against the spool for setting an extent of the opening; and a pressure compensating valve disposed between the inlet chamber and the communicating passage for holding constant a pressure difference between a pressure in the communicating passage and the outlet chamber, i.e., a differential pressure across the opening. The flow control valve portion includes a spring for urging the spool in a direction to open the opening until the spool abuts against the adjuster, and the opening extent is set by manually operating the adjuster from the exterior.
DISCLOSURE OF THE INVENTION
When an optional hydraulic actuator is mounted to a hydraulic drive system, a directional control valve is also provided on the optional hydraulic actuator. In the case of providing the directional control valve on the optional hydraulic actuator, there is a demand on the side of designers and manufacturers to provide a directional control valve of open center type that is more general and more easily available as mentioned before. The same demand is seen in the case of mounting the optional hydraulic actuator to a hydraulic drive system of load sensing type. However, when the directional control valve of open center type is attached to the hy
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"Practical Oil Hydraulic Pocketbook", (1986), Hydraulic Industries Association of Japan, pp. 190-191.
"Oil Hydraulic Power and Its Industrial Applications", McGraw-Hill Book Company, Inc., 1960, pp.246, 249-250.
Ino Kazuyuki
Nozawa Yusaku
Takahashi Kinya
Hitachi Construction Machinery Co. Ltd.
Look Edward K.
Ryznic John
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