Motors: expansible chamber type – With motive fluid valve – Relatively movable serial valves
Patent
1997-02-04
1998-11-10
Nguyen, Hoang
Motors: expansible chamber type
With motive fluid valve
Relatively movable serial valves
91421, 91436, 91461, 13762563, 13762566, F15B 1108
Patent
active
058328084
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a directional control valve unit for supplying a pressure oil to a cylinder of a working machine. Specifically the cylinder is for moving the working machine up and down. The working machine may be an arm or a boom of a hydraulic shovel.
BACKGROUND ART
A working machine is moved up and down by extending or retracting a working machine cylinder through the supply of a drain pressure oil from a hydraulic pump to a raising (to move the machine up) side chamber and a lowering (to move the machine down) side chamber of the working machine cylinder. A directional control valve unit is used to supply the drain pressure oil. In order to increase a lowering speed of the working machine (i.e., the retracting operation speed of the working machine cylinder) a portion of a return flow rate from the raising side chamber is supplied (i.e., reproduced) to the lowering side chamber, thus rapidly contracting the working machine cylinder.
For example, as disclosed in Japanese Patent Laid-open Publication No. HEI 3-28501, there is known a directional control valve unit in which a first port is connected to a lowering side chamber of a working machine cylinder and is in communication with a regeneration port via a regeneration passage provided with a check valve. A second port is connected to a raising side chamber of the working, machine cylinder and is in communication with a tank port. The second port is also in communication with the regeneration port. Thus, regeneration of a portion of a return flow rate from the raising side chamber to the first port through the regeneration passage occurs. Hence, the lowering speed of the working machine is increased.
According to the directional control valve unit of the structure described above, the lowering speed of the working machine cylinder can be increased by an amount corresponding to the regeneration flow rate of a pressure oil flowing from the raising side chamber to the lowering side chamber without increasing the flow rate from the hydraulic pump.
In such a directional control valve unit, an opening area between the second port and the tank port (i.e., the meter-out opening area) and an opening area between the second port and the regeneration port (i.e., the regeneration opening area) are increased or decreased in accordance with the moving distance (displacement) of the spool. Accordingly, the regeneration flow rate is determined by the moving distance of the spool. Hence, the lowering speed of the working machine cylinder is univocally determined by the moving distance of the spool.
Furthermore, since the spool of the directional control valve unit is moved by a pilot pressure from a hydraulic pilot valve, the moving distance of the spool may be changed by adjusting the pilot pressure. However, it is difficult to always univocally change the moving distance, and moreover, it is impossible to change the moving distance to a different predetermined value. Therefore, it is impossible to change the lowering speed of the working machine cylinder to a different speed.
Further, in cases where a deep excavation is performed by a hydraulic shovel, since a bucket is moved a long distance vertically, it is necessary to increase the lowering speed of the working machine cylinder to a level greater than that in a usual excavation in order to improve the excavating efficiency.
In view of the above problems, an object of the present invention is, therefore, to provide a directional control valve unit capable of changing a lowering speed of a working machine cylinder in a plurality of stages. The lowering speed is changed by increasing or decreasing a meter-out opening area and a regeneration opening area through the changing of the maximum moving distance of a main spool in a plurality of stages in one direction. The lowering speed is also changed by increasing and decreasing the flow rate of a return oil from a raising side chamber of the working machine cylinder to a lowering side chamber and the flow rate to a tank.
SUMMARY OF
REFERENCES:
patent: 4450865 (1984-05-01), Tardy
patent: 4623003 (1986-11-01), Leonard
patent: 4782859 (1988-11-01), Constantinian
patent: 5022434 (1991-06-01), Tsukimoto
patent: 5036750 (1991-08-01), Katayama
patent: 5386697 (1995-02-01), Claudinon et al.
Ishizaki Naoki
Takano Toshiro
Komatsu Ltd.
Nguyen Hoang
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