Motors: expansible chamber type – With motive fluid valve – Pilot valve
Patent
1988-10-17
1992-01-21
Look, Edward K.
Motors: expansible chamber type
With motive fluid valve
Pilot valve
91433, 137102, 1376256, 13762564, F15B 1108
Patent
active
050819054
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a hydraulic pilot operation circuit for remote-controlling, by means of a hydraulic pilot pressure output from a remote control valve, a hydraulic control valve which controls the operation of driving a hydraulic actuator for use in a construction machine such as a hydraulic power shovel. The present invention also relates to a valve for quickly discharging an oil (referred to as a hydraulic pressure quick discharge valve hereinafter) suitable for improving the change-over response of the hydraulic control valve, the hydraulic pressure quick discharge valve being disposed, for example, in a line which connects the remote control valve and a pilot port of the hydraulic control valve to each other.
2. Description of the Prior Art
FIG. 4 shows a conventional hydraulic pilot operation circuit for controlling a change-over of a directional control valve which is a hydraulic control valve, by a hydraulic pressure supplied from a remote control valve.
When an operation lever 1 is operated so as to be turned in a direction R as viewed in FIG. 4, the pressure of oil ejected from a hydraulic pump 2 for operating-system is reduced at a rate in proportion to the amount of operation of a remote control valve 3, introduced via a line 4 to a pilot port 5a of a directional control valve 5 which is changed over by a hydraulic pilot pressure, so that the directional control valve 5 is changed from a position B (neutral position) to a position A. As a result, pressurized oil is supplied from a hydraulic pump 6 for cylinder driving system to a rod chamber of a hydraulic cylinder 7 so that a piston rod 7a retracts. When the operation lever 1 is returned to the neutral position while the directional control valve 5 is maintained at the position A after changing-over thereto, the line 4 communicates with a tank 9 via the remote control valve 3 and a line 8. The directional control valve 5 is changed to the position B by a force of a return spring 5c, thereby stopping the movement of the piston rod 7a. During this sequence of operations, the other pilot port 5b of the directional control valve 5 communicates with the tank via a line 10, a remote control valve 11, and the line 8. When the operation lever 1 is turned in a direction L, each component operates as described above, thereby extending the piston rod 7a.
If the hydraulic pilot operation circuit shown in FIG. 4 is applied to a large sized construction machine, the length of each of the lines 4 and 10 connecting the remote control valves 3 and 11 to the pilot ports 5a and 5b of the directional control valve 5 is increased, so that the resistance to an oil flowing through each of the lines 4 and 10 increases. There is therefore a possibility of occurrence of a response retardation in returning of the directional control valve 5 to the neutral position from the position A or C.
If the operation lever 1 is gradually returned to the neutral position, the directional control valve 5 is gradually changed to the neutral position generally in response to change in the pressure output from the remote control valve 3 or 11. In this case, there is no problem in terms of response retardation. If the operation lever 1 is rapidly operated when returned to the neutral position, returning of the directional control valve 5 to the neutral position is retarded. That is, the pressure output from the remote control valve 3 abruptly decreases to the tank pressure in response to an abrupt operation of the operation lever 1, so that the directional control valve 5 starts returning to the neutral position by a force of a return spring 5c. During returning of the directional control valve 5 to the neutral position, oil is discharged from the pilot port 5a (5b) into the line 4 (10) as a spool of the directional control valve 5 moves, and this oil flows to the tank via the remote control valve 3 (11) and the line 8. If the resistance to the oil flowing through the line 4 (10) undesirably increases due to increase of the
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Katsuki Kimio
Tanaka Soutarou
Yagyu Takashi
Hitachi Construction Machinery Co. Ltd.
Kapsalas George
Look Edward K.
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