Claims
- 1. A hydraulic circuit apparatus for supplying fluid under pressure into a plurality of hydraulic cylinders for a work implement, each cylinder having a different load pressure, arranged so as to connect a discharge passage of a variable displacement pump through operating valves with the cylinders for the work implement, said apparatus comprising:
- a large diameter piston for actuating a displacement regulating member of said variable displacement pump in such a direction as to reduce the displacement of the pump;
- a small diameter piston having a pressure receiving chamber connected with said discharge passage of the pump for actuating the displacement regulating member of said pump in such a direction as to increase the displacement of the pump;
- a load sensing valve for connecting or disconnecting the pressure receiving chamber of said large diameter piston with or from the discharge passage of said pump; and
- means for applying pushing forces to the load sensing valve for pushing its spool in such a direction as to selectively establish and block communication of the discharge passage of said pump with the pressure receiving chamber of said large diameter piston; and
- wherein during normal operation of the work implement the flow rate of fluid discharged by the pump is controlled depending upon a pressure difference at said load sensing valve in such a manner that the difference between the discharge pressure of the pump and the highest of the load pressures from said plurality of hydraulic cylinders is always kept constant, while during inching operation of the work implement the flow rate of fluid discharged by the pump is reduced.
- 2. A hydraulic circuit apparatus for supplying fluid under pressure into hydraulic cylinders for a work implement as claimed in claim 1, wherein said pushing force applying means comprises: a proportional position action electromagnetic solenoid provided on one side of said load sensing valve; a mode change-over switch for the electromagnetic solenoid; and a controller for receiving an inching operation mode signal transmitted by the mode change-over switch and send an electric current to said electromagnetic solenoid.
- 3. A hydraulic circuit apparatus for supplying fluid under pressure into hydraulic cylinders for a work implement as claimed in claim 1, wherein said pushing force applying means comprises: a pilot pump; a conduit for introducing pilot fluid under pressure discharged by the pilot pump into a pressure receiving section provided on one side of said load sensing valve; a change-over valve provided in the conduit; a proportional position action electromagnetic solenoid provided on one side of the change-over valve; a mode change-over switch for the electromagnetic solenoid; and a controller for receiving an inching operation mode signal transmitted by the mode change-over switch and send an electric current to said electromagnetic solenoid.
- 4. A hydraulic circuit apparatus for supplying fluid under pressure into a plurality of hydraulic cylinders for a work implement, each cylinder having a different load pressure, arranged so as to connect a discharge passage of a variable displacement pump through operating valves with the cylinders for the work implement, said apparatus comprising:
- a variable displacement pump connected to said hydraulic cylinders for supplying pressurized working fluid thereto;
- a displacement adjusting means cooperating with said variable displacement pump for adjusting displacement of said pump;
- a valve means disposed between said variable displacement pump and said hydraulic cylinders for regulating a pressure difference at the pump side connected to said variable displacement pump and the load side connected to said hydraulic cylinders, said valve means including a valve member responsive to hydraulic pressures at said pump and load sides;
- means for cooperating said displacement adjusting means with said valve member for operating said displacement adjusting means depending upon the position of said valve member for maintaining said valve member at a predetermined neutral position where a predetermined pressure difference between said pump side and load side is established; and
- an electrically operated actuator means cooperating with said valve member and responsive to an electric command for inching operating of said work implement, for forcedly shifting said valve to a predetermined shift position for operating said displacement adjusting means via said cooperating means to reduce displacement of said variable displacement pump irrespective of the pressure difference between said pump and load sides for reducing discharge of said pump.
- 5. A hydraulic circuit apparatus as set forth in claim 4, wherein said valve member comprises a first valve component responsive to said hydraulic pressure at said pump side and a second valve component responsive to said hydraulic pressure at said load side, said first valve component being active at one end of said cooperating means for driving said cooperating means in a first direction in response to increasing of the hydraulic pressure at said pump side for reducing displacement of said variable displacement pump and said second valve component being active at the other end of said cooperating means for driving said cooperating means in a second direction opposite to said first direction in response to increasing of said hydraulic pressure at said load side for increasing the displacement of said variable displacement pump.
- 6. A hydraulic circuit apparatus for supplying fluid under pressure into a plurality of hydraulic cylinders for a work implement, each cylinder having a different load pressure, arranged so as to connect a discharge passage of a variable displacement pump through operating valves with the cylinders for the work implement, said apparatus comprising:
- a variable displacement pump connected to said hydraulic cylinders for supplying pressurized working fluid thereto;
- a displacement adjusting means cooperating with said variable displacement pump for adjusting displacement of said pump;
- a valve means disposed between said variable displacement pump and said hydraulic cylinders for regulating a pressure difference at the pump side connected to said variable displacement pump and the load side connected to said hydraulic cylinders, said valve means including a valve member responsive to hydraulic pressures at said pump and load sides and having a force balance established between the pump side and the load side at a predetermined pressure difference between the hydraulic pressure at said pump side and the hydraulic pressure at said load side;
- means for cooperating said displacement adjusting means with said valve member for operating said displacement adjusting means depending upon the position of said valve member for maintaining said valve member at a predetermined neutral position where a predetermined pressure difference between said pump side and load side is established; and
- an electrically operated actuator means cooperating with said valve member and responsive to an electric command for inching operation of said work implement, for forcedly shifting said valve to a predetermined shift position with an actuation force active for nominally reducing the pressure difference between said pump side and load side for operating said displacement adjusting means via said cooperating means to reduce displacement of said variable displacement pump irrespective of the pressure difference between said pump and load sides.
- 7. A hydraulic circuit system including a variable displacement pump means for discharging controlled displacement of working fluid through a discharge passage terminating at a plurality of hydraulic loads for work, a pressure controlling arrangement for adjusting hydraulic pressure at said hydraulic loads comprising:
- a valve means disposed within said discharge passage for adjusting the hydraulic pressure to be introduced into said hydraulic loads, said valve means defining a predetermined pressure difference between said pump side and said load side;
- a displacement adjusting means cooperating with said variable displacement pump for adjusting displacement thereof depending upon its position, said displacement adjusting means being coupled with said first valve member at one end so as to be driven in a first direction depending upon variation of the hydraulic pressure at said pump side and being coupled with said second valve member at the other end so as to be driven in a second direction opposite to said first direction in response to variation of the hydraulic pressure at said load side, said displacement adjusting means being operated by said first and second valve means for adjusting displacement of said variable displacement pump to establish a force balance at said first and second valve members at a predetermined pressure difference; and
- an electrically operated actuator means cooperating with one of said first and second valve members and responsive to an electric command for performing inching operation of said work implement, for forcedly shifting the associated one of said first and second valve members to a predetermined shift position with an actuation force active for nominally reducing the pressure difference between said pump side and load side for operating said displacement adjusting means to reduce displacement of said variable displacement pump irrespective of the pressure difference between said pump and load sides.
- 8. A hydraulic circuit apparatus for supplying fluid under pressure into a plurality of hydraulic cylinders for a work implement, each cylinder having a different load pressure, arranged so as to connect a discharge passage of a variable displacement pump through operating valves with the cylinders for the work implement, said apparatus comprising:
- a large diameter piston for actuating a displacement regulating member of said variable displacement pump in such a direction as to reduce the displacement of the pump;
- a small diameter piston having a pressure receiving chamber connected with said discharge passage of the pump for actuating the displacement regulating member of said pump in such a direction so as to increase the displacement of the pump;
- a load sensing valve for connecting or disconnecting the pressure receiving chamber of said large diameter piston with or from the discharge passage of said pump;
- means for applying pushing forces to the load sensing valve so as to push its spool in such a direction as to selectively establish and block communication of the discharge passage of said pump with the pressure receiving chamber of said large diameter piston said pushing force applying means comprising:
- a proportional position action electromagnetic solenoid provided on one side of said load sensing valve;
- a mode change-over switch for the electromagnetic solenoid; and
- a controller adapted to receive an inching operation mode signal transmitted by the mode change over switch and send an electric current to said electromagnetic solenoid,
- wherein during normal operation of the work implement the flow rate of fluid discharged by the pump is controlled in such a manner that the difference between the discharge pressure of the pump and the load pressure is always kept constant, while during inching operation of the work implement the flow rate of the fluid discharged by the pump is reduced by an actuation force active on said large diameter piston for nominally reducing the pressure difference between said pump side and load side.
Priority Claims (1)
Number |
Date |
Country |
Kind |
1-210053 |
Aug 1989 |
JPX |
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Parent Case Info
This application is a continuation of application Ser. No. 07/651,268 filed as PCT/JP90/01050 on Aug. 16, 1990, now abandoned.
US Referenced Citations (12)
Foreign Referenced Citations (3)
Number |
Date |
Country |
3713824 |
Nov 1988 |
DEX |
0167501 |
Oct 1982 |
JPX |
59-69505 |
Apr 1984 |
JPX |
Continuations (1)
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Number |
Date |
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Parent |
651268 |
Apr 1991 |
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