WO2024135005A1 - Hydraulic system - Google Patents

Hydraulic system Download PDF

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Publication number
WO2024135005A1
WO2024135005A1 PCT/JP2023/032406 JP2023032406W WO2024135005A1 WO 2024135005 A1 WO2024135005 A1 WO 2024135005A1 JP 2023032406 W JP2023032406 W JP 2023032406W WO 2024135005 A1 WO2024135005 A1 WO 2024135005A1
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WO
WIPO (PCT)
Prior art keywords
line
discharge line
bidirectional pump
pressure
head side
Prior art date
Application number
PCT/JP2023/032406
Other languages
French (fr)
Japanese (ja)
Inventor
良 山本
英紀 田中
広明 三井
Original Assignee
川崎重工業株式会社
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Publication date
Application filed by 川崎重工業株式会社 filed Critical 川崎重工業株式会社
Publication of WO2024135005A1 publication Critical patent/WO2024135005A1/en

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B11/00—Servomotor systems without provision for follow-up action; Circuits therefor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B11/00—Servomotor systems without provision for follow-up action; Circuits therefor
    • F15B11/02—Systems essentially incorporating special features for controlling the speed or actuating force of an output member
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B11/00—Servomotor systems without provision for follow-up action; Circuits therefor
    • F15B11/08—Servomotor systems without provision for follow-up action; Circuits therefor with only one servomotor

Definitions

  • This disclosure relates to a hydraulic system for a single rod cylinder.
  • Patent Document 1 discloses a hydraulic system 100 as shown in FIG. 7.
  • This hydraulic system 100 includes a first bidirectional pump 110 and a second bidirectional pump 120.
  • the first bidirectional pump 110 is connected to the head side chamber 210 of the single-rod cylinder 200 by a head side line 111, and is connected to the rod side chamber 220 of the single-rod cylinder 200 by a rod side line 112.
  • the second bidirectional pump 120 is for eliminating the flow rate difference between the head side chamber 210 and the rod side chamber 220 of the single-rod cylinder 200, i.e., the difference between the inflow flow rate and the outflow flow rate, and is connected to the head side line 111 by a supply and discharge line 121.
  • the first bidirectional pump 110 and the second bidirectional pump 120 are driven in the same direction by the electric motor 130. More specifically, the electric motor 130 drives the first bidirectional pump 110 and the second bidirectional pump 120 in a first direction when the single-rod cylinder 200 is extended, i.e., when the rod is advanced, and drives the first bidirectional pump 110 and the second bidirectional pump 120 in a second direction opposite to the first direction when the single-rod cylinder 200 is shortened, i.e., when the rod is retreated.
  • the first bidirectional pump 110 and the second bidirectional pump 120 When the first bidirectional pump 110 and the second bidirectional pump 120 are driven in the first direction, they discharge the working fluid to the head side chamber 210, and when the first bidirectional pump 110 and the second bidirectional pump 120 are driven in the second direction, they suck the working fluid from the head side chamber 210.
  • the second bidirectional pump 120 is a variable displacement pump, and the displacement of the second bidirectional pump 120 is changed by the regulator 140.
  • hydraulic system 100 if the capacity of second bidirectional pump 120 when there is no excess or deficiency in the inflow flow rate to or outflow flow rate from single-rod cylinder 200 is taken as the reference capacity, if the capacity of second bidirectional pump 120 is greater than the reference capacity when single-rod cylinder 200 extends, pressure trapping occurs on the rod side or head side which has the lower pressure.
  • the rod side is rod side chamber 220 and rod side line 112
  • the head side is head side chamber 210 and head side line 111.
  • the capacity of second bidirectional pump 120 is less than the reference capacity when single-rod cylinder 200 extends, cavitation occurs on the rod side or head side which has the lower pressure.
  • the single-rod cylinder 200 when the single-rod cylinder 200 is contracted, if the capacity of the second bidirectional pump 120 is greater than the reference capacity, cavitation occurs on the rod side or head side, whichever has the lower pressure, and if the capacity of the second bidirectional pump 120 is less than the reference capacity, pressure trapping occurs on the rod side or head side, whichever has the lower pressure.
  • the regulator 140 is controlled based on the pressure in the head side chamber 210 or rod side chamber 220 of the single-rod cylinder 200 so that this pressure trapping or cavitation is suppressed.
  • FIG. 2 of Patent Document 2 discloses, as a conventional technique, a hydraulic circuit in which only one bidirectional pump is used for a single-rod cylinder and a low-pressure selection valve (called a "flushing valve” in Patent Document 2) is employed that enables the discharge of hydraulic fluid from either the head side line or the rod side line, whichever has the lower pressure, into the tank.
  • this hydraulic circuit does not have a second bidirectional pump added to the first bidirectional pump, as in hydraulic system 100 of Patent Document 1.
  • the present disclosure therefore aims to provide a hydraulic system that can easily prevent pressure trapping from occurring on the lower pressure side, either the rod side or the head side, in a configuration in which a second bidirectional pump is added to a first bidirectional pump.
  • the present disclosure relates to a hydraulic system for a single-rod cylinder including a head side chamber and a rod side chamber, comprising a first bidirectional pump connected to the head side chamber by a head side line and connected to the rod side chamber by a rod side line, a second bidirectional pump connected to the head side line by a first supply and discharge line, an accumulator connected to the second bidirectional pump by a second supply and discharge line, an electric motor that drives the first bidirectional pump and the second bidirectional pump in the same direction, and a third bidirectional pump connected to the head side line by a first discharge line and to the rod side line by a second discharge line.
  • a hydraulic system includes a low pressure selection valve that is connected to the second supply/discharge line by a discharge line, communicates the second discharge line with the third discharge line when the pressure in the rod side chamber is lower than the pressure in the head side chamber, and communicates the first discharge line with the third discharge line when the pressure in the head side chamber is lower than the pressure in the rod side chamber, and a pair of check valves in mutually opposite directions that are provided in a bridge line that connects the head side line and the rod side line, and the second supply/discharge line is connected to a portion of the bridge line between the pair of check valves by a relay line.
  • the present disclosure provides a hydraulic system that can easily prevent pressure trapping on the lower pressure side of the rod side or head side in a configuration in which a second bidirectional pump is added to a first bidirectional pump.
  • FIG. 1 is a schematic configuration diagram of a hydraulic system according to a first embodiment.
  • FIG. FIG. 11 is a schematic configuration diagram of a hydraulic system according to a second embodiment.
  • FIG. 11 is a schematic configuration diagram of a hydraulic system according to a third embodiment.
  • FIG. 13 is a schematic configuration diagram of a hydraulic system according to a fourth embodiment.
  • FIG. 13 is a diagram showing a modified low pressure selection valve.
  • FIG. 13 is a diagram showing another modified example of a low pressure selection valve.
  • FIG. 1 is a schematic diagram of a conventional hydraulic system.
  • First Embodiment 1 shows a hydraulic system 1A according to a first embodiment.
  • the hydraulic system 1A is a hydraulic system for a single-rod cylinder 4 including a head side chamber 4h and a rod side chamber 4r.
  • the hydraulic fluid used in the hydraulic system 1A is typically oil.
  • the hydraulic system 1A includes a first bidirectional pump 2 connected to the single-rod cylinder 4 to form a closed loop, and a second bidirectional pump 3 for eliminating the flow rate difference between the head side chamber 4h and the rod side chamber 4r of the single-rod cylinder 4, i.e., the difference between the inflow flow rate and the outflow flow rate.
  • the hydraulic system 1A also includes an accumulator 7 for storing pressurized hydraulic fluid.
  • the single-rod cylinder 4, the first bidirectional pump 2, the second bidirectional pump 3, and the accumulator 7 form a closed circuit together with multiple lines described below.
  • the first bidirectional pump 2 is connected to the head side chamber 4h of the single-rod cylinder 4 by a head side line 21, and is connected to the rod side chamber 4r of the single-rod cylinder 4 by a rod side line 22.
  • the second bidirectional pump 3 is connected to the head side line 21 by a first supply/discharge line 31, and is connected to the accumulator 7 by a second supply/discharge line 71.
  • the set pressure of the accumulator 7 is, for example, within the range of 0.1-2 MPa.
  • the "set pressure of the accumulator 7" is the pressure at which the hydraulic fluid can flow into the accumulator 7.
  • the head side line 21 and the rod side line 22 are provided with lock valves 23, 24, which are on-off valves.
  • the lock valves 23, 24 are controlled by the control device 10. Note that in FIG. 1, some signal lines are not shown to simplify the drawing.
  • the control device 10 opens the lock valves 23, 24 when the single rod cylinder 4 is operated, i.e., when it is extended or retracted, and closes the lock valves 23, 24 at other times.
  • the head side line 21 and the rod side line 22 are connected to each other by a first bridge line 51 and a second bridge line 54.
  • a pair of relief valves 52, 53 are provided in the first bridge line 51 in the opposite directions, and a pair of check valves 55, 56 are provided in the second bridge line 54 in the opposite directions.
  • first bridge line 51 and the second bridge line 54 are connected to the head side line 21 and the rod side line 22 between the lock valves 23, 24 and the first bidirectional pump 2, but the first bridge line 51 and the second bridge line 54 may be connected to the head side line 21 and the rod side line 22 between the lock valves 23, 24 and the single-rod cylinder 4. Also, parts of the first bridge line 51 and the second bridge line 54, for example both ends and the center parts, may merge with each other to form a common flow path.
  • the relief valve 52 opens when the pressure in the head side line 21 becomes too high, and the relief valve 53 opens when the pressure in the rod side line 22 becomes too high.
  • the relief pressures of the relief valves 52 and 53 are set relatively high, for example, within the range of 25-35 MPa.
  • Check valve 55 allows flow from the center of second bridge line 54 toward head side line 21 but prohibits flow in the opposite direction.
  • Check valve 56 allows flow from the center of second bridge line 54 toward rod side line 22 but prohibits flow in the opposite direction.
  • the portion between the relief valves 52 and 53 in the first bridge line 51 and the portion between the check valves 55 and 56 in the second bridge line 54 are connected to the second supply and discharge line 71 by a relay line 72.
  • the first bidirectional pump 2 and the second bidirectional pump 3 are, for example, axial piston pumps.
  • the axial piston pump is, for example, a swash plate pump or a bent-axis pump.
  • the first bidirectional pump 2 is a fixed displacement pump
  • the second bidirectional pump 3 is a variable displacement pump.
  • the first bidirectional pump 2 may also be a variable displacement pump.
  • both the first bidirectional pump 2 and the second bidirectional pump 3 may be fixed displacement pumps.
  • the capacity of the second bidirectional pump 3 is changed by the regulator 35.
  • the regulator 35 is controlled by the control device 10.
  • the regulator 35 may be a device that electrically changes the hydraulic pressure acting on a servo piston connected to the swash plate of the second bidirectional pump 3, or may be an electric actuator connected to the swash plate of the second bidirectional pump 3.
  • the first bidirectional pump 2 and the second bidirectional pump 3 are driven in the same direction by an electric motor 9.
  • the first bidirectional pump 2 and the second bidirectional pump 3 may be arranged so that their central axes are aligned coaxially, or so that their central axes are aligned in parallel.
  • the former is a tandem type, and the latter is a parallel type.
  • the electric motor 9 is controlled by a control device 10.
  • the electric motor 9 drives the first bidirectional pump 2 and the second bidirectional pump 3 in a first direction when the single-rod cylinder 4 is extended, and drives the first bidirectional pump 2 and the second bidirectional pump 3 in a second direction opposite to the first direction when the single-rod cylinder 4 is retracted.
  • the first bidirectional pump 2 and the second bidirectional pump 3 are driven in the first direction, they discharge working fluid into the head side chamber 4h, and when the first bidirectional pump 2 and the second bidirectional pump 3 are driven in the second direction, they suck working fluid from the head side chamber 4h.
  • a low pressure selection valve 6 is used that is connected to the head side line 21 by a first discharge line 61 and to the rod side line 22 by a second discharge line 62.
  • the low pressure selection valve 6 is connected to the second supply and discharge line 71 by a third discharge line 63.
  • a relief valve 64 is provided in the third discharge line 63.
  • the relief valve 64 serves to maintain a relatively high low pressure in the closed loop consisting of the single-rod cylinder 4, the head side line 21, the rod side line 22, and the first bidirectional pump 2.
  • the relief pressure of the relief valve 64 is set relatively low, for example, within the range of 0.1-2 MPa.
  • the low pressure in the closed loop is the sum of the set pressure of the accumulator 7 and the set pressure of the relief valve 64, and is, for example, 1-2 MPa. Note that if the set pressure of the accumulator 7 is relatively high, the relief valve 64 can be omitted.
  • the low pressure selection valve 6 can be switched between a neutral position, a head side discharge position, and a rod side discharge position.
  • the center position is the neutral position
  • the right position is the head side discharge position
  • the left position is the rod side discharge position.
  • the low pressure selection valve 6 blocks the first discharge line 61 and the second discharge line 62.
  • the low pressure selection valve 6 blocks the second discharge line 62 while connecting the first discharge line 61 to the third discharge line 63.
  • the low pressure selection valve 6 blocks the first discharge line 61 while connecting the second discharge line 62 to the third discharge line 63.
  • the low pressure selection valve 6 is a pilot type three-position valve. Therefore, the pressure Ph of the head side chamber 4h is guided to the low pressure selection valve 6 through the first pilot line 65, and the pressure Pr of the rod side chamber 4r is guided to the low pressure selection valve 6 through the second pilot line 66.
  • the first pilot line 65 is for switching the low pressure selection valve 6 from the neutral position to the rod side discharge position
  • the second pilot line 66 is for switching the low pressure selection valve 6 from the neutral position to the head side discharge position.
  • first pilot line 65 and the second pilot line 66 branch off from the first discharge line 61 and the second discharge line 62, respectively, but the first pilot line 65 may branch off from the head side line 21, and the second pilot line 66 may branch off from the rod side line 22.
  • the low pressure selection valve 6 is switched to the rod side discharge position when the pressure Pr in the rod side chamber 4r is lower than the pressure Ph in the head side chamber 4h, and is switched to the head side discharge position when the pressure Ph in the head side chamber 4h is lower than the pressure Pr in the rod side chamber 4r.
  • the threshold value Pt is within the range of 0.5-3 MPa. The threshold value Pt may be different when the cylinder is extended and when it is retracted.
  • control performed by the control device 10 is not limited to the one described below, and the control device 10 may perform other controls.
  • circuits or processing circuits including general purpose processors, special purpose processors, integrated circuits, ASICs (Application Specific Integrated Circuits), conventional circuits, and/or combinations thereof, configured or programmed to perform the disclosed functions.
  • a processor is considered a processing circuit or circuit because it includes transistors and other circuitry.
  • a circuit, unit, or means is hardware that performs the recited functions or hardware that is programmed to perform the recited functions.
  • the hardware may be hardware disclosed herein or other known hardware that is programmed or configured to perform the recited functions. Where the hardware is a processor, which is considered a type of circuit, the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and/or the processor.
  • the control device 10 receives a first operation signal, which is an extension command for the single-rod cylinder 4, and a second operation signal, which is a contraction command for the single-rod cylinder 4.
  • the control device 10 also receives the pressure Ph in the head side chamber 4h and the pressure Pr in the rod side chamber 4r measured by a pressure sensor, or the differential pressure ⁇ P between the pressure Ph in the head side chamber 4h and the pressure Pr in the rod side chamber 4r measured by a differential pressure gauge.
  • the control device 10 controls the regulator 35 so that the capacity q2 of the second bidirectional pump 3 becomes the reference capacity qr.
  • the control device 10 controls the regulator 35 so that the capacity q2 of the second bidirectional pump 3 is greater than the reference capacity qr by a first predetermined amount ⁇ q1.
  • q2 qr + ⁇ q1.
  • ⁇ q1 is within the range of 1-10% of qr.
  • the pressure Ph in the head side chamber 4h becomes higher than the pressure Pr in the rod side chamber 4r by at least the threshold Pt
  • the pressure Pr in the rod side chamber 4r becomes higher than the pressure Pr in the head side chamber 4h by at least the threshold Pt
  • the low pressure selection valve 6 is switched to the rod side discharge position.
  • the surplus corresponding to the first predetermined amount ⁇ q1 is discharged from the rod side line 22 through the second discharge line 62, the low pressure selection valve 6, the third discharge line 63, and a part of the second supply/discharge line 71 to the accumulator 7.
  • the low pressure selection valve 6 is switched to the head side discharge position.
  • the surplus corresponding to the first predetermined amount ⁇ q1 is discharged from the head side line 21 through the first discharge line 61, the low pressure selection valve 6, the third discharge line 63, and a part of the second supply/discharge line 71 to the accumulator 7.
  • the control device 10 controls the regulator 35 so that the capacity q2 of the second bidirectional pump 3 becomes the reference capacity qr.
  • the control device 10 controls the regulator 35 so that the capacity q2 of the second bidirectional pump 3 is less than the reference capacity qr by a second predetermined amount ⁇ q2.
  • q2 qr - ⁇ q2.
  • the second predetermined amount ⁇ q2 may be the same as or different from the first predetermined amount ⁇ q1 described above.
  • ⁇ q2 is within the range of 1-10% of qr.
  • the pressure Pr in the rod side chamber 4r becomes higher than the pressure Ph in the head side chamber 4h by more than the threshold value Pt
  • the pressure Ph in the head side chamber 4h becomes higher than the pressure Pr in the rod side chamber 4r by more than the threshold value Pt
  • the low pressure selection valve 6 When the pressure Pr in the rod side chamber 4r becomes higher than the pressure Pr in the head side chamber 4h by the threshold value Pt or more, the low pressure selection valve 6 is switched to the head side discharge position. As a result, the surplus corresponding to the second predetermined amount ⁇ q2 is discharged from the head side line 21 through the first discharge line 61, the low pressure selection valve 6, the third discharge line 63, and a part of the second supply/discharge line 71 to the accumulator 7.
  • the low pressure selection valve 6 is switched to the rod side discharge position.
  • the surplus corresponding to the second predetermined amount ⁇ q2 is discharged from the rod side line 22 through the second discharge line 62, the low pressure selection valve 6, the third discharge line 63, and a part of the second supply/discharge line 71 to the accumulator 7.
  • the low pressure selection valve 6 is provided, so that in a configuration in which the second bidirectional pump 3 is added to the first bidirectional pump 2, it is possible to simply prevent pressure trapping from occurring on the rod side or head side, whichever has the lower pressure.
  • the rod side is the rod side chamber 4r and the rod side line 22, and the head side is the head side chamber 4h and the head side line 21.
  • the second bidirectional pump 3 is connected to the accumulator 7 by the second supply/discharge line 71, it is possible to prevent cavitation due to a drop in pressure on the suction side of the second bidirectional pump 3 when the second bidirectional pump 3 starts to rotate in the direction of discharging working fluid through the first supply/discharge line 31. Furthermore, when the pressure on the suction side drops due to a delay in the return of working fluid to the suction side when the first bidirectional pump 2 starts to rotate, pressurized working fluid from the accumulator 7 is supplied to the suction side via the check valve 55 or 56, so it is also possible to prevent cavitation on the suction side of the first bidirectional pump 2.
  • a relief valve 64 is provided in the third discharge line 63, so the pressure at which the hydraulic fluid is discharged from the head side line 21 or the rod side line 22 through the first discharge line 61 or the second discharge line 62 can be set separately from the set pressure of the accumulator 7.
  • Second Embodiment 2 shows a hydraulic system 1B according to a second embodiment.
  • the same components as those in the first embodiment are denoted by the same reference numerals, and duplicated explanations will be omitted.
  • the hydraulic system 1B differs from the hydraulic system 1A of the first embodiment in that it further includes a tank 11 and a charge pump 8.
  • the charge pump 8 is connected to the tank 11 by a suction line 81, and is connected to the second supply/discharge line 71 by a discharge line 82.
  • the discharge line 82 does not necessarily have to be connected to the second supply/discharge line 71, and may be connected to the third discharge line 63 between the relief valve 64 and the second supply/discharge line 71, or may be connected to the relay line 72.
  • the discharge line 82 is provided with a check valve 83 that allows flow from the charge pump 8 to the second supply/discharge line 71 but prohibits flow in the opposite direction.
  • a relief line 84 branches off from the discharge line 82 between the charge pump 8 and the check valve 83, and the relief line 84 is connected to the tank 11.
  • a relief valve 85 is provided in the relief line 84.
  • the relief pressure of the relief valve 85 is, for example, in the range of 0.1-2 MPa.
  • the hydraulic fluid can be replenished when the amount of hydraulic fluid in the closed circuit consisting of the single-rod cylinder 4, first bidirectional pump 2, second bidirectional pump 3, and accumulator 7 decreases.
  • first bidirectional pump 2 and second bidirectional pump 3 are of the external drain type, the amount of hydraulic fluid in the closed circuit gradually decreases.
  • the charge pump 8 may be operated manually, but when the control device 10 controls the charge pump 8, for example, the control device 10 may operate the charge pump 8 when the amount of hydraulic fluid in the accumulator 7 falls below a predetermined value or when the pressure at a predetermined position in the closed circuit falls below a predetermined value.
  • the discharge line 82 does not necessarily need to be constantly connected to the second supply/discharge line 71, and may be connected to the second supply/discharge line 71 only when the hydraulic fluid is replenished.
  • the relief valve 64 can be omitted when the set pressure of the accumulator 7 is relatively high. The fact that the relief valve 64 can be omitted is also the case in the third and fourth embodiments described below.
  • Third Embodiment 3 shows a hydraulic system 1C according to the third embodiment.
  • the hydraulic system 1C differs from the hydraulic system 1B of the second embodiment in that a discharge line 82 is connected to the third discharge line 63 between the relief valve 64 and the second supply/discharge line 71, and that a relief line 84 branches off from the second supply/discharge line 71.
  • the relief line 84 branches off from the second supply/discharge line 71 on the opposite side to the discharge line 82, with a part of the third discharge line 63 and a part of the second supply/discharge line 71 in between.
  • the relief line 84 may branch off from the relay line 72 on the opposite side to the discharge line 82, sandwiching part of the third discharge line 63, part of the second supply/discharge line 71, and part of the relay line 72.
  • the discharge line 82 may be connected to the second supply/discharge line 71 or the relay line 72, and the relief line 84 may branch off from the third discharge line 63 between the relief valve 64 and the second supply/discharge line 71.
  • the charge pump 8 operates at all times. In other words, while the second bidirectional pump 3 is stopped, the hydraulic fluid discharged from the charge pump 8 flows into the accumulator 7 as shown by the solid arrows in FIG. 3, and after the accumulator 7 becomes full, the hydraulic fluid in the tank 11 circulates through the suction line 81, the charge pump 8, the discharge line 82, part of the third discharge line 63, part of the second supply/discharge line 71, and the relief line 84, in that order.
  • the charge pump 8 can circulate the hydraulic fluid from the discharge line 82 through a part of the closed circuit made up of the single-rod cylinder 4, the first bidirectional pump 2, the second bidirectional pump 3, and the accumulator 7 to the relief line 84. This makes it possible to cool the hydraulic fluid in the closed circuit.
  • Fourth Embodiment 4 shows a hydraulic system 1D according to the fourth embodiment.
  • the hydraulic system 1D differs from the hydraulic system 1C of the third embodiment in that the accumulator 7 is disposed near the second bidirectional pump 3, a cooler 12 is interposed between the charge pump 8 and the accumulator 7, and a relief line 84 branches off from the relay line 72.
  • the cooler 12 is provided in the third discharge line 63.
  • the relief valve 85 is located on the opposite side of the accumulator 7 from the cooler 12. In other words, the working fluid discharged from the charge pump 8 and passing through the cooler 12 flows through a portion of the second supply/discharge line 71 adjacent to the accumulator 7, and then flows into the relief line 84 via a portion of the relay line 72.
  • the cooling effect of the working fluid in the closed circuit described in the third embodiment can be improved by the cooler 12. Moreover, since the accumulator 7 is located between the cooler 12 and the relief valve 85, the working fluid stored in the accumulator 7 can also be cooled as the working fluid circulates.
  • the cooler 12 is provided in the third discharge line 63, so the working fluid is also cooled when it is returned to the accumulator 7 through the third discharge line 63.
  • the cooler 12 may be provided in the discharge line 82, etc.
  • a low-pressure selection valve 6A which is an electromagnetic three-position valve as shown in FIG. 5, may be used instead of the pilot-type low-pressure selection valve 6, a low-pressure selection valve 6A, which is an electromagnetic three-position valve as shown in FIG. 5, may be used.
  • a low-pressure selection valve 6B which is an electromagnetic two-position valve including a first solenoid valve 6a and a second solenoid valve 6b, as shown in FIG. 6, may be used.
  • a first discharge line 61 and a third discharge line 63 are connected to the first solenoid valve 6a, and a second discharge line 62 and a third discharge line 63 are connected to the second solenoid valve 6b.
  • the present disclosure provides a hydraulic system for a single-rod cylinder including a head side chamber and a rod side chamber, the hydraulic system including a first bidirectional pump connected to the head side chamber by a head side line and connected to the rod side chamber by a rod side line, a second bidirectional pump connected to the head side line by a first supply and discharge line, an accumulator connected to the second bidirectional pump by a second supply and discharge line, an electric motor that drives the first bidirectional pump and the second bidirectional pump in the same direction, and a hydraulic system connected to the head side line by a first discharge line and to the rod side line by a second discharge line.
  • a low pressure selection valve connected to the second supply/discharge line by a third discharge line, communicating the second discharge line with the third discharge line when the pressure in the rod side chamber is lower than the pressure in the head side chamber, and communicating the first discharge line with the third discharge line when the pressure in the head side chamber is lower than the pressure in the rod side chamber; and a pair of check valves oriented in opposite directions and provided in a bridge line connecting the head side line and the rod side line, wherein the second supply/discharge line is connected to a portion of the bridge line between the pair of check valves by a relay line.
  • the above configuration provides a low pressure selection valve, which makes it possible to easily prevent pressure trapping on the lower pressure side of the rod side or head side in a configuration in which a second bidirectional pump is added to a first bidirectional pump. Moreover, since the second bidirectional pump is connected to the accumulator by the second supply and discharge line, it is possible to prevent cavitation due to a drop in pressure on the suction side of the second bidirectional pump when the second bidirectional pump starts to rotate in the direction of discharging hydraulic fluid through the first supply and discharge line.
  • the hydraulic system of the first aspect may further include a charge pump that is connected to a tank by a suction line and is connected to the second supply/discharge line, the third discharge line, or the relay line by a discharge line.
  • a charge pump that is connected to a tank by a suction line and is connected to the second supply/discharge line, the third discharge line, or the relay line by a discharge line.
  • the hydraulic system may further include a relief valve provided in a relief line that branches off from the discharge line and leads to the tank.
  • the hydraulic system may further include a relief valve provided in a relief line that branches off from any one of the second supply/discharge line, the third discharge line, and the relay line and leads to the tank.
  • the charge pump can circulate the hydraulic fluid from the discharge line through a part of the closed circuit to the relief line. This makes it possible to cool the hydraulic fluid in the closed circuit.
  • the hydraulic system may further include a cooler interposed between the charge pump and the accumulator, and the relief valve may be located on the opposite side of the accumulator to the cooler.
  • the cooler can improve the cooling effect of the working fluid in the closed circuit.
  • the accumulator is located between the cooler and the relief valve, the working fluid stored in the accumulator can also be cooled as the working fluid circulates.
  • the hydraulic system may further include a relief valve provided in the third discharge line.
  • the low pressure selection valve may be an electromagnetic three-position valve.
  • the low pressure selection valve may include a first solenoid valve and a second solenoid valve which are electromagnetic two-position valves, the first discharge line and the third discharge line being connected to the first solenoid valve, and the second discharge line and the third discharge line being connected to the second solenoid valve.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Fluid-Pressure Circuits (AREA)

Abstract

A hydraulic system (1A) according to one embodiment includes: a first bi-directional pump (2) that is connected to a single rod cylinder (4) by a head-side line (21) and a rod-side line (22); a second bi-directional pump (3) that is connected to the head-side line (21) by a first supply/discharge line (31); and an accumulator (7) that is connected to the second bi-directional pump (3) by a second supply/discharge line (71). Further, the hydraulic system (1A) includes a low-pressure selection valve (6) that is connected to the head-side line (21), the rod-side line (22), and the second supply/discharge line (71). The second supply/discharge line (71) is connected through a relay line (72) to a portion between a pair of check valves (55, 56) in a bridge line (54) connecting the head-side line (21) and the rod-side line (22).

Description

液圧システムHydraulic System
　本開示は、片ロッドシリンダ用の液圧システムに関する。 This disclosure relates to a hydraulic system for a single rod cylinder.
　従来から、片ロッドシリンダと閉ループを形成するように接続される両方向ポンプを含む片ロッドシリンダ用の液圧システムが知られている。例えば、特許文献１には、図７に示すような液圧システム１００が開示されている。 Conventionally, hydraulic systems for single-rod cylinders that include a bidirectional pump connected to the single-rod cylinder to form a closed loop have been known. For example, Patent Document 1 discloses a hydraulic system 100 as shown in FIG. 7.
　この液圧システム１００は、第１両方向ポンプ１１０および第２両方向ポンプ１２０を含む。第１両方向ポンプ１１０は、ヘッド側ライン１１１により片ロッドシリンダ２００のヘッド側室２１０と接続されるとともに、ロッド側ライン１１２により片ロッドシリンダ２００のロッド側室２２０と接続される。第２両方向ポンプ１２０は、片ロッドシリンダ２００のヘッド側室２１０とロッド側室２２０の間の流量差、すなわち流入流量と流出流量との差を解消するためのものであり、給排ライン１２１によりヘッド側ライン１１１と接続される。 This hydraulic system 100 includes a first bidirectional pump 110 and a second bidirectional pump 120. The first bidirectional pump 110 is connected to the head side chamber 210 of the single-rod cylinder 200 by a head side line 111, and is connected to the rod side chamber 220 of the single-rod cylinder 200 by a rod side line 112. The second bidirectional pump 120 is for eliminating the flow rate difference between the head side chamber 210 and the rod side chamber 220 of the single-rod cylinder 200, i.e., the difference between the inflow flow rate and the outflow flow rate, and is connected to the head side line 111 by a supply and discharge line 121.
　第１両方向ポンプ１１０および第２両方向ポンプ１２０は、電動モータ１３０により同方向に駆動される。より詳しくは、電動モータ１３０は、片ロッドシリンダ２００を伸長させる際、すなわちロッドを前進させる際に第１両方向ポンプ１１０および第２両方向ポンプ１２０を第１方向に駆動し、片ロッドシリンダ２００を短縮させる際、すなわちロッドを後退させる際に第１両方向ポンプ１１０および第２両方向ポンプ１２０を第１方向と反対の第２方向に駆動する。第１両方向ポンプ１１０および第２両方向ポンプ１２０が第１方向に駆動されるとそれらがヘッド側室２１０へ作動液を吐出し、第１両方向ポンプ１１０および第２両方向ポンプ１２０が第２方向に駆動されるとそれらがヘッド側室２１０から作動液を吸入する。また、液圧システム１００では、第２両方向ポンプ１２０が可変容量型ポンプであり、第２両方向ポンプ１２０の容量がレギュレータ１４０によって変更される。 The first bidirectional pump 110 and the second bidirectional pump 120 are driven in the same direction by the electric motor 130. More specifically, the electric motor 130 drives the first bidirectional pump 110 and the second bidirectional pump 120 in a first direction when the single-rod cylinder 200 is extended, i.e., when the rod is advanced, and drives the first bidirectional pump 110 and the second bidirectional pump 120 in a second direction opposite to the first direction when the single-rod cylinder 200 is shortened, i.e., when the rod is retreated. When the first bidirectional pump 110 and the second bidirectional pump 120 are driven in the first direction, they discharge the working fluid to the head side chamber 210, and when the first bidirectional pump 110 and the second bidirectional pump 120 are driven in the second direction, they suck the working fluid from the head side chamber 210. In addition, in the hydraulic system 100, the second bidirectional pump 120 is a variable displacement pump, and the displacement of the second bidirectional pump 120 is changed by the regulator 140.
　液圧システム１００では、片ロッドシリンダ２００への流入流量または片ロッドシリンダ２００からの流出流量に過不足がないときの第２両方向ポンプ１２０の容量を基準容量とすると、片ロッドシリンダ２００の伸長時に第２両方向ポンプ１２０の容量が基準容量よりも多い場合はロッド側およびヘッド側のうちの圧力の低い方に圧力の閉じ込みが発生する。ロッド側はロッド側室２２０およびロッド側ライン１１２であり、ヘッド側はヘッド側室２１０およびヘッド側ライン１１１である。逆に、片ロッドシリンダ２００の伸長時に第２両方向ポンプ１２０の容量が基準容量よりも少ない場合はロッド側およびヘッド側のうちの圧力の低い方にキャビテーションが発生する。また、片ロッドシリンダ２００の短縮時には、第２両方向ポンプ１２０の容量が基準容量よりも多い場合はロッド側およびヘッド側のうちの圧力の低い方にキャビテーションが発生し、第２両方向ポンプ１２０の容量が基準容量よりも少ない場合はロッド側およびヘッド側のうちの圧力の低い方に圧力の閉じ込みが発生する。レギュレータ１４０は、これらの圧力の閉じ込みまたはキャビテーションが抑制されるように、片ロッドシリンダ２００のヘッド側室２１０またはロッド側室２２０の圧力に基づいて制御される。 In hydraulic system 100, if the capacity of second bidirectional pump 120 when there is no excess or deficiency in the inflow flow rate to or outflow flow rate from single-rod cylinder 200 is taken as the reference capacity, if the capacity of second bidirectional pump 120 is greater than the reference capacity when single-rod cylinder 200 extends, pressure trapping occurs on the rod side or head side which has the lower pressure. The rod side is rod side chamber 220 and rod side line 112, and the head side is head side chamber 210 and head side line 111. Conversely, if the capacity of second bidirectional pump 120 is less than the reference capacity when single-rod cylinder 200 extends, cavitation occurs on the rod side or head side which has the lower pressure. In addition, when the single-rod cylinder 200 is contracted, if the capacity of the second bidirectional pump 120 is greater than the reference capacity, cavitation occurs on the rod side or head side, whichever has the lower pressure, and if the capacity of the second bidirectional pump 120 is less than the reference capacity, pressure trapping occurs on the rod side or head side, whichever has the lower pressure. The regulator 140 is controlled based on the pressure in the head side chamber 210 or rod side chamber 220 of the single-rod cylinder 200 so that this pressure trapping or cavitation is suppressed.
特開２０１３－２４５７４０号公報JP 2013-245740 A 特開２００２－５４６０２号公報JP 2002-54602 A
　上述したように、特許文献１の液圧システム１００では、ロッド側およびヘッド側のうちの圧力の低い方に圧力の閉じ込みが発生することが制御的に抑制される。これに対し、ロッド側およびヘッド側のうちの圧力の低い方に圧力の閉じ込みが発生することを簡易的に防止したいという要望がある。 As described above, in the hydraulic system 100 of Patent Document 1, the occurrence of pressure trapping on the lower pressure side of the rod side or the head side is controlled to be suppressed. In response to this, there is a demand for a simple method of preventing pressure trapping on the lower pressure side of the rod side or the head side.
　なお、特許文献２の図２には、従来技術として、片ロッドシリンダに対して両方向ポンプが１つだけ用いられるとともに、ヘッド側ラインとロッド側ラインのうちの圧力の低い方からタンクへの作動液の排出を可能とする低圧選択弁（特許文献２では「フラッシング弁」と称呼）が採用された液圧回路が開示されている。しかし、この液圧回路は、特許文献１の液圧システム１００のように第１両方向ポンプに対して第２両方向ポンプが付加されたものではない。 Incidentally, FIG. 2 of Patent Document 2 discloses, as a conventional technique, a hydraulic circuit in which only one bidirectional pump is used for a single-rod cylinder and a low-pressure selection valve (called a "flushing valve" in Patent Document 2) is employed that enables the discharge of hydraulic fluid from either the head side line or the rod side line, whichever has the lower pressure, into the tank. However, this hydraulic circuit does not have a second bidirectional pump added to the first bidirectional pump, as in hydraulic system 100 of Patent Document 1.
　そこで、本開示は、第１両方向ポンプに対して第２両方向ポンプが付加された構成においてロッド側およびヘッド側のうちの圧力の低い方に圧力の閉じ込みが発生することを簡易的に防止することができる液圧システムを提供することを目的とする。 The present disclosure therefore aims to provide a hydraulic system that can easily prevent pressure trapping from occurring on the lower pressure side, either the rod side or the head side, in a configuration in which a second bidirectional pump is added to a first bidirectional pump.
　本開示は、ヘッド側室およびロッド側室を含む片ロッドシリンダ用の液圧システムであって、ヘッド側ラインにより前記ヘッド側室と接続されるとともに、ロッド側ラインにより前記ロッド側室と接続される第１両方向ポンプと、第１給排ラインにより前記ヘッド側ラインと接続される第２両方向ポンプと、第２給排ラインにより前記第２両方向ポンプと接続されるアキュムレータと、前記第１両方向ポンプおよび前記第２両方向ポンプを同方向に駆動する電動モータと、第１排出ラインにより前記ヘッド側ラインと接続され、第２排出ラインにより前記ロッド側ラインと接続され、第３排出ラインにより前記第２給排ラインと接続され、前記ロッド側室の圧力が前記ヘッド側室の圧力よりも低いときは前記第２排出ラインを前記第３排出ラインと連通させ、前記ヘッド側室の圧力が前記ロッド側室の圧力よりも低いときは前記第１排出ラインを前記第３排出ラインと連通させる低圧選択弁と、前記ヘッド側ラインと前記ロッド側ラインとを接続するブリッジラインに設けられた、互いに逆向きの一対のチェック弁と、を備え、前記第２給排ラインは、中継ラインにより前記ブリッジラインにおける前記一対のチェック弁の間の部分と接続されている、液圧システムを提供する。 The present disclosure relates to a hydraulic system for a single-rod cylinder including a head side chamber and a rod side chamber, comprising a first bidirectional pump connected to the head side chamber by a head side line and connected to the rod side chamber by a rod side line, a second bidirectional pump connected to the head side line by a first supply and discharge line, an accumulator connected to the second bidirectional pump by a second supply and discharge line, an electric motor that drives the first bidirectional pump and the second bidirectional pump in the same direction, and a third bidirectional pump connected to the head side line by a first discharge line and to the rod side line by a second discharge line. A hydraulic system is provided that includes a low pressure selection valve that is connected to the second supply/discharge line by a discharge line, communicates the second discharge line with the third discharge line when the pressure in the rod side chamber is lower than the pressure in the head side chamber, and communicates the first discharge line with the third discharge line when the pressure in the head side chamber is lower than the pressure in the rod side chamber, and a pair of check valves in mutually opposite directions that are provided in a bridge line that connects the head side line and the rod side line, and the second supply/discharge line is connected to a portion of the bridge line between the pair of check valves by a relay line.
　本開示によれば、第１両方向ポンプに対して第２両方向ポンプが付加された構成においてロッド側およびヘッド側のうちの圧力の低い方に圧力の閉じ込みが発生することを簡易的に防止することができる液圧システムが提供される。 The present disclosure provides a hydraulic system that can easily prevent pressure trapping on the lower pressure side of the rod side or head side in a configuration in which a second bidirectional pump is added to a first bidirectional pump.
第１実施形態に係る液圧システムの概略構成図である。1 is a schematic configuration diagram of a hydraulic system according to a first embodiment. FIG. 第２実施形態に係る液圧システムの概略構成図である。FIG. 11 is a schematic configuration diagram of a hydraulic system according to a second embodiment. 第３実施形態に係る液圧システムの概略構成図である。FIG. 11 is a schematic configuration diagram of a hydraulic system according to a third embodiment. 第４実施形態に係る液圧システムの概略構成図である。FIG. 13 is a schematic configuration diagram of a hydraulic system according to a fourth embodiment. 変形例の低圧選択弁を示す図である。FIG. 13 is a diagram showing a modified low pressure selection valve. 別の変形例の低圧選択弁を示す図である。FIG. 13 is a diagram showing another modified example of a low pressure selection valve. 従来の液圧システムの概略構成図である。FIG. 1 is a schematic diagram of a conventional hydraulic system.
　＜第１実施形態＞
　図１に、第１実施形態に係る液圧システム１Ａを示す。この液圧システム１Ａは、ヘッド側室４ｈおよびロッド側室４ｒを含む片ロッドシリンダ４用の液圧システムである。液圧システム１Ａに用いられる作動液は、典型的には油である。 First Embodiment
1 shows a hydraulic system 1A according to a first embodiment. The hydraulic system 1A is a hydraulic system for a single-rod cylinder 4 including a head side chamber 4h and a rod side chamber 4r. The hydraulic fluid used in the hydraulic system 1A is typically oil.
　具体的に、液圧システム１Ａは、片ロッドシリンダ４と閉ループを形成するように接続される第１両方向ポンプ２と、片ロッドシリンダ４のヘッド側室４ｈとロッド側室４ｒの間の流量差、すなわち流入流量と流出流量との差を解消するための第２両方向ポンプ３を含む。また、液圧システム１Ａは、加圧された作動液を貯留するアキュムレータ７を含む。片ロッドシリンダ４、第１両方向ポンプ２、第２両方向ポンプ３およびアキュムレータ７は、後述する複数のラインと共に閉回路を構成する。 Specifically, the hydraulic system 1A includes a first bidirectional pump 2 connected to the single-rod cylinder 4 to form a closed loop, and a second bidirectional pump 3 for eliminating the flow rate difference between the head side chamber 4h and the rod side chamber 4r of the single-rod cylinder 4, i.e., the difference between the inflow flow rate and the outflow flow rate. The hydraulic system 1A also includes an accumulator 7 for storing pressurized hydraulic fluid. The single-rod cylinder 4, the first bidirectional pump 2, the second bidirectional pump 3, and the accumulator 7 form a closed circuit together with multiple lines described below.
　より詳しくは、第１両方向ポンプ２は、ヘッド側ライン２１により片ロッドシリンダ４のヘッド側室４ｈと接続されるとともに、ロッド側ライン２２により片ロッドシリンダ４のロッド側室４ｒと接続される。第２両方向ポンプ３は、第１給排ライン３１によりヘッド側ライン２１と接続されるとともに、第２給排ライン７１によりアキュムレータ７と接続される。 More specifically, the first bidirectional pump 2 is connected to the head side chamber 4h of the single-rod cylinder 4 by a head side line 21, and is connected to the rod side chamber 4r of the single-rod cylinder 4 by a rod side line 22. The second bidirectional pump 3 is connected to the head side line 21 by a first supply/discharge line 31, and is connected to the accumulator 7 by a second supply/discharge line 71.
　アキュムレータ７の設定圧は、例えば０．１－２ＭＰａの範囲内である。ここで、「アキュムレータ７の設定圧」とは、アキュムレータ７への作動液の流入が可能となる圧力である。 The set pressure of the accumulator 7 is, for example, within the range of 0.1-2 MPa. Here, the "set pressure of the accumulator 7" is the pressure at which the hydraulic fluid can flow into the accumulator 7.
　ヘッド側ライン２１およびロッド側ライン２２には、開閉弁であるロック弁２３，２４がそれぞれ設けられている。ロック弁２３，２４は、制御装置１０により制御される。なお、図１では、図面の簡略化のために一部の信号線の作図を省略する。制御装置１０は、片ロッドシリンダ４を動作させるとき、すなわち伸長または短縮させるときにロック弁２３，２４を開き、それ以外のときはロック弁２３，２４を閉じる。 The head side line 21 and the rod side line 22 are provided with lock valves 23, 24, which are on-off valves. The lock valves 23, 24 are controlled by the control device 10. Note that in FIG. 1, some signal lines are not shown to simplify the drawing. The control device 10 opens the lock valves 23, 24 when the single rod cylinder 4 is operated, i.e., when it is extended or retracted, and closes the lock valves 23, 24 at other times.
　ヘッド側ライン２１とロッド側ライン２２とは、第１ブリッジライン５１および第２ブリッジライン５４により互いに接続されている。第１ブリッジライン５１には一対のリリーフ弁５２，５３が互いに逆向きに設けられ、第２ブリッジライン５４には一対のチェック弁５５，５６が互いに逆向きに設けられている。 The head side line 21 and the rod side line 22 are connected to each other by a first bridge line 51 and a second bridge line 54. A pair of relief valves 52, 53 are provided in the first bridge line 51 in the opposite directions, and a pair of check valves 55, 56 are provided in the second bridge line 54 in the opposite directions.
　図例では第１ブリッジライン５１および第２ブリッジライン５４がロック弁２３，２４と第１両方向ポンプ２との間でヘッド側ライン２１およびロッド側ライン２２と接続されているが、第１ブリッジライン５１および第２ブリッジライン５４はロック弁２３，２４と片ロッドシリンダ４との間でヘッド側ライン２１およびロッド側ライン２２と接続されてもよい。また、第１ブリッジライン５１と第２ブリッジライン５４の一部同士、例えば両端部同士および中央部同士が互いに合流して共通の流路となってもよい。 In the illustrated example, the first bridge line 51 and the second bridge line 54 are connected to the head side line 21 and the rod side line 22 between the lock valves 23, 24 and the first bidirectional pump 2, but the first bridge line 51 and the second bridge line 54 may be connected to the head side line 21 and the rod side line 22 between the lock valves 23, 24 and the single-rod cylinder 4. Also, parts of the first bridge line 51 and the second bridge line 54, for example both ends and the center parts, may merge with each other to form a common flow path.
　リリーフ弁５２はヘッド側ライン２１の圧力が高くなりすぎたときに開き、リリーフ弁５３はロッド側ライン２２の圧力が高くなりすぎたときに開く。リリーフ弁５２，５３のリリーフ圧は、例えば２５－３５ＭＰａの範囲内と比較的に高く設定される。 The relief valve 52 opens when the pressure in the head side line 21 becomes too high, and the relief valve 53 opens when the pressure in the rod side line 22 becomes too high. The relief pressures of the relief valves 52 and 53 are set relatively high, for example, within the range of 25-35 MPa.
　チェック弁５５は、第２ブリッジライン５４の中央からヘッド側ライン２１へ向かう流れは許容するがその逆の流れは禁止する。チェック弁５６は、第２ブリッジライン５４の中央からロッド側ライン２２へ向かう流れは許容するがその逆の流れは禁止する。 Check valve 55 allows flow from the center of second bridge line 54 toward head side line 21 but prohibits flow in the opposite direction. Check valve 56 allows flow from the center of second bridge line 54 toward rod side line 22 but prohibits flow in the opposite direction.
　第１ブリッジライン５１におけるリリーフ弁５２，５３の間の部分および第２ブリッジライン５４におけるチェック弁５５，５６の間の部分は、中継ライン７２により第２給排ライン７１と接続されている。 The portion between the relief valves 52 and 53 in the first bridge line 51 and the portion between the check valves 55 and 56 in the second bridge line 54 are connected to the second supply and discharge line 71 by a relay line 72.
　第１両方向ポンプ２および第２両方向ポンプ３は、例えば、アキシャルピストンポンプである。アキシャルピストンポンプは、例えば、斜板ポンプまたは斜軸ポンプである。本実施形態では、第１両方向ポンプ２が固定容量型ポンプであり、第２両方向ポンプ３が可変容量型ポンプである。ただし、第１両方向ポンプ２は可変容量型ポンプであってもよい。あるいは、第１両方向ポンプ２と第２両方向ポンプ３の双方が固定容量型ポンプであってもよい。 The first bidirectional pump 2 and the second bidirectional pump 3 are, for example, axial piston pumps. The axial piston pump is, for example, a swash plate pump or a bent-axis pump. In this embodiment, the first bidirectional pump 2 is a fixed displacement pump, and the second bidirectional pump 3 is a variable displacement pump. However, the first bidirectional pump 2 may also be a variable displacement pump. Alternatively, both the first bidirectional pump 2 and the second bidirectional pump 3 may be fixed displacement pumps.
　第２両方向ポンプ３の容量は、レギュレータ３５により変更される。レギュレータ３５は、制御装置１０により制御される。例えば、第２両方向ポンプ３が斜板ポンプである場合、レギュレータ３５は、第２両方向ポンプ３の斜板と連結されたサーボピストンに作用する液圧を電気的に変更するものであってもよいし、第２両方向ポンプ３の斜板と連結された電動アクチュエータであってもよい。 The capacity of the second bidirectional pump 3 is changed by the regulator 35. The regulator 35 is controlled by the control device 10. For example, if the second bidirectional pump 3 is a swash plate pump, the regulator 35 may be a device that electrically changes the hydraulic pressure acting on a servo piston connected to the swash plate of the second bidirectional pump 3, or may be an electric actuator connected to the swash plate of the second bidirectional pump 3.
　第１両方向ポンプ２および第２両方向ポンプ３は、電動モータ９により同方向に駆動される。第１両方向ポンプ２および第２両方向ポンプ３は、それらの中心軸が同軸上に並ぶように配置されもよいし、それらの中心軸が平行に並ぶように配置されてもよい。前者はタンデム型、後者はパラレル型である。 The first bidirectional pump 2 and the second bidirectional pump 3 are driven in the same direction by an electric motor 9. The first bidirectional pump 2 and the second bidirectional pump 3 may be arranged so that their central axes are aligned coaxially, or so that their central axes are aligned in parallel. The former is a tandem type, and the latter is a parallel type.
　電動モータ９は、制御装置１０により制御される。電動モータ９は、片ロッドシリンダ４を伸長させる際に第１両方向ポンプ２および第２両方向ポンプ３を第１方向に駆動し、片ロッドシリンダ４を短縮させる際に第１両方向ポンプ２および第２両方向ポンプ３を第１方向と反対の第２方向に駆動する。第１両方向ポンプ２および第２両方向ポンプ３が第１方向に駆動されるとそれらがヘッド側室４ｈへ作動液を吐出し、第１両方向ポンプ２および第２両方向ポンプ３が第２方向に駆動されるとそれらがヘッド側室４ｈから作動液を吸入する。 The electric motor 9 is controlled by a control device 10. The electric motor 9 drives the first bidirectional pump 2 and the second bidirectional pump 3 in a first direction when the single-rod cylinder 4 is extended, and drives the first bidirectional pump 2 and the second bidirectional pump 3 in a second direction opposite to the first direction when the single-rod cylinder 4 is retracted. When the first bidirectional pump 2 and the second bidirectional pump 3 are driven in the first direction, they discharge working fluid into the head side chamber 4h, and when the first bidirectional pump 2 and the second bidirectional pump 3 are driven in the second direction, they suck working fluid from the head side chamber 4h.
　さらに、本実施形態では、第１排出ライン６１によりヘッド側ライン２１と接続されるとともに第２排出ライン６２によりロッド側ライン２２と接続された低圧選択弁６が採用されている。低圧選択弁６は、第３排出ライン６３により第２給排ライン７１と接続されている。 Furthermore, in this embodiment, a low pressure selection valve 6 is used that is connected to the head side line 21 by a first discharge line 61 and to the rod side line 22 by a second discharge line 62. The low pressure selection valve 6 is connected to the second supply and discharge line 71 by a third discharge line 63.
　本実施形態では、第３排出ライン６３にリリーフ弁６４が設けられている。リリーフ弁６４は、片ロッドシリンダ４、ヘッド側ライン２１、ロッド側ライン２２および第１両方向ポンプ２で構成される閉ループ内の低圧をある程度高く保つ役割を果たす。リリーフ弁６４のリリーフ圧は、例えば０．１－２ＭＰａの範囲内と比較的に低く設定される。閉ループ内の低圧はアキュムレータ７の設定圧とリリーフ弁６４の設定圧の和であり、例えば１－２ＭＰａである。なお、アキュムレータ７の設定圧が比較的に高い場合、リリーフ弁６４は省略可能である。 In this embodiment, a relief valve 64 is provided in the third discharge line 63. The relief valve 64 serves to maintain a relatively high low pressure in the closed loop consisting of the single-rod cylinder 4, the head side line 21, the rod side line 22, and the first bidirectional pump 2. The relief pressure of the relief valve 64 is set relatively low, for example, within the range of 0.1-2 MPa. The low pressure in the closed loop is the sum of the set pressure of the accumulator 7 and the set pressure of the relief valve 64, and is, for example, 1-2 MPa. Note that if the set pressure of the accumulator 7 is relatively high, the relief valve 64 can be omitted.
　低圧選択弁６は、中立位置とヘッド側排出位置とロッド側排出位置との間で切り換えられる。図１では、中央位置が中立位置、右側位置がヘッド側排出位置、左側位置がロッド側排出位置である。中立位置では低圧選択弁６が第１排出ライン６１および第２排出ライン６２をブロックする。ヘッド側排出位置では低圧選択弁６が第２排出ライン６２をブロックしつつ第１排出ライン６１を第３排出ライン６３と連通させる。ロッド側排出位置では低圧選択弁６が第１排出ライン６１をブロックしつつ第２排出ライン６２を第３排出ライン６３と連通させる。 The low pressure selection valve 6 can be switched between a neutral position, a head side discharge position, and a rod side discharge position. In FIG. 1, the center position is the neutral position, the right position is the head side discharge position, and the left position is the rod side discharge position. In the neutral position, the low pressure selection valve 6 blocks the first discharge line 61 and the second discharge line 62. In the head side discharge position, the low pressure selection valve 6 blocks the second discharge line 62 while connecting the first discharge line 61 to the third discharge line 63. In the rod side discharge position, the low pressure selection valve 6 blocks the first discharge line 61 while connecting the second discharge line 62 to the third discharge line 63.
　本実施形態では、低圧選択弁６がパイロット式の三位置弁である。このため、低圧選択弁６には、第１パイロットライン６５を通じてヘッド側室４ｈの圧力Ｐｈが導かれるとともに、第２パイロットライン６６を通じてロッド側室４ｒの圧力Ｐｒが導かれる。第１パイロットライン６５は低圧選択弁６を中立位置からロッド側排出位置へ切り換えるためのものであり、第２パイロットライン６６は低圧選択弁６を中立位置からヘッド側排出位置へ切り換えるためのものである。図例では第１パイロットライン６５および第２パイロットライン６６が第１排出ライン６１および第２排出ライン６２からそれぞれ分岐しているが、第１パイロットライン６５がヘッド側ライン２１から分岐してもよいし、第２パイロットライン６６がロッド側ライン２２から分岐してもよい。 In this embodiment, the low pressure selection valve 6 is a pilot type three-position valve. Therefore, the pressure Ph of the head side chamber 4h is guided to the low pressure selection valve 6 through the first pilot line 65, and the pressure Pr of the rod side chamber 4r is guided to the low pressure selection valve 6 through the second pilot line 66. The first pilot line 65 is for switching the low pressure selection valve 6 from the neutral position to the rod side discharge position, and the second pilot line 66 is for switching the low pressure selection valve 6 from the neutral position to the head side discharge position. In the illustrated example, the first pilot line 65 and the second pilot line 66 branch off from the first discharge line 61 and the second discharge line 62, respectively, but the first pilot line 65 may branch off from the head side line 21, and the second pilot line 66 may branch off from the rod side line 22.
　低圧選択弁６は、ロッド側室４ｒの圧力Ｐｒがヘッド側室４ｈの圧力Ｐｈよりも低いときにロッド側排出位置に切り換えられ、ヘッド側室４ｈの圧力Ｐｈがロッド側室４ｒの圧力Ｐｒよりも低いときにヘッド側排出位置に切り換えられる。本実施形態では、ヘッド側室４ｈの圧力Ｐｈとロッド側室４ｒの圧力Ｐｒとの差圧ΔＰ、すなわち圧力Ｐｈと圧力Ｐｒの偏差の絶対値が閾値Ｐｔ以上となったときに、低圧選択弁６が中立位置からロッド側排出位置またはヘッド側排出位置に切り換えられる。例えば、閾値Ｐｔは、０．５－３ＭＰａの範囲内である。なお、閾値Ｐｔは、シリンダ伸長時とシリンダ短縮時とで異なってもよい。 The low pressure selection valve 6 is switched to the rod side discharge position when the pressure Pr in the rod side chamber 4r is lower than the pressure Ph in the head side chamber 4h, and is switched to the head side discharge position when the pressure Ph in the head side chamber 4h is lower than the pressure Pr in the rod side chamber 4r. In this embodiment, when the pressure difference ΔP between the pressure Ph in the head side chamber 4h and the pressure Pr in the rod side chamber 4r, i.e., the absolute value of the deviation between the pressure Ph and the pressure Pr, becomes equal to or greater than the threshold value Pt, the low pressure selection valve 6 is switched from the neutral position to the rod side discharge position or the head side discharge position. For example, the threshold value Pt is within the range of 0.5-3 MPa. The threshold value Pt may be different when the cylinder is extended and when it is retracted.
　次に、制御装置１０が行う制御の一例を説明する。ただし、制御装置１０が行う制御は以下で説明するものに限られず、制御装置１０は別の制御を行ってもよい。 Next, an example of the control performed by the control device 10 will be described. However, the control performed by the control device 10 is not limited to the one described below, and the control device 10 may perform other controls.
　制御装置１０に関し、本明細書で開示する要素の機能は、開示された機能を実行するよう構成またはプログラムされた汎用プロセッサ、専用プロセッサ、集積回路、ASIC（Application Specific Integrated Circuits）、従来の回路、および/または、それらの組み合わせ、を含む回路または処理回路を使用して実行できる。プロセッサは、トランジスタやその他の回路を含むため、処理回路または回路と見なされる。本開示において、回路、ユニット、または手段は、列挙された機能を実行するハードウエアであるか、または、列挙された機能を実行するようにプログラムされたハードウエアである。ハードウエアは、本明細書に開示されているハードウエアであってもよいし、あるいは、列挙された機能を実行するようにプログラムまたは構成されているその他の既知のハードウエアであってもよい。ハードウエアが回路の一種と考えられるプロセッサである場合、回路、手段、またはユニットはハードウエアとソフトウエアの組み合わせであり、ソフトウエアはハードウエアおよび/またはプロセッサの構成に使用される。 With respect to the control device 10, the functions of the elements disclosed herein may be performed using circuits or processing circuits, including general purpose processors, special purpose processors, integrated circuits, ASICs (Application Specific Integrated Circuits), conventional circuits, and/or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuitry. In this disclosure, a circuit, unit, or means is hardware that performs the recited functions or hardware that is programmed to perform the recited functions. The hardware may be hardware disclosed herein or other known hardware that is programmed or configured to perform the recited functions. Where the hardware is a processor, which is considered a type of circuit, the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and/or the processor.
　制御装置１０には、片ロッドシリンダ４に対する伸長指令である第１操作信号と、片ロッドシリンダ４に対する短縮指令である第２操作信号が入力される。また、制御装置１０には、圧力センサで計測されるヘッド側室４ｈの圧力Ｐｈおよびロッド側室４ｒの圧力Ｐｒ、または差圧計で計測されるヘッド側室４ｈの圧力Ｐｈとロッド側室４ｒの圧力Ｐｒとの差圧ΔＰが入力される。 The control device 10 receives a first operation signal, which is an extension command for the single-rod cylinder 4, and a second operation signal, which is a contraction command for the single-rod cylinder 4. The control device 10 also receives the pressure Ph in the head side chamber 4h and the pressure Pr in the rod side chamber 4r measured by a pressure sensor, or the differential pressure ΔP between the pressure Ph in the head side chamber 4h and the pressure Pr in the rod side chamber 4r measured by a differential pressure gauge.
　１．シリンダ伸長
　制御装置１０へ第１操作信号が入力されると、制御装置１０は電動モータ９を第１方向に回転させる。これにより、第１両方向ポンプ２および第２両方向ポンプ３が第１方向に駆動され、第１両方向ポンプ２がロッド側ライン２２を通じて作動液を吸入するとともに、第２両方向ポンプ３が第２給排ライン７１を通じて作動液を吸入する。また、第１両方向ポンプ２はヘッド側ライン２１を通じて作動液を吐出し、第２両方向ポンプ３は第１給排ライン３１を通じて作動液を吐出する。 1. Cylinder extension When a first operation signal is input to the control device 10, the control device 10 rotates the electric motor 9 in the first direction. This drives the first bidirectional pump 2 and the second bidirectional pump 3 in the first direction, and the first bidirectional pump 2 draws in working fluid through the rod side line 22, while the second bidirectional pump 3 draws in working fluid through the second supply/discharge line 71. In addition, the first bidirectional pump 2 discharges working fluid through the head side line 21, and the second bidirectional pump 3 discharges working fluid through the first supply/discharge line 31.
　ヘッド側室４ｈの圧力Ｐｈとロッド側室４ｒの圧力Ｐｒとの差圧ΔＰが閾値Ｐｔ未満である場合、制御装置１０は第２両方向ポンプ３の容量ｑ２が基準容量ｑｒとなるようにレギュレータ３５を制御する。基準容量ｑｒは、第１両方向ポンプ２の容量ｑ１にロッド側室４ｒの受圧面積Ａｒに対する片ロッドシリンダ４のロッドの断面積Ａｃの比を乗算したものである。ｑｒ＝Ａｃ／Ａｒ×ｑ１。すなわち、ｑ２＝ｑｒである場合、理論的には片ロッドシリンダ４への流入流量または片ロッドシリンダ４からの流出流量に過不足がない。このため、第２ブリッジライン５４の一部および中継ライン７２および第２給排ライン７１の一部を通じたアキュムレータ７からヘッド側ライン２１またはロッド側ライン２２への作動液の供給、および第１排出ライン６１または第２排出ライン６２を通じたヘッド側ライン２１またはロッド側ライン２２からの作動液の排出は行われない。 When the pressure difference ΔP between the pressure Ph of the head side chamber 4h and the pressure Pr of the rod side chamber 4r is less than the threshold value Pt, the control device 10 controls the regulator 35 so that the capacity q2 of the second bidirectional pump 3 becomes the reference capacity qr. The reference capacity qr is the capacity q1 of the first bidirectional pump 2 multiplied by the ratio of the cross-sectional area Ac of the rod of the single-rod cylinder 4 to the pressure-receiving area Ar of the rod side chamber 4r. qr = Ac/Ar x q1. In other words, when q2 = qr, theoretically there is no excess or deficiency in the inflow flow rate to the single-rod cylinder 4 or the outflow flow rate from the single-rod cylinder 4. For this reason, the supply of the working fluid from the accumulator 7 to the head side line 21 or the rod side line 22 through a part of the second bridge line 54, the relay line 72, and a part of the second supply/discharge line 71, and the discharge of the working fluid from the head side line 21 or the rod side line 22 through the first discharge line 61 or the second discharge line 62 are not performed.
　一方、差圧ΔＰが閾値Ｐｔ以上である場合、制御装置１０は第２両方向ポンプ３の容量ｑ２が基準容量ｑｒよりも第１所定量Δｑ１だけ多くなるようにレギュレータ３５を制御する。ｑ２＝ｑｒ＋Δｑ１。例えば、Δｑ１は、ｑｒの１－１０％の範囲内である。 On the other hand, when the pressure difference ΔP is equal to or greater than the threshold value Pt, the control device 10 controls the regulator 35 so that the capacity q2 of the second bidirectional pump 3 is greater than the reference capacity qr by a first predetermined amount Δq1. q2 = qr + Δq1. For example, Δq1 is within the range of 1-10% of qr.
　例えば、片ロッドシリンダ４に短縮方向への負荷がかかっている場合にはヘッド側室４ｈの圧力Ｐｈがロッド側室４ｒの圧力Ｐｒよりも閾値Ｐｔ以上高くなり、片ロッドシリンダ４に伸長方向への負荷がかかっている場合にはロッド側室４ｒの圧力Ｐｒがヘッド側室４ｈの圧力Ｐｒよりも閾値Ｐｔ以上高くなる。 For example, when a load is applied to the single-rod cylinder 4 in the shortening direction, the pressure Ph in the head side chamber 4h becomes higher than the pressure Pr in the rod side chamber 4r by at least the threshold Pt, and when a load is applied to the single-rod cylinder 4 in the extending direction, the pressure Pr in the rod side chamber 4r becomes higher than the pressure Pr in the head side chamber 4h by at least the threshold Pt.
　ヘッド側室４ｈの圧力Ｐｈがロッド側室４ｒの圧力Ｐｒよりも閾値Ｐｔ以上高くなる場合、低圧選択弁６がロッド側排出位置に切り換えられる。これにより、第１所定量Δｑ１に応じた余剰分がロッド側ライン２２から第２排出ライン６２、低圧選択弁６、第３排出ライン６３および第２給排ライン７１の一部を通じてアキュムレータ７へ排出される。 When the pressure Ph in the head side chamber 4h becomes higher than the pressure Pr in the rod side chamber 4r by the threshold value Pt or more, the low pressure selection valve 6 is switched to the rod side discharge position. As a result, the surplus corresponding to the first predetermined amount Δq1 is discharged from the rod side line 22 through the second discharge line 62, the low pressure selection valve 6, the third discharge line 63, and a part of the second supply/discharge line 71 to the accumulator 7.
　逆に、ロッド側室４ｒの圧力Ｐｒがヘッド側室４ｈの圧力Ｐｒよりも閾値Ｐｔ以上高くなる場合、低圧選択弁６がヘッド側排出位置に切り換えられる。これにより、第１所定量Δｑ１に応じた余剰分がヘッド側ライン２１から第１排出ライン６１、低圧選択弁６、第３排出ライン６３および第２給排ライン７１の一部を通じてアキュムレータ７へ排出される。 On the other hand, when the pressure Pr in the rod side chamber 4r becomes higher than the pressure Pr in the head side chamber 4h by the threshold value Pt or more, the low pressure selection valve 6 is switched to the head side discharge position. As a result, the surplus corresponding to the first predetermined amount Δq1 is discharged from the head side line 21 through the first discharge line 61, the low pressure selection valve 6, the third discharge line 63, and a part of the second supply/discharge line 71 to the accumulator 7.
　２．シリンダ短縮
　制御装置１０へ第２操作信号が入力されると、制御装置１０は電動モータ９を第２方向に回転させる。これにより、第１両方向ポンプ２および第２両方向ポンプ３が第２方向に駆動され、第１両方向ポンプ２がヘッド側ライン２１を通じて作動液を吸入するとともに、第２両方向ポンプ３が第１給排ライン３１を通じて作動液を吸入する。また、第１両方向ポンプ２はロッド側ライン２２を通じて作動液を吐出し、第２両方向ポンプ３は第２給排ライン７１を通じて作動液を吐出する。 2. Cylinder Retraction When a second operation signal is input to the control device 10, the control device 10 rotates the electric motor 9 in the second direction. This drives the first bidirectional pump 2 and the second bidirectional pump 3 in the second direction, and the first bidirectional pump 2 draws in working fluid through the head side line 21, while the second bidirectional pump 3 draws in working fluid through the first supply/discharge line 31. In addition, the first bidirectional pump 2 discharges working fluid through the rod side line 22, and the second bidirectional pump 3 discharges working fluid through the second supply/discharge line 71.
　ヘッド側室４ｈの圧力Ｐｈとロッド側室４ｒの圧力Ｐｒとの差圧ΔＰが閾値Ｐｔ未満である場合、制御装置１０は第２両方向ポンプ３の容量ｑ２が基準容量ｑｒとなるようにレギュレータ３５を制御する。すなわち、ｑ２＝ｑｒである場合、理論的には片ロッドシリンダ４への流入流量または片ロッドシリンダ４からの流出流量に過不足がない。このため、第２ブリッジライン５４の一部および中継ライン７２および第２給排ライン７１の一部を通じたアキュムレータ７からヘッド側ライン２１またはロッド側ライン２２への作動液の供給、および第１排出ライン６１または第２排出ライン６２を通じたヘッド側ライン２１またはロッド側ライン２２からの作動液の排出は行われない。 When the pressure difference ΔP between the pressure Ph in the head side chamber 4h and the pressure Pr in the rod side chamber 4r is less than the threshold value Pt, the control device 10 controls the regulator 35 so that the capacity q2 of the second bidirectional pump 3 becomes the reference capacity qr. In other words, when q2=qr, theoretically there is no excess or deficiency in the inflow flow rate to the single-rod cylinder 4 or the outflow flow rate from the single-rod cylinder 4. For this reason, the supply of hydraulic fluid from the accumulator 7 to the head side line 21 or the rod side line 22 through a part of the second bridge line 54, the relay line 72, and a part of the second supply/discharge line 71, and the discharge of hydraulic fluid from the head side line 21 or the rod side line 22 through the first discharge line 61 or the second discharge line 62 are not performed.
　一方、差圧ΔＰが閾値Ｐｔ以上である場合、制御装置１０は第２両方向ポンプ３の容量ｑ２が基準容量ｑｒよりも第２所定量Δｑ２だけ少なくなるようにレギュレータ３５を制御する。ｑ２＝ｑｒ－Δｑ２。第２所定量Δｑ２は、上述した第１所定量Δｑ１と同じであっても異なってもよい。例えば、Δｑ２は、ｑｒの１－１０％の範囲内である。 On the other hand, when the pressure difference ΔP is equal to or greater than the threshold value Pt, the control device 10 controls the regulator 35 so that the capacity q2 of the second bidirectional pump 3 is less than the reference capacity qr by a second predetermined amount Δq2. q2 = qr - Δq2. The second predetermined amount Δq2 may be the same as or different from the first predetermined amount Δq1 described above. For example, Δq2 is within the range of 1-10% of qr.
　例えば、片ロッドシリンダ４に伸長方向への負荷がかかっている場合にはロッド側室４ｒの圧力Ｐｒがヘッド側室４ｈの圧力Ｐｈよりも閾値Ｐｔ以上高くなり、片ロッドシリンダ４に短縮方向への負荷がかかっている場合にはヘッド側室４ｈの圧力Ｐｈがロッド側室４ｒの圧力Ｐｒよりも閾値Ｐｔ以上高くなる。 For example, when a load is applied to the single-rod cylinder 4 in the extension direction, the pressure Pr in the rod side chamber 4r becomes higher than the pressure Ph in the head side chamber 4h by more than the threshold value Pt, and when a load is applied to the single-rod cylinder 4 in the contraction direction, the pressure Ph in the head side chamber 4h becomes higher than the pressure Pr in the rod side chamber 4r by more than the threshold value Pt.
　ロッド側室４ｒの圧力Ｐｒがヘッド側室４ｈの圧力Ｐｒよりも閾値Ｐｔ以上高くなる場合、低圧選択弁６がヘッド側排出位置に切り換えられる。これにより、第２所定量Δｑ２に応じた余剰分がヘッド側ライン２１から第１排出ライン６１、低圧選択弁６、第３排出ライン６３および第２給排ライン７１の一部を通じてアキュムレータ７へ排出される。 When the pressure Pr in the rod side chamber 4r becomes higher than the pressure Pr in the head side chamber 4h by the threshold value Pt or more, the low pressure selection valve 6 is switched to the head side discharge position. As a result, the surplus corresponding to the second predetermined amount Δq2 is discharged from the head side line 21 through the first discharge line 61, the low pressure selection valve 6, the third discharge line 63, and a part of the second supply/discharge line 71 to the accumulator 7.
　逆に、ヘッド側室４ｈの圧力Ｐｈがロッド側室４ｒの圧力Ｐｒよりも閾値Ｐｔ以上高くなる場合、低圧選択弁６がロッド側排出位置に切り換えられる。これにより、第２所定量Δｑ２に応じた余剰分がロッド側ライン２２から第２排出ライン６２、低圧選択弁６、第３排出ライン６３および第２給排ライン７１の一部を通じてアキュムレータ７へ排出される。 On the other hand, when the pressure Ph in the head side chamber 4h becomes higher than the pressure Pr in the rod side chamber 4r by the threshold value Pt or more, the low pressure selection valve 6 is switched to the rod side discharge position. As a result, the surplus corresponding to the second predetermined amount Δq2 is discharged from the rod side line 22 through the second discharge line 62, the low pressure selection valve 6, the third discharge line 63, and a part of the second supply/discharge line 71 to the accumulator 7.
　以上説明したように、本実施形態の液圧システム１Ａでは、低圧選択弁６が設けられているので、第１両方向ポンプ２に対して第２両方向ポンプ３が付加された構成においてロッド側およびヘッド側のうちの圧力の低い方に圧力の閉じ込みが発生することを簡易的に防止することができる。ロッド側はロッド側室４ｒおよびロッド側ライン２２であり、ヘッド側はヘッド側室４ｈおよびヘッド側ライン２１である。 As described above, in the hydraulic system 1A of this embodiment, the low pressure selection valve 6 is provided, so that in a configuration in which the second bidirectional pump 3 is added to the first bidirectional pump 2, it is possible to simply prevent pressure trapping from occurring on the rod side or head side, whichever has the lower pressure. The rod side is the rod side chamber 4r and the rod side line 22, and the head side is the head side chamber 4h and the head side line 21.
　しかも、第２両方向ポンプ３は第２給排ライン７１によりアキュムレータ７と接続されているので、第２両方向ポンプ３が第１給排ライン３１を通じて作動液を吐出する方向に回転し始めるときに第２両方向ポンプ３の吸入側での圧力の低下によるキャビテーションを防止することができる。さらには、第１両方向ポンプ２の回転開始時に吸入側への作動液の戻りの遅れによって吸入側の圧力が低下したときには、アキュムレータ７から加圧された作動液がチェック弁５５または５６を介して吸入側に供給されるので、第１両方向ポンプ２の吸入側でのキャビテーションも防止することができる。 Moreover, because the second bidirectional pump 3 is connected to the accumulator 7 by the second supply/discharge line 71, it is possible to prevent cavitation due to a drop in pressure on the suction side of the second bidirectional pump 3 when the second bidirectional pump 3 starts to rotate in the direction of discharging working fluid through the first supply/discharge line 31. Furthermore, when the pressure on the suction side drops due to a delay in the return of working fluid to the suction side when the first bidirectional pump 2 starts to rotate, pressurized working fluid from the accumulator 7 is supplied to the suction side via the check valve 55 or 56, so it is also possible to prevent cavitation on the suction side of the first bidirectional pump 2.
　また、本実施形態では、第３排出ライン６３にリリーフ弁６４が設けられているので、ヘッド側ライン２１またはロッド側ライン２２から第１排出ライン６１または第２排出ライン６２を通じて作動液が排出されるときの圧力を、アキュムレータ７の設定圧とは別に設定することができる。 In addition, in this embodiment, a relief valve 64 is provided in the third discharge line 63, so the pressure at which the hydraulic fluid is discharged from the head side line 21 or the rod side line 22 through the first discharge line 61 or the second discharge line 62 can be set separately from the set pressure of the accumulator 7.
　＜第２実施形態＞
　図２に、第２実施形態に係る液圧システム１Ｂを示す。なお、本実施形態ならびに後述する第３実施形態および第４実施形態において、第１実施形態と同一構成要素には同一符号を付し、重複した説明は省略する。 Second Embodiment
2 shows a hydraulic system 1B according to a second embodiment. In this embodiment as well as in a third and fourth embodiment described later, the same components as those in the first embodiment are denoted by the same reference numerals, and duplicated explanations will be omitted.
　液圧システム１Ｂが第１実施形態の液圧システム１Ａと異なる点は、タンク１１およびチャージポンプ８をさらに含む点である。チャージポンプ８は、吸入ライン８１によりタンク１１と接続されるとともに、吐出ライン８２により第２給排ライン７１と接続されている。ただし、吐出ライン８２は必ずしも第２給排ライン７１に接続される必要はなく、リリーフ弁６４と第２給排ライン７１の間で第３排出ライン６３に接続されてもよいし、中継ライン７２に接続されてもよい。 The hydraulic system 1B differs from the hydraulic system 1A of the first embodiment in that it further includes a tank 11 and a charge pump 8. The charge pump 8 is connected to the tank 11 by a suction line 81, and is connected to the second supply/discharge line 71 by a discharge line 82. However, the discharge line 82 does not necessarily have to be connected to the second supply/discharge line 71, and may be connected to the third discharge line 63 between the relief valve 64 and the second supply/discharge line 71, or may be connected to the relay line 72.
　吐出ライン８２には、チャージポンプ８から第２給排ライン７１へ向かう流れは許容するがその逆の流れは禁止するチェック弁８３が設けられている。また、吐出ライン８２からはチャージポンプ８とチェック弁８３の間でリリーフライン８４が分岐しており、リリーフライン８４はタンク１１へつながっている。 The discharge line 82 is provided with a check valve 83 that allows flow from the charge pump 8 to the second supply/discharge line 71 but prohibits flow in the opposite direction. In addition, a relief line 84 branches off from the discharge line 82 between the charge pump 8 and the check valve 83, and the relief line 84 is connected to the tank 11.
　リリーフライン８４には、リリーフ弁８５が設けられている。リリーフ弁８５のリリーフ圧は、例えば０．１－２ＭＰａの範囲内である。 A relief valve 85 is provided in the relief line 84. The relief pressure of the relief valve 85 is, for example, in the range of 0.1-2 MPa.
　本実施形態のようにチャージポンプ８が設けられていれば、片ロッドシリンダ４、第１両方向ポンプ２、第２両方向ポンプ３およびアキュムレータ７で構成される閉回路内の作動液の量が減少したときに、作動液を補給することができる。例えば、第１両方向ポンプ２および第２両方向ポンプ３が外部ドレン式である場合には、閉回路内の作動液の量が徐々に減少する。 If a charge pump 8 is provided as in this embodiment, the hydraulic fluid can be replenished when the amount of hydraulic fluid in the closed circuit consisting of the single-rod cylinder 4, first bidirectional pump 2, second bidirectional pump 3, and accumulator 7 decreases. For example, if the first bidirectional pump 2 and second bidirectional pump 3 are of the external drain type, the amount of hydraulic fluid in the closed circuit gradually decreases.
　チャージポンプ８は手動で操作されてもよいが、制御装置１０がチャージポンプ８を制御する場合、例えば、アキュムレータ７内の作動液の量が所定値を下回った場合や、閉回路内の所定位置の圧力が所定値を下回った場合に、制御装置１０がチャージポンプ８を稼働させてもよい。 The charge pump 8 may be operated manually, but when the control device 10 controls the charge pump 8, for example, the control device 10 may operate the charge pump 8 when the amount of hydraulic fluid in the accumulator 7 falls below a predetermined value or when the pressure at a predetermined position in the closed circuit falls below a predetermined value.
　なお、吐出ライン８２は、必ずしも第２給排ライン７１に常時接続されている必要はなく、作動液を補給するときにだけ第２給排ライン７１に接続されてもよい。また、第１実施形態で説明したのと同様に、アキュムレータ７の設定圧が比較的に高い場合、リリーフ弁６４は省略可能である。リリーフ弁６４が省略可能である点は、後述する第３実施形態および第４実施形態でも同様である。 The discharge line 82 does not necessarily need to be constantly connected to the second supply/discharge line 71, and may be connected to the second supply/discharge line 71 only when the hydraulic fluid is replenished. As explained in the first embodiment, the relief valve 64 can be omitted when the set pressure of the accumulator 7 is relatively high. The fact that the relief valve 64 can be omitted is also the case in the third and fourth embodiments described below.
　＜第３実施形態＞
　図３に、第３実施形態に係る液圧システム１Ｃを示す。液圧システム１Ｃが第２実施形態の液圧システム１Ｂと異なる点は、吐出ライン８２がリリーフ弁６４と第２給排ライン７１の間で第３排出ライン６３に接続されている点と、リリーフライン８４が第２給排ライン７１から分岐する点である。換言すれば、リリーフライン８４は第３排出ライン６３の一部および第２給排ライン７１の一部を挟んで吐出ライン８２と反対側で第２給排ライン７１から分岐している。 Third Embodiment
3 shows a hydraulic system 1C according to the third embodiment. The hydraulic system 1C differs from the hydraulic system 1B of the second embodiment in that a discharge line 82 is connected to the third discharge line 63 between the relief valve 64 and the second supply/discharge line 71, and that a relief line 84 branches off from the second supply/discharge line 71. In other words, the relief line 84 branches off from the second supply/discharge line 71 on the opposite side to the discharge line 82, with a part of the third discharge line 63 and a part of the second supply/discharge line 71 in between.
　ただし、リリーフライン８４は、第３排出ライン６３の一部、第２給排ライン７１の一部および中継ライン７２の一部を挟んで吐出ライン８２と反対側で中継ライン７２から分岐してもよい。あるいは、図３とは逆に、吐出ライン８２が第２給排ライン７１または中継ライン７２に接続され、リリーフライン８４がリリーフ弁６４と第２給排ライン７１の間で第３排出ライン６３から分岐してもよい。 However, the relief line 84 may branch off from the relay line 72 on the opposite side to the discharge line 82, sandwiching part of the third discharge line 63, part of the second supply/discharge line 71, and part of the relay line 72. Alternatively, in the opposite arrangement to FIG. 3, the discharge line 82 may be connected to the second supply/discharge line 71 or the relay line 72, and the relief line 84 may branch off from the third discharge line 63 between the relief valve 64 and the second supply/discharge line 71.
　本実施形態では、チャージポンプ８が常時稼働する。つまり、第２両方向ポンプ３が停止中は、図３中に実線の矢印で示すように、チャージポンプ８から吐出された作動液がアキュムレータ７へ流入し、アキュムレータ７が満杯となった後は、タンク１１内の作動液が吸入ライン８１、チャージポンプ８、吐出ライン８２、第３排出ライン６３の一部、第２給排ライン７１の一部、リリーフライン８４をこの順に通過するように循環する。 In this embodiment, the charge pump 8 operates at all times. In other words, while the second bidirectional pump 3 is stopped, the hydraulic fluid discharged from the charge pump 8 flows into the accumulator 7 as shown by the solid arrows in FIG. 3, and after the accumulator 7 becomes full, the hydraulic fluid in the tank 11 circulates through the suction line 81, the charge pump 8, the discharge line 82, part of the third discharge line 63, part of the second supply/discharge line 71, and the relief line 84, in that order.
　一方、第２両方向ポンプ３が第１給排ライン３１を通じて作動液を吐出する方向に回転すると、図３中に破線の矢印で示すように、第２両方向ポンプ３にはチャージポンプ８およびアキュムレータ７から作動液が供給される。 On the other hand, when the second bidirectional pump 3 rotates in a direction to discharge hydraulic fluid through the first supply/discharge line 31, hydraulic fluid is supplied to the second bidirectional pump 3 from the charge pump 8 and the accumulator 7, as shown by the dashed arrow in Figure 3.
　本実施形態のような構成であれば、チャージポンプ８によって、作動液を吐出ライン８２から、片ロッドシリンダ４、第１両方向ポンプ２、第２両方向ポンプ３およびアキュムレータ７で構成される閉回路の一部を通ってリリーフライン８４へ流れるように循環させることができる。これにより、閉回路内の作動液を冷却することができる。 In the configuration of this embodiment, the charge pump 8 can circulate the hydraulic fluid from the discharge line 82 through a part of the closed circuit made up of the single-rod cylinder 4, the first bidirectional pump 2, the second bidirectional pump 3, and the accumulator 7 to the relief line 84. This makes it possible to cool the hydraulic fluid in the closed circuit.
　＜第４実施形態＞
　図４に、第４実施形態に係る液圧システム１Ｄを示す。液圧システム１Ｄが第３実施形態の液圧システム１Ｃと異なる点は、アキュムレータ７が第２両方向ポンプ３の近傍に配置されている点と、チャージポンプ８とアキュムレータ７との間にクーラー１２が介在する点と、リリーフライン８４が中継ライン７２から分岐する点である。 Fourth Embodiment
4 shows a hydraulic system 1D according to the fourth embodiment. The hydraulic system 1D differs from the hydraulic system 1C of the third embodiment in that the accumulator 7 is disposed near the second bidirectional pump 3, a cooler 12 is interposed between the charge pump 8 and the accumulator 7, and a relief line 84 branches off from the relay line 72.
　本実施形態では、クーラー１２が第３排出ライン６３に設けられている。また、本実施形態では、リリーフ弁８５がアキュムレータ７を挟んでクーラー１２と反対側に位置する。つまり、チャージポンプ８から吐出されてクーラー１２を通過した作動液は、第２給排ライン７１におけるアキュムレータ７に隣接する部分を流れた後に、中継ライン７２の一部を経てリリーフライン８４に流入する。 In this embodiment, the cooler 12 is provided in the third discharge line 63. Also, in this embodiment, the relief valve 85 is located on the opposite side of the accumulator 7 from the cooler 12. In other words, the working fluid discharged from the charge pump 8 and passing through the cooler 12 flows through a portion of the second supply/discharge line 71 adjacent to the accumulator 7, and then flows into the relief line 84 via a portion of the relay line 72.
　本実施形態では、第３実施形態で説明した閉回路内の作動液の冷却効果をクーラー１２によって向上させることができる。しかも、アキュムレータ７がクーラー１２とリリーフ弁８５の間にあるので、作動液が循環する際に、アキュムレータ７に貯留される作動液も冷却することができる。 In this embodiment, the cooling effect of the working fluid in the closed circuit described in the third embodiment can be improved by the cooler 12. Moreover, since the accumulator 7 is located between the cooler 12 and the relief valve 85, the working fluid stored in the accumulator 7 can also be cooled as the working fluid circulates.
　さらに、本実施形態ではクーラー１２が第３排出ライン６３に設けられているので、作動液が第３排出ライン６３を通じてアキュムレータ７へ戻される際にも冷却される。ただし、作動液の循環時の冷却効果を向上させるという観点からは、クーラー１２は吐出ライン８２などに設けられてもよい。 Furthermore, in this embodiment, the cooler 12 is provided in the third discharge line 63, so the working fluid is also cooled when it is returned to the accumulator 7 through the third discharge line 63. However, from the viewpoint of improving the cooling effect when the working fluid is circulating, the cooler 12 may be provided in the discharge line 82, etc.
　＜その他の実施形態＞
　本開示は上述した実施形態に限定されるものではなく、本開示の要旨を逸脱しない範囲で種々の変形が可能である。 <Other embodiments>
The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present disclosure.
　例えば、パイロット式の低圧選択弁６に換えて、図５に示すような電磁式の三位置弁である低圧選択弁６Ａが採用されてもよい。あるいは、図６に示すような電磁式の二位置弁である第１電磁弁６ａおよび第２電磁弁６ｂを含む低圧選択弁６Ｂが採用されてもよい。第１電磁弁６ａには第１排出ライン６１および第３排出ライン６３が接続され、第２電磁弁６ｂには第２排出ライン６２および第３排出ライン６３が接続される。 For example, instead of the pilot-type low-pressure selection valve 6, a low-pressure selection valve 6A, which is an electromagnetic three-position valve as shown in FIG. 5, may be used. Alternatively, a low-pressure selection valve 6B, which is an electromagnetic two-position valve including a first solenoid valve 6a and a second solenoid valve 6b, as shown in FIG. 6, may be used. A first discharge line 61 and a third discharge line 63 are connected to the first solenoid valve 6a, and a second discharge line 62 and a third discharge line 63 are connected to the second solenoid valve 6b.
　＜まとめ＞
　第１の態様として、本開示は、ヘッド側室およびロッド側室を含む片ロッドシリンダ用の液圧システムであって、ヘッド側ラインにより前記ヘッド側室と接続されるとともに、ロッド側ラインにより前記ロッド側室と接続される第１両方向ポンプと、第１給排ラインにより前記ヘッド側ラインと接続される第２両方向ポンプと、第２給排ラインにより前記第２両方向ポンプと接続されるアキュムレータと、前記第１両方向ポンプおよび前記第２両方向ポンプを同方向に駆動する電動モータと、第１排出ラインにより前記ヘッド側ラインと接続され、第２排出ラインにより前記ロッド側ラインと接続され、第３排出ラインにより前記第２給排ラインと接続され、前記ロッド側室の圧力が前記ヘッド側室の圧力よりも低いときは前記第２排出ラインを前記第３排出ラインと連通させ、前記ヘッド側室の圧力が前記ロッド側室の圧力よりも低いときは前記第１排出ラインを前記第３排出ラインと連通させる低圧選択弁と、前記ヘッド側ラインと前記ロッド側ラインとを接続するブリッジラインに設けられた、互いに逆向きの一対のチェック弁と、を備え、前記第２給排ラインは、中継ラインにより前記ブリッジラインにおける前記一対のチェック弁の間の部分と接続されている、液圧システムを提供する。 <Summary>
In a first aspect, the present disclosure provides a hydraulic system for a single-rod cylinder including a head side chamber and a rod side chamber, the hydraulic system including a first bidirectional pump connected to the head side chamber by a head side line and connected to the rod side chamber by a rod side line, a second bidirectional pump connected to the head side line by a first supply and discharge line, an accumulator connected to the second bidirectional pump by a second supply and discharge line, an electric motor that drives the first bidirectional pump and the second bidirectional pump in the same direction, and a hydraulic system connected to the head side line by a first discharge line and to the rod side line by a second discharge line. a low pressure selection valve connected to the second supply/discharge line by a third discharge line, communicating the second discharge line with the third discharge line when the pressure in the rod side chamber is lower than the pressure in the head side chamber, and communicating the first discharge line with the third discharge line when the pressure in the head side chamber is lower than the pressure in the rod side chamber; and a pair of check valves oriented in opposite directions and provided in a bridge line connecting the head side line and the rod side line, wherein the second supply/discharge line is connected to a portion of the bridge line between the pair of check valves by a relay line.
　上記の構成によれば、低圧選択弁が設けられているので、第１両方向ポンプに対して第２両方向ポンプが付加された構成においてロッド側およびヘッド側のうちの圧力の低い方に圧力の閉じ込みが発生することを簡易的に防止することができる。しかも、第２両方向ポンプは第２給排ラインによりアキュムレータと接続されているので、第２両方向ポンプが第１給排ラインを通じて作動液を吐出する方向に回転し始めるときに第２両方向ポンプの吸入側での圧力の低下によるキャビテーションを防止することができる。さらには、第１両方向ポンプの回転開始時に吸入側への作動液の戻りの遅れによって吸入側の圧力が低下したときには、アキュムレータから加圧された作動液がチェック弁を介して吸入側に供給されるので、第１両方向ポンプの吸入側でのキャビテーションも防止することができる。 The above configuration provides a low pressure selection valve, which makes it possible to easily prevent pressure trapping on the lower pressure side of the rod side or head side in a configuration in which a second bidirectional pump is added to a first bidirectional pump. Moreover, since the second bidirectional pump is connected to the accumulator by the second supply and discharge line, it is possible to prevent cavitation due to a drop in pressure on the suction side of the second bidirectional pump when the second bidirectional pump starts to rotate in the direction of discharging hydraulic fluid through the first supply and discharge line. Furthermore, when the pressure on the suction side drops due to a delay in the return of hydraulic fluid to the suction side when the first bidirectional pump starts to rotate, pressurized hydraulic fluid from the accumulator is supplied to the suction side via the check valve, so cavitation on the suction side of the first bidirectional pump can also be prevented.
　第２の態様として、第１の態様において、上記の液圧システムは、吸入ラインによりタンクと接続されるとともに、吐出ラインにより前記第２給排ライン、前記第３排出ラインおよび前記中継ラインのいずれかと接続されるチャージポンプをさらに備えてもよい。この構成によれば、閉回路内の作動液の量が減少したときに、作動液を補給することができる。 As a second aspect, the hydraulic system of the first aspect may further include a charge pump that is connected to a tank by a suction line and is connected to the second supply/discharge line, the third discharge line, or the relay line by a discharge line. With this configuration, the hydraulic fluid can be replenished when the amount of hydraulic fluid in the closed circuit decreases.
　第３の態様として、第２の態様において、例えば、上記の液圧システムは、前記吐出ラインから分岐して前記タンクにつながるリリーフラインに設けられたリリーフ弁をさらに備えてもよい。 As a third aspect, in the second aspect, for example, the hydraulic system may further include a relief valve provided in a relief line that branches off from the discharge line and leads to the tank.
　第４の態様として、第２の態様において、上記の液圧システムは、前記第２給排ライン、前記第３排出ラインおよび前記中継ラインのいずれかから分岐して前記タンクにつながるリリーフラインに設けられたリリーフ弁をさらに備えてもよい。この構成によれば、チャージポンプによって、作動液を吐出ラインから閉回路の一部を通ってリリーフラインへ流れるように循環させることができる。これにより、閉回路内の作動液を冷却することができる。 As a fourth aspect, in the second aspect, the hydraulic system may further include a relief valve provided in a relief line that branches off from any one of the second supply/discharge line, the third discharge line, and the relay line and leads to the tank. With this configuration, the charge pump can circulate the hydraulic fluid from the discharge line through a part of the closed circuit to the relief line. This makes it possible to cool the hydraulic fluid in the closed circuit.
　第５の態様として、第４の態様において、上記の液圧システムは、前記チャージポンプと前記アキュムレータとの間に介在するクーラーをさらに備え、前記リリーフ弁は、前記アキュムレータを挟んで前記クーラーと反対側に位置してもよい。この構成によれば、クーラーによって、閉回路内の作動液の冷却効果を向上させることができる。しかも、アキュムレータがクーラーとリリーフ弁の間にあるので、作動液が循環する際に、アキュムレータに貯留される作動液も冷却することができる。 As a fifth aspect, in the fourth aspect, the hydraulic system may further include a cooler interposed between the charge pump and the accumulator, and the relief valve may be located on the opposite side of the accumulator to the cooler. With this configuration, the cooler can improve the cooling effect of the working fluid in the closed circuit. Moreover, since the accumulator is located between the cooler and the relief valve, the working fluid stored in the accumulator can also be cooled as the working fluid circulates.
　第６の態様として、第１乃至第５の態様の何れかにおいて、上記の液圧システムは、前記第３排出ラインに設けられたリリーフ弁をさらに備えてもよい。この構成によれば、ヘッド側ラインまたはロッド側ラインから第１排出ラインまたは第２排出ラインを通じて作動液が排出されるときの圧力を、アキュムレータの設定圧とは別に設定することができる。 As a sixth aspect, in any of the first to fifth aspects, the hydraulic system may further include a relief valve provided in the third discharge line. With this configuration, the pressure at which the hydraulic fluid is discharged from the head side line or the rod side line through the first discharge line or the second discharge line can be set separately from the set pressure of the accumulator.
　第７の態様として、第１乃至第６の態様の何れかにおいて、例えば、前記低圧選択弁は、電磁式の三位置弁であってもよい。 As a seventh aspect, in any of the first to sixth aspects, for example, the low pressure selection valve may be an electromagnetic three-position valve.
　第８の態様として、第１乃至第７の態様の何れかにおいて、例えば、前記低圧選択弁は、電磁式の二位置弁である第１電磁弁および第２電磁弁を含み、前記第１電磁弁に前記第１排出ラインおよび前記第３排出ラインが接続され、前記第２電磁弁に前記第２排出ラインおよび前記第３排出ラインが接続されてもよい。
  As an eighth aspect, in any of the first to seventh aspects, for example, the low pressure selection valve may include a first solenoid valve and a second solenoid valve which are electromagnetic two-position valves, the first discharge line and the third discharge line being connected to the first solenoid valve, and the second discharge line and the third discharge line being connected to the second solenoid valve.

Claims (8)

  1. 　ヘッド側室およびロッド側室を含む片ロッドシリンダ用の液圧システムであって、
    　ヘッド側ラインにより前記ヘッド側室と接続されるとともに、ロッド側ラインにより前記ロッド側室と接続される第１両方向ポンプと、
    　第１給排ラインにより前記ヘッド側ラインと接続される第２両方向ポンプと、
    　第２給排ラインにより前記第２両方向ポンプと接続されるアキュムレータと、
    　前記第１両方向ポンプおよび前記第２両方向ポンプを同方向に駆動する電動モータと、
    　第１排出ラインにより前記ヘッド側ラインと接続され、第２排出ラインにより前記ロッド側ラインと接続され、第３排出ラインにより前記第２給排ラインと接続され、前記ロッド側室の圧力が前記ヘッド側室の圧力よりも低いときは前記第２排出ラインを前記第３排出ラインと連通させ、前記ヘッド側室の圧力が前記ロッド側室の圧力よりも低いときは前記第１排出ラインを前記第３排出ラインと連通させる低圧選択弁と、
    　前記ヘッド側ラインと前記ロッド側ラインとを接続するブリッジラインに設けられた、互いに逆向きの一対のチェック弁と、を備え、
    　前記第２給排ラインは、中継ラインにより前記ブリッジラインにおける前記一対のチェック弁の間の部分と接続されている、液圧システム。     A hydraulic system for a single rod cylinder including a head side chamber and a rod side chamber,
    a first bidirectional pump connected to the head side chamber by a head side line and connected to the rod side chamber by a rod side line;
    a second bidirectional pump connected to the head side line by a first supply/discharge line;
    an accumulator connected to the second bidirectional pump by a second supply/discharge line;
    an electric motor that drives the first bidirectional pump and the second bidirectional pump in the same direction;
    a low pressure selection valve connected to the head side line by a first discharge line, connected to the rod side line by a second discharge line, and connected to the second supply/discharge line by a third discharge line, for communicating the second discharge line with the third discharge line when the pressure in the rod side chamber is lower than the pressure in the head side chamber, and for communicating the first discharge line with the third discharge line when the pressure in the head side chamber is lower than the pressure in the rod side chamber;
    a pair of check valves arranged in opposite directions and provided in a bridge line connecting the head side line and the rod side line;
    A hydraulic system, wherein the second supply/discharge line is connected to a portion of the bridge line between the pair of check valves by a relay line.
  2. 　吸入ラインによりタンクと接続されるとともに、吐出ラインにより前記第２給排ライン、前記第３排出ラインおよび前記中継ラインのいずれかと接続されるチャージポンプをさらに備える、請求項１に記載の液圧システム。 The hydraulic system of claim 1, further comprising a charge pump connected to a tank by a suction line and connected to the second supply/discharge line, the third discharge line, or the relay line by a discharge line.
  3. 　前記吐出ラインから分岐して前記タンクにつながるリリーフラインに設けられたリリーフ弁をさらに備える、請求項２に記載の液圧システム。 The hydraulic system of claim 2, further comprising a relief valve provided in a relief line that branches off from the discharge line and leads to the tank.
  4. 　前記第２給排ライン、前記第３排出ラインおよび前記中継ラインのいずれかから分岐して前記タンクにつながるリリーフラインに設けられたリリーフ弁をさらに備える、請求項２に記載の液圧システム。 The hydraulic system according to claim 2, further comprising a relief valve provided in a relief line that branches off from either the second supply/discharge line, the third discharge line, or the relay line and leads to the tank.
  5. 　前記チャージポンプと前記アキュムレータとの間に介在するクーラーをさらに備え、
    　前記リリーフ弁は、前記アキュムレータを挟んで前記クーラーと反対側に位置する、請求項４に記載の液圧システム。     a cooler interposed between the charge pump and the accumulator;
    The hydraulic system according to claim 4 , wherein the relief valve is located on an opposite side of the accumulator from the cooler.
  6. 　前記第３排出ラインに設けられたリリーフ弁をさらに備える、請求項１～５の何れか一項に記載の液圧システム。 The hydraulic system according to any one of claims 1 to 5, further comprising a relief valve provided in the third discharge line.
  7. 　前記低圧選択弁は、電磁式の三位置弁である、請求項１～５の何れか一項に記載の液圧システム。 The hydraulic system according to any one of claims 1 to 5, wherein the low pressure selection valve is an electromagnetic three-position valve.
  8. 　前記低圧選択弁は、電磁式の二位置弁である第１電磁弁および第２電磁弁を含み、前記第１電磁弁に前記第１排出ラインおよび前記第３排出ラインが接続され、前記第２電磁弁に前記第２排出ラインおよび前記第３排出ラインが接続される、請求項１～５の何れか一項に記載の液圧システム。
          The hydraulic system according to any one of claims 1 to 5, wherein the low pressure selection valve includes a first solenoid valve and a second solenoid valve which are electromagnetic two-position valves, the first discharge line and the third discharge line are connected to the first solenoid valve, and the second discharge line and the third discharge line are connected to the second solenoid valve.
PCT/JP2023/032406 2022-12-21 2023-09-05 Hydraulic system WO2024135005A1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5263575A (en) * 1975-11-15 1977-05-26 Hitachi Constr Mach Co Ltd Hydraulic circuit and directional control valve
JPS5612102U (en) * 1979-07-09 1981-02-02
JP2014185696A (en) * 2013-03-22 2014-10-02 Sumitomo Heavy Ind Ltd Hydraulic circuit, hydraulic cylinder, processor including hydraulic cylinder, and control method of hydraulic circuit

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5263575A (en) * 1975-11-15 1977-05-26 Hitachi Constr Mach Co Ltd Hydraulic circuit and directional control valve
JPS5612102U (en) * 1979-07-09 1981-02-02
JP2014185696A (en) * 2013-03-22 2014-10-02 Sumitomo Heavy Ind Ltd Hydraulic circuit, hydraulic cylinder, processor including hydraulic cylinder, and control method of hydraulic circuit

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