hydraulic system

Abstract

To provide a hydraulic system which can cool hydraulic fluid in constitution in which a first bidirectional pump and a second bidirectional pump are used for a single-rod cylinder.SOLUTION: A hydraulic system 1A in one embodiment includes: a first bidirectional pump 2 connected to a head side chamber 4h of a single rod cylinder 4 by a head side line 21, and also connected to a rod side chamber 4r of the single rod cylinder 4 by a rod side line 22, and a second bidirectional pump 3 connected to the head side line 21 by a first supply / discharge line 31 and also connected to a reservoir 7 by a second supply / discharge line 32. The hydraulic system 1A further includes an electric motor 9 driving the first bidirectional pump 2 and the second bidirectional pump 3 in the same direction, and a cooler 8 provided in the second supply / discharge line 32.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a hydraulic system for a single-rod cylinder. Background Art

[0002] Conventionally, there has been known a hydraulic system for a single-rod cylinder that includes a bi-directional pump connected to form a closed loop with the single-rod cylinder. For example, Patent Document 1 discloses a hydraulic system 100 as illustrated in FIG. 7.

[0003] This hydraulic system 100 includes a first bi-directional pump 110 and a second bi-directional pump 120. The first bi-directional pump 110 is connected to a head-side chamber 210 of the single-rod cylinder 200 via a head-side line 111, and is connected to a rod-side chamber 220 of the single-rod cylinder 200 via a rod-side line 112. The second bi-directional pump 120 is configured to eliminate a flow difference between the head-side chamber 210 and the rod-side chamber 220 of the single-rod cylinder 200, that is, a difference between an inflow flow rate and an outflow flow rate. The second bi-directional pump 120 is connected to the head-side line 111 via a first supply / discharge line 121, and is connected to a tank via a second supply / discharge line 122.

[0004] The first bi-directional pump 110 and the second bi-directional pump 120 are driven in the same direction by an electric motor 130. More specifically, when extending the single-rod cylinder 200, that is, when advancing the rod, the electric motor 130 drives the first bi-directional pump 110 and the second bi-directional pump 120 in a first direction, and when retracting the single-rod cylinder 200, that is, when retracting the rod, the electric motor 130 drives the first bi-directional pump 110 and the second bi-directional pump 120 in a second direction opposite to the first direction. When the first bi-directional pump 110 and the second bi-directional pump 120 are driven in the first direction, they discharge hydraulic fluid into the head-side chamber 210, and when the first bi-directional pump 110 and the second bi-directional pump 120 are driven in the second direction, they suck hydraulic fluid from the head-side chamber 210. Prior Art Documents Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2013-245740 [Overview of the project] [Problems that the invention aims to solve]

[0006] In a hydraulic system 100 as shown in Figure 7, it is desirable to cool the working fluid.

[0007] Therefore, the present disclosure aims to provide a hydraulic system capable of cooling the working fluid in a configuration using a first bidirectional pump and a second bidirectional pump for a single-rod cylinder. [Means for solving the problem]

[0008] This disclosure provides, in one aspect, 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 / discharge line and connected to a reservoir by a second supply / discharge line; an electric motor that drives the first bidirectional pump and the second bidirectional pump in the same direction; and a cooler provided on the second supply / discharge line.

[0009] This disclosure also provides a hydraulic system for a single-rod cylinder including a head chamber and a rod chamber, comprising: a first bidirectional pump connected to the head chamber by a head line and to the rod chamber by a rod line; a second bidirectional pump connected to the head line by a first supply / discharge line and to a reservoir by a second supply / discharge line; an electric motor for driving the first and second bidirectional pumps in the same direction; a low-pressure selector valve connected to the head line by a first discharge line, connected to the rod line by a second discharge line, and connected to the second supply / discharge line by a third discharge line, which connects the second discharge line to the third discharge line when the pressure in the rod chamber is lower than the pressure in the head chamber, and connects the first discharge line to the third discharge line when the pressure in the head chamber is lower than the pressure in the rod chamber; and a cooler provided on the third discharge line. [Effects of the Invention]

[0010] According to this disclosure, a hydraulic system is provided that can cool the working fluid in a configuration using a first bidirectional pump and a second bidirectional pump for a single-rod cylinder. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of the hydraulic system according to the first embodiment. [Figure 2] This is a schematic diagram of a modified hydraulic system. [Figure 3] This is a schematic diagram of the hydraulic system according to the second embodiment. [Figure 4] This is a schematic diagram of the hydraulic system according to the third embodiment. [Figure 5] This diagram shows a modified low-pressure selector valve. [Figure 6] This diagram shows another modified example of a low-pressure selector valve. [Figure 7] This is a schematic diagram of a conventional hydraulic system. [Modes for carrying out the invention]

[0012] <First Embodiment> Figure 1 shows a hydraulic system 1A according to the first embodiment. This 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 working fluid used in the hydraulic system 1A is typically oil.

[0013] Specifically, the hydraulic system 1A includes a first bidirectional pump 2 connected to a 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 a reservoir 7 for storing the working fluid.

[0014] In this embodiment, the reservoir 7 is an accumulator 7A that stores pressurized working fluid. The single-rod cylinder 4, the first bidirectional pump 2, the second bidirectional pump 3, and the accumulator 7A, together with a plurality of lines described later, form a closed circuit.

[0015] More specifically, the first bidirectional pump 2 is connected to the head-side chamber 4h of the single-rod cylinder 4 by the head-side line 21 and to the rod-side chamber 4r of the single-rod cylinder 4 by the rod-side line 22. The second bidirectional pump 3 is connected to the head-side line 21 by the first supply / discharge line 31 and to the accumulator 7A by the second supply / discharge line 32.

[0016] The set pressure of accumulator 7A is, for example, within the range of 0.1-2 MPa. Here, "set pressure of accumulator 7A" refers to the pressure at which working fluid can flow into accumulator 7A.

[0017] In the present embodiment, a cooler 8 is provided on the second supply / discharge line 32. A parallel line 33 is connected to the second supply / discharge line 32 so as to bypass the cooler 8, and a check valve 34 is provided on the parallel line 33. The check valve 34 allows flow from the accumulator 7A toward the second bidirectional pump 3, but blocks flow in the reverse direction. The cracking pressure of the check valve 34 is set to be lower than the pressure loss of the cooler 8.

[0018] A first lock valve 23, which is an on-off valve, is provided on the head side line 21, and a second lock valve 24, which is an on-off valve, is provided on the rod side line 22. The first lock valve 23 and the second lock valve 24 are controlled by the control device 10. In FIG. 1, illustration of some signal lines is omitted for simplification of the drawing. The control device 10 opens the first lock valve 23 and the second lock valve 24 when operating the single-rod cylinder 4, that is, when extending or retracting the cylinder, and closes the first lock valve 23 and the second lock valve 24 in other cases.

[0019] 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 and 53 are provided on the first bridge line 51 in opposite directions to each other, and a pair of check valves 55 and 56 are provided on the second bridge line 54 in opposite directions to each other.

[0020] 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 first lock valve 23, the second lock valve 24 and the first bidirectional pump 2, but the first bridge line 51 and the second bridge line 54 may alternatively be connected to the head side line 21 and the rod side line 22 between the first lock valve 23, the second lock valve 24 and the single-rod cylinder 4. Further, parts of the first bridge line 51 and the second bridge line 54, for example, both end portions and central portions thereof, may merge with each other to form a common flow path.

[0021] Relief valve 52 opens when the pressure in the head-side line 21 becomes too high, and relief valve 53 opens when the pressure in the rod-side line 22 becomes too high. The relief pressures of relief valves 52 and 53 are set relatively high, for example, within the range of 25-35 MPa.

[0022] The check valve 55 allows flow from the center of the second bridge line 54 towards the head-side line 21, but prohibits flow in the reverse direction. The check valve 56 allows flow from the center of the second bridge line 54 towards the rod-side line 22, but prohibits flow in the reverse direction.

[0023] The portion between relief valves 52 and 53 in the first bridge line 51 and the portion between check valves 55 and 56 in the second bridge line 54 are connected by a relay line 71 to the portion between the cooler 8 and the accumulator 7A in the second supply and discharge line 32.

[0024] The first bidirectional pump 2 and the second bidirectional pump 3 are, for example, axial piston pumps. An axial piston pump is, for example, a swashplate pump or a slanted shaft 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 be a variable-displacement pump. Alternatively, both the first bidirectional pump 2 and the second bidirectional pump 3 may be fixed-displacement pumps.

[0025] The capacity of the second bidirectional pump 3 is changed by a regulator 35. The regulator 35 is controlled by a control device 10. For example, if the second bidirectional pump 3 is a swashplate pump, the regulator 35 may electrically change the hydraulic pressure acting on a servo piston connected to the swashplate of the second bidirectional pump 3, or it may be an electric actuator connected to the swashplate of the second bidirectional pump 3.

[0026] 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 coaxial, or they may be arranged so that their central axes are parallel. The former is a tandem type, and the latter is a parallel type.

[0027] The electric motor 9 is controlled by the control device 10. When extending the single-rod cylinder 4, the electric motor 9 drives the first bidirectional pump 2 and the second bidirectional pump 3 in the first direction, and when shortening the single-rod cylinder 4, it drives the first bidirectional pump 2 and the second bidirectional pump 3 in the second direction opposite to the first direction. 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 draw working fluid from the head side chamber 4h.

[0028] Furthermore, in this embodiment, a low-pressure selector valve 6 is employed, which 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 selector valve 6 is connected to the portion of the second supply / discharge line 32 between the cooler 8 and the accumulator 7A by a third discharge line 63.

[0029] In this embodiment, a relief valve 64 is provided in the third discharge line 63. The relief valve 64 plays a role in maintaining 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 3. 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 7A and the set pressure of the relief valve 64, for example, 1-2 MPa. Note that if the set pressure of the accumulator 7A is relatively high, the relief valve 64 can be omitted.

[0030] The low-pressure selector valve 6 can be switched between a neutral position, a head-side discharge position, and a rod-side discharge position. In Figure 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 selector valve 6 blocks the first discharge line 61 and the second discharge line 62. In the head-side discharge position, the low-pressure selector 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 selector valve 6 blocks the first discharge line 61 while connecting the second discharge line 62 to the third discharge line 63.

[0031] In this embodiment, the low-pressure selector valve 6 is a pilot-operated three-position valve. Therefore, the pressure Ph of the head-side chamber 4h is introduced to the low-pressure selector valve 6 through the first pilot line 65, and the pressure Pr of the rod-side chamber 4r is introduced through the second pilot line 66. The first pilot line 65 is for switching the low-pressure selector valve 6 from the neutral position to the rod-side discharge position, and the second pilot line 66 is for switching the low-pressure selector 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, or the second pilot line 66 may branch off from the rod-side line 22.

[0032] The low-pressure selector 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 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, the low-pressure selector valve 6 is switched from the neutral position to the rod-side discharge position or the head-side discharge position when the differential pressure 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 pressure Ph and pressure Pr, becomes greater than or equal to the threshold Pt. For example, the threshold Pt is in the range of 0.5-3 MPa. Note that the threshold Pt may differ between cylinder extension and cylinder retraction.

[0033] 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 what is described below and can be changed as appropriate.

[0034] With respect to the control device 10, the functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, dedicated 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 circuits. In this disclosure, a circuit, unit, or means is hardware that performs the enumerated functions, or hardware programmed to perform the enumerated functions. The hardware may be hardware disclosed herein, or other known hardware that is programmed or configured to perform the enumerated functions. If the hardware is a processor, which is considered a type of circuit, then 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.

[0035] The control device 10 receives a first operation signal, which is an extension command for one rod cylinder 4, and a second operation signal, which is a shortening command for one rod cylinder 4. The control device 10 also receives the pressure Ph of the head side chamber 4h and the pressure Pr of the rod side chamber 4r, measured by a pressure sensor, or the differential pressure ΔP between the pressure Ph of the head side chamber 4h and the pressure Pr of the rod side chamber 4r, measured by a differential pressure gauge.

[0036] 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 a first direction. This drives the first bidirectional pump 2 and the second bidirectional pump 3 in the first direction, causing the first bidirectional pump 2 to draw in working fluid through the rod-side line 22, and the second bidirectional pump 3 to draw in working fluid through the second supply / discharge line 32 and the parallel line 33. The first bidirectional pump 2 also 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.

[0037] More specifically, regarding the suction of the working fluid by the second bidirectional pump 3, the second bidirectional pump 3 suctions the working fluid from the accumulator 7A through a portion of the second supply / discharge line 32 on the accumulator 7A side, the parallel line 33, and a portion of the second supply / discharge line 32 on the second bidirectional pump 3 side. This is because, as mentioned above, the cracking pressure of the check valve 34 is set lower than the pressure loss of the cooler 8. In other words, when the second bidirectional pump 3 is driven in the first direction, the working fluid hardly passes through the cooler 8.

[0038] If the differential pressure 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 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 obtained by multiplying the capacity q1 of the first bidirectional pump 2 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 × q1. That is, if 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 working fluid from the accumulator 7A to the head-side line 21 or the rod-side line 22 through a part of the second bridge line 54, the relay line 71 and a part of the second supply / discharge line 32, and the discharge of 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.

[0039] On the other hand, if the differential pressure ΔP is greater than or equal to the threshold 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.

[0040] For example, when a load is applied to one 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 a threshold Pt or more, and when a load is applied to one rod cylinder 4 in the extension direction, the pressure Pr in the rod side chamber 4r becomes higher than the pressure Pr in the head side chamber 4h by a threshold Pt or more.

[0041] When the pressure Ph in the head-side chamber 4h becomes higher than the pressure Pr in the rod-side chamber 4r by a threshold Pt or more, the low-pressure selector valve 6 is switched to the rod-side discharge position. As a result, the excess amount corresponding to the first predetermined amount Δq1 is discharged from the rod-side line 22 to the accumulator 7A through the second discharge line 62, the low-pressure selector valve 6, the third discharge line 63, and a portion of the second supply and discharge line 32.

[0042] Conversely, if the pressure Pr in the rod-side chamber 4r becomes higher than the pressure Pr in the head-side chamber 4h by a threshold Pt or more, the low-pressure selector valve 6 is switched to the head-side discharge position. As a result, the excess amount corresponding to the first predetermined amount Δq1 is discharged from the head-side line 21 to the accumulator 7A through the first discharge line 61, the low-pressure selector valve 6, the third discharge line 63, and a portion of the second supply and discharge line 32.

[0043] 2. Cylinder shortening 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. As a result, the first bidirectional pump 2 and the second bidirectional pump 3 are driven in the second direction, causing the first bidirectional pump 2 to draw in working fluid through the head-side line 21 and the second bidirectional pump 3 to draw in working fluid through the first supply / discharge line 31. The first bidirectional pump 2 also discharges working fluid through the rod-side line 22, and the second bidirectional pump 3 discharges working fluid through the second supply / discharge line 32.

[0044] More specifically, regarding the discharge of the working fluid from the second bidirectional pump 3, the second bidirectional pump 3 discharges the working fluid to the accumulator 7A through the entire length of the second supply and discharge line 32. In other words, when the second bidirectional pump 3 is driven in the second direction, the working fluid discharged from the second bidirectional pump 3 passes through the cooler 8.

[0045] If the differential pressure 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 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. That is, if 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 working fluid from the accumulator 7A to the head-side line 21 or the rod-side line 22 through a portion of the second bridge line 54, the relay line 71, and a portion of the second supply / discharge line 32, as well as the discharge of 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, does not occur.

[0046] On the other hand, if the differential pressure ΔP is greater than or equal to the threshold 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.

[0047] For example, when an extensional load is applied to one rod cylinder 4, the pressure Pr in the rod-side chamber 4r becomes higher than the pressure Ph in the head-side chamber 4h by a threshold Pt or more. When a shortening load is applied to one rod cylinder 4, the pressure Ph in the head-side chamber 4h becomes higher than the pressure Pr in the rod-side chamber 4r by a threshold Pt or more.

[0048] When the pressure Pr in the rod-side chamber 4r becomes higher than the pressure Pr in the head-side chamber 4h by a threshold Pt or more, the low-pressure selector valve 6 is switched to the head-side discharge position. As a result, the excess amount corresponding to the second predetermined amount Δq2 is discharged from the head-side line 21 to the accumulator 7A through the first discharge line 61, the low-pressure selector valve 6, the third discharge line 63, and a portion of the second supply and discharge line 32.

[0049] Conversely, if the pressure Ph in the head chamber 4h becomes higher than the pressure Pr in the rod chamber 4r by a threshold Pt or more, the low-pressure selector valve 6 is switched to the rod-side discharge position. As a result, the excess amount corresponding to the second predetermined amount Δq2 is discharged from the rod-side line 22 to the accumulator 7A through the second discharge line 62, the low-pressure selector valve 6, the third discharge line 63, and a portion of the second supply and discharge line 32.

[0050] As described above, in the hydraulic system 1A of this embodiment, a cooler 8 is provided in the second supply and discharge line 32, so the working fluid is cooled when it is returned from the second bidirectional pump 3 to the accumulator 7A. Therefore, the working fluid can be cooled in a configuration using the first bidirectional pump 2 and the second bidirectional pump 3 for a single-rod cylinder 4.

[0051] Furthermore, in this embodiment, the operation of the low-pressure selector valve 6 makes it possible to easily prevent pressure conflation from occurring on the lower-pressure side of the rod side and the head side. The rod side consists of the rod side chamber 4r and the rod side line 22, and the head side consists of the head side chamber 4h and the head side line 21.

[0052] <Variation> As shown in the modified hydraulic system 1B in Figure 2, the reservoir 7 may be a tank 7B. That is, the second bidirectional pump 3 may be connected to the tank 7B by a second supply / discharge line 32. In this case, the parallel line 33 and the third discharge line 63 are connected to the tank 7B, and 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 also connected to the tank 7B. With this configuration, the working fluid is cooled when it is returned from the second bidirectional pump 3 to the tank 7B. This modified example, in which the reservoir 7 may be a tank 7B, is also applicable to the second and third embodiments described later.

[0053] However, if the reservoir 7 is an accumulator 7A as in the above embodiment, cavitation due to a drop in pressure on the suction side of the second bidirectional pump 3 can be prevented when the second bidirectional pump 3 starts rotating in the direction of discharging the 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 the working fluid to the suction side at the start of rotation of the first bidirectional pump 2, pressurized working fluid from the accumulator 7A is supplied to the suction side via the check valve 55 or 56, thus preventing cavitation on the suction side of the first bidirectional pump 2.

[0054] <Second Embodiment> Figure 3 shows the hydraulic system 1C according to the second embodiment. In this embodiment and the third embodiment described later, the same reference numerals are used for components that are the same as in the first embodiment, and redundant explanations are omitted.

[0055] The difference between the hydraulic system 1C and the hydraulic system 1A of the first embodiment is that the cooler 8 is located in the third discharge line 63, between the relief valve 64 and the second supply / discharge line 32, rather than in the second supply / discharge line 32. For this reason, the parallel line 33 shown in Figure 1 is not used in the hydraulic system 1C.

[0056] In this embodiment, a cooler 8 is provided in the third discharge line 63, so the working fluid is cooled when it is returned to the accumulator 7A through the third discharge line 63. Therefore, the working fluid can be cooled in a configuration using the first bidirectional pump 2 and the second bidirectional pump 3 for a single-rod cylinder 4. Also, similar to the first embodiment, the operation of the low-pressure selector valve 6 makes it easy to prevent pressure lock-in on the lower pressure side of the rod side and the head side.

[0057] <Third Embodiment> Figure 4 shows the hydraulic system 1D according to the third embodiment. The difference between the hydraulic system 1D and the hydraulic system 1C of the third embodiment is that bypass lines 91 are connected to the head-side line 21 and the rod-side line 22 so as to bypass the single-rod cylinder 4. The first lock valve 23 is located between the connection point of the bypass line 91 in the head-side line 21 and the single-rod cylinder 4, and the second lock valve 24 is located between the connection point of the bypass line 91 in the rod-side line 22 and the single-rod cylinder 4.

[0058] A bypass valve 92, which is an on / off valve, is provided in the bypass line 91. In this embodiment, the bypass valve 92 functions as a throttle when it is open. However, the bypass valve 92 does not necessarily have to function as a throttle when it is open; a throttle may be provided in the bypass line 91 between the head-side line 21 and the bypass valve 92, or between the bypass valve 92 and the rod-side line 22.

[0059] The bypass valve 92 is controlled by the control device 10. When the single-rod cylinder 4 is stopped, the first lock valve 23 and the second lock valve 24 are closed, as described in the first embodiment. When the single-rod cylinder 4 is stopped, the control device 10 opens the bypass valve 92 and rotates the second bidirectional pump 3 in the direction of discharging the working fluid through the first supply and discharge line 31. As a result, as shown by the arrows in Figure 4, the working fluid discharged from the second bidirectional pump 3 circulates in the order of the first supply and discharge line 31, part of the head-side line 21, the bypass line 91, part of the rod-side line 22, the second discharge line 62, the third discharge line 63, and part of the second supply and discharge line 32, passing through the cooler 8 along the way. Therefore, the working fluid can be cooled by utilizing the time when the single-rod cylinder 4 is stopped. Moreover, the working fluid 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 can also be cooled.

[0060] Furthermore, in this embodiment, since the bypass valve 92 functions as a throttle when it is open, the pressure difference created by the working fluid passing through the bypass valve 92 can operate the low-pressure selector valve 6, which is a pilot-operated three-position valve.

[0061] In addition, the bypass line 91 and bypass valve 92 are used in the first embodiment, and in the first embodiment as well, the bypass valve 92 may be opened when the single-rod cylinder 4 stops, and the second bidirectional pump 3 may be rotated in a direction that discharges the working fluid through the first supply / discharge line 31. Furthermore, the bypass line 91 and bypass valve 92 can also be used in the modified version of the first embodiment shown in Figure 2.

[0062] <Other Embodiments> This disclosure is not limited to the embodiments described above, and various modifications are possible without departing from the gist of this disclosure.

[0063] For example, instead of the pilot-operated low-pressure selector valve 6, a solenoid three-position low-pressure selector valve 6A, as shown in Figure 5, may be used. Alternatively, a low-pressure selector valve 6B, which includes a first solenoid valve 6a and a second solenoid valve 6b, as shown in Figure 6, may be used. The first solenoid valve 6a is connected to the first discharge line 61 and the third discharge line 63, and the second solenoid valve 6b is connected to the second discharge line 62 and the third discharge line 63.

[0064] <Summary> In a first aspect, the present disclosure provides a hydraulic system for a single-rod cylinder including a head chamber and a rod chamber, comprising: a first bidirectional pump connected to the head chamber by a head line and to the rod chamber by a rod line; a second bidirectional pump connected to the head line by a first supply / discharge line and to a reservoir by a second supply / discharge line; an electric motor for driving the first bidirectional pump and the second bidirectional pump in the same direction; and a cooler provided on the second supply / discharge line.

[0065] With the above configuration, a cooler is provided in the second supply and discharge line, so the working fluid is cooled when it is returned from the second bidirectional pump to the reservoir. Therefore, the working fluid can be cooled in a configuration using a first bidirectional pump and a second bidirectional pump for a single-rod cylinder.

[0066] In a second embodiment, the hydraulic system described above may further include a low-pressure selector valve connected to the head-side line by a first discharge line, the rod-side line by a second discharge line, and the second supply / discharge line by a third discharge line, wherein the second discharge line is connected to the third discharge line when the pressure in the rod-side chamber is lower than the pressure in the head-side chamber, and the first discharge line is connected to the third discharge line when the pressure in the head-side chamber is lower than the pressure in the rod-side chamber. With this configuration, the operation of the low-pressure selector valve makes it easy to prevent pressure confinement from occurring on the side with the lower pressure between the rod side and the head side.

[0067] In a third aspect, the present disclosure provides a hydraulic system for a single-rod cylinder including a head chamber and a rod chamber, comprising: a first bidirectional pump connected to the head chamber by a head line and to the rod chamber by a rod line; a second bidirectional pump connected to the head line by a first supply / discharge line and to a reservoir by a second supply / discharge line; an electric motor for driving the first bidirectional pump and the second bidirectional pump in the same direction; a low-pressure selector valve connected to the head line by a first discharge line, connected to the rod line by a second discharge line, and connected to the second supply / discharge line by a third discharge line, which connects the second discharge line to the third discharge line when the pressure in the rod chamber is lower than the pressure in the head chamber, and connects the first discharge line to the third discharge line when the pressure in the head chamber is lower than the pressure in the rod chamber; and a cooler provided on the third discharge line.

[0068] With the above configuration, a cooler is provided in the third discharge line, so the working fluid is cooled when it is returned to the reservoir through the third discharge line. Therefore, the working fluid can be cooled in a configuration using a first bidirectional pump and a second bidirectional pump for a single-rod cylinder. Moreover, the operation of the low-pressure selector valve makes it easy to prevent pressure lock-up on the lower pressure side of the rod side or the head side.

[0069] In a fourth embodiment, in any of the first to third embodiments, the reservoir may be an accumulator. With this configuration, cavitation due to a drop in pressure on the suction side of the second bidirectional pump can be prevented when the second bidirectional pump begins to rotate in the direction of discharging the working fluid through the first supply and discharge line.

[0070] In a fifth embodiment, in any of the first to fourth embodiments, the hydraulic system may further include a bypass valve, which is an on-off valve, provided in a bypass line connected to the head-side line and the rod-side line so as to bypass the single-rod cylinder; a first lock valve, which is an on-off valve, provided in the head-side line between the connection point of the bypass line and the single-rod cylinder; and a second lock valve, which is an on-off valve, provided in the rod-side line between the connection point of the bypass line and the single-rod cylinder. With this configuration, if the second bidirectional pump is rotated in the direction of discharging the working fluid through the first supply and discharge line with the first lock valve and the second lock valve closed and the bypass valve open, the working fluid discharged from the second bidirectional pump circulates so as to flow through the first supply and discharge line, part of the head-side line, the bypass line, part of the rod-side line, the second discharge line, the third discharge line, and part of the second supply and discharge line in this order, passing through the cooler along the way. Therefore, the working fluid can be cooled by utilizing the time when the single-rod cylinder is stopped.

[0071] In a sixth aspect, as in the fifth aspect, the bypass valve may function as a throttle when open. With this configuration, if the low-pressure selector valve is a pilot-operated three-position valve, the low-pressure selector valve can be operated by the pressure difference created by the working fluid passing through the bypass valve.

[0072] In a seventh aspect, in any of the second to sixth aspects, for example, the low-pressure selector valve may be an electromagnetic three-position valve.

[0073] In an eighth aspect, in any of the second to sixth aspects, for example, the low-pressure selector valve may include a first solenoid valve and a second solenoid valve, which are electromagnetic two-position valves, with the first solenoid valve being connected to the first discharge line and the third discharge line, and the second solenoid valve being connected to the second discharge line and the third discharge line. [Explanation of Symbols]

[0074] 1A to 1D Hydraulic Systems 2. First bidirectional pump 21 Head-side line 22 Rod-side line 23. First lock valve 24. Second locking valve 3. Second bidirectional pump 31. First supply and discharge line 32. Second supply and discharge line 4 Single-rod cylinder 4h Head side chamber 4r rod side chamber 6, 6A, 6B Low-pressure selector valve 61 First Emission Line 62 Second Emission Line 63 Third Emission Line 7 Storage container 7A Accumulator 7B Tank 8 Cooler 9 Electric motor 91 Bypass Line 92 Bypass valve

Claims

1. A hydraulic system for a single-rod cylinder, including a head side chamber and a rod side chamber, A first bidirectional pump is connected to the head side chamber by a head side line and to the rod side chamber by a rod side line, A second bidirectional pump is connected to the head-side line by a first supply / discharge line and to the storage container 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 cooler installed in the second supply and exhaust line, A hydraulic system comprising: a low-pressure selector valve connected to the head-side line by a first discharge line, connected to the rod-side line by a second discharge line, connected to the second supply / discharge line by a third discharge line, which connects the second discharge line to the third discharge line when the pressure in the rod-side chamber is lower than the pressure in the head-side chamber, and connects the first discharge line to the third discharge line when the pressure in the head-side chamber is lower than the pressure in the rod-side chamber.

2. A hydraulic system for a single-rod cylinder, including a head side chamber and a rod side chamber, A first bidirectional pump is connected to the head side chamber by a head side line and to the rod side chamber by a rod side line, A second bidirectional pump is connected to the head-side line by a first supply / discharge line and to the storage container 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 selector valve is provided, which is connected to the head-side line by a first discharge line, to the rod-side line by a second discharge line, and to the second supply / discharge line by a third discharge line, and when the pressure in the rod-side chamber is lower than the pressure in the head-side chamber, the second discharge line is connected to the third discharge line, and when the pressure in the head-side chamber is lower than the pressure in the rod-side chamber, the first discharge line is connected to the third discharge line. A cooler provided in the third discharge line, A hydraulic system equipped with...

3. The hydraulic system according to claim 1 or 2, wherein the storage device is an accumulator.

4. A bypass line connected to the head-side line and the rod-side line so as to bypass a single-rod cylinder, and a bypass valve which is an on / off valve provided in the bypass line, A first lock valve, which is an on / off valve, is provided on the head-side line between the connection point of the bypass line and the single-rod cylinder, The hydraulic system according to claim 1 or 2, further comprising a second lock valve, which is an on / off valve, provided on the rod-side line between the connection position of the bypass line and the single-rod cylinder.

5. The hydraulic system according to claim 4, wherein the bypass valve functions as a throttle when opened.

6. The hydraulic system according to claim 1 or 2, wherein the low-pressure selector valve is an electromagnetic three-position valve.

7. The hydraulic system according to claim 1 or 2, wherein the low-pressure selector valve includes a first solenoid valve and a second solenoid valve, which are electromagnetic two-position valves, the first solenoid valve is connected to the first discharge line and the third discharge line, and the second solenoid valve is connected to the second discharge line and the third discharge line.

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