Hydraulic system

Abstract

A hydraulic system (1A) according to one embodiment is provided with: a first two-way pump (2) connected to a single-rod cylinder (4) via a head-side line (21) and a rod-side line (22); a second two-way pump (3) connected to the head-side line (21) via a first supply / discharge line (31); and the energy accumulator (7) is connected with the second two-way pump (3) through a second feeding and discharging pipeline (71). The hydraulic system (1A) is further provided with a low-pressure selection valve (6) 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 by 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

Technical Field

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

[0002] Conventionally, a hydraulic system for a single-rod cylinder including a two-way pump connected to the single-rod cylinder in a form of forming a closed loop has been known. For example, a hydraulic system 100 as shown in Figure 7 is disclosed in Patent Document 1.

[0003] The hydraulic system 100 includes a first two-way pump 110 and a second two-way pump 120. The first two-way pump 110 is connected to a head-side chamber 210 of the single-rod cylinder 200 through a head-side pipe 111 and is connected to a rod-side chamber 220 of the single-rod cylinder 200 through a rod-side pipe 112. The second two-way pump 120 is for eliminating a flow rate 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 rate and an outflow rate, and is connected to the head-side pipe 111 through a supply / discharge pipe 121.

[0004] The first two-way pump 110 and the second two-way pump 120 are driven in the same direction by an electric motor 130. More specifically, when the single-rod cylinder 200 is extended, that is, when the rod advances, the electric motor 130 drives the first two-way pump 110 and the second two-way pump 120 in a first direction, and when the single-rod cylinder 200 is contracted, that is, when the rod retracts, the electric motor 130 drives the first two-way pump 110 and the second two-way pump 120 in a second direction opposite to the first direction. When the first two-way pump 110 and the second two-way pump 120 are driven in the first direction, they discharge a working fluid into the head-side chamber 210, and when the first two-way pump 110 and the second two-way pump 120 are driven in the second direction, they suck the working fluid from the head-side chamber 210. Further, in the hydraulic system 100, the second two-way pump 120 is a variable-capacity type pump, and the capacity of the second two-way pump 120 is changed by a regulator 140.

[0005] In the hydraulic system 100, if the capacity of the second bidirectional pump 120 when there is no excess or deficiency in the inflow rate into the single-rod cylinder 200 or the outflow rate from the single-rod cylinder 200 is taken as the reference capacity, when the single-rod cylinder 200 extends and the capacity of the second bidirectional pump 120 is more than the reference capacity, pressure residue occurs in the side with the lower pressure among the rod side and the head side. The rod side includes the rod side chamber 220 and the rod side pipeline 112, and the head side includes the head side chamber 210 and the head side pipeline 111. Conversely, when the single-rod cylinder 200 extends and the capacity of the second bidirectional pump 120 is less than the reference capacity, cavitation occurs in the side with the lower pressure among the rod side and the head side. Also, when the single-rod cylinder 200 contracts and the capacity of the second bidirectional pump 120 is more than the reference capacity, cavitation occurs in the side with the lower pressure among the rod side and the head side, and when the capacity of the second bidirectional pump 120 is less than the reference capacity, pressure residue occurs in the side with the lower pressure among the rod side and the head side. The regulator 140 is controlled based on the pressure in the head side chamber 210 or the rod side chamber 220 of the single-rod cylinder 200 to suppress these pressure residues or cavitation.

[0006] Prior art documents: Patent documents: Patent document 1: Japanese Patent Application Laid-Open No. 2013-245740; Patent document 2: Japanese Patent Application Laid-Open No. 2002-54602. Summary of the invention

[0007] Problems to be solved by the invention: As described above, in the hydraulic system 100 of Patent Document 1, the residual pressure generated in the side with the lower pressure among the rod side and the head side is controllably suppressed. In this regard, it is desired to simply prevent the generation of residual pressure in the side with the lower pressure among the rod side and the head side.

[0008] In addition, in Patent Document 2 Figure 2 it is disclosed as the prior art a hydraulic circuit that uses only one bidirectional pump for a single-rod cylinder and employs a low-pressure selection valve (referred to as a "flushing valve" in Patent Document 2) capable of discharging the working fluid from the side with the lower pressure between the head side pipeline and the rod side pipeline to the tank. However, this hydraulic circuit does not add a second bidirectional pump to the first bidirectional pump like the hydraulic system 100 of Patent Document 1.

[0009] Therefore, an object of the present disclosure is to provide a hydraulic system that can simply prevent the generation of residual pressure in the side with the lower pressure among the rod side and the head side in a structure where a second bidirectional pump is added to the first bidirectional pump.

[0010] Means for solving the problems: The present disclosure provides a hydraulic system, which is a hydraulic system for a single-rod cylinder including a head-side chamber and a rod-side chamber, and includes: a first bidirectional pump connected to the head-side chamber through a head-side pipeline and to the rod-side chamber through a rod-side pipeline; a second bidirectional pump connected to the head-side pipeline through a first supply / discharge pipeline; an accumulator connected to the second bidirectional pump through a second supply / discharge pipeline; an electric motor for driving the first bidirectional pump and the second bidirectional pump in the same direction; a low-pressure selection valve connected to the head-side pipeline through a first discharge pipeline, to the rod-side pipeline through a second discharge pipeline, and to the second supply / discharge pipeline through a third discharge pipeline, and configured to connect the second discharge pipeline and the third discharge pipeline when the pressure in the rod-side chamber is lower than the pressure in the head-side chamber, and connect the first discharge pipeline and the third discharge pipeline when the pressure in the head-side chamber is lower than the pressure in the rod-side chamber; and a pair of check valves disposed on opposite sides of a bridge pipeline connecting the head-side pipeline and the rod-side pipeline, and the second supply / discharge pipeline is connected to a portion between the pair of check valves in the bridge pipeline through a relay pipeline.

[0011] Advantages of the Invention: According to the present disclosure, there is provided a hydraulic system that can simply prevent pressure residue from occurring in the lower-pressure side of the rod side and the head side in a structure where a second bidirectional pump is added to a first bidirectional pump. Description of the Drawings

[0012] Figure 1 is a schematic structural diagram of the hydraulic system according to the first embodiment; Figure 2 is a schematic structural diagram of the hydraulic system according to the second embodiment; Figure 3 is a schematic structural diagram of the hydraulic system according to the third embodiment; Figure 4 is a schematic structural diagram of the hydraulic system according to the fourth embodiment; Figure 5 is a diagram showing the low-pressure selection valve of a modification; Figure 6 is a diagram showing the low-pressure selection valve of another modification; Figure 7 is a schematic structural diagram of a conventional hydraulic system. Detailed Description of the Embodiments

[0013] <First Embodiment> Figure 1 The hydraulic system 1A of the first embodiment is shown. 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 working fluid used in the hydraulic system 1A is typically oil.

[0014] Specifically, the hydraulic system 1A includes: a first two-way pump 2 connected to a single-rod cylinder 4 in a closed-loop form; and a second two-way pump 3 for eliminating the flow difference between the head side chamber 4h and the rod side chamber 4r of the single-rod cylinder 4, that is, the difference between the inflow and outflow flows. Further, the hydraulic system 1A includes an accumulator 7 for storing the pressurized working fluid. The single-rod cylinder 4, the first two-way pump 2, the second two-way pump 3, and the accumulator 7 together with a plurality of pipelines described later constitute a closed loop.

[0015] More specifically, the first two-way pump 2 is connected to the head side chamber 4h of the single-rod cylinder 4 through the head side pipeline 21, and is connected to the rod side chamber 4r of the single-rod cylinder 4 through the rod side pipeline 22. The second two-way pump 3 is connected to the head side pipeline 21 through the first supply / discharge pipeline 31, and is connected to the accumulator 7 through the second supply / discharge pipeline 71.

[0016] The set pressure of the accumulator 7 is, for example, in the range of 0.1 - 2 MPa. Here, the "set pressure of the accumulator 7" refers to the pressure that enables the working fluid to flow into the accumulator 7.

[0017] Lock valves 23 and 24 as on-off valves are respectively provided on the head side pipeline 21 and the rod side pipeline 22. The lock valves 23 and 24 are controlled by the control device 10. In addition, Figure 1 In the figure, the drawing of a part of the signal lines is omitted for simplicity. When the control device 10 operates the single-rod cylinder 4, that is, when it extends or retracts, the lock valves 23 and 24 are opened, and at other times, the lock valves 23 and 24 are closed.

[0018] The head side pipeline 21 and the rod side pipeline 22 are connected to each other through a first bridge pipeline 51 and a second bridge pipeline 54. A pair of overflow valves 52 and 53 are provided on the first bridge pipeline 51 in opposite directions to each other, and a pair of check valves 55 and 56 are provided on the second bridge pipeline 54 in opposite directions to each other.

[0019] In the legend, the first bridge pipeline 51 and the second bridge pipeline 54 are connected to the head side pipeline 21 and the rod side pipeline 22 between the lock valves 23 and 24 and the first two-way pump 2, but the first bridge pipeline 51 and the second bridge pipeline 54 can also be connected to the head side pipeline 21 and the rod side pipeline 22 between the lock valves 23 and 24 and the single-rod cylinder 4. Further, it can also be that a part of the first bridge pipeline 51 and the second bridge pipeline 54, for example, their ends and their central parts, merge with each other to form a common flow path.

[0020] The overflow valve 52 opens when the pressure in the head side pipeline 21 is too high, and the overflow valve 53 opens when the pressure in the rod side pipeline 22 is too high. The overflow pressures of the overflow valves 52 and 53 are set relatively high, for example, in the range of 25 - 35 MPa.

[0021] The check valve 55 allows the flow from the center of the second bridge pipeline 54 towards the head-side pipeline 21 but prohibits the reverse flow. The check valve 56 allows the flow from the center of the second bridge pipeline 54 towards the rod-side pipeline 22 but prohibits the reverse flow.

[0022] The part between the relief valves 52 and 53 in the first bridge pipeline 51 and the part between the check valves 55 and 56 in the second bridge pipeline 54 are connected to the second supply and discharge pipeline 71 through the relay pipeline 72.

[0023] The first double-direction pump 2 and the second double-direction pump 3 are, for example, axial piston pumps. The axial piston pump is, for example, a swash plate pump or a swash shaft pump. In the present embodiment, the first double-direction pump 2 is a fixed-capacity pump, and the second double-direction pump 3 is a variable-capacity pump. However, the first double-direction pump 2 may also be a variable-capacity pump. Or, both the first double-direction pump 2 and the second double-direction pump 3 may be fixed-capacity pumps.

[0024] The capacity of the second double-direction pump 3 is changed by the regulator 35. The regulator 35 is controlled by the control device 10. For example, when the second double-direction pump 3 is a swash plate pump, the regulator 35 may be a regulator that electrically changes the hydraulic pressure acting on the servo piston connected to the swash plate of the second double-direction pump 3, or may be an electric actuator connected to the swash plate of the second double-direction pump 3.

[0025] The first double-direction pump 2 and the second double-direction pump 3 are driven in the same direction by the electric motor 9. The first double-direction pump 2 and the second double-direction pump 3 may be arranged in such a way that their central axes are coaxially arranged, or may be arranged in such a way that their central axes are parallelly arranged. The former is a series type, and the latter is a parallel type.

[0026] The electric motor 9 is controlled by the control device 10. When the single rod cylinder 4 is extended, the electric motor 9 drives the first double-direction pump 2 and the second double-direction pump 3 in the first direction, and when the single rod cylinder 4 is shortened, the electric motor 9 drives the first double-direction pump 2 and the second double-direction pump 3 in the second direction opposite to the first direction. When the first double-direction pump 2 and the second double-direction pump 3 are driven in the first direction, they discharge the working fluid into the head-side chamber 4h, and when the first double-direction pump 2 and the second double-direction pump 3 are driven in the second direction, they suck the working fluid from the head-side chamber 4h.

[0027] In addition, in the present embodiment, a low-pressure selection valve 6 that is connected to the head-side pipeline 21 through the first discharge pipeline 61 and is connected to the rod-side pipeline 22 through the second discharge pipeline 62 is adopted. The low-pressure selection valve 6 is connected to the second supply and discharge pipeline 71 through the third discharge pipeline 63.

[0028] In this embodiment, an overflow valve 64 is provided on the third discharge pipeline 63. The overflow valve 64 serves to maintain the low pressure within the closed loop formed by the single-rod cylinder 4, the head-side pipeline 21, the rod-side pipeline 22, and the first two-way pump 2 at a certain relatively high level. The overflow pressure of the overflow valve 64 is set relatively low, for example, within the range of 0.1 - 2 MPa. The low pressure within the closed loop is the sum of the set pressure of the accumulator 7 and the set pressure of the overflow valve 64, for example, 1 - 2 MPa. Additionally, when the set pressure of the accumulator 7 is relatively high, the overflow valve 64 can be omitted.

[0029] The low-pressure selection valve 6 switches between a neutral position, a head-side discharge position, and a rod-side discharge position. In Figure 1 the figure, the central 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 pipeline 61 and the second discharge pipeline 62. In the head-side discharge position, the low-pressure selection valve 6 blocks the second discharge pipeline 62 and simultaneously connects the first discharge pipeline 61 to the third discharge pipeline 63. In the rod-side discharge position, the low-pressure selection valve 6 blocks the first discharge pipeline 61 and simultaneously connects the second discharge pipeline 62 to the third discharge pipeline 63.

[0030] In this embodiment, the low-pressure selection valve 6 is a pilot-operated three-position valve. Therefore, the pressure Ph in the head-side chamber 4h is introduced into the low-pressure selection valve 6 through the first pilot pipeline 65, and the pressure Pr in the rod-side chamber 4r is introduced into the low-pressure selection valve 6 through the second pilot pipeline 66. The first pilot pipeline 65 is used to switch the low-pressure selection valve 6 from the neutral position to the rod-side discharge position, and the second pilot pipeline 66 is used to switch the low-pressure selection valve 6 from the neutral position to the head-side discharge position. In the illustrated example, the first pilot pipeline 65 and the second pilot pipeline 66 branch from the first discharge pipeline 61 and the second discharge pipeline 62 respectively, but the first pilot pipeline 65 can also branch from the head-side pipeline 21, and the second pilot pipeline 66 can also branch from the rod-side pipeline 22.

[0031] The low-pressure selection valve 6 switches 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 switches 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, that is, 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 switches 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. Additionally, the threshold value Pt can also be different when the cylinder extends and when the cylinder contracts.

[0032] 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 content described below, and the control device 10 may also perform other controls.

[0033] Regarding the control device 10, the functions of the elements disclosed in this specification can be executed using a general-purpose processor, a dedicated processor, an integrated circuit, an ASIC (Application Specific Integrated Circuits), existing circuits, and / or a combination of them, or a processing circuit that is configured or programmed to execute the disclosed functions. Since a processor includes transistors and other circuits, it can be regarded as a processing circuit or a circuit. In this disclosure, a circuit, a unit, or a means is hardware that executes the listed functions, or hardware that is programmed to execute the exemplified functions. The hardware can be the hardware disclosed in this specification, or it can also be other known hardware that is programmed or configured to execute the listed functions. When the hardware is a processor that is considered a type of circuit, the circuit, the means, or the unit is a combination of hardware and software, and the software is used for the configuration of the hardware and / or the processor.

[0034] A first operation signal as an elongation instruction for the single-rod cylinder 4 and a second operation signal as a shortening instruction for the single-rod cylinder 4 are input to the control device 10. Also, 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 pressure difference 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 are input to the control device 10.

[0035] 1. Cylinder elongation If a first operation signal is input to the control device 10, the control device 10 causes the electric motor 9 to rotate in the first direction. As a result, the first bi-directional pump 2 and the second bi-directional pump 3 are driven in the first direction. The first bi-directional pump 2 sucks the working fluid through the rod-side pipeline 22, and the second bi-directional pump 3 sucks the working fluid through the second supply / discharge pipeline 71. Also, the first bi-directional pump 2 discharges the working fluid through the head-side pipeline 21, and the second bi-directional pump 3 discharges the working fluid through the first supply / discharge pipeline 31.

[0036] 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 in such a way that the capacity q2 of the second bi-directional pump 3 becomes the reference capacity qr. The reference capacity qr is obtained by multiplying the capacity q1 of the first bi-directional pump 2 by the ratio of the cross-sectional area Ac of the rod portion of the single rod cylinder 4 to the pressure receiving area Ar of the rod side chamber 4r. qr = Ac / Ar × q1. That is, when q2 = qr, theoretically, there is no excess or shortage in the inflow or outflow of the working fluid to or from the single rod cylinder 4. Therefore, the supply of the working fluid from the accumulator 7 to the head side pipeline 21 or the rod side pipeline 22 through a part of the second bridge pipeline 54, the relay pipeline 72 and a part of the second supply and discharge pipeline 71, and the discharge of the working fluid from the head side pipeline 21 or the rod side pipeline 22 through the first discharge pipeline 61 or the second discharge pipeline 62 are not carried out.

[0037] On the other hand, when the pressure difference ΔP is equal to or higher than the threshold value Pt, the control device 10 controls the regulator 35 in such a way that the capacity q2 of the second bi-directional pump 3 is only more than the reference capacity qr by the first specified amount Δq1. q2 = qr + Δq1. For example, Δq1 is in the range of 1 - 10% of qr.

[0038] For example, when a load in the shortening direction is applied to the single rod cylinder 4, the pressure Ph in the head side chamber 4h is higher than the pressure Pr in the rod side chamber 4r by more than the threshold value Pt. When a load in the extending direction is applied to the single rod cylinder 4, the pressure Pr in the rod side chamber 4r is higher than the pressure Pr in the head side chamber 4h by more than the threshold value Pt.

[0039] When the pressure Ph in the head side chamber 4h is higher than the pressure Pr in the rod side chamber 4r by more than the threshold value Pt, the low pressure selection valve 6 switches to the rod side discharge position. As a result, the remaining part corresponding to the first specified amount Δq1 is discharged from the rod side pipeline 22 through the second discharge pipeline 62, the low pressure selection valve 6, the third discharge pipeline 63 and a part of the second supply and discharge pipeline 71 to the accumulator 7.

[0040] Conversely, when the pressure Pr in the rod side chamber 4r is higher than the pressure Ph in the head side chamber 4h by more than the threshold value Pt, the low pressure selection valve 6 switches to the head side discharge position. As a result, the remaining part corresponding to the first specified amount Δq1 is discharged from the head side pipeline 21 through the first discharge pipeline 61, the low pressure selection valve 6, the third discharge pipeline 63 and a part of the second supply and discharge pipeline 71 to the accumulator 7.

[0041] 2. Cylinder shortening If a second operation signal is input to the control device 10, the control device 10 causes the electric motor 9 to rotate in the second direction. As a result, the first bi-directional pump 2 and the second bi-directional pump 3 are driven in the second direction. The first bi-directional pump 2 sucks the working fluid through the head-side pipe 21, and the second bi-directional pump 3 sucks the working fluid through the first supply / discharge pipe 31. Also, the first bi-directional pump 2 discharges the working fluid through the rod-side pipe 22, and the second bi-directional pump 3 discharges the working fluid through the second supply / discharge pipe 71.

[0042] 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 in such a way that the capacity q2 of the second bi-directional pump 3 becomes the reference capacity qr. That is, when q2 = qr, theoretically there is no excess or shortage in the inflow or outflow of the working fluid to or from the single-rod cylinder 4. Therefore, the supply of the working fluid from the accumulator 7 to the head-side pipe 21 or the rod-side pipe 22 through a part of the second bridge pipe 54, the relay pipe 72, and a part of the second supply / discharge pipe 71, and the discharge of the working fluid from the head-side pipe 21 or the rod-side pipe 22 through the first discharge pipe 61 or the second discharge pipe 62 are not performed.

[0043] 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 in such a way that the capacity q2 of the second bi-directional pump 3 is less than the reference capacity qr by only the second specified amount Δq2. q2 = qr - Δq2. The second specified amount Δq2 may be the same as or different from the above-mentioned first specified amount Δq1. For example, Δq2 is in the range of 1 - 10% of qr.

[0044] For example, when a load in the extending direction is applied to the single-rod cylinder 4, the pressure Pr in the rod-side chamber 4r is higher than the pressure Ph in the head-side chamber 4h by more than the threshold value Pt. When a load in the shortening direction is applied to the single-rod cylinder 4, the pressure Ph in the head-side chamber 4h is higher than the pressure Pr in the rod-side chamber 4r by more than the threshold value Pt.

[0045] When the pressure Pr in the rod-side chamber 4r is higher than the pressure Pr in the head-side chamber 4h by more than the threshold value Pt, the low-pressure selection valve 6 switches to the head-side discharge position. As a result, the remaining part corresponding to the second specified amount Δq2 is discharged from the head-side pipe 21 to the accumulator 7 through the first discharge pipe 61, the low-pressure selection valve 6, the third discharge pipe 63, and a part of the second supply / discharge pipe 71.

[0046] Conversely, when the pressure Ph in the head-side chamber 4h is higher than the pressure Pr in the rod-side chamber 4r by more than the threshold value Pt, the low-pressure selection valve 6 switches to the rod-side discharge position. As a result, the remaining part corresponding to the second specified amount Δq2 is discharged from the rod-side pipe 22 to the accumulator 7 through the second discharge pipe 62, the low-pressure selection valve 6, the third discharge pipe 63, and a part of the second supply / discharge pipe 71.

[0047] As described above, in the hydraulic system 1A of the present embodiment, since the low-pressure selection valve 6 is provided, it is possible to simply prevent the residual pressure from occurring in the side with the lower pressure between the rod side and the head side in the structure where the second bi-directional pump 3 is added to the first bi-directional pump 2. The rod side includes the rod-side chamber 4r and the rod-side pipeline 22, and the head side includes the head-side chamber 4h and the head-side pipeline 21.

[0048] Moreover, since the second bi-directional pump 3 is connected to the accumulator 7 through the second supply / discharge pipeline 71, it is possible to prevent cavitation caused by the pressure reduction on the suction side of the second bi-directional pump 3 when the second bi-directional pump 3 starts to rotate in the direction of discharging the working fluid through the first supply / discharge pipeline 31. In addition, when the pressure on the suction side of the first bi-directional pump 2 is reduced due to the delay in the return of the working fluid to the suction side at the start of rotation of the first bi-directional pump 2, the pressurized working fluid is supplied from the accumulator 7 to the suction side via the check valve 55 or 56, so that cavitation on the suction side of the first bi-directional pump 2 can also be prevented.

[0049] Also, in the present embodiment, since the relief valve 64 is provided on the third discharge pipeline 63, it is possible to separately set the pressure when discharging the working fluid from the head-side pipeline 21 or the rod-side pipeline 22 through the first discharge pipeline 61 or the second discharge pipeline 62 and the set pressure of the accumulator 7.

[0050] <Second Embodiment> Figure 2 The hydraulic system 1B of the second embodiment is shown. In addition, in the present embodiment and the third and fourth embodiments described later, the same reference numerals are given to the same structural elements as those in the first embodiment, and repeated descriptions are omitted.

[0051] The difference between the hydraulic system 1B and the hydraulic system 1A of the first embodiment is that it further includes a tank 11 and a supply pump 8. The supply pump 8 is connected to the tank 11 through the suction pipeline 81 and is connected to the second supply / discharge pipeline 71 through the discharge pipeline 82. However, the discharge pipeline 82 does not necessarily have to be connected to the second supply / discharge pipeline 71, and it may be connected to the third discharge pipeline 63 between the relief valve 64 and the second supply / discharge pipeline 71, or may be connected to the relay pipeline 72.

[0052] A check valve 83 that allows the flow from the supply pump 8 to the second supply / discharge pipeline 71 but prohibits the reverse flow is provided on the discharge pipeline 82. Also, an overflow pipeline 84 branches from the discharge pipeline 82 between the supply pump 8 and the check valve 83, and the overflow pipeline 84 is connected to the tank 11.

[0053] A relief valve 85 is provided on the overflow pipeline 84. The overflow pressure of the relief valve 85 is, for example, in the range of 0.1 - 2 MPa.

[0054] If the replenishing pump 8 is provided as in the present embodiment, the working fluid can be replenished when the amount of working fluid in the closed circuit formed by the single-rod cylinder 4, the first two-way pump 2, the second two-way pump 3 and the accumulator 7 decreases. For example, when the first two-way pump 2 and the second two-way pump 3 are of external discharge type, the amount of working fluid in the closed circuit gradually decreases.

[0055] The feed pump 8 can be manually operated, but it can also be that the control device 10 controls the feed pump 8, for example, when the amount of working fluid in the accumulator 7 is lower than a specified value, or when the pressure at a specified position in the closed circuit is lower than a specified value, the control device 10 operates the feed pump 8.

[0056] In addition, the discharge conduit 82 does not necessarily have to be connected to the second supply and discharge conduit 71 at all times, and may be connected to the second supply and discharge conduit 71 only when the working fluid is replenished. In addition, similarly to the content described in the first embodiment, when the set pressure of the accumulator 7 is relatively high, the relief valve 64 may be omitted. The point that the relief valve 64 can be omitted is also the same in the third embodiment and the fourth embodiment described later.

[0057] <Third embodiment> Figure 3 , a hydraulic system 1C of the third embodiment is shown. The hydraulic system 1C is different from the hydraulic system 1B of the second embodiment in that the discharge line 82 is connected to the third discharge line 63 between the relief valve 64 and the second supply and discharge line 71, and the overflow line 84 is branched from the second supply and discharge line 71. In other words, the overflow line 84 is branched from the second supply and discharge line 71 on the side opposite to the discharge line 82 across a portion of the third discharge line 63 and a portion of the second supply and discharge line 71.

[0058] However, the overflow conduit 84 may be branched from the relay conduit 72 on the opposite side of the discharge conduit 82 via a portion of the third discharge conduit 63, a portion of the second supply and discharge conduit 71, and a portion of the relay conduit 72. Figure 3 On the contrary, the discharge line 82 is connected to the second supply and discharge line 71 or the relay line 72 , and the relief line 84 branches from the third discharge line 63 between the relief valve 64 and the second supply and discharge line 71 .

[0059] In this embodiment, the replenishment pump 8 is always running. That is, when the second bidirectional pump 3 is stopped, Figure 3 As shown by the solid arrow in the middle, the working fluid discharged from the supply pump 8 flows into the accumulator 7. After the accumulator 7 becomes full, the working fluid in the tank 11 circulates in the form of passing through the suction pipeline 81, the supply pump 8, the discharge pipeline 82, a part of the third discharge pipeline 63, a part of the second supply and discharge pipeline 71, and the overflow pipeline 84 in sequence.

[0060] On the other hand, if the second two-way pump 3 rotates in the direction of discharging the working fluid through the first supply and discharge pipeline 31, as shown by the dashed arrow in Figure 3 , the working fluid is supplied from the supply pump 8 and the accumulator 7 to the second two-way pump 3.

[0061] If the structure is like this embodiment, the working fluid can be circulated in such a form that the supply pump 8 makes the working fluid flow from the discharge pipeline 82 through a part of the closed loop composed of the single-rod cylinder 4, the first two-way pump 2, the second two-way pump 3 and the accumulator 7 to the overflow pipeline 84. Thus, the working fluid in the closed loop can be cooled.

[0062] <Fourth Embodiment> Figure 4 The hydraulic system 1D of the fourth embodiment is shown in. The difference between the hydraulic system 1D and the hydraulic system 1C of the third embodiment is that the accumulator 7 is arranged near the second two-way pump 3, a cooler 12 is interposed between the supply pump 8 and the accumulator 7, and the overflow pipeline 84 branches from the relay pipeline 72.

[0063] In this embodiment, the cooler 12 is arranged on the third discharge pipeline 63. Also, in this embodiment, the overflow valve 85 is located on the side opposite to the cooler 12 across the accumulator 7. That is, the working fluid discharged from the supply pump 8 and passing through the cooler 12 flows through the part adjacent to the accumulator 7 in the second supply and discharge pipeline 71 and then flows into the overflow pipeline 84 through a part of the relay pipeline 72.

[0064] In this embodiment, the cooling effect of the working fluid in the closed loop described in the third embodiment can be improved by the cooler 12. Moreover, since the accumulator 7 is between the cooler 12 and the overflow valve 85, the working fluid stored in the accumulator 7 can also be cooled when the working fluid circulates.

[0065] In addition, in this embodiment, since the cooler 12 is arranged on the third discharge pipeline 63, the working fluid is also cooled when it returns to the accumulator 7 through the third discharge pipeline 63. However, from the viewpoint of improving the cooling effect when the working fluid circulates, the cooler 12 can also be arranged on the discharge pipeline 82 or the like.

[0066] <Other Embodiments> The present disclosure is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present disclosure.

[0067] For example, a low-pressure selection valve 6A as an electromagnetic three-way valve as shown in Figure 5 can be adopted to replace the pilot-operated low-pressure selection valve 6. Or, a Figure 6A low-pressure selection valve 6B including a first electromagnetic valve 6a and a second electromagnetic valve 6b, which are electromagnetic two-way valves, as shown. A first discharge pipe 61 and a third discharge pipe 63 are connected to the first electromagnetic valve 6a, and a second discharge pipe 62 and a third discharge pipe 63 are connected to the second electromagnetic valve 6b.

[0068] <Summary> As 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, which includes: a first two-way pump connected to the head-side chamber through a head-side pipe and connected to the rod-side chamber through a rod-side pipe; a second two-way pump connected to the head-side pipe through a first supply / discharge pipe; an accumulator connected to the second two-way pump through a second supply / discharge pipe; an electric motor that drives the first two-way pump and the second two-way pump in the same direction; a low-pressure selection valve that is connected to the head-side pipe through a first discharge pipe, connected to the rod-side pipe through a second discharge pipe, connected to the second supply / discharge pipe through a third discharge pipe, and connects the second discharge pipe and the third discharge pipe when the pressure in the rod-side chamber is lower than the pressure in the head-side chamber, and connects the first discharge pipe and the third discharge pipe when the pressure in the head-side chamber is lower than the pressure in the rod-side chamber; and a pair of check valves disposed on the bridge pipe connecting the head-side pipe and the rod-side pipe and facing each other in opposite directions, and the second supply / discharge pipe is connected to a portion between the pair of check valves in the bridge pipe through a relay pipe.

[0069] According to the above structure, since the low-pressure selection valve is provided, it is possible to simply prevent the residual pressure from occurring in the lower-pressure side of the rod side and the head side in the structure where the second two-way pump is added to the first two-way pump. Moreover, since the second two-way pump is connected to the accumulator through the second supply / discharge pipe, it is possible to prevent cavitation caused by the pressure reduction on the suction side of the second two-way pump when the second two-way pump starts to rotate in the direction of discharging the working fluid through the first supply / discharge pipe. In addition, when the first two-way pump starts to rotate and the pressure on the suction side decreases due to the delay in the return of the working fluid to the suction side, the pressurized working fluid is supplied from the accumulator to the suction side through the check valve, so it is also possible to prevent cavitation on the suction side of the first two-way pump.

[0070] As a second aspect, in the first aspect, the above hydraulic system may further include: a supply pump connected to the tank through a suction pipe and connected to any one of the second supply / discharge pipe, the third discharge pipe, and the relay pipe through a discharge pipe. According to this structure, it is possible to supply the working fluid when the amount of the working fluid in the closed loop decreases.

[0071] As a third aspect, it can also be in the second aspect. For example, the above hydraulic system further includes an overflow valve provided in an overflow pipe that branches from the discharge pipe and is connected to the tank.

[0072] As a fourth aspect, it can also be in the second aspect. The above hydraulic system further includes: an overflow valve provided in an overflow pipe that branches from any one of the second supply / discharge pipe, the third discharge pipe, and the relay pipe and is connected to the tank. According to this structure, the working fluid can be circulated in a form that flows from the discharge pipe through a part of the closed loop to the overflow pipe by the supply pump. Thus, the working fluid in the closed loop can be cooled.

[0073] As a fifth aspect, it can also be in the fourth aspect. The above hydraulic system further includes a cooler interposed between the supply pump and the accumulator, and the overflow valve is located on the side opposite to the cooler with the accumulator in between. According to this structure, the cooling effect of the working fluid in the closed loop can be improved by the cooler. Moreover, since the accumulator is between the cooler and the overflow valve, the working fluid stored in the accumulator can also be cooled when the working fluid circulates.

[0074] As a sixth aspect, it can also be in any one of the first to fifth aspects. The above hydraulic system further includes an overflow valve provided in the third discharge pipe. According to this structure, the pressure when discharging the working fluid from the head-side pipe or the rod-side pipe through the first discharge pipe or the second discharge pipe can be set separately from the set pressure of the accumulator.

[0075] As a seventh aspect, it can also be in any one of the first to sixth aspects. For example, the low-pressure selection valve is an electromagnetic three-way valve.

[0076] As an eighth aspect, it can also be in any one of the first to seventh aspects. For example, the low-pressure selection valve includes a first electromagnetic valve and a second electromagnetic valve that are electromagnetic two-way valves. The first discharge pipe and the third discharge pipe are connected to the first electromagnetic valve, and the second discharge pipe and the third discharge pipe are connected to the second electromagnetic valve.

Claims

1. A hydraulic system, characterized in that it is a hydraulic system for a single-rod cylinder including a head-side chamber and a rod-side chamber, and comprises: a first bidirectional pump connected to the head-side chamber through a head-side pipeline and to the rod-side chamber through a rod-side pipeline; a second bidirectional pump connected to the head-side pipeline through a first supply / discharge pipeline; an accumulator connected to the second bidirectional pump through a second supply / discharge pipeline; an electric motor for driving the first bidirectional pump and the second bidirectional pump in the same direction; a low-pressure selection valve connected to the head-side pipeline through a first discharge pipeline, to the rod-side pipeline through a second discharge pipeline, and to the second supply / discharge pipeline through a third discharge pipeline, which makes the second discharge pipeline communicate with the third discharge pipeline when the pressure in the rod-side chamber is lower than the pressure in the head-side chamber, and makes the first discharge pipeline communicate with the third discharge pipeline when the pressure in the head-side chamber is lower than the pressure in the rod-side chamber; and a pair of check valves disposed on a bridge pipeline connecting the head-side pipeline and the rod-side pipeline and facing opposite directions, the second supply / discharge pipeline is connected to a portion between the pair of check valves in the bridge pipeline through a relay pipeline.

2. The hydraulic system according to claim 1, characterized in that it further comprises: a supply pump connected to a tank through a suction pipeline and connected to any one of the second supply / discharge pipeline, the third discharge pipeline, and the relay pipeline through a discharge pipeline.

3. The hydraulic system according to claim 2, characterized in that it further comprises: an overflow valve disposed on an overflow pipeline branched from the discharge pipeline and connected to the tank.

4. The hydraulic system according to claim 2, characterized in that it further comprises: an overflow valve disposed on an overflow pipeline branched from any one of the second supply / discharge pipeline, the third discharge pipeline, and the relay pipeline and connected to the tank.

5. The hydraulic system according to claim 4, characterized in that it further comprises a cooler interposed between the supply pump and the accumulator, the overflow valve is located on the side opposite to the cooler with the accumulator in between.

6. The hydraulic system according to any one of claims 1 to 5, characterized in that , It further comprises an overflow valve disposed on the third discharge pipeline.

7. The hydraulic system according to any one of claims 1 to 5, characterized in that the low-pressure selection valve is an electromagnetic three-position valve.

8. The hydraulic system according to any one of claims 1 to 5, characterized in that the low-pressure selection 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 pipeline and the third discharge pipeline, and the second solenoid valve is connected to the second discharge pipeline and the third discharge pipeline.

Images