Fluid pressure circuit

Abstract

Provided is a fluid pressure circuit with high energy recovery efficiency.　In a fluid pressure circuit 100, a relief valve 54 is connected to flow paths 23, 50, 51, 52 connecting a cylinder device 5 and a booster 40, and a piston 42-2 of the booster 40 moves with a fluid body flowing in from the flow path 52. A pressure accumulator 74 is connected to the flow path 51.

Description

Fluid Pressure Circuit

[0001] The present invention relates to a fluid pressure circuit, and more particularly to a fluid pressure circuit having a pressure booster device for boosting the pressure of a fluid.

[0002] Generally, hydraulic pressure circuits that control the rod stroke of a cylinder device in response to an operation command are used in work machines, construction machines, cargo handling vehicles, automobiles, etc. Energy conservation is required for hydraulic pressure circuits, and some hydraulic pressure circuits use the fluid flowing out of the cylinder device to drive a pressure booster device, thereby making effective use of energy (see Patent Document 1).

[0003] A known example of such a fluid pressure circuit is a hydraulic circuit 101 shown in Figure 8. In the hydraulic circuit 101, when the hydraulic remote control valve 106 is operated in the retraction direction E, pressure oil is supplied from the pump 102 to the rod chamber 105-1 of the cylinder device 105, causing the piston rod 105-3 to retract inside. As a result, oil flows out from the head chamber 105-2 of the cylinder device 105 to a return oil passage 123, which is part of the return line of the cylinder device 105.

[0004] An oil line 140 is connected to the return oil line 123 via a pressure-compensated electromagnetic proportional control type flow rate adjustment valve 139. An electromagnetic switching valve 141, a pressure booster 142, and a relief valve 149 are connected to the oil line 140.

[0005] The electromagnetic switching valve 141 can be switched between a return position 141-1 when de-energized and a pressurized position 141-2 when energized. The booster 142 has a case 142-1 whose interior space is divided by a piston 142-2 enclosed therein into a first oil chamber 142-3, a second oil chamber 142-4, and a third oil chamber 142-5. The first oil chamber 142-3 is connected to an accumulator 143.

[0006] When the electromagnetic switching valve 141 is switched to the pressurized position 141-2 and oil is supplied to the second oil chamber 142-4, the booster 142 sends oil from the first oil chamber 142-3 to the accumulator 143 and discharges oil from the third oil chamber 142-5 to the tank 111, causing the piston 142-2 to move from the start position to the end position.

[0007] Furthermore, when the electromagnetic switching valve 141 is switched to the return position 141-1 and oil is supplied to the third oil chamber 142-5, the piston 142-2 of the pressure booster 142 moves from the terminal position to the start position while oil is drawn into the first oil chamber 142-3 and oil is discharged from the second oil chamber 142-4 to the tank 111. In other words, by continuing to switch the electromagnetic switching valve 141, the piston 142-2 can be reciprocated.

[0008] Furthermore, the area of ​​the pressure-receiving surface of the piston 142-2 facing the second oil chamber 142-4 is larger than the area of ​​the pressure-receiving surface facing the first oil chamber 142-3, which enables the pressure booster 142 to boost the oil in the first oil chamber 142-3 to a pressure higher than that of the oil in the second oil chamber 142-4 and supply it to the accumulator 143.

[0009] JP 2017-15130 A (pages 7 and 8, Figure 2)

[0010] In the hydraulic circuit 101 shown in FIG. 8, high-pressure oil flows into the oil passage 140 from the return line of the cylinder device 105, and when the piston 142-2 in the pressure booster 142 moves, oil that exceeds the relief pressure is discharged from the relief valve 149 to the tank 111 to compensate for the high pressure in the return line of the cylinder device 105 and to protect the circuit.

[0011] In particular, when the electromagnetic directional control valve 141 is switched to the pressurized position 141-2, the piston 142-2 moves against the force generated by the pressure in the first oil chamber 142-3, so the amount of oil discharged from the relief valve 149 to the tank 111 is greater than when the electromagnetic directional control valve 141 is switched to the return position 141-1. As a result, although the hydraulic circuit 101 can continue to maintain smooth operation of the cylinder device 105, it cannot be said that the oil that has flowed from the cylinder device 105 into the oil passage 140 is fully utilized.

[0012] The present invention has been made in view of the above-mentioned problems, and has as its object to provide a fluid pressure circuit with high energy recovery efficiency.

[0013] To solve the above problems, the present invention provides a fluid pressure circuit in which a relief valve is connected to a flow path connecting a cylinder device and a pressure booster device, and a piston of the pressure booster device is moved by fluid flowing in from the flow path, and a pressure accumulator is connected to the flow path. This makes it possible to store in the accumulator at least a portion of the high-pressure fluid that flows into the flow path from the cylinder device when the cylinder device is operating, regardless of whether the piston in the pressure booster is moving. This reduces the amount of fluid discharged through the relief valve to compensate for high pressure generated in the return line of the cylinder device, thereby improving energy recovery efficiency.

[0014] A check valve may be provided in the flow path upstream of the pressure booster, the relief valve, and the pressure accumulator. This prevents the fluid stored in the pressure accumulator from flowing back toward the cylinder device. This prevents interference with the operation of the cylinder device and increases energy recovery efficiency.

[0015] A switching valve may be provided between the pressure accumulator and the relief valve, whereby a pressure of fluid equal to or greater than the relief pressure of the relief valve can be accumulated in the pressure accumulator.

[0016] The pressure accumulator may further include a pressure detection device capable of detecting the fluid pressure of the pressure accumulator, and a switching valve that opens and closes in response to the fluid pressure detected by the pressure detection device and is provided between the pressure accumulator and the pressure booster. This not only allows the pressure booster to be operated independently of the operation of the cylinder device, but also ensures free volume in the pressure accumulator.

[0017] The fluid pressure circuit may include an operating valve that operates the cylinder device with a fluid, and a diversion valve that diverts a portion of the fluid flowing out of the cylinder device may be provided between the operating valve and the cylinder device. This allows the cylinder device to operate smoothly while recovering energy using the surplus fluid.

[0018] A downstream diverter valve may be provided between the flow diverter valve and the pressure booster device to divert a portion of the fluid remaining after the portion of the outflow fluid is diverted by the flow diverter valve and guide it to the second relief valve. This makes it possible to protect the pressure booster device while enabling smooth operation of the cylinder device.

[0019] FIG. 1 is a schematic diagram showing a fluid pressure circuit in an embodiment of the present invention. FIG. 2 is a graph showing the flow rate control characteristics of a variable throttle in a flow dividing valve. FIG. 3 is a graph showing the flow rate control characteristics of a solenoid valve. FIG. 4 is a graph showing the electrical signal characteristics of a remote control valve. FIG. 5 is a graph showing the pressure boost characteristics of a pressure accumulator upstream of a pressure booster. (a) and (b) are diagrams showing a state in which fluid is flowing into the pressure booster from the cylinder device, (a) is a diagram showing a state in which the piston in the pressure booster is moved to an end position, and (b) is a diagram showing a state in which the piston in the pressure booster is moved to a start position. (a) and (b) are diagrams showing a state in which fluid is not flowing into the pressure booster from the cylinder device, and (a) is a diagram showing a state in which the fluid pressure in the pressure accumulator is at a pressure value P ＺＸ 1(b) is a diagram showing the state in which the fluid pressure in the pressure accumulator reaches a pressure value P ＺＸ 1 is a schematic diagram showing a conventional hydraulic circuit.

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fluid pressure circuit according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

[0021] A fluid pressure circuit according to an embodiment of the present invention will be described with reference to Figures 1 to 7. In the following description, the left and right sides of the pressure booster device will be taken as the left and right sides when viewed from the front of Figure 1.

[0022] The hydraulic circuit as a fluid pressure circuit according to the embodiment is a hydraulic circuit that controls the stroke of a cylinder device in response to an operation command in a work machine such as a press, a construction machine such as a power shovel, a cargo handling vehicle such as a forklift, or a brake device of an automobile.

[0023] As shown in FIG. 1, the hydraulic circuit 100 includes a drive mechanism 1, a variable displacement hydraulic pump 2, a fixed displacement hydraulic pump 3, an electromagnetic directional control valve 4 as an operating valve, a cylinder device 5, a hydraulic remote control valve 6, relief valves 7, 8, 54, 59, 77, pressure sensors 9, 10, 60, 61, 75, a tank 11, oil passages 12 to 18, 22 to 25, 50 to 53, 55, 57, 73, 76, check valves 26, 58, 71, a controller 28, electric signal lines 33 to 38, flow control valves 39, 70 as dividing valves, a pressure booster device 40, an electromagnetic switching valve 56, an electromagnetic proportional valve 72, and an accumulator 74.

[0024] The variable displacement hydraulic pump 2 and the fixed displacement hydraulic pump 3 are connected to a drive mechanism 1 such as an electric motor or an internal combustion engine, and are driven by power from the drive mechanism 1 to supply oil downstream. In the following description, the variable displacement hydraulic pump 2 and the fixed displacement hydraulic pump 3 will be simply referred to as "pumps 2, 3" etc.

[0025] Oil discharged from the pump 2 flows through oil passages 12 and 14 into the electromagnetic directional control valve 4. Hereinafter, the electromagnetic directional control valve 4 will be simply referred to as the "control valve 4."

[0026] Furthermore, a relief oil passage having a relief valve 7 is branched and connected to the oil passage 12. The relief valve 7 opens when the pressure in the oil passage 12 becomes abnormally high, and discharges the oil into the tank 11.

[0027] The switching valve 4 is a six-port, three-position open-center type switching valve that can be switched between a neutral position, an extension position 4E, and a retraction position 4C. The switching valve 4 is switched in response to the operation of a hydraulic remote control valve 6, as will be described later.

[0028] The switching valve 4 in the neutral position connects the oil passages 12 and 13. As a result, all of the oil discharged from the pump 2 flows into the tank 11 through the oil passage 13.

[0029] The switching valve 4 in the extension position 4E connects the oil passages 14 and 22 and also connects the oil passages 24 and 15. The oil passage 24 is connected to the rod chamber 5-1 in the cylinder device 5. The oil passage 15 is in communication with the tank 11.

[0030] The oil passage 22 is connected to a flow rate adjustment valve 39. The flow rate adjustment valve 39 is further connected to an oil passage 23 connected to the head chamber 5-2 in the cylinder device 5 and an oil passage 50 that can communicate with a pressure booster device 40.

[0031] When the switching valve 4 is in the extension position 4E, the flow rate adjustment valve 39 is in a state where no electrical signal is input from the controller 28, and the flow rate adjustment valve 39 cuts off the oil passages 22, 23 and the oil passages 23, 50. The flow rate adjustment valve 39 will be described in detail later.

[0032] An oil passage 25 is branched and connected to the oil passages 22 and 23 so as to bypass the flow rate adjustment valve 39. The oil passage 25 is provided with a check valve 26 that allows oil to pass only from the oil passage 22 to the oil passage 23.

[0033] A pressure sensor 61 is connected to the oil passage 23. The pressure sensor 61 outputs an electric signal corresponding to the pressure in the head chamber 5-2 of the cylinder device 5 to the controller 28.

[0034] The switching valve 4 in the retraction position 4C connects the oil lines 14 and 24 and the oil lines 22 and 15. The flow rate adjustment valve 39 receives an electrical signal from the controller 28 and connects the oil lines 23 and 22 and the oil lines 23 and 50. The oil lines 23 and 50 and the oil lines 51 and 52 described below are flow paths in this embodiment, and these flow paths can be said to be oil paths that supply oil from the cylinder device 5 to the pressure booster device 40. The oil lines 50 to 52 are branched and connected to the oil lines 23 and 22 via the flow rate adjustment valve 39. In this way, the oil line 23 also serves as part of the return line formed by the so-called oil lines 23, 22, and 15.

[0035] The flow rate control valve 39 is a pressure-compensated electromagnetic proportional control flow rate control valve, and is electrically connected to the controller 28 via an electric signal line 35 .

[0036] 6, the flow rate control valve 39 has a first flow path 39-1 connecting the oil paths 23 and 22, a second flow path 39-2 connecting the oil paths 23 and 50, a fixed throttle 39-3 provided in the first flow path 39-1, and a variable throttle 39-4 provided in the second flow path 39-2. The flow rate control valve 39 is capable of dividing the oil flowing in from the oil path 23 into the first flow path 39-1 and the second flow path 39-2.

[0037] 2, and is capable of variably adjusting the flow rate of oil flowing into the oil passage 50 in accordance with an electrical signal input from the controller 28. The strength of the electrical signal output from the controller 28 is determined by an arithmetic circuit pre-installed in the controller 28 based on the electrical signal input to the controller 28 from the pressure sensor 10. Hereinafter, the flow rate of oil passing through the second passage 39-2 will be simply referred to as the "priority flow rate to the pressure booster 40 side."

[0038] 6, the oil passage 50 is connected to a flow rate adjustment valve 70. Oil passages 51 and 76 are further connected downstream of the flow rate adjustment valve 70. The flow rate adjustment valve 70 is a downstream branch valve in this embodiment.

[0039] The oil passage 76 is a relief oil passage having a relief valve 77, and is branched and connected to the oil passages 50 and 51 via the flow rate adjustment valve 70. The relief valve 77 is a second relief valve in this embodiment that is different from a relief valve 54 described later.

[0040] The flow control valve 70 is a pressure-compensated electromagnetic proportional control type flow control valve, similar to the flow control valve 39, and is electrically connected to the controller 28 via an electric signal line 37. Note that explanations of the flow control valve 70 that overlap with those of the flow control valve 39 will be simplified or omitted.

[0041] The flow rate control valve 70 has a first flow path 70-1 connecting the oil paths 50, 51, a second flow path 70-2 connecting the oil paths 50, 76, a fixed throttle 70-3 provided in the first flow path 70-1, and a variable throttle 70-4 provided in the second flow path 70-2. The flow rate control valve 70 is capable of dividing the oil flowing in from the oil path 50 into the first flow path 70-1 and the second flow path 70-2. Hereinafter, the flow rate of oil passing through the second flow path 70-2 will be simply referred to as the "priority flow rate to the relief valve 77 side."

[0042] The oil passage 51 is connected to an electromagnetic proportional valve 72 serving as a switching valve. The oil passage 52 is connected downstream of the electromagnetic proportional valve 72.

[0043] The electromagnetic proportional valve 72 is an electromagnetic proportional control type flow control valve, and is electrically connected to the controller 28 via the electric signal line 38. The electromagnetic proportional valve 72 has the flow control characteristics shown in Fig. 3 and is capable of variably adjusting the amount of oil flowing into the oil passage 52 in response to an electric signal from the controller 28. Furthermore, when no electric signal is input from the controller 28, the electromagnetic proportional valve 72 cuts off the oil passages 51, 52.

[0044] Further, the oil passage 51 is provided with a check valve 71 that allows oil to pass only from the flow rate adjustment valve 70 toward the electromagnetic proportional valve 72. With reference to Fig. 6(a), the oil passage 51 (see Fig. 6(b)) may be particularly referred to as an upstream oil passage 51-1 on the upstream side of the check valve 71, and as a downstream oil passage 51-2 on the downstream side of the check valve 71.

[0045] An oil passage 73 is branched and connected to the downstream oil passage 51-2. An accumulator 74 as a pressure accumulation device and a pressure sensor 75 as a pressure detection device are connected to the oil passage 73. A check valve 71 is provided in the oil passage 51, so that the oil stored in the accumulator 74 is prevented from flowing back to the upstream oil passage 51-1, i.e., the flow rate adjustment valve 70 side. The pressure in the oil passage 73 is determined by the pressure P of the oil stored in the accumulator 74. ＡＣＣ It is approximately the same as

[0046] The pressure sensor 75 detects the pressure in the oil passage 73, i.e., the pressure P ＡＣＣThe controller 28 outputs an electrical signal according to the signal.

[0047] The oil passage 52 is connected to the electromagnetic switching valve 41 in the pressure booster 40. An oil passage 53 is branched and connected to the oil passage 52. The oil passage 53 is a relief oil passage having a relief valve 54.

[0048] The pressure booster 40 includes an electromagnetic switching valve 41 , a pressure booster 42 , an accumulator 43 , oil passages 44 to 47 , and check valves 48 and 49 .

[0049] An oil passage 52, an oil passage 55, and oil passages 44 and 45 are connected to the electromagnetic switching valve 41. The electromagnetic switching valve 41 is electrically connected to the controller 28 through an electric signal line 34.

[0050] When no electric signal is input from the controller 28, i.e., when the electromagnetic switching valve 41 is in a non-energized state, the electromagnetic switching valve 41 switches to a return position 41-1 where oil is passed from the oil passage 52 to the oil passage 45 and oil is passed from the oil passage 44 to the oil passage 55. The oil passage 55 is in communication with the tank 11.

[0051] In addition, when an electrical signal is input from the controller 28, i.e., when the electromagnetic switching valve 41 is energized, it switches to the pressurized position 41-2, which allows oil to pass from oil passage 52 to oil passage 44 and from oil passage 45 to oil passage 55.

[0052] The intensifier 42 has a stepped cylindrical case 42-1 formed by a series of cylinders with different radial dimensions, and a stepped cylindrical piston 42-2 formed by a series of columns with different radial dimensions. The piston 42-2 is enclosed in the case 42-1 so as to be movable in the axial direction.

[0053] The space of the case 42-1 is divided by the piston 42-2 into a first oil chamber 42-3, a second oil chamber 42-4, and a third oil chamber 42-5. According to Pascal's theorem, the pressure intensifier 42 is able to intensify the pressure of the first oil chamber 42-3 relative to the pressure of the second oil chamber 42-4 at a ratio between the pressure-receiving surface of the piston 42-2 facing the first oil chamber 42-3 and the pressure-receiving surface of the piston 42-2 facing the second oil chamber 42-4.

[0054] The first oil chamber 42-3 is connected to oil passages 46 and 47. The second oil chamber 42-4 is connected to an oil passage 44. The third oil chamber 42-5 is connected to an oil passage 45.

[0055] The oil passage 46 is in communication with the tank 11. The oil passage 46 is provided with a check valve 48 that allows oil to pass only from the tank 11 toward the first oil chamber 42-3.

[0056] 1, the oil passage 47 is connected to the accumulator 43, a pressure sensor 60, and an electromagnetic switching valve 56. The pressure sensor 60 outputs an electric signal corresponding to the pressure of the accumulator 43 to the controller 28.

[0057] In addition, a check valve 49 is provided in the oil passage 47 between the first oil chamber 42-3 and the accumulator 43. The check valve 49 allows oil to pass only from the first oil chamber 42-3 toward the accumulator 43 and the electromagnetic switching valve 56. This prevents the oil stored in the accumulator 43 from flowing back toward the booster 42.

[0058] Furthermore, a relief flow passage having a relief valve 59 is connected to the oil passage 47 between the accumulator 43 and the electromagnetic switching valve 56 .

[0059] An oil passage 57 is connected to the electromagnetic switching valve 56. A check valve 58 is provided in the oil passage 57, which allows oil to pass only from the electromagnetic switching valve 56 toward the oil passage 23. The oil passage 57 is also branched off and connected to the oil passage 23.

[0060] The electromagnetic switching valve 56 is electrically connected to the controller 28 through the electric signal line 36. When an electric signal is input from the controller 28, the electromagnetic switching valve 56 connects the oil passages 47, 57. As a result, the oil stored in the accumulator 43 is supplied to the head chamber 5-2 in the cylinder device 5.

[0061] Oil discharged from the pump 3 is supplied to the hydraulic remote control valve 6 through an oil passage 16. A relief oil passage having a relief valve 8 is branched and connected to the oil passage 16.

[0062] The hydraulic remote control valve 6 is a variable pressure reducing valve. When the operating lever 6-1 of the hydraulic remote control valve 6 is operated in the extension direction E or the retraction direction C, the hydraulic remote control valve 6 reduces the pressure of the oil in accordance with the amount of lever operation. The reduced pressure oil is supplied to the signal port 4-1 or the signal port 4-2 of the switching valve 4 through either the signal oil passage 17 or 18. In response to this, the switching valve 4 switches to the "extension position 4E" or the "retraction position 4C."

[0063] Further, pressure sensors 9 and 10 are provided in the signal oil passages 17 and 18. The pressure sensors 9 and 10 have the electrical signal characteristics shown in Fig. 4 and output to the controller 28 an electrical signal corresponding to the pressure in the signal oil passages 17 and 18, in other words, an electrical signal corresponding to the amount of operation of the operating lever 6-1.

[0064] Next, the operation of the cylinder device 5 will be described.

[0065] First, we will explain the extension of the cylinder device 5. Referring to Figure 1, when the operating lever 6-1 is operated in the extension direction E, the switching valve 4 switches to the extension position 4E. Oil delivered from the pump 2 flows through oil passages 12, 14, 22, 25, and 23 into the head chamber 5-2 of the cylinder device 5.

[0066] The piston rod 5-3 in the cylinder device 5 moves toward the extension end when the pressure in the head chamber 5-2 exceeds the sum of the pressure in the rod chamber 5-1 and the load W. In other words, the cylinder device 5 extends.

[0067] As the piston rod 5-3 moves, oil flows out of the rod chamber 5-1 into the oil passage 24, passes through the oil passage 15 and is discharged into the tank 11.

[0068] The controller 28 outputs an electric signal corresponding to the amount of operation of the hydraulic remote control valve 6 to the drive mechanism 1 via an electric signal line 33. In response to this electric signal, the drive mechanism 1 adjusts the drive force and sends out an amount of oil corresponding to the drive force from the pump 2. This allows the cylinder device 5 to extend at a speed corresponding to the amount of operation of the hydraulic remote control valve 6.

[0069] When the controller 28 determines from the electrical signal input from the pressure sensor 60 that the pressure in the accumulator 43 can contribute to the movement of the piston rod 5-3, it outputs an electrical signal to the solenoid controlled directional control valve 56. As a result, the solenoid controlled directional control valve 56 connects the oil passages 47, 57, and supplies the oil delivered from the accumulator 43 to the head chamber 5-2.

[0070] The controller 28 also outputs an electric signal to the drive mechanism 1 to reduce the drive force, thereby reducing the energy required to operate the drive mechanism 1 while maintaining the extension speed of the cylinder device 5 according to the amount of operation of the hydraulic remote control valve 6.

[0071] Next, we will explain the retraction of the cylinder device 5. When the operating lever 6-1 is operated in the retraction direction C, the switching valve 4 switches to the retraction position 4C. Oil delivered from the pump 2 flows into the rod chamber 5-1 in the cylinder device 5 through oil passages 12, 14, and 24. Note that when the operating lever 6-1 is operated in the retraction direction C, the controller 28 does not output an electrical signal to the solenoid switching valve 56.

[0072] When the sum of the pressure in the rod chamber 5-1 and the load W exceeds the pressure in the head chamber 5-2, the piston rod 5-3 in the cylinder device 5 moves toward the contraction end. In other words, the cylinder device 5 retracts.

[0073] As the piston rod 5-3 moves, oil flows out from the rod chamber 5-1 into the oil passage 23. Hereinafter, the oil flowing into the oil passage 23 from the rod chamber 5-1 will be described in detail.

[0074] When the operating lever 6-1 is operated in the retraction direction C, the controller 28 outputs an electric signal input from the pressure sensor 61, i.e., an electric signal corresponding to the pressure in the rod chamber 5-1, to each of the flow rate control valves 39 and 70. In addition, the controller 28 outputs an electric signal input from the pressure sensor 75, i.e., an electric signal corresponding to the pressure in the oil passage 73, to the solenoid proportional valve 72.

[0075] 6, when an electrical signal is input, the flow rate control valve 39 connects the oil passages 23 and 22 and also connects the oil passages 23 and 50. The flow rate control valve 39 also adjusts the opening of the variable throttle 39-4 in response to the electrical signal from the controller 28, thereby adjusting the priority flow rate to the pressure booster 40 side.

[0076] The oil that flows from the oil passage 23 into the first flow path 39-1 is reduced in pressure by the fixed throttle 39-3 while the amount that flows into the oil passage 22 is limited. The oil that flows into the oil passage 22 is discharged to the tank 11 through the oil passage 15.

[0077] The oil flowing from the oil passage 23 into the second flow path 39-2 is reduced in pressure according to the opening of the variable throttle 39-4, while the amount of oil flowing into the oil passage 50 is limited by the variable throttle 39-4 to a priority flow rate toward the pressure booster 40.

[0078] As a result, the head chamber 5-2 is maintained at approximately the same pressure as before the hydraulic remote control valve 6 was operated, even though part of the oil flowing from the head chamber 5-2 through the oil passage 23 is diverted to the oil passage 50. In other words, the flow rate control valve 39 generates a so-called brake pressure, and can move the piston rod 5-3 toward the contraction end at a speed according to the amount of operation of the hydraulic remote control valve 6 regardless of the load W.

[0079] In addition, the flow control valve 39 divides the oil flowing in from the oil passage 23 into oil that passes through the fixed orifice 39-3 and oil that passes through the variable orifice 39-4, thereby reducing the oil pressure acting on the oil passage 50 and the flow control valve 70, i.e., the oil pressure acting on the downstream side of the pressure booster device 40, to the desired pressure.

[0080] The flow rate control valve 70, to which the electrical signal is input, connects the oil passages 50 and 51 and also connects the oil passages 50 and 76. The flow rate control valve 70 also adjusts the opening of the variable throttle 70-4 in response to the electrical signal from the controller 28, thereby adjusting the priority flow rate to the relief valve 77 side.

[0081] The oil that has flowed from the oil passage 50 into the first flow passage 70-1 is reduced in pressure while the amount that flows into the oil passage 51 is restricted by the fixed throttle 70-3.

[0082] In addition, the oil that flows from the oil passage 50 into the second flow path 70-2 is reduced in pressure according to the opening of the variable throttle 70-4, while the amount of oil that flows into the oil passage 76 is limited by the variable throttle 70-4 to a priority flow rate toward the relief valve 77 side.

[0083] In this way, the oil that has passed through the flow rate adjustment valve 39 and flowed into the oil line 50 is partially diverted by the flow rate adjustment valve 70 to the oil line 76. Furthermore, even if the pressure of the oil that has passed through the flow rate adjustment valve 39 and flowed into the oil line 50 exceeds the pressure resistance of the pressure booster 40, the fixed throttle 70-3 reduces the pressure of the oil flowing into the pressure booster 40, thereby protecting the solenoid proportional valve 72, the pressure booster 40, etc. In other words, it is possible to use a pressure booster or a switching valve that has a lower pressure resistance than the expected braking pressure.

[0084] Furthermore, the priority flow rate to the pressure booster 40 and the priority flow rate to the relief valve 77 are adjusted so as to maintain the brake pressure in accordance with the electrical signal input from the pressure sensor 61, as described above. When the pressure in the oil passage 76 becomes high, the relief valve 77 opens and discharges oil into the tank 11. This allows the piston rod 5-3 to move smoothly toward the retraction end while maintaining an appropriate brake pressure.

[0085] The oil that has passed through the fixed throttle 70-3 and the oil that has been delivered from the accumulator 74 flow into the downstream oil passage 51-2. ＡＣＣ When the pressure exceeds 0.05, oil flows from the oil passage 73 into the accumulator 74 and is stored therein.

[0086] The accumulator 74 has the pressure increase characteristics shown in Figure 5, and can make the pressure increase in the oil passages 51 and 73 gentle. ＡＣＣ is the pressure value P shown by the dashed line in FIG. ＺＸ When the pressure exceeds this value, the increase becomes gentle and reaches the upper limit. ＺＸ is the pressure required to boost the oil pressure in the pressure booster 40, as will be described later.

[0087] The oil flowing into oil passage 51 flows into oil passage 52 in accordance with the aperture of electromagnetic proportional valve 72. As described above, the aperture of electromagnetic proportional valve 72 is set to an aperture corresponding to the pressure in oil passages 51-2 and 73. As a result, electromagnetic proportional valve 72 makes it difficult for oil in excess of the amount necessary to operate pressure booster 40 to flow into oil passage 52, causing the pressure in oil passages 52 and 53 to exceed the pressure set in relief valve 54, thereby preventing excessive oil from being discharged.

[0088] Here, the controller 28 can identify the position of the piston 42-2 using a position sensor (not shown) provided in the pressure intensifier 42. In this embodiment, the position where the piston 42-2 has moved to the leftmost position is the start position, and the position where the piston 42-2 has moved to the rightmost position is the end position. Note that the type of sensor may be changed as appropriate as long as the position of the piston 42-2 can be identified.

[0089] 6(a), when the controller 28 determines that the piston 42-2 is at the start end position, it switches the electromagnetic switching valve 41 to the pressurizing position 41-2. As a result, the oil that has flowed from the oil passage 51 into the oil passage 52 flows into the second oil chamber 42-4 in the pressure booster 42 through the oil passage 44. In addition, the pressure of the oil in the third oil chamber 42-5 becomes the same as the pressure in the tank 11 because the third oil chamber 42-5 is connected to the tank 11.

[0090] The piston 42-2 moves to the right when the pressure in the first oil chamber 42-3 exceeds the pressure in the accumulator 43 and the force of the pressure in the second oil chamber 42-4 acting on the pressure-receiving surface to push the piston 42-2 to the right exceeds the force of the pressure in the first oil chamber 42-3 acting on the pressure-receiving surface to push the piston 42-2 to the left.

[0091] Accordingly, the oil in the first oil chamber 42-3 is sent to the oil passage 47 and stored in the accumulator 43. Because the pressure of the oil in the first oil chamber 42-3 exceeds the pressure of the accumulator 43, it tends to hinder the piston 42-2 from moving to the right.

[0092] Additionally, as the piston 42-2 moves toward the right, the oil in the third oil chamber 42-5 is discharged to the tank 11 through the oil passages 45 and 55. Because the pressure in the tank 11 is approximately the same as atmospheric pressure, it is unlikely to impede the movement of the piston 42-2.

[0093] When the controller 28 determines that the piston 42-2 is at the end position, it switches the solenoid controlled directional control valve 41 to the return position 41-1. As a result, the oil that has flowed from the oil passage 51 to the oil passage 52 flows into the third oil chamber 42-5 in the pressure booster 42 through the oil passage 45. The piston 42-2 moves toward the left.

[0094] In the pressure intensifier 42, when the piston 42-2 moves to the left, the pressure in the first oil chamber 42-3 momentarily becomes lower than the pressure in the tank 11, and the first oil chamber 42-3 can suck up oil from the tank 11. At this time, the movement of the piston 42-2 is hindered, but this is minor compared to the effect of the pressure in the first oil chamber 42-3 acting on the piston 42-2 during pressure boosting.

[0095] The pressure of the oil in the second oil chamber 42-4 becomes equal to the pressure in the tank 11 because the second oil chamber 42-4 is connected to the tank 11. The oil in the second oil chamber 42-4 is discharged into the tank 11 through the oil passages 44 and 55 as the piston 42-2 moves toward the left.

[0096] As a result, the pressure in the oil passages 52 and 53 is more likely to rise when the piston 42-2 moves to the right than when it moves to the left.

[0097] 1, the switching valve 4 is switched to the neutral position when the operation of the hydraulic remote control valve 6 is released, whereby the operation of the cylinder device 5 is stopped.

[0098] When the controller 28 determines that the operation of the hydraulic remote control valve 6 has been released, it stops outputting electrical signals to the flow rate control valves 39, 70. This stops the flow of oil from the head chamber 5-2 into the oil passage 23.

[0099] Furthermore, when the controller 28 determines that the operation of the hydraulic remote control valve 6 has been released, it detects the pressure P ＡＣＣ is the pressure value P ＺＸ (See FIG. 5) It is determined whether or not it is equal to or greater than this.

[0100] Referring to FIG. 7( a ), the controller 28 controls the pressure P ＡＣＣ is the pressure value P ＺＸ If it is determined that this is the case, an electric signal corresponding to the electric signal input from the pressure sensor 75 is output to the electromagnetic proportional valve 72, just as when the operating lever 6-1 is operated in the retraction direction C.

[0101] As a result, even when the flow of oil from the head chamber 5-2 to the oil passage 23 is stopped, the pressure booster 40 can be operated using the oil stored in the accumulator 74.

[0102] Furthermore, by sending out the oil stored in the accumulator 74, it is possible to ensure a free volume for storing the oil that subsequently flows into the oil passage 23 from the head chamber 5-2.

[0103] Referring to FIG. 7B, the controller 28 controls the pressure P ＡＣＣ is the pressure value P ＺＸ If it is determined that the difference is less than the predetermined value, the output of the electric signal to the electromagnetic proportional valve 72 is stopped.

[0104] This prevents the amount of oil stored in the accumulator 74 from being less than the minimum hydraulic oil amount of the pressure booster 42, preventing the pressure boosting operation from being insufficient. ＺＸ is set to a pressure that can sufficiently boost the pressure of the booster 42. The boost operation occurs when, for example, the piston 42-2 moving toward the right in less than one reciprocation stops midway.

[0105] As described above, the hydraulic circuit 100 can store in the accumulator 74 at least a portion of the high-pressure oil that flows from the cylinder device 5 into the oil passage 23 when the cylinder device 5 is operating, regardless of whether the piston 42-2 in the pressure booster device 40 is moving or not. This reduces the amount of oil discharged through the relief valve 54 that compensates for the high pressure generated in the oil passage 23, which is part of the return line of the cylinder device 5. This increases the energy recovery efficiency of the hydraulic circuit 100.

[0106] Furthermore, in the hydraulic circuit 100, the check valve 71 provided upstream of the pressure booster 40, the relief valve 54, and the accumulator 74 prevents oil stored in the accumulator 74 from flowing back toward the cylinder device 5. This prevents interference with the operation of the cylinder device 5 and increases the energy recovery efficiency.

[0107] Furthermore, the hydraulic circuit 100 is provided with an electromagnetic proportional valve 72 between the accumulator 74 and the relief valve 54. This allows the accumulator 74 to accumulate oil at a pressure equal to or greater than the relief pressure of the relief valve 54.

[0108] The hydraulic circuit 100 is also connected to the downstream oil passage 51-2 and includes a pressure sensor 75 that can detect the fluid pressure of the accumulator 74, i.e., the pressure of the oil stored in the accumulator 74, and an electromagnetic proportional valve 72 that opens and closes in response to the pressure of the accumulator 74 detected by the pressure sensor 75 and is provided between the accumulator 74 and the pressure booster 40. This not only makes it possible to operate the pressure booster 40 regardless of the operation of the cylinder device 5, but also ensures that the free volume of the accumulator 74 is sufficient.

[0109] Furthermore, the hydraulic circuit 100 is provided with a flow control valve 39 between the switching valve 4 and the cylinder device 5, which diverts a portion of the oil that has flowed from the cylinder device 5 into the oil passage 23 to the oil passage 22. This allows for smoother operation of the cylinder device 5, while also enabling energy recovery using the surplus oil.

[0110] Although the embodiments of the present invention have been described above with reference to the drawings, the specific configuration is not limited to these embodiments, and the present invention also includes modifications and additions that do not deviate from the gist of the present invention.

[0111] For example, in the above embodiment, the fluid pressure circuit has been described as a hydraulic circuit in which oil is pumped, but this is not limited to this, and the working fluid may be a fluid other than oil, and the fluid to be applied may be changed as appropriate.

[0112] In addition, in the above embodiment, the case has been described as having a stepped cylindrical shape formed by connecting cylinders with different radial dimensions, but this is not limited to this and any shape that allows the area ratio to be changed may be used.

[0113] Furthermore, in the above embodiment, the piston has been described as being a stepped cylinder formed by a series of cylinders with different radial dimensions, but this is not limited to this. The piston may also be configured such that a plurality of discs are fixed to the rod at axial intervals, with one axial end face of each disc functioning as a pressure-receiving surface on the input chamber side and the other axial end face functioning as a pressure-receiving surface on the output chamber side.

[0114] More specifically, the shapes of the case and piston may be changed as appropriate as long as the sum of the pressure-receiving areas arranged in the output chamber is smaller than the sum of the pressure-receiving areas arranged in the input chamber.

[0115] Furthermore, in the above embodiment, the pressure booster device is described as being a so-called single-acting type that boosts pressure only when moving in one axial direction, but this is not limited to this, and the pressure booster device may be a double-acting type that boosts pressure both when moving in one axial direction and when moving in the other axial direction.

[0116] In addition, in the above embodiment, the pressure accumulator is described as an accumulator, but this is not limited to this and may be any device that can temporarily hold and discharge the working fluid, such as an air chamber or a damper, and may be modified as appropriate.

[0117] In the above embodiment, the pressure booster device has been described as having the accumulator 43, but this is not limiting, and an accumulator may not be provided, or a regenerative device such as a generator may be provided instead of the accumulator 43. In other words, any appropriate modification may be made as long as the fluid pressurized by the pressure booster device can be utilized.

[0118] In addition, in the above embodiment, the accumulator 74 as a pressure storage device has been described as having a pressure storage capacity capable of storing a pressure higher than the pressure resistance capacity of the pressure booster 40, but this is not limited to this, and the accumulator 74 may have a pressure storage capacity capable of storing a pressure equal to or lower than the pressure resistance capacity of the pressure booster 40, and this may be changed as appropriate.

[0119] In addition, in the above embodiment, a configuration has been described in which oil flowing from the head chamber in the cylinder device into the oil passage is diverted by the flow control valve 39 as a diverter valve and flows into the pressure booster device side, but this is not limited to this, and the entire amount of oil flowing from the head chamber into the oil passage may flow into the pressure booster device side.

[0120] In addition, in the above embodiments, many of the valves have been described as solenoid valves, but this is not a limitation and they may be hydraulic valves or may be modified as appropriate. Similarly, the valves described as hydraulic valves may also be solenoid valves or may be modified as appropriate.

[0121] Furthermore, in the above embodiment, a structure in which a downstream diverter valve is provided has been described, but this is not limiting, and the downstream diverter valve may be omitted. In such a configuration, when the pressure in the accumulator reaches its upper limit, control is required, such as widening the opening of the switching valve to discharge the pressure through the relief valve 54. On the other hand, the above embodiment is preferable from the viewpoints of simplifying control and facilitating protection of the switching valve and the pressure booster device.

[0122] 4 Electromagnetic directional control valve (operating valve) 5 Cylinder device 23, 50 to 53 Oil passage (flow path) 39 Flow rate adjustment valve (dividing valve) 40 Pressure booster device 54 Relief valve 70 Flow rate adjustment valve (downstream dividing valve) 71 Check valve 72 Electromagnetic proportional valve (switching valve) 74 Accumulator (pressure storage device) 75 Pressure sensor (pressure detection means) 77 Relief valve (second relief valve) 100 Hydraulic circuit (fluid pressure circuit)

Claims

1. A fluid pressure circuit in which a relief valve is connected to a flow path connecting a cylinder device and a pressure booster device, and a piston of the pressure booster device is moved by fluid flowing in from the flow path, and a pressure accumulator is connected to the flow path.

2. A fluid pressure circuit according to claim 1, wherein a check valve is provided in the flow path upstream of the pressure booster, the relief valve and the pressure accumulator.

3. The fluid pressure circuit according to claim 2, wherein a switching valve is provided between the pressure accumulator and the relief valve.

4. A fluid pressure circuit as claimed in any one of claims 1 to 3, comprising a pressure detection device capable of detecting the fluid pressure of the pressure accumulator, and a switching valve disposed between the pressure accumulator and the pressure booster, which opens and closes in response to the fluid pressure detected by the pressure detection device.

5. A fluid pressure circuit according to claim 1, wherein the fluid pressure circuit comprises an operating valve that operates the cylinder device with a fluid, and a flow dividing valve that divides a portion of the fluid flowing out of the cylinder device is provided between the operating valve and the cylinder device.

6. A fluid pressure circuit as claimed in claim 5, wherein a downstream diverter valve is provided between the diverter valve and the pressure booster, for diverting a portion of the fluid remaining after the diverter valve has diverted a portion of the outflowing fluid and directing it to a second relief valve.

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