Fluid pressure circuit

Abstract

Provided is a fluid pressure circuit capable of accurately controlling an actuator.　A fluid pressure circuit 101 comprises: fluid supply sources 1, 2; an actuator 6 connected to the fluid supply sources 1, 2; a directional switching valve 5 that is provided in a flow passage between the fluid supply sources 1, 2 and the actuator 6 and switches the supply destination of the fluid supplied from the fluid supply sources 1, 2; an output control means that controls output of the fluid supply sources 1, 2; and an accumulator 34 provided to be able to supply accumulated pressure fluid to the flow passage. The fluid pressure circuit 101 includes: an actuator pressure detection means 43 that detects the pressure of the actuator 6; and an accumulator pressure detection means 42 that detects the pressure of the accumulator 34. The output control means is capable of controlling the output of the fluid supply sources 1, 2 on the basis of the pressure of the actuator 6 and the pressure of the accumulator 34.

Description

Hydraulic circuit

[0001] The present invention relates to a hydraulic circuit, for example, a hydraulic circuit that controls an actuator according to an operation command.

[0002] Generally, a hydraulic circuit that controls an actuator according to an operation command is used in a working machine, a construction machine, a cargo handling and transport vehicle, an automobile, etc.

[0003] For example, a hydraulic circuit that employs a so-called positive flow control circuit capable of varying the operating speed of an actuator based on the manipulated amount of an operating means is known (see Patent Document 1). The hydraulic circuit shown in FIG. 9, which is an example of such a hydraulic circuit, mainly includes a drive mechanism 201, a variable displacement main hydraulic pump 202, a pilot hydraulic pump 203, a boom remote control valve 204 (hereinafter referred to as remote control valve 204), a boom direction changeover valve 205 (hereinafter referred to as direction changeover valve 205), a boom cylinder 206 (hereinafter referred to as cylinder 206), and a shuttle valve 207.

[0004] The remote control valve 204 is a variable type pressure reducing valve. The remote control valve 204 converts the pilot fluid supplied from the pilot hydraulic pump 203 through the oil passage 208 into an operating hydraulic signal that reduces the pressure from the pilot primary pressure to the pilot secondary pressure in proportion to the operating amount of the lever 204-1 (see FIG. 3). The operating hydraulic signal flows into one of the signal oil passages 209 and 210 according to the operating direction of the lever 204-1 and is supplied to the signal port 205-1 or the signal port 205-2 in the direction changeover valve 205.

[0005] Note that all of the surplus oil discharged from the pilot hydraulic pump 203 that is not supplied to the signal ports 205-1 and 205-2 is discharged to the tank 214 through the oil passage 211 and the relief valve 212.

[0006] The direction changeover valve 205 is a 6-port 3-position type normally open pilot changeover valve. When the direction changeover valve 205 is in the neutral position, the pressure oil discharged from the main hydraulic pump 202 is discharged to the tank 214 through the oil passage 215, the direction changeover valve 205, and the oil passage 216.

[0007] The directional control valve 205 switches to the extended position 205-3 when an operating hydraulic signal is supplied to the signal port 205-1. When the directional control valve 205 is in the extended position 205-3, pressurized oil discharged from the main hydraulic pump 202 flows into the head chamber 206-1 of the cylinder 206 through oil passages 215, 217, check valve 218, directional control valve 205, and 219. In response, as the cylinder rod 206-3 moves in the extended direction, the oil in the rod chamber 206-2 of the cylinder 206 is discharged to the tank 214 through oil passage 220, directional control valve 205, and 221.

[0008] Furthermore, the directional control valve 205 switches to the retracted position 205-4 when an operating hydraulic signal is supplied to the signal port 205-2. When the directional control valve 205 is in the retracted position 205-4, the pressurized oil discharged from the main hydraulic pump 202 flows into the rod chamber 206-2 through the oil passage 215, oil passage 217, check valve 218, directional control valve 205, and oil passage 220. In response, when the cylinder rod 206-3 moves in the retracted direction, the oil in the head chamber 206-1 of the cylinder 206 is discharged to the tank 214 through the oil passage 219, directional control valve 205, and oil passage 221.

[0009] Furthermore, a portion of the operating hydraulic signals are supplied to the signal pressure control unit 202-3 via the shuttle valve 207 and signal oil passage 224, which are connected to the signal oil passages 209 and 210 via signal oil passages 222 and 223.

[0010] The signal pressure control unit 202-3 functions as a pressure reducing valve whose opening degree is adjusted according to the pilot signal pressure Pp of the operating hydraulic pressure signal, and reduces the pressure of the pressurized oil supplied from the signal oil passage 225, which is branched and connected to the oil passage 215, to obtain a swash plate control hydraulic pressure signal. The swash plate control hydraulic pressure signal is supplied to the swash plate control unit 202-4.

[0011] The swash plate control unit 202-4 adjusts the swash plate angle of the swash plate 202-1 in the main hydraulic pump 202 according to the pressure of the swash plate control hydraulic signal. The pump flow rate Q of the main hydraulic pump 202 is controlled according to the swash plate angle of the swash plate 202-1 (see Figure 6).

[0012] When the lever 204-1 is operated in the extension direction, the extension speed Ve of the cylinder rod 206-3 with respect to the amount of operation L results in a characteristic curve as shown in Figure 7.

[0013] Furthermore, the main circuit, which includes the main hydraulic pump 202, is provided with an oil passage 227 in which a relief valve 226 is installed. The relief valve 226 opens when the pressurized oil in the circuit becomes blocked and abnormally high pressure is generated. As a result, the high-pressure oil is discharged to the tank 214 through the oil passage 227 and the relief valve 226, thereby preventing damage to the hydraulic equipment in the circuit.

[0014] Incidentally, to improve energy efficiency, a fluid pressure circuit with an accumulator added, as shown in Figure 9, is also known. In such a fluid pressure circuit, the pressurized oil stored in the accumulator can be regenerated into the pump line via a supply switching valve to drive the actuator.

[0015] Japanese Patent No. 4067596 (pages 5 and 6, Figure 1)

[0016] In such fluid pressure circuits, when pressurized oil stored in the accumulator is regenerated into the pump line via a supply switching valve, the supply switching valve is uniformly controlled by the pilot pressure of the remote control valve. As a result, the amount of oil supplied changes depending on the pressure difference between the accumulator's internal pressure and the pump line's pressure, making optimal energy regeneration and pump control difficult, and thus preventing accurate control of the actuator.

[0017] This invention was made in view of these problems, and aims to provide a fluid pressure circuit capable of accurately controlling an actuator.

[0018] To solve the above problems, the fluid pressure circuit of the present invention comprises a fluid supply source, an actuator connected to the fluid supply source, a directional control valve provided in a flow path between the fluid supply source and the actuator for switching the destination of the fluid supplied from the fluid supply source, output control means for controlling the output of the fluid supply source, and an accumulator provided to supply pressurized fluid to the flow path, wherein the fluid pressure circuit comprises an actuator pressure detection means for detecting the pressure of the actuator and an accumulator pressure detection means for detecting the pressure of the accumulator, and the output control means is capable of controlling the output of the fluid supply source based on the pressure of the actuator and the pressure of the accumulator. According to this, by sequentially adjusting the output of the fluid supply source based on the pressure of the actuator and the pressure of the accumulator, it is possible to match the output of the fluid supply source according to the capacity of the accumulator, and thus the actuator can be accurately controlled.

[0019] The output control means includes a control mechanism that controls the output of the fluid supply source by receiving pilot pressure, and a pressure reducing valve that reduces the pilot pressure, wherein the opening of the pressure reducing valve may be adjusted based on the pressure of the actuator and the pressure of the accumulator. This simplifies the configuration.

[0020] The system may have an operating means that outputs the pilot pressure corresponding to the amount of manipulation, and the actuator may be driven according to the amount of manipulation. This makes it less likely for the operator to feel any discomfort when using an accumulator in conjunction with the system.

[0021] The accumulator may be connected between the directional control valve and the actuator in the flow path. This makes it possible to use a small directional control valve.

[0022] The actuator may also be a cylinder. This allows the cylinder to be driven smoothly.

[0023] This figure shows a hydraulic excavator incorporating the hydraulic circuit according to an embodiment of the present invention. This is a schematic diagram showing the hydraulic circuit in the embodiment. This is a graph showing the relationship between the lever operation amount and the pilot secondary pressure output to the switching valve. This is a graph showing the relationship between the electrical signal and the opening degree in the electromagnetic switching valve. This is a graph showing the relationship between the electrical signal and the secondary pressure in the electromagnetic proportional pressure reducing valve. This is a graph showing the relationship between the pilot pressure and the flow rate delivered from the main hydraulic pump. This is a graph showing the relationship between the lever operation amount and the cylinder operating speed. This is a graph showing the relationship between the signal pressure and the secondary pressure in the hydraulic proportional pressure reducing valve. This is a schematic diagram showing a conventional hydraulic circuit.

[0024] Embodiments for implementing the fluid pressure circuit according to the present invention will be described below based on examples.

[0025] A fluid pressure circuit according to an embodiment of the present invention will be described with reference to Figures 1 to 7. Hereinafter, the left and right sides of Figure 2, as viewed from the front, will be described as the valve positions of the electromagnetic directional control valves.

[0026] The hydraulic circuit, as a fluid pressure circuit in this embodiment, is a hydraulic circuit that controls the stroke of a cylinder in response to an operation command in work machines, construction machines, material handling vehicles, automobiles, etc. The hydraulic circuit in this embodiment is incorporated into the powertrain of the hydraulic excavator 100 shown in Figure 1 and is used to control multiple actuators driven by pressurized oil.

[0027] Examples of such actuators include cylinders and motors. In this embodiment, a boom cylinder 6, which is an example of a cylinder, will be used as an example of an actuator. The actuator may also be other cylinders such as an arm cylinder 50 or a bucket cylinder 51, or it may be a motor such as a slewing motor 52 or a travel motor 53.

[0028] As shown in Figure 2, the hydraulic circuit 101 mainly consists of a drive mechanism 1 as a fluid supply source, a variable displacement main hydraulic pump 2 as a fluid supply source, a pilot hydraulic pump 3 as an operating means, a boom hydraulic remote control valve 4 (hereinafter referred to as remote control valve 4) as an operating means, a boom directional control valve 5 (hereinafter referred to as directional control valve 5), a boom cylinder 6 (hereinafter referred to as cylinder 6), a shuttle valve 7, oil passages 8, 11, 15-17, 19-21, 27-29, 31, 33, signal oil passages 9, 10, 22-25, 45-48, relief valves 12, 26, a tank 14, a check valve 18, solenoid valves 30, 32, an accumulator 34, pressure detectors 35, 36, 42, 43, a controller 37, electrical signal lines 39, 40, 44, and a solenoid proportional pressure reducing valve 41.

[0029] The main hydraulic pump 2 is connected to a drive mechanism 1 such as an internal combustion engine, and operates using power from the drive mechanism 1, supplying pressurized oil to the downstream side through the oil passage 15.

[0030] The pilot hydraulic pump 3, like the main hydraulic pump 2, is powered by the drive mechanism 1 and supplies pressurized oil to the downstream side through the oil passage 8.

[0031] The pressurized oil discharged from the pilot hydraulic pump 3 flows through the oil passage 8 into the remote control valve 4. The remote control valve 4 is a variable pressure reducing valve and is used to control the extended or retracted position, i.e., the amount of extension or retraction, of the rod 6-3.

[0032] The remote control valve 4 converts the pilot fluid supplied from the pilot hydraulic pump 3 through the oil passage 8 into an operating hydraulic signal, which is reduced from the primary pilot pressure to the secondary pilot pressure in proportion to the amount L operated by the lever 4-1 (see Figure 3).

[0033] When lever 4-1 is operated in the extension direction A, the operating hydraulic signal flows into the signal oil passage 9 and is supplied to the signal port 5-1 of the directional control valve 5. Furthermore, when lever 4-1 is operated in the retraction direction B, the operating hydraulic signal flows into the signal oil passage 10 and is supplied to the signal port 5-2 of the directional control valve 5.

[0034] Furthermore, any excess pressurized oil discharged from the pilot hydraulic pump 3 that is not supplied to the signal ports 5-1 and 5-2 is discharged to the tank 14 through the oil passage 11, which is equipped with a relief valve 12.

[0035] The directional control valve 5 is a 6-port, 3-position normally open type pilot control valve. When the spool in the directional control valve 5 is in the neutral position, the pressurized oil that flows into the directional control valve 5 through the oil passage 15 is entirely discharged into the tank 14 through the oil passage 16.

[0036] When an operating hydraulic signal is supplied to the signal port 5-1, the spool of the directional control valve 5 moves to the right and switches to the extended position 5-3.

[0037] When the directional control valve 5 is in the extended position 5-3, the pressurized oil discharged from the main hydraulic pump 2 flows into the head chamber 6-1 of the cylinder 6 through oil passage 15, oil passage 17, check valve 18, directional control valve 5, and oil passage 19. In response, as the cylinder rod 6-3 moves in the extended direction, the oil in the rod chamber 6-2 of the cylinder 6 is discharged into the tank 14 through oil passage 20, directional control valve 5, and oil passage 21.

[0038] Furthermore, when an operating hydraulic signal is supplied to the signal port 5-2, the spool of the directional control valve 5 moves to the left and switches to the retracted position 5-4.

[0039] When the directional control valve 5 is in the retracted position 5-4, the pressurized oil discharged from the main hydraulic pump 2 flows into the rod chamber 6-2 through the oil passage 15, oil passage 17, check valve 18, directional control valve 5, and oil passage 20. In response, when the cylinder rod 6-3 moves in the retracted direction, the oil in the head chamber 6-1 of the cylinder 6 is discharged into the tank 14 through the oil passage 19, directional control valve 5, and oil passage 21.

[0040] In the main circuit equipped with the main hydraulic pump 2, a relief valve 26 is installed in the oil passage 27 that is branched and connected to the oil passage 15. The relief valve 26 is opened when, for example, when the cylinder rod 6-3 reaches the extension end or the contraction end, or when a sudden load is applied to the cylinder 6, the pressure oil in the circuit becomes blocked and an abnormal high pressure occurs. As a result, the high-pressure oil is discharged to the tank 14 through the oil passage 27, thereby preventing the oil machine in the circuit from being damaged.

[0041] Also, in the oil passage 19 between the direction control valve 5 and the cylinder 6 in the main circuit, the oil passages 28 and 31 in the regeneration circuit are branched and connected. The oil passage 28 is provided on the cylinder 6 side, that is, on the head chamber 6-1 side, rather than the oil passage 31. In other words, the oil passage 31 is provided on the direction control valve 5 side rather than the oil passage 28.

[0042] An electromagnetic switching valve 30 is connected to the oil passage 28. Also, an oil passage 29 is connected to the electromagnetic switching valve 30. The electromagnetic switching valve 30 is a 2-port 2-position type normally closed electromagnetic switching valve and has a solenoid 30-1. The solenoid 30-1 is electrically connected to the controller 37 through the electrical signal line 39.

[0043] The controller 37 can output an electrical signal to the electromagnetic switching valves 30, 32 and the electromagnetic proportional pressure reducing valve 41 from a pre-built arithmetic circuit.

[0044] The electromagnetic switching valve 30 in the offset position makes the oil passage 28 in a non-communicating state with the oil passage 29. The oil passage 29 is branched and connected to the oil passage 33. An accumulator 34 and an electromagnetic switching valve 32 are connected to the oil passage 33. That is, the electromagnetic switching valve 30 in the offset position makes it impossible for the pressure oil to flow from the oil passage 19 to the accumulator 34.

[0045] When an electrical signal from the controller 37 is applied to the solenoid 30-1 through the electrical signal line 39 and the solenoid 30-1 is excited, the electromagnetic switching valve 30 moves the spool and switches to the onset position 30-2.

[0046] At the onset position 30-2, it has an opening degree corresponding to the electrical signal from the controller 37 (see FIG. 4). Also, a check valve 30-3 configured to allow oil to pass from the oil passage 28 toward the oil passage 29 is built into the onset position 30-2. That is, the electromagnetic switching valve 30 at the onset position 30-2 enables the inflow of pressure oil from the oil passage 19 to the accumulator 34.

[0047] An oil passage 31 is connected to the electromagnetic switching valve 32. The electromagnetic switching valve 32 is a 2-port 2-position type normally closed electromagnetic switching valve and has a solenoid 32-1. The solenoid 32-1 is electrically connected to the controller 37 through an electrical signal line 40.

[0048] The electromagnetic switching valve 32 at the offset position makes the oil passage 33 non-communicating with the oil passage 31. That is, the electromagnetic switching valve 32 at the offset position prevents the supply of pressure oil from the accumulator 34 to the oil passage 19.

[0049] When an electrical signal from the controller 37 is applied to the solenoid 32-1 through the electrical signal line 40 and the solenoid 32-1 is excited, the electromagnetic switching valve 32 moves the spool and switches to the onset position 32-2.

[0050] At the onset position 32-2, it has an opening degree corresponding to the electrical signal from the controller 37 (see FIG. 4). Also, a check valve 32-3 configured to allow oil to pass from the oil passage 33 toward the oil passage 31 is built into the onset position 32-2. That is, the electromagnetic switching valve 32 at the onset position 32-2 enables the supply of pressure oil from the accumulator 34 to the oil passage 19.

[0051] Also, a pressure detector 42 as accumulator pressure detection means and a pressure detector 43 as actuator pressure detection means are provided in the regeneration system circuit.

[0052] The pressure detector 42 is provided in the oil passage 33, detects the pressure PA in the oil passage 33, and outputs an electrical signal capable of specifying the pressure PA to the controller 37. The pressure PA in the oil passage 33 is substantially the same pressure as the pressure of the oil stored in the accumulator 34.

[0053] The pressure detector 43 is installed in the oil passage 31 and detects the pressure Ph in the oil passage 31, outputting an electrical signal that can identify the pressure Ph to the controller 37. The pressure Ph in the oil passage 31 is approximately the same as the pressure in the head chamber 6-1, which is connected via the oil passage 19.

[0054] The pilot circuit, which includes the pilot hydraulic pump 3, is equipped with pressure sensors 35 and 36.

[0055] The pressure detector 35 is located in the signal oil passage 9 and detects the pilot secondary pressure Px, which is the pilot pressure of the operating hydraulic signal in the signal oil passage 9. It then outputs an electrical signal that can identify the pilot secondary pressure Px to the controller 37.

[0056] The pressure detector 36 is installed in the signal oil passage 10 and detects the pilot secondary pressure Py, which is the pilot pressure of the operating hydraulic signal in the signal oil passage 10, and outputs an electrical signal that can identify the pilot secondary pressure Py to the controller 37.

[0057] Signal oil passage 9 is branched to signal oil passage 22. Signal oil passage 10 is branched to signal oil passage 23. Signal oil passages 22 and 23 are connected to shuttle valve 7. In other words, signal oil passages 9 and 10 are connected in parallel to shuttle valve 7. Also, signal oil passage 24 is connected to shuttle valve 7. Shuttle valve 7 is configured to allow the signal oil passage with the higher pilot pressure among signal oil passages 9 and 10 to be connected to signal oil passage 24.

[0058] In the following explanation, regardless of whether the oil flows from signal oil passage 9 to signal oil passage 24 or from signal oil passage 10 to signal oil passage 24, the pilot pressure of the operating hydraulic signal after passing through shuttle valve 7 will be referred to as the pilot signal pressure Pp.

[0059] The signal oil passage 24 is connected to an electromagnetic proportional pressure reducing valve 41, which acts as a pressure reducing valve. The electromagnetic proportional pressure reducing valve 41 is connected to a signal oil passage 45, which is connected to a signal pressure control unit 2-3, which is composed of a switching valve in the control mechanism 2-2, and a signal oil passage 46, which is connected to the tank 14.

[0060] The electromagnetic proportional pressure reducing valve 41 is a normally open type electromagnetic proportional pressure reducing valve and has a solenoid 41-1. The solenoid 41-1 is electrically connected to the controller 37 via an electrical signal line 44.

[0061] When no electrical signal is input from the controller 37 to the solenoid 41-1, the electromagnetic proportional pressure reducing valve 41 opens to its maximum degree, connecting signal oil passages 24 and 45, and disconnecting signal oil passages 45 and 46. The pilot signal pressure Pp of the operating hydraulic pressure signal acting on the signal pressure control unit 2-3 becomes a secondary pressure that is approximately the same as the pressure when passing through the shuttle valve 7 (see Figure 5).

[0062] Furthermore, if the secondary pressure after passing the electromagnetic proportional pressure reducing valve 41 when no electrical signal is input to the solenoid 41-1 is greater than the pressure after passing the electromagnetic proportional pressure reducing valve 41 when an electrical signal is input to the solenoid 41-1, then it may be less than the primary pressure when passing the shuttle valve 7, i.e., it may be reduced.

[0063] When an electrical signal from the controller 37 is applied to the solenoid 41-1 via the electrical signal line 44 and the electromagnetic proportional pressure reducing valve 41 is energized, it opens the signal oil passages 24 and 45 and opens the signal oil passages 45 and 46 to an opening degree corresponding to the electrical signal from the controller 37.

[0064] As a result, the electromagnetic proportional pressure reducing valve 41 reduces the pilot signal pressure Pp of the operating hydraulic pressure signal that is flowing from the signal oil passage 24 into the signal oil passage 45 to a secondary pressure corresponding to the electrical signal (see Figure 5), while releasing a portion of the operating hydraulic pressure signal into the tank 14, thereby maintaining the pilot signal pressure Pp acting on the signal pressure control unit 2-3 at a secondary pressure corresponding to the electrical signal.

[0065] The control mechanism 2-2 includes a signal pressure control unit 2-3 and a swash plate control unit 2-4, which is composed of a cylinder device. The signal pressure control unit 2-3 functions as a pressure reducing valve whose opening degree is adjusted according to the pilot signal pressure Pp of the operating hydraulic signal. The signal pressure control unit 2-3 is connected to a signal oil passage 25 that is branched and connected to the oil passage 15, a signal oil passage 47 that is connected to the swash plate control unit 2-4, and a signal oil passage 48 that is connected to the tank 14.

[0066] The signal pressure control unit 2-3 deconnects signal oil passages 25 and 47 and connects signal oil passages 47 and 48 if the pilot signal pressure Pp is the same dynamic pressure as the pressure when the remote control valve 4 is not operated. As a result, the pressure of the swash plate control hydraulic signal acting on the swash plate control unit 2-4 becomes approximately the same dynamic pressure as the pressure in tank 14.

[0067] Furthermore, if the pilot signal pressure Pp is higher than the pressure when the remote control valve 4 is not operated, and its opening force exceeds the force of the return spring, the signal pressure control unit 2-3 will connect the signal oil passages 25 and 47 and connect the signal oil passages 47 and 48.

[0068] As a result, the signal pressure control unit 2-3 reduces the pressure oil flowing from the signal oil passage 25 to the signal oil passage 47 from the primary pressure Pin at the time of discharge of the main hydraulic pump 2 to the secondary pressure, while releasing a portion of the operating hydraulic signal into the tank 14. This maintains the pressure of the swash plate control hydraulic signal acting on the swash plate control unit 2-4 at a secondary pressure corresponding to the pilot signal pressure Pp.

[0069] The swash plate control unit 2-4 adjusts the swash plate angle of the swash plate 2-1 in the main hydraulic pump 2 according to the pressure of the swash plate control hydraulic signal. The pump flow rate Q of the main hydraulic pump 2 is controlled according to the swash plate angle of the swash plate 2-1, in other words, according to the pilot signal pressure Pp of the operating hydraulic signal. As shown in Figure 6, the pump flow rate Q of the main hydraulic pump 2 increases in proportion to the increase in the pilot signal pressure Pp.

[0070] Next, the operation of the accumulator 34 will be explained. When the lever 4-1 in the remote control valve 4 is operated in the contraction direction B, an electrical signal is output from the pressure detector 36 to the controller 37. When the controller 37 receives an electrical signal from the pressure detector 36, it determines whether or not it is necessary to accumulate pressure in the accumulator 34 based on the electrical signal input from the pressure detector 42, i.e., the pressure PA.

[0071] When the controller 37 determines that the accumulator 34 needs to accumulate pressure, that is, that the allowable pressure level has not been reached, it outputs an electrical signal to the electrical signal line 39. In response to this electrical signal, the electromagnetic switching valve 30 switches to the onset position 30-2 and opens to the degree corresponding to the electrical signal. As a result, some of the return oil discharged from the head chamber 6-1 into the oil passage 19 flows into the accumulator 34 through the oil passages 28, 29, the electromagnetic switching valve 30, and the oil passage 33.

[0072] It goes without saying that the opening of the electromagnetic switching valve 30 is adjusted so that the retraction speed Ve of the cylinder rod 6-3 does not exceed the retraction speed Ve with respect to the operating amount L of the lever 4-1.

[0073] Furthermore, if the controller 37 determines that pressure accumulation in the accumulator 34 is unnecessary, that is, that the allowable pressure level has been reached, it stops sending an electrical signal to the electrical signal line 39. In response, the electromagnetic switching valve 30 switches to the offset position. As a result, the return oil discharged from the head chamber 6-1 into the oil passage 19 is discharged to the tank 14 through the directional switching valve 5 and the oil passage 21. The same applies when, after an electrical signal is input from the pressure detector 36, it is determined that pressure accumulation in the accumulator 34 is unnecessary.

[0074] Furthermore, when the lever 4-1 in the remote control valve 4 is operated in the contraction direction B, that is, when an electrical signal is input from the pressure detector 36 to the controller 37, the controller 37 does not output an electrical signal to the electromagnetic switching valve 32 and the electromagnetic proportional pressure reducing valve 41.

[0075] As a result, when operating in the retraction direction B, a pump flow rate Q corresponding to the amount L operated by lever 4-1 is discharged from the main hydraulic pump 2 (see Figure 4). The retraction speed Ve of the cylinder rod 6-3 with respect to the amount L operated in the retraction direction B has a characteristic curve as shown in Figure 7.

[0076] When the lever 4-1 in the remote control valve 4 is operated in the extension direction A, an electrical signal is output from the pressure detector 35 to the controller 37. When the controller 37 receives an electrical signal from the pressure detector 35, it determines whether or not pressurized oil can be supplied from the accumulator 34 to the head chamber 6-1 based on the electrical signals input from the pressure detectors 42 and 43, i.e., the pressures PA and Ph.

[0077] When the controller 37 determines that it is unable to supply pressurized oil from the accumulator 34 to the head chamber 6-1, that is, that the pressure PA is less than or equal to the sum of the pressure Ph and a predetermined value α (PA ≤ Ph + α), it does not output an electrical signal to any of the electromagnetic switching valves 30, 32 and the electromagnetic proportional pressure reducing valve 41. Note that the value α may be zero.

[0078] In this case, a pump flow rate Q corresponding to the amount L of the lever 4-1 is discharged from the main hydraulic pump 2 (see Figure 4). The extension speed Ve of the cylinder rod 6-3 with respect to the amount L of the extension direction A has a characteristic curve as shown in Figure 7.

[0079] Furthermore, when the controller 37 determines that pressurized oil can be supplied from the accumulator 34 to the head chamber 6-1, that is, that the pressure PA exceeds the sum of the pressure Ph and a predetermined value α (PA > Ph + α), it outputs an electrical signal to the electrical signal line 40. In response to this electrical signal, the electromagnetic switching valve 32 switches to the onset position 32-2 and opens to the degree corresponding to the electrical signal.

[0080] It goes without saying that the opening degree of the electromagnetic switching valve 32 is adjusted so that the extension speed Ve of the cylinder rod 6-3 does not exceed the extension speed Ve with respect to the operating amount L of the lever 4-1.

[0081] Furthermore, the controller 37 calculates the flow rate Qx of pressurized oil supplied from the accumulator 34 to the head chamber 6-1 at that moment using the pressures PA and Ph.

[0082] Regarding the flow rate Qx, it is known that when the sealed gas pressure in the accumulator 34 is P1, the minimum operating pressure is P2, the maximum operating pressure is P3, and the volume of the accumulator 34 is V1, a volume Vw expressed by the following equation 1 is discharged from the accumulator 34. However, m and n are the polytropic indices during accumulation and discharge, respectively.

[0083] If we reflect the minimum operating pressure at that moment as Ph, the maximum operating pressure as PA, and the volume discharged from the accumulator 34 as the flow rate Qx in Equation 1, the flow rate Qx becomes Equation 2 below.

[0084] The controller 37 then outputs an electrical signal to the electrical signal line 44 based on the calculated flow rate Qx in order to reduce the pump flow rate Q of the main hydraulic pump 2 by the calculated flow rate Qx. The electrical signal output based on the flow rate Qx may be an electrical signal extracted from a correspondence table of electrical signals set in advance for each value of flow rate Qx, according to the value of flow rate Qx at that moment, or it may be an electrical signal calculated from the value of flow rate Qx at that moment based on a pre-registered calculation formula, and may be changed as appropriate.

[0085] In response to this electrical signal, the electromagnetic proportional pressure reducing valve 41 reduces the pilot signal pressure Pp of the operating hydraulic signal acting on the signal pressure control unit 2-3 by a pressure of Ppx (see Figure 6). As a result, the pump flow rate Q decreases by a flow rate of Qx.

[0086] Referring to Figure 6, in the state before pressurized oil is supplied from the accumulator 34 to the head chamber 6-1, the operating amount L of lever 4-1 is at its maximum Lm, the pilot signal pressure Pp is at its maximum value Ppmax, and the pump flow rate Q is at Qmax.

[0087] As described above, the controller 37 calculates the flow rate Qx discharged from the accumulator 34, and when an electrical signal based on the flow rate Qx is input to the electromagnetic proportional pressure reducing valve 41, even though the operating amount L of lever 4-1 is at its maximum Lm, the pilot signal pressure Pp is reduced to Pp1 (Pp1 = Ppmax - Ppx), and the pump flow rate Q decreases to Q1 (Q1 = Qmax - Qx). In other words, the power required for the main hydraulic pump 2 can be reduced.

[0088] The flow rate supplied to the head chamber 6-1 is the sum of the flow rate Qx discharged from the accumulator 34 and the pump flow rate Q1, so the flow rate is Qmax (Qmax = Q1 + Qx). In other words, the pump flow rate Qmax can be made approximately the same as when the lever 4-1 is operated to its maximum Lm and no pressurized oil is supplied from the accumulator 34 to the head chamber 6-1.

[0089] As a result, the extension speed Ve of the cylinder rod 6-3 becomes the same extension speed Vemax as when the accumulator 34 is not used.

[0090] Furthermore, the controller 37 calculates the instantaneous flow rate Qx at predetermined intervals (for example, every 0.1 seconds) and outputs an electrical signal based on the flow rate Qx to the electrical signal line 44. Therefore, even if the flow rate Qx changes, the pump flow rate Q can be controlled accordingly.

[0091] This makes it possible to set the flow rate supplied from the main hydraulic pump 2 and the accumulator 34 to the head chamber 6-1 to approximately the same as the pump flow rate Q when the accumulator 34 is not supplying pressurized oil to the head chamber 6-1. In other words, the extension speed Ve of the cylinder rod 6-3 when the accumulator 34 is used can be maintained at the same extension speed Ve as when the accumulator 34 is not used.

[0092] Furthermore, the timing at which the controller 37 calculates the instantaneous flow rate Qx is not limited to predetermined intervals, but may also be changed as appropriate, for example, when the pressure PA changes by more than a predetermined value.

[0093] As described above, the hydraulic circuit 101 of this embodiment can accurately control the cylinder 6 by sequentially adjusting the output of the main hydraulic pump 2 based on the pressure Ph in the head chamber 6-1 of the cylinder 6 and the pressure PA of the accumulator 34, thereby matching the output of the main hydraulic pump 2 according to the capacity of the accumulator 34.

[0094] Furthermore, the hydraulic circuit 101 has a control mechanism 2-2 as an output control means and an electromagnetic proportional pressure reducing valve 41 whose opening degree is adjusted based on pressures PA and Ph, making its configuration simple.

[0095] Furthermore, since the hydraulic circuit 101 has a controller 37 as an output control means, it can adjust the opening degree of the electromagnetic proportional pressure reducing valve 41 based on the pressures PA and Ph with good accuracy.

[0096] Furthermore, the hydraulic circuit 101 includes a pilot hydraulic pump 3 for outputting a pilot signal pressure Pp corresponding to the amount L of operation of the lever 4-1, and a remote control valve 4. The actuator is a cylinder 6 driven by the amount L of operation of the lever 4-1. This makes it less likely for the operator to feel any discomfort when using the accumulator 34 and the main hydraulic pump 2 together.

[0097] Furthermore, the accumulator 34 is connected to the oil passage 19 between the directional control valve 5 and the cylinder 6. This eliminates the need to employ a directional control valve capable of handling the sum of the pressure Pin of the pressurized oil discharged from the main hydraulic pump 2 and the pressure PA of the pressurized oil discharged from the accumulator 34 (Pin + PA), thus allowing the use of a compact directional control valve 5.

[0098] Furthermore, since the hydraulic circuit 101 uses a cylinder 6 as the actuator and allows pressurized oil to flow between the head chamber 6-1 and the accumulator 34 through the oil passage 19, its configuration and control are simpler than those of a hydraulic circuit that allows pressurized oil to flow between the rod chamber 6-2 and the accumulator 34. As a result, the hydraulic circuit 101 can drive the cylinder 6 more smoothly than a hydraulic circuit that allows pressurized oil to flow between the rod chamber 6-2 and the accumulator 34.

[0099] Although embodiments of the present invention have been described above with reference to the drawings, the specific configurations are not limited to these embodiments, and any changes or additions that do not depart from the spirit of the present invention are also included.

[0100] For example, in the above embodiment, the fluid pressure circuit was described as a hydraulic circuit in which oil is pumped, but it 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.

[0101] Furthermore, although an electromagnetic proportional pressure reducing valve was exemplified as a pressure reducing valve in the above embodiment, the invention is not limited to this, and any pressure reducing valve may be appropriately modified. For example, a pilot-operated pressure reducing valve that operates in response to an external hydraulic signal, as shown in Figure 8, may also be used.

[0102] Furthermore, although the operating means in the above embodiment were described as a remote control valve and a pilot hydraulic pump, they are not limited to these, and may be, for example, an electric remote control. With such a configuration, the output of the fluid supply source may be controlled based on an electrical signal directly input to the controller from the electric remote control.

[0103] Furthermore, although the above embodiment described the pressure detector for detecting the accumulator pressure as being connected to an oil passage communicating with the accumulator, it is not limited to this configuration, and the connection destination may be changed as appropriate as long as the internal pressure of the accumulator can be measured. For example, the internal pressure of the accumulator may be estimated from the accumulator's sealed gas pressure, or a switching valve may be switched according to the change in the accumulator's sealed gas pressure. The same applies to the pressure detector for detecting the actuator pressure.

[0104] 1 Drive mechanism (fluid supply source) 2 Main hydraulic pump (fluid supply source) 2-2 Control mechanism 3 Pilot hydraulic pump (operating means) 4 Hydraulic remote control valve for boom (operating means) 5 Directional control valve for boom (directional control valve) 6 Boom cylinder (actuator, cylinder) 34 Accumulator 37 Controller (output control means) 41 Electromagnetic proportional pressure reducing valve (output control means) 42 Pressure detector (accumulator pressure detection means) 43 Pressure detector (actuator pressure detection means) 101 Hydraulic circuit (fluid pressure circuit) L Operating amount PA Pressure (accumulator pressure) Ph Pressure (actuator pressure) Pp Pilot signal pressure (pilot pressure) Px, Py Pilot secondary pressure (pilot pressure)

Claims

1. A fluid pressure circuit comprising: a fluid supply source; an actuator connected to the fluid supply source; a directional control valve provided in a flow path between the fluid supply source and the actuator for switching the destination of the fluid supplied from the fluid supply source; output control means for controlling the output of the fluid supply source; and an accumulator provided to supply pressurized fluid to the flow path, wherein the fluid pressure circuit further comprises: an actuator pressure detection means for detecting the pressure of the actuator; and an accumulator pressure detection means for detecting the pressure of the accumulator, and the output control means is capable of controlling the output of the fluid supply source based on the pressure of the actuator and the pressure of the accumulator.

2. The fluid pressure circuit according to claim 1, wherein the output control means comprises a control mechanism that receives pilot pressure and controls the output of the fluid supply source, and a pressure reducing valve that reduces the pilot pressure, and the opening of the pressure reducing valve is adjusted based on the pressure of the actuator and the pressure of the accumulator.

3. The fluid pressure circuit according to claim 2, comprising an operating means for outputting the pilot pressure corresponding to the operating amount, wherein the actuator is driven according to the operating amount.

4. The fluid pressure circuit according to any one of claims 1 to 3, wherein the accumulator is connected between the directional control valve and the actuator in the flow path.

5. The fluid pressure circuit according to claim 1, wherein the actuator is a cylinder.

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