JP2008014440A - Hydraulic control system of working machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a pressure loss generated at the passing of a valve when installing the valve for controlling the flow-in/flow-out of oil to/from an accumulator, in a hydraulic control system which is constituted in such a manner that the discharged oil of a hydraulic cylinder is accumulated in the accumulator when a working part descends, and when the working part ascends, the accumulated oil in the accumulator is fed to the hydraulic cylinder. <P>SOLUTION: An accumulator check valve 45 is constituted in such a manner that, a nonreturn state for blocking the flow-out of oil from the accumulator and an open state for reducing a force acting on a valve path closing side on the basis of an external signal are freely switchable, the flow-out of the oil from the accumulator 36 is blocked by turning the accumulator check valve 45 nonreturnable when a boom is stopped, and when the boom ascends, the flow-out of the oil form the accumulator 36 or the flow-in of the oil to the accumulator 36 is allowed by turning the accumulator check valve 45 open. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention belongs to the technical field of a hydraulic control system in a working machine that can recover and reuse the potential energy of the working part in a working machine that includes a working part that moves up and down.

In general, a work machine such as a hydraulic excavator or a crane includes a working unit that can freely move up and down, and the working unit is configured to be lifted and lowered based on an expansion and contraction operation of a hydraulic cylinder supplied with pressure oil from a hydraulic pump. However, in this case, conventionally, the oil discharged from the hydraulic cylinder weight holding side oil chamber to the oil tank when the working unit is lowered is supplied to the hydraulic cylinder in order to prevent a sudden drop due to its own weight. Meter-out control is performed by a throttle provided in a control valve that performs discharge control. That is, the working unit located above the ground has potential energy, but the potential energy is converted into thermal energy when passing through the throttle of the control valve, and the thermal energy is further converted into an oil cooler. Will be discharged into the atmosphere, resulting in wasted energy loss.
Therefore, in order to recover and reuse the potential energy of the working unit, an auxiliary hydraulic cylinder (assist cylinder) is provided in addition to the normal hydraulic cylinder, and when the working unit is lowered, the auxiliary hydraulic cylinder is moved from the weight holding side oil chamber. A technique is disclosed in which the discharged oil is accumulated in an accumulator and the pressure oil accumulated in the accumulator is supplied to the weight holding side of the auxiliary hydraulic cylinder when the working unit is raised (for example, Patent Document 1). reference.). In this device, a pilot type check valve is arranged between the weight holding side oil chamber of the auxiliary hydraulic cylinder and the accumulator, and the pilot type check valve allows the oil from the auxiliary hydraulic cylinder to the accumulator when the working part is lowered. It is configured to prevent flow of oil from the accumulator to the auxiliary hydraulic cylinder when the working unit is stopped while allowing flow of oil from the accumulator to the auxiliary hydraulic cylinder when the working unit is raised. Yes.
Patent Document 1 discloses a technique using a spool switching valve in place of the pilot check valve. However, the spool switching valve is a kind of slip valve, and a minute leak cannot be avoided. There is a problem that oil cannot be reliably prevented from leaking from the accumulator to the auxiliary hydraulic cylinder when the working unit is stopped.
Japanese Patent No. 2582310

  By the way, the valve body of the pilot type check valve is generally pressed to the valve path opening side by the upstream pressure, while being pressed to the valve path closing side by the downstream pressure and the pressing force of the spring. The valve body can be moved to the valve path opening side by the input of pressure. When such a pilot type check valve is arranged between the hydraulic cylinder and the accumulator as in Patent Document 1, the oil discharged from the hydraulic cylinder and accumulated in the accumulator when the working unit is lowered is stored in the accumulator pressure and the accumulator. There is a problem that the valve path is opened while resisting the spring pressing force and passes through the pilot type check valve, causing a small pressure loss, and the oil discharged from the hydraulic cylinder cannot be efficiently accumulated in the accumulator. There is a problem to be solved by the present invention.

The present invention has been created in order to solve these problems in view of the above situation, and the invention of claim 1 is directed to the oil discharged from the hydraulic cylinder when the working unit that moves up and down is lowered. In the hydraulic control system for a work machine configured to store oil accumulated in the accumulator while supplying the oil accumulated in the accumulator to the hydraulic cylinder when the working unit is raised, the accumulator is connected to the oil flowing into the accumulator and from the accumulator. The accumulator check valve valve is connected to the inflow / outflow oil passage that becomes the oil outflow passage of the accumulator, and has a valve passage that opens and closes between the accumulator and the inflow / outflow oil passage, In addition, when the inflow / outflow passage pressure is higher than the accumulator pressure by a predetermined pressure or higher, the The oil is allowed to flow into the motor, but the non-return state that prevents the oil from flowing into the inflow / outflow oil passage from the accumulator and the force acting on the valve closing side based on the external signal is reduced or the valve opening is operated By increasing the force, it is possible to switch between an open state allowing oil inflow from the inflow / outflow oil passage to the accumulator and oil outflow from the accumulator to the inflow / outflow oil passage, and an accumulator check valve is provided when the working part is stopped. While preventing the oil outflow from the accumulator to the inflow / outflow oil passage in the non-return state, the accumulator check valve is opened when the working part is raised and lowered, and the oil outflow from the accumulator to the inflow / outflow oil passage It is the hydraulic control system in the working machine characterized by performing the oil inflow to the accumulator.
By doing so, when the working part is stopped, the check-out accumulator check valve prevents oil from flowing out from the accumulator to the inflow / outflow oil path, and reliably holds the high-pressure oil accumulated in the accumulator. On the other hand, when the working part is raised, the accumulator check valve in the open state allows the oil to flow out from the accumulator to the inflow / outflow oil passage, and the oil accumulated in the accumulator can be supplied to the hydraulic cylinder. Furthermore, when the working unit is lowered, by opening the accumulator check valve, the oil discharged from the hydraulic cylinder can pass through the accumulator check valve with almost no resistance. The discharged oil can be efficiently accumulated in the accumulator.
According to a second aspect of the present invention, the accumulator check valve has a valve path that opens and closes between the accumulator and the inflow / outflow oil path, and is pressed toward the valve path side by the inflow / outflow oil path pressure and the accumulator pressure. On the other hand, a poppet valve that is pressed to the valve path closing side by a pressing force of the spring and an accumulator pressure that is introduced into the spring chamber via the introduction oil path, and a control valve that opens and closes the introduction oil path based on an external signal The control valve is opened and the accumulator pressure is introduced into the spring chamber, and the check valve is brought into a non-return state, while the control valve is closed to stop introducing the accumulator pressure into the spring chamber, and the spring chamber 2. The hydraulic control system for a work machine according to claim 1, wherein when the pressure oil is drained, the force acting on the valve path closing side is reduced and the valve is opened. 3.
In this manner, the accumulator check valve can be configured to be switchable between a check state and an open state based on an external signal.
According to a third aspect of the present invention, the hydraulic control system includes a hydraulic pump that sucks oil accumulated in the accumulator when the working unit is raised and supplies the hydraulic cylinder to the hydraulic cylinder, while the inflow / outflow oil passage is oil discharged from the hydraulic cylinder. The hydraulic control system for a work machine according to claim 1 or 2, wherein the hydraulic control system is connected to a recovery oil passage that guides oil to an accumulator, and a suction oil passage that guides oil accumulated in the accumulator to the suction side of the hydraulic pump. is there.
And by doing in this way, when the working part descends, the hydraulic oil flows into the accumulator when accumulating the oil discharged from the hydraulic cylinder in the accumulator, and when the working part rises, the accumulator accumulated oil is fed through the hydraulic pump via the hydraulic pump. The accumulator check valve can control the oil outflow from the accumulator when supplied to the engine and the prevention of the accumulator pressure oil outflow when the working unit is stopped.

  Next, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, reference numeral 1 denotes a hydraulic excavator that is an example of a work machine. The hydraulic excavator 1 includes a crawler-type lower traveling body 2 and an upper revolving body 3 that is rotatably supported above the lower traveling body 2. The working unit 4 is composed of various parts such as a working unit 4 mounted on the front of the upper swing body 3, and the working unit 4 further includes a boom 5 whose base end portion is supported by the upper swing body 3 so as to swing up and down, The arm 5 is supported at the front end of the boom 5 so as to be swingable back and forth, and the bucket 7 is attached to the front end of the arm 6.

  Reference numeral 8 denotes a pair of left and right boom cylinders (corresponding to the hydraulic cylinders of the present invention) that extend and contract to swing the boom 5 up and down. The boom cylinder 8 is operated by the pressure of the head side oil chamber 8a. And the boom 5 is lifted by the pressure oil supply to the head side oil chamber 8a and the oil discharge from the rod side oil chamber 8b, and the pressure oil supply to the rod side oil chamber 8b. Further, the boom 5 is lowered by being reduced by discharging the oil from the head side oil chamber 8a. As the boom 5 rises, the potential energy of the working unit 4 increases. The potential energy is recovered when the boom 5 is lowered by a hydraulic control system, which will be described later. It is used when the boom 5 is raised.

  Next, the hydraulic control system will be described with reference to the circuit diagrams of FIGS. 2 and 3. In these drawings, numerals 9 and 10 are connected to an engine E mounted on the hydraulic excavator 1 via a pump drive gear portion G. The first and second main pumps are configured such that the first and second main pumps 9 and 10 suck the hydraulic oil from the oil tank 11 and discharge it to the first and second pump oil passages 12 and 13. It is configured. 2 and 3, circled numbers are connector symbols, and the corresponding circled numbers are connected to each other.

  Reference numerals 14 and 15 denote first and second regulators for controlling the discharge flow rates of the first and second main pumps 9 and 10, respectively. The first and second regulators 14 and 15 are controlled by a controller 16 described later. In response to the control signal pressure from the main pump control electromagnetic proportional pressure reducing valve 17, the pump operates to produce a pump output corresponding to the engine speed and the work load, and the discharge pressures of the first and second main pumps 9 and 10. In response to constant horsepower control. Further, the first and second regulators 14 and 15 are configured to perform negative control flow rate control for increasing or decreasing the pump flow rate in accordance with the movement strokes of the spools of the first and second control valves 18 and 19 described later. .

  On the other hand, the first and second control valves 18 and 19 are direction switching valves respectively connected to the first and second pump oil passages 12 and 13, and the first and second control valves 18 and 19 The oil discharged from the first and second main pumps 9 and 10 is operated to be supplied to the boom cylinder 8. The first and second main pumps 9 and 10 are not only the boom cylinder 8 but also a plurality of other hydraulic actuators (not shown, travel motor, swing motor, arm cylinder, bucket cylinder) provided in the hydraulic excavator 1. Etc.), and control valves for other hydraulic actuators are connected to the first and second pump oil passages 12 and 13, but these are omitted.

  The first control valve 18 is composed of a spool valve having ascending and descending pilot ports 18a and 18b. When no pilot pressure is input to the pilot ports 18a and 18b, the boom cylinder 8 is located at a neutral position N where oil is not supplied or discharged, but when the pilot pressure is input to the ascending pilot port 18a, the spool moves, and the pressure oil of the first main pump 9 is transferred to the cylinder head side. While supplying oil to the head side oil chamber 8a of the boom cylinder 8 via the oil passage 20, oil discharged from the rod side oil chamber 8b to the cylinder rod side oil passage 21 is returned to the oil tank 11 via the return oil passage 22. The position is switched to the ascending side position X. Further, when the pilot pressure is input to the descending pilot port 18b, the spool moves to the side opposite to the ascending position X, and the oil discharged from the head side oil chamber 8a to the cylinder head side oil passage 20 is discharged. Is switched to a descending position Y to be supplied from the cylinder rod side oil passage 21 to the rod side oil chamber 8b via the regeneration valve passage 18c. The cylinder head side oil passage 20 is an oil passage connected to the head side oil chamber 8a to supply and discharge oil to the head side oil chamber 8a of the boom cylinder 8, and the cylinder rod side oil passage 21 is a boom. This is an oil passage connected to the rod side oil chamber 8b to supply and discharge oil to the rod side oil chamber 8b of the cylinder 8.

  Here, the regeneration valve path 18c provided in the first control valve 18 at the descending position Y is a valve path that communicates the head side oil chamber 8a and the rod side oil chamber 8b of the boom cylinder 8, The regeneration valve path 18c is provided with a check valve 18d that restricts the flow of oil from the head-side oil chamber 8a to the rod-side oil chamber 8b but prevents the reverse flow, and a throttle 18e. Thus, as described above, when the first control valve 18 is at the lowering position Y, the oil discharged from the head side oil chamber 8a is supplied to the rod side oil chamber 8b via the regeneration valve path 18c. However, the flow rate depends on the opening characteristic of the throttle 18e arranged in the regeneration valve path 18c (the opening characteristic of the throttle 18e is set according to the spool movement stroke of the first control valve 18), and the head side It changes with the differential pressure | voltage of the oil chamber 8a and the rod side oil chamber 8b.

  On the other hand, the second control valve 19 is constituted by a spool valve provided with an ascending pilot port 19a, and when no pilot pressure is input to the ascending pilot port 19a, the oil supply / discharge of the boom cylinder 8 is performed. The spool is moved by the pilot pressure being input to the ascending-side pilot port 19a, and the pressure oil of the second main pump 10 passes through the cylinder head-side oil passage 20. The boom cylinder 8 is configured to switch to the ascending position X supplied to the head side oil chamber 8a.

  Reference numerals 23, 24, and 25 denote first ascending side, first descending side, and second ascending side electromagnetic proportional pressure reducing valves. These electromagnetic proportional pressure reducing valves 23, 24, and 25 are controlled by a control signal from the controller 16. Based on this, the first control valve 18 operates to output pilot pressure to the ascending pilot port 18a, the descending pilot port 18b, and the ascending pilot port 19a of the second control valve 19, respectively. The first and second control valves 18, 19 correspond to the increase / decrease in the pilot pressure output from the first ascending side, first descending side, and second ascending electromagnetic proportional pressure reducing valves 23, 24, 25. The movement stroke of the spool is increased or decreased, whereby the flow rate of the supply / discharge oil from the first and second control valves 18 and 19 to the boom cylinder 8 is controlled. 2 and 3, reference numeral 26 denotes a pilot pump serving as a pilot hydraulic pressure source.

  Further, the first and second control valves 18 and 19 have a center bypass for flowing the pressure oil of the first and second main pumps 9 and 10 to the oil tank 11 via the first and second negative control valves 27 and 28. Valve paths 18f and 19b are formed. The opening amount of the center bypass valve passages 18f and 19b is the largest when the first and second control valves 18 and 19 are in the neutral position N, and becomes smaller as the moving stroke of the spool switched to the rising side position X becomes larger. However, the center bypass valve path 18f of the first control valve 18 at the descending position Y has a characteristic of maintaining a large opening regardless of the movement stroke of the spool. The passage flow rate of the center bypass valve path 18f of the first control valve 18 at the position Y is set so as not to change from the passage flow rate at the neutral position N. The passage flow rate of the center bypass valve passages 18f and 19b is input to the first and second regulators 14 and 15 as a negative control control signal, and the first passage flow rate of the center bypass valve passages 18f and 19b decreases. The so-called negative control flow rate control in which the discharge flow rate of the second main pumps 9 and 10 is increased is performed. Here, as described above, the passage flow rate of the center bypass valve passage 18f of the first control valve 18 does not change from that at the neutral position N even when the first control valve 18 is switched to the descending position Y. The discharge flow rate of the first main pump 9 when the valve 18 is in the descending position Y is controlled to be minimized by negative control flow rate control.

  Further, 29 is a drift reduction valve disposed in the cylinder head side oil passage 20, and 30 is an electromagnetic switching valve for a drift reduction valve that switches from the OFF position N to the ON position X based on the ON signal from the controller 16. The drift reducing valve 29 always allows the flow of oil from the first and second control valves 18 and 19 and the third control valve 37 described later to the head side oil chamber 8a of the boom cylinder 8, but in the reverse direction. This flow is configured to be blocked when the drift reducing valve electromagnetic switching valve 30 is in the OFF position N and allowed only when it is in the ON position X. Reference numeral 31 denotes a relief valve connected to the cylinder head side oil passage 20, and the maximum pressure of the cylinder head side oil passage 20 is limited by the relief valve 31.

  On the other hand, 32 is a dedicated pump (corresponding to the hydraulic pump of the present invention), which is also connected to the engine E via the pump drive gear portion G. The dedicated pump 32 is connected to the suction oil passage 33. The oil supplied from the pump is sucked and discharged to the dedicated pump oil passage 34, and the discharge flow rate control of the dedicated pump 32 is performed by a dedicated pump regulator 35 that operates based on a control signal output from the controller 16. It is configured.

  Here, as will be described later, the accumulated oil of the accumulator 36 or the discharged oil from the head side oil chamber 8a of the boom cylinder 8 is guided to the suction oil passage 33, and thus the dedicated pump. 32 is configured to suck in the accumulated oil in the accumulator 36 or the oil discharged from the head side oil chamber 8a of the boom cylinder 8 and discharge it to the dedicated pump oil passage 34.

  Reference numeral 37 denotes a third control valve connected to the dedicated pump oil passage 34. The third control valve 37 supplies pressure oil discharged from the dedicated pump 32 to the boom based on a control signal from the controller 16. Actuate to feed cylinder 8.

  The third control valve 37 will be described in detail. The third control valve 37 is based on the operation of the third ascending side and third descending electrooil conversion valves 38 and 39 to which a control signal from the controller 16 is input. When the operation signal is not input to both the electro-hydraulic conversion valves 38 and 39, the spool is moved in the neutral position N where no oil is supplied to or discharged from the boom cylinder 8. When the operation signal is input to the third ascending-side electro-oil conversion valve 38, the spool moves, and the discharge oil of the dedicated pump 32 passes through the cylinder head-side oil passage 20 to the head-side oil chamber of the boom cylinder 8. While being supplied to 8 a, the oil discharged from the rod side oil chamber 8 b to the cylinder rod side oil passage 21 is switched to the ascending position X through which the oil flows to the oil tank 11 via the return oil passage 22. Further, when an operation control signal is input to the third lowering-side electrooil conversion valve 39, the spool moves to the side opposite to the ascending-side position X, and the discharge oil of the dedicated pump 32 is supplied to the cylinder rod-side oil. It is configured to switch to a lower position Y to be supplied to the rod side oil chamber 8b of the boom cylinder 8 via the path 21.

  The movement stroke of the spool of the third control valve 37 is controlled to increase / decrease according to the signal value of the operation signal input from the controller 16 to the third ascending side and third descending electrooil conversion valves 38, 39. The flow rate of the supply / discharge oil from the third control valve 37 to the boom cylinder 8 is controlled by increasing / decreasing the movement stroke of the spool.

  Further, reference numeral 40 denotes a recovery oil passage branched from the cylinder head side oil passage 20, and a recovery valve 41 is arranged in the recovery oil passage 40, and a downstream side of the recovery valve 41. Is connected to the suction oil passage 33, and is further connected to an accumulator oil passage 42 via an inflow / outlet oil passage 62 described later. The recovery oil passage 40 is provided with a check valve 43 that allows oil flow from the cylinder head side oil passage 20 to the accumulator oil passage 42 and the suction oil passage 33 but prevents reverse flow. . Thus, the oil discharged from the head side oil chamber 8 a of the boom cylinder 8 to the cylinder head side oil passage 20 can be guided to the accumulator oil passage 42 and the suction oil passage 33 via the recovery oil passage 40. It is like that.

  The recovery valve 41 is an open / close valve in which the spool moves based on the operation of the recovery electro-oil conversion valve 44 to which a control signal from the controller 16 is input. In a state in which no input is made, the recovery oil passage 40 is positioned at the closed position N. However, when the operation signal is input to the recovery electro-oil conversion valve 44, the spool moves and the recovery oil passage 40 is It is configured to switch to the open position X to be opened.

  The movement stroke of the spool of the recovery valve 41 is controlled to increase or decrease according to the signal value of the operation signal input from the controller 16 to the recovery electro-oil conversion valve 44. By the increase / decrease control, the flow rate of the oil flowing from the head side oil chamber 8a of the boom cylinder 8 to the accumulator oil passage 42 and the suction oil passage 33 via the recovery oil passage 40 is controlled.

  On the other hand, the inflow / outflow oil passage 62 is an oil passage whose one end is connected to the recovered oil passage 40 and the suction oil passage 33 and whose other end is connected to an accumulator check valve 45 described later, and an accumulator oil passage 42. Is an oil passage from the accumulator check valve 45 to the accumulator 36, and the maximum pressure of the accumulator oil passage 42 is limited by a relief valve 46 connected to the accumulator oil passage 42. In the present embodiment, the accumulator 36 is an optimal bladder type for storing hydraulic energy, but is not limited thereto, and may be a piston type, for example.

  The accumulator check valve 45 is a valve for controlling the oil inflow from the inflow / outflow oil passage 62 to the accumulator 36 and the oil outflow from the accumulator 36 to the inflow / outflow oil passage 62. And an electromagnetic switching valve for an accumulator check valve (corresponding to the control valve of the present invention) 48 that switches from the OFF position N to the ON position X based on a signal output from 16 (corresponding to an external signal of the present invention). Configured.

  As shown in FIG. 4, the poppet valve 47 includes a poppet 47a, a first port 47b connected to the inflow / outflow oil passage 62, a second port 47c connected to the accumulator oil passage 42, and these first ports 47b. 47d for opening and closing between the second port 47c and the second port 47c (corresponding to a valve path for opening and closing between the accumulator and the inflow / outflow oil passage of the present invention) 47d, a spring 47e, and a spring in which the spring 47e is housed A chamber 47f and an introduction oil passage 47g for introducing the pressure of the accumulator oil passage 42 input from the second port 47c into the spring chamber 47f, and the poppet 47a has an inflow / outflow oil input from the first port 47b. The pressure of the passage 62d (pressure receiving area A) and the pressure of the accumulator oil passage 42 (pressure receiving area B) input from the second port 47c are pressed to the side where the valve passage 47d opens. That one, so that the valve passage 47d is pressed close to the side by the pressing force and the pressure of the spring chamber 47f of the spring 47e (pressure receiving area C). In this case, the poppet 47a is designed such that the pressure receiving area (A + B) of the oil pressure acting on the valve path opening side is equal to the pressure receiving area C of the oil pressure acting on the valve path closing side (C = A + B).

  On the other hand, the accumulator check valve electromagnetic switching valve 48 is disposed in the middle of the introduction oil passage 47g, and switches from the OFF position N to the ON position X based on the ON signal output from the controller 16. When the accumulator check valve electromagnetic switching valve 48 is in the OFF position N, the introduction oil passage 47g is opened, that is, the pressure in the accumulator oil passage 42 is introduced into the spring chamber 47f. However, by switching to the ON position X, the introduction oil passage 47g is closed and the spring chamber 47f is communicated with the oil tank 11, that is, the pressure in the accumulator oil passage 42 is not introduced into the spring chamber 47f, and the pressure in the spring chamber 47f is The oil is drained.

In the state where the accumulator check valve electromagnetic switching valve 48 is located at the OFF position N where the introduction oil passage 47g is opened, the pressure of the accumulator oil passage 42 introduced into the spring chamber 47f causes the poppet 47a to move to the valve passage closing side. Works as a pressing force. As a result, the accumulator check valve 45 is in a state where the pressure in the inflow / outflow oil passage 62 is higher than the pressure in the accumulator oil passage 42 by a predetermined pressure (the predetermined pressure is determined by the pressure receiving area A and the pressing force of the spring 47e). The valve passage 47d is opened to allow the inflow of oil from the inflow / outflow oil passage 62 to the accumulator oil passage 42, but when the pressure in the accumulator oil passage 42 is higher than the pressure in the inflow / outflow oil passage 62 (and inflow / outflow oil) When the pressure in the passage 62 is not higher than the pressure in the accumulator oil passage 42 by a predetermined pressure or higher), the valve passage 47d is closed, thereby preventing the oil from flowing out from the accumulator oil passage 42 to the inflow / outflow oil passage 62. It becomes a state.
On the other hand, in the state where the accumulator check valve electromagnetic switching valve 48 is located at the ON position X that closes the introduction oil passage 47g, the pressure in the accumulator oil passage 42 is not introduced into the spring chamber 47f, and the pressure oil in the spring chamber 47f is Therefore, the pressure in the accumulator oil passage 42 does not act as a force for pressing the poppet 47a toward the valve passage closing side. Thereby, the accumulator check valve 45 reduces the force acting on the valve path closing side (the force acting on the valve path closing side is only the pressing force of the spring 47e), while the accumulator oil path 42 and the inflow / outlet oil path 62 Both pressures act on the valve path opening side, and therefore, an opening that allows the flow in both directions from the accumulator oil path 42 to the inflow / outflow oil path 62 or from the inflow / outflow oil path 62 to the accumulator oil path 42 is allowed. It becomes a state.
Here, the flow of the oil from the inflow / outflow oil passage 62 to the accumulator oil passage 42 is such that the accumulator check valve 45 is non-returned when the pressure in the inflow / outflow oil passage 62 is higher than the pressure of the accumulator oil passage 42 by a predetermined pressure or more. However, as described above, when the accumulator check valve 45 is in the non-return state, the pressure of the accumulator oil passage 42 presses the poppet 47a toward the valve passage closing side. On the other hand, in the open state, the pressure in the accumulator oil passage 42 does not work as a force for pressing the poppet 47a toward the valve passage closing side. For this reason, by opening the accumulator check valve 45, the force acting on the valve path closing side is reduced, and the accumulator oil is discharged from the inflow / outflow oil path 62 with almost no resistance, that is, almost no pressure loss. Oil can flow through the passage 42.

  Further, 49 is a discharge oil passage that is branched from the suction oil passage 33 and reaches the oil tank 11, and a tank check valve 50 is disposed in the discharge oil passage 49.

  The tank check valve 50 includes a poppet valve 51 and a tank check valve electromagnetic switching valve 52 that switches from an OFF position N to an ON position X based on an ON signal output from the controller 16. The poppet valve 51 allows oil flow from the suction oil passage 33 to the oil tank 11 only when the tank check valve electromagnetic switching valve 52 is located at the ON position X, and is located at the OFF position N. It is designed to stop when you are. For example, when the excavator 1 is finished or maintained, the accumulator check valve electromagnetic switching valve 48 and the tank check valve electromagnetic switching valve 52 are both switched to the ON position X to accumulate pressure in the accumulator 36. The pressurized oil can be discharged to the oil tank 11.

  On the other hand, the controller 16 is configured by using a microcomputer or the like, and as shown in the block diagram of FIG. 5, a boom operation detecting means 53 for detecting an operation direction and an operation amount of a boom operation lever (not shown). The first discharge side pressure sensor 54 connected to the first pump oil passage 12 to detect the discharge pressure of the first main pump 9, and the second discharge side pump oil passage to detect the discharge pressure of the second main pump 10. 13, a second discharge side pressure sensor 55 connected to 13, a third discharge side pressure sensor 56 connected to the dedicated pump oil passage 34 to detect the discharge pressure of the dedicated pump 32, and a suction side pressure of the dedicated pump 32 are detected. The suction side pressure sensor 57 connected to the suction oil passage 33 and the cylinder head side oil passage 20 are contacted to detect the pressure of the head side oil chamber 8a of the boom cylinder 8. The cylinder head side pressure sensor 58, the cylinder rod side pressure sensor 59 connected to the cylinder rod side oil passage 21 to detect the pressure of the rod side oil chamber 8b of the boom cylinder 8, and the accumulator to detect the pressure of the accumulator 36. A signal from an accumulator pressure sensor 60 or the like connected to the oil passage 42 is input, and based on these input signals, the main pump control electromagnetic proportional pressure reducing valve 17, the first ascending electromagnetic proportional pressure reducing valve 23, the first 1 descending electromagnetic proportional pressure reducing valve 24, 2nd ascending electromagnetic proportional pressure reducing valve 25, electromagnetic switching valve 30 for drift reduction valve, dedicated pump regulator 35, 3rd ascending side electro-oil conversion valve 38, 3rd descending side electro-oil Conversion valve 39, recovery electrooil conversion valve 44, accumulator check valve electromagnetic switching valve 48, tank check valve electromagnetic switching valve 52, etc. It outputs a control signal.

  Here, 61 is a pressure accumulation state calculation unit provided in the controller 16, and the pressure accumulation state calculation unit 61 is an accumulator oil passage input from an accumulator pressure sensor 60 (corresponding to the pressure accumulation state detection means of the present invention). Based on the pressure of 42, the current pressure accumulation state (%) of the accumulator 36 is calculated. The accumulator state (%) is set in advance, for example, as 0% if the pressure in the accumulator oil passage 42 is equal to the precharge pressure (accumulation start setting pressure) of the accumulator 36, and sufficiently accumulated in the accumulator 36. If the pressure is higher than the set pressure, it is calculated to be 100%, and if it is between the precharge pressure and the set pressure, it is calculated so that the percentage increases as the pressure in the accumulator oil passage 42 increases. Depending on the temperature correction.

  Next, the control of the controller 16 when the boom operating lever is operated to the boom raising side, that is, when the boom raising side operation detection signal is input from the boom operation detecting means 53 will be described. In this case, since the control of the controller 16 differs depending on the pressure accumulation state of the accumulator 36 calculated by the pressure accumulation state calculation unit 61, first, a case where the pressure accumulation state is 100%, that is, when the pressure is sufficiently accumulated in the accumulator 36 will be described.

  When the accumulator 36 is operated to the boom raising side when the pressure accumulation state is 100%, the controller 16 outputs a control signal to the main pump control electromagnetic proportional pressure reducing valve 17 so that the pump output corresponds to the engine speed. Then, a control signal is output to the ascending pilot port 19a of the second control valve 19 so that a pilot pressure corresponding to the operation amount of the boom operating lever is output to the second ascending electromagnetic proportional pressure reducing valve 25. As a result, the spool of the second control valve 19 is moved by the stroke corresponding to the operation amount of the boom operation lever, and is switched to the ascending position X. Thus, the oil discharged from the second main pump 10 flows into the cylinder head side oil passage 20 via the second control valve 19 at the ascending side position X, and is supplied to the head side oil chamber 8a of the boom cylinder 8. The

  Furthermore, the controller 16 outputs a control command to the dedicated pump regulator 35 so that the discharge flow rate of the dedicated pump 32 becomes a flow rate corresponding to the operation amount of the boom operation lever. 38, an operation signal having a signal value corresponding to the operation amount of the boom operation lever is output. As a result, the spool of the third control valve 37 is moved by the stroke corresponding to the operation amount of the boom operation lever, and is switched to the ascending position X. Thus, the oil discharged from the dedicated pump 32 flows into the cylinder head side oil passage 20 via the third control valve 37 at the ascending side position X, and in the cylinder head side oil passage 20, the second main pump 10 described above. It merges with the discharged oil and is supplied to the head side oil chamber 8 a of the boom cylinder 8. On the other hand, the oil in the rod side oil chamber 8 b of the boom cylinder 8 is discharged to the oil tank 11 via the third control valve 37 at the ascending side position X.

  Further, the controller 16 outputs an ON signal to the accumulator check valve electromagnetic switching valve 48 so as to switch to the ON position X. As a result, the accumulator check valve 45 is opened, and oil flows out from the accumulator oil passage 42 to the suction oil passage 33 via the inflow / outflow oil passage 62. Thus, the pressure oil accumulated in the accumulator 36 is supplied to the suction side of the dedicated pump 32 via the suction oil passage 33.

  Further, when the boom control lever is operated to the boom raising side in the pressure accumulation state 100%, a control signal for pilot pressure output is output from the controller 16 to the first raising side and first lowering electromagnetic proportional pressure reducing valves 23 and 24. First, the first control valve 18 is held at the neutral position N. As a result, the oil discharged from the first main pump 9 is not supplied to the boom cylinder 8, and the flow rate of the first main pump 9 is controlled to be minimized by the negative control flow rate control.

  Further, no operation signal is output from the controller 16 to the recovery electro-oil conversion valve 44, and the recovery valve 41 is located at the closed position N where the recovery oil passage 40 is closed. Thereby, the supply pressure oil from the second control valve 19 and the third control valve 37 is supplied to the head side oil chamber 8a of the boom cylinder 8 without flowing into the accumulator oil passage 42 and the suction oil passage 33. It has become.

  Next, a case where the accumulator 36 is operated at the boom raising side when the pressure accumulation state is 0% will be described. In this case, the main pump controlling electromagnetic proportional pressure reducing valve 17, the second raising side electromagnetic proportional pressure reducing valve 25, the accumulator check valve will be described. The electromagnetic switching valve 48 and the recovery electro-hydraulic conversion valve 44 are controlled in the same manner as when operated to the boom raising side in the pressure accumulation state 100% described above.

  Further, when the pressure accumulation state is 0% and the controller 16 is operated to the boom raising side, the controller 16 connects the boom operating lever to the raising pilot port 18a of the first control valve 18 with respect to the first raising electromagnetic proportional pressure reducing valve 23. A control signal is output so as to output a pilot pressure corresponding to the operation amount. As a result, the spool of the first control valve 18 is moved by the stroke corresponding to the operation amount of the boom operation lever, and is switched to the ascending position X. Thus, the oil discharged from the first main pump 9 flows into the cylinder head side oil passage 20 via the first control valve 18 at the ascending side position X, and the second main pump 10 is supplied to the cylinder head side oil passage 20. And is supplied to the head side oil chamber 8a of the boom cylinder 8. On the other hand, the oil in the rod side oil chamber 8 b of the boom cylinder 8 is discharged to the oil tank 11 via the first control valve 18 at the ascending side position X.

  Further, the controller 16 outputs a control command to the dedicated pump regulator 35 so that the discharge flow rate of the dedicated pump 32 becomes zero, that is, the pressure oil supply of the dedicated pump 32 is stopped. Further, no operation command is output from the controller 16 to the third ascending side and third descending electrohydraulic conversion valves 38, 39, and the third control valve 37 is held at the neutral position N. Thereby, pressure oil is not supplied from the dedicated pump 32 to the head side oil chamber 8a of the boom cylinder 8.

  On the other hand, when the pressure accumulation state of the accumulator 36 is between 0% and 100% (however, 0% and 100% are not included), the controller 16 controls the first ascending electromagnetic proportional pressure reduction when operated on the boom raising side. The control signal is output to the valve 23 and the third ascending-side electro-oil conversion valve 38, and the first control valve 18 and the third control valve 37 are switched to the ascending-side position X. Further, control is performed so that the supply pressure oil from the first main pump 9 is joined and supplied to the head side oil chamber 8a of the boom cylinder 8. In this case, as the pressure accumulation state of the accumulator 36 decreases, the dedicated pump 32 The discharge flow rate and the movement stroke of the spool of the third control valve 37 are reduced, while the movement of the spool of the first control valve 18 is reduced. Stroke is controlled to increase. That is, as the pressure accumulation state of the accumulator 36 decreases, the supply flow rate from the dedicated pump 32 decreases while the supply flow rate from the first main pump 9 increases. Is added to the supply flow rate from the first main pump 9 to control the flow rate for one pump.

  Further, even when the pressure accumulation state is between 0% and 100%, the main pump control electromagnetic proportional pressure reducing valve 17, the second ascending electromagnetic proportional pressure reducing valve 25, the accumulator check valve electromagnetic switching valve 48, the recovery electro-oil conversion Control similar to that when the valve 44 is operated to the boom raising side in the pressure accumulation state 100% is performed.

  Thus, when the accumulator 36 is at 100% accumulated pressure when the boom 5 is raised, the flow rate for one pump supplied from the dedicated pump 32 and the flow rate for one pump supplied from the second main pump 10 Are combined and supplied to the head side oil chamber 8a of the boom cylinder 8, and when the pressure accumulation state of the accumulator 36 is 0%, pressure oil is not supplied from the dedicated pump 32 but supplied from the first main pump 9. The flow rate for one pump and the flow rate for one pump supplied from the second main pump 9 are merged and supplied to the head side oil chamber 8a, and the accumulator 36 has a pressure accumulation state of 0% to 100%. When the flow rate for one pump supplied from the dedicated pump 32 and the first main pump 9 and the flow rate for one pump supplied from the second main pump 10 merge. It is supplied to the head-side oil chambers 8a Te. Therefore, when the boom 5 is raised, regardless of the pressure accumulation state of the accumulator 36, the flow of two pumps can always be supplied to the head-side oil chamber 8a, and the boom 5 rises against the weight load of the working unit 4. Even in this case, the boom 5 can be raised at a desired speed corresponding to the operation amount of the boom operation lever. In this case, the dedicated pump 32 uses the high-pressure pressure oil accumulated in the accumulator 36. Since the suction and discharge are performed, the pressure difference between the suction side and the discharge side is small, and the pressure oil can be supplied with much less required power than the first and second main pumps 9 and 10.

  Next, the control of the controller 16 when the boom operation lever is operated to the boom lowering side, that is, when the boom lowering operation detection signal is input from the boom operation detecting means 53 will be described. In this case, the control of the controller 16 is the same regardless of the pressure accumulation state of the accumulator 36.

That is, when the boom operating lever is operated to the boom lowering side, the controller 16 outputs a control signal to the main pump control electromagnetic proportional pressure reducing valve 17 so as to reduce the pump output and the first lowering side electromagnetic. A control signal is output to the proportional pressure reducing valve 24 so as to output a pilot pressure corresponding to the operation amount of the boom operation lever to the descending pilot port 18 b of the first control valve 18. As a result, the spool of the first control valve 18 is moved by the stroke corresponding to the operation amount of the boom operation lever, and is switched to the descending position Y. Thus, the discharged oil from the head side oil chamber 8a of the boom cylinder 8 is supplied to the rod side oil chamber 8b via the regeneration valve path 18c at the descending position Y, and as described above, Since the passage flow rate of the center bypass valve path 18f at the descending position Y does not change, the discharge flow rate of the first main pump 9 is controlled to be minimized by negative control flow rate control.
The second control valve 19 is held at the neutral position N when the boom 5 is lowered, and therefore does not supply / discharge oil to / from the boom cylinder 8, and the discharge flow rate of the second main pump 10 is also the negative control flow rate. It is controlled to be minimized by the control.

  Furthermore, the controller 16 outputs a control command to the dedicated pump regulator 35 so that the discharge flow rate of the dedicated pump 32 becomes a flow rate corresponding to the operation amount of the boom operation lever. 39, an operation signal having a signal value corresponding to the operation amount of the boom operation lever is output. As a result, the spool of the third control valve 37 is moved by the stroke corresponding to the operation amount of the boom operation lever, and is switched to the lower position Y. Thus, the oil discharged from the dedicated pump 32 flows into the cylinder rod side oil passage 21 via the third control valve 37 at the descending position Y, and is supplied to the rod side oil chamber 8 b of the boom cylinder 8.

  Further, the controller 16 outputs an ON signal to the drift reducing valve electromagnetic proportional pressure reducing valve 30 so as to switch to the ON position X. As a result, the drift reduction valve 29 is allowed to discharge oil from the head side oil chamber 8a of the boom cylinder 8.

  Further, the controller 16 outputs an operation signal having a signal value corresponding to the operation amount of the boom operation lever to the collecting electro-oil conversion valve 44. Thus, the recovery valve 41 is switched to the open position X in which the spool is moved by a stroke corresponding to the operation amount of the boom operation lever, and the recovery oil passage 40 is opened. Thus, the oil discharged from the head side oil chamber 8a of the boom cylinder 8 flows from the inflow / outflow oil passage 62 to the accumulator oil passage 42 via the recovery oil passage 40 and the accumulator check valve 45, It flows into the suction oil passage 33. The oil flowing in the accumulator oil passage 42 is accumulated in the accumulator 36, while the oil flowing in the suction oil passage 33 is supplied to the suction side of the dedicated pump 32.

  Further, at this time, the controller 16 outputs an ON signal to the accumulator check valve electromagnetic switching valve 48 so as to switch to the ON position X. As a result, the accumulator check valve 45 is in an open state in which the force acting on the valve path closing side is reduced, and therefore, there is almost no pressure loss when passing through the accumulator check valve 45, and the accumulator check valve 45 is in the open state. The oil can flow into 36.

  Thus, when the boom 5 is lowered, the pressure oil from the dedicated pump 32 is supplied to the rod side oil chamber 8b of the boom cylinder 8. In this case, the dedicated pump 32 is connected to the head side oil chamber 8a. Since the high pressure oil discharged from the pump is sucked and discharged, the pressure difference between the suction side and the discharge side is small, and the pressure oil can be supplied with much less required power than the first main pump 9. .

On the other hand, when the boom 5 is lowered, the oil discharged from the head-side oil chamber 8a of the boom cylinder 8 is at a high pressure due to the potential energy of the working unit 4, and the rod is in consideration of the pressure receiving area acting on the piston 8c. The amount of oil discharged is approximately twice the amount supplied to the side oil chamber 8b, but the oil discharged from the head side oil chamber 8a is supplied to the suction side of the dedicated pump 32, and as described above, the dedicated pump. 32 is supplied to the rod side oil chamber 8 b and is accumulated in the accumulator 36. As described above, the pressure oil accumulated in the accumulator 36 is supplied from the dedicated pump 32 to the head-side oil chamber 8a when the boom 5 is raised. Thus, the potential energy of the working unit 4 can be recovered and reused without being wasted.
When the boom 5 is lowered, a part of the oil discharged from the head side oil chamber 8 a is supplied to the rod side oil chamber 8 b via the regeneration valve path 18 c of the first control valve 18.

When the boom operating lever is not operated on either the ascending side or the descending side, the controller 16 controls the first ascending side, the first descending side, the second ascending electromagnetic proportional pressure reducing valves 23, 24, 25, and No signal is output to the third ascending side and third descending electro-hydraulic conversion valves 38 and 39, and the first, second and third control valves 18, 19 and 37 are all held at the neutral position N. As a result, no pressure oil is supplied to the boom cylinder 8 and no oil is discharged from the boom cylinder 8, and the boom 5 is stopped. At this time, the controller 16 turns on the electromagnetic switching valve 48 for the accumulator check valve. No signal is output, and the accumulator check valve electromagnetic switching valve 48 is in the OFF position N. As a result, the accumulator check valve 45 is in a non-return state, and oil can be prevented from flowing out from the accumulator oil passage 42 to the suction oil passage 33 via the inflow / outflow oil passage 62, and thus the accumulator The high-pressure oil accumulated in 36 can be reliably held.
When the boom 5 is stopped, the controller 16 outputs a control command to the dedicated pump regulator 35 so that the discharge flow rate of the dedicated pump 32 becomes zero. Further, the ON signal for the drift reducing electromagnetic switching valve 30 is not output, and the operation signal for the recovery electro-oil conversion valve 44 is not output.

  In the present embodiment configured as described, the oil discharged from the head side oil chamber 8a of the boom cylinder 8 when the boom 5 is lowered is accumulated in the accumulator 36, while the oil accumulated in the accumulator 36 is When the boom 5 is raised, it is supplied to the head-side oil chamber 8a of the boom cylinder 8 via the dedicated pump 32. Thus, the potential energy of the working unit 4 can be effectively recovered and reused. In this case, the oil discharged from the head side oil chamber 8a of the boom cylinder 8 passes through the recovery oil passage 40, the inflow / outflow oil passage 62, and the accumulator oil passage 42. On the other hand, the accumulated oil in the accumulator 36 passes through the accumulator oil passage 42, the inflow / outlet oil passage 62, and the suction oil passage 33. Only supplied to the suction side of the pump 32, further will be supplied to the head-side oil chambers 8a of the boom cylinders 8 from the dedicated pump 32 Te. Thus, the oil inflow to the accumulator 36 and the oil outflow from the accumulator 36 are performed via the inflow / outflow oil passage 62, and the accumulator 36 is connected to the inflow / outflow oil passage 62. And an accumulator check valve 45 for controlling oil inflow and oil outflow. The accumulator check valve 45 has a valve path 47d that opens and closes between the accumulator 36 and the inflow / outflow oil path 62, and is pressed against the valve path open side by the pressure of the inflow / outflow oil path 62 and the pressure of the accumulator 36. On the other hand, the poppet valve 47 that is pressed to the valve path closing side by the pressure of the accumulator 36 and the pressing force of the spring 47e introduced into the spring chamber 47f via the introduction oil path 47g, and the controller 16 outputs it. The accumulator check valve electromagnetic switching valve 48 opens and closes the introduction oil passage 47g based on the signal. In the accumulator check valve 45, when the introduction oil passage 47g is opened and the pressure of the accumulator 36 is introduced into the spring chamber 47f, the pressure of the inflow / outflow oil passage 62 is higher than the pressure of the accumulator 36 by a predetermined pressure or more. The valve passage 47d is sometimes opened to allow the oil inflow from the inflow / outflow oil passage 62 to the accumulator 36, but the oil outflow from the accumulator 36 to the inflow / outflow oil passage 62 closes the valve passage 47d and prevents the oil outflow. On the other hand, when the introduction oil passage 45g is closed and pressure introduction into the spring chamber 47f is interrupted and the pressure oil in the spring chamber 47f is drained, the force acting on the valve passage closing side is reduced and the valve passage 47d is opened. An open state in which oil inflow from the inflow / outflow oil passage 62 to the accumulator 36 and oil outflow from the accumulator 36 to the inflow / outflow oil passage 62 is permitted.

  Thus, when the boom 5 is stopped, the accumulator check valve 45 is set in the non-return state, so that the pressure oil can be prevented from flowing out from the accumulator 36 into the inflow / outflow oil passage 62. Accumulated high-pressure oil can be reliably held. On the other hand, when the boom 5 is raised, by opening the accumulator check valve 45, the pressure oil flows out from the accumulator 36 to the suction oil passage 33 via the inflow / outflow oil passage 62, and thus into the accumulator 36. The accumulated oil can be supplied to the boom cylinder 8 via the dedicated pump 32. Further, even when the boom 5 is lowered, by opening the accumulator check valve 45, the force on the valve path closing side acting on the accumulator check valve 45 is reduced, and thus the accumulator 36 is discharged from the boom cylinder 8 and discharged. The oil flowing into the accumulator can be passed through the accumulator check valve 45 with almost no resistance, that is, with almost no pressure loss, so that the oil discharged from the boom cylinder 8 can be efficiently accumulated in the accumulator 36. it can.

Of course, the present invention is not limited to the above-described embodiment. In the above-described embodiment, the boom cylinder hydraulic control system of the excavator has been described as an example. The present invention can be implemented in various hydraulic control systems configured to accumulate oil discharged from the hydraulic cylinder when descending in the accumulator while supplying the oil accumulated in the accumulator to the hydraulic cylinder when the working unit is raised.
Further, the accumulator check valve is not limited to the one using the poppet valve and the electromagnetic switching valve for the accumulator check valve as in the above-described embodiment. For example, the valve path is obtained by inputting a pilot pressure based on an external signal. It can also be configured using a pilot type check valve that increases the force acting on the open side and thereby opens. In addition, the external signal for switching the accumulator check valve from the non-return state to the open state is not limited to the output signal from the controller, for example, an electric signal output in accordance with the operation of the operation tool for moving the working unit up and down. Of course, it may be a hydraulic signal or the like.

It is a side view of a hydraulic excavator. It is a circuit diagram of a hydraulic control system. It is a circuit diagram of a hydraulic control system. It is a partially expanded circuit diagram of a hydraulic control system. It is a block diagram which shows the input / output of a controller.

Explanation of symbols

4 Working section 8 Boom cylinder 32 Dedicated pump 33 Suction oil path 36 Accumulator 40 Recovery oil path 45 Accumulator check valve 47 Poppet valve 47d Valve path 47f Spring 47g Introducing oil path 48 Electromagnetic switching valve for accumulator check valve 62 Inlet / outlet oil path

Claims (3)

Hydraulic control of a working machine configured to accumulate oil discharged from the hydraulic cylinder when the working unit that moves up and down descends in the accumulator while supplying the oil accumulated in the accumulator to the hydraulic cylinder when the working unit ascends In the system,
The accumulator is connected via an accumulator check valve to an inflow / outflow oil passage which is a flow path of oil inflow to the accumulator and oil outflow from the accumulator,
The accumulator check valve valve,
It has a valve path that opens and closes between the accumulator and the inflow / outflow oil path, and permits oil inflow from the inflow / outflow oil path to the accumulator when the inflow / outflow oil path pressure is higher than the accumulator pressure by a predetermined pressure or more. However, a non-return state that prevents oil outflow from the accumulator to the inflow and outflow passages,
Allowing oil inflow from the inflow / outflow oil passage to the accumulator and oil outflow from the accumulator to the inflow / outflow oil passage by reducing the force acting on the valve closing side or increasing the force acting on the valve opening side based on the external signal It is configured to be switchable to an open state, and
When the working part is stopped, the accumulator check valve is set in a non-return state to prevent oil from flowing out from the accumulator to the inflow / outflow oil passage, while when the working part is raised or lowered, the accumulator check valve is opened to enter the inflow / outflow oil passage A hydraulic control system for a work machine, characterized in that an oil outflow or an oil inflow from an inflow / outflow oil passage to an accumulator is performed. The accumulator check valve
It has a valve path that opens and closes between the accumulator and the inflow / outflow oil path, and is pressed against the valve path open side by the inflow / outflow oil path pressure and the accumulator pressure, while passing through the spring pressing force and the introduction oil path A poppet valve that is pressed to the valve closing side by the accumulator pressure introduced into the spring chamber,
It is configured using a control valve that opens and closes the introduction oil passage based on an external signal,
Opening the control valve and introducing the accumulator pressure into the spring chamber results in a non-return state, while closing the control valve to stop introducing the accumulator pressure into the spring chamber and draining the pressure oil in the spring chamber 2. The hydraulic control system for a work machine according to claim 1, wherein a force acting on the road closing side is reduced to be in an open state.   The hydraulic control system includes a hydraulic pump that sucks oil accumulated in the accumulator when the working unit is raised and supplies the hydraulic cylinder to the hydraulic cylinder, while an inflow / outflow oil path is a recovery oil path that guides oil discharged from the hydraulic cylinder to the accumulator And a hydraulic control system for a working machine according to claim 1, wherein the hydraulic pressure control system is connected to a suction oil passage that guides oil accumulated in the accumulator to the suction side of the hydraulic pump.

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