JP2010060057A - Hydraulic control system in working machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accumulate high-pressurized oil which can be applied to a high load work, when potential energy possessed by a vertically moving working portion is collected and accumulated in an accumulator. <P>SOLUTION: A hydraulic system in a utility machine includes an unload oil passage 41 (a first head-side oil passage 19, a first flow-regulating valve 33 a first flow control valve 40, a head-side discharge oil passage and an unload valve) for flowing the pressurized oil of the head-side first boom cyclinder to an oil tank 12, capable of being opened/closed for allowing pressurized oil in a head-side oil chamber of a first boom cylinder, i.e., one of a pair of the first and a second boom cylinders 8, 9, for lifting the working portion 4. The weight of the working portion is held by pressure of head-side oil chambers of the first and second boom cylinders, by opening the unload oil passage when vertical the working portion is stopped to move vertically and is lifted. The weight of the working portion is held by pressure of the head-side oil chamber of the second boom cylinder, by opening the unload oil passage when the working portion is lowered. The system further includes an accumulator 59 for accumulating and pressurizing discharged oil from the head-side oil chamber of the second boom cylinder, when the working portion is lowered. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention belongs to a technical field of a hydraulic control system in a work machine that is capable of recovering and reusing potential energy of a work part in a work machine having a work part that can be raised and lowered.

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, conventionally, oil discharged from the hydraulic cylinder head side oil chamber to the oil tank when the working unit is lowered is prevented from dropping suddenly due to its own weight. Meter-out control is performed by a throttle provided in a control valve that performs 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 wasted into the atmosphere, resulting in wasted energy loss.
Therefore, in order to recover and reuse the potential energy of the working unit, an assist cylinder is provided in addition to the conventional hydraulic cylinder, and oil discharged from the head side oil chamber of the assist cylinder when the working unit is lowered. Is accumulated in the accumulator, and the pressure oil accumulated in the accumulator is supplied to the head-side oil chamber of the assist cylinder when the working unit is raised (see, for example, Patent Document 1).
However, according to Patent Document 1, the oil discharged from the assist cylinder is accumulated in the accumulator when the working unit is lowered, but the oil discharged from the hydraulic cylinder that has been conventionally provided to raise and lower the working unit is The oil is discharged to the oil tank via the control valve, and only a part of the potential energy of the working machine is recovered. In addition, if the accumulator is not sufficiently accumulating when the working unit is raised, a part of the pressure oil supplied from the hydraulic pump to the hydraulic cylinder via the control valve is supplied to the assist cylinder and used for accumulator accumulator Therefore, there is a problem that the ascending speed of the working unit becomes slow and the working efficiency is lowered.
On the other hand, without providing an assist cylinder, the oil discharged from the hydraulic cylinder is accumulated in the accumulator when the working part is lowered, and the pressure oil accumulated in the accumulator is supplied to the hydraulic cylinder when the working part is raised. In this case, the pressure of the accumulated oil in the accumulator is not higher than the holding pressure at which the hydraulic cylinder holds the weight of the working part. The pressure of pressure oil used during high-load work may be insufficient. In view of this, a technique has been proposed in which the accumulated oil in the accumulator is supplied to a hydraulic cylinder by making it high pressure with a dedicated pump driven by engine power (see, for example, Patent Document 2).
Japanese Patent No. 2582310 JP 2008-14468 A

  However, in Patent Document 2, a dedicated pump for increasing the pressure of the accumulator accumulated oil and a power transmission device (gear device, etc.) for transmitting engine power to the pump are required, which increases costs. In addition, there is a problem of energy loss such as torque reduction in the power transmission device and idling torque due to inertial mass of the pump itself, and further energy saving is required. There are challenges.

The present invention has been created in view of the above circumstances and has been created for the purpose of solving these problems. The invention of claim 1 includes a working unit that can be raised and lowered and a pair of raising and lowering the working unit. In the hydraulic control system for a work machine including the first and second hydraulic cylinders, the hydraulic control system includes an openable and closable unload oil passage that allows the pressure oil in the head side oil chamber of the first hydraulic cylinder to flow to the oil tank. And a control device for controlling opening and closing of the unload oil passage, and when the unload oil passage is closed, the weight of the working portion is held by the pressure of the head side oil chambers of the first and second hydraulic cylinders. In the state in which the unload oil passage is open, the weight of the working part is held by the pressure of the oil chamber on the head side of the second hydraulic cylinder, and the first and second that hold the weight when the working part is lowered, Or the second hydraulic system A hydraulic control system in a working machine, characterized in that a accumulator for accumulating oil discharged from the head-side oil chamber of Sunda.
According to a second aspect of the present invention, the hydraulic control system is controlled by a control device for opening and closing the head side communication oil passage for communicating the head side oil chambers of the first and second hydraulic cylinders, and the head side communication oil passage. And the control device opens the head side communication oil passage in a state in which the unload oil passage is closed while the unload oil passage opens and closes the head side communication oil passage on / off valve. 2. The hydraulic control system for a work machine according to claim 1, wherein control is performed so that the head side communication oil passage is closed in a state in which is opened. 3.
According to a third aspect of the present invention, the control device controls to open the unload oil passage when the working portion is lowered and close the unload oil passage when the working portion is stopped and raised. Or it is a hydraulic control system in the working machine of 2.
According to a fourth aspect of the present invention, in the hydraulic control system, accumulator pressure detecting means for detecting the pressure of the accumulator, and first and second head side pressures for detecting the pressures of the head side oil chambers of the first and second hydraulic cylinders, respectively. The control device is configured to preset a differential pressure between the average value of the pressure in the head side oil chambers of the first and second hydraulic cylinders and the pressure of the accumulator even when the working unit is lowered. 4. The hydraulic control system for a work machine according to claim 3, wherein control is performed so that the unload oil passage is closed when the set value is equal to or greater than a predetermined value.
According to a fifth aspect of the present invention, in the hydraulic control system, a second head side pressure detecting means for detecting the pressure of the head side oil chamber of the second hydraulic cylinder, and a second relief for setting the head side relief pressure of the second hydraulic cylinder. In addition to providing a valve, the control device presets the differential pressure between the head-side relief pressure of the second hydraulic cylinder and the pressure of the head-side oil chamber of the second hydraulic cylinder even when the working unit is lowered. 5. The hydraulic control system for a work machine according to claim 3, wherein control is performed so that the unload oil passage is closed when the set value is not more than the set value.
According to a sixth aspect of the present invention, the hydraulic control system is provided with first and second flow rate control valves that respectively control the discharge flow rates from the head side oil chambers of the first and second hydraulic cylinders when the working unit is lowered. The hydraulic control system for a work machine according to any one of claims 1 to 5, wherein the hydraulic control system is a work machine.
According to the seventh aspect of the present invention, the oil flow from the head side oil chambers of the first and second hydraulic cylinders to the accumulator and the oil from the accumulator to the head side oil chambers of the first and second hydraulic cylinders is provided in the hydraulic control system. The hydraulic control system for a work machine according to any one of claims 1 to 6, further comprising a valve unit capable of preventing the flow of the working machine.
According to an eighth aspect of the present invention, in the hydraulic control system, accumulator pressure detecting means for detecting the pressure of the accumulator, and first and second head side pressures for detecting the pressures of the head side oil chambers of the first and second hydraulic cylinders, respectively. A detecting means, and an openable and closable tank oil passage for flowing oil discharged from the head side oil chambers of the first and second hydraulic cylinders to the oil tank via the first and second flow rate control valves; And a valve means capable of preventing the flow of oil from the head side oil chamber of the hydraulic cylinder to the accumulator and the flow of oil from the accumulator to the head side oil chamber of the first and second hydraulic cylinders, and a control device. When the pressure of the head side oil chambers of the first and second or second hydraulic cylinders that hold the weight is lower than the pressure of the accumulator when the working unit is lowered, The oil flow from the head side oil chamber of the pressure cylinder to the accumulator and the oil flow from the accumulator to the head side oil chamber of the first and second hydraulic cylinders are blocked, and the tank oil passage is opened to The hydraulic control system for a work machine according to claim 6, wherein the pressure oil in the head side oil chamber of the second hydraulic cylinder is caused to flow to the oil tank via the first and second flow rate control valves.

According to the first aspect of the present invention, when the working part is lowered, the unloading oil passage is opened and the pressure oil in the head side oil chamber of the first hydraulic cylinder is caused to flow into the oil tank, so that the weight of the working part is second. While being held at the pressure of the head side oil chamber of the hydraulic cylinder, the discharged oil from the head side oil chamber of the second hydraulic cylinder is accumulated in the accumulator. Since the pressure of the oil chamber, that is, the holding pressure for holding the weight of the working part is doubled with respect to the holding pressure when the weight of the working part is held by both the first and second hydraulic cylinders, High-pressure oil that can handle high-load work is accumulated, and thus the accumulator pressure-accumulated oil can be used as it is without increasing the pressure separately for various operations. Moreover, there is no loss of idling torque due to the torque drop in the power transmission path from the engine to the pump or the inertia mass of the pump itself, as in the case of increasing the pressure accumulation oil of the accumulator using the pump driven by engine power, The potential energy of the working part collected in the accumulator can be used with as little loss as possible, and can greatly contribute to cost reduction.
According to the invention of claim 2, in the state where the unload oil passage is closed, that is, in the state where the weight of the working part is held in the head side oil chambers of the first and second hydraulic cylinders, The head side oil chambers of the second hydraulic cylinder are in communication with each other, and the working portion can be supported by the first and second hydraulic cylinders in a well-balanced manner, while the unload oil passage is open, that is, the second hydraulic cylinder In a state where the weight of the working part is held in the head side oil chamber, the head side oil chamber of the second hydraulic cylinder and the head side oil chamber of the first hydraulic cylinder can be shut off.
According to the invention of claim 3, the unloading oil passage is opened, that is, the weight of the working part is held by the second hydraulic cylinder when the working part for accumulating pressure in the accumulator is lowered. When lifting and lowering the part, the unloading oil passage is closed, that is, the weight of the working part is held by the first and second hydraulic cylinders. Therefore, except when the working part that accumulates pressure on the accumulator is lowered In this case, the loss of flowing the pressure oil in the head side oil chamber of the first hydraulic cylinder to the oil tank can be eliminated, and the force may be insufficient or the balance may be lost when the working part is raised. There is nothing.
According to the fourth aspect of the present invention, when the pressure of the head side oil chambers of the first and second hydraulic cylinders is higher than the pressure of the accumulator even when the working part is lowered, the unloading is performed. The oil passage is closed, the weight of the working part is held by the pressure of the head side oil chambers of the first and second hydraulic cylinders, and the oil discharged from the head side oil chambers of the first and second hydraulic cylinders is transferred to the accumulator. As a result, the loss of flowing the pressure oil in the head side oil chamber of the first hydraulic cylinder to the oil tank due to the opening of the unload oil passage can be reduced.
According to the fifth aspect of the present invention, when the differential pressure between the head-side relief pressure of the second hydraulic cylinder and the pressure of the head-side oil chamber becomes equal to or less than a set value even when the working unit is lowered, the unload oil The path is closed, and the weight of the working part is held by the first and second hydraulic cylinders. As a result, the pressure in the head side oil chamber of the second hydraulic cylinder rises too much and the second head side relief valve It can prevent operating.
According to the sixth aspect of the present invention, the lowering speed of the working portion can be controlled by the first and second flow rate control valves.
According to the seventh aspect of the present invention, when the working unit is stopped to be raised and lowered, the valve means causes the oil flow from the head side oil chamber of the first and second hydraulic cylinders to the accumulator, and the first and second hydraulic cylinders from the accumulator. By blocking the flow of oil to the head side oil chamber, the pressure oil in the head side oil chamber of the first and second hydraulic cylinders flows out to the accumulator, or the accumulated oil in the accumulator is the first and second hydraulic pressure Problems such as being supplied to the cylinder head side oil chamber can be reliably avoided.
According to the invention of claim 8, when the pressure of the head side oil chamber of the first and second or second hydraulic cylinders holding the weight of the working part is lower than the pressure of the accumulator when the working part is lowered. Can prevent the oil from flowing back from the accumulator to the head side oil chambers of the first and second hydraulic cylinders by the valve means, and even in this case, the speed is controlled by the first and second flow control valves. In this state, the working part can be lowered.

  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.

  8 and 9 are a pair of left and right first and second boom cylinders (corresponding to the first and second hydraulic cylinders of the present invention) for swinging the boom 5 up and down. The two boom cylinders 8 and 9 hold the weight of the working unit 4 by the pressure of the head side oil chambers 8a and 9a, supply pressure oil to the head side oil chambers 8a and 9a, and from the rod side oil chambers 8b and 9b. So that the boom 5 is lifted by being discharged, and the boom 5 is lowered by being contracted by pressure oil supply to the rod-side oil chambers 8b and 9b and oil discharge from the head-side oil chambers 8a and 9a. It is configured. The working unit 4 as a whole moves up and down as the boom 5 moves up and down, and the potential energy of the working unit 4 increases as the boom 5 moves up. The positional energy is recovered by a hydraulic control system described later. Are being reused. The first boom cylinder 8 is one of the pair of boom cylinders 8 and 9, and the second boom cylinder 9 is the other boom cylinder 9. In FIG. Although one boom cylinder 8 is provided and the right boom cylinder 9 is provided on the right side, it may of course be reversed left and right.

  Next, the hydraulic control system will be described with reference to the hydraulic circuit diagram of FIG. 2. In FIG. 2, 8 and 9 are the first and second boom cylinders, and 10 is the engine E mounted on the hydraulic excavator 1. A variable displacement main pump to be driven, 11 is a pilot pump serving as a pilot hydraulic pressure source, and 12 is an oil tank. The main pump 10 includes not only the first and second boom cylinders 8 and 9, but also a plurality of other hydraulic actuators provided in the excavator 1 (not shown in FIG. Cylinder, bucket cylinder, etc.).

  Further, 13 is a regulator for controlling the discharge flow rate of the main pump 10, and the regulator 13 receives the control signal pressure from the main pump output control electromagnetic proportional pressure reducing valve 14 and controls the engine speed and the work load. While operating to obtain a corresponding pump output, constant horsepower control is performed by receiving the discharge pressure of the main pump 10. Further, the regulator 13 also performs flow control based on the negative control signal pressure Pn or the flow control signal pressure Pc, which will be described later.

  On the other hand, 15 is a discharge line of the main pump 10, and the discharge line 15 joins a merging oil passage 16 to be described later and reaches a pressure oil supply oil passage 17. The boom cylinder control valve 18 is connected to perform oil supply / discharge control for the first and second boom cylinders 8 and 9. Further, in the pressure oil supply oil passage 17, not only the boom cylinder control valve 18, but also a hydraulic actuator control valve (travel motor) that respectively performs oil supply / discharge control for a plurality of other hydraulic actuators provided in the hydraulic excavator 1. Control valve, swivel motor control valve, arm cylinder control valve, bucket cylinder control valve, etc.) are also connected, but are omitted in FIG.

  The boom cylinder control valve 18 is composed of a spool valve having ascending and descending pilot ports 18a and 18b. In a state where no pilot pressure is input to both the pilot ports 18a and 18b, Although it is located at a neutral position N where oil is not supplied to or discharged from the second boom cylinders 8 and 9, the pilot pressure is input to the ascending pilot port 18a, so that the pressure oil in the pressure oil supply oil passage 17 is The first boom cylinders 8 and 9 are supplied to the head-side oil chambers 8a and 9a, while the oil discharged from the rod-side oil chambers 8b and 9b is switched to the ascending position X that flows into the oil tank 12, When the pilot pressure is input to the descending pilot port 18b, the pressure oil in the pressure oil supply oil passage 17 is supplied to the rod side oil chambers of the first and second boom cylinders 8 and 9. b, it is configured Setsu換Ru so the descending side position Y to be supplied to 9b.

  Here, the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 and the boom cylinder control valve 18 are the same as the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9. The first and second head side oil passages 19 and 20 are connected to the first and second head side oil passages 19 and 20, respectively, and the first and second boom cylinders 8 and 9 have a head side oil chamber 8a. , 9a are connected to each other via a head side communication oil passage 21, and a head side main oil passage 22 connecting the head side communication oil passage 21 and the boom cylinder control valve 18. The rod-side oil chambers 8b, 9b of the first and second boom cylinders 8, 9 and the boom cylinder control valve 18 are connected to the rod-side communication oil passage 23 that connects the rod-side oil chambers 8b, 9b, and The rod side communication oil passage 23 and the boom cylinder control valve 18 are connected via a rod side main oil passage 24. Thus, oil is supplied and discharged between the first and second boom cylinders 8 and 9 and the boom cylinder control valve 18 through these oil passages.

  On the other hand, 25 and 26 are ascending and descending electromagnetic proportional pressure reducing valves. These electromagnetic proportional pressure reducing valves 25 and 26 are controlled by the boom cylinder control valve 18 based on a control signal from a control device 27 described later. Each of the ascending pilot port 18a and descending pilot port 18b operates to output pilot pressure. The pilot pressure output from the ascending and descending electromagnetic proportional pressure reducing valves 25 and 26 is controlled so as to increase / decrease according to the operation amount of the boom operation lever (not shown), and the increase / decrease of the pilot pressure is also controlled. Accordingly, the opening area of the boom cylinder control valve 18 is controlled to increase / decrease by increasing / decreasing the movement stroke of the spool. Accordingly, the boom cylinder control valve 18 controls the first and second boom cylinders. Increase / decrease control of the supply / discharge flow rate to 8, 9 is performed.

  Further, the boom cylinder control valve 18 is formed with a center bypass valve path 18c for allowing the pressure oil in the pressure oil supply oil path 17 to flow to the oil tank 12 via the negative control valve 28. The flow rate through the center bypass valve passage 18c is the highest when the boom cylinder control valve 18 is in the neutral position N, and decreases as the spool movement stroke increases, that is, the operation amount of the boom operation lever increases. Control is performed so that the passage flow rate of the center bypass valve passage 18c decreases. Then, the passage flow rate of the center bypass valve path 18c is output as a negative control signal pressure Pn to one input port 29a of the shuttle valve 29 described later.

  Reference numeral 30 denotes a main pump flow control electromagnetic proportional pressure reducing valve that outputs a flow control signal pressure Pc based on a control signal from the control device 27, and is output from the main pump flow control electromagnetic proportional pressure reducing valve 30. The flow control signal pressure Pc is input to the other input port 29 b of the shuttle valve 29.

  The shuttle valve 29 selects the high pressure side of the negative control signal pressure Pn and the flow rate control signal pressure Pc input from the input ports 29 a and 29 b and outputs the selected pressure to the regulator 13 of the main pump 10. The regulator 13 controls the flow rate of the main pump 10 so that the higher the input signal pressure, the lower the pump flow rate. That is, of the negative control signal pressure Pn and the flow rate control signal pressure Pc, the signal pressure for decreasing the discharge flow rate of the main pump 10 is selected by the shuttle valve 29 and input to the regulator 13, and the regulator 13 When the negative control signal pressure Pn is input, the pump flow rate is increased or decreased in response to the increase or decrease of the operation amount of the boom operation lever. When the flow control signal pressure Pc is input, the flow control is performed. The flow rate control based on the signal pressure Pc is performed. The flow rate control signal pressure Pc will be described later.

  On the other hand, the first and second head side oil passages 19 and 20 are oil passages connected to the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9, as described above. The first and second head side oil passages 19 and 20 allow the oil supply to the head side oil chambers 8a and 9a, but prevent the oil discharge from the head side oil chambers 8a and 9a. Check valves 31 and 32 and first and second flow rate control valves 33 and 34 for controlling the discharge flow rate from the head side oil chambers 8a and 9a are arranged in parallel. Thus, the oil supply to the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 is performed via the first and second check valves 31, 32, while the head side oil chamber 8a is supplied. , 9a is discharged via the first and second flow control valves 33, 34.

  The first and second flow control valves 33 and 34 are spool valves provided with pilot ports 33a and 34a. When no pilot pressure is input to the pilot ports 33a and 34a, the first and second heads are controlled. Although it is located at the closed position N for closing the side oil passages 19 and 20, the open position X for opening the first and second head side oil passages 19 and 20 by inputting pilot pressure to the pilot ports 33a and 34a. It is comprised so that it may switch to.

  Reference numerals 35 and 36 denote first and second electromagnetic proportional pressure reducing valves. These electromagnetic proportional pressure reducing valves 35 and 36 are based on a control signal from the control device 27, respectively. It operates to output pilot pressure to the pilot ports 33a, 34a of 33, 34. The opening areas of the first and second flow rate control valves 33 and 34 are controlled to increase or decrease in response to the increase or decrease of the pilot pressure output from the first and second electromagnetic proportional pressure reducing valves 35 and 36. ing.

  Further, 37 and 38 are first and second relief valves respectively connected to the first and second head side oil passages 19 and 20, and the first and second relief valves 37 and 38 respectively The head side relief pressure of the second boom cylinders 8 and 9 is set.

  On the other hand, as described above, the head side communication oil passage 21 is connected to the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 via the first and second head side oil passages 19 and 20, respectively. The head side communication oil passage 21 is provided with a head side communication oil passage opening / closing valve 39 for opening and closing the head side communication oil passage 21 based on a control signal from the control device 27. ing. Thus, the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 are located at the open position X where the head side communication oil passage opening / closing valve 39 opens the head side communication oil passage 21. In this state, the first and second head side oil passages 19 and 20 communicate with each other, but the head side communication oil passage opening / closing valve 39 is located at the closed position N where the head side communication oil passage 21 is closed. Therefore, it is configured to be in a blocked state. The rod side communication oil passage 23 is not provided with an on / off valve such as the head side communication oil passage on / off valve 39, and the rod side oil chambers 8b, 9b of the first and second boom cylinders 8, 9 are connected to each other. Is always in communication.

  Further, reference numeral 40 denotes a head side discharge oil passage from the first head side oil passage 19 to the oil tank 12, and an unload valve 41 is disposed in the head side discharge oil passage 40. The second head side oil passage 20 is connected to the head side discharge oil passage 40 via the head side communication oil passage 21, so that the head side communication oil passage opening / closing valve 39 is closed. In this state, the second head side oil passage 20 and the head side discharge oil passage 40 are blocked, but the head side communication oil passage opening / closing valve 39 is positioned at the open position X, so that The oil in the two-head-side oil passage 20 can be made to flow to the head-side discharge oil passage 40.

  The unload valve 41 includes a poppet valve 42 and an unload valve electromagnetic switching valve 43 that switches from the OFF position N to the ON position X based on a control signal output from the control device 27. . The unload valve 41 prevents the flow of oil from the first head side oil passage 19 to the oil tank 12 when the unload valve electromagnetic switching valve 43 is in the OFF position N, that is, the head The side discharge oil passage 40 is kept closed, but the unloading valve electromagnetic switching valve 43 is switched to the ON position X, whereby the oil flow from the first head side oil passage 19 to the oil tank 12 is reduced. It is allowed, that is, the head side discharge oil passage 40 is opened. Thus, by placing the unload valve electromagnetic switching valve 43 at the ON position X and opening the unload valve 41, the pressure oil in the head side oil chamber 8a of the first boom cylinder 8 is changed to the first position. The oil can be supplied to the oil tank 12 via the one flow rate control valve 33 and the head side discharge oil passage 40. As described above, since the second head side oil passage 20 is connected to the head side discharge oil passage 40 via the head side communication oil passage 21, the head side communication oil passage opening / closing valve 39 is set to the open position X. When the unload valve 41 is in the open state, the pressure oil in the head side oil chamber 9a of the second boom cylinder 9 is supplied to the oil tank via the second flow rate control valve 34 and the head side discharge oil passage 40. 12 can be made to flow.

  Here, as described above, when the unload valve 41 is in the open state, the pressure oil in the head side oil chamber 8a of the first boom cylinder 8 passes through the first flow control valve 33 and the head side discharge oil passage 40. In this case, by maximizing the opening area of the first flow control valve 33, the pressure oil in the head-side oil chamber 8a of the first boom cylinder 8 is substantially unloaded. It can be made to flow in the oil tank 12. In the present embodiment, the first head side oil passage 19, the first flow rate control valve 33, the head side discharge oil passage 40, and the unload valve 41 constitute the openable and closable unload oil passage of the present invention. However, the state in which the unload oil passage of the present invention is open is when the opening area of the first flow control valve 33 is the maximum and the unload valve 41 is in the open state. In this case, the unload oil passage is closed.

  Further, 44 is a recovery oil passage connected to the second head side oil passage 20, and the recovery oil passage 44 has a head side oil of the second boom cylinder 8 passing through the second head side oil passage 20. The oil discharged from the chamber 8a and the oil discharged from the head side oil chamber 8a of the first boom cylinder 8 via the first head side oil passage 19 and the head side communication oil passage 21 are supplied. The passage 44 is connected to the accumulator oil passage 45 via a cylinder side check valve 46 and an accumulator side check valve 49 which will be described later. Here, the accumulator oil passage 45 is an oil passage connected to the accumulator 59 in order to supply / discharge pressure oil to / from the accumulator 59.

  The cylinder-side check valve 46 includes a poppet valve 47 and a cylinder-side check valve electromagnetic switching valve 48 that switches from the OFF position N to the ON position X based on a control signal output from the control device 27. ing. The cylinder-side check valve 46 is in a closed state in which the flow of oil from the recovery oil passage 44 to the accumulator oil passage 45 is blocked when the cylinder-side check valve electromagnetic switching valve 48 is in the OFF position N. However, when the cylinder-side check valve electromagnetic switching valve 48 is switched to the ON position X, the two-way flow between the recovery oil passage 44 and the accumulator oil passage 45 is permitted.

  The accumulator-side check valve 49 includes a poppet valve 50 and an accumulator-side check valve electromagnetic switching valve 51 that switches from the OFF position N to the ON position X based on a control signal output from the control device 27. It is configured. The accumulator side check valve 49 is in a closed state that prevents the flow of oil from the accumulator oil passage 45 to the recovery oil passage 44 when the accumulator side check valve electromagnetic switching valve 51 is in the OFF position N. However, when the accumulator-side check valve electromagnetic switching valve 51 is switched to the ON position X, the two-way flow between the recovery oil passage 44 and the accumulator oil passage 45 is permitted. The accumulator side check valve 49 allows oil to flow from the recovery oil passage 44 to the accumulator oil passage 45 even when the accumulator side check valve electromagnetic switching valve 51 is in the OFF position N. However, in the state where the accumulator side check valve electromagnetic switching valve 51 is in the ON position X, the pressure in the accumulator oil passage 45 is not introduced into the spring chamber 50a of the poppet valve 50, and is thus recovered with almost no pressure loss. Oil can flow from the oil passage 44 to the accumulator oil passage 45.

  Thus, when the cylinder side check valve 46 and the accumulator side check valve 49 are both kept closed, the oil flow from the recovery oil passage 44 to the accumulator oil passage 45 and the recovery from the accumulator oil passage 45 are performed. While the flow of oil to the oil passage 44 is both blocked, the cylinder side check valve 46 and the accumulator side check valve 49 are both opened, so that the head side oil chambers of the first and second boom cylinders 8 and 9 are opened. The discharged oil from 8a and 9a can be accumulated in the accumulator 59 via the recovery oil passage 44 and the accumulator oil passage 45. The cylinder-side check valve 46 and the accumulator-side check valve 49 are arranged so that the oil flows from the head-side oil chambers of the first and second hydraulic cylinders of the first and second hydraulic cylinders of the present invention to the accumulator and the first and second hydraulic cylinders. The valve means which can prevent the oil flow to the head side oil chamber is constituted. In the present embodiment, the accumulator 59 is an optimum bladder type for storing hydraulic energy, but is not limited thereto, and may be a piston type, for example.

  On the other hand, 16 is a merging oil passage formed so as to reach the discharge line 15 of the main pump 10 from the accumulator oil passage 45, and a merging valve 52 is arranged in the merging oil passage 16.

  The merging valve 52 is an open / close valve in which the spool moves based on the operation of the merging valve electro-oil conversion valve 53 to which a control signal from the control device 27 is input. In the operating state, the merging oil passage 16 is located at the closed position N, but when the merging valve electro-hydraulic conversion valve 53 is actuated, the spool is moved to the opening position X where the merging oil passage 16 is opened. It is comprised so that it may switch. Further, the merging valve 52 incorporates a check valve 54 that allows oil flow from the accumulator oil passage 45 to the discharge line 15 but prevents reverse flow. Thus, when the merging valve 52 is switched to the open position X, the pressure oil accumulated in the accumulator 59 is merged into the discharge line 15 of the main pump 10 via the accumulator oil path 45 and the merging oil path 16. It can be made to.

  The opening area of the merging valve 52 is controlled to be increased or decreased by the signal value of the control signal input from the control device 27 to the merging valve electro-hydraulic conversion valve 53, and the opening area of the merging valve 52 is The increase / decrease control of the flow rate is configured to increase / decrease the flow rate that flows from the accumulator 59 to the discharge line 15 of the main pump 10 via the merged oil passage 16.

  An accumulator discharge oil passage 55 is branched from the accumulator oil passage 45 and reaches the oil tank 12, and a tank check valve 56 is disposed in the accumulator discharge oil passage 55.

  The tank check valve 56 includes a poppet valve 57 and a tank check valve electromagnetic switching valve 58 that switches from the OFF position N to the ON position X based on a control signal output from the control device 27. . The tank check valve 56 prevents the flow of oil from the accumulator oil passage 45 to the oil tank 12 when the tank check valve electromagnetic switching valve 58 is in the OFF position N, that is, the accumulator discharge oil. Although the passage 55 is kept closed, the tank check valve electromagnetic switching valve 58 is switched to the ON position X to allow the oil flow from the accumulator oil passage 45 to the oil tank 12, that is, the accumulator. The exhaust oil passage 55 is opened. Thus, by placing the tank check valve electromagnetic switching valve 58 at the ON position X and opening the tank check valve 56, the accumulated oil in the accumulator 59 is passed through the discharge oil passage 55 for the accumulator. The tank 12 can be discharged.

  On the other hand, the control device 27 is configured using a microcomputer or the like, and as shown in the block diagram of FIG. 3, a boom operation detecting means 60 for detecting the operation direction and the operation amount of the boom operation lever, A pump pressure sensor 61 for detecting the discharge pressure of the main pump 10 and a first head side pressure sensor for detecting the pressure in the head side oil chamber 8a of the first boom cylinder 8 (corresponding to the first head side pressure detecting means of the present invention). 62), a second head side pressure sensor (corresponding to the second head side pressure detecting means of the present invention) 63 for detecting the pressure of the head side oil chamber 9a of the second boom cylinder 9, and the pressure of the accumulator 59 are detected. A signal from an accumulator pressure sensor (corresponding to the accumulator pressure detection means of the present invention) 64 or the like is input, and the above-mentioned rise is made based on these input signals An electromagnetic proportional pressure reducing valve 25, a descending electromagnetic proportional pressure reducing valve 26, an electromagnetic proportional pressure reducing valve 30 for main pump flow control, a first electromagnetic proportional pressure reducing valve 35, a second electromagnetic proportional pressure reducing valve 36, a head side communication oil passage opening / closing valve 39, Control signal to unloading valve electromagnetic switching valve 43, cylinder side check valve electromagnetic switching valve 48, accumulator side check valve electromagnetic switching valve 51, merging valve electro-hydraulic conversion valve 53, tank check valve electromagnetic switching valve 58, etc. Is output.

  Of the controls performed by the control device 27, first, cantilever control and double-sided control will be described. The control device 27 operates the operation of the boom operation lever input from the boom operation detection means 60 and the first head side pressure. The pressure Ph1 of the head side oil chamber 8a of the first boom cylinder 8 input from the sensor 62, the pressure Ph2 of the head side oil chamber 9a of the second boom cylinder 9 input from the second head side pressure sensor 63, and an accumulator Based on the pressure Pa of the accumulator 59 input from the pressure sensor 64, both the weights of the working unit 4 are held by the pressures of the head side oil chambers 8a, 9a of both the first and second boom cylinders 8, 9. The pressure of the head side oil chamber 9a of the second boom cylinder 9 of one of the first and second boom cylinders 8 and 9 is controlled. It determines whether to cantilever control to maintain.

  That is, as shown in the flowchart of FIG. 4, the control device 27 determines whether or not the boom operation lever is operated to the boom lowering side (step S <b> 1), the head side oil chambers of the first and second boom cylinders 8 and 9. Whether the differential pressure between the average value ((Ph1 + Ph2) / 2) of the pressures Ph1 and Ph2 of 8a and 9a and the pressure Pa of the accumulator 59 is smaller than a preset set value C1 ({(Ph1 + Ph2) / 2) } −Pa <C1?) (Step S2), the difference between the head-side relief pressure Pr2 of the second boom cylinder 9 set by the second relief valve 38 and the pressure Ph2 of the head-side oil chamber 9a of the second boom cylinder 9 It is determined whether or not the pressure is larger than a preset set value C2 (Pr2-Ph2> C2?) (Step S3), and all the determinations in steps S1, S2, and S3 are “YE”. In the case of "it is determined to perform the control cantilevered, if even one of the" NO "is determined to perform the inboard control.

  When it is determined that the both-end control is to be performed based on the determinations of steps S1, S2, and S3, the control device 27 sends a control signal to the OFF position N with respect to the electromagnetic switching valve 43 for unloading valve. The unloading valve 41 is closed (the unloading oil passage is closed). Further, the control device 27 outputs a control signal so as to be positioned at the open position X with respect to the head side communication oil passage opening / closing valve 39. Thereby, the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 are in communication with each other via the first and second head side oil passages 19 and 20. In this state, both the first and second boom cylinders 8 and 9 are responsible for holding the weight of the working unit 4, and thus the head side of both the first and second boom cylinders 8 and 9. A double-sided control for holding the weight of the working unit 4 with the pressure of the oil chambers 8a and 9a is executed.

  On the other hand, when it is determined that the cantilever control is performed based on the determinations of steps S1, S2, and S3, the control device 27 sends a control signal so that the head side communication oil passage opening / closing valve 39 is positioned at the closed position N. Output. As a result, the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 are shut off. Further, the control device 27 outputs a control signal of maximum pilot pressure output to the first electromagnetic proportional pressure reducing valve 35 to maximize the opening area of the first flow rate control valve 33, and the unloading valve electromagnetic switching valve 43. On the other hand, a control signal is output so as to be in the ON position X to open the unload valve 41 (open the unload oil passage). Thereby, the oil in the head side oil chamber 8a of the first boom cylinder 8 flows to the oil tank 12 via the first head side oil passage 19 and the head side discharge oil passage 40, and the first boom cylinder. The pressure in the head side oil chamber 8a is reduced to substantially the tank pressure. In this state, the weight of the working unit 4 is not held by the first boom cylinder 8, and only the second boom cylinder 9 is responsible for holding the weight of the working unit 4. Thus, the first and second boom cylinders are used. The cantilever control for holding the weight of the working unit 4 by the pressure of the head side oil chamber 9a of one of the second boom cylinders 9 is performed. By performing the cantilever control, the pressure in the head side oil chamber 9a of the second boom cylinder 9 is adjusted so that the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 during the both-end control. The pressure is increased about twice as much as the pressure.

  Here, as described above, the determination of the cantilever control and the double-sided control is performed based on the determinations in steps S1 to S3. The cantilever control is executed based on the determination in step S1. When the operating lever is operated to the boom lowering side, that is, when the working unit 4 is lowered, and when the boom operating lever is not operated to the boom lowering side, that is, when the working unit 4 is stopped to be lifted and At the time of ascent, double-sided control is executed.

  Even when the working unit 4 is lowered, the cantilever control is executed according to the determination in step S2. The pressure Ph1 of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 is determined. , When the differential pressure between the average value of Ph2 and the pressure Pa of the accumulator 59 is smaller than the set value C1 ({(Ph1 + Ph2) / 2} −Pa <C1), and when it is greater than the set value C1 ({(Ph1 + Ph2 ) / 2} −Pa ≧ C1), both-end control is executed. Here, the set value C1 is a value set in advance as a differential pressure necessary for flowing pressure oil from the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 to the accumulator 59. If the set value C1 is too small, the descending speed of the working unit 4 may be slow. Therefore, the heads of the first and second boom cylinders 8 and 9 can be secured in a state in which the descending speed of the working unit 4 can be secured. A differential pressure required to flow the pressure oil from the side oil chambers 8a, 9a to the accumulator 59 is set as a set value C1. That is, when the differential pressure between the average value of the pressures Ph1 and Ph2 of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 and the pressure Pa of the accumulator 59 is equal to or higher than the set value C1, Even in the case of the cantilever control, the cantilever control is not executed because the oil discharged from the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 can be accumulated in the accumulator 59. . In order to prevent hunting, the set value C1 is set to be slightly different between the case of shifting from the cantilever control to the cantilever control and the case of shifting from the cantilever control to the cantilever control.

  Further, even when the working unit 4 is lowered, the cantilever control is executed according to the determination in step S3, and the head side relief pressure Pr2 of the second boom cylinder 9 and the head side oil of the second boom cylinder 9 are executed. When the differential pressure with respect to the pressure Ph2 in the chamber 9a is larger than the set value C2 (Pr2-Ph2> C2) and not more than the set value C2 (Pr2-Ph2 ≦ C2), the double-sided control is executed. The Here, the set value C2 is a value of a differential pressure that is set in advance to prevent inadvertent operation of the second relief valve 38. That is, when the pressure difference between the head-side relief pressure Pr2 of the second boom cylinder 9 and the pressure Ph2 of the head-side oil chamber 9a of the second boom cylinder 9 is equal to or less than the set value C2, the second relief valve 38 is not prepared. Therefore, the possibility that the oil in the head-side oil chamber 9a of the second boom cylinder 9 flows into the oil tank 12 increases, so that the cantilever control is not executed.

Next, the control of the control device 27 based on the operation of the boom operation lever will be described.
First, when the boom control lever is not operated on either the boom lowering side or the raising side, that is, when the working unit 4 is stopped to be raised or lowered, the control device 27 performs the raising electromagnetic proportional pressure reducing valve 25, the lowering electromagnetic proportional. A pilot pressure output control signal is not output to the pressure reducing valve 26, the first electromagnetic proportional pressure reducing valve 35, and the second electromagnetic proportional pressure reducing valve 36, whereby the boom cylinder control valve 18 is positioned at the neutral position N, and The first and second flow control valves 33 and 34 are located at the closed position N. Further, the control signal for the flow control signal pressure Pc is not output to the main pump flow control electromagnetic proportional pressure reducing valve 30, and the negative control signal pressure Pn is input to the regulator 13 of the main pump 10. Further, the cylinder side check valve electromagnetic switching valve 48, the accumulator side check valve electromagnetic switching valve 51, and the tank check valve electromagnetic switching valve 58 are all controlled to be located at the OFF position N, whereby the cylinder side check valve is controlled. 46, accumulator side check valve 49 and tank check valve 56 are all kept closed. Further, no actuation signal is output to the electro-hydraulic conversion valve 53 for the merging valve. Further, as described above, when the raising / lowering of the working unit 4 is stopped, since the both-end control is executed, the head side communication oil passage opening / closing valve 39 is located at the open position X, and the unloading valve 41 is controlled to be in a closed state.

  On the other hand, when the boom operation lever is operated to the boom lowering side, that is, when the working unit 4 is lowered, as described above, the pressures of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 are as described above. Depending on the pressure Ph1, Ph2 and the pressure Pa of the accumulator 59, there are cases where both-end support control is executed and cantilever control is executed. When both-end control is executed, the head-side communication oil passage opening / closing valve 39 is controlled to be in the open position X, and the unload valve 41 is controlled to be in the closed state. On the other hand, when the cantilever control is executed, the head side communication oil passage opening / closing valve 39 is located at the closed position N, the opening area of the first flow control valve 33 is maximized, and the unload valve 41 is controlled to be in the open state.

  Further, when operated to the boom lowering side, the control device 27 corresponds to the operation amount of the boom operating lever to the lowering pilot port 18b of the boom cylinder control valve 18 with respect to the lowering electromagnetic proportional pressure reducing valve 26. A control signal is output so as to output the pilot pressure. As a result, the boom cylinder control valve 18 is switched to the lowering position Y, and the pressure oil in the pressure oil supply oil passage 17 is changed to the boom cylinder control valve 18 and the rod side main oil passage at the lowering position Y. 24, supplied to the rod side oil chambers 8b, 9b of the first and second boom cylinders 8, 9 via the rod side communication oil passage 23. As will be described later, when the boom operation lever is operated to the boom lowering side, only the discharge oil of the main pump 10 is supplied to the pressure oil supply oil passage 17.

  Further, when operated to the boom lowering side, the control device 27 does not output a control signal of the flow control signal pressure Pc output to the main pump flow control electromagnetic proportional pressure reducing valve 30. As a result, the pressure input to the other port 29a of the shuttle valve 29 becomes the tank pressure, and thus the shuttle valve 29 selects the negative control signal pressure Pn and inputs it to the regulator 13 of the main pump 10. As a result, the main pump 10 is controlled so that the discharge flow rate increases or decreases in accordance with the increase or decrease of the operation amount of the boom operation lever.

  Further, when operated to the boom lowering side, the control device 27 outputs a control signal to the first and second electromagnetic proportional pressure reducing valves 35 and 36. In this case, both-end control is executed. The control is different from the case where cantilever control is executed. First, a description will be given of the case of both-end control. The control device 27 is connected to the pilot ports 33a and 34a of the first and second flow rate control valves 33 and 34 with respect to the first and second electromagnetic proportional pressure reducing valves 35 and 36, respectively. A control signal is output so as to output a pilot pressure corresponding to the operation amount of the boom operation lever. As a result, the first and second flow control valves 33 and 34 are switched to the open position X for opening the first and second head-side oil passages 19 and 20, and the opening area is determined by the operation amount of the boom operation lever. It is controlled to correspond to. Thus, the pressure oil discharged from the head-side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 is recovered via the first and second flow control valves 33, 34 at the open position X. Although supplied to the oil passage 44, the flow rate is controlled by the opening areas of the first and second flow control valves 33 and 34. In the case of both-end control, as described above, the head side communication oil passage opening / closing valve 39 is controlled to be in the open position X, and the unload valve 41 is controlled to be in the closed state. The oil discharged from the head side oil chamber 8a of the one boom cylinder 8 and passing through the first flow control valve 33 does not flow to the oil tank 12 via the head side discharge oil path 40, but the head side communication oil path 21. The oil is supplied to the recovered oil passage 44 via

  Next, the case of cantilever control will be described. The control device 27 applies a pilot pressure corresponding to the operation amount of the boom operation lever to the pilot port 34a of the second flow rate control valve 34 with respect to the second electromagnetic proportional pressure reducing valve 36. A control signal is output so as to output. As a result, the second flow rate control valve 34 is switched to the open position X where the second head side oil passage 20 is opened. Thus, the pressure oil discharged from the head-side oil chamber 9a of the second boom cylinder 9 is supplied to the recovery oil passage 44 via the second flow rate control valve 34 at the open position X. It is controlled by the opening area of the second flow control valve 34. In the case of cantilever control, as described above, the head side communication oil passage opening / closing valve 39 is located at the closed position N, and the opening area of the first flow rate control valve 33 is maximized. The load valve 41 is controlled to be in an open state, whereby the discharged oil from the head side oil chamber 8a of the first boom cylinder 8 flows into the oil tank 12 via the head side discharged oil passage 40. On the other hand, the oil discharged from the head-side oil chamber 9a of the second boom cylinder 9 has a high pressure approximately twice that in the case of the double-sided control, and the high-pressure oil is supplied to the recovery oil passage 44. The

  Further, when operated to the boom lowering side, the control device 27 outputs a control signal so that the cylinder side check valve electromagnetic switching valve 48 and the accumulator side check valve electromagnetic switching valve 51 are switched to the ON position X. To do. Thereby, both the cylinder side check valve 46 and the accumulator side check valve 49 are opened, and the flow of oil from the recovery oil passage 44 to the accumulator oil passage 45 is allowed. Thus, in the case of double-end control, the pressure oil discharged from the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 and supplied to the recovery oil passage 44 is also cantilever controlled. In this case, the oil discharged from the head-side oil chamber 9a of the second boom cylinder 9 and supplied to the recovery oil passage 44 flows into the accumulator oil passage 45, and is accumulated in the accumulator 59 via the accumulator oil passage 45. It has become so.

  Thus, when the working unit 4 is lowered, in the double-sided control, the oil discharged from the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 is accumulated in the accumulator 59 and cantilevered. In the control, the oil discharged from the head side oil chamber 9a of the second boom cylinder 9 is accumulated in the accumulator 59. In this case, the oil discharged from the head side oil chambers 8a, 9a The first boom boom 8 and the second boom cylinder 9 hold the weight of the working unit 4 by the potential energy of the two-clamp control, and the second boom cylinder 9 on one side further weights the working unit 4. Since the cantilever control for holding the pressure is higher than that of the double-sided control (about twice), the accumulator 59 accumulates high-pressure pressure oil that can handle high-load work.

  Further, when operated to the boom lowering side, the control device 27 does not output an operation signal to the electro-hydraulic conversion valve 53 for the merging valve. To be controlled. Accordingly, only the discharge oil of the main pump 10 is supplied to the pressure oil supply oil passage 17 without being supplied from the accumulator oil passage 45 to the pressure oil supply oil passage 17 via the merging oil passage 16. It has become so.

  Further, when operated to the boom lowering side, the control device 27 controls the tank check valve electromagnetic switching valve 58 so as to be positioned at the OFF position N. As a result, the tank check valve 56 is held in a closed state in which the accumulator discharge oil passage 55 is closed.

  Here, when the working unit 4 is lowered, as described above, the oil discharged from the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 is accumulated in the accumulator 59. In this case, in order to prevent the backflow from the accumulator 59 to the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9, the control device 27 includes the first and second head side pressure sensors 62, 63. Back flow prevention control based on the pressures Ph1 and Ph2 of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 and the pressure Pa of the accumulator 59 input from the accumulator pressure sensor 64. Is configured to run. The backflow prevention control is executed when the pressures Ph1 and Ph2 of the head-side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 are smaller than the pressure Pa of the accumulator 59 during both-end control. During the cantilever control, the control is performed when the pressure Ph2 of the head side oil chamber 9a of the second boom cylinder 9 is smaller than the pressure Pa of the accumulator 59. In this case, the control of each valve in the backflow prevention control is described above. Priority is given to control of each valve in both-end control and cantilever control.

  When performing the backflow prevention control, the control device 27 outputs a control signal to the cylinder side check valve electromagnetic switching valve 48 and the accumulator side check valve electromagnetic switching valve 51 so as to switch to the OFF position N. Thereby, both the cylinder side check valve 46 and the accumulator side check valve 49 are closed, and the flow of oil from the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 to the accumulator 59, and Oil flow from the accumulator 59 to the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 is both blocked. In addition, a control signal is output to the first and second electromagnetic proportional pressure reducing valves 35 and 36 so as to output a pilot pressure corresponding to the operation amount of the boom operation lever. The valves 33 and 34 are controlled so as to have an opening area corresponding to the operation amount of the boom operation lever. Further, a control signal is output to the head side communication oil passage opening / closing valve 39 so as to be positioned at the open position X where the head side communication oil passage 21 is opened, and the unloading valve electromagnetic switching valve 43 is turned on. A control signal is output so as to be positioned at the position X, whereby the unload valve 41 enters an open state in which the head side discharge oil passage 40 is opened. Then, the first and second flow control valves 33 and 34 are opened, the head side communication oil passage 21 is opened, and the head side discharge oil passage 40 is opened, whereby the first and second boom cylinders 8 and 9 are opened. The oil discharged from the head side oil chambers 8a, 9a flows into the oil tank 12 in a state where the flow rate is controlled by the first and second flow rate valves 33, 34.

In other words, when the backflow prevention control is executed when the working unit 4 is lowered, the cylinder side check valve 46 and the accumulator side check valve 49 in the closed state cause the head side oil of the first and second boom cylinders 8 and 9 to move. The flow of oil from the chambers 8a and 9a to the accumulator 59 and the flow of oil from the accumulator 59 to the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 are blocked, and the first and second The pressure oil in the head side oil chambers 8a, 9a of the two boom cylinders 8, 9 is discharged to the oil tank 12 in a state where the flow rate is controlled by the first and second flow rate control valves 33, 24.
When the double-sided control is executed when the working unit 4 is lowered, the head-side relief pressure Pr2 of the second boom cylinder 9 and the second boom cylinder 9 The pressure Ph1 of the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 is excluding the case where the differential pressure from the pressure Ph2 of the head side oil chamber 9a is not more than the set value C2 (Pr2-Ph2 ≦ C2). When the differential pressure between the average value of Ph2 and the pressure Pa of the accumulator 59 becomes smaller than the set value C1 ({(Ph1 + Ph2) / 2} −Pa <C1), the control shifts from the both-end control to the cantilever control. For this reason, there is a possibility that the backflow prevention control may be executed during the both-end control. The head-side relief pressure Pr2 of the second boom cylinder 9 and the pressure Ph2 of the head-side oil chamber 9a of the second boom cylinder 9 This is only when the differential pressure is less than the set value C2.
In the present embodiment, the first and second head side oil passages 19 and 20, the head side communication oil passage 21, and the head side communication oil passage opening / closing valve in which the first and second flow control valves 33 and 34 are arranged. 39, the head side oil discharge passage 40, and the unload valve 41 are oil tanks for discharging oil from the head side oil chambers of the first and second hydraulic cylinders of the present invention via the first and second flow control valves. A tank oil passage that can be freely opened and closed is configured. In other words, in the present embodiment, the head-side communication oil passage 21, the head-side communication oil passage opening / closing valve 39, the head-side discharge oil passage 40, and the unload valve 41 that are used when performing both-end control and cantilever control are used as they are. Thus, a tank oil passage that can be freely opened and closed when the backflow prevention control is performed is formed, thereby simplifying the circuit.

  Next, the control when the boom operating lever is operated to the boom raising side, that is, the control when the working unit 4 is raised will be described. When the working unit 4 is raised, as described above, the both-end control is executed. Therefore, the head side communication oil passage opening / closing valve 39 is controlled to be in the open position X, and the unload valve 41 is controlled to be closed.

  Further, when operated to the boom raising side, the control device 27 corresponds to the operation amount of the boom operation lever to the up / down pilot port 18a of the boom cylinder control valve 18 with respect to the ascending electromagnetic proportional pressure reducing valve 25. A control signal is output so as to output the pilot pressure. As a result, the boom cylinder control valve 18 is switched to the ascending position X, so that the pressure oil in the pressure oil supply oil passage 17 passes through the boom cylinder control valve 18 at the ascending position X. The oil is supplied to the head side oil chambers 8 a and 9 a of the second boom cylinder 8 and the oil discharged from the rod side oil chambers 8 b and 9 b is discharged to the oil tank 12. As will be described later, when operated to the boom raising side, not only the discharge oil of the main pump 10 but also the pressure accumulation oil of the accumulator 59 is supplied to the pressure oil supply oil passage 17.

  Further, at this time, the control device 27 does not output a pilot pressure output control signal to the first and second electromagnetic proportional pressure reducing valves 35 and 36, so that the first and second flow rate control valves 33 and 34 are Control is performed so as to be in the closed position N. Further, as described above, the head-side communication oil passage opening / closing valve 39 is located at the open position X, and the unload valve 41 is closed. Thus, the pressure oil supplied to the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 via the boom cylinder control valve 18 at the ascending side position X is the head side discharged oil. Without flowing into the oil tank 12 via the path 40, the head side main oil path 22, the head side communication oil path 21, and the first and second check valves 31 of the first and second head side oil paths 19 and 20 are provided. , 32 to the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9.

  Further, when operated to the boom raising side, the control device 27 controls the cylinder side check valve electromagnetic switching valve 48 and the accumulator side check valve electromagnetic switching valve 51 to be positioned at the OFF position N. As a result, the cylinder side check valve 46 and the accumulator side check valve 49 are held in a closed state, so that the recovery oil passage 44 and the accumulator oil passage 45 are shut off.

  Furthermore, when operated to the boom raising side, the control device 27 outputs an operation signal to the merging valve electro-hydraulic conversion valve 53 so as to switch the merging valve 52 to the open position X. As a result, the merging valve 52 opens the merging oil passage 16 extending from the accumulator oil passage 45 to the discharge line 15 of the main pump 10. The opening area of the merging valve 52 depends on the amount of operation of the boom operation lever, the pressure Pa of the accumulator 59 and the main pressure. It is controlled according to the differential pressure from the discharge pressure Pp of the pump 10. Thus, the pressure oil accumulated in the accumulator 59 is joined to the discharge line 15 of the main pump 10 via the accumulator oil passage 45 and the joining oil passage 16, and as described above, the pressure oil supply oil passage 17, the boom cylinder control valve 18 at the ascending position X is supplied to the head side oil chambers 8 a and 9 a of the first and second boom cylinders 8 and 9.

  Further, when operated to the boom raising side, the control device 27 outputs a control signal to the main pump flow rate control electromagnetic proportional pressure reducing valve 30 so as to output the flow rate control signal pressure Pc. In this case, the control device 27 sets the discharge flow rate of the main pump 10 to a flow rate obtained by subtracting the combined flow rate from the accumulator 59 from the pump flow rate required according to the operation amount of the boom operation lever and the pump output. Therefore, the value of the flow control signal pressure Pc is controlled.

  The flow control signal pressure Pc output from the main pump flow control electromagnetic proportional pressure reducing valve 30 is input to the other input port 29 b of the shuttle valve 29. On the other hand, the negative control signal pressure Pn is input to one input port 29a of the shuttle valve 29. However, when the supply pressure oil from the accumulator 59 is merged into the discharge line 15, the flow control signal pressure Pc Since the signal pressure that reduces the pump flow rate than the negative control signal pressure Pn, that is, the flow control signal pressure Pc is higher than the negative control signal pressure Pn, the flow control signal pressure Pc is selected by the shuttle valve 29. And input to the regulator 13 of the main pump 10. Thus, the discharge flow rate of the main pump 10 is controlled to be a flow rate that is reduced by the combined flow rate from the accumulator 59.

  That is, when the working unit 4 is raised, the accumulated oil in the accumulator 59 merges with the discharge oil of the main pump 10 via the merged oil passage 16, and the merged pressure oil is the boom cylinder control valve at the ascending position X. 18 is supplied to the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9. Further, at this time, the discharge flow rate of the main pump 10 is controlled to be a flow rate reduced by the combined flow rate from the accumulator 59. Thus, the potential energy recovered by the accumulator 59 when the working unit 4 is lowered can be reused when the working unit 4 is raised, and the discharge flow rate of the main pump 10 can be reduced accordingly. .

  Further, when operated to the boom raising side, the control device 27 controls the tank check valve electromagnetic switching valve 58 so as to be positioned at the OFF position N. As a result, the tank check valve 56 is held in a closed state in which the accumulator discharge oil passage 55 is closed.

Next, accumulator discharge control performed by the control device 27 will be described.
The control device 27 switches the tank check valve electromagnetic switching valve 58 to the ON position X for a predetermined time when an operator operates an accumulator discharge operation switch (not shown) or when the engine E is stopped. As a result, the tank check valve 56 opens to open the accumulator discharge oil passage 55, and thus the accumulated oil in the accumulator 59 is discharged to the oil tank 12 via the accumulator discharge oil passage 55. . In other words, when the operation switch for discharging the accumulator is operated or the engine E is stopped, the accumulated oil in the accumulator 59 is automatically discharged to the oil tank 12 to be in a state suitable for long-term storage. Even when the excavator 1 is not used for a long time, it is possible to reliably avoid a problem that the accumulator 59 is left for a long time while the oil is accumulated in the accumulator 59 and the gas amount of the accumulator 59 decreases. Yes.

  Furthermore, when the engine E is stopped, the control device 27 sets the cylinder side check valve electromagnetic switching valve 48, the accumulator side check valve electromagnetic switching valve 51, and the tank check valve electromagnetic switching valve 58 for a predetermined time. While switching to the ON position X, the first and second electromagnetic proportional pressure reductions can be performed so that the first and second flow rate control valves 33 and 34 can be switched to the open position X based on the lowering operation of the boom operation lever. The valves 35 and 36 are controlled. Thus, based on the lowering operation of the boom operation lever, the oil in the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 is supplied to the recovery oil passage 44, the accumulator oil passage 45, and the accumulator. It is possible to flow to the oil tank 12 via the discharge oil passage, and thereby, even after the stop operation of the engine E, the working unit 4 is operated based on the lowering operation of the boom operation lever for a predetermined time. Can be lowered.

  In the present embodiment configured as described, the working unit 4 of the excavator 1 moves up and down as the boom 5 constituting the working unit 4 moves up and down. The first boom cylinder of the pair of first and second boom cylinders 8 and 9 is included in the hydraulic control system of the hydraulic excavator 1. 8 open / close unload oil passages (first head side oil passage 19, first flow rate control valve 33, head side discharge oil passage 40, and unload valve) for flowing the pressure oil in the head side oil chamber 8a to the oil tank 12. 41) and a control device 27 for performing opening / closing control of the unload oil passage, and when the unload oil passage is closed, the first and second boom cylinders 8 are provided. , 9 heads While the weight of the working unit 4 is maintained by the pressure of the chambers 8a and 9a, the unload oil passage is open (the opening area of the first flow control valve 33 is maximum and the unload valve 41 is open). ), The pressure of the head side oil chamber 9a of the second boom cylinder 9 holds the weight of the working unit 4 and the first and second hold the weight of the working unit 4 when the working unit 4 is lowered. Oil discharged from the head side oil chambers 8 a and 9 a of the boom cylinders 8 and 9 or the head side oil chamber 9 a of the second boom cylinder 9 is accumulated in the accumulator 59.

  Thus, when the working unit 4 is lowered, the unloading oil passage is opened and the pressure oil in the head-side oil chamber 8a of the first boom cylinder 8 is caused to flow into the oil tank 12, so that the weight of the working unit 4 is the second boom. While being held at the pressure of the head side oil chamber 9a of the cylinder 9, the oil discharged from the head side oil chamber 9a of the second boom cylinder 9 is accumulated in the accumulator 59. In this case, the second boom The pressure of the head side oil chamber 9a of the cylinder 9, that is, the holding pressure for holding the weight of the working unit 4, is the holding pressure when the weight of the working unit 4 is held by both the first and second boom cylinders 8 and 9. Therefore, the accumulator 59 accumulates high-pressure oil that can handle high-load work.

  As a result, the accumulator 59 can accumulate high-pressure oil that can be used even during high-load work such as excavation work and lifting swivel. Therefore, the accumulator 59 can be used as it is without increasing pressure separately. It can be used for work. Thus, as in the case where the accumulator pressure accumulation oil is increased using a pump driven by engine power, there is a decrease in torque in the power transmission path from the engine to the pump, loss of idling torque due to the inertial mass of the pump itself, etc. In addition, the potential energy of the working unit 4 collected in the accumulator 59 can be used with as little loss as possible and can greatly contribute to cost reduction.

  Further, the hydraulic control system of the excavator 1 includes a head side communication oil passage 21 that communicates between the head side oil chambers 8a of the first and second boom cylinders 8 and 9, and the head side communication oil passage 21. A head side communication oil passage opening / closing valve 39 controlled by the control device 27 to be opened and closed is provided, and the head side communication oil passage opening / closing valve 39 is connected to the head side communication when the unload oil passage is closed. While the oil passage 21 is opened, the head side communication oil passage 21 is controlled to be closed when the unload oil passage is open. Thus, the state in which the unload oil passage is closed, that is, the double-sided control that holds the weight of the working unit 4 in the head side oil chambers 8a, 9a of both the first and second boom cylinders 8, 9 is performed. In the executed state, the head side oil chambers 8a and 9a are in communication with each other, and the working unit 4 can be supported by the pair of first and second boom cylinders 8 and 9 in a well-balanced manner. Is open, that is, in a state where the cantilever control for holding the weight of the working unit 4 is performed in the head side oil chamber 9a of the second boom cylinder 9, the head side oil chamber of the second boom cylinder 9 is performed. 9a and the head side oil chamber 8a of the first boom cylinder 8 can be shut off.

  Further, the unload oil passage is opened, that is, the cantilever control is executed when the working unit 4 that accumulates pressure on the accumulator 59 is lowered, and when the working unit 4 is stopped and raised, the unloading oil passage is unloaded. Since the load oil passage is closed, that is, the both-end support control is executed, the pressure oil in the head-side oil chamber 8a of the first boom cylinder 8 is not used except when accumulator 59 is accumulating. The loss flowing into the oil tank 12 can be eliminated, and there is no fear that the force will be insufficient or the balance will be lost when the working unit 4 is raised.

  Further, in this case, even when the working unit 4 is lowered, the average value of the pressures Ph1 and Ph2 of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 and the pressure Pa of the accumulator 59 is obtained. When the differential pressure is greater than or equal to the set value C1 ({(Ph1 + Ph2) / 2} −Pa ≧ C1), the unload oil passage is closed, that is, both-end control is executed, and the first and second boom cylinders are executed. The oil discharged from the head-side oil chambers 8 a and 9 a of 8 and 9 is accumulated in the accumulator 59. Thus, the pressures Ph1 and Ph2 of the head-side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 are higher than the pressure Pa of the accumulator 59, and can be accumulated in the accumulator 59 even in both-end control. In this case, the cantilever control will not be executed, thereby causing a loss that causes the pressure oil in the head side oil chamber 8a of the first boom cylinder 8 to flow into the oil tank 12 due to the opening of the unload oil passage. Can be reduced.

  Furthermore, in this case, even when the working unit 4 is lowered, the differential pressure between the head-side relief pressure Pr2 of the second boom cylinder 9 and the pressure Ph2 of the head-side oil chamber 9a of the second boom cylinder 9 is a set value. In the case of C2 or less (Pr2-Ph2 ≦ C2), the unload oil passage is closed, that is, both-end control is executed. As a result, it is possible to prevent the pressure Ph2 in the head-side oil chamber 9a of the second boom cylinder 9 from rising excessively and the second relief valve 38 from being inadvertently operated, and thus the second relief. It is possible to eliminate the loss that the valve 38 operates and the oil discharged from the head side oil chamber 9a of the second boom cylinder 9 flows into the oil tank 12.

  Further, the hydraulic control system of the excavator 1 includes first and second flow rate controls for controlling the discharge flow rates from the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 when the working unit 4 is lowered. Valves 33 and 34 are provided, and the first and second flow control valves 33 and 34 can control the lowering speed of the working unit 4 during both-end control or cantilever control.

  Furthermore, the hydraulic control system of the hydraulic excavator 1 includes a cylinder side check valve 46 that can block the flow of oil from the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 to the accumulator 59. The accumulator 59 is provided with an accumulator check valve 49 that can prevent the flow of oil from the accumulator 59 to the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9. By the valve 46 and the accumulator side check valve 49, when the working unit 4 stops moving up and down, the pressure oil in the head side oil chambers 8 a and 9 a of the first and second boom cylinders 8 and 9 flows into the accumulator 59, or the accumulator It is ensured that 59 pressure accumulation oil is supplied to the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9. It can be avoided.

  Furthermore, when the working unit 4 is lowered, the pressures Ph1 and Ph2 of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 are lower than the pressure Pa of the accumulator 59 during both-end control. During cantilever control, if the pressure Ph2 in the head-side oil chamber 9a of the second boom cylinder 9 is lower than the pressure Pa in the accumulator 59, backflow prevention control is executed. That is, the cylinder side check valve 46 and the accumulator side check valve 49 allow the oil flow from the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 to the accumulator 59, and from the accumulator 59 to the first. The flow of oil to the head side oil chambers 8a, 9a of the second boom cylinders 8, 9 is blocked, and the oil discharged from the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9 is prevented. The oil flows into the oil tank 12 in a state where the flow rate is controlled by the first and second flow rate control valves 33 and 34. Thus, even when the pressures Ph1 and Ph2 of the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 are transiently lower than the pressure Pa of the accumulator 59 when the working unit 4 is lowered, the accumulator 59, it is possible to reliably prevent the pressure oil from flowing back to the head side oil chambers 8a, 9a of the first and second boom cylinders 8, 9, and even in this case, The working unit 4 can be lowered while the speed is controlled by the two flow control valves 33 and 34.

Needless to say, the present invention is not limited to the above embodiment, and in the above embodiment, the accumulated oil of the accumulator 59 is joined to the discharge line 15 of the main pump 10 via the joining oil passage 16. The working unit 4 is configured to be supplied to the head side oil chambers 8a and 9a of the first and second boom cylinders 8 and 9 without being limited thereto. For example, the pressure accumulation oil of the accumulator 59 is used. Can be used as pressure oil supplied to a plurality of other hydraulic actuators provided on the work machine (in the case where the work machine is a hydraulic excavator, for example, a travel motor, a swing motor, an arm cylinder, and a bucket cylinder). In this case, the potential energy collected when the working unit 4 is lowered can be used for the operation of other hydraulic actuators.
Furthermore, the present invention can be implemented not only in a hydraulic excavator but also in a hydraulic control system for various work machines provided with a pair of hydraulic cylinders that raise and lower a working unit.
In the hydraulic circuit diagram of FIG. 2, one main pump is shown as a hydraulic pump that supplies pressure oil to a plurality of hydraulic actuators, but it is needless to say that two or more main pumps may be provided.

It is a perspective view of a hydraulic excavator. It is a hydraulic circuit diagram of a hydraulic control system. It is a block diagram which shows the input / output of a control apparatus. It is a flowchart figure which shows judgment of cantilever control and double-sided control.

Explanation of symbols

4 Working Unit 8 First Boom Cylinder 8a First Boom Cylinder Head Side Oil Chamber 9 Second Boom Cylinder 9a Second Boom Cylinder Head Side Oil Chamber 12 Oil Tank 19 First Head Side Oil Path 21 Head Side Communication Oil Path 27 Control Device 33 First flow control valve 34 Second flow control valve 38 Second relief valve 39 Head side communication oil passage opening / closing valve 40 Head side discharge oil passage 41 Unload valve 46 Cylinder side check valve 49 Accumulator side check valve 59 Accumulator 62 First Head side pressure sensor 63 Second head side pressure sensor 64 Accumulator pressure sensor

Claims (8)

  In a hydraulic control system for a working machine comprising a working unit that can be raised and lowered and a pair of first and second hydraulic cylinders that raise and lower the working unit, the hydraulic control system includes a head side oil chamber of the first hydraulic cylinder. An open / close unload oil passage that allows the pressure oil to flow into the oil tank and a control device that performs open / close control of the unload oil passage are provided, and when the unload oil passage is closed, the first and second hydraulic cylinders While holding the weight of the working part with the pressure of the head side oil chamber, while the unload oil passage is open, the weight of the working part is held with the pressure of the head side oil chamber of the second hydraulic cylinder, A hydraulic control system for a working machine, comprising an accumulator for accumulating discharged oil from a head side oil chamber of a first hydraulic cylinder, a second hydraulic cylinder, or a second hydraulic cylinder that holds weight when the working unit is lowered. .   A head-side fluid passage that communicates between the head-side fluid chambers of the first and second hydraulic cylinders to the hydraulic control system, and a head-side fluid passage that is controlled by a controller to open and close the head-side fluid passage. And the control device opens the head side communication oil passage opening / closing valve when the unload oil passage is closed while opening the head side communication oil passage, while the unload oil passage is open. 2. The hydraulic control system for a work machine according to claim 1, wherein control is performed so as to close the side communication oil passage.   3. The work machine according to claim 1, wherein the control device performs control so that the unload oil passage is opened when the working portion is lowered, and the unload oil passage is closed when the working portion is lifted and stopped. Hydraulic control system in.   The hydraulic control system is provided with accumulator pressure detecting means for detecting the pressure of the accumulator, and first and second head side pressure detecting means for detecting the pressure of the head side oil chambers of the first and second hydraulic cylinders, respectively. Even when the working unit is descending, the control device detects that the difference between the average value of the pressure in the head side oil chambers of the first and second hydraulic cylinders and the pressure in the accumulator is equal to or higher than a preset value. 4. The hydraulic control system for a work machine according to claim 3, wherein the control is performed to close the unload oil passage.   The hydraulic control system is provided with a second head side pressure detecting means for detecting the pressure of the head side oil chamber of the second hydraulic cylinder and a second relief valve for setting the head side relief pressure of the second hydraulic cylinder. Even when the working unit is descending, the device is used when the differential pressure between the head-side relief pressure of the second hydraulic cylinder and the pressure of the head-side oil chamber of the second hydraulic cylinder is not more than a preset set value. 5. The hydraulic control system for a work machine according to claim 3, wherein the control is performed so as to close the unload oil passage.   The first and second flow rate control valves that respectively control the discharge flow rates from the head side oil chambers of the first and second hydraulic cylinders when the working unit is lowered in the hydraulic control system. The hydraulic control system for the work machine according to any one of claims 5 to 6.   The hydraulic control system can prevent the flow of oil from the head side oil chambers of the first and second hydraulic cylinders to the accumulator, and the flow of oil from the accumulator to the head side oil chambers of the first and second hydraulic cylinders. The hydraulic control system for a work machine according to any one of claims 1 to 6, further comprising a valve means that can be used.   In the hydraulic control system, accumulator pressure detecting means for detecting the pressure of the accumulator, first and second head side pressure detecting means for detecting the pressure of the head side oil chambers of the first and second hydraulic cylinders, respectively, Openable and closable tank oil passage for flowing oil discharged from the head side oil chamber of the second hydraulic cylinder to the oil tank via the first and second flow control valves, and the head side oil chamber of the first and second hydraulic cylinders Valve means capable of preventing the flow of oil from the accumulator to the accumulator and the oil flow from the accumulator to the head side oil chamber of the first and second hydraulic cylinders. When the pressure of the head side oil chamber of the first and second or second hydraulic cylinders holding the weight is smaller than the pressure of the accumulator, the valve means causes the first and second hydraulic cylinder heads to The oil flow from the side oil chamber to the accumulator and the oil flow from the accumulator to the head side oil chambers of the first and second hydraulic cylinders are blocked, and the tank oil passage is opened to open the first and second hydraulic pressures. 7. The hydraulic control system for a work machine according to claim 6, wherein the pressure oil in the cylinder head side oil chamber is caused to flow to the oil tank via the first and second flow rate control valves.

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