JP2008101414A - Hydraulic control system in hydraulic excavator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To recover and recycle the potential energy of a working part and smoothly raise a frame in a hydraulic excavator having the working part with a boom, an arm, and a bucket. <P>SOLUTION: The hydraulic control system comprises a frame raising operation determination part 74 for determining whether a frame raising operation is performed. When the boom is lowered except when the frame raising operation is performed, the oil discharged from the head side oil chamber of a boom cylinder is accumulated in an accumulator and supplied to the rod side oil chamber of the boom cylinder. When the frame raising operation is performed, the pressure oil supplied from a dedicated pump is supplied to the rod side oil chamber of the boom cylinder, and the oil discharged from the head side oil chamber of the boom cylinder is returned to an oil tank. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention belongs to the technical field of a hydraulic control system in a hydraulic excavator when performing a body lifting operation.

In general, a hydraulic excavator is a boom body that is pivotally supported by a machine body that includes a lower traveling body and an upper swing body, and a base end of which is swingably supported by the machine body. A working part consisting of an arm that is pivotally supported and a work attachment (for example, a bucket) attached to the tip of the arm is mounted. In such a hydraulic excavator, it escapes from a dent or soft ground. If the crawler that constitutes the lower traveling body 2 is clogged with mud or gravel, the boom is further lowered with the work attachment grounded (boom cylinder). So that the boom is lowered relative to the airframe body, thereby lifting the airframe body. There is a case of performing (see Figure 1). This airframe lifting operation reduces the boom cylinder against the weight of the airframe body. Therefore, a large thrust is required to reduce the boom cylinder. In this case, the boom cylinder rod-side oil chamber and head The greater the differential pressure with the side oil chamber, the greater the thrust.
Therefore, conventionally, during the body lifting operation, the port relief valve that sets the maximum pressure when the boom of the boom cylinder descends, and the set pressure of the main relief valve that sets the maximum pressure of the hydraulic pump that is the hydraulic pressure supply source of the boom cylinder, A technique configured to switch to the high voltage side is disclosed (for example, see Patent Document 1).
On the other hand, when the boom is lowered while the work attachment is not in contact with the ground, the oil discharged from the head side oil chamber of the boom cylinder is at a high pressure due to the potential energy of the working unit, but the potential energy is recovered. In order to reuse the boom, conventionally, a boom raising / lowering assist cylinder is provided in addition to the boom cylinder, and when the boom is lowered, the oil discharged from the head side oil chamber of the boom raising / lowering assist cylinder is accumulated in the accumulator. A technique has been disclosed in which pressure oil accumulated in an accumulator is supplied to a head side oil chamber of a boom raising / lowering assist cylinder when rising (see, for example, Patent Document 2).
JP 2003-20692 A Japanese Patent No. 2582310

However, according to Patent Document 2, the oil discharged from the boom lifting assist cylinder is accumulated in the accumulator when the boom is lowered, but the oil discharged from the head side oil chamber of the boom cylinder passes through the control valve. Therefore, only a part of the potential energy of the work machine is recovered. Therefore, it is proposed to accumulate the discharged oil from the head side oil chamber of the boom cylinder in the accumulator when the boom is lowered without providing the boom raising / lowering assist cylinder.
By the way, as described in Patent Document 2, in the case where the oil discharged from the head side oil chamber of the boom lifting assist cylinder is accumulated in the accumulator, or as proposed, the head side oil chamber of the boom cylinder. When the boom is lowered, the boom lifting assist cylinder or the boom cylinder head side oil chamber is connected to the accumulator when the boom is lowered. When an attempt is made to lift the fuselage, the boom lifting assist cylinder or the boom cylinder head side oil chamber is connected to the accumulator and is therefore at a high pressure. Therefore, as in Patent Document 1, the rod side oil chamber is used. Even if it is configured so that high pressure oil is supplied to the boom, the boom lifting assist cylinder Rui has a problem that it is difficult to obtain a large thrust for reducing the boom cylinder, there is a problem to be present invention is resolved here.

The present invention has been made in view of the above circumstances and has been created for the purpose of solving these problems. The invention of claim 1 is such that the base body is swingable to the body body. A working part equipped with a boom supported by a boom cylinder that moves up and down by the expansion and contraction of the boom cylinder, an arm that is pivotally supported at the tip of the boom, and a work attachment that is attached to the tip of the arm is mounted. Whether the hydraulic excavator is in a body lifting operation in which the boom main body is lifted by lowering the boom relative to the body main body while the work attachment is grounded. When the boom is lowered when it is determined that it is not during the airframe lifting operation, oil discharged from the head side oil chamber of the boom cylinder is On the other hand, when it is determined that the airframe is being lifted, the pressure oil supplied from the hydraulic pump is supplied to the rod side oil of the boom cylinder. A hydraulic control system for a hydraulic excavator, characterized in that the oil discharged from the head side oil chamber of the boom cylinder is allowed to flow into an oil tank while being supplied to the chamber.
And by doing in this way, the oil discharged | emitted from the head side oil chamber of a boom cylinder at the time of boom lower than the time of airframe lifting operation is accumulate | stored in an accumulator, and is supplied to the rod side oil chamber of a boom cylinder. Therefore, the potential energy of the working unit can be effectively recovered and reused, while the oil discharged from the head side oil chamber flows into the oil tank during the aircraft lifting operation, and the pressure in the head side oil chamber As a result, the differential pressure between the rod-side oil chamber and the head-side oil chamber is increased, and a large thrust force for reducing the boom cylinder can be obtained. Can be done.
The invention according to claim 2 is characterized in that the judging means judges whether or not the body is being lifted based on the differential pressure between the rod side oil chamber and the head side oil chamber of the boom cylinder. 1 is a hydraulic control system for a hydraulic excavator according to 1;
And by doing in this way, the judgment whether it is at the time of a body lifting operation | movement can be performed exactly.
According to a third aspect of the present invention, the hydraulic control system is provided with a control valve for performing oil supply / discharge control with respect to the boom cylinder based on the operation of the boom operation lever and the determination by the determination means. During boom lowering operation other than the above, it is located at the first lowering position where oil discharged from the head side oil chamber of the boom cylinder does not flow to the oil tank, while during boom lowering operation during body lifting operation, the boom cylinder head side 3. The hydraulic control system for a hydraulic excavator according to claim 1, wherein the hydraulic control system is controlled so as to be positioned at a second descending position where the oil discharged from the oil chamber flows into the oil tank. 4.
In this way, the control valve can perform two types of control, that is, when the boom operating lever is operated to the lower side, except when the aircraft is being lifted and when the aircraft is not being lifted. It can be carried out.
According to a fourth aspect of the present invention, the control valve is formed by a spool valve in which the spool moves based on the operation of the boom operation lever and the determination by the determination means, and the first lowering side as the movement stroke of the spool increases. The hydraulic control system for a hydraulic excavator according to claim 3, wherein the hydraulic control system is configured to be switched from a position to a second descending position.
And, in this way, when the aircraft is lifted after the boom is lowered in the air, the switching from the first descending side position to the second descending side position is smoothly performed, which is good. Operability can be obtained.
According to a fifth aspect of the present invention, the hydraulic pump sucks the accumulator accumulated oil and supplies it to the rod side oil chamber of the boom cylinder during the body lifting operation, while the boom cylinder head side when the boom is lowered except during the body lifting operation. The hydraulic control system for a hydraulic excavator according to any one of claims 1 to 4, characterized in that the oil discharged from the oil chamber is sucked and supplied to the rod side oil chamber.
And by doing in this way, the hydraulic pump sucks and discharges high-pressure oil both during the aircraft lifting operation and other than during the aircraft lifting operation, and hardly requires the required power, It can greatly contribute to the reduction of energy consumption.
The invention according to claim 6 is characterized in that the hydraulic control system is provided with pump control means for controlling the discharge flow rate of the hydraulic pump during the airframe lifting operation so as to be a discharge flow rate suitable for the airframe lifting operation. Item 6. A hydraulic control system for a hydraulic excavator according to any one of Items 1 to 5.
By doing so, the hydraulic pump is controlled so as to have a discharge flow rate suitable for the aircraft lifting operation during the aircraft lifting operation, and thus the amount of operation of the boom operation lever is reduced. Even if it is small, the aircraft can be lifted smoothly.
According to a seventh aspect of the present invention, when the boom is raised, the hydraulic pump sucks the oil accumulated in the accumulator and supplies it to the head side oil chamber of the boom cylinder. Is a hydraulic control system.
By doing so, the oil discharged from the boom-side oil chamber of the boom cylinder and accumulated in the accumulator when the boom is lowered, except during the airframe lifting operation, is collected by the dedicated pump when the boom is raised. As a result, the potential energy of the working unit can be effectively reused without waste, which can greatly contribute to energy saving.

  Next, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, reference numeral 1 denotes a hydraulic excavator. The hydraulic excavator 1 includes a crawler-type lower traveling body 2, an upper revolving body 3 that is pivotably supported above the lower traveling body 2, and the upper revolving body 3. The working unit 4 includes a boom 5 whose base end is supported by the upper swing body 3 so as to be swingable up and down, and a distal end of the boom 5. The arm 6 is supported in such a manner that it can swing back and forth, and a bucket (an example of a work attachment according to the present invention) 7 attached to the tip of the arm 6. FIG. 1 shows a state in which the excavator 1 is performing a body lifting operation described later. The machine body of the present invention includes the lower traveling body 2 and the upper swing body 3.

  Reference numeral 8 denotes a pair of left and right boom cylinders that extend and contract to move the boom 5 up and down. The boom cylinder 8 is configured so that the pressure of the head-side oil chamber 8a is adjusted by the pressure of the head side oil chamber 8a when the bucket 7 is not grounded. While maintaining the weight, the boom 5 is raised by extending the pressure oil supply to the head side oil chamber 8a and the oil discharge from the rod side oil chamber 8b, and the pressure oil supply to the rod side oil chamber 8b The boom 5 is lowered by being reduced by discharging the oil from the head side oil chamber 8a. 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 lowered by the hydraulic control system described later. While sometimes recovered, the recovered energy is used when the boom 5 is raised.

Next, the hydraulic control system will be described with reference to the circuit diagrams of FIGS. 2 and 3. In these drawings, numerals 9 and 10 are connected to an engine E mounted on the hydraulic excavator 1 via a pump drive gear portion G. The first and second main pumps are configured such that the first and second main pumps 9 and 10 suck the hydraulic oil from the oil tank 11 and discharge it to the first and second pump oil passages 12 and 13. It is configured.
Here, the first and second main pumps 9 and 10 are not only the boom cylinder 8 but also various hydraulic actuators provided in the hydraulic excavator 1 (not shown, travel motor, swing motor, arm cylinder, bucket cylinder, etc.) This is a variable displacement pump serving as a hydraulic pressure supply source. 2 and 3, circled numbers are connector symbols, and the corresponding circled numbers are connected to each other.

  Reference numerals 14 and 15 denote first and second regulators for controlling the discharge flow rates of the first and second main pumps 9 and 10, respectively. The first and second regulators 14 and 15 are controlled by a control device 16 to be described later. In response to the control signal pressure from the main pump control electromagnetic proportional pressure reducing valve 17, the pump is operated to produce a pump output corresponding to the engine speed and the work load, and the first and second main pumps 9 and 10 are discharged. Constant horsepower control is performed under pressure. Further, the first and second regulators 14 and 15 perform negative control flow rate control for increasing or decreasing the pump flow rate corresponding to the opening amounts of the center bypass valve passages 18f and 19b of the first and second control valves 18 and 19, as will be described later. Also configured to do.

  On the other hand, the first and second control valves 18 and 19 are direction switching valves respectively connected to the first and second pump oil passages 12 and 13, and the first and second control valves 18 and 19 The oil discharged from the first and second main pumps 9 and 10 is operated to be supplied to the boom cylinder 8. Since the first and second main pumps 9 and 10 serve as hydraulic supply sources for various hydraulic actuators provided in the hydraulic excavator 1 as described above, the first and second pump oil passages 12 and 13 have other components. A control valve for the hydraulic actuator is also connected, but these are omitted.

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

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

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

  Reference numerals 23, 24, and 25 are first ascending side, first descending side, and second ascending side electromagnetic proportional pressure reducing valves. These electromagnetic proportional pressure reducing valves 23, 24, and 25 are control signals from the control device 16. Is operated to output a pilot pressure to the ascending pilot port 18a, the descending pilot port 18a of the first control valve 18 and the ascending pilot port 19a of the second control valve 19, respectively. The control signal is set so as to increase or decrease in accordance with the increase or decrease of the control signal value output from the control device 16. The first and second control valves 18, 19 correspond to the increase / decrease in the pilot pressure output from the first ascending side, first descending side, and second ascending electromagnetic proportional pressure reducing valves 23, 24, 25. The movement stroke of the spool is increased or decreased, and thereby, the increase / decrease control of the supply / discharge flow rate from the first and second control valves 18, 19 to the boom cylinder 8 is performed. 2 and 3, reference numeral 26 denotes a pilot pump serving as a pilot hydraulic pressure source.

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

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

  On the other hand, 32 is a dedicated pump (corresponding to the hydraulic pump of the present invention), which is also a variable displacement pump connected to the engine E via the pump drive gear section G. In addition, the oil supplied from the suction oil passage 33 is sucked and discharged to the dedicated pump oil passage 34, and the discharge flow rate control of the dedicated pump 32 is operated based on the control signal output from the control device 16. 35.

  Here, the suction oil passage 33 is supplied with pressure accumulation oil of the accumulator 36 or oil discharged from the head side oil chamber 8a of the boom cylinder 8, as will be described later. The pump 32 sucks the accumulated oil in the accumulator 36 or the discharged oil from the head side oil chamber 8 a of the boom cylinder 8 and discharges it to the dedicated pump oil passage 34.

  37 is a third control valve connected to the dedicated pump oil passage 34, and the third control valve 37 receives pressure oil discharged from the dedicated pump 32 based on a control signal from the control device 16. Although it operates to supply the boom cylinder 8, the third control valve 37 of the first and second control valves 18, 19 and the third control valve 37 corresponds to the control valve of the present invention.

  The third control valve 37 will be described in detail. The third control valve 37 is used to operate the third ascending side and third descending electrooil conversion valves 38 and 39 to which a control signal from the control device 16 is input. The spool valve moves on the basis of this, and when the control signal is not input to both the electro-hydraulic conversion valves 38 and 39, the spool valve is positioned at the neutral position N where the oil supply / discharge of the boom cylinder 8 is not performed. When the control signal is input to the third ascending-side electro-oil conversion valve 38, the spool is moved, and the discharge oil of the dedicated pump 32 is passed through the cylinder head-side oil passage 20 to the head-side oil chamber of the boom cylinder 8. While being supplied to 8 a, the oil discharged from the rod side oil chamber 8 b to the cylinder rod side oil passage 21 is switched to the ascending position X through which the oil flows to the oil tank 11 via the return oil passage 22. Further, when a control signal is input to the third descending electro-hydraulic conversion valve 39, the spool moves to the side opposite to the ascending position X, and the first descending position Y1 or The third control valve 37 at the first descending side position Y1 switches to the second descending side position Y2, but the rod side oil chamber of the boom cylinder 8 passes the oil discharged from the dedicated pump 32 via the cylinder rod side oil passage 21. The third control valve 37 at the second descending position Y2 supplies the oil discharged from the dedicated pump 32 to the rod side oil chamber 8b of the boom cylinder 8 via the cylinder rod side oil passage 21. At the same time, the oil discharged from the head side oil chamber 8 a to the cylinder head side oil passage 20 is made to flow to the oil tank 11 via the return oil passage 22.

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

  Here, the spool movement stroke of the first lower side position Y1 and the second lower side position Y2 of the third control valve 37 and the supply oil supplied from the dedicated pump 32 to the rod side oil chamber 8b of the boom cylinder 8 are supplied. FIG. 4 shows the relationship between the opening amount of the valve passage 37a and the opening amount of the discharge valve passage 37b for flowing the oil discharged from the head side oil chamber 8a to the oil tank. As shown in FIG. The three control valves 37 are switched from the first descending position Y1 to the second descending position Y2 as the spool moving stroke increases, and the opening amount of the supply valve passage 37a is determined by the spool moving stroke. On the other hand, the discharge valve passage 37b is closed when the spool is moved within the range of the first descending position Y1 (that is, the third con- trol at the first descending position Y1). The roll valve 37 does not flow the oil discharged from the head side oil chamber 8a into the oil tank 11), but the amount of opening increases as the movement stroke of the spool increases after switching to the second descending position Y2. It is configured as follows.

  Further, reference numeral 40 denotes a recovery oil passage branched from the cylinder head side oil passage 20, and a recovery valve 41 is arranged in the recovery oil passage 40, and a downstream side of the recovery valve 41. The accumulator oil passage 42 and the suction oil passage 33 are connected to each other. Further, the recovery oil passage 40 is provided with a check valve 43 that allows oil flow from the cylinder head side oil passage 20 to the accumulator oil passage 42 and the suction oil passage 33 but prevents reverse flow. . Thus, the oil discharged from the head side oil chamber 8 a of the boom cylinder 8 to the cylinder head side oil passage 20 can be supplied to the accumulator oil passage 42 and the suction oil passage 33 via the recovery oil passage 40. It can be done.

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

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

  On the other hand, the accumulator oil passage 42 is an oil passage from the recovery oil passage 40 to the accumulator 36 via the accumulator check valve 45, and the maximum pressure of the accumulator oil passage 42 is connected to the accumulator oil passage 42. Limited by the relief valve 46. In the present embodiment, the accumulator 36 is an optimal bladder type for storing hydraulic energy, but is not limited thereto, and may be a piston type, for example.

  The accumulator check valve 45 is a valve for performing oil supply / discharge control with respect to the accumulator 36, and is an accumulator that switches from the OFF position N to the ON position X based on the poppet valve 47 and the ON signal output from the control device 16. The check valve electromagnetic switching valve 48 is used. The poppet valve 47 allows the flow of oil from the recovered oil passage 40 to the accumulator 36 regardless of whether the accumulator check valve electromagnetic switching valve 48 is in the OFF position N or the ON position X. The flow of oil to the suction oil passage 33 is blocked when the accumulator check valve electromagnetic switching valve 48 is located at the OFF position N and allowed only when it is located at the ON position X. Yes. Note that the flow of oil from the recovered oil passage 40 to the accumulator 36 is allowed regardless of whether the accumulator check valve electromagnetic switching valve 48 is in the OFF position N or the ON position X as described above, but the accumulator check valve In the state where the electromagnetic switching valve 48 is in the ON position X, the pressure in the accumulator oil passage 42 is not introduced into the spring chamber 47a of the poppet valve 47, and therefore the accumulator oil is discharged from the recovery oil passage 40 with almost no pressure loss. Oil can flow through the passage 42.

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

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

  On the other hand, the control device 16 is configured by using a microcomputer or the like, and as shown in the block diagram of FIG. 5, a boom operation detecting means for detecting an operation direction and an operation amount of a boom operation lever (not shown). 53, a first discharge side pressure sensor 54 connected to the first pump oil passage 12 to detect the discharge pressure of the first main pump 9, and a second discharge side pump oil to detect the discharge pressure of the second main pump 10. The second discharge side pressure sensor 55 connected to the passage 13, the third discharge side pressure sensor 56 connected to the dedicated pump oil passage 34 to detect the discharge pressure of the dedicated pump 32, and the suction side pressure of the dedicated pump 32. A suction side pressure sensor 57 connected to the suction oil passage 33 to detect, and a cylinder head side oil passage 20 to detect the pressure of the head side oil chamber 8a of the boom cylinder 8. Cylinder head side pressure sensor 58, cylinder rod side pressure sensor 59 connected to the cylinder rod side oil passage 21 to detect the pressure of the rod side oil chamber 8b of the boom cylinder 8, and accumulator oil to detect the pressure of the accumulator 36. Signals from an accumulator pressure sensor 60 connected to the passage 42, an accumulator temperature sensor 61 for detecting the temperature of the gas charged in the accumulator 36, and the like are input, and based on these input signals, the above-mentioned electromagnetic proportional pressure reduction for main pump control Valve 17, first ascending electromagnetic proportional pressure reducing valve 23, first descending electromagnetic proportional pressure reducing valve 24, second ascending electromagnetic proportional pressure reducing valve 25, electromagnetic switching valve 30 for drift reduction valve, dedicated pump regulator 35, third Ascending-side electro-oil conversion valve 38, third descending-side electro-oil conversion valve 39, recovery electro-oil conversion valve 44, accumulator Ekkubarubu selector valve 48, and outputs a control signal to the electromagnetic switching valve 52 or the like for the tank check valve.

  Here, 62 is a pressure accumulation amount calculation unit provided in the control device 16, and the pressure accumulation amount calculation unit 62 calculates the current pressure accumulation amount of the accumulator 36 based on the detection signal input from the accumulator pressure sensor 60. Calculate. In this embodiment, the accumulated pressure amount of the accumulator 36 calculated is the accumulated pressure ΔP accumulated in the accumulator 36 exceeding the accumulated pressure start setting pressure, and the accumulated pressure ΔP is the current pressure of the accumulator 36. Calculated by subtracting the current accumulation start setting pressure (Po, pressure obtained by converting the precharge pressure at 20 degrees Celsius into the current temperature) from Pa (detected by the pressure sensor 60 for the accumulator). (ΔP = Pa−Po).

  Reference numeral 63 denotes a required pump capacity calculation unit. The request pump capacity calculation unit 63 inputs an operation signal for the boom operation lever output from the boom operation detection means 53 as shown in the block diagram of FIG. The required pump capacity DR is calculated by the gain control 64. The required pump capacity DR is a pump capacity required by the operation amount of the boom operation lever, and is set to increase as the operation amount of the boom operation lever increases, and is operated to the boom raising side. The value is set to be “positive” when it is operated, and is output as “negative” when operated to the boom lowering side.

  In addition, 65 is a share ratio calculation unit, and as shown in the block diagram of FIG. 7, the share ratio calculation unit 65 is configured so that the accumulated pressure ΔP calculated by the accumulated pressure calculation unit 62 and the boom 5 are raised. There is an assist table 66 in which the relationship with the assist ratio α (α = “0” to “1”) of the first main pump 9 is set. The sharing ratio calculation unit 65 obtains the assist ratio α based on the assist table 66. In the present embodiment, the assist ratio α is obtained when the pressure accumulation ΔP is sufficient and the pressure accumulation amount of the accumulator 36 is sufficient. "0" when reaching a preset high set pressure PH as the pressure of "1", "1" when less than the preset low set pressure PL as the pressure when there is almost no accumulator pressure accumulation, the above high When the pressure is between the set pressure PH and the low set pressure PL, the assist ratio α is set to increase as the pressure accumulation pressure ΔP decreases. Further, the sharing ratio calculation unit 65 calculates the supply ratio β (β = 1−α) of the dedicated pump 32 when the boom 5 is raised by subtracting the assist ratio α from “1”. The assist ratio α and the supply ratio β obtained based on these assist tables 66 are output from the sharing ratio calculation unit 65 when the boom operation lever is operated to the boom raising side, and will be described later. It is used for flow control of the first control valve 18 and third control valve 37 and discharge flow control of the dedicated pump 32. On the other hand, when the boom operation lever is operated to the boom lowering side, the assist ratio α and the supply ratio β output from the sharing ratio calculation unit 65 are always “1” regardless of the accumulated pressure ΔP of the accumulator 36. Is set to

  Further, 74 is an airframe lifting operation determination unit (corresponding to the determination means of the present invention), and the airframe lifting operation determination unit 74 is detected by a cylinder rod side pressure sensor 59 as shown in the block diagram of FIG. The pressure PBR of the rod side oil chamber 8b of the boom cylinder 8 (hereinafter referred to as rod side pressure PBR) and the pressure PBH of the head side oil chamber 8a of the boom cylinder 8 detected by the cylinder head side pressure sensor 58 (hereinafter referred to as Head pressure PBH), and a differential pressure ΔPB (ΔPB = PBR−PBH) between the rod side pressure PBR and the head side pressure PBH is obtained by the subtractor 75, and the difference obtained by the subtractor 75 is obtained. Based on the pressure ΔPB, it is determined by the determination table 76 whether or not it is during the body lifting operation. When it is determined that the airframe lifting operation is being performed, the airframe lifting operation ON signal is output, and when it is determined that the airframe lifting operation is not being performed, the airframe lifting operation OFF signal is output. .

  Here, the airframe lifting operation means that the crawler is lifted one by one when the hydraulic excavator 1 escapes from a depression or soft ground, or when the crawler constituting the lower traveling body 2 is clogged with mud or gravel. In such a case, the boom 5 is further lowered with respect to the main body by lowering the boom 5 with the bucket 7 in contact with the ground (the reduction operation of the boom cylinder 8), thereby lifting the main body. It is an operation. In order to perform the airframe lifting operation, the boom 5 is lowered against the weight of the airframe body. Therefore, the differential pressure ΔPB obtained by subtracting the head side pressure PBH from the rod side pressure PBR of the boom cylinder 8 is large. Become. Therefore, in the determination table 76 of the airframe lifting operation determination unit 74, when the differential pressure ΔPB is equal to or lower than the first predetermined pressure ΔPB1 set in advance, it is determined that the airframe lifting operation is not performed, and the airframe lifting operation is turned off. On the other hand, when the differential pressure ΔPB is equal to or higher than a second predetermined pressure ΔPB2 set in advance, it is determined that the airframe lifting operation is being performed, and the airframe lifting operation ON signal is output. In the present embodiment, the differential pressure ΔPB is set to be OFF when the differential pressure ΔPB is increased and ON when the differential pressure ΔPB is decreased between the first set pressure ΔPB1 and the second set pressure ΔPB2. Yes.

  On the other hand, 67 is a first control valve control unit, and the first control valve control unit 67, as shown in the block diagram of FIG. The requested pump displacement DR output from the calculation unit 63 is input, and the assist ratio α and the requested pump displacement DR are multiplied by the multiplier 68 to obtain the requested requested pump displacement DRα. Further, the first control valve control unit 67 converts the requested pump capacity for assist DRα into a control signal value for the first ascending side and first descending electromagnetic proportional pressure reducing valves 23, 24. Based on the first valve table 69, control signal values for the first ascending side and first descending electromagnetic proportional pressure reducing valves 23, 24 are obtained. Then, the first control valve control unit 67 outputs the control signal value to the first ascending electromagnetic proportional pressure reducing valve 23 when the boom operating lever is operated to the boom raising side, and operates to the boom lowering side. In this case, the first descending electromagnetic proportional pressure reducing valve 23 is set to output to the first lowering electromagnetic proportional pressure reducing valve 24. However, the first raising side electromagnetic proportional pressure reducing valve 23 is controlled by the control signal value from the first control valve 18 when the boom is raised. Control is performed so as to output a pilot pressure for changing the supply flow rate to the boom cylinder 8 to a flow rate obtained by multiplying the flow rate required according to the operation amount of the boom operation lever by the assist ratio α.

  Further, reference numeral 70 denotes a third control valve control unit. The third control valve control unit 70, as shown in the block diagram of FIG. The signal, the supply ratio β output from the sharing ratio calculator 65, and the required pump capacity DR output from the required pump capacity calculator 63 are input. First, the third control valve control unit 70 multiplies the supply ratio β and the required pump capacity DR by the multiplier 71 to obtain the required pump capacity DRβ for supply. Further, the third control valve control unit 70 converts the above-mentioned requested pump capacity for supply DRβ into control signal values for the third ascending side, third descending side electro-hydraulic conversion valves 38, 39. Based on the third valve table 72, the control signal values for the third ascending side and third descending side electro-hydraulic conversion valves 38, 39 are obtained. When a signal indicating that the airframe lifting operation is OFF is input (when the airframe lifting operation is not performed, that is, when the boom is raised or when the boom is lowered other than during the airframe lifting operation), the control indicated by the solid line in FIG. On the other hand, when the airframe lifting operation ON signal is input from the airframe lifting operation determination unit 74, the signal value is converted into the control signal value indicated by the dotted line in FIG. It has become to so that. The control signal value (control signal value marked with a dotted line) when the airframe lifting operation is ON is set only when the required pump displacement DR is a negative value, that is, when the boom is lowered. The control signal value is set to be larger than the control signal value (control signal value indicated by a solid line) when the airframe lifting operation is OFF. The third control valve control unit 70 outputs the control signal value to the third ascending-side electro-hydraulic conversion valve 38 when the boom operating lever is operated to the boom ascending side, and operates the boom control side as the boom descending side. In this case, it is output to the third descending electro-oil conversion valve 39, but the movement stroke of the spool of the third control valve 37 that moves according to the control signal value output to the third descending electro-oil conversion valve 39 is: The control signal value that is output when the airframe lifting operation is OFF is a movement stroke within the range of the first descending position Y1, even when the operation amount of the boom control lever is maximum (full stroke operation). The control signal value when the operation is ON is set to be the moving stroke of the second descending position Y2. Thus, when the third control valve 37 is operated to the boom lowering side, it switches to the first lowering position Y1 when the aircraft lifting operation is OFF, and the second lowering when the aircraft lifting operation is ON. It is configured to switch to the side position Y2. On the other hand, the third ascending-side electro-hydraulic conversion valve 38 controls the supply flow rate from the third control valve 37 to the boom cylinder 8 when the boom is raised according to the control signal value output from the third control valve control unit 70. Control is performed to obtain a flow rate obtained by multiplying the flow rate required according to the operation amount of the operation lever by the supply ratio β.

  Reference numeral 73 denotes a dedicated pump control unit (corresponding to the pump control means of the present invention). The dedicated pump control unit 73 is output from the airframe lifting operation determination unit 74 as shown in the block diagram of FIG. The airframe lifting operation ON / OFF signal and the airframe lifting pump capacity DL described later are input. Then, when the aircraft lifting operation ON signal is input from the aircraft lifting operation determination unit 74, the dedicated pump controller 73 sets the dedicated pump regulator 35 so that the capacity of the dedicated pump 32 becomes the aircraft lifting pump capacity DL. A control signal is output. Here, the airframe lifting pump capacity DL is a pump capacity that is set so that the discharge flow rate of the dedicated pump 32 is an appropriate discharge flow rate for performing the airframe lifting operation, and the airframe lifting pump capacity By outputting the DL control signal to the dedicated pump regulator 35, the dedicated pump 32 is controlled to have a discharge flow rate suitable for performing the body lifting operation. On the other hand, when the aircraft lifting operation OFF signal is input from the aircraft lifting operation determination unit 74, the dedicated pump control unit 73 is not shown, but the requested pump capacity DR output from the requested pump capacity calculation unit 63 and the sharing ratio are not shown. A control signal for normal control for controlling the flow rate of the dedicated pump 32 based on the supply ratio β output from the calculation unit 65, the discharge pressure of the dedicated pump 32 input from the third discharge side pressure sensor 56, and the like is output. It is configured.

  The control device 16 controls the second control valve 19, the recovery valve 41, the drift reduction valve 29, the accumulator check valve 45, the tank check valve 50, etc., in addition to the calculation unit and control unit described above. Although it has various control parts (not shown), control in these control parts is explained as control of control device 16, without explaining individually.

Next, the control of the control device 16 based on the operation on the raising side and the lowering side of the boom operation lever will be described.
First, the case where the boom operation lever is operated to the upward side will be described. The control device 16 outputs the pump outputs of the first and second main pumps 9 and 10 to the engine relative to the main pump control electromagnetic proportional pressure reducing valve 17. A control signal is output to correspond to the rotation speed and the work load.

  Further, when the boom operation lever is operated to the upward side, the control device 16 outputs a control signal value set according to the operation amount of the boom operation lever to the second upward electromagnetic proportional pressure reducing valve 25. To do. As a result, the pilot pressure is output from the second ascending electromagnetic proportional pressure reducing valve 25, the second control valve 19 is switched to the ascending position X, and the discharge oil of the second main pump 10 is thus increased. It flows into the cylinder head side oil passage 20 via the second control valve 19 at the position X, and is supplied to the head side oil chamber 8a of the boom cylinder 8, from the second control valve 19 to the head side oil chamber 8a. The supply flow rate is controlled to be a flow rate required according to the operation amount of the boom operation lever.

Further, when the boom operation lever is operated to the ascending side, the control device 16 controls the first ascending-side electromagnetic proportional pressure reducing valve 23 based on the control executed by the first control valve control unit 67. Output a signal. The supply flow rate from the first control valve 18 to the boom cylinder 8 according to the control signal value output to the first ascending electromagnetic proportional pressure reducing valve 23 is a flow rate required according to the operation amount of the boom operation lever. The flow rate is controlled to be multiplied by the assist ratio α.
That is, when the assist ratio α is “1”, the pilot pressure is output from the first ascending electromagnetic proportional pressure reducing valve 23 according to the control signal output from the control device 16, whereby the first control valve 18 is moved to the ascending position. Thus, the oil discharged from the first main pump 9 flows into the cylinder head side oil passage 20 via the first control valve 18 at the ascending side position X, and the head side oil of the boom cylinder 8 is switched to X. Although supplied to the chamber 8a, the supply flow rate from the first control valve 18 to the head side oil chamber 8a is controlled to be a flow rate required according to the operation amount of the boom operation lever.
When the assist ratio α is between “1” and “0” (however, “1” and “0” are not included), as in the case where the assist ratio α is “1”, the control device The pilot pressure is outputted from the first ascending electromagnetic proportional pressure reducing valve 23 by the control signal outputted from 16, whereby the first control valve 18 is switched to the ascending position X, and the discharged oil of the first main pump 9 is discharged. Although supplied to the head side oil chamber 8a of the boom cylinder 8, the supply flow rate from the first control valve 18 to the head side oil chamber 8a is an assist ratio to the flow rate required according to the operation amount of the boom operation lever. As the flow rate multiplied by α, that is, the assist ratio α decreases, the flow rate is controlled to be smaller than the flow rate required according to the operation amount of the boom operation lever.
Further, when the assist ratio α is “0”, the control for reducing the supply flow rate from the first control valve 18 to the boom cylinder 8 from the control device 16 to the first ascending electromagnetic proportional pressure reducing valve 23 is zero. A signal is output. As a result, the first control valve 37 is held at the neutral position N. Thus, no pressure oil is supplied from the first main pump 9 to the head side oil chamber 8a of the boom cylinder 8, and the first control valve 37 is controlled by negative control flow rate control. The discharge flow rate of the main pump 9 is controlled to be a minimum.

  Further, when the boom operation lever is operated to the ascending side, the control device 16 makes a request pump capacity DR, a supply ratio to the dedicated pump regulator 35 based on the control executed by the dedicated pump control unit 73. A control signal for normal control for controlling the flow rate of the dedicated pump 32 is output based on β, the discharge pressure of the dedicated pump 32, and the like.

Further, when the boom operation lever is operated to the ascending side, the control device 16 controls the third ascending-side electro-oil conversion valve 38 based on the control executed in the third control valve control unit 70. Output a signal. The supply flow rate from the third control valve 37 to the boom cylinder 8 according to the control signal value output to the third ascending-side electro-oil conversion valve 38 is a flow rate required according to the operation amount of the boom operation lever. The flow rate is controlled to be multiplied by the supply ratio β.
That is, when the supply ratio β is “1”, the third control valve 37 is switched to the ascending side position X by the control signal output from the control device 16 to the third ascending side electro-hydraulic conversion valve 38. Then, the discharge oil of the dedicated pump 32 flows into the cylinder head side oil passage 20 via the third control valve 37 at the ascending position X, and is supplied to the head side oil chamber 8a of the boom cylinder 8. The supply flow rate from the third control valve 37 to the head side oil chamber 8a is controlled to be a flow rate required in accordance with the operation amount of the boom operation lever.
Further, when the supply ratio β is between “1” and “0” (however, “1” and “0” are not included), as in the case where the supply ratio β is “1”, the control device The third control valve 37 is switched to the ascending position X by a control signal output from 16 to the third ascending-side electro-oil conversion valve 38, and the discharge oil of the dedicated pump 32 is supplied to the head-side oil chamber 8a of the boom cylinder 8. However, the supply flow rate from the third control valve 19 to the head side oil chamber 8a is the flow rate obtained by multiplying the flow rate required according to the operation amount of the boom operation lever by the supply rate β, that is, the supply rate. As β decreases, the flow rate is controlled to be smaller than the flow rate required in accordance with the operation amount of the boom operation lever.
Further, when the supply ratio β is “0”, the control for reducing the supply flow rate from the third control valve 37 to the boom cylinder 8 from the control device 16 to the third ascending-side electro-hydraulic conversion valve 38 is zero. A signal is output. As a result, the third control valve 37 is held at the neutral position N, and pressure oil is not supplied from the dedicated pump 32 to the head side oil chamber 8a of the boom cylinder 8.

   Further, when the boom operation lever is operated to the ascending side, the control device 16 outputs an ON signal to the accumulator check valve electromagnetic switching valve 48 so as to be switched to the ON position X. As a result, the accumulator check valve 45 is in a state of allowing the oil flow from the accumulator oil passage 42 to the suction oil passage 33. Thus, the pressure oil accumulated in the accumulator 36 is supplied to the suction side of the dedicated pump 32 via the suction oil passage 33.

  When the boom operation lever is operated to the ascending side, no control signal is output from the control device 16 to the recovery electro-oil conversion valve 44, and the recovery valve 41 is in the closed position N where the recovery oil passage 40 is closed. positioned. As a result, the pressure oil supplied from the first, second, and third control valves 18, 19, and 37 described above does not flow into the accumulator oil passage 42 and the suction oil passage 33, and the head side oil chamber of the boom cylinder 8. 8a is supplied.

  Next, the pressure oil supply to the boom cylinder 8 that is executed based on the control of the control device 16 described above when the boom operation lever is operated to the boom raising side will be described for each pressure accumulation amount of the accumulator 36.

First, when the accumulated pressure of the accumulator 36 is sufficient and the accumulated pressure ΔP has reached the high set pressure PH, the supply ratio β is “1” and the assist ratio α is “0”. The control valve 37 is controlled so as to supply a flow rate required according to the operation amount of the boom operation lever to the head side oil chamber 8a. The flow rate for one pump is supplied to the head side oil chamber 8a.
On the other hand, the first control valve 18 is held at the neutral position N, and therefore no pressure oil is supplied from the first main pump 9 to the head side oil chamber 8a.
Further, the second control valve 19 is controlled so as to supply the flow rate required according to the operation amount of the boom operation lever to the head side oil chamber 8a. The flow rate for one pump is supplied to the head side oil chamber 8a (when the operation amount of the boom operation lever is maximum).
The oil discharged from the rod side oil chamber 8b of the boom cylinder 8 flows into the oil tank 11 via the third control valve 37 at the ascending position X.

  Thus, when the accumulator 36 is operated to the boom raising side with a sufficient pressure accumulation amount, the head side oil chamber 8a of the boom cylinder 8 has a flow rate corresponding to the maximum one pump supplied from the second main pump 10. And the flow rate for one pump supplied from the dedicated pump 32 are combined and supplied, and even if the boom 5 is lifted against the heavy load of the working unit 4, The boom 5 can be raised at a desired speed corresponding to the operation amount. In this case, the dedicated pump 32 sucks and discharges the high-pressure oil accumulated in the accumulator 36, so that the suction side and the discharge side The differential pressure is small and the pressure oil can be supplied with less required power.

On the other hand, when there is almost no pressure accumulation amount of the accumulator 36 and the pressure accumulation pressure ΔP is equal to or lower than the low set pressure PL, the supply rate β is “0” and the assist rate α is “1”. In addition, the first control valve 18 is controlled so as to supply the flow rate required according to the operation amount of the boom operation lever to the head side oil chamber 8a. The flow rate for one pump is supplied to the head side oil chamber 8a (when the operation amount of the boom operation lever is maximum).
On the other hand, the third control valve 37 is held at the neutral position N, and therefore no pressure oil is supplied from the dedicated pump 32 to the head side oil chamber 8a.
The second control valve 19 is controlled so as to supply a flow rate required according to the operation amount of the boom operation lever to the head side oil chamber 8a. The flow rate for the pump is supplied to the head side oil chamber 8a.
The oil discharged from the rod side oil chamber 8b of the boom cylinder 8 flows to the oil tank 11 via the first control valve 18 at the ascending position X.

  Thus, when the accumulator 36 is operated to the boom ascending side with almost no pressure accumulation amount, pressure oil is supplied from the first main pump 9 instead of being supplied from the dedicated pump 32, so that the boom cylinder 8 The head-side oil chamber 8a is supplied with the flow rate for the maximum one pump supplied from the second main pump 10 and the flow rate for the maximum one pump supplied from the first main pump 9 combined. Therefore, even when the accumulator 36 is not accumulating pressure, the boom 5 can be raised at a desired speed corresponding to the operation amount of the boom operation lever, as in the case where the accumulator 36 is accumulating enough pressure. it can.

When the accumulated pressure ΔP of the accumulator 36 is between the high set pressure PH and the low set pressure PL, the supply ratio β and the assist ratio α are values between “1” and “0” (where β = α−1). In this case, the third control valve 37 has a boom in which the supply flow rate from the three control valves 37 to the head side oil chamber 8a decreases as the supply ratio β decreases (that is, as the accumulated pressure ΔP decreases). The flow rate is controlled to be less than the required flow rate according to the operation amount of the control lever.
On the other hand, in the first control valve 18, the amount of operation of the boom control lever is decreased as the assist rate α decreases (that is, the accumulated pressure ΔP increases) in the supply flow rate from the three control valves 18 to the head side oil chamber 8a. Accordingly, the discharge flow rate is controlled to be less than that required.
Here, the supply flow rate from the third control valve 37 to the head side oil chamber 8a is a flow rate obtained by multiplying the flow rate required according to the operation amount of the boom operation lever by the supply ratio β, The supply flow rate from the control valve 18 to the head side oil chamber 8a is a flow rate obtained by multiplying the flow rate required according to the operation amount of the boom operation lever by the assist rate α, and the assist rate α and the supply rate β. Since it is set to be “1” (α + β = 1) when added, the supply flow rate from the first control valve 18 increases as the supply flow rate from the third control valve 37 decreases, and the third control When the supply flow rate from the valve 37 and the supply flow rate from the first control valve 18 are added, the flow rate required according to the boom operating lever is obtained. Thus, the maximum flow rate (when the operation amount of the boom operation lever is maximum) added from the dedicated pump 32 and the first main pump 9 is supplied to the head-side oil chamber 8a.
The second control valve 19 is controlled so as to supply a flow rate required according to the operation amount of the boom operation lever to the head side oil chamber 8a. The flow rate for the pump is supplied to the head side oil chamber 8a.
The oil discharged from the rod side oil chamber 8b of the boom cylinder 8 flows into the oil tank 11 via the first control valve 18 at the ascending position X and the third control valve 37 at the ascending position X.

  Therefore, when the pressure accumulation pressure ΔP of the accumulator 36 is operated to the boom raising side when the pressure is between the high set pressure PH and the low set pressure PL, the second main pump is provided in the head side oil chamber 8a of the boom cylinder 8. 10 and the maximum flow rate of one pump supplied from the dedicated pump 32 and the first main pump 9 are combined and supplied, and accordingly, the accumulator 36 is supplied. Even if the pressure accumulation amount fluctuates, the boom 5 can be raised at a desired speed corresponding to the operation amount of the boom operation lever, as in the case where the accumulator 36 is sufficiently accumulated.

  Next, the control of the control device 16 when the boom operation lever is operated to the boom lowering side will be described. The operations on the boom lowering side are performed in the case of performing the above-described aircraft lifting operation and the operations other than the aircraft lifting operation described above. There are cases (such as when the boom 5 is lowered in the air, or when excavation work or transport work is performed). The aircraft lifting operation determination unit 74 determines whether or not it is during the aircraft lifting operation. If it is during the aircraft lifting operation, an aircraft lifting operation ON signal is output. Otherwise, the airframe lifting operation OFF signal is output, but the control of the control device 16 differs depending on the determination result of the operation determination unit 74. The case of the body lifting operation OFF signal output from the lifting operation determination unit 74 will be described. As described above, the assist ratio α and the supply ratio β output from the sharing ratio calculation unit 65 when operated to the boom lowering side are always “1” regardless of the accumulated pressure ΔP of the accumulator 36. Is set to

  扨 When the body lifting operation is turned off and the boom is lowered, the control device 16 causes the main pump control electromagnetic proportional pressure reducing valve 17 to reduce the pump output of the first and second main pumps 9 and 10. Output a control signal.

Further, when the aircraft is lifted off and operated to the boom lowering side, the control device 16 controls the first lowering electromagnetic proportional pressure reducing valve 24 based on the control executed by the first control valve control unit 67. Output a control signal. As a result, the first control valve 18 is switched to the lower side position Y, and the oil discharged from the head side oil chamber 8a of the boom cylinder 8a passes through the regeneration valve path 18c at the lower side position Y. Although supplied to the rod-side oil chamber 8b, the flow rate is controlled to be a flow rate required according to the operation amount of the boom operation lever. Further, as described above, the discharge flow rate of the first main pump 9 when the first control valve 18 is at the lowering position Y is controlled to be minimized by the negative control flow rate control.
The second control valve 19 is held at the neutral position N when the boom 5 is lowered, and therefore does not supply and discharge oil to the boom cylinder 8, and the discharge flow rate of the second main pump 9 is also the negative control flow rate. It is controlled to be minimized by the control.

  Further, when the aircraft is lifted off and operated to the boom lowering side, the control device 16 supplies the required pump capacity DR, supply to the dedicated pump regulator 35 based on the control executed by the dedicated pump control unit 73. A control signal for normal control for controlling the flow rate of the dedicated pump 32 is output based on the ratio β, the discharge pressure of the dedicated pump 32, and the like.

  Further, when the aircraft is lifted off and operated to the boom lowering side, the control device 16 controls the third lowering-side electro-oil conversion valve 39 based on the control executed by the third control valve control unit 70. Output a control signal. The control signal for the third descending electro-oil conversion valve 39 is a control signal value for switching the third control valve to the first descending position Y1, as described above, when the aircraft lifting operation is OFF. The oil discharged from the dedicated pump 32 flows into the cylinder rod side oil passage 21 via the supply valve passage 37a of the third control valve 37 at the first descending position Y1, and the rod side oil chamber 8b of the boom cylinder 8 is supplied. However, the supply flow rate from the third control valve 37 to the rod-side oil chamber 8b is controlled to be a flow rate required according to the operation amount of the boom operation lever. In this case, the third control valve 37 at the first descending position Y1 closes the discharge valve path 37b for flowing the oil discharged from the head side oil chamber 8a to the oil tank 11, and thus the head side oil chamber. The oil 8 a is prevented from flowing into the oil tank 11 via the third control valve 37.

  Furthermore, when the body lifting operation is turned OFF and the boom is lowered, the control device 16 outputs an ON signal to the drift reducing valve electromagnetic proportional pressure reducing valve 30 so as to switch to the ON position X. As a result, the drift reduction valve 29 is allowed to discharge oil from the head side oil chamber 8a of the boom cylinder 8.

  Furthermore, when the body lifting operation is turned OFF and the boom is lowered, the control device 16 outputs a control signal to the recovery electro-oil conversion valve 44 so as to switch the recovery valve 41 to the open position X. As a result, the recovery valve 41 switches to the open position X where the recovery oil passage 40 is opened, and thus the oil discharged from the head side oil chamber 8a of the boom cylinder 8 passes through the recovery oil passage 40 and is stored in the accumulator. The oil flows into the oil passage 42 and the suction oil passage 33, is accumulated in the accumulator 36, and is supplied to the suction side of the dedicated pump 32. The flow rate of the recovery oil passage 40 is controlled by the boom operating lever. The flow rate is controlled according to the operation amount. Further, at this time, the control device 16 outputs an ON signal to the accumulator check valve electromagnetic switching valve 48 so as to switch to the ON position X. As a result, oil can flow from the recovery oil passage 40 to the accumulator oil passage 42 with almost no pressure loss.

  Thus, when the boom 5 is lowered except during the airframe lifting operation, the pressure oil from the dedicated pump 32 via the third control valve 37 is supplied to the rod side oil chamber 8b of the boom cylinder 8. In this case, since the dedicated pump 32 sucks and discharges the high-pressure oil discharged from the head-side oil chamber 8a, the differential pressure between the suction side and the discharge side is small and almost no required power is required. Pressure oil can be supplied.

On the other hand, the oil discharged from the head side oil chamber 8a of the boom cylinder 8 at the time of lowering of the boom 5 other than during the body lifting operation becomes high pressure due to the potential energy of the working unit 4 and acts on the piston 8c. The amount of oil discharged from the head side oil chamber 8a is approximately twice as large as the amount supplied to the rod side oil chamber 8b due to the pressure receiving area. 33 and the accumulator oil passage 42. The oil flowing in the suction oil passage 33 is supplied to the suction side of the dedicated pump 32 and supplied from the dedicated pump 32 to the rod-side oil chamber 8b, while the pressure oil supplied to the accumulator oil passage 42 is stored in the accumulator. As described above, the pressure is accumulated in 36 and supplied from the dedicated pump 32 to the head side oil chamber 8a when the boom 5 is raised. Thus, the potential energy of the working unit 4 can be recovered and reused without being wasted.
In addition, when the boom 5 is lowered other than during the airframe lifting operation, a part of the oil discharged from the head side oil chamber 8a passes through the regeneration valve path 18d of the first control valve 18 to the rod side oil chamber 8b. Supplied.

  Next, a description will be given of the control of the control device 16 when the airframe lifting operation is ON (the airframe lifting operation determining unit 74 outputs the airframe lifting operation ON signal) when operated to the boom lowering side. The electromagnetic proportional pressure reducing valve 17 is controlled in the same manner as when the airframe lifting operation is turned off and operated to the boom lowering side, thereby reducing the pump output of the first and second main pumps 9 and 10. . Also, the electromagnetic proportional pressure reducing valve 30 for the drift reduction valve is controlled in the same manner as when the body lifting operation is turned off and the boom lowering side is operated, so that the head side oil chamber 8a of the boom cylinder 8 is controlled. Oil drainage is allowed. Further, the same control as when the first lowering electromagnetic proportional pressure reducing valve 24 is operated to the boom lowering side with the body lifting operation OFF is performed, whereby the first control valve 18 is switched to the lowering position Y. In other words, when the airframe lifting operation is ON, the rod-side pressure PBR of the boom cylinder 8 is higher than the head-side pressure PBH, so that the oil in the head-side oil chamber 8a passes through the regeneration valve path 18c to the rod. Since oil does not flow into the side oil chamber 8b and the flow of oil from the rod side oil chamber 8b to the head side oil chamber 8a is blocked by the check valve 18d, the oil to the boom cylinder 8 by the first control valve 18 is prevented. Supply and discharge are not performed. Further, the oil supply / discharge to the boom cylinder 8 by the second control valve 19 is not performed as in the case where the boom lifting operation is turned off and the boom lowering side is operated.

  Furthermore, when the body lifting operation is turned on and the boom is lowered, the control device 16 outputs a control signal to the dedicated pump regulator 35 based on the control executed by the dedicated pump control unit 73. The control signal for the dedicated pump regulator 35 is a control signal for setting the discharge flow rate of the dedicated pump 32 to a discharge flow rate suitable for performing the body lifting operation, as described above, when the body lifting operation is ON. Therefore, the pressure oil having a flow rate suitable for performing the body lifting operation is discharged from the dedicated pump 32.

  Further, when the body lifting operation is turned on and operated to the boom lowering side, the control device 16 controls the third lowering-side electro-oil conversion valve 39 based on the control executed by the third control valve control unit 70. Output a control signal. As described above, the control signal for the third lower-side electro-oil conversion valve 39 is a control signal value for switching the third control valve to the second lower-side position Y2 in the case where the body lifting operation is ON. The oil discharged from the dedicated pump 32 flows into the cylinder rod side oil passage 21 via the supply valve passage 37a of the third control valve 37 at the second descending position Y2, and the rod side oil chamber 8b of the boom cylinder 8 is supplied. And the oil discharged from the head side oil chamber 8a to the cylinder head side oil passage 20 via the discharge valve passage 37b of the third control valve 37 at the second descending position Y2 is supplied to the oil tank 11. Flowing into.

  Further, when the body lifting operation is turned on and operated to the boom lowering side, the control device 16 makes the recovery electro-hydraulic conversion valve 44 the same as when the body lifting operation is turned off and operated to the boom lowering side. A control signal is output so as to switch the valve 41 to the open position X. As a result, the recovery valve 41 is switched to the open position X that opens the recovery oil passage 40, but as described above, the oil discharged from the head-side oil chamber 8a to the cylinder head-side oil passage 20 is in the second descending position. Since it flows to the oil tank 11 via the Y2 third control valve, when the machine lifting operation is ON, the oil discharged from the head side oil chamber 8a passes through the recovery oil passage 40 and the accumulator oil passage 42 and the suction oil. It is not supplied to the path 33. It should be noted that the flow of oil from the accumulator oil passage 42 or the suction oil passage 33 to the cylinder head side oil passage 20 is blocked by the check valve 43.

  Further, when the body lifting operation is turned on and operated to the boom lowering side, the control device 16 outputs an ON signal to the accumulator check valve electromagnetic switching valve 48 so as to switch to the ON position X. As a result, the accumulator check valve 45 is in a state of allowing the oil flow from the accumulator oil passage 42 to the suction oil passage 33. Thus, the pressure oil accumulated in the accumulator 36 is supplied to the suction side of the dedicated pump 32 via the suction oil passage 33.

  Thus, during the airframe lifting operation, the pressure oil from the dedicated pump 32 is supplied to the rod side oil chamber 8b of the boom cylinder 8 via the third control valve 37 at the second descending position Y2. However, the discharge flow rate of the dedicated pump 32 is controlled so as to be a discharge flow rate suitable for the airframe lifting operation, so that the pressure oil having a flow rate suitable for the airframe lifting operation can be supplied to the rod side oil chamber 8b. Further, in this case, the dedicated pump 32 sucks and discharges the high pressure oil accumulated in the accumulator 36, so that the differential pressure between the suction side and the discharge side is small and the required pressure is not required. Supply can be made.

  On the other hand, during the airframe lifting operation, the oil discharged from the head side oil chamber 8a of the boom cylinder 8 flows into the oil tank 11 via the third control valve 37 at the second lower movement side position Y2, thereby the head side. The pressure in the oil chamber 8a decreases. As the pressure in the head side oil chamber 8a decreases, the differential pressure ΔPB between the rod side pressure PBR and the head side pressure PBH increases, and the thrust acting on the piston 8c to reduce the boom cylinder 8 increases. . Thus, the airframe lifting operation can be performed smoothly.

  In this embodiment configured as described, the excavator 1 is equipped with a working unit 4 including a boom 5, an arm 6, and a bucket 7. In the excavator 1, the bucket 7 is grounded. Thus, there is a case where a so-called body lifting operation is performed in which the body 5 is lifted by lowering the boom 5 relative to the body. Since the boom lifting operation reduces the boom cylinder 8 against the weight of the fuselage main body, a large thrust is required to reduce the boom cylinder 8, but whether or not it is during the aircraft lifting operation. Is determined by the airframe lifting operation determination unit 74 of the control device 16. Then, when the boom 5 is lowered when it is determined that it is not during the airframe lifting operation, the oil discharged from the head side oil chamber 8a of the boom cylinder 8 is accumulated in the accumulator 36 and also to the suction side of the dedicated pump 32. Supplied and supplied from the dedicated pump 32 to the rod side oil chamber 8b via the third control valve 37, so that the potential energy of the working unit 4 can be effectively recovered and reused. This can greatly contribute to energy saving. On the other hand, when it is determined that the airframe is being lifted, the pressure oil supplied from the dedicated pump 32 is supplied to the rod side oil chamber 8b via the third control valve 37, while the head side oil chamber 8a is supplied. The oil discharged from the oil flows into the oil tank 11 via the third control valve 37.

  As a result, the oil discharged from the head side oil chamber 8a of the boom cylinder 8 when the boom 5 is lowered is accumulated in the accumulator 36 in order to recover and reuse the potential energy of the working unit 4. However, during the airframe lifting operation, the pressure of the head side oil chamber 8a is lowered by flowing the oil discharged from the head side oil chamber 8a to the oil tank 11, thereby the rod side oil chamber 8b and the head side oil chamber 8a. The pressure difference ΔPB is increased, and a large thrust for contracting the boom cylinder 8 can be obtained, so that the airframe lifting operation can be performed smoothly.

  In addition, in this configuration, the determination as to whether or not the body is being lifted is made based on the differential pressure between the rod side oil chamber 8b and the head side oil chamber 8a of the boom cylinder 8, so that it is accurate. Therefore, it is possible to reliably prevent a problem that the oil in the head side oil chamber 8a flows into the oil tank 11 and is not accumulated in the accumulator 36 when the boom is lowered when the aircraft is not being lifted. be able to.

  Furthermore, oil is discharged from the head side oil chamber 8a to the oil tank 11 during the body lifting operation through the third control valve 37 that performs oil supply / discharge control on the boom cylinder 8. The control valve 37 includes a first lowering position Y1 at which the oil discharged from the head side oil chamber 8a does not flow to the oil tank 11, and a second lowering position at which the oil discharged from the head side oil chamber 8a flows to the oil tank 11. Y2 is provided, and is controlled to be positioned at the first lowering position Y1 during the boom lowering operation other than during the aircraft lifting operation, and at the second lowering position Y2 during the aircraft lifting operation. become. Thus, the third control valve 37 can perform two kinds of control, that is, when the boom operating lever is operated to the lowering side, except when the aircraft is lifted and when the aircraft is not lifted. become.

  In addition, the switching of the third control valve 37 from the first lowering position Y1 to the second lowering position Y2 is performed as the moving stroke of the spool of the third control valve 37 increases. Therefore, when the aircraft is lifted after the boom 5 is lowered in the air, the switching from the first lowering side position Y1 to the second lowering side position Y2 is performed smoothly, and good operability is achieved. Obtainable.

  Further, the dedicated pump 32 sucks the accumulated oil in the accumulator 36 during the body lifting operation and supplies it to the rod side oil chamber 8a of the boom cylinder 8, while the dedicated pump 32 removes from the head side oil chamber 8a during the boom lowering except during the body lifting operation. It is configured to suck the discharged oil and supply it to the rod side oil chamber 8b, and thus sucks and discharges high-pressure oil both during the aircraft lifting operation and during other than the aircraft lifting operation. As a result, almost no required power is required, which can greatly contribute to reduction of energy consumption.

  Further, the dedicated pump 32 is controlled by the dedicated pump control unit 73 so that the discharge flow rate during the airframe lifting operation is a discharge flow rate suitable for the airframe lifting operation, so the operation amount of the boom operation lever is small. Even in such a case, a large thrust for reducing the boom cylinder 8 can be obtained with certainty, and the airframe lifting operation can be performed smoothly.

  Further, the oil discharged from the head side oil chamber 8a of the boom cylinder 8 and accumulated in the accumulator 36 when the boom is lowered other than during the body lifting operation is not only used during the aforementioned body lifting operation, but also when the boom 5 is raised. In this case, the dedicated pump 32 supplies the oil to the head side oil chamber 8a of the boom cylinder 8, so that the potential energy of the working unit 4 can be effectively reused without waste, thereby saving energy. Can contribute greatly.

  Needless to say, the present embodiment is not limited to the above-described embodiment. For example, the third control valve is not provided with the second descending side position, and instead, the cylinder head side oil passage is connected to the fuselage. It is also possible to arrange a valve that is controlled so that the oil in the head side oil chamber of the boom cylinder flows into the oil tank during the lifting operation. Even in such a configuration, the pressure in the head side oil chamber can be reduced during the airframe lifting operation, but in this case, a separate valve is required in addition to the third control valve.

It is a side view of a hydraulic excavator. It is a circuit diagram of a hydraulic control system. It is a circuit diagram of a hydraulic control system. It is a figure which shows the opening characteristic of the 3rd control valve of a 1st descent | fall side position and a 2nd descent | fall side position. It is a block diagram which shows the input / output of a control apparatus. It is a block diagram which shows the control procedure of a request | requirement pump capacity | capacitance calculating part. It is a block diagram which shows the control procedure of a share ratio calculating part. It is a block diagram which shows the control procedure of a body lifting operation | movement judgment part. It is a block diagram which shows the control procedure of a 1st control valve control part. It is a block diagram which shows the control procedure of a 3rd control valve control part. It is a block diagram which shows the control procedure of a dedicated pump control part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 4 Working part 5 Boom 6 Arm 7 Bucket 8 Boom cylinder 8a Head side oil chamber 8b Rod side oil chamber 11 Oil tank 16 Controller 32 Dedicated pump 36 Accumulator 37 Third control valve Y1 First lower side position Y2 Second lower side position 70 Third control valve control unit 73 Dedicated pump control unit 74 Airframe lifting operation determination unit 73 Dedicated pump control unit

Claims (7)

  A boom whose body end is pivotally supported by the fuselage main body and swings up and down by the expansion and contraction of the boom cylinder, an arm pivotally supported by the tip of the boom, and the tip of the arm In a hydraulic excavator having a working part equipped with a work attachment attached to the part, the boom is lowered relative to the main body of the hydraulic excavator with the work attachment grounded to the hydraulic control system of the hydraulic excavator. Therefore, there is provided a judging means for judging whether or not the airframe lifting operation is performed to lift the airframe body, and the oil discharged from the head side oil chamber of the boom cylinder when the boom is lowered when it is determined not to be the airframe lifting operation. Is stored in the accumulator and supplied to the rod-side oil chamber of the boom cylinder. When it is cut off, the pressure oil supplied from the hydraulic pump is supplied to the rod side oil chamber of the boom cylinder, and the oil discharged from the head side oil chamber of the boom cylinder is made to flow to the oil tank. A hydraulic control system in a hydraulic excavator.   2. The hydraulic excavator according to claim 1, wherein the determination unit determines whether or not the body is being lifted based on a differential pressure between the rod side oil chamber and the head side oil chamber of the boom cylinder. Hydraulic control system.   The hydraulic control system is provided with a control valve for performing oil supply / discharge control on the boom cylinder based on the operation of the boom operation lever and the determination by the determination means, and the control valve is operated during the boom lowering operation other than during the body lifting operation. The oil discharged from the head side oil chamber of the boom cylinder is located at the first lower side position where the oil discharged from the head side oil chamber of the boom cylinder does not flow to the oil tank. The hydraulic control system for a hydraulic excavator according to claim 1 or 2, wherein the hydraulic control system is controlled so as to be positioned at a second descending position where the oil flows through the oil tank.   The control valve is formed by a spool valve in which the spool moves based on the operation of the boom operation lever and the judgment by the judgment means, and the first lower side position to the second lower side position as the spool movement stroke increases. The hydraulic control system for a hydraulic excavator according to claim 3, wherein the hydraulic control system is configured to be switched to.   The hydraulic pump sucks the accumulator accumulated oil during the body lifting operation and supplies it to the rod side oil chamber of the boom cylinder, while the oil discharged from the head side oil chamber of the boom cylinder when the boom is lowered except during the body lifting operation. The hydraulic control system for a hydraulic excavator according to any one of claims 1 to 4, wherein the hydraulic control system is configured to suck in and supply to the rod side oil chamber.   6. The hydraulic control system according to claim 1, further comprising pump control means for controlling the discharge flow rate of the hydraulic pump during the airframe lifting operation so as to be a discharge flow rate suitable for the airframe lifting operation. Hydraulic control system for hydraulic excavators.   The hydraulic control system for a hydraulic excavator according to any one of claims 1 to 6, wherein when the boom is raised, the hydraulic pump sucks the oil accumulated in the accumulator and supplies the oil to the head side oil chamber of the boom cylinder.

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