shovel

Abstract

To provide a shovel enabling a hydraulic actuator to efficiently operate.SOLUTION: A shovel 100 comprises: a first hydraulic pump 14A; meter-in valves corresponding to a boom cylinder 7 and an arm cylinder 8, respectively (a hydraulic control valve HV3, a hydraulic control valve HV5); meter-out valves corresponding to the boom cylinder 7 and the arm cylinder 8, respectively (a hydraulic control valve HV4, a hydraulic control valve HV6); and a controller 30 to control the meter-in valves, the meter-out valves, and the first hydraulic pump 14A, respectively. The controller 30 is constituted so as to be switchable between a normal circuit to return a hydraulic oil flowing out of the boom cylinder 7 and the arm cylinder 8 respectively to a hydraulic oil tank T and a difference circuit to make a portion of the hydraulic oil flowing out of at least either one of the boom cylinder 7 or the arm cylinder 8 join the hydraulic oil discharged from the first hydraulic pump 14A.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present disclosure relates to a shovel. [Background technology]

[0002] Conventionally, a shovel is known as an excavator for excavating the ground (see Patent Document 1). This shovel is configured to be able to excavate earth and sand by moving an excavation attachment attached to an upper rotating body.

[0003] This excavator is configured so that, when the hydraulic actuator is operated, the opening area (meter-in opening area) of the first oil passage connecting the hydraulic pump and the hydraulic actuator and the opening area (meter-out opening area) of the second oil passage connecting the hydraulic actuator and the hydraulic oil tank can be simultaneously controlled by a single spool valve. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 164169 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above-described configuration, the correspondence between the displacement of the spool valve and the opening areas of the first and second oil passages is uniquely determined by the physical shape of the spool valve, so depending on how the spool valve is moved, there is a risk that the hydraulic actuator will not operate efficiently.

[0006] Therefore, it is desirable to provide a shovel that can operate the hydraulic actuator more efficiently. [Means for solving the problem]

[0007] An excavator according to an embodiment of the present disclosure includes a hydraulic oil tank, a first hydraulic actuator, a second hydraulic actuator, a hydraulic pump capable of supplying hydraulic oil in the hydraulic oil tank to each of the first hydraulic actuator and the second hydraulic actuator, a meter-in valve corresponding to each of the first hydraulic actuator and the second hydraulic actuator, a meter-out valve corresponding to each of the first hydraulic actuator and the second hydraulic actuator, and a control device that controls each of the meter-in valve, the meter-out valve, and the hydraulic pump, and the control device is configured to be capable of switching between a first hydraulic circuit that returns hydraulic oil flowing out from each of the first hydraulic actuator and the second hydraulic actuator to the hydraulic oil tank, and a second hydraulic circuit that merges a portion of the hydraulic oil flowing out from at least one of the first hydraulic actuator and the second hydraulic actuator with the hydraulic oil discharged by the hydraulic pump. Effect of the Invention

[0008] The above-mentioned means provide a shovel that can operate the hydraulic actuator more efficiently. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a side view of a shovel according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a schematic diagram of a hydraulic circuit mounted on the excavator. [Diagram 3] FIG. 2 is a diagram illustrating an example of the configuration of a hydraulic control valve. [Figure 4] FIG. 13 is a diagram showing an example of a control flow for operating a shovel. [Diagram 5] FIG. 3 is a schematic diagram of a portion of the hydraulic circuit shown in FIG. 2. [Figure 6] FIG. 3 is a schematic diagram of a portion of the hydraulic circuit shown in FIG. 2. [Figure 7] 13 is a flowchart showing an example of the flow of a circuit selection process. [Figure 8] FIG. 4 is a diagram showing the relationship between the pressure of hydraulic oil, the flow rate of hydraulic oil, and energy consumption. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] First, with reference to FIG. 1, an excavator (shovel 100) as a construction machine according to an embodiment of the present disclosure will be described. FIG. 1 is a side view of the excavator 100 according to an embodiment of the present disclosure. An upper rotating body 3 is rotatably mounted on a lower traveling body 1 of the excavator 100 shown in FIG. 1 via a rotating mechanism 2. A boom 4 is attached to the upper rotating body 3, an arm 5 is attached to the tip of the boom 4, and a bucket 6 is attached to the tip of the arm 5. The boom 4, the arm 5, and the bucket 6 as working elements constitute an excavation attachment, which is an example of an attachment. The boom 4 is driven by a boom cylinder 7, the arm 5 is driven by an arm cylinder 8, and the bucket 6 is driven by a bucket cylinder 9. A cabin 10 is provided on the upper rotating body 3, and a power source such as an engine 11 is mounted on the upper rotating body 3. The engine 11 is a drive source for the excavator 100, and is, for example, a diesel engine that operates to maintain a predetermined rotation speed. The drive source may be a hydrogen engine, an electric motor, or the like.

[0011] Next, a hydraulic circuit mounted on the excavator 100 will be described with reference to Fig. 2 and Fig. 3. Fig. 2 is a schematic diagram of the hydraulic circuit mounted on the excavator 100. The basic system of the excavator 100 mainly includes a hydraulic pump 14, a pilot pump 15, an operating device 26, a controller 30, hydraulic control valves HV, and pressure sensors S1 to S7. Fig. 3 is a diagram showing an example of the configuration of a hydraulic control valve HV1, which is one of the hydraulic control valves HV.

[0012] The hydraulic pump 14 is a hydraulic pump that supplies hydraulic oil to the hydraulic control valve HV via a hydraulic oil line. In the example shown in FIG. 2, the hydraulic pump 14 is a swash plate type variable displacement hydraulic pump that is driven by the engine 11, and the input shaft of the hydraulic pump 14 is connected to the output shaft of the engine 11. In the swash plate type variable displacement hydraulic pump, the stroke length of the piston that determines the displacement volume changes according to a change in the swash plate tilt angle, and the pump discharge amount per one rotation changes. The swash plate tilt angle is controlled by the regulator 13. The regulator 13 changes the swash plate tilt angle according to a change in the control current from the controller 30. For example, the regulator 13 is configured to increase the swash plate tilt angle according to an increase in the control current, thereby increasing the pump discharge amount of the hydraulic pump 14. Specifically, the hydraulic pump 14 includes a first hydraulic pump 14A and a second hydraulic pump 14B, and the regulator 13 includes a first regulator 13A and a second regulator 13B.

[0013] 2 and 3, the boom cylinder 7 and the arm cylinder 8 are driven by the hydraulic oil discharged by the first hydraulic pump 14A and the hydraulic oil discharged by the second hydraulic pump 14B. Furthermore, the bucket cylinder 9 is driven by the hydraulic oil discharged by the first hydraulic pump 14A and the hydraulic oil discharged by the second hydraulic pump 14B when contracting, but is driven only by the hydraulic oil discharged by the second hydraulic pump 14B when extending.

[0014] The pressure sensors S1 to S7 are devices for detecting the pressure of the hydraulic oil in each part of the hydraulic circuit.

[0015] The pressure sensor S1 is a device for detecting the pressure of hydraulic oil related to the operation of the left traveling hydraulic motor 1M. Specifically, the pressure sensor S1 includes a pressure sensor S1L and a pressure sensor S1R. The pressure sensor S1L detects the pressure of hydraulic oil in a first port (left port) of the left traveling hydraulic motor 1M. The pressure sensor S1R detects the pressure of hydraulic oil (right port pressure) in a second port (right port) of the left traveling hydraulic motor 1M.

[0016] The pressure sensor S2 is a device for detecting the pressure of hydraulic oil related to the operation of the right traveling hydraulic motor 2M. Specifically, the pressure sensor S2 includes a pressure sensor S2L and a pressure sensor S2R. The pressure sensor S2L detects the pressure of hydraulic oil at a first port (left port) of the right traveling hydraulic motor 2M. The pressure sensor S2R detects the pressure of hydraulic oil at a second port (right port) of the right traveling hydraulic motor 2M.

[0017] The pressure sensor S3 is a device for detecting the pressure of hydraulic oil related to the operation of the swing hydraulic motor 3M. Specifically, the pressure sensor S3 includes a pressure sensor S3L and a pressure sensor S3R. The pressure sensor S3L detects the pressure of hydraulic oil at a first port (left port) of the swing hydraulic motor 3M. The pressure sensor S3R detects the pressure of hydraulic oil at a second port (right port) of the swing hydraulic motor 3M.

[0018] The pressure sensor S4 is a device for detecting the pressure of hydraulic oil related to the operation of the boom 4. Specifically, the pressure sensor S4 includes a pressure sensor S4B and a pressure sensor S4R. The pressure sensor S4B detects the boom bottom pressure, which is the pressure of hydraulic oil in the bottom side oil chamber of the boom cylinder 7. The pressure sensor S4R detects the boom rod pressure, which is the pressure of hydraulic oil in the rod side oil chamber of the boom cylinder 7.

[0019] The pressure sensor S5 is a device for detecting the pressure of hydraulic oil related to the operation of the arm 5. Specifically, the pressure sensor S5 includes a pressure sensor S5B and a pressure sensor S5R. The pressure sensor S5B detects the arm bottom pressure which is the pressure of hydraulic oil in the bottom side oil chamber of the arm cylinder 8. The pressure sensor S5R detects the arm rod pressure which is the pressure of hydraulic oil in the rod side oil chamber of the arm cylinder 8.

[0020] The pressure sensor S6 is a device for detecting the pressure of hydraulic oil related to the operation of the bucket 6. Specifically, the pressure sensor S6 includes a pressure sensor S6B and a pressure sensor S6R. The pressure sensor S6B detects the bucket bottom pressure, which is the pressure of hydraulic oil in a bottom-side oil chamber of the bucket cylinder 9. The pressure sensor S6R detects the bucket rod pressure, which is the pressure of hydraulic oil in a rod-side oil chamber of the bucket cylinder 9.

[0021] The pressure sensor S7 is a device (discharge pressure sensor) for detecting the pump discharge pressure of the hydraulic pump 14. Specifically, the pressure sensor S7 includes a pressure sensor S7A and a pressure sensor S7B. The pressure sensor S7A detects the pump discharge pressure of the first hydraulic pump 14A. The pressure sensor S7B detects the pump discharge pressure of the second hydraulic pump 14B.

[0022] The hydraulic control valve HV is configured to be able to control the flow of hydraulic oil related to the hydraulic actuators. In this embodiment, the hydraulic control valve HV includes hydraulic control valves HV1 to HV20 of the same structure that are individually controlled by solenoid valves EV. The hydraulic control valve HV is configured to selectively supply hydraulic oil received from the hydraulic pump 14 through a hydraulic oil line to one or more hydraulic actuators in response to a change in pressure (pilot pressure) corresponding to the operation direction and operation amount of the operating device 26. The hydraulic actuators include, for example, a boom cylinder 7, an arm cylinder 8, a bucket cylinder 9, a left traveling hydraulic motor 1M, a right traveling hydraulic motor 2M, and a swing hydraulic motor 3M.

[0023] The hydraulic control valve HV1 is disposed in a pipeline connected to a first port (left port) of the swing hydraulic motor 3M, and is configured to selectively connect the first port (left port) of the swing hydraulic motor 3M to the first hydraulic pump 14A or the hydraulic oil tank T. The hydraulic control valve HV1 functions as a meter-in valve for the swing hydraulic motor 3M when the swing hydraulic motor 3M rotates in a first direction, and functions as a meter-out valve for the swing hydraulic motor 3M when the swing hydraulic motor 3M rotates in a second direction that is opposite to the first direction.

[0024] The hydraulic control valve HV2 arranged in the pipeline connected to the second port (right port) of the swing hydraulic motor 3M, the hydraulic control valve HV3 arranged in the pipeline connected to the bottom side oil chamber of the boom cylinder 7, the hydraulic control valve HV4 arranged in the pipeline connected to the rod side oil chamber of the boom cylinder 7, the hydraulic control valve HV5 arranged in the pipeline connected to the bottom side oil chamber of the arm cylinder 8, the hydraulic control valve HV6 arranged in the pipeline connected to the rod side oil chamber of the arm cylinder 8, the hydraulic control valve HV7 arranged in the pipeline connected to the first port (left port) of the left traveling hydraulic motor 1M, the hydraulic control valve HV8 arranged in the pipeline connected to the second port (right port) of the left traveling hydraulic motor 1M, the hydraulic control valve HV9 arranged in the pipeline connected to the rod side oil chamber of the bucket cylinder 9, the hydraulic control valve HV10 arranged in the pipeline connected to the oil chamber of the hydraulic actuator, the hydraulic control valve HV11 arranged in the pipeline connected to the rod side oil chamber of the bucket cylinder 9, The same is true for the hydraulic control valve HV11 arranged in the pipeline connected to the bottom oil chamber of the bucket cylinder 9, the hydraulic control valve HV12 arranged in the pipeline connected to the bottom oil chamber of the bucket cylinder 9, the hydraulic control valve HV13 arranged in the pipeline connected to the rod side oil chamber of the arm cylinder 8, the hydraulic control valve HV14 arranged in the pipeline connected to the bottom oil chamber of the arm cylinder 8, the hydraulic control valve HV15 arranged in the pipeline connected to the rod side oil chamber of the boom cylinder 7, the hydraulic control valve HV16 arranged in the pipeline connected to the bottom oil chamber of the boom cylinder 7, the hydraulic control valve HV17 arranged in the pipeline connected to the first port (left port) of the right traveling hydraulic motor 2M, the hydraulic control valve HV18 arranged in the pipeline connected to the second port (right port) of the right traveling hydraulic motor 2M, and the hydraulic control valve HV19 and the hydraulic control valve HV20 arranged in the pipelines connected to hydraulic actuators other than the above-mentioned hydraulic actuators.

[0025] The pilot pump 15 is a hydraulic pump for supplying hydraulic oil to various hydraulic control devices such as the operating device 26 via a pilot line. In the example shown in Fig. 3, the pilot pump 15 is a fixed displacement hydraulic pump that is driven by the engine 11, and an input shaft of the pilot pump 15 is connected to an output shaft of the engine 11. Note that the hydraulic pump 14 may be configured to supply hydraulic oil to various hydraulic control devices such as the operating device 26 via a pilot line after reducing the pressure of the discharged hydraulic oil by throttling or the like. In this case, the pilot pump 15 may be omitted.

[0026] The operation device 26 is a device used by an operator to operate the hydraulic actuator. The operation device 26 is, for example, an operation lever or an operation pedal. In the example shown in FIG. 3, the operation device 26 is an electric operation device, and outputs information on the operation direction and operation amount of the operation device 26 to the controller 30 as an electric signal (operation command value). The controller 30 can adjust the magnitude of the pilot pressure acting on the hydraulic control valve HV by adjusting the opening area of ​​the solenoid valve EV in response to the electric signal received from the operation device 26. The operation device 26 also includes a left operation lever for operating the swing hydraulic motor 3M and the arm cylinder 8, and a right operation lever for operating the boom cylinder 7 and the bucket cylinder 9.

[0027] The controller 30 is a control device for controlling the shovel 100. In this embodiment, the controller 30 is configured with a computer including a CPU, a volatile storage medium, a nonvolatile storage medium, etc. The CPU of the controller 30 reads out programs corresponding to various functions from the nonvolatile storage medium, loads them into the volatile storage medium, and executes them to realize the functions corresponding to each of the programs.

[0028] For example, the controller 30 realizes a function of controlling the pump discharge amount of the hydraulic pump 14. Specifically, the controller 30 changes the magnitude of the control current to the regulator 13, and controls the pump discharge amount of the hydraulic pump 14 via the regulator 13.

[0029] Here, the hydraulic control valve HV will be described in detail with reference to Fig. 3. Note that the following description relates to the hydraulic control valve HV1, but is similarly applicable to each of the hydraulic control valves HV2 to HV20.

[0030] The hydraulic control valve HV1 is a 3-port, 3-position spool valve. In Fig. 3, (1) indicates the first position (first valve position), (2) indicates the second position (second valve position), and (3) indicates the third position (third valve position).

[0031] When the hydraulic control valve HV1 is positioned at the second position, which is the neutral position, it blocks communication between the left port of the swing hydraulic motor 3M and each of the first hydraulic pump 14A and the hydraulic oil tank T. In other words, when the hydraulic control valve HV1 is positioned at the second position, which is the neutral position, the opening area of ​​the first oil passage connecting the left port of the swing hydraulic motor 3M and the first hydraulic pump 14A and the opening area of ​​the second oil passage connecting the left port of the swing hydraulic motor 3M and the hydraulic oil tank are each minimized (zero).

[0032] Furthermore, when the hydraulic control valve HV1 is positioned at the first position, it communicates the left port of the swing hydraulic motor 3M with the first hydraulic pump 14A, and when the hydraulic control valve HV1 is positioned at the third position, it communicates the left port of the swing hydraulic motor 3M with the hydraulic oil tank T. That is, the hydraulic control valve HV1 is configured so that when the hydraulic control valve HV1 is positioned at the first position, the opening area of ​​the first oil passage is maximized, and when the hydraulic control valve HV1 is positioned at the third position, the opening area of ​​the second oil passage is maximized.

[0033] In addition, the hydraulic control valve HV1 is configured such that, in an intermediate position between the second position and the first position, the opening area of ​​the first oil passage becomes larger the further away from the neutral position, and, in an intermediate position between the second position and the third position, the opening area of ​​the second oil passage becomes larger the further away from the neutral position.

[0034] In addition, the hydraulic control valve HV1 is configured to move to the right when the pilot pressure at the left pilot port PL (left pilot pressure) becomes greater than the pilot pressure at the right pilot port PR (right pilot pressure), to move to the left when the left pilot pressure becomes smaller than the right pilot pressure, and to return to the neutral position when the left pilot pressure and the right pilot pressure become equal.

[0035] The left pilot pressure and the right pilot pressure are controlled by a solenoid valve EV. Specifically, the solenoid valve EV is a device for adjusting the pilot pressure, and is disposed between the hydraulic control valve HV1 and the pilot pump 15. In the example shown in FIG. 3, the solenoid valve EV operates in response to a current command from a controller 30. The solenoid valve EV is basically configured to operate the hydraulic control valve HV1 in response to the contents of an operation input to the operating device 26. Typically, the solenoid valve EV is configured to increase the amount of movement of the hydraulic control valve HV1 as the operation amount of the operating device 26 increases. In addition, the solenoid valve EV is configured to forcibly operate the hydraulic control valve HV1 regardless of the contents of the operation input to the operating device 26.

[0036] Specifically, the solenoid valve EV is a 4-port, 3-position spool valve. In Fig. 3, (1) indicates the first position (first valve position), (2) indicates the second position (second valve position), and (3) indicates the third position (third valve position).

[0037] When the solenoid valve EV is located at the second position, which is the neutral position, it connects the left pilot port PL and right pilot port PR of the hydraulic control valve HV1 to the hydraulic oil tank T, and blocks communication between the left pilot port PL and right pilot port PR and the pilot pump 15. At this time, both the left pilot pressure and the right pilot pressure acting on the hydraulic control valve HV1 become the hydraulic oil tank pressure (atmospheric pressure), so the hydraulic control valve HV1 returns to the neutral position.

[0038] Furthermore, when the solenoid valve EV is positioned at the first position, it communicates the left pilot port PL with the pilot pump 15, and also communicates the right pilot port PR with the hydraulic oil tank T. That is, when the solenoid valve EV is positioned at the first position, the opening area of ​​the first oil passage connecting the left pilot port PL with the pilot pump 15 is maximized, and the opening area of ​​the second oil passage connecting the right pilot port PR with the hydraulic oil tank T is maximized. At this time, the left pilot pressure acting on the hydraulic control valve HV1 becomes larger than the right pilot pressure, so the hydraulic control valve HV1 moves to the right.

[0039] Furthermore, when the solenoid valve EV is positioned at the third position, it communicates the left pilot port PL with the hydraulic oil tank T, and also communicates the right pilot port PR with the pilot pump 15. That is, when the solenoid valve EV is positioned at the third position, the opening area of ​​the third oil passage connecting the left pilot port PL with the hydraulic oil tank T is maximized, and the opening area of ​​the fourth oil passage connecting the right pilot port PR with the pilot pump 15 is maximized. At this time, the left pilot pressure acting on the hydraulic control valve HV1 becomes smaller than the right pilot pressure, so the hydraulic control valve HV1 moves to the left.

[0040] In addition, the solenoid valve EV is configured such that, in an intermediate position between the second position and the first position, the opening area of ​​the first oil passage and the second oil passage increases the further away from the neutral position, and, in an intermediate position between the second position and the third position, the opening area of ​​the third oil passage and the fourth oil passage increases the further away from the neutral position.

[0041] Next, an example of a control flow for operating the shovel 100 will be described with reference to FIG. 4. FIG. 4 is a diagram showing an example of a control flow for operating the shovel 100. This control is executed by the controller 30. In the example shown in FIG. 4, a control flow when a combined operation including a boom raising operation, an arm closing operation, and a bucket closing operation is performed is shown. In addition, in FIG. 4, the control flow executed by the controller 30 is represented by a plurality of functional blocks. In the example shown in FIG. 4, the functions represented by each functional block are realized by software. However, the functions represented by each functional block may be realized by hardware, or may be realized by a combination of software and hardware. In addition, in FIG. 4, for clarity, the meter-in valve is represented by an "MI valve" and the meter-out valve is represented by an "MO valve".

[0042] The boom required flow rate derivation unit F2 is configured to derive the boom required flow rate based on the boom operation amount and the boom thrust. The value of the boom operation amount is an example of an operation command value, and is the value of the operation amount of the operation device 26 for operating the boom 4. In the example shown in Fig. 4, the boom operation amount is a value corresponding to the tilt angle when the right operation lever is tilted in the forward / rearward direction.

[0043] Boom thrust is a thrust for moving the boom 4. Boom thrust is expressed, for example, by a value obtained by multiplying the pressure difference between the boom bottom pressure and the boom rod pressure by a pressure-receiving area. The pressure difference between the boom bottom pressure (meter-in pressure) and the boom rod pressure (meter-out pressure) is a value obtained by subtracting the meter-out pressure from the meter-in pressure, and is also called the "boom effective pressure", which is one of the "effective pressures". The pressure-receiving area is the pressure-receiving area of ​​the piston that constitutes the boom cylinder 7. In the example shown in FIG. 4, the pressure-receiving area in the rod-side oil chamber is smaller than the pressure-receiving area in the bottom-side oil chamber by the cross-sectional area of ​​the rod.

[0044] The boom required flow rate is a required flow rate of the boom cylinder 7. Specifically, the boom required flow rate is a target value for the amount of hydraulic oil flowing into the boom cylinder 7 per unit time.

[0045] The flow command generating unit F1 is configured to calculate a target value of the flow rate of the hydraulic oil to be supplied to each hydraulic actuator based on the required flow rate of each hydraulic actuator and the pump discharge pressure. In the example shown in Fig. 4, the flow command generating unit F1 is configured to output a command value corresponding to the target value.

[0046] 4, flow command generating unit F1 outputs a first boom inflow, which is an example of a flow command, to MI valve opening area calculating unit F5 and MO valve opening area calculating unit F6. The first boom inflow is a target value related to the flow rate of hydraulic oil supplied from the first hydraulic pump 14A through a first meter-in valve (in this example, hydraulic control valve HV3) to the boom cylinder 7. The first meter-in valve is one of two meter-in valves related to the boom cylinder 7.

[0047] The MI valve opening area calculation unit F5 is configured to control a first meter-in valve disposed between the first hydraulic pump 14A and the boom cylinder 7. For example, the MI valve opening area calculation unit F5 is configured to calculate the opening area of ​​the first meter-in valve. In the example shown in Fig. 4, the MI valve opening area calculation unit F5 calculates the opening area of ​​the hydraulic control valve HV3 that functions as the first meter-in valve during the boom raising operation.

[0048] Specifically, the MI valve opening area calculation unit F5 calculates the opening area of ​​the first meter-in valve (hydraulic control valve HV3) based on the first boom inflow volume, the first boom MI pressure, the pump discharge pressure of the first hydraulic pump 14A, and a predetermined calculation formula.

[0049] The first boom MI pressure is a detection value of the pressure sensor S4B, and the pump discharge pressure of the first hydraulic pump 14A is a detection value of the pressure sensor S7A.

[0050] The predetermined calculation formula is, for example, a flow rate calculation formula for an orifice shown in the following formula (1), where the first boom inflow amount is Qb, the pump discharge pressure of the first hydraulic pump 14A is Pa, the first boom MI pressure is Pb, and the opening area of ​​the first meter-in valve (hydraulic control valve HV3) is A1, then the opening area A1 of the first meter-in valve (hydraulic control valve HV3) is expressed by formula (2), where C is a flow coefficient and ρ is a fluid density.

[0051]

number

[0052] In this way, the MI valve opening area calculation unit F5 controls the opening area of ​​the first meter-in valve so that hydraulic oil can flow into the bottom side oil chamber of the boom cylinder 7 at a desired flow rate (first boom inflow amount Qb).

[0053] The flow rate command generating unit F1 is configured to similarly output flow rate commands to an MI valve opening area calculation unit F7 that controls the opening area of ​​the remaining one of the two meter-in valves related to the boom cylinder 7, an MO valve opening area calculation unit F6 and an MO valve opening area calculation unit F8 that control the opening areas of the two meter-out valves related to the boom cylinder 7, two MI valve opening area calculation units (not shown) that control the opening area of ​​the two meter-in valves related to the arm cylinder 8, two MO valve opening area calculation units (not shown) that control the opening area of ​​the two meter-out valves related to the arm cylinder 8, an MI opening area calculation unit (not shown) that controls the meter-in valve related to the bucket cylinder 9, and two MO valve opening area calculation units (not shown) that control the opening area of ​​the two meter-out valves related to the bucket cylinder 9.

[0054] Moreover, the flow command generating unit F1 is configured to output a command for determining the pump discharge rate of the hydraulic pump 14. Specifically, the flow command generating unit F1 outputs a pump discharge rate determination command to the maximum MI pressure selecting unit F9.

[0055] The maximum MI pressure selection unit F9 is configured to select the maximum value of one or more meter-in pressures as the maximum MI pressure. The meter-in pressure is the pressure of hydraulic oil downstream of the meter-in valve. Specifically, the meter-in pressure is the pressure of hydraulic oil in a pipe connecting the meter-in valve and the hydraulic actuator. In the example shown in FIG. 4 in which the boom raising operation is performed, the meter-in pressure includes the pressure of hydraulic oil in the pipe connecting the hydraulic control valve HV3 functioning as a meter-in valve and the bottom side oil chamber of the boom cylinder 7, i.e., the boom bottom pressure detected by the pressure sensor S4B.

[0056] When a combined operation consisting of a boom raising operation, an arm closing operation, and a bucket closing operation is performed, the maximum MI pressure selection unit F9 selects the maximum value among the boom bottom pressure, the arm bottom pressure, and the bucket bottom pressure as the maximum MI pressure.

[0057] 4, the maximum MI pressure selection unit F9 selects the maximum value of one or more meter-in pressures related to the first hydraulic pump 14A as the first maximum MI pressure, and selects the maximum value of one or more meter-in pressures related to the second hydraulic pump 14B as the second maximum MI pressure. The one or more meter-in pressures related to the first hydraulic pump 14A are the meter-in pressures related to one or more of the hydraulic control valves HV1 to HV10. The one or more meter-in pressures related to the second hydraulic pump 14B are the meter-in pressures related to one or more of the hydraulic control valves HV11 to HV20.

[0058] Then, the maximum MI pressure selection unit F9 outputs the selected maximum MI pressure to the pump discharge rate control unit F10.

[0059] The pump discharge rate control unit F10 is configured to control the pump discharge rate of the hydraulic pump 14. In the example shown in Fig. 4, the pump discharge rate control unit F10 calculates a command value to be output to the regulator 13 of the hydraulic pump 14 serving as a swash plate type variable displacement hydraulic pump, based on the maximum MI pressure output by the maximum MI pressure selection unit F9. In this case, the command value is, for example, the swash plate tilt angle.

[0060] Specifically, the pump discharge control unit F10 calculates the swash plate tilt angle to be output to the first regulator 13A of the first hydraulic pump 14A based on the first maximum MI pressure output by the maximum MI pressure selection unit F9. The pump discharge control unit F10 also calculates the swash plate tilt angle to be output to the second regulator 13B of the second hydraulic pump 14B based on the second maximum MI pressure output by the maximum MI pressure selection unit F9.

[0061] The regulator 13 changes the swash plate tilt angle of the hydraulic pump 14 in response to a command value from the pump discharge rate control unit F10 to change the pump discharge rate of the hydraulic pump 14. Specifically, the first regulator 13A changes the pump discharge rate of the first hydraulic pump 14A, and the second regulator 13B changes the pump discharge rate of the second hydraulic pump 14B.

[0062] In this way, the controller 30 can appropriately control the flow rate of hydraulic oil flowing into the hydraulic actuator, the flow rate of hydraulic oil flowing out of the hydraulic actuator, and the pump discharge rate of the hydraulic pump 14.

[0063] Next, with reference to Figs. 5 to 8, an example of a process in which the controller 30 controls the movement of the solenoid valve EV will be described. Figs. 5 and 6 are schematic diagrams of a part of the hydraulic circuit shown in Fig. 2, showing the flow of hydraulic oil when the boom cylinder 7 and the arm cylinder 8 are extended. That is, Figs. 5 and 6 are schematic diagrams of a hydraulic circuit including the hydraulic control valves HV3 to HV6, the boom cylinder 7, the arm cylinder 8, the first hydraulic pump 14A, and the hydraulic oil tank T, showing the flow of hydraulic oil when a combined operation including a boom raising operation and an arm closing operation is performed. In Figs. 5 and 6, for clarity, the flow of hydraulic oil from the first hydraulic pump 14A toward the boom cylinder 7 and the arm cylinder 8 is represented by a thick solid arrow, and the flow of hydraulic oil from the boom cylinder 7 and the arm cylinder 8 toward the hydraulic oil tank T is represented by a thick dashed arrow. In addition, although the boom cylinder 7 is actually composed of two hydraulic cylinders, in the following, it is represented by one hydraulic cylinder for simplicity of explanation. In addition, the boom cylinder 7 and the arm cylinder 8 actually operate using hydraulic oil discharged from the first hydraulic pump 14A and the second hydraulic pump 14B, respectively, but in the following, for simplicity of explanation, they are represented as operating using hydraulic oil discharged from the first hydraulic pump 14A.

[0064] 5 and 6, the hydraulic control valve HV6 is configured to be able to utilize an intermediate position between the first position (see FIG. 3) and the third position (see FIG. 3). That is, the hydraulic control valve HV6 can cause a portion of the hydraulic oil flowing out from the rod-side oil chamber of the arm cylinder 8 to flow toward the hydraulic oil tank T, and the remaining portion to flow toward the first hydraulic pump 14A. The same is true for the hydraulic control valves HV3 to HV5. Therefore, in FIG. 5 and 6, for the sake of clarity, the hydraulic control valves HV3 to HV6 are illustrated as 3-port 2-position spool valves.

[0065] Specifically, Fig. 5 shows the flow of hydraulic oil when the normal circuit is selected. The "normal circuit" is one of the paths through which hydraulic oil flows to operate a hydraulic actuator, and refers to a path when the hydraulic oil flowing out of the hydraulic actuator is not merged with the hydraulic oil discharged by the first hydraulic pump 14A. Fig. 5 shows how all of the hydraulic oil flowing out of the first port 7P1 of the boom cylinder 7 is discharged into the hydraulic oil tank T through the hydraulic control valve HV4, and how all of the hydraulic oil flowing out of the first port 8P1 of the arm cylinder 8 is discharged into the hydraulic oil tank T through the hydraulic control valve HV6.

[0066] FIG. 6 also shows the flow of hydraulic oil when the first differential circuit, which is one of the differential circuits, is selected. The "differential circuit" is another of the paths through which hydraulic oil flows to operate the hydraulic actuators, and means a path when hydraulic oil flowing out from at least one of the two hydraulic actuators is merged with hydraulic oil discharged by the first hydraulic pump 14A. The function of merging hydraulic oil flowing out from at least one of the two hydraulic actuators with hydraulic oil discharged by the first hydraulic pump 14A is also called a differential function. The differential function includes a regeneration function of returning hydraulic oil flowing out from one hydraulic actuator to that hydraulic actuator, and a regeneration function of causing hydraulic oil flowing out from one hydraulic actuator to flow into another hydraulic actuator. In the illustrated example, the differential circuit includes a first differential circuit and a second differential circuit. The "first differential circuit" means a path when using a function (first differential function) of causing at least a part of hydraulic oil flowing out from the first port 8P1 of the arm cylinder 8 to flow into the arm cylinder 8 via the second port 8P2. FIG. 6 shows how the flow of hydraulic oil flowing out from the first port 8P1 of the arm cylinder 8 is branched by the hydraulic control valve HV6, with half of it joining the hydraulic oil from the first hydraulic pump 14A and flowing toward the second port 8P2, and the remaining half being discharged into the hydraulic oil tank T.

[0067] Although not shown, the second differential circuit has a similar configuration to the first differential circuit. Note that the "second differential circuit" refers to a path when a function (second differential function) of causing at least a portion of the hydraulic oil flowing out from the first port 7P1 of the boom cylinder 7 to flow into the boom cylinder 7 via the second port 7P2 is used.

[0068] FIG. 5 also includes cross-sectional views of the boom cylinder 7 and the arm cylinder 8. Specifically, FIG. 5 includes a view of the cross section of the bottom-side oil chamber of the arm cylinder 8 in a virtual plane including the dashed line AA when viewed from below, and a view of the cross section of the rod-side oil chamber of the arm cylinder 8 in a virtual plane including the dashed line BB when viewed from above. Then, "A11" represents the pressure-receiving area (surface area of ​​the area represented by the dot pattern) in the rod-side oil chamber of the piston 8S sliding in the arm cylinder 8, and "A12" represents the pressure-receiving area (surface area of ​​the area represented by the dot pattern) in the bottom-side oil chamber of the piston 8S. FIG. 5 also includes a view of the cross section of the bottom-side oil chamber of the boom cylinder 7 in a virtual plane including the dashed line CC when viewed from below, and a view of the cross section of the rod-side oil chamber of the boom cylinder 7 in a virtual plane including the dashed line DD when viewed from above. Furthermore, "A21" represents the pressure-receiving area (the surface area of ​​the area represented by the dot pattern) in the rod side oil chamber of the piston 7S sliding inside the boom cylinder 7, and "A22" represents the pressure-receiving area (the surface area of ​​the area represented by the dot pattern) in the bottom side oil chamber of the piston 7S.

[0069] 7 is a flowchart showing an example of the flow of a process (hereinafter, referred to as a "circuit selection process") in which the controller 30 selects one of the normal circuit, the first differential circuit, and the second differential circuit when extending each of the boom cylinder 7 and the arm cylinder 8. In the illustrated example, the controller 30 repeatedly executes this circuit selection process at a predetermined control period.

[0070] First, the controller 30 measures the first cylinder pressure P1, the pump discharge pressure PS, the second cylinder pressure P2, the first cylinder inflow amount Q1, and the second cylinder inflow amount Q2 (steps ST1 to ST5).

[0071] In the illustrated example, the first cylinder pressure P1 is the pressure of the hydraulic oil in the bottom side oil chamber of the arm cylinder 8, and the second cylinder pressure P2 is the pressure of the hydraulic oil in the bottom side oil chamber of the boom cylinder 7. The pump discharge pressure PS is the pressure of the hydraulic oil discharged by the first hydraulic pump 14A. Furthermore, the first cylinder inflow Q1 of the first hydraulic pump 14A is the amount of hydraulic oil per unit time flowing into the bottom side oil chamber of the arm cylinder 8, and the second cylinder inflow Q2 is the amount of hydraulic oil per unit time flowing into the bottom side oil chamber of the boom cylinder 7.

[0072] In the illustrated example, the controller 30 measures the first cylinder pressure P1 based on the output of the pressure sensor S5B, and measures the second cylinder pressure P2 based on the output of the pressure sensor S4B. The controller 30 also measures the first cylinder inflow Q1 based on the opening area of ​​the PC port of the hydraulic control valve HV5 and the differential pressure before and after the hydraulic control valve HV5. The PC port of the hydraulic control valve HV5 is a port that connects the first hydraulic pump 14A and the arm cylinder 8. Specifically, the controller 30 calculates the opening area of ​​the PC port of the hydraulic control valve HV5 based on the output of a pilot pressure sensor that detects the pilot pressure of the hydraulic control valve HV5, and measures the first cylinder inflow Q1 based on the opening area and the outputs of the pressure sensors S5B and S7A. The controller 30 may derive the opening area of ​​the PC port of the hydraulic control valve HV5 from the value of the MI valve opening command. Similarly, the controller 30 measures the second cylinder inflow amount Q2 based on the opening area of ​​the PC port of the hydraulic control valve HV3 and the pressure difference before and after the hydraulic control valve HV3. Specifically, the controller 30 calculates the opening area of ​​the PC port of the hydraulic control valve HV3 based on the output of a pilot pressure sensor that detects the pilot pressure of the hydraulic control valve HV3, and measures the second cylinder inflow amount Q2 based on the opening area and the respective outputs of the pressure sensors S4B and S7A. Note that the controller 30 may measure the first cylinder inflow amount Q1 and the second cylinder inflow amount Q2 based on the output of a cylinder stroke sensor that detects the extension and contraction amounts of the boom cylinder 7 and the arm cylinder 8, respectively.

[0073] Thereafter, the controller 30 calculates an estimated value P1c of the first cylinder pressure P1 and an estimated value Q1c of the first cylinder inflow amount Q1 when the first differential circuit is selected, and calculates an estimated value P2c of the second cylinder pressure P2 and an estimated value Q2c of the second cylinder inflow amount Q2 when the second differential circuit is selected (steps ST6 to ST9).

[0074] Specifically, the estimated value P1c of the first cylinder pressure P1 when the first differential circuit is selected is calculated using the following equation (3), as shown in step ST6.

[0075] P1c = P1 + A12 / A11 * PS + PD (3) That is, the estimated value P1c of the first cylinder pressure P1 is calculated as the sum of a value obtained by multiplying the pump discharge pressure PS of the first hydraulic pump 14A by a first area ratio (A12 / A11), which is the ratio of the pressure receiving area A12 in the rod side oil chamber to the pressure receiving area A11 in the bottom side oil chamber of the piston 8S of the arm cylinder 8, the first cylinder pressure P1, and a predetermined margin pressure PD. The predetermined margin pressure PD is a pressure value that is set so that the hydraulic actuator can be operated reliably, and the pump discharge pressure PS of the first hydraulic pump 14A is controlled to be a pressure that is higher than the larger of the first cylinder pressure P1 and the second cylinder pressure P2 by the margin pressure PD.

[0076] Similarly, the estimated value P2c of the second cylinder pressure P2 when the second differential circuit is selected is calculated using the following equation (4) as shown in step ST7.

[0077] P2c=P2+A22 / A21*PS+PD (4) That is, the estimated value P2c of the second cylinder pressure P2 is calculated as the sum of the second cylinder pressure P2 and a predetermined margin pressure PD, the value obtained by multiplying the pump discharge pressure PS of the first hydraulic pump 14A by a second area ratio (A22 / A21), which is the ratio of the pressure-receiving area A22 in the rod side oil chamber to the pressure-receiving area A21 in the bottom side oil chamber of the piston 7S of the boom cylinder 7.

[0078] Further, the estimated value Q1c of the first cylinder inflow amount Q1 when the first differential circuit is selected is calculated using the following equation (5) as shown in step ST8.

[0079] Q1c = (A11 - A12) / A11 * Q1 (5) That is, the estimated value Q1c of the first cylinder inflow Q1 is calculated as the product of the third area ratio (A11-A12) / A11, which is the ratio of the difference (A11-A12) between the pressure-receiving area A11 and the pressure-receiving area A12 to the pressure-receiving area A11 in the bottom oil chamber of the piston 8S of the arm cylinder 8, and the first cylinder inflow Q1.

[0080] Similarly, the estimated value Q2c of the second cylinder inflow amount Q2 when the second differential circuit is selected is calculated using the following equation (6), as shown in step ST9.

[0081] Q2c = (A21 - A22) / A21 * Q2 (6) That is, the estimated value Q2c of the second cylinder inflow Q2 is calculated as the product of the fourth area ratio (A21-A22) / A21, which is the ratio of the difference (A21-A22) between the pressure-receiving area A21 and the pressure-receiving area A22 to the pressure-receiving area A21 in the bottom oil chamber of the piston 7S of the boom cylinder 7, and the second cylinder inflow Q2.

[0082] Thereafter, the controller 30 calculates an estimated value PSc1 of the pump discharge pressure PS and an estimated value QSc1 of the pump discharge volume QS when the first differential circuit is selected, calculates an estimated value PSc2 of the pump discharge pressure PS and an estimated value QSc2 of the pump discharge volume QS when the second differential circuit is selected, and calculates the pump discharge volume QS when the normal circuit is selected (steps ST10 to ST14).

[0083] Specifically, the estimated value PSc1 of the pump discharge pressure PS when the first differential circuit is selected is calculated using the following equation (7) as shown in step ST10.

[0084] PSc1 = MAX(P1c,P2) + PD (7) That is, the estimated value PSc1 of the pump discharge pressure PS is calculated as the sum of the larger of the estimated value P1c of the first cylinder pressure P1 calculated in step ST6 and the second cylinder pressure P2, and the margin pressure PD.

[0085] Similarly, the estimated value PSc2 of the pump discharge pressure PS when the second differential circuit is selected is calculated using the following equation (8) as shown in step ST11.

[0086] P2c2 = MAX(P2c,P1) + P D (8) That is, the estimated value PSc2 of the pump discharge pressure PS is calculated as the sum of the larger of the estimated value P2c of the second cylinder pressure P2 calculated in step ST7 and the first cylinder pressure P1, and the margin pressure PD.

[0087] Moreover, the estimated value QSc1 of the pump discharge amount QS when the first differential circuit is selected is calculated using the following equation (9) as shown in step ST12.

[0088] QSc1 = Q1c + Q2 (9) That is, the estimated value QSc1 of the pump discharge amount QS is calculated as the sum of the estimated value Q1c of the first cylinder inflow amount Q1 calculated in step ST8 and the second cylinder inflow amount Q2 measured in step ST5.

[0089] Similarly, the estimated value QSc2 of the pump discharge amount QS when the second differential circuit is selected is calculated using the following formula (10) as shown in step ST14.

[0090] QSc2 = Q1 + Q2c (10) That is, the estimated value QSc2 of the pump discharge amount QS is calculated as the sum of the estimated value Q2c of the second cylinder inflow amount Q2 calculated in step ST9 and the first cylinder inflow amount Q1 measured in step ST4.

[0091] Moreover, when the normal circuit is selected, the pump discharge amount QS is calculated using the following formula (11) as shown in step ST13.

[0092] QS = Q1 + Q2 (11) That is, the pump discharge amount QS is calculated as the sum of the first cylinder inflow amount Q1 measured in step ST4 and the second cylinder inflow amount Q2 measured in step ST5.

[0093] After that, the controller 30 calculates the pump output Wc1 when the first differential circuit is selected, the pump output Wc2 when the second differential circuit is selected, and the pump output W when the normal circuit is selected (steps ST15 to ST17).

[0094] Specifically, the pump output Wc1 when the first differential circuit is selected is calculated using the following equation (12), as shown in step ST15.

[0095] Wc1 = PSc1 * QSc1 (12) That is, the pump output Wc1 when the first differential circuit is selected is calculated as the product of the estimated value PSc1 of the pump discharge pressure PS when the first differential circuit is selected, calculated in step ST10, and the estimated value QSc1 of the pump discharge volume QS when the first differential circuit is selected, calculated in step ST12.

[0096] Similarly, the pump output Wc2 when the second differential circuit is selected is calculated using the following equation (13), as shown in step ST17.

[0097] Wc2 = PSc2 * QSc2 (13) That is, the pump output Wc2 when the second differential circuit is selected is calculated as the product of the estimated value PSc2 of the pump discharge pressure PS when the second differential circuit is selected, calculated in step ST11, and the estimated value QSc2 of the pump discharge volume QS when the second differential circuit is selected, calculated in step ST14.

[0098] Moreover, when the normal circuit is selected, the pump output W is calculated using the following formula (14) as shown in step ST16.

[0099] W = P S * Q S (14) That is, the pump output W when the normal circuit is selected is calculated as the product of the pump discharge pressure PS measured in step ST2 and the pump discharge amount QS calculated in step ST13.

[0100] After that, the controller 30 selects which of the normal circuit, the first differential circuit, and the second differential circuit to use (step ST18).

[0101] In the illustrated example, the controller 30 compares the pump output Wc1 when the first differential circuit is selected, the pump output Wc2 when the second differential circuit is selected, and the pump output W when the normal circuit is selected. Then, the controller 30 selects the normal circuit when it determines that the pump output W is minimum, selects the first differential circuit when it determines that the pump output Wc1 is minimum, and selects the second differential circuit when it determines that the pump output Wc2 is minimum. When the controller 30 selects the normal circuit, it realizes the normal circuit by setting the hydraulic control valves HV3 to HV6 to the state shown in FIG. 5. The same applies when the first differential circuit or the second differential circuit is selected.

[0102] Here, the effect of the circuit selection process will be described with reference to FIG. 8. FIG. 8 is a diagram showing the relationship between the pressure of the hydraulic oil (first cylinder pressure P1, second cylinder pressure P2, pump discharge pressure PS, etc.), the flow rate of the hydraulic oil (first cylinder inflow amount Q1, second cylinder inflow amount Q2, pump discharge amount QS, etc.), and the consumed energy (first pump output W1, second pump output W2, output loss LS, etc.). Specifically, the upper diagram of FIG. 8 shows an example of the relationship between the pressure and flow rate of the hydraulic oil when the normal circuit is selected, and the center diagram of FIG. 8 and the lower diagram of FIG. 8 show an example of the relationship between the pressure and flow rate of the hydraulic oil when the first differential circuit is selected and the output loss LS is reduced, and the lower diagram of FIG. 8 shows an example of the relationship between the pressure and flow rate of the hydraulic oil when the first differential circuit is selected and the output loss LS is increased.

[0103] Specifically, when the boom cylinder 7 and the arm cylinder 8 are driven simultaneously by the hydraulic oil discharged from the first hydraulic pump 14A, the hydraulic loads of the two are different, so the controller 30 controls the pump discharge volume QS to achieve a pump discharge pressure PS capable of driving the hydraulic cylinder with the higher hydraulic load. In the illustrated example, the controller 30 controls the pump discharge volume QS so that the pump discharge pressure PS of the first hydraulic pump 14A becomes the sum of the second cylinder pressure P2 and the margin pressure PD so that the boom cylinder 7 with the higher hydraulic load can be driven.

[0104] Therefore, the arm cylinder 8 with a lower hydraulic load generates an output loss (first output loss LS1) that is larger than the output loss (second output loss LS2) in the boom cylinder 7 with a higher hydraulic load. In the illustrated example, the output loss LS corresponds to the pump output W of the first hydraulic pump 14A that is wasted without being used by either the boom cylinder 7 or the arm cylinder 8, and includes the first output loss LS1 and the second output loss LS2. In the illustrated example, the pump output W of the first hydraulic pump 14A is calculated as the product of the pump discharge pressure PS and the pump discharge amount QS, the first pump output W1 used in the arm cylinder 8 is calculated as the product of the first cylinder pressure P1 and the first cylinder inflow amount Q1, the second pump output W2 used in the boom cylinder 7 is calculated as the product of the second cylinder pressure P2 and the second cylinder inflow amount Q2, and the pump output W is calculated as the sum of the first pump output W1, the second pump output W2, and the output loss LS. The pump output W corresponds to the energy consumed in the hydraulic circuit installed in the shovel 100, the first pump output W1 corresponds to the energy consumed in the arm cylinder 8, and the second pump output W2 corresponds to the energy consumed in the boom cylinder 7.

[0105] For clarity in Fig. 8, the area representing the power loss LS is marked with a dot pattern, the area representing the first pump power W1 is marked with a cross pattern, and the area representing the second pump power W2 is marked with a diagonal line pattern. Also, in the upper diagram of Fig. 8, the area representing the power loss LS is surrounded by a dashed line, and in the center and lower diagrams of Fig. 8, for comparison, an area of ​​the same size as the area surrounded by the dashed line in the upper diagram of Fig. 8 is surrounded by a dashed line.

[0106] As can be seen by comparing the upper diagram in FIG. 8 with the center diagram in FIG. 8, in the illustrated example, the controller 30 can reduce the output loss LS by selecting the first differential circuit instead of the normal circuit.

[0107] Specifically, the controller 30 operates the hydraulic control valve HV6 by controlling the solenoid valve EV corresponding to the hydraulic control valve HV6, and can switch the hydraulic circuit installed in the excavator 100 from a state in which a normal circuit as shown in FIG. 5 is selected to a state in which a first differential circuit as shown in FIG. 6 is selected.

[0108] When the normal circuit is switched to the first differential circuit, the controller 30 increases the first cylinder pressure P1 to the estimated value P1c as shown in the upper diagram and the center diagram of FIG. 8, but can reduce the first cylinder inflow amount Q1 to the estimated value Q1c. That is, when the differential circuit related to the arm cylinder 8 with the lower hydraulic load is used, the controller 30 can reduce the overall energy consumption in the hydraulic circuit mounted on the excavator 100 when the reduction effect of the pump discharge amount QS exceeds the effect of the increase in the pump discharge pressure PS. The increase in the first cylinder pressure P1 is caused by the increase in the rod side oil chamber of the arm cylinder 8, which increases by selecting the first differential circuit. In the illustrated example, the pump discharge pressure PS when the first differential circuit is selected is the same as the pump discharge pressure PS when the normal circuit is selected, and the increase in the first cylinder pressure P1 does not cause an increase in the pump discharge pressure PS.

[0109] On the other hand, even if the normal circuit is switched to the first differential circuit, when the effect of reducing the pump discharge volume QS is less than the effect of increasing the pump discharge pressure PS, the controller 30 cannot reduce the overall energy consumption in the hydraulic circuits installed in the shovel 100.

[0110] Specifically, as shown in the lower diagram of Fig. 8, when the estimated value P1c of the first cylinder pressure P1 after the increase is greater than the second cylinder pressure P2, the controller 30 increases the pump discharge pressure PS of the first hydraulic pump 14A to an estimated value PSc1 obtained by adding the margin pressure PD to the estimated value P1c. In this case, the larger the estimated value P1c, the greater the second output loss LS2 in the boom cylinder 7, and depending on the magnitude of the estimated value P1c, the output loss LS when the first differential circuit is selected may exceed the output loss LS when the normal circuit is selected. That is, the reduction effect of the pump discharge amount QS may be less than the effect of the increase in the pump discharge pressure PS.

[0111] Therefore, the controller 30 is configured to execute a circuit selection process as shown in FIG. 7 to determine in advance whether or not energy consumption can be reduced, and then select an optimal hydraulic circuit (path through which the hydraulic oil flows).

[0112] With this configuration, for example, when the normal circuit is selected, if the controller 30 determines that energy consumption can be reduced by switching to the first differential circuit, the controller 30 can switch the normal circuit to the first differential circuit. Alternatively, when the first differential circuit is selected, if the controller 30 determines that energy consumption can be reduced by switching to the normal circuit, the controller 30 can switch the first differential circuit to the normal circuit.

[0113] Note that the above description with reference to FIG. 8 relates to the relationship between the normal circuit and the first differential circuit, but the same applies to the relationship between the normal circuit and the second differential circuit, and the relationship between the first differential circuit and the second differential circuit, etc.

[0114] In the above embodiment, the controller 30 is configured to select one of the normal circuit, the first differential circuit, and the second differential circuit, but may be configured to select one of the normal circuit, the first differential circuit, the second differential circuit, and the third differential circuit. In this case, the third differential circuit may be a combination of the first differential circuit and the second differential circuit. That is, the third differential circuit can merge at least a part of the hydraulic oil flowing out from the arm cylinder 8 and at least a part of the hydraulic oil flowing out from the boom cylinder 7 into the hydraulic oil discharged by the first hydraulic pump 14A.

[0115] Furthermore, the hydraulic control valve HV may be an electromagnetic control valve. In this case, the electromagnetic valve EV may be omitted, because the controller 30 can directly control the electromagnetic control valve without the intervention of the electromagnetic valve EV.

[0116] As described above, the excavator 100 according to an embodiment of the present disclosure includes, as shown in FIG. 5, a hydraulic oil tank T, a first hydraulic actuator (arm cylinder 8), a second hydraulic actuator (boom cylinder 7), a hydraulic pump (first hydraulic pump 14A) capable of supplying hydraulic oil in the hydraulic oil tank T to each of the first hydraulic actuator and the second hydraulic actuator, meter-in valves (hydraulic control valve HV3 and hydraulic control valve HV5) corresponding to each of the first hydraulic actuator and the second hydraulic actuator, meter-out valves (hydraulic control valve HV4 and hydraulic control valve HV6) corresponding to each of the first hydraulic actuator and the second hydraulic actuator, and a control device (controller 30) that controls each of the meter-in valves, the meter-out valves, and the hydraulic pump. The control device is configured to be able to switch between a first hydraulic circuit (normal circuit in FIG. 5) that returns the hydraulic oil flowing out from each of the first hydraulic actuator and the second hydraulic actuator to the hydraulic oil tank T, and a second hydraulic circuit (first differential circuit in FIG. 6) that merges a portion of the hydraulic oil flowing out from at least one of the first hydraulic actuator and the second hydraulic actuator with the hydraulic oil discharged by the hydraulic pump.

[0117] With this configuration, the excavator 100 can select and use a hydraulic circuit suitable for the current operating state from a plurality of hydraulic circuits (paths through which hydraulic oil flows), such as the first hydraulic circuit and the second hydraulic circuit, at any timing, and can therefore reduce the output loss LS and operate the hydraulic actuator more efficiently, as compared to a configuration in which the hydraulic circuit cannot be selected at any timing. Therefore, for example, when the engine 11 is a diesel engine, the control device (controller 30) can improve the fuel efficiency of the engine 11. This is because the fuel efficiency of an engine improves as the output loss LS becomes smaller, and being able to select an optimal hydraulic circuit means that the output loss LS can be reduced.

[0118] The control device (controller 30) may be configured to calculate a first consumed energy (pump output W) which is the energy consumed when the first hydraulic circuit (normal circuit in FIG. 5) is selected, and a second consumed energy (pump output Wc1) which is the energy consumed when the second hydraulic circuit (first differential circuit in FIG. 6) is selected, and select the first hydraulic circuit or the second hydraulic circuit based on the first consumed energy and the second consumed energy. Note that the first consumed energy and the second consumed energy are typically calculated so that the movement of the hydraulic actuator when the first hydraulic circuit is employed is the same as the movement of the hydraulic actuator when the second hydraulic circuit is employed.

[0119] This configuration allows the excavator 100 to select, at any timing, a hydraulic circuit (path through which the hydraulic oil flows) that reduces energy consumption (pump output), thereby enabling the hydraulic actuator to operate more efficiently.

[0120] In addition, the control device (controller 30) may be configured to determine whether or not to switch the first hydraulic circuit (the first differential circuit in FIG. 6) to the second hydraulic circuit (the first differential circuit in FIG. 6) based on the first consumed energy (the pump output W) and the second consumed energy (the pump output Wc1) when the first hydraulic circuit (the normal circuit in FIG. 5) is selected.

[0121] With this configuration, the shovel 100 can determine whether or not to switch from the first hydraulic circuit to the second hydraulic circuit before switching from the first hydraulic circuit to the second hydraulic circuit. Therefore, the shovel 100 can prevent a non-optimal hydraulic circuit (path through which the hydraulic oil flows) from being erroneously selected. In addition, the shovel 100 can prevent unnecessary switching of the hydraulic circuit from being repeated multiple times in a short period of time.

[0122] In addition, the control device (controller 30) may be configured to determine whether or not to switch the second hydraulic circuit (the first differential circuit in FIG. 6) to the first hydraulic circuit (the normal circuit in FIG. 5) based on the first consumed energy (pump output W) and the second consumed energy (pump output Wc1) when the second hydraulic circuit (the first differential circuit in FIG. 6) is selected.

[0123] With this configuration, the excavator 100 can switch from the second hydraulic circuit to the first hydraulic circuit as necessary, even after switching from the first hydraulic circuit to the second hydraulic circuit. Therefore, when the second energy consumption (pump output Wc1) when the second hydraulic circuit is employed exceeds the first energy consumption (pump output Wc) when the first hydraulic circuit is employed, the excavator 100 can quickly switch from the second hydraulic circuit to the first hydraulic circuit. Therefore, the excavator 100 can avoid a situation in which the output loss LS becomes large due to the selection of the second hydraulic circuit.

[0124] 5, the excavator 100 may include pressure sensors (pressure sensor S5B and pressure sensor S4B) for detecting the pressure of the hydraulic oil in each of the first hydraulic actuator (arm cylinder 8) and the second hydraulic actuator (boom cylinder 7), and a discharge pressure sensor (pressure sensor S7A) for detecting the pump discharge pressure of the hydraulic pump (first hydraulic pump 14A). In this case, the control device (controller 30) may be configured to calculate the flow rate (first cylinder inflow amount Q1) of the hydraulic oil flowing into the first hydraulic actuator (arm cylinder 8), the flow rate (second cylinder inflow amount Q2) of the hydraulic oil flowing into the second hydraulic actuator (boom cylinder 7), the first energy consumption (pump output W) when the first hydraulic circuit (normal circuit in FIG. 5) is selected, and the second energy consumption (pump output Wc1) when the second hydraulic circuit (first differential circuit in FIG. 6) is selected, based on the output of the pressure sensor and the output of the discharge pressure sensor.

[0125] Specifically, the control device (controller 30) may measure the first cylinder inflow amount Q1 based on the opening area of ​​the PC port of the hydraulic control valve HV5 and the differential pressure before and after the hydraulic control valve HV5. In this case, the opening area of ​​the PC port of the hydraulic control valve HV5 may be derived based on the output of the pilot pressure sensor, or may be derived based on the operation amount of the operating device 26 (left operation lever). In addition, the differential pressure before and after the hydraulic control valve HV5 may be calculated based on the output of the pressure sensor S5B (first cylinder pressure P1) and the output of the pressure sensor S7A (pump discharge pressure PS). Similarly, the control device (controller 30) may measure the second cylinder inflow amount Q2 based on the opening area of ​​the PC port of the hydraulic control valve HV3 and the differential pressure before and after the hydraulic control valve HV3. In this case, the opening area of ​​the PC port of the hydraulic control valve HV3 may be derived based on the output of the pilot pressure sensor, or may be derived based on the operation amount of the operating device 26 (right operation lever). Also, the pressure difference across the hydraulic control valve HV3 may be calculated based on the output of the pressure sensor S4B (the second cylinder pressure P2) and the output of the pressure sensor S7A (the pump discharge pressure PS).

[0126] With this configuration, the shovel 100 can calculate the first energy consumption (pump output W) and the second energy consumption (pump output Wc1) based on the outputs of the pressure sensor and the discharge pressure sensor that are attached as standard parts. The shovel 100 can also calculate the energy consumption (pump output Wc2) when the second differential circuit is selected in the same manner. Therefore, the shovel 100 can select an optimal hydraulic circuit by using the outputs of the pressure sensor and the discharge pressure sensor that are attached as standard parts, and can therefore operate the hydraulic actuator more efficiently. Furthermore, since the shovel 100 does not require special sensors or the like, it is possible to suppress an increase in the manufacturing cost of the shovel 100 that would be associated with the introduction of the above-mentioned configuration.

[0127] In addition, the second hydraulic circuit (first differential circuit in FIG. 6) may include a first differential circuit that merges a portion of the hydraulic oil flowing out from the first hydraulic actuator (arm cylinder 8) with the hydraulic oil discharged by the hydraulic pump (first hydraulic pump 14A), and a second differential circuit that merges a portion of the hydraulic oil flowing out from the second hydraulic actuator (boom cylinder 7) with the hydraulic oil discharged by the hydraulic pump (first hydraulic pump 14A).

[0128] With this configuration, the excavator 100 can improve the efficiency of the operation of the hydraulic actuator not only by merging the hydraulic oil flowing out of the arm cylinder 8 with the hydraulic oil discharged by the first hydraulic pump 14A, but also by merging the hydraulic oil flowing out of the boom cylinder 7 with the hydraulic oil discharged by the first hydraulic pump 14A.

[0129] The preferred embodiments of the present invention have been described above in detail. However, the present invention is not limited to the above-described embodiments, nor to the embodiments described below. Various modifications or substitutions may be applied to the above-described or following embodiments without departing from the scope of the present invention. Furthermore, features described separately may be combined unless technical contradictions arise. [Explanation of symbols]

[0130] 1···Lower traveling body 1M···Left traveling hydraulic motor 2···Slewing mechanism 2M···Right traveling hydraulic motor 3···Upper rotating body 3M···Slewing hydraulic motor 4···Boom 5···Arm 6···Bucket 7···Boom cylinder 7P1···First port 7P2···Second port 7S···Piston 8···Arm cylinder 8P1···First port 8P2···Second port 8S···Piston 9···Bucket cylinder 10···Cabin 11··Engine 13···Regulator 13A···First regulator 13B···Second regulator 14···Hydraulic pump 14A···First hydraulic pump 14B···Second hydraulic pump 15···Pilot pump 26···Operating device 30···Controller 100···Excavator EV··Solenoid valve F1···Flow rate command generation section F2···Boom required flow rate derivation section F3···Arm required flow rate derivation section F4···Bucket required flow rate derivation section F5, F7···MI valve opening area calculation section F6, F8···MO valve opening area calculation section F9···Maximum MI pressure selection section F10···Pump discharge rate control section HV, HV1~HV20··Hydraulic control valve PL··Left pilot port PR··Right pilot port S1L, S1R, S2L, S2R, S3L, S3R, S4B, S4R, S5B, S5R, S6B, S6R, S7A, S7B··Pressure sensor T··Hydraulic oil tank

Claims

1. A hydraulic oil tank; A first hydraulic actuator; A second hydraulic actuator; a hydraulic pump capable of supplying hydraulic oil in the hydraulic oil tank to each of the first hydraulic actuator and the second hydraulic actuator; a meter-in valve corresponding to each of the first hydraulic actuator and the second hydraulic actuator; a meter-out valve corresponding to each of the first hydraulic actuator and the second hydraulic actuator; A control device that controls each of the meter-in valve, the meter-out valve, and the hydraulic pump, The control device is configured to be able to switch between a first hydraulic circuit that returns hydraulic oil flowing out from each of the first hydraulic actuator and the second hydraulic actuator to the hydraulic oil tank, and a second hydraulic circuit that merges a portion of the hydraulic oil flowing out from at least one of the first hydraulic actuator and the second hydraulic actuator with the hydraulic oil discharged by the hydraulic pump. Shovel.

2. The control device is configured to calculate a first consumed energy when the first hydraulic circuit is selected and a second consumed energy when the second hydraulic circuit is selected, and to select the first hydraulic circuit or the second hydraulic circuit based on the first consumed energy and the second consumed energy. The shovel according to claim 1.

3. the control device, when the first hydraulic circuit is selected, determines whether or not to switch the first hydraulic circuit to the second hydraulic circuit based on the first consumed energy and the second consumed energy. The shovel according to claim 2.

4. the control device, when the second hydraulic circuit is selected, determines whether or not to switch the second hydraulic circuit to the first hydraulic circuit based on the first consumed energy and the second consumed energy. The shovel according to claim 2.

5. a pressure sensor that detects a pressure of hydraulic oil in each of the first hydraulic actuator and the second hydraulic actuator; a discharge pressure sensor for detecting a pump discharge pressure of the hydraulic pump, the control device calculates a flow rate of hydraulic oil flowing into the first hydraulic actuator, a flow rate of hydraulic oil flowing into the second hydraulic actuator, the first consumed energy, and the second consumed energy based on an output of the pressure sensor and an output of the discharge pressure sensor. The shovel according to claim 2.

6. The second hydraulic circuit includes a first differential circuit that merges a portion of the hydraulic oil flowing out from the first hydraulic actuator with the hydraulic oil discharged by the hydraulic pump, and a second differential circuit that merges a portion of the hydraulic oil flowing out from the second hydraulic actuator with the hydraulic oil discharged by the hydraulic pump. A shovel according to any one of claims 1 to 5.

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