Hydraulic circuits for construction machinery

Abstract

To provide a hydraulic circuit of a construction machine in which a low-capacity relief valve can be used in a work tool circuit.SOLUTION: A hydraulic circuit 2 of a construction machine comprises a variable capacity type hydraulic pump 4, a work tool 6 to be operated by hydraulic oil discharged by the hydraulic pump 4, a work tool operation device 10 for outputting a signal for operating the work tool 6, a control valve 14 for allowing supply of the hydraulic oil from the hydraulic pump 4 to the work tool 6 on the basis of the signal outputted by the work tool operation device 10, a tool relief valve 44 for releasing the hydraulic oil flowing between the control valve 14 and the work tool 6, a pressure sensor 46 for detecting a pressure of the hydraulic oil flowing into the work tool 6, and a controller 48 for reducing a discharge rate of the hydraulic pump 4 when the pressure detected by the pressure sensor 46 exceeds a predetermined value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hydraulic circuit for a construction machine to which various work tools are detachably attached. [Background technology]

[0002] A hydraulic excavator, a typical example of construction machinery, comprises a lower traveling body, an upper rotating body rotatably supported on the lower traveling body, and a front working implement attached to the upper rotating body. The front working implement of the hydraulic excavator includes a boom swingably connected to the upper rotating body, an arm swingably connected to the tip of the boom, and a work tool detachably attached to the tip of the arm.

[0003] Many hydraulic excavators are equipped with a bucket for excavation work as a work tool, but various other work tools can be attached besides the bucket. Examples of work tools other than the bucket include a hydraulic hammer for breaking concrete, rocks, etc., and a grapple for gripping wood, etc. (See, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-168738 Summary of the Invention [Problem to be solved by the invention]

[0005] Some work tools (e.g., grapples) are used by releasing hydraulic fluid from the circuit that operates the work tool (work tool circuit) through a relief valve. When using such a work tool, a large-capacity relief valve that can release the entire pump discharge volume during relief must be installed in the work tool circuit. However, large-capacity relief valves are expensive, which contributes to the increased cost of the work tool circuit.

[0006] Furthermore, some work tools require a relief pressure that is set lower than the relief pressure of the entire circuit of the hydraulic excavator. When such a work tool is used together with an actuator other than the work tool, the pressure in the entire circuit only rises to the relief pressure of the work tool, which can cause a problem of degraded operability of the other actuator.

[0007] In view of the above, a first object of the present invention is to provide a hydraulic circuit for a construction machine that enables the use of a low-capacity relief valve in the work tool circuit. A second object of the present invention is to provide a hydraulic circuit that is easy to operate when simultaneously operating a work tool and another actuator. [Means for solving the problem]

[0008] According to a first aspect of the present invention, there is provided the following hydraulic circuit for a construction machine that solves the first problem described above. "A hydraulic circuit of a construction machine, A variable displacement hydraulic pump; a work tool operated by the hydraulic fluid discharged by the hydraulic pump; and a work tool operating device that outputs a signal to operate the work tool; a control valve that allows hydraulic oil to be supplied from the hydraulic pump to the work tool based on a signal output from the work tool operating device; a tool relief valve that releases hydraulic fluid flowing between the control valve and the work tool; a pressure sensor for detecting a pressure of hydraulic oil flowing into the work tool; a controller that reduces the discharge amount of the hydraulic pump when the pressure detected by the pressure sensor exceeds a predetermined value. 、 The control valve includes a meter-in valve that controls the amount of hydraulic oil flowing into the work tool, and a meter-out valve that controls the amount of hydraulic oil flowing out of the work tool. A hydraulic circuit for a construction machine is provided.

[0009] Preferably, the predetermined value is set to be equal to or lower than the relief pressure of the tool relief valve. 。

[0010] Furthermore, according to a second aspect of the present invention, there is provided the following hydraulic circuit for a construction machine that solves the second problem described above. "A hydraulic circuit of a construction machine, A hydraulic pump; a work tool and an actuator, both of which are actuated by hydraulic fluid discharged by the hydraulic pump; a work tool operating device that outputs a signal to operate the work tool; an actuator operating device that outputs a signal to operate the actuator; a control valve that allows hydraulic oil to be supplied from the hydraulic pump to the work tool and the actuator based on signals output from the work tool operating device and the actuator operating device; a main relief valve disposed upstream of the control valve for releasing hydraulic oil discharged by the hydraulic pump; a tool relief valve that releases hydraulic fluid flowing between the control valve and the work tool; a controller for controlling the operation of the control valve; the control valve includes a meter-in valve that controls the amount of hydraulic oil flowing into the work tool, and a meter-out valve that controls the amount of hydraulic oil flowing out of the work tool; When signals are output from both the work tool operation device and the actuator operation device, the controller reduces the opening area of ​​the meter-in valve to make the pressure downstream of the meter-in valve lower than the pressure upstream of the meter-in valve.

[0011] Desirably, when signals are output from both the work tool operation device and the actuator operation device, the controller reduces the opening area of ​​the meter-in valve to make the pressure downstream of the meter-in valve lower than the pressure upstream of the meter-in valve so that the pressure downstream of the meter-in valve does not reach the relief pressure of the tool relief valve before the pressure upstream of the meter-in valve reaches the relief pressure of the main relief valve.

[0012] Advantageously, the hydraulic pump is of a variable displacement type and includes a pressure sensor that detects the pressure of hydraulic fluid flowing into the work tool, and the controller reduces the discharge rate of the hydraulic pump when the pressure detected by the pressure sensor exceeds a predetermined value.

[0013] Preferably, both the first and second aspects of the present invention include a first conduit and a second conduit connecting the control valve and the work tool, a first relief conduit branching from the first conduit and extending to a hydraulic fluid tank, and a second relief conduit branching from the second conduit and extending to the hydraulic fluid tank, and the tool relief valve is provided in each of the first relief conduit and the second relief conduit. Alternatively, both may include a first conduit and a second conduit connecting the control valve and the work tool, a connecting conduit connecting the first conduit and the second conduit, a shuttle valve disposed in the connecting conduit, and a relief conduit extending from an outlet of the shuttle valve to the hydraulic fluid tank, and the tool relief valve is provided in the relief conduit.

[0014] Preferably, the tool relief valve is an electromagnetic proportional relief valve. [Effects of the Invention]

[0015] According to the first aspect of the present invention, when the pressure of the hydraulic oil flowing into the work tool exceeds a predetermined value, the discharge rate of the hydraulic pump is reduced, thereby suppressing the amount of hydraulic oil passing through the tool relief valve and enabling the tool relief valve to have a low capacity.

[0016] According to the second aspect of the present invention, when signals are output from both the work tool operating device and the actuator operating device, the opening area of ​​the meter-in valve is reduced to make the pressure downstream of the meter-in valve lower than the pressure upstream of the meter-in valve. Therefore, even if the relief pressure of the tool relief valve is set to a value lower than the relief pressure of the main relief valve, the pressure of the hydraulic oil flowing into the actuator can be increased to equal to or higher than the relief pressure of the tool relief valve, resulting in good operability when operating the work tool and actuator simultaneously.

[0017] In addition, the present invention No. 1 According to the second aspect, the work tool is provided with a meter-in valve that controls the amount of hydraulic oil flowing into the work tool, and a meter-out valve that controls the amount of hydraulic oil flowing out of the work tool. Therefore, the opening of the meter-out valve can be reduced in conjunction with the reduction in the opening of the meter-in valve. of There is no need to make the work tool smaller, and an increase in back pressure in the work tool circuit can be suppressed. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a circuit diagram showing a hydraulic circuit of a construction machine configured according to the present invention. [Figure 2] FIG. 2 is a circuit diagram showing a first modified example of the hydraulic circuit shown in FIG. [Figure 3] FIG. 2 is a circuit diagram showing a second modified example of the hydraulic circuit shown in FIG. [Figure 4] FIG. 2 is a circuit diagram showing a third modified example of the hydraulic circuit shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0019] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a hydraulic circuit for a construction machine configured according to the present invention will now be described with reference to the drawings.

[0020] (Hydraulic circuit 2) As shown in FIG. 1, hydraulic circuit 2 that can be mounted on construction machinery such as a hydraulic excavator includes variable displacement hydraulic pump 4, work tool 6 and actuator 8, both of which are operated by hydraulic oil (discharge oil) discharged by hydraulic pump 4, work tool operating device 10 that outputs a signal to operate work tool 6, actuator operating device 12 that outputs a signal to operate actuator 8, control valve 14 that allows the supply of hydraulic oil from hydraulic pump 4 to work tool 6 and actuator 8 based on the signals output by work tool operating device 10 and actuator operating device 12, and first and second pipelines 16 and 18 that both connect control valve 14 to work tool 6.

[0021] (Hydraulic pump 4) Hydraulic pump 4 is driven by engine 20, and draws hydraulic oil from hydraulic oil tank 22 and discharges it to pump line 24. As shown in FIG. 1, pump line 24 is a line that connects hydraulic pump 4 and control valve 14. As described above, hydraulic pump 4 supplies hydraulic oil to work tool 6 and actuator 8, but a separate pilot pump may also be provided.

[0022] (Work Tool 6) The work tool 6 detachably attached to the hydraulic circuit 2 is either a single-action work tool 6a (see FIG. 1) or a double-action work tool 6b (see FIG. 2). The single-action work tool 6a shown in FIG. 1 uses either the first conduit 16 or the second conduit 18 only as an inlet line, and uses the other of the first conduit 16 or the second conduit 18 only as an outlet line. An example of the single-action work tool 6a is a hydraulic hammer for breaking concrete, rocks, etc.

[0023] 2 alternately uses the first conduit 16 and the second conduit 18 as an inlet line and alternately uses the first conduit 16 and the second conduit 18 as an outlet line. An example of the double-action work tool 6b is a grapple for gripping wood or the like. The actuator of the double-action work tool 6b may be either a hydraulic cylinder or a hydraulic motor.

[0024] (Actuator 8) 1 and 2 are shown as hydraulic cylinders, but are not limited to hydraulic cylinders and may be hydraulic motors. Also, in the illustrated embodiment, only one actuator 8 is shown, but two or more actuators 8 may be provided. For example, if the hydraulic circuit 2 is for a hydraulic excavator, such actuators 8 may include a boom cylinder that swings the boom, an arm cylinder that swings the arm, a travel motor that travels the hydraulic excavator, a swing motor that swings the upper swing body, etc.

[0025] (Work tool operating device 10, actuator operating device 12) The work tool operating device 10 and the actuator operating device 12 may be configured to have input devices (e.g., joysticks, slide switches, pedals, etc.) that output signals with increasing strength as the amount of operation increases. Although only one actuator operating device 12 is shown in the illustrated embodiment, two or more actuator operating devices 12 may be provided.

[0026] When operated by an operator, work tool operating device 10 outputs an electrical signal or hydraulic signal for operating work tool 6. Similarly, when operated by an operator, actuator operating device 12 outputs an electrical signal or hydraulic signal for operating actuator 8. FIG. 1 shows how work tool operating device 10 and actuator operating device 12 output electrical signals. The electrical signals output by work tool operating device 10 and actuator operating device 12 are sent to control valve 14 via controller 48, which will be described later.

[0027] Unlike the illustrated embodiment, the work tool operating device 10 and the actuator operating device 12 may output hydraulic pressure signals to the control valve 14. In this case, the hydraulic pressure signals output from the work tool operating device 10 and the actuator operating device 12 are detected by a pressure sensor (not shown), and the detection results of the pressure sensor are input to the controller 48.

[0028] (Control valve 14) Control valve 14 in the illustrated embodiment includes a meter-in valve 26 that controls the amount of hydraulic oil flowing into work tool 6, a meter-out valve 28 that controls the amount of hydraulic oil flowing out of work tool 6, an actuator valve 30 that controls the amount of hydraulic oil flowing into actuator 8 and the amount of hydraulic oil flowing out of actuator 8, a first check valve 32 installed upstream of meter-in valve 26, and a second check valve 34 installed upstream of actuator valve 30.

[0029] The meter-in valve 26 and the meter-out valve 28 in the illustrated embodiment are electromagnetic proportional valves whose opening areas are controlled by the controller 48 based on an electrical signal output from the work tool operation device 10 to the controller 48, but they may also be hydraulic pilot valves that are actuated by a hydraulic signal output from the work tool operation device 10.

[0030] 1, meter-in valve 26 is a two-port selector valve and is installed in pump line 24. When work tool operating device 10 outputs a signal, controller 48 opens meter-in valve 26.

[0031] Meter-out valve 28 is a four-port selector valve and is provided between meter-in valve 26 and work tool 6. Meter-out valve 28 connects pump line 24 to either first or second line 16, 18, and connects the other of first or second line 16, 18 to first return line 36, which leads from meter-out valve 28 to hydraulic oil tank 22.

[0032] The actuator valve 30 in the illustrated embodiment is an electromagnetic proportional type in which the opening area is controlled by the controller 48 based on an electrical signal output from the actuator operating device 12 to the controller 48, similar to the meter-in valve 26, etc., but it may also be a hydraulic pilot type valve that is operated by a hydraulic signal output from the actuator operating device 12.

[0033] The actuator valve 30 is a four-port selector valve and is disposed in the pump line 24. In response to a signal output from the actuator operating device 12, the actuator valve 30 connects the pump line 24 to one of the third and fourth lines 38, 40, and also connects the other of the third and fourth lines 38, 40 to a second return line 42.

[0034] The third and fourth pipelines 38 and 40 are both pipelines that connect the actuator valve 30 and the actuator 8 , and the second return pipeline 42 leads from the actuator valve 30 to the hydraulic oil tank 22 .

[0035] As shown in FIG. 1 , the hydraulic circuit 2 of the illustrated embodiment further includes a tool relief valve 44 that releases hydraulic oil flowing between the control valve 14 and the work tool 6, a pressure sensor 46 that detects the pressure of hydraulic oil flowing into the work tool 6, a controller 48, a first relief line 50 that branches off from the first line 16 and extends to the hydraulic oil tank 22, and a second relief line 52 that branches off from the second line 18 and extends to the hydraulic oil tank 22.

[0036] (Tool Relief Valve 44) In the illustrated embodiment, the first and second relief lines 50, 52 are each provided with a tool relief valve 44. The tool relief valve 44 is configured to release the hydraulic oil flowing through the first and second relief lines 50, 52 to the hydraulic oil tank 22 when the pressure of the hydraulic oil in the first and second relief lines 50, 52 exceeds the relief pressure.

[0037] The relief pressure of the tool relief valve 44 is set in advance to a required value (initial value), but if the tool relief valve 44 is an electromagnetic proportional type, the initial value can be changed as appropriate by the controller 48 based on the type of work tool 6 input into the controller 48 by the operator.

[0038] Furthermore, if the tool relief valve 44 is an electromagnetic proportional type, the relief pressure of the tool relief valve 44 can be changed by the controller 48 not only when the type of work tool 6 is input, but also when a required signal is output from the work tool operating device 10.

[0039] For example, when a signal is output from work tool operating device 10, the relief pressure of tool relief valve 44 provided on the outlet side of work tool 6 can be reduced. This causes return oil from work tool 6 to be divided into a route that passes through meter-out valve 28 and a route that passes through tool relief valve 44 on the outlet side, thereby suppressing a rise in back pressure in the work tool circuit. Note that there is no need to change the relief pressure of tool relief valve 44 on the inlet side of work tool 6, as this does not affect the suppression of back pressure rise.

[0040] (Pressure Sensor 46) Pressure sensor 46 is attached to meter-out valve 28 and detects the pressure of hydraulic oil flowing from meter-out valve 28 toward work tool 6, regardless of whether first or second pipeline 16, 18 is the inlet path. The result detected by pressure sensor 46 is sent to controller 48.

[0041] (Controller 48) Controller 48 is composed of a computer having a processing unit and a storage unit. Controller 48 controls the operation of control valve 14 and the discharge rate of hydraulic pump 4 based on signals output from work tool operating device 10 and actuator operating device 12.

[0042] 1, the first and second pipelines 16, 18 are also connected to the hydraulic oil tank 22 by a makeup pipeline 54. A pair of makeup check valves 56 are disposed in the makeup pipeline 54 to prevent cavitation from occurring in the first and second pipelines 16, 18 when negative pressure occurs in the pipelines 16, 18.

[0043] The hydraulic circuit 2 in the illustrated embodiment includes a pressure sensor 58 that detects the pressure of the hydraulic oil in the pump line 24, a bypass line 60 that branches off from the pump line 24 and extends to the hydraulic oil tank 22, an electromagnetic proportional bypass valve 62 that controls the amount of hydraulic oil that passes through the bypass line 60 and returns to the hydraulic oil tank 22, and a main relief valve 64 that is located upstream of the control valve 14 and releases the hydraulic oil discharged by the hydraulic pump 4.

[0044] The main relief valve 64 is configured to release the hydraulic oil flowing through the pump line 24 to the hydraulic oil tank 22 when the pressure of the hydraulic oil in the pump line 24 exceeds the relief pressure. In general, the relief pressure of the main relief valve 64 is set to a value higher than the relief pressure of the tool relief valve 44.

[0045] 1, the first and second return lines 36, 42, the first and second relief lines 50, 52, and the makeup line 54, all of which are connected to the hydraulic oil tank 22, converge before the hydraulic oil tank 22. The hydraulic oil returning to the hydraulic oil tank 22 returns to the hydraulic oil tank 22 through either a cooled line 68 that passes through an oil cooler 66, or a non-cooled line 70 that does not pass through the oil cooler 66.

[0046] Next, the operation of the hydraulic circuit 2 of the construction machine as described above will be explained.

[0047] When the work tool operating device 10 and the actuator operating device 12 are not being operated, no signals are output from the work tool operating device 10 and the actuator operating device 12. In this case, the meter-in valve 26, the meter-out valve 28, and the actuator valve 30 are closed, the oil discharged from the hydraulic pump 4 does not flow into the work tool 6 and the actuator 8, and the work tool 6, etc. do not operate.

[0048] Furthermore, when the work tool operating device 10, etc. is not being operated, the controller 48 opens the bypass valve 62. This causes the oil discharged from the hydraulic pump 4 to return to the hydraulic oil tank 22 through the bypass line 60.

[0049] (Work Tool 6 Operation) When work tool operating device 10 is operated, a signal is output from work tool operating device 10. In response, controller 48 actuates meter-in valve 26 and meter-out valve 28 to open the oil passage leading from hydraulic pump 4 to work tool 6 and reduces the opening area of ​​bypass valve 62. As a result, oil discharged from hydraulic pump 4 is supplied to work tool 6, causing work tool 6 to operate.

[0050] When the amount of operation applied to the work tool operation device 10 increases, the strength of the signal output from the work tool operation device 10 also increases in accordance with the increase in the amount of operation. Then, as the strength of the signal from the work tool operation device 10 increases, the controller 48 increases the discharge rate of the hydraulic pump 4, increases the opening area of ​​the meter-in valve 26 and the meter-out valve 28, and decreases the opening area of ​​the bypass valve 62. Therefore, the operating speed of the work tool 6 increases in accordance with the increase in the amount of operation of the work tool operation device 10.

[0051] However, when the pressure detected by the pressure sensor 46 (the pressure of the hydraulic oil flowing from the meter-out valve 28 to the work tool 6) exceeds a predetermined value, the controller 48 reduces the discharge volume of the hydraulic pump 4 compared to when the pressure detected by the pressure sensor 46 is equal to or less than the predetermined value, even if the operation amount of the work tool operating device 10 has not changed.

[0052] As a result, when the pressure of the hydraulic oil in the inlet path (first pipeline 16 or second pipeline 18) to the work tool 6 exceeds a predetermined value, the amount of hydraulic oil passing through the tool relief valve 44 on the inlet path side of the work tool 6 can be reduced, allowing the tool relief valve 44 to have a low capacity. Furthermore, because the amount of hydraulic oil passing through the tool relief valve 44 is reduced, energy loss during relief is reduced.

[0053] It is preferable that the discharge rate of the hydraulic pump 4 after the discharge rate has been reduced be equal to or less than the capacity (passable flow rate) of the tool relief valve 44, and that all of the hydraulic oil discharged from the hydraulic pump 4 after the discharge rate has been reduced be able to pass through the tool relief valve 44.

[0054] The predetermined value for starting the discharge rate reduction control of the hydraulic pump 4 can be set to any value equal to or less than the relief pressure (initial value) of the tool relief valve 44. However, from the viewpoint of minimizing the effect on the operation of the work tool 6, it is preferable that the predetermined value be as large as possible.

[0055] When the relief pressure of the tool relief valve 44 is changed from the initial value by the controller 48 based on the type of work tool 6, the predetermined value can also be changed in accordance with the change in the relief pressure.

[0056] However, if the relief pressure of tool relief valve 44 provided on the outlet path side of work tool 6 is reduced during operation of work tool 6 to suppress an increase in back pressure in the work tool circuit, it is not necessary to change the predetermined value in accordance with the reduction in relief pressure. This is because the predetermined value is a value for suppressing the amount of hydraulic oil passing through tool relief valve 44 on the inlet path side of work tool 6, and is not closely related to the relief pressure of tool relief valve 44 on the outlet path side of work tool 6.

[0057] The above-mentioned control by the controller 48 (control to reduce the discharge rate of the hydraulic pump 4 when the pressure detected by the pressure sensor 46 exceeds a predetermined value) is executed in either case where a signal is output from only the work tool operation device 10, or where signals are output from both the work tool operation device 10 and the actuator operation device 12.

[0058] (Work Tool 6 and Actuator 8 Operation) When the work tool operating device 10 and the actuator operating device 12 are operated, signals are output from both the work tool operating device 10 and the actuator operating device 12. In response, the controller 48 actuates the meter-in valve 26, the meter-out valve 28, and the actuator valve 30 to open the oil passages leading from the hydraulic pump 4 to the work tool 6 and the actuator 8, and also reduces the opening area of ​​the bypass valve 62. As a result, oil discharged from the hydraulic pump 4 is supplied to the work tool 6 and the actuator 8, causing the work tool 6 and the actuator 8 to operate.

[0059] As described above, as the strength of the signal output from the work tool operation device 10 increases, the opening area of ​​the meter-in valve 26 is increased by the controller 48. However, when signals are output from both the work tool operation device 10 and the actuator operation device 12, the opening area of ​​the meter-in valve 26 is controlled by the controller 48 to be smaller than when a signal is output from only the work tool operation device 10.

[0060] That is, when comparing (1) a case where a signal is output only from the work tool operating device 10 and (2) a case where a signal is output from both the work tool operating device 10 and the actuator operating device 12, even if the strength of the signal output from the work tool operating device 10 is the same in cases (1) and (2), the controller 48 controls so that the opening area of ​​the meter-in valve 26 in case (2) is smaller than the opening area of ​​the meter-in valve 26 in case (1).

[0061] More specifically, when signals are output from both the work tool operating device 10 and the actuator operating device 12, the controller 48 executes the following control. That is, the opening area of ​​the meter-in valve 26 is reduced so that the pressure downstream of the meter-in valve 26 (the pressure of the hydraulic oil flowing into the work tool 6) does not reach the relief pressure of the tool relief valve 44 before the pressure upstream of the meter-in valve 26 (the pressure of the hydraulic oil flowing into the actuator 8) reaches the relief pressure of the main relief valve 64, and control is executed to make the pressure downstream of the meter-in valve 26 lower than the pressure upstream of the meter-in valve 26.

[0062] As a result, even if the relief pressure of the tool relief valve 44 is set to a value lower than the relief pressure of the main relief valve 64, the pressure of the hydraulic oil flowing into the actuator 8 can be increased to a value equal to or higher than the relief pressure of the tool relief valve 44 (to the relief pressure of the main relief valve 64 in the illustrated embodiment). Therefore, operability is improved when operating the work tool 6 and the actuator 8 simultaneously.

[0063] Furthermore, the illustrated embodiment is equipped with meter-in valve 26 that controls the amount of hydraulic oil flowing into work tool 6, and meter-out valve 28 that controls the amount of hydraulic oil flowing out of work tool 6. Therefore, when the opening of meter-in valve 26 is reduced, there is no need to reduce the opening of meter-out valve 28, and an increase in back pressure in the work tool circuit can be suppressed.

[0064] The present invention is not limited to the above-described embodiment and various modifications are possible. For example, in the above-described embodiment, an example in which two tool relief valves 44 are provided has been described, but the number of tool relief valves 44 may be one.

[0065] 2, a hydraulic circuit generally designated by reference numeral 72 includes a connecting pipe 74 connecting the first pipe 16 and the second pipe 18, a shuttle valve 76 disposed in the connecting pipe 74, and a relief pipe 78 extending from the outlet of the shuttle valve 76 to the hydraulic oil tank 22. One tool relief valve 44 is provided in the relief pipe 78. In the example shown in FIG. 2, since there is one tool relief valve 44, costs can be kept lower than when two tool relief valves 44 are provided (the embodiment shown in FIG. 1).

[0066] Another modified example is one in which two hydraulic pumps 4 are provided, as shown in Fig. 3. In the hydraulic circuit 80 shown in Fig. 3, in addition to the two hydraulic pumps 4 (4a, 4b), two pump lines 24 (24a, 24b), meter-in valves 26 (26a, 26b), actuators 8 (8a, 8b), actuator valves 30 (30a, 30b), bypass valves 62 (62a, 62b), etc. are also provided.

[0067] 3 is provided with a connecting line 82 that connects one pump line 24a and the other pump line 24b, a shuttle valve 84 disposed in the connecting line 82, and a main relief line 86 that extends from the outlet of the shuttle valve 84 to the hydraulic oil tank 22. The main relief valve 64 is disposed in the main relief line 86.

[0068] In FIG. 3, the work tool operating device 10, the actuator operating device 12, and the controller 48 are omitted from the view point of avoiding complexity.

[0069] When two hydraulic pumps 4a, 4b are provided as shown in FIG. 3, hydraulic oil can be supplied to the work tool 6 only from one hydraulic pump 4a, or only from the other hydraulic pump 4b, or hydraulic oil can be supplied to the work tool 6 from both hydraulic pumps 4a, 4b.

[0070] For example, when the same amount of hydraulic oil is supplied to the work tool 6 from both hydraulic pumps 4a, 4b, as the strength of the signal output from the work tool operating device 10 increases, the opening area of ​​each bypass valve 62a, 62b gradually decreases, and the opening area of ​​each meter-in valve 26a, 26b gradually increases.

[0071] When the pressure detected by the pressure sensor 46 exceeds a predetermined value set to be equal to or lower than the relief pressure of the tool relief valve 44, the discharge rate of each of the hydraulic pumps 4a, 4b is reduced.

[0072] Furthermore, in the example shown in FIG. 3, when signals are output from both the work tool operation device 10 and the actuator operation device 12, control is executed to reduce the opening areas of the meter-in valves 26a, 26b and make the pressure downstream of the meter-in valves 26a, 26b lower than the pressure upstream of the meter-in valves 26a, 26b so that the pressure downstream of the meter-in valves 26a, 26b does not reach the relief pressure of the tool relief valve 44 before the pressure upstream of the meter-in valves 26a, 26b reaches the relief pressure of the main relief valve 64.

[0073] When hydraulic oil is supplied to work tool 6 from only one hydraulic pump 4a, the opening area of ​​one meter-in valve 26a is controlled in accordance with the operation of work tool operating device 10, and the other meter-in valve 26b is maintained in a closed state.

[0074] Conversely, when hydraulic oil is supplied to the work tool 6 only from the other hydraulic pump 4b, the opening area of ​​the other meter-in valve 26b is controlled in accordance with the operation of the work tool operating device 10, and the one meter-in valve 26a is maintained in a closed state.

[0075] Furthermore, in addition to the example shown in FIG. 3, when two hydraulic pumps 4 (4a, 4b) are provided as in a hydraulic circuit 90 shown in FIG. 4, the number of tool relief valves 44 may be one. [Explanation of symbols]

[0076] 2: Hydraulic circuit 4: Hydraulic pump 6: Work tools 8: Actuator 10: Work tool operating device 12: Actuator operating device 14: Control valve 16: First pipeline 18: Second pipeline 22: Hydraulic oil tank 26: Meter-in valve 28: Meter-out valve 44: Tool relief valve 46: Pressure sensor 48: Controller 50: First relief pipe 52: Second relief line 64: Main relief valve 74: Connecting pipe 76: Shuttle valve 78: Relief pipeline

Claims

1. A hydraulic circuit of a construction machine, A variable displacement hydraulic pump; a work tool operated by the hydraulic fluid discharged by the hydraulic pump; and a work tool operating device that outputs a signal to operate the work tool; a control valve that allows hydraulic oil to be supplied from the hydraulic pump to the work tool based on a signal output from the work tool operating device; a tool relief valve that releases hydraulic fluid flowing between the control valve and the work tool; a pressure sensor for detecting a pressure of hydraulic oil flowing into the work tool; a controller that reduces the discharge amount of the hydraulic pump when the pressure detected by the pressure sensor exceeds a predetermined value; The control valve is a hydraulic circuit for a construction machine that includes a meter-in valve that controls the amount of hydraulic oil flowing into the work tool, and a meter-out valve that controls the amount of hydraulic oil flowing out of the work tool.

2. 2. The hydraulic circuit for a construction machine according to claim 1, wherein the predetermined value is set to a value equal to or lower than the relief pressure of the tool relief valve.

3. A hydraulic circuit of a construction machine, A hydraulic pump; a work tool and an actuator, both of which are actuated by hydraulic fluid discharged by the hydraulic pump; a work tool operating device that outputs a signal to operate the work tool; an actuator operating device that outputs a signal to operate the actuator; a control valve that allows hydraulic oil to be supplied from the hydraulic pump to the work tool and the actuator based on signals output from the work tool operating device and the actuator operating device; a main relief valve disposed upstream of the control valve for releasing hydraulic oil discharged by the hydraulic pump; a tool relief valve that releases hydraulic fluid flowing between the control valve and the work tool; a controller for controlling the operation of the control valve; the control valve includes a meter-in valve that controls the amount of hydraulic oil flowing into the work tool, and a meter-out valve that controls the amount of hydraulic oil flowing out of the work tool; When signals are output from both the work tool operation device and the actuator operation device, the controller reduces the opening area of ​​the meter-in valve to make the pressure downstream of the meter-in valve lower than the pressure upstream of the meter-in valve.

4. 4. The hydraulic circuit for a construction machine according to claim 3, wherein, when signals are output from both the work tool operation device and the actuator operation device, the controller reduces the opening area of ​​the meter-in valve to make the pressure downstream of the meter-in valve lower than the pressure upstream of the meter-in valve so that the pressure downstream of the meter-in valve does not reach the relief pressure of the tool relief valve before the pressure upstream of the meter-in valve reaches the relief pressure of the main relief valve.

5. the hydraulic pump is a variable displacement type; a pressure sensor for detecting a pressure of hydraulic fluid flowing into the work tool; 5. The hydraulic circuit for a construction machine according to claim 3, wherein the controller reduces the discharge rate of the hydraulic pump when the pressure detected by the pressure sensor exceeds a predetermined value.

6. a first conduit and a second conduit, both connecting the control valve and the work tool; a first relief line branching from the first line and extending to a hydraulic oil tank; a second relief line branching from the second line and extending to the hydraulic oil tank; 6. The hydraulic circuit for a construction machine according to claim 1, wherein the tool relief valve is provided in each of the first relief line and the second relief line.

7. a first conduit and a second conduit, both connecting the control valve and the work tool; a connecting pipe that connects the first pipe and the second pipe; a shuttle valve disposed in the connecting pipeline; a relief line extending from the outlet of the shuttle valve to a hydraulic oil tank; 6. The hydraulic circuit for a construction machine according to claim 1, wherein the tool relief valve is provided in the relief pipe line.

8. 8. The hydraulic circuit for a construction machine according to claim 1, wherein the tool relief valve is an electromagnetic proportional relief valve.

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