Work machine

Abstract

The present application aims to enable a work implement to appropriately and efficiently perform work even if a hydraulic cylinder of the work implement becomes an overload state regardless of an operating condition of the work implement. A work machine is provided with: a boom cylinder and a stick cylinder; a hydraulic pump; a boom direction control valve and a stick direction control valve; and a first communication pipe that communicates a bottom-side oil chamber of the boom cylinder, which is an elongation-side oil chamber when the boom cylinder is elongated by a digging operation, and a bottom-side oil chamber of the stick cylinder, which is an elongation-side oil chamber when the stick cylinder is elongated by the digging operation.

Description

Technical Field

[0001] This invention relates to a work machine. Background Technology

[0002] Hydraulic excavators, as a representative example of construction machinery, have working devices with a multi-joint structure. Such working devices are configured to include, for example, a boom, a stick, and a bucket, as well as boom cylinders, stick cylinders, and bucket cylinders that drive them.

[0003] During excavation operations, the operator needs to perform the following operations as part of the excavation process: boom raising (rotating the boom upwards), stick retraction (rotating the stick in the retracting direction), and bucket retraction (rotating the bucket in the retracting direction). The primary operation in excavation is stick retraction, while boom raising and bucket retraction are secondary operations.

[0004] If the operator does not raise the boom during excavation, the digging resistance becomes excessive, and any one of the boom cylinder, stick cylinder, or bucket cylinder becomes overloaded. Sometimes, high-pressure working oil is discharged from the overload relief valve into the working oil tank, or the machine body floats up. As a result, the machine may sometimes be unable to operate properly and efficiently.

[0005] Patent Document 1 discloses the following technology: During a combined digging operation involving boom retraction or bucket retraction and boom raising, the pressure of the bottom oil chamber of the boom cylinder is controlled to prevent the pressure from exceeding the maximum allowable pressure due to digging resistance, thereby preventing the vehicle from floating. In the technology disclosed in Patent Document 1, when the operator's boom raising operation is small and the vehicle floats, the pilot pressure of the boom raising operation is controlled to be above the operator's operation amount, increasing the boom raising speed. In the technology disclosed in Patent Document 1, when the operator's boom retraction operation is large and the vehicle floats, the pilot pressure involved in the boom retraction operation is controlled to be below the operator's operation amount, slowing down the boom retraction speed. Thus, in the technology disclosed in Patent Document 1, vehicle float is prevented.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent No. 5969379 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] However, in the technology disclosed in Patent Document 1, the aforementioned control to prevent the vehicle body from floating is performed during combined excavation operations. That is, in the technology disclosed in Patent Document 1, the pilot pressure control involved in the boom raising operation is not performed when the operator does not perform the boom retraction operation, and the pilot pressure control involved in the stick retraction operation is not performed when the operator does not perform the stick retraction operation. Therefore, for example, if a hydraulic cylinder becomes overloaded during a separate stick retraction operation, it is impossible to prevent the discharge of high-pressure working oil from the overload relief valve and the vehicle body from floating.

[0011] Furthermore, in the technology disclosed in Patent Document 1, when controlling the pilot pressure involved in the boom lifting operation, a portion of the working oil discharged from the hydraulic pump is directed to the circuit involved in the boom lifting operation. Therefore, in a work machine equipped with a control valve device that forms a series circuit between the circuit involved in the stick retraction operation or the circuit involved in the bucket retraction operation and the circuit involved in the boom lifting operation, the stick retraction speed or the bucket retraction speed will be reduced.

[0012] In view of the above, the object of the present invention is that the working device can perform its work appropriately and efficiently, regardless of the operating condition of the working device, even if the hydraulic cylinder of the working device becomes overloaded.

[0013] Solution for solving the problem

[0014] To address the aforementioned issues, the work machinery of the present invention is characterized by comprising: a work device including: a boom rotatably connected to the vehicle body; a stick rotatably connected to the boom; a boom cylinder driving the boom; and a stick cylinder driving the stick; a hydraulic pump supplying working oil to the boom cylinder and the stick cylinder; and a control valve device including: a boom direction control valve disposed between the hydraulic pump and the boom cylinder, controlling the supply of hydraulic oil from the hydraulic pump to the boom cylinder. The flow direction of the working oil; and a boom direction control valve, which is disposed between the hydraulic pump and the boom cylinder, controls the flow direction of the working oil supplied from the hydraulic pump to the boom cylinder; and a first connecting pipe, which connects the bottom oil chamber of the boom cylinder to the bottom oil chamber of the boom cylinder, the bottom oil chamber of the boom cylinder being the extension side oil chamber when the boom cylinder extends by digging operation, and the bottom oil chamber of the boom cylinder being the extension side oil chamber when the boom cylinder extends by digging operation.

[0015] Invention Effects

[0016] According to the present invention, regardless of the operating condition of the working device, even if the hydraulic cylinder of the working device becomes overloaded, the working device can still perform the operation appropriately and efficiently. Attached Figure Description

[0017] Figure 1 This is a diagram showing the right-side view of the operating machinery.

[0018] Figure 2 This is a diagram showing the structure of the hydraulic drive circuit used in the working device.

[0019] Figure 3 This diagram illustrates the operation of the hydraulic drive circuit when the stick cylinder is overloaded during the individual stick retraction operation.

[0020] Figure 4 This diagram illustrates the operation of the hydraulic drive circuit when the bucket cylinder is overloaded during the individual operation of stick retraction.

[0021] Figure 5 This diagram illustrates the operation of the hydraulic drive circuit when the stick cylinder is in an overloaded state during combined stick and bucket operation.

[0022] Figure 6 This diagram illustrates the operation of the hydraulic drive circuit when the bucket cylinder is in an overloaded state during combined boom and bucket operation.

[0023] Figure 7 These are diagrams showing other examples of operating machinery. Detailed Implementation

[0024] Hereinafter, embodiments of the present invention will be described using the accompanying drawings. Unless otherwise specified, elements labeled with the same reference numerals in each embodiment are identical and their descriptions are omitted.

[0025] Figure 1 This is a diagram showing the right-side view of the operating machine 1.

[0026] The working machine 1 is a working machine such as a hydraulic excavator used for excavation operations. In this embodiment, a hydraulic excavator will be used as an example of the working machine 1.

[0027] Figure 1 The illustrated work machine 1 is a hydraulic excavator with an extra-large backhoe bucket 14. The work machine 1 comprises: a self-propelled tracked lower traveling body 2; an upper slewing body 3 rotatably mounted on top of the lower traveling body 2; and a working device 11 having a multi-jointed structure rotatably connected to the front of the upper slewing body 3. The lower traveling body 2 and the upper slewing body 3 constitute the body of the work machine 1.

[0028] The working device 11 is configured to include working machines 12-14 and hydraulic cylinders 15-17 that drive the working machines 12-14. The working machines 12-14 include: a boom 12 rotatably connected to the vehicle body; a stick 13 rotatably connected to the boom 12; and a bucket 14 rotatably connected to the stick 13. The hydraulic cylinders 15-17 include: a boom cylinder 15 that drives the boom 12; a stick cylinder 16 that drives the stick 13; and a bucket cylinder 17 that drives the bucket 14.

[0029] The base end of the boom 12 is connected to the slewing frame 5 of the upper slewing body 3, and rotates relative to the slewing frame 5 through the extension and retraction of the boom cylinder 15. The base end of the stick 13 is connected to the front end of the boom 12, and rotates relative to the boom 12 through the extension and retraction of the stick cylinder 16. The base end of the bucket 14 is connected to the front end of the stick 13, and rotates relative to the stick 13 through the extension and retraction of the bucket cylinder 17.

[0030] The boom cylinder 15, stick cylinder 16, and bucket cylinder 17 extend and retract via working oil supplied from the hydraulic pump 33. This causes a change in the posture of the working device 11. The boom cylinder 15, stick cylinder 16, and bucket cylinder 17 extend and retract by a stroke corresponding to the operating amount of the left and right control levers described later.

[0031] An operator's seat is provided inside the cab 6 located on the upper slewing body 3. Left and right control levers, which are operated by the operator, are located on either side of the operator's seat. These control levers are operated during the slewing motion of the upper slewing body 3 and the rotation motion of the working device 11. The left control lever is, for example, composed of a slewing control lever that indicates the operation of the slewing hydraulic motor of the slewing device 4 and a stick control lever that indicates the operation of the stick cylinder 16 of the working device 11. The right control lever is, for example, composed of a boom control lever that indicates the operation of the boom cylinder 15 of the working device 11 and a bucket control lever that indicates the operation of the bucket cylinder 17 of the working device 11.

[0032] The left and right lever devices are connected to a control device (not shown) and output operation signals representing commands corresponding to the operator's actions to the control device. Based on the operation signals output from these lever devices, the control device controls multiple proportional solenoid valves (not shown). As a result, the working oil discharged from the pilot pump is output as a pilot pressure corresponding to the operator's actions to the control valve device 38 (boom direction control valve 38A, stick direction control valve 38B, and bucket direction control valve 38C) via the proportional solenoid valves. Thus, the operator can drive the hydraulic cylinders 15-17 of the working device 11, including the boom cylinder 15, stick cylinder 16, and bucket cylinder 17.

[0033] Figure 2This is a diagram showing the structure of the hydraulic drive circuit 31 used in the working device 11. Furthermore, in Figure 2 The diagram of the circuit related to the opening and closing cylinder that enables the opening and closing of the opening and closing bucket 14 of the working device 11 of the hydraulic excavator is omitted.

[0034] The working machine 1 is equipped with a hydraulic drive circuit 31 for the working machines 12-14 that drive the working device 11. In addition, the working machine 1, besides... Figure 2 In addition to the hydraulic drive circuit 31 for the working device 11 shown, it also includes a hydraulic drive circuit for a driving device that drives the driving device that moves the lower driving body 2, and a hydraulic drive device for a slewing device that drives the slewing device 4.

[0035] In addition to the hydraulic cylinders 15-17, the left operating lever device, and the right operating lever device, the hydraulic drive circuit 31 used in the working device 11 also has the following components: a hydraulic pump 33 that supplies working oil to the hydraulic cylinders 15-17; a prime mover 32 that is the power source for the hydraulic pump 33; a working oil tank 34 that stores working oil; a control valve device 38 that is located between the hydraulic pump 33 and the hydraulic cylinders 15-17; a discharge pipe 36 that connects the hydraulic pump 33 and the control valve device 38; first oil passages 39 and 40; second oil passages 41 and 42; and third oil passages 43 and 44.

[0036] Hydraulic pump 33 is driven by prime mover 32. Driven by prime mover 32, hydraulic pump 33 draws in working oil from working oil tank 34 and discharges the drawn-in working oil to discharge line 36, also known as the delivery line. A control valve device 38 is connected to the front end of discharge line 36. Working oil discharged from hydraulic pump 33 to discharge line 36 is supplied to control valve device 38.

[0037] The control valve device 38 distributes the working oil supplied from the hydraulic pump 33 to the hydraulic cylinders 15-17 according to the operation of the left and right operating lever devices. The control valve device 38 includes: a boom direction control valve 38A, located between the hydraulic pump 33 and the boom cylinder 15; a stick direction control valve 38B, located between the hydraulic pump 33 and the stick cylinder 16; and a bucket direction control valve 38C, located between the hydraulic pump 33 and the bucket cylinder 17. The control valve device 38 is formed by a series circuit in which the stick direction control valve 38B and the bucket direction control valve 38C are connected in parallel to each other downstream of the boom direction control valve 38A.

[0038] The boom directional control valve 38A is composed of a pilot-operated directional control valve. For example, the boom directional control valve 38A is composed of a 5-port 3-position (or 6-port 3-position or 4-port 3-position) pilot-operated directional control valve.

[0039] The boom directional control valve 38A controls the flow direction of the working oil supplied from the hydraulic pump 33 to the boom cylinder 15 based on the operation signal output from the boom operating lever device. Specifically, the control device controls the proportional solenoid valve based on the operation signal output from the boom operating lever device, and the pilot pressure generated by controlling the proportional solenoid valve is supplied to the boom directional control valve 38A. In the boom directional control valve 38A, by switching the position of the spool valve within the boom directional control valve 38A according to the pilot pressure, the supply and discharge of working oil relative to the boom cylinder 15 can be switched. As a result, the working oil in the bottom oil chamber 15A and the rod-side oil chamber 15B of the boom cylinder 15 changes, causing the boom cylinder 15 to extend and retract. In this way, the boom directional control valve 38A can control the working oil supplied to the boom cylinder 15 according to the operation signal output from the boom operating lever device.

[0040] Similar to boom direction control valve 38A, stick direction control valve 38B controls the flow direction of working oil supplied from hydraulic pump 33 to stick cylinder 16 based on the operation signal output from stick operating lever device. Similarly, similar to boom direction control valve 38A, bucket direction control valve 38C controls the flow direction of working oil supplied from hydraulic pump 33 to bucket cylinder 17 based on the operation signal output from bucket operating lever device. Stick direction control valve 38B and bucket direction control valve 38C are identical to boom direction control valve 38A except for the different targets of working oil supply (hydraulic cylinders 15-17), therefore further explanation is omitted.

[0041] It should be noted that during excavation operations, the boom raising operation, stick retraction operation, and bucket retraction operation are performed individually or in combination. That is, during excavation operations, it is assumed that any one of the hydraulic cylinders 15-17, such as the boom cylinder 15, stick cylinder 16, and bucket cylinder 17, extends.

[0042] Therefore, the bottom oil chamber 15A of the boom cylinder 15 is the oil chamber on the extended side when the boom cylinder 15 extends during digging operations, and is also referred to as the "extending side oil chamber" of the boom cylinder 15. The rod side oil chamber 15B of the boom cylinder 15 is the oil chamber on the retracted side when the boom cylinder 15 extends during digging operations, and is also referred to as the "retracting side oil chamber" of the boom cylinder 15. Similarly, the bottom oil chamber 16A of the stick cylinder 16 is the extending side oil chamber when the stick cylinder 16 extends during digging operations, and the rod side oil chamber 16B of the stick cylinder 16 is the retracting side oil chamber when the stick cylinder 16 extends during digging operations. The bottom oil chamber 17A of the bucket cylinder 17 is the extending side oil chamber when the bucket cylinder 17 extends during digging operations, and the rod side oil chamber 17B of the bucket cylinder 17 is the retracting side oil chamber when the bucket cylinder 17 extends during digging operations.

[0043] The first oil circuits 39 and 40 are pipelines connecting the boom direction control valve 38A to the boom cylinder 15. The first oil circuits 39 and 40 include: BMCB pipeline 39, which connects the boom direction control valve 38A to the bottom side oil chamber 15A of the boom cylinder 15; and BMCR pipeline 40, which connects the boom direction control valve 38A to the rod side oil chamber 15B of the boom cylinder 15.

[0044] The second oil circuits 41 and 42 are pipelines connecting the stick directional control valve 38B to the stick cylinder 16. The second oil circuits 41 and 42 include: an AMCB pipeline 41, which connects the stick directional control valve 38B to the bottom oil chamber 16A of the stick cylinder 16; and an AMCR pipeline 42, which connects the stick directional control valve 38B to the rod-side oil chamber 16B of the stick cylinder 16. An overload relief valve 41A is installed in the AMCB pipeline 41, which releases the working oil from the bottom oil chamber 16A to the working oil tank 34 when the bottom oil chamber 16A of the stick cylinder 16 becomes overloaded. An overload relief valve 42A is installed in the AMCR pipeline 42, which releases the working oil from the rod-side oil chamber 16B of the stick cylinder 16 to the working oil tank 34 when the rod-side oil chamber 16B of the stick cylinder 16 becomes overloaded.

[0045] The third oil circuits 43 and 44 are pipelines connecting the bucket directional control valve 38C to the bucket cylinder 17. The third oil circuits 43 and 44 include: a BKCB pipeline 43, which connects the bucket directional control valve 38C to the bottom oil chamber 17A of the bucket cylinder 17; and a BKCR pipeline 44, which connects the bucket directional control valve 38C to the rod-side oil chamber 17B of the bucket cylinder 17. An overload relief valve 43A is installed in the BKCB pipeline 43, which releases the working oil from the bottom oil chamber 17A to the working oil tank 34 when the bottom oil chamber 17A of the bucket cylinder 17 becomes overloaded. An overload relief valve 44A is installed in the BKCR pipeline 44, which releases the working oil from the rod-side oil chamber 17B of the bucket cylinder 17 to the working oil tank 34 when the rod-side oil chamber 17B of the bucket cylinder 17 becomes overloaded.

[0046] However, in the technology disclosed in Patent Document 1, during a combined digging operation involving boom retraction or bucket retraction and boom raising, the pressure in the bottom oil chamber of any of the boom cylinder, stick cylinder, and bucket cylinder rises due to digging resistance. If the conditions for vehicle levitation are met, the pilot pressure for boom raising is controlled to be greater than or equal to the operator's input, while the pilot pressure for boom retraction is controlled to be less than or equal to the operator's input. Therefore, in the technology disclosed in Patent Document 1, it is possible to prevent each hydraulic cylinder from becoming overloaded, and to prevent high-pressure working oil from being discharged from the overload relief valve into the working oil tank or for the vehicle levitation to occur.

[0047] However, in the technology disclosed in Patent Document 1, for example, when any hydraulic cylinder becomes overloaded due to a separate operation of the boom retraction, without controlling the pilot pressure involved in the boom lifting operation, it is impossible to prevent the discharge of high-pressure working oil from the overload relief valve and the lifting of the vehicle body. Therefore, in the technology disclosed in Patent Document 1, energy efficiency is low, or the working device cannot perform its operations properly.

[0048] Furthermore, in the technology disclosed in Patent Document 1, when the circuit involved in the stick retraction operation or the circuit involved in the bucket retraction operation and the circuit involved in the boom lifting operation form a series circuit in the control valve device, when the pilot pressure involved in the boom lifting operation is controlled to be greater than or equal to the operator's operating amount, the stick retraction speed is reduced, and the work efficiency may be reduced.

[0049] Therefore, the working machine 1 of this embodiment includes a hydraulic drive circuit 31 for the working device 11. This hydraulic drive circuit 31 is configured such that, regardless of whether it is performed individually or in combination as a digging operation, if the bottom oil chambers 16A and 17A of either the boom cylinder 16 or the bucket cylinder 17 are overloaded, it automatically performs a boom lifting action that rotates the boom 13 upwards. Furthermore, the hydraulic drive circuit 31 of the working device 11 in this embodiment is configured such that the boom retraction speed or bucket retraction speed is not decelerated due to the diversion of working oil in the control valve device 38 accompanying the boom lifting operation.

[0050] Specifically, the hydraulic drive circuit 31 includes a first connecting pipe 20 that connects the extension side oil chamber (bottom side oil chamber 15A) of the boom cylinder 15 to the extension side oil chamber (bottom side oil chamber 16A) of the stick cylinder 16. The first connecting pipe 20 connects the bottom side oil chamber 15A of the boom cylinder 15 and the bottom side oil chamber 16A of the stick cylinder 16 without passing through the control valve device 38. A first valve 20A is provided on the first connecting pipe 20. This first valve 20A opens when the pressure in the bottom side oil chamber 16A of the stick cylinder 16 reaches an overload state exceeding a first threshold, allowing working oil to flow from the bottom side oil chamber 16A of the stick cylinder 16 to the bottom side oil chamber 15A of the boom cylinder 15.

[0051] A return circuit 21 is connected to the rod-side oil chamber 15B of the boom cylinder 15. The return circuit 21 includes a first pipe 24, which connects the retraction-side oil chamber 15B of the boom cylinder 15 (rod-side oil chamber) to the retraction-side oil chamber 16B of the boom cylinder 16 (rod-side oil chamber). The first pipe 24 is connected to the rod-side oil chamber 15B of the boom cylinder 15 and the AMCR pipe 42, connecting the rod-side oil chamber 15B of the boom cylinder 15 and the rod-side oil chamber 16B of the boom cylinder 16 via the AMCR pipe 42. A third valve 21A is provided on the first pipe 24. This third valve 21A opens when the pressure in the bottom-side oil chamber 16A of the boom cylinder 16 exceeds a first threshold, indicating an overload state, allowing working oil to flow from the rod-side oil chamber 15B of the boom cylinder 15 to the rod-side oil chamber 16B of the boom cylinder 16. A check valve 24A is installed on the first pipeline 24 between the third valve 21A and the AMCR pipeline 42 to restrict the flow direction of the working oil. The first pipeline 24 between the third valve 21A and the check valve 24A branches off and connects to the working oil tank 34.

[0052] Additionally, the hydraulic drive circuit 31 includes a second connecting pipe 22 that connects the extension side oil chamber (bottom side oil chamber 15A) of the boom cylinder 15 to the extension side oil chamber (bottom side oil chamber 17A) of the bucket cylinder 17. The second connecting pipe 22 connects the bottom side oil chamber 15A of the boom cylinder 15 and the bottom side oil chamber 17A of the bucket cylinder 17 without passing through the control valve device 38. A second valve 22A is provided on the second connecting pipe 22. This second valve 22A opens when the pressure in the bottom side oil chamber 17A of the bucket cylinder 17 reaches an overload state exceeding a second threshold, allowing working oil to flow from the bottom side oil chamber 17A of the bucket cylinder 17 to the bottom side oil chamber 15A of the boom cylinder 15.

[0053] A return circuit 23 is connected to the rod-side oil chamber 15B of the boom cylinder 15. The return circuit 23 includes a second pipe 25 connecting the retraction-side oil chamber 15B (rod-side oil chamber) of the boom cylinder 15 to the retraction-side oil chamber 17B (rod-side oil chamber) of the bucket cylinder 17. The second pipe 25 is connected to the rod-side oil chamber 15B of the boom cylinder 15 and the BKCR pipe 44, connecting the rod-side oil chamber 15B of the boom cylinder 15 and the rod-side oil chamber 17B of the bucket cylinder 17 via the BKCR pipe 44. A fourth valve 23A is provided on the second pipe 25. This fourth valve 23A opens when the pressure in the bottom oil chamber 17A of the bucket cylinder 17 becomes overloaded, exceeding a second threshold, allowing working oil to flow from the rod-side oil chamber 15B of the boom cylinder 15 to the rod-side oil chamber 17B of the bucket cylinder 17. A check valve 25A is installed on the second pipeline 25 between the fourth valve 23A and the BKCR pipeline 44 to restrict the flow direction of the working oil. The second pipeline 25 between the fourth valve 23A and the check valve 25A branches off and connects to the working oil tank 34.

[0054] The first valve 20A, the second valve 22A, the third valve 21A, and the fourth valve 23A are each composed of sequence valves. The first valve 20A and the third valve 21A are opened by the same pilot pressure. The second valve 22A and the fourth valve 23A are opened by the same pilot pressure. Alternatively, the first valve 20A, the second valve 22A, the third valve 21A, and the fourth valve 23A can also be composed of solenoid valves.

[0055] Figure 3 This diagram illustrates the operation of the hydraulic drive circuit 31 when the stick cylinder 16 is in an overload state during the individual stick retraction operation.

[0056] The stick retraction operation is a type of excavation operation, meaning that only the boom 12, stick 13, and stick 13 of the bucket 14 are operated in the retraction direction, while the boom 12 and bucket 14 are not operated. The overload state of the stick cylinder 16 refers to the state where the pressure in the extension side oil chamber, i.e., the bottom oil chamber 16A, of the stick cylinder 16 exceeds a first threshold. The first threshold is less than the permissible pressure value of the bottom oil chamber 16A of the stick cylinder 16.

[0057] exist Figure 3 In the case shown, working oil is supplied from hydraulic pump 33 to the bottom oil chamber 16A of boom cylinder 16 via boom directional control valve 38B. Figure 3 In the case shown, the second valve 22A and the fourth valve 23A are closed, but the first valve 20A and the third valve 21A are open.

[0058] When the first valve 20A and the third valve 21A are opened, at least a portion of the working oil supplied from the hydraulic pump 33 to the bottom oil chamber 16A of the boom cylinder 16 via the boom direction control valve 38B is supplied to the bottom oil chamber 15A of the boom cylinder 15 via the first connecting pipe 20. Thus, in the working machine 1, although no boom lifting operation is performed, a boom lifting action of rotating the boom 12 upward is performed. The working oil in the boom cylinder 15's rod-side oil chamber 15B is discharged to the working oil tank 34 via the first pipe 24.

[0059] If the overload state of the boom cylinder 16 is eliminated by lifting the boom, then the first valve 20A and the third valve 21A will be closed.

[0060] Figure 4 This diagram illustrates the operation of the hydraulic drive circuit 31 when the bucket cylinder 17 is in an overload state during the individual operation of the boom retraction.

[0061] The overload state of the bucket cylinder 17 refers to the state in which the pressure in the bottom oil chamber 17A of the bucket cylinder 17 exceeds the second threshold. The second threshold is smaller than the allowable pressure value of the bottom oil chamber 17A of the bucket cylinder 17.

[0062] exist Figure 4In the case shown, working oil is supplied from hydraulic pump 33 to the bottom oil chamber 16A of boom cylinder 16 via boom directional control valve 38B. Figure 4 In the case shown, the first valve 20A and the third valve 21A are closed, but the second valve 22A and the fourth valve 23A are open.

[0063] When the second valve 22A and the fourth valve 23A are opened, the working oil in the bottom oil chamber 17A of the bucket cylinder 17 is supplied to the bottom oil chamber 15A of the boom cylinder 15 via the second connecting pipe 22 due to overload. Thus, in the working machine 1, although no boom lifting operation is performed, a boom lifting action is performed by rotating the boom 12 upwards. At this time, based on the amount of working oil flowing out of the bottom oil chamber 17A of the bucket cylinder 17 due to overload, the working oil in the rod-side oil chamber 15B of the boom cylinder 15 flows into the rod-side oil chamber 17B of the bucket cylinder 17 via the second pipe 25. As a result, the bucket cylinder 17 retracts.

[0064] When the overload condition of the bucket cylinder 17 is eliminated by the boom lifting action, the second valve 22A and the fourth valve 23A are closed.

[0065] Figure 5 This diagram illustrates the operation of the hydraulic drive circuit 31 when the stick cylinder 16 is in an overload state during the combined stick and bucket operation.

[0066] The combined stick and bucket operation is a type of excavation operation, which means that the stick 13 and bucket 14 are operated in both directions of retraction, while the boom 12 is not operated.

[0067] exist Figure 5 In the illustrated case, working oil is supplied from hydraulic pump 33 to the bottom oil chamber 16A of boom cylinder 16 via boom direction control valve 38B, and working oil is supplied from hydraulic pump 33 to the bottom oil chamber 17A of bucket cylinder 17 via bucket direction control valve 38C. Figure 5 In the case shown, the second valve 22A and the fourth valve 23A are closed, but the first valve 20A and the third valve 21A are open.

[0068] If the first valve 20A and the third valve 21A are open, then... Figure 3 Similarly, the working oil in the bottom oil chamber 16A of the boom cylinder 16 is supplied to the bottom oil chamber 15A of the boom cylinder 15 via the first connecting pipe 20. Thus, in the working machine 1, although no boom lifting operation is performed, a boom lifting action is performed by rotating the boom 12 upwards. The working oil in the rod-side oil chamber 15B of the boom cylinder 15 is discharged to the working oil tank 34 via the first pipe 24.

[0069] Furthermore, even if the control valve device 38 is configured as a series circuit as described above, it does not perform a boom lifting operation. Therefore, the working oil is not diverted from the boom direction control valve 38A to the boom cylinder 15. As a result, the amount of working oil supplied to the bucket cylinder 17 is not affected in the working machine 1. Therefore, compared with the case where a boom lifting operation is performed, the bucket retraction speed is not reduced when performing the boom lifting operation.

[0070] It should be noted that sometimes the load increase effect of the bucket loading action on the bottom oil chamber 16A of the stick cylinder 16 exceeds the load reduction effect of the boom lifting action on the bottom oil chamber 16A of the stick cylinder 16. In this case, all the working oil supplied from the hydraulic pump 33 to the bottom oil chamber 16A via the stick direction control valve 38B merges with the working oil flowing out of the bottom oil chamber 16A due to overload, and flows out from the bottom oil chamber 16A to supply the bottom oil chamber 15A of the boom cylinder 15 to perform the boom lifting action. At this time, based on the amount of working oil flowing out of the bottom oil chamber 16A of the stick cylinder 16, the working oil in the rod side oil chamber 15B of the boom cylinder 15 flows into the rod side oil chamber 16B of the stick cylinder 16 via the first pipeline 24. As a result, the stick cylinder 16 retracts.

[0071] If the overload state of the boom cylinder 16 is eliminated by lifting the boom, then the first valve 20A and the third valve 21A will be closed.

[0072] Figure 6 This diagram illustrates the operation of the hydraulic drive circuit 31 when the bucket cylinder 17 is in an overload state during the combined boom and bucket operation.

[0073] exist Figure 6 In the illustrated case, working oil is supplied from hydraulic pump 33 to the bottom oil chamber 16A of boom cylinder 16 via boom direction control valve 38B, and working oil is supplied from hydraulic pump 33 to the bottom oil chamber 17A of bucket cylinder 17 via bucket direction control valve 38C. Figure 6 In the case shown, the first valve 20A and the third valve 21A are closed, but the second valve 22A and the fourth valve 23A are open.

[0074] When the second valve 22A and the fourth valve 23A are opened, with Figure 4 Similarly, as shown, the working oil in the bottom oil chamber 17A of the bucket cylinder 17 is supplied to the bottom oil chamber 15A of the boom cylinder 15 via the second connecting pipe 22. Thus, in the working machine 1, although no boom lifting operation is performed, a boom lifting action is performed by rotating the boom 12 upwards. The working oil in the rod-side oil chamber 15B of the boom cylinder 15 is discharged to the working oil tank 34 via the second pipe 25.

[0075] Furthermore, even if the control valve device 38 is configured as a series circuit as described above, it does not perform a boom lifting operation. Therefore, the working oil is not diverted from the boom direction control valve 38A to the boom cylinder 15. As a result, the amount of working oil supplied to the stick cylinder 16 is not affected in the working machine 1. Therefore, compared with the case where a boom lifting operation is performed, the boom lifting operation is performed without slowing down the stick retraction speed.

[0076] It should be noted that sometimes the increased load on the bottom oil chamber 17A of the bucket cylinder 17 caused by the stick retraction action exceeds the reduced load on the bottom oil chamber 17A of the bucket cylinder 17 caused by the boom raising action. In this case, all the working oil supplied from the hydraulic pump 33 to the bottom oil chamber 17A via the bucket direction control valve 38C merges with the working oil flowing out of the bottom oil chamber 17A due to overload, and flows out of the bottom oil chamber 17A to supply the bottom oil chamber 15A of the boom cylinder 15 to perform the boom raising action. At this time, based on the amount of working oil flowing out of the bottom oil chamber 17A of the bucket cylinder 17, the working oil in the rod side oil chamber 15B of the boom cylinder 15 flows into the rod side oil chamber 17B of the bucket cylinder 17 via the second pipe 25. As a result, the bucket cylinder 17 retracts.

[0077] When the overload condition of the bucket cylinder 17 is eliminated by the boom lifting action, the second valve 22A and the fourth valve 23A are closed.

[0078] Figure 7 The diagram shows other examples of operating machinery 1.

[0079] Operating machinery 1 may not be Figure 1 A backhoe-type hydraulic excavator as shown, but rather like... Figure 7 A hydraulic excavator with a loading bucket 14 as shown. Figure 7 The machine shown, 1, basically has the same functions as... Figure 1 The hydraulic drive circuit 31 is the same as that of the machine shown in the diagram 1.

[0080] However, in Figure 7 In the excavating machine 1 shown, during the excavation operation, the boom lifting operation, the stick pushing operation (the operation of rotating the stick 13 forward), and the bucket retraction operation are performed individually or in combination. That is, in the loading type hydraulic excavator, it is also envisioned that any one of the hydraulic cylinders 15 to 17, such as the boom cylinder 15, the stick cylinder 16, and the bucket cylinder 17, will extend during the excavation operation.

[0081] Therefore, in Figure 7In the illustrated work machine 1, the bottom oil chamber 15A of the boom cylinder 15 is the extension side oil chamber when the boom cylinder 15 extends during digging operations, and the rod side oil chamber 15B of the boom cylinder 15 is the retraction side oil chamber when the boom cylinder 15 extends during digging operations. Similarly, the bottom oil chamber 16A of the stick cylinder 16 is the extension side oil chamber when the stick cylinder 16 extends during digging operations, and the rod side oil chamber 16B of the stick cylinder 16 is the retraction side oil chamber when the stick cylinder 16 extends during digging operations. The bottom oil chamber 17A of the bucket cylinder 17 is the extension side oil chamber when the bucket cylinder 17 extends during digging operations, and the rod side oil chamber 17B of the bucket cylinder 17 is the retraction side oil chamber when the bucket cylinder 17 extends during digging operations.

[0082] exist Figure 7 In the operating machine 1 shown, the first connecting pipe 20 connects the bottom oil chamber 15A of the boom cylinder 15 to the bottom oil chamber 16A of the stick cylinder 16. The second connecting pipe 22 connects the bottom oil chamber 15A of the boom cylinder 15 to the bottom oil chamber 17A of the bucket cylinder 17.

[0083] exist Figure 7 In the operating machine 1 shown, the first pipeline 24 connects the rod-side oil chamber 15B of the boom cylinder 15 to the rod-side oil chamber 16B of the stick cylinder 16. The second pipeline 25 connects the rod-side oil chamber 15B of the boom cylinder 15 to the rod-side oil chamber 17B of the bucket cylinder 17.

[0084] exist Figure 7 In the illustrated machine 1, the overload state of the boom cylinder 16 refers to the state in which the pressure in the extension side oil chamber, i.e., the bottom side oil chamber 16A, of the boom cylinder 16 exceeds a first threshold. The overload state of the bucket cylinder 17 refers to the state in which the pressure in the extension side oil chamber, i.e., the bottom side oil chamber 17A, of the bucket cylinder 17 exceeds a second threshold.

[0085] Furthermore, in Figure 7 In the illustrated machine 1, when the stick push is operated alone, or when the stick and bucket are combined, and the stick cylinder 16 is in an overloaded state, the working oil in the extension side oil chamber (bottom side oil chamber 16A) of the stick cylinder 16 is supplied to the extension side oil chamber (bottom side oil chamber 15A) of the boom cylinder 15 via the first connecting pipe 20. Thus, even without boom lifting, the boom 12 rotates upward. When the bucket cylinder 17 is in an overloaded state, the working oil in the extension side oil chamber (bottom side oil chamber 17A) of the bucket cylinder 17 is supplied to the extension side oil chamber (bottom side oil chamber 15A) of the boom cylinder 15 via the second connecting pipe 22. Thus, even without boom lifting, the boom 12 rotates upward.

[0086] As described above, the work machine 1 of this embodiment includes a work device 11, which includes a boom 12 rotatably connected to the vehicle body 2 and 3, a stick 13 rotatably connected to the boom 12, a boom cylinder 15 for driving the boom 12, and a stick cylinder 16 for driving the stick 13. The work machine 1 includes a hydraulic pump 33 that supplies working oil to the boom cylinder 15 and the stick cylinder 16. The work machine 1 includes a control valve device 38, which includes a boom direction control valve 38A, which is disposed between the hydraulic pump 33 and the boom cylinder 15 and controls the flow direction of the working oil supplied from the hydraulic pump 33 to the boom cylinder 15; and a stick direction control valve 38B, which is disposed between the hydraulic pump 33 and the stick cylinder 16 and controls the flow direction of the working oil supplied from the hydraulic pump 33 to the stick cylinder 16. The working machine 1 has a first oil passage 39 and 40 connecting the boom direction control valve 38A to the boom cylinder 15, and a second oil passage 41 and 42 connecting the stick direction control valve 38B to the stick cylinder 16. The working machine 1 also has a first connecting pipe 20 connecting the extension side oil chamber (bottom oil chamber 15A of the boom cylinder 15 when extended by digging operation) to the extension side oil chamber (bottom oil chamber 16A of the stick cylinder 16 when extended by digging operation.

[0087] Therefore, regardless of whether the machine 1 is operating alone or in combination as an excavation operation, it can automatically raise the boom when the boom cylinder 16 or bucket cylinder 17 is overloaded, thus eliminating the overload condition. Therefore, the machine 1 can prevent high-pressure working oil from being discharged from the overload relief valves 41A-44A into the working oil tank 34, or prevent the machine body 2 and 3 from floating. Therefore, regardless of the operating condition of the working device 11, even if the hydraulic cylinders 16 and 17 of the working device 11 are overloaded, the working device 11 can still operate appropriately and efficiently.

[0088] Furthermore, in the working machine 1 of this embodiment, the working device 11 includes a bucket 14 rotatably connected to the boom 13 and a bucket cylinder 17 that drives the bucket 14. A hydraulic pump 33 supplies working oil to the bucket cylinder 17. A control valve device 38 includes a bucket direction control valve 38C, which is disposed between the hydraulic pump 33 and the bucket cylinder 17, controlling the flow direction of the working oil supplied from the hydraulic pump 33 to the bucket cylinder 17. The bucket direction control valve 38C and the bucket cylinder 17 are connected via third oil passages 43 and 44. The extension side oil chamber 17A of the bucket cylinder 17 when it extends during digging operations, i.e., the bottom oil chamber 17A of the bucket cylinder 17, is connected to the bottom oil chamber 15A of the boom cylinder 15 via a second connecting pipe 22. A first valve 20A is provided on the first connecting pipe 20. The first valve 20A opens when the pressure in the bottom oil chamber 16A of the boom cylinder 16 exceeds a first threshold, allowing working oil to flow from the bottom oil chamber 16A of the boom cylinder 16 to the bottom oil chamber 15A of the boom cylinder 15. A second valve 22A is provided on the second connecting pipe 22. The second valve 22A opens when the pressure in the bottom oil chamber 17A of the bucket cylinder 17 exceeds a second threshold, allowing working oil to flow from the bottom oil chamber 17A of the bucket cylinder 17 to the bottom oil chamber 15A of the boom cylinder 15.

[0089] Therefore, regardless of whether the machine 1 is operating alone or in combination as an excavation operation, it can reliably perform boom lifting even when the boom cylinder 16 or bucket cylinder 17 is overloaded, and can reliably eliminate the overload condition. Thus, the machine 1 can reliably prevent high-pressure working oil from being discharged from the overload relief valves 41A to 44A into the working oil tank 34, or prevent the machine body 2 and 3 from floating. Therefore, even if the hydraulic cylinders 16 and 17 of the working device 11 are overloaded, the working device 11 can operate more appropriately and efficiently.

[0090] Furthermore, the working machine 1 of this embodiment includes a first pipeline 24, which connects the retractable side oil chamber 15B of the boom cylinder 15 (i.e., the rod side oil chamber 15B) when it extends during digging operations to the retractable side oil chamber 16B of the stick cylinder 16 (i.e., the stick side oil chamber 16B) when it extends during digging operations. The working vehicle 1 includes a second pipeline 25, which connects the retractable side oil chamber 17B of the bucket cylinder 17 (i.e., the rod side oil chamber 17B) when it extends during digging operations to the rod side oil chamber 15B of the boom cylinder 15.

[0091] Therefore, regardless of whether the machine 1 is operating alone or in a combined operation as an excavation operation, it can perform the aforementioned boom lifting action without supplying working oil from the hydraulic pump 33 to the extension side oil chamber of the boom cylinder 15 via the control valve device 38. Thus, the machine 1 can prevent, for example, deceleration of the stick retraction speed or bucket retraction speed during combined stick and bucket operation, and can prevent high-pressure working oil from being discharged from the overload relief valves 41A to 44A into the working oil tank 34, or the machine body 2 and 3 from floating. Therefore, even if the hydraulic cylinders 16 and 17 of the working device 11 are overloaded, the working device 11 can operate appropriately and more efficiently.

[0092] Furthermore, in the working machine 1 of this embodiment, a third valve 21A is provided on the first pipeline 24. This third valve 21A opens when the pressure in the bottom oil chamber 16A of the boom cylinder 16 exceeds a first threshold, allowing working oil to flow from the rod-side oil chamber 15B of the boom cylinder 15 to the rod-side oil chamber 16B of the boom cylinder 16. A fourth valve 23A is provided on the second pipeline 25. This fourth valve 23A opens when the pressure in the bottom oil chamber 17A of the bucket cylinder 17 exceeds a second threshold, allowing working oil to flow from the rod-side oil chamber 15B of the boom cylinder 15 to the rod-side oil chamber 17B of the bucket cylinder 17.

[0093] Therefore, regardless of whether the machine 1 is operating alone or in a combined operation as an excavation operation, it can reliably perform the aforementioned boom lifting action without supplying working oil from the hydraulic pump 33 to the boom cylinder 15 rod-side oil chamber 15B via the control valve device 38. Thus, the machine 1 can reliably prevent, for example, deceleration of the stick retraction speed or bucket retraction speed during combined stick and bucket operation, and can prevent high-pressure working oil from being discharged from the overload relief valves 41A to 44A into the working oil tank 34, or the machine body 2 and 3 from floating. Therefore, even if the hydraulic cylinders 16 and 17 of the working device 11 are overloaded, the working device 11 can operate appropriately and more efficiently.

[0094] Furthermore, in the machine tool 1 of this embodiment, the first valve 20A, the second valve 22A, the third valve 21A, and the fourth valve 23A are configured as sequence valves. The first valve 20A and the third valve 21A are opened by the same pilot pressure. The second valve 22A and the fourth valve 23A are opened by the same pilot pressure.

[0095] Therefore, the working machine 1 can drive the first valve 20A to the fourth valve 23A via mechanical hydraulics. Furthermore, the working machine 1 can determine the opening state of the first valve 20A or the second valve 22A, which allows working oil to flow into the bottom oil chamber 15A of the boom cylinder 15, and the opening state of the third valve 21A or the fourth valve 23A, which allows working oil to flow out of the rod-side oil chamber 15B, under the same pressure conditions. Therefore, it is not necessary to monitor the establishment of these pressure conditions using electrical control methods such as sensors. Thus, the working machine 1 can minimize the electrical control associated with the first valve 20A to the fourth valve 23A, ensuring the robustness of the hydraulic drive circuit 31, and thus enabling more reliable boom lifting operations. Therefore, even if the hydraulic cylinders 16 and 17 of the working device 11 are overloaded, the working device 11 can operate more appropriately and efficiently.

[0096] Furthermore, in the working machine 1 of this embodiment, the first valve 20A, the second valve 22A, the third valve 21A, and the fourth valve 23A are composed of solenoid valves.

[0097] Therefore, even in models where it is difficult to configure a pilot circuit, the working machine 1 can be equipped with a hydraulic drive circuit 31 to perform the aforementioned boom lifting action. Thus, in various models of the working machine 1, even if the hydraulic cylinders 16 and 17 of the working device 11 are overloaded, the working device 11 can still perform operations appropriately and efficiently.

[0098] Furthermore, in the working machine 1 of this embodiment, the control valve device 38 is composed of a series circuit in which the boom direction control valve 38B and the bucket direction control valve 38C are connected in parallel to each other on the downstream side of the boom direction control valve 38A.

[0099] Therefore, even if the control valve device 38 is configured with this series circuit, the machine tool 1 can prevent, for example, deceleration of the stick retraction speed or bucket retraction speed during combined stick and bucket operation, and can prevent high-pressure working oil from being discharged from the overload relief valves 41A to 44A into the working oil tank 34 or the machine body 2 and 3 from floating. Therefore, even if the hydraulic cylinders 16 and 17 of the working device 11 are overloaded, the working device 11 can still operate appropriately and more efficiently.

[0100] Furthermore, the working machine 1 in this embodiment is a backhoe type hydraulic excavator. When the working machine 1 performs a single operation of retracting the boom 12, stick 13, and bucket 14 in the retraction direction during excavation, or a combined operation of retracting both the stick 13 and bucket 14 during excavation, if the pressure in the bottom oil chamber 16A of the stick cylinder 16 exceeds a first threshold and the stick cylinder 16 is in an overload state, the working oil in the bottom oil chamber 16A of the stick cylinder 16 is supplied to the bottom oil chamber 15A of the boom cylinder 15 via the first connecting pipe 20. As a result, the boom 12 rotates upward even when no boom lifting operation is performed. When the pressure in the bottom oil chamber 17A of the bucket cylinder 17 becomes overloaded and exceeds the second threshold, the working oil in the bottom oil chamber 17A of the bucket cylinder 17 is supplied to the bottom oil chamber 15A of the boom cylinder 15 via the second connecting pipe 22, so that the boom 12 rotates upward even without boom lifting operation.

[0101] Therefore, regardless of whether the machine 1 is operating alone or in combination as a digging operation, it can automatically raise the boom and eliminate the overload condition if the boom cylinder 16 or bucket cylinder 17 is overloaded. Regardless of the operating status of the working device 11, even if the hydraulic cylinders 16 and 17 of the working device 11 are overloaded, the working device 11 can still operate appropriately and efficiently.

[0102] The embodiments of the present invention have been described in detail above, but the present invention is not limited to each embodiment, and various modifications can be made without departing from the spirit of the present invention. The present invention can add a component of one embodiment to a component of another embodiment, or replace a component of one embodiment with a component of another embodiment, or delete a portion of a component of one embodiment.

[0103] Symbol Explanation

[0104] 1—Working machinery, 2—Lower traveling body, 3—Upper slewing body, 4—Slewing device, 5—Slewing frame, 6—Cab, 11—Working device, 12—Boom, 13—Stick, 14—Bucket, 15—Boom cylinder, 15A—Bottom side oil chamber, 15B—Stick side oil chamber, 16—Stick cylinder, 16A—Bottom side oil chamber, 16B—Stick side oil chamber, 17—Bucket cylinder, 17A—Bottom side oil chamber, 17B—Stick side oil chamber, 20—First connecting pipe, 20A—First valve, 21—Return circuit, 21A—Third valve, 22—Second connecting pipe, 22A—Second valve, 23—Return circuit, 23A—Fourth valve, 24— First pipeline, 24A—Check valve, 25—Second pipeline, 25A—Check valve, 31—Hydraulic drive circuit, 32—Prime mover, 33—Hydraulic pump, 34—Working oil tank, 36—Discharge pipeline, 38—Control valve device, 38A—Boom direction control valve, 38B—Stick direction control valve, 38C—Bucket direction control valve, 39—BMCB pipeline, 40—BMCR pipeline, 41—AMCB pipeline, 41A—Overload relief valve, 42—AMCR pipeline, 42A—Overload relief valve, 43—BKCB pipeline, 43A—Overload relief valve, 44—BKCR pipeline, 44A—Overload relief valve.

Claims

1. A type of operating machinery, characterized in that, have The working device includes: a boom rotatably connected to the vehicle body; a stick rotatably connected to the boom; a boom cylinder for driving the boom; and a stick cylinder for driving the stick. A hydraulic pump supplies working oil to the boom cylinder and the stick cylinder; A control valve device includes: a boom direction control valve disposed between the hydraulic pump and the boom cylinder, controlling the flow direction of the working oil supplied from the hydraulic pump to the boom cylinder; and a stick direction control valve disposed between the hydraulic pump and the stick cylinder, controlling the flow direction of the working oil supplied from the hydraulic pump to the stick cylinder; and The first connecting pipe connects the bottom oil chamber of the boom cylinder to the bottom oil chamber of the stick cylinder. The bottom oil chamber of the boom cylinder is the extension side oil chamber when the boom cylinder extends through the digging operation, and the bottom oil chamber of the stick cylinder is the extension side oil chamber when the stick cylinder extends through the digging operation.

2. The operating machinery according to claim 1, characterized in that, The working device includes a bucket rotatably connected to the boom and a bucket cylinder for driving the bucket. The hydraulic pump supplies the working oil to the bucket cylinder. The control valve device includes a bucket direction control valve, which is disposed between the hydraulic pump and the bucket cylinder to control the flow direction of the working oil supplied from the hydraulic pump to the bucket cylinder. The extension side oil chamber of the bucket cylinder, which extends during the digging operation (i.e., the bottom side oil chamber of the bucket cylinder), is connected to the bottom side oil chamber of the boom cylinder via a second connecting pipe. A first valve is provided on the first connecting pipe. This first valve opens when the pressure in the bottom oil chamber of the boom cylinder exceeds a first threshold, allowing the working oil to flow from the bottom oil chamber of the boom cylinder to the bottom oil chamber of the boom cylinder. A second valve is provided on the second connecting pipe. The second valve opens when the pressure in the bottom oil chamber of the bucket cylinder exceeds a second threshold, so that the working oil flows from the bottom oil chamber of the bucket cylinder to the bottom oil chamber of the boom cylinder.

3. The operating machinery according to claim 2, characterized in that, have: A first pipeline connects the rod-side oil chamber of the boom cylinder to the rod-side oil chamber of the stick cylinder, wherein the rod-side oil chamber of the boom cylinder is the retracted side oil chamber when the boom cylinder extends during the digging operation, and the rod-side oil chamber of the stick cylinder is the retracted side oil chamber when the stick cylinder extends during the digging operation; and The second pipeline connects the rod-side oil chamber of the bucket cylinder to the rod-side oil chamber of the boom cylinder. The rod-side oil chamber of the bucket cylinder is the retractable side oil chamber when the bucket cylinder extends through the digging operation.

4. The operating machinery according to claim 3, characterized in that, A third valve is provided on the first pipeline. This third valve opens when the pressure in the bottom oil chamber of the boom cylinder exceeds a first threshold, allowing the working oil to flow from the rod-side oil chamber of the boom cylinder to the rod-side oil chamber of the boom cylinder. A fourth valve is provided on the second pipeline. When the pressure in the bottom oil chamber of the bucket cylinder exceeds the second threshold, the fourth valve opens, allowing the working oil to flow from the rod-side oil chamber of the boom cylinder to the rod-side oil chamber of the bucket cylinder.

5. The operating machinery according to claim 4, characterized in that, The first valve, the second valve, the third valve, and the fourth valve are sequential valves. The first valve and the third valve open with the same pilot pressure. The second valve and the fourth valve are opened by the same pilot pressure.

6. The operating machinery according to claim 4, characterized in that, The first valve, the second valve, the third valve, and the fourth valve are all composed of solenoid valves.

7. The operating machinery according to claim 2, characterized in that, The control valve device consists of a series circuit in which the boom direction control valve and the bucket direction control valve are connected in parallel to each other on the downstream side of the boom direction control valve.

8. The operating machinery according to claim 2, characterized in that, The bucket is a backhoe bucket. When the digging operation involves only retracting the boom, stick, and bucket in the retraction direction, or when the digging operation involves a combined boom-bucket operation that retracts both the stick and the bucket in the retraction direction, the digging operation is performed as follows: In the case of an overloaded state where the pressure in the bottom oil chamber of the boom cylinder exceeds a first threshold, the working oil in the bottom oil chamber of the boom cylinder is supplied to the bottom oil chamber of the boom cylinder via the first connecting pipe. Thus, even without a boom lifting operation to move the boom upwards, the boom rotates upwards. In the case of an overloaded state where the pressure in the bottom oil chamber of the bucket cylinder exceeds a second threshold, the working oil in the bottom oil chamber of the bucket cylinder is supplied to the bottom oil chamber of the boom cylinder via the second connecting pipe, thereby causing the boom to rotate upward even without the boom lifting operation.

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