Work machine

Abstract

To provide a work machine capable of securing the pressure of an accumulator even when the accumulator cannot be charged by a main pump.SOLUTION: A control device 20 controls switching devices 13 and 14 so that a supply destination of pressurized oil discharged from a pilot pump 11 is switched from a pilot circuit 12 to a high-pressure accumulator 7 when the pressure of the high-pressure accumulator 7 detected by a pressure sensor 18 is lower than a threshold value T1 set higher than the relief set pressure of a pilot relief valve 16, and when the pressure of a low-pressure accumulator 15 detected by a pressure sensor 19 is higher than a threshold value T2 set lower than the relief set pressure.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a work machine such as a hydraulic excavator. [Background technology]

[0002] An example of a document disclosing prior art related to a hydraulic drive system mounted on a work machine such as a hydraulic excavator is Patent Document 1. Patent Document 1 describes a hydraulic drive system including a hydraulic pump (main pump), a hydraulic actuator that receives a supply of pressurized oil from the hydraulic pump and is driven by the pump, a first pipe that supplies the pressurized oil from the hydraulic pump to the hydraulic actuator, a pump flow rate adjustment device that is installed in the first pipe and adjusts the flow of pressurized oil from the hydraulic pump to the hydraulic actuator, an accumulator that accumulates the pressurized oil discharged from the hydraulic pump, and an accumulator flow rate adjustment device that adjusts the flow of pressurized oil from the hydraulic pump to the accumulator, the hydraulic drive system being characterized in that it further includes an accumulator flow rate supply device that supplies the pressurized oil accumulated in the accumulator to the hydraulic actuator via a second pipe that is different from the first pipe. According to this hydraulic drive system, the more efficient circuit can be selected from either the circuit that supplies pressure oil from the main pump to the hydraulic actuator via the first pipe line, or the circuit that supplies pressure oil from the accumulator to the hydraulic actuator via the second pipe line, depending on the operation of the work machine, thereby achieving a significant improvement in the efficiency of the work machine as a whole and enabling a significant reduction in fuel consumption. Also, if the pressure in the accumulator drops due to the supply of pressure oil to the hydraulic actuator from the accumulator device, the accumulator device can be charged (accumulated pressure) by supplying pressure oil from the main pump to the accumulator device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 061165 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the hydraulic drive system described in Patent Document 1, when the pressure in the accumulator is reduced and an instruction to operate the hydraulic actuator is given via the operating device, pressurized oil is supplied to the hydraulic actuator only from the main pump. During this time, the main pump cannot charge the accumulator, which poses a problem in that efficiency is not improved as expected.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a work machine that can ensure accumulator pressure even when the accumulator cannot be charged by the main pump. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention provides a working machine comprising a prime mover, a hydraulic oil tank for storing hydraulic oil, a main pump driven by the prime mover for drawing in and discharging hydraulic oil from the hydraulic oil tank, a hydraulic actuator, a control valve for controlling the flow of pressurized oil supplied from the main pump to the hydraulic actuator, a pilot pump driven by the prime mover, a pilot circuit to which pressurized oil discharged from the pilot pump is supplied and which supplies pilot pressure to the control valve, a pilot relief valve provided in an oil passage connecting the pilot circuit and the hydraulic oil tank and which opens when the pressure in the pilot circuit exceeds a predetermined relief set pressure, and a first accumulator for accumulating pressurized oil discharged from the main pump, the working machine further comprising a first pressure detection device for detecting the pressure of the first accumulator, and a pilot relief valve connected to the pilot circuit and configured to open when the pressure in the pilot circuit exceeds a predetermined relief set pressure. The system includes a second accumulator that accumulates pressurized oil discharged from a pilot pump, a second pressure detection device that detects the pressure of the second accumulator, a switching device that can switch the supply destination of the pressurized oil discharged from the pilot pump to either the pilot circuit or the first accumulator, and a control device that receives signals from the first pressure detection device and the second pressure detection device and outputs a control signal to the switching device, wherein the control device controls the switching device so that the supply destination of the pressurized oil discharged from the pilot pump is switched from the pilot circuit to the first accumulator when the pressure of the first accumulator detected by the first pressure detection device is lower than a first threshold value that is set higher than the relief set pressure and when the pressure of the second accumulator detected by the second pressure detection device is higher than a second threshold value that is set lower than the relief set pressure. [Effects of the Invention]

[0007] According to the present invention, even when the accumulator cannot be charged by the main pump in a work machine, pressure oil can be supplied to the accumulator from the pilot pump, so that the pressure in the accumulator can be ensured. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a perspective view of a hydraulic excavator according to a first embodiment of the present invention. [Figure 2] 1 is a hydraulic circuit diagram of a hydraulic drive system according to a first embodiment of the present invention. [Figure 3] FIG. 3 is a flowchart showing the processing of a control device in the first embodiment of the present invention. [Figure 4] FIG. 4 is a hydraulic circuit diagram of a hydraulic drive system according to a second embodiment of the present invention. [Figure 5] FIG. 10 is a flowchart showing the processing of a control device in a second embodiment of the present invention. [Figure 6] FIG. 10 is a hydraulic circuit diagram of a hydraulic drive system according to a third embodiment of the present invention. [Figure 7] FIG. 10 is a flowchart showing the processing of a control device in a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, a hydraulic excavator will be described as an example of a work machine, but the present invention can also be applied to other work machines such as a wheel loader, a dump truck, and a hydraulic crane. [Example]

[0010] Fig. 1 is a perspective view of a hydraulic excavator according to a first embodiment of the present invention. The hydraulic excavator 100 comprises a lower traveling structure 101, an upper rotating structure 102, and a working device 103. The upper rotating structure 102 is driven by a traveling motor 104 (hydraulic actuator). The upper rotating structure 102 is rotatably mounted on the lower traveling structure 101, and is driven by a swing motor (hydraulic actuator) (not shown).

[0011] The work device 103 has a boom 105, an arm 106, and a bucket 107. The boom 105 is rotatably supported on the upper rotating body 102, and is driven by a boom cylinder 108 (hydraulic actuator). The arm 106 is rotatably supported on the boom 105, and is driven by an arm cylinder 109 (hydraulic actuator). The bucket 107 is rotatably supported on the arm 106, and is driven by a bucket cylinder 110 (hydraulic actuator).

[0012] Fig. 2 is a hydraulic circuit diagram of a hydraulic drive system mounted on the hydraulic excavator 100. Note that Fig. 2 shows only the parts related to the drive of the hydraulic cylinder 5, which is any one of the boom cylinder 108, arm cylinder 109, and bucket cylinder 110, and omits the parts related to the drive of the other actuators.

[0013] The hydraulic drive unit 200 includes an engine 1 as a prime mover, a hydraulic oil tank 2 that stores hydraulic oil, a main pump 3 driven by the engine 1, a pump regulator 4 that controls the flow rate of the main pump 3, a hydraulic cylinder 5 that is driven by pressure oil from the main pump 3, a center bypass type control valve 6 that controls the flow rate of pressure oil supplied from the main pump 3 to one side (bottom side or rod side) of the hydraulic cylinder 5 and also controls the flow rate of pressure oil discharged from the other side (rod side or bottom side) of the hydraulic cylinder 5 to the hydraulic oil tank 2, a high-pressure accumulator 7 that stores pressure oil from the main pump 3, a control valve 8 that controls the flow rate of pressure oil flowing from the main pump 3 into the high-pressure accumulator 7, and a control valve 9 that controls the flow rate of pressure oil supplied from the high-pressure accumulator 7 to one side (bottom side or rod side) of the hydraulic cylinder 5 and also controls the flow rate of pressure oil discharged from the other side (rod side or bottom side) of the hydraulic cylinder 5 to the hydraulic oil tank 2. the control device 20 receives signals from the control lever 17 and the pressure sensors 18 and 19 and outputs control signals to the pump regulator 4, the control valves 6, 8, 9 and 10, and the switching valves 13 and 14. The control device 20 receives signals from the control lever 17 and the pressure sensors 18 and 19 and outputs control signals to the pump regulator 4, the control valves 6, 8, 9 and 10, and the switching valves 13 and 14. The control device 20 is equipped with an arithmetic unit such as a CPU, memory devices such as ROM and RAM, and an input / output interface for signal input / output between external devices, and realizes the functions described below by executing programs stored in ROM, etc.

[0014] The discharge port of the main pump 3 is connected to the hydraulic oil tank 2 via a center bypass oil passage 21. Control valves 6 and 10 are arranged in this order from the upstream side in the center bypass oil passage 21. The control valve 6 is an open-center type flow control valve, and the control valve 10 is a center bypass cut valve. The control valve 6 is connected to the bottom side of the hydraulic cylinder 5 via an oil passage 22, and is connected to the rod side of the hydraulic cylinder 5 via an oil passage 23.

[0015] Pilot circuit 12 is connected to pilot pump 11 via oil passage 24. Switching valve 13 is disposed in oil passage 24 and switches between open position 13a and closed position 13b in response to a control signal from control device 20. Pilot relief valve 16 is disposed in oil passage 25 connecting pilot circuit 12 and hydraulic oil tank 2 and opens when the pressure in pilot circuit 12 exceeds a predetermined relief set pressure (for example, 4 MPa) to release the pressurized oil in pilot circuit 12 to hydraulic oil tank 2. The pressure in pilot circuit 12 is reduced by a solenoid valve (not shown) that is driven in response to a control signal from control device 20, thereby generating pilot pressure for driving control valves 6, 8 to 10 and switching valves 13, 14.

[0016] The high-pressure accumulator 7 is connected via an oil passage 26 to a portion of the center bypass oil passage 21 that connects the main pump 3 and the control valve 6. The control valve 8 is arranged in the oil passage 26 and is switched to an open position 8a or a closed position 8b in response to a control signal from the control device 20. The high-pressure accumulator 7 is also connected to the pilot pump 11 via an oil passage 27. The switching valve 14 is arranged in the oil passage 27 and is switched to an open position 14a or a closed position 14b in response to a control signal from the control device 20. The switching valves 13 and 14 in this embodiment constitute a switching device that can switch the supply destination of the pressurized oil discharged from the pilot pump 11 to either the pilot circuit 12 or the high-pressure accumulator 7.

[0017] Next, the operation of the hydraulic cylinder 5 will be described. When a signal from the operating lever 17 is input, the control device 20 increases the flow rate of the main pump 3 according to the amount of lever operation, and switches at least one of the control valves 6, 9 in a direction according to the direction of lever operation. As a result, pressure oil is supplied from the main pump 3 to one side (bottom side or rod side) of the hydraulic cylinder 5, and pressure oil is discharged from the other side (rod side or bottom side) of the hydraulic cylinder 5 to the hydraulic oil tank 2, causing the hydraulic cylinder 5 to extend or retract.

[0018] Next, we will explain the operation of charging the high-pressure accumulator 7 with the main pump 3. When the control device 20 determines via the pressure sensor 18 that the pressure in the high-pressure accumulator 7 is decreasing, the control device 20 opens the control valve 8 and closes the control valve 10. As a result, the pressurized oil from the main pump 3 is sent to the high-pressure accumulator 7, and the high-pressure accumulator 7 is charged.

[0019] Next, the operation related to the pilot pump 11 will be described. When the control device 20 determines that the pressure in the high-pressure accumulator 7 has dropped and that the pressure in the low-pressure accumulator 15 is sufficient, it closes the switching valve 13 and opens the switching valve 14 to send pressurized oil from the pilot pump 11 to the high-pressure accumulator 7 and charge the high-pressure accumulator 7. This ensures the pressure in the high-pressure accumulator 7 even when the main pump 3 is supplying pressurized oil to the hydraulic cylinder 5 and the main pump 3 is unable to charge the high-pressure accumulator 7. Note that while the pilot pump 11 is charging the high-pressure accumulator 7, the pressure in the pilot circuit 12 is maintained by the low-pressure accumulator 15, so there is no problem in driving the control valves 6, 8 to 10 and the switching valves 13, 14. Furthermore, the charging of the high-pressure accumulator 7 by the pilot pump 11 may be performed while the control valve 8 is opened to supply pressure oil from the main pump 3 to the high-pressure accumulator 7, or while the control valve 9 is opened to supply pressure oil from the high-pressure accumulator 7 to the hydraulic cylinder 5.

[0020] Furthermore, when the control device 20 determines that the pressure in the high-pressure accumulator 7 is sufficient or that the pressure in the low-pressure accumulator 15 is dropping, it closes the selector valve 14 and opens the selector valve 13 to send the pressure oil from the pilot pump 11 to the pilot circuit 12 and charge the low-pressure accumulator 15. This ensures the pressure in the pilot circuit 12 and prevents the pressure in the pilot pump 11 from rising unnecessarily, resulting in excessive consumption of power from the engine 1.

[0021] Fig. 3 is a flow chart showing the processing of the control device 20 in the first embodiment. Note that Fig. 3 shows only the processing related to the control of the switching valves 13 and 14, and omits the processing related to the control of other devices.

[0022] When a key switch (not shown) is operated in the hydraulic excavator 100, the processing of the control device 20 is started (step S101).

[0023] Following step S101, it is determined whether the pressure of the low-pressure accumulator 15 is higher than a predetermined threshold value T2 (step S102). The threshold value T2 is a threshold value for determining whether the pressure of the low-pressure accumulator 15 is sufficient, and is set to a value lower than the relief setting pressure (e.g., 4 MPa) of the pilot relief valve 16 and equal to or higher than the pilot pressure (e.g., 3 MPa) required to drive the control valves 6, 8 to 10 and the switching valves 13, 14.

[0024] If the determination result in step S102 is No, the switching valve 14 is closed and the switching valve 13 is opened (step S103), and the process returns to step S102. As a result, if the pressure in the low-pressure accumulator 15 (= the pressure in the pilot circuit 12) becomes equal to or lower than the threshold value T2 while the high-pressure accumulator 7 is being charged by the pilot pump 11, the supply destination of the pressure oil discharged from the pilot pump 11 is switched from the high-pressure accumulator 7 to the pilot circuit 12, and therefore the pressure in the pilot circuit 12 can be secured.

[0025] If the determination result in step S102 is Yes, it is determined whether the pressure in the high-pressure accumulator 7 is lower than a predetermined threshold T1 (step S104). The threshold T1 is a threshold for determining that the pressure in the high-pressure accumulator 7 is insufficient, and is set to a value approximately equal to the pressure required to drive the hydraulic cylinder 5 (for example, 10 to 15 MPa).

[0026] If the determination result in step S104 is No, the process proceeds to step S103, whereby consumption of the power of the engine 1 due to an unnecessary increase in the pressure of the pilot pump 11 can be prevented.

[0027] If the determination result in step S104 is Yes, the switching valve 13 is closed and the switching valve 14 is opened (step S105), and the process returns to step S101. As a result, when the pressure in the low-pressure accumulator 15 exceeds the threshold value T2 and the pressure in the high-pressure accumulator 7 falls below the threshold value T1, the supply destination of the pressure oil discharged from the pilot pump 11 is switched from the pilot circuit 12 to the high-pressure accumulator 7, so that the high-pressure accumulator 7 can be charged by the pilot pump 11.

[0028] (summary) In the first embodiment, a hydraulic excavator 100 (working machine) includes an engine 1 (prime mover), a hydraulic oil tank 2 for storing hydraulic oil, a main pump 3 driven by the engine 1 and sucking in and discharging hydraulic oil from the hydraulic oil tank 2, a hydraulic cylinder 5 (hydraulic actuator), a control valve 6 for controlling the flow of pressurized oil supplied from the main pump 3 to the hydraulic cylinder 5, a pilot pump 11 driven by the engine 1, a pilot circuit 12 to which the pressurized oil discharged from the pilot pump 11 is supplied and which supplies pilot pressure to the control valve 6, a pilot relief valve 16 provided in an oil passage 25 connecting the pilot circuit 12 and the hydraulic oil tank 2 and which opens when the pressure in the pilot circuit 12 exceeds a predetermined relief set pressure, and a high-pressure accumulator 7 (first accumulator) for storing pressurized oil discharged from the main pump 3. In this hydraulic excavator 100, a pressure sensor 18 (first pressure detection device) is connected to the pilot circuit 12. The relief set pressure detection device includes a low-pressure accumulator 15 (second pressure accumulator) that accumulates pressurized oil discharged from the pilot pump 11, a pressure sensor 19 (second pressure detection device) that detects the pressure of the low-pressure accumulator 15, switching devices 13 and 14 that can switch the supply destination of the pressurized oil discharged from the pilot pump 11 to either the pilot circuit 12 or the high-pressure accumulator 7, and a control device 20 that receives signals from the pressure sensors 18 and 19 and outputs control signals to the switching devices 13 and 14. The control device 20 controls the switching devices 13 and 14 so that the supply destination of the pressurized oil discharged from the pilot pump 11 is switched from the pilot circuit 12 to the high-pressure accumulator 7 when the pressure of the high-pressure accumulator 7 detected by the pressure sensor 18 is lower than a threshold value T1 (first threshold value) that is set higher than the relief set pressure and when the pressure of the low-pressure accumulator 15 detected by the pressure sensor 19 is higher than a threshold value T2 (second threshold value) that is set lower than the relief set pressure.

[0029] According to the first embodiment configured as described above, even when the main pump 3 cannot charge the high-pressure accumulator 7, pressure oil can be supplied from the pilot pump 11 to the high-pressure accumulator 7, making it possible to ensure the pressure in the high-pressure accumulator 7. As a result, the frequency and time for which the high-pressure accumulator 7 is charged by the main pump 3 are reduced, thereby improving the efficiency of the hydraulic excavator 100.

[0030] In the first embodiment, the switching devices 13, 14 include a switching valve 13 (first switching valve) that is arranged in an oil passage 24 (first oil passage) connecting the pilot pump 11 and the pilot circuit 12 and that switches to either an open position 13a that allows the flow of pressure oil through the oil passage 24 or a closed position 13b that prohibits the flow of pressure oil through the oil passage 24 in response to a control signal from the control device 20, and a switching valve 14 (second switching valve) that is arranged in an oil passage 27 (second oil passage) connecting the pilot pump 11 and the high-pressure accumulator 7 (first pressure accumulator) and that switches to either an open position 14a that allows the flow of pressure oil through the oil passage 27 or a closed position 14b that prohibits the flow of pressure oil through the oil passage 27 in response to a control signal from the control device 20. This makes it possible to configure the switching devices 13, 14 with the switching valves 13, 14. [Example]

[0031] The second embodiment of the present invention will be described, focusing on the differences from the first embodiment.

[0032] FIG. 4 is a hydraulic circuit diagram of a hydraulic drive system 200 according to a second embodiment. The hydraulic drive system 200 according to this embodiment includes a two-position, three-port switching valve 28 instead of the switching valves 13 and 14 (shown in FIG. 2). The switching valve 28 is switched, in response to a control signal from the control device 20, to either a first position 28a that allows the flow of pressure oil between the pilot pump 11 and the pilot circuit 12 and prohibits the flow of pressure oil between the pilot pump 11 and the high-pressure accumulator 7, or a second position 28b that allows the flow of pressure oil between the pilot pump 11 and the high-pressure accumulator 7 and prohibits the flow of pressure oil between the pilot pump 11 and the pilot circuit 12. The switching valve 28 according to this embodiment constitutes a switching device that can switch the supply destination of pressure oil discharged from the pilot pump 11 to either the pilot circuit 12 or the high-pressure accumulator 7.

[0033] Fig. 5 is a flow chart showing the processing of the control device 20 in the second embodiment. In Fig. 5, the control device 20 executes steps S103A and S105A instead of steps S103 and S105 (shown in Fig. 3).

[0034] In step S103A, the switching valve 28 is switched to the first position 28a. As a result, when the pressure in the low-pressure accumulator 15 becomes equal to or lower than the threshold value T2 or when the pressure in the high-pressure accumulator 7 becomes equal to or higher than the threshold value T1, the supply destination of the pressure oil discharged from the pilot pump 11 is switched from the high-pressure accumulator 7 to the pilot circuit 12.

[0035] In step S105A, the switching valve 28 is switched to the second position 28b. As a result, when the pressure in the low-pressure accumulator 15 exceeds the threshold value T2 and the pressure in the high-pressure accumulator 7 falls below the threshold value T1, the supply destination of the pressure oil discharged from the pilot pump 11 is switched from the pilot circuit 12 to the high-pressure accumulator 7.

[0036] (summary) In the second embodiment, the switching devices 13, 29, which can switch the supply destination of the pressurized oil discharged from the pilot pump 11 to either the pilot circuit 12 or the high-pressure accumulator 7 (first pressure accumulator), have a switching valve 28 that switches, in response to a control signal from the control device 20, to either a first position 28a that allows the flow of pressurized oil between the pilot pump 11 and the pilot circuit 12 and prohibits the flow of pressurized oil between the pilot pump 11 and the high-pressure accumulator 7, or a second position 28b that allows the flow of pressurized oil between the pilot pump 11 and the high-pressure accumulator 7 and prohibits the flow of pressurized oil between the pilot pump 11 and the pilot circuit 12.

[0037] In the second embodiment configured as described above, similarly to the first embodiment, even when the main pump 3 cannot charge the high-pressure accumulator 7, pressure oil can be supplied from the pilot pump 11 to the high-pressure accumulator 7, making it possible to ensure the pressure in the high-pressure accumulator 7. Furthermore, by replacing the switching valves 13, 14 (shown in FIG. 2) in the first embodiment with a single switching valve 28, the circuit configuration of the hydraulic drive system 200 and the control of the control device 20 are simplified. [Example]

[0038] The third embodiment of the present invention will be described, focusing on the differences from the first embodiment.

[0039] 6 is a hydraulic circuit diagram of a hydraulic drive system 200 in a third embodiment. The hydraulic drive system 200 in this embodiment is provided with a check valve 29 instead of the switching valve 14 (shown in FIG. 2). The check valve 29 allows the flow of pressure oil from the pilot pump 11 to the high-pressure accumulator 7, and prohibits the flow of pressure oil from the high-pressure accumulator 7 to the pilot pump 11. The switching valve 13 and the check valve 29 in this embodiment constitute a switching device that can switch the supply destination of pressure oil discharged from the pilot pump 11 to either the pilot circuit 12 or the high-pressure accumulator 7.

[0040] Fig. 7 is a flow chart showing the processing of the control device 20 in the third embodiment. In Fig. 7, the control device 20 executes steps S103B and S105B instead of steps S103 and S105 (shown in Fig. 3).

[0041] In step S103B, the switching valve 13 is opened. As a result, when the pressure in the low-pressure accumulator 15 becomes equal to or lower than the threshold value T2, or when the pressure in the high-pressure accumulator 7 becomes equal to or higher than the threshold value T1, the supply destination of the pressure oil discharged from the pilot pump 11 is switched from the high-pressure accumulator 7 to the pilot circuit 12.

[0042] In step S105B, the switching valve 13 is closed. As a result, when the pressure in the low-pressure accumulator 15 exceeds the threshold value T2 and the pressure in the high-pressure accumulator 7 falls below the threshold value T1, the supply destination of the pressure oil discharged from the pilot pump 11 is switched from the pilot circuit 12 to the high-pressure accumulator 7.

[0043] (summary) In the third embodiment, a switching device 13, 29 capable of switching the supply destination of pressurized oil discharged from a pilot pump 11 to either a pilot circuit 12 or a high-pressure accumulator 7 (first pressure accumulator) is arranged in an oil passage 24 (first oil passage) connecting the pilot pump 11 and the pilot circuit 12, and has a switching valve 13 that switches to either an open position 13a that allows the flow of pressurized oil in the oil passage 24 or a closed position 13b that prohibits the flow of pressurized oil in the oil passage 24 in response to a control signal from a control device 20, and a check valve 29 that is arranged in an oil passage 27 (second oil passage) connecting the pilot pump 11 and the high-pressure accumulator 7, and allows the flow of pressurized oil from the pilot pump 11 to the high-pressure accumulator 7 and prohibits the flow of pressurized oil from the high-pressure accumulator 7 to the pilot pump 11.

[0044] In the third embodiment configured as described above, similarly to the first embodiment, even when the main pump 3 cannot charge the high-pressure accumulator 7, pressure oil can be supplied from the pilot pump 11 to the high-pressure accumulator 7, making it possible to ensure the pressure in the high-pressure accumulator 7. Furthermore, by replacing the switching valve 14 (shown in FIG. 2) in the first embodiment with a check valve 29 that does not need to be controlled by the control device 20, the circuit configuration of the hydraulic drive system 200 and the control by the control device 20 are simplified.

[0045] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments are presented to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0046] 1... engine (prime mover), 2... hydraulic oil tank, 3... main pump, 4... pump regulator, 5... hydraulic cylinder (hydraulic actuator), 6... control valve, 7... high-pressure accumulator (first pressure accumulator), 8... control valve, 8a... open position, 8b... closed position, 9, 10... control valve, 11... pilot pump, 12... pilot circuit, 13... switching valve (switching device), 13a... open position, 13b... closed position, 14... switching valve (switching device), 14a... open position, 14b... closed position, 15... low-pressure accumulator (second pressure accumulator), 16... pilot relief valve, 17... operation lever, 18... pressure sensor (first pressure detection device), 19... pressure sensor (second pressure detection device ), 20...control device, 21...center bypass oil passage, 22, 23...oil passage, 24...oil passage (first oil passage), 25, 26...oil passage, 27...oil passage (second oil passage), 28...switching valve (switching device), 28a...first position, 28b...second position, 29...check valve (switching device), 100...hydraulic excavator, 101...lower traveling body, 102...upper rotating body, 103...working device, 104...traveling motor (hydraulic actuator), 105...boom, 106...arm, 107...bucket, 108...boom cylinder (hydraulic actuator), 109...arm cylinder (hydraulic actuator), 110...bucket cylinder (hydraulic actuator), 200...hydraulic drive unit.

Claims

1. The prime mover and a hydraulic oil tank for storing hydraulic oil; a main pump driven by the prime mover, which draws hydraulic oil from the hydraulic oil tank and discharges it; A hydraulic actuator; a control valve for controlling the flow of pressure oil supplied from the main pump to the hydraulic actuator; a pilot pump driven by the prime mover; a pilot circuit to which pressure oil discharged from the pilot pump is supplied and which supplies a pilot pressure to the control valve; a pilot relief valve that is provided in an oil passage connecting the pilot circuit and the hydraulic oil tank and that opens when the pressure in the pilot circuit exceeds a predetermined relief set pressure; a first accumulator that accumulates pressure oil discharged from the main pump, a first pressure detection device that detects the pressure of the first pressure accumulator; a second accumulator connected to the pilot circuit and configured to accumulate pressure oil discharged from the pilot pump; a second pressure detection device that detects the pressure of the second pressure accumulator; a switching device that switches a supply destination of the pressure oil discharged from the pilot pump to either the pilot circuit or the first pressure accumulator; a control device that receives signals from the first pressure detection device and the second pressure detection device and outputs a control signal to the switching device, The control device controls the switching device so that a supply destination of the pressure oil discharged from the pilot pump is switched from the pilot circuit to the first accumulator when the pressure of the first accumulator detected by the first pressure detection device is lower than a first threshold value set higher than the set relief pressure and when the pressure of the second accumulator detected by the second pressure detection device is higher than a second threshold value set lower than the set relief pressure. A work machine characterized by:

2. A work machine according to claim 1. The switching device is a first switching valve that is disposed in a first oil passage connecting the pilot pump and the pilot circuit, and that switches between an open position that allows the flow of pressure oil through the first oil passage and a closed position that prohibits the flow of pressure oil through the first oil passage in response to a control signal from the control device; a second switching valve that is arranged in a second oil passage connecting the pilot pump and the first pressure accumulator and that switches between an open position that allows the flow of pressure oil through the second oil passage and a closed position that prohibits the flow of pressure oil through the second oil passage in response to a control signal from the control device; A work machine characterized by:

3. A work machine according to claim 1. The switching device has a switching valve that switches, in response to a control signal from the control device, to either a first position that allows the flow of pressure oil between the pilot pump and the pilot circuit and prohibits the flow of pressure oil between the pilot pump and the first pressure accumulator, or a second position that allows the flow of pressure oil between the pilot pump and the first pressure accumulator and prohibits the flow of pressure oil between the pilot pump and the pilot circuit. A work machine characterized by:

4. A work machine according to claim 1. The switching device is a switching valve that is disposed in a first oil passage connecting the pilot pump and the pilot circuit, and that switches between an open position that allows the flow of pressure oil through the first oil passage and a closed position that prohibits the flow of pressure oil through the first oil passage in response to a control signal from the control device; a check valve that is disposed in a second oil passage that connects the pilot pump and the first pressure accumulator, and that allows a flow of pressure oil from the pilot pump toward the first pressure accumulator and prohibits a flow of pressure oil from the first pressure accumulator toward the pilot pump. A work machine characterized by:

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