Work machine and method for driving hydraulic breaker in work machine

Abstract

Provided is a work machine comprising: a hydraulic breaker (431) that is used as a tip attachment; a breaker drive line (LB) that supplies hydraulic fluid discharged from a second hydraulic pump (52) to the hydraulic breaker (431) and returns the hydraulic fluid to a tank (50) without passing the hydraulic fluid through a cooler (54); a merging line (LC) that merges first hydraulic fluid discharged from a first hydraulic pump (51) with second hydraulic fluid flowing through the breaker drive line (LB); a first hydraulic fluid cooling line (LU1) that passes the first hydraulic fluid through the cooler (54) and then returns the first hydraulic fluid to the tank (50); switching units (60, 61) that switch the line, through which the first hydraulic fluid flows, between the merging line (LB) and the first hydraulic fluid cooling line (LU1); and a controller (80) that controls the switching of the line by the switching units (60, 61) on the basis of a first hydraulic fluid cooling condition.

Description

Working machine and method for driving a hydraulic breaker in a working machine

[0001] The present invention relates to a working machine and a method for driving a hydraulic breaker in the working machine.

[0002] In a working machine such as an excavator, a hydraulic breaker may be used as its tip attachment. The hydraulic breaker is used for work such as crushing rocks, etc., and depending on the work, a large output may be required for the hydraulic breaker.

[0003] On the other hand, in the working machine, as described in Patent Document 1, it is required to cool the hydraulic oil to suppress the temperature rise of the hydraulic oil. [[ID=ll]]

[0004] Japanese Patent Application Laid-Open No. 2014-101940

[0005] As a means for increasing the output of the hydraulic breaker, the inventors have come up with the idea of combining the hydraulic oil from two hydraulic pumps and supplying it to the breaker. However, this may be accompanied by a significant increase in the hydraulic oil temperature. Specifically, if a cooler such as an oil cooler is provided in the return oil passage from the hydraulic breaker to the tank, there is a risk that the cooler will be damaged due to the significant pulsation of the hydraulic oil caused by the driving of the hydraulic breaker. Therefore, it is desirable that the hydraulic oil discharged from the hydraulic breaker returns to the tank without passing through the oil cooler. Therefore, supplying the hydraulic oil discharged from the two hydraulic pumps and merged to the hydraulic breaker makes it impossible for any of the hydraulic oil discharged from the two hydraulic pumps to pass through the oil cooler. This, regardless of the improvement in the capacity of the cooling fan (such as an oil cooler) as described in Patent Document 1, prevents the capacity from contributing to the cooling of the hydraulic oil, thereby potentially significantly increasing the temperature of the hydraulic oil.

[0006] An object of the present invention is to provide a working machine equipped with a hydraulic breaker, which can increase the output of the hydraulic breaker while avoiding a significant increase in the temperature of the hydraulic oil.

[0007] Provided is a work machine, the work machine comprising a lower traveling body, an upper rotating body rotatably mounted on the lower traveling body, a work arm connected to the upper rotating body, and a tip attachment attached to the tip of the work arm, wherein a hydraulic breaker capable of being driven by hydraulics can be attached to the work arm as the tip attachment, a tank for storing hydraulic fluid, a cooler that allows hydraulic fluid to pass through and cools the hydraulic fluid passing through, a first hydraulic pump for discharging the hydraulic fluid from the tank, a second hydraulic pump for discharging the hydraulic fluid from the tank, and a second hydraulic fluid, which is the hydraulic fluid discharged from the second hydraulic pump, attached to the work arm as the tip attachment. The system includes: a breaker drive line that guides the second hydraulic fluid to be supplied to the attached hydraulic breaker and to return to the tank without passing through the cooler; a confluence line that guides the first hydraulic fluid, which is hydraulic fluid discharged from the first hydraulic pump, to merge with the second hydraulic fluid flowing through the breaker drive line and to be supplied to the hydraulic breaker together with the second hydraulic fluid; a first hydraulic fluid cooling line that guides the first hydraulic fluid to be cooled by passing through the cooler without passing through the hydraulic breaker and then to return to the tank; a switching unit that switches the line through which the first hydraulic fluid flows between the confluence line and the first hydraulic fluid cooling line; and a controller. The controller controls the switching of the line by the switching unit so that when the operating state of the work machine meets a predetermined first hydraulic fluid cooling condition, the line through which the first hydraulic fluid flows becomes the first hydraulic fluid cooling line, and when the operating state of the work machine does not meet the first hydraulic fluid cooling condition, the line through which the first hydraulic fluid flows becomes the confluence line.

[0008] Also provided is a method for hydraulically driving a hydraulic breaker used as an end attachment in a work machine. The method includes: discharging hydraulic fluid from a first hydraulic pump and a second hydraulic pump, respectively; guiding the hydraulic fluid discharged from the second hydraulic pump to the hydraulic breaker to drive the hydraulic breaker; returning the hydraulic fluid discharged from the hydraulic breaker to a tank without passing it through a cooler; when the operating state of the work machine corresponds to a predetermined first hydraulic fluid cooling condition, passing the first hydraulic fluid, which is the hydraulic fluid discharged from the first hydraulic pump, through a cooler without passing it through the hydraulic breaker to cool the first hydraulic fluid before returning it to the tank; and when the operating state does not correspond to the cooling condition, merging the first hydraulic fluid with the second hydraulic fluid, which is the hydraulic fluid discharged from the second hydraulic pump and supplied to the hydraulic breaker, so that the first hydraulic fluid is supplied to the hydraulic breaker together with the second hydraulic fluid.

[0009] This is a side view of a work machine according to an embodiment of the present invention. This diagram shows the first hydraulic oil cooling line of a hydraulic circuit according to an embodiment of the present invention, indicated by a thick line. This diagram shows the breaker drive line of the hydraulic circuit, indicated by a thick line. This diagram shows the second hydraulic oil cooling line of the hydraulic circuit, indicated by a thick line. This is a flowchart showing the control performed by the controller when a hydraulic breaker is used in the first embodiment of the present invention. This diagram shows the oil passage through which hydraulic oil flows in the standby state of the hydraulic circuit, indicated by a thick line. This diagram shows the lines through which the first and second hydraulic oils flow when combined supply control is performed in the hydraulic circuit, indicated by a thick line. This diagram shows the lines through which the first and second hydraulic oils flow when single-flow supply control is performed in the hydraulic circuit, indicated by a thick line. This is a flowchart showing the control performed by the controller according to the second embodiment of the present invention. This is a flowchart showing the control performed by the controller according to the third embodiment of the present invention. This is a flowchart showing the control performed by the controller according to the fourth embodiment of the present invention. This is a flowchart showing the control performed by the controller according to the fifth embodiment of the present invention.

[0010] Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as "embodiments") will be described in detail with reference to the attached drawings.

[0011] Figure 1 is a side view of a work machine 100 according to each of the embodiments described below. The work machine 100 comprises a crawler-type lower traveling body 10, an upper rotating body 30 rotatably mounted on the lower traveling body 10, and a work device 40 connected to the upper rotating body 30 in a manner that allows for luffing and unluffing.

[0012] The upper rotating body 30 includes a rotating frame 34, an operator's cab 31, and a machine room 32. The rotating frame 34 is positioned above the lower traveling body 10 and is connected to the lower traveling body 10 via a rotating section 20 so as to be able to rotate relative to the lower traveling body 10. The operator's cab 31 is positioned on the front portion of the rotating frame 34 and defines an operating space in which an operator can sit. An operating unit (not shown) is located in the operating space and controls for operating the work machine 100 are provided to the operating unit. The machine room 32 is positioned on the rear portion of the rotating frame 34 and houses the power source 36 and hydraulic circuit shown in Figure 2.

[0013] The working device 40 includes a boom 41, an arm 42, and a tip attachment 43, the boom 41 and the arm 42 constituting a working arm. The boom 41 has a boom base end and a boom tip end, and the boom base end is connected to the slewing frame 34 of the upper slewing body 30 so that the boom 41 can perform luffing movements relative to the upper slewing body 30. The arm 42 has an arm base end and an arm tip end, and the arm base end is connected to the boom tip end so that the arm 42 can rotate relative to the boom 41. The tip attachment 43 is rotatably and detachably attached to the tip of the arm.

[0014] Multiple work tools are selectively, i.e., detachably attached to the tip of the work arm, in this embodiment, the arm tip, as the tip attachment 43, and the multiple work tools include the hydraulic breaker 431 shown in Figure 1. That is, the hydraulic breaker 431 can be attached to the tip of the work arm, in this embodiment, the arm tip, as the tip attachment 43 and used.

[0015] The hydraulic breaker 431 is driven by the supply of hydraulic fluid to the hydraulic breaker 431, thereby performing an action to crush the object. The hydraulic breaker 431 illustrated in Figure 2 includes a piston that moves back and forth for the purpose of crushing, and this reciprocating motion generates pulsation in the hydraulic fluid discharged from the hydraulic breaker 431.

[0016] The work machine 100 includes a plurality of hydraulic actuators for moving the work device 40, specifically a plurality of hydraulic cylinders, each of which is extendable and retractable, and the plurality of hydraulic cylinders include a boom cylinder 41A, an arm cylinder 42A, and a tip attachment cylinder 43A. The boom cylinder 41A extends and retracts to cause the boom 41 to perform the luffing motion relative to the upper slewing body 30. The arm cylinder 42A extends and retracts to cause the arm 42 to rotate relative to the boom 41. The tip attachment cylinder 43A extends and retracts to cause the tip attachment 43 (or the hydraulic breaker 431 if the hydraulic breaker 431 is attached to the tip of the arm) to rotate relative to the arm 42.

[0017] Figure 2 shows the hydraulic circuit included in the work machine 100. The hydraulic circuit includes a tank 50, a first hydraulic pump 51, a second hydraulic pump 52, an oil cooler 54, a breaker switching valve 56, a confluence switching valve 60, a first unload valve 61, and a second unload valve 62.

[0018] The tank 50 is mounted on the upper rotating body 30 and stores hydraulic fluid for driving each of the multiple actuators, including the hydraulic breaker.

[0019] The first hydraulic pump 51 and the second hydraulic pump 52 are mounted on the upper rotating body 30 and connected to the power source 36. Each of the first and second hydraulic pumps is driven by power generated by the power source 36, thereby drawing in and discharging hydraulic fluid from the tank 50. The first and second hydraulic pumps 51 and 52, as illustrated in Figures 2 to 4 and Figures 6 to 8, are each composed of variable displacement hydraulic pumps.

[0020] The power source 36 is, for example, an internal combustion engine or a motor. The power source 36 only needs to generate power to drive the first and second hydraulic pumps 51 and 52, respectively.

[0021] The oil cooler 54 is a cooler for cooling the hydraulic fluid. Specifically, the oil cooler 54 is installed in the middle of the tank line connected to the tank 50, allowing the hydraulic fluid to be returned to the tank 50 through the oil cooler 54, and cooling the hydraulic fluid as it passes through the oil cooler 54. The specific configuration of the oil cooler 54 is not limited. The oil cooler 54 is, for example, composed of a heat exchanger that causes heat exchange between the hydraulic fluid and a cooling medium. The cooling medium may be cooling air supplied from a cooling fan or the like, or a cooling liquid such as water.

[0022] The hydraulic circuit includes a plurality of lines through which the hydraulic fluid discharged from the first and second hydraulic pumps 51 and 52 can flow. The plurality of lines include a breaker drive line LB, a first actuator drive line LA1, a second actuator drive line LA2, a merging line LC, a first unload line LU1, and a second unload line LU2. Each of the plurality of lines is composed of piping members and the like that surround a flow path space through which the hydraulic fluid can flow.

[0023] The breaker drive line LB guides the second hydraulic fluid discharged from the second hydraulic pump 52 to the hydraulic breaker 431 and returns to the tank 50 without passing through the oil cooler 54, as shown by the thick line in Figure 3 when the hydraulic breaker 431 is in use.

[0024] The breaker switching valve 56 is installed in the middle of the breaker drive line LB. The breaker switching valve 56 switches the part to which hydraulic fluid is supplied in the breaker 431 between the head chamber and the rod chamber, which are defined on both sides of the piston, respectively. As a result, the piston is driven back and forth, and the hydraulic breaker 431 performs a crushing operation.

[0025] The first actuator drive line LA1 guides the first hydraulic fluid discharged from the first hydraulic pump 51 so that it is supplied to at least one first hydraulic actuator other than the hydraulic breaker, cooled by passing through the oil cooler 54, and then returned to the tank 50. Similarly, the second actuator drive line LA2 guides the second hydraulic fluid discharged from the second hydraulic pump 52 so that it is supplied to at least one second hydraulic actuator other than the hydraulic breaker, cooled by passing through the oil cooler 54, and then returned to the tank 50.

[0026] Examples of the first and second hydraulic actuators, i.e., hydraulic actuators other than the hydraulic breaker 431, include a pair of travel motors which are a pair of hydraulic motors for causing the lower travel body 10 to perform a travel operation, a hydraulic motor for rotating the upper slewing body 30, the boom cylinder 41A, the arm cylinder 42A, and the tip attachment cylinder 43A.

[0027] The confluence line LC guides the first hydraulic fluid discharged from the first hydraulic pump 51 to merge with the second hydraulic fluid flowing through the breaker drive line LB and to be supplied together with the second hydraulic fluid to the hydraulic breaker 431. The confluence line LC illustrated in Figure 3 is connected to the breaker drive line LB such that the second hydraulic fluid merges with the first hydraulic fluid at a position upstream of the breaker switching valve 56 in the breaker drive line LB.

[0028] As shown by the thick line in Figure 2, the first unload line LU1 guides the first hydraulic fluid discharged from the first hydraulic pump 51 so that it passes through the oil cooler 54 without passing through the hydraulic breaker 431 (i.e., bypassing the hydraulic breaker 431) and is cooled before returning to the tank 50. In other words, the first unload line LU1 functions as a first hydraulic fluid cooling line for cooling the first hydraulic fluid.

[0029] As shown by the thick line in Figure 4, the second unload line LU2 guides the second hydraulic fluid discharged from the second hydraulic pump 52 so that it passes through the oil cooler 54 without passing through the hydraulic breaker 431 (i.e., bypassing the hydraulic breaker 431) and is cooled before returning to the tank 50. In other words, the second unload line LU2 functions as a second hydraulic fluid cooling line for cooling the second hydraulic fluid discharged from the second hydraulic pump 52.

[0030] The confluence switching valve 60 and the first unloading valve 61 constitute a switching unit that switches the line through which the first hydraulic fluid discharged from the first hydraulic pump 51 flows.

[0031] The confluence switching valve 60 is installed in the middle of the confluence line LC and can be switched between a confluence-allowed position and a confluence-blocking position. In the confluence-allowed position, the confluence switching valve 60 opens the confluence line LC, allowing the first hydraulic fluid discharged from the first hydraulic pump 51 to pass through the confluence line LC and merge with the second hydraulic fluid flowing through the breaker drive line LB, as shown by the thick line in Figure 7. In the confluence-blocking position, the confluence switching valve 60 shuts off the confluence line LC, preventing the first hydraulic fluid from merging with the second hydraulic fluid.

[0032] The first unload valve 61 is located in the middle of the first unload line LU1 and is switchable between a first unload position and a first unload blocking position. In the first unload position, the first unload valve 61 opens the first unload line LU1, thereby allowing the first hydraulic fluid discharged from the first hydraulic pump 51 to be returned directly to the tank 50 through the first unload line LU1, as shown by the thick lines in Figures 2 and 8. That is, it is cooled by passing through the oil cooler 54 without passing through the hydraulic breaker 431 before returning to the tank 50. In the first unload blocking position, the first unload valve 61 blocks the first unload line LU1, preventing the first hydraulic fluid from flowing through the first unload line LU1.

[0033] By switching the positions of the confluence switching valve 60 and the first unload valve 61, which constitute the switching unit, the line through which the first hydraulic fluid flows is selectively switched. Specifically, when the confluence switching valve 60 is switched to the confluence-allowing position and the first unload valve 61 is switched to the first unload-blocking position, the first hydraulic fluid is allowed to flow through the first actuator drive line LA1 and the confluence line LC, thereby allowing it to be supplied to the first actuator and to confluence with the second hydraulic fluid in the breaker drive line LB through the confluence line LC. Conversely, when the confluence switching valve 60 is switched to the confluence-blocking position and the first unload valve 61 is switched to the first unload position, the first hydraulic fluid is allowed to be cooled through the oil cooler 54 without passing through the hydraulic breaker 431, and then returned to the tank 50. Furthermore, when the confluence switching valve 60 is switched to the confluence blocking position and the first unload valve 61 is switched to the first unload blocking position, the first hydraulic fluid is allowed to flow to the first actuator drive line LA1 without passing through either the confluence line LC or the first unload line LU1, and return to the tank 50 through the oil cooler 54.

[0034] On the other hand, the second unload valve 62 is provided in the middle of the second unload line LU2 and can be switched between a second unload position and a second unload blocking position. In the second unload position, the second unload valve 62 opens the second unload line LU2, allowing the second hydraulic fluid discharged from the second hydraulic pump 52 to be returned directly to the tank 50 through the second unload line LU2, as shown by the thick line in Figure 4. That is, it is cooled by passing through the oil cooler 54 without passing through the hydraulic breaker 431 before returning to the tank 50. In the second unload blocking position, the second unload valve 62 blocks the second unload line LU2, preventing the second hydraulic fluid from flowing through the second unload line LU2.

[0035] In other words, the second unload valve 62 constitutes a switching unit for the second hydraulic pump 52 that switches the line through which the hydraulic fluid discharged from the second hydraulic pump 52 flows. Specifically, when the second unload valve 62 is switched to the second unload blocking position, the second hydraulic fluid is allowed to flow through the second actuator drive line LA2 and the hydraulic breaker drive line LB. On the other hand, when the second unload valve 62 is switched to the second unload position, the second hydraulic fluid is allowed to be cooled by passing through the second unload line LU2 before returning to the tank 50.

[0036] Each of the illustrated breaker switching valve 56, the merging switching valve 60, the first unloading valve 61, and the second unloading valve 62 is an electromagnetic switching valve having a solenoid, and is switched to a position corresponding to a switching command signal input to the solenoid from the controller 80. Each of the valves 56, 60-62 may also be a pilot-operated hydraulic switching valve having a pilot port and being switched to a position corresponding to the pilot pressure input to the pilot port. In this case, preferably, an electromagnetic valve that converts an electrical signal output from the controller 80 into the pilot pressure is attached to each of the valves 56, 60-62.

[0037] The aforementioned work machine 100 further includes a breaker operator 66 shown in Figures 2 to 4 and Figures 6 to 8, a plurality of detectors, a controller 80, and a display device (not shown).

[0038] The breaker operator 66 is located in the operator's cab 31 and allows breaker operations to be performed on the breaker operator 66 to operate the hydraulic breaker 432. The breaker operator 66 generates an operation signal corresponding to the breaker operation and inputs it to the controller 80.

[0039] The plurality of detectors include a temperature sensor 70, a first pump pressure sensor 71, and a second pump pressure sensor 72.

[0040] The temperature sensor 70 generates a temperature detection signal corresponding to the temperature of the hydraulic fluid in the tank 50 and inputs it to the controller 80, and functions as a temperature measuring unit that measures the temperature value corresponding to the temperature of the hydraulic fluid in the tank 50.

[0041] The first pump pressure sensor 71 detects the first pump pressure, which is the pressure of the hydraulic fluid discharged from the first hydraulic pump 51. Similarly, the second pump pressure sensor 72 detects the second pump pressure, which is the pressure of the hydraulic fluid discharged from the second hydraulic pump 52. The first and second pump pressure sensors 71 and 72 each generate pump pressure detection signals corresponding to the first and second pump pressures and input them to the controller 80. The first and second pump pressure sensors 71 and 72 are arranged, for example, in the machine room 32.

[0042] The controller 80 controls the switching of the line by the switching unit, thereby controlling the flow of the first and second hydraulic oils discharged from the first and second hydraulic pumps 51 and 52 respectively. Specifically, the controller 80 switches the positions of the merging switching valve 60 and the first and second unloading valves 61 and 62 based on the operation signal and the detection signal input from the breaker operator 66 and the plurality of detectors respectively. Further, the controller 80 inputs a capacity command signal to each of the first and second hydraulic pumps 51 and 52, thereby controlling the pump capacity of each of the first and second hydraulic pumps 51 and 52.

[0043] The controller 80 is constituted by, for example, a computer including a storage unit and an arithmetic unit, and the functions of the controller 80 are realized by the program stored in the storage unit being executed by the arithmetic unit. The program includes conditions for executing the control. The storage unit may be configured independently of the controller 80.

[0044] The display device is provided in the cab 31 and displays information corresponding to the signal input from the controller 80 to the operator.

[0045] Next, the control operation performed by the controller 80 when the hydraulic breaker 431 is used will be described while referring to the flowchart of FIG. 5.

[0046] The control operation starts in the standby state. The standby state is a state in which, for example, the driving of the first hydraulic pump 51 and the second hydraulic pump 52 has been started by an operation of turning on the key, but the driving of all hydraulic actuators including the hydraulic breaker 431, the first hydraulic actuator, and the second hydraulic actuator has not been performed. In the standby state, the controller 80 sets the capacities of the first hydraulic pump 51 and the second hydraulic pump 52 to the minimum capacities.

[0047] Generally, when the hydraulic breaker 431 is in operation, other hydraulic actuators are not driven. Therefore, in the standby state immediately before the hydraulic breaker 431 is driven, the flow rate of the hydraulic oil discharged from the first and second hydraulic pumps 51, 52 is minimized.

[0048] In the standby state, the controller 80 sets the line through which the first hydraulic oil flows to the first unloading line LU1 and the line through which the second hydraulic oil flows to the second unloading line LU2. Specifically, as shown by the thick line in FIG. 6, the controller 80 sets the confluence switching valve 60 to the confluence blocking position and the first unloading valve 61 to the first unloading position so that the first hydraulic oil discharged from the first hydraulic pump 51 flows through the first unloading line LU1, and sets the second unloading valve 62 to the second unloading position so that the second hydraulic oil discharged from the second hydraulic pump 52 flows through the second unloading line LU2, and controls the switching of the lines. Therefore, the hydraulic oil discharged from the first and second hydraulic pumps 51, 52 both returns to the tank 50 through the oil cooler 54 without passing through either the hydraulic breaker 431 or other hydraulic actuators. That is, in the standby state, the hydraulic oil discharged from the first and second hydraulic pumps 52 flows through the first and second unloading lines LU1, LU2 at a small flow rate respectively, passes through the oil cooler 54, and then returns to the tank 50.

[0049] When a breaker drive operation, which is an operation to drive the hydraulic breaker 431 by an operator in the standby state, is given to the breaker actuator 66 (YES in step S10), the controller 80 increases the capacity of the first and second hydraulic pumps 51 and 52 to secure the output required to drive the hydraulic breaker 431, and performs merged supply control on the flow of hydraulic fluid discharged from the first and second hydraulic pumps 51 and 52 (step S11). As shown by the thick line in Figure 7, the merged supply control allows the second hydraulic fluid discharged from the second hydraulic pump 52 to flow through the breaker drive line LB, and also allows the first hydraulic fluid discharged from the first hydraulic pump 51 to merge with the second hydraulic fluid flowing through the breaker drive line LB and be supplied to the hydraulic breaker 431 together with the second hydraulic fluid.

[0050] Specifically, the controller 80 switches the second unload valve 62 to the second unload blocking position to allow the second hydraulic fluid to flow through the breaker drive line LB, and switches the confluence switching valve 60 and the first unload valve 61 to the confluence allowing position and the first unload blocking position, respectively, to allow the first hydraulic fluid discharged from the first hydraulic pump 51 to merge with the second hydraulic fluid flowing through the breaker drive line LB. As a result, the flow rate of the hydraulic fluid supplied to the hydraulic breaker 431 becomes the sum of the flow rates of the first hydraulic fluid and the second hydraulic fluid, and the output of the hydraulic breaker 431 is increased by the amount of the confluence of the first hydraulic fluid compared to when only the second hydraulic fluid is supplied to the hydraulic breaker 431.

[0051] On the other hand, in the combined supply control, both the first and second hydraulic fluids are returned to the tank 50 without passing through the oil cooler 54, so the hydraulic fluids are not cooled by the oil cooler 54. This causes the temperature of the hydraulic fluids in the tank 50 to rise.

[0052] The controller 80 monitors the tank temperature, which is the temperature of the hydraulic fluid in the tank 50 detected by the temperature sensor 70. As long as the tank temperature is below a predetermined temperature threshold (specifically stored in the memory unit) (YES in step S12), the controller 80 continues the current combined supply control (NO in step S13). Conversely, if the tank temperature rises and exceeds the temperature threshold, which is a first hydraulic fluid cooling condition (NO in step S12), the controller 80 performs single-flow supply control, setting the line through which the first hydraulic fluid discharged from the first hydraulic pump 51 flows to the first unload line LU1, so that the hydraulic breaker 432 is driven only by the second hydraulic fluid (step S14). Specifically, the controller 80 switches the confluence switching valve 60 from the confluence-allowed position to the confluence-blocking position and switches the first unload valve 61 from the first unload-blocking position to the first unload position, thereby directing the first hydraulic fluid discharged from the first hydraulic pump 51 to the first unload line LU1, so that only the second hydraulic fluid is supplied to the hydraulic breaker 432. As a result, the output of the hydraulic breaker 431 decreases, but the first hydraulic fluid can be cooled by passing through the oil cooler 54 before returning to the tank 50. This suppresses the rise in temperature inside the tank, making it possible to continue operations without stopping the hydraulic breaker 431.

[0053] Meanwhile, the controller 80 inputs a display command signal to the display device, causing the display device to show that the line through which the first hydraulic fluid flows has switched from the merging line LC to the first unload line (first hydraulic fluid cooling line) LU1. This display allows the operator of the work machine 100 to recognize that although the output of the hydraulic breaker 431 has decreased, the first hydraulic fluid is being cooled.

[0054] The switching of the line from the merging line LC to the first unload line LU1 is for the purpose of cooling the first hydraulic fluid, and therefore it is preferable to increase the flow rate of the hydraulic fluid discharged from the first hydraulic pump 51 to pass more hydraulic fluid through the oil cooler 54. Accordingly, it is preferable that the controller 80 is configured to perform flow rate increase control in the single-flow supply control so that the flow rate of the hydraulic fluid discharged from the first hydraulic pump 51 is greater than the flow rate in the standby state. For example, it is preferable that the controller 80, in the single-flow supply control as in the merging supply control, performs flow rate increase control so that the flow rate of the first hydraulic fluid discharged from the first hydraulic pump 51 is greater than the flow rate of the first hydraulic fluid in the standby state.

[0055] When the temperature inside the tank drops below the temperature threshold due to the switching from the merging line LC to the first unload line LU1, that is, the switching from the merging supply control to the single-flow supply control (YES in step S12 and YES in step S13), the controller 80 re-executes the merging supply control (step S15).

[0056] It is preferable that the controller 80 also displays the re-execution of the merging supply control on the display device. The controller 80 may be configured to inform the operator of the restoration of the merging drive control by stopping the display that a switch has been made from the merging supply control to the single-flow supply control when the merging supply control is re-executed. Alternatively, the controller 80 may be configured to constantly display on the display device whether the merging supply control or the single-flow supply control is being executed.

[0057] The controller 80 continues the above control until the breaker operator 66 is given a breaker stop operation, that is, an operation to stop the driving of the hydraulic breaker 431 (NO in step S16). When the breaker stop operation is given (YES in step S16), the controller 80 terminates control over the driving of the hydraulic breaker 431. For example, the controller 80 returns the operating state to the standby state and monitors whether or not there is another breaker drive operation (step S10).

[0058] According to the work machine 100 described above, when the first hydraulic oil cooling conditions are not met, the hydraulic oil discharged from the first hydraulic pump 51 and the second hydraulic pump 52 are combined and supplied to the hydraulic breaker 431, thereby increasing the output of the hydraulic breaker 431. On the other hand, when the first hydraulic oil cooling conditions are met, in this embodiment, if the temperature of the hydraulic oil in the tank 50 exceeds the temperature threshold, the hydraulic oil discharged from the first hydraulic pump 51 is not passed through the hydraulic breaker 431 but is passed through the oil cooler 54 in the first unload line LU1 to cool it before being returned to the tank 50, thereby suppressing the rise in the temperature of the hydraulic oil and allowing the work by the hydraulic breaker 431 to continue. In this way, both ensuring work efficiency and suppressing the rise in the temperature of the hydraulic oil are achieved.

[0059] Moreover, the above-mentioned effects can be achieved at low cost by simply switching the line through which the first hydraulic fluid discharged from the first hydraulic pump 51 flows between the confluence line LC and the first unload line LU1.

[0060] The controller 80 may be configured to store a plurality of different selectable temperature thresholds (for example, in the memory unit) and to determine the first hydraulic fluid cooling conditions based on a temperature threshold selected from the plurality of selectable temperature thresholds. The selectable temperature thresholds may be selected by the operator, for example, according to the type and specifications of the hydraulic breaker 431, or the controller 80 may be configured to automatically select them based on information output from the installed hydraulic breaker 431. In the former case, the controller 80 may be configured to display a touch panel operation screen on the display device, enabling the operator to select a desired selectable temperature threshold. The operation screen may also display information that is helpful to the operator in selecting a selectable temperature threshold, such as the model and operating conditions of the hydraulic breaker 431. In either case, the controller 80 can determine the first hydraulic fluid cooling conditions for switching between the combined supply control and the single-flow supply control based on the selected selectable temperature threshold.

[0061] Furthermore, the first hydraulic fluid cooling condition is not limited to conditions relating to the temperature inside the tank. For example, the first hydraulic fluid cooling condition may be a condition in which the time elapsed since the start of operation of the hydraulic breaker 431 exceeds a predetermined elapsed time threshold. Alternatively, the first hydraulic fluid cooling condition may be a combination of a temperature condition relating to the temperature inside the tank and a time condition relating to the elapsed time. For example, the first hydraulic fluid cooling condition may be a condition in which both the temperature condition and the time condition are satisfied, or a condition in which at least one of the temperature condition and the time condition is satisfied.

[0062] Figure 9 shows the control operation performed by the controller 80 according to the second embodiment of the present invention.

[0063] The controller 80 according to the second embodiment is configured, for example, to store in its memory a shutdown condition in addition to the first hydraulic fluid cooling condition, and to forcibly stop the operation of the hydraulic breaker 431 when the shutdown condition is met.

[0064] Specifically, the control operation shown in Figure 9 includes, in addition to the steps included in the control operation shown in Figure 5, a step of determining whether the operating state meets the operation stop condition, more specifically, a step of determining whether the continuous operating time of the hydraulic breaker 431 exceeds a predetermined operating time threshold (step S20). If the controller 80 determines that the operation stop condition is met, namely that the continuous operating time exceeds the operating time threshold (NO in step S20), it forcibly stops the operation of the hydraulic breaker 431 without waiting for the breaker stop operation (step S16) and terminates the control operation.

[0065] The controller 80 may be configured to display a notification on the display device to inform the operator that the hydraulic breaker 431 will soon be forcibly shut down when the continuous operating time approaches the operating time threshold, for example, a countdown to the scheduled breaker shutdown time. In other words, the controller 80 may be configured to display information on the display device regarding the remaining time until the hydraulic breaker 431 is forcibly shut down based on the operating shutdown conditions.

[0066] The controller 80 may be configured to store a plurality of different selectable operating time thresholds (for example, in the memory unit) and to determine the operation stop condition based on the operating time threshold selected from the plurality of selectable operating time thresholds. The selectable operating time threshold may be selected by the operator, for example, according to the type and specifications of the hydraulic breaker 431, or the controller 80 may be configured to automatically select it based on information output from the installed hydraulic breaker 431. In the former case, the controller 80 may be configured to display a touch panel operation screen on the display device, enabling the operator to select a desired selectable operating time threshold. The operation screen may also display information that is helpful to the operator in selecting the selectable operating time threshold, such as the model and operating conditions of the hydraulic breaker 431. In either case, the controller 80 can determine the operation stop condition for forcibly stopping the operation of the hydraulic breaker 431 based on the selected selectable operating time threshold.

[0067] The forced cessation of the operation of the hydraulic breaker 431 based on the continuous operating time prevents the hydraulic breaker 431 from operating continuously for an excessive amount of time, and allows the operator to recognize when continuous operation has occurred for a long period of time. This enables proper protection of the hydraulic breaker 431 and suppression of the rise in the temperature of the hydraulic fluid.

[0068] Figure 10 shows the control operation performed by the controller 80 according to the third embodiment of the present invention.

[0069] The controller 80 according to the third embodiment is configured such that, for example, in its storage unit, it stores a restart permission condition in addition to the first hydraulic oil cooling condition and the operation stop condition, and only when the restart permission condition is met does it permit restart by a breaker operation operation (step S10) after the operation of the hydraulic breaker 431 has been stopped. The restart permission condition is that the breaker stop time, which is the time elapsed since the operation of the hydraulic breaker 431 was stopped, exceeds a first stop time threshold, and the first stop time threshold is stored in advance in the storage unit, for example.

[0070] Specifically, the control operation shown in Figure 10 includes, in addition to the steps included in the control operation shown in Figure 9, a step (step S30) of determining whether the breaker stop time exceeds the first stop time threshold. If the breaker stop time is less than or equal to the first stop time threshold (YES in step S30), the controller 80 does not permit the restart of the hydraulic breaker 431 by the breaker operation (step S10), and from the point when the breaker stop time exceeds the first stop time threshold (NO in step S30), it permits the restart of the hydraulic breaker 431 by the breaker drive operation. The control operation after the breaker drive operation is performed (YES in step S10) is the same as the control operation according to the second embodiment.

[0071] The controller 80 allows the hydraulic breaker 431 to restart only when the restart permission conditions are met, thereby ensuring a sufficient downtime between the shutdown and restart of the hydraulic breaker 431. This prevents, for example, the restart of the hydraulic breaker 431 from starting before the hydraulic fluid temperature has sufficiently decreased after the restart of the hydraulic breaker 431 has been forcibly stopped (NO in step S20).

[0072] Figure 11 shows the control operation performed by the controller 80 according to the fourth embodiment of the present invention.

[0073] The controller 80 according to the fourth embodiment is configured such that, for example, in its storage unit, it stores a second stop time threshold smaller than the first stop time threshold as a stop time threshold for determining the restart permission condition according to the third embodiment, and if a hydraulic actuator other than the hydraulic breaker 431 is driven after the operation of the hydraulic breaker 431 has stopped, it determines the restart permission condition based on the second stop time threshold, in other words, it reduces the stop time threshold. The reason is as follows.

[0074] In the hydraulic circuit shown in Figure 2, the hydraulic fluid supplied to the first and second hydraulic actuators, which are hydraulic actuators other than the hydraulic breaker 431, returns to the tank 50 via the oil cooler 54, similar to the hydraulic fluid that flows through the first and second unload lines LU1 and LU2, respectively, in the standby state. The flow rate of the hydraulic fluid supplied to the first and second actuator drive lines LA1 and LA2 to operate the first and second hydraulic actuators is generally greater than the standby flow rate, which is the flow rate of hydraulic fluid that flows through the first and second unload lines LU1 and LU2 in the standby state. Therefore, the flow rate of hydraulic fluid flowing through the oil cooler 54 is also greater. Consequently, when the operation of the hydraulic breaker 431 is stopped and, for example, the first hydraulic actuator or the second hydraulic actuator, which are hydraulic actuators other than the hydraulic breaker 431, are driven to change the position of the work machine 100 or the posture of the work device 40, it can be expected that the hydraulic fluid will be cooled more than when it is waiting in the normal standby state. For these reasons, the controller 80 according to the fourth embodiment determines the restart permission condition based on a second stop time threshold that is smaller than the first stop time threshold that applies when the hydraulic actuator other than the hydraulic breaker 431 is not being driven, if the hydraulic breaker 431 is stopped and a hydraulic actuator other than the hydraulic breaker 431 is being driven, that is, it reduces the stop time threshold, thereby allowing the restart of the hydraulic breaker 431 with a short stop time.

[0075] Specifically, the control operation shown in Figure 11 includes steps S40 to S42 in place of step S30 shown in Figure 10. The controller 80 determines whether any hydraulic actuators other than the hydraulic breaker 431 are operating after stopping the operation of the hydraulic breaker 431 (step S40). If the controller 80 determines that none of the hydraulic actuators other than the hydraulic breaker 431 are operating (NO in step S40), it determines whether to allow the restart of the hydraulic breaker 431 by a breaker drive operation (step S10), based on whether the breaker stop time exceeds the first stop time threshold, that is, based on whether the restart permission condition determined by the first stop time threshold is met (step S41), as in the third embodiment. In response, if the controller 80 determines that any hydraulic actuator other than the hydraulic breaker 431 is operating (YES in step S40), it determines whether or not to allow the restart of the hydraulic breaker 431 by a breaker drive operation (step S10) based on whether or not the breaker stop time exceeds the second stop time threshold, that is, whether or not the restart permission condition determined by the second stop time threshold is met (step S41).

[0076] Thus, in the fourth embodiment, by reducing the stop time threshold, taking into account the cooling effect of the hydraulic fluid due to the operation of other hydraulic actuators after the operation of the hydraulic breaker 431 has been stopped according to the operation stop conditions, the time from the stop of operation of the hydraulic breaker 431 to restarting can be shortened, thereby improving work efficiency.

[0077] Figure 12 shows the control operation performed by the controller 80 according to the fifth embodiment of the present invention.

[0078] The controller 80 according to the fifth embodiment is configured to perform flow rate increase control so that, after stopping the operation of the hydraulic breaker in accordance with the operation stop conditions, at least one of the first unload flow rate, which is the flow rate of hydraulic fluid discharged from the first hydraulic pump 51 shown in Figure 2 and flowing through the first unload line LU1, and the second unload flow rate, which is the flow rate of hydraulic fluid discharged from the second hydraulic pump 52 and flowing through the second unload line LU2, is greater than the flow rate in the standby state. This makes it possible to cool the hydraulic fluid more efficiently.

[0079] Taking such cooling effects into consideration, in the fifth embodiment, a third stop time threshold smaller than the first stop time threshold in the third embodiment is applied as the stop time threshold constituting the restart permission condition. In other words, the controller 80 in the fifth embodiment decreases the stop time threshold as the flow rate increase control is executed. The controller 80 determines whether or not to allow the restart of the hydraulic breaker 431 based on whether or not the breaker stop time, which is the elapsed time since the hydraulic breaker 431 stopped, exceeds the third stop time threshold (step S50). Specifically, the controller 80 does not allow the restart of the hydraulic breaker 431 by a breaker drive operation (step S10) if the breaker stop time is less than or equal to the third stop time threshold (YES in step S50), and only allows the restart of the hydraulic breaker 431 if the breaker stop time exceeds the third stop time threshold (NO in step S50).

[0080] Furthermore, if the controller 80 determines that the continuous operating time of the hydraulic breaker 431 after restart exceeds the operating time threshold, which is a stop condition (NO in step S20), it performs flow rate increase control to make at least one of the first unload flow rate and the second unload flow rate greater than the flow rate in the standby state (step S51). For example, the controller 80 is configured to stop the operation of the hydraulic breaker 431 by switching the state of the switching unit so that the hydraulic fluid flows through the first and second unload lines LU1 and LU2 while maintaining the capacity of the first hydraulic pump 51 and the second hydraulic pump 52 when the hydraulic breaker 431 is operating.

[0081] The flow rate increase control described above may be performed on at least one of the first unload flow rate and the second unload flow rate, but it is preferable from the viewpoint of improving cooling efficiency to perform it on both the first and second unload flow rates.

[0082] The controller 80 may automatically determine whether or not to perform the flow rate increase control in step S51. Alternatively, the system may be configured so that when the operation stop condition is met (NO in step S20), the operator can input an instruction to the controller 80 regarding whether or not to perform the flow rate increase control. In other words, the work machine 100 may be configured so that when the operation of the hydraulic breaker 431 is stopped in accordance with the operation stop condition, the operator can perform an operation to cause the controller 80 to perform the flow rate increase control (step S51).

[0083] The present invention has been described above based on specific embodiments, but the present invention is not limited to the above embodiments. The present invention also includes modifications and improvements to the above embodiments, which will be clear to those skilled in the art from the description of the claims.

[0084] As described above, a work machine equipped with a hydraulic breaker is provided, which is capable of increasing the output of the hydraulic breaker while avoiding a significant rise in the temperature of the hydraulic fluid. The work machine includes a lower traveling body, an upper rotating body rotatably mounted on the lower traveling body, a working arm connected to the upper rotating body and a tip attachment attached to the tip of the working arm, a working device in which a hydraulically driven hydraulic breaker can be attached to the working arm as the tip attachment, a tank for storing hydraulic fluid, a cooler that allows hydraulic fluid to pass through and cools the hydraulic fluid passing through, a first hydraulic pump for discharging the hydraulic fluid in the tank, a second hydraulic pump for discharging the hydraulic fluid in the tank, and the second hydraulic fluid, which is the hydraulic fluid discharged from the second hydraulic pump, is attached to the working arm as the tip attachment. The hydraulic circuit includes: a breaker drive line that guides the second hydraulic fluid to be supplied to a pressure breaker and to return to the tank without passing through the cooler; a confluence line that guides the first hydraulic fluid, which is hydraulic fluid discharged from the first hydraulic pump, to merge with the second hydraulic fluid flowing through the breaker drive line and to be supplied to the hydraulic breaker together with the second hydraulic fluid; a first hydraulic fluid cooling line that guides the first hydraulic fluid to be cooled by passing through the cooler without passing through the hydraulic breaker and then to return to the tank; a switching unit that switches the line through which the first hydraulic fluid flows between the confluence line and the first hydraulic fluid cooling line; and a controller. The controller controls the switching of the line by the switching unit so that when the operating state of the work machine meets a predetermined first hydraulic fluid cooling condition, the line through which the first hydraulic fluid flows becomes the first hydraulic fluid cooling line, and when the operating state of the work machine does not meet the first hydraulic fluid cooling condition, the line through which the first hydraulic fluid flows becomes the confluence line.

[0085] The aforementioned work machine further includes a temperature measuring unit that measures a temperature value corresponding to the temperature of the hydraulic oil in the tank, and preferably the first hydraulic oil cooling condition includes a condition in which the temperature value measured by the temperature measuring unit exceeds a predetermined temperature threshold.

[0086] The controller may be configured to store a plurality of different selectable temperature thresholds and to determine the first hydraulic fluid cooling conditions based on a temperature threshold selected from the plurality of selectable temperature thresholds.

[0087] Preferably, the work machine further includes a display device that indicates that the line through which the first hydraulic fluid flows has been switched from the merging line to the first hydraulic fluid cooling line.

[0088] Preferably, the controller is configured to set the flow rate of the first hydraulic fluid supplied from the first hydraulic pump to the first hydraulic fluid cooling line to be greater than the flow rate of the first hydraulic fluid supplied to the first hydraulic fluid cooling line in the standby state. The standby state is a state in which the first hydraulic pump and the second hydraulic pump are driven, but the hydraulic fluid discharged from the first hydraulic pump and the second hydraulic pump is returned to the tank without being supplied to any of the hydraulic actuators, including the hydraulic breaker.

[0089] Preferably, the controller is configured to stop the operation of the hydraulic breaker by stopping the supply of hydraulic fluid from the second hydraulic pump to the hydraulic breaker when an operation stop condition is met, which includes the condition that the continuous operating time of the breaker exceeds a predetermined operating time threshold.

[0090] For example, the controller may be configured to store a plurality of different selectable operating time thresholds and to determine the shutdown condition based on an operating time threshold selected from among the plurality of selectable operating time thresholds.

[0091] The controller may be configured to allow the restart of the breaker by supplying hydraulic fluid from the second hydraulic pump to the breaker drive line only when the restart permission condition is met, which is that the time elapsed after the operation of the hydraulic breaker has been stopped in accordance with the stop condition exceeds a predetermined stop time threshold.

[0092] If the work machine further includes a hydraulic actuator separate from the hydraulic breaker, and an actuator drive line that guides at least one of the first and second hydraulic fluids to the hydraulic actuator, cool through the cooler, and then return to the tank, the controller may be configured to set the stop time threshold lower when hydraulic fluid is supplied to the actuator drive line after the breaker has been stopped in accordance with the stop conditions, compared to when hydraulic fluid is not supplied to the actuator drive line.

[0093] Furthermore, the controller may be configured to perform flow rate increase control, which increases the flow rate of the first hydraulic fluid supplied from the first hydraulic pump to the first hydraulic fluid cooling line to a level greater than the flow rate of the first hydraulic fluid supplied to the first hydraulic fluid cooling line in the standby state. In this case, the controller may be configured to set the stop time threshold lower when performing the flow rate increase control after stopping the operation of the breaker in accordance with the stop conditions, compared to when the flow rate increase control is not performed.

[0094] Furthermore, if the work machine further includes a second hydraulic oil cooling line that passes the hydraulic oil discharged from the second hydraulic pump through the cooler without passing it through the hydraulic breaker and then back to the tank, the controller may be configured to perform flow rate increase control so that the flow rate of the hydraulic oil supplied from the second hydraulic pump to the second hydraulic oil cooling line is greater than the flow rate of the hydraulic oil supplied to the second hydraulic oil cooling line in the standby state, and the controller may be configured to make the stop time threshold smaller when the flow rate increase control is performed after the operation of the breaker has been stopped in accordance with the operation stop conditions, compared to when the flow rate increase control is not performed.

[0095] Furthermore, a method is provided for hydraulically driving a hydraulic breaker used as an end attachment in a work machine. The method includes: discharging hydraulic fluid from a first hydraulic pump and a second hydraulic pump, respectively; guiding the hydraulic fluid discharged from the second hydraulic pump to the hydraulic breaker to drive the hydraulic breaker; returning the hydraulic fluid discharged from the hydraulic breaker to a tank without passing it through a cooler; when the operating state of the work machine corresponds to a predetermined first hydraulic fluid cooling condition, passing the first hydraulic fluid, which is the hydraulic fluid discharged from the first hydraulic pump, through a cooler without passing it through the hydraulic breaker to cool the first hydraulic fluid before returning it to the tank; and when the operating state does not correspond to the cooling condition, merging the first hydraulic fluid with the second hydraulic fluid, which is the hydraulic fluid discharged from the second hydraulic pump and supplied to the hydraulic breaker, so that the first hydraulic fluid is supplied to the hydraulic breaker together with the second hydraulic fluid.

[0096] In the above method, it is preferable that the cooling conditions include a condition in which the temperature value corresponding to the temperature of the hydraulic fluid in the tank exceeds a predetermined temperature threshold.

Claims

1. A work machine, the work machine comprising: a lower traveling body; an upper rotating body rotatably mounted on the lower traveling body; a work device comprising a working arm connected to the upper rotating body and a tip attachment attached to the tip of the working arm, wherein a hydraulically driven hydraulic breaker can be attached to the working arm as the tip attachment; a tank for storing hydraulic fluid; a cooler that allows hydraulic fluid to pass through and cools the hydraulic fluid passing through it; a first hydraulic pump for discharging the hydraulic fluid from the tank; a second hydraulic pump for discharging the hydraulic fluid from the tank; and a breaker drive line that guides the second hydraulic fluid, which is the hydraulic fluid discharged from the second hydraulic pump, to the hydraulic breaker attached to the working arm as the tip attachment, and to return the second hydraulic fluid to the tank without passing through the cooler. A work machine comprising: a confluence line that guides the first hydraulic fluid, which is a hydraulic fluid discharged from the first hydraulic pump, to merge with the second hydraulic fluid flowing through the breaker drive line and supply together with the second hydraulic fluid to the hydraulic breaker; a first hydraulic fluid cooling line that guides the first hydraulic fluid to be cooled by passing through the cooler without passing through the hydraulic breaker and then returned to the tank; a switching unit that switches the line through which the first hydraulic fluid flows between the confluence line and the first hydraulic fluid cooling line; and a controller, wherein the controller controls the switching of the line by the switching unit so that when the operating state of the work machine is in use the hydraulic breaker, the line through which the first hydraulic fluid flows becomes the first hydraulic fluid cooling line, and when the operating state of the work machine is not in use the first hydraulic fluid cooling condition, the line through which the first hydraulic fluid flows becomes the confluence line.

2. A work machine according to claim 1, further comprising a temperature measuring unit that measures a temperature value which corresponds to the temperature of the hydraulic oil in the tank, wherein the first hydraulic oil cooling condition includes the condition that the temperature value measured by the temperature measuring unit exceeds a predetermined temperature threshold.

3. A work machine according to claim 2, wherein the controller is configured to store a plurality of selectable temperature thresholds that are different from each other, and to determine the first hydraulic oil cooling condition based on a temperature threshold selected from the plurality of selectable temperature thresholds.

4. A work machine according to any one of claims 1 to 3, further comprising a display unit that indicates that the line through which the first hydraulic fluid flows has been switched from the merging line to the first hydraulic fluid cooling line.

5. A work machine according to any one of claims 1 to 4, wherein the controller is configured to increase the flow rate of the first hydraulic fluid supplied from the first hydraulic pump to the first hydraulic fluid cooling line compared to the flow rate of the first hydraulic fluid supplied to the first hydraulic fluid cooling line in a standby state, the standby state being a state in which the first hydraulic pump and the second hydraulic pump are driven, but the hydraulic fluid discharged from the first hydraulic pump and the second hydraulic pump is returned to the tank without being supplied to any hydraulic actuator, including the hydraulic breaker.

6. A work machine according to any one of claims 1 to 4, wherein the controller is configured to stop the operation of the hydraulic breaker by stopping the supply of hydraulic fluid from the second hydraulic pump to the hydraulic breaker when an operation stop condition is met, which includes the condition that the continuous operating time of the hydraulic breaker exceeds a predetermined operating time threshold.

7. A work machine according to claim 6, wherein the controller stores a plurality of different selectable operating time thresholds, and determines the operating stop condition based on an operating time threshold selected from the plurality of selectable operating time thresholds.

8. A work machine according to claim 6 or 7, wherein the controller is configured to permit the restart of the hydraulic breaker by supplying hydraulic fluid from the second hydraulic pump to the breaker drive line when the breaker stop time, which is the time elapsed after the operation of the hydraulic breaker has been stopped in accordance with the operation stop condition, exceeds a predetermined stop time threshold, which is a restart permission condition.

9. A work machine according to claim 8, further comprising: a hydraulic actuator separate from the hydraulic breaker; and an actuator drive line that supplies at least one of the first hydraulic fluid and the second hydraulic fluid to the hydraulic actuator and guides the at least one hydraulic fluid through the cooler and back to the tank, wherein the controller is configured to reduce the stop time threshold when hydraulic fluid is supplied to the actuator drive line after the operation of the hydraulic breaker has been stopped in accordance with the stop condition, compared to when hydraulic fluid is not supplied to the actuator drive line.

10. A work machine according to claim 8, wherein the controller is configured to perform flow rate increase control such that the flow rate of the first hydraulic fluid supplied from the first hydraulic pump to the first hydraulic fluid cooling line is greater than the flow rate of the first hydraulic fluid supplied to the first hydraulic fluid cooling line in a standby state, the standby state is a state in which the first hydraulic pump and the second hydraulic pump are driven, but the hydraulic fluid discharged from the first hydraulic pump and the second hydraulic pump is returned to the tank without being supplied to the hydraulic actuator including the hydraulic breaker, and the controller is configured to reduce the stop time threshold when performing the flow rate increase control after stopping the operation of the hydraulic breaker in accordance with the operation stop condition, compared to when the flow rate increase control is not performed.

11. A work machine according to claim 8, further comprising a second hydraulic oil cooling line that passes the hydraulic oil discharged from the second hydraulic pump through the cooler without passing it through the hydraulic breaker and then back to the tank, wherein the controller is configured to perform flow rate increase control such that the flow rate of the hydraulic oil supplied from the second hydraulic pump to the second hydraulic oil cooling line is greater than the flow rate of the hydraulic oil supplied to the second hydraulic oil cooling line in a standby state, the standby state is a state in which the first hydraulic pump and the second hydraulic pump are driven, but the hydraulic oil discharged from the first hydraulic pump and the second hydraulic pump is returned to the tank without being supplied to a hydraulic actuator including the hydraulic breaker, and the controller is configured to reduce the stop time threshold when performing the flow rate increase control after stopping the operation of the hydraulic breaker in accordance with the operation stop condition, compared to when the flow rate increase control is not performed.

12. A method for hydraulically driving a hydraulic breaker used as an end attachment in a work machine, comprising: discharging hydraulic fluid from a first hydraulic pump and a second hydraulic pump, respectively; guiding the second hydraulic fluid discharged from the second hydraulic pump to the hydraulic breaker to drive the hydraulic breaker, and returning the hydraulic fluid discharged from the hydraulic breaker to a tank without passing it through a cooler; when the operating state of the work machine corresponds to predetermined cooling conditions, passing the first hydraulic fluid, which is the hydraulic fluid discharged from the first hydraulic pump, through a cooler without passing it through the hydraulic breaker to cool the first hydraulic fluid before returning it to the tank; and when the operating state does not correspond to the cooling conditions, merging the first hydraulic fluid with the second hydraulic fluid discharged from the second hydraulic pump and supplied to the hydraulic breaker, thereby enabling the first hydraulic fluid to be supplied to the hydraulic breaker together with the second hydraulic fluid.

13. A circuit breaker driving method according to claim 12, wherein the cooling condition includes a condition that the temperature value corresponding to the temperature of the hydraulic fluid in the tank exceeds a predetermined temperature threshold.

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