Work machine

Abstract

To provide a work machine capable of improving operational accuracy of automatic control of a work device by making temperature of hydraulic oil flowing through a hydraulic circuit uniform.SOLUTION: A hydraulic shovel 1 equipped with a function to automatically limit an operation of a work device 13 separately from an operation control of the work device 13 through operation of an operator includes: an electromagnetic switching valve 44 provided between a second directional control valve 42 and a hydraulic oil tank 40 and switched between a first switching position 44A that directs pilot pressure oil P to a first return line 451 and a second switching position 44B that directs the pilot pressure oil P to a second return line 452; and a controller 5 that controls the electromagnetic switching valve 44. The controller 5 outputs a switching command signal to switch a switching position of the electromagnetic switching valve 44 to the first switching position 44A or the second switching position 44B based on an oil temperature Tp detected by a pilot oil temperature sensor 42A and an oil temperature Tt detected by a tank oil temperature sensor 40A.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a work machine equipped with a function for automatically controlling the operation of a work implement. [Background technology]

[0002] In a work machine such as a hydraulic excavator, a bucket constituting a working device attached to the vehicle body may interfere with the driver's cab depending on its posture or operation. In order to avoid interference between the working device and the driver's cab, a work machine equipped with an interference prevention function that limits the operation of the working device has been conventionally known.

[0003] For example, Patent Document 1 discloses an interference prevention device that detects hydraulic oil temperature, which affects the operating characteristics of a working device, corrects the position of the working device at the start of interference prevention control according to the detected hydraulic oil temperature, and then performs interference prevention control. For example, when a work machine works in winter or in cold regions, the hydraulic oil temperature drops and the fluidity of the hydraulic oil decreases, which may delay the operation of the working device, but this interference prevention device corrects the interference prevention control according to the hydraulic oil temperature, making it possible to accurately avoid interference between the working device and the driver's cab. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-256403 Summary of the Invention [Problem to be solved by the invention]

[0005] When interference prevention control is corrected based on the hydraulic oil temperature detected in the main hydraulic circuit for driving the work machine, as in the interference prevention device described in Patent Document 1, the temperature of the hydraulic oil flowing through the pilot hydraulic circuit, which is independent of the main hydraulic circuit (pilot oil temperature), is not taken into account, which can lead to a discrepancy with the actual operation of the work machine, resulting in reduced workability.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a work machine capable of improving the operational accuracy of the automatic control of a work device by making the temperature of hydraulic oil flowing through a hydraulic circuit uniform. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides a work machine including a machine body, a working device attached to the machine body, a hydraulic actuator for driving the working device, a directional control valve for controlling the drive of the hydraulic actuator, a hydraulic oil tank for storing hydraulic oil, a pilot pump for drawing in the hydraulic oil from the hydraulic oil tank and supplying pilot pressure oil to the directional control valve, and a first return pipe that is connected to one side of the hydraulic oil tank and is a return pipe for returning the pilot pressure oil to the hydraulic oil tank, the work machine including a pilot oil temperature sensor that detects the temperature of the pilot pressure oil supplied to the directional control valve, a tank oil temperature sensor that detects the temperature of the hydraulic oil stored in the hydraulic oil tank, and a first return pipe that is connected to one side of the hydraulic oil tank and is a return pipe for returning the pilot pressure oil to the hydraulic oil tank, the work machine including a machine body including a machine body having a work device attached to the machine body, a working device attached to the machine body the hydraulic oil tank having a return line different from the first return line and connected to one side of the hydraulic oil tank at a predetermined distance in the height direction from the first return line; an electromagnetic switching valve provided between the directional control valve and the hydraulic oil tank and switching between a first switching position that directs the pilot pressure oil to the first return line and a second switching position that directs the pilot pressure oil to the second return line; and a controller that controls the electromagnetic switching valve, wherein the controller outputs a switching command signal to switch the switching position of the electromagnetic switching valve to the first switching position or the second switching position based on an oil temperature detected by the pilot oil temperature sensor and an oil temperature detected by the tank oil temperature sensor. Effect of the Invention

[0008] According to the present invention, the temperature of the hydraulic oil flowing through the hydraulic circuit can be made uniform, thereby improving the operational accuracy of the automatic control of the working device. Problems, configurations, and effects other than those described above will become apparent from the description of the following embodiments. [Brief description of the drawings]

[0009] [Figure 1] 1 is an external side view showing one configuration example of a hydraulic excavator according to an embodiment of the present invention. FIG. [Diagram 2] FIG. 2 is a diagram showing an example of a system configuration relating to a hydraulic oil tank, showing a case where a solenoid switching valve is switched to a first switching position. [Diagram 3] FIG. 4 is a schematic diagram of the hydraulic oil tank as viewed from above, illustrating the state in which the second return line is connected to the hydraulic oil tank. [Figure 4] FIG. 2 is a functional block diagram showing functions of a controller. [Diagram 5] 4 is a flowchart showing a flow of processing executed by a controller. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In the following, a crawler type hydraulic excavator will be described as an example of one aspect of a work machine according to an embodiment of the present invention.

[0011] <Configuration of Hydraulic Excavator 1> First, the overall configuration of a hydraulic excavator 1 will be described with reference to FIG.

[0012] The hydraulic excavator 1 comprises a crawler-type running body 11 which forms the lower part of the machine body, a rotating body 12 which is rotatably mounted above the running body 11 and forms the upper part of the machine body, and a hydraulically-driven working device 13 which is attached to the rotating body 12 (machine body) and performs work such as excavation and leveling.

[0013] The running body 11 includes a pair of crawlers 111 extending in the traveling direction of the machine body, and a pair of travel motors 112 that drive the pair of crawlers 111, and moves the machine body by rotating the pair of crawlers 111 in contact with the ground by the driving force of the pair of travel motors 112. The pair of travel motors 112 are mounted on the running body 11 corresponding to each of the pair of crawlers 111, and can rotate the pair of crawlers 111 forward and backward independently by driving them independently of each other. Note that FIG. 1 shows only one of the pair of crawlers 111 and the pair of travel motors 112.

[0014] The rotating body 12 comprises a rotating frame 21 which is a base frame, a cab 22 in which the operator sits, a counterweight 23 which maintains balance with the work implement 13 to prevent the hydraulic excavator 1 from tipping over, and a machine room 24 which houses various devices for driving the hydraulic excavator 1.

[0015] On the revolving frame 21, the operator's cab 22 is placed at the front, the counterweight 23 is placed at the rear end, and the machine room 24 is placed between the operator's cab 22 and the counterweight 23. In addition, the working device 13 is attached to one side of the operator's cab 22 at the front of the revolving frame 21.

[0016] The working device 13 comprises a boom 31 whose base end is rotatably attached to the swivel frame 21, an arm 32 rotatably attached to the tip of the boom 31, and a bucket 33 rotatably attached to the tip of the arm 32.

[0017] The boom 31 is driven by a boom cylinder 31A. Specifically, one end of the boom cylinder 31A is connected to the revolving frame 21, and the other end is connected to the boom 31. The boom cylinder 31A rotates (elevates) the boom 31 in the vertical direction relative to the revolving body 12 by expanding and contracting a rod due to the inflow and outflow of hydraulic oil.

[0018] The arm 32 is driven by an arm cylinder 32A. Specifically, one end of the arm cylinder 32A is connected to the boom 31, and the other end is connected to the arm 32, and the arm 32 is rotated in the front-rear direction relative to the boom 31 by the rod extending and contracting due to the inflow and outflow of hydraulic oil.

[0019] The bucket 33 is driven by a bucket cylinder 33A. Specifically, one end of the bucket cylinder 33A is connected to the arm 32, and the other end is connected to the bucket 33. The bucket 33 is rotated in the front-rear direction relative to the arm 32 by the rod extending and contracting due to the inflow and outflow of hydraulic oil.

[0020] It should be noted that the boom cylinder 31A, the arm cylinder 32A, and the bucket cylinder 33A are each an example of a hydraulic actuator that drives the working device 13.

[0021] The bucket 33 is a working tool that scoops up loads such as soil and minerals and drops them at a designated location, and that levels the ground. Note that the bucket 33 can be changed to various attachments, such as a grapple for grabbing wood, rocks, waste, etc., a wide special bucket, or a breaker for excavating rock, and thus the hydraulic excavator 1 can perform various tasks, including excavation and crushing, using an attachment suited to the type of work.

[0022] The working device 13 is operated by the operator by operating an operating device provided in the cab 22, but if the bucket 33 is changed to one of the various attachments listed above, there is a possibility that it may collide with the cab 22 depending on its posture and operation.

[0023] For example, when a wide special bucket is attached in place of the standard bucket 33 attached to the tip of the working implement 13, the widthwise length of the wide special bucket becomes longer than the widthwise length of the standard bucket 33. When an attachment with a longer width is used in this way, there is a possibility that the special bucket will interfere with the cab 22 when the operator performs an operation to retract the arm 32 toward the cab 22 or an operation to retract the special bucket toward the cab 22.

[0024] Therefore, the hydraulic excavator 1 is provided with an interference prevention function that automatically limits the operation of the work implement 13 in order to prevent collision between the operator's cab 22 and an attachment such as a special bucket.

[0025] <System configuration related to hydraulic oil tank 40> Next, the system configuration relating to the hydraulic oil tank 40 will be described with reference to FIGS.

[0026] Fig. 2 is a diagram showing an example of a system configuration related to the hydraulic oil tank 40, showing a case where the solenoid switching valve 44 is switched to a first switching position 44A representing a normal state. Fig. 3 is a schematic diagram showing the hydraulic oil tank 40 as viewed from above, showing a state in which the second return pipe 452 is connected to the hydraulic oil tank 40.

[0027] The hydraulic actuator that drives the working device 13 is controlled by a pilot-type first directional control valve 41. Specifically, as shown in Fig. 2, the flow (direction and flow rate) of hydraulic oil supplied from the main pump 430 to the bucket cylinder 33A is controlled by the first directional control valve 41, and the flow (direction and flow rate) of hydraulic oil supplied from the main pump 430 to the arm cylinder 32A is controlled by the second directional control valve 42.

[0028] Note that while FIG. 2 shows a first directional control valve 41 that controls the drive of the bucket cylinder 33A and a second directional control valve 42 that controls the drive of the arm cylinder 32A, in reality, the hydraulic excavator 1 also includes a directional control valve that controls the drive of the boom cylinder 31A, which is not shown in the figure.

[0029] A pair of branch pilot lines 61A, 61B are connected to the first directional control valve 41. The branch pilot lines 61A, 61B branch off from a main pilot line 60 connected to the discharge side of the pilot pump 43 and are bifurcated via a bucket operating lever 121 that constitutes a pilot valve for the bucket 33.

[0030] The first directional control valve 41 moves a spool (not shown) provided therein by guiding pilot pressure oil P discharged from the pilot pump 43 to one of a pair of branch pilot lines 61A, 61B based on the amount of operation of the bucket operating lever 121. This makes it possible to switch the operating direction of the rod of the bucket cylinder 33A.

[0031] Similarly, a pair of branch pilot lines 62A, 62B branching off from the main pilot line 60 and splitting into two via an arm operating lever 122 constituting a pilot valve for the arm 32 are connected to the second directional control valve 42.

[0032] The second directional control valve 42 moves a spool (not shown) provided therein by guiding the pilot pressure oil P discharged from the pilot pump 43 to one of a pair of branch pilot lines 62A, 62B based on the amount of operation of the arm operating lever 122. This makes it possible to switch the operating direction of the rod of the arm cylinder 32A.

[0033] Here, of the pair of branch pilot lines 62A, 62B connected to the second directional control valve 42, an electromagnetic switching valve 62C for preventing interference is provided on the branch pilot line 62B, which switches the direction to extend the rod of the arm cylinder 32A.

[0034] This solenoid switching valve 62C has a blocking position 621 for blocking the pilot pressure oil for switching to a direction for extending the rod of the arm cylinder 32A, and a communication position 622 for communicating the pilot pressure oil for switching to a direction for extending the rod of the arm cylinder 32A. The solenoid switching valve 62C switches between the blocking position 621 and the communication position 622 based on a switching signal output from the controller 5.

[0035] When the solenoid switching valve 62C is switched to the shut-off position 621, the rod of the arm cylinder 32A cannot be extended, thereby restricting the operation of the work device 13 and preventing attachments such as special buckets from colliding with the operator's cab 22.

[0036] The pilot pump 43 is driven by the engine 43A, sucks in the hydraulic oil X stored in the hydraulic oil tank 40, and supplies pilot pressure oil P to each of the first directional control valve 41 and the second directional control valve 42. At this time, the hydraulic oil X stored in the hydraulic oil tank 40 flows out from an outlet 400A provided in the bottom 400 of the hydraulic oil tank 40.

[0037] The pilot pump 43 supplies pilot pressure oil P not only to the first directional control valve 41 and the second directional control valve 42, but also to a swing control valve 45 that controls the flow (direction and flow rate) of hydraulic oil supplied to the swing motor 34 that swings the swing body 12. As shown in Fig. 2, the first directional control valve 41, the second directional control valve 42, and the swing control valve 45 are connected in parallel with each other.

[0038] A first return pipeline 451 and a second return pipeline 452 that return the pilot pressure oil P to the hydraulic oil tank 40 are connected to one side portion 401 of the hydraulic oil tank 40. The first return pipeline 451 and the second return pipeline 452 are disposed at one side portion 401 of the hydraulic oil tank 40 at a predetermined distance in the height direction (corresponding to the up-down direction of the aircraft body).

[0039] In this embodiment, the connection position of the first return pipe 451 on one side 401 of the hydraulic oil tank 40 is above the oil level (oil surface) Y of the hydraulic oil X stored in the hydraulic oil tank 40. Also, the connection position of the second return pipe 452 on one side 401 of the hydraulic oil tank 40 is between the oil level Y of the hydraulic oil X and the bottom 400 of the hydraulic oil tank 40, on the bottom 400 side of the oil level Y. That is, on one side 401 of the hydraulic oil tank 40, the first return pipe 451 is connected to a position on the upper part 402 side, and the second return pipe 452 is connected to a position on the bottom 400 side.

[0040] 3, the second return pipe 452 is connected to the one side 401 of the hydraulic oil tank 40 at an angle. That is, the angle θ between the one side 401 of the hydraulic oil tank 40 and the second return pipe 452 is less than 90 degrees (θ<90°).

[0041] Further, a pilot relief valve 46 is provided downstream of the main pilot line 60 for discharging the pilot pressure oil P to the hydraulic oil tank 40 when the pilot pressure reaches a predetermined relief pressure. An electromagnetic switching valve 44 is provided between the pilot relief valve 46 and the hydraulic oil tank 40.

[0042] In this embodiment, since the electromagnetic switching valve 44 is located between the pilot relief valve 46 and the hydraulic oil tank 40, the lengths of the first return line 451 and the second return line 452 can be made as short as possible, thereby reducing the pilot pressure oil P remaining in each line 451, 452 and making it easier to drain it.

[0043] The solenoid switching valve 44 is controlled based on a switching command signal output from the controller 5, and switches between a first switching position 44A in which the pilot pressure oil P is guided to a first return line 451 and a second switching position 44B in which the pilot pressure oil P is guided to a second return line 452.

[0044] The pilot pressure oil P discharged from the pilot pump 43 flows separately toward the first directional control valve 41, the second directional control valve 42, and the swing control valve 45, which are connected in parallel to each other, and after being supplied to each of the first directional control valve 41, the second directional control valve 42, and the swing control valve 45, the pilot pressure oil P joins together upstream of the solenoid switching valve 44 and is discharged into the hydraulic oil tank 40 via the first return line 451 or the second return line 452.

[0045] 2, the pilot pressure oil P flows through the first return pipe 451 and is discharged into the hydraulic oil tank 40. Therefore, the pilot pressure oil P discharged into the hydraulic oil tank 40 flows into the upper region of the hydraulic oil X stored in the hydraulic oil tank 40.

[0046] On the other hand, when the solenoid switching valve 44 is switched to the second switching position 44B, the pilot pressure oil P flows through the second return pipe 452 and is discharged into the hydraulic oil tank 40. Therefore, the pilot pressure oil P discharged to the hydraulic oil tank 40 flows into a lower region of the hydraulic oil X stored in the hydraulic oil tank 40.

[0047] The controller 5 outputs a switching command signal to switch the switching position of the electromagnetic switching valve 44 to the first switching position 44A or the second switching position 44B based on the oil temperature Tt of the hydraulic oil X stored in the hydraulic oil tank 40 (hereinafter referred to as the "tank oil temperature Tt") and the oil temperature of the pilot pressure oil P supplied to the second directional control valve 42 (hereinafter referred to as the "pilot oil temperature Tp").

[0048] The tank oil temperature Tt is detected by a tank oil temperature sensor 40A provided on the bottom 400 side of the hydraulic oil tank 40. The pilot oil temperature Tp is detected by a pilot oil temperature sensor 42A provided between the interference prevention solenoid switching valve 62C and the second directional control valve 42. The pilot oil temperature sensor 42A may be provided integrally with the second directional control valve 42, or may be provided on the branch pilot line 62B.

[0049] Data relating to the tank oil temperature Tt detected by the tank oil temperature sensor 40A and the pilot oil temperature Tp detected by the pilot oil temperature sensor 42A are output to the controller 5.

[0050] <Controller 5 Configuration> Next, the configuration of the controller 5 will be described with reference to FIGS.

[0051] Fig. 4 is a functional block diagram showing functions of the controller 5. Fig. 5 is a flowchart showing the flow of processing executed by the controller 5.

[0052] The controller 5 is configured by connecting a CPU, RAM, ROM, HDD, input I / F, and output I / F via a bus. Various operating devices and various sensors such as a tank oil temperature sensor 40A and a pilot oil temperature sensor 42A are connected to the input I / F, and an electromagnetic switching valve 44 and the like are connected to the output I / F.

[0053] In such a hardware configuration, the CPU reads out a control program (software) stored on a recording medium such as a ROM, HDD, or optical disk, expands it on the RAM, and executes the expanded control program, whereby the control program and the hardware work together to realize the functions of the controller 5.

[0054] In this embodiment, the configuration of the controller 5 is described as a combination of software and hardware, but this is not limited to the above, and the controller 5 may be configured using an integrated circuit that realizes the functions of a control program executed on the hydraulic excavator 1 side.

[0055] As shown in FIG. 4, the controller 5 includes a data acquisition unit 51, an oil temperature determination unit 52, and a signal output unit 53.

[0056] In the controller 5, as shown in FIG. 5, first, the data acquisition unit 51 acquires the pilot oil temperature Tp detected by the pilot oil temperature sensor 42A and the tank oil temperature Tt detected by the tank oil temperature sensor 40A (step S501).

[0057] Next, the oil temperature determination unit 52 determines whether the pilot oil temperature Tp acquired in step S501 is lower than the tank oil temperature Tt (step S502).

[0058] If it is determined in step S502 that the pilot oil temperature Tp is lower than the tank oil temperature Tt (Tp < Tt) (step S502 / YES), the signal output unit 53 outputs a switching command signal for instructing switching to the second switching position 44B to the electromagnetic switching valve 44 (step S503).

[0059] On the other hand, if it is determined in step S502 that the pilot oil temperature Tp is equal to or higher than the tank oil temperature Tt (Tp ≥ Tt) (step S502 / NO), the signal output unit 53 outputs a switching command signal for instructing switching to the first switching position 44A to the electromagnetic switching valve 44 (step S504).

[0060] When the signal output unit 53 outputs a switching command signal in step S503 or step S504, the processing in the controller 5 ends.

[0061] In this way, when the pilot pressure oil P has a pilot oil temperature Tp equal to or higher than the tank oil temperature Tt (Tp ≥ Tt), the electromagnetic switching valve 44 switches to the first switching position 44A, so that it flows into the upper region of the hydraulic oil X stored in the hydraulic oil tank 40. On the other hand, when the pilot oil temperature Tp is lower than the tank oil temperature Tt (Tp < Tt), the electromagnetic switching valve 44 switches to the second switching position 44B, so that it flows into the lower region of the hydraulic oil X stored in the hydraulic oil tank 40.

[0062] Here, when the pilot oil temperature Tp is lower than the tank oil temperature Tt (Tp < Tt), it means that the circuit on the side of the second direction control valve 42 is not warmed up or the warm-up is insufficient. In this case, by allowing the pilot pressure oil P whose temperature has risen due to warm-up to flow into the lower region of the hydraulic oil X in the hydraulic oil tank 40 (the region on the side of the outlet 400A in the hydraulic oil tank 40) via the second return pipeline 452, the temperature of the hydraulic oil X flowing out from the outlet 400A rises. As a result, the warmed pilot pressure oil P flows into the branch pilot line 62B that switches in the direction of extending the rod of the arm cylinder 32A among the pair of branch pilot lines 62A and 62B, the response of the second direction control valve 42 becomes good, and the accuracy of the operation control of the working device 13 related to preventing interference between the working device 13 and the cab 22 can be improved.

[0063] Also, when the pilot oil temperature Tp is lower than the tank oil temperature Tt (Tp < Tt), if the pilot pressure oil P whose temperature has risen due to warm-up is allowed to flow into the upper region of the hydraulic oil X in the hydraulic oil tank 40 via the first return pipeline 451, only the upper region of the hydraulic oil X in the hydraulic oil tank 40 is warmed and the lower region is not warmed, and it is difficult for the temperature of the hydraulic oil X in the hydraulic oil tank 40 to become uniform. However, in the present embodiment, since the pilot pressure oil P whose temperature has risen due to warm-up is allowed to flow into the lower region of the hydraulic oil X in the hydraulic oil tank 40 via the second return pipeline 452, it is possible to efficiently make the temperature of the hydraulic oil X in the hydraulic oil tank 40 uniform.

[0064] Furthermore, in the present embodiment, as described above, the connection position of the first return pipeline 451 at the one side portion 401 of the hydraulic oil tank 40 is above the oil level Y of the hydraulic oil X in the hydraulic oil tank 40, while the connection position of the second return pipeline 452 at the one side portion 401 of the hydraulic oil tank 40 is on the bottom 400 side with respect to the oil level Y. Therefore, the pilot pressure oil P whose temperature has risen due to warm-up can be surely made to flow into the lower regions with different temperature zones of the hydraulic oil X in the hydraulic oil tank 40.

[0065] In addition, in this embodiment, as described above, the second return pipe 452 is connected at an angle to one side 401 of the hydraulic oil tank 40, so that as shown in FIG. 4, a spiral convection is generated in the hydraulic oil X in the hydraulic oil tank 40, making it possible to more efficiently equalize the oil temperature of the hydraulic oil X in the hydraulic oil tank 40.

[0066] The embodiments of the present invention have been described above. Note that the present invention is not limited to the above-described embodiments, and various modified examples are included. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those having all of the configurations described. In addition, it is possible to replace a part of the configuration of this embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of this embodiment. Furthermore, it is possible to add, delete, or replace a part of the configuration of this embodiment with another configuration.

[0067] For example, in the above embodiment, an interference prevention function for avoiding collision between the working device 13 and the cab 22 has been described as an example of a function for limiting the drive of the hydraulic actuator, but this is not limited to this, and the function may be, for example, a machine control function that automatically controls (limits) the operation of the working device 13 according to a preset trajectory.

[0068] In addition, in the above embodiment, the hydraulic excavator 1 has been described as an example of one type of work machine, but this is not limited to this, and there are no particular limitations as long as the work machine is equipped with a function (e.g., an interference prevention function or a machine control function) that automatically limits the operation of the work implement 13 in addition to the operation control of the work implement 13 by the operator. [Explanation of symbols]

[0069] 1: Hydraulic excavator (working machine) 5: Controller 11: Running body (aircraft) 12: Rotating body (aircraft) 13: Working equipment 31A: Boom cylinder (hydraulic actuator) 32A: Arm cylinder (hydraulic actuator) 33A: Bucket cylinder (hydraulic actuator) 40: Hydraulic oil tank 40A: Tank oil temperature sensor 42: Second directional control valve (directional control valve) 42A: Pilot oil temperature sensor 43: Pilot pump 44: Solenoid valve 44A: 1st switching position 44B: 2nd switching position 400: Bottom 401: One side 451: First return line 452: Second return line P: Pilot pressure oil X: Hydraulic oil

Claims

1. The aircraft and A working device attached to the machine body; A hydraulic actuator that drives the working device; A directional control valve for controlling the drive of the hydraulic actuator; A hydraulic oil tank for storing hydraulic oil; a pilot pump that draws the hydraulic oil from the hydraulic oil tank and supplies pilot pressure oil to the directional control valve; a first return line that is connected to one side of the hydraulic oil tank and that is a return line for returning the pilot pressure oil to the hydraulic oil tank; In a work machine equipped with a pilot oil temperature sensor for detecting a temperature of the pilot pressure oil supplied to the directional control valve; a tank oil temperature sensor for detecting a temperature of the hydraulic oil stored in the hydraulic oil tank; a second return pipe that is different from the first return pipe and is connected to the one side of the hydraulic oil tank at a predetermined distance in a height direction from the first return pipe; an electromagnetic switching valve that is provided between the directional control valve and the hydraulic oil tank and that switches between a first switching position at which the pilot pressure oil is guided to the first return line and a second switching position at which the pilot pressure oil is guided to the second return line; A controller for controlling the solenoid switching valve, The controller: a switching command signal for switching the switching position of the solenoid switching valve to the first switching position or the second switching position based on the oil temperature detected by the pilot oil temperature sensor and the oil temperature detected by the tank oil temperature sensor; A working machine characterized by:

2. 2. The work machine according to claim 1, The connection position of the first return pipe at the one side is Above the oil level of the hydraulic oil stored in the hydraulic oil tank, The connection position of the second return pipe at the one side is Between the oil level and a bottom of the hydraulic oil tank, the oil level is on the bottom side of the oil level, The controller: When the oil temperature detected by the pilot oil temperature sensor is lower than the oil temperature detected by the tank oil temperature sensor, the switching command signal is output to switch the solenoid switching valve to the second switching position. A working machine characterized by:

3. 2. The work machine according to claim 1, The second return line is The hydraulic oil tank is connected to the one side at an angle. A working machine characterized by:

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