Working machine and method for controlling working machine

Abstract

To suppress temperature rise of a fluid to be cooled in a heat exchanger.SOLUTION: A working machine is equipped with an engine, a heat exchanger through which a fluid to be cooled flows internally, a cooling fan that sends outside air to the heat exchanger by rotating forward and cools the fluid to be cooled, and a controller that limits a torque of the engine when the cooling fan rotates in reverse.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a work machine and a method for controlling a work machine. [Background technology]

[0002] As an example of the prior art, a work machine described in JP 2023-50941 A (Patent Document 1) is exemplified. This work machine is equipped with a controller that changes the rotation of multiple cooling fans from forward to reverse while controlling at least one other cooling fan to rotate forward or reverse when the rotation of at least one cooling fan stops when changing from forward to reverse. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-50941 A Summary of the Invention [Problem to be solved by the invention]

[0004] Reversing the rotation of the cooling fan reduces the heat exchanger's ability to cool the fluid being cooled. The heat exchanger includes a CAC (Charge Air Cooler). The CAC cools the heated air compressed by the turbocharger before it is supplied to the engine. When the CAC's cooling capacity decreases, the air temperature at the CAC outlet rises. The air temperature at the CAC outlet is the engine's intake air temperature. As the engine intake air temperature rises, the exhaust temperature also rises, resulting in hot exhaust gas being discharged from the engine.

[0005] The present disclosure proposes a work machine and a method for controlling a work machine that can suppress a rise in temperature of a fluid to be cooled in a heat exchanger. [Means for solving the problem]

[0006] According to the present disclosure, there is proposed a work machine including an engine, a heat exchanger through which a fluid to be cooled flows, a cooling fan that rotates forward to send outside air to the heat exchanger to cool the fluid to be cooled, and a controller. The controller limits the torque of the engine when the cooling fan rotates in reverse.

[0007] A control method for a work machine according to the present disclosure comprises rotating a cooling fan in the forward direction to send outside air to a heat exchanger through which the fluid to be cooled flows, thereby cooling the fluid to be cooled, and limiting the torque of the engine when the cooling fan rotates in the reverse direction. Effect of the Invention

[0008] According to the work machine and the control method for the work machine of the present disclosure, it is possible to suppress a rise in the temperature of the fluid to be cooled in the heat exchanger. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a side view showing a schematic configuration of a hydraulic excavator. [Diagram 2] FIG. 1 is a schematic block diagram showing a system configuration of a hydraulic excavator. [Diagram 3] 5 is a flowchart showing a process for controlling engine output in accordance with the rotation speed of a cooling fan. [Figure 4] FIG. 4 is a diagram illustrating an example of control of a cooling fan and an engine. [Diagram 5] FIG. 4 is a diagram showing an engine output torque curve before restriction. [Figure 6] FIG. 13 is a diagram showing an engine output torque curve during limitation. [Figure 7] FIG. 11 is a diagram illustrating a comparative example of control of a cooling fan and an engine. [Figure 8] FIG. 2 is a diagram illustrating an example of a display unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments will be described with reference to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated. In the drawings, configurations may be omitted or simplified for convenience of explanation. It is also intended from the beginning that any configurations may be extracted from the embodiments and arbitrarily combined.

[0011] <Overall composition> In the embodiment, a hydraulic excavator 1 will be described as an example of a work machine. Fig. 1 is a side view showing a schematic configuration of the hydraulic excavator 1.

[0012] 1, the hydraulic excavator 1 includes a work machine 2 and a vehicle body 3. The vehicle body 3 includes a traveling body 31, a swing circle 32, a rotating body 33, and a rotating motor 35.

[0013] The traveling body 31 has a pair of left and right track belt devices 311. Each of the pair of left and right track belt devices 311 has a travel motor 312 and tracks. The pair of left and right tracks are rotationally driven by the travel motors 312, causing the hydraulic excavator 1 to self-propel.

[0014] The swing circle 32 is connected to a swing motor 35. The swing circle 32 rotates by the rotational drive of the swing motor 35. The travel motor 312 and the swing motor 35 are hydraulic motors driven by hydraulic oil supplied from a hydraulic source (hydraulic pump 45 and hydraulic oil tank 46; see FIG. 2).

[0015] The rotating body 33 is installed on the running body 31 via the swing circle 32. The rotating body 33 rotates with respect to the running body 31 as the swing circle 32 rotates.

[0016] The rotating body 33 has a frame 331 to which the work machine 2 is attached, a cab 332, and an engine room 333. The cab 332 is disposed, for example, on the front left side (front side of the vehicle) of the rotating body 33. The engine room 333 is disposed at the rear of the rotating body 33 (rear side of the vehicle).

[0017] The work machine 2 is supported by a frame 331 on the front side of the rotating body 33, for example on the right side of a driver's cab 332. The work machine 2 is supported by the vehicle body 3 and disposed in front of the vehicle body 3. The work machine 2 has a boom 21, an arm 22, a bucket 23, etc. The bucket 23 is an example of an attachment that can be attached to the tip of the work machine 2.

[0018] In this embodiment, the positional relationship of each part of the hydraulic excavator 1 will be described with reference to the work machine 2.

[0019] The boom 21 of the work machine 2 rotates around a boom foot pin provided at the base end of the boom 21 relative to the rotating body 33. A specific part of the boom 21 that rotates relative to the rotating body 33, for example the tip of the boom 21, moves along a circular arc, and a plane including the circular arc is specified. When the hydraulic excavator 1 is viewed in a plan view, the plane is expressed as a straight line. The direction in which this straight line extends is the front-rear direction of the vehicle body 3 of the hydraulic excavator 1, or the front-rear direction of the rotating body 33, and will hereinafter also be referred to simply as the front-rear direction. The left-right direction (vehicle width direction) of the vehicle body 3 of the hydraulic excavator 1, or the left-right direction of the rotating body 33, is a direction perpendicular to the front-rear direction in a plan view, and will hereinafter also be referred to simply as the left-right direction.

[0020] In the front-to-rear direction, the side where the work machine 2 protrudes from the vehicle body 3 of the hydraulic excavator 1 is the front direction, and the direction opposite to the front direction is the rear direction. Looking forward, the right side and the left side in the left-right direction are the right direction and the left direction, respectively.

[0021] The front-to-rear direction is the front-to-rear direction of the operator seated in the driver's seat in the driver's cab 332. The direction facing the operator seated in the driver's seat is the forward direction, and the direction behind the operator seated in the driver's seat is the rearward direction. The left-to-right direction is the left-to-right direction of the operator seated in the driver's seat. The right and left sides of the operator seated in the driver's seat when facing directly ahead are the right direction and the left direction, respectively.

[0022] In FIG. 1, the front-rear direction is indicated by an arrow X, the left-right direction is indicated by an arrow Y, and the up-down direction is indicated by an arrow Z.

[0023] The boom 21 is attached to the rotating body 33. A base end of the boom 21 is rotatably connected to the rotating body 33 by a boom foot pin (not shown). The boom 21 can be driven by a boom cylinder 211. The boom cylinder 211 is driven by hydraulic oil supplied from a hydraulic source. This drive allows the boom 21 to rotate up and down relative to the rotating body 33 around the boom foot pin.

[0024] The arm 22 is attached to the tip of the boom 21. A base end of the arm 22 is rotatably connected to the tip of the boom 21 by a boom tip pin 242. The arm 22 can be driven by an arm cylinder 221. The arm cylinder 221 is driven by hydraulic oil supplied from a hydraulic source. This drive allows the arm 22 to rotate up and down relative to the boom 21 around the boom tip pin 242.

[0025] The bucket 23 is attached to the tip of the arm 22. The bucket 23 is rotatably connected to the tip of the arm 22 by an arm tip pin 243. The bucket 23 can be driven by a bucket cylinder 231. The bucket cylinder 231 is driven by hydraulic oil supplied from a hydraulic source. This drive allows the bucket 23 to rotate vertically relative to the arm 22 around the arm tip pin 243. The work machine 2 can be driven in this manner.

[0026] <System configuration> FIG. 2 is a schematic block diagram showing the system configuration of the hydraulic excavator 1. The hydraulic excavator 1 is equipped with an engine 40. The engine 40 is accommodated in an engine room 333 (FIG. 1). The engine 40 is disposed in the center of the engine room 333 in the left-right direction. The engine 40 is a drive source for the operation of the hydraulic excavator 1. The engine 40 is an internal combustion engine, such as a diesel engine. The rotation speed of the engine 40 is controlled by adjusting the amount of fuel injected into the cylinder. This adjustment is performed by controlling a governor attached to a fuel injection pump of the engine 40.

[0027] An output shaft 41 of the engine 40 is connected to a power takeoff 43. A driving force generated by the engine 40 is transmitted to a hydraulic pump 45 via the power takeoff 43. The hydraulic pump 45 is driven by the engine 40. The hydraulic pump 45 draws in and discharges hydraulic oil contained in a hydraulic oil tank 46.

[0028] Hydraulic oil discharged from hydraulic pump 45 is supplied to various hydraulic actuators via main valve 47. The hydraulic actuators include a boom cylinder 211, an arm cylinder 221, a bucket cylinder 231, a swing motor 35, and a traveling motor 312, which are also shown in Fig. 1. The engine 40 is a drive source for operation of the work machine 2, rotation of the swing body 33, and travel of the traveling body 31.

[0029] The operation of the hydraulic excavator 1 is controlled by controlling the supply and discharge of hydraulic oil to the hydraulic actuators. The hydraulic oil is oil that is supplied to the hydraulic actuators in order to operate the actuators. The hydraulic oil discharged from the hydraulic actuators is returned to the hydraulic oil tank 46 via the main valve 47.

[0030] An alternator 44 is connected to the power takeoff section 43. The alternator 44 operates as a generator that generates electricity using the driving force generated by the engine 40. The rotation speed of the alternator 44 is set according to the rotation speed of the engine 40. The higher the rotation speed of the engine 40, the higher the rotation speed of the alternator 44 becomes, and the amount of electricity generated by the alternator 44 also increases.

[0031] The alternator 44 and the battery 50 are electrically connected. Electric power generated by the alternator 44 is stored in the battery 50. The battery 50 is an electricity storage device that stores electric power. The battery 50 is a secondary battery such as a nickel-metal hydride battery or a lithium-metal hydride battery.

[0032] The hydraulic excavator 1 is equipped with a cooling device 60. The cooling device 60 is accommodated in the engine room 333. The cooling device 60 is disposed to the left of the engine 40. The cooling device 60 is disposed toward the left side of the engine room 333. The cooling device 60 is disposed closer to the left side surface of the rotating body 33 than the engine 40. The cooling device 60 of the embodiment is equipped with a heat exchanger 70. The heat exchanger 70 of the embodiment has a radiator 71, an oil cooler 72, and a CAC (Charge Air Cooler) 73.

[0033] Cooling water for the engine 40 flows inside the radiator 71. The cooling water for the engine 40 is the fluid to be cooled by the radiator 71. Hydraulic oil supplied to the hydraulic actuator flows inside the oil cooler 72. The hydraulic oil is the fluid to be cooled by the oil cooler 72. Air supplied to the engine 40 flows inside the CAC 73. The intake air of the engine 40 is the fluid to be cooled by the CAC 73.

[0034] The cooling device 60 includes a plurality of cooling fans including a first cooling fan 61 and a second cooling fan 62. The cooling fans 61, 62 are each disposed facing the heat exchanger 70. The cooling fans 61, 62 are configured to be capable of switching the direction of rotation. The cooling fans 61, 62 are each configured to be capable of rotating in both forward and reverse directions.

[0035] The cooling fans 61, 62 rotate forward to take in outside air from a left vent port formed on the left side surface of the revolving body 33 into the engine compartment 333 and send the outside air to the heat exchanger 70. The air flow generated by the cooling fans 61, 62 cools the fluid to be cooled flowing through the heat exchanger 70. The fluid to be cooled exchanges heat with the outside air in the heat exchanger 70, and the fluid to be cooled is cooled by dissipating heat from the fluid to be cooled to the outside air.

[0036] The cooling fans 61 and 62 are electric fans. The electric motors 64 and 65 are electrically connected to the battery 50. The cooling fan 61 is driven by the electric motor 64. The cooling fan 62 is driven by the electric motor 65.

[0037] Electric power stored in the battery 50 or electric power generated by the alternator 44 is supplied to the electric motors 64, 65 to drive the electric motors 64, 65. The cooling fans 61, 62 are driven by the power supplied from the battery 50 or the alternator 44 to generate an air flow that passes through the heat exchanger 70. When the fluid to be cooled passes through the heat exchanger 70, heat is released to the air, thereby cooling the fluid to be cooled.

[0038] The hydraulic excavator 1 further includes a controller 80, a reverse rotation switch 81, and a display unit 90.

[0039] The controller 80 controls the overall operation of the hydraulic excavator 1 and includes a CPU (Central Processing Unit), a non-volatile memory, a timer, etc. The controller 80 is capable of transmitting control signals to the engine 40, the electric motors 64, 65, etc. The controller 80 stores in advance programs for controlling the engine 40 and the cooling fans 61, 62, and various data required for executing the programs.

[0040] The controller 80 in the embodiment is mounted on the hydraulic excavator 1. The controller 80 does not have to be mounted on the hydraulic excavator 1. The controller 80 may be arranged outside the hydraulic excavator 1. The controller 80 may be arranged at the work site of the hydraulic excavator 1, or may be arranged in a remote location away from the work site of the hydraulic excavator 1. The hydraulic excavator 1 and the controller 80 arranged outside the hydraulic excavator 1 may constitute a control system for the hydraulic excavator 1.

[0041] The controller 80 transmits an engine control signal SE to the engine 40 to control the rotation speed and output torque of the engine 40. The controller 80 transmits a motor control signal SM1 to the electric motor 64 to control the rotation direction and rotation speed of the cooling fan 61. The controller 80 transmits a motor control signal SM2 to the electric motor 65 to control the rotation direction and rotation speed of the cooling fan 62.

[0042] The reverse rotation switch 81 is disposed near the driver's seat where the operator sits. The reverse rotation switch 81 is disposed, for example, inside the driver's cab 332. The reverse rotation switch 81 may be displayed on a touch panel or may be a push button type switch. The reverse rotation switch 81 is operated by the operator to rotate the cooling fans 61, 62 in the reverse direction.

[0043] The display unit 90 displays various types of information related to the hydraulic excavator 1. The display unit 90 is disposed in front of the driver's seat where the operator sits. The display unit 90 is disposed, for example, inside the driver's cab 332. The display unit 90 may include a liquid crystal display, an organic EL display, or the like. The display unit 90 receives command signals as input from the controller 80 and displays various types of information on the screen.

[0044] <Control of Cooling Fans 61, 62 and Engine 40> The control of the cooling fans 61, 62 and the engine 40 by the controller 80 in the hydraulic excavator 1 of the embodiment having the above configuration will be described below. FIG. 3 is a flowchart showing a process flow for controlling the output of the engine 40 according to the rotation speed of the cooling fans 61, 62. FIG. 4 is a diagram showing an example of the control of the cooling fans 61, 62 and the engine 40. The horizontal axis of the three graphs shown in FIG. 4 is time. The vertical axis of the upper graph is the rotation speed of the cooling fans 61, 62. The vertical axis of the middle graph is the output torque of the engine 40. The vertical axis of the lower graph is the temperature of the air, which is the fluid to be cooled by the CAC 73, at the outlet of the CAC 73. A judgment value is specified for the air temperature.

[0045] In step S1 shown in Fig. 3, the cooling fans 61, 62 rotate forward at a constant rotation speed. The engine 40 outputs a rated torque. Until the "deceleration start" time shown in Fig. 4, the cooling fans 61, 62 rotate forward at a constant rotation speed, and the engine 40 outputs a constant torque.

[0046] In step S2, it is determined whether or not the control for rotating the cooling fans 61, 62 in reverse has been turned ON. When the operator operates the reverse rotation switch 81, an operation signal is sent to the controller 80. If the controller 80 does not receive an operation signal from the reverse rotation switch 81, it determines that the control for rotating the cooling fans 61, 62 in reverse has not been turned ON (NO in the determination in step S2). In this case, the determination in step S2 is repeated. During this time, the cooling fans 61, 62 maintain forward rotation at a constant rotation speed, and the engine 40 maintains a constant torque output.

[0047] When the controller 80 receives the operation signal of the reverse rotation switch 81, it determines that the control for rotating the cooling fans 61, 62 in reverse has been turned ON (YES in step S2). In step S3, the controller 80 starts reverse operation of the cooling fans 61, 62. The controller 80 sends motor control signals SM1, SM2 to the electric motors 64, 65, respectively, thereby changing the rotation direction of the cooling fans 61, 62, which had been rotating forward, and rotates the cooling fans 61, 62 in reverse.

[0048] 4, at the time of "deceleration start", the cooling fans 61, 62 start to decelerate. The cooling fans 61, 62 rotating in the forward direction decelerate in order to switch to reverse rotation. The forward rotation speed of the cooling fans 61, 62 decreases.

[0049] In step S4, the controller 80 starts limiting the torque of the engine 40 when the cooling fans 61, 62 start to decelerate. As shown in Fig. 4, the controller 80 performs torque limiting of the engine 40 while the cooling fans 61, 62 are decelerating in order to switch the cooling fans 61, 62 from rotating in the forward direction to rotating in the reverse direction.

[0050] In step S5, the controller 80 judges whether the cooling fans 61, 62 have completely returned to normal rotation. If the cooling fans 61, 62 have not completely returned to normal rotation (NO in step S5), the judgment in step S5 is repeated. During this time, the output torque of the engine 40 remains limited.

[0051] 4, the cooling fans 61, 62 stop rotating in the forward direction. The cooling fans 61, 62 stop rotating in the reverse direction to switch between the forward rotation and the reverse rotation. The controller 80 limits the torque of the engine 40 while the cooling fans 61, 62 are stopped to switch from the forward rotation to the reverse rotation.

[0052] Next, the cooling fans 61, 62 start rotating in reverse. The cooling fans 61, 62 rotating in reverse accelerate. The rotation speed of the cooling fans 61, 62 in reverse increases. The controller 80 limits the torque of the engine 40 while the cooling fans 61, 62 are rotating in reverse and accelerating.

[0053] When the rotation speed of the cooling fans 61, 62 in the reverse rotation reaches a specified value, the cooling fans 61, 62 stop accelerating and maintain the rotation speed. The cooling fans 61, 62 rotate in the reverse direction at a constant speed. The controller 80 limits the torque of the engine 40 while the cooling fans 61, 62 rotate in the reverse direction at the constant speed.

[0054] When a predetermined time has elapsed, the cooling fans 61, 62 rotating in the reverse direction slow down. The number of rotations of the cooling fans 61, 62 rotating in the reverse direction decreases. The controller 80 limits the torque of the engine 40 while the cooling fans 61, 62 are rotating in the reverse direction and decelerating.

[0055] The cooling fan 61 stops reverse rotation. The cooling fans 61, 62 stop to switch between forward and reverse rotation. The controller 80 limits the torque of the engine 40 while the cooling fans 61, 62 are stopped to switch from reverse rotation to forward rotation.

[0056] The cooling fans 61, 62 start rotating in the forward direction. The cooling fans 61, 62 rotating in the forward direction accelerate. The forward rotation speed of the cooling fans 61, 62 increases. The controller 80 limits the torque of the engine 40 while the cooling fans 61, 62 are accelerating after the reverse rotation has been switched to the forward rotation.

[0057] When the rotation speed of the cooling fans 61, 62 in the forward rotation reaches the specified value, the determination in step S5 is YES. The cooling fans 61, 62 stop accelerating and maintain the rotation speed. The cooling fans 61, 62 rotate in the forward direction at a constant speed. The rotation speed of the cooling fans 61, 62 in the forward rotation at this time may be equal to the rotation speed of the cooling fans 61, 62 in the forward rotation up to the time of "deceleration start". The cooling fans 61, 62 stop accelerating at the time of "full return to forward rotation" and rotate in the forward direction at a constant rotation speed after that time. In step S6, the controller 80 releases the torque limit of the engine 40 when the cooling fans 61, 62, which have been switched from reverse rotation to forward rotation, stop accelerating. Then, the process is returned.

[0058] The controller 80 limits the output torque of the engine 40 when the cooling fans 61, 62 rotate in reverse. The "engine torque limit period" shown in Fig. 4 is the time from "start of deceleration" of the cooling fans 61, 62 to "complete return to forward rotation". The controller 80 continues to limit the output torque of the engine 40 from when the cooling fans 61, 62 rotating in the forward direction start to decelerate, until the cooling fans 61, 62 rotate in the reverse direction, resume forward rotation, and the forward rotation speed reaches a specified value.

[0059] The torque limit of the engine 40 will now be described. Fig. 5 is a diagram showing an engine output torque curve before limiting. The horizontal axis of Fig. 5 is the rotation speed of the engine 40, and the vertical axis is the output torque of the engine 40. The engine output torque curve L1 shown in Fig. 5 indicates the relationship between the rotation speed and output torque of the engine 40 in a state in which no torque limiting is being performed. The engine output torque curve L1 is stored in the controller 80.

[0060] Fig. 6 is a diagram showing an engine output torque curve during restriction. The horizontal axis of Fig. 6 is the rotation speed of the engine 40, and the vertical axis is the output torque of the engine 40. An engine output torque curve L2 shown by a solid line in Fig. 6 indicates the relationship between the rotation speed and output torque of the engine 40 in a state in which torque restriction is being performed. The engine output torque curve L2 is stored in the controller 80. A dashed line in Fig. 6 indicates the engine output torque curve L1 shown in Fig. 5. The engine output torque curve L2 during restriction limits the output torque of the engine 40 to a value smaller than the engine output torque curve L1 before restriction.

[0061] At the start of the engine torque limit period shown in Fig. 4, the torque curve used to control the engine 40 is changed from the engine output torque curve L1 to the engine output torque curve L2. In a state where torque limit is being performed, the output torque corresponding to the rotation speed of the engine 40 is made smaller than in a state where torque limit is not being performed. During the engine torque limit period, the controller 80 reduces the output torque of the engine 40 by sending an engine control signal SE according to the engine output torque curve L2 to the engine 40. At the end of the engine torque limit period, the torque curve used to control the engine 40 is returned from the engine output torque curve L2 to the engine output torque curve L1.

[0062] In the process of switching the cooling fans 61, 62 from forward rotation to reverse rotation and then back to forward rotation, the rotation speed of the cooling fans 61, 62 decreases, and the flow rate of air sent to the heat exchanger 70 decreases. During the reverse rotation of the cooling fans 61, 62, the direction of the air flow generated by the cooling fans 61, 62 becomes opposite to that during the forward rotation, and high-temperature air around the engine 40 that has received heat radiated by the engine 40 is sent to the heat exchanger 70. Due to these factors, when the cooling fans 61, 62 rotate in the reverse direction, their ability to cool the fluid to be cooled decreases.

[0063] By limiting the output torque of the engine 40, the amount of air intake (compression pressure) can be suppressed, and the amount of heat generated by the engine 40 is reduced. A rise in temperature of the air around the engine 40 that is supplied to the heat exchanger 70 during the reverse rotation of the cooling fans 61, 62 is suppressed. Air with a lower temperature is supplied to the heat exchanger 70, and the fluid to be cooled is cooled by heat exchange between the air supplied to the heat exchanger 70 and the fluid to be cooled. A decrease in the ability of the heat exchanger 70 to cool the fluid to be cooled is suppressed. The temperature of the air, which is the fluid to be cooled by the CAC 73, at the outlet of the CAC 73 can be reduced.

[0064] FIG. 7 is a diagram showing a comparative example of control of cooling fans 61, 62 and engine 40. As in FIG. 4, the horizontal axis of the three graphs shown in FIG. 7 is time. The vertical axis of the upper graph is the rotation speed of cooling fans 61, 62. The vertical axis of the middle graph is the output torque of engine 40. The vertical axis of the lower graph is the temperature of air, which is the fluid to be cooled by CAC 73, at the outlet of CAC 73. A judgment value is set for the air temperature.

[0065] 7, the output torque of the engine 40 is not limited when the cooling fans 61, 62 rotate in reverse. When the cooling fans 61, 62 are operated in reverse rotation, the cooling capacity decreases, and the outlet temperature of the CAC 73 starts to rise from the point when the cooling fans 61, 62 "start to decelerate". Since the output torque of the engine 40 is not limited and the temperature of the air supplied to the CAC 73 is high, the outlet temperature of the CAC 73 continues to rise, and a situation occurs in which the outlet temperature of the CAC 73 exceeds the judgment value before "complete return to normal rotation".

[0066] On the other hand, in the example shown in Fig. 4, the output torque of the engine 40 is limited when the cooling fans 61, 62 rotate in the reverse direction. The controller 80 starts limiting the output torque of the engine 40, triggered by outputting a command to decelerate the cooling fans 61, 62 that are rotating in the forward direction. The controller 80 releases the limit on the output torque of the engine 40, triggered by outputting a command to set the forward rotation speed of the cooling fans 61, 62 to a specified value. During the "engine torque limit period" shown in Fig. 4, the output torque of the engine 40 is limited.

[0067] The outlet temperature of the CAC 73 increases from the point when the cooling fans 61, 62 "start to decelerate." The temperature of the air supplied to the CAC 73 is lowered by limiting the output torque of the engine 40. As a result, even at the point when the CAC 73 "completely returns to normal rotation" when the outlet temperature of the CAC 73 is at its highest, the outlet temperature of the CAC 73 is kept lower than the determination value.

[0068] 8 is a diagram showing an example of the display unit 90. During an engine torque limiting period, the controller 80 displays a message 91 for calling attention on the display unit 90. The controller 80 outputs a command to the display unit 90 to display the message 91, triggered by outputting a command to decelerate the cooling fans 61, 62 rotating in the forward direction. The controller 80 outputs a command to the display unit 90 to erase the message 91, triggered by outputting a command to set the forward rotation speed of the cooling fans 61, 62 to a specified value.

[0069] The controller 80 displays a message 91 on the display unit 90 to alert the operator that the torque of the engine 40 is being limited. The operator can recognize that the torque of the engine 40 is being limited by looking at the display unit 90. This reduces the discomfort felt by the operator due to the engine 40 not outputting the torque value according to the operator's operation.

[0070] <Action and Effects> Although some of the description herein overlaps with the above description, the characteristic configuration and effects of this embodiment can be summarized as follows.

[0071] 2, the hydraulic excavator 1 includes an engine 40, a heat exchanger 70 through which a fluid to be cooled flows, cooling fans 61, 62 which rotate forward to send outside air to the heat exchanger 70 to cool the fluid to be cooled, and a controller 80. As shown in FIGS. 3 and 4, the controller 80 limits the torque of the engine 40 when the cooling fans 61, 62 rotate in reverse.

[0072] In the hydraulic excavator 1, the cooling fans 61, 62 may be rotated in reverse to clean the heat exchanger 70. When the cooling fans 61, 62 are rotated in reverse, the cooling capacity of the fluid to be cooled in the heat exchanger 70 decreases. During the reverse rotation of the cooling fans 61, 62, the temperature of the fluid to be cooled at the outlet of the heat exchanger 70 increases. As shown in FIGS. 3 and 4, the torque of the engine 40 is temporarily limited when the cooling fans 61, 62 rotate in reverse, thereby lowering the temperature of the air sent to the heat exchanger 70. Since the cooling capacity of the heat exchanger 70 for the fluid to be cooled can be ensured, the temperature increase of the fluid to be cooled at the outlet of the heat exchanger 70 can be suppressed.

[0073] 4, the controller 80 may limit the torque of the engine 40 while the cooling fans 61, 62 are rotating in reverse at a constant speed. While the cooling fans 61, 62 are rotating in reverse at a constant speed, the air around the engine 40 is sent to the heat exchanger 70, so that the cooling capacity of the heat exchanger 70 for the fluid to be cooled decreases. By limiting the torque of the engine 40 at this time, the cooling capacity of the heat exchanger 70 for the fluid to be cooled can be ensured.

[0074] 4, the controller 80 may limit the torque of the engine 40 while the cooling fans 61, 62 are rotating in reverse and accelerating. While the rotation speed of the cooling fans 61, 62 in reverse is increasing toward a certain speed, the flow rate of air sent to the heat exchanger 70 decreases, and the cooling capacity of the heat exchanger 70 for the fluid to be cooled decreases. By limiting the torque of the engine 40 at this time, the cooling capacity of the heat exchanger 70 for the fluid to be cooled can be ensured.

[0075] 4, the controller 80 may limit the torque of the engine 40 while the cooling fans 61, 62 are rotating in reverse and accelerating. While the rotation speed of the cooling fans 61, 62 in reverse rotation is decreasing from a constant speed, the flow rate of air sent to the heat exchanger 70 decreases, and the cooling capacity of the heat exchanger 70 for the fluid to be cooled decreases. By limiting the torque of the engine 40 at this time, the cooling capacity of the heat exchanger 70 for the fluid to be cooled can be ensured.

[0076] 4, the controller 80 may limit the torque of the engine 40 while the cooling fans 61, 62 are stopped to switch between forward and reverse rotation. While the cooling fans 61, 62 are stopped, the flow of air to the heat exchanger 70 is stopped, and the cooling capacity of the heat exchanger 70 for the fluid to be cooled is reduced. By limiting the torque of the engine 40 while the cooling fans 61, 62 are stopped in addition to while the cooling fans 61, 62 are rotating in the reverse direction, the cooling capacity of the heat exchanger 70 for the fluid to be cooled can be ensured.

[0077] 4, the controller 80 may limit the torque of the engine 40 while the cooling fans 61, 62 are decelerating in order to switch the cooling fans 61, 62 from rotating in the forward direction to rotating in the reverse direction. While the forward rotation speed of the cooling fans 61, 62 is decreasing, the flow rate of air sent to the heat exchanger 70 decreases, and the cooling capacity of the heat exchanger 70 for the fluid to be cooled is reduced. By limiting the torque of the engine 40 while the cooling fans 61, 62 are rotating in the forward direction and decelerating in addition to during the reverse rotation of the cooling fans 61, 62, the cooling capacity of the heat exchanger 70 for the fluid to be cooled can be ensured.

[0078] 3 and 4, the controller 80 may start limiting the torque of the engine 40 when the cooling fans 61, 62 start to decelerate. By starting to limit the torque of the engine 40 at the timing when the flow rate of air sent to the heat exchanger 70 starts to decrease, it is possible to ensure the cooling capacity of the heat exchanger 70 for the fluid to be cooled.

[0079] 4, the controller 80 may limit the torque of the engine 40 while the cooling fans 61, 62 are accelerating after switching from reverse rotation to forward rotation. While the forward rotation speed of the cooling fans 61, 62 is increasing toward a specified value, the flow rate of air sent to the heat exchanger 70 decreases, and the cooling capacity of the heat exchanger 70 for the fluid to be cooled is reduced. By limiting the torque of the engine 40 while the cooling fans 61, 62 are accelerating in the forward direction in addition to while the cooling fans 61, 62 are rotating in the reverse direction, the cooling capacity of the heat exchanger 70 for the fluid to be cooled can be ensured.

[0080] 3 and 4, the controller 80 may release the torque limit of the engine 40 when the cooling fans 61, 62 stop accelerating. When the forward rotation speed of the cooling fans 61, 62 reaches a specified value, a sufficient flow rate of outside air is sent to the heat exchanger 70. Since the heat exchanger 70 is in a state where it can fully exert its cooling capacity for the fluid to be cooled, it is not necessary to limit the torque of the engine 40 in order to ensure the cooling capacity of the heat exchanger 70 for the fluid to be cooled. By releasing the torque limit of the engine 40 in this state, the engine 40 can output torque in accordance with the operation of the operator, and the hydraulic excavator 1 can work efficiently.

[0081] 2, the cooling fans 61, 62 may be electric fans. The controller 80 appropriately transmits motor control signals SM1, SM2 to the electric motors 64, 65, so that the rotation direction of the cooling fans 61, 62 can be freely switched between forward and reverse rotation.

[0082] 8, the controller 80 may alert the operator to the state in which the torque of the engine 40 is being limited. This allows the operator to recognize that the torque of the engine is being limited.

[0083] 8, the controller 80 may display a message 91 for calling attention on the display unit 90. When the operator sees the message 91 for calling attention displayed on the display unit 90, the operator can reliably recognize that the torque of the engine is being limited.

[0084] The hydraulic excavator 1 of the embodiment includes a plurality of cooling fans 61, 62. The timing at which the plurality of cooling fans 61, 62 are switched from forward rotation to reverse rotation may be shifted, and the plurality of cooling fans 61, 62 may be switched from forward rotation to reverse rotation one by one in sequence. In this case, the timing of "deceleration start" shown in FIG. 4 is the time at which the cooling fan that is switched to reverse rotation first among the plurality of cooling fans 61, 62 starts to decelerate. The timing of "complete return to forward rotation" is the time at which the forward rotation speed of the cooling fan that is switched to reverse rotation last among the plurality of cooling fans 61, 62 reaches a specified value. Alternatively, the plurality of cooling fans 61, 62 may be switched from forward rotation to reverse rotation simultaneously.

[0085] Although the hydraulic excavator 1 in the embodiment is provided with two cooling fans 61, 62, it is sufficient that the hydraulic excavator 1 is provided with at least one cooling fan. The hydraulic excavator 1 may be provided with only one cooling fan, or may be provided with three or more cooling fans.

[0086] In the embodiment, an example has been described in which the output torque of the engine 40 is continuously limited from when the cooling fans 61, 62 rotating in the forward direction start to decelerate in order to switch to reverse rotation, until the cooling fans 61, 62, which are accelerating as the reverse rotation is switched to forward rotation, stop accelerating. The timing to start limiting the output torque of the engine may be set after the cooling fans 61, 62 start to decelerate. The timing to release the limit on the output torque of the engine may be set before the cooling fans 61, 62 stop accelerating. The period during which the output torque of the engine is limited can be shortened as much as possible within a range in which the temperature of the fluid to be cooled by the heat exchanger 70 can be kept lower than the judgment value. This can reduce the influence of the limit on the output torque of the engine on the operator.

[0087] In the embodiment, the hydraulic excavator 1 has been described as an example of a work machine, but the invention is not limited to the hydraulic excavator 1 and the concept of the present disclosure may be applied to other types of work machines such as wheel loaders and bulldozers.

[0088] <Additional Notes> The above description includes the following additional features.

[0089] (Appendix 1) The engine, a heat exchanger through which a fluid to be cooled flows; a cooling fan that rotates in a forward direction to send outside air to the heat exchanger to cool the fluid to be cooled; and a controller that limits the torque of the engine when the cooling fan rotates in reverse.

[0090] (Appendix 2) 2. The work machine of claim 1, wherein the controller limits the torque of the engine while the cooling fan is rotating in reverse at a constant speed.

[0091] (Appendix 3) 3. The work machine of claim 1 or 2, wherein the controller limits torque of the engine while the cooling fan is rotating in reverse and accelerating.

[0092] (Appendix 4) 4. The work machine according to any one of claims 1 to 3, wherein the controller limits torque of the engine while the cooling fan is rotating in reverse and decelerating.

[0093] (Appendix 5) The work machine according to any one of Supplementary Note 1 to Supplementary Note 4, wherein the controller limits the torque of the engine while the cooling fan is stopped for switching between forward rotation and reverse rotation.

[0094] (Appendix 6) The work machine according to any one of Supplementary Note 1 to Supplementary Note 5, wherein the controller limits the torque of the engine while decelerating in order to switch the cooling fan, which has been rotating in a forward direction, to a reverse direction.

[0095] (Appendix 7) 7. The work machine of claim 6, wherein the controller initiates torque limiting of the engine when the cooling fan begins to decelerate.

[0096] (Appendix 8) The work machine according to any one of Supplementary Note 1 to Supplementary Note 7, wherein the controller limits the torque of the engine while the cooling fan is accelerating after reverse rotation is switched to forward rotation.

[0097] (Appendix 9) 9. The work machine of claim 8, wherein the controller releases torque limiting of the engine when the cooling fan stops accelerating.

[0098] (Appendix 10) 10. The work machine according to any one of claims 1 to 9, wherein the cooling fan is an electric fan.

[0099] (Appendix 11) 11. The work machine according to any one of Supplementary Note 1 to Supplementary Note 10, wherein the controller alerts an operator to a state in which torque of the engine is being limited.

[0100] (Appendix 12) Further comprising a display unit for displaying information, The work machine according to claim 11, wherein the controller displays a message for calling attention on the display unit.

[0101] The embodiments disclosed herein are illustrative in all respects and should not be considered as limiting. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0102] 1 hydraulic excavator, 2 work machine, 3 vehicle body, 21 boom, 22 arm, 23 bucket, 31 travel unit, 33 swing unit, 35 swing motor, 40 engine, 41 output shaft, 45 hydraulic pump, 46 hydraulic oil tank, 47 main valve, 50 battery, 60 cooling device, 61, 62 cooling fan, 64, 65 electric motor, 70 heat exchanger, 71 radiator, 72 oil cooler, 73 CAC, 80 controller, 81 reverse rotation switch, 90 display unit, 91 message, 211 boom cylinder, 221 arm cylinder, 231 bucket cylinder, 311 track device, 312 travel motor, 331 frame, 332 cab, 333 engine room, L1, L2 engine output torque curve, SE engine control signal, SM1, SM2 motor control signal.

Claims

1. The engine, a heat exchanger through which a fluid to be cooled flows; a cooling fan that rotates in a forward direction to send outside air to the heat exchanger to cool the fluid to be cooled; and a controller that limits the torque of the engine when the cooling fan rotates in reverse.

2. The work machine of claim 1 , wherein the controller performs torque limiting of the engine while the cooling fan is rotating in reverse at a constant speed.

3. The work machine of claim 1 , wherein the controller torque limits the engine while the cooling fan is rotating in reverse and accelerating.

4. The work machine of claim 1 , wherein the controller torque limits the engine while the cooling fan is rotating in reverse and decelerating.

5. The work machine according to claim 1 , wherein the controller limits the torque of the engine while the cooling fan is stopped for switching between forward and reverse rotation.

6. 2. The work machine according to claim 1, wherein the controller limits the torque of the engine while the engine is decelerating in order to switch the cooling fan from rotating in a forward direction to rotating in a reverse direction.

7. The work machine of claim 6 , wherein the controller initiates torque limiting of the engine when the cooling fan begins to decelerate.

8. The work machine according to claim 1 , wherein the controller limits the torque of the engine while the cooling fan is accelerating after reverse rotation is switched to forward rotation.

9. The work machine of claim 8 , wherein the controller releases torque limiting of the engine when the cooling fan stops accelerating.

10. The work machine according to any one of claims 1 to 9, wherein the cooling fan is an electric fan.

11. The work machine according to claim 1 , wherein the controller issues a warning to an operator when the torque of the engine is being limited.

12. Further comprising a display unit for displaying information, The work machine according to claim 11, wherein the controller displays a message for calling attention on the display unit.

13. Rotating a cooling fan in a forward direction to send outside air to a heat exchanger through which a fluid to be cooled flows, thereby cooling the fluid to be cooled; limiting the torque of the engine when the cooling fan rotates in reverse.

Images