Work machine and method for controlling work machine

Abstract

The invention suppresses a temperature rise in a fluid to be cooled by a heat exchanger. This work machine is provided with: an engine; a heat exchanger inside 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 that limits the torque of the engine when the cooling fan rotates in the reverse direction.

Description

Work machine and work machine control method

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

[0002] An example of prior art is the work machine described in Japanese Patent Laid-Open Publication No. 2023-50941 (Patent Document 1). 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 continue rotating forward or reverse when the rotation of at least one cooling fan stops during the change from forward to reverse rotation.

[0003] Japanese Patent Application Laid-Open No. 2023-50941

[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 supplying it 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's 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.

[0006] According to the present disclosure, there is provided 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, wherein the controller limits the torque of the engine when the cooling fan rotates reversely.

[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.

[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.

[0009] FIG. 1 is a side view showing a schematic configuration of a hydraulic excavator. FIG. 2 is a schematic block diagram showing a system configuration of a hydraulic excavator. FIG. 3 is a flowchart showing a process flow for controlling engine output according to the rotation speed of a cooling fan. FIG. 4 is a diagram showing an example of control of a cooling fan and an engine. FIG. 5 is a diagram showing an engine output torque curve before restriction. FIG. 6 is a diagram showing an engine output torque curve during restriction. FIG. 7 is a diagram showing a comparative example of control of a cooling fan and an engine. FIG. 8 is a diagram showing an example of a display unit.

[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 descriptions thereof will not be repeated. In the drawings, configurations may be omitted or simplified for the sake of convenience. It is also intended from the beginning that any configurations may be extracted from the embodiments and arbitrarily combined.

[0011] <Overall Configuration> In this 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 implement 2 and a vehicle body 3. The vehicle body 3 includes a running body 31, a swing circle 32, a swing body 33, and a swing motor 35.

[0013] The running body 31 has a pair of left and right track devices 311. Each of the pair of left and right track devices 311 has a travel motor 312 and a track. 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 due to the rotational drive of the swing motor 35. The travel motor 312 and the swing motor 35 are hydraulic motors that are driven by hydraulic oil supplied from a hydraulic source (a hydraulic pump 45 and a hydraulic oil tank 46; see FIG. 2).

[0015] The revolving body 33 is installed on the running body 31 via the swing circle 32. The revolving body 33 revolves relative to the running body 31 as the swing circle 32 rotates.

[0016] The revolving unit 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 located, for example, on the front left side (front side of the vehicle) of the revolving unit 33. The engine room 333 is located at the rear of the revolving unit 33 (rear side of the vehicle).

[0017] The work implement 2 is supported by the frame 331 on the front side of the revolving unit 33, for example, on the right side of the operator's cab 332. The work implement 2 is supported by the vehicle body 3 and is disposed in front of the vehicle body 3. The work implement 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 implement 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 implement 2 rotates around a boom foot pin provided at the base end of the boom 21 relative to the rotating unit 33. A specific portion of the boom 21 that rotates relative to the rotating unit 33, for example the tip of the boom 21, moves along an arc-shaped trajectory, and a plane that includes this arc is identified. When the hydraulic excavator 1 is viewed from above, this plane is represented as a straight line. The direction in which this straight line extends is the fore-and-aft direction of the vehicle body 3 of the hydraulic excavator 1 or the fore-and-aft direction of the rotating unit 33, and will hereinafter also be referred to simply as the fore-and-aft direction. The left-and-right direction (vehicle width direction) of the vehicle body 3 of the hydraulic excavator 1 or the left-and-right direction of the rotating unit 33 is a direction perpendicular to the fore-and-aft direction in a plan view, and will hereinafter also be referred to simply as the left-and-right direction.

[0020] In the front-to-rear direction, the side where the work implement 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 and left sides 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 and left directions, 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 revolving unit 33. The base end of the boom 21 is rotatably connected to the revolving unit 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 revolving unit 33 around the boom foot pin.

[0024] The arm 22 is attached to the tip of the boom 21. The 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 power source. This drive allows the bucket 23 to rotate vertically relative to the arm 22 around the arm tip pin 243. The work implement 2 can be driven in this manner.

[0026] <System Configuration> Figure 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 housed in the engine compartment 333 (Figure 1). The engine 40 is disposed in the center of the engine compartment 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. The 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] The hydraulic oil discharged from the hydraulic pump 45 is supplied to various hydraulic actuators via a 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 travel motor 312, which are also shown in Figure 1. The engine 40 is a drive source for operating the work implement 2, for rotating the swing unit 33, and for traveling the travel unit 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 to operate the hydraulic 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, and the greater the amount of electricity generated by the alternator 44.

[0031] The alternator 44 and the battery 50 are electrically connected. The electric power generated by the alternator 44 is stored in the battery 50. The battery 50 is an electric power 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 housed in the engine compartment 333. The cooling device 60 is arranged to the left of the engine 40. The cooling device 60 is arranged closer to the left side of the engine compartment 333 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 and 62 are each disposed opposite the heat exchanger 70. The cooling fans 61 and 62 are configured so that their rotation directions can be switched. Each of the cooling fans 61 and 62 is configured so that it can rotate forward and backward.

[0035] The cooling fans 61, 62 rotate forward to draw outside air into the engine compartment 333 through a left air vent formed on the left side of the revolving body 33 and send the outside air to the heat exchanger 70. The airflow generated by the cooling fans 61, 62 cools the fluid to be cooled flowing through the heat exchanger 70. In the heat exchanger 70, heat is exchanged between the fluid to be cooled and the outside air, 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, and generate a flow of air that passes through the heat exchanger 70. When the fluid to be cooled passes through the heat exchanger 70, heat is released into 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, as well as 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 external to 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 external to 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 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 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 this embodiment having the above configuration will be described below. FIG. 3 is a flowchart showing the flow of a process for controlling the output of the engine 40 in accordance with the rotation speeds of the cooling fans 61, 62. FIG. 4 is a diagram showing an example of control of the cooling fans 61, 62 and the engine 40. The horizontal axis of the three graphs shown in FIG. 4 represents time. The vertical axis of the upper graph represents the rotation speed of the cooling fans 61, 62. The vertical axis of the middle graph represents the output torque of the engine 40. The vertical axis of the lower graph represents the temperature of air, which is the fluid to be cooled by the CAC 73, at the outlet of the CAC 73. A judgment value is defined for the air temperature.

[0045] In step S1 shown in Fig. 3, the cooling fans 61 and 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 and 62 rotate forward at a constant rotation speed, and the engine 40 outputs a constant torque.

[0046] In step S2, it is determined whether 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 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 reverse rotation of the cooling fans 61, 62 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 causing the cooling fans 61, 62 to rotate in the reverse direction.

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

[0049] In step S4, when the cooling fans 61, 62 start to decelerate, the controller 80 starts limiting the torque of the engine 40. As shown in Fig. 4, the controller 80 limits 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.

[0050] In step S5, controller 80 determines whether cooling fans 61, 62 have completely returned to normal rotation. If cooling fans 61, 62 have not completely returned to normal rotation (NO in step S5), the determination in step S5 is repeated. During this time, the output torque of 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. The controller 80 limits the torque of the engine 40 while the cooling fans 61, 62 are stopped in order to switch from forward rotation to reverse rotation.

[0052] Next, the cooling fans 61, 62 start to rotate in reverse. The cooling fans 61, 62 that are 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 direction reaches a predetermined value, the cooling fans 61, 62 stop accelerating and maintain their 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 are rotating in the reverse direction at a constant speed.

[0054] After a predetermined time has elapsed, the cooling fans 61, 62 that are rotating in the reverse direction slow down, and the rotation speed of the cooling fans 61, 62 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 rotating in reverse. The cooling fans 61 and 62 stop to switch between forward and reverse rotation. The controller 80 limits the torque of the engine 40 while the cooling fans 61 and 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 that are 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 direction reaches the specified value, a YES determination is made in step S5. The cooling fans 61, 62 stop accelerating and maintain their 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 direction at this time may be equal to the rotation speed of the cooling fans 61, 62 in the forward direction up to the "deceleration start" time. The cooling fans 61, 62 stop accelerating at the "full return to forward rotation" time and rotate in the forward direction at a constant rotation speed thereafter. In step S6, the controller 80 releases the torque limit on the engine 40 when the cooling fans 61, 62, which have been switched from reverse rotation to forward rotation, stop accelerating. The process then returns.

[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 when the cooling fans 61, 62 start to decelerate until they completely return to normal rotation. The controller 80 continues to limit the output torque of the engine 40 from when the cooling fans 61, 62 start to decelerate while rotating in the forward direction, until the cooling fans 61, 62 rotate in the reverse direction, resume normal rotation, and reach a specified rotation speed.

[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 represents the rotation speed of the engine 40, and the vertical axis represents the output torque of the engine 40. The engine output torque curve L1 shown in Fig. 5 represents the relationship between the rotation speed and output torque of the engine 40 when no torque limiting is 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 represents the rotation speed of the engine 40, and the vertical axis represents the output torque of the engine 40. The engine output torque curve L2 shown by a solid line in Fig. 6 represents the relationship between the rotation speed and output torque of the engine 40 when torque restriction is being performed. The engine output torque curve L2 is stored in the controller 80. The dashed line in Fig. 6 represents the engine output torque curve L1 shown in Fig. 5. The engine output torque curve L2 during restriction restricts 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 limiting period shown in Figure 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. When torque limiting is being performed, the output torque corresponding to the engine 40 rotation speed is made smaller than when torque limiting is not being performed. During the engine torque limiting period, the controller 80 reduces the output torque of the engine 40 by sending an engine control signal SE to the engine 40 that conforms to the engine output torque curve L2. At the end of the engine torque limiting 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 is opposite to that during forward rotation, and high-temperature air around the engine 40 that has absorbed 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, thereby reducing the amount of heat generated by the engine 40. The temperature rise 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. The 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 lowered.

[0064] FIG. 7 is a diagram showing a comparative example of control of the cooling fans 61, 62 and the engine 40. As in FIG. 4, the horizontal axis of the three graphs shown in FIG. 7 represents time. The vertical axis of the upper graph represents the rotation speed of the cooling fans 61, 62. The vertical axis of the middle graph represents the output torque of the engine 40. The vertical axis of the lower graph represents 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 defined 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, the cooling capacity decreases, and the outlet temperature of the CAC 73 begins to rise from the point when the cooling fans 61, 62 start to "deceleration." Because 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 determination value before "full 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 when it is 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 when it is 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 rises from the point at which 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 at which the outlet temperature of the CAC 73 reaches its highest point at which the engine 40 has completely returned to normal rotation, the outlet temperature of the CAC 73 is kept lower than the reference value.

[0068] 8 is a diagram showing an example of the display unit 90. During the 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 slow down the cooling fans 61, 62 that are 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. By looking at the display unit 90, the operator can recognize that the torque of the engine 40 is being limited. This alleviates the discomfort felt by the operator when the engine 40 is not outputting the torque value in accordance with the operator's operation.

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

[0071] As shown in Fig. 2, the hydraulic excavator 1 includes an engine 40, a heat exchanger 70 through which a fluid to be cooled flows, cooling fans 61 and 62 that 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 and 62 rotate reversely.

[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 , by temporarily limiting the torque of the engine 40 when the cooling fans 61, 62 rotate in reverse, the temperature of the air sent to the heat exchanger 70 is lowered. 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, air around the engine 40 is sent to the heat exchanger 70, reducing the cooling capacity of the heat exchanger 70 for the fluid to be cooled. 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 speeds of the cooling fans 61, 62 are increasing toward a certain speed in the reverse rotation, the flow rate of air sent to the heat exchanger 70 decreases, thereby reducing the cooling capacity of the heat exchanger 70 for the fluid to be cooled. 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 decelerating. While the rotation speeds of the cooling fans 61, 62 in reverse rotation are decreasing from a constant speed, the flow rate of air sent to the heat exchanger 70 decreases, thereby reducing the cooling capacity of the heat exchanger 70 for the fluid to be cooled. 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, thereby reducing the cooling capacity of the heat exchanger 70 for the fluid to be cooled. 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 from rotating in the forward direction to rotating in the reverse direction. While the rotation speeds of the cooling fans 61, 62 are decreasing in the forward direction, the flow rate of air sent to the heat exchanger 70 decreases, thereby reducing the cooling capacity of the heat exchanger 70 for the fluid to be cooled. By limiting the torque of the engine 40 while the cooling fans 61, 62 are rotating in the forward direction and decelerating, as well as 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.

[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 when the flow rate of air sent to the heat exchanger 70 starts to decrease, the cooling capacity of the heat exchanger 70 for the fluid to be cooled can be ensured.

[0079] 4, the controller 80 may limit the torque of the engine 40 while the cooling fans 61, 62 are switched from reverse rotation to forward rotation and accelerating. While the forward rotation speeds of the cooling fans 61, 62 are increasing toward a specified value, the flow rate of air sent to the heat exchanger 70 decreases, thereby reducing the cooling capacity of the heat exchanger 70 for the fluid to be cooled. By limiting the torque of the engine 40 while the cooling fans 61, 62 are rotating forward and accelerating, as well as while the cooling fans 61, 62 are rotating reversely, 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 on the engine 40 when the cooling fans 61, 62 stop accelerating. When the forward rotation speeds of the cooling fans 61, 62 reach a specified value, a sufficient flow rate of outside air is sent to the heat exchanger 70. Because the heat exchanger 70 is in a state where it can fully demonstrate 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 on the engine 40 in this state, the engine 40 can output torque in accordance with the operator's operation, allowing the hydraulic excavator 1 to work efficiently.

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

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

[0085] Although the hydraulic excavator 1 of 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 the time when the cooling fans 61, 62, which are rotating in the forward direction, start to decelerate in order to switch to reverse rotation, until the cooling fans 61, 62, which are accelerating, stop accelerating after the reverse rotation is switched to forward rotation. The timing for starting to limit the engine output torque may be set to be later than the time when the cooling fans 61, 62 start to decelerate. The timing for releasing the limit on the engine output torque may be set to be earlier than the time when the cooling fans 61, 62 stop accelerating. The period during which the engine output torque is limited can be shortened as long as the temperature of the fluid to be cooled in the heat exchanger 70 can be kept lower than the judgment value. This reduces the impact of the limit on the engine output torque on the operator.

[0087] In the embodiment, a hydraulic excavator 1 has been described as an example of a work machine, but the concept of the present disclosure may be applied to other types of work machines, such as wheel loaders and bulldozers, without being limited to the hydraulic excavator 1.

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

[0089] (Supplementary Note 1) A work machine comprising: 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 that limits the torque of the engine when the cooling fan rotates reversely.

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

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

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

[0093] (Supplementary Note 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 to switch between forward rotation and reverse rotation.

[0094] (Supplementary Note 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 the engine is decelerating in order to switch the cooling fan from forward rotation to reverse rotation.

[0095] (Supplementary Note 7) The work machine according to Supplementary Note 6, wherein the controller starts limiting the torque of the engine when the cooling fan starts to decelerate.

[0096] (Supplementary Note 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 the reverse rotation has been switched to the forward rotation.

[0097] (Supplementary Note 9) The work machine according to Supplementary Note 8, wherein the controller releases the torque limit on the engine when the cooling fan stops accelerating.

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

[0099] (Supplementary Note 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] (Supplementary Note 12) The work machine according to Supplementary Note 11, further comprising a display unit that displays information, wherein the controller displays a message for calling attention on the display unit.

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

[0102] 1 Hydraulic excavator, 2 Work machine, 3 Body, 21 Boom, 22 Arm, 23 Bucket, 31 Traveling body, 33 Swing body, 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 Operator's cab, 333 Engine room, L1, L2 Engine output torque curve, SE Engine control signal, SM1, SM2 Motor control signal.

Claims

1. A work machine comprising: an engine; a heat exchanger through which a fluid to be cooled flows; a cooling fan that rotates in the 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 according to claim 1, wherein said controller limits the torque of said engine while said cooling fan is rotating in reverse at a constant speed.

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

4. The work machine of claim 1, wherein the controller performs torque limiting of 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. 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 the torque limit of the engine when the cooling fan stops accelerating.

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

11. A work machine according to any one of claims 1 to 9, wherein the controller alerts an operator to a state in which torque of the engine is being limited.

12. A work machine as set forth in claim 11, further comprising a display unit for displaying information, wherein the controller displays a message for calling attention on the display unit.

13. A control method for a work machine, comprising: rotating a cooling fan in the 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; and limiting the torque of the engine when the cooling fan rotates in the reverse direction.

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