Working machinery and control methods

Abstract

Operate the compressor properly when the cooling fan is rotating in reverse. [Solution] The air conditioner includes a compressor that compresses the refrigerant and a condenser that cools the refrigerant. The cooling fan blows outside air to the condenser by rotating forward. When the controller switches the forward-rotating cooling fan to reverse rotation, it outputs a signal to stop the compressor after the rotation speed of the cooling fan has decreased.

Description

Technical Field

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

Background Art

[0002] Japanese Patent Application Laid-Open No. 2020-84520 (Patent Document 1) discloses a construction machine capable of removing dust from a heat exchanger unit by reversing a cooling fan.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the cooling fan rotates reversely, the high-temperature air in the engine room is sent to the condenser of the air conditioner, resulting in a decrease in the cooling capacity of the refrigerant. To suppress the pressure increase of the refrigerant, if the compressor of the air conditioner is stopped during the reverse rotation of the cooling fan, the air conditioning becomes ineffective, deteriorating the habitability in the cab.

[0005] The present disclosure proposes a technique for appropriately operating the compressor when the cooling fan rotates reversely.

Means for Solving the Problems

[0006] A work machine according to an aspect of the present disclosure includes an air conditioner, at least one cooling fan, and a controller. The air conditioner includes a compressor that compresses a refrigerant and a condenser that cools the refrigerant. The cooling fan sends outside air to the condenser by rotating forward. When the controller switches the cooling fan that is rotating forward to rotate reversely, after the rotation speed of the cooling fan decreases, the controller outputs a signal to stop the compressor.

[0007] A control method relating to a certain aspect of the present disclosure comprises the following steps: A first step is to supply outside air to the condenser of an air conditioner, which includes a compressor for compressing a refrigerant and a condenser for cooling the refrigerant, by rotating at least one cooling fan in the forward direction. A second step is to initiate a process to switch the forward-rotating cooling fan to reverse direction. A third step is to output a signal to stop the compressor after the rotational speed of the cooling fan has decreased. [Effects of the Invention]

[0008] According to this disclosure, the compressor can be operated properly when the cooling fan is rotating in reverse. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic side view showing the configuration of a hydraulic excavator. [Figure 2] This is a schematic block diagram showing the system configuration of a hydraulic excavator. [Figure 3] This is a schematic diagram showing the arrangement of equipment inside the engine compartment, as viewed from the rear. [Figure 4] This flowchart shows the process of stopping the compressor according to the rotation speed of the cooling fan. [Figure 5] This figure shows an example of the control of a cooling fan and compressor. [Figure 6] This is a diagram showing an example of a display unit. [Figure 7] This flowchart shows the process flow for stopping the compressor according to the rotation speed of the cooling fan according to the second embodiment. [Modes for carrying out the invention]

[0010] The embodiments will be described below 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 of them will not be repeated. In the drawings, some configurations may be omitted or simplified for the sake of explanation. It is also intended from the outset that any configuration may be extracted from the embodiments and combined in any way.

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

[0012] As shown in Figure 1, the hydraulic excavator 1 comprises a work implement 2 and a body 3. The body 3 includes a travel body 31, a swing circle 32, a slewing body 33, and a slewing motor 35.

[0013] The vehicle 31 has a pair of left and right tracked devices 311. Each of these left and right tracked devices 311 has a travel motor 312 and a track. The hydraulic excavator 1 moves under its own power as the left and right tracked devices are rotated by the travel motor 312.

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

[0015] The rotating body 33 is attached to the traveling body 31 via a swing circle 32. The rotating body 33 rotates relative to the traveling body 31 as the swing circle 32 rotates.

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

[0017] The working machine 2 is supported by the frame 331 on the front side of the revolving body 33 and, for example, on the right side of the cab 332. The working machine 2 is supported by the vehicle body 3 and is arranged in front of the vehicle body 3. The working 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 working machine 2.

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

[0019] The boom 21 of the working machine 2 rotates with respect to the revolving body 33 about a boom foot pin provided at the base end of the boom 21. The locus of a specific part of the boom 21 that rotates with respect to the revolving body 33, for example, the tip of the boom 21, is an arc, and a plane including the arc is specified. When the hydraulic excavator 1 is viewed in plan view, the plane is represented 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 revolving body 33, and hereinafter is simply referred to 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 revolving body 33 is the direction orthogonal to the front - rear direction in plan view, and hereinafter is simply referred to as the left - right direction.

[0020] In the front - rear direction, the side where the working 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 in the front direction, the right side and the left side in the left - right direction are the right direction and the left direction, respectively.

[0021] The forward / backward direction refers to the direction in which the operator is seated in the driver's seat within the driver's cab 332. The direction directly 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 rear direction. The left / right direction refers to the left / right direction from the perspective of the operator seated in the driver's seat. The right and left directions are to the right and left of the operator seated in the driver's seat, respectively, when the operator is facing directly forward.

[0022] In Figure 1, the front-to-back direction is indicated by arrow X, the left-to-right direction by arrow Y, and the up-to-down direction by arrow Z.

[0023] The boom 21 is attached to the slewing body 33. The base end of the boom 21 is rotatably connected to the slewing body 33 by a boom foot pin (not shown). The boom 21 is drivable by a boom cylinder 211. The boom cylinder 211 is driven by hydraulic fluid supplied from a hydraulic source. This drive allows the boom 21 to rotate vertically relative to the slewing body 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 is drivable by an arm cylinder 221. The arm cylinder 221 is driven by hydraulic fluid supplied from a hydraulic source. This drive allows the arm 22 to rotate vertically relative to the boom 21 around the boom tip pin 242.

[0025] The bucket 23 is attached to the end of the arm 22. The bucket 23 is rotatably connected to the end of the arm 22 by an arm end pin 243. The bucket 23 is drivable by a bucket cylinder 231. The bucket cylinder 231 is driven by hydraulic fluid supplied from a hydraulic power source. This drive allows the bucket 23 to rotate vertically relative to the arm 22 around the arm end pin 243. In this way, the work machine 2 is drivable.

[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 the power source of the hydraulic excavator 1. The engine 40 is the driving force behind the operation of the hydraulic excavator 1. The engine 40 is an internal combustion engine, such as a diesel engine. The rotational 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 the fuel injection pump of the engine 40.

[0027] The output shaft 41 of the engine 40 is connected to the power take-off unit 43. The driving force generated by the engine 40 is transmitted to the hydraulic pump 45 via the power take-off unit 43. The hydraulic pump 45 is driven by the engine 40. The hydraulic pump 45 draws in and discharges hydraulic fluid contained in the hydraulic fluid tank 46.

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

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

[0030] An alternator 44 is connected to the power take-off unit 43. The alternator 44 operates as a generator that produces electricity using the driving force generated by the engine 40. The rotational speed of the alternator 44 is set according to the rotational speed of the engine 40. The higher the rotational speed of the engine 40, the higher the rotational 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 electricity generated by the alternator 44 is stored in the battery 50. The battery 50 is an energy storage device that stores electricity. 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 system 60. The cooling system 60 is equipped with a heat exchanger 70. The heat exchanger 70 in this embodiment includes a radiator 71, an oil cooler 72, and a CAC (Charge Air Cooler) 73.

[0033] Coolant from the engine 40 flows through the radiator 71. The coolant from the engine 40 is the fluid that the radiator 71 cools. Hydraulic fluid supplied to the hydraulic actuator flows through the oil cooler 72. Hydraulic fluid is the fluid that the oil cooler 72 cools. Air supplied to the engine 40 flows through the CAC 73. The intake air from the engine 40 is the fluid that the CAC 73 cools.

[0034] The cooling device 60 includes a plurality of cooling fans, including a first cooling fan 61 and a second cooling fan 62. The first cooling fan 61 and the second cooling fan 62 are configured to have their rotation direction switchable. The first cooling fan 61 and the second cooling fan 62 are each configured to rotate in both forward and reverse directions.

[0035] The first cooling fan 61 and the second cooling fan 62 are each positioned facing the heat exchanger 70. The airflow generated by the first cooling fan 61 and the second cooling fan 62 cools the fluid to be cooled that flows through the heat exchanger 70. Heat exchange occurs between the fluid to be cooled and the outside air in the heat exchanger 70, and the fluid to be cooled is cooled by releasing heat from the fluid to the outside air.

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

[0037] The power stored in the battery 50 or generated by the alternator 44 is supplied to the first electric motor 64 and the second electric motor 65, driving them. The first cooling fan 61 and the second cooling fan 62 are driven by power supplied from the battery 50 or the alternator 44 to generate airflow through the heat exchanger 70. As the fluid to be cooled passes through the heat exchanger 70, it dissipates heat into the air, thereby cooling the fluid.

[0038] The hydraulic excavator 1 further includes a controller 80, a reverse rotation switch 81, and a display unit 82.

[0039] Controller 80 is a controller that controls the overall operation of the hydraulic excavator 1 and includes a CPU (Central Processing Unit), non-volatile memory, timer, etc. Controller 80 can transmit control signals to the engine 40, the first electric motor 64, the second electric motor 65, and the compressor 91, which will be described later. Controller 80 has programs for controlling the engine 40, the first cooling fan 61, the second cooling fan 62, and the compressor 91, as well as various data necessary for executing those programs, pre-stored in Controller 80.

[0040] In this embodiment, the controller 80 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 located outside the hydraulic excavator 1. The controller 80 may be located at the work site of the hydraulic excavator 1, or it may be located in a remote location away from the work site of the hydraulic excavator 1. The hydraulic excavator 1 and the controller 80 located outside the hydraulic excavator 1 may constitute the control system for the hydraulic excavator 1.

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

[0042] The reverse rotation switch 81 is located around the driver's seat where the operator sits. For example, the reverse rotation switch 81 is located inside the driver's cab 332. The reverse rotation switch 81 may be displayed on a touch panel or it may be a push-button switch. The reverse rotation switch 81 is operated by the operator to reverse the rotation of the first cooling fan 61 and the second cooling fan 62.

[0043] The display unit 82 displays various information related to the hydraulic excavator 1. The display unit 82 is located in front of the operator's seat where the operator sits. The display unit 82 is located, for example, inside the operator's cabin 332. The display unit 82 may include a liquid crystal display, an organic EL display, etc. The display unit 82 receives command signals from the controller 80 and displays various information on its screen.

[0044] A fan speed sensor 66 is attached to the first cooling fan 61. The fan speed sensor 66 detects the rotational speed of the first cooling fan 61. The fan speed sensor 66 outputs the detected rotational speed to the controller 80. A fan speed sensor 67 is attached to the second cooling fan 62. The fan speed sensor 67 detects the rotational speed of the second cooling fan 62. The fan speed sensor 67 outputs the detected rotational speed to the controller 80.

[0045] A temperature sensor 74 is attached to the radiator 71. The temperature sensor 74 detects the temperature of the coolant for the engine 40, which is the fluid to be cooled flowing through the radiator 71. The temperature sensor 74 outputs the detected temperature to the controller 80. A temperature sensor 75 is attached to the oil cooler 72. The temperature sensor 75 detects the temperature of the hydraulic oil, which is the fluid to be cooled flowing through the oil cooler 72. The temperature sensor 75 outputs the detected temperature to the controller 80. A temperature sensor 76 is attached to the CAC 73. The temperature sensor 76 detects the temperature of the air supplied to the engine 40, which is the fluid to be cooled flowing through the CAC 73. The temperature sensor 76 outputs the detected temperature to the controller 80.

[0046] Hydraulic excavator 1 is further equipped with an air conditioner 90. The air conditioner 90 includes a compressor 91, a condenser 92, an expansion valve 93, and an evaporator 94. The compressor 91, condenser 92, expansion valve 93, and evaporator 94 are connected in series via a pipeline.

[0047] The compressor 91 uses the driving force of the engine 40 to compress the refrigerant into a high-temperature, high-pressure gas. The controller 80 sends a compressor control signal SC to the compressor 91 to start and stop it. The refrigerant compressed by the compressor 91 is sent to the condenser 92.

[0048] The condenser 92 cools and liquefies the gaseous refrigerant. The first cooling fan 61 and the second cooling fan 62 supply outside air to the condenser 92. The refrigerant passing through the condenser 92 is cooled by dissipating heat into the air. The cooled refrigerant is then sent to the expansion valve 93.

[0049] The expansion valve 93 adiabatically expands the high-pressure liquid refrigerant, creating a low-temperature, low-pressure gas-liquid mixture. The throttling action of the expansion valve 93 reduces the refrigerant pressure to a level at which it can easily evaporate. The reduced-pressure refrigerant is then sent to the evaporator 94.

[0050] The evaporator 94 cools the air by absorbing heat from the surrounding air through vaporization of the liquid refrigerant. The air cooled by the evaporator 94 is then sent into the operator's chamber 332. The refrigerant is circulated to the compressor 91.

[0051] As the first cooling fan 61 and the second cooling fan 62 rotate in the forward direction, outside air is drawn into the engine compartment 333 and sent to the heat exchanger 70 and the condenser 92. The outside air temperature sensor 84 detects the temperature of the outside air. The outside air temperature sensor 84 outputs the detected outside air temperature T to the controller 80.

[0052] <Arrangement of cooling device 60> The arrangement of the cooling system 60 will now be described. Figure 3 is a schematic diagram showing the arrangement of equipment inside the engine compartment 333, viewed from the rear. The engine 40 and the cooling system 60 are housed inside the engine compartment 333. The engine 40 is located in the center of the engine compartment 333 in the left-right direction. The engine 40 has a right side surface 40R that faces to the right. The hydraulic pump 45 is located to the right of the engine 40 and faces the right side surface 40R of the engine 40.

[0053] The cooling unit 60 is located to the left of the engine 40. The cooling unit 60 is located towards the left side of the engine compartment 333. The cooling unit 60 is located closer to the left side 33L of the slewing body 33 than to the engine 40. A left vent is formed on the left side 33L of the slewing body 33. The heat exchanger 70 and condenser 92 are positioned facing the left vent. The first cooling fan 61 and the second cooling fan 62 rotate in the forward direction to draw outside air into the engine compartment 333 from the left vent and send the outside air to the heat exchanger 70 and condenser 92.

[0054] The engine 40 has a left side surface 40L that faces to the left. The first cooling fan 61 and the second cooling fan 62 are located to the left of the engine 40 and face the left side surface 40L of the engine 40. The outside air temperature sensor 84 is mounted on the left side surface 33L of the rotating body 33. Inside the engine compartment 333, the outside air temperature sensor 84, condenser 92, heat exchanger 70, cooling fans 61 and 62, engine 40, and hydraulic pump 45 are arranged in that order from left to right.

[0055] The first cooling fan 61 and the second cooling fan 62, when rotating in the forward direction, generate an airflow within the engine compartment 333 from left to right. The forward-rotating first cooling fan 61 and the second cooling fan 62 generate an airflow that passes through the condenser 92 and the heat exchanger 70 and then heads towards the engine 40. The air that has passed through the condenser 92 and the heat exchanger 70 is blown towards the engine 40, generating an airflow that circulates around the engine 40.

[0056] The first cooling fan 61 and the second cooling fan 62 rotate in opposite directions, generating an airflow within the engine compartment 333 from right to left.

[0057] Within the engine compartment 333, the radiator 71, CAC 73, and oil cooler 72 are arranged in that order from front to back. The radiator 71 includes a cooling core containing multiple heat exchange tubes. The heat exchange tubes form the flow path for the engine 40 coolant, from the inlet at the top of the radiator 71 to the outlet at the bottom. The radiator 71 is designed so that the engine 40 coolant enters from the top and exits from the bottom.

[0058] The oil cooler 72 includes a cooling core containing multiple heat exchange tubes. The heat exchange tubes form the flow path for hydraulic fluid from the inlet at the top of the oil cooler 72 to the outlet at the bottom. The oil cooler 72 is designed so that hydraulic fluid enters from the top and exits from the bottom. The CAC 73 also includes a cooling core containing multiple heat exchange tubes. The heat exchange tubes form the flow path for air from the inlet at the top of the CAC 73 to the outlet at the bottom. The CAC 73 is designed so that air enters from the top and exits from the bottom.

[0059] The first cooling fan 61 and the second cooling fan 62 supply outside air to the cooling core of the radiator 71, the cooling core of the oil cooler 72, the cooling core of the CAC 73, and the condenser 92.

[0060] <Control of cooling fans 61, 62 and compressor 91> The control of the first cooling fan 61, the second cooling fan 62, and the compressor 91 by the controller 80 in the hydraulic excavator 1 having the above configuration will be described below.

[0061] Figure 4 is a flowchart showing the process of stopping the compressor 91 according to the rotation speed of the cooling fans 61 and 62. Figure 5 is a diagram showing an example of the control of the cooling fans 61 and 62 and the compressor 91. Figure 5 shows four graphs arranged vertically in the figure. The horizontal axis of the four graphs is time. The vertical axis of the top graph is the rotation speed of the cooling fans 61 and 62. The vertical axis of the second graph from the top is the refrigerant pressure of the air conditioner 90. The vertical axis of the third graph from the top is the ambient temperature detected by the ambient temperature sensor 84. The vertical axis of the bottom graph is the operating state of the compressor 91.

[0062] In step S1 shown in Figure 4, the controller 80 rotates the first cooling fan 61 and the second cooling fan 62 in the forward direction while maintaining a constant rotational speed +R1. The outside air temperature drawn into the engine compartment 333 by the forward-rotating first cooling fan 61 and the second cooling fan 62 is kept constant at temperature T1. The refrigerant is sufficiently cooled by the outside air supplied to the condenser 92, and the refrigerant pressure is kept constant at pressure P1. The compressor 91 is operating and in the ON state.

[0063] In step S2, the controller 80 starts the process of switching the first cooling fan 61 and the second cooling fan 62, which are rotating in the forward direction, to reverse direction. When the operator operates the reverse rotation switch 81, an operation signal is sent to the controller 80. Upon receiving the operation signal from the reverse rotation switch 81, the controller 80 starts the process of switching the first cooling fan 61 and the second cooling fan 62, which are rotating in the forward direction, to reverse direction. Alternatively, the controller 80 may determine that the first cooling fan 61 and the second cooling fan 62 have been operating in the forward direction for a predetermined time and automatically start the process of switching the first cooling fan 61 and the second cooling fan 62, which are rotating in the forward direction, to reverse direction.

[0064] At time t1 shown in Figure 5, the controller 80 starts the first cooling fan 61 and the second cooling fan 62 to rotate in the reverse direction. The controller 80 transmits motor control signals SM1 and SM2 to the electric motors 64 and 65, respectively, to decelerate the forward-rotating cooling fans 61 and 62 in order to switch them to reverse rotation. As shown in Figure 5, after time t1, the forward rotation speed of the first cooling fan 61 and the second cooling fan 62 decreases from rotation speed + R1 and approaches zero.

[0065] As the rotational speeds of the first cooling fan 61 and the second cooling fan 62 decrease, the flow rate of outside air taken into the engine compartment 333 is reduced. This reduces the ability of the condenser 92 to cool the refrigerant. The refrigerant pressure increases from pressure P1.

[0066] Even after time t1 has elapsed, when the rotation speed of the first cooling fan 61 and the second cooling fan 62 begins to decrease, the compressor 91 continues to operate and remains in the ON state. By not stopping the compressor 91 and not stopping the flow of refrigerant at time t1, the operation of the air conditioner 90 continues. As a result, the time during which the air conditioning is not effective is shortened, the temperature rise in the operator's cab 332 is suppressed, and the deterioration of habitability is suppressed.

[0067] In step S3, the controller 80 determines whether the rotational speed of the first cooling fan 61 and the second cooling fan 62 has reached a threshold rotational speed RTH. The rotational speed of the first cooling fan 61 and the second cooling fan 62 may be an actual value detected by the fan speed sensors 66 and 67, or it may be a command value based on the motor control signals SM1 and SM2 transmitted from the controller 80 to the first electric motor 64 and the second electric motor 65.

[0068] If it is determined that the rotational speeds of the first cooling fan 61 and the second cooling fan 62 have not decreased to the threshold rotational speed RTH (NO in the determination in step S3), the determination in step S3 is repeated.

[0069] When it is determined that the rotational speeds of the first cooling fan 61 and the second cooling fan 62 have reached a threshold rotational speed RTH (YES in the determination in step S3), in step S4, the controller 80 outputs a signal to stop the compressor 91. At time t2 shown in Figure 5, the controller 80 determines that the forward rotational speeds of the first cooling fan 61 and the second cooling fan 62 have decreased to the threshold rotational speed RTH. While the controller 80 is decelerating the first cooling fan 61 and the second cooling fan 62, which are rotating forward, to reverse rotation, it sends a compressor control signal SC to the compressor 91 to stop the compressor 91. The operating state of the compressor 91 switches from the ON state to the OFF state.

[0070] If the forward rotation speeds of the first cooling fan 61 and the second cooling fan 62 become too low, the flow rate of outside air sent to the condenser 92 of the air conditioner 90 decreases, resulting in insufficient cooling of the refrigerant. The refrigerant pressure rises, and a refrigerant pressure abnormality error is triggered. If the compressor 91 continues to operate without stopping even when the forward rotation speeds of the first cooling fan 61 and the second cooling fan 62 fall below the threshold rotation speed RTH, the refrigerant pressure will continue to rise, as shown by the dashed line in the second graph from the top in Figure 5, until it reaches a level that triggers an error.

[0071] When the forward rotation speeds of the first cooling fan 61 and the second cooling fan 62 decrease to a threshold rotation speed RTH, the compressor 91 is stopped, which prevents the refrigerant pressure from rising, as shown by the solid line in the second graph from the top in Figure 5. Since the refrigerant pressure rise can be kept at a pressure P2 that does not trigger an error, the triggering of a refrigerant pressure abnormality error can be avoided, and the discomfort to the operator caused by the error can be mitigated.

[0072] In step S5, the controller 80 displays the operating status of the compressor 91 on the display unit 82. Figure 6 shows an example of the display unit 82. While the compressor 91 is stopped, the controller 80 displays a notification message 83 on the display unit 82. The controller 80 triggers a command to the display unit 82 to display the message 83 when the rotational speeds of the first cooling fan 61 and the second cooling fan 62 drop to a threshold rotational speed RTH.

[0073] The controller 80 notifies the operator that the compressor 91 has stopped and the air conditioning function of the air conditioner 90 has stopped by displaying message 83 on the display unit 82. The operator can recognize that the air conditioning function has stopped by looking at the display unit 82. The operator can recognize that the air conditioning function will be resolved in a short time because the first cooling fan 61 and the second cooling fan 62 are rotating in reverse, thus alleviating the operator's discomfort. In addition to the message 83 shown in Figure 6, the controller 80 may also display the approximate estimated time until the compressor 91 restarts on the display unit 82.

[0074] As shown in Figure 5, at time t3, the rotational speeds of the first cooling fan 61 and the second cooling fan 62 decrease to zero, and the first cooling fan 61 and the second cooling fan 62 stop rotating in the forward direction. The first cooling fan 61 and the second cooling fan 62 stop in order to switch between forward and reverse rotation.

[0075] After time t3, the first cooling fan 61 and the second cooling fan 62 begin to rotate in the opposite direction. The first cooling fan 61 and the second cooling fan 62, which are now rotating in the opposite direction, accelerate. The rotational speed of the first cooling fan 61 and the second cooling fan 62 in the opposite direction increases.

[0076] While the first cooling fan 61 and the second cooling fan 62 are rotating in the forward direction, even if the rotational speed decreases, the direction of the outside air flow is from outside to inside the engine compartment 333, so the outside air temperature does not rise from temperature T1. When the first cooling fan 61 and the second cooling fan 62 start rotating in the reverse direction at time t3, the direction of the air flow generated by the first cooling fan 61 and the second cooling fan 62 becomes the opposite direction to when they are rotating in the forward direction. While the first cooling fan 61 and the second cooling fan 62 are rotating in the reverse direction, the hot air around the engine 40, which has been heated by the engine 40, flows through the heat exchanger 70 and the condenser 92 to the outside air temperature sensor 84. As a result, the outside air temperature detected by the outside air temperature sensor 84 rises.

[0077] At time t4, when the reverse rotation speed of the first cooling fan 61 and the second cooling fan 62 reaches a specified rotation speed -R1, the first cooling fan 61 and the second cooling fan 62 stop accelerating and maintain that rotation speed -R1. The first cooling fan 61 and the second cooling fan 62 rotate in reverse at a constant speed. While the first cooling fan 61 and the second cooling fan 62 are rotating in reverse at a constant speed between times t4 and t5, the controller 80 maintains the compressor 91 in a stopped state.

[0078] When a predetermined time has elapsed for the reverse rotation and it is time t5, the process proceeds to step S6, and the controller 80 starts the process of switching the first cooling fan 61 and the second cooling fan 62, which are rotating in reverse, to forward rotation. The first cooling fan 61 and the second cooling fan 62, which are rotating in reverse, decelerate. The rotational speed of the first cooling fan 61 and the second cooling fan 62 in reverse rotation decreases. The compressor 91 remains stopped at the time the process of switching the first cooling fan 61 and the second cooling fan 62, which are rotating in reverse, to forward rotation begins. While the first cooling fan 61 and the second cooling fan 62 are rotating in reverse and decelerating between times t5 and t6, the controller 80 maintains the compressor 91 in a stopped state.

[0079] At time t6, the rotational speeds of the first cooling fan 61 and the second cooling fan 62 decrease to zero, and the first cooling fan 61 and the second cooling fan 62 stop rotating in the reverse direction. The first cooling fan 61 and the second cooling fan 62 stop in order to switch between forward and reverse rotation. At time t6, the compressor 91 remains stopped. The controller 80 maintains the state in which the compressor 91 is stopped while the first cooling fan 61 and the second cooling fan 62 are stopped in order to switch from reverse to forward rotation.

[0080] After time t6, the first cooling fan 61 and the second cooling fan 62 begin to rotate in the forward direction. The first cooling fan 61 and the second cooling fan 62, whose direction of rotation has been changed and are now rotating in the forward direction, accelerate. The forward rotation speed of the first cooling fan 61 and the second cooling fan 62 increases. Even after time t6, when the first cooling fan 61 and the second cooling fan 62 begin to rotate in the forward direction, has passed, the compressor 91 remains stopped. The controller 80 maintains the compressor 91 stopped for at least a portion of the time while the reverse rotation of the first cooling fan 61 and the second cooling fan 62 is switched to forward rotation and accelerates.

[0081] Immediately after the first cooling fan 61 and the second cooling fan 62 return to forward rotation, the high-temperature outside air remains around the condenser 92 due to the inertia of the airflow, causing the outside air temperature detected by the outside air temperature sensor 84 to continue rising. At time t7, the outside air temperature rises to its peak value, temperature T2. As the forward rotation speed of the first cooling fan 61 and the second cooling fan 62 increases, the direction of the outside air flow changes, and outside air flows from outside to inside the engine compartment 333. As a result, the outside air temperature begins to decrease from its peak value, temperature T2.

[0082] In step S7, the controller 80 determines whether the ambient temperature detected by the ambient temperature sensor 84 has dropped to the threshold temperature TTH. If it is determined that the ambient temperature has not dropped to temperature TTH (NO in the determination in step S7), the determination in step S7 is repeated.

[0083] When it is determined that the ambient temperature has fallen from its peak temperature T2 to the threshold temperature TTH (YES in the determination in step S7), in step S8, the controller 80 outputs a signal to restart the compressor 91. At time t8 shown in Figure 5, the controller 80 determines that the ambient temperature has fallen to the threshold temperature TTH. Triggered by the ambient temperature dropping to temperature TTH, the controller 80 sends a compressor control signal SC to the compressor 91, starting the compressor 91. The operating state of the compressor 91 switches from OFF to ON.

[0084] If the compressor 91 is started when the outside air temperature is high, the hot outside air is sent to the condenser 92 of the air conditioner 90, resulting in insufficient cooling of the refrigerant. The refrigerant pressure rises, and a refrigerant pressure abnormality error is triggered. If the compressor 91 is restarted when the outside air temperature is higher than the threshold temperature TTH, the refrigerant pressure rises to a level that triggers an error.

[0085] By restarting the compressor 91 when the ambient temperature drops to the threshold temperature TTH and cooler ambient air is supplied to the condenser 92, a rise in refrigerant pressure can be avoided. As shown in Figure 5, by starting the compressor 91 after the condenser 92 has regained its ability to cool the refrigerant with ambient air, the refrigerant pressure can be reduced from the time t8 when the compressor 91 is started. The refrigerant pressure can be kept at a level that does not trigger an error alarm, thus mitigating operator discomfort caused by error alarms.

[0086] The controller 80, triggered by the ambient temperature dropping to a threshold temperature TTH, outputs a command to the display unit 82 to clear the notification message 83 shown in Figure 6. When the forward rotation speed of the first cooling fan 61 and the second cooling fan 62 reaches a specified rotation speed + R1, the first cooling fan 61 and the second cooling fan 62 stop accelerating and rotate forward while maintaining a constant rotation speed + R1. The first cooling fan 61 and the second cooling fan 62 fully return to forward rotation. The refrigerant pressure returns to the normal pressure P1. The ambient temperature returns to the normal temperature T1. Then, the process ends.

[0087] [Second Embodiment] The hydraulic excavator 1 according to the second embodiment does not need to be equipped with the ambient air temperature sensor 84 shown in Figures 2 and 3. The temperature of the ambient air supplied to the heat exchanger 70 and condenser 92 does not need to be detected. If the ambient air temperature is not used, the compressor 91 may be restarted after a predetermined time has elapsed from the time t2 when the compressor 91 is stopped. The predetermined time is determined in advance by experimentation or the like and stored in the controller 80. The starting point of the predetermined time is not limited to the time t2 when the compressor 91 is stopped, but may be the time t5 when the process of switching the fan that is rotating in reverse to forward rotation starts, or it may be the time t1 when the process of switching the fan that is rotating in forward rotation starts.

[0088] Figure 7 is a flowchart showing the process flow for stopping the compressor 91 according to the rotation speed of the cooling fans 61 and 62 according to the second embodiment. The control method of the second embodiment shown in Figure 7 does not include step S7, which was described with reference to Figure 4, for determining whether the ambient temperature has dropped to a threshold temperature TTH. When the controller 80 starts the process of switching the first cooling fan 61 and the second cooling fan 62, which are rotating in reverse, to forward rotation in step S6, the process proceeds to step S17, where the controller 80 determines whether a predetermined time has elapsed since the compressor 91 was stopped.

[0089] If it is determined that the predetermined time has not yet elapsed (NO in the determination in step S17), the determination in step S17 is repeated. If it is determined that the predetermined time has elapsed (YES in the determination in step S17), in step S8, the controller 80 outputs a signal to restart the compressor 91. The controller 80 uses the elapsed time as a trigger to start the compressor 91 by sending a compressor control signal SC to the compressor 91.

[0090] In the second embodiment, the timing for restarting the compressor 91 can be determined with a simple configuration that does not use an outside air temperature sensor 84 for detecting the outside air temperature. By starting the compressor 91 at a timing that ensures the cooling capacity of the refrigerant in the condenser 92, the rise in refrigerant pressure can be suppressed. It is possible to reliably avoid the refrigerant pressure rising to a level that triggers an error alert.

[0091] <Mechanism of Action and Effects> Although some of the above description overlaps with the above, the characteristic configuration and effects of this embodiment can be summarized as follows.

[0092] As shown in Figure 2, the hydraulic excavator 1 is equipped with an air conditioner 90, cooling fans 61 and 62, and a controller 80. The air conditioner 90 includes a compressor 91 for compressing the refrigerant and a condenser 92 for cooling the refrigerant. The cooling fans 61 and 62 supply outside air to the condenser 92 by rotating in the forward direction. As shown in Figures 4 and 5, when the controller 80 switches the forward-rotating cooling fans 61 and 62 to reverse rotation, it outputs a compressor control signal SC that stops the compressor 91 after the rotational speed of the cooling fans 61 and 62 has decreased.

[0093] In hydraulic excavator 1, the cooling fans 61 and 62 are sometimes rotated in reverse to clean the heat exchanger 70. When the cooling fans 61 and 62 are rotated in reverse, the timing of outputting the compressor control signal SC to stop the compressor 91 of the air conditioner 90 is delayed compared to the timing of commanding the switching from forward rotation to reverse rotation of the cooling fans 61 and 62, so that the signal is sent only after the rotational speed of the cooling fans 61 and 62 has started to decrease. By delaying the timing at which the compressor 91 stops and the air conditioning becomes ineffective, the downtime of the compressor 91 is shortened, and the time during which the air conditioning is ineffective is reduced. By properly operating the compressor 91 when the cooling fans 61 and 62 are rotated in reverse, the temperature rise in the operator's cab 332 can be suppressed, and the deterioration of the habitability of the operator's cab 332 can be suppressed.

[0094] The timing for stopping the compressor 91 can be either the timing for switching the cooling fans 61 and 62 from forward rotation to reverse rotation (time t3 shown in Figure 5), or after the cooling fans 61 and 62 have started to rotate in reverse (after time t3). This is preferable because it allows for further delay in stopping the compressor 91. On the other hand, when the forward rotation speed of the cooling fans 61 and 62 decreases, the flow rate of outside air sent to the condenser 92 decreases. While the cooling fans 61 and 62 are rotating in reverse, hot air from around the engine 40 flows into the condenser 92. As a result, the cooling capacity of the refrigerant in the condenser 92 decreases. If the refrigerant is not sufficiently cooled in the condenser 92, the refrigerant pressure will rise. When the refrigerant pressure rises, an error will be triggered.

[0095] As shown in Figure 5, the controller 80 may output a compressor control signal SC to stop the compressor 91 while it is decelerating the cooling fans 61 and 62, which are rotating in the forward direction, to switch them to reverse direction. The time t2 at which the compressor 91 is stopped, as shown in Figure 5, is earlier than the time t3 at which the rotational speed of the cooling fans 61 and 62 becomes zero, and is set to the timing when the rotational speed of the cooling fans 61 and 62 is decreasing from rotational speed + R1 towards zero. In this way, the rise in refrigerant pressure can be suppressed, and it is possible to reliably avoid the refrigerant pressure rising to a level that would trigger an error.

[0096] As shown in Figure 5, the controller 80 may stop the compressor 91 at time t2 and maintain the stopped state of the compressor 91 at time t5, when it starts the process of switching the cooling fans 61 and 62, which are rotating in reverse, to forward rotation. At time t5, when it starts the process of returning the cooling fans 61 and 62 to forward rotation, the cooling fans 61 and 62 are rotating in reverse, and hot air from around the engine 40 is flowing through the condenser 92. At time t5, the refrigerant cannot be sufficiently cooled by the condenser 92, so the compressor 91 is kept stopped without being restarted. In this way, the rise in refrigerant pressure can be suppressed, and the issuance of an error can be avoided.

[0097] As shown in Figure 5, the ambient temperature rises while the cooling fans 61 and 62 are rotating in reverse. The controller 80 may output a compressor control signal SC to restart the compressor 91 after the ambient temperature sensor 84 detects that the ambient temperature has fallen from its peak temperature T2. If the compressor 91 is restarted when the ambient temperature is high, the high temperature of the ambient air sent to the condenser 92 reduces the cooling capacity of the refrigerant in the condenser 92. If the refrigerant is not sufficiently cooled in the condenser 92, the refrigerant pressure will rise, and an error will be triggered. By starting the compressor 91 when the ambient temperature has dropped sufficiently, the rise in refrigerant pressure can be suppressed. This ensures that the refrigerant pressure does not rise to a level that triggers an error.

[0098] As shown in Figures 2 and 3, the hydraulic excavator 1 may be equipped with multiple cooling fans 61 and 62. In this case, the multiple cooling fans 61 and 62 may be switched from forward rotation to reverse rotation simultaneously, but it is possible to stagger the timing of switching the multiple cooling fans 61 and 62 from forward rotation to reverse rotation. For example, by delaying the switching of one cooling fan positioned opposite the condenser 92 to reverse rotation, the timing of stopping the compressor 91 can be delayed. By switching the multiple cooling fans from forward rotation to reverse rotation one by one in sequence, and operating so that at least one cooling fan continues to supply outside air to the condenser 92, the time during which the air conditioning is not effective can be further reduced.

[0099] As shown in Figure 2, the cooling fans 61 and 62 may be electric fans. The controller 80 can appropriately transmit motor control signals SM1 and SM2 to the electric motors 64 and 65, allowing the rotation direction of the cooling fans 61 and 62 to be freely switched between forward and reverse rotation.

[0100] As shown in Figures 2 and 6, the controller 80 may display a message 83 indicating the operating status of the compressor 91 on the display unit 82. By viewing the message 83 displayed on the display unit 82, the operator can reliably recognize that the compressor 91 is stopped.

[0101] Although the hydraulic excavator 1 in this embodiment is equipped with two cooling fans 61 and 62, the hydraulic excavator 1 only needs to be equipped with at least one cooling fan. The hydraulic excavator 1 may be equipped with only one cooling fan, or it may be equipped with three or more cooling fans.

[0102] In this embodiment, a hydraulic excavator 1 was described as an example of a work machine, but the concept of this disclosure may be applied not only to the hydraulic excavator 1 but also to other types of work machines such as wheel loaders and bulldozers.

[0103] <Note> The above description includes the following features.

[0104] (Note 1) An air conditioner including a compressor for compressing a refrigerant and a condenser for cooling the refrigerant, A cooling fan that rotates in the forward direction to send outside air to the condenser, A work machine comprising: a controller that, when switching the forward-rotating cooling fan to reverse rotation, outputs a signal to stop the compressor after the rotational speed of the cooling fan has decreased.

[0105] (Note 2) The working machine as described in Appendix 1, wherein the controller outputs a signal to stop the compressor while it is decelerating to switch the forward-rotating cooling fan to reverse rotation.

[0106] (Note 3) The working machine as described in Appendix 1 or Appendix 2, wherein the controller maintains the compressor in a stopped state when it starts the process of switching the cooling fan, which is rotating in reverse, to rotating in the forward direction.

[0107] (Note 4) The capacitor further comprises an outside air temperature sensor that detects the temperature of the outside air supplied to the capacitor, The working machine according to any one of Appendix 1 to 3, wherein the outside air temperature sensor detects that the outside air temperature, which rises while the cooling fan is rotating in reverse, has fallen from its peak value, and then the controller outputs a signal to restart the compressor.

[0108] (Note 5) The aforementioned at least one cooling fan is a working machine according to any one of the appendices 1 to 4, comprising a plurality of cooling fans.

[0109] (Note 6) The cooling fan is an electric fan, as described in any one of the items in Appendix 1 to Appendix 5 of the work machine.

[0110] (Note 7) It further includes a display unit for displaying information, The controller is a working machine as described in any one of the appendices 1 to 6, which displays the operating status of the compressor on the display unit.

[0111] (Note 8) A step of supplying outside air to the condenser of an air conditioner, which includes a compressor for compressing a refrigerant and a condenser for cooling the refrigerant, by rotating at least one cooling fan in the forward direction; The steps include: starting a process to switch the cooling fan, which is rotating in the forward direction, to rotate in the reverse direction; A control method comprising the step of outputting a signal to stop the compressor after the rotation speed of the cooling fan has decreased.

[0112] (Note 9) The control method described in Appendix 8, wherein in the output step, a signal to stop the compressor is output while the cooling fan is decelerating to switch from forward rotation to reverse rotation.

[0113] (Note 10) The control method according to Appendix 8 or Appendix 9, wherein the compressor is kept stopped at the time the process of switching the cooling fan, which is rotating in reverse, to rotating in the forward direction is initiated.

[0114] (Note 11) The control method according to any one of appendices 8 to 10, further comprising the step of restarting the compressor after the temperature of the outside air supplied to the condenser, which rises while the cooling fan is rotating in reverse, has fallen from its peak value.

[0115] (Note 12) The control method described in any one of appendices 8 to 11, wherein the at least one cooling fan includes a plurality of cooling fans.

[0116] (Note 13) The control method described in any one of Appendix 8 to Appendix 12, wherein the cooling fan is an electric fan.

[0117] (Note 14) The control method according to any one of the appendices 8 to 13, further comprising the step of displaying the operating status of the compressor on a display unit that displays information.

[0118] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the claims rather than the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended. [Explanation of Symbols]

[0119] 1 Hydraulic excavator, 2 Work equipment, 3 Body, 31 Running body, 33 Slewing body, 33L, 40L Left side, 40 Engine, 44 Alternator, 47 Main valve, 50 Battery, 60 Cooling system, 61 First cooling fan, 62 Second cooling fan, 64 First electric motor, 65 Second electric motor, 70 Heat exchanger, 71 Radiator, 72 Oil cooler, 73 CAC, 80 Controller, 81 Reverse rotation switch, 82 Display unit, 83 Message, 84 Outside air temperature sensor, 90 Air conditioner, 91 Compressor, 92 Condenser, 93 Expansion valve, 94 Evaporator, 333 Engine room, SC Compressor control signal.

Claims

1. An air conditioner including a compressor for compressing a refrigerant and a condenser for cooling the refrigerant, A cooling fan that rotates in the forward direction to send outside air to the condenser, A work machine comprising: a controller that, when switching the forward-rotating cooling fan to reverse rotation, outputs a signal to stop the compressor after the rotational speed of the cooling fan has decreased.

2. The working machine according to claim 1, wherein the controller outputs a signal to stop the compressor while it is decelerating to switch the cooling fan, which is rotating in the forward direction, to reverse direction.

3. The working machine according to claim 1, wherein the controller maintains the compressor in a stopped state when it starts the process of switching the cooling fan, which is rotating in reverse, to rotating in the forward direction.

4. The capacitor further comprises an outside air temperature sensor that detects the temperature of the outside air supplied to the capacitor, The working machine according to claim 1, wherein the outside air temperature sensor detects that the outside air temperature, which rises while the cooling fan is rotating in reverse, has fallen from its peak value, and then the controller outputs a signal to restart the compressor.

5. The work machine according to claim 1, wherein the at least one cooling fan includes a plurality of cooling fans.

6. The working machine according to claim 1, wherein the cooling fan is an electric fan.

7. It further includes a display unit for displaying information, The work machine according to claim 1, wherein the controller displays the operating status of the compressor on the display unit.

8. A step of supplying outside air to the condenser of an air conditioner, which includes a compressor for compressing a refrigerant and a condenser for cooling the refrigerant, by rotating at least one cooling fan in the forward direction; The steps include: starting a process to switch the cooling fan, which is rotating in the forward direction, to rotate in the reverse direction; A control method comprising the step of outputting a signal to stop the compressor after the rotation speed of the cooling fan has decreased.

9. The control method according to claim 8, wherein in the output step, a signal to stop the compressor is output while the cooling fan is decelerating to switch from forward rotation to reverse rotation.

10. The control method according to claim 8, wherein the compressor is kept stopped at the time the process of switching the cooling fan, which is rotating in reverse, to rotating in the forward direction is initiated.

11. The control method according to claim 8, further comprising the step of restarting the compressor after the temperature of the outside air supplied to the condenser, which rises while the cooling fan is rotating in reverse, has fallen from its peak value.

12. The control method according to claim 8, wherein the at least one cooling fan includes a plurality of cooling fans.

13. The control method according to claim 8, wherein the cooling fan is an electric fan.

14. The control method according to claim 8, further comprising the step of displaying the operating status of the compressor on a display unit that displays information.

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