Control system for industrial machinery

Abstract

It suppresses the pressure rise of the refrigerant in the air conditioner. [Solution] The air conditioner that cools the driver's cab where the operator of the work machine sits includes a compressor that compresses the refrigerant and a condenser that cools the refrigerant. The control system of the work machine includes a cooling fan that blows air onto the condenser, a pressure switch that detects the refrigerant pressure, and a controller. The cooling fan can switch the direction of airflow between forward and reverse. The period from when the airflow of the cooling fan starts to decrease in order to switch the airflow direction from forward to reverse until the airflow returns to the forward direction and the airflow returns to normal is defined as the airflow adjustment period. During the airflow adjustment period, the controller stops the compressor when the refrigerant pressure rises to the first pressure PR1, and starts the compressor when the refrigerant pressure drops from the first pressure PR1 to the second pressure PR2.

Description

Technical Field

[0001] The present disclosure relates to a control system for a work machine.

Background Art

[0002] Japanese Patent Application Laid-Open No. 2014-167286 (Patent Document 1) discloses a work vehicle that performs forward and reverse rotation of a cooling fan. A compressor compresses the refrigerant from a condenser through which the refrigerant of the air conditioning equipment flows. When the fan is driven in reverse, the drive of the compressor is stopped.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When switching the blowing direction of a cooling fan that blows air to a condenser that cools the refrigerant of an air conditioner, the pressure of the refrigerant may increase, and the air conditioner may stop, resulting in a decrease in the habitability of the operation room.

[0005] In the present disclosure, a control system for a work machine that can suppress an increase in the pressure of the refrigerant of an air conditioner is proposed.

Means for Solving the Problems

[0006] A control system for a work machine according to this disclosure comprises a cab in which an operator sits to operate the work machine, and an air conditioner for cooling the cab. The air conditioner includes a compressor for compressing a refrigerant and a condenser for cooling the refrigerant. The control system for the work machine comprises a cooling fan for blowing air onto the condenser, a pressure switch for detecting the refrigerant pressure, and a controller. The cooling fan is switchable between forward and reverse airflow directions. The period from when the airflow of the cooling fan begins to decrease in order to switch the airflow direction from forward to reverse until the airflow returns to the forward direction and the airflow returns to normal is defined as the airflow adjustment period. During the airflow adjustment period, the controller stops the compressor when the refrigerant pressure rises to a first pressure, and starts the compressor when the refrigerant pressure drops from the first pressure to a second pressure. [Effects of the Invention]

[0007] According to the control system described in this disclosure, it is possible to suppress the pressure rise of the refrigerant in an air conditioner. [Brief explanation of the drawing]

[0008] [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 machine room, as viewed from the rear. [Figure 4] This flowchart shows the process flow for controlling the compressor according to the refrigerant pressure. [Figure 5] This figure shows an example of the control of a cooling fan and compressor. [Modes for carrying out the invention]

[0009] 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.

[0010] <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.

[0011] 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.

[0012] 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.

[0013] 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).

[0014] 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.

[0015] The revolving body 33 has a frame 331 to which the working machine 2 is attached, a cab 332, and a machine 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 machine room 333 is arranged at the rear part (rear side of the vehicle) of the revolving body 33.

[0016] 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.

[0017] In this embodiment, the positional relationship of each part of the hydraulic excavator 1 will be described with reference to the working machine 2.

[0018] 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 portion of the boom 21. The locus of a specific portion of the boom 21 that rotates with respect to the revolving body 33, for example, the tip portion of the boom 21, is an arc shape, 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 is hereinafter 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 a direction orthogonal to the front-rear direction in plan view, and is hereinafter simply referred to as the left-right direction.

[0019] 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. When 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.

[0020] The front-back direction is the front-back direction of the operator sitting on the driver's seat in the cab 332. The direction facing the operator sitting on the driver's seat is the front direction, and the direction behind the operator sitting on the driver's seat is the back direction. The left-right direction is the left-right direction of the operator sitting on the driver's seat. When the operator sitting on the driver's seat faces forward, the right side and the left side are the right direction and the left direction respectively.

[0021] In the drawings, the front-back direction is indicated by arrow X in the figure, the left-right direction is indicated by arrow Y in the figure, and the up-down direction is indicated by arrow Z in the figure.

[0022] The boom 21 is attached to the revolving body 33. The base end portion of the boom 21 is rotatably connected to the revolving 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 oil supplied from a hydraulic source. By this drive, the boom 21 is rotatable in the up-down direction with respect to the revolving body 33 about the boom foot pin.

[0023] The arm 22 is attached to the tip of the boom 21. The base end portion of the arm 22 is rotatably connected to the tip portion 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 oil supplied from a hydraulic source. By this drive, the arm 22 is rotatable in the up-down direction with respect to the boom 21 about the boom tip pin 242.

[0024] The bucket 23 is attached to the tip of the arm 22. The bucket 23 is rotatably connected to the tip portion of the arm 22 by an arm tip pin 243. The bucket 23 is drivable by a bucket cylinder 231. The bucket cylinder 231 is driven by hydraulic oil supplied from a hydraulic source. By this drive, the bucket 23 is rotatable in the up-down direction with respect to the arm 22 about the arm tip pin 243. Thus, the working machine 2 is drivable.

[0025] <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 electric motor 40. The electric motor 40 is the power source of the hydraulic excavator 1. The electric motor 40 is driven by power supplied to the electric motor 40 from power stored in a 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. The hydraulic excavator 1 may also receive power from an external power source via a power cable, and the electric motor 40 may be driven and controlled by a control panel.

[0026] The output shaft 41 of the electric motor 40 is connected to the hydraulic pump 45. The driving force generated by the electric motor 40 is transmitted to the hydraulic pump 45 via the output shaft 41. The hydraulic pump 45 is driven by the electric motor 40. The hydraulic pump 45 draws in and discharges the hydraulic fluid contained in the hydraulic fluid tank 46.

[0027] 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 electric motor 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.

[0028] 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.

[0029] 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 has an oil cooler. Hydraulic fluid supplied to the hydraulic actuator flows through the inside of the oil cooler. The hydraulic fluid is the fluid to be cooled by the oil cooler.

[0030] The cooling device 60 is equipped with a cooling fan 61. The cooling fan 61 is positioned opposite the heat exchanger 70. The airflow generated by the cooling fan 61 cools the fluid to be cooled that flows through the heat exchanger 70. In the heat exchanger 70, the fluid to be cooled and the outside air exchange heat, and the fluid to be cooled is cooled by releasing heat from the fluid to the outside air.

[0031] The cooling fan 61 is configured to allow switching of its rotation direction. The cooling fan 61 is configured to allow forward and reverse rotation. By switching the rotation direction of the cooling fan 61, the direction of airflow can be switched.

[0032] The cooling fan 61 is an electric fan. The electric motor 64 is electrically connected to the battery 50. The cooling fan 61 is driven by the electric motor 64. Power stored in the battery 50 is supplied to the electric motor 64, which drives the electric motor 64. The cooling fan 61 is driven by power supplied from the battery 50 and generates an airflow that passes 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 to be cooled.

[0033] The hydraulic excavator 1 is further equipped with controllers, namely a fan controller 80 and an air conditioning controller 82. The fan controller 80 and the air conditioning controller 82 may be an integrated controller. The fan controller 80 and the air conditioning controller 82 are connected to each other so that they can send and receive signals. Such a controller controls the overall operation of the hydraulic excavator 1, including at least the cooling fan 61, and is composed of a CPU (Central Processing Unit), non-volatile memory, a timer, etc. The controller is capable of transmitting control signals to the electric motor 40, the electric motor 64, and the compressor 91, which will be described later. The controller has programs for controlling the electric motor 40, the cooling fan 61, and the compressor 91, as well as various data necessary for executing those programs, pre-stored in the controller.

[0034] The fan controller 80 and air conditioner controller 82 in this embodiment are mounted on the hydraulic excavator 1. The fan controller 80 and air conditioner controller 82 do not necessarily have to be mounted on the hydraulic excavator 1. The fan controller 80 and air conditioner controller 82 may be located outside the hydraulic excavator 1. The fan controller 80 and air conditioner controller 82 may be located at the work site of the hydraulic excavator 1, or they may be located in a remote location away from the work site of the hydraulic excavator 1. The hydraulic excavator 1 and the fan controller 80 and air conditioner controller 82 located outside the hydraulic excavator 1 may constitute the control system of the hydraulic excavator 1.

[0035] The fan controller 80 sends a motor control signal SM to the electric motor 64 to control the rotation direction and rotation speed of the cooling fan 61.

[0036] The hydraulic excavator 1 is further equipped with a reverse rotation switch 81. The reverse rotation switch 81 is located around the operator's seat where the operator sits. The reverse rotation switch 81 is located, for example, inside the operator'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 reverse the rotation of the cooling fan 61.

[0037] 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.

[0038] The compressor 91 uses the driving force of the electric motor 40 to compress the refrigerant into a high-temperature, high-pressure gas. The air conditioner controller 82 sends a compressor control signal SC1 to the compressor 91 to start and stop it. The refrigerant compressed by the compressor 91 is sent to the condenser 92.

[0039] The condenser 92 cools and liquefies the gaseous refrigerant. The cooling fan 61 blows outside air into 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.

[0040] 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 evaporation is easily achieved. The expansion valve 93 corresponds to an example of a pressure reducer that reduces the pressure of the refrigerant. The expansion valve 93 may also be a thermostatic expansion valve that adjusts its valve opening according to the refrigerant temperature at the outlet of the evaporator 94. The pressure reducer may also be a capillary tube. The reduced-pressure refrigerant is then sent to the evaporator 94.

[0041] 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.

[0042] The pressure switch 84 has the function of detecting the pressure of the high-pressure refrigerant compressed by the compressor 91. The pressure switch 84 detects the pressure of the refrigerant in the path connecting the condenser 92 and the expansion valve 93. The pressure switch 84 also has the function of shutting off the power supplied to the compressor 91 when the detected refrigerant pressure P is high.

[0043] <Arrangement of cooling device 60> The arrangement of the cooling device 60 will now be described. Figure 3 is a schematic diagram showing the arrangement of equipment inside the machine room 333, viewed from the rear of the machine room 333. The electric motor 40 and the cooling device 60 are housed inside the machine room 333. The electric motor 40 is located in the center of the machine room 333 in the left-right direction. The electric motor 40 has a right side surface 40R that faces to the right.

[0044] The hydraulic pump 45 is positioned to the right of the electric motor 40 and faces the right side surface 40R of the electric motor 40. The hydraulic pump 45 is positioned closer to the right side surface 33R of the slewing body 33 than to the electric motor 40. A right vent is formed on the right side surface 33R of the slewing body 33.

[0045] The cooling device 60 is located to the left of the electric motor 40. The cooling device 60 is located towards the left side of the machine room 333. The cooling device 60 is located closer to the left side 33L of the slewing body 33 than the electric motor 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.

[0046] The electric motor 40 has a left side surface 40L that faces to the left. The cooling fan 61 is located to the left of the electric motor 40 and faces the left side surface 40L of the electric motor 40. Inside the machine room 333, the condenser 92, heat exchanger 70, cooling fan 61, electric motor 40, and hydraulic pump 45 are arranged in that order from left to right.

[0047] The cooling fan 61, by rotating in the forward direction, generates an airflow within the machine room 333 from left to right. The forward-rotating cooling fan 61 draws outside air into the machine room 333 through the left vent on the left side 33L and sends it to the heat exchanger 70 and the condenser 92. After passing through the condenser 92 and the heat exchanger 70, the air is blown towards the electric motor 40, generating an airflow around the electric motor 40. The air is then discharged from the machine room 333 through the right vent on the right side 33R.

[0048] The cooling fan 61 rotates in the reverse direction, generating an airflow from right to left within the machine room 333. The reverse-rotating cooling fan 61 draws outside air into the machine room 333 through the right vent on the right side 33R. The outside air is blown towards the electric motor 40, generating an airflow around the electric motor 40. After passing around the electric motor 40, the air is sent to the heat exchanger 70 and the condenser 92. After passing through the condenser 92 and the heat exchanger 70, the air is discharged from the machine room 333 through the left vent on the left side 33L.

[0049] In this specification, the direction of airflow from the cooling fan 61 when it is rotating in the forward direction is referred to as the forward direction. The forward direction is the -Y direction. The forward direction is the direction of airflow toward the right. In this specification, the direction of airflow from the cooling fan 61 when it is rotating in the reverse direction is referred to as the reverse direction. The reverse direction is the +Y direction. The reverse direction is the direction of airflow toward the left.

[0050] The heat exchanger 70 includes a cooling core containing multiple heat exchange tubes. The heat exchange tubes serve as pathways for the hydraulic fluid flowing from the inlet at the bottom of the heat exchanger 70 to the outlet at the top. The heat exchanger 70 is designed so that the hydraulic fluid enters from the bottom and exits from the top. The cooling fan 61 blows air into the cooling core of the heat exchanger 70, cooling the hydraulic fluid flowing through the cooling core.

[0051] The cooling fan 61 blows air to the condenser 92 of the air conditioner 90. The cooling fan 61 sends air to the condenser 92 and cools the refrigerant flowing through the condenser 92.

[0052] When the cooling fan 61 is blowing air in the forward direction, the condenser 92 is positioned upstream of the cooling fan 61 in the direction of airflow. When the cooling fan 61 is blowing air in the forward direction, the electric motor 40 is positioned downstream of the heat exchanger 70 and the condenser 92 in the direction of airflow. When the cooling fan 61 is blowing air in the reverse direction, the condenser 92 is positioned downstream of the cooling fan 61 in the direction of airflow. When the cooling fan 61 is blowing air in the reverse direction, the electric motor 40 is positioned upstream of the heat exchanger 70 and the condenser 92 in the direction of airflow.

[0053] The arrangement of the heat exchanger 70 and condenser 92 relative to the cooling fan 61 is not limited to the example shown in Figure 3. The heat exchanger 70 and condenser 92 may be positioned to the right of the cooling fan 61. The heat exchanger 70 and condenser 92 may be positioned downstream of the cooling fan 61 in the direction of airflow when the airflow direction of the cooling fan 61 is positive, and upstream of the cooling fan 61 in the direction of airflow when the airflow direction of the cooling fan 61 is reversed.

[0054] <Control of cooling fan 61 and compressor 91> The control of the cooling fan 61 and compressor 91 by the fan controller 80 and air conditioner controller 82 in the hydraulic excavator 1 having the above configuration will be described below.

[0055] Figure 4 is a flowchart showing the process flow for controlling the compressor 91 according to the refrigerant pressure. Figure 5 is a diagram showing an example of the control of the cooling fan 61 and the compressor 91. Figure 5 shows three graphs arranged vertically in the figure. The horizontal axis of the three graphs is time. The vertical axis of the top graph is the airflow generated by the cooling fan 61. The vertical axis of the middle graph is the refrigerant pressure of the air conditioner 90, detected by the pressure switch 84. The vertical axis of the bottom graph is the operating state of the compressor 91.

[0056] The airflow generated by the cooling fan 61 is a command value based on the motor control signal SM transmitted from the fan controller 80 to the electric motor 64. Two thresholds are set for the refrigerant pressure of the air conditioner 90. The first threshold is the first pressure PR1. The second threshold is the second pressure PR2.

[0057] If the difference between the first pressure PR1 and the second pressure PR2 is too small, the compressor 91 will start and stop more frequently, shortening the lifespan of the air conditioner 90. Therefore, the second pressure PR2 is set to a lower pressure than the first pressure PR1. On the other hand, if the second pressure PR2 is set too low, the period of time during which the air conditioner 90's ability to cool the conditioned air supplied to the operating chamber 332 is reduced will be longer. For example, the second pressure PR2 may be set to 0.8 times the value of the first pressure PR1. Since the refrigerant pressure fluctuates with the influence of the outside temperature, the values ​​of the first pressure PR1 and the second pressure PR2 may be changed according to the outside temperature by detecting the outside temperature.

[0058] In step S1 shown in Figure 4, the fan controller 80 rotates the cooling fan 61 in the forward direction while maintaining a constant airflow + V1. The forward-rotating cooling fan 61 draws outside air into the machine room 333, and the outside air is sent to the condenser 92, where the refrigerant is sufficiently cooled. The refrigerant pressure detected by the pressure switch 84 fluctuates depending on the ambient temperature, but is basically considered constant unless the ambient temperature fluctuates significantly in a short period of time. The refrigerant pressure may also be considered constant at an intermediate value between the second pressure PR2 and the first pressure PR1. The compressor 91 is operating and in the ON state.

[0059] In step S2, the fan controller 80 determines whether or not to start the process of switching the forward-rotating cooling fan 61 to reverse rotation. When an operator in the driver's cab 332 operates the reverse rotation switch 81, an operation signal is sent to the fan controller 80. Upon receiving the operation signal from the reverse rotation switch 81, the fan controller 80 starts the process of switching the forward-rotating cooling fan 61 to reverse rotation. Alternatively, the fan controller 80 may automatically start the process of switching the forward-rotating cooling fan 61 to reverse rotation if it determines that the cooling fan 61 has been operating in the forward rotation for a predetermined time. In other words, the fan controller 80 may switch the forward rotation of the cooling fan 61 to reverse rotation using a timer function.

[0060] At time t1 shown in Figure 5, the fan controller 80 starts the cooling fan 61 to rotate in reverse. The fan controller 80 generates a reverse command to switch the airflow direction of the cooling fan 61 from forward to reverse. The fan controller 80 transmits a motor control signal SM based on the reverse command to the electric motor 64, thereby decelerating the cooling fan 61, which is rotating forward, in order to switch it to reverse rotation. After time t1, the forward rotation speed of the cooling fan 61 decreases and approaches zero.

[0061] As shown in Figure 5, after time t1, the rotational speed of the cooling fan 61 decreases, which reduces the airflow generated by the cooling fan 61. Time t1 is the time when the airflow of the cooling fan 61 begins to decrease in order to switch the airflow direction of the cooling fan 61 from forward to reverse. Time t1 is the start time of the airflow adjustment period. During the airflow adjustment period, the airflow generated by the cooling fan 61 is changed from the specified airflow + V1 generated by the cooling fan 61 when it is rotating in the forward direction.

[0062] During the airflow adjustment period, the airflow rate of the cooling fan 61 blowing air in the forward direction is lower than the airflow rate +V1. At this time, the flow rate of outside air taken into the machine room 333 is reduced. During the airflow adjustment period, the cooling fan 61 may also blow air in the reverse direction. When the cooling fan 61 is blowing air in the reverse direction, the air that has passed around the electric motor 40 and received heat dissipation from the electric motor 40 flows to the condenser 92. During the airflow adjustment period, the cooling capacity of the refrigerant in the condenser 92 is reduced compared to when the cooling fan 61 is blowing air at an airflow rate of +V1 in the forward direction. The pressure of the refrigerant increases.

[0063] Even after time t1, when the airflow of the cooling fan 61 begins to decrease, the compressor 91 continues to operate and remains ON as long as the refrigerant pressure is below the first pressure PR1. By not stopping the compressor 91 and thus not stopping the flow of refrigerant at time t1, the operation of the air conditioner 90 continues. This shortens the time during which the air conditioning is not effective, thereby suppressing the temperature rise in the operator's cab 332 and preventing deterioration of habitability.

[0064] The rotation speed of the cooling fan 61 decreases to zero, and the cooling fan 61 stops rotating in the forward direction. The cooling fan 61 stops in order to switch between forward and reverse rotation. The cooling fan 61 starts rotating in the reverse direction. When the cooling fan 61 starts rotating in the reverse direction, the direction of the airflow generated by the cooling fan 61 becomes the opposite direction to when it was rotating in the forward direction. The cooling fan 61, which is rotating in the reverse direction after its rotation direction has changed, accelerates. The rotation speed of the cooling fan 61 in the reverse direction increases. The amount of airflow generated by the cooling fan 61 in the reverse direction increases.

[0065] If it is determined in step S2 shown in Figure 4 that the cooling fan 61 should be switched to reverse rotation (YES in the determination in step S2), the process proceeds to step S3. In step S3, the fan controller 80 receives a signal P from the pressure switch 84 indicating the magnitude of the refrigerant pressure. Based on the signal P, the fan controller 80 determines the refrigerant pressure.

[0066] If the refrigerant pressure is determined to be equal to or greater than the first pressure PR1 in step S3, the process proceeds to step S4. In step S4, the fan controller 80 outputs a signal to stop the compressor 91. In the example shown in Figure 5, the first pressure PR1 is set to a pressure higher than the refrigerant pressure at time t1, which is the start time of the airflow adjustment period. At time t2, which is after time t1, the fan controller 80 determines that the refrigerant pressure has risen to the threshold first pressure PR1. The fan controller 80 sends a compressor control signal SC2 to the compressor 91 to stop it. The operating state of the compressor 91 switches from the ON state to the OFF state.

[0067] If the refrigerant pressure becomes too high, the air conditioner 90 will stop due to a refrigerant pressure abnormality error, reducing the habitability of the operator's room 332. By stopping the compressor 91 when the refrigerant pressure rises to the threshold pressure PR1, the rise in refrigerant pressure can be stopped, as shown in Figure 5. Since the refrigerant pressure can be kept within a range where a refrigerant pressure abnormality error does not occur, the air conditioner 90 can be prevented from stopping, and a comfortable temperature can be maintained inside the operator's room 332.

[0068] As shown in Figure 5, while the compressor 91 is stopped, the refrigerant pressure gradually decreases from the first pressure PR1. The cooling fan 61 continues to operate even when the compressor 91 is stopped, supplying air to the condenser 92, so the refrigerant is cooled to some extent in the condenser 92. In addition, even when the compressor 91 is not pressurizing the refrigerant, the expansion valve 93 may open due to the temperature difference of the refrigerant, and a flow of refrigerant through the expansion valve 93 is generated. As a result, the refrigerant pressure upstream of the expansion valve 93, as detected by the pressure switch 84, gradually decreases.

[0069] When the airflow generated by the cooling fan 61 in the reverse direction reaches a specified airflow -V1, the cooling fan 61 stops accelerating and rotates in the reverse direction while maintaining that airflow -V1. The cooling fan 61 rotates in the reverse direction at a constant speed.

[0070] If the refrigerant pressure is determined to be below the second pressure PR2 in step S3, the process proceeds to step S6. In step S6, the air conditioner controller 82 outputs a signal to start the compressor 91. At time t3 shown in Figure 5, the air conditioner controller 82 determines that the refrigerant pressure has dropped to the threshold second pressure PR2. The fan controller 80 sends a compressor control signal SC2 to the compressor 91 to start it. The operating state of the compressor 91 switches from the OFF state to the ON state.

[0071] By starting the compressor 91, the air conditioner 90 is operated, and the temperature of the air supplied to the operator's chamber 332 can be lowered. This allows the operator's chamber 332 to be maintained at a comfortable temperature. As shown in Figure 5, when the compressor 91 is started, the refrigerant pressure gradually rises from the second pressure PR2.

[0072] In step S7, the fan controller 80 determines whether the process of switching the cooling fan 61, which is rotating in reverse, to forward rotation has already started. After a predetermined time for reverse rotation has elapsed and it is time t4, the fan controller 80 starts the process of switching the cooling fan 61, which is rotating in reverse, to forward rotation. The cooling fan 61, which is rotating in reverse, slows down. The rotational speed of the cooling fan 61 in reverse decreases. As long as time t4 has not been reached and the cooling fan 61 is rotating in reverse at a constant speed and generating an airflow of -V1, it is determined that the switching of the cooling fan 61 to forward rotation has not started (NO in the determination in step S7), and the process returns to step S3. The determination of the refrigerant pressure in step S3 and the starting and stopping of the compressor 91 according to the refrigerant pressure in steps S4 and S6 are repeated.

[0073] If it is determined that time t4 has already passed and the switching of the cooling fan 61 to forward rotation has already begun (YES in the determination in step S7), the process proceeds to step S8. In step S8, the fan controller 80 determines whether the airflow of the cooling fan 61 has returned to the specified airflow + V1 for forward rotation. If it is determined that the airflow of the cooling fan 61 has not returned to + V1 (NO in the determination in step S8), the process returns to step S3. The determination of the refrigerant pressure in step S3 and the starting and stopping of the compressor 91 according to the refrigerant pressure in steps S4 and S6 are repeated.

[0074] At time t5 shown in Figure 5, the fan controller 80 determines that the refrigerant pressure has risen to the threshold first pressure PR1. The air conditioner controller 82 sends a compressor control signal SC1 to the compressor 91, stopping the compressor 91. The operating state of the compressor 91 switches from ON to OFF. The refrigerant pressure detected by the pressure switch 84 gradually decreases from the first pressure PR1.

[0075] The rotational speed of the cooling fan 61 decreases to zero, and the cooling fan 61 stops rotating in the reverse direction. The cooling fan 61 stops in order to switch between forward and reverse rotation. The cooling fan 61 starts rotating in the forward direction. The cooling fan 61, which is rotating in the forward direction after the change in rotational direction, accelerates. The rotational speed of the cooling fan 61 in the forward direction increases. The amount of airflow generated by the cooling fan 61 in the forward direction increases.

[0076] At time t6 shown in Figure 5, the airflow of the cooling fan 61 reaches the specified airflow + V1 when it is rotating in the forward direction. The cooling fan 61 stops accelerating and rotates in the forward direction while maintaining that airflow + V1. The cooling fan 61 rotates in the forward direction at a constant speed. The airflow generated by the cooling fan 61 in the forward direction returns completely to the specified airflow + V. Time t6 is the time when the decrease in airflow of the cooling fan 61 ends. Time t6 is the end time of the airflow adjustment period. The airflow adjustment period is the time from time t1, when the airflow of the cooling fan 61 begins to decrease in order to switch the airflow direction of the cooling fan 61 from the forward direction to the reverse direction, to time t6, when the airflow direction of the cooling fan 61 returns to the forward direction and the airflow returns to normal.

[0077] When the process first proceeds to step S8 after time t6, it is determined that the airflow of the cooling fan 61 has returned to +V1 (YES in the determination of step S8). The process proceeds to step S9, where the air conditioner controller 82 determines whether the compressor 91 is stopped at the end of the airflow adjustment period. If the compressor 91 is stopped at the end of the airflow adjustment period (YES in the determination of step S9), the process proceeds to step S10. The air conditioner controller 82 outputs a signal to start the compressor 91.

[0078] In the example shown in Figure 5, the compressor 91 is stopped at time t6, which is the end of the airflow adjustment period. Therefore, the air conditioner controller 82 sends a compressor control signal SC1 to the compressor 91 to start it up. The operating state of the compressor 91 switches from OFF to ON. The cooling fan 61 generates a specified airflow +V in the forward direction, supplying cool outside air to the condenser 92. Cooling of the refrigerant in the condenser 92 is promoted, and the refrigerant pressure detected by the pressure switch 84 decreases.

[0079] If the compressor 91 is not stopped at the end of the airflow adjustment period, that is, if the compressor 91 is started at the end of the airflow adjustment period (NO in the judgment of step S9), the process of step S10 is skipped. The process of starting the compressor 91 in step S10 is not performed.

[0080] If it is determined in step S2 that the cooling fan 61 will not be switched to reverse rotation (the determination in step S2 is NO), then steps S3 to S8 are skipped. The process then proceeds to step S9, where it is determined whether the compressor is stopped or not. If the compressor 91 is stopped, the process proceeds to step S10 to restart the compressor 91; if the compressor 91 is not stopped, the process to start the compressor 91 is not performed. Then the process ends ("End" in Figure 4).

[0081] <Mechanism of Action and Effects> Although some of the above description overlaps with the above, the characteristic configuration and effects of this embodiment are summarized as follows.

[0082] In hydraulic excavator 1, the cooling fan 61 may be reversed to clean the heat exchanger 70. During the airflow adjustment period when the direction of airflow from the cooling fan 61 is switched, the cooling performance of the refrigerant in the condenser 92 decreases. As shown in Figures 4 and 5, the fan controller 80 stops the compressor 91 that compresses the refrigerant when the refrigerant pressure rises to a threshold pressure PR1 during the airflow adjustment period. This prevents the refrigerant pressure from rising, as shown in Figure 5. Since the refrigerant pressure can be kept within a range that does not trigger a refrigerant pressure abnormality error, the air conditioner 90 can be stopped, and a comfortable temperature can be maintained inside the operator's cab 332.

[0083] The timing of stopping the compressor 91 of the air conditioner 90 is delayed compared to the timing at which the airflow of the cooling fan 61 begins to decrease in order to switch the direction of airflow from the cooling fan 61. 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. This suppresses the temperature rise inside the operator's cab 332 and prevents a decrease in the habitability inside the operator's cab 332.

[0084] As shown in Figures 4 and 5, the air conditioner controller 82 starts the compressor 91 when the refrigerant pressure drops from the first pressure PR1 to the second pressure PR2 during the airflow adjustment period. When the refrigerant pressure has dropped sufficiently low, the compressor 91 is started to operate the air conditioner 90, thereby lowering the temperature of the air delivered into the control room 332. By properly operating the compressor 91 during the airflow adjustment period, a comfortable temperature can be maintained inside the control room 332.

[0085] The first pressure PR1, which is the threshold for stopping the compressor 91, may be preset so that the temperature of the conditioned air supplied by the air conditioner 90 into the operator's cab 332 is kept lower than the room temperature inside the operator's cab 332. If the operator in the operator's cab 332 wants to cool the cab 332 but is supplied with conditioned air that is higher than the room temperature, the room temperature will rise, the habitability of the operator's cab 332 will decrease, and the operator's discomfort will increase. The compressor 91 is operated within a range that keeps the temperature of the conditioned air lower than the room temperature inside the operator's cab 332, and the compressor 91 is stopped when the temperature of the conditioned air rises or exceeds the room temperature inside the operator's cab 332. This maintains the environment inside the operator's cab 332 and keeps the habitability of the operator's cab 332 comfortable.

[0086] The fan controller 80 may switch the airflow direction of the cooling fan 61 from forward to reverse if it determines that the forward airflow direction has continued for a predetermined period of time. By periodically reversing the airflow direction of the cooling fan 61, the heat exchanger 70 can be cleaned periodically. Alternatively, the fan controller 80 may switch the airflow direction of the cooling fan 61 from forward to reverse according to the operation of an operator in the operator's cab 332. The heat exchanger 70 can be cleaned by reversing the airflow direction when the operator intends to remove dust and debris from the heat exchanger 70.

[0087] As shown in Figure 3, the condenser 92 that cools the refrigerant of the air conditioner 90 may be positioned upstream of the cooling fan 61 in the direction of airflow when the cooling fan 61 is blowing air in the forward direction, and downstream of the cooling fan 61 in the direction of airflow when the airflow direction is reversed. When the cooling fan 61 is blowing air in the forward direction, cool outside air can be supplied to the condenser 92 to efficiently cool the refrigerant of the air conditioner 90. Even when the cooling fan 61 is blowing air in the reverse direction, an airflow is generated that passes through the condenser 92, and although the cooling capacity of the refrigerant is reduced compared to when the airflow direction is forward, a certain degree of cooling capacity for the refrigerant can be ensured in the condenser 92.

[0088] As shown in Figure 2, the air conditioner 90 further includes an expansion valve 93 for reducing the pressure of the refrigerant, and a pressure switch 84 may detect the pressure of the refrigerant in the path connecting the condenser 92 and the expansion valve 93. The pressure switch 84 can detect the pressure of the relatively high-pressure refrigerant, which has been compressed by the compressor 91 and isobarically cooled in the condenser 92. The fan controller 80 can start and stop the compressor 91 in a timely manner according to the refrigerant pressure detected by the pressure switch 84.

[0089] As shown in Figures 4 and 5, the air conditioner controller 82 may, during the airflow adjustment period, stop the compressor 91 again after the pressure has dropped to the second pressure PR2 and the compressor 91 has started, if the refrigerant pressure rises to the first pressure PR1. By repeatedly stopping and starting the compressor 91 during the airflow adjustment period according to the detection result of the refrigerant pressure of the air conditioner 90, an error indicating abnormal refrigerant pressure can be avoided, and a comfortable temperature can be maintained inside the operating chamber 332.

[0090] As shown in Figure 2, the cooling fan 61 may be an electric fan. By appropriately transmitting a motor control signal SM to the electric motor 64, the fan controller 80 can switch the rotation direction of the cooling fan 61 between forward and reverse rotation, thereby freely switching the airflow direction of the cooling fan 61 between forward and reverse directions.

[0091] As shown in Figures 4 and 5, the air conditioner controller 82 may start the compressor 91 if it has stopped at the end of the airflow adjustment period. When the airflow direction of the cooling fan 61 returns to the positive direction and the airflow returns to normal, cooler outside air is sent to the condenser 92. If the compressor 91 has stopped at this point, restarting the compressor 91 will allow the refrigerant in the condenser 92 to be cooled and the refrigerant pressure to be reduced.

[0092] As shown in Figure 2, the hydraulic excavator 1 may be equipped with an electric motor 40 as a power source. As shown in Figure 3, the electric motor 40 may be positioned downstream of the condenser 92 in the direction of airflow when the airflow direction of the cooling fan 61 is in the forward direction, and upstream of the condenser 92 in the direction of airflow when the airflow direction is in the reverse direction. When the airflow direction is in the reverse direction, the air around the electric motor 40 flows to the heat exchanger 70 and the condenser 92. Although the temperature of the air rises due to the heat dissipated by the electric motor 40, which is the power source, the amount of heat dissipated by the power source is smaller compared to the case where the power source is an internal combustion engine, so the rise in the temperature of the air is kept to a minimum. Even when the airflow direction is in the reverse direction, air at a temperature sufficient to cool the refrigerant in the condenser 92 is supplied to the condenser 92, so the refrigerant can be cooled and the pressure of the refrigerant can be reduced.

[0093] The hydraulic excavator 1 in this embodiment is equipped with one cooling fan 61, but the hydraulic excavator 1 only needs to be equipped with at least one cooling fan. The hydraulic excavator 1 may be equipped with two or more cooling fans. If the hydraulic excavator 1 is equipped with multiple cooling fans, the airflow direction of the multiple cooling fans may be switched simultaneously from the forward direction to the reverse direction, but it becomes possible to stagger the timing of switching the airflow direction for each cooling fan. By switching the airflow direction of the multiple cooling fans one by one in sequence from the forward direction to the reverse direction, 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.

[0094] The cooling fan 61 is not limited to an electric fan. The cooling fan 61 may be a fan that can rotate in both forward and reverse directions by hydraulic drive. The cooling fan 61 does not necessarily have to be able to switch the direction of rotation. The cooling fan 61 may be a fan that can switch the airflow direction between forward and reverse by mechanically reversing the blades.

[0095] 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.

[0096] 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]

[0097] 1 Hydraulic excavator, 2 Work equipment, 3 Body, 31 Traveling body, 33 Slewing body, 33L, 40L Left side, 33R, 40R Right side, 40 Electric motor, 41 Output shaft, 45 Hydraulic pump, 46 Hydraulic oil tank, 47 Main valve, 50 Battery, 60 Cooling system, 61 Cooling fan, 64 Electric motor, 70 Heat exchanger, 80 Fan controller, 81 Reverse rotation switch, 82 Air conditioning controller, 84 Pressure switch, 90 Air conditioner, 91 Compressor, 92 Condenser, 93 Expansion valve, 94 Evaporator, 332 Operator's cab, 333 Machine room, P Pressure, PR1 First pressure, PR2 Second pressure, SC1, SC2 Compressor control signal, SM Motor control signal.

Claims

1. The driver's cab where the operator of the work machine sits, An air conditioner comprising a compressor for compressing a refrigerant and a condenser for cooling the refrigerant, for cooling the operating chamber, A cooling fan that blows air onto the condenser, A pressure switch that detects the refrigerant pressure, Equipped with a controller, The cooling fan is capable of switching the airflow direction between forward and reverse. The controller is a control system for a working machine, wherein, during the airflow adjustment period from when the airflow of the cooling fan begins to decrease in order to switch the airflow direction from the forward direction to the reverse direction until the airflow direction returns to the forward direction and the airflow returns to normal, the controller stops the compressor when the pressure rises to a first pressure, and starts the compressor when the pressure falls from the first pressure to a second pressure.

2. The control system for a work machine according to claim 1, wherein the first pressure is set in advance so that the temperature of the conditioned air supplied by the air conditioner to the operating chamber is kept lower than the room temperature of the operating chamber.

3. The control system for a work machine according to claim 1, wherein the controller determines that the state in which the airflow direction is in the forward direction has continued for a predetermined time, or switches the airflow direction from the forward direction to the reverse direction according to the operation of an operator in the operator's cab.

4. The control system for a work machine according to claim 1, wherein the capacitor is positioned upstream of the cooling fan in the airflow direction when the airflow direction is the forward direction, and downstream of the cooling fan in the airflow direction when the airflow direction is the reverse direction.

5. The aforementioned air conditioner further includes a pressure reducer for reducing the pressure of the refrigerant, The control system for a work machine according to claim 1, wherein the pressure switch detects the pressure of the refrigerant in the path connecting the condenser and the pressure reducer.

6. The control system for a working machine according to claim 1, wherein the controller, during the airflow adjustment period, stops the compressor again when the pressure rises to the first pressure after the pressure has dropped to the second pressure and the compressor has started.

7. The control system for a work machine according to claim 1, wherein the cooling fan is an electric fan.

8. The control system for a work machine according to claim 1, wherein the controller starts the compressor if the compressor is stopped at the end of the airflow adjustment period.

9. The aforementioned work machine is equipped with an electric motor which is the power source for the work machine, The control system for a work machine according to claim 1, wherein the electric motor is positioned downstream of the capacitor in the airflow direction when the airflow direction is the forward direction, and upstream of the capacitor in the airflow direction when the airflow direction is the reverse direction.

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