Electrically powered tug and computer readable medium

Abstract

An electrically driven tractor has a vehicle body, an electric motor, a battery, a converter that controls input and output electric power of the battery, wheels for traveling, and a control device. The control device controls the converter so that the input and output electric power of the battery is within a predetermined prescribed power range, with one of the conditions being that the electrically driven tractor is traveling within a predetermined restricted area. The control device determines whether the electrically driven tractor is likely to move from the restricted area to outside the restricted area. In the case where a positive determination is made in the determination processing during the restricted processing, the control device expands the prescribed power range compared to the case where a negative determination is made in the determination processing.

Description

TECHNICAL FIELD

[0001] The present application relates to an electrically driven tractor and a computer readable medium. BACKGROUND

[0002] The tractor disclosed in Japanese Patent Application Publication No. 2014-143965 is provided with a battery, an electric motor, wheels, and a work machine. The battery supplies electric power to the electric motor. The electric motor is driven by receiving the supply of electric power from the battery. The driving force from the electric motor is transmitted to the wheels and the work machine. That is, the tractor disclosed in Japanese Patent Application Publication No. 2014-143965 travels with the electric motor as a driving source. SUMMARY

[0003] In the technology of the tractor disclosed in Japanese Patent Application Publication No. 2014-143965, for example, the following technology is known: in a case where the traveling condition of the tractor becomes a specific condition, and in a case where the state of charge of the battery becomes a specific state, and so on, the input and output electric power of the battery is limited to a given range. On the other hand, as the tractor separates from mud, and as the tractor separates from a farm to a road, and so on, a larger torque than usual is required as the output torque of the electric motor. Thus, in a state where the input and output electric power of the battery is limited as described above, if the tractor is to separate from mud, a farm, and so on, it is possible that the output torque of the electric motor is insufficient and the tractor cannot separate.

[0004] To solve the above problem, the present application is an electrically driven tractor provided with: a vehicle body capable of being coupled to a work machine; an electric motor; a battery that accumulates electric power supplied to the electric motor; a converter that controls the input and output electric power of the battery; wheels for traveling that rotate by driving force from the electric motor; and a control device that takes the converter as a control object, wherein the control device executes: a limiting process that controls the converter so that the input and output electric power of the battery becomes within a predetermined prescribed electric power range, with the electrically driven tractor being within a predetermined limited area as one of the conditions; a determination process that determines whether or not the electrically driven tractor is likely to move from the limited area to outside the limited area; and a mitigation process that, during the limiting process, expands the prescribed electric power range in a case where a positive determination is made in the determination process, compared to a case where a negative determination is made in the determination process.

[0005] Further, in order to solve the above problem, the present application is a computer-readable medium storing a control program for an electrically driven tractor, the control program being applied to a control device of an electrically driven tractor, the electrically driven tractor including: a vehicle body capable of being coupled to a work machine; an electric motor; a battery that accumulates electric power supplied to the electric motor; a converter that controls input and output electric power of the battery; a wheel for traveling that rotates by drive force from the electric motor; and the control device that takes the converter as a control target, the control program causing the control device to execute: a restriction process that controls the converter so that the input and output electric power of the battery is within a predetermined prescribed electric power range as one of conditions that the electrically driven tractor is traveling within a predetermined restricted area; a determination process that determines whether the electrically driven tractor is likely to move from the restricted area to outside the restricted area; and a mitigation process that, during the restriction process, expands the prescribed electric power range when a positive determination is made in the determination process, compared to when a negative determination is made in the determination process.

[0006] According to the above configuration, when the electrically driven tractor is likely to move outside the restricted area in the restriction process, the restriction of the input and output electric power of the battery is mitigated. As a result, the electric motor is able to output a high torque, and thus the electrically driven tractor is more likely to escape from the restricted area, compared to when the mitigation process is not performed.

[0007] The electrically driven tractor can also be configured such that, in the above configuration, the control device prohibits execution of the mitigation process when the number of times a positive determination is made in the determination process exceeds a predetermined prescribed number of times during execution of the restriction process from start to end. According to the above configuration, it is possible to suppress a situation in which the state of charge of the battery is too low or the battery is subjected to excessive load due to repeated performance of the mitigation process.

[0008] The electrically driven tractor can also be configured such that, in the above configuration, the control device stores a farm map in which, in each of a plurality of sub-areas obtained by dividing a farm into the sub-areas, a position of the sub-area and slip information indicating whether the wheel slips in the sub-area are associated, and the restricted area is the sub-area associated with occurrence of a slip in the farm map.

[0009] According to the above configuration, when the wheel escapes from a location where the wheel slips, i.e., mud, the restriction of the input and output electric power of the battery is mitigated. Thus, it is possible to suppress a situation in which the output torque from the electric motor is insufficient when a relatively large torque as the output torque from the electric motor is required to escape from the mud.

[0010] The electrically driven tractor can also be configured such that, in the above-described configuration, a switch that can be switched on / off by an occupant of the electrically driven tractor is further provided, and in the determination processing, in a case where the switch is on, the control device determines that the electrically driven tractor is likely to move from the restricted area to outside the restricted area. According to the above-described configuration, it is possible to determine that the electrically driven tractor is to escape from the restricted area by on / off operation of the switch by the occupant.

[0011] The electrically driven tractor can also be configured such that, in the above-described configuration, in the determination processing, in a case where the state in which the wheels are slipping continues for a predetermined prescribed period, the control device determines that the electrically driven tractor is likely to move from the restricted area to outside the restricted area. According to the above-described configuration, it is possible to accurately determine that the electrically driven tractor is to escape from mud or the like based on the slipping of the wheels.

[0012] The electrically driven tractor can also be configured such that, in the above-described configuration, the control device further executes the restriction processing with the condition that the state of charge of the battery is equal to or lower than a predetermined first prescribed state of charge. According to the above-described configuration, it is possible to restrict the input and output of the battery power in conjunction with a decrease in the state of charge of the battery. Thus, it is possible to suppress overdischarge of the battery.

[0013] The electrically driven tractor can also be configured such that, in the above-described configuration, an inclination sensor that detects an inclination of the vehicle body is further provided, and the restricted area is a farm, and in the determination processing, based on a detection result of the inclination sensor, the control device determines whether the electrically driven tractor is likely to move from the restricted area to outside the restricted area. According to the above-described configuration, it is possible to accurately determine that the electrically driven tractor is to escape from a farm to a road or the like based on the inclination sensor.

[0014] The electrically driven tractor can also be configured such that, in the above-described configuration, a system main relay that is located between the battery and the converter and that can switch on / off of electrical conduction is further provided, and the control device executes: a reset processing that sets the system main relay to off in a case where the state of charge of the battery is equal to or lower than a predetermined second prescribed state of charge after the mitigation processing is executed; and a recalculation processing that recalculates the state of charge of the battery in a state where the system main relay is off after the reset processing is executed, and sets the system main relay to on in a case where the state of charge of the battery recalculated in the recalculation processing is greater than the second prescribed state of charge.

[0015] According to the above configuration, after the mitigation process, the battery becomes in a state of being electrically disconnected from the converter, and thus the open-circuit voltage of the battery is stabilized. Also, since the state of charge of the battery is recalculated in this state, even if the detected values of the voltage and current of the battery are not stabilized along with the mitigation process, an accurate state of charge can be calculated again. BRIEF DESCRIPTION OF DRAWINGS

[0016] The features, advantages, and technical and industrial significance of exemplary embodiments of the application will be described in connection with the attached drawings, in which like numbering represents similar parts, and in which:

[0017] Figure 1 is a schematic configuration view of an electrically driven tractor.

[0018] Figure 2 is a view showing the electric structure and power transmission path of the electrically driven tractor.

[0019] Figure 3 is a flowchart of farm map creation control performed by the control device of the electrically driven tractor of the first embodiment.

[0020] Figure 4 is a flowchart of slip escape control performed by the control device of the electrically driven tractor of the first embodiment.

[0021] Figure 5 is a flowchart of farm escape control performed by the control device of the electrically driven tractor of the second embodiment. DETAILED DESCRIPTION

[0022] <First Embodiment>

[0023] <Overall Configuration of Electrically Driven Tractor>

[0024] As shown in Figure 1 , an electrically driven tractor 10 is provided with a vehicle 11, a work machine 20, and a support mechanism 30. The vehicle 11 has a plurality of wheels 12 and a vehicle body 13. The plurality of wheels 12 are linked to the vehicle body 13. The vehicle body 13 can be linked to the work machine 20 via the support mechanism 30.

[0025] The work machine 20 is located at the rear when viewed from the vehicle 11. The work machine 20 is provided with a plurality of blades 21 for plowing. The work machine 20 can plow a farm by rotating the blades 21 in a state in which the blades 21 are in contact with the ground GR of the farm. In addition, in Figure 1 , the plurality of blades 21 are simply illustrated as cylindrical shapes.

[0026] The support mechanism 30 connects the vehicle body 13 to the working machine 20. The support mechanism 30 has a support shaft 31. Although not shown in the figure, the support mechanism 30 includes multiple rods, a hydraulic circuit, a control valve, a hydraulic cylinder, etc., in addition to the support shaft 31. The hydraulic cylinder is actuated by switching the control valve on / off in the support mechanism 30. As a result, the working machine 20 rotates around the support shaft 31. Specifically, the working machine 20 rotates multiple blades 21 around the support shaft 31 in either the approach direction D1 or the departure direction D2. The approach direction D1 is the direction that brings the multiple blades 21 closer to the ground GR. The departure direction D2 is the direction that moves the multiple blades 21 away from the ground GR.

[0027] <Power transmission path of electric tractor>

[0028] like Figure 2 As shown, the electric tractor 10 includes a first electric motor 41, a second electric motor 42, a third electric motor 43, a power transmission mechanism 19, a PTO 25, and a hydraulic device 35. The first electric motor 41, the second electric motor 42, and the third electric motor 43 are generator motors. It should be noted that "PTO" stands for "power take-off".

[0029] The first electric motor 41 is the drive source for moving the electric tractor 10. The first electric motor 41 is connected to the wheel 12 via a power transmission mechanism 19. That is, the wheel 12 is a driving wheel that rotates by the driving force from the first electric motor 41. The power transmission mechanism 19 includes, for example, a reduction mechanism that increases and outputs torque.

[0030] The second electric motor 42 is the drive source for the working machine 20. The second electric motor 42 is connected to the blades 21 of the working machine 20 via a PTO 25. The PTO 25 is a device for transmitting the torque of the second electric motor 42 to the blades 21. The PTO 25 includes, for example, a reduction gear mechanism.

[0031] The third electric motor 43 is the drive source for the hydraulic device 35. The third electric motor 43 drives the hydraulic device 35. The hydraulic device 35 generates hydraulic pressure based on the driving force from the third electric motor 43. The hydraulic pressure generated by the hydraulic device 35 is supplied to the support mechanism 30. As described above, the support mechanism 30 can rotate the working machine 20 in the approach direction D1 and the departure direction D2 based on the supplied hydraulic pressure.

[0032] It should be noted that, as described above, the first motor 41 is a generator motor. Therefore, the first motor 41 can function as a generator. Specifically, the first motor 41 can function as a generator when the electric tractor 10 decelerates. At this time, regenerative braking force corresponding to the power generated by the first motor 41 is generated in the electric tractor 10.

[0033] <Structure of the electric traction vehicle>

[0034] As shown in FIG. 1, the electric traction vehicle 10 is provided with a power supply circuit 99. The power supply circuit 99 is provided with a battery 77, a positive electrode line 81, a negative electrode line 82, and a system main relay 80. In addition, the power supply circuit 99 is provided with a converter 85, a first converter 71, a second converter 72, and a third converter 73. Figure 2

[0035] The battery 77 is a secondary battery. The battery 77 is a high-voltage battery that is responsible for the running of the electric traction vehicle 10, the driving of the working machine 20, and the driving of the support mechanism 30. The battery 77 stores electric power that is supplied to the first motor 41, the second motor 42, and the third motor 43.

[0036] A terminal on the high-potential side of the battery 77 is connected to the converter 85 via the positive electrode line 81. In addition, a terminal on the low-potential side of the battery 77 is connected to the converter 85 via the negative electrode line 82. The converter 85 converts the magnitude of voltage to output electric current.

[0037] The system main relay 80 is provided with a positive electrode relay 83 and a negative electrode relay 84. The positive electrode relay 83 is located on the positive electrode line 81. The negative electrode relay 84 is located on the negative electrode line 82. The system main relay 80 turns on / off the electric conduction between the battery 77 and the converter 85.

[0038] The first converter 71 and the second converter 72 are connected to the converter 85. The first converter 71 and the second converter 72 are connected in parallel to each other. The first converter 71 is connected to the first motor 41. The first converter 71 performs DC / AC power conversion between the converter 85 and the first motor 41. The second converter 72 is connected to the second motor 42. The second converter 72 performs DC / AC power conversion between the converter 85 and the second motor 42.

[0039] The third converter 73 is connected to the battery 77. The third converter 73 is connected in parallel to the converter 85. The third converter 73 is connected to the third motor 43. The third converter 73 performs DC / AC power conversion between the battery 77 and the third motor 43.

[0040] The electric traction vehicle 10 is provided with a rotation sensor 61, a battery temperature sensor 62, a current voltage sensor 63, an acceleration sensor 64, and an accelerator pedal sensor 65. The rotation sensor 61 is located near the rotation axis of the corresponding wheel 12. The rotation sensor 61 detects the rotation speed Al of the corresponding wheel 12.

[0041] ​The battery temperature sensor 62 is built in the battery 77. The battery temperature sensor 62 detects the temperature Tl of the battery 77. The current voltage sensor 63 detects the voltage of the battery 77 and the current from the battery 77 as the battery information BI.

[0042] The acceleration sensor 64 is located in the vehicle body 13 of the electrically driven tractor 10. The acceleration sensor 64 detects an acceleration IA generated in the vehicle body 13. The acceleration IA is a vector value, and includes information on the orientation. In addition, the gravitational acceleration acts on the electrically driven tractor 10. Thus, the acceleration sensor 64 also functions as a tilt sensor that detects the tilt angle of the vehicle body 13. The accelerator pedal sensor 65 detects the operation amount ACCP of the accelerator pedal operated by the occupant of the electrically driven tractor 10.

[0043]

[0044] The electrically driven tractor 10 is provided with the control device 100, the operation section 90, the GPS device 50, and the wireless communication machine 51.

[0045] The operation section 90 is mounted to the vehicle body 13. Specifically, the operation section 90 is mounted to the vehicle body 13 at a position operable by the occupant of the electrically driven tractor 10. The operation section 90 is provided with a map switch SI and a slip control switch S2.

[0046] The map switch SI is switched on / off by the occupant of the electrically driven tractor 10. The map switch SI is a switch for starting and ending the farm map creation control described later. The map switch SI is switched on, for example, when the electrically driven tractor 10 is performing tillage work in the farm. In the case where the map switch SI is turned on, the map switch SI outputs a first signal SIGl.

[0047] The slip control switch S2 is switched on / off by the occupant of the electrically driven tractor 10. The slip control switch S2 is a switch for starting and ending the slip control described later. The slip control switch S2 is switched on, for example, when the electrically driven tractor 10 enters the farm from outside the farm. In the case where the slip control switch S2 is turned on, the slip control switch S2 outputs a second signal SIG2.

[0048] The GPS device 50 receives a signal related to the current position information PI of the electrically driven tractor 10 from a GPS satellite.

[0049] The wireless communication machine 51 can communicate with a weather server not shown via a wireless communication network. The wireless communication machine 51 receives weather information WI corresponding to the current position determined from the position information PI. The weather information WI includes information on the presence or absence of precipitation.

[0050] ​The control device 100 takes the first converter 71, the second converter 72, the third converter 73, and the like as control targets. The control device 100 causes the electric traction vehicle 10 to travel or causes the electric traction vehicle 10 to stop traveling by controlling the first converter 71. In addition, the control device 100 causes the work machine 20 to act or stop by controlling the second converter 72. That is, the control device 100 controls the input and output power of the battery 77 by the control of the first converter 71 and the second converter 72.

[0051] In addition, the control device 100 takes the system main relay 80 as a control target. That is, the control device 100 switches the on / off of the electrical connection by the positive electrode relay 83 and the negative electrode relay 84. Note that if the electrical connection by the positive electrode relay 83 and the negative electrode relay 84 is on, the battery 77 becomes a power-on state. That is, the battery 77 supplies power to each machine to which the battery 77 is connected. On the other hand, if the electrical connection by the positive electrode relay 83 and the negative electrode relay 84 is off, the battery 77 becomes a power-off state. Note that the control device 100 operates by receiving power from a low-voltage battery, not shown, other than the battery 77.

[0052] The control device 100 acquires a signal indicating the rotation speed Al of the wheel 12 from the rotation sensor 61. The control device 100 acquires a signal indicating the temperature Tl of the battery 77 from the battery temperature sensor 62. The control device 100 acquires a signal indicating the battery information BI from the current voltage sensor 63. Note that, as described above, the battery information BI includes information on the voltage and the current of the battery 77. The control device 100 acquires a signal indicating the acceleration IA of the vehicle body 13 from the acceleration sensor 64. The control device 100 acquires a signal indicating the operation amount ACCP of the accelerator pedal from the accelerator pedal sensor 65. The control device 100 receives a signal related to the position information PI via the GPS device 50. Note that the control device 100 repeatedly acquires the signals from each of the above-described sensors at a unit time interval.

[0053] The control device 100 requests weather information WI of the current position to a weather server, not shown, via the wireless communication machine 51. The control device 100 receives the weather information WI transmitted in response to the request via the wireless communication machine 51.

[0054] The control device 100 stores a farm map M in which slip information is recorded, the slip information indicating whether or not the wheels 12 slipped in a farm in which tillage is scheduled to be performed. The farm map M is virtually obtained in a two-dimensional manner with respect to the farm. In addition, in the farm map M, the farm is divided into a plurality of zones in a matrix form. In each zone, information related to the position of the zone is associated. In addition, in each zone, slip information indicating whether or not the wheels 12 slipped is associated. In the farm map M, when the slip flag is ON, it is indicated that the wheels 12 slipped. In addition, in the farm map M, when the slip flag is OFF, it is indicated that the wheels 12 did not slip. The control device 100 stores, as the farm map M, a first farm map Ml used in the absence of precipitation and a second farm map M2 used in the presence of precipitation. In the first farm map Ml and the second farm map M2, the positions of the zones are the same. Note that in an initial state in which the electric tractor 10 is shipped from a factory or the like, the slip flags of the zones in the farm map M are all set to OFF.

[0055] The control device 100 can be configured as one or more processors that execute various processes according to a computer program (software). Note that the control device 100 can also be configured as one or more dedicated hardware circuits such as an application specific integrated circuit (ASIC) that executes at least a part of the various processes or a circuitry including a combination thereof. The processor includes a CPU, a RAM, a ROM, and the like. The memory stores program codes or instructions that cause the CPU to execute the processes. The memory, which is a computer readable medium, includes various available media that can be accessed by a computer, which are general or specific. The control device 100 has a nonvolatile memory, which is a storage device, that can be electrically rewritten. The control device 100 stores, in the nonvolatile memory, which is a storage device, programs for performing the farm map creation control, the slip escape control, and the farm escape control described later.

[0056] <Outline of the control related to escape from the slip state>

[0057] The control device 100 has the farm map creation control and the slip escape control as the control related to escape from the slip state. By executing the farm map creation control, the control device 100 updates the farm map M in which slip information of a farm in which tillage is scheduled to be performed by the electric tractor 10 is stored. By executing the slip escape control, the control device 100 executes the restriction process, the determination process, and the mitigation process.

[0058] <Regarding the farm map creation control>

[0059] Farm map creation control begins when the occupant of the electric tractor 10 turns on the map switch S1. That is, the control device 100 executes farm map creation control when it receives the first signal SIG1 from the map switch S1. Conversely, farm map creation control ends when the occupant of the electric tractor 10 turns off the map switch S1. That is, the control device 100 terminates farm map creation control when it no longer receives the first signal SIG1 from the map switch S1.

[0060] like Figure 3 As shown, if farm map creation control begins, the control device 100 first executes step S10. In step S10, the control device 100 determines whether the position of the electric tractor 10 is located on the boundary of an adjacent partition in the farm map M. Specifically, the control device 100 obtains location information PI from the GPS device 50. Then, the control device 100 determines whether the current position shown by the location information PI is located on the boundary of an adjacent partition. At this time, if the current position is within a given allowable distance from the boundary of the partition, the control device 100 determines that it is located on the boundary. The allowable distance at this time is, for example, several tens of centimeters. If a negative determination is made in step S10 (S10: No), the control device 100 executes step S10 again. That is, the control device 100 repeats step S10 until the electric tractor 10 is located on the boundary line of the partition. If a positive determination is made in step S10 (S10: Yes), the control device 100's process jumps to step S11.

[0061] In step S11, the control device 100 determines whether the electric tractor 10 has traveled a predetermined distance. Specifically, the control device 100 calculates the distance traveled by the electric tractor 10 since the start of step S10 based on the rotational speed A1 of the wheel 12 detected by the rotation sensor 61, the acceleration IA detected by the acceleration sensor 64, and the location information PI from the GPS device 50. Then, the control device 100 determines whether the calculated travel distance is greater than a predetermined distance. It should be noted that the predetermined distance is determined as the distance of one of the multiple zones into which the farm is divided. An example of this predetermined distance is, for example, a few meters.

[0062] If a negative determination is made in step S11 (S11: No), the control device 100 executes the process of step S11 again. That is, the control device 100 repeats the process of step S11 before the electric tractor 10 has traveled a given distance. If a positive determination is made in step S11 (S11: Yes), the process of the control device 100 jumps to step S12.

[0063] In step S12, the control device 100 determines which section on the farm map M the traveled place corresponds to. Specifically, the control device 100 acquires the current position information PI by the GPS device 50. In addition, the control device 100 acquires the position information PI at the time of execution of step S10. Then, the control device 100 determines which section on the farm map M the travel trajectory of the electric tractor 10 corresponds to at the time of repeated execution of step S11, based on these position information PI. Then, the processing of the control device 100 jumps to step S13.

[0064] In step S13, the control device 100 requests the weather server for the weather information WI corresponding to the current position of the electric tractor 10 via the wireless communication machine 51. Then, the control device 100 receives the weather information WI via the wireless communication machine 51. The control device 100 judges whether there is precipitation or not, based on the received weather information WI. Then, the processing of the control device 100 jumps to step S14.

[0065] In step S14, the control device 100 determines whether the state in which the electric tractor 10 slips continues for a predetermined prescribed period or more during the period in which the electric tractor 10 travels for the given distance, for which the affirmative determination is made in step S11. Specifically, the control device 100 acquires the rotation speed Al detected by the rotation sensor 61 in the travel for the given distance. Then, the control device 100 calculates the change in the travel speed of the electric tractor 10 based on the rotation speed Al of the wheel 12. On the other hand, the control device 100 acquires the position information PI detected by the GPS device 50 in the travel for the given distance. The control device 100 calculates the change in the travel distance per unit time of the electric tractor 10, that is, the change in the travel speed, from the change in the position information PI. The control device 100 compares the change in the travel speed calculated based on the rotation sensor 61 with the change in the travel speed calculated based on the GPS device 50. Also, the control device 100 determines whether the state in which the travel speed calculated based on the rotation sensor 61 is greater than the travel speed calculated based on the GPS device 50 continues for a predetermined prescribed period or more. In the case where the determination is affirmative, the control device 100 determines that the electric tractor 10 slips in the travel for the prescribed period. Note that one example of the above-described prescribed period is several seconds. In the case where the affirmative determination is made in step S14 (S14: YES), the processing of the control device 100 jumps to step S15.

[0066] In step S15, the control device 100 refers to the farm map M corresponding to the weather information WI obtained in step S13. Specifically, if the weather information WI contains information indicating no precipitation, the control device 100 refers to the first farm map M1. Conversely, if the weather information WI contains information indicating precipitation, the control device 100 refers to the second farm map M2. Then, the control device 100 sets the slip flag of the zone determined in step S12 to ON on the referenced farm map M. The processing of the control device 100 then returns to step S10.

[0067] On the other hand, if a negative determination is made in step S14 (S14: No), the processing of the control device 100 jumps to step S16. In step S16, similarly to step S15, the control device 100 refers to the farm map M corresponding to the weather information WI obtained in step S13. Then, the control device 100 sets the slip flag of the zone determined in step S12 to OFF on the referenced farm map M. Then, the processing of the control device 100 returns to step S10.

[0068] <Regarding slippage and loss of control>

[0069] The slippage disengagement control is initiated when the occupant of the electric tractor 10 turns on the disengagement control switch S2. That is, the control device 100 executes slippage disengagement control when it receives the second signal SIG2 from the disengagement control switch S2. Conversely, the slippage disengagement control is terminated when the occupant of the electric tractor 10 turns off the disengagement control switch S2. That is, the control device 100 terminates slippage disengagement control when it no longer receives the second signal SIG2 from the disengagement control switch S2.

[0070] like Figure 4 As shown, if slippage begins and the vehicle loses control, the control device 100 executes step S100. In step S100, the control device 100 obtains the current location information PI from the GPS device 50. Then, the control device 100 calculates the current location of the electric tractor 10 based on the location information PI. Then, the processing of the control device 100 jumps to step S101.

[0071] In step S101, the control device 100 requests weather information WI corresponding to the current location of the electric tractor 10 from the weather server via the wireless communication device 51. Then, the control device 100 receives the weather information WI via the wireless communication device 51. Based on the received weather information WI, the control device 100 determines whether there is precipitation or not. Then, the processing of the control device 100 jumps to step S102.

[0072] In step S102, the control device 100 refers to the farm map M corresponding to the weather information WI. That is, if the weather information WI contains information that there is no precipitation, the control device 100 refers to the first farm map Ml. In addition, if the weather information WI contains information that there is precipitation, the control device 100 refers to the second farm map M2. Then, the control device 100 determines the zone on the farm map M corresponding to the current position of the electric tractor 10. In addition, the control device 100 determines whether the slip flag of the zone determined on the farm map M is ON or OFF. In the case where the slip flag is ON (S102: YES), the processing of the control device 100 jumps to step S103.

[0073] In step S103, the control device 100 controls the first converter 71 and the second converter 72 so that the input and output power of the battery 77 is within a predetermined prescribed power range. Here, the prescribed power range is prescribed to be a narrower range than the input and output power range determined at the time of normal travel before the execution of the restriction processing. For example, the prescribed power range is prescribed to be a range in which the battery 77 and the peripheral circuit thereof do not suffer damage even if unexpected sharp turning and sharp braking of the wheels 12 occur. Note that the processing of step S103 is the restriction processing. In addition, the restriction processing of step S103 is executed in the case where the slip flag of the zone on the farm map is ON. Thus, the zone where the slip flag is ON is a restricted area. After the execution of the restriction processing, the processing of the control device 100 jumps to step S104.

[0074] In step S104, the control device 100 determines whether the state in which the wheels 12 of the electric tractor 10 are slipping has continued for a predetermined prescribed period. Specifically, the control device 100 acquires the rotation speed Al detected by the rotation sensor 61. On the other hand, the control device 100 determines the current position based on the position information PI detected by the GPS device 50. The control device 100 calculates the distance between the position before the unit time and the current position determined this time as the travel distance per unit time of the electric tractor 10, that is, the travel speed. The control device 100 determines whether the state in which the travel speed calculated based on the rotation sensor 61 is greater than the travel speed calculated based on the position information PI from the GPS device 50 has continued for a predetermined prescribed period or more. In the case where this determination is affirmative, the control device 100 determines that the electric tractor 10 is slipping. One example of the prescribed period is the same as that in step S13, and is several seconds.

[0075] Note that even if the wheels 12 are slipping, in a case where the state of slipping continues for a prescribed period or more, it is possible that the occupant has stepped on the accelerator pedal of the electrically propelled vehicle 10 to want to escape from the zone where slipping has occurred. Thus, the processing of step S104 is determination processing that determines whether the electrically propelled vehicle 10 is likely to move from the restricted area to outside the restricted area.

[0076] In a case where a negative determination is made in step S104 (S104: NO), the series of slip escape controls returns to step S100. On the other hand, in a case where a positive determination is made in step S104 (S104: YES), the processing of the control device 100 jumps to step S105.

[0077] In step S105, the control device 100 determines whether the mitigation count value is below a prescribed number of times that is determined in advance. The mitigation count value indicates the number of times that the mitigation processing described later is performed. The initial value of the mitigation count value is 0. The prescribed number of times is determined through experiments or the like as a number of times at which an excessive burden is not imposed on the battery 77 even if the mitigation processing is performed. One example of the prescribed number of times is 2 to 3 times.

[0078] In a case where a negative determination is made in step S105 (S105: NO), the series of slip escape controls returns to step S100. In a case where a positive determination is made in step S105 (S105: YES), the processing of the control device 100 jumps to step S106.

[0079] In step S106, the control device 100 expands the prescribed power range that is set in the restriction processing. Specifically, the control device 100 sets the prescribed power range to the same range as the power range at the time of normal travel before the prescribed power range is set. That is, even during the execution of the restriction processing, the control device 100 temporarily mitigates the range of the power that can be input and output from the battery 77 to the same range as at the time of normal travel. That is, the processing of step S106 is mitigation processing that expands the prescribed power range. Then, the processing of the control device 100 jumps to step S107.

[0080] In step S107, the control device 100 increments the mitigation count value by 1. Then, the processing of the control device 100 jumps to step S108.

[0081] In step S108, the control device 100 determines whether the slip of the wheel 12 is eliminated. Specifically, the control device 100 calculates the travel speed based on the rotation sensor 61 as in step S104. In addition, the control device 100 calculates the travel speed based on the position information PI from the GPS device 50. Then, if both the travel speed calculated based on the rotation sensor 61 and the travel speed calculated based on the position information PI from the GPS device 50 are positive values and the difference between the two travel speeds is smaller than a given value, the control device 100 determines that the slip state has been eliminated.

[0082] In the case where the affirmative determination is made in step S108 (S108: YES), the processing of the control device 100 jumps to step S109.

[0083] In step S109, the control device 100 releases the mitigation processing. That is, the control device 100 sets the prescribed power range temporarily enlarged in the mitigation processing to the original prescribed power range determined in advance. Specifically, the control device 100 controls the 1st converter 71 and the 2nd converter 72 so that the input and output power of the battery 77 becomes within the original prescribed power range. Then, the processing of the control device 100 jumps to step S110.

[0084] In step S110, the control device 100 clears the mitigation count value. Then, the processing of the control device 100 returns to step S100.

[0085] On the other hand, in the case where the negative determination is made in step S108 (S108: NO), the processing of the control device 100 jumps to step S130.

[0086] In step S130, the control device 100 determines whether the time from when the mitigation processing is executed in step S106 is greater than a prescribed period set in advance. One example of the prescribed period is several seconds to several tens of seconds or the like. In the case where the negative determination is made in step S130 (S130: NO), the control device 100 executes again the processing of step S130. In the case where the affirmative determination is made in step S130 (S130: YES), the processing of the control device 100 jumps to step S109.

[0087] On the other hand, in the case where the negative determination is made in step S102 (S102: NO), the processing of the control device 100 jumps to step S120.

[0088] In step S120, the control device 100 releases the restriction processing. Note that in a case where the restriction processing is not executed at the start time of step S120, the control device 100 maintains the current control of the input and output power of the battery 77. That is, the control device 100 maintains the state where the restriction processing is not executed. Then, the processing of the control device 100 returns to step S100.

[0089] <Effects of the First Embodiment>

[0090] In the above-described first embodiment, it is assumed that the electrically driven tractor 10 is located in a subarea where the slip flag is ON on the farm map M. In this case, it is possible that the condition where the wheel 12 of the electrically driven tractor 10 slips, the slip is eliminated, and the wheel 12 suddenly grips the ground is repeated. If the state where the wheel 12 slips changes to the state where the wheel 12 suddenly grips the ground, large power is supplied from the first electric motor 41 to the battery 77. In the above-described embodiment, by executing the restriction processing, that is, by not supplying excessive power to the battery 77 in this condition, the input and output power of the battery 77 is restricted to the prescribed power range.

[0091] On the other hand, in a case where the wheel 12 is slipping in the subarea where the slip flag is ON, in order to escape from the subarea, it is necessary to transmit large torque to the wheel 12 that does not slip. That is, it is necessary to supply large power from the battery 77 to the first electric motor 41.

[0092] <Effects of the First Embodiment>

[0093] (1-1) In the above-described embodiment, in a case where the electrically driven tractor 10 can possibly move to the outside of the subarea where the slip flag is ON, even during the restriction processing, the restriction of the input and output power of the battery 77 is relaxed. As a result, the necessary power is supplied to the first electric motor 41, and the possibility that the electrically driven tractor 10 can escape from the subarea is increased.

[0094] (1-2) In the above-described embodiment, in a case where the count value exceeds the prescribed number of times during the period from the start of the execution of the restriction processing to the end, the execution of the relaxation processing is prohibited. Thus, it is possible to suppress the case where the state of charge SOC of the battery 77 is excessively low and an excessive burden is applied to the battery 77 due to the repeated execution of the relaxation processing.

[0095] (1-3) In the above-described embodiment, the control device 100 executes the farm map creation control. Also, the farm map M indicates the subarea where the wheel 12 actually slips, that is, the subarea where mud can possibly exist, with the slip flag. If the above-described relaxation processing is executed in accordance with these farm maps M, it is possible to suppress the case where the output torque of the first electric motor 41 is insufficient when large torque that is necessary as the output torque from the first electric motor 41 is required to escape from the mud.

[0096] (1-4) In the above-described embodiment, the control device 100 determines in the determination process that the electrically propelled vehicle 10 is likely to move outside the division for which the slip flag is ON in a case where the state in which the wheel 12 is slipping continues for a prescribed period. According to this configuration, it is possible to accurately determine a situation to be escaped from mud or the like based on the slipping of the wheel 12.

[0097] (1-5) The muddy state of a farm differs between a case where it is raining and a case where it is not raining. For example, in a case where it is raining, the degree of mud and the number of muddy locations are higher than in a case where it is not raining. In the above-described embodiment, the control device 100 can selectively refer to the first farm map Ml or the second farm map M2 when executing the restriction process. That is, the control device 100 can execute the restriction process based on the farm map M that more appropriately represents the state of the actual farm.

[0098] <2nd Embodiment>

[0099] Hereinafter, a 2nd embodiment of the electrically propelled vehicle and the control program of the electrically propelled vehicle will be described. In the 2nd embodiment, the schematic configuration of the electrically propelled vehicle 10, the power transmission path of the electrically propelled vehicle 10, the electrical structure of the electrically propelled vehicle 10, and the schematic configuration of the control device 100 are the same as those of the 1st embodiment.

[0100] <About Farm Escape Control>

[0101] The control device 100 executes farm escape control. The farm escape control is started on the condition that the electrically propelled vehicle 10 is located within a farm. That is, the control device 100 acquires the current position information PI of the electrically propelled vehicle 10 from the GPS device 50. In addition, the control device 100 starts the farm escape control on the condition that the current position of the electrically propelled vehicle 10 based on the acquired position information PI is located within the region shown by the farm map M. In addition, the farm escape control is ended on the condition that the electrically propelled vehicle 10 is located outside the farm. That is, the control device 100 ends the farm escape control on the condition that the current position of the electrically propelled vehicle 10 determined based on the current position information PI is located outside the region shown by the farm map M.

[0102] As Figure 5If the farm escape control is started, the control device 100 performs the process of step S200 as shown. In step S200, the control device 100 determines whether the current state of charge SOC of the battery 77 is equal to or lower than a first prescribed state of charge X that is predetermined. Specifically, the control device 100 acquires the battery information BI from the battery 77. In addition, the control device 100 acquires the temperature Tl from the battery temperature sensor 62. The control device 100 calculates the current state of charge SOC of the battery 77 based on the battery information BI and the temperature Tl. The first prescribed state of charge X is determined as a lower limit value of the state of charge SOC at which the battery 77 can output the electric power required for the electric traction vehicle 10 to travel normally and at which the battery 77 does not deteriorate excessively.

[0103] In the case where the determination in step S200 is negative (S200: No), the process of the control device 100 returns to step S200. In the case where the determination in step S200 is affirmative (S200: Yes), the process of the control device 100 branches to step S201.

[0104] In step S201, the control device 100 controls the first converter 71 and the second converter 72 so that the input and output electric power of the battery 77 is within a prescribed electric power range that is predetermined. Here, the prescribed electric power range is prescribed as a narrower range than the input and output electric power prescribed before the restriction process is performed. For example, the prescribed electric power range is prescribed as a range in which the battery 77 does not undergo overdischarge in a state where the state of charge SOC of the battery 77 is equal to or lower than the first prescribed state of charge X. Note that the process of step S201 is a restriction process. In addition, as shown above, the series of farm escape control including the restriction process of step S201 is performed on the condition that the electric traction vehicle 10 is located within the farm. Thus, the farm is a restricted area. After the restriction process is performed, the process of the control device 100 branches to step S202.

[0105] In step S202, the control device 100 determines whether or not the state in which the electrically driven tractor 10 is to be detached from the farm has continued for a predetermined prescribed period. Specifically, the control device 100 acquires the acceleration IA from the acceleration sensor 64. Then, the control device 100 calculates the inclination angle of the vehicle body 13 on the basis of the acceleration IA. Here, the inclination angle of the vehicle body 13 refers to the angle of the acute angle among the angles formed by the up-and-down axis of the vehicle body 13 and the plumb axis extending in the direction of gravity. Thus, when the electrically driven tractor 10 is running on a horizontal plane, the inclination angle of the vehicle body 13 is 0. The control device 100 determines whether or not the state in which the inclination angle of the vehicle body 13 is greater than a predetermined prescribed angle has continued for a predetermined prescribed period or more. In the case where the determination is affirmative, the control device 100 determines that the electrically driven tractor 10 is to be detached from the farm. One example of the prescribed period is several seconds. Thus, the process of step S202 is a determination process that determines whether or not the electrically driven tractor 10 is likely to move from the restricted area to outside the restricted area.

[0106] In the case where the determination in step S202 is negative (S202: No), the series of farm detachment control returns to step S200. On the other hand, in the case where the determination in step S202 is affirmative (S202: Yes), the process of the control device 100 branches to step S203.

[0107] In step S203, the control device 100 expands the prescribed electric power range set in the restriction process. Specifically, the control device 100 sets the prescribed electric power range to the same range as the electric power range at the time of normal running before the prescribed electric power range is set. That is, the control device 100 temporarily relaxes the input-outputable electric power range of the battery 77 to the same range as at the time of normal running even during the execution of the restriction process. That is, the process of step S203 is a relaxation process that expands the prescribed electric power range. Then, the process of the control device 100 branches to step S204.

[0108] In step S204, the control device 100 determines whether or not the electrically driven tractor 10 has completed detachment from the farm. Specifically, the control device 100 acquires the acceleration IA from the acceleration sensor 64. The control device 100 determines whether or not the state in which the inclination angle of the vehicle body 13 is the prescribed angle or less has continued for a prescribed period. In the case where the determination is affirmative, the control device 100 determines that the electrically driven tractor 10 has completed detachment from the farm. One example of the prescribed period is several seconds.

[0109] In the case where the determination in step S204 is affirmative (S204: Yes), the process of the control device 100 branches to step S205. On the other hand, in the case where the determination in step S204 is negative (S204: No), the process of the control device 100 branches to step S220.

[0110] In step S220, the control device 100 determines whether the time from when the mitigation process was executed in step S203 has continued for a predetermined prescribed period. An example of the prescribed period is several seconds to several tens of seconds, etc. In the case where a negative determination is made in step S220 (S220: NO), the control device 100 executes the process of step S220 again. In the case where an affirmative determination is made in step S220 (S220: YES), the process of the control device 100 jumps to step S205.

[0111] In step S205, the control device 100 determines whether the current state of charge SOC of the battery 77 is below a predetermined second prescribed state of charge Y. Specifically, the control device 100 acquires the battery information BI from the battery 77. In addition, the control device 100 acquires the temperature Tl from the battery temperature sensor 62. The control device 100 calculates the current state of charge SOC of the battery 77 based on the battery information BI and the temperature Tl. The second prescribed state of charge Y is prescribed as a lower limit value of the state of charge SOC at which the battery 77 does not become an overdischarged state. That is, the second prescribed state of charge Y is a value that is smaller than the first prescribed state of charge X.

[0112] In the case where a negative determination is made in step S205 (S205: NO), the process of the control device 100 returns to step S200. In the case where an affirmative determination is made in step S205 (S205: YES), the process of the control device 100 jumps to step S206.

[0113] In step S206, the control device 100 opens the system main relay 80. That is, the control device 100 opens the electrical connection between the battery 77 and the inverter 85. Note that the process of step S206 is a reset process in which the system main relay 80 is opened in the case where the state of charge SOC of the battery 77 is below the predetermined second prescribed state of charge Y. Then, the process of the control device 100 jumps to step S207.

[0114] In step S207, the control device 100 determines whether a predetermined prescribed period has elapsed after the system main relay 80 was opened. The prescribed period is determined through experiments, etc., as a period until the open-circuit voltage OCV of the battery 77 stabilizes.

[0115] In the case where a negative determination is made in step S207 (S207: NO), the control device 100 executes the process of step S207 again. In the case where an affirmative determination is made in step S207 (S207: YES), the process of the control device 100 jumps to step S208.

[0116] In step S208, the control device 100 acquires the open-circuit voltage OCV of the battery 77. The process of the control device 100 jumps to step S209.

[0117] In step S209, the control device 100 calculates the state of charge SOC of the battery 77 based on the open-circuit voltage OCV. That is, the process of step S209 is a recalculation process in which the state of charge SOC of the battery 77 is recalculated in a state in which the system main relay 80 is turned off after the reset process. Then, the process of the control device 100 jumps to step S210.

[0118] In step S210, the control device 100 determines whether the state of charge SOC of the battery 77 recalculated in the recalculation process is greater than the second prescribed state of charge Y. In the case where the affirmative determination is made in step S210 (S210: YES), the process of the control device 100 jumps to step S211.

[0119] In step S211, the control device 100 turns on the system main relay 80. That is, the control device 100 turns on the electrical connection between the battery 77 and the inverter 85. Then, the process of the control device 100 returns to step S200.

[0120] On the other hand, in the case where the negative determination is made in step S210 (S210: NO), the process of the control device 100 jumps to step S212.

[0121] In step S212, the control device 100 keeps the system main relay 80 turned off. Also, the control device 100 notifies the occupant of the electrically driven tractor 10 of the fact that the power supply circuit 99 of the electrically driven tractor 10 cannot be started again. As one example of the notification, the control device 100 causes the vehicle-mounted indicator lamp or the like using a battery other than the battery 77 as a driving source to light up. Then, the series of farm departure control ends. Note that in the case where the series of farm departure control ends through step S212, the system main relay 80 is kept turned off, and thus the control device 100 cannot perform the normal control of the electrically driven tractor 10. Thus, the battery 77 of the electrically driven tractor 10 needs to be charged using an external power source or the like.

[0122] <Effects of the Second Embodiment>

[0123] In the above-described second embodiment, the electrically driven tractor 10 is located within the farm, and the state of charge SOC of the battery 77 is the first prescribed state of charge X or less. In this case, if the electrically driven tractor 10 is running at high speed, or the load of the work machine 20 is large, the state of charge SOC of the battery 77 can be below the second prescribed state of charge Y, and overdischarge can occur. Therefore, in the second embodiment, if the state of charge SOC of the battery 77 is the first prescribed state of charge X or less, the input and output power of the battery 77 is limited to the prescribed power range.

[0124] On the other hand, when the electrically driven tractor 10 moves from within the farm to outside the farm, it mostly climbs a slope or a step. Thus, in order for the electrically driven tractor 10 to escape from the farm, a large torque needs to be transmitted to the wheels 12. That is, a large power needs to be supplied from the battery 77 to the first electric motor 41.

[0125] <Effects of the Second Embodiment>

[0126] Next, the effects of the second embodiment will be described. The electrically driven tractor 10 of the second embodiment and the control program of the electrically driven tractor 10 achieve the following effects in addition to the effects of (1-5) of the first embodiment.

[0127] (2-1) In the above-described embodiment, the control device 100 executes the limiting process with the condition that the state of charge SOC of the battery 77 is the first prescribed state of charge X or less. According to this configuration, the input and output of the power of the battery 77 is limited in conjunction with the decrease in the state of charge SOC of the battery 77. Thus, overdischarge of the battery 77 can be suppressed.

[0128] (2-2) In the above-described embodiment, the restriction of the input and output power of the battery 77 is relaxed even during the limiting process, in the case where the electrically driven tractor 10 is likely to move outside the farm. Therefore, the case where the output torque of the first electric motor 41 is insufficient when the electrically driven tractor 10 escapes from the farm can be suppressed. As a result, even if only the state of charge SOC of the battery 77 remains that enables the electrically driven tractor 10 to escape from the farm, the situation where the electrically driven tractor 10 cannot escape from the farm due to being in the limiting process is less likely to occur.

[0129] (2-3) In the above-described embodiment, the electrically driven tractor 10 can determine whether the electrically driven tractor 10 is likely to move from within the farm to outside the farm, based on the detection result of the acceleration IA detected by the acceleration sensor 64. According to this configuration, the control device 100 can accurately determine the case where the electrically driven tractor 10 is running on a slope within the farm and is about to escape to a road or the like, based on the acceleration sensor 64.

[0130] (2-4) Since the battery 77 is able to temporarily output more electric power after the mitigation processing is performed, the calculated state of charge SOC is sometimes calculated as a value smaller than the original state of charge SOC. Therefore, it is possible that even if the original state of charge SOC is a state greater than the second prescribed state of charge Y, the state of charge SOC is erroneously determined to be the second prescribed state of charge Y or less. If such an erroneous determination occurs, the travel of the electrically propelled vehicle 10 is prohibited even if it is actually still possible to travel.

[0131] In the above-described embodiment, the control device 100 performs the reset processing and the recalculation processing after the mitigation processing. In addition, in a case where the state of charge SOC recalculated in the recalculation processing is greater than the second prescribed state of charge Y, the control device 100 turns on the system main relay 80.

[0132] Thus, after the mitigation processing, the battery 77 is brought to a state electrically disconnected from the first converter 71 by the reset processing, and thus the open-circuit voltage OCV of the battery 77 is stabilized. Then, the state of charge SOC is calculated based on the open-circuit voltage OCV in the stabilized state, and thus the above-described erroneous determination is less likely to occur.

[0133]

[0134] The present embodiment can be implemented by being changed as follows. The present embodiment and the following modified examples can be implemented after being combined with each other within a range where there is no technical contradiction.

[0135] • In the above-described embodiment, the restricted area is not limited to a farm and a section in which the slip flag is ON. As long as an area in which it is effective to travel the electrically propelled vehicle 10 in a state in which the input and output of electric power is restricted is set as the restricted area.

[0136] • In the above-described embodiment, the condition for performing the restriction processing can include at least the condition that the electrically propelled vehicle 10 travels in the restricted area. That is, the restriction processing can be performed when the electrically propelled vehicle 10 travels in the restricted area and one or more other conditions are satisfied.

[0137] • In the above-described embodiment, the determination of the slip state is not limited to the example of the above-described embodiment. It can be determined that the electrically propelled vehicle 10 is in the slip state when the travel speed of the electrically propelled vehicle 10 calculated based on the rotation speed Al of the rotation sensor 61 is the prescribed travel speed or less and the operation amount ACCP of the accelerator pedal of the accelerator pedal sensor 65 is the prescribed amount or more for a prescribed period.

[0138] ​• In the above embodiment, the control device 100 can further have a map other than the first farm map Ml and the second farm map M2. For example, the control device 100 can further have a map at the time of snowfall. In addition, the control device 100 can further have a farm map M that differs according to each season. Further, the control device 100 can have one farm map M. In the case where the control device 100 has one farm map M, the processing related to the acquisition of the weather information WI can be omitted.

[0139] • In the above embodiment, the control device 100 can perform the determination processing by processing other than the above embodiment. For example, the electrically driven tractor 10 can further have a switch other than the map switch SI and the disengagement control switch S2, which can switch on / off, and when the switch is operated, a positive determination is made in the determination processing.

[0140] • In the first embodiment, the control device 100 can omit the processing related to the mitigation count value. That is, the control device 100 can omit the processing of step S105, step S107, and step S110.

[0141] • In the mitigation processing of the above embodiment, the prescribed power range can not be set to the same range as the power range at the time of normal travel before the prescribed power range is set. That is, in the mitigation processing, it is only necessary to be set to a range larger than the prescribed power range set in the restriction processing.

[0142] • In the second embodiment, the control device 100 can omit the processing from step S206. That is, the control device 100 can prohibit the travel of the electrically driven tractor 10 in the case where the state of charge SOC of the battery 77 is the second prescribed state of charge Y or less after the mitigation processing is performed.

[0143] • In the second embodiment, the processing related to the mitigation count value of the first embodiment can be applied. Specifically, the control device 100 can increase the mitigation count value after the processing of step S203, and prohibit the next mitigation processing in the case where the mitigation count value is the prescribed value or more.

Claims

1. An electrically driven tractor comprising: a vehicle body capable of being coupled to a work machine; an electric motor; a battery that accumulates electric power supplied to the electric motor; a converter that controls input and output electric power of the battery; a wheel for traveling that rotates by drive force from the electric motor; and a control device that takes the converter as a control target, the control device storing a first farm map used in the absence of precipitation and a second farm map used in the presence of precipitation as a farm map, wherein the control device executes: a restriction process that requests weather information corresponding to a current position of the electrically driven tractor via a wireless communication machine, refers to the farm map corresponding to the weather information, and controls the converter so that the input and output electric power of the battery becomes within a predetermined prescribed electric power range that is a narrower range than an input and output electric power range determined at the time of normal travel before the execution of the restriction process, as one of conditions that the electrically driven tractor is traveling within a predetermined restricted area; a determination process that determines whether the electrically driven tractor is likely to move from the restricted area to outside the restricted area; and a mitigation process that, in the case where the determination process makes a positive determination during the restriction process, expands the prescribed electric power range to a range that is the same as the electric power range at the time of normal travel before the prescribed electric power range is set, compared to the case where the determination process makes a negative determination, wherein the control device prohibits the execution of the mitigation process in the case where the number of times that the determination process makes a positive determination exceeds a predetermined prescribed number of times during the period from the start to the end of the restriction process.

2. The electrically driven tractor according to claim 1, wherein in the farm map, in each of a plurality of sub-areas obtained by dividing a farm into the sub-areas, a position of the sub-area and slip information indicating whether the wheel slips in the sub-area are associated, and the restricted area is the sub-area in the farm map with which the information that the wheel slips is associated.

3. The electrically driven tractor according to claim 1 or 2, further comprising a switch capable of being switched on / off by an occupant of the electrically driven tractor, wherein in the determination process, in the case where the switch is on, the control device determines that the electrically driven tractor is likely to move from the restricted area to outside the restricted area.

4. The electrically driven tractor according to claim 1 or 2, wherein in the determination process, in the case where a state in which the wheel is slipping continues for a predetermined prescribed period of time, the control device determines that the electrically driven tractor is likely to move from the restricted area to outside the restricted area.

5. The electrically driven tractor according to claim 1 or 2, wherein the control device further executes the restriction process with a condition that a state of charge of the battery is below a predetermined first prescribed state of charge.

6. The electrically driven tractor according to claim 5, further comprising a tilt sensor that detects a tilt angle of the vehicle body, wherein the restricted area is a farm. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ In the determination processing, the control device determines whether the electrically powered tractor is likely to move from the restricted area to outside the restricted area, based on a detection result of the tilt sensor.

7. The electrically powered tractor according to claim 1 or 2, wherein a system main relay is further provided between the battery and the converter, and is capable of switching on / off of electric conduction, the control device executes: reset processing for setting the system main relay to off in a case where the state of charge of the battery is below a predetermined second specified state of charge after the mitigation processing is executed; and recalculation processing for recalculating the state of charge of the battery in a case where the system main relay is set to off after the reset processing is executed, the control device sets the system main relay to on in a case where the state of charge of the battery recalculated in the recalculation processing is greater than the second specified state of charge.

8. A computer-readable medium storing a control program for an electrically powered tractor, the control program is applied to a control device of an electrically powered tractor, the electrically powered tractor being provided with: a vehicle body capable of being coupled to a work machine; an electric motor; a battery that accumulates electric power supplied to the electric motor; a converter that controls input and output electric power of the battery; a travel wheel that rotates by drive power from the electric motor; and the control device controls the converter as a control target, the control device stores a first farm map used in the absence of precipitation and a second farm map used in the presence of precipitation as a farm map, the control program causes the control device to execute: restriction processing for requesting weather information corresponding to a current position of the electrically powered tractor via a wireless communication device, referring to the farm map corresponding to the weather information, and controlling the converter so that the input and output electric power of the battery is within a predetermined specified electric power range as one of conditions that the electrically powered tractor is traveling within a predetermined restricted area, the specified electric power range being a narrower range than an input and output electric power range determined during normal travel before the restriction processing is executed; determination processing for determining whether the electrically powered tractor is likely to move from the restricted area to outside the restricted area; and mitigation processing for expanding the specified electric power range to a range identical to an electric power range during normal travel before the specified electric power range is set, in a case where the determination processing determines positively during the restriction processing, the control device prohibits execution of the mitigation processing in a case where the determination processing determines positively a predetermined specified number of times during a period from the start to the end of the restriction processing. ​ ​

Images