Work vehicle and method for controlling the work vehicle

Abstract

This makes it easier to turn on the PTO axis without causing damage. [Solution] The work vehicle comprises a traveling device, a PTO shaft that supplies power to the work machine, a first electric motor that drives the traveling device, a second electric motor that drives the PTO shaft, a PTO switch for switching the rotation of the PTO shaft on and off, a PTO clutch disposed between the second electric motor and the PTO shaft, and a control device. When the PTO switch is switched from off to on while the rotation speed of the second electric motor is higher than a reference value, the control device reduces the rotation speed of the second electric motor to the reference value, and then switches the PTO clutch from a disengaged state to a engaged state.

Description

【Technical Field】 【0001】 The present invention relates to a work vehicle and a method for controlling the work vehicle. 【Background Art】 【0002】 In the field of automobiles whose main purpose is to move people or objects, electric vehicles (EVs) that generate driving force (traction) for driving by an electric motor (hereinafter sometimes simply referred to as a "motor") instead of an internal combustion engine are becoming widespread. 【0003】 On the other hand, in order to realize a decarbonized society, it is required to reduce the amount of carbon dioxide (CO2) emitted by work vehicles such as tractors used in fields. Different from general automobiles, work vehicles such as tractors need to tow work implements (agricultural implements) to perform agricultural work such as tilling. Therefore, in order to realize the electrification of work vehicles, there are problems to be solved different from the electrification of passenger cars. 【0004】 Patent Document 1 discloses an electric tractor that distributes and supplies electric power from a battery to a plurality of electric motors. The electric tractor includes a hydraulic pump, a pump motor, a PTO motor, a traveling motor, a battery, and an electric drive controller. The pump motor is an electric motor that drives the hydraulic pump. The PTO motor is an electric motor that drives the PTO shaft. The traveling motor is an electric motor that drives the traveling body to travel. The battery supplies electric power to the pump motor, the PTO motor, and the traveling motor. The electric drive controller controls the distribution of electric power to the pump motor, the PTO motor, and the traveling motor. 【Prior Art Documents】 【Patent Documents】 【0005】 【Patent Document 1】 Japanese Unexamined Patent Application Publication No. 2023-66721 【Summary of the Invention】 [Problems that the invention aims to solve] 【0006】 Electric work vehicles that drive the PTO shaft with a PTO motor may be equipped with a clutch (hereinafter referred to as "PTO clutch") for switching the transmission of power from the PTO motor to the PTO shaft. The PTO clutch can be switched off and on by the user operating a switch (hereinafter referred to as "PTO switch") provided on the work vehicle. For example, when the PTO shaft is rotating at high speed for work, if the user switches the PTO switch from on to off, the PTO clutch is disengaged, and the transmission of power from the PTO motor to the PTO shaft is interrupted. As a result, the rotation of the PTO shaft stops. When the PTO shaft is to be rotated again from that state, the user switches the PTO switch back on to switch the PTO clutch from the disengaged state to the engaged state. This transmits power from the rotation of the PTO motor to the PTO shaft, and the PTO shaft rotates again. However, if the PTO clutch is engaged when the PTO motor is rotating at a relatively high rotational speed, it may cause damage to the work vehicle and parts of the work machine (e.g., blades). [Means for solving the problem] 【0007】 This disclosure provides solutions as described in the following items. 【0008】 [Item 1] Traveling device and The PTO shaft that supplies power to the implement, A first electric motor that drives the aforementioned traveling device, A second electric motor that drives the PTO shaft, A PTO switch for switching the rotation of the PTO shaft on and off, A PTO clutch is positioned between the second electric motor and the PTO shaft, Control device and Equipped with, When the PTO switch is switched from off to on while the rotational speed of the second electric motor is higher than a reference value, the control device reduces the rotational speed of the second electric motor to the reference value, and then switches the PTO clutch from the disengaged state to the engaged state. Work vehicle. [Item 2] The work vehicle as described in item 1, wherein the control device, after switching the PTO clutch from the disengaged state to the engaged state and a predetermined time has elapsed, returns the rotational speed of the second electric motor to the rotational speed before the PTO switch was switched. [Item 3] The work vehicle described in item 2, wherein the predetermined time is 1 second or more and 5 seconds or less. [Item 4] The control device changes the predetermined time based on input from the user, as described in item 2 or 3 for the work vehicle. [Item 5] The control device is Information indicating the type of the aforementioned work machine is obtained, The predetermined time is changed according to the type of work machine. Work vehicles as described in item 2 or 3. [Item 6] The aforementioned reference value for rotational speed is 0 rpm or more and 2000 rpm or less, as described in any one of items 1 to 5, for the work vehicle. [Item 7] The control device, when the PTO switch is switched from on to off, switches the PTO clutch from a connected state to a disconnected state while maintaining the rotational speed of the second electric motor, as described in any one of items 1 to 6, for the work vehicle. [Item 8] The control device, when the PTO switch is switched from on to off while the rotational speed of the second electric motor is higher than the reference value, reduces the rotational speed of the second electric motor to the reference value, and then switches the PTO clutch from the engaged state to the disengaged state, as described in any one of items 1 to 6. [Item 9] The control device, when the PTO switch is switched from on to off while the rotational speed of the second electric motor is higher than the reference value, switches the PTO clutch from the connected state to the disconnected state, and then reduces the rotational speed of the second electric motor to the reference value, as described in any one of items 1 to 6. [Item 10] The control device switches, in response to user input, whether to enable or disable the function that reduces the rotational speed of the second electric motor to the reference value before switching the PTO clutch from a disengaged state to a engaged state when the PTO switch is switched from off to on, the work vehicle according to any one of items 1 to 9. [Item 11] The control device, according to item 8, switches, in response to user input, whether to enable or disable the function that reduces the rotational speed of the second electric motor to the reference value before switching the PTO clutch from the engaged state to the disengaged state when the PTO switch is switched from on to off. [Item 12] The control device, according to item 9, switches, in response to user input, whether to enable or disable the function that switches the PTO clutch from a connected state to a disconnected state and then reduces the rotational speed of the second electric motor to the reference value when the PTO switch is switched from on to off. [Item 13] It further includes a meter panel unit with a digital display, The control device displays a graphical user interface on the digital display that allows the user to set whether to enable or disable the function. A work vehicle as described in any one of items 10 to 13. [Item 14] The work vehicle according to item 13, wherein the meter panel unit further has an indicator that shows whether the function is enabled or disabled. [Item 15] The work vehicle further includes a meter panel unit including an indicator indicating an operating state of the PTO shaft. When the control device connects the PTO clutch, the control device lights the indicator, and when the control device disconnects the PTO clutch, the control device turns off the indicator. The work vehicle according to any one of Items 1 to 14. [Item 16] A method executed by a computer that controls a work vehicle, The work vehicle includes a traveling device, a PTO shaft that supplies power to a work implement, a first electric motor that drives the traveling device, a second electric motor that drives the PTO shaft, a PTO switch for switching on and off the rotation of the PTO shaft, and a PTO clutch disposed between the second electric motor and the PTO shaft. The method includes when the PTO switch is switched from off to on while the rotational speed of the second electric motor is higher than a reference value, reducing the rotational speed of the second electric motor to the reference value; after reducing the rotational speed to the reference value, switching the PTO clutch from a disengaged state to an engaged state; and the method includes the above steps. [Item 17] A computer program executed by a computer that controls a work vehicle, The work vehicle includes a traveling device, a PTO shaft that supplies power to a work implement, a first electric motor that drives the traveling device, a second electric motor that drives the PTO shaft, a PTO switch for switching on and off the rotation of the PTO shaft, and a PTO clutch disposed between the second electric motor and the PTO shaft. The computer program causes the computer to when the PTO switch is switched from off to on while the rotational speed of the second electric motor is higher than a reference value, reduce the rotational speed of the second electric motor to the reference value; After reducing the rotational speed to the reference value, the PTO clutch is switched from the disengaged state to the engaged state. A computer program that executes an action. [Item 18] Traveling device and The PTO shaft that supplies power to the implement, The aforementioned traveling device and power source for driving the PTO shaft, A PTO switch for switching the rotation of the PTO shaft on and off, A PTO clutch is positioned between the power source and the PTO shaft, Control device and A work vehicle equipped with, The control device, when the PTO switch is switched from off to on while the rotational speed of the power source is higher than a reference value, reduces the rotational speed of the power source to the reference value only when the work vehicle is not moving, and then switches the PTO clutch from the disengaged state to the engaged state. Work vehicle. [Item 19] A method performed by a computer that controls the work vehicle, The aforementioned work vehicle comprises a traveling device, a PTO shaft that supplies power to the work machine, a power source that drives the traveling device and the PTO shaft, a PTO switch for switching the rotation of the PTO shaft on and off, and a PTO clutch positioned between the power source and the PTO shaft. The aforementioned method, To determine whether the aforementioned work vehicle is in motion, When the PTO switch is switched from off to on while the aforementioned work vehicle is not moving and the rotational speed of the power source is higher than the reference value, the rotational speed of the power source is reduced to the reference value, and then the PTO clutch is switched from the disengaged state to the engaged state. Methods that include... [Item 20] A computer program executed by a computer that controls a work vehicle, The aforementioned work vehicle comprises a traveling device, a PTO shaft that supplies power to the work machine, a power source that drives the traveling device and the PTO shaft, a PTO switch for switching the rotation of the PTO shaft on and off, and a PTO clutch positioned between the power source and the PTO shaft. The computer program is installed on the computer. To determine whether the aforementioned work vehicle is in motion, When the PTO switch is switched from off to on while the aforementioned work vehicle is not moving and the rotational speed of the power source is higher than the reference value, the rotational speed of the power source is reduced to the reference value, and then the PTO clutch is switched from the disengaged state to the engaged state. A computer program that executes something. 【0009】 Comprehensive or specific embodiments of the present invention may be realized by apparatus, systems, methods, integrated circuits, computer programs, or computer-readable non-temporary storage media, or any combination thereof. Computer-readable storage media may include volatile storage media or non-volatile storage media. An apparatus may consist of multiple devices. If an apparatus consists of two or more devices, these two or more devices may be located in a single device or in two or more separate devices. [Effects of the Invention] 【0010】 According to embodiments of the present invention, it is possible to prevent damage to a work vehicle or work machine caused by engaging the PTO clutch when the PTO motor is rotating at high speed. [Brief explanation of the drawing] 【0011】 [Figure 1] This is a schematic plan view illustrating an example of the basic configuration of a work vehicle according to an exemplary embodiment of the present invention. [Figure 2] This is a side view of a work vehicle according to an exemplary embodiment of the present invention. [Figure 3] This is a top view of the work vehicle. [Figure 4] A block diagram showing the main components of a work vehicle and an example of their connection relationships. [Figure 5] This block diagram shows an example of the configuration of a power converter and its connection to other equipment. [Figure 6] Block diagram showing examples of hardware configurations for each ECU. [Figure 7] This is a block diagram showing an example of the configuration of a power distribution unit. [Figure 8] This is a block diagram showing some of the components of a work vehicle. [Figure 9A] This is a diagram illustrating an example of operation by a control device. [Figure 9B] This is a diagram illustrating another example of operation by a control device. [Figure 9C] This figure shows yet another example of operation by a control device. [Figure 9D] This figure shows yet another example of operation by a control device. [Figure 10A] This flowchart shows an example of an operation performed by the control device. [Figure 10B] This flowchart shows other examples of actions performed by the control device. [Figure 11] This is a front view showing a specific example of a meter panel unit. [Figure 12] This figure shows an example of a GUI displayed on a screen. [Modes for carrying out the invention] 【0012】 Embodiments of the present invention will be described below. However, unnecessarily detailed descriptions may be omitted. For example, detailed descriptions of already well-known matters and redundant descriptions of substantially identical configurations may be omitted. This is to avoid the following description becoming unnecessarily verbose and to facilitate understanding for those skilled in the art. The inventors provide the accompanying drawings and the following description so that those skilled in the art can fully understand the present invention, and not to limit the subject matter described in the claims. In the following description, components having the same or similar function are denoted by the same reference numerals. 【0013】 The following embodiments are illustrative examples for realizing the technical concept of the present invention, and the present invention is not limited to these embodiments. For example, the numerical values, shapes, materials, steps, and order of steps shown in the following embodiments are merely examples, and various modifications are possible as long as they do not create a technical inconsistency. Furthermore, it is possible to combine one embodiment with other embodiments. The size and positional relationships of the components shown in each drawing may be exaggerated for ease of understanding. 【0014】 (Definition of terms) In this specification, “work vehicle” means a vehicle used for a specific task, such as agricultural work or construction work. “Work” could be, for example, agricultural work, construction work, rubble removal work, or snow removal work. Agricultural work vehicles could be, for example, tractors, combine harvesters, rice transplanters, riding cultivators, vegetable transplanters, vegetable harvesters, lawnmowers, seeders, or fertilizer spreaders. Construction work vehicles could be, for example, backhoes, wheel loaders, or carriers. An agricultural work vehicle such as a tractor or combine harvester, or a construction work vehicle, may function as a “work vehicle” on its own, or the work vehicle and any implements attached to or towed by it may function as a single “work vehicle.” Agricultural work vehicles perform agricultural tasks on the ground in a field, such as tilling, sowing, pest control, fertilizing, planting crops, or harvesting. Construction work vehicles perform tasks such as transporting soil, rubble, and other materials at a construction site. These tasks are sometimes referred to as "ground work" or simply "work." The act of a work vehicle moving while performing work is sometimes referred to as "work driving." 【0015】 An "electric work vehicle" refers to a work vehicle that runs using an electric motor as its power source. An electric work vehicle may also be equipped with an internal combustion engine as an auxiliary power source in addition to the electric motor. Alternatively, an electric work vehicle may be equipped with an electric motor as an auxiliary power source in addition to the internal combustion engine. An electric work vehicle is equipped with an electrical energy source, such as a battery or fuel cell, to supply power to the electric motor. In the following description, an "electric work vehicle" may be simply referred to as a "work vehicle." 【0016】 Electric motors can be synchronous motors such as permanent magnet synchronous motors or reluctance motors, or asynchronous motors such as induction motors. 【0017】 A battery is an energy storage device that stores the electrical energy necessary for the operation of electric motors and other electrical components mounted on a work vehicle and / or work machine. A fuel cell is a power generation device that generates such electrical energy from a fuel such as hydrogen. An electrical energy source can be realized by an energy storage device, a power generation device, or a combination of an energy storage device and a power generation device. Furthermore, an electric work vehicle may obtain electrical energy from an electrical energy source located at a distance from the vehicle (e.g., on the ground or on another vehicle) via wired or wireless means. 【0018】 When an electric work vehicle performs various "tasks" while moving or stationary, the power required for those tasks may be obtained from electric motors. An electric work vehicle may be equipped with one or more electric motors. If an electric work vehicle is equipped with multiple electric motors, certain electric motors may output the driving force required for movement, while other electric motors may output the driving force required for the "tasks." If some or all of the "tasks" are performed by a work machine, the driving force may be mechanically transmitted from one or more electric motors on the electric work vehicle to the work machine. Such mechanical transmission of driving force may be achieved via a power transmission shaft called a power take-off (PTO) shaft. 【0019】 The work machine itself may be equipped with an electric motor for the work. In this case, power may be supplied to the electric motor of the work machine from an electrical energy source such as a battery or fuel cell equipped in the electric work vehicle. The work machine may also be equipped with an electrical energy source that stores the power required for the work. 【0020】 A "control device" (controller) is a device that controls the operation of part or all of a work vehicle. One example of a "control device" is a computing device comprising at least one processor and at least one memory that stores a computer program (code) that defines the control process executed by the processor. Another example of a "control device" is a computing device with a hardware accelerator such as an FPGA (Field-Programmable Gate Array), ASSP (Application Specific Standard Product), or ASIC (Application-Specific Integrated Circuit) configured or programmed to execute the control process. A control device may also be a collection of multiple devices. For example, several computing devices such as physically separated electronic control units (ECUs) may work together to function as a "control device". 【0021】 A "processor" is a hardware electronic circuit such as a CPU (Central Processing Unit), GPU (Graphics Processing Unit), DSP (Digital Signal Processor), ISP (Image Signal Processor), or NPU (Neural Network Processing Unit). 【0022】 "Memory" refers to hardware electronic circuits such as ROM (Read Only Memory) or RAM (Random Access Memory). Part of the memory may be a storage medium connected to the processor via wiring or a network. These hardware electronic circuits may be implemented by one or more integrated circuits (ICs) or large-scale integrated circuits (LSIs). Each functional unit or block and associated component within the electronic circuit may be manufactured individually as separate integrated circuit chips, or some or all of these functional units or blocks may be combined and manufactured as a single integrated circuit chip. Memory may store computer programs (hereinafter sometimes simply referred to as "programs") that define the operation of the processor. The programs are designed so that the processor performs one or more functions, operations, steps, or processes in embodiments of the present invention. 【0023】 (Embodiment) The following describes several embodiments of the present invention applied to an electric agricultural tractor, an example of an electric work vehicle, with reference to the drawings. The various technologies described for tractors in the following description can also be applied to agricultural machinery other than tractors, construction vehicles used at construction sites, work vehicles used at disaster sites, snowplows used in heavy snow areas, and vehicles for transporting goods. 【0024】 In the following explanation, the direction of arrow F in the diagram will be referred to as "forward," the direction of arrow B as "backward," the direction of arrow L as "left," the direction of arrow R as "right," the direction of arrow U as "up," and the direction of arrow D as "down." 【0025】 <1. Basic configuration of work vehicles> Figure 1 is a schematic plan view illustrating an example of the basic configuration of a work vehicle 10 according to an exemplary embodiment of the present invention. The illustrated work vehicle 10 is an electric tractor for agricultural use. The work vehicle 10 can travel within a field while carrying or towing implements and performing agricultural work according to the type of implement. The work vehicle 10 can also travel within and outside of a field (including roads) with the implement lifted or without the implement attached. 【0026】 The work vehicle 10 is equipped with a body (vehicle frame) 11 that rotatably supports the left and right front wheels 14F and the left and right rear wheels 14R. The body 11 includes a front frame 12 on which the front wheels 14F are mounted and a transmission case 13 on which the rear wheels 14R are mounted. The front frame 12 is fixed to the front of the transmission case 13. The front wheels 14F and the rear wheels 14R may be collectively referred to as "wheels 14". Strictly speaking, wheels 14 are wheels, and wheels 14 are fitted with tires. In this disclosure, "wheels" generally means the entire "wheel and tire". One or both of the front wheels 14F and the rear wheels 14R may be replaced with multiple wheels fitted with tracks (crawlers) instead of wheels with tires. 【0027】 The work vehicle 10 in the example in Figure 1 is equipped with a battery 20 and an electric motor 30 (hereinafter simply referred to as "motor 30") which are directly or indirectly supported by a front frame 12. The battery 20 may be configured as a battery pack including, for example, multiple cells connected in series. The battery 20 is a rechargeable battery that outputs a relatively high voltage, such as a lithium-ion battery or an all-solid-state battery. The battery 20 stores power to drive the motor 30. The battery 20 may be housed in a front housing called a "bonnet". The front housing is supported by a front frame 12 located at the front of the vehicle body 11. 【0028】 The motor 30 is electrically connected to the battery 20. The motor 30 can convert the power output from the battery 20 into mechanical motion (power) to generate the driving force (traction) necessary for the work vehicle 10 to move. The motor 30 may be, for example, an AC synchronous motor. The battery 20 generates DC current. For this reason, if the motor 30 is an AC synchronous motor, a group of electrical circuits including an inverter device (hereinafter sometimes simply referred to as "inverter") may be provided between the battery 20 and the motor 30. The inverter device converts the DC current into AC current. Part of such a group of electrical circuits may be located inside the battery 20. Another part of the group of electrical circuits may be attached to the motor 30 as a drive circuit for the motor 30. 【0029】 The motor 30 has a rotating output shaft 33. The torque of the output shaft 33 is transmitted to the rear wheels 14R via mechanical components such as a transmission (speed changer) and a rear wheel differential (differential gear device) located inside the transmission case 13. In other words, the power generated by the motor 30, which is the power source, is transmitted to the rear wheels 14R by a power transmission system (drivetrain) 34, including a transmission, located inside the transmission case 13. For this reason, the "transmission case" is sometimes called a "transmission case". In four-wheel drive mode, a portion of the power from the motor 30 is also transmitted to the front wheels 14F. In this way, the motor 30 drives a running gear including multiple wheels 14. 【0030】 The power of the motor 30 may be used not only for the travel of the work vehicle 10 but also for driving the work implement. A PTO shaft 40 is provided at the rear end of the transmission case 13. A work implement can be connected to the PTO shaft 40. The PTO shaft 40 may be driven by the motor 30 that drives the travel device, or by other electric motors not shown in Figure 1. Torque from the output shaft 33 of the motor 30 or the output shaft of another motor is transmitted to the PTO shaft 40. The work implement attached to or towed by the work vehicle 10 receives power from the PTO shaft 40 and can perform operations according to various tasks. The motor 30 and the power transmission system 34 are sometimes collectively referred to as an electric powertrain. 【0031】 As shown in Figure 1, the work vehicle 10 does not have an internal combustion engine such as a diesel engine, but is equipped with a battery 20 and a motor 30. The output shaft 33 of the motor 30 is mechanically coupled to a power transmission system 34, such as a transmission, in a transmission case 13. The motor 30 can efficiently generate torque over a relatively wide range of rotational speeds compared to an internal combustion engine. By using the power transmission system 34, including the transmission, it becomes easy to adjust the torque and rotational speed from the motor 30 over an even wider range by performing multi-stage or continuously variable speed changes. Therefore, it is possible to efficiently perform not only the movement of the work vehicle 10 but also a variety of tasks using work equipment. 【0032】 Depending on the intended use or size of the work vehicle 10, some functions of the power transmission system 34 may be omitted. For example, some or all of the transmission responsible for the gear shifting function may be omitted. The number and mounting positions of the motors 30 are not limited to the example shown in Figure 1. Furthermore, the work vehicle may be a hybrid electric vehicle (HEV) equipped with an internal combustion engine such as a diesel engine as a power source in addition to the electric motors. 【0033】 The work vehicle 10 shown in Figure 1 is equipped with one motor 30. However, the work vehicle 10 may be equipped with multiple electric motors. For example, the work vehicle 10 may be equipped with a drive electric motor that drives a running gear including four wheels 14, and a PTO electric motor that drives the PTO shaft 40. The work vehicle 10 may be equipped with multiple PTO shafts (e.g., a rear PTO shaft, a mid PTO shaft, a front PTO shaft, etc.). In that case, one electric motor may drive multiple PTO shafts, or multiple electric motors may drive multiple PTO shafts. For example, the work vehicle 10 may be equipped with multiple electric motors, each driving a corresponding one of the multiple PTO shafts. The work vehicle 10 may be equipped with a front wheel electric motor that drives two front wheels 14F, and a rear wheel electric motor that drives two rear wheels 14R. Alternatively, the work vehicle 10 may be equipped with two electric motors for the front wheels, each driving one of the two front wheels 14F, and two electric motors for the rear wheels, each driving one of the two rear wheels 14R. In other words, the work vehicle 10 may be equipped with four electric motors, each driving one of the four wheels 14. Thus, the work vehicle 10 may be equipped with one or more electric motors for driving the running gear and one or more electric motors for driving one or more PTO shafts. By providing multiple electric motors, the work vehicle 10 can control the rotation of multiple wheels 14 and one or more PTO shafts more flexibly. In the following description, electric motors for driving may be referred to as "driving motors," and electric motors for PTOs may be referred to as "PTO motors" or "PTO motors." 【0034】 <2. Specific examples of work vehicles> Next, we will describe a more specific example of the configuration of the work vehicle 10. 【0035】 Figure 2 is a side view of a work vehicle 10 according to an exemplary embodiment of the present invention. Figure 3 is a top view of the work vehicle 10 according to this embodiment. 【0036】 The work vehicle 10 shown in Figures 2 and 3 comprises a vehicle body 11 and a running gear supported by the vehicle body 11. The running gear includes various devices necessary for driving, such as left and right front wheels 14F, left and right rear wheels 14R, front axle 15F, rear axle 15R, and a rear wheel differential. 【0037】 The vehicle body 11 comprises a front frame 12, a transmission case 13, and a housing frame 16. The front frame 12 is connected to the front of the housing frame 16. The transmission case 13 is connected to the rear of the housing frame 16. A first electric motor 30A and a second electric motor 30B are housed inside the housing frame 16. The first electric motor 30A is a traction motor and drives the traction device via a power transmission system in the transmission case 13. The second electric motor 30B is a PTO motor and drives the PTO shaft 40 and one or more hydraulic pumps. The first electric motor 30A and the second electric motor 30B may be electric motors capable of relatively high efficiency and high torque output, such as permanent magnet synchronous motors. 【0038】 The front frame 12 is fitted with the front axle case 17F. The front axle case 17F supports the left and right front wheels 14F. The transmission case 13 includes the rear axle case 17R. The rear axle case 17R supports the left and right rear wheels 14R and transmits power to the rear wheels 14R. 【0039】 A battery 20 is mounted on the front frame 12. The battery 20 is supported by the front frame 12 and housed inside the front housing 19 (bonnet). The battery 20 stores the power supplied to the first electric motor 30A and the second electric motor 30B. In other words, the battery 20 stores power for driving, operation, and hydraulic drive. In the following description, the battery 20 may be referred to as the "drive battery 20". 【0040】 Above the housing frame 16 and the transmission case 13 are a steering wheel 53, a meter panel unit 54, a group of pedals 55 including the accelerator and brake, a group of switches 56 for work driving, and a driver's seat 52. A safety frame 51 is provided behind the driver's seat 52. The safety frame 51 is attached to the transmission case 13 and has a structure that extends upward. Inside the housing frame 16 are the first electric motor 30A and the second electric motor 30B. 【0041】 The switch group 56 includes various operating devices such as multiple switches, levers, and dials for adjusting the operation of the work vehicle 10 and the work implement. The switch group 56 includes various operating devices such as an accelerator lever for adjusting the travel speed, a switch for switching the PTO shaft 40 on and off, a dial for adjusting the rotational speed of the PTO shaft 40, and a lever for adjusting the height of the three-point linkage supporting the work implement. By operating the switch group 56, the driver can give various instructions to the work vehicle 10 for travel and work. 【0042】 The meter panel unit 54 displays information regarding the status of the work vehicle 10. For example, the meter panel unit 54 displays various information such as the travel speed, the rotational speed of the PTO shaft 40, the height of the three-point linkage, the output of motors 30A and 30B, the charge status of the battery 20, and the temperature of the battery 20. The meter panel unit 54 may be equipped with analog meters and / or a digital display (hereinafter sometimes simply referred to as "display") for displaying this information. The display of the meter panel unit 54 may display a graphical user interface (GUI) that allows the user to perform various setting operations related to the work vehicle 10. The user can perform various settings related to the work vehicle 10 on the display screen using input means such as an input device connected to the meter panel unit 54 or a touchscreen mounted on the display. 【0043】 As shown in Figure 3, a charging inlet 57 is provided to the right of the steering wheel 53. The charging inlet 57 is a device that includes a socket configured to allow connection of a charging adapter extending from an external power source or charging device. Near the charging inlet 57, a device for the user to initiate charging, such as a charging start button, may be provided. When the user connects the charging adapter to the charging inlet 57 and performs a predetermined operation, such as pressing the charging start button, charging of the battery 20 begins. 【0044】 The battery 20 can be charged using either normal charging or rapid charging. In normal charging, AC power supplied from an external AC power source is converted to high-voltage DC power (e.g., around 350V to 450V), and this DC power is supplied to the battery 20. In rapid charging, high-voltage DC power is directly supplied to the battery 20 from an external DC power source. The charging inlet 57 in this embodiment supports both normal and rapid charging. For normal charging, a commercial AC power source outputting an AC voltage of, for example, 200V or 100V may be used. For rapid charging, a DC power source outputting a DC voltage of, for example, around 350V to 450V may be used. Rapid charging can be performed using protocols compliant with standards such as CHAdeMO, NACS, CCS1, CCS2, GB / T, or ChaoJi. 【0045】 The power stored in the battery 20 can also be output to external electrical equipment via the charging inlet 57. Such external power output is referred to herein as "external power supply." External power supply is performed with an external power supply adapter connected to the charging inlet 57. The DC power from the battery 20 can be converted to AC power by a power converter in the work vehicle 10. This AC power can then be supplied to external equipment via the charging inlet 57 and the external power supply adapter. 【0046】 As shown in Figure 3, the first electric motor 30A and the second electric motor 30B in this embodiment are arranged side by side. The first electric motor 30A and the second electric motor 30B are rotated by power supplied from the battery 20. The first electric motor 30A drives the running gear via a power transmission system in the transmission case 13. The second electric motor 30B drives the PTO shaft 40 and the hydraulic pump via a power transmission system in the transmission case 13. Thus, the second electric motor 30B drives the work implement and various hydraulic devices. The hydraulic devices may be used, for example, to change the height of the three-point linkage supporting the work implement. The work vehicle 10 may be equipped with a power steering system that assists the driver's steering wheel operation. In this case, the hydraulic devices may also be used in the power steering system to supply auxiliary force to change the steering angle of the front wheels 104F. 【0047】 <3. System Configuration of Work Vehicles> Figure 4 is a block diagram showing the main components of the work vehicle 10 and an example of their connection relationships. In Figure 4, connection relationships for power transmission, high-voltage drive power, and low-voltage auxiliary power are represented by solid lines of different thicknesses. Connection relationships for signals (digital and analog signals) are represented by dotted lines. Coolant flow is represented by thick dashed lines. 【0048】 As shown in Figure 4, the work vehicle 10 is equipped with a first inverter 35A and a second inverter 35B. The first inverter 35A is connected to the first electric motor 30A. The second inverter 35B is connected to the second electric motor 30B. Each of the first inverter 35A and the second inverter 35B converts the DC voltage from the battery 20 into a three-phase AC voltage. The first inverter 35A supplies the converted three-phase AC voltage to the first electric motor 30A. This causes the first electric motor 30A to rotate and drive the traction device. The second inverter 35B also supplies the converted three-phase AC voltage to the second electric motor 30B. This causes the second electric motor 30B to rotate and drive the hydraulic pump 36 and the PTO shaft 40. 【0049】 The transmission case 13 houses the power transmission system 34A for driving, the power transmission system 34B for work, and the hydraulic pump 36. The power transmission system 34A for driving may include components such as a reduction gear, a sub-transmission, and a differential. The power transmission system 34A for driving transmits power from the rotation of the first electric motor 30A to the rear wheels 14R. In four-wheel drive mode, the power transmission system 34A for driving also transmits a portion of the power from the rotation of the first electric motor 30A to the front wheels 14F. The power transmission system 34B for work may include components such as a reduction gear, a PTO clutch, and a PTO transmission. The power transmission system 34B for work transmits power from the rotation of the second electric motor 30B to the hydraulic pump 36 and the PTO shaft 40. The PTO shaft 40 supplies power for work to the work implement. 【0050】 The PTO shaft 40 shown in Figure 4 is the rear PTO shaft. In addition to the rear PTO shaft, the work vehicle 10 may also have a mid-PTO shaft or a front PTO shaft. If the work vehicle 10 has multiple PTO shafts, the power transmission system 34B may be configured to distribute the power generated by the rotation of the second electric motor 30B to the multiple PTO shafts. Alternatively, the work vehicle 10 may include other electric motors to drive the other PTO shafts in addition to the second electric motor 30B that drives the PTO shaft 40. 【0051】 The implements connected to the PTO shaft 40 may include, for example, a rotary tiller, a seeder, a spreader, a transplanter, a mower, a rake, a baler, a harvester, a spreader, or a harrow. Any implement can be connected to the work vehicle 10 and used. 【0052】 The hydraulic pump 36 is driven by power from the second electric motor 30B. The hydraulic pump 36 pressurizes the hydraulic fluid, thereby changing the height of the three-point linkage to which the work equipment is connected. Alternatively, the hydraulic pump 36 may be used in a hydraulic power steering system. If a front loader is mounted as the work equipment, the hydraulic pump 36 may be used in a hydraulic system that enables the lifting and lowering of the front loader. Power from the second electric motor 30B may be transmitted to multiple hydraulic pumps to drive these multiple hydraulic systems. Alternatively, the work vehicle 10 may have one or more electric motors for hydraulics separate from the second electric motor 30B. 【0053】 In the example shown in Figure 4, the work vehicle 10 further comprises a power converter 58, a power distribution unit (PDU) 80, an auxiliary battery 21, and a battery temperature control system 70. 【0054】 The power converter 58 is positioned between the charging inlet 57 and the battery 20 and performs power conversions such as AC to DC conversion and voltage conversion. Figure 5 shows an example of the configuration of the power converter 58 and its connection to other equipment. The power converter 58 shown in Figure 5 includes an onboard charger (OBC) 81 and a DC-DC converter 82. During normal charging, the OBC 81 converts AC power from the charging inlet 57 to DC power and supplies it to the drive battery 20 via the power distribution unit 80. The drive battery 20 is charged by this DC power. The DC-DC converter 82 is connected to the OBC 81 and also to the battery 20 via the power distribution unit 80. The DC-DC converter 82 converts the relatively high-voltage DC power output from the OBC 81 or the drive battery 20 to lower-voltage DC power (e.g., 12V or 24V). The low-voltage DC power converted by the DC-DC converter 82 is supplied to the auxiliary battery 21 and the auxiliary components 84. The auxiliary components 84 include several devices that operate on the relatively low voltage output from the DC-DC converter 82 or the battery 21. For example, the auxiliary components 84 include several electronic control units (ECUs) and other electrical components. The auxiliary battery 21 is charged by the DC voltage output from the DC-DC converter 82. The auxiliary battery 21 stores the power supplied to each ECU, the meter panel unit 54, the pumps 67 and 77, and the auxiliary components 84 such as the air conditioner. The battery 21 may be, for example, a lead-acid battery. 【0055】 Refer to Figure 4 again. The work vehicle 10 is equipped with multiple ECUs. These multiple ECUs include a main ECU 61, an electric ECU 62, and a charging ECU 63. The main ECU 61 controls the overall operation of the work vehicle 10 based on signals generated by the user operating the pedal group 55, the switch group 56, and the meter panel unit 54. The electric ECU 62 mainly controls the charging and discharging of the battery 20 and the operation of the electric motors 30A and 30B. The charging ECU 63 communicates with an external charger (external power supply) and performs control to ensure smooth charging by appropriately controlling the relay 64. 【0056】 In this embodiment, the combination of the main ECU 61, the electric ECU 62, and the charging ECU 63 functions as a "control device" that controls the operation of the work vehicle 10. Therefore, in the following description, the operations performed by the main ECU 61, the electric ECU 62, and the charging ECU 63 all correspond to operations performed by the "control device". These ECUs can communicate with each other according to a vehicle bus standard such as CAN (Controller Area Network). A faster communication method such as onboard Ethernet (registered trademark) may be used instead of CAN. An onboard computer integrating at least some of the functions of the main ECU 61, the electric ECU 62, and the charging ECU 63 may be provided as the "control device". The control device may include ECUs other than the main ECU 61, the electric ECU 62, and the charging ECU 63. Each ECU may be a computing device including one or more processors and one or more memories. Each ECU can perform the operations described later by having the processor execute a computer program stored in the memory. 【0057】 The electric ECU 62 sends control signals to the first inverter 35A and the second inverter 35B in response to signals from the pedal group 55 and the switch group 56. The electric ECU 62 can perform motor control based on a rotational speed command value or a torque command value determined, for example, according to the amount of operation of the pedal group 55 by the driver. 【0058】 The electric ECU 62 controls the switching operation of multiple switching elements (e.g., MOSFETs) in the first inverter 35A and the second inverter 35B, respectively. Specifically, the electric ECU 62 generates control signals to control the switching operation of each switching element and outputs them to each inverter. The first inverter 35A, in accordance with the control signals from the electric ECU 62, converts the DC power from the battery 20 into three-phase AC power, which is a pseudo-sine wave of, for example, u-phase, v-phase, and w-phase, and supplies this three-phase AC power to the first electric motor 30A. Similarly, the second inverter 35B, in accordance with the control signals from the electric ECU 62, converts the DC power from the battery 20 into three-phase AC power, which is a pseudo-sine wave of, for example, u-phase, v-phase, and w-phase, and supplies this three-phase AC power to the second electric motor 30B. As a result, the electric ECU 62 can rotate the electric motors 30A and 30B at appropriate rotational speeds and torques according to the driver's operation. 【0059】 While the work vehicle 10 is in operation, the main ECU 61 causes the meter panel unit 54 to display information regarding the status of the work vehicle 10. For example, the main ECU 61 displays information such as the travel speed, the operating status of motors 30A and 30B, the charge status of the battery 20, and the status of the power transmission system 34A and the transmission included in 34A on the meter panel unit 54. 【0060】 Figure 6 is a block diagram showing an example of the hardware configuration of each ECU. Each ECU includes a processor 434, ROM 435, RAM 436, external I / F 437, and communication I / F 438. These components are interconnected via a bus 439. 【0061】 ROM435 is, for example, writable memory (e.g., PROM), rewritable memory (e.g., flash memory), or read-only memory. ROM435 stores a program that controls the operation of processor 434. ROM435 does not have to be a single recording medium; it may be a collection of multiple recording media. Some of these multiple storage media may be removable memory. 【0062】 RAM436 provides a workspace for temporarily unpacking programs stored in ROM435 during boot-up. RAM436 does not need to be a single storage medium; it may be a collection of multiple storage mediums. 【0063】 External I / F437 is an interface for connecting to external devices. Communication I / F438 is an interface for communicating with other electronic devices (e.g., sensors and other ECUs). For example, communication I / F438 can perform wired communication compliant with various protocols such as CAN or Ethernet®. Communication I / F438 may also perform wireless communication compliant with wireless communication standards such as Bluetooth® and / or Wi-Fi®. 【0064】 The ECU may further include a storage device for storing data generated by the processor 434 for a relatively long period of time. Such a storage device may be, for example, a semiconductor storage device, a magnetic storage device, or an optical storage device, or a combination thereof. 【0065】 The power distribution unit 80 shown in Figure 4 is a device that electrically connects equipment such as the charging inlet 57, power converter 58, battery 20, inverters 35A and 35B, and heater 72. 【0066】 Figure 7 shows an example of the configuration of the power distribution unit 80. The power distribution unit 80 may have a plurality of relay circuits 83 (83a to 83g) that operate under the control of the electric ECU 62. During charging, the power distribution unit 80 is configured to supply power from the charging inlet 57 or power converter 58 to the battery 20, and to the heater 72 when the temperature is low. On the other hand, during discharging, the power distribution unit 80 is configured to distribute power from the battery 20 to the first inverter 35A, the second inverter 35B, and the power converter 23. The electric ECU 62 may be configured or programmed to control the charging and discharging of the battery 20 by appropriately switching the on and off of the plurality of relay circuits 83a to 83g in the power distribution unit 80. In this specification, relay circuits may be simply referred to as "relays". 【0067】 As shown in Figure 4, the battery 20 includes a battery management system (BMS) 22 and a temperature sensor 24. The BMS 22 is configured to monitor the status of the battery 20, such as its input voltage, output voltage, and temperature, and to control the charging and discharging currents to the battery 20 based on these statuses. The temperature sensor 24 may be configured to measure the temperature of each of the multiple cells contained in the battery 20. 【0068】 The work vehicle 10 illustrated in Figure 4 is equipped with a cooling system 60 for high-voltage equipment and a battery temperature control system 70. The cooling system 60 is used to cool equipment to which high voltage is applied (also referred to as "high-voltage equipment"). The cooling system 60 comprises a radiator 65, a reservoir tank 66, a pump 67, and a cooling fan 68. In the example in Figure 4, the cooling system 60 is connected via hoses to the first inverter 35A, the first electric motor 30A, the second electric motor 30B, the second inverter 35B, and the power converter 58 in that order. This forms a flow path through which the coolant circulates. The coolant in the cooling system 60 is, for example, water or oil. The cooling system 60 cools these high-voltage equipment by circulating the coolant through the flow path. The coolant heated by the high-voltage equipment is cooled by heat dissipation in the radiator 65. The cooling fan 68 generates cooling air to cool the coolant inside the radiator 65. The cooling airflow promotes heat dissipation from the radiator 65. 【0069】 The battery temperature control system 70 is used to cool or heat (also referred to as "heating") the battery 20. The battery temperature control system 70 comprises a heater 72, a radiator 75, a reservoir tank 76, and a pump 77. The battery temperature control system 70 is connected to the battery 20 via a hose, which forms a passage through which the coolant circulates. The coolant in the battery temperature control system 70 is, for example, water or oil. The battery temperature control system 70 cools the battery 20 by circulating the coolant through the passage. The coolant heated by the battery 20 is cooled by heat dissipation in the radiator 75. Cooling air from the cooling fan 68 also plays a role in cooling the coolant inside the radiator 75. The heater 72 raises the temperature of the battery 20 by warming the coolant. This makes it possible to suppress a decrease in the charge and discharge performance of the battery 20 even in low-temperature environments where the ambient temperature is, for example, below 0 degrees Celsius (°C). 【0070】 The operation of the cooling system 60 and the battery temperature control system 70 is controlled by the electric ECU 62. For example, the electric ECU 62 is configured or programmed to maintain the temperature of the battery 20 within an appropriate range by controlling the battery temperature control system 70 based on the temperature of the battery 20 measured by the temperature sensor 24. In addition to the measurement value of the temperature sensor 24, the electric ECU 62 may also control the battery temperature control system 70 based on the measurement value of a temperature sensor 25 that measures the ambient temperature and is installed in the work vehicle 10. 【0071】 The flow paths of the coolant in the cooling system 60 and the battery temperature control system 70 are not limited to the illustrated paths and can be changed as appropriate. The cooling method in the cooling system 60 and the battery temperature control system 70 is not limited to water cooling or oil cooling, but may also be air cooling. Alternatively, the refrigerant used in an air conditioner may be used instead of the above-mentioned coolant. 【0072】 <4. Examples of operation when the PTO switch is turned on or off> Next, we will explain the function for preventing damage to the work vehicle or work equipment caused by switching the PTO clutch from the engaged state to the disengaged state when the PTO motor is rotating at high speed. 【0073】 Figure 8 is a block diagram showing an example of components of a work vehicle 10 related to this function. Figure 8 shows a more detailed example of the configuration of the power transmission systems 34A, 34A shown in Figure 4. In this example, the first power transmission system 34A includes a reduction gear 37A, a clutch 38A, a transmission 39A, and a differential 41. The second power transmission system 34B includes a PTO reduction gear 37B, a PTO clutch 38B, and a PTO transmission 39B. Each component of the power transmission systems 34A, 34B can be controlled by a control device 200, which includes a main ECU 61 and an electric ECU 62. 【0074】 The reduction gear 37A is connected to the first electric motor 30A. The clutch 38A is positioned between the reduction gear 37A and the transmission 39A and connects the reduction gear 37A and the transmission 39A. Through this mechanical connection, when the clutch 38A is engaged, power is transmitted from the reduction gear 37A to the transmission 39A. When the clutch is disengaged, the transmission of power from the reduction gear 37A to the transmission 39A is interrupted. 【0075】 The reduction gear 37B is connected to the second electric motor 30B. The PTO clutch 38B is positioned between the reduction gear 37B and the PTO transmission 39B and connects the reduction gear 37B and the PTO transmission 39B. Through this mechanical connection, when the PTO clutch 38B is engaged, power is transmitted from the reduction gear 37B to the PTO transmission 39B. When the PTO clutch 38B is disengaged, the transmission of power from the reduction gear 37B to the PTO transmission 39B is interrupted. 【0076】 Each of the clutches 38A and 38B operates, for example, under hydraulic control and is equipped with an ON / OFF solenoid valve. The control device 200 can switch the connected and disconnected states of clutches 38A and 38B by sending a control signal to the solenoid valve and controlling the ON / OFF state of the solenoid valve. This control can be performed, for example, by the main ECU 61 in the control device 200. Each of the clutches 38A and 38B may be an electromagnetic clutch. 【0077】 Figure 8 also illustrates a PTO switch 91 and an instrument panel unit 54. The PTO switch 91 is a switch for turning the rotation of the PTO shaft 40 on and off, and is operated by the user. The instrument panel unit 54 may include a PTO operating indicator that shows the operating status of the PTO shaft. The PTO operating indicator may be controlled to illuminate when the PTO clutch 38B is engaged and to turn off when the PTO clutch 38B is disengaged. 【0078】 In this embodiment, the control device 200 is configured to reduce the rotational speed of the second electric motor 30B to the reference value when the PTO switch 91 is switched from off to on while the rotational speed of the second electric motor 30B is higher than a reference value, and then switch the PTO clutch 38B from the disengaged state to the engaged state. This operation prevents damage to the work vehicle 10 or work machine caused by the PTO clutch 38B being engaged when the second electric motor 30B is rotating at high speed. Here, the rotational speed can be expressed as the number of rotations per unit time (e.g., rotations per minute, unit: rpm). In the following description, the number of rotations per unit time may be simply referred to as "rotational speed". 【0079】 In work vehicles powered by an internal combustion engine such as a diesel engine or a single electric motor, the running gear and the PTO shaft are driven by a single power source. Therefore, the rotational speed of the electric motor is linked to the rotational speed of the running gear (e.g., the wheels). In this case, before the user operates the PTO switch to engage the PTO clutch, it was necessary to manually reduce the rotational speed of the power source to a sufficiently low speed (e.g., idling speed) to prevent damage to the work vehicle 10 or the work implement. 【0080】 In contrast, in this embodiment, the first electric motor 30A that drives the traveling device and the second electric motor 30B that drives the PTO shaft 40 are provided separately, so that changes in the rotational speed of the second electric motor 30B do not affect the rotational speed of the traveling device. For this reason, it is possible to implement a function that automatically reduces the rotational speed of the second electric motor 30B in response to the user's operation of the PTO switch 91. With this function, the user can switch the rotation of the PTO shaft 40 on and off simply by operating the PTO switch 91, without having to perform any operation to reduce the rotational speed of the power source, and without causing damage to the work vehicle 10 or the work machine. 【0081】 The operation of the control device 200 in this embodiment will be described in more detail below. 【0082】 Figure 9A is a diagram illustrating an example of operation by the control device 200. Figure 9A shows an example of the time variation of the on / off state of the PTO switch 91, the rotational speed of the second electric motor 30B, the on / off state of the PTO clutch 38B, and the on / off state of the PTO operation indicator. Hereinafter, the second electric motor 30B will also be referred to as the "PTO motor 30B". The reference value of the rotational speed of the PTO motor 30B (i.e., rotations per unit time) is called the "idle speed" and is expressed as "IDLE". In this embodiment, since the PTO motor 30B drives not only the PTO shaft 40 but also the hydraulic pump 36, a state of being above the idle speed is maintained even when the PTO switch 91 is in the OFF state. The "idle speed" is the minimum rotational speed required to drive the hydraulic pump and enable steering and other operations to be performed without problems. 【0083】 In the example shown in Figure 9A, the PTO switch 91 is switched from off to on when the rotational speed of the PTO motor 30B is higher than the reference value (indicated as "TARGET"). TARGET could be, for example, the rated rotational speed. In response to this switch, the control device 200 controls the second inverter 35B to reduce the rotational speed of the PTO motor 30B to the reference value, the idle speed (IDLE). Subsequently, the control device 200 switches the PTO clutch 38B from the disengaged state (off) to the engaged state (on). At this time, the control device 200 illuminates the PTO operation indicator. 【0084】 The reference value for rotational speed (idle speed) can be set to a value such as 0 rpm to 3000 rpm or 500 rpm to 2000 rpm. In one example, the idle speed may be set to a value of approximately 1000 rpm. 【0085】 Thus, in the example shown in Figure 9A, when the PTO switch 91 is switched from off to on, the control device 200 does not immediately engage the PTO clutch 38B, but rather reduces the rotational speed of the PTO motor 30B to a reference value before engaging the PTO clutch 38B. This prevents damage to the work vehicle 10 or work equipment when the PTO clutch 38B is engaged. 【0086】 In the example shown in Figure 9A, the control device 200 switches the PTO clutch 38B from off to on, and after a predetermined time t1 has elapsed, it returns the rotational speed of the PTO motor 30B to the rotational speed (TARGET) before the PTO switch 91 was switched. The time t1 can be set to a value of, for example, 0.5 seconds or more and 10 seconds or less, and in some examples, 1 second or more and 5 seconds or less. In some examples, the time t1 can be set to 2.5 seconds or 3 seconds. 【0087】 In the example shown in Figure 9A, when the PTO switch 91 is switched from on to off, the control device 200 switches the PTO clutch 38B from the connected state (on) to the disconnected state (off) while maintaining the rotational speed of the PTO motor 30B. At this time, the control device 200 switches the PTO operation indicator from on to off. Such an operation may be performed, for example, when temporarily interrupting work performed by a work implement connected to the PTO shaft 40. If work is temporarily stopped and then resumed after a while, the rotational speed of the PTO motor 30B may be maintained without decreasing even after the PTO clutch 38B is disconnected, as shown in Figure 9A. 【0088】 Figure 9B is a diagram illustrating another example of operation by the control device 200. In the example shown in Figure 9B, the control device 200 controls the rotational speed of the PTO motor 30B to a reference value (idle speed) not only when the PTO switch 91 is switched from off to on, but also when it is switched from on to off. More specifically, when the rotational speed of the PTO motor 30B is higher than the reference value and the PTO switch 91 is switched from on to off, the control device 200 reduces the rotational speed of the PTO motor 30B to the reference value. Subsequently, the control device 200 switches the PTO clutch 38B from the connected state (on) to the disconnected state (off). At this time, the control device 200 turns off the PTO operation indicator. 【0089】 Thus, in the example shown in Figure 9B, the control device 200 reduces the rotational speed of the PTO motor 30B to a reference value not only when the PTO switch 91 is switched from off to on, but also when the PTO switch 91 is switched from on to off, and then switches the PTO clutch 38B on and off. This prevents the PTO clutch 38B from disengaging while the PTO shaft is rotating at high speed. 【0090】 Figure 9C shows yet another example of operation by the control device 200. In the example shown in Figure 9C, when the PTO switch 91 is switched from on to off while the rotational speed of the PTO motor 30B is higher than the reference value, the control device 200 first switches the PTO clutch 38B from the connected state (on) to the disconnected state (off) and turns off the PTO operation indicator. Furthermore, the control device 200 reduces the rotational speed of the PTO motor 30B to the reference value (IDLE), and after a predetermined time t2 has elapsed, returns the rotational speed of the PTO motor 30B to the original rotational speed (TARGET). 【0091】 The operation shown in Figure 9C prevents "co-rotation," where the PTO shaft 40 continues to rotate even after the PTO clutch 38B is disengaged, mainly in cold climates. In cold climates, the viscosity of the hydraulic fluid increases, which can cause the PTO shaft to continue rotating even after the PTO clutch 38B is disengaged. As shown in the example in Figure 9C, by disengaging the PTO clutch 38B and reducing the rotational speed of the PTO motor 30B, co-rotation of the PTO shaft can be prevented. 【0092】 In the examples of Figures 9B and 9C, the control device 200 switches the PTO clutch 38B from on to off, and after a predetermined time t2 has elapsed, it returns the rotational speed of the PTO motor 30B to the rotational speed (TARGET) before the PTO switch 91 was switched. Time t2 may be the same as or different from the aforementioned time t1. Time t2 may be set to a value of, for example, 0.5 seconds or more and 10 seconds or less, and in some examples, 1 second or more and 5 seconds or less. In some examples, time t2 may be set to 2.5 seconds or 3 seconds. 【0093】 The control device 200 may change times t1 and t2 based on user input. For example, the user may be able to set times t1 and t2 by operating the meter panel unit 54. Alternatively, the control device 200 may acquire information indicating the type of work equipment and change times t1 and t2 according to the type of work equipment. Information indicating the type of work equipment may be input, for example, by user operation using the meter panel unit 54, and stored in the meter panel unit 54 or a storage device within the control device 200. 【0094】 Figure 9D shows yet another example of operation by the control device 200. Figure 9D shows an example where the PTO switch 91 is switched on and off when the rotational speed of the PTO motor 30B is below a reference value. In such a case, since the rotational speed of the PTO motor 30B is sufficiently low, there is no problem of damage to the device. Therefore, the control device 200 may immediately switch the PTO clutch between disconnected and connected in response to the operation of switching the PTO switch 91 on and off. When the PTO clutch 38B is connected, the control device 200 turns on the PTO work light, and when the PTO clutch 38B is disconnected, it turns off the PTO work light. 【0095】 Next, the operation of the control device 200 will be described in more detail with reference to Figures 10A and 10B. 【0096】 Figure 10A is a flowchart showing an example of an operation performed by the control device 200. The operation shown in Figure 10A corresponds to the example in Figure 9A. The operation of each step shown in Figure 10A will be described below. 【0097】 In step S101, the control device 200 determines whether the PTO switch 91 has been switched from OFF to ON. If the PTO switch 91 has been switched from OFF to ON, the process proceeds to step S102. If the PTO switch 91 has not been switched from OFF to ON, the process proceeds to step S111. 【0098】 In step S102, the control device 200 determines whether the rotational speed of the PTO motor 30B is higher than a reference value. If the rotational speed of the PTO motor 30B is higher than a reference value, the process proceeds to step S103. If the rotational speed of the PTO motor 30B is less than or equal to the reference value, the process proceeds to step S109. 【0099】 In step S103, the control device 200 reduces the rotational speed of the PTO motor 30B to a reference value. Once the rotational speed has decreased to the reference value, the process proceeds to step S104. 【0100】 In step S104, the control device 200 switches the PTO clutch 38B and the PTO operation indicator from OFF to ON. Then, the process proceeds to step S105. 【0101】 In step S105, the control device 200 determines whether a predetermined time t1 has elapsed since the rotational speed of the PTO motor 30B decreased to a reference value. If the predetermined time t1 has elapsed, the process proceeds to step S106. 【0102】 In step S106, the control device 200 returns the rotational speed of the PTO motor 30B to the speed it was at before it was reduced in step S103. Then, the process proceeds to step S111. 【0103】 In step S109, the control device 200 switches the PTO clutch 38B and the PTO operation indicator from OFF to ON. Then, the process proceeds to step S110. 【0104】 In step S110, the control device 200 determines whether the PTO switch 91 has been switched from ON to OFF. If the PTO switch 91 has been switched from ON to OFF, the process proceeds to step S111. If the PTO switch 91 has not been switched from ON to OFF, the process proceeds to step S120. 【0105】 In step S111, the control device 200 switches the PTO clutch 38B and the PTO operation indicator from ON to OFF. 【0106】 In step S120, the control device 200 determines whether or not to terminate the operation. For example, if the user performs an operation such as turning off the power switch of the work vehicle 10, the control device 200 terminates the operation. If the operation is not terminated, the process returns to step S101. 【0107】 As a result of the above operation, if the PTO switch 91 is switched from OFF to ON while the rotational speed of the PTO motor 30B exceeds the standard value, the rotational speed will be reduced to the standard value before the PTO clutch 38B is engaged. This prevents damage to the work vehicle 10 or work equipment caused by the PTO clutch 38B being engaged while the PTO motor 30B is rotating at high speed. Since this control is performed automatically, the user does not need to reduce the rotational speed of the PTO motor 30B to below the standard value before turning on the PTO switch 91, or increase the rotational speed of the PTO motor 30B after the PTO clutch 38B is engaged. Furthermore, even while driving, the PTO clutch 38B can be engaged without affecting the feel of the driving pedal. This greatly improves convenience. 【0108】 Figure 10B is a flowchart showing another example of the operation performed by the control device 200. The operation shown in Figure 10B corresponds to the example in Figure 9B. In the example in Figure 10B, the operation after determining Yes in step S111 differs from the example in Figure 10A. The operations in steps S101-S106, S109, S110, and S120 are the same as the operations in the corresponding steps shown in Figure 10A. The differences from the operation shown in Figure 10A will be explained below. 【0109】 In the example shown in Figure 10B, if it is determined in step S110 that the PTO switch has been switched from ON to OFF, the process proceeds to step S112. 【0110】 In step S112, the control device 200 determines whether the rotational speed of the PTO motor 30B is greater than a reference value. If the rotational speed of the PTO motor 30B is greater than a reference value, the process proceeds to step S113. If the rotational speed of the PTO motor 30B is less than or equal to the reference value, the process proceeds to step S119. 【0111】 In step S113, the control device 200 reduces the rotational speed of the PTO motor 30B to a reference value. Once the rotational speed has decreased to the reference value, the process proceeds to step S114. 【0112】 In step S114, the control device 200 switches the PTO clutch 38B and the PTO operation indicator from ON to OFF. Then, the process proceeds to step S115. 【0113】 In step S115, the control device 200 determines whether a predetermined time t2 has elapsed since the rotational speed of the PTO motor 30B decreased to a reference value. This predetermined time t2 may be the same as or different from the predetermined time t1 in step S105. If the predetermined time t2 has elapsed, the process proceeds to step S116. 【0114】 In step S116, the control device 200 returns the rotational speed of the PTO motor 30B to the rotational speed it was at before it was reduced in step S113. Then, the process proceeds to step S120. 【0115】 In step S119, the control device 200 switches the PTO clutch 38B and the PTO operation indicator from ON to OFF. Then, the process proceeds to step S120. 【0116】 As a result of the above operation, the rotation speed of the PTO motor 30B is reduced to the standard value before the PTO clutch 38B is engaged, not only when the PTO switch 91 is switched from OFF to ON while the rotation speed of the PTO motor 30B exceeds the standard value, but also when the PTO switch 91 is switched from ON to OFF. This prevents damage to the work vehicle 10 or work implement caused by the PTO clutch 38B being disengaged while the PTO motor 30B is rotating at high speed. Since this control is performed automatically, the user does not need to reduce the rotation speed of the PTO motor 30B to below the standard value before turning off the PTO switch 91, or increase the rotation speed of the PTO motor 30B after disengaging the PTO clutch 38B. Furthermore, the PTO clutch 38B can be disengaged even while driving without affecting the feel of the driving pedal. This greatly improves convenience. 【0117】 Note that in the example shown in Figure 10B, the order of steps S113 and S114 may be reversed. In that case, as shown in Figure 9C, the rotational speed of the PTO motor 30B decreases to the reference value after the PTO clutch 38B is disengaged. 【0118】 In the examples shown in Figures 10A and 10B, the control device 200 may be configured to enable or disable, in response to user input, a function that reduces the rotational speed of the PTO motor 30B to a reference value before switching the PTO clutch 38B from a disengaged state to a connected state when the PTO switch 91 is switched from off to on. Similarly, the control device 200 may be configured to enable or disable, in response to user input, a function that reduces the rotational speed of the PTO motor 30B to a reference value before switching the PTO clutch 38B from a connected state to a disengaged state when the PTO switch 91 is switched from on to off. Alternatively, the control device 200 may be configured to enable or disable, in response to user input, a function that switches the PTO clutch 38B from a connected state to a disengaged state before reducing the rotational speed of the PTO motor 30B to a reference value when the PTO switch 91 is switched from on to off. For example, the user may be able to set whether to enable or disable the above functions by operating the meter panel unit 54. The control device 200 may be configured to display a graphical user interface (GUI) on the digital display of the meter panel unit 54, which allows the user to set whether to enable or disable those functions. Such a meter panel unit 54 may further have indicators that show whether those functions are enabled or disabled. 【0119】 <5. Example of display on the meter panel unit> The following describes examples of displays on the meter panel unit 54, with reference to Figures 11 and 12. 【0120】 Figure 11 is a front view showing a specific example of the meter panel unit 54. The meter panel unit 54 is located in front of the driver's seat of the work vehicle 10. In this example, the meter panel unit 54 has a first analog meter 111, a second analog meter 112, and a display 113. The display 113 is located between the first analog meter 111 and the second analog meter 112. 【0121】 The display 113 is a digital display. The display 113 is, for example, an active-matrix display such as a liquid crystal display panel or an OLED (Organic Light Emitting Diode). The display 113 has a large number of pixels arranged two-dimensionally in the display area, and a display visible to the human eye is realized by the light emitted from the large number of pixels. In the display 113 in this embodiment, each pixel includes RGB subpixels and can display a color image. The display 113 can display numbers, characters, figures, icons, symbols, still images, or moving images of any size at any position within the display area. 【0122】 The meter panel unit 54 shown in Figure 10 has an indicator area 114T located above the display 113 and indicator areas 114L and 114R located below the display 113. Various indicators are provided in each of the indicator areas 114T, 114L, and 114R. Each indicator displays predetermined information, such as a warning, when a light-emitting element such as an LED behind it is lit. In this embodiment, two indicator areas 114L and 114R, which are divided left and right, are located below the display 113, but a single indicator area that integrates the two indicator areas may also be provided. 【0123】 Each indicator located in indicator areas 114T, 114L, and 114R consists of a translucent area shaped to define a characteristic figure (including icons and / or letters) and a light-emitting element located behind it. The indicator can be turned on or off by the on / off of the light-emitting element behind it. Behind each individual indicator, for example, one or two light-emitting elements are located. 【0124】 In the example shown in Figure 11, the indicator area 114R contains two PTO operation indicators 115 (one for the front and one for the rear). In this example, the work vehicle has a front PTO shaft and a rear PTO shaft. The two PTO operation indicators 115 are controlled to illuminate when their respective PTO shafts are driven. If the work vehicle has a single PTO shaft for either the front or rear, a single PTO operation indicator 115 may be provided in the instrument panel unit 54. Instead of the PTO operation indicators 115, a similar indicator may be displayed on the display 113. 【0125】 In the example shown in Figure 11, the display area of ​​the display 113 is divided into several regions. Each region displays an image showing information such as the gear shift stage, vehicle speed, various function performance indicators, and an hour meter. This image contains various types of information represented by letters, numbers, shapes, icons, symbols, etc. To enhance visibility, the diverse digital images may be shown in different colors. Furthermore, when it is particularly important to attract the user's attention, the position, size, or color of at least one of the letters, numbers, shapes, icons, or symbols may be changed to provide a highlighted display. When such a highlighted display is performed, sound or audio may be emitted from an audio device such as a speaker. 【0126】 In the example shown in Figure 11, an input device 170 enabling user-interactive operation is connected to the meter panel unit 54 via a communication cable 160. The input device 170 includes a selector switch 171, such as a jog dial, and an operation switch 172. The input device 170 may be connected to the meter panel unit 54 wirelessly or via a wired connection. Any device that accepts user input can be used as the input device 170. The input device 170 may be, for example, a rotary switch, a slide switch, a push-button switch, a touchscreen, a joystick, or a combination of two or more of these. 【0127】 Figure 12 shows an example of a GUI for setting whether or not to enable the aforementioned function that automatically reduces the rotational speed of the PTO motor 30B to below a reference value when the PTO switch 91 is switched on and off. In this example, toggle switches 113a and 113b for selecting whether to enable or disable the above function are displayed on the display 113. By operating toggle switch 113a, the user can switch between enabling and disabling the function that automatically reduces the rotational speed of the PTO motor 30B to below a reference value before engaging the PTO clutch 38B when the PTO switch 91 is turned on. Similarly, by operating toggle switch 113b, the user can switch between enabling and disabling the function that automatically reduces the rotational speed of the PTO motor 30B to below a reference value before disengaging the PTO clutch 38B when the PTO switch 91 is turned off. 【0128】 <6. Variation> In the embodiment described with reference to Figures 2 to 12, the work vehicle is equipped with a first electric motor for travel and a second electric motor for the PTO. However, the work vehicle does not necessarily need to be equipped with these two electric motors. For example, as shown in Figure 1, the work vehicle may be equipped with a single electric motor. Alternatively, the work vehicle may be equipped with an internal combustion engine such as a diesel engine as a power source instead of an electric motor. In a work vehicle equipped with such a single power source, the rotational speed of the travel system and the rotational speed of the PTO are linked. Therefore, if the rotational speed of the power source is reduced prior to engaging or disengaging the PTO clutch while traveling, it will affect the feel of operating the travel pedal. To avoid this, in a work vehicle equipped with a single power source, the control described with reference to Figures 9A to 10B may be applied only when the work vehicle is not traveling. Such a work vehicle is equipped with a travel system, a PTO shaft that supplies power to the work machine, a power source that drives the travel system and the PTO shaft, a PTO switch for switching the rotation of the PTO shaft on and off, a PTO clutch positioned between the power source and the PTO shaft, and a control device. The control device may be configured to reduce the rotational speed of the power source to the reference value when the PTO switch is switched from off to on while the rotational speed of the power source is higher than a reference value, and only if the work vehicle is not moving, and then switch the PTO clutch from the disengaged state to the engaged state. The control device can determine whether or not the work vehicle has stopped moving based on signals from, for example, the driving pedal or a vehicle speed sensor. When the work vehicle is moving and the PTO switch is switched from off to on while the rotational speed of the power source is higher than a reference value, the control device may perform an action to notify the user without engaging the PTO clutch. For example, the control device may notify the user by displaying a message on a display such as the meter panel unit 54 prompting the user to stop driving, or a message asking whether it is really okay to engage or disengage the PTO clutch. 【0129】 The systems including the control devices in the above embodiments can also be retrofitted to work vehicles that do not have those functions. Such systems can be manufactured and sold independently of the work vehicles. Computer programs used in such systems can also be manufactured and sold independently of the work vehicles. Computer programs can be provided, for example, stored in a computer-readable non-temporary storage medium. Computer programs can also be provided by download via telecommunications lines (e.g., the Internet). [Industrial applicability] 【0130】 The present invention can be applied to agricultural tractors equipped with electric motors for driving, and to electric work vehicles such as construction vehicles. [Explanation of symbols] 【0131】 10...Work vehicle, 11...Body, 12...Front frame, 13...Transmission case, 14...Wheels, 14F...Front wheel, 14R...Rear wheel, 15F...Front axle, 15R...Rear axle, 16...Housing frame, 17F...Front axle case, 17R...Rear axle case, 19...Front housing, 20...Battery, 22...Battery management system (BMS), 24...Temperature sensor, 30, 30A, 30B...Electric motor, 33...Output shaft, 34...Power transmission system, 35A, 35B...Inverter, 36...Hydraulic pump, 37A, 37B...Gear reducer, 38A, 38B...Clutch, 39A, 39B...Transmission, 40...PTO shaft, 41...Differential, 51...Rops frame, 52...Driver's seat, 53...Steering wheel, 54...Instrument panel unit, 55...Pedal group, 56...Switch group, 57...Charging inlet, 58...Power converter, 60...Cooling system for high-voltage equipment, 61...Main ECU, 62...Electric ECU, 63...Charging ECU, 64...Relay, 65...Radiator for high-voltage equipment, 66...Reservoir tank, 67...Pump, 68...Cooling fan, 70...Battery temperature control system, 72...Heater, 75...Radiator for battery 76...Reservoir tank, 77...Pump, 80...Power distribution unit, 81...Onboard charger (OBC), 82...DC-DC converter, 91...PTO switch, 200...Control unit

Claims

[Claim 1] Traveling device and The PTO shaft that supplies power to the implement, A first electric motor that drives the aforementioned traveling device, A second electric motor that drives the PTO shaft, A PTO switch for switching the rotation of the PTO shaft on and off, A PTO clutch is positioned between the second electric motor and the PTO shaft, Control device and Equipped with, When the PTO switch is switched from off to on while the rotational speed of the second electric motor is higher than a reference value, the control device reduces the rotational speed of the second electric motor to the reference value, and then switches the PTO clutch from the disengaged state to the engaged state. Work vehicle. [Claim 2] The work vehicle according to claim 1, wherein the control device, after switching the PTO clutch from the disengaged state to the engaged state and a predetermined time has elapsed, returns the rotational speed of the second electric motor to the rotational speed before the PTO switch was switched. [Claim 3] The work vehicle according to claim 2, wherein the predetermined time is 1 second or more and 5 seconds or less. [Claim 4] The work vehicle according to claim 2, wherein the control device changes the predetermined time based on input from the user. [Claim 5] The control device is Information indicating the type of the aforementioned work machine is obtained, The predetermined time is changed according to the type of work machine. The work vehicle according to claim 2. [Claim 6] The work vehicle according to claim 1, wherein the reference value of the rotational speed is 0 rpm or more and 2000 rpm or less. [Claim 7] The work vehicle according to claim 1, wherein the control device switches the PTO clutch from a connected state to a disconnected state while maintaining the rotational speed of the second electric motor when the PTO switch is switched from on to off. [Claim 8] The work vehicle according to claim 1, wherein when the PTO switch is switched from on to off while the rotational speed of the second electric motor is higher than the reference value, the control device reduces the rotational speed of the second electric motor to the reference value, and then switches the PTO clutch from the engaged state to the disengaged state. [Claim 9] The work vehicle according to claim 1, wherein the control device switches the PTO clutch from a connected state to a disconnected state when the PTO switch is switched from on to off while the rotational speed of the second electric motor is higher than the reference value, and then reduces the rotational speed of the second electric motor to the reference value. [Claim 10] The work vehicle according to claim 1, wherein the control device switches, in response to user input, whether to enable or disable the function that reduces the rotational speed of the second electric motor to the reference value before switching the PTO clutch from a disengaged state to a engaged state when the PTO switch is switched from off to on. [Claim 11] The work vehicle according to claim 8, wherein the control device switches, in response to user input, whether to enable or disable the function that reduces the rotational speed of the second electric motor to the reference value before switching the PTO clutch from the engaged state to the disengaged state when the PTO switch is switched from on to off. [Claim 12] The work vehicle according to claim 9, wherein the control device switches, in response to user input, whether to enable or disable the function that switches the PTO clutch from a connected state to a disconnected state and then reduces the rotational speed of the second electric motor to the reference value when the PTO switch is switched from on to off. [Claim 13] It further includes a meter panel unit with a digital display, The control device displays a graphical user interface on the digital display that allows the user to set whether to enable or disable the function. A work vehicle according to any one of claims 10 to 12. [Claim 14] The work vehicle according to claim 13, wherein the meter panel unit further includes an indicator that shows whether the function is enabled or disabled. [Claim 15] The unit further includes a meter panel unit that includes an indicator showing the operating status of the PTO shaft, The control device illuminates the indicator when the PTO clutch is engaged, and turns off the indicator when the PTO clutch is disengaged. A work vehicle according to any one of claims 1 to 12. [Claim 16] A method performed by a computer that controls the work vehicle, The aforementioned work vehicle comprises a traveling device, a PTO shaft for supplying power to the work machine, a first electric motor for driving the traveling device, a second electric motor for driving the PTO shaft, a PTO switch for switching the rotation of the PTO shaft on and off, and a PTO clutch positioned between the second electric motor and the PTO shaft. The aforementioned method, When the PTO switch is switched from off to on while the rotational speed of the second electric motor is higher than a reference value, the rotational speed of the second electric motor is reduced to the reference value. After reducing the rotational speed to the reference value, the PTO clutch is switched from the disengaged state to the engaged state. A method that includes this. [Claim 17] A computer program executed by a computer that controls a work vehicle, The aforementioned work vehicle comprises a traveling device, a PTO shaft for supplying power to the work machine, a first electric motor for driving the traveling device, a second electric motor for driving the PTO shaft, a PTO switch for switching the rotation of the PTO shaft on and off, and a PTO clutch positioned between the second electric motor and the PTO shaft. The computer program is installed on the computer. When the PTO switch is switched from off to on while the rotational speed of the second electric motor is higher than a reference value, the rotational speed of the second electric motor is reduced to the reference value. After reducing the rotational speed to the reference value, the PTO clutch is switched from the disengaged state to the engaged state. A computer program that executes an action. [Claim 18] Traveling device and The PTO shaft that supplies power to the implement, The aforementioned traveling device and power source that drives the PTO shaft, A PTO switch for switching the rotation of the PTO shaft on and off, A PTO clutch is positioned between the power source and the PTO shaft, Control device and A work vehicle equipped with, The control device, when the PTO switch is switched from off to on while the rotational speed of the power source is higher than a reference value, reduces the rotational speed of the power source to the reference value only if the work vehicle is not moving, and then switches the PTO clutch from the disengaged state to the engaged state. Work vehicle.

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