Drive systems, work vehicles, control methods, and computer programs

Abstract

The rotation of the electric motors installed in the work vehicles is appropriately controlled. [Solution] A drive system for a work vehicle according to one embodiment comprises an electric motor that generates a driving force to move the work vehicle, and a control device that controls the electric motor. The work vehicle comprises an operating device that accepts user operation for driving the electric motor, and a transmission provided in a power transmission path that transmits the rotation of the electric motor to the wheels. The transmission is switchable between an engaged state in which the rotation of the electric motor is transmitted to the wheels via the transmission, and a neutral state in which the rotation of the electric motor is not transmitted to the wheels via the transmission. When the electric motor is rotated in response to user operation of the operating device while the transmission is in the neutral state, the control device limits the rotation speed of the electric motor to a predetermined rotation speed or less.

Description

【Technical Field】 【0001】 The present invention relates to a drive system, a work vehicle, a control method, and a computer program. 【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 running by an electric motor (hereinafter sometimes simply referred to as "motor") instead of an internal combustion engine are becoming popular. 【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 to run the traveling body. 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. For example, when an overload state of the battery is detected, the electric drive controller reduces the electric power supplied to the traveling motor. If the overload state continues, the electric drive controller further reduces the electric power supplied to the PTO motor. Thereby, it is possible to prevent an overload of the battery while ensuring the stability of the operation of the hydraulic equipment. 【Prior Art Documents】 [Patent Documents] 【0005】 [Patent Document 1] Japanese Patent Publication No. 2023-66721 [Overview of the Initiative] [Problems that the invention aims to solve] 【0006】 It is required to properly control the rotation of the electric motors installed in work vehicles. [Means for solving the problem] 【0007】 This disclosure provides solutions as described in the following items. 【0008】 [Item 1] A drive system for work vehicles, An electric motor that generates the driving force to move the aforementioned work vehicle, A control device for controlling the electric motor, Equipped with, The aforementioned work vehicle is An operating device that accepts user input for driving the aforementioned electric motor, A transmission is provided in the power transmission path that transmits the rotation of the electric motor to the wheels, Equipped with, The transmission is switchable between an engaged state in which the rotation of the electric motor is transmitted to the wheel via the transmission, and a neutral state in which the rotation of the electric motor is not transmitted to the wheel via the transmission. A drive system in which, when the transmission is in the neutral position and the electric motor is rotated in response to the user's operation of the control device, the control device limits the rotational speed of the electric motor to a predetermined rotational speed or less. 【0009】 [Item 2] The drive system according to item 1, wherein when the transmission is in the neutral position and the electric motor is rotated in response to the user's operation of the operating device, the control device limits the rotational speed of the electric motor to a predetermined rotational speed or less, even when the user's operation of the operating device is at its maximum. 【0010】 [Item 3] The drive system according to item 1 or 2, wherein the control device reduces the rotational speed of the electric motor when the transmission is in the neutral state compared to when the transmission is in the engaged state, for the same amount of operation by the user to the operating device. 【0011】 [Item 4] The drive system according to any one of items 1 to 3, wherein the predetermined rotational speed is 50 rpm or more and 200 rpm or less. 【0012】 [Item 5] The drive system according to any one of items 1 to 4, wherein the transmission is the auxiliary transmission among the main transmission and auxiliary transmission provided in the work vehicle. 【0013】 [Item 6] The aforementioned work vehicle is an agricultural machine, and the drive system is one of the items 1 to 5. 【0014】 [Item 7] The aforementioned work vehicle comprises a PTO (Power Take Off) shaft that supplies power to the work machine and an electric motor that drives the PTO shaft, the drive system according to any one of items 1 to 6. 【0015】 [Item 8] A work vehicle equipped with a drive system as described in any of items 1 through 7. 【0016】 [Item 9] A control method for controlling the operation of a work vehicle, which is executed by one or more computers, The aforementioned work vehicle is An electric motor that generates a driving force for driving the work vehicle, An operating device that receives an operation by a user for driving the electric motor, A transmission provided in a power transmission path that transmits the rotation of the electric motor to the wheels, and is provided with, The transmission can be switched between an engaged state in which the rotation of the electric motor is transmitted to the wheels via the transmission and a neutral state in which the rotation of the electric motor is not transmitted to the wheels via the transmission, The control method is, When the electric motor is rotated in response to an operation of the operating device by the user when the transmission is in the neutral state, the rotation speed of the electric motor is limited to a predetermined rotation speed or less, A control method including this. 【0017】 [Item 10] A computer program that causes one or more computers to execute a process for controlling the operation of a work vehicle, The work vehicle is, An electric motor that generates a driving force for driving the work vehicle, An operating device that receives an operation by a user for driving the electric motor, A transmission provided in a power transmission path that transmits the rotation of the electric motor to the wheels, and is provided with, The transmission can be switched between an engaged state in which the rotation of the electric motor is transmitted to the wheels via the transmission and a neutral state in which the rotation of the electric motor is not transmitted to the wheels via the transmission, The computer program is, When the electric motor is rotated in response to an operation of the operating device by the user when the transmission is in the neutral state, the rotation speed of the electric motor is limited to a predetermined rotation speed or less, Causes the one or more computers to execute this, a computer program. 【0018】 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] 【0019】 When the work vehicle's transmission is in neutral, power consumption can be reduced by stopping the electric motor. However, when the electric motor is stopped, it may not be possible to smoothly switch the transmission from neutral to engaged. In such cases, the user can operate a control device to rotate the electric motor and rotate the gears in the transmission, thereby enabling a smoother transmission shift. At this time, by limiting the rotation speed of the electric motor to below a predetermined speed, it is possible to prevent the work vehicle from accelerating suddenly when the transmission enters the engaged state. 【0020】 Furthermore, even if the transmission gears are lightly engaged while the vehicle is in neutral, this system can prevent the work vehicle from accelerating suddenly. [Brief explanation of the drawing] 【0021】 [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 circuit diagram showing an example of a charging circuit configuration. [Figure 9] This block diagram shows an example of a drive system used in a work vehicle. [Figure 10] This flowchart shows an example of the control of the first electric motor. [Figure 11] This flowchart shows another example of the control of the first electric motor. [Modes for carrying out the invention] 【0022】 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. 【0023】 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. 【0024】 (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." 【0025】 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." 【0026】 Electric motors can be synchronous motors such as permanent magnet synchronous motors or reluctance motors, or asynchronous motors such as induction motors. 【0027】 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. 【0028】 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. 【0029】 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. 【0030】 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". 【0031】 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). 【0032】 "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. 【0033】 (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. 【0034】 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." 【0035】 <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. 【0036】 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. 【0037】 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. 【0038】 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. 【0039】 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. 【0040】 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. 【0041】 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. 【0042】 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. 【0043】 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." 【0044】 <2. Specific examples of work vehicles> Next, we will describe a more specific example of the configuration of the work vehicle 10. 【0045】 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. 【0046】 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. 【0047】 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. 【0048】 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. 【0049】 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". 【0050】 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. 【0051】 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. 【0052】 In the following description, devices used by the user to operate the work vehicle 10, such as the steering wheel 53, pedal group 55, and switch group 56, may be collectively referred to as the "operating device group." 【0053】 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 show 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. 【0054】 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. 【0055】 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. 【0056】 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. 【0057】 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. 【0058】 <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. 【0059】 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. 【0060】 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 brake. 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. 【0061】 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. 【0062】 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. 【0063】 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. 【0064】 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. 【0065】 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. 【0066】 Refer to Figure 4 again. The work vehicle 10 is equipped with multiple ECUs. The multiple ECUs include a main ECU 61, an electric ECU 62, a charging ECU 63, and a meter ECU 151. 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 controls the relay 64 appropriately to perform controls for smooth charging. The meter ECU 151 controls the operation of the meter panel unit 54. For example, the meter ECU 151 controls the display of various information on the meter panel unit 54 and controls various settings in response to user operations on the meter panel unit 54. 【0067】 In this embodiment, the combination of the main ECU 61, electric ECU 62, charging ECU 63, and meter ECU 151 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, electric ECU 62, charging ECU 63, and meter ECU 151 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, electric ECU 62, charging ECU 63, and meter ECU 151 may be provided as the "control device". The control device may include ECUs other than the main ECU 61, electric ECU 62, charging ECU 63, and meter ECU 151. 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 its processor execute a computer program stored in memory. 【0068】 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, by the amount of operation of the pedal group 55 by the driver. In this specification, the former control based on the rotational speed command value may be referred to as "speed control," and the latter control based on the torque command value may be referred to as "torque control." 【0069】 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. 【0070】 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 transmissions included in the power transmission systems 34A and 34B on the meter panel unit 54. 【0071】 Figure 6 is a block diagram showing an example of the hardware configuration of each ECU. The main ECU 61, electric ECU 62, charging ECU 63, and meter ECU 151 each include the various components shown in Figure 6. The ECU 400 shown in Figure 6 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. 【0072】 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. 【0073】 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. 【0074】 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®. 【0075】 The ECU400 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. 【0076】 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. 【0077】 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". 【0078】 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. 【0079】 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 refrigerant inside the radiator 65. The cooling airflow promotes heat dissipation from the radiator 65. 【0080】 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). 【0081】 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. 【0082】 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. 【0083】 Next, we will explain an example of a charging circuit configuration that switches between normal charging and fast charging. 【0084】 Figure 8 is a circuit diagram showing an example of a charging circuit configuration. The charging circuit 700 illustrated in Figure 8 is a circuit that enables rapid charging in accordance with the NACS standard. The charging circuit 700 comprises a pair of power pins 710a and 710b, a relay circuit 720, a contactor 730, an OBC 81, and a controller 750. The controller 750 may be, for example, the charging ECU 63 or the electric ECU 62 shown in Figure 4. The relay circuit 720 and the contactor 730 operate under the control of the controller 750. The charging circuit 700 is connected to the battery 20 and enables normal and rapid charging of the battery 20. Communication takes place between the charging circuit and the charging station, thereby controlling the charging process. 【0085】 During rapid charging, a relatively high DC voltage (e.g., 450V) is applied to a pair of power pins 710a and 710b. If high-voltage DC power is supplied to the OBC 81, the OBC 81 may fail. To avoid this, the charging circuit 700 in this embodiment is provided with a relay circuit 720. During rapid charging, the controller 750 supplies DC power from an external DC power source to the battery 20 by bringing contact 721a of the relay circuit 720 into contact with contact 721b and closing contactor 730. On the other hand, during normal charging, the controller 750 inputs AC power from an external AC power source to the OBC 81 by bringing contact 721a of the relay circuit 720 into contact with contact 721c and opening contactor 730. The controller 750 converts the AC power to DC power by controlling the OBC 81 and supplies the DC power to the battery 20. In this way, a relatively simple circuit like the relay circuit 720 can reliably prevent high-voltage DC power from being supplied to the OBC 740 during rapid charging. <4. Controlling the rotation of the electric motor> Next, we will explain an example of controlling the rotation of the first electric motor 30A. 【0086】 Figure 9 is a block diagram showing an example of a drive system 100 provided by a work vehicle 10. The control device 110 shown in Figure 9 is a control unit including a main ECU 61 and an electric ECU 62. The control device 110 may further include a charging ECU 63 and / or a meter ECU 151, or other ECUs. The control device 110 controls the operation of the first electric motor 30A and the second electric motor 30B. 【0087】 The power transmission system 34A includes a transmission 134A. The transmission 134A is located in the power transmission path that transmits the rotation of the electric motor 30A to the rear wheel 14R and / or the front wheel 14F. The transmission 134A is capable of switching between multiple gears. For example, the transmission 134A can have two gears (low, high) or three gears (low, medium, high). The transmission 134A may also be capable of four or more gears. 【0088】 In an embodiment where the work vehicle 10 is equipped with a main transmission and an auxiliary transmission, the transmission 134A may be the auxiliary transmission. The main transmission is capable of shifting between, for example, 4, 6, or 8 speeds. In a configuration combining a main transmission and an auxiliary transmission, for example, the auxiliary transmission sets the shifting range, and the main transmission shifts within the shifting range set by the auxiliary transmission. By combining a main transmission and an auxiliary transmission, the gear ratio can be set more precisely. 【0089】 The drive system 100 includes operating devices 150 and 160. Operating device 150 is, for example, a gear shift lever or gear shift switch that accepts user operation to switch gears of the transmission 134A. The gears of the transmission 134A are switched in response to the user's operation of operating device 150. Operating device 160 is, for example, an accelerator pedal or accelerator lever that accepts user operation to drive the electric motor 30A. The rotational speed of the electric motor 30A changes in response to the user's operation of operating device 160. 【0090】 The control device 110 can detect the user's operating state to the operating devices 150 and 160 based on the output signals of sensors provided on each of the operating devices 150 and 160. These sensors are, for example, position sensors. 【0091】 The transmission 134A can switch between an engaged state, in which the rotation of the electric motor 30A is transmitted to the wheels via the transmission 134A, and a neutral state, in which the rotation of the electric motor 30A is not transmitted to the wheels via the transmission 134A. In this embodiment, when the transmission 134A is in the neutral state and there is no operation of the operating device 160 by the user, the control device 110 stops the electric motor 30A. This reduces power consumption. 【0092】 On the other hand, when the electric motor 30A is stopped, even if the user operates the control device 150, the gears of the transmission 134A may not mesh properly, making it difficult to switch smoothly from the neutral state to the engaged state. In such cases, the user can operate the control device 160 to rotate the electric motor 30A, thereby rotating the gears in the transmission 134A, which makes it easier for the gears to mesh properly and allows for a smooth switch from the neutral state to the engaged state. 【0093】 Figure 10 is a flowchart showing an example of the control of the electric motor 30A when switching the transmission 134A from the neutral state to the engaged state. 【0094】 The control device 110 determines whether the transmission 134A is in neutral (step S101). As described above, in this embodiment, if the transmission 134A is in neutral and there is no operation of the operating device 160 by the user, the control device 110 stops the electric motor 30A. 【0095】 The control device 110 determines whether to rotate the electric motor 30A when the transmission 134A is in neutral (step S102). For example, if the user operates the operating device 160 when the transmission 134A is in neutral, the electric motor 30A is rotated. At this time, the control device 110 controls the inverter 35A to limit the rotational speed of the electric motor 30A to a predetermined rotational speed P1 or less (step S103). The predetermined rotational speed P1 is, for example, between 50 rpm and 200 rpm, but is not limited to this value. As an example, here the predetermined rotational speed P1 is set to 100 rpm. 【0096】 For example, even when the user's input to the control device 160 is at its maximum, the control device 110 limits the rotational speed of the electric motor 30A to a predetermined rotational speed P1 or less. The control device 110 reduces the rotational speed of the electric motor 30A when the transmission 134A is in neutral compared to when it is in engaged, for the same amount of input from the user to the control device 160. 【0097】 By limiting the rotational speed of the electric motor 30A when it is in neutral to a predetermined rotational speed P1 or less, it is possible to suppress the sudden acceleration of the work vehicle 10 when the transmission 134A switches from neutral to engaged while the electric motor 30A is rotating. 【0098】 Furthermore, even if the transmission 134A is in neutral but the gears are lightly engaged, it is possible to prevent the work vehicle 10 from accelerating suddenly. 【0099】 The control device 110 determines whether the transmission 134A has switched from the neutral state to the engaged state (step S104). 【0100】 When the transmission 134A switches from the neutral state to the engaged state, the control device 110 determines whether a predetermined time has elapsed since the transmission 134A switched to the engaged state (step S105). The predetermined time is, for example, 1 second or more and 3 seconds or less, but is not limited to that value. As an example, the predetermined time here is set to 2 seconds. 【0101】 After a predetermined time has elapsed since the transmission 134A switched to the engaged state, the control device 110 turns off the control that limits the rotational speed of the electric motor 30A to a predetermined rotational speed P1 or less, and releases the restriction (step S106). After releasing the restriction, the control device 110 controls the rotational speed of the electric motor 30A according to the amount of operation performed by the user on the operating device 160. At this time, by gradually increasing the rotational speed of the electric motor 30A, it is possible to suppress the sudden acceleration of the work vehicle 10. 【0102】 Figure 11 is a flowchart showing another example of the control of the electric motor 30A when switching the transmission 134A from the neutral state to the engaged state. 【0103】 In the example shown in Figure 11, in step S104, if the control device 110 determines that the transmission 134A has switched from the neutral state to the engaged state, it then determines whether the user has stopped operating the operating device 160 (step S115). 【0104】 After the transmission 134A switches to the engaged state, if the user stops operating the control device 160, the control device 110 turns off the control that limits the rotational speed of the electric motor 30A to a predetermined rotational speed P1 or less, and releases the restriction (step S106). This prevents the work vehicle 10 from accelerating suddenly. When the user operates the control device 160 again, the control device 110 controls the rotational speed of the electric motor 30A according to the amount of operation the user has performed on the control device 160. 【0105】 The drive system 100 according to this embodiment can also be retrofitted to a work vehicle that does not have those functions. Such a system can be manufactured and sold independently of the work vehicle. The computer program used in such a system can also be manufactured and sold independently of the work vehicle. The computer program can be provided, for example, stored in a computer-readable non-temporary storage medium. The computer program can also be provided by download via a telecommunications line (e.g., the Internet). [Industrial applicability] 【0106】 The present invention is particularly useful in the field of electric work vehicles such as agricultural tractors and construction vehicles equipped with electric motors for driving. [Explanation of symbols] 【0107】 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, 40...PTO shaft, 51...Loops 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...Battery radiator, 76...Reservoir tank, 77...Pump, 80...Power distribution unit, 81...Onboard charger (OBC), 82...DC-DC converter, 83...Relay circuits, 84...Auxiliary equipment, 100...Drive systems, 110...Control devices, 134A...Transmissions, 150...Operating devices, 160...Operating devices

Claims

[Claim 1] A drive system for work vehicles, An electric motor that generates the driving force to move the aforementioned work vehicle, A control device for controlling the electric motor, Equipped with, The aforementioned work vehicle is An operating device that accepts user input for driving the aforementioned electric motor, A transmission is provided in the power transmission path that transmits the rotation of the electric motor to the wheels, Equipped with, The transmission is switchable between an engaged state in which the rotation of the electric motor is transmitted to the wheel via the transmission, and a neutral state in which the rotation of the electric motor is not transmitted to the wheel via the transmission. A drive system in which, when the transmission is in the neutral position and the electric motor is rotated in response to the user's operation of the control device, the control device limits the rotational speed of the electric motor to a predetermined rotational speed or less. [Claim 2] The drive system according to claim 1, wherein when the transmission is in the neutral position and the electric motor is rotated in response to the user's operation of the operating device, the control device limits the rotational speed of the electric motor to a predetermined rotational speed or less, even when the user's operation of the operating device is at its maximum. [Claim 3] The drive system according to claim 1 or 2, wherein the control device reduces the rotational speed of the electric motor when the transmission is in the neutral state compared to when the transmission is in the engaged state, for the same amount of operation by the user to the operating device. [Claim 4] The drive system according to claim 1 or 2, wherein the predetermined rotational speed is 50 rpm or more and 200 rpm or less. [Claim 5] The drive system according to claim 1 or 2, wherein the transmission is the auxiliary transmission among the main transmission and auxiliary transmission provided in the work vehicle. [Claim 6] The drive system according to claim 1 or 2, wherein the work vehicle is agricultural machinery. [Claim 7] The drive system according to claim 1 or 2, wherein the work vehicle comprises a PTO (Power Take Off) shaft that supplies power to the work machine and an electric motor that drives the PTO shaft. [Claim 8] A work vehicle equipped with the drive system according to claim 1 or 2. [Claim 9] A control method for controlling the operation of a work vehicle, which is executed by one or more computers, The aforementioned work vehicle is An electric motor that generates the driving force to move the aforementioned work vehicle, An operating device that accepts user input for driving the aforementioned electric motor, A transmission is provided in the power transmission path that transmits the rotation of the electric motor to the wheels, Equipped with, The transmission is switchable between an engaged state in which the rotation of the electric motor is transmitted to the wheel via the transmission, and a neutral state in which the rotation of the electric motor is not transmitted to the wheel via the transmission. The control method described above is When the transmission is in the neutral position and the electric motor is rotated in response to the user's operation of the control device, the rotational speed of the electric motor is limited to a predetermined rotational speed or less. A control method including [Claim 10] A computer program that causes one or more computers to execute a process to control the operation of a work vehicle, The aforementioned work vehicle is An electric motor that generates the driving force to move the aforementioned work vehicle, An operating device that accepts user input for driving the aforementioned electric motor, A transmission is provided in the power transmission path that transmits the rotation of the electric motor to the wheels, Equipped with, The transmission is switchable between an engaged state in which the rotation of the electric motor is transmitted to the wheel via the transmission, and a neutral state in which the rotation of the electric motor is not transmitted to the wheel via the transmission. The aforementioned computer program, When the transmission is in the neutral position and the electric motor is rotated in response to the user's operation of the control device, the rotational speed of the electric motor is limited to a predetermined rotational speed or less. A computer program that causes one or more computers to execute the aforementioned program.

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