Work vehicle and motor control method

Abstract

This work vehicle is provided with: an electric motor that drives a travel device; a transmission that is connected to an output shaft of the electric motor; and a control device that controls the electric motor. The control device is configured to control the electric motor, upon detecting a stop of the vehicle, such that the torque of the electric motor becomes less than or equal to a torque threshold at which a transmission gear can be shifted.

Description

Work vehicle and motor control method

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

[0002] In the field of automobiles, whose main purpose is to transport people or goods, electric vehicles (EVs), which generate driving force (traction) for running by electric motors (hereinafter sometimes simply referred to as "motors") instead of internal combustion engines, are becoming more common.

[0003] On the other hand, in order to realize a decarbonized society, carbon dioxide (CO ) emitted by work vehicles such as tractors used in fields is being reduced. ２ There is a demand to reduce the amount of fuel used. Unlike ordinary automobiles, work vehicles such as tractors need to tow agricultural implements to perform farm work such as plowing. Therefore, in order to realize the electrification of work vehicles, there are challenges that need to be overcome that are different from those faced by passenger cars.

[0004] Patent Document 1 discloses an electric tractor that distributes and supplies power from a battery to multiple electric motors. The electric tractor includes a hydraulic pump, a pump motor, a PTO motor, a traction 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 a PTO shaft. The traction motor is an electric motor that is driven to propel the traveling vehicle. A battery supplies power to the pump motor, the PTO motor, and the traction motor. The electric drive controller controls the distribution of power to the pump motor, the PTO motor, and the traction motor. For example, if the electric drive controller detects a battery overload state, it reduces the power supplied to the traction motor. If the overload state continues, the electric drive controller further reduces the power supplied to the PTO motor. This prevents battery overload while ensuring stable operation of the hydraulic equipment.

[0005] JP 2023-66721 A

[0006] While conventional work vehicles equipped with internal combustion engines inevitably consume fossil fuels and emit greenhouse gases, electric work vehicles face a variety of challenges that must be resolved, including ensuring safety, improving driving performance, reducing environmental impact, improving convenience, and reducing costs.

[0007] The present disclosure provides an electric work vehicle that can solve at least one of these problems.

[0008] The present disclosure provides the solutions described in the following items.

[0009] [Item 1] A work vehicle comprising: a travel device; an electric motor that drives the travel device; a transmission connected to an output shaft of the electric motor; and a control device that controls the electric motor, wherein the control device is configured to, after detecting a stop of the vehicle, control the electric motor so that the torque of the electric motor becomes equal to or less than a torque threshold that enables gear switching of the transmission.

[0010] [Item 2] The work vehicle according to item 1, wherein the torque threshold is zero.

[0011] [Item 3] The work vehicle according to item 1 or 2, wherein the control device includes one or more processors and one or more memories that store programs for controlling the operation of the one or more processors, and the one or more processors, after detecting a stop of the vehicle, control the electric motor in accordance with the program so that the torque of the electric motor becomes equal to or less than the torque threshold value.

[0012] [Item 4] The work vehicle according to item 1 or 2, wherein when rotation of the electric motor is detected while the control device is controlling the electric motor so that the torque of the electric motor is equal to or less than the torque threshold value, the control device switches control of the electric motor so that the torque of the electric motor is greater than the torque threshold value.

[0013] [Item 5] The work vehicle according to Item 4, wherein the control device detects rotation of the electric motor, switches control of the electric motor so that the torque of the electric motor is greater than the torque threshold value, and then, when stoppage of rotation of the electric motor is detected, switches control of the electric motor so that the torque of the electric motor is equal to or less than the torque threshold value.

[0014] [Item 6] The work vehicle according to item 1 or 2, further comprising a parking brake, wherein the control device issues a warning to prompt a user to apply the parking brake when rotation of the electric motor is detected while the control device is controlling the electric motor so that the torque of the electric motor is equal to or less than the torque threshold value.

[0015] [Item 7] The work vehicle according to Item 6, further comprising a meter panel having a display that displays various information related to the work vehicle, wherein the control device causes the display to display a warning message urging the user to apply the parking brake.

[0016] [Item 8] The work vehicle according to item 1 or 2, further comprising an electric parking brake, wherein the control device activates the electric parking brake when rotation of the electric motor is detected while the control device is controlling the electric motor so that the torque of the electric motor is equal to or less than the torque threshold value.

[0017] [Item 9] The work vehicle according to any one of items 1 to 8, wherein the electric motor is a first electric motor, and the work vehicle comprises: a PTO shaft that supplies power to a work implement; and a second electric motor that drives the PTO shaft.

[0018] [Item 10] The work vehicle according to any one of items 1 to 9, wherein the transmission is connected to the output shaft of the electric motor without a clutch.

[0019] [Item 11] A motor control method implemented in a computer for controlling an electric motor that drives a traveling device of a work vehicle, the motor control method including: determining whether the vehicle has stopped; and, when it is determined that the vehicle has stopped, controlling the electric motor so that the torque of the electric motor is equal to or less than a torque threshold that enables gear switching of a transmission of the work vehicle.

[0020] [Item 12] A control device configured to carry out the method of item 11.

[0021] [Item 13] A computer program comprising a group of instructions for causing a computer to execute the method described in Item 11.

[0022] [Item 14] A computer-readable non-transitory storage medium storing a computer program including instructions for causing a computer to execute the method described in Item 11.

[0023] [Item 15] A system comprising: the control device according to item 12; and an electric motor.

[0024] [Item 16] A control device for controlling an electric motor mounted on a work vehicle, the control device including: a determination means for determining whether the vehicle has stopped; and a control means for controlling the electric motor, when it is determined that the vehicle has stopped, so that the torque of the electric motor becomes equal to or less than a torque threshold value that enables gear switching of a transmission of the work vehicle.

[0025] [Item 17] A system comprising: the control device according to item 16; and an electric motor.

[0026] A general or specific aspect of the present invention may be realized by an apparatus, a system, a method, an integrated circuit, a computer program, or a computer-readable non-transitory storage medium, or any combination thereof. The computer-readable storage medium may include a volatile storage medium or a non-volatile storage medium. The apparatus may be composed of multiple devices. When the apparatus is composed of two or more devices, the two or more devices may be located in a single device or may be located separately in two or more separate devices.

[0027] According to an embodiment of the present disclosure, an electric work vehicle is provided that can achieve at least one of ensuring safety, improving driving performance, reducing environmental impact, improving convenience, and reducing costs.

[0028] FIG. 1 is a plan view schematically showing an example of the basic configuration of a work vehicle according to an exemplary embodiment of the present invention. FIG. 2 is a side view of a work vehicle according to an exemplary embodiment of the present invention. FIG. 3 is a top view of a work vehicle. FIG. 4 is a block diagram showing an example of the main components of a work vehicle and their connection relationships. FIG. 5 is a block diagram showing an example of the configuration of a power conversion device and connections with other devices. FIG. 6 is a block diagram showing an example of the hardware configuration of each ECU. FIG. 7 is a block diagram showing an example of the configuration of a power distribution unit. FIG. 8 is a circuit diagram showing an example of the configuration of a charging circuit. FIG. 9 is a block diagram showing an example of the configuration of a power transmission system for traveling. FIG. 10 is a flowchart showing the procedure of a process for controlling the drive of an electric motor when the work vehicle is stopped.

[0029] Hereinafter, embodiments of the present invention will be described. However, more detailed descriptions than necessary may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the inventors provide the accompanying drawings and the following description to enable those skilled in the art to fully understand the present invention, and do not intend for them to limit the subject matter described in the claims. In the following description, components having the same or similar functions are designated by the same reference numerals.

[0030] The following embodiments are examples for embodying the technical concept of the present invention, and the present invention is not limited to the following embodiments. For example, the numerical values, shapes, materials, steps, and step orders shown in the following embodiments are merely examples, and various modifications are possible as long as no technical contradictions arise. Furthermore, one embodiment can be combined with another embodiment. The size and positional relationship of components shown in each drawing may be exaggerated to facilitate understanding.

[0031] (Definition of Terms) In this specification, a "work vehicle" refers to a vehicle used for a specific task, such as agricultural work or construction work. The "task" may be, for example, agricultural work, construction work, debris removal, or snow removal. Agricultural work vehicles may be, for example, tractors, combine harvesters, rice transplanters, riding tillers, vegetable transplanters, vegetable harvesters, mowers, seed sowing machines, or fertilizer applicators. Construction work vehicles may 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 alone as a "work vehicle," or the entire combination of the work vehicle and a work implement attached to or towed by the work vehicle may function as a single "work vehicle." Agricultural work vehicles perform agricultural tasks, such as plowing, sowing, pest control, fertilizing, planting crops, or harvesting, on the ground in a field. Construction work vehicles perform tasks such as transporting soil, rubble, and other materials at construction sites. These operations are sometimes referred to as "ground operations" or simply "operations." When a work vehicle travels while performing work, this is sometimes referred to as "work travel."

[0032] An "electric work vehicle" refers to a work vehicle that travels using an electric motor as a power source. An electric work vehicle may 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 electric energy source such as a battery or fuel cell that supplies power to the electric motor. In the following description, an "electric work vehicle" may be simply referred to as a "work vehicle."

[0033] The electric motor may be, for example, a synchronous motor, such as a permanent magnet synchronous motor or a reluctance motor, or an asynchronous motor, such as an induction motor.

[0034] A battery is an electricity storage device that stores the electrical energy required to operate the electric motor and other electrical equipment mounted on the 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. The electrical energy source can be realized by an electricity storage device, a power generation device, or a combination of an electricity storage device and a power generation device. Note that an electric work vehicle may obtain electrical energy via wired or wireless connections from an electrical energy source located remotely from the vehicle (e.g., on the ground or on another vehicle).

[0035] When an electric work vehicle performs various "tasks" while traveling or stopped, the power required for the tasks may be obtained from the electric motor. An electric work vehicle is equipped with one or more electric motors. When an electric work vehicle is equipped with multiple electric motors, some specific electric motors may output the driving force required for traveling, while other electric motors may output the driving force required for the "task." When some or all of the "tasks" are performed by a work machine, the driving force may be mechanically transmitted to the work machine from one or more electric motors provided on the electric work vehicle. This mechanical transmission of driving force may be achieved via a power transmission shaft called a power take-off (PTO) shaft.

[0036] The work machine itself may be equipped with an electric motor for work. In this case, power may be supplied to the electric motor of the work machine from an electric energy source such as a battery or fuel cell provided in the electric work vehicle. The work machine may also be equipped with an electric energy source that stores the power required for work.

[0037] A "controller" is a device that controls the operation of a part or the entire work vehicle. One example of a "controller" is a computing device that includes at least one processor and at least one memory that stores a computer program (code) that defines a control process executed by the processor. Another example of a "controller" is a computing device that includes a hardware accelerator, such as a field-programmable gate array (FPGA), an application-specific standard product (ASSP), or an application-specific integrated circuit (ASIC), configured or programmed to execute the control process. A control device may also be a collection of multiple devices. For example, multiple physically separated computing devices, such as electronic control units (ECUs), may work together to function as a "controller."

[0038] A "processor" is a hardware electronic circuit such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), a DSP (Digital Signal Processor), an ISP (Image Signal Processor), or an NPU (Neural Network Processing Unit).

[0039] "Memory" refers to hardware electronic circuits such as read-only memory (ROM) or random-access memory (RAM). Part of the memory may be storage media 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 related components in the electronic circuit may be manufactured individually as a separate integrated circuit chip, or some or all of these functional units or blocks may be combined and manufactured as a single integrated circuit chip. The memory may store a computer program (hereinafter simply referred to as a "program") that defines the operation of the processor. The program is designed to cause the processor to perform one or more functions, operations, steps, or processes in embodiments of the present invention.

[0040] (Embodiments) Hereinafter, with reference to the drawings, several embodiments in which the technology of the present invention is applied to an electric agricultural tractor, which is an example of an electric work vehicle, will be described. The various technologies described in the following description for tractors 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 areas with heavy snowfall, vehicles for transporting goods, and the like.

[0041] In the following description, the direction of arrow F in the figure will be referred to as "front," the direction of arrow B as "back," 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."

[0042] 1. Basic Configuration of Work Vehicle Figure 1 is a plan view that schematically shows an example of the basic configuration of a work vehicle 10 according to an exemplary embodiment of the present invention. The work vehicle 10 shown in the figure is an electric agricultural tractor. The work vehicle 10 can be attached to or towed with a work implement and travel within a field while performing agricultural work according to the type of work implement. The work vehicle 10 can also travel within and outside a field (including on roads) with the work implement lifted or without the work implement attached.

[0043] The work vehicle 10 includes a vehicle body (vehicle frame) 11 that rotatably supports left and right front wheels 14F and left and right rear wheels 14R. The vehicle 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 portion of the transmission case 13. The front wheels 14F and the rear wheels 14R may be collectively referred to as "wheels 14." Strictly speaking, the wheels 14 are wheels, and tires are attached to the wheels 14. In this disclosure, "wheels" generally refers to the entire "wheels and tires." One or both of the front wheels 14F and the rear wheels 14R may be replaced with multiple wheels (crawlers) equipped with tracks rather than with tires.

[0044] The work vehicle 10 in the example of FIG. 1 is equipped with a battery 20 and an electric motor 30 (hereinafter simply referred to as the "motor 30") that are supported directly or indirectly by a front frame 12. The battery 20 may be configured, for example, as a battery pack including a plurality of 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, for example, in a front housing called a "bonnet." The front housing is supported by a front frame 12 that is located at the front of the vehicle body 11.

[0045] The motor 30 is electrically connected to the battery 20. The motor 30 converts the electric power output from the battery 20 into mechanical motion (power) and is able to generate the driving force (traction) required for the travel of the work vehicle 10. The motor 30 may be, for example, an AC synchronous motor. The battery 20 generates DC current. For this reason, when the motor 30 is an AC synchronous motor, a group of electrical circuits including an inverter device (hereinafter sometimes simply referred to as an "inverter") may be provided between the battery 20 and the motor 30. The inverter device converts DC current into AC current. A portion of this group of electrical circuits may be located inside the battery 20. Furthermore, another portion of the group of electrical circuits may be attached to the motor 30 as a drive circuit for the motor 30.

[0046] 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) provided 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 (drive train) 34 including the transmission provided inside the transmission case 13. For this reason, the "transmission case" is sometimes called a "transmission case." Note that in four-wheel drive mode, a portion of the power of the motor 30 is also transmitted to the front wheels 14F. In this way, the motor 30 drives the running device including the multiple wheels 14.

[0047] The power of the motor 30 may be used not only to propel the work vehicle 10 but also to drive a 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 can be driven by the motor 30 that drives the travel device, or by another electric motor not shown in FIG. 1 . Torque from an output shaft 33 of the motor 30 or an output shaft of another motor is transmitted to the PTO shaft 40. A 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.

[0048] As such, the work vehicle 10 shown in FIG. 1 is not equipped with an internal combustion engine such as a diesel engine, but rather is equipped with a battery 20 and a motor 30. Furthermore, the output shaft 33 of the motor 30 is mechanically coupled to a power transmission system 34, such as a transmission, inside the 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 utilizing the power transmission system 34, which includes a transmission, multi-stage or continuously variable speed change operations can be performed, making it easy to adjust the torque and rotational speed from the motor 30 over an even wider range. This makes it possible not only to drive the work vehicle 10, but also to efficiently perform a variety of tasks using the work equipment.

[0049] Depending on the application or size of the work vehicle 10, some functions of the power transmission system 34 may be eliminated. For example, part or all of the transmission responsible for the speed change function may be omitted. The number and mounting positions of the motors 30 are also not limited to the example shown in Figure 1. Furthermore, the work vehicle may be a hybrid electric vehicle (HEV) that is equipped with an internal combustion engine such as a diesel engine as a power source in addition to the electric motor.

[0050] The work vehicle 10 shown in FIG. 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 travel electric motor that drives a travel device including four wheels 14, and a PTO electric motor that drives a 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 this 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 the two front wheels 14F and a rear wheel electric motor that drives the two rear wheels 14R. Alternatively, the work vehicle 10 may be equipped with two front electric motors that respectively drive the two front wheels 14F, and two rear electric motors that respectively drive the two rear wheels 14R. That is, the work vehicle 10 may be equipped with four electric motors that respectively drive the four wheels 14. In this manner, the work vehicle 10 may be equipped with one or more traction electric motors that drive the travel gear, and one or more PTO electric motors that drive one or more PTO axles. By being equipped with multiple electric motors, the work vehicle 10 can more flexibly control the rotation of the multiple wheels 14 and one or more PTO axles. In the following description, the traction electric motor may be referred to as the "traffic motor," and the PTO electric motor may be referred to as the "PTO motor."

[0051] 2. Specific Example of Work Vehicle Next, a more specific example of the configuration of the work vehicle 10 will be described.

[0052] 2 and 3 are side and top views of work vehicle 10 according to an exemplary embodiment of the present invention.

[0053] 2 and 3 includes a vehicle body 11 and a traveling device supported by the vehicle body 11. The traveling device includes various devices necessary for traveling, such as left and right front wheels 14F, left and right rear wheels 14R, a front axle 15F, a rear axle 15R, and a rear wheel differential.

[0054] The vehicle body 11 includes a front frame 12, a transmission case 13, and a storage frame 16. The front frame 12 is connected to the front portion of the storage frame 16. The transmission case 13 is connected to the rear portion of the storage frame 16. A first electric motor 30A and a second electric motor 30B are housed inside the storage frame 16. The first electric motor 30A is a travel motor that drives the travel device via a power transmission system in the transmission case 13. The second electric motor 30B is a PTO motor that drives a PTO shaft 40 and one or more hydraulic pumps. The first electric motor 30A and the second electric motor 30B may be electric motors that are capable of outputting high torque with relatively high efficiency, such as permanent magnet synchronous motors.

[0055] A front axle case 17F is attached to the front frame 12. The front axle case 17F supports left and right front wheels 14F. The transmission case 13 includes a rear axle case 17R. The rear axle case 17R supports left and right rear wheels 14R and transmits power to the rear wheels 14R.

[0056] A battery 20 is provided on the front frame 12. The battery 20 is supported by the front frame 12 and housed inside the front housing 19 (hood). The battery 20 stores electric power to be supplied to the first electric motor 30A and the second electric motor 30B. In other words, the battery 20 stores electric power for traveling, working, and hydraulic drive. In the following description, the battery 20 may be referred to as the "driving battery 20."

[0057] Above the storage frame 16 and transmission case 13 are provided a steering wheel 53, an instrument panel unit 54, pedals 55 such as accelerator and brake, switches 56 for driving for work, and a driver's seat 52. A safety frame 51 (ROPS frame) is provided behind the driver's seat 52. The safety frame 51 is attached to the transmission case 13 and extends upward. A first electric motor 30A and a second electric motor 30B are disposed inside the storage frame 16.

[0058] The switch group 56 includes various operating devices such as a plurality of switches, levers, dials, etc. for adjusting the operation of the work vehicle 10 and the work equipment. The switch group 56 includes various operating devices such as an accelerator lever for adjusting the traveling speed, a switch for switching the PTO shaft 40 on and off, a dial for adjusting the rotation speed of the PTO shaft 40, and a lever for adjusting the height of the three-point linkage that supports the work equipment. By operating the switch group 56, the driver can give various instructions for traveling and working to the work vehicle 10.

[0059] In the following description, devices used by the user to operate the work vehicle 10, such as the steering wheel 53, pedals 55, and switches 56, may be collectively referred to as an "operation device group."

[0060] The meter panel unit 54 displays information related to 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 the motors 30A, 30B, the charge state 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 simply referred to as the "display") for displaying this information. The display of the meter panel unit 54 may display a graphical user interface (GUI) that enables 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 an input device connected to the meter panel unit 54 or input means such as a touch screen mounted on the display.

[0061] As shown in FIG. 3 , a charging inlet 57 is provided to the right of the steering wheel 53. The charging inlet 57 is a device including a socket configured to allow connection of a charging adapter extending from an external power source or charging device. A device such as a charging start button that allows the user to instruct the start of charging may be provided near the charging inlet 57. 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.

[0062] Charging methods for the battery 20 include normal charging and rapid charging. In normal charging, AC power supplied from an external AC power source is converted into high-voltage DC power (e.g., approximately 350 V to 450 V), and the DC power is supplied to the battery 20. In rapid charging, high-voltage DC power is directly supplied from an external DC power source to the battery 20. The charging inlet 57 in this embodiment is compatible with both normal charging and rapid charging. A commercial AC power source that outputs an AC voltage of, for example, 200 V or 100 V may be used as the power source for normal charging. A DC power source that outputs a DC voltage of, for example, approximately 350 V to 450 V may be used as the power source for rapid charging. Rapid charging may be performed using a protocol that complies with standards such as CHAdeMO, NACS, CCS1, CCS2, GB / T, or ChaoJi.

[0063] It is also possible to output the power stored in battery 20 to external electrical equipment via charging inlet 57. Such an output of power to the outside is referred to in this specification as "external power supply." External power supply is performed when an external power supply adapter is connected to charging inlet 57. DC power from battery 20 can be converted to AC power by a power conversion device in work vehicle 10. This AC power can be supplied to external equipment via charging inlet 57 and the external power supply adapter.

[0064] As shown in FIG. 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 electric power supplied from the battery 20. The first electric motor 30A drives the traveling device via a power transmission system within the transmission case 13. The second electric motor 30B drives the PTO shaft 40 and the hydraulic pump via the power transmission system within the transmission case 13. In this way, the second electric motor 30B drives the work equipment and various hydraulic devices. The hydraulic device can be used, for example, to change the height of a three-point linkage that supports the work equipment. The work vehicle 10 can be equipped with a power steering device that assists the driver in operating the steering wheel. In this case, the hydraulic device can also be used to supply an auxiliary force to the power steering device to change the steering angle of the front wheels 104F.

[0065] 3. System Configuration of Work Vehicle Figure 4 is a block diagram showing an example of the main components of the work vehicle 10 and their interconnections. In Figure 4, the interconnections related to power transmission, high-voltage drive power, and low-voltage auxiliary power are represented by solid lines of different thicknesses. The interconnections related to signals (digital signals and analog signals) are represented by dotted lines. The flow of coolant is represented by thick dashed lines.

[0066] As shown in FIG. 4 , the work vehicle 10 includes 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 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 travel device. Furthermore, the second inverter 35B 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.

[0067] The transmission case 13 houses a traveling power transmission system 34A, a work power transmission system 34B, and a hydraulic pump 36. The traveling power transmission system 34A may include components such as a speed reducer, an auxiliary transmission, and a differential brake. The traveling power transmission system 34A transmits power generated by the rotation of the first electric motor 30A to the rear wheels 14R. In four-wheel drive mode, the traveling power transmission system 34A also transmits a portion of the power generated by the rotation of the first electric motor 30A to the front wheels 14F. The work power transmission system 34B may include components such as a speed reducer, a PTO clutch, and a PTO transmission. The work power transmission system 34B transmits power generated by the rotation of the second electric motor 30B to the hydraulic pump 36 and the PTO shaft 40. The PTO shaft 40 supplies work power to the work equipment.

[0068] The PTO shaft 40 shown in FIG. 4 is a rear PTO shaft. In addition to the rear PTO shaft, the work vehicle 10 may also be equipped with a mid PTO shaft or a front PTO shaft. If the work vehicle 10 is equipped with multiple PTO shafts, the power transmission system 34B may be configured to distribute power generated by the rotation of the second electric motor 30B to the multiple PTO shafts. Alternatively, the work vehicle 10 may include, in addition to the second electric motor 30B that drives the PTO shaft 40, other electric motors that drive other PTO shafts.

[0069] The work implement connected to the PTO shaft 40 may be, for example, a rotary tiller, a seeder, a spreader, a transplanter, a mower, a rake, a baler, a harvester, a sprayer, or a harrow. Any work implement can be connected to the work vehicle 10 and used.

[0070] The hydraulic pump 36 is driven by power from the second electric motor 30B. The hydraulic pump 36 pressurizes hydraulic oil, thereby changing the height of the three-point link to which the work machine is connected. Alternatively, the hydraulic pump 36 may be used in a hydraulic power steering device. When a front loader is attached as the work machine, the hydraulic pump 36 may be used in a hydraulic system that realizes the lifting and lowering operation of the front loader. The power of the second electric motor 30B may be transmitted to multiple hydraulic pumps for driving these multiple hydraulic systems. Alternatively, the work vehicle 10 may be equipped with one or more electric motors for hydraulic pressures different from the second electric motor 30B.

[0071] In the example shown in FIG. 4 , the work vehicle 10 further includes a power conversion device 58 , a power distribution unit (PDU) 80 , an auxiliary battery 21 , and a battery temperature regulation system 70 .

[0072] The power conversion device 58 is disposed between the charging inlet 57 and the battery 20 and performs power conversion, such as AC-DC conversion and voltage conversion. FIG. 5 shows an example of the configuration of the power conversion device 58 and its connection to other devices. The power conversion device 58 shown in FIG. 5 includes an on-board charger (OBC) 81 and a DC-DC converter 82. During normal charging, the OBC 81 converts AC power from the charging inlet 57 into DC power and supplies it to the drive battery 20 via the power distribution unit 80. The drive battery 20 is charged with this DC power. The DC-DC converter 82 is connected to the OBC 81 and 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 into DC power of a lower voltage (e.g., 12 V or 24 V). The low-voltage DC power converted by the DC-DC converter 82 is supplied to the auxiliary battery 21 and auxiliary equipment 84. The auxiliary equipment 84 includes a plurality of devices that operate on the relatively low voltage output from the DC-DC converter 82 or the battery 21. For example, the auxiliary equipment 84 includes a plurality of electronic control units (ECUs) and other electrical equipment. The auxiliary battery 21 is charged by the DC voltage output from the DC-DC converter 82. The auxiliary battery 21 stores the power to be supplied to the auxiliary equipment 84, such as each ECU, the meter panel unit 54, the pumps 67 and 77, and the air conditioner. The battery 21 may be, for example, a lead battery.

[0073] Referring again to Figure 4, the work vehicle 10 is equipped with multiple ECUs. The multiple ECUs include a main ECU 61, an electric motor 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 motor ECU 62 mainly controls the charging and discharging of the battery 20 and the operation of the electric motors 30A, 30B. The charging ECU 63 communicates with an external charger (external power source) and appropriately controls a relay 64, thereby executing control to ensure smooth charging.

[0074] In this embodiment, the combination of the main ECU 61, the electric ECU 62, and the charging ECU 63 functions as a "controller" 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 a "controller." 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 In-Vehicle Ethernet (registered trademark) may be used instead of CAN. An on-board computer that integrates 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 "controller." 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 below by the processor executing a computer program stored in the memory.

[0075] The electric motor 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 motor ECU 62 can perform motor control based on a rotation speed command value or a torque command value determined according to the amount of operation of the pedal group 55 by the driver, for example. In this specification, the former control based on the rotation 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."

[0076] The electric motor ECU 62 controls the switching operation of a plurality of switch elements (e.g., MOSFETs) included in each of the first inverter 35A and the second inverter 35B. Specifically, the electric motor ECU 62 generates control signals for controlling the switching operation of each switch element and outputs the control signals to each inverter. The first inverter 35A converts DC power from the battery 20 into three-phase AC power, e.g., a pseudo-sine wave having u-, v-, and w-phases, in accordance with the control signal from the electric motor ECU 62, and supplies the three-phase AC power to the first electric motor 30A. Similarly, the second inverter 35B converts DC power from the battery 20 into three-phase AC power, e.g., a pseudo-sine wave having u-, v-, and w-phases, in accordance with the control signal from the electric motor ECU 62, and supplies the three-phase AC power to the second electric motor 30B. This allows the electric motor ECU 62 to rotate the electric motors 30A, 30B at an appropriate rotational speed and torque according to the driver's operation.

[0077] While the work vehicle 10 is in operation, the main ECU 61 causes the meter panel unit 54 to display information relating to the state of the work vehicle 10. For example, the main ECU 61 causes the meter panel unit 54 to display information relating to the traveling speed, the operating state of the motors 30A, 30B, the charging state of the battery 20, the state of the transmissions included in the power transmission systems 34A, 34A, and the like.

[0078] 6 is a block diagram showing an example of the hardware configuration of each ECU 400. Each ECU 400 includes a processor 434, a ROM 435, a RAM 436, an external I / F 437, and a communication I / F 438. These components are connected to each other via a bus 439.

[0079] The ROM 435 is, for example, a writable memory (e.g., a PROM), a rewritable memory (e.g., a flash memory), or a read-only memory. The ROM 435 stores a program that controls the operation of the processor 434. The ROM 435 does not have to be a single recording medium, but may be a collection of multiple recording media. Some of the multiple storage media may be removable memories.

[0080] The RAM 436 provides a working area for temporarily loading, at boot time, the programs stored in the ROM 435. The RAM 436 does not have to be a single recording medium, but may be a collection of multiple recording media.

[0081] The external I / F 437 is an interface for connecting to external devices. The communication I / F 438 is an interface for communicating with other electronic devices (e.g., sensors, other ECUs, etc.). For example, the communication I / F 438 can perform wired communication in accordance with various protocols such as CAN or Ethernet (registered trademark). The communication I / F 438 may also perform wireless communication in accordance with wireless communication standards such as Bluetooth (registered trademark) and / or Wi-Fi (registered trademark).

[0082] The ECU 400 may further include a storage device that stores, for a relatively long period of time, data generated by the processor 434. Such a storage device may be, for example, a semiconductor storage device, a magnetic storage device, an optical storage device, or a combination thereof.

[0083] The power distribution unit 80 shown in FIG. 4 is a device that electrically connects devices such as the charging inlet 57, the power conversion device 58, the battery 20, the inverters 35A and 35B, and the heater 72 to one another.

[0084] FIG. 7 is a diagram showing an example of the configuration of the power distribution unit 80. The power distribution unit 80 may have multiple relay circuits 83 (83a to 83g) that operate under the control of the electric power ECU 62. During charging, the power distribution unit 80 is configured to supply power from the charging inlet 57 or the power conversion device 58 to the battery 20, and to the heater 72 when the temperature is low. 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 conversion device 23. The electric power ECU 62 may be configured or programmed to control charging and discharging of the battery 20 by appropriately switching on and off the multiple relay circuits 83a to 83g in the power distribution unit 80. In this specification, the relay circuits may be simply referred to as "relays."

[0085] 4 , the battery 20 includes a battery management system (BMS) 22 and a temperature sensor 24. The BMS 22 is configured to monitor conditions of the battery 20, such as the input voltage, output voltage, and temperature, and to control the charge current and discharge current to the battery 20 based on these conditions. The temperature sensor 24 may be configured to measure the temperature of each of the multiple cells included in the battery 20.

[0086] The work vehicle 10 illustrated in FIG. 4 includes a cooling system 60 for high-voltage equipment and a battery temperature control system 70. The cooling system 60 is used to cool devices to which high voltage is applied (also referred to as "high-power devices"). The cooling system 60 includes a radiator 65, a reservoir tank 66, a pump 67, and a cooling fan 68. In the example illustrated in FIG. 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 conversion device 58 in this 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-power devices by circulating the coolant through the flow path. The coolant heated by the high-power devices is cooled by dissipating heat in the radiator 65. The cooling fan 68 generates cooling air to cool the coolant inside the radiator 65. The cooling air promotes heat dissipation from the radiator 65 .

[0087] The battery temperature regulation system 70 is used to cool or heat (also referred to as "warming") the battery 20. The battery temperature regulation system 70 includes a heater 72, a radiator 75, a reservoir tank 76, and a pump 77. The battery temperature regulation system 70 is connected to the battery 20 via a hose. This forms a flow path through which a coolant circulates. The coolant in the battery temperature regulation system 70 is, for example, water or oil. The battery temperature regulation system 70 cools the battery 20 by circulating the coolant through the flow path. The coolant heated by the battery 20 is cooled by dissipating heat in the radiator 75. The cooling air from the cooling fan 68 also serves to cool the coolant inside the radiator 75. The heater 72 heats the coolant, thereby increasing the temperature of the battery 20. This makes it possible to prevent a decrease in the charge / discharge performance of the battery 20, even in a low-temperature environment where the outside air temperature is, for example, below 0°C.

[0088] The operation of the cooling system 60 and the battery temperature regulation 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 regulation system 70 based on the temperature of the battery 20 measured by the temperature sensor 24. The electric ECU 62 may control the battery temperature regulation system 70 based on the measurement value of a temperature sensor 25 that is provided in the work vehicle 10 and measures the outside air temperature, in addition to the measurement value of the temperature sensor 24.

[0089] The coolant flow paths in the cooling system 60 and the battery temperature regulation system 70 are not limited to the illustrated flow paths and can be modified as appropriate. The cooling method in the cooling system 60 and the battery temperature regulation system 70 is not limited to water cooling or oil cooling, and air cooling may also be used. Alternatively, the refrigerant used in an air conditioner may be used instead of the above-mentioned coolant.

[0090] Next, an example of the configuration of a charging circuit that switches between normal charging and rapid charging will be described.

[0091] FIG. 8 is a circuit diagram showing an example configuration of a charging circuit. The charging circuit 700 shown in FIG. 8 is a circuit that enables rapid charging in accordance with the NACS standard. The charging circuit 700 includes a pair of power pins 710a, 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 FIG. 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 charging and rapid charging of the battery 20. Charging control is performed through communication between the charging circuit and a charging station.

[0092] When rapid charging is performed, a relatively high DC voltage (e.g., 450 V) is applied to the pair of power pins 710 a, 710 b. Supplying high-voltage DC power to the OBC 81 may cause the OBC 81 to malfunction. To avoid this, the charging circuit 700 of this embodiment is provided with a relay circuit 720. During rapid charging, the controller 750 brings the contact 721 a of the relay circuit 720 into contact with the contact 721 b and closes the contactor 730, thereby supplying DC power supplied from an external DC power source to the battery 20. During normal charging, the controller 750 brings the contact 721 a of the relay circuit 720 into contact with the contact 721 c and opens the contactor 730, thereby inputting AC power supplied from an external AC power source to the OBC 81. The controller 750 controls the OBC 81 to convert AC power into DC power and supply the DC power to the battery 20. In this way, a relatively simple circuit such as the relay circuit 720 can reliably prevent high-voltage DC power from being supplied to the OBC 740 during fast charging.

[0093] 4. Control of the Electric Motor A typical agricultural machine equipped with an internal combustion engine is provided with a transmission and a clutch for shifting gears in the transmission. In an electric work vehicle, the output shaft of the electric motor may be connected to the transmission via a clutch, for example, to enable smooth starting and stopping of the work machine or to protect the PTO shaft from a high workload. On the other hand, in cases where an electric motor for travel and an electric motor for work are provided independently, as in the electric work vehicle of this embodiment, the output shaft of the electric motor may be directly connected to the transmission without a clutch. However, in this embodiment, strictly speaking, the output shaft of the electric motor may be connected to the transmission via a reducer.

[0094] In this embodiment, speed control or torque control can be applied to the drive control of the electric motor. Speed ​​control is motor control based on a rotational speed command value determined in accordance with the accelerator operation amount (e.g., accelerator pedal depression angle). On the other hand, torque control is motor control based on a torque command value determined in accordance with the accelerator operation amount.

[0095] When motor control is performed using speed control, if the rotational speed command value indicates 0 revolutions per minute (rpm) under speed control after the work vehicle has stopped, the transmission in the driving powertrain may not shift into gear. As described above, the output shaft of the electric motor is constantly connected to the transmission. Therefore, when shifting gears from a disengaged state to an engaged state, assistance is required to slightly rotate the transmission shaft so that one of the pair of gears can clear the chamfered portion at the end of the tooth flank of the other gear. As a result, if the rotational speed command value is set to 0 rpm under speed control after the work vehicle has stopped, interference may occur between the motor speed control and the gear shift operation. In other words, when the work vehicle stops and the actual measured value of the electric motor rotational speed becomes zero, the torque command value in the torque control for maintaining the rotational speed at zero may have a non-zero value. However, the magnitude of the non-zero torque command value in the control operation for maintaining the rotational speed at zero may be at a level that makes it impossible to change the gear ratio of the transmission. In such a state, it can be difficult for the user to operate the transmission. Therefore, in a work vehicle in which the electric motor for driving and the transmission are connected without a clutch, a technology is desired that reduces or prevents interference between motor speed control and the operation of shifting gears.

[0096] The work vehicle in this embodiment includes a travel device, an electric motor that drives the travel device, a transmission connected to the output shaft of the electric motor, and a control device that controls the electric motor. After detecting a stop of the vehicle, the control device controls the electric motor so that the torque of the electric motor is equal to or less than a torque threshold that enables gear switching of the transmission. The electric motor may be a first electric motor for travel. The work vehicle may further include a PTO shaft that supplies power to the work equipment, and a second electric motor that drives the PTO shaft. In this embodiment, stopping the vehicle mainly means stopping to operate the transmission.

[0097] The motor control method in this embodiment can be applied when the output shaft of the electric motor is connected to the transmission without a clutch. When the work vehicle is equipped with one electric motor, the control device is configured to, after detecting a stop of the vehicle, control the electric motor so that the torque of the electric motor is equal to or less than a torque threshold value that enables gear shifting in the transmission. When the work vehicle is equipped with multiple electric motors, including a motor for travel and a motor for work, the control device is configured to, after detecting a stop of the vehicle, control the motor for travel so that the torque of at least the motor for travel among the multiple electric motors is equal to or less than a torque threshold value that enables gear shifting in the transmission.

[0098] The control device generates a torque command value or a rotational speed command value based on the actual current value or the actual rotational speed, and controls the torque and rotational speed of the electric motor, for example, by vector control. Vector control is a method of decomposing the current flowing through the electric motor into a current component that contributes to torque generation and a current component that contributes to magnetic flux generation, and independently controlling each of the mutually orthogonal current components. This method is not limited to vector control, and other closed-loop control methods may also be used. The actual current value is detected by a current sensor such as a shunt resistor. The actual rotational speed is detected based on sensor data indicating the rotational angle of the motor rotor output from an angle sensor such as a resolver or Hall IC, or may be detected by a speed sensor.

[0099] The control device may include one or more processors and one or more memories that store programs for controlling the operation of the one or more processors. After detecting a stop of the vehicle, the one or more processors execute a process for controlling the electric motor so that the torque of the electric motor is equal to or less than a torque threshold value in accordance with the program.

[0100] According to the work vehicle of this embodiment, after a stop of the vehicle is detected, a torque command value or a rotational speed command value is generated so that the torque of the electric motor for traveling is equal to or less than a torque threshold value that enables gear shifting of the transmission. This makes it possible to reduce or prevent interference that may occur between motor speed control and the operation of shifting gears. This can make it easier for the user to operate, for example, the auxiliary transmission.

[0101] FIG. 9 is a block diagram showing an example configuration of a power transmission system for traveling. The power transmission system 34A in the example of FIG. 9 includes a speed reducer 101, an auxiliary transmission 102, and a differential brake 103 equipped with a differential gear and a brake mechanism. The auxiliary transmission 102 may be connected directly or indirectly to the output shaft OS of the first electric motor 30A. In the example shown, the auxiliary transmission 102 is connected to the output shaft OS of the first electric motor 30A via the speed reducer 101. In this way, the auxiliary transmission 102 in this embodiment is connected to the output shaft OS of the first electric motor 30A without via a clutch.

[0102] 10 is a flowchart showing the procedure for controlling the drive of the electric motor when the work vehicle is stopped. The control device in this embodiment controls the drive of the motor by speed control while the work vehicle is traveling. However, speed control is just one example, and the control device may also perform torque control.

[0103] A motor control method for controlling an electric motor that drives a traveling device of a work vehicle is implemented in a computer according to the processing procedure shown in Fig. 10. An example of controlling the first electric motor 30A for traveling is shown below.

[0104] When the first electric motor 30A for traveling is activated (step S101), the control device begins monitoring the traveling state of the work vehicle while the work vehicle is traveling. When the control device detects that the work vehicle has stopped (YES in step S102), it proceeds to the next process (step S103). For example, the control device determines whether the work vehicle has stopped based on the actual rotational speed of the rotor of the first electric motor 30A. The control device waits until it detects that the work vehicle has stopped (NO in step S102).

[0105] In this embodiment, when the control device detects that the work vehicle has stopped, it waits until a predetermined time (e.g., several seconds) has elapsed. The control device controls the motor using speed control while the vehicle is not stopped, in other words, while the vehicle is moving. When the control device detects that the vehicle has stopped, it switches motor control from speed control to torque control and can perform control to set the torque command value to zero. The control device can, for example, refer to a table that defines the correspondence between the accelerator pedal operation amount and the rotational speed command value and determine the rotational speed command value in accordance with the accelerator pedal operation amount. Similarly, the control device can, for example, refer to a table that defines the correspondence between the accelerator pedal operation amount and the torque command value and determine the torque command value in accordance with the accelerator pedal operation amount. The rotational speed command value or torque command value relative to the accelerator pedal operation amount can vary depending on the motor characteristics. The table is stored in a memory provided in the control device.

[0106] After a predetermined time has elapsed, the control device controls the driving of the first electric motor 30A so that the motor torque determined from the actual current value becomes equal to or less than the torque threshold value (step S103). The torque threshold value is a torque value that enables gear switching of the auxiliary transmission 102. The torque threshold value can be determined appropriately depending on the characteristics of the motor, transmission, and other devices. The torque threshold value is, for example, zero. For example, to stop the vehicle, the control device can set the rotational speed command value under speed control to 0 rpm, and after the actual rotational speed of the motor becomes 0 rpm, switch the motor control from speed control to torque control. After a predetermined time has elapsed, the control device can set the torque command value under torque control to a value equal to or less than the torque threshold value.

[0107] The control device may continue speed control even after detecting that the work vehicle has stopped. In other words, the control device does not need to switch motor control from speed control to torque control. In this case, by setting the upper limit of the torque value under speed control to essentially zero, the control device can control the drive of the first electric motor 30A so that the motor torque becomes zero. In other words, the control device can control the drive of the first electric motor 30A so that no motor torque is generated.

[0108] In this way, in a configuration in which the transmission is connected to the output shaft of the motor without a clutch, it is possible to reduce or prevent interference that may occur between motor speed control and gear engagement, which may make it easier for the user to operate, for example, the auxiliary transmission when the vehicle is stopped.

[0109] The control device then continues to monitor the traveling state of the work vehicle. If the control device detects movement of the work vehicle while controlling the first electric motor 30A so that the motor torque is equal to or less than the torque threshold value (YES in step S104), the control device proceeds to the next process (step S105). For example, the control device determines whether the work vehicle is moving or traveling based on the actual rotational speed of the rotor of the first electric motor 30A.

[0110] In this embodiment, when the control device detects rotation of the first electric motor 30A while controlling the first electric motor 30A so that the motor torque is equal to or less than the torque threshold, the control device switches the control of the first electric motor 30A so that the motor torque is greater than the torque threshold (step S105). In other words, the control device controls the drive of the first electric motor 30A so that the motor torque is generated. Hereinafter, controlling the motor so that no motor torque is generated or so that the motor torque is equal to or less than the torque threshold may be referred to as "torque-off control," and controlling the motor so that the motor torque is generated or so that the motor torque is greater than the torque threshold may be referred to as "torque-on control."

[0111] If the motor torque is maintained at zero after the work vehicle has stopped, for example, a work vehicle stopped on a downhill slope may repeatedly go down the slope and then stop. This phenomenon can be avoided by applying torque-on control to the first electric motor 30A when movement of the work vehicle is detected. For example, the work vehicle can be prevented from going down the slope while stopped on a downhill slope.

[0112] The work vehicle may be equipped with a parking brake. A brake pedal may be included in the pedal group 55, and a brake lever may be included in the switch group 56 (see FIG. 4 ). The combination of the brake pedal and the brake lever may function as the parking brake. If the control device detects rotation of the first electric motor 30A while controlling the first electric motor 30A so that the motor torque is equal to or less than a torque threshold, the control device may issue a warning urging the user to apply the parking brake. The warning may be realized by emitting sound, light, or vibration using a warning device such as a buzzer, speaker, vibration device, or light-emitting device. Such a warning can prevent the work vehicle from descending a slope, for example, by urging the user to apply the parking brake when there is a possibility that the work vehicle will descend a slope.

[0113] A work vehicle may be equipped with a meter panel having a display that displays various information related to the work vehicle. An example of a meter panel is the meter panel unit 54 shown in FIG. 4. The control device may cause the display to display a warning message urging the user to apply the parking brake. In this case, the display functions as the warning device described above. The warning message may include, for example, a message saying, "Apply the parking brake immediately." Such a warning message may be displayed as a pop-up on the display that is displaying various information related to the work vehicle.

[0114] The work vehicle may be equipped with an electric parking brake. The electric parking brake may be configured to be activated by operating a switch, button, or lever included in the switch group 56 shown in FIG. 4. The control device may activate the electric parking brake when rotation of the first electric motor 30A is detected while the control device is controlling the first electric motor 30A so that the motor torque is equal to or less than a torque threshold. This makes it possible to automatically activate the parking brake when, for example, there is a possibility that the work vehicle will descend a slope.

[0115] When the control device detects rotation of the first electric motor 30A (YES in step S104), it switches the control of the first electric motor 30A so that the motor torque is greater than the torque threshold value (step S105), and when it detects that rotation of the first electric motor 30A has stopped (YES in step S102), it switches the control of the first electric motor 30A so that the motor torque is equal to or less than the torque threshold value (step S103). In this way, when the control device detects movement of the work vehicle and is applying torque-on control to the first electric motor 30A, if it again detects that the work vehicle has stopped, it can apply torque-off control to the first electric motor 30A.

[0116] The control device repeatedly executes the processes of steps S102 to S105 while monitoring the running state of the work vehicle until the power source is stopped (step S106).

[0117] By following the procedure for processing to control the drive of such an electric motor, the following examples of control are possible.

[0118] When the work vehicle stops on a slope, the control device applies torque-off control to the first electric motor 30A (step S103), and when the work vehicle begins to descend the slope, the control device may apply torque-on control to the first electric motor 30A (step S105). Thereafter, the control device continues to execute torque-on control until the user operates the transmission, thereby generating motor torque. In this case, the control device may issue a warning urging the user to apply the parking brake, as described above.

[0119] As another example, when the work vehicle stops on a slope, the control device may apply torque-off control to the first electric motor 30A (step S103), and when the work vehicle begins to descend the slope, the control device may apply torque-on control to the first electric motor 30A (step S105). Thereafter, the control device may continue to execute torque-on control until the user operates the transmission, thereby generating a motor torque sufficient to allow the work vehicle to slowly descend the slope.

[0120] As yet another example, when the work vehicle stops on a slope, the control device may apply torque-off control to the first electric motor 30A (step S103), and when the work vehicle starts to descend the slope, the control device may apply torque-on control to the first electric motor 30A (step S105). Thereafter, when the work vehicle stops again, the control device may apply torque-off control to the first electric motor 30A (step S103). In this case, the control device continues to maintain torque-off control, allowing the work vehicle to descend the slope. Alternatively, while the control device is applying torque-off control to the first electric motor 30A (step S103), when the work vehicle starts to descend the slope, the control device may apply torque-on control to the first electric motor 30A (step S105). By repeating these processes, the control device can cause the work vehicle to repeatedly move a short distance and then come to a stop.

[0121] The systems in the above embodiments can also be retrofitted to work vehicles that do not have these functions. Such systems can be manufactured and sold independently of the work vehicle. The computer programs used in such systems can also be manufactured and sold independently of the work vehicle. The computer programs can be provided, for example, by being stored on a computer-readable non-transitory storage medium. The computer programs can also be provided by downloading via a telecommunications line (for example, the Internet).

[0122] The present invention can be applied to electric work vehicles such as agricultural tractors and construction vehicles that are equipped with an electric motor for driving.

[0123] REFERENCE SIGNS LIST 10...Work vehicle, 11...Vehicle body, 12...Front frame, 13...Transmission case, 14...Wheels, 14F...Front wheels, 14R...Rear wheels, 15F...Front axle, 15R...Rear axle, 16...Storage 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...ROPS frame, 52...Driver's seat, 53...Steering wheel, 54...Meter panel unit, 55...Pedals, 56...Switches, 57...Charging inlet, 58...Power conversion device 60...Cooling system for high-pressure equipment, 61...Main ECU, 62...Electric ECU, 63...Charging ECU, 64...Relay, 65...Radiator for high-pressure 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...On-board charger (OBC), 82...DC-DC converter, 83...Relay circuit, 84...Auxiliary equipment

Claims

1. A work vehicle comprising: a traveling device; an electric motor that drives the traveling device; a transmission connected to the output shaft of the electric motor; and a control device that controls the electric motor, wherein the control device is configured to, after detecting a stop of the vehicle, control the electric motor so that the torque of the electric motor becomes equal to or less than a torque threshold that enables gear switching of the transmission.

2. The work vehicle of claim 1, wherein the torque threshold is zero.

3. A work vehicle as described in claim 1 or 2, wherein the control device includes one or more processors and one or more memories that store programs that control the operation of the one or more processors, and the one or more processors control the electric motor in accordance with the programs after detecting a stop of the vehicle so that the torque of the electric motor is equal to or less than the torque threshold value.

4. A work vehicle as described in claim 1 or 2, wherein when rotation of the electric motor is detected while the control device is controlling the electric motor so that the torque of the electric motor is equal to or less than the torque threshold value, the control device switches control of the electric motor so that the torque of the electric motor is greater than the torque threshold value.

5. A work vehicle as described in claim 4, wherein the control device detects rotation of the electric motor, switches control of the electric motor so that the torque of the electric motor is greater than the torque threshold, and then, when it detects that rotation of the electric motor has stopped, switches control of the electric motor so that the torque of the electric motor is equal to or less than the torque threshold.

6. A work vehicle as described in claim 1 or 2, which is equipped with a parking brake, and wherein the control device issues a warning to prompt a user to use the parking brake when rotation of the electric motor is detected while the control device is controlling the electric motor so that the torque of the electric motor is equal to or less than the torque threshold value.

7. A work vehicle as described in claim 6, further comprising a meter panel having a display that displays various information related to the work vehicle, and wherein the control device causes the display to display a warning message urging the user to apply the parking brake.

8. A work vehicle as described in claim 1 or 2, which is equipped with an electric parking brake, and wherein the control device activates the electric parking brake when rotation of the electric motor is detected while controlling the electric motor so that the torque of the electric motor is equal to or less than the torque threshold value.

9. A work vehicle according to claim 1 or 2, wherein the electric motor is a first electric motor, and the work vehicle comprises: a PTO shaft that supplies power to a work implement; and a second electric motor that drives the PTO shaft.

10. A work vehicle according to claim 1 or 2, wherein the transmission is connected to the output shaft of the electric motor without a clutch.

11. A motor control method implemented in a computer for controlling an electric motor that drives a traveling device of a work vehicle, the motor control method comprising: determining whether the vehicle has stopped; and, when it is determined that the vehicle has stopped, controlling the electric motor so that the torque of the electric motor is equal to or less than a torque threshold that enables gear shifting in a transmission of the work vehicle.

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