Work vehicle, motor control method, and computer program

Abstract

This work vehicle comprises: a steering wheel; a hydraulic power steering device that is mechanically connected to the steering wheel and that has a hydraulic pump; a travel device; a first electric motor that drives the hydraulic pump; a second electric motor that drives the travel device; and a control device that controls the first electric motor and the second electric motor. The control device stops the first electric motor after stopping the second electric motor if stopping the work vehicle, and starts the second electric motor after starting the first electric motor if starting traveling of the work vehicle.

Description

Work vehicle, motor control method, and computer program

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

[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 (CO ２ ) emitted by work vehicles such as tractors used in fields. Different from general automobiles, work vehicles such as tractors need to tow a work implement (agricultural implement) to perform agricultural work such as tilling. Therefore, in order to realize the electrification of work vehicles, there are problems to be solved that are 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.

[0005] Japanese Patent Application Laid-Open No. 2023-66721

[0006] In a conventional work vehicle equipped with an internal combustion engine, consumption of fossil fuel and emission of greenhouse gases are inevitable. On the other hand, in an electric work vehicle, various problems to be solved such as ensuring safety, improving running performance, reducing environmental load, improving convenience, or reducing costs remain.

[0007] This disclosure provides an electric work vehicle capable of solving at least one of these problems.

[0008] This disclosure provides solutions as described in the following items.

[0009] [Item 1] An electric work vehicle comprising: a steering wheel; a hydraulic power steering device having a hydraulic pump and mechanically connected to the steering wheel; a running device; a first electric motor for driving the hydraulic pump; a second electric motor for driving the running device; and a control device for controlling the first electric motor and the second electric motor, wherein the control device stops the second electric motor and then the first electric motor when stopping the work vehicle, and starts the first electric motor and then the second electric motor when starting the work vehicle to run.

[0010] [Item 2] The work vehicle according to Item 1, wherein, while the work vehicle is in motion, the control device starts control to stop the second electric motor in response to a command to stop driving, and after detecting that the rotational speed of the second electric motor is below a first threshold, controls to stop the first electric motor and stops the operation of the hydraulic pump.

[0011] [Item 3] The work vehicle according to item 1 or 2, wherein, while the work vehicle is stopped, the control device starts control to start the first electric motor in response to a command to start driving, and after detecting that the rotational speed of the first electric motor exceeds a second threshold, controls to start the second electric motor to drive the driving device.

[0012] [Item 4] The work vehicle according to Item 1, wherein, while the work vehicle is in motion, the control device starts control to stop the second electric motor in response to a command to stop driving, and when it receives a request to release the command to stop driving before the rotation speed of the second electric motor falls below a first threshold, it releases the control to stop the second electric motor in response to the release request and restarts the second electric motor.

[0013] [Item 5] The work vehicle according to Item 1, wherein, while the work vehicle is in motion, the control device starts control to stop the second electric motor in response to a command to stop driving, detects that the rotational speed of the second electric motor is below a first threshold, and then starts control to stop the first electric motor, and when it receives a request to release the command to stop driving, it releases the control to stop the first electric motor in response to the release request and restarts the first electric motor.

[0014] [Item 6] The work vehicle according to Item 5, wherein the control device restarts the first electric motor in response to the release request, and then, after detecting that the rotational speed of the first electric motor exceeds a second threshold, restarts the second electric motor.

[0015] [Item 7] The work vehicle according to item 4 or 6, wherein the control device restarts the second electric motor in response to the release request and then controls the second electric motor to limit the acceleration of the work vehicle until the rotational speed of the second electric motor reaches a target rotational speed.

[0016] [Item 8] The work vehicle described in any one of items 2, 4, and 5, wherein the first threshold is zero rpm.

[0017] [Item 9] A work vehicle according to any one of items 5 to 7, comprising a driver's seat and a sensor for detecting whether a driver is seated or unseated in the driver's seat, wherein the sensor transmits the command to stop driving to the control device when it detects that the driver has left the seat, and transmits the release request to the control device when it detects that the driver has sat down after detecting that the driver has left the seat.

[0018] [Item 10] The work vehicle according to Item 2, wherein the control device controls the second electric motor to generate torque in the deceleration direction in response to the command to stop the vehicle, thereby stopping the vehicle.

[0019] [Item 11] The work vehicle according to Item 2, wherein the control device, in response to the command to stop driving, causes the second electric motor to regenerate with a predetermined torque to stop the driving device.

[0020] [Item 12] The work vehicle according to Item 2, wherein the control device controls the rotational speed of the second electric motor at a constant deceleration rate in response to the command to stop driving, thereby stopping the driving device.

[0021] [Item 13] The work vehicle according to Item 1, comprising a PTO shaft for supplying power to the work machine, and a third electric motor for driving the PTO shaft, wherein the control device controls the third electric motor, and when stopping the work vehicle, stops the second electric motor and the third electric motor, and then stops the first electric motor.

[0022] [Item 14] The work vehicle according to Item 13, wherein the control device controls the second electric motor and the third electric motor so that the rotational speed of the second electric motor and the rotational speed of the third electric motor decrease in synchronous manner, thereby stopping the second electric motor and the third electric motor.

[0023] [Item 15] 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, wherein the one or more processors execute the process of stopping the second electric motor and then stopping the first electric motor when stopping the work vehicle, and starting the first electric motor and then starting the second electric motor when starting the work vehicle to move, according to the program, the work vehicle as described in Item 1.

[0024] [Item 16] A motor control method executed by a computer for use in a work vehicle comprising a steering wheel, a hydraulic power steering device mechanically connected to the steering wheel and having a hydraulic pump, a running gear, a first electric motor for driving the hydraulic pump, and a second electric motor for driving the running gear, the motor control method comprising: when stopping the work vehicle, stopping the second electric motor and then stopping the first electric motor; and when starting the work vehicle to run, starting the first electric motor and then starting the second electric motor.

[0025] [Item 17] A computer program used for motor control of a work vehicle comprising a steering wheel, a hydraulic power steering device mechanically connected to the steering wheel and having a hydraulic pump, a running gear, a first electric motor for driving the hydraulic pump, and a second electric motor for driving the running gear, wherein the computer causes the computer to: stop the work vehicle by stopping the second electric motor and then stopping the first electric motor; and start the work vehicle by starting the first electric motor and then starting the second electric motor.

[0026] [Item 18] A control device configured to perform the method described in Item 17.

[0027] [Item 19] A computer-readable non-temporary storage medium that stores a computer program containing instructions for causing a computer to perform the method described in Item 17.

[0028] [Item 20] A system comprising the control device described in Item 15, and two or more electric motors.

[0029] [Item 21] A control device for controlling the first and second electric motors mounted on a work vehicle comprising a steering wheel, a hydraulic power steering device mechanically connected to the steering wheel and having a hydraulic pump, a running gear, a first electric motor for driving the hydraulic pump, and a second electric motor for driving the running gear, the control device comprising: stop control means for stopping the second electric motor and then stopping the first electric motor when stopping the work vehicle; and start control means for starting the first electric motor and then starting the second electric motor when starting the work vehicle to travel.

[0030] [Item 22] A system comprising the control device described in Item 21, and two or more electric motors.

[0031] 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. The computer-readable storage media may include volatile storage media or non-volatile storage media. The apparatus may consist of multiple devices. If the 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.

[0032] According to embodiments of this disclosure, an electric work vehicle is provided that can improve the operability of the steering wheel when the work vehicle is stopped or started.

[0033] This is a schematic plan view showing an example of the basic configuration of a work vehicle according to an exemplary embodiment of the present invention. This is a side view of a work vehicle according to an exemplary embodiment of the present invention. This is a top view of a work vehicle according to an exemplary embodiment of the present invention. This is a block diagram showing an example of the main components of a work vehicle and their connection relationships. This is a block diagram showing an example of the configuration of a power converter and its connection to other equipment. This is a block diagram showing an example of the hardware configuration of each ECU. This is a block diagram showing an example of the configuration of a power distribution unit. This is a block diagram showing an example of the connection between the control device and each motor. This is a flowchart showing the procedure for sequence control of a motor according to a first implementation example in an exemplary embodiment of the present invention. This is a flowchart showing the procedure for sequence control of a motor according to a second implementation example in an exemplary embodiment of the present invention. This is a flowchart showing the procedure for sequence control of a motor according to a third implementation example in an exemplary embodiment of the present invention. This is a flowchart showing the procedure for sequence control of a motor according to a fourth implementation example in an exemplary embodiment of the present invention. This is a flowchart showing the procedure for sequence control of a motor according to a fourth implementation example in an exemplary embodiment of the present invention. This is a flowchart showing the procedure for sequence control of a motor according to a fourth implementation example in an exemplary embodiment of the present invention.

[0034] 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.

[0035] 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.

[0036] (Definition of Terms) In this specification, “work vehicle” means a vehicle used for a specific task, such as agricultural work or construction work. “Work” may be, for example, agricultural work, construction work, rubble removal work, or snow removal work. Agricultural work vehicles may be, for example, tractors, combine harvesters, rice transplanters, riding cultivators, vegetable transplanters, vegetable harvesters, mowers, seeders, fertilizer spreaders, sprayers, or broadcasters. 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 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 within a field (or work area), such as tilling, sowing, pest control, fertilizing, planting crops, or harvesting. Construction vehicles perform tasks such as transporting soil, rubble, and other materials at construction sites. These tasks are sometimes referred to as "ground work" or simply "work." When a construction vehicle moves while performing work, it is sometimes referred to as "work driving."

[0037] 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."

[0038] Electric motors can be synchronous motors such as permanent magnet synchronous motors or reluctance motors, or asynchronous motors such as induction motors.

[0039] 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.

[0040] 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 is 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 can be mechanically transmitted from one or more electric motors on the electric work vehicle to the work machine. Such mechanical transmission of driving force can be achieved via a power transmission shaft called a power take-off (PTO) shaft.

[0041] 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.

[0042] 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".

[0043] 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).

[0044] "Memory" is a hardware electronic circuit such as ROM (Read Only Memory) or RAM (Random Access Memory). A part of the memory may be storage media connected to the processor via wiring or a network. These hardware electronic circuits can be implemented by one or more integrated circuits (ICs) or large-scale integrated circuits (LSIs). Each functional unit or block within the electronic circuit, and related components, 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. A computer program (hereinafter sometimes simply referred to as "program") that defines the operation of the processor may be stored in the memory. The program is designed such that the processor executes one or more functions, operations, steps, or processes in the embodiments of the present invention.

[0045] (Embodiment) Hereinafter, several embodiments in which the technology of the present invention is applied to an agricultural electric tractor, which is an example of an electric work vehicle, will be described while referring to the drawings. Various technologies described for the tractor in the following description can also be applied to agricultural machinery other than tractors, construction work vehicles used at construction sites, work vehicles used at disaster sites, snow removal vehicles used in heavy snow areas, and vehicles for transporting goods, etc.

[0046] In the following description, the direction of arrow F in the figure is referred to as "front", the direction of arrow B as "rear", 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".

[0047] <1. Basic Configuration of Work Vehicle> FIG. 1 is a plan view schematically showing 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 agricultural electric tractor. The work vehicle 10 can travel in a field while mounting or towing a work implement and performing farm work according to the type of the work implement. The work vehicle 10 can also travel in the field and outside the field (including roads) with the work implement lifted or without mounting the work implement.

[0048] 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 tires are mounted on the wheels 14. 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 a plurality of wheels (crawlers) equipped with a track instead of wheels with tires.

[0049] The work vehicle 10 in the example shown 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 the 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, for example, called a "bonnet." The front housing is supported by the front frame 12 located at the front of the vehicle body 11.

[0050] 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.

[0051] 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.

[0052] The power of the motor 30 may be used not only for the movement 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 another electric motor 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 the electric powertrain.

[0053] 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.

[0054] 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 electric motors.

[0055] 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."

[0056] <2. Specific Examples of Work Vehicles> Next, we will explain a more specific example of the configuration of work vehicle 10.

[0057] 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.

[0058] 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.

[0059] 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 driving motor and drives the running gear 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.

[0060] The front frame 12 is fitted with a front axle case 17F. The front axle case 17F supports the left and right front wheels 14F. The transmission case 13 includes a 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.

[0061] 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".

[0062] 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.

[0063] The switch group 56 includes various operating devices such as 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.

[0064] 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 the motors 30A and 30B, the charge status of the battery 20, and the temperature of the battery 20. The meter panel unit 54 may be equipped with analog meters and / or a digital display (hereinafter sometimes simply referred to as "display") for displaying this information. The display of the meter panel unit 54 may display a graphical user interface (GUI) that allows the user to perform various setting operations related to the work vehicle 10. The user can perform various settings related to the work vehicle 10 on the display screen using an input device connected to the meter panel unit 54 or an input means such as a touchscreen mounted on the display.

[0065] 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.

[0066] 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 that outputs an AC voltage of, for example, 200V or 100V may be used as the power source. For rapid charging, a DC power source that outputs a DC voltage of, for example, around 350V to 450V may be used as the power source. Rapid charging can be performed using protocols compliant with standards such as CHAdeMO, NACS, CCS1, CCS2, GB / T, or ChaoJi.

[0067] 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 as "external power supply" in this specification. 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.

[0068] 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. As a result, 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.

[0069] <3. System Configuration of the Work Vehicle> 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 related to power transmission, high-voltage drive power, and low-voltage auxiliary power are represented by solid lines of different thicknesses. Connection relationships related to signals (digital signals and analog signals) are represented by dotted lines. Coolant flow is represented by thick dashed lines.

[0070] 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 the traction device to be driven. 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 the hydraulic pump 36 and the PTO shaft 40 to be driven.

[0071] The transmission case 13 houses the power transmission system 34A for driving, the power transmission system 34B for work, and the hydraulic pump 36. The power transmission system 34A for driving may include components such as a reduction gear, a sub-transmission, and a differential. The power transmission system 34A for driving transmits power from the rotation of the first electric motor 30A to the rear wheels 14R. In four-wheel drive mode, the power transmission system 34A for driving also transmits a portion of the power from the rotation of the first electric motor 30A to the front wheels 14F. The power transmission system 34B for work may include components such as a reduction gear, a PTO clutch, and a PTO transmission. The power transmission system 34B for work transmits power from the rotation of the second electric motor 30B to the hydraulic pump 36 and the PTO shaft 40. The PTO shaft 40 supplies power for work to the work implement.

[0072] 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, in addition to the second electric motor 30B that drives the PTO shaft 40, the work vehicle 10 may include other electric motors that drive the other PTO shafts.

[0073] 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 sprayer, or a harrow. Any implement can be connected to the work vehicle 10 and used.

[0074] 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.

[0075] 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.

[0076] 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 the auxiliary components 84, such as each ECU, the meter panel unit 54, the pumps 67, 77, and the air conditioner. The battery 21 may be, for example, a lead-acid battery.

[0077] 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, and a charging ECU 63. The main ECU 61 controls the overall operation of the work vehicle 10 based on signals generated by the user operating the pedal group 55, the switch group 56, and the meter panel unit 54. The electric ECU 62 mainly controls the charging and discharging of the battery 20 and the operation of the electric motors 30A and 30B. The charging ECU 63 communicates with an external charger (external power supply) and performs control to ensure smooth charging by appropriately controlling the relay 64.

[0078] In this embodiment, the combination of the main ECU 61, the electric ECU 62, and the charging ECU 63 functions as a "control device" that controls the operation of the work vehicle 10. Therefore, in the following description, the operations performed by the main ECU 61, the electric ECU 62, and the charging ECU 63 all correspond to operations performed by the "control device". These ECUs can communicate with each other according to a vehicle bus standard such as CAN (Controller Area Network). Instead of CAN, a faster communication method such as on-board Ethernet (registered trademark) may be used. An on-board computer integrating at least some of the functions of the main ECU 61, the electric ECU 62, and the charging ECU 63 may be provided as the "control device". The control device may include ECUs other than the main ECU 61, the electric ECU 62, and the charging ECU 63. Each ECU may be a computing device including one or more processors and one or more memories. Each ECU can perform the operations described later by having the processor execute a computer program stored in the memory.

[0079] The electric ECU 62 sends control signals to the first inverter 35A and the second inverter 35B in response to signals from the pedal group 55 and the switch group 56. The electric ECU 62 can perform motor control based on a rotational speed command value or a torque command value determined, for example, according to the amount of operation of the pedal group 55 by the driver. In this specification, the control based on the former rotational speed command value may be referred to as "speed control".

[0080] The electric ECU 62 controls the switching operation of multiple switch 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 switch element and outputs them to each inverter. The first inverter 35A 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, according to the control signals from the electric ECU 62, and supplies this three-phase AC power to the first electric motor 30A. Similarly, the second inverter 35B 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, according to the control signals from the electric ECU 62, 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.

[0081] 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 the motors 30A and 30B, the charge status of the battery 20, and the status of the power transmission system 34A and the transmission included in 34A on the meter panel unit 54.

[0082] Figure 6 is a block diagram showing an example of the hardware configuration of each ECU. Each ECU 400 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.

[0083] ROM 435 is, for example, writable memory (e.g., PROM), rewritable memory (e.g., flash memory), or read-only memory. ROM 435 stores a program that controls the operation of the processor 434. ROM 435 does not have to be a single recording medium; it may be a collection of multiple recording media. Some of the multiple storage media may be removable memory.

[0084] RAM 436 provides a working area for temporarily unpacking the program stored in ROM 435 at boot time. RAM 436 does not need to be a single recording medium; it may be a collection of multiple recording media.

[0085] External I / F 437 is an interface for connecting to external devices. Communication I / F 438 is an interface for communicating with other electronic devices (e.g., sensors and other ECUs). For example, communication I / F 438 can perform wired communication compliant with various protocols such as CAN or Ethernet®. Communication I / F 438 may also perform wireless communication compliant with wireless communication standards such as Bluetooth® and / or Wi-Fi®.

[0086] The ECU may further include a storage device for storing data generated by the processor 434 for a relatively long period of time. Such a storage device may be, for example, a semiconductor storage device, a magnetic storage device, or an optical storage device, or a combination thereof.

[0087] 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.

[0088] 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 the 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".

[0089] 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 state of the battery 20, such as the input voltage, output voltage, and temperature, and to control the charging and discharging currents to the battery 20 based on these states. The temperature sensor 24 may be configured to measure the temperature of each of the multiple cells contained in the battery 20.

[0090] The work vehicle 10 illustrated in Figure 4 is equipped with a cooling system 60 for high-voltage equipment and a battery temperature control system 70. The cooling system 60 is used to cool equipment to which high voltage is applied (also referred to as "high-voltage equipment"). The cooling system 60 comprises a radiator 65, a reservoir tank 66, a pump 67, and a cooling fan 68. In the example in Figure 4, the cooling system 60 is connected via hoses to the first inverter 35A, the first electric motor 30A, the second electric motor 30B, the second inverter 35B, and the power converter 58 in that order. This forms a flow path through which the coolant circulates. The coolant in the cooling system 60 is, for example, water or oil. The cooling system 60 cools these high-voltage equipment by circulating the coolant through the flow path. The coolant heated by the high-voltage equipment is cooled by heat dissipation in the radiator 65. The cooling fan 68 generates cooling air to cool the coolant inside the radiator 65. The cooling air promotes heat dissipation from the radiator 65.

[0091] 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. This creates 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).

[0092] 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.

[0093] 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.

[0094] <4. Control of Starting and Stopping of Work Vehicles> Work vehicles are equipped with a power steering system to assist the driver's steering force. Power steering systems can greatly improve the stability or comfort of steering operations. There are two types of power steering systems: hydraulic and electric. Hydraulic systems are equipped with a hydraulic pump that is driven by a pump motor (or hydraulic motor). Such systems are called hydraulic power steering systems or hydraulic power steering.

[0095] Electric work vehicles may be equipped with a hydraulic power steering system. Such work vehicles are equipped with a drive motor and a pump motor. Conventionally, when the work vehicle starts, the drive motor and pump motor are started simultaneously, and when the work vehicle stops, the drive motor and pump motor are stopped simultaneously. Such motor control can result in reduced steering wheel operability when the work vehicle starts or stops.

[0096] To solve the above problems, the work vehicle in this embodiment includes a steering wheel, a hydraulic power steering device mechanically connected to the steering wheel and having a hydraulic pump, a running gear, a first electric motor that drives the hydraulic pump, a second electric motor that drives the running gear, and a control device that controls the first electric motor and the second electric motor. The control device is configured or programmed to stop the second electric motor and then the first electric motor when stopping the work vehicle, and to start the first electric motor and then the second electric motor when starting the work vehicle.

[0097] The pump motor and the drive motor mentioned above are examples of the first electric motor and the second electric motor, respectively. Hereafter, the first electric motor and the second electric motor will be referred to as the pump motor and the drive motor, respectively.

[0098] In one embodiment, 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. The one or more processors execute processes according to the program, such as stopping the drive motor and then the pump motor when stopping the work vehicle, and starting the pump motor and then the drive motor when starting the work vehicle.

[0099] The motor control method executed by (or implemented in) the computer in this embodiment is used for a work vehicle comprising a steering wheel, a hydraulic power steering system mechanically connected to the steering wheel and having a hydraulic pump, a running gear, a pump motor for driving the hydraulic pump, and a running motor for driving the running gear. The method includes stopping the running motor and then stopping the pump motor when stopping the work vehicle, and starting the pump motor and then starting the running motor when starting the work vehicle.

[0100] A computer program containing a set of instructions for causing one or more computers to execute the above-described method for controlling the pump motor and the drive motor may be manufactured and sold independently of the work vehicle. The computer program may be provided, for example, by being stored in a computer-readable non-temporary storage medium. The computer program may also be provided by download via a telecommunications line (e.g., the Internet).

[0101] According to the electric work vehicle, motor control method, or computer program of this embodiment, a novel motor control is provided for stopping or starting the pump motor and the drive motor when the work vehicle starts or stops, thereby improving the operability of the steering wheel.

[0102] In this embodiment, the control for stopping or starting two or more motors when a work vehicle is started or stopped is described as "sequence control".

[0103] The work vehicle in this embodiment may optionally include a PTO shaft for supplying power to the work machine and a third electric motor for driving the PTO shaft. The PTO motor mentioned above is an example of the third electric motor. Hereafter, the third electric motor will be referred to as the PTO motor. In this example, the control device may further control the PTO motor and, when stopping the work vehicle, stop the pump motor after stopping the travel motor and the PTO motor. Such control provides a novel sequence control for stopping or starting the pump motor, travel motor and PTO motor when the work vehicle is starting or stopping, thereby improving the operability of the steering wheel and the safety of driving or working.

[0104] Figure 8 is a block diagram showing an example of the connection between the control device and each motor. Strictly speaking, inverters are connected between the control device and each motor, but these are omitted for simplicity.

[0105] The work vehicle 10 shown in Figure 8 comprises a steering wheel 53, a hydraulic power steering system 90 mechanically connected to the steering wheel 53 and having a hydraulic pump 36, a travel device 91, a pump motor 30C that drives the hydraulic pump 36, a travel motor 30A that drives the travel device 91, and a control device 400 that controls the travel motor 30A and the pump motor 30C.

[0106] In this embodiment, the electric ECU 62 shown in Figure 4 can function as a control device 400 that controls the driving motor 30A and the pump motor 30C.

[0107] The control device 400 is configured or programmed to stop the drive motor 30A and then the pump motor 30C when stopping the work vehicle 10, and to start the pump motor 30C and then the drive motor 30A when starting the work vehicle to move.

[0108] In the control system for stopping the work vehicle, the pump motor 30C is assumed to stop before the drive motor 30A. In that case, steering assistance from the hydraulic power steering system 90 is not available, and for example, while the work vehicle is coasting, the operability of the steering wheel temporarily decreases, making it difficult to operate the steering wheel. On the other hand, according to this embodiment, the operation of the pump motor 30C is guaranteed until the drive motor 30A stops and the work vehicle comes to a stop, so steering assistance from the hydraulic power steering system 90 is maintained. Therefore, even if coasting occurs, the driver can continue to operate the steering wheel.

[0109] In this embodiment, stopping the drive motor means that the rotational speed of the drive motor is below a first threshold. The first threshold is, for example, zero rpm (revolutions per minute). In this embodiment, when the rotational speed of the drive motor becomes zero rpm, the work vehicle comes to a complete stop.

[0110] Figure 9 is a flowchart showing the procedure for motor sequence control according to the first implementation example in this embodiment.

[0111] While the work vehicle is in motion, the control device may, in response to a command to stop the vehicle, initiate control to stop the travel motor, and after detecting that the rotational speed of the travel motor is below a first threshold, initiate control to stop the pump motor, thereby stopping the operation of the hydraulic pump.

[0112] In this embodiment, for example, when the ignition switch or starter is turned on and the work vehicle is started, a start-to-travel command is issued. In response to the start-to-travel command, the control device starts the pump motor first among the pump motor and the travel motor (step S101). The control device may apply speed control to the pump motor. In response to the start-to-travel command, the control device may operate the hydraulic pump by controlling the torque of the pump motor to generate torque in the acceleration direction.

[0113] The control device starts the pump motor, and then starts the drive motor (step S102). The control device may apply speed control to the drive motor, similar to the pump motor. The control device may operate the drive system by controlling the torque of the drive motor to generate torque in the acceleration direction.

[0114] This sequence control ensures that the hydraulic pump is already operating when the work vehicle starts moving, providing steering assistance from the hydraulic power steering system while the vehicle is in motion.

[0115] If a command to stop the vehicle is issued while the vehicle is in motion (YES in step S103), the control device starts control to stop the drive motor in response to the command to stop the vehicle (step S104). For example, in response to the command to stop the vehicle, the control device may stop the vehicle by controlling the drive motor to generate torque in the deceleration direction.

[0116] As another example, the control device may, in response to a command to stop travel, regenerate the drive motor with a predetermined torque to stop the travel system. Such control makes it possible to prevent sudden stops of the work vehicle.

[0117] As yet another example, the control device may, in response to a stop command, control the rotational speed of the drive motor at a constant deceleration rate to stop the drive system. Such control makes it possible to stop the vehicle properly, for example, even when the vehicle is traveling downhill.

[0118] Refer again to Figure 8. As shown in Figure 8, the work vehicle 10 may be equipped with a sensor 95 for detecting whether the driver is seated or unseated in the driver's seat. An example of the sensor 95 is a seating sensor. The sensor 95 may be configured to transmit a stop command to the control device 400 when it detects that the driver has left the seat. The sensor 95 may be further configured to transmit a request to release the stop command to the control device 400 when it detects that the driver has sat back in the vehicle after detecting that the driver has left the seat.

[0119] Furthermore, a stop command or a request to release a stop command is not limited to being issued in synchronization with the driver's seating event detected by sensor 95, but may also be issued due to other factors. For example, a stop command may be issued due to the detection of a malfunction in electronic equipment or electronic components installed in the work vehicle. A request to release a stop command may be issued in accordance with a direct request from the user who has confirmed the safety of driving.

[0120] After the control device starts control to stop the drive motor, it detects whether the rotational speed of the drive motor is below a first threshold (step S105). If the control device detects that the rotational speed of the drive motor is below the first threshold (YES in step S105), it performs control to stop the pump motor and stops the operation of the hydraulic pump (step S106). For example, if the control device detects that the rotational speed of the drive motor is below the first threshold, it may control the pump motor to generate torque in the deceleration direction and stop the operation of the hydraulic pump.

[0121] This sequence control ensures that the hydraulic pump continues to operate until the work vehicle comes to a stop, thus providing steering assistance from the hydraulic power steering system until the vehicle comes to a complete halt.

[0122] Figure 10 is a flowchart showing the procedure for sequence control of the motor according to the second implementation example in this embodiment.

[0123] While the work vehicle is stopped, the control device may initiate control to start the pump motor in response to a command to start driving, and after detecting that the rotational speed of the pump motor exceeds a second threshold, it may perform control to start the driving motor to drive the driving device.

[0124] When a command to start driving is issued while the work vehicle is stopped (YES in step S201), the device starts control to start the pump motor in response to the command to start driving (step S202). For example, the control device may operate the hydraulic pump by controlling the torque of the pump motor to generate torque in the acceleration direction.

[0125] The control device detects whether the rotational speed of the pump motor exceeds a second threshold (step S203). The second threshold can be determined, for example, in the range of 1 to 800 rpm. However, the second threshold can be determined appropriately according to the specifications of the work vehicle. When the control device detects that the rotational speed of the pump motor exceeds the second threshold (YES in step S203), it performs control to start the travel motor and drives the travel device (step S204). For example, when the rotational speed of the pump motor exceeds the second threshold, the control device may operate the travel device by controlling the torque of the travel motor to generate torque in the acceleration direction.

[0126] Figure 11 is a flowchart showing the procedure for motor sequence control according to the third implementation example in this embodiment.

[0127] While the work vehicle is in motion, the control device may initiate control to stop the drive motor in response to a command to stop driving, and if it receives a request to release the command to stop driving before the rotational speed of the drive motor reaches zero rpm, it may release the control to stop the drive motor in response to the release request and restart the drive motor.

[0128] If a command to stop travel is issued while the work vehicle is in motion (YES in step S301), the control device starts control to stop the travel motor in response to the command to stop travel (step S302).

[0129] If the control device receives a request to release the drive stop command before the rotation speed of the drive motor reaches zero rpm (NO in step S303) (YES in step S304), it may respond to the release request by releasing the control to stop the drive motor and restarting the drive motor (step S305). On the other hand, if no release request is issued and the rotation speed of the drive motor reaches zero rpm (YES in step S303), the control device stops the pump motor (step S306).

[0130] Figures 12A to 12C are flowcharts showing the procedure for sequence control of the motor according to the fourth implementation example in this embodiment.

[0131] While the work vehicle is in motion, the control device may, in response to a command to stop the vehicle, initiate control to stop the drive motor, and after detecting that the rotational speed of the drive motor is zero rpm, initiate control to stop the pump motor. If it receives a request to release the command to stop the vehicle, it may, in response to the release request, release the control to stop the pump motor and restart the pump motor.

[0132] If a command to stop travel is issued while the work vehicle is in motion (YES in step S401), the control device starts control to stop the travel motor in response to the command to stop travel (step S402).

[0133] The control device detects that the rotational speed of the drive motor is zero rpm (YES in step S403) and then starts control to stop the pump motor (step S404).

[0134] If the control device receives a request to release the stop command after initiating control to stop the pump motor (YES in step S405), it may respond to the release request by releasing the control to stop the pump motor and restarting the pump motor (step S406).

[0135] As shown in Figure 12B, after restarting the pump motor in response to the release request, the control device may restart the drive motor (step S408) after detecting that the rotational speed of the pump motor has exceeded a second threshold (YES in step S407).

[0136] The control device may, after restarting the drive motor in response to a release request, control the drive motor to limit the acceleration of the work vehicle until the drive motor's rotational speed reaches a target rotational speed.

[0137] As shown in Figure 12C, after restarting the drive motor in response to a release request (step S408 in Figure 12B), the control device may control the drive motor to limit the acceleration of the work vehicle until the drive motor's rotational speed reaches a target rotational speed (NO in step S409) (step S410). The target rotational speed may be determined, for example, in the range of 500 to 4000 rpm. However, the target rotational speed may be appropriately determined according to the specifications of the work vehicle. When the drive motor's rotational speed reaches the target rotational speed (YES in step S409), the control device may release the limit on the acceleration of the work vehicle (step S411). The control device may also control the drive motor so that the acceleration limit value smoothly changes according to the difference between the drive motor's rotational speed and the target rotational speed.

[0138] The conditions for acceleration limiting are not limited to comparing the rotational speed of the drive motor with a target rotational speed. For example, the control device may, after restarting the drive motor in response to a release request, control the drive motor to limit the acceleration of the work vehicle until a predetermined time has elapsed. This predetermined time may be, for example, 3 to 10 seconds.

[0139] In addition to the condition in step S409 that the rotational speed of the travel motor reaches the target rotational speed, the control device may also control the travel motor to limit the acceleration of the work vehicle for a predetermined time (for example, several seconds) after restarting the travel motor in response to a release request.

[0140] Refer to Figure 8 again. The work vehicle may further include a PTO shaft 40 that supplies power to the work machine and a PTO motor 30B that drives the PTO shaft 40.

[0141] The control device 400 can control the travel motor 30A, the PTO motor 30B, and the pump motor 30C. When stopping the work vehicle 10, the control device 400 can stop the travel motor 30A and the PTO motor 30B, and then stop the pump motor 30C. For example, the control device 400 can stop the travel motor 30A and the PTO motor 30B by controlling them so that their rotational speeds decrease in synchronously.

[0142] If the work vehicle is allowed to move after the work machine has stopped, the work machine may be dragged. For example, if the work vehicle is allowed to move after a rotary tiller has stopped, the rotary tiller may be dragged, which could result in damage to the tilling tines, for example. As another example, if the work vehicle is allowed to move after a broadcast that requires speed-linked control for fertilization work has stopped, it may result in the wasteful spreading or consumption of fertilizer. To avoid such situations, it is preferable to control the rotational speed of the travel motor 30A and the rotational speed of the PTO motor 30B to decrease in synchronously, and to stop the travel motor 30A and the PTO motor 30B at the same time.

[0143] The present invention is applicable to all types of work vehicles equipped with a drive motor and a hydraulic motor.

[0144] 10...Work vehicle, 11...Body, 12...Front frame, 13...Transmission case, 14...Wheels, 14F...Front wheels, 14R...Rear wheels, 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, 30C...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...Pedal group, 56...Switch group, 57...Charging inlet 58... Power converter, 60... Cooling system for high-voltage equipment, 61... Main ECU, 62... Electric ECU, 63... Charging ECU, 64... Relay, 65... Radiator for high-voltage equipment, 66... ​​Reservoir tank, 67... Pump, 68... Cooling fan, 70... Battery temperature control system, 72... Heater, 75... Radiator for battery, 76... Reservoir tank, 77... Pump, 80... Power distribution unit, 81... Onboard charger (OBC), 82... DC-DC converter, 90... Hydraulic power steering system, 91... Running gear, 95... Seat sensor

Claims

1. An electric work vehicle comprising: a steering wheel; a hydraulic power steering device having a hydraulic pump and mechanically connected to the steering wheel; a running gear; a first electric motor for driving the hydraulic pump; a second electric motor for driving the running gear; and a control device for controlling the first electric motor and the second electric motor, wherein the control device stops the second electric motor and then the first electric motor when stopping the work vehicle, and starts the first electric motor and then the second electric motor when starting the work vehicle to run.

2. The work vehicle according to claim 1, wherein, while the work vehicle is in motion, the control device starts control to stop the second electric motor in response to a command to stop driving, and after detecting that the rotational speed of the second electric motor is below a first threshold, it performs control to stop the first electric motor and stops the operation of the hydraulic pump.

3. The work vehicle according to claim 1 or 2, wherein, while the work vehicle is stopped, the control device initiates control to start the first electric motor in response to a command to start driving, and after detecting that the rotational speed of the first electric motor exceeds a second threshold, it performs control to start the second electric motor to drive the driving device.

4. The work vehicle according to claim 1, wherein, while the work vehicle is in motion, the control device initiates control to stop the second electric motor in response to a command to stop driving, and when it receives a request to release the command to stop driving before the rotation speed of the second electric motor falls below a first threshold, it releases the control to stop the second electric motor in response to the release request and restarts the second electric motor.

5. The work vehicle according to claim 1, wherein, while the work vehicle is in motion, the control device starts control to stop the second electric motor in response to a command to stop driving, detects that the rotational speed of the second electric motor is below a first threshold, and then starts control to stop the first electric motor, and upon receiving a request to release the command to stop driving, the control device releases the control to stop the first electric motor in response to the release request and restarts the first electric motor.

6. The work vehicle according to claim 5, wherein the control device restarts the first electric motor in response to the release request, and then restarts the second electric motor after detecting that the rotational speed of the first electric motor has exceeded a second threshold.

7. The work vehicle according to claim 4 or 6, wherein the control device, after restarting the second electric motor in response to the release request, controls the second electric motor to limit the acceleration of the work vehicle until the rotational speed of the second electric motor reaches a target rotational speed.

8. The work vehicle according to any one of claims 2, 4, and 5, wherein the first threshold is zero rpm.

9. A work vehicle according to claim 5 or 6, comprising a driver's seat and a sensor for detecting whether a driver is seated or unseated in the driver's seat, wherein the sensor transmits the command to stop driving to the control device when it detects that the driver has left the seat, and transmits the release request to the control device when it detects that the driver has sat in the seat after detecting that the driver has left the seat.

10. The work vehicle according to claim 2, wherein the control device controls the second electric motor to generate torque in the deceleration direction in response to the command to stop the vehicle, thereby stopping the vehicle.

11. The work vehicle according to claim 2, wherein the control device, in response to the command to stop the vehicle, causes the second electric motor to regenerate with a predetermined torque to stop the vehicle.

12. The work vehicle according to claim 2, wherein the control device, in response to the command to stop travel, controls the rotational speed of the second electric motor at a constant deceleration rate to stop the travel device.

13. A work vehicle according to claim 1, comprising: a PTO shaft for supplying power to a work machine; and a third electric motor for driving the PTO shaft, wherein the control device controls the third electric motor, and when stopping the work vehicle, stops the second electric motor and the third electric motor, and then stops the first electric motor.

14. The work vehicle according to claim 13, wherein the control device controls the second electric motor and the third electric motor so that the rotational speed of the second electric motor and the rotational speed of the third electric motor decrease in synchronous manner, thereby stopping the second electric motor and the third electric motor.

15. The control device includes one or more processors and one or more memories for storing a program for controlling the operation of the one or more processors, wherein the one or more processors execute the process of stopping the second electric motor and then stopping the first electric motor when stopping the work vehicle, and starting the first electric motor and then starting the second electric motor when starting the work vehicle to move, according to the program, the work vehicle according to claim 1.

16. A motor control method executed by a computer for use in a work vehicle comprising a steering wheel, a hydraulic power steering device mechanically connected to the steering wheel and having a hydraulic pump, a running gear, a first electric motor for driving the hydraulic pump, and a second electric motor for driving the running gear, the motor control method comprising: when stopping the work vehicle, stopping the second electric motor and then stopping the first electric motor; and when starting the work vehicle to run, starting the first electric motor and then starting the second electric motor.

17. A computer program used for motor control of a work vehicle comprising a steering wheel, a hydraulic power steering device mechanically connected to the steering wheel and having a hydraulic pump, a running gear, a first electric motor for driving the hydraulic pump, and a second electric motor for driving the running gear, wherein the computer causes the computer to: stop the second electric motor and then stop the first electric motor when stopping the work vehicle; and start the first electric motor and then start the second electric motor when starting the work vehicle to run.

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