Drive system, work vehicle, control method, and computer program

Abstract

A drive system for a work vehicle according to an embodiment comprises: a first electric motor for generating driving force for propelling a work vehicle; a second electric motor for generating driving force for rotating a PTO shaft; a battery for supplying electric power to the first and second electric motors; and a control device for controlling the operation of the first and second electric motors. Control modes for controlling the first and second electric motors include a first mode, in which a restriction is placed which restricts a total power, which is the sum of the power supplied to the first electric motor and the power supplied to the second electric motor, to or below a first upper limit value, and a second mode, in which the restriction is lifted. When a predetermined condition is satisfied while the first and second electric motors are being controlled in the first mode, the control device controls the first and second electric motors by switching the control mode from the first mode to the second mode.

Description

Drive system, work vehicle, control method and computer program

[0001] The present invention relates to a drive system, a work vehicle, a control method, and a computer program.

[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] There is a demand for appropriate control of the outputs of multiple electric motors equipped in electric work vehicles.

[0007] The present disclosure provides the solutions described in the following items.

[0008] [Item 1] A drive system for a work vehicle, comprising: a first electric motor that generates a drive force for propelling the work vehicle; a second electric motor that generates a drive force for rotating a PTO (Power Take Off) shaft; a battery that supplies power to the first and second electric motors; and a control device that controls operation of the first and second electric motors, wherein the control modes in which the control device controls the first and second electric motors include a first mode in which a limit is imposed on total power, which is the sum of power supplied to the first electric motor and power supplied to the second electric motor, so that the total power is equal to or less than a first upper limit value, and a second mode in which the limit is lifted, and wherein when a predetermined condition is satisfied while the control device is controlling the first and second electric motors in the first mode, the control mode is switched from the first mode to the second mode to control the first and second electric motors.

[0009] According to one embodiment of the present invention, the control modes of the first and second electric motors include a first mode in which a limit is imposed to keep the total electric power at or below a first upper limit value, and a second mode in which the limit is lifted. If a predetermined condition is satisfied while the first and second electric motors are being controlled in the first mode, the control mode is switched from the first mode to the second mode. By limiting the total electric power to a low level during normal operation, power consumption and the load on various components of the work vehicle can be reduced, while the output of the first and second electric motors can be increased when necessary.

[0010] [Item 2] The drive system according to item 1, wherein the control device counts a time during which the first and second electric motors are controlled in the second mode, and when the counted time reaches a first predetermined time, switches the control mode from the second mode to the first mode and controls the first and second electric motors.

[0011] [Item 3] The drive system according to item 1 or 2, further comprising a first switch that accepts operation by a user to turn on the second mode, wherein when the control device detects operation of the first switch by the user while controlling the first and second electric motors in the first mode, the control device switches the control mode from the first mode to the second mode and controls the first and second electric motors.

[0012] [Item 4] The drive system according to Item 3, wherein the control device maintains control of the first and second electric motors in the first mode while not detecting operation of the first switch by the user.

[0013] [Item 5] The drive system according to item 1 or 2, further comprising a second switch that accepts a user operation to turn on the second mode when the total electric power reaches the first upper limit value, wherein the control device detects an operation of the second switch by the user while controlling the first and second electric motors in the first mode, and when the total electric power reaches the first upper limit value, switches the control mode from the first mode to the second mode to control the first and second electric motors.

[0014] [Item 6] The drive system according to Item 5, wherein even when the control device detects an operation of the second switch by the user, the control device maintains control of the first and second electric motors in the first mode while the total electric power does not reach the first upper limit value.

[0015] [Item 7] The drive system according to Item 5 or 6, wherein the control device maintains control of the first and second electric motors in the first mode while not detecting operation of the second switch by the user.

[0016] [Item 8] The drive system according to item 1 or 2, wherein, when the total electric power reaches the first upper limit value while the control device is controlling the first and second electric motors in the first mode, the control device switches the control mode from the first mode to the second mode to control the first and second electric motors.

[0017] [Item 9] The drive system according to item 8, wherein the control device maintains control of the first and second electric motors in the first mode when the total electric power is less than the first upper limit value.

[0018] [Item 10] The drive system according to item 8 or 9, wherein when the control mode is switched from the first mode to the second mode, the control device increases the total electric power so that the rotation speed of at least one of the first and second electric motors can be maintained at a target rotation speed.

[0019] [Item 11] The drive system according to any one of Items 1 to 10, wherein the control device maintains control of the first and second electric motors in the first mode until a second predetermined time has elapsed after switching the control mode from the second mode to the first mode.

[0020] [Item 12] The drive system according to Item 11, further comprising a display device that displays information about the work vehicle, wherein the control device causes the display device to display information indicating that the first and second electric motors will not be controlled in the second mode until the second predetermined time has elapsed after switching the control mode from the second mode to the first mode.

[0021] [Item 13] The drive system according to any one of Items 1 to 12, wherein when the control mode is switched from the first mode to the second mode, the control device increases the electric power supplied to the first electric motor at different rates from the rate at which the electric power supplied to the second electric motor is increased.

[0022] [Item 14] The drive system according to any one of Items 1 to 13, wherein when the control mode is switched from the first mode to the second mode, the control device prioritizes increasing the electric power supplied to the second electric motor over the electric power supplied to the first electric motor.

[0023] [Item 15] The drive system according to any one of Items 1 to 14, wherein the control device reduces the total electric power at a slower pace when the control mode is switched from the second mode to the first mode than when the control mode is switched from the first mode to the second mode.

[0024] [Item 16] The drive system according to any one of items 1 to 15, wherein the control device sets the upper limit value of the total electric power in the second mode to a second upper limit value that is greater than the first upper limit value.

[0025] [Item 17] The drive system according to Item 2, wherein the first predetermined time is not less than 3 seconds and not more than 60 seconds.

[0026] [Item 18] The drive system according to Item 11, wherein the second predetermined time is not less than 3 seconds and not more than 60 seconds.

[0027] [Item 19] The drive system according to any one of Items 1 to 18, wherein the work vehicle is a mobile agricultural machine.

[0028] [Item 20] The drive system according to any one of items 1 to 19, wherein the work vehicle is a tractor.

[0029] [Item 21] A work vehicle equipped with the drive system according to any one of items 1 to 18.

[0030] [Item 22] A control method for controlling the operation of a work vehicle, executed by one or more computers, wherein the work vehicle comprises: a first electric motor that generates a driving force for propelling the work vehicle; a second electric motor that generates a driving force for rotating a PTO (Power Take Off) shaft; and a battery that supplies power to the first and second electric motors; control modes for controlling the first and second electric motors include a first mode in which a limit is imposed on total power, which is the sum of power supplied to the first electric motor and power supplied to the second electric motor, to be equal to or less than a first upper limit value, and a second mode in which the limit is lifted; and the control method includes: when a predetermined condition is satisfied while the first and second electric motors are being controlled in the first mode, switching the control mode from the first mode to the second mode to control the first and second electric motors.

[0031] [Item 23] A computer program that causes one or more computers to execute a process for controlling the operation of a work vehicle, wherein the work vehicle comprises: a first electric motor that generates a driving force for propelling the work vehicle; a second electric motor that generates a driving force for rotating a PTO (Power Take Off) shaft; and a battery that supplies power to the first and second electric motors; control modes for controlling the first and second electric motors include a first mode in which a limit is imposed on total power, which is the sum of power supplied to the first electric motor and power supplied to the second electric motor, to be equal to or less than a first upper limit value, and a second mode in which the limit is lifted; and the computer program that causes the one or more computers to execute the following process: when a predetermined condition is satisfied while the first and second electric motors are being controlled in the first mode, the control mode is switched from the first mode to the second mode to control the first and second electric motors.

[0032] [Item 24] A computer-readable non-transitory storage medium that stores a computer program that causes one or more computers to execute a process for controlling the operation of a work vehicle, wherein the work vehicle comprises: a first electric motor that generates a driving force for propelling the work vehicle; a second electric motor that generates a driving force for rotating a PTO (Power Take Off) shaft; and a battery that supplies power to the first and second electric motors, and the control modes for controlling the first and second electric motors include a first mode that imposes a limit on total power, which is the sum of power supplied to the first electric motor and power supplied to the second electric motor, to be equal to or less than a first upper limit value, and a second mode that removes the limit, and the computer program causes the one or more computers to switch the control mode from the first mode to the second mode and control the first and second electric motors when a predetermined condition is satisfied while the first and second electric motors are being controlled in the first mode.

[0033] [Item 25] A control device for controlling the operation of a work vehicle, wherein the work vehicle comprises: a first electric motor that generates a driving force for propelling the work vehicle; a second electric motor that generates a driving force for rotating a PTO (Power Take Off) shaft; and a battery that supplies power to the first and second electric motors, and control modes for controlling the first and second electric motors include a first mode in which a limit is imposed on total power, which is the sum of power supplied to the first electric motor and power supplied to the second electric motor, to be equal to or less than a first upper limit value, and a second mode in which the limit is lifted, the control device comprises: one or more processors; and one or more memories, wherein a computer program that causes the one or more processors to execute the following when a predetermined condition is satisfied while the first and second electric motors are being controlled in the first mode, is stored in the one or more memories.

[0034] [Item 26] A control system for controlling the operation of a work vehicle, wherein the work vehicle comprises: a first electric motor that generates a driving force for propelling the work vehicle; a second electric motor that generates a driving force for rotating a PTO (Power Take Off) shaft; and a battery that supplies power to the first and second electric motors; control modes for controlling the first and second electric motors include a first mode in which a limit is imposed on total power, which is the sum of power supplied to the first electric motor and power supplied to the second electric motor, to be equal to or less than a first upper limit value, and a second mode in which the limit is lifted; and the control system comprises means for switching the control mode from the first mode to the second mode and controlling the first and second electric motors when a predetermined condition is satisfied while the first and second electric motors are being controlled in the first mode.

[0035] 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.

[0036] According to one embodiment of the present invention, the control modes of the first and second electric motors include a first mode in which a limit is imposed to keep the total power at or below a first upper limit value, and a second mode in which the limit is lifted. If a predetermined condition is satisfied while the first and second electric motors are being controlled in the first mode, the control mode is switched from the first mode to the second mode. By limiting the total output to a low level during normal operation, power consumption and the load on various components of the work vehicle can be reduced, while the output of the first and second electric motors can be increased when necessary.

[0037] 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 a drive system equipped in a work vehicle. FIG. 10 is a flowchart showing an example of control of a first electric motor and a second electric motor. FIG. 11 is a diagram showing an example of changes in the upper limit value of total power when the control mode is switched between a first mode and a second mode. FIG. 12 is a flowchart showing another example of control of the first electric motor and the second electric motor. FIG. 13 is a flowchart showing yet another example of control of the first electric motor and the second electric motor.

[0038] 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.

[0039] 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.

[0040] (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."

[0041] 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."

[0042] 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.

[0043] 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).

[0044] 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.

[0045] 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.

[0046] 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."

[0047] 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).

[0048] "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.

[0049] (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.

[0050] 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."

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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 change device) and a rear wheel differential device (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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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."

[0060] 2. Specific Example of Work Vehicle Next, a more specific example of the configuration of the work vehicle 10 will be described.

[0061] 2 and 3 are side and top views of work vehicle 10 according to an exemplary embodiment of the present invention.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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."

[0066] 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.

[0067] 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.

[0068] 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."

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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 .

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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."

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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).

[0091] 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.

[0092] 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.

[0093] 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."

[0094] 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.

[0095] 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 of 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 refrigerant inside the radiator 65. The cooling air promotes heat dissipation from the radiator 65 .

[0096] 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 low-temperature environments where the outside air temperature is, for example, below 0 degrees Celsius (°C).

[0097] 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.

[0098] 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.

[0099] Next, an example of the configuration of a charging circuit that switches between normal charging and rapid charging will be described.

[0100] 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.

[0101] 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.

[0102] 4. Electric Motor Output Control Next, an example of control of the outputs of the first electric motor 30A and the second electric motor 30B will be described.

[0103] Fig. 9 is a block diagram showing an example of a drive system 100 provided in a work vehicle 10. The control device 110 shown in Fig. 9 is a control unit including a main ECU 61 and an electric motor ECU 62. The control device 110 may further include a charging ECU 63 and / or other ECUs. The control device 110 controls the operation of the first electric motor 30A and the second electric motor 30B.

[0104] The current sensor 121 and the voltage sensor 122 are provided at any position on the electrical path between the battery 20 and the first electric motor 30A. The current sensor 121 and the voltage sensor 122 are also provided at any position on the electrical path between the battery 20 and the second electric motor 30B. The control device 110 can calculate the power supplied to the first electric motor 30A and the power supplied to the second electric motor 30B based on the output signals of the current sensor 121 and the voltage sensor 122. The control device 110 may also calculate the power supplied to the first electric motor 30A and the power supplied to the second electric motor 30B based on command values ​​output to the first inverter 35A and the second inverter 35B.

[0105] The control device 110 can control the first and second electric motors 30A and 30B in a plurality of control modes. The plurality of control modes includes a first mode in which a total electric power Wo, which is the sum of the electric power supplied to the first electric motor 30A and the electric power supplied to the second electric motor 30B, is limited to be equal to or less than a first upper limit value W1, and a second mode in which this limitation is lifted.

[0106] In order to reduce power consumption and extend the life of various components of work vehicle 10, first and second electric motors 30A and 30B may be operated with the upper limit value of the output of first and second electric motors 30A and 30B suppressed. On the other hand, during operation of work vehicle 10, there may arise a situation where it is desired to increase the output of first electric motor 30A and / or second electric motor 30B.

[0107] In this embodiment, when a predetermined condition is satisfied while controlling first and second electric motors 30A and 30B in the first mode, control device 110 switches the control mode from the first mode to the second mode to control first and second electric motors 30A and 30B. By limiting the total output to a low level during normal operation, power consumption and the load on various components of work vehicle 10 can be reduced, while the output of first electric motor 30A and / or second electric motor 30B can be increased when necessary.

[0108] The boost switch (first switch) 131 is a switch that accepts a user operation to turn on the second mode. For example, when the user presses the boost switch 131, the control device 110 turns on the second mode.

[0109] The boost reservation switch (second switch) 132 is a switch that accepts a user operation to reserve turning on the second mode. For example, when the user presses the boost reservation switch 132, the control device 110 turns on the second mode when the total power Wo reaches the first upper limit value W1. The boost switch 131 and the boost reservation switch 132 may be included in the switch group 56.

[0110] Fig. 10 is a flowchart showing an example of control of the first electric motor 30A and the second electric motor 30B. In the example shown in Fig. 10, the second mode is turned on based on the operation of the boost switch 131 by the user.

[0111] Control device 110 normally controls first and second electric motors 30A and 30B in the first mode (step S101). During normal operation, total electric power Wo is limited to a first upper limit value W1 or less, thereby reducing power consumption and the load on various components of work vehicle 10.

[0112] The control device 110 determines whether or not the user has operated the boost switch 131 (step S102). While the control device 110 does not detect the user's operation of the boost switch 131, it maintains control of the first and second electric motors 30A and 30B in the first mode.

[0113] If the control device 110 determines that the user has operated the boost switch 131, the process proceeds to step S103.

[0114] The control device 110 counts the elapsed time since the previous control in the second mode ended and the control mode was switched from the second mode to the first mode. In step S103, the control device 110 determines whether a second predetermined time or more has elapsed since the previous control in the second mode ended and the control mode was switched from the second mode to the first mode. The second predetermined time is, for example, between 3 and 60 seconds, but is not limited to this value. Note that if control in the second mode has never been performed, it is determined that the second predetermined time has elapsed, and the process proceeds to step S104.

[0115] If the control device 110 determines that the second predetermined time has not elapsed since the previous control in the second mode ended and the control mode was switched from the second mode to the first mode, the control device 110 maintains control of the first and second electric motors 30A and 30B in the first mode. In this case, the control device 110 notifies the user that the second mode will not be turned on (step S107). For example, the control device 110 displays information on the display of the meter panel unit 54 indicating that control in the second mode will not be performed until the second predetermined time has elapsed since the previous control in the second mode ended and the control mode was switched from the second mode to the first mode. For example, the control device 110 displays text information and / or an icon indicating that control in the second mode will not be performed on the display.

[0116] In this embodiment, after the previous control in the second mode ends and the control mode is switched from the second mode to the first mode, control in the second mode is not performed until a second predetermined time has elapsed. By providing such a cool down time, frequent switching on of the second mode is suppressed, and power consumption and the load on various components of the work vehicle 10 can be reduced.

[0117] When the control device 110 determines that a second predetermined time or more has elapsed since the previous control in the second mode ended and the control mode was switched from the second mode to the first mode, the control device 110 switches the control mode from the first mode to the second mode and controls the first and second electric motors 30A and 30B (step S104). The control device 110 sets the upper limit of the total electric power Wo in the second mode to a second upper limit W2 that is greater than the first upper limit W1. By increasing the upper limit of the total electric power Wo in the second mode, the output of the first electric motor 30A and / or the second electric motor 30B can be increased.

[0118] The control device 110 counts the time during which the first and second electric motors 30A and 30B are controlled in the second mode. In step S105, the control device 110 determines whether the counted time has reached a first predetermined time. The first predetermined time is, for example, between 3 and 60 seconds, but is not limited to this value.

[0119] When control device 110 determines that the counted time has reached the first predetermined time, it ends control in the second mode. Control device 110 switches the control mode from the second mode to the first mode and controls first and second electric motors 30A and 30B (step S106). By setting a time limit for control in the second mode in this way, it is possible to reduce power consumption and the load on various components of work vehicle 10.

[0120] When the control mode is switched from the first mode to the second mode, the control device 110 may increase the electric power supplied to the first electric motor 30A at different rates from the rate at which the electric power supplied to the second electric motor 30B is increased. For example, when the control mode is switched from the first mode to the second mode, the electric power supplied to the second electric motor 30B may be increased preferentially over the electric power supplied to the first electric motor 30A. This allows sufficient driving force to be supplied to the work equipment. Furthermore, sudden changes in the traveling speed of the work vehicle 10 can be suppressed.

[0121] 11 is a diagram showing an example of how the upper limit of the total power Wo changes when the control mode is switched between the first mode and the second mode, where the vertical axis represents the upper limit and the horizontal axis represents time.

[0122] 11 , at time T1, the control device 110 switches the control mode from the first mode to the second mode and changes the upper limit of the total electric power Wo from the first upper limit W1 to the second upper limit W2. At time T2, the control device 110 switches the control mode from the second mode to the first mode and changes the upper limit of the total electric power Wo from the second upper limit W2 to the first upper limit W1.

[0123] As shown in FIG. 11, the control device 110 may decrease the upper limit value of the total power Wo when the control mode is switched from the second mode to the first mode at a slower pace than the pace at which the upper limit value of the total power Wo is increased when the control mode is switched from the first mode to the second mode.

[0124] When the control mode is switched from the first mode to the second mode, the upper limit value of the total electric power Wo is quickly increased, thereby quickly responding to the user's request to increase the motor output.

[0125] When the control mode is switched from the second mode to the first mode, the upper limit value of the total power Wo is slowly reduced, thereby preventing the motor output from suddenly decreasing and causing discomfort to the user.

[0126] Next, another example of control of the first electric motor 30A and the second electric motor 30B will be described.

[0127] Fig. 12 is a flowchart showing another example of control of the first electric motor 30A and the second electric motor 30B. In the example shown in Fig. 12, the second mode is turned on based on the operation of the boost reservation switch 132 by the user.

[0128] The control device 110 normally controls the first and second electric motors 30A and 30B in the first mode (step S111). The control device 110 determines whether or not the user has operated the boost reservation switch 132 (step S112). The control device 110 maintains control of the first and second electric motors 30A and 30B in the first mode while it does not detect the user's operation of the boost reservation switch 132.

[0129] If the control device 110 determines that the user has operated the boost reservation switch 132, the process proceeds to step S113.

[0130] In step S113, the control device 110 determines whether the total electric power Wo, which is the sum of the electric power supplied to the first electric motor 30A and the electric power supplied to the second electric motor 30B, has reached a first upper limit W1. Even if the control device 110 detects that the user has operated the boost reservation switch 132, the control device 110 continues to control the first and second electric motors 30A and 30B in the first mode as long as the total electric power Wo has not reached the first upper limit W1. If the control device 110 determines that the total electric power Wo has reached the first upper limit W1, the control device 110 proceeds to the processing of step S114.

[0131] In step S114, the control device 110 determines whether or not a second predetermined time has elapsed since the previous control in the second mode ended and the control mode was switched from the second mode to the first mode. If control in the second mode has never been performed, it is determined that this is equivalent to the second predetermined time having elapsed, and the process proceeds to step S115.

[0132] If the control device 110 determines that the second predetermined time has not elapsed since the previous control in the second mode ended and the control mode was switched from the second mode to the first mode, the control device 110 maintains the control of the first and second electric motors 30A and 30B in the first mode. In this case, the control device 110 notifies the user that the second mode will not be turned on (step S118).

[0133] When the control device 110 determines that a second predetermined time or more has elapsed since the previous control in the second mode ended and the control mode was switched from the second mode to the first mode, the control device 110 switches the control mode from the first mode to the second mode and controls the first and second electric motors 30A and 30B (step S115). The control device 110 sets the upper limit of the total electric power Wo in the second mode to a second upper limit W2 that is greater than the first upper limit W1.

[0134] The control device 110 counts the time during which the first and second electric motors 30A and 30B are controlled in the second mode, and then determines whether the counted time has reached a first predetermined time (step S116).

[0135] When the control device 110 determines that the counted time has reached the first predetermined time, it ends the control in the second mode. The control device 110 switches the control mode from the second mode to the first mode and controls the first and second electric motors 30A and 30B (step S117).

[0136] 12, the motor output can be increased when necessary by the user operating the boost reservation switch 132 in advance. For example, when the load on the work vehicle 10 and / or the work equipment increases and it is desired to increase the motor output, the motor output can be increased.

[0137] Next, another example of control of the first electric motor 30A and the second electric motor 30B will be described.

[0138] Fig. 13 is a flowchart showing another example of the control of the first electric motor 30A and the second electric motor 30B. In the example shown in Fig. 13, if the total electric power Wo reaches the first upper limit value W1 while the first and second electric motors 30A and 30B are being controlled in the first mode, the control mode is switched from the first mode to the second mode to control the first and second electric motors 30A and 30B.

[0139] The control device 110 normally controls the first and second electric motors 30A and 30B in the first mode (step S121). The control device 110 determines whether the total electric power Wo, which is the sum of the electric power supplied to the first electric motor 30A and the electric power supplied to the second electric motor 30B, has reached a first upper limit value W1 (step S122). The control device 110 maintains control of the first and second electric motors 30A and 30B in the first mode while the total electric power Wo is less than the first upper limit value W1. If the control device 110 determines that the total electric power Wo has reached the first upper limit value W1, the control device 110 proceeds to the processing of step S123.

[0140] In step S123, the control device 110 determines whether or not a second predetermined time has elapsed since the previous control in the second mode ended and the control mode was switched from the second mode to the first mode. If control in the second mode has never been performed, it is determined that this is equivalent to the second predetermined time having elapsed, and the process proceeds to step S124.

[0141] If the control device 110 determines that the second predetermined time has not elapsed since the previous control in the second mode ended and the control mode was switched from the second mode to the first mode, the control device 110 maintains the control of the first and second electric motors 30A and 30B in the first mode. In this case, the control device 110 notifies the user that the second mode will not be turned on (step S127).

[0142] When the control device 110 determines that a second predetermined time or more has elapsed since the previous control in the second mode ended and the control mode was switched from the second mode to the first mode, the control device 110 switches the control mode from the first mode to the second mode and controls the first and second electric motors 30A and 30B (step S124). The control device 110 sets the upper limit of the total electric power Wo in the second mode to a second upper limit W2 that is greater than the first upper limit W1.

[0143] The control device 110 counts the time during which the first and second electric motors 30A and 30B are controlled in the second mode, and then determines whether the counted time has reached a first predetermined time (step S125).

[0144] When the control device 110 determines that the counted time has reached the first predetermined time, it ends the control in the second mode. The control device 110 switches the control mode from the second mode to the first mode and controls the first and second electric motors 30A and 30B (step S126).

[0145] 13, total power Wo is limited to a low level during normal operation, thereby reducing power consumption and the load on various components of work vehicle 10, while also allowing motor output to be increased when necessary. For example, when the load on work vehicle 10 and / or work equipment increases and it is desired to increase motor output, motor output can be increased.

[0146] In contrast to control in which the upper limit of total power Wo is always high, in this embodiment, a time limit is set for control in the second mode, which reduces power consumption and the load on various components of work vehicle 10.

[0147] When the control mode is switched from the first mode to the second mode, the control device 110 may increase the total electric power Wo so that the rotation speed of at least one of the first and second electric motors 30A and 30B can be maintained at the target rotation speed. In this embodiment, the upper limit of the total electric power Wo is reduced during control in the first mode to provide a margin in the output of the battery 20. This makes it possible to ensure electric power to maintain the rotation speed at the target rotation speed even when the load on the first electric motor 30A and / or the second electric motor 30B increases.

[0148] The drive system 100 according to this embodiment can also be retrofitted to a work vehicle that does not have these functions. Such a system can be manufactured and sold independently of the work vehicle. The computer program used in such a system can also be manufactured and sold independently of the work vehicle. The computer program can be provided, for example, by being stored on a computer-readable non-transitory storage medium. The computer program can also be provided by downloading via a telecommunications line (for example, the Internet).

[0149] The present invention is particularly useful in the field of electric work vehicles such as agricultural tractors and construction vehicles that are equipped with electric motors for driving.

[0150] 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 DESCRIPTION OF THE SYMBOLS 60...Cooling system for high-voltage equipment, 61...Main ECU, 62...Electric ECU, 63...Charging ECU, 64...Relay, 65...Radiator for high-voltage equipment, 66...Reservoir tank, 67...Pump, 68...Cooling fan, 70...Battery temperature control system, 72...Heater, 75...Battery radiator, 76...Reservoir tank, 77...Pump, 80...Power distribution unit, 81...On-board charger (OBC), 82...DC-DC converter, 83...Relay circuit, 84...Auxiliary equipment, 100...Drive system, 110...Control device, 121...Current sensor, 122...Voltage sensor, 131...Boost switch, 132...Boost reservation switch

Claims

1. A drive system for a work vehicle, comprising: a first electric motor that generates a drive force for propelling the work vehicle; a second electric motor that generates a drive force for rotating a PTO (Power Take Off) shaft; a battery that supplies power to the first and second electric motors; and a control device that controls the operation of the first and second electric motors, wherein the control modes in which the control device controls the first and second electric motors include a first mode in which a limit is imposed on total power, which is the sum of power supplied to the first electric motor and power supplied to the second electric motor, so that the total power is equal to or less than a first upper limit value, and a second mode in which the limit is lifted, and wherein when the control device is controlling the first and second electric motors in the first mode, if a predetermined condition is satisfied, the control device switches the control mode from the first mode to the second mode and controls the first and second electric motors.

2. A drive system as described in claim 1, wherein the control device counts the time during which the first and second electric motors are controlled in the second mode, and when the counted time reaches a first predetermined time, switches the control mode from the second mode to the first mode and controls the first and second electric motors.

3. A drive system as described in claim 1 or 2, further comprising a first switch that accepts operation by the user to turn on the second mode, and when the control device detects operation of the first switch by the user while controlling the first and second electric motors in the first mode, it switches the control mode from the first mode to the second mode and controls the first and second electric motors.

4. The drive system according to claim 3, wherein the control device maintains control of the first and second electric motors in the first mode while it does not detect operation of the first switch by the user.

5. A drive system as described in claim 1 or 2, further comprising a second switch that accepts user operation to turn on the second mode when the total power reaches the first upper limit value, wherein the control device detects operation of the second switch by the user while controlling the first and second electric motors in the first mode, and when the total power reaches the first upper limit value, switches the control mode from the first mode to the second mode to control the first and second electric motors.

6. A drive system as described in claim 5, wherein the control device maintains control of the first and second electric motors in the first mode even when it detects operation of the second switch by the user, as long as the total power does not reach the first upper limit value.

7. The drive system according to claim 5, wherein the control device maintains control of the first and second electric motors in the first mode while it does not detect operation of the second switch by the user.

8. A drive system as described in claim 1 or 2, wherein, when the total electric power reaches the first upper limit value while the control device is controlling the first and second electric motors in the first mode, the control device switches the control mode from the first mode to the second mode and controls the first and second electric motors.

9. The drive system of claim 8, wherein the controller maintains control of the first and second electric motors in the first mode when the total electric power is less than the first upper limit.

10. A drive system according to claim 8, wherein when the control mode is switched from the first mode to the second mode, the control device increases the total electric power so that the rotation speed of at least one of the first and second electric motors can be maintained at a target rotation speed.

11. A drive system as described in claim 1 or 2, wherein the control device maintains control of the first and second electric motors in the first mode until a second predetermined time has elapsed after switching the control mode from the second mode to the first mode.

12. A drive system as described in claim 11, further comprising a display device that displays information about the work vehicle, wherein the control device causes the display device to display information indicating that the first and second electric motors will not be controlled in the second mode until the second predetermined time has elapsed after switching the control mode from the second mode to the first mode.

13. A drive system as described in claim 1 or 2, wherein when the control mode is switched from the first mode to the second mode, the control device increases the power supplied to the first electric motor at different rates from the power supplied to the second electric motor.

14. A drive system as described in claim 1 or 2, wherein when the control mode is switched from the first mode to the second mode, the control device preferentially increases the amount of power supplied to the second electric motor over the amount of power supplied to the first electric motor.

15. A drive system according to claim 1 or 2, wherein the control device reduces the total power when the control mode is switched from the second mode to the first mode at a slower pace than the pace at which the total power is increased when the control mode is switched from the first mode to the second mode.

16. The drive system according to claim 1 or 2, wherein the control device sets the upper limit value of the total electric power in the second mode to a second upper limit value that is greater than the first upper limit value.

17. The drive system according to claim 2, wherein the first predetermined time is greater than or equal to 3 seconds and less than or equal to 60 seconds.

18. The drive system according to claim 11, wherein the second predetermined time is greater than or equal to 3 seconds and less than or equal to 60 seconds.

19. The drive system of claim 1 or 2, wherein the work vehicle is a mobile agricultural machine.

20. The drive system of claim 1 or 2, wherein the work vehicle is a tractor.

21. A work vehicle equipped with a drive system according to claim 1 or 2.

22. A control method executed by one or more computers for controlling the operation of a work vehicle, wherein the work vehicle comprises: a first electric motor that generates driving force for propelling the work vehicle; a second electric motor that generates driving force for rotating a PTO (Power Take Off) shaft; and a battery that supplies power to the first and second electric motors; control modes for controlling the first and second electric motors include a first mode in which a limit is imposed on total power, which is the sum of power supplied to the first electric motor and power supplied to the second electric motor, to be equal to or less than a first upper limit value, and a second mode in which the limit is lifted; and the control method includes: when a predetermined condition is satisfied while the first and second electric motors are being controlled in the first mode, switching the control mode from the first mode to the second mode to control the first and second electric motors.

23. A computer program that causes one or more computers to execute processing for controlling the operation of a work vehicle, wherein the work vehicle comprises: a first electric motor that generates driving force for propelling the work vehicle; a second electric motor that generates driving force for rotating a PTO (Power Take Off) shaft; and a battery that supplies power to the first and second electric motors; control modes for controlling the first and second electric motors include a first mode in which a limit is imposed on total power, which is the sum of power supplied to the first electric motor and power supplied to the second electric motor, to be equal to or less than a first upper limit value, and a second mode in which the limit is lifted; and the computer program that causes the one or more computers to execute the following processing: when a predetermined condition is satisfied while the first and second electric motors are being controlled in the first mode, the control mode is switched from the first mode to the second mode and the first and second electric motors are controlled.

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