Electric work vehicle, and system and method for controlling electric work vehicle

Abstract

This system for controlling charging of a battery for driving in an electric work vehicle comprises: a temperature sensor for measuring the temperature of the battery; a heater for heating the battery; and a control device for controlling charging of the battery and operation of the heater. When starting charging of the battery, the control device turns on the heater to heat the battery without charging the battery if the temperature of the battery is less than a first threshold value. If the temperature of the battery is greater than or equal to the first threshold value and less than a second threshold value that is greater than the first threshold value, the control device turns on the heater to heat the battery and starts charging the battery. If the temperature of the battery is greater than or equal to the second threshold value, the control device starts charging the battery with the heater off.

Description

Electric work vehicle, system and method for controlling an electric work vehicle

[0001] The present invention relates to an electric work vehicle, and a system and method for controlling an electric work vehicle.

[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] Patent Document 2 discloses a technique for solving the problem of reduced charging efficiency when an electric work vehicle is used in a low-temperature environment (for example, below -10°C), due to a decrease in the maximum charging current that can be passed through the battery. The electric work vehicle disclosed in Patent Document 2 executes temperature rise control to warm the battery until it reaches a target temperature before charging it when the battery temperature is below a set temperature. By raising the battery temperature, the maximum charging current that can be passed through the battery is increased, thereby improving charging efficiency.

[0006] JP 2023-66721 A JP 2023-113437 A

[0007] In a work vehicle equipped with a battery that supplies electric energy to an electric motor, it is required to be able to stably charge and discharge (hereinafter also referred to as "charge and discharge") even in a low-temperature environment, for example, below 0°C.

[0008] The present invention provides an electric work vehicle that is capable of stably charging and discharging a battery even in a low-temperature environment.

[0009] The present disclosure provides the solutions described in the following items.

[0010] [Item 1] A system for controlling charging of a drive battery in an electric work vehicle, comprising: a temperature sensor that measures the temperature of the battery; a heater that warms the battery; and a control device that controls charging of the battery and operation of the heater, wherein when charging of the battery is started, the control device: if the temperature of the battery is below a first threshold, turns on the heater to warm the battery without charging the battery; if the temperature of the battery is equal to or higher than the first threshold and lower than a second threshold that is higher than the first threshold, turns on the heater to warm the battery and start charging the battery; and if the temperature of the battery is equal to or higher than the second threshold, turns off the heater and starts charging the battery.

[0011] [Item 2] The system according to Item 1, further comprising another temperature sensor that measures an outside air temperature, wherein, after the charging is completed, if the outside air temperature is less than a third threshold that is lower than the first threshold, the control device turns on the heater to warm the battery and maintain the temperature of the battery at or above the third threshold.

[0012] [Item 3] The system according to Item 2, wherein the control device acquires information about the time when the charging is completed, and determines whether to maintain the temperature of the battery at or above the third threshold based on the time, or determines a time for which the temperature of the battery is maintained at or above the third threshold.

[0013] [Item 4] The system according to Item 2, wherein the control device determines whether to maintain the temperature of the battery at or above the third threshold, or the time for which the temperature of the battery is maintained at or above the third threshold, further based on the outside air temperature when the charging is completed.

[0014] [Item 5] The system according to any one of items 1 to 4, further comprising: an on-board charger (OBC) that converts AC power output from an external AC power source into first DC power for charging the battery and outputs the first DC power; and a DC-DC converter that converts the first DC power into second DC power used by one or more electronic control units (ECUs) included in the electric work vehicle and outputs the second DC power, wherein when starting to charge the battery with the first DC power output from the OBC, if the temperature of the battery is below a first threshold, the control device supplies the first DC power to the heater and the DC-DC converter without supplying the first DC power to the battery; if the temperature of the battery is equal to or greater than the first threshold and less than the second threshold, the control device supplies the first DC power to the heater, the DC-DC converter, and the battery; and if the temperature of the battery is equal to or greater than the second threshold, the control device supplies the first DC power to the DC-DC converter and the battery without supplying the first DC power to the heater.

[0015] [Item 6] The system according to any one of items 1 to 4, further comprising a DC-DC converter that converts first DC power output from an external DC power source and supplied to the battery into second DC power used by one or more electronic control units (ECUs) included in the electric work vehicle and outputs the second DC power, wherein the control device, when starting to charge the battery with the first DC power output from the DC power source, if the temperature of the battery is below a first threshold, supplies the first DC power to the heater and the DC-DC converter without supplying the first DC power to the battery; if the temperature of the battery is equal to or greater than the first threshold and less than the second threshold, supplies the first DC power to the heater, the DC-DC converter, and the battery; and if the temperature of the battery is equal to or greater than the second threshold, supplies the first DC power to the DC-DC converter and the battery without supplying the first DC power to the heater.

[0016] [Item 7] The system according to any one of items 1 to 6, further comprising a battery management system with a passive cell balancing function, wherein the heater is part of the battery management system and warms the battery by heat generated by discharging at least some of the cells included in the battery.

[0017] [Item 8] The system described in any one of items 1 to 7, wherein the electric work vehicle includes at least one of an electric traction motor and an electric PTO motor that are operated by power from the battery, and when the temperature of the battery is below a fourth threshold when discharging from the battery to at least one of the electric traction motor and the electric PTO motor, the control device preferentially distributes the output of the battery to the heater and distributes surplus output to at least one of the electric traction motor and the electric PTO motor.

[0018] [Item 9] The system described in Item 8, wherein the electric work vehicle includes the electric motor for traveling, and when the temperature of the battery is below the fourth threshold while the electric work vehicle is traveling, the control device preferentially distributes the output of the battery to the heater and distributes any surplus output to the electric motor for traveling.

[0019] [Item 10] The system described in Item 8, wherein the electric work vehicle includes the electric traction motor and the electric PTO motor, and when the temperature of the battery is below the fourth threshold value during discharge from the battery to the electric traction motor and the electric PTO motor, the control device preferentially distributes the output of the battery to the heater, preferentially distributes surplus output to the electric PTO motor, and distributes the remaining output to the electric traction motor.

[0020] [Item 11] A work vehicle comprising: the system according to any one of items 1 to 10; a traveling device; and an electric traveling motor that drives the traveling device.

[0021] [Item 12] A control device used in a system for controlling charging of a drive battery in an electric work vehicle, the system comprising: a temperature sensor that measures the temperature of the battery; and a heater that warms the battery, the control device comprising: one or more processors; and a memory that stores a computer program, the computer program causing the one or more processors to execute the following when starting charging of the battery: if the temperature of the battery is below a first threshold, turn on the heater to warm the battery without charging the battery; if the temperature of the battery is equal to or higher than the first threshold and less than a second threshold that is higher than the first threshold, turn on the heater to warm the battery and start charging the battery; and if the temperature of the battery is equal to or higher than the second threshold, turn off the heater and start charging the battery.

[0022] [Item 13] A method executed by a computing device that controls charging of a battery in an electric work vehicle that is equipped with a drive battery, a temperature sensor that measures the temperature of the battery, and a heater that warms the battery, the method including the steps of: when starting charging of the battery, if the temperature of the battery is below a first threshold, turning on the heater to warm the battery without charging the battery; if the temperature of the battery is equal to or greater than the first threshold and less than a second threshold that is greater than the first threshold, turning on the heater to warm the battery and starting charging the battery; and if the temperature of the battery is equal to or greater than the second threshold, turning off the heater and starting charging the battery.

[0023] [Item 14] A computer program executed by a computing device that controls charging of a battery in an electric work vehicle that is equipped with a drive battery, a temperature sensor that measures the temperature of the battery, and a heater that warms the battery, the computer program causing the computing device to execute the following steps when starting charging of the battery: if the temperature of the battery is below a first threshold, turn on the heater to warm the battery without charging the battery; if the temperature of the battery is equal to or higher than the first threshold and lower than a second threshold that is higher than the first threshold, turn on the heater to warm the battery and start charging the battery; and if the temperature of the battery is equal to or higher than the second threshold, turn off the heater and start charging the battery.

[0024] [Item 15] A computer-readable non-transitory storage medium storing a computer program executed by a computing device that controls charging of a battery in an electric work vehicle that is equipped with a drive battery, a temperature sensor that measures the temperature of the battery, and a heater that warms the battery, wherein the computer program causes the computing device to execute the following when starting charging of the battery: if the temperature of the battery is below a first threshold, turn on the heater to warm the battery without charging the battery; if the temperature of the battery is equal to or higher than the first threshold and less than a second threshold that is higher than the first threshold, turn on the heater to warm the battery and start charging the battery; and if the temperature of the battery is equal to or higher than the second threshold, turn off the heater and start charging the battery.

[0025] [Item 16] A system for controlling charging of a drive battery in an electric work vehicle, comprising: a temperature measurement means for measuring the temperature of the battery; a heating means for heating the battery; and a control means for controlling charging of the battery and operation of the heater, wherein when charging of the battery is started, if the temperature of the battery is below a first threshold, the control means turns on the heater to warm the battery without charging the battery; if the temperature of the battery is equal to or higher than the first threshold and lower than a second threshold that is higher than the first threshold, the control means turns on the heater to warm the battery and start charging the battery; and if the temperature of the battery is equal to or higher than the second threshold, the control means turns off the heater and start charging the battery.

[0026] [Item 17] A system for controlling an electric work vehicle equipped with a drive battery and at least one of an electric traction motor and an electric PTO motor that are operated by power from the battery, the system comprising: a temperature sensor that measures the temperature of the battery; a heater that heats the battery; and a control device, wherein if the temperature of the battery is below a fourth threshold when discharging from the battery to at least one of the electric traction motor and the electric PTO motor, the control device preferentially distributes the output of the battery to the heater, and distributes surplus output to at least one of the electric traction motor and the electric PTO motor.

[0027] [Item 18] The system described in Item 17, wherein the electric work vehicle includes both the traction electric motor and the PTO electric motor, and when the temperature of the battery is below the fourth threshold value during discharge from the battery to the traction electric motor and the PTO electric motor, the control device preferentially distributes the output of the battery to the heater, preferentially distributes surplus output to the PTO electric motor, and distributes the remaining output to the traction electric motor.

[0028] 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.

[0029] According to an embodiment of the present invention, an electric work vehicle can be realized that is capable of stably charging and discharging the battery even in a low-temperature environment.

[0030] 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 flowchart showing an example of a method for controlling charging of a battery; and FIG. 10 is a flowchart showing another example of a method for controlling charging of a battery.

[0031] 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.

[0032] 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.

[0033] (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."

[0034] 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."

[0035] 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.

[0036] 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).

[0037] 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.

[0038] 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.

[0039] 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."

[0040] 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).

[0041] "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.

[0042] (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.

[0043] 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."

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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."

[0053] 2. Specific Example of Work Vehicle Next, a more specific example of the configuration of the work vehicle 10 will be described.

[0054] 2 and 3 are side and top views of work vehicle 10 according to an exemplary embodiment of the present invention.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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."

[0059] 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.

[0060] 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.

[0061] 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."

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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 .

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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."

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] The RAM 436 provides a working area for temporarily loading the programs stored in the ROM 435 at boot time. The RAM 436 does not have to be a single recording medium, but may be a collection of multiple recording media.

[0083] 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).

[0084] 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.

[0085] 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.

[0086] 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."

[0087] 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.

[0088] The work vehicle 10 illustrated in FIG. 4 includes a cooling system 60 for high-voltage equipment and a battery temperature control system 70. The cooling system 60 is used to cool devices to which high voltage is applied (also referred to as "high-power devices"). The cooling system 60 includes a radiator 65, a reservoir tank 66, a pump 67, and a cooling fan 68. In the example illustrated in FIG. 4, the cooling system 60 is connected via hoses to the first inverter 35A, the first electric motor 30A, the second electric motor 30B, the second inverter 35B, and the power conversion device 58 in this order. This forms a flow path through which the coolant circulates. The coolant in the cooling system 60 is, for example, water or oil. The cooling system 60 cools these high-power devices by circulating the coolant through the flow path. The coolant heated by the high-power devices is cooled by dissipating heat in the radiator 65. The cooling fan 68 generates cooling air to cool the coolant inside the radiator 65. The cooling air promotes heat dissipation from the radiator 65 .

[0089] 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).

[0090] 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.

[0091] 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.

[0092] Next, an example of the configuration of a charging circuit that switches between normal charging and rapid charging will be described.

[0093] 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.

[0094] 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.

[0095] 4. Charge / Discharge Control in a Low-Temperature Environment Next, an example of a method for controlling charging of the driving battery 20 in a low-temperature environment will be described.

[0096] The work vehicle 10 in this embodiment is equipped with a system that controls charging of the drive battery 20. In the example shown in FIGS. 4 and 5 , the system includes a group of ECUs (i.e., control devices) such as temperature sensors 24, 25, a heater 72, a power conversion device 58 (OBC 81 and DC-DC converter 82), a BMS 22, a power distribution unit 80, and an electric ECU 62. The temperature sensor 24 measures the temperature of the battery 20. The temperature sensor 25 measures the outside air temperature. The heater 72 is used to warm the battery 20 when its temperature is low. The OBC 81 is a circuit that converts AC power output from an external AC power source into first DC power for charging the battery 20 during normal charging and outputs the first DC power. The DC-DC converter 82 is a circuit that converts DC power into DC power of a different voltage. During normal charging, the DC-DC converter 82 converts the first DC power into second DC power used by one or more ECUs included in the work vehicle 10 and outputs the converted power. On the other hand, during rapid charging, the DC-DC converter 82 converts the first DC power output from an external DC power source and supplied to the battery 20 into second DC power used by one or more ECUs included in the work vehicle 10 and outputs the converted power. The BMS 22 is a system that manages the charging and discharging of the battery 20 under the control of the electric ECU 62. The electric ECU 62 is a control device that controls multiple devices, such as the OBC 81, the DC-DC converter 82, the BMS 22, the heater 72, and multiple relays in the power distribution unit 80. The electric ECU 62 controls these devices to charge the battery 20 and operate the heater 72.

[0097] The electric ECU 62 can be configured or programmed to perform the following operations when starting to charge the battery 20. If the temperature of the battery 20 is below a first threshold (e.g., 0°C), turn on the heater 72 to warm the battery 20 without charging the battery 20. If the temperature of the battery 20 is equal to or higher than the first threshold and lower than a second threshold (e.g., 20°C) that is higher than the first threshold, turn on the heater 72 to warm the battery 20 and start charging the battery 20. If the temperature of the battery 20 is equal to or higher than the second threshold, turn off the heater 72 and start charging the battery 20.

[0098] Here, the "temperature of the battery 20" may be, for example, the lowest temperature among the temperatures of the multiple cells included in the battery 20. The temperature of each cell is measured by the temperature sensor 24 and transmitted to the electric ECU 62 via the BMS 22. Note that the "temperature of the battery 20" is not limited to the lowest value of the temperatures of the multiple cells included in the battery 20, and may be, for example, an average value.

[0099] The first threshold value may be set to, for example, a temperature value below which charging of the battery 20 becomes substantially impossible. The first threshold value may be set to, for example, a lower limit of the temperature at which charging is possible as determined by the specifications of the battery 20 or a value close to that limit. The first threshold value may be set to, for example, a value within a range of -10°C to 10°C. In the following description, the first threshold value is set to 0°C as an example.

[0100] The second threshold value may be set to a temperature value at which the charging efficiency of the battery 20 is sufficiently high and further heating is unnecessary. The second threshold value may be set to a value within a range of, for example, 10° C. to 30° C., more preferably, a value within a range of 15° C. to 25° C. In the following description, the second temperature is set to 20° C. as an example.

[0101] 9 is a flowchart showing an example of a method for controlling charging of the battery 20 in this embodiment. The operation shown in FIG. 9 is executed by the electric ECU 62. The operation of each step shown in FIG. 9 will be described below.

[0102] In step S101, the electric ECU 62 starts the charging mode. The charging mode can be started by a predetermined operation, such as a user connecting a charging adapter to the charging inlet 57 and pressing a charging start button. The electric ECU 62 can be configured or programmed to start the charging mode in response to a signal input from an external charger (i.e., an external power source), for example. Alternatively, the electric ECU 62 can be configured or programmed to start the charging mode based on a preset timer or a signal input by remote control.

[0103] In step S102, the electric ECU 62 determines whether the temperature of the battery 20 (hereinafter also referred to as "battery temperature") is lower than a first threshold value Th1 (e.g., 0°C). If the battery temperature is lower than the first threshold value Th1, the process proceeds to step S103. If the battery temperature is equal to or higher than the first threshold value Th1, the process proceeds to step S111.

[0104] In step S103, the electric ECU 62 turns on the heater 72. If the heater 72 is already on, it remains on. During normal charging, the electric ECU 62 turns on relays 83a and 83b in the power distribution unit 80 shown in FIG. 7, for example, and turns off relays 83c, 83d, 83e, 83f, and 83g. This operation allows current flowing from the charging inlet 57 via the power conversion device 58 to be supplied to the heater 72, thereby operating the heater 72. At this time, the electric ECU 62 controls the OBC 81 and the DC-DC converter 82 in the power conversion device 58 to supply DC power to the heater 72 and the auxiliary devices 84. On the other hand, during rapid charging, the electric ECU 62 turns on relays 83a, 83b, 83c, and 83d in the power distribution unit 80 shown in FIG. 7, and turns off relays 83e, 83f, and 83g. This operation allows the current flowing in from charging inlet 57 to be supplied to heater 72, thereby operating heater 72. During rapid charging, electric motor ECU 62 stops control of OBC 81 in power conversion device 58, and controls DC-DC converter 82 to maintain the supply of low-voltage power to accessories 84. After step S103, the process returns to step S102.

[0105] If it is determined in step S102 that the battery temperature is equal to or higher than the first threshold value Th1, the process proceeds to step S111.

[0106] In step S111, the electric ECU 62 determines whether the battery temperature is lower than a second threshold value Th2 (e.g., 20° C.). If the battery temperature is lower than the second threshold value Th2, the process proceeds to step S112. If the battery temperature is equal to or higher than the second threshold value Th2, the process proceeds to step S113.

[0107] In step S112, the electric motor ECU 62 turns on the heater 72. For example, by turning on the relay 83a shown in FIG. 7, the electric motor ECU 62 supplies the current flowing from the charging inlet 57 or the power conversion device 58 to the heater 72, thereby operating the heater 72. If the heater 72 is already on, the heater 72 remains on.

[0108] In step S113, the electric ECU 62 turns off the heater 72. For example, by turning off the relay 83a shown in FIG. 7, the supply of current to the heater 72 is stopped, thereby stopping the operation of the heater 72. If the heater 72 is already off, the heater 72 remains off.

[0109] After steps S112 and S113, the process proceeds to step S114.

[0110] In step S114, the electric power ECU 62 executes charging of the battery 20. For example, by turning on the relay 83g shown in FIG. 7, the electric current flowing from the charging inlet 57 or the power conversion device 58 is supplied to the battery 20. This charges the battery 20. After step S114, the process proceeds to step S115.

[0111] In step S115, the electric ECU 62 determines whether charging has ended. For example, the electric ECU 62 determines that charging has ended when it detects via the BMS 22 that the battery 20 is fully charged, or when it detects that the user has performed an operation to stop charging. If charging has ended, the process proceeds to step S116. If charging has not ended, the process returns to step S111. Thereafter, until charging ends, the ECU 62 executes control to turn on the heater 72 when the battery temperature is below the second threshold value Th2, and to turn off the heater 72 when the battery temperature is equal to or higher than the second threshold value Th.

[0112] In step S116, the electric motor ECU 62 stops charging the battery 20. For example, the electric motor ECU 62 stops the flow of current into the battery 20 by turning off the relay 83g shown in FIG. 7. When stopping normal charging, the electric motor ECU 62 stops the power conversion operation by the OBC 81 in the power conversion device 58. When stopping rapid charging, the electric motor ECU 62 stops the flow of high-voltage current from the charge inlet 57 by turning off the relays 83c and 83d.

[0113] As described above, in the example shown in Fig. 9, the electric ECU 62 (i.e., the control device) executes the following controls (S1) to (S3) in the charge mode. (S1) If the temperature of the battery 20 is less than the first threshold value Th1 (e.g., 0°C), the heater 72 is turned on to warm the battery 20 without charging the battery 20. (S2) If the temperature of the battery 20 is equal to or greater than the first threshold value Th1 (e.g., 0°C) and less than the second threshold value (e.g., 20°C), the heater 72 is turned on to warm the battery 20 and charge the battery 20. (S3) If the temperature of the battery 20 is equal to or greater than the second threshold value Th2, the heater 72 is turned off and charging the battery 20 is executed.

[0114] By the above control (S1), when the battery temperature is too low to charge (below the first threshold Th1), charging is suspended and the battery 20 is warmed up, thereby enabling charging. Furthermore, by the above control (S2), when the battery temperature is in a range where charging is possible but charging efficiency is low (above the first threshold and below the second threshold), charging efficiency can be gradually improved by warming the battery 20 while charging. Furthermore, by the above control (S3), when the battery temperature is high enough to achieve sufficiently high charging efficiency (above the second threshold), unnecessary power consumption can be avoided by turning off the heater 72, thereby enabling charging of the battery 20.

[0115] 9, while operating in the charging mode, the electric ECU 62 continuously supplies and controls power from the external power source to the DC-DC converter 82, regardless of the temperature of the battery 20. As a result, even when the temperature is so low that charging or discharging of the battery 20 is not possible, power supply to the auxiliary machinery 84, including the ECU group, in the work vehicle 10 is maintained, and the control in this embodiment can be executed.

[0116] The electric ECU 62 can be configured or programmed to execute the following controls (S11) to (S13) when starting normal charging, i.e., charging of the battery 20 with the first DC power output from the OBC 81. (S11) If the temperature of the battery 20 is less than the first threshold value Th1, the first DC power is supplied to the heater 72 and the DC-DC converter 82 without supplying the first DC power to the battery 20. (S12) If the temperature of the battery 20 is equal to or greater than the first threshold value Th1 and less than the second threshold value Th2, the first DC power is supplied to the heater 72, the DC-DC converter 82, and the battery 20. (S13) If the temperature of the battery 20 is equal to or greater than the second threshold value Th2, the first DC power is supplied to the DC-DC converter 82 and the battery 20 without supplying the first DC power to the heater 72.

[0117] On the other hand, when starting rapid charging, i.e., charging of the battery 20 with first DC power output from an external DC power supply, the electric ECU 62 can be configured or programmed to execute the following controls (S21) to (S23): (S21) If the temperature of the battery 20 is less than the first threshold value Th1, the first DC power is supplied to the heater 72 and the DC-DC converter 82 without supplying the first DC power to the battery 20. (S22) If the temperature of the battery 20 is equal to or greater than the first threshold value Th1 and less than the second threshold value TH2, the first DC power is supplied to the heater 72, the DC-DC converter 82, and the battery 20. (S23) If the temperature of the battery 20 is equal to or greater than the second threshold value Th2, the first DC power is supplied to the DC-DC converter 82 and the battery 20 without supplying the first DC power to the heater 72.

[0118] By the above control, even if the battery 20 is at a low temperature, power supply to the auxiliary machinery 84 including the ECU group is maintained, and the above control can be smoothly executed.

[0119] (Modifications) Next, several modifications of the control method in this embodiment will be described.

[0120] In the above embodiment, the electric ECU 62 (i.e., the control device) controls the power supply to devices such as the battery 20 and the heater 72 by switching on and off the multiple relays 83 in the power distribution unit 80. However, the method of controlling the power supply is not limited to this method. For example, instead of controlling the multiple relays 83, the power supply may be controlled by controlling one or more switch elements included in the internal circuits of the power conversion device 58, the heater 72, and the battery 20. For example, in a low-temperature environment, the electric ECU 62 may adjust the charging current so that almost all of the power from the charging inlet 57 or the OBC 81 is consumed by the heater 72 and the DC-DC converter 82 until the temperature of the battery 20 reaches a temperature at which charging is possible (i.e., equal to or higher than the first threshold Th1). In this case, some or all of the relays 83 in the power distribution unit 80 may be omitted. For example, the relay 83g in the power distribution unit 80 may be omitted. In this case, the battery 20 is electrically connected to the charging inlet 57 or the power conversion device 58, but almost all of the incoming power is consumed by the heater 72 and the DC-DC converter 82, and no current flows through the battery 20. Therefore, the battery 20 can be heated without damaging it.

[0121] 9, when charging is stopped in step S116, the process ends. Instead of this operation, the heater 72 may continue to heat the battery 20 as needed even after charging is stopped. An example of such an operation will be described below.

[0122] As shown in Fig. 4, the work vehicle 10 is equipped with a temperature sensor 25 that measures the outside air temperature. After charging is completed, if the outside air temperature measured by the temperature sensor 25 is less than a third threshold value Th3 that is lower than the first threshold value Th1, the electric ECU 62 may turn on the heater 72 to heat the battery 20 and maintain the temperature of the battery 20 at or above the third threshold value. The third threshold value Th3 may be set to a value ranging from -20°C to 0°C, for example, and preferably to a value ranging from -15°C to -5°C. In the following description, the third threshold value Th3 is set to -10°C, as an example.

[0123] Figure 10 is a flowchart showing an example of control for continuing to heat the battery 20 by the heater 72 when the outside air temperature is low after charging has stopped. The operations from steps S101 to S116 shown in Figure 10 are the same as those shown in Figure 9. In the example of Figure 10, after charging is stopped in step S116, the operations from steps S120 to S123 are executed. These steps will be described below.

[0124] In step S120, the electric ECU 62 determines whether the outside air temperature measured by the temperature sensor 25 is lower than a third threshold value Th3 (e.g., −10° C.). If the outside air temperature is lower than the third threshold value Th3, the process proceeds to step S121. If the outside air temperature is equal to or higher than the third threshold value Th3, the process proceeds to step S123.

[0125] In step S121, the electric ECU 62 turns on the heater 72 and sets the heater 72 to ON to maintain the temperature of the battery 20 at or above the third threshold value Th3. After step S121, the process proceeds to step S122.

[0126] In step S122, the electric ECU 62 determines whether a predetermined time has elapsed since the setting for maintaining the temperature was turned on. The predetermined time may be set to any value, such as 8 hours, 12 hours, or 15 hours. This time may be set, for example, by the user. The user can set the time by operating an input device such as the meter panel unit 54. If the predetermined time has elapsed since the setting for maintaining the temperature was turned on, the process proceeds to step S123.

[0127] In step S123, the electric ECU 62 turns off the heater 72 and ends the process.

[0128] 10, if the outside temperature is low after charging is completed, the heater 72 continues to heat the battery 20. As a result, for example, when the battery 20 of the work vehicle 10 is charged after work for the day is finished, even if the outside temperature is low, the deterioration of the discharge performance of the battery 20 is suppressed, and the work vehicle 10 can be used immediately the next day.

[0129] In the example shown in FIG. 10 , the electric ECU 62 turns off the heater 72 when a predetermined time has elapsed after step S121, but this is merely an example. For example, the electric ECU 62 may obtain information about the time when charging is completed and, based on that time, determine whether or not to maintain the temperature of the battery 20 at or above the third threshold value Th3. Alternatively, the electric ECU 62 may determine the time for which the temperature of the battery 20 is maintained at or above the third threshold value Th3 based on the time when charging is completed. Since the time when work is performed the next day is often roughly fixed, knowing the time when charging is completed makes it possible to estimate the time until the work vehicle 10 will be used the next day. The longer that time is, the longer the control can be, such as lengthening the time for warming the battery 20. The electric ECU 62 can obtain the time information, for example, from the main ECU 61 or an external time server.

[0130] The electric ECU 62 may determine whether to maintain the temperature of the battery 20 at or above the third threshold value Th3 or the time for which the temperature of the battery 20 is maintained at or above the third threshold value Th3 further based on the outside air temperature when charging is completed. By taking into account the time when charging is completed and the outside air temperature, it is possible to more precisely determine whether or not heating of the battery 20 is necessary or the time for which heating is necessary.

[0131] The electric ECU 62 may obtain the outside air temperature information from an external server computer that manages meteorological conditions such as temperature and weather, instead of from the temperature sensor 25. In this case, the temperature sensor 25 does not need to be included in the system.

[0132] The work vehicle 10 shown in Figure 4 is equipped with a traction electric motor 30A and a PTO electric motor 30B that are powered by electric power from the battery 20. At low temperatures, the discharge performance of the battery 20 also decreases, so the output of the battery 20 is limited. In such a situation, it is desirable to be able to operate the work vehicle 10 or the work equipment by driving at least one of the traction electric motor 30A and the PTO electric motor 30B while warming the battery 20 with a heater 72. To enable such operation, the electric ECU 62 may set a minimum guaranteed output of the heater 72 and allocate electric power from the battery 20 to the heater 72 preferentially.

[0133] More specifically, if the temperature of battery 20 is below fourth threshold Th4 (e.g., −15° C.) when discharging from battery 20 to at least one of traction electric motor 30A and PTO electric motor 30B, electric ECU 62 may preferentially distribute the output of battery 20 to heater 72 and distribute surplus output to at least one of traction electric motor 30A and PTO electric motor 30B. For example, if the temperature of battery 20 is below fourth threshold Th4 when work vehicle 10 is traveling, electric ECU 62 may preferentially distribute the output of battery 20 to heater 72 and distribute surplus output to traction electric motor 30A. Alternatively, if the temperature of battery 20 is below fourth threshold Th4 when discharging from battery 20 to PTO electric motor 30B, electric ECU 62 may preferentially distribute the output of battery 20 to heater 72 and distribute surplus output to PTO electric motor 30B. In addition, if the temperature of the battery 20 is less than the fourth threshold value Th4 when discharging from the battery 20 to the traction electric motor 30A and the PTO electric motor 30B, the electric ECU 62 may preferentially distribute the output of the battery 20 to the heater 72, preferentially distribute the surplus output to the PTO electric motor 30B, and distribute the remaining output to the traction electric motor 30A.

[0134] The fourth threshold value Th4 may be set to, for example, a value equal to or higher than the lower limit of the temperature at which the battery 20 can be discharged. The fourth threshold value Th4 may be set to, for example, a value between −20° C. and −10° C.

[0135] The above-described priority control of power distribution can be achieved by the electric power ECU 62 controlling the multiple relays 83 in the power distribution unit 80 and the multiple switch elements in the first inverter 35A and the second inverter 35B. Through the above-described control, the heater 72 heats the battery 20 at low temperatures, enabling the work vehicle 10 to travel or the work equipment to be driven. Such priority control of power distribution may be performed independently of the charge control illustrated in FIG. 9 or 10 . That is, a control device according to an embodiment of the present disclosure may be configured or programmed to perform control such that, when the temperature of the battery 20 is below threshold value Th4 during discharge from the battery 20 to at least one of the traction electric motor 30A and the PTO electric motor 30B, the output of the battery 20 is preferentially distributed to the heater 72 and the surplus output is distributed to at least one of the traction electric motor 30A and the PTO electric motor 30B. Such a control device does not necessarily have to have a function for performing the charge control illustrated in FIG. 9 or 10 . An electric work vehicle in which such a system is implemented includes a drive battery 20 and at least one of a traveling electric motor 30A and a PTO electric motor 30B that are operated by power from the battery 20.

[0136] In each of the above embodiments, the battery 20 is heated by a heater 72 in a temperature control system 70 shown in FIG. 4 . The heater 72 heats the battery 20 by increasing the temperature of the coolant flowing through the battery 20. However, the method for heating the battery 20 is not limited to this. For example, if the battery management system (BMS) 22 has a passive cell balancing function, each cell of the battery 20 may be heated by heat generated by passive cell balancing. Passive cell balancing is a function that discharges charge from some cells with a large amount of stored charge in order to equalize the voltages of the multiple cells in the battery 20. Each cell is provided with an electrical resistance for discharge. Heat is generated from the electrical resistance during discharge, and this heat can be used to warm the battery 20. In this case, the “heater” is part of the battery management system 22 and heats the battery 20 by heat generated by discharging at least some of the multiple cells included in the battery 20. In this manner, the heater does not necessarily have to be a separate device external to the battery 20, but may be part of the battery 20 (i.e., the battery pack).

[0137] The charging control system in the above embodiments 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).

[0138] The present invention can be applied to electric work vehicles such as agricultural tractors and construction vehicles that are equipped with an electric motor for driving.

[0139] REFERENCE SIGNS LIST 10...Work vehicle, 11...Vehicle body, 12...Front frame, 13...Transmission case, 14...Wheels, 14F...Front wheels, 14R...Rear wheels, 15F...Front axle, 15R...Rear axle, 16...Storage frame, 17F...Front axle case, 17R...Rear axle case, 19...Front housing, 20...Battery, 22...Battery management system (BMS), 24...Temperature sensor, 30, 30A, 30B...Electric motor, 33...Output shaft, 34...Power transmission system, 35A, 35B...Inverter, 36...Hydraulic pump, 40...PTO shaft, 51...ROPS frame, 52...Driver's seat, 53...Steering wheel, 54...Meter panel unit, 55...Pedals, 56...Switches, 57...Charging inlet, 58...Power conversion device 60...Cooling system for high-pressure equipment, 61...Main ECU, 62...Electric ECU, 63...Charging ECU, 64...Relay, 65...Radiator for high-pressure equipment, 66...Reservoir tank, 67...Pump, 68...Cooling fan, 70...Battery temperature control system, 72...Heater, 75...Battery radiator, 76...Reservoir tank, 77...Pump, 80...Power distribution unit, 81...On-board charger (OBC), 82...DC-DC converter, 83...Relay circuit, 84...Auxiliary equipment

Claims

1. A system for controlling the charging of a drive battery in an electric work vehicle, comprising: a temperature sensor for measuring the temperature of the battery; a heater for heating the battery; and a control device for controlling the charging of the battery and the operation of the heater, wherein when charging of the battery is started, if the temperature of the battery is below a first threshold, the control device turns on the heater to warm the battery without charging the battery; if the temperature of the battery is equal to or higher than the first threshold and lower than a second threshold that is higher than the first threshold, the control device turns on the heater to warm the battery and start charging the battery; and if the temperature of the battery is equal to or higher than the second threshold, the control device turns off the heater and starts charging the battery.

2. The system described in claim 1, further comprising another temperature sensor that measures the outside air temperature, wherein, after the charging is completed, if the outside air temperature is less than a third threshold that is lower than the first threshold, the control device turns on the heater to warm the battery and maintain the temperature of the battery at or above the third threshold.

3. The system described in claim 2, wherein the control device acquires information on the time when the charging is completed, and determines, based on the time, whether to maintain the temperature of the battery at or above the third threshold, or the time for which the temperature of the battery is to be maintained at or above the third threshold.

4. The system described in claim 2, wherein the control device determines whether to maintain the battery temperature at or above the third threshold, or the time for which the battery temperature is to be maintained at or above the third threshold, further based on the outside air temperature when the charging is completed.

5. The system according to any one of claims 1 to 4, further comprising: an on-board charger (OBC) that converts AC power output from an external AC power source into first DC power for charging the battery and outputs the first DC power; and a DC-DC converter that converts the first DC power into second DC power used by one or more electronic control units (ECUs) included in the electric work vehicle and outputs the second DC power, wherein the control device, when starting to charge the battery with the first DC power output from the OBC, if the temperature of the battery is below a first threshold, supplies the first DC power to the heater and the DC-DC converter without supplying the first DC power to the battery; if the temperature of the battery is equal to or greater than the first threshold and less than the second threshold, supplies the first DC power to the heater, the DC-DC converter, and the battery; and if the temperature of the battery is equal to or greater than the second threshold, supplies the first DC power to the DC-DC converter and the battery without supplying the first DC power to the heater.

6. The system described in any one of claims 1 to 4, further comprising a DC-DC converter that converts first DC power output from an external DC power source and supplied to the battery into second DC power used by one or more electronic control units (ECUs) included in the electric work vehicle and outputs the second DC power, wherein the control device, when starting to charge the battery with the first DC power output from the DC power source, if the temperature of the battery is below a first threshold, supplies the first DC power to the heater and the DC-DC converter without supplying the first DC power to the battery; if the temperature of the battery is equal to or greater than the first threshold and less than the second threshold, supplies the first DC power to the heater, the DC-DC converter, and the battery; and if the temperature of the battery is equal to or greater than the second threshold, supplies the first DC power to the DC-DC converter and the battery without supplying the first DC power to the heater.

7. The system according to any one of claims 1 to 4, further comprising a battery management system with a passive cell balancing function, wherein the heater is part of the battery management system and warms the battery by heat generated by discharging at least some of the cells included in the battery.

8. The system described in any one of claims 1 to 4, wherein the electric work vehicle is equipped with at least one of an electric traction motor and an electric PTO motor that are operated by power from the battery, and if the temperature of the battery is below a fourth threshold when discharging from the battery to at least one of the electric traction motor and the electric PTO motor, the control device preferentially distributes the output of the battery to the heater and distributes surplus output to at least one of the electric traction motor and the electric PTO motor.

9. The system described in claim 8, wherein the electric work vehicle is equipped with the electric motor for driving, and when the temperature of the battery is below the fourth threshold while the electric work vehicle is driving, the control device preferentially distributes the output of the battery to the heater and distributes any surplus output to the electric motor for driving.

10. The system described in claim 8, wherein the electric work vehicle is equipped with the electric traction motor and the electric PTO motor, and if the temperature of the battery is below the fourth threshold when discharging from the battery to the electric traction motor and the electric PTO motor, the control device preferentially distributes the output of the battery to the heater, preferentially distributes surplus output to the electric PTO motor, and distributes the remaining output to the electric traction motor.

11. A work vehicle comprising: a system according to any one of claims 1 to 4; a traveling device; and an electric traveling motor that drives the traveling device.

12. A control device used in a system that controls charging of a drive battery in an electric work vehicle, the system comprising: a temperature sensor that measures the temperature of the battery; and a heater that warms the battery, the control device comprising: one or more processors; and a memory that stores a computer program, the computer program causing the one or more processors to execute the following operations when starting charging of the battery: if the temperature of the battery is below a first threshold, turn on the heater to warm the battery without charging the battery; if the temperature of the battery is equal to or higher than the first threshold and less than a second threshold that is higher than the first threshold, turn on the heater to warm the battery and start charging the battery; and if the temperature of the battery is equal to or higher than the second threshold, turn off the heater and start charging the battery.

13. A method executed by a computing device that controls charging of a battery in an electric work vehicle that is equipped with a drive battery, a temperature sensor that measures the temperature of the battery, and a heater that warms the battery, the method including the steps of: when starting charging of the battery, if the temperature of the battery is below a first threshold, turning on the heater to warm the battery without charging the battery; if the temperature of the battery is equal to or greater than the first threshold and less than a second threshold that is greater than the first threshold, turning on the heater to warm the battery and starting charging the battery; and if the temperature of the battery is equal to or greater than the second threshold, turning off the heater and starting charging the battery.

14. A computer program executed by a computing device that controls charging of a battery in an electric work vehicle that is equipped with a drive battery, a temperature sensor that measures the temperature of the battery, and a heater that warms the battery, the computer program causing the computing device to execute the following steps when starting charging of the battery: if the temperature of the battery is below a first threshold, turn on the heater to warm the battery without charging the battery; if the temperature of the battery is equal to or higher than the first threshold and lower than a second threshold that is higher than the first threshold, turn on the heater to warm the battery and start charging the battery; and if the temperature of the battery is equal to or higher than the second threshold, turn off the heater and start charging the battery.

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