JP7788949B2 - electric work vehicle - Google Patents

Description

The present invention relates to an electric work vehicle that manages the battery's charge/discharge state, preventing overcharging and over-discharging of the battery and reducing unexpected stops.

Patent Document 1 discloses a battery management device that includes a voltage sensor that detects the electromotive force (cell voltage) of each of the multiple battery units (battery cells) that make up the battery, a voltage sensor failure detection means that detects failures in the voltage sensors, and a battery current suppression means. This battery current suppression means suppresses the battery current if a failure in any of the voltage sensors is detected. This suppresses heat generation due to Joule heat, preventing further deterioration of the battery unit even if an abnormality occurs.

Japanese Patent Application Laid-Open No. 2000-357541

In the battery management device disclosed in Patent Document 1, when a voltage sensor failure detection means detects a failure in the voltage sensor that detects the voltage of a battery unit, the battery current is suppressed. However, because the battery supplies reduced power to the motor, there is a risk that fatal over-discharge or over-charge may occur in the battery unit assigned to the failed voltage sensor.

In light of these circumstances, the object of the present invention is to provide an electric work vehicle that can appropriately manage the output of the driving battery even when it becomes impossible to detect the cell voltage of the battery cells that make up the driving battery.

The electric work vehicle according to the present invention comprises an electric motor that is driven to propel the vehicle body, a traction battery consisting of a plurality of battery cells, an inverter that supplies driving power to the electric motor using power from the traction battery, a cell voltage detector that detects the cell voltages of the battery cells, a control device that stops the output of the electric motor or limits the output of the electric motor to a preset limit output value when the cell voltage detector is unable to detect at least one of the cell voltages, and an inverter voltage detection unit that detects the total inverter voltage of the inverter , and the control device limits the output of the electric motor to the preset limit output value when it is unable to detect the cell voltages and the total inverter voltage of the inverter is within a preset inverter total voltage allowable range .
Moreover, an electric work vehicle according to the present invention comprises an electric motor that is driven to propel the vehicle body, a traction battery consisting of a plurality of battery cells, an inverter that supplies driving power to the electric motor using power from the traction battery, a cell voltage detector that detects the cell voltages of the battery cells, a control device that stops the output of the electric motor or limits the output of the electric motor to a preset limit output value if the cell voltage detector is unable to detect at least one of the cell voltages, and a DC/DC converter that is powered by the traction battery, and the control device limits the output of the electric motor to a preset limit output value if it is unable to detect the cell voltage and the input voltage of the DC/DC converter is within a preset converter input voltage allowable range.

With this configuration, if the cell voltage detector is unable to detect at least one of the cell voltages, either the electric motor output is stopped or the electric motor output is limited. If it is determined that there is a high possibility of fatal over-discharge or over-charge of the drive battery, the electric motor output is stopped and the vehicle is brought to a halt. The state of the drive battery and the state of battery-related equipment, such as the cell voltage detector, are then checked. Furthermore, if it is determined that the drive battery is not imminent to fatally over-discharge or over-charge, the electric motor output is limited, allowing the electric work vehicle to travel to a location (such as a parking lot or maintenance and inspection service center) suitable for checking the drive battery, cell voltage detector, etc.

Whether the electric motor output is stopped or limited, this has a significant impact on the driving of the electric work vehicle. Therefore, it is preferable to notify the driver that the cell voltage detector is unable to detect at least one cell voltage, or the resulting selection (output stop or output limit). For this reason, in the present invention, the driver is notified via a notification unit when the control device has decided to stop the electric motor output or limit the electric motor output.

The battery state of the traction battery, which is the criterion for determining whether to stop or limit the output of the electric motor, can be estimated, for example, from the inverter total voltage. For this reason, the present invention is provided with an inverter voltage detection unit that detects the inverter total voltage of the inverter, and the control device stops the output of the electric motor if the inverter total voltage of the inverter falls outside a preset inverter total voltage tolerance range. In other words, if the inverter total voltage is low enough to indicate over-discharge of the traction battery, for example, the vehicle is stopped to avoid the danger of over-discharge. However, to avoid unexpected stops in inappropriate locations, it is preferable to set the inverter total voltage tolerance range large enough to allow for some leeway.

The battery state of the drive battery, which is the criterion for determining whether to stop or limit the output of the electric motor, can also be estimated from the input voltage of a DC/DC converter powered by the drive battery. For this reason, the present invention is equipped with a DC/DC converter powered by the drive battery, and the control device stops the output of the electric motor if the input voltage of the DC/DC converter falls outside a preset converter input voltage allowable range. Even in this configuration, it is preferable to set the converter input voltage allowable range large enough to allow for a margin of error in order to avoid unexpected stops in inappropriate locations.

Since the basic element of a traction battery is the battery cell, if the cell voltage of one battery cell falls outside a specified range (cell voltage tolerance range), it has a significant impact on the state of the traction battery. To resolve this problem and properly manage the output of the traction battery, in this invention, the control device stops the output of the electric motor or limits the output of the electric motor to the limited output value when the cell voltage falls outside the preset cell voltage tolerance range. The cell voltage tolerance range, like the inverter total voltage tolerance range and converter input voltage tolerance range, is determined experimentally and empirically, taking into account factors such as the type of vehicle being worked on.

FIG. 2 is a left side view of the tractor. FIG. 2 is a left side view showing the arrangement of the motor and the driving battery. FIG. 2 is a schematic diagram showing the flow of power transmission. FIG. 2 is a functional block diagram showing functional units of the battery system. 10 is a flowchart illustrating an example of battery management control. 10 is a flowchart illustrating another example of battery management control.

The following description will discuss an embodiment of the present invention with reference to the drawings. In the following description, unless otherwise specified, the direction of arrow F in the drawings will be referred to as "front," the direction of arrow B as "rear," the direction of arrow L as "left," and the direction of arrow R as "right." The direction of arrow U in the drawings will be referred to as "up," and the direction of arrow D as "down."

[Overall configuration of the tractor]
The following describes a tractor as an example of an electric work vehicle according to the present invention. As shown in Figure 1, the tractor has left and right front wheels 10, left and right rear wheels 11, and a cover member 12.

The tractor comprises a machine frame 2 and a driving section 3. The machine frame 2 is supported by left and right front wheels 10 and left and right rear wheels 11. A cover member 12 is located at the front of the machine. The driving section 3 is located behind the cover member 12.

The driver's unit 3 has a protective frame 30, a driver's seat 31, and a steering wheel 32. The steering wheel 32 is provided so that it can be operated by a driver sitting in the driver's seat 31 while in the driver's unit 3. The left and right front wheels 10 are steered by operating the steering wheel 32. The driver can perform various driving operations using the driver's unit 3.

The tractor is equipped with a traction battery 4. The cover member 12 is configured to be able to swing around an opening/closing axis Q that runs along the left-right direction of the vehicle body. This allows the cover member 12 to be opened and closed. When the cover member 12 is in the closed state, the traction battery 4 is covered by the cover member 12.

As shown in FIG. 2, the tractor is equipped with an inverter 14 and an electric motor 1. The traction battery 4 supplies power to the inverter 14. The inverter 14 converts DC power from the traction battery 4 into AC power to generate drive power that is supplied to the electric motor 1. The drive power is AC power generated by the inverter 14.

As shown in Figures 2 and 3, the tractor is equipped with a hydrostatic continuously variable transmission 15 and a transmission 16. As shown in Figure 3, the hydrostatic continuously variable transmission 15 has a hydraulic pump 15a and a hydraulic motor 15b.

The hydraulic pump 15a is driven by rotational power from the electric motor 1. When the hydraulic pump 15a is driven, rotational power is output from the hydraulic motor 15b. The hydrostatic continuously variable transmission 15 is configured to continuously change the speed of the rotational power between the hydraulic pump 15a and the hydraulic motor 15b.

The rotational power output from the hydraulic motor 15b is transmitted to the transmission 16. The rotational power transmitted to the transmission 16 is changed in speed by the gear-type speed change mechanism of the transmission 16 and distributed to the left and right front wheels 10 and the left and right rear wheels 11. This drives the left and right front wheels 10 and the left and right rear wheels 11.

As shown in Figures 2 and 3, the tractor is equipped with a mid-PTO shaft 17 and a rear PTO shaft 18. The rotational power output from the electric motor 1 is distributed to the hydraulic pump 15a, the mid-PTO shaft 17, and the rear PTO shaft 18. This causes the mid-PTO shaft 17 and the rear PTO shaft 18 to rotate.

If a work device is connected to the mid-PTO shaft 17 or rear PTO shaft 18, the work device will be driven by the rotational power of the mid-PTO shaft 17 or rear PTO shaft 18. For example, as shown in Figure 2, in this embodiment, a brush cutter 19 is connected to the mid-PTO shaft 17. The brush cutter 19 is driven by the rotational power of the mid-PTO shaft 17.

[Motor/battery control system configuration]
FIG. 4 schematically shows the configuration related to the control of the traction battery 4 and the electric motor 1. The motor/battery control system includes an accelerator device 33, a key controller 34, a control device 6 that controls the operation of the electric motor 1, and an inverter 14. The accelerator device 33 is provided near the steering wheel 32. Although not shown, the accelerator device 33 includes a lever that can be swung and a potentiometer that is operated by swung operation of the lever. The accelerator device 33 is connected to the control device 6. The key controller 34 is also connected to the control device 6 and provides a key operation signal to the control device 6 based on the movement of a main key operated by the driver. The control device 6 is connected to the inverter 14 and provides a drive command to the inverter 14 in response to a command from the accelerator device 33. The inverter 14 adjusts the power supplied from the traction battery 4 to the electric motor 1 in response to a command from the control device 6 to control the output of the electric motor 1.

The control device 6 is also connected to the notification unit 35. The notification unit 35 is a general term for devices that notify the driver of information, such as an operation panel, meter panel, lamps, and buzzers, and visually or audibly notifies the driver of, for example, the vehicle's driving status, operating status, and information about the driving battery 4 (charge level and temperature).

The driving battery 4 can be charged from an external power source 44 via the charging unit 43. The charging unit 43 is provided with a power supply socket (not shown). The power supply socket can be connected to a power supply connector (not shown) of a charging cable from the external power source 44. The power supply socket is located inside the cover member 12 and is exposed to the outside when the cover member 12 is swung open. The control device 6 controls the operation of the inverter 14 and also controls the charging of the driving battery 4 by the charging unit 43.

The driving battery 4 is, for example, a lithium-ion battery, and is composed of a large number of battery cells 40, which are small, low-voltage unit cells, stacked one on top of the other. The driving battery 4 is stored in a storage case, with the outside covered and sealed.

A battery voltage detection unit 5 is provided to detect the battery voltage of the driving battery 4. In this embodiment, the battery voltage detection unit 5 is equipped with a cell voltage detector 51 that detects the voltage at the connection point between multiple battery cells 40 connected in series as the cell voltage. In FIG. 4, the cell voltage detector 51 is configured to detect the cell voltage of each battery cell 40, but it may also be configured to detect the cell voltage of two or more battery cells 40 as a unit. The cell voltage detected by the cell voltage detector 51 is input to the control device 6. Although not shown, a temperature detection sensor is also provided to detect the temperature of the battery cells 40 and other internal temperatures of the driving battery 4, and its detection signal is also input to the control device 6.

In addition to the traction battery 4, the tractor is equipped with an electrical equipment battery 41 that supplies power to the control device 6 and other electrical equipment. The electrical equipment battery 41 supplies low-voltage (12 volts) power to drive the electrical equipment. The electrical equipment battery 41 is charged with power supplied from the traction battery 4 via a DC/DC converter 42. The DC/DC converter 42 is driven and controlled by the control device 6.

The control device 6 has the function of stopping the output of the electric motor 1 or limiting the output of the electric motor 1 to a preset limit output value based on the power supply status of the drive battery 4 when the cell voltage detector 51 is unable to detect at least one cell voltage. To achieve this function, the control device 6 is equipped with a battery management unit 60, an inverter voltage detection unit 61, a DC/DC converter voltage detection unit 62, and a motor drive management unit 63 to manage the output (discharge) of the drive battery 4 according to its charge state.

The inverter voltage detection unit 61 detects the total inverter voltage of the inverter 14. The DC/DC converter voltage detection unit 62 detects the converter input voltage of the DC/DC converter 42. In FIG. 4, the inverter voltage detection unit 61 and the DC/DC converter voltage detection unit 62 are provided inside the control device 6, but they may also be provided outside the control device 6. The battery management unit 60 manages the charging and discharging of the traction battery 4 based on the cell voltage, total inverter voltage, converter input voltage, signals from the accelerator device 33, signals from the key controller 34, etc. The motor drive management unit 63 generates a drive signal for driving the electric motor 1 based on a signal from the accelerator device 33 and provides it to the inverter 14.

When a charging command is input while the power cable from the external power source 44 is plugged into the socket of the charging unit 43, the control device 6 executes a charging program and charges the driving battery 4.

The control device 6 determines whether to stop the output of the electric motor 1 or limit the output of the electric motor 1 based on pre-set control rules, and the driver is notified of this decision via the notification unit 35.

If the cell voltage detector 51 is unable to detect the cell voltage of at least one battery cell 40, the control device 6 limits the output of the electric motor 1 to a preset limit output value. Even if the cell voltage cannot be detected, this does not necessarily mean that the battery cell 40 is in an abnormal state. However, as a safety measure, the output of the electric motor 1 is first limited to take relief measures against an unexpected battery cell 40 abnormality, i.e., an abnormality in the drive battery 4. Furthermore, a secondary method other than cell voltage detection by the cell voltage detector 51 is used to determine whether the drive battery 4 is abnormal, and based on the results of this determination, the output of the electric motor 1 is stopped, if necessary, as a secondary relief measure.

In this embodiment, an example of the secondary rescue measure, that is, the determination rule for determining whether to stop the output of the electric motor 1, is as follows.
(1) When the inverter total voltage falls outside a preset inverter total voltage allowable range, the control device 6 stops the output of the electric motor 1 .
(2) When the input voltage of the DC/DC converter 42 falls outside the preset allowable range of the converter input voltage, the control device 6 stops the output of the electric motor 1 .

Even if the cell voltage detector 51 is unable to detect the cell voltage of at least one battery cell 40, this does not necessarily mean that it will be unable to detect the cell voltages of all battery cells 40. Therefore, the control device 6 may determine whether to limit the output of the electric motor 1 or stop the output of the electric motor 1 based on the cell voltage of the battery cells 40 for which the cell voltage can be detected. In other words, if the cell voltage falls outside the preset cell voltage tolerance range, the control device 6 will stop the output of the electric motor 1 or limit the output of the electric motor 1 to a preset limit output value.

Next, an example of the management process for the driving battery 4 (output management of the electric motor 1) performed by the control device 6 configured as described above will be described with reference to the flowchart in Figure 5.

When this battery management process is initiated, the control device 6 checks whether there are any battery cells 40 for which the cell voltage cannot be detected (#01). This cell voltage undetectable check can be performed based on the detection results of the cell voltage detector 51. If the cell voltage undetectable check does not detect any battery cells 40 for which the cell voltage cannot be detected (#01: No branch), a further check is performed to see whether there are any battery cells 40 for which the detected cell voltage is outside the preset cell voltage tolerance range (overcharged or overdischarged state) (#02). If all cell voltages are within the cell voltage tolerance range in this cell voltage out-of-range check (#02: No branch), the battery condition of the drive battery 4 is deemed normal (#03), and motor output control of the electric motor 1 is performed normally (#04).

If at least one battery cell 40 with an undetectable cell voltage is detected during the cell voltage detection check in step #01 (#01 Yes branch), the control device 6 notifies the alarm unit 35 that a battery cell 40 with an undetectable cell voltage has been detected (#10). Furthermore, the control device 6 uses the inverter voltage detection unit 61 to check whether the inverter total voltage is outside the preset inverter total voltage tolerance range (#11). If this inverter total voltage check finds that the inverter total voltage is within the inverter total voltage tolerance range (#11 No branch), the traction battery 4 is deemed usable for at least a short time, even though cell voltage detection is not possible (#13). However, because future deterioration of the traction battery 4 is anticipated, the control device 6 limits the motor output of the electric motor 1 so that it does not exceed a preset output limit value (#14). At the same time, the control device 6 notifies the alarm unit 35 that motor output control of the electric motor 1 will be performed (#15). This notification allows the driver to move the tractor to a suitable location for maintenance, such as a barn or repair center, without having to stop unexpectedly.

If, in the cell voltage out-of-range check in step #02, any one cell voltage is outside the allowable cell voltage range (#02 Yes branch), the drive battery 4 is deemed to be abnormal (#20). In other words, if at least one battery cell 40 whose cell voltage cannot be detected is detected and any one cell voltage is outside the allowable cell voltage range, the drive battery 4 is deemed to be abnormal, and motor output control for the electric motor 1 is stopped (#21). Furthermore, the control device 6 notifies the alarm unit 35 that the drive battery 4 is deemed to be abnormal and motor output control for the electric motor 1 will be stopped (#22).

Similarly, if the inverter total voltage check in step #11 finds that the inverter total voltage is outside the inverter total voltage tolerance range (#11 Yes branch), the power supply from the drive battery 4 is insufficient, the drive battery 4 is deemed to be abnormal (#20), and motor output control of the electric motor 1 is stopped (#21). The control device 6 determines that the drive battery 4 is abnormal, and issues a notification via the notification unit 35 that motor output control of the electric motor 1 will be stopped (#22).

Next, another example of the management process for the driving battery 4 (the output management process for the electric motor 1), which differs from the flowchart in Figure 5, will be described with reference to the flowchart in Figure 6.

The management process shown in FIG. 6 differs from the management process shown in FIG. 5 in that, instead of checking whether the inverter total voltage is outside the preset inverter total voltage tolerance range in step #11 of FIG. 5, in step #12, the control device 6 uses the DC/DC converter voltage detection unit 62 to check whether the converter input voltage is outside the preset converter input voltage tolerance range. If the converter input voltage check finds that the converter input voltage is within the converter input voltage tolerance range (No branch in #12), the traction battery 4 is deemed usable for at least a short time, even though cell voltage detection is not possible (#13). If the converter input voltage check in step #12 finds that the converter input voltage is outside the converter input voltage tolerance range (Yes branch in #12), the power supply from the traction battery 4 is insufficient, and the traction battery 4 is deemed to be abnormal (#20). Otherwise, the flowchart in FIG. 6 is identical to the flowchart in FIG. 5. In other words, the management process shown in Figure 6 checks the converter input voltage instead of checking the inverter total voltage as in the management process shown in Figure 5.

Another possible management process for the traction battery 4 is a combination of the flowcharts in Figures 5 and 6, that is, a process that incorporates both a check of the inverter total voltage in step #11 of Figure 5 and a check of the converter input voltage in step #12 of Figure 6. In such a management process, if the inverter total voltage is not outside the allowable range and the converter input voltage is not outside the allowable range, the traction battery 4 is considered usable, at least for a while. If either the inverter total voltage or the converter input voltage is outside the allowable range, the traction battery 4 is considered to be abnormal.

In the flowchart of the management process for the driving battery 4 described above, if there is at least one battery cell 40 whose cell voltage cannot be detected and the cell voltage of at least one of the remaining battery cells 40 whose cell voltage can be detected is outside the cell voltage allowable range, i.e., if the "Yes" branch is returned in step #02, motor output control is stopped. Alternatively, the allowable cell voltage range may be configured to include a first allowable range and a second allowable range, and motor output control may be stopped if the cell voltage is outside the second allowable range, and motor output may be limited if the cell voltage is within the second allowable range but outside the first allowable range. Furthermore, if the "Yes" branch is returned in step #02, a jump to step #11 (Figure 5) or step #12 (Figure 6) may be performed.

In the cell voltage detection undetectable check in step #01, if even one battery cell 40 is detected whose cell voltage cannot be detected, it is determined that the cell voltage cannot be detected. However, it may also be determined that the cell voltage cannot be detected if the cell voltage of a small number of battery cells 40 (two or more) cannot be detected.

[Another embodiment]
(1) In the above embodiment, the driving battery 4 was located in front of the driving unit 3. However, instead, it may be located below the driving unit 3 or behind the driving unit 3, or it may be divided into multiple units and each unit may be located in a different location.

(2) The criteria for the cell voltage tolerance range, inverter total voltage tolerance range, converter input voltage tolerance range, etc. may be changed depending on whether a work implement such as a grass cutting implement 19 or a tilling implement is attached to the tractor or not, or may also be changed depending on the type of work implement attached.

The configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, provided that no contradictions arise. Furthermore, the embodiments disclosed in this specification are merely examples, and the present invention is not limited to these embodiments. They can be modified as appropriate within the scope of the purpose of the present invention.

The present invention can be applied not only to tractors, but also to various electric work vehicles such as rice transplanters, combine harvesters, and construction machinery.

1: Electric motor 14: Inverter 35: Notification unit 4: Driving battery 40: Battery cell 41: Battery for electrical equipment 42: DC/DC converter 43: Charging unit 44: External power supply 5: Battery voltage detection unit 51: Cell voltage detector 6: Control device 60: Battery management unit 61: Inverter voltage detection unit 62: DC/DC converter voltage detection unit 63: Motor drive management unit

Claims (5)

an electric motor that is driven to drive the vehicle;
a driving battery consisting of a plurality of battery cells;
an inverter that uses electric power from the driving battery to supply drive electric power to the electric motor;
a cell voltage detector for detecting a cell voltage of the battery cell;
a control device that stops the output of the electric motor or limits the output of the electric motor to a preset limit output value when the cell voltage detector becomes unable to detect at least one of the cell voltages;
an inverter voltage detection unit that detects a total inverter voltage of the inverter;
Equipped with
When the cell voltage cannot be detected and the inverter total voltage of the inverter is within a preset inverter total voltage allowable range, the control device limits the output of the electric motor to a preset limit output value . 2. The electric work vehicle according to claim 1, wherein the control device stops output of the electric motor when the cell voltage cannot be detected and the inverter total voltage of the inverter falls outside a preset inverter total voltage allowable range . an electric motor that is driven to drive the vehicle;
a driving battery consisting of a plurality of battery cells;
an inverter that uses electric power from the driving battery to supply drive electric power to the electric motor;
a cell voltage detector for detecting a cell voltage of the battery cell;
a control device that stops the output of the electric motor or limits the output of the electric motor to a preset limit output value when the cell voltage detector becomes unable to detect at least one of the cell voltages ;
a DC/DC converter powered by the driving battery;
Equipped with
The control device limits the output of the electric motor to a preset limit output value when the cell voltage cannot be detected and the input voltage of the DC/DC converter is within a preset converter input voltage allowable range. 4. The electric work vehicle according to claim 3, wherein the control device stops the output of the electric motor when the cell voltage cannot be detected and the input voltage of the DC/DC converter is outside a preset converter input voltage allowable range . The electric work vehicle according to any one of claims 1 to 4, wherein a notification unit notifies a driver that the control device has decided to stop output of the electric motor or to limit output of the electric motor.