JP2022171216A - electric tractor - Google Patents

Abstract

To accurately determine whether a current position is a farm field or not.SOLUTION: An electric tractor includes: a first electric motor 41; rear wheels 12R that rotate according to drive force from the first electric motor 41; and a control device 100 controlling the first electric motor 41. The control device 100 executes farm field determination processing of determining that a current position is a farm field, if a state in which a change amount of rotational speed of the first electric motor 41 is equal to a specified value or greater continues for a prescribed period.SELECTED DRAWING: Figure 2

Description

The present invention relates to electric tractors.

The electric tractor disclosed in Patent Literature 1 includes a battery, an electric motor as a drive source, drive wheels driven by the electric motor, and a work machine.

JP 2015-22662 A

In the electric tractor disclosed in Patent Document 1, it is determined whether the current position of the electric tractor is in a field or on a general road, based on the gear ratio of the transmission provided in the power transmission mechanism.

Here, during field driving, a gear ratio on the low speed side is often used compared to when driving on a general road. However, the gear ratio on the low speed side may be used even while traveling on a general road. Therefore, in the determination based on the gear ratio, for example, there is a risk of erroneously determining that the electric tractor is traveling on a field even though it is traveling on a general road. is difficult to determine with high accuracy.

An electric tractor that solves the above problems includes a vehicle body that can be connected to a work machine, an electric motor, a battery that supplies electric power to the electric motor, driving wheels for traveling that are rotated by the driving force from the electric motor, and a control device that controls the electric motor. Then, the control device executes an agricultural field determination process for determining that the current position is an agricultural field when the amount of change in the rotation speed of the electric motor is equal to or greater than a specified value for a specified period of time.

In agricultural fields, the rotational resistance of drive wheels tends to fluctuate more than ordinary roads, so the rotational speed of an electric motor that drives such drive wheels tends to fluctuate more easily. Therefore, in the same configuration, when the amount of change in the rotation speed of the electric motor continues to be equal to or greater than a specified value for a specified period of time, determination processing is executed to determine that the current position is in a field. It is possible to accurately determine whether or not the current position of the tractor is in a field.

Schematic configuration diagram of a tractor. The figure showing the electric composition of a tractor, and a power transmission path. 4 is a flowchart showing the procedure of agricultural field determination processing executed by the control device for an electric tractor according to one embodiment.

<Overall configuration of electric tractor>
As shown in FIG. 1, the electric tractor 10 includes a vehicle 11, a working machine 20, and a support mechanism 30. The vehicle 11 has front wheels 12</b>F as steering wheels, rear wheels 12</b>R as drive wheels for running, and a vehicle body 13 . A work machine 20 can be connected to the vehicle body 13 via a support mechanism 30 . The front wheel 12F may be the drive wheel, or both the front wheel 12F and the rear wheel 12R may be drive wheels.

The working machine 20 is positioned behind the vehicle 11 . The work machine 20 includes a plurality of blades 21 for tillage, for example. The work machine 20 can cultivate a field by rotating the blade 21 while the blade 21 is in contact with the ground GR of the field. In addition, in FIG. 1 , the plurality of blades 21 are illustrated in a simplified columnar shape.

The electric tractor 10 has a support mechanism 30 . The support mechanism 30 connects the vehicle body 13 and the work machine 20 . The support mechanism 30 has a support shaft 31 . Although not shown, the support mechanism 30 also includes a plurality of rods, hydraulic circuits, control valves, hydraulic cylinders, and the like. In the support mechanism 30, the hydraulic cylinders are operated by opening and closing control valves and the like. As a result, the work machine 20 rotates around the support shaft 31 . Specifically, the work machine 20 rotates the plurality of blades 21 about the support shaft 31 in the approaching direction D1 or the separating direction D2. The approach direction D1 is the direction in which the blade 21 approaches the ground GR. The separation direction D2 is the direction in which the blade 21 is separated from the ground GR.

<Power transmission path of electric tractor>
As shown in FIG. 2 , the electric tractor 10 includes a first electric motor 41 , a second electric motor 42 , a third electric motor 43 , a power transmission mechanism 19 , a PTO 25 and a hydraulic device 35 . The first electric motor 41, the second electric motor 42, and the third electric motor 43 are generator motors. "PTO" means "power take off".

The first electric motor 41 is a drive source for causing the electric tractor 10 to travel. The first electric motor 41 is connected through the power transmission mechanism 19 to the rear wheel 12R. The power transmission mechanism 19 includes, for example, a speed reduction mechanism that amplifies and outputs torque.

The second electric motor 42 is a drive source for the working machine 20 . The second electric motor 42 is connected to the blade 21 of the work machine 20 via the PTO 25. The PTO 25 is a device for transmitting the torque of the second electric motor 42 to the blades 21 . The PTO 25 includes, for example, a speed reduction mechanism.

The third electric motor 43 is a drive source for the hydraulic device 35 . The third electric motor 43 drives the hydraulic device 35 . The hydraulic device 35 generates hydraulic pressure based on the driving force from the third electric motor 43 . The hydraulic pressure generated by the hydraulic device 35 is supplied to the support mechanism 30 . The support mechanism 30 rotates the work machine 20 in the approach direction D1 and the separation direction D2 based on the supplied hydraulic pressure.

Since the first electric motor 41 is a generator motor, the first electric motor 41 functions as a generator when the electric tractor 10 decelerates. At that time, the electric tractor 10 generates a regenerative braking force according to the amount of power generated by the first electric motor 41 .

<Electrical Configuration of Electric Tractor>
As shown in FIG. 2 , the electric tractor 10 has a power supply circuit 99 . The power supply circuit 99 includes a battery 77 , a positive line 81 , a negative line 82 and a system main relay 80 . The power supply circuit 99 also includes a converter 85 , a first inverter 71 , a second inverter 72 and a third inverter 73 .

Battery 77 is a secondary battery. The battery 77 is a high-voltage battery that drives the electric tractor 10 , the work machine 20 , and the support mechanism 30 . The battery 77 stores electric power to be supplied to the first electric motor 41 , the second electric motor 42 and the third electric motor 43 .

A terminal on the high potential side of the battery 77 is connected to the converter 85 via the positive electrode line 81 . A terminal on the low potential side of the battery 77 is connected to a converter 85 via a negative electrode line 82 . The converter 85 converts the magnitude of the voltage and outputs it.

The system main relay 80 has a positive relay 83 and a negative relay 84 . The positive electrode relay 83 is positioned in the middle of the positive electrode line 81 . The negative relay 84 is located in the middle of the negative line 82 . System main relay 80 turns on and off electrical continuity between battery 77 and converter 85 .

The first inverter 71 and the second inverter 72 are connected in parallel to the converter 85 . The first inverter 71 is connected to the first electric motor 41 . The first inverter 71 performs DC/AC power conversion between the converter 85 and the first electric motor 41 . The second inverter 72 is connected to the second electric motor 42 . The second inverter 72 performs DC/AC power conversion between the converter 85 and the second electric motor 42 .

The third inverter 73 and converter 85 are connected in parallel with the battery 77 . The third inverter 73 is connected to the third electric motor 43 . The third inverter 73 performs DC/AC power conversion between the battery 77 and the third electric motor 43 .

<Configuration of control device, etc.>
The electric tractor 10 includes a control device 100 , an operation section 90 and a GPS device 50 .

The operation unit 90 is attached to the vehicle body 13 . Specifically, the operation unit 90 is attached to the vehicle body 13 at a position that can be operated by the rider of the electric tractor 10 .
The operation unit 90 includes an agricultural field switch S1. The field switch S<b>1 is a switch that can be turned on and off by the rider of the electric tractor 10 . The farm field switch S1 is turned on, for example, when the electric tractor 10 is performing plowing work in the field. When the agricultural field switch S1 is turned on, the agricultural field switch S1 outputs the first signal SIG1.

The GPS device 50 receives signals regarding the current position information PI of the electric tractor 10 from GPS satellites. The position information PI is information including latitude and longitude.
The control device 100 controls the first inverter 71, the second inverter 72, the third inverter 73, and the like. The control device 100 causes the electric tractor 10 to run or stops the electric tractor 10 to run by controlling the first inverter 71 . In addition, control device 100 operates or stops working machine 20 by controlling second inverter 72 . That is, the control device 100 controls input/output power of the battery 77 through control of the first inverter 71 and the second inverter 72 .

Control device 100 also controls system main relay 80 . That is, the control device 100 switches ON/OFF of the electrical connection by the positive electrode relay 83 and the negative electrode relay 84 . Note that if the electrical connection by the positive electrode relay 83 and the negative electrode relay 84 is ON, the battery 77 is in an energized state. That is, the battery 77 supplies power to each device connected to the battery 77 . On the other hand, if the electrical connection by the positive electrode relay 83 and the negative electrode relay 84 is off, the battery 77 is in a non-energized state. Control device 100 operates by receiving power from a low-voltage battery (not shown) that is different from battery 77 .

The control device 100 includes a central processing unit (hereinafter referred to as CPU) 110 and a memory 120 in which control programs and data are stored. The CPU 110 executes the programs stored in the memory 120 to control the above-described controlled objects.

The control device 100 refers to the rotation angle A1 of the rotor of the first electric motor 41 detected by the first rotation sensor 61 when controlling the control target. The control device 100 also refers to the rotation angle A2 of the rotor of the second electric motor 42 detected by the second rotation sensor 62 . The control device 100 also refers to the rotation angle A3 of the rotor of the third electric motor 43 detected by the third rotation sensor 63 . Control device 100 also refers to temperature TI of battery 77 detected by battery temperature sensor 64 . Control device 100 also refers to battery information BI detected by current/voltage sensor 65 . The battery information BI includes information on the voltage and current of the battery 77 . The control device 100 also refers to the acceleration IA of the vehicle body 13 detected by the acceleration sensor 66 . Further, the control device 100 refers to the accelerator operation amount ACCP, which is the operation amount of the accelerator pedal detected by the accelerator position sensor 67 . Also, the control device 100 receives a signal regarding the position information PI via the GPS device 50 .

Note that the control device 100 calculates a first rotation speed Nm1, which is the rotation speed of the rotor of the first electric motor 41, based on the rotation angle A1. Similarly, the control device 100 calculates a second rotation speed Nm2, which is the rotation speed of the rotor of the second electric motor 42, based on the rotation angle A2. Similarly, the control device 100 calculates a third rotation speed Nm3, which is the rotation speed of the rotor of the third electric motor 43, based on the rotation angle A3. Control device 100 also calculates the current state of charge SOC of battery 77 based on battery information BI and temperature TI.

<Regarding farm field determination processing>
The control device 100 executes an agricultural field determination process for determining whether or not the current position of the electric tractor 10 is an agricultural field.

FIG. 2 shows the procedure of the farm field determination process. This processing is realized by CPU 110 repeatedly executing a program stored in memory 120 at predetermined intervals, for example. Also, hereinafter, the step number of each process is represented by a number prefixed with "S".

When this process is started, first, the CPU 110 acquires the first rotation speed Nm1 (S100).
Next, the CPU 110 calculates the speed change amount ΔNm (S110). The CPU 110 calculates the absolute value of a value obtained by subtracting the first rotation speed Nm1 obtained during the previous execution of this process from the first rotation speed Nm1 obtained in S100, and uses the calculated value as the speed change amount ΔNm. do. That is, the speed change amount ΔNm is a value indicating the change amount of the rotation speed of the first electric motor 41 during the execution cycle of this process.

Next, the CPU 110 determines whether or not agricultural field determination conditions including the following condition A are satisfied (S120).
Condition A: The state in which the calculated speed change amount ΔNm is equal to or greater than the specified value ΔNmref continues for the specified period Tp.

As the specified value ΔNmref, based on the fact that the speed change amount ΔNm is equal to or greater than this specified value ΔNmref, the speed change amount ΔNm has changed to such an extent that it can be determined that the electric tractor 10 is currently traveling in a field. The magnitude of the value is set so that it can be accurately determined that the Further, as the specified period Tp, the electric tractor 10 is currently running in the field based on the fact that the period during which the condition of "speed variation ΔNm≧specified value ΔNmref" is continuously satisfied is equal to or longer than the specified period Tp. The magnitude of the value is set so that it can be determined accurately.

When the condition A is satisfied and the field determination condition is satisfied (S120: YES), the CPU 110 determines that the current position of the electric tractor 10 is a field (S130). Then, the CPU 110 adds an agricultural field flag indicating that the current position is an agricultural field to the position information PI acquired from the GPS device 50 (S140), and ends this process.

On the other hand, when it is determined in the process of S120 that the above determination condition is not satisfied (S120::NO), the CPU 110 determines that the current position of the electric tractor 10 is on a general road (S150). Then, the CPU 110 once terminates this process.

<About the action and effect of the present embodiment>
The operation and effects of this embodiment will be described.
(1) Compared to ordinary roads, the rotation resistance of the rear wheels 12R, which are driving wheels, tends to fluctuate more easily in fields, so the rotational speed of the first electric motor 41 that drives these driving wheels tends to fluctuate more easily. Therefore, in the present embodiment, the speed change amount ΔNm indicating the change amount of the rotational speed of the first electric motor 41 is calculated (S110 in FIG. 3). Then, when the state in which the speed change amount ΔNm is equal to or greater than the specified value ΔNmref continues for the specified period Tp, determination processing is performed to determine that the current position is an agricultural field (S120, S130 in FIG. 3). Therefore, it is possible to accurately determine whether or not the current position of the electric tractor 10 is in a field.

<Change example>
It should be noted that the above embodiment can be implemented with the following modifications. The above embodiments and the following modifications can be combined with each other within a technically consistent range.

When it is determined that the current position of the electric tractor 10 is in a field in the field determination process shown in FIG. 3, the process of S140 is executed. processing may be performed.

When the electric tractor 10 is traveling in a field, even if the accelerator operation amount ACCP is kept substantially constant, the rotation speed of the first electric motor 41 tends to fluctuate due to the unevenness of the road surface. Therefore, the following condition B is added as the agricultural field determination condition. Then, it may be determined that the current position of the electric tractor 10 is in the field when both the condition A and the condition B are satisfied.

Condition B: The accelerator operation amount ACCP is within the specified range R for the specified time Tpac. As the specified time Tpac and the specified range R, suitable values suitable for field determination are set in advance. According to such a modification, it is possible to more accurately determine that the current position of the electric tractor 10 is an agricultural field.

- When the accelerator operation amount ACCP is large, the speed change amount ΔNm tends to be large. Therefore, by variably setting the specified value ΔNmref so that the specified value ΔNmref increases as the accelerator operation amount ACCP increases, the accuracy of agricultural field determination can be further enhanced.

- During the work in the field, the electric power change due to the use and stoppage of use of the second electric motor 42 and the third electric motor 43 increases. Therefore, when the vehicle is traveling in a field, the amount of change in the charging rate SOC per hour is greater than when traveling on a general road. Therefore, the following condition C is set as an agricultural field determination condition in place of the condition A described above. Then, when the condition C is satisfied, it may be determined that the current position of the electric tractor 10 is in the field.

Condition C: The amount of change per time in the charging rate SOC is equal to or greater than a predetermined specified value SOCref.
However, when the state of charge SOC is in a low or high region, the amount of change in the state of charge SOC per hour may increase even when traveling on a general road, which may lead to erroneous determination. Therefore, the determination based on the condition C may not be performed in such a low region or high region of the state of charge SOC.

Further, when the accelerator operation amount ACCP is large, the amount of change in the charging rate SOC per hour tends to increase. Therefore, by variably setting the specified value SOCref so that the value of the specified value SOCref increases as the accelerator operation amount ACCP increases, the accuracy of agricultural field determination can be further enhanced.

・The friction coefficient μ of the road surface tends to be larger when driving on a field than when driving on a general road. In addition, when traveling in a field, the amount of change in the friction coefficient μ of the road surface tends to be greater than when traveling on a general road. Therefore, the following condition D or condition E is set as the agricultural field determination condition instead of the condition A. Then, it may be determined that the current position of the electric tractor 10 is in the field when the condition D is satisfied or when the condition E is satisfied.

Condition D: The coefficient of friction μ is equal to or greater than a predetermined specified value μref1.
Condition E: The amount of change per hour in the coefficient of friction μ is equal to or greater than a predetermined specified value μref2.
Note that the coefficient of friction μ may be obtained in an appropriate manner. For example, it may be calculated using the following equations (1) and (2).

Tm1=I×dω/dt (1)
I: Rotational inertia of rear wheel 12R Tm1: Output torque of first electric motor 41 dω/dt: Time differential value of rotation angle A1 μ=(Tm1/r−m×a)/(m×g) (2)
μ: coefficient of friction r: radius of rear wheel 12R m: weight of electric tractor 10 a: acceleration of electric tractor 10 in traveling direction g: coefficient of gravity (=9.8)
It should be noted that when the accelerator operation amount ACCP is large, the drive wheels tend to idle, and the value of "mxa" in the above equation (2) increases, so the calculated friction coefficient µ tends to decrease. Therefore, by variably setting the specified value μref1 so that the value of the specified value μref1 increases as the accelerator operation amount ACCP increases, the accuracy of agricultural field determination can be further enhanced.

Further, when the accelerator operation amount ACCP is large, the drive wheels tend to idle, and the value of "mxa" in the above formula (2) tends to fluctuate, so the amount of change in the calculated friction coefficient μ tends to increase. There is Therefore, by variably setting the specified value μref2 so that the value of the specified value μref2 increases as the accelerator operation amount ACCP increases, the accuracy of field determination can be further enhanced.

When the electric tractor 10 is working in a field, the blade 21 of the work machine 20 is often driven while the electric tractor 10 is running. Therefore, as the agricultural field determination condition, the following condition F is set instead of the above condition A. Then, when the condition F is satisfied, it may be determined that the current position of the electric tractor 10 is in the field.

Condition F: The value of the first rotation speed Nm1, which is the rotation speed of the first electric motor 41, is equal to or greater than a predetermined specified value Nm1ref, and the value of the second rotation speed Nm2, which is the rotation speed of the second electric motor 42, is Greater than '0'. Note that the specified value Nm1ref is a value suitable for determining whether or not the electric tractor 10 is running.

If the above condition F is satisfied, the current position of the electric tractor 10 is the position where the work is completed. Therefore, the current position is grasped by acquiring the position information PI. Then, work completion information indicating work completion may be added to the current position in the field map stored in the memory 120 and indicating the range of the field on the map.

- The control device 100 is not limited to one that includes the CPU 110 and the memory 120 and executes software processing. For example, a dedicated hardware circuit such as an ASIC may be provided to perform hardware processing at least part of what is software processed in the above embodiments. That is, the execution device may have any one of the following configurations (a) to (c). (a) A processing device for executing all of the above processes according to a program and a program storage device such as a ROM for storing the program. (b) A processing device and a program storage device for executing part of the above processing according to a program, and a dedicated hardware circuit for executing the remaining processing. (c) provide dedicated hardware circuitry to perform all of the above processing; Here, there may be a plurality of software execution devices provided with a processing device and a program storage device, or a plurality of dedicated hardware circuits.

DESCRIPTION OF SYMBOLS 10... Electric tractor 12R... Rear wheel 20... Working machine 25... PTO
REFERENCE SIGNS LIST 30 support mechanism 41 first electric motor 42 second electric motor 43 third electric motor 50 GPS device 61 first rotation sensor 62 second rotation sensor 63 third rotation sensor 64 battery temperature sensor 65 Current/Voltage Sensor 66 Acceleration Sensor 67 Accelerator Position Sensor 71 First Inverter 72 Second Inverter 73 Third Inverter 77 Battery 80 System Main Relay 85 Converter 99 Power Supply Circuit 100 Control Device 110 Center Processing unit (CPU)
120 memory

Claims (1)

A vehicle body that can be connected to a working machine, an electric motor, a battery that supplies electric power to the electric motor, drive wheels for traveling that are rotated by driving force from the electric motor, and a control device that controls the electric motor. , an electric tractor comprising
The control device is
An electric tractor that executes agricultural field determination processing for determining that the current position is an agricultural field when a state in which the amount of change in the rotation speed of the electric motor is equal to or greater than a specified value continues for a specified period of time.

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