Electric Tractor

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

[Technical field]

[0001] The present invention relates to an electric tractor. [Background technology]

[0002] The electric tractor disclosed in Patent Document 1 includes a battery, an electric motor as a drive source, and drive wheels and a work machine driven by the electric motor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-22662 A Summary of the Invention [Problem to be solved by the invention]

[0004] The electric tractor disclosed in Patent Document 1 is configured to determine whether the current position of the electric tractor is in a farm field or on an ordinary road based on the gear ratio of a transmission included in a power transmission mechanism.

[0005] Here, a lower gear ratio is often used when traveling in a farm field compared to when traveling on a general road. However, a lower gear ratio may also be used when traveling on a general road. Therefore, in a determination based on the gear ratio, for example, there is a risk of erroneously determining that the electric tractor is traveling in a farm field even when it is traveling on a general road, making it difficult to accurately determine whether the current position of the electric tractor is in a farm field. [Means for solving the problem]

[0006] The electric tractor that solves the above problem includes a vehicle body connectable to a work machine, an electric motor, a battery that supplies power to the electric motor, drive wheels that rotate by the driving force from the electric motor, and a control device that controls the electric motor. The control device executes a field determination process that determines that the current position is a 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.

[0007] In a farm field, the rotational resistance of the drive wheels is more likely to fluctuate than on a general road, and therefore the rotational speed of the electric motor that drives the drive wheels is more likely to fluctuate. Therefore, in this configuration, a determination process is executed to determine that the current position is in a farm field if the change in the rotational speed of the electric motor is equal to or greater than a specified value for a specified period of time, so that it is possible to accurately determine whether the current position of the electric tractor is in a farm field. [Brief description of the drawings]

[0008] [Figure 1] FIG. [Diagram 2] FIG. 2 is a diagram showing the electrical configuration and power transmission path of the tractor. [Diagram 3] 4 is a flowchart showing the procedure of a field determination process executed by a control device of an electric tractor according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] <Overall configuration of electric tractor> As shown in Fig. 1, the electric tractor 10 includes a vehicle 11, a work machine 20, and a support mechanism 30. The vehicle 11 has front wheels 12F which are steered wheels, rear wheels 12R which are drive wheels for traveling, and a vehicle body 13. The work machine 20 can be connected to the vehicle body 13 via the support mechanism 30. Note that the front wheels 12F may be drive wheels, or both the front wheels 12F and the rear wheels 12R may be drive wheels.

[0010] The work machine 20 is located rearward as viewed from the vehicle 11. The work machine 20 is equipped with a plurality of blades 21 for, for example, tilling. The work machine 20 can till the field by rotating the blade 21 while the blade 21 is in contact with the ground surface GR of the field. Note that in Fig. 1, the plurality of blades 21 are illustrated simply as cylindrical.

[0011] The electric tractor 10 is equipped with 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 in the figure, the support mechanism 30 also includes a plurality of rods, a hydraulic circuit, a control valve, a hydraulic cylinder, etc. In the support mechanism 30, the hydraulic cylinder operates when the control valve, etc. is opened and closed. This causes the work machine 20 to rotate about the support shaft 31. Specifically, the work machine 20 rotates the multiple blades 21 about the support shaft 31 in an approaching direction D1 or a separating direction D2. The approaching direction D1 is a direction in which the blades 21 approach the ground surface GR. The separating direction D2 is a direction in which the blades 21 are separated from the ground surface GR.

[0012] <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. Note that "PTO" stands for "power take-off."

[0013] The first electric motor 41 is a drive source for propelling the electric tractor 10. The first electric motor 41 is connected to the rear wheel 12R via a power transmission mechanism 19. The power transmission mechanism 19 includes, for example, a reduction gear mechanism that amplifies and outputs torque.

[0014] The second electric motor 42 is a drive source for the work 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 blade 21. The PTO 25 includes, for example, a reduction gear mechanism.

[0015] 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 drive 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 approaching direction D1 and the separating direction D2 based on the supplied hydraulic pressure.

[0016] In addition, 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, a regenerative braking force corresponding to the amount of power generated by the first electric motor 41 is generated in the electric tractor 10.

[0017] <Electric configuration of electric tractor> 2, the electric tractor 10 includes 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.

[0018] The 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.

[0019] A high potential terminal of the battery 77 is connected to the converter 85 via a positive line 81. A low potential terminal of the battery 77 is connected to the converter 85 via a negative line 82. The converter 85 converts the magnitude of the voltage and outputs it.

[0020] The system main relay 80 includes a positive relay 83 and a negative relay 84. The positive relay 83 is located midway along the positive line 81. The negative relay 84 is located midway along the negative line 82. The system main relay 80 turns on and off electrical continuity between the battery 77 and the converter 85.

[0021] 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.

[0022] The third inverter 73 and the converter 85 are connected in parallel to 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.

[0023] <Configuration of control device, etc.> The electric tractor 10 includes a control device 100, an operation unit 90, and a GPS device 50.

[0024] 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 where the operation unit 90 can be operated by a driver of the electric tractor 10. The operation unit 90 includes a field switch S1. The field switch S1 is a switch that can be switched on and off by a driver of the electric tractor 10. The field switch S1 is switched to the on state, for example, when the electric tractor 10 is performing tilling work in a field. When the field switch S1 is switched to the on state, the field switch S1 outputs a first signal SIG1.

[0025] The GPS device 50 receives signals from GPS satellites that indicate the current position information PI of the electric tractor 10. The position information PI is information that includes latitude, longitude, and the like. The control device 100 controls the first inverter 71, the second inverter 72, the third inverter 73, etc. The control device 100 controls the first inverter 71 to run the electric tractor 10 or stop the electric tractor 10 from running. The control device 100 also controls the second inverter 72 to operate or stop the work machine 20. That is, the control device 100 controls the input / output power of the battery 77 through the control of the first inverter 71 and the second inverter 72.

[0026] The control device 100 also controls the system main relay 80. That is, the control device 100 switches on and off the electrical connection by the positive relay 83 and the negative relay 84. When the electrical connection by the positive relay 83 and the negative relay 84 is on, the battery 77 is in a conducting state. That is, the battery 77 supplies power to each device connected to the battery 77. On the other hand, when the electrical connection by the positive relay 83 and the negative relay 84 is off, the battery 77 is in a non-conducting state. The control device 100 operates by receiving power from a low-voltage battery (not shown) separate from the battery 77.

[0027] 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-mentioned controlled objects.

[0028] When controlling the above-mentioned controlled object, 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. 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. The control device 100 also refers to the temperature TI of the battery 77 detected by the battery temperature sensor 64. The control device 100 also refers to the battery information BI detected by the 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. The control device 100 also refers to the accelerator operation amount ACCP, which is the operation amount of the accelerator pedal, detected by the accelerator position sensor 67. The control device 100 also receives a signal related to the position information PI via the GPS device 50.

[0029] 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. The control device 100 also calculates the current charging rate SOC of the battery 77 based on the battery information BI and the temperature TI.

[0030] <About the field determination process> The control device 100 executes a farm field determination process to determine whether the current position of the electric tractor 10 is in a farm field.

[0031] The procedure for the field determination process is shown in Fig. 2. This process is realized by the CPU 110 repeatedly executing a program stored in the memory 120, for example, at a predetermined interval. In the following, the step number of each process is represented by a number preceded by "S".

[0032] When this process starts, first, the CPU 110 obtains 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 the difference between the first rotation speed Nm1 acquired in S100 and the first rotation speed Nm1 acquired the previous time this process was executed, and sets the calculated value as the speed change amount ΔNm. In other words, this speed change amount ΔNm is a value indicating the amount of change in the rotation speed of the first electric motor 41 during the execution cycle of this process.

[0033] Next, the CPU 110 determines whether or not the farm field determination conditions including the following condition A are met (S120). Condition A: The state in which the calculated speed change amount ΔNm is equal to or greater than a specified value ΔNmref continues for a specified period Tp.

[0034] The specified value ΔNmref is set to a value that allows accurate determination that the speed change amount ΔNm has changed to such an extent that it is possible to determine that the electric tractor 10 is currently traveling in a field, based on the speed change amount ΔNm being equal to or greater than this specified value ΔNmref. Also, the specified period Tp is set to a value that allows accurate determination that the electric tractor 10 is currently traveling in a field, based on the period during which the condition "speed change amount ΔNm≧specified value ΔNmref" is continuously satisfied being equal to or greater than this specified period Tp.

[0035] If the condition A is satisfied, and thus the field determination condition is established (S120: YES), the CPU 110 determines that the current position of the electric tractor 10 is a field (S130). The CPU 110 then assigns a field flag indicating that the current position is a field to the position information PI acquired from the GPS device 50 (S140), and temporarily ends this process.

[0036] On the other hand, when it is determined in the process of S120 that the above-mentioned 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 temporarily ends this process.

[0037] <Actions and Effects of the Present Embodiment> The operation and effects of this embodiment will be described. (1) In a farm field, the rotational resistance of the rear wheels 12R, which are the driving wheels, tends to fluctuate more easily than on a general road, and therefore the rotational speed of the first electric motor 41 that drives the driving wheels tends to fluctuate more easily. Therefore, in this embodiment, a speed change amount ΔNm that indicates the amount of change in the rotational speed of the first electric motor 41 is calculated (S110 in FIG. 3). Then, if the speed change amount ΔNm is equal to or greater than a specified value ΔNmref for a specified period Tp, a determination process is executed to determine that the current position is a farm field (S120, S130 in FIG. 3). Therefore, it is possible to accurately determine whether the current position of the electric tractor 10 is a farm field.

[0038] <Example of change> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other to the extent that no technical contradiction occurs.

[0039] In the farm field determination process shown in FIG. 3, when it is determined that the current position of the electric tractor 10 is a farm field, the process of S140 described above is executed. However, other processes different from the process of S140 may be executed.

[0040] When the electric tractor 10 is traveling in a field, even if the accelerator operation amount ACCP is kept almost constant, the rotation speed of the first electric motor 41 is likely to fluctuate due to the influence of unevenness of the road surface, etc. Therefore, the following condition B is added as the field determination condition. Then, when both the above conditions A and B are satisfied, it may be determined that the current position of the electric tractor 10 is in a field.

[0041] Condition B: The accelerator operation amount ACCP is within a specified range R for a specified time Tpac. Note that suitable values ​​suitable for determining a farm field are set in advance as the specified time Tpac and the specified range R. According to this modification example, it is possible to more accurately determine that the current position of the electric tractor 10 is a farm field.

[0042] When the accelerator operation amount ACCP is large, the speed change amount ΔNm tends to be large. Therefore, for example, by variably setting the specified value ΔNmref so that the value of the specified value ΔNmref increases as the accelerator operation amount ACCP increases, the accuracy of the field judgment can be further improved.

[0043] During work in a farm field, the change in power due to the use and stop of the second electric motor 42 and the third electric motor 43 becomes large. Therefore, the amount of change per hour in the state of charge SOC becomes larger when traveling in a farm field compared to when traveling on an ordinary road. Therefore, the following condition C is set as the farm field determination condition instead of the above condition A. Then, when condition C is satisfied, it may be determined that the current position of the electric tractor 10 is in a farm field.

[0044] Condition C: The amount of change per unit time in the state of charge SOC is equal to or greater than a predetermined value SOCref. However, when the SOC is in a low or high range, the amount of change in the SOC per hour may be large even when driving on a general road, which may lead to erroneous determination. Therefore, in such a low or high range of the SOC, the determination based on condition C may not be performed.

[0045] In addition, when the accelerator operation amount ACCP is large, the amount of change in the charging rate SOC per unit time tends to be large. Therefore, for example, 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 the farm field determination can be further improved.

[0046] When traveling on a farm field, the friction coefficient μ of the road surface tends to be larger than when traveling on a general road. Also, when traveling on a farm field, the amount of change in the friction coefficient μ of the road surface tends to be larger than when traveling on a general road. Therefore, instead of the above condition A, the following condition D or condition E is set as the farm field determination condition. Then, when condition D is satisfied or when condition E is satisfied, it may be determined that the current position of the electric tractor 10 is a farm field.

[0047] Condition D: The friction coefficient μ is equal to or greater than a predetermined specified value μref1. Condition E: The change in the friction coefficient μ per unit time is equal to or greater than a predetermined value μref2. The friction coefficient μ may be obtained in any suitable manner. For example, it may be calculated using the following formulas (1) and (2).

[0048] Tm1 = I × dω / dt … (1) I: Rotational inertia of rear wheel 12R Tm1: output torque of the first electric motor 41 dω / dt: Time differential value of rotation angle A1 μ = (Tm1 / rm × a) / (m × g) … (2) μ: Friction coefficient r: Radius of rear wheel 12R m: weight of electric tractor 10 a: Acceleration in the direction of travel of the electric tractor 10 g: Gravity coefficient (=9.8) When the accelerator operation amount ACCP is large, the drive wheels are more likely to spin, and the value of "m×a" in the above formula (2) becomes larger, so the calculated friction coefficient μ tends to become smaller. Therefore, for example, by variably setting the above-mentioned specified value μref1 so that the value of the specified value μref1 becomes larger as the accelerator operation amount ACCP becomes larger, the accuracy of the field judgment can be further improved.

[0049] In addition, when the accelerator operation amount ACCP is large, the drive wheels are more likely to spin, and the value of "m×a" in the above formula (2) is more likely to fluctuate, so the amount of change in the calculated friction coefficient μ tends to be large. Therefore, for example, by variably setting the above-mentioned specified value μref2 so that the value of this specified value μref2 increases as the accelerator operation amount ACCP increases, the accuracy of the field judgment can be further improved.

[0050] When the electric tractor 10 is working in a farm field, the electric tractor 10 is often in a traveling state and the blade 21 of the work machine 20 is driven. Therefore, the following condition F is set as the farm field determination condition instead of the above condition A. Then, if condition F is satisfied, it may be determined that the current position of the electric tractor 10 is in a farm field.

[0051] 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. The specified value Nm1ref is a value suitable for determining whether the electric tractor 10 is traveling or not.

[0052] When the above condition F is satisfied, the current position of the electric tractor 10 is the position where the work is completed. Therefore, the above position information PI is acquired to grasp the current position. Then, work completion information indicating the completion of the work may be added to the current position on the field map, which is a map stored in the memory 120 and shows the range of the field on the map.

[0053] The control device 100 is not limited to a device equipped with a CPU 110 and a memory 120 and executing software processing. For example, a dedicated hardware circuit such as an ASIC may be provided for performing hardware processing of at least a part of what was processed by software in the above embodiment. That is, the execution device may have any of the following configurations (a) to (c). (a) A processing device that executes all of the above processing according to a program, and a program storage device such as a ROM that stores the program. (b) A processing device and a program storage device that execute a part of the above processing according to a program, and a dedicated hardware circuit that executes the remaining processing. (c) A dedicated hardware circuit that executes all of the above processing. Here, there may be a plurality of software execution devices equipped with a processing device and a program storage device, and a dedicated hardware circuit. [Explanation of symbols]

[0054] 10. Electric tractor 12R…Rear wheel 20...Work machinery 25…PTO 30…Support mechanism 41…First electric motor 42...Second electric motor 43…Third electric motor 50...GPS device 61…1st rotation sensor 62…Second rotation sensor 63…Third rotation sensor 64…Battery temperature sensor 65...Current / voltage sensor 66…Accelerometer 67...Accelerator position sensor 71…First inverter 72…Second inverter 73…Third inverter 77…Battery 80…System main relay 85…Converter 99…Power circuit 100...Control device 110...Central Processing Unit (CPU) 120…Memory

Claims

[Claim 1] An electric tractor including a vehicle body connectable to a work machine, an electric motor, a battery supplying power to the electric motor, drive wheels for traveling rotated by a driving force from the electric motor, and a control device for controlling the electric motor, The control device includes: A field determination process is executed to determine that the current location is a 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. Electric tractor.

Images