Control device and control method for performing steering control of a vehicle

Abstract

The steering angle is corrected in real time based on information obtained during normal driving. [Solution] A control device for performing steering control of a vehicle is disclosed. The control device comprises one or more processors and one or more memories for storing computer programs executed by the one or more processors. The one or more processors, by executing the computer programs, perform the following: acquire sensor data from one or more sensors provided on the vehicle to be used to determine the curvature of the path the vehicle is traveling; determine the curvature based on the sensor data; and correct the steering angle of the vehicle's steering wheels based on the curvature.

Description

Technical Field

[0001] The present disclosure relates to a control device and a control method for performing steering control of a vehicle.

Background Art

[0002] Research and development for automating work vehicles such as agricultural tractors are underway. For example, vehicles that travel by automatic steering using a positioning device such as GNSS (Global Navigation Satellite System) capable of precise positioning have been put into practical use. Vehicles that automatically perform speed control in addition to automatic steering have also been put into practical use.

[0003] Patent Document 1 discloses an example of a system for controlling an off-road vehicle (such as an agricultural vehicle or a construction vehicle) that performs automatic driving. The system disclosed in Patent Document 1 has a function of estimating in real time the tire parameters (such as cornering stiffness and tire type) of the vehicle. The system estimates the tire parameters based on the difference between the predicted position of the vehicle predicted based on the motion characteristics of the vehicle and the measured position of the vehicle.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] A vehicle that travels by automatic steering estimates its own position and orientation using various sensors and travels along a predetermined target path. In order to make the vehicle travel along the target path, it is required to accurately adjust the steering angle of the steering wheel (for example, the front wheels) so as to match the curvature of the target path. However, since there is generally a difference between the theoretical movement of the vehicle and the actual movement of the vehicle, it is important to appropriately correct the steering angle according to the difference.

[0006] The present invention provides a vehicle capable of correcting the steering angle in real time based on information obtained during normal driving, without performing special driving to determine correction parameters for steering angle correction, and a control device and control method for said vehicle. [Means for solving the problem]

[0007] This disclosure provides solutions as described in the following items.

[0008] [Item 1] A control device that performs steering control of a vehicle, One or more processors, One or more memories for storing computer programs executed by the one or more processors, Equipped with, The one or more processors execute the computer program, The vehicle is provided with one or more sensors to acquire sensor data used to determine the curvature of the path the vehicle is traveling. Determining the curvature based on the aforementioned sensor data, Based on the curvature, the steering angle of the vehicle's steering wheels is corrected. A control device that performs this operation.

[0009] [Item 2] The control device according to item 1, wherein the one or more processors perform steering angle correction based on the curvature and the wheelbase of the vehicle.

[0010] [Item 3] The above-mentioned sensor 1 or more, A vehicle speed sensor for measuring the vehicle's speed, An angular velocity sensor for measuring the angular velocity of the vehicle around its yaw axis, Includes, The one or more processors determine the curvature based on the travel speed and the angular velocity. The control device according to item 1 or 2.

[0011] [Item 4] With the traveling speed being v, the angular velocity being ω, and the curvature being κ, The control device according to item 3, wherein the one or more processors determine the curvature κ based on the relationship κ = ω / v.

[0012] [Item 5] With the steering angle of the vehicle before correction being δ, the wheelbase being L, the first error coefficient being α, and the second error coefficient being β, The one or more processors κ = tan(δ×β + α) / L ··· (Equation 1) determine the first error coefficient α and the second error coefficient β based on the relationship of and correct the steering angle based on the first error coefficient α and the second error coefficient β, The control device according to item 4.

[0013] [Item 6] The one or more sensors include a steering angle sensor that measures the steering angle of the vehicle, The one or more processors determine the curvature κ based on the traveling speed v and the angular velocity ω during a period in which the vehicle is traveling with the absolute value of the measured steering angle being smaller than a first threshold value, and approximate δ = 0 in Equation 1 κ = tan(α) / L to determine the first error coefficient α based on the relationship of The control device according to item 5.

[0014] [Item 7] The control device according to item 6, wherein the one or more processors determine the second error coefficient β based on the determined first error coefficient α, the curvature κ determined based on the traveling speed v and the angular velocity ω during a period in which the vehicle is traveling with the absolute value of the steering angle being larger than a second threshold value, and Equation 1.

[0015] [Item 8] While the vehicle is traveling, the one or more processors sequentially update the first error coefficient α and the second error coefficient β, and correct the steering angle based on the updated first error coefficient α and second error coefficient β. The control device according to any one of Items 5 to 7.

[0016] [Item 9] The one or more processors select, according to the content of the sensor data and / or the traveling state of the vehicle, a data portion used to determine the curvature from the sensor data acquired when the vehicle is traveling. The control device according to any one of Items 1 to 8.

[0017] [Item 10] The vehicle is operable in an automatic steering mode. The one or more processors Determine a steering angle command value based on a target path and the position of the vehicle. Determine a steering angle correction parameter based on the curvature. Correct the steering angle command value based on the steering angle correction parameter. Execute steering control of the vehicle based on the corrected steering angle command value. The control device according to any one of Items 1 to 9.

[0018] [Item 11] The vehicle is operable in an automatic steering mode. In the automatic steering mode, the one or more processors Acquire information indicating the measured position of the vehicle from a positioning device provided in the vehicle. Acquire information indicating the target path of the vehicle from a storage device. Determine a steering angle command value based on the measured position and the target path. Determine a steering angle correction parameter based on the curvature. Correct the steering angle command value based on the steering angle correction parameter. Based on the corrected steering angle command value, the steering control of the vehicle is performed. A control device as described in any one of items 1 through 9.

[0019] [Item 12] The vehicle is an agricultural tractor, and the control device is as described in any one of items 1 to 11.

[0020] [Item 13] A control device as described in any one of items 1 to 12, The one or more sensors, Running gear including the steering wheels, An actuator that drives the steering wheel according to a command from the control device, A vehicle equipped with the following features.

[0021] [Item 14] A method performed by one or more computers to control the steering of a vehicle, The vehicle is provided with one or more sensors to acquire sensor data used to determine the curvature of the path the vehicle is traveling. Determining the curvature based on the aforementioned sensor data, The steering angle of the vehicle is corrected based on the curvature, A method that includes this.

[0022] [Item 15] A computer program that is executed by one or more computers that perform steering control of a vehicle, wherein the one or more computers The vehicle is provided with one or more sensors to acquire sensor data used to determine the curvature of the path the vehicle is traveling. Determining the curvature based on the aforementioned sensor data, The steering angle of the vehicle is corrected based on the curvature, A computer program that executes an action.

[0023] The comprehensive or specific embodiments of this disclosure may be implemented by apparatus, systems, methods, integrated circuits, computer programs, or computer-readable non-temporary storage media, or any combination thereof. Computer-readable storage media may include volatile storage media or non-volatile storage media. Apparatus may consist of multiple devices. If apparatus consists of two or more devices, these two or more devices may be located in a single device or in two or more separate devices. [Effects of the Invention]

[0024] According to embodiments of the present invention, it is possible to correct the steering angle in real time based on information obtained during normal driving, without having to perform any special driving to determine the correction value for steering angle correction. [Brief explanation of the drawing]

[0025] [Figure 1] This is a block diagram showing a schematic configuration of a vehicle according to an exemplary embodiment of the present invention. [Figure 2] This flowchart shows an example of an operation performed by the processor of the control unit. [Figure 3A] This diagram schematically illustrates the steering angle offset error that occurs when a vehicle is moving in a straight line. [Figure 3B] This diagram schematically illustrates the scale factor error of the steering angle that occurs when a vehicle is turning. [Figure 4] This figure shows an example of vehicle geometry for a vehicle with front-wheel steering. [Figure 5] This flowchart shows an example of a method for determining correction parameters by the processor of a control device. [Figure 6] This is a perspective view showing an example of the exterior of a work vehicle. [Figure 7] This is a schematic side view showing an example of a work vehicle and a work machine attached to the work vehicle. [Figure 8]This is a block diagram showing an example of a schematic configuration of a work vehicle and work machine. [Figure 9] This is a conceptual diagram showing an example of a work vehicle that performs positioning using RTK-GNSS. [Figure 10] This is a schematic diagram showing an example of an operating terminal and a group of operating switches installed inside the cabin. [Figure 11] This is a block diagram showing an example of an ECU (control unit) configuration. [Figure 12A] This figure shows an example of how a work vehicle moves in automatic steering mode. [Figure 12B] This figure shows another example of a work vehicle driving in auto-steering mode. [Figure 12C] This figure shows yet another example of a work vehicle driving in automatic steering mode. [Figure 13] This diagram schematically shows an example of a target route for a work vehicle that travels through a field using automatic steering. [Figure 14] This flowchart shows examples of actions performed by the control system during automatic steering. [Figure 15A] This figure shows an example of a work vehicle traveling along a target route. [Figure 15B] This figure shows an example of a work vehicle positioned to the right of the target path. [Figure 15C] This figure shows an example of a work vehicle positioned to the left of the target path. [Figure 15D] This figure shows an example of a work vehicle facing in a direction inclined relative to the target path. [Modes for carrying out the invention]

[0026] Embodiments of the present disclosure are described below. However, descriptions that are unnecessarily detailed may be omitted. For example, detailed descriptions of already well-known matters and redundant descriptions of substantially identical configurations may be omitted. This is to avoid the following description becoming unnecessarily verbose and to facilitate understanding for those skilled in the art. The inventors provide the accompanying drawings and the following description so that those skilled in the art can fully understand the present disclosure, and not to limit the subject matter described in the claims. In the following description, components having the same or similar function are denoted by the same reference numerals.

[0027] The following embodiments are illustrative, and the technology of this disclosure is not limited to these embodiments. For example, the numerical values, shapes, steps, the order of those steps, the layout of the display screen, etc., shown in the following embodiments are merely examples and can be modified in various ways. Furthermore, it is possible to combine one embodiment with another.

[0028] In this specification, "autonomous driving" means controlling the vehicle's movement through the operation of a control device, without manual operation by a driver (operator). During autonomous driving, not only the vehicle's movement but also the operation of work (e.g., the operation of work equipment) may be controlled automatically. The movement of the vehicle under autonomous driving conditions is referred to as "autonomous driving." The control device can control at least one of the following necessary for the vehicle's movement: steering, adjustment of the driving speed, starting and stopping the vehicle. Steering the vehicle through the operation of the control device, without manual operation by a driver, is referred to as "automatic steering." When controlling a work vehicle equipped with work equipment, the control device may control operations such as raising and lowering the work equipment and starting and stopping the operation of the work equipment. Autonomous driving may include not only driving the vehicle along a predetermined route toward a destination but also driving while following a target. In addition to autonomous driving mode, a vehicle performing autonomous driving may also operate in manual driving mode, where the vehicle is driven by the driver's manual operation. Driving by the driver's manual operation is referred to as "manual driving." "Manual operation by the driver" includes not only manual operation by a driver on board the vehicle, but also remote operation by a driver outside the vehicle. An autonomous vehicle may operate based in part on manual operation by the driver. Some or all of the control devices may be located outside the vehicle. Communication of control signals, commands, or data may take place between the external control devices and the vehicle. An autonomous vehicle may operate autonomously while sensing the surrounding environment without human intervention in controlling the vehicle's movement. A vehicle capable of autonomous operation can operate unmanned. Obstacle detection and obstacle avoidance actions may be performed during autonomous operation.

[0029] Figure 1 is a block diagram showing a schematic configuration of a vehicle 10 according to an exemplary embodiment of the present invention. The vehicle 10 may be, for example, an agricultural work vehicle such as an agricultural tractor. However, the vehicle 10 is not limited to an agricultural work vehicle, and may be other types of vehicles such as a construction work vehicle, a truck, or a passenger car.

[0030] The vehicle 10 shown in Figure 1 comprises a positioning device 30, a sensor group 40, a control device 50, an actuator 60, and a driving device 65. The positioning device 30 measures the position of the vehicle 10 and outputs information indicating the measured position. The sensor group 40 includes various sensors such as a vehicle speed sensor 42, an angular velocity sensor 44, and a steering angle sensor 46. An inertial measurement unit (IMU) including the vehicle speed sensor 42 and the angular velocity sensor 44 may be provided in the vehicle 10. The control device 50 includes one or more processors 52 and one or more memories 54. The driving device 65 includes various devices necessary for driving, such as four wheels (i.e., two front wheels and two rear wheels) and front and rear axles. The driving device 65 includes, for example, two front wheels as drive wheels. The actuator 60 is configured to drive the steering wheels according to commands from the control device 50.

[0031] The control device 50 may be configured to operate in both automatic steering mode and manual steering mode. The control device 50 can switch between automatic steering mode and manual steering mode, for example, in response to driver input. In automatic steering mode, the control device 50 controls the steering of the steering wheels (e.g., left and right front wheels) included in the running gear 65 via the actuator 60 so that the vehicle 10 travels along the target path, based on the position of the vehicle 10 identified by the positioning device 30 and the target path stored in a storage device such as memory 54.

[0032] The positioning device 30 is located inside or outside the vehicle 10. The positioning device 30 may include, for example, a GNSS receiver. The positioning device 30 determines the position of the vehicle 10 based on signals from multiple GNSS satellites and outputs time-series position data. The positioning device 30 may also include devices other than a GNSS receiver, such as a LiDAR sensor or a camera. The position of the vehicle 10 can be estimated by matching data acquired by the LiDAR sensor or camera with a pre-prepared environmental map. The target route is a target route set within the area on which the vehicle 10 travels. The target route may be set before starting automatic steering operation, for example, based on user input, and recorded in a storage device such as memory 54. If the vehicle 10 is an agricultural vehicle such as a tractor, the target route may be set on farm roads within and / or outside the field.

[0033] The control device 50 is a computer configured or programmed to perform steering control for automatic steering. The control device 50 may be, for example, an electronic control unit (ECU) located inside the vehicle 10. At least some of the functions of the control device 50 may be realized by a device located outside the vehicle 10. That is, the functions of the control device 50 may be realized by a collection of computers located inside or outside the vehicle 10.

[0034] As shown in Figure 1, the control device 50 comprises one or more processors 52 and one or more memories 54. Although Figure 1 illustrates one processor 52 and one memory 54, the control device 50 may have multiple processors and / or multiple memories. The memory 54 stores computer programs executed by the processor 52, data referenced by the processor 52, and data generated by the processor 52. The processor 52 may be configured to perform operations including steering control of the vehicle 10 by executing computer programs stored in the memory 54.

[0035] Figure 2 is a flowchart showing an example of an operation performed by the processor 52 of the control device 50. In the example shown in Figure 2, the processor 52 performs the following operations by executing a program stored in memory 54. Step S11: Sensor data is acquired from one or more sensors included in the sensor group 20 installed on the vehicle 10 to be used in determining the curvature of the path the vehicle 10 is traveling along. Based on the acquired sensor data, the curvature of the path that vehicle 10 is traveling is determined (step S12). Based on the determined curvature, the steering angle of the steering wheels of vehicle 10 is corrected (step S13).

[0036] "One or more sensors" could be, for example, a vehicle speed sensor 42 and an angular velocity sensor 44. These sensors can measure the vehicle speed (also referred to as "vehicle speed") and the angular velocity of the vehicle 10 around its yaw axis (also referred to as "yaw rate"). As will be described later, the processor 52 can determine the curvature of the path the vehicle 10 is traveling (hereinafter sometimes referred to as "travel curvature") based on the vehicle speed measured by the vehicle speed sensor 42 and the angular velocity (yaw rate) measured by the angular velocity sensor 44.

[0037] The processor 52 may also determine the curvature using signals from sensors other than the vehicle speed sensor 42 and the angular velocity sensor 44. For example, if the sensor group 40 includes an acceleration sensor, the curvature may be determined based on its measured value. Alternatively, if the positioning device 30 is capable of high-precision positioning such as RTK-GNSS, the driving curvature of the vehicle 10 may be determined based on the time change of position measured by the positioning device 30.

[0038] "Steering angle correction" is a process that adjusts the steering angle so that the vehicle travels with the target curvature by correcting the command values ​​of the steering angles of the steering wheels (for example, the left and right front wheels) of the vehicle 10. As will be described later, the processor 52 can perform steering angle correction based on the curvature determined in step S12 and the wheelbase of the vehicle 10.

[0039] If the vehicle 10 is capable of operating in automatic steering mode, the processor 52 may be configured to perform the following operations in automatic steering mode. • Information indicating the measured position of the vehicle 10 is obtained from the positioning device 30. • Information indicating the target route of vehicle 10 is obtained from a storage device (e.g., memory 54). Based on the measurement position and target path, the rudder angle command value is determined by a predetermined algorithm. The steering angle value of the front wheels of vehicle 10 is obtained from the steering angle sensor 46. Based on the curvature determined in step S12 and the front wheel steering angle obtained from the steering angle sensor 46, the steering angle correction parameters are determined. The steering angle command value is corrected based on the determined steering angle correction parameters. Based on the corrected steering angle command value, the vehicle's steering control is executed.

[0040] The "rudder angle correction parameters" are parameters used to correct the rudder angle. These parameters may include, for example, the error coefficients α and β described later, or any parameters derived from them.

[0041] On the other hand, in manual steering mode, no steering angle correction is performed, but it is possible to perform processing to determine the steering angle correction parameters used in automatic steering mode. In manual steering mode, the processor 52 may be configured to perform the following operations. The steering angle value of the front wheels of the vehicle 10, which changes based on the steering operation of the vehicle by the driver, is obtained from the steering angle sensor 46. Based on the curvature determined in step S12 and the front wheel steering angle obtained from the steering angle sensor 46, steering angle correction parameters are determined and recorded in the storage device.

[0042] Through the above operation, the control device 50 can acquire steering angle correction parameters for optimizing the steering angle in automatic steering mode based on the actual curvature of the path the vehicle 10 is traveling. This allows for real-time steering angle correction during normal driving without having to perform any special driving to acquire correction values ​​for steering angle correction.

[0043] As mentioned above, there is generally a difference between the theoretical movement of a vehicle and the actual movement of a vehicle. For example, due to various factors such as unevenness of the ground, mounting errors of components, and detection errors of sensors, the curvature of the vehicle 10 during travel may deviate from the curvature calculated based on the theoretical movement of the vehicle. Therefore, in order to make the vehicle travel along the target path, it is necessary to appropriately determine the steering angle correction value to reduce the difference between the theoretical movement and the actual movement of the vehicle.

[0044] Examples of correction values ​​include a straight-line correction value to correct offset errors during straight-line driving, and a turning correction value to correct scale factor errors during turning. These errors and correction values ​​will be explained below with reference to Figures 3A and 3B.

[0045] Figure 3A schematically shows the steering angle offset error that occurs when vehicle 10 is moving in a straight line. Figure 3B schematically shows the steering angle scale factor error that occurs when vehicle 10 is turning. In Figures 3A and 3B, the target path P0 is shown by a dashed arrow, and the actual path P1 of vehicle 10 is illustrated by a solid arrow. The steering angle corresponding to the target path P0 is represented by δ, the coefficient of the offset error when moving in a straight line (first error coefficient) is represented by α, and the coefficient of the scale factor error when turning (second error coefficient) is represented by β.

[0046] As shown in Figure 3A, even if the steering angle command value is set to 0 degrees (δ=0) to make the vehicle 10 move in a straight line, the actual trajectory of the vehicle 10 may correspond to the trajectory when the steering angle is α (≠0) due to offset errors. Also, as shown in Figure 3B, even if the steering angle command value is set to δ to make the vehicle 10 turn along a predetermined target path P0, the actual trajectory of the vehicle 10 may correspond to the trajectory when the steering angle is δ×β+α due to scale factor errors and offset errors. Therefore, it is necessary to correct the steering angle command value to eliminate the effects of these errors. The correction of the steering angle command value can be done by identifying coefficients α and β and using those values ​​to correct the steering angle command value, for example, from δ to δ'=(δ-α) / β.

[0047] Conventionally, the above-mentioned problems have been addressed by implementing a special mode in the vehicle, separate from the normal driving mode, for determining correction parameters such as coefficients α and β. In such a mode, the vehicle is driven manually or automatically along one of several predetermined paths, such as a straight path or a circular arc with a predetermined curvature, and the correction parameters are determined based on the data obtained during this process. For example, the offset error coefficient α can be determined by driving the vehicle manually or automatically along a straight path and using the commanded or measured steering angle during the drive. Alternatively, the scale factor error coefficient β can be determined by driving the vehicle at a predetermined steering angle and using the curvature of the actual driving trajectory measured during that time (hereinafter also referred to as "driving curvature"), the steering angle command, and the previously determined coefficient α. This operation of driving the vehicle in such a special mode to determine the correction parameters may be performed, for example, by the manufacturer or dealer before the vehicle is sold, or by the service provider or user during maintenance, modification, or repair.

[0048] Appropriate correction parameters can vary from aircraft to aircraft. Furthermore, even within the same aircraft, these parameters can change due to aging, modifications, or repairs. Therefore, it is necessary to update the correction parameters as needed. However, determining or updating these parameters using the special modes described above is a complex process, requiring more than 10 minutes per operation even for experienced operators. Moreover, if the operation is not performed correctly, the correction parameters may not be updated properly, potentially leading to a decrease in the accuracy or precision of steering control.

[0049] Therefore, the embodiments of this disclosure provide a method for automatically determining correction parameters based on information obtained during normal driving of the vehicle 10. This makes it possible to determine correction parameters without performing predetermined operations that were necessary in conventional methods using modes for acquiring correction parameters.

[0050] Now, with reference to Figure 4, the method of steering angle correction according to this embodiment will be explained in more detail.

[0051] Figure 4 shows an example of vehicle geometry in a front-wheel steering vehicle with an Ackermann-Jant mechanism. Figure 4 shows the front wheel 62 and rear wheel 64, which are located on the outside during turns and are part of the vehicle's running gear. Let r be the turning radius of the vehicle, L be the distance between the axles of the front wheel 62 and the rear wheel 64 (i.e., the wheelbase), and δ be the steering angle of the front wheel 62 (i.e., the steering wheel). Theoretical driving curvature κ based on vehicle geometry. theory This is calculated by the following formula (1).

number

[0052] In actual vehicles, equation (1) does not necessarily hold due to various factors such as tire slip or mounting errors of components such as actuators or sensors. The actual driving curvature κ of a vehicle can be expressed, for example, by the following equation (2), which includes the aforementioned error coefficients α and β.

number

[0053] Here, α represents the offset error coefficient that causes curvature error when the rudder angle δ is zero (0), and β represents the scale factor error coefficient that causes curvature error proportional to the rudder angle δ. The error coefficients α and β are related to the straight-line correction value and the turning correction value, respectively.

[0054] On the other hand, the following relationship (3) holds between the vehicle speed v, the angular velocity (yaw rate) around the yaw axis (yaw rate) of a moving vehicle, and the curvature κ of the vehicle.

number

[0055] In this embodiment, the processor 52 of the control device 50 may be configured to determine error coefficients α and β based on the relationship between equations (1) to (3) and the vehicle speed v, angular velocity ω, and steering angle δ while the vehicle 10 is traveling in manual or automatic driving mode. The vehicle speed v may be measured by the vehicle speed sensor 42. The angular velocity ω may be measured by the angular velocity sensor 44. When the vehicle 10 is traveling with automatic steering, the steering angle δ may be a steering angle command value determined by the processor 52 according to a predetermined algorithm based on the current position and orientation of the vehicle 10 and the target path. When the vehicle 10 is traveling with manual steering, the steering angle δ may be a front wheel steering angle value determined based on the steering operation by the driver.

[0056] The processor 52 can determine correction parameters (error coefficients α and β) by, for example, the process shown in Figure 5. Figure 5 is a flowchart showing an example of how the processor 52 of the control device 50 determines the error coefficients α and β. The operation shown in Figure 5 is performed when the vehicle 10 is traveling by automatic or manual driving. The travel path of the vehicle 10 is arbitrary. In the example in Figure 5, the processor 52 performs the following operations.

[0057] In step S21, the processor 52 determines whether the absolute value of the steering angle is smaller than a first threshold. The steering angle may be a value measured by the steering angle sensor 46, or, in the case of autonomous driving, a steering angle command value determined by the processor 52. The first threshold may be set to a positive value close to zero. For example, the first threshold may be set to a value within the range of 0.01° to 1°. That is, the processor 52 determines whether the vehicle 10 is traveling with a steering angle δ that is substantially zero. Based on this determination, the processor 52 detects a section in which the vehicle 10 is traveling in a straight line. If the steering angle δ is smaller than the first threshold, the process proceeds to step S22. The operation of step S21 is repeated until it is determined that the steering angle δ is smaller than the first threshold. Note that the processor 52 does not immediately proceed to step S22 when the steering angle δ is smaller than the first threshold, but may proceed to step S22 only if the condition in which the steering angle δ is smaller than the first threshold continues for a predetermined time (for example, several seconds) or longer.

[0058] In step S22, the processor 52 acquires the measured values ​​of the vehicle 10's travel speed v and angular velocity ω. The processor 52 acquires the measured value of the travel speed v from the vehicle speed sensor 42 and the measured value of the angular velocity ω from the angular velocity sensor 44.

[0059] In step S23, the processor 52 determines the actual curvature κ of the vehicle 10 using the relationship in equation (3) based on the travel speed v and angular velocity ω.

[0060] In step S24, the processor 52 determines a first error coefficient α based on the driving curvature κ determined in step S23 and the relationship κ = tan(α) / L, which is approximated as δ = 0 in equation (2). Here, the wheelbase L is a known value and is pre-stored in a memory device such as memory 54. The processor 52 stores the determined coefficient α in the memory device.

[0061] In step S25, the processor 52 determines whether the absolute value of the steering angle or steering angle command value measured by the steering angle sensor 46 is greater than the second threshold. Based on this determination, the processor 52 detects the section in which the vehicle 10 is turning. The second threshold may be the same value as the first threshold, or it may be a value greater than the first threshold. The second threshold may be set to a value within the range of, for example, 0.01° to 30°. If the steering angle δ is greater than the second threshold, the process proceeds to step S26. The operation of step S25 is repeated until it is determined that the steering angle δ is greater than the threshold.

[0062] In step S26, the processor 52 determines whether the time variation of the rudder angle δ is small and stable. For example, the processor 52 may determine whether the rudder angle δ is stable by determining whether the value obtained by averaging the rate of change of the rudder angle δ over a predetermined time is small or less than a threshold close to zero. If the rudder angle δ is stable, the process proceeds to step S27. If the rudder angle δ is not stable, the process returns to step S25.

[0063] In step S27, the processor 52 acquires the measured values ​​of the vehicle 10's travel speed v and angular velocity ω. The processor 52 acquires the measured value of the travel speed v from the vehicle speed sensor 42 and the measured value of the angular velocity ω from the angular velocity sensor 44.

[0064] In step S28, the processor 52 determines the actual curvature κ of the vehicle 10 using the relationship in equation (3) based on the travel speed v and angular velocity ω.

[0065] In step S29, the processor 52 determines a second error coefficient β based on the first error coefficient α determined in step S24, the driving curvature κ determined in step S27, and the relationship shown in equation (2). The processor 52 stores the determined coefficient β in the memory.

[0066] Once step S29 is completed, the processor 52 can start automatic steering control, including rudder angle correction using the determined error coefficients α and β. For example, the processor 52 can achieve steering control that reduces the effects of offset error and scale factor error by correcting the rudder angle δ (command value) to δ' calculated by δ' = (δ - α) / β.

[0067] The operation shown in Figure 5 may be performed repeatedly while the vehicle 10 is in motion. The processor 52 may determine the final coefficients α and β by averaging the coefficients α and β that have been repeatedly calculated over a predetermined period of time. For example, the coefficient α may be calculated multiple times by repeating the process from steps S22 to S24 during the period when the vehicle 10 is substantially moving in a straight line, and the average value of these coefficients may be determined as the final coefficient α. Similarly, the coefficient β may be calculated multiple times by repeating the process from steps S27 to S29 during the period when the time change of the steering angle δ is small, and the average value of these coefficients may be determined as the final coefficient β. The processor 52 may perform the operation to determine the coefficients α and β at regular intervals while the vehicle 10 is in motion, or only within a relatively short time after the vehicle 10 starts moving. Alternatively, the processor 52 may perform the operation to determine the coefficients α and β at a timing specified by the user.

[0068] The processor 52 may sequentially update the first error coefficient α and the second error coefficient β while the vehicle 10 is in motion, and correct the steering angle based on the updated first error coefficient α and the second error coefficient β. This allows the steering angle to be optimized in real time in response to changes in the state of the vehicle 10 or the surrounding environment while it is in motion.

[0069] The processor 52 may select a portion of the sensor data acquired while the vehicle 10 is in motion to be used to determine the curvature, depending on the content of the sensor data and / or the driving state of the vehicle 10. For example, the processor 52 may determine the curvature using only the data acquired from the vehicle speed sensor 42 and / or the angular velocity sensor 44 during a period in which at least one of the vehicle speed, acceleration, and angular velocity satisfies a predetermined condition. The predetermined condition may include, for example, at least one of the following: the vehicle speed is lower than the reference speed, the rate of change of acceleration over time is lower than the reference value, and the rate of change of angular velocity over time is lower than the reference value. This makes it possible to determine the curvature more accurately based on sensor data acquired during periods of little curvature fluctuation or periods of little acceleration or deceleration.

[0070] Through the above operation, the processor 52 can determine the error coefficients α and β while the user is driving the vehicle 10 in a normal, everyday manner, without having to drive the vehicle 10 in a special mode for determining the error coefficients α and β. Since information necessary for steering angle correction can be collected during the normal driving of the vehicle 10, the need for driving in a special mode, which was previously required, can be eliminated.

[0071] In conventional methods, the actual driving curvature can be calculated with high accuracy by retrospectively processing information obtained during driving along a predetermined trajectory, thereby obtaining parameters for steering angle correction. On the other hand, as in this embodiment, when driving is not performed along a predetermined trajectory, it is necessary to obtain the actual driving curvature without knowing what path the driver will take, and a method for obtaining the actual driving curvature in real time rather than retrospectively is required. In this embodiment, by newly using the relationship in equation (3), the actual driving curvature can be dynamically estimated based on information obtained from the vehicle speed sensor 42 and the angular velocity sensor 44. This eliminates the need to perform driving operations along a predetermined trajectory, improving convenience. In this embodiment, the correction parameters can be updated sequentially during daily driving, not limited to the timing of vehicle maintenance, repair, or modification. This effectively prevents a decrease in the accuracy of steering control due to aging deterioration, and eliminates the need for the user to periodically perform operations to update the correction parameters.

[0072] Next, a more specific embodiment in which the technology of this disclosure is applied to an agricultural work vehicle, which is an example of vehicle 10, will be described.

[0073] <Structure> Figure 6 is a perspective view showing an example of the external appearance of the work vehicle 100. Figure 7 is a schematic side view showing an example of the work vehicle 100 and an implement 300 connected to the work vehicle 100. In this embodiment, the work vehicle 100 is a tractor used in a field. The work vehicle 100 is equipped with an automatic steering function.

[0074] The work vehicle 100 in this embodiment includes a positioning device 120 and one or more obstacle sensors 130. Figure 7 illustrates one obstacle sensor 130, but the obstacle sensors 130 may be provided at multiple locations on the work vehicle 100. The obstacle sensors 130 are provided as needed. If they are not needed, the work vehicle 100 does not need to be equipped with obstacle sensors 130.

[0075] As shown in Figure 7, the work vehicle 100 comprises a vehicle body 101, a prime mover (engine) 102, and a transmission 103. The vehicle body 101 is provided with wheels 104 with tires and a cabin 105. The wheels 104 include a pair of front wheels 104F and a pair of rear wheels 104R. These wheels 104, along with the front and rear axles, are components of the running gear. Inside the cabin 105 are a driver's seat 107, a steering gear 106, several pedals 109, an operating terminal 200, and a group of switches for operation. One or both of the front wheels 104F and the rear wheels 104R may be replaced with crawlers in which tracks are mounted on multiple wheels instead of wheels with tires.

[0076] The positioning device 120 in this embodiment includes a GNSS receiver. The GNSS receiver may include an antenna that receives signals from GNSS satellites and a processor that determines the position of the work vehicle 100 based on the signals received by the antenna. The positioning device 120 receives GNSS signals transmitted from multiple GNSS satellites and performs positioning based on the GNSS signals. GNSS is a general term for satellite positioning systems such as GPS (Global Positioning System), QZSS (Quasi-Zenith Satellite System, e.g., Michibiki), GLONASS, Galileo, and BeiDou. The positioning device 120 in this embodiment is located on top of the cabin 105, but it may be located in other positions.

[0077] The positioning device 120 may include, in addition to or instead of a GNSS receiver, other types of devices such as a LiDAR sensor or a camera (including an image sensor). If there are features that function as feature points in the environment in which the work vehicle 100 is traveling, the position of the work vehicle 100 can be estimated with high accuracy based on data acquired by the LiDAR sensor or camera and an environmental map previously recorded in the storage device 170. The LiDAR sensor or camera may be used in combination with the GNSS receiver. By correcting or supplementing the position data based on the GNSS signal using the data acquired by the LiDAR sensor or camera, the position of the work vehicle 100 can be determined with even higher accuracy.

[0078] The prime mover 102 may be, for example, a diesel engine. An electric motor may be used instead of a diesel engine. The transmission 103 can change the propulsion force and travel speed of the work vehicle 100 by shifting gears. The transmission 103 can also switch the work vehicle 100 between forward and reverse.

[0079] The steering system 106 includes a steering wheel, a steering shaft connected to the steering wheel, and a power steering system that assists steering by the steering wheel. The front wheels 104F are steering wheels, and by changing their steering angle, the direction of travel of the work vehicle 100 can be changed. The steering angle of the front wheels 104F can be changed by operating the steering wheel. The power steering system includes a hydraulic system or electric motor that supplies auxiliary force to change the steering angle of the front wheels 104F. When automatic steering is performed, the steering angle is automatically adjusted by the force of the hydraulic system or electric motor under control from a control device located inside the work vehicle 100.

[0080] The multiple pedals 109 include an accelerator pedal, a clutch pedal, and a brake pedal. Each pedal may be equipped with a sensor to detect when it is pressed.

[0081] A coupling device 108 is provided at the rear of the vehicle body 101. The coupling device 108 includes, for example, a three-point support device (also referred to as a "three-point link" or "three-point hitch"), a PTO (Power Take Off) shaft, a universal joint, and a communication cable. The coupling device 108 allows the work implement 300 to be attached to and detached from the work vehicle 100. The coupling device 108 can control the position or posture of the work implement 300 by raising and lowering the three-point link, for example, by a hydraulic system. Power can also be supplied from the work vehicle 100 to the work implement 300 via the universal joint. The work vehicle 100 can pull the work implement 300 and cause the work implement 300 to perform a predetermined operation. The coupling device may be provided at the front of the vehicle body 101. In that case, the work implement can be connected to the front of the work vehicle 100.

[0082] The implement 300 shown in Figure 7 is a rotary tiller, but the implement 300 is not limited to a rotary tiller. For example, any implement such as a mower, seeder, spreader, rake, baler, harvester, spreader, or harrow can be connected to the work vehicle 100 and used.

[0083] Figure 8 is a block diagram showing an example of a schematic configuration of a work vehicle 100 and a work machine 300. The work vehicle 100 and the work machine 300 can communicate with each other via a communication cable included in the coupling device 108.

[0084] In the example shown in Figure 8, the work vehicle 100 includes a positioning device 120, an obstacle sensor 130, and an operating terminal 200, as well as an inertial measurement unit (IMU) 125, a drive unit 140, a sensor group 150, a control system 160, a communication interface (I / F) 190, an operating switch group 210, and a buzzer 220. These components can be connected to each other via a bus so as to be able to communicate with one another.

[0085] The positioning device 120 comprises a GNSS receiver 121, an RTK receiver 122, and a processor 123. The inertial measurement unit 125 comprises an acceleration sensor 126, an angular velocity sensor 127, and a processor 128. The sensor group 150 includes, for example, a steering wheel sensor 152, a steering angle sensor 154, and a vehicle speed sensor 156. The control system 160 comprises a storage device 170 and a control device 180. The control device 180 comprises a plurality of electronic control units (ECUs) 182, 183, 184, and 185. The work machine 300 comprises a drive unit 340, a control device 380, and a communication interface (I / F) 390. Note that Figure 8 shows components that are relatively highly related to the automatic steering or automatic driving operation of the work vehicle 100, and other components are not shown.

[0086] The GNSS receiver 121 in the positioning device 120 receives satellite signals (also referred to as "GNSS signals") transmitted from multiple GNSS satellites and generates GNSS data based on the satellite signals. The GNSS data is generated in a predetermined format, such as the NMEA-0183 format. The GNSS data may include, for example, the identification number, elevation angle, azimuth angle, and received signal strength of each satellite from which the satellite signal was received. The received signal strength may be expressed by a value such as the carrier noise power density ratio (C / N0). The GNSS data may also include position information of the work vehicle 100 calculated based on the received satellite signals, and information indicating the reliability of said position information. The position information may be expressed by, for example, latitude, longitude, and height above mean sea level. The reliability of the position information may be expressed by, for example, a DOP value indicating the satellite configuration.

[0087] The positioning device 120 shown in Figure 8 uses RTK (Real Time Kinematic)-GNSS to position the work vehicle 100. Figure 9 is a conceptual diagram showing an example of a work vehicle 100 performing RTK-GNSS positioning. In RTK-GNSS positioning, in addition to satellite signals transmitted from multiple GNSS satellites 90, a correction signal transmitted from a base station 92 is used. The base station 92 may be installed near the field where the work vehicle 100 is performing its work (for example, within 10 km of the work vehicle 100). Based on the satellite signals received from multiple GNSS satellites 90, the base station 92 generates a correction signal, for example, in RTCM format and transmits it to the positioning device 120. The RTK receiver 122 includes an antenna and a modem and receives the correction signal transmitted from the base station 92. The processor 123 of the positioning device 120 corrects the positioning result from the GNSS receiver 121 based on the correction signal. By using RTK-GNSS, positioning can be performed with an accuracy of, for example, a few centimeters. Position information, including latitude, longitude, and altitude, is acquired by high-precision positioning using RTK-GNSS. The processor 123 of the positioning device 120 calculates the position of the work vehicle 100 at a frequency of, for example, 1 to 10 times per second. The positioning device 120 outputs time-series data containing the calculated position (coordinate) information.

[0088] Furthermore, the positioning method is not limited to RTK-GNSS; any positioning method that can obtain the necessary accuracy of positional information (such as interferometric positioning or relative positioning) can be used. For example, positioning may be performed using VRS (Virtual Reference Station) or DGPS (Differential Global Positioning System). If the necessary accuracy of positional information can be obtained without using the correction signal transmitted from the base station 92, the positioning device 120 may be generated without using the correction signal. In that case, the positioning device 120 does not need to be equipped with an RTK receiver 122.

[0089] Instead of the inertial measurement unit 125, an acceleration sensor 126 and an angular velocity sensor 127 may be separately provided on the work vehicle 100. Such acceleration sensor 126 and angular velocity sensor 127 are included in the sensor group 150. The acceleration sensor 126 is, for example, a 3-axis acceleration sensor. The angular velocity sensor 127 is, for example, a 3-axis gyroscope. The processor 128 can output time-series data including position and orientation information of the work vehicle 100 by performing processing such as integrating the measured values ​​of the acceleration sensor 126 and the measured values ​​of the angular velocity sensor 127 over time. Instead of performing the above processing, the processor 128 may perform necessary correction processing on the measured values ​​of the acceleration sensor 126 and the angular velocity sensor 127 and output data including corrected acceleration and angular velocity and measurement time information. The inertial measurement unit 125 may also be equipped with an orientation sensor such as a 3-axis geomagnetic sensor. The inertial measurement unit 125 functions as a motion sensor and can output signals indicating various quantities such as acceleration, velocity, displacement, and posture of the work vehicle 100. The inertial measurement unit 125 can output these signals at a frequency of, for example, several tens to several thousand times per second.

[0090] The positioning device 120 and the inertial measurement unit 125 may be integrated as a single device. The processing of processors 123 and 128 may be performed by a single processor. At least part of the processing of processors 123 and 128 may be performed by a processor included in the control unit 180. Such a processor can estimate the position and orientation of the work vehicle 100 with higher accuracy based on the signal output from the inertial measurement unit 125 in addition to the GNSS signal and correction signal. The signal output from the inertial measurement unit 125 can be used to correct or complement the position calculated based on the GNSS signal and correction signal. The inertial measurement unit 125 can output signals at a higher frequency than the positioning device 120. Its high-frequency signals can be used to measure the position and orientation of the work vehicle 100 at a higher frequency (e.g., 10 Hz or higher).

[0091] The positioning device 120 may include, in addition to or instead of, the GNSS receiver 121 and the RTK receiver 122, other types of sensors such as a LiDAR sensor or an image sensor. If there are landmarks in the environment in which the work vehicle 100 is traveling, the position and orientation of the work vehicle 100 can be estimated by matching the sensor data output from these sensors with an environmental map. In such a configuration, external sensors such as a LiDAR sensor or an image sensor may be included in the positioning device.

[0092] The drive system 140 includes various devices necessary for the movement of the work vehicle 100 and the driving of the work equipment 300, such as the prime mover 102, transmission 103, steering system 106, and coupling device 108. The prime mover 102 may be an internal combustion engine, such as a diesel engine. The drive system 140 may also be equipped with an electric motor for traction, either in place of or in conjunction with the internal combustion engine.

[0093] The steering wheel sensor 152 measures the rotation angle of the steering wheel of the work vehicle 100. The steering angle sensor 154 measures the steering angle of the front wheels 104F, which are the steering wheels. The vehicle speed sensor 156 is a sensor that measures the travel speed (vehicle speed) of the work vehicle 100.

[0094] The vehicle speed sensor 156 may be configured to measure, for example, the rotational speed of an axle connected to a wheel 104, i.e., the number of rotations per unit time. Such a vehicle speed sensor 156 may include, for example, a magnetoresistive element (MR), a Hall element, or an electromagnetic pickup. The vehicle speed sensor 156 may be configured to output a pulse signal proportional to the rotational speed of a gear included in the transmission, for example.

[0095] The values ​​measured by the steering wheel sensor 152, steering angle sensor 154, and vehicle speed sensor 156 are used for steering control by the control device 180.

[0096] The storage device 170 includes one or more storage media, such as flash memory or magnetic disks. The storage device 170 stores various data generated by each sensor and the control device 180. The data stored in the storage device 170 may include map data of the environment in which the work vehicle 100 travels, and data of the target route for automatic steering. The storage device 170 also stores computer programs that cause each ECU in the control device 180 to perform various operations described later. Such computer programs may be provided to the work vehicle 100 via a storage medium (e.g., semiconductor memory or optical disk) or a telecommunications line (e.g., the Internet). Such computer programs may be sold as commercial software.

[0097] The control device 180 includes multiple ECUs. These multiple ECUs include ECU 182 for driving control, ECU 183 for automatic steering control, ECU 184 for work equipment control, and ECU 185 for display control. ECU 182 controls the speed of the work vehicle 100 by controlling the prime mover 102, transmission 103, accelerator, and brakes included in the drive unit 140. ECU 182 also controls the steering of the work vehicle 100 by controlling the hydraulic system or electric motor included in the steering unit 106 based on the measurement value of the steering wheel sensor 152. ECU 183 performs calculations and controls to realize automatic steering operation based on signals output from the positioning device 120, inertial measurement unit 125, steering wheel sensor 152, steering angle sensor 154, vehicle speed sensor 156, etc. ECU 183 functions as the control device 50 shown in Figure 1 and corrects the steering angle in the manner described with reference to Figures 2 to 5. During automatic steering operation, ECU 183 sends a command to ECU 182 to change the steering angle. ECU 182 changes the steering angle by controlling the steering device 106 in response to the command. ECU 184 controls the operation of the coupling device 108 to cause the implement 300 to perform the desired operation. ECU 184 also generates signals to control the operation of the implement 300 and transmits these signals to the implement 300 via the communication I / F 190. ECU 185 controls the display on the operation terminal 200. ECU 185 enables various displays on the display device of the operation terminal 200, such as a field map, the position and target route of the work vehicle 100 on the map, pop-up notifications, and a settings screen.

[0098] Through the operation of these ECUs, the control device 180 enables driving by manual or automatic steering. During automatic steering operation, the control device 180 determines the steering angle command value of the steering wheels based on the position and orientation of the work vehicle 100 measured or estimated by the positioning device 120 and the inertial measurement unit 125, and the target path stored in the memory device 170. The control device 180 corrects the determined steering angle command value in the manner described with reference to Figures 2 to 5, and controls the drive unit 140 based on the corrected steering angle command value. As a result, the control device 180 can drive the work vehicle 100 along the target path. The control device 180 may also automatically control the vehicle speed as well as the steering of the work vehicle 100. In other words, the control device 180 may be configured to operate in an automatic driving mode that automatically drives the work vehicle 100 along a preset target path.

[0099] Multiple ECUs included in the control unit 180 can communicate with each other according to a vehicle bus standard such as CAN (Controller Area Network). In Figure 8, ECUs 182, 183, 184, and 185 are shown as separate blocks, but the functions of each of these may be realized by multiple ECUs. In addition, an on-board computer integrating at least some of the functions of ECUs 182, 183, 184, and 185 may be provided. The control unit 180 may also include ECUs other than ECUs 182, 183, 184, and 185. Any number of ECUs can be provided depending on the function. Each ECU includes a control circuit that includes one or more processors.

[0100] The communication interface 190 is a circuit that communicates with the communication interface 390 of the implement 300. The communication interface 190 transmits and receives signals compliant with the ISOBUS standard, such as ISOBUS-TIM, to and from the communication interface 390 of the implement 300. This allows the implement 300 to perform desired operations or to acquire information from the implement 300. The communication interface 190 may also communicate with an external computer via a wired or wireless network. The external computer may be, for example, a server computer in an agricultural support system that centrally manages field-related information on the cloud and supports agriculture by utilizing the data on the cloud.

[0101] The operation terminal 200 is a terminal for the user to perform operations related to the movement of the work vehicle 100 and the operation of the work equipment 300, and is also called a virtual terminal (VT). The operation terminal 200 may be equipped with a display device such as a touchscreen and / or one or more buttons. By operating the operation terminal 200, the user can perform various operations such as switching the automatic steering mode on / off, setting the initial position of the work vehicle 100, setting a target route, recording or editing a map, and switching the work equipment 300 on / off. At least some of these operations can also be performed by operating the operation switch group 210. The display on the operation terminal 200 is controlled by the ECU 185.

[0102] The buzzer 220 is an audio output device that emits a warning sound to notify the user of an abnormality. For example, during automatic steering operation, the buzzer 220 emits a warning sound if the work vehicle 100 deviates from the target path by a predetermined distance or more. Instead of the buzzer 220, a similar function may be achieved by the speaker of the operation terminal 200.

[0103] The drive unit 340 in the work implement 300 performs the operations necessary for the work implement 300 to perform a predetermined operation. The drive unit 340 includes devices such as a hydraulic system, an electric motor, or a pump, depending on the application of the work implement 300. The control device 380 controls the operation of the drive unit 340. The control device 380 causes the drive unit 340 to perform various operations in response to signals transmitted from the work vehicle 100 via the communication interface 390. It can also transmit signals corresponding to the status of the work implement 300 to the work vehicle 100 via the communication interface 390.

[0104] Figure 10 shows an example of an operating terminal 200 and a group of operating switches 210 located inside the cabin 105. Inside the cabin 105 is a group of switches 210, which includes a number of switches that can be operated by the user. The group of switches 210 may include, for example, a switch for switching between automatic steering mode and manual steering mode, a switch for switching between forward and reverse (e.g., a shuttle lever or shuttle switch), a switch for selecting the gear of the main or auxiliary transmission, and a switch for raising and lowering the work equipment 300.

[0105] Figure 11 is a block diagram showing an example of the hardware configuration of each ECU. Each ECU comprises a processor 434, ROM 435, RAM 436, external I / F 437, and communication I / F 438. These components are interconnected via a bus 439.

[0106] ROM435 is, for example, writable memory (e.g., PROM), rewritable memory (e.g., flash memory), or read-only memory. ROM435 stores a program that controls the operation of processor 434. ROM435 does not have to be a single recording medium; it may be a collection of multiple recording media. Some of these multiple storage media may be removable memory.

[0107] RAM436 provides a workspace for temporarily unpacking programs stored in ROM435 during boot-up. RAM436 does not need to be a single storage medium; it may be a collection of multiple storage mediums.

[0108] External I / F437 is an interface for connecting to external devices. Communication I / F438 is an interface for communicating with other electronic devices (e.g., sensors and other ECUs). For example, communication I / F438 can perform wired communication compliant with various protocols such as CAN or Ethernet®. Communication I / F438 may also perform wireless communication compliant with wireless communication standards such as Bluetooth® and / or Wi-Fi®.

[0109] The ECU may further include a storage device for storing data generated by the processor 434 for a relatively long period of time. Such a storage device may be, for example, a semiconductor storage device, a magnetic storage device, or an optical storage device, or a combination thereof.

[0110] <Operation> Next, the operation of the work vehicle 100 will be described. In this embodiment, the control device 180 can switch between manual steering mode and automatic steering mode in response to the operation of the user (e.g., driver) of the work vehicle 100. In manual steering mode, the control device 180 controls steering by driving the power steering system in response to the user's operation of the steering wheel. In automatic steering mode, the control device 180 controls steering by driving the power steering system based on the position and orientation (heading) of the work vehicle 100 estimated based on data output from the positioning device 120 and the inertial measurement unit 125, and a pre-recorded target path. Even in automatic steering mode, the speed is adjusted by the user's accelerator and brake operations.

[0111] Figures 12A to 12C illustrate examples of the movement of the work vehicle 100 in automatic steering mode. Figure 12A schematically shows the work vehicle 100 traveling along a straight target path P. Figure 12B schematically shows the work vehicle 100 traveling along a curved target path P. Figure 12B schematically shows the work vehicle 100 traveling along a target path P that includes two adjacent straight paths and a curved path connecting them. The target path P is pre-set and recorded in the storage device 170. When the work vehicle 100 is traveling in automatic steering mode, the control device 180 calculates the deviation between the position and orientation of the work vehicle 100 estimated based on data output from the positioning device 120 and the inertial measurement unit 125 and the target path P, and repeatedly controls the steering device to reduce the deviation. This causes the work vehicle 100 to travel along the target path P.

[0112] Figure 13 schematically shows an example of a target route for a work vehicle 100 that travels through a field using automatic steering. In this example, the field includes a work area 70 where the work vehicle 100 and implement 300 perform their work, and a headland 80 located near the outer edge of the field. The user can pre-set which areas on the field map correspond to the work area 70 and the headland 80 by operating the operation terminal 200. The target route includes a plurality of parallel main routes P1 and a plurality of turning routes P2 connecting the plurality of main routes P1. The main routes P1 are located within the work area 70, and the turning routes P2 are located in the headland 80. The spacing of the dashed lines in Figure 13 represents the working width of the implement 300. The working width is pre-set and recorded in the storage device 170. The working width can be set by the user operating the operation terminal 200 and recorded in the storage device 170. Alternatively, the working width may be automatically recognized when the work implement 300 is connected to the work vehicle 100 and recorded in the storage device 170. The spacing between the multiple main paths P1 is adjusted to match the working width. The target path may be determined based on user input before automatic steering operation is initiated.

[0113] Next, an example of control during automatic steering by the control device 180 will be explained.

[0114] Figure 14 is a flowchart showing an example of the operation performed by the control device 180 during automatic steering. The control device 180 may be configured to perform automatic steering operation while the work vehicle 100 is in motion by performing the operations from steps S101 to S105 shown in Figure 14. Before the operations shown in Figure 14, the control device 180 determines the steering angle correction parameters in the manner described with reference to Figures 2 to 5. Then, the control device 180 performs the operations from steps S101 to S105.

[0115] First, the control device 180 determines the position and bearing (orientation) of the work vehicle 100 based on the data output from the positioning device 120 and the inertial measurement unit 125 (step S101). Next, the control device 180 calculates the deviation between the position and bearing of the work vehicle 100 and the target path (step S102). The position deviation represents the distance between the position of the work vehicle 100 at that time and the target path. The bearing deviation represents the magnitude of the angle between the bearing of the work vehicle 100 at that time and the direction of the target path. The control device 180 determines whether the calculated position deviation exceeds a preset threshold, and whether the calculated bearing deviation exceeds other preset thresholds (step S103). If at least one of the position deviation and the bearing deviation exceeds their respective thresholds, the control device 180 changes the steering angle by changing the control parameters of the steering device included in the drive device 140 so that the deviations become smaller. This change in steering angle reflects the result of the steering angle correction based on the correction parameters described above. If neither the position nor the bearing deviation exceeds the respective threshold in step S103, the operation in step S104 is omitted. In the following step S105, the control device 180 determines whether or not it has received a command to terminate the operation. A command to terminate the operation may be issued, for example, when a user instructs the automatic steering mode to stop using the operation terminal 200, or when the work vehicle 100 reaches its destination. If no command to terminate the operation has been issued, the process returns to step S101 and performs the same operation based on the newly measured position of the work vehicle 100. The control device 180 repeats the operations from steps S101 to S105 until a command to terminate the operation is issued. The above operations are performed by the ECU 183 in the control device 180.

[0116] Below, we will explain in more detail an example of steering control by the control device 180, referring to Figures 15A to 15D.

[0117] Figure 15A shows an example of a work vehicle 100 traveling along a target path P. Figure 15B shows an example of a work vehicle 100 positioned to the right of the target path P. Figure 15C shows an example of a work vehicle 100 positioned to the left of the target path P. Figure 15D shows an example of a work vehicle 100 facing inclined relative to the target path P. In these figures, the position and orientation of the work vehicle 100, estimated based on signals output from the positioning device 120 and the inertial measurement unit 125, is represented as r(x,y,θ). (x,y) are coordinates representing the position of the reference point of the work vehicle 100 in the XY coordinate system, which is a two-dimensional coordinate system fixed to the Earth. In the examples shown in Figures 15A to 15D, the reference point of the work vehicle 100 is located where the GNSS antenna is installed on the cabin, but the position of the reference point is arbitrary. θ is an angle representing the measured orientation of the work vehicle 100. In the illustrated example, the target path P is parallel to the Y-axis, but generally, the target path P is not necessarily parallel to the Y-axis.

[0118] As shown in Figure 15A, if the position and orientation of the work vehicle 100 are not deviating from the target path P, the control device 180 maintains the steering angle and speed of the work vehicle 100 without changing them.

[0119] As shown in Figure 15B, if the position of the work vehicle 100 is shifted to the right of the target path P, the control device 180 changes the steering angle by changing the rotation angle of the steering wheel included in the drive unit 140 so that the direction of travel of the work vehicle 100 is tilted to the left and closer to path P. At this time, the speed may also be changed in addition to the steering angle. The magnitude of the steering angle can be adjusted, for example, according to the magnitude of the position deviation Δx.

[0120] As shown in Figure 15C, if the position of the work vehicle 100 is shifted to the left from the target path P, the control device 180 changes the steering angle by changing the rotation angle of the steering wheel so that the direction of travel of the work vehicle 100 is tilted to the right and closer to path P. In this case as well, the speed may be changed in addition to the steering angle. The amount of change in the steering angle can be adjusted, for example, according to the magnitude of the position deviation Δx.

[0121] As shown in Figure 15D, if the position of the work vehicle 100 is not significantly off the target path P, but its orientation differs from that of the target path P, the control device 180 changes the steering angle to reduce the azimuth deviation Δθ. In this case as well, the speed may be changed in addition to the steering angle. The magnitude of the steering angle can be adjusted, for example, according to the magnitudes of the position deviation Δx and the azimuth deviation Δθ. For example, the smaller the absolute value of the position deviation Δx, the larger the amount of change in the steering angle corresponding to the azimuth deviation Δθ may be. When the absolute value of the position deviation Δx is large, the steering angle will be changed significantly in order to return to path P, so the absolute value of the azimuth deviation Δθ will inevitably be large. Conversely, when the absolute value of the position deviation Δx is small, it is necessary to bring the azimuth deviation Δθ closer to zero. For this reason, it is appropriate to relatively increase the weight (i.e., control gain) of the azimuth deviation Δθ used to determine the steering angle.

[0122] Control technologies such as PID control or MPC control (model predictive control) can be applied to the steering and speed control of the work vehicle 100. By applying these control technologies, the control of the work vehicle 100 to approach the target path P can be made smoother.

[0123] Through the above operations, automatic steering is achieved, causing the work vehicle 100 to travel along the target path P. According to this embodiment, in step S104, steering angle correction is performed based on correction parameters α and β determined in advance, for example, by the method shown in Figure 5. This further reduces the deviation from the target path P during automatic steering operation. As mentioned above, since the parameters α and β can be updated sequentially during normal driving, the deterioration of steering control accuracy due to aging can be suppressed. In the above embodiment, the work vehicle 100 may be an unmanned work vehicle that operates automatically. In that case, components necessary only for manned operation, such as a cabin, driver's seat, steering wheel, and operating terminal, do not need to be provided on the work vehicle 100. The unmanned work vehicle may perform operations similar to those in the above embodiment by autonomous driving or remote operation by a user.

[0124] The control devices in the above embodiments can also be retrofitted to vehicles that do not possess those functions. Such control devices can be manufactured and sold independently of the vehicles. Computer programs used in such control devices can also be manufactured and sold independently of the vehicles. Computer programs can be provided, for example, stored in a computer-readable non-temporary storage medium. Computer programs can also be provided by download via telecommunications lines (e.g., the Internet). [Industrial applicability]

[0125] The technology disclosed herein can be applied to work vehicles used in agricultural applications, such as tractors, transplanters, or harvesters. The technology disclosed herein can also be applied to work vehicles used in non-agricultural applications, such as construction vehicles or snowplows. Furthermore, the technology disclosed herein can also be applied to general vehicles, such as passenger cars. [Explanation of Symbols]

[0126] 10: Vehicle, 30: Positioning device 40: Sensor group, 42: Vehicle speed sensor, 44: Angular velocity sensor, 46: Steering angle sensor, 50: Control device, 52: Processor, 54: Memory, 60: Actuator, 65: Running gear, 70: Working area, 80: Headland, 90: GNSS satellite, 92: Base station, 100: Work vehicle, 101: Vehicle body, 102: Engine, 103: Transmission, 104: Wheels, 105: Cabin, 106: Steering gear, 107: Driver's seat, 108: Coupling device, 109: Pedals, 120: Positioning device, 121: GNSS receiver, 122: RTK receiver, 1 23: Processor, 126: Accelerometer, 127: Angular velocity sensor, 130: Obstacle sensor, 140: Drive unit, 150: Sensor group, 152: Steering wheel sensor, 154: Steering angle sensor, 156: Vehicle speed sensor, 160: Control system, 170: Memory device, 180: Control device, 182, 183, 184, 185: ECU, 190: Communication interface, 200: Operating terminal, 210: Operating switch group, 220: Buzzer, 300: Work machine, 340: Drive unit, 360: Control device, 390: Communication interface

Claims

1. A control device that performs steering control of a vehicle, One or more processors, One or more memories for storing computer programs executed by the one or more processors, Equipped with, The one or more processors execute the computer program, The vehicle is provided with one or more sensors to acquire sensor data used to determine the curvature of the path the vehicle is traveling. Determining the curvature based on the aforementioned sensor data, Based on the curvature, the steering angle of the vehicle's steering wheels is corrected. A control device that performs this operation.

2. The control device according to claim 1, wherein the one or more processors perform steering angle correction based on the curvature and the wheelbase of the vehicle.

3. The one or more sensors mentioned above are: A vehicle speed sensor for measuring the vehicle's speed, An angular velocity sensor for measuring the angular velocity of the vehicle around its yaw axis, Includes, The one or more processors determine the curvature based on the travel speed and the angular velocity. The control device according to claim 1.

4. Let v be the aforementioned travel speed, ω be the aforementioned angular velocity, and κ be the aforementioned curvature. The control device according to claim 3, wherein the one or more processors determine the curvature κ based on the relationship κ = ω / v.

5. Let δ be the steering angle of the vehicle before correction, L be the wheelbase, α be the first error coefficient, and β be the second error coefficient. The one or more processors mentioned above are: κ=tan(δ×β+α) / L...(Formula 1) Based on the relationship, the first error coefficient α and the second error coefficient β are determined. The steering angle is corrected based on the first error coefficient α and the second error coefficient β. The control device according to claim 4.

6. The one or more sensors mentioned above include a steering angle sensor for measuring the steering angle of the vehicle. The one or more processors mentioned above are: The curvature κ is determined based on the driving speed v and angular velocity ω during the period when the vehicle is traveling with the measured absolute value of the steering angle being smaller than a first threshold. In the above equation 1, we approximated δ = 0. κ = tan(α) / L The first error coefficient α is determined based on the relationship. The control device according to claim 5.

7. The control device according to claim 6, wherein the one or more processors determine the second error coefficient β based on the determined first error coefficient α, the curvature κ determined based on the driving speed v and the angular velocity ω during the period when the vehicle is traveling with the absolute value of the steering angle greater than the second threshold, and the formula 1.

8. The control device according to claim 5, wherein the one or more processors sequentially update the first error coefficient α and the second error coefficient β while the vehicle is in motion, and correct the steering angle based on the updated first error coefficient α and the second error coefficient β.

9. The control device according to claim 1, wherein the one or more processors select a data portion to be used to determine the curvature from the sensor data acquired while the vehicle is in motion, according to the content of the sensor data and / or the driving state of the vehicle.

10. The aforementioned vehicle is capable of operating in automatic steering mode. The one or more processors mentioned above are: The steering angle command value is determined based on the target path and the position of the vehicle. Based on the curvature, the steering angle correction parameters are determined. The steering angle command value is corrected based on the steering angle correction parameter. Based on the corrected steering angle command value, the steering control of the vehicle is performed. The control device according to claim 1.

11. The aforementioned vehicle is capable of operating in automatic steering mode. In the automatic steering mode, the one or more processors Information indicating the measurement position of the vehicle is obtained from a positioning device installed on the vehicle. Information indicating the target route of the vehicle is obtained from the storage device, Based on the measurement position and the target path, the rudder angle command value is determined. Based on the curvature, the steering angle correction parameters are determined. The steering angle command value is corrected based on the steering angle correction parameter. Based on the corrected steering angle command value, the steering control of the vehicle is performed. The control device according to claim 1.

12. The control device according to claim 1, wherein the vehicle is an agricultural tractor.

13. A control device according to any one of claims 1 to 12, The one or more sensors mentioned above, Running gear including the steering wheels, An actuator that drives the steering wheel according to a command from the control device, A vehicle equipped with the following features.

14. A method performed by one or more computers to control the steering of a vehicle, The vehicle is provided with one or more sensors to acquire sensor data used to determine the curvature of the path the vehicle is traveling. Determining the curvature based on the aforementioned sensor data, The steering angle of the vehicle is corrected based on the curvature, A method that includes this.

15. A computer program that is executed by one or more computers that perform steering control of a vehicle, wherein the one or more computers The vehicle is provided with one or more sensors to acquire sensor data used to determine the curvature of the path the vehicle is traveling. Determining the curvature based on the aforementioned sensor data, The steering angle of the vehicle is corrected based on the curvature, A computer program that executes an action.

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