Driving assistance method and driving assistance device

Abstract

Provided are a driving assistance method and a driving assistance device (14) that: predict whether a vehicle (V) being driven by the steering operation of a driver will depart from the lane (L) during travel; acquire a departure direction in which the vehicle (V) departs from the lane (L) and the turning direction of the vehicle (V), when it is predicted that the vehicle (V) will depart from the lane (L), and determine whether the departure direction and the turning direction are the same direction; and, when it is determined that the departure direction and the turning direction are the same direction, execute a steering control such that the steering wheel of the vehicle (V) does not turn in the departure direction and the vehicle (V) does not depart from the lane (L).

Description

[Technical Field]

[0001] The present invention relates to a driving assistance method and a driving assistance device. [Background technology]

[0002] Lane departure prevention control, which prevents a vehicle from departing from the lane in which it is traveling, is known (see Patent Document 1). In lane departure prevention control, a target yaw rate for departure prevention control, which prevents the vehicle from departing from the lane, and a target yaw rate for attitude determination control, which controls the vehicle's attitude after departure prevention control, are calculated as target yaw rates for the vehicle to travel along a target course. The target yaw rate for attitude determination control is calculated by multiplying the deviation between the target lane-to-lane yaw angle at the end of control and the lane-to-lane yaw angle during attitude determination control by a predetermined feedback gain, and dividing the result by the target time required to reach the target lane-to-lane yaw angle. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6637952 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-described conventional technology, if the absolute value of the target lane-to-lane yaw angle at the time of control termination is greater than the absolute value of the lane-to-lane yaw angle during attitude determination control, the steering wheel will rotate in the turning direction during attitude determination control. In this case, the steering wheel will rotate in the direction opposite to the turning direction due to departure prevention control, and then rotate in the turning direction, and when attitude determination control terminates, the steering wheel will rotate again in the direction opposite to the turning direction due to self-aligning torque.

[0005] As described above, if the driver turns the steering wheel in the turning direction before the attitude determination control is completed, the driver will mistakenly recognize the rotation of the steering wheel due to the self-aligning torque after the attitude determination control is completed as a series of steering controls due to the attitude determination control. As a result, the timing at which the driver starts operating the steering wheel after the attitude determination control is completed will be delayed, and the vehicle behavior will change significantly to avoid deviation from the lane.

[0006] The problem to be solved by the present invention is to provide a driving assistance method and a driving assistance device that can prevent the driver from misunderstanding the timing when steering control ends and the timing when the steering operation by the driver begins. [Means for solving the problem]

[0007] The present invention solves the above problem by monitoring the driving state of a vehicle that is traveling due to steering operations by the driver, and when it is predicted that the vehicle will deviate from the lane in which it is traveling, executing steering control to maintain the lane-to-lane yaw angle, which is the angle between the vehicle's direction of travel and the tangent direction to the lane at the position on the lane in which the vehicle is traveling, within a range of angles that allows the vehicle to travel along the lane, and continuing steering control until a predetermined time has passed since the lane-to-lane yaw angle changes from decreasing to increasing, and when it is determined that the direction in which the vehicle will deviate from the lane and the direction in which the vehicle is turning are the same direction, not rotating the steering wheel of the vehicle in the direction of departure. [Effects of the Invention]

[0008] According to the present invention, it is possible to prevent the driver from misperceiving the timing when steering control ends and transitions to the driver's steering operation. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a block diagram showing an example of a driving assistance system including a driving assistance device according to the present invention; [Figure 2]2A to 2C are diagrams showing an example of a driving scene in which steering control is performed as driving assistance using the driving assistance system shown in FIG. 1, and a time chart showing the movement of the steering wheel during, before, and after the steering control. [Figure 3] 3 is a diagram showing a time chart when the vehicle travels at a higher speed in the traveling scene shown in FIG. 2. FIG. [Figure 4] 3 is a diagram showing an example of steering control executed in a driving scene where the curvature of a curve is larger than that of the driving scene shown in FIG. 2, and a time chart showing the movement of the steering wheel during, before and after the steering control. [Figure 5A] 2 is a flowchart showing an example of a processing procedure in the driving assistance system of FIG. 1 (part 1). [Figure 5B] 2 is a flowchart showing an example of a processing procedure in the driving assistance system of FIG. 1 (part 2). [Figure 5C] 10 is a flowchart showing an example of a processing procedure in the driving assistance system of FIG. 1 (part 3). [Figure 6] 10A and 10B are diagrams illustrating an example of steering control according to a comparative example of the present invention and a time chart showing the movement of the steering wheel in the steering control according to the comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] [Driver assistance system configuration] FIG. 1 is a block diagram showing a driving assistance system 1 according to the present invention. The driving assistance system 1 is an in-vehicle system that monitors the driving state of a vehicle driven by a driver's steering operation, and, if it is predicted that the vehicle will deviate from the lane in which it is traveling, steers the vehicle's steering wheels to prevent the vehicle from deviating from the lane. The steering wheels are wheels that change the direction of travel of the vehicle, and are also called steered wheels. A steering operation is, for example, the driver turning the steering wheel. The driving state of the vehicle is a parameter detected by a vehicle state detection device (described later), and examples include the vehicle's driving speed, acceleration, lateral speed, lateral acceleration, yaw rate, and steering wheel rotation angle (hereinafter also referred to as "steering angle").

[0012] A vehicle deviating from a lane means that the vehicle crosses a boundary that defines a lane and, in a plan view, part or all of the vehicle body is outside the lane. For example, if a vehicle is traveling in a lane defined by a boundary line such as a white line and crosses the boundary line to enter an adjacent lane, the vehicle is determined to have deviated from the lane. Note that the boundary that defines a lane is not limited to a boundary line such as a white line, but may also be a boundary between a drivable area and an impassable area. For example, a guardrail, a curb on the shoulder of the road, a median strip, or the boundary between a paved road and an unpaved road (e.g., a gravel road) is also included in the boundary that defines a lane.

[0013] 1, the driving assistance system 1 includes an imaging device 11, a vehicle state detection device 12, a steering control device 13, and a driving assistance device 14. The devices that make up the driving assistance system 1 are connected by a CAN (Controller Area Network) or other in-vehicle LAN, and can exchange information with each other.

[0014] The imaging device 11 is a device that recognizes objects around the vehicle using images, and is, for example, a camera equipped with an imaging element such as a CCD, an ultrasonic camera, etc. A single vehicle can be provided with a plurality of imaging devices 11, and they may be located, for example, near the front grille, under the left and right door mirrors, and near the rear bumper of the vehicle.

[0015] Objects detected by the imaging device 11 include the boundaries that define the lanes described above, as well as lane boundaries, center lines, road markings, medians, guardrails, curbs, highway sidewalls, road signs, traffic lights, crosswalks, construction sites, accident sites, traffic restrictions, etc. Objects also include obstacles that may affect the travel of a vehicle, such as automobiles (other vehicles) other than the vehicle itself, motorcycles, bicycles, pedestrians, etc.

[0016] The detection results of the imaging device 11 are acquired at predetermined time intervals by the driving assistance device 14 as needed. This predetermined time interval can be set to an appropriate value depending on the processing capacity of the driving assistance device 14. Furthermore, the detection results of the multiple imaging devices 11 can be integrated or synthesized in the driving assistance device 14 to supplement missing information about the detected object.

[0017] The vehicle state detection device 12 is a device for detecting the running state of the vehicle, and examples thereof include a speed sensor, an acceleration sensor, a yaw rate sensor (e.g., a gyro sensor), a steering angle sensor, and an inertial measurement unit. There are no particular limitations on these devices, and known devices can be used. The locations and numbers of these devices can be set appropriately within a range that allows appropriate detection of the running state of the vehicle. The detection results of each device are acquired by the driving assistance device 14 at predetermined time intervals as necessary.

[0018] The steering control device 13 is an on-board computer for electronically controlling the steering device, and is, for example, an electronic control unit (ECU). Information necessary for steering control by the steering control device 13, such as the vehicle's running speed, acceleration, steering angle, and attitude, is obtained from the host vehicle state detection device 12. The steering device may, for example, be a steering actuator (motor) attached to a steering column shaft that steers the steered wheels according to the steering angle. Alternatively, the steering actuator may be attached to a steering rack or pinion gear of a mechanism that steers the steered wheels. Furthermore, as a steer-by-wire system in which the mechanism that steers the steered wheels is mechanically separated from the steering wheel, both a steering actuator attached to a steering rack or pinion gear of a mechanism that steers the steered wheels and a steering actuator attached to a steering column shaft may be provided.

[0019] The driving assistance device 14 is a device that monitors the driving state of the vehicle steered by the driver and executes steering control to prevent the vehicle from leaving its lane by controlling and cooperating with the devices that make up the driving assistance system 1. The driving assistance device 14 is, for example, a computer, and includes a CPU (Central Processing Unit) 141 that is a processor, a ROM (Read Only Memory) 142 that stores programs, and a RAM (Random Access Memory) 143 that functions as an accessible storage device. The CPU 141 is an operating circuit that executes the programs stored in the ROM 142 to execute the above-mentioned monitoring and steering control.

[0020] The driving assistance device 14 has a monitoring function for monitoring the driving state and a steering control function for executing steering control, and these functions are realized by the CPU 141 executing a program stored in the ROM 142. Fig. 1 shows functional blocks that realize each function, extracted for convenience. Below, the functions of each functional block of the assistance unit 2, recognition unit 21, prediction unit 22, acquisition unit 23, and control unit 24 shown in Fig. 1 will be described.

[0021] [Functions of each function block] The support unit 2 has the function of acquiring information from each device constituting the driving support system 1, processing the acquired information, outputting instructions to each device, and cooperating with each other among the devices constituting the driving support system 1. Fig. 2 is a plan view showing an example of a driving scene in which the driving support device 14 performs monitoring using the monitoring function and steering control using the steering control function.

[0022] The driving scene shown in Fig. 2 is a driving scene in which a vehicle V is driving in a lane L in the direction of an arrow X. That is, the vehicle V shown in Fig. 2 is driving from the left side to the right side of the drawing in the lane L defined by a boundary line B1 on the left side of the vehicle V's traveling direction and a boundary line B2 on the right side of the vehicle V's traveling direction.

[0023] In the driving scene of Fig. 2, the driver steers vehicle V, enters a left curve turning left as shown in Fig. 2, and is currently traveling at position P1. Furthermore, if the steering angle after entering the left curve is large and the driving assistance device 14 does not steer the steered wheels, vehicle V will turn to the left from position P1 in the traveling direction, cross boundary line B1, and deviate from lane L. In this case, driving assistance device 14 predicts the departure of vehicle V from lane L using a monitoring function, and performs steering control using a steering control function as necessary.

[0024] The recognition unit 21 has a function of recognizing the driving environment around the vehicle V in order to predict deviation of the vehicle V from the lane L. The driving assistance device 14 recognizes the driving environment around the vehicle V using the imaging device 11 through the function of the recognition unit 21. The driving environment is information for determining whether the vehicle V can maintain its current driving state or needs to change its driving state, and includes information such as the type and position of objects, the type and position of obstacles if any, and road conditions. The driving assistance device 14 recognizes the driving environment by performing appropriate processing such as pattern matching on the detection results of the imaging device 11.

[0025] In the driving scene shown in FIG. 2, the driving assistance device 14 performs edge extraction processing and the like on the detection result of the imaging device 11 using the function of the recognition unit 21 to recognize boundary lines B1 and B2.

[0026] Furthermore, the driving assistance device 14 may acquire the distance in the width direction between the vehicle V and the boundary lines B1, B2 in accordance with the rotation direction of the steering wheel or the turning direction of the vehicle V. In the driving scene shown in Fig. 2, the driver inputs a rotation torque in the left direction to the steering wheel, causing the vehicle V to turn left, and when this torque is detected, the driving assistance device 14 acquires the distance D in the width direction between the vehicle V and the boundary line B1 on the left side of the traveling direction. Note that the process of acquiring the distance D in the width direction is not an essential component of the present invention and may be provided as needed.

[0027] The prediction unit 22 has a function of predicting whether the vehicle V, which is traveling due to the driver's steering operation, will deviate from the lane L in which it is traveling. The driving assistance device 14 acquires the traveling direction of the vehicle V using the function of the prediction unit 22, and predicts whether the vehicle V will deviate from the lane L by crossing the boundary that defines the lane L if it continues to travel along that traveling direction. The traveling direction of the vehicle V is recognized from the yaw rate acquired from a yaw rate sensor, the steering angle acquired from a steering angle sensor, etc.

[0028] As an example of a method for predicting deviation of the vehicle V, the driving assistance device 14 detects the boundary of the lane L on which the vehicle V is traveling from image data acquired from the imaging device 11, and recognizes the positional relationship between the boundary and the vehicle V. That is, based on the distance D in the width direction described above, the driving assistance device 14 recognizes whether the vehicle V is far from the boundary, whether the vehicle V is approaching the boundary, and how far the vehicle V is from the boundary. The driving assistance device 14 also calculates the lane yaw angle, which is the angle between the traveling direction of the vehicle V and the tangent direction of the lane L at the position on the lane L where the vehicle V is traveling. Then, it predicts whether the vehicle V will cross the boundary that defines the lane L if it travels while maintaining the calculated lane yaw angle. The tangent direction of the lane L is calculated from the positional relationship between the boundary and the vehicle V described above.

[0029] For example, the driving assistance device 14 calculates the lane yaw angle formed by a line C1 parallel to the traveling direction of the vehicle V and a tangent line C2 to the boundary line B1 at the traveling position of the vehicle V, as shown in FIG. 2, and obtains the distance D in the width direction between the vehicle V and the boundary line B1. An example of the lane yaw angle is shown as α in FIG. 2. Then, deviation of the vehicle V is predicted from the lane yaw angle and the distance D. If the lane yaw angle is within a range in which the vehicle V can travel along the lane L and the distance D is long (i.e., the vehicle V is farther away from the boundary line B1), the driving assistance device 14 predicts that the vehicle V will not deviate from the lane L. On the other hand, when the lane-to-lane yaw angle of the vehicle V is larger or smaller than the range in which the vehicle V can travel along the lane L (i.e., when the steering angle is too large or too small for the required lane-to-lane yaw angle), or when the distance D is shortened (i.e., when the vehicle V and boundary line B1 are approaching), it is predicted that the vehicle V will deviate from the lane L. Note that the tangent line C2 to the boundary line B1 is, for example, the tangent line at the point on the boundary line B1 that is closest to the body of the vehicle V.

[0030] Furthermore, the driving assistance device 14 may determine whether the vehicle V will enter a curve, and if it determines that the vehicle V will enter a curve, it may predict deviation of the vehicle V. For example, when the vehicle V is traveling straight and the boundary line of the lane L ahead of the vehicle V is curved, it may determine that the vehicle V will enter a curve, and if the boundary line is not curved, it may determine that the vehicle V will not enter a curve. Alternatively or in addition to this, the driving assistance device 14 may acquire the current position of the vehicle V from a GPS unit (not shown), acquire road information around the vehicle V from map information (not shown), and determine whether the vehicle V will enter a curve based on the road information ahead of the vehicle V. Note that the determination of entering a curve is not an essential component of the present invention and may be provided as needed.

[0031] In the driving scene shown in Fig. 2, the driver has turned the steering wheel too far to the left, causing the lane-to-lane yaw angle of vehicle V to be larger than the range in which vehicle V can travel along lane L. Therefore, if vehicle V continues to travel while maintaining the lane-to-lane yaw angle, it will cross boundary line B1 that defines lane L and head outside lane L, and so driving assistance device 14 predicts that vehicle V will deviate from lane L. Then, when it is predicted that vehicle V will deviate from lane L, the steering control function of driving assistance device 14 is activated, and steering control is performed.

[0032] The acquisition unit 23 has a function of acquiring the departure direction in which the vehicle V deviates from the lane L. The departure direction of the vehicle V is the direction in which the vehicle V will head if it deviates from the lane L on which the vehicle V is traveling, and indicates whether the vehicle V will deviate to the right or left of the traveling direction. In other words, the departure direction indicates whether the vehicle V will cross the boundary on the right side of the traveling direction or the boundary on the left side of the traveling direction among the boundaries that define the lane L when it is predicted that the vehicle V will deviate from the lane L. If the departure direction is to the left, the vehicle V will deviate from the lane L by crossing the boundary on the left side of the traveling direction, and if the departure direction is to the right, the vehicle V will deviate from the lane L by crossing the boundary on the right side of the traveling direction.

[0033] The driving assistance device 14 acquires the departure direction in which the vehicle V will depart from the lane L from the information on the traveling direction of the vehicle V that was used when predicting the departure of the vehicle V from the lane L. For example, when it is predicted that the vehicle V will depart from the lane L, if the traveling direction of the vehicle V is to the left front or to the left side of the vehicle V, the departure direction is the leftward direction, and if the traveling direction of the vehicle V is to the right front or to the right side of the vehicle V, the departure direction is the rightward direction.

[0034] The control unit 24 has a function of executing steering control to prevent the vehicle V from deviating from the lane L. Steering control to prevent the vehicle V from deviating from the lane L means using a steering mechanism to rotate the steered wheels to increase or decrease the steering angle in order to align the vehicle V's traveling direction with the lane L. The driving assistance device 14 operates the steering actuator via the steering control device 13 to rotate the steered wheels left or right (i.e., point the steered wheels in the target direction) and adjust the steering angle so that the vehicle V maintains a sufficient distance in the width direction between the vehicle V and the boundary of the lane L and the lane yaw angle of the vehicle V is within a range that allows the vehicle V to travel along the lane L. The above-mentioned range is set appropriately based on the traveling speed of the vehicle V and the curvature of the lane L.

[0035] Note that the driving assistance device 14 may control the traveling speed of the vehicle V using a speed control device (not shown) while steering control is being performed. When traveling speed control is not being performed, the traveling speed of the vehicle V is controlled by the driver's operation. Also, the steering actuator may be operated via the steering control device 13 to rotate the steered wheels left or right to adjust the steering angle. In the case of a steer-by-wire system in which the mechanism for steering the steered wheels is mechanically separated from the steering wheel, it is possible to adjust one or both of the steering angle of the steering actuator attached to the steering rack or pinion gear of the mechanism for steering the steered wheels and the steering angle of the steering actuator attached to the steering column shaft.

[0036] In the driving scene shown in Fig. 2, it is assumed that when the vehicle V is traveling at position P1, it is predicted that the vehicle V will deviate leftward from the lane L. In this case, the driving assistance device 14 acquires the departure direction using the function of the acquisition unit 23, and executes steering control to avoid departure from the lane L using the function of the control unit 24. Specifically, since the departure direction is leftward, an instruction to turn the steered wheels rightward is output to the steering control device 13.

[0037] The steering control executed in the driving scene shown in Figure 2 will be explained in detail using timing diagrams. Figure 2 shows five timing diagrams, which, from top to bottom, are (1) a diagram of the steering control state, (2) a diagram of the departure direction of vehicle V, (3) a diagram of the steering angle command value in steering control, (4) a diagram of the steering angle, and (5) a diagram of the distance D in the width direction between vehicle V and boundary line B1. The horizontal axis of each diagram indicates time, and this time corresponds to the elapsed time in the driving scene shown in the upper part of Figure 2.

[0038] The diagram of the steering control state is a diagram showing whether the steering control is enabled (ON) or disabled (OFF), and takes the value "enabled (ON)" if the steering control is enabled, and takes the value "disabled (OFF)" if the steering control is disabled. The diagram of the departure direction of vehicle V takes the value "left departure" or "right departure" depending on the departure direction of vehicle V, and takes the value "non-departure" if it is predicted that vehicle V will not depart from lane L.

[0039] The diagram of the steering angle command value is a diagram showing the command value of the steering angle output from the driving assistance device 14 to the steering control device 13 in the steering control. In the diagram of the steering angle command value and the diagram of the steering angle, a left turn is represented by a positive value, and a right turn is represented by a negative value. In the driving scene shown in FIG. 2, the steering wheel and the steered wheels are connected, and the turning angle also changes in accordance with changes in the steering angle. Below, the processing in the steering control will be explained using a timing diagram.

[0040] In the driving scene shown in Fig. 2, when the vehicle V is traveling at position P1, it is predicted that the vehicle V will deviate leftward from the lane L, so as shown in the diagram of the steering control state, the steering control is enabled (ON) at position P1. Next, in the driving scene shown in Fig. 2, the vehicle V is heading left and forward, so as shown in the diagram of the departure direction of the vehicle V, the departure direction is determined to be leftward. The driving assistance device 14 acquires information indicating that the departure direction is leftward.

[0041] Because the departure direction of vehicle V is to the left, driving assistance device 14 outputs an instruction to steering control device 13 to rotate the steering wheel to the right so that vehicle V can travel along lane L. Specifically, as shown in the diagram of steering angle command value, driving assistance device 14 outputs an instruction having a command value to decrease the steering angle to the left. As a result, the steering wheel is rotated to the right, and the steering angle to the left becomes smaller as shown in the diagram of steering angle. In the case of steer-by-wire, the steering angle command value becomes a turning angle command value, and the steered wheels are rotated by the steering mechanism in accordance with this command value. At the same time, a target steering angle is set, and the steering wheel is rotated by a steering actuator attached to the column shaft.

[0042] In the driving scene of FIG. 2, the steering wheel is rotated rightward at a constant angular velocity by the steering control device 13, and when the vehicle V is traveling at position P2, the lane-to-lane yaw angle of the vehicle V becomes an angle within a range that allows the vehicle V to travel along the lane L. In this case, when the traveling position of the vehicle V reaches position P2, the driving assistance device 14 outputs an instruction to the steering control device 13 to stop the rotation of the steering wheel and maintain the steering angle. This stops the rotation of the steering wheel to the right, and the steering angle is maintained as shown in the steering angle diagram. The vehicle V maintains the steering angle shown in FIG. 2 and travels to position P3, where the lane-to-lane yaw angle of the vehicle V changes from decreasing to increasing and begins to increase. Note that position P3 is also the position where the vehicle V is closest to the boundary line B1 that defines the lane L.

[0043] As shown in the diagram of the distance D in the width direction, the distance between the vehicle V and the boundary line B1 gradually decreases while the vehicle V travels from position P1 to position P3, so the driving assistance device 14 continues to repeatedly perform departure determination for the vehicle V. While the departure determination is being performed, as shown in the diagram of the departure direction of the vehicle V, the departure direction takes the value of departure to the left. Note that it is not necessarily necessary to stop turning the steering wheel at position P2.

[0044] After the vehicle V passes position P3 where the lane-to-lane yaw angle begins to increase, the distance D between the vehicle V and boundary line B1 gradually increases. After the vehicle V passes position P3, the driving assistance device 14 predicts that the vehicle V will not deviate from lane L when it determines that the vehicle V continues to travel away from boundary line B1 and has exited the traveling state in which the vehicle V deviates from lane L. For example, the driving assistance device 14 predicts that the vehicle V will not deviate from lane L when the vehicle V is traveling at position P4, a predetermined time after the vehicle V passed position P3. In this case, the driving assistance device 14 ends steering control at position P4 and transitions to traveling under steering operation by the driver.

[0045] As before passing position P3, if the lane-to-lane yaw angle of vehicle V is controlled to maintain an angle within a range that allows vehicle V to travel along lane L, the steering wheel may be turned left after passing position P3. Fig. 6 is a diagram showing steering control according to a comparative example of the present invention, and the driving scene shown in Fig. 6 is a driving scene in which the lane-to-lane yaw angle of vehicle V is controlled to maintain an angle within the above-mentioned range even after vehicle V passes position P3 in the driving scene shown in Fig. 2.

[0046] As shown in the diagram of the steering angle command value in FIG. 6, in the steering control according to the comparative example, after passing position P3, an instruction to rotate the steering wheel left is output to the steering control device 13, and the steering angle to the left increases in accordance with the command value. Then, at position Px, a predetermined time after passing position P3, the distance D between the vehicle V and boundary line B1 increases, and it is predicted that the vehicle V will not deviate from lane L. In this case, the steering control ends at position Px, and the state of the steering control becomes disabled (OFF) as shown in the diagram of the steering control state. Furthermore, the departure direction assumes a non-departure value. If the driver does not start a steering operation after the steering control ends at position Px, the steering wheel rotates rightward due to the self-aligning torque, as shown in FIG. 6. If the vehicle continues traveling in this state, the steering angle becomes 0° when the vehicle V reaches position Py, and the rotation of the steering wheel stops.

[0047] In the steering control shown in FIG. 6 , the steering wheel rotates left while traveling from position P3 to position Px, and rotates right while traveling from position Px to position Py. If the leftward rotation due to the steering control occurs before the rightward rotation due to the self-aligning torque, the driver may mistakenly perceive the rightward rotation due to the self-aligning torque as a series of steering controls, following the leftward rotation due to the steering control. Furthermore, the driver may expect the steering control to continue even after a predetermined time has elapsed since passing position P3, and the steering wheel to automatically rotate again even after passing position Py and the steering wheel rotation stops. Therefore, the driver does not initiate a steering operation even when the vehicle V passes position Py, but instead initiates a steering operation after the vehicle V approaches boundary line B2. In this case, the vehicle V is turned left in a relatively short time, resulting in a significant change in the behavior of the vehicle V.

[0048] Therefore, the driving assistance device 14 of this embodiment acquires the turning direction of the vehicle V using the function of the acquisition unit 23, and determines whether the departure direction of the vehicle V and the turning direction are the same using the function of the control unit 24. If it is determined that the departure direction and the turning direction are the same, steering control is executed to prevent the steering wheel from being rotated in the departure direction. In other words, if the vehicle V departs in the turning direction, the steering wheel is not rotated in the departure direction from the start to the end of the steering control, and is rotated only in the direction opposite to the departure direction.

[0049] In contrast, if it is determined that the departure direction and the turning direction are not the same, normal steering control is performed to suppress departure from lane L. If vehicle V departs in the opposite direction to the turning direction, the steering angle is insufficient to turn along lane L, so the steering angle is increased so that vehicle V heads in the opposite direction to the predicted departure direction. When the lane-to-lane yaw angle begins to increase, the steering angle of vehicle V is greater than the range in which vehicle V can travel along lane L. Therefore, the steering angle is decreased, causing vehicle V to travel along lane L. In other words, in a driving scenario in which the departure direction and turning direction are different, the steering angle is only increased once and then decreased, and steering control is not performed to decrease the steering angle and then increase it again, so the driver will not mistakenly recognize the rotation of the steering wheel due to self-aligning torque as rotation due to steering control.

[0050] The driving assistance device 14 acquires whether the turning direction of the vehicle V is to the left or to the right from the detection result of the steering angle sensor. The driving assistance device 14 may acquire the departure direction and the turning direction simultaneously, or may acquire either the departure direction or the turning direction first. The turning direction of the vehicle V may also be recognized from the yaw rate acquired from a yaw rate sensor, the lane-to-lane yaw angle calculated from the detection result of the imaging device 11, the lateral acceleration acquired from an acceleration sensor, etc.

[0051] In the driving scene shown in FIG. 2, as shown in the diagram of the steering angle command value, the same steering angle command value is output as the command value even after the vehicle V passes position P3. Therefore, the steering wheel does not rotate, and the steering angle is maintained. Then, at position P4, a predetermined time after passing position P3, the steering control ends and the steering control state becomes inactive (OFF). If the driver does not start steering after the steering control ends at position P4, the steering wheel will rotate to the right due to the self-aligning torque, as shown in FIG. 2. If the vehicle continues driving in this state, the steering angle will become 0° when the vehicle V is driving to position P5, and the rotation of the steering wheel will stop.

[0052] In the steering control shown in FIG. 2, the steering wheel does not rotate to the left, which is the departure direction, while traveling from position P3 to position P4. Therefore, the driver recognizes that the steering control has ended when the right rotation due to the self-aligning torque begins, and can start steering. Furthermore, even if the driver does not notice that the steering control has ended and the vehicle V travels to position P5, unlike the steering control according to the comparative example, the driver does not expect the steering wheel to automatically rotate again. Therefore, the driver can start steering promptly when the vehicle V passes position P5.

[0053] Alternatively, the driving assistance device 14 may stop the rotation of the steering wheel at a timing between when the lane-to-vehicle yaw angle starts to increase and when the increment of the lane-to-vehicle yaw angle reaches a predetermined angle, thereby maintaining the steering angle. In this case, the steering control ends when the steering wheel is stopped. The predetermined angle is, for example, 0.05 to 0.2 degrees. Alternatively, the driving assistance device 14 may stop the rotation of the steering wheel at a timing between when the lane-to-vehicle yaw angle starts to increase and when a certain period of time has elapsed, thereby maintaining the steering angle. In this case, the steering control ends when the steering wheel is stopped. The certain period of time is, for example, 0.1 to 1 second.

[0054] 2, the steering angle is maintained from position P2, where the lane-to-lane yaw angle of vehicle V is within a range that allows vehicle V to travel along lane L, to position P3, where the lane-to-lane yaw angle of vehicle V begins to increase, but it is not necessary to maintain the steering angle between positions P2 and P3, and the steering angle may change between positions P2 and P3. Furthermore, these exemplified steering controls are not essential configurations for the present invention and may be provided as needed.

[0055] Next, using FIG. 3, steering control when the vehicle V travels at a higher speed in the driving scene shown in FIG. 2 will be described. The driving scene shown in FIG. 3 is similar to the driving scene shown in FIG. 2, except that the driving speed of the vehicle V is faster than that in the driving scene shown in FIG. 2. When following a certain driving trajectory, the faster the driving speed, the larger the steering angle must be. Therefore, in the driving scene shown in FIG. 3, the steering angle is larger than in the driving scene shown in FIG. 2. If steering control is terminated in this large steering angle state, the self-aligning torque increases the rotation speed of the steering wheel, causing a significant change in the behavior of the vehicle V.

[0056] Therefore, the driving assistance device 14 acquires the traveling speed of the vehicle V, and if the traveling speed of the vehicle V is equal to or lower than a predetermined speed, rotates the steering wheel in the direction opposite to the departure direction and calculates the lane-to-lane yaw angle of the vehicle V. Then, at a certain timing between when the lane-to-lane yaw angle starts to increase and when the increment of the lane-to-lane yaw angle reaches a predetermined angle, the driving assistance device 14 stops the rotation of the steering wheel and ends steering control while maintaining the steering angle.

[0057] In contrast, if the traveling speed of the vehicle V is faster than a predetermined speed, the steering wheel is rotated in the direction opposite to the departure direction, and the lane-to-lane yaw angle of the vehicle V is calculated. Then, at a certain timing between when the lane-to-lane yaw angle starts to increase and when the increment of the lane-to-lane yaw angle reaches a predetermined angle, the rotation of the steering wheel is stopped and the steering angle is maintained. Furthermore, from a predetermined timing after the start of maintaining the steering angle, the steering wheel is rotated in the direction opposite to the departure direction, and steering control is terminated with the steering wheel rotating in the direction opposite to the departure direction. This allows the steering angle to be reduced before the steering control is terminated, thereby preventing the behavior of the vehicle V from being significantly changed by the self-aligning torque.

[0058] The predetermined speed can be set to an appropriate value within a range in which changes in behavior due to the self-aligning torque do not cause discomfort to occupants of the vehicle V. The predetermined timing is a timing between when the steering angle starts to be maintained and when the steering control ends, for example, when the vehicle V passes a position where the lane-to-lane yaw angle starts to increase. Furthermore, when the traveling speed is faster than the predetermined speed, the driving assistance device 14 may set a speed at which the steering wheel is turned in the direction opposite to the departure direction to be greater the faster the traveling speed.

[0059] In the driving scene shown in FIG. 3, the driving assistance device 14 performs steering control similar to that shown in FIG. 2 up to position P3. After the vehicle V passes position P3, a command value to decrease the steering angle to the left is output, as shown in the diagram of the steering angle command value. Therefore, the steering wheel rotates to the right and continues to rotate at a constant angular velocity until position P4, a predetermined time after passing position P3. If the driver does not start steering after the steering control ends at position P4 and the steering control state becomes disabled (OFF), the steering wheel will rotate to the right due to self-aligning torque, as shown in FIG. 3. If the vehicle continues to drive in this state, the steering angle will become 0° when the vehicle V is driving to position P5, and the rotation of the steering wheel will stop.

[0060] Next, using Figure 4, steering control when traveling on a curve with a larger curvature than the curve shown in Figure 2 will be described. The traveling scene shown in Figure 4 is similar to the traveling scene shown in Figure 2, except that the curvature of the curve is larger than that of the curve shown in Figure 2. In the traveling scene shown in Figure 4, a vehicle V is traveling in a lane La in the direction of arrow Xa, and the lane La is defined by a boundary line B1a on the left side of the traveling direction of the vehicle V and a boundary line B2a on the right side of the traveling direction.

[0061] In the driving scene shown in Fig. 4, the curvature of the curve is greater than in the driving scene shown in Fig. 2, so if the vehicle is driven at the same speed as in the driving scene shown in Fig. 2, the steering angle needs to be greater than the angle shown in Fig. 2. Therefore, in the driving scene shown in Fig. 4, the steering angle is greater than in the driving scene shown in Fig. 2. In this case, as in the driving scene shown in Fig. 3, if steering control is terminated when the steering angle is large, the behavior of the vehicle V will change significantly due to the self-aligning torque.

[0062] Therefore, the driving assistance device 14 acquires the curvature of the lane La, and if the curvature of the lane La is equal to or less than a predetermined value, rotates the steering wheel in the direction opposite to the departure direction and calculates the lane-to-lane yaw angle of the vehicle V. Then, at a certain timing between when the lane-to-lane yaw angle starts to increase and when the increment of the lane-to-lane yaw angle reaches a predetermined angle, the driving assistance device 14 stops the rotation of the steering wheel and ends steering control while maintaining the steering angle.

[0063] On the other hand, if the curvature of lane La is greater than a predetermined value, the steering wheel is rotated in the direction opposite to the departure direction, and the lane-to-lane yaw angle of vehicle V is calculated. Then, at a certain timing between when the lane-to-lane yaw angle starts to increase and when the increment of the lane-to-lane yaw angle reaches a predetermined angle, the rotation of the steering wheel is stopped to maintain the steering angle. Furthermore, from a predetermined timing after the start of maintaining the steering angle, the steering wheel is rotated in the direction opposite to the departure direction, and steering control is terminated with the steering wheel rotating in the direction opposite to the departure direction. This allows the steering angle to be reduced before the steering control is terminated, thereby preventing the behavior of vehicle V from being significantly changed by the self-aligning torque.

[0064] The predetermined value can be set appropriately within a range in which changes in behavior due to the self-aligning torque do not cause discomfort to occupants of the vehicle V. As described above, the predetermined timing is a timing between the timing at which maintenance of the steering angle begins and the timing at which steering control ends, for example, the timing at which the vehicle V passes a position at which the lane-to-lane yaw angle begins to increase. Furthermore, when the curvature of the lane La is greater than the predetermined value, the driving assistance device 14 may set a speed at which the steering wheel is turned in the direction opposite to the departure direction to increase as the curvature increases.

[0065] In the driving scene shown in FIG. 4, the driving assistance device 14 performs steering control similar to that shown in FIG. 2 up to position P3a. After the vehicle V passes position P3a, a command value to decrease the steering angle to the left is output, as shown in the diagram of the steering angle command value. Therefore, the steering wheel rotates to the right and continues to rotate at a constant angular velocity until position P4a, a predetermined time after passing position P3a. If the driver does not start steering after the steering control ends at position P4a and the steering control state becomes disabled (OFF), the steering wheel will rotate to the right due to self-aligning torque, as shown in FIG. 4. If the vehicle continues driving in this state, the steering angle will become 0° when the vehicle V reaches position P5a, and the rotation of the steering wheel will stop.

[0066] Note that the following are not essential components of the present invention and may be added as needed: acquiring the curvature of lane La; acquiring the traveling speed of vehicle V; rotating the steering wheel in the direction opposite to the departure direction from a predetermined timing after starting to maintain the steering angle; terminating steering control while the steering wheel is rotating in the direction opposite to the departure direction; terminating steering control while the steering angle is maintained; rotating the steering wheel in the direction opposite to the departure direction and stopping the rotation of the steering wheel at a certain timing between when the lane-to-vehicle yaw angle starts to increase and when the increment of the lane-to-vehicle yaw angle reaches a predetermined angle.

[0067] [Processing in driving assistance systems] 5A to 5C, the procedure for processing information by the driving assistance device 14 will be described. FIGS. 5A to 5C are examples of flowcharts showing information processing executed in the driving assistance system 1 of this embodiment. The processing described below is executed at predetermined time intervals by the CPU 141, which is the processor of the driving assistance device 14.

[0068] First, in step S1 of Fig. 5A, the recognition unit 21 detects the boundary of the lane L on which the vehicle V is traveling from the detection result of the imaging device 11, and then in step S2, the prediction unit 22 determines whether or not the vehicle will enter a curve. If it is determined that the vehicle V will not enter a curve, the process proceeds to step S6, where the support unit 2 determines whether or not the vehicle V has reached its destination. If it is determined that the vehicle V has reached its destination, the process ends execution of the routine, and if it is determined that the vehicle V has not reached its destination, the process proceeds to step S1.

[0069] If it is determined in step S2 that the vehicle V will enter a curve, the process proceeds to step S3, where the direction of travel of the vehicle V is obtained using the function of the prediction unit 22, and in the following step S4, it is predicted whether or not the vehicle V will deviate from the lane L. If it is predicted that the vehicle V will not deviate from the lane L, the process proceeds to step S5, where it is determined whether or not the vehicle V has passed through a curve. If the vehicle V is traveling straight and the boundary of the lane L is not curved, it is determined that the vehicle V has passed through a curve, and the process proceeds to step S6, and if it is determined that the vehicle V has not passed through a curve, the process proceeds to step S3.

[0070] If it is predicted in step S4 that the vehicle V will deviate from the lane L, the process proceeds to step S11 in FIG. 5B. In step S11, steering control is started using the function of the control unit 24, and in the following step S12, the departure direction of the vehicle is acquired using the function of the acquisition unit 23, and in step S13, the turning direction of the vehicle V is acquired. In the following step S14, it is determined whether the departure direction and the turning direction are the same direction, and if the departure direction and the turning direction are different directions, the process proceeds to step S15. In step S15, normal steering control is executed to suppress departure from the lane L, and the process proceeds to step S6 in FIG. 5A.

[0071] On the other hand, if the departure direction and the turning direction are the same, the process proceeds to step S16, where the steering actuator is operated via the steering control device 13 to rotate the steering wheel in the direction opposite to the departure direction. In the following step S17, the lane-to-lane yaw angle is calculated, and in step S18, it is determined whether the lane-to-lane yaw angle has increased. If it is determined that the lane-to-lane yaw angle has not increased, the process proceeds to step S16, where the steering control device 13 is used to rotate the steering wheel in the direction opposite to the departure direction. On the other hand, if it is determined that the lane-to-lane yaw angle is increasing (or has started to increase), the process proceeds to step S19, where the rotation of the steering wheel is stopped until the increment of the lane-to-lane yaw angle reaches a predetermined angle, and the steering angle is maintained.

[0072] Proceeding to step S20 in Fig. 5C, the curvature of the lane L is acquired using the function of the acquisition unit 23, and in the following step S21, it is determined whether or not the curvature is equal to or less than a predetermined value using the function of the control unit 24. If the curvature is equal to or less than the predetermined value, the process proceeds to step S22, and if the curvature is greater than the predetermined value, the process proceeds to step S24. In step S22, the traveling speed of the vehicle V is acquired, and in step S23, it is determined whether or not the traveling speed of the vehicle V is equal to or less than a predetermined speed. If the traveling speed is equal to or less than the predetermined speed, the process proceeds to step S26, and if the traveling speed is greater than the predetermined speed, the process proceeds to step S24.

[0073] In step S24, the control unit 24 determines whether or not a predetermined timing has been reached, and if it determines that the predetermined timing has not been reached, step S24 is repeated until the predetermined timing is reached. On the other hand, if it determines that the predetermined timing has been reached, the process proceeds to step S25, where the steering actuator is operated via the steering control device 13, and the steering wheel begins to rotate in the direction opposite to the departure direction. In the following step S26, it is determined whether or not a predetermined time has elapsed since the lane-to-lane yaw angle began to increase. If it determines that the predetermined time has not elapsed, step S26 is repeated, and if it determines that the predetermined time has elapsed, the process proceeds to step S27, where steering control is terminated. Thereafter, the process proceeds to step S6 in FIG. 5A.

[0074] Note that steps S20 to S25 are not essential steps and may be added or omitted as necessary. Specifically, only steps S20 and S21 may be omitted, only steps S22 and S23 may be omitted, or all of steps S20 to S25 may be omitted.

[0075] [Embodiments of the present invention] As described above, according to the present embodiment, a driving assistance method is provided in which the processor predicts whether the vehicle V, which is traveling due to a steering operation by a driver, will deviate from the lane L in which the vehicle is traveling, and, if it predicts that the vehicle V will deviate from the lane L, acquires a departure direction in which the vehicle V will deviate from the lane L and a turning direction of the vehicle V, determines whether the departure direction and the turning direction are the same, and, if it determines that the departure direction and the turning direction are the same, does not rotate the steering wheel of the vehicle V in the departure direction, thereby executing steering control to prevent the vehicle V from deviating from the lane L. This makes it possible to prevent the driver from misunderstanding the timing at which steering control ends and the transition to steering operation by the driver occurs.

[0076] Furthermore, according to the driving assistance method of this embodiment, when the processor determines that the departure direction and the turning direction are the same, it rotates the steering wheel in the direction opposite to the departure direction, and maintains the rotation angle of the steering wheel from a certain timing between when a lane-to-lane yaw angle, which is the angle between the traveling direction of the vehicle V and the tangent direction of the lane L at the position on the lane L where the vehicle V is traveling, begins to increase and when the increment of the lane-to-lane yaw angle reaches a predetermined angle. This makes it possible to prevent the vehicle V from departing in the direction opposite to the departure direction.

[0077] Furthermore, according to the driving assistance method of this embodiment, the processor acquires the curvature of the lane L, and if the curvature is equal to or less than a predetermined value, rotates the steering wheel in a direction opposite to the departure direction, and maintains the rotation angle of the steering wheel from a certain timing between when a lane-to-lane yaw angle, which is the angle between the traveling direction of the vehicle V and a tangent direction of the lane L at the position on the lane L where the vehicle V is traveling, begins to increase and when the increment of the lane-to-lane yaw angle reaches a predetermined angle, and terminates the steering control with the rotation angle maintained; if the curvature is greater than the predetermined value, rotates the steering wheel in a direction opposite to the departure direction, and maintains the rotation angle of the steering wheel from a certain timing between when the lane-to-lane yaw angle begins to increase and when the increment of the lane-to-lane yaw angle reaches the predetermined angle, rotates the steering wheel in the direction opposite to the departure direction from a certain timing after starting to maintain the rotation angle, and terminates the steering control with the steering wheel rotating in the direction opposite to the departure direction. This allows the rotation speed of the steering wheel caused by the self-aligning torque to be controlled, thereby suppressing changes in the behavior of the vehicle V.

[0078] Furthermore, according to the driving assistance method of this embodiment, when the curvature is greater than the predetermined value, the processor sets a speed at which the steering wheel is rotated in the direction opposite to the departure direction to be greater the greater the curvature, thereby controlling the rotation speed of the steering wheel due to self-aligning torque and suppressing changes in the behavior of the vehicle V.

[0079] Furthermore, according to the driving assistance method of this embodiment, the processor acquires the traveling speed of the vehicle V, and if the traveling speed is equal to or less than a predetermined speed, rotates the steering wheel in a direction opposite to the departure direction, and maintains the rotation angle of the steering wheel from a certain timing between when a lane yaw angle, which is the angle between the traveling direction of the vehicle V and a tangent direction of the lane La at the position on the lane La where the vehicle V is traveling, begins to increase and when the increment of the lane yaw angle reaches a predetermined angle, and terminates the steering control with the rotation angle maintained; if the traveling speed is faster than the predetermined speed, rotates the steering wheel in a direction opposite to the departure direction, and maintains the rotation angle of the steering wheel from a certain timing between when the lane yaw angle begins to increase and when the increment of the lane yaw angle reaches the predetermined angle, rotates the steering wheel in the direction opposite to the departure direction from a certain timing after starting to maintain the rotation angle, and terminates the steering control with the steering wheel rotating in the direction opposite to the departure direction. This allows the rotation speed of the steering wheel caused by the self-aligning torque to be controlled, thereby suppressing changes in the behavior of the vehicle V.

[0080] Furthermore, according to the driving assistance method of this embodiment, when the traveling speed is faster than the predetermined speed, the processor sets a speed at which the steering wheel is rotated in the direction opposite to the departure direction to be larger the faster the traveling speed is, thereby controlling the rotation speed of the steering wheel due to the self-aligning torque and suppressing changes in the behavior of the vehicle V.

[0081] Furthermore, according to this embodiment, a driving assistance device 14 is provided, which includes: a prediction unit 22 that predicts whether a vehicle V traveling due to a steering operation by a driver will deviate from a lane L in which the vehicle V is traveling; an acquisition unit 23 that, when the prediction unit 22 predicts that the vehicle V will deviate from the lane L, acquires a departure direction in which the vehicle V will deviate from the lane L and a turning direction of the vehicle V; and a control unit 24 that determines whether the departure direction and the turning direction are the same, and, when it is determined that the departure direction and the turning direction are the same, does not rotate the steering wheel of the vehicle V in the departure direction, thereby executing steering control to prevent the vehicle V from deviating from the lane L. This makes it possible to prevent the driver from misunderstanding the timing at which steering control ends and the transition to steering operation by the driver occurs. [Explanation of symbols]

[0082] 1... driving assistance system, 11... imaging device, 12... vehicle state detection device, 13... steering control device, 14... driving assistance device, 141... CPU (processor), 142... ROM, 143... RAM 2...Support unit, 21...Recognition unit, 22...Prediction unit, 23...Acquisition unit, 24...Control unit B1, B2, B1a, B2a...boundary line, C1...line parallel to the front and rear direction of the vehicle, C2...tangent to the boundary, D...distance, L, La...lane, P1~P5, P1a~P5a, Px, Py...position, V...vehicle, X, Xa...arrow, α...lane yaw angle

Claims

1. A driving assistance method executed by a processor, comprising: monitoring a driving state of a vehicle that is traveling in response to a steering operation by a driver; and, when it is predicted that the vehicle will deviate from the lane in which it is traveling, performing steering control to maintain a lane-to-lane yaw angle, which is an angle formed between a traveling direction of the vehicle and a tangent direction of the lane at a position on the lane in which the vehicle is traveling, within an angle range in which the vehicle can travel along the lane; and continuing the steering control until a predetermined time has elapsed since the lane-to-lane yaw angle changes from a decrease to an increase, The processor: predicting whether the vehicle, which is traveling due to the steering operation of the driver, will deviate from the lane in which it is traveling; When it is predicted that the vehicle will deviate from the lane, a departure direction in which the vehicle will deviate from the lane and a turning direction of the vehicle are acquired; determining whether the departure direction and the turning direction are the same direction; When it is determined that the departure direction and the turning direction are the same, the steering control is executed to prevent the vehicle from departing from the lane by not rotating the steering wheel of the vehicle in the departure direction.

2. The processor: When it is determined that the departure direction and the turning direction are the same direction, the steering wheel is rotated in a direction opposite to the departure direction, 2. The driving assistance method according to claim 1, wherein the rotation angle of the steering wheel is maintained from a certain timing between when the lane-to-vehicle yaw angle starts to increase and when the increment of the lane-to-vehicle yaw angle reaches a predetermined angle.

3. The processor: Obtaining the curvature of the lane; If the curvature is equal to or less than a predetermined value, rotating the steering wheel in a direction opposite to the departure direction; maintaining the rotation angle of the steering wheel from a certain timing between when the lane-relative yaw angle starts to increase and when the increment of the lane-relative yaw angle reaches a predetermined angle; Ending the steering control while maintaining the rotation angle, If the curvature is greater than the predetermined value, rotating the steering wheel in a direction opposite to the departure direction; maintaining the rotation angle of the steering wheel from a certain timing between when the lane-relative yaw angle starts to increase and when the increment of the lane-relative yaw angle reaches the predetermined angle; The steering wheel is rotated in a direction opposite to the departure direction from a predetermined timing after the start of maintaining the rotation angle.

3. The driving assistance method according to claim 1, wherein the steering control is terminated in a state where the steering wheel is rotating in a direction opposite to the departure direction.

4. The driving assistance method according to claim 3 , wherein, when the curvature is greater than the predetermined value, the processor sets a speed at which the steering wheel is rotated in the direction opposite to the departure direction to be greater as the curvature increases.

5. The processor: Acquire the traveling speed of the vehicle; If the traveling speed is equal to or lower than a predetermined speed, rotating the steering wheel in a direction opposite to the departure direction; maintaining the rotation angle of the steering wheel from a certain timing between when the lane-relative yaw angle starts to increase and when the increment of the lane-relative yaw angle reaches a predetermined angle; Ending the steering control while maintaining the rotation angle, If the traveling speed is faster than the predetermined speed, rotating the steering wheel in a direction opposite to the departure direction; maintaining the rotation angle of the steering wheel from a certain timing between when the lane-relative yaw angle starts to increase and when the increment of the lane-relative yaw angle reaches the predetermined angle; The steering wheel is rotated in a direction opposite to the departure direction from a predetermined timing after the start of maintaining the rotation angle.

3. The driving assistance method according to claim 1, wherein the steering control is terminated in a state where the steering wheel is rotating in a direction opposite to the departure direction.

6. 6. The driving assistance method according to claim 5, wherein, when the traveling speed is higher than the predetermined speed, the processor sets a speed at which the steering wheel is rotated in the direction opposite to the departure direction to be larger as the traveling speed is higher.

7. A driving assistance device that monitors a driving state of a vehicle that is traveling due to a steering operation by a driver, and when it is predicted that the vehicle will deviate from the lane in which it is traveling, executes steering control to maintain a lane-to-lane yaw angle, which is an angle formed by a traveling direction of the vehicle and a tangent direction of the lane at a position on the lane in which the vehicle is traveling, within an angle range in which the vehicle can travel along the lane, and continues the steering control until a predetermined time has elapsed since the lane-to-lane yaw angle changes from a decrease to an increase, a prediction unit that predicts whether the vehicle, which is traveling due to the steering operation of the driver, will deviate from the lane in which the vehicle is traveling; an acquisition unit that acquires, when the prediction unit predicts that the vehicle will deviate from the lane, a departure direction in which the vehicle will deviate from the lane and a turning direction of the vehicle; determining whether the departure direction and the turning direction are the same direction; a control unit that, when it is determined that the departure direction and the turning direction are the same, executes the steering control to prevent the vehicle from deviating from the lane by not rotating the steering wheel of the vehicle in the departure direction.

Images