LANE KEEPING ASSISTANT

Abstract

Lane Keeping Assist with: - a lane line detection unit (21) attached to a vehicle (90) and configured to detect at least one lane line (BO) present in a destination area (RE) which describes an area in front of the vehicle in the direction of travel; - a lane departure detection unit (23) attached to the vehicle and configured to determine whether or not there is a probability that the vehicle will leave a lane (TL) based on at least one lane boundary line detected by the boundary line detection unit; - a lane keeping unit (25) attached to the vehicle and configured to allow the vehicle, when the lane departure determination unit determines that there is a probability that the vehicle will leave the lane, to perform a lane keeping operation which changes the direction of travel of the vehicle in order to prevent the vehicle from leaving the lane it is traveling in; and - a lane condition determination unit (23) attached to the vehicle and configured to determine a lane condition in front of the vehicle based on at least one lane boundary line detected by the boundary line detection unit and to execute at least one of the following restriction provisions: (i) a crossing rule stating that two lane boundary lines or their extension lines (BO1a, BO2a) cross in front of the vehicle, (ii) a distribution rule stating that the width of a lane in front of the vehicle increases in a direction away from the vehicle compared to an area close to the vehicle, and (iii) a narrowing provision such that the width of a lane in front of the vehicle decreases in a direction away from the vehicle compared with an area close to the vehicle, wherein - the lane keeping unit is configured to suppress or restrict the lane keeping operation performed by the vehicle when at least one of the restriction provisions is executed by the lane condition determination unit, - the lane keeping operation includes: - a first change operation that changes the direction of travel of the vehicle from a direction towards an outside of the lane to an inside of the lane; and - a second change operation that changes the vehicle's direction of travel to a direction along the lane, after the vehicle's direction of travel has been changed by the first change operation, and - if the distribution determination is carried out by the lane condition determination unit, the suppression or restriction of the lane keeping operation is carried out by suppressing or restricting the second change operation in an area of ​​the at least one lane boundary line detected by the boundary line detection unit, which extends in one direction to an outside of the lane in the direction of travel of the vehicle.

Description

BACKGROUND OF (Field of Invention)

[0001] The present invention relates to a technology for preventing a vehicle from leaving a lane. [State of the art]

[0002] In a driving assistance device disclosed in JP 2011-233151 A, when a branching section exists ahead on a traveling lane of a vehicle, operation information such as steering torque information and turn signal information generated by a driver's operations is acquired. Based on the acquired operation information, a traveling direction of the vehicle at the branching section is estimated. Subsequently, based on the estimated traveling direction of the vehicle, a virtual lane division line (lane boundary line) is generated. Then, based on the generated virtual lane division line, it is determined whether or not the probability (probability or possibility) that the vehicle will leave the traveling lane (deviate from the traveling lane) is high.If it is determined that the probability of the vehicle leaving the lane is high, a warning or the like is issued to prevent the vehicle from leaving the lane.

[0003] Furthermore, the following technology is known as a technology for preventing a vehicle from leaving a lane (see JP H11-91606 A). With this technology, when the probability of lane departure is high, a steering torque is generated to return the vehicle to the inside (center) of the lane (lane keeping control).

[0004] Operational information, such as steering torque information and turn signal information, is generated based on the driver's actions. Consequently, due to driver inattention, such as driving erratically, the operational information may display information that differs from the intended direction. Therefore, in an area where the direction of travel is split into multiple directions, a direction of travel that differs from the driver's intended direction may be erroneously estimated based on the operational information.

[0005] If the vehicle's traveling direction is incorrectly estimated and lane departure control is performed based on the estimated traveling direction, a steering torque may be generated that the driver does not intend. This may cause anxiety or discomfort to the driver. Furthermore, in certain zones, such as construction zones, multiple lane boundary lines (such as white and yellow lines) may be drawn in an intersecting manner on the road surface. If lane departure control is performed in a vehicle traveling in such a specific zone based on the incorrectly estimated traveling direction, driving operations may be performed that cause discomfort or endanger the driver. Therefore, there is a need for lane departure control technology that improves driver safety.

[0006] Furthermore, DE 10 2012 004 791 A1 discloses a method for warning the driver of a motor vehicle of an impending dangerous situation as a result of an unintentional drift into an oncoming traffic lane.

[0007] A method and a device for carrying out an automatic steering intervention, in particular for lane keeping assistance, are known from WO 2006 / 081 936 A1. SUMMARY OF THE INVENTION

[0008] It is an object of the present invention to provide a lane keeping assistant and a lane keeping method which are capable of improving driving safety.

[0009] The problem is solved by the subject matter of the independent claims. Advantageous further developments are specified in the dependent claims.

[0010] According to the invention, the likelihood of driving operations that cause driver discomfort or endanger the driver due to lane-keeping operations can be reduced. Consequently, a lane-keeping assistant and a lane-keeping method capable of improving driver safety can be provided.

[0011] The present invention can be implemented in various aspects other than the lane keeping assistant. For example, the present invention can be implemented in aspects such as a method for controlling a lane keeping assistant, a program that enables a lane keeping assistant to execute a control method, or a vehicle with a lane keeping assistant. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The attached drawings show: Fig. 1 shows a configuration of a vehicle according to an embodiment; Fig. 2 a figure illustrating the conditions for a crossing presence determination; Fig. 3 a figure illustrating the conditions for a distribution-presence determination; Fig. 4 a figure illustrating the conditions for a constriction presence determination; Fig. 5 is a diagram illustrating a lane departure determination and a lane keeping operation; Fig. 6 is a diagram illustrating the details of lane keeping operation; Fig. 7 a flow diagram of a lane keeping assistant; Fig. 8 is a diagram illustrating a first detailed example of lane keeping control and its effects; Fig. 9 is a diagram illustrating a second detailed example of lane keeping control and its effects; Fig. 10 is an illustration of the case where a normal lane keeping operation is carried out in a vehicle; and Fig. 11 is a figure illustrating a third detailed example of lane keeping control and its effects. DESCRIPTION OF THE EMBODIMENTS

[0013] An embodiment of the present invention will be described below with reference to the drawings. (Device configuration and processing steps)

[0014] A vehicle 90 according to the embodiment has, as shown in Fig. 1, a camera 12, a vehicle speed sensor 14, a yaw rate sensor 16, a steering angle sensor 18, a driver assistance ECU (ECU = electronic control unit) 20, a steering ECU 30, and a steering actuator 32. The driver assistance ECU 20 serves as a lane departure prevention system.

[0015] The camera 12 captures an image of an area (road surface) in the direction of travel in front of the vehicle 90. The camera 12 then sends the captured image (image information) to the driving assistance ECU 20. The image area of ​​the camera 12 serves as a determination area, which will be described later. The vehicle speed sensor 14 detects the speed of the vehicle 90. The vehicle speed sensor 14 then sends the detected speed information of the vehicle 90 to the driving assistance ECU 20. The yaw rate sensor 16 detects the rotational angular velocity (yaw rate) of the vehicle 90. The yaw rate sensor 16 then sends the detected rotational angular velocity information to the driving assistance ECU 20. The steering angle sensor 18 detects the steering angle of the vehicle 90. The steering angle sensor 18 then sends the detected steering angle information to the driving assistance ECU 20.

[0016] The steering ECU 30 provides a steering angle control function for sending steering angle commands (steering torque commands) to the steering actuator 32. The steering actuator 32 controls the steering angle of the vehicle 90. Furthermore, the steering ECU 30 provides a function (steering angle calculation function) for calculating the steering angle to satisfy a target yaw rate based on a target yaw rate received more quickly from an external source (such as a steering wheel operation). The steering angle calculation function is set to output a corresponding steering angle when the target yaw rate is input. The steering angle control function controls the steering actuator 32 to achieve the output steering angle.

[0017] The driving assistance ECU 20 includes a boundary line detection unit 21, a lane departure determination unit 22, a lane state determination unit 23, and a lane keeping unit 25. The lane keeping unit 25 includes an operation suspension unit 26.

[0018] The boundary line detection unit 21 detects a lane boundary line present within a destination area based on image information. The lane boundary line is a marker used to divide lanes. The lane boundary lines include currently used lane boundaries and previously used lane boundaries.

[0019] The lane boundary lines include, for example, white and yellow lines continuously drawn linearly on the road. The lane boundary lines also include white and yellow dashed lines that form a linear shape by connecting adjacent line segments. The lane boundary lines further include Botts' points, cat's eyes (reflective plates), repair sections, and the like. Lane boundary lines used in the past indicate repair sections and white lines, yellow lines, and the like that have been removed by road repair and the like. Even if a white line or the like is over-tarred (removed using tar) or the like, the deleted portion (repair section) may appear. In such cases, the boundary line detecting unit 21 detects the removed portion as a lane boundary line, if any.

[0020] The lane departure determination unit 22 determines whether or not there is a probability that the vehicle 90 will leave the lane based on the lane boundary line detected by the boundary line detection unit 21. Specifically, the lane departure determination unit 22 makes the determination as follows.

[0021] The vehicle 90 proceeds as in Fig. 5, in a direction approaching a lane boundary line BO1 (in a direction away from a traveling lane TL). A distance DY between the lane boundary line BO1 and the vehicle 90 in a lane width direction is determined to be less than or equal to a predetermined value DYS. In this case, the lane departure determination unit 22 determines that there is a probability that the vehicle 90 will leave the traveling lane TL.

[0022] When it is determined that there is a probability that the vehicle 90 will leave the traveling lane TL, the lane departure determination unit 22 sets a lane departure request flag SSRF to ON. The lane departure request flag SSRF is used to cause the vehicle 90 to perform a lane departure operation. Herein, "determining that there is a probability of departure" is also referred to as a "lane departure presence determination." Hereinafter, when referring to the lane boundary lines without distinction, the reference symbol "BO" is used. When referring to the traveling lane without distinction, the reference symbol "TL" is used.

[0023] According to the present embodiment, a measurement reference for the distance DY ( Fig. 5) intended for the following sections of vehicle 90. (i) When the lane boundary line BO is located on the left side in the traveling direction of the vehicle 90, the left front wheel of the vehicle 90 serves as the reference. (ii) When the lane boundary line BO is located on the right side in the traveling direction of the vehicle 90, the right front wheel of the vehicle 90 serves as the reference.

[0024] The Fig. The lane state determination unit 23 shown in FIG. 1 determines the state of the lane TL in front of the vehicle 90 based on the lane boundary line BO detected by the boundary line detection unit 21. The lane state determination unit 23 then sets an intersection flag CF, a widening flag WF, and a narrowing flag RF. The intersection flag CF, the widening flag WF, and the narrowing flag RF restrict the lane keeping operation performed by the lane keeping unit 25. "Restricting the lane keeping operation" includes suppressing or prohibiting the lane keeping control operation.

[0025] Specifically, the lane state determination unit 23 makes a determination regarding the following three states of the lane TL. (i) It is determined whether or not two lane boundary lines BO cross in front of the vehicle 90 (crossing determination). (ii) It is determined whether or not the width of the lane TL in front of the vehicle 90 increases (widening determination). (iii) It is determined whether or not the width of the lane TL in front of the vehicle 90 decreases (narrowing determination).

[0026] If any of the Fig. 2 are met, the lane state determination unit 23 determines that two lane boundary lines BO or extension lines BO1a and BO2a of the lane boundary lines BO cross in front of the vehicle. The lane state determination unit 23 then sets the crossing flag CF ( Fig. 1) ON (intersection presence determination). Conditions (i-1) to (i-3) are as follows.

[0027] Condition (i-1): Two lane boundary lines BO1 and BO2 existing within the determination area (image area) RE cross each other.

[0028] Condition (i-2): An extension line BO2a of one lane boundary line BO2, of the two lane boundary lines BO1 and BO2 existing within the determination area RE, crosses the other lane boundary line BO1.

[0029] Condition (i-3): Respective extension lines BO1a and BO2a of the two lane boundary lines BO1 and BO2 existing within the determination area RE intersect.

[0030] Herein, the determination area RE is the entire area of ​​a rectangular image taken by the camera 12 and converted to the road surface by a perspective transformation.

[0031] In this specification, the term "cross" (broad definition) describes two conditions: the merging of two lines with a non-zero degree angle at the merging point (narrow definition of "cross"); and the merging of two lines with a zero degree angle at the merging point (referred to as a "branch"). In this application, unless otherwise stated, "cross" is used as this broadly defined term.

[0032] Furthermore, the lane state determination unit 23 determines when one of the Fig. 3, the conditions (ii-1) and (ii-2) are satisfied, that the width of the lane TL in front of the vehicle 90 increases in the direction away from the vehicle 90 compared to near the vehicle 90. The lane state determination unit 23 then sets the widening flag WF ( Fig. 1) to ON (Broadening-Presence-Determination).

[0033] Condition (ii-1): A width La of the lane TL at a first predetermined point FP within the determination range RE is greater than or equal to a first predetermined value greater than a width Lb of the lane TL at a second predetermined point SP within the determination range RE. The second point SP is closer to the vehicle 90 in the traveling direction than the first point FP.

[0034] Condition (ii-2): The lane boundary line BO1 within the determination area RE has a first curved portion CP1 curved toward the outside of the lane TL in the traveling direction of the vehicle 90. Further, the first curved portion CP1 has a curvature greater than or equal to a first threshold value.

[0035] The first predetermined value in condition (ii-1) and the first threshold value in condition (ii-2) are preferably set to values ​​greater than or equal to values ​​that allow an assumption that the probability of branching of the lane TL in front of the vehicle 90 is high. Further, the first predetermined value and the first threshold value are preferably set to values ​​greater than or equal to values ​​that allow an assumption that there is a probability that a driving operation contrary to the driver's intentions will occur when an ordinary lane keeping operation as described below is performed.

[0036] Further, according to the present embodiment, for example, the first point FP in the above-described condition (ii-2) is set to a point farthest in the traveling direction within the determination range RE. The second point SP is set to a point closest in the traveling direction within the determination range RE.

[0037] Furthermore, the lane state determination unit 23 determines when one of the Fig. 4, the conditions (iii-1) and (iii-2) are satisfied, that the width of the lane TL in front of the vehicle 90 decreases in the direction away from the vehicle 90 compared to near the vehicle 90. The lane state determination unit 23 sets the narrowing flag RF ( Fig. 1) to ON (narrowing presence determination).

[0038] Condition (iii-1): The width of the lane TL at the first predetermined point FP within the determination range RE is greater than or equal to a second predetermined value smaller than the width Lb of the lane TL at the second predetermined point SP within the determination range RE. The second point SP is closer to the vehicle 90 in the traveling direction than the first point FP.

[0039] Condition (iii-2): A lane boundary line BO3 within the determination area RE has a second curved section CP2 that is curved toward the inside of the lane TL in the traveling direction of the vehicle 90. Furthermore, the second curved section CP1 has a curvature greater than or equal to a second threshold value.

[0040] The second predetermined value in condition (iii-1) and the second threshold value in condition (iii-2) are preferably set to values ​​greater than or equal to values ​​that allow an assumption that the probability of the lane TL merging with another lane TL ahead of the vehicle 90 is high. Furthermore, the second predetermined value and the second threshold value are preferably set to values ​​greater than or equal to values ​​that allow an assumption that there is a probability of a driving operation contrary to the driver's intentions occurring when an ordinary lane keeping operation, which will be described later, is executed.

[0041] Furthermore, according to the present embodiment, for example, the first point FP in the above-described condition (iii-1) is set to a point located farthest in the traveling direction within the determination range RE. The second point SP is set to a point located closest in the traveling direction within the determination range RE.

[0042] The intersection presence determination, the widening presence determination, or the narrowing presence determination described above, which are executed by the lane state determination unit 23, serve as a trigger for restricting lane keeping operation. Accordingly, these determinations are each also referred to as a "restriction determination." The lane state determination unit 23 can execute only one or two of the three determinations.

[0043] The Fig. The lane keeping unit 25 shown in FIG. 1 executes lane keeping control when the lane keeping request flag SSRF is set to ON. The lane keeping control is performed to prevent the vehicle 90 from leaving the traveling lane TL. The lane keeping control causes the vehicle 90 to perform a lane keeping operation that changes the traveling direction of the vehicle 90. The lane keeping operation is an operation performed to return the vehicle 90 to the inside (center) of the traveling lane TL. Specific examples of the lane keeping operation are described below.

[0044] The operation cancellation unit 26 detects a manual steering torque generated by the driver's steering (steering wheel operation). If the manual steering torque detected during execution of the lane keeping operation is greater than or equal to a predetermined threshold, the operation cancellation unit 26 cancels the lane keeping operation. The predetermined threshold is preferably set to a value greater than or equal to a value that allows a determination that the driver intentionally operated the steering wheel. The predetermined threshold is also referred to as the "lane keeping cancellation threshold value (SSCT)."

[0045] The following describes a lane keeping operation in an ordinary situation (when the restriction flags CF, WF and RF are not set to ON) with reference to the Fig. 5 and Fig. 6. The vehicle 90 is designed to perform lane keeping operation by means of the lane keeping unit 25.

[0046] If the vehicle is 90, as in Fig. 5, is returned to the inside of the lane TL, the lane keeping unit 25 changes the direction of travel of the vehicle 90 by a suppression angle (α + β) to the inside of the lane TL (first change operation). The suppression angle (α + β) describes the sum of a lane departure angle α and an assistance angle β. The lane departure angle α is formed by a lane boundary line BO1 and the direction of travel of the vehicle 90. The assistance angle β is formed by the lane boundary line BO1 and a desired direction of travel of the vehicle 90.

[0047] Subsequently, the lane keeping unit 25 regresses the traveling direction of the vehicle 90 by a final angle γ near a virtual line VL (second change operation). The virtual line VL is located closer to the inside of the lane TL than the other lane boundary line BO2. The final angle γ is formed by the virtual line VL and the traveling direction. By causing the vehicle 90 to perform the first and second change operations, the lane keeping unit 25 causes the vehicle 90 to travel along the virtual line VL. After causing the lane keeping unit 25 to perform the first and second change operations, the lane keeping unit 25 ends the lane keeping control.

[0048] Herein, the phrase "toward the inside (center) of the lane TL" describes the side of the lane TL on which the vehicle 90 is located farther from the lane boundary line BO than at the point at which the lane keeping operation is started. The phrase "toward the inside (center) of the lane TL" does not describe a position in the center of the lane TL in the width direction. According to the present embodiment, the virtual line VL is set to a position located a predetermined distance PDS further toward the inside of the lane TL from the lane boundary line BO1. According to the present embodiment, the first and second changing operations are realized by the steering actuator 32 ( Fig. 1), which is controlled. Consequently, the first change mode is also referred to as a first steering mode. The second change mode is also referred to as a second steering mode.

[0049] To make the vehicle 90 the Fig. 5, the lane keeping unit 25 determines, as shown in Fig. 6 shows a comparison expression. The comparison expression is described by a yaw rate Yr on the vertical axis and time on the horizontal axis. The lane keeping unit 25 controls the operation of the vehicle 90 based on the determined comparison expression. According to the present embodiment, the first steering process is performed as follows during execution of the lane keeping operation. According to the present embodiment, the yaw rate has a positive value during a left turn. (i) The yaw rate Yr is increased such that the rate of change of the yaw rate Yr is constant until a maximum yaw rate YrMax1 is reached. (ii) After the maximum yaw rate YrMax1 is reached, the yaw rate Yr is maintained at the maximum yaw rate YrMax1 until the yaw rate Yr is reduced so that the passengers do not experience excessive acceleration. (iii) After the maximum yaw rate YrMax1 is maintained for a predetermined period of time, the yaw rate Yr is reduced such that the rate of change of the yaw rate Yr is constant until the second steering operation occurs.

[0050] Further, according to the present embodiment, the second steering operation during execution of the lane keeping operation is performed as follows. (i) The yaw rate Yr is reduced such that the rate of change of the yaw rate Yr is constant until a maximum yaw rate YrMax2 is reached. (ii) After the maximum yaw rate YrMax2 is reached, the yaw rate Yr is maintained at the maximum yaw rate YrMax2 until the yaw rate Yr is increased so that the passengers do not experience excessive acceleration. (iii) After the maximum yaw rate YrMax2 is maintained for a predetermined period of time, the yaw rate Yr is increased such that the rate of change of the yaw rate Yr is constant until the second steering operation is completed.

[0051] Instead of being implemented using the steering actuator 32, the lane keeping operation that the vehicle performs under the control of the lane keeping unit 25 can be implemented using a braking mechanism. The braking mechanism can change the traveling direction of the vehicle 90 by applying the brake only to the right wheels or only to the left wheels. Specifically, an actuator that provides a function for changing the traveling direction of the vehicle 90 can be used instead of the steering actuator 32. Furthermore, multiple functions for changing the traveling direction of the vehicle 90 can be used.

[0052] The following is a processing flow of a lane keeping control executed by the driving assistance ECU 20 with reference to Fig. 7. For example, the lane departure control processing sequence is started when the driving assistance ECU 20 is turned ON. Subsequently, the processing sequence is repeatedly executed at a fixed time interval (e.g., every 50 ms).

[0053] The lane state determination unit 23 ( Fig. 1) executes the above-described determination and setting process for the restriction flags CF, WF, and RF (the crossing flag CF, the widening flag WF, and the narrowing flag RF) (step S20).

[0054] The restriction flags CF, WF, and RF are processed as follows, taking into account the time lag between the start of lane departure control and the setting process for the restriction flags CF, WF, and RF. Specifically, when the restriction flags CF, WF, and RF are set to ON, the restriction flags CF, WF, and RF remain ON for a predetermined period of time without being reset. Specifically, even if a determination is made to set the restriction flags CF, WF, and RF to OFF during the predetermined period of time, the restriction flags CF, WF, and RF remain ON. The restriction flags CF, WF, and RF that are set to ON are subsequently set to OFF after the predetermined period of time has elapsed.

[0055] After step S20, the lane keeping unit 25 determines whether the intersection flag CF is ON (step S22). If it is determined that the intersection flag CF is ON, the lane keeping unit 25 determines whether the lane keeping request flag SSRF is ON (step S24). More specifically, in step S24, the lane keeping unit 25 determines whether the lane keeping operation (lane keeping control) is being executed.

[0056] If it is determined that the lane keeping request flag SSRF is ON, the lane keeping unit 25 restricts the lane keeping operation (step S26). The following two methods can be provided as specific methods for restricting the lane keeping operation. (i) First intersection restriction procedure: Lane keeping operation is prohibited (execution of lane keeping operation by vehicle 90 is prohibited) (ii) Second crossing restriction procedure: the crossing restriction procedure in the operation cancellation unit 26 ( Fig. 1) set lane departure warning threshold SSCT is decreased.

[0057] Here, the second intersection restriction method is, for example, a method of reducing the value of an ordinary lane departure control threshold value SSCT by 10 to 30%. This results in the lane departure control operation being canceled by a smaller manual steering torque.

[0058] According to the present embodiment, the lane keeping unit 25 restricts the lane keeping operation due to the application of the first intersection restriction method. When the first intersection restriction method is applied, the driving assistance ECU 20 does not need to include the operation cancellation unit 26.

[0059] If it is determined in step S24 that the lane keeping request flag SSRF is not set to ON, the lane keeping unit 25 executes the setting of the next operation restriction (step S27). The setting of the next operation restriction is a setting for restricting the lane keeping operation when the lane keeping request flag SSRF is set to ON (when the lane departure presence determination is made) during a processing routine subsequently executed by the drive assistance ECU 20 during a period in which the intersection flag CF is continuously set to ON (during the period in which the intersection presence determination is maintained). The following third intersection restriction method can be applied, in addition to the above-described first and second intersection restriction methods in step S26, as a method for restricting the lane keeping operation by setting the next operation restriction. (iii) Third intersection restriction method: At least either the maximum yaw rate YrMax1 of the first steering operation or the maximum yaw rate YrMax2 ( Fig. 3) of the second steering operation is reduced.

[0060] In the third intersection restriction method, the value of the maximum yaw rate YrMax1 or YrMax2 is reduced by 10 to 30% from the maximum yaw rate YrMax1 or YrMax2 set during ordinary lane keeping control. Specifically, the third intersection restriction method suppresses the lane keeping operation by reducing the degree of change in the traveling direction of the vehicle 90. According to the present embodiment, the first intersection restriction method (lane keeping operation prohibition method) is used as the next operation restriction method.

[0061] If it is determined in step S22 that the intersection flag CF is not set to ON, the lane keeping unit 25 determines whether or not the widening flag WF is set to ON (step S32). If it is determined that the widening flag WF is set to ON, the lane keeping unit 25 determines whether or not the lane keeping request flag SSRF is set to ON (step S34).

[0062] If it is determined that the lane keeping request flag SSRF is set to ON, the lane keeping unit 25 restricts the lane keeping operation with respect to the second steering operation (step S36). Specifically, the following two methods can be provided as the method for restricting the lane keeping operation with respect to the second steering operation. (i) First widening restriction procedure: The second steering operation ( Fig. 5 and Fig. 6) with respect to the lane boundary line BO extending in a direction to the outside of the lane TL in the traveling direction of the vehicle 90 is prevented (the vehicle 90 is prevented from performing the second steering operation) (ii) Second widening restriction procedure: The procedure established in the operation suspension unit 26 ( Fig. 1) The lane departure cancellation threshold SSCT set is decreased. The lane departure cancellation threshold SSCT is used when the second steering operation is performed with respect to the lane boundary line BO extending in a direction toward the outside of the lane TL in the traveling direction of the vehicle 90.

[0063] The second widening restriction method applied in step S36 is, for example, a method of reducing the value of a usual lane departure cancellation threshold value SSCT used during execution of the second steering operation by 10 to 30%. This results in the lane departure operation being suppressed with respect to the second steering operation. According to the present embodiment, the lane departure unit 25 restricts the lane departure operation using the first widening restriction method.

[0064] If it is determined in step S34 that the lane departure request flag SSRF is not set to ON, the lane departure unit 25 executes the setting of the next operation restriction with respect to the second steering operation (step S37). The setting of the next operation restriction with respect to the second steering operation is a setting for restricting the lane departure operation with respect to the second steering operation when the lane departure request flag SSRF is set to ON during a processing routine subsequently executed by the drive assistance ECU 20 (when the lane departure presence determination is made) during a period in which the widening flag WF is continuously set to ON (during the period in which the widening presence determination is maintained).

[0065] The following third widening restriction method may be applied, in addition to the above-described first and second widening restriction methods in step S36, as a method for restricting the lane keeping operation by setting the next operation restriction with respect to the second steering operation. (iii) Third widening restriction method: The maximum yaw rate YrMax2 ( Fig. 2) of the second steering operation is reduced.

[0066] In the third widening restriction method, the value of the maximum yaw rate YrMax2 is reduced by 10 to 30% from the maximum yaw rate YrMax2 set during ordinary lane keeping control. Specifically, the third widening restriction method suppresses the lane keeping operation by reducing the degree of change in the traveling direction of the vehicle 90.

[0067] If it is determined in step S32 that the widening flag WF is not set to ON, the lane keeping unit 25 determines whether or not the narrowing flag RF is set to ON (step S42). If it is determined that the narrowing flag RF is set to ON, the lane keeping unit 25 determines whether or not the lane keeping request flag SSRF is set to ON (step S44).

[0068] If it is determined in step S44 that the lane keeping request flag SSRF is ON, the lane keeping unit 25 restricts the lane keeping operation (step S46). The determined method for restricting the lane keeping operation is the same as that in step S26. More specifically, the lane keeping operation is restricted by prohibiting the lane keeping operation. Alternatively, the lane keeping operation is restricted by decreasing the lane keeping cancellation threshold value SSCT set in the operation cancellation unit 26.

[0069] According to the present embodiment, the lane keeping unit 25 restricts the lane keeping operation by prohibiting the lane keeping operation. Herein, "the process in which the lane keeping operation is restricted" applied in step S46 is also referred to as a first narrowing restricting process. "The process in which the lane keeping cancellation threshold value SSCT is reduced" applied in step S46 is also referred to as a second narrowing restricting process.

[0070] If it is determined in step S44 that the lane departure request flag SSRF is not set to ON, the lane departure unit 25 executes the next operation restriction setting (step S47). The next operation restriction setting is a setting for restricting the lane departure operation when the lane departure request flag SSRF is set to ON during a processing routine subsequently executed by the drive assistance ECU 20 (when the lane departure presence determination is made) during a period in which the narrowing flag RF is continuously set to ON (during the period in which the narrowing presence determination is maintained).

[0071] The method for restricting lane keeping operation by setting the next operation restriction is the same as the restriction methods (first to third intersection restriction methods) of the next operation restriction executed in step S27. Herein, the method corresponding to the third intersection restriction method applied in step S47 is also referred to as a third narrowing restriction method.

[0072] If it is determined in step S42 that the narrowing flag RF is not set to ON, the lane keeping unit 25 executes an ordinary lane keeping control ( Fig. 5 and Fig. 6) (Step S50). (Intersection determination and lane keeping control)

[0073] A first specific example of lane keeping control executed by the driving assistance ECU 20 and its effects are described below with reference to the Fig. 8. In the first specific example, the intersection flag CF is set to ON. The lane keeping unit 25 executes the setting for the next operation restriction in step S27 ( Fig. 7).

[0074] Vehicle 90 travels in a lane TLa. Lane TLa curves sharply to the left. Lane boundary lines BLa and BRa on both sides of lane TLa also curve. Furthermore, a lane TLb branches off from lane TLa. From the intersection points CPa and CPb forward, lane TLb and the lane boundary lines BLb and BRb extend in a straight line. The intersection point CPa is the point where the two lane boundary lines BLa and BLb intersect. The intersection point CPb is the point where the two lane boundary lines BRa and BRb intersect. Fig. 8 shows the image area (determination area) of the camera 12 provided on the vehicle 90, which is located at point P5.

[0075] In the Fig. In the lane state shown in Figure 8, the two lane boundary lines BLa and BLb intersect, as described above, in front of the vehicle 90 located at point P5. Furthermore, the two lane boundary lines BRa and BRb also intersect in front of the vehicle 90.

[0076] The lane condition, such as the one described above where the two lane boundary lines BLa and BLb (BRa and BRb) intersect, may occur, for example, in European construction zones or branching zones leading to highway rest areas. A European construction zone is considered below as an example. The lane TLb is a temporary road. The lane TLb extends in a straight line from the intersection points CPa and CPb. In this case, the lane boundary lines BLb and BRb, which mark the temporary lane TLb, are drawn using yellow lines. In addition, the lane boundary lines BLa and BRa, which mark the actual lane TLa under construction, are drawn using white lines.

[0077] In this case, after the intersection points CPa and CPb, the vehicle 90 must travel in the lane TLb marked by the yellow lines. When ordinary lane keeping control is performed in such a lane state, the first steering operation is initially performed as the lane keeping operation when the vehicle 90 reaches the point P6. As a result of the first steering operation, the vehicle 90 is guided to the lane TLa, which is different from the lane TLb in which the vehicle 90 should travel. The vehicle 90 begins to travel to the left.

[0078] Meanwhile, according to the present embodiment, the boundary line detection unit 21 provided in the vehicle 90 located at point P5 detects the lane boundary lines BLa, BLb, BRa, and BRb present in the determination area RE. The lane state determination unit 23 determines, based on the detected lane boundary lines BLa, BLb, BRa, and BRb, that the two lane boundary lines BLa and BLb (BRa and BRb) intersect. The lane state determination unit 23 sets the intersection flag CF to ON (step S20 in Fig. 7). The ON setting of the intersection flag CF at this point P5 is continuously maintained even when the vehicle 90 advances to point P6.

[0079] Meanwhile, at point P5, the lane departure request flag SSRF is not set to ON (step S24 in Fig. 7). Consequently, the lane keeping unit 25 executes the setting for the next operation restriction (step S27 in Fig. 7). When the vehicle 90 reaches point P6, the lane departure determination unit 22 sets the lane keeping request flag SSRF to ON. However, the lane keeping unit 25 has executed the setting for the next operation restriction at point P5. Consequently, even if the vehicle 90 reaches point P6 and the lane keeping request flag SSRF is set to ON, the lane keeping operation (lane keeping control) is prohibited (step S27 in the Fig. 7).

[0080] In this way, when the intersection flag CF is set to ON, the lane keeping operation is prohibited even if the lane keeping request flag SSRF is set to ON (step S26 or S27 in the Fig. 7). Accordingly, the steering torque generated by the lane departure control system, which is not desired by the driver, does not occur. This reduces the likelihood of the driver experiencing undesirable driving experiences, such as feelings of discomfort, anxiety, or fear.

[0081] Furthermore, similar effects can be achieved if the method (second intersection restriction method) in which the signal stored in the operation cancellation unit 26 ( Fig. 1) set lane departure cancellation threshold SSCT is reduced when the lane departure control operation restriction method is applied, instead of the method (first intersection restriction method) in which the lane departure control operation is restricted.

[0082] Specifically, even if the ordinary lane keeping operation (ordinary lane keeping control) is started at point P6, the lane keeping operation can be easily canceled by the driver performing a steering operation (steering wheel operation) that generates a manual steering torque greater than or equal to the lane keeping cancellation threshold SSCT, which is set to a low value. As a result, the probability of the driver experiencing undesirable driving experiences, such as feelings of discomfort, anxiety, or fright, can be reduced.

[0083] Furthermore, similar effects can be achieved if the method (third intersection restriction method) in which the maximum yaw rate YrMax1 or YrMax2 ( Fig. 6) is reduced when the lane keeping operation restriction process in step S27 of the Fig. 7 is applied. More specifically, even if the first steering operation occurs at point P6, the maximum yaw rate YrMax1 or YrMax2 is lower than the maximum yaw rate YrMax1 or YrMax2 during ordinary lane keeping operation.

[0084] Consequently, the driver can easily change the direction of travel of the vehicle 90 by a steering operation. This reduces the likelihood of the driver experiencing an undesirable experience during driving, such as feelings of discomfort, fear, or anxiety. (Widerness determination and lane keeping control)

[0085] The following is a second specific example of lane keeping control executed by the driving assistance ECU 20 and its effects with reference to the Fig. 9 and Fig. 10 described. Fig. 9 shows an example in which the widening flag WF is set to ON. The lane keeping unit 25 executes the setting of the next operation restriction with respect to the second steering operation in step S37 ( Fig. 7). Fig. Figure 10 shows the case where the usual lane keeping operation is carried out in a road condition similar to that in the Fig. 9 is in vehicle 90.

[0086] In the Fig. In the lane state shown in Figure 9, the lane TLc branches into two lanes TLd and TLe. Two lane boundary lines BLa and BRa mark the lane TLc. Of the two lane boundary lines BLa and BRa, one lane boundary line BLa has a first curved section CP1 in front of the vehicle 90, located at point P15. The first curved section CP1 curves toward the outside of the lane TLc in the direction of travel. The first curved section CP1 has a curvature that is greater than or equal to a first threshold value.

[0087] In contrast, the lane boundary line BRa extends in a straight line. Furthermore, the width La of the lane TLc at a first point FP within the determination range RE is greater than or equal to a first predetermined value than a width Lb of the lane TLc at a second point SP within the determination range RE. Specifically, the width of the lane TLc widens in the traveling direction ahead of the vehicle 90 located at point P15. Here, from the lane boundary line BLa, the portion where the width of the lane TLc widens is also referred to as a widening boundary line EBLa. Fig. 9 shows the image area (determination area) RE of the camera 12 provided in the vehicle 90 located at the point P15.

[0088] The lane departure request flag SSRF is set as in Fig. 10, the lane keeping unit 25 is set to ON at point P16 due to the vehicle 90 approaching the lane boundary line BLa due to careless driving or the like. In this case, the lane keeping unit 25 first causes the vehicle 90 to perform the first steering operation as the lane keeping operation. The traveling trajectory of the vehicle 90 is changed back to the inside of the traveling lane TLc. Subsequently, when the vehicle 90 reaches point P17, the lane keeping unit 25 causes the vehicle 90 to perform the second steering operation.

[0089] However, at points P16 and P17, it is difficult for the driving assistance ECU 20 to accurately determine which of the two branch lanes TLd and TLe the driver intends to continue driving based on operation information (such as turn signal information) generated based on the driver's driving operations. In this case, when the lane keeping operation is performed, the vehicle 90 is guided to the lane TLe on the left side by the second steering operation, even if the driver intends to continue driving toward the lane TLd that continues straight ahead.

[0090] Furthermore, even when the driver intends to advance to the left-side lane TLe, the traveling direction of the vehicle 90 is a direction largely along the widening limit line EBLa. At this time, driving operations that are not desired by the driver occur due to the acceleration generated by the second steering operation becoming excessively high or the rate of change of the yaw rate Yr becoming excessively high during the second steering operation.

[0091] Consequently, when the vehicle 90 is to be moved toward the left-side lane TLe, a situation may arise in which the driver has difficulty moving the vehicle 90 along an ordinary traveling line De. Consequently, the driver may not be able to smoothly steer the vehicle toward the left-side lane TLe.

[0092] In this way, depending on the road conditions (the condition of the lane boundary lines BO), the driver may experience undesirable driving experiences, such as feelings of discomfort, anxiety, or fear, due to the execution of ordinary lane-keeping operations. Furthermore, the driver may be endangered due to undesirable driving operations being performed under the control of the lane-keeping unit 25.

[0093] However, according to the present embodiment, the lane state determination unit 23 determines, as shown in Fig. 9, at point P15, the width LA of the lane TLc at the first point FP within the determination range RE is greater than or equal to the first predetermined value than the width Lb of the lane TLc at the second point SP within the determination range RE, based on the lane boundary lines BLa and BRa detected by the lane boundary line detection unit 21. Subsequently, the lane state determination unit 23 sets the widening flag WF to ON (step S20 in the Fig. 7). The widening flag WF being ON at this point P15 is continuously maintained even when the vehicle 90 advances to point P16.

[0094] Meanwhile, at point P15, the lane departure request flag SSRF is not set to ON (step S34 in the Fig. 7). Accordingly, the lane keeping unit 25 carries out the setting for the next operation restriction with respect to the second steering operation (step S37 in the Fig. 7).

[0095] When the vehicle 90 reaches point P16, the lane departure determination unit 22 sets the lane keeping request flag SSRF to ON. However, the lane keeping unit 25 has executed the setting for the next operation restriction with respect to the second steering operation at point P15. Consequently, even when the vehicle 90 reaches point P16 and the lane keeping request flag SSRF is set to ON, the second steering operation among the lane keeping operations is prohibited (step S37 in Fig. 7).

[0096] In this way, when the widening flag WF is set to ON, the second steering operation with respect to the widening boundary line EBLa extending in a direction to the outside of the lane TLc in the traveling direction of the vehicle 90 is prohibited even if the lane departure request flag SSRF is set to ON (step S36 or S37 in the Fig. 7).

[0097] Consequently, the driver can smoothly move the vehicle 90 toward the desired lane TLd or TLe while preventing the vehicle 90 from leaving the lane TLc. Specifically, the probability of the driver experiencing an undesirable experience during driving can be reduced by preventing the second steering operation.

[0098] Furthermore, similar effects can be achieved if the method (second widening restriction method) in which the lane departure cancellation threshold value SSCT used when the second steering operation is performed is reduced is adopted as the method for restricting the lane departure operation instead of the method (first widening restriction method) in which the second steering operation is prohibited.

[0099] Specifically, even if the usual second steering operation is started at point P17, the lane keeping operation can be easily canceled by the driver performing a steering operation (steering wheel operation) that generates a manual steering torque greater than or equal to the lane keeping cancellation threshold SSCT, which is set to a low value. This results in reducing the probability that the driver will experience an undesirable driving experience.

[0100] Furthermore, similar effects can be achieved if the method (third widening restriction method) in which the maximum yaw rate YrMax2 ( Fig. 6) is reduced when the lane keeping operation restriction process in step S37 of the Fig. 7 is applied. More specifically, even if the second steering operation is performed at point P17, the maximum yaw rate YrMax2 is lower than the maximum yaw rate YrMax2 during ordinary lane keeping operation.

[0101] Consequently, the driver can easily change the direction of travel of the vehicle 90 by a steering operation (steering wheel operation). As a result, the likelihood of the driver experiencing an undesirable experience during driving can be reduced. (Narrowing detection and lane keeping control)

[0102] The following is a third specific example of lane keeping control executed by the driving assistance ECU 20 and its effects with reference to the Fig. 11. In the Fig. In the lane state shown in Figure 11, vehicle 90 is traveling in a lane TLf. In front of vehicle 90, lane TLf and a lane TLg on the left side merge into a single lane TLh. The lane TLf, on which vehicle 90 is traveling, is marked by two straight lane boundary lines BLf and BRf. The lane TLg on the left side is marked by two straight lane boundary lines BL1 and BR1.

[0103] Furthermore, the lane TLh is marked by two straight lane boundary lines BL1 and BRh after the merging point. A lane TLi at the merging point is marked by two lane boundary lines BL1 and RBRf. The lane boundary line RBRf is located in front of the vehicle 90 located at point P25. The lane boundary line RBRf connects the two lane boundary lines BRf and BRh. The lane boundary line RBRf has a second curved section CP2, which is curved toward the inside of the lane TLi in the direction of travel, in front of the vehicle 90 located at point P25. The curved section CP2 has a curvature greater than or equal to a second threshold value.

[0104] More specifically, the width of the lane TLi decreases in the direction of travel in front of vehicle 90 located at point P25. Here, the lane boundary line RBRf is also referred to as a narrowing boundary line RBRf. Fig. 11 shows the image area (determination area) RE of the camera 12 provided in the vehicle 90 located at point P25.

[0105] If a normal lane keeping control system in the Fig. 11, the first steering operation is executed as the lane keeping operation when the vehicle 90 reaches the point P26. As a result of the first steering operation, the vehicle 90 advances in a direction away from the narrowing boundary line RBRf. However, if the curvature of the narrowing boundary line RBRf is large, an acceleration generated by the first steering operation may become excessively high.

[0106] Alternatively, the rate of change in the yaw rate Yr may become excessively high during the initial steering operation. This may cause the driver to have difficulty moving the vehicle 90 along an ordinary driving line Df when moving the vehicle 90 toward the driving lane TLh after merging.

[0107] Meanwhile, according to the present embodiment, the lane condition determination unit 23 determines at point P25 that the second curved portion CP2 of the lane boundary line RBRf within the determination range RE has a curvature greater than or equal to the second threshold value based on the lane boundary line RBRf detected by the boundary line detection unit 21. Subsequently, the lane condition determination unit 23 sets the narrowing flag RF to ON (step S20 in the Fig. 7). The ON setting of the narrowing flag RF at this point P25 is continuously maintained even when the vehicle 90 advances to point P26.

[0108] At point P25, the lane departure request flag SSRF is not set to ON (step S44 in the Fig. 7). Consequently, the lane keeping unit 25 executes the setting for the next operation restriction (step S47 in the Fig. 7).

[0109] When the vehicle 90 reaches point P26, the lane departure determination unit 22 sets the lane keeping request flag SSRF to ON. However, the lane keeping unit 25 has executed the setting for the next operation restriction at point P25. Consequently, even if the vehicle 90 reaches point P26 and the lane keeping request flag SSRF is set to ON, the lane keeping operation is prohibited (step S47 in the Fig. 7).

[0110] In this way, when the narrowing flag RF is set to ON, the lane keeping operation with respect to the narrowing boundary line RBRf extending in the direction toward the inside of the lane TLi in the traveling direction of the vehicle 90 is prohibited even if the lane keeping request flag SSRF is set to ON (step S46 or S47 in the Fig. 7).

[0111] Accordingly, the driver can easily move the vehicle 90 along the desired driving line DF. Specifically, the probability of the driver experiencing an undesirable driving experience can be reduced.

[0112] Furthermore, similar effects can be achieved if the method (second narrowing restriction method) in which the lane departure cancellation threshold value SSCT in the operation cancellation unit 26 ( Fig. 1) is set, is reduced when the lane keeping operation restriction method is applied instead of the method (first narrowing restriction method) in which the lane keeping operation is restricted.

[0113] Specifically, even if the ordinary lane keeping operation (ordinary lane keeping control) is started at point P26, the lane keeping operation can be easily canceled by performing a steering operation (steering wheel operation) that generates a manual steering torque greater than or equal to the lane keeping cancellation threshold SSCT, which is set to a low value. This results in reducing the probability that the driver will experience an undesirable driving experience.

[0114] Furthermore, similar effects can be achieved if the method (third constriction restriction method) in which the maximum yaw rate YrMax1 or YrMax2 ( Fig. 6) is reduced when the lane keeping operation restriction process in step S37 of the Fig. 7 is applied. More specifically, even if the first steering operation occurs at point P26, the maximum yaw rate YrMax1 or YrMax2 is lower than the maximum yaw rate YrMax1 or YrMax2 during ordinary lane keeping operation.

[0115] Consequently, the driver can easily change the direction of travel of the vehicle 90 by a steering operation (steering wheel operation). As a result, the likelihood of the driver experiencing an undesirable experience during driving can be reduced.

[0116] When the narrowing flag RF is set to ON, the crossing flag CF is also set to ON in some cases. However, the same control (steps S26, S27, S46, and S47) is performed both when the narrowing flag RF is set to ON and when the crossing flag CF is set to ON in the process of Fig. 7.

[0117] More specifically, control similar to that when the narrowing flag RF is set to ON is performed even if the intersection flag CF is set to ON in the lane state of the Fig. 11 is set to ON. Consequently, when lane TL merges in front of the vehicle 90, the probability of the driver having an undesirable experience during driving can be reduced. (Modifications)(First Modification)

[0118] According to the above-described embodiment, the second steering operation is prohibited or suppressed when the widening flag WF is set to ON. However, the lane keeping operation itself, which consists of the first steering operation and the second steering operation, may be prohibited or suppressed. More specifically, the lane keeping operation may be restricted by a method similar to that when the intersection flag CF is set to ON. In this case, too, effects similar to those of the above-described embodiment can be achieved. (Second modification)

[0119] The lane state determination unit 23 makes the intersection presence determination when one of the Fig. 2 conditions (i-1) to (i-3) are met. However, the lane state determination unit 23 may make the intersection presence determination if any of the conditions shown in the Fig. 2, conditions (i-1) to (i-3) are met in both areas to the left and right of the vehicle 90 on the lane TL traveled by the vehicle 90 within the determination area RE.

[0120] Below is a specific example with reference to the Fig. 8. Within the determination area RE, the lane boundary line BLa and the lane boundary line BLb intersect in the area to the left of the vehicle 90. Within the determination area RE, the lane boundary line BRa and the lane boundary line BRb intersect in the area to the right of the vehicle 90. In this way, the intersection presence determination is made when any of the Fig. 2 is satisfied in both the left and right areas of the vehicle 90, the accuracy of the intersection presence determination can be improved.

[0121] Furthermore, the lane state determination unit 23 may make the intersection presence determination when a following condition (i-4) is satisfied, in addition to the case that any of the conditions set forth in the Fig. 2 are satisfied. Then, the lane state determination unit 23 may set the intersection flag CF to ON.

[0122] Condition (i-4): Within the determination area RE, another lane boundary line BO exists on the lane TL, which is marked by two lane boundary lines.

[0123] Below is a specific example with reference to the Fig. 8. The lane TLb is marked by two lane boundary lines BLb and BRb. Within the destination area RE, the lane boundary line BRa, which is different from the lane boundary lines BLb and BRb, is present on the lane TLb.

[0124] By adding the above-described condition (i-4) to the conditions for making the intersection-existence determination in this way, it is possible to easily distinguish between the case where the lane boundary line BO marking the lane TL has only a curved shape (such as when the widening boundary line EBLa is in the Fig. 9 is present), and the case where two lane boundary lines BO intersect. The occurrence of incorrect determination can be reduced. (Third modification)

[0125] When the process for restricting the lane keeping operation in steps S26, S36 and S46 in the Fig. 7, according to the embodiment described above, a method can be applied in which the maximum yaw rates YrMax1 and YrMax2 ( Fig. 6). In this case, too, effects similar to those of the above-described embodiment can be achieved. For example, the method is implemented by reducing the values ​​of the maximum yaw rates YrMax1 and YrMax2, which are set for ordinary lane keeping control, by 10 to 30%.

[0126] Furthermore, the various restriction methods can be applied in combination as the lane departure restriction method. For example, when the intersection flag CF is set to ON, the second intersection restriction method (the method in which the lane departure cancellation threshold value SSCT is reduced) and the method in which the maximum yaw rates YrMax1 and YrMax2 are reduced ( Fig. 6) can be combined to limit lane keeping operation. (Fourth modification)

[0127] According to the above-described embodiment, the lane state determination unit 23 determines the state of the lane TL based on image information acquired by the camera 12, and then sets the restriction flags CF, WF, and RF. However, the lane state determination unit 23 may determine the state of the lane TL based on various types of information that enable determination of the lane TL, instead of the image information.

[0128] For example, if the vehicle 90 has a GPS (Global Positioning System) receiver and a map database displaying road networks, the boundary line detection unit 21 can detect the lane TL present in the area ahead of the vehicle 90 based on boundary line data and information about the current position of the vehicle 90. The boundary line data indicates the lane boundary lines BO and is retained in the map database. The information about the current position of the vehicle 90 is detected via the GPS receiver. The state of the lane TL can be determined based on the detection results. The restriction flags CF, WF, and RF can then be set.

[0129] Furthermore, various types of devices for detecting the lane boundary lines BO can be used instead of the camera 12. For example, a radar sensor such as a millimeter-wave radar or an image sensor can be used as the various types of devices. Furthermore, the camera or the various types of devices can be provided with the function of the boundary line detection unit 21. (Fifth Modification)

[0130] The intersection determination according to the embodiment described above can be made with respect to two lane boundary lines drawn in different colors. For example, the intersection determination can be made with respect to a white lane boundary line BO and a yellow lane boundary line BO. In Europe, the yellow lane boundary line BO is used as a lane boundary line BO for a temporary lane during construction work.

[0131] Consequently, the accuracy of intersection determination can be further improved by performing the intersection determination with respect to lane boundary lines drawn in different colors. A camera configured to capture color images is preferably used as the camera 12 to determine whether or not a white lane boundary line BO and a yellow lane boundary line BO intersect. (Sixth Modification)

[0132] According to the above-described embodiment, the lane state determination unit 23 performs three determinations: the intersection determination, the widening determination, and the narrowing determination. Subsequently, the lane state determination unit 23 sets the intersection flag CF, the widening flag WF, and the narrowing flag RF. However, the lane state determination unit 23 may perform at least one determination.

[0133] For example, if the lane state determination unit 23 does not perform the intersection determination, steps S22 to S27 are skipped. In this case, the lane state determination unit 23 first executes step S32. In addition, if the lane state determination unit 23 does not perform the spread determination, the Fig. 7 are omitted. In this case, if the determination in step S22 is NO, the lane condition determination unit 23 then executes step S42. Further, if the lane condition determination unit 23 does not execute the narrowing determination, the Fig. 7 are not executed. In this case, if the determination in step S32 is NO, the lane condition determination unit 23 then executes step S50.

[0134] The present invention is not limited to the above-described embodiment, examples, and modifications, but can be implemented in various ways without departing from the scope thereof. The technical features in the embodiment, examples, and modifications corresponding to the technical features of each of the aspects described in the summary of the invention can be exchanged or combined as appropriate in order to overcome some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, unless described as an essential feature in the present application, the technical features may be omitted as appropriate.

Claims

[1] Lane keeping assistant with: - a boundary line detection unit (21) attached to a vehicle (90) and configured to detect at least one lane boundary line (BO) present in a determination area (RE) that describes an area in front of the vehicle in the direction of travel of the vehicle; - a lane departure determination unit (23) mounted on the vehicle and configured to determine whether or not there is a probability that the vehicle will leave a lane (TL) based on the at least one lane boundary line detected by the boundary line detection unit; - a lane keeping unit (25) mounted on the vehicle and configured to, when the lane departure determination unit determines that there is a probability that the vehicle will leave the lane, allow the vehicle to perform a lane keeping operation that changes the traveling direction of the vehicle to prevent the vehicle from leaving the lane traveled by the vehicle; and - a lane state determination unit (23) mounted on the vehicle and configured to determine a state of the lane ahead of the vehicle based on the at least one lane boundary line detected by the boundary line detection unit and to perform at least one of the following restriction determinations: (i) an intersection determination that two lane boundary lines or their extension lines (BO1a, BO2a) cross in front of the vehicle, (ii) a spreading determination that a width of a lane in front of the vehicle increases in a direction away from the vehicle compared to an area near the vehicle, and (iii) a narrowing determination that a width of a lane in front of the vehicle decreases in a direction away from the vehicle compared to an area near the vehicle, where - the lane keeping unit is configured to suppress or restrict the lane keeping operation performed by the vehicle when the at least one of the restriction determinations is performed by the lane state determination unit, - Lane keeping mode includes: - a first change operation that changes the direction of travel of the vehicle from a direction toward an outside of the lane to an inside of the lane; and - a second change operation which changes the direction of travel of the vehicle to a direction along the lane after the direction of travel of the vehicle has been changed by the first change operation, and - when the propagation determination is made by the lane state determination unit, the suppression or restriction of the lane keeping operation is made by suppressing or restricting the second change operation in a range of the at least one lane boundary line detected by the boundary line detection unit, which extends in a direction toward an outside of the lane in the traveling direction of the vehicle. [2] Lane keeping assistant according to claim 1, wherein the lane keeping unit comprises: - an operation cancellation unit (26) configured to detect a steering torque generated by a driver's operation and to cancel the lane keeping operation when the steering torque detected during execution of the lane keeping operation is greater than or equal to a predetermined lane keeping cancellation threshold, wherein - the lane keeping operation is suppressed by setting the lane keeping cancellation threshold to be lower than the lane keeping cancellation threshold used when the at least one of the restriction determinations is not carried out by the lane state determination unit. [3] Lane departure warning system according to claim 1 or 2, wherein - the lane keeping operation is suppressed by reducing a degree of change in the direction of travel of the vehicle caused by the lane keeping operation. [4] Lane keeping assistant according to one of claims 1 to 3, wherein - when the narrowing determination is made by the lane state determination unit, the suppression or restriction of the lane keeping operation is carried out for the at least one lane boundary line detected by the boundary line detection unit, which extends in a direction toward an inner side of the lane in the traveling direction of the vehicle. [5] Lane departure warning system according to one of claims 1 to 4, wherein - the lane departure determination unit is configured to determine whether or not there is a probability that the vehicle will leave the lane at a predetermined time; - when the at least one of the restriction determinations of the intersection determination, the widening determination, and the narrowing determination is made, the lane state determination unit is configured to continuously maintain a result of the at least one of the restriction determinations for a predetermined period; and - when the lane departure determination unit does not determine that there is a probability that the vehicle will leave the lane during a period in which the result of the at least one of the restriction determinations is maintained, and subsequently determines that there is a probability that the vehicle will leave the lane, the lane keeping unit is configured to perform suppression or restriction of the lane keeping operation performed by the vehicle. [6] The lane departure warning system according to claim 1, wherein the lane state determination unit is configured to perform the intersection determination: - if the two lane boundary lines present within the designation area cross each other; or - when an extension line of one of the two lane boundary lines present within the designation area and the other of the two lane boundary lines cross; or - when respective extension lines of the two lane boundary lines existing within the designation area cross each other. [7] The lane departure warning system according to any one of claims 1 to 3, wherein the lane state determining unit is configured to perform the propagation determination: - if a width (La) of the lane at a first predetermined point (FP) in the determination area is greater than or equal to a first predetermined value greater than a width (Lb) of the lane at a second predetermined point (SP) within the determination area (RE) which is positioned closer to the vehicle in the direction of travel than the first point; or - if the at least one lane boundary line within the determination range has a first curved portion (CP1) that curves toward an outside of the lane in the traveling direction of the vehicle, and the first curved portion has a curvature that is greater than or equal to a first predetermined threshold value. [8] The lane departure warning system according to claim 4, wherein the lane state determination unit is configured to perform the narrowing determination: - if a width (La) of the lane at a first predetermined point (FP) within the determination area is greater than or equal to a second predetermined value less than a width (Lb) of the lane at a second predetermined point (SP) within the determination area (RE) which is positioned closer to the vehicle in the direction of travel than the first point; or - when a lane boundary line within the determination range has a second curved portion (CP2) curved toward an inside of the lane in the traveling direction of the vehicle, and the second curved portion has a curvature greater than or equal to a second predetermined threshold. [9] Lane keeping procedure comprising the following steps: - detecting, by means of a boundary line detection unit (21) which is attached to a vehicle (90), at least one lane boundary line (BO) which is present in a determination area (RE) which describes an area in front of the vehicle in the direction of travel of the vehicle; - determining, by means of a lane departure determination unit (23) attached to the vehicle, whether or not there is a probability that the vehicle will leave a lane (TL) based on the at least one lane boundary line detected by the boundary line detection unit; - when the lane departure determination unit determines that there is a probability that the vehicle will leave the lane, allowing, by means of a lane keeping unit (25) attached to the vehicle, the vehicle to perform a lane keeping operation that changes the traveling direction of the vehicle to prevent the vehicle from leaving the lane traveled by the vehicle; - determining, by means of a lane state determining unit (23) attached to the vehicle, a state of the lane in front of the vehicle on the basis of the at least one lane boundary line detected by the boundary line detecting unit; - Executing, based on the lane state determination unit, at least one of the following restriction determinations: (i) an intersection determination that two lane boundary lines or their extension lines (BO1a, BO2a) cross in front of the vehicle, (ii) a spreading determination that a width of a lane in front of the vehicle increases in a direction away from the vehicle compared to an area near the vehicle, and (iii) a narrowing determination that a width of a lane in front of the vehicle decreases in a direction away from the vehicle compared to an area near the vehicle; and - when the at least one of the restriction determinations is carried out by the lane state determination unit, carrying out, by means of the lane keeping unit, a suppression or restriction of the lane keeping operation carried out by the vehicle, wherein - Lane keeping mode includes: - a first change operation that changes the direction of travel of the vehicle from a direction toward an outside of the lane to an inside of the lane; and - a second change operation which changes the direction of travel of the vehicle to a direction along the lane after the direction of travel of the vehicle has been changed by the first change operation, and - when the propagation determination is made by the lane state determination unit, the suppression or restriction of the lane keeping operation is made by suppressing or restricting the second change operation in a range of the at least one lane boundary line detected by the boundary line detection unit, which extends in a direction toward an outside of the lane in the traveling direction of the vehicle.

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