JP7459445B2 - Route planning system and vehicle driving assistance system - Google Patents

Description

The present invention relates to a driving route generation system that generates a driving route for a vehicle, and a vehicle driving assistance system that provides driving assistance for the vehicle based on the driving route.

Conventionally, a target driving route for the own vehicle is set based on the surrounding conditions of the own vehicle and the state of the own vehicle, and based on this target driving route, driving support (specifically, driving assist control) is applied to the vehicle. technology for autonomous driving and automatic driving control) is being developed. For example, Patent Documents 1 and 2 disclose techniques for setting a target travel route using a clothoid curve.

JP 2019-194844 A JP2018-79823A

In general, in order to allow a vehicle to travel safely, a target driving path is set along a center line (lane center line) located in the center of the width direction of a lane. Here, when a vehicle is turned at an intersection, etc., since lanes are not clearly defined within the intersection, the lane center line for setting the target driving path is considered to be defined as follows. That is, the lane center line for setting the target driving path when the vehicle is turned at an intersection is considered to be defined by a straight line corresponding to the lane center line of the straight driving path before turning, a straight line corresponding to the lane center line of the straight driving path after turning, and an arc corresponding to the driving path to be turned that is defined within the intersection and has both ends connected to these straight lines. According to the target driving path set by this lane center line, the vehicle can be turned safely. However, since the path is discontinuous at the connection between the straight line and the arc on the lane center line, it is difficult to achieve smooth vehicle behavior when turning.

On the other hand, if the vehicle turns along a clothoid curve (for example, see Patent Documents 1 and 2 above), smooth vehicle behavior can be realized. This is because the clothoid curve is a trajectory drawn by the vehicle when turning the steering wheel at a constant angular velocity. Therefore, when the vehicle is to turn at an intersection or the like, it is considered that the target travel route may be set based on the clothoid curve. However, if smooth vehicle behavior is prioritized and the target travel route is set based on a clothoid curve that deviates relatively largely from the lane center line as described above, safety during turns may not be ensured. Therefore, it is considered desirable to set the target travel route based on an appropriate clothoid curve determined in consideration of the lane center line.

The present invention has been made to solve the above-mentioned problems, and aims to provide a driving path generation system that can generate a target driving path that can achieve safe and smooth vehicle behavior based on lane center lines and clothoid curves when the vehicle turns, and a vehicle driving assistance system that can provide vehicle driving assistance based on this target driving path.

In order to achieve the above object, the present invention provides a driving route generation system, comprising: a driving route information acquisition device that acquires driving route information related to a vehicle's driving route; and a calculation device configured to generate a target driving route for the vehicle to travel on the driving route based on the driving route information, wherein the calculation device acquires, when the vehicle turns, information on a lane centerline related to the driving route on which the vehicle turns based on the driving route information, generates a plurality of clothoid curves whose start points and end points are located on the acquired lane centerline, and calculates an error indicating a difference between the clothoid curve and the lane centerline for each of the generated plurality of clothoid curves. The method calculates an error integral value, which is a value obtained by integrating the entire clothoid curve, determines the clothoid curve among the multiple clothoid curves which has the smallest calculated error integral value, and generates a target driving path for the vehicle to travel when turning based on the determined clothoid curve.If there are two or more clothoid curves which have the smallest error integral value, the calculation device calculates an error integral value in a predetermined range near the starting point for each of the two or more clothoid curves, and determines the clothoid curve among the two or more clothoid curves which has the smallest calculated error integral value .

In the present invention configured as described above, the arithmetic device generates a plurality of clothoid curves whose starting and ending points are located on the lane center line of the roadway on which the vehicle turns, calculates an error integral value between the clothoid curve and the lane center line for each of the plurality of clothoid curves, and generates a target driving path along which the vehicle will turn based on the clothoid curve with the smallest error integral value (corresponding to the clothoid curve closest to the lane center line). When the vehicle is caused to run along such a target driving path, since the clothoid curve is applied to the target driving path, the vehicle can be turned by steering at a constant angular velocity, and smooth vehicle behavior can be realized when turning. In addition, since the clothoid curve with the starting and ending points located on the lane center line and with the smallest error integral value with the lane center line is applied to the target driving path, it is possible to suppress a large deviation of the vehicle from the lane center line, and safety during turning can be ensured. Therefore, according to the present invention, a target driving path that can realize a safe and smooth vehicle behavior when the vehicle turns can be generated.
In addition, according to the present invention, at the beginning of a turn when accurate information is required when driving a vehicle along a target driving path, it is possible to appropriately generate a target driving path that corresponds to a clothoid curve that is closest to the lane center line.
In another aspect, the present invention is a driving route generation system, comprising: a driving route information acquisition device that acquires driving route information related to a vehicle's driving route; and a calculation device configured to generate a target driving route for the vehicle to drive on the driving route based on the driving route information, wherein the calculation device acquires information on a lane center line related to the driving route on which the vehicle turns based on the driving route information, generates a plurality of clothoid curves whose start points and end points are located on the acquired lane center line, calculates an error integral value, which is a value obtained by integrating an error indicating a difference between the clothoid curve and the lane center line over the entire clothoid curve, determines a clothoid curve among the plurality of clothoid curves for which the calculated error integral value is the smallest, and generates a target driving route for the vehicle to drive when turning based on the determined clothoid curve, and when there are two or more clothoid curves with the smallest error integral value, determines a clothoid curve among the two or more clothoid curves for which the steering angle when the vehicle turns is the smallest.
According to the present invention configured as described above, since the clothoid curve that minimizes the steering angle is determined, the radius of curvature of the target driving path for turning the vehicle is increased. As a result, the lateral acceleration generated in the vehicle during turning can be reduced, that is, the vehicle behavior during turning can be improved.

In the present invention, preferably, the lane center lines obtained by the arithmetic device include a first straight line which is the lane center line of the straight traveling path before the turn, and a first straight line which is the lane center line of the straight traveling path after the turn. It is formed from two straight lines and an arc corresponding to the lane center line of the traveling path to be turned, which has one end connected to the first straight line and the other end connected to the second straight line, and the arithmetic device calculates the starting point from the lane. A plurality of clothoid curves are generated whose end points are located on a first straight line of the center line and whose end points are located on a second straight line of the lane center line.
According to the present invention configured in this way, it is possible to generate an appropriate clothoid curve according to the lane center line of the travel path when the vehicle turns.

In the present invention, the calculation device preferably generates a plurality of clothoid curves by changing the curve length and the curvature radius from the starting point of the clothoid curve, under the condition that the starting point and the ending point are located on the center line of the lane.
According to the present invention configured in this manner, it is possible to accurately generate a plurality of clothoid curve candidates that satisfy desired conditions.

In a preferred example of the present invention, when a vehicle turns left or right at an intersection, the calculation device determines a clothoid curve that has the smallest error integral value among multiple clothoid curves, and generates a target driving route based on the determined clothoid curve.

In another aspect, in the present invention, the vehicle driving support system includes a control device configured to control the driving of the vehicle so that the vehicle travels along the travel route generated by the above-described travel route generation system. It is characterized by

The driving path generation system of the present invention can generate a target driving path that can achieve safe and smooth vehicle behavior based on the lane center line and clothoid curve when the vehicle turns, and the vehicle driving assistance system of the present invention can appropriately provide vehicle driving assistance based on such a target driving path.

1 is a block diagram showing a schematic configuration of a vehicle driving assistance system to which a driving route generation system according to an embodiment of the present invention is applied. FIG. 2 is an explanatory diagram of a lane centerline according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of a clothoid curve according to a first example of an embodiment of the present invention. FIG. 11 is an explanatory diagram of a clothoid curve according to a second example of an embodiment of the present invention. FIG. 13 is an explanatory diagram of a clothoid curve according to a third example of an embodiment of the present invention. FIG. 2 is an explanatory diagram of a clothoid curve expressed in an SL coordinate system in an embodiment of the present invention. 4 is a flowchart relating to target driving route generation and driving assistance according to an embodiment of the present invention. 11 is an explanatory diagram of a method for determining a clothoid curve according to a first modified example of an embodiment of the present invention. FIG. 13 is an explanatory diagram of a method for determining a clothoid curve according to a second modified example of an embodiment of the present invention. FIG.

The following describes a driving route generation system and a vehicle driving assistance system according to an embodiment of the present invention, with reference to the attached drawings.

[System configuration]
First, with reference to FIG. 1, the configuration of a vehicle driving support system to which a driving route generation system according to an embodiment of the present invention is applied will be described. FIG. 1 is a block diagram showing a schematic configuration of a vehicle driving support system to which a driving route generation system according to an embodiment of the present invention is applied.

The vehicle driving assistance system 100 functions as a driving route generation system that sets a target driving route for the vehicle 1 to drive on a road, and is configured to perform driving assistance control (driving assist control or automatic driving control) to drive the vehicle 1 along this target driving route. As shown in FIG. 1, the vehicle driving assistance system 100 has an ECU (Electronic Control Unit) 10 as a calculation device and control device, multiple sensors, and multiple control systems.

Specifically, the multiple sensors include a camera 21, a radar 22, a vehicle speed sensor 23 for detecting the behavior of the vehicle 1 and driving operations by the occupants, an acceleration sensor 24, a yaw rate sensor 25, a steering angle sensor 26, an accelerator sensor 27, and a brake sensor 28. Furthermore, the multiple sensors include a positioning system 29 for detecting the position of the vehicle 1, and a navigation system 30. The multiple control systems include an engine control system 31, a brake control system 32, and a steering control system 33.

Other sensors may include a surrounding sonar that measures the distance and position of surrounding structures relative to the vehicle 1, a corner radar that measures the proximity of surrounding structures at the four corners of the vehicle 1, and an inner camera that captures images of the interior of the vehicle 1.

The ECU 10 executes various calculations based on signals received from a plurality of sensors, and controls the engine system, brake system, and steering system appropriately for the engine control system 31, brake control system 32, and steering control system 33, respectively. Sends a control signal to operate the device. The ECU 10 is composed of a computer including one or more processors (typically a CPU), a memory (ROM, RAM, etc.) that stores various programs, an input/output device, and the like. Note that the ECU 10 corresponds to an example of a "computation device" and a "control device" in the present invention.

The camera 21 photographs the surroundings of the vehicle 1 and outputs image data. Based on the image data received from the camera 21, the ECU 10 detects objects (for example, a preceding vehicle (vehicle in front), a following vehicle (vehicle in the rear), a parked vehicle, a pedestrian, a driving path, a marking line (lane boundary line, a white line), etc. , yellow lines), traffic signals, traffic signs, stop lines, intersections, obstacles, etc.). Note that the ECU 10 may acquire information about the object from outside through traffic infrastructure, inter-vehicle communication, or the like. As a result, the type, relative position, moving direction, etc. of the object are specified.

The radar 22 measures the position and speed of objects (particularly, preceding vehicles, following vehicles, parked vehicles, pedestrians, fallen objects on the road, etc.). As the radar 22, for example, a millimeter wave radar can be used. The radar 22 transmits radio waves in the traveling direction of the vehicle 1, and receives reflected waves generated when the transmitted waves are reflected by objects. Then, the radar 22 measures the distance between the vehicle 1 and the object (for example, the inter-vehicle distance) and the relative speed of the object with respect to the vehicle 1 based on the transmitted wave and the received wave. In this embodiment, instead of the radar 22, a laser radar, an ultrasonic sensor, or the like may be used to measure the distance and relative speed to the object. Further, the position and velocity measuring device may be configured using a plurality of sensors.

Note that the camera 21 and the radar 22 correspond to an example of a "driving route information acquisition device" in the present invention. In addition, "driving road information" includes, for example, the shape of the driving road (straight line, curve, curve curvature), driving road width, number of lanes, lane width, road regulation information (speed limit, etc.) specified by signs, etc. , intersections, crosswalks, etc. In addition to such travel route information, the ECU 10 sets a target travel route for the vehicle 1 based on obstacle information. This obstacle information includes information such as the presence or absence of an obstacle on the travel path of the vehicle 1 (for example, objects that may become an obstacle to the vehicle 1, such as a preceding vehicle, a following vehicle, a parked vehicle, or a pedestrian), the moving direction of the obstacle, and the like. Contains information regarding the moving speed of obstacles, etc.

Vehicle speed sensor 23 detects the absolute speed of vehicle 1. Acceleration sensor 24 detects the acceleration of vehicle 1. This acceleration includes acceleration in the longitudinal direction and acceleration in the lateral direction (that is, lateral acceleration). Note that the acceleration includes not only the rate of change in speed in the direction in which the speed increases, but also the rate of change in speed in the direction in which the speed decreases (that is, deceleration).

Yaw rate sensor 25 detects the yaw rate of vehicle 1. The steering angle sensor 26 detects the rotation angle (steering angle) of the steering wheel of the vehicle 1. The ECU 10 can obtain the yaw angle of the vehicle 1 by executing a predetermined calculation based on the absolute speed detected by the vehicle speed sensor 23 and the steering angle detected by the steering angle sensor 26. The accelerator sensor 27 detects the amount of depression of the accelerator pedal. Brake sensor 28 detects the amount of depression of the brake pedal.

The positioning system 29 is a GPS system and/or a gyro system, and detects the position of the vehicle 1 (current vehicle position information). The navigation system 30 stores map information internally and can provide the map information to the ECU 10. The ECU 10 identifies roads, intersections, traffic signals, buildings, etc. that exist around the vehicle 1 (particularly in the direction of travel) based on the map information and the current vehicle position information. The map information may be stored in the ECU 10. The navigation system 30 also corresponds to an example of a "roadway information acquisition device" in the present invention.

The engine control system 31 controls the engine of the vehicle 1. The engine control system 31 is a component that can adjust the engine output (driving force), and includes, for example, a spark plug, a fuel injection valve, a throttle valve, and a variable valve mechanism that changes the opening and closing timing of the intake and exhaust valves. When it is necessary to accelerate or decelerate the vehicle 1, the ECU 10 sends a control signal to the engine control system 31 to change the engine output.

The brake control system 32 controls the brake device of the vehicle 1. The brake control system 32 is a component that can adjust the braking force of the brake device, and includes, for example, a hydraulic pump and a valve unit. When it is necessary to decelerate the vehicle 1, the ECU 10 sends a control signal to the brake control system 32 to generate a braking force.

Steering control system 33 controls the steering device of vehicle 1 . The steering control system 33 is a component that can adjust the steering angle of the vehicle 1, and includes, for example, an electric motor of an electric power steering system. When the traveling direction of the vehicle 1 needs to be changed, the ECU 10 transmits a control signal to the steering control system 33 to change the steering direction.

[Generation of target driving route]
Next, a description will be given of generation of a target driving route executed by the above-described ECU 10 in the embodiment of the present invention. Here, a description will be given of a target driving route generated when the vehicle 1 turns left at an intersection.

First, referring to FIG. 2, we will explain the lane centerline used as a reference for setting a target driving path when vehicle 1 turns left at an intersection. Basically, the lane centerline is a centerline located in the center of the width direction within the lane of the driving path. On the other hand, since lanes are not clearly defined within an intersection, a lane centerline is virtually defined within the intersection for the driving path where vehicle 1 turns left at the intersection, as shown in FIG. 2.

In FIG. 2, straight line L01 (corresponding to the "first straight line" in this invention) indicates the lane centerline of the straight road before turning left (i.e., before entering the intersection), and straight line L03 (corresponding to the "second straight line" in this invention) indicates the lane centerline of the straight road after turning left (i.e., after leaving the intersection). When vehicle 1 turns left at an intersection, a lane centerline for turning left is defined within the intersection by arc L02, one end of which is connected to the end point (terminal end) of lane centerline L01 and the other end of which is connected to the end point (starting end) of lane centerline L03. This lane centerline L02 is connected to lane centerline L01 at connection point P01 and to lane centerline L03 at connection point P02.

The ECU 10 acquires information on the lane center lines L01, L02, and L03 based on the traveling route information from the aforementioned traveling route information acquisition device. In one example, information about lane center lines L01, L02, and L03 is included in map information stored in navigation system 30, and ECU 10 receives information about lane center lines L01, L02, and L03 from navigation system 30. get. In another example, the ECU 10 calculates the lane center lines L01, L02, and L03 based on the driving path information acquired by the camera 21 or the like, specifically, the shape of the driving path, the driving path width, the lane width, and the like. In this example, the ECU 10 may use map information stored in the navigation system 30 as appropriate when calculating the lane center lines L01, L02, and L03. Further, the ECU 10 may obtain the straight lane center lines L01 and L03 from the navigation system 30 and calculate the arc lane center line L02.

When vehicle 1 turns left at an intersection, it is conceivable to set lane center line L0, which connects lane center lines L01, L02, and L03, as a target driving route, and perform driving assistance (automatic driving or driving assistance) to drive vehicle 1 along this target driving route. According to the target driving route set by lane center line L0 in this way, vehicle 1 can turn left safely. However, since the route becomes discontinuous at connection points P01 and P02 between straight lines L01 and L03 and arc L02 on lane center line L0, it is difficult to achieve smooth vehicle behavior when turning left.

Therefore, in this embodiment, a clothoid curve (corresponding to the path that vehicle 1 traces when the steering wheel is turned at a constant angular velocity) is used to set a target driving route to be applied when vehicle 1 turns left at an intersection, so that smooth vehicle behavior is achieved when turning left at an intersection. Here, if the target driving route is set based on a clothoid curve that deviates relatively significantly from the lane center line L0, prioritizing smooth vehicle behavior, there is a possibility that safety during left turns will not be ensured. Therefore, in this embodiment, the target driving route is set based on an appropriate clothoid curve determined after taking into account the above-mentioned lane center line L0.

Specifically, in this embodiment, the ECU 10 sets the target travel route based on a clothoid curve whose starting point and end point are located on the lane center line L0. Specifically, the ECU 10 uses a clothoid curve whose starting point and end point are respectively located on lane center lines L01 and L03, which are straight portions of lane center line L0. In other words, the ECU 10 has a starting point located before the connecting point P01 of the lane center lines L01 and L02 on the lane center line L0, and behind the connecting point P02 of the lane center lines L02 and L03 on the lane center line L0. A clothoid curve is used where the end point is located.

In this embodiment, under the condition that the start and end points are located on the lane center line L0 as described above, the ECU 10 generates multiple clothoid curves by varying the curve length L from the start point of the clothoid curve and the curvature radius R in various ways, determines the clothoid curve closest to the lane center line L0 among the multiple clothoid curves, and sets the target driving route based on this clothoid curve. In detail, the ECU 10 calculates an error integral value, which is a value obtained by integrating the error indicating the difference between the clothoid curve and the lane center line L0 over the entire clothoid curve, for each of the multiple clothoid curves, determines the clothoid curve with the smallest error integral value among the multiple clothoid curves, and sets the target driving route based on this clothoid curve. If driving assistance is provided to turn left at an intersection based on such a target driving route, safe and smooth vehicle behavior can be achieved.

Note that the clothoid curve is generally expressed by the formula "RL=A ² " based on the curve length L from the starting point, the radius of curvature R, and the clothoid parameter A. From this equation, when the curve length L and the radius of curvature R from the starting point are set, the clothoid parameter A is determined and the clothoid curve is specified.

Next, specific examples (first to third examples) of clothoid curve candidates for setting a target travel route for causing the vehicle 1 to turn left at an intersection will be described with reference to FIGS. 3 to 5.

First, as shown in Fig. 3, the start point and end point of the clothoid curve L1 in the first example are located at connection points P01 and P02 on the lane center line L0, respectively. The radius of curvature R1 of this clothoid curve L1 (if the clothoid parameter is "A1", the radius of curvature R1 is "R1 = A1 ² /L") is considerably smaller than the radius of curvature R0 of the arc portion of the lane center line L0 (lane center line L02 in Fig. 2). Therefore, when the vehicle 1 is turned left based on the target driving route corresponding to this clothoid curve L1, the vehicle behavior tends to become large.

Next, as shown in FIG. 4, the clothoid curve L2 according to the second example has its start point P21 and end point P22 located on the lane center line L0 ( Specifically, it is located on the lane center lines L01 and L03 in FIG. 2). The radius of curvature R2 of this clothoid curve L2 (if the clothoid parameter is "A2", the radius of curvature R2 is "R2 = A2 ² /L") is the arc portion of the lane center line L0 (the lane center line L02 in Fig. 2). ) is the same as the radius of curvature R0. Further, the clothoid curve L2 has a relatively large error E2 with respect to the lane center line L0. In such a clothoid curve L2, the starting point P21 is located considerably before the connection point P01 of the lane center line L0, so when the vehicle 1 is turned left based on the target travel route according to the clothoid curve L2, the vehicle 1 This may cause the vehicle 1 to start turning earlier, causing the vehicle 1 to go off course.

Next, as shown in Fig. 5, the clothoid curve L3 according to the third example has a start point P31 and an end point P32 each located on the lane center line L0 (specifically, on the lane center lines L01 and L03 in Fig. 2) at a certain distance from the connection points P01 and P02 on the lane center line L0. The radius of curvature R3 of this clothoid curve L3 (when the clothoid parameter is "A3", the radius of curvature R3 is "R3 = A3 ² /L") is almost the same as the radius of curvature R0 of the arc part of the lane center line L0 (the lane center line L02 in Fig. 2). The clothoid parameter A3 of the clothoid curve L3 is almost the same as the clothoid parameter A2 of the clothoid curve L2 in Fig. 4. On the other hand, the error E3 of the clothoid curve L3 with respect to the lane center line L0 is relatively small. In detail, the error integral value S3 (=ΣE3) obtained by integrating the error E3 between the clothoid curve L3 and the lane center line L0 over the entire clothoid curve L3 is smaller than the error integral value S2 (=ΣE2) obtained by integrating the error E2 between the clothoid curve L2 and the lane center line L0 in FIG. 4 over the entire clothoid curve L2. In particular, the clothoid curve L3 is assumed to have the smallest error integral value S3 among multiple assumed clothoid curves. Therefore, when the vehicle 1 is turned left based on the target driving route corresponding to such a clothoid curve L3, a safe and smooth vehicle behavior can be realized.

Basically, the ECU 10 calculates the distance between each of the points on the clothoid curve and the points on the lane center line L0 corresponding to the points on the clothoid curve as an error, and calculates the error integral value by integrating the calculated errors. If a point on the clothoid curve is expressed as "Xn, Yn" and a point on the lane center line L0 corresponding to the point on the clothoid curve is expressed as "Xc, Yc", the error is expressed as "{(Xn-Xc) ²⁺ (Yn-Yc) ² } ^1/2 ". Note that the points set on the clothoid curve and the lane center line L0 for calculating the error integral value are, for example, specified at 1 cm intervals in the horizontal direction and at 0.5 to 1 m intervals in the vertical direction.

Here, in calculating the error integral value between the plurality of clothoid curves and the lane center line L0, the plurality of clothoid curves are defined by a direction along the lane center line L0 and a direction perpendicular to the lane center line L0. It may also be expressed in a coordinate system (hereinafter referred to as "SL coordinate system"). That is, the ECU 10 converts a clothoid curve expressed by a general orthogonal coordinate system (xy coordinate system) defined in the horizontal direction (x axis) and the vertical direction (y axis) into the SL coordinate system, and determines the lane center. An error integral value with respect to line L0 may be calculated. In the SL coordinate system, "S" indicates the coordinate axis of "station" that defines the distance along the lane center line L0, and "L" indicates the distance in the vertical direction (lateral direction) from the lane center line L0. It shows the ``lateral'' coordinate axes that define .

With reference to Figure 6, a method for calculating the error integral value between the lane center line L0 and the clothoid curve converted into the SL coordinate system will be described. In Figure 6, the horizontal axis (S axis) shows the distance along the lane center line L0 (path length), and the vertical axis (L axis) shows the vertical distance from the lane center line L0 (offset amount from the lane center line L0). Note that the lane center line L0 corresponds to the horizontal axis (S axis) itself.

6(A) shows a clothoid curve L2' obtained by converting the clothoid curve L2 of FIG. 4 into the SL coordinate system, and FIG. 6(B) shows a clothoid curve L3 obtained by converting the clothoid curve L3 of FIG. 5 into the SL coordinate system. ' is shown. The error integral values S2 and S3 between the clothoid curves L2' and L3' expressed in the SL coordinate system and the lane center line L0 are expressed in the hatched area in the figure, that is, between the clothoid curves L2' and L3' and the horizontal axis. This is the area of the region surrounded by (S axis). The ECU 10 converts the plurality of clothoid curves into the SL coordinate system, and calculates the area of the region surrounded by the plurality of clothoid curves converted into the SL coordinate system and the horizontal axis (S axis) corresponding to the lane center line L0. , can be calculated as an error integral value. Thereby, it is possible to easily determine the clothoid curve with the minimum error integral value among the plurality of clothoid curves.

Next, a flowchart relating to target driving route generation and driving assistance according to an embodiment of the present invention will be described with reference to FIG. 7. The process according to this flowchart is repeatedly executed by the ECU 10 at a predetermined interval (e.g., every 0.05 to 0.2 seconds).

First, in step S1, the ECU 10 acquires various types of information from a plurality of sensors (particularly the camera 21, the radar 22, the navigation system 30, etc.) shown in FIG. In this case, the ECU 10 acquires at least the above-mentioned traveling route information.

Next, in step S2, the ECU 10 determines whether an intersection exists in front of the vehicle 1 based on the travel route information acquired in step S1. In one example, the ECU 10 determines whether an intersection exists in front of the vehicle 1 by analyzing an image in front of the vehicle 1 taken by the camera 21. In another example, the ECU 10 determines whether an intersection exists in front of the vehicle 1 by referring to map information around the vehicle 1 stored in the navigation system 30. In this case, the ECU 10 uses the current position of the vehicle 1 detected by the positioning system 29 to obtain map information around the current position of the vehicle 1 from the navigation system 30 . Alternatively, the ECU 10 can identify the current position of the vehicle 1 by comparing the result of analyzing the image in front of the vehicle 1 taken by the camera 21 with the map information acquired from the navigation system 30. Map information around the current location of the vehicle 1 is acquired from the navigation system 30 by performing so-called map matching.

If, as a result of step S2, an intersection exists ahead of the vehicle 1 (step S2: Yes), the ECU 10 proceeds to step S3, and if an intersection does not exist ahead of the vehicle 1 (step S2: No), the ECU 10 ends the processing related to the flowchart shown in FIG. 7. In step S3, the ECU 10 determines whether the vehicle 1 will turn left or right at the intersection. For example, the ECU 10 determines that the vehicle 1 will turn left or right at the intersection if the currently set target driving route includes a route that turns left or right at the intersection, or if the driver of the vehicle 1 has operated the blinker to turn left or right at the intersection.

As a result of step S3, if the vehicle 1 turns left or right at the intersection (step S3: Yes), the ECU 10 proceeds to step S4, and if the vehicle 1 does not turn left or right at the intersection (step S3: No), that is, When the vehicle 1 goes straight at the intersection, the process according to the flowchart shown in FIG. 7 ends.

In step S4, the ECU 10 acquires a lane center line L0 that is a reference for setting a target driving route for turning the vehicle 1 left or right at the intersection. Specifically, the ECU 10 acquires a lane center line L0 that is composed of a lane center line L01 of a straight driving path before turning left or right (i.e., before entering the intersection), a lane center line L03 of a straight driving path after turning left or right (i.e., after leaving the intersection), and a lane center line L02 of a driving path to be turned in the intersection that is formed by an arc whose both ends are connected to the endpoints of these straight lane center lines L01 and L03 (see FIG. 2). In one example, the ECU 10 acquires information on the lane center line L0 from the navigation system 30. In another example, the ECU 10 calculates the lane center line L0 based on driving path information acquired by the camera 21 or the like, specifically, the shape of the driving path, the driving path width, the lane width, etc. In this case, the ECU 10 may use map information stored in the navigation system 30 as appropriate when calculating the lane center line L0.

Next, in step S5, the ECU 10 generates a plurality of clothoid curves that are candidates for setting a target travel route for causing the vehicle 1 to turn left or right at the intersection, based on the lane center line L0 acquired in step S4. do. Specifically, the ECU 10 generates a plurality of clothoid curves whose start and end points are located on the lane center line L0. Specifically, the ECU 10 generates a plurality of clothoid curves whose starting point is located on the straight line L01 in front of the circular arc L02 at the lane center line L0, and whose end point is located on the straight line L03 behind the circular arc L02 at the lane center line L0. do. Further, under the condition that the starting point and the ending point are located on the lane center line L0 as described above, the ECU 10 creates a plurality of clothoid curves by variously changing the curve length L and the radius of curvature R from the starting point of the clothoid curve. generate. Note that by varying the curve length L and radius of curvature R, the positions of the starting point and ending point on the lane center line L0 of the clothoid curve will vary.

Next, in step S6, the ECU 10 calculates an error integral value, which is a value obtained by integrating the error indicating the difference between the clothoid curve and the lane center line L0 over the entire clothoid curve, for each of the multiple clothoid curves generated in step S5. Specifically, the ECU 10 calculates the distance between each of the multiple points on the clothoid curve and the multiple points on the lane center line L0 corresponding to the multiple points on the clothoid curve as an error, and calculates the error integral value by integrating the multiple calculated errors. The ECU 10 may also convert the multiple clothoid curves into the SL coordinate system and calculate the area of the region surrounded by the clothoid curve converted into the SL coordinate system and the horizontal axis (S axis) corresponding to the lane center line L0 as the error integral value (see FIG. 6).

Next, in step S7, the ECU 10 determines, from among the multiple clothoid curves generated in step S5, the clothoid curve that minimizes the error integral value calculated in step S6. The ECU 10 then proceeds to step S8, where it generates a driving route corresponding to the clothoid curve determined in step S7 as a target driving route for turning the vehicle 1 left or right at the intersection.

Next, in step S9, the ECU 10 performs driving control including speed control and steering control of the vehicle 1 so that the vehicle 1 travels along the target travel route generated in step S8. Specifically, the ECU 10 transmits a control signal to at least one of the engine control system 31, brake control system 32, and steering control system 33, and executes at least one of engine control, braking control, and steering control. do.

[Action and Effect]
Next, the operation and effects of the embodiment of the present invention will be described.

In the present embodiment, the ECU 10 generates a plurality of clothoid curves whose starting points and end points are located on the lane center line L0 of the travel path on which the vehicle 1 turns left or right, and for each of the plurality of clothoid curves, the ECU 10 generates a plurality of clothoid curves and a lane center line. The error integral value with respect to the line L0 is calculated, and a target travel route for the vehicle 1 to travel when turning left or right is generated based on the clothoid curve with the minimum error integral value. When the vehicle 1 is controlled to travel along such a target travel route, since a clothoid curve is applied to the target travel route, the vehicle 1 is made to turn left or right by steering operation at a constant angular velocity. This makes it possible to achieve smooth vehicle behavior when turning left or right. In addition, since the starting point and the ending point are located on the lane center line L0 and a clothoid curve with the minimum error integral value with the lane center line L0 is applied to the target travel route, the vehicle 1's starting point and end point are located on the lane center line L0. Large deviations can be suppressed, and safety can be ensured when turning left or right. Therefore, according to the present embodiment, it is possible to generate a target travel route that can realize safe and smooth vehicle behavior when the vehicle 1 turns left or right.

In addition, in this embodiment, the ECU 10 generates multiple clothoid curves whose starting points are located on the straight lane centerline L01 and whose ending points are located on the straight lane centerline L03, using a lane centerline L0 consisting of a lane centerline L01 corresponding to the straight road before a left or right turn, a lane centerline L03 corresponding to the straight road after a left or right turn, and a lane centerline L02 formed by an arc with both ends connected to the lane centerlines L01 and L03, respectively, corresponding to the road on which the vehicle is to turn. This makes it possible to generate an appropriate clothoid curve according to the lane centerline L0 of the road when the vehicle is turning.

Furthermore, in the present embodiment, the ECU 10 creates a plurality of clothoid curves by variously changing the curve length L and the radius of curvature R from the start point of the clothoid curve under the condition that the start point and the end point are located on the lane center line L0. generate. Thereby, it is possible to accurately generate a plurality of clothoid curve candidates that satisfy the desired conditions.

[Modification]
Below, a modification of the above-described embodiment will be described.

(Variation 1)
The first modification relates to a method for determining a clothoid curve to be applied to a target driving route when there are two or more clothoid curves for which the error integral value between the lane center line L0 and each of a plurality of clothoid curves is smallest when the error integral value between each of the clothoid curves and the lane center line L0 is calculated. In the first modification, the ECU 10 calculates an error integral value in a predetermined range near the start point of the clothoid curve for each of the two or more clothoid curves for which the error integral value is smallest, and determines the clothoid curve for which the calculated error integral value is smallest among the two or more clothoid curves.

Figure 8 is an explanatory diagram of a method for determining a clothoid curve to be applied to a target driving route according to a first modified example of an embodiment of the present invention. In Figures 8(A) and (B), the horizontal axis indicates the distance along the lane center line L0, and the vertical axis indicates the vertical distance from the lane center line L0. Also, Figures 8(A) and (B) respectively show clothoid curves L4 and L5 converted into the SL coordinate system. These clothoid curves L4 and L5 have the same error integral values S4 and S5, respectively, and these two error integral values S4 and S5 are assumed to be the smallest among the error integral values obtained from multiple clothoid curves.

In this case, in the first modification, the ECU 10 calculates the error integral values S4a and S5a in a predetermined range near the start point of each of the clothoid curves L4 and L5 (the region where the distance from the start point of the clothoid curve along the lane center line L0 is equal to or less than "D1"). In the example shown in FIG. 8, since the error integral value S5a is smaller than the error integral value S4a, the ECU 10 determines the clothoid curve L5 corresponding to the error integral value S5a to be applied to the target driving path. According to the first modification, at the beginning of a turn when accurate information is required to drive the vehicle 1 along the target driving path, it is possible to appropriately generate a target driving path corresponding to a clothoid curve that is closer to the lane center line L0.

(Variation 2)
Similar to the first modification, the second modification also relates to a method for determining a clothoid curve to be applied to a target driving path when there are two or more clothoid curves that have the smallest error integral value. In the second modification, the ECU 10 determines the clothoid curve that has the smallest steering angle when the vehicle 1 turns, from among the two or more clothoid curves that have the smallest error integral value.

FIG. 9 is an explanatory diagram of a method for determining a clothoid curve applied to a target travel route according to a second modification of the embodiment of the present invention. In FIGS. 9A and 9B, the horizontal axis shows the distance along the lane center line L0, and the vertical axis shows the distance in the vertical direction from the lane center line L0. Moreover, FIGS. 9(A) and 9(B) respectively show clothoid curves L6 and L7 converted to the SL coordinate system. These clothoid curves L6 and L7 have the same error integral values S6 and S7, and these two error integral values S6 and S7 are the smallest among the error integral values obtained from a plurality of clothoid curves. shall be taken as a thing.

In this case, in Modification 2, the ECU 10 determines the clothoid curve with a smaller steering angle when the vehicle 1 turns, of the two clothoid curves L6 and L7. For example, when the vehicle 1 turns left, the clothoid curve L6 shifts to the right with respect to the lane center line L0, rather than the clothoid curve L6, which shifts to the left with respect to the lane center line L0 (the horizontal axis (S axis) itself). The clothoid curve L7 has a smaller steering angle when the vehicle 1 turns to the left. In this case, the ECU 10 determines that the clothoid curve L7 is to be applied to the target travel route. On the other hand, when the vehicle 1 turns to the right, the clothoid curve L6 shifts to the left with respect to the lane center line L0 rather than the clothoid curve L7 which shifts to the right with respect to the lane center line L0. In this case, the steering angle when the vehicle 1 turns to the right becomes smaller. In this case, the ECU 10 determines that the clothoid curve L6 is to be applied to the target travel route. According to such modification example 2, the radius of curvature of the target travel path for turning the vehicle 1 is increased, and the lateral acceleration generated in the vehicle 1 during the turn can be reduced, that is, the vehicle behavior during the turn can be reduced. It can be improved.

Regarding two or more clothoid curves with the minimum error integral value, if the clothoid curves converted to the SL coordinate system are shifted in the same direction, the amount of offset (shift amount) from the lane center line L0 is The minimum clothoid curve can be determined as the clothoid curve with the minimum steering angle when the vehicle 1 turns.

(Variation 3)
In the above embodiment, an example is shown in which the present invention is applied when the vehicle 1 turns left or right at an intersection, but the application of the present invention is not limited to this. The present invention can also be applied to turning at a place other than an intersection on a road. For example, the present invention can also be applied to turning right or left when the vehicle 1 enters a store or the like on the road.

(Modification 4)
In the above-described embodiment, an example was shown in which a target travel route is generated based on a clothoid curve expressed by the formula "RL=A ² ", but in other examples, a clothoid curve approximated by a formula such as a cubic function is used. A target travel route may be generated based on the curve. In still another example, the target travel route may be generated based on a predetermined transition curve other than a clothoid. For example, the transition curve may be a cubic curve, a quintic curve, or various spline curves.

(Modification 5)
In the embodiment described above, an example was shown in which the present invention is applied to a vehicle 1 that uses an engine as a drive source (see FIG. 1), but the present invention also applies to a vehicle that uses an electric motor as a drive source (an electric vehicle or a hybrid vehicle). It is also applicable to In addition, in the embodiment described above, the braking force is applied to the vehicle 1 by the brake device (brake control system 32), but in other examples, the braking force may be applied to the vehicle by regeneration of the electric motor. .

1 vehicle 10 ECU
21 Camera 22 Radar 30 Navigation System 31 Engine Control System 32 Brake Control System 33 Steering Control System 100 Vehicle Driving Support System (Driving Route Generation System)

Claims (6)

A driving route generation system,
A road information acquisition device that acquires road information related to a road on which a vehicle is traveling;
a calculation device configured to generate a target driving route for the vehicle to travel on the driving route based on the driving route information,
The computing device includes:
When the vehicle is turning, information on a lane center line regarding the road on which the vehicle is turning is acquired based on the road information;
Generate a plurality of clothoid curves whose start points and end points are located on the acquired lane center line;
For each of the generated clothoid curves, an error integral value is calculated by integrating an error indicating a difference between the clothoid curve and the lane center line over the entire clothoid curve;
determining a clothoid curve among the plurality of clothoid curves, which minimizes the calculated error integral value;
generating the target driving path along which the vehicle is to travel when turning based on the determined clothoid curve;
The calculation device, when there are two or more clothoid curves for which the error integral value is the smallest, calculates the error integral value in a predetermined range near the starting point for each of the two or more clothoid curves, and determines the clothoid curve among the two or more clothoid curves for which the calculated error integral value is the smallest. A driving route generation system,
a driving path information acquisition device that acquires driving path information regarding a driving path of a vehicle;
a calculation device configured to generate a target driving route for the vehicle to travel on the driving route based on the driving route information,
The arithmetic device is
When the vehicle is turning, information on a lane center line regarding the road on which the vehicle is turning is acquired based on the road information;
generating a plurality of clothoid curves whose start and end points are located on the acquired lane center line;
For each of the generated clothoid curves, an error integral value is calculated by integrating an error indicating a difference between the clothoid curve and the lane center line over the entire clothoid curve;
determining a clothoid curve among the plurality of clothoid curves, which minimizes the calculated error integral value;
generating the target driving path along which the vehicle is to travel when turning based on the determined clothoid curve;
The calculation device is configured to calculate, when there are two or more clothoid curves with which the error integral value is the minimum, a steering angle when the vehicle turns is the minimum among the two or more clothoid curves. A travel route generation system characterized by determining a clothoid curve. the lane center line acquired by the calculation device is formed of a first straight line which is a lane center line of a straight road before turning, a second straight line which is a lane center line of a straight road after turning, and a circular arc which corresponds to the lane center line of the road to be turned, one end of which is connected to the first straight line and the other end of which is connected to the second straight line;
The calculation device generates the plurality of clothoid curves, the start point of which is located on the first straight line of the lane center line, and the end point of which is located on the second straight line of the lane center line.
The driving route generation system according to claim 1 or 2 . The driving route generation system according to any one of claims 1 to 3, wherein the calculation device generates the plurality of clothoid curves by changing a curve length and a curvature radius from a start point of the clothoid curve under the condition that the start point and the end point are located on the lane center line. The calculation device determines a clothoid curve with the minimum error integral value among the plurality of clothoid curves when the vehicle turns left or right at an intersection, and calculates the target travel based on the determined clothoid curve. The travel route generation system according to any one of claims 1 to 4 , which generates a route. A vehicle driving assistance system comprising a control device configured to drive and control a vehicle so that the vehicle travels along a target driving route generated by the driving route generation system according to any one of claims 1 to 5 .

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