Course prediction method and course prediction device

A course prediction method uses a position acquisition circuit configured to acquire a position of a surrounding vehicle and a course prediction circuit configured to predict a course of a host vehicle based on a traveling path of the surrounding vehicle obtained from a history of the position of the surrounding vehicle. In the course prediction method, the course of the host vehicle is predicted by increasing or reducing the size of the traveling path of the surrounding vehicle, based on a turning direction and a lateral position of the surrounding vehicle.

TECHNICAL FIELD

The present invention relates to a course prediction method and a course prediction device.

BACKGROUND

There has been conventionally known a steering control technique in which a traveling path of a preceding vehicle is acquired or calculated and a curve shape of a lane on which a host vehicle is traveling (host vehicle lane) is predicted from the traveling path of the preceding vehicle (see Japanese Patent Application Publication No. 2013-226973).

However, in Japanese Patent Application Publication No. 2013-226973, it is difficult to predict the curve shape of the host vehicle lane from a traveling path of a surrounding vehicle traveling in a lane other than the host vehicle lane.

SUMMARY

The present invention has been made in view of the aforementioned problem and an object thereof is to provide a course prediction method and a course prediction device which can predict a course of a host vehicle from a traveling path of a surrounding vehicle.

In one aspect of the present invention, a course of a host vehicle is predicted by increasing or reducing the size of a traveling path of a surrounding vehicle, based on a turning direction and a lateral position of the surrounding vehicle.

According to one aspect of the present invention, since the course of the host vehicle is predicted by increasing or reducing the size of the traveling path of the surrounding vehicle, the course of the host vehicle can be predicted by using the traveling path of the surrounding vehicle traveling in a lane other than a host vehicle lane.

DETAILED DESCRIPTION

First Embodiment

Next, an embodiment is described in detail with reference to the drawings.

An overall configuration of a course prediction device1aaccording to a first embodiment is described with reference toFIG. 1. The course prediction device1apredicts a course of a host vehicle from a position of a surrounding vehicle. The “surrounding vehicle” refers to another vehicle which travels around the host vehicle in a lane (adjacent lane) adjacent to a lane (host vehicle lane) in which the host vehicle is traveling, a lane adjacent to the adjacent lane, or the like.

The course prediction device1aincludes a position detection sensor9which detects the position of the surrounding vehicle and a microcomputer8which executes a series of information computation processes to predict the course of the host vehicle from the position of the surrounding vehicle detected by the position detection sensor9. The position detection sensor9and the microcomputer8are both mounted in the host vehicle and are connected to each other by a cable for receiving and sending the position of the surrounding vehicle.

Specific examples of the position detection sensor9include a radar, a laser radar, a laser range finder (LRF), and a camera but the position detection sensor9is not limited to these and may use other known methods. Note that means for acquiring depth information by using a camera include not only means using a stereo camera but also means using a monocular camera.

The microcomputer8can be implemented by using a general-purpose microcomputer including a CPU (central processing unit), a memory, and input and output units. A computer program (course prediction program) for executing the series of information computation processes for predicting the course of the host vehicle from the position of the surrounding vehicle is installed in the microcomputer8and the microcomputer8executes the computer program. The microcomputer8thereby functions as information computation circuits (10,20,30,40) which execute the series of information computation processes. Note that, although an example in which the course prediction device1ais implemented by software is explained in this description, the information computation circuits (10,20,30,40) described below may be configured as dedicated hardware such as an ASIC, instead of the general-purpose microcomputer, as a matter of course. Alternatively, the information computation circuits (10,20,30,40) which are otherwise implemented by the microcomputer8may be configured by individual pieces of hardware. Furthermore, the microcomputer8may be used also as an electronic control unit (ECU) used for other control relating to the vehicle.

The microcomputer8functions as a position acquisition circuit10, a traveling path calculation circuit20, a lateral deviation amount calculation circuit30, and a course prediction circuit40.

The position acquisition circuit10acquires the position of the surrounding vehicle. The position acquisition circuit10may acquire the position of the surrounding vehicle detected by the position detection sensor9from the position detection sensor9. As a matter of course, the position acquisition circuit10may externally acquire information indicating the position of the surrounding vehicle via a radio communication network.

The traveling path calculation circuit20calculates the traveling path of the surrounding vehicle from a history of the position of the surrounding vehicle acquired by the position acquisition circuit10. Specifically, the traveling path calculation circuit20calculates the traveling path of the surrounding vehicle by connecting the positions of the surrounding vehicle detected at multiple consecutive time points. For example, as illustrated inFIG. 4, the traveling path calculation circuit20may repeatedly plot the position (P1, P2, P3, P4, P5, . . . ) of the surrounding vehicle relative to the host vehicle which is detected every predetermined time, on a map in consideration of the moving direction and moving distance of the host vehicle within the predetermined time, and perform curve approximation for multiple positions (path points: P1to P5, . . . ) plotted on the map. An approximate curve83Mthus obtained forms the traveling path of the surrounding vehicle.

The lateral deviation amount calculation circuit30calculates the position (hereafter referred to as “lateral position”) of the traveling path calculated by the traveling path calculation circuit20, relative to the host vehicle in a vehicle width direction of the host vehicle. For example, in a two-dimensional coordinate system in which the origin is the host vehicle and a vehicle front-rear direction and the vehicle width direction are an x-axis and a y-axis, respectively, the lateral position can be indicated by an intersection between the traveling path and the y-axis, that is a y-coordinate of a y-intercept. The lateral position is described later with reference toFIG. 3.

Alternatively, the lateral deviation amount calculation circuit30may determine a lane in which the traveling path is located as the lateral position of the traveling path. For example, the lateral deviation amount calculation circuit30detects a lane marker provided on a road surface by using a camera or the like mounted in the host vehicle and calculates the position of the lane marker relative to the host vehicle. Then, the lateral deviation amount calculation circuit30determines the lane in which the surrounding vehicle is traveling, that is the lane (adjacent lane, lane adjacent to the adjacent lane, or the like) in which the traveling path is located, based on the position of the lane marker and the position of the traveling path. Since the width of the lane varies depending on a road section, the lateral deviation amount calculation circuit30may set the lateral position of the traveling path determined to be in the adjacent lane to, for example, 3 m and set the lateral position of the traveling path determined to be in the lane adjacent to the adjacent lane to, for example, 6 m, instead of an actually measured value.

The course prediction circuit40predicts the course of the host vehicle by increasing or reducing the size of the traveling path of the surrounding vehicle based on the turning direction of the surrounding vehicle and the lateral position calculated by the lateral deviation amount calculation circuit30. Note that the course prediction circuit40determines the turning direction of the surrounding vehicle from the traveling path of the surrounding vehicle calculated by the traveling path calculation circuit20. For example, when the traveling path has a right curve shape, the course prediction circuit40may determine that the turning direction is right and, when the traveling path has a left curve shape, determine that the turning direction is left.

The course prediction circuit40includes a base traveling path selector40a, a base traveling path corrector40b, and a course determiner40c.

The base traveling path selector40aselects a traveling path (hereafter, referred to as “base traveling path”) to be used as a base in estimation of the course, from traveling paths of multiple surrounding vehicles. When the position acquisition circuit10acquires the positions of the multiple surrounding vehicles, multiple traveling paths and multiple lateral positions are calculated. In this case, the base traveling path selector40aselects a traveling path suitable for the estimation of course, based on the lateral positions of the traveling paths. The selection of the base traveling path is described later with reference toFIG. 3.

The base traveling path corrector40bcorrects the base traveling path selected by the base traveling path selector40a, based on the turning direction of the surrounding vehicle and the lateral position of the base traveling path. The correction of the base traveling path is described later with reference toFIG. 4.

The course determiner40csets the base traveling path corrected by the base traveling path corrector40bas the course of the host vehicle.

The lateral positions (Di, Dj) of the traveling paths (83i,83j) and a method of selecting the base traveling path are specifically described with reference toFIG. 3. In the example illustrated inFIG. 3, the position acquisition circuit10acquires the positions of multiple surrounding vehicles (82i,82j) and the traveling path calculation circuit20calculates the traveling paths (83i,83j) of the respective surrounding vehicles (82i,82j). Then, the lateral deviation amount calculation circuit30calculates the lateral positions (Di, Dj) of the respective traveling paths (83i,83j) relative to a host vehicle81. Note that, since the traveling paths (83i,83j) have left curve shapes as illustrated inFIG. 3, the course prediction circuit40determines that the turning directions of the surrounding vehicles are left.

The base traveling path selector40aselects the base traveling path from the multiple traveling paths (83i,83j), based on the lateral positions (Di, Dj) of the traveling paths. Specifically, the base traveling path selector40aselects the traveling path (83i,83j) of the surrounding vehicle away from the host vehicle81by a distance smaller than a predetermined reference distance, as the base traveling path. For example, when there are multiple surrounding vehicles, the base traveling path selector40aselects traveling paths (83i,83j) whose absolute values of the lateral positions (Di, Dj) are smaller than a first reference distance (3 m), from multiple traveling paths, so as to select the base traveling path from the traveling paths of the surrounding vehicles in the host vehicle lane and the adjacent lane. When the absolute values of the lateral positions (Di, Dj) of multiple traveling paths (83i,83j) are smaller than the first reference distance (3 m), the base traveling path selector40aselects a traveling path of the surrounding vehicle (82i,82j) whose distance from the host vehicle81is smaller than a second reference distance, from the multiple traveling paths (83i,83j). Here, the “distance of the surrounding vehicle (82i,82j) from the host vehicle81” is a concept including not only the distance in the vehicle width direction but also the distance in a traveling direction. For example, the base traveling path selector40aselects the traveling path83jof the surrounding vehicle82jclosest to the host vehicle81as the base traveling path, from the traveling paths (83i,83j) whose the absolute values of the lateral positions (Di, Dj) are smaller than the first reference distance (3 m).

Alternatively, the base traveling path selector40amay select the traveling path83jwhose absolute value of the lateral position (Di, Dj) is the smallest, as the base traveling path. In this case, the base traveling path selector40adoes not consider the “distance of the surrounding vehicle (82i,82j) from the host vehicle81.” As another alternative, the base traveling path selector40amay select the traveling path of “the surrounding vehicle (82i,82j) whose distance from the host vehicle81” is the smallest, as the base traveling path. In this case, the base traveling path selector40adoes not consider the “absolute values of the lateral positions (Di, Dj).”

Note that, when the lane (adjacent lane, lane adjacent to the adjacent lane, or the like) in which each traveling path is located is used as the lateral position of the traveling path, for example, the base traveling path selector40aselects the traveling path located in the adjacent lane and does not select the traveling path located in the lane adjacent to the adjacent lane.

An example of a specific method of predicting the course of the host vehicle81by correcting a base traveling path83Mis described with reference toFIG. 4. The base traveling path corrector40bincreases or reduces the size of the base traveling path83Mselected by the base traveling path selector40a, based on the turning direction of the surrounding vehicle and the lateral position DMof the base traveling path83M.

First, the base traveling path corrector40bcalculates a turning radius R and a turning center84at each of path points (P1to P5, . . . ). For example, the base traveling path corrector40bcalculates the turning radius R and the coordinates of the turning center84by using the path point P3being the calculation target and the points preceding and following the path point P3by means of a least squares method or the like. The base traveling path corrector40bcalculates the turning radius R and the turning center84for each of the path points (P1to P5, . . . ) in a similar way.

Next, the base traveling path corrector40bincreases the turning radius R about the turning center84at each path points (P1to P5, . . . ) to a turning radius (R+DM) or reduces the turning radius R to a turning radius (R−DM). The base traveling path corrector40bdetermines whether to increase or reduce the turning radius R, based on the turning direction and the lateral position DMof the base traveling path83M.

For example, as in the traveling path83iofFIG. 3, when the turning direction is left and the lateral position Di of the traveling path83iis on the left side of the host vehicle81, the host vehicle81is located outside the traveling path83iof the surrounding vehicle82iin the turning direction. In this case, as inFIG. 4, the turning radius at each path point (P1to P5, . . . ) of the traveling path83iis increased to a turning radius (R+Di).

Meanwhile, as in the traveling path83jofFIG. 3, when turning direction is left and the lateral position Dj of the traveling path83jis on the right side of the host vehicle81, the host vehicle81is located inside the traveling path83jof the surrounding vehicle82jin the turning direction. In this case, contrary toFIG. 4, the turning radius at each path point (P1to P5, . . . ) of the traveling path83jis reduced to a turning radius (R−Dj).

As described above, the base traveling path corrector40bchanges the distance (turning radius) from the turning center84to each path point (P1to P5, . . . ) without changing the turning center84. When the host vehicle81is located outside the traveling path in the turning direction, the base traveling path corrector40bincreases the turning radius and, when the host vehicle81is located inside the traveling path, reduces the turning radius. Then, the base traveling path corrector40bperforms the curve approximation again on the path points (P3′) subjected to the turning radius increase or reduction and can thereby correct the base traveling path83M.

The larger the turning radius R of the base traveling path83Mis, the smaller the degree of increasing or reducing by the base traveling path corrector40bis made. In other words, provided that the lateral position D is constant, the larger the turning radius R is, the smaller the increase ratio (=(R+DM)/R) and the reduction ratio (=(R−DM)/R) are.

The greater the distance from the host vehicle81to the lateral position DMof the surrounding vehicle82is, the greater the degree of increasing or reducing by the base traveling path corrector40bis made. In other words, provided that the turning radius R is constant, the larger the absolute value of the lateral position DMis, the larger the increase ratio and the reduction ratio are.

In the first embodiment, the course determiner40cdetermines a base traveling path91corrected by the base traveling path corrector40bas the course of the host vehicle as it is.

An example of a course prediction method using the course prediction device1aillustrated inFIG. 1is described with reference to the flowchart ofFIG. 2. Here, operation steps of the microcomputer8in the course prediction device1aillustrated inFIG. 1are described. The processing illustrated inFIG. 2is repeatedly executed at a predetermined cycle.

First, in step S110, the position acquisition circuit10acquires the position of each surrounding vehicle.

Proceeding to step S120, as illustrated inFIG. 4, the traveling path calculation circuit20calculates the traveling path (approximate curve83M) of each surrounding vehicle from the history (traveling points: P1to P5, . . . ) of the position of the surrounding vehicle acquired by the position acquisition circuit10.

Proceeding to step S130, as illustrated inFIG. 3, the lateral deviation amount calculation circuit30calculates the lateral position (Di, Dj) of each traveling path (83i,83j) calculated by the traveling path calculation circuit20relative to the host vehicle81.

Proceeding to step S140, as illustrated inFIG. 3, the base traveling path selector40aselects the base traveling path from the multiple traveling paths (83i,83j), based on the lateral positions (Di, Dj) of the traveling paths. For example, the base traveling path selector40aselects the traveling paths (83i,83j) whose absolute values of the lateral positions (Di, Dj) are smaller than the first reference distance (3 m) and selects the traveling path83jof the surrounding vehicle82jclosest to the host vehicle81, as the base traveling path83M. However, the method of selecting the base traveling path is not limited to this and the other methods described above may be used. Note that the selection of the base traveling path may be performed only when the positions of multiple surrounding vehicles are acquired in step S110. When the position of only one surrounding vehicle is acquired, the base traveling path selector40amay select the traveling path of this surrounding vehicle as the base traveling path. Moreover, when there is no traveling path whose absolute value of the lateral position is smaller than the first reference distance, the processing may be aborted and restarted from step S110or the traveling path whose absolute value of the lateral position is the smallest may be selected as the base traveling path.

Proceeding to step S150, as illustrated inFIG. 4, the base traveling path corrector40bcalculates the turning radius R and the turning center84at each path point (P1to P5, . . . ).

Proceeding to step S160, as illustrated inFIG. 4, the base traveling path corrector40bincreases the turning radius R about the turning center84at each path point (P1to P5, . . . ) to the turning radius (R+DM) or reduces the turning radius R to the turning radius (R−DM). The base traveling path corrector40bdetermines whether to increase or reduce the turning radius R, based on the turning direction and the lateral position of the base traveling path83M. Then, the base traveling path corrector40bperforms the curve approximation again on the path points (P3′) subjected to the turning radius increase or reduction and thereby corrects the base traveling path83M.

Proceeding to step S170, the course determiner40cdetermines the base traveling path91corrected by the base traveling path corrector40bas the course of the host vehicle as it is.

Proceeding to step S180, the microcomputer8determines whether an ignition switch of the host vehicle81is turned off and repeatedly executes steps S110to S170described above at a predetermined cycle until the ignition switch is turned off. When the ignition switch is turned off (YES in step S180), the aforementioned processing cycle is terminated.

As described above, in the first embodiment, the following operations and effects are obtained.

The microcomputer8predicts the course of the host vehicle81by increasing or reducing the size of the traveling path (83i,83j) of the surrounding vehicle (82i,82j). The microcomputer8can thereby predict the course of the host vehicle81by using the traveling path (83i,83j) of the surrounding vehicle (82i,82j) traveling in the lane other than the host vehicle lane. For example, as illustrated inFIG. 5A, assume a situation where the host vehicle81cannot detect the position of a preceding vehicle89due to the surrounding vehicle82or the like. A curve shape of a traveling path (adjacent lane) of the surrounding vehicle82is different from a curve shape of a traveling path (host vehicle lane) of the preceding vehicle89. Accordingly, when a conventional method of predicting the course of the host vehicle81from the traveling path of the preceding vehicle89is applied, as illustrated inFIG. 5B, a curve shape90of the host vehicle lane cannot be appropriately predicted. In the first embodiment, also in the situation illustrated inFIG. 5A, the microcomputer8can accurately predict the curve shape of the host vehicle81by using the traveling path83of the surrounding vehicle82traveling in the adjacent lane or the like.

As illustrated inFIG. 4, the larger the turning radius of the traveling path83Mis, the smaller the degree of increasing or reducing by the base traveling path corrector40bis made. The base traveling path corrector40bcan thereby appropriately predict the course depending on the curve shape.

As illustrated inFIG. 4, the greater the distance from the host vehicle81to the lateral position DMof the surrounding vehicle82is, the greater the degree of increasing or reducing by the base traveling path corrector40bis made. The base traveling path corrector40bcan thereby appropriately predict the course also when the lane in which the host vehicle81is traveling is different from the lane in which the surrounding vehicle82is traveling (the adjacent lane or the lane adjacent to the adjacent lane).

The microcomputer8predicts the course based on the traveling path (83i,83j) of the surrounding vehicle whose distance from the host vehicle81is the smallest. The closer the position of the surrounding vehicle (82i,82j) to the host vehicle81is, the higher the detection accuracy of this position is. Accordingly, the microcomputer8predicts the course based on the traveling path (83i,83j) of the surrounding vehicle (82i,82j) whose distance from the host vehicle81is the smallest, and can thereby appropriately predict the course from the highly-accurate traveling path (83i,83j).

Moreover, the microcomputer8predicts the course based on the traveling path83jof the surrounding vehicle in the lane adjacent to the lane in which the host vehicle81is traveling. The microcomputer8can thereby appropriately predict the course from the highly-accurate traveling path83j.

Second Embodiment

An overall configuration of a course prediction device1baccording to a second embodiment is described with reference toFIG. 6. The course prediction device1bacquires map information including at least branching information of roads and does not predict the course of the host vehicle when determining that the host vehicle81is to pass a branching point. When the course prediction device1bdetermines that the host vehicle81is to pass no branching point, the course determiner40cdetermines the base traveling path91corrected by the base traveling path corrector40bas the course of the host vehicle.

As illustrated inFIG. 6, the course prediction device1bfurther includes a map database7. The map database7and the microcomputer8are both mounted in the host vehicle81and are connected each other by a cable for receiving and sending the map information including at least the branching information of roads.

The microcomputer8functions not only as the information computation circuits (10,20,30,40) but also as a map acquisition circuit50. The map acquisition circuit50acquires the map information including at least the branching information of roads, from the map database7.

The other configurations of the course prediction device1bare the same as those of the course prediction device1ainFIG. 1and description thereof is omitted.

An example of a course prediction method using the course prediction device1billustrated inFIG. 6is described with reference to the flowchart ofFIG. 7. Here, operation steps of the microcomputer8in the course prediction device1billustrated inFIG. 6are described. The processing illustrated inFIG. 7is repeatedly executed at a predetermined cycle.

In comparison withFIG. 2, the flowchart ofFIG. 7further includes step S165and is different in the contents of step S170. The contents of processing in steps S110to S160and S180inFIG. 7are the same as those inFIG. 2and description thereof is omitted.

After step S160, the processing proceeds to step S165and the map acquisition circuit50acquires the map information including at least the branching information of roads, from the map database7. Specifically, the map acquisition circuit50reads the map information including the branching information of a road on which the host vehicle81is traveling, from the map database7.

Proceeding to step S170, the course determiner40cpredicts the course of the host vehicle from the corrected base traveling path91, the map information, and the absolute value of the lateral position DM. The course determiner40cdetermines whether the host vehicle81is to pass a branching point within a predetermined time. Specifically, as illustrated inFIG. 8, the course determiner40cdetermines whether a road on which the host vehicle81is traveling includes a point (branching point87) where the road branches into two or more roads (85,86) in front of the host vehicle81within a predetermined distance therefrom. When the course determiner40cdetermines that the absolute value of the lateral position DMof the base traveling path83Mis a third reference distance (1.5 m) or more and that the host vehicle81is to pass the branching point87within the predetermined time, the course determiner40cdoes not predict the course of the host vehicle81. Specifically, when the course determiner40cdetermines that the surrounding vehicle for which the traveling path can be calculated is traveling in a lane other than the host vehicle lane (the distance to the lateral position DMis the third reference distance (1.5 m) or more) and that the host vehicle81is to pass the branching point87, the course determiner40cdoes not set the base traveling path91corrected by the base traveling path corrector40bas the course of the host vehicle81. Meanwhile, when the course determiner40cdetermines that the absolute value of the lateral position DMof the base traveling path83Mis less than the third reference distance (1.5 m) or that the host vehicle81is to pass no branching point87within the predetermined time, the course determiner40csets the base traveling path91corrected by the base traveling path corrector40bas the course of the host vehicle81. Specifically, when the course determiner40cdetermines that the surrounding vehicle for which the traveling path can be calculated is traveling in the host vehicle lane (the distance to the lateral position DMis less than the third reference distance (1.5 m)) or that the host vehicle81is to pass no branching point, the course determiner40csets the base traveling path91corrected by the base traveling path corrector40bas the course of the host vehicle81.

As described above, in the second embodiment, the course is not predicted when the host vehicle81is to pass the branching point87. Accordingly, as illustrated inFIG. 8, erroneous course prediction can be prevented when the surrounding vehicle82leaves in a direction (road86) different from the course (road85) of the host vehicle81at the branching point87. Specifically, when the traveling path83of the surrounding vehicle and the course of the host vehicle are to be located in different roads (85,86) from the branching point87, the course determiner40cprevents the corrected base traveling path91from being set as the course of the host vehicle81. Erroneous course prediction can be thereby avoided.

Note that, in step S170, the course determiner40cmay determine the course based only on the presence or absence of the branching point87. For example, no matter where the position of the lane of the surrounding vehicle for which the traveling path can be calculated is, the course determiner40cmay not predict the course of the host vehicle81irrespective of the lateral position DMof the base traveling path83Mwhen determining that the host vehicle81is to pass the branching point87within the predetermined time.

Third Embodiment

An overall configuration of a course prediction device1caccording to a third embodiment is described with reference toFIG. 9. The course prediction device1cacquires at least travel route information of the host vehicle81on a map and predicts the course based on the traveling path83of the surrounding vehicle82similar to a travel route of the host vehicle81. The course determiner40cdetermines the base traveling path91corrected by the base traveling path corrector40bas the course of the host vehicle only when the corrected base traveling path91is determined to be similar to the travel route of the host vehicle81.

As illustrated inFIG. 9, the course prediction device1cfurther includes a navigation device6. The navigation device6, the map database7, and the microcomputer8are all mounted in the host vehicle81. The navigation device6and the microcomputer8are connected to each other by a cable for receiving and sending the traveling route information of the host vehicle81.

The microcomputer8functions not only as the information computation circuits (10,20,30,40,50) but also as a route acquisition circuit60. The route acquisition circuit60acquires the travel route information of the host vehicle81from the navigation device6. Moreover, the map acquisition circuit50acquires map information including the branching information of roads, intersection information, and shape information (including turning radius information) of roads.

The other configurations of the course prediction device1care the same as those of the course prediction device1binFIG. 6and description thereof is omitted.

An example of a course prediction method using the course prediction device1cillustrated inFIG. 9is described with reference to the flowchart ofFIG. 10. Here, operation steps of the microcomputer8in the course prediction device1cillustrated inFIG. 9are described. The processing illustrated inFIG. 10is repeatedly executed at a predetermined cycle.

In comparison withFIG. 7, the flowchart ofFIG. 10further includes step S100and is different in the contents of step S170. The contents of processing in steps S110to S160and S180inFIG. 10are the same as those inFIG. 7and description thereof is omitted.

In step S100, the route acquisition circuit60acquires the travel route information of the host vehicle81from the navigation device6. Then, the processing proceeds to step S110.

In step S170, when the course determiner40cdetermines that the absolute value of the lateral position DMof the base traveling path83Mis the third reference distance or more and that the host vehicle81is to pass the branching point87, the course determiner40cdoes not set the corrected base traveling path91as the course of the host vehicle81. This is the same as the second embodiment.

In the third embodiment, in step S170, the course determiner40cfurther determines whether the branching point87is an intersection88. Then, when the branching point87is the intersection88, the course determiner40cdetermines whether the base traveling path91corrected in the step S160is similar to the travel route of the host vehicle81acquired in step S100.

Then, when the course determiner40cdetermines that the branching point87is the intersection88and that the corrected base traveling path91is similar to the travel route of the host vehicle81, the course determiner40csets the base traveling path91corrected in step S160as the course of the host vehicle81.

Note that, even if the course determiner40cdetermines that the branching point87is the intersection88and that the corrected base traveling path91is similar to the travel route of the host vehicle81, the course determiner40cmay not set the corrected base traveling path91as the course of the host vehicle81when the following condition is established. Specifically, the course determiner40cmay not set the corrected base traveling path91as the course of the host vehicle lane when a state where the absolute value of the lateral position DMof the base traveling path83Mis the third reference distance (1.5 m) or more continues for a predetermined time (for example, 5 seconds) or more.

As described above, in the third embodiment, since the traveling path of the surrounding vehicle similar to the traveling route of the host vehicle81is used, the course can be appropriately predicted by using the traveling path of the surrounding vehicle which runs parallel to the traveling route of the host vehicle81.

Although the third embodiment is described as an example based on the second embodiment, the third embodiment may be carried out based on the first embodiment. Specifically, in step S170, the course determiner40cdetermines whether the base traveling path91corrected in step S160is similar to the traveling route of the host vehicle81acquired in step S100. When the base traveling path91is not similar, the course determiner40cdoes not set the base traveling path91corrected by the base traveling path corrector40bas the course of the host vehicle. Meanwhile, when the base traveling path91is similar, the course determiner40csets the base traveling path91corrected by the base traveling path corrector40bas the course of the host vehicle.

In step S170, the course determiner40cdoes not determine whether the absolute value of the lateral position DMis the third reference distance or more, whether the host vehicle81passes the branching point87, or whether the branching point87is the intersection88. Step S165(reading of the map) is also unnecessary.

Note that the course prediction device (1a,1b,1c) may include no position detection sensor9. In this case, for example, the course prediction device (1ato1c) includes a radio communication unit and the position acquisition circuit10can externally acquire information indicating the position of the surrounding vehicle via a radio communication network. Similarly, the course prediction device (1ato1c) may include neither map database7nor navigation device6. In this case, for example, the map acquisition circuit50and the route acquisition circuit60may externally acquire the map information and the travel route information via a computer network.

Furthermore, the course prediction device (1ato1c) may not be mounted in the host vehicle81. For example, the course prediction device (1ato1c) may be a backend (cloud itself) in a cloud computing model. The host vehicle81being a frontend is connected to the course prediction device (1ato1c) being the backend via a network such as the Internet. The course prediction device (1ato1c) may predict the course of the host vehicle81by acquiring the information indicating the position of the surrounding vehicle82from the surrounding vehicle82itself or from the host vehicle81(the detection result of the position detection sensor9) to predict the course of the host vehicle81and provide the predicted course to the host vehicle81via the network.

The functions described in the aforementioned embodiments can be implemented by one or multiple processing circuits. The processing circuit includes a programed processing device such as a processing device including an electric circuit. Moreover, the processing device includes devices such as an application-specific integrated circuit (ASIC) and conventional circuit parts which are designed to execute the functions described in the embodiments.

Although the contents of the present invention have been explained above according to the examples, the present invention is not limited to this explanation. It is apparent to those skilled in the art that various changes and modifications can be made.

REFERENCE SIGNS LIST