Abstract:
Provided are a lane separation line detection correcting device/method and an automatic driving system for stabilizing the behavior of a vehicle by correcting overestimated curvature information resulting from an erroneous detection of a curvature of a lane separation line. A travel speed detecting circuit detects, for example, a target travel speed as vehicle sensor information. A maximum curvature estimating circuit estimates, based on the target travel speed, a maximum curvature of a road along which an own vehicle is traveling. A curvature correcting circuit corrects a curvature of a lane separation line input thereto based on the maximum curvature. A control unit controls steering of the own vehicle based on the lane separation line having a corrected curvature. As a result, vehicle steering can be automatically controlled so as to prevent the own vehicle while traveling from departing from a driving lane.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
       [0001]    The present invention relates to a lane separation line detection correcting device and a lane separation line detection correcting method, which are used upon automatic control of a steering angle of a vehicle so that the vehicle is may be prevented from departing from a driving lane when the vehicle has almost departed from the driving lane during traveling, and to an automatic driving system including the lane separation line detection correcting device. 
       2. Description of the Related Art 
       [0002]    Hitherto, there has been a technology for detecting a position, an inclination, and a curvature of a lane separation line, which is represented by a white line, based on image information taken by a camera, and for automatically controlling the steering angle of a vehicle by using the detected position, inclination, and curvature so that the vehicle may not depart from a driving lane, as seen from e.g. Japanese Patent Application Laid-open No. 2015-197794. 
         [0003]    However, the image information taken by the camera is greatly influenced by the surrounding environment, such as road surface glare from the sun, the lights of an oncoming vehicle, shadows on the road surface, paint, etc. As a result, when the position, inclination, and curvature of the lane separation line are detected in the environment that is constantly changing during traveling, accuracy of the detection often deteriorates. 
         [0004]    In particular respect of the lane separation line, there is a need to detect the curvature far away. In such a case, a phenomenon may occur in which the curvature is detected as being several times larger than that of the actual road shape due to an erroneous detection caused by obstruction to the curvature detection by a preceding vehicle, an oncoming vehicle, etc. At the time when the steering angle of the vehicle is automatically controlled by using overestimated curvature information resulting from that erroneous detection, there is a problem in that the behavior of the vehicle becomes unstable. 
       SUMMARY OF THE INVENTION 
       [0005]    Having been made in order to solve the above-mentioned problem, the present invention has an object to provide a lane separation line detection correcting device, a lane separation line detection correcting method, and an automatic driving system for stabilizing the behavior of a vehicle by correcting overestimated curvature information resulting from an erroneous detection of a curvature of a lane separation line. 
         [0006]    For achieving the above object, the present invention provides a lane separation line detection correcting device, comprising: a maximum curvature estimating circuit to estimate a maximum curvature of a road along which an own vehicle is traveling based on vehicle sensor information; and a curvature correcting circuit to correct a curvature of a lane separation line input to the curvature correcting circuit, based on the maximum curvature. 
         [0007]    Also, for achieving the above object, the present invention provides a lane separation line detection correcting method, comprising: estimating, by a maximum curvature estimating circuit, a maximum curvature of a road along which an own vehicle is traveling, based on vehicle sensor information; and correcting, by a curvature correcting circuit, a curvature of a lane separation line input to the curvature correcting circuit, based on the maximum curvature. 
         [0008]    Further, for achieving the above object, the present invention provides an automatic driving system, comprising: the lane separation line detection correcting device of claim  1 ; and a control circuit to control steering of the own vehicle based on a lane separation line having a curvature corrected by the curvature correcting circuit. 
         [0009]    According to the present invention, the maximum curvature of the road along which the vehicle is traveling is estimated based on vehicle sensor information, and based on that maximum curvature estimated, the curvature of the lane separation line input is corrected. As a result, an overestimated curvature caused by an erroneous detection can be suppressed, and vehicle steering control that utilizes the information on the lane separation line can be stabilized. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a block diagram for illustrating a configuration of a lane separation line detection correcting device and a lane separation line detection correcting method according to a first embodiment of the present invention; 
           [0011]      FIG. 2  is a flowchart for illustrating an algorithm according to the first embodiment illustrated in  FIG. 1 ; 
           [0012]      FIG. 3  is a block diagram for illustrating a configuration of a lane separation line detection correcting device and a lane separation line detection correcting method according to a second embodiment of the present invention; 
           [0013]      FIG. 4  is a flowchart for illustrating an algorithm according to the second embodiment illustrated in  FIG. 3 ; 
           [0014]      FIG. 5  is a block diagram for illustrating a configuration of a lane separation line detection correcting device and a lane separation line detection correcting method according to a third embodiment of the present invention; 
           [0015]      FIG. 6  is a flowchart for illustrating an algorithm according to the third embodiment illustrated in  FIG. 5 ; 
           [0016]      FIG. 7  is a block diagram for illustrating a configuration of a lane separation line detection correcting device and a lane separation line detection correcting method according to a fourth embodiment of the present invention; 
           [0017]      FIG. 8  is a flowchart for illustrating an algorithm according to the fourth embodiment illustrated in  FIG. 7 ; 
           [0018]      FIG. 9  is a block diagram for illustrating a configuration of a lane separation line detection correcting device and a lane separation line detection correcting method according to a fifth embodiment of the present invention; 
           [0019]      FIG. 10  is a flowchart for illustrating an algorithm according to the fifth embodiment illustrated in  FIG. 9 ; 
           [0020]      FIG. 11A  is a block diagram for illustrating a configuration of a lane separation line detection correcting device and a lane separation line detection correcting method according to a sixth embodiment of the present invention; 
           [0021]      FIG. 11B  is a schematic diagram of travel around a curve for illustrating a relation between a preceding vehicle and an own vehicle according to the sixth embodiment of the present invention; 
           [0022]      FIG. 12  is a flowchart for illustrating an algorithm according to the sixth embodiment illustrated in  FIG. 11 ; 
           [0023]      FIG. 13A  is a block diagram for illustrating a configuration of a lane separation line detection correcting device and a lane separation line detection correcting method according to a seventh embodiment of the present invention; 
           [0024]      FIG. 13B  is a schematic diagram of travel around a curve for illustrating a travel track of the own vehicle according to the seventh embodiment of the present invention; 
           [0025]      FIG. 14  is a flowchart for illustrating an algorithm according to the seventh embodiment illustrated in  FIG. 13 ; 
           [0026]      FIG. 15A  is a block diagram for illustrating a configuration of a lane separation line detection correcting device and a lane separation line detection correcting method according to an eighth embodiment of the present invention; 
           [0027]      FIG. 15B  is a schematic diagram of travel around a curve for illustrating the travel track of the own vehicle between road edges according to the eighth embodiment of the present invention; and 
           [0028]      FIG. 16  is a flowchart for illustrating an algorithm according to the eighth embodiment illustrated in  FIG. 15 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0029]    A lane separation line detection correcting device, a lane separation line detection correcting method, and an automatic driving system according to a first embodiment to a ninth embodiment of the present invention will now be described in detail with reference to the above drawings attached. In each of the first to ninth embodiments, because the lane separation line detection correcting device and the lane separation line detection correcting method correspond to each other, the following descriptions will be made based on the lane separation line detection correcting device. 
       First Embodiment 
     &lt;Configuration of Lane Separation Line Detection Correcting Device  1 &gt; 
       [0030]    A lane separation line detection correcting device  1  illustrated in  FIG. 1  according to a first embodiment of the present invention includes a travel speed detecting circuit  11 , a maximum curvature estimating circuit  12 , and a curvature correcting circuit  13 . The travel speed detecting circuit  11  is configured to acquire a current travel speed from an own vehicle  2 . The maximum curvature estimating circuit  12  is configured to estimate a maximum curvature of a road based on the current travel speed acquired by the travel speed detecting circuit  11 . The curvature correcting circuit  13  is configured to correct, based on the maximum curvature obtained from the maximum curvature estimating circuit  12 , a curvature of a lane separation line input from a lane separation line detecting circuit  41  of an image processing device  4 , and to output detection information on the lane separation line to an external lane departure prevention control device  5 . The lane separation line detecting circuit  41  is configured to detect the lane separation line by image processing with an image taken by an external camera  3 . The lane departure prevention control device  5  may also be a lane departure prevention warning device. 
       &lt;Operation of Lane Separation Line Detection Correcting Device  1 &gt; 
       [0031]    An operation flowchart of the lane separation line detection correcting device  1  is illustrated in  FIG. 2 . First, the lane separation line detection correcting device  1  waits for input of lane separation line detection information from the image processing device  4  (Steps Si-i and S 1 - 2 ). At the time when the lane separation line detection information is input, the maximum curvature estimating circuit  12  calculates an estimation value of the maximum curvature based on, for example, the newest or latest travel speed input last via the travel speed detecting circuit  11 , and transmits to the curvature correcting circuit  13  the calculated estimation value as the maximum curvature (Step S 1 - 3 ). The curvature correcting circuit  13  uses the maximum curvature to correct the curvature in the lane separation line detection information input from the lane separation line detecting circuit  41  (Step S 1 - 4 ). The lane separation line detection information containing the corrected curvature is then output from the curvature correcting circuit  13  to the external lane departure prevention control device  5  (Step S 1 - 5 ). 
       &lt;Operation of Maximum Curvature Estimating Circuit  12 &gt; 
       [0032]    The maximum curvature estimating circuit  12  is configured to calculate an estimation value of the maximum curvature of the lane separation line based on the input travel speed. The maximum curvature estimating circuit  12  is configured to calculate an estimation value k of the maximum curvature based on Expression (1), and to transmit the calculated estimation value k to the curvature correcting circuit  13 : 
         [0000]    
       
         
           
             
               
                 
                   κ 
                   = 
                   
                     
                       1 
                       R 
                     
                     = 
                     
                       α 
                        
                       
                         
                           gf 
                           
                             v 
                             2 
                           
                         
                          
                         
                           [ 
                           
                             m 
                             1 
                           
                           ] 
                         
                       
                     
                   
                 
               
               
                 
                   Expression 
                    
                   
                       
                   
                    
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
     
         [0000]    where v represents a speed (m/s), R represents a minimum flat curve radius (m), g represents a gravitational acceleration (m/s 2 ), and f represents a side slip friction coefficient between a road surface and tires. 
         [0033]    A coefficient α is an experimentally-determined value. Because a road curvature at a design speed of a road varies depending on the country or region in which the lane separation line detection correcting device of the present invention is assumed to be used, a value of “1” or less is specified in accordance with that road curvature. A specified value of “1” represents the curvature at which the vehicle can travel at its actual speed without side-slip. 
       &lt;Operation of Curvature Correcting Circuit  13 &gt; 
       [0034]    The curvature correcting circuit  13  is configured to calculate a corrected curvature L i  by correcting a curvature K i  in the lane separation line detection information in accordance with Expression (2) based on the estimated value k of the maximum curvature calculated by the maximum curvature estimating circuit  12 , and to output lane separation line detection information containing the calculated curvature L i  to the external lane departure prevention control device  5 : 
         [0000]    
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           
                             L 
                             i 
                           
                           = 
                           
                             K 
                             i 
                           
                         
                       
                       
                         
                           ( 
                           
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                             ≥ 
                             
                               K 
                               i 
                             
                           
                           ) 
                         
                       
                     
                     
                       
                         
                           
                             L 
                             i 
                           
                           = 
                           
                             L 
                             
                               i 
                               - 
                               1 
                             
                           
                         
                       
                       
                         
                           ( 
                           
                             κ 
                             &lt; 
                             
                               K 
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                   Expression 
                    
                   
                       
                   
                    
                   
                     ( 
                     2 
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         [0000]    where L i-1  represents the curvature of the lane separation line detection information corrected last time. 
       Second Embodiment 
     &lt;Configuration of Lane Separation Line Detection Correcting Device  1 &gt; 
       [0035]    The lane separation line detection correcting device  1  illustrated in  FIG. 3  according to a second embodiment of the present invention includes a travel speed detecting circuit  11   a,  the maximum curvature estimating circuit  12 , and the curvature correcting circuit  13 . The travel speed detecting circuit  11   a  is configured to acquire relative speeds of preceding vehicles with respect to the own vehicle output from a vehicle detecting circuit  42  of the image processing device  4 , which is configured to perform image processing by using an image taken by the external camera  3 , as well as the current travel speed of the own vehicle  2 . Then, the travel speed detecting circuit  11   a  calculates one of an average travel speed and a maximum travel speed of the preceding vehicles, to be notified to the maximum curvature estimating circuit  12 . The maximum curvature estimating circuit  12  is configured to estimate the maximum curvature of a travel path based on the travel speed of the own vehicle. The curvature correcting circuit  13  is configured to correct, based on the maximum curvature obtained from the maximum curvature estimating circuit  12 , the curvature of the lane separation line acquired from the image processing device  4 , which includes the lane separation line detecting circuit  41  configured to acquire an image from the external camera  3  and to detect the lane separation line by image processing, and to output the corrected lane separation line detection information to the lane departure prevention control device  5 . The lane departure prevention control device  5  may also be a lane departure prevention warning device. 
       &lt;Operation of Lane Separation Line Detection Correcting Device  1 &gt; 
       [0036]    An operation flowchart of the lane separation line detection correcting device  1  is illustrated in  FIG. 4 . First, the lane separation line detection correcting device  1  waits for input of lane separation line detection information from the lane separation line detecting circuit  41  of the image processing device  4  (Steps S 2 - 1  and S 2 - 2 ). At the time when the lane separation line detection information is input, the travel speed detecting circuit  11   a  calculates one of an average value and a maximum value of the travel speeds of a plurality of preceding vehicles based on the relative speeds of the plurality of preceding vehicles received from the vehicle detecting circuit  42  of the image processing device  4  and the travel speed of the own vehicle input from the own vehicle  2  (Step S 2 - 3 ). For a single preceding vehicle, the relative speed of that vehicle assumes the calculation result. For no preceding vehicles, the relative speed is calculated as “0”. 
         [0037]    Next, the travel speed detecting circuit  11   a  notifies the maximum curvature estimating circuit  12  of the calculated travel speed (Step S 2 - 4 ). The maximum curvature estimating circuit  12  calculates the estimation value of the maximum curvature of the road based on the average speed or maximum speed of the preceding vehicles input immediately before that notification, and transmits the calculated estimation value to the curvature correcting circuit  13  (Step S 2 - 5 ). The curvature correcting circuit  13  then uses the maximum curvature to correct the curvature of the lane separation line input from the lane separation line detecting circuit  41  of the image processing device  4  (Step S 2 - 6 ), and outputs the corrected lane separation line detection information to the external lane departure prevention control device  5  (Step S 2 - 7 ). 
       &lt;Operation of Maximum Curvature Estimating Circuit  12 &gt; 
       [0038]    The maximum curvature estimating circuit  12  is configured to calculate the estimation value of the maximum curvature of the lane separation line based on the input average speed or maximum speed of the preceding vehicles. The maximum curvature estimating circuit  12  is configured to calculate the estimation value k of the maximum curvature based on Expression (1) mentioned in the first embodiment, and to transmit the calculated estimation value k to the curvature correcting circuit  13 . 
       &lt;Operation of Curvature Correcting Circuit  13 &gt; 
       [0039]    The curvature correcting circuit  13  is configured to calculate the corrected curvature L i  by correcting the curvature K 1  in the lane separation line detection information in accordance with Expression (3) based on the estimation value k of the maximum curvature calculated by the maximum curvature estimating circuit  12 , and to output lane separation line detection information containing the calculated curvature L i  to the external lane departure prevention control device  5 : 
         [0000]    
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           
                             L 
                             i 
                           
                           = 
                           
                             K 
                             i 
                           
                         
                       
                       
                         
                           ( 
                           
                             κ 
                             ≥ 
                             
                               K 
                               i 
                             
                           
                           ) 
                         
                       
                     
                     
                       
                         
                           
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                             i 
                           
                           = 
                           
                             
                               L 
                               
                                 i 
                                 - 
                                 1 
                               
                             
                             + 
                             
                               ( 
                               
                                 
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                                     i 
                                     - 
                                     1 
                                   
                                 
                                 - 
                                 
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                                     - 
                                     2 
                                   
                                 
                               
                               ) 
                             
                           
                         
                       
                       
                         
                           ( 
                           
                             κ 
                             &lt; 
                             
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                               i 
                             
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   Expression 
                    
                   
                       
                   
                    
                   
                     ( 
                     3 
                     ) 
                   
                 
               
             
           
         
       
     
         [0000]    where L i-1  represents the curvature of the lane separation line detection information corrected the previous time. 
       Third Embodiment 
     &lt;Configuration of Lane Separation Line Detection Correcting Device  1 &gt; 
       [0040]    The lane separation line detection correcting device  1  illustrated in  FIG. 5  according to a third embodiment of the present invention includes a speed limit detecting circuit  14 , the maximum curvature estimating circuit  12 , and the curvature correcting circuit  13 . The speed limit detecting circuit  14  is configured to detect a speed limit based on road sign/marking information from a road sign detecting circuit  43  of the image processing device  4 , which is configured to perform image processing by using an image taken by the camera  3 . The maximum curvature estimating circuit  12  is configured to estimate the maximum curvature of the road along which the own vehicle is traveling, based on the detected speed limit. The curvature correcting circuit  13  is configured to correct the curvature of the lane separation line obtained from the lane separation line detecting circuit  41  of the image processing device  4  such that the curvature of the lane separation line may be confined within the maximum curvature calculated by the maximum curvature estimating circuit  12 , and to output information on the lane separation line to the lane departure prevention control device  5 . The lane departure prevention control device  5  may also be a lane departure prevention warning device. 
       &lt;Operation of Lane Separation Line Detection Correcting Device  1 &gt; 
       [0041]    An operation flowchart of the lane separation line detection correcting device  1  is illustrated in  FIG. 6 . First, the lane separation line detection correcting device  1  waits for input of lane separation line detection information from the lane separation line detecting circuit  41  of the image processing device  4  (Steps S 3 - 1  and S 3 - 2 ). At the time when the lane separation line detection information is input, the speed limit detecting circuit  14  confirms whether or not, from among the road sign/marking information from the road sign detecting circuit  43  of the image processing device  4 , information on the speed limit is input even once previously (Steps S 3 - 3  and S 3 - 4 ). At the time when information on the speed limit is input even once previously, the maximum curvature estimating circuit  12  calculates the maximum curvature of the road along which the own vehicle is traveling or driving based on that speed limit (Step S 3 - 5 ). Next, the curvature correcting circuit  13  corrects the curvature in the lane separation line detection information such that the curvature may be confined within the maximum curvature (Step S 3 - 6 ). Finally, the curvature correcting circuit  13  outputs the corrected lane separation line detection information to the lane departure prevention control device  5  (Step S 3 - 7 ). On the other hand, in Step S 3 - 4 , when information on the speed limit has not been input even once previously, the curvature correcting circuit  13  outputs uncorrected lane separation line detection information to the lane departure prevention control device  5  (Step S 3 - 8 ). 
       &lt;Operation of Maximum Curvature Estimating Circuit  12 &gt; 
       [0042]    The maximum curvature estimating circuit  12  is configured to estimate the maximum curvature of the road based on speed limit information input from a road sign. In general, the speed limit is set to be lower than the design speed of the road. Therefore, the maximum curvature estimating circuit  12  is configured to look up and output the curvature from table data of the maximum curvature at the design speed for input speed limit each. For example, the road curvature with respect to the road design speed as indicated in the Road Structure Ordinance defined by the Japanese Ministry of Land, Infrastructure, Transport and Tourism shown in Table 1 may be applied as the table data. 
         [0000]    
       
         
               
             
               
               
             
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Maximum Curvature with Respect to Speed Limit 
               
             
          
           
               
                 Speed Limit [km/h] 
                   
               
               
                 (road design speed) 
                 Maximum Curvature [1/m] 
               
               
                   
               
             
          
           
               
                 120 
                 1/570 
               
               
                 100 
                 1/380 
               
               
                 80 
                 1/230 
               
               
                 60 
                 1/120 
               
               
                 50 
                 1/80 
               
               
                 40 
                 1/50 
               
               
                 30 
                 1/30 
               
               
                 20 
                 1/15 
               
               
                   
               
             
          
         
       
     
       &lt;Operation of Curvature Correcting Circuit  13 &gt; 
       [0043]    The curvature correcting circuit  13  is configured to calculate the corrected curvature L i  by correcting the curvature K i  in the lane separation line detection information in accordance with Expression (1) or Expression (2) based on the estimation value k of the maximum curvature calculated by the maximum curvature estimating circuit  12 . 
       Fourth Embodiment 
     &lt;Configuration of Lane Separation Line Detection Correcting Device  1 &gt; 
       [0044]    The lane separation line detection correcting device  1  illustrated in  FIG. 7  according to a fourth embodiment of the present invention includes the speed limit detecting circuit  14 , the maximum curvature estimating circuit  12 , and the curvature correcting circuit  13 . The speed limit detecting circuit  14  is configured to obtain from an external communication device  6 , e.g., a road-to-vehicle communication system, information on the speed limit of the road currently being traveled along. The maximum curvature estimating circuit  12  is configured to estimate the maximum curvature of the road along which the own vehicle is traveling based on the obtained speed limit. The curvature correcting circuit  13  is configured to correct the curvature of the lane separation line obtained from the lane separation line detecting circuit  41  of the image processing device  4 , which is configured to perform image processing with an image taken by the camera  3 , to be confined within the maximum curvature calculated by the maximum curvature estimating circuit  12 , and to output information on the lane separation line to the lane departure prevention control device  5 . The lane departure prevention control device  5  may also be a lane departure prevention warning device. 
       &lt;Operation of Lane Separation Line Detection Correcting Device  1 &gt; 
       [0045]    An operation flowchart of the lane separation line detection correcting device  1  is illustrated in  FIG. 8 . First, the lane separation line detection correcting device  1  waits for input of lane separation line detection information from the lane separation line detecting circuit  41  of the image processing device  4  (Steps S 4 - 1  and S 4 - 2 ). At the time when the lane separation line detection information is input, the speed limit detecting circuit  14  acquires the speed limit of the road along which the vehicle is currently traveling from the external communication device  6  (Step S 4 - 3 ). At the time when the speed limit is acquired, the maximum curvature estimating circuit  12  calculates the maximum curvature of the traveling road based on the speed limit (Step S 4 - 4 ). Next, the curvature correcting circuit  13  corrects the curvature in the lane separation line detection information such that the curvature may be confined within the maximum curvature (Step S 4 - 5 ). Finally, the curvature correcting circuit  13  outputs the corrected lane separation line detection information to the lane departure prevention control device  5  (Step S 4 - 6 ). 
         [0046]    It is to be noted that the operation of the maximum curvature estimating circuit  12  and the operation of the curvature correcting circuit  13  are the same as in the third embodiment. 
       Fifth Embodiment 
     &lt;Configuration of Lane Separation Line Detection Correcting Device  1 &gt; 
       [0047]    The lane separation line detection correcting device  1  illustrated in  FIG. 9  according to a fifth embodiment of the present invention includes a road curvature detecting circuit  12   a  and the curvature correcting circuit  13 . The road curvature detecting circuit  12   a  is configured to extract information on the road curvature from road sign information output from the road sign detecting circuit  43  of the image processing device  4 , which is configured to perform image processing by using an image taken by the camera  3 . The curvature correcting circuit  13  is configured to correct the curvature of the lane separation line obtained from the lane separation line detecting circuit  41  of the image processing device  4  to be confined within the curvature extracted by the road curvature detecting circuit  12   a,  and to output information on the lane separation line to the lane departure prevention control device  5 . The lane departure prevention control device  5  may also be a lane departure prevention warning device. 
       &lt;Operation of Lane Separation Line Detection Correcting Device  1 &gt; 
       [0048]    An operation flowchart of the lane separation line detection correcting device  1  is illustrated in  FIG. 10 . First, the lane separation line detection correcting device  1  waits for input of lane separation line detection information from the lane separation line detecting circuit  41  of the image processing device  4  (Steps S 5 - 1  and S 5 - 2 ). At the time when the lane separation line detection information is input, the road curvature detecting circuit  12   a  confirms whether or not information on a road curvature sign among the road sign/marking information from the road sign detecting circuit  43  of the image processing device  4 , is input even once previously (Steps S 5 - 3  and S 5 - 4 ). At the time when information on a road curvature sign is input even once previously, the road curvature detecting circuit  12   a  extracts the information on the road curvature sign, and outputs the extracted information to the curvature correcting circuit  13  (Step S 5 - 5 ). Next, the curvature correcting circuit  13  corrects the curvature in the lane separation line detection information so that the curvature may be confined within the maximum curvature (Step S 5 - 6 ). Finally, the curvature correcting circuit  13  outputs the corrected lane separation line detection information to the lane departure prevention control device  5  (Step S 5 - 7 ). On the other hand, in Step S 5 - 4 , when information on a road curvature sign has not been input even once previously, the curvature correcting circuit  13  outputs uncorrected lane separation line detection information to the lane departure prevention control device  5  (Step S 5 - 8 ). 
       Sixth Embodiment 
     &lt;Configuration of Lane Separation Line Detection Correcting Device  1 &gt; 
       [0049]    The lane separation line detection correcting device  1  illustrated in  FIG. 11A  according to a sixth embodiment of the present invention includes a preceding vehicle detecting circuit  15 , a maximum curvature estimating circuit  12   b,  and the curvature correcting circuit  13 . The preceding vehicle detecting circuit  15  is configured to acquire a position of a preceding vehicle (front-and-rear distance and right-and-left distance) from the vehicle detecting circuit  42  of the image processing device  4 , which is configured to perform image processing by using an image taken by the camera  3 . The maximum curvature estimating circuit  12   b  is configured to estimate the maximum curvature of the traveling road based on the position of the preceding vehicle. The curvature correcting circuit  13  is configured to correct the curvature of the lane separation line input from the lane separation line detecting circuit  41  of the image processing device  4  to be confined within the maximum curvature calculated by the maximum curvature estimating circuit  12   b,  and to output information on the lane separation line to the lane departure prevention control device  5 . The lane departure prevention control device  5  may also be a lane departure prevention warning device. 
       &lt;Operation of Lane Separation Line Detection Correcting Device  1 &gt; 
       [0050]    An operation flowchart of the lane separation line detection correcting device  1  is illustrated in  FIG. 12 . First, the lane separation line detection correcting device  1  waits for input of lane separation line detection information from the lane separation line detecting circuit  41  of the image processing device  4  (Steps S 6 - 1  and S 6 - 2 ). At the time when the lane separation line detection information is input, the preceding vehicle detecting circuit  15  confirms whether or not information on a preceding vehicle is currently being periodically input from the vehicle detecting circuit  42  of the image processing device  4  (Steps S 6 - 3  and S 6 - 4 ). At the time when information on a preceding vehicle is input, the preceding vehicle detecting circuit  15  then confirms based on the input lane separation line detection information input next, whether or not the traveling lane is a single lane (Step S 6 - 5 ). If it is determined that the position information on the preceding vehicle is not input, or that the traveling lane is not a single lane, this means that there is no preceding vehicles. In such a case, the curvature correcting circuit  13  outputs uncorrected lane separation line detection information (Step S 6 - 9 ). If it is determined that the traveling lane is a single lane, the maximum curvature estimating circuit  12   b  estimates the maximum curvature of the driving lane based on the position information on the preceding vehicle (Step S 6 - 6 ). If it is not the case, the processing is advanced to Step S 6 - 9 , and correction of the lane separation line detection information is not performed. Next, in Step S 6 - 7 , the curvature correcting circuit  13  corrects the curvature in the lane separation line detection information so that the curvature may be confined within the estimated maximum curvature. Finally, the curvature correcting circuit  13  outputs the corrected lane separation line detection information to the lane departure prevention control device  5  (Step S 6 - 8 ). 
         [0000]    &lt;Operation of Maximum Curvature Estimating Circuit  12   b&gt;   
         [0051]    The maximum curvature estimating circuit  12   b  is configured to estimate the maximum curvature of the driving lane based on preceding vehicle detection position information in which the input position of the own vehicle is made the original point. As illustrated in  FIG. 11B , the maximum curvature estimating circuit  12   b  is configured to calculate a curvature 1 −1  [l/m] by calculating a turning radius [m]=y/sin θ of a curve  1  based on a relation between the detected position input of a preceding vehicle  2   a  and the position of the own vehicle  2 . The calculated curvature 1 −1  [l/m] is output to the curvature correcting circuit  13  as the estimation value of the maximum curvature. 
       Seventh Embodiment 
     &lt;Configuration of Lane Separation Line Detection Correcting Device  1 &gt; 
       [0052]    The lane separation line detection correcting device  1  illustrated in  FIG. 13A  according to a seventh embodiment of the present invention includes a travel path track detecting circuit  16 , a maximum curvature estimating circuit  12   c,  and the curvature correcting circuit  13 . The travel path track detecting circuit  16  is configured to acquire range information on a travel path output from a travel path detecting circuit  44  of the image processing device  4 , which is configured to perform image processing with an image taken by the camera  3 . The maximum curvature estimating circuit  12   c  is configured to estimate the maximum curvature of the traveling lane based on the acquired range information on the travel path. The curvature correcting circuit  13  is configured to correct the curvature of the lane separation line obtained from the lane separation line detecting circuit  41  of the image processing device  4  to be confined within the maximum curvature calculated by the maximum curvature estimating circuit  12   c,  and to output information on the lane separation line to the lane departure prevention control device  5 . The lane departure prevention control device  5  may also be a lane departure prevention warning device. 
       &lt;Operation of Lane Separation Line Detection Correcting Device  1 &gt; 
       [0053]    An operation flowchart of the lane separation line detection correcting device  1  is illustrated in  FIG. 14 . First, the lane separation line detection correcting device  1  waits for input of lane separation line detection information from the travel path detecting circuit  44  of the image processing device  4  (Steps S 7 - 1  and S 7 - 2 ). At the time when the lane separation line detection information is input, the maximum curvature estimating circuit  12   c  inputs the range information on the travel path from the travel path detecting circuit  44  of the image processing device  4  via the travel path track detecting circuit  16 , and estimates the maximum curvature of the driving lane (Step S 7 - 3 ). Next, in Step S 7 - 4 , the curvature correcting circuit  13  corrects the curvature in the lane separation line detection information such that the curvature may be confined within the maximum curvature. Finally, the curvature correcting circuit  13  outputs the corrected lane separation line detection information to the lane departure prevention control device  5  (Step S 7 - 5 ). 
         [0000]    &lt;Operation of Maximum Curvature Estimating Circuit  12   c&gt;   
         [0054]    The maximum curvature estimating circuit  12   c  is configured to estimate the maximum curvature of the driving lane based on the input range information on the travel path. As illustrated in  FIG. 13B , the maximum curvature estimating circuit  12   c  is configured to extract, from a travel path range A detected, a plurality of coordinate points P 1  that lie in the center of the width of the road, and to calculate a curvature 1 −1  [l/m] of a curve with the least square error distance from those coordinate points P 1  by using least square method. This calculated curvature 1 −1  [l/m] is output to the curvature correcting circuit  13  as the maximum curvature. 
       Eighth Embodiment 
       [0055]    The lane separation line detection correcting device  1  illustrated in  FIG. 15A  according to an eighth embodiment of the present invention includes the travel path track detecting circuit  16 , the maximum curvature estimating circuit  12   c , and the curvature correcting circuit  13 . The travel path track detecting circuit  16  is configured to acquire position information on road edges output from a road edge detecting circuit  81  of a data processing device  8 , which is configured to process detection data, such as millimeter wave radar data and laser radar data. The maximum curvature estimating circuit  12   c  is configured to estimate the maximum curvature of the traveling lane. The curvature correcting circuit  13  is configured to correct the curvature of the lane separation line obtained from the lane separation line detecting circuit  41  of the image processing device  4  to be confined within the maximum curvature calculated by the maximum curvature estimating circuit  12   c,  and to output information on the lane separation line to the lane departure prevention control device  5 . The lane departure prevention control device  5  may also be a lane departure prevention warning device. 
       &lt;Operation of Lane Separation Line Detection Correcting Device  1 &gt; 
       [0056]    An operation flowchart of the lane separation line detection correcting device  1  is illustrated in  FIG. 16 . First, the lane separation line detection correcting device  1  waits for input of lane separation line detection information from the lane separation line detecting circuit  41  of the image processing device  4  (Steps S 8 - 1  and S 8 - 2 ). At the time when the lane separation line detection information is input, the maximum curvature estimating circuit  12   c  inputs via the travel path track detecting circuit  16  the position information on the road edges input from the road edge detecting circuit  81  of the image processing device  4 , and estimates the maximum curvature of the driving lane (Step S 8 - 3 ). Next, in Step S 8 - 4 , the curvature correcting circuit  13  corrects the curvature in the lane separation line detection information so that the curvature may be confined within the maximum curvature, and outputs the corrected lane separation line detection information to the lane departure prevention control device  5  (Step S 8 - 5 ). 
         [0000]    &lt;Operation of Maximum Curvature Estimating Circuit  12   c&gt;   
         [0057]    The maximum curvature estimating circuit  12   c  is configured to estimate the maximum curvature of the driving lane based on the input position information on the road edges. As illustrated in  FIG. 15B , the maximum curvature estimating circuit  12   c  is configured to extract from the position of road edges B a plurality of coordinate points P 2  that lie in the center between both road edges, and to calculate a curvature 1 −1  [l/m] of a curve with the least square error distance from those coordinate points P 2  by using least square method. The calculated curvature 1 −1  [l/m] is output to the curvature correcting circuit  13  as the maximum curvature. 
       Ninth Embodiment 
     &lt;Configuration of Automatic Driving System&gt; 
       [0058]    In an automatic driving system according to a ninth embodiment of the present invention, the lane separation line detection correcting device  1  described in the first to eighth embodiments is mounted as it is. The automatic driving system includes a control unit configured to control the travel of the own vehicle  2  based on the curvature of the lane separation line corrected by the curvature correcting circuit  13  of the lane separation line detection correcting device  1 . 
       &lt;Operation of Lane Separation Line Detection Correcting Device  1 &gt; 
       [0059]    Operation of the lane separation line detection correcting device  1  is the same as that of the lane separation line detection correcting devices  1  described in the first to eighth embodiments. 
         [0060]    The control unit is configured to control the travel of the own vehicle  2  based on the curvature of the lane separation line corrected by the curvature correcting circuit  13  of the lane separation line detection correcting device  1 . 
       &lt;Modified Examples of Various Embodiments&gt; 
       [0061]    The curvature correcting circuit  13  of the first to ninth embodiments may be configured to preliminarily store a plurality of maximum curvatures from the maximum curvature estimating circuits  12 ,  12   b,  and  12   c  or from the road curvature detecting circuit  12   a,  and to perform, when the curvature in the input lane separation line detection information exceeds the maximum curvature determined last, correction by using the latest maximum curvature that does not exceed the above maximum curvature among the stored maximum curvatures. 
         [0062]    The curvature correcting circuit  13  may also be configured to store a plurality of maximum curvatures from the maximum curvature estimating circuits  12 ,  12   b,  and  12   c  or from the road curvature detecting circuit  12   a,  and to perform, when the curvature in the input lane separation line detection information exceeds the maximum curvature determined last, correction by calculating, in accordance with Expression (3), the maximum curvature at the current point among the plurality of maximum curvatures stored based on a change amount in the maximum curvature obtained from a difference among the maximum curvatures stored.