Patent Publication Number: US-11396288-B2

Title: Parking assistance device

Description:
TECHNICAL FIELD 
     The present invention relates to a parking assistance device. 
     BACKGROUND ART 
     There is a parking assistance device that automatically parks a vehicle at a target parking position by automatic steering. This parking assistance device recognizes the surrounding area of the vehicle by an external environment recognition device, geometrically calculates a route and a steering angle from a parking start position to the target parking position, and generates a parking route. The driver performs the automatic parking without steering operation. As such a parking assistance device, PTL 1 discloses a technique of performing more accurate parking assistance as the target parking position is approached. 
     CITATION LIST 
     Patent Literature 
     PTL 1: JP 2017-30567 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     In a general automatic parking, a route from a parking start position to a target parking position is calculated prior to the start of parking. However, there are cases where an external environment recognition device cannot detect an obstacle at a distant or blind spot. In such a case, smooth parking is hindered when the vehicle is actually automatically parked. 
     Solution to Problem 
     A parking assistance device according to the invention includes a candidate route calculation unit that generates a candidate route from a current position of a vehicle to a target parking position based on a drivable area of the vehicle that is recognized based on external environment information, a turning position calculation unit that provides a turning position at a predetermined position on the candidate route generated by the candidate route calculation unit, and a preliminary route calculation unit that generates a preliminary route from the turning position to the target parking position. The candidate route in which the preliminary route can be generated by the preliminary route calculation unit is set to a parking route of automatic parking. 
     Advantageous Effects of Invention 
     According to the invention, it is possible to make automatic parking smoothly. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram for explaining general automatic parking. 
         FIG. 2  is a diagram for explaining general automatic parking. 
         FIG. 3  is a diagram illustrating a configuration of a vehicle with a parking assistance device mounted thereon. 
         FIG. 4  is a block diagram illustrating a configuration of a vehicle control device. 
         FIG. 5  is a block diagram illustrating a configuration of a route generation unit. 
         FIG. 6  is a flowchart illustrating a processing procedure of a candidate route calculation unit. 
         FIG. 7  is a diagram for explaining a delivery route. 
         FIG. 8  is a diagram illustrating one-side steering connection. 
         FIG. 9  is a diagram illustrating S-shaped steering connection. 
         FIG. 10  is a diagram for explaining a backward route. 
         FIG. 11  is a flowchart illustrating a processing procedure of preliminary route generation. 
         FIG. 12  is a diagram illustrating a parking route and a turning position. 
         FIG. 13  is a diagram illustrating the parking route and the turning position of a modification. 
         FIG. 14  is a block diagram illustrating a configuration of a route generation unit in a second embodiment. 
         FIG. 15  is a flowchart illustrating a processing procedure of a preliminary route generation in the second embodiment. 
         FIG. 16  is a diagram illustrating a display example of an input/output device in the second embodiment. 
         FIG. 17  is a block diagram illustrating a configuration of a vehicle control device in a third embodiment. 
         FIG. 18  is a flowchart illustrating a processing procedure of an automatic parking stop/interruption determination unit in the third embodiment. 
         FIG. 19  is a diagram illustrating a parking route in the automatic parking stop/interruption determination unit in the third embodiment. 
         FIG. 20  is a diagram illustrating a parking route in a modification. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     Prior to the description of the embodiment, a general automatic parking will be described with reference to  FIGS. 1 and 2 . 
     As illustrated in  FIG. 1 , based on an external environment recognition device such as a camera or an ultrasonic sensor installed in a vehicle  101 , an area  104  (indicated by hatching in the diagram) in which the vehicle  101  can travel is calculated at a parking start position based on position information  103  of an obstacle  102  such as a parked vehicle. Next, a parking route  105  (dotted line) to a target parking position  106  is calculated based on the calculated drivable area  104 . When the route search is successful, the movement control of the vehicle  101  is performed according to the parking route  105 . 
     However, as illustrated in  FIG. 2( a ) , the route may not be detected at the parking start position with respect to an obstacle  202  that is out of the area  104 . In such a case, as illustrated in  FIG. 2( b ) , when the vehicle  101  is moved to a point where the obstacle  202  can be detected, it is necessary to correct a parking route such as a turning route from that position. At that time, when the movable space of the vehicle  101  is narrow, the correction amount is limited, the vehicle cannot move backward in a large turn to avoid a collision, a correction route  203  is inflated, or parking is stalled. Therefore, parking is not made smoothly. In this embodiment, as described below, such a situation does not occur, and smooth parking is possible. 
       FIG. 3  is a diagram illustrating a configuration of a vehicle  300  with a parking assistance device according to an embodiment of the invention mounted. 
     The vehicle  300  includes a driving force generation mechanism  310  that is a power source, a brake  311  that brakes the vehicle  300 , and a transmission  312  that has a gear for switching the driving force generated by the driving force generation mechanism  310  to move forward and backward. The driving force generated by the driving force generation mechanism  310  rotates left and right wheels  314  via the transmission  312 , thereby causing the vehicle  300  to travel. Further, a braking force is generated and the vehicle  300  is decelerated by controlling the brake  311 . Here, the driving force generation mechanism  310  may be an engine, a hybrid mechanism of an engine and a motor, or a motor alone. 
     The vehicle  300  is equipped with a steering  313 . When the steering  313  is turned, the direction of the wheels  314  is changed, and the vehicle  300  turns. 
     A driving force control device  320  controls the driving force generated by the driving force generation mechanism  310 . A brake control device  321  controls the brake  311  so that a predetermined braking force is generated. In the case of automatic parking, a steering control device  322  controls the steering  313  so that a predetermined wheel angle is obtained even if the driver does not operate the steering  313 . A transmission control device  323  controls the transmission  312  to switch forward and backward movements of the vehicle  300 . Further, the vehicle  300  is provided with an external environment recognition device  325  that acquires external environment information around the vehicle  300  and recognizes a drivable area of the vehicle  300  based on the external environment information, and a vehicle speed sensor  326  that acquires speed information of the vehicle  300 . The external environment recognition device  325  is configured by cameras which are installed on the front and rear sides and the right and left side surfaces of the vehicle  300  to acquire, for example, captured images around the vehicle  300  as external environment information, and a sonar which acquires distance information to an obstacle around the vehicle  300  as external environment information. 
     Further, the vehicle speed sensor  326  that acquires the speed information of the vehicle  300  is not limited to wheel speed pulse information, and the speed information may be indirectly calculated using a resolver rotation speed sensor of the motor, a rotation speed sensor of the transmission  312 , or the like. 
     A vehicle control device  324  transmits a command value to the driving force control device  320 , the brake control device  321 , the steering control device  322 , and the transmission control device  323  based on the information of an external environment recognition device  325  and the vehicle speed sensor  326 . Further, an input/output device  328  for inputting/outputting input information from the driver and output information to the driver is provided for the information related to the automatic parking. Specifically, the input information includes the determination of a parking position, the start of automatic parking, etc., and the output information includes a bird&#39;s-eye view that combines a parking frame, route information, a turning position, and an image of the surroundings of the vehicle during automatic parking. 
     Hereinafter, details of the vehicle control device  324  which is an application of the parking assistance device according to an embodiment of the invention will be described.  FIG. 4  is a block diagram illustrating a configuration of the vehicle control device  324 . 
     The vehicle control device  324  includes a parking target candidate presentation unit  401 , a self-position estimation unit  402 , a route generation unit  403 , a target steering angle calculation unit  404 , a target vehicle speed calculation unit  405 , a target braking/driving force calculation unit  406 , and a forward/backward switching determination unit  407 . 
     The parking target candidate presentation unit  401  calculates a parking space based on the position of the obstacle, the position of the white line, and the like obtained from the external environment recognition device  325 , and presents it to the driver as a parking target candidate. Specifically, the parking target candidate is displayed on a screen of a navigation system or the like of the input/output device  328 , and the driver selects a parking target position to park from the parking target candidates. 
     When the automatic parking is started, the self-position estimation unit  402  calculates the self-position of the vehicle  300 , specifically, the coordinates and the drive distance, and the like based on the vehicle speed information acquired from the vehicle speed sensor  326  and the steering angle information acquired from the steering  313 . 
     The route generation unit  403  calculates a route that can be moved from the parking start position to the parking target position without hitting an obstacle or the like based on the parking target position and the position of the obstacle. When the route can be generated, the curvature information and the turning position with respect to the drive distance are output. Further, when it is determined that the height of the detected step is a height that can be overcome, it is not recognized as an obstacle, and when it is determined that the step cannot be overcome, it is recognized as an obstacle. 
     The target steering angle calculation unit  404  calculates a target steering angle based on the curvature information for the drive distance, which is the output result of the route generation unit  403 , and transmits it to the steering control device  322 . Here, the target steering angle is not limited to the output result of the route generation unit  403 , and the target steering angle may be used in which the correction value of the steering amount when the relative relationship with the parking frame and the obstacle is deviated during the automatic parking. 
     The target vehicle speed calculation unit  405  determines a target vehicle speed in the actual drive control based on the magnitude of the curvature and the position of the obstacle, which are the output results of the route generation unit  403 . At this time, when the target vehicle speed during drive control changes, smooth acceleration and deceleration are realized by correcting the target vehicle speed in consideration of an acceleration and also an acceleration increasing rate. Here, after the automatic parking is started, when the external environment recognition device  325  detects a step or a wheel clasp on the parking route, the target vehicle speed is reduced. As a result, the vehicle can be parked without giving an unpleasant shock to the driver at the time of a step or a wheel-clamping collision. 
     The target braking/driving force calculation unit  406  calculates the required braking/driving force based on the difference between the target vehicle speed and the vehicle speed information. At this time, when the braking force is generated, the braking torque is transmitted to the brake control device  321 , and when the driving force is generated, the driving torque is transmitted to a driving force control device  120 . Here, when the external environment recognition device  325  detects a slope, a step, or the like, the driving force corrected. Specifically, the driving force is corrected to increase when the slope is upward, and the driving force is corrected to decrease when the slope is downward. When a step is detected, the higher the step, the larger the driving force. As a result, the ability to follow the target vehicle speed can be improved. 
     The forward/backward switching determination unit  407  transmits the forward/backward switching to the transmission control device  323  based on the forward/backward switching information that the output result of the route generation unit  403 . 
       FIG. 5  is a block diagram illustrating a configuration of the route generation unit  403 . As illustrated in  FIG. 5 , the route generation unit  403  includes a candidate route calculation unit  501 , a turning position calculation unit  502 , a preliminary route calculation unit  503 , and a candidate route adoption determination unit  504 . 
     The candidate route calculation unit  501  calculates a movable candidate route from the parking start position to the target parking position without colliding with the obstacle based on the position information of the obstacle recognized at the parking start position. A specific process of the candidate route calculation unit  501  will be described later with reference to  FIG. 6 . 
     As will be described later with reference to  FIG. 11 , the turning position calculation unit  502  sets the turning position at a predetermined position on the candidate route output by the candidate route calculation unit  501 . 
     The preliminary route calculation unit  503  calculates a route (preliminary route) when the vehicle is turned back at the set turning position. 
     The candidate route adoption determination unit  504  determines whether the preliminary route can be generated and outputs either the candidate route or the preliminary route. 
       FIG. 6  is a flowchart of the candidate route calculation unit  501 . Further, the program illustrated in this flowchart and the program illustrated in the flowchart described later can be executed by a computer including a CPU, a memory, and the like. The whole process or a part of the process may be realized by a hardware logic circuit. Further, this program can be stored in a storage medium of the vehicle control device  324  in advance and provided. Alternatively, the program may be stored and provided in an independent recording medium, or the program may be recorded and stored in the storage medium of the vehicle control device  324  through a network line. It may be provided as various forms of computer-readable computer program products such as data signals (carrier waves). 
     The processing procedure of the candidate route calculation unit  501  will be described with reference to  FIG. 6 . 
     In Step S 601 , reference vehicle speed pattern calculation is performed. First, a reference vehicle speed pattern Vbase for traveling on a route is calculated. Specifically, with reference to an upper limit vehicle speed Vmax with respect to the parking space, the vehicle speed is divided at predetermined intervals Vd, and the reference vehicle speed pattern Vbase is generated as illustrated in the following Expression (1).
 
[Math. 1]
 
 V   base =[ V   max   ,V   max   −V   d   ,V   max −2 V   d , . . . ]  (1)
 
     The upper limit of the speed set for the parking space is as follows in this embodiment. The upper limit vehicle speed Vmax is set smaller as a road width becomes narrower. Further, as the distance to the obstacle becomes shorter, the upper limit vehicle speed Vmax is set smaller. Specifically, the candidate route calculation unit  501  sets the reference vehicle speed smaller as the road width becomes narrower or as the distance to the obstacle becomes shorter. For example, if the road width is 10 m, the upper limit vehicle speed Vmax is set, and if it is 6 m, Vmax−2Vd is set. Alternatively, if the distance to the obstacle is 3 m, the upper limit vehicle speed Vmax is set, and if it is 0.5 m, Vmax−3Vd is set. As a result, the speed can be slowed down when the road is narrow or the distance to the obstacle is short, and the driver&#39;s fear can be alleviated. 
     Further, by setting the upper limit vehicle speed Vmax in the backward direction to be smaller than the forward direction, it is possible to slow down the backward speed, which is difficult for the driver to confirm, and to alleviate the driver&#39;s fear. 
     Further, even with the same curvature, the lateral acceleration increases as the vehicle speed increases, so the reference vehicle speed is set smaller as the curvature increases. This improves the drivability without giving an excessive lateral acceleration to the driver. 
     Furthermore, the speed is reduced in an environment in which it is difficult for the driver to visually recognize the surrounding situations of the vehicle. Specifically, the speed is set low based on the information from the illuminance sensor or the external environment recognition device  325  when a dark surrounding environment is detected, or when a wiper signal or raindrops is detected by the external environment recognition device  325 . The driver&#39;s fear can be suppressed by reducing the speed in a situation where it is difficult for the driver to recognize the surrounding situation. 
     In Step S 602 , the reference vehicle speed used in the automatic parking control calculation is selected. Specifically, one of the reference vehicle speed patterns that has not been subjected to a route generation process is selected, and the candidate route generation process illustrated in and after Step S 603  is executed based on the reference vehicle speed. For example, in a case where a first upper limit vehicle speed set based on the road width, a second upper limit vehicle speed set based on the distance to the obstacle, a third upper limit vehicle speed set based on the curvature of the route, and a fourth upper limit vehicle speed set based on the brightness of the surrounding environment are set, the route generation process is performed using the first to fourth upper limit vehicle speeds. Therefore, Vmax of the reference vehicle speed pattern is the upper limit vehicle speed determined by the surrounding environment. Then, with the upper limit vehicle speed Vmax as a reference, the reference vehicle speed at the time of calculating the candidate route is changed as Vmax−Vd, Vmax−2×Vd, and so on. 
     For example, the route generation process can be performed with two reference vehicle speeds of Vmax−Vd and Vmax−2×Vd, or with three reference vehicle speeds of Vmax, Vmax−Vd, and Vmax−2×Vd. 
     In Step S 603 , the delivery route is calculated.  FIG. 7  is a diagram for explaining a delivery route. 
       FIG. 7  illustrates routes  704  to  707  capable of leaving the vehicle without being brought into contact with an obstacle  703  on the left and right (such as a parked vehicle) from the state where the vehicle is accurately placed in a parking frame  702 . 
     Here, in order to shorten the route length, it is desirable to sequentially calculate the delivery route based on a minimum turning radius at the time of turning, but the radius of the delivery route may be calculated by increasing the turning radius. 
     Furthermore, the radius at the time of turning may be increased as the road width in front of the parking frame  702  is wider. As a result, when the parking space is large, the vehicle turns gently and the drivability is improved. 
     In Step S 603 , the delivery route is calculated until a predetermined ending condition is satisfied. Here, the delivery route is calculated until at least one of the ending conditions such as a condition that the direction of the vehicle after leaving is perpendicular to the parking orientation of the parking frame  702 , parallel to the aisle orientation, and the same direction as the direction of the vehicle at the parking start position  701 , or a condition that the left vehicle arrives at a point away from the parking frame  702  by a predetermined distance Wth. 
     Next, the process proceeds to Step S 604  to generate a connection route by one-sided steering. 
     Specifically, it is determined whether it is possible to connect by the one-sided steering to a delivery completion position  707  of the vehicle that has moved along the delivery route from the parking start position  701  illustrated in  FIG. 7 , and if the connection is possible, the route information is stored. Here, the one-sided steering is an operation (one-sided steering) of turning the steering  313  of the host vehicle to only one of the left and right sides. The connectable route information means a route that the vehicle can move from the parking start position  701  to the delivery completion position  707  by the one-sided steering without interfering with an obstacle. 
       FIG. 8  is a diagram illustrating a one-sided steering connection. As illustrated in  FIG. 8 , in order to generate a route from one-side steering (entry preparation route) from the parking start position A to an arrival target position T, the following calculation processes (1) to (3) are executed. 
     (1) An intersection X of an axis L 1  of the vehicle at the parking start position A and an axis L 2  of the vehicle at the arrival target position T is obtained. 
     (2) Then, a distance Ls between the intersection X and the parking start position A and a distance Le between the intersection X and the arrival target position T are calculated, and the shorter one is selected. 
     (3) in the example illustrated in  FIG. 8 , the distance Le is selected. Then, a circle C having two axes L 1  and L 2  as common tangents is drawn. A radius R of the circle C at that time is calculated by the following Expression (2). 
     
       
         
           
             
               
                 
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     In this way, the straight line and the circular arc are combined to generate the route from the parking start position A to the arrival target position T. Here, the connection by the one-sided steering is not limited to a straight line and a circular arc, and a route may be generated using a relaxation curve such as clothoid. 
     The delivery route obtained by the calculation of the delivery route in Step S 603  and the entry preparation route obtained by the generation of the connection route by the one-side steering in Step S 604  are combined and stored in the memory as a first parking route. 
     In Step S 605 , a process of generating a connection route by S-shaped steering is executed. In this Step S 605 , it is determined whether connection is possible by the S-shaped steering from the parking start position  701  illustrated in  FIG. 7  to the delivery completion position  707  calculated on the delivery route, and if connection is possible, the route information is stored. 
       FIG. 9  is a diagram illustrating an S-shaped steering connection. As illustrated in  FIG. 9 , in order to generate an S-shaped steering route from the parking start position A to the arrival target position T, a radius for drawing an S-shape is calculated. Here, the calculation can be facilitated by setting the turning radius of the S-shaped steering to the same radius R, but the connection route by the S-shaped steering may be generated using different radii. By setting different radii, the degree of freedom of the route by the S-shaped steering increases and it becomes easier to reach. Here, the case of the same radius R will be described. The coordinates of the parking start position A are A(0, 0), the coordinates of the reaching target position T are T(Xe, Ye), and the angle with respect to the reaching target position T, that is, the angle e indicating the direction of the vehicle at the arrival target position T when the direction of the vehicle at the parking start position A is 0. In this case, the radius R of the common circle is obtained by the center coordinates C 1  and C 2  of the respective circles, and therefore the following Expression (3) is established from the distance between the center coordinates. Then, R is obtained by the following Expression (4). 
     
       
         
           
             
               
                 
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     The calculated turning radius R is used to generate a connection route for the S-shaped steering. Here, the S-shaped connection is not limited to a circular arc, and a route may be generated using a smoothing curve such as clothoid. 
     In this way, not only the one-sided steering but also the S-shaped steering is used to generate the connection route, so that the degree of freedom is increased and the connection route is easily generated. 
     The delivery route obtained by the calculation of the delivery route in Step S 603  and the entry preparation route obtained by the generation of the connection route by the S-shaped steering in Step S 605  are combined and stored in the memory as a second parking route. 
     Next, the process proceeds to Step S 606  to determine the end of the route generation process by starting the backward movement. In this Step S 606 , if the generation process by the backward movement start is not executed, the process proceeds to the route generation by the backward movement start in Step S 607 , and if the generation process by the backward movement start has been already executed, the process proceeds to Step S 608  to determine the end of the route generation by the total reference vehicle speed pattern. 
     In Step S 607 , the route is generated by the backward movement start.  FIG. 10  is a diagram illustrating route generation by the backward movement start. As illustrated in  FIG. 10 , when the own vehicle position  1001  at the start of parking passes through the parking frame, it is difficult to connect with the routes  704  to  708  capable of leaving by the one-side steering and S-shaped steering, and as indicated by the connection route  1002 , the vehicle can be connected only to the route  708  capable of leaving the parking frame  702 , which gives the driver a feeling of discomfort. Therefore, as illustrated by the backward route  1003 , a connection route from an own vehicle position  1004  that has been retracted by a predetermined amount to the routes  704  to  708  capable of leaving the vehicle is searched. As a result, the parking route can be made compact and the driver&#39;s discomfort can be reduced. 
     Here, the backward position is within a predetermined value from the lateral obstacle  703 , or a vehicle front position of the own vehicle is on the right side of the lateral obstacle  703 . This reduces the driver&#39;s discomfort due to the backward movement. 
     Furthermore, when the own vehicle position  1001  at the start of parking is not parallel to the road, the vehicle angle is adjusted when moving backward so that it is parallel to the road. As a result, the next time when the vehicle moves forward, it will be easier to successfully search for a connection route to the routes  704  to  708  that can leave. 
     In Step S 607 , when the connection route by the one-sided steering in Step S 604 , and the connection route by the S-shaped steering in Step S 605  are successfully generated after generating a backward route for retracting the vehicle from the own vehicle position  1001  at the start of parking to the own vehicle position  1004 , a route obtained by combining the first parking route and the backward route including the entry preparation route by one-side steering and a route obtained by combining the second parking route and the backward route including the entry preparation route by the S-shaped steering are stored in the memory as a first candidate route and a second candidate route, respectively. 
     In Step S 608 , it is determined whether to finish the route generation based on all the reference vehicle speed patterns. In this Step S 608 , if the route generation for each reference vehicle speed is completed, the generation of the candidate route is ended, and if not completed, the process turns back to Step S 602 . 
     The candidate route calculation unit  501  executes the process of the flowchart illustrated in  FIG. 6  as described above to generate a plurality of candidate routes. Thereby, the candidate route calculation using the entry preparation route by the one-sided steering and the entry preparation route by the S-shaped steering is performed, and it is possible to calculate an automatic parking method in which a plurality of parking patterns based on the plurality of route shapes, that is, the reference vehicle speed is the same and the route shape is different. 
       FIG. 11  is a flowchart illustrating a processing procedure for generating a preliminary route, which is a process performed by the turning position calculation unit  502 , the preliminary route calculation unit  503 , and the candidate route adoption determination unit  504 . 
     In Step S 1101 , the candidate routes generated by the candidate route calculation unit  501  are read. In next Step S 1102 , the turning position calculation unit  502  sets the turning position to a predetermined position on the parking route. The setting of the turning position will be described with reference to  FIG. 12 . 
       FIG. 12  is a diagram illustrating a parking route and a turning position. Based on the external environment recognition device  325  installed in a vehicle  101 , an area  1202  (indicated by hatching in the diagram) in which the vehicle  101  can travel is calculated at a parking start position  1201  based on position information  103  of an obstacle  102  such as a parked vehicle. Next, a parking route  1205  (dotted line) to a target parking position  1207  is calculated based on the calculated drivable area  1202 . The turning position calculation unit  502  virtually moves the vehicle from the parking start position  1201  toward a turning point  1203 , and calculates a turning position  1206  on the parking route  1205 . 
     As the turning position  1206 , at least one or more positions are set between the turning point  1203  of the parking route  1205  and the boundary of the area  1202 , where the vehicle can drive, detected at the parking start position  1201  by the external environment recognition device  325 . It is guaranteed that there is no obstacle even from the parking start position  1201  up to the drivable area  1202  detected by the external environment recognition device  325 . However, this is because the vehicle may need to turn back while driving on a route exceeding the area  1202  without detecting an obstacle away from this area  1202 . As an example, it is assumed that the vehicle has moved on the parking route  1205 , and when a part of the vehicle is at a position  1204  outside the area  1202 , the position at that time is set as the turning position  1206 . 
     In Step S 1103  of FIG. , the preliminary route calculation unit  503  calculates a preliminary route when the vehicle turns back at the turning position  1206 . As a specific processing content, a backward movement start process (Step S 607 ) similar to that illustrated in  FIG. 6  is performed with the turning position  1206  as an initial position. When a route can be generated by the backward movement start process, a connection route generation by the one-side steering (Step S 604 ) and a connection route generation by the S-shaped steering (Step S 605 ) are performed from the retracted position, and the connection route with the delivery route is calculated, so that the route to the target parking position  1207  is calculated. 
     In the next Step S 1104 , the candidate route adoption determination unit  504  determines whether a preliminary route can be generated. In the candidate route adoption determination unit  504 , when the calculated preliminary route satisfies a predetermined condition, the candidate route calculated by the candidate route calculation unit  501  is adopted as a parking route for automatic parking. If not satisfying, it is considered that the route generation has failed. Here, as an example of the case where the predetermined condition is satisfied, a preliminary route can be generated from the turning position to the target parking position. An example of a case where the predetermined condition is not satisfied is a route that the vehicle moves backward from the parking start position  1201  by the preliminary route and leaves the target parking position. This is because the driver feels uncomfortable if a route passes through a position retracted from the position instructed to start parking. 
     If a preliminary route can be generated in Step S 1104 , the process advances to Step S 1105  to start automatic parking alone the initial parking route  1205 . If it is not possible to generate a preliminary route in Step S 1104 , this parking route  1205  is not adopted and the process illustrated in  FIG. 11  is repeated to read the next candidate route generated by the candidate route calculation unit  501  in Step S 1101  so as to obtain a candidate route that can generate a preliminary route. With such a candidate route, even if there is an obstacle slightly ahead of the outside of the detection area of the external environment recognition device  325 , it is possible to park on the preliminary route without being stuck, so smooth automatic parking is possible. 
     The turning position  1206  is not limited to the position  1204  where a part of the vehicle is outside the detection area of the external environment recognition device  325 , and in addition, the turning position may be set to a position determined that the distance accuracy of the external environment information acquired by the external environment recognition device  325  is low. This is because if the automatic parking is started with a poor accuracy in distance to an obstacle detected based on the external environment information in the parking start position  1201 , and there is an obstacle closer to the assumed position when approaching the obstacle, the parking route may not be recalculated. Therefore, if it is determined that the distance accuracy of the external environment information acquired by the external environment recognition device  325  is low, the turning position  1206  is provided. Therefore, it is possible to suppress a failure in recalculation of the parking route. 
       FIG. 13  is a diagram illustrating a parking route and a turning position, illustrating a modification. Based on the external environment recognition device  325  installed in a vehicle  101 , an area  1308  (indicated by hatching in the diagram) in which the vehicle  101  can travel is calculated at a parking start position  1301  based on position information  103  of an obstacle  102  such as a parked vehicle. Next, a parking route  1305  (dotted line) to a target parking position  1307  is calculated based on the calculated drivable area  1308 . The final turning point  1306  of the vehicle on the parking route  1305  is at the position illustrated in  FIG. 13 . The turning position calculation unit  502  provides turning positions  1302 ,  1303 , and  1304  on the parking route  1305  from the parking start position  1301  to the turning point  1306  at predetermined intervals, and when the vehicle turns at each of the turning positions  1302 ,  1303 , and  1304 , it is calculated whether a preliminary route to the target parking position  1307  can be generated. By turning, it is determined whether each position is the position  1302  (white circle) or  1304  (white circle) where the preliminary route can be generated and the position  1303  (black circle) where the preliminary route cannot be generated, and the position  1304  which is closest to the turning point  1306  and can generate the preliminary route is set as the turning position. Accordingly, in the parking route  1305 , the reliability of the automatic parking can be improved by previously grasping the position where the preliminary route due to the turning back cannot be generated. 
     In addition, when passing the vicinity of the turning position  1303  where the preliminary route cannot be generated, or the position deeper than the turning position  1304 , the vehicle  101  may suppress the speed of the vehicle  101  from being lowered compared to a case where the vehicle passes the position before the turning position  1304 . When the vehicle speed of the vehicle  101  is high, the vehicle passes through the turning positions  1302  and  1304  at a high speed, so when the external environment recognition device  325  detects a new obstacle, the braking distance increases and the vehicle  101  advances to the turning position  1303  where a route cannot be generated. Thus, there is also the possibility of stopping. 
     Therefore, when driving near the turning position  1304  where there is a possibility that the preliminary route cannot be generated and at the back of the turning position  1304 , the speed is lowered compared to a time when driving at the front turning position  1302 . As a result, the braking distance is shortened, the vehicle can be stopped before reaching a point where a route cannot be generated, and the reliability of automatic parking is improved. 
     Second Embodiment 
     Hereinafter, a second embodiment of the invention will be described with reference to  FIGS. 14 to 16 . The diagram illustrating the configuration of the vehicle equipped with the parking assistance device of  FIG. 3  and the block diagram illustrating the configuration of the vehicle control device of  FIG. 4  described in the first embodiment are the same in the second embodiment. The second embodiment is different in the configuration of the route generation unit  403  illustrated in the first embodiment. 
       FIG. 14  is a block diagram illustrating the configuration of the route generation unit  1403  in the second embodiment. As illustrated in  FIG. 14 , a route generation unit  1403  includes a candidate route calculation unit  501 , a turning position calculation unit  502 , a preliminary route calculation unit  503 , a route selection unit  1401 , and a second candidate route calculation unit  1402 . 
     For the candidate route output by the candidate route calculation unit  501 , as described in the first embodiment, the preliminary route calculation unit  503  calculates the preliminary route based on the turning position calculated by the turning position calculation unit  502 . 
       FIG. 15  is a flowchart illustrating a processing procedure for generating a preliminary route, which is processed by the candidate route calculation unit  501 , the turning position calculation unit  502 , the preliminary route calculation unit  503 , the route selection unit  1401 , and the second candidate route calculation unit  1402 . 
     In Step S 1501 , the candidate route calculation unit  501  calculates a candidate route by making maximum use of the empty space, and sets this as the candidate route  1 . The calculation of the candidate route by the candidate route calculation unit  501  is the same as in the first embodiment. 
     Next, in Step S 1502 , the generated candidate route  1  is read. Then, in Step S 1503 , turning position calculation unit  502  sets the turning position at a predetermined position on the parking route. Next, in Step S 1504 , the preliminary route calculation unit  503  calculates a preliminary route when the vehicle turns back at the turning position. The processes of Steps S 1502  to S 1504  are the same as the processes of Steps S 1101  to S 1103  described in the first embodiment, and thus details thereof will be omitted. 
     In the next Step S 1505 , it is determined whether a preliminary route can be generated. If the calculated preliminary route satisfies a predetermined condition, the preliminary route calculation unit  503  adopts the calculated candidate route  1  as the parking route for automatic parking in Step S 1506 , and if not satisfying, the candidate route  1  is not adopted, and the process proceeds to Step S 1507 . Here, as an example of the case where the predetermined condition is satisfied, a preliminary route can be generated from the turning position to the target parking position. An example of a case where the predetermined condition is not satisfied is a route that the vehicle moves backward from the parking start position by the preliminary route and leaves the target parking position. 
     In Step S 1507 , the second candidate route calculation unit  1402  calculates the candidate route as the drivable area of the vehicle within the area corresponding to the acquisition range of the external environment information of the external environment recognition device  325 , and sets this as a candidate route  2 . Specifically, the second candidate route calculation unit  1402  generates, for example, the parking route  105  with the area where the external environment recognition device  325  can acquire the external environment information and the area without obstacles as the drivable area  104  as illustrated in  FIG. 1 , and output this as the candidate route  2 . As a result, the candidate route  2  calculated by the second candidate route calculation unit  1402  is adopted to perform the automatic parking rather than adopting the candidate route  1  for which the preliminary route cannot be generated even if the candidate route  1  is calculated by utilizing the most of the free space. Thus, it is possible to execute the automatic parking more reliably. 
     Next, in Step S 1508 , the route selection unit  1401  performs route evaluation to evaluate which preliminary route of candidate route  1  and the candidate route  2  is superior or inferior. The route evaluation is calculated based on at least one index of the number of times of turning, a route length, and a parking time. 
     Here, the parking time is calculated by adding a route passing time based on the calculated length of the route and the speed at which the vehicle passes the route, and a state switching time required to change the steering angle to a predetermined value by performing the forward and backward switching of the vehicle or the steering (hereinafter, steering without driving) with the vehicle stopped. The smaller the number of times of turning and the shorter the parking time or the shorter the route length, the higher the route evaluation. The more the number of times of turning and the longer the parking time or the longer the route length, the lower the route evaluation. Further, in the route evaluation, the weighting of the index may be set in consideration of the driver&#39;s preference. Specifically, the driver may operate an input device  328  to set a priority index in advance. 
     In Step S 1509 , the route selection unit  1401  determines whether the preliminary route of the candidate route  1  is higher than or equal to the route evaluation of the candidate route  2 , and if higher or equal, the process proceeds to Step S 1510 , and if not higher, the process proceeds to Step S 1511 . In Step S 1510 , the automatic parking is started on the preliminary route of the candidate route  1 , and the automatic parking is started on the candidate route  2  in Step S 1511 . This is because even if the candidate route  1  has a higher route evaluation than the candidate route  2 , if the preliminary route of the candidate route  1  has a lower evaluation than the candidate route  2 , the candidate route  2  is more likely to smoothly perform the automatic parking. This can prevent the smooth automatic parking from being disturbed. 
     Another example of the route evaluation will be described with reference to  FIG. 16 .  FIG. 16  is a diagram illustrating a display example of the input/output device  328 . As illustrated in  FIG. 16 , the input/output device  328  has a route display area  3281  for displaying a candidate route and a data display area  3282  for displaying data of the candidate route. 
     Based on the external environment recognition device  325 , the obstacle  102  such as a parked vehicle, the area  104  in which the vehicle  101  can drive (indicated by hatching in the diagram), and a preliminary route of the candidate route  1  to the target parking position  106  and the candidate route  2  are displayed in the route display area  3281 . In the data display area  3282 , the number of times of turning and parking time of each candidate route are displayed. At this time, when the evaluation of the preliminary route is lower than the evaluation of the candidate route  2 , the candidate route  1  may not be displayed and only the candidate route  2  may be displayed. As a result, the candidate route  1  is selected, and the vehicle is actually turned back. Therefore, when the number of times of turning is increased, it is possible to prevent the driver from feeling distrust of the automatic parking. The driver selects a desired candidate route from the displayed information. The vehicle starts the automatic parking on the selected candidate route. 
     By realizing the above route generation, even if there is an empty space, if there is a possibility that the route evaluation will be lower than the conventional route, the reliability of the automatic parking can be improved by selecting a route that does not use the empty space. 
     Third Embodiment 
     Hereinafter, a third embodiment of the invention will be described with reference to  FIGS. 17 to 20 . The diagram illustrating the configuration of the vehicle equipped with the parking assistance device of  FIG. 3  described in the first embodiment are the same in the second embodiment. The second embodiment is different in the configuration of the vehicle control device  324  illustrated in the first embodiment. 
       FIG. 17  is a block diagram illustrating a configuration of a vehicle control device  1724  in this embodiment. The same parts as those of the vehicle control device  324  illustrated in the first embodiment are designated by the same reference numerals, the description thereof will be omitted, and different parts will be described. 
     The vehicle control device  1724  includes an automatic parking stop/interruption determination unit  1701  in addition to the configuration of the vehicle control device  324  in the first embodiment. 
     The automatic parking stop/interruption determination unit  1701  stops or interrupts the automatic parking when the distance of an obstacle or the target parking position recognized at the parking start position and the distance actually recognized after starting the automatic parking are different and the automatic parking is hard to continue. Here, stopping indicates that the automatic parking is stopped and the control is transferred to the driver, and interruption indicates that the automatic parking process is temporarily stopped and is restarted when there is a restart request (for example, pressing a restart button, switching the shift, etc.) from the driver or there is no obstacle on the route in the advancing direction. 
       FIG. 18  is a flowchart illustrating a processing procedure of the automatic parking stop/interruption determination unit  1701 . In Step S 1801 , it is determined whether there is an obstacle on the parking route. If it is determined that there is no obstacle, the process proceeds to Step S 1802  to continue automatic parking on the parking route. On the other hand, if it is determined that there is an obstacle, the process proceeds to Step S 1803 . 
     In Step S 1803 , when an obstacle is detected, it is determined whether the vehicle is passing through the turning position. Specifically, as illustrated in  FIG. 19 , when an obstacle  1903  is detected, if the own vehicle position is a position  1902  before a turning position  1901 , it is determined that the vehicle has not passed, the process proceeds to Step S 1804 , and the automatic parking is interrupted. Here, when the own vehicle position is before the turning position  1901 , it can be more likely to generate a parking route on the preliminary route by interrupting the automatic parking without approaching the obstacle until the collision to the obstacle is determined. 
     In the next Step S 1805 , if it is determined that there is a restart request from the driver or that there is no obstacle left, the automatic parking is restarted according to the parking route. 
     On the other hand, in Step S 1803 , if it is at a position  1904  deeper than the turning position  1901 , it is determined that the turning position  1901  has passed, and the process proceeds to Step S 1806 . 
     In Step S 1806 , when the driver requests a backward movement, the process proceeds to Step S 1807 , and the vehicle moves backward to a turning position where a preliminary route can be generated. If the driver does not request the backward movement, the process advances to Step S 1808  to stop the automatic parking and transfer the control to the driver. 
     In Step S 1809 , the vehicle is moved backward to the turning position and the parking route is updated to the preliminary route, thereby restarting the automatic parking using the preliminary route. As a result, even if the obstacle  1903  appears, the automatic parking can be continued as long as possible, and the reliability of the automatic parking is improved. 
     The vehicle control devices  324  and  1724  according to the first to third embodiments have been described by way of an example in which the automatic parking is started by obtaining the turning position at the parking start position. However, the invention is not limited to this, and the automatic parking may be started and the turning position may be sequentially obtained while the vehicle is moving. Specifically, as illustrated in  FIG. 20( a ) , at the parking start position  2001 , a turning position  2002  at which a preliminary route can be generated is calculated. Then, the drivable area is sequentially updated as the vehicle moves on the parking route. Then, based on the updated drivable area, as illustrated in  FIG. 20( b ) , a turning position  2004  is updated, and at the same time a preliminary route that can be generated is also calculated. If a preliminary route can be generated, the automatic parking is continued, and if the position where a preliminary route cannot be generated can be detected in advance, the route is switched to the preliminary route before reaching the position, and if the preliminary route cannot be detected, the automatic parking is stopped. As a result, when the vehicle moves to a position  2005  illustrated in  FIG. 20( b ) , it finally moves to the turning position  2002  where a preliminary route can be generated. This improves the reliability of the automatic parking. Further, if such process is used for the stop/interruption determination of the automatic parking described in the third embodiment, it is possible to detect the position where a preliminary route cannot be generated in advance during driving. Therefore, the situation where the automatic parking is stopped can be reduced as much as possible, and the reliability of the automatic parking is improved. 
     According to the above embodiment, the following operational effects are obtained. 
     (1) The parking assistance device includes the candidate route calculation unit  501  which generates a candidate route from the current position of the vehicle to the target parking position based on the drivable area of the vehicle recognized based on the external environment information in the external environment recognition device  325 , the turning position calculation unit  502  which provides a turning position at a predetermined position on the candidate route generated by the candidate route calculation unit  501 , and the preliminary route calculation unit  503  which generates a preliminary route from the turning position to the target parking position. The candidate route in which the preliminary route can be generated by the preliminary route calculation unit  503  is set to a parking route of the automatic parking. This enables smooth automatic parking. 
     The invention is not limited to the above embodiments, and includes other forms considered within the scope of the technical ideas of the invention as long as the features of the invention are not degraded. In addition, the above embodiments and the modifications may be combined. 
     REFERENCE SIGNS LIST 
     
         
           101  vehicle 
           102  obstacle 
           103  obstacle position information 
           104  drivable area 
           105  parking route 
           106  target parking position 
           310  driving force generation mechanism 
           311  brake 
           312  transmission 
           313  steering 
           314  wheel 
           320  driving force control device 
           321  brake control device 
           322  steering control mechanism 
           323  transmission control device 
           324  vehicle control device 
           325  external environment recognition device 
           326  vehicle speed sensor 
           401  parking target candidate presentation unit 
           402  self-position estimation unit 
           403  route generation unit 
           404  target steering angle calculation unit 
           405  target vehicle speed calculation unit 
           406  target braking/driving force calculation unit 
           407  forward/backward switching determination unit 
           501  candidate route calculation unit 
           502  turning position calculation unit 
           503  preliminary route calculation unit 
           504  candidate route adoption determination unit 
           1401  route selection unit 
           1402  second candidate route calculation unit 
           1701  automatic parking stop/interruption determination unit