Patent Publication Number: US-11390273-B2

Title: Parking assistance apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a U.S. National Phase Patent Application and claims priority to and the benefit of International Application Number PCT/JP2019/009918, filed on Mar. 12, 2019, which claims priority of Japanese Patent Application Number 2018-070438, filed on Mar. 30, 2018, the entire contents of all of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a parking assistance apparatus for assisting parallel parking of a driver&#39;s own vehicle. 
     BACKGROUND ART 
     PTL 1 describes a technology of a parking assistance apparatus for calculating a guiding route including turning of a steering wheel to one direction and to the other direction to move a vehicle forward and backward to park the vehicle and assisting the vehicle to reach a target position along that guiding route. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Patent Application Laid-Open (Kokai) Publication No. 2010-208392 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     The technology of PTL 1 generates a parking route by linking a circular arc which connects from an initial position where the parking assistance is started, to a turning back position and a circular arc which connects from the turning back position to a target parking position. When the technology of PTL 1 is applied to parallel parking, there is a fear that the turning back position may become farther away from the target parking position towards a passage direction and the route may become longer, thereby resulting in a fear of causing anxiety to a driver and a problem of difficulty in conveying the driver&#39;s intention of where to park his/her own vehicle to other surrounding vehicles. Furthermore, a case where each circular arc becomes large and the route cannot be set due to the relation to obstacles happens very often and the number of scenes where the parking assistance can be actually used may decrease, so that there is a fear that the parking assistance may not be user-friendly and, as a result, may no longer be used. 
     The present invention was devised in light of the above-described circumstances and it is an object of the present invention to provide a parking assistance apparatus capable of making a parking route much shorter when providing the parking assistance for the parallel parking. 
     Means to Solve the Problems 
     The parking assistance apparatus of the present invention to solve the above-described problems is a parking assistance apparatus for assisting parallel parking of a driver&#39;s own vehicle, wherein the parking assistance apparatus includes: an escapable position calculation unit that calculates an escapable position where the driver&#39;s own vehicle can escape from a parking area to a passage area by moving the driver&#39;s own vehicle on the basis of a target parking position; 
     a parking-space leaving route calculation unit that calculates a parking-space leaving route where the driver&#39;s own vehicle can be moved from the escapable position to an initial position in the passage area; and 
     a parking route setting unit that sets a parking route for moving the driver&#39;s own vehicle from the initial position to the target parking position according to the parking-space leaving route, 
     wherein the parking-space leaving route calculation unit calculates the parking-space leaving route by using a first turning circle when turning from the escapable position to a passage side, a second turning circle when turning in a direction of the target parking position at the initial position of the driver&#39;s own vehicle, and a third turning circle which is a locus of a turning center when the vehicle has moved along the first turning circle and turns in a direction different from the first turning circle. 
     Advantageous Effects of the Invention 
     The parking route for providing the parking assistance for the parallel parking can be further shortened according to the present invention. Further features related to the present invention will be made clear by the description of this specification and the attached drawings. Furthermore, objects, configurations, and advantageous effects other than those described above will be made clear by the following explanation of embodiments. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a functional block diagram of a parking assistance apparatus according to an embodiment of the present invention; 
         FIG. 2  is a diagram for explaining movements of a driver&#39;s own vehicle upon parallel parking; 
         FIG. 3  is a diagram for explaining an example of movements of the driver&#39;s own vehicle until it reaches an escapable route; 
         FIG. 4  is a diagram for explaining positions to switch between a forward movement and a backward movement in the escapable route; 
         FIG. 5  is a diagram for explaining a movement amount upon the forward movement; 
         FIG. 6  is a diagram for explaining a movement amount upon the backward movement; 
         FIG. 7  is a diagram for explaining the escapable position; 
         FIG. 8  is a flowchart explaining a method for calculating the escapable position; 
         FIG. 9  is a flowchart explaining a method for calculating a parking-space leaving route; 
         FIG. 10  is a flowchart explaining a method for calculating a first turning movement route; 
         FIG. 11  is a diagram for explaining an example of the method for calculating the parking-space leaving route; 
         FIG. 12  is a diagram for explaining an example of the method for calculating the parking-space leaving route; 
         FIG. 13  is a diagram for explaining an example of the method for calculating the parking-space leaving route; 
         FIG. 14  is a diagram for explaining an example of the method for calculating the parking-space leaving route; 
         FIG. 15  is a diagram for explaining an example of the method for calculating the parking-space leaving route; 
         FIG. 16  is a diagram for explaining an example of the method for calculating the parking-space leaving route; 
         FIG. 17  is a diagram for explaining an example of the method for calculating the parking-space leaving route; 
         FIG. 18  is a diagram for explaining an example of the method for calculating the parking-space leaving route; 
         FIG. 19  is a diagram for explaining an example of the method for calculating the parking-space leaving route; 
         FIG. 20  is a diagram for explaining an example of the method for calculating the parking-space leaving route; 
         FIG. 21  is a diagram for explaining an example of the method for calculating the parking-space leaving route; 
         FIG. 22  is a diagram for explaining another example of the method for calculating the parking-space leaving route; 
         FIG. 23  is a diagram for explaining another example of the method for calculating the parking-space leaving route; 
         FIG. 24  is a diagram for explaining another example of the method for calculating the parking-space leaving route; 
         FIG. 25  is a diagram for explaining another example of the method for calculating the parking-space leaving route; 
         FIG. 26  is a diagram for explaining another example of the method for calculating the parking-space leaving route; 
         FIG. 27  is a diagram for explaining another example of the method for calculating the parking-space leaving route; 
         FIG. 28  is a diagram for explaining another example of the method for calculating the parking-space leaving route; 
         FIG. 29  is a diagram for explaining another example of the method for calculating the parking-space leaving route; 
         FIG. 30  is a diagram for explaining another example of the method for calculating the parking-space leaving route; 
         FIG. 31  is a diagram for explaining another example of the method for calculating the parking-space leaving route; 
         FIG. 32  is a diagram for explaining another example of the method for calculating the parking-space leaving route; and 
         FIG. 33  is a diagram for explaining another example of the method for calculating the parking-space leaving route. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Next, embodiments of the present invention will be explained by using the drawings. Incidentally, in the following description, an explanation will be provided about a case of parallel parking a driver&#39;s own vehicle in a parking area on the left side of a passage from an initial position in a passage area; however, the present invention can be also similarly applied to a case of parallel parking the driver&#39;s own vehicle in a parking area on the right side of the passage from the initial position in the passage area. 
       FIG. 1  is a functional block diagram of a parking assistance apparatus according to an embodiment of the present invention; and  FIG. 2  is a diagram for explaining movements of the driver&#39;s own vehicle upon parallel parking. 
     In a case of an example illustrated in  FIG. 2 , a road has a passage area Sr on the right side in a traveling direction of the road (the right side in a road-width direction) and has a parking area Sp on the left side in the traveling direction of the road (the left side in the road-width direction). Regarding the parking area Sp, a forward obstacle  22  and a backward obstacle  23  are placed in front of and behind the parking area Sp and a lateral-side obstacle  24  is placed on the left side of the parking area Sp, so that three sides of the parking area Sp are blocked and only the right side in the road-width direction, that is, only the passage area Sr side is open. The forward obstacle  22  and the backward obstacle  23  are, for example, other vehicles and the lateral-side obstacle  24  is, for example, a curbstone or a wall. The parking area Sp is an area for parallel parking and its parking direction is set so that the direction of the driver&#39;s own vehicle  21  becomes parallel to the traveling direction in the passage area Sr when the driver&#39;s own vehicle  21  is parked at a target parking position P 1  in the parking area Sp. 
     The parallel parking is to, for example, cause the driver&#39;s own vehicle  21 , which is in a stopped state at an initial position P 0  in the passage area Sr ahead of the target parking position P 1  ( FIG. 2 ( 1 )), to move backward and turn to the left to make the back part of the driver&#39;s own vehicle  21  enter the parking area Sp ( FIG. 2 ( 2 )) as illustrated in  FIG. 2 . Then, the driver&#39;s own vehicle  21  is located so that its facing direction at the target parking position P 1  in the parking area Sp is aligned with the parking direction ( FIG. 2 ( 3 )). If the facing direction of the driver&#39;s own vehicle  21  at the target parking position P 1  is not aligned with the parking direction, actions to turn the steering wheel to one direction and then to the other direction are performed to move the driver&#39;s own vehicle  21  forward and backward between the forward obstacle  22  and the backward obstacle  23  until the facing direction of the driver&#39;s own vehicle  21  becomes aligned with the parking direction. Incidentally, in this embodiment, whether or not the driver&#39;s own vehicle  21  is located at each position such as the initial position P 0 , the target parking position P 1 , or an escapable position P 2  described later (see  FIG. 7 ) is judged based on a reference point which is an intermediate position between the right and left rear wheels of the driver&#39;s own vehicle  21 . Furthermore, turning is performed along, for example, a steady-state circle or a clothoid curve. 
     A parking assistance apparatus  1  according to the present invention is designed to assist the parallel parking of the driver&#39;s own vehicle  21  to reach the target parking position P 1  from the initial position P 0  and is suited for assisting actions of the parallel parking, which starts with a backward movement. The parking assistance apparatus  1  can calculate a parking route for guiding the driver&#39;s own vehicle  21  and cause the driver&#39;s own vehicle  21  to perform the parallel parking by guiding and moving the driver&#39;s own vehicle  21  along the calculated parking route. A system for causing the driver&#39;s own vehicle  21  to automatically or semi-automatically perform the parallel parking at the target parking position P 1  may be implemented by outputting information of the parking route from the parking assistance apparatus  1 . In a case of the semi-automatic parking, for example, steering wheel operations may be conducted by automatic control and accelerator operations and brake operations are conducted by the driver. 
     The parking assistance apparatus  1  is mounted in the driver&#39;s own vehicle  21  and is implemented by cooperation between hardware such as a microcomputer and software programs. The parking assistance apparatus  1  includes, as illustrated in  FIG. 1 , an escapable position calculation unit  11 , a parking-space leaving route calculation unit  12 , and a parking route setting unit  13 . 
     The escapable position calculation unit  11  calculates an escapable position where the driver&#39;s own vehicle  21  can escape from the parking area Sp to the passage area Sr by a steering-wheel-turning-and-advance movement or a straight advance movement of the driver&#39;s own vehicle  21  on the basis of the target parking position P 1 . The parking-space leaving route calculation unit  12  calculates a parking-space leaving route where the driver&#39;s own vehicle  21  can be moved from the escapable position P 2  to the initial position P 0  in the passage area Sr. The parking route setting unit  13  sets a parking route for moving the driver&#39;s own vehicle  21  from the initial position P 0  to the target parking position P 1  on the basis of the parking-space leaving route. 
     Referring to  FIG. 1 , target parking space information  141 , target parking position information  142 , the driver&#39;s own vehicle information  143 , and the driver&#39;s own vehicle position information  144  are input to the parking assistance apparatus  1 . The target parking space information  141  includes information which serves as constraint conditions for a parking space such as distances to surrounding walls and other vehicles. The target parking space information  141  can be acquired from, for example, a detection signal of an ultrasonic wave sensor mounted in the driver&#39;s own vehicle  21  and images from an in-vehicle camera and may be acquired via road-to-vehicle communications and inter-vehicle communications. 
     The target parking position information  142  includes information such as coordinate information of the target parking position P 1  and a relative position with the driver&#39;s own vehicle  21  and the driver&#39;s own vehicle information  143  includes information which serves as behavior constraint conditions of the driver&#39;s own vehicle such as a turning radius of the driver&#39;s own vehicle  21 . Then, dead reckoning calculated by a vehicle model from a steering angle and speed of the driver&#39;s own vehicle  21  and a rotation amount of wheels may be utilized and positional information acquired by a sensor such as a GPS and positional information of the driver&#39;s own vehicle which is obtained via the road-to-vehicle and inter-vehicle communications may be utilized as the driver&#39;s own vehicle position information  144 . 
     The operation input unit  15  inputs, for example, information of the target parking position P 1 , which is selected by a user, to the parking assistance apparatus  1 . The route display unit  16 : is an in-vehicle monitor which the driver can watch inside the vehicle; and can display a position(s) to turn the steering wheel in a target parking route by overlaying it/them on a video from the camera. Furthermore, not only the steering-wheel-turning position(s), but also the entire parking route may be displayed. 
     The driver can check the steering-wheel-turning position(s) and the parking route by watching the steering-wheel-turning position(s) and the parking route which are displayed on the in-vehicle monitor. 
     &lt;Escapable Position Calculation Unit&gt; 
     The escapable position calculation unit  11  calculates the escapable position P 2  based on the target parking position P 1 . Specifically speaking, the escapable position P 2  is calculated based on the target parking space information  141  about, for example, obstacles in front of and behind the target parking position P 1  where the parallel parking is to be performed, the target parking position information  142  such as coordinate position information of the target parking position P 1 , and the driver&#39;s own vehicle information  143  about vehicle specifications such as the size and minimum rotation radius of the driver&#39;s own vehicle. 
       FIG. 8  is a flowchart explaining a method for calculating the escapable position. The escapable position calculation unit  11  judges whether or not the driver&#39;s own vehicle  21  can directly escape from the parking area Sp to the passage area Sr by a steering-wheel-turning-and-advance movement or a straight advance movement from the target parking position P 1 , on the basis of the target parking space information  141 , the target parking position information  142 , and the driver&#39;s own vehicle information  143  (S 101 ). Then, if it is determined that the driver&#39;s own vehicle  21  can be made to directly escape from the target parking position P 1  in the parking area Sp to the passage area Sr without turning the steering wheel to one direction and then to the other direction to move forward and backward (YES in S 101 ), the target parking position P 1  is set as the escapable position P 2  (S 102 ). In other words, if the driver&#39;s own vehicle  21  can be made to escape from the parking area Sp to the passage area Sr simply by the steering-wheel-turning-and-advance movement of the driver&#39;s own vehicle  21  from the target parking position P 1 , the target parking position P 1  is set as the escapable position P 2 . 
     On the other hand, if it is determined that the driver&#39;s own vehicle  21  cannot be made to directly escape from the target parking position P 1  to the passage area Sr (NO in S 101 ), an escapable route for moving the driver&#39;s own vehicle from the target parking position P 1  to the escapable position P 2  is calculated (S 103 ). For example, in a case of the steering-wheel-turning-and-advance movement or the straight advance movement of the driver&#39;s own vehicle  21  from the target parking position P 1 , if the forward obstacle  22  becomes an impediment and the driver&#39;s own vehicle  21  cannot be made to directly escape from the parking area Sp to the passage area Sr, it is determined that it is impossible to escape. 
     If it is determined that it is impossible to escape, a route capable of locating the driver&#39;s own vehicle  21  at the escapable position P 2  by moving the driver&#39;s own vehicle  21  forward or backward from the target parking position P 1  at least once and then turning the steering wheel is calculated and the calculated route is set as an escapable route. 
     The escapable route is a virtual moving route which is an estimated route for the driver&#39;s own vehicle  21  in a state of being parked with a correct facing direction at the target parking position P 1  to reach the escapable position P; and the escapable route includes at least one or more turns of the steering wheel to one direction and to the other direction to move the driver&#39;s own vehicle  21  forward and backward. The escapable route is calculated based on the parking space and the driver&#39;s own vehicle behavior constraint conditions. The escapable route is calculated completely regardless of, and without the constraint of, the initial position of the driver&#39;s own vehicle  21 . 
       FIG. 3  is a diagram for explaining an example of movements of the driver&#39;s own vehicle until it reaches the escapable route;  FIG. 4  is a diagram for explaining positions to switch between a forward movement and a backward movement in the escapable route;  FIG. 5  is a diagram for explaining a movement amount upon the forward movement;  FIG. 6  is a diagram for explaining a movement amount upon the backward movement; and  FIG. 7  is a diagram for explaining the escapable position. 
     If the escapable position calculation unit  11  determines that the driver&#39;s own vehicle  21  cannot be made to escape from the parking area Sp to the passage area Sr by the steering-wheel-turning-and-advance movement or the straight advance movement from the state illustrated in  FIG. 3 ( 1 ), the escapable position calculation unit  11  calculates a route for moving the driver&#39;s own vehicle  21  straight backward from the target parking position P 1  ( FIG. 3 ( 2 )) and turning the steering wheel at a backward movable limit position and then turning to the right while moving forward ( FIG. 3 ( 3 )). 
     Then, if the forward obstacle  22  becomes an impediment and it is impossible to make the driver&#39;s own vehicle  21  escape from the parking area Sp, the escapable position calculation unit  11  calculates a route for turning the steering wheel at a forward movable limit position, turning to the left while moving backward ( FIG. 3 ( 4 )), and repeatedly turning the steering wheel to one direction and then to the other direction alternately as illustrated in  FIG. 3 ( 3 ) and  FIG. 3 ( 4 ) until the driver&#39;s own vehicle reaches the escapable position. Then, a locus of movements to reach the escapable position P 2  as illustrated in  FIG. 7 ( 1 ) and  FIG. 7 ( 2 ) is further calculated as the escapable route. 
     The escapable position calculation unit  11  recognizes a position where the front part of the driver&#39;s own vehicle  21  comes close to a limit distance to the forward obstacle  22  as indicated with the reference numeral  31  in  FIG. 4 ( 1 ) as a forward movable limit position. Then, either a position where the back part of the driver&#39;s own vehicle  21  comes close to a limit distance to the lateral-side obstacle  24  as indicated with the reference numeral  32  in  FIG. 4 ( 2   a ), or a position where the back part of the driver&#39;s own vehicle  21  comes close to a limit distance to the backward obstacle  23  as indicated with the reference numeral  33  in  FIG. 4 ( 2   b ), whichever has a shorter movement distance from the limit distance, is adopted as a backward movable limit position. 
     The forward movable limit position is set at a position with a specified gap δ 1  of, for example, approximately 1 cm to 50 cm away from a position where the front part of the driver&#39;s own vehicle  21  enters into contact with the forward obstacle  22  by a forward movement as illustrated in  FIG. 5 . Then, the backward movable limit position is set at a position with a specified gap δ 2  or δ 3  of, for example, approximately 5 cm to 10 cm away from a position where the back part of the driver&#39;s own vehicle  21  enters into contact with the lateral-side obstacle  24  or the backward obstacle  23  by a backward movement as illustrated in  FIG. 6 ( 1 ) and  FIG. 6 ( 2 ). 
     The escapable position P 2  is: a position where the driver&#39;s own vehicle  21  has a gap δ 4  from the forward obstacle  22  and can escape from the parking area Sp to the passage area Sr when the driver&#39;s own vehicle  21  turns to the right while moving forward (advance movement and turning the steering wheel) as illustrated in  FIG. 7 ( 1 ); and a position where the driver&#39;s own vehicle  21  has a gap δ 4  from the forward obstacle  22  and can escape from the parking area Sp to the passage area Sr when the driver&#39;s own vehicle moves straight forward (straight advance movement) as illustrated in  FIG. 7 ( 2 ). This gap δ 4  includes a margin in consideration of an error or the like so that the driver&#39;s own vehicle  21  would not enter into contact with the forward obstacle  22 ; and the gap δ 4  should preferably be as small as possible and is set as, for example, approximately 1 cm to 50 cm. 
     &lt;Parking-Space Leaving Route Calculation Unit&gt; 
       FIG. 9  is a flowchart explaining a method for calculating a parking-space leaving route. Then,  FIG. 11  to  FIG. 33  are diagrams for explaining a method for calculating the parking-space leaving route.  FIG. 11  to  FIG. 21  are diagrams for explaining examples of the method for calculating the parking-space leaving route when the target parking position P 1  is set as the escapable position P 2 . Then,  FIG. 22  to  FIG. 33  are diagrams for explaining examples of the method for calculating the parking-space leaving route when the escapable route is calculated and the escapable position P 2  is set at a place different from the target parking position P 1 . 
     The parking-space leaving route calculation unit  12  calculates a parking-space leaving route E by using: a first turning circle C 1  when turning from the escapable position towards the passage side; a second turning circle C 2  when turning at the initial position P 0  of the driver&#39;s own vehicle  21  to a direction of the target parking position P; and a third turning circle C 3  which is a locus of a turning center when the driver&#39;s own vehicle  21  has moved along the first turning circle C 1  and turns to a direction different from the first turning circle C 1 . 
     The parking-space leaving route calculation unit  12  performs coordinate transformation of first normal coordinates, whose origin is the escapable position P 2 , into second normal coordinates whose origin is the initial position P 0  of the driver&#39;s own vehicle  21  (S 111 ). The first normal coordinates are a coordinate system regarding which a front-back direction relative to the vehicle&#39;s facing direction at the escapable position P 2  is a vertical axis Y and a vehicle width direction relative to the vehicle&#39;s facing direction is a horizontal axis X; and the second normal coordinates are a coordinate system regarding which the direction of the front-back direction of the driver&#39;s own vehicle  21  at the initial position is a vertical axis y and the direction of the vehicle width direction of the driver&#39;s own vehicle  21  is a horizontal axis x. 
     For example, when the target parking position P 1  is set as the escapable position P 2  as illustrated in  FIG. 11  and  FIG. 12  or when the escapable route is calculated and the escapable position P 2  is set separately from the target parking position as illustrated in  FIG. 22  to  FIG. 24 , the first normal coordinates whose origin is the target parking position P 1  are coordinate-transformed to the second normal coordinates whose origin is the initial position P 0  of the driver&#39;s own vehicle  21 . Then, for example, as illustrated in  FIG. 13  and  FIG. 25 , the first turning circle C 1  is set which has a minimum turning radius R to pass through the escapable position P 2  and whose center O 1  is a position separated from the escapable position P 2  by the minimum turning radius R, which is a reference distance, in the horizontal-axis X-direction of the first normal coordinates and on the passage area Sr side; and the second turning circle C 2  is set which has the minimum turning radius R to pass through the initial position P 0  and whose center O 2  is a position separated from the initial position P 0  by the minimum turning radius R in the horizontal-axis X-direction of the second normal coordinates and on the parking area Sp side (S 112 ). 
     Incidentally, in this embodiment, the radius of the first turning circle C 1  and the radius of the second turning circle C 2  are set as the minimum turning radius R of the driver&#39;s own vehicle  21 ; however, any radius may be used as long as the above-mentioned radius is equal to or more than the minimum turning radius R and the radius of the first turning circle C 1  is the same as the radius of the second turning circle C 2 . 
     Then, whether the first turning circle C 1  and the second turning circle C 2  intersect each other at two points or not is judged (S 113 ). Under this circumstance, if the first turning circle C 1  and the second turning circle C 2  intersect each other at two points, the parking-space leaving route to the target parking position P 1  cannot be calculated at the initial position P 0 . In other words, it is determined that the parking-space leaving route cannot be calculated; and then the flow is terminated. On the other hand, if the first turning circle C 1  and the second turning circle C 2  are separated from each other and do not intersect each other or intersect each other only at one point, it is determined that the parking-space leaving route can be calculated; and then the processing proceeds to processing in step S 114  and subsequent steps. 
     In the processing of step S 114  and subsequent steps, a route for turning the steering wheel continuously to the right and the left with the minimum turning radius R and moving forward from the escapable position P 2  to the initial position P 0  is calculated as the parking-space leaving route. The parking-space leaving route E has, for example, as illustrated in  FIG. 21  and  FIG. 33 , a first turning movement route E 1  for moving from the escapable position P 2  to a first turning movement position P 3 , a second turning movement route E 2 , which continuously follows the first turning movement route E 1 , for moving from the first turning movement position P 3  to a second turning movement position P 4 , and a straight advance movement route E 3 , which continuously follows the second turning movement route E 2 , for moving from the second turning movement position P 4  to the initial position P 0 , each of which is calculated by the processing from step S 114  to step S 116 . 
     Firstly, the processing for calculating the first turning movement route E 1  is executed (S 114 ). 
     The first turning movement route E 1  is a route for moving from the escapable position P 2  to the first turning movement position P 3  by turning with the minimum turning radius R towards the passage area Sr side around the center O 1  of the first turning circle C 1  (which is also the center of the third turning circle C 3 ) as the turning center. 
     The first turning movement position P 3  is a position moved from the escapable position P 2  by a first turning movement amount D 1  by turning the steering wheel to the right (see  FIG. 18  and  FIG. 30 ). 
       FIG. 10  is a flowchart for explaining a method for calculating the first turning movement position P 3 . 
     Firstly, as illustrated in  FIG. 14  and  FIG. 26 , the third turning circle C 3  which is a concentric circle of the first turning circle C 1  and is a double-sized circle having a radius  2 R that is twice as large as the radius R of the first turning circle C 1  is set (S 121 ). In other words, the third turning circle C 3  whose center is the position (center O 1 ) separated from the escapable position P 2  by the specified reference distance (the radius R) in the horizontal-axis X-direction of the first normal coordinates and on the passage area Sr side, and which has the radius  2 R that is twice as large as the reference distance is set. 
     The third turning circle C 3  forms a shape that matches the locus of the center of a turning circle that is drawn when the driver&#39;s own vehicle moving along the first turning circle C 1  turns in a reverse direction. For example, when the driver&#39;s own vehicle  21  which is moving along the first turning circle C 1  turns with the radius R in a direction to move away from the first turning circle C, a turning circle which has the same size as that of the first turning circle C 1  and contacts the first turning circle is formed outside the first turning circle C 1 . When a plurality of such turning circles which contact the first turning circle are located to surround the outside of the first turning circle, a circular locus which is drawn with the centers of the plurality of these turning circles forms the third turning circle C 3 . 
     Then, a first reference line B 1  which passes through the position (the center O 2 ) separated from the initial position P 0  by the reference distance (the radius R) in the horizontal-axis X-direction of the second normal coordinates and on the parking area Sp side and extends in the vertical-axis Y-direction of the second normal coordinates is set; and a first intersection point A 1  at which the first reference line B 1  intersects with the third turning circle C 3  is calculated (S 122 ). Although there are two intersection points where the first reference line B 1  and the third turning circle C 3  intersect each other, the intersection point positioned ahead of the escapable position P 2  in the vertical-axis Y-direction of the first normal coordinates is adopted as the first intersection point A 1 . In other words, the parking-space leaving route calculation unit  12 : calculates the first reference line B 1  which is a front-back direction of the driver&#39;s own vehicle  21  and passes through the center of the second turning circle C 2 ; and sets the intersection point which is an intersection point between the first reference line B 1  and the third turning circle C 3  and is located in a direction closer to the driver&#39;s own vehicle  21 , as the first intersection point A 1 . 
     Next, as illustrated in  FIG. 15  and  FIG. 27 , a second reference line B 2  which passes from the center O 1  of the first turning circle C 1  through the escapable position P 2  and extends in the horizontal-axis X-direction of the first normal coordinates is set; and the position of a second intersection point A 2  where the second reference line B 2  and the third turning circle C 3  intersect each other is calculated (S 123 ). 
     Then, as illustrated in  FIG. 16  and  FIG. 28 , the distance L between the intersection points, the first intersection point A 1  and the second intersection point A 2  (S 124 ). 
     Assuming that coordinate positions of the first intersection point A 1  and the second intersection point A in the second normal coordinates are (x 1 , y 1 ) and (x 2 , y 2 ), the distance L between the intersection points can be calculated according to Expression (1) below.
 
[Math. 1]
 
 L =√{square root over (( x   1   −x   2 ) 2 +( y   1   −y   2 ) 2 )}   Expression (1)
 
     Then, as illustrated in  FIG. 17  and  FIG. 29 , an included angle θ which is an angle between the first intersection point A 1  and the second intersection point A 2  at the center O 1  of the first turning circle C 1  is calculated by using the distance L between the intersection points and the radius  2 R of the third turning circle C 3  (S 125 ). The included angle θ can be calculated according to Expression (2) below. 
     
       
         
           
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                     2 
                     ) 
                   
                 
               
             
           
         
       
     
     Then, as illustrated in  FIG. 18  and  FIG. 30 , a first turning movement amount D 1  by turning the steering wheel to the right is calculated by using the included angle θ and the radius R of the first turning circle C 1  (the reference distance) (S 126 ). The first turning movement amount D 1  is a movement amount from the escapable position P 2  to the first turning movement position P 3  and can be calculated according to Expression (3) below.
 
[Math. 3]
 
 D 1=   R θ    Expression (3)
 
     The first turning movement position P 3  is calculated by using this first turning movement amount D 1  (S 127 ). Then, the first turning movement route E 1  (see  FIG. 21  and  FIG. 33 ) is calculated based on the first turning movement position P 3 . 
     Next, the processing for calculating the second turning movement route E 2  is executed (S 115  in  FIG. 9 ). The second turning movement route E 2  is a route for moving from the first turning movement position P 3  to the second turning movement position P 4  by turning with the minimum turning radius R around the first intersection point A 1  as the center towards the parking area Sp side. The second turning movement position P 4  is, for example, as illustrated in  FIG. 19  and  FIG. 31 , a position moved from the first turning movement position P 3  by the second turning movement amount D 2  by turning the steering wheel to the left. Regarding the second turning movement route E 2 , when the vehicle is moved from the first turning movement position P 3  to the second turning movement position P 4 , the vehicle is positioned on the vertical axis y of the second normal coordinates, which passes through the initial position P 0 , and the vehicle&#39;s facing direction th becomes the same facing direction as that of the driver&#39;s own vehicle  21  at the initial position P 0 . 
     In order to calculate the second turning movement position P 4 , the vehicle&#39;s facing direction th at the first turning movement position P 3  is firstly calculated. The vehicle&#39;s facing direction th at the first turning movement position P 3  is an inclination angle φ relative to the horizontal axis x of the second normal coordinates and can be expressed by Expression (4) below.
 
[Math. 4]
 
φ= th    Expression (4)
 
     Next, the second turning movement amount D 2  which is a movement amount from the first turning movement position P 3  to the second turning movement position P 4  is calculated. A turning angle around the first intersection point A 1  as the center to move from the first turning movement position P 3  to the second turning movement position P 4  is the inclination angle φ relative to the horizontal axis x of the second normal coordinates and the distance between the first intersection point A 1  and the first turning movement position P 3  is equal to the radius R of the first turning circle C 1 . Therefore, the second turning movement amount D 2  can be calculated according to Expression (5) below on the basis of the inclination angle φ and the radius R.
 
[Math. 5]
 
 D 2=    Expression (5)
 
     The second turning movement position P 4  is calculated by using this second turning movement amount D 2 . Then, the second turning movement route E 2  (see  FIG. 21  and  FIG. 33 ) is calculated based on the second turning movement position P 4 . 
     Next, the processing for calculating the straight advance movement route E 3  is executed (S 116  in  FIG. 9 ). The straight advance movement route E 3  is, for example, a route for a straight advance movement from the second turning movement position P 4  to the initial position P 0 , that is, a route which connects the second turning movement route and the initial position P 0  of the driver&#39;s own vehicle as illustrated in  FIG. 20  and  FIG. 32 . The second turning movement position P 4  exists on the vertical axis y which passes through the initial position P 0 . Therefore, the straight advance movement amount D 3  from the second turning movement position P 4  to the initial position P 0  is represented by a vertical-direction difference distance from the second turning movement position P 4  to the initial position P 0  in the second normal coordinates. The straight advance movement route E 3  is calculated by using this straight advance movement amount D 3 . 
     The parking-space leaving route is generated by connecting the first turning movement route E 1 , the second turning movement route E 2 , and the straight advance movement route E 3  together as illustrated in  FIG. 21  and  FIG. 33 . 
     Incidentally, if it is determined in step S 113  in  FIG. 9  that the first turning circle and the second turning circle intersect each other at one point, the straight advance movement amount D 3  does not exist. Therefore, the processing of step S 116  for calculating the straight advance movement route E 3  is omitted and the parking-space leaving route E is calculated by using the first turning movement route E 1  and the second turning movement route E 2 . 
     &lt;Parking Route Setting Unit&gt; 
     The parking route setting unit  13  sets the parking route by using the escapable route from the target parking position P 1  to the escapable position P 2  and the parking-space leaving route E from the escapable position P 2  to the initial position P 0 . The parking route is a route for reverse running by connecting the escapable route and the parking-space leaving route E. 
     Next, operational advantages of the parking assistance apparatus according to this embodiment will be explained. The parking assistance apparatus according to this embodiment: calculates the first turning movement route E 1  for moving forward and turning towards the passage area Sr side with the minimum turning radius R from the escapable position P 2 , the second turning movement route E 2  for moving forward and turning towards the parking area Sp side with the minimum turning radius R continuously following the first turning movement route E 1 , and the straight advance movement route E 3  for moving straight forward to the initial position P 0  continuously following the second turning movement route E 2 ; and calculates the parking-space leaving route E by using the first turning movement route E 1 , the second turning movement route E 2 , and the straight advance movement route E 3 . The parking-space leaving route E is configured by continuously linking the second turning movement route E 2  with the same minimum turning radius R to the first turning movement route E 1  with the minimum turning radius R and further continuously linking the straight advance movement route E 3  to the second turning movement route E 2 . 
     Therefore, as compared with a conventional parking route that connects a circular arc, which passes through the target parking position, to a circular arc which passes through the initial position, it is easy to shorten the route length and it is possible to calculate a more compact parking-space leaving route and generate the route without moving further away from the target parking position towards the passage direction than the conventional route. Furthermore, since the parking-space leaving route is generated by continuously connecting the routes both having the minimum turning radius R, the initial position can be also set at a position away from the parking area Sp in a passage-width direction, so that the initial position can be set with a wider degree of freedom and a route generation rate can be increased more than the conventional one. 
     The embodiments of the present invention have been described above in detail; however, the present invention is not limited to the aforementioned embodiments and various design changes can be made within the range not departing from the spirit of the present invention as described in the claims. For example, the aforementioned embodiments have been described in detail in order to explain the present invention in an easily comprehensible manner and are not necessarily limited to those having all the configurations explained above. Furthermore, part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment and the configuration of another embodiment can be added to the configuration of a certain embodiment. Also, another configuration can be added to, deleted from, or replaced with part of the configuration of each embodiment. 
     REFERENCE SIGNS LIST 
     
         
           21 : driver&#39;s own vehicle 
           22 : forward obstacle 
           23 : backward obstacle 
           24 : lateral-side obstacle 
         A 1 : first intersection point 
         A 2 : second intersection point 
         B 1 : first reference line 
         B 2 : second reference line 
         C 1 : first turning circle 
         C 2 : second turning circle 
         C 3 : third turning circle (double-sized circle) 
         D 1 : first turning movement amount 
         D 2 : second turning movement amount 
         D 3 : straight advance movement amount 
         O 1 : center of first turning circle (center of third turning circle) 
         O 2 : center of second turning circle 
         P 0 : initial position 
         P 1 : target parking position 
         P 2 : escapable position 
         R: radius (reference distance) 
         Sp: parking area 
         Sr: passage area 
         θ: included angle 
         φ: inclination angle