Patent Publication Number: US-2021179089-A1

Title: Parking assistance device, parking assistance method, and computer program product

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-225911 filed Dec. 13, 2019, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     The disclosure relates to a parking assistance device, parking assistance method, and computer program product. 
     Related Art 
     Patent Literature 1 (Japanese Unexamined Patent Application Publication No. 2016-016681) discloses a technology for detecting parking space boundary lines using an image captured with an imager of a vehicle. 
     Patent Literature 2 (Japanese Unexamined Patent Application Publication No. 2014-019305) discloses a technology to establish a parking location of a host vehicle by deriving a corner portion or center position of another vehicle when boundary lines separating a parking area are angled obliquely (see paragraph 0042 and FIG. 5). 
     Patent Literature 3 (WO 2019/008757) discloses a technology for aligning a reference location of a host vehicle with a virtual line L by detecting front end portions of white lines W1 and W2 that separates a parking area (see FIG. 13A). 
     Patent Literature 4 (WO 2019/064907) discloses a technology for automatic parking when boundary lines separating a parking area are angled obliquely. 
     However, there are parking areas with different types of parking regions. For example, some parking areas separate individual parking regions with boundary lines whereas some do not. And although with the technologies of Patent Literatures 1-4 a parking region is set as a parking target, these literatures do not disclose a technology for automatically parking a vehicle within a parking region at a parking location that is appropriate for each type of parking region. 
     SUMMARY 
     One aspect of the disclosure provides a parking assistance device including a recognition part configured to acquire recognition information through recognition of surroundings of a host vehicle, a maneuver controller configured to perform maneuver control to park the host vehicle in a parking region based on the recognition information, a maintain stop position controller configured to keep the host vehicle stationary after the host vehicle is stopped by the maneuver control of the maneuver controller until a predetermined operation is received from a driver, a determination part configured to determine a type of the parking region in which the host vehicle is to be parked with the maneuver controller, and a decision part configured to determine, in accordance with the type of the parking region that is determined by the determination part, a parking reference location that is used to park the host vehicle in the parking region. In response to determining that the type of the parking region is a demarcated parking region that is demarcated by at least left and right boundary lines, the decision part is configured to set the parking reference location to a location that is a first predetermined distance apart from a first virtual line joining front ends of the left and right boundary lines. In response to determining that the type of the parking region is a parking region that is not demarcated by the at least left and right boundary lines, the decision part is configured to set the parking reference location to a location based on a second virtual line joining front ends of other vehicles on a left and right of the parking region. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of a system configuration in accordance with at least one embodiment centered on an automatic parking control unit according to at least one embodiment. 
         FIG. 2  is a top view of a vehicle installed with an automatic parking control unit according to at least one embodiment showing the positions of cameras and sonars installed on the vehicle. 
         FIG. 3A  is a top view of a parking area for explaining a situation where a vehicle installed with an automatic parking control unit according to at least one embodiment searches for a space to perform a parking maneuver. 
         FIG. 3B  is a top view of a parking area for explaining a situation where a vehicle installed with an automatic parking control unit according to at least one embodiment searches for a space to perform a parking maneuver. 
         FIG. 3C  is a top view of a parking area for explaining a situation where a vehicle installed with an automatic parking control unit according to at least one embodiment searches for a space to perform a parking maneuver. 
         FIG. 4  is a flowchart for explaining a process executed by an automatic parking control unit according to at least one embodiment. 
         FIGS. 5A and 5B  are flowcharts for explaining a process executed by an automatic parking control unit according to at least one embodiment. 
         FIG. 6  is a top view of a parking area for explaining a process executed by an automatic parking control unit according to at least one embodiment. 
         FIG. 7  is a top view of a parking area for explaining a process executed by an automatic parking control unit according to at least one embodiment. 
         FIG. 8  is a top view of a parking area for explaining a process executed by an automatic parking control unit according to an embodiment. 
         FIG. 9  is a top view of a parking area for explaining a process executed by an automatic parking control unit according to at least one embodiment. 
         FIG. 10  is a plan view of a selection screen that is displayed on a touch panel by a process that is executed by an automatic parking control unit according to at least one embodiment. 
         FIG. 11  is a flowchart of a subroutine for a parking reference location determination process of S 6  that is executed by an automatic parking control unit according to at least one embodiment. 
         FIG. 12  is a plan view of a parking region for explaining a parking reference location determination process that is executed by an automatic parking control unit according to at least one embodiment. 
         FIG. 13  is a plan view of a parking region for explaining a parking reference location determination process that is executed by an automatic parking control unit according to at least one embodiment. 
         FIG. 14  is a plan view of a parking region for explaining a parking reference location determination process that is executed by an automatic parking control unit according to at least one embodiment. 
         FIG. 15  is a plan view of a parking region for explaining a parking reference location determination process that is executed by an automatic parking control unit according to at least one embodiment. 
         FIG. 16  is a plan view of a parking region for explaining a parking reference location determination process that is executed by an automatic parking control unit according to at least one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An object of the disclosure is to provide a parking assistance device that is able to perform automatic parking of a vehicle at an appropriate parking location in accordance with a type of a parking region where the vehicle is to park. 
     One aspect of the disclosure provides a parking assistance device that is configured to perform automatic parking of a vehicle at an appropriate parking location in accordance with a type of a parking region where the vehicle is to park. 
     In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing. 
     Embodiments according to the disclosure is described below with reference to drawings. Directions to the front, back, left, and right referred to in the description are in accordance with the arrows shown in the drawings. 
       FIG. 1  is a block diagram showing a system configuration of an embodiment centered on an automatic parking control unit  1 .  FIG. 2  is a top view of a host vehicle  100  equipped with the system of  FIG. 1 . 
     The automatic parking control unit  1  is an electronic control unit (ECU) for automatic parking that is installed on board a host vehicle  100 . The automatic parking control unit  1  is an embodiment of a parking assistance device according to the disclosure and is configured mainly from a microcomputer and realizes the functions of the following various control parts through executing a process based on a control program. The automatic parking control unit  1  operates based on a program characteristic to the disclosure and carries out a parking assistance method according to the disclosure through execution of the process of the program. A recognition part  11  acquires recognition information including image data and sonar data by recognizing the surroundings with a camera group  21  and sonar group  22  (the camera group  21  and sonar group  22  are described later). Based on this recognition information, a maneuver controller  12  performs maneuver control for the automatic parking of the host vehicle  100  in a parking region by maneuvering the host vehicle  100  into the parking region using the following systems (described in detail later). The maneuver control controls a brake system  41 , a drive system  51 , a transmission system  61 , and an EPS system  71  based on information including detection results of an inertial sensor  23 , a wheel speed sensor  24 , and a driver presence determiner  65  and an operation result of a brake hold switch  45 . A “parking region” refers to a region for parking the host vehicle  100 . For example, for a parking space whose boundary is delineated by a boundary line, a parking region is the parking space for a single vehicle that is demarcated by the boundary line. The maneuver controller  12  includes a maintain stop position controller  13 . The maintain stop position controller  13  maintains the host vehicle  100  at the same location from when the host vehicle  100  stops through maneuver control of the host vehicle  100  by the maneuver controller  12  to when a predetermined operation from the driver is received. The determination part  14  determines the type of a parking region where the host vehicle  100  is to be parked by the maneuver controller  12 . A “type of a parking region” may refer, for example, to a parking region among a number of parking regions arranged next to one another and demarcated by left and right boundary lines, or a parking region without left and right boundary lines (i.e., a parking region that is not separated from an adjacently parked vehicle with a demarcation). The decision part  15  determines a parking reference location for the automatic parking of the host vehicle  100  in a parking region according to the type of the parking region as determined by the determination part  14 . A “parking reference location” refers to a location that is used as reference when deciding a location of the front end or rear end of the host vehicle  100  when parking the host vehicle  100  in a parking region. The operations executed by the recognition part  11 , maneuver controller  12 , maintain stop position controller  13 , determination part  14 , and decision part  15  will be described in detail later. 
     The automatic parking control unit  1  is connected to a camera group  21  and sonar group  22 . In some embodiments, each component that is connected to the automatic parking control unit  1  (with the connection as indicated by a line in the drawing of  FIG. 1 ) has a wire connection with the automatic parking control unit  1 . In some embodiments, each component connected to the automatic parking control unit  1  has a connection via a Controller Area Network (a CAN). 
     The camera group  21  is a group of cameras that the host vehicle  100  is installed with as shown in  FIG. 2 . The host vehicle  100  is equipped at the front thereof with a front camera  2 IF that captures an image of a view in front of the host vehicle  100 . Furthermore, the host vehicle  100  is equipped at the rear thereof with a rear camera  21 R that captures an image of a view at the back of the host vehicle  100 . Yet further, the host vehicle  100  is equipped on the right side thereof towards the front with a side camera  21 RF that captures an image of a view to the right of the host vehicle  100 . Yet further, the host vehicle  100  is equipped on the left side thereof towards the front with a side camera  21 LF that captures an image of a view to the left of the host vehicle  100 . In some embodiments, the side cameras  21 RF and  21 LF are each installed at the tip of a side mirror or away from a side mirror to prevent the side mirrors from obstructing the views that are captured by the cameras. In some embodiments, the side cameras  21 RF and  21 LF are each installed some distance away from a side mirror. 
     The sonar group  22  is a group of cameras that the host vehicle  100  is installed with as shown in  FIG. 2 . The host vehicle  100  is equipped at the front thereof with four front sonars  22 F that are arranged apart at substantially equal intervals. The four front sonars  22 F detect an obstacle in front of the host vehicle  100 . Furthermore, the host vehicle  100  is equipped at the rear thereof with four rear sonars  22 R that are arranged apart at substantially equal intervals. The four rear sonars  22 R detect an obstacle at the back of the host vehicle  100 . The front sonars  22 F detect an obstacle in the direction of travel when the host vehicle  100  is moving forward. The rear sonars  22 R detect an obstacle in the direction of travel when the host vehicle  100  is moving in reverse. 
     Furthermore, the host vehicle  100  is equipped with a single side sonar  22 RF on a front portion of the right side of the host vehicle  100 . The side sonar  22 RF detects an obstacle at the front right of the host vehicle  100  to the right of the host vehicle  100 . Yet further, the host vehicle  100  is equipped with a single side sonar  22 LF on a front portion of the left side of the host vehicle  100 . The side sonar  22 LF detects an obstacle at the front left of the host vehicle  100  to the left of the host vehicle  100 . Yet further, the host vehicle  100  is equipped with a single side sonar  22 RR on a back portion of the right side of the host vehicle  100 . The side sonar  22 RR detects an obstacle at the back right of the host vehicle  100  to the right of the host vehicle  100 . Yet further, the host vehicle  100  is equipped with a single side sonar  22 LR on a back portion of the left side of the host vehicle  100 . The side sonar  22 LR detects an obstacle at the back left of the host vehicle  100  to the left of the host vehicle  100 . Each of the side sonars  22 RF,  22 LF,  22 RR, and  22  LR detects an obstacle that may come in the path of the host vehicle  100 . In  FIG. 2 , a broken line S indicates a spatial range where the individual sonars detect an obstacle. The broken line V indicates a range of view of individual cameras. 
     Note that the number of cameras and sonars and their installed locations are not limited to the description given above. The number of cameras and sonars may be increased or decreased. The locations of the cameras and sonars may be changed. In some embodiments, the numbers and locations of one or more cameras and one or more sonars may be selected so that the situation around the circumference of the host vehicle  100  is detectable. 
     In some embodiments, a sensor other than a camera or a sonar is used to detect the surrounding situation of the host vehicle  100 . For example, the host vehicle  100  may be equipped with a radar. The radar includes a function to acquire distribution information of a target by irradiating a target with a radar wave and receiving a radar wave reflected from the target, the target including another vehicle driving in front of the host vehicle  100 , and the distribution information of the target including a distance to the target and a direction of the target. For the radar wave, a laser, a microwave, a millimeter-wave, or an ultrasonic wave may for example be used as deemed appropriate. 
     In some embodiments, the host vehicle  100  is equipped with a LIDAR (Light Detection and Ranging). The LIDAR includes, for example, a function to detect a presence of a target and a distance to the target by measuring the time taken to detect scattered light in response to irradiation of light. 
     In the description that follows, an example is used where the host vehicle  100  detects its surrounding area through a combined used of the camera group  21  and sonar group  22 . 
     Referring back to  FIG. 1 , the automatic parking control unit I is connected to an inertial sensor  23  and a wheel speed sensor  24 . The inertial sensor  23  is a sensor that detects the acceleration of the host vehicle  100 . The wheel speed sensor  24  is a sensor that detects the wheel speed of each of the wheels of the host vehicle  100 . 
     Furthermore, the automatic parking control unit  1  is connected to an information input and output device  31 . The information input and output device  31  includes a touch panel  32  and a speaker  33 . The main body of the information input and output device  31  is arranged in the vicinity of a driver&#39;s seat to allow the driver to operate, for example, the touch panel  32 . The information input and output device  31  may display various information on the touch panel  32 , output various audio output with the speaker  33 , and accept various operations through the touch panel  32 . 
     In other words, through the use of the information input and output device  31 , car navigation information that has been prepared, for example, based on information from a satellite navigation system, may be displayed on the touch panel  32  or output as audio from the speaker  33  or both. This car navigation information may also include information received from the Vehicle Information and Communication System (VICS [a registered trademark]). 
     Furthermore, the information input and output device  31  may receive TV and radio broadcast and display images on the touch panel  32  and output audio from the speaker  33 . Yet further, the information input and output device  31  may include an optical disc drive (not shown) and read data from media such as a CD (a compact disc), DVD (a digital versatile disc or digital video disc), and BD (a Blu-ray Disc). Yet further, the information input and output device  31  may include an HDD (a hard disk drive, not shown) and play music recorded thereon. 
     Yet further, the information input and output device  31  may be used to output various messages from the host vehicle  100  or a device installed on the host vehicle  100  (e.g., an ETC [Electronic Toll Collection] in-vehicle device) and accept various operations for the installed device. 
     The automatic parking control unit  1  is connected to a brake system  41 . The brake system  41  is a system for performing the braking of the host vehicle  100 . The brake system  41  includes a brake device  42  that performs the braking of the host vehicle  100  and a brake controller  43  that controls the brake device  42 . The brake controller  43  includes a function of an automatic brake hold controller  44 . The automatic brake hold controller  44  realizes an automatic brake hold control part. The brake device  42  generates hydraulic pressure (oil pressure) thereby supplying hydraulic pressure to a wheel cylinder of each wheel to generate friction braking force. Note that the brake system  41  may use a regenerative brake in conjunction when the host vehicle  100  is, for example, a hybrid vehicle. The brake device  42  is, for example, a device where a brake-by-wire system is applied. Therefore, the brake device  42  may generate braking force irrespective of a brake pedal operation (a brake pedal is not shown in drawings). Furthermore, the brake device  42  may be a system installed with an electric brake booster. In this case, braking force may be generated with the electric brake booster irrespective of a brake pedal operation. The brake controller  43  is a controller for controlling the brake device  42 . 
     The automatic brake hold controller  44  is a function that is included as part of the brake controller  43  and controls an automatic brake hold function. The automatic brake hold function is a function for maintaining a braking state of the host vehicle  100  when the driver releases his foot from a brake pedal (not shown) after the brake pedal has been pressed. Note that with the automatic brake hold function, the host vehicle  100  is released from the automatic brake hold state when a predetermined condition is met, such as when an accelerator pedal (not shown) is operated. The automatic brake hold state may be turned on and off by operating a brake hold switch  45  installed close to the driver&#39;s seat of the host vehicle  100 . 
     The automatic parking control unit  1  is connected to a drive system  51 . The drive system  51  is a system to drive the host vehicle  100 . In the given example, the host vehicle  100  is a hybrid vehicle that includes as its driving source an engine  52  and a motor generator  53 . A hybrid controller  54  drives the host vehicle  100  by controlling the engine  52  and motor generator  53 . Note that the host vehicle  100  is not limited to a hybrid vehicle. When, for example, the host vehicle  100  is a gasoline-powered vehicle, the engine  52  is the driving source. When, as another example, the host vehicle  100  is an electric vehicle including a fuel-cell vehicle, a motor is the driving source. 
     A transmission system  61  is a system for carrying out gear changes of the host vehicle  100 . The transmission system  61  includes a transmission  62  that performs a gear change of the host vehicle  100 , a transmission controller  63  that controls the transmission  62 , and a gearshift  64  that is connected to the transmission  62 . The transmission  62  may be an automatic transmission or a manual transmission. With the transmission system  61  described here, a gear change may be carried out without driver operation and through the transmission controller  63  controlling the transmission  62 , in which case the transmission controller  63  moves the position of the gearshift  64  in accordance with the gear change. 
     The automatic parking control unit  1  is connected to a driver presence determiner  65 . The driver presence determiner  65  determines whether a driver is present in the driver&#39;s seat. 
     The automatic parking control unit  1  is connected to an electric power steering system  71  (an EPS system  71 ). The EPS system  71  is a system configured to assist the steering of a driver. The EPS system  71  includes a steering axle  73  with a steering wheel  72 , a drive motor  74  that drives the rotation of the steering axle  73 , and an EPS controller  75  that controls the drive motor  74 . The EPS system  71  rotates the steering axle  73  using the drive motor  74  as a driving source thereby assisting the steering operation of the driver turning the steering wheel  72 . 
     Next, the effect of the system centered on the automatic parking control unit I is described. 
     In the subsequent description, the phrase “automatic parking operation” refers to a series of operations described in the flowcharts of  FIGS. 4 and 5  (described later) that involves the automatic parking control unit  1  performing automatic operation of the host vehicle  100  through the control of individual systems and driving the host vehicle  100  to perform automatic parking. The phrase “automatic parking function” refers to the entire process indicated by the flowcharts of  FIGS. 4 and 5  concerning automatic parking that the automatic parking control unit  1  takes a central role executing (note that the entire process includes the “automatic parking operation”). 
     The automatic parking control unit  1  carries out the control of automatic parking. To do this, the automatic parking control unit  1  detects a space to perform a parking maneuver in a place such as a parking area by using the camera group  21  and sonar group  22 .  FIGS. 3A-3C  are top views of the host vehicle  100  for explaining a situation where the host vehicle  100  searches for a space to perform a parking maneuver. 
       FIG. 3A  is a top view showing a situation where the host vehicle  100  searches for a space to carry out a parking maneuver in a parking area  200  through the use mainly of the front camera  21 F of the camera group  21 . To the host vehicle  100  that has entered the parking area  200 , there are multiple parking spaces  202  (parking regions) separated by white lines  201  (boundary lines) that are arranged on the left and right. Some parking spaces  202  are already in use by other vehicles  203  but some are vacant. A driver of the host vehicle  100  drives the host vehicle  100  to advance slowly along a way  210  of the parking area  200  in a direction of travel  208 . Although the parking area  200  of the drawing shows parking spaces  202  on both sides of the way  210 , there are cases where parking spaces  202  are available on one side and not on the other. 
     From an image captured by the front camera  21 F ( FIG. 2 ), a region  211  may be recognized as a space that is available for the host vehicle  100  to perform a parking maneuver. By performing predetermined image processing on the image captured by the front camera  21 F, a difference in luminance levels may be recognized, and in this way, the host vehicle  100  may recognize the region  211  that is available for use to perform a parking maneuver. Camera recognition is good at recognizing a white line  201 . Camera recognition also includes a space recognition function. However, camera recognition is not good at recognizing objects such as snow, a white wall, and another vehicle close by. For this reason, control of the brake to avoid colliding with obstacles when performing automatic parking is difficult with only the image captured by the front camera  21 . 
     The sonar group  22  is therefore used in combination.  FIG. 3B  is a top view showing a situation where all the sonars of the sonar group  22  are used to search for a space to perform a parking maneuver in the parking area  200 . Sonars are capable of detecting an obstacle by transmitting and receiving sound waves and, in comparison to a camera, is good at detecting an obstacle close by. Therefore, a sonar may be used to accurately perform brake control against an obstacle. Furthermore, because a sonar has a higher space recognition function than a camera, the sonar group  22  is useful when deriving various parking patterns.  FIG. 3B  shows a region  261  that is available for use when performing a parking maneuver as recognized by the sonar group  22 . 
       FIG. 3C  is a top view showing both the region  211  and region  261 . Through the combined use of the front camera  21 F and sonar group  22 , a wide space may be recognized as a space available for use to perform a parking maneuver. Furthermore, the combined use enables a better brake control for avoiding an obstacle. In the example of  FIG. 3C , a parking space  202   a  is decided as a parking region in which the host vehicle  100  is to park through automatic parking. A space further down on the right as viewed from the host vehicle  100  is unoccupied and this location is decided as a location (a “change-to-reverse location”) where the host vehicle  100  stops before moving in reverse. The example shows how the host vehicle  100  may be parked through automated parking by (a) moving and steering the host vehicle  100  forward to the right (as shown by an arrow  263 ), (b) stopping the host vehicle  100  temporarily at the change-to-reverse location  262 , and (c) turning back the steering wheel and moving the host vehicle  100  in reverse so that the host vehicle  100  enters the parking space  202   a  (a parking region) (as shown by an arrow  264 ). 
     The above has been an outline of automated parking in which the front camera  21 F is used in combination with the sonar group  22 . A detailed description of a process of automated parking now follows. 
       FIGS. 4, 5A, and 5B  are flowcharts that explain a process carried out by the automatic parking control unit  1 .  FIGS. 6-9  are top views of a parking area for describing the process that the automatic parking control unit  1  carries out. Note that the flowcharts illustrate an outline of a series of operational steps described below and does not include every detail of the operational steps that the automatic parking control unit  1  performs. Operations not included in the flowcharts are included in the below description as deemed appropriate. 
     To begin with, as shown in  FIG. 6 , a driver of the host vehicle  100  drives the host vehicle  100  into a parking area  200  as shown by an arrow indicating a direction of travel  208 . During this time, the driver instructs the automatic parking function to be activated by, for example, operating the touch panel  32  (“Yes” of S 1 ). The instruction to activate the automatic parking function is received by the maneuver controller  12 . Upon receiving the instruction, the maneuver controller  12  displays a predetermined screen for the automatic parking function on the touch panel  32  (S 2 ). Note that during the series of operational steps, various types of automatic parking function screens are displayed as deemed appropriate. 
     The recognition part  11  makes a combined use of the front camera  21 F and the sonar group  22  with a method such as that described above with reference to  FIGS. 3A-3C . The recognition information acquired by the recognition part  11  is used by the maneuver controller  12  to search for a parking maneuver space that the host vehicle  100  is able to use when performing a parking maneuver (S 3 ). 
     Furthermore in S 3 , based on the result of the search, the following operations are carried out. First, the maneuver controller  12  determines a parking region (a parking space  202 ) where the host vehicle  100  is possible to park. In the example of  FIG. 7 , parking spaces  202   a  and  202   b  are candidates for a parking-target parking region. Furthermore, based on the detection results of the front camera  21 F and sonar group  22 , the maneuver controller  12  calculates paths that avoid an obstacle for the host vehicle  100  to park in the parking space  202   a  and in the parking space  202   b.    
     Next, the maneuver controller  12  estimates the current location of the host vehicle  100  based on the detection results of the inertial sensor  23  and wheel speed sensor  24 . Using this location as reference, the maneuver controller  12  calculates each of the target movement paths of the host vehicle  100  to park in the parking space  202   a  and in the parking space  202   b.  The maneuver controller  12  provides a display on the touch panel  32  of relative locations of the host vehicle  100  and the parking spaces  202   a  and  202   b  such as that shown in  FIG. 7 . For ease of recognition by the driver, the parking spaces  202   a  and  202   b  are indicated on a displayed image with a mark such as a frame  205 . 
     Since the “Yes” of Sl, the driver has been driving the host vehicle  100  to move through the parking area  200 , and during this time the operations of S 3  continue to be performed (“No” of S 4 ). However, when the brake pedal (not shown) is operated by the driver (“Yes” of S 4 ) and the host vehicle  100  stops, the maneuver controller  12  performs the following operations. When the driver operates the touch panel  32  and selects one candidate (in this example, the parking space  202   a  or  202   b ) as the parking-target parking region (“Yes” of S 5 ), the maneuver controller  12  determines that the selected candidate is the parking-target parking region. The selection may, for example, be carried out by touching a region indicated by a frame  205  mentioned above. When the selection is not made (“No” of S 5 ), the abovementioned operations of S 3  are continued. Note that the operational steps of S 4  and S 5  may be reversed in order. 
     When the parking-target parking region is determined as above (“Yes” of S 5 ), the maneuver controller  12  displays a mark  271 , such as the one shown in  FIG. 8 , on an image of the parking region (in this example, the parking space  202   a ) displayed on the touch panel  32 . 
     The maintain stop position controller  13  instructs the automatic brake hold controller  44  to turn on the automatic brake hold function (S 6 ). As a result of turning on the automatic brake hold function, the brake state of the host vehicle  100  is automatically maintained when a foot of the driver is removed from the brake pedal (not shown). 
     Furthermore, a travel route indicated by arrows  263  and  264  in  FIG. 3C  and a change-to-reverse location indicated by the number “ 262 ” also in  FIG. 3C  are determined by the determination part  14  and decision part  15 . When the travel route and change-to-reverse location are determined, a parking reference location for the parking-target parking region that was selected in S 5  is determined (S 6 ). The determination process of the parking reference location is described later. 
     Subsequently, the maneuver controller  12  starts measuring an elapsed time, a first length of time, with a timer (S 7 ). Then, the maneuver controller  12  displays a message on automatic parking on the touch panel  32  and outputs an audio message with the speaker  33  (S 8 ). In some embodiments, the message on automatic parking is output on the touch panel  32  only. The message notified to the driver contains information to the following effect: “The automatic brake hold has been turned on. To begin automatic parking, press the brake hold switch, release your hands from the steering wheel, and remove your foot from the brake pedal”. 
     If the driver follows all the instructions given in the message, the brake hold switch  45  will be pressed thereby releasing the brake hold switch  45  (i.e., the brake hold switch  45  will be released from a “pressed” state; “Yes” of S 9 ). When the brake hold switch  45  is not released (“No” of S 9 ), the abovementioned message continues to be displayed on the touch panel  32 . 
     Note that when a predetermined operation is performed during the operational steps S 2 -S 8  that have been described, the series of operational steps for automatic parking is terminated. This may occur, for example, when the driver operates the automatic parking function screen displayed on the touch panel  32  to terminate the operation of the automatic parking function, or when the driver intentionally operates the gearshift  64 . 
     When the brake hold switch  45  is released (“Yes” of S 9 ), the operations of SI  0  are carried out. That is, the maintain stop position controller  13  instructs the automatic brake hold controller  44  to turn off the automatic brake hold function (S 10 ). This causes the brake on the host vehicle  100  to be released. Furthermore, the maintain stop position controller  13  stores a record of operation of the automatic brake hold function in S 6  in storage such as a non-volatile memory (S 10 ). Yet further, the maneuver controller  12  starts the automatic parking operation (S 10 ). (Details of the automatic parking operation is described later.) Yet further, the maneuver controller  12  starts measuring another elapsed time, a second length of time, with a timer (S 10 ). Note that when the brake pedal (not shown) is not released, the maneuver controller  12  performs control as follows. Even when the brake hold switch  45  is released (S 9 ), the maneuver controller  12  does not start the automatic parking operation (S 10 ). The automatic brake hold function (S 6 ) remains turned on. 
     The automatic parking operation started by the maneuver controller  12  includes the following operations. As shown in  FIG. 9 , the maneuver controller  12  controls the host vehicle  100  to travel along the target movement path that has been decided in S 3 . That is, the maneuver controller  12  controls the brake system  41 , drive system  51 , transmission system  61 , and EPS system  71 . Through this control, the host vehicle  100  reverse parks in the parking space  202   a,  the parking-target parking region. 
     Described in more detail, the maneuver controller  12  controls these systems so that the host vehicle  100  travels forward in D range as shown by the arrow  263  until the change-to-reverse location  262  is reached, at which point the host vehicle  100  stops temporarily. Next, the maneuver controller  12  controls these systems so that the host vehicle  100  (i) travels backwards in R range and into the parking space  202   a,  the parking-target parking region, and (ii) stops when the host vehicle  100  has entered the parking space  202   a.    
     Once the automatic parking operation has been started (S 10 ), whether a condition to suspend the automatic parking function has been met while the automatic parking operation is taking place is determined (S 11 ). 
     In S 11 , an operation of the steering wheel  72  is one action that meets the condition to suspend the automatic parking function and a shifting of the gearshift  64  to the N range is another action that meets the condition to suspend the automatic parking function. 
     Furthermore, in S 11 , the maneuver controller  12  determines whether the first length of time, whose measurement started in S 7 , has reached a predetermined length of time. The first length of time is a period of time from when the parking-target parking region is decided (S 5 , S 7 ) to when the operation to remove the automatic brake hold with the brake hold switch  45  is received (“Yes” of S 9 ). The condition to suspend the automatic parking function is also met if the first length of time is equal to or greater than the predetermined length of time. Yet further, in S 11 , the maneuver controller  12  determines whether the second length of time whose measurement started in S 10  has reached a predetermined length of time. The second length of time is a period of time from when the brake hold switch  45  is operated (“Yes” of S 9 ) to when a released state of the brake pedal (not shown) is detected. The condition to suspend the automatic parking function is also met if the second length of time is equal to or greater than the predetermined length of time. 
     Furthermore, the condition to suspend the automatic parking function is also met if, through the driver presence determiner  65 , it is determined that a driver seat is without a driver. The driver presence determiner  65  may be configured from a device such as a seating sensor that detects whether a driver is seated in the driver&#39;s seat, an on-board camera that takes an image of the vehicle interior (the presence of a seated driver may be determined through image processing), or a door-opening sensor that detects whether the door next to the driver&#39;s seat is opened or closed. Yet further, various other conditions under which suspending the automatic parking function is considered sensible may be used as a criterion to meet the condition to suspend the automatic parking function. 
     When the automatic parking operation is completed with the condition to suspend the automatic parking function not being met (“Yes” of S 12 ), a message to notify the completion of the automatic parking operation is output through the touch panel  32 , speaker  33 , or the like. The next operational step becomes S 13 . If the condition to suspend the automatic parking function has been met during the automatic parking operation (“No” of S 12 ), the next operational step becomes S 16 . The automatic parking operation is complete (“Yes” of S 12 ) when the host vehicle  100  comes to a stop inside the parking-target parking region (in this example, the parking space  202   a ). The location within the parking region where the host vehicle  100  stops is based on the parking reference location determined in S 6 . 
     In S 13 , the maneuver controller  12  determines whether a record of an automatic brake hold operation has been stored in S 10 . If there is a stored record of an automatic brake hold operation (“Yes” of S 13 ), the brake system  41  is controlled to turn on the automatic brake hold function once again. The operational step then advances to S 15 . Therefore, even if the driver is not pressing down on the brake pedal (not shown), the host vehicle  100  is applied with a brake and stops. If there is no stored record (“No” of S 13 ), the process advances to S 15 . In this case, the automatic brake hold function stays turned off. An example of when a record of an automatic brake hold operation is not stored is when, even though the automatic brake hold function is turned on in S 6 , the driver operates the brake hold switch  45  to turn off the function. In S 15 , the maneuver controller  12  controls the gearshift  64  so that the gearshift position shifts to the P range to end the automatic parking. 
     In S 16 , on the other hand, because the condition to suspend the automatic parking function has been met (“Yes” of S 11 ), the maneuver controller  12  suspends the automatic parking function. Then, the maneuver controller  12  determines whether a condition to resume the automatic parking function exists (S 17 ). A condition to resume exists if a predetermined criterion is met. The predetermined criterion may be met if a predetermined operation is carried out on a selection screen  81  of  FIG. 10 , the selection screen  81  being one type of automatic parking function screens that are displayed on the touch panel  32 . The selection screen  81  displays a “Resume” button  82  and “Terminate” button  83 . If the driver operates the “Resume” button  82 , the predetermined criterion is met and the condition to resume the automatic parking function exists. If the “Terminate” button  83  is operated, then a termination of the automatic parking function is selected. 
     If the condition to resume the automatic parking function exists (“Yes” of S 17 ), the process returns to S 2  and the automatic parking function resumes. If a predetermined amount of time elapses without the condition to resume the automatic parking function arising (“No” of S 17  and “Yes” of S 18 ), the maneuver controller  12  makes a decision to terminate the automatic parking function (S 19 ), and the series of operational steps comes to an end. If the predetermined amount of time has not yet elapsed and the condition to resume the automatic parking function has not arisen (“No” of S 17  and “No” of S 18 ), the maneuver controller  12  returns to S 16 . Note that if the “Terminate” button  83  is operated, the maneuver controller  12  terminates the automatic parking function without waiting for the predetermined amount of time referred to in S 18  to elapse. 
     Note that when the condition to suspend the automatic parking function exists (“Yes” of S 11 ), the maneuver controller  12  may resume the automatic parking function from S 2  if the condition to resume the automatic parking function is met (“Yes” of S 17 ). On the other hand, if a condition to terminate is met during the series of operations of the automatic parking function, the maneuver controller  12  terminates the process of  FIGS. 4 and 5  and does not resume the process. When the automatic parking function is to start again, the maneuver controller  12  begins the operational steps from S 1 . The “condition to terminate” may be met if, for example, one of the following criteria is met during the series of operations of the automatic parking function: (a) the gearshift  64  is shifted to a P range; (b) an electric park brake comes into operation; and (c) an instruction to operate the parking brake function has been input via the touch panel  32 . Furthermore, if a condition to halt the automatic parking function is met during the series of operations of the automatic parking function, the series of operations of the automatic parking function is brought to a halt. However, in this case, the series of operations of the automatic parking function is resumed from the point at which the operation has been halted if the condition to halt is removed. The “condition to halt” exists if a criterion is met such as an operation of the brake pedal (not shown). 
       FIG. 11  is a flowchart of a subroutine for the determination process of the parking reference location of S 6 . Words expressing directions such as “front” and “back” are used to describe directions from the viewpoint of the host vehicle  100  that is pausing at the change-to-reverse location  262  (see  FIG. 9 ). The process of  FIG. 11  is performed based on a situation of the surroundings of the host vehicle  100  as recognized by the recognition part  11 . First, as shown in  FIG. 12 , the determination part  14  determines whether a solid line (or a broken line [the same hereinafter])  221  joining the rear ends of the left and right boundary lines  201  at the rear of the parking space  202   a  (a parking region) where the host vehicle  100  is to park (S 21 ). A white line that marks the boundary of the parking space  202   a  at the rear side thereof may be regarded as a solid line  221 . An edge of an obstacle such as a fence, a building, or another vehicle may also be regarded as a solid line  221 . In other words, a solid line  221  is a mark or an object that indicates a location of a limit of a parking space  202   a  on the rear side thereof. If a solid line  221  exists at the rear of the parking region (“Yes” of S 21 ), the decision part  15  sets the parking reference location  222  to a location that is a predetermined distance L 1  away (for example, towards the front of the parking region) from the solid line  221  at the rear as shown in  FIG. 12 . This parking reference location  222  is where the rear end of the host vehicle  100  is to be positioned when parking the host vehicle  100  in the parking space  202   a  (a parking region). 
     Next, the determination part  14  determines whether the host vehicle  100  will protrude from a virtual line  231  when the parking reference location  222  remains at the location that has been decided in S 22  (S 23 ). A virtual line  231  refers to a line joining the front ends  201   a  of the left and right white lines (boundary lines)  201  of the parking space  202   a  (a parking region) as shown in  FIG. 13 . Whether or not the host vehicle  100  will protrude from the virtual line  231  may be determined from the depth (the length from the entry side to the rear side) of the parking space  202   a,  the predetermined distance L 1 , and the length of the host vehicle  100 . 
     When it is determined that the host vehicle  100  will protrude from the virtual line  231  (“Yes” of S 23 ), the parking reference location  222  of  FIG. 12  is modified to a parking reference location  223  of  FIG. 13  that is further to the back (in the direction that prevents the host vehicle  100  from protruding) of the parking space  202   a  than the parking reference location  222 . The modified parking reference location  223  is a predetermined distance L 2 (&lt;L 1 ) to the front from the solid line  221  at the rear. The parking reference location  223  is a location that prevents the host vehicle  100  from protruding from the virtual line  231  when the rear end of the host vehicle  100  is aligned with the parking reference location  223  when the host vehicle  100  is parked in the parking space  202   a  (the parking region). 
     When a solid line  221  does not exist at the rear of the parking space  202   a  (a parking region) where the host vehicle  100  is to park (“No” of S 21 ), the determination part  14  determines whether the parking space  202   a  (a parking region) is a demarcated parking region with boundary lines including at least left and right white lines (boundary lines)  201  ( FIGS. 14 and 15 ) (S 25 ). A “demarcated parking region” refers to a parking region whose region is demarcated by boundary lines including left and right white lines (boundary lines)  201  that is in a parking area  200  where vehicles park side to side such as those shown in  FIGS. 6-9 . 
     When the parking space  202   a  (a parking region) is a demarcated parking region where left and right white lines (boundary lines)  201  exist (“Yes” of S 25 ), the determination part  14  determines whether the left and right boundary lines are angled obliquely at a predetermined angle (S 26 ). The determination part  14  determines whether the left and right boundary lines are angled obliquely at the predetermined angle by determining whether the left and right boundary lines  201  are, for example, substantially at an angle between 45 and 60 degrees to the direction of travel  208  of the way  210  (i.e., a lengthwise direction of the way  210 ) in the parking area  200  or not (for example, the left and right boundary lines  201  are at an angle that is at or is close to substantially 90 degrees to the direction of travel  208 ).  FIG. 14  shows an example where the left and right boundary lines  201  are angled obliquely at the predetermined angle.  FIG. 15  shows an example where the left and right boundary lines  201  are not angled obliquely. 
     When the left and right boundary lines  201  are angled obliquely at the predetermined angle (“Yes” of S 26 ), a perpendicular line  232  is set by the decision part  15  as the parking reference location (S 27 ). The perpendicular line  232  is a line that extends perpendicularly from the front end  201   a  of one of the left and right white lines (boundary lines)  201  to the other one of the left and right white lines (boundary lines)  201 . This parking reference location that is set to the perpendicular line  232  becomes a reference location where the front end of the host vehicle  100  is positioned when parking the host vehicle  100  in the parking space  202   a  (the parking region). 
     When the left and right boundary lines  201  are not angled obliquely at the predetermined angle (“No” of S 26 ), and hence the left and right boundary lines  201  are at an angle that is at or is close to substantially 90 degrees to the direction of travel  208 , the operational step advances to S 28 . In S 28 , the parking reference location  234  is set by the decision part  15  to a location that is a predetermined distance L 3  away from a virtual line  233  that joins the front ends  201   a  of the left and right white lines (boundary lines)  201  as shown in  FIG. 15 . More specifically, the parking reference location  234  is set to a location that is further to the rear side of the parking space  202   a  (a parking region) from the virtual line  233  by the predetermined distance L 3 . This parking reference location  234  becomes a reference location where the front end of the host vehicle  100  is positioned when parking the host vehicle  100  in the parking space  202   a  (the parking region). 
     When the parking space  202   a  (a parking region) is not a demarcated parking region with left and right white lines (boundary lines)  201  (“No” of S 25 ), the parking space  202   a  (a parking region) is in a parking area in which no left and right white lines (boundary lines)  201  exist that separate parking regions of individual vehicles parked side by side. 
     In this case, as shown in  FIG. 16 , the decision part  15  sets the parking reference location to a virtual line  241  that joins the front ends  203   a  of other vehicles  203  on the left and right of the parking space  202   a  (a parking region) (S 29 ). This parking reference location that is set to the virtual line  241  is a straight line across front ends  203   a  of the other vehicle  203  on the left and right that runs in parallel with the direction of travel  208  of the way  210 . This parking reference location that is set to the virtual line  241  becomes a reference location where the front end of the host vehicle  100  is positioned when parking the host vehicle  100  in the parking space  202   a  (a parking region). In the example of  FIG. 16 , there are other vehicles  203  on the left and right of the parking space  202   a  (a parking region), and a virtual line  241  that joins the front ends  203   a  of the pair of other vehicles  203  are in parallel to the direction of travel  208 . When a front end  203   a  of one of the pair of other vehicles  203  is further out to the front, a line that extends from the front end  203   a  of the one of the pair of other vehicles  203  (i.e., the other vehicle  203  whose front end  203   a  is further out to the front) and is parallel to the direction of travel  208  becomes the virtual line  241 . When there is only another vehicle  203  on either the left or right of the parking space  202   a  (a parking region), a line that extends from the front end  203   a  of the another vehicle  203  and is parallel to the direction of travel  208  becomes the virtual line  241 . The same applies when one of the other vehicles  203  on the left and right is parked at a distance from the parking space  202   a  (a parking region) in which the host vehicle  100  is to park. 
     According to the automatic parking control unit  1  (the parking assistance device) described above, a parking reference location for parking the host vehicle  100  in a parking region is determined (S 27 -S 29 ) according to the type of the parking region (the parking space  202   a ) (S 25 , S 26 ). In this way, the automatic parking control unit  1  performs automatic parking of the host vehicle  100  at a suitable parking location that is in accordance with the type of a parking region (a parking space  202   a ) in which the host vehicle  100  is to be parked. 
     When the parking region (the parking space  202   a ) is a demarcated parking region with boundary lines including at least left and right boundary lines  201  (“Yes” of S 25  and “No” of S 26 ), the parking reference location  234  is set to a location that is a predetermined distance L 3  further to the rear of a virtual line  233  joining the front ends  201   a  of the left and right boundary lines  201  (S 28 ,  FIG. 15 ). If the host vehicle  100  parked with the front end thereof close to the virtual line  233  or protruding from the virtual line  233 , there is a rise in risk of the host vehicle  100  coming into contact with another vehicle while the other vehicle parks or leaves on the left or right of the host vehicle  100 . The parking reference location  234  is intended to avoid this rise. 
     When the parking region (the parking space  202   a ) is a parking region with no boundary lines on the left and right  201  (“No” of S 25 ,  FIG. 16 ), the parking reference location  234  is set to a virtual line  241  joining the front ends  203   a  of the other vehicles on the left and right  203  (S 29 ). In this way, when at least one of the other vehicles  203  on the left and right are parked somewhat towards the front to avoid an obstacle or another object at the back, by aligning the front end of the host vehicle  100  with the front end of the at least one of the other vehicles  203  when parking, the risk of the host vehicle  100  coming into contact with an obstacle at the back will be reduced. 
     When the automatic parking control unit  1  recognizes that the left and right boundary lines  201  of the parking region (parking space  202   a ) are angled obliquely at the predetermined angle with respect to the way  210  that the host vehicle  100  is travelling inside the parking area (“Yes” of S 26 ,  FIG. 14 ), the operational step of S 27  is performed. In other words, a parking reference location is set to a perpendicular line  232  that extends perpendicularly from a front end  201   a  of one of the left and right boundary lines  201  of the parking region (parking space  202   a ) to the other one of the left and right boundary lines  201 . If the host vehicle  100  is parked with front end thereof protruding from the perpendicular line  232 , there is a rise in risk of the host vehicle  100  coming into contact with another vehicle while the other vehicle leaves or parks on the left or right of the host vehicle  100 . Selecting the parking reference location of S 27  is intended to reduce this risk. 
     When the automatic parking control unit  1  determines that a solid line  221  exists at the back of the parking region (the parking space  202   a ) (“Yes” of S 21 ,  FIG. 12 ), the solid line  221  is prioritized and the parking reference location is determined based on the solid line  221 . More specifically, the parking reference location  222  is set to a location that is a predetermined distance L 1  away from (i.e., further to the front of) the solid line  221  (S 22 ). If the host vehicle  100  is parked too closely to the solid line  221  such as a white line or an obstacle, the risk of the host vehicle  100  coming into contact with an obstacle including another vehicle parked at the back of the host vehicle  100  increases. Prioritizing the solid line  221  when determining the parking reference location is intended to avoid this increase. 
     However, when, by adopting the parking reference location  222 , the host vehicle  100  protrudes from the virtual line  231  that joins the front ends  201   a  of the left and right boundary lines  201  of the parking region (the parking space  202   a ), instead of the predetermined distance L 1 , a shorter predetermined distance L 2  is adopted. The reference location of the host vehicle  100  in the parking region (the parking space  202   a ) is changed from the parking reference location  222  that has been decided in S 22  to a parking reference location  223  (for example, the reference location is moved further back from the parking reference location  222 ) (S 24 ). If the parked host vehicle  100  protrudes from the virtual line  231 , there is a rise in risk of the host vehicle  100  coming into contact with another vehicle while the other vehicle parks or leaves on the left or right of the host vehicle  100 . Changing the parking reference location is intended to avoid this rise. 
     Note that although in the example described above, the host vehicle  100  enters the parking region (the parking space  202   a ) by reverse parking, the host vehicle  100  may be enter with the front end of the host vehicle  100  entering first (i.e., forward parking). In this case, the parking reference location where the front end of the host vehicle  100  is aligned in the above description becomes a parking reference location where the back end of the host vehicle  100  is aligned, and the parking reference location where the rear end of the host vehicle  100  is aligned becomes the parking reference location where the front end of the host vehicle  100  is aligned. 
     Note that when the parking space  202   a  (a parking region) is not a demarcated parking region where left and right white lines (boundary lines)  201  exist, (“No” of S 25 ), and one or both of the other vehicles  203  on the left and right of the parking space  202   a  (a parking region) are parked with the rear facing the way  210 , the front end  203   a  of the above description for the one or both of the other vehicles  203  is replaced by the rear end of the one or both of the other vehicles  203  that faces the way  210 .