Patent Publication Number: US-10308283-B2

Title: Parking assist apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 U.S.C. § 119 to Japanese Patent Application 2017-017208, filed on Feb. 2, 2017, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     This disclosure relates to a parking assist apparatus. 
     BACKGROUND DISCUSSION 
     There is known a parking assist apparatus that assists parking or exit by a driver by being mounted on a vehicle such as an automobile and displaying a host vehicle image and an overhead image of a periphery of the vehicle on a display device. 
     Examples of related art include JP 2009-49943A (Reference 1) and JP 2016-66322A (Reference 2). 
     However, in a case of forward parking, backward exit, or the like, in which the parking assist apparatus described above requires a movement distance up to the maximum steering angle and a set path from an assist starting point to a target frame for parking is lengthened (for example, about 7 m), the host vehicle image and the target frame become outside the display image. Therefore, there is a problem that it is difficult for the parking assist apparatus described above to display an appropriate display image including the host vehicle image and the target frame on the display device. 
     Thus, a need exists for a parking assist apparatus which is not susceptible to the drawback mentioned above. 
     SUMMARY 
     A parking assist apparatus according to an aspect of this disclosure includes: a peripheral image generation portion that generates an overhead image of a periphery viewed from above based on a captured image of a periphery of a vehicle; and a display image generation portion that generates a display image by superimposing a host vehicle image displaying a host vehicle on one of left and right sides in the overhead image and superimposing a target frame displaying a target of a movement destination of the vehicle on the other of the left and right sides in the overhead image in an assist mode of a forward parking or a backward exit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and additional features and characteristics of this disclosure will become more apparent from the following detailed description considered with the reference to the accompanying drawings, wherein: 
         FIG. 1  is a plan view of a vehicle according to an embodiment; 
         FIG. 2  is a block diagram illustrating a configuration of a parking assist system mounted on the vehicle; 
         FIG. 3  is a functional block diagram explaining functions of the parking assist apparatus; 
         FIG. 4  is a diagram illustrating an example of a display image in a left forward parking mode in parking assist for automatic driving; 
         FIG. 5  is a diagram illustrating an example of a display image in a left backward exit mode in the parking assist for automatic driving; 
         FIG. 6  is a diagram illustrating an example of a display image in a left backward parking mode in parking assist for automatic driving; 
         FIG. 7  is a flowchart illustrating assist processing executed by a controller; 
         FIG. 8  is a flowchart illustrating left forward parking assist processing which is a portion of assist processing executed by the controller; and 
         FIG. 9  is a flowchart illustrating left backward exit assist processing executed by the controller. 
     
    
    
     DETAILED DESCRIPTION 
     The same reference numerals are given to the same constituent elements in the following exemplary embodiments and the like, and redundant explanation will be appropriately omitted. 
     Embodiment 
       FIG. 1  is a plan view of a vehicle  10  according to the embodiment. As illustrated in  FIG. 1 , the vehicle  10  includes a vehicle body  12  and four imaging portions  14   a ,  14   b ,  14   c , and  14   d . In a case where it is not necessary to distinguish the imaging portions  14   a ,  14   b ,  14   c , and  14   d , they are described as the imaging portion  14 . 
     The vehicle body  12  constitutes an occupant compartment where occupants ride. The vehicle body  12  accommodates and holds the imaging portion  14  and the like. 
     The imaging portion  14  is, for example, a digital camera incorporating an imaging device such as a charge coupled device (CCD) or CMOS image sensor (CIS). The imaging portion  14  can output a moving image including a plurality of frame images generated at a predetermined frame rate or data of a still image as data of a captured image. Each of the imaging portions  14  has a wide angle lens or a fisheye lens, and can image a range of 140° to 190° in the horizontal direction. The optical axis of the imaging portion  14  is set obliquely downward. Therefore, the imaging portion  14  outputs captured image data imaged the periphery including the road surface of a periphery of the vehicle  10 . 
     The imaging portion  14  is provided on a periphery of the vehicle body  12 . For example, the imaging portion  14   a  is provided at a center portion (for example, front bumper) of the front end portion of the vehicle body  12  in the lateral direction. The imaging portion  14   a  generates a captured image obtained by imaging a periphery of the front side of the vehicle  10 . The imaging portion  14   b  is provided at a center portion (for example, rear bumper) of the rear end portion of the vehicle body  12  in the lateral direction. The imaging portion  14   b  generates a captured image obtained by imaging a periphery of the rear side of the vehicle  10 . The imaging portion  14   c  is provided at a center portion (for example, left side mirror  12   a ) of the left end portion of the vehicle body  12  in the front and rear direction. The imaging portion  14   c  generates a captured image obtained by imaging a periphery of the left side of the vehicle  10 . The imaging portion  14   d  is provided at a center portion (for example, right side mirror  12   b ) of the right end portion of the vehicle body  12  in the front and rear direction. The imaging portion  14   d  generates a captured image obtained by imaging a periphery of the right side of the vehicle  10 . 
       FIG. 2  is a block diagram illustrating the configuration of a parking assist system  30  mounted on the vehicle  10 . As illustrated in  FIG. 2 , the parking assist system  30  further includes an automatic driving portion  32 , a monitor device  34 , a parking assist apparatus  36 , and an in-vehicle network  38 . 
     The automatic driving portion  32  controls an accelerator, a brake, a steering wheel, and the like based on an instruction from the parking assist apparatus  36  to automatically drive the vehicle  10  during the parking and during the exit, or the like. 
     The monitor device  34  is provided in a dashboard or the like in the occupant compartment. The monitor device  34  includes a display portion  40 , a voice output portion  42 , and an operation input portion  44 . 
     The display portion  40  displays an image based on the image data transmitted by the parking assist apparatus  36 . The display portion  40  is, for example, a display device such as a liquid crystal display (LCD) or an organic electro luminescence display (OELD). 
     The voice output portion  42  outputs voice based on the voice data transmitted by the parking assist apparatus  36 . The voice output portion  42  is, for example, a speaker. The voice output portion  42  may be provided at a different position from the display portion  40  in the occupant compartment. 
     The operation input portion  44  receives an input by an occupant. The operation input portion  44  is, for example, a touch panel. The operation input portion  44  is provided on a display screen of the display portion  40 . The operation input portion  44  is configured to be capable of transmitting the image displayed by the display portion  40 . Accordingly, the operation input portion  44  can visually recognize the image displayed on the display screen of the display portion  40  by the occupant. The operation input portion  44  receives an instruction input by touching the position corresponding to the image displayed on the display screen of the display portion  40  by the occupant and thus transmits the instruction to the parking assist apparatus  36 . 
     The parking assist apparatus  36  is a computer including a microcomputer such as an electronic control unit (ECU). The parking assist apparatus  36  acquires data of the captured image from the imaging portion  14 . The parking assist apparatus  36  transmits data relating to an image or voice generated based on the captured image or the like to the monitor device  34 . The parking assist apparatus  36  controls the automatic driving portion  32  to assist the vehicle  10  by automatically driving the vehicle  10  during the parking or during the exit. The parking assist apparatus  36  includes a central processing unit (CPU)  36   a , a read only memory (ROM)  36   b , a random access memory (RAM)  36   c , a display controller  36   d , a voice controller  36   e , a solid state drive (SSD)  36   f . The CPU  36   a , the ROM  36   b  and the RAM  36   c  may be integrated in the same package. 
     The CPU  36   a  is an example of a hardware processor, reads a program stored in a nonvolatile storage device such as the ROM  36   b , and executes various calculation processing and control according to the program. For example, the CPU  36   a  executes image processing such as an image for parking assist to be displayed on the display portion  40 . 
     The ROM  36   b  stores each program and parameters necessary for executing the program and the like. The RAM  36   c  temporarily stores various data used in the calculation in the CPU  36   a . The display controller  36   d  mainly executes processing of the image obtained by the imaging portion  14 , the data conversion of the display image to be displayed on the display portion  40  among the calculation processing by the parking assist apparatus  36 . The voice controller  36   e  mainly executes processing of the voice to be output to the voice output portion  42  among the calculation processing by the parking assist apparatus  36 . The SSD  36   f  is a rewritable nonvolatile storage portion and maintains data even in a case where the power source of the parking assist apparatus  36  is turned off. 
     In the embodiment, the parking assist apparatus  36  cooperates with hardware and software (control program) to manage assist processing during parking and exit of the vehicle  10 . The parking assist apparatus  36  generates display images  68  and  70  in which the host vehicle image and the target frame are superimposed on the top view type peripheral image generated based on the captured image including the peripheral image captured by the imaging portion  14  and thus displays the display images on the display portion  40 . The parking assist apparatus  36  controls the automatic driving portion  32  to move the vehicle  10  to the target frame by automatic driving to assist the parking and the exit. 
     The in-vehicle network  38  is, for example, a controller area network (CAN). The in-vehicle network  38  electrically connects the automatic driving portion  32 , the parking assist apparatus  36 , and the operation input portion  44  so that signals and information can be transmitted and received with each other. 
       FIG. 3  is a functional block diagram explaining the function of the parking assist apparatus  36 . As illustrated in  FIG. 3 , the parking assist apparatus  36  includes a controller  50  and a storage portion  52 . 
     The controller  50  is realized, for example, using a function of the CPU  36   a . The controller  50  includes a mode determination portion  54 , a peripheral image generation portion  56 , a display image generation portion  58 , and a driving controller  60 . By reading the automatic driving assist program stored in the storage portion  52 , the controller  50  may realize the functions of the mode determination portion  54 , the peripheral image generation portion  56 , the display image generation portion  58 , and the driving controller  60 . A portion or all of the mode determination portion  54 , the peripheral image generation portion  56 , the display image generation portion  58 , and the driving controller  60  may be configured by hardware such as a circuit including an application specific integrated circuit (ASIC). 
     For example, in a state such as a navigation mode in which a navigation image is displayed, the mode determination portion  54  receives from the operation input portion  44  instructions of mode switching to an assist mode that assists the parking or the exit by automatic driving by an occupant. Furthermore, after the mode switching from the navigation mode to the assist mode, the mode determination portion  54  determines the parking assist mode or the exit assist mode selected by the occupant based on the input from the operation input portion  44 . The assist mode includes a forward parking mode and a backward parking mode. Further, the forward parking mode includes a left forward parking mode for parking to the left front target frame, a right forward parking mode for parking to the right front target frame, a right backward exit mode for exiting to the right rear target frame, and left backward exit mode for exiting to the left rear target frame. The backward parking mode includes a left backward parking mode for parking to the left rear target frame, a right backward parking mode for parking to the right rear target frame, a right forward exit mode for exiting to the right front target frame, and a left forward exit mode for exiting to the left front target frame. 
     In the assist mode of forward parking or backward exit, the peripheral image generation portion  56  generates an overhead image of the periphery viewed from above, based on the captured image of the periphery of the vehicle  10  acquired from the imaging portion  14 . The overhead image is also referred to as a top view image or a bird&#39;s eye image. The peripheral image generation portion  56  generates the overhead image by executing image processing and synthesis processing on a plurality of captured images obtained from the plurality of imaging portions  14 . Specifically, the peripheral image generation portion  56  generates an overhead image centered on the parking direction side or the exit direction side as viewed from the vehicle  10 , that is, the overhead image centered on a direction side where the target frame is set as viewed from the vehicle  10 . For example, in a case of the left forward parking mode, since the target frame is set to the left front, the peripheral image generation portion  56  generates an overhead image centered on the left front of the vehicle  10 . The peripheral image generation portion  56  generates an overhead image of the vehicle  10  in all directions based on the captured image and then trims a necessary region on the traveling direction side of the vehicle  10 , and thus an overhead image  72  centered on the traveling direction side of the vehicle  10  may be generated. In addition, in the backward parking or forward exit assist mode, the peripheral image generation portion  56  generates an overhead image centered on the position of the vehicle  10  based on the captured image. The peripheral image generation portion  56  outputs the generated overhead image together with the captured image to the display image generation portion  58 . In the following description, the position in the overhead image will be described based on the front, rear, left and right directions of the vehicle  10 . 
     In the assist mode of the forward parking or the backward exit, the display image generation portion  58  generate a first display image by superimposing the host vehicle image on one of left and right sides of the overhead image and by superimposing the target frame displaying the target of the movement destination of the vehicle  10  on the other of the left and right sides in the overhead image. 
     Specifically, in the forward parking assist mode, the display image generation portion  58  superimposes the host vehicle image on the rear side in the overhead image. In the backward exit assist mode, the display image generation portion  58  superimposes the host vehicle image on the front side in the overhead image. In other words, in a case of forward parking and backward exit, the display image generation portion  58  superimposes the host vehicle image on a side opposite to the traveling direction in the overhead image as viewed from the center of the overhead image. 
     In a case of the assist mode for assisting the forward parking or the backward exit to the target frame on the left side of the vehicle  10 , the display image generation portion  58  superimposes the target frame on the left side in the overhead image. In a case of the assist mode for assisting the forward parking or the backward exit to the target frame on the right side of the vehicle  10 , the display image generation portion  58  superimposes the target frame on the right side in the overhead image. In other words, the display image generation portion  58  superimposes the target frame on a portion on a side opposite to the host vehicle image in the overhead image. 
     For example, in a case of the left forward parking mode, since the vehicle  10  is moved to the left front and is parked, the display image generation portion  58  superimposes the host vehicle image on the right rear side of the overhead image. The display image generation portion  58  superimposes the target frame on a preset set path in which the host vehicle image is set in the overhead image as a starting point based on set path data  66   d  in the storage portion  52 . For example, in a case of the left forward parking mode, the display image generation portion  58  superimposes the target frame on the left front position in the overhead image. 
     In the assist mode of the backward parking and the forward exit, the display image generation portion  58  generates a first display image by superimposing the host vehicle image on the center in the overhead image and superimposing the target frame on the set path in which the host vehicle image is set in the overhead image as a starting point. 
     The display image generation portion  58  generates a second display image in which the target frame is superimposed on the captured image. Specifically, the display image generation portion  58  superimposes the target frame on the captured image so that it is at the same position as the real world position of the target frame in the first display image in the real world and thus the second display image is generated. 
     The display image generation portion  58  stores the first display image data  68   d  and the second display image data  70   d  which are the data of the generated first display image and the generated second display image in the storage portion  52  and displays the first display image and the second display image on the display portion  40 . 
     When the driving controller  60  determines the start of the automatic driving based on the position of the target frame and the like and starts the automatic driving, the driving controller  60  controls the automatic driving portion  32  to automatically drive the vehicle  10  and moves the vehicle  10  to the target frame along the preset set path. 
     The storage portion  52  stores programs to be executed by the controller  50 , data necessary for execution of the programs, data generated by execution of the programs, and the like. For example, the storage portion  52  stores an assist processing program  62  executed by the controller  50 . The storage portion  52  stores the host vehicle image data  64   d  necessary for executing the assist processing program  62  and the set path data  66   d  from the host vehicle position to the target frame. The set path data  66   d  may include data of a plurality of set paths associated with any one of the vehicle speed at the time of starting the assist, the steering angle of the steering wheel, and the like. The storage portion  52  temporarily stores the first display image data  68   d  and the second display image data  70   d  generated by execution of the assist processing program  62 . 
       FIG. 4  is a diagram illustrating an example of the display images  68  and  70  in the left forward parking mode in the parking assist of automatic driving. In the left forward parking mode, the display image generation portion  58  generates the first display image  68  including the overhead image  72  illustrated in  FIG. 4  and the second display image  70  including a captured image  75  and thus displays the first display image  68  and the second display image  70  on the display portion  40 . 
     Specifically, the peripheral image generation portion  56  generates an overhead image  72  which is a peripheral image centered on the left front which is the parking direction of the vehicle  10  from the captured images of the periphery acquired by the imaging portions  14   a ,  14   b , and  14   c  and outputs the overhead image  72  to the display image generation portion  58 . The display image generation portion  58  superimposes a portion of the host vehicle image  64  (for example, front half portion of host vehicle image  64 ) on the right rear end portion of the overhead image  72  which is a side opposite to the parking direction. In addition, the display image generation portion  58  superimposes a target frame  76   a  on the set path (for example, end point of set path) in which the host vehicle image  64  of the overhead image  72  is set as a starting point in the parking direction side in the overhead image  72 . Accordingly, the display image generation portion  58  generates the first display image  68 . An example of the shape of the target frame  76   a  in the real world is 5.1 m in length in the front and rear direction of the vehicle  10  after parking, 30° in inclination with respect to the front and rear direction of the vehicle  10 , and 2.9 m in length in a direction inclined with respect to the front and rear direction of the vehicle  10 . The shape of the target frame  76   a  may be appropriately changed according to the size of the vehicle  10  and the shape of the parking frame line  82  or the like indicated by a white line or the like in a parking lot. 
     The display image generation portion  58  superimposes the target frame  76   b  on the captured image  75  captured by the imaging portion  14   b  and thus generates the second display image  70 . Here, the display image generation portion  58  superimposes the target frame  76   b  on the captured image  75  and thus generates the second display image  70  so that the positions of the target frame  76   a  of the first display image  68  and the target frame  76   b  of the second display image  70  in the real world are at the same position. 
     The display image generation portion  58  may display a mode switching button on the second display image  70 . For example, the display image generation portion  58  may display a forward parking button  78   a  for selecting the forward parking mode and a backward parking button  78   b  for selecting the backward parking mode as the mode switching buttons. Further, in the forward parking mode, the display image generation portion  58  may display a left forward parking button  80   a  for selecting the left forward parking mode, a right forward parking button  80   b  for selecting the right forward parking mode, a right backward exit button  80   c  for selecting the right backward parking mode, and a left backward exit button  80   d  for selecting the left backward parking mode. In the example illustrated in  FIG. 4 , the occupant selects the left forward parking mode by operating the forward parking button  78   a  and the left forward parking button  80   a  as indicated by the thick frame. In a case where it is unnecessary to distinguish the buttons  78   a  and  78   b  and the buttons  80   a  to  80   d , it is described as a button  78  or a button  80 . 
       FIG. 5  is a diagram illustrating an example of the display images  68  and  70  in the left backward exit mode in the parking assist for automatic driving. In the left backward exit mode, the display image generation portion  58  generates the first display image  68  including the overhead image  72  illustrated in  FIG. 5  and the second display image  70  including the captured image  75  and thus displays the first display image  68  and the second display image  70  on the display portion  40 . 
     Specifically, the peripheral image generation portion  56  generates an overhead image  72  which is a peripheral image centered on the left rear which is the exit direction of the vehicle  10 , from captured images of the periphery acquired from the imaging portions  14   b ,  14   c , and  14   d  and thus outputs the overhead image  72  to the display image generation portion  58 . The display image generation portion  58  superimposes a portion of the host vehicle image  64  (for example, rear half portion of host vehicle image  64 ) on the right front end portion of the overhead image  72 . In addition, the display image generation portion  58  superimposes the target frame  76   a  on the set path (for example, end point of set path) in which the host vehicle image  64  of the overhead image  72  is set as a starting point. Accordingly, the display image generation portion  58  generates the first display image  68 . An example of the shape of the target frame  76   a  in the real world is 5.1 m in length in the front and rear direction of the vehicle  10  after the parking and 2.5 m in length in the lateral direction of the vehicle  10 . The shape of the target frame  76   a  may be appropriately changed according to the size of the vehicle  10  and the shape of the parking frame line  82  or the like indicated by a white line or the like in the parking lot. 
     The display image generation portion  58  may display the exit start frame  84  on the overhead image  72 . The exit start frame  84  is in a position to move the parked vehicle  10  by straight traveling so as to avoid contact with an adjacent vehicle or the like. Therefore, the driving controller  60  starts turning of the vehicle  10  after exceeding the exit start frame  84 . The display image generation portion  58  may recognize the parking frame line  82  of the parking lot from the captured image and display the exit start frame  84  on the parking frame line  82  or may display the exit start frame  84  based on the preset exit start frame  84 . The shape of the exit start frame  84  in the real world may be configured by a side having a length of 1 m parallel to the front and rear direction of the vehicle  10  during the parking and a side having a length of 1 m inclined by 30° from the lateral direction of the vehicle  10 . The shape of the exit start frame  84  may be appropriately changed according to the size of the vehicle  10  and the shape of the parking frame line  82  or the like indicated by a white line or the like in the parking lot. 
     The display image generation portion  58  superimposes the target frame  76   b  on the captured image  75  captured by the imaging portion  14   b  and generates the second display image  70 . Here, the display image generation portion  58  superimposes the target frame  76   b  on the captured image  75  so that the positions of the target frame  76   a  of the first display image  68  and the target frame  76   b  of the second display image  70  in the real world are at the same position and thus generates the second display image  70 . 
     The display image generation portion  58  may display buttons  78  and  80  for switching same mode as in  FIG. 4  on the second display image  70 . In the example illustrated in  FIG. 5 , the occupant selects the left backward exit mode by operating the forward parking button  78   a  and the left backward exit button  80   d  as indicated by the thick frame. 
       FIG. 6  is a diagram illustrating an example of the display images  68  and  70  in the left backward parking mode in the parking assist for automatic driving. In the left backward parking mode, the display image generation portion  58  generates the first display image  68  including the overhead image  72  illustrated in  FIG. 6  and the second display image  70  including the captured image  75  and displays the first display image  68  and the second display image  70  on the display portion  40 . 
     Specifically, the peripheral image generation portion  56  generates the overhead image  72  which is a peripheral image centered on the vehicle  10  from the captured images of the periphery acquired from the imaging portions  14   a ,  14   b ,  14   c , and  14   d  and outputs the overhead image  72  to the display image generation portion  58 . The display image generation portion  58  superimposes the host vehicle image  64  on the center of the overhead image  72 . In addition, the display image generation portion  58  superimposes the target frame  76   a  on the set path (for example, end point of set path) in which the host vehicle image  64  of the overhead image  72  is set as a starting point. Accordingly, the display image generation portion  58  generates the first display image  68 . Here, in the backward parking, since the turning radius is small and the movement distance of the vehicle  10  is short, the display image generation portion  58  can contain the target frame  76   a  in the first display image  68 , even in the overhead image  72  centered on the vehicle  10 . 
     The display image generation portion  58  superimposes the target frame  76   b  on the captured image  75  captured by the imaging portion  14   b , and generates the second display image  70 . Here, the display image generation portion  58  superimposes the target frame  76   b  on the captured image  75  so that the positions of the target frame  76   a  of the first display image  68  and the target frame  76   b  of the second display image  70  in the real world are at the same position and thus generates the second display image  70 . 
     The display image generation portion  58  may display the mode switching button in the second display image  70  in the backward parking mode. For example, the display image generation portion  58  may display the forward parking button  78   a  for selecting the forward parking mode and the backward parking button  78   b  for selecting the backward parking mode as the mode switching button. Further, in the backward parking mode, the display image generation portion  58  may display a left backward parking button  80   e  for selecting the left backward parking mode, a right backward parking button  80   f  for selecting the right backward parking mode, a right forward exit button  80   g  for selecting a right forward exit mode, and the left forward exit button  80   h  for selecting the left forward exit mode. In the example illustrated in  FIG. 6 , the occupant selects the left backward parking mode by operating the backward parking button  78   b  and the left backward parking button  80   e  as indicated by the thick frame. 
       FIG. 7  is a flowchart illustrating assist processing executed by the controller  50 . The controller  50  starts the assist processing by reading the assist processing program  62 . In the assist processing, the controller  50  receives and executes the selection of the parking assist mode or the exit assist mode by the occupant. 
     In a state where the navigation image is being displayed, the mode determination portion  54  of the controller  50  determines whether or not selection of the assist mode by automatic driving is received (S 102 ). The mode determination portion  54  is in a standby state until selection of the assist mode is received (S 102 : No). 
     For example, when the occupant operates the assist mode button displayed together with the navigation image, the mode determination portion  54  determines that the assist mode is selected (S 102 : Yes), and outputs the display instructions of the buttons  78  and  80  to the display image generation portion  58 . 
     When acquiring the display instruction of the buttons  78  and  80 , the display image generation portion  58  displays the parking button  78  and the exit button  80  (S 104 ). The display image generation portion  58  may display the display images  68  and  70  illustrated in  FIG. 4  to  FIG. 6  together with the buttons  78 ,  80  on the display portion  40 . 
     The mode determination portion  54  determines whether or not the occupant has selected any one of the parking assist mode or the exit assist mode by the buttons  78  and  80  (S 106 ). The mode determination portion  54  is in a standby state until being determined that the parking assist mode or the exit assist mode is selected (S 106 : No). 
     When the occupant selects any one of the buttons  78  and  80  by the operation input portion  44 , the mode determination portion  54  determines that the occupant has selected any one of the parking assist mode or the exit assist mode (S 106 : Yes), and then outputs the information of the parking assist mode or the exit assist mode which is selected to the peripheral image generation portion  56 . 
     The peripheral image generation portion  56 , the display image generation portion  58 , and the driving controller  60  execute the parking assist processing or the exit assist processing according to the parking assist mode or the exit assist mode selected by the occupant (S 108 ). 
       FIG. 8  is a flowchart of the left forward parking assist processing which is a portion of the parking assist processing executed by the controller  50 . In a case where the occupant selects the left forward parking button  80   a , the controller  50  executes the left forward parking assist processing which is one of the parking assist processing (S 108 ). 
     The peripheral image generation portion  56  of the parking assist apparatus  36  acquires a captured image from the imaging portion  14  (S 202 ). Based on the captured image, the peripheral image generation portion  56  generates an overhead image  72  centered on the left front which is the traveling direction side of the vehicle  10  and then outputs the overhead image  72  and the captured image to the display image generation portion  58  (S 204 ). 
     The display image generation portion  58  superimposes a portion of the host vehicle image  64  on the end portion of the right rear side of the overhead image  72  (S 206 ). The display image generation portion  58  sets a set path in which the position of the vehicle  10  is set as a starting point, based on the set path data  66   d  in the storage portion  52  (S 208 ). The display image generation portion  58  superimposes the target frame  76   a  on the set path of the overhead image  72  to generate the first display image  68  as illustrated in  FIG. 4  (S 210 ). 
     The display image generation portion  58  superimposes the target frame  76   b  on the position on the captured image  75  corresponding to the position of the target frame  76   a  of the first display image  68 , installs the buttons  78  and  80  above the captured image  75 , and generates a second display image  70  as illustrated in  FIG. 4  (S 212 ). 
     As illustrated in  FIG. 4 , the display image generation portion  58  displays the display images  68  and  70  on the display portion  40  (S 214 ). 
     The driving controller  60  determines whether or not automatic driving is started (S 216 ). For example, the driving controller  60  may determine start of automatic driving when the target frames  76   a  and  76   b  overlap with the parking frame line  82  indicated by a white line or the like of the parking lot or the vehicle  10  stops. In addition, when the occupant touches the positions of the target frames  76   a  and  76   b  on the operation input portion  44  in a state where the target frames  76   a  and  76   b  overlap the parking frame line  82  of the white line of the parking lot, the driving controller  60  may determine start of the automatic driving. 
     When the driving controller  60  determines that automatic driving is not started (S 216 : No), the driving controller  60  repeats step S 202  and the following steps. Accordingly, the peripheral image generation portion  56  and the display image generation portion  58  repeat generation of the display images  68  and  70  according to the movement of the vehicle  10  until the start of automatic driving and updates and displays the display images  68  and  70 . 
     If the driving controller  60  determines the start of the automatic driving (S 216 : Yes), the driving controller  60  controls the automatic driving portion  32  to automatically drive the vehicle  10  and to move the vehicle  10  to the target frames  76   a  and  76   b  for parking (S 218 ). Accordingly, the parking assist apparatus  36  ends the left forward parking assist processing which is one of the parking assist processing and ends the assist processing. 
     In the right forward parking assist processing which is one of the parking assist processing, the left forward parking assist processing and processing with respect to positions of left and right sides are different and the description with respect to the same processing except for the portion described above is omitted. 
       FIG. 9  is a flowchart of the left backward exit assist processing executed by the controller  50 . In a case where the occupant selects the left backward exit button  80   d , the controller  50  executes the left backward exit assist processing, which is one of the exit assist processing (S 108 ). 
     The peripheral image generation portion  56  of the parking assist apparatus  36  acquires a captured image from the imaging portion  14  (S 302 ). Based on the captured image, the peripheral image generation portion  56  generates an overhead image  72  centered on the left rear side which is the traveling direction side of the vehicle  10  and then outputs the overhead image  72  and the captured image to the display image generation portion  58  (S 304 ). 
     The display image generation portion  58  superimposes a portion of the host vehicle image  64  on the end portion of the right front side of the overhead image  72  (S 306 ). The display image generation portion  58  sets a set path in which the position of the vehicle  10  is set as a starting point (S 308 ). The display image generation portion  58  superimposes the exit start frame  84  on the overhead image  72  (S 310 ) and superimposes the target frame  76   a  on the set path of the overhead image  72  to generate the first display image  68  (S 312 ). 
     The display image generation portion  58  superimposes the target frame  76   b  on the position on the captured image  75  corresponding to the position of the target frame  76   a  of the first display image  68  and installs the buttons  78  and  80  above the captured image  75 , and generates the second display image  70  (S 314 ). 
     As illustrated in  FIG. 5 , the display image generation portion  58  displays the display images  68  and  70  on the display portion  40  (S 316 ). 
     The driving controller  60  determines whether or not to start automatic driving (S 318 ). For example, when the occupant touches the positions of the target frames  76   a  and  76   b  on the operation input portion  44 , the driving controller  60  may determine to start the automatic driving. 
     If the driving controller  60  determines that automatic driving is not started (S 318 : No), step S 302  and the following steps are repeated. Accordingly, the peripheral image generation portion  56  and the display image generation portion  58  repeat the generation of the display images  68  and  70  until the automatic driving is started. 
     If the driving controller  60  determines start of the automatic driving (S 318 : Yes), the driving controller  60  controls the automatic driving portion  32  to automatically drive the vehicle  10  and move the vehicle  10  to the target frames  76   a  and  76   b  and causes the vehicle  10  to execute backward exit (S 320 ). Accordingly, the parking assist apparatus  36  ends the left backward exit assist processing which is one of the exit assist processing and ends the assist processing. 
     In the right backward exit assist processing which is one of the exit assist processing, the left backward exit assist processing and the processing with respect to positions of left and right sides are different and thus description with respect to the same portion except for the portion described above is omitted. 
     As described above, in the parking assist apparatus  36 , the display image generation portion  58  superimposes the host vehicle image  64  on one of the left and right sides of the overhead image  72 , and superimposes the target frame  76   a  on the other of the left and right sides to generate the first display image  68  in the assist mode of the forward parking and the backward exit. Accordingly, the parking assist apparatus  36  can more reliably contain the host vehicle image  64  and the target frame  76   a  in the first display image  68  as compared with a case where the host vehicle image  64  is displayed at the center of the overhead image  72 . As a result, even in the forward parking and the backward parking in which the field of view range of the overhead image  72  is narrow and the set path is long, the parking assist apparatus  36  can display the appropriate first display image  68  including the host vehicle image  64  and the target frame  76   a  on the display portion  40 . Further, the parking assist apparatus  36  reduces the processing load of the controller  50  configured by the processor such as the CPU  36   a  by narrowing the field of view range of the overhead image  72 , and thus the above effect can be realized by the microcomputer including the inexpensive CPU  36   a  and the like and the imaging portion  14  having a narrow angle of view. 
     The display image generation portion  58  superimposes the host vehicle image  64  on the rear side in the overhead image  72  in the forward parking mode in the parking assist apparatus  36  and superimposes the host vehicle image  64  on the front side in the overhead image  72  in the backward exit mode. Accordingly, in the assist mode, the parking assist apparatus  36  omits the overhead image  72  of the region on a side opposite to the traveling direction of the vehicle  10  and thus the host vehicle image  64  and the target frame  76   a  can be more reliably displayed in the first display image  68  by the overhead image  72  with emphasis on the region on the traveling direction side of the vehicle  10 . 
     In the parking assist apparatus  36 , the display image generation portion  58  superimposes the target frame  76   a  on the left side in the overhead image  72  in the forward parking mode and the backward exit mode to the target frame  76   a  of the left side of the vehicle  10  and superimposes the target frame  76   a  on the right side in the overhead image  72  in the forward parking mode and the backward exit mode to the target frame  76   a  of right side of the vehicle  10 . Accordingly, the parking assist apparatus  36  can more reliably display the host vehicle image  64  and the target frame  76   a , even with the first display image  68  including the overhead image  72  having a narrow field of view range. 
     In the parking assist apparatus  36 , since the display image generation portion  58  superimposes the target frame  76   a  on the preset set path based on the set path data  66   d , processing load required for calculation of the set path for setting the position where the target frame  76   a  is superimposed can be reduced. 
     The functions, connection relationships, number, arrangement, or the like of the configurations of each the embodiment described above may be appropriately changed, deleted, or the like within a range equivalent to the range of this disclosure and the scope of this disclosure. Each embodiment may be appropriately combined. The order of each step of each embodiment may be appropriately changed. 
     In the above embodiment, although an example of the parking assist system  30  having the four imaging portions  14  is given, this disclosure is not limited thereto. For example, the parking assist system  30  may have three or less or five or more imaging portions  14 . 
     A parking assist apparatus according to an aspect of this disclosure includes: a peripheral image generation portion that generates an overhead image of a periphery viewed from above based on a captured image of a periphery of a vehicle; and a display image generation portion that generates a display image by superimposing a host vehicle image displaying a host vehicle on one of left and right sides in the overhead image and superimposing a target frame displaying a target of a movement destination of the vehicle on the other of the left and right sides in the overhead image in an assist mode of a forward parking or a backward exit. 
     According to the aspect of this disclosure, by superimposing the host vehicle image and the target frame on both sides of left and right sides of the overhead image, even in an assist mode of the forward parking or the backward exit which increases the set path to the target frame, an appropriate display image including the host vehicle image and the target frame can be displayed. 
     In the aspect of this disclosure, the display image generation portion may superimpose the host vehicle image on a rear side in the overhead image in the assist mode of the forward parking and may superimpose the host vehicle image on a front side in the overhead image in the assist mode of the backward exit. 
     According to the aspect of this disclosure with this configuration, in the assist mode, the overhead image of a region on the traveling direction side of the vehicle can be further displayed on the display image by the overhead image of a region on a side opposite to a traveling direction of the vehicle being omitted. 
     In the aspect of this disclosure, the display image generation portion may superimpose the target frame on a left side in the overhead image in a case of the assist mode for assisting the forward parking or the backward exit with respect to the target frame on a left side of the vehicle and may superimpose the target frame on a right side in the overhead image in a case of the assist mode for assisting the forward parking or the backward exit with respect to the target frame on a right side of the vehicle. 
     Accordingly, according to the aspect of this disclosure with this configuration, the host vehicle image and the target frame can be more reliably displayed even in the display image by an overhead image having a narrow field of view range. 
     In the aspect of this disclosure, the display image generation portion may superimpose the target frame on a preset set path in which the host vehicle image is set as a starting point. 
     Accordingly, according to the aspect of this disclosure with this configuration, since the target frame is superimposed on the preset set path, it is possible to reduce processing load required for setting the set path for setting a position where the target frame is superimposed. 
     The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.