Abstract:
In the back monitoring apparatus for a vehicle, a path loci of a minimum cornering portion and a maximum cornering portion of the vehicle is predicted, superposed on a back image and then displayed simultaneously superposed on the back image. In this configuration, the safety confirmation and operation by a driver can be improved when a vehicle is backed up by displaying a predicted path locus with excellent visibility.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a back monitoring apparatus for a vehicle, and more particularly to a back monitoring apparatus for a vehicle for displaying a predicted path of the vehicle according to a steering angle when the vehicle is backed up in such a manner that it is superposed on a back image on a monitor. 
     In recent years, a back monitoring apparatus for confirming the back of a vehicle has become prevalent. The feature of a back monitoring apparatus resides in that it permits a vehicle driver to confirm the back (environment) easily in such a manner that the blind spot of a rearview mirror is monitored by a video camera. This feature is efficient the case where the environment of a direct back corner of the vehicle is hidden from view by a cabin as in a truck. Some back monitor apparatus not only displays a back image for a driver, but also displays a predicted path locus of a rear wheel according to a steering angle when the vehicle is backed up which is superposed on the image on a monitor, thereby improving the operability of a driver. An example of these monitoring apparatus is disclosed in JPA64-14700. 
     The display of the predicted path locus of the rear wheel disclosed in the above prior art permits the moving direction and vehicle width of one&#39;s own vehicle to be visually recognized at first sight. Therefore, the driver can easily back up the vehicle for parking. However, as shown in FIG. 11, in backing-up of the vehicle, when a vehicle  100  is turned clockwise rearwards, a front wheel  101   a  located outside of the turning turns widely unlike the path of a rear wheel  102   a  corresponding to it. Therefore, when the driver is plunged into the operation of driving carefully viewing only the interior of the predicted path lines of the rear wheels  102   a  and  102   b,  a front body  100   a  which turns more widely than the rear wheel  102   a  may be brought into contact with an obstacle  103 . 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a back monitor which can improve the safety confirmation and operation by a driver when a vehicle is backed up, by displaying a predicted path locus with excellent visibility in order to display a predicted path of the vehicle according to a steering angle when the vehicle is backed up in such a manner that it is superposed on a back image picked up by a video camera on a monitor. 
     In order to attain the above object, in accordance with the present invention, there is provided a back monitoring apparatus for a vehicle comprising: 
     a predicted path locus computing means for computing a predicted path locus of a vehicle corresponding to a steering angle when the vehicle is backed up; 
     a signal processing means for processing the predicted path locus so as to be superposed on a back image picked up by an image pick-up means; and 
     a monitoring means for displaying an image from the data thus superposed, 
     wherein the predicted path locus computing means computes predicted path loci of a minimum cornering portion and a maximum cornering portion of the vehicle, 
     the signal processing means processes the predicted path loci of the minimum cornering portion and the maximum cornering portion so as to be superposed on data of the back image; and 
     the monitoring means simultaneously displays the predicted path loci of the minimum cornering portion and the maximum cornering portion superposed the back image, which are supplied from the signal processing means. 
     In this configuration, since the predicted path loci of the minimum cornering portion and the maximum cornering portion superposed on the back image are simultaneously displayed, the predicted path direction of the vehicle and vehicle width can be known so that the back confirmation and operability by the driver can be improved. 
     Preferably, the minimum cornering portion of the vehicle is an inner rear wheel, the maximum cornering portion of the vehicle is a front corner of an outer shape of the vehicle, the predicted path locus of the vehicle includes that of an outer rear wheel. 
     In this configuration, since the predicted path loci of both rear wheels and the maximum cornering portion are simultaneously displayed, a driver can discern the back-up direction and presence or absence of accessible space of the vehicle. 
     Preferably, the predicted loci are displayed in display formats in which they are distinguishable from each other. 
     In this configuration, since the predicted path loci of both rear wheels and the maximum cornering portion which are simultaneously displayed can be recognized individually according to their different display formats, they can be displayed with good visibility so that the predicted path loci of the rear wheels can be distinguishable from the maximum cornering portion. 
     Preferably, the display format is composed of a line type, a display color, a line width and a combination thereof. In this configuration, since the predicted path loci of both rear wheels and the maximum cornering portion are displayed in different display formats each composed of a line type, a display color, a line width and a combination thereof, a difference in the predicted path loci can be made clear and the driver can easily discern the difference. 
     Preferably, the predicted path locus of the maximum cornering portion has a turning radius computed from          R                 max     =            (       Rout   2     +     L   2       )                                   
     where Rout: a turning radius of an outer rear wheel when a vehicle is backed up, L: a distance between a rear wheel shaft and a front corner of an outer shape of the vehicle. 
     In this configuration, the predicted path locus of the maximum cornering portion can be displayed using the computed turning radius. 
     The above and other objects and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a basic arrangement of the back monitoring apparatus for a vehicle according to the present invention; 
     FIG. 2 is a block diagram of an embodiment of the back monitoring apparatus for a vehicle according to the present invention; 
     FIG. 3 is a schematic diagram for explaining the turning manner of the front and rear wheels and their turning radii when a vehicle is backed up; 
     FIG. 4 is a schematic diagram for explaining a method of computing predicted path loci; 
     FIGS. 5A and 5B are schematic plan and side views for explaining the state where a video camera is attached, respectively; 
     FIGS. 6 and 7 are schematic diagrams for explaining coordinate conversion from a spatial coordinate to an image pick-up plate, respectively; 
     FIG. 8 is a schematic diagram for explaining the coordinate standard point on an image pick-up plate of a video camera; 
     FIG. 9 is a schematic diagram for explaining the standard point of a monitor screen; 
     FIG. 10 is a flowchart showing the operation in the block diagram of FIG. 2; and 
     FIG. 11 is a schematic diagram for explaining the predicted path locus of a conventional back monitoring apparatus for a vehicle. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now referring to FIGS. 2-10, an explanation will be given of an embodiment of the back monitoring apparatus for a vehicle according to the present invention. 
     FIG. 2 is a block diagram showing an embodiment of the back-monitoring apparatus for a vehicle according to the present invention. In FIG. 2, the back monitoring apparatus includes a controller  1 , a video camera  2  serving as an image pick-up means and a monitor  3  serving as display means. The controller  1  includes a steering sensor  4 , a back sensor  5 , a storage unit  6 , a control unit  7  serving as a means for computing a predicted path locus and a signal processing unit  8 . The video camera  2 , which is attached to the outside of the vehicle, for example, supplies image data obtained by picking up the back scene of the vehicle to the controller  1 . The monitor  3  displays a superposed image of the back image taken by the video camera  2  and supplied from the controller  1  and a predicted path locus when the vehicle is backed up which is computed by the controller  7 . 
     In the controller  1 , a steering sensor  4  produces a signal indicative of turning information of a vehicle according to a handling helm angle (steering angle) which varies by a handling operation when the vehicle is backed up. The back sensor  5  produces an ON/OFF signal for determining whether or not the vehicle is being backed up. The back sensor  5  is attached to e.g. a transmission mechanism (not shown) of the vehicle. When the gear position of the transmission mechanism is shifted to the back (reverse) position which is used when the vehicle is backed up, an ON signal is produced. When it is shifted to the other position than the reverse, an OFF signal is produced. 
     The storage unit  6  stores parameter values required to compute the exhibition position of the predicted path locus of a vehicle on a monitor screen of the monitor  3 . The storage unit  6  stores a display format selecting table which includes a plural kinds of lines (e.g. solid line, dotted line, etc.), a plurality of display colors (white, black, red, etc.), and a plurality of line widths). The storage unit  6  is a frame memory which temporarily stores image data captured from the video camera  2 . 
     The control section  7 , which can be constructed of a microcomputer, etc., serves to compute the plotting position on the monitor screen of the monitor  3  of the predicted path locus of the vehicle according to the steering angle when the vehicle is backed up. The signal processing unit  8  superposes data of the plotting position thus computed on the image signal outputted from the video camera  2  and sends the resultant image to the monitor  3 . 
     Referring to FIG. 3, an explanation will be given of the summary of the present invention. 
     As shown in FIG. 3, during a low speed running (slippage of tires is negligible), when a vehicle  100  moves to turn backward, it turns around a certain point p (center point) extended from a rear wheel shaft  102   c.  In this case, the turning radius of the vehicle is determined by the distance between the center point p and each of wheels  101   a,    101   b;  and  102   a,    102   b.  Therefore, the turning radii R 1 , R 2 , R 3  and R 4  of the predicted path loci  103   a,    103   b,    103   c  and  103   d  of the wheels  101   a,    101   b,    102   a  and  102   b  are from one another. The inner rear wheel  102   b  turns along the innermost line. Likewise, the car body provides a minimum turning radius in the vicinity of the inner side  100   b  of the inner rear wheel. Further, it provides a maximum turning radius in the vicinity of the a front bumper corner  100   a.  Therefore, the vehicle  100  passes the back space confined by the minimum turning radius and the maximum turning radius. For this reason, the car body will not be brought into contact with an obstacle as long as the driver can monitor such a back space through the video camera. 
     In view of such a fact, the present invention superposedly displays the predicted path loci  103   a,    103   c  of the rear wheels  102   a  and  102   b  and a part of the car body providing the maximum turning radius (hereinafter referred to as a maximum cornering portion) (i.e. predicted path locus of the front corner  100   a  of the outer shape of the vehicle) on a back image taken from the video camera  2 . Thus, the driver can confirm the running direction and the presence or absence of a vehicle traveling space. In addition, the driver can know his monitoring rage through the exhibition of the maximum cornering portion, i.e. the predicted path locus of the front corner  100   a.    
     In this case, if the predicted path loci of the rear wheels and the maximum cornering portion are exhibited in the same line, the driver may confuse these loci. Taking this into consideration, in accordance with the present invention, these predicted path loci are discriminated from one another using different exhibition formats with respect to a line kind, line color, width, etc. For example, the predicted paths of the rear wheels  102   a  and  102   b  are exhibited in solid line, whereas that of the maximum cornering portion  100   a  is exhibited in dotted line. In this way, the driver can easily discriminate these predicted path loci from one another. 
     A detailed explanation will be given of the operation of the present invention. 
     When the vehicle is backed up, the control section  7  receives an ON signal from the back sensor  5  representative of that the vehicle is being moved backward and also receives the signal from the steering sensor  4  representative of the turning information of the vehicle corresponding to the steering angle. 
     On the basis of the signal representative of the turning information of the vehicle according to the steering angle from the steering sensor  4  and the parameter values read from the storage unit  6 , the control section  7  computes the plotting positions of the monitoring screen of the monitor  3  of the predicted path loci of the rear wheels  102   a  and  102   b  and the maximum cornering portion  100   a.    
     An explanation will be given of a method of computing the plotting positions of the predicted path loci. 
     As shown in FIG. 4, it is assumed that the vehicle  100  corners around a point P (Xr, 0) on an X-Y coordinate with an origin of the mid point of the rear wheel shaft  102   c.  Further, it is assumed that the turning radius of the inner rear wheel  102   b  is Rin, that of the outer rear wheel  102   a  is Rout, and that of the maximum cornering portion of the vehicle is Rmax. Incidentally, these turning radii can be computed using equations representative of the relationship between the steering angle and the turning radii which have been acquired experimentally. By replacing the vehicle by a tricycle, the turning radii R 1 n, Rout and Rmax can be approximated as represented by Equations (1), (2), (3) and (4).                x   r     =     B     tan                 θ               (   1   )                                
     (leftward steering θ&gt;0, rightward steering θ&lt;0)                R   in     =            x   r          -     W   /   2               (   2   )                 R   out     =            x   r          +     W   /   2               (   3   )                 R   max     =            (       R   out   2     +     L   2       )                    (   4   )                                
     where B: a distance between a front wheel shaft  101   c  and the rear wheel shaft  102   c , θ: a steering angle, W: vehicle width (distance between the outer walls of left and right tires), L: front corner of the outer shape of the vehicle (i.e. the front bumper corner on the side of the outer rear wheel in this example) and the rear wheel shaft  102   c.    
     The locus coordinate of the vehicle which corners with the turning radius R around the point P (Xr, 0) can be obtained from Equation (5) 
     
       
         ( x−x   r ) 2   +y   2   =R   2   (5) 
       
     
     (R=Rin, Rout, Rmax) 
     Now, as shown in FIGS. 5A and 5B, it is assumed that the locus computed by Equation (5) is picked up by a video camera installed at a position displaced from the center of the back of the vehicle  100  by dx in a X-direction and dy in a Y-direction in a direction of an optical axis having a lying angle of φ. In this case, as shown in FIGS. 6 and 7, the respective points P(x, y) on the locus are converted from a spatial coordinate to a plane coordinate (pick-up plate) by Equation (7). The coordinate standard point of the pick-up plate  2   a  is an optical axis of the video camera  2 .                [       p   x     ,     p   y       ]     =     [                   CP   x     ·   tan                     ϕ   x                     {     1   +       k   ·     f   2                       (         tan   2                     ϕ   x       +       tan   2          ϕ   y         )         }         2                 tan                     W   x     2                     {     1   +       k   ·     f   2                       (         tan   2                       W   x     2       +       tan   2                       W   y     2         )         }                         CP   y     ·   tan                     ϕ   y                     {     1   +       k   ·     f   2                       (         tan   2                     ϕ   x       +       tan   2          ϕ   y         )         }         2                 tan                     W   y     2                     {     1   +       k   ·     f   2                       (         tan   2                       W   x     2       +       tan   2                       W   y     2         )         }               ,     ]             (   6   )                 ϕ   x     =         tan     -   1          x     -          x                    h   2     +       (     y   -   E   -        y       )     2         ·   cos                     ϕ   y                        (   7   )                   (       if                 y     ≧     E   +        y         )                     ϕ   y       =     φ   -       tan     -   1                       h     y   -   E   -        y                     (   8   )                   (       if                 y     &lt;     E   +        y         )                     ϕ   y       =     π   -   φ   +       tan     -   1            h     y   -   E   -        y                     (   9   )                                
     where Wx: a horizontal view angle of the video camera  2 , Wy: a vertical view angle of the video camera  2 , k: a lens aberration coefficient, f: a focal distance of the video camera, Cpx: number of pixels on the pick-up plate  2   a  of the video camera in a horizontal direction, Cpy: number of pixels on the pick-up plate  2   a  of the video camera in a vertical direction, E: a distance between the back of the vehicle  100  and the rear wheel axis  102   c,  h: a vehicle height of the vehicle  100 . 
     Further, coordinate conversion is made from the image pick-up plate  2   a  to the monitor  3 . Therefore, the points of the locus are displayed on the coordinate computed by Equation (10). The coordinate standard point on the monitor is an optical axis of the video camera  2  (see FIG.  9 ).                [       g   x     ,     g   y       ]     =     [           CG   x       CP   x       ·     p   x       ,         CG   y       CP   y       ·     p   y         ]             (   10   )                                
     where CGx: number of pixels on the monitor in the horizontal direction, Cgy: number of pixels on the monitor in the vertical direction. 
     Thus, on the basis of the coordinates of the locus points computed from Equations (1)-(10), the predicted path loci of the vehicle rear wheels  102   a  and  102   b  according to the steering angle and that of the maximum cornering portion  100   a  of the car body can be displayed on the monitor  3 . 
     The control section  7  supplies to the signal processing section  8  the position data the predicted path loci of the vehicle rear wheels  102   a  and  102   b  according to the steering angle and that of the maximum cornering portion  100   a  of the car body, and display format information of the kind of line, display color or line width or any combination thereof which is read from the display format table stored in the storage unit  6 . The signal processing unit  8  superposes the data of the respective path loci inclusive of the selected display format on the back image signal produced from the video camera  2 , and send the superposed data to the monitor  3 . The monitor  3  displays the predicted path loci superposed on the back image on the monitoring screen. For example, the predicted path loci of the vehicle rear wheels  102   a  and  102   b  are displayed in white solid line, and that of the maximum cornering portion  100   a  of the car body is displayed in red dotted line. 
     Therefore, by confirming the predicted path loci of the vehicle rear wheels  102   a,    102   b  and the maximum cornering portion  100   a,  the driver can know the space through the vehicle passes. This makes it easy to ensure the back safety and improve the operability. 
     Referring to the flowchart shown in FIG. 10, an explanation will be given of the above operation. 
     When the vehicle starts to backup (step S 1 ), the control section  7  starts to acquire the signal according to the steering angle from the steering sensor  4  (step S 2 ). In accordance with the turning information from the steering sensor  4 , the control section  7  computes the predicted path loci of the vehicle rear wheels  102   a,    102   b  and supplies these computed predicted path loci to the signal processing section  8  as information to be displayed in solid line (step S 3 ). 
     The signal processing section  8  superposes the predicted path loci information of the vehicle rear wheels  102   a,    102   b  supplied from the control section  7  on the back image data produced from the video camera  2 , and supplies the information thus created to the monitor  3 . The monitor  3  displays the predicted path loci of the vehicle rear wheels  102   a,    102   b  superposed in solid line on the back image on the monitor screen. Next, the control section  7  computes the predicted path locus of the maximum cornering portion  100   a  and supplies the computed locus to the signal processing section  8  as information to be exhibited in dotted line (step S 5 ). 
     The signal processing section  8  superposes the predicted path locus information of the maximum cornering portion  100   a  supplied from the control section  7  on the back image data produced from the video camera  2 , and supplies the information thus created to the monitor  3 . The monitor  3  displays the predicted path locus of the maximum cornering portion  100   a  superposed in dotted line on the back image and the predicted loci of the vehicle path rear wheels  102   a,    102   b  (step S 6 ).