Abstract:
An object of the present invention is to provide a design-superposing display apparatus for superposing a design above a part of a display surface of a display device. The design-superposing display apparatus includes a design display portion disposed above the display surface for accepting a transmitted light from a rear thereof; a light source disposed outside of the display device for emitting the transmitted light of the design display portion; and a light guide portion extending from the rear of the design display portion toward the light source and guiding the emitted light toward the rear of the design display portion.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a design-superposing display apparatus to superpose a design onto a part of a display surface of a display device, and a vehicle display unit utilizing the same. 
     2. Description of the Related Art 
     A projection type display unit such as head-up display (HUD) has been mounted on a vehicle. The HUD displays a virtual image on a windshield and superposes the virtual image on a foreground. The displayed virtual image is information which can not be displayed on a meter unit due to limited space therein. JP-2002-293162-A discloses a liquid crystal display (LCD) and a vacuum fluorescent display (VFD) as a display device for a HUD apparatus. 
     The colors of green, red, and blue are available for the VFD. Maximum luminance and lifetime of the respective colors is different. Only green has a required luminance for the HUD apparatus. 
       FIGS. 10A and 10B  show a conventional VFD  100 . A design W is formed in a display plane  101  transparent to a light emitted from an LED backlight  110  having a diffusion portion  112  and an LED  111 . 
     The backlight method needs a space in a rear of the VFD  100 . A heat sink is usually attached to a rear surface of the high luminance VFD  100 . It is preferable to make a large contact area between the VFD  100  and the heat sink. The backlight method reduces the contact area due to a window in the heat sink to allow passage of the LED light, causing reduction of heat dissipation. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a design-superposing display apparatus to superpose a design above a display device without reducing performance of the display device, and a vehicle display unit. 
     According to a first aspect of the present invention, a design-superposing display apparatus for superposing a design above a part of a display surface of a display device includes a design display portion disposed above the display surface for accepting a transmitted light from a rear thereof; a light source disposed outside of the display device for emitting the transmitted light of the design display portion; and a light guide portion extending from the rear of the design display portion toward the light source and guiding the emitted light toward the rear of the design display portion. 
     Preferably, the light guide portion has a hollow tube shape for reflecting the light emitted from the light source at an inner wall thereof. 
     Preferably, the light guide portion includes a first light guide portion and a second light guide portion, the first light guide portion being disposed between the design display portion and the display device, and the second light guide portion extending from the first light guide portion and having a cross-sectional area intersecting a light guide direction larger than that of the first light guide portion. 
     Preferably, the second light guide portion intersects the first light guide portion with a prescribed angle so that the center light of the light source is reflected to the center of the design display portion. 
     According to a second aspect of the present invention, a vehicle display unit having the design-superposing display apparatus described above superposes a virtual image on a windshield projected with the display device on a foreground of a vehicle, a superposed image being recognized by a driver. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic drawing of a vehicle display unit having a design-superposing display apparatus of the present invention; 
         FIG. 2  is a perspective view of an outer appearance of the design-superposing display apparatus and a display device of  FIG. 1 ; 
         FIG. 3  is an exploded perspective view of the design-superposing display apparatus of the present invention; 
         FIG. 4  is a schematic cross-sectional view of the design-superposing display apparatus and the display device; 
         FIG. 5  illustrates a distribution of luminance of light emitted from a light source; 
         FIG. 6  shows schematic cross-sectional views of a first embodiment (upper drawing) and a second embodiment (lower drawing) for comparison; 
         FIG. 7  shows another embodiment of a light guide portion having a tube shape of the design-superposing display apparatus; 
         FIG. 8  is a schematic configuration of a design superposing display apparatus utilizing a light guide plate as the light guide portion; 
         FIG. 9  is a perspective view showing that the design-superposing display apparatus is disposed on a surface of a display device; 
         FIG. 10A  is a top view of a configuration to superpose a design on a conventional display device; and 
         FIG. 10B  is a perspective view of the configuration of  FIG. 10A . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1-9  show embodiments of a design-superposing display apparatus and a vehicle display unit utilizing the same. 
     Example 1 
     Referring to  FIG. 1 , a vehicle display unit  1  is a head-up display (HUD) apparatus and is disposed in an instrument panel  2  of the vehicle. The vehicle display unit  1  includes a display device  10 , a reflector  20 , and a design-superposing display apparatus  30 . The vehicle display unit  1  is received in a receiving case  5 . 
     The display device  10  is a vacuum fluorescent display (VFD) having a high luminance of tens of thousands cd/m 2 . For example, the display device  10  is formed in a way that a fluorescent material is applied on a ceramic substrate to form anode segments and selectively emit lights. The display device  10  is LCD, TFT, or the like. 
     The reflector  20  is a mirror, a magnifying mirror, or the like, and is disposed opposite to the display device  10  in the receiving case  5  so that a display light L can project an image on the display device  10  onto a projection area E of a windshield  3  of the vehicle. The embodiment illustrated in  FIG. 1  has one reflector  20  but is only exemplary and not limited thereto. A plurality of reflectors  20  may be utilized to reflect the display light L several times. The display light L may be directly projected to the windshield  3  without the reflector  20 . 
     The display device  10  displays the image controlled with a control unit, not shown, and the image is projected onto the windshield  3  through an opening  2   a  of the instrument panel  2 . The image is then reflected by the projection area E and a virtual image S is formed at foreground. An eye point I of a driver recognizes a superposed image of the virtual image S and the foreground through the windshield  3 . 
     The design-superposing display apparatus  30  superposes the design above a part of a display surface  11  of the display device  10 . Referring to  FIGS. 2-4 , the design-superposing display apparatus  30  includes a design display portion  31 , a light source  32 , and a light guide portion  33 . The design-superposing display apparatus  30  is held in the receiving case  5  so that the design is not overlapped a number and unit of a speed as shown in  FIG. 10A . 
     The design display portion  31  includes a design pattern portion and other portions formed with a transparent material, such as polycarbonate or optical film. The design display portion  31  is disposed above the surface  11  of the display device  10  to allow passage of the light from behind. 
     The design display portion  31  is changeable with respect to the light guide portion  33  corresponding to the design pattern, a specification and a kind of the vehicle display unit  1 . 
     The light source  32  is LED and is mounted on a board  34 . The control device, not shown, controls light-on/off of the light source  32  via an electrical wire patterned on the board  34 . A plurality of light sources  32  may be disposed and the light source  32  may be a bulb. 
     The light guide portion  33  extends from a rear of the design display portion  31  toward the light source  32  to guide the light along the extension thereof. The light guide portion  33  is made of a synthetic resin or a metal and formed in a hollow tube and an inner wall thereof is covered with a reflection member  35  achieved with reflection treatment of the inner wall, reflecting sheet, or white paint treatment. The reflection member  35  thus guides the light emitted from the light source  32  to the rear of the design display portion  31  without attenuation. 
     The light guide portion  33  includes a first light guide portion  33   a  and a second light guide portion  33   b . The first light guide portion  33   a  is disposed between the design display portion  31  and the display device  10 . The second light guide portion  33   b  extends from the first light guide portion  33   a  to the light source  32  and has a cross-sectional area, which intersects a light guide direction A indicated in  FIG. 4 , larger than that of the first light guide portion  33   a.    
     The first light guide portion  33   a  has a mounting portion  33   c  at a prescribed distance t apart from the display surface  11  to mount the design display portion  31 . The mounting portion  33   c  has an opening a little smaller than the design display portion  31 . The first light guide portion  33   a  is attached to the part of the display surface  11  of the display device  10  so that the light reflected from the light source  32  emits from the opening of the mounting portion  33   c  in a direction B same as the direction of the display light L. 
     The light guided in the light guide portion  33  permeates the design display portion  31  and transmits toward the windshield  3 . It is apparent that the shorter distance of the prescribed distance t provides an almost same distance from the eye point I to the display device  10  and the design display portion  31 . It is essential to make the prescribed distance t as small as possible when a projection type display unit utilizes a magnified image of the display device  10 . 
     The smaller distance t reduces covering of the design display portion  31  over the display light L emitted from the display device  10  and projected toward the eye point I. 
     The second light guide portion  33   b  is connected with the first light guide portion  33   a  with a prescribed angle θ against the display surface  11 . The first and second light portions  33   a  and  33   b  thus are substantially formed in L shape. This configuration makes the prescribed distance t smaller, or the first light guide portion  33   a  thinner. One end portion  33   d  of the second light guide portion  33   b  abuts on the board  34  and completely covers the light source  32 . 
     A long length L of the second light guide portion  33   b  attains uniformity of the luminance but reduces the luminance. The short length L reduces uniformity of the luminance but attains a high luminance. The length L of the second light guide portion  33   b  is adjusted to achieve a desired display luminance of the design display portion  31 . 
     An example of assembly of the design-superposing display apparatus  30  is explained below. 
     The design display portion  31  having the design pattern portion and the other portions is mounted on the mounting portion  33   c  of the light guide portion  33 . The board  34  mounted with the light source  32  is attached to the end portion  33   d  of the second light guide portion  33   b . The assembly of the design-superposing display apparatus  30  is attached on the receiving case  5 . 
     An operation of the design-superposing display apparatus  30  of the vehicle display unit  1  is explained below. 
     The display light L of the display device  10  is reflected by the reflector  20  and projected onto the windshield  3 . The virtual image S of the image of the display device  10  and the foreground are superposed together through the windshield  3  to the eye point I of the driver. 
     The design-superposing display apparatus  30  turns on the light source  32  in response to request of a warning display. The light source  32  is positioned outside of the display light L of the display device  10 . The light from the light source  32  is guided in the second light guide portion  33   b  and reflected by the inner wall of the first light guide portion  33   a  and guided to the rear of the design display portion  31 . The light permeates through the design display portion  31  and projects the design pattern portion onto the windshield  3 . The driver recognizes the superposed image of the virtual image S such as shown in  FIG. 10A . 
     The design-superposing display apparatus  30  of the present invention is not provided with the backlight source disposed on the rear thereof, so that the display device  10  achieves the high luminance design display without limitation of the rear space. The heat sink can be arranged at the rear of the display device  10 , so that the VFD can also be adapted to the display device  10  and keep performance by virtue of the heat sink. 
     The hollow tube structure of the light guide portion  33  keeps the light from the light source  32  therein and reduces attenuation of the light so as to achieve the high luminance superposed display. 
     The distance between the design display portion  31  and the display device  10  can be made smaller so as to decrease reduction of the light of the display device around the design-superposing display apparatus  30 . 
     Example 2 
     A second embodiment of the design-superposing display apparatus  30  is explained. Like parts of the first embodiment are given the same references and explanations are omitted. 
     A vehicle display unit  1  includes a display device  10 , a reflector  20 , and a design-superposing display apparatus  30  similar to the first embodiment. The design-superposing display apparatus  30  includes a design display portion  31 , a light source  32 , and a light guide portion  33 . 
       FIG. 5  shows a general distribution of luminance of an emitting light, where the center light has the highest luminance and other lights away from the center light have smaller luminance. 
     The upper figure of  FIG. 6  shows the design-superposing display apparatus  30  of the first embodiment in order to compare with that of the second embodiment of the lower figure. In the first embodiment, the center light R of the light source  32  is reflected in the first light guide portion  33   a  and toward a position P 1  of the design display portion  31 . The position P 1  is apart from the center position P 0  by a distance a. 
     The second embodiment of the design-superposing display apparatus  30  includes a step portion  33   e  between the first and second light guide portions  33   a  and  33   b  so that the center light R of the light source  32  is reflected by an inner wall of the first light guide portion  33   a  and forwarded to the center position P 0  of the design display portion  31 . This configuration thereby keeps uniformity of luminance of the design display portion  31  and achieves high luminance display. 
     An operation of the second embodiment is explained. 
     Upon a request of a warning display, the light source  32  disposed outside of the display device  10  is turned on. The light is guided in the second light guide portion  33   b  and reflected at the inner wall of the first light guide portion  33   a  and guided at a rear of the design display portion  31 . The center light R is positioned to the center position P 0  of the design display portion  31 . The guided light lights the design display portion  31  to project a design pattern portion onto a windshield  3 . A driver recognizes a virtual image S as shown in  FIG. 10A  on the windshield  3 . 
     The design-superposing display apparatus  30  of the present invention is not provided a backlight source disposed on a rear thereof, so that the display device  10  achieves a high luminance design display without limitation of a rear space. A heat sink can be arranged at the rear of the display device  10 , so that the VFD can also be adapted to the display device  10  and keep a specified performance by virtue of the heat sink. 
     The second light guide portion  33   b  intersects the first light guide portion  33   a  with a prescribed angle so that the center light R of the light source  32  is reflected to the center position P 0  of the design display portion  31 . The increase of light intensity at the design display portion  31  achieves superposing display of the design pattern portion with uniform and high luminance. 
     In the first and second embodiments, it is made to effort the prescribed distance t between the design display portion  31  and the display device  10  shorter. A light guide portion  33  shown in  FIG. 7  can be utilized for the vehicle display unit  1  when the display unit  1  has no restriction about the prescribed distance t. 
     The light guide portion  33  includes a first light guide portion  33   a  having a reflecting surface  33   f  and a second light guide portion  33   b . A light emitted from a light source  32  is reflected by the reflecting surface  33   f  and the center light is projected onto a center position P 0  of a design display portion  31 . 
     The light guide portion  33  of  FIG. 7  achieves the same effect as the first and second embodiments of the design-superposing display apparatus  30 . The light guide portion  33  of  FIG. 7  does not include the bending portion included in the first and second embodiments, so that the manufacturing becomes simple, resulting low cost product. It is preferable to utilize the design-superposing display apparatus  30  of  FIG. 7  for the vehicle display unit  1  when the vehicle display unit  1  has no restriction about the prescribed distance t. 
     The embodiments described above have the light guide portions  33  with the hollow tube shape but the invention is not limited thereto. The light guide portion  33  may have a light guide plate  33 ′ as shown in  FIGS. 8-9 . 
     A design-superposing display apparatus  30  includes a design display portion  31 , light sources  32 , the light guide plate  33 ′ as the light guide portion. The light guide plate  33 ′ has the same shape as the design display portion  31 . The light sources  32  disposed aside of a display device  10  emit lights into the light guide plate  33 ′ and the lights are guided to a rear of the design display portion  31 . The plurality of light sources  32  achieve high luminance. 
     The configuration of  FIGS. 8-9  provides also the same function as the first and second embodiments. The embodiment of  FIGS. 8-9  is adapted to the vehicle display unit  1  having restriction about the prescribed distance t. 
     The embodiments shown are purely exemplary and not limited thereto. Any modification and alteration are within spirit and scope of the present invention.