Abstract:
An image illumination apparatus for backlighting a portion of a liquid crystal display. The apparatus includes a light source generating an illuminating light, a light shielding medium located between the light source and a display grid, and an aperture formed in the light shielding medium for allowing the transmission of light generated by the light source to pass to a lighted portion of the display grid. The light shielding medium prevents light from being transmitted to a non-lighted portion of the display grid.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/317,001, filed Sep. 4, 2001. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to lighted displays for displaying images, and more particularly to the backlighting of image generating displays, such as active matrix liquid crystal displays which are useful for head up displays. 
     BACKGROUND OF THE INVENTION 
     Electronic image displays are commonly illuminated by backlighting the display for direct viewing from the front or for viewing in a head up display (HUD) system. HUD systems have been widely known and used in military and commercial aircraft applications. More recently, HUD systems have been employed in automotive vehicles to project an image for display in front of the vehicle driver so that the image is viewable through the front windshield. The HUD system thus serves as an alternative to displaying the image on a display unit generally located in the instrument panel of the vehicle. 
     In automotive applications, passive displays, such as active matrix liquid crystal displays (AMLCD), are illuminated by applying backlight illumination to the backside of the electronic display. Since HUDs typically project a light pattern generated by an image source and reflect the light pattern from a windshield generally having a low reflectivity, it becomes necessary to provide a high intensity light source, especially during daylight driving conditions which demand a very bright image source. Typically, the image source for a HUD includes a halogen bulb and an elliptical reflector such as is disclosed in U.S. Pat. No. 5,709,463. The aforementioned patent is hereby incorporated by reference. 
     In many conventional HUD systems, multiple images are generated by a single electronic display and only a portion of the display grid is actually used to project the images. The remaining portion of the display grid, which is not used to display any image, is generally colored black. With conventional backlighting approaches, the light pattern is generally configured to illuminate the entire backside of the electronic display grid. Accordingly, not only is the lighted portion of the display grid illuminated, but the black non-lighted portion of the grid is also illuminated in many conventional displays. The non-lighted black colored portion of the display grid absorbs light energy illuminated thereon, and the absorbed light energy is converted to heat energy. Not only is this light not used for generating an image, but the heat build-up in the electronic display raises the operating temperature to excessive levels which may lead to damage or inoperability of the display. 
     It is therefore desirable to provide backlighting for a display, such as a liquid crystal display, which avoids problems associated with overheating of the display. It is further desirable to provide for backlighting for such a display which more efficiently utilizes the light energy. It is particularly desirable to provide for such backlighting for a display for use in HUD systems, such as those used in automotive vehicles. 
     SUMMARY OF THE INVENTION 
     The present invention provides for an image illumination apparatus for backlighting a portion of an electronic display. The apparatus comprises a light source for generating illuminating light, a light shielding medium located between the light source and a display, and an aperture formed in the light shielding medium for allowing the transmission of light generated by the light source to pass to a lit portion of the display. The light shielding medium prevents some of the light from being transmitted to non-lit portions of the display. 
     These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic diagram of a HUD system employed in an automotive vehicle; 
     FIG. 2 is a side view of the image source display having a backlighting apparatus according to the present invention; 
     FIG. 3 is a partial exploded view of the display and backlighting apparatus shown in FIG. 2; and 
     FIG. 4 is a front view of displayed images generated by the display, according to one example. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, an automotive vehicle  10  is generally shown equipped with a head up display (HUD) system  15 . The HUD system  15  displays to the vehicle operator  24  one or more images  20  projected in front of the operator  24  and generally aligned with the operator&#39;s line of sight. As is evident in vehicle applications, the HUD system  15  allows the operator  24  to view the displayed image without requiring the operator to remove his/her eyes from the view through the front window  18  of the vehicle. According to the present invention, the HUD system  15  employs an image source display  12 , particularly an active matrix liquid crystal display (AMLCD), having a backlighting apparatus as described herein. 
     The HUD system  15  generally includes a video processor  14 , the image source display unit  12 , a mirror  16 , and a combiner or windshield  18 . The video processor  14  receives data from multiple systems and sensors in the automotive vehicle  10  and formats the data into a suitable display signal that is communicated to the display unit  12 . For example, data may be received from an infrared sensor for detecting objects in the roadway ahead of the vehicle, a vehicle speed sensor, engine sensors, light sensors, and GPS related data, amongst other data. The video processor  14  may be of a conventional design having a digital microprocessor, memory, and related circuitry, and therefore is not described in detail herein. 
     Processor  14  receives a light signal from light sensor  22  which is indicative of the sensed ambient light conditions in front of the vehicle. The processor  14  generates signals responsive to the light signal for controlling the brightness of the backlight source which illuminates the backside of the display unit  12  as described herein. In order to generate a sufficiently viewable image, the brightness of the light source may need to be adjusted depending upon the ambient light conditions. It should also be apparent that a relatively bright light source may be needed, considering the light losses that may occur at the reflection of the image off of the combiner or windshield  18 . 
     The display unit  12  generates a lighted image and projects the lighted image from a front side of the display. Display unit  12  may be of a conventional design, except for the backlighting apparatus of the present invention. Display unit  12  includes an electronic display having a grid of pixels that may be illuminated with light from the backside to generate a lighted image on the front side. The electronic display further has a masked area that does not generate an image. One example of the display unit may include a liquid crystal display. Liquid crystal displays may employ a passive matrix or an active matrix display grid. According to a more specific embodiment, the liquid crystal display may include an AMLCD. While the present embodiment illustrates the use of an AMLCD having a backlighting apparatus according to the present invention, it should be appreciated that the display may include other types of displays employing backlighting. 
     Referring to FIGS. 2 and 3, the backlighting apparatus  12  is shown positioned against the backside of an AMLCD  50 . The backlighting apparatus  12  includes a light source, such as first and second lamps  32 A and  32 B, for generating illuminating light. Each of the first and second lamps include a bulb supported in an elliptical reflector for shaping the light beam emitted therefrom. The first and second lamps  32 A and  32 B may employ halogen bulbs according to one embodiment. While the light source is shown having first and second lamps  32 A and  32 B, it should be appreciated that one or more lamps may be employed to generate a source of illuminating light. 
     The backlighting apparatus further includes a light engine  34  in optical communication with the first and second lamps  32 A and  32 B. The light engine  34  has inner reflective walls  36  which define a light guide for transmitting illuminating light from the lamps  32 A and  32 B toward the AMLCD  50 . According to one embodiment, the inner reflective walls  36  define a generally rectangular shape to provide a generally rectangularly configured light guide. 
     Coupled between the light engine  34  and the backside of AMLCD  50  are three planar mediums  40 ,  42 , and  44 , each having first and second apertures  46  and  48  extending therethrough and aligned with one another. Medium  40  is a heat shielding reflector having a generally planar shape and a reflective surface facing lamps  32 A and  32 B for recycling light energy illuminated thereon. Light generated by the lamps  32 A and  32 B is transmitted through light guide  36 . Some of the light passing through light guide  36  will pass through apertures  46  and  48 , while a substantial amount of the light which illuminates the remainder of light recycling reflector  40  is reflected back into the light engine  34 . Thus, the light energy may be recycled within light engine  34 , until such light energy exits apertures  46  and  48 . 
     Medium  42  is a thermal insulation layer disposed between mediums  40  and  44 . The insulation layer  42  may include a high temperature polymeric or glass material, generally in the shape of a substantially flat panel. Insulation layer  42  provides thermal insulation to prevent or reduce the transfer of heat between mediums  40  and  44 . 
     Medium  44  is a heat sink having a conductive material that physically contacts the back surface of the display grid  50  to collect and remove heat from the display grid  50  and dissipate the collected heat to the outer surrounding environment. The heat sink  44  may include a heat transmissive conductive material such as aluminum or copper and may further include radially extending arms with an enlarged surface area for effectively dissipating heat energy. Accordingly, the use of a heat sink  44  reduces the heat energy generated at the display grid  50 , thus preventing overheating of the display. 
     It should be appreciated that each of mediums  40 ,  42 , and  44  has apertures  46  and  48  extending therethrough so as to allow for the transmission of illuminating light to pass from the light engine  34  through apertures  46  and  48  to only designated lighted areas at the backside of display grid  50  which are intended to be lit to provide displayed images. The remaining non-lighted area of the display grid is masked so as not to receive light or display a light image. Thus, by only lighting those portions of the backside of display grid  50  that are intended to generate an image, the remaining portions which are not illuminated with light do not absorb light energy. 
     Planar mediums  40 ,  42 , and  44  are stacked one on top another and directly against the backside of display grid  50 . Thus, light passing through apertures  46  and  48  illuminates only the grid area exposed to apertures  46  and  48 . According to one embodiment, the active matrix display grid  50  has a thickness of approximately 5 mils, while each of the mediums  40 ,  42 , and  44  has an individual thickness of approximately 1 mil. 
     Referring to FIG. 4, one example of lighted images generated on display grid  50  are illustrated therein. According to the example shown, a first image  56  is generated by illuminating the backside of display grid  50  by transmitting light through aperture  46  to the backside of display grid  50 . Similarly, a second image  58  is generated by passing light through aperture  48  to the backside of display grid  50 . The size, shape, and location of images  56  and  58  are determined by the apertures  46  and  48 , respectively. Accordingly, only those portions containing images  56  and  58  are illuminated with light, while the remaining portions  52  of the display are not illuminated with light. While two rectangularly shaped images  56  and  58  are shown herein, it should be appreciated that one or more images having various shapes and sizes may be employed by forming aperture  46  and  48  to have a select size and shape. 
     Accordingly, the backlighting apparatus of the present invention advantageously illuminates only select designated portions of the backside of display  50  with light, thereby maintaining a lower operating temperature of the display. By maintaining a lower operating temperature, it should be appreciated that increased reliability of the display may be realized. Further, by providing a heat sink as a conductive medium contacting the back surface of display grid  50 , further reduced operating temperature may thereby be achieved. In addition, by directing the light to only those regions where an image is to be generated, the backlighting system efficiently utilizes the light source energy and operates with reduced power consumption. 
     It will be understood by those who practice the invention and those skilled in the art, that various modifications and improvements may be made to the invention without departing from the spirit of the disclosed concept. The scope of protection afforded is to be determined by the claims and by the breadth of interpretation allowed by law.