Patent Publication Number: US-2009231720-A1

Title: Heads up display

Description:
BACKGROUND 
     The present invention relates, in general, to heads up displays (HUD) and, more particularly, to heads up displays for automotive applications. 
     Heads up displays or HUD are known and are currently used in many military and commercial aircraft. HUDs are also finding application in automobiles. In an automotive application, a HUD unit is mounted in the automobile dashboard to project an image in front of the driver. 
     A HUD typically includes a video processor, a display unit or image source, a mirror and a combiner or windshield. Data is received from one or more vehicle computers or directly from various sensors to enable one or more types of data pertaining to vehicle operating conditions to be displayed by the HUD. Such data can include the vehicle speed, tachometer reading, turn signal operation, low/high beam headlight operation, fuel level, etc. to name a few. 
     While HUDs significantly enhance vehicle safety by minimizing driver distraction caused by having to look down at the instrument panel to determine the engine speed, or other vehicle operating parameters, only a fraction of vehicles on the road today are equipped with HUD technology. One of the reasons for poor market penetration for such a useful technology is cost. Consumers may like the HUE technology, but are not willing to pay a perceived high price for a HUD system. If the cost of the HUD system could be considerably lower, there would be the potential for a very large market for HUD systems in automotive applications. Thus, it would be desirable to provide HUD system for automotive applications which has a low cost. 
     SUMMARY 
     A heads up display apparatus for a vehicle having a windshield includes an LED display mounted in the vehicle to reflect an alphanumeric output of the display from a vehicle windshield toward the vehicle driver. 
     In one aspect, a vehicle operating parameter input is coupled to the display. The vehicle operating parameter input may be at least one of the vehicle speed, the vehicle tachometer output, fuel quantity and vehicle turn signal condition. 
     In another aspect, a variable brightness control input is coupled to the display for controlling the brightness level of the LED display. The variable brightness input may be a user manipulated control member and/or an ambient light signal coupled to the display. 
     In another aspect, a control member is connected between a power source and the display for turning the display on and off. 
     Each element of each LED character includes a reflected element image and an at least partially refracted and reflected ghost element image which have juxtaposed and overlapped elements to form a combined single image to the viewer. 
     The present HUD apparatus has a low cost since a simple LED display is used thereby eliminating the complex imaging, mirror and processing required by prior art HUD systems which project an image in front of the driver. The present HUD system utilizes the inherent partial reflective property of a vehicle windshield thereby eliminating the need for special reflective coatings required in prior art HUED systems. 
     In addition, the present HUD system may receive inputs from a variety of vehicle operating parameter sensors, such as tachometer reading, fuel quantity, turn signal or headlight operation as well as vehicle speed. The brightness of the display may be adjusted manually by the operator or automatically via an ambient light sensor to brighten. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The various features, advantages, and other uses of the disclosed HUD apparatus will become more apparent by referring to the following detailed description and drawing in which: 
         FIG. 1  is a side elevational view of a heads up display apparatus mounted in the vehicle; 
         FIG. 2  is a pictorial representation of the HUD with inputs; 
         FIG. 3  is a pictorial representation of the image of the HUD display reflected from a vehicle windshield; 
         FIG. 4  is a pictorial representation of one of the HUD display LED elements; 
         FIG. 5  is a pictorial representation of one HUD display LED element which has non-optimized dimensions producing spaced reflected and ghost images; 
         FIG. 6  is a pictorial representation of one HUD display LED element having optimized dimensions producing overlapped reflected and ghost image; and 
         FIG. 7  is an enlarged front pictorial view of the overlapped reflected and ghost images of one entire HUD display character. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1 , an automobile  10  is shown equipped with a heads up display apparatus (HUD)  12 . The HUD  12  communicates information to the vehicle operator via an image reflected off of the inner surface of the vehicle windshield  18  within the driver&#39;s visual line of sight. The HUD  12  allows the driver to receive vehicle operating information without taking his eyes off of the road or from the forward direction of movement of the vehicle. 
     The HUD  12 , as shown in  FIG. 2 , includes a luminous LED digital display  20  capable of forming one or more independent alphanumeric characters  22  in a housing  14  mounted on or in a vehicle dashboard  16 . Three characters  22  are shown by way of example only. Seven elements  22 A,  22 B,  22 C,  22 D,  22 E,  22 F and  22 G make up each LED character  22  to enable alphanumeric characters to be generated. 
     The seven LED elements  22 A,  22 B,  22 C,  22 D,  22 E,  22 F and  22 G are arranged in a general figure eight pattern as shown in  FIG. 4 . Each LED element,  22 A,  22 B,  22 C,  22 D,  22 E,  22 F and  22 G, is discrete and contacts other LED elements  22   a - 22 G only at one edge, as also shown in the  FIG. 4 . 
     Each LED character  22  is symmetrical both in longitudinal and lateral directions. As the display  20  is mounted on a generally horizontally extending surface, such as the vehicle dashboard  16 , the laterally extending LED elements,  22 A,  22 B, and  22 C of each LED character  20  are horizontally oriented, from the reference point of the vehicle driver, and will be reflected and refracted, as described hereafter, from the vehicle windshield  18  to appear in a laterally or horizontally extending direction to the vehicle driver. However, the horizontal reflected and refracted LED elements  22 A and  22 C will be inverted from the same element in the display  20 . Likewise, the longitudinally extending LED elements  22 B,  22 E,  22 F and  22 G, when viewed in a mounting orientation on the vehicle dashboard  16 , are reflected and refracted from the vehicle windshield  82  to appear in a vertically extending orientation to the driver. 
     Electrical power  24 , such as a 12-volt d.c. power, is input to the HUD  12  from the vehicle electrical system or vehicle battery. 
     A vehicle operating parameter input  26  is also input to the display  20 . The display  20  includes circuitry for converting the input  26  to a single or multi-character alphanumeric display. For example, the input  26 , i.e., numerals, letters, etc., can be the vehicle speed sensor data received directly from the vehicle speed sensor or from one of the vehicle computers which receives the vehicle speed sensor data directly from the speed sensor. The input  26  may also be other vehicle operating parameters, such as dynamic parameters, i.e., tachometer output, fuel level sensor output, engine fluid pressure levels, tire pressure, etc., as well as more static parameters, such as turn signal or headlight state, door lock or unlock state, etc. 
     A control member, such as an on/off switch  28 , is also input to the display  20  for controlling the application of electric power through the power source input  24  to the display  20 . The control member  28  may be a rotary knob having circumferentially spaced on and off positions. 
     The control member or rotary knob input  28  may also be connected to a voltage control circuit to vary the voltage applied to the display  20  from the power source  24  in order to control the brightness of the display characters  22  to accommodate ambient light conditions or according to the driver&#39;s preference. 
     The display  20  may also receive an input  30  which provides ambient data, such as the output of a photocell mounted on the vehicle dashboard  16  or at any of other suitable locations within the vehicle. The ambient light input  30  controls the voltage applied to the display characters  22  in the same manner as the brightness control member input  28  by varying the voltage applied to the display characters  22 . 
     The display  20  is also adaptable to receiving multiple vehicle operating parameters similar to the input  26 . Such parameters can be controlled by a selector switch, such as a slide switch or a rotary switch, to enable the vehicle driver to select between various vehicle parameters for display on the display characters  22 . As mentioned previously, such other inputs can include the tachometer output, fuel level, turn signal or headlight operation, engine oil pressure, etc. 
     To generate a clear image  40  in the driver&#39;s field of view, as shown in  FIG. 3 , each LED element  24 A,  24 B,  24 C,  24 D,  24 E,  24 F and  24 G of each LED character  22  have uniform illumination throughout the display surface of each element rather than being brighter toward the center region of each display surface. This could eliminate the need for a lens or a coating on the LED display  20  or a coating  18  on the vehicle windshield. It may also be possible to vary or increase the width of the vertical elements  22 D,  22 E,  22 F, and  22 G as compared to the width of the horizontally extending LED elements  22 A,  22 B, and  22 C to produce an optimized, clear image. In the following example, for example only, the length of each element  22 A,  22 B,  22 C,  22 D,  22 E,  22 F, and  22 G is held at a constant, identical dimension. 
     The following equations are employed to optimize the dimensions of each LED element  22 A,  22 B,  22 C,  22 D,  22 E,  22 F, and  22 G of each LED character  20 . 
         W 1= t *tan(θ)/cos(α) 
       Where θ=sin −1 (sin(α)/μ) 
         W 2=4* t *tan(θ)*sin(α) 
     In the above formulas:
         α is the windshield inclination angle shown in  FIGS. 5 and 6     t is the windshield thickness   μ is the Refractive Index of the windshield  18  glass   w 1  is the width of the horizontal LED elements  22 A,  22 B,  22 C   w 2  is the width of the vertical LED elements  22 D,  22 G,  22 F,  22 CA       

     EXAMPLE 
     Consider the case where α is 30 degrees, μ is 1.5 (typical for glass windshields) and the thickness (t) of the windshield  18  is 8 mm 
       Computing θ=sin −1 (sin(30)/1.5),         this makes θ=19.47.       
     Inserting this into the equation for w 1  yields: 
         w 1=8*tan(19.47)/cos(30)         which makes w 1 ==3.265 mm.       
     The optimal value of w 2  is computed using 
         w 2=4*8tan(19.47)*sin(30)         which makes w 2 =5.656 mm
 
Therefore, for the given windshield  18  parameters, the optimal dimensions of the LED elements  22 A- 22 G are w 1 =3.265 mm and w 2 =5.656 mm.
       
     Referring briefly to  FIG. 5 , if LED elements  22 A- 22 G of each LED character  22  have the same width dimensions as shown pictorially in  FIG. 2 , an image of the LED characters  22  will be reflected from the inner surface  19  of the windshield  18  as a reflected image  42  toward the driver&#39;s eyes  44 . In addition, the LED characters  22  will be refracted as rays  47  by the inner surface  19  of the windshield  18  through the windshield  18  and reflected at points  46  by the outer surface  21  of the windshield  18  to form second reflected rays  48 . The second reflected rays  48  will pass back through the thickness of the windshield  18  to the inner surface  19  of the windshield  18  where again they will be refracted by the inner surface  19  of the windshield  18  towards the driver&#39;s eye  44  as a ghost image  50  separate and spaced from the reflected image  42  at the driver&#39;s eyes  44 . The reflected image  42  and the ghost image  50  are seen by the driver&#39;s eyes  44  as a composite image which, due to the spaced nature of the reflected image  42  and the ghost image  50 , are seen by the driver&#39;s eyes  44  as a blurred or double image. 
     In  FIG. 6 , the optimized dimensions described above for the width of each LED element  22 A- 22 G are employed. Each LED element  22 A- 22 G is again reflected off of the inner surface  19  of the windshield  18  to form a reflected image  52  at the driver&#39;s eyes  44 . The images of the LED element  22 A- 22 G are also refracted by the inner surface  19  through the windshield  18  and are reflected at points  56  from the outer surface  21  of the windshield  18 . The reflections form second reflected rays  58  which are again refracted by the inner surface  19  of the windshield  18  and directed toward the driver&#39;s eyes  44  as a ghost image  60 . 
     The ghost image  60  will have less brightness or intensity than the reflected image  52 . The amount of decrease in the brightness of the ghost image  60  relative to the reflected image  50  will depend on the type of glass used in the windshield  18  and the design of the windshield  18 , such as the angle or inclination of the windshield  18  relative to the vehicle dashboard  16 . 
     However, due to the optimized dimensions described above in which the vertically oriented LED elements  22 D,  22 E,  22 F, and  22 G have width larger that the width of the horizontally extending LED elements  22 A,  22 B, and  22 C of each LED display character  22 , the ghost image  60  is overlapped or juxtaposed horizontally and superimposed or overlaid vertically with the reflected image  52  at the driver&#39;s eyes  44 , as pictorially shown in  FIG. 7 , to form a composite image  6 . That is, the lower edge of the bottommost LED element  22 C of the ghost image  60  is disposed immediately adjacent to or superimposed over the upper edge of the uppermost LED element  22 C′ of the reflected image  52 . 
     It should be noted that the arrangement of the LED elements  22 A- 22 G shown in  FIG. 4 , which are as they appear when looking down at the upper surface of the display  12 , are inverted by the windshield  18  to the arrangement shown in  FIG. 7 . The driver&#39;s eyes  44  combined the reflected image  52  and the ghost image  60  into a composite, single image  62  having clearly defined edges. 
     It should also be noted that the dimension w 1  shown in  FIG. 6  is the width w 1  of one of the horizontally extending LED elements  22 A,  22 B, and  22 C. For clarity in  FIG. 7 , these elements, which are inverted, as described above, by reflection and refraction by the windshield  18 , are relabeled  22 A′,  22 B′, and  22 C′. Likewise, the horizontally extending ghost image of each LED element  60 A,  60 B, and  60 C is also inverted as shown in  FIG. 7 . 
     As clearly shown in  FIG. 7 , the ghost images of each LED element  60 A,  60 B, and  60 C, which are of slightly less brightness or intensity than the corresponding horizontally extending elements  22 A′,  22 B′, and  22 C′ of the reflected image  52 , are juxtaposed or immediately adjacent to the horizontally elements  22 A′,  22 B′, and  22 C′ of the reflected image  52  to form a combined horizontally extending element of the composite image  50 . 
     Meanwhile, the vertically extending element of the reflected image  52 , namely, LED elements  22 B,  22 E,  22 F, and  22 G, overlap corresponding vertically extending elements  60 D,  60 E,  60 F and  60 G of the ghost image  60 . In the areas of overlap, denoted by combined element locations  22 D′ and  60 B,  22 E′ and  60 E,  22 F′ and  60 F, and  22 G′ and  60 G, the brightness or intensity of the corresponding reflected image elements and the ghost image elements combine and are additives to form bright elements in the composite image  62 . Non-overlapped regions  23 D′,  23 E′,  60 D′,  60 E′,  60 F′, and  60 G′ which are formed by only a portion of one of the reflected image  52  or the ghost image  60  element, have a brightness or intensity substantially the same as the adjacent horizontally extending elements  22 A′,  22 B′, and  22 C′ of the reflected image  52  or the adjacent portion of the ghost image  60  elements  60 D,  60 D,  60 F and  60 G. 
     While edge blurring of the LED elements forming the composite image  62  can occur, such as where a portion of a ghost image of the LED characters is juxtaposed or immediately adjacent to the reflected image  50 , larger size LED&#39;s may be employed to minimize the effects of such edge blurring. 
     If low power LED&#39;s are employed in the display  14 , increased the brightness of the composite image  62  may be attained by forming a translucent portion on the inner surface  19  of the windshield  18  which has increased reflectivity. This makes at least the reflected image  52  of the composite image  62  brighter. 
     It should be noted that the over all dimensions of the LED characters are not constrained by the above described optimization method. This permits greater flexible for designers because the overall dimension can be set to any desired size to match a given application configuration.