Abstract:
A heads-up display comprises a monochrome display device for generating an image and an optical device for generating a virtual image from the image of the display device. The monochrome display device comprises a display and a backlight for illuminating the display from its backside. The backlight comprises a first light source emitting light of a first color, a second light source emitting light of a second color, a first light guide coupled to the first light source, and a second light guide coupled to the second light source. The first and second light guides are disposed in such close juxtaposition behind the display so that they illuminate together the entire backside of the display and illuminate a first region of the display associated with the first light guide with the first color and a second region of the display associated with the second light guide with the second color.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This Utility Patent Application claims priority to German Patent Application No. DE 10 2006 014394.9, filed Mar. 29, 2006. 
     FIELD OF THE INVENTION 
     The invention relates to a heads-up display, to a motor vehicle and to a method of operating a heads-up display. 
     BACKGROUND OF THE INVENTION 
     What is known as a heads-up display (HUD) is a display system in which information is projected into the field of vision of a user, for example the driver of a car or the pilot of an airplane. Pilots have had such systems since the 1940s, when they were known as reflex visors. 
     A heads-up display generally comprises a display device and an optical device which cooperate with what is known as a combiner. The display device generates an image from which the optical device, comprising for example a lens and a concave mirror, generates a virtual image which the driver or pilot views in a reflective, transparent screen: the combiner. The combiner therefore superimposes on the virtual image the environmental information appearing through the combiner. 
     If a heads-up display is installed in a motor vehicle, the windscreen of the motor vehicle may be used as the combiner. 
     For relatively good readability of the virtual image, the display device should generate not only a sufficiently bright image but also, if possible, a color image. 
     Published European application for patent EP 1 143 288 A1 discloses a heads-up display in which the light from a light source is transmitted through a liquid crystal display (LCD) screen and the image which may be seen on the liquid crystal display screen is projected on the windscreen of a motor vehicle as a virtual image. The light source comprises a plurality of red, blue and green light-emitting diodes disposed on a common carrier. 
     Published European application for patent EP 0 570 037 A1 discloses a further heads-up display comprising a monochrome or a polychrome display device. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the invention, a heads-up display comprises a monochrome display device for generating an image and comprising an optical device for generating a virtual image from the image of the display device, wherein the monochrome display device comprises a display and background lighting provided for backlighting the display and the background lighting comprises a first light source emitting light of a first color, a second light source emitting light of a second color, a first light guide coupled to the first light source and a second light guide coupled to the second light source, wherein the two light guides are disposed in such close juxtaposition behind the display of the display device that they backlight the entire area of the display and backlight a region of the display associated with the first light guide with the first color and a region of the display associated with the second light guide with the second color. This allows the two regions to be backlit with different colors and at the same time the entire area of the display to be backlit without the means for lighting the two regions affecting one another or, if they do affect one another, then doing so only slightly. The prerequisites for generating a multicolored image using the monochrome display device, which is relatively inexpensive to produce, are thus met and this is, in turn, a prerequisite for generating a multicolored virtual image. The term “image” or “projected image” refers to any type of displayed information, i.e. including numbers, letters or symbols. 
     According to an embodiment of the inventive heads-up display, the risk of the two regions affecting one another may be reduced if the two light guides are separated from one another by a non-transparent and/or light-reflecting layer. The layer is, for example, a thin film or may preferably be applied by means of color printing. 
     The two colors may be different, identical and/or adjustable. 
     If the display used is a liquid crystal display screen in an embodiment of the inventive heads-up display, then the heads-up display may be produced particularly inexpensively. 
     The inventive heads-up display may be configured in a particularly attractive manner if, according to a variation, at least one of the two light guides takes the form of a symbol. A symbol of this type is, for example, a trade mark. 
     The inventive heads-up display may, in particular, be used in a motor vehicle, for example as an instrument cluster for displaying various vehicle parameters. When used in a motor vehicle, the inventive heads-up display may be used, in particular, for carrying out a method comprising the following method steps: injecting light of the first color into the first light guide and into the second light guide, which are juxtaposed in such a way behind the display of the display device that they backlight substantially the entire area of the display with the first color, and changing the color of the light injected into the second light guide from the first color to a second color differing from the first color on the basis of a signal emitted by a control device of the vehicle, so that a region of the display associated with the first light guide is backlit with the first color and a region of the display associated with the second light guide is backlit with the second color. 
     This method allows substantially the entire display initially to be backlit with the first color. If the control device emits the signal, the second color changes, i.e. the display is backlit with the second color in the region of the second light guide. However, owing to the two light guides, which are preferably isolated from one another by a non-transparent and/or light-reflecting layer, the second color does not disturb, or hardly disturbs, the region of the display that is backlit by the first light guide. The region of the display that is backlit by the second light guide is, for example, associated with a warning signal, so the control device emits the signal when a driver of the motor vehicle is to be warned. The region of the display that is backlit by the second light guide is then backlit with the second color, for example red. 
     The inventive heads-up display therefore provides, inter alia, a heads-up display comprising a backlit display device, the light of which is injected into the two light guides and is emitted therefrom behind the display, for example the glass of a liquid crystal display screen. The display comprises a plurality of lighting zones, each of which is backlit by one of the two light guides. The light guides are joined directly adjacent to one another. In order to rule out the risk of light transferring from one light guide to the other light guide, the thin, non-transparent or light-reflecting layer is inserted at the interface of the two light guides. This allows, in particular, the following use: 
     The entire display of the display device may be completely utilized with its conventional backlighting color. Light of a single color is therefore initially injected in the two light guides. The entire display is then substantially backlit with this color. If a warning display is to be presented, for example in the color red, then the associated symbol is generated in the region of the second light guide. Only in this region is the red backlighting, instead of the yellow backlighting, then activated by injecting a red light into the second light guide. 
     Since the interface between the two light guides may be relatively thin, the entire display of the display device is backlit uniformly substantially over its entire area if a light of a single color is injected in both light guides. 
     The invention also provides a heads-up display comprising a display device for generating an image and an optical device for generating a virtual image from the image of the display device, wherein the display device comprises a first light guide, a second light guide, a first light source that injects light of a first color into the first light guide and a second light source that injects light of a second color into the second light guide, wherein the two light guides are disposed in such close juxtaposition that they form substantially an area designed as a display area and are separated from one another by a non-transparent and/or light-reflecting layer. The light-absorbing or light-reflecting layer, which may preferably be a thin film or may be applied by means of color printing, on the one hand, prevents overlapping of two different-colored lights injected into the two light guides and, on the other hand, provides a visually continuous display surface which is not interrupted by any non-lighting demarcations. 
     Advantages of the inventive heads-up display include: 
     There are cost advantages owing to the use of a monochrome display device for a heads-up display for displaying color information. In comparison to conventional color display devices, the background lighting of the inventive heads-up display may be less powerful, since a monochrome display has relatively high transmission. This has a positive effect on the price of the light source used. 
     Owing to the relatively high transmission of the monochrome display, prerequisites for a relatively bright image, and therefore for a relatively bright virtual image, are met. Despite the use of the monochrome display, the light guide structure according to the invention produces a multicolored image. 
     Specific symbols, such as for example a warning symbol, circles or curves, may be fixed in the light guide structure. A relatively low-resolution monochrome display may thus be used and this, again, may reduce costs. 
     Relatively simple scaling of the color range of the heads-up display according to the invention is obtained. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
         FIG. 1  is a passenger car; 
         FIG. 2  is a portion of the passenger car of  FIG. 1  having a heads-up display; 
         FIGS. 3 ,  4  are different views of the display device for the heads-up display of  FIG. 2 ; and 
         FIG. 5  is a further display device for the heads-up display of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention. 
       FIG. 1  shows a passenger car having a windscreen  2  and a dashboard  3  on which there is disposed a steering wheel  4  and to which, in the case of the present embodiment, a heads-up display  5 , illustrated in greater detail in  FIG. 2 to 4 , is attached. The heads-up display  5  is provided to project an image in a projection region  6  of the windscreen  2 . 
     The heads-up display  5  comprises an optical device  7  and a display device  8 , illustrated in greater detail in  FIG. 3 and 4 , for generating an image. The image generated by the display device  8  is injected into the optical device  7  which then generates from the image of the display device  8  in a generally known manner, such as is known, for example, from published European application for patent EP 1 143 288 A1, a virtual image projected onto the projection region  6  of the windscreen  2 . The optical device  7  comprises, for example, a lens and a concave mirror. 
     The projection region  6  is located in the field of vision of a driver (not illustrated in greater detail) of the passenger car, so the projection region  6  superimposes on the virtual image the environmental information appearing through the windscreen  2 . In the case of the present embodiment, the heads-up display  5  is provided to inform the driver about vehicle parameters of the passenger car. 
     The display device  8  comprises, in the case of the present embodiment, a liquid crystal display screen  9  as the display and a background lighting means, disposed on the back of the liquid crystal display screen  9 , for backlighting the liquid crystal display screen  9 . The background lighting means has, in the case of the present embodiment, a light guide  10  made from plexiglass. The light guide  10  has, in the case of the present embodiment, four part light guides  11 - 14  which jointly extend over substantially the entire area of the back of the liquid crystal display screen  9 . 
     The light guide  10  is disposed on a printed circuit board  15  having light-emitting diodes  16 - 23  which each inject light laterally into the light guide  10 . In the case of the present embodiment, four respective light-emitting diodes, which emit light of different colors, are associated with each of the four part light guides  11 - 14 . In the case of the present embodiment, yellow light-emitting diodes  16  and red light-emitting diodes  17  are disposed laterally on the first part light guide  13 . Yellow light-emitting diodes  18  and green light-emitting diodes  19  are disposed laterally on the second part light guide  12 . Yellow light-emitting diodes  20  and red light-emitting diodes  21  are disposed laterally on the third part light guide  13 . Yellow light-emitting diodes  22  and green light-emitting diodes  23  are disposed laterally on the fourth part light guide  14 . 
     The background lighting means further comprises a reflector  24  which laterally frames the light guide  10 . In addition, the four part light guides  11 - 14  are isolated at those interfaces at which the part light guides  11 - 14  respectively make contact, by thin, non-transparent layers  26 - 29  which, in the case of the present embodiment, were applied to the first part light guide  11  and the third part light guide  13  by means of color printing. 
     The light-emitting diodes  16 - 23  are connected in a non-illustrated manner to a control device  25  which is disposed below the dashboard  3  of the passenger car and individually activates the light-emitting diodes  16 - 23 . In the case of the present embodiment, the control device  25  may be used to adjust the intensity of the light issuing from the light-emitting diodes  16 - 23  or the light-emitting diodes  16 - 23  may be switched on and off. 
     In the case of the present embodiment, the background lighting means may be operated in various operating states. In a first operating state, it is provided that only the yellow light-emitting diodes  16 ,  18 ,  20 ,  22  are activated by the control device  25  and the remaining light-emitting diodes are switched off. In this operating state, the entire liquid crystal display screen  9  is backlit yellow. 
     In a second operating state, the driver is also able to adjust the background colors of the partial display areas of the liquid crystal display screen  9  associated with the individual part light guides  11 - 14 . Provision is therefore made, in the case of the present embodiment, for the yellow light-emitting diodes  16  of the first part light guide  11  to be switched off, while the red light-emitting diodes  17  of the first part light guide  11  are switched on. It is also possible to switch on the green light-emitting diodes  19  of the second part light guide  12 , rather than the yellow light-emitting diodes  18 , as a result of which the portion of the liquid crystal display screen  9  that is associated with the second part light guide  12  is backlit green. The same accordingly applies to the third part light guide  13  and the fourth part light guide  14 . 
     The interfaces coated with the thin, non-transparent layers  26 - 29 , at which interfaces the part light guides  11 - 14  respectively make contact, prevent light injected into one of the part light guides from also being injected into one of the other part light guides. 
     In the case of the present embodiment, the heads-up display  5  may be operated in a third operating state. In the third operating state, only the yellow light-emitting diodes  16 ,  18 ,  20 ,  22  are switched on and the remaining light-emitting diodes are switched off. If the driver&#39;s attention is to be drawn, for example, to the backlit image content associated with the first part light guide  11 , the control device  25  automatically switches the yellow light-emitting diodes  16  of the first part light guide  11  off and the red light-emitting diodes  17  of the first part light guide  11  on. 
     Owing to the interfaces coated with the thin, non-transparent layers  26 - 29 , at which interfaces the part light guides  11 - 14  respectively make contact, the red light injected into the first part light guide  11  does not disturb the partial display areas which are associated with the remaining part light guides  12 - 14  and backlight the liquid crystal display screen  9  yellow. 
       FIG. 5  shows a further display device  50  which may be used instead of the display device  8  shown in  FIG. 2 to 4  for the heads-up display  5 . Unless otherwise specified, components of the display device  50  shown in  FIG. 5  which are identical in terms of construction and functioning to components of the display device  8  shown in  FIG. 2 to 4  are provided with the same reference numerals. 
     The display device  50  illustrated in  FIG. 5  differs substantially from the display device  8  shown in  FIG. 2 to 5  in terms of its background lighting means. Said means comprises, in addition to the four part light guides  11 - 14 , a fifth part light guide  51  which is inserted in the first part light guide  11  and, in the case of the present embodiment, is in the form of a vehicle having an open rear door. The interface between the fifth part light guide  51  and the first part light guide  11  is provided, in the case of the present embodiment, with a non-transparent layer  52  which isolates the fifth part light guide  51  from the first part light guide  11 . The non-transparent layer  52  was attached to the fifth part light guide  51  by means of color printing. 
     The display device  50  comprises, in addition to the light-emitting diodes  16 - 23 , which are connected to the control device  25  and disposed on printed circuit boards  53 , a further yellow light-emitting diode  54  and red light-emitting diode  55 . The two light-emitting diodes  54 ,  55  are provided to inject their light into the fifth part light guide  51  and are also connected to the control device  25 . In the case of the present embodiment, the control device  25  is configured in such a way that it activates the yellow light-emitting diode  54  of the fifth part light guide  51  when the rear door  30  of the passenger car is locked. As a result, the fifth part light guide  51  backlights the liquid crystal display screen  9  yellow. If, on the other hand, the rear door  30  of the passenger car is not locked, the control device  25  activates the red light-emitting diode  55 , so the fifth part light guide  51  backlights the liquid crystal display screen  9  red. A red-lit projected image of a vehicle having an opened rear door on a yellow background thus appears in the projection region  6  of the windscreen  2  when the first part light guide  11  backlights the liquid crystal display screen yellow. Owing to the non-transparent layer  52  of the fifth part light guide  51 , the injected colors of the first and fifth part light guides  11 ,  51  do not disturb one another—and if they do, then they do so only slightly—as a result of which the projected image of the vehicle having an open rear door is relatively clearly defined. 
     Although the present invention has been described with reference to preferred embodiments, the invention is not restricted thereto, but rather may be modified in many ways. In particular, the selected colors of the yellow and red light-emitting diodes are intended merely as examples. In addition, the two light guides  5  and  6  may also be isolated from one another by other methods, for example by a light-reflecting layer or a thin film. The two light guides do not have to be rectangular either. In particular, it is possible for at least one of the two light guides to take the form of a symbol, so a symbol of a color differing from the color of the remainder of the background lighting means appears on the liquid crystal display screen. More than two light guides may also be used. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.