Head-up display

[0001] This is a U.S. national stage of application No. PCT/DE03/02891, filed on 1 Sep. 2003. Priority is claimed on the following application(s): Country: Germany, Application No.: 102 45 933.9, Filed: 30 Sep. 2002 the content of which is/are incorporated herein by reference.

[0002] 1. Field of the Invention

[0003] The invention relates to a head up display with a device for producing a focused light flux, having a light source and having an image reproduction apparatus including light valves.

[0004] 2. Description of the Prior Art

[0005] In order to convey information to vehicle drivers without the need for them to avert their gaze from the road to be driven or the air space to be flown, so-called head up displays have become known that are used to fade in an image representing information into the windshield of a vehicle. In order for the image still to remain visible in bright ambient light, there is an additional need for it to have a high luminous density. Focused light fluxes are also required for other illumination purposes, for example as reading lamps or as emitters for show-windows and expositions.

[0006] Devices for producing a focused light flux have already been disclosed in U.S. Pat. Nos. 5,836,676, 5,043,716 and 5,617,131 in an application for a display, in each case. A luminaire with focusing of the light beam is known from U.S. Pat. No. 4,935,665. However, the arrangements shown exhibit scarcely any suitability for use in a head-up display, because of their respective focusing and scattering characteristics.

[0007] It is therefore an object of the invention to produce a light flux with the aid of devices that exhibit, in particular, a low overall size and low weight, consume, and/or output as heat, as little power loss as possible, and are therefore also suitable for operation in a vehicle.

[0008] This object is achieved according to the invention by a head up display including a device for producing a focused light flux, the display comprising a light source having a plurality of light emitting diodes arranged in points of a light emitting diode matrix, an optical device arranged and dimensioned for focusing and scattering light produced by the light source, the optical device including a grid reflector comprising walls reflecting the light produced by the light source and forming light channels for each point of the light emitting diode matrix, the light channels each having a first end facing the light source and a second end at a light exit opening of the optical device, and a positive lens arranged at the first end of each of the light channels, an image reproduction apparatus including light valves arranged proximate the light exit opening of the optical device, and a diffusing screen arranged between the image reproduction apparatus and the light exit opening.

[0009] According to the invention, a matrix point is formed in each ease from a number of light-emitting diodes, which can also be of different color. Furthermore, the invention is not restricted to the application of in each ease a single lens per light channel.

[0010] A cost effective fabrication of the device according to the invention is possible when the positive lenses of all the light channels are integrally connected to a plate arranged between the light source and the grid reflector. However, this plate permits an undesired conduction of light in a transverse direction, and this can be prevented when the positive lenses are integrally connected in groups to webs arranged between the light source and the grid reflector.

[0011] An advantageous refinement of the invention consists in that the radii of curvature of the lens differ in different directions (astigmatic lenses). The light distribution can thereby be improved, particularly in elongated light exit openings.

[0012] The image reproduction apparatus including light valves and arranged at the light exit opening permits a compact device for producing high-resolution images of high luminous density and with a uniform distribution of luminous density over the entire image area. The device for focusing and scattering ensures in this case that the light produced by the light-emitting diodes is concentrated onto the surface of the image reproduction apparatus without the individual light emitting diodes being disturbingly imaged. A preferred field of application of the device according to the invention are graphical head up displays for vehicle applications.

[0013] The image reproduction apparatus lends the device according to the invention a few more advantages, which are set forth below. Thus, the coordination between RGB light source and color display renders possible the display of graphic color images in a head up display in conjunction with adequate luminous density. A uniform distribution of color and luminous density of the background lighting on the area of the liquid crystal display is achieved in cooperation with the reflector and the lens.

[0014] Configurable image contents can be displayed in color in the liquid crystal color display. The image content can therefore be adapted to the driving situation. The installation space for the entire image generating device is only a few cubic centimeters in the case of the example executed in practice. It is possible to influence the color space respectively to be displayed by selecting the colors of the light emitting diodes and of the associated display. For example, instead of an RGB light emitting diode matrix it is possible to select a red/green light emitting diode matrix and, in a corresponding way, to replace the blue filter elements by green ones in the liquid crystal display. This results in a restricted color space with a luminous density that has been further substantially increased.

[0022] Provided as light source in the exemplary embodiment according to FIGS. 1 and 2 is a matrix of 4×8 groups of in each case four light emitting diodes 1 that are mounted on a support 2. Webs 3 whose oblique surface serves as reflector are located between the groups.

[0023] A lens array 4 adjoined by a grid reflector 5 lies over the light source 1, 2, 3.

[0024] The webs 3, the lens matrix 4 and the obliquely running surfaces 6 of the grid reflector 5 effect uniform light distribution. In order to avoid shading by the webs 7 of the reflector 5, a frame 8 is provided that effects a spacing between the reflector 5 and the liquid crystal display 9. Located below the liquid crystal display 9 is a diffusing screen 10 which serves the purpose of further improving the uniformity of the backlighting of the liquid crystal display 9.

[0025] The frame 8 positions the liquid crystal display obliquely such that the light incident from above is not reflected in the same direction in which the light also leaves the liquid crystal display in order to reach the viewer.

[0026] FIG. 2 shows the device according to FIG. 1 with the liquid crystal display 9 removed and with the diffusing screen 10 removed. The light emitting diodes 1 are visible per se through the lens matrix 4 in the case of the illustration according to FIG. 2.

[0027] However, for the sake of simplicity a corresponding distortion of the light emitting diodes 1 has not been illustrated.

[0028] The exemplary embodiment according to FIG. 3 illustrates an illuminating device where the light exit opening comprises a glass plate 18 resting on a frame 17. Otherwise, this exemplary embodiment is constructed like that according to FIG. 1.

[0029] FIG. 4 essentially illustrates an enlarged detail from FIG. 1, and serves to explain details of the liquid crystal display and of the light source. The liquid crystal display 9 has a liquid crystal 13 and a color filter 14 between two glass plates 11, 12. Said color filter consists of an array of three differently colored color points, which is marked in FIG. 4 by different hatching. Control electrodes (not illustrated) are provided in a fashion correlating with the array of the color filter, and form a light valve in each case with the liquid crystal. Located outside the glass plates 11, 12 are polarizers 15, 16 with mutually perpendicular polarization planes.

[0030] The light source briefly described in conjunction with FIG. 1 is illustrated in FIG. 4, likewise in more detail.

[0031] Four light emitting diodes 1 are arranged on a submount 20 in a fashion raised in the middle of a hole formed by webs 3. The light emitting diodes are connected to lines 25 via bonding wires 21 that are illustrated only schematically by hatching the area they occupy. In a preferred embodiment, one of the light emitting diodes shines red, two shine green, and the fourth shines blue. In this arrangement, light is mixed to form white. The space between the submount 20 and the webs 3 is filled up with a white potting compound 22 whose surface 24 serves as reflector for the light emitted laterally from the light emitting diodes 1.

[0032] A transparent potting compound 23 prevents the formation of a cavity.

[0033] In the case of the exemplary embodiment illustrated in FIG. 4, the connection between the light source 1, 2 3 and the lens matrix 4 is performed via a layer 26 made from silicone gel, a PCF layer 27 and a suitable adhesive 28.

[0034] The PCF layer 27 has the effect that from the light which is produced by means of the light emitting diodes, only that is allowed through which is polarized in the direction of the lower polarizer 15, so that no light is lost by the polarization in the PCF layer 27. The differently polarized light is reflected by the PCF layer 27 and subsequently re-emitted from the surface 24. Of this, the component with the appropriate polarization in turn additionally passes through the PCF layer 27 such that, overall, the PCF layer contributes to increasing the brightness.

[0035] FIG. 5 shows an exemplary embodiment without a PCF layer. The illustrated detail at the edge of the device is also to be found in FIG. 5.

[0036] FIG. 6 shows a lens matrix 31 with eight lenses that are held together by webs 32. Four of the lens matrices illustrated in FIG. 6 are arranged next to one another in the exemplary embodiment according to FIGS. 4 and 5.