Lighting device for a motor vehicle

Abstract

A lighting device for a motor vehicle has a laser light source for producing laser light and a converting unit having a reflective converting layer, at which laser light originating from the laser light source is directed, during operation of the lighting device, such that a white light source is produced at the converting layer. A reflector is provided, which has an elliptical reflection surface, which corresponds to a portion of an ellipsoid containing a vertex of the ellipsoid. The reflector is shaped and arranged such that a first focal point of the ellipsoid lies within the white light source and the white light source is optically imaged in the form of a real intermediate image, which includes a second focal point of the ellipsoid, by way of the reflector. The lighting device also has a secondary optical unit, by which a light distribution in the environment of the motor vehicle is produced from the real intermediate image. An aperture for limiting the light distribution in the environment of the motor vehicle is arranged at the location of the real intermediate image.

Claims

1. A lighting device for a motor vehicle, comprising: a laser light source for generating laser light; a conversion unit comprising a reflecting conversion layer, onto which, during operation of the lighting device, laser light originating from the laser light source is directed such that a white light source is generated at the conversion layer; a reflector comprising an elliptical reflection surface corresponding to a subregion of an ellipsoid containing a vertex of the ellipsoid, wherein the reflector is formed and arranged such that a first focal point of the ellipsoid is located within the white light source, all light beams reflected by the reflector converge at a second focal point of the ellipsoid, and the white light source is optically imaged in the form of a real intermediate image via the reflector, the real intermediate image being formed at the second focal point of the ellipsoid; and a secondary optical unit, by which a light distribution is generated in a vicinity of the motor vehicle from the real intermediate image, wherein a stop for limiting the light distribution in the vicinity of the motor vehicle is arranged at a position of the real intermediate image.

2. The lighting device according to claim 1, wherein a ratio of a first distance, which represents the distance of a target plane from the vertex of the elliptical reflection surface of the reflector, to a second distance, which represents the distance of a source plane from the vertex of the elliptical reflection surface of the reflector, is located in a range of values between 0.8 and 1.2, the first focal point is arranged in the source plane and the source plane spans perpendicular to the semi-axis of the ellipsoid, the axis running through the vertex of the elliptical reflection surface, and the second focal point is arranged in the target plane and the target plane spans perpendicular to the semi-axis of the ellipsoid, the axis running through the vertex of the elliptical reflection surface.

3. The lighting device according to claim 2, wherein the ratio of the first distance to the second distance is substantially equal to one.

4. The lighting device according to claim 3, wherein of the pair of the semi-axis of the ellipsoid which runs through the vertex of the elliptical reflection surface and the semi-axis of the ellipsoid which runs through the first and second focal point, the semi-axis running through the vertex is the minor semi-axis.

5. The lighting device according to claim 1, wherein the lighting device comprises a front headlight for a motor vehicle and is configured to generate at least one part of a dipped beam light distribution and/or full beam light distribution as a light distribution in the vicinity of the motor vehicle.

6. The lighting device according to claim 1, wherein the elliptical reflection surface of the reflector has a reflectance of 90% or more.

7. The lighting device according to claim 1, wherein the elliptical reflection surface of the reflector has a reflectance of 95% of more.

8. The lighting device according to claim 1, further comprising: an optical light guide, via which laser light originating from the laser light source is guided to the reflecting conversion layer.

9. The lighting device according to claim 1, wherein the secondary optical unit comprises one or more additional reflectors and/or one or more lenses.

10. The lighting device according to claim 9, wherein at least one additional reflector has a reflection surface with a reflectance of 90% or more, and at least one lens has an anti-reflection coating.

11. The lighting device according to claim 9, wherein at least one additional reflector has a reflection surface with a reflectance of 90% or more, or at least one lens has an anti-reflection coating.

12. The lighting device according to claim 1, wherein at least two elements selected from a group comprising the reflector, the stop and at least one part of the secondary optical unit, form an integral structural component.

13. A motor vehicle, comprising one or more lighting devices according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 is a schematic section view of an embodiment of a lighting device according to the invention.

DETAILED DESCRIPTION OF THE DRAWING

(2) The invention is explained in exemplary fashion with the aid of a lighting device in the form of a front headlight. This front headlight is rendered only schematically in FIG. 1 and designated by reference sign 1. For reasons of clarity, the housing of the front headlight and its transparent cover pane, via which the front headlight light emerges from the housing, are omitted.

(3) The front headlight 1 comprises a laser light source 2, which generates monochromatic laser light, such as for example blue laser light. For this purpose, the laser light source comprises one or, if necessary, a plurality of laser diodes. This laser light is guided toward a conversion unit or a conversion module 4 via an optical light guide 3 made of one or more optical fibers. By means of the connection of the laser light source 2 via the light guide 3, the laser light source can be arranged at a distance from the rest of the headlight if necessary.

(4) The laser light guided in the light guide 3 exits via the end of the light guide which is arranged at a distance from the laser light source 2, and is incident on a conversion element or a conversion layer 5, which is a constituent part of the conversion module 4. The conversion layer consists of intrinsically known conversion material. For example, a phosphor conversion layer of nitride phosphor, oxynitride phosphor or cerium-doped YAG phosphor is used for a blue/violet laser light source with an emission wavelength of 450 nm/405 nm. The conversion layer converts the laser light that is incident thereon into white light. In this case, the conversion layer is reflecting, i.e., the converted white light leaves the conversion layer from the same side on which the laser light is incident on the conversion layer. The use of a reflecting conversion layer enables efficient cooling of this layer, as heat can be dissipated from the whole rear side of the conversion layer.

(5) In the embodiment in FIG. 1, a substantially point-like white light source is provided by means of the conversion layer 5, which is indicated by a black circle and is designated by the reference sign Q. In this case, the point-like white light source is located in a focal point f1 of the elliptical reflector 6 described further below. The light of the white light source emerges from the conversion unit 4 through a light output window (not shown). The beam path of the white light source is schematically indicated by means of a plurality of solid lines L, which are partially rendered as arrows. The lines represent the route of the light beams of the white light source Q.

(6) In the lighting device in FIG. 1, the light of the white light source Q is incident on a reflector 6, which is rendered in the section and forms a subregion of an (imaginary) ellipsoid E. For a typical distance of 3 to 5 mm between the conversion layer 4 and the light output window, the reflector 6 typically has a diameter between 20 mm and 40 mm. The ellipsoid is likewise shown in the section in FIG. 1 and indicated by a dashed line. On the inner side, the reflector 6 has a reflection surface 7 with a highly-reflecting coating in order to keep power losses in the lighting device low because of this. A single vertex SP of the ellipsoid E is located on the reflection surface 7.

(7) The form and arrangement of the reflector 6 or of the ellipsoid E is selected in such a way that the white light source Q is located in a first focal point f1 of the three focal points of the ellipsoid E so that an optical image of the white light source Q is generated in the form of a real intermediate image Q′ at the position of a second focal point f2 of the ellipsoid E, by means of the reflector 6. The real intermediate image is indicated by a black circle in FIG. 1, analogous to the white light source. The axis a running through the two focal points f1 and f2 represents a semi-axis of the ellipsoid E. The axis b running perpendicular through the vertex SP also represents a semi-axis of the ellipsoid E. Here, axis a is the major semi-axis and axis b is the minor semi-axis.

(8) According to the illustration in FIG. 1, the white light source Q lies in a source plane E1, which spans perpendicular to the minor semi-axis b and is indicated by a dashed line. Analogously, the intermediate image Q′ lies in a target plane E2, which spans perpendicular to the minor semi-axis b and is indicated by a dashed-dotted line. In the embodiment in FIG. 1, the source plane E1 coincides with the target plane E2. This means that the distance s of the source plane E1 from the vertex SP is exactly as large as the distance s′ of the target plane E2 from the vertex SP. The distances s and s′ represent the back focal lengths of the optical imaging of the reflector 6. Their ratio determines the imaging scale β of the optical imaging, i.e., β=s′/s applies. The optical imaging of the reflector 6 thus has an imaging scale of one. By means of the previously described embodiment and arrangement of the reflector 6, in which the minor semi-axis b extends through the reflection surface 7, a much lower construction depth of the lighting device 1 can be achieved, as the two focal points f1 and f2 can be positioned near to each other.

(9) As already mentioned, a real intermediate image Q′ is generated at the second focal point f2 by the reflector 6. From this intermediate image, a light distribution is generated by means of a secondary optical unit in the form of a further curved reflector 9 with reflection surface 10, the light distribution being cast onto the road 11 by the motor vehicle. Depending on the embodiment, a dipped beam and/or a full beam light distribution can be generated as a light distribution. Thus, a light distribution with very high luminance is achieved by using laser light.

(10) An aspect of the embodiment in FIG. 1, which is essential to the invention, is that a stop 8 is positioned in the vicinity of Q′, which limits the intermediate image Q′ and thus effects shadowing, which in turn manifests itself in a dark region in the light distribution, as indicated by the vertical line 8′. With the stop, the light distribution that is cast onto the road can be suitably limited. For example, a suitable light/dark boundary can be generated when a dipped (low) beam light distribution is generated by means of a corresponding stop shape, thereby preventing blinding of approaching road users. Also, in the case that the headlight generates a glare-free full (high) beam by means of a variable headlight adjustment, a glare-free region of the full beam is realized by means of the stop 8.

(11) By means of using the stop 8 in the vicinity of the intermediate image Q′, shadowing is effected very simply and flexibly, without needing to make changes to the conversion module 4. Furthermore, undesirable monochromatic reflections due to scattering of laser light at the stop edges are prevented.

(12) In a preferred variant of the embodiment just described, at least two elements selected from the reflector 6, the stop 8 and the reflector 9 form a monolithic structure, which for example can be achieved by means of the integral embodiment of these elements by means of injection molding. In this way, exact relative positioning of optical elements is ensured, without these having to be adjusted relative to each other in a complex fashion. Preferably a holder also has an integral embodiment with the elements mentioned, in which the conversion module 4 is positioned, whereby the adjustment effort is further reduced.

(13) The lighting device in FIG. 1 generates an optical image with the reflector 6, the imaging scale of which has the value 1. However, the invention is not restricted to an arrangement in which the imaging scale is equal to one. Rather, reflectors with other imaging scales can also be used in the lighting device according to the invention. For a low construction depth of the lighting device according to the invention, the imaging scale should preferably be between 0.8 and 1.2.

(14) The previously described embodiments of the invention have a number of advantages. In particular, a motor vehicle lighting device with lower construction depth is provided. By means of using a reflector with a high refractive power, short focal lengths and low self-shadowing and an almost aberration-free image are thus ensured, despite a small construction space. By arranging the stop in the plane of the intermediate image, it is possible to prevent monochromatic diffraction effects which occur when positioning the stop at the conversion layer because of light scattering at the stop edge. By using a laser light source, the generation of luminous fluxes with a high luminance is further ensured. Optionally, the adjustment effort can be minimized or the problem of an increased requirement for the adjustment precision can be controlled by means of a monolithic structure, in which a plurality of elements of the lighting device form an integral structural component. Furthermore, using a reflecting conversion layer enables very good cooling of this layer.

REFERENCE SIGNS

(15) 1 lighting device 2 laser light source 3 light guide 4 conversion unit 5 conversion layer 6 reflector 7 elliptical reflection surface 8 stop (aperture) 8′ dark region 9 reflector 10 reflection surface 11 road Q white light source Q′ real intermediate image E ellipsoid SP vertex f1 first focal point f2 second focal point a major semi-axis b minor semi-axis s, s′ back focal lengths L light beams