Patent Publication Number: US-6991354-B2

Title: Light-emitting diode module for vehicle headlamps, and a vehicle headlamp

Description:
I. TECHNICAL FIELD 
     The invention relates to a light-emitting diode module for a vehicle headlamp, wherein the light-emitting diode module has a carrier for a number of light-emitting diodes, and to a vehicle headlamp. 
     II. BACKGROUND ART 
     The laid-open specification WO 01/01037 A1 discloses a vehicle headlamp with a multiplicity of light-emitting diodes serving as light source. The light bundle emitted by the light-emitting diodes has at least two segments with light from different spectral regions. A first segment of the light bundle has a high proportion of white or yellow-orange light, and a second segment has a high proportion of blue-green light. 
     The laid-open specification EP 1 298 382 A1 describes a light-emitting diode module for a vehicle luminaire having a reflector and a carrier for light-emitting diodes, the carrier having a plane surface on which the light-emitting diodes are arranged. 
     III. DISCLOSURE OF THE INVENTION 
     It is the object of the invention to provide a light-emitting diode module for a vehicle headlamp that is suitable for producing various light distributions typical of a vehicle headlamp. Moreover, it is the object of the invention to provide a vehicle headlamp that permits the production of the typical light distributions of a vehicle headlamp solely with the aid of light-emitting diodes as light sources. 
     This object is achieved by a light-emitting diode module for a vehicle headlamp, the light-emitting diode module having a carrier for a number of light-emitting diodes, wherein the carrier is provided with at least one light directing means in order to direct in prescribed spatial directions the light emitted by the light-emitting diodes. Particularly advantageous designs of the invention are described in the dependent patent claims. 
     The light-emitting diode module according to the invention has a carrier for a number of light-emitting diodes, the carrier being provided in accordance with the invention with at least one light directing means in order to direct in prescribed spatial directions the light emitted by the light-emitting diodes. 
     The light emitting diode module according to the invention permits optimum adaptation of the shape of the spatially extended light source, which consists here of a number of light-emitting diodes, to the reflector of the vehicle headlamp. It has emerged that the inventive light-emitting diode module in a vehicle headlamp can be used to produce different light distributions, in particular for dimmed headlight, high beam, fog lamp, parking light and daytime running light. The inventive light-emitting diode module serves in this case as light source in the vehicle headlamp and replaces the conventional halogen incandescent lamp or the high-pressure discharge lamp containing metal halides and xenon. The light-emitting diodes have a substantially longer service life than the above named lamps. 
     The carrier of the inventive light emitting diode module is preferably of axially symmetrical, in particular rotationally symmetrical design. It has a lateral surface of axially symmetrical design relative to a longitudinal axis on which a number of light-emitting diodes and the at least one light directing means are arranged, in order to direct in directions transverse to the longitudinal axis of the carrier the light emitted by the light-emitting diodes. The light-emitting diodes of the inventive light-emitting diode module are preferably arranged along at least one ring the axis of which runs parallel to the longitudinal axis of the carrier or on the longitudinal axis of the carrier. It is thereby possible to ensure optimum cooperation between the light-emitting diode module and the reflector of the vehicle headlamp. 
     In accordance with a preferred exemplary embodiment, the at least one light directing means is designed as a reflecting surface. The at least one light reflecting surface preferably faces the annularly arranged light-emitting diodes in order to focus their light in directions transverse to the longitudinal axis of the carrier. There are provided in accordance with a preferred exemplary embodiment two light reflecting surfaces that face the light-emitting diodes arranged along at least one ring in order to direct their light transverse to the longitudinal direction of the carrier on to the reflector of the vehicle headlamp. These light reflecting surfaces are preferably designed in such a way that they surround the carrier annularly in order to minimize the light losses. 
     However, the light directing means can also be designed as transparent refractor elements, for example as optical lenses, that are arranged in each case directly on the annularly arranged light-emitting diodes and focus light in directions transverse to the longitudinal axis of the carrier. However, it is also possible for the refractor element to be designed as an annular light guide that is fixed directly on the annularly arranged light-emitting diodes and whose lateral annular surfaces are designed to be totally reflecting and whose circumferential surface is transparent, in order to focus in directions transverse to the longitudinal axis of the carrier the light emitted by the light-emitting diodes. 
     The inventive vehicle headlamp has a light-emitting diode module that has a carrier for a number of light-emitting diodes, a reflector for reflecting the light emitted by the light-emitting diode module, and at least one optical lens for imaging the light reflected by the reflector. According to the invention, the carrier of the light-emitting diode module of the vehicle headlamp is provided with at least one light directing means in order to direct in prescribed spatial directions the light emitted by the light-emitting diodes. 
     The carrier preferably has a lateral surface of axially symmetrical design relative to an axis, a number of diodes and the at least one light directing means being arranged on the lateral surface in order to direct onto the reflector of the vehicle headlamp in directions transverse to the longitudinal axis of the carrier the light emitted by the light-emitting diodes. 
     The same light distributions as are produced with the aid of the conventional vehicle headlamps that are fitted with incandescent lamps or discharge lamps can be produced by means of the inventive vehicle headlamp, which contains exclusively light-emitting diodes as light source. In order to produce the largely mirror symmetric light distribution of the high beam, fog lamp, parking light and daytime running light, the inventive vehicle headlamp advantageously has at least one optical lens that projects onto the roadway the light emitted by the light-emitting diode module and reflected by the vehicle headlamp reflector. In addition, the inventive vehicle headlamp also has a shading device for producing the asymmetric light distribution of the dimmed headlight. 
     The light-emitting diodes mounted on the lateral surface of the carrier of the light-emitting diode module are preferably arranged along a number of rings running concentrically with the longitudinal axis of the carrier, in order to produce as high a luminous flux as possible and as high a luminous intensity as possible. The spacing between the above named rings is selected such that the light directing means do not cause any, or any appreciable shading of the light. For the same reason, and in order to ensure satisfactory imaging of the light-emitting diode module serving as light source by the reflector and the at least one optical lens of the vehicle headlamp, the dimensions of the carrier of the light-emitting diode module are as small as possible. 
    
    
     
       IV. BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail below with the aid of a preferred exemplary embodiment. In the drawing: 
         FIG. 1  shows a side view of a light-emitting diode module in accordance with the preferred exemplary embodiment of the invention, and 
         FIG. 2  shows a side view of a vehicle headlamp having the light-emitting diode module depicted in  FIG. 1 . 
     
    
    
     V. BEST MODE FOR CARRYING OUT THE INVENTION 
     The preferred exemplary embodiment of the inventive light-emitting diode module is illustrated schematically in  FIG. 1 . The light-emitting diode module  1  has an axially symmetric carrier  10  with a lateral surface  11  on which a total of sixty four light-emitting diodes are mounted. The carrier  10  is of rotationally symmetrical design relative to its longitudinal axis A-A. Of the above named sixty four light-emitting diodes, sixteen light-emitting diodes  21  are arranged equidistantly along a first ring of which the axis is identical to the longitudinal axis A-A of the carrier  10 . Twenty four light-emitting diodes  22  and  23 , respectively, are arranged equidistantly along a second and third ring of which the axis is likewise identical to the longitudinal axis A-A of the carrier  10 . The spaces between the above named rings of light-emitting diodes  21 ,  22  and  23  are 9.9 mm in each case. 
     The total length of the carrier  10  is 30 mm, and its greatest outside diameter is 10 mm. Arranged in each case on both sides of each ring of light-emitting diodes  21 ,  22 ,  23  are two shields each having a light reflecting surface  311 ,  312 ,  321 ,  322 ,  331 ,  332  facing the light-emitting diodes  21 ,  22 ,  23 . The light-emitting diodes  21 ,  22 ,  23  are therefore arranged between the respective pairs of light reflecting surfaces  311 ,  312 ;  321 ,  322 ; and  331 ,  332  forming in each case two adjacent screens for the respective diodes. The screens having the light reflecting surfaces  311 ,  312 ,  321 ,  322 ,  331 ,  332  are fixed on the lateral surface  11  of the carrier  10 , annularly surround the carrier  10 , and are inclined to the longitudinal axis A-A of the carrier  10  such that the interspace between the light reflecting surfaces  311 ,  312 ,  321 ,  322 ,  331 ,  332  in which the light-emitting diodes  21 ,  22 ,  23  are arranged, is of conical design. Consequently, the light emitted by the light-emitting diodes  21 ,  22 ,  23  is directed in directions transverse to the longitudinal axis A-A. The screens with the light reflecting surfaces  311 ,  312 ,  321 ,  322 ,  331 ,  332  in each case have an outside diameter of 20 mm. The carrier  10  is of hollow design. The electrical leads for the light-emitting diodes  21 ,  22 ,  23  run in the interior of the carrier  10 . 
     Illustrated schematically in  FIG. 2  is a side view of a vehicle headlamp having the light-emitting diode module  1  described above. This vehicle headlamp has a freeform surface reflector  4  of conical design with a structural depth of at least 65 mm. The light-emitting diode module  1  is arranged entirely in the freeform surface reflector  4  and is therefore not visible in  FIG. 2 . The longitudinal axis A-A of the light-emitting diode module  1  is identical to the optical axis A-A of the freeform surface reflector  4 . The spacing between the first ring of light-emitting diodes  21  and the apex of the freeform surface reflector  4  is 9.81 mm. The spacing between the second and the third rings of light-emitting diodes  22  and  23 , respectively, from the apex of the freeform surface reflector is correspondingly 19.7 mm and 28.6 mm. The vehicle headlamp further has an optical lens  5  arranged in front of the light exit opening of the freeform surface reflector  4  in order to project onto the roadway the light reflected by the freeform surface reflector  4 . In order to produce the light/dark boundary of the dimmed headlight, an opaque diaphragm  6  is arranged between the optical lens  5  and the freeform surface reflector  4  at a spacing of 100 mm from the apex of the reflector  4 .