Patent Abstract:
A method produces a lighting element that includes at least one luminescent diode and an inserted light-guiding body. The light-guiding body receives light emitted by the luminescent diode. The luminescent diodes are secured to the light-guiding body by an injection molding process of a transparent plastic material such that at least 50% of the surface of the light emitting diode is covered by the injected material during the manufacturing thereof, and that the maximum wall thickness of the injected layer does not exceed three-times the minimum wall-thickness of the layer.

Full Description:
BACKGROUND ART  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a method for the production of a lighting element including at least one luminescent light source and an inserted light-guiding body. More particularly, the invention relates to a lighting element of uniform construction and a method of making same.  
         [0003]     2. Description of the Related Art  
         [0004]     Such a method for the production of a lighting element is known from the German patent specification DE 101 63 117. Here, a first LED-partial body is permanently connected to a second, larger light-guiding body by injection molding. However, a special component is used here as the LED-partial body. This solution also results in portions of large material build-ups in the injection mold. This requires inter alia a longer cooling-off time and brings about an uneven cooling.  
         [0005]     Therefore the problem underlying the present invention is to develop a method for the production of light-guiding lighting elements by using at least one inserted light-guiding body, wherein the transparent partial illuminating bodies are connected to one another in a safe, rapid and precise manner with respect to the form thereof with the usual capacity of the known injection methods.  
       SUMMARY OF THE INVENTION  
       [0006]     A method produces a lighting element that includes at least one luminescent diode and an inserted light-guiding body. The light-guiding body receives light emitted by the luminescent diode. The luminescent diodes are secured to the light-guiding body by an injection molding process of a transparent plastic material such that at least 50% of the surface of the light emitting diode is covered by the injected material during the manufacturing thereof, and that the maximum wall thickness of the injected layer does not exceed three-times the minimum wall-thickness of the layer. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     Advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:  
         [0008]      FIG. 1  is a cross-sectional end view of one embodiment of the invention; and  
         [0009]      FIG. 2  is a cross-sectional side view of the embodiment shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0010]      FIGS. 1 and 2  show a lighting element  70 . In the embodiment shown, the lighting element  70  is a raised automobile brake light. The lighting element  70 , which is arranged here, for example, with the help of a housing  50  in a trunk lid  60  of a motor vehicle, is made of a group of individual lighting elements  10 , wherein every element  10  includes at least one light source  11 . In the preferred embodiment, the light source  11  is a light emitting diode (LED). The lighting element  70  has a diffusing screen  40 , the outer surface of which is adapted to the shape of the surrounding surface curvature of the trunk lid  60 .  
         [0011]     In this context, the individual LED  11  can be a standard LED or a preliminary stage LED. The latter is produced only for installation in the brake light  70 . The LED  11  usually includes the electrical terminals  1 ,  4  located in one plane, the light-emitting chip  6 , a bond wire  2 , and a reflector dish  5 . The latter is a part of the cathode  4 . The chip  6  is seated in the reflector dish  5 . The chip  6  contacts the anode  1  using the bond wire  2 . The bond wire  2  is thereby preferably located in the plane, which is defined by the centerlines of the electrodes  1 ,  4 . The zone located above the chip  6  transports the light emitted by the chip  6  losslessly, as far as possible, to the outer surface  12  of the LED  11 .  
         [0012]     The standard LED used in  FIG. 1  has a geometric form, which is substantially made of three geometric bodies arranged on top of one another. The first geometric body is a short, at least approximately straight cylinder  13 , which includes, if desired, two planar flat portions, which are aligned generally parallel to the LED centerline  7 . The second geometric body is a truncated cone  15  arranged on the upper end face  14  of the cylinder  13  or a comparable rotational body, which tapers away from the cylinder  13 . The third geometric body is a calotte and/or a comparable rotationally symmetrical cap, which is positioned on the upper, smaller end face of the truncated cone. The surface line of the truncated cone thereby passes tangentially into the contour of the cap. The upper end face  14  of the cylinder  13  is larger than the lower end face of the truncated cone  15 . The centerlines of the cylinder  13  and of the truncated cone  15  are located on the LED centerline  7 .  
         [0013]     If desired, a notch  16 , a channel or a waist, shown as a dashed line in  FIG. 2 , which ends on the end face  14 , is present in the lower regions of the truncated cone  15 .  
         [0014]     Should the individual lighting element  10  be used in a group of several individual lighting elements, the LEDs  11  are arranged on a lamellar circuit board  18 . For this purpose, the LEDs  11  are soldered permanently on the circuit board  18  after being previously glued thereon. The circuit board  18  connects the individual LEDs  11  using superimposed conductor tracks. If desired, every other electronic component, such as multipliers, blocking diodes or integrated circuits, are arranged on the circuit board  18  in known manners. The circuit board  18  positions the LEDs  11  in relation to one another and later—during the coating—in the injection molding device. If desired, the electrodes  1 ,  4  of the LEDs  11  are also discretely connected electrically using individual cables.  
         [0015]     In the embodiment shown, the inserted light-guiding body  21  located opposite to the respective LED  11  has the shape of a partial paraboloid, which is flattened on both sides and also truncated at the top and at the bottom. The flattened lateral surfaces  26 ,  27  are located approximately parallel to a midplane, which is located according to  FIG. 1  on the centerline  7  of the respective individual lighting element  10 . The minimum distance of the lateral surfaces  26 ,  27  from the midplane amounts, e.g. to 50% of the maximum LED diameter or the maximum LED width. In the example embodiment, the distance between the lateral surfaces  26 ,  27  is larger towards the main light exit surface  41 .  
         [0016]     A spherical concave recess  25  is present in the end face  24  of the lower truncation according to  FIG. 2 . In this context, the recess  25  is curved in such a way that the gap  19  lying between the recess  25  and the LED  11  has an at substantially constant width.  
         [0017]     The other end face  23  is a top face, planar and oriented normal to the centerline  7  of the individual lighting element  10 . If desired, a short pin  29 , cf.  FIG. 2 , is molded in the middle region, e.g. centrally, wherein the short pin  29  facilitates the handling and positioning when coating by means of injection molding. The length of the pin  29 —measured in the longitudinal extension along the centerline  7 —is shorter than the thickness of the diffusing screen  40  in the vicinity of the pin. A transparent, colorless plastic is provided as the material for the diffusing screen.  
         [0018]     Should several individual lighting elements  10  be combined in a group  70  and should these lighting elements  10  be located adjoining one another, each would be connected to one another using at least one web  28 . In this context, each web  28  has a semi-circular cross-section. The webs  28  adjoin flush to the end faces  23  wherein they form a planar or curved surface with the latter.  
         [0019]     For the purpose of coating by means of injection molding, the circuit board  18  is inserted with the LEDs  11  and the group consisting of inserted light-guiding bodies  21  into an injection mold. In this context, the distance of individual LED  11  from the inserted light-guiding body  21  at the narrowest place amounts to between 0.3 mm and 3 mm. The injection mold is designed in such a way that the finished injected layer for each pair of LED and inserted light-guiding body in turn forms a partial paraboloid  30 , which is flattened on both sides and truncated at least at the top. The lower edge of this partial paraboloid rests against the LED  11  below a plane, which extends through the center of gravity of the LED chip  6  and, secondly, is aligned normal to the centerline  7 . In the example embodiment, the lower edge  32  of the injected layer  30  rests against the end face  14  of the cylinder  13  of the LED  11 . For example, the edge  32  is located directly in the geometrical cut edge, which is formed by the penetration of the cylinder  13  and of the rotational body and/or of the truncated cone  15 .  
         [0020]     The surface of the partial paraboloid  30  is located at a distance from the surface of the partial paraboloid of the inserted light-guiding body  21 , said distance corresponding to e.g. two-times the width of the gap  19 . The injected layer  30  has an almost constant wall-thickness over large regions. In zones of strong curvature, the wall-thickness can increase up to three-times the width of the gap. These small differences in the wall-thickness enable a production of the individual lighting element  10  without any problems.  
         [0021]     The injected layer  30  positively engages behind the corresponding LED in case of LEDs having a notch  16 . The inserted light-guiding bodies  21  can also have notches, channels or annular grooves of the same function. The injected layer  30  may be a colorless, transparent plastic is used for the coating by means of injection molding.  FIG. 2  illustrates the injected layer  30  only in case of the first inserted light-guiding body  21 .  
         [0022]     In another step, the diffusing screen  40  is sprayed onto the end surfaces  23  of the inserted light-guiding body  21 . In this context, the diffusing screen  40  engages around the injected layer  30 , in the upper fifth part. The diffusing screen  40  accordingly covers the inserted light-guiding body  21  on the end face  23  and the injected layer  30  on the upper edge completely. It has a flange-shaped installation edge  42 , which is parallelly displaced in relation to its main light exit surface  41  and which surrounds the entire brake light  70 . The main light exit surface  41  is designed with a smooth or structured surface. For example, a red, transparent thermoplastic is used as the material.  
         [0023]     The light-guiding and current-carrying components  11 ,  21 ,  30 ,  18  of the middle, raised brake light  70  are surrounded by the housing  50  on the rear side as shown in  FIG. 1 . The housing  50  made from a hard substance, e.g., a metal, is a dish which can be closed with a lid. In this context, the lid is a diffusing screen  40  seated tightly on the dish. For this purpose, sealing contours  45 ,  51  contacting one another flatly are embodied on the diffusing screen  40  and on the housing  50 . For the protection of these sealing contours  45 ,  51  and for holding a sealing ring  48 , the housing  50  is partially guided around the diffusing screen  40  as a supporting edge as shown in  FIG. 1 .  
         [0024]     The brake light  70  is installed in the trunk lid, in the tailgate or on the rear roof edge in such a way that the surface of the diffusing screen  40  adjoins tangentially to the surface of the autobody sheet steel  60  carrying the brake light  70 . In this context, the autobody sheet steel  60  can also be manufactured from a non-metallic material. The diffusing screen  40  is inserted from the rear side together with the housing  50  into a recess  61  and is clamped there by means of a leaf spring  63  (with a two-fold curvature here) against a mounting bracket  62 , which is stationary in relation to the autobody sheet steel  60 . In the installed state, the recess  61  is sealed by the diffusing screen  40  and the sealing ring  48  resting on the flange-type edge  42  of the diffusing screen  40  against the intrusion of water and dirt.  
         [0025]     In order to create the typical appearance of a middle brake light, the colors of the individual components  11 ,  21 ,  30 ,  40  can be used in different variations.  
         [0026]     Certain substances, which change the wavelength of the light emitted from the chip  6  can be combined with the materials of the individual transparent components of the brake light  70 , as a result of which the subjectively recognizable luminous color corresponds to that of a typical brake light  70 , although the material of the unlighted brake light has another color, e.g. the color of the surrounding autobody sheet steel  60 .  
         [0027]     An individual lighting element  10  can naturally also be used separately.  
         [0028]     The invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation.  
         [0029]     Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.

Technology Classification (CPC): 5