Patent Publication Number: US-2007121333-A1

Title: Semiconductor light engine for automotive lighting

Description:
FIELD OF THE INVENTION  
      The present invention relates to a light source for automotive lighting systems and the like. More specifically, the present invention relates to a semiconductor light engine to provide light for automotive lighting systems and the like.  
     BACKGROUND OF THE INVENTION  
      Automotive lighting systems, and in particular headlamp systems, require light sources capable of producing relatively bright light which can be formed into the necessary beam patterns, as defined and required by various safety regulations. Incandescent bulbs were employed as light sources for headlamp systems for many years with reasonably acceptable results.  
      To provide more light to improve the beam patterns produced by headlamp systems, quartz halogen (“Halogen”) and high intensity discharge (“HID”) bulbs are now commonly used instead of incandescent bulbs, as Halogen and HID bulbs produce significantly more light than incandescent bulbs. However, such Halogen and HID light sources suffer from disadvantages in that they create a significant amount of waste heat which the headlamp must be designed to withstand. Further, Halogen and HID headlamps require carefully designed optics to remove defects, from bulb filaments or bulb envelope influences, in the pattern of light they produce.  
      Accordingly, to withstand this heat and/or to provide the necessary optics, the enclosures of Halogen and HID headlamps must be relatively large and such large enclosures limit the aesthetic and/or aerodynamic designs which automotive designers could otherwise produce.  
      More recently, interest has developed in employing semiconductor light sources, such as light emitting diodes (“LED”s), as light sources for headlamp systems. LEDs which produce white light have become available and the amount of light produced by such LEDs has increased significantly in recent years. Ideally, headlamps employing LEDs as light sources will be able to be constructed with smaller enclosures than those required for conventional headlamps, allowing for the variety of aesthetic and aerodynamic vehicle designs to be increased.  
      However, LED-based headlamp systems also suffer from some disadvantages. The amount of light produced by available white LEDs is still insufficient to produce the required headlamp beam patterns and thus several closely positioned LEDs must be jointly employed to produce sufficient light. Further, the semiconductor junction in each LED produces a relatively large amount of waste heat when operating and this heat must be removed, by heat sinks, heat pipes and/or cooling fans and the like or the junction will fail. Thus, to provide for the proper arrangement of the multiple LED sources with respect to the lens of the LED headlamp and to provide adequate cooling of the LED sources, the enclosure of LED headlamps tend to be larger than is otherwise desired.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to provide a novel light engine which obviates or mitigates at least one disadvantage of the prior art.  
      According to a first aspect of the present invention, there is provided a light engine for an automotive lighting system, comprising: at least one substrate; a plurality of semiconductor light sources mounted to each of the at least one substrates, each adjacent semiconductor light source being spaced from each other adjacent semiconductor light source on the substrate to enhance cooling of the semiconductor light sources during operation thereof; and at least one a transfer device operable to receive light emitted by the semiconductor light sources on the at least one substrate and to transfer the received light to at least one location spaced from the substrate, wherein the transfer device comprises at least one light pipe, each light pipe having a receiving end to receive light emitted from a semiconductor light source and an emitting end to emit the received light. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Preferred embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:  
       FIG. 1  shows a schematic representation of a light engine in accordance with the present invention;  
       FIG. 2  shows a front view of a substrate and semiconductor light sources used in the light engine of  FIG. 1 ;  
       FIG. 3  shows a side section taken along line  3 - 3  of  FIG. 2 ;  
       FIG. 4  shows a section similar to that of  FIG. 3  wherein one method of attaching light pipes to the semiconductor light sources of the substrate is shown;  
       FIG. 5  shows a front view of an emitter end of a transfer device of the light engine of  FIG. 1 ;  
       FIG. 6  shows a side view of the emitter end of  FIG. 5  and a portion of the bundle of light pipes of the light engine of  FIG. 1 ;  
       FIG. 7  shows a front view of another embodiment of an emitter end of a transfer device of the light engine of  FIG. 1 ;  
       FIG. 8  shows a mixer attached to the emitter end of a light pipe to provide a portion of diffuse light;  
       FIG. 9  shows a schematic representation of another embodiment of a light engine in accordance with the present invention; and  
       FIG. 10  shows a side view of another embodiment of a light engine in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      A first embodiment of a light engine in accordance with the present invention is indicated generally at  20  in  FIG. 1 . Light engine  20  includes two or more substrates  24   a ,  24   b  and a transfer device  28  which includes a receiving end  32  and an emitter end  36 .  
      As shown in  FIGS. 2 and 3 , substrate  24   a  includes a plurality of semiconductor light sources  40 , such as LEDs emitting white light, mounted thereon. Preferably, substrate  24   a  further includes a reflector  44  which surrounds each semiconductor light source  40  to direct the light emitted by each semiconductor light source  40  to the receiving end  32  of transfer device  28 , as described in more detail below. Reflectors  44  are not essential to the operation of light engine  20 , but can improve the efficiency of light engine  20 . Substrate  24   a  preferably further includes a series of apertures  46 , through substrate  24   a , the purpose of which apertures  46  is discussed below.  
      Substrate  24   b  is substantially the same as substrate  24   a  but, if light engine  20  contains no additional substrates  24  to be stacked with substrate  24   b  or if substrates  24   a  or  24   b  are not to be stacked at all, then substrates  24   a  or  24   b  need not include apertures  46 , but such apertures can be included in substrates  24   a  and  24   b  without harm, to allow for uniformity of manufacture of substrates  24 .  
      Semiconductor light sources  40  are mounted to each substrate  24  with sufficient spacing between adjacent semiconductor light sources  40  to ensure that their junction temperatures can be maintained within the acceptable operating temperature range.  
      Substrates  24  can be formed of any suitable material as will be apparent to those of skill in the art and examples of such materials include ceramics, such as those used in packaging semiconductor integrated circuits, phenolics and/or epoxies, such as those used to fabricate printed circuit boards, etc.  
      Preferably, substrates  24  include at least one layer  48  of a heat transfer material, such as copper or aluminum, which assists in the removal of waste heat generated within semiconductor light sources  40 . Layer  48  can be connected to a suitable heat sink, heat pipe or heat wick when substrates  24  are mounted in a headlamp system. Layer  48 , in combination with the above mentioned spacing of semiconductor light sources  40  on substrates  24 , ensures that semiconductor light sources  40  can be operated within their specified operating temperature range.  
      By employing more than one substrate  24  on which to mount semiconductor light sources  40 , the necessary number of semiconductor light sources  40  to provide the desired amount of illumination from light engine  20  can be spaced across the faces each substrate  24 , which are separated from each other substrate  24 . In this manner, a less dense arrangement of semiconductor light sources  40  on each substrate  24  can be obtained to enhance cooling of the junctions of semiconductor light sources  40 .  
      Each substrate  24  also preferably includes at least two electrical layers  52  and  56 , each being a respective one of a positive and negative electrical conductor to which semiconductor light sources  40  are connected and are powered thereby. Alternatively, positive and negative electrical conductors can be provided as conductive traces on the top, bottom or both of the top and bottom of substrate  24 .  
      It is contemplated that it may be desired to illuminate semiconductor light sources  40  in groups, for example to form low beam or high beam lighting patterns. In such case additional electrical conductors, whether in the form of conducting layers in substrate  24 , conducting traces on the top or bottom of substrate  24 , etc. can be provided to supply energy to such groups of semiconductor light sources  40 .  
      Each reflector  44  preferably includes a parabolic shaped surface which surrounds its respective semiconductor light source  40  and reflectors  44  can be fabricated from any suitable material, such as acrylic, epoxy or polycarbonate, to which a suitable reflective coating can be applied or reflectors  44  can be fabricated from a reflective material such as aluminum.  
      In the illustrated embodiment, each reflector  44  is shown as being a separate component mounted to a substrate  24  individually, but it is also contemplated that reflectors  44  can be fabricated as a unit. For example, reflectors  44  can be molded as an assembly from an epoxy material, to which a reflective material is then applied, and the assembly being mounted to a substrate  24 , over semiconductor light sources  40 , after semiconductor light sources  40  have been mounted to substrate  24 .  
      Similarly, reflectors  44  can be machined and polished as an assembly from a piece of aluminum, or the like, and then mounted to substrate  24 . In this latter case, the assembly of reflectors  44  can also assist in the removal of waste heat produced by semiconductor light sources  40 .  
      As shown in  FIGS. 1, 4  and  6 , transfer device  28  comprises at least one light pipe  60 , such as fiber optic cable, light guides manufactured from polycarbonate or silicone rubber or moldable acrylic resins, such as Acrymid™ 815, sold by CYRO Industries of Rockaway, N.J., or any other suitable method of transferring light from a light source to a desired location. In a present embodiment, at least one light pipe  60  is provided for each semiconductor light source  40  but it is also contemplated that in some circumstances one light pipe  60  may be provided for two or more light sources  40 .  
      At receiving end  32  of transfer device  28 , best shown in  FIG. 4 , each respective light pipe  60  is positioned adjacent a respective semiconductor light source  40  and reflector  44  (if present). In the embodiment of  FIG. 1 , some of light pipes  60  extend through apertures  46  in substrate  24   a  such that the ends of those light pipes can be positioned adjacent a respective semiconductor light source  40  and reflector  44  (if present) on substrate  24   b.    
      Preferably, the receiving ends of the light pipes  60  include surfaces  64  which are shaped and positioned with respect to semiconductor light sources  40  on each substrate to capture a substantial portion of the light emitted by semiconductor light sources  40 . The receiving ends of the light pipes are maintained in place by any suitable means, such as epoxy  68  or by mechanical means (not shown).  
      Preferably, the receiving ends of the light pipes are tapered, from a geometry (size and shape) substantially corresponding to the geometry of the outer end of reflector  44  (if present) or substantially corresponding to the geometry of semiconductor light source  40  (if no reflector  44  is present) to a larger geometry along the length of light pipe  60  to emitter end  36 . As will be understood by those of skill in the art, such a taper will improve the amount of the light, emitted by semiconductor light source  40 , which is received by the respective light pipe  60  and transmitted along its length.  
      As will also be understood by those of skill in the art, the length of light pipe  60  need not have the same cross-sectional shape as the receiver end of light pipe  60 , for example the receiver end of light pipe  60  can have a rectangular geometry, in cross section, to correspond to the semiconductor light source while the length of light pipe  60  can be circular in cross-sectional shape, etc.  
      While in the illustrated embodiment substrates  24   a  and  24   b  are shown as being planar, the present invention is not so limited and either or both substrates  24  can include a curved surface, etc. if required to fit within a headlamp system with a small, or irregular, volume. In such a case, the length of the light pipes  60  in transfer device  28  may not all be the same.  
      As shown in  FIGS. 5 and 6 , emitting end  36  of transfer device  28  preferably includes a forming member  72  which maintains the emitting ends of each light pipe  60  in their desired configuration. It is contemplated that in many circumstances the emitting ends of light pipes  60  will be maintained in a closely spaced configuration and substantially aligned, such that the light emitted from each light pipe  60  is substantially parallel to the light emitting by each other light pipe  60 , but such a configuration is only one of many possible configurations of emitting end  36  of transfer device  28 .  
      Forming member  72  can be an epoxy member cast about the ends of the light pipes  60  in transfer device  28 , or can be a phenolic or epoxy board, aluminum sheet, etc. with suitably sized apertures to receive and maintain the respective ends of light pipes  60  in their desired configuration. As will be apparent, forming member  72  need not hold the individual light pipe ends of emitting end  36  in a planar arrangement and can instead hold the individual light pipe ends in convex, concave or another arrangement as might be desired.  
      Forming member  72  can also be used as a mounting member to retain emitter ends  36  in a desired position with respect to a lens system  76 , or other component, within a headlamp system or the like. It is contemplated that forming member  72  can be mechanically mounted to one or more stepper motors  80 , or other devices, to allow forming member  72  and the emitter ends of light pipes  60  to be moved with respect to lens system  76  to, for example, alter the emitted beam pattern and/or to compensate for loading and/or pitch or roll of a vehicle.  
      While not illustrated, it is also contemplated that light pipes  60  at emitting end  36  can taper from the above-mentioned larger geometry of the majority of their run length to a geometry which is smaller and/or a different cross sectional shape at their ends adjacent forming member  72  to increase the amount of light emitted from each light pipe  60 .  
      As will be apparent, the spacing between the emitting ends of light pipes  60  can be much closer than the spacing of semiconductor light sources  40  on substrates  24 . Thus, transfer device  28  allows semiconductor light sources  40  to be spaced and or located, on one or more substrates  24 , to meet thermal requirements and yet allows the light emitted by semiconductor light sources  40  to be provided to a headlamp lens system in a much closer spaced configuration.  
      Further, the arrangement of emitter ends  36  of light pipes  60  in forming member  72  need not be the same as the arrangement of the receiving ends  32  of light pipes  60  at substrates  24 . For example, light pipes  60  whose receiving ends  32  are located by adjacent semiconductor light sources  40  on a substrate  24  can be located non-adjacently on forming member  72 . It is contemplated that this non-symmetry of the arrangement of the receiving ends  32  and emitter ends  36  of light pipes  60  provides numerous advantages.  
      For example, if light engine  20  includes a first set of semiconductor light sources  40  which are only illuminated to form a portion of a low beam headlamp pattern and a second set of semiconductor light sources  40  which are only illuminated to form a portion of a high beam headlamp pattern, the semiconductor light sources  40  in the first set can be mounted intermixed with the semiconductor light sources  40  of the second set, on one or both of substrates  24   a  and  24   b . As only one set of semiconductor light sources  40  is illuminated at a given time, the spacing provided by the non-illuminated, but intermixed, semiconductor light sources  40  of the other set help reduce the thermal density of the waste heat produced by the operating semiconductor light sources  40 .  
      In addition, by having differing arrangements of the emitter ends  36  and receiver ends  32  of light pipes  60 , substrates  24  can be fabricated in different shapes to make better use of available space in a vehicle or other location. For example, while many headlamp beam patterns are substantially rectangular in shape, with the major axis of the rectangle being generally horizontal, substrates  24  can be square, round, rectangular, elliptical, irregular or any other shape which is desired. Further, substrates  24  can be oriented in any orientation which provides for efficient or desired use of the available volume for a headlamp or other vehicle lighting system using light engine  20 .  
      Another contemplated advantage of light engine  20  is that, while receiving ends  32  of light pipes  60  preferably have a cross section which is selected to enhance the capture of the light emitted by their respective semiconductor light sources  40 , the cross section and other characteristics of the emitter ends  36  can be varied as desired. For example, in some illumination patterns, such as a low beam headlamp pattern, sharp transitions or gradients between lighted and unlighted portions of the beam pattern are undesired.  
      Accordingly;  FIG. 7  shows another embodiment of the emitter end  36  of lights pipes  60  in transfer device  28  wherein some of the emitter ends  36   a  are generally rectangular in shape and other emitter ends  36   b  are generally triangular in shape to provide a gentler transition from lighted to unlighted parts of the resulting beam pattern. As will be apparent to those of skill in the art, a variety of other relative sizes, shapes and combinations of shapes can be employed for emitter ends  36 . Similarly, emitted ends  36  can be located on forming member  72  with varying spacing to provide a desired varying density of illumination.  
      It is also contemplated that, if desired, emitter ends  36  can be treated to obtain desired beam pattern effects. Such treatments can include coatings applied to emitter ends  36  to diffuse their emitted light and/or other treatments as will occur to those of skill in the art.  
       FIG. 8  shows a mixer  84  which can be attached to, or integrally formed with, emitter ends  36  of light pipes  60 . Mixer  84  can be fabricated from the same, or a different, material than light pipes  60  provided only that its refractive index is similar to the refractive index of light pipes  60 . As shown, mixer  84  has at least one cross sectional dimension which is larger than the cross sectional dimensions of emitter end  36 , resulting in an additional surface area  88  from which light from light pipe  60  will be emitted. As will be apparent, due to the internal reflection of the light rays in mixer  84 , light emitted from surface area  88  of mixer  84  will be more diffuse than the light emitted from the surface area  92  of mixer  84  that corresponds to the cross section of emitter ends  36 .  
      It is contemplated that a single mixer  84  can have two or more emitter ends  36  connected to it, or that an emitter end  36  can have its own mixer  84  connected to it to provide diffuse light, as needed, for forming a desired beam pattern.  
       FIG. 9  shows another embodiment of a light engine  20   a  in accordance with the present invention. In this Figure, elements which are similar to those described above with reference to  FIGS. 1 through 6  are indicated with like reference numerals. In light engine  20   a , substrate  24   a  need not include apertures  46  as substrate  24   b  is located adjacent substrate  24   a , rather than under it. As is illustrated, the receiving ends  32  of light pipes  60  of transfer device  28  extend, respectively, to semiconductor light sources  40  on each of substrates  24   a  and  24   b . As should now be apparent, light engine  20   a  affords a great amount of flexibility in the size and positioning of substrates  24  to allow light engine  20   a  to be manufactured to fit within a wide variety of volumes on vehicles, or other desired locations.  
       FIG. 10  shows yet another embodiment of a light engine  20   b  in accordance with the present invention. In this Figure, elements which are similar to those described above with reference to  FIGS. 1 through 6  are indicated with like reference numerals. In light engine  20   b , two transfer devices  28   a  and  28   b  are provided, each having a respective emitting end  36   a  and  36   b , and a respective forming member  72   a  and  72   b . The receiver end (not shown) of each transfer device  28   a  and  28   b  can be supplied with light from the same substrate (also not shown) or different substrates, as required.  
      In the illustrated embodiment, emitter ends  36   a  and  36   b , and their respective forming members  72   a  and  72   b  are located at different distances from lens system  76 . Assuming that emitter ends  36   a  are at the focal point of lens system  76 , focused light will be provided from emitter ends  36   a  and transfer device  28   a . If emitter ends  36   b  are located outside the focal point of lens system  76 , unfocussed (diffuse) light will be provided from emitter ends  36   b  and transfer device  28   b.    
      It is also contemplated that emitter ends  36   a  and  36   b  can be located at different distances and/or orientations with respect to lens system  76  and that one or more additional optical elements, such as mixer plates, diffusers, lenses, etc., can be interposed between one or the other or both of emitter ends  36   a  and  36   b  to alter the beam pattern produced by lens system  76  as desired and, for example, to simultaneously provide focused and diffuse beam patterns.  
      As should now be apparent to those of skill in the art, a light engine in accordance with the present invention provides several advantages for semiconductor-based headlamps. In prior art semiconductor headlamp systems, the semiconductor light sources had to be located adjacent the lens of the headlamp system to form the desired beam patterns. Electrical connections and heat removal systems thus had to be designed and arranged to work with the location of the light sources and the resulting heat transfer characteristics would often be less efficient than desired while the overall enclosure size and/or shape for the headlamp system would also be less favorable than desired.  
      In contrast, with a light engine in accordance with the present invention, transfer device  28  removes the need for the semiconductor light sources themselves to be located at any specific location with respect to the lens of the headlamp system. Instead, emitter end  36  of transfer device  28  can be appropriately positioned with respect to the lens, but one or more substrates  24 , with semiconductor light sources  40  and the required electrical and heat transfer connections thereto, can be located in a variety of locations within the enclosure of the headlamp system. For example, a substrate  24  can be located horizontally along the bottom of a headlamp enclosure and another substrate  24  “stacked” behind it while emitter end  36  of transfer device  28  is located at the front of the headlamp enclosure, adjacent the lens. In such a configuration, each substrate  24  can be thermally connected to one or more heat sinks which extend from the bottom of the headlamp enclosure, etc.  
      Further, light engine  20  can be used as a standard light engine from which a wide variety of headlamp or other lighting systems can be constructed. Light engine  20  provides a known amount of light and a headlamp system can employ one or more light engines  20 , as needed, to produce a required lighting level. By producing standardized light engines  20 , manufacturing costs can be reduced, design processes simplified and repair of headlamp systems simplified.  
      The above-described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto.