Abstract:
A device for the emission of light, in particular for the generation of an image, the device including at least one light source, at least one heat sink, a diffusor for diffusing and homogenizing the light emitted from the light source and comprises a thermal conduction device, is provided herein. The light source is constructed to be thermally coupled to a heat sink. The thermal conduction device is also constructed to be thermally coupled to a heat sink so that heat generated by the light source is transmitted to the thermal conduction device and from the thermal conduction device to the heat sink. The thermal conduction device is additionally constructed as a diffusor for diffusing and homogenizing the light emitted from the light source.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This patent application claims priority to German Patent Application No. DE 10 2015 106 708 0, filed Apr. 30, 2015, entitled “DEVICE FOR THE EMISSION OF LIGHT, IN PARTICULAR FOR THE GENERATION OF AN IMAGE,” the entire disclosure of the application being considered part of the disclosure of this application and hereby incorporated by reference. 
       BACKGROUND 
       [0002]    Known systems from the prior art for the generation of images, also known as “Picture Generating Units” (PGUs) or Image Generating Units” (IGUs), are constructed with light emitting diodes with increasing power and luminous intensity and special lenses, in particular collimator lenses. The construction of the systems for image generation with high-performance light emitting diodes, also called high-performance LEDs, serves to increase the intensity of the display illumination and therefore the brightness of a generated virtual image. 
         [0003]    The use of high-performance LEDs can cause a rise in the emission of heat inside the systems, in particular in the area in front of the light-emitting element, that is, especially in the area between the light-emitting element, the collimator lens, and a display device. Due to the increasing emission of heat, the temperature rises in the area in front of the light-emitting element in such a manner that the admissible limit of the working temperature of the display device is exceeded. The display device can fail or be destroyed. The area is also designated as a high-temperature area. 
         [0004]    Traditional systems for image generation comprise a heat sink constructed as a cooling body. However, a cooling body thermally coupled to the light-emitting element cannot completely remove the heat emitted from high-performance LEDs, so that the temperature inside the high-temperature area between the collimator lens and the display device sharply rises. 
         [0005]    The systems for image generation are also used as components of display devices such as a so-called “head-up-display” and are arranged, for example, in the area of the windshield of a motor vehicle. The term head-up-display, also abbreviated as HUD, denotes a display system in this context with which the user can retain the position of his head and/or the direction of view in the original alignment when observing the displayed information since the information is projected into his field of view. HUDs generally comprise an image-forming unit which generates an image, a lens module and a projection surface. The lens module guides the image onto the projection surface, which is constructed as a reflecting, transparent plate. The vehicle driver sees the reflected information of the image-forming unit and at the same time the actual environment behind the disk. 
         [0006]    US 2007/0064174 A1 teaches a device with a light unit and a display unit, in particular a HUD. The light unit comprises illumination elements arranged between a reflector and a heat-blocking layer, through which a liquid crystal panel is illuminated. 
         [0007]    EP 1 865 534 B1 discloses a light emission device with a light emission panel and a diffuser plate for diffusing the light emitted by the light emission panel. The device comprises a heat dissipation plate arranged between the light emission panel and the diffuser plate and which is constructed from a material with high thermal conductivity. 
         [0008]    Moreover, in addition to the heat blocking layer and heat dissipation plate, ventilators, cooling coils and heat-absorbing filters are used in the prior art. 
         [0009]    The systems known from the prior art comprise a plurality of components that are arranged inside the beam of the light emitted by the light-emitting elements and which reduce the intensity of the light exiting from the device. The components provided in the prior art devices can just adequately dissipate the emitted heat. Furthermore, the light emission devices have no connection to a display device which is to be protected from overheating. 
         [0010]    There exists a need for a device for the emission of light, in particular to generate an image, in which the heat emitted by light-emitting elements, for example, high-performance LEDs, is more effectively dissipated from a high-temperature area in order to avoid destruction of or damage to the device. Elements for dissipating the heat are to be constructed in combination with a device for generating an image in such a manner that limit temperatures of individual components are not achieved or exceeded. The number of components of the device for the emission of light should be minimal in order to minimize the manufacturing costs. On the other hand the components for removing the heat should be constructed so that the light intensity is not additionally influenced or reduced. 
       SUMMARY 
       [0011]    The aspects disclosed herein include a device for the emission of light, in particular for the generation of an image, comprising at least one light source thermally coupled to a heat sink, and a diffusor comprising a thermally conductive device for diffusing and homogenizing the light emitted by the light source. 
         [0012]    The thermal coupling makes possible a thermal transfer between the components that are connected to one another not only by thermal radiation or convection but also by direct thermal conduction. Thermally coupled components are therefore connected in a thermally conductive manner to each other. 
         [0013]    The thermally conductive device is designed to be thermally coupled to a heat sink so that emitted heat generated by the light source is transferred to the thermally conductive device and from the thermally conductive device to the heat sink. In addition, the thermally conductive device also functions as a diffusor for diffusing and homogenizing the light emitted by the light source. 
         [0014]    A light source or a light unit in this connection is an element that emits heat and light. High-performance LEDs are preferably used as light source. 
         [0015]    According to an embodiment, the device comprises a first heat sink and a second heat sink. The light source is constructed to be thermally coupled to the first heat sink. The thermally conductive device is constructed to be thermally coupled to the second heat sink and disposed a distance from the light source so that heat generated by the light source is transmitted to the thermally conductive device and from the thermally conductive device to the second heat sink. 
         [0016]    According to an embodiment, the first heat sink and the second heat sink are spatially separated from one another. No direct thermally conductive connection is formed between the heat sinks. 
         [0017]    According to another embodiment, the first heat sink and the second heat sink are thermally coupled to one another and are constructed in one piece. Therefore, the thermally conductive device thermally coupled to the second thermally conductive device is also thermally connected via the second heat sink to the first heat sink. The second heat sink is advantageously constructed as a wall of the device. 
         [0018]    According to a further embodiment, the thermally conductive device is thermally coupled, at least in sections, to the heat sink. The thermally conductive device may also be completely thermally coupled to the heat sink. 
         [0019]    According to an embodiment, the device is constructed with a reflector. The reflector radially surrounds the light source, includes an opening on an end distal to the light source, and is thermally coupled to the heat sink. Therefore, heat emitted by the light source and building up inside the volume surrounded by the reflector is transferred to the heat sink. 
         [0020]    According to a further development, the device includes a collimator for aligning the light in parallel, which is arranged in the direction of the light emitted by the light source. In addition, the thermally conductive device may be constructed in a plane aligned perpendicularly to the light directed in parallel by the collimator. 
         [0021]    According to an embodiment, the device comprises a display device for generating an image. The thermally conductive device may be disposed in the path of the light emitted by the light source in front of the display device. In other words, the thermally conductive device is located between the light source and the display device so that the light passing the thermally conductive device shines through the display device. 
         [0022]    Therefore, this design includes a light source with a display device, such as in a projector unit or a system for image generation, preferably with high-performance LEDs, and a device for the dissipation of heat for the thermal protection of individual components. The projector unit and the system for image generation may be used, for example, as a HUD in motor vehicles, airplanes, ships or the like. 
         [0023]    The display device is advantageously constructed as a TFT display. 
         [0024]    According to an embodiment, the heat sink is constructed as a cooling body that includes ribs for transferring heat to the ambient air. 
         [0025]    According to an embodiment, the thermally conductive device is constructed from a good heat-conducting material such as aluminium, copper, titanium, magnesium or an alloy of one or more that includes such heat-conducting materials. In other words, the thermally conductive device should be conducted of a material having a high thermal conductivity of at least 19 W/(m·K). Other materials having a higher thermal conductivity may be used as well. 
         [0026]    The design, especially as regards the small number of components with an effective removal of the heat generated by the light-emitting elements with high luminous power, makes possible the use of the device in combination with optical components for generating a virtual image in a motor vehicle. The virtual image is projected onto the windshield in a direction of view of a vehicle driver when looking in the direction of travel through a windshield. The device and the additional optical components are disposed inside a dashboard. 
         [0027]    In sum, the device has advantages, including:
       small number of components,   minimal costs incurred during the manufacture,   no reduction of luminous intensity by additional components with an effective removal of the heat generated by the light-emitting elements with high luminous power and therefore protection of a display device against damage due to overheating and the ensuring of a long service life.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    Other details, features and advantages of embodiments of the invention result from the following description of exemplary embodiments with reference made to the associated drawings wherein: 
           [0032]      FIG. 1  is a schematic diagram of optical components for a device for the emission of light, in particular for showing information as a virtual image in a motor vehicle; 
           [0033]      FIG. 2  is a perspective cut-away view of a device for the emission of light, in particular for generating an image, with a first and a second deflection mirror arranged inside a dashboard; 
           [0034]      FIG. 3  is a sectional view of a device for the emission of light, in particular for generating an image, showing an area of high temperatures; 
           [0035]      FIG. 4  is a sectional view of a device for the emission of light, in particular for generating an image, with a thermally conductive device disposed in the area of high temperatures; 
           [0036]      FIG. 5  is a sectional perspective view of a device for the emission of light, in particular for generating an image, with a thermally conductive device; 
           [0037]      FIG. 6  is a magnified view of one embodiment of a thermally conductive device; 
           [0038]      FIG. 7  is a magnified view of another embodiment of a thermally conductive device. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, a device  1  for the emission of light, in particular for the generation of an image is generally shown. 
         [0040]      FIG. 1  shows a device  1  for the emission of light, in particular for generating a virtual image  11  inside an arrangement with optical components for displaying information in a motor vehicle. The virtual image  11  is projected by the windshield  9  in the direction of view of the vehicle driver  2  looking in the direction of travel. 
         [0041]    The device  1  with the optical components, in particular a first deflection mirror  3  and a second deflection mirror  4 , is arranged inside the dashboard  8 . The beam  7  consisting of light rays emitted by the device  1  is conducted via the first deflection mirror  3 , which is constructed in a planar or aspherical and convex manner, to the second deflection mirror  4 , which is constructed aspherically and concavely. The beam  7  consisting of light rays exits out of the dashboard  8  through a glare light trap (not shown). Another light trap  6  arranged adjacent to the glare light trap prevents in combination with the glare light trap the exit of light rays which can cause irritations of and reflections to the vehicle driver  2 . 
         [0042]    The beam  7  of light rays is conducted against a predetermined area of the windshield  9  of the motor vehicle, also designated as the projection surface in which the windshield  9  is formed with optical components for displaying the image. The device  1  for the emission of light and for generating the virtual image  11  and the deflection mirrors  3 ,  4  act in combination with the projection surface formed on the front pane  9  as a HUD. 
         [0043]    The vehicle driver  2  is given the possibility of not increasing the area of his head movement and his eye movement  10  in order to perceive the virtual image  11  and the information contained in it. The vehicle driver  2  can retain his head position and his direction of view since the information is projected into his field of vision, which minimizes the deflection of the vehicle driver  2  for receiving the information. 
         [0044]    The device  1  generates the virtual image  11 , which is conducted onto the reflecting, transparent projection surface of the windshield  9 . The vehicle driver  2  sees as a user of the windshield projector the reflected information of the device  1  and at the same time the real environment in the direction of view behind the windshield  9 . 
         [0045]    The virtual image  11  is displayed at a perceptible distance, the so-called projection distance S, from the vehicle driver  2  on an optical path  12 . 
         [0046]      FIG. 2  shows the device  1  for the emission of light, in particular for generating a virtual image  11 , in the assembled state in combination with the first deflection mirror  3  and the second deflection mirror  4 , which are arranged inside the dashboard  8 . 
         [0047]    The device  1  transmits the generated beam  7  of light rays in the direction of the vehicle driver  2  onto the first deflection mirror  3 , which reflects the light rays onto the second deflection mirror  4 . 
         [0048]      FIG. 3  shows the device  1  for the emission of light in a sectional view with characterization of an area  21  of high temperatures.  FIG. 4  shows the device  1  for the emission of light with a thermally conductive device  22  arranged in the area of high temperatures  21 . 
         [0049]    The light source  13  is arranged on a circuit board  18  and thermally and mechanically coupled via the circuit board  18  to a first heat sink  19  constructed as a cooling body. The cooling body of the first heat sink  19 , which cooling body is constructed on the back side of the light source  13 , comprises air-loaded ribs. In particular, a plurality of high-performance light-emitting diodes also designated in the following as high-performance LEDs, serve as light source  13 . 
         [0050]    The circuit board  18 , which can be programmed and is constructed as a power relay, is connected on the one hand to the light source  13  and on the other hand to the heat sink  19  so that heat generated by the light source  13  is transferred via thermal conduction and thermal radiation onto the cooling body. The heat is dissipated from the cooling body to the outside to the air surrounding the device  1 . 
         [0051]    The light source  13  is surrounded in the area facing away from the circuit board  18  by a reflector  14  which comprises an opening on the end distal to the light source  13 . Therefore, the entire light emitted from the light source  13  is conducted to the opening of the reflector  14 . 
         [0052]    A lens constructed as collimator  15  is arranged on the opening of the reflector  14  for generating a parallel course of the light rays or a parallel beam of light rays. The collimator  15  covers substantially the entire opening of the reflector  14  in order to conduct all light rays emitted from the light source  13  directed in parallel to a display device  17 . An optical filter  16  is constructed between the collimator  15  and the display device  17 . The display device  17  is, for example, constructed as a high-resolution color TFT display, that is, as a display with a thin-film transistor control or as a thin-film transistor display. 
         [0053]    The light rays emitted by the light source  13  and directed in parallel by the collimator  15  shine through the display device  17  in order to generate the virtual image  11 . 
         [0054]    Since the high-performance LEDs generate and emit light with a very high intensity but, on the other hand, also generate a large amount of heat, the temperature rises inside the device  1 , in particular in the area in front of the light source  13 . The area of high temperatures  21  extends substantially from the light source  13  and the collimator  15  to the display device  17 . 
         [0055]    In the area of high temperatures  21  of the device  1  at an ambient temperature of 55° C., temperatures of the collimator  15  and of the filter  16  of approximately 130° C. are achieved and at an ambient temperature of 44° C., approximately 120° C. is achieved. The limit temperature of the collimator  15  is approximately 120° C. The limit temperature of the filter  16  is, in comparison to the above, between 95° C. and 105° C. Therefore, the admissible limits of the working temperatures of the display device  17  and of the filter  16  are exceeded, which can result in destruction and failure of the display device  17  and therefore of the device  1 . 
         [0056]    As is apparent from  FIG. 4 , a thermally conductive device  22  is formed in the area of high temperatures  21  which is arranged between the collimator  15  and the display device  17 , in particular between the collimator  15  and the filter  16 . The thermally conductive device  22  is formed in a plane aligned perpendicular to the light beams directed in parallel by the collimator  15  and extends up to the boundaries of the area of high temperatures  21  and therefore up to the housing of device  1 . The housing wall advantageously consists of metal. 
         [0057]    The thermally conductive device  22  serves to dissipate the heat rays emitted by the light sources  13  in the direction of the display device  17  and by the filter  16  in order to protect the display device  17  and the filter  16  against too great an incidence of heat and therefore against exceeding the limit temperatures. 
         [0058]    The thermally conductive device  22  is coupled thermally and mechanically to a second heat sink  20  constructed as a cooling body so that heat generated by the light source  13  is transferred to the thermally conductive device  22  and from the thermally conductive device  22  substantially via thermal conduction to the heat sink  20 . From the cooling body the heat is removed to the outside to the air surrounding the device  1 . The cooling body of the second heat sink  19 , which body is formed on the side surfaces, in particular on the top and the bottom of the device  1 , comprises air-loaded ribs. 
         [0059]    In an embodiment which is not shown, the first heat sink  19  and the second heat sink  20  are thermally coupled to one another or constructed in one piece as a heat sink so that the thermally conductive device  22  is also thermally connected via the second heat sink  20  to the first heat sink  19 . 
         [0060]    The thermally conductive device  22  is constructed on the one hand for dissipating heat to the second heat sink  20  and on the other hand as a diffuser for the light emitted by the light source  13 . The diffuser is suitable as a light-scattering element for making hard direct light softer and for reducing strong light-shadow contrasts and disturbing reflexes. In combination with the device  1 , the diffuser brings about a uniform illumination of the display device  17 . 
         [0061]      FIG. 5  shows the device  1  for the emission of light, in particular for generating an image  11 , in a sectional perspective view. The circuit board  18  is thermally and mechanically coupled by the first heat sink  19  to the light sources  13  arranged on the front side. The back side of the circuit board  18  facing away from the light source  13  lies flatly on the cooling body of the first heat sink  19 . The circuit board  18  is fastened to the cooling body by holding elements which are not shown. 
         [0062]    The reflector  14  arranged around the light source  13  lies with a very large part of its entire surface on the cooling body of the second heat sink  20  and is consequently thermally coupled to the cooling body so that the heat emitted by the light sources  13  and building up inside the volume surrounded by the reflector  14  is removed to the outside to the air of the environment. 
         [0063]    The thermally conductive device  22  is disposed in the area of high temperatures  21  and aligned perpendicularly to the light rays directed in parallel extends up to the housing of device  1 , which housing is constructed on all sides as a cooling body of the second heat sink  20 . Therefore, the device  1  is surrounded on its back side by the cooling body of the first heat sink  19  and on all sides and the faces or front side by the cooling body of the second heat sink  19 . The cooling body of the second heat sink  20 , which cooling body is formed on the side surface and the front side of device  1 , comprises air-loaded ribs. 
         [0064]    The thermally conductive device  22  is thermally coupled on all edge areas to the cooling body of the second heat sink  20  so that the heat taken up by the thermally conductive device  22  is transferred by thermal conduction to the cooling body and from the cooling body to the air surrounding the device  1 . 
         [0065]    The light rays emitted by the light source  13  and directed in parallel pass through the collimator (not shown) and the thermally conductive device  22  to the filter  16  and through the display device  17  in order to generate the virtual image  11 . The display device  17  is secured by fastening element  23  on the front side of the device  1 . In the area of the display device  17  the housing, in particular the cooling body of the second heat sink  20 , is designed with an opening through which the light rays emitted by the light source  13  and shining through the display device  17  exit from the device  1 . 
         [0066]      FIGS. 6 and 7  show thermally conductive devices  22 ′,  22 ″ constructed as diffusers in different embodiments. 
         [0067]    The thermally conductive devices  22 ′,  22 ″ are constructed as a network, grid or fabric, which may consist of metal. The thermally conductive devices  22 ′,  22 ″ function, in addition to the removal of heat, also as a light diffuser which is permanently connected to a cooling body. The thermally conductive device  22 ′,  22 ″ conducts the heat from a central axis of the beam consisting of light rays to the outside down to the cooling body of the second heat sink  20 . 
         [0068]    The thermally conductive devices  22 ′,  22 ″ are constructed from a good heat-conducting material, that is, from a material with a high coefficient of thermal conductivity such as aluminium, copper, titanium, or magnesium. 
         [0069]    The light rays are substantially perpendicular to the thermally conductive device  22 ′,  22 ″ and pass through the openings formed inside the network, grid or fabric. The light rays are thereby evened-out and conducted further to the display device  17 . The thermally conductive devices  22 ′,  22 ″ each have a shape that is homogenizing for the light. 
         [0070]    The device  1  can be used in all systems for generating images such as HUD, PGU, IGU, light units, and projector units with high-performance LEDs or other light-emitting elements which also emit heat in addition to light.