Abstract:
A headlamp assembly for a motor vehicle having a light source, a chamber that receives the light source and a cooling channel for removing heat from the chamber. A conductive wall and an insulating wall cooperate to define the chamber and the channel. The conductive wall has a substantially higher thermal conductivity than the insulating wall to promote the heat exchange between the chamber and the cooling channel and to reduce heat exchange between the cooling channel and the relatively hot engine compartment.

Description:
BACKGROUND 
     1. Field of the Invention 
     The invention relates generally to a headlamp assembly for a motor vehicle. More specifically, the invention relates to the cooling of a headlamp assembly by conducting heat from the light source to the exterior of the headlamp assembly via conductive heat sinks. 
     2. Related Technology 
     Headlamp assemblies have a light source, such as an incandescent lamp, a light emitting diode (LED) or high intensity discharge (HID) lamp, positioned within a headlamp chamber and electrically connected to a power source. The headlamp chamber is typically defined by a transparent or translucent lens, located forward of the light source, and a reflector located rearward and/or surrounding the light source. As used herein, the terms forward and rearward are referenced with respect to the position of the light source and the direction in which the light from the source is intended to be seen. Thus, light from the assembly is intended to be seen from a forward position. 
     During an operation cycle of the headlamp assembly, the light sources and other components of the lamp generate heat while “on” and cool while “off”, causing the chamber to undergoes temperature fluctuation and causing the air located within to expand and contract. To maintain a relative-constant chamber pressure, the chamber typically includes at least one opening that permits an air exchange between the chamber and the ambient air. However, to prevent contaminants, such as dust and debris, from entering the chamber, the opening is typically relatively small and is covered with an air-permeable membrane. 
     In order to attain designed optimal performance of newer light sources, LED&#39;S and their electrical components in the lamp assembly, it is desirable to maintain the internal temperature of the lamp assembly below the maximum operating temperature Therefore, it is advantageous to provide the headlamp assembly with a mechanism that cools the chamber and the LED&#39;S located therein. 
     Headlamp assemblies are typically secured to a portion of the vehicle frame that is adjacent to the engine compartment. The temperature within the engine compartment is often significantly higher than the temperature outside of the engine compartment (the ambient temperature). For example, during operation of the vehicle various components, such as the engine and the engine cooling system, output heated air into the engine compartment. As another example, during periods of vehicle use and non-use, the air trapped within the engine compartment may become heated by solar energy. Therefore, it is advantageous to provide the headlamp assembly with a mechanism that isolates the chamber and the light sources located therein from the relatively high temperatures of the engine compartment. 
     In view of the above, it is beneficial to have a headlamp assembly that has a mechanism that effectively cools the mechanism&#39;s internal components while minimizing air exchange between the headlamp assembly chamber and the atmosphere and while isolating the chamber from the engine compartment and the relatively high temperatures associated therewith. 
     SUMMARY 
     In overcoming the above limitations and other drawbacks, a headlamp assembly for a motor vehicle is provided that includes a lens and a housing that define an inner chamber that is generally fluidly isolated from the atmosphere. The housing includes portions that extend from an interior surface of the housing into the inner chamber to define a base having a light source mounted thereon. The housing further includes portions that extend from an exterior surface of the housing to define a plurality of fins exposed to ambient air. A reflector is positioned behind the light source and is adapted to reflect light from the light source forward. 
     In one aspect, the headlamp assembly includes a flow channel positioned adjacent the exterior surface of the housing. The flow channel is adapted to direct ambient air flowing therethrough. The fins extend into the flow channel such that heat from within the inner chamber is conducted through the base portion of the housing to the fins of the housing to the air flowing through the flow channel. 
     In another aspect, air flow through the flow channel can be achieved by natural convention, forced convection, induced forced convection, or any combination thereof. 
     In yet another aspect, the flow channel is positioned behind the headlamp assembly and is at least partially defined by the exterior surface of the housing. 
     In still another aspect, the flow channel includes an inlet and an outlet. The inlet of the flow channel includes venturi openings and the outlet of the flow channel is positioned in a low pressure region within the motor vehicle. Air air is drawn in through the venturi openings at the inlet and flows toward the low pressure region at the outlet. The venturi openings at the inlet of the flow channel include one way valves. 
     In still another aspect, the housing is made from a conductive material selected from the group: metal, metal alloy, silicon, and graphite. 
     Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front schematic view of a headlamp assembly for a motor vehicle embodying the principles of the present invention; 
         FIG. 2  is a sectional view taken generally along line  2 - 2  of the headlamp assembly shown in  FIG. 1 ; 
         FIG. 3  is a rear view of the housing of the headlamp assembly shown in  FIG. 1 ; 
         FIG. 4  is a sectional view of an alternative embodiment, having forced air moving through the flow channel; 
         FIG. 5  is a sectional view of an alternative embodiment, having venturi openings positioned at the inlet of the flow channel, the outlet of the flow channel being positioned at a low pressure region; and 
         FIG. 6  is a sectional view of an alternative embodiment that does not include a flow channel. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , a headlamp assembly for a motor vehicle in accordance with the teachings of the claims herein is shown generally at  10 . The headlamp assembly  10  includes a lens  12  and a housing  14  that cooperate to at least partially define an inner chamber  16  that is generally fluidly isolated from the atmosphere. The housing  14  is preferably opaque, and the lens  12  is preferably formed from a transparent or translucent plastic material, such as polycarbonate. 
     The housing  14  includes an interior surface  18  and an exterior surface  20 . Portions of the housing  14  extend from the interior surface  18  into the inner chamber  16  to define a base  22  that operates as a support and mount for a light source  24 . Portions of the housing  14  also extend from the exterior surface  20  to define a plurality of fins  26  that are exposed to ambient air outside of the chamber  16 , as shown in  FIGS. 1 ,  2 , and  3 , and further described below. 
     As shown in  FIGS. 1 and 2 , the housing  14  includes portions that define two bases  22 , one positioned immediately above the other. Each base  22  includes a plurality, four as shown, of light sources  24  mounted thereon. 
     The headlamp assembly  10  further includes surfaces that cooperate to focus light rays  28  from the light sources  24  into a beam having desired characteristics and direct the light rays  28  towards the lens  12 . As shown, a plurality of reflectors  30  are positioned within the inner chamber  16 , one reflector  30  being positioned relative to each light source  24 , to achieve this. The reflectors  30  re-direct the light rays  28  received thereby in a forward direction and through the lens  12 . 
     The housing  14  and the lens  12  are connected with one another such that the inner chamber  16  is substantially sealed from the atmosphere. The inner chamber  16  is, however, provided with pressure vents (not shown) that permit a relatively small amount of airflow into and out of the inner chamber  16  to account for air pressure fluctuations during temperature changes therein. 
     The light sources  24 , are preferably light emitting diodes (LEDs). Each light source  24 , hereinafter just “LED  24 ”, is attached to a printed circuit board (PCB)  32  that includes electronic controls and connections for the LED  24 . Furthermore, each LED  24  and PCB  32  are supported on the base portion  22  of the interior surface  18  of the housing  14  in a well known manner. Preferably, the housing  14  is constructed of a material having a relatively high thermal conductivity, such as metals, metal alloys, silicon, and graphite. 
     During operation of the headlamp assembly  10 , each LED  24  generates heat and increases the temperature of the air, components and structures located within the inner chamber  16 . However, the LED  24  and/or other electronic components may experience diminished performance or failure if their maximum operating temperature is exceeded. To reduce the temperature of these components, the LEDs  24  and PCBs  32  are mounted onto the base portion  22  of the interior surface  18  of the housing  14  such that heat from the light sources  24  will be conducted through the base  22  to the fins  26  extending from the exterior surface  20  of the housing  14 , and thus outside of the inner chamber  16 . Ambient air flowing across the fins  26  will cool the fins  26 , thereby dissipating the heat conducted from within the inner chamber  16 . 
     To insure that ambient air is directed over and around the fins  26 , the headlight assembly  10  may include a flow channel  34  positioned adjacent the housing  14 . As shown in  FIG. 2 , a flow channel wall  36  is positioned adjacent to and spaced from the exterior surface  20  of the housing  14 , thereby defining the flow channel  34 . The flow channel wall  36  and the exterior surface  20  of the housing  14  are preferably spaced apart from each other along their respective lengths so that the flow channel  34  has a substantially constant width, thereby minimizing flow loss across the flow channel  34 . 
     The flow channel  34  is adapted to direct ambient air flowing therethrough, wherein the fins  26  extend into the flow channel  34  such that heat from within the inner chamber  16  is conducted through the base  22 , to the fins  26 , and to the air flowing through the flow channel  34 . 
     Referring to  FIG. 2 , the flow channel  34  includes an inlet  38  and an outlet  40 . The inlet  38  of the flow channel  34  is oriented in the forward direction and is positioned near the front bottom of the headlamp assembly  10 . The outlet  40  of the flow channel  34  is oriented in the rearward direction and is positioned near the rear top of the headlamp assembly  10 . With the headlamp assembly  10  placed near the front of the motor vehicle  42 , when the motor vehicle  42  is moving in a forward direction, a stream of fresh ambient air flows into the inlet  38  of the headlamp assembly  10  and into the flow channel  34 , as indicated by arrows  44 . In this way, cooling of the fins  26  is achieved by “forced” convection. An air duct or opening  46  defined by the front portion of the motor vehicle  42 , such as a bumper  48 , may be positioned near the inlet  38  to further promote the inflow of ambient air. 
     Referring to  FIG. 4 , an alternative embodiment of the headlamp assembly is shown generally at  10   a . A flow channel  34   a  for the headlamp assembly  10   a  includes an inlet  34   a  that is located near the bottom of the headlamp assembly  10   a , but is not exposed openly to the front of the vehicle  42 . The flow channel  34   a  has an outlet  40   a  that is again positione assembly  10   a . In this instance, as the fins  26  heat up, the air within the flow channel  34   a  will also heat up, by convection. The heated air will rise upward, causing a draft that will pull cooler air up from the inlet  38   a , as cooler air comes upward into contact with the fins  26 , it will in turn be heated and rise upward, thereby creating a flow of air through the flow channel  34   a  by natural convention, as indicated by arrows  50 . 
     In either instance, the headlamp assembly  10  shown in  FIG. 2  or the headlamp assembly  10   a  shown in  FIG. 4  could include a fan  52  (shown in phantom) mounted near the inlet  38 ,  38   a  or the outlet  40 ,  40   a  to force air to flow through the flow channels  34 ,  34   a . An electric fan  52  would provide selective induced forced convection to draw ambient air in through the inlets  38 ,  38   a  and push air through the flow channels  34 ,  34   a  to the outlets  40 ,  40   a.    
     Referring to  FIG. 5 , another embodiment of the headlamp assembly is shown generally at  10   b . A flow channel  34   b  for the headlamp assembly  10   b  includes an inlet  38   b  that is located near the bottom of the headlamp assembly  10   b , but is not exposed openly to the front of the vehicle  42 . The inlet  38   b  comprises a plurality of venturi openings  54  formed within the flow channel wall  36   b . The flow channel  34   b  has an outlet  40   b  that is again positioned near the rear top of the headlamp assembly  10   b . In this instance, the outlet  40   b  is strategically positioned within an area that is a low pressure region when the vehicle  42  is moving forward. 
     When the vehicle  42  is moving, air will naturally flow from higher pressure to the low pressure region at the outlet  40   b  of the flow channel  34   b . The low pressure region will draw air in through the venturi openings  54  in the flow channel wall  36   b , as indicated by arrows  56 , and through the flow channel  34   b , thereby developing a flow of air from the region near the inlet  38   b , which is relatively higher pressure than the low pressure region near the outlet  40   b . Heat from within the inner chamber  16  is conducted through the base  22 , to the fins  26 , and to the air flowing through the flow channel  34   b , as indicated by arrows  58 , to cool the inner chamber  16  and the housing  14 . One way valves (not shown) could be placed at the venturi openings  54  to insure that the flow of air is restricted to only flowing into the flow channel  34   b  through the venturi openings  54 . 
     Referring to  FIG. 6 , still another embodiment of the headlamp assembly is shown generally at  10   c . The headlamp assembly  10   c  does not have a flow channel wall or a flow channel. Cooling of the fins  26  comes only from natural convection as discussed previously. As heat is conducted to the fins  26  from the inner chamber  16 , the fins  26  heat up. The air near and around the fins  26  is heated by the fins  26  and begins to rise upward. The heated air will rise upward, causing a draft that will pull cooler air up and into the spaces between and around the fins  26 . As cooler air comes into contact with the fins  26 , it will in turn be heated and rise upward, thereby creating a flow of air through and around the fins  26  by natural convention, as indicated by arrows  60 . 
     By making the housing  14  from a thermally conductive material and using portions of the interior surface  18  to define the base  22  and portions of the exterior surface  20  to define the fins  26 , the housing  14  acts both as the housing  14  and as an additional heat sink to conduct heat away from the inner chamber  16 . The housing  14  can be made from any suitable thermally conductive materials such as metal, metal alloy, silicon, or graphite material, and more specifically, aluminum. Alternatively, the housing  14  may include a plurality of conductive components, such as a metal, a metal alloy, or a graphite material, embedded within a base material, such as a polymer. In this design, the benefits discussed above are equally applicable. 
     It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the scope of this invention.