Abstract:
An automotive headlamp assembly having a closed-loop cooling circuit. The headlamp assembly includes a housing cooperating with a transparent lens cover to define a chamber. At least one light source is located within the chamber. The cooling circuit has at least one cold plate thermally coupled to the light source. A radiator is fluidly coupled to the cold plate by a plurality of tubes. The tubes are oriented at least partially upwardly and configured to circulate a fluid through the cooling circuit as a result of heating and cooling of the fluid therein.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 12/194,663, filed Aug. 20, 2008, now U.S. Pat. No. 7,883,251, the entire contents of which are herein incorporated by reference. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention generally relates to an automotive exterior lamp assembly. More particularly, the invention relates to heat dissipation from an automotive headlamp assembly. 
     2. Description of the Known Technology 
     In recent years, light emitting diodes (LEDs), individually and in arrays, have become a popular light source for automotive lighting applications. LEDs are typically used in automobiles to provide lighting for the interior cluster of a Center High Mount Stop Lamp (CHMSL) and the rear lamps of an automobile. Used in such applications, LEDs have several advantages over traditional incandescent light bulbs. For example, LEDs have increased efficiency, faster response times, low electrical current requirements, longer operating life, and can be surface mounted and manufactured using techniques well developed in electronic manufacturing unlike traditional incandescent bulbs which typically require through-hole mounts. 
     Even with the above advantages, one drawback with the use of LEDs as a light source is that, during operation, the LEDs and associated electrical components generate a significant amount of heat for their physical size. If the heat generated by the LED is not efficiently dissipated, internal temperature of the LED will exceed the safe limits and the LED will degrade and possibly fail. In addition, excessive LED temperatures generally cause LED efficiency to decline and change the color of the light produced. 
     Since the performance of an LED depends, in part, on maintaining the temperature of the LED below a maximum operating temperature, it is advantageous to provide the headlamp assembly with a means for cooling the LED, its associated electronics, and potentially the chamber within which it is located. 
     Thus, there exists a need for a solution that provides LEDs with enhanced heat dissipation capabilities. 
     SUMMARY 
     In overcoming the drawbacks and the limitations of the known technologies, an automotive headlamp assembly with enhanced heat dissipation capabilities is disclosed. 
     In one embodiment, the headlamp assembly comprises a housing having a housing wall defining an opening. A transparent lens cover is coupled to the housing wall and covers the opening forming a chamber. At least one light source is disposed within the chamber and a reflector is positioned within the chamber and adapted to reflect light from the light source. A partially vertically arranged cooling circuit is also at least partially disposed within the chamber. The cooling circuit comprises at least one cold plate thermally coupled to the light source. At least one radiator is partially vertically connected to the cold plate. Tubes are configured to circulate a fluid through the cooling circuit in a partially vertical direction to effectively cool the light source. 
     In another embodiment, the headlamp assembly comprises a housing defining an opening. A transparent lens cover is coupled to the housing wall and covers the opening forming a chamber. A plurality of light sources is disposed within the chamber and a reflector is positioned within the chamber to reflect light from at least one of the light sources. A partially vertically arranged cooling circuit is also at least partially disposed within the chamber. The cooling circuit comprises a plurality of cold plates, each of which is thermally coupled to at least one of the light sources. At least one radiator is partially vertically connected to the cold plates. Tubes are configured to circulate a fluid through the cooling circuit in a partially vertical direction to effectively cool the light sources. 
     In another embodiment, the headlamp assembly comprises a housing defining an opening. A transparent lens cover is coupled to the housing wall and covers the opening forming a chamber. Disposed within the chamber is a plurality of light sources and a reflector is positioned within the chamber to reflect light from at least one of the light sources. A cooling circuit is at least partially disposed within the chamber and partially vertically arranged. The cooling circuit includes a plurality of cold plates, each of which is thermally coupled to at least one of the light sources. Each of the cold plates includes a cold plate channel having a cold plate inlet and a cold plate outlet. The cooling circuit further includes at least one radiator connected to the plurality of cold plates. The radiator is generally vertically oriented and includes a radiator channel having a radiator inlet and a radiator outlet. A plurality of at least partially vertically oriented tubes circulates a fluid through the cooling circuit to effectively cool at least one of the light sources. The plurality of tubes includes a series of tubes that connect the cold plates in series. The plurality of tubes further includes a tube connecting the outlet of the last cold plate with the inlet of the radiator. A further tube connects the outlet of the radiator to the inlet of the first in the series of cold plates. Other arrangements for the cooling circuit include a parallel arrangement, wherein the cold plates are arranged in parallel, or a combination of a series arrangement and a parallel arrangement. 
     Further, a method of dissipating heat inside an automotive headlamp assembly is disclosed. The headlamp assembly includes a housing, a chamber formed within the housing, a plurality of light sources within the chamber, and an at least partially vertically arranged cooling circuit. The cooling circuit includes one or more cold plates thermally coupled to the light sources, at least one radiator, and a plurality of tubes configured to circulate a fluid through the cooling circuit. In one embodiment, the method comprises providing a flow of fluid through the cooling circuit. Heat is collected from at least one light source by providing the flow of fluid through a cold plate, wherein the heat is conducted to the fluid. The heated flow of fluid is provided to a radiator, wherein the heat is conducted to the outside environment and the fluid is cooled. The fluid continuously flows through the closed circuit while at least one of the light sources is in operation. As the heated fluid rises within the cold plates, the fluid travels in a partially vertical direction through the tubes to the radiator. As the cooled fluid falls within the radiator, the fluid travels in a partially vertical direction through the tubes back to the cold plates. 
     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 diagrammatic side view of an embodiment of a light assembly incorporating the principles of the present invention; and 
         FIG. 2  is a diagrammatic side view of another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings,  FIGS. 1 and 2  illustrate a headlamp assembly  10  having a housing  12  including a housing wall  14  defining a chamber  16  and an opening  18 . Generally, the housing wall  14  is composed of a rigid and/or thermally-insulating material, such as plastic. However, the housing wall  14  may be made of any material suitable for this purpose, such as metal materials. A transparent lens cover  20  is coupled to the housing  12  so as to extend over the opening  18  and enclose the chamber  16 . The transparent lens cover  20  is preferably made of a transparent plastic, but may be made of any transparent material, such as glass. 
     The headlamp assembly  10  includes a light source  22 , such as a light emitting diode array (hereinafter “LEDs  22 ”), and a reflector  24  adapted to reflect light from the LEDs  22 . As shown in  FIGS. 1 and 2 , the headlamp assembly  10  may include a plurality of individual LEDs  22   a ,  22   b ,  22   c ,  22   d . During operation of the headlamp assembly  10 , the LEDs  22  generate heat and increase the temperature of the air located within the chamber  16  and the components defining the chamber  16 . However, the LEDs  22  and/or the electronic components connected to the LEDs  22  may experience diminished performance or failure if their maximum operating temperature is exceeded. To avoid this, the headlamp assembly  10  includes a liquid cooling circuit  26  disposed wholly ( FIG. 1 ) or partially ( FIG. 2 ) within the chamber  16 . 
     The liquid cooling circuit  26  is a closed circuit and includes at least one cold plate  28  connected to at least one radiator  30  through partially vertically oriented tubes  32 . The tubes  32  are partially vertically oriented to circulate a coolant through the circuit in a vertical or partially vertical direction. Acceptable coolants include water, ethylene glycol, a mixture of water and ethylene glycol, or other proprietary heat transfer fluids used in the industry for such purpose. As shown in  FIGS. 1 and 2 , the liquid cooling circuit  26  may include a series of cold plates  28   a ,  28   b ,  28   c ,  28   d  connected to the radiator  30  through a series of tubes  32   a ,  32   b ,  32   c ,  32   d ,  32   e . In  FIG. 2 , the radiator  30  is positioned outside of the housing  12  and tubes  32   d  and  32   e  extend from within the chamber  16  through a rear portion of the housing wall  14 . As will be appreciated, it is also within the scope of the present invention for the radiator  30  to be positioned partially inside and partially outside the housing  12 . 
     The cooling circuit  26  may be supported within the housing  12  in a number of ways. Each of the cold plates  28  and the radiator  30  may be individually mounted in the housing  12  by any support means, such as a support post, bracket or other structure. However, this can become very complex if there are many cold plates  28  within the cooling circuit  26 . Another option is to support the plurality of cold plates  28  via a bezel or an adjustable frame and mount the bezel within the housing  12  by any common support mechanisms. The tubes  32   a - c  then connect each of the cold plates  28  and the tubes  32   d - e  connect the cold plates  28  to the radiator  30  to complete the cooling circuit  26 . In this instance, the tubes  32  may be supported by the cold plates  28  and radiator  30 . 
     At least one LED  22  is thermally coupled to each of the cold plates  28 . In achieving this, LEDs  22  may be directly mounted to the cold plates  28 , or they may be indirectly mounted to the cold plates  28  via a substrate. For example, a retainer clip may attach an LED substrate to a face of the cold plate  28  and the LED  22  may be attached to the LED substrate by a solder joint or a thermally conductive adhesive. The faces of the cold plates  28  that come in contact with the LED or LED substrate are made of highly conductive material, such as copper, aluminum, or any other suitable conductive material in the art. The other faces of the cold plate may or may not be made of highly conductive material. 
     Each of the cold plates  28   a - d  includes a cold plate channel  34  defined and passing therethrough and having an inlet  36  and an outlet  38  (see cold plate  28   a ), wherein the outlet  38  is located above the inlet  36 . The radiator  30  includes a radiator channel  40 , also having an inlet  42  and an outlet  44 , wherein the outlet  44  is located below the inlet  42 . The cold plate channel  34  and the radiator channel  40  may include more than one channel joined together by air convection fins within the cold plate and the radiator, respectively. 
     As fluid circulates within the cooling circuit  26 , the fluid inside the cold plate channels  34  warms as heat generated by the LEDs  22  is conducted through the cold plates  28  to the fluid within the channel  34 . Being heated, the fluid is less dense and tends to rise in the circuit  26 . Upon reaching the radiator  30 , the fluid enters the radiator channel  40  and cools as heat from the heated fluid is conducted through the radiator  30  to the surrounding environment. Preferably, the radiator  30  is disposed at or outside of the housing wall  14  and conducts heat from the fluid, and the air within the chamber  16 , to the outside environment, which is at a lower temperature. 
     As the fluid within the cold plate channels  34  is heated, it rises in the circuit  26  due to a reduction in its density. Conversely, as the fluid within the radiator channel  40  cools, it falls in the circuit  26  due to an increase in its density. The rising fluid is propelled through the cold plates  28 , traveling in a partially vertical direction through tubes  32 . For example, the fluid rises within each of the cold plate channels  34 , traveling from each of the cold plate inlets  36  to each of the cold plate outlets  38 . As the fluid inside each cold plate channel  34  rises, it displaces the fluid above into the next sequential tube, i.e., the fluid within the cold plate  28   a  is displaced into the tube  32   a , which displaces fluid into the cold plate  28   b , which displaces fluid into the tube  32   b , which displaces fluid into the cold plate  28   c , which displaces fluid into the tube  32   c  and so on until reaching the radiator  30 . Inside the radiator  30  the fluid cools and falls from the radiator inlet  42  to the radiator outlet  44 . In doing so, it displaces the fluid below into the tube below, i.e., the fluid within the radiator  30  is displaced into the tube  32   e . Thereafter, the fluid travels in a partially vertical direction through the tube  32   e  back to the first of the cold plates  28 , cold plate  28   a.    
     The fluid traveling within the cooling circuit  26  is coolest when traveling from the radiator  30  to the first cold plate  28   a  and warmest when traveling from the last cold plate  28   d  to the radiator  30  through the tube  32   d . Thus, the cold plate  28   a  is cooled first and the cold plate  28   d  is cooled last. 
     The continuous heating and cooling, and resultant gravity assisted rising and falling of the fluid in the partially vertical circuit  26 , are what drives the fluid through the cooling circuit  26 , creating a self-stabilizing, closed-loop cooling system. The movement of the fluid is proportional to the heat generated by the LEDs  22  and transferred through to the fluid. If desired, the cooling circuit  26  may include a pump to increase the flow rate of the fluid circulating within the circuit  26 . 
     As a person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles of this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from spirit of this invention, as defined in the following claims.