Patent Description:
Many different types of heat dissipation devices are known. For example, <CIT> discloses a heat pipe for a light-emitting diode (LED) lighting device. <CIT>discloses a LED optical unit of a vehicle headlight including a heat pipe. <CIT> discloses a vehicle headlamp comprising a light source, heat pipe, and a heat radiating member. <CIT> discloses a LED assembly including a heat-absorbing member in the form of a heat pipe. A plurality of LEDs is directly attached to the heat pipe, each LED being connected by wires to a printed circuit board (PCB). A heat sink is provided having a groove for receiving the heat pipe therein. The PCB has a number of through holes for receiving the LEDs and is mounted directly to the heat pipe close to the heat sink. <CIT> discloses a LED assembly wherein the LEDs are mounted on PCBs which are interconnected via leads. The PCBs are mounted on a cooling base, the cooling base being connected to a folded shaped radiator comprising a heat pipe and a heat radiation. <CIT> discloses a diode lamp having a heat-dissipating module, a LED light module, an optical module, and a control circuit module. The control circuit module is arranged with a distance to the LED light module, which is mounted to one end of a heat-conducting pipe, while the control circuit module is mounted to the other end of the heat-conducting pipe. In CN <NUM><NUM><NUM> B a LED module is mounted to a heat sink via a link block plate, which is connected to the LED module, and a support unit, which is connected to the link block plate.

Other aspects and advantages of the invention will be apparent from the following detailed description of the embodiments and the accompanying drawing figures.

The present invention provides a vehicle lamp heat dissipation system according to claim <NUM>. The vehicle lamp heat dissipation system includes a heat pipe, a heat sink having a slot adapted to receive the heat pipe, and a light-emitting diode (LED) mounted directly to the heat pipe. The heat pipe is disposed in the slot such that heat is transferred from the LED to the heat sink via the heat pipe for effectively cooling the LED.

Also described herein is a passive-cooling illumination system including a heat pipe embedded in a heat sink. The heat sink includes a slot adapted to receive the heat pipe. A light-emitting diode (LED) is mounted directly to a central portion of the heat pipe such that heat from the LED is transferred to the heat sink via the heat pipe for passively cooling the LED in the absence of forced convective air flow.

Also described herein is a passive heat dissipation system for a vehicle lamp including a heat pipe having a substantially rectangular cross section, a light-emitting diode (LED) mounted directly to a central portion of the heat pipe, a heat sink having a substantially rectangular slot adapted to receive the heat pipe such that heat from the LED is transferred to the heat sink via the heat pipe, and a printed circuit board electrically bonded to the LED for electrically and communicatively coupling the LED to a controller for controlling operation of the LED. The printed circuit board is mounted to the heat sink adjacent the heat pipe.

Illustrative embodiments are described in detail below with reference to the attached drawing figures, which are incorporated by reference herein and wherein:.

The drawing figures do not limit the invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention.

The following detailed description references the accompanying drawings that illustrate specific embodiments in which the invention can be practiced. The embodiments are intended to describe aspects of the invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be utilized and changes can be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense. The scope of the invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.

In this description, references to "one embodiment", "an embodiment", or "embodiments" mean that the feature or features being referred to are included in at least one embodiment of the technology. Separate references to "one embodiment," "an embodiment," or "embodiments" in this description do not necessarily refer to the same embodiment and are also not mutually exclusive unless so stated and/or except as will be readily apparent to those skilled in the art from the description. For example, a feature, structure, act, etc. described in one embodiment may also be included in other embodiments, but is not necessarily included. Thus, the technology can include a variety of combinations and/or integrations of the embodiments described herein.

Embodiments disclosed herein provide a heat dissipation system for removing heat from a light-emitting diode (LED) by mounting the LED directly to a heat pipe embedded in a heat sink. Without the use of a fan, embodiments disclosed herein provide heat transfer away from the LED at comparable levels to a traditional heat exchanger in which a fan is used to pull heat from a heat sink. Heat removal is needed to reduce the p-n junction temperature of the LED to prevent overheating and damage to the LED.

<FIG> is a perspective view of an exemplary vehicle lamp heat dissipation system <NUM>. A light-emitting diode (LED) <NUM> is mounted directly on the surface of a heat pipe <NUM> for rapidly dissipating heat produced by LED <NUM>. A heat sink <NUM> is configured for dissipating heat from heat pipe <NUM> to surrounding air via natural convection. A printed circuit board (PCB) <NUM> provides electrical power to LED <NUM>, and PCB <NUM> communicatively couples LED <NUM> to a controller (not shown) via electrical connector <NUM>. A fastener <NUM> is used to mount PCB <NUM> directly to heat sink <NUM>. Fastener <NUM> may be a screw or bolt for example.

<FIG> is a perspective view of heat sink <NUM>. A slot <NUM> is adapted for receiving heat pipe <NUM> of <FIG>. In certain embodiments, heat sink <NUM> is made of aluminum by subtractive manufacturing techniques (e.g., machining). In other words, heat sink <NUM> is extruded from a block of aluminum material. Heat sink <NUM> may include a plurality of vertically aligned fins configured for dissipating heat to ambient air via natural convection. Slot <NUM> is machined into the aluminum block such that heat pipe <NUM> may be disposed in the slot. In embodiments, slot <NUM> is formed into a substantially rectangular or square elongated channel in a top side of heat sink <NUM>.

Referring again to <FIG>, heat pipe <NUM> has been pressed into slot <NUM> with three sides of heat pipe <NUM> in direct contact with inner walls of slot <NUM> and a fourth (e.g., top) side of heat pipe <NUM> being exposed. In embodiments, heat pipe <NUM> is formed from a cylindrical pipe that is subsequently flattened into a more rectangular or square cross-section and bent towards each end to form a U-shape. See also <FIG>. The flattened shape of heat pipe <NUM> provides a substantially flat surface for LED <NUM> to be placed upon for providing thermal contact with the lower surface of LED <NUM>. In certain embodiments, a top surface of heat pipe <NUM> is machined down prior to attaching LED <NUM> to further flatten the surface and to accurately achieve a highly finished surface suitable for placing LED <NUM>. The top surface of heat pipe <NUM> may be machined down before and/or after installation into heat sink <NUM>. Prior to insertion into heat sink <NUM>, any side or portion of heat pipe <NUM> may be machined down to provide a proper fit within slot <NUM> to ensure that heat pipe <NUM> remains wedged in slot <NUM> after being pressed therein. Optionally, a thermal adhesive may be applied within slot <NUM> for securing heat pipe <NUM> thereto.

Internally, heat pipe <NUM> may include radially-extending finger elements adapted for wicking fluid. The fluid, in embodiments, is water. Alternatively, the fluid may be an aqueous solution containing mostly water mixed with another solvent (e.g., alcohol). Heat pipe <NUM> includes a first end <NUM> and a second end <NUM> opposite first end <NUM>.

In operation, heat pipe <NUM> functions generally by absorbing heat from a heat source adjacent a portion of heat pipe <NUM>. In portions of heat pipe <NUM> located close to the heat source the fluid evaporates, whereas distal portions of heat pipe <NUM> that are further from the heat source remain cooler allowing the fluid to condense to a liquid. The condensed fluid may then be returned towards the heat source by gravity, capillary action, or some other means (e.g., centrifugal force). As the fluid changes phase from liquid to gas, the latent heat transfer removes a much larger amount of heat from LED <NUM> compared to conduction alone. The result is a substantially increased effective heat flux away from LED <NUM>.

Specifically, heat pipe <NUM> is heated by LED <NUM> such that fluid evaporates locally from a portion of heat pipe <NUM> nearby LED <NUM>. Along distal portions of heat pipe <NUM> where the temperature is cooler, for example towards first end <NUM> and second end <NUM> (see <FIG>), the evaporated fluid condenses. The condensed fluid returns toward the center of heat pipe <NUM> via capillary action (e.g., wicking) along internal radially-extending finger elements and towards the region near LED <NUM>. The internal radially-extending finger elements act as wicks that help distribute liquid from a cooler portion of heat pipe <NUM> to a warmer portion. A thickness of the internal radially-extending finger elements is based upon a width of heat pipe <NUM>. The process continually repeats to remove heat from LED <NUM> and transport it to heat sink <NUM>, which transfers the heat to surrounding air via natural convection (e.g., or optionally via forced convection by using a fan).

Heat pipe <NUM> effectively increases the heat flux compared to using heat sink <NUM> alone by more than an order of magnitude. In certain embodiments, heat sink <NUM> provides a heat flux of approximately <NUM> W/mm<NUM>, whereas heat pipe <NUM> coupled with heat sink <NUM> increases the heat flux to approximately <NUM> W/mm<NUM>, providing a <NUM>-fold increase. The increased heat flux is due to the effective increase in thermal conductivity of heat pipe <NUM>. In certain embodiments, the thermal conductivity of heat pipe <NUM> is approximately <NUM>,<NUM> W/m-K compared to only about <NUM> W/m-K for aluminum.

A thermal adhesive having a thin bond line may be used to secure LED <NUM> to the surface of heat pipe <NUM> such that thermal resistance between LED <NUM> and heat pipe <NUM> is negligible. By mounting LED <NUM> directly to heat pipe <NUM>, thermal resistance between LED <NUM> and heatsink <NUM> is minimized. The effect of using heat pipe <NUM> is to increase the effective surface area for dissipating heat from LED <NUM>. In certain embodiments, the effective surface area of LED <NUM>, in terms of heat dissipation, is increased from about <NUM><NUM> to about <NUM><NUM>.

<FIG> is a close-up perspective view showing a portion of vehicle lamp heat dissipation system <NUM> of <FIG>. LED <NUM> is electrically coupled to PCB <NUM> via first ribbon bond <NUM> and a second ribbon bond <NUM>. First and second ribbon bonds <NUM>, <NUM> are for example wedge bonds in which flat metal wires are bonded at each end to LED <NUM> and PCB <NUM>, respectively, using ultrasonic energy and/or heat. The ribbon bonds <NUM>, <NUM> may be applied via a robotic arm using an automated process.

Traditionally, LEDs are mounted directly to a PCB and electrically bonded thereto (e.g., using wire bonds). In contrast, LED <NUM> is located off of PCB <NUM> which enables it to be thermally connected directly with heat pipe <NUM> for conduction of heat away from LED <NUM>. With this configuration, heat transfer away from LED <NUM> is accomplished directly via heat pipe <NUM> rather than having indirect heat transfer via PCB <NUM>. Because the thermal mass of LED <NUM> is much smaller than that of PCB <NUM>, this greatly reduces the heat transfer requirement for cooling LED <NUM> to acceptable temperatures.

PCB <NUM> is mounted directly to heat sink <NUM> (e.g., via fastener <NUM> into a threaded hole in heat sink <NUM>). This provides a secure mechanical connection for supporting PCB <NUM> and also provides heat transfer via conduction away from PCB <NUM> to heat sink <NUM>. In certain embodiments (see e.g., <FIG>, <FIG>, and <FIG>), PCB <NUM> includes an extension <NUM> for thermally coupling a PCB-mounted temperature sensor directly with heat pipe <NUM>. In embodiments, extension <NUM> makes direct thermal contact with heat pipe <NUM> immediately adjacent LED <NUM> as shown in <FIG>, <FIG>, and <FIG>, such that the PCB-mounted temperature sensor makes direct thermal contact with heat pipe <NUM> nearby LED <NUM>. This enables a more accurate temperature measurement for LED <NUM> compared to having a temperature sensor located on the main portion of PCB <NUM> since the PCB-mounted temperature sensor is in direct thermal contact with heat pipe <NUM> adjacent LED <NUM>.

In certain embodiments, LED <NUM> includes a plurality of LEDs. For example, LED <NUM> may include an array or matrix of LEDs that are each independently ribbon bonded to PCB <NUM>.

<FIG> and <FIG> provide perspective views from opposite directions of an exemplary projector module <NUM> configured for projecting light from a vehicle. <FIG> shows a top-down view of projector module <NUM>, which is attached (e.g., via bolts) directly to heat sink <NUM> of heat dissipation system <NUM> and is configured to project light emitted from LED <NUM>. <FIG>, <FIG>, and <FIG> show the heat dissipation system <NUM> with the components of the projector module <NUM> removed from the viewpoints of <FIG>, <FIG>, and <FIG>, respectively. <FIG> are best viewed together with the following description.

A reflector <NUM> is configured to reflect light from LED <NUM> towards an outer lens <NUM>. Specifically, LED <NUM> emits light generally upwards (e.g., in the vertical direction along the Z-axis depicted in the figures), and reflector <NUM> redirects the light in a generally horizontally direction (e.g., in the longitudinal direction along the X-axis depicted in the figures).

Outer lens <NUM> is mechanically coupled with a lens holder <NUM>, which is configured to provide structural support for securing outer lens <NUM> and for enclosing a light path between reflector <NUM> and outer lens <NUM>. Outer lens <NUM> is formed of a transparent material and configured to shape light emitted from projector module <NUM>. For example, outer lens <NUM> may be configured to condense light and flip the projected image upside down.

Projector module <NUM> of <FIG>, <FIG>, and <FIG> is configured as an automotive vehicle headlamp; however, heat dissipation system <NUM> is not limited to use in a vehicle headlamp, and other types of vehicle and non-vehicle lighting assemblies that use one or more LEDs as their light source may benefit from system <NUM>. For example, system <NUM> may be incorporated into a taillight assembly without departing from the scope hereof.

While heat dissipation system <NUM> obviates the need for a fan in projector module <NUM>, a fan could be used in conjunction with system <NUM> in other embodiments having higher heat removal requirements.

<FIG> is a perspective view of an exemplary heat pipe <NUM> configured for use in heat dissipation system <NUM> of <FIG>. In the embodiment depicted in <FIG>, heat pipe <NUM> has been flattened from a tube having a circular cross-section to a tube having a substantially rectangular cross-section with rounded corners. Along a longitudinal direction, heat pipe <NUM> has been bent to form a first corner <NUM> and a second corner <NUM>, such that first end <NUM> and second end <NUM> both extend transversely in the same direction from a central portion <NUM>. In other words, heat pipe <NUM> has two bends along its longitudinal axis with both ends pointed generally towards one side of heat pipe <NUM> thereby forming a U-shape. The U-shaped heat pipe <NUM> is adapted for fitting into slot <NUM> of heat sink <NUM> (see e.g., <FIG> and <FIG>). In embodiments, the first and second ends <NUM>, <NUM> extend perpendicular to the central portion <NUM>.

<FIG> also includes a contour plot illustrating a temperature gradient along a surface of heat pipe <NUM> to show how heat spreads from central portion <NUM> towards first and second ends <NUM>, <NUM>. A legend <NUM> shows a temperature range in degrees Celsius along the external top surface of the solid material of heat pipe <NUM>. Heat pipe <NUM> is heated by LED <NUM> along central portion <NUM>, as illustrated in <FIG>, such that central portion <NUM> has a high temperature and first and second ends <NUM>, <NUM> have a substantially cooler temperature. Internally, as the temperature inside heat pipe <NUM> approaches the phase transition temperature of the working fluid (e.g., <NUM> for water), fluid adjacent central portion <NUM> evaporates. As the fluid vapor diffuses towards distal portions of heat pipe <NUM> where the temperature is cooler, for example along the transversely extending arms past first and second corners <NUM>, <NUM>, the evaporated fluid condenses. The condensed fluid then returns toward central portion <NUM> via capillary action (e.g., wicking), as described above, enabling the cycle to be repeated.

<FIG> is a perspective view of an exemplary heat sink <NUM> and heat pipe <NUM> configured for use in heat dissipation system <NUM> of <FIG>. <FIG> is a contour plot illustrating a temperature gradient of heat sink <NUM> as heat from heat pipe <NUM> conducts to heat sink <NUM> and is dissipated to the surrounding air. Legend <NUM> shows a temperature range corresponding to the contour plot in degrees Celsius. <FIG> shows how heat sink <NUM> is heated by heat pipe <NUM> and how the heat distributes to the fins for transferring to surrounding air via radiation and convection (e.g., via natural convection without a fan). Distal portions of the fins maintain a colder temperature compared to areas of heat sink <NUM> that are proximate to heat pipe <NUM>. This temperature gradient drives heat transfer from the proximate regions to the distal regions via conduction through the aluminum material of heat sink <NUM>.

Use of heat dissipation system <NUM> enables an efficient and relatively high heat flux that eliminates the need for an actively cooled system, which greatly reduces manufacturing and maintenance costs. Advantages provided by system <NUM> include that it is provides a passively cooled illumination system, meaning that forced convective air flow is not used to provide active heat removal. Instead, natural convection (i.e., gravity-driven motion of less dense hot air rising and more dense cold air sinking) transfers heat to the surrounding ambient air. Without providing forced convection, neither a fan nor external air flow from a moving vehicle is needed. This makes the system operable while a vehicle is stationary and more reliable and less likely to require maintenance (e.g., when the fan motor needs replacing) due to lack of a fan.

Claim 1:
A vehicle lamp heat dissipation system (<NUM>) comprising:
a heat pipe (<NUM>);
a heat sink (<NUM>) having a slot (<NUM>) adapted to receive the heat pipe; and
a light-emitting diode (LED) (<NUM>) mounted directly to the heat pipe, wherein the heat pipe is disposed in the slot such that heat is transferred from the LED to the heat sink via the heat pipe for effectively cooling the LED;
wherein the heat pipe comprises a first end (<NUM>) and a second end (<NUM>), characterized in that the heat pipe is bent in two locations along a longitudinal axis such that the first end and the second end extend in a transverse direction perpendicular to the longitudinal axis thereby forming a U-shape; and
wherein the LED is located inside of a projector module (<NUM>) and the first end and the second end of the heat pipe extend in the transverse direction away from the projector module for transferring heat away from the projector module; and further comprising:
a printed circuit board (PCB) (<NUM>) located off of the LED (<NUM>) and mounted directly to the heat sink (<NUM>) outside of and adjacent to the heat pipe (<NUM>),
wherein the LED is electrically bonded to the printed circuit board, the printed circuit board (<NUM>) being mounted to the heat sink (<NUM>) adjacent the slot (<NUM>); and
a first ribbon bond (<NUM>) electrically coupling the LED to the printed circuit board and a second ribbon bond (<NUM>) electrically coupling the LED to the printed circuit board.