Cooling of LED headlamp in automotive by heat pipes

Trends in automotive headlamps are changing from halogen/xeon towards light emitting diode (LED) type light functions. LEDs have 2 times higher light efficiency, longer illumination distance, 10-15 times longer lifetime and better styling features than halogen lamps. Unlike halogens, LEDs need temperature control to maintain their monochromaticity, light intensity and longevity. A typical LED headlamp can dissipate 25 to 70 W heat load depending on light functions and styling features. Traditionally, aluminum die cast heat sinks are used as cooling solution for LEDs, which are thermally low efficient and structurally heavy and space intensive. In the present investigation, heat pipe based cooling systems for different designs and styles of LED headlamps and thermal capability of up to 20 W/per-module have been proposed, designed and characterized. Heat pipe configurations include 6-8 mm diameter, 200-400 mm length, copper wick/container and water as working fluid. In combination with different heat sink designs and cooling options, heat pipes can provide 2 to 3 times higher heat capability and up to 50% lighter cooling module, as compared to die cast heat sinks. Based on requirements from headlamp manufacturers, different innovative designs of heat pipes, including high-performance cylindrical/flattened copper-water heat pipe for low/high beam cooling, hinge heat pipe for adaptive headlamp with swivel function cooling and flexible heat pipe for remotely mounted heat sink, has been developed. Heat pipes due to their ultra-high thermal conductivity (similar to 5000 W/m.K or higher) can drastically improve heat dissipation capability of heat sink (natural or fan cooled) and allow different heat sink design options (chassis/frame type, die cast type, stacked-thin-fin type). This allows for better space utilizations inside headlamps, possibility of fully passively cooled headlamps and shared heat sinks between different light functions. LED headlamp with heat pipe thermal modules will tend to be cooler, lightweight and compact.