Patent Application
20140071707
1. Technical Field
The technical field relates generally vehicle lighting temperature control and more particularly to temperature control of light emitting diode based lamps.
2. Description of the Technical Field
Light emitting diodes (LED) are a type of semi-conductor device which emits light when electricity flows through them. LED efficiency in terms of conversion of power to light in the visible spectrum decreases with increasing temperature, with the decrease in efficiency accelerating dramatically when temperature increases above a particular threshold temperature. At the same time heat generation tends to increase. Removing heat from LEDs increasingly important at high power level operation of LEDs to keep operating temperature below the threshold.
LED temperature has been controlled using many of the same techniques used to control semi-conductor device temperature. These techniques generally rely on increasingly heavy heat sinks and more complex heat transfer systems as the amount of heat to be removed increases. A basic heat sink for an LED may provide a heat conducting metal substrate on which the LED is mounted. The metal substrate provides an increased area from heat is radiated to the environment. The metal substrate may be cast with heat radiating fins to increase its radiating area. If fins alone are insufficient to reject the heat produced by an LED a temperature actuated fan may be employed to force air across the fins. Improved transmission of heat from an LED to the heat sink may be achieved by circulation of a liquid between the LED and the heat sink. Such an LED package includes a built in finned radiator, circulation paths for the liquid coolant and electronics to detect temperature and to drive circulation of air and possibly coolant. Each gradation of heat removal adds to the expense and to the power consumption of the device. Such heat sinks tend to become increasingly heavy which is a consideration in motor vehicle applications.
A temperature control system for a light emitting diode assembly and associated comprises a circuit board for supporting one or more light emitting diodes and a housing supporting the circuit board. A coolant circulation path is routed through the housing. The coolant circulation path is provided with connectors for connection to an external source of a substantially constant temperature, circulating coolant. The coolant is maintained at a constant temperature by an internal combustion engine and an associated radiator.
In the following detailed description, like reference numerals and characters may be used to designate identical, corresponding, or similar components in differing drawing figures.
Referring now to the figures and in particular to
Control over the coolant circulation system 11 resides in an engine control unit (ECU) 24 which, responsive to sensed coolant temperature from temperature sensor 15 can activate or deactivate a fan 28 positioned to force air through radiator 12. Variance of coolant temperature above the limit T results in fan 28 being turned on. Coolant temperature below T less an offset results in the fan being turned off if it is already on. After a warm up period radiator 12 usually operates in a constant temperature range.
ECU 24 communicates with an electrical system controller (ESC) 26 which in turn provides control signals for turning exterior lamp 10 on and off and which is connected to receive temperature measurements from lamp 10 from a temperature sensor 13. In some applications ESC 26 can control the amount of power delivered to lamp 10. ESC 26 can reduce the amount of power delivered to lamp 10, or turn lamp 10 off, in response to measured temperature from temperature sensor 13 exceeding a maximum limit.
Lamp 10 includes a light emitting diode (LED) assembly 30 which is shown in
Reference to the liquid circulated through lamp 10 as “coolant” is conventional terminology for the water/alcohol mix used in engine cooling systems, however, the coolant can serve to transport heat either to or from LED assembly 30. For example, coolant serves to transport heat from radiator 12 to lamp 10 when the LED's 36 are off. This allows for conduction of heat to the exterior surface 17 which can keep the surface warmed and prevent ice and snow buildup on the exterior surface under cold weather conditions.
Referring to
As illustrated in the partially exploded view of
When IC engine 20 is on and engine coolant has reached in normal operating range, circulation of the coolant through lamp 10 keeps the lamp 10 and LED assembly 30 in a temperature range with an upper limit, but warm enough to prevent ice and snow accumulation even when the LED's 36 are not energized. No convection heating of the exterior surface 17 need be provided and the LED's 36 do not need to be turned on to keep ice and snow off the lamp 10. The close proximity of the LED's 36 should keep the temperature of LED's 36 close to the coolant temperature under most conditions.
