Aircraft light

An aircraft light consists of a housing containing a light source, a heat sink element forming at least part of the exterior surface of the housing and an auxiliary thermal capacitor that is thermally decoupled from the heat sink element. A thermally expandable medium is coupled to the heat sink element and operates to thermally decouple the light source from the heat sink element and thermally couple the light source to the auxiliary thermal capacitor and vice versa, depending on the actual temperature of the heat sink element.

BACKGROUND OF THE INVENTION

The present invention relates to an aircraft light which can withstand temporary extreme thermal peak loads.

DESCRIPTION OF THE PRIOR ART

Typically, an aircraft light comprises a housing and at least one light source located within the housing for emitting light. High intensity light sources can be rather sensitive to thermal loads so that heat generated upon operation of the light sources has to be dissipated. To this end, an aircraft light typically comprises a heat sink element for cooling the at least one light source. Part of the heat sink element forms at least a portion of the outer side of the housing which is exposed to the environment around the light in order to dissipate heat into this environment.

This type of cooling concept is designed for cases in which the environment around the heat sink element can still receive thermal energy dissipated from the heat sink element. However, if the environment around the heat sink element for whatever reasons is overheated, the heat sink element cannot be used to transfer heat from the heat sink element to the environment. Depending on the time period for which these conditions last, this can result in a thermal distortion of the light sources.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to overcome the above-identified disadvantages and to design an aircraft light in which also in temporary extreme thermal environmental conditions the at least one light source can be sufficiently cooled in order to prevent a distortion or degradation of the at least one light source.

To this end, the present invention provides an aircraft light comprising

a housing having an outer side,

at least one light source located within the housing for emitting light,

a heat sink element for cooling the at least one light source, wherein at least a portion of the heat sink element forms at least a portion of the outer side of the housing,

an auxiliary thermal capacitor for receiving thermal energy from the at least one light source, wherein the auxiliary thermal capacitor is thermally decoupled from the heat sink element, and

actuator means thermally coupled to the heat sink element and operable to thermally decouple the at least one light source from the heat sink element and thermally couple the at least one light source to the auxiliary thermal capacitor and vice versa, depending on the actual temperature of the heat sink element becoming higher or lower than a threshold value,

wherein the actuator means comprises a volume of a thermally expandable medium for displacing the at least one light source out of thermal coupling to the heat sink element and towards thermal coupling to the auxiliary thermal capacitor.

The present invention solves the above-identified issue by thermally decoupling the at least one light source from the heat sink element during the time of an external extreme thermal energy input to the heat sink element. Thermal decoupling is performed with the aid of an actuator means which is thermally operated automatically in order to displace the at least one light source out of thermal coupling to the heat sink element and into thermal coupling to an internal auxiliary thermal capacitor for receiving thermal energy from the at least one light source. The auxiliary thermal capacitor is thermally decoupled from the heat sink element. The actuator means comprises a volume of a thermally expandable medium for displacing the at least one light source out of thermal coupling to the heat sink element and towards thermal coupling to the auxiliary thermal capacitor and vice versa, depending on the actual temperature of the heat sink element becoming higher or lower than a threshold value. Accordingly, during the period of time in which the at least one light source is thermally decoupled from the heat sink element, the self-induced thermal energy from the at least one light source is buffered in the auxiliary internal thermal capacitor until the housing and, in particular, the heat sink element forming at least a part of the outer side of the housing, is cooled off again. At this time the thermally expandable medium no longer is expanded so that the at least one light source again becomes thermally decoupled from the auxiliary thermal capacitor and thermally coupled to the heat sink element. Also a discharge of the thermal capacitor to the housing (and, if necessary, the heat sink element) takes place again so that the auxiliary thermal capacitor is ready again for receiving thermal energy from the at least one light source in case that the heat sink element is exposed to external thermal energy inputs.

The structure according to the invention can also be described as a smart thermal switch that couples and decouples the at least one temperature-sensitive light source in the manner of a dual clutch. If the exterior housing and exterior heat sink element portion get too hot, the energy path from the at least one light source is decoupled from the heat sink element and coupled to the inner thermal capacitor. This process is reversible and occurs once the exterior housing or heat sink element portion is cooling off again.

However, what is not known from the prior art is thermally decoupling a thermal heat generating element from its associated heat sink element if the same itself is exposed to external thermal energy inputs, and thermally coupling the heat generating element to an auxiliary thermal capacitor thermally decoupled from the heat sink element.

In one aspect of the present invention, the thermally expandable medium can be a wax and/or can be encompassed by an elastic enclosure. The elastic enclosure can further be fixed to the at least one light source or an intermediate element to which the at least one light source is mounted. In this embodiment, the light source is moved back and forth depending on the actual degree of expansion of the thermally expandable medium.

In another embodiment of the present invention the thermally expandable medium is in mechanical contact with the at least one light source or an intermediate element to which the at least one light source is mounted, wherein the actuator means comprises a resilient element for displacing the at least one light source for thermally decoupling it from the auxiliary thermal capacitor and for thermally coupling it with the heat sink element. The resilient element can be a spring element or the like elastically deformable element.

According to a further aspect of the present invention, the heat sink element comprises a contact side for thermally contacting the at least one light source or an intermediate element to which the at least one light source is mounted, wherein the contact side of the heat sink element comprises a recess accommodating the thermally expandable medium.

Finally, in a further embodiment according to the invention, a plurality of light sources are provided and mounted to a support element acting as an intermediate element for transmitting heat energy from the light sources to the heat sink element as long as in thermal contact with the same or from the light sources to the auxiliary thermal capacitor as long as in thermal contact therewith.

DESCRIPTION ON A PREFERRED EMBODIMENT

FIG. 1shows the tail portion of an aircraft10comprising an auxiliary power unit (APU)12having an outlet14located at the tail end16of the aircraft10. In the vicinity of the APU outlet14, there is arranged an external aircraft light18used as tail light in this embodiment. The aircraft light18comprises a housing20formed at least in part by a portion22of a heat sink element24and a transparent cover26. The aircraft light18is shown in more detail in the cross-sectional views ofFIGS. 1 and 2.

The portion22of the heat sink element24exposed to the environment around the aircraft light18is used to dissipate thermal energy from the heat sink element24to the environment. However, if the heat sink element is exposed to external thermal inputs, unfortunately it can no longer serve as a heat dissipating element. This can happen e.g. if the exhaust gas of the APU12due to the actual wind conditions are directed (back) towards the heat sink element portion22. Also in this condition, the light sources of the aircraft light18have to be effectively cooled to avoid degradation or in the extreme case distortion.

The construction of the aircraft light18is shown in more detail inFIGS. 2 and 3. The heat sink element24comprises the portion22as well as another portion28as shown inFIGS. 1 and 2. This other plate-like portion28which also can have other geometric configurations, is provided with at least one recess30(in this embodiment there are two recesses30) filled by a thermally expandable medium32which e.g. can be a wax. The thermally expandable medium32is included in an elastic envelope or enclosure33.

Arranged within the housing20of the aircraft light18is an auxiliary thermal capacitor34which is thermally decoupled from the heat sink element24. To this end, the auxiliary thermal capacitor34is located spaced apart from the heat sink element24so that a gap exists between both which can be filled by an insulator36.

Finally, the aircraft light18also comprises at least one light source38, which in this embodiment can be formed by an LED. In this embodiment according toFIGS. 2 and 3, a plurality of light sources38, i.e. a plurality of LEDs is provided. These light sources38are mounted to a common support40which in this embodiment is designed as a printed circuit board layer. The support40under normal thermal conditions is in contact with the heat sink element portion28so that the light sources38are thermally coupled to the heat sink element24.

FIG. 2shows the operational situation of the aircraft light18under normal thermal conditions in which the heat sink element24is used to dissipate thermal energy from the light sources38via the heat sink element portion22to the environment (see heat flow arrows42inFIG. 2). The support40of the light sources38is in thermal (and mechanical) contact with the heat sink element24as shown inFIG. 2. The support40can be regarded as an intermediate element41for thermally coupling the light sources38to the heat sink element24(and, if necessary, to the thermal capacitor34). A resilient element44(spring or the like) is used so as to push the support40against the heat sink element portion22.

FIG. 3shows the situation in which the heat sink element portion22is exposed to an external thermal energy input (see the heat flow arrows46inFIG. 3). Due to the external heat energy input, the heat sink element24is heated up to an extent beyond a threshold value beyond which the support40is displaced from the heat sink element24towards thermal contact with the auxiliary thermal capacitor34. This is performed with the aid of the heat expandable medium32which under the influence of the increased temperatures expands and thereby pushes the support40against the spring biasing force of the resilient element44into thermal contact with the auxiliary thermal capacitor34. Now the self-induced heat energy of the light sources38is received by the auxiliary thermal capacitor34, resulting in a cooling effect to the light sources38.

After a certain period of time when the external heat energy input does no longer exist, the heat sink element24cools off and the expandable medium32contracts so that the support40is urged again against the heat sink element24by means of the resilient element44. Accordingly, in this condition the situation as shown inFIG. 2applies.

The volume of the thermally expandable medium32(with or without the elastic envelope or enclosure33) described above can be regarded as a thermal actuator means acting as a thermal switch for thermally coupling and decoupling the light sources28in a dual clutch way.

Although the invention has been described and illustrated with reference to specific illustrative embodiments thereof, it is not intended that the invention be limited to those illustrative embodiments. Those skilled in the art will recognize that variations and modifications can be made without departing from the true scope of the invention as defined by the claims that follow. For example, the aircraft light typically can be provided with a unit connector which is not shown in detail in the above-mentioned Figures. Also, in these Figures the wiring is not shown in detail. Finally, in this embodiment the use of the aircraft light as a tail light is described. It is self-explanatory that also other applications of the aircraft light (both external and internal) are possible. It is also clear that there are a plurality of embodiments in which the principles of the invention can be used in that all of them can use the thermal actuator as described above in which a volumetric extension of a thermally expandable material within the actuator leads to a relative movement of a component to be cooled out of thermal coupling to an external heat sink element and into thermal coupling to an inner auxiliary thermal capacitor. The actuator is thermally coupled to the exterior heat sink element. A robust approach for using the invention in an aircraft light is described above in connection with the Figures because in this embodiment the masses and movements are reduced to a relatively small amount and configuration.