Headlamp assemblies have, since the inception of the automobile and the adoption of lighting on bicycles and motorcycles, been ancillary devices designed to provide functional forward lighting as well as required lighted and non-lighted signaling and positioning functions, and fulfilling vehicular styling considerations.
At the dawn of the automotive age, carriage lamps were incorporated onto vehicle design. These were followed by electrically-powered lighting systems.
Irrespective of the type of illumination source and lamp construction methodology, headlamps have and remain ancillary elements mechanically attached to the vehicle architecture and usually primarily serving the lighting and illumination functions, with secondary considerations, such as environmental, safety, aerodynamic, and other functional considerations addressed where applicable.
During the late 1960's, primarily in Western Europe marketplace, automotive companies sought to incorporate more styling freedom onto headlamp design, thus shifting away from standardized lighting devices to vehicle-specific designs. To this point headlamps were generally external devices aimed and adjusted via external mechanical means.
The quest to better integrate the headlamp onto the vehicle's overall shape led to the development of headlamp designs having encapsulated reflector assemblies and internal adjustment devices. In so doing, the outer headlamp lens, now fixed in a specific position, could thus be better integrated onto the overall vehicle design with the aiming/adjustment function fitted within an overall headlamp enclosure.
While such design originally incorporated mainly metal construction, the quest for increased design and fitment flexibility led to the development of injection molded plastic headlamp housings. Modern headlamp designs essentially follow this practice with plastic headlamp housings, featuring lighting components packaged within, or attached to, the headlamp enclosure being the norm.
Contemporary styling, aerodynamic and safety regulatory requirements, along with newly developed technologies such as LED forward lighting, continue to increase the complexity, and oftentimes the size, of headlamps. As the headlamp size, positioning on the vehicle and overall geometry grows in complexity, the headlamp attachment support structure experiences a concomitant level of complexity, cost and weight impact.
Plastic materials, whether natural, alloyed or reinforced (e.g., fiber-reinforced plastic) do not usually exhibit the type of long term durability required to be used as structural components, and have thus proved impractical for such applications. Multi-material approaches, such as insert-molding of reinforced metal components, composite construction method and the like can alleviate such deficiencies, yet invariably drive up the cost of the items in question.
Another primary consideration regards the established design hierarchy within the automotive industry, whereby lighting components are designed as separate entities from the vehicle's primary structure. As such, lighting suppliers routinely have only limited involvement with vehicle structural considerations, save for safety and other functional considerations that directly affect a particular vehicular application.
Yet another consideration is the rapidly escalating cost of vehicle headlamp assemblies. The cost of such assemblies has been increasing so rapidly that a replacement pair of luxury vehicle headlamp replacement fixtures can now cost more than the purchase of a new economy automobile. Consequently, the reparability and reusability of components has become an important design consideration.
United States Published Patent Application No. US 2002/0015310, published Feb. 7, 2002, discloses a vehicle's front-end structural support featuring integral headlamps. The integration of the headlamp housing onto the front-end structural support (front-end module) provides a substantive reduction in the overall volume and cost, and yielded increased usable space within the front/engine compartment of the vehicle. The headlamps are integrated onto a single molding encompassing an overall structural component. Yet, the headlamp housings themselves are not structural in nature. Instead, they are simply integrated onto a metal/plastic matrix structural element.
Thixoformed magnesium support bracket structures, which locate and support the headlamp, fairings, instrument cluster and mirror assemblies, are also known in the art for use with motorcycles, for example, the Buell Motorcycle Company.
A still further complicating factor of modern headlamp applications is the increasing use of LED lighting. LEDs, unlike more conventional light sources such as tungsten, halogen or HID light sources, emit essentially no infrared radiation and are, therefore, “cold” on their optical output side. Nevertheless, LEDs do generate heat at their electrical junction, the so-called “back side,” of the LED proper. This is particularly significant as the drive current increases in order to achieve greater LED optical output. Control of this thermal output, referred to as “junction temperature,” is critical so as to ensure proper operating performance of the LED and avoid either premature degradation or failure.
With the “back side” of the LEDs being housed within the lamp housing, which housing is conventionally made primarily of plastic, the heat generated is “trapped” within the housing. This thermal output on the “back side” of LEDs must be removed in order to prevent overheating and, relatedly, premature failure of the LED lamp. Accordingly, LEDs do require cooling via the introduction of heat sinks.
Conventionally, it is the practice to place such heat sinks within the housing of the LED lamp, where the LEDs themselves are housed. For instance, the head and tail-lamps for the CADILLAC CTS brand automobile utilize a single, high-power LED and a die-cast heat sink that dissipates heat within the housing of the lamp. Given that there is, for these particular applications, a sufficient amount of interior volume in which to dissipate this energy, such heat sinks serve their purpose. However, either for smaller volumes or applications generating additional thermal output, adequate dissipation of heat internally is complicated, thereby forcing the adoption of more elaborate thermal management solutions, such as exposing the heat sink to the outside of the housing or utilizing “heat pipes” (liquid filled thermal conductors) or cooling fans to circulate air within the lamp housing.
Still another solution, disclosed in United States Patent Application Pub. No. US 2007/0127252 A1 to Fallahi et al., published Jun. 7, 2007, comprises an LED headlamp assembly for a motor vehicle having a plastic lens and a plastic lamp housing cooperating with the lens to define an inner chamber that is generally fluidly isolated from the atmosphere. An injection molded metal reflector is mounted to the lamp housing and has a polished reflective portion that reflects light forward through the lens. A separate heat sink portion of the reflector includes fins that extend through the lamp housing and are exposed to the atmosphere outside the lamp housing, such that heat from the inner chamber is transmitted from the fins to the atmosphere.
The foregoing thermal management solutions notwithstanding, it is desirable to have a lamp assembly, for automotive as well as other applications, that is able to effectively dissipate heat energy generated by LEDs or other light sources.