Optically-coated dual-filament bulb for single compartment headlamp

#The present invention generally is related to automotive lighting, and more particularly is related to headlamps employing a single compartment or housing for both high and low beam filaments.

#In a conventional halogen bulb, approximately less than 20 percent of the energy output is radiated as visible light. The remaining approximately greater than 80 percent is radiated as infrared light. Since the purpose of a halogen bulb in a vehicle headlamp application is to illuminate the roadway, the infrared radiation is substantially wasted energy. Hence, such bulb designs are generally considered to be relatively inefficient light providers.

#Reflective infrared (hereafter RIR) bulbs are known which employ multi-layer dichroic coatings on the outer surface of the bulb. The dichroic coatings generally are adapted to pass wavelengths of visible light and to reflect back wavelengths of infrared light. The structure of the filament and bulb enclosure is such that reflected infrared light is relatively well focused upon the filament along substantially its entire length. Such arrangement provides for filament heating resulting in a more efficient bulb. This all translates into more visible light output for a given power consumption or less power consumption at a given light output. Such designs may be acceptable for relatively long filaments since end losses are a relatively small fraction of the total infrared radiation.

#The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

#FIG. 1 is a view of an axial twin-filament RIR bulb assembly in accord with the present invention;

#FIG. 2 is a side view of the axial twin-filament RIR bulb assembly in accord with the present invention;

#Referring to FIG. 1, a preferred embodiment of an RIR bulb assembly generally designated by the numeral 10 in accord with the present invention is illustrated in an intended application as the illumination source of a single compartment headlamp. A complementary headlamp enclosure 11 including reflective surfaces is illustrated in broken lines. An exemplary bulb mounting provision is also illustrated and comprises a base 13 carrying three terminals. The terminals in the present embodiment are designated 15, 17, and 19 and correspond, respectively to a common ground lead, a high beam lead and a low beam lead for the bulb and interfaced vehicle harness (not shown).

#With reference now to FIGS. 1 through 5 wherein like numerals used between the various views correspond to like features, a preferred embodiment of the invention is portrayed. An RIR bulb assembly 10 is generally defined along a major longitudinal axis. A pair of filaments 21 and 23 are substantially aligned or coextensive with the axis. Functionally, filament 21 corresponds to high beam illumination while filament 23 corresponds to low beam illumination. The filaments 21 and 23 are preferably formed of tungsten. The filaments are further characterized by spaced adjacency with respect to their cooperative placement along the axis. That is to say, the high beam filament 21 and low beam filament 23 are separated by a distance along the common longitudinal axis. The filaments are electrically coupled at respective adjacent opposing ends 21A and 23A by conductor 25. The conductor 25 is common in the physical sense that it joins the two filaments and in the electrical sense that it provides an electrical ground node for both filaments. Conductor 25 is further electrically coupled to ground conductor 27 comprising, in the preferred structure, a first portion formed as an internal bulb lead 29 directly coupled at one end to conductor 25 and at the other end to a second portion formed as a foil strip 31 for example from molybdenum. The foil strip 31 is also coupled, opposite the internal bulb lead coupling, to a third portion formed as an externalizing lead 33. The first portion 29 of the ground conductor is importantly located significantly off-axis with respect to the longitudinal axis.

#Each of the high beam filament 21 and low beam filament 23 has a power conductor, 35 and 37 respectively, coupled to corresponding non-adjacent opposing ends 21B and 23B respectively. In the preferred structure, respective first portions formed as internal bulb leads 39 and 45 directly couples at one end to the non-adjacent opposing ends 21B and 23B and at the other end to a respective second portion formed as a foil strip 41 and 47 for example from molybdenum. Each foil strip 41 and 47 is also coupled, opposite the respective internal bulb lead coupling, to a third portion formed as an externalizing leads 43 and 49. All conductors are preferably formed from molybdenum.