Patent Publication Number: US-6659829-B2

Title: Single-ended halogen lamp with IR coating and method of making the same

Description:
TECHNICAL FIELD 
     This invention relates to halogen lamps of the type that are used in vehicle headlights and to manufacturing methods for making such lamps. 
     BACKGROUND OF THE INVENTION 
     Halogen filament lamps generally comprise tubular vitreous envelopes enclosing a filament which is surrounded by an inert halogen gas. Such lamps are used in headlight systems for vehicles and have replaced traditional incandescent lamps which have lower light output with a higher energy consumption. Halogen incandescent lamps generally utilize a tungsten filament which is supported and connected to electrical lead wires which supply the filament with current and cause the filament to produce incandescent light. The presence of a halogen gas within the vitreous envelope allows for the recycling of the tungsten atoms which are released into the surrounding volume as the filament is heated to increase the life of a lamp. 
     A more recent development for increasing the efficiency of such halogen lamps has been to include a coating or filter which transmits visible light radiation but reflects infrared radiation back to the filament thereby decreasing the amount of electrical power used by the lamp without a significant decrease in the amount of visible light output. Such coatings or filters are known in the art and maybe found for example in U.S. Pat. Nos. 4,663,557 and 4,701,663. 
     When such infrared reflective coatings are utilized, it is necessary that the filament be centered or aligned along the optical axis of the vitreous tube for the coating to effectively reflect the infrared radiation back onto the filament. 
     U.S. Pat. No. 4,942,331 to Bergman et al. discloses a double ended HIR (halogen infrared) filament lamp including a quartz glass tubular envelope having an infrared reflective coating and enclosing an axially-oriented tungsten filament that is connected to a molybdenum foil inlead. The inlead is connected to the filament utilizing plasma or laser welding to join the ends of the filaments and inleads. The inleads include spuds which generally comprise a refractory metal wire in the shape of a circular ring that is connected to the filament and allows for positioning of the filament within a central portion of the quartz tube. The lamp manufacturing technique of the U.S. Pat. No. 4,942,331 patent utilizes plasma or laser welding operations to connect the spud with the filament which is enclosed in a high melt temperature quartz glass. This combination of quartz glass tubing, spuds, and molybdenum foil inleads can be difficult and expensive to manufacture. 
     In non-HIR automotive headlamp applications where relative positioning of multiple filaments is needed, it is known to form a single-ended halogen lamp using a positioning device that is inserted into a first end of a glass tube to hold high and low beam filaments in a set position during sealing of a second end of the tube. See, for example, U.S. Pat. No. 4,305,632 to de La Chapelle. For transverse mounted filaments, the positioning device includes a pair of transverse slots in its lower end. The slots are spaced apart by a separator having a width suitable for maintaining the desired spacing of the filaments. For axially-oriented filaments, the patent states that the positioning device would have longitudinal grooves or holes to contain the filaments during the press sealing operation. The positioning devices disclosed in this patent are used to set the position of one filament relative to another within a generally cylindrical glass envelope that does not have an infrared reflective coating and that does not have a spherical or ellipsoidal shape suitable for use with such coatings. 
     There is therefore a need in the art for producing a cost effective halogen lamp having an enlarged envelope that includes an infrared coating and a filament that is precisely centered within the envelope. It is therefore a general object of the present invention to provide a method of producing a single ended tungsten halogen lamp having an enlarged envelope with an infrared reflective coating and a filament radially centered within the envelope. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, there is provided a method of making a halogen lamp having an axially-oriented filament. The method includes the steps of: 
     (a) providing a glass tube having first and second ends and an enlarged section located between the first and second ends; 
     (b) providing a filament assembly that includes a filament supported on one or more lead wires; 
     (c) inserting the filament assembly into the first end of the glass tube such that the filament is oriented axially within the enlarged section of the glass tube; 
     (d) centering the filament within the enlarged section of the glass bulb using a mandrel alignment tool that is inserted into the second end of the glass tube; 
     (e) sealing the first end of the glass tube around the filament assembly; 
     (f) removing the mandrel alignment tool from the glass tube; 
     (g) filling the glass tube with a halogen gas; and 
     (h) sealing the glass tube at a location between the enlarged section and the second end. 
     Preferably, the mandrel alignment tool has a base with tip that extends down from the base and into the center of the filament which is preferably in the conventional form of a coil. At least a section of the base has an outer diameter that is the same as the inner diameter of the glass tube so that when that section of the base is inserted into the glass tube, the tip is centered radially and the mandrel alignment tool is restricted from any radial movement. The enlarged section of the glass tube preferably has a spherical or ellipsoidal shape and is coated on its exterior surface with an infrared reflective material. 
     In accordance with another aspect of the present invention, there is provided a single-ended halogen lamp that can be manufactured according to the inventive method disclosed herein. The lamp includes a glass envelope having first and second sealed ends and a spherical or ellipsoidal region located between the first and second ends. A pair of leads extend through the first sealed end from an exterior, exposed location to an interior located within the glass envelope. A filament is electrically connected to the leads, with the filament being oriented along an axis extending between the first and second ends and being radially centered within the glass envelope. A halogen gas fill is contained within the glass envelope and an infrared reflective coating is disposed on a surface of the spherical or ellipsoidal region to reflect infrared light back onto the filament for increased efficiency. 
     Preferably, the filament is a coiled tungsten filament axially oriented within the glass envelope and the region is ellipsoidal in shape with its two foci each located at the filament proximate an opposite end of the filament. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred exemplary embodiments of the invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein: 
     FIGS. 1A through 1H illustrates various steps involved in a preferred embodiment of the manufacturing method of the present invention; 
     FIG. 2 is a enlarged, cross-sectional view taken along the  2 — 2  line of FIG.  1 E and depicting the interaction of the mandrel alignment tool with the coil portion of the filament; and 
     FIG. 3 is a perspective view of a completed halogen lamp manufactured according to the steps of FIGS.  1 A through  1 H. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIGS. 1A through 1C, there is shown a glass tube  10  that is first cut to an appropriate (initial) length and then has an enlarged section  15  formed in the glass tube  10 . The glass tube  10  is then cut to a final working length after the section  15  has been formed. The glass tube  10  can be any of a variety of different glass compositions, including quartz glass or an aluminosilicate glass that has a lower melting temperature than quartz glass and therefore simplifies the manufacturing process. The aluminosilicate glass is also less expensive. 
     The aluminosilicate glass can be Corning™ 1724 glass tubing having a 10.5 mm outside diameter with a thickness of 0.9 mm. The enlarged section  15  can be a spherical or ellipsoidal section formed while the tubing is installed on a glass lathe and rotated while heating. Utilizing a two piece mold and pressurizing the interior, a spherical or ellipsoidal section preferably having a 16 mm diameter is blown into the tube  10 . For an ellipsoidal shape, the foci of the ellipsoid are preferably spaced by a distance equal to the length of the filament coil  45  shown in subsequent figures. After the section  15  is formed, the glass tube  10  is then cut to a smaller working size for subsequent processing. 
     With reference to FIG. 1D, a filament assembly  20  that includes a lead portion  22  and a filament portion  24  is inserted into a first end  35  of the glass tube  10 . The filament leads  22  are preferably simple molybdenum wire leads that are commonly used in the lamp manufacturing industry. The filament  24  is preferably made of tungsten in the form of a coil, and is welded or otherwise attached to the leads  22  using known techniques. As shown, the coil portion  45  of the filament  24  is attached to the leads  22  such that it has an axial orientation; that is, it is oriented along a central axis extending between the first and second ends of the glass tube  10 . The filament  24  is axially centered within the envelope and, for an ellipsoidal section  15 , is centered axially so that the two foci of the ellipsoid are located at the filament proximate opposite ends of the filament. 
     After the filament assembly  20  has been inserted into and axially centered within the enlarged section  15  of the glass tube  10 , a mandrel alignment tool  25  is inserted into the glass tube  10  from a second end  30  such that the mandrel alignment tool  25  engages the filament to center it radially within the spherical or ellipsoidal section  15 . This is shown in FIG.  1 E and in the cross-section of FIG.  2 . The mandrel alignment tool  25  includes a base portion  50  and a filament engaging portion, or tip,  55 . A section of the base  50  has a reduced outer diameter that is equal to the inner diameter of the glass tube  10  so that, once this section of the base enters the glass tube, the mandrel alignment tool including, in particular, the tip  55 , can freely move axially within the tube, but is substantially restricted from radial movement. The length of the tip can be selected so that the reduced diameter portion of the base  50  enters the glass tube before the tip  55  engages the coil  45 . In this way, the tip is radially centered when it engages the filament and is maintained centered as it slides through the center of the coil to the final position shown in FIG.  1 E. The reduced portion of the base  50  defines a shoulder (shown engaging the second end  30 ) and this can be used to limit the downward travel of the tool. It will, however, be appreciated that the entire base could have a fixed diameter with other means being used to limit the extent of downward travel. The tip  55  of the mandrel alignment tool is tapered to facilitate entry into the coil portion  45  of the filament  24 , and the outer diameter of the tip is selected relative to the inner diameter of the coil such that it engages the filament  24  in a slip fit that does not place any significant stress on the filament. 
     With reference to both FIGS. 1E and 1F, after the mandrel alignment tool  25  has been inserted into the glass tube  10  to maintain the centered location of the filament  24 , the glass tube is placed in a single head press machine mount holding fixture (not shown) wherein the first end  35  of the glass tube  10  is heated by opposing gas burners. While the glass is heated, nitrogen is injected into the bulb interior through the fixture to protect the mount assembly from oxidation. When the glass reaches a sufficient temperature, the machine jaws of the press machine (not shown) closes to form the press area  56  of the lamp  5 . This seals the first end  35 , locking the filament assembly  20  (and, thus, filament  24 ) in place relative to the envelope. After the pressing operation, the mandrel alignment tool  25  is removed from the glass tube  10 . 
     With reference to FIG. 1G, the second end  30  of the glass tube  10  is then necked down to form an exhaust tube  40 . This can be done by mounting the glass tube  10  on a glass lathe (not shown) with heat being applied while the bulb assembly is rotated and nitrogen is injected into the interior of the bulb to protect the mount from oxidation. Again, when the glass is sufficiently hot, the upper portion of the second end  30  is pulled away from the bottom portion, stretching the glass and forming the exhaust tube  40  and the corresponding narrowed portion  42 . After the exhaust tube  40  has been formed in the glass tube  10 , the glass tube is then heated, flashed, flushed, and filled with an appropriate halogen gas. The glass tube is then immersed in liquid nitrogen (not shown) and tipped off to form the completed lamp  5 , as shown in FIG.  1 H. These final steps shown in FIGS. 1G and 1H can be done using conventional techniques. 
     After the bulb has been tipped off, the lamp  5  is coated with an infrared reflective coating  60  using a multi-layer thin film process. Such processes are commonly known in the art. 
     The resulting single-ended halogen lamp  5  is shown in FIG.  3 . The lamp includes a glass envelope having first and second sealed ends and a spherical or ellipsoidal region  15  located between the first and second ends. A pair of leads  22  extend through the first sealed end  56  from an exterior, exposed location to an interior located within the glass envelope. A filament  45  is electrically connected to the leads, with the filament being oriented along an axis extending between the first and second ends and being radially centered within the glass envelope. A halogen gas fill is contained within the glass envelope and an infrared reflective coating  60  is disposed on a surface of the envelope region  15  to reflect infrared light back onto the filament for increased efficiency. 
     It will thus be apparent that there has been provided in accordance with the present invention a single-ended halogen lamp and manufacturing method therefor which achieves the aims and advantages specified herein. It will of course be understood that the foregoing description is of preferred exemplary embodiments of the invention and that the invention is not limited to the specific embodiments shown. Various changes and modifications will become apparent to those skilled in the art. For example, although the leads  22  of the illustrated embodiment are electrically connected directly to the filament, it will be understood that they could be connected indirectly to the filament to supply current through one or more intermediate elements. Also, while the leads  22  mechanically support the filament, one or more other mechanical supports could be used in addition to or in lieu of these leads  22 . All such variations and modifications are intended to come within the scope of the appended claims.