Abstract:
A lamp includes a light transmissive envelope comprising two spaced apart elliptical portions that together form a hollow interior. The envelope has sealed end portions. Leads are in electrical contact with the filament near the end portions of the envelope for providing power to the lamp. There is a central portion of the envelope that spaces apart the elliptical portions. An electrically conductive filament is disposed in the interior of the envelope. The filament includes coiled-coil portions disposed in the elliptical portions in a coiled-coil shape and a single coil interval portion disposed between the coiled-coil portions at the central portion of the envelope. At least one filament support positions the filament near a center of the envelope. Gas is contained in the interior of the envelope.

Description:
FIELD OF THE INVENTION 
     The field of the invention is lamps, in particular, halogen lamps, that have high efficiency. This high efficiency can be brought about by the shape of the envelope of the lamp and the configuration and position of the filament in the lamp. 
     BACKGROUND OF THE INVENTION 
     As shown in  FIG. 1 , in Europe 230-240V line voltage halogen lamps today are in the lower range of the C class range close to the D class range boundary. However, B class efficiency is the most desirable. The application of an infrared reflecting coating to the lamp can improve lamp efficiency, so to reach the B energy class is theoretically possible. 
     There are several major requirements of the halogen lamp design with infrared (IR) reflecting technology developed to produce higher efficiency halogen lamps. IR reflectivity and visible transmission of the infrared reflecting multilayer should be increased. Bulb and filament shape should be optimized to reflect infrared radiation back to the filament as much as possible. Also, the filament should be maintained in the designed place, namely, in center of the bulb both during manufacturing and throughout its lifetime. Nevertheless, to reach B class is a huge step, even for low wattage lamps, where wire and coil dimensions are small. Small wire and coil size can easily cause the misfit and deformation of the filament during manufacturing and throughout its lifetime. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment the lamp of this disclosure includes a light transmissive (e.g., glass) envelope comprising two spaced apart, connected elliptical portions that together form a hollow interior. The envelope has sealed end portions. There is a central portion of the envelope that spaces apart the elliptical portions. An electrically conductive filament is disposed in the interior of the envelope. Leads are in electrical contact with the filament near the end portions of the envelope for providing power to the lamp. The filament includes coiled-coil portions disposed in the elliptical portions in a coiled-coil shape and a single coil interval portion disposed between the coiled-coil portions at the central portion of the envelope. That is, the coiled-coil portions of the filament are where a coil of the filament is in turn coiled. The single coil interval portion of the filament is where there is only a single coil in the filament. At least one filament support positions the filament near a center of the envelope. Gas is hermetically sealed in the interior of the envelope. 
     Referring to specific aspects of the lamp described above, each of the elliptical portions has a major axis and a minor axis, wherein the major axis can be between about 12 mm and 17 mm and the minor axis (mm) can be approximately equal to 1.2*(major axis−5). The central portion of the envelope can be in a shape of a cylindrical tube. The filament support can be made of metal having a high melting point (e.g., above 1800-2000° C.), for example, tungsten or molybdenum. The filament can be designed for a line voltage of 230-240 volts and the lamp can be operated at 25-150 W. An infrared radiation reflecting coating can be disposed on a surface of the envelope. The lamp can be a halogen lamp in which case the gas comprises an inert gas containing halogen. For example, the gas may contain Ar, Kr, Xe, or N 2 , or combinations thereof as inert gases, and Cl, I, Br or F, or combinations thereof as halogens. 
     The filament can include single coil interval portions near the end portions of the envelope. The filament support can comprise side filament supports located near each of the end portions of the envelope and a central filament support located at the central portion of the envelope. The envelope can include outer tubular portions near the end portions adjacent and outside of the elliptical portions. The side filament supports can be disposed in the elliptical portions of the envelope, as well as in the outer tubular portions. Each of the side filament supports can be welded to one of the single coil intervals near the end portions of the envelope in close proximity to one of the coiled-coil portions of the filament. The envelope can include pinch portions located near its end portions. The side filament supports can extend within an inner space of the envelope in the elliptical portions and so as not to touch the pinch portions. The side filament supports are separated from the pinch portion, even from the Mo foil in the pinch portion, to prevent high current arcing at end of life, which may cause explosion of the lamp. On the other hand, the inner surface of the pinch portion is curved, which could cause deformation of the filament support during manufacturing. 
     The filament support can be a foil. The foil can have a thickness ranging from 0.01 to 0.3 mm. Near to the edge of the foil the glass of the envelope can be melted embedding the foil partially. The filament support can comprise a single foil welded to the filament or two foils (or folded single foil) that sandwich the filament therebetween and are welded to the filament. The two foils or folded single foil can also be welded together. 
     Another embodiment of the lamp of this disclosure includes a light transmissive (e.g., glass) envelope comprising two connected elliptical portions that together form a hollow interior. Each elliptical portion including a major axis and a minor axis, wherein the major axis is between about 12 mm and 17 mm and the minor axis (mm) is approximately equal to 1.2*(major axis−5). An electrically conductive filament is disposed in the interior of the envelope. The envelope includes sealed end portions. Leads are in electrical contact with the filament near the end portions of the envelope for providing power to the lamp. At least one filament support is used for positioning the filament near a center of the envelope. A gas is hermetically sealed in the interior of the envelope. 
     All of the specific aspects of the lamp of this disclosure discussed above in connection with the first embodiment can apply to this embodiment in any combination. For example, there can be a central (e.g., cylindrical tubular) portion of the envelope between the elliptical portions. The filament can include coiled-coil portions disposed in the elliptical portions in a coiled-coil shape and a single coil interval portion disposed between the coiled-coil portions at the central portion of the envelope. Also, the filament support can include side filament supports near the end portions of the envelope and a central filament support in the central portion of the envelope. 
     Many additional features, advantages and a fuller understanding of the invention will be had from the accompanying drawings and the detailed description that follows. It should be understood that the above Brief Description of the Invention describes the invention in broad terms while the following Detailed Description of the Invention describes the invention more narrowly and presents specific embodiments that should not be construed as necessary limitations of the invention as broadly defined in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Prior Art  FIG. 1  is a graph showing efficiency of halogen lamps as a function of wattage; 
         FIG. 2  shows a double ellipse lamp of this disclosure with attached tube for adding fill gas to the lamp; 
         FIG. 3(   a ) is an enlarged side view of a double ellipse lamp of this disclosure after the fill gas tube has been removed;  FIG. 3(   b ) is a side view of the lamp of  FIG. 3(   a ) rotated 90 degrees; and  FIG. 3(   c ) is a further enlarged view of a central portion of the envelope, a central filament support and coiled-coil portions of the filament of the lamp shown in  FIG. 3(   b ); 
         FIG. 4  shows a schematic of optical coupling that can occur between the elliptical portions of the lamp of  FIG. 3 ; 
         FIG. 5  is a graph showing infrared radiation (IR) gain as a function of the ellipse minor axis and distance between elliptical portions of the envelope D; 
         FIG. 6  is a graph showing the ellipse minor axis as a function of the ellipse major axis, and resulting IR gain; 
         FIG. 7(   a ) shows one aspect of the double filament support foil;  FIG. 7(   b ) shows another aspect of the double filament support foil; and  FIG. 7(   c ) shows yet another aspect of the double filament support foil; and 
         FIGS. 8(   a )-( c ) show aspects of a single, folded filament support foil. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 2 and 3 , a lamp  10  of this disclosure includes a heat resistant, light transmissive bulb or envelope  12  having two connected elliptical portions  14 ,  16  forming a hollow interior  18 . The envelope  12  is made of fused or synthetic silica (quartz). The lamp  10  of this disclosure ideally has two elliptical portions  14 ,  16  in particular, not one, and not three or more. The lamp disclosed here can be used in A-shaped bulbs, spherical shaped bulbs or candle shaped bulbs, for example. The two elliptical bulb portions can be connected with a central cylindrical tubular portion  20 , all of which have an IR radiation reflecting coating on their outer surfaces (not shown). The central connecting bulb portion  20  is not distorted with, for example dunching. A fill gas tube  19  is shown centrally located in  FIG. 2 , but can instead be located between one of the elliptical portions and a pinch portion of the lamp shown in  FIG. 3  in which case a longer side filament support  44  and longer tubular portion  45  between the ellipse and pinch portion would be used to receive the exhaust tube. The lamp  10  includes an electric light source or filament  22  in the interior  18  of the double ellipse envelope. The lamp includes a current conductor  24  comprising an outer lead  26 , seal foil  28  and the filament  22 . The lamp shown in  FIG. 2  includes only a central filament support  46  while the lamp shown in  FIG. 3  also includes side filament supports  44 . 
     The lamp is hermetically sealed at the end portions of the envelope by pinch portions  30  at which the glass envelope is pressed together closed into flattened cross-sections. The flattened pinch portion  30  is shown in  FIG. 2 ,  3   a  or  3   b . At each end of the envelope, the welded outer lead  26 , seal foil  28  and interval single coil portion  32  of the filament  22  are sealed by quartz of the bulb itself in the pinch portion  30 , which is pressed together. The seal foil  28  is known in the art and can be made of a first seal foil  34  welded to the outer lead wire  26  comprising molybdenum, alternatively molybdenum alloy or molybdenum doped with yttrium and/or yttrium oxides. The outer lead wire  26  can be made of molybdenum. An optional second seal foil  36  of tantalum or platinum, for example, is welded to the first seal foil  34  and in turn is welded to the single coil end portion  32  of the filament  22  on both sides of the lamp. The second seal foil  36  can be omitted or replaced by another welding aid besides the second seal foil  36 . When the second seal foil  36  is omitted, the single coil end portions are welded to the first seal foil  34 . The current conductor  24  connects the filament or electric light source  22  to an external power source. 
     The filament is disposed at a center of the envelope (i.e., close to a central axis extending between the end portions of the envelope in the interior of the envelope and located at a center C of the elliptical portions, represented by the cross C in  FIG. 7(   a ) and the line C in  FIG. 3(   b )). The central axis C extends along the major axes, a, of the elliptical portions, the minor axis, b, being perpendicular thereto. There are two coiled coil (CC) portions  38  of the filament  22  separated by a central single coil interval portion  40  of the filament  22 . The single coil interval portions  32  of the filament are also disposed at end portions  42  of the envelope  12 . The single coil portions  32 ,  40  are much cooler than the active coiled coil (CC) portions  38  of the filament  22 . The CC-portions  38  of the filament  22  function as a burner or radiator that reach an optimum operating temperature and are centered in each elliptical portion  14 ,  16 . The filament  22  can reach temperatures of 2700-3000° C. The filament  22  is suitable for a line voltage of 230-240V, which dictates that the filament have a certain length. This in turn affects the length of the envelope  12  that is needed. The CC portions  38  of the filament  22  are centered in the elliptical portions  14 ,  16  of the envelope  12 . There is an optical coupling of the CC-filament portions  38  between the two elliptical portions  14 ,  16  through the central portion  20  (e.g., the connecting cylindrical part) of the bulb. The CC portions  38  of the filament  22  are kept in the center by filament supports made from metallic, e.g., tungsten, foil, which include side filament supports  44  and a central filament support  46  therebetween. The central filament support  46  is a foil that fits into the connecting central portion  20 . The side filament supports  44  are foils that fit into the end portions  42  of the envelope  12  (e.g., inside tubular portions  45 ), within the inner space  18  of the lamp. The side filament support foils  44  do not touch the pinch portion  30  from inside. The central filament support foil  46  and the side filament support foils  44  may penetrate to the ellipsoid parts of the bulbs, and are welded to the intervals of the filament as close to the CC part  38  of the filament  22  as possible. The filament support foils  44 ,  46  may include one or two parts. The double filament support foils  48   a ,  48   b ,  48   c  ( FIG. 7(   a )-( c )) (or folded single support foils shown in  FIG. 8(   a )-( c )) can provide better centricity of the filament relative to the central axis C of the envelope. The glass of the bulb can be melted to the edge of the filament support foil in a very small area to prevent axial movement of the filament support foils. 
     In the case of 230-240 line voltage filaments a coiled coil segment  38  of the filament  22 , which is the active (radiating) part of the filament, is too long to mount into a single ellipsoid bulb in contrast to 120V filaments. Therefore, the coiled coil (CC) segment  38  is separated into two parts with a central single coiled (SC) segment (interval)  40  in the middle. The two separated active CC parts  38  are mounted to separate ellipsoid parts  14 ,  16  of the halogen burner ( FIG. 2 ). 
     One way to increase the efficiency of the double elliptical design is to increase the ellipse surface, but this is limited by the diameter of the tube from which the bulb is formed. The infrared radiation from the filament to the direction of the open ends of the ellipsoids cannot be reflected back to the filament. Efficiency is increased by optical coupling between the two CC segments through the cylindrical portion of the envelope between the elliptical portions, as shown schematically in  FIG. 4 . The infrared radiation coming from the first CC segment goes to the second CC segment directly or after one or more reflections on the surface of the connecting central cylindrical portion  20 . Although the central portion  20  need not have an exactly cylindrical geometry, a distorted or other irregular surface, e.g. dunching, can destroy this coupling. Therefore, no dunching is used for coil support in this design. 
     The efficiency increment (IR gain) depends on the ellipse geometry (the major and minor axis), coil geometry, and significantly on the distance between elliptical portions (D, mm) as shown in  FIGS. 5 and 6 . With decreasing D the IR gain increases, and this effect is higher for smaller ellipsoids. However, D can be only decreased to a point where the two elliptical portions still do not touch each other. In  FIG. 5 , D=∞ means that there is no optical coupling between two ellipsoids. Otherwise, the central filament support or coil holder  46  cannot be fit between the elliptical portions. 
     Although many different ellipse geometries are possible, for the usual 230-240 V CC filaments in the 25-150 W wattage range a, the major axis of the elliptical portions  14 ,  16 , ranges between 12 mm and 17 mm. To maximize IR gain the minor axis of the elliptical portions, b, is approximately equal to 1.2*(a−5). The relevant IR gain map is shown in  FIG. 6 . The target region of the higher IR gain is shown 31.2% and 31.8%. The major axis, a, of the elliptical portions  14 ,  16  leading to this higher gain ranges from about 13.6 mm to 14.5 mm and above, in particular from about 14.1 to 14.5 and above, and the minor axis, b, of the elliptical portions  14 ,  16  ranges from about 10.5 mm to about 12 mm and above, in particular from about 10.8 mm to about 11.8 mm and above. 
     Gain is maximized by keeping the filament  22  in the center of the envelope (along the central axis C of the elliptical portions). Misfit of the filament can occur during manufacturing due to improper coil support design and during burning throughout lifetime due to deformation of the coil caused by gravity force. To resolve both issues, filament coil supports  44 ,  46  can be made from an appropriately formed metal foil, onto which the intervals  32 ,  40  are welded at  50  as seen in  FIGS. 3 and 7 . The circles in  FIGS. 7(   a )-( c ) show the contour of the coiled coil part of the filament. The CC segments  38  of coil can be kept in the center of the envelope if the filament support  44 ,  46  is as close as possible to the CC segment (see  FIG. 3) . The deformation caused by gravity is also much less in this case. The central filament support foil  46  is applied to hold the filament central interval  40  between the two elliptical portions as shown in  FIG. 2 . A better solution is to use  3  filament supports, one on the central interval, and two on the side intervals as shown in  FIGS. 3(   a ) and ( b ). Better center positioning can be achieved if centering foils penetrate into the ellipsoids (e.g., see  FIG. 3(   c )), and the welding points are as close to the CC segment as they can be. This is shown in  FIGS. 3(   b ) and ( c ). 
     The material of the foil is a metal or metallic alloy with high melting temperature (e.g., at least 1800-2000° C.), for example, tungsten or possibly molybdenum. The thickness of the filament support foils  44 ,  46  can be between 0.01 and 0.3 mm. Single or double foils can be used depending on the centering requirements, but the double foil filament supports (sandwich structure)  48   a ,  48   b ,  48   c  may provide better centricity. Different double foil filament supports are shown in  FIG. 7 . The foils  48   a  in the “sandwich” can be unshaped and parallel, surrounding the coil interval that has to be supported ( FIG. 7(   a )). When applying shaped foil  48   b  with an axial dip  52  in the middle, the positioning of the coil interval is easier before welding. This also includes portions  51  (on top and bottom) shaped to extend at an angle away from the dip portion  52 . In addition, not only can the foil-coil-foil welding be performed, but the two filament support foils  48   c  can be welded to each other at the contacting points ( FIG. 7(   b )). A simple solution, if the foils  48   c  are shaped to have portions  53  extending at an angle away from the center (on top and bottom), but in which there is no dip in the middle  54  for the filament interval, is shown in  FIG. 7(   c )). 
     The sandwich foil structure can be made from one piece, if double wide foil is folded in half as shown in  FIGS. 8(   a )-( c ), which have foil shapes similar to those of  FIGS. 7(   a )-( c ), respectively. Rather than using two foils, the shapes are achieved using a single wider foil  56  that is folded at fold  58 . 
     To fix the filament support foil  44 ,  46  in the axial direction, the bulb or envelope glass can be melted onto the edge of the foils in one or more small areas during manufacturing. This can prevent the displacement of the support foils in the axial direction. An advantage of this filament support solution is that it prevents forming a high current arc at end of life, because there are no thick wires required coming into the inner space  18  of the lamp from the pinch portion from the lead wires. In the exemplary design of the lamp shown in the drawings there are two free single coiled parts  32  of the filament at both side of the inner space of the lamp close to the pinch portion (see  FIGS. 3(   a ) and ( b )). These single coiled parts  32  can act as fuses preventing high current surge during burn out of the lamp. 
     In a conventional halogen lamp, evaporated material of the filament can condense on the inner surface of the envelope causing it to darken. Filament evaporation and envelope darkening results in loss of light or less lamp efficiency. The envelope may be filled with a fill gas which helps to reduce evaporation of the filament, such as an inert gas, e.g., Ar, Kr or Xe or combinations thereof, nitrogen and halogen. One example of the fill gas includes about 5% N 2  and about 95% Xe (volume percent) and some halogen. A part of the Xe can be replaced by Kr, e.g. about 65% Xe, 30% Kr. The halogen can be, for example, Br, Cl or I or combinations thereof. Halogens can be filled in very different compounds in gas form or even in liquid. Other components might be added to the fill gas in very small amounts, for example, O 2 , H 2  or other compounds containing Si or P. 
     Many modifications and variations of the invention will be apparent to those of ordinary skill in the art in light of the foregoing disclosure. Therefore, it is to be understood that, within the scope of the appended claims, the invention can be practiced otherwise than has been specifically shown and described.