Patent Publication Number: US-7211954-B2

Title: Discharge tubes

Description:
FIELD OF THE INVENTION 
   The present invention relates to illumination components, and more particularly to discharge tubes for a lamp. 
   BACKGROUND OF THE INVENTION 
   Certain lamps are known to include a discharge tube to facilitate the illumination function. For example, U.S. Pat. No. 6,137,229 discloses a conventional metal halide lamp with a ceramic discharge tube. As shown in U.S. Pat. No. 6,137,229, end portions of conventional discharge tubes are known to comprise ring portions with a wall thickness based on the power supplied to the lamp. 
     FIGS. 1 and 2  depict a further example of a conventional ceramic discharge tube  160 . As shown, the discharge tube  160  includes end portions  164   a ,  164   b  disposed on opposite circumferential end portions of a substantially cylindrical tubular member  162 . The discharge tube  160  is symmetrically disposed about an elongated axis  158  and includes an outer radius “r” of 9.35 millimeters. Each end portion  164   a ,  164   b  is substantially identical and includes a transition section  168  between a ring portion  173  and a tubular extension  166 . The transition section spans between a maximum extent  168   a  in the direction of the elongated axis  158  and a minimum extent  168   b  in the direction of the elongated axis  158 . The minimum extent  168   b  has a first dimension “d 1 ” of 1.5 millimeters with respect to an interior surface  172 . The maximum extent  168   a  has a second dimension “d 2 ” of 3.4 millimeters with respect to the interior surface  172 . 
   Conventional end portions can have features that result in cracking due to heat-cycles during the lamp lifetime. There is a continued need to provide discharge tubes with features that inhibit cracking of one or more end portions of discharge tubes. 
   SUMMARY OF THE INVENTION 
   In accordance with one aspect, a discharge tube for a lamp comprises a body portion including a first end, a second end, and a tubular member defining an interior area. The tubular member extends along an elongated axis between the first end and the second end. The discharge tube includes a first end portion provided at the first end of the body portion. The first end portion includes a first tapered portion that is tapered in a direction extending substantially perpendicular from the elongated axis. The first tapered portion includes an interior surface facing the interior area. The tapered portion spans between a maximum extent in the direction of the elongated axis and a minimum extent in the direction of the elongated axis. The minimum extent includes a first dimension D 1  with respect to the interior surface and the maximum extent includes a second dimension D 2  with respect to the interior surface. The ratio D 1 /D 2  is from about 0.07 to 0.43. 
   In accordance with another aspect, a discharge tube for a lamp comprises a body portion including a first end, a second end, and a tubular member defining an interior area. The tubular member extends along an elongated axis between the first end and the second end and the discharge tube has a circular periphery disposed at a radius “R” about the elongated axis. The discharge tube further comprises a first end portion provided at the first end of the body portion. The first end portion includes a first tapered portion that is tapered in a direction extending substantially perpendicular from the elongated axis. The first tapered portion includes an interior surface facing the interior area. The tapered portion spans between a maximum extent in the direction of the elongated axis and a minimum extent in the direction of the elongated axis. The minimum extent includes a first dimension D 1  with respect to the interior surface and the maximum extent includes a second dimension D 2  with respect to the interior surface wherein the ratio D 2 /R is from 0.40 to about 2.2. 
   In accordance with a further aspect, a discharge tube for a lamp comprises a body portion including a first end, a second end, and a tubular member defining an interior area. The tubular member extends along an elongated axis between the first end and the second end and the discharge tube has a circular periphery disposed at a radius “R” about the elongated axis. The discharge tube further includes a first end portion provided at the first end of the body portion. The first end portion includes a first tapered portion that is tapered in a direction extending substantially perpendicular from the elongated axis. The first tapered portion includes an interior surface facing the interior area and the tapered portion spans between a maximum extent in the direction of the elongated axis and a minimum extent in the direction of the elongated axis. The minimum extent includes a first dimension D 1  with respect to the interior surface and the maximum extent includes a second dimension D 2  with respect to the interior surface, wherein the ratio D 1 /D 2  is from about 0.18 to about 0.25 and the ratio D 2 /R is from about 0.8 to about 0.9. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross sectional view of a conventional discharge tube; 
       FIG. 2  is an enlarged view of portions of the conventional discharge tube taken at view  2  of  FIG. 1 ; 
       FIG. 3  is a partial sectional view of an exemplary lamp including a discharge tube assembly with a discharge tube in accordance with an exemplary embodiment of the invention; 
       FIG. 4  is a partial sectional view of the discharge tube assembly of  FIG. 3 ; 
       FIG. 5  is a sectional view of the discharge tube illustrated in  FIGS. 3 and 4 ; and 
       FIG. 6  is an enlarged view of portions of the discharge tube taken at view  6  of  FIG. 5 . 
   

   DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
   Discharge tubes of the present invention may be used as an illumination component in a wide variety of lamps having various structures, shapes, sizes, components and/or configurations. Just one example of a lamp  20  incorporating concepts of the present invention is illustrated in  FIG. 3 . The illustrative lamp  20  incorporates a discharge tube assembly  50  comprising a discharge tube  60  in accordance with the present invention. The lamp  20  can include an optional protective feature, such as a transparent quartz shroud  26 , designed to contain explosions that might occur during a failure of the discharge tube  50 . The lamp  20  can also include a support structure  24  designed to suspend the discharge tube assembly  50  within the interior area defined by outer bulb  22 . Discharge tubes in accordance with the present invention may be used with a lamp having a power level of about 150 Watts or greater. In further examples, discharge tubes in accordance with the present invention may be used with a lamp having a power level of about 250 Watts or greater. In still further embodiments, discharge tubes in accordance with the present invention may be used with lamps having a lower power level. 
   Discharge tubes of the present invention may also be used as an illumination component in a wide variety of discharge tube assemblies having various structures, shapes, sizes, components and/or configurations.  FIG. 4  illustrates just one example of a discharge tube assembly  50  having an exemplary discharge tube  60  incorporating aspects of the present invention. The discharge tube  60  defines an interior area  74  that can act as a discharge location for the lamp. The interior area  74  may be filled with an ionizable filling, such as various metal halides that are known for use with metal halide lamps. A first electrode  56   a  and a second electrode  56   b  can be positioned within the interior area  74 . The first and second electrodes  56   a ,  56   b  can comprise a winding of tungsten wire that is wrapped around respective lead-in wires  52   a ,  52   b . The lead-in wires might be formed of a niobium material and can include a winding  53  of molybdenum material. Each lead-in wire  52   a ,  52   b  extends through respective through passages  67  of end portions  64   a ,  64   b  of the discharge tube  60 . Once appropriately positioned, a seal  54   a ,  54   b  may be applied to seal any interstitial space between the lead-in wires and the through passage. The seals  54   a ,  54   b  can comprise a ceramic sealing compound in exemplary embodiments. 
     FIGS. 5 and 6  illustrate the exemplary discharge tube  60  incorporating concepts of the present invention. As shown, the discharge tube  60  includes a body portion  61  with a first end  61   a  and a second end  61   b . The body portion  61  further includes a tubular member  62  defining the interior area  74 . The tubular member  62  extends along an elongated axis  58  between the first end  61   a  and the second end  61   b  of the body portion  61 . 
   Exemplary discharge tubes in accordance with the present invention can comprise tubular members having a wide variety of shapes, sizes and can be oriented in a variety of positions with respect to other components of the discharge tube. In the illustrated embodiment, the tubular member  62  is substantially symmetrically disposed about the elongated axis  58  although it is contemplated that the tubular members may also be asymmetrically or otherwise disposed about the elongated axis  58  in further embodiments of the present invention. In the illustrated embodiment, the tubular members comprise circular peripheries along cross sections that are substantially perpendicular to the elongated axis  58 . The circular peripheries may have a constant radius or a varying radius. In the illustrated embodiment, the radius is smaller towards a central section of the tubular member and gets larger toward each end (e.g., see reference number  63  in  FIG. 6 ). It is contemplated that the tubular member may have substantially the same radius along the entire length. The tubular member can also be formed as a bulbous portion or may be formed without circular peripheries and therefore might not include a radius dimension from the elongated axis. For example, the tubular members can have an at least partially rectilinear periphery such as a polygonal periphery (e.g., triangular, rectangular, square or other polygonal arrangement). 
   Discharge tubes in accordance with the present invention can include an end portion or a plurality of end portions. For example, a plurality of end portions can be provided with similar or substantially identical structural features. Alternatively, the plurality of end portions may comprise different structural features wherein at least one end portion incorporates aspects of the present invention. Discharge tubes can also include a single end portion incorporating aspects of the present invention. For example, the tubular member can comprise a closed end tube wherein only one end of the tube includes an end portion in accordance with aspects of the present invention. 
   As shown in  FIG. 5 , the illustrated example depicts a first end portion  64   a  provided at the first end  61   a  of the body portion  61  and a second end portion  64   b  provided at the second end  61   b  of the body portion  61 . In the illustrated example, the first and second end portions  64   a ,  64   b  are substantially identical to one another. As shown in  FIG. 6 , the first end portion  64   a  includes a tapered portion  68  that is tapered in a direction  59  extending substantially perpendicular from the elongated axis  58 . The tapered portion  68  includes an interior surface  72  facing the interior area  74 . The interior surface  72  can comprise a substantially flat surface and can extend substantially perpendicular from the elongated axis  58 . In alternative embodiments, the interior surface  72  may comprise a nonplanar surface and/or can extend at an angle other than 90 degrees from the elongated axis  58 . 
   The tapered portion  68  spans between a maximum extent  68   a  in the direction of the elongated axis  58  and a minimum extent  68   b  in the direction of the elongated axis  58 . For example, as shown the maximum and minimum extent  68   a ,  68   b  can extend substantially parallel with respect to the elongated axis. The minimum extent  68   b  includes a first dimension D 1  with respect to the interior surface  72  and the maximum extent  68   a  includes a second dimension D 2  with respect to the interior surface  72 . For example, as shown, the first and second dimensions D 1 , D 2  can be measured with respect to a plane  71  along which the interior surface  72  extends. 
   Discharge tubes in accordance with aspects of the present invention can have various shapes and sizes depending how the tapered portion spans from the maximum extent to the minimum extent. As shown in  FIG. 6 , the tapered portion tapers in the direction  59  that is perpendicular from the elongated axis to form a surface  70 . In exemplary embodiments, the surface  70  can comprise a flat surface when the tapered portion does not extend perpendicularly from the elongated axis in all directions. In the illustrated embodiment, the tapered portion tapers in all directions that are perpendicular from the elongated axis to form a conical surface  70 . The conical surface  70  can have a variety of surface characteristics to provide a linear, convex, concave, stepped or other conical surface arrangements. In the illustrated embodiment, the tapered portion  68  comprises a linear conical surface  70  that faces away from the interior area  74  of the tubular member. 
   The first and second dimensions can have a wide range of values depending on the size of the discharge tube. Regardless of the size of the discharge tube, exemplary embodiments of discharge tubes in accordance with the present invention can be arranged with a ratio between D 1  and D 2  that can inhibit cracking of the end portion. For example, a ratio D 1 /D 2  from about 0.07 to 0.43 can inhibit cracking of the end portion during heating and/or cooling. In another example, a ratio D 1 /D 2  from about 0.15 to about 0.3 can inhibit cracking of the end portion during heating and/or cooling. In a further example, a ratio D 1 /D 2  from about 0.18 to about 0.25 can inhibit cracking of the end portion during heating and/or cooling. Providing ratios D 1 /D 2  within the ranges above can reduce stresses resulting from temperature differentials as the discharge tube heats when the lamp is turned on and/or as the discharge tube cools after the lamp is turned off. 
   In exemplary embodiments, the first dimension D 1  can range from about 1 millimeter to about 4 millimeters. In additional embodiments, the first dimension D 1  can range from about 1 millimeter to about 2 millimeters. In further embodiments, the first dimension D 1  can range below 1 millimeter or above 4 millimeters depending on the size of the lamp. One example of a discharge tube can have a first dimension D 1  of about 1.5 millimeters and a second dimension D 2  of about 8 millimeters wherein the ratio D 1 /D 2  is about 0.19. It is further understood that the first dimension D 1  can be selected based on the desired size of the lamp wherein the second dimension D 2  can be determined to provide a ratio D 1 /D 2  within a range discussed above to inhibit cracking of the discharge tube. 
   Exemplary embodiments of the invention can also include a discharge tube that has various periphery shapes, such as a circular periphery disposed at a radius “R” about the elongated axis. If the discharge tube has a circular periphery, the ratio between the second dimension D 2  and the radius “R” can be provided within a range to reduce stresses after the lamp is turned off. Thus, if the discharge tube has a circular periphery, the ratio D 2 /R and/or the ratio D 1 /D 2  can be provided within ranges discussed herein to reduce stresses when turning the lamp on and/or when turning the lamp off. For example, in the illustrated embodiment, the discharge tube  60  has a circular periphery  63  disposed at a radius “R” about the elongated axis  58 . The radius “R” can have a wide range of values depending on the size of the discharge tube. Regardless of the size of the discharge tube, exemplary embodiments of discharge tubes in accordance with the present invention can have a ratio between D 2  and “R” that can inhibit cracking of the end portion. For example, a ratio D 2 /R from 0.40 to about 2.2 can inhibit cracking of the end portion during heating and/or cooling. In another example, a ratio D 2 /R from about 0.5 to about 1 can inhibit cracking of the end portion during heating and/or cooling. In a further example, a ratio D 2 /R from about 0.8 to about 0.9 can inhibit cracking of the end portion during heating and/or cooling. Providing a ratio D 2 /R within the ranges above can reduce stresses resulting from temperature differentials as the discharge tube heats when the lamp is turned on and/or as the discharge tube cools after the lamp is turned off. 
   In exemplary embodiments, the radius “R” can range from about 4 millimeters to about 15 millimeters. In further embodiments, the radius “R” can range below 4 millimeters or above 15 millimeters depending on the size of the lamp. One example of a discharge tube can have a radius “R” of about 9.35 millimeters and a second dimension D 2  of about 8 millimeters wherein the ratio D 2 /R is about 0.86. It is further understood that the radius “R” can be selected based on the desired size of the lamp wherein the second dimension D 2  can be determined to provide a ratio D 2 /R within a range discussed above to inhibit cracking of the discharge tube. 
   If the discharge tube has a circular periphery, the ratio D 2 /R and/or the ratio D 1 /D 2  can be provided within ranges discussed above. In addition, a discharge tube with a circular periphery can include ratios D 2 /R and D 1 /D 2  that both fall within any of the ranges discussed above to inhibit cracking during heating and/or cooling of the end portion. For example, a discharge tube may be provided wherein the ratio D 2 /R is from 0.40 to about 2.2 and the ratio D 1 /D 2  is from about 0.07 to 0.43. In another example, the ratio D 2 /R is from about 0.5 to about 1 and the ratio D 1 /D 2  is from about 0.15 to about 0.3. In a further example, the ratio D 2 /R is from about 0.8 to about 0.9 and the ratio D 1 /D 2  is from about 0.18 to about 0.25. 
   In further exemplary embodiments, the end portions can include a tubular extension extending from the tapered portion. For example, as shown in  FIG. 6 , the first end portion  64   a  includes a tubular extension  66  extending from the tapered portion  68 . The first end portion  64   a  can further include one or more through passages to accommodate one or more lead-in wires. In embodiments with a single end portion, two or more through passages may be provided or a single through passage can be provided that is sufficient to accommodate both lead-in wires. In the illustrated exemplary embodiment, each end portion  64   a  includes a single through passage  67  that extends through the tubular extension  66  and the tapered portion  68  along the elongated axis  58 . 
   The discharge tube in accordance with the present invention may be formed from a wide range of materials and processes while incorporating the concepts of the present invention. For example, the discharge tube can be formed from a ceramic material although other materials can be used to facilitate appropriate lamp function. If fabricated from ceramic, the ceramic material can comprise AL203, Y203 or YAG ceramic material although other ceramic materials are contemplated. The tubular member can also be initially formed separately from the end portions for later assembly. For example, the tubular member  62  can be formed and cut to the desired length. As shown in  FIG. 6 , each end portion can have a circumferential lip  69  designed to fit within a corresponding end of the tubular member  62 . Once the end portions are in place, the assembly can be sintered together wherein the end portions are attached to the tubular member at a sintered location  65 . It is understood that other process techniques may be used to form the discharge tube in accordance with concepts of the present invention. 
   From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.