Sheathed glow plug

Abstract

A glow plug which includes an annular metal shell, thermally conductive tubular sheath, central electrode; resistance heating element, and electrically insulating, thermally conductive powder includes a glass seal in sealing engagement with the sheath and the electrode to form a sealed cavity within the sheath. The glass seal may include silicate, borate and borosilicate glasses, and may include one or more transition metal oxides, such as oxides of chromium, cobalt, nickel, iron and copper. The glass may also include a filler, including a ceramic oxide, such as one selected from a group consisting of quartz, eucryptites, leucites, cordierites, beta-spodumene, glass-ceramics, low-expansion glass(CTE<5 ppm/° C.), mullite, zircon, zirconia and alumina. The sealed cavity may house a protective inert gas. The resistance heating element may be formed from a metal selected from a group consisting of tungsten, molybdenum, or alloys containing tungsten, molybdenum, nickel, iron, tantalum, niobium, titanium, vanadium, osmium and chromium.

1 . A glow plug, comprising:
 an annular metal shell having an axially extending bore;   an electrically and thermally conductive tubular sheath having an open end disposed within said bore in electrical contact with said shell and a closed end projecting from said bore;   an electrode extending into said open end of said sheath;   a resistance heating element disposed in said sheath having a proximal end which is electrically connected to said electrode and a distal end which is electrically connected to said closed end of said sheath;   an electrically insulating, thermally conductive powder disposed within said sheath and surrounding said resistance heating element; and   a glass seal disposed in said open end and in sealing engagement with said sheath and said electrode.   
   
   
       2 . The glow plug of  claim 1 , wherein said glass seal comprises a glass selected from a group consisting of a silicate glass, a borate glass and a borosilicate glass. 
   
   
       3 . The glow plug of  claim 2 , further comprising an oxide of a transition metal as a constituent of said glass. 
   
   
       4 . The glow plug of  claim 3 , wherein said transition metal is selected from a group consisting of chromium, cobalt, nickel, iron and copper. 
   
   
       5 . The glow plug of  claim 3 , wherein said oxide comprises 10 mole percent or less of said glass. 
   
   
       6 . The glow plug of  claim 2 , wherein said glass comprises a recrystallized microstructure. 
   
   
       7 . The glow plug of  claim 6 , wherein said recrystallized microstructure comprises greater than 90 volume percent of said glass. 
   
   
       8 . The glow plug of  claim 2 , wherein said glass is substantially lead free. 
   
   
       9 . The glow plug of  claim 2 , further comprising a filler as a constituent of said glass. 
   
   
       10 . The glow plug of  claim 9 , wherein said filler is a ceramic oxide. 
   
   
       11 . The glow plug of  claim 10 , wherein said ceramic oxide is selected from a group consisting of quartz, eucryptites, leucites, cordierites, beta-spodumene, glass-ceramics, low-expansion glass(CTE<5 ppm/° C.) , mullite, zircon, zirconia and alumina. 
   
   
       12 . The glow plug of  claim 1 , wherein said sheath has an outer diameter that varies along its length such that said outer diameter has a reduced diameter portion proximate said open end. 
   
   
       13 . The glow plug of  claim 12 , wherein said glass seal has a length, and said reduced diameter portion has a length, and said length of said reduced diameter portion is greater than said length of said glass seal. 
   
   
       14 . The glow plug of  claim 1 , further comprising a protective gas disposed in said cavity. 
   
   
       15 . The glow plug of  claim 14 , wherein said protective gas is selected from a group consisting of nitrogen, helium, neon, argon, krypton and xenon. 
   
   
       16 . The glow plug of  claim 1 , wherein said resistance heating element comprises a metal wire spiral. 
   
   
       17 . The glow plug of  claim 16 , wherein said metal wire spiral comprises a metal selected from a group consisting of pure nickel, a nickel alloy, a nickel-iron-chromium alloy and an iron-cobalt alloy. 
   
   
       18 . The glow plug of  claim 16 , wherein said metal wire spiral comprises a metal selected from a group consisting of tungsten, molybdenum, or alloys containing tungsten, molybdenum, nickel, iron, tantalum, niobium, titanium, vanadium, osmium and chromium. 
   
   
       19 . A heater assembly for a glow plug, comprising:
 an electrically and thermally conductive tubular sheath having an open end and a closed end;   an electrode extending into said open end of said sheath;   a resistance heating element disposed in said sheath and having a proximal end electrically connected to said electrode and a distal end electrically connected to said closed end of said sheath;   an electrically insulating, thermally conductive powder disposed within said sheath and surrounding said resistance heating element; and   a glass seal disposed in said open end and in sealing engagement with said sheath and said electrode.   
   
   
       20 . The heater assembly of  claim 19 , wherein said glass seal comprises a glass selected from a group consisting of a silicate glass, a borate glass and a borosilicate glass. 
   
   
       21 . The heater assembly of  claim 20 , further comprising an oxide of a transition metal as a constituent of said glass. 
   
   
       22 . The heater assembly of  claim 21 , wherein said transition metal is selected from a group consisting of chromium, cobalt, nickel, iron and copper. 
   
   
       23 . The heater assembly of  claim 20 , further comprising a filler as a constituent of said glass. 
   
   
       24 . The heater assembly of  claim 23 , wherein said filler is a ceramic oxide. 
   
   
       25 . The heater assembly of  claim 24 , wherein said ceramic oxide is selected from a group consisting of quartz, eucryptites, leucites, cordierites, beta-spodumene, glass-ceramics, low-expansion glass(CTE<5 ppm/° C.) , mullite, zircon, zirconia and alumina. 
   
   
       26 . The heater assembly of  claim 19 , wherein said sheath has an outer diameter that varies along its length such that said outer diameter has a reduced diameter portion proximate said open end. 
   
   
       27 . The heater assembly of  claim 26 , wherein said glass seal has a length, and said reduced diameter portion has a length, and said length of said reduced diameter portion is greater than said length of said glass seal. 
   
   
       28 . The heater assembly of  claim 19 , further comprising a protective gas disposed in said cavity. 
   
   
       29 . The heater assembly of  claim 28 , wherein said protective gas is selected from a group consisting of nitrogen, helium, neon, argon, krypton and xenon. 
   
   
       30 . The heater assembly of  claim 19 , wherein said resistance heating element comprises a metal wire spiral selected from a group consisting of pure nickel, a nickel alloy, a nickel-iron-chromium alloy and an iron-cobalt alloy. 
   
   
       31 . The heater assembly of  claim 19 , wherein said resistance heating element comprises a metal wire spiral selected from a group consisting of tungsten, molybdenum, or alloys containing tungsten, molybdenum, nickel, iron, tantalum, niobium, titanium, vanadium, osmium and chromium. 
   
   
       32 . A method of making a heater assembly for a glow plug comprising the steps of:
 forming a tubular sheath preform, electrode and resistance heating element;   attaching a distal end of the electrode to a proximal end of the resistance heating element;   inserting the resistance heating element and electrode into the tubular sheath preform;   attaching the distal end of the resistance heating element to the distal end of the tubular sheath preform to form the closed end of the sheath;   disposing electrically insulating, thermally conductive powder into the sheath preform to surround the resistance heating element;   inserting a glass preform into the open end; and   heating the glass preform for a time and temperature sufficient to melt the glass and form the glass seal.   
   
   
       33 . The method of  claim 32 , further comprising a step of reducing an outer diameter of the sheath preform to form the tubular sheath. 
   
   
       34 . The method of  claim 32 , further comprising performing the heating in vacuum or under a blanket of a protective gas. 
   
   
       35 . The method of  claim 34 , further comprising selecting the protective gas from a group consisting of nitrogen, helium, neon, argon, krypton and xenon. 
   
   
       36 . The method of  claim 32 , further comprising a step of forming an oxide layer on one of the electrode or the sheath proximate the location of the glass seal. 
   
   
       37 . The method of  claim 32 , further comprising forming the resistance heating element from a metal selected from a group consisting of tungsten, molybdenum, or alloys containing tungsten, molybdenum, nickel, iron, tantalum, niobium, titanium, vanadium, osmium and chromium.