Patent Publication Number: US-10784655-B2

Title: Corona igniter with hermetic combustion seal on insulator inner diameter

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This U.S. Divisional patent application claims the benefit of U.S. Utility patent application Ser. No. 15/409,694, filed Jan. 19, 2017, now U.S. Pat. No. 10,211,605, issued Feb. 19, 2019, which claims the benefit of U.S. provisional patent application No. 62/281,856, filed Jan. 22, 2016, the entire contents of both which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to corona igniters with combustion seals, and methods of manufacturing corona igniters with combustion seals. 
     2. Related Art 
     Glass seals are oftentimes used to bond an electrically conductive component, such as center electrode, and an insulator of an ignition device, for example a corona igniter. The glass seal of the corona igniter is typically formed by disposing a glass powder in a bore of the insulator, and then subsequently firing the insulator, center electrode, and glass powder together in a furnace. The heat causes certain components of the glass seal to expand and thus form the bond between the insulator and center electrode. Another option is to use a brass seal between the center electrode and the inner surface of the insulator. However, manufacturers are continuously trying to improve the quality and reliability of the bond, and thus always achieve a hermetic combustion seal along the inner surface of the insulator, while also keeping production time and costs to a minimum. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention provides a corona igniter comprising an insulator and a center electrode. The insulator includes an inner surface surrounding a bore and extending from an upper connection end to an insulator nose end. The inner surface of the insulator includes an electrode seat between the upper connection end and the insulator nose end. The inner surface of the insulator also presents an inner diameter, and the inner diameter decreases along the electrode seat in a direction moving toward the insulator nose end. The center electrode is disposed in the bore of the insulator. The center electrode includes a head disposed on the electrode seat of the inner surface of the insulator. A metallic coating is disposed on the inner surface of the insulator between the electrode seat and the upper connection end, and the metallic coating not disposed on the inner surface of the insulator below the electrode seat. A braze is disposed along the inner surface of the insulator between the electrode seat and the upper connection end. 
     Another embodiment of the invention provides a corona igniter comprising an insulator including an inner surface surrounding a bore. A metallic coating is disposed on the inner surface of the insulator, a center electrode is disposed in the bore of the insulator, and a braze is disposed between the center electrode and the metallic coating. 
     Another aspect of the invention provides a method of manufacturing a corona igniter. The method comprises providing an insulator including an inner surface surrounding a bore and extending from an upper connection end to an insulator nose end, the inner surface of the insulator including an electrode seat between the upper connection end and the insulator nose end, the inner surface of the insulator presenting an inner diameter, and the inner diameter decreasing along the electrode seat in a direction moving toward the insulator nose end. The method also includes disposing a metallic coating on the inner surface of the insulator between the electrode seat and the upper connection end and not below the electrode seat; and disposing a center electrode in the bore of the insulator, the center electrode including a head. The step of disposing the center electrode in the bore of the insulator includes disposing the head of the center electrode on the electrode seat of the insulator. The method further includes brazing the metallic coating on the inner surface of the insulator between the electrode seat and the upper connection end. 
     Another embodiment of the invention provides a method for manufacturing a corona igniter comprising the steps of: providing an insulator including an inner surface surrounding a bore; disposing a metallic coating on the inner surface of the insulator; disposing a center electrode in the bore of the insulator; and brazing the center electrode to the metallic coating. 
     The combination of the metallic coating and braze provides an economical and reliable hermetic combustion seal between the center electrode and the inner surface of the insulator. The metallic coating can be applied to the inner surface of the insulator at the same time that a metal coating is applied to an outer surface of the insulator. In addition, the brazing step can be performed while brazing the metal coating on the outer surface of the insulator to a metal shell. Since processes currently used to manufacture corona igniters already include the steps of applying the metal coating to the outer surface of the insulator and brazing the metal coating on the outer surface of the insulator to the shell, no additional process time is typically required to implement the steps of the present invention. In addition, the corona igniter will not require a Kovar wire on the center electrode, thereby eliminating the cost of welding the Kovar to the center electrode. The metallic coating on the inner surface of the insulator also eliminates the need for a glass material, and helps provide electrical continuity within the insulator, thus eliminating the need for brass powder. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is a cross-sectional view of an insulator and center electrode of a corona igniter according to one example embodiment including a metallic coating and braze providing a hermetic combustion seal between the center electrode and inner surface of the insulator; 
         FIG. 2  a cross-sectional view of an insulator and center electrode of a corona igniter of another example embodiment including a metallic coating and copper-based powder brazed to the inner surface of the insulator to provide a hermetic combustion seal between the center electrode and the insulator; 
         FIG. 3  is a cross-sectional view of a corona igniter according to another example embodiment including a metallic coating and braze providing a hermetic combustion seal between the center electrode and insulator; 
         FIG. 4  is a cross-sectional view of an insulator and center electrode of a corona igniter of another example embodiment including a braze between the center electrode and metallic coating; 
         FIG. 5  is a cross-sectional view of an insulator and center electrode of a corona igniter of another example embodiment including a braze between the center electrode and a metallic coating; and 
         FIG. 6  is a cross-sectional view of an insulator and center electrode of a corona igniter of another example embodiment including a braze between the center electrode and a metallic coating. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     One aspect of the invention includes a corona igniter  20  for an internal combustion engine including a metallic coating  22  and braze  23  providing a hermetic combustion seal between a center electrode  24  and insulator  26  to prevent gases located in a combustion chamber of the engine from entering the igniter  20 .  FIGS. 1, 2, and 4-6  are examples of the center electrode  24  and insulator  26  with the hermetic combustion seal therebetween, and  FIG. 3  is an example of a corona igniter  20  including the combustion seal. 
     The corona igniter  20  including the hermetic combustion seal can have various different designs, including, but not limited to the designs shown in the Figures. In the example embodiments of  FIGS. 1-3 , the center electrode  24  is disposed in the bore of the insulator  26 , and the center electrode  24  extends along a center axis A from a head  28  to a firing end  32 . The center electrode  24  is formed of an electrically conductive material, such as nickel or a nickel alloy. In the example embodiment of  FIGS. 1-3 , the head  28  of the center electrode  24  is supported and maintained in a predetermined axial position by a reduced diameter of the insulator  26 , referred to as an electrode seat  33 , and an electrical terminal  30  rests on the head  28  of the center electrode  24 . A majority of the length of the center electrode  24  is surrounded by the insulator  26 . Also in this example embodiment, the center electrode  24  includes a firing tip  34  at the firing end  32 . The firing tip  34  has a plurality of branches each extending radially outwardly from the center axis A for emitting an electric field and providing the corona discharge during use of the corona igniter  20  in the internal combustion engine. 
     The insulator  26  of  FIG. 3  extends longitudinally along the center axis A from an upper connection end  38  to an insulator nose end  40 . The insulator  26  is formed of an insulating material, typically a ceramic such as such as alumina. The insulator  26  also presents an inner surface  42  surrounding the bore which extends longitudinally from the upper connection end  38  to the insulator nose end  40  for receiving the center electrode  24  and possibly other electrically conductive components. The firing tip  34  of the center electrode  24  is typically disposed longitudinally past the insulator nose end  40 . As mentioned above, in the embodiment of  FIGS. 1-3 , the insulator inner surface  42  presents an inner diameter Di which decreases along a portion of the insulator  26  moving toward the insulator nose end  40  to form the electrode seat  33  which supports the electrode head  28 . The inner diameter Di extends across and perpendicular to the center axis A. The insulator inner diameter Di decreases from a top of the electrode seat  33  to a base of the electrode seat  33 , which is in the direction moving toward the insulator nose end  40 . 
     The insulator  26  of the example embodiment also presents an insulator outer surface  44  having an insulator outer diameter D o  extending across and perpendicular to the center axis A. The insulator outer surface  44  extends longitudinally from the upper connection end  38  to the insulator nose end  40 . In the exemplary embodiments, the insulator outer diameter D o  decreases along a portion of the insulator  26  moving toward the insulator nose end  40  to present an insulator nose region  46 . The insulator outer diameter D o  can also vary along other portions of the length, as shown in the Figures. 
     The corona igniter  20  also includes a shell  52  formed of metal and surrounding a portion of the insulator  26 . The shell  52  is typically used to couple the insulator  26  to a cylinder block (not shown) of the internal combustion engine. The shell  52  extends along the center axis A from a shell upper end  54  to a shell lower end  56 . The shell upper end  54  is disposed between an insulator upper shoulder  50  and the insulator upper end  38  and engages the insulator  26 . The shell lower end  56  is disposed adjacent the insulator nose region  46  such that at least a portion of the insulator nose region  46  extends axially outwardly of the shell lower end  56 . 
     As mentioned above, the hermetic combustion seal between the insulator  26  and center electrode  24  is provided by applying the metallic coating  22  to the inner surface  42  of the insulator  26 , and then brazing. In the example embodiments of  FIGS. 1-3 , the metallic coating  22  is located between the electrode seat  33  and the upper connection end  38 . The metallic coating  22  can be formed of various different compositions. According to one embodiment, the metallic coating  22  includes a layer of molybdenum and manganese. For example, the metallic coating  22  can consist of molybdenum and manganese. However, the layer of molybdenum and manganese could include trace amounts of other elements or components. The layer of molybdenum and manganese typically includes an oxide when applied, but the oxide is not present after heating in a furnace. According to another embodiment, the metallic coating  22  is a nickel-based layer, such as electroless nickel plating. For example, the metallic coating  22  can consist of nickel. However, the nickel-based layer can include trace amounts of other elements or components. The nickel-based layer is typically referred to as a nickel overlay, and can be applied by an electroplating process, an electrolytic process, an electroless process, or by a chemical reaction. The nickel-based layer is typically applied as a nickel oxide material, but the oxide is not present after heating in a furnace. Preferably, the metallic coating  22  includes the nickel-based layer applied to the layer of molybdenum and manganese. 
     In the embodiments of  FIGS. 1-3 , the metallic coating  22  is applied along only a portion of the insulator inner surface  42  for example in a region extending from the electrode seat  33 , or slightly above the electrode seat  33 , to the upper connection end  38 , or around the upper connection end  38 . In these embodiments, the metallic coating  22  is not located below the electrode seat  33  which supports the electrode head  28 , and the inner surface  42  of the insulator  26  is not coated in the region extending from the base of the electrode seat  33  to the insulator nose end  40 . The length L 1  of the metallic coating  23  of the example embodiments is identified in  FIGS. 1 and 2 . The thickness of the metallic coating  22  can vary, but it is typically less than 0.1 mm. 
     The hermetic combustion seal further includes the braze  23  disposed along the insulator inner surface  42  between the center electrode  24  and the insulator inner surface  42 . In the embodiments of  FIGS. 1-3 , the braze is between the electrode seat  33  and the upper connection end  38 . In the example of  FIG. 1 , the head  28  of the center electrode  24  is brazed directly to the metallic coating  22  on the insulator inner surface  42 . In this case, the braze  23  is located along the head  28  of the center electrode  24  but not along other portions of the insulator inner surface  42 . In the example of  FIG. 2 , a shot of copper-based powder  64  is disposed along the center axis A on the head  28  of the center electrode, and the copper-based powder  64  is then brazed to the metallic coating  22  on the inner surface  42  of the insulator  26 . The copper-based powder  64  can consist of copper or a copper alloy. In this case, the braze  23  is located along the copper-based powder  64  but not along other portions of the insulator inner surface  42 . Due to the combination of the metallic coating  22  and the braze  23 , the corona igniter  20  does not require a Kovar wire on the center electrode  24 , thereby eliminating the cost of welding the Kovar to the center electrode  24 . In addition to a reliable combustion seal, the metallic coating  22  and braze  23  helps provide electrical continuity within the insulator  26 , thus eliminating the need for glass material or brass powder. 
     Other example embodiments of the insulator  26  and center electrode  24  of the corona igniter  20  are shown in  FIGS. 4-6 . According to this embodiment, the insulator  26  includes the inner surface  42  surrounding the bore, the metallic coating  22  disposed on the inner surface  42 , the center electrode  24  disposed in the bore of the insulator  26 , and the braze  23  disposed between the center electrode  24  and the metallic coating  22 . However, in this case, the center electrode  24  does not include the head  28 , and the inner surface  42  of the insulator  26  does not include the electrode seat  33  to support the center electrode  24 , as in the embodiments of  FIGS. 1-3 . Rather, in the embodiments of  FIGS. 4-6 , the inner surface  42  of the insulator  26  extends straight from the upper connection end  38  to the insulator nose end  40 , such that the diameter of the bore is constant, and the braze  23  secures the center electrode  24  to the metallic coating  22  on the inner surface  42 . 
     In the embodiments of  FIGS. 4-6 , the metallic coating  22  can include the layer of molybdenum and manganese and/or the nickel-based layer, as described above. According to these example embodiments, the inner surface  42  of the insulator  26  has a length L 2  extending from the upper connection end  38  to the insulator nose end  40 , and the metallic coating  22  is located along at least 50% of the length of the inner surface  42 . In the embodiment of  FIG. 5 , the metallic coating  22  is located on greater than 50%, but less than 100% of the length L 2  of the inner surface  42 . In the embodiments of  FIGS. 4 and 6 , the metallic coating  22  extends continuously from the upper connection end  38  to the insulator nose end  40 . 
     Also in the embodiments of  FIGS. 4-6 , the braze  23  can be located in one or more various locations along the center electrode  24 , and not necessarily at the top of the center electrode  24 , as in the embodiments of  FIGS. 1-3 . Typically, the braze  23  is located along less than 50% of said length L 2  of the inner surface  42  of the insulator  26 . In the embodiments of  FIGS. 4-6 , the braze  23  located in a single distinct location along the inner surface  42  of the insulator  26 , between the center electrode  24  and the metallic coating  22 .  FIGS. 4-6  show examples of where the braze  23  may be located, but the braze  23  is typically only in one location along the inner surface  42  of the insulator  26 . 
     Also in the embodiments of  FIGS. 4-6 , the center electrode  22  presents a length L 3  extending from a top end  60  to the firing end  32 , and the length L 3  of the center electrode  22  can vary. As shown in  FIGS. 4 and 5 , the length L 3  of the center electrode  24  is less than the length L 2  of the insulator inner surface  42 . Alternatively, the length L 3  of the center electrode  22  could equal the length L 2  of the insulator inner surface  42 . In the embodiment of  FIG. 6 , the length L 3  of the center electrode  22  is greater than the length L 2  of the insulator inner surface  42 . Also in the embodiments of  FIGS. 4-6 , brass powder  62  is located along an uppermost portion of the center electrode  22  and fills a portion of the insulator bore. 
     According to the example embodiments, in addition to applying the metallic coating  20  to the inner surface  42  of the insulator  26 , an outer metal coating  58  is applied to the outer surface  44  of the insulator  26 . Typically, the outer metal coating  58  is in contact with the metal shell  52 , but could be applied to other areas which do not contact the metal shell  52 . Preferably, a nickel-based layer is also applied to the inner surface  42  of the metal shell  52 . The outer metal coating  58  is then brazed to the inner surface  42  of the shell  52 , or the nickel-based layer on the inner surface  42  of the metal shell  52 , to provide another hermetic combustion seal between the insulator  26  and shell  52  to prevent gases from the combustion chamber from entering the corona igniter  20 . The outer metal coating  58  applied to the outer surface  44  and the metallic coating  22  applied to the inner surface  42  can have the same composition or a different composition. Preferably, the coatings  22 ,  58  are applied to the inner and outer surfaces  42 ,  44  of the insulator  26  during the same process step to reduce time and costs. The step of brazing the electrode head  28  to the inner surface  42  of the insulator  26  and the step of brazing the outer surface  44  of the insulator  26  to the shell  52  can also be conducted during the same process step to further reduce time and costs. In addition, limiting the number of firing steps is expected to improve the quality of the seals. 
     Another aspect of the invention provides a method of manufacturing the corona igniter  20  with the hermetic combustion seal. To manufacture the corona igniter  20  of  FIGS. 1-3 , the method includes applying the metallic coating  22  to the inner surface  42  of the insulator  26  in the region extending from or around the electrode seat  33  to our around the upper connection end  38  while applying the outer metal coating  58  to the outer surface  42  of the insulator  26 . In these embodiments, the method does not include applying the metallic coating  22  below the electrode head  28 . The method of these embodiments then includes disposing the center electrode  24  in the bore of the insulator  26  such that the head  28  of the center electrode  24  rests on the electrode seat  33 . 
     Once the center electrode  24  is disposed in the insulator  26 , the method further includes a brazing step along the inner surface  42  of the insulator  26 . For example, the method can include brazing head  28  of the center electrode  24  and/or the shot of copper-based powder  64  to the inner surface  42  of the insulator  26 . Preferably, this step is conducted simultaneously with the step of brazing the outer metal coating  58  on the outer surface  44  of the insulator  26  to the metal shell  52 . During this step, one hermetic combustion seal is formed between the inner surface  42  of the insulator  26  and the center electrode  24 , and another hermetic combustion seal is formed between the outer surface  44  of the insulator  26  and the metal shell  52  to prevent combustion gases from entering the igniter  20 . Since processes currently used to manufacture corona igniters already include the step of applying the outer metal coating  58  to the outer surface of the insulator  26  and brazing the outer surface  42  of the insulator  26  to the shell  52 , no additional process time is be required to implement the steps of the present invention. Accordingly, the reliable hermetic combustion seal is obtained without a significant increase in process time or costs. 
     Another aspect of the invention provides a method of manufacturing the corona igniter  20  including the insulator  26  and center electrode  24  of  FIGS. 4-6 . In this case, the method includes providing the insulator  26  including the inner surface  42  surrounding the bore; disposing the metallic coating  22  on the inner surface  42  of the insulator  26 ; disposing the center electrode  24  in the bore of the insulator  26 ; and brazing the center electrode  24  to the metallic coating  22 . According to these embodiments, the inner surface  42  of the insulator  26  extends straight from upper connection end  38  to the insulator nose end  40 , the inner surface  42  does not include the electrode seat  33 , and the center electrode  24  does not include the head  28 . According to these embodiments, the braze  23  secures the center electrode  24  to the metallic coating  22  on the insulator inner surface  42 . The step of brazing the center electrode  24  to the metallic coating  22  can include disposing the braze  23  in a single distinct location along the length L 2  of the inner surface  42 . 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings and may be practiced otherwise than as specifically described while within the scope of the claims.