This invention relates generally to a corona igniter for emitting a radio frequency electric field to ionize a fuel-air mixture and provide a corona discharge, and a method of forming the igniter.
Corona discharge ignition systems include an igniter with a central electrode charged to a high radio frequency voltage potential, creating a strong radio frequency electric field in a combustion chamber. The electric field causes a portion of a mixture of fuel and air in the combustion chamber to ionize and begin dielectric breakdown, facilitating combustion of the fuel-air mixture. The electric field is preferably controlled so that the fuel-air mixture maintains dielectric properties and corona discharge occurs, also referred to as a non-thermal plasma. The ionized portion of the fuel-air mixture forms a flame front which then becomes self-sustaining and combusts the remaining portion of the fuel-air mixture. Preferably, the electric field is controlled so that the fuel-air mixture does not lose all dielectric properties, which would create a thermal plasma and an electric arc between the electrode and grounded cylinder walls, piston, or other portion of the igniter. An example of a corona discharge ignition system is disclosed in U.S. Pat. No. 6,883,507 to Freen.
The corona igniter typically includes the central electrode formed of an electrically conductive material for receiving the high radio frequency voltage and emitting the radio frequency electric field to ionize the fuel-air mixture and provide the corona discharge. The electrode typically includes a high voltage corona-enhancing electrode tip emitting the electrical field. The igniter also includes a shell formed of a metal material receiving the central electrode and an insulator formed of an electrically insulating material is disposed between the shell and the central electrode. The igniter of the corona discharge ignition system does not include any grounded electrode element intentionally placed in close proximity to a firing end of the central electrode. Rather, the ground is preferably provided by cylinder walls or a piston of the ignition system. An example of a corona igniter is disclosed in U.S. Patent Application Publication No. 2010/0083942 to Lykowski and Hampton.
During operation of high frequency corona igniters, there is an electrical advantage if the insulator outer diameter increases in a direction moving away from the grounded metal shell and towards the high voltage electrode tip. An example of this design is disclosed in U.S. Patent Application Publication No. 2012/0181916. For maximum benefit it is often desirable to make the outer diameter larger than the inner diameter of the grounded metal shell. This design has resulted in the need to assemble the igniter by inserting the insulator into the shell from the direction of the combustion chamber, referenced to as “reverse-assembly”.
One aspect of the invention provides a corona igniter comprising a central electrode, an insulator surrounding the central electrode, and a conductive component surrounding the insulator. The central electrode is formed of an electrically conductive material for receiving a high radio frequency voltage and emitting a radio frequency electric field. The insulator is formed of an electrically insulating material and extends longitudinally along a center axis from an insulator upper end to an insulator nose end. The insulator includes an insulator outer surface extending from the insulator upper end to the insulator nose end, and the insulator outer surface presents an insulator outer diameter extending across and perpendicular to the center axis. The insulator also includes an insulator body region and an insulator nose region. The insulator outer surface includes a lower ledge extending outwardly away from the center axis between the insulator body region and the insulator nose region. The lower ledge presents an increase in the insulator outer diameter.
The conductive component is formed of electrically conductive material and surrounds at least a portion of the insulator body region such that the insulator nose region extends outwardly of the conductive component. The conductive component includes a shell surrounding at least a portion of the insulator body region and extending from a shell upper end to a shell firing end. The shell presents a shell inner surface facing the center axis and extending along the insulator outer surface from the shell upper end to the shell firing end. The shell inner surface also presents a shell inner diameter extending across and perpendicular to the center axis.
The conductive component also includes an intermediate part surrounding a portion of the insulator body region and extending longitudinally from an intermediate upper end to an intermediate firing end. For example, the intermediate part can be layer of metal which brazes the insulator to the shell. The intermediate part includes an intermediate inner surface facing the center axis and extending longitudinally along the insulator outer surface from the intermediate upper end to the intermediate firing end. The intermediate inner surface presents a conductive inner diameter extending across and perpendicular to the center axis, and the conductive inner diameter is less than the insulator outer diameter along a portion of the insulator located between the lower ledge and the insulator nose end. The intermediate part is disposed between the insulator upper end and the lower ledge.
Another aspect of the invention provides a method of forming the corona igniter. The method comprises disposing the intermediate part between the insulator upper end and the lower ledge; and disposing a shell formed of an electrically conductive material around the intermediate part and the insulator.
The corona igniter of the present invention provides exceptional electrical performance because the conductive inner diameter is less than the insulator outer diameter adjacent the insulator nose region. The corona igniter can also be reverse-assembled.
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:
Exemplary embodiments of a corona igniter 20 are shown in
The central electrode 22 of the corona igniter 22 is formed of an electrically conductive material for receiving the high radio frequency voltage, typically in the range of 20 to 75 KV peak/peak. The central electrode 22 also emits a high radio frequency electric field, typically in the range of 0.9 to 1.1 MHz. The central electrode 22 extends longitudinally along a center axis A from a terminal end 38 to an electrode firing end 40. The central electrode 22 typically includes a corona enhancing tip 24 at the electrode firing end 40, for example a tip including a plurality of prongs, as shown in
The insulator 26 of the corona igniter 20 is formed of an electrically insulating material. The insulator 26 surrounds the central electrode 22 and extends longitudinally along the center axis A from an insulator upper end 42 to an insulator nose end 44. The electrode firing end 40 is typically disposed outwardly of the insulator nose end 44, as shown in
The insulator inner surface 46 also presents an insulator inner diameter Dii extending across and perpendicular to the center axis A. The insulator 26 includes an insulator outer surface 50 extending from the insulator upper end 42 to the insulator nose end 44. The insulator outer surface 50 also presents the insulator outer diameter Dio extending across and perpendicular to the center axis A. The insulator inner diameter Dii is preferably 15 to 25% of the insulator outer diameter Dio.
As shown in
The conductive component of the corona igniter 20 surrounds at least a portion of the insulator body region 28 such that the insulator nose region 30 extends outwardly of the conductive component, as shown in the Figures. The conductive component includes the shell 34 and the intermediate part 36, both formed of electrically conductive metal. The shell 34 and the intermediate part 36 can be formed of the same or different electrically conductive materials.
The shell 34 is typically formed of a metal material, such as steel, and surrounds at least a portion of the insulator body region 28. The shell 34 extends along the center axis A from a shell upper end 54 to a shell firing end 56. The shell 34 presents a shell inner surface 58 facing the center axis A and extending along the insulator outer surface 50 from the shell upper end 54 to the shell firing end 56. The shell 34 also includes a shell outer surface 60 facing opposite the shell inner surface 58 and presenting a shell outer diameter Dso. The shell inner surface 58 presents a shell bore surrounding the center axis A and a shell inner diameter Dsi extending across and perpendicular to the center axis A. The shell inner diameter Dsi is typically greater than or equal to the insulator outer diameter Dio along the entire length l of the insulator 26 from the insulator upper end 42 to the insulator nose end 44, so that the corona igniter 20 can be forward-assembled. The length of the insulator 26 includes both the body region 28 and the nose region 30. The term “forward-assembled” means that the insulator nose end 44 can be inserted into the shell bore through the shell upper end 54, rather than through the shell firing end 56. However, in an alternate embodiment, the shell inner diameter Dsi is less than or equal to the insulator outer diameter Dio along a portion of the length l of the insulator 26 from the insulator upper end 42 to the insulator nose end 44, and that the corona igniter 20 is reversed assembled. The term “reverse-assembled” means that the insulator upper end 42 is inserted into the shell bore through the shell firing end 56.
The intermediate part 36 of the corona igniter 20 is disposed inwardly of the shell 34 and surrounds a portion of the insulator body region 28. The intermediate part 36 is disposed along the insulator body region 28 directly above the insulator nose region 30. It extends longitudinally from an intermediate upper end 64 to an intermediate firing end 66. The intermediate part 36 is rigidly attached to the insulator outer surface 50. Preferably, the intermediate inner surface 68 is hermetically sealed to the insulator outer surface 50, to close the axial joint and avoid gas leakage during use of the corona igniter 20 in a combustion engine.
The intermediate part 36 is typically formed of a metal or metal alloy containing one or more of nickel, cobalt, iron, copper, tin, zinc, silver, and gold. The metal or metal alloy can be cast into place on the insulator outer surface 50. Alternatively, the intermediate part 36 can be glass or ceramic based and made conductive by the addition of one or more of the above metals or metal alloys. The glass or ceramic based intermediate part 36 can be formed and sintered directly into place on the insulator outer surface 50. The intermediate part 36 can also be provided as a metal ring attached in place to the insulator outer surface 50 by soldering, brazing, diffusion bonding, high temperature adhesive, or another method. The intermediate part 36 is also attached to the shell inner surface 58, preferably by any suitable method, including soldering, brazing, welding, interference fit, and thermal shrink fit. The material used to form the intermediate part 36 is preferably conformable and is able to absorb stresses occurring during operation, without passing them to the insulator 26.
In another embodiment, the intermediate part 36 brazes the insulator 26 to the shell 34. In this embodiment, the intermediate part 36 is a thin layer of metal containing one or more of nickel, cobalt, iron, copper, tin, zinc, silver, and gold. The metal is provided in liquid form and flows between the insulator 26 and the shell 34, and then allowed to solidify to braze the insulator 26 to the shell 34. The layer of metal can be applied before or after disposing the insulator 26 in the shell 34. In addition, the intermediate part 28 can be used to braze the insulator 26 to the shell 34 in either the forward or reverse assembly igniters 22.
In one example embodiment, the intermediate part 28 is formed from a solid piece of metal, specifically a solid ring formed of a silver (Ag) and/or copper (Cu) alloy disposed around the insulator 26. Next, the shell 34 is disposed around the insulator 26, and the assembly is heated at which time the solid ring, referred to as a braze, becomes liquid and is wicked into an area, referred to as a “braze area,” through capillary action. As the parts cool, the liquid alloy solidifies to provide the intermediate part 36 brazed to the insulator 26 and to the shell 34. This process puts the ceramic insulator 26 in compression because of the differences in shrinkage of the components after the alloy solidifies and as the parts cool. During operation, the engine temperature does not reach the melting point of the braze alloy used to form intermediate part 36, so that it stays solid during engine operation. Alternatively, the intermediate part 36 could be formed by brazing the solid ring to the insulator 26 and shell 34 by another metal material, such as another metal having a lower melting point than the solid ring, using the brazing process described above.
The intermediate inner surface 68 of the intermediate part 36 faces the center axis A and extends longitudinally along the insulator outer surface 50 from the intermediate upper end 64 to the intermediate firing end 66. The intermediate part 36 also includes an intermediate outer surface 70 facing opposite the intermediate inner surface 68 and extending longitudinally from the intermediate upper end 64 to the intermediate firing end 66. The intermediate outer diameter Dint is typically less than or equal to the shell outer diameter Dso, as shown in
The conductive inner diameter Dc is typically equal to 75 to 90% of the shell inner diameter Dsi along the intermediate part 36. As shown in
The exemplary embodiments of the corona igniter 20 can include various different features. In the exemplary embodiments of
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Another aspect of the invention provides a method of forming the corona igniter 20. The method can be a forward-assembly method, which includes inserting the insulator nose end 44 into the shell bore through the shell upper end 54, rather than the shell firing end 56 as in the reverse-assembly method. However, the method could alternatively comprise a reverse assembly method, wherein the shell inner diameter Dsi is less than or equal to the insulator outer diameter Dio along a portion of the insulator 26, and the method includes inserting the insulator nose end 44 into the shell bore through the shell firing end 56.
The method of forming the corona igniter 20 includes control of forces and material temperatures such that the insulator 26 is not placed in tension, either during assembly, or due to differential thermal expansion during operation.
The method includes providing the insulator 26 formed of the electrically insulating material extending along the center axis A from the insulator upper end 42 to the insulator nose end 44. The insulator 26 includes the insulator outer surface 50 extending from the insulator upper end 42 to the insulator nose end 44. The insulator outer surface 50 presents the insulator outer diameter Dio and includes the lower ledge 52 extending outwardly away from and transverse to the center axis A between the insulator body region 28 and the insulator nose region 30.
The method also includes disposing the intermediate part 36 formed of the electrically conductive material on the lower ledge 52 of the insulator 26. This step is typically conducted before the insulator 26 is inserted into the shell 34. However, if the intermediate outer diameter Dint is greater than the shell inner diameter Dsi, as in the corona igniter 20 of
The method also includes rigidly attaching the intermediate part 36 to the insulator outer surface 50, typically before inserting the insulator 26 into the shell 34. The attaching step typically includes casting, sintering, brazing, soldering, diffusion bonding, or applying a high temperature adhesive between the intermediate part 36 and insulator outer surface 50. If the intermediate part 36 is a metal or metal alloy, the attaching step typically includes casting. If the intermediate part 36 is glass or ceramic based, the attaching step typically includes forming and sintering directly into place around the insulator outer surface 50. If the intermediate part 36 is a metal ring, then the attaching step typically includes soldering, diffusion bonding, or applying a high temperature adhesive between the intermediate part 36 and insulator outer surface 50. The method typically includes hermetically sealing the intermediate part 36 to the insulator 26 to close the axial joint and avoid gas leakage during use of the corona igniter 20.
The method also includes providing the shell 34 formed of the electrically conductive material extending along and around the center axis A from the shell upper end 54 to the shell firing end 56. The shell 34 includes the shell inner surface 58 extending from the shell upper end 54 to the shell firing end 56, and the shell inner surface 58 presents the shell bore extending along the center axis A. In each exemplary embodiment, the shell inner diameter Dsi is greater than or equal to the insulator outer diameter Dio.
The method next includes inserting the insulator 26 into the shell 34 in the forward-assembly direction. This step is typically conducted after attaching the intermediate part 36 to the insulator 26, but may be done before. This step includes inserting the insulator nose end 44 through the shell upper end 54 into the shell bore. The insulator 26 should be moved along the shell inner surface 58 until the insulator nose end 44 extends outwardly of the shell firing end 56. To manufacture the exemplary embodiments of
The method may also include disposing the filler material 88 in the crevices 76 between the insulator 26 and shell upper end 54. This step may include filling at least a portion of the crevice 76 with the filler material 88. Alternatively, the filler material 88 can be applied to both the insulator outer surface 50 and shell inner surface 58 before inserting the insulator 26 into the shell 34, such that when the insulator 26 and shell 34 are connected, the filler material 88 at least partially fills the crevice 76. If the filler material 88 provides a gas-tight seal, then it is possible to omit the step of rigidly attaching the intermediate part 36 to the insulator 26.
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 appended claims.
This continuation application claims the benefit of U.S. continuation application Ser. No. 16/041,209, filed Jul. 20, 2018, which claims the benefit of U.S. continuation-in-part application Ser. No. 15/240,652, filed Aug. 18, 2016, which claims the benefit of U.S. continuation application Ser. No. 14/742,064, filed Jun. 17, 2015, which claims the benefit of U.S. application Ser. No. 13/843,336, filed Mar. 15, 2013, now U.S. Pat. No. 9,088,136, which claims the benefit of U.S. provisional application Ser. No. 61/614,808, filed Mar. 23, 2012, the entire contents of which are hereby incorporated by reference.
Number | Date | Country | |
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61614808 | Mar 2012 | US |
Number | Date | Country | |
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Parent | 16041209 | Jul 2018 | US |
Child | 16661275 | US | |
Parent | 15240652 | Aug 2016 | US |
Child | 16041209 | US | |
Parent | 13843336 | Mar 2013 | US |
Child | 14742064 | US |
Number | Date | Country | |
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Parent | 14742064 | Jun 2015 | US |
Child | 15240652 | US |