Patent Publication Number: US-10774805-B2

Title: Igniter assembly with improved insulation and method of insulating the igniter assembly

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This U.S. Divisional application claims priority to U.S. Utility patent application Ser. No. 15/935,540, filed Mar. 26, 2018, which claims the benefit of U.S. Provisional Patent Application Ser. No. 62/477,299, filed Mar. 27, 2017, the entire disclosure of the application being considered part of the disclosure of this application, and hereby incorporated by reference. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     This invention relates generally to corona ignition assemblies, and methods of manufacturing the corona ignition assemblies. 
     2. Related Art 
     Corona discharge ignition systems typically include a corona igniter assembly typically with a firing end assembly and an ignition coil assembly attached to one another and inserted into a combustion chamber of an engine. The firing end assembly includes 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 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. The electric field is also preferably 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. Ideally, the field is also controlled so that the corona discharge only forms at the firing end and not along other portions of the corona igniter assembly. However, such control is oftentimes difficult to achieve. 
     For example, a significant amount of energy that should be transferred from the coil of the ignition coil assembly to the igniter of the firing end assembly through an insulating medium can be lost through the insulating medium used to connect the coil and the igniter, referred to as an extension. The energy loss can occur due to capacitive and dissipative losses and loss due to formation of corona in the extension. 
     SUMMARY 
     One aspect of the invention provides an igniter assembly, for example a corona igniter assembly. The igniter assembly comprises an ignition coil assembly including a coil, a firing end assembly including an igniter and coupled to the ignition coil assembly by an extension, and the extension contains a pressure chamber. A central conductor is disposed between the ignition coil assembly and the firing end assembly for transferring energy from the coil to the igniter. A valve assembly is disposed in the pressure chamber of the extension for allowing evacuation of contents of the pressure chamber and allowing the pressure chamber to be filled with an insulating medium. The valve assembly seals the insulating medium in the pressure chamber. The valve assembly includes a valve stem, and the valve stem is biased toward the ignition coil assembly by a spring to maintain the sealing of the pressure chamber. 
     The valve assembly together with the ignition coil assembly, extension and firing end assembly can provide for improved sealing, reduced packaging, and thus lower energy loss in the extension, as well as a compact packaging of the igniter with the coil. The valve assembly can also contribute to improved electrical fields and can mitigate problems that typically occur using an external fill valve. 
     Another aspect of the invention provides a method of manufacturing an igniter assembly. The method comprises the steps of coupling a central conductor to a firing end assembly including an igniter, coupling the firing end assembly to an extension containing a pressure chamber, and disposing a valve assembly in the pressure chamber of the extension. The valve assembly includes a valve stem, and the valve stem and/or a sealing device located around the valve stem seals the pressure chamber when the valve stem is biased away from the firing end assembly by a spring. The method also includes evacuating contents of the pressure chamber by pressing the valve stem toward the spring and allowing contents of the pressure chamber to travel past the valve stem and out of the pressure chamber, and filling the pressure chamber with an insulating medium by pressing the valve stem toward the spring and allowing the insulating medium to travel past the valve stem and into the pressure chamber after evacuating the contents out of the pressure chamber. The method further includes biasing the valve stem away from the firing end assembly with the spring so that the valve stem maintains a seal of the pressure chamber containing the insulating medium, and coupling an ignition coil assembly including a coil to the central conductor and the extension. 
     Yet another aspect of the invention provides a method for providing an insulating medium to an igniter assembly. The igniter assembly comprises a firing end assembly including an igniter, and the igniter is coupled to a central conductor and an extension containing a pressure chamber with a valve assembly disposed in the pressure chamber of the extension. The method comprises the steps of pressing a valve stem of the valve assembly into a spring, providing the insulating medium past the valve stem to fill the pressure chamber of the extension with the insulating medium, and sealing the pressure chamber containing the insulating medium with the valve stem and/or a sealing device located around the valve stem. 
    
    
     
       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 a corona igniter assembly including an ignition coil extension, firing end assembly, extension, and valve assembly according to an example embodiment; 
         FIG. 2  is an enlarged view of the valve assembly of the example embodiment; 
         FIG. 3A  is an enlarged view of the valve assembly of the example embodiment in a closed configuration; 
         FIG. 3B  is an enlarged view of the valve assembly of  FIG. 3A  in an open configuration; 
         FIG. 4A  illustrates a vacuum and pressurizing assembly fixture connected to the valve assembly according to an example embodiment in a closed configuration; 
         FIG. 4B  illustrates the vacuum and pressurizing assembly fixture of  FIG. 4A  in an open configuration; 
         FIGS. 5A and 5B  are partial view of the assembly according to an example embodiment; 
         FIG. 6A  is a partial view of the assembly according to an example embodiment; 
         FIGS. 6B and 6C  are FEA models showing the electrical field in portions of the assembly of  FIG. 6A ; 
         FIGS. 7A and 7B  are partial view of the assembly according to an example embodiment; 
         FIG. 8A  is a partial view of the assembly according to an example embodiment; 
         FIGS. 8B and 8C  are FEA models showing the electrical field in portions of the assembly of  FIG. 8A ; 
         FIG. 9A  is a partial view of the assembly according to an example embodiment; 
         FIG. 9B  is a FEA model showing the electrical field in portions of the assembly of  FIG. 9A ; 
         FIG. 10A  illustrates a valve stem of the valve assembly and an upper connector according to an example embodiment; 
         FIG. 10B  shows the valve stem and the upper connector and illustrates gas flow through the valve stem when pressurizing a pressure chamber of the extension; 
         FIG. 10C  is a cross-section of the valve stem and the upper connector and illustrates gas flow through the valve stem when vacuuming the pressure chamber; and 
         FIG. 10D  is another cross-section of the valve stem and the upper connector. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     One aspect of the invention provides an igniter assembly for an internal combustion engine, such as a corona igniter assembly  20  as shown in  FIG. 1 . The corona igniter assembly  20  includes an ignition coil assembly  22  producing a high radio frequency and high voltage electrical field, and a firing end assembly  24  distributing the electrical field in the combustion chamber for fuel ignition. An extension  26  connects the ignition coil assembly  22  to the firing end assembly  24 . The firing end assembly  24  includes a corona igniter  28 , the ignition coil assembly  22  includes a coil  30 , and energy is transferred from the coil  30  to the corona igniter  28  through a central conductor  32 . In the example embodiment, the central conductor  32  is formed of brass. The extension  26  includes a tube  34  containing a sealed pressure chamber  36  which surrounds the central conductor  32 . The tube  34  could be rigid or flexible made of any impermeable material. In the example embodiment, the tube  34  is formed of steel. 
     A valve assembly  38  is connected to the central conductor  32  and the tube  34  for evacuating contents of the sealed pressure chamber of the tube  34 , and then filling the sealed pressure chamber  36  of the tube  34  with an insulating medium, such as pressurized gas. The ignition coil assembly  22  is also typically connected to the valve assembly  38  after the sealed pressure chamber  36  is filled with the insulating medium. Although the valve assembly  38  is described in connection with the corona igniter assembly  20 , it is noted that the valve assembly  38  could be used with other types of igniter assemblies. 
     In the example embodiment shown in  FIG. 1 , the firing end assembly  24  includes an insulator  40 , typically formed of ceramic, disposed around a bottom portion of the central conductor  32  and around a central electrode  42  of the corona igniter  28 . The central electrode  42  is coupled to the central conductor  32  for receiving energy from the coil  30 . In the example embodiment, the corona igniter  28  includes a firing tip  44  including a plurality of prongs at a firing end of the central electrode  42 . The firing end assembly  24  of this embodiment also includes a metal shell  46  surrounding the insulator  40  and connected to the tube  24  of the extension  26 . The ignition coil assembly  22  and the firing end assembly  24  shown in  FIG. 1  are only example embodiments, and the ignition coil assembly  22  and the firing end assembly  24  can have various other designs and include various other components. 
     The valve assembly  38  is shown in the Figures and includes a valve stem  48  surrounded by a valve housing  50 . The valve housing  50  can be formed of a single piece, or more than one piece. The valve housing  50  can also include an inner portion, referred to as a valve body, which is sealed to an outer portion of the valve housing  50 . The valve housing  50  is disposed in the sealed pressure chamber  36  of the extension  26  adjacent an upper end of the extension  26  and is also connected to the ignition coil assembly  22 . 
       FIG. 2  is an enlarged view of the valve assembly  38  according to the example embodiment. The valve assembly  28  of this embodiment includes the valve housing  50  which is typically formed of a plastic or other insulating material. The valve stem  48  is typically formed of metal, such as brass, or other highly conductive material, and is disposed in a bore of the valve housing  50 . A conductive coating can be applied along the bore of the valve housing  50  to further reduce electric field. In the example embodiment, an O-ring  51 , in this case a male static O-ring seal, is disposed around the valve stem  48  to seal the valve stem  48  against the valve housing  50 . One or more additional O-rings are also disposed around the valve housing  50  to seal the valve housing  50  against the tube  34 . 
     A lower end of the valve stem  48  is connected to a spring  52  formed of metal. The spring  52  can be a coil spring, as shown in the drawings, or another type of spring. Although the spring  52  is coupled to the central conductor  32 , the spring  52  is not directly connected to the central conductor  32 , but rather is electrically connected to the central conductor  32  through a spring seat  54  on which it rests, which is explained further below. In the example embodiment, the spring seat  54  is located adjacent an upper end of a sleeve  56  which surrounds the central conductor  32 . The sleeve  56  is typically made of conductive silicon, PTFE, or any other low dielectric insulating material. The spring seat  54  is preferably conductive. The spring seat  54  extends upward from the sleeve  56  and surrounds the spring  52 . The spring seat  54  is preferably conductive and helps mitigate corona formation in a cavity formed between the spring  52  and the valve housing  50 . 
     A lower connector  58 , referred to as a slip connector, is disposed along the spring seat  54  between the spring  52  and the sleeve  56 . The central conductor  32  is attached to the lower portion of the spring seat  54  by the lower connector  58 . In the example embodiment, a spring seat cover  60  formed of plastic or other insulating material is disposed around the spring  52 . A top end of the spring seat cover  60  is received in the bore of the valve housing  50 , and a bottom end of the spring seat cover  60  is located near the base of the spring seat  54 . In an another example embodiment, the bore of the valve housing  50  could have a conductive plating to further reduce corona formation losses and failure paths initiating in a cavity formed between the spring  52  and the valve housing  50 . The spring seat  54  could then be made of an insulating material with a conductive bore and will help eliminate the spring seat cover  60 . In the example embodiment of the Figures, an upper connector  62  connects the valve stem  48  to the ignition coil assembly  22 . 
     In the example embodiment, the valve stem  48  is free to move axially only, concentrically sliding against the bore in the valve housing  50 . The spring  52  helps to hold or bias the valve stem  48  in its closed position, which is away from the igniter assembly  20  and toward the ignition coil assembly  22 . The spring  52  is supported by the spring seat  54  which is press fitted and bonded to the valve housing  50 . As discussed above, the valve assembly  38  sits in the sealed pressure chamber  36  of the tube  34 . The extension  26 , with the valve assembly  38  attached, is attached to the firing end assembly  24 . More specifically, a lower end of the tube  34  is attached to the metal shell  46  of the corona igniter  28  with the help of a weld and O-rings  51  to seal the sealed pressure chamber  36 . 
     The valve stem  48  according to an example embodiment is shown in  FIGS. 10A-10D . The valve stem  48  has an axial hole  67  in which the upper connector  62  is fitted. Two holes  66 , orthogonally offset, are cross-drilled perpendicular to the axis of the valve stem  48  in a manner such that they intersect with the axial hole  67  of the valve stem  48 . In this embodiment, the O-ring  51  on the valve stem  48  seals against the valve housing  50  and is located below the cross drilled holes  66 . Once the valve stem  48  is assembled in the valve housing  50 , and when put in the open configuration ( FIG. 3B ), these three holes  66 ,  67  together create a passage way for gas to flow from the top of the valve assembly  38  into the pressure chamber  36  or for gas from the pressure chamber  36  to flow out through the valve assembly  38 . The passageway is sealed off to the pressure chamber  36  by the O-ring  51  in the closed position ( FIG. 3A ).  FIG. 10A  illustrates the valve stem  48  with the holes  66 ,  67  and the upper connector  62 .  FIG. 10B  shows the valve stem  48  and the upper connector  62  and illustrates the gas flow through the valve stem  48  when pressurizing the pressure chamber  36 .  FIG. 10C  is a cross-section of the valve stem  48  and the upper connector  62  and illustrates the gas flow through the valve stem  48  when vacuuming the pressure chamber  36 .  FIG. 10D  is another cross-section of the valve stem  48  and upper connector  62 . 
     The valve assembly  38  and a vacuum and pressurizing fixture assembly  64  are used to provide the insulating medium in the sealed pressure chamber  36 . The example embodiment is shown in  FIGS. 3 and 4 . In its closed position, the O-ring  51  located around the valve stem  48  seals pressure chamber  36  formed in the tube  34 . Alternatively, the valve stem  48  and/or another sealing device seals off the pressure chamber  36 . The valve stem  48  and O-ring could also together seal the pressure chamber  36 . During the vacuuming or pressurizing process, the valve assembly  38  is set to its open position, as shown  FIGS. 3B and 4B , by pushing the valve stem  48  down against the spring  52  to a defined position which exposes at least one opening, for example the cross drilled holes  66  and axial hole  67  in the valve stem  48 , to a cavity in a seat region  68 . This cavity connects the pressure chamber  36  in the tube  34  below (to be vacuumed or pressurized) to an opening  70  on the top face of the valve housing  50 . Once the insulating medium is provided and the pressure chamber  36  is pressurized, the differential force of the spring  52  along with the pressure in the sealed pressure chamber  36  forces the spring  52  upward and closes the valve assembly  38  shut. The valve assembly  38  in the closed position is shown in  FIGS. 3A and 4A . The valve stem  38  is coupled to the coil assembly  22 . In the example embodiment, the upper connector  62  on the top of the valve stem  48  is attached to the coil  30  via a pin  72  and acts as another central conductive element. The central conductor  32  is allowed to have floating contact in the bore of the insulator  40  of the corona igniter  28 , providing for movement of the valve stem  48 , thermal expansion, and electrical continuity. 
     As shown in  FIGS. 4A and 4B , the combined vacuum and pressurizing assembly fixture  64  of the example embodiment is made up of an aluminum manifold  74 , a steel push screw  76 , and brass fixture stem  78 . The vacuum and pressurizing assembly fixture  64  is screwed on to a coil receptacle nut  80  for operation. The push screw  76  is attached to the brass fixture stem  78  via a snap ring arrangement  82 . When tightened to a stop, the push screw  76  pushes the brass fixture stem  78  to an open position, as shown in  FIG. 4B . This in turn pushes the valve stem  48  in the open position, as shown in  FIG. 3B . When the vacuum and pressurizing assembly fixture  64  is in the open position, all ports are open and the vacuum and pressurizing operation is carried out. In the open position, a pressurized gas inlet  84  is located along a first valve connector  86 , and a vacuum outlet  88  is located along a second valve connector  86 . Once the vacuum and pressurizing operation is done, the push screw  76  is brought to its original position and all ports are now in the closed sealed position, as shown in  FIG. 4A . 
     The design described above can provide numerous advantages, including a very low loss, low dielectric constant fluid insulating medium in the extension  26  used to transfer of energy from the coil  30  to the corona igniter  28 . The unique valve assembly  38  which is incorporated in the central conducting element of the extension  26  facilities compact packaging of the corona igniter  28  with the coil  30 , which in the example embodiment is detachable. 
     The valve assembly  38  can also improve electrical fields and mitigate problems arising by attaching an external fill valve. The single vacuum and pressurizing assembly fixture  64  is designed to evacuate contents of the extension  26  and then fill the extension  26  with pressurized gas, such as nitrogen, through the valve assembly  38  (two-way application). More specifically, the advantages include reduced electric field in the valve assembly  38  and components surrounding the valve assembly  38 . The valve assembly  38  is able to operate without moving the central conductor  32  where it passes out of the valve assembly  38 , such that the central conductor  32  and center electrode  42  can be covered with insulating medium from top to bottom and occurrence of corona from the surfaces of the central conductor  32  and the central electrode  42  is reduced. 
     As indicated above, the improved design provides for reduced electrical fields in the valve assembly  52  and immediately surrounding the valve assembly  52 . In addition, the valve assembly  52  can operate without moving the central conductor  32  where passes out of the value assembly  52 . Thus, it is possible to surround the entire central conductor  32  in the tube  34  with the insulating medium and reduce the occurrence of corona discharge from the surface of the central conductor  32 . 
     In comparative designs, a significant amount of energy transferred from the coil  30  to the corona igniter  28  is lost through the insulating medium and the extension  26  used to connect the coil  30  and the corona igniter  28 . This can occur due to capacitive and dissipative losses, and possible loss due to formation of corona in the extension  26 . Highly pressurized gas or fluid, such as greater than 30 bar, preferably having a low dielectric constant and loss factor, can suppress formation of corona or discharges from the central conductor  32  to ground. Thus, the pressurized gas or fluid can be used as the insulating medium in the extension  26 . One example of such a gas is dry nitrogen gas at a pressure of greater than 30 bar, which is known to have a very low dielectric constant (such as ˜1 or near 1). It is not trivial to pressurize and hold pressure in the extension  26  over the lifetime of the coil  30 , extension  26 , and corona igniter  28 . By incorporating the pressurizing valve assembly  38  in to the central conductor  32  in the extension  26 , the sealing surfaces are reduced and overall packaging of the corona igniter  28  is made compact which helps in better sealing of the components. The dual purpose of the valve assembly  38  as another centralized conductor lends to electrical field improvements when compared to attaching an external fill valve. As designed, the insulating medium, such as the pressurized gas, can fill the minutest of the crevices in the extension  26  and provides optimal insulation. The assembly can be made impermeable by using a combination of O-rings  51 , sealant, and a rubber puck  90 . In the example embodiment, the O-rings  50  are formed of a silicon-based material. The extension  26  is designed in such a way that the coil  30  is attached after the extension  26  is pressurized. The coil  30  is also detachable from the valve assembly  38  without de-pressurizing the extension  26 . This feature enables improved maintenance capabilities of the igniter  28 , such as removal, cleaning and replacement of the coil  30  without changing other components, and improved installation through the coil  30 . 
       FIGS. 5A-9B  include example embodiments of the valve assembly  38  and FEA models showing the effects of the reduced electrical field provided by the valve assembly  38  design. It is noted that the metal components of  FIGS. 5A-9B , which are not conductors, are not modeled in the FEA results. 
     The designs included in  FIGS. 7A-9B  are preferred over the design of  FIGS. 5A-6C  because the design of  FIGS. 5A-6C  typically have movement of the central conductor  32  and higher electrical field throughout the valve assembly  38 . 
     In the design of  FIGS. 5A-6C , the valve stems  48  move ups and down when the valve assembly  38  operates. Hence, the central conductor  32  and the sleeve  56  also move up and down, and the sleeve  56  cannot completely cover the central conductor  32  as it approaches and goes into the firing end assembly  24 . This can lead to flashover at the lower joint between the central conductor  32  and the firing end assembly  24 . Also, the design of  FIGS. 5A-6C  typically has a higher electrical field than the designs of  FIG. 7A-9B  because of the clearances in the valve assembly  38 , and the high electric field typically appears in these small clearances or gaps. Due to the electrical field level, the O-rings  51  typically have a reduced life and higher parasitic loss, compared to the O-rings  51  of  FIGS. 7A-9B . 
     In the designs of  FIGS. 7A-8C , movement of the central conductor  32  is avoided, and the electric field is reduced throughout the valve assembly  38 . In these embodiments, the valve stem  48  moves up and down inside of the stationary valve housing  50 . Thus, the central conductor  32  remains completely covered by the sleeve  56  and electric field throughout the valve assembly  38  is reduced, including everywhere inside the valve housing  50 . It has been found that the electric field in the valve assembly  38  of  FIGS. 7A-8C  is actually zero in the valve housing  50 . An electrical field does remain above the valve housing  50 . It is noted that in the design of  FIGS. 7A-8C , the plastic valve housing  50  can include a conductive coating along the bore of the plastic valve housing  50 . A FEA analysis of this design is shown in  FIG. 8B . In this case, the electric field is reduced, as shown by the FEA model. For example, the peak electric field can be approximately 3 times less when the conductive coating is applied, as in the design in  FIG. 8B , compared to the design in  FIG. 8A . 
     In the design of  FIGS. 9A and 9B , the conductive valve housing  50  completely covers the valve mechanism. The valve housing  50  can be one or more pieces. In the embodiment of  FIGS. 9A and 9B , the valve housing  50  includes the inner portion  50   a , in this case a plastic valve body, which completely covers the valve mechanism and is sealed to the outer portion  50   b  of the valve housing  50 . For example, the inner and outer portions  50   a ,  50   b  of the valve housing  50  can be co-molded. In the design of  FIGS. 9A and 9B , the electric field is reduced everywhere inside the valve housing  50 , compared to other designs The FEA model shows the electric field is actually zero inside the valve housing  50  of  FIGS. 9A and 9B . In addition, the peak electric field drops throughout the design of  FIGS. 9A and 9B . It was found the peak electric field is about three times less than a similar design without the elongated plastic valve body  50   a , similar to the embodiment of  FIGS. 8A-8C  with the conductive coating along the bore. 
     The design described above can be translated to work over various sizes of extension  26  length and corona igniter  28  sizes without significant modifications to the assembly. As discussed above, either a rigid or flexible air tight tube  34  could be used for the extension  26 . The single vacuum and pressurizing assembly fixture  64  facilitates pulling a vacuum in the extension  26  and pressurizing the extension  26  by connecting to the valve assembly  38  in the same location where the coil  30  will be attached to the extension  26 . This helps reduce assembly fixturing and components and expedites the assembly process. 
     The design described above includes a combination of metallic and plastic or other non metallic components. The valve assembly  38  is incorporated in to part of the central conductive element and is spring loaded. It is also noted that the valve assembly  38  can be used with the extension  26  when the extension  26  is flexible, the fluid medium is used as insulation, and the extension  26  can be of any overall length without modifications to the connecting features or the valve assembly  38 . The coil  30  is detachable without depressurizing the assembly, and evacuation of the sealed pressure chamber  36  of the tube  34  and pressurizing of the tube  34  are carried out with the same vacuum and pressurizing assembly fixture  64 . The valve assembly  38  is also scalable to different sized corona igniters  28 . 
     It is noted that the extension  26 , the valve assembly  38 , and the combined vacuum and pressurizing assembly fixture  64  described herein are only example embodiments, and modifications of the example extension  26 , the valve assembly  38 , and the vacuum and pressurizing assembly fixture  64  described herein can be made. 
     Another aspect of the invention provides a method of manufacturing the corona igniter assembly  20 . The method includes connecting the metal shell  46  of the firing end assembly  24  to the tube  34  of the extension  26 , disposing the valve assembly  38  in the tube  34  of the extension  26 , and connecting the valve assembly  38  to the central conductor  32 . The method further includes connecting the valve assembly  38  to the ignition coil assembly  22  after filling the sealed pressure chamber  36  of the tube  34  with the insulating medium. 
     Yet another aspect of the invention provides a method for providing the insulating medium around the central conductor  32  of the corona igniter assembly  20 . The extension  26  contains the sealed pressure chamber  36  which surrounds the central conductor  32 . The valve assembly  38  is connected to the central conductor  32  and the extension  26 . The method includes evacuating contents of the sealed pressure chamber  36 , and then filling the sealed pressure chamber  36  with the insulating medium using the vacuum and pressurizing fixture  64  and the valve assembly  38 . After filling the sealed pressure chamber  36 , the vacuum and pressurizing fixture  64  and the valve assembly  38  is disconnected from the valve assembly  38 , and the ignition coil assembly  22  is connected to the valve assembly  38 . 
     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 invention. It is contemplated that all features of all claims and of all embodiments can be combined with each other, so long as such combinations would not contradict one another.