Patent Description:
This invention relates generally to corona igniters with combustion seals, and methods of manufacturing corona igniters with combustion seals.

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. Document <CIT> discloses a device according to the preamble of claim <NUM>.

One aspect of the invention provides a corona igniter according to claim <NUM>.

Another aspect of the invention provides a method of manufacturing a corona igniter. The method is described in claim <NUM>.

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.

One aspect of the disclosure includes a corona igniter <NUM> for an internal combustion engine including a metallic coating <NUM> and braze <NUM> providing a hermetic combustion seal between a center electrode <NUM> and insulator <NUM> to prevent gases located in a combustion chamber of the engine from entering the igniter <NUM>. <FIG>, <FIG>, and <FIG> are examples of the center electrode <NUM> and insulator <NUM> with the hermetic combustion seal therebetween, and <FIG> is an example of a corona igniter <NUM> including the combustion seal.

The corona igniter <NUM> 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 <FIG>, the center electrode <NUM> is disposed in the bore of the insulator <NUM>, and the center electrode <NUM> extends along a center axis A from a head <NUM> to a firing end <NUM>. The center electrode <NUM> is formed of an electrically conductive material, such as nickel or a nickel alloy. In the example embodiment of <FIG>, the head <NUM> of the center electrode <NUM> is supported and maintained in a predetermined axial position by a reduced diameter of the insulator <NUM>, referred to as an electrode seat <NUM>, and an electrical terminal <NUM> rests on the head <NUM> of the center electrode <NUM>. A majority of the length of the center electrode <NUM> is surrounded by the insulator <NUM>. Also in this example embodiment, the center electrode <NUM> includes a firing tip <NUM> at the firing end <NUM>. The firing tip <NUM> 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 <NUM> in the internal combustion engine.

The insulator <NUM> of <FIG> extends longitudinally along the center axis A from an upper connection end <NUM> to an insulator nose end <NUM>. The insulator <NUM> is formed of an insulating material, typically a ceramic such as such as alumina. The insulator <NUM> also presents an inner surface <NUM> surrounding the bore which extends longitudinally from the upper connection end <NUM> to the insulator nose end <NUM> for receiving the center electrode <NUM> and possibly other electrically conductive components. The firing tip <NUM> of the center electrode <NUM> is typically disposed longitudinally past the insulator nose end <NUM>. As mentioned above, in the embodiment of <FIG>, the insulator inner surface <NUM> presents an inner diameter Di which decreases along a portion of the insulator <NUM> moving toward the insulator nose end <NUM> to form the electrode seat <NUM> which supports the electrode head <NUM>. 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 <NUM> to a base of the electrode seat <NUM>, which is in the direction moving toward the insulator nose end <NUM>.

The insulator <NUM> of the example also presents an insulator outer surface <NUM> having an insulator outer diameter Do extending across and perpendicular to the center axis A. The insulator outer surface <NUM> extends longitudinally from the upper connection end <NUM> to the insulator nose end <NUM>. In the examples the insulator outer diameter Do decreases along a portion of the insulator <NUM> moving toward the insulator nose end <NUM> to present an insulator nose region <NUM>. The insulator outer diameter Do can also vary along other portions of the length, as shown in the Figures.

The corona igniter <NUM> also includes a shell <NUM> formed of metal and surrounding a portion of the insulator <NUM>. The shell <NUM> is typically used to couple the insulator <NUM> to a cylinder block (not shown) of the internal combustion engine. The shell <NUM> extends along the center axis A from a shell upper end <NUM> to a shell lower end <NUM>. The shell upper end <NUM> is disposed between an insulator upper shoulder <NUM> and the insulator upper end <NUM> and engages the insulator <NUM>. The shell lower end <NUM> is disposed adjacent the insulator nose region <NUM> such that at least a portion of the insulator nose region <NUM> extends axially outwardly of the shell lower end <NUM>.

As mentioned above, the hermetic combustion seal between the insulator <NUM> and center electrode <NUM> is provided by applying the metallic coating <NUM> to the inner surface <NUM> of the insulator <NUM>, and then brazing. In the examples of <FIG>, the metallic coating <NUM> is located between the electrode seat <NUM> and the upper connection end <NUM>. The metallic coating <NUM> can be formed of various different compositions. According to one example the metallic coating <NUM> includes a layer of molybdenum and manganese. For example, the metallic coating <NUM> 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 <NUM> is a nickel-based layer, such as electroless nickel plating. For example, the metallic coating <NUM> 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 <NUM> includes the nickel-based layer applied to the layer of molybdenum and manganese.

In the examples of <FIG>, the metallic coating <NUM> is applied along only a portion of the insulator inner surface <NUM> for example in a region extending from the electrode seat <NUM>, or slightly above the electrode seat <NUM>, to the upper connection end <NUM>, or around the upper connection end <NUM>. In these examples the metallic coating <NUM> is not located below the electrode seat <NUM> which supports the electrode head <NUM>, and the inner surface <NUM> of the insulator <NUM> is not coated in the region extending from the base of the electrode seat <NUM> to the insulator nose end <NUM>. The length L1 of the metallic coating <NUM> of the example embodiments is identified in <FIG> and <FIG>. The thickness of the metallic coating <NUM> can vary, but it is typically less than <NUM>.

The hermetic combustion seal further includes the braze <NUM> disposed along the insulator inner surface <NUM> between the center electrode <NUM> and the insulator inner surface <NUM>. In the examples of <FIG>, the braze is between the electrode seat <NUM> and the upper connection end <NUM>. In the example of <FIG>, the head <NUM> of the center electrode <NUM> is brazed directly to the metallic coating <NUM> on the insulator inner surface <NUM>. In this case, the braze <NUM> is located along the head <NUM> of the center electrode <NUM> but not along other portions of the insulator inner surface <NUM>. In the example of <FIG>, a shot of copper-based powder <NUM> is disposed along the center axis A on the head <NUM> of the center electrode, and the copper-based powder <NUM> is then brazed to the metallic coating <NUM> on the inner surface <NUM> of the insulator <NUM>. The copper-based powder <NUM> can consist of copper or a copper alloy. In this case, the braze <NUM> is located along the copper-based powder <NUM> but not along other portions of the insulator inner surface <NUM>. Due to the combination of the metallic coating <NUM> and the braze <NUM>, the corona igniter <NUM> does not require a Kovar wire on the center electrode <NUM>, thereby eliminating the cost of welding the Kovar to the center electrode <NUM>. In addition to a reliable combustion seal, the metallic coating <NUM> and braze <NUM> helps provide electrical continuity within the insulator <NUM>, thus eliminating the need for glass material or brass powder.

Embodiments of the insulator <NUM> and center electrode <NUM> of the corona igniter <NUM> are shown in <FIG>. According to this embodiment, the insulator <NUM> includes the inner surface <NUM> surrounding the bore, the metallic coating <NUM> disposed on the inner surface <NUM>, the center electrode <NUM> disposed in the bore of the insulator <NUM>, and the braze <NUM> disposed between the center electrode <NUM> and the metallic coating <NUM>. However, in this case, the center electrode <NUM> does not include the head <NUM>, and the inner surface <NUM> of the insulator <NUM> does not include the electrode seat <NUM> to support the center electrode <NUM>, as in the embodiments of <FIG>, Rather, in the embodiments of <FIG>, the inner surface <NUM> of the insulator <NUM> extends straight from the upper connection end <NUM> to the insulator nose end <NUM>, such that the diameter of the bore is constant, and the braze <NUM> secures the center electrode <NUM> to the metallic coating <NUM> on the inner surface <NUM>.

In the embodiments of <FIG>, the metallic coating <NUM> 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 <NUM> of the insulator <NUM> has a length L2 extending from the upper connection end <NUM> to the insulator nose end <NUM>, and the metallic coating <NUM> is located along at least <NUM>% of the length of the inner surface <NUM>. In the embodiment of <FIG>, the metallic coating <NUM> is located on greater than <NUM>%, but less than <NUM>% of the length L2 of the inner surface <NUM>. In the embodiments of <FIG> and <FIG>, the metallic coating <NUM> extends continuously from the upper connection end <NUM> to the insulator nose end <NUM>.

Also in the embodiments of <FIG>, the braze <NUM> can be located in one or more various locations along the center electrode <NUM>, and not necessarily at the top of the center electrode <NUM>, as in the embodiments of <FIG>. Typically, the braze <NUM> is located along less than <NUM>% of said length L2 of the inner surface <NUM> of the insulator <NUM>. In the embodiments of <FIG>, the braze <NUM> located in a single distinct location along the inner surface <NUM> of the insulator <NUM>, between the center electrode <NUM> and the metallic coating <NUM>. <FIG> show examples of where the braze <NUM> may be located, but the braze <NUM> is typically only in one location along the inner surface <NUM> of the insulator <NUM>.

Also in the embodiments of <FIG>, the center electrode <NUM> presents a length L3 extending from a top end <NUM> to the firing end <NUM>, and the length L3 of the center electrode <NUM> can vary. As shown in <FIG> and <FIG>, the length L3 of the center electrode <NUM> is less than the length L2 of the insulator inner surface <NUM>. Alternatively, the length L3 of the center electrode <NUM> could equal the length L2 of the insulator inner surface <NUM>. In the embodiment of <FIG>, the length L3 of the center electrode <NUM> is greater than the length L2 of the insulator inner surface <NUM>. Also in the embodiments of <FIG>, brass powder <NUM> is located along an uppermost portion of the center electrode <NUM> and fills a portion of the insulator bore.

According to the example embodiments, in addition to applying the metallic coating <NUM> to the inner surface <NUM> of the insulator <NUM>, an outer metal coating <NUM> is applied to the outer surface <NUM> of the insulator <NUM>. Typically, the outer metal coating <NUM> is in contact with the metal shell <NUM>, but could be applied to other areas which do not contact the metal shell <NUM>. Preferably, a nickel-based layer is also applied to the inner surface <NUM> of the metal shell <NUM>. The outer metal coating <NUM> is then brazed to the inner surface <NUM> of the shell <NUM>, or the nickel-based layer on the inner surface <NUM> of the metal shell <NUM>, to provide another hermetic combustion seal between the insulator <NUM> and shell <NUM> to prevent gases from the combustion chamber from entering the corona igniter <NUM>. The outer metal coating <NUM> applied to the outer surface <NUM> and the metallic coating <NUM> applied to the inner surface <NUM> can have the same composition or a different composition. Preferably, the coatings <NUM>, <NUM> are applied to the inner and outer surfaces <NUM>, <NUM> of the insulator <NUM> during the same process step to reduce time and costs. The step of brazing the electrode head <NUM> to the inner surface <NUM> of the insulator <NUM> and the step of brazing the outer surface <NUM> of the insulator <NUM> to the shell <NUM> 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 disclosure provides a method of manufacturing the corona igniter <NUM> with the hermetic combustion seal. To manufacture the corona igniter <NUM> of <FIG>, the method includes applying the metallic coating <NUM> to the inner surface <NUM> of the insulator <NUM> in the region extending from or around the electrode seat <NUM> to our around the upper connection end <NUM> while applying the outer metal coating <NUM> to the outer surface <NUM> of the insulator <NUM>. In these embodiments, the method does not include applying the metallic coating <NUM> below the electrode head <NUM>. The method of these embodiments then includes disposing the center electrode <NUM> in the bore of the insulator <NUM> such that the head <NUM> of the center electrode <NUM> rests on the electrode seat <NUM>.

Once the center electrode <NUM> is disposed in the insulator <NUM>, the method further includes a brazing step along the inner surface <NUM> of the insulator <NUM>. For example, the method can include brazing head <NUM> of the center electrode <NUM> and/or the shot of copper-based powder <NUM> to the inner surface <NUM> of the insulator <NUM>. Preferably, this step is conducted simultaneously with the step of brazing the outer metal coating <NUM> on the outer surface <NUM> of the insulator <NUM> to the metal shell <NUM>. During this step, one hermetic combustion seal is formed between the inner surface <NUM> of the insulator <NUM> and the center electrode <NUM>, and another hermetic combustion seal is formed between the outer surface <NUM> of the insulator <NUM> and the metal shell <NUM> to prevent combustion gases from entering the igniter <NUM>. Since processes currently used to manufacture corona igniters already include the step of applying the outer metal coating <NUM> to the outer surface of the insulator <NUM> and brazing the outer surface <NUM> of the insulator <NUM> to the shell <NUM>, 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 <NUM> including the insulator <NUM> and center electrode <NUM> of <FIG>. In this case, the method includes providing the insulator <NUM> including the inner surface <NUM> surrounding the bore; disposing the metallic coating <NUM> on the inner surface <NUM> of the insulator <NUM>; disposing the center electrode <NUM> in the bore of the insulator <NUM>; and brazing the center electrode <NUM> to the metallic coating <NUM>. According to these embodiments, the inner surface <NUM> of the insulator <NUM> extends straight from upper connection end <NUM> to the insulator nose end <NUM>, the inner surface <NUM> does not include the electrode seat <NUM>, and the center electrode <NUM> does not include the head <NUM>. According to these embodiments, the braze <NUM> secures the center electrode <NUM> to the metallic coating <NUM> on the insulator inner surface <NUM>. The step of brazing the center electrode <NUM> to the metallic coating <NUM> can include disposing the braze <NUM> in a single distinct location along the length L2 of the inner surface <NUM>.

Claim 1:
A corona igniter (<NUM>), comprising:
an insulator (<NUM>) including an inner surface (<NUM>) surrounding a bore;
a metallic coating (<NUM>) disposed on said inner surface (<NUM>) of said insulator (<NUM>);
a center electrode (<NUM>) disposed in said bore of said insulator (<NUM>)); and
a braze (<NUM>) disposed between said center electrode (<NUM>) and said metallic coating (<NUM>),
wherein the corona igniter (<NUM>) is characterized in that
the inner surface (<NUM>) of the insulator (<NUM>) extends straight along the center axis (A) from an upper connection end (<NUM>) to an insulator nose end (<NUM>), such that a diameter of the bore is constant, and the braze (<NUM>) secures the center electrode (<NUM>) to the metallic coating (<NUM>) on the inner surface (<NUM>).