Corona ignition device with improved electrical performance

A method of forming a corona igniter, comprising the steps of:

• providing an insulator formed of an electrically insulating material extending along a center axis from an insulator upper end to and insulator nose end, the insulator including an insulator outer surface extending from the insulator upper end to the insulator nose end and presenting an insulator outer diameter, the insulator outer surface including a lower ledge extending outwardly away from and transverse to the center axis between an insulator body region and an insulator nose region;
• disposing an intermediate part formed of an electrically conductive material on the lower ledge of the insulator;
• and
• disposing a shell formed of an electrically conductive material around the intermediate part and the insulator.

A corona igniter for emitting a radio frequency electric field to ionize a fuel-air mixture and provide a corona discharge, comprising:

• a central electrode formed of an electrically conductive material for receiving a high radio frequency voltage and emitting the radio frequency electric;
• said central electrode extending longitudinally along a center axis from a terminal end to an electrode firing end;
• an insulator formed of an electrically insulating material and extending longitudinally along said center axis from an insulator upper end to an insulator nose end;
• said electrode firing end disposed outwardly of said insulator nose end;
• a corona enhancing tip disposed at said firing end of said central electrode;
• said insulator including an insulator inner surface surrounding said central electrode and presenting an insulator inner diameter extending across and perpendicular to said center axis;
• said insulator inner surface surrounding an insulator bore receiving said central electrode;
• said insulator including an insulator outer surface extending from said insulator upper end to said insulator nose end;
• said insulator outer surface presenting an insulator outer diameter extending across and perpendicular to said center axis;
• said insulator inner diameter being 15 to 25% of said insulator outer diameter;
• said insulator including an insulator body region and an insulator nose region;
• said insulator outer surface including a lower ledge extending outwardly away from and transverse to said center axis between said insulator body region and said insulator nose region;
• said lower ledge presenting an increase in said insulator outer diameter;
• a conductive component formed of electrically conductive material surrounding at least a portion of said insulator body region such that said insulator nose region extends outwardly of said conductive component;
• said conductive component including a shell surrounding at least a portion of said insulator body region and extending from a shell upper end to a shell firing end;
• said shell presenting a shell inner surface facing said center axis and extending along said insulator outer surface from said shell upper end to said shell firing end;
• said shell inner surface presenting a shell bore surrounding said center axis and a shell inner diameter extending across and perpendicular to said center axis;
• said shell inner diameter being greater than or equal to said insulator outer diameter from said insulator upper end to said insulator nose end;
• said shell including a shell outer surface facing opposite said shell inner surface and presenting a shell outer diameter;
• said conductive component including an intermediate part surrounding a portion of said insulator body region and extending longitudinally from an intermediate upper end to an intermediate firing end;
• said intermediate part including an intermediate inner surface facing said center axis and extending longitudinally along said insulator outer surface said from said intermediate upper end to said intermediate firing end;
• said intermediate inner surface being hermetically sealed to said insulator outer surface;
• said intermediate inner surface presenting a conductive inner diameter extending across and perpendicular to said center axis;
• said conductive inner diameter being less than said insulator outer diameter below said lower ledge of said insulator;
• said conductive inner diameter being 80 to 90% of said insulator outer diameter below said lower ledge and being 75 to 90% of said shell inner diameter along said intermediate part;
• said intermediate firing end engaging said lower ledge of said insulator and being longitudinally aligned with said shell firing end.