Small-diameter spark plug with resistive seal

A spark plug assembly for a spark-ignited combustion event, said assembly comprising:

• a generally tubular insulator having an upper terminal end and a lower nose end, and a central passage extending longitudinally between said terminal and nose ends;
• a conductive shell surrounding at least a portion of said insulator, said shell including at least one ground electrode proximate said nose end of said insulator;
• a center electrode disposed in said central passage of said insulator, said center electrode having a lower sparking end exposed through said nose end and presented in opposing relation to said ground electrode so as to establish a spark gap in the space therebetween, said center electrode further including an electrode head seated in said central passage;
• an intermediate connecting pin disposed in said central passage, said connecting pin having a shank spaced from said electrode head of said center electrode;
• a fired-in suppressor seal electrically interconnecting said electrode head and said shank of said connecting pin within said central passage;
• said central passage including an intermediate tapered section generally midway between said terminal end and said electrode head, and said connecting pin having a tapered pin head seated in said tapered section of said central passage;
• wherein said intermediate tapered section is generally frustoconical and establishes a transition between a first larger diameter of said central passage and a second smaller diameter of said central passage, and wherein said pin head of said connecting pin has a diameter less than said first diameter but greater than said second diameter;
• wherein said shank of said connecting pin extends longitudinally from said pin head and has a maximum lateral dimension less than said second diameter of said central passage;
• wherein said shank includes surface discontinuities;
• and
• wherein said fired-in suppressor seal includes an upper layer of glass material having a longitudinal depth dimension (SL), and said shank of said connecting pin extends longitudinally into said upper layer of glass material a longitudinal distance (PL) according to the formula:
• 0.7*SL≦PL≦SL.