Small-diameter spark plug with resistive seal
View Patent ↗A spark plug ( 10 ) includes an intermediate connecting pin ( 54 ) disposed in the central passage ( 28 ) of an the insulator body ( 12 ). The connecting pin ( 54 ) seats in an intermediate taper section ( 72 ) within the central passage ( 28 ), which is generally frustoconical and establishes a transition between a first larger diameter of the central passage ( 28 ) and a second smaller diameter. The intermediate tapered section ( 72 ) is located longitudinally above a filleted transition ( 26 ) feature of the insulator body ( 12 ) exterior. A pin head ( 53 ) of the connecting pin ( 54 ) has a complementary tapered under-cut and seats against the intermediate tapered section ( 72 ) to provide self-centering of the connecting pin ( 54 ) without trapping gas during the assembly process. The intermediate taper section ( 72 ) also provides an increase in insulator wall thickness which improves dielectric capacity and structural integrity of the insulator ( 12 ).
1. 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;
and 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; and
a conductive terminal stud partially disposed in said terminal end of said central passage, and wherein said connecting pin is fabricated from a metallic material dissimilar to the material composition of said terminal stud.
2. The spark plug assembly of claim 1 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.
3. The spark plug assembly of claim 2 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.
4. The spark plug assembly of claim 3 wherein said shank includes surface discontinuities.
5. The spark plug assembly of claim 4 wherein said surface discontinuities include at least one helical thread form.
6. The spark plug assembly of claim 4 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.
7. The spark plug assembly of claim 1 wherein said fired-in suppressor seal has a coefficient of thermal expansion, and said connecting pin is selected from a metallic material having a coefficient of thermal expansion generally equal to the coefficient of thermal expansion of said fired-in suppressor seal.
8. The spark plug assembly of claim 1 further including a conductive compression spring disposed in said central passage between said terminal stud and said connecting pin.
9. The spark plug assembly of claim 1 further including a conductive compression spring and an electronic capsule disposed in end-to-end fashion within said central passage between said terminal stud and said connecting pin.
10. The spark plug assembly of claim 1 wherein said insulator includes a large upper shoulder, a small lower shoulder, and a filleted transition therebetween, and wherein said intermediate tapered section is disposed longitudinally between said filleted transition and said terminal end.
11. 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.