Small diameter/long reach spark plug
View Patent ↗A spark plug ( 10 ) having an elongated ceramic insulator ( 12 ) includes numerous design features in various strategic locations. At least the ground electrode ( 26 ) is fitted with a rimmed, hemispherical metallic sparking tip ( 56 ) which controls rogue electrical arcing ( 62 ) and facilitates attachment techniques due to increased surface contact with the ground electrode ( 26 ). The various features of the spark plug ( 10 ) cooperate with one another so that the physical dimensions of the spark plug ( 10 ) can be reduced to meet current demands of newer engines without sacrificing mechanical strength or performance.
1. A spark plug for a spark-ignited combustion event, said spark plug comprising:
an elongated ceramic insulator having an upper terminal end, a lower nose end, and a central passage extending longitudinally between said terminal and nose ends;
said insulator including an exterior surface presenting a generally circular large shoulder proximate said terminal end and a generally circular small shoulder proximate said nose end, said large shoulder having a diameter greater than the diameter of said small shoulder;
a conductive shell surrounding at least a portion of said insulator, said shell including at least one ground electrode;
a conductive center electrode disposed in said central passage and having an exposed sparking tip proximate said ground electrode;
said insulator having a nose region extending from said nose end, said nose region having a maximum outer diameter d(base) measured adjacent said small shoulder and a minimum outer diameter d(tip) measured adjacent said sparking tip of said center electrode; and
said shell including an inner bore diameter ID (shell) surrounding said nose region of said insulator, and wherein a spatial relationship is established according to the formula:
0.05
≤
(
d
(
base
)
+
d
(
tip
)
2
)
÷
ID
(
shell
)
≤
0.7
said insulator including a rounded transition and a filleted transition, said rounded transition spaced from said filleted transition by a transition length (L), both said rounded and filleted transitions located longitudinally between the disparate diameters of said large and small shoulders, said rounded transition having a major diameter D 2 and said filleted transition having a minor diameter D 1 , and wherein a spatial relationship is established according to the formula:
0.5
≤
(
D
2
-
D
1
)
L
(
transition
)
≤
3.5
.
2. The spark plug of claim 1 further including a metallic sparking tip attached to said distal end of said ground electrode, said sparking tip having a convex dome and a rim surrounding said dome, said rim disposed in surface-to-surface contact with said ground electrode.
3. The spark plug of claim 2 wherein said rim of said metallic sparking tip has a generally annular configuration.
4. The spark plug of claim 3 wherein said dome and said rim are generally aligned with one another along an imaginary central axis.
5. The spark plug of claim 4 wherein said shell includes upper and lower compression flanges bearing in pressing contact with said respective large and small shoulders of said insulator to place said insulator in compression between said large and small shoulders.
6. The spark plug of claim 5 wherein said lower compression flange of said shell includes an inner peripheral lip, said lip being spaced from said lower nose end of said insulator such that combustion gases may occupy the space and enhance the dielectric properties therein.
7. A spark plug for a spark-ignited combustion event, said spark plug comprising:
an elongated ceramic insulator having an upper terminal end, a lower nose end, and a central passage extending longitudinally between said terminal and nose ends;
said insulator including an exterior surface presenting a generally circular large shoulder proximate said terminal end and a generally circular small shoulder proximate said nose end, said large shoulder having a diameter greater than the diameter of said small shoulder;
a conductive shell surrounding at least a portion of said insulator, said shell including at least one ground electrode;
a conductive center electrode disposed in said central passage and having an exposed sparking tip proximate said ground electrode;
said insulator having a nose region extending from said nose end, said nose region having a maximum outer diameter d(base) measured adjacent said small shoulder and a minimum outer diameter d(tip) measured adjacent said sparking tip of said center electrode; and
said shell including an inner bore diameter ID (shell) surrounding said nose region of said insulator, and wherein a spatial relationship is established according to the formula:
0.057
≤
(
d
(
base
)
+
d
(
tip
)
2
)
÷
ID
(
shell
)
≤
0.66
said insulator including a rounded transition and a filleted transition, said rounded transition spaced from said filleted transition by a transition length (L), both said rounded and filleted transitions located longitudinally between the disparate diameters of said large and small shoulders, said rounded transition having a major diameter D 2 and said filleted transition having a minor diameter D 1 , and wherein a spatial relationship is established according to the formula:
0.5
≤
(
D
2
-
D
1
)
L
(
transition
)
≤
3.5
.
8. The spark plug of claim 7 further including a metallic sparking tip attached to said distal end of said ground electrode, said sparking tip having a convex dome and a rim surrounding said dome, said rim disposed in surface-to-surface contact with said ground electrode.
9. The spark plug of claim 8 wherein said rim of said metallic sparking tip has a generally annular configuration.
10. The spark plug of claim 7 wherein said dome and said rim are generally aligned with one another along an imaginary central axis.
11. The spark plug of claim 7 wherein said shell includes upper and lower compression flanges bearing in pressing contact with said respective large and small shoulders of said insulator to place said insulator in compression between said large and small shoulders.
12. The spark plug of claim 7 wherein said lower compression flange of said shell includes an inner peripheral lip, said lip being spaced from said lower nose end of said insulator such that combustion gases may occupy the space and enhance the dielectric properties therein.