Spark plug

Abstract

A spark plug has a central electrode and a plurality of peripheral electrodes. The central electrode has a proximal portion and a distal portion. The distal portion of the central electrode has a circular cross-section with a longitudinal axis and terminates in a distal end. Each peripheral electrode has a lower portion and an upper portion. Each upper portion has a distal-most point. Each distal-most point is disposed in a central plane within which the longitudinal axis of the distal portion of the central electrode is wholly disposed. The cross-section of each upper portion taken along its central plane defines a convex outer side and a non-convex inner side. Each convex outer side has a curved surface which is tangent to a plurality of tangent planes, all of which intersect the longitudinal axis of the distal portion of the central electrode at points at or above the distal end of the distal point of the central electrode.

What is claimed is: 
     
       1. A spark plug comprising:
 (a) a threaded cylindrical body; 
 (a)(b) a central electrode disposed within the cylindrical body along a central axis of the cylindrical body, the central electrode having a proximal portion and a distal portion, the proximal portion of the central electrode surrounded by an insulating material, the distal portion extending beyond the insulating material and having a circular cross section with a longitudinal axishaving a circumference centered about the central axis and terminating in a distal end; 
 (b)(c) an upper end of the cylindrical body terminating in a plurality of peripheral electrodes radially disposed around the central electrode and equally spaced apart from one another, each peripheral electrode having a lower portion and an upper portion and being substantially identical in shape and dimensions, each peripheral electrode having an upper portion and a lower portion, each upper portion having converging to a distal-most point, each distal-most point being disposed in a central plane within which the longitudinal axis of the distal portion of the central electrode is wholly disposed, the cross-section of that intersects the insulating material below the distal portion of the central electrode, each upper portion taken along its central plane defining a convex outer side surface and a non-convex inner side surface, each convex outer side having a curved surface which is tangent to a plurality of tangent planes, all of which tangent planes intersect the longitudinal axis of the distal portion of the central electrode at points at or above the distal end of the distal point of the central electrode the inner surfaces of all of the peripheral electrodes being integral with and one piece with the cylindrical body, the inner surface of each peripheral electrode terminating in a flat section at a distal end thereof, the flat section lying in an inclined plane, a distal end of the flat section being further away from the central electrode than a proximal end of the flat section. 
 
     
     
       2. The spark plug of  claim 1  wherein the distal portion of the central electrode has a diameter between about 0.125 inches and about 0.265 inches. 
     
     
       3. The spark plug of  claim 1  wherein the distal end of the central electrode has a distal end which is dome-shaped comprises rounded edges. 
     
     
       4. The spark plug of  claim 1  wherein the number of the plurality of peripheral electrodes is between about 3 and about 12 peripheral electrodes. 
     
     
       5. The spark plug of  claim 1  wherein the lower portion of each of the peripheral electrodes has a square cross-section. 
     
     
       6. The spark plug of  claim 1  wherein the lower portion of each of the peripheral electrodes has a rectangular cross-section. 
     
     
       7. The spark plug of  claim 1  wherein the lower portion of each of the peripheral electrodes has a generally oval cross-section. 
     
     
       8. The spark plug of  claim 1  wherein the lower portion of each of the peripheral electrodes has a circular cross-section. 
     
     
       9. The spark plug of  claim 1  wherein the lower portion of each of the peripheral electrodes has a generally square cross-section with rounded corners. 
     
     
       10. The spark plug of  claim 1  wherein the lower portion of each of the peripheral electrodes has a generally rectangular cross-section with rounded corners. 
     
     
       11. The spark plug of  claim 1  wherein the lower portion of each of the peripheral electrodes has a generally triangular cross-section with rounded corners. 
     
     
       12. The spark plug of  claim 1  wherein the upper portion of each of the peripheral electrodes has the shape of an eccentric cone. 
     
     
       13. The spark plug of  claim 1  wherein the convex outer side surface is smooth. 
     
     
       14. The spark plug of  claim 13  wherein the convex outer side surface forms an arc of a circle. 
     
     
       15. The spark plug of claim 1 wherein the distal end of the central electrode has a diameter substantially equal to the diameter of a distal end of the insulating material.