Spark plug having ground electrode tip attached to free end surface of ground electrode

1. A spark plug, comprising:

a metallic shell having an axial bore;

an insulator having an axial bore and being disposed at least partially within said axial bore of said metallic shell;

a center electrode body disposed at least partially within said axial bore of said insulator;

a ground electrode body attached to said metallic shell and having a radially-facing free end surface; and

a ground electrode tip including a non-precious metal piece and a precious metal piece attached together, said non-precious metal piece having a side surface attached to said radially-facing free end surface of said ground electrode body.

2. A spark plug as defined in claim 1 , wherein said insulator has a rib extending circumferentially therearound and protruding radially outwardly therefrom, and said rib is located axially on said insulator in general alignment with an open end of said metallic shell.

3. A spark plug as defined in claim 1 , wherein said ground electrode body includes an end portion that tapers in axial thickness toward said radially-facing free end surface.

4. A spark plug as defined in claim 3 , wherein said end portion of said ground electrode body also tapers in radial width toward said radially-facing free end surface.

5. A spark plug as defined in claim 3 , wherein an axial thickness dimension of said radially-facing free end surface is less than a longitudinal length of said non-precious metal piece.

6. A spark plug as defined in claim 1 , wherein said radially-facing free end surface is generally planar and free of notches.

7. A spark plug as defined in claim 1 , wherein said radially-facing free end surface has a notch located therein to facilitate placement of said ground electrode tip.

8. A spark plug as defined in claim 1 , wherein said ground electrode tip has a longitudinal axis that is generally parallel with a center axis of the spark plug.

9. A spark plug as defined in claim 1 , further comprising a center electrode tip attached to said center electrode body and having a longitudinal axis generally parallel with a longitudinal axis of said ground electrode tip.

10. A spark plug as defined in claim 1 , wherein said non-precious metal piece is a Ni-alloy piece and said precious metal piece is an Ir-alloy piece.

11. A spark plug as defined in claim 9 , wherein said precious metal piece of said ground electrode tip has an axially-facing free end surface, and said center electrode tip has an axially-facing free end surface, and said axially-facing free end surfaces of said precious metal piece and of said center electrode tip directly confront each other and generate a spark therebetween during use of the spark plug.

12. A spark plug as defined in claim 1 , wherein said precious metal piece does not directly contact said radially-facing free end surface of said ground electrode body.

13. A spark plug as defined in claim 1 , wherein a weldment portion is located at the attachment between said non-precious metal piece and said precious metal piece, and said weldment portion does not directly contact said radially-facing free end surface of said ground electrode body.

14. A spark plug, comprising:

a metallic shell having an axial bore;

an insulator having an axial bore and being disposed at least partially within said axial bore of said metallic shell;

a center electrode body disposed at least partially within said axial bore of said insulator;

a ground electrode body attached to said metallic shell and having an end portion tapering in size toward a radially-facing free end surface; and

a ground electrode tip having a side surface attached to said radially-facing free end surface of said ground electrode body, wherein an axial extent of attachment between said side surface and said radially-facing free end surface constitutes a first axial extent L 1 of said ground electrode tip, an axial extent of said ground electrode tip free of the attachment between said side surface and said radially-facing free end surface constitutes a second axial extent L 2 of said ground electrode tip, and said first axial extent L 1 is less than said second axial extent L 2 in order to facilitate flame kernel growth in a combustion chamber.

15. A spark plug as defined in claim 14 , wherein said end portion of said ground electrode body tapers in axial thickness toward said radially-facing free end surface.

16. A spark plug as defined in claim 15 , wherein said ground electrode tip includes a Ni-alloy piece and a precious metal piece, said Ni-alloy piece and said precious metal piece are attached together, said Ni-alloy piece is attached to said radially-facing free end surface of said ground electrode body and said precious metal piece is not attached to said radially-facing free end surface.

17. A spark plug as defined in claim 16 , wherein an axial thickness dimension of said radially-facing free end surface is less than a longitudinal length of said Ni-alloy piece.

18. A method of assembling a ground electrode body and a ground electrode tip, the method comprising the steps of:

providing a non-precious metal piece and a precious metal piece;

welding said non-precious metal piece and said precious metal piece together to form said ground electrode tip; and

welding a side surface of said non-precious metal piece to a free end surface of said ground electrode body.

19. A method as defined in claim 18 , further comprising the step of trimming said ground electrode body wherein an end portion of said ground electrode body tapers in axial thickness toward said radially-facing free end surface.

20. A method as defined in claim 18 , wherein the step of welding a side surface of said non-precious metal piece to a free end surface of said ground electrode body is performed after said ground electrode body is attached to a metallic shell and is bent to its final position.