Spark plug with combustion sensor

1. A spark plug assembly, comprising:

a generally annular ceramic insulator having an annular surface extending between an upper mast portion and a lower distal end, said annular surface transitioning via a shoulder to a reduced diameter nose portion;

a metal annular outer shell surrounding at least a portion of said ceramic insulator;

a ground electrode operatively attached to said outer shell;

a center electrode received in said ceramic insulator, said center electrode extending between an upper terminal end and a lower firing end, said lower firing end extending out of said nose portion of said insulator, said lower firing end of said center electrode and said ground electrode providing a spark gap;

a force sensor disposed about said insulator;

an annular inner shell received between said outer shell and said insulator, said inner shell having a first surface configured to confront said shoulder of said insulator along an axial direction;

wherein said inner shell extends to a lower end, said inner shell being fixed to said outer shell adjacent said lower end and the remaining portion of said inner shell remaining spaced from said outer shell by a gap; and

said inner shell has a radially outwardly extending shoulder and said outer shell has a radially outwardly extending flange, said shoulder and said flange being axially spaced from one another by said gap.

2. A spark plug assembly, comprising:

a generally annular ceramic insulator having an annular surface extending between an upper mast portion and a lower distal end, said annular surface transitioning via a shoulder to a reduced diameter nose portion;

a metal annular outer shell surrounding at least a portion of said ceramic insulator;

a ground electrode operatively attached to said outer shell;

a center electrode received in said ceramic insulator, said center electrode extending between an upper terminal end and a lower firing end, said lower firing end extending out of said nose portion of said insulator, said lower firing end of said center electrode and said ground electrode providing a spark gap;

a force sensor disposed about said insulator;

an annular inner shell received between said outer shell and said insulator, said inner shell having a first surface configured to confront said shoulder of said insulator along an axial direction; wherein

said inner shell extends to an upper end, said inner shell being fixed to said outer shell adjacent said upper end and the remaining portion of said inner shell remaining spaced from said outer shell by a gap; and

said inner shell has a radially outwardly extending shoulder adjacent said upper end and said outer shell has a radially inwardly extending shoulder fixed to said radially outwardly extending shoulder.

3. The spark plug assembly of claim 2 wherein said radially inwardly extending shoulder of said outer shell is provided by a radially outwardly extending flange providing a sealing seat, and said radially outwardly extending shoulder of said inner shell confronting said flange.

4. The spark plug assembly of claim 2 wherein the force sensor is disposed between said outer shell and said insulator.

5. The spark plug assembly of claim 4 wherein said outer shell has an end configured to confront said force sensor along an axial direction.

6. The spark plug assembly of claim 2 wherein an annular gap extends between said inner shell and said outer shell from said first surface to a second surface.

7. The spark plug assembly of claim 6 wherein said inner shell is fixed to said outer shell adjacent said second surface.

8. The spark plug assembly of claim 7 wherein said outer shell has an end configured to confront said insulator along an axial direction.