Spark plug having specific gasket structure and orientation
A spark plug includes a metal shell and a gasket. The metal shell includes a thread portion, a seat portion, and a thread root portion. The gasket has an inner diameter smaller than a thread size of the thread portion. The relationships 0.8L≦C≦L−2A and B≦0.75L are satisfied in a case where: in the seat portion, an outer diameter of a seating portion is L (mm); the maximum value of a relatively shiftable distance is A (mm), the gasket is shiftable along a direction orthogonal to the axis relative to the metal shell by the maximum value; in the gasket, an outer diameter is C (mm); and in the gasket, an inner diameter is B (mm).
1. A spark plug comprising:
a tubular metal shell extending along an axis; and
a solid annular gasket disposed at an outer periphery of the metal shell, wherein
the metal shell includes:
a thread portion formed at an outer periphery on a tip end side of the metal shell;
a seat portion formed on a rear end side with respect to the thread portion, the seat portion bulging radially outward; and
a thread root portion disposed between the thread portion and the seat portion, wherein
the gasket has an inner diameter smaller than a thread size of the thread portion, the gasket being disposed at an outer periphery of the thread root portion, and
0.8L≦C≦L−2A and B≦0.75L are satisfied in a case where:
in the seat portion, an outer diameter of a seating portion that is a surface positioned at the gasket side is L (mm);
when the gasket contacts the seating portion, a maximum value of a relatively shiftable distance is A (mm), the gasket being shiftable along a direction orthogonal to the axis relative to the metal shell by the maximum value from a state where the axis and a central axis of the gasket coincide with each other;
in the gasket, an outer diameter of a face in contact with the seating portion is C (mm); and
in the gasket, an inner diameter of a face in contact with the seating portion is B (mm).
2. The spark plug according to claim 1 , wherein
in the gasket, an outer diameter of a face at an opposite side from the seating portion is larger than an outer diameter of a face of the gasket in contact with the seating portion.
3. The spark plug according to claim 1 , wherein
the thread portion has a thread size equal to or less than M12.
4. The spark plug according to claim 1 , wherein
the thread portion has a thread size equal to or less than M10.
5. The spark plug according to claim 2 , wherein
the thread portion has a thread size equal to or less than M12.
6. The spark plug according to claim 2 , wherein
the thread portion has a thread size equal to or less than M10.