Patent ID: 9620935
Date: 2017-04-11
CPC Classifications: H01T

Claim:
1. A spark plug, comprising: a center electrode extending in an axial line direction; an insulator that includes an axial hole extending in the axial line direction, the center electrode being arranged at a front end side of the axial hole, the insulator including an outer-diameter-contracted portion and a nose portion, the outer-diameter-contracted portion having an outer diameter decreased toward the front end side in the axial line direction, the nose portion being a part disposed at a front end side of the outer-diameter-contracted portion; a metal shell arranged at an outer periphery of the insulator, the metal shell including an inner-diameter-contracted portion, the inner-diameter-contracted portion having an internal diameter decreased toward the front end side in the axial line direction; and a packing arranged between the outer-diameter-contracted portion of the insulator and the inner-diameter-contracted portion of the metal shell, wherein assuming that in a contact portion of the packing and the insulator, a position at a most front end side is set as a first position, in a surface of the nose portion of the insulator, a position where a length from a front end of the insulator parallel to the axial line direction is 1 mm is set as a second position, a length between the first position and the second position parallel to the axial line direction is set as a first length, in a case where a load perpendicular to the axial line direction is applied to the second position in a state where the insulator is secured at the first position of the insulator and the front end of the insulator is a free end, a ratio of stress at a surface position that is a position on a surface of the insulator to stress at the first position is set as a stress ratio, and in a range of the surface position where the stress ratio is 0.8 or more to 1.15 or less, a length in a continuous range from the first position toward a front end side parallel to the axial line direction is set as a second length, a ratio of the second length to the first length is 0.7 or more.