| 摘要 |
A spark plug includes a center electrode, an insulator, a metallic shell, and a seal member for providing a seal between the insulator and the metallic shell. The insulator includes a first portion, a second portion located axially forward of the first portion and being smaller than the first portion, and an insulator first-diameter-reducing-portion whose outside diameter reduces forward and which connects the first portion and the second portion. The metallic shell includes a protrusion that includes a metallic shell diameter-reducing-portion whose inside diameter reduces forward. The seal member is disposed between the insulator first-diameter-reducing-portion and the metallic shell diameter-reducing-portion. A relationship θ21>θ22 is satisfied, where the angle θ21 is an angle between a straight line orthogonal to the axial line and the outline of the metallic shell diameter-reducing-portion, and the angle θ22 is an angle between the straight line and an outline of the insulator first-diameter-reducing-portion. |
| 主权项 |
1. A spark plug comprising:
a center electrode extending along an axial line; an insulator having an axial hole extending along the axial line and holding the center electrode in the axial hole in such a manner that the center electrode protrudes axially forward from the axial hole; a metallic shell holding the insulator in such a manner as to circumferentially surround a portion of the insulator; and an annular seal member that seals a gap between the insulator and the metallic shell, wherein the insulator includes a first portion, a second portion located axially forward of the first portion and being smaller in outside diameter than the first portion, and an insulator first-diameter-reducing-portion whose outside diameter reduces axially forward and which connects the first portion and the second portion, the metallic shell includes a protrusion protruding radially inward, said protrusion having a metallic shell diameter-reducing-portion whose inside diameter reduces axially forward, the seal member is disposed between the insulator first-diameter-reducing-portion and the metallic shell diameter-reducing-portion at such a position as to cross an extension line formed by imaginarily extending an outer surface of the first portion in an axially forward direction, a first angle θ21 and a second angle θ22 satisfy a relational expression θ21>θ22, where, on a section which contains the axial line, the first angle θ21 is an acute angle between a straight line orthogonal to the axial line and an outline of the metallic shell diameter-reducing-portion, and the second angle θ22 is an acute angle between a straight line orthogonal to the axial line and an outline of the insulator first-diameter-reducing-portion, and the first angle θ21 and the second angle θ22 satisfy a relational expression θ21−θ22≦7°. |
