| 主权项 |
1. A glow plug comprising:
a housing having an axial hole, a screw portion, and a tool engagement portion, the axial hole extending in a direction of an axis, the screw portion being on an outer circumferential surface of the housing, said screw portion being dimensioned to be screwed into a mounting hole of an internal combustion engine, the tool engagement portion being provided at a rear end side of the screw portion, said tool engagement portion being dimensioned to engage a tool when said housing is mounted to the internal-combustion engine; a heater member inserted into the axial hole in a state where at least a front end portion thereof projects from a front end of the housing; a center pole extending in the direction of the axis, inserted through the axial hole and electrically connected with the heater member; and an annular seal member in contact with an inner circumference of the tool engagement portion and an outer circumference of the center pole, wherein, along an axial length of the tool engagement portion, the inner circumference of the tool engagement portion has a shape that follows a shape of an outer circumference of the tool engagement portion, wherein the housing further has an annular step portion that is located on the inner circumference of the tool engagement portion, the annular step portion projecting radially inwards and being in contact with the seal member, and wherein, when a surface of the outer circumference of the tool engagement portion, a surface of the outer circumference of the center pole, and a surface of an outer circumference of the step portion are projected along the axis on a plane perpendicular to the axis, an area of a first projected region defined between the outer circumferential surface of the center pole and the outer circumferential surface of the step portion is 30% or more of an area of a second projected region defined by the outer circumferential surface of the tool engagement portion. |
