| 摘要 |
A spark plug includes a center electrode, an insulator, a metallic shell, and a ground electrode which has a noble metal tip at the other end portion. A gap is formed between a forward end portion of the center electrode and a discharge surface of the noble metal tip. When an acute angle formed by the forward end surface and the discharge surface is θ1, a point on the forward end surface closest to the noble metal tip is A, opposite ends of the discharge surface are B1 and B2, and an angle formed by a first line segment connecting A and B1 and a second line segment connecting A and B2 is θ2, 35°≦θ1≦55°, 85°≦θ2≦90°, and the difference in length between the first and second line segments is equal to or less than 10% of the longer line segment. |
| 主权项 |
1. A spark plug comprising:
a center electrode extending in the direction of an axial line; an insulator disposed around the center electrode such that a forward end portion of the center electrode is exposed; a metallic shell disposed around the insulator; and a ground electrode whose one end portion is joined to the metallic shell and which has a noble metal tip at the other end portion thereof, wherein a gap is formed between a forward end portion of the center electrode and a discharge surface of the noble metal tip, and wherein on a cross section which passes through the center of the discharge surface and includes the axial line, an acute angle formed by a forward end surface of the center electrode and the discharge surface of the noble metal tip is defined as θ1, a point on the forward end surface of the center electrode closest to the noble metal tip is defined as a point A, opposite end points of the discharge surface are defined as points B1 and B2, a line segment connecting the point A and the point B1 is defined as a first line segment, a line segment connecting the point A and the point B2 is defined as a second line segment, and an angle formed by the first line segment and the second line segment is defined as θ2; and under the above definitions, 35°≦θ1≦55°, 85°≦θ2≦90°, and a difference in length between the first and second line segments is equal to or less than 10% of the length of a longer line segment. |
