Abstract: A spark plug includes a tubular metal shell, an insulator, a cylindrical center electrode, and a ground electrode. The ground electrode has an inclined portion, a straight portion, and a bend between the inclined and straight portions. The inclined portion extends obliquely with respect to the axial direction of the center electrode from a base end of the ground electrode, which is joined to an end of the metal shell, to the bend that is positioned closer to the center electrode in the radial direction of the center electrode than the base end. The straight portion extends substantially parallel to the axial direction of the center electrode from the bend to a tip end of the ground electrode. The straight portion has an inner side surface facing the side surface of an end portion of the center electrode through a spark gap in the radial direction of the center electrode.

Abstract: A method of manufacturing a spark plug having an attachment fitting 2, an insulator 3, a center electrode 4 and an earth electrode 5. While fixed to attachment fitting 2, earth electrode 5 has a convex part 510 formed by projecting a part of an opposed surface 51 toward center electrode 4, and a concave part 520 formed toward the opposed surface 51 from the earth electrode's back surface 52. The convex part 510 is disposed so that the extension of a shaft center of the convex part 510 passes through the area in which the concave part 520 is formed. The relation S1>=s is realized when an area of an opening of the concave part 520 is set to S1 and an average cross-section area of a cross section of the convex part 510 perpendicular to an axial direction of the spark plug is set to s.

Abstract: A spark plug for an internal-combustion engine comprises an attachment fitting 2, an insulator 3, a center electrode 4 and an earth electrode 5. While fixed to the attachment fitting 2, the earth electrode 5 has a convex part 510 formed by projecting toward the center electrode 4 a part of the opposed surface 51, which faces the center electrode 4, of the earth electrode and a concave part 520 formed toward the opposed surface 51 from the earth electrode's back surface 52 which is the reverse side of the opposed surface 51 of the earth electrode 5. The convex part 510 is disposed so that the extension of a shaft center of the convex part 510 may pass through the area in which the concave part 520 is formed. A relation of S1>=s is realized when an area of an opening of the concave part 520 is set to S1 and an average cross-section area of a cross section of the convex part 510 perpendicular to an axial direction of the spark plug is set to s.

Abstract: A spark plug includes a tubular metal shell, an insulator, a cylindrical center electrode, and a ground electrode. The ground electrode has an inclined portion, a straight portion, and a bend between the inclined and straight portions. The inclined portion extends obliquely with respect to the axial direction of the center electrode from a base end of the ground electrode, which is joined to an end of the metal shell, to the bend that is positioned closer to the center electrode in the radial direction of the center electrode than the base end. The straight portion extends substantially parallel to the axial direction of the center electrode from the bend to a tip end of the ground electrode. The straight portion has an inner side surface facing the side surface of an end portion of the center electrode through a spark gap in the radial direction of the center electrode.

Abstract: A spark plug includes a tubular metal shell, an insulator, a cylindrical center electrode, and a ground electrode. The ground electrode has an inclined portion, a straight portion, and a bend between the inclined and straight portions. The inclined portion extends obliquely with respect to the axial direction of the center electrode from a base end of the ground electrode, which is joined to an end of the metal shell, to the bend that is positioned closer to the center electrode in the radial direction of the center electrode than the base end. The straight portion extends substantially parallel to the axial direction of the center electrode from the bend to a tip end of the ground electrode. The straight portion has an inner side surface facing the side surface of an end portion of the center electrode through a spark gap in the radial direction of the center electrode.

Abstract: A method of manufacturing a spark plug having an attachment fitting 2, an insulator 3, a center electrode 4 and an earth electrode 5. While fixed to attachment fitting 2, earth electrode 5 has a convex part 510 formed by projecting a part of an opposed surface 51 toward center electrode 4, and a concave part 520 formed toward the opposed surface 51 from the earth electrode's back surface 52. The convex part 510 is disposed so that the extension of a shaft center of the convex part 510 passes through the area in which the concave part 520 is formed. The relation S1>=s is realized when an area of an opening of the concave part 520 is set to S1 and an average cross-section area of a cross section of the convex part 510 perpendicular to an axial direction of the spark plug is set to s.

Abstract: A spark plug for an internal-combustion engine comprises an attachment fitting 2, an insulator 3, a center electrode 4 and an earth electrode 5 . While fixed to the attachment fitting 2, the earth electrode 5 has a convex part 510 formed by projecting toward the center electrode 4 a part of the opposed surface 51, which faces the center electrode 4, of the earth electrode and a concave part 520 formed toward the opposed surface 51 from the earth electrode's back surface 52 which is the reverse side of the opposed surface 51 of the earth electrode 5 . The convex part 510 is disposed so that the extension of a shaft center of the convex part 510 may pass through the area in which the concave part 520 is formed. A relation of S1>=s is realized when an area of an opening of the concave part 520 is set to S1 and an average cross-section area of a cross section of the convex part 510 perpendicular to an axial direction of the spark plug is set to s.

Abstract: A spark plug includes a tubular metal shell, an insulator, a cylindrical center electrode, and a ground electrode. The ground electrode has an inclined portion, a straight portion, and a bend between the inclined and straight portions. The inclined portion extends obliquely with respect to the axial direction of the center electrode from a base end of the ground electrode, which is joined to an end of the metal shell, to the bend that is positioned closer to the center electrode in the radial direction of the center electrode than the base end. The straight portion extends substantially parallel to the axial direction of the center electrode from the bend to a tip end of the ground electrode. The straight portion has an inner side surface facing the side surface of an end portion of the center electrode through a spark gap in the radial direction of the center electrode.