| 摘要 |
PROBLEM TO BE SOLVED: To suppress deposition of carbon on an insulator.SOLUTION: The main body metal fitting of a spark plug forms an annular gap between the outer peripheral surface of the leg of an insulator and itself. Between the reduced outer diameter portion of the insulator and the reduced inner diameter portion of the main body metal fitting, a packing is disposed. The position of the contact part of the packing and main body metal fitting, closest to the tip side, is the contact end position, the distance in the radial direction between the outer peripheral surface of the leg of an insulator and the inner peripheral surface of the main body metal fitting is the gap distance, and the position of the rear end of a maximum part where the gap distance is maximum out of the annular gaps is the maximum end position. The gap distance at the tip of the main body metal fitting is larger than the distance of the gap between the center electrode and ground electrode. The main body metal fitting includes an enlarged inner diameter portion where the inner diameter increases toward the rear end side in the axial direction, on the side closer to the tip than the contact end position. The maximum end position is located closer to the rear end side than the middle position, where the distance between the contact end position and the tip of the main body metal fitting in the axial direction is divided equally into two parts.SELECTED DRAWING: Figure 2 |
