| 摘要 |
PROBLEM TO BE SOLVED: To provide a glow plug which rigidly joins a middle shaft to a ceramic heater, has a constricted part on the middle shaft and has a small risk of breakage of a heater in an actual usage environment.SOLUTION: A glow plug 1 includes: a ceramic heater 2 having a heat generator 2b which generates heat by energization; a metal fitting 3 which receives a rear end part of the heater 2 into a shaft hole 5; and a middle shaft 4 which is inserted to the shaft hole 5, is formed of a terminal part 4a for supplying an electric power to the rear end part projected from the shaft hole 5, on the other hand, rigidly joins the rear end part of the heater 2 to the tip and is formed of a constricted part 4c on a part from the constricted part to the rear end part of the main metal fitting 3. Therein, when the length of the heater 2 is Lh, the length from the rigid joint part of the middle shaft 4 to the rear end part of the main metal fitting 3 is La, the length from the rigid joint part to the tip part of the constricted part 4c is Lb1 and the length from the rigid joint part to the rear end part of the constricted part is Lb2, Lh>La and Lz/(La×R)≤0.03 (*R is an outer diameter on the position corresponding to the length of Lz on the basis of the rigid joint part of the constricted part) and Lb1≤Lz≤Lb2 are satisfied. |
