Abstract: A spark plug includes an insulator, and a metal shell disposed at an outer periphery of the insulator and including a shoulder. The insulator includes a trunk portion, and a leg formed at the tip end side of the trunk portion. The shoulder of the metal shell includes a first shoulder, and a second shoulder formed at the tip end side of the first shoulder. A distance Da between the tip end of the second shoulder and the leg and a distance Db between the tip end of the trunk portion and the second shoulder satisfy a relationship of Da/Db?1.1. A distance T between the rear end of the first shoulder and the tip end of the second shoulder and a distance L between the rear end of the first shoulder and a tip end face of the metal shell satisfy a relationship of T/L?0.5.

Abstract: A spark plug includes an insulator, and a metal shell disposed at an outer periphery of the insulator and including a shoulder. The insulator includes a trunk portion, and a leg formed at the tip end side of the trunk portion. The shoulder of the metal shell includes a first shoulder, and a second shoulder formed at the tip end side of the first shoulder. A distance Da between the tip end of the second shoulder and the leg and a distance Db between the tip end of the trunk portion and the second shoulder satisfy a relationship of Da/Db?1.1. A distance T between the rear end of the first shoulder and the tip end of the second shoulder and a distance L between the rear end of the first shoulder and a tip end face of the metal shell satisfy a relationship of T/L?0.5.

Abstract: A method for manufacturing a spark plug includes an assembling step of assembling an insulator into a metallic shell by insertion of the insulator into the metallic shell from an axially rear end opening portion of the metallic shell. The assembling step includes a displacement restricting step of restricting a relative positional displacement between the metallic shell and the insulator in a radial direction intersecting with the axial direction so as to reduce eccentricity between the axis of the metallic shell and the axis of the insulator to a predetermined value or less, while allowing a relative positional displacement between the metallic shell and the insulator in the axial direction. In the assembling step, whether or not the insulator is cracked in the assembling step is judged by detecting acoustic emission from the insulator.

Abstract: A spark plug includes a ceramic insulator extending in the direction of an axis (CL1) and a metallic shell provided around the ceramic insulator. Talc is pressed charged between the ceramic insulator and the metallic shell and a crimp portion is formed for fixing the metallic shell and the ceramic insulator while the metallic shell having the ceramic insulator inserted thereinto is supported by a tubular receiving member. The receiving member is made movable in relation to a pressing jig in its radial direction. Thus, at the time of pressing of the talc, etc., the eccentricity between the center axis (CL2), (CL3) of the pressing jig and the axis (CL1) in the radial direction can be reduced, whereby the misalignment between the axis (CL1) and the center axis of the metallic shell or the like assembly error can be suppressed.

Abstract: A spark plug having a combustion pressure detecting function, including a tip end portion in an axial direction of the spark plug capable of generating a spark discharge, a male thread adapted for attaching the spark plug to an internal combustion engine and a metal shell including, at a rear end side of the male thread, a brim portion projecting perpendicularly to the axial direction; an annular, flat gasket provided on a tip side of the brim portion; and a pressure sensor including a pressure-sensitive element, wherein the gasket has a Young's modulus E (kN/mm2) satisfying a relationship, 100?E?170.

Abstract: A glow plug comprising: a cylindrical housing; a heater member as defined herein; a conductive center pole as defined herein; a first piezoelectric element as defined herein; and a second piezoelectric element as defined herein, wherein each of said first piezoelectric element and said second piezoelectric element is subjected to a preload for compressing it in said axial direction and is arranged such that, when said center pole is displaced to a root-end side, a load to be applied to one of said first piezoelectric element and said second piezoelectric element for compressing the same in said axial direction increases whereas a load to be applied to the other for compressing the same in said axial direction decreases.

Abstract: A spark plug having a combustion pressure detecting function, including a tip end portion in an axial direction of the spark plug capable of generating a spark discharge, a male thread adapted for attaching the spark plug to an internal combustion engine and a metal shell including, at a rear end side of the male thread, a brim portion projecting perpendicularly to the axial direction; an annular, flat gasket provided on a tip side of the brim portion; and a pressure sensor including a pressure-sensitive element, wherein the gasket has a Young's modulus E (kN/mm2) satisfying a relationship, 100?E?170.

Abstract: A glow plug comprising: a cylindrical housing; a heater member as defined herein; a conductive center pole as defined herein; a first piezoelectric element as defined herein; and a second piezoelectric element as defined herein, wherein each of said first piezoelectric element and said second piezoelectric element is subjected to a preload for compressing it in said axial direction and is arranged such that, when said center pole is displaced to a root-end side, a load to be applied to one of said first piezoelectric element and said second piezoelectric element for compressing the same in said axial direction increases whereas a load to be applied to the other for compressing the same in said axial direction decreases.