Ignition plug and method of manufacturing the same

An ignition plug according to claim I, further comprising:

• a center electrode inserted into a forward end portion of the axial hole;
• and
• a ground electrode disposed at a forward end portion of the metallic shell and forming a gap in cooperation with a forward end portion of the center electrode,
• wherein a length L along the axial line of that portion of the filling member which is located rearward of the crimped portion is greater than a dimension G of the gap.

A method of manufacturing an ignition plug utilized for detecting ionic current, the ignition plug comprising:

• a tubular metallic shell;
• an insulator having an axial hole extending therethrough in a direction of an axial line, provided internally of an inner circumference of the metallic shell, and having a rear trunk portion formed at a rear end portion thereof and protruding in an exposed condition from a rear end of the metallic shell,
• wherein the metallic shell and the insulator are fixed together by means of a crimped portion provided at a rear end portion of the metallic shell and bent radially inward;
• and
• an electrically insulative filling member which fills a space formed between the crimped portion and the insulator,
• wherein the filling member covers at least a portion of an outer circumferential surface of the rear trunk portion along the entire circumference and the entirety of a rear end surface of the crimped portion, which surface is a portion of an outer surface of the crimped portion and is visible from a rear side with respect to the direction of the axial line,
• said method comprising:
• a filling member forming step of forming the filling member, wherein the filling member forming step comprises:
• a step of filling under pressure a plastic material which is to become the filling member after curing, into a cavity defined by the metallic shell, the insulator, and a mold disposed around outer circumferences of the crimped portion and the rear trunk portion.

A method of manufacturing an ignition plug utilized for detecting ionic current, the ignition plug comprising:

• a tubular metallic shell;
• an insulator having an axial hole extending therethrough in a direction of an axial line, provided internally of an inner circumference of the metallic shell, and having a rear trunk portion formed at a rear end portion thereof and protruding in an exposed condition from a rear end of the metallic shell,
• wherein the metallic shell and the insulator are fixed together by means of a crimped portion provided at a rear end portion of the metallic shell and bent radially inward;
• and
• an electrically insulative filling member which fills a space formed between the crimped portion and the insulator,
• wherein the filling member covers at least a portion of an outer circumferential surface of the rear trunk portion along the entire circumference and the entirety of a rear end surface of the crimped portion, which surface is a portion of an outer surface of the crimped portion and is visible from a rear side with respect to the direction of the axial line,
• said method comprising:
• a filling member forming step of forming the filling member, wherein the filling member forming step comprises:
• a step of charging a plastic material which is to become the filling member after curing, into a cavity defined by the metallic shell, the insulator, and a mold disposed around outer circumferences of the crimped portion and the rear trunk portion;
• and
• a step of performing vacuum defoaming on the plastic material.

A method of manufacturing an ignition plug utilized for detecting ionic current, the ignition plug comprising:

• a tubular metallic shell;
• an insulator having an axial hole extending therethrough in a direction of an axial line, provided internally of an inner circumference of the metallic shell, and having a rear trunk portion formed at a rear end portion thereof and protruding in an exposed condition from a rear end of the metallic shell,
• wherein the metallic shell and the insulator are fixed together by means of a crimped portion provided at a rear end portion of the metallic shell and bent radially inward;
• and
• an electrically insulative filling member which fills a space formed between the crimped portion and the insulator,
• wherein the filling member covers at least a portion of an outer circumferential surface of the rear trunk portion along the entire circumference and the entirety of a rear end surface of the crimped portion, which surface is a portion of an outer surface of the crimped portion and is visible from a rear side with respect to the direction of the axial line, and
• wherein the insulator comprises a body formed of an electrically insulative ceramic, and at least a portion of that region of the filling member which covers an outer circumferential surface of the rear trunk portion is in direct contact with the body,
• said method comprising:
• a glaze layer forming step of forming a glaze layer on an outer circumferential surface of the body;
• and
• a glaze layer removing step of removing a portion of the glaze layer for allowing direct contact between the outer circumferential surface of the body and at least a portion of that region of the filling member which covers an outer circumferential surface of the rear trunk portion.