Glow plug with built-in combustion pressure sensor and manufacturing method thereof

A method of manufacturing a glow plug, comprising:

• disposing a heater in a sheath;
• fitting a rear end portion of the sheath into a cylindrical housing shell, the housing shell having a rear end portion formed with a sensor seat on an inner surface thereof;
• inserting an electrode rod into the housing shell;
• after said inserting, placing a first piece that defines an outward protrusion on the electrode rod, a pressure-sensitive element and a second piece that defines an inward protrusion on the housing shell, on the sensor seat of the housing shell so as to hold the pressure-sensitive element between a rear surface of the outward protrusion and a front surface of the inward protrusion;
• while pushing the second piece toward the front and applying compressive stress to the pressure-sensitive element, fixing the second piece to the housing shell;
• and
• fixing the first piece to the electrode rod.

A glow plug for an internal combustion engine, comprising:

• a cylindrical housing having front and rear end portions, a threaded portion formed between the front end and rear end portions for screwing the glow plug into a plug hole of the engine and a sealing portion formed on a front side of the threaded portion for engaging the housing with a given portion of the plug hole to form an airtight seal between the housing and the plug hole;
• a sheath having a front sheath end portion projecting from the housing and a rear sheath end portion airtightly fixed in the front end portion of the housing;
• a heater disposed in the sheath and generating heat upon energization thereof;
• a center electrode disposed in the housing and having a rear electrode end portion projecting from the housing, the center electrode being electrically connected with the heater and mechanically connected with the sheath or the sheath and the heater;
• and
• a combustion pressure sensor including a pressure-sensitive element that converts an axial displacement of the sheath or the sheath and the heater caused by a variation in combustion pressure into an electrical signal and being configured to have compressive stress increasingly applied to the pressure-sensitive element by screwing the glow plug into the plug hole and increased with increase in the combustion pressure.