Ngk Spark Plug Company, Limited

Toru Moriya

Mitsutaka Yoshida

Makoto Sugimoto

Akihiro Toya

Eigo Goto

Akihisa Harada

Tunekazu Enomoto

A spark plug for attachment to a cylinder head includes a metallic shell including a tip-end side having an open tip end and a tail-end side having an open tail end. The metallic shell has an attachment screw portion peripherally formed at the tip-end side thereof. The spark plug also includes a ground electrode attached onto the tip-end side of the metallic shell, and an insulator including an axial through-hole formed therein and a tail end portion having a tail end. The insulator is disposed within the metallic shell such that the tail end portion of the insulator substantially projects from the tail end of the metallic shell. A center electrode has a tip end and being disposed within the through-hole and facing the ground electrode to define a spark discharge gap therebetween, and a metallic terminal has a tail end and being disposed within the through-hole of the insulator such that the tail end of the metallic terminal is set back from the tail end of the insulator into the through-hole. The metallic terminal is electrically connected with the center electrode. The metallic terminal and the tail end of the metallic shell are separated with a distance for preventing an electrical discharge therebetween, and wherein, when A represents a distance between the tail end of the insulator and the tail end of the metallic terminal disposed within the through-hole, and B represents a length of the tail end portion of the insulator projecting from the tail end of the metallic shell along the axial direction of the through-hole of the insulator, a length of (A&plus;B) is at least 20 mm.

Spark plug having a metallic terminal within a through-hole

A distributorless ignition system is provided which includes an ignition coil for firing a pair of first and second spark plugs at the same time. The ignition system includes a changeover switch which, when assuming one operating position, causes the first spark plug to produce negative polarity spark and the second spark plug to produce positive polarity spark and, when assuming another operating position, causes the first spark plug to produce positive polarity spark and the second spark plug to produce negative polarity spark. The operating position of changeover switch is changed every time the number of sparks produced by each of the first and second spark plugs becomes two. By this, the number of negative polarity sparks and the number of positive polarity sparks produced by each of the first and second spark plugs on compression stroke at its corresponding cylinder over a long period of time are the same. This enables the center electrode and ground electrode of each of the first and second spark plugs to wear away equally. An ignition method is also provided.

Waste-spark engine ignition

A spark plug (,) has an outer tube member (,) that covers the outer peripheral surface of the projecting part (,) of an insulator (,) beyond a metallic shell (,), with its front end being coupled to the metallic shell (,). A hexagonal tool engaging portion (,) is formed in the rear end portion of the outer tube member (,). No tool engaging hexagonal portion is formed in the metallic shell (,). Accordingly, even if a plug hole (PH) of a smaller diameter is formed, the outside diameter of the insulator (,) need not be reduced accordingly since the heretofore required hexagonal portion is eliminated. As a result, the mechanical strength and withstand voltage of the insulator (,) can be ensured at adequately high levels.

Spark plug

A spark plug for an internal combustion engine includes a metallic shell within which a tubular insulator is placed, a center electrode is provided within the insulator to form a spark gap between a front end of the center electrode and an outer electrode extending from the metallic shell. First and second stepped portions are provided near a front portion of the center electrode to form a clearance between an outer wall of the center electrode and an inner wall of the insulator. The stepped portions have a progressively decreasing diameter toward the front end of the center electrode. A tapered portion is provided at an inner wall of the insulator by bevelling a front open end of the insulator. This maintains high insulation of the insulator with significantly low carbon deposit, thus avoiding ignition failure of the spark plug.

Spark plug for use in internal combustion engine

A spark plug for an internal combustion engine is disclosed. A semiconductor material having a resistance of 5.times.10.sup.2 -5.times.10.sup.4 M.OMEGA./mm is coated or baked in the form of a band on the peripheral surface of a basal part of a leg portion of an insulator of the spark plug. Preferably, at least the basal part of the leg portion, including the band, is covered with a water-repellant insulating coating. An inner wall of a metal shell of the spark plug is desirably coated with a water-repellant material at an area facing at least the peripheral surface of the basal part of the leg portion of the insulator.

Growing community of inventors

Aichi, Japan

Toru Moriya