Denso Corporation

Nippon Soken, Inc.

Hiroshi Araki

Hirofumi Suzuki

Tomoyuki Watanabe

Masamichi Shibata

Kenji Hattori

Itsuhei Ogata

Naoto Hayashi

Yasuomi Imanaka

Shota Imada

Toshiya Nakamura

Yasuki Aoi

Hikaru Takashima

Katsumasa Koeda

Shin Hase

In a method for manufacturing a spark plug, a space on a proximal end side of a center electrode in a shaft hole of an insulator is filled with first electrically conductive glass powder. A space on the proximal end side of the first electrically conductive glass powder in the shaft hole is filled with resistor composition powder. A space on the proximal end side of the resistor composition powder in the shaft hole is filled with second electrically conductive glass powder. The first electrically conductive glass powder, the resistor composition powder, and the second electrically conductive glass powder are sintered in the shaft hole. Prior to filling of the resistor composition powder, at least one of the insulator and the first electrically conductive glass powder is placed in an uncharged state, or the insulator and the first electrically conductive glass powder are placed in the same charged state.

Method for manufacturing spark plug with peripheral edge of proximal end surface of sealing distal-end layer prevented from significantly rising toward proximal end

Provided are a molding step (A) of preparing an alumina molded bodyfrom a molding raw material which contains an alumina raw material powder having an average particle size of 2 &#x3bc;m to 5 &#x3bc;m and a molding additive, and a sintering step (B) of preparing an alumina molded body, which becomes a spark plug insulator, by sintering the alumina molded body. At the sintering step (B), the alumina molded bodyis conveyed to a continuous furnaceprovided with a heating zone Zwhich is heated to 700&#xb0; C. to 1600&#xb0; C. by a heating means, followed by introducing oxygen gas to control the heating zone Zto have a high oxygen atmosphere with an oxygen concentration exceeding 20 mol %.

Method of producing spark plug insulator

A spark plugincludes a cylindrical housing, a cylindrical insulator, a center electrode, a terminal bracket, a ground electrode, and a resistor. The insulator is held on the inside of the housing. The center electrodeis held on the inside of the insulator, with a tip end being projected therefrom. The terminal bracket is held on the inside of the insulator, with a base end part and being projected therefrom. The ground electrode forms a spark discharge gap G between itself and the center electrode. The resistor contains carbon and is disposed on the inside of the insulator so as to be located between the center electrodeand the terminal bracket. In an axial direction X of the spark plug, the resistor has a higher carbon content in a first region positioned on a tip side, compared to a second region positioned on a base end side.

Spark plug for internal combustion engine

The spark plug has a shaft shaped center electrode, insulator, terminal fitting, ground electrode and resistor. The insulator has an axially penetrating shaft hole, and the center electrode is held in a tip end side of the shaft hole. The terminal fitting has a shaft and a terminal part. The shaft is held in a base end side of the shaft hole. The terminal part is projected from a base end of the shaft hole to a base end side of the spark plug. The ground electrode faces the center electrode in a tip end side of the shaft hole. The resistor is disposed between the center electrode and the terminal fitting in the shaft hole. An axial length L of the resistor is 15 mm&#x2266;L&#x2266;22.5 mm. An axial length T of the shaft satisfies a relation of 1.25&#x2266;T/L.

Spark plug

An alumina sintered body has a main phase made of alumina crystals, a first dispersed phase made of MgAlOdispersed in the main phase, and a second dispersed phase made of SiOand/or CaO dispersed in the main phase. A content ratio of the main phase is within a range from not less than 98% to less than 98%. The alumina sintered body satisfies a relationship of 100&#xd7;I/I&#x2267;5.5%, where Iindicates a maximum peak height intensity derived from alumina, and Iindicates a maximum peak height intensity derived from MgAlOin a X-ray diffraction of the alumina sintered body. An area ratio of the second dispersed phase on a surface of the alumina sintered body is not more than 15.2%. A spark plug has a central electrode, a ground electrode and an insulator made of the alumina sintered body having the specific features previously described.

Alumina sintered body and spark plug using the same

An alumina sintered body comprises alumina crystals as a main phase and a grain boundary phase made up of crystalline YSiOand amorphous SiOat grain boundaries of the alumina crystals wherein when the alumina sintered body is taken as 100 wt %, the high melting phase is present in the range of from 0.1 wt % to 15 wt %. There is also provided a method for preparing the alumina sintered body, which method comprising a first mixing step Pof mixing, at least, a yttria powder having an average particle size of 60 to 100 nm and a silica powder having a given average particle size to provide a mixed slurry and a second mixing step of further mixing an alumina powder having an average particle size of 0.5 to 1.0 &#x3bc;m in the mixed slurry.

Growing community of inventors

Kariya, Japan

Hiroshi Araki