Ngk Spark Plug Company, Limited

Atsushi Tsukada

Haruki Yoshida

Takamitsu Mizuno

Tsutomu Shibata

Satoru Ochiai

Ryoji Kato

A spark plug, comprised of: an insulator having an axial bore extending in the direction of an axis, a first inner circumferential surface extending at a forward side of the axial bore, a second inner circumferential surface extending at a rear side of the axial bore and having a diameter greater than that of the first inner circumferential surface, and a ledge connecting the first inner circumferential surface and the second inner circumferential surface; a center electrode having a head supported by the ledge and extending in a space surrounded by the second inner circumferential surface, and a circular columnar leg extending continuously from the forward end of the head in a space surrounded by the first inner circumferential surface; and a seal material for holding the center electrode in the axial bore.

Spark plug

A spark plug includes an insulator having an axial hole, a first inner circumferential surface, a second inner circumferential surface whose diameter is greater than that of the first inner circumferential surface, and a ledge portion connecting the first and the second inner circumferential surfaces. The spark plug also includes a center electrode having a large-diameter portion, a projection portion, and a circular columnar leg portion that projects into a space surrounded by the first inner circumferential surface. The spark plug includes a seal portion which fixes the center electrode within the axial hole. When C&#x3c;A, A&#x2212;C&#x2266;B&#x2212;A, where A represents a diameter of an imaginary cylinder having the minimum diameter required for surrounding the projection portion, B represents a maximum diameter of the large-diameter portion, and C represents an average diameter of the leg portion present in the space surrounded by the first inner circumferential surface.

A decrease in yield and degradation of productivity can be avoided when a spark plug having an insulator with low mechanical strength is manufactured. In a second process, a terminal electrodeis inserted to a predetermined position in a state where an insulatoris heated to a temperature equal to or greater than the softening temperatures of first to third powder materialsP,P, andP such that the first powder materialP becomes a first conductive sealing material layer, the second powder materialP becomes a resistor, and the third powder materialP becomes a second conductive sealing material layer. In addition, a speed at which the terminal electrodeis inserted is reduced between the start and the end of the second process.

Growing community of inventors

Yokkaichi, Japan

Atsushi Tsukada