Low noise resistance containing spark plug

Claim 1

In a resistance containing spark plug comprising an elongated hollow cylindrical heat resisting insulator having a central longitudinal through hole; a spark electrode received in and partially exposed from the spark end of the insulator through hole; a noise suppressing resistance material inserted into the through hole of the insulator and having a predetermined height starting from the upper end of the spark electrode; a terminal electrode having an inner portion secured in the through hole of the insulator in contact with the resistance material and an outer portion adapted to be connected to an external power source; and a ground electrode spaced by a predetermined gap from the spark electrode, the improvement characterized by: (a) said spark electrode comprising a semiconductive material having a relatively low electrical resistance, relatively high resistances to sparking and heat deterioration, relatively high thermal conductivity, and relatively high resistance to oxidation, said semiconductive material comprising a first main component of high melting point sealing glass composition containing SiO 2 , Al 2 O 3 and B 2 O 3 , a second main component of metal alloy powder having a high oxidation resistance at high temperatures, and lesser amounts of oxides and inorganic substances, (b) said noise suppressing resistance material comprising a carbonaceous layer above the spark electrode and having a relatively high electrical resistance, and a sealing layer above the carbonaceous layer and having a relatively low electrical resistance and high adhesion properties, said sealing layer being in contact with the terminal electrode, and (c) the spark end of the insulator through hole being at least partially closed to define a reduced diameter end opening.