Glow plug for an internal combustion engine

Claim 1

A glow plug mounted in a combustion chamber of an internal combustion engine, comprising: (1) a heater support member projecting into the combustion chamber of the internal combustion engine, said heater support member being formed of a mixture containing alumina and silicon nitride; (2) a heater member affixed to the surface of said heater support member, said heater member being formed of a mixture containing molybdenum disilicate and silicon nitride, said heater support member and said heater member being integrally sintered; said heater support member being in the form of a rod, and said heater member covering in a U-shaped form the tip end face of said heater support member and the upper and lower face portions of said heater support member contiguous to said end face; (3) first, second and third lead wires for power supply embedded in said heater support member; one end of said first lead wire being connected embeddedly to one end portion of said heater member, one end of said second lead wire being connected embeddedly to the other end portion of said heater member and one end of said third lead wire being connected embeddedly to the central portion of said heater member, thereby forming two heater elements having substantially the same resistance value between the lead wires; (4) a power source; and (5) a power switching means for connecting said power source selectively between said lead wires for power supply according to the state of preheating in said combustion chamber, said power switching means having a switching relay contact for connecting said power source selectively between said third lead wire and the other two lead wires and between said other two lead wires.