Abstract: A platinum reference electrode is disposed on the surface of a blind bore formed in a body of solid zirconia electrolyte and two semi cylindrically shaped measuring electrodes one platinum the other gold are disposed on the outer surface of the body. A first annular insulator supports the body within the casing and defines two chambers on either side thereof while a second annular insulator supports and presses lead wires against the measuring electrodes. A cylindrical connector is inserted into the blind bore to provide good electrical connection between the platinum reference electrode and a lead line.Atmospheric air enters the first chamber and the blind bore while exhaust gases enter the second chamber and contact the measuring electrodes; the platinum/platinum and platinum/gold electrodes produce markedly different signals one of which is used to recalibrate the other as the peak output voltages decrease with time and temperature.

Abstract: A temperature sensor is disposed at the upstream or middle portion of a reactor for oxidizing the unburned constituents contained in the exhaust gases discharged from the combustion chambers of the engine. The air-fuel ratio of the air-fuel mixture supplied to the combustion chambers is controlled so as to maintain the temperature of the upstream or middle portion of the reactor at the predetermined level in the vicinity of but higher than the temperature corresponding to the critical point where the temperature of the downstream portion of the reactor begins to decrease.