Device for producing control signal for feedback control of air/fuel ratio

A device to produce a control signal for feedback control of the air/fuel ratio of an air-fuel mixture supplied to a combustor, the device comprising:

• an oxygen-sensitive element which is to be disposed in a combustion gas exhausted from the combustor and comprises two oxygen concentration cells each constituted of a layer of an oxygen ion conductive solid electrolyte, a measurement electrode layer formed on one side of the solid electrolyte layer, a reference electrode layer formed-on the other side of the solid electrolyte layer and a shield layer provided on the reference electrode side of the solid electrolyte layer so as to closely cover the reference electrode layer, at least one of the solid electrolyte layer and the shield layer of each concentration cell having a microscopically porous and gas permeable structure, one of the measurement electrode layer and the reference electrode layer of one concentration cell being electrically connected to the corresponding one of the other concentration cell;
• a constant voltage DC power source connected to the unconnected electrode layers of the respective concentration cells of the oxygen-sensitive element to force a DC current to flow through the solid electrolyte layers of the two concentration cells from the measurement electrode layer to the reference electrode layer in one cell and from the reference electrode layer to the measurement electrode layer in the other cell;
• and
• a signal-producing circuit having comparing means for making a comparison between a predetermined reference voltage and an output voltage of the oxygen-sensitive element developed between the measurement and reference electrode layers of a predetermined one of the two concentration cells to examine which one of the reference voltage and the output voltage is higher than the other and signal-generating means for producing a control signal which varies according to a high-low relationship between the reference voltage and the output voltage examined by the comparing means.