| 摘要 |
PURPOSE:To stably control an air-fuel ratio to be close to a theoretical air-fuel ratio only by integral control, by laying a protective layer having gas-permeability and a fine structure so that it covers an electrode on the inner surface side or a platinum catalyst layer on the outer surface side. CONSTITUTION:Inside and outside electrodes 22 and 23 made of Pt respectively are formed in parts of the inner and outer surfaces of a ceramic tube 21 containing ZrO2 being a solid electrolyte of oxygen ion conductivity, as a main component, and a Pt catalyst layer 24 is formed on the outer surface of the ceramic tube 21. Then, a protective layer 31 is formed on the outer surface of the catalyst layer 24 by flame- spraying Rh contained in a metal oxide. On the other hand, a protective layer 32 is laid on the inner surface of the ceramic tube 21 whereon the electrode 22 is formed. The protective layer 32 is formed, for instance, by sintering alumina attached on the inner surface of the ceramic tube 21 to turn it into alpha alumina having a fine crystal structure. By covering the electrode 22 with the fine protective layer 32, O<-> ions capable of penetrating into the ceramic tube 31 through the protective layer 32 are reduced, and an output characteristic of the movement of the O<-> ions varying gently in relation to the variation in an air-fuel ratio is obtained. Thereby a stable air-fuel ratio control can be realized. |
