Electrochemical oxygen sensor, particularly for analysis of combustion cases from internal combustion engines

Claim 1

Electrochemical sensor to determine the oxygen content of test gases, particularly to analyze exhaust gases from a combustion process, especially from an internal combustion engine, having a tubular housing (12); a plate-like sensing element (11, 511) retained in the housing and having a sensing end portion (11/1; 511/1) adapted to be exposed to the gas to be analyzed, an intermediate holding portion (11/2) and a connecting portion (11/3) adapted to be connected to an electrical circuit (B, E), wherein the sensing end portion of the plate-like sensing element comprises an oxygen ion conductive solid electrolyte plate-like carrier (35) having terminal edges; two layer-like porous electrodes (39, 48; 539, 548), applied to the plate-like carrier and positioned inwardly of the edges of the solid electrolyte plate-like carrier (35), one of the electrodes forming a sensing electrode and being in communication with the gas to be analyzed, and comprising, in accordance with the invention, a sintered, porous, gas-pervious filler material (42, 49) covering at least one of the electrodes (39, 48; 539, 548) and a portion of the carrier, and extending towards and adjacent to a neighboring edge (40) of the carrier; and a gas-tight covering (44, 51) placed over said porous filler material and the at least one electrode covered by said filler material (42, 49), the edge of the gas-tight covering (44) being forward of the edge of said at least one electrode beneath the filler material to force the gas to flow at least for some distance along the plane of the carrier and hence over said at least one layer-like porous electrode beneath the porous filler material, said gas-tight covering being mechanically supported by the porous filler material over the layer-like electrode applied to the plate-like carrier, and forming a tunnel cover over said porous filler material, the respective electrode therebeneath and said portion of the carrier, the tunnel being filled by said porous filler material, said tunnel extending essentially parallel to the major surface of said electrolyte plate-like carrier (35); said gas-tight covering leaving exposed a portion of the sintered, porous, gas-pervious filler material in a region adjacent said edge (40) to expose said filler material to the gas to be applied to the electrode in, and beneath the tunnel, to permit access of said gas to the filler material and to conduct said gas along the surface of said carrier portion and hence to the electrode positioned beneath the tunnel cover, said gas-tight covering protecting the electrode and isolating the porous filler material over the carrier portion and over the electrode, and hence the electrode, from contact with gas surrounding said sensing elmeent except at the zone of exposure adjacent said edge.