Patent ID: 6344119
Filing Date: 2002-02-05
Classification: G01N

Abstract:
A NOx gas sensor comprising:a main pumping means including an inner pumping electrode and an outer pumping electrode arranged on inner and outer surfaces of an outer substrate composed of an oxygen ion-conductive solid electrolyte comprising ZrO2, for pumping-processing oxygen contained in a measurement gas introduced from external space on the basis of a control voltage applied between said inner pumping electrode and said outer pumping electrode; an auxiliary pumping means including an inner auxiliary electrode and an outer auxiliary electrode arranged on said inner and outer surfaces of said substrate composed of said oxygen ion-conductive solid electrolyte, for pumping-processing oxygen contained in said measurement gas after being pumping-processed by said main pumping means on the basis of an auxiliary pumping voltage applied between said inner auxiliary electrode and said outer auxiliary electrode; an electric signal-generating conversion means including an inner detecting electrode and an outer detecting electrode arranged on inner and outer surfaces of an inner substrate composed of an oxygen ion-conductive solid electrolyte, said inner detecting electrode provided in a processing space, for decomposing a predetermined gas component contained in said measurement gas after being pumping-processed by said main pumping means, by means of a catalytic action and/or electrolysis to make conversion into an electric signal corresponding to an amount of oxygen produced by said decomposition; and insulative layers and conductive layers formed on a plurality of solid electrolyte green sheets comprising ZrO2, said plurality of green sheets being stacked and integrated into one unit followed by being sintered to form said outer substrate and said inner substrate, wherein: at least a lead wire connected to said inner detecting electrode of said electric signal-generating conversion means, which is exposed to said measurement gas introduced into said processing space, comprises a cermet comprising densified ZrO2 and a metal of the platinum group, said ZrO2 having a sintering degree not less than a sintering degree of ZrO2 in said solid electrolyte substrate; said densified lead wire having a porosity of not more than 10% whereby the ease of O2 entry into the densified lead wire is represented by 1/R where 1/R=(r)(S/L) andr=porosity, S=the cross-sectional area of the lead wire, L=the length of the lead wire, and wherein said ease of O2 entry 1/R is less than or equal to 6.0Ã—10âˆ’6; said densified lead wire has a covering of densified insulated material that surrounds the lead wire, which extends from the processing space where the detecting electrode is provided to a short, predetermined distance from the end of the lead wire, and which maintains said densified lead wire electrically insulated, said densified lead wire and surrounding densified insulated material being maintained between solid electrolyte sheets on either side of the densified lead wire; and said predetermined gas component contained in said measurement gas is measured on the basis of said electric signal detected by said electric signal-generating conversion means.