Patent ID: 8052862

Claim:
A limiting current type oxygen sensor, comprising: an ion conductor composed of a solid electrolyte; a porous electrode pair comprising a first electrode and a second electrode, wherein the ion conductor is disposed between the first and second electrodes and the porous electrode pair is adapted to apply an electric field between the first and second electrodes; a cap configured to supply a diffusion-rate-determined gas to a face of the first electrode; and a heater arranged to heat the ion conductor, wherein the cap includes an internal space in contact with the face of the first electrode, and a gas diffusion bore formed to communicate the internal space with a space outside of the cap, wherein the cap is configured such that an oxygen concentration gradient within the internal space satisfies the following expression: 1 /I lim =(1/4 FDC o2 ){( l/S )+( l in /S in )} which is based on a relationship between the Faraday constant (F); a diffusion coefficient (D); an oxygen concentration (C o2 ); a bore area (S) of the gas diffusion bore; a bore length (l) in the axial direction of the gas diffusion bore; a distance (l in ) in the internal space between the first electrode and the inner surface opposed thereto; an effective cross section (S in ) of the internal space; and an output current value (I lim ); wherein the cap is configured such that the bore area (S) and the bore length (l) of the gas diffusion bore have a ratio (S/l) of 50-250 μm.