OXYGEN SENSOR PARTICULARLY USEFUL IN EXHAUST SYSTEM OF AUTOMOTIVE ENGINE

摘要

A solid electrolyte tube closed at one end and two porous electrode layers respectively coated on the outer and inner surfaces of the electrolyte tube constitute a known oxygen concentration cell. A tubular metal shell encloses the electrolyte tube partly such that a closed end portion of the tube protrudes from the shell and that the outer electrode coating is locally in contact with the inside of the shell. To protect the open end of the electrolyte tube against splashing of water during use without interrupting the admission of atmospheric air as a reference gas into the inside of the electrolyte tube, a tubular cap member of a metal is coaxially fixed to and electrically connected at its one end to the shell at one end portion surrounding the open end of the electrolyte tube, and a cross-sectionally circular plug of an insulating material is coaxially and tightly received in and fixed to the cap member to occupy an end portion, contiguous to the free end, of the interior of the cap member. This plug has two axial bores which respectively allow two cable wires of the sensor to tightly pass therethrough and an air-admitting passage formed therein independently of these two bores in such an arrangement and cross-sectional area that unpressurized water does not pass therethrough from the atmosphere to the unoccupied portion of the interior of the cap member.