Abstract: An oxygen sensor is constituted by a ceramic separator being placed so that the rear thereof enters the inside of a filter holding part and the front enters the inside of a casing and formed with a plurality of lead insertion holes axially penetrating the ceramic separator and an elastic seal member being fitted elastically into a rear opening of the filter holding part and having seal lead insertion holes for inserting leads for sealing the gap between the outer faces of the leads and the inner face of the filter holding part. The rear end face of the ceramic separator is positioned on the rear side behind a gas introduction hole in the axial direction and a predetermined gap is formed between the elastic seal member and the ceramic separator at least at the lead insertion position.

Abstract: A gas sensor 1 includes a casing 10 which covers a sensing element 2 and includes two cylindrical members. The cylindrical members are axially disposed in such a manner as to overlap each other. Examples of the cylindrical members are a protector 11 (outer member) and a protector attachment portion 9a (inner member) of a metallic shell 9. A diameter-reduced portion 81 is circumferentially formed on the outer member 11 through, for example, caulking. A weld zone 83 is circumferentially formed at the diameter-reduced portion 81 so as to weld the outer member 11 onto the inner member 9a. Through formation of the diameter-reduced portion 81, a gap between the outer member 11 and the inner member 9a as measured at the position of the weld zone is reduced, thereby improving adhesion therebetween. As a result, possibility of a weld defect arising can be suppressed.

Abstract: An oxygen sensor is constituted by a ceramic separator being placed so that the rear thereof enters the inside of a filter holding part and the front enters the inside of a casing and formed with a plurality of lead insertion holes axially penetrating the ceramic separator and an elastic seal member being fitted elastically into a rear opening of the filter holding part and having seal lead insertion holes for inserting leads for sealing the gap between the outer faces of the leads and the inner face of the filter holding part. The rear end face of the ceramic separator is positioned on the rear side behind a gas introduction hole in the axial direction and a predetermined gap is formed between the elastic seal member and the ceramic separator at least at the lead insertion position.

Abstract: A rotary valve made of ceramics has edges at the junctions between a generally cylindrical outer periphery and opposite ends of a through hole. Each of the edges has a leading edge portion at which the valve starts opening and a leading edge portion at which the valve finishes closing. The leading edge portions are chamferred in such a way as to form part of surfaces of right circular cones whose vertexes are contained in an axis of rotation of the rotary valve and whose axes coincide with the center axis of the through hole.