Patent ID: 7565826

Claim:
A gas sensor comprising: a gas sensor element for detecting a concentration of specified gas in measuring gases; a cylindrical housing through which the sensor element extends and is fixedly supported; an atmosphere-side cover fixedly secured to a base end of the cylindrical housing so as to cover a base end portion of the gas sensor element; a seal member fixedly supported with a base end of the atmosphere-side cover and having a ventilation bore, through which atmospheric air is introduced to the cylindrical housing, and a plurality of lead wire inserting bores formed around the ventilation bore; and a filter member, made of porous material and covering the ventilation bore so as to permeate atmospheric air, which has a fusion-bonded area in which the filter member is fusion bonded to an end face of the seal member at temperatures above 300° C.; wherein the fusion-bonded area is formed in an entire circumference in gastight effect at an area outside an outer periphery of the ventilation bore covered with the filter member and has no clearance; wherein suppose that the ventilation bore has an opening surface area A at the end face of the seal member and a region surrounded with the fusion-bonded area has a surface area B, the relationship is established as A<B≦ 9 A.