Patent ID: 7722750

Claim:
A gas sensor comprising: a sensing element that detects a concentration of a particular gas component within a gas to be measured and outputs an electric signal corresponding to the detected concentration; a housing in which the sensing element is inserted and held, the sensing element held in the housing having a length direction defining an axial direction of the housing, the housing having both a radial direction perpendicular to the axial direction and a circumferential direction encircling the axial direction, the housing having a base end and a tip end both located along the axial direction; an atmosphere-side cover formed as an approximately cylindrical member having i) a first section of a first diameter which is located on a tip-end side in the axial direction and which is fixed on the base end of the housing, ii) a second section of a second diameter smaller than the first diameter, the second section being located on a base-end side in the axial direction and having an outer periphery, iii) a stepped section formed between the first and second sections to connect both the first and second sections with each other, and iv) a plurality of ribs each protruding outward in the radial direction from an axial end portion of the second section so that the plurality of ribs are located next to the stepped section in the axial direction and spaced apart from one another in the circumferential direction, each rib having a base-end section in the axial direction; a ventilation filter mounted on the outer periphery of the second section and formed to have a tip-end section in the axial direction, the tip-end section of the ventilation filter being in contact with the base-end section of the ribs; and a filter cover that covers the ventilation filter so that the ventilation filter is fixedly placed between the second section of the atmosphere-side cover and the filter cover, the filter cover having a tip-end section in the axial direction, the tip-end section being in contact with the ribs so that a space is defined by the second section of the atmosphere-side cover, adjacent two ribs of the ribs, and the filter cover, the space communicating with an outside of the gas sensor, wherein a circumferential length A of a rib-formation area of the second section that is protruded to form each rib and a circumferential length B of a non-ribbed area of the second section that is between adjacent two ribs have the relationship: 0.15≦ A/B≦ 1.