Abstract: [Objective] To provide a gas sensor in which a filter member provided in an aerial communication hole adapted to introduce the air for exposing a reference electrode of a detection element to the air is reliably protected through simple configuration. [Means for Solution] A filter member 87 having air permeability and waterproofness is disposed in an aerial communication hole 91 formed in a grommet 9 disposed in a rear end portion 38 of a housing tube 3. The housing tube 3 has a vent portion 34 provided for ensuring aerial communication while protecting the filter member 87. The vent portion 34 is connected, by means of arm portions 33, to an end portion (an opening end 32) of a side wall 39 of the housing tube 3. The side wall 39 surrounds the circumference of the grommet 9. Since the arm portions 33 are disposed in respective grooves 93 of the grommet 9, the grommet 9 is positioned relative to the housing tube 3.

Abstract: A sensor including a tubular casing having an open rear end; and a first elastic member having a through hole so as to introduce ambient air into the casing and disposed so as to block the rear end opening of the casing.

Abstract: A gas sensor having an axis including a detecting element; a metal shell; an outer cylinder; and a plug member, as defined herein, and the gas sensor includes a first protective member that covers an air vent of the plug member so as to protect the filter member, the protective member having a ventilation portion having an opening smaller than an opening of the air vent and at least partially overlapping the air vent in the axial direction, and at least one of the outer cylinder and the plug member is provided with a locking portion that limits rotation of the protective member around the axis.

Abstract: A sensor including a tubular casing having an open rear end; and a first elastic member having a through hole so as to introduce ambient air into the casing and disposed so as to block the rear end opening of the casing.

Abstract: A gas sensor having an axis including a detecting element; a metal shell; an outer cylinder; and a plug member, as defined herein, and the gas sensor includes a first protective member that covers an air vent of the plug member so as to protect the filter member, the protective member having a ventilation portion having an opening smaller than an opening of the air vent and at least partially overlapping the air vent in the axial direction, and at least one of the outer cylinder and the plug member is provided with a locking portion that limits rotation of the protective member around the axis.