Gas generator

A gas generator, comprising

• a cylindrical housing with an ignition device attached at one end and a diffuser portion, which has a gas discharge port, attached at the other end,
• a first combustion chamber formed inside the cylindrical housing at the one end to which the ignition device is attached, being defined by a first porous plate member, and being charged with a molded article of first gas generating agent,
• a second combustion chamber formed in the cylindrical housing and defined by a second porous plate member, which is disposed axially at a distance from the first porous plate member and has a second through hole, the second combustion chamber being charged with a molded article of second gas generating agent,
• the ignition device provided by fixing an igniter main body with a columnar ignition portion, to a fixing member including an igniter collar, the ignition portion disposed to protrude inside the first combustion chamber,
• the first porous plate member having first through holes, a proportion of a first total opening area of only outer first through holes arranged in the vicinity of a peripheral edge portion and in a circumferential direction of the first porous plate member to a total opening area of the first through holes in the first porous plate member being not less than 95%,
• axial end surfaces of the first combustion chamber, respectively, formed by the first porous plate member, and the ignition portion of the igniter main body and the igniter collar,
• an annular space formed between an outer peripheral surface of the ignition portion and an inner peripheral wall surface of the cylindrical housing, which radially faces the outer peripheral surface of the ignition portion, the annular space having a bottom surface defined by the igniter collar,
• a height (H) of a top surface of the ignition portion from the bottom surface and a smallest length (Lmin) of the molded article of first gas generating agent charged in the first combustion chamber satisfying a relation of Lmin<H, and
• an axis X of the cylindrical housing being coincident with a central line of the ignition portion of the igniter main body, the first porous plate member, and the second porous plate member.