Gas generator

1. A gas generator comprising:

a gas generating agent that generates gas as the gas generating agent burns;

an igniter including an ignition portion loaded with a terminal pin connected to the ignition portion;

a cylindrical cup having a bottom portion configured to accommodate the gas generating agent, the cylindrical cup including one axial end as an opening end; and

a columnar holder to which the cup is coaxially assembled to close the opening end, the columnar holder holding the igniter such that the ignition portion faces the gas generating agent, wherein

an annular step portion is provided at a periphery of an axial end of the holder on a side facing the cup, and

the cup is fixed to the holder by fitting the opening end to the annular step portion and providing an annular welded portion at the opening end, the annular welded portion being, joined to the annular step portion so as to extend along a circumferential direction of the cup,

wherein a maximum outer dimension in a radial direction of the cup including the annular welded portion is equal to or smaller than a maximum outer dimension in the radial direction of the holder,

wherein a maximum outer dimension in a radial direction of the cup in a portion fitted to the annular step portion except for the annular welded portion is smaller than a maximum outer dimension in the radial direction of the holder,

wherein the opening end of the cup is substantially in a straight cylindrical shape,

wherein the annular step portion is defined by a first step forming surface formed from a peripheral surface of the holder continuous to the axial end surface of the holder on the side facing the cup and an annular planar second step forming surface continuous to the first step forming surface and continuous to the outer peripheral surface of the holder, and

wherein the annular welded portion is provided at the opening end of the cup in a portion facing the first step forming surface, at a position distant from a tip end surface of the opening end of the cup, so as to be joined to the first step forming surface without being joined to the second step forming surface.

2. The gas generator according to claim 1 , wherein

the igniter further includes a base in which the terminal pin is inserted and held,

the holder includes

a first recess provided at the axial end on the side facing the cup, the first recess accepting and holding the base,

a second recess provided at an axial end on a side not facing the cup, the terminal pin being arranged in the second recess, and

a partition portion that serves as a partition between the first recess and the second recess by defining a bottom surface of the first recess and a bottom surface of the second recess, the partition portion being provided with an opening in which the igniter is inserted, and

the annular step portion is provided to reach an outer peripheral surface of the holder in a portion of the holder surrounding the partition portion, and the annular welded portion is provided in a portion of the opening end that surrounds the partition portion.

3. The gas generator according to claim 1 , wherein

the annular welded portion is a laser welded portion where the opening end is joined to the annular step portion by laser welding.

4. The gas generator according to claim 1 , wherein

the cup and the holder are both made of an iron-based material.