Airbag device

1. An airbag device for protecting an occupant seated on a vehicle seat of a vehicle from an impact by deploying and inflating an airbag with an inflation gas in a case where the impact is applied to the vehicle from an obliquely front outer side of the vehicle seat or in a case where it is predicted that the impact is to be applied to the vehicle, wherein

when in a width direction of a seatback of the vehicle seat, a side closer to a central portion of the seatback in the width direction is defined as an inner side and a side farther from the central portion of the seatback in the width direction is defined as an outer side, the airbag includes

a main inflation portion that is configured to be deployed and inflated and adapted so as to be positioned when deployed and inflated at the outer side of an upper body of the occupant, and

an auxiliary inflation portion that is disposed at a position adjacent to the inner side of the main inflation portion and is configured to be deployed and inflated and adapted so as to be positioned when deployed and inflated at an obliquely front outer side of a head portion of the occupant by the inflation gas passing through the main inflation portion,

the auxiliary inflation portion is joined to the main inflation portion in a joining area, in a state of being in communication with the main inflation portion,

the auxiliary inflation portion includes an annular side portion constituting an outer peripheral portion, an outer main body portion surrounded by an outer edge portion of the annular side portion, and an inner main body portion surrounded by an inner edge portion of the annular side portion,

in the auxiliary inflation portion whose deployment and inflation are completed, a maximum dimension in a facing direction in which the outer main body portion and the inner main body portion face each other is set to be smaller than a dimension in a direction orthogonal to the facing direction, and

the outer main body portion is joined to the main inflation portion as the joining area of the auxiliary inflation portion.

2. The airbag device according to claim 1 , wherein

when deployment and inflation of the main inflation portion and the auxiliary inflation portion are completed, both the main inflation portion and the auxiliary inflation portion are inclined with respect to a front-rear direction such that a front side of the main inflation portion and a front side of the auxiliary inflation portion are positioned at a front outer side.

3. The airbag device according to claim 1 , wherein

an auxiliary communication hole, with which an inside and an outside of the auxiliary inflation portion communicate with each other, is formed in the outer main body portion,

a main communication hole, with which an inside and an outside of the main inflation portion communicate with each other, is formed in a portion of the main inflation portion adjacent to the auxiliary communication hole, and

a peripheral portion of the main communication hole in the main inflation portion and a peripheral portion of the auxiliary communication hole in the outer main body portion are overlapped with each other and joined to each other by an annular joint portion.

4. The airbag device according to claim 3 , wherein

a combination of the main communication hole, the auxiliary communication hole, and the annular joint portion is provided at a plurality of positions in the joining area.

5. The airbag device according to claim 3 , wherein

when a distance between a front end portion of the annular joint portion positioned at a foremost position and a rear end portion of the annular joint portion positioned at a rearmost position in the joining area is defined as a front-rear length of joining area, the maximum dimension in the facing direction is set to be smaller than the front-rear length of the joining area.