In-seat airbag device

1. An in-seat airbag device having an airbag main body that is structured so as to comprise:

an outer side airbag portion having a front-rear chamber that, due to gas jetted-out from an inflator that operates due to a collision of a vehicle being detected or predicted, is configured to expand past one side of a head of a passenger toward a seat front side and is configured to be disposed at the one side of the head of the passenger, a left-right chamber that expands from a seat front side end portion of the front-rear chamber toward a seat width direction inner side and is configured to be disposed at a seat front side of a face of the passenger, a distal end chamber that expands from a seat width direction inner side end portion of the left-right chamber toward a seat rear side and is configured to be disposed at another side of the head of the passenger, and a tether that joins the front-rear chamber and the distal end chamber; and

an inner side airbag portion that, due to gas that flows therein from the outer side airbag portion, expands and is disposed between the front-rear chamber, the left-right chamber and the distal end chamber, and has a head restraining surface that is configured to retrain the head of the passenger.

2. The in-seat airbag device of claim 1 , wherein, as seen in plan view, a projecting portion, which projects-out further toward a seat rear side than a front-rear chamber side, is formed at a distal end chamber side of the head restraining surface of the inner side airbag portion.

3. The in-seat airbag device of claim 2 , wherein, as seen in plan view, a length in a seat front-rear direction of the inner side airbag portion except for the projecting portion is made to be longer than a length in a seat width direction.

4. The in-seat airbag device of claim 1 , wherein, as seen in plan view, the inner side airbag portion is formed substantially in a shape of an oval having a predetermined thickness in a seat width direction, and a seat rear side end portion of the inner side airbag portion is disposed at an incline with respect to a seat front-rear direction so as to move away from the front-rear chamber.

5. The in-seat airbag device of claim 1 , wherein:

a vent hole through which the gas is discharged is formed in the inner side airbag portion, and

an opening surface area of the vent hole is made to be larger than an opening surface area of a flow-in port that is for the gas to flow-in from the outer side airbag portion into the inner side airbag portion.

6. The in-seat airbag device of claim 1 , wherein:

a check valve, which permits flowing-in of the gas from the outer side airbag portion into the inner side airbag portion and restricts flowing-out of the gas from the inner side airbag portion to the outer side airbag portion, is provided at a flow-in port that is for the gas to flow-in from the outer side airbag portion into the inner side airbag portion, and

a variable vent hole, which is closed while the gas is flowing in from the outer side airbag portion into the inner side airbag portion and is configured to be opened when the head of the passenger is restrained, is provided at the inner side airbag portion.

7. The in-seat airbag device of claim 1 , wherein the tether is formed in a substantial “Y” shape as seen in plan view, the tether having one end portion attached to the distal end chamber, and having a front side other end portion and a rear side other end portion, which are separated from each other in a seat front-rear direction and are respectively attached to the front-rear chamber.