Seat cushion airbag apparatus

1. A seat cushion airbag apparatus for a conveyance seat having a cushion portion configured such that an occupant is seated thereon, the seat cushion airbag apparatus comprising:

a support portion that is arranged below the cushion portion;

an airbag that is arranged between the cushion portion and the support portion and at a center portion in a width direction of the conveyance seat, the seat cushion airbag apparatus being configured to inflate the airbag with inflation gas to restrict forward movement of the lumbar region of the occupant;

a fastening portion that fastens the airbag to the support portion, the fastening portion being disposed rearward of a center in a front-rear direction of a lower portion of the airbag in an inflated state; and

a band-shaped tether arranged about the airbag, wherein

the tether includes two tilted portions respectively arranged at opposite sides in the width direction of the airbag,

a rear end of each tilted portion is fixed to the support portion,

a front end of the tether is fixed to a front portion of the airbag, and

each tilted portion is tilted to rise toward a front side when the airbag is inflated.

2. The seat cushion airbag apparatus according to claim 1 , wherein the fastening portion is disposed at a rear end of the airbag in the inflated state.

3. The seat cushion airbag apparatus according to claim 1 , wherein the airbag in the inflated state has such a shape that a height from the support portion is highest at a rear end.

4. The seat cushion airbag apparatus according to claim 3 , wherein the airbag in the inflated state has such a shape that the height decreases toward a front side with distance from the rear end.

5. The seat cushion airbag apparatus according to claim 1 , wherein

the airbag before being inflated includes

a first inflatable portion that is arranged on the support portion, and

a second inflatable portion that is folded to be located on top of the first inflatable portion, and

the first inflatable portion and the second inflatable portion communicate with each other at rear ends.

6. The seat cushion airbag apparatus according to claim 1 , wherein

the support portion includes a wall plate portion extending upward, and

the wall plate portion is located at a position that is forward of and adjacent to the airbag in the inflated state.

7. The seat cushion airbag apparatus according to claim 1 , wherein

the fastening portion is a rear fastening portion, and

the seat cushion airbag apparatus further comprises a front fastening portion that fastens the airbag to the support portion, the front fastening portion being disposed forward of the rear fastening portion.

8. The seat cushion airbag apparatus according to claim 1 , wherein

the tether is formed by a single band that includes the two tilted portions and a connecting portion that is arranged forward of the airbag and connects front ends of the tilted portions to each other, and

the tether is fixed to a front end of the airbag at least at the connecting portion.

9. The seat cushion airbag apparatus according to claim 8 , wherein a length of the tether is set to be shorter than a peripheral length of a part of the airbag over which the tether is placed.

10. The seat cushion airbag apparatus according to claim 1 , wherein the front end of the tether is fixed to the front portion of the airbag by a sewing thread that sews the tether and the airbag together.

11. The seat cushion airbag apparatus according to claim 1 , wherein a rear end of each tilted portion is fastened to the support portion by the fastening portion together with the airbag.

12. The seat cushion airbag apparatus according to claim 1 , wherein

the airbag in the inflated state includes a tilted surface that is lowered toward the front side, and

the front end of the tether is arranged at a position that is forward of and below a center in the front-rear direction of the tilted surface.