Passenger seat airbag

1. A passenger-seat airbag that is folded and stored in an airbag case fixed in an instrument panel, and that is protruded from a bag-protrusion opening formed in the instrument panel, and is deployed toward a passenger seat when a frontal collision occurs, comprising:

a left airbag and a right airbag that correspond to shoulders of an occupant seated at the passenger seat;

a root portion that receives gas injected from an inflator when the inflator operates, and that connects a left-airbag root portion and a right-airbag root portion; and

a strap that connects a base-end portion of the root portion to a connection root portion positioned between the left-airbag root portion and the right-airbag root portion, wherein in a lateral view, the root portion is heart shaped when inflated, and a peripheral length from a junction portion between the connection root portion and the strap to a front edge of the bag-protrusion opening is longer than or equal to a peripheral length from the junction portion between the connection root portion and the strap to a rear edge of the bag-protrusion opening.

2. The passenger-seat airbag according to claim 1 , wherein:

a volume of one of the left and right airbags, which is positioned on an inner side in a vehicle-width direction, is larger than a volume of another of the left and right airbags, which is positioned on an outer side in the vehicle-width direction; and

the strap has a substantially trapezoid shape in which a vehicle front-side base is longer than a vehicle rear-side upper side, and the vehicle rear-side upper side is offset to the airbag positioned on the outer side in the vehicle-width direction, with respect to the vehicle front-side base.

3. The passenger-seat airbag according to claim 1 , wherein:

a volume of one of the left and right airbags, which is positioned on an inner side in a vehicle-width direction, is larger than a volume of another of the left and right airbags, which is positioned on an outer side in the vehicle-width direction; and

gas supply holes, through which the gas is supplied to the left and right airbags, are formed in the strap, opening areas of the gas supply holes are different from each other, and the opening areas correspond to the volumes of the left and right airbags.

4. The passenger-seat airbag according to claim 1 , wherein:

a length of the strap and a position of the junction portion are set such that the inflated root portion does not contact a windshield, and

upper edges of the left and right airbags contact the windshield at two left and right positions when the passenger-seat airbag is completely deployed.

5. The passenger-seat airbag according to claim 1 , wherein an airbag folded portion is formed by folding an airbag body which is positioned closer to a rear of a vehicle than the root portion is when the passenger-seat airbag is provided in the vehicle.

6. The passenger-seat airbag according to claim 5 , wherein the airbag folded portion is formed mainly by rolling up the airbag body.

7. The passenger-seat airbag according to claim 5 , wherein the airbag folded portion is formed mainly by accordion-folding the airbag body.

8. The passenger-seat airbag according to claim 5 , wherein the airbag folded portion is formed by rolling up the airbag body and accordion-folding the airbag body substantially the same number of times.

9. The passenger-seat airbag according to claim 5 , wherein a tip portion of the root portion is accordion-folded once toward the airbag folded portion.

10. The passenger-seat airbag according to claim 5 , wherein a tip portion of the root portion is bent toward the airbag folded portion at a substantially right angle.

11. The passenger-seat airbag according to claim 5 , wherein the root portion, which is positioned closer to a front of the vehicle than the airbag body is when the passenger-seat airbag is provided in the vehicle, is made slack to form a slack portion, and the slack portion is folded separately from the airbag folded portion.

12. The passenger-seat airbag according to claim 11 , wherein:

the slack portion is made upright along the airbag folded portion.

13. The passenger-seat airbag according to claim 11 , wherein the airbag folded portion is formed mainly by rolling up the left and right airbags which are positioned closer to a rear of a vehicle than the root portion is when the passenger-seat airbag is provided in the vehicle; the root portion which is positioned closer to a front of the vehicle than the left and right airbags are when the passenger-seat airbag is provided in the vehicle, is made slack to form the slack portion; the slack portion is made upright along the airbag folded portion that is formed mainly by rolling up the left and right airbags; and a tip portion of the slack portion is accordion-folded.

14. A passenger-seat airbag that is folded and stored in an airbag case fixed in an instrument panel, and that is protruded from a bag-protrusion opening formed in the instrument panel, and is deployed toward a passenger seat when a frontal collision occurs, comprising:

a left airbag and a right airbag that correspond to shoulders of an occupant seated at the passenger seat;

a root portion that receives gas injected from an inflator when the inflator operates, and that connects a left-airbag root portion and a right-airbag root portion; and

a strap that connects a base-end portion of the root portion to a connection root portion positioned between the left-airbag root portion and the right-airbag root portion, wherein in a lateral view, the root portion is substantially heart shaped when inflated, and a peripheral length from a junction portion between the connection root portion and the strap to a front edge of the bag-protrusion opening is longer than or equal to a peripheral length from the junction portion between the connection root portion and the strap to a rear edge of the bag-protrusion opening;

wherein:

the volume of one of the left and right airbags, which is positioned on an inner side in a vehicle-width direction, is larger than the volume of another of the left and right airbags, which is positioned on an outer side in the vehicle-width direction; and

the strap has a rectangular shape, gas supply holes, through which the gas is supplied to the left and right airbags, are formed in the strap, and an opening area of the gas supply hole corresponding to the airbag positioned on the inner side in the vehicle-width direction is larger than an opening area of the gas supply hole corresponding to the airbag positioned on the outer side in the vehicle-width direction.