Airbag equipped with sub-chamber

1. An airbag equipped with a sub-chamber, comprising:

a main chamber expanding by being injected with gas in a collision; and

a sub-chamber formed by folding a panel-shaped chamber to be combined with the main chamber and have self-supporting force, the sub-chamber assisting supporting force of the main chamber by expanding with the main chamber,

wherein the sub-chamber is folded and coupled to the main chamber and has an M-shape when completely expanded in the collision,

wherein the sub-chamber is formed as a rectangle having a width larger than a height thereof and comprises a front part and a rear part,

wherein the front part and the rear part are coupled at upper and lower portions thereof and include a plurality of vertical seams having a predetermined length, and

wherein first and second sides and a center of the sub-chamber are coupled to sides of the main chamber.

2. The airbag of claim 1 , wherein the sub-chamber is coupled to side parts of the main chamber to increase side supporting force of the main chamber and support a passenger turning in the collision.

3. The airbag of claim 1 , wherein the main chamber and the sub-chamber each include an inflator, and the main chamber and the sub-chamber simultaneously expand via respective inflators and support a passenger in the collision.

4. The airbag of claim 1 , wherein vents are formed through a side of the main chamber and gas injection holes are formed at positions corresponding to the vents in the sub-chamber, gas is supplied into the sub-chamber through the vents when gas is injected into the main chamber, the gas is supplied into the sub-chamber through the vents.

5. The airbag of claim 1 , wherein the sub-chamber is coupled to the main chamber to turn at a predetermined angle with respect to the main chamber so that a folded portion of the sub-chamber supports a passenger.

6. The airbag of claim 1 , wherein the sub-chamber is folded and coupled to the main chamber, has the M-shape when completely expanded in the collision, both ends of the M-shape are coupled to a side part of the main chamber, and a bending portion of the M-shape faces outside from the main chamber.

7. The airbag of claim 1 , wherein the sub-chamber is folded and coupled to the main chamber and has a C-shaped cross-section cut in a width direction of a vehicle, and at least one folded part of the sub-chamber is protruded toward a passenger when completely expanded in the collision.

8. The airbag of claim 1 , wherein the sub-chamber is folded and coupled to the main chamber and has a U-shaped cross-section cut in a width direction of a vehicle, and at least one folded part of the sub-chamber is protruded toward a passenger when completely expanded in the collision.

9. The airbag of claim 1 , wherein the sub-chamber is coupled to the main chamber to further protrude by a predetermined distance toward a passenger than toward the main chamber when the main chamber and the sub-chamber expand.

10. The airbag of claim 1 , wherein a pair of head protection chambers for protecting a head of a passenger is formed in the main chamber.

11. The airbag of claim 1 wherein the center of the sub-chamber is directly coupled to one of the sides of the main chamber by the vertical seams.