Vehicle occupant restraint system

1. A vehicle occupant restraint system comprising an airbag module and a backrest of a vehicle seat, wherein the airbag module is arranged at the backrest, and wherein the airbag module comprises an inflatable gas bag main chamber and an inflatable gas bag secondary chamber, wherein in the inflated condition the gas bag main chamber has a larger volume than the gas bag secondary chamber and wherein the gas bag main chamber and the gas bag secondary chamber are fluidically connected to each other via an overflow opening, wherein the airbag module is arranged at the backrest of the vehicle seat in such a way that in the inflated condition the gas bag secondary chamber is supported at the backrest of the vehicle seat, wherein in the inflated condition the gas bag main chamber is supported on a side of the gas bag secondary chamber that faces away from the backrest so that the gas bag secondary chamber is arranged between the gas bag main chamber and the backrest.

2. The vehicle occupant restraint system according to claim 1 , wherein the gas bag main chamber is attached to the backrest at a point of attachment, wherein the point of attachment is provided at or close to an edge of the backrest that is defined by a front side of the backrest and a left or right side of the backrest.

3. The vehicle occupant restraint system according to claim 1 , wherein the gas bag main chamber and the gas bag secondary chamber are formed by a folded inflatable gas bag, wherein the gas bag main chamber and the gas bag secondary chamber are configured on either side of the fold thus formed, or that the gas bag main chamber and the gas bag secondary chamber are formed by one inflatable gas bag each.

4. The vehicle occupant restraint system according to claim 3 , wherein the gas bag that forms the gas bag main chamber and the gas bag that forms the gas bag secondary chamber each include an opening, wherein the two openings are fluidically connected to each other.

5. The vehicle occupant restraint system according to claim 1 , wherein the gas bag main chamber and the gas bag secondary chamber are connected to each other by a connector so that in the inflated condition the gas bag main chamber and the gas bag secondary chamber have a defined alignment relative to each other.

6. The vehicle occupant restraint system according to claim 1 , wherein the airbag module comprises a gas generator that is arranged in the gas bag main chamber or in the gas bag secondary chamber or that protrudes into the gas bag main chamber or into the gas bag secondary chamber.

7. The vehicle occupant restraint system according to claim 1 , wherein the airbag module is arranged laterally on the backrest.

8. The vehicle occupant restraint system according to claim 7 , wherein the airbag module faces a vehicle interior space and faces away from a vehicle door.

9. The vehicle occupant restraint system according to claim 1 , wherein the gas bag secondary chamber is laterally supported on the backrest.

10. The vehicle occupant restraint system according to claim 1 , wherein in the inflated condition the gas bag main chamber has a larger expansion along the direction of travel than the gas bag secondary chamber.

11. The vehicle occupant restraint system according to claim 1 , wherein in the inflated condition the gas bag main chamber protrudes beyond the gas bag secondary chamber and the backrest in the direction of travel.

12. The vehicle occupant restraint system according to claim 1 , wherein the gas bag main chamber is attached to the backrest in front of the gas bag secondary chamber in the direction of travel.

13. The vehicle occupant restraint system according to claim 12 , wherein the gas bag main chamber is attached to the backrest at a point of attachment and in the inflated condition is rotatable about this point of attachment.

14. The vehicle occupant restraint system according to claim 1 , wherein the gas bag main chamber is laterally supported on the backrest, while the gas bag secondary chamber is supported on a rear side of the backrest.

15. A vehicle occupant restraint system comprising an airbag module and a backrest of a vehicle seat, wherein the airbag module is arranged at the backrest, and wherein the airbag module comprises an inflatable gas bag main chamber and an inflatable gas bag secondary chamber, wherein in the inflated condition the gas bag main chamber has a larger volume than the gas bag secondary chamber and wherein the gas bag main chamber and the gas bag secondary chamber are fluidically connected to each other via an overflow opening, wherein the airbag module is arranged at the backrest of the vehicle seat in such a way that in the inflated condition the gas bag secondary chamber is supported at the backrest of the vehicle seat, wherein the airbag module comprises at least two gas bag secondary chambers, wherein in the inflated condition a first gas bag secondary chamber of the at least two gas bag secondary chambers is supported on the backrest of the vehicle seat and in the inflated condition the gas bag main chamber is supported on a second gas bag secondary chamber of the at least two gas bag secondary chambers, which is arranged between the first gas bag secondary chamber and the gas bag main chamber.

16. The vehicle occupant restraint system according to claim 15 , wherein the gas bag main chamber is attached to the backrest in front of the at least two gas bag secondary chambers in the direction of travel, wherein in particular the gas bag main chamber is attached to the backrest at a point of attachment and in the inflated condition is rotatable about this point of attachment.