Airbag

1. An airbag for a motor vehicle for supporting knees of a vehicle occupant in an event of a crash, comprising:

an inflatable portion;

a first fastening region for fastening the airbag to a motor vehicle part;

at least one second, detachable fastening region for fastening the airbag to the same or different motor vehicle part; and

a given connection located between the second, detachable fastening region and the inflatable portion,

wherein the second, detachable fastening region and the first fastening region are formed at spaced-apart points on the airbag,

wherein the second, detachable fastening region is configured to detach from the inflatable portion if a force exceeding a predetermined value acts on the given connection between the second, detachable fastening region and the inflatable portion,

wherein the first fastening region and the second, detachable fastening region are formed from a fabric from which the inflatable portion is also formed,

wherein two side regions of the inflatable portion in an installed state of the airbag are turned inward or folded over in a direction of a central point of the airbag along two side folds which extend in a vehicle longitudinal direction,

wherein the inflatable portion comprises two airbag layers connected by a first connection which extends substantially transversely with respect to the vehicle longitudinal direction and substantially between the two side folds, and

wherein detachable connections extending substantially along the two side folds connect the two airbag layers.

2. The airbag as claimed in claim 1 , wherein the force that detaches the second, detachable fastening region from the inflatable portion is a tensile force, and wherein the tensile force acts on the given connection when the airbag is partially filled with gas.

3. The airbag as claimed in claim 1 , wherein the second, detachable fastening region is detachably connected to the inflatable portion by a tear line, a tear seam, a perforation, or any combination thereof as a separating point formed on the given connection.

4. The airbag as claimed in claim 3 , wherein the first fastening region is configured to be fastened to its respective motor vehicle part even in an inflated state of the airbag.

5. The airbag as claimed in claim 1 , wherein the airbag is configured such that the intended detachment of the second, detachable fastening region from the inflatable portion as a result of the force exceeding the predetermined value takes place such that the airbag itself remains capable of supporting the knees of the vehicle occupant.

6. The airbag as claimed in claim 1 , wherein the second, detachable fastening region is configured to detach from the inflatable portion at lower forces than for detachment of the first fastening region.

7. The airbag as claimed in claim 1 , wherein the second, detachable fastening region comprises a projection on the inflatable portion.

8. The airbag as claimed in claim 7 , wherein the projection of the second, detachable fastening region comprises at least one lug-shaped projection.

9. The airbag as claimed in claim 1 , wherein the first and second fastening regions are formed on opposite ends of the airbag.

10. The airbag as claimed in claim 9 , wherein the first and second fastening regions are formed on opposite ends of the airbag in the vehicle longitudinal direction in an unfolded state of the airbag.

11. The airbag as claimed in claim 1 , wherein the first fastening region comprises a retaining plate, a housing, or a combination thereof.

12. The airbag as claimed in claim 11 , wherein the second, detachable fastening region comprises a retaining plate, a housing, or a combination thereof.

13. The airbag as claimed in claim 1 , wherein the first fastening region comprises a first gas inlet opening through which the inflatable portion can be inflated with gas originating from an inflating device.

14. The airbag as claimed in claim 13 , wherein the second, detachable fastening region comprises a second gas inlet opening arranged on the first gas inlet opening of the first fastening region in the installed state of the airbag such that the inflatable portion can be inflated with gas which flows in through both first and second gas inlet openings.

15. The airbag as claimed in claim 14 , wherein the airbag is folded such that, in the installed state, the first fastening region and the second, detachable fastening region are arranged congruently on one another.

16. The airbag as claimed in claim 1 , wherein the first fastening region and the second, detachable fastening region have same dimensions.

17. The airbag as claimed in claim 1 , wherein the airbag is folded along one fold such that the first and second fastening regions are formed on regions of the airbag which are separated from one another by the one fold.

18. The airbag as claimed in claim 17 , wherein the one fold substantially divides the airbag in half, wherein the first and second fastening regions are arranged substantially axially symmetrically on the airbag.

19. The airbag as claimed in claim 17 , wherein, in the installed state of the airbag, the one fold is formed substantially transversely with respect to the vehicle longitudinal direction.

20. The airbag as claimed in claim 17 , further comprising a gas inlet opening and an additional fold extending substantially parallel to the one fold wherein the additional fold is formed in a region that faces away from the gas inlet opening, wherein the region that faces away from the gas inlet is rolled up.

21. The airbag as claimed in claim 1 , wherein, in the installed state of the airbag, the second, detachable fastening region is arranged above the first fastening region.

22. The airbag as claimed in claim 1 , wherein the two side regions of the inflatable portion in the installed state are turned inward in the direction of the central point of the airbag along the two side folds which extend in the vehicle longitudinal direction.

23. The airbag as claimed in claim 1 , wherein the inflatable portion comprises a gas inlet opening and wherein the first connection extends substantially transversely with respect to the vehicle longitudinal direction and substantially between the two side folds such that gas flowing into the inflatable portion through the gas inlet opening is conducted into the turned-inward or folded-over side regions.

24. The airbag as claimed in claim 23 , wherein the inflatable portion comprises a gas inlet opening, and wherein the detachable connections are arranged at a side of the first connection which faces away from the gas inlet opening and extend substantially along the two side folds.

25. The airbag as claimed in claim 24 , wherein one of the detachable connections is reinforced.

26. A knee air bag module for a motor vehicle for supporting knees of a vehicle occupant in an event of a crash, comprising:

an airbag, wherein the air bag comprises:

an inflatable portion;

a first fastening region for fastening the airbag to a motor vehicle part;

at least one second, detachable fastening region for fastening the airbag to the same or different motor vehicle part; and

a given connection located between the second, detachable fastening region and the inflatable portion,

wherein the second, detachable fastening region and the first fastening region are formed at spaced-apart points on the airbag,

wherein the second, detachable fastening region is configured to detach from the inflatable portion if a force exceeding a predetermined value acts on the given connection between the second, detachable fastening region and the inflatable portion,

wherein the first fastening region and the second, detachable fastening region are formed from a fabric from which the inflatable portion is also formed,

wherein two side regions of the inflatable portion in an installed state of the airbag are turned inward or folded over in a direction of a central point of the airbag along two side folds which extend in a vehicle longitudinal direction,

wherein the inflatable portion comprises two airbag layers connected by a first connection which extends substantially transversely with respect to the vehicle longitudinal direction and substantially between the two side folds, and

wherein detachable connections extending substantially along the two side folds connect the two airbag layers.

27. The knee air bag module as claimed in claim 26 , further comprising a gas generator.

28. The knee air bag module as claimed in claim 27 , wherein the knee air bag module is configured to be arranged in an instrument panel of the motor vehicle.

29. A vehicle, comprising:

a knee air bag module for supporting knees of a vehicle occupant in an event of a crash comprising an airbag, wherein the airbag comprises:

an inflatable portion;

a first fastening region for fastening the airbag to a motor vehicle part;

at least one second, detachable fastening region for fastening the airbag to the same or different motor vehicle part; and

a given connection located between the second, detachable fastening region and the inflatable portion,

wherein the second, detachable fastening region and the first fastening region are formed at spaced-apart points on the airbag,

wherein the second, detachable fastening region is configured to detach from the inflatable portion if a force exceeding a predetermined value acts on the given connection between the second, detachable fastening region and the inflatable portion, and

wherein the first fastening region and the second, detachable fastening region are formed from a fabric from which the inflatable portion is also formed,

wherein two side regions of the inflatable portion in an installed state of the airbag are turned inward or folded over in a direction of a central point of the airbag along two side folds which extend in a vehicle longitudinal direction,

wherein the inflatable portion comprises two airbag layers connected by a first connection which extends substantially transversely with respect to the vehicle longitudinal direction and substantially between the two side folds, and

wherein detachable connections extending substantially along the two side folds connect the two airbag layers.

30. The airbag as claimed in claim 1 , wherein the first connection is a first connecting seam.

31. The airbag as claimed in claim 1 , wherein the detachable connections are detachable connecting seams.