Airbag and airbag apparatus

1. An airbag, including a vent hole and a restriction mechanism for restricting outflow of gas through the vent hole, wherein

the vent hole is formed in a surface opposite to an occupant facing surface of the airbag in the inflated state or in a side surface of the airbag in the inflated state, wherein

the restriction mechanism comprises:

a lid member which is disposed inside the airbag to cover the vent hole; and

a tethering member which extends inside the airbag to connect the lid member and said occupant facing surface, wherein

when the airbag is inflated, the lid member is prevented from moving to outside of the airbag and is overlaid on said vent hole by the tethering member so that the vent hole is closed or slightly opened, and

as an occupant collides with the inflated airbag to depress said occupant facing surface, the lid member is pushed out of the airbag through the vent hole by the inner gas pressure of the airbag so as to open or widely open the vent hole.

2. An airbag as claimed in claim 1 , further including an insertion loop through which said tethering member is inserted and which is formed on an inner surface of said surface opposite to the occupant facing surface or on an inner surface of said side surface, wherein

said tethering member has one end portion which is connected to said occupant facing surface, a midway portion which is inserted through the insertion loop, and the other end portion which continues to a first end of said lid member, and wherein

a second end of the lid member on the side opposite to the tethering member relative to the vent hole is connected to a portion in the vicinity of the vent hole of the airbag.

3. An airbag as claimed in claim 2 , further including a first window formed in said lid member, and

a cover panel which is overlaid on the lid member to cover the first window, wherein

one end of said cover panel is connected to a portion of the lid member on the tethering member side relative to the first window, and the other end of said cover panel is connected to a portion of the lid member on the side opposite to the tethering member side relative to the first window, wherein

a second window is formed in the cover panel at a position not corresponding to the first window, wherein

when the airbag is inflated, the lid member is pulled by the tethering member and is thus tensioned and, according to the tension of the lid member, the cover panel is also tensioned to be overlaid on the lid member so that the first window and the second window are both closed, and wherein

when the occupant collides with the inflated airbag to depress said occupant facing surface, the tension of the lid member is canceled so that the lid member is pushed out of the airbag through the vent hole by the inner gas pressure of the airbag, and the tension of the cover panel is also cancelled so that the cover panel is spaced apart form the lid member so as to open the first window and the second window.

4. An airbag as claimed in claim 3 , wherein said first window and said second window are slits extending in the longitudinal direction of said tethering member.

5. An airbag as claimed in claim 2 , further including a sub vent hole which is formed in said surface opposite to the occupant facing surface or said side surface at a position between the vent hole and said insertion loop, for allowing the communication between the inside and the outside of the airbag, wherein

said lid member is arranged to cover both the vent hole and the sub vent hole continuously, and wherein

a release hole is formed in a portion of said lid member between an area thereof facing the sub vent hole and said tethering member or in a midway portion in the longitudinal direction of said tethering member, and is positioned to correspond to the sub vent hole so as to open the sub vent hole when said lid member is pushed out through the vent hole.

6. An airbag as claimed in claim 5 , wherein a plurality of the sub vent holes are formed at positions shifted in a direction from said insertion loop to said vent hole, and wherein

said release hole is an elongated hole extending in the longitudinal direction of the tethering member.

7. An airbag as claimed in claim 2 , wherein at least two said vent holes are formed in said surface opposite to the occupant facing surface or said side surfaces, wherein

said lid members are provided to cover the vent holes, respectively, and said first ends of said lid members are connected to said occupant facing surface via tethering members, wherein

midway portions in the longitudinal direction of the tethering members are detachably connected to each other by a connecting mechanism, and wherein

said connecting mechanism cancels the connection between said tethering members when the inner pressure of the airbag reaches a predetermined value or more.

8. An airbag as claimed in claim 1 , further including an inner member which is arranged inside the airbag to connect the occupant facing surface and the surface opposite to the occupant facing surface of the airbag in the inflated state, wherein

said tethering member is connected to said inner member.

9. An airbag as claimed in claim 8 , wherein said inner member is an inner panel for partitioning the inside of the airbag into a first chamber centrally located and a second chamber surrounding the first chamber, wherein

said inner panel is provided with a communication hole formed therein for allowing communication between the first chamber and the second chamber, wherein

said airbag is structured such that gas is first introduced into the first chamber so as to inflate the first chamber and the gas is then introduced from the first chamber to the second chamber through the communication hole so as to inflate the second chamber, and wherein

said vent hole is arranged to allow communication between the second chamber and the outside of the airbag.

10. An airbag as claimed in claim 8 , wherein said inner member is a restriction strap of which one end is connected to the occupant facing surface of the airbag and the other end is connected to the surface opposite to the occupant facing surface.

11. An airbag as claimed in claim 1 , further including an inner member which is arranged to extend across the inside of the airbag to connect side portions of the airbag in the inflated state, wherein

said tethering member is connected to said inner member.

12. An airbag as claimed in claim 8 , wherein said tethering member and said inner member are integrally formed.

13. An airbag as claimed in claim 1 , wherein a first end of said tethering member is connected to said lid member and a second end of said tethering member is connected to said occupant facing surface.

14. An airbag as claimed in claim 13 , further including a gas inlet for introducing gas from a gas generator or a gas generator receiving portion where the gas generator is received and which is formed in the surface opposite to said occupant facing surface of the airbag, wherein

the second end of the tethering member is connected to a portion confronting to the gas inlet or the gas generator receiving portion of said occupant facing surface.

15. An airbag as claimed in claim 1 , wherein said tethering member and said lid member are integrally formed.

16. An airbag as claimed in claim 1 , further including a deflection loop through which said tethering member is inserted and which is provided on the inner surface of said occupant facing surface, wherein one end of said tethering member is connected to said lid member and a midway portion in the longitudinal direction of said tethering member is inserted into said deflection loop.

17. An airbag as claimed in claim 16 , further comprising a plurality of deflection loops, the deflection loops are a plurality of occupant-side deflection loops that are disposed on said occupant facing surface at different positions and a plurality of opposite-occupant-side deflection loops that are disposed on the surface opposite to said occupant facing surface, and wherein

the midway portion of said tethering member is inserted through the occupant-side deflection loops and the opposite-occupant-side deflection loops alternately.

18. An airbag as claimed in claim 1 , further including a pulling member which is arranged inside the airbag for pulling a midway portion in the longitudinal direction of said tethering member to the side opposite to the occupant facing surface, wherein

said pulling member is connected at its proximal end to the inner surface of the airbag at the side opposite to the occupant facing surface and is provided at its distal end with a guide loop through which the tethering member is inserted, and wherein

a midway portion in the longitudinal direction of said tethering member is inserted through the guide loop.

19. An airbag as claimed in claim 1 , wherein said lid member does not protrude outside the airbag through the vent hole and is overlaid on the vent hole from the inside of the airbag at the start of inflation of the airbag.

20. An airbag as claimed in claim 19 , the airbag is in the folded state before the inflation, and the airbag is folded keeping the state that the lid member does not protrude outside the airbag through the vent hole and is overlaid on the vent hole from the inside of the airbag.

21. An airbag as claimed in claim 1 , further including an open type vent hole which always allows communication between the inside and the outside of the airbag.

22. An airbag apparatus comprising:

an airbag as claimed in claim 1 ;

a gas generator for supplying gas into the airbag;

a retainer to which the airbag is mounted; and

a fixing member for fixing the airbag to the retainer.

23. An airbag apparatus as claimed in claim 22 , wherein said fixing member is arranged inside the airbag, wherein

said fixing member is provided with an insertion loop through which said tethering member is inserted, wherein

said tethering member has a first end portion which is connected to said occupant facing surface of the airbag, a midway portion which is inserted through the insertion loop, and a second end portion which continues to a first end of said lid member, and wherein

a second end of the lid member on the side opposite to the tethering member relative to the vent hole is connected to a portion near the vent hole of the airbag.