Air bag
FIELD OF THE INVENTION 
     The present invention concerns an air bag for protecting an occupant in a driver&#39;s seat upon emergency such as collision of a vehicle. 
     More specifically, it relates to an air bag suitable to a case in which a steering wheel is disposed at a horizontal state as in a truck or a bus. 
     DESCRIPTION OF THE RELATED ART 
     In the air bag device of this type used generally, an air bag usually folded and attached so as to surround an inflator is covered with a cover member referred to as a module reciver which can be broken upon emergency. 
     When collision of a vehicle is detected by a sensor, the inflator is actuated to inflate the air bag by a gas generated from the inflator (inflation gas). 
     In a case of a vehicle such as a truck in which a steering wheel is disposed at a horizontal state, when the air bag is expanded upon collision of the vehicle, even if the air bag is interposed between an occupant and a steering wheel as shown in FIG. 2, the air bag 1 tends to deform in the direction escaping from the occupant 2 by the force applied from the occupant 2 to the air bag 1. Reference numeral 3 denotes a steering wheel. 
     OBJECT AND SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an air bag capable of reliably protecting a driver even when a steering wheel is situated substantially horizontally. 
     In accordance with the first aspect of the present invention, an air bag is disposed on the side od a steering wheel and has a first annular cloth member having an opening for an inflator or introduction of an inflation gas in the central portion and a second circular cloth disposed on the side of an occupant joined at the circumferential edge to the circumferential edge of the first cloth member, the diameter upon full expansion being greater than the diameter of the steering wheel, wherein a radial midway of the first cloth member and a radial midway of the second cloth are connected by means of a connection piece and, the length of the connection piece is such that a portion protruding more than the central portion of the second cloth is formed at the outer circumferential side of the connection portion of the second cloth when the air bag is fully inflated. 
     In accordance with the second aspect of the present invention, the connection portion between the connection piece and the first cloth member is located near a steering wheel portion, and the connection portion between the connection piece and the second cloth is located closer to the central side than the steering wheel. 
     In the third aspect of the present invention, the connection piece comprises a cloth having an aperture through which the inflation gas passes. 
     With the air bag according to the present invention, even when the steering wheel is disposed at a horizontal state, the air bag is expanded sufficiently at the outside of the steering wheel, and the air bag is prevented from moving to either of the side as shown in FIG. 1 to be described later. Accordingly, a largely expanded air bag is present between an occupant dashing to the air bag and the steering wheel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view illustrating an expanded state of an air bag according to a preferred embodiment of the present invention; 
     FIG. 2 is a side elevational view illustrating an expanded state of an air bag in the prior art; 
     FIG. 3 is a side elevational view illustrating an expanded state of an air bag according to a preferred embodiment of the present invention; 
     FIG. 4 is a cross sectional view in a non-expanded state of an air bag according to a preferred embodiment of the present invention; 
     FIG. 5 is an exploded perspective view of the air bag; 
     FIG. 6 is a cross sectional view of an air bag device; 
     FIG. 7 is an exploded perspective view of the air bag device. 
    
    
     PREFERRED EMBODIMENTS 
     Description will now be made more specifically for the preferred embodiment according to the present invention with reference to the accompanying drawings. 
     FIG. 6 is a side elevational view of an air bag device having an air bag of a preferred embodiment according to the present invention and FIG. 7 is a exploded perspective view of the air bag device. 
     In Figs, 6 and 7, there are shown a steering wheel 11 and spokes 13 of the steering wheel, a retainer plate 12 mounted at the base of the spokes 13 opposing to an upper half body of an occupant and an inflator 14 inserted from the rear face into a hole 15 perforated at the center of the retainer plate 12. Reference numeral 16 denotes an air bag. The air bag 16 is attached to an occupant-opposing retaining face 17 of the retainer plate 12. More specifically, the air bag 16 is secured to the retainer plate 12 by inserting rivets 24 through apertures 21 of the retainer plate 12, and apertures 23 perforated in the circumferential flange 22 of the inflator 14 and clamping the rivets 24. 
     The air bag 16 is folded so as to surround gas injection apertures 26 of the inflator 14. The air bag 16 is covered by a module cover 25. 
     An easily breakable recessed groove 30 extending in an H-shaped, radial or any other shape is formed to the inner wall surface of an occupant-opposing portion of the module cover 25, and a thin-walled portion formed by the recessed groove 30 is broken upon inflation of the air bag 16 to develop the entire module cover 25 outward in a petal-like shape. 
     An erected portion 31 is disposed to the retainer plate 12 be bent substantially at a right angle and in the direction parting from the occupant (hereinafter sometimes referred to as rearward). The base end 32 of the module cover 25 is appended on the side of the erected portion 31. More specifically, the module cover 25 is secured to the retainer plate 12 by passing the rivets 35 through the apertures 34 of the erected portion 31 and fastening the rivets 35. 
     In the drawing, a bracket 36 is extended further backward from the erected portion 31 of the retainer plate 12, and it is secured to the steering wheel by bolts (not illustrated) inserted through the apertures 37 of the bracket 36. An under cover 38 is attached so as to cover the gap formed on the side of the base end of the module cover 25. 
     As shown also in FIGS. 3 to 5, the air bag 16 mainly comprises a first cloth member 41 on the side of the steering wheel and a second cloth 42 on the side of the occupant. The second cloth 42 has a circular shape. 
     As clearly shown in FIG. 5, the first cloth member 41 comprises two annular support cloths 44 each of a small diameter, a circular cloth 46 having openings 45 and a patch cloth 47. The openings 45 are gas passing holes for introducing the inflation gas to the outer peripheral region in the air bag 16. The patch cloth 47 is for the reinforcement of the edge of the opening 43. The opening 43 and rivets holes 18 are formed to the patch cloth 47 and the two support cloths 44. The patch cloth 47 and the two support cloths 44 are stitched at the stitch portions 47A, 47B along the inner circumferential edge and the outer circumferential edge of the patch cloth 47. 
     The openings 45 in the circular cloth 46 are four in this embodiment and they are arranged at positions equally divided by four in the circumferential direction with respect to the center for the circular cloth 46. The outer circumferential edges of the two support cloths 44 are stitched with the circular cloth 46 along the stitch 46A that turns around the outer circumference of the four openings 45. The outer circumferential edge of the circular cloth 46 is stitched with the outer circumferential, edge of the second cloth 42 at the stitch 42A. The outer circumferential edges of the cloths 42 46 are stitched in a state to be located inside the airbag. 
     The circular cloth 46 is stitched with the second sloth 42, at a stitch 46B along the inner circumference of the four openings 45. 
     In the circular cloth 46, a portion between the stitches 46A and 46B functions as a connection piece 50. 
     In the air bag device having thus been constituted, when a vehicle collides, the inflator 14 is actuated to generate a gas. Thus, the air bag 16 starts expansion, and the module cover 25 tears along the recessed groove 30 and expands. Then, the air bag 16 inflates as shown in FIGS. 1 and 3. 
     In this state, an outer portion 51 of the connection piece 50 protrudes greater than the central side 52 of the air bag (region inward of the stitch 46B) to the side of the occupant 2. Further, the outer portion 51 covers the steering wheel 11 from the outer side of the steering wheel 11. In addition, the connection piece 50 inhibits the air bag 16 from escaping from a portion between the occupant 2 and the steering wheel 11. As a result, even when the occupant 2 is dashed to the air bag 16 as shown in FIG. 1, a sufficient amount of the air bag 16 is interposed also at a portion 60 between the occupant and the steering wheel 11 to sufficiently absorb impact shocks exerting on the occupant. 
     In the above-mentioned embodiment, although the connection piece 50 is constituted with a portion of the circular cloth 46 that constitutes a portion of the first cloth 41 member, it may be constituted with a cloth separated from the first cloth member 41. 
     Further, although the connection piece 50 is made of cloth in the above embodiment, it may be constituted with a belt or string. In a case of using the connection piece 50 made of cloth, the first cloth member and the second cloth can be connected uniformly in the circumferential direction of the air bag. Further, as compared with a belt or string, there is no localization of stresses. 
     As has been described above in the air bag according to the present invention, even in a vehicle such as a truck in which the steering wheel is disposed at to a horizontal state, an air bag can expand greatly between the steering wheel and the occupant, is interposed upon expansion of the air bag and the occupant can be protected sufficiently. 
     The air bag according to the present invention is free from local stress concentration.