Abstract:
The invention relates to an airbag, especially a lateral airbag, preferably in the shape of a tube, which is connected to at least two points on the motor vehicle and accommodated in its non-inflated state in a curved storage area. The invention provides for at least one tensioning cord ( 3 ) between the gas bag and a point of attachment to the motor vehicle, whereby said tensioning cord ( 3 ) can be tautened by the inflating gas bag. A preferred version provides for the tensioning cord ( 3 ) to be attached with one end to the gas bag ( 8 ) and with the other end to the motor vehicle (F 1 ), whereby, when the gas bag inflates, the cord&#39;s point of attachment on the gas bag, together with the gas bag, is able to move away from the point (F 1 ) where the tensioning cord ( 3 ) is attache to the motor vehicle. In this way the gas bag can be tautened without the need for additional mechanical or electrical components.

Description:
BACKGROUND OF THE INVENTION 
     Lateral airbags are known to protect the occupant of a vehicle in the event of lateral impact. Lateral airbags are provided for example in doors or in the side trims of the vehicle. These lateral airbags spread out and upwards in the event of a crash so that parts of the body lying level with the window are also protected. 
     The lateral airbags arranged in this way, however, are not suitable to protect the head of the occupant. Therefore airbags are known which are integrated in the vehicle seat. Thus a head restraint with integrated gas bag is known from DE 94 15 511.9 U1. This gas bag extends in the inflated state sideways from the head area and in the forward travel direction. The drawback with an airbag of this kind provided in the seat is that the sensor required for detonation of the gas generator has to be connected to the energy supply of the vehicle through a cable. Since vehicle seats are however in most cases movable and even removable these cables become in the way. 
     Therefore lateral airbags are also known which are mounted level with the head at the side in the vehicle. Here the gas bag extends between the A- and B-pillar or the B- and C-pillar of the vehicle. In the inflated state the gas bag covers the area of a side window. In the folded state the gas bag is stowed away above the window frame, i.e., it extends along a curve. In this curved position therefore the distance between the fastening points is greater than in the case where the gas bag runs straight in the inflated state. From this there is the need to tauten the gas bag or fastening sections of the gas bag in its inflated position. 
     To this end it is known from DE 195 19 297 to provide the gas bag on the A-pillar with a cable which runs over a tautening device. This has a guide pulley where the cable is deflected round 180°. The guide pulley is displaceable by means of a further mechanical device which is electronically controlled whereby the deflected part of the cable is extended and thus a tautening effect is achieved. This tautening device is operated during the inflation process. The drawback here is that a tautening device of this kind means extra mechanical and electronic expense. 
     Furthermore a lateral airbag is known from WO 94/19215 for protecting the head wherein this airbag likewise extends between two pillars of the vehicle, e.g., between the A and B pillars. The gas bag is tubular and consists of two crisscrossing threads with an elastic material extending inbetween. When the gas bag is not inflated but is stowed in this state above a vehicle window the threads lie practically parallel to each other. After inflation the threads rotate into the main unfolding direction of the gas bag. The diameter of the gas bag thereby increases whilst the length reduces. Thus a tautening effect likewise occurs without special additional mechanical or electronic aids. The drawback here, however, is that the gas bag has to be made from the said special material. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to achieve a tautening action in an airbag, more particularly a lateral airbag, without additional mechanical devices and the electronics associated therewith and without having to use special material for the gas bag. 
     The present invention relates to an airbag, more particularly a lateral airbag with a tubular shape, which is connected to at least two points of the motor vehicle and in the non-inflated state is stored in a curved storage area. According to the invention at least one tensioning cord for shortening the unfolded gas bag is provided between the gas bag and a fastening point on the vehicle whereby the tensioning cord can be tautened through the inflating gas bag. 
     More particularly at least one tensioning cord is provided which is fixed at one end on the gas bag and at the other end on the vehicle whereby the fixing point on the gas bag can be moved together with the gas bag away from the cord&#39;s fixing point on the vehicle as the gas bag inflates. 
     Furthermore the invention can be designed so that the tensioning cord is fixed at one end to the gas bag and at the other end to the vehicle and that the tensioning cord has at least one guide point on the gas bag which during inflation of the gas bag can be moved away from the point of attachment of the tensioning cord on the gas bag. 
     With the airbag according to the invention, the movement of part of the gas bag and in particular a movement away from the point of attachment of the tensioning cord on the vehicle or on the gas bag during inflation of the gas bag is thus utilised to tauten the tensioning cord and thus the gas bag as it unfolds. The length of the tensioning cord can remain unchanged or can be shortened as the gas bag unfolds. The advantage of using the movement of the gas bag to tauten the cord is that no additional mechanical devices and associated electronics are required and that the gas bag can be made from conventional materials. 
     In a first embodiment, it is proposed that the gas bag is bottle-shaped and has inside a tensioning cord which is shorter than the gas bag and is connected at one end in the area of the bottle neck to the gas bag and at the other end in the non-inflated state of the gas bag to the inverted end of same which corresponds to the bottle base wherein the end of the tensioning cord is connected to the vehicle in the area of the bottle neck and the gas bag is connected to the vehicle in the area of its inflation mouth which is set at a distance from the bottle base. 
     With this embodiment, the distance between the fastening points of the gas bag at the inflation mouth and at the end of the bottle neck during inflation of the gas bag is reduced to the debit of the distance between the inflation mouth and the bottle base in that this distance is increased by the stretching of the gas bag while the bottle neck is simultaneously folded and thereby shortened. 
     The tensioning cord can both end at the bottle-shaped end of the gas bag and also extend beyond the gas bag and only there be connected to the vehicle. 
     In a second embodiment, at least one connecting cord or at least one contraction cord is provided which runs at least approximately in the main unfolding direction of the gas bag and is fixed on opposite parts of the gas bag, and the tensioning cord is fixed roughly in the middle of the connecting cord/contraction cord. The point of attachment of the tensioning cord on the connecting cord moves away from the fixing point of the tensioning cord on the gas bag as the gas bag inflates. The displacement path of the point of attachment thereby corresponds to the slack in the tensioning cord which is to be compensated. 
     It is expedient if the connecting cord is provided approximately in the center of the gas bag and is designed as a closed ring. 
     In a first design of this embodiment, the connecting cord runs inside the gas bag and the tensioning cord extends out from the gas bag and is connected to the gas bag at the point where it emerges from the same. 
     In a second design, the connecting and tensioning cords are provided outside of the gas bag and the tensioning cord is guided at the end of the gas bag between this and a shackle. With this design, the tensioning cord is thus not connected to the end of the gas bag but is guided round the same through the shackle. 
     In a further embodiment, it is proposed that the tensioning cords are formed at their fastening points with the gas bag as guide shackles for each other tensioning cord. 
     When using a contraction cord which acts similar to the connecting cord, the tensioning cord is connected to opposite ends of the gas bag. The contraction cord is attached to predefined points of the gas bag so that it gathers together individual sections of the gas bag during unfolding and in this way compensates for the slack in the tensioning cord. 
     In a third embodiment, the tensioning cord is guided at one end of the gas bag in a shackle and in its non-inflated state is connected to the other end of the gas bag which is folded towards the shackle. As the gas bag unfolds, the folded end of the gas bag moves away from the shackle and away from the fastening point of the tensioning cord on the vehicle and thereby transfers this movement to the tensioning cord. 
     In a further design of this embodiment, it is proposed that each tensioning cord has at least one return lock which prevents the tensioning cord from moving back against the unfolding direction of the gas bag but allows the tensioning cord to move in the unfolding direction of the gas bag and/or that at least one additional support shackle is provided for guiding the tensioning cord in the middle area of the gas bag which is likely to bend. 
     Providing a return lock or an additional tensioning cord support shackle prevents the tubular gas bag from bending in through the strain of the occupant once it has unfolded. The protection of the occupant would be impaired if the gas bag were to bend inwards. 
     In a preferred embodiment, the return lock is formed as a guide shackle and is fixed on the gas bag in place of a guide shackle. 
     Where two tensioning cords are provided, each tensioning cord has a return lock. 
     Where two tensioning cords are provided criss-crossing each other, it is expedient to provide one double return lock at the cross-over point. 
     In a preferred embodiment, the return lock has two relatively movable wedges wherein the tensioning cord runs between opposite wedge faces and these can be pressed against each other by at least one elastically deformable fastening means. During unfolding of the gas bag, the tensioning cords press the wedge faces away from each other against the force of the elastically deformable fastening means, and the tensioning cord is drawn along with the end of the gas bag to which it is fixed, and tautens the unfolded gas bag. As the gas escapes from the gas bag at the end of the unfolding process, the wedge faces are pressed against each other under the action of the elastically deformable fastening means. The tensioning cord is thereby fixed at this point. The tensioning cord thereby remains tensioned between its fastening point on the motor vehicle and the wedge faces even if the gas bag collapses as a result of the escaping gas. This substantially prevents the gas bag from bending inwards. 
     It is expedient if one wedge is arranged fixed while the other wedge is displaceable relative to the fixed wedge and has the elastically deformable fastening means. As elastically deformable fastening means, a draw spring can be provided whose active direction runs substantially opposite the traction direction of the tensioning cord during unfolding of the gas bag. 
     To increase the clamping action of the wedge faces, it is expedient if the opposing wedge faces have grooves which run at least approximately cross-wise to the direction of movement of the tensioning cord. 
     In a further design, it is proposed that at least one additional support shackle is provided between the guide shackles or return locks provided at the ends of the gas bag. Where return locks are used, this support shackle represents an additional means for preventing the gas bag from bending in. In the event that guide shackles are used in place of return locks, the support shackle is the sole means for preventing the gas bag from bending in. 
     In one embodiment, the tensioning cord is guided on the gas bag and in the non-inflated state is connected to the other end of the gas bag which has been folded towards the fastening point on the vehicle. 
     In a fourth embodiment, the tensioning cord is connected to the gas bag at the site where the gas bag changes shape the most during inflation and is guided from there towards the end of the gas bag in at least one shackle. It is expedient if the site of the greatest change of shape is formed by a peak-like irregularity in the contour of the gas bag which can be provided as an indent or bulge in the gas bag. In the folded state, the shackles, as well as the fastening point of the tensioning cord on the vehicle, are mounted substantially along a straight line. During unfolding, the tensioning cord is drawn along as a result of the irregular airbag contour through the shackles in the direction of the fastening point of the tensioning cord on the gas bag and the slack in the tensioning cord is thereby compensated. 
     In a fifth embodiment, the gas bag is fixed in the area of its inflation mouth on the vehicle and extends to each side of the inflation mouth. The tensioning cord is fixed at one end inside the gas bag and with its other end runs out of the gas bag where it is connected to the vehicle outside of the gas bag. For assembly, the gas bag is gathered up in the area next to the inflation mouth which is remote from the fastening point of the tensioning cord on the vehicle. During unfolding of the gas bag, the gathered gas bag material expands and thereby draws in a corresponding piece of the tensioning cord. The tensioning cord can in this embodiment be guided to the outside from the gas bag through an outlet opening, valve opening or through the fabric of the gas bag. 
     In a sixth embodiment, a gas bag which during folding has been wound up through rotation about the unfolding axis is connected to the tensioning cord on the outside by at least one section which is opposite the fastening point of the tensioning cord on the vehicle. During unfolding the gas bag spreads out in the direction of the useful position and thus in the direction of the fastening point of the tensioning cord on the vehicle. At the same time the gas bag turns back into its original alignment and the slack of the tensioning cord winds up over the circumference of the gas bag. 
     In one embodiment two tensioning cords are provided of which each one is connected to the vehicle in the area of one end of two opposite ends of the gas bag. 
     The tensioning cords can be substantially non-deformable, but can however also be made from elastically deformable material. 
     The invention will now be explained with reference to the embodiments shown in the drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 a-c  show the principal construction of a bottle-shaped bag; 
     FIGS. 2 a, b  show the gas bag according to FIGS. 1 a-c  in the folded and unfolded positions; 
     FIG. 3 shows a variation of the gas bag according to FIGS. 1 a-c;    
     FIGS. 4 a-c  show the gas bag according to FIG. 3 fitted in a vehicle in the folded and unfolded positions; 
     FIG. 4 d  shows a variation of the gas bag with the inflation mouth at the narrow end of the gas bag; 
     FIGS. 5 a-c  show an embodiment with two connecting cords mounted in the gas bag in the folded and unfolded positions; 
     FIGS. 6 a, b  show an embodiment with a connecting cord mounted outside of the gas bag in the folded and unfolded positions; 
     FIGS. 7 a, b  show side views of an embodiment with criss-crossing contraction cords in the folded and unfolded positions; 
     FIG. 7 c  shows a plan view of the embodiment of FIGS. 7 a ,  7   b;    
     FIGS. 8 a, b  show an embodiment wherein a tensioning cord connected at one end to the gas bag forms a guide shackle; 
     FIG. 8 c  shows a section through FIG. 8 a  in the direction of the arrow VIII—VIII on an enlarged scale; 
     FIGS. 9 a, b  show an embodiment wherein each tensioning cord is guided loose at one end of the gas bag and is fixed at its other end, in the folded and unfolded positions; 
     FIGS. 10 a, b  show an embodiment with an inwardly bulging gas bag; 
     FIGS. 11 a, b  show an embodiment with a specially guided tensioning cord; 
     FIGS. 12 a-c  show an embodiment with a gas bag fixed at its inflation mouth on the vehicle, and a tensioning cord which is fixed at one end on the vehicle and at the other end in the gas bag at its end on the other side of the inflation mouth; 
     FIG. 12 d  shows an embodiment with a gas bag fixed at its inflation mouth on the vehicle, and a tensioning cord fixed outside on the gas bag; 
     FIGS. 13 a, b  show diagrammatically a gas bag folded by inward rotation and with tensioning cords; 
     FIGS. 14 a ,  14   b  show the gas bag according to FIGS. 13 a, b  after partial unfolding; 
     FIGS. 14 c, d  show the gas bag according to FIGS. 13 a, b  in the unfolded state; 
     FIGS. 15 a-c  show diagrammatically a gas bag installed in the vehicle according to the active principle of FIGS. 13 and 14 in various unfolding positions; 
     FIG. 16 shows a gas bag in the inflated state which has a return lock at opposite ends for each tensioning cord; 
     FIG. 17 shows a section on an enlarged scale through a return lock according to the detail E 1  of FIG. 16; 
     FIG. 18 shows a gas bag in the inflated state which has a double return lock; 
     FIG. 19 shows an enlarged sectional view through the double return lock according to the detail E 2  of FIG. 18; and 
     FIG. 20 shows a gas bag in the inflated state with two guide and one support shackles. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The gas bag illustrated in FIGS. 1 a  to  1   c  has a bottle shape and is comprised of an upper plate  1  and a lower plate  2  between which is provided a tensioning cord  3  which has a shorter length than the gas bag. In the lower plate  2  is an inflation mouth  4  to which an inflation device (not shown) can be attached. The upper and lower plates  1 ,  2  are connected together by a seam  5 . The tensioning cord  3  is connected at one end by a seam  7  to the end of the bottle neck  6 . The bottle base  8  is then inverted until the outer edge of the gas bag can be stitched to the second end of the tensioning cord. The upper and lower plates are thereby also stitched by a seam  9  to this side of the gas bag. 
     The gas bag is connected by its inflation mouth area  4  to the vehicle and the tensioning cord  3  is connected to the gas bag at the end of the bottle neck  6 . The distance a exists between the two. The gas bag has the length b to the right of the inflation mouth  4  in the unstitched state. The tensioning cord  3  ends at a distance c from the unstitched right end of the gas bag. After inverting and stitching the bottle base  8  its distance from the inflation mouth  4  is reduced by the distance c (FIG. 2 a ). 
     When the gas bag inflates it cannot expand completely since the tensioning cord inside the gas bag restricts the expansion of the gas bag. As a result of the larger cross-sectional surface of the wide gas bag part opposite the bottle neck  6  and the greater force arising therefrom in the wider gas bag part, as the internal pressure rises, so the wider gas bag part is extended up to reaching the distance b (FIG. 2 b ) to the debit of the distance a which is reduced by the value c. 
     The same effect is achieved if the tensioning cord is extended beyond the bottle neck as shown in FIG.  3 . This embodiment is shown in the installed position in FIGS. 4 a  to  4   c . The end of the tensioning cord projecting out of the gas bag is connected to the A-pillar  10  of the vehicle at its fastening point F 1 . On the other side, the gas bag is connected by a fastening point F 2  to the vehicle by its inflation mouth  4  in the area of the B-pillar  11 . As can be seen in FIG. 4 a  the gas bag is stowed in the folded state above the window  12  along the roof bar. Owing to the curved storage area, the gas bag extends with the tensioning cord over a greater length than the straight connecting line between the fastening points F 1  and F 2 . This embodiment is shown in the installed position in FIGS. 4 a  to  4   c  The end of the tensioning cord projecting out of the gas bag is connected to the A-pillar  10  of the vehicle at its fastening point F 1 . On the other side, the gas bag is connected by a fastening point F 2  to the vehicle by its inflation mouth  4  in the area of the B-pillar  11 . As can be seen in FIG.,  4   a  the gas bag is stowed in the folded state above the window  12  along the roof bar. Owing to the curved storage area, the gas bag extends with the tensioning cord over a greater length than the straight connecting line between the fastening points F 1  and F 2 . 
     When propellant gas flows into the folded gas bag after the cover (not shown) has been ripped open, the gas bag is unfolded into the inside of the vehicle as shown in FIG. 4 b . The gas bag thereby first extends more loosely between the fastening points F 1  and F 2  and the tensioning cord  3  likewise loosely in the gas bag as can be seen from FIG. 4 b . As the pressure in the gas bag increases, a greater force engages on an engagement point A 2  than on an engagement point A 1  at the bottle neck so that A 2  moves away outwards from the fastening point F 2  at the inflation mouth  4  and the movement is transferred through the tensioning cord  3  to A 2 . The bottle neck  6  is gathered as a result of the adjusting force equilibrium and the shortening resulting therefrom (FIG. 4 c ) so that the gas bag is tensioned taut between the fastening points F 1  and F 2 . Through the displacement of the engagement point A 2  to the right, the tensioning cord between the fastening points F 1  and F 2  is quasi shortened. 
     A further variation is shown in FIG. 4 d  in the inflated state. With this variation the inflation mouth  4  is located at the narrow gas bag end. The gas bag is connected to the A-pillar  10  at fastening point F 1  and to the B-column  11  at the fastening point F 2 . The tautening strip  3  is connected to the gas bag on one side at the engagement point A 1  in the bottle neck  6  and on the other side at the engagement point A 2 . The method of action corresponds to the embodiment of FIGS. 4 a  to  4   c.    
     With the embodiment of FIGS. 5 a  to  5   c  two connecting cords  13 ,  14  are provided inside the gas bag  19  and are fixed on parts  15 ,  16  and  17 ,  18  of the gas bag  19  which are opposite one another in the main unfolding direction. Tensioning cords  22 ,  23  are fixed in the middle between the fastening points on the gas bag to the connecting cords at the fastening points  20 ,  21 . These tensioning cords extend through two opposite ends of the gas bag which are closest to the fastening points  24 ,  25  of the tensioning cords on the vehicle side. These ends are formed as imprinted projections  26 ,  27  of the gas bag and the tensioning cords are connected, e.g. stitched, there to the gas bag. Therefore the length of the tensioning cords remains constant between the points  24  and  26  or  25  and  27  on one side and between the points  20  and  26  or  21  and  27  during unfolding of the gas bag. 
     FIG. 5 a  shows the gas bag first in the folded state above the window  12  wherein the fastening point  24  is on the A pillar  10  and the fastening point  25  is on the B pillar  11  of the vehicle. In this position the connecting cords  13 ,  14  extend in the direction of the fastening points  24 ,  25 . 
     During inflation of the gas bag, the connecting cords  13 ,  14  are stretched in the main unfolding direction whereby the fastening points  20 ,  21  of the tensioning cords  22 ,  23  are moved away from the fastening points  24 ,  25 . The projections  26 ,  27  of the gas bag are thereby stretched at first (FIG. 5 b ) and with full unfolding of the gas bag are inverted into the gas bag (FIG. 5 c ). Where the gas bag is designed without projections, the gas bag would be inverted to a greater extent. Through the depicted displacement of the fastening points  20 ,  21 , the gas bag is tautened in the unfolded position by means of the tensioning cords. 
     With the embodiment of FIGS. 6 a  and  6   b , a closed ring  28  is provided as a connecting cord outside of the gas bag and around the same. A ring of this kind could also be provided inside the gas bag as a connecting cord. This ring is connected to the gas bag  31  at fastening points  29 ,  30 . Tensioning cords  32 ,  33  are fixed offset 90° to the ring  28  on opposite points  34 ,  35 . The tensioning cords are guided on opposite ends of the gas bag in shackles  36 ,  37  and are connected to the vehicle at fastening points  38 ,  39 . 
     As can be seen from FIG. 6 a  the fastening points  34 ,  35  in the folded state of the gas bag face towards the fastening points  38 ,  39 . During inflation the fastening points  34 ,  35  of the tensioning cords are moved away from their fastening points  38 ,  39  on the vehicle whereby the gas bag is tautened in the inflated state. 
     FIGS. 7 a  and  7   b  show an embodiment with criss-crossing contraction cords  40 ,  41  which are connected to the gas bag  42  to fastening points  43 ,  44 ,  45 ,  46  inside same. The contraction cords gather up individual sections  47 ,  48  of the gas bag as it unfolds whereby the slack of the tensioning cords which are fixed on the vehicle at fastening pints  38 ,  39  is compensated. 
     The plan view of FIG. 7 b  shown in FIG. 7 c  shows the section of the contraction cords  40 ,  41  running on the upper side of the gas bag  42  as well as the section of the contraction cords  49 ,  50  which runs on the upper side. The latter cannot be seen from the side views of FIGS. 7 a  and  7   b  since only one side of the gas bag is shown there. 
     In the embodiment of FIGS. 8 a  to  8   c , two tensioning cords  51 ,  52  are provided outside of the gas bag  53 . These are fixed at one end on the vehicle and at the other end on the gas bag in the form of shackles  54 ,  55 . One tensioning cord runs in each shackle of the other tensioning cord, i.e., the tensioning cord  52  runs in the shackle of the tensioning cord  51  and vice versa. In FIG. 8 a , the gas bag  53  is shown in the folded position. During unfolding of the gas bag as a result of the gas emerging from the gas generator  53   a , the tensioning cords  51 ,  52  are drawn along and deflected through the shackles  54 ,  55  until in the inflated state of the gas bag the position of the tensioning cords is reached as shown in FIG. 8 b . The path of the tensioning cord  52  in the shackle  54  can be seen from the sectional view of FIG. 8 c.    
     Also, with the embodiment of FIGS. 9 a  and  9   b , two tensioning cords  56 ,  57  are provided outside of the gas bag  60  and are guided through shackles  58 ,  59  at one end of the gas bag to opposite ends  61 ,  62  of the gas bag. The ends  61 ,  62  are, in the folded state of the gas bag, folded in the direction of the fastening point of the relevant tensioning cord on the vehicle, as can be seen from FIG. 9 a . During unfolding of the gas bag, the ends  61 ,  62  are removed from the fastening point of the relevant tensioning cord. The movement of the gas bag during unfolding is transferred to the tensioning cords which are deflected round by means of the relevant shackles  58 ,  59  to the fastening points  38 ,  39  on the vehicle side. 
     In the embodiment of FIGS. 10 a  and  10   b , a gas bag  63  is provided which bulges inwards on one side in the unfolded state. With this embodiment, a tensioning cord  64  is provided which is connected to the gas bag at the most heavily curved area  65 . On either side of this connecting point, the tensioning cord is guided in the shackles  66  to  69  up to the fastening points  38 ,  39  on the vehicle. In the folded state, as shown in FIG. 10 a , the shackles as well as the area  65  of the gas bag, lie substantially in a straight line. During unfolding the tensioning cord is drawn as a result of the inward curvature of the gas bag through the shackles in the direction of the area  65  and thereby compensates the slack in the tensioning cord. 
     With the embodiment of FIGS. 11 a  and  11   b , the active mechanism is similar to that in the embodiment of FIGS. 10 a  and  10   b . A gas bag  70  is provided which is connected to the vehicle at its area of maximum shape change during inflation. A tensioning cord  72  is also fixed there outside on the gas bag and is guided at inclined opposite points of the gas bag through shackles  73 ,  74  to the fastening areas  38 ,  39  on the vehicle. In the folded state of the gas bag, the tensioning cord runs between the shackles  73  and  74  substantially along a straight line. During unfolding, the shackles  73 ,  74  move away from the point  71  whereby the tensioning cord is drawn through the shackles towards the point  71  so that the slack in the tensioning cord is compensated. 
     With the embodiments of FIGS. 12 a  to  12   c , a gas bag  75  is fixed around its inflation mouth area  76  to the B-pillar of the vehicle whereby the tubular gas bag extends in the direction of its center line on either side of the inflation mouth. The gas bag is associated with a tensioning cord  77  which is fixed by one end  78  to the A pillar of the vehicle. The tensioning cord enters into the gas bag at one end and is connected to the gas bag at the other end  82  on the other side of the inflation mouth. As with the embodiment of FIGS. 1 and 2, a minimum spacing b is provided between this end  82  and the inflation mouth  76 . The point of entry can be formed by a penetration point  79  (FIG. 12 a ) through which the tensioning cord is rammed. The point of entry can however also be formed by an outflow opening  80  (FIG. 12 b ) or a valve  81  (FIG. 12 c ). 
     For fitting, the minimum distance b of the gas bag end is gathered up. During unfolding of the gas bag the gathered gas bag material expands and thereby draws a corresponding piece of the tensioning cord into the gas bag whereby the tautening of the tensioning cord takes place as shown in FIGS. 12 a  to  12   c.    
     In the embodiment of FIG. 12 d  a tensioning cord  83  runs out along the gas bag starting from its end  78  which is fixed on the A pillar. The tensioning cord is thereby guided at one end of the gas bag in a shackle  84  and at the other end of the gas bag is fixed outside on the gas bag by its end  82 . The method of operation corresponds. to the embodiments of FIGS. 12 a  to  12   c.    
     With the embodiment of FIGS. 13 to  15 , a rotation of the gas bag about an unfolding axis during folding is used to tauten the gas bag. The principle is explained in FIGS. 13 a ,  13   b  and  14   a  to  14   d . FIG. 13 b  shows a side view of the gas bag  86  turned about the unfolding axis  85 . In this folded position, tensioning cords  89 ,  90  extend freely away from the gas bag away from the fastening points  87 ,  88  of the gas bag, as shown in particular in FIG. 13 a . The tensioning cords  89 ,  90  run, in this embodiment in the folded position of the gas bag  86 , from the fastening points  87 ,  88  in plan view (FIG. 13 a ) in the radial direction and in side view (FIG. 13 b ) inclined to the unfolding axis  85 . 
     During unfolding of the gas bag, the gas bag turns back into its original position. The slack of the tensioning cords is thereby wound up on the gas bag as can be seen from FIGS. 14 a  to  14   d . The tensioning cords are in this embodiment thus torsion cords. It can be seen that the gas bag during unfolding spreads out both in the direction of the unfolding axis  85  and crosswise relative to same. FIGS. 14 c  and  14   d  show the fully unfolded gas bag. 
     FIGS. 15 a - 15   c  show the unfolding phases of a further embodiment of the gas bag with torsion cords. The tensioning cords  91 ,  92  extend left and right of the inflation mouth  93  of the gas bag  94 . The gas bag includes an upper and lower plate wherein the tensioning cord  91  is fixed on the lower plate at the fastening point  95  and the tensioning cord  92  is fixed on the upper plate at the fastening point  96 . Furthermore the tensioning cords are connected to the vehicle at the fastening points  97 ,  98 . In FIG. 15 a , the gas bag is shown in the folded and thereby turned-in state. In FIG. 15 b  the gas bag is partially unfolded. During unfolding, the gas bag has spread out in the direction of the fastening points of the tensioning cords on the vehicle side. At the same time the gas bag is turned back into its original orientation and winds up the slack of the tensioning cords over the circumference. FIG. 15 c  shows the gas bag in the fully unfolded state. 
     FIG. 16 shows a gas bag  101  in the inflated state. Tensioning cords  104  and  105  are fixed on the gas bag at fastening points  102  and  103  and are connected by their other ends at fastening points  106  and  107  to the vehicle. Each tensioning cord  104  and  105  is associated with a return lock  108  and  109  respectively in the area of the ends of the gas bag. A support shackle  110  is associated with both tensioning cords and is fixed on the gas bag between the return locks. Thus the tensioning cord  104  thus runs from the fastening point  106  on the vehicle over the return lock  108  and the support shackle  110  to the fastening point  102  on the gas bag. The tensioning cord  105  runs from a fastening point  107  on the vehicle opposite the fastening point  106  over the return lock  109  and the support shackle  110  to the fastening point  103  on the gas bag. 
     FIG. 17 shows the return lock  109  on an enlarged scale. It is fixed on the gas bag  101  at the fastening point  102  together with the tensioning cord  104  and is further connected to same at a fastening point  111 . The return lock has a base body  112  with webs  113 ,  114  on which a wedge  115  is fixed. The wedge face  116  is provided with grooves  117  running across the pull direction of the tensioning cord  105 . A movable wedge  118  is associated with the fixed wedge  115 . This is connected to the base body  112  through a draw spring  119  and the draw spring runs in the pull direction of the tensioning cord  105 . The wedge face  120  of the wedge  118  likewise has grooves  121  running across the pull direction of the tensioning cord  105 . 
     In the folded state of the gas bag (not shown) in which this occupies a curved position for example above a door frame, the sections of the tensioning cords  104  and  105  provided between the fastening points  106 ,  107  and the associated return locks  108  and  109 , respectively, are longer than in the unfolded state of the gas bag shown in FIG.  16 . The relevant section of the tensioning cords between the return lock and the fastening points  102  and  103  is correspondingly shorter. 
     The method of functioning of the return locks will be explained with reference to the return lock  109 . During unfolding of the gas bag, the tensioning cord  105  connected to the gas bag at the fastening point  103  is drawn as a result of this part of the gas bag spreading out to the right into the pull direction shown in FIG.  17  through the return lock. This is possible since through the action of the tensioning cord  105 , the movable wedge  118  is moved away from the fixed wedge  115  against the action of the draw spring  119 . The return lock acts in this phase as a guide shackle. If immediately after unfolding, the gas bag collapses as a result of the gas escaping, then the tensioning cord  105  is relaxed. The movable wedge  118  is then pressed by the draw spring  119  against the fixed wedge  115  and clamps the tensioning cord  105  between its wedge faces  116  and  120 . This action is assisted by the grooves  117  and  121 . If instead of the return lock only a guide shackle were to be provided, then in the relaxation phase of the gas bag, as a result of the displacement of the fastening point  103  of the tensioning cord  105  to the left, the section of the tensioning cord  105  between its fastening point  107  on the vehicle and the guide shackle could be extended again. The danger would then arise of the gas bag bending in upwards and thus the danger that the gas bag no longer protects the body of the occupant. 
     This action which is described for the return lock  109  also occurs for the return lock  108  for the tensioning cord  104  and thus for the other side of the gas bag  101 . 
     The bending in of the gas bag is additionally prevented by the support shackle  110  which is located in the middle of the gas bag, i.e., at the site where the gas bag is most likely to bend in. 
     A further embodiment of the invention is shown in FIGS. 18 and 19. There guide shackles  122  and  123  are provided in place of the return locks. A double return lock  124  is attached to the gas bag  101  between these shackles. This double return lock has pairs of wedges arranged side by side. Thus a fixed wedge  125 , a movable wedge  126  and a draw spring  127  are provided for the tensioning cord  105 . Next to this pair of wedges, i.e., in FIG. 19 behind the first-mentioned pair of wedges in the viewing direction, a fixed wedge  128 , a movable wedge  129  and a draw spring  130  are provided for the tensioning cord  104 . The method of operation of the double return lock corresponds to the method of operation previously described for the return locks  108  and  109 . 
     Bending in of the gas bag can also be prevented to a certain extent if a support shackle  110  is provided between two guide shackles  122  and  123 , as shown in FIG.  20 . The two tensioning cords  104  and  105  run through this.