Abstract:
A device for folding a gas bag ( 10 ) comprises a positioning means for the gas bag ( 10 ) with a tubular folding device ( 32 ). The positioning means positions the gas bag ( 10 ) such that upon an axial movement of the tubular folding device ( 32 ), the gas bag ( 10 ) is turned over the tubular folding device ( 32 ). A method of folding a gas bag ( 10 ) having an inflation opening, using a device of this type comprises the following steps: 
       positioning the tubular folding device ( 32 ) on the side of the gas bag ( 10 ) opposite the inflation opening;    axially displacing the tubular folding device ( 32 ) through the inflation opening, so that the gas bag ( 10 ) is turned over the tubular folding device ( 32 ); and    withdrawing the tubular folding device ( 32 ) from the inflation opening.

Description:
TECHNICAL FIELD  
       [0001]     The invention relates to a device and a method for folding a gas bag. The invention further relates to a method of assembling a gas bag module and a gas bag module assembled in accordance with this method.  
       BACKGROUND OF THE INVENTION  
       [0002]     Numerous methods are known for folding a gas bag, which are used during the positioning of a gas bag into a mounting of a gas bag module. Generally, during the assembly of the module, the gas bag is clamped with a gas bag holding plate or with a flange of the gas generator of the module by screws or rivets against a gas generator carrier. This requires manual work and additional expenditure of time, materials, tools and hence costs.  
         [0003]     It is an object of the invention to enable an automated gas bag module assembly, in which in particular the gas bag folding and gas bag fastening can be embedded into the automated assembly process.  
       BRIEF SUMMARY OF THE INVENTION  
       [0004]     For this purpose, according to the invention, a device for folding a gas bag is provided. The device comprises a positioning means for the gas bag and a tubular folding device. The positioning means positions the gas bag such that upon an axial displacement of the tubular folding device, the gas bag is turned over the tubular folding device.  
         [0005]     In a preferred embodiment of the device according to the invention, the tubular folding device includes an outer tube having several bores. The tubular folding device is adapted to be connected to a suction pump.  
         [0006]     The invention further provides a method of folding a gas bag having an inflation opening. The method uses a device according to the invention and comprises the following steps:  
         [0007]     positioning the tubular folding device on the side of the gas bag opposite the inflation opening;  
         [0008]     axially displacing the tubular folding device through the inflation opening, so that the gas bag is turned over the tubular folding device and turned inside out; and  
         [0009]     withdrawing the tubular folding device from the inflation opening.  
         [0010]     In a preferred embodiment of the method according to the invention, prior to withdrawal of the tubular folding device, air present in the gas bag is sucked out, in particular through the tubular folding device.  
         [0011]     The invention also provides for a method of assembling a gas bag module. The method comprises the step of folding the gas bag in accordance with the folding method according to the invention. The axial displacement of the tubular folding device causes the gas bag to be pushed through an opening into a mounting, preferably a gas generator carrier.  
         [0012]     Finally, the invention also provides a gas bag module which is assembled in accordance with the assembly method according to the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     FIGS.  1  to  6  show various successive steps in the assembly of a gas bag module according to the invention;  
         [0014]      FIGS. 7 and 8  show perspective views of the two opposite ends of a tubular folding device;  
         [0015]      FIG. 9  shows a lateral sectional view of a gas bag module with an alternative gas bag fastening;  
         [0016]      FIG. 10  shows a perspective view of the fastening ring used in the gas bag module of  FIG. 9 ;  
         [0017]      FIG. 11  shows a lateral sectional view of a gas bag module with a further alternative gas bag fastening;  
         [0018]      FIG. 12  shows a perspective view of the fastening ring used in the gas bag module of  FIG. 11 ;  
         [0019]      FIG. 13  shows a lateral sectional view of a gas bag module, with the gas bag inflated, with an alternative arrangement of the limiting strap; and  
         [0020]      FIG. 14  shows a top view onto a spread-out gas bag with an alternative design of the inflation opening. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]      FIG. 1  shows a gas bag  10  which is formed from two fabric blanks  12 ,  14 . The two fabric blanks  12 ,  14  are connected with each other at their edges by sewing, gluing or in some other manner. A sheet metal, plastic or wire part  16  was previously automatically arranged on one of the blanks. The part  16  corresponds to the later inflation opening contour of the gas bag. The shape of part  16  can be seen from the turned-down detail view of  FIG. 1  (viewed from the interior of the gas bag  10 ). Through an automated sewing or gluing process and by the folding over of wings  18 , the part  16  is fastened to the blank  14 .  
         [0022]     A limiting strap  20  can optionally be provided on the outer side of the other blank  12 . The limiting strap  20  is both automatically cut to size and also arranged on the blank  12 . The central section of the limiting strap  20  is sewn on or glued on, and the two ends  22  of the limiting strap  20  remain loose.  
         [0023]     The gas bag  10  of  FIG. 1  is conveyed by a conveyor belt to a folding station, at which a cup-shaped gas generator carrier  24  is provided. The gas bag  10 , as shown in  FIG. 2 , is positioned so that the inflation opening of the gas bag  10  lies precisely opposite a corresponding opening  26  of the gas generator carrier  24 . Plastic pins  28 , which project from the gas generator carrier  24 , engage into corresponding holes  30  of the gas bag  10  and of the part  16 . On the other side of the gas bag  10 , between the limiting strap ends  22 , a tubular folding device  32  is aligned coaxially to the inflation opening and to the opening  26  in the gas generator carrier  24 .  
         [0024]     Details of the tubular folding device  32  can be seen in  FIGS. 7 and 8 . The device  32  consists of an outer tube  34  and an inner tube  36 , which are both provided with a plurality of bores  38  and  40 , respectively. In the illustrated example, the bores of the outer tube  34  and of the inner tube  36  are arranged in several axial rows and can be aligned to each other. The tubes  34 ,  36  are both rotatable and also axially displaceable relative to each other. Whereas the lower end of the tubular folding device  32  according to  FIG. 2  is open (see  FIG. 7 ), at the upper end a controllable flap  42  is provided (see  FIG. 8 ), with which the tubular folding device  32  can be closed.  
         [0025]      FIG. 3  shows how the gas bag  10  is pulled through the opening  26  into the gas generator carrier  24  by means of the tubular folding device  32  while it is turned inside out at the inflation opening. In the process, the holes  44  of the gas bag  10  still situated outside the inflation opening before the pushing-in of the tubular folding device  32 , are automatically drawn over the pins  28  of the gas generator carrier  24 , which pins  28  already engage into the holes  30 . The tubular folding device  32  is moved upwards up to a limit which is produced through the vertical height (in relation to the illustration of  FIG. 4 ) of the non-inflated gas bag  10  not restrained by the limiting strap  20 . The blanks  12 ,  14  are then passed practically completely through the opening  26  in the gas generator carrier  24  (see  FIG. 4 ). The loose ends  22  of the limiting strap  20 , on the other hand, are longer than the displacement path of the tubular folding device  32 , so that the ends  22  still project out from the opening  26 .  
         [0026]     Whilst the tubular folding device  32  lies against the stop, all or part of the air present in the gas bag  10  is sucked off through the open lower end by means of a suction pump connected to the tubular folding device  32 . The bores  40  of the inner tube  36  are aligned to the bores  38  of the outer tube  34  during the sucking out. Owing to the bores  38 ,  40  arranged in axial rows, a folding of the gas bag  10  occurs as in an umbrella. Through a defined turning and/or axial displacement of the two tubes  34 ,  36  and also through a defined controlling of the flap  42 , the gas bag can be folded in a defined and reproducible manner into the free interior of the gas generator carrier  24 , as is shown in  FIG. 5 , when the tubular folding device  32 , which is still connected to the suction pump, is drawn out.  
         [0027]     If necessary, the folding can take place in an axial extension of the side wall of the gas generator carrier  24  provided for this, and the folded gas bag  10  can be pressed down by means of a plate or the like adapted to the diameter of the gas generator carrier  24 , in order to achieve the desired packing height and packing density of the gas bag package. In addition, the upper end of the tubular folding device  32  can serve as “space keeper” for the gas generator  46  which is to be inserted later.  
         [0028]     The loose limiting strap ends  22  are drawn out up to a predetermined length with the tubular folding device  32  and are then fixed. This length of the limiting strap ends  22  determines the maximum axial extent of the gas bag  10  on its unfolding. The fixing can advantageously take place by clamping in the compound of the gas generator carrier  24  and a covering cap  48  placed thereon, so that an additional screwing, welding or the like can be dispensed with.  
         [0029]     Finally, the gas generator  46  is inserted into the gas generator carrier  24 , after the tubular folding device  32  has been removed ( FIG. 6 ). The gas generator  46  has at the bottom a fastening flange  50  provided with bores, which is placed onto the pins  28 . The protruding sections of the pins  28  are used for fastening the gas generator  46  by ultrasonic welding or hot calking (see right-hand pin  28  in  FIG. 6 ), the gas bag  10  being securely clamped between the gas generator carrier  24  and the fastening flange  50  by means of the sheet metal, plastic or wire part  16 . Furthermore, the outer contour of the part  16  is constructed so as to be larger than the through-bore  26  of the gas generator carrier  24 , so that the base of the gas generator carrier  24  undertakes the function of a hitherto usual gas bag holding plate, and forces are passed on to the steering wheel and hence to the vehicle via known types of fastening such as snap-in or screw fastenings.  
         [0030]     In  FIGS. 9 and 11 , two alternative types of fastening of the gas bag  10  and of the gas generator  46  are shown. In both cases, the gas bag  10  and the fastening flange  50  of the gas generator  46  are fastened by means of a fastening ring  52  and  54 , respectively (see  FIGS. 10 and 12 ). The fastening ring can be a component part of the gas generator carrier  24 . The fastening ring forms a kind of shaft which is constricted towards the top by cross-pieces  56  and  58 , respectively, of the fastening ring  52  and  54 , respectively. In each of these embodiments, the gas bag  10  is wound around a wire ring  60  which is held between the cross-pieces  56  and  58  respectively, and the flange  50  of the gas generator  46 . Towards the bottom, the shaft is constricted either by a securing ring  62  ( FIG. 9 ) or by clips  64  ( FIG. 11 ). Provision can also be made to fasten only the gas bag  10  or only the gas generator  46  in this manner.  
         [0031]      FIG. 13  shows an alternative possibility for arranging the limiting strap  20 . In this case, the limiting strap  20  is not designed to have loose ends, but rather as a closed loop. The limiting strap  20  is suspended into a bracket  66 , hook or the like arranged on or above the gas generator  46 . The bracket  66  can be formed onto the gas generator  46  or be constructed in one piece therewith, or it may be fastened as a type of clip to the gas generator  46  or to the gas generator carrier  24 . During the folding process, the limiting strap loop, which is shorter than the height of the gas bag  10  when pushed in to a maximum, can be held in the tubular folding device  32  e.g. by the partial vacuum, guided and, when the tubular folding device  32  is withdrawn, can also be brought outside again, in order to then be suspended on the bracket  66 .  
         [0032]     The steps as described for assembling the gas bag module are all suited for an automated assembly.  
         [0033]     The methods as described for folding the gas bag  10  and for assembling the gas bag module can basically also be implemented without sucking air out of the gas bag  10  (after the axial displacement of the tubular folding device  32 ). In this case, the tubular folding device  32  may be constructed to be simpler (without bores) and does not have to be connected to a suction pump.  
         [0034]      FIG. 14  shows a gas bag  10  which has a slit shaped inflation opening area  68  which is suitable in particular for a folding and an assembly which does not involve sucking out air.