Abstract:
The invention relates to a vehicle occupant protection system, comprising a gas bag which has at least one inflatable chamber defined by a wall. The protection system further comprises a tensioning strap which fixes the gas bag in position in an inflated state. The tensioning strap is fully looped around the wall of the chamber and fastened to the wall and to the vehicle in such a manner that inflating the chamber causes a displacement of the tensioning strap and a tightening of the tensioning strap.

Description:
TECHNICAL FIELD  
         [0001]    The invention relates to a vehicle occupant protection system comprising a gas bag, in particular a side gas bag.  
         BACKGROUND OF THE INVENTION  
         [0002]    Especially in vehicle occupant protection systems with side window gas bags, frequently tensioning straps are used to fix the gas bag in position in a vehicle. In the case of side window gas bags which in the unfolded state extend from the A-to the C-column of the vehicle and which in the folded state are arranged in the region of the vehicle roof, the problem exists that owing to the curvature of the roof frame, the length of the gas bag in the folded state is greater than the desired length in the inflated state. It is known to achieve an anchoring of the gas bag via a shortening of the length of the tensioning straps which are used for fixing in position. This can take place for example by a spring mechanism arranged in the region of the A- or C-column or a piston/cylinder device. Such devices for tensioning the tensioning strap are expensive to produce and are complicated to install on the vehicle.  
         BRIEF SUMMARY OF THE INVENTION  
         [0003]    The invention is faced with the problem of providing a vehicle occupant protection device which offers a simple and favorably-priced anchoring of the gas bag.  
           [0004]    This is achieved in a vehicle occupant protection system comprising a gas bag which has at least one inflatable chamber including a wall. The protection system further comprises a tensioning strap which fixes the gas bag in position in an inflated state. The tensioning strap is fully looped around the wall of the inflatable chamber and fastened to the wall and to the vehicle in such a manner that inflating the chamber causes a displacement of the tensioning strap and a tightening of the tensioning strap. The looping around the chamber, with the tensioning strap going completely around the chamber, allows to make a particularly good use of an increase in volume of the chamber. During filling of the gas bag, the increase in volume of the chamber which has the tensioning strap looped around it provides for those sections of the tensioning strap which are located in direct vicinity to the chamber, to experience a force oriented towards the chamber and to be pulled into the section of the tensioning strap which loops around the chamber. These sections of the tensioning strap are regarded as being located in direct vicinity which before or during the filling of the gas bag adjoin directly to the section looping around the chamber. Thus, an effective “shortening” of the tensioning strap and with this an anchoring of the gas bag can be achieved. As in this way the gas bag itself is brought in for tightening the tensioning strap, a further mechanism can be dispensed with, which reduces costs and effort.  
           [0005]    The tensioning strap is displaceable with respect to the wall of the chamber, so that during filling of the chamber the tensioning strap can be “pulled into” the section looping around the chamber.  
           [0006]    In order to not hinder the tensioning strap from moving relative to the chamber, it is favorable if the tensioning strap loops around the chamber in a spiral fashion.  
           [0007]    The distance, contributing to the anchoring, by which the tensioning strap is shortened through the increase in volume of the chamber which has the strap looped around it, can be increased in that the tensioning strap is laid around the chamber in at least two loops.  
           [0008]    Preferably the gas bag has several chambers, and the chamber which has the tensioning strap looped around it, hereinafter named the anchoring chamber, serves principally for tightening the tensioning strap, whilst the other chambers are provided for restraining purposes.  
           [0009]    Preferably the anchoring chamber has a higher internal pressure and, where appropriate, a wall which is more gas-tight than the other chambers. As no consideration has to be given to the restraining characteristics of the anchoring chamber, it can be optimized to its anchoring purpose by adjusting the pressure and the gas-tightness.  
           [0010]    For this purpose, preferably a gas distributor is provided via which gas, which is generated by a gas generator in the case of restraint, is directed into the individual chambers, the gas distributor being designed such that in the inflated state a different pressure can prevail in the individual chambers. By means of such a known gas distributor, which may also be embodied as a gas lance, the higher internal pressure of the anchoring chamber can be realized, as compared with the other restraint chambers.  
           [0011]    In a preferred embodiment of the invention, the gas bag is a side window gas bag. The tensioning strap preferably runs substantially parallel to the lower edge of the side windows of the vehicle. It is particularly advantageous if the side window gas bag has three inflatable chambers arranged adjacent each other, the tensioning strap being looped around the central chamber. The anchoring effect occurs particularly clearly if the chambers of the gas bag are connected with each other at the lower edge only by means of the tensioning strap. As seen in a projection onto a plane parallel to the side windows of the vehicle, the section of the tensioning strap looping around the chamber runs in this embodiment preferably parallel to a lower edge of the side windows of the vehicle, so that the tensioning strap extends along an imaginary straight line between fastening points on the vehicle, whereby a uniform anchoring of the lower edge of the gas bag can be achieved.  
           [0012]    Preferably the ends of the tensioning strap are fastened to the walls of the two outer chambers. The walls of the outer chambers can be fastened in addition by means of further tensioning straps to vehicle-fixed parts. In this way, the overall length of the tensioning strap can be kept as short as possible, and a correct unfolding of the gas bag can be achieved.  
           [0013]    Another alternative makes provision that the ends of the tensioning strap are connected directly to vehicle-fixed parts. In this case, only a single long tensioning strap can be provided which loops around the central chamber and runs for example through eyes on the outer chambers and can be fastened to the A- and C-column of the vehicle. Thereby, sewing the tensioning strap to the individual walls of the chambers can be avoided.  
           [0014]    In a further preferred embodiment of the invention a deflection is provided which is connected to a vehicle part such as the A- or the C-column and which is arranged in the run of the tensioning strap between the chamber which has the strap looped around it and a fastening point of the tensioning strap on the gas bag. That is, the tensioning strap can run from a fastening point on the gas bag through the deflection to the chamber. A particularly suitable variant makes provision that the tensioning strap runs from the chamber which has the strap looped around it, to a second deflection and from there to a second fastening point located at the other end of the gas bag. In this way the gas bag can be anchored by means of only one tensioning strap.  
           [0015]    Preferably, the chamber which has the tensioning strap looped around it extends only in the region of the roof frame, i.e. it does not reach the lower edge of the side windows. As this chamber mainly serves for anchoring the gas bag and not so much for restraining, gas bag volume can be saved in this way. An additional advantage of this arrangement lies in the fact that, with the above-mentioned three-chamber design of the gas bag, a run of the tensioning strap may be chosen in which the tensioning strap extends obliquely along the restraint chambers and thus the latter can be fixed in position when the side windows are destroyed, for example. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 shows a vehicle with a vehicle occupant protection system according to the invention and according to a first embodiment, in diagrammatic representation; and  
         [0017]    [0017]FIGS. 2 a  and  2   b  show a section along the line X-X of FIG. 1 in folded state and also in inflated state of the gas bag;  
         [0018]    [0018]FIG. 3 shows a vehicle with a vehicle occupant protection system according to the invention and according to a second embodiment, in diagrammatic representation;  
         [0019]    [0019]FIG. 4 shows a detail from FIG. 3; and  
         [0020]    [0020]FIGS. 5 a  and  5   b  show different variants of how to lay the tensioning strap around the chamber which is looped around by it. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    [0021]FIG. 1 shows a vehicle occupant protection system in a first embodiment, comprising an inflated side window gas bag  10  which extends in the region of the side windows  12  of a vehicle substantially from the A-column  14  to the C-column  16  of the vehicle. The gas bag  10  has three chambers, a front and a rear restraint chamber  18 ,  20  and a tubular anchoring chamber  22  extending approximately vertically downwards and arranged between the two restraint chambers  18 ,  20 . At the lower edge of the gas bag, the chambers  18 ,  20 ,  22  are separated from each other by breaks. In the case of restraint, the chambers of the gas bag  10  are supplied with gas by a gas generator  24  with a gas distributor  26  which is arranged in the region of the roof frame  28  above the B-column  30  of the vehicle. The gas distributor  26  is designed here in a known manner such that in the individual chambers  18 ,  20 ,  22  a different internal pressure is set. Provision is made that the anchoring chamber  22  has a higher internal pressure than the two restraint chambers  18 ,  20 . The wall of the anchoring chamber  22  may also have a higher gas-tightness than the walls of the chambers  18  and  20 .  
         [0022]    The anchoring of the gas bag is achieved by tensioning straps  32 ,  34 . The tensioning straps  32  are fastened to the A- and C-column, respectively, and also to the walls of the restraint chambers  18 ,  20  e.g. by seams, whilst the tensioning strap  34  is looped around the anchoring chamber  22  in the region of the lower edge of the gas bag  10 . The ends  36  of the tensioning strap  34  are fastened for example by seams to the walls of the chambers  18 ,  20  directed towards the anchoring chamber  22 . The tensioning straps  32 ,  34  run substantially parallel to the lower edge of the side windows  12 . The tensioning strap  34  is fastened such that it can move in relation to the wall of the chamber  22 , e.g. by means of eyes  38 .  
         [0023]    Instead of three tensioning straps, a single continuous tensioning strap can also be provided, which is fastened by its ends  36  to A- and C-column. This tensioning strap can then be guided on the restraint chambers  18 ,  20  in eyes.  
         [0024]    The achieving of the anchoring effect is described hereinbelow. The tensioning strap fully loops around the anchoring chamber  22  in terms of circumference already in the folded state of the gas bag, as is illustrated in FIG. 2 a . The tensioning strap  34  lies here closely against the folded chamber  22 . On inflation of the chamber  22  by gas from the gas generator  24 , the diameter of the chamber  22  enlarges and the ends  36  of the tensioning strap  34  are moved towards each other in the arrow direction (FIG. 2 b ). Hereby, a shortening of that section of the tensioning strap  34  takes place which is not in contact with the wall of the chamber  22 , whereby due to the connection of the tensioning strap  34  to the restraint chambers  18 ,  20  the lower edges of the restraint chambers  18 ,  20  are moved towards each other and so a tightening of the tensioning strap  34  and an anchoring of the gas bag is achieved. The amount of shortening can be set via the diameter of the anchoring chamber  22  at that point at which it is looped around by the tensioning strap  34 .  
         [0025]    In FIGS.  3  to  5  there is illustrated a second embodiment of the invention. For already known components, the already used reference numerals are maintained, for modified and new components an apostrophe is added to the reference numeral.  
         [0026]    The gas bag  10 ′ used in this embodiment likewise has three chambers  18 ,  20 ,  22 ′, of which two extend in the region of the front and rear side windows  12  and which are constructed as restraint chambers, whilst the third one, lying between the restraint chambers  18 ,  20 , is constructed as an anchoring chamber  22 ′. In the inflated state the chamber  22 ′ is arranged in the region of the roof frame  28  and extends not so far towards the lower edge of the side windows  12  than the restraint chambers  18 ,  20 . Chamber  22 ′ may have, for instance, the shape of a horizontally arranged, short hose.  
         [0027]    In the case of restraint, the gas bag  10 ′ is filled with gas from a gas generator  24 . The gas preferably flows through a gas lance  36 ′ and openings  38 ′ into the chambers  18 ,  20 ,  22 ′. By selecting the number and the diameter of the openings  38 ′ to the individual chambers, a pressure may be realized in the anchoring chamber  22 ′ which is higher than in the restraint chambers  18 ,  20 .  
         [0028]    A tensioning strap  34 ′ is fastened to the gas bag at fastening points  40 ′ on both ends of the latter, as seen in the direction of the longitudinal axis of the vehicle. The tensioning strap  34 ′ runs from the fastening points  40 ′ through deflections  42 ′ mounted to the A-column  14  and the C-column  16 , respectively (in detail in FIG. 4). From the deflections  42 ′, sections of the tensioning strap  34 ′ run each obliquely across the restraint chambers  18 ,  20 , up to the chamber  22 ′ which has the tensioning strap  34 ′ looped around it. The looping around takes place preferably in a spiral fashion, so that the tensioning strap does not contact itself in the region of the looped portion. The tensioning strap may either be laid around the chamber  22 ′ once (FIG. 5 a ) or twice (FIG. 5 b ). A higher number of loops is also conceivable. Preferably a narrow belt webbing is selected as the material for the tensioning strap.  
         [0029]    In order to prevent a displacement of the tensioning strap  34 ′ in relation to the chamber  22 ′, the tensioning strap  34 ′ may be guided for the looped portions through eyes  44 ′ constructed on the chamber  22 ′.  
         [0030]    All three chambers  18 ,  20 ,  22 ′ of the gas bag  10 ′ are connected with each other preferably by non-inflatable sections. The eyes  44 ′ through which the tensioning strap runs for looping around the chamber  22 ′, may be manufactured in a known manner in a non-inflatable section.  
         [0031]    When not inflated, the gas bag  10 ′ is stowed in the region of the roof frame. The sections of the tensioning strap  34 ′ that run to the deflections  42 ′ may, for instance, be accommodated in the lining of the A-column  14  and the C-column  16 .  
         [0032]    If the gas bag is inflated in the case of restraint, inflation of the chamber  22 ′ causes a retraction of the tensioning strap  34 ′ towards the chamber  22 ′ and thus provides for a shortening of the effective length of the tensioning strap  34 ′. Since the tensioning strap  34 ′ runs through the deflections  42 ′, a force is exerted on the fastening points  40 ′ which acts in the direction towards the deflections, whereby the gas bag  10 ′ is anchored. The two fastening points  40 ′ are preferably arranged so as to be relatively close to the gas bag lower edge, in order to anchor the gas bag across an as large an area as possible. As is preferred, the fastening points  40 ′ lie on one level with respect to the lower edge of gas bag  10 ′, to receive an optimum distribution of anchoring forces in the gas bag. The sections of the tensioning strap  34 ′ that run obliquely along the restraint chambers  18 ,  20  cause an additional stiffening of the gas bag  10 ′.  
         [0033]    The state of the chamber  22 ′ having the strap looped around it exists already in the non-inflated, folded state of the gas bag, so that the increase in length of the section, looping around the chamber  22 ′, of the tensioning strap  34 ′ is maximum on inflation. Selecting the diameter of chamber  22 ′ and the number of loops determines the length by which the tensioning strap is shortened. In the embodiment illustrated, the shortening may amount to approximately 10-50 cm.  
         [0034]    Of course, also in the first embodiment the tensioning strap can be looped several times around the chamber  22 .