Abstract:
Disclosed is a fabric comprising first and second warp threads and first and second weft threads. Said fabric is characterized in that the first warp threads and the first weft threads form a basic fabric while the second warp threads, along with the second weft threads, form a covering fabric that adjoins the basic fabric, the second warp threads also being interwoven with the first weft threads.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a National Phase of PCT/EP2007/003263, filed Apr. 12, 2007, which claims priority to German Application No. 10 2006 017 270.1, filed Apr. 12, 2006; both of these applications are incorporated by reference herein. 
     
    
     BACKGROUND AND SUMMARY 
       [0002]    The present invention relates to a stretchable fabric comprising first and second warp threads and first and second weft threads. 
         [0003]    Fabrics are known which are employed in the production of air bags for automotive passenger restraint systems and incorporated uncoated. An air bag made of such a fabric is inflated instantly by a gas being jetted thereinto in application, the resulting pressure stressing the air bag in tension, opening up the fabric structure, i.e. increasing its air permeance by stretching its structure, permitting the outflow of inflation gas. This can greatly retard the response of the air bag, for example, because of it being deployed slower and because of it losing air all the time as a consequence. As a result of this, the air bag is delayed in developing its cushioning effect to protect the passenger, possibly also with a risk of injury from escape of the inflation gas. 
         [0004]    It has been attempted to make up for critical losses of inflation gas by using larger inflators. The drawback here, however, is the module ultimately becoming cost-prohibitive. Another approach to avoid the negative consequences as described was to coat or laminate the air bag fabric. Although this actually does achieve a near optimum fabric as regards air permeance, this adds to the costs of producing such a fabric immensely, the additional step in production “coating or laminating” complicating fabrication in all in thus automatically becoming critical. 
         [0005]    The invention is based on the object of proposing a fabric which avoids, or at least greatly reduces, the drawbacks known from prior art. 
         [0006]    This object is achieved firstly by a fabric as set forth in claim  1  comprising first and second warp threads and first and second weft threads, characterized in that the first warp threads and the first weft threads form a basic ply and the second warp threads and second weft threads form a ply topping the basic ply, the second warp threads being interwoven also with the first weft threads and the first weft threads and the second weft threads are arranged so that they, after stretching of the fabric, lie alternatingly substantially juxtaposed so that a second weft thread always locates alongside a first weft thread. With the fabric in accordance with the invention there is now the advantage that when the fabric is used to make an air bag, such that the two topping plies face each other, an air cushion can be produced, the topping ply of which is each first impacted by the gas of the inflator when the air bag is deployed. When impacted by the gas of the inflator in deployment of the air bag, the design of the fabric in accordance with the invention results in the first warp threads as well as the first weft threads stretching under the load, the second warp threads drawing in the second weft threads into interspaces resulting between the first weft threads because of the basic ply being stretched. With increasing pressure these “gaps” or “holes” in the fabric are “plugged” by means of the second weft threads which because of this could also be termed sealing threads, preventing or at least greatly delaying any further increase in air permeance with the result that due to the fabric forming or remaining a seal under loading an escape of the inflation gas is restricted. 
         [0007]    This object is achieved secondly by a fabric as set forth in claim  2  comprising first and second warp threads and first and second weft threads, characterized in that the modulus of elasticity of the first warp threads is lower than the modulus of elasticity of the second warp threads and that the second warp threads are woven with a lower warp tension than the first warp threads and that the first weft threads lie in a basic plane and the weft threads lie in a topping plane along with the basic plane, the first weft threads and the second weft threads being arranged so that after stretching of the fabric they lie alternatingly substantially juxtaposed so that a second weft thread always locates alongside a first weft thread. The advantages of this fabric in accordance with the invention are the same as those as it reads from claim  1 . In the second achievement of the fabric its response when employed in an air bag is different, however, although in principle the result is the same as with the first fabric, namely preventing a further increase in the air permeance of the fabric when in action so that there is no substantial increase in the escape of the inflation gas during deployment and the necessary active life of the air bag. The design of the fabric in accordance with the invention as it reads from claim  2  produces a much stronger crimp of the second warp threads since they, as compared to the first warp threads, have a higher modulus of elasticity and are interwoven with a lower weft tension. When in application of the fabric in an air bag the fabric is subjected to tensile loading, the first warp threads having the lower modulus of elasticity are stretched more than the second warp threads having the higher modulus of elasticity so that the spacing growing between the first weft threads when the fabric is tensile loaded is compensated that the second weft threads previously located in the topping plane become more or less arranged in the increasing gaps between the first weft threads, resulting in the absolute spacing between two juxtaposed weft threads remaining roughly the same. This now makes it possible to advantage to maintain the interspace and thus also the air permeance between warp threads and weft threads roughly constant or to be controlled over the loading profile individually by the gas pressure materializing in the air bag. 
         [0008]    Throughout this description there is repeated reference to first and second warp threads and weft threads. It is to be noted that this does not exclusively involve individual threads, but is also intended to include threads in a multiple lay or shedded, in other words, threads located multiply juxtaposed. When formulated e.g. as “a first warp thread,” “a” is intended functionally and not numerically. 
         [0009]    In both variants of the achievement the fabric in accordance with the invention may be provided as a piece, for example as a filter piece or gas jetting mechanism in an air bag both fabricated and in one-piece woven (OPW) air bags. The air bag may also be made totally of such a fabric. 
         [0010]    It is to be noted that threads of differing design and/or stretch can be put to use in accordance with the invention in a fabric in the warp and/or weft direction. It is understood that this is not exclusively intended for application in automotive passenger restraint systems but may find application in many technical fields for the use of textiles. 
         [0011]    It is also possible in accordance with the invention to employ in the weft direction, for example, a strongly texturized material for the first weft threads (sealing threads) and load the first warp threads (lacing threads) with a very high warp tension so that the second warp threads (sealing threads) during production due to the stretchability of the texturized material are lifted out from the basic ply interlock in thus tending to be arranged more above (topping) than in the plane of the basic ply. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention will now be detailed by way of examples with reference to the drawing for a better appreciation in which: 
           [0013]      FIG. 1  is a diagrammatic view of a fabric as known from prior art in the unstretched condition. 
           [0014]      FIG. 2  is a diagrammatic view of the fabric as shown in  FIG. 1  but in the stretched condition as occurs in its application as an air bag. 
           [0015]      FIG. 3  is a diagrammatic view of one example embodiment of the fabric in accordance with the invention in the unstretched condition. 
           [0016]      FIG. 4  is a diagrammatic view of the fabric as shown in  FIG. 3  but in the stretched condition. 
           [0017]      FIG. 5  is a diagrammatic view of another example embodiment of the fabric in accordance with the invention in the unstretched condition. 
           [0018]      FIG. 6  is a diagrammatic view of the fabric as shown in  FIG. 5  but in the stretched condition. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Referring now to  FIG. 1  there is illustrated weft threads  3  greatly magnified as circles interwoven by warp threads  1  and  2  in a fabric woven in usual L 1/1 plain weave, the spacing of two weft threads being identified by the reference numeral  6 . The upper illustration of  FIG. 1  shows a section through a fabric along a first warp thread in which a first warp thread  1  entwines weft threads  3 . 
         [0020]    The lower illustration of a section of fabric known from prior art in a plain weave shows a section through the fabric along a second warp thread  2 . The spacing  6  between the weft threads  3  (the response being the same between warp threads) is as designed. 
         [0021]    Referring now to  FIG. 2  there are illustrated the sections of the fabric as shown in  FIG. 1  but in the stretched condition, i.e. for example in application of the fabric in an air bag during or after inflation. Jetting the air bag (not shown) with gas by an inflator (not shown) and/or cushioning the impact of the vehicle occupant results in tensile loading of the fabric, extending the spacing  6  between the weft threads indexed “a” to indicate the stretched condition in  FIG. 2 . The spacing  6   a  is greater than the spacing  6  and the weft threads in the position  3   a  have a correspondingly larger spacing. This increase in the spacing  6   a  between the  3   a  increases the air permeance of the fabric, a designed and substantial stretch resulting, in the course of which the threads (warp threads and weft threads) also become thinner. 
         [0022]    Referring now to  FIG. 3  there is illustrated one embodiment of a new fabric comprising first weft threads  13  topped by second weft threads  15  (so-called sealing threads). Analogous to the illustration as shown in  FIGS. 1 and 2  again the upper illustration of  FIG. 3  shows how the first weft threads  13  and second weft threads  15  are picked in connection with warp threads  11  and  14 , the first weft threads  13  forming likewise a basic ply  17  over which an actual not truly juxtaposed topping ply  19  is arranged. The lower illustration of  FIG. 3  shows warp threads  12  and  14 . As is clearly evident from  FIG. 3  the warp threads  11  and  12  crimp only the first weft threads  13  whereas the second warp thread  14 , in this case having likewise the function of a lacing thread, laces the second weft threads  15  in forming a topping ply  19  on the basic ply  17 . In this arrangement, the second weft threads  15 , in other words, the sealing threads, lie more on instead of in the basic ply  17  in forming a “topping ply”  19 . Actually, the topping ply  19  is not a woven in its own right but a topping  19  lying on the basic ply  17 , represented by the second weft threads  15  and the second warp threads  14  (lacing threads). Whilst the fabric is shown in  FIG. 3  in the unstretched condition, referring now to  FIG. 4  there is illustrated the fabric of  FIG. 3  in the stretched condition, showing how the first and second warp threads  11 ,  12  are stretched to the left and right. The spacing between the weft threads  13   a  has increased to that as shown by interspace dimension  16   a  and in the interspace between the second weft threads  13   a  the weft threads  15   a  (sealing threads) are drawn by the lacing threads (second warp threads  14   a ) into the interspaces  16   a . This makes it possible to maintain the interspacing between the threads constant in thus rendering the air permeance of the fabric in the stretched condition practically constant. 
         [0023]    This special design of the fabric in accordance with the invention now makes it possible by presetting the running length of the second warp thread (lacing thread  14 ) lacing the weft threads  13  and  15  to maintain constant the interspace  16  resulting from stretch under loading and thus also the air permeance between the threads of the fabric, to reduce it with increasing stress, or to increase it in accordance with requirements or to tailor it individually via the loading profile. Referring now to  FIGS. 3 and 4  it is thus, for example, possible to set the smallest spacing (spacing  16  in  FIG. 3 , spacing  16   b  in  FIG. 4 ) between two sealing weft threads. In the aspect as shown here, the spacing in  FIG. 3  between two first weft threads  13  (=spacing  16 ) equals the spacing  16   b  in  FIG. 4  between two weft threads  13   a  and weft threads  15   a , assuming the air permeance maintained constant. When the running length of the second warp threads  14  (lacing thread) is selected longer than in the variant as shown in  FIG. 3 , then when the fabric is stressed analagous to the illustration of  FIG. 4  a spacing  16   b  materializes which is larger than the spacing  16  as shown in  FIG. 3 . In the woven structure as shown in  FIG. 3  the spacing between the plies  17  and  19  would be larger. Conversely, the spacing between the plies  17  and  19  could also be made smaller, the loading of the fabric analagous to that as shown in  FIG. 4  results in the spacing  16   b  becoming smaller than the spacing  16  as shown in  FIG. 3  in thus reducing the air permeance with increasing loading. 
         [0024]    It is, of course, just as possible to apply the application of the fabric design as described and shown in  FIGS. 3 and 4  conversely, i.e. with the warp threads and weft threads the other way round. This could involve employing a strongly texturized material for the lacing threads in the weft direction and apply a very high warp tension to the analogous sealing threads so that, as made possible by the stretch capacity of the texturized material the sealing threads are lifted out from the basic ply interlock in production in thus tending to be arranged more above the basic ply (topping) than therein. 
         [0025]    Referring now to  FIG. 5  there is illustrated a second example aspect of a fabric in accordance with the invention in the unloaded condition with a response similar to that of the first example aspect, but without separate lacing and sealing threads. As evident from  FIG. 5  two different yarn materials are employed in the warp, namely first warp threads  21  and second warp threads  24 , the second warp threads  24  having a higher modulus of elasticity than that of the first warp threads  21 . As already evident from the illustration of  FIG. 5  the second warp threads  24  are woven with a lower warp tension than the first warp threads  21 , resulting in a fabric situation the first weft threads  23  being woven in a basic plane  27  and the weft threads  25  in a topping plane  29 . The first warp threads  21  with a lower modulus of elasticity than that of the second warp threads  24  are placed with a warp tension for fabricating the fabric and the second warp threads  24  having a modulus of elasticity higher than the modulus of elasticity of the first warp threads  21  are placed with a warp tension lower than that of the first warp threads  21 . This results in the condition of the fabric as shown in  FIG. 5  in which the weft threads  25  likewise lie on the first weft threads  23  as a topping plane  29  lying on a basic plane  27 . 
         [0026]    Referring now to  FIG. 6  there is illustrated the fabric as shown in  FIG. 5  but in the loaded condition. For the same absolute loading of the fabric the first warp threads  21   a  having the smaller modulus of elasticity are stretched more than the second warp threads  24   a  having the higher modulus of elasticity so that the increase in the spacing ( 26  becomes  26   a ) between the first weft threads  23   a  when the fabric is subjected to tensile loading is compensated by the previously topping weft threads  25  becoming arranged more or less in the gaps  26   a  becoming larger and the absolute spacing  28  between adjoining weft threads  23   a ,  25   a  remaining the same in thus making it possible to maintain the interspace  26 / 28  and accordingly also the air permeance between the weft threads constant. 
         [0027]    In one advantageous aspect of the invention a fabric as shown in  FIG. 6 , for example, is characterized by it being woven in the unloaded condition with the same crimp of the first warp threads  21  and second warp threads  24 , the strain of the material of the second warp threads  24 ,  24   a  being higher than the strain capacity of the first warp threads  21 ,  21   a . To advantage in this fabric, second weft threads (sealing threads  25 ) can be lifted out from the plane of the first weft threads as a result of the difference in the capacity of the warp threads when loaded to accommodate strain. 
         [0028]    However, the spacing may also be made larger or smaller than that of the fabric shown unloaded in  FIG. 5 . The design in accordance with the invention permits enhancing the air permeance out of all proportion when weaving a fabric similar to that as shown in  FIG. 6 , i.e. with the same crimp of the warp threads  21  and  24 , but now in the unloaded condition. Nevertheless the second weft threads (sealing threads  25 ) because of the difference in the strain capacity (that of the second warp threads  24 , second warp threads  24   a  is higher and that of the first warp threads  21 , first warp threads  21   a  is lower) can be lifted out from the plane of the first weft threads  23  when loaded (analagous to the illustration as shown in  FIG. 5  but with an even greater spacing in the levels  27  and  29 , but in the loaded condition). 
         [0029]    In another advantageous aspect of the invention a fabric is proposed in which the profile of the stretch curve is set up individually or tweaked by the fabric comprising in predefined portions warp threads and weft threads with specifically selected parameters such as the modulus of elasticity or also in a specifically selected sequence. With fabrics as designed in accordance with the invention other technical parameters—such as for example the profile of the stretch curve—can be tweaked or individually set up to subsequently also influence, for example, the deployment response of air bags by sections of the fabric stretching more or less individually. These smart fabrics pave the way to tweaking or setting up individually the parameters of the fabric each independent of the other in the future as are currently functionally dependent on each by design. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           1 ,  1   a  first warp thread 
           2 ,  2   a  first warp thread 
           3 ,  3   a  weft thread 
           6 ,  6   a  spacing 
           11 ,  11   a  first warp thread 
           12 ,  12   a  first warp thread 
           13 ,  13   a  first weft thread 
           14 ,  14   a  second warp thread (lacing thread) 
           15 ,  15   a  second weft thread (sealing thread) 
           16 ,  16   a  spacing 
           16   b  spacing 
           17  basic ply 
           19  topping ply 
           21 ,  21   a  first warp thread 
           23 ,  23   a  first weft thread 
           24 ,  24   a  second warp thread 
           25 ,  25   a  second weft thread (sealing thread) 
           26 ,  26   a  spacing 
           27  basic plane 
           28  spacing 
           29  topping plane