Patent Publication Number: US-6660668-B2

Title: Woven webbing structure

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to webbing, and in particular to woven webbing structures for vehicle occupant restraining used in a vehicle seat belt device. 
     2. Description of the Related Art 
     An example of a vehicle seat belt device is a three point seat belt type using a continuous webbing. 
     In this type of seat belt device, one end of the webbing is fastened to a take-up mechanism and another end of the webbing is fastened to an anchor plate via a through anchor. In order to apply the webbing to a vehicle occupant, a tongue plate provided at an intermediate portion of the webbing between the anchor plate and the through anchor is engaged with a buckle device and the webbing is thereby pulled out from the take-up device. 
     A type of webbing used in the above-described seat belt device is known as so-called energy absorbing webbing, which has a function of reducing (absorbing) energy that acts on a vehicle occupant at the time of sudden deceleration of a vehicle. This type of webbing is comprised of different kinds of yarns running along a longitudinal direction of the webbing and having different elongation percentages or different extensional rigidities. For example, the warps are formed by cored yarns whose elongation percentage is relatively small or whose extensional rigidity is relatively large, along with side yarns having a large elongation percentage or a small extensional rigidity. 
     As a result, when a large load acts on the webbing, the cored yarns are broken earlier than the side yarns and absorb the load, thereby reducing energy applied to the vehicle occupant. 
     In such a type of conventional energy absorbing webbing, it is thus possible to reduce energy acting on the vehicle occupant due to the cored yarns being broken and absorbing the load. However, the cored yarns interwoven within the webbing come out from the surface of the webbing due to friction caused by the webbing sliding on the through anchor or the anchor plate, or bending of the webbing caused by applying the webbing to the vehicle occupant. As a result, the yarns fray, or deterioration in appearance occurs. 
     SUMMARY OF THE INVENTION 
     In view of the above-described facts, an object of the present invention is to provide a woven webbing structure, in which the risk of (often referred to herein as “webbing” for convenient reference) interwoven cored yarns coming out from a surface of the webbing due to friction caused by the webbing sliding on a through anchor, or bending of the webbing caused by applying the webbing to a vehicle occupant, is reduced. The advantage thereof is to thereby prevent occurrence of frayed yarns or deterioration in appearance. It is intended to achieve these effects without significantly reducing strength or energy absorptivity of the webbing. 
     A woven webbing structure according to the present invention comprises plural types of warps interwoven along a longitudinal direction of the webbing and having different elongation percentages or extensional rigidities, and wefts interwoven along a transverse direction with respect to the warps. In this woven webbing structure, among the plural kinds of warps, there is at least one kind of warp whose elongation percentage is relatively small or extensional rigidity is relatively large, and which has been subjected to twist processing. 
     In the woven webbing structure according to the present invention, the warps interwoven along the longitudinal direction of the webbing each include plural kinds of yarns having different elongation percentages or extensional rigidities. Among these warps, a yarn whose elongation percentage is relatively small or extensional rigidity is relatively large has been subjected to twist processing. 
     The above-described webbing is used in, for example, a vehicle safety restraint belt device. When a large load acts on the webbing, the yarn whose elongation percentage is relatively small or extensional rigidity is relatively large among the warps breaks earlier than other yarns and absorbs the load, thereby reducing energy that would act on the vehicle occupant. 
     Further, in the woven webbing structure according to the present invention, the warp whose elongation percentage is relatively small or extensional rigidity is relatively large has been subjected to twist processing. Therefore, unevenness is formed on the surface of this warp and friction between this yarn and other yarns (other warps or wefts) increases. The frictional force functions for preventing free movement of the twisted warp due to bending of the webbing, or the like. Accordingly, even if the webbing is bent by friction due to the webbing sliding on a through anchor or applying the webbing to a vehicle occupant, the above-described twisted warp resists coming out from the surface of the webbing. 
     Particularly, when plural kinds of warps having different thicknesses are subjected to twisting processing (for example, when two kinds of warps having different thicknesses are twisted together), the entire surface of these warps is made uneven still more so as to further increase the frictional force between yarns, which is even more effective. 
     As described above, in the woven webbing structure according to the present invention, there is reduced possibility that the interwoven yarns will come out from the surface of the webbing due to bending of the webbing, or the like, such as when the webbing is applied to a vehicle occupant. As a result, fraying of yarns and deterioration in appearance is reduced, and is achieved without any significant reduction in the strength and energy absorptivity of the webbing. 
     Further, according to another aspect of the present invention, in the above-described woven webbing structure, the warp is subjected to single twisting or plying and is set such that a twist coefficient thereof, K, is at least 1200, where the number of twists per meter is T, the denier number of the warp is D, and the twist coefficient defined by 
     
       
           T{square root over ( )}D  is  K.    
       
     
     When the twist coefficient K is set as described above, friction between yarns due to surface unevenness of the warp increases in rapid proportion to K, so that the warp resists coming out from the surface of the webbing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal cross-sectional view taken along the line  1 — 1  in FIG. 2, wherein FIG. 2 shows a webbing formed with a woven structure according to a first preferred embodiment of the present invention. 
     FIG. 2 is a plan view of webbing according to a first preferred embodiment of the present invention. 
     FIG. 3A is a diagram which shows data obtained by measuring the force required for pulling out cored yarns from webbing according to the first embodiment of the present invention, versus the relationship between a twist coefficient of cored yarns and the frictional force between the cored yarns in the webbing. 
     FIG. 3B is a plan view which schematically shows a method for measuring the data shown in FIG.  3 A. 
     FIG. 4 is a longitudinal cross-sectional view corresponding to FIG. 1, which shows webbing formed with a woven structure according to a second preferred embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a longitudinal cross-sectional view (taken along the line  1 — 1  in FIG. 2) of webbing  10  formed with a woven structure according to a first preferred embodiment of the present invention. FIG. 2 shows a plan view of the webbing  10 . In FIG. 1, the components are each shown exaggerated for the purposes of clarification in the following description thereof. 
     The webbing  10  is comprised of two kinds of warps  12  interwoven along a longitudinal direction of the webbing, and wefts  14  interwoven along a transverse direction of the webbing  10  with respect to the warps  12 . 
     The warps  12  each include a cored yarn  16 , for example, made of polyester or aramide, and a side yarn  18 , for example, made of polyester. These yarns have different elongation percentages or extensional rigidities. Namely, the cored yarn  16  is formed so as to have a relatively small elongation percentage or a large extensional rigidity and is interwoven in a central portion of the webbing  10 . The side yarn  18  is formed so as to have a large elongation percentage or a small extensional rigidity and is interwoven at the side of the surface of the webbing  10 . 
     The cord yarn  16  is inserted or laid-in to the webbing  10 . By contrast, the side yarn  18  is interwoven with the wefts  14 . 
     Further, the cored yarn  16  whose elongation percentage (or extensional rigidity) is relatively smaller (or larger) than that of the side yarn  18  is twisted by, for example, “single twisting”. The twisted cored yarn  16  is set such that twist coefficient K≧1200 assuming that the number of twist per meter is T, the number of denier of the cored yarn  16  is D, and a twist coefficient defined by T{square root over ( )} D is K. 
     For example, it is preferable that the number of twist T is 110, the number of denier D is 1250, and the twist coefficient K is 3900. 
     The above-described webbing  10  is useful, for example, in a vehicle seat belt device. When a large load acts on the webbing  10  at the time of sudden deceleration of the vehicle, the cored yarns  16  whose elongation percentage (or extensional rigidity) is relatively small (or large) among the warps  12  breaks earlier than the side yarns  18  and absorb the load, thereby reducing energy applied to the vehicle occupant. 
     In the webbing  10  according to the first embodiment of the present invention, the cored yarn  16  is subjected to the twist processing, and therefore, unevenness or roughness is formed on the surface of the cored yarn  16  and the frictional force between yarns (between the cored yarn  16  and the side yarn  18  (or the weft  14 )) thereby increases. The frictional force functions for preventing free movement of the twisted cored yarns  16  caused by bending of the webbing  10 , or the like. Accordingly, even if the webbing  10  is bent due to applying the webbing to a vehicle occupant, the cored yarns  18  resist coming out from the surface of the webbing  10 . 
     Further, in this case, the twisted cored yarn  16  is set so as to satisfy the expression, K≧1200, assuming that the number of twist per meter is T, the number of denier of the warp is D, and the twist coefficient defied by T{square root over ( )} D is K. The frictional force between yarns is increased due to the unevenness on the surface of the cored yarn  16 , thereby making it possible to reliably prevent the cored yarn  16  form coming out from the surface of the webbing. 
     Here, FIG. 3A shows data obtained by measuring the frictional force between the cored yarn  16  and other yarns (the side yarn  18  or the weft  14 ), measured as the force F (that is, difficulty in pulling out) required for pulling out the cored yarn  16  from the webbing  10  as shown in FIG.  3 B. 
     It can be seen from FIG. 3A that so long as the twist coefficient K is set such that K≧1200, the force F required for pulling out the cored yarn  16  from the webbing  10  rapidly increases in proportion to K. Namely, the frictional force between the cored yarn  16  and other yarn (the side yarn  18  or the weft  14 ) is reliably caused to be relatively large. 
     As described above, in the webbing  10  (woven structure) according to the first embodiment of the present invention, there is reduced possibility that the cored yarn  16  among the interwoven yarns will come out from the surface of the webbing due to bending of the webbing caused by applying the webbing to a vehicle occupant. The result is reduced fraying of yarns and deterioration in appearance. These effects are achieved without significant reduction in the strength and energy absorptivity of the webbing. 
     Next, a second preferred embodiment of the present invention will be described. 
     FIG. 4 is a longitudinal cross-sectional view of webbing  20  formed with a woven structure according to the second preferred embodiment of the present invention. In FIG. 4, the components are each again shown exaggerated for the purpose of clarification in description. 
     The webbing  20  includes warps  22  interwoven along the longitudinal direction thereof. The warps  22  each include cored yarns  24  and  26  having different thicknesses, and a side yarn  28 . The cored yarns  24  and  26 , and the side yarn  28  have different elongation percentages or extensional rigidities. Namely, the cored yarns  24  and  26  are set such that the elongation percentages thereof are relatively small or the extensional rigidities thereof are relatively large, and these cored yarns are interwoven at a central portion of the webbing  20 . Further, the side yarn  28  is set such that the elongation percentage thereof is relatively large or the extensional rigidity thereof is relatively small, and the side yarn is interwoven on the side of the surface of the webbing  20 . 
     The cored yarns  24  and  26  whose elongation percentages are relatively smaller than, or whose extensional rigidities are relatively larger than, the side yarn  28  are twisted by a so-called “mixed twisting”, and the thin cored yarn  26  is twisted around and into the thick cored yarn  24 . The twisted cored yarns  24  and  26  are each set so that a twist coefficient K satisfies an expression, K≧1200, assuming that the number of twist per meter is indicated by T, the number of denier of the cored yarns is indicated by D, and the twist coefficient defined by T{square root over ( )} D is indicated by K. 
     In the webbing  20  having the above-described structure, when a large load acts on the webbing  20 , among the warps  22 , the cored yarns  24  and  26  whose elongation percentages are relatively small or extensional rigidities are relatively large, break earlier than the side yarn  28  and absorb the load, thereby reducing the energy acting on a vehicle occupant. 
     In the webbing  20  according to the second embodiment of the present invention, the cored yarns  24  and  26  are subjected to twist processing, and therefore, unevenness is caused on the entire surface of the twisted cored yarns  24  and  26  so that friction between the cored yarns  24  and  26 , and other yarn (the side yarn  28  or a weft  30 ) increases. Particularly, when two kinds of cored yarns  24  and  26  having different thicknesses are twisted, the entire surface of the cored yarns  24  and  26  becomes uneven still further. Therefore, the frictional force further increases. The frictional force functions for preventing free movement of the twisted cored yarns  24  and  26  caused by bending of the webbing  20 , or the like. Accordingly, even if the webbing  20  is bent due to an operation of applying the webbing to a vehicle occupant, the cored yarns  24  and  26  have increased resistance to coming out from the surface of the webbing  20 . 
     In this case as well, the twisted cored yarns  24  and  26  are set so as to satisfy the expression, K≧1200, assuming that the number of twisting per meter is indicated by T, the number of denier of the warp is indicated by D, and the twist coefficient defined by T{square root over ( )} D is indicated by K. Therefore, friction increases between yarns due to the unevenness around substantially the entire surface of the cored yarns  24  and  26 , thereby making it possible to reliably prevent the cored yarns  24  and  26  from coming out from the surface of the webbing. 
     As described above, in the webbing  20  (woven structure) according to the second embodiment, there is reduced possibility that the cored yarns  24  and  26  among the interwoven yarns will come out from the surface of the webbing due to bending of the webbing, or the like, caused by applying the webbing to a vehicle occupant. As a result, fraying of yarns and deterioration in appearance is reduced without significant reduction in strength or energy absorptivity of the webbing. 
     The above-described first embodiment is constructed in such a manner that one kind of cored yarn  16  among the warp  12  is set and subjected to twist processing. Further, the second embodiment is constructed in such a manner that two kinds of cored yarns  24  and  26  among the warp  22  are set and subjected to twist processing. However, the present invention is not limited to the foregoing, and three or more kinds of cored yarns among the warp may be set and subjected to twist processing. 
     As described above, the webbing woven structure according to the present invention has an advantage in that there is reduced possibility of interwoven yarns coming out from the surface of the webbing due to bending or friction caused by the webbing sliding on a through anchor or applying the webbing to a vehicle occupant. Fraying of yarns or deterioration in appearance is thus reduced, and further, this advantage is achieved without any significant decrease in the strength or energy absorptivity of the webbing.