Abstract:
A gasbag for a pedestrian protection system, when in the inflated state encompasses a first, oblong central section and end sections angled away from the ends of the first central section. At least one first and one second membrane with differing permeability values are distributed over the sections in such a way that an average permeability of the end sections is lower than an average permeability of the first central section.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to German Patent Application No. 102011119564.9, filed Nov. 26, 2011, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     This application relates to a gasbag for a pedestrian protection system on a motor vehicle, which is provided so as to be inflated immediately when the vehicle comes into contact with a pedestrian, thereby cushioning the impact of the latter on the body. 
     BACKGROUND 
     For example, such a gasbag or a motor vehicle equipped therewith is known from DE 10 2005 041 274 A1. This conventional gasbag is tightly folded together under the rear edge of a front opening hood of the motor vehicle in an idle state, and when inflated, it first lifts up the front opening hood, to then expand through a gap created by lifting the hood, over a lower edge of a windshield adjoining the front opening hood and over the A-column that laterally encases the windshield. When the head of a pedestrian strikes the rear edge of the front opening hood, the hood is to yield at least at the point of impact, and the gasbag made flexible by the compressibility of the gas contained therein is to decelerate the penetrating motion of the head and, if at all possible, prevent it from breaking through into non-deformable fixtures in the engine compartment. Since the front opening hood disperses the force of impact over a large surface, a slight excess pressure in the gasbag is sufficient to build up the counterforce required to decelerate the impact. 
     However, if the head hits one of the end regions of the gasbag covering the A-columns, there is no structure to disperse the force of impact. Therefore, the deceleration experienced by the head given the same excess pressure in the gasbag is less when it strikes the end regions than when it hits the hood, and the danger of the head breaking through all the way to the A-column already exists at a relatively low speed of impact. 
     Made known by EP 1 072 479 B1 was a gasbag for installation in a motor vehicle steering wheel, which is comprised of cloth panels varying in permeability, so as to achieve a desired overall permeability for the gasbag. 
     Accordingly, it is desirable to provide improved gasbags for a pedestrian protection system that is able to effectively protect the head of a pedestrian, regardless of whether the latter strikes the front opening hood or parts of the motor vehicle body adjoining the latter. Furthermore, other desirable features and characteristics of the present invention will be apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. 
     SUMMARY 
     In accordance with various embodiments, a gasbag for a pedestrian protection system is provided. The gasbag in the inflated state encompasses a first, oblong central section and end sections angled away from the ends of the first central section, in which the first central section is more strongly cushioned than the end sections. While a strong cushioning in the central section allows the latter to yield more easily when exposed to the force of an impact dispersed over a large area by the front opening hood, this is not the case at the end sections. In this way, the gasbag can be inflated with a high pressure required for effective protection at the end sections without the inherently desired flexibility of the first central section being lost as a result. 
     The desired cushioning can be realized with a variety of means, e.g., by arranging valves between the sections of the gasbag and the environment, so that gas can escape to the outside when a limiting pressure is exceeded via weak spots in the membrane that tear open when exposed to a high enough stress. In one embodiment, the gasbag exhibits at least one first and one second membrane with differing permeability values, and the membranes are distributed in such a way that an average permeability of the end sections is lower than an average permeability of the first central section. 
     A second central section can extend next to the first central section between the end sections, so as to cover the lower edge of a windshield adjoining the front opening hood during use. In order to be able to maintain a high pressure here as well, and thereby diminish the risk of penetration, the average permeability of the second central section may be lower than for the first central section. 
     In order to be able to inflate the gasbag in the shortest possible time when needed, a supply port can be provided for a gas generator, which can be located centrally on the first central section, and at least one of the other sections of the gasbag can be supplied with gas via the first central section. All other sections can be supplied via the first central section. 
     It is also conceivable to provide a distributor, which exhibits a supply port for a gas generator on the one hand, and ports connected with the central section and end sections on the other. By suitably selecting the length and cross section of the lines leading from the supply port to the ports of the individual sections, such a distributor makes it possible to control the deployment behavior of the individual sections. 
     In order to be able to simultaneously inflate the individual sections from the same gas generator, pathways are present for the gas to get from the gas generator to each section of the gasbag. However, to prevent a high permeability in the first central section from also leading to a premature pressure drop at the end sections, for example, two of the gasbag sections can be interconnected by a check valve, which only allows the respective gas to flow from an upstream to a downstream location of the two sections. 
     The downstream location of the two sections should exhibit a lower average permeability than the upstream section. In this way, a high pressure can initially be generated in both sections when igniting the gas generator, e.g., which in the case of the first central section is beneficial in quickly lifting up the front opening hood, and the pressure in the upstream section can again be allowed to fall shortly thereafter, while the high pressure remains intact in the downstream section, or the pressure at least drops more slowly than in the upstream section. 
     The two sections can extend on different sides of a membrane that partitions the gasbag; in this case, the check valve can be situated at a passageway of the membrane. 
     In particular a flap valve can be used as the check valve. One flap of this flap valve can be flexible like the membrane of the gasbag, so that it can deploy in conjunction with the latter while the gasbag inflates. 
     In another embodiment, the two sections border each other along a seam, and the check valve is situated in a gap in the seam. 
     In particular a lip valve is suitable for this type of attachment. 
     The first and second membrane with the different permeability values can be obtained from an identical initial fabric through varying impregnation, wherein the more permeable membrane can also remain unimpregnated. 
     In further embodiments, a motor vehicle with a gasbag of the kind described above is provided, wherein, in the inflated state, the first central section of the gasbag supports a front opening hood of the motor vehicle, and the end sections cover A-columns of the motor vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and: 
         FIG. 1  is a schematic, perspective partial view of the body of a motor vehicle according to various exemplary embodiments with a lifted hood and inflated gasbag; 
         FIG. 2  is a schematic top view of the isolated gasbag of the motor vehicle from  FIG. 1  according to a first embodiment; 
         FIG. 3  is a schematic cross section through the inflated gasbag along line III-III from  FIG. 2 ; and 
         FIG. 4  is a schematic section along the IV-IV line from  FIG. 2  and  FIG. 3 ; 
         FIG. 5  is a schematic view along the IV-IV line according to a second embodiment; 
         FIG. 6  is a top view analogous to  FIG. 2  according to a third embodiment; and 
         FIG. 7  is a schematic section along the VII-VII line from  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the disclosure or the application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
     In a simplified, perspective view,  FIG. 1  shows part of the body of a motor vehicle with a gasbag  1  according to the present disclosure as configured immediately after contact with a pedestrian. A front opening hood  3  normally flush with adjoining fenders  2  is lifted by the inflated gasbag  1  into a position where a portion of the gasbag  1 , which is concealed under the rear edge of the hood  3  when not inflated and folded together in the idle state, has exited through a gap between the rear edge of the hood  3  and a windshield  4 . A first, central section  6  of the gasbag  1  that supports the rear edge of the front opening hood  3  is for the most part concealed under the front opening hood  3 . A second, central section  7  has positioned itself over the lower edge of the windshield  4 , and end sections  8  each cover the lower regions of the A-columns  5  that laterally encase the windshield  4 . 
       FIG. 2  shows a schematic top view of the inflated gasbag  1  separated from the motor vehicle. Viewed from the top, the gasbag is roughly U-shaped, wherein the end sections  8  each comprise the lateral legs, and the central sections  6 ,  7  comprise a central piece of the U. The two central sections  6 ,  7  are delineated from each other by a seam  9 . Pieces of fabric membrane that together form a cover for the gasbag  1  can be sewn and/or welded together along the seam  9 . 
     The membrane on the lower side of the central section  6  incorporates an opening  10 , to which the gas generator  11  is connected. 
     Stretched inside the gasbag  1  at the lateral ends of the central section  6  are internal membranes  12 , which separate the central section  6  from the end sections  8 . A respective check valve  13  is formed in the membranes  12 , which allows the gas fed into the first central section  6  by the gas generator  11  to flow over into the end sections  8 , but blocks the way back to the central section  6 . 
     Another check valve  14  is arranged in an interrupted segment of the seam  9  between the central sections  6 ,  7 , so as to allow gas to flow over from the first into the second central section  7 , but block a return flow to the central section  6 . Secured between the end sections  8  and the second central section  7  are impermeable membranes  15 , so that no gas exchange takes place there. 
     The impermeability referenced here with respect to the gasbag  1  and the membranes that comprise it should not necessarily be taken to mean hermetic impermeability. In order to be regarded as impermeable within the context of the present disclosure, it is sufficient that the permeability of a membrane be so low that pressure changes owing to the passage of gas through the membrane during the time elapsed from the point where gas generator  11  is activated to the point where the impacting pedestrian has stopped decelerating are low enough not to significantly influence the deceleration process. 
       FIG. 3  shows a cross section through the inflated gasbag  1  along the III-III plane from  FIG. 2 . The sections  6 ,  7  are inflated into cylindrical hoses. The walls of sections  6 ,  7  are formed by two types of membranes  16 ,  17 . While the membranes  16 ,  17  here consist of an identical backing fabric, the membrane  17  comprising the wall of the section  7  exhibits a diminished permeability relative to the membrane  16  comprising the majority of the wall of section  6  due to impregnation with a polymer solution in which the plastic has accumulated on its fibers and constricted the gaps between them. The membrane  17  can be impregnated so strongly that the gaps between the fibers of the fabric are essentially sealed by the impregnating plastic. However, in one embodiment the membrane  17  enveloping the section  7  also exhibits a non-zero permeability, so that impact energy can be dissipated by forcing gas through the membrane  17  during the deceleration process. 
     The two membranes  16 ,  17  are here attached to each other by the seam  9  interrupted at the level of sectional plane III-III; overlapping portions of the membranes  16 ,  17  can also be flatly adhesively bonded or welded, e.g., on edge strips  18  of the membrane  17  that protrude over the seam  9 . However, in the case shown on  FIG. 3 , where the edge strips  18  of the less permeable membrane  17  comprise part of the wall of the section  6 , care must be taken that the membranes  16 ,  17  not overlap so much that the average permeability of section  6  becomes less than that of section  7 . 
     The check valve  14  that joins the two sections  6 ,  7  is here designed as a lip valve. Two lips  19  of the valve  14  are here each formed by edge strips of the membrane  16 , which instead of being joined together by the seam  9 , protrude into the second central section  7 .  FIG. 3  shows the lip valve  14  in an open state, while gas streams over from the first central section  6  to the second central section  7 . As soon as the gasbag  1  has completely inflated, and the flow through the valve  14  has subsided, the first central section  6  begins to lose pressure due to the relatively high permeability of its membrane  16 . The resultant excess pressure in the second central section  7  presses the lips  19  against each other, thereby closing the valve  14 . 
     A passage with an inserted mesh  20  is visible in the membrane  12  on a bulkhead of the first central section  6 . Situated opposite the mesh  20 , on the side of the membrane  12  facing the end section  8 , is a flexible, possibly also elastically extensible, impermeable membrane piece  21 , which completely covers the passage provided with the mesh  20 . The mesh  20  and membrane piece  21  together form the check valve  13 . 
       FIG. 4  shows this check valve  13  and the end section  8  supplied with gas by way of the check valve  13  in a cross section along the IV-IV plane recorded on  FIG. 3  and  FIG. 2 . An outer wall of the end section  8  is composed of an edge of the membrane  16  protruding over the membrane  12  and a membrane  22  whose permeability is less than that of the membrane  16 , and which is joined with the membrane  16  by way of a stitched or welded seam  30 . 
     In the configuration on  FIG. 4 , the membrane piece  21  is forced apart from the mesh  20  by gas flowing through the mesh  20 . The membrane piece  21  is secured to the membrane  15  at two opposing edges of the mesh  20 , here at the upper and lower edges. As the flow of gas through the valve  13  subsides, this ensures that the excess pressure that then arises in the end section  8  presses the membrane piece  21  against the mesh  20 , thereby closing the valve  13 . Because the mesh  20  supports the membrane piece  21  over its entire expansion, the membrane piece  21  is prevented from being pressed into the section  6  through the passage of the membrane  12  when excess pressure prevails in the section  8 , which would cause the valve  13  to leak. 
       FIG. 5  shows a section along the IV-IV plane according to a second embodiment. As opposed to  FIG. 4 , where the membrane  16  of the section  6  transitions into the membrane enveloping the end section  8  as a single piece, the end section  8  is here bordered by a separate membrane  22 , which contacts the membrane  16  of the first central section on its face  23  over a large surface. The membranes  16 ,  22  can be attached to each other by a seam  24  running all around the face  23 , and a second seam envelops the opening of the valve  13 , whose membrane piece  21  can here be a one-piece constituent of the membrane  22  of the end section  8 . 
       FIG. 6  shows a third embodiment of the gasbag  1  in a top view analogous to  FIG. 2 . A first difference relative to the embodiment on  FIG. 2  is that the gas generator  11  is here not hooked up directly to the inlet opening  10  of the first central section  6 , but rather that the two instead have arranged between them a distributor  25  with branched, tubular lines  26 ,  27 , one of which,  26 , is connected in the first central section  6 , and the other,  27 , is connected to the end sections  8 . Check valves  13  that prevent gas from flowing back from the relatively sparingly permeable end sections  8  to the more permeable first, central section  6  are situated in the lines  27  or on the lines  27  with the ports joining the end sections  8 . 
     As in the first embodiment, the second central section  7  is joined indirectly with the gas generator  11  by way of a valve  14  inserted in the seam  9  between the sections  6 ,  7 . 
     A second difference independent of the presence or absence of the distributor  25  has to do with the fact that, as evident in particular in the cross section on  FIG. 7 , a seam  28  is provided between the sections  6 ,  8  instead of the large-surface membrane  12 . 
     A third difference lies in the fact that, as opposed to the seam  9  in the cross section on  FIG. 3 , the membranes of different sections are not connected with each other along the seam  28 ; instead, the membrane  16  of the first, central section  6  and a membrane  29  of the end section  8  are here joined as a single piece over the seam  28 . A varying permeability is here achieved for the first central section  6  and end section  8  by locally impregnating a backing fabric comprising both membranes  16 ,  29  before generating the seam  28 , e.g., via silk-screen printing, whereupon a region of the backing fabric that was slightly impregnated or not at all becomes the membrane  16 , while an impregnated or strongly impregnated region becomes the membrane  29 . 
     In the embodiment on  FIG. 7 , the check valve  14  is designed as a flap valve at the point where the line  27  is connected to the end section  8 . 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.