Abstract:
A gasbag for a pneumatic personal protection device on a motor vehicle is provided. The gasbag has a membrane at least locally comprising an inner layer and an outer layer that exhibits a higher tolerance to a frictional load than the inner layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to German Patent Application No. 102011121724.3, filed Dec. 20, 2011, which is incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The technical field relates to a gasbag for a pneumatic personal protection device on a motor vehicle, as well as to a motor vehicle equipped therewith. 
       BACKGROUND 
       [0003]    Gasbags or airbags can be sheathed and integrated into various hollow spaces on a motor vehicle, from which they must expand as rapidly as possible when needed, so as to establish a buffer between hard sections of the motor vehicle body and persons that might need to be protected, in particular passengers inside the vehicle or pedestrians. Such a gasbag is exposed to significant mechanical loads not just at the moment where it cushions a person in an expanded state, but conceivably even before that point, e.g., when the expanding gasbag has to force its way out of its installation space into the open through a narrow opening, during which it is exposed to potentially significant friction at the edges of the opening. In particular given a gasbag for protecting pedestrians, strong frictional loads can also arise when it is pressed against the roadway during its expansion or even only after cushioning a pedestrian. If the frictional load tears open the gasbag, it becomes ineffective. 
         [0004]    It is at least object to improve the operational reliability of such a gasbag. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. 
       SUMMARY 
       [0005]    In an exemplary embodiment, the membrane of a gasbag at least locally encompasses an inner layer and an outer layer, which exhibits a higher tolerance to a frictional load than the inner layer. 
         [0006]    Such an elevated tolerance can come about in different ways, e.g., by using a material with a low coefficient of friction and/or higher resistance to wear for the outer layer, or, while accepting the wear on the outer layer, instead giving it thick enough dimensions to protect the inner layer against a frictional load for at least the time it takes the gasbag to decelerate a person impacting it. 
         [0007]    At least in the areas of the membrane that are expected to be exposed to wear and preferably also a bit beyond that, the outer layer can form a closed layer, so as to protect the inner layer over its entire threatened region. For example, such a closed layer can be composed of a lubricant like fat or wax, which is slightly abraded when in contact with a frictional surface; however, it can also be a low-abrasion layer consisting of a durable material like aramide, wherein the closed nature of the layer here prevents projections of a frictional surface from potentially getting caught in the layer and ripping it open. 
         [0008]    In order to economize on installation space, it may be best for the outer layer to be comprised of discrete wearing bodies individually secured to the inner layer. Even if they do not completely cover the inner layer with the gasbag in an expanded state, the latter can effectively keep it away from a frictional surface. 
         [0009]    In order to prevent the wearing bodies from getting caught on projections of a frictional surface, it may be best to scale the wearing bodies. 
         [0010]    The wearing bodies can be adhesively bonded to the inner layer of the membrane; if the membrane exhibits openings, in particular if the membrane is a fabric and the openings are gaps between threads of the fabric, effectively anchoring the wearing bodies may involve having them exhibit fastening sections that pass through openings in the inner layer. 
         [0011]    In another modification, the outer layer can also be designed as a fabric. 
         [0012]    The outer and inner layer can also be joined together to form a uniform fabric. 
         [0013]    Varying tolerances to a frictional load for the outer and inner layer can be obtained in particular by having the inner layer and outer layer be comprised of different types of threads. 
         [0014]    A high tolerance to frictional loads can be achieved by having the outer layer consist at least partially of aramide or PTFE. 
         [0015]    In another exemplary embodiment, a motor vehicle with a gasbag of the kind described above is provided. Such a gasbag for protecting pedestrians can be arranged on a bumper, in particular the front bumper, of the motor vehicle. 
         [0016]    In a gasbag for protecting pedestrians, in an embodiment the outer layer is provided on at least a part of the membrane that faces the roadway in an expanded state, and can come into frictional contact with the latter. Parts of the gasbag facing away from the roadway preferably do not exhibit the outer layer, so as to minimize the space required by the gasbag when not expanded and its weight. 
         [0017]    If the gasbag is arranged in such a way as to expand through an opening, in an embodiment the outer layer is provided on at least a part of the gasbag that comes into frictional contact with an edge of the opening during expansion. Once again, parts of the gasbag for which there is no risk of frictional contact are preferably free of the outer layer. 
         [0018]    Structured surfaces often exhibit an anisotropic coefficient of friction. Since the direction in which the gasbag moves relative to a frictional surface is generally determined by its installation, it is possible to orient the membrane of the gasbag in such a way that it moves, if necessary relative to the frictional surface, in the direction where its coefficient of friction is minimal 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The various embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein: 
           [0020]      FIG. 1  is a schematic side view of a front portion of a motor vehicle according to a first embodiment; 
           [0021]      FIG. 2  is a schematic cross section through the dashboard of a motor vehicle according to a second embodiment; 
           [0022]      FIG. 3  is a first exemplary embodiment for the structural design of the membrane of a gasbag in a schematic section; 
           [0023]      FIG. 4  is a second example for the structure of the membrane in a section analogous to  FIG. 3 ; 
           [0024]      FIG. 5  is a third exemplary embodiment for the membrane structure; 
           [0025]      FIG. 6  is a fourth exemplary embodiment; 
           [0026]      FIG. 7  is a magnified section through a membrane according to a fifth exemplary embodiment; 
           [0027]      FIG. 8  is a magnified section through a membrane according to a sixth exemplary embodiment; and 
           [0028]      FIG. 9  is a magnified section through a membrane according to a seventh exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    The following detailed description is merely exemplary in nature and is not intended to limit the various embodiments or the application and uses thereof. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description. 
         [0030]      FIG. 1  shows the front portion of a motor vehicle in a first typical situation involving a gasbag as contemplated herein. A large segment of the front portion of the motor vehicle is taken up by a bumper  1  made out of plastic. The front side of the bumper  1  exhibits a pocket or recess not visible on the figure, which incorporates a gasbag  2  in a tightly folded configuration and a pyrotechnic gas generator for supplying gas to the gasbag  2 , if necessary protected by a lid. A control circuit known in the art (not shown) is provided for igniting the gas generator if a strong collision pointing to contact between the driving vehicle and an outside obstacle, such as a pedestrian  3 , was registered or, preferably, if an approach toward such an obstacle at a speed roughly corresponding to the traveling velocity of the motor vehicle was registered. In the latter case, the gasbag  2  can expand even before the vehicle touches the pedestrian  3 , and thereby achieve the configuration depicted on  FIG. 1 . 
         [0031]    The expanded gasbag  2  extends to the bottom beyond the lower edge of the bumper  1 , and as a consequence is diverted downward by the turbulence, against the road surface  4 . In this way, the gasbag  2  engages the legs of the pedestrian  3  at a slight distance from the road surface  4 , reliably preventing the latter from being pulled under the vehicle. On the other hand, given a more prolonged, tight contact between the gasbag  2  and road surface  4 , there is a danger that it will be abraded and become less effective if no suitable countermeasures are taken. Examples of such countermeasures will be outlined below based on  FIG. 3 . 
         [0032]      FIG. 2  shows a second, typical situation involving a gasbag contemplated herein. A dashboard panel  6  is located under a sectionally depicted windshield  5  of the motor vehicle. In an idle state, a gas generator  7  and folded gasbag  2  are accommodated inside the dashboard, and an elongated weak point is formed in the dashboard panel  6 . When the gas generator  7  is actuated and the gasbag  2  begins to expand in response to a strong collision, the dashboard panel  6  tears along the weak point under the pressure exerted by the gasbag  2 . An outlet opening  10  forms between the upwardly diverted section  8  and an immovable section  9  of the panel  6 , through which the gasbag  2  penetrates into the passenger cabin, and continues to expand there. The edges  12  of the outlet opening often have sharp edges given the way they come about, and parts of the membrane of the gasbag  11  that are abraded over the edges  12  as the gasbag  11  exits the opening  10  run the danger of becoming damaged in the process if they have no suitable protection. 
         [0033]      FIG. 3  shows a schematic section through a cutout of the expanded gasbag  2  according to a first exemplary embodiment. A flexible membrane  13  forming the outer wall of one or more chambers of the gasbag  2  encompasses an inner layer  14  and an outer layer  15  in a region facing the road surface  4  in the expanded state. The inner layer  14  can be a tight fabric, a film or a composite material, such as a film comprised of rubbery elastic material, which is limited in terms of its extensibility by an embedded fabric layer. The outer layer  15  is here a layer of fat or wax. While such an outer layer  15  can abrade quickly when in contact with the road surface  4 , it still provides the inner layer  14  with effective protection if its thickness is dimensioned so as to prevent the inner layer  14  from coming into contact with the road at least until the gasbag  2  has effectively cushioned the pedestrian  3 . 
         [0034]    In an upper region  16  (see  FIG. 1 ) of the gasbag  2  facing away from the road surface  4  in an expanded state, the membrane  13  lacks the outer layer, so as not to unnecessarily elevate the space required by the gasbag when not expanded in the idle state. As an alternative, the outer layer  15  can also be a film made out of a tough, flexible material, such as aramide. Such a film can be adhesively bonded with the inner layer  14  over a large surface, or a film can be formed that at least partially penetrates the fabric of the inner layer  14 , e.g., by applying an aramide solution to the inner layer  14 . 
         [0035]    In order to achieve a long-lasting resistance to frictional wear, possibly even one that enables a reversal and renewed use of the gasbag  2  for another expansion process, the outer layer  15  may have to exhibit a thickness that would stiffen a continuous film to where it no longer could readily be folded together as tightly as required for the gasbag  2  when in an idle state. One remedy would here be the modification shown on  FIG. 4 , as a result of which the outer layer  15  is composed of discrete, block-shaped wearing bodies  17  each individually attached to the inner layer  14 . The wearing bodies  17  can each be adhesively bonded to the inner layer  14  or, if the inner layer  14  is a fabric, the material of the wearing body  17  can penetrate into respective gaps between the warp and weft threads of the fabric, so as to become anchored in a positively and materially bonded way. 
         [0036]    If the wearing bodies  17  are pressed into the inner layer  14  while in contact with the road surface  4 , it may happen that the inner layer  14  will still come into contact with the road surface  4  in a gap  18  between two wearing bodies  17 . In order to reliably preclude this possibility, the wearing bodies can be scaled, as depicted on  FIG. 5 , with a respective base section  19  reliably secured to the inner layer  14  via adhesive bonding or penetration through the fabric of the inner layer  14 , and a wing  20  that is joined with the inner layer  14  via the base section  19 , and whose edge facing away from the base section  19  overlaps the respective base section  19  of an adjacent wearing body  17 . The scaled arrangement shown on  FIG. 5  is especially insusceptible to a movement by the gasbag  2  relative to the road surface  4 , in a direction where the base sections  19  are situated in the front in the direction of movement, and the wings  20  are situated toward the back, i.e., toward the left on  FIG. 5 , as denoted by an arrow. At the same time, this is also the direction in which the frictional coefficient of the gasbag  2  relative to the road surface  4  is minimal. For this reason, the gasbag  2  should be mounted to the vehicle in such a way that the base sections  19  of the wearing bodies  17  each lie in front of the wings  20  relative to the traveling direction of the vehicle in an expanded state. 
         [0037]      FIG. 6  shows a variant in which the wearing bodies  17  have a rounded cross section, so as to minimize the danger of getting caught on a projection of the road surface  4 . Partially recessing the wearing body  17  in the inner layer  14  while attaching it thereto enlarges the contact surface to the inner layer  14 , and thereby provides the wearing bodies  17  with a secure fit. 
         [0038]      FIG. 7  shows a cutout from the membrane  13  in a highly magnified, schematic cross section. As clearly evident, the inner layer  14  of the membrane  13  is here designed as a fabric with warp and weft threads  21  or  22 . A wearing body  17  is injection molded onto the fabric of the membrane  13 , where part of the material of the block  17  has penetrated through the gaps  23  between the threads  21 ,  22  of the fabric, so that they become locally embedded in a fastening section  24  of the block  17 . The outer layer  14  tolerant to abrasive wear is here formed by a wearing layer  25  on the exterior side of the fastening section  24 . The wearing layer  25  can be designed as a single piece with the fastening section, or form an especially low-friction or abrasion protective layer over the fastening section  24 . In order to keep friction or abrasion low, the wearing layer  25  can be made out of PTFE or aramide, for example. 
         [0039]      FIG. 8  illustrates, according to another embodiment, the inner layer  14  of the membrane  13  again designed as a fabric. The fabric here has a pelt-like structure, with incorporated fibers  26 , e.g. comprised of aramide, whose free ends form the outer layer  15 . Because they become tightly nestled against the inner layer  14  upon contact with the floor, the fibers  56  deliver effective protection against damage while simultaneously ensuring minimal friction. 
         [0040]    In the embodiment on  FIG. 9 , the inner and outer layers  14 ,  15  are integrated into a uniform fabric. The depicted fabric exhibits a satin weave. This weave is characterized by the fact that warp and weft threads extend essentially on different sides of the fabric and, by each running parallel to each other, generate a high frictional anisotropy. The warp threads  21  shown in section on the figure are kept under a high stress while weaving, so that they are significantly less curved in the finished fabric than the weft threads  22  depicted in a top view. Therefore, the weft threads  22  form only the outer layer  15  facing the road surface  4 , and the warp threads  21  only come into contact with the road  4  when the weft threads  22  have largely been abraded. Using a tough, highly resilient material like aramide makes it possible to achieve a strong resistance to friction here as well. 
         [0041]    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.