Patent Publication Number: US-2003222446-A1

Title: Inflator insertion apparatus and method for airbag systems

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to systems and methods for protecting vehicle occupants from injury. More specifically, the present invention relates to openings that facilitate inflator insertion into airbag cushions.  
       [0003] 2. Description of Related Art  
       [0004] The inclusion of inflatable safety restraint devices, or airbags, is now a legal requirement for many new vehicles. Airbags are typically installed in the steering wheel and in the dashboard on the passenger side of a car. Additionally, airbags may be installed to inflate beside the passenger to provide side impact protection, in front of the knees to protect the knees from impact, or at other strategic locations.  
       [0005] In the event of an accident, an accelerometer within the vehicle measures the abnormal deceleration and triggers the ignition of an explosive charge. Expanding gases from the charge fill the airbags, which immediately inflate to protect the driver and/or passengers from impact against the interior surfaces of the vehicle. During normal vehicle operation, airbags are typically stowed behind covers to protect them from tampering and provide a more attractive interior facade for the vehicle.  
       [0006] Typically, the expanding gases are expelled into the cushion from an inflator that contains the gas in compressed form or generates gas through the ignition of a pyrotechnic. In certain airbag modules, the inflator is positioned within the cushion. Thus, the inflation gas is able to reach the cushion faster, and installation of the module may be simplified.  
       [0007] Unfortunately, insertion of the inflator into the airbag cushion, according to known methods, adds to the cost and difficulty of the manufacturing process. For example, some known processes require installation of the inflator prior to attachment of the various portions of the cushion. Some processes require that separate portions of the cushion be only partially attached together so that the inflator can be inserted through the unattached portion. The cushion must then be sealed shut with the inflator inside. In either case, the presence of the inflator in the cushion during processing adds to the complexity of the remaining operations.  
       [0008] Other known cushion designs include a hole into which the inflator is to be inserted after the other parts of the cushion have been attached together. Many such holes are oriented or shaped in such a manner that tears are likely to propagate outward from the hole due to the tensile stresses that are present in the cushion during deployment. Some holes are shaped in a manner that is awkward to create through known manufacturing processes. Furthermore, some such holes have a mechanism designed to seal the hole during deployment; however, many such mechanisms are not reliable or predictable in their operation.  
       [0009] Accordingly, a need exists for an airbag module and associated manufacturing method by which an inflator can be inserted into an airbag cushion after all other cushion elements have been fully assembled and attached together. Preferably, the airbag module provides a cushion that is resistant to tearing during deployment, and that reliably inflates with the proper sealing and/or venting characteristics. Furthermore, the airbag module should be inexpensive and easy to manufacture.  
       SUMMARY OF THE INVENTION  
       [0010] The apparatus and method of the present invention have been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available airbag modules. Thus, it is an overall objective of the present invention to provide an airbag module that remedies the shortcomings of the prior art. Such an airbag module may permit insertion of the inflator into a fully assembled cushion, and may reduce the danger of inadequate cushion sealing or venting during deployment.  
       [0011] To achieve the foregoing objective, and in accordance with the invention as embodied and broadly described herein in the preferred embodiment, an enhanced airbag module is provided. The airbag module may have a cushion and an inflator designed to be seated within the cushion. The cushion may be folded around the inflator to pack the module for installation in a vehicle. According to one exemplary embodiment, the airbag module is a front impact airbag module designed to protect the upper body of a passenger from forward impact.  
       [0012] The cushion may have a front panel designed to receive impact from the vehicle occupant, and a rear panel that faces toward the dash board or steering wheel when the cushion deploys. The panels may be generally circular in shape, and may be attached at their outer edges. The panels may cooperate to form an insertion passageway that can be sealed after the remainder of the panel edges have been attached together.  
       [0013] If desired, the cushion may include a tether disposed within the cushion to attach the first and second panels together toward the center of the cushion, so that expansion of the cushion toward the vehicle occupant is limited. The tether may include a first tether portion attached to the first cushion and a second tether portion attached to the second cushion. Each of the tether portions may have an attachment flap, so that the tether portions can be attached together to form a complete loop.  
       [0014] The rear panel may also have one or more vents designed to permit gas to escape from the cushion at a measured rate. Each of the vents may include a hole in the rear panel. The hole may be surrounded by one or more reinforcement discs of fabric material that reduce the probability of tearing from the vents.  
       [0015] Furthermore, the rear panel may have an inflator insertion portion designed to permit insertion of the inflator through the rear panel. The inflator insertion portion may have an elongated opening. According to one embodiment, the elongated opening is fully covered by a flap attached around the elongated opening on three sides to create a pocket. The side furthest from the center of the cushion may be left open, so that the inflator may be inserted through the elongated opening, removed from the pocket by moving the inflator away from the center of the cushion, and then moved to its final position at the center of the cushion.  
       [0016] The rear panel may have a projection designed to fit through an inflator attachment aperture in the center of the rear panel. The inflator may be retained in place through the use of anchoring arms extending from the projection, or through another suitable anchoring mechanism. Hence, after removal from the inflator insertion portion, the inflator may be moved into alignment with the inflator attachment aperture, and the projection may be inserted through the aperture and retained in place.  
       [0017] The elongated opening may be very narrow, so as to essentially form a slit. The elongated opening may even be formed by cutting a straight line in a single direction of the cushion, so that the two sides of the elongated opening lie flush with each other when the cushion is flat. The elongated opening may be oriented generally in-line with the center of the rear panel, so that stresses radiating outward from the center do not tend to induce tearing of the cushion outward from the elongated opening.  
       [0018] The length of the elongated opening may be just large enough to enable comparatively easy manual insertion of the inflator. The flap may entirely cover the elongated opening, with an overlap sufficient to substantially seal the elongated opening during deployment of the cushion.  
       [0019] According to another embodiment of the invention, the elongated opening may be disposed at some angle with respect to an intersecting radius of the rear panel. The elongated opening may thus be neither parallel nor perpendicular to the radius. The elongated opening may have a thin central portion, with a first end and a second end that are somewhat wider than the central portion. Each of the first and second ends may even have a circular shape to further prevent tear propagation from the ends of the elongated opening.  
       [0020] In another embodiment, the elongated opening may extend beyond the flap so as to provide venting of the gas within the cushion. Hence, separate vents need not be provided. If desired, the first end of the elongated opening may extend beyond the edge of the flap, and may have a circular shape large enough to provide the desired mass flow rate of gas from the cushion during deployment. The remainder of the elongated opening, i.e., the central portion and the second end, may be comparatively thin, and may be covered by the flap. Thus, the elongated opening is still long enough to receive the inflator, but a portion of the elongated opening is covered during deployment to prevent excess venting.  
       [0021] In yet another embodiment, both first and second ends of the elongated opening extend from the flap to provide venting. Thus, both ends may have wide, circular shapes, while the central portion is thin. The central portion may be covered by the flap. If desired, the flap may be attached through the central portion. Hence, the central portion may, exclusively, be used for inflator insertion, while the first and second ends simply provide venting.  
       [0022] According to another embodiment, the flap may be omitted entirely, so that the full length of the elongated opening is used for both inflator insertion and venting. The first and second ends may thus have wide circular shapes, as with the previous embodiment. The central portion may remain thin. The wide shape of the first and second ends also serves to prevent tearing; hence, the elongated opening may be oriented perpendicular to the radius. Venting may be expected to occur through the first and second ends, and also through the central portion, which may open somewhat during deployment of the cushion to release gas.  
       [0023] In still another embodiment, the flap may once again be omitted. The elongated opening may have first and second ends with a somewhat smaller circular configuration. The elongated opening may be disposed parallel to the radius. In this embodiment, the central portion is once again narrow, and provides the majority of the venting area. The first and second ends restrain tear propagation, but are not large enough to serve as vents without gas flow through the central portion. Reinforcement seams may be disposed around three sides of each of the first and second ends to further restrict the propagation of any tears originating at the elongated opening.  
       [0024] According to one exemplary manufacturing process, the airbag module may be manufactured through a number of steps. The front and rear panels may first be provided by cutting them into the desired shape. The rear panel may further be cut to form the elongated opening, the vents (if used), and the inflator attachment opening. The flap may be attached to the rear panel, over the elongated opening. The first and second tether portions may then be attached to the first and second panels, respectively.  
       [0025] The panels may then be attached together at their outer edges, with the exception of the insertion passageway. The panels may be attached with the internal components on the outside, i.e., with the flap, tether portions, and reinforcement elements attached to the outside of the rear panel. The first and second tether portions may then be attached together. The cushion may then be turned inside out by pushing the panels, the flap, and the tether through the insertion passageway, after which the insertion passageway may be sewn shut. In the alternative, the panels may initially be fully attached in such a manner that the insertion passageway is omitted; the cushion may then be turned inside out via the inflator attachment opening.  
       [0026] The inflator may then be inserted into the cushion through the elongated opening. The inflator may be maneuvered into alignment with the inflator attachment opening. Such maneuvering may entail moving the inflator out of the pocket formed by the flap, and then moving the inflator toward the inflator attachment opening. The projection of the inflator may be inserted through the inflator attachment opening and anchored in place. The cushion may then be folded around the inflator to provide a compact module that is ready for installation in a vehicle.  
       [0027] Through the use of the airbag modules and associated manufacturing methods of the present invention, airbags may be produced in a more convenient and cost-effective manner. Furthermore, such airbag modules may provide more reliable gas retention and/or venting characteristics. Additionally, the cushions provided by the present invention may have a lower likelihood of failure due to tearing of the cushion material.  
       [0028] These and other features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0029] In order that the manner in which the above-recited and other features and advantages of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:  
     [0030]FIG. 1 is a cutaway, perspective view of one embodiment of an airbag module within the scope of the invention;  
     [0031]FIG. 2 is a side elevation, section view of the airbag module of FIG. 1;  
     [0032]FIG. 3 is a front elevation view of the inflator insertion portion of the airbag module of FIGS. 1 and 2;  
     [0033]FIG. 4 is a front elevation view of the inflator insertion portion of an airbag module according to an alternative embodiment of the invention;  
     [0034]FIG. 5 is a front elevation view of an inflator insertion portion of an airbag module according to another alternative embodiment of the invention;  
     [0035]FIG. 6 is a front elevation view of an inflator insertion portion of an airbag module according to another alternative embodiment of the invention;  
     [0036]FIG. 7 is a front elevation view of an inflator insertion portion of an airbag module according to yet another alternative embodiment of the invention; and  
     [0037]FIG. 8 is a front elevation view of an inflator insertion portion of an airbag module according to still another alternative embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0038] The presently preferred embodiments of the present invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the apparatus, system, and method of the present invention, as represented in FIGS. 1 through 8, is not intended to limit the scope of the invention, as claimed, but is merely representative of presently preferred embodiments of the invention.  
     [0039] The present invention utilizes a number of physical principles to enhance the cost-effectiveness and operation of airbag modules. For example, crack and tear propagation have the greatest tendency to originate from an opening that is disposed perpendicular to the direction along which tensile stress is greatest. Tears propagate more readily from openings with narrow ends than from those with enlarged ends.  
     [0040] Furthermore, air flow through an opening will generally be proportional to the size of the area encompassed by the opening. In the case of flexible materials such as fabric, deformation of the opening due to tensile and bending stresses may tend to increase the size of the opening, thereby permitting significant gas flow through an otherwise narrow opening. Additionally, some flexible materials may be used to substantially seal an opening by ensuring that the flexible material overlaps the opening by a sufficient distance. In general, a larger overlap produces a better seal.  
     [0041] Such principles may be applied to many types of airbags, including driver&#39;s side airbags, passenger&#39;s side airbags, overhead airbags, knee bolsters and inflatable curtains. The manner in which the present invention utilizes these principles to provide cost-effective, reliable impact protection will be shown and described in greater detail with reference to FIGS. 1 through 8.  
     [0042] For this application, the phrases “connected to,” “coupled to,” and “in communication with” refer to any form of interaction between two or more entities, including mechanical, electrical, magnetic, electromagnetic, and thermal interaction. The phrase “attached to” refers to a form of mechanical coupling that restricts relative translation or rotation between the attached objects. The phrases “pivotally attached to” and “slidably attached to” refer to forms of mechanical coupling that permit relative rotation or relative translation, respectively, while restricting other relative motion.  
     [0043] The phrase “attached directly to” refers to a form of attachment by which the attached items are either in direct contact, or are only separated by a single fastener, adhesive, or other attachment mechanism. The term “abutting” refers to items that are in direct physical contact with each other, although the items may not be attached together.  
     [0044] Referring to FIG. 1, a cutaway, perspective view shows one embodiment of an airbag module  10  within the scope of the present invention. The airbag module  10  is depicted in fully assembled, deployed form. The airbag module  10  of FIG. 1 is of a type that protects the upper body of a vehicle occupant from forward impact. However, those of skill in the art will recognize that the present invention is equally applicable to other types of airbags, such as knee bolsters, overhead airbags, and inflatable curtains. The airbag module  10  may have a longitudinal direction  12 , a lateral direction  14 , and a transverse direction  16 .  
     [0045] The airbag module  10  may include a cushion  20  and an inflator  22 . The cushion  20  may have a generally circular shape when laid flat. The inflator  22  may be disc-shaped, and may be configured to expel inflation gases radially into the cushion  20 . The cushion  20  may have a first panel  24  and a second panel  26 . The first panel  24  is a “front” panel, i.e., a panel facing the vehicle occupant to receive impact. The second panel  26  is a “rear” panel that faces the dashboard (not shown) or steering wheel (not shown) of the vehicle.  
     [0046] Each of the panels  24 ,  26  may have an outer edge  30  with a generally circular shape. The outer edges  30  may be attached together in gastight fashion, i.e., so that significant quantities of gas are unable to escape between the outer edges  30  during deployment of the cushion  20 . Each of the outer edges  30  may have an extension  32  that protrudes outward. The extensions  32  may cooperate to define an insertion passageway  34 , which may simply be a region in which the outer edges  30  are attached together through the use of a separate operation subsequent to that used to attach the remainder of the outer edges  30 . The insertion passageway  34  may thus be sealed shut by a seam  36  when the cushion  20  is in its fully assembled state. The purpose and operation of the insertion passageway  34  will be described in greater detail subsequently.  
     [0047] The cushion  20  may also have a tether  38  designed to limit the longitudinal distance between the first and second panels  24 ,  26 . The purpose of the tether  38  is to define the deployed shape of the cushion  20  to ensure that the cushion  20  does not inflate too far toward the vehicle occupant, thereby intensifying the impact of the occupant against the cushion  20 . Of course, the tether  38  is optional, and may not be present in every embodiment of the invention.  
     [0048] The tether  38  may include a first tether portion  40  and a second tether portion  42 . The first and second tether portions  40 ,  42  may each have a pair of attachment flaps  44 ; the attachment flaps  44  of the first tether portion  40  may be attached to those of the second tether portion  42  via seams  46 , which may be sewn in place. Alternatively, the seams  46  may be replaced with different forms of attachment such as thermal welds, RF welds, ultrasonic welds, adhesives, or the like. The first and second tether portions  40 ,  42  may be attached to the centers of the first and second cushions  24 ,  26 , respectively, via attachment portions  48 . Each attachment portion  48  may have a circular shape, and may be sewn to the corresponding panel  24  or  26 .  
     [0049] The second panel  26 , or rear panel, may also have one or more vents  60  that permit the escape of a measured quantity of inflation gas during deployment and impact of the occupant against the first panel  24 . Since stresses tend to concentrate at the edges of holes, each of the vents  60  may have some type of reinforcement structure designed to ensure that the tears are unable to propagate through the material of the second panel  26  from the vents  60 . For example, each of the vents  60  may have a reinforcement disc  62  attached by a sew line  64  to the second panel  26 . Each of the reinforcement discs  62  may simply take the form of a circular, fabric sheet.  
     [0050] Holes  66  may extend through the reinforcement disc  62  as well as the material of the second panel  26 . The holes  66  may provide an open area sized to release gas rapidly enough to cushion the impact of the occupant against the airbag, but not so rapidly that the occupant strikes the steering wheel or dashboard through the cushion  20 . According to one embodiment, the holes  66  may each have a diameter of about thirty millimeters.  
     [0051] Of course, the vents  60  are optional. In certain embodiments, the cushion may inflate in such a manner that venting is not necessary or desirable. In other embodiments, the cushion may have a somewhat permeable construction so that venting occurs directly through the first and second panels  24 ,  26 . In still other embodiments, venting may occur through an opening that permits passage of the inflator  22  in the cushion  20 . Such dual purpose openings will be shown and described subsequently, with reference to FIGS. 5 through 8.  
     [0052] The second panel  26  may have an inflator insertion portion  70 , through which the inflator  22  can be inserted into the cushion  20 . The inflator insertion portion  70  may have an elongated opening  72  covered by a flap  74 . The flap  74  may be attached to the inside of the second panel  26  by attachment lines  76 , which may be formed by sewing, adhesive bonding, RF welding, thermal welding, or the like. The attachment lines  76  may be disposed on three sides of the elongated opening  72 , so that only the side of the flap  74  furthest from the center of the second panel  26  is open to the interior of the cushion  20 . Thus, the attachment lines  76  may form a pocket that contains the elongated opening  72 .  
     [0053] Hence, the inflator  22  may be inserted into the cushion  20  along an insertion pathway indicated by the arrow  77 . As shown, the elongated opening  72  may be oriented radially, or generally parallel to a radius  78  of the second panel  26  that intersects or nearly intersects the elongated opening  72 . Thus, the inflator  22  may be inserted in a direction generally perpendicular to the radius  78 , moved toward the edge  30  of the second panel  26  to remove the inflator  22  from the pocket created by the panel  74 , and then moved to the center of the second panel  26  for anchoring.  
     [0054] Referring to FIG. 2, a side elevation, section view illustrates the airbag module  10 . The airbag module  10  may have seam  79  that attaches the outer edges  30  of the panels  24 ,  26  to each other. The seam  79  may be formed through sewing, one piece weaving, RF welding, ultrasonic welding, adhesive bonding, chemical bonding, or any other known method. As shown, the seam  79  is sewn. The seam  79  may be formed in such a manner that the outer edges  30  are turned inward against each other, as depicted in FIG. 2. One possible method of forming the seams  79  with such an inward disposition will be described subsequently.  
     [0055] The inflator  22  may be designed to help anchor the cushion  20  in place within the vehicle; this may be accomplished with or without extra plates or other attachments. The inflator  22  may have a projection  80  that extends longitudinally, rearward of the main body of the inflator  22 . The projection  80  may have a plurality of anchoring arms  82  designed to keep the inflator  22  in position against the second panel  26 . The anchoring arms  82  may, for example, deflect to permit passage of the projection  80  into an opening, after which the anchoring arms  82  extend outward to preclude retraction of the projection  80  through the opening. Of course, other anchoring devices, such as crimped extensions,  11  threaded fasteners, or the like may be used in addition to or in place of the anchoring arms  82 .  
     [0056] The rear panel  26  may have an inflator attachment aperture  84  sized to receive the projection  80 . If desired, the inflator attachment aperture  84  may be reinforced against tearing through the use of a reinforcement disc  86  disposed between the main body of the inflator  22  and the attachment portion  48  of the second tether portion  42 . The reinforcement disc  86  may simply take the form of a circular piece of sturdy fabric. Of course, the reinforcement disc  86  is optional; the same function may additionally or alternatively be performed by the attachment portion  48  of the second tether portion  42 .  
     [0057] If desired, the inflator attachment aperture  84  may be sized to perform the same function as the insertion passageway  34 . With such a configuration, the panels  24 ,  26  may be pushed through the inflator attachment aperture  84  to turn the cushion  20  inside out. The insertion passageway  84  may then be omitted entirely, and the outer edges  30  of the panels  24 ,  26  may initially be sewn together along their entire length.  
     [0058] The attachment portion  48  of the second tether portion  42  and the reinforcement disc  86  may be attached to the second panel  26 , around the inflator attachment aperture  84 , by sewing, one-piece weaving, RF welding, ultrasonic welding, chemical bonding, adhesive bonding, or any other suitable method known in the art. The attachment portion  48  and the reinforcement disc  86  may have apertures  88 ,  90 , respectively, with the same size and alignment as the inflator attachment aperture  84 , to permit passage of the projection  80 .  
     [0059] The elongated opening  72  is shown in phantom; as depicted, the elongated opening  72  may extend through the second panel  26  to permit insertion of the inflator  22  through the second panel  26 . The inflator insertion portion  70  may be configured in a large number of ways, and may be adapted to suit many different cushion designs. The inflator insertion portion  70  of FIGS. 1 and 2 will be shown and described in greater detail in FIG. 3; FIGS. 4 through 8 present several alternative inflator insertion portion configurations. The configurations presented are only examples; many additional embodiments may be implemented through the application of the principles of the present invention.  
     [0060] Referring to FIG. 3, a plan view illustrates the inflator insertion portion  70  of FIGS. 1 and 2. As mentioned previously, the inflator insertion portion  70  includes the elongated opening  72 , formed in the rear panel  26 , and the flap  74 , which is attached on three sides of the elongated opening  72  by the attachment lines  76 . The flap  74  may be constructed of a fabric material, such as that used to form the panels  24 ,  26 . The attachment lines  76  may thus take the form of stitching, welded interfaces, bonded interfaces, or the like. As shown in FIG. 3, the attachment lines  76  are formed by stitching.  
     [0061] In the alternative to the configuration shown, the attachment lines  76  may form a “V” shape rather than the “U” shape shown in FIG. 3, and still surround the elongated opening  72  on three sides. The attachment lines  76  also include curved shapes such as semicircles, partial ellipses, or the like. The attachment lines  76  also need not be open on the side furthest from the inflator attachment aperture  84 , but may instead be open on either lateral side. However, it may be beneficial to leave the side of the flap  74  nearest the inflator attachment aperture  84  affixed to the second panel  26  because inflation gas flowing from the inflator  22  may otherwise flow directly into the gap between the flap  74  and the second panel  26  during inflation.  
     [0062] The elongated opening  72  may have a central portion  98  with a comparatively small width  99 . Additionally, the elongated opening  72  may have a first end  100  and a second end  102  disposed on either side of the central portion  98 . The first and second ends  100 ,  102  may each have width equal to the central portion  98 , so that the entire elongated opening  72  has a substantially uniform width  99 .  
     [0063] The width  99  may be small enough that the central portion  98 , and indeed the entire elongated opening  72 , takes the form of a slit. A “slit” may be defined as an opening with a width small enough to be formed with a cutting motion that moves only one way, along the length of the opening. Hence, a circuitous incision, in which the end of the incision intersects the beginning, need not be made. Slits are, therefore, generally easier to form than openings with significant width.  
     [0064] A slit may not have a width of zero, because a flexible material may bend or contract around the edges of the cut. Hence, the central portion  98  may, for example, have a width of less than five millimeters when the cushion  20  is laid flat. Further, the central portion  98  may have a width of less than two millimeters. Yet further, if the fabric of the second panel  26  is somewhat inelastic, the central portion  98  may have a negligible width, so that opposite edges of the central portion  98  lie flush with each other when the cushion  20  is laid flat.  
     [0065] Thus, the elongated opening  72  may be formed relatively easily by slicing the second panel  26  with one single, linear motion. Of course, the elongated opening  72  need not be performed through a mechanical cutting operation. Lasers, reactive chemicals, or other devices that are able to form an incision may also be used.  
     [0066] The elongated opening  72  may have a length  104  selected to permit relatively easy passage of the inflator  22 . More specifically, the length  104  may be selected such that the perimeter of the elongated opening  72  is slightly larger than the largest cross section of the inflator  22  that must pass through the elongated opening  72 .  
     [0067] For example, with the short, cylindrical shape of the inflator  22  depicted in FIGS. 1 and 2, the inflator  22  may most easily pass through the elongated opening  72  if the flat faces on the top and bottom of the inflator  22  are oriented generally perpendicular to the second panel  26  during insertion. Thus, the elongated opening  72  should be slightly longer than the height of the inflator  22  plus the diameter of the inflator  22 . Some additional length may be needed to ensure that the elongated opening  72  is large enough to permit passage of the projection  80 .  
     [0068] Of course, other inflator shapes may be used, and the length of the elongated opening  72  may be similarly adapted to ensure that the elongated opening is able to open enough to receive the inflator. If desired, the length  104  may be further increased to permit an operator to grip the inflator  22  and insert the inflator  22  into the opening  72  without releasing the grip. The operator may then insert the inflator  22  through the second panel  26  and maneuver the inflator  22  into engagement with the inflator attachment aperture  84  with one continuous motion, without letting go of the inflator  22 .  
     [0069] In the embodiment shown, the length  104  may range from about 70 to about 200 millimeters. Furthermore, the length  104  may range from about 90 to about 150 millimeters. Yet further, the length  104  may be about 110 millimeters.  
     [0070] The flap  74  may be positioned and dimensioned in such a manner that the elongated opening  72  is fully covered by the flap  74 , with an overlap  106 . The overlap  106  may be selected such that the area of the pocket outside the first end  100  of the elongated opening  72  is large enough to form a substantially gastight seal. When the airbag module  10  deploys, the high pressure within the cushion  20  presses the flap  74  against the elongated opening  72 . The pressure tends to form a seal between the flap  74  and the second flap  26 ; the integrity of the seal is proportional to the pressure and the area of the fabric surfaces that are pressed against each other.  
     [0071] Hence, the overlap  106  can be lengthened to reduce the likelihood that gas will escape through the elongated opening  72  during deployment. Alternatively, the overlap  106  can be shortened to permit some gas to escape or to reduce the amount of material required to form the flap  74 . In the embodiment shown in FIG. 3, the overlap  106  may range from about five millimeters to about fifty millimeters. Further, the overlap  106  may range from about ten millimeters to about thirty-five millimeters. Yet further, the overlap  106  may be about twenty millimeters.  
     [0072] The flap  74  may generally be dimensioned such that the flap  74  is large enough to cover the elongated opening  72  and provide the overlap  106 , yet not large enough to waste significant material or add excessively to the weight or volume of the airbag module  10 . The flap  74  may have a width  108  sufficient to provide the desired amount of inflator maneuvering room within the pocket created by the flap  74 . According to one example, the width  108  may be about 160 millimeters. A height  109  of the flap  74  may also be about 160 millimeters.  
     [0073] As mentioned previously, the elongated opening  72  is nearly aligned with the radius  78  that extends outward from the inflator attachment aperture  84 , parallel to the elongated opening  72 . When the inflator  22  deploys, pressurized gas forces the cushion  20  to expand. Hence, the maximum tensile stress on the fabric of the cushion  20  is typically directed radially, i.e., along lines running from the inflator attachment aperture  84  to the outer edge  30 . Hence, at the inflator insertion portion  70 , the greatest tensile stress on the material of the second panel  26  runs generally parallel to the radius  78 .  
     [0074] Orienting the elongated opening  72  generally parallel to the radius  78  ensures that the greatest tensile stress on the elongated opening  72  does not tend to widen the opening, but rather tends to elongate the opening  72 . Hence, crack propagation is less likely to occur than if the elongated opening  72  were disposed at a different orientation. Orienting the elongated opening  72  perpendicular to the radius  78  would generally be the least favorable alternative because the maximum tensile stress would tend to directly widen the opening  72 , thereby causing tears to propagate through the second panel  26  from the ends of the elongated opening  72 .  
     [0075] The airbag module  10  may be relatively easily manufactured. According to one manufacturing method, the panels  24 ,  26  may first be formed, for example, by cutting circular shapes from a larger sheet of fabric. The elongated opening  72 , the holes  66  of the vents  60 , and the inflator attachment aperture  84  may then be formed in the second panel  26 , for example, by cutting the desired shapes in the fabric of the second panel  26  with a die, laser, or mechanized blade.  
     [0076] The flap  74  may then be affixed to the inflator insertion portion  70 , for example, by sewing the flap  74  in place to form the attachment lines  76 . Similarly, the attachment portions  48  of the first and second tether portions  40 ,  42  may be attached to the centers of the first and second panels  24 ,  26 , respectively. Again, sewing may be used to provide the attachment, although many alternative forms of attachment may also be used.  
     [0077] After the flap  74  and the first and second tether portions  40 ,  42  have been attached to the panels  24 ,  26 , the panels  24 ,  26  may be aligned with each other, back-to-back (i.e., with the outer surfaces facing each other). The panels  24 ,  26  may then be attached together at the outer edges  30 . Sewing may be used to form the seam  79 . The seam  79  may extend around all but a small length of the outer edges  30  to leave the insertion passageway  34  open.  
     [0078] The attachment flaps  44  of the tether portions  40 ,  42  may be aligned with each other and attached together, for example, by sewing. The panels  24 ,  26  may then be pushed through the insertion passageway  34 , together with the flap  74  and the attached tether  38 , to turn the cushion  20  inside-out. The edges  30  of the cushion panels  24 ,  26  then obtain the inward orientation depicted in FIG. 2. The insertion passageway  34  may then be closed, for example, through sewing to form the seam  36 , thereby ensuring that significant quantities of gas are unable to escape the cushion  20  through the insertion passageway  34  during deployment.  
     [0079] After the cushion  20  has been fully formed, in the manner described above, the inflator  22  may be inserted into the cushion  20 . More specifically, as described previously, the inflator  22  may be inserted through the elongated opening  72 , into the pocket created by attachment of the flap  74  to the second panel  26 . The inflator  22  may then be moved toward the outer edge  30  to remove the inflator  22  from the pocket so that the inflator  22  can be freely moved within the interior of the cushion  20 .  
     [0080] The inflator  22  may then be maneuvered to the center of the second panel  26 , so that the projection  80  is aligned with the inflator attachment aperture  84 . The inflator  22  may then be moved toward the second panel  26  so that the projection  80  extends through the aperture  88  of the attachment portion  48  of the second tether portion  42 , the aperture  90  of the reinforcement disc  86 , if used, and the inflator attachment aperture  84  of the second panel  26 .  
     [0081] Once the projection  80  has been fully inserted, the anchoring arms  82  may extend outward to fix the position of the projection  80  relative to the inflator attachment aperture  84 , thereby keeping the inflator  22  properly positioned within the cushion  20 . The cushion  20  may then be folded around the inflator  22  to form a compact module that is ready for rapid installation in a vehicle.  
     [0082] The elongated opening  72  may also be used to facilitate insertion of other internal components of the cushion  20 , such as heat shields, module attachment features, and the like. The configuration of the elongated opening  72 , and of the inflator insertion portion  70  in general, may be adjusted to enable convenient passage of such components.  
     [0083] Of course, the manufacturing method described above is only one of many possible methods that may be used to form the airbag module  10 . Furthermore, the system and method of the present invention may be used with a wide variety of cushion types. In addition to front impact airbags, side impact airbags, or “inflatable curtains,” knee bolsters, and overhead airbags may incorporate an inflator insertion portion designed to permit installation of an inflator within the cushion after the cushion has been substantially assembled. Such inflator insertion portions may be configured in a manner similar to the inflator insertion portion  70  described above, or like the inflator insertion portions that will be shown and described in connection with FIGS. 4 through 8.  
     [0084] Referring to FIG. 4, a plan view illustrates an alternative embodiment of an inflator insertion portion  110 . The inflator insertion portion  110  may be used with a cushion similar to the cushion  20  of FIGS. 1 and 2, or with a wide variety of other cushion types, as mentioned previously. For the sake of description, FIGS. 4 through 8 assume that a cushion like the cushion  20  of FIGS. 1 and 2 is used.  
     [0085] The inflator insertion portion  110  may have an elongated opening  112  oriented at some angle with respect to the radius  78 . The angle may be non-parallel, yet non-perpendicular to the radius  78 . Hence, the elongated opening  112  may be oriented in a direction that is neither the most nor the least effective for resisting tear propagation.  
     [0086] The angle of the elongated opening  112  may facilitate insertion of the inflator  22  by simplifying the insertion pathway. More specifically, the insertion pathway  77  of the previous embodiment requires motion of the inflator  22  perpendicular to the radius  78  to enter the elongated opening  72 , and then parallel to the radius  78  to remove the inflator  22  from the pocket created by the flap  74 . The insertion pathway of the elongated opening  112  has no right angle, and therefore provides for insertion and anchoring of the inflator  22  with a more continuous motion.  
     [0087] A flap  114  may be attached to the second panel  26  via attachment lines  116  to cover the elongated opening  112 . Like the flap  74 , the flap  114  may be formed from a piece of fabric material. The elongated opening  112  may have a central portion  118  with a width  119  narrow enough to form a slit, like the central portion  98  of the previous embodiment.  
     [0088] However, the elongated opening  112  may also have a first end  120  with a width  121  somewhat larger than the width  119 , and a second end  122  with a width  123  approximately equal to the width  121  of the first end  120 . The first and second ends  120 ,  122  may each have a generally circular configuration so that the widths  121 ,  123  are diameters of the circles. The enlargement of the first and second ends  120 ,  122  facilitates spreading of the elongated opening  112  for insertion of the inflator  22  and restricts tear propagation from the first and second ends  120 ,  122 .  
     [0089] More specifically, cracks, tears, or narrow openings tend to spread more easily under stress when their tips are comparatively sharp, because the sharpened tip is a location at which stresses gather to continually cause further tearing. The circular shape of the first and second ends  120 ,  122  spreads the tensile stresses to substantially prevent tear propagation from the first and second ends  120 ,  122 .  
     [0090] Of course, the widths  121 ,  123  of the first and second ends  120 ,  122  need not be equal. Rather, the widths  121 ,  123  may be made different to provide different manufacturing or tear resistance characteristics.  
     [0091] The elongated opening  112  may have a length  124  selected to permit passage of the inflator  22  through the elongated opening  112 . As with the previous embodiment, the length  124  may be selected such that the circumference of the elongated opening  112  is larger than that of the largest cross section of the inflator  22  that must pass through the opening  112 . Like the elongated opening  72  of the previous embodiment, the length  124  of the elongated opening  112  may be about  110  millimeters.  
     [0092] The flap  114  may be positioned to fully cover the elongated opening  112 , with an offset  126  large enough to substantially seal the elongated opening  112  against the escape of pressurized gas during inflation. As with the previous embodiment, the offset  126  may be about twenty millimeters. The flap  114  may also have a width  128  and a height  129  that are selected such that the pocket created by the flap  114  and the second panel  26  is large enough to avoid obstructing the insertion pathway of the inflator  22 . According to one example, the width  128  may be about 180 millimeters, and the height may be about 130 millimeters.  
     [0093] Referring to FIG. 5, a plan view illustrates another alternative embodiment of an inflator insertion portion  130  according to the present invention. The inflator insertion portion  130  may have an elongated opening  132  that performs a dual function. More specifically, the elongated opening  132  may be only partially covered by a flap  134  attached to the second panel  26  by attachment lines  136 . Hence, the elongated opening  132  may permit passage of the inflator  22  into the cushion  20 , and may also serve as a vent for the cushion  20 .  
     [0094] The elongated opening  132  may have a central portion  138  with a width  139  small enough to form a slit. Additionally, the elongated opening  132  may have a first end  140  with a width  141  large enough to not only restrain tear propagation, but also to enable the first end  140  to serve as a vent. The first end  140  may also have a substantially circular shape to provide effective venting. The first end  140  may be entirely outside the flap  134  so that the flap  134  will not interfere with venting of inflation gas through the first end  140 . A second end  142  may be disposed underneath the flap  134 , and may be narrow enough to form a slit, like the central portion  138 .  
     [0095] The venting capability of the first end  140  may enable the vents  60  to be omitted entirely. Hence, the width  141  of the first end  140  may be sufficient to provide an airflow area approximately equal to the combined flow areas of the holes  66  of the vents. For example, the width  141  may be about forty millimeters. Thus, the first end  140  may provide a flow area of about 1250 square millimeters, while each hole  66  of the vents  60  has a diameter of about thirty millimeters, for a combined flow area of about 1400 square millimeters.  
     [0096] The elongated opening  132  may have a length  144  sufficient to permit passage of the inflator  22  through the elongated opening  132 . As with the previous embodiment, the length  144  may be about 110 millimeters. Due to the fact that the elongated opening  132  is not fully covered by the flap  134 , no overlap may be present. Rather, the elongated opening  132  has an offset  146  equivalent to the length of the elongated opening  132  that protrudes from underneath the flap  134 .  
     [0097] As shown, only the circular shape of the first end  140  protrudes from underneath the flap  134 . Hence, the offset  146  may be approximately equal to the width  141  of the first end  140 . However, in alternative embodiment, the flap  134  may cover more or less than the circular shape of the first end  140 ; hence, the offset  146  may not be the same as the width  141 .  
     [0098] As with the elongated opening  72  of FIG. 3, the elongated opening  132  may be disposed generally along the radius  78  for enhanced tear propagation resistance. The elongated opening  132  may alternatively have an orientation non-parallel to the radius  78 , like that of the elongated opening  112  of FIG. 4. The inflator  22  may be inserted through the inflator insertion portion  130  in much the same manner as with the inflator insertion portion  70 . The flap  134  may have a width  148  that provides the desired amount of inflator maneuvering room within the pocket created by attachment of the flap  134  to the second panel  26 . Additionally, the flap  134  may have a height  149  selected to provide the desired degree of coverage of the elongated opening  132 . The width  148  may be about 160 millimeters, while the height  149  may be about 100 millimeters.  
     [0099] Referring to FIG. 6, a plan view illustrates another embodiment of an inflator insertion portion  150  that may be used for the cushion  20 , or for an airbag cushion with a different configuration. The inflator insertion portion  150  may have an elongated opening  152 . Like the elongated opening  132 , the elongated opening  152  provides venting in addition to inflator installation capability. The elongated opening  152  may be partially covered by a flap  154 , which is attached to the second panel  26  by attachment lines  156 .  
     [0100] The elongated opening  152  may have a central portion  158  disposed underneath the flap  154 . The central portion  158  may have a width  159  small enough to form a slit. Furthermore, the elongated opening  152  may have a first end  160  with a width  161 , and a second end  162  with a width  163 . Each of the first and second ends  160 ,  162  may have a generally circular shape, and each may be disposed outside the flap  154 .  
     [0101] The first and second ends  160 ,  162  may cooperate to provide airflow area for venting. Thus, like the first end  140  of the previous embodiment, the first and second ends  160 ,  162  may effectively replace the vents  60 . In order to provide about the same airflow area as the vents  60 , the first and second ends  160 ,  162  may each be sized about the same as the holes  66  of the vents  60 , i.e., about thirty millimeters in diameter. Thus, the widths  161 ,  163  may each be about thirty millimeters.  
     [0102] The elongated opening  152  may have a length  164  that is somewhat greater than those of the previously disclosed elongated openings  72 ,  112 ,  132 . More particularly, the central portion  158  intersects the attachment lines  156  of the flap  154 . Hence, the entire length  164  of the elongated opening  152  may not be able to open to receive the inflator  22 . Rather, only an insertion length  165 , disposed between the attachment lines  156  that intersect the central portion  158 , may be available for inflator insertion.  
     [0103] Hence, the insertion length  165  may be long enough to receive the inflator  22 , and may thus be about 110 millimeters in length. The length  164  of the entire elongated opening  152  may include the insertion length  165  as well as the widths  161 ,  163  of the first and second ends  160 ,  162 . Hence, the length  164  of the elongated opening  152  may be about 190 millimeters.  
     [0104] The first and second ends  160 ,  162  may protrude from underneath the flap  154  by offsets  166 ,  167 , respectively, that are generally equal to the widths  161 ,  163  of the first and second ends  160 ,  162 . Of course, somewhat larger or smaller offsets  166 ,  167  may be used if the first and second ends  160 ,  162  are to be partially covered, or if the central portion  158  is to be partially exposed.  
     [0105] The inflator  22  may be inserted through the central portion  158  of the elongated opening  152  and moved out of the pocket created by the flap  154  and the second panel  26  with one continuous motion. The inflator  22  may then be moved into alignment with the inflator attachment aperture  84  and anchored in place. The flap  154  may have a width  168  sufficient to substantially seal the central portion  158  during deployment of the cushion  20 ; the width  168  may be about eighty millimeters. The flap  154  may also have a height  169  slightly larger than the insertion length  165 ; the height  169  may be about 130 millimeters.  
     [0106] Referring to FIG. 7, a plan view depicts another alternative embodiment of an inflator insertion portion  170  according to the present invention. As with the previous two embodiments, the inflator insertion portion  170  may have an elongated opening  172  that provides for passage of the inflator  22  into the cushion  20  as well as airflow area for venting. However, the elongated opening  172  may not be covered by any type of flap. Rather, the elongated opening  172 , in its entirety, may serve as a vent.  
     [0107] The elongated opening  172  may have a central portion  178  with a width  179  narrow enough to form a slit. The elongated opening  172  may have a first end  180  with a width  181  and a second end  182  with a width  183 . The widths  181 ,  183  of the first and second ends  180 ,  182  may be somewhat larger than the width  179  of the central portion  178 .  
     [0108] More specifically, the first and second ends  180 ,  182  may each have a circular shape large enough to provide venting. For example, as with the previous embodiment, the widths  181 ,  183  may each be approximately equal to the diameter of each hole  66  of the vents  60 , so that the first and second ends  180 ,  182  are able to replace the vents  60 . Hence, each of the widths  181 ,  183  may be about thirty millimeters.  
     [0109] The central portion  178  may also be expected to open somewhat during deployment to release gas. If desired, the widths  181 ,  183  may be decreased to compensate for the increased airflow area provided by opening of the central portion  178 . The narrow width  179  of the central portion  178  may restrict gas flow through the central portion  178  enough to make a cover flap unnecessary.  
     [0110] The elongated opening  172  may have a length  184  large enough to permit passage of the inflator  22  through the elongated opening  172 . Hence, as with some of the previous embodiments, the elongated opening  172  may be about 110 millimeters. As shown, the elongated opening  172  may be oriented generally perpendicular to the radius  78 . Although such an orientation is not generally favorable for tear propagation from the first and second ends  180 ,  182 , the large widths  181 ,  183  of the first and second ends  180 ,  182  serve as deterrents to tear propagation. Hence, the elongated opening  172  may not pose a significant risk of damage to the cushion  20 , despite its orientation perpendicular to the radius  78 . Of course, the orientation of the elongated opening  172  may be altered so that the elongated opening  172  is parallel to the radius  78  or disposed at some other non-perpendicular, non-parallel angle, like that of the elongated opening  112  of FIG. 4.  
     [0111] The insertion pathway (not shown) of the inflator  22  may be simplified for the inflator insertion portion  170  of FIG. 7. More specifically, the inflator  22  may be inserted through the elongated opening  172  and moved into alignment with the inflator attachment aperture  84  with one single, generally linear motion. Since no flap is used, the inflator  22  need not be moved out from any pocket within the cushion  20 . Hence, installation of the inflator  22  may be facilitated by the configuration of the inflator insertion portion  170 .  
     [0112] Referring to FIG. 8, a plan view shows still another embodiment of an inflator insertion portion  190  according to the invention. As with the previous three embodiments, the inflator insertion portion  190  may have an elongated opening  192  that serves two purposes. The elongated opening  192  may permit passage of the inflator  22  into the cushion  20  and to vent measured quantities of pressurized gas from the cushion  20  during deployment and/or impact of the vehicle occupant against the cushion  20 .  
     [0113] As shown, the elongated opening  192  may have a central portion  198  with a small width  199 , so that the central portion  198  comprises a slit. The elongated opening  192  may also have a first end  200  with a width  201  and a second end  202  with a width  203 . The widths  201 ,  203  of the first and second ends  200 ,  202  may be larger than the width  199  of the central portion  198 . More specifically, the widths  201 ,  203  may be large enough to restrict tear propagation from the first and second ends  200 ,  202 , but not large enough to provide sufficient airflow area for venting through the first and second ends  200 ,  202 . For example, the widths  201 ,  203  may each be about five to ten millimeters.  
     [0114] Rather, the majority of the venting may occur through the central portion  198 , which may open significantly during deployment of the cushion  20 . The elongated opening  192  may have a length  204  sufficient to receive the inflator  22 ; as with several of the previous embodiments, the length  204  may be about 110 millimeters. The central portion  192  may include most of the length  204 , and may thus open significantly in response to the pressure increase within the cushion  20  to release gas.  
     [0115] The central portion  192  may be structured such that, under the pressure within the cushion  20 , the central portion  192  opens to provide approximately the same airflow area as the vents  60 . Hence, the elongated opening  192  may be used in place of the vents  60 . Of course, the elongated opening  192  also receives the inflator  22 . More specifically, the inflator  22  may be inserted through the elongated opening  192  in a direction generally perpendicular to the radius  78 , and then moved generally along the radius  78 , into alignment with the inflator attachment aperture  84 . Again, the absence of a flap simplifies the insertion pathway for the inflator  22 .  
     [0116] The elongated opening  192  is oriented generally along the radius  78  to reduce the possibility of tear propagation from the first and second ends  200 ,  202 . Additionally, despite their small size by comparison with some of the previous embodiments, the generally circular shape of the first and second ends  200 ,  202  also provides a deterrent against tear propagation. Furthermore, if desired, first and second reinforcement seams  206 ,  208  may be disposed to partially encircle each of the first and second ends  200 ,  202 , respectively. More particularly, the reinforcement seams  206 ,  208  may hold the material outside the first and second ends  200 ,  202  together, so that the reinforcement seams  206 ,  208  serve as boundaries beyond which tears are unable to propagate. The reinforcement seams  206 ,  208  may simply be stitched into place.  
     [0117] Of course, the inflator insertion portions  70 ,  110 ,  130 ,  150 ,  170 ,  190  of FIGS. 3 through 8 are simply examples. The inflator design and module requirements may necessitate additional changes to the embodiments shown. Many other inflator insertion portions may be created within the scope of the present invention by combining, isolating, or otherwise modifying the features depicted in the figures.  
     [0118] The airbag modules and associated methods of the present invention present significant improvements in airbag design. Through the use of elongated openings, inflators may be inserted into the airbag cushion after the cushion has been substantially assembled. The elongated opening shapes and/or flap configurations enable the cushions of the present invention to provide reliable sealing and venting of inflation gases. Through the use of radial orientation and/or enlarged opening ends, the probability of tear propagation through the cushion may be minimized.  
     [0119] The present invention may be embodied in other specific forms without departing from its structures, methods, or other essential characteristics as broadly described herein and claimed hereinafter. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.  
     [0120] What is claimed and desired to be secured by United States Letters Patent is: