Abstract:
An airbag module for protecting the knees of an occupant of a vehicle includes an airbag formed by at least one panel of material, an inflator that produces gas that inflates the airbag into a deployed condition, a tether connected to the airbag for restraining upward movement of the airbag when the airbag begins to deploy, and a housing. Prior to deployment, the airbag is compacted in the storage condition. In the storage condition, the airbag includes a rolled portion and a folded portion, where the folded portion includes a half Z-shape fold.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application is a continuation of application Ser. No. 12/289,710 filed on Oct. 31, 2008, which is now patented as U.S. Pat. No. 8,096,578, and also claims priority to and the benefit of Provisional Application No. 60/996,148, filed on Nov. 2, 2007. Both of the foregoing applications are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     The present disclosure relates generally to the field of vehicle airbags. More particularly, the present disclosure relates to the field of knee airbags with improved deployment. 
     Airbags are provided in vehicles to protect occupants from injury in the event of a vehicle crash. Knee airbags in particular can help prevent injury to an occupant&#39;s legs by preventing the legs from hitting the dash or an instrument panel in the event of a crash. 
     SUMMARY 
     One exemplary embodiment provides a knee airbag apparatus. The knee airbag apparatus comprises a front panel configured to face toward an occupant when the knee airbag deploys, and a rear panel configured to face toward an instrument panel when the knee airbag deploys. The rear panel is joined to the front panel to form an inflatable knee cushion configured to inflate to protect an occupant&#39;s knees during a crash event. The knee airbag apparatus includes a first internal tether extending between the front and rear panels. The first internal tether is attached to the front panel at a front panel attachment location offset from a rear panel attachment location. 
     Another exemplary embodiment provides method of forming a knee airbag. The method comprises: joining a front panel to a rear panel to form a knee cushion; laying the knee cushion flat such that the rear panel is on top of the front panel; and folding the knee cushion. Folding of the knee cushion includes rolling the knee cushion beginning at a top end of the knee cushion toward a bottom end of the knee cushion with a mounting bracket. After rolling the knee cushion toward the bottom end, the knee cushion is folded back towards the front end in a Z-type fold. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below. 
         FIG. 1  is a perspective view of the interior of a vehicle illustrating a location of a knee airbag assembly according to an exemplary embodiment. 
         FIG. 2  is a side view of a vehicle interior showing a knee airbag in a stowed configuration and a trajectory of the knee airbag according to an exemplary embodiment. 
         FIG. 3  is a side view of a vehicle interior showing a deploying knee airbag illustrating the external tether before the tether ruptures according to an exemplary embodiment. 
         FIG. 4  is a side view of a vehicle interior showing a deployed knee airbag illustrating the relationship between chamber and the cushion/housing according to an exemplary embodiment. 
         FIG. 5  is a front view of a flattened, uninflated knee airbag cushion illustrating a trapezoidal shaped external tether according to an exemplary embodiment. 
         FIG. 6  is a front view of a flattened, uninflated knee airbag cushion illustrating the trapezoidal shaped external tether wrapped around the airbag cushion and coupled to a housing according to an exemplary embodiment. 
         FIG. 7A  is a side view of a partially assembled knee airbag cushion illustrating internal tethers according to an exemplary embodiment. 
         FIG. 7B  is a side view of a knee airbag cushion including a plurality of offset internal tethers according to an exemplary embodiment. 
         FIG. 7C  is a side view of a known knee airbag cushion including a plurality of parallel tethers according to prior art. 
         FIG. 8  is a side view of a process for the folding of a knee airbag according to an exemplary embodiment. 
         FIGS. 9A-9F  are front views of an external tether for a knee airbag according to other exemplary embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Airbags may be provided in a vehicle to protect the occupants of the vehicle in a collision. The airbags generally comprise a fabric bag or cushion that is inflated with gas from a gas generator (e.g., a pyrotechnic gas generator). The airbags are often stored out of sight, such as behind trim pieces, and are inflated to occupy the space between an occupant of the vehicle and a structure that may injure the occupant in a collision (e.g., a steering wheel, the vehicle dash, instrument panel, doors, windows, etc.) 
     Knee airbags are provided in vehicles to help prevent an occupant&#39;s legs from hitting a dash or instrument panel in the event of a vehicle collision. However, the force of a still-inflating airbag may injure the occupant, especially in an out-of-position (OOP) situation, such as if the occupant is not wearing a safety belt and is too close to the dash when the airbag deploys. In order to decrease possible injury to an occupant&#39;s legs occurring from the force of the deploying airbag, it is desirable to minimize the interaction between a deploying airbag cushion and occupants&#39; legs. In an embodiment, the trajectory of the airbag is in a generally vertical direction. With the vertical trajectory, the airbag deploys upward, following the instrument panel surface, rather than toward the occupant&#39;s legs, thus decreasing the interaction between the deploying airbag cushion and the occupant&#39;s legs. 
     Referring to  FIG. 1 , the location of a knee airbag assembly  20  in the interior of a vehicle  10  is shown according to an exemplary embodiment. The airbag assembly  20  is stored and concealed in a housing  12  (e.g., recess, socket, compartment, etc.) in a dash panel  14 . According to one exemplary embodiment, the dash panel  14  may be below an instrument panel (e.g., for a driver&#39;s side knee airbag assembly). Thus, the knee airbag assembly  20  may be a driver or passenger side airbag assembly. 
     Referring now to  FIGS. 2-4 , the knee airbag assembly  20  is shown according to an exemplary embodiment. The knee airbag assembly  20  includes an airbag cushion  30 , that remains folded in the housing  12  awaiting deployment, and an inflator  22  to inflate the airbag cushion  30  once a collision is sensed. The inflator  22  is, for example, a conventional pyrotechnic gas generator, or any other suitable type of inflator. The inflator  22  is coupled to the airbag cushion  30  with a diffuser bracket  24 . When a collision is detected, the inflator  22  generates a gas that fills the airbag cushion  30 . As the airbag cushion  30  is filled, the cushion  30  expands to deploy out of the housing  12  and between the occupant  16  and the vehicle dash panel  14 . 
     Referring to  FIGS. 5-6 , a knee airbag cushion  30  is shown in more detail according to an exemplary embodiment. The cushion  30  is formed from several panels of a fabric such as nylon that are sewn together. Airbag cushions such as cushion  30  are generally formed with at least a front panel  32  and a rear panel  34  that are coupled together at a first seam  33  that extends generally around the periphery of the cushion  30 . When the airbag cushion  30  is deployed, the rear panel  34  is proximate to the dash panel  14  with the front panel  32  remote from the dash panel  14 , proximate to the occupant  16 . An opening in the cushion  30  is aligned with the inflator  22 . A portion of the inflator  22  extends through an opening  36  in the rear panel  34  so that gas generated by the inflator  22  can enter the cushion  30 . The cushion  30  is trapped between the inflator  22  and the bracket  24 . The bracket  24  extends through openings  38  in the rear panel  34  and is coupled to the inflator  22  to hold the cushion  30  in place. 
     The cushion  30  further includes an external tether  40  to help control the trajectory of airbag cushion  30  during deployment. More specifically, the tether  40  is configured to direct the airbag cushion  30  to deploy in a generally vertical direction, along the dash panel  14  rather than in a horizontal direction, towards the legs of the occupant  16 . The tether  40  may be formed from the same material as the front panel  32  and the rear panel  34  such as a nylon fabric, or any other suitable type of material. 
     The external tether  40  is coupled to at least one of the front panel  32  or the rear panel. The tether  40  is releasably coupled to cushion  30  such that it may rip or tear away from the cushion  30  during the deployment of the cushion  30 . This releasable coupling is provided along a relatively wide area so that the external tether  40  may more effectively compensate for lateral (e.g., left, right, center) variations in deployment speed of the cushion  30 . 
     In an exemplary embodiment, the external tether  40  is a trapezoidal fabric panel with a wide end  42  and a narrow end  46 . The narrow end  46  may have one or more openings  48  that are similar to the openings  36  and  38  in the rear panel  34 . The openings  48  are aligned with the openings  36  and  38  in the rear panel  34  such that the narrow end  46  of the external tether  40  may be trapped between the inflator  22  and the bracket  24  along with the rear panel  34  to hold the external tether  40  in place (e.g., generally coupled to the inflator  22  and the bracket  24 ). The wide end  42  of the external tether  40  is coupled to the front panel  32 . According to an exemplary embodiment, the wide end  42  is stitched to the front panel  32  at a second seam  43 . The wide end  42  is first sewn to the cushion  30  and then the external tether  40  is wrapped around the cushion  30  so that the narrow end  46  may be coupled to the bracket  24 , a fixed part of the knee cushion  30  near the housing, or the housing itself. 
     When wrapped around the cushion  30 , the external tether  40  constrains the cushion  30  so that it may not fully inflate (see  FIG. 3 ). The constraining of the cushion during deployment causes it to first deploy in a lateral direction (e.g., out to the side) and facilitates the deployment of the cushion  30  along a generally vertical trajectory. A multitude of frangible regions or break points  44  are provided proximate to the second seam  43  along which the external tether  40  may be torn or otherwise ruptured to allow the cushion  30  to fully deploy. While the external tether  40  is shown with three break points  44  in  FIGS. 5 and 6 , according to other exemplary embodiments, the external tether  50  may include more or fewer break points  44 . 
     According to an exemplary embodiment, as shown in  FIGS. 5 ,  6 , and  9 B, the break points  44  are provided in the form of narrow frangible portions. According to other exemplary embodiments, the break points  44  may be other structures (i.e., tear tabs, detachable stitches, etc.). By being located proximate to the wide end  42 , the break points  44  are arranged over a wide range of areas. The gas generated by the inflator  22  may apply an uneven outward force on the cushion  30  causing an uneven deployment speed across the width of the cushion. The break points  44  can have a determined strength pre-set to control deployment trajectory of cushion  30  and balance the left-center-right speed of cushion  30 . 
     Referring to  FIGS. 9A-9F , external tethers  40  are shown according to several exemplary embodiments. For example, the break points  44  may be formed by narrow portions of the tether  40  formed by large openings (see  FIG. 9C ) or may be narrow portions of the tether  40  that connect the main body of the tether  40  to tabs that are coupled to the airbag cushion at seams  43 . 
     According to other exemplary embodiments, the break points  44  may be provided in the form of frangible seams  47  (see  FIGS. 9A ,  9 D, and  9 F) that are configured to couple the tether  40  to the airbag cushion  30  and tear or burst during the deployment of the airbag cushion  30 . The frangible seams  47  may be several discreet stitches provided along the wide end  42  of the tether  40  or may be a continuous stitch provided along the wide end  42  of the tether  40 . 
     According to another exemplary embodiment, the external tether  40  may comprise one or more generally narrow strips that are coupled on a first end  46  to the bracket  24  and on a second end  42  to the airbag cushion  30  (see  FIG. 9F ). The second end  42  may be coupled to the airbag cushion at a fixed seam  43  and include break points  44  or may be coupled to the airbag cushion  30  with at frangible seam  47 . 
     Referring now to  FIGS. 7A and 7B , according to another exemplary embodiment, an airbag cushion  30  may include one or more internal tethers  50  to help control the trajectory of airbag cushion  30  during deployment. More specifically, the tethers  50  are configured to direct the airbag cushion  30  to deploy in a generally vertical direction, along the dash panel  14  rather than in a horizontal direction, towards the legs of the occupant  16 . 
     The tethers  50  may be formed from the same material as the front panel  32  and the rear panel  34  such as a nylon fabric. 
     Internal tethers  50  are shifted between front and rear panel to pull the cushion  30  upward against the dash panel  14  surface, improving deployment trajectory and reducing the interaction of the cushion with the occupant&#39;s legs. The distance between the point at which the internal tethers  50  are coupled to the rear panel  34  and the bracket  24  is less than the distance between the point at which the internal tethers  50  are coupled to the front panel  32  and the bracket  24  such that the tethers  50  form an acute angle (θ) with the rear panel  34 . The angle (θ) is determined by the length of the internal tether  50  and the offset between the points at which the internal tether  50  is coupled to the rear panel  34  and the front panel  32 . The difference in distance of each end of the tethers  50  to the bracket  24  urges the rear panel  34  to contract and be pulled upward. This pulling force helps to control the trajectory of the airbag cushion  30 . According to an exemplary embodiment, at least one of the internal tethers  50  has an offset in a range of approximately 15 to 60 mm; or more specifically in a range of 20 to 50 mm, or more specifically of approximately 40 mm. For example, a distance from a bottom seam  33  to the first tether  50  in the first panel  32  is about 40 mm different from a distance from a bottom seam  33  to the first tether  50  on the rear panel  34 . According to an exemplary embodiment, the angle (θ) formed between the internal tethers  50  and the rear panel  34  is between five to 85 degrees, or in a range of 9 to 85 degrees, or more specifically in a range of 9 degrees to 81 degrees. According to a preferred embodiment, the angle (Θ) formed between the internal tethers  50  and the rear panel  34  is between 35 degrees and 80 degrees. 
     The internal tethers  50  and the geometry of the cushion  30  are configured to facilitate the generally vertical deployment of the knee airbag cushion  30  along the surface of the dash panel  14 . An upward cushion  30  along the dash panel  14  rather than towards the occupant&#39;s legs provides decreased interaction between the airbag cushion  30  and the occupant&#39;s legs. 
     As shown in  FIG. 4 , the distance  60  from the center line of the bracket  24  to the seam  33  between the front panel  32  and the rear panel  34  is greater than the distance  62  between the center line of the bracket  24  and the lower edge  13  of the housing  12 . The cushion  30  bears against the lower edge  13  of the housing  12 , which adds support to the cushion  30  and helps to support it in a generally vertical orientation (e.g., along the surface of the dash panel  14 ). 
     As shown best in  FIG. 7A and 7B , the front panel  32  extends longer than the rear panel  34  during inflation. The difference in extended lengths urges the cushion  30  to curve convexly outward (e.g., toward the occupant  16 ) and more closely follow the contour of the dash panel  14 . The offset internal tethers  50  allow the front panel  32  to extend farther upward such that the cushion  30  inflates upward and follows the dash panel  14  as opposed to extending more toward an occupant. The panels  32 ,  34  can have the same length prior to inflation or different lengths. However, the offset tethers  50  (in conjunction with the external tether  40 ) is what creates the inflation shape of the knee airbag cushion  30 .  FIG. 7C  illustrates a conventional knee airbag that includes parallel internal tethers (no offset angle, or offset angle is equal to 90 degrees). 
     Referring now to  FIG. 8 , a method of folding the knee airbag cushion  30  is shown. The airbag cushion  30  is folded to better control trajectory and deployment of the cushion  30 . The cushion is laid out flat in uninflated state with the rear panel  34  facing upward and the wide end  42  an external tether  40  coupled to the front panel  34 . The sides of the knee cushion  30  may be tucked into the cushion to reduce the width of the cushion  30 . 
     The end of the cushion  30  remote from the bracket  24  (e.g., the top of the cushion  30 ) are then folded back on itself a number of times. According to an exemplary embodiment, the cushion  30  is folded back five times. According to other exemplary embodiments, the cushion  30  may be folded back more or fewer times, for example, depending on the length of the cushion  30  and the desired size of the stowed cushion  30 . The narrow end  46  of the external tether  40  is then coupled to the bracket  24 . The final fold of the cushion  30  and the tether  40  is a half fold in the opposite direction (e.g., a half “Z” fold). Additional “Z” folds may be used. When the cushion  30  and the tether  40  are folded, they are held in the housing  12  proximate to the inflator  22 , with the bracket  24  coupled to the inflator  22 . 
     It should be recognized that the front and rear panels may be formed of one single sheet that is folded over and sewn together to from the knee cushion. Alternatively, the knee cushion  30  may be formed from any suitable number of sheets (panels). 
     It is important to note that the construction and arrangement of the attachment method of an airbag inflator to an airbag module housing as shown in the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the description. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of the elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments.