Abstract:
An airbag housing having elastically deflectable mounting tabs is disclosed. The mounting tabs allow for positionable attachment of an airbag module to a vehicle structural member. The mounting tabs may be defined by U-shaped slots in the airbag housing. The semi-flexible mounting tabs deflect during attachment of the airbag module to the steering wheel to provide good fit and finish between an associated decorative airbag cover and the steering wheel. The mounting tabs may also include attachment members to provide attachment location for coupling the airbag housing to the vehicle structural member.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to airbag modules. More specifically, the present invention relates to a system of deflectable mounting tabs located on an airbag housing to provide good fit and finish between a decorative airbag cover and a vehicle steering wheel. 
   2. Description of Related Art 
   Throughout recent decades, airbags have proven to be an effective tool in preventing death and injuries caused by vehicle collisions. In order to provide increased protection for vehicle occupants, airbag modules are currently being employed in multiple locations within a vehicle. Often, airbag modules are placed in highly visible locations of the vehicle, such as the steering wheel or instrument panel. If a highly visible airbag module is not attached properly, the airbag module may have a poor appearance. Attachment problems can result in airbag modules having gaps at their perimeters or not having a flush alignment with adjacent components. 
   One cause of attachment problems within airbag modules is selecting an appropriate tolerance range for the airbag module components. Generally, airbag module components, as with most components, must balance between tight tolerances and low cost. Tight tolerances are desirable because the attachment fit and size of multiple components are controlled. Tight tolerances also prevent attachable parts from being too large or too small to properly couple corresponding parts. However, obtaining tight tolerances is often very expensive because of the machinery, tools, and materials needed to obtain such tolerances. 
   While tight tolerances are desirable, processes that are not capable of tight tolerances are commonly employed because of their low cost and short manufacturing time. Processes such as injection molding and metal stamping allow complex components to be manufactured with minimal time and material, resulting in a low cost component. Yet, these processes are not always capable of maintaining tight tolerances. While the inexpensive processes may not have tight tolerances, the tolerances are often within a range that does not cause any attachment or appearance problems. 
   However, if multiple components having loose tolerances are attached together, the loose tolerances of the individual components may combine to create a product that is out of the overall tolerance range of the part. For example, an airbag module may include an airbag housing made through a stamping process, an airbag cover, and airbag fasteners made by an injection molding processes. Typically, any one of these components may have an acceptable tolerance range. But when all three components are attached together, the overall airbag module may exceed acceptable tolerance ranges. This is known as tolerance stacking. 
   Tolerance stacking occurs when two or more components are attached to one another where both components are near the extreme allowable tolerances. For example, an airbag housing may have a height of 5 cm±0.2 cm and a airbag cover may have a height of 8 cm±0.3 cm. If both the airbag housing and the airbag cover are at their largest allowable tolerances, the assembled airbag module has a height of 13.5 cm. If both the airbag housing and the airbag cover are at the lowest allowable tolerances, the assembled airbag has a height of 12.5 cm. The difference between the largest and smallest assembled airbag modules is ±0.5 cm. Thus, the tolerances of two objects may have a tolerance range that is outside the allowable range of any one of the individual components. 
   In an airbag module, the airbag cover is generally attached to the airbag housing, creating the potential for tolerance stacking between the two components. Additionally, the airbag housing may be attached to a vehicle structural member through injection molded fasteners, possibly creating additional tolerance stacking. If all three of the components are at their high end of allowable tolerances, the airbag module may extend above adjacent components and may also have a gap around its perimeter. If all three components are at their low end of allowable tolerances, the airbag module may be recessed too far into the vehicle attachment structure. 
   Thus, the cost and fit of an airbag module are often weighed against each other. If the tolerances on the airbag module components are tight, the airbag module will have a proper fit, but the overall cost of the airbag module will be high. Alternatively, if the tolerances of the airbag module components are loose, the overall cost of the airbag module will be low, but may have a poor fit. 
   Therefore, what is needed in the art is an airbag module capable of a properly aligned fit within a vehicle. What is also needed in the art is an airbag module that may be manufactured using inexpensive processes. What is further needed is a system for inexpensively correcting the result of tolerance stacking in an airbag module. Such a system and apparatus is disclosed herein. 
   SUMMARY OF THE INVENTION 
   The apparatus of the present invention has 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 may inexpensively overcome tolerance stacking. 
   The present invention is comprised of an airbag housing having deflectable mounting tabs. The deflectable mounting tabs provide a mechanism for attaching the airbag module to a vehicle structural member, such as a steering wheel. As the airbag module is attached to a vehicle structural member, the deflectable mounting tabs elastically deform until the airbag is in flush alignment with the steering wheel or other vehicle structural member. Thus, the attachment of the airbag module overcomes any tolerance stacking to provide a good fit and finish with the steering wheel. 
   The mounting tabs may be comprised of U-shaped slots located in the base surface of the airbag module. The U-shaped slots may define mounting tabs that cantilever substantially in-plane from the base surface. The cantilevering configuration allows the mounting tabs to bend about the cantilevering location defined by the U-shaped slots. Additionally, the mounting tabs may be positioned within the perimeter of the airbag housing. 
   In order for the mounting tabs to couple to a vehicle structural member, the mounting tabs may include attachment members. The attachment member may be an aperture or protrusion configured to engage a corresponding attachment member in the vehicle structural member. Various fasteners, including slidably attaching snap-locking fasteners, may be employed to attach the airbag housing to the vehicle structural member via the mounting tabs. 
   An embossment may also be present at the location where the mounting tabs cantilevers from the base surface. The embossment may provide additional strength and control for bending the deflectable mounting tabs. Various shapes of embossment may also be employed, such as an S-shaped embossment. 
   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 
     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: 
       FIG. 1  is a perspective view of an airbag housing according to one embodiment of the invention. 
       FIG. 2  is a perspective view of an airbag module according to one embodiment of the invention. 
       FIG. 3   a  is a cross-sectional view of an airbag module and a vehicle structural member in an unassembled configuration. 
       FIG. 4  is a cross-sectional view of the airbag module of  FIG. 3  attached to a vehicle structural member in an undeflected configuration. 
       FIG. 5  is a cross-sectional view of an airbag module of  FIG. 3 and a  vehicle structural member in an assembled and deflected configuration. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   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 5 , is not intended to limit the scope of the invention, as claimed, but is merely representative of presently preferred embodiments of the invention. 
   The present invention provides for an airbag module having a low cost system for correcting the negative effects of tolerance stacking in airbag module assembly applications. Tolerance stacking occurs when the actual measurement of various components are near their extreme end of allowable tolerance ranges, such that in an assembled configuration the component as a whole is outside an allowable tolerance range. In an airbag module, tolerance stacking can prevent a flush alignment of the airbag module to a steering wheel or other vehicle structural member, causing unsightly gaps around the perimeter of the airbag module. 
   In order to overcome the associated problems with tolerance stacking without tightening the tolerances of the airbag components, an airbag housing having deflectable mounting tabs is provided. The deflectable mounting tabs provide a mechanism for attaching the airbag module to a vehicle structural member, such as a steering wheel. If a gap is present between the airbag module and the vehicle structural member, the elastically deflectable mounting tabs are deformed until the airbag is in flush alignment with the steering wheel or other vehicle structural member. 
   Referring now to  FIG. 1 , a perspective view of an airbag housing  112  is illustrated. The airbag housing  112  is a generally rigid member configured to support various airbag module components. The airbag housing  112  may support an airbag, airbag cover, and inflator. The airbag housing  112  may also function as a base for attaching the airbag module to a vehicle structural member. By attaching the various airbag module components to the airbag housing  112 , the airbag module may be assembled separately from the vehicle and then attached to the vehicle via the airbag housing  112 . 
   The present airbag housing  112  incorporates plastically deflectable mounting tabs  110  to allow adjustment of the airbag module in the presence of tolerance stacking. The mounting tabs  110  are configured to define an adjustable mounting member to attach the airbag housing  112  to a vehicle structural member. In the embodiment illustrated in  FIG. 1 , the mounting tabs  110  are defined by U-shaped slots  116  stamped into the base surface  120  of the airbag housing  112 . The base surface  120  may be defined as the generally broad face of the airbag housing  112 . 
   The U-shape slots  116  allow the mounting tabs  110  to have a cantilevering configuration, where one end of the mounting tabs  110  is attached to the housing  112  and the other end of the mounting tabs  110  is free to deflect. The mounting tabs  110  may be located within the perimeter  122  of the airbag housing  112 . Locating the mounting tabs  110  within the perimeter of the airbag housing  112  allows the mounting tabs  110  to be incorporated into the airbag housing  112  without the need to increase the outline size of the airbag housing  112 . Furthermore, locating the mounting tabs  110  within the perimeter of the airbag housing  112  reduces the length of a moment arm created between the attached mounting tabs  110  and a thrust producing inflator. By reducing the moment arm length, the torsional force applied to the mounting tabs  110  can be reduced. 
   The mounting tabs  110  are configured to elastically deflect about the cantilevering location  124  when mounting fasteners (shown in FIG.  2 ), are tightened. The mounting tabs  110  return generally to their original positions after the mounting fasteners are removed for serviceability. 
   The degree of deflection will depend upon amount of tolerance stacking in the airbag module and the initial position of the mounting tabs  110 . Because the mounting tabs  110  may be defined by U-shaped slots  116  in the base surface  120  of the airbag housing  112 , the mounting tabs  110  may be generally in-plane with the base surface  120 . Upon deflection of the mounting tabs  110 , the mounting tabs  110  bend to an orientation that is at least partially out-of-plane with the base surface  120 . However, in other embodiments the mounting tabs may be initially positioned out-of-plane with the base surface  120  and then deflect to an in-plane position. In yet another configuration, the mounting tabs  110  may be positioned out-of-plane in both the deflected and non-deflected positions. 
   The initial positioning and orientation of the mounting tabs  110  can be easily established when manufacturing the airbag housing  112  through a stamping process. Stamping is the process by which a generally flat plate can be manufactured into a complex, three-dimensional structure by cutting the plate and bending the cutout shapes of the plate into the desired orientation. Through stamping, the shape and orientations of the mounting tabs  110  may be established through changes in the tooling. 
   Stamping will create mounting tabs  110  that are integrally formed to the airbag housing  112 . However, non-integrally formed mounting tabs  110  may also be employed in the airbag housing  112 . A non-integrally formed mounting tab  110  would be a tab that is welded, adhered, or otherwise attached to the airbag housing  112 . The non-integrally formed mounting tab  110  would be able to deflect about the location where the non-integrally formed mounting tab  110  is attached to the airbag housing  112 . 
   The mounting tabs  110  may also have various shapes and positions other than those illustrated in FIG.  1 . Generally, the mounting tabs  110  may be any shape that allows the mounting tabs  110  to be attached to a vehicle structural member and to deflect once attached. Furthermore, the position of the mounting tabs  110  may be located anywhere on the airbag housing  112 . However, it is preferred that the position of the mounting tabs  110  not interfere with attachment of the inflator, airbag cover, or airbag. 
   The airbag housing  112  may include various numbers of mounting tabs  110 . For example, the airbag housing  112  may only require one mounting tab  110  to attach the airbag housing  112  to the vehicle structural member. Alternatively, more than two mounting tabs  110  may be employed in an airbag housing  112 . Additionally, when multiple mounting tabs  110  are employed, the individual mounting tabs  110  need not be identical. The mounting tabs  110  may be individually configured for individual applications and for any number of locations on the airbag housing.  112   
   The mounting tabs  110  may further include embossments  128  at the cantilevering locations  124 . The embossments  128  are indentations present in the airbag housing  112  that are convex on one side of the airbag housing  112  and concave on the other. In the airbag housing illustrated in  FIG. 1 , the embossments  128  are stamped into the base surface  120  of the airbag housing  112 , where the convex side is visible. The embossments  128  may have any number of shapes, such as an S-shape, or C-shape. 
   The embossments  128  are indentations present in the airbag housing  112 , being convex on one side of the airbag housing  112  and concave on the other. In the airbag housing illustrated in  FIG. 1 , the embossments  128  are stamped into the base surface  120  of the airbag housing, where the convex side is visible. The embossments  128  may have any number of shapes, such as an S-shape, or C-shape. 
   The embossments  128  provide several functions for the mounting tabs  110 . One function of the embossments  128  is to distribute the stresses created at the cantilevering locations  124  of the mounting tabs  110  when the mounting tabs  110  are deflected. The embossments  128  allow some of the bending of the airbag housing  112  material to occur in the raised sections of the embossments  128  and not entirely at the cantilevering locations  124 . By distributing the bending across the embossments  128 , the stresses at any one location may be lower than if only the cantilevering locations  124  of the mounting tabs  110  were bent. 
   Another function of the embossments  128  is to provide a desirable grain orientation in the metal at the cantilevering location  124  of the mounting tabs  110 . When the embossments  128  are stamped into the airbag housing  112 , some of the grains in the metal will orient to conform to the contours of the embossments  128 . By reorienting the grains in the metal, the mounting tabs  110  are able to have a large deflection with a reduced possibility of tearing the housing. 
   The mounting tabs  110  may further include airbag module attachment members  132 . The airbag module attachment members  132  are configured to provide a mechanism to attach the airbag module to the vehicle structural member. In the mounting tabs  110  illustrated in  FIG. 1 , the airbag module attachment members  132  are apertures. The apertures may receive corresponding fastener members of the vehicle structural member. The airbag module attachment members  132  may also incorporate protrusions in place of apertures, or other similar male-type fasteners. However, apertures may be generally preferred because they may be easily stamped into the mounting tabs  110  when the mounting tabs  110  are being formed. 
   Various other components may also be formed into the airbag housing  112  to facilitate attachments of other components to the airbag housing  112 . The airbag housing may include brackets  136  that facilitate attachment of a cover (shown in  FIG. 2 ) to the airbag housing  112 . The brackets  136  may be stamped into the housing when the airbag housing  112  is formed. The brackets  136  illustrated in  FIG. 1  are out-of-plane with the base surface  120  and positioned around the perimeter of the inflator opening  138  in the center of the airbag housing  112 . 
   The airbag housing  112  may also include apertures  140  for receiving and mounting an inflator. The apertures  140  may be positioned around the inflator opening  138 . The apertures  140  may be sized to receive fasteners to attach an inflator to the airbag housing  112 . 
   The airbag housing  112  may also include airbag cover fasteners. In the embodiment illustrated in  FIG. 1 , the airbag cover fasteners are a plurality of hook fasteners  144  that attach to window fasteners in the airbag cover (shown in FIG.  2 ). The hook fasteners  144  are generally broad hooks that are stamped and integrally formed into the airbag housing  112 . The hooks engage the edges of window openings in the airbag cover. 
   Referring now to  FIG. 2 , an assembled airbag module  200  is illustrated. The airbag module  200  has an airbag cover  212  and an inflator  216  attached to the airbag housing  112 . The airbag cover  212  is attached to the airbag housing  112  through hook  144  and window  220  fasteners. The airbag cover  212  provides the aesthetic exterior of the airbag module  200  which is exposed to the interior the vehicle. The airbag cover  212  may be made of an injection molded plastic or other injection molded material. 
   Similar to the stamping process used in manufacturing the airbag housing  112 , injection molding is a fast and cost-effective method for manufacturing a complex shape. However, both the stamping and injection molding processes have generally loose tolerances, such that the attachment of the stamped housing  112  to the molded cover  212  has the potential for significant tolerance stacking. 
   While the tolerance stacking created by the airbag housing  112  and the airbag cover  212  will affect the overall tolerance of the airbag module  200 , the tolerances in the mechanisms that attach the airbag module  200  to a vehicle structural member will affect the allowable tolerance range between the airbag module and a vehicle structural member. The mounting tabs  110  should have a deflection range that is greater than the largest tolerance extremes in the airbag module  200  members. Also, the deflection of the mounting tabs  110  should be greater than the largest allowable tolerances in the attachment of the airbag module  200  to the vehicle structural member. 
   Referring now to  FIG. 3 , a cross-sectional view of an airbag module  200  and a steering wheel structure  250  is illustrated. The airbag module  200  and the steering wheel structure  250  incorporate airbag module mounting fasteners  224  and steering wheel mounting fasteners  228  to attach the airbag module  200  to the steering wheel structure  250 . 
   Alternatively, the airbag module mounting fasteners  224  and the steering wheel mounting fasteners  228  may be employed in attaching the airbag module  200  to the steering wheel structure  250 . A threaded nut may be pressed into the mounting tabs  110 , where the threaded nut is configured to receive a threaded nut or screw. The fastener  228  may be accessed from behind the steering wheel structure  250  to attach the airbag module  200 . In alternative embodiments, different fastening schemes may be used within the scope of the present invention. 
   The airbag module mounting fasteners  224  are attached to the airbag housing  112  on the mounting tabs  110 . The airbag module mounting fasteners  224  may be coupled to the attachment members  132  of the mounting tabs  110 . For example, the airbag module mounting fasteners  224  may have a snap-locking end which locks in to the attachment member  132  aperture. Such snap-locking mechanisms allow the airbag module mounting fasteners  224  to be easily and quickly attached to the mounting tabs  110 . 
   Similarly the steering wheel structure  250  may incorporate snap-locking steering wheel mounting fasteners  228  configured to attach to the airbag module mounting fasteners  224 . The steering wheel mounting fasteners  228  receive and lock to the airbag module mounting fasteners  224 . The steering wheel mounting fasteners  228  may extend from the steering wheel structure  250 , such that the airbag module  200  may be slidably attached to the steering wheel structure  250 . 
   Referring now to  FIG. 4 , once the steering wheel fasteners  228  and the airbag module mounting fasteners  224  are aligned, the female-type mounting fasteners  224  and male-type mounting fasteners  228  are attached but not yet torqued. A gap  254  may be present between the airbag cover  212  and the steering wheel structure  250 . The gap  254  may be caused by the edge  258  of the airbag cover  212  not touching the front  262  of the steering wheel structure  250 . The gap  254  may be present around the entire perimeter of the airbag module  200 , creating a non-aesthetic appearance. The gap  254  may be particularly noticeable on a steering wheel mounted airbag, where the vehicle occupant is looking directly at the airbag cover  212 . 
   Through the use of the deflectable mounting tabs  110 , the gap  254  may be closed such that the edge  258  of the airbag cover  212  touches the front  262  of the steering wheel structure  250 . Referring now to  FIG. 5 , the mounting fasteners  228  are tightened to a torque sufficient to deflect the mounting tabs  110 . As the mounting tabs  110  deflect, the airbag module  200  moves into flush alignment with the steering wheel structure  250 . Thus, the gap  254  created by excessive tolerance stacking may be inexpensively sealed by plastically deflecting the mounting tabs  110 . 
     FIGS. 3-5  have illustrated an airbag module  200  attached to a steering wheel structure  250 . However, the deflectable mounting tabs  110  may be employed in airbag modules  200  that are positioned throughout various locations of the vehicle, such as the instrument panel. 
   Generally, the present invention provides a cost-effective system for correcting tolerance stacking within airbag modules. The airbag housing employs elastically deflectable mounting tabs that deform while the airbag module is attached to a vehicle structural member to bring the airbag module into a flush alignment with the vehicle structural member. 
   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.