Abstract:
Instrument panels integrated with passenger airbag modules and methods of producing such modules are provided. The integrated instrument panels and passenger airbag modules of the invention provide modules that may be closely integrated with the instrument panel during its construction, thus simplifying attachment of the module to the instrument panel and rendering potential cost savings. The application also provides methods of construction and assembly of such integrated instrument panels and passenger airbag modules.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Safety belts are designed to protect the occupants of a vehicle during events such as automobile collisions. In low-speed collisions, the occupants are generally protected from impact with objects located inside the vehicle such as the windshield, the instrument panel, a door, the side windows, or the steering wheel by the action of the safety belt. In more severe collisions, however, even belted occupants may experience an impact with the car&#39;s interior. Airbag systems were developed to supplement conventional safety belts by deploying into the space between an occupant and an interior object or surface in the vehicle during a collision event. The airbag acts to decelerate the occupant, thus reducing the chances of injury to the occupant caused by contact with the vehicle&#39;s interior.  
         [0002]     Many typical airbag systems consist of several individual components joined to form an operational airbag module. Such components generally include an airbag cushion, an airbag inflator, a sensor, and an electronic control unit. Airbag cushions are typically made of a thin, durable fabric that is folded to fit into a compartment of a steering wheel, dashboard, interior compartment, roof, roof rail, roof compartment, or other space in a vehicle. The airbag inflator is in fluid communication with the airbag cushion, and is configured to produce a gas to inflate the cushion when it is needed. The sensors detect sudden decelerations of the vehicle that are characteristic of an impact. The readings taken by the sensors are processed in the electronic control unit using an algorithm to determine whether a collision has occurred.  
         [0003]     Upon detection of an impact of sufficient severity, the control unit sends an electrical signal to the inflator. The inflator uses one of many technologies currently known in the art to produce a volume of an inflation gas. The inflation gas is channeled into the airbag, inflating it. Inflation of the airbag causes it to deploy, placing it in a position to receive the impact of a vehicle occupant. After contact of the occupant with the airbag and the corresponding deceleration of the occupant, the airbag rapidly deflates. To accomplish this, the inflation gas is vented from openings in the airbag, deflating it and freeing the occupant to exit the vehicle.  
         [0004]     As experience in the manufacture and use of airbags has increased, the engineering challenges involved in their design, construction, and use have become better understood. Most airbag systems are designed to rapidly inflate and provide a cushion in proximity to a vehicle occupant. Many such cushions are configured to be placed in front of a vehicle occupant. Placement of the cushions is determined based on presumptions made of the position occupied by a vehicle occupant in a vehicle during normal operation of the vehicle. Thus, a vehicle occupant enjoys optimal protection from a specific airbag when the occupant is in the presumed range of positions when the airbag deploys.  
         [0005]     In some situations, injuries have been noted to occur when a vehicle occupant is “out of position” with regard to the presumed position discussed above. Some such injuries have been attributed to incidents in which vehicle occupants located out-of-position during the deployment of an airbag cushion are located in the path of the inflating cushion. Currently available airbag systems rapidly inflate a cushion in front of an occupant during a collision. This inflation process is generally difficult to regulate, however, and some regions of the cushion may inflate before others, increasing the risk of injury to out-of-position occupants located near these early-filling portions of the cushion.  
         [0006]     Potential injury to out-of-position occupants could be reduced and/or avoided by the use of systems capable of causing full radial expansion of an airbag cushion prior to placement of the cushion in front of the vehicle occupant. Similarly, injury could be reduced by the use of systems capable of reducing the forward momentum with which an airbag cushion is directed toward a vehicle occupant. Some systems currently available to regulate cushion expansion and deployment often utilize passive tether systems such as “break-tethers”—tethers configured to first hold an airbag cushion at a specified state and then to rupture at a specified load to release the cushion and allow full cushion deployment. Although useful, such systems have proven complex, with a large number of variables present in configuring a break tether for a specific application, and a large number of variables which may affect the performance of the tethers. Other technologies utilize active tether systems which have several characteristics which may be actively controlled by systems of the vehicle. These technologies are also very complex and more expensive to implement and use in a vehicle.  
         [0007]     Accordingly, a need exists for airbag deployment restraint devices for use in vehicles to regulate the deployment characteristics of an airbag cushion such that out-of-position vehicle occupants receive a more even load during inflation of the airbag cushion. It would be specifically beneficial to provide an airbag deployment restraint device capable of forcing the deploying airbag cushion to assume its fullest radial width prior to fully expanding toward a vehicle occupant, thus presenting a broad surface area for potential contact with the vehicle occupant. There is a similar need for devices capable of regulating the momentum with which an airbag cushion expands toward a vehicle occupant. It would be a further advantage in the art to provide such an airbag deployment restraint device that is compatible with existing airbag cushion and housing designs to avoid the costs associated with the customization of existing airbag modules. Such airbag cushion deployment restraint devices and methods for their use are provided herein.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     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 passenger airbag modules, instrument panels, and airbag module and instrument panel assembly methods. Thus, the present invention provides novel integrated passenger airbag and instrument panel assemblies and methods of their assembly for use in vehicles to protect a vehicle occupant during a collision event.  
         [0009]     In one embodiment, the invention provides an airbag module for protecting a vehicle occupant. The airbag module first includes an airbag module cover. The airbag module cover has a substrate surface, an instrument panel adapter, and an airbag housing interlock. The airbag module cover of the invention is adapted to be integrated with an instrument panel substrate to provide a surface suitable for receiving a decorative overlay. The airbag module also includes an airbag module housing having an airbag case portion and an airbag module cover interlock portion. The module housing is adapted to be coupled to the airbag module cover. The airbag modules of the invention further include an airbag cushion configured to be deployed from the airbag module housing. In some specific embodiments of the invention, the airbag cushion is configured for use as a passenger airbag cushion.  
         [0010]     According to the invention, the substrate surface of the airbag module cover may be configured to receive a decorative overlay such as a skin-and-foam overlay that may produce a class A surface suitable for use as an exposed surface in a vehicle. In some instances, the substrate surface of the inflatable airbag module may have a class A surface.  
         [0011]     As discussed above, the airbag module cover of the inflatable airbag modules of the invention may include an instrument panel adapter. In some instances, the instrument panel adapter may simply comprise a surface of the module cover sized, shaped, and otherwise adapted to be attached to the instrument panel. In other embodiments of the invention, the instrument panel adapter may comprise a radial flange extending from the substrate surface of the airbag module cover.  
         [0012]     The airbag module cover further includes an airbag housing interlock to allow the airbag module cover to be attached to an airbag module housing. In some configurations, the airbag housing interlock of the module cover may include a plurality of locking fingers projecting from the module cover. These locking fingers may be configured to extend into an airbag module cover interlock of an airbag module housing. Once in place, the locking fingers may function to securely join the module cover and the module housing for use in a vehicle.  
         [0013]     The inflatable airbag module of the invention may also include a tear seam in the airbag module cover to allow proper deployment of the airbag cushion of the module. More specifically, the airbag module cover of the airbag modules of the invention may include a tear seam which may be invisible to a vehicle occupant from the exposed surface of the instrument panel housing the airbag cushion. In some instances, the tear seam may be placed in the airbag module cover during the construction of the cover itself. Such tear seams may be molded, stamped, or punched into the airbag module cover during its construction, after its construction, or even after its integration with the instrument panel. In some instances, the tear seam may be added to the airbag module after its integration with the instrument panel, and after a decorative overlay such as a skin-and-foam cover has been added. In one such embodiment, the airbag module cover may be scored using a laser to provide a proper tear seam. The depth of the scoring may be varied, as is known to one of skill in the art. In many instances, however, the laser-scoring completely penetrates the airbag module cover and may even extend into the decorative overlay to weaken it. In these ways, the tear seams provide an exit route for an inflating airbag cushion during cushion deployment in a collision event.  
         [0014]     The invention further provides airbag module covers suitable according to the invention. As described as components of the module noted above, these airbag module covers of the invention have a substrate surface configured to receive a decorative overlay, an instrument panel adapter, and a plurality of locking fingers extending from the cover in a direction substantially opposite the substrate surface. As above, the substrate surface may be configured to receive a skin-and-foam overlay to provide a surface suitable for use in the interior of a vehicle, and the cover may be provided with a tear seam using the methods described above.  
         [0015]     The invention may further include a vehicular instrument panel having an integral airbag module cover for use in a vehicle. Such dashboards may be constructed in a manner simpler than many methods currently in use, and may ease the installation of a passenger airbag cushion into a vehicle. Such instrument panels may first include a primary dashboard panel that provides the base structure for the instrument panel. The primary dashboard panel includes a substrate surface configured to receive a decorative overlay and an airbag module cover adapter. The substrate surface may be a class A surface, or it may be configured to receive an overlay providing a class A surface. The instrument panels next include an airbag module cover having a substrate surface configured to receive a decorative overlay, an instrument panel adapter, and an airbag housing interlock. The primary dashboard panel and the airbag module cover may be joined to provide a unitary instrument panel which may receive a decorative overlay such as a skin-and-foam overlay. Subsequent to the attachment of such an overlay, an airbag module may be attached to the locking fingers of the airbag module cover.  
         [0016]     The primary dashboard panel may first include an orifice sized to receive the airbag module cover. The primary dashboard panel may further comprise an adapter channel having a depth sufficient to allow the airbag module cover to nest into the substrate surface of the primary dashboard panel without substantial outward protrusion into the space of the cabin of the vehicle. This may result in a combination substrate surface that is sufficiently even that the application of a decorative overlay results in a substantially even surface with no obvious seams. As above, the instrument panel adapter of the airbag module cover may comprise a radial flange extending from the substrate surface of the airbag module cover or a face of the module cover configured to be attached to an instrument panel.  
         [0017]     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 SEVERAL VIEWS OF THE DRAWINGS  
       [0018]     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:  
         [0019]      FIG. 1  is a partial perspective view of the interior of a vehicle including a partially-cutaway view of an integrated instrument panel and passenger airbag module according to the invention;  
         [0020]      FIG. 2  is an isolated perspective view of the integrated instrument panel and passenger airbag module of  FIG. 1  shown exploded to illustrate the relation of its components;  
         [0021]      FIG. 3A  is a cross-sectional view of the integrated instrument panel and passenger airbag module of  FIG. 2  taken at line  3 A- 3 A of  FIG. 2 ;  
         [0022]      FIG. 3B  is a detail of the cross-sectional view of the integrated instrument panel and passenger airbag module of  FIG. 3A ;  
         [0023]      FIG. 4A  is a cross-sectional view of another integrated instrument panel and passenger airbag module taken from a perspective similar to that of  FIG. 2  taken at line  3 A- 3 A of  FIG. 2 ;  
         [0024]      FIG. 4B  is a detail of the cross-sectional view of the integrated instrument panel and passenger airbag module of  FIG. 4A ;  
         [0025]      FIG. 5A  is a cross-sectional view of still another integrated instrument panel and passenger airbag module taken from a perspective similar to that of  FIG. 2  taken at line  3 A- 3 A of  FIG. 2 ; and  
         [0026]      FIG. 5B  is a detail of the cross-sectional view of the integrated instrument panel and passenger airbag module of  FIG. 5A . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     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 integrated passenger airbag and instrument panel and assembly method of the present invention, as represented in  FIGS. 1 through 3 B, is not intended to limit the scope of the invention, as claimed, but is merely representative of presently preferred embodiments of the invention.  
         [0028]     Referring first to  FIG. 1 , a partial perspective view of the interior of a vehicle  12  is shown including a partially-cutaway view of an integrated instrument panel and passenger airbag module  10  according to the invention. A portion of the instrument panel  14  is shown with an integrated airbag module  10 , along with a portion of the windshield  16 , A-pillar  18 , side door  22 , and side window  20 . The instrument panel  14  is shown to be composed of a plurality of layers, in this instance including a primary instrument panel substrate layer  48  and an associated airbag module cover  52  covered by a decorative overlay  38 . Although many suitable decorative overlays  38  are known to one of ordinary skill in the art, the integrated airbag module  10  of  FIG. 1  is shown to include a decorative overlay  38  taking the form of an instrument panel skin layer  40  and a foam layer  44 .  
         [0029]     The integrated airbag module  10  further includes an airbag module housing  60  for enclosing an inflatable airbag cushion such as a passenger-side airbag cushion (not shown). The module housing  60  is configured to be attached to a module cover  52  (shown in phantom) of the module  10  integrated with the instrument panel substrate layer  48  under the decorative overlay  38 . In some embodiments of the integrated airbag module  10  of the invention, the housing  60  may be attached to the module cover  52  in a snap-fit fashion using at least one module lock  64 . The module lock  64  may include locking fingers  66  extending from one of the components of the module  10 , here the module cover. The module lock  64  may further include locking gates  68 , here shown positioned on the module housing  60 . The locking fingers  66  may specifically be configured to enter the locking gates  68  and be engaged such that the module cover  52  and housing  60  are held together. The module housing  60  further includes a contact surface  78  that is pressed against an outer substrate contact surface  58   b  of the substrate panel  48  during assembly of the module  10 .  
         [0030]     The integrated airbag module  10  may further include an airbag inflator  90  to provide inflation gas to the airbag cushion during deployment. In the airbag module  10  of  FIG. 1 , an airbag inflator  90  is shown linked to the module  10  by bracket  94  attached to the airbag module housing  60  by inflator attachments  92 . The module  10  may be attached to a cross-vehicle beam by a bracket  94 . Suitable inflators  90  may be mounted to the module  10  within the scope of the invention in a variety of ways known to one of ordinary skill in the art.  
         [0031]     The individual components of the integrated airbag module  10  of the invention are also shown in  FIG. 2  in which the integrated instrument panel and passenger airbag module  10  of  FIG. 1  is shown isolated in a perspective view and partially exploded. In  FIG. 2 , the decorative overlay  38  has been separated from the upper surface  50   a  of the primary instrument panel substrate layer  48  and from the upper surface  54   a  of the airbag module cover  52 . The decorative overlay  38  is shown to include a skin layer  40  having an upper surface  42   a  and a lower surface  42   b . The upper surface  42   a  is generally a surface suitable for presentation in the cabin of the vehicle. Such high-quality surfaces are often referred to as “class A surfaces.” The lower surface  42   b  of the skin layer  40  is attached to a foam layer  44  of the decorative overlay  38 . The foam layer  44  is optionally included in the overlay  38  to add depth and cushioning characteristics to the decorative overlay  38 . The foam layer  44  has an upper surface  46   a  that is attached to the skin layer  40  and a lower layer  46   b  that attaches the decorative overlay  38  to the primary instrument panel substrate  48  and the airbag module cover  52 .  
         [0032]     The primary instrument panel substrate  48  and the airbag module cover  52  are configured to be joined to provide a substantially level upper face including the upper surface  50   a  of the substrate  48  and the upper surface  54   a  of the module cover  52 . This presents a combined upper surface  50   a ,  54   a  suitable for receiving a decorative overlay  38  here shown to be a skin-and-foam overlay  38 . Other decorative overlays  38  suitable for use with the present invention are known to one of ordinary skill in the art. As a result of this configuration, according to the invention, at least a portion of the airbag module  10  is joined to the instrument panel  14  during the assembly of the instrument panel  14 . This results in a final module product  10  having a closely-integrated airbag module  10  and instrument panel  14 .  
         [0033]     More specifically, in the embodiment illustrated in  FIGS. 1-2 , at least a portion of the airbag module  10  such as the module cover  52  is placed into association with the primary substrate layer  48  prior to deposition of the decorative overlay  38 . Following this, the decorative overlay  38 , here foam and skin layers  44 ,  40  may be added over the top. This produces an integrally-linked instrument panel and airbag module assembly  10 . The module housing  60  and other components of the module  10  may be attached to the module cover  52  after deposition of the decorative overlay  38 . Alternatively, if convenient and practicable, the module housing  60  may be attached to the module cover  52  prior to the addition of the decorative overlay  38 . As a result, the module housing  60  may be either present or absent during deposition of the decorative overlay  38 , here comprising foam and skin layers  44 ,  40 .  
         [0034]     One factor that may be used in determining when the airbag module housing  60  is attached to the module cover  52  is whether or not the module cover  52  has been provided with a tear seam  72  configured to rupture on deployment of the airbag module  10  to permit the cushion  80  to escape the module  10 . In some embodiments of the modules  10  of the invention, the tear seam  72  may be molded into the airbag module cover  52 . In such modules  10 , the module housing  60  may be attached to the airbag module cover  52  of the instrument panel  14  prior to addition of the decorative overlay  38 . In such modules  10 , the force of the deployment of the airbag cushion (not shown) is sufficient to rupture the tear seam  72  and sufficiently disrupt the decorative overlay  38  to provide for proper deployment of the airbag cushion.  
         [0035]     In alternate embodiments of the modules of the invention, a tear seam  72  may be produced in the final module cover  52  and the associated decorative overlay  38  following deposition of the decorative overlay  38 . In some circumstances, the tear seam  72  could be produced by using a laser to score the seam  72  into the cover  52 . Alternatively, the tear seam  72  could be scored completely through the cover  52  and partially through the overlay  38  to further help assure proper egress of the deploying airbag cushion. Such scoring would generally not pass completely through the overlay  38 . These methods would produce a hidden tear seam in the final integrated instrument panel and airbag module  10  that is functional, but not visible from the cabin of the vehicle  12 . Laser scoring technology suitable for the practice of the invention is taught in U.S. Pat. No. 5,744,776.  
         [0036]     As briefly described above, following attachment of the decorative overlay  38  to the combination of the instrument panel substrate  48  and the module cover  52 , the airbag module housing  60  and the associated cushion  80  may be attached to the cover  52 . In some embodiments of the invention, the module cover  52  and housing  60  are configured to allow their assembly in a snap-fit manner. More specifically, the module locks  64  may be configured to operate based on snap-fit principles. In some instances, this may simplify the assembly process and potentially reduce the labor and cost associated with assembly. Often, conventional assembly methods require hand-labor in attaching airbag modules using bolts or other labor-intensive fasteners. Use of snap-fit attachment structures in the module locks  64 , although not required to be within the scope of the invention, may decrease labor costs and simplify the design of module components such as the module cover  52  and housing  60 .  
         [0037]     As briefly discussed above, the module locks  64  illustrated in  FIGS. 1-3B  include locking fingers  66  extending from the lower surface  54   b  of the module cover  52 . As briefly mentioned above, the locking fingers  66  are configured to extend into the locking gates  68  present on the housing  60 . As illustrated in  FIGS. 3A and 3B , the locking fingers  66  are configured to enter the locking gates  68 , and in some embodiments, to be engaged by biased locking clips  70 . In some embodiments, the locking clip  70  may be an integral component of the locking gates  68 . The specific structure and arrangement of the module locks  64  may be varied widely within the scope of the invention. In some embodiments of the invention, the module locks  64  may vary the position of the locking components, such as by placing locking fingers  66  on the module housing  60  and gates on the module cover  52 . Similarly, the structure of the module locks  64  themselves may be varied within the scope of the invention as known to one of ordinary skill in the art.  
         [0038]      FIG. 3A  provides a cross-sectional view of the integrated instrument panel and passenger airbag module  10  of  FIG. 2  taken at line  3 A- 3 A of  FIG. 2 , and  FIG. 3B  provides a detailed view of a portion of this cross-sectional view indicated by the dashed circle  30  present in  FIGS. 3A and 3B .  FIG. 3A  shows a cross-section of the module  10 . The module  10  comprises a decorative overlay  38 , an instrument panel substrate  48  integrated with an airbag module cover  52 , and an airbag module housing  60 . The module cover  52  and panel substrate  48  are configured to be placed together. More specifically, the panel substrate  48  has a substrate adaptor channel  56  having a size, depth, and shape configured to accommodate the module cover  52  and to provide a substantially flat combined surface. This is illustrated in detail in  FIG. 3B . More specifically, the primary substrate panel  48  includes a substrate adaptor channel  56 . The channel  56  has a contact surface  58   a . This contact surface  58   a  is adapted to receive the module cover  52 , with contact with the lower surface  54   b  of the module cover  52 . The substrate panel  48  may additionally include an alignment ridge  76  projecting outwardly from the panel  48 . Such a ridge  76  may operate to reduce movement of the airbag module housing  60 , and may additionally assist in proper alignment of the components of the module  10  during assembly. The combined upper surfaces  50   a ,  54   a  of the substrate panel  48  and module cover  52  may then receive a decorative overlay  38  such as this one including a skin layer  40  and a foam layer  44 .  
         [0039]     As illustrated in  FIGS. 3A and 3B , the substrate panel  48  includes an orifice  62 . The orifice  62  is configured to be smaller than the module cover  52  such that the cover  52  cannot pass through it. It is, however, configured to allow portions of the module cover  52  to pass through it, including, but not limited to, elements of the module locks  64  such as locking fingers  66 . As discussed above, the module  10  may be assembled by attaching the housing  60  to the assembled instrument panel substrate  48  and module cover  52 . In doing so, a contact surface  78  of the module housing  60  is pressed against an outer substrate contact surface  58   b  of the substrate panel  48 .  
         [0040]     In this embodiment of the module  10  of the invention, the orifice  62  may also be used to provide access to the module cover  52  and decorative overlay  38  for the purposes of adding a tear seam  72 , which may pass completely or partially through the cover  52 , and potentially into the foam and skin layers  44 ,  40 . As illustrated, the tear seam  72  has been cut completely through the cover  52  and partially into the foam layer  44 , leaving the skin layer  40  intact. The overall shape of such a tear seam  72  may be varied widely within the scope of the invention as is known to one of skill in the art, but may include a substantially-U-shaped configuration to form a region of the module that will rupture to form an instrument panel flap  74  when the airbag cushion  80  deploys.  
         [0041]     Referring next to  FIG. 4A , yet another embodiment of the inflatable airbag modules  110  of the invention is shown. As in  FIG. 3A , this Figure shows a cross-sectional view of this embodiment of the airbag module  110  is shown in a cross-sectional view taken from a perspective similar to that used to produce  FIG. 3A , namely along a plane such as that defined by line  3 A- 3 A of  FIG. 2 .  FIG. 4B  provides a detailed view of a portion of the cross-sectional view indicated by the dashed circle  130  present in both  FIGS. 4A and 4B . The module  110  of  FIG. 4A  is in many respects similar to module  10  of  FIGS. 3A and 3B . The module  110  first includes a decorative overlay  138 , an instrument panel substrate  148  integrated with an airbag module cover  152 , and an airbag module housing  160 . In module  110 , however, the module cover  152  and panel substrate  148  are produced and integrated using techniques such as injection molding. Such techniques allow the parts  148 ,  152  to be formed in an integrated manner. This may be done in a stepwise manner, i.e., one of the parts is first produced, and the second part is subsequently injection-molded in place. Alternately, this may be accomplished in a nearly simultaneous co-injection process that forms both parts  148 ,  152  in an integrated manner nearly simultaneously.  
         [0042]     Thus, in  FIGS. 4A and 4B , the panel substrate  148  of the module  110  conforms to the shape of the airbag module cover  152 . While the module  10  of the previous Figures included an adaptor channel  56 , the module  110  of  FIGS. 4A and 4B  instead includes a seam  158   a  at the interface of the upper surface  150   a  of the instrument panel substrate  148  and the lower surface  154   b  of the module cover  152 . As in the previously-described embodiment, the substrate panel  148  may additionally include an alignment ridge  176  projecting outwardly from the panel  148 . Similarly, as before, the combined upper surfaces  150   a ,  154   a  of the substrate panel  148  and module cover  152  may then receive a decorative overlay  138  such as this one including a skin layer  140  and a foam layer  144 .  
         [0043]     As previously discussed, the substrate panel  148  may be adapted to permit portions of the module cover  152  to extend therethrough. Structures such as elements of the locks  164 , including locking fingers  166  may specifically be permitted to pass through the substrate panel  148 . The resulting configuration allows the module  110  to be assembled by attaching the housing  160  to the unitary instrument panel substrate  148  and module cover  152  by allowing the locking fingers  166  to enter the locking gates  168  of the housing  160 . The locking fingers  166  culminate with locking clips  170  that engage the locking gates  168 . During assembly, a contact surface  178  of the module housing  160  is pressed against an outer substrate contact surface  158   b  of the substrate panel  148 .  
         [0044]     In this embodiment of the module  110  of the invention, the substrate panel  148  may also be adapted used to provide access to the module cover  152  and decorative overlay  138  for the purposes of adding a tear seam  172 , which may pass completely or partially through the cover  152 , and potentially into the foam and skin layers  144 ,  140 . As illustrated, the tear seam  172  has been cut completely through the cover  152 , disrupting the upper and lower surfaces  154   a ,  154   b , and cut partially into the foam layer  144 , disrupting the lower layer  146   b , but not disrupting the upper layer  146   a , and leaving the skin layer  140  with its upper and lower surfaces  142   a ,  142   b  intact. The overall shape of such a tear seam  172  may be varied widely within the scope of the invention as is known to one of skill in the art, but may include a substantially-U-shaped configuration to form a region of the module that will rupture to form an instrument panel flap  174  when the airbag cushion  180  deploys.  
         [0045]      FIG. 5A  illustrates still another embodiment of the inflatable airbag module  210  of the invention.  FIG. 5A  shows a cross-sectional view of this airbag module  210  taken from a perspective similar to that used to produce  FIGS. 3A and 4A . More specifically, this view is obtained from a plane such as that defined by line  3 A- 3 A of  FIG. 2 . As previous  FIGS. 3B and 4B ,  FIG. 5B  provides a detailed view of a selected portion of the cross-sectional view of  FIG. 5A . The specific section viewed is indicated by the dashed circle  230  present in  FIGS. 5A and 5B . The module  210  of  FIG. 4A  is in many respects similar to modules  10  and  110  of  FIGS. 3A-3B  and  FIGS. 4A-4B , respectively.  
         [0046]     The airbag module  210  of  FIGS. 5A and 5B  first includes a decorative overlay  238 , an instrument panel substrate  248 , and an airbag module housing  260 . In module  210 , the instrument panel substrate  248  has been designed to incorporate features found in the module covers  52  and  152  of the previously-described embodiments. Such features include the locking fingers  266 , which here extend from the substrate  248 , and a module housing contact surface  278 . The panel substrate  248  also extends across the space occupied by module covers  52  and  152  in previously-described configurations. As a result, it is the substrate  248  which may be cut to form the tear seam  272 .  
         [0047]     Module  210  of  FIGS. 5A and 5B  includes a module housing contact surface  278  at the interface of the lower surface  250   b  of the instrument panel substrate  248  and the module housing  260 . As illustrated in  FIGS. 5A and 5B , the contact surface  278  may take the form of an indentation into the substrate  248 . This provides an alignment ridge  276  that projects outwardly from the panel  248  to retain the module housing  260  in proper alignment. The upper surface  250   a  may additionally be configured to receive a decorative overlay  238 . As previously described, the decorative overlay  238  such may include a skin layer  240  with an upper surface  242   a  and a lower surface  242   b ; and a foam layer  244  with an upper surface  246   a  and a lower surface  246   b.    
         [0048]     The substrate panel  248  includes elements of the locks  264  of the module  210 , including locking fingers  266  which extend from the substrate panel  248 . The resulting configuration allows the housing  260  to be attached to the instrument panel substrate  248  by allowing the locking fingers  266  to enter the locking gates  268  of the housing  260 . The locking fingers  266  culminate in locking clips  270  that engage the locking gates  268 .  
         [0049]     In this embodiment of the module  210  of the invention, the substrate panel  248  may receive a tear seam  272 , which may pass completely or partially through the substrate panel  248 , and potentially into the foam and skin layers  244 ,  240 . In  FIGS. 5A and 5B , the tear seam  272  has been cut completely through the substrate panel  248 , disrupting the upper and lower surfaces  250   a ,  250   b , and cut partially into the foam layer  244 , disrupting the lower layer  246   b , but not disrupting the upper layer  246   a , and leaving the skin layer  240  with its upper and lower surfaces  242   a ,  242   b  intact. The overall shape of such a tear seam  272  may be varied widely within the scope of the invention as is known to one of skill in the art, but may include a substantially-U-shaped configuration to form a region of the module that will rupture to form an instrument panel flap  274  when the airbag cushion  280  deploys.  
         [0050]     The present invention thus provides an inflatable airbag module for protecting a vehicle occupant which may be integrated with a vehicular instrument panel. The invention further provides methods of assembling such an integrated airbag module and instrument panel. According to the invention, the airbag module generally first includes a module cover suitable for being integrated with an instrument panel during the manufacture of the instrument panel. The module cover generally has a substrate surface, an instrument panel adapter, and an airbag housing interlock. The module covers of the invention are integrated with an instrument panel substrate to form a composite substrate surface which may then receive a decorative overlay. In many cases the decorative overlay is a foam and skin overlay that provides an attractive and tactilely pleasing surface suitable for use in the exposed interior of a vehicle. The airbag module of the invention also includes an airbag case portion suited to enclose a folded airbag cushion, and an airbag module cover interlock. The airbag module cover is configured to engage the airbag module cover interlock to attach the module housing to the instrument panel of the invention. According to the invention, such an interlock may utilize snap-fit fasteners to allow simple, predictable, and low-labor assembly of the airbag module cover and instrument panel of the invention.  
         [0051]     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.