Patent Publication Number: US-2012038133-A1

Title: Invisible Tear Seam for an Air Bag Deployment Door

Description:
RELATED APPLICATIONS 
     This application is related to commonly assigned non-provisional application U.S. Ser. No. 12/111,684 filed Apr. 29, 2008, and published as 2009/0267329 on Oct. 29, 2009; non-provisional application U.S. Ser. No. 12/335,795 filed Dec. 15, 2008, and published as 2010/0147129 on Jun. 17, 2010; and U.S. Pat. No. 7,631,890, which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Field of the Invention 
     This invention relates to the field of air bag deployment covers for an automotive vehicle and more particularly to the area of a door panel structure that has a pre-weakened hinge and tearable seams formed for air bag deployment. 
     SUMMARY 
     The described embodiment is directed to an improved apparatus and method for providing invisible hinge and seams to define the air bag opening cover such as is located on the passenger side instrument panel of an automotive vehicle. The embodiment is also suited for a driver side steering wheel mounted air bag system or any other location where a pre-weakened and externally invisible tear seam is required. 
     With the variety of materials increasing for automotive interiors, it has been found that conventional scoring and pre-weakening techniques are not always effective to ensure that a deployment door can be formed which is invisible to the vehicle occupants, has the strength properties to resist inward pressures and opens properly during air bag deployment. The described embodiment is preferably implemented by forming the hinge and tear seams into the substrate layer as the substrate is being molded and prior to flowing the foam layer between the substrate and outer skin for the instrument panel. However, the hinge and tear seams could be machined into the substrate layer following molding. 
     It is an object of the described embodiments to provide a defined air bag deployment door for an automotive vehicle that is substantially invisible from the occupant section of the vehicle and that functions to properly open upon air bag deployment. The deployment door includes a relatively rigid base substrate structure having an outer surface and an inner surface and a relatively constant thickness between the surfaces surrounding a defined deployment door. A foam layer is adhesively attached to the outer surface of the substrate and an outer finish skin material is adhesively attached to and overlies the foam layer. 
     The base substrate structure is molded to define the inner and outer surfaces and the deployment door section. The deployment door section is defined in the molded structure by reduced thicknesses along the tear seam path formed into the inner surface. Elongated and spaced apart bridge elements formed at the top of the base substrate are separated along the tear seam path by complete voids in the substrate that combine to define the tear path for the air bag deployment door. The bridge elements are pre-weakened by a both a single reduced length dimension and a reduced thickness dimension, each of which run along the defined tear path. 
     It is another object of the described embodiments to provide a method of forming and defining an air bag deployment door in an automotive vehicle that allows the deployment of an air bag and comprises the following steps: 
     providing a mold for a panel substrate having a plurality of mold preforms placed in a spaced apart configuration for forming the substrate with upper and lower surfaces in an area that will define the deployment door of a first predetermined thickness; providing a mold preform for forming the lower substrate surface in the area that will define the deployment door; providing an opposing mold preform for forming the upper substrate surface in the area that will define the deployment door; providing the lower surface mold preform with a plurality of spaced apart and elongated protrusion elements entering the space between the mold preforms to define a plurality of tear seam indentations in the lower surface, wherein the protrusion elements alternate between a partial protrusion element and a complete protrusion element of the space between the preforms; providing the opposing perform to form a non-indented and smooth substrate surface at least in those areas facing where protrusion elements enter the space between the performs; flowing a liquid phase of the substrate material between the mold preforms; and allowing substrate material between the mold preforms to set to a self-supporting solid before removing the panel substrate from the mold preforms. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a portion of an interior of an automotive vehicle with defined air bag deployment doors. 
         FIG. 2  is a perspective view of a die that may be used to form a defined tear seam or hinge portion of an air bag deployment door. 
         FIG. 2A  is a top view of a portion of the die shown in  FIG. 2 . 
         FIG. 3  is a cross-sectional view taken along section line III-III in  FIG. 2  of a portion of the mold preforms placed for molding the base substrate of the airbag deployment door to illustrate the effect of the partial protrusion on the base substrate. 
         FIG. 4  is a cross-sectional view taken along section line IV-IV in  FIG. 2  of a portion of the mold preforms placed for molding the base substrate of the airbag deployment door to illustrate the effect of the full protrusion element on the base structure. 
         FIG. 5  is a lengthwise cross-sectional view taken along section line V-V in  FIG. 2  of a portion of the mold preforms placed for molding the base substrate of the airbag deployment door to illustrate the tear seam formed in the base substrate. 
         FIG. 6  is a cross-sectional view of a portion of the laminated layers of the airbag deployment door following forming of the base substrate, taken along the same section line as  FIG. 3  to illustrate the reduced thickness of a bridge element formed in the base substrate. 
         FIG. 7  is a cross-sectional view of a portion of the laminated layers of the airbag deployment door following forming of the base substrate, taken along the same section line as  FIG. 4  to illustrate the void created between bridge elements formed in the base substrate. 
         FIG. 8  is a lengthwise cross-sectional view of a portion of the laminated layers of the airbag deployment door following forming of the base substrate, taken along the same section line as  FIG. 5  to illustrate both the bridges and voids that define the tear seam path. 
         FIG. 9  is a perspective view of a portion of an alternative die that may be used to form a defined tear seam of an air bag deployment door in a base substrate. 
         FIG. 10  is a representation of the instrument panel and air bag deployment door containing disclosed embodiments. 
         FIG. 10A  is an enlarged view of a portion of a first embodiment of the pre-weakened seam in the air bag deployment door shown in  FIG. 10 . 
         FIG. 10B  is an enlarged view of a portion of an alternative embodiment of the pre-weakened seam in the air bag deployment door shown in  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  represents a typical vehicle instrument panel  10  in an automotive vehicle  100  into which any of the described embodiments may be included. Additionally, the embodiments are suitable for inclusion in a steering wheel air bag module  20 . An air bag deployment door  16  is shown as being defined by tear seams  12  and a hinge portion  14 . In  FIGS. 10 ,  10 A and  10 B, first and second embodiments of a pre-weakened tear seam and hinge are represented enlarged and as invisible to the vehicle occupant.  FIGS. 2-8  are enlargement views of elements from a sample portion of a mold preform used to define the tear seam  12 . Similar tear seams can be defined in the steering wheel hub substrate. While the instrument panel air bag deployment door  16  typically may have a “C” shaped configuration with a single hinge portion, the steering wheel air bag deployment door typically may have an “H” shaped configuration with two hinges. The described embodiments are suitable for any air bag deployment door configurations. 
     In  FIG. 3 , a base substrate  161  is shown which is first molded to a predetermined configuration employing a pre-weakened seam, prior to being used for the base of the instrument panel and an air bag deployment door. The base substrate is formed by a method that includes providing a mold for a panel substrate having a plurality of mold preforms  100  and  200  placed in a spaced apart configuration for forming the substrate  161  with upper and lower surfaces in an area that will define the deployment door of a first predetermined thickness. A mold preform, such as die plate  200  shown in  FIGS. 2 and 2A , is used for forming the lower substrate surface  162  in the area that will define the deployment door. An opposing mold preform  100  is used for forming the upper substrate surface  164  in the area that will define the deployment door. Die plate  200  is provided with an elongated partial protrusion element  220  and plurality of spaced apart and elongated full protrusion elements  230   a - 230   n  entering the space between the mold preforms to define at least one hinge seam  14  and a plurality of tear seam  12 . Partial die protrusion element  220  defines a door seam tear path with a triangular cross-section in the form of a polyhedron that enters lower surface  162  and extends partially through the thickness of the substrate. When molded, partial die protrusion element  220  forms a void  404  in the molded base substrate  161  that runs continuously along the tear path. Full protrusion elements  230   a - 230   n  extend from the upper edge  218  of partial protrusion element  220  and are separated by spaces  201   a - 201   n . In the mold, the full protrusion elements  230   a - 230   n  preferably abut the underside of mold preform  100  and provide an elongated series of voids in the base substrate  161  that alternate between a partial void  404  and a complete void of combined  404 / 402  as seen in  FIGS. 6-8 . The spaces  201   a - 201   n  result in base substrate material forming bridges  165  that are pre-weakened by a reduced length dimension and reduced thickness dimension along the tear path line. 
     The substrate base  161  is formed by flowing a liquid phase plastic material—preferably a TPO (Thermoplastic Olefin)—between the mold preforms  100  and  200 . By allowing substrate material between the mold preforms to cool and set for a predetermined period of time before removing the panel substrate from the mold preforms, a self-supporting solid base structure  161  is formed with pre-weakened tear seams  12  and hinge  14 . 
       FIGS. 2 and 2A  provide detail of a first embodiment of the die configuration utilized to achieve the molded in a pre-weakened tear seam path that defines an air bag deployment door in base substrate  161 . The protrusion part of die  200  includes an elongated partial protrusion element  220  which has a generally polyhedron prism shape with a triangular cross-section containing faces  214  and  216  that run along its length. Although only a small section is shown in  FIGS. 2 and 2A , it is understood that protrusion element  220  continuously extends along a path to outline and define tearable seam  12  of air bag deployment door  16 . 
     Elongated full protrusion elements  230   a - 230   n  extend from upper edge  218  of partial protrusion element  220  and are separated by spaces  201   a - 201   n . Each full protrusion element  230  contains a top portion  231  that abuts the surface of upper mold preform  100 . Upright end walls  232 ,  233 ,  234  and  235  combine with side surfaces  236  and  238  to provide an elongated polyhedral or diamond shape to the voids  402  ( FIGS. 7 and 8 ) that are molded into base substrate  161 . The planar end walls  232 / 233  and  234 / 235  of elongated full protrusion elements  230   a - 230   n  meet at acute angels to define narrow ends aligned along the tear seam path. With that elongated and generally pointed shape, bridge  165  of base material that is left between each void  402  created by each full protrusion element  230  has a narrowed and diminished length dimension of substrate material that runs along the defined tear seam path. 
     Since it is desirable to create a hinge seam that freely flexes but does not separate or tear during air bag deployment, the hinge portion  14  of die  200  would include a partial protrusion element  220  extending along and defining the hinge path. In most cases, it would not be necessary to include full protrusion elements when forming a hinge path. 
     In  FIGS. 6 ,  7  and  8 , the completed laminated structure of the panel containing the air bag deployment door is shown in various cross-sections. 
     Subsequent to forming the base substrate  161 , an intermediate TPO foam layer  181  is adhesively attached to the upper surface  164  of base substrate  161 . A class “A” outer skin  111 , also preferably a TPO material, is adhesively attached to foam layer  181  to complete the lamination process. During implementation of the laminating process, the layers are subjected to a vacuum applied to the underside of the base layer  161  to draw down the layers during curing of the adhesive layers. While it is common to provide vent holes in the base to support the vacuum lamination process, voids  402  created along the tear seams and hinge provide additional access for vacuum to be applied to the layers. 
     In  FIG. 6 , the cross-section illustrates the triangular polyhedral shaped void  404 , created by elongated partial protrusion element  220 , extends from break  405  to break  406  in lower surface  162  of base substrate  161 . Void  404  is separated from upper surface  164  of base substrate  161  by a bridge of base substrate material  165  that was allowed to flow into each space  201  defined between each full protrusion element  230 . The top ridge of void  404  runs along the defined tear seam and extends into each bridge element  165 , resulting in a reduced thickness along the length of bridge  165 . 
     In  FIG. 7 , the cross-section illustrates how each void  404 / 402 , created by elongated partial protrusion element  220  and a full protrusion element  230 , provide a complete opening in the base structure  161 . These voids are located between each bridge  165  and, together with the bridges  165 , define the weakened tear seam path  12  of the air bag deployment door  16 . 
     In  FIG. 8 , the cross-section of the laminated structure taken lengthwise along a seam portion illustrates voids  402  above partial voids  404  separated by bridges  165  of substrate material  161 . In this embodiment, the bridges are of equal length and the voids are of equal length in a hinge path. The same may be provided for a tear seam path, except where the designer of the system may want to vary the weakness of the seam in order to determine which portion opens first during an air bag deployment. In such as case, the length of bridges may be decreased or voids may be lengthened or some combination to achieve the desired result. 
     The series of bridges  165  along the tear seam path together provide the strength necessary to maintain smooth and invisible tear seam structure of the base material. Because of the elongated and generally pointed shape of the voids  402  shown in  FIGS. 6-8 , as viewed through the cross-section of the base substrate  161  and  FIGS. 10 and 10A  (as invisibly viewed from above the instrument panel  10 ), the bridge element  165  of base material  161  that is left between each void  402  has a narrowed and diminished material composition that extends from break  405  to break  406 . This results in a single reduced dimension that runs along the centerline  166  of the defined tear seam path, from one bridge  165  to another. Combined with the reduced thickness line, the pre-weakened path in each bridge  165  becomes predictable and defined. 
     The series of bridges  165  are at the top of the substrate, flush with the upper surface  164 , and are pre-weakened both by the reduction in length between the indentations formed at each end and by the reduced thickness dimension provided by the top of triangular void  404  formed in their lower surfaces. The weakening end indentations as well as the top of the triangular void  404  each run along the centerline of the tear seam path. This combination of indented ends, triangular thicknesses, along with adjacent voids provide a tear seam that is weak enough to cleanly and precisely control the tear path for the defined deployment door during an air bag deployment event. 
     An alternative embodiment configuration for the elongated full protrusion elements of a die  300  are shown in  FIG. 9 . In  FIG. 9 , full protrusion elements  330   a - 330   n  are illustrated as ellipses or ovals extending upwards from the upper edge  318  of a prism shaped partial protrusion element  320  having side faces  314  and  316 . In this embodiment, full protrusion elements  330 - 330   n  are separated by spaces  301   a - 301   n , which result in bridge elements  165 ′ being formed during molding of the base substrate (also see  FIGS. 10 and 10B ). 
     As further illustrated in  FIGS. 10 and 10B , the series of bridges  165 ′ and voids  402 ′ along the tear seam path together provide the strength necessary to maintain smooth and invisible seam structure of the base substrate. Because of the elongated and generally truncated shape of the ends of voids  402 ′, as invisibly viewed from above the instrument panel  10 , the bridge  165 ′ of base substrate material that is present between each void  402 ′ has a narrowed and diminished material composition that results in a single reduced dimension running along the centerline  166 ′ of the defined tear seam path from one bridge  165 ′ to another. 
     The series of bridges  165 ′ are at the top of the substrate, flush with the upper surface  164 , and are pre-weakened both by the reduction in length between the indentations formed at each end by protrusion elements  330  and by the top of triangular void  404 ′ formed in their lower surfaces by partial protrusion element  320 . The weakest portion of each bridge  165 ′ is defined by the least length dimension provided by the end indentations, as well as the least thickness defined by the top of the triangular void  404  to purposely coincide with the centerline  166 ′ of each bridge  165 ′ and precisely define the tear seam path. This combination of indented ends, triangular thicknesses, along with adjacent voids provide seams that are weak enough to cleanly and precisely control the tear path for the defined deployment door during an air bag deployment event. The combination also coincides with the center line of each bridge and is strong enough to provide support for the laminated layers that provide the desired smooth surface in which the tear seam is invisible to the vehicle occupant. 
     Each embodiment has the common characteristic of providing in-mold pre-weakened tear seam of an air bag deployment door in the base substrate material of a subsequently laminated panel structure, wherein each seam is made up of a continuous void path that extends into a portion of the substrate and a series of spaced apart and elongated voids that extend through only the base substrate of the laminated panel structure. This configuration provides a series of pre-weakened substrate bridge elements which are able to fracture and separate during air bag deployment along a predetermined and precise tear seam path. 
     As can be seen by the drawings and accompanying explanation, the described embodiments are unique improvements over conventional air bag deployment door path configurations. And while the embodiments shown here are preferred, they shall not be considered to be a restriction on the scope of the claims set forth below.