Abstract:
An air bag deployment apparatus is provided for use in an air bag deployment system of an automotive vehicle. The apparatus has a support base for attachment to a rear surface of an occupant facing substrate. A door support panel has upper and lower surfaces and four side edges for attachment to the rear surface of the substrate within the area of an air bag deployment door. An air bag chute extends downward from the support base and contains a plurality of skirt walls for defining a path for deployment of an air bag from beneath the substrate. A hinge element extends from one of the skirt walls to one edge of the door support panel wherein the hinge element has upper and lower surfaces joined by a left side surface and a right side surface. At least one of the side surfaces protruding from the skirt wall includes an undercut so that a lower corner of the hinge element forms an obtuse angle, resulting in better transfer of deployment forces through the hinge element.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates in general to air bag deployment systems for automotive vehicles, and, more specifically, to a door support panel structure that has an energy transmitting hinge formed integral with an air bag chute. 
     Air bag deployment chute assemblies have been put into commercial use for the passenger side of an instrument panel of automotive vehicles. The chute assembly couples an air bag module (typically containing a folded bag and chemical propellants for inflating the bag on command) to a door support panel (i.e., substrate) of the instrument panel. A typical structure for a chute assembly includes a tubular outer wall, one or more door flaps, and one or more hinge members connecting the door flaps to the outer wall. The hinge can be formed with a dual curved configuration that allows the hinge to straighten out as the air bag is deployed. 
     In copending published application US2010/0109296A1, a hinge element is disclosed that extends between a skirt wall of the air bag chute tube and one edge of a door support panel, and that includes a pair of pivoting elements and an arm extension. A first pivoting element is formed with a downwardly directed curve having one end connected to the inner side of the skirt wall and the other end connected to the second pivot element. The second pivot element is formed with an upwardly directed curve having one end connected to the first pivot element and the other end connected to an extension arm that extends upwards to the edge of the door support panel. During deployment of the associated air bag, the integrated structure allows energy forces presented to the door support panel to be partially dissipated into the structure via the hinge element. 
     The air bag module is typically required to be mounted with its top edge in a horizontal plane so that the chemical reaction and air bag expansion can be properly directed and controlled. The door support substrate, however, is typically not horizontal. Instead, it usually slopes from the center of the vehicle toward the passenger side of the vehicle. Since the door flap(s) and hinge member(s) follow the shape of the door support substrate, they are also not horizontal. As a result, the deployment forces from the expanding air bag can create a torque on the hinge member that could impair the hinge operation or even cause breakage of the hinge which reduces the dissipation of energy into the skirt wall. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, an air bag deployment apparatus is provided for use in an air bag deployment system of an automotive vehicle. The apparatus has a support base for attachment to a rear surface of an occupant facing substrate of the vehicle, wherein the support base has upper and lower surfaces and is configured to surround an air bag deployment door in the substrate defined by an area that is pre-weakened. A door support panel has upper and lower surfaces and four side edges for attachment to the rear surface of the substrate within the area of the air bag deployment door, wherein the door support panel is generally co-planar with the support base when attached to the rear substrate surface and all four side edges are separated from the support base along the rear substrate surface. An air bag chute extends downward from the support base and contains a plurality of skirt walls for defining a path for deployment of an air bag from beneath the substrate. A hinge element extends from one of the skirt walls to one edge of the door support panel wherein the hinge element has upper and lower surfaces joined by a left side surface and a right side surface. At least one of the side surfaces protruding from the skirt wall includes an undercut so that a lower corner of the hinge element forms an obtuse angle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a vehicle instrument panel illustrating air bag deployment areas. 
         FIG. 2  is a cross-sectional view of an air bag system having a chute connected to a substrate. 
         FIG. 3  is a top plan view of an embodiment of the air bag deployment apparatus with chute prior to installation in a vehicle. 
         FIG. 4  is a cross-sectional perspective view taken along section line  4 - 4  in  FIG. 3 . 
         FIG. 5  is diagram showing uneven deployment forces. 
         FIG. 6A  is a front plan view of a generic example of an undercut hinge according to one embodiment of the present invention. 
         FIG. 6B  is side view taken along section line  6 B- 6 B in  FIG. 6A . 
         FIG. 7  is a partial sectional view of an undercut hinge of another embodiment. 
         FIG. 8  illustrates the obtuse angle of the embodiment of  FIG. 7 . 
         FIG. 9  is another partial cross sectional view of the undercut hinge of  FIG. 7  taken at a position farther from the skirt wall. 
         FIG. 10  is a side view showing a varying position of a parting line for another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1-4 , a vehicle instrument panel  10  receives an air bag deployment structure  100 . A support base  101  is shown attached to the lower surface of a substrate  14  that forms part of the instrument panel  10 . A door support panel  104  is shown as also attached to the lower surface of the substrate, but positioned below an air bag deployment door that is defined by pre-weakened door seam  12  and hinge seam  13 . 
     Support base  101  is shown to have upper and lower surfaces. The upper surface of support base  101  contains a plurality of welding ribs  118  to facilitate attachment to the lower surface  11  of substrate  14  with a vibration welding process. (Of course other types of attachment such as ultrasonic welding, adhesives and other commonly known techniques may be acceptable substitutes, provided they preserve the energy absorbing characteristics described herein.) Door support panel  104  also contains welding ribs which are attached to the lower surface  11  of substrate  14  within an area defined as the air bag deployment door by the pre-weakened seams  12  and  13 . In this configuration, the door tear seam  12  is pre-weakened to the extent that the outer surface of instrument panel  10  and the substrate  14  will completely rupture upon deployment of the air bag. Seam  13  is a hinge seam and is only required to provide a pivot point for the substrate and outer skin of the instrument panel  10 . Therefore, it may be pre-weakened to a lesser extent than door seam  12 . 
     Air bag deployment structure  100  is preferably formed as a one piece molding of a flexible material such as Dexflex™ or other material that exhibits good ductility at very cold temperatures at least to −30° C. and good toughness at high temperatures at least to 90° C. Other materials such as TPO (Thermoplastic Olefin), TPE (Thermoplastic Elastomer), or TEO (Thermoplastic Elastomer Olefin) could be used. Various pieces could be separately formed and joined together to replicate a one-piece molded component. If that is done, care will have to be made in order to obtain the energy management that is offered by the integration of the various elements that make up the disclosed structure. 
     Support base  101  is a generally planar flange that is substantially coplanar with door support panel  104 . As shown in the figures, there is a slight curvature that is intended to correspond to the styled substrate surface to which the structure  100  attaches. 
     In the depicted embodiment, an alignment slot  137  is provided in an extension from support base  101 . Although not shown, the substrate  12  may have a protrusion formed therein and extending from its lower surface to provide a keying feature to be received in slot  137  in order to assist in the placement of the support structure  100  prior to being welded to the substrate. Apertures on tabs  131 ,  133 , and  135  extending from support base  101  are used to perform the same function as alignment slot  137  with protrusions extending from the lower surface of substrate  12 . 
     A test tab extension  139  is shown as having deformable ribs  136  that are is identical in content to weldable ribs  118  on support base  101  for attachment to the corresponding lower surface area of the substrate  12  during the same vibration welding process. The test tab extension  139  allows the welding vendor or subsequent customer to perform non-destructive quality control testing by applying a pull pressure to the tab and thereby ensure that the entire weld of the support structure  100  to the substrate is acceptable. 
     Door support panel  104  and support base  101  are separated by a gap  112  so that door support panel  104  is not directly attached to the support base  101 . The support base  101  extends under the pre-weakened door seams  12  and  13  and therefore provides resistance to inward pressures that may be applied to the outer surface of the instrument panel. In the depicted embodiment, several apertures  110  are shown in door support panel  104 . Apertures  110  are positioned to reduce the mass of the door support panel  104  without affecting its support or attachment properties. 
     An air bag chute tube is formed by skirt walls  105 ,  106 ,  107 , and  108  which extend downward from support base  101 . In this embodiment, the air bag chute tube has a substantially rectangular configuration defined by side skirt walls  105  and  107  and front and back skirt walls  106  and  108 . Angle gussets such as  128  are spaced along the skirt walls to provide added strength and some rigidity between the support base  101  and the air bag chute tube. 
     A hinge element  200  extends between skirt wall  108  and hinge edge  109  of door support panel  104 . Hinge element  200  includes respective first and second pivoting elements “A” and “B” and an arm extension  103 . From the end, it can be seen that the first pivoting element A is formed with a downwardly directed curve having one end connected to the inner side  111  of side skirt wall  108  and the other end connected to the second pivot element B. The second pivot element B is formed with an upwardly directed curve having one end connected to the first pivot element A and the other end connected to extension arm  103 . Extension arm  103  extends upwards from second pivot element B to hinge edge  109  of the door support panel  104 . Each pivot element is an axial extension substantially parallel to each other and to the edge of the door panel to which the arm extension  103  is connected. Each pivot element, as well as arm extension  103 , extends approximately the full length of the hinge edge  109 . 
     The longer side skirt walls  106  and  108  contain several window apertures  114  and  116  for engagement with a corresponding number of attachment hooks  304  and  306  extending from an air bag container  300 . Each window aperture  114  and  116  has a tab  115  and  117  that bear against the inserted hooks to tighten the engagement connections and prevent rattling from occurring between the air bag container and the air bag chute during vehicle operation prior to air bag deployment. 
     The lower portions of the side skirt walls  106  and  108  (below the windows  114  and  116 ) contain reinforcement barriers  122  and  124 . Reinforcement barriers  122  and  124  are formed as a doubled thickness of the side skirt wall material and are formed along the entire length of side skirt walls  106 / 108 . Reinforcement barriers act to prevent hooks  304  and  306  from completely tearing through the side skirt walls from their positions in the windows  114  and  116  when the air bag is deployed. When an air bag is deployed, there is severe pressure initially present from a gas canister  305  within the air bag container and chute. Because the air bag container  300  is fixed to the structure of the vehicle at mounting structure  307 , the hooks  304  and  306  prevent separation of the air bag support structure  100  and the instrument panel from their intended locations during air bag deployment. Hooks  304  and  306  interact with side skirt walls  106  and  108  below the windows  114  and  116  to contain the pressure and allow the chute to remain intact and direct the pressure to the door support panel  104 , which will force rupturing of the tear seams  12  and allow the air bag to deploy. Some prior art applications use metal side walls in air bag chutes to prevent tearing. In the present inventive concept where a thermoplastic material, such as noted above, is molded to form an integrated structure  100 , the double thickness reinforcement barriers  122  and  124  function to prevent the hooks from completely tearing through and allowing separation of the air bag support structure. 
     Referring to  FIG. 5 , an air bag container  20  has a top edge  21  that must be maintained horizontal for proper operation. An upper instrument panel surface  22  is typically not horizontal since a typical instrument panel is styled to be highest along a center line of the vehicle and to slope downward toward the driver&#39;s side and passenger&#39;s side of the vehicle. An air bag chute  23  attaches to container  20  and instrument panel  22  in a manner that accommodates for the difference in height at each end of container  20 . Upon deployment of the air bag, the inflating air bag fills a space  24  within the interior of chute  23 . As space  24  is filled with the expanding air bag such that a substantially equally rising pressure is present throughout space  24 , a sideways rotational torque  25  may result since one side of the deploying air bag extends to a higher elevation along the sloped inner surface of instrument panel  22  thereby causing uneven deployment forces. Torque  25  has a pivot axis that is perpendicular to the axis of the hinge element. Torque  25  is undesirable as it could create a tear along the hinge element where it attaches the air bag door to the chute. 
     The present invention handles the uneven forces by applying a special undercut at the end of the hinge experiencing the torque forces (i.e., the hinge corresponding to the higher end of the instrument panel substrate, as shown in  FIG. 6A . In an integrally molded plastic unit, a hinge  30  protrudes from a skirt wall  26  of an air bag chute between skirt walls  27  and  28 . Where it emerges from skirt wall  26 , hinge  30  has an upper surface  31  and a lower surface  32  joined by a left side surface  33  and a right side surface  34 . Both side surfaces  33  and  34  are shown with an undercut even though the increased torque forces would be applied only to one side surface. For purposes of standardizing design practices, facilitating mold design, and maintaining design flexibility, it is desirable to provide the undercut on both side surfaces. However, only the side surface corresponding to the end where the instrument panel is highest needs to have an undercut. 
     The top of left side surface  33  is defined by an upper cusp  35  extending away from skirt wall  26  as shown in  FIG. 6B . The bottom edge of side surface  33  provides a lower cusp  36 . According to the present invention, the undercut is comprised of an obtuse angle (i.e., greater than 90°) of the side surface with respect to is the bottom surface. Thus, the angle at lower cusp  36  is greater than 90°. The obtuse angle is preferably in the range of about 100° to about 150°, and more preferably within the range of about 115° to about 135°. 
       FIG. 7  shows the present invention used with a hinge element  200  having pivot elements of  FIGS. 2-4 . Where hinge element  200  protrudes from skirt wall  108 , it has an undercut side surface  40  between an upper cusp  41  and a lower cusp  42 . Due to the undercut, side surface  40  emerges from skirt wall  108  at an obtuse angle shown at  43 . As shown in  FIG. 8 , a lower left corner  44  of the side surface coincides with the lower cusp  42 . An imaginary line  45  passes through point  44  and an upper left corner where the side surface emerges from the skirt wall. An imaginary line  46  coincides with point  44  and the bottom surface of the hinge element. An angle  47  between imaginary lines  45  and  46  forms an obtuse angle. The obtuse angle provides an increased amount of material at the base of the hinge element for transmitting forces in a manner that provides greater resistance to tearing of the hinge element. As a result, the uneven deployment forces are better transferred to the skirt wall and the integrity of the hinge element is maintained. 
     To best utilize the added material from the undercut toward the top surface of the hinge element, the side surface preferably terminates with an acute edge at the upper cusp. However, maintaining a sharp edge at the upper cusp along the entire side surface of the hinge may be undesirable since it would provide a place where the air bag could bind during inflation. As shown in  FIG. 9 , a radius  50  may be provided in the upper cusp for portions of the hinge element away from skirt wall  108 . In connection with an integrally molded part, the parting line (corresponding to the break in the mold tooling used to manufacture the part) preferably coincides with the upper cusp at the point where it emerges from the skirt wall. As shown in  FIG. 10 , with increasing distances away from skirt wall  108 , a parting line  51  transitions from the upper cusp toward the lower cusp with increasing distance from skirt wall  108  so that the radius as shown in  FIG. 9  is achieved at or prior to the point where the parting line reaches door support panel  104 .