Abstract:
A cover panel for the air bag in an automotive vehicle with an invisible deployment door section defined by pre-weakened hinge and tear seam formed on the underside of the instrument panel base substrate during the base substrate molding process. The hinge and tear seams are formed into the underside of the base substrate by projections extending from a lower surface mold preform and are differently proportioned in size to provide sequentially operating functions during air bag deployment. Flowing the liquid substrate material into opposing sides of the mold allow for more even cooling and smooth upper surface over the reduced thicknesses of the invisible door hinge and seams.

Description:
BACKGROUND 
   1. 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. 
   2. Description of the Prior Art 
   Most recently in this technology field, there is a desire to make the air bag deployment door in instrument panels and other locations invisible to occupants of the vehicle and achieve a desired aesthetic for vehicle interiors. Several patents show various techniques and materials used to form cover panels with invisible air bag deployment doors. 
   U.S. Pat. No. 6,453,535 discloses a process that employs a laser to provide a concealed deployment door and opening in a substrate panel. In that patent, the pre-weakened scoring traces out the door except for bridging tabs which remain to provide support for the door member. 
   U.S. Pat. No. 6,808,197 discloses a process that employs a multi-axis laser manipulator for providing continuous controlled scoring of the inside of an instrument panel to form a pre-weakened pattern. 
   U.S. Pat. No. 7,100,941 discloses various techniques of pre-weakening an outer woven material, including weakening the fabric from either the front or backsides by thinning, cutting or melting and by weaving in weaker yarns to define the pre-weakened pattern. 
   Each of the prior art attempts to provide a pre-weakened area that defines the door for air bag deployment requires post-processing steps that follow the manufacturing process for the instrument panel. 
   SUMMARY OF THE INVENTION 
   The present invention 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 invention 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 occupant, has the strength properties to resist inward pressures and opens properly during air bag deployment. The present invention is preferably implemented by molding in the hinge and tear seams at the same time the substrate for the instrument panel is being formed by a molding process. 
   It is an object of the present invention to provide an instrument panel for an automotive vehicle with a defined air bag deployment door including a relatively rigid base substrate structure having an outer surface and an inner surface and a relatively constant thickness between the surfaces surrounding the defined deployment door. An outer finish skin material is adhered to and overlies the outer surface. The base structure is molded to define the inner and outer surfaces and a deployment door section. The deployment door section is defined in the molded structure by reduced thicknesses in tear seams and hinge portions formed into the inner surface and maintaining the defined deployment door invisible from the outer surface. 
   It is another object of the present invention to provide a method of forming an invisible door in an instrument panel of an automotive vehicle that allows the deployment of an air bag and comprises the following steps: 
   providing a mold for an instrument 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 protrusions entering the space between the mold preforms to define at least one hinge seam and a plurality of tear seam indentations in the lower surface; providing said opposing perform to form a non-indented and smooth substrate surface at least in those areas facing where protrusions enter the space between the performs; providing the protrusion for the at least one hinge seam at a predetermined first height extending into the space between the mold preforms; providing the protrusions for the tear seams at predetermined heights that are greater than the first height; providing a protrusion for one of the tear seams opposing the at least one hinge seam at a second predetermined height that is greater than all other heights; 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 instrument panel from the mold preforms. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a portion of an interior cover panel having an air bag deployment door formed according to the present invention. 
       FIG. 2  is a cross-sectional view taken along section line  2 - 2  in  FIG. 1 . 
       FIG. 3  is a cross-sectional view taken along section line  3 - 3  in  FIG. 1 . 
       FIG. 4  is a cross-sectional view taken along section line  4 - 4  in  FIG. 1 . 
       FIG. 5  is a representation of liquid phase flow into a mold utilizing components of the present invention. 
   

   DETAILED DESCRIPTION 
   The cover panel  100 , shown in  FIG. 1 , is a portion of a larger structure such as a passenger side instrument panel, as viewed from its underside. However, it equally represents a driver side knee bolster panel, a steering wheel hub cover, or any other interior panel of an automotive vehicle through which an air bag can be deployed. Cover panel  100  is formed of a relatively rigid base structure  120  such as plastic or other material that provides the desired strength and rigidity for the panel. In the preferred embodiment, a thermoplastic substrate having a thickness t 0  of approximately 4 mm is utilized. The thickness t 0  of the base substrate structure  120  surrounding the defined door  110  is substantially constant. Base structure  120  has an inner surface  112  and an outer surface  114  ( FIG. 2 ). An external skin material  130  is attached to the outer surface  114  of the base structure  120  and is typically made as a laminate, as is described below with reference to  FIG. 2 . 
   An air bag deployment door  110  is defined by a hinge  210 , side tear seams  212   a  and  212   b  and initial tear seam  214 . Hinge  210 , and the tear seams  212   a ,  212   b  and  214  are formed in the lower surface  112  of the base structure  120 . In this invention, the hinge and tear seams are formed during the substrate molding process to define the deployment door. Several section lines  2 - 2 ,  3 - 3  and  4 - 4  are shown in  FIG. 1  to provide a basis for  FIGS. 2 ,  3 ,  3  and  4 , respectively. 
   In  FIG. 2 , the cross-section illustrates the initial rupturable tear seam  214  as molded into the base substrate  120 . The rear seam is formed in the base substrate  120  during the substrate molding process by use of a mold preform in the having a protrusion provided with a height and in the shape of the preferred cross-section of the initial rupturable tear seam  214 . In this illustration, the thickness t 1  of the base substrate above the initial rupturable tear seam  214  is approximately 0.25 mm or, in this case within the range on approximately 5%-10% of thickness to t 0  ensure that it will be weak enough to fracture and rupture when the underlying air bag is deployed from its storage container and chute  100 . The deployment door  110  as defined by the hinge  210  and the tear seams is shown on the left side of  FIG. 2 . The molded angle of approach α 1  for tear seam  214  is formed to be approximately 21° to provide a tapered thinness to the seam and extend the weakened area towards the door and away from the surrounding substrate  120 . Outer edge angle α 2  is approximately 1° from the vertical in order to facilitate withdrawal of the mold preform containing the protrusion for initial rupturable tear seam  214 . Pre-weakened fabric seam  132  in external skin material  130  is outwardly offset from the deployment door tear seam so as to be supported by the base substrate  120  during normal use prior to deployment of the air bag. This location resists inward pressures that may cause premature fracturing of the tear seam  214 . 
     FIG. 3  is a cross-sectional view taken along section lines  3 - 3  in  FIG. 1  and illustrates a side tear seam  212 . In this case, the side tear seam  212  is molded into the base substrate  120  so that the thickness t 2  between the protrusion from the lower mold preform and the upper mold preform is approximately twice the thickness t 1  of initial rupturable tear seam  214 . Here, the angle of approach α 3  is much steeper than α 1 —approximately 60°—to provide less area to be weakened along the tear seam  212 . Outer edge angle α 4  is approximately 1° from the vertical in order to facilitate withdrawal of the mold preform containing the protrusion for the side tear seam  212 . As in  FIG. 2 , the angle of approach is towards the defined deployment door  110 , rather than the surrounding base substrate  120 . Pre-weakened fabric seam  134  is formed in external skin material  130  and is outwardly offset from the side tear seams  212  so as to be supported by the base substrate  120  during normal use and prior to deployment of the air bag. 
   Pre-weakened fabric seams  132  and  134  may be created by several methods. In the preferred embodiment of the present invention, a mechanical weakening technique is used to satisfy the invisible seam requirement. Seams  132  and  134  are formed as a series of very small holes created in external skin material  130  in a pattern that generally corresponds to the tear seams of the deployment door while being offset outwardly from the tear seams. Holes are created by use of a highly focused laser beam tuned to provide substantially invisible holes that penetrate the skin material  130  sufficiently to allow tearing when the deployment door is being forced open due to air bag deployment. Such mechanical creation of seams  32  and  134  can be performed externally after the external skin material  130  is applied to the base substrate  120  or internally prior to applying the external skin material  130  to the base substrate  120 . 
   External skin material  130  may be of any conventional or non-conventional material, provided it can be pre-weakened in the fashion described herein to result in an invisible tear seam. For instance, a woven multilayered fabric, with a foam layer, leather, or foam underlayment and a hand-wrapped vinyl skin could be suitable. 
   In  FIG. 4 , a cross-sectional view of pre-weakened hinge  210  is shown which has a much wider dimension than the tear seams and has an upper thickness t 3  that is approximately twice the that of t 2 . When combined with a relatively high approach angle α 5  of approximately 60°, an outer edge angle α 6  of approximately 21° and a width l 1  that is approximately 2 mm at the hinge apex, this portion will result in a tethered hinge. That is, the base substrate  102  will bend at the apex area of  210  and will not fracture and separate during deployment of the air bag. 
   In  FIG. 5 , a representation is made of the preferred flow of liquid substrate material into a mold that comprises upper and lower mold preforms. The representation shows the lower mold preform  300  having a hinge projection  210 ′ that extends linearly between its ends  308  and  308 . The lower mold preform also has a pair of projections  212   a ′ and  212   b ′ that extend between their respective ends  308  and  311  and  309  and  310 . In addition, lower mold preform has with a projection  214 ′ that extends between its ends  310  and  311 . The projections correspond to the similarly non-prime numbered hinge and seams discussed above. Although not shown, it is understood that an upper mole preform of a relatively smooth surface is used to define the upper surface of the door  110  during the substrate molding process and is positions in opposition across a defined space equal to the thickness of the base substrate  120 . 
   It has been found that a superior mold is achieved when the liquid is forced at “A” into the deployment door mold area from opposite sides across the gates formed by projections  212   a ′ and  212   b ′. (Although the drawing shows flow direction at arrow A, it is understood that the flow over projections  212   a ′ and  21   b ′ is not confined to the arrow area, but rather is spread across the entire width of the projections.) Since the height of projections  212   a ′ and  212   b ′ are less than the height of projection  214 ′ and higher than projection  210 ′, there is an imbalance in resistance when the flow “B” enters into the door area. This imbalance allows greater flow to pass out of the door area at “C” and a lesser flow “D” to pass projection  214 ′. As a result, if the imbalance of flow at the gates of varying heights, there tends to be a balance of heat dissipating energy present at the gates which allows for more even curing and resultant quality in the molded product. A more even curing results in no or insignificant dimpling on the top surface of the hinge and seams that in turn allows the hinge and seams to be invisible. 
   As can be seen by the drawings and accompanying explanation, the present invention is a unique improvement over conventional air bag cover panels. And while the embodiment shown here is the preferred embodiment, it shall not be considered to be a restriction on the scope of the claims set forth below.