Patent Publication Number: US-2004051280-A1

Title: Air bag door

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates to an air bag door for helping to enclose an air bag in a vehicle.  
       BACKGROUND OF THE INVENTION  
       [0002] It is known to provide an inflatable vehicle occupant protection device, such as an air bag, for helping to protect an occupant of a vehicle. One particular type of air bag is a front impact air bag inflatable between an occupant of a front seat of the vehicle and an instrument panel of the vehicle. Such air bags may be driver side air bags or passenger side air bags. When inflated, the air bags help protect the occupant from impacts with parts of the vehicle, such as the instrument panel.  
       [0003] Passenger side air bags are typically stored in a deflated condition in a housing that is mounted in the vehicle instrument panel. An air bag door is connectable to the housing and/or instrument panel to help conceal and enclose the air bag in a stored condition. The air bag door has a surface that forms a portion of a surface of the instrument panel that is visible to vehicle occupants. These visible surfaces are sometimes referred to as “class A” surfaces of the vehicle. Since the class A surface is visible to vehicle occupants, it is desirable for the class A surface of the air bag door to have an attractive aesthetic appearance.  
       [0004] Upon deployment of the passenger side air bag, the air bag door opens to permit the air bag to move to an inflated position. The air bag door opens as a result of forces exerted on the door by the inflating air bag. In order to help prevent injury to the vehicle occupant, the air bag door is structurally reinforced so that the door does not break apart or fragment during deployment of the air bag. The air bag door may also be connected to the instrument panel by means, such as a hinge or strap, so that the door is retained near the instrument panel during air bag deployment.  
       [0005] Known air bag doors have a multi-piece construction including a base or frame structure constructed of a high strength material, such as metal. A layer of foam material is fixed to the base by means such as molding the foam around the base. The foam material is then coated with a layer of skin material, such as vinyl, which forms the class A surface of the air bag door. The frame structure helps provide the requisite strength for withstanding deployment of the air bag.  
       SUMMARY OF THE INVENTION  
       [0006] The present invention relates to an apparatus for helping to protect an occupant of a vehicle. The apparatus includes an inflatable vehicle occupant protection device inflatable from a stored position to an inflated position. The apparatus also includes an inflation fluid source that is actuatable to provide inflation fluid for inflating the inflatable vehicle occupant protection device. The apparatus further includes a molded portion molded as a single piece of plastic material and associated with the inflatable vehicle occupant protection device. The molded portion includes a base portion and a reinforcing portion. The base portion has a first surface, an opposite second surface, and a first thickness measured between the first and second surfaces. The first surface forms a class A surface in the vehicle. The reinforcing portion includes a main wall portion spaced from the second surface and at least one side wall extending from the main wall portion to the second surface and merging with the second surface. The at least one side wall has a second thickness about equal to the first thickness. The main wall portion, base portion, and at least one side wall define a chamber in the molded portion.  
       [0007] The present invention also relates to an apparatus that that includes an inflatable vehicle occupant protection device inflatable from a stored position to an inflated position. An inflation fluid source provides inflation fluid for inflating the protection device. A door helps to enclose the protection device in the stored position. The door includes a molded portion molded as a single piece of plastic material, a bracket at least partially embedded in the molded portion, and a tether secured to the bracket for connecting the door to the vehicle. The molded portion includes a base portion and a reinforcing portion. The base portion has a first surface and a second surface opposite the first surface. The first surface forms a class A surface in the vehicle. The base portion has a first thickness measured between the first and second surfaces. The reinforcing portion includes a main wall portion spaced from the second surface and at least one side wall extending from the main wall portion to the second surface and merging with the second surface. The at least one side wall has a second thickness about equal to the first thickness. The main wall portion, base portion, and the at least one side wall define a chamber in the door.  
       [0008] The present invention also relates to a door for helping to enclose an air bag in a vehicle. The door includes a molded portion and a bracket at least partially embedded in the molded portion. The molded portion includes a base portion and a reinforcing portion. The base portion has a first thickness measured between a first class A surface and an opposite second surface of the base portion. The reinforcing portion includes a main wall portion spaced from the second surface and at least one side wall extending from the main wall portion, merging with the second surface, and having a second thickness about equal to the first thickness. The main wall portion, base portion, and at least one side wall define a chamber that receives a pressurized gas during molding of the door. The pressurized gas exerts a force on the main wall, base portion, and at least one side wall during cooling of the plastic material.  
       [0009] The present invention further relates to a method for producing an air bag door for helping to enclose an air bag in a stored position in a vehicle. The method includes the step of providing a mold including a first mold piece and a second mold piece, the mold having a closed condition in which a mold cavity is defined between the first and second mold pieces. The method also includes the steps of placing a metal bracket in the mold cavity, placing the mold in the closed condition, and injecting a molten plastic material into the mold cavity to fill the mold cavity at least partially. The molten plastic material forms a molded portion of the air bag door in the mold cavity that at least partially surrounds the bracket. The molded portion includes a base portion having a first surface, a second surface opposite the first surface, and a first thickness measured between the first and second surfaces. The molded portion further includes at least one side wall for reinforcing the air bag door and supporting the bracket. The at least one side wall extends transverse to the base portion, merges with the second surface, and has a second thickness about equal to the first thickness. The method further includes the step of injecting a pressurized gas into the mold cavity. The gas when injected into the mold cavity helps form a chamber of the air bag door, the chamber being bounded by the at least one side wall, the second surface, and a portion of the molded portion overlying the bracket. The pressurized gas pressurizes the chamber and exerts a force on the main wall portion, the base portion, and the at least one side wall during cooling of the plastic material. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010] The foregoing and other features of the present invention will become apparent to one skilled in the art to which the present invention relates upon consideration of the following description of the invention with reference to the accompanying drawings, in which:  
     [0011]FIG. 1 is a schematic illustration of a vehicle including an air bag in a stored condition enclosed by an air bag door constructed in accordance with an illustrated embodiment of the present invention;  
     [0012]FIG. 2 is a schematic illustration of the vehicle of FIG. 1, illustrating the air bag in a deployed condition;  
     [0013]FIG. 3 is a rear plan view of the air bag door of FIGS. 1 and 2;  
     [0014]FIG. 4 is a sectional view taken generally along line  4 - 4  in FIG. 3;  
     [0015]FIG. 5 is a sectional view taken generally along line  5 - 5  in FIG. 3;  
     [0016]FIG. 6 is a sectional view taken generally along line  6 - 6  in FIG. 3;  
     [0017]FIG. 7 is a sectional view taken generally along line  7 - 7  in FIG. 3;  
     [0018]FIG. 8 is a sectional view taken generally along line  8 - 8  in FIG. 3;  
     [0019]FIG. 9 is a side plan view of a portion of a known molded plastic structure; and  
     [0020]FIG. 10 is a schematic representation of a mold used to construct a portion of the air bag door of FIGS.  1 - 8 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0021] The present invention relates to an inflatable vehicle occupant protection device for helping to protect an occupant of a vehicle. More particularly, the present invention relates to an apparatus for helping to enclose an air bag in a vehicle. As illustrated in FIGS. 1 and 2, the apparatus  10  comprises an air bag door  40  for helping to enclose an air bag  14  in a vehicle  12 . In the illustrated embodiment, the air bag  14  is a passenger side front impact air bag for helping to protect an occupant  20  in a passenger side  24  of the vehicle  12 . In the illustrated embodiment, the occupant  20  is positioned in a seat  22  in the passenger side  24  of the vehicle  12 .  
     [0022] As illustrated in FIGS. 1 and 2, the air bag  14  may be part of an air bag module  30  that includes an inflator  32  and a housing  34 . The air bag  14  has a stored condition in which the air bag is folded and placed in the housing  34 . The housing  34  and thus the module  30  is connected to an instrument panel  36  of the vehicle  12  on the passenger side  24  of the vehicle. The housing  34  helps contain and support the air bag  14  and inflator  24  in the instrument panel  36 .  
     [0023] The air bag door  40  is releasably connected to the instrument panel  36  and/or the housing  34 . The air bag door  40  forms a cover for the module  30  and helps enclose the air bag  14  in the stored condition in the housing  34 . An outer surface (FIG. 1) of the air bag door  40  forms a class A surface  42  of the instrument panel  36  that is visible to passengers  20  of the vehicle  12 .  
     [0024] The inflator  32  (FIGS. 1 and 2) is actuatable to provide inflation fluid for inflating the air bag  14 . The inflator  32  may be of any known type, such as stored gas, solid propellant, augmented, and hybrid. The apparatus  10  includes a sensor, illustrated schematically at  50 , for sensing an event for which occupant protection is desired, such as a collision. The inflator  32  is operatively connected to the sensor  50  via lead wires  52 .  
     [0025] Upon sensing the occurrence of an event for which occupant protection is desired, the sensor  50  provides a signal to the inflator  32  via the lead wires  52 . Upon receiving the signal from the sensor  50 , the inflator  32  is actuated in a known manner and provides inflation fluid to the air bag  14 . The air bag  14  inflates from the stored condition of FIG. 1 to a deployed condition illustrated in FIG. 2. The air bag  14 , while inflated, helps protect the vehicle occupant  20  from impacts with parts of the vehicle  12 , such as the instrument panel  36 .  
     [0026] As the air bag  14  inflates, the inflating air bag exerts a force on the air bag door  40 . This force causes the door  40  to disengage from the instrument panel  36  and/or housing  34 , which allows the air bag  14  to inflate from the stored position (FIG. 1) to the deployed position of FIG. 2. The module  30  also includes means, such as a tether  44 , for connecting the door  40  to the instrument panel  36  and/or housing  34 . The tether  44  helps retain the door  40  near the instrument panel  36  when the air bag  14  is deployed. This helps prevent the air bag door  40  from hitting or otherwise contacting the occupant  20  when the air bag  14  is deployed.  
     [0027] Referring to FIGS.  3 - 8 , the air bag door  40  includes a molded portion  60  and a bracket  62 . The molded portion  60  supports the bracket  62  in the illustrated position relative to the molded portion. The molded portion  60  is constructed of an elastomeric material, such as plastic. Examples of such plastic materials are polyvinyl chloride (PVC), thermoplastic elastomers (TPE) such as polypropylene and polypropylene copolymers, thermoplastic polyolefin elastomers (TPO) such as polypropylene and ethylene propylene diene monomers (EPDM), thermoplastic elastomers based on polyether esters and polyester esters (TPEE), copolyester (TEEE), thermoplastic vulcanizates (RPV), rubber modified polypropylene (EMPP), and PA6/PA66 nylon. Other suitable elastomeric materials may also be used.  
     [0028] The bracket  62  is constructed of a generally strong and rigid material, such as steel. The molded portion  60  is molded around the bracket by means such as insert molding. In this instance, the bracket  62  is placed in a mold and molten plastic material, referred to as “melt”, is injected into the mold. The melt at least partially fills the mold cavity and at least partially surrounds the bracket  62 , forming the molded portion  60 . The bracket  62  is thus at least partially embedded in the molded portion  60 . The molded portion  60  forms a single piece of material that at least partially surrounds the bracket  62  and supports the bracket in the air bag door  40 .  
     [0029] In the illustrated embodiment, the air bag door  40  has a generally rectangular configuration. It will be appreciated, however, that the door  40  may have any desired shape depending on a variety of factors, such as the shape or configuration of the structure (e.g., the instrument panel  36 ) in which the door is implemented. The molded portion  60  of the air bag door  40  includes a base portion  64  and a rim portion  66  that extends transverse to the base portion along a periphery  68  of the base portion. The base portion  64  has a generally planar configuration and may be slightly curved as shown in FIGS. 4 and 5. One surface of the base portion  64  forms the class A surface  42  of the air bag door  40 . The base portion  64  includes an inner surface  80  opposite the class A surface  42 .  
     [0030] The rim portion  66  includes an upper side wall  70 , an opposite lower side wall  72  and spaced end walls  74  and  76  of the air bag door  40 . As viewed in FIG. 3, the air bag door  40  has a length measured in a direction parallel to the upper and lower side walls  70  and  72  from the end wall  74  to the end wall  76 . The air bag door  40  also has a width measured in a direction perpendicular to the length and parallel to the end walls  74  and  76  from the upper side wall  70  to the lower side wall  72 . In the illustrated embodiment, the rim portion  66  extends along the entire periphery  68  of the base portion  64 . The rim portion  66  could, however, extend along a portion or selected portions of the periphery  68 .  
     [0031] The air bag door  40  also includes a plurality of fastener support portions  90  molded integrally with the molded portion  60  of the door. In the illustrated embodiment, the air bag door  40  includes six fastener support portions  90 . The support portions  90  are spaced along the upper side wall  70  and lower side wall  72  and merge with the rim portion  66 . It will be appreciated, however, that the number and positioning of the support portions  90  may vary.  
     [0032] Referring to FIGS. 3, 5, and  6 , each support portion  90  includes a planar, generally rectangular, main portion  92  that merges with a terminal edge  98  of the rim portion  66  and extends transverse to the rim portion. A pair of support legs  94  extend from opposite edges of the main portion  92  and diverge from each other at an acute angle relative to the main portion. The support legs  94  merge with the inner surface  80  of the base portion  64 . The support legs  94  may also merge with the rim portion  66 , as best shown in FIG. 3.  
     [0033] Each support portion  90  also includes an aperture  96  that extends through the main portion  92 . The apertures  96  are adapted to receive means (not shown) for releasably connecting the air bag door  40  to the vehicle  12 , i.e., to the housing  34  and/or instrument panel  36  (see FIGS. 1 and 2). Such means may include, for example, fasteners or pins extendable through the aperture  96  to connect the door  40  to the vehicle  12 .  
     [0034] Referring to FIGS.  3 - 5  and  7 , a reinforcing portion  100  of the air bag door  40  is positioned within the periphery  68  of the base portion  64 . The reinforcing portion  100  helps bolster the structural integrity of the air bag door  40  so that the door may withstand forces experienced during deployment of the air bag  14 . The reinforcing portion  100  also helps provide means by which to connect the air bag door  40  to the vehicle  12  via the tether  44 .  
     [0035] As shown in FIGS.  3 - 5  and  7 , the reinforcing portion  100  comprises a portion of the molded portion  60  that projects from the inner surface  80  of the base portion  64 . The reinforcing portion  100  is molded around the bracket  62  and thus connects the bracket to the door  40 . The reinforcing portion  100  includes a main portion  102  and a pair of ribs  104  that extend from the main portion.  
     [0036] The main portion  102  includes spaced first and second side walls  110  and  112 , respectively, that extend parallel to the length of the air bag door  40 . The main portion  102  also includes third and fourth side walls  114  and  116 , respectively, that extend transverse to the first and second side walls  110  and  112  in a direction parallel to the width of the air bag door  40 . The third and fourth side walls  114  and  116  intersect the second side wall  112  and extend toward the first side wall  110 . One of the ribs  104  merges with the first and third side walls  110  and  114 . The other rib  104  merges with the first and fourth side walls  110  and  116 .  
     [0037] Referring to FIGS. 3 and 5, the bracket  62  has a bent configuration and includes a main portion  120 , a flange portion  122 , and an angled portion  124  that extends between the main portion and flange portion. The main portion  120  is spaced from the inner surface  80  of the base portion  64 . The flange portion  122  engages and overlies the inner surface  80  of the base portion  64 . The bracket  62  is sandwiched between layers  130  and  132  of the reinforcing portion  100 . The layers  130  and  132  follow the contour of the main portion  120 , flange portion  122 , and angled portion  124 .  
     [0038] The portions of the layers  130  and  132  extending along the main portion  120  of the bracket  62  form a main wall  126  of the reinforcing portion  100 . The portions of the layers  130  and  132  extending along the flange portion  122  and angled portion  124  help define the first side wall  110  of the reinforcing portion  100 . The side walls  110 ,  112 ,  114 , and  116  extend from peripheral edges of the main wall  126  to the base portion  64  and merge with the inner surface  80  of the base portion. As shown in FIG. 3, one of the support portions  90  positioned centrally along the lower edge  72  merges with the main wall  126  and the second side wall  112  of the reinforcing portion  100 .  
     [0039] Referring to FIG. 7, the bracket  62  includes means for connecting the tether  44  to the air bag door  40 . In the illustrated embodiment, the bracket  62  includes a plurality of studs  140  that extend from the main portion  120  through the layer  130  of the reinforcing portion  100 . It will be appreciated, however, that the bracket  62  may include various alternative means for connecting the air bag door  40  to the tether  44 .  
     [0040] Each stud  140  has a shaft portion  142  that extends through the main portion  120  of the bracket  62 . A head portion  144  of each stud engages the main portion  120  and is positioned between the main portion and the layer  132  of the reinforcing portion  100 . As shown in FIG. 7, the layer  132  may be contoured around the head portions  144  of the studs  140 . The studs  140  are connected to the main portion  120  by known means, such as welding, adhesives, and mechanical clinch fit.  
     [0041] The tether  44  is constructed of a flexible material, such as fabric, so as to permit movement of the air bag door  40  during deployment of the air bag  14 . Alternative materials, such as elastomers, could also be used to construct the tether  44 . In the embodiment illustrated in FIG. 7, a single tether  44  is connected to all four studs  140 . It will be appreciated, however, that multiple tethers (not shown) could be used to connect the air bag door  40  to the vehicle. For example, four separate tethers could be connected individually to respective ones of the four studs  140 .  
     [0042] The reinforcing portion  100  includes a pair of apertures  150  that extend through the layer  130  and expose the main portion  120  of the bracket  62 . The apertures  150  provide access to the bracket  62  to help position the bracket while molding the molded portion  60  around the bracket. The location and number of apertures  150  may vary.  
     [0043] Referring to FIG. 8, each rib  104  includes a pair of opposing side walls  160  that merge with the inner surface  80  of the base portion  64 . The side walls  160  extend at acute angles from the inner surface  80  and converge towards each other. The side walls  160  meet at an intersection  162  spaced from the inner surface  80 . The ribs  104  help reinforce the air bag door  40  to help provide the door with a desired strength and rigidity. This helps the air bag door  40  withstand forces associated with air bag deployment.  
     [0044] Referring to FIGS. 4, 5, and  7 , the air bag door  40  includes a chamber  170  positioned between the base portion  64  and the reinforcing portion  100 . The chamber  170  is defined by the spaced base portion  64  and main wall  126 , and by the first, second, third and fourth side walls  110 ,  112 ,  114 , and  116 , which extend from the base portion to the main wall. The chamber  170  thus has a generally rectangular configuration as viewed in the plan view of FIG. 3. The chamber  170  could, however, have an alternative configuration depending on factors such as the size or shape of the reinforcing portion  100  and/or the air bag door  40 .  
     [0045] Those skilled in the art will appreciate that, when providing a molded vehicle part that forms a class A surface in the vehicle, it is desirable that the class A surface have an attractive aesthetic appearance. One particular problem known in the field of providing molded vehicle parts is referred to as sink marks. This problem is illustrated by way of example in FIG. 9.  
     [0046] Referring to FIG. 9, a vehicle part  200  constructed of a molded plastic material has a nominal wall  202  and a projection  204 , such as a rib. In this example, the nominal wall  202  forms a class A surface  206 . As illustrated in FIG. 9, the thickness of the nominal wall  202  and the thickness of the projection  204  are about equal to each other. As a result, a sink mark  210  is formed in the class A surface  202  during molding of the part  200 . The sink mark  210  is formed on the class A surface  202  opposite the intersection of the nominal wall  202  and the projection  204 . The sink mark  210 , being located on the class A surface  202 , would thus be visible to a vehicle occupant and would thus be considered an undesirable aesthetic defect in the class A surface  202 .  
     [0047] The sink mark  210  occurs because the intersecting nominal wall  202  and projection  204  form a section of material, indicated generally at  212 , that has a large cross-sectional area relative to the thickness of the nominal wall. When the hot melt is injected into the mold, the section  212 , having a large area relative to surrounding portions (i.e., the nominal wall  202  and the projection  204 ) of the part  200 , cools at a slower rate than the surrounding portions. The surrounding portions also help insulate the section  212 , which further slows the cooling rate of the section. Thus, as the section  212  cools, it shrinks at a different rate than the surrounding portions. This difference in cooling rates causes the section  212  to draw inward and create the sink mark  210  on the class A surface  206  the part  200 .  
     [0048] In order to help eliminate sink marks in molded plastic parts, it is known to limit the thickness of projections from the nominal wall to help reduce the cross-sectional area at the intersection of the nominal wall and the projection. For example, a general rule for preventing sink marks is to limit the thickness of projections to about 50% to 60% of the thickness of the nominal wall. This rule may vary depending on the particular type of material. For example, high shrinkage materials (e.g., nylon, polypropylene) are prone to sink marks and thus may require a lower projection thickness. Low shrinkage materials (e.g., polycarbonate, polystyrene) may withstand a higher projection thickness without producing sink marks. The example materials cited above (PVC, TPE, TPO, EPDM, TPEE, TEEE, RPV, EMPP, and PA6/PA66 nylon) adhere to the general 50% to 60% rule.  
     [0049] The general rule stated above may be implemented in portions of the illustrated embodiment of the present invention. For example, the support walls  94  of the support portions  90  and the side walls  160  of the ribs  104  (see FIGS. 6 and 8) comprise projections from the nominal wall, i.e., the base portion  64  of the air bag door  40 . It will be appreciated that the support walls  94  and the side walls  160  each have a thickness of about 50% to 60% of the thickness of the base portion  64 , as dictated by the general rule. This helps to prevent sink marks on the class A surface  42  of the air bag door  40  opposite the support walls  94  and side walls  106 .  
     [0050] As a feature of the present invention, the air bag door  40  is constructed of a plastic material using a gas assisted molding technique. The gas assisted molding technique allows the projection thickness dictated by the general rule to be increased without producing sink marks. According to the present invention, the air bag door  40  is constructed via a gas assisted injection molding process in which the molded portion  60  is molded around the bracket  62  to support the bracket. This is commonly referred to as insert molding. A gas assisted insert molding process used to produce the air bag door  40  of the present invention is described herein with reference to FIG. 10.  
     [0051] Referring to FIG. 10, a mold  220  for producing the air bag door  40  includes first and second mold pieces  222  and  224 , respectively. In a closed position of the mold  220  illustrated in FIG. 10, a mold cavity  226  is formed between the first and second mold pieces  222  and  224 . The bracket  62  is placed in the mold cavity  226 , and the mold  220  is placed in the closed position. A hot melt injector, illustrated schematically at  230 , injects hot melted plastic material (“melt”) into the mold cavity  226  through a machine nozzle (not shown) in a known manner. The melt surrounds the bracket  62  and is formed in the shape of the molded portion  60  of the air bag door  40 . Prior to opening the mold and before the hot melt solidifies, a pressurized gas injector, illustrated schematically at  232 , injects a pressurized gas, such as nitrogen, into the mold cavity  226 .  
     [0052] The mold  220  includes a gas conduit, illustrated schematically at  240 , through which the gas injector  232  injects the gas into the mold cavity  226 . The gas conduit  240  may comprise any known means for delivering the pressurized gas to the mold cavity  226 . For example, the gas conduit  240  may comprise the machine nozzle through which the hot melt material is injected into the mold cavity  226 . Alternatively, the gas conduit  240  may comprise a gas needle, separate from the machine nozzle. Although the mold  220  is illustrated in FIG. 10 as having a single, centrally located gas conduit  240 , it will be appreciated that the mold  220  may include a plurality of gas conduits spaced about the mold.  
     [0053] Referring to FIGS. 3, 5,  7 , and  10 , the air bag door  40  includes a gas injection aperture  242  through which the pressurized gas is injected. The gas injection aperture  242  is in fluid communication with the chamber  170 . In the illustrated embodiment, the gas injection aperture  242  extends through the main portion  120  of the bracket  62 . Those skilled in the art will appreciate, however, that the gas injection aperture  242  may have a different position on the air bag door  40  and that the air bag door may include more than one gas injection aperture.  
     [0054] The pressurized gas is injected into the mold cavity  226  while the hot melt is still molten. When injected, the pressurized gas takes the path of least resistance in the mold cavity  226 . Thus, the pressurized gas may tend to flow into areas of the mold cavity in which the hot melt has a low pressure and/or high temperature. The pressurized gas displaces thicker sections of the hot melt, which helps distribute the hot melt in the mold cavity  226 . The pressurized gas thus helps to form the walls of the chamber  170  and the ribs  104  of the air bag door  40 .  
     [0055] The gas also pressurizes the chamber  170  (FIGS.  3 - 5  and  7 ) and exerts a pressure on the hot melt as the hot melt cools. More specifically, the pressurized gas exerts a pressure on the layer  132 , on the base portion  64 , and on the first, second, third, and fourth side walls  110 ,  112 ,  114 , and  116 . At intersections between the nominal wall and the projections that are exposed to the gas pressure, i.e., at the intersection of the base portion  64  and the side walls  110 ,  112 ,  114 , and  116 , the pressure of the gas exerts a force on the hot melt in directions that oppose the “drawing in” of the melt in the direction in which the sinking occurs. This helps prevent the formation of sink marks. Thus, at intersections exposed to the gas pressure, the projection thickness may be increased without producing sink marks.  
     [0056] After the hot melt solidifies and/or cools to a predetermined point, the mold  220  is opened, and the pressurized gas is released. At this point, the air bag door  40  may be removed from the mold  220 . The air bag door  40 , having been constructed in accordance with the procedure outlined above, has a construction in which projections (i.e., side walls  110 ,  112 ,  114 ,  116 ) have a thickness about equal to the thickness of the nominal wall (i.e., the base portion  64 ). This is illustrated in FIGS. 4, 5, and  7 .  
     [0057] According to the general rule discussed herein above, in order to avoid sink marks, the projections, i.e., the side walls  110 ,  112 ,  114 , and  116 , should have a thickness that is 50% to 60% of the thickness of the base portion  64 . It will be appreciated, however, that the gas assisted injection molding technique used to construct the air bag door  40  allows avoidance of the general rule and permits the projections to have a thickness about equal to the thickness of the base portion  64  without producing sink marks. The prevention of sink marks helps provide an attractive aesthetic appearance for the class A surface  42 . The thick projections are advantageous for several reasons.  
     [0058] In addition to providing support for the main wall  126  of the reinforcing portion  100 , the side walls  110 ,  112 ,  114 , and  116  serve as ribs for helping to reinforce the door  40 . The side walls  110 ,  112 ,  114 , and  116 , having an increased thickness, are stronger than side walls constructed in accordance with the 50% to 60% general rule. This provides for a stronger and more robust construction of the air bag door  40 . This also allows for a simpler construction since fewer reinforcing members, e.g., ribs, may be required to provide the required structural integrity.  
     [0059] The thicker side walls  110 ,  112 ,  114 , and  116  provide a strong connection between the reinforcing portion  100  and the base portion  64 . As a result, there is a strong connection between the bracket  62 , the reinforcing portion  100 , and the base portion  64 . These strong connections allow the tether  44  (FIG. 1) to connect the air bag door  40  to the instrument panel  36  in a strong and reliable manner so as to help retain the door during deployment of the air bag  14 .  
     [0060] The air bag door  40  constructed in accordance with the gas assisted injection molding technique of the present invention also helps simplify the construction of the door in comparison to prior art air bag doors. The molded portion  60  is molded around the bracket  62  in a single molding procedure to form the air bag door  40 . This simple two-piece construction may thus provide benefits in terms of reduced material costs, manufacturing costs, and time savings.  
     [0061] In accordance with the preceding, it will be appreciated that the present invention also relates to an air bag door  40  and a method for producing the air bag door. The method includes the step of providing the mold  220 , which includes the first mold piece  222  and the second mold pieces  224 . The mold  220  has a closed condition in which a mold cavity  226  is defined between the first and second mold pieces  222  and  224 . The method also includes the step of placing the metal bracket  62  in the mold cavity  226 . The method also includes the steps of placing the mold  220  in the closed condition and injecting the hot melt into the mold cavity  226  to fill the mold cavity at least partially. The hot melt forms the molded portion  60  of the air bag door  40 , which at least partially surrounds the bracket  62 . The method further includes the step of injecting pressurized gas into the mold cavity  226 . The pressurized gas pressurizes the chamber  170  and exerts a force on the main wall portion  126 , the base portion  64 , and the side walls  110 ,  112 ,  114 , and  116  of the air bag door  40  while the hot melt cools. The method also includes the steps of cooling the hot melt to solidify the plastic material and releasing the pressurized gas from the chamber  170 .  
     [0062] From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. For example, it will be appreciated that the air bag door construction of the present invention may be implemented to construct air bag doors other than the illustrated passenger side air bag door. These alternative air bag doors may include driver side air bag doors, and side impact air bag doors. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.