Patent Publication Number: US-9409468-B2

Title: Liftgate inner die cast with integrated glass urethane bonding surface

Description:
The present disclosure relates to vehicle liftgates having die cast inner panels. 
     BACKGROUND 
     This section provides background information related to the present disclosure and is not necessarily prior art. 
     Vehicles that have flip-up style rear doors (i.e. liftgates), such as SUVs, vans, or hatchbacks for example, are typical constructed with an inner panel disposed toward an interior side of the vehicle, an outer panel disposed toward an exterior side of the vehicle, and a window pane disposed in an upper section of the liftgate. The inner panel is typically stamped or pressed from a single sheet of metal, such as steel or aluminum, into a shape that generally contours to an opening to the rear of the passenger compartment or trunk area of the vehicle. The shape of conventional inner panels includes a large, generally rectangular opening for the rear window in the upper section of the inner panel. The liftgate is typically hinged to the vehicle structure, such as at a header of a vehicle body, to allow pivotal movement of the liftgate to open the liftgate. The liftgate and vehicle body typically include a latching mechanism to secure the liftgate to the vehicle body when closed. Conventionally constructed liftgates pose a number of issues that are improved upon by the present teachings. 
     Conventional liftgates contribute significantly to the overall weight of the vehicle. With increasing demand for greater fuel economy, reducing the weight of the liftgate is one target for increasing fuel economy. One method of reducing the weight of the liftgate is to cast the inner panel from a lighter material, such as magnesium for example, instead of press molding or stamping it from steel or aluminum. Magnesium casting is a relatively new method in the art of vehicle liftgates, and due to the size and complexity of liftgates relative to conventionally die cast parts, it raises many new challenges. The size of the rear window pane is also a significant target for reducing the weight of the liftgate. However, the sprue and gates of the casting die and platen are typically located within the envelope of the rear window opening. Decreasing the size of the inner panel&#39;s rear window opening reduces the area available for introducing the molten magnesium into the mold through the sprue and gates. Decreasing the size of the rear window opening also increases the size of the liftgate&#39;s lower section (i.e. the area below the rear window opening). The larger the lower section of the inner panel, the further that the molten magnesium must travel through the casting mold to reach the outer periphery of the inner panel. Long travel distances can cause the molten metal to cool and begin to solidify before reaching all portions of the mold. This cooling can prevent adequate flow through narrower areas of the mold, thus effectively limiting the minimum nominal thickness of the inner panel, and thus the minimum weight achievable. 
     Conventionally constructed liftgates can vibrate and move relative to the vehicle&#39;s body or can have internal vibrations relative to different parts of the liftgate. Stabilization of the liftgate is important to reduce undesirable noise of the vehicle and wear on the liftgate and vehicle body. To stabilize the liftgate, the liftgate should be prevented from traveling cross-vehicle, fore/aft, and vertically during movement and vibration of the vehicle body and liftgate. Various components of the liftgate (e.g. speakers, inner or outer panels) should be prevented from moving relative to other proximate components (e.g. inner or outer panel). Prior attempts at stabilizing the liftgate involved draft angles and geometry that required separate parts to be mounted to the liftgate. These additional parts increase the time and cost of assembling the liftgate. 
     Conventionally constructed liftgates that include taillights typically have a set of taillight cans into which the taillights are mounted. Conventional taillights require a taillight can of a significant depth. To achieve such a depth, conventionally constructed liftgates require taillight cans that are separately stamped parts, as the depth and draft angles are too severe for stamping into the inner panel. These separate taillight cans are subsequently mounted to the liftgate and seal with the outer panel of the liftgate to prevent liquid from getting between the inner and outer panels. These separate taillight cans add cost and time to the manufacturing process. 
     SUMMARY 
     In accordance with an aspect of the present disclosure a liftgate for a vehicle includes an inner panel. The inner panel includes an upper section and a lower section. The upper section has a header member and a pair of supports that extends from opposite ends of the header member. The lower section is coupled to the supports and is spaced apart from the header member by the supports to partially define a window aperture. The lower section defines a rim, a pair of taillight cans, and a pair of first bridge members. The rim is disposed about a periphery of the lower section. The rim has a generally “U” shaped cross-section that protrudes in a fore direction from a fore face of the lower section to define a trough in an aft face of the lower section. Each taillight can has an inner portion and an outer portion separated by the trough. Each inner and outer portion has a side wall and a back wall. The side walls offset the back walls in the fore direction from the aft face. Each first bridge member spans the trough between a respective set of the inner and outer portions of each taillight can. 
     In accordance with an aspect of the present disclosure the first bridge members are flush with a surrounding portion of the aft face. 
     In accordance with an aspect of the present disclosure the first bridge members are upper bridges that span between the respective set of the inner and outer portions of each taillight can proximate to a top of the taillight can. At least one bonding surface is disposed about an upper periphery of each taillight can and across each upper bridge, the bonding surface forming a seal between a window pane and the inner panel. 
     In accordance with an aspect of the present disclosure the liftgate includes an outer panel and the first bridge members are upper bridges that span between the respective set of the inner and outer portions of each taillight can proximate to a top of the taillight can. At least one bonding surface is disposed about an upper periphery of each taillight can and across each upper bridge, and the bonding surface forms a seal between the inner and outer panels along an upper periphery of a respective one of the taillight cans. 
     In accordance with an aspect of the present disclosure the liftgate includes an outer panel and the first bridge members are lower bridges that span between the respective set of the inner and outer portions of each taillight can proximate to a bottom of the taillight can. The inner panel includes a pair of bonding surfaces. Each of the bonding surfaces forms a seal between the inner and outer panels along a lower periphery of a respective one of the taillight cans and across each lower bridge. 
     In accordance with an aspect of the present disclosure the liftgate includes an outer panel and the inner panel includes a pair of bonding surfaces. Each of the bonding surfaces forms a seal between the inner and outer panels along a periphery of a respective one of the taillight cans. The outer panel includes a pair of flanges that extend into a respective one of the taillight cans to overlap with a respective one of the first bridge members. 
     In accordance with an aspect of the present disclosure the first bridge members are upper bridges that span between the respective set of the inner and outer portions of each taillight can proximate to a top of the taillight can. 
     In accordance with an aspect of the present disclosure the first bridge members are lower bridges that span between the respective set of the inner and outer portions of each taillight can proximate to a bottom of the taillight can. 
     In accordance with an aspect of the present disclosure the lower section defines a pair of second bridge members, and wherein the second bridge members are upper bridges that span between the respective set of the inner and outer portions of each taillight can proximate to a top of the taillight can. 
     In accordance with an aspect of the present disclosure the first bridge members have a solid cross-section when cut along the trough. 
     In accordance with an aspect of the present disclosure the inner panel has a surface texture having a depth value of at least a 0.003″ and a draft value of at least 4.5°. 
     In accordance with an aspect of the present disclosure the taillight cans are integrally formed with the rim and the first bridge members. 
     In accordance with an aspect of the present disclosure a liftgate for a vehicle includes an outer panel, and an inner panel. The inner panel includes an upper section, a lower section, a pair of first bonding surfaces, and a pair of second bonding surfaces. The upper section has a header member and a pair of supports extending from opposite ends of the header member. The lower section is coupled to the supports and spaced apart from the header member by the supports to partially define a window aperture. The lower section includes a peripheral wall, an inner wall, a trough, a pair of taillight cans, a pair of upper bridges, and a pair of lower bridges. The peripheral wall extends about the periphery of the lower section. The inner wall is interior of the peripheral wall. The trough has a generally “U” shaped cross-section that protrudes in a fore direction from the peripheral wall and the inner wall to separate the inner wall from the peripheral wall. Each taillight can has an inner cavity and an outer cavity. The inner cavity protrudes into the peripheral wall. The outer cavity protrudes into the inner wall. Each upper bridge is a solid mass that spans the trough between the inner wall and the peripheral wall proximate to an upper periphery of a respective taillight can. Each lower bridge is a solid mass that spans the trough between the inner wall and the peripheral wall proximate to a lower periphery of the respective taillight can. Each of the first bonding surfaces is disposed along the lower periphery of the respective taillight can and a respective one of the lower bridges to form a seal between the inner and outer panels. Each second bonding surface is disposed along the upper periphery of the respective taillight can and across a respective one of the upper bridges. 
     In accordance with an aspect of the present disclosure each lower bridge extends from a base of the trough in the aft direction a distance that is less than a distance from the base of the trough to the lower periphery of the taillight can. The outer panel includes a pair of flanges that extend into a respective one of the taillight cans to overlap and seal with a respective one of the lower bridges. 
     In accordance with an aspect of the present disclosure each lower bridge extends from a base of the trough in the aft direction to be flush with the lower periphery of the respective taillight can. 
     In accordance with an aspect of the present disclosure the inner panel has a surface texture having a depth value of at least a 0.003″ and a draft value of at least 4.5°. 
     In accordance with an aspect of the present disclosure the inner and outer cavities of each taillight can are integrally formed with the peripheral wall and the inner wall. 
     In accordance with an aspect of the present disclosure the inner cavity of each taillight can has a side wall and a back wall. The sidewall offsets the back wall in a fore direction from the inner wall. 
     In accordance with an aspect of the present disclosure the inner cavity has a profile length “L 5 ” and a distance “L 4 ”. The profile length L 5  includes a length of two opposing portions of the sidewall and the length of a portion of the back wall that is between the opposing portions of the sidewall. The distance L 4  is the distance between the opposing portions of the sidewall. A relationship between L 4  and L 5  is defined by 100*(L 5 −L 4 )/L 4 &gt;20%. 
     In accordance with an aspect of the present disclosure the relationship between L 4  and L 5  is defined by 100*(L 5 −L 4 )/L 4 &gt;50%. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is perspective view of a vehicle that has a liftgate in accordance with the present teachings; 
         FIG. 2  is an exploded view of the liftgate of  FIG. 1  showing an inner panel of the liftgate; 
         FIG. 3  is an elevated view of an aft side of the inner panel of  FIG. 2 ; 
         FIG. 4  is an elevated view of a fore side of the inner panel of  FIG. 2 ; 
         FIG. 5  is a perspective of a portion of the fore side of the inner panel of  FIG. 2 , showing a stability shoulder of the inner panel and a shuffle bumper; 
         FIG. 6  is a sectional view of the stability shoulder and shuffle bumper of  FIG. 5 ; 
         FIG. 7  is a perspective view of a portion of the inner panel of  FIG. 2 , showing a taillight can integrally formed in the inner panel; 
         FIG. 8  is a sectional view of the taillight can of  FIG. 7 ; 
         FIG. 9  is a sectional view of a portion of the inner panel of  FIG. 2 , showing a lower bridge of a first construction integrally formed in the inner panel; 
         FIG. 10  is a sectional view similar to  FIG. 9 , showing a lower bridge of a second construction integrally formed in the inner panel; 
         FIG. 11  is a perspective view of a portion of the fore side of the inner panel of  FIG. 2 , showing a speaker housing of the inner panel; 
         FIG. 12  is a perspective view of a portion of the aft side of the inner panel of  FIG. 2 , showing a stiffener of a header portion of the inner panel; 
         FIG. 13  is a sectional view of the header portion and stiffener of  FIG. 12 , showing an outer header panel of the liftgate; and 
         FIG. 14  is a schematic view of a set of die-cast dies showing a plurality of gates used in forming the inner panel of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is directed toward a liftgate design for a vehicle that permits the inner panel to be die cast from a metal material, such as magnesium, while having a decreased rear window envelope and flow-through areas of the inner panel having nominal wall thicknesses of equal to or less than 2 mm. It will be appreciated that the liftgates of the present disclosure can be formed from any other suitable material and/or may have nominal wall thicknesses of more or less than 2 mm. In one example, the liftgate of the present disclosure has a nominal wall thickness of 2.3 mm or less. 
     With reference to  FIG. 1 , a vehicle  10  is shown having a vehicle body  14  and a flip-up style rear door or liftgate  18  in a closed position. The vehicle  10  has a rear window pane  22 , a pair of outer taillights  26 , a pair of inner taillights  30 , and a wiper assembly  34 . The vehicle body  14  includes a roof  38  and defines a rear opening  42  that permits access to the vehicle&#39;s  10  passenger compartment and/or trunk area (not specifically shown) when the liftgate  18  is in an open position (not shown). The liftgate  18  closes the rear opening  42  to inhibit access to the passenger compartment and/or trunk area when in the closed position. The liftgate  18  is coupled to the vehicle body  14  such that the liftgate  18  pivots about an axis  50  via a hinge (not shown) that is located proximate to the roof  38 . 
     The liftgate  18  includes a window aperture  54 . The rear window pane  22  is mounted to the liftgate  18  to cover the window aperture  54  while permitting sight from the passenger compartment and/or trunk area, to the exterior of the vehicle  10 . The outer taillights  26  are mounted to the vehicle body  14  on opposite (e.g. left and right) sides of the rear opening  42  and generally terminate at the rear opening  42 . The inner taillights  30  are mounted to the liftgate  18  on opposite sides of the liftgate  18 , such that each of the inner taillights  30  is adjacent to and generally aligned with one of the outer taillights  26  when the liftgate  18  is in the closed position. The inner taillights  30  generally terminate at the periphery of the liftgate  18 . The inner taillights  30  are positioned below the rear window pane  22 . The wiper assembly  34  is mounted to the liftgate  18  and includes a blade  58  and a motor (not shown). The motor is coupled to the blade  58  to rotate or move the blade  58  in a conventional manner. In the example provided, the wiper assembly  34  is mounted to the liftgate above the inner taillights  30  and through the rear window pane  22 , though other configurations can be used. 
     With additional reference to  FIG. 2 , the liftgate  18  is shown in greater detail. The liftgate  18  includes an inner panel  110 , a beltline panel  114 , an outer header panel  118 , and an outer lower panel  122 . The inner panel  110  is a single piece, unitarily formed body. The inner panel  110  is formed in a single, die-casting process and is a metal, such as magnesium. The beltline panel  114 , outer header panel  118 , and outer lower panel  122  are each individual parts that are formed separately from the inner panel  110 . The inner panel  110  has a fore face  126  and an aft face  130 . The inner panel  110  has an upper section  134  and a lower section  138  that provide the structure and shape of the liftgate  18 . In the example provided, the liftgate  18  has a generally rectangular overall shape when viewed from a front or rear view (e.g.  FIGS. 3 and 4 ), and the liftgate  18  is angled in the fore direction at a juncture of the upper and lower sections  134 ,  138  of the inner panel  110 . 
     The upper section  134  includes a header member  150  and a pair of vertical supports  154 . The header member  150  is disposed along the top of the inner panel  110  proximate to the roof  38  of the vehicle  10  and is coupled to the vehicle body  14  or roof  38  by the hinge (not shown). The header member  150  has a fore face  158  and an aft face  162 . The vertical supports  154  join the lower section  138  of the inner panel  110  to the header member  150 . The vertical supports  154  extend between the header member  150  and the lower section  138  at an angle relative to the lower section  138 , such that the header member  150  and lower section  138  are offset in the fore/aft directions. The vertical supports  154  are disposed on opposite (e.g. left and right) sides of the inner panel  110  to partially define the shape of the liftgate  18 . The vertical supports  154  space the lower section  138  apart from the header member  150 , such that the vertical supports  154 , header member  150 , and lower section  138  partially define the window aperture  54 . The header member  150  is described in greater detail below with reference to  FIGS. 12 and 13 . 
     The lower section  138  is a generally “U” shaped structure including a pair of side portions  210  that form the sides of the “U” shape, and a base portion  214  that forms the bottom of the “U” shape. Each of the side portions  210  is connected to one of the vertical supports  154  at a upper end of the side portion  210  (i.e. the end that is distal to the base portion  214 ) to join the upper and lower sections  134 ,  138 . Each side portion  210  defines a taillight can  218  proximate to each upper end of the side portion  210  and disposed above the base portion  214 . The lower section  138  is described in greater detail below with reference to  FIGS. 3 and 4 . 
     The beltline panel  114  is a separately formed structure that is mounted to the lower section  138  of the inner panel  110  by any suitable means, such as rivets, welds, or bolts for example. In the example provided, the beltline panel  114  is press molded or stamped from a steel or aluminum sheet. In an alternative construction, the beltline panel  114  is die-cast separately from the inner panel  110 . Left and right sides  230 ,  234  of the beltline panel  114  are coupled to a respective one of the side portions  210  of the lower section  138  proximate to the upper ends of the side portions  210 . The beltline panel  114  spans across the top of the lower section  138  to close the “U” shape and to define a portion of the window aperture  54 . Thus, the beltline panel  114 , header member  150 , upper ends of the side portions  210 , and vertical supports  154  define the window aperture  54 . The beltline panel  114  includes a mount (not specifically shown) and a wiper aperture  238 . The motor (not shown) is connected to the mount and disposed on a fore side of the beltline panel  114 , proximate to the passenger compartment and/or trunk area. A shaft member (not shown) extends through the wiper aperture  238  and is drivingly coupled to the blade  58  to rotate the blade  58 . 
     The outer header panel  118  is a separately formed structure that is mounted to the header member  150  by any suitable means, such as rivets, welds, crimping, or bolts for example. In the example provided, the outer header panel  118  is press molded or stamped from a steel or aluminum sheet, though it is understood that other materials or constructions can be used. The outer header panel  118  has a fore face  250  and an aft face  254 . The fore face  250  opposes the aft face  162  of the header member  150  when mounted to the header member  150 . The aft face  254  of the outer header panel  118  faces toward the exterior of the vehicle  10  and may be a Class A surface prepared or painted to be visible from the exterior of the vehicle. 
     The outer lower panel  122  is a separately formed structure that is mounted to the lower section  138  of the inner panel  110  by any suitable means, such as rivets, welds, crimping, or bolts for example. In the example provided, the outer lower panel  122  is press molded or stamped from a steel or aluminum sheet, though it is understood that other materials or constructions can be used. The outer lower panel  122  has a fore face  270  and an aft face  274 . The fore face  270  opposes the aft face  130  of the lower section  138  of the inner panel  110 . The aft face  274  of the outer lower panel  122  faces exterior of the vehicle  10  and may be a Class A surface prepared or painted to be visible from the exterior of the vehicle. The outer lower panel  122  has a shape that substantially covers the lower section  138  of the inner panel  110 , generally excluding the taillight cans  218 , such that the aft face  130  of the lower section  138  of the inner panel  110  is hidden by the inner taillights  30 , the window pane  22 , and the outer lower panel  122  when viewed from the exterior of the vehicle  10 . The outer lower panel  122  has a first area  278 , a second area  282 , and a pair of flanges  286 . The first area  278  spans across the lower section  138 , below the taillight cans  218 . The second area  282  extends up from the first area  278 , between the taillight cans  218 . The second area  282  covers the beltline panel  114  to border the rear window pane  22 . The flanges  286  extend slightly into a respective one of the taillight cans  218  as described below and shown with reference to  FIG. 9 . 
     With additional reference to  FIGS. 3 and 4 , the lower section  138  of the inner panel  110  is described in greater detail. The lower section  138  has a generally rectangular shape when viewed from the fore or aft directions, with a pair of outer edges  310  joined by a bottom edge  314  that form the periphery of the lower section  138 . The lower section  138  includes a rim  318  ( FIG. 4 ) that extends vertically along the sides and horizontally along the bottom of the lower section  138 , proximate to the periphery of the lower section  138  and offset interior of the outer and bottom edges  310 ,  314 . The rim  318  contacts weather stripping (not shown) on the vehicle body  14  around the rear opening  42  to seal the passenger compartment and/or trunk area from the exterior of the vehicle  10 . 
     The lower section  138  further includes a pair of stability shoulders  322  ( FIG. 4 ), a pair of upper bridges  326  ( FIG. 3 ), a pair of lower bridges  330  ( FIG. 3 ), and a pair of speaker housings  334 . The upper end of each side portion  210  includes a first edge  338  that extends generally inward from each vertical support  154  toward the middle of the liftgate  18  (e.g. in the right direction for the left side portion  210  and in the left direction for the right side portion  210 ) to partially define the bottom border of the window aperture  54 . Each side portion  210  includes a second edge  342  that extends generally downward from the first edge  338  to form an interior side of the “U” shape. The base portion  214  includes a third edge  346  that extends in the left and right directions between the second edges  342  to form an interior bottom of the “U” shape. The second edge  342  extends downward a vertical length L 1  and the third edge  346  extends across the lower section  138  a horizontal length L 2 . The horizontal length L 2  may be greater than the vertical length L 1 , such that the bottom of the “U” shape is wider than the height of the sides of the “U” shape. The base portion  214  may be configured such that the horizontal length L 2  is longer than a maximum horizontal distance between each second edge  342  and the respective outer edge  310 . The “U” shape is such that a maximum distance radially outward from the second or third edges  342 ,  346  is a length L 3 . Length L 3  is the maximum distance that molten metal must flow through the dies from any particular gate  710  during the casting process, which is described in greater detail below. This maximum distance may be described by an equation where L 3  is less than or equal to 200*T, where T is equal to the nominal wall stock thickness of the inner panel  110  in millimeters. In the example provided, the nominal wall stock thickness is 2 mm and L 3  is approximately 400 mm. 
     With additional reference to  FIGS. 5 and 6 , the rim  318  has a generally “U” shaped cross-section, with the tops of the “U” shape extending from the surrounding fore face  126  of the inner panel  110  to offset the bottom of the “U” shape from the surrounding fore face  126  in the fore direction. Thus the rim  318  forms a trough  350  in the aft face  130  and a protrusion in the fore face  126  of the inner panel  110 . The rim  318  has a first rim surface  354  and a second rim surface  358 . The first rim surface  354  faces in the fore direction and the second rim surface  358  extends from the first rim surface  354  in the aft direction. The second rim surface  358  faces outward toward the outer edge  310  (e.g. in the right and left directions for the left and right sections of the rim  318  respectively). The stability shoulders  322  are located approximately midway along the length of each outer edge  310  and are formed into or protrude from the second rim surface  358 , between the rim  318  and the outer edge  310 . The stability shoulder  322  has a first shoulder surface  362  and a second shoulder surface  366 . The first shoulder surface  362  is offset in the aft direction from the first rim surface  354  and extends outward from the second rim surface  358 . The second shoulder surface  366  is offset in the outward direction from the second rim surface  358 . Those of skill in the art will appreciate that the first shoulder surface  362 , second shoulder surface  366 , first rim surface  354 , second rim surface  358 , and outer edge  310 , are formed at angles that cannot be formed by stamping a single sheet of material. The first and second shoulder surfaces  362 ,  366  are configured to abut against a shuffle bumper  370  when the liftgate  18  is in the closed position. 
     The shuffle bumper  370  is a resilient member formed from rubber for example, that is mounted to the vehicle body  14 . The shuffle bumper  370  includes a first bumper surface  374  and a lip  378 . The first bumper surface  374  abuts against the first shoulder surface  362 . The lip  378  extends in the aft direction from the outer side of the first bumper surface  374  to abut against the second shoulder surface  366 . The shuffle bumper  370  has a cavity  382  that permits the shuffle bumper  370  to compress when the liftgate  18  is moved from the open position to the closed position. The compression of the shuffle bumper  370  biases the first bumper surface toward the first shoulder surface  362  to remain in contact with the first shoulder surface  362  and inhibit vibration of the liftgate  18  in the fore/aft direction. The respective lips  378  of the left and right shuffle bumpers  370  inhibit vibration of the liftgate  18  in the respective left/right directions. 
     With additional reference to  FIGS. 7-9 , each taillight can  218  is embossed into the aft face  130  of the lower section  138 . The taillight can  218  has an outer periphery  410 , a side wall  414 , a back wall  418 , and an aperture  422  for permitting power cables (not shown) or a portion of the inner taillights  30  to pass through the inner panel  110 . The side wall  414  protrudes in the fore direction from the outer periphery  410  and the surrounding area of the aft face  130  of the inner panel  110 . The outer periphery  410  and side wall  414  form a generally sideways “U” shape, such that the tops of the “U” shape are open to and terminate at the outer edge  310  of the lower section  138 . The side wall  414  terminates in the fore direction at the back wall  418 . The distance across the taillight can  218  between the top and bottom or opposite sides of the outer periphery  410  is denoted by L 4  and the length of the taillight can&#39;s  218  profile, i.e. along each side wall  414  and the back wall  418  from the opposite sides of the outer periphery  410 , is denoted by L 5 . The taillight can  218  may be embossed into the aft face  130 , such that 100*(L 5 −L 4 )/L 4  is at least greater than 20%. In the example provided L 4  and L 5  are such that 100*(L 5 −L 4 )/L 4  is greater than 53%. Those of skill in the art will appreciate that such a taillight can  218  cannot be unitarily formed into a liftgate inner panel by a traditional stamping of a single sheet of steel or aluminum, as the sheet would stretch and break due to the inability to feed additional material from the area surrounding the taillight can  218  into the area of the stamp tooling that would form the taillight can  218 . Those of skill in the art will appreciate that the additional material would be prevented from being fed into the area of the stamp tooling that would form the taillight can  218  due to the surrounding material being clamped by the stamp tooling in order to form the features that surround the taillight can  218 . 
     The portions of the outer periphery  410  and the side wall  414  that form the upper side of the “U” shape includes the upper bridge  326  that spans across the trough  350  of the rim  318 . The upper bridge  326  is a solid body of metal having a cross-sectional area that fills a length of the trough  350  to be flush with the surrounding aft face  130  of the inner panel  110 . The length of the trough  350  that is filled by the upper bridge  326  is sufficient to apply a first bonding material (not shown). The first bonding material is applied to a first area or bonding surface A 1  that extends around the window aperture  54  and along the top of the outer periphery  410  of the taillight can  218 . In the example provided, the first bonding material seals the rear window pane  22  to the inner panel  110  in some areas and to a portion of the outer lower panel  122  in others to inhibits liquid from entering the space between the inner panel  110  and the rear window pane  22  or between the inner panel  110  and the outer lower panel  122 . In the example provided, the first bonding material is a glass urethane material. 
     The portion of the side wall  414  that forms the lower side of the “U” shape includes the lower bridge  330  that spans across the trough  350  of the rim  318 . The lower bridge  330  is a wedge shaped, solid body of metal having a first side  450 , a second side  454 , and a tip  458 . The first side  450  forms a portion of the side wall  414  and is flush with the surrounding portions of the side wall  414 . The first and second sides  450 ,  454  converge to join at the tip  458 . The lower bridge  330  has a cross-sectional area such that the tip  458  does not extend to the outer periphery  410  of the taillight can  218 . In this way, the trough  350  causes a break in the outer periphery  410  proximate to the bottom of the taillight can  218 , but only a partial break in the side wall  414 . The flange  286  of the outer lower panel  122  extends in the fore direction partially into the taillight can  218  along the outer periphery  410 . The flange  286  has an extension  462  that extends inward from the outer periphery  410  and along the side wall  414  to cover the break in the side wall  414  caused by the trough  350  and lower bridge  330 . A second bonding material (not shown), such as a pumpable adhesive for example, is applied to a second area or bonding surface A 2  along the outer periphery  410 , the lower side wall  414  and up the aft face  130  to intersect with the first area A 1 . The second bonding material seals the flange  286  of the outer lower panel  122  to the inner panel  110  to inhibit liquid from entering the space between the inner panel  110  and the outer lower panel  122 . In this way, the taillight cans  218  are unitarily formed in the inner panel  110 , while the space between the inner panel  110  and the outer lower panel  122  remains a dry environment. 
     In an alternate construction, not specifically shown, the upper bridge  326  is constructed in a similar manner to the lower bridge  330  described above. In this construction, the upper bridge  326  does not extend to the outer periphery  410  of the taillight can  218 . In this way, the trough  350  causes a break in the outer periphery  410  proximate to the top of the taillight can  218 , but only a partial break in the side wall  414 . In this construction, a Class A surface seals along the first area A 1  and includes an upper extension (not shown) that is similar to the extension  462 . The upper extension extends inward from the outer periphery  410  and along the side wall  414  to cover the break in the side wall  414  caused by the trough  350  and upper bridge  326  and seals on a portion of the side wall  414  and the upper bridge  326  similar to the extension  462 . 
     With reference to  FIG. 10 , a lower bridge  330 ′ and flange  286 ′ of a second construction are shown. The lower bridge  330 ′ and flange  286 ′ are similar to the lower bridge  330  and flange  286  with the exceptions shown in  FIG. 10  and described herein. The tip  458 ′ of the lower bridge  330 ′ has a first flat surface  510  and a second flat surface  514  formed at angles relative to the first and second sides  450 ′,  454 ′ of the lower bridge  330 ′. The tip  458 ′ extends to the outer periphery  410  and forms a portion of the outer periphery  410 . The flange  286 ′ does not include the extension  462  to overlap with the side wall  414  and instead, seals along the outer periphery  410  including at least one of the first and second flat surfaces  510 ,  514  of the lower bridge  330 ′. 
     With additional reference to  FIG. 11 , each speaker housing  334  is formed into one of the side portions  210  of the inner panel  110 , below the taillight can  218 . The speaker housing  334  is disposed partially above and partially below the third edge  346  of the base portion  214 . The speaker housing  334  includes a plateau surface  550  that is offset in the fore direction from the fore face  126  of the inner panel  110  by a plateau wall  554 . The plateau wall  554  is formed at a depth and draft angle relative to the fore face  126  and the plateau surface  550  such that the speaker housing  334  could not be unitarily formed with the inner panel  110  from a stamping of a single sheet of material. The plateau surface  550  includes a plurality of speaker mounting holes  558 . A speaker (not shown) is mounted in the speaker housing  334 . The plateau wall  554  supports the plateau surface  550  to prevent the speaker from pumping the lower section  138  and producing undesired vibrations in the inner panel  110 . 
     With additional reference to  FIGS. 12 and 13 , the header member  150  is described in greater detail. The header member  150  has an outer edge  610  that extends along the top of the header member  150  and an inner edge  614  that extends along the bottom of the header member  150 . The outer header panel  118  is attached to the header member  150  at the outer and inner edges  610 ,  614 . The outer header panel  118  is spaced apart from the header member  150  between the outer and inner edges  610 ,  614  to define a header cavity  618 . The header member  150  includes at least one stiffener  622 . The stiffener  622  is a hollow wedge shaped protrusion formed in the header member  150  between the outer and inner edges  610 ,  614 . The stiffener  622  can alternatively be other shapes such as a rectangular protrusion (not specifically shown) for example. The stiffener  622  protrudes from the header member  150  in the aft direction into the header cavity  618 . The stiffener does not extend the entire length of the header member  150  and is located between the ends of the header member  150  that are coupled to the vertical supports  154 . The stiffener  622  includes a shelf surface  626 . The shelf surface  626  is coupled to a middle portion of the outer header panel  118  by an adhesive  630  placed between the shelf surface  626  and the fore face  250  of the outer header panel  118 . The middle portion of the outer header panel  118  is the portion of the outer header panel  118  that is between the outer and inner edges  610 ,  614  and partially defines the header cavity  618 . The stiffener  622  provides structural support to the outer header panel  118  to prevent pumping relative to the inner panel  110  during vibration of the liftgate  18 . In the example provided, the header member  150  includes two stiffeners  622 , equally spaced apart from a center of the header member  150 . 
     In manufacturing the liftgate  18 , the inner panel  110  is formed by a die-casting process. With additional reference to  FIG. 14 , an amount of magnesium is heated until molten, then injected through a sprue  710  and a plurality of gates  714  (also shown in  FIG. 3 ) of a platen (not specifically shown) and a set of dies  718 . Those of skill in the art will appreciate that the set of dies  718  include two dies (only one of which is schematically shown) that have a pair of opposing faces (not shown) that are substantially the negative of the inner panel  110 . The gates  714  are connected to the sprue  710  by a plurality of pathways (not shown) to deposit the molten metal within the dies  718  along the window aperture  54  and second and third edges  342 ,  346 . In the example provided, there are four gates  714  along the header member  150 , one gate along each first edge  338 , one gate along each second edge  342 , two gates along the third edge  346 , and one gate  714  at the juncture of each second edge  342  and the bottom edge  346 . 
     Pressure is applied to the molten metal entering the dies  718  such that the molten metal travels radially outward from the gates  714 , through the dies  718  until the dies  718  are filled with molten metal. The gates  714  are positioned such that the molten metal does not need to travel a distance greater than L 3 , i.e. 200 times the nominal wall stock thickness. The dies  718  are heated to minimize premature solidification of the molten metal. The dies  718  may have a surface texture or roughness having a depth of approximately 0.003 inches and a draft angle of 4.5°, which gives the inner panel  110  a similar, mating surface texture. In the example provided, the surface texture is on the opposing faces of both of the dies  718 . The surface texture of the dies  718  decreases the surface tension of the flowing molten metal to improve flow through areas of the dies  718  including areas that are a nominal thickness of 2 mm or less. The molten metal then solidifies in the dies  718  and the inner panel  110  is ejected therefrom. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.