Abstract:
A composite liftgate system with an inner panel construction having a strengthening channel structure. Structural composite reinforcements are bonded to the inner panel where additional strength is needed to meet predetermined performance requirements. Where the extra structure is needed, no steel or a minimum amounts of steel is used and the structural reinforcements are bonded in place using adhesive prior to application of additional fasteners.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation-In-Part of Application No. PCT/US2015/015413, filed Feb. 11, 2015, which claims priority to U.S. Provisional Patent Application No. 61/938,452 filed Feb. 11, 2014. The disclosures of the above applications are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to liftgate systems for automobiles. More specifically, to a composite liftgate and method of manufacture. 
       BACKGROUND OF THE INVENTION 
       [0003]    One of the current trends in the automobile industry is to lower vehicle weight to help achieve better fuel economy, thus helping to meet fuel economy standards and to offset the higher fuel prices. Another trend is that there is a broader range of vehicle models, which in turn reduces the volume of vehicles produced on a per model basis. Sport utility and crossover vehicles remain popular and typically include fairly heavy rear liftgates making this part of the vehicle a target area for weight reduction. Liftgates are traditionally made from stamped steel panels that are heavy and have a high tooling cost. Traditional steel liftgates are expensive investments, heavy, take up a lot of OEM floor space in areas from stamping plant, body shop, paint shop, and trim line. Further, steel liftgates have limited styling flexibility, take a lot of time to tool, and have corrosion concerns. Sheet Molding Compound (SMC) is an alternative to steel for the inner and outer panels of the liftgate. Using SMC has several manufacturing concerns related to the material and process. Steel and SMC liftgates have a mass penalty over thermoplastics. There are also styling restrictions with traditional sheet metal components. Thermoplastic composite type materials used for liftgate applications also have difficulty meeting customer performance specifications. 
         [0004]    Another concern with the manufacture of liftgates is that typical liftgates are manufactured as a relatively flat or smoothly contoured panel, with structural reinforcements such as ribs added onto the panel. This will also add weight and increase manufacturing complexity as well and when thermoplastics are used there are read through areas where the ribs are placed which must be dealt with by design modifications or expensive processes such as gas assist injection molding. Ribs are also weaker and do not carry the load through the liftgate panel. Recently magnesium inner reinforcement panels have been used with an outer polymer skin in order to reduce weight. While such panels are an improvement in weight, this is an expensive solution. Another concern with typical liftgates is that the structural reinforcements are steel or larger steel structures adding weight and increased manufacturing complexity. Another concern is typically reinforcement material is used for reinforcement in the structural areas and attachment structures are fixed using bolts. However, the use of bolts does not provide a continuous attachment structure and improved strength since there is distance between the bolts. Yet another concern with the manufacture of liftgates is that typical liftgates are manufactured as relatively solid with no access features such as access doors added into the panel to allow for easy access for general maintenance and repair of built in components. 
         [0005]    A known 2008 Nissan Murano composite liftgate system helped to satisfy the weight savings and the tooling cost concerns, but utilized a typical bolt in small steel reinforcement at the latch which secures one end of the liftgate to the vehicle. This does not meet the higher load requirements desired in some applications, such as the latch pull test. A known Nissan Rogue composite liftgate system utilizes a steel one-piece outer panel and steel brackets. This does not improve density, painting efficiency, hold tighter tolerances, is more expensive and complex to manufacture, and adds weight to the liftgate/vehicle. 
         [0006]    Accordingly, there exists a need for a composite liftgate which is both lightweight, as well as structurally sound enough to meet various load requirements, while being more mass and cost effective. 
       SUMMARY OF THE INVENTION 
       [0007]    In accordance with the present invention, there is provided a composite liftgate system with inner panel construction including at least one strengthening channel structure and at least one reinforcement connected to the inner panel. The reinforcement is structural composite preform reinforcement bonded to the inner panel. The structural composite reinforcements are woven glass reinforcement. Tapping plates are minimized in size to minimize the use of steel. The present inventive provides extra strength when compared to steel or conventional composite liftgates while reducing overall weight by several pounds. 
         [0008]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0010]      FIG. 1  is a front perspective view of a composite liftgate assembly with D-pillars removed to depict the inner structure including struts, in accordance with the present invention; 
           [0011]      FIG. 2  is a front elevation view of an inner panel sub-assembly for the liftgate system, in accordance with the present invention; 
           [0012]      FIG. 3  is a front elevation view of the inner panel with a strut reinforcement bracket connected to a strut preform reinforcement, hinge reinforcement bracket, connected to a hinge preform reinforcement, and structural channel reinforcements in accordance with the present invention; 
           [0013]      FIG. 4  is a front elevation view of an upper outer panel connected to the inner panel, in accordance with the present invention; 
           [0014]      FIG. 5  is a front elevation view of the upper outer panel and a lower outer panel connected to the inner panel, in accordance with the present invention; 
           [0015]      FIG. 6  is a rear perspective view depicting the inner panel sub-assembly for the liftgate system, in accordance with the present invention; 
           [0016]      FIG. 7  is a front perspective view of the composite liftgate assembly of  FIG. 1 ; 
           [0017]      FIG. 8  is a rear perspective view of a lower trim panel connected to the inner panel for the composite liftgate assembly, in accordance with the present invention; 
           [0018]      FIG. 9  is an exploded elevation view of the composite liftgate system, in accordance with the present invention; 
           [0019]      FIG. 10  is a sectional view taken alone section A-A of  FIG. 1 ; and 
           [0020]      FIG. 11  is a sectional view taken alone section B-B of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0022]    Referring to the figures generally, there is provided a composite liftgate assembly with bonded composite preform reinforcements. Structural channels molded into an inner panel of the liftgate add structure where needed and manage the main loading paths as the liftgate is utilized in the various load cases. Also composite preforms structurally bonded in place (or Insert molded) to add structure where needed are used, allowing for the need for no steel reinforcements and/or minimization of the size of steel tapping plates. Bonding through the use of adhesive provides a more continuous attachment structure and improved strength over bolting alone. A two-piece outer panel allows for styling, molding, painting, tolerance, weight, and assembly advantages. The features and process of the present invention help to achieve desired weight targets, while keeping costs at target levels. In addition, the composite liftgate has several business case advantages for supplying a module, and reducing assembly plant complexity and improving throughput. Additionally, the present invention improves styling options and flexability when compared to sheet metal and one-piece panels. Corrosion and durability are also improved. 
         [0023]    An embodiment of a composite liftgate system is shown in the Figures generally at  10 . The liftgate  10  includes an outer panel  12  formed of an upper outer panel, shown generally at  14 , and a lower outer panel, shown generally at  16 . A spoiler  18  is incorporated into the upper outer panel  14 . A glass window  20  or rear window liftgate of the tailgate  10  is adhered to the upper and lower outer panels  14 , 16  and to an inner panel. The upper outer panel  14  and separate lower panel  16  thereby form a two-piece outer panel. This has significant benefits and superior results over having a one-piece panel (especially over one that is also steel or not bonded in place), including, but not limited to, improved density, more efficient painting, tighter tolerances, less manufacturing issues, and more cost effectiveness. Alternatively, the outer panel  12  may be formed as a single piece. 
         [0024]    The spoiler  18  incorporated with the upper outer panel  14  has significant benefits and superior results over having a separate spoiler, including, but not limited to, optimized structure and strength and efficient processing. 
         [0025]    The inner panel  22  is formed with a channel pattern arrangement including a plurality of structural channels molded into the inner panel  22  to manage the loading paths as the liftgate is utilized in various load cases. The channel pattern of the present invention provides more structural shape where needed and allows for carrying the full thickness and load through the part, whereas ribbing is weaker and will not carry the load. The channels have significant benefits and superior results over ribbing. The channels will now be explained in greater detail. 
         [0026]    Molded into the inner panel  22  are at least one first pair of channels  24  that run horizontally, substantially parallel to and below a horizontal plane of the viewing opening  25  formed in the inner panel  22 . The channels of the first pair  24  are substantially centrally located in the portion of the inner panel  22  below the opening  25  and an upper first pair channel  26  is longer than a lower first pair channel  28 . The first pair of channels  24  are raised, as in substantially extending outward generally toward the rear of the vehicle (See  FIGS. 2 and 6 ). 
         [0027]    The first pair of channels  24  terminate at a second pair of channels  30  that run in a diagonal pattern at a predetermined angle, substantially in diagonal directions away from each other with the largest distance apart being toward the opening  25 . The second pair of channels  30  are depressed, as in substantially extending inward generally toward the interior of the vehicle (See  FIGS. 2 and 6 ). 
         [0028]    A third pair of channels  32  extend substantially along each side of the second pair of channels  30  on the side away from the center of the inner panel  22 . The third pair of channels  32  are raised, as in substantially extending outward generally toward the rear of the vehicle (See  FIGS. 2 and 6 ). Preferably, the second pair of channels  30  and fourth pair of channels  32  have one side wall longer than the other side wall, sharing the common of the longer wall. 
         [0029]    Each of the channels in the second pair of channels  30  is substantially a mirror image of the other channel of the pair  30 . Each of the channels in the third pair of channels  32  is substantially a mirror image of the other channel of the pair  32 . 
         [0030]    A fourth pair of channels  33  run substantially vertically from the lower first pair channel  28  to the upper first pair channel  26  of the first pair of channels  24 . The fourth pair of channels  33  are depressed, as in substantially extending inward generally toward the interior of the vehicle (See  FIGS. 2 and 6 ). 
         [0031]    Each of the pairs of channels  24  and  30 - 33  have predetermined lengths, widths, depths, and material thickness suitable to provide structural support and strength for the inner panel  22 , including under predetermined load conditions. Optionally, additional channels can be formed as part of the inner panel  22 . 
         [0032]    Formed as part of the inner panel  22  is an upper trim ring portion, generally shown at  34 , incorporated into a D-pillar area (‘D’  FIG. 8 ) rather than providing the upper trim ring as a separate panel. The upper trim ring  34  incorporated into the inner panel  22  in the D-pillar area has significant benefits and superior results over having a separate panel, including, but not limited to, optimized structure and strength. The upper trim ring portion  34  has a predetermined size that is small suitable for access, e.g., for a lower trim panel installation and retention. 
         [0033]    The liftgate  10  is additionally reinforced in areas where extra structure is needed. There is provided a plurality of composite preforms or composite reinforcements to add structure where needed to reinforce areas such as the D-pillar, top corners of the inner panel  22  at the hinge nuts, side nuts, backlight, and/or latch areas, as will be described further below. Composite preforms have significant benefits and superior results over steel reinforcements, which steel, among other things, adds weight. 
         [0034]    All of the composite reinforcements are bonded directly to the inner panel  22  such that the composite reinforcements are structurally bonded in place (or, alternatively, insert molded to connect the reinforcements to the inner panel  22 ) to add structure where needed. This allows for the elimination of steel reinforcements and to minimize the size of a plurality of tapping plates made of metal. The bonding of the present invention uses predetermined adhesive(s) applied to select the areas of the inner panel  22 . Most preferably, the adhesive is a structural two-part urethane adhesive. The bonding with the use of adhesives has significant benefits and superior results over steel reinforcements connected to the inner panel by bolts. Tapping plates that are formed of steel are minimized in size and are not only bolted in place—but additionally bonded with adhesive for added strength and structure, as will be described further below. This has significant benefits and superior results over the conventional need for larger steel tapping plates that are merely bolted. 
         [0035]    One of the composite preforms connected to the inner panel  22  is a pair of strut reinforcements  36  or strut preforms. The pair of strut reinforcements  36  are bonded to the inner panel  22  using adhesive. These are located generally in the area adjacent to the lower corner of the opening  25 . 
         [0036]    A pair of strut reinforcement brackets  44  or tapping plates, preferably formed of steel, are bonded to the pair of strut reinforcements  36  using adhesive. A first plurality of fasteners  46 , e.g., push nuts, are added to further hold the strut reinforcements  36  and strut reinforcement brackets  44  in position. 
         [0037]    Another one of the composite preforms connected to the inner panel  22  is a pair of hinge reinforcements  38  or hinge preforms. These are located generally in the area adjacent to the upper corner of the opening  25 . The pair of hinge reinforcements  38  are bonded to the inner panel  22  using adhesive. A second plurality of fasteners  50 , e.g., push nuts, are added to further hold the hinge reinforcements  38  in position. The lower end portion  40  of each hinge reinforcement  38  overlaps an upper end portion  42  ( FIG. 9 ) of each strut reinforcement  36 . Preferably, this upper end portion  42  has a lower profile for connecting to the inner panel  22  below the lower end portion  40  of hinge reinforcement  38  and provide a butting engagement with the hinge reinforcement  38 . Most preferably, the lower end portion  40  is bonded to the upper end portion  42  with adhesive. 
         [0038]    A pair of hinge reinforcement brackets  48  or tapping plates, preferably formed of steel, are bonded to the pair of hinge reinforcements  38  using adhesive. A third plurality of fasteners  52 , e.g., screws, are added to further hold the hinge reinforcements  38  and hinge reinforcement brackets  48  in position. 
         [0039]    Each hinge reinforcement bracket  48  also has a hinge assembly  54  coupled thereto. Each hinge reinforcement  38  and strut reinforcement  36  also has at least one compression limiter  56  coupled thereto. At least one compression limiter  56  is coupled near the bottom rear edge of the inner panel  22 . 
         [0040]    A latch reinforcement bracket  58  or tapping plate, preferably formed of steel, is bonded to the inner panel  22  using adhesive in the area where a latch handle  60  is connected to the lower outer panel  16 . Optionally, a fourth plurality of fasteners, e.g., screws, are added to further hold the latch reinforcement bracket  58  in position. The latch handle  60  actuates a latch manual and/or power liftgate device  62  coupled to the inner panel  22  generally adjacent to the latch reinforcement bracket  58  when engaged by an operator of the liftgate  10 . 
         [0041]    Formed as part of the inner panel  22  are additional structural reinforcements such as ribs and fins. A set of sloped fin-like shaped  64  ridges are each connected to a top surface of both channels of the fourth pair of channels  33  and within the upper first pair channel  26  ( FIG. 6 ). At least one pair of first ribs  66  are connected to a bottom surface of the fourth pair of channels  33 . A plurality of second ribs  68 , e.g., at least three ribs, are connected within each of the second pair of channels  30 . A plurality of third ribs  70 , e.g., two pairs of two ribs, are connected to a top surface of the upper first pair channel  26  and run generally vertically to a predetermined distance below the opening  25 . A plurality of fourth rips  72 , e.g., at least three ribs, run substantially diagonal across the lower inside corner areas of the inner panel  22 . Each fin or rib in the respective sets and pairs are substantially parallel with one another. 
         [0042]    Each fin or rib in the respective sets and pairs have predetermined lengths, widths, depths, and material thickness suitable to provide structural support and strength for the inner panel  22  and improve the rigidity of the liftgate  10  system, including under predetermined load conditions. Optionally, additional fins and/or ribs can be formed as part of the inner panel  22 . 
         [0043]    There is provided a main wiring harness  74  and a washer device  76  with a motor and wider coupled to the inner panel  22 . The outer panel  12  is bonded to the inner panel  22  by using adhesive  78  (“ 78 ” indicates adhesive for various components, e.g.,  FIGS. 4 and 9 ) applied in a predetermined pattern and locations on the inner panel  22 . Also provided is a center high-mount stop light (CHMSL) device  80  connected to the upper outer panel  14 . A tail light assembly  82  is operably connected to the lower outer panel  16 . Preferably, the tail light assembly  82  is bonded to the lower outer panel  16  with adhesive and additionally a plurality of fasteners. 
         [0044]    As further illustrated in  FIG. 10 , the inner panel  22  is bonded to the glass panel  20  and reinforcement brackets, e.g., each strut reinforcement bracket  44 , through the use of adhesive  78  such that packaging for wiring, e.g., the main wiring harness  74 , and an adjacent gas strut is provided. The reinforcement has a predetermined thickness and is bonded, rather than merely bolting in a few locations, with structural adhesive to bond in place with continuous attachment of the structure. The inner panel connected to the brackets and outer panel forms predetermined operable cross sections. 
         [0045]    Also connected to the inner panel  22  is a lower trim panel, shown generally at  84 , substantially facing toward the vehicle interior and running generally from the D-pillar to near the bottom edge of the inner panel  22 . The lower trim panel has class A surfaces and at least one access panel  86  or door. A pair of handle pockets  88  is also provided in the lower trim panel  84  for an operator to selectively grasp when operating the liftgate  22 , in particular to cycle to the liftgate  10  from an open to a closed position. 
         [0046]    The access door  86  is removable and/or rotatable for gaining access to at least the latch mechanism assembly  62  for maintenance and/or repair. The access panel  86  is a significant benefit over conventional liftgates requiring disassembly and maintenance/repair complexity. Preferably, there are at least five access panels  86  suitably situated where maintenance and repair of various components not otherwise easily accessible is desired. Most preferably, at least one access panel  86  is located in each of the following areas: the latch mechanism assembly  62 , tail light assembly  82  (e.g., for changing both burnt out tail lights), CHMSL  80 , and wiper device  76  (e.g., to access a wiper motor) areas. 
         [0047]    A pair of gas struts  90  is operably connected to the inner panel  22  and/or a hinge system. The gas strut and hinge system are connected to the vehicle. 
         [0048]    By non-limiting example, the inner panel  22  is bonded to the outer panel  12  to using urethane bonding. The inner panel  22  provides structural support for the composite liftgate of the present invention not only through the shape of the inner panel as described above, but the material used to make the inner panel provides structural support as well. The inner panel  22  is made of a structural thermoplastic, such as a polypropylene, a thermoset or thermoplastic such as a reinforced polypropylene (RPP), and is preferably a 40% glass-filled polypropylene. The inner panel  22  is preferably thermoplastic 0.5 inch long glass filament filled polypropylene. By way of non-limiting example, the outer panel  12  is made of a suitable thermoplastic used as a show surface, such as a thermoplastic polyolefin (TPO). The structural composite reinforcements preferably comprise woven glass reinforcement. 
         [0049]    The inner panel  22  is preferably thermoplastic injection molded with mold-in color, and grain in areas of class A surface(s). Thereafter, the inner panel  22  is painted and bonded with the structural composite reinforcements. Alternatively, the structural composite reinforcements are insert molded to connect the reinforcements to the inner panel  22 . At least the hitch reinforcement brackets are additionally affixed with fasteners. The reinforcement brackets are bonded in place and further held in position with fasteners. Bonding is substantially beneficial over conventional liftgates. The outer panel  12  is painted prior to connecting to the inner panel  22 . The outer panel  12  is bonded to the inner panel  22  and the glass pane  20  is bonded to the inner panel  22  and outer panel  12  (fasteners are additionally contemplated in addition to the adhesive). The lower trim panel  84  is operably connected to the inner panel  22  by at least adhesive. 
         [0050]    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.