Abstract:
The present invention is a thermoplastic composite liftgate system with reinforcements in key areas to allow the system to meet performance requirements, while lowering the tooling investment, lowering the system mass, and improving the styling flexibility. The present invention includes an inner panel and at least one bracket or reinforcement member connected to the inner panel such that when a force is applied to the bracket, the force is distributed to the inner panel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/130,489, filed May 30, 2008. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to liftgates for automobiles. More specifically, the present invention relates to a composite liftgate for an automobile. 
     BACKGROUND OF THE INVENTION 
     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. Liftgates are traditionally made from stamped steel panels that are heavy and have a high tooling cost. 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. 
     Another concern with the manufacture of liftgates is that typical lifgates are manufactured as a relatively flat or smoothly contoured panel, with structural reinforcements such as ribs being added onto the panel. This will also add weight and increase manufacturing complexity as well. 
     One solution to this problem has been the 2008 Nissan Murano composite liftgate system, which has helped to satisfy the weight savings and the tooling cost concerns, but utilizes 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. 
     Accordingly, there exists a need for a composite liftgate which is both lightweight, as well as structurally sound enough to meet various load requirements. 
     SUMMARY OF THE INVENTION 
     The present invention is a thermoplastic composite liftgate system with reinforcements in key areas to allow the system to meet performance requirements, while lowering the tooling investment, lowering the system mass, and improving the styling flexibility. The present ivention includes an inner panel, and at least one bracket, or reinforcement, connected to the inner panel such that when a force is applied to the bracket, the force is distributed to the inner panel. 
     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 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a rear view of an inner panel having multiple reinforcements used in a liftgate system, according to the present invention; 
         FIG. 2  is an enlarged perspective view of a lower pillar reinforcement used for a composite liftgate system, according to the present invention; 
         FIG. 3  is an enlarged perspective view of an upper pillar reinforcement used for a composite liftgate system, according to the present invention; 
         FIG. 4  is an enlarged perspective view of a wide reinforcing bracket used for a composite liftgate system, according to the present invention; 
         FIG. 5  is a perspective view of an inner panel used for a composite liftgate system, according to the present invention; 
         FIG. 6  is a rear view of an inner panel used for a composite liftgate system, according to the present invention; 
         FIG. 7  is a front view of an inner panel used for a composite liftgate system, according to the present invention; 
         FIG. 8  is a side view of an inner panel used for a composite liftgate system, according to the present invention; 
         FIG. 9  is an exploded perspective view of a first embodiment of an outer panel used in a composite liftgate system, according to the present invention; and 
         FIG. 10  is a perspective view of a second embodiment of an outer panel used in a composite liftgate system, according to a first embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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. 
     The composite liftgate system of the present invention utilizes a wide reinforcing bracket along with a latch which aids in spreading the load applied to the bracket over a larger area. The wide reinforcement bracket adds more structure by attaching to the inner panel with structural adhesive or insert molding. Additionally, the wide reinforcing bracket is also tied into other reinforcing brackets with steel tethers. The other reinforcing brackets are also connected to a hinge system through the use of additional steel tethers. The steel tethers are in the form of cables, stampings, tubes, etc., which reinforce the composite gate and the latch system (which ties to the body) to a counter balance system and the hinge system (which also ties back into the body structure). 
     The composite liftgate of the present invention provides the advantage over other inventions through the use of a wide steel reinforcement in the area of the latch. The wide steel reinforcement is installed with structural adhesive, or in another embodiment is insert molded for added structure. Mechanical fasteners are used as a temporary connection to hold the wide steel reinforcement in place until the structural adhesive sets up and cures. Tethers, similar to the tethers mentioned above, tie the lower reinforcement in the latch area to other important reinforced areas that extend to other reinforcements and to the upper hinges that again tie into the metallic body structure. 
     Another feature of the present invention is that the liftgate includes an inner composite panel. The structure of the inner composite panel includes various shapes and ribs which transfer the load path up through key structural areas of the assembly. 
     The inner panel is connected to an outer panel to form the composite liftgate of the present invention. The inner panel and outer panel are bonded together through the use of a urethane bonding. The inner panel 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 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 outer panel is made of a typical thermoplastic used as a show surface, such as a thermoplastic polyolefin (TPO), and provides no significant structural support for the composite liftgate of the present invention. 
     An embodiment of a composite liftgate system is shown in the Figures generally at  10 . The liftgate  10  includes a bracket  12 , which is connected to an inner panel  14 . In this embodiment, the bracket  12  is structurally bonded using an adhesive  16 , but it is within the scope of the invention that the bracket  12  could be insert molded to connect the bracket  12  to the inner panel  14 . 
     Also connected to the inner panel  14  are a set of lower pillar reinforcements  18  and a set of upper pillar reinforcements  20 ; both the reinforcements  18 , 20  are connected to the inner panel  14  in a similar manner as the bracket  12 . Each of the lower pillar reinforcements  18  are typically connected to a gas strut (not shown), and the upper pillar reinforcements are typically attached to a hinge system (not shown), with the hinge system and gas strut connected to a vehicle. 
     The liftgate  10  of the present invention also includes a series of reinforcement members  22 . The reinforcement members  22  will keep the liftgate  10  together even if the inner panel  14  becomes cracked or deformed from being subjected to an impact. In this embodiment, the reinforcement members  22  are in the form of tethers  22 . The tethers  22  may be braded stainless steel cable, stainless steel tubing, a rolled or stamped steel channel, or a wide webbing material, similar to what is used in common seat belts. 
     Formed as part of the inner panel  14  are a first pair of channels or latch channels  24 . The channels  24  run in a substantially diagonal pattern from the near the center of the bracket  12  to the lower pillar reinforcements  18 . In this embodiment, the channels are 70 mm wide and 70 mm deep, but it is within the scope of the invention that other dimensions may be used as well. The two channels  24  shown in the Figures produce substantially a “V-pattern.” 
     There are also two second channels  26  which are substantially perpendicular to the latch channels  24 . Again, the additional channels  26  are 70 mm wide and 70 mm deep, but it is within the scope of the invention that other dimensions be used as well. 
     The inner panel  14  also includes a pair of third channels, or side channels  28 , which again are 70 mm wide and 70 mm deep, and provide further structural support for the inner panel  14 . The side channels  28  extend along each side of the inner panel  14 , and intersect the latch channels  24  respectively in the general area of the lower pillar reinforcements  18 . 
     To further improve the structural integrity of the inner panel  14 , there is also a plurality of secondary reinforcement members, or ribs  30 . The ribs  30  are also formed as part of the inner panel  14 , similar to the channels  24 , 26 , 28 . The ribs  30  are incorporated into all of the channels  24 , 26 , 28 , and improve the rigidity of the entire lift gate  10 . 
     The liftgate  10  also includes an outer panel, generally shown at  32  in  FIGS. 9 and 10 . The outer panel  32  is connected to the inner panel  14  such that a cavity is formed between the inner panel  14  and outer panel  32 . The outer panel  32  may be formed of two separate pieces, as shown in  FIG. 9 , or may be formed as a single piece, as shown in  FIG. 10 . 
     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.