Abstract:
An automotive tailgate includes a door adapted to pivot about a generally horizontal pivot axis, with the door including a shell defining an interior space. The door is pivoted upon bearings mounted upon bearing retainers located at each end of the door. A full floating torsion bar is provided and includes a first end rotationally grounded within the interior of the door shell and a second end engaged with and rotationally locked with one of the bearing inserts so that the torsion bar will be subjected to torsional loading as the door is pivoted. Because the torsion bar is full floating, the operation of the tailgate hinges will not be impaired even if the torsion bar were to become fractured.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to a door or tailgate for vehicle such as a pickup truck, having a torsion bar for assisting the closure of the tailgate. 
     2. Disclosure Information 
     Tailgates used with large pickup trucks present a challenge to the operator of the truck insofar as the weight of such tailgates and the height of such vehicles frequently result in the necessity of expending considerable effort to close the tailgate. U.S. Pat. No. 5,358,301, which is shown in FIG. 6, discloses a torsion bar system for assisting the closure of a tailgate. Unfortunately, the system disclosed in the &#39;301 patent suffers from several drawbacks. First, the system would have high cost because the torsion bar is itself used as a hinge pin and this necessitates that the torsion bar be sufficiently large to not only function in torsion, but also in shear so as to support the tailgate itself. Secondly, the fact that the torsion bar functions not only as a torsion element but also as a pivot for tailgate means that in the event that the torsion bar breaks, the tailgate&#39;s pivot function may be impaired, with the result that the tailgate could separate from the vehicle in a unwanted manner. 
     A torsion bar tailgate lift assist system according to the present invention solves the problems inherent in the previously described system, but at a lower cost, while providing a torsion bar which is full floating. This means that if the torsion bar of the present inventive system were to break, the pivoting function and retention of the tailgate to the body of the pickup truck would not be adversely affected. 
     SUMMARY OF INVENTION 
     An automotive closure panel includes a door, typically a tailgate adapted to pivot about a generally horizontal pivot axis, with the door having a shell defining an interior space. A first hinge bearing retainer is attached to a first end of the door and has a first bearing insert housed within the retainer. A first pivot post is rigidly attached to a structure such as a side pillar adjoining a first end of the pivot axis, with the pivot post engaging a bore formed in the interior of the said first bearing insert. A second hinge bearing retainer is attached to the second end of the door and has a second bearing insert housed therein. A second pivot post is rigidly attached to a structure such as a second side pillar adjoining a second end of the pivot axis. The second post engages the second bearing insert such that the second pivot post and the second bearing insert are rotationally locked. This means as the tailgate is pivoted, the second bearing insert will rotate within the second bearing retainer. In other words, the second bearing insert will rotate with respect to the second bearing retainer because the second bearing insert will not rotate at with respect to the tailgate. This means that the tailgate itself, including the second bearing retainer, will rotate about the second bearing insert. 
     The present automotive closure panel further includes a full floating torsion bar having a first end rotationally grounded within the interior of the door, and a second end engaged with and rotationally locked with the previously described second bearing insert such that the torsion bar will be subjected to torsional loading as the door is pivoted. The second pivot post is oriented so that the torsion bar is subjected to a minimal torsional load tending to open the door when the door is in a closed position. The orientation of the second pivot post further allows the torsion bar to be subjected to a maximum torsional load tending to close the door when the door is in a fully open position, which normally corresponds to about 90Â° of rotation from the closed position. 
     The torsion bar of the present system is situated such that the first end of the torsion bar is grounded within an anchoring member located within the interior of the door, wherein the anchoring member passes through an aperture of the door shell during assembly. The anchoring member may take a variety of forms such as a bracket, mounting block, or a pinch block. The anchoring member may be affixed to a portion of the first bearing retainer via a hinge bracket or the like, or directly to the first bearing retainer. 
     The first bearing insert and first pivot post are keyed in a manner used with 2003 model year pickup trucks produced by Ford Motor Company, so as to allow the closure panel to be removed from a vehicle when the panel has been opened to a predetermined position. 
     According to another aspect of the present invention, a method for constructing an automotive tailgate includes the steps of fabricating a door adapted to pivot about a generally horizontal pivot axis, with the door having a shell defining an interior space, and with the shell having a first end and a second end, and attaching first and second bearing retainers to the shell, with each of the bearing retainers housing a bearing insert. The present method further includes providing a first pivot post rigidly attached to a body structure adjoining a first end of the door shell when the door is in a closed position. The first pivot post engages a bore formed the interior of said first bearing insert. A second pivot post is attached to a pillar structure adjoining the second end of the door when the door or tailgate is in a closed position, with the second pivot post engaging the second bearing insert such that the second pivot post and second bearing insert are rotationally locked. 
     According to another aspect of the present invention, a cargo box for an automotive vehicle includes left and right pickup box sides, a first side pillar attached to the right pickup box side, and a second side pillar attached to the left pickup box side. A first pivot post is attached to the first side pillar, and a second pivot post is attached to the second side pillar. A tailgate is hingedly attached to the first and second pivot posts, with the tailgate having a full floating torsion bar lift assist. The torsion bar has a first end rotationally grounded within the interior of the tailgate, and a second end rotationally locked with the second pivot post such that the torsion bar will be subjected to torsional loading as the tailgate is pivoted to an open position. 
     Finally, according to the present invention, a full floating torsion bar is provided, with the bar housed entirely within the interior space of the door and with the torsion bar having a first end rotationally grounded within the interior of the door and a second end engaged with and rotationally locked with the second bearing insert such that the torsion bar will be subjected to torsional loading as the door is pivoted. 
     It is an advantage of the present invention that an automotive tailgate may be provided with a lift assist system having less weight than other known lift assist systems. 
     It is a further advantage of the present invention that the present lift assist system is less costly than known lift assist systems. 
     It is a further advantage of the present invention that the present lift assist system will not impair the basic functions of the tailgate even if the torsion bar should fail during normal operation of the vehicle. 
     It is a further advantage of the present invention that the torsion bar employed in the inventive lift assist system may be readily changed in diameter, or in length, or both, so as to alter the effective spring rate of the torsion bar, without the necessity of retooling the tailgate hardware. This change is not easily accommodated by prior art designs. 
     It is a further advantage that a vehicular door, such as a tailgate, equipped according to this invention has a self-contained torsion bar mechanism, allowing the tailgate to be removed without the use of tools. 
     Other advantages, as well as objects and features of the present invention, will become apparent to the reader of this specification. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view of a pickup truck having a tailgate lift assist system according to the present invention. 
     FIG. 2 is a cut-away plan view of a tailgate as shown in FIG.  1 . 
     FIG. 3 is a blown-up perspective view of the tailgate lift assist system shown in FIGS. 1 and 2. 
     FIG. 4 illustrates a driver&#39;s side pivot post according to one aspect of the present invention. 
     FIG. 5 illustrates a pivot for a tailgate having an assist system according to the present invention. 
     FIG. 6 illustrates a prior art tailgate assist system according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     As shown in FIG. 1, vehicle  10  has rear roadwheels  12  and tailgate  14  including shell  18  and torsion bar  70 . Tailgate  14  pivots about axis A 1 -A 2  (FIG.  2 ). Note that torsion bar  70  does not extend across the entire width of tailgate  14 . This means that the length of torsion bar  70  may easily changed, so as to change the effective spring rate of torsion bar  70  to compensate for changes in the weight of tailgate  14 . Tailgate  14  is hingedly attached to a pickup box having a left pickup box side  90  and a right pickup box side  92 . 
     FIGS. 2 and 3 illustrate various details of the present system. Shell  18  is pivoted upon two pivots which define the generally horizontal pivot axis shown as A 1 -A 2  in FIG.  2 . At the right side of vehicle  10 , a first hinge bearing retainer  22  is applied to the first end  26  of shell  18 . Bearing retainer  22  is cup-shaped and may be either mechanically joined or welded, or for that matter, molded from metal or plastic integrally with hinge bracket  24  which is applied to the outer or exterior surface of shell  18 . First bearing insert  30  is located within hinge bearing retainer  22 . First bearing insert  30  has bore  32  therein which allows first bearing insert  30  to engage first pivot post  34 , which is rigidly attached to first side pillar  38 , which is in turn rigidly attached to right pickup box side  92 . First hinge bearing retainer  22  and first bearing insert  30 , as well as first pivot post  34  are made in conventional fashion so as to allow tailgate  14  including shell  18  to be removed from vehicle  10  when tailgate  14  has been rotated to a prescribed partially open position. 
     Those skilled in the art will appreciate in view of this disclosure that the tailgate removal technique (i.e. permitting removal at a predetermined opening position lying between fully open and fully closed) described herein has been used in the past by Ford Motor Company and others and is intended to be adopted with the present system. This provides additional advantages because the right side hinge mechanism of tailgate  14  according to present invention may be made for the most part according to known methods with known materials with a resulting labor and materials saving over known alternative torsion bar assist systems. And, the vehicle operator will be able to remove tailgate  14  by using a familiar technique, thereby promotion owner satisfaction. 
     At the second end  48  of shell  18 , second hinge bearing retainer  44 , which too is cup-shaped, is mounted upon hinge bracket  46 , in a manner previously described with respect to first hinge bearing retainer  22 . Second bearing insert  52  is rotatably received within second hinge bearing retainer  44 . Second bearing insert  52  includes a rigid substrate such as a metallic or non-metallic material having a generally cylindrical outer surface  53 , which preferably has a dense resin coating  54  applied thereto to combat corrosion and to permit a close fit between the inner diameter of second hinge bearing retainer  44  and the outer diameter of second bearing insert  52 . Bearing insert  52  also has bore  55 (FIG. 5) to permit torsion bar  70  to be slidably engaged therewith. The slidable engagement should preferably be a press fit. Bore  55  has a non-circular cross section which matches a non-circular cross section of torsion bar  70 . Torsion bar  70  has first end  72  with a flat surface  76  formed thereon and a second end  74  with a flat surface  77  formed thereon. Flat surface  77  allows torsion bar  70  and second bearing insert  52  to be rotationally locked. In other words, torsion bar  70  and second bearing insert  52  cannot rotate with respect to each other. Moreover, rotation of second bearing insert  52  with respect to the body of vehicle  10  and more precisely, with respect to second pivot post  56 , is prevented by the cooperation of oblong bore  58  formed in second bearing insert  52 , which receives an oblong projection  62  extending from the base of second pivot post  56 . As shown in FIGS. 2 and 3, second pivot post  56  is attached to second side pillar  60  by fasteners such that the pivot post cannot rotate with respect to side pillar  60 , which is rigidly attached to left pickup box side  90  (FIGS.  1  &amp;  3 ). As noted above, second bearing insert  52  is overmolded, preferably with a plastic  54  such as the urethane composition currently used for automotive bushings, so as to prevent corrosion of second bearing insert  52 , while allowing a close, noise free fit of insert  52 . 
     The present torsion bar system is said to be full floating because even torsion bar  70  were to break, second bearing insert  52  will not become disengaged from second hinge bearing retainer  44  and second pivot post  56 . This full floating feature means that the pivoting function of the tailgate system and, for that matter, the retention of tailgate  14  upon vehicle  10 , will not be adversely affected by breakage of torsion bar  70 . 
     First end  72  of torsion bar  70  is rotationally grounded within the interior of shell  18  by means of an anchoring member  78  such as a bracket or the like (shown in FIG. 2 as a pinch block), which is mounted to hinge bracket  24 . Anchoring member  78  extends into the interior of shell  18  through aperture  82 . Where anchoring member  78  is a pinch block, pinch block  78  has a bore  80  formed therein. Bore  80  has a semi circular cross section. Pinch block  78  further has a torsion bar retainer  84  which is maintained in place by means of fasteners such as rivet  86  and bolt  88 . Once fasteners  86  and  88  have been placed, torsion bar  70  is grounded or non-rotationally locked to pinch block  78 , and as a result, pivoting of shell  18  about axis A 1 -A 2  will cause torsion bar  70  to be subjected to torsional windup sufficient to produce the desired assist for the operator of the vehicle opening or closing tailgate  14 . 
     The present invention may be employed as follows. After a portion of shell  18  including ends  26  and  48  has been formed, hinge brackets  24  and  46  including first and second hinge bearing retainers  22  and  44  will be applied to the exterior surface of shell  18  either by welding, bonding, riveting, bolting or by other means known to those skilled in the art and suggested by this disclosure. In a preferred embodiment, hinge bracket  24  includes pinch block  78 , which passes into the interior of the tailgate through port  83  formed in shell  18 . Alternatively, first and second hinge bearing retainers  22  and  44  could be integrally formed with the ends of shell  18 . These and other such modifications will be suggested to those skilled in the art by this disclosure. Once second hinge bearing retainer  44  has been mounted to shell  18 , torsion bar  70  may be slidably engaged with both pinch block  78  and with second bearing insert  52 . The slidable engagement between end  74  of torsion bar  70  and end bore  55  formed in second bearing insert  52  would normally be to be an interference fit sufficient to assure the retention of torsion bar  70  within bore  55  with a minimum retention force of about 100 lbs. In any event, once torsion bar  70  has been mounted within pinch block  78  and pinch bolt  88  has been tightened, torsion bar  70  is not free to move axially. 
     Engagement of end  74  of torsion bar  70  with bore  80  of pinch block  78  is promoted by a chamfered section of bore  80  at the end of pinch block  78  which is first entered by bar end  74 . Engagement of torsion bar  70  with pinch block  78  is further promoted by the fact that torsion bar  70  is a straight rod. 
     Although the present invention has been described in connection with particular embodiments thereof, it is to be understood that various modifications, alterations, and adaptations may be made by those skilled in the art without departing from the spirit and scope of the invention set forth in the following claims.