Patent Document

RELATED APPLICATION 
   This application claims the benefit of U.S. Provisional Application No. 60/546,102, filed on Feb. 18, 2004 the entire teachings of that are incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   Typically, a tailgate is pivotally mounted between body side panels forming the pillars at the rear of the vehicle. The tailgate pivots about a hinge axis between a horizontal, open position and a vertical, closed position. Preferably, the mounting assemblies for the tailgate permit the tailgate to be removed, removal typically being accomplished when the tailgate is pivoted to a position between the fully open or fully closed position. For example, the tailgate may include hinge pins that extend outwardly along the hinge axis that removably connect into brackets carried on the truck body. When the tailgate is pivoted to a predetermined intermediate position, for example, 15° away from the fully closed position, at least one of the hinge pins slips through a slot in the connecting bracket as the tailgate is lifted at one end from the truck body. 
   Some of the tailgate mounting assemblies include counterbalance mechanisms, such as torque rods for assisting with the opening and closing of the tailgate. These torque rods are located, at least in part, within the tailgate for spring biasing between the tailgate and the body panel pillars. These torque rods typically require numerous components to assemble the torque rod to the tailgate. 
   In some instances, it may be desirable to keep the tailgate in the open position, such as for transporting material having a greater length than vehicle&#39;s bed. As such, the tailgate can be susceptible to closing by way of the counterbalancing mechanism. For example, the tailgate might bounce in a direction toward closure if the vehicle were to inadvertently go over a bump or into a pothole, and the counterbalancing mechanism would then assist in potentially closing the tailgate. 
   SUMMARY OF THE INVENTION 
   The present invention provides a counterbalancing system that can be easily installed to an exterior of a tailgate and provide a mechanism for arresting the tailgate in an open position. The system includes a stop assembly coupled to the vehicle and a counterbalance assembly adapted to be coupled in an optional pretensioned position to an outer periphery of the tailgate, the counterbalance assembly providing a counterbalance force when engaged with the stop assembly while the tailgate is opened or closed. 
   The stop assembly can be adapted to be coupled to an existing hinge pin of the vehicle. The stop assembly can include a semicircular groove for slidably engaging the counterbalance assembly. 
   The counterbalance assembly can include a spring member comprising a first portion and a second portion that extends traversely from the first portion. The second portion can include a first notch positioned proximal to and below an end of the spring member for engaging the stop assembly and arresting the tailgate in a first position, wherein the first position can allow the tailgate to be arrested in a partially opened position. The second portion can further include a second notch positioned proximal to and below the first notch for engaging the stop assembly and arresting the tailgate in a second position, wherein the second position can allow the tailgate to be arrested in a fully opened position. The spring member can be a torque rod. 
   The stop assembly and the counterbalance assembly can be coupled as not to interfere with removal of the tailgate from the vehicle. The stop assembly and or the counterbalance assembly can be adapted to be spring-loaded for ease of installation of the tailgate to the vehicle. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in that like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
       FIG. 1A  shows an exploded perspective view of a counterbalance assembly of the present invention; 
       FIG. 1B  shows an exploded perspective view a stop assembly of the present invention; 
       FIG. 2  shows a pretension angle “A” of a counterbalance assembly of  FIG. 1 ; 
       FIGS. 3A–3B  illustrate installation of the present invention to a tailgate of a vehicle; 
       FIG. 3C  illustrates installation of the tailgate to the vehicle; 
       FIGS. 4A–4D  illustrate the opening of the tailgate using the crank arm of  FIG. 2 ; 
       FIG. 5  shows another embodiment of a crank arm of the invention; and 
       FIGS. 6A–6D  illustrate the opening of the tailgate using the crank arm of  FIG. 5 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A description of preferred embodiments of the invention follows. 
   Generally, an externally mounted counterbalance mechanism is provided to assist with the opening and closing of a tailgate of a vehicle, such as a truck, minivan, station wagon, etc. The counterbalance mechanism can also include a series of safety stops that arrest the tailgate in predetermined positions. 
     FIG. 1A  shows an exploded perspective view of a counterbalance assembly  11  of the present invention. The counterbalance assembly  11  includes a spring member  12 , a plurality of brackets ( 20 ,  22 ,  34 ), and bracket screws ( 24 ,  26 ,  32 ,  40 ) for attaching the counterbalance assembly  11  to an exterior of the tailgate in an optional pretensioned position as will be explained in further detail below. In one embodiment, the spring member  12  is a torque rod. The material used for the spring member  12  should be chosen as not to fatigue as the spring member is rotated. 
     FIG. 1B  shows an exploded perspective view of a stop assembly  13  of the present invention. The stop assembly  13  includes a stop bracket  44 , a stop pin  42 , stop pin screws ( 46 ,  48 ), and bracket screws ( 52 ,  54 ) for attaching the stop assembly  13  to an existing hinge pin  50  on the vehicle. The stop bracket  44  includes an upper portion  62 , a lower portion  64 , and an intermediate portion  60 . The intermediate portion  60  provides an offset between the upper portion  62  and the lower portion  64 . The stop pin  42  fastens to the upper portion  62  of the stop bracket  44 . As a result, the stop pin  42  can easily flex outward laterally, but is relatively rigid in the fore and aft direction. The stop pin  42  includes a semicircular groove  56  facing forward and a tapered face  58  facing backward. The semicircular groove  56  is positioned laterally to cradle a section of the spring member  12  ( FIG. 1A ) once the tailgate is installed. The semicircular groove can be replaced by a roller assembly, such as a one way roller. 
     FIG. 2  shows a pretension angle “A” of the counterbalance assembly  11 . The spring member  12  is bent 90° to create a straight section  14  and a crank arm  16 . Typically, a length of the straight section  14  is greater than a length of the crank arm  16 . The straight section  14  includes a flat portion  30  that is disposed at an angle “A” (zero torque position) relative to a center axis of the crank arm  16 , typically in the range of 60°. Bracket  22  includes a flat surface  28  for mating with the flat surface  30  of the straight section  14  such that free rotation of the counterbalance assembly  11  is prevented. Bracket  34  includes a lip  36  for holding the spring member  12  in a pretensioned position as described in further detail below. Pretensioning of the counterbalance assembly  11  is optional and provides for a greater restoring force than that of an assembly having no pretension. 
     FIGS. 3A–3B  illustrate the installation of the spring member  12  of the preceding figures. Brackets  20 ,  22  are attached to the bottom  8  of a tailgate  18  and bracket  34  is attached to a side  38  of the tailgate. The lip  36  of the bracket  34  should be on an edge inward toward a bed of a vehicle. Once the brackets  22 ,  24 ,  34  have been installed, the spring member  12  is inserted into brackets  20 ,  22  with the flat portion  30  of the straight section  14  aligned to fit into the respective flat mating surface  28  of the bracket  22  until the crank arm  16  hits the side  38  of the tailgate  18  as shown in  FIG. 3A . The spring member  12  can freely slide in and out of the brackets  20 ,  22 , but cannot rotate once the spring member  12  is engage with bracket  22 . 
   The crank arm  16  can then be forced in a counterclockwise direction relative to  FIGS. 3A and 3B  until it clears the top of the lip  36  on the retaining bracket  34 . At that time, the spring member  12  can be fully inserted into bracket  22  and secured with screw  32 , as shown in  FIG. 3B . The rotation of the crank arm  16  reduces angle “A” ( FIG. 2 ) to approximately 0°. This reduction creates an amount of torque on the spring member  12  that left unrestrained by the lip  36  would restore the spring member  12  to its normal or zero torque position. Although the straight section  14  of the spring member  12  is shown across the entire length of the tailgate  18 , it should be understood the length of the straight section  14  can be any length that provides a sufficient restoring force. 
     FIG. 3C  shows a cutaway view of the tailgate  18  mounted to a vehicle  10 . The tailgate  18  of  FIGS. 3A and 3B  is rotated to align with the vehicle  10  as shown. The stop assembly  13  can be mounted to an existing hinge pin  50  located on the vehicle  10 . It should be understood that the tailgate  18  is mounted to the vehicle  10  in the conventional manner as known in the art. Installation of the tailgate  18  is described with reference to the preceding figures. First, a first trunnion  66  ( FIG. 3B ) can be inserted over a respective hinge pin  50  on a body of the vehicle  10 , and while holding the tailgate  18  at an approximately 45° slant, a second trunnion (not shown) can slid over a slanted hinge pin (not shown), at that point the tailgate  18  can be closed. 
   In some instances, the stop pin  42  can obstruct the crank arm  16  as the tailgate  18  is lifted, but by virtue of its tapered face  58  ( FIG. 1B ) the stop bracket  44  and the crank arm  16  flex laterally out and in, respectively, to allow the crank arm  16  to pass into position. Once the crank arm  16  is past the stop pin  42 , the stop bracket  44  and the crank arm  16  spring back into position laterally, and the crank arm  16  is captured by the groove  56  ( FIG. 1B ) of the stop pin  42 . It should be realized that the flexing action described above is merely a convenience feature during the installation of the tailgate  18 . The operation of the present invention would remain unchanged if the stop bracket  44  were rigid. Thus, the operator would merely be forced to hold the tailgate  18  straight up and down as he engages the first hinge pin, then lower it approximately 45 degrees to engage the second hinge pin. 
     FIGS. 4A–4D  illustrate the opening of the tailgate  18  using the crank arm  16  of  FIG. 2 . The viewing angle of this illustration is looking through the near side of the vehicle  10  ( FIG. 3C ) in the direction of the hinge pin  50 . The stop pin  42  is attached to the vehicle  10  and is stationary relative to movement of the tailgate  18 . 
     FIG. 4A  shows the tailgate  18  in a closed position with the crank arm  16  remaining in the pretensioned position by the lip  36  of the bracket  34 . There is approximately 15° of free travel of the tailgate  18  between the closed position and engagement of the spring member  12  and the stop pin  42 . In this position the opening gravitational moment acting on the tailgate is very slight and the pretensioning of the torsion rod can be chosen to exceed it easily such that the tailgate is arrested in a “safety stop” position. As shown in  FIG. 4B , the tailgate is engaged with the crank arm  16 . Once the spring member  12  and the stop pin  42  are engaged, a counterbalance force or restoring force is applied to the tailgate  18  to assist an operator with either opening or closing the tailgate  18 . That is, the spring member  12  tries to restore itself to the normal position as shown in  FIG. 2 . As the tailgate  18  is lowered further as shown in  FIG. 4C , the amount of restoring force on the spring member  12  increases since the spring member  12  is rotated further from its normal position. The tailgate  18  is then dropped to the fully open position shown in  FIG. 4D . At this point the amount of restoring force on the spring member  12  is greatest since the spring member  12  is rotated furthest from its normal position. 
     FIG. 5  shows another embodiment of the crank arm  16  of the preceding figures. The crank arm  16 ′ is shaped to include two curved notches “B” and “D” and a curved section “C” for arresting or locking the tailgate  18  in predetermined positions as explained with reference to  FIGS. 6A–6D . The notches “B” and “D” prevent the tailgate from inadvertent closure. It should be understood that any number of notches or curves can be used to arrest the tailgate in a predetermined position. Further, the deeper the notches the more force is required to move the tailgate from the predetermined position. 
     FIGS. 6A–6D  illustrate the opening of the tailgate  18  using the crank arm  16 ′ of  FIG. 5 . The viewing angle of this illustration is the same as the viewing angle as described with reference to  FIGS. 4A–4D .  FIG. 6A  shows the tailgate  18  in a closed position with the crank arm  16 ′ remaining in the pretensioned position by the lip  36  of bracket  34 . There is approximately 15° of free travel of the tailgate  18  between the closed position and engagement of the spring member  12  and the stop pin  42 . Once the spring member  12  and the stop pin  42  are engaged, a counterbalance force or restoring force is applied to the tailgate  18  to assist an operator with either opening or closing the tailgate  18 . In this position the opening gravitational moment acting on the tailgate is very slight and the pre tensioning of the torsion rod can be chosen to exceed it easily such that tailgate is arrested in a “safety stop” position. As shown in  FIG. 6B , the tailgate is held or locked in a “safety stop” or arrested position once the stop pin  42  engages notch “B” of the crank arm  16 ′. The notch “B” further enhances arresting the drop of the tailgate. The notch “B” of the crank arm  16 ′ can be either straight or curved as shown. The curvature makes it possible to better counterbalance the sinusoidal gravitational pull by the linear stress-strain characteristic of the spring member  12 . To lower the tailgate beyond this point requires the operator to pull the tailgate  18  in a downward direction past notch “B” as shown in  FIG. 6C . The amount of restoring force on the spring member  12  increases since the spring member  12  is rotated further from its normal position. The tailgate  18  can then be dropped to the fully open position shown in  FIG. 6D  as the notch “D” of the crank arm  16 ′ engages the stop pin  42 . At this point the amount of restoring force on the spring member  12  is greatest since the spring member  12  is rotated furthest from its normal position. The depth of the notch “D” determines how firmly the tailgate is restrained in the open position, such as to prevent an inadvertent closure of the tailgate. 
   As an additional feature to cushion the drop of the tailgate, the sliding action of the crank arm  16  can be utilized to push against a viscous damper mounted on the truck just above the stop pin  42  (not shown). 
   While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. For example, the crank arm may terminate in a laterally positioned pin that rides up and down over a shaped cam surface mounted to the truck. Although the counterbalance assembly is shown to be in a pretension position, it should be understood that pretension is not necessary to provide the counterbalancing means.

Technology Category: b