Abstract:
A control mechanism for controlling movement of a vehicle gate between a first and a second position comprises a dampener assembly and a lift assembly that are incorporated within the gate. The dampener assembly has a first component mountable to a vehicle structure and a second component supportable by the vehicle gate mounted for pivotal movement relative to the vehicle structure. The first and second components cooperate to control vehicle gate speed as the vehicle gate is moved from the second position to the first position. The lift assembly includes a spring operatively coupled to the dampener assembly to reduce lifting effort as the vehicle gate is moved from the first position to the second position.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to a lift assist system for a tailgate of a vehicle, such as a pickup truck or sport utility vehicle. 
   A tailgate for a vehicle, such as a pickup truck or sport utility vehicle, is typically hinged to a vehicle support or frame member and may be opened and closed by pivoting the tailgate about its hinge to facilitate access to a truck bed or passenger compartment. A tailgate may be very heavy, particularly in the case of sport utility vehicles, because window lift and position control components are often housed within the tailgate. As a consequence, some assistance may be necessary to open and close the tailgate. 
   Systems do exist that provide lift assistance for the tailgate of the vehicle. Indeed, several known systems employ springs to counterbalance the weight of the tailgate. These springs are located in the sidewalls of the bed of the vehicle. One such system attaches one end of a cable to a spring in the sidewall of the vehicle and the other end to the tailgate. When the tailgate is lowered, the spring expands. Lift assistance to the tailgate is then provided by the returning spring as the tailgate is lifted. 
   Such a system, however, has several drawbacks. The spring force must be closely balanced with the weight of the tailgate so that a vehicle occupant may easily close the tailgate. However, as a consequence, very little upward lift may cause the tailgate to close quickly. 
   In addition, a driver of the vehicle may desire to keep the tailgate open during vehicle operation, so as to accommodate oversized loads that may extend beyond the vehicle bed or to allow loading or unloading of the vehicle while moving. Due to the counterbalancing effect of the spring, over rough roads, the tailgate may close when the driver prefers it to remain open. The tailgate may also bounce up and down on these roads more so than without the lift assistance. A fluctuating tailgate places stress on the tailgate hinge as well as the lift assist system. 
   Moreover, it is very difficult to install the spring in the sidewall during vehicle production. Specifically, the spring must be mounted to the sidewall during assembly of the vehicle body, which is difficult to access because the sidewalls typically form an integral part of the body. Sidewalls for a sport utility vehicle are especially difficult to access because of the integration of the sidewalls with a vehicle roof. Installing a spring inside the sidewall accordingly interferes with the assembly of the vehicle body. 
   Another option would be to install the assist spring outside the sidewall, which avoids interruption of body assembly. However, the spring is then open to the environment and more susceptible to wear and damage. Thus, it is preferable to keep the spring housed and protected. 
   Another disadvantage with existing systems is that when the tailgate is opened, the weight of the tailgate is supported in part by the compressed spring. This design places significant stress on the spring and housing for the spring and requires significant reinforcement. As a result, installation of the lift system is time consuming and expensive. 
   A need therefore exists for a tailgate assembly that incorporates a lift assist system without the drawbacks encountered by existing systems. 
   SUMMARY OF THE INVENTION 
   The present invention comprises a control mechanism for controlling movement of a vehicle tailgate between open and closed positions. In contrast to existing assemblies, the invention combines a dampener assembly with a lift assembly. The dampener has a first component mounted to a vehicle structure, such as a vehicle sidewall, and a second component supported by a tailgate and mounted for pivotal movement relative to the vehicle structure. The first and second components cooperate to slow tailgate speed as the tailgate is moved between a closed position and an open position. The lift assembly includes a spring that is coupled to the dampener assembly to reduce lifting effort as the tailgate is moved from the open position to the closed position. Preferably, the spring and dampener assembly are incorporated into the tailgate. 
   The spring stores energy when the vehicle tailgate moves toward the open position and releases energy when the vehicle tailgate moves toward the closed position. The damper assembly helps slow movement of the tailgate as the tailgate is pivoted from the closed position to the open position. In this way, the invention prevents the tailgate from closing upon the slightest disturbance or opening too quickly while still providing adequate lift assistance. 
   In one disclosed embodiment, the dampener assembly includes a cable and a piston slidably received within a cylinder. The cable is attached to the piston by a rod. The rod moves in a linear direction parallel to a lateral axis about which the tailgate pivots. A guide is used to redirect the cable to the vehicle structure along a long axis that is transverse to the lateral axis. 
   As discussed above, the lift spring and related components are preferably enclosed within the tailgate, which facilitates assembly because the tailgate is not an integral part of the vehicle body. Moreover, enclosing the spring and dampener assembly within the tailgate provides a protected environment. The spring is further protected from the environment by being enclosed within the dampening cylinder. 
   In one disclosed embodiment, a rigid stop is used to prevent a catch on the cable from moving beyond an end of travel position. The stop is preferably mounted to the tailgate. The stop and catch cooperate to prevent the piston and the rod from bearing the load of the tailgate and any associated payload weight when in the open position. 
   A latching device is also preferably incorporated within the control mechanism. The latching device is movable between a first position in which the spring is prohibited from providing lift assistance and a second position in which the spring is released to provide lift assistance. The latching device prevents an unloaded tailgate from bouncing up and down as the vehicle is driven with the tailgate in the open position and further prevents the tailgate from inadvertently closing. The latching device is preferably actuated by the tailgate latch handle. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
       FIG. 1  illustrates a side view of a vehicle and a tailgate in an open position. 
       FIG. 2  illustrates a side view of the vehicle and the tailgate of  FIG. 1  with the tailgate in a closed position. 
       FIG. 3  illustrates an overhead view of the inventive lift assembly, including cable stop, catch, decoupling device, and dampener with the tailgate in the open position of FIG.  1 . 
       FIG. 4  illustrates the lift assistance device of  FIG. 3  in its retracted position with the tailgate closed. 
       FIG. 5  shows a piston of the lift assistance device with the rod compressed in the cylinder. 
       FIG. 6  shows the piston of  FIG. 5  with the rod extended from the cylinder. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2  show a side view of tailgate assembly  10  for vehicle body  18 . The tailgate assembly  10  comprises tailgate  14  attached to vehicle body  18  with a hinge  16 . In  FIG. 1 , tailgate  14  pivots about hinge  16  in a direction indicated by arrow A to closed position  21  (see  FIG. 2 ) while in  FIG. 2 , tailgate  14  pivots in a direction indicated by arrow B to open position  15  (see FIG.  1 ). Although tailgate  14  is shown here as part of a pickup truck, tailgate  14  may also be used with other vehicles, such as a sport utility vehicle. 
   As shown in  FIG. 3 , tailgate assembly  10  employs a spring  22  to provide lift assistance to tailgate  14  and a dampener  101  to control the opening speed of the tailgate  14 . The dampener  101  comprises a piston and cylinder assembly that utilizes a dampening effect to reduce the speed at which the tailgate  14  opens. This prevents a heavy tailgate from opening too quickly. Spring  22  is housed within cylinder  54  between a spring retainer  55  and a first piston  58 . Of course, spring  22  may also be mounted outside of cylinder  54  as well. The spring retainer  55  is fixed within cylinder  54 , while the first piston  58  is free to move axially within cylinder  54 . Moreover, the first piston  58  is attached to a rod  62  such that when rod  62  extends in a linear direction indicated by arrow C out of cylinder  54 , the first piston  58  compresses spring  22  to store energy for lift assistance. Spring  22  decompresses to release energy for lift assistance when rod  62  moves in a direction indicated by arrow D as shown in FIG.  4 . 
   Hydraulic fluid may be provided within cylinder  54  to dampen movement of rod  62  from its extended and retracted position. While cylinder  54  is shown here as a hydraulic cylinder, other dampeners, such as a pneumatic dampener, may be employed. The invention is not limited to any particular type of dampener. 
     FIGS. 5 and 6  show a particular cylinder design for a hydraulic dampener. Cylinder  54  has rod  62  disposed therein. Rod  62  may compress into cylinder  54  as shown in  FIG. 5  in the direction of arrow D and may extend from cylinder  54  as shown in  FIG. 6  in the direction of arrow C. Rod  62  is attached to first piston  58 . First piston  58  has O-ring  80 , valve disc  82  and orifice plate  81 . O-ring  80  prevents hydraulic fluid flew around the outside of first piston  58 . When rod  62  compresses within cylinder  54 , O-ring  80  and valve disc  82  are forced away from orifice plate  81 , thereby producing a large non-restrictive flow path  79  for hydraulic fluid  77 . At extension, friction on O-ring  80  forces valve disc  82  against the coined orifice plate  81  to restrict flow path  79  thereby slowing down the motion of rod  62  during extension, such as when tailgate  14  is opened along the direction of arrow B (see FIG.  2 ). 
   As shown in  FIGS. 3 and 4 , a second piston  56  and a second spring  57  are also disposed within cylinder  54  and serve to control hydraulic fluid pressure within cylinder  54 . The second piston  56  is located-near one end  63  of cylinder  54  and is spaced apart from the first piston  58  and spring retainer  55 . While hydraulic fluid fills cylinder  54  between the rod seal  53  and the second piston  56 , no hydraulic fluid fills cylinder  54  between the second piston  56  and end  63 . Instead, the second spring  57  extends between the second piston  56  and end  63 . The second spring  57  exerts force on the second piston  56 , which, in turn, exerts pressure on hydraulic fluid between the rod seal  53  and the second piston  56 . This pressure helps prevent cavitation of the hydraulic fluid  77  as it passes through the orifice of orifice plate  81  when the first piston  58  moves in a direction indicated by arrow C. The second piston  56  is free to move axially in cylinder  54  in relation to the movement of rod  62 . As rod  62  moves in direction C, second piston  56  moves in direction C, and likewise for direction D. Hydraulic fluid  77  is incompressible, therefore, as rod  62  moves in and out of cylinder  54  the volume it displaces must be offset by a like volume from the movement of second piston  56  in cylinder  54 . 
   In contrast to existing systems, spring  22  and cylinder  54  are mounted to tailgate  14  at mounting  61 . As shown, mounting  61  may comprise a pivot that connects cylinder  54  to tailgate  14 . The location of spring  22  on tailgate  14  greatly simplifies installation of spring  22  to the vehicle, as tailgate  14  is separately installed from vehicle body  18 . Moreover, assembly of spring  22  to tailgate  14  does not interfere with the construction of vehicle body  18 . As shown by cutaway in  FIG. 3 , spring  22 , cylinder  54 , and other associated components are installed within interior  23  of tailgate  14  between a first exterior surface  13  of tailgate  14  and a second exterior surface  19  of tailgate  14 . Thus, spring  22  and other components are protected from the environment without having to install them into sidewalls  17  of vehicle body  18 . However, although this protected mounting arrangement is a desirable feature, it is not necessary for the lift assist system to operate. 
   As shown in  FIG. 3 , tailgate  14  utilize first cable  26  and second cable  27  to control movement of the tailgate  14  and to support the actual weight of the tailgate in addition to any payload positioned on the tailgate when in the open position. Second cable  27  extends from sidewall  17  to tailgate  14  along longitudinal axis  31  and supports part of the weight of tailgate  14 . The other part of the weight of tailgate  14  is supported by first cable  26 . First cable  26  and second cable  27  are attached at side walls  17  at attachment points  85  as shown in  FIGS. 1 and 3 . The connections  86  used at attachment points  85  are the standard types used in conventional pickup trucks for easy removal of tailgate  14 . The installation of spring  22  and dampener  101  to tailgate  14  facilitates the removal of tailgate  14  in the conventional manner. 
   First cable  26  extends from sidewall  17  along longitudinal axis  31  to pulley  66 . Pulley  66  directs cable  26  from a lateral axis  30  to a longitudinal axis  31  that is transverse to lateral axis  30 . In this way, pulley  66  permits spring  22  and dampener  101  to extend and compress along lateral axis  30 , rather than along longitudinal axis  31 , thereby allowing storage of spring  22  and dampener  101  in tailgate  14 . 
   First cable  26  serves as a draw cable to draw tailgate  14  to sidewalls  17  of vehicle body  18  as spring  22  decompresses (see  FIG. 4 ) when the tailgate  14  is moved toward the closed position  21  (see FIG.  2 ). In this way, spring  22  provides lift assistance to tailgate  14 . A catch  34  is attached to rod  62 . When tailgate  14  moves to open position  15 , as shown in  FIGS. 1 and 3 , first cable  26  pulls catch  34 , rod  62  and first piston  58  along arrow C, thereby compressing spring  22  (see FIG.  3 ). The compression of spring  22  slows movement of tailgate  14  to open position  15 . The dampening effect of dampener  101  acts to slow movement of tailgate  14  by slowing movement of first piston  58  and consequently rod  62 . 
   Cable stop  38  is mounted within the interior  23  of tailgate  14  and is used to stop movement of first cable  26  and catch  34  along lateral axis  30  as tailgate  14  is extended to open position  15 . In so doing, cable stop  38  prevents a significant portion of weight of tailgate  14  and any associated payload from being exerted on the dampener  101  and spring  22 . The second cable  27  is used to support these heavy loads. 
   In addition, when catch  34  is stopped by cable stop  38  in open position  15 , latching device  46  may serve to lock catch  34  in place. By locking catch  34  in place, spring  22  is held in position and is disengaged from providing lift assistance to tailgate  14 . Latching device  46  may comprise a latching pawl that simply blocks movement of catch  34  along arrow D. Latching device  46  may be linked to a vehicle gate latch actuator  70  so that when vehicle gate latch actuator  70  is actuated, latching device  46  may also be actuated automatically. After tailgate  14  is lowered, an operator may toggle vehicle gate latch actuator  70  to lock latching device  46 , or latching device  46  may be spring-loaded to lock automatically, and thereby disengage lift assistance by locking spring  22  into its compressed state. In this way, the lift assistance provided by spring  22  is decoupled thereby permitting the full weight of tailgate  14  to keep tailgate  14  in its open position (see  FIG. 1 ) and helping to avoid the fluttering of tailgate  14  during vehicle operation. When lift assistance is required, door latch  70  may be toggled to unlock latching device  46  and thereby permit movement of catch  34  in the direction of arrow D and thereby allow spring  22  to provide lift assistance. 
   The aforementioned description is exemplary rather that limiting. Many modifications and variations of the present invention arepossible in light of the above teachings. The preferred embodiments of this invention have been disclosed. However, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. Hence, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For this reason the following claims should be studied to determined the true scope and content of this invention.