Abstract:
A lift assembly connects to a receiver hitch and utilizes a plurality of parallel arms connecting a vertical mounting post to a center support in a lift frame that is raised and lowered by the lift assembly. The lift assembly is configured so that the parallel arms rotate from vertical to an inclined angle as the lift frame is lowered, but the arms do not extend below the horizontal as they extend rearward from the mounting post.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The subject patent application is a continuation of co-pending U.S. patent application Ser. No. 12/423,634, filed on Apr. 14, 2009, which is now U.S. Pat. No. 9,096,160, the disclosure of which is hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a lift assembly that may be mounted on a vehicle and particularly to an assembly mounted to a trailer hitch in a fashion providing mechanical advantage to facilitate lifting and lowering of the assembly. 
       BACKGROUND OF THE INVENTION 
       [0003]    Numerous lift assemblies have been designed for attachment to vehicles and most commonly to facilitate loading and unloading from a truck tailgate. Many of the prior art tailgate lift assemblies require integration into the side wall or bed of the vehicle in order to adequately support the lift assembly and weighted load. Powerful hydraulics or lift drives are also required for many of these lift assemblies, if the lifts are intended to be used with substantial loads. 
         [0004]    The integration of lift assembly mounts into the side rail or bed of a vehicle is difficult and expensive, both in time and material. Devices have been provided where a mechanism for a tailgate lift utilizes cables, such as in U.S. Pat. No. 4,601,485, screw drives as shown in U.S. Pat. No. 3,180,503; and power from a winch mounted on the vehicle as shown in U.S. Pat. No. 6,609,481. 
         [0005]    Some devices have even been designed to mount on a trailer hitch as in U.S. Publication No. 2007/0280807 disclosing a carrier with a screw drive to adjust the height, and U.S. Publication No. 2001/0014272 disclosing a lift connected to its hitch mounted yoke by pairs of parallel support bars. However, this latter publication is inoperable in practice because the lift is allowed to pivot so that the support bars extend both upward and downward from the yoke, causing a situation that requires vertical force to raise and lower the lift. 
         [0006]    These and other devices of the prior art fail to be easily integrated with presently existing vehicles and require extensive engineering and manufacturing to mount and operate effectively. 
         [0007]    In the prior art there does not exist a simplified unit for providing a vehicle mounted lift assembly, that can be hitch mounted, and providing mechanical advantage so that loads may be lifted manually or with relatively small motors contained within the lift assembly. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0008]    The present invention resolves at least some of the above disclosed shortcomings of the prior art. A vehicle mounted lift assembly of the present invention may be adapted to easily fasten to a vehicle, and preferably to a hitch assembly, provides mechanical advantage that permits manual lifting or lifting with a motor contained within the lift assembly, of loads up to at least about 500 pounds, utilizes pairs of parallel support arms to connect the vehicle mounting section to the lift frame, and does not permit the pairs of parallel connecting arms to extend from the mounting section at an angle below the vertical. The lift assembly is especially adapted for the carriage of a portable grill apparatus, however, the lift frame is easily adapted to carry conventional loads. 
         [0009]    It is, therefore, an object of the present invention to provide a removable vehicle mounted lift assembly that does not require special integration into the bed, side rails or frame of the vehicle. It is a further object of the invention to provide a vehicle mounted lift assembly which may be easily manufactured and that may provide for mechanical advantage in lifting a load of significant weight for carriage by the vehicle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    These and other objectives of the invention may be more readily seen in the accompanying figures of an exemplary lift assembly in which: 
           [0011]      FIG. 1A  is a top side perspective view of a vehicle mounted lift assembly according to the invention utilized to carry a portable grill in raised position. 
           [0012]      FIG. 1B  is a top perspective view of the vehicle mounted lift assembly of  FIG. 1A  in lowered position. 
           [0013]      FIG. 2  is a side perspective view of a vehicle mounted lift assembly according to the invention carrying a lift frame in raised position. 
           [0014]      FIG. 3  is a side perspective view of the lift assembly of  FIG. 2  in a partially lowered position. 
           [0015]      FIG. 4  is a side perspective view of the lift assembly of  FIG. 2  in a fully lowered position. 
           [0016]      FIG. 5  is a side plan view of the hitch mount of the lift assembly of  FIG. 2 . 
           [0017]      FIG. 6  is a reverse angle view of the lift assembly of  FIG. 4  with the vehicle tailgate in its lowered position. 
           [0018]      FIG. 7  is an exploded perspective view of an exemplary lift assembly with parallel arm structure and lift frame. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Turning then to  FIG. 1A , a representative vehicle  10  with hitch receiver  13  mounted below bumper  11  is shown. The illustrated vehicle has a tailgate  12  and a trailer step  18  above the hitch receiver  13 . Preferably the usual trailer hitch is removed from hitch receiver  13  and in this fashion the lift assembly  20  can be readily mounted. In particular, the horizontal attaching member  21  of the mounting portion of the lift assembly is fitted in the hitch receiver  13 . As shown in detail in  FIG. 5 , the hitch receiver  13  preferably has opposed openings and the horizontal attaching member  21  may have similar opposed openings that may be aligned and secured through the use of a hitch cross pin  15 . In turn, the hitch cross pin  15  may be secured in place through the use of cross pin retainers  16 . To insure that there is no unnecessary movement of the lift assembly  20  when the vehicle  10  is in motion, a tightening mechanism such as a hitch adjusting screw  17  is provided that may be tightened against hitch receiver lip  14  and thereby minimize any movement of the lift assembly  20  and its attendant load when the vehicle  10  is in motion. The horizontal attaching member  21  is secured to vertical mounting post  23  that preferably extends both above and below the attaching number  21  received within the hitch receiver  13 . The bottom  26  of the vertical mounting post has a ground clearance that will vary depending upon the vehicle, but should be about one foot or more. The attaching member  21  is preferably attached to the vertical mounting post  23  in a reinforced fashion as through the use of multiple supporting angles  22 . 
         [0020]    Turning again to  FIG. 1A , an exemplary lift frame load for lift assembly  20  is shown in the form of a grill having a center grill unit  60  connected by hinges  65  to folded right grill unit  61  and left folded grill unit  62  and having folding top panels  63 . When the grill unit is in its folded position for transport, latch  67  secures the left and right folded grill units  61 ,  62  from opening. When lowered, the grill units are moveable on wheels  66  so that the grill may be disengaged from vehicle  10  and easily positioned as desired, even if weighting several hundred pounds. Within the lift frame of the lift assembly  20  is defined as a rear vertical plane by a center support member  40 , preferably having a center support channel  41  shown in  FIG. 3  and top center support openings  42 . The vertical mounting post  23  has a post top  25  and post bottom  26  and at least a pair of bottom post openings  27  (shown in  FIG. 7 ). Extending between bottom post openings  27  and top center support openings  42  are first parallel arm  30  and second parallel arm  31 . The use of two parallel arms  30 ,  31 , allows the lift frame to be raised and lowered in a constant vertical orientation without substantial swinging. A first bottom retaining axis in the form of first bolt  32  passes through first bottom end or arm opening  34  and bottom post opening  27  to secure first parallel arm  30  to the vertical mounting post. Similarly, a second bottom retaining axis in the form of second bolt  33  passes through a second bottom end or arm opening  35  and bottom post opening  27  to secure the second parallel arm to the vertical mounting post  23 . The first  38  and second  39  opposite ends of first and second parallel arms  30 ,  31  are secured with first and second top retaining axes in the form of first and second bolts  43 ,  44  passing through top center support openings  42  and first arm top opening  38  and second arm top opening  39 . In the raised position, it is preferred that the load carried by the lift frame not extend significantly below the bottom of vertical mounting post  23 . The bottom of vertical mounting post  23  preferably has about a foot or more of clearance from the ground. 
         [0021]    In order to operate the lift assembly  20  and lower the lift frame, the first and second parallel arms  30 ,  31  are moved from a vertical position in the forward plane of the lift frame where in the illustrated embodiment, arm channels  36  receive the vertical mounting post  23 , and in turn the first and second parallel arms  30 ,  31  and mounting post  23  are received within the center support channel  41 , to the extended position shown in  FIG. 1B . In this lowered position, it can be seen that the wheels  66  of the lift frame are resting on the ground. When the lift assembly  20  is in its fully lowered position, as illustrated in  FIG. 1B , the first and second parallel arms  30 ,  31  extend rearward from the mounting post  23  at a positive acute angle β upward from the horizontal. Similarly, those same first and second parallel arms  30 ,  31  extend forward from the vertical center support member  40  or forward plane at a positive acute angle α. Because the parallel arms  30 ,  31  do not extend from the mounting post  23  below the horizontal, pressure exerted on the carried load or lift assembly frame, tending to push the frame towards the rear of vehicle  10 , illustrated as force F in  FIG. 1B , tends to cause the lift assembly to return to its raised position of  FIG. 1A . Therefore, because the parallel arms  30 ,  31  are not allowed to descend below the horizontal, force only need be applied in the horizontal plane to raise the lift frame and it is not necessary to mount mechanisms on the vehicle to provide vertical lifting force to the lift frame. It will be appreciated that when the angle β remains near 45°, the lift assembly achieves the optimum combination of ease of lifting the lift assembly with horizontal force and lift height. Depending upon the weight of the load carried by the lift frame and whether a motor  45  is available to assist in the raising and lowering of the lift frame, the optimum angle β may vary, typically between about 25° and 60°. 
         [0022]      FIG. 2  shows an exemplary lift assembly in raised position where the lift assembly  20  includes not only the center support  40 , but also a front bottom frame member  51  extending on either side of the center support  40 , a top frame member  50  extending to either side of the center support  40 , a right forward vertical support  52  connecting the top frame member  50  and bottom frame member  51  and a left forward vertical support  53  again connecting top frame member  50  to bottom frame member  51 . Members  50 ,  51 ,  52  and  53  define the forward plane of the illustrated lift frame. Alternative constructions of lift frames are possible so that the forward plane does not extend across the entire width of the frame. Extending rearward from the bottom frame member  51  are right bottom horizontal support  54  and left bottom horizontal support  55  and these are connected by rear bottom frame member  56  at their opposite ends. To provide the frame with proper support, the top frame member  50  is preferably connected to the rear bottom frame member  56  either in an angular fashion as illustrated, or by a more diagonal connection. 
         [0023]    Turning then to  FIG. 3 , the lift assembly  20  is shown in a partially descended position and the top post openings  24   a,    24   b  of the vertical mounting post  23  are illustrated. In the illustrated embodiment, top post opening  24   a  is preferably utilized to connect with a cable  46  running to drive assembly of motor  45  to allow for mechanized raising and lowering of the lift frame. The top post opening  24   b  is preferably aligned with lower center support opening  47  of center support  40  when in the fully raised position. In this fashion, locking pin  48  can be passed through center support opening  47  (shown in  FIG. 7 ) and vertical mounting post opening  24   b  to securely hold the lift assembly in raised position for transport. Even in the fully lowered position of  FIG. 4 , the mechanical advantage provided by the arrangement of the lift mechanism is such that the electrical connection  49  for motor  45  can be extended from the electrical connection provided for trailer lights, the motor  45  needing no more power than the typical windshield wiper motor of a passenger vehicle. 
         [0024]      FIG. 6  shows a reverse angle view of the lift assembly in its lowered position and it can be seen that in a preferred embodiment, the post top  25  of vertical mounting post  23  is below the height of an open tailgate  12  when lift assembly  20  is utilized with a pickup truck type vehicle.  FIG. 7  shows first and second parallel arms  30 ,  31  in an exploded view of the lift assembly so that bottom arm openings  34  and top arm openings  38  and channels  36  are clearly seen. 
         [0025]    Therefore, in transport mode, the vertical mounting post  23 , parallel arms  30 ,  31  and center support  40 , are all preferably aligned in a substantially vertical orientation about one another, or at least within the forward plane of the lift frame, and the bottom frame member  51  of the lift assembly  20  is carried at a safe clearance distance  29  above the ground. When lowered, the center support member  40  is unlocked from the vertical mounting post  23  and the first and second parallel arms are rotated out of vertical into a angular orientation rising at angle βfrom the attachment of bottom arm openings  34 ,  35  near post bottom  26  to top arm openings  38 ,  39  that are fastened at the top center support openings  42  of the lift frame. It will be seen that according to the Pythagorean theorem, the length L of the displacement of center support post  40  from vertical mounting post  23  can be computed according to the formula where the sum of the displacement length squared plus the square of the difference V in vertical height between top center support openings  42  of the lowered lift frame and bottom post openings  27  of the vertical mounting post  23  is equal to the square of the length of the parallel arms,  30 ,  31  between their opposed retaining axis points. This provides the designers of lift assemblies according to the present invention with guidance in optimizing the lift design for various functions such as the illustrated portable grill carrier, a game lift for hunters, a frame for cargo transport, and other lift assembly uses. 
         [0026]    All publications, patent, and patent documents mentioned herein are incorporated by reference herein as though individually incorporated by reference. Although preferred embodiments of the present invention have been disclosed in detail herein, it will be understood that various substitutions and modifications may be made to the disclosed embodiment described herein without departing from the scope and spirit of the present invention as recited in the appended claims.