Patent Publication Number: US-2009226290-A1

Title: Liftgate for use with dock lock mechanisms

Description:
This application claims priority to U.S. Ser. No. 60/971,413, entitled LIFTGATE FOR USE WITH DOCK LOCK MECHANISMS, filed Sep. 11, 2007, which is incorporated herein by reference. 
    
    
     I. BACKGROUND OF THE INVENTION 
     A. Field of Invention 
     This invention pertains to the art of methods and apparatuses regarding liftgates, and more specifically, to methods and apparatuses regarding the use of a liftgate with a dock lock mechanism and adjustment characteristics permitting normal operation even when encountering ground obstacles. 
     B. Description of the Related Art 
     It is well known in the art to attach liftgates to vehicle trailers or other forms of vehicle cargo holds to assist with loading and unloading of the vehicles. In general, liftgates include a platform or deck (platform assembly) and some motorized system, often including a hydraulic system, used to move the platform (lift assembly). To load cargo from a ground surface to the vehicle bed, the platform assembly is positioned in a lowered position where it is generally parallel with, and just above or on the same plane as, the ground surface. The cargo can then be easily placed onto the platform. The platform assembly is then lifted to a raised position generally parallel with the vehicle and generally on the same plane as the vehicle bed. The cargo can then be easily loaded into the vehicle. To unload cargo from the vehicle, the reverse steps are taken. 
     Various types and styles of liftgates are known in the art. Some liftgates, sometimes referred to as flip-a-way or fold-up liftgates, are foldable or collapsible into a stowed or storage condition. Often this storage condition is positioned underneath the vehicle cargo hold. When it is desirable to use the liftgate, it can be unfolded out of the storage condition. 
     A recent development in the field of loading docks is the use of a dock lock mechanism. Dock lock mechanisms generally are attached to the loading dock and have a hook member that swings outwardly from the loading dock to engage a portion of a truck or trailer (a dock lock engagement member) in order to hold or secure the truck or trailer to the loading dock. Dock lock mechanisms also generally have some type of indicating device, such as a colored light panel, that indicates to dock workers when the truck or trailer is in the proper secured-to-the-loading-dock position. In this way, dock workers receive a signal indicating that it is safe to begin loading and/or unloading operations with the truck or trailer. In order to be engaged to the dock lock mechanism, however, the dock lock engagement member must meet certain design criteria. The design criteria generally include: (1) a height requirement range (the dock lock engagement member must be within a specified height range from the ground surface); and, (2) a distance requirement range (the dock lock engagement member must be within a specified distance range from the back surface of the truck or trailer). For example, one type of dock lock mechanism requires that the dock lock engagement member have a height from the ground surface within the range of 20½ inches to 22½ inches and a distance from the back of the trailer within the range of 8½ inches to 9½ inches. 
     Because liftgate assemblies are often stowed or stored to the back, underneath portion of a truck or trailer, there is the possibility of interference with dock lock mechanisms. One solution to this interference problem is to provide the liftgate assembly with its own dock lock engagement member. In this way, the truck or trailer can be secured to the dock by engaging the dock lock mechanism directly to the liftgate assembly. This solution, however, may create additional problems. More specifically, the height and length range requirements of dock lock mechanisms may make normal operation of the liftgate (folding and unfolding of the liftgate, for example) more difficult. For example, designing a liftgate with a dock lock engagement member in the appropriate height and length range while the liftgate is in a stored position may cause the lift assembly to interfere with ground obstacles when lowering the platform into the lowered position. Interference with ground obstacles may prevent the platform from achieving the complete lowered position required for easy loading and unloading of cargo. 
     As a result, there is a need in the art for a liftgate assembly, with a dock lock engagement member residing at the correct height and distance in a stored position for engagement with a dock lock mechanism, that is also capable of the full range of normal operation even when presented with ground obstacles that might otherwise be an impediment. This invention provides methods and apparatuses regarding a liftgate assembly that can easily engage with a dock lock mechanism without the problems described above. This invention thus overcomes the foregoing difficulties and others while providing better and more advantageous overall results. 
     II. SUMMARY OF THE INVENTION 
     According to one embodiment of this invention, a liftgate assembly for use with: (1) an associated loading dock having a dock surface and a dock lock mechanism; and, (2) an associated vehicle having a cargo hold with a vehicle bed, may comprise: (A) a mount assembly for use in mounting the liftgate assembly to the associated vehicle; (B) a platform assembly supported to the mount assembly and comprising a platform having a traffic surface for use in receiving traffic for loading and unloading associated cargo; (C) a lift assembly supported to the mount assembly for use in moving the platform between: (1) a storage position at least partially under the associated vehicle; (2) a lowered position juxtaposed to an associated ground surface; and, (3) a raised position juxtaposed to the vehicle bed; (D) a dock lock engagement mechanism supported to the mount assembly and comprising a dock lock engagement member that is operatively engagable to the associated dock lock mechanism to secure the associated vehicle to the loading dock; and, (E) an adjustment mechanism that: (1) when the dock lock engagement member contacts an obstruction on the associated ground surface as the platform is moved toward the lowered position, places the dock lock engagement member in a first position with respect to the platform when the platform is placed into the lowered position; and, (2) when the dock lock engagement member does not contact an obstruction on the associated ground surface as the platform is moved toward the lowered position, places the dock lock engagement member in a second position, that is substantially different than the first position, with respect to the platform when the platform is placed into the lowered position. 
     According to another embodiment of this invention, a liftgate assembly for use with: (1) an associated loading dock having a dock surface and a dock lock mechanism; and, (2) an associated vehicle having a cargo hold with a vehicle bed, may comprise: (A) a mount assembly for use in mounting the liftgate assembly to the associated vehicle; (B) a platform assembly supported to the mount assembly and comprising a platform having a traffic surface for use in receiving traffic for loading and unloading associated cargo; (C) a lift assembly supported to the mount assembly for use in moving the platform between: (1) a storage position at least partially under the associated vehicle; (2) a lowered position juxtaposed to an associated ground surface; and, (3) a raised position juxtaposed to the vehicle bed; (D) a dock lock engagement mechanism supported to the mount assembly and comprising a dock lock engagement member that is operatively engagable to the associated dock lock mechanism to secure the associated vehicle to the loading dock; and, (E) wherein the lift assembly moves the platform into the lowered position both: (1) when the dock lock engagement member does not contact an obstruction as the platform is placed into the lowered position; and, (2) when the dock lock engagement member contacts an obstruction on the associated ground surface as the platform is placed into the lowered position. 
     According to still another embodiment of this invention, a method may comprise the steps of: (A) providing a vehicle having a cargo hold with a vehicle bed; (B) providing the vehicle with a liftgate assembly for use with an associated loading dock having a dock surface and a dock lock mechanism; (C) providing the liftgate assembly with: (1) a mount assembly for use in mounting the liftgate assembly to the vehicle; (2) a platform assembly supported to the mount assembly and comprising a platform having a traffic surface for use in receiving traffic for loading and unloading associated cargo; (3) a lift assembly supported to the mount assembly for use in moving the platform between: (a) a storage position at least partially under the associated vehicle; (b) a lowered position juxtaposed to an associated ground surface; and, (c) a raised position juxtaposed to the vehicle bed; and, (4) a dock lock engagement mechanism supported to the mount assembly and comprising a dock lock engagement member that is operatively engagable to the associated dock lock mechanism to secure the associated vehicle to the loading dock; (D) moving the platform toward the lowered position; (E) contacting an obstruction on the associated ground surface with the dock lock engagement member; and, (F) discontinuing downward motion of the dock lock engagement member while moving the platform into the lowered position. 
     One advantage of this invention is that it provides a liftgate assembly with an integrated dock lock engagement member situated at the appropriate height and distance for easy operative engagement with an associated dock lock mechanism. 
     Another advantage of this invention is that it incorporates an adjustment mechanism that permits the liftgate assembly to engage in normal operation—including fully lowering the platform onto the ground surface—even when the dock lock engagement mechanism encounters ground obstructions. 
     Still other benefits and advantages of the invention will become apparent to those skilled in the art to which it pertains upon a reading and understanding of the following detailed specification. 
    
    
     
       III. BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may take physical form in certain parts and arrangement of parts, embodiments of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and wherein: 
         FIG. 1  is a partial side view of a liftgate assembly in the storage position and attached to a vehicle that is near a loading dock. 
         FIG. 2  is a perspective bottom view of the liftgate assembly of this invention. 
         FIG. 3  is a partial side view of the liftgate assembly shown in  FIG. 1 . 
         FIG. 4  is a perspective top of view of the liftgate assembly of this invention; shown with the platform in a lowered position. 
         FIG. 5  is a partial cut-a-way side view of the liftgate assembly of this invention; with the platform shown in a lowered position on an even surface. 
         FIG. 6  is a partial cut-a-way side view of the liftgate assembly of this invention; with the platform shown in a lowered position on an uneven surface. 
     
    
    
     III. DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings wherein the showings are for purposes of illustrating embodiments of the invention only, and not for purposes of limiting the same,  FIG. 1  shows a loading dock  10  equipped with a dock lock mechanism  20  which can be of any known design. As shown, the loading dock  10  has a dock surface  12  that extends above a ground surface  14  upon which a vehicle  50  such as a truck or trailer is supported as it is positioned near the loading dock  10 . As the operation and use of a dock  10  is well known, further details will not be provided here. 
     With continuing reference to  FIG. 1 , the vehicle  50  may include a cargo hold  52  having a vehicle bed  54 . The vehicle  50  may also have a sill at the outer edge of the cargo hold  52  and conventional vehicle frame members  58 . Any type and style of vehicle will work well with this invention when applied with the sound judgment of a person of skill in the art. The vehicle  50  may be positioned relatively close to the outer edge of the loading dock  10  so that the dock surface  12  and the vehicle bed  54  are substantially parallel and substantially on the same plane. This is the well known appropriate position for loading and/or unloading cargo into the vehicle  50 .  FIG. 1  also indicates the appropriate height HT and distance DC, according to one non-limiting embodiment of this invention, at which a dock lock engagement member  210  must reside when the liftgate assembly is in a stored position, so that it properly engages with the dock lock mechanism  20 . 
     With reference now to  FIGS. 1-4 , a liftgate assembly  100 , including a dock lock engagement mechanism  200  according to one embodiment of this invention, may be mounted to the vehicle&#39;s mount assembly  110 , such as to the vehicle frame members  58 , in any conventional manner. While the liftgate assembly  100  shown is the style known as flip-a-way or fold-up, it is to be noted that this invention may be used with any liftgate style, type and size, when applied with the sound judgment of a person of skill in the art. The liftgate assembly  100  may include a mount assembly  110  (having first and second sides  110   a ,  110   b ), a platform assembly  130  including a platform or deck  132 , a lift assembly  150  (having first and second sides  150   a ,  150   b ), a bed extension  170 , and the previously noted dock lock engagement mechanism  200 . The mount assembly  110  may include one or more mounting tubes  112 , one or more mounting plates  114 , and one or more plates  252 , as well as other components shown but not referenced. The mount assembly  110  is used to mount the liftgate assembly  100  to the vehicle frame in any conventional manner and thus will not be described in detail. The platform  132  may have a traffic surface  134  that may be used to receive traffic for loading and unloading cargo as is well known. The bed extension  170  may have a first side  172  that abuts the vehicle  50 , such as along the sill, as shown, and a second side  174  that may abut a first end of the platform  132  when the platform  132  is in a raised position (not shown). The second side  174  of the bed extension  170  may be positioned near the outer edge of the dock  10  for loading and unloading purposes. The bed extension  170  may also have a traffic surface  176  that may be used to receive traffic for loading and unloading cargo. It should be noted that a bed extension  170  is not required for this invention because in an alternate embodiment, not shown, the platform  132  may have a first side  133  that abuts the vehicle  50 , such as along the sill, making the use of a bed extension  170  unnecessary. 
     With continuing reference to  FIGS. 1-4 , the lift assembly  150  may be used to move the platform  132  between a folded storage position (shown in  FIGS. 1 ,  2 , and  3 ), a lowered position (shown in  FIG. 4 ) and a raised position (not shown but, as is well known, where the traffic surface  134  of the platform or deck  132  is substantially parallel with the traffic surface  176  of the bed extension  170  and substantially on the same plane as the vehicle bed  54 ). The lift assembly  150  may include a control system (not shown) and a hydraulic system (not shown) used to operate one or more cylinders  152  (referenced in  FIGS. 2 and 4 ) to move the platform  132 . The control and hydraulic systems raise and lower the platform assembly  130  by raising and lowering lift arms  156 , and the lift tube  154  extending between and connected to the lift arms  156 . The basic operation of the control and hydraulic systems are well known and will not be described in detail. 
     Still referring to  FIGS. 1-4 , the dock lock engagement mechanism  200  is used to engage with the dock lock mechanism  20 . The dock lock engagement mechanism  200  may include a dock lock engagement member  210  (having first and second sides  210   a ,  210   b ) that engages the hook of the dock lock mechanism  20  in a known manner. The dock lock engagement member  210  may be of any size and shape chosen with the sound judgment of a person of skill in the art. For the embodiment shown, the dock lock engagement member  210  is a tube with a circular cross-section. The dock lock engagement member  210  of this invention advantageously also serves as a bumper for the vehicle  50 , although that is not necessary for this invention. The dock lock engagement mechanism  200  also may include a first brace  260  for use in attaching the dock lock engagement member  210  to the mount assembly  110 . The first brace  260  also works with the lift assembly  150  to properly position the dock lock engagement member  210  as the platform  132  is raised, lowered, and folded into the storage position. 
     With continuing reference to  FIGS. 1-4 , the first brace  260  has a first end  260   a  that pivotally connects the first brace  260  to the first side of the mount assembly  110   a , and a second end  260   b  that operatively attaches the first brace  260  to the first side of the dock lock engagement member  210   a . In the embodiment shown in  FIG. 4 , a second brace  261  is shown; the second brace  261  also has a first end  261   a  that pivotally connects the second brace to the second side of the mount assembly  110   b , and a second end  261   b  that operatively attaches the second brace  261  to the second side of the dock lock engagement member  210   b . Each brace  260 ,  261  may be attached at its second end  260   b ,  261   b , such as by welding, to the dock lock engagement member  210 . Each brace  260 ,  261  may be attached at its first end  260   a ,  261   a  with a pivotal connection to the mount assembly  110 . For the embodiment shown, the mount assembly  110  comprises at least a plate  252  that may be fixedly attached to a mount plate  114  such as by welding. The plate  252  may have a hole that receives a pivot pin  254  which is also received in a hole formed in the brace  260 ,  261 . This attachment allows the brace  260  to pivot about pivot axis A 2  with respect to the plate  252  about the pivot pin  254 . In one embodiment, the pivot pin  254  is not in line with the pivot axis A 1  of the lift arms  156  which are well-known components used to lift and lower liftgate platform assemblies  130 . As a result, this pivotal connection provides an independent pivot point for the brace  260  that permits pivoting motion independent of the lift arms  156  (that is, a different rotation arc). This independent pivot point allows the lift assembly&#39;s  150  lift arms  156  to continue to lower the platform assembly  130  to a position substantially in contact with the ground surface  14 , even after movement of the dock lock engagement mechanism  200  has been halted (by a ground obstruction, for example). A stop member  158  may also be attached to the plate  252  and used to stop or limit the upward rotation of the brace  260 . 
     Still referring to  FIGS. 1-4 , the independent movement of the lift assembly  150  and dock lock engagement mechanism  200  is possible because of this invention&#39;s adjustment mechanism  280 . The adjustment mechanism  280  comprises at least a first link  270 , having a first end  270   a  that may be pivotally attached to the first brace  260 , and a second end  270   b  that may be attached to the first side of the lift assembly  150   a . In another embodiment of this invention, the adjustment mechanism  280  also comprises a second link  271 , having a first end  271   a  that may be pivotally attached to the second brace  261 , and a second end  271   b  that may be attached to the second side of the lift assembly  150   b . In the embodiment shown in  FIGS. 2 and 4 , each link  270 ,  271  includes first and second plates  272 ,  273 , whereby first pins  274   a ,  274   b  pass through holes in the first ends  270   a ,  271   a  and second pins  275   a ,  275   b  pass through holes in the second ends  270   b ,  271   b ; the first and second pins  274 ,  275  being substantially positioned between the plates  272 ,  273 . In the embodiment shown in  FIG. 4 , the links&#39;  270 ,  271  first pins  274   a ,  274   b  are pivotal and slidable within a groove  262  formed in the braces  260 ,  261 , while the links&#39;  270 ,  271  second pins  275   a ,  275   b  are pivotally attached within an opening formed on the lift assembly  150 . For the embodiment shown in  FIG. 4 , the links  270 ,  271  pivot about second pins  275   a ,  275   b  passing through its plates  272 ,  273  and openings in an ear  155   a ,  155   b  formed on the lift assembly&#39;s  150  lift tube  154 . This attachment configuration allows the links  270 ,  271  to pivot with respect to the lift tube  154 , and to pivot or slide with respect to the grooves  262  formed in the braces  260 ,  261 . 
     The liftgate assembly of this invention utilizes the cooperative movements of the lift assembly  150 , adjustment mechanism  180 , and dock lock engagement mechanism  200  to adapt to disparate operational conditions. For example, this invention moves the lift assembly  150  and attached platform assembly  130  into a fully lowered position irrespective of ground conditions. As shown in  FIG. 5 , when the dock lock engagement member  210  does not encounter a ground obstruction  15 , the liftgate assembly  100  operates in a normal fashion whereby the platform  130  is fully lowered into a second position P 2 . As shown in  FIG. 6 , however, when the dock lock engagement member  210  does encounter a ground obstruction  15 , the platform assembly  130  is still capable of being fully lowered onto the ground surface  14  by virtue of adjustment mechanism  280  movement; but the dock lock engagement member  210  now resides in a first position P 1  that is substantially different than the position of the dock lock engagement member  210  in the second position P 2 . Adjustment mechanism  280  movement is appropriately characterized as follows: A) when the liftgate assembly  100  is being moved towards a lowered position, and the dock lock engagement member  210  encounters a ground obstruction  15  that prematurely halts the downward movement of the dock lock engagement mechanism  200 , B) the links  270 ,  271  and first pins  274   a ,  274   b  pivot and/or slide within the braces&#39; grooves  262 , C) while the links  270 ,  271  and second pins  275   a ,  275   b  also pivot with respect to the attached lift tube  154  in order to accommodate the continued downward movement of the lift assembly  150 . 
     The advantages of this invention can be appreciated by comparing  FIG. 5  to  FIG. 6 . Both of these figures show the liftgate assembly  100  in the lowered position.  FIG. 6 , however, shows an obstruction  15  extending above the ground surface  14 . This obstruction  15  may be a rock, a piece of asphalt or concrete, or any other cause of an uneven ground surface. When the liftgate assembly  100  is used on an even surface, as shown in  FIG. 5 , its operation goes smoothly. When the liftgate assembly  100  is used on an uneven surface, as shown in  FIG. 6 , its operation still goes smoothly because of this invention. More specifically, as the liftgate assembly  100  is pivoted downward the dock lock engagement member  210  may contact the obstruction  15 . This does not prevent the continued rotation downward of the platform  132 , however, because each link  270 ,  271  simply slides within the corresponding groove  262 , and/or pivots with respect to the lift tube  154 . 
     Multiple embodiments have been described, hereinabove. It will be apparent to those skilled in the art that the above methods and apparatuses may incorporate changes and modifications without departing from the general scope of this invention. It is intended to include all such modifications and alterations in so far as they come within the scope of the appended claims or the equivalents thereof. 
     Having thus described the invention, it is now claimed: