Abstract:
A sideloader liftgate system automatically extends a stabilizer leg when a liftgate is deployed, and automatically retracts the stabilizer leg when the liftgate is stored. Adjustment of the liftgate and stabilizer leg is carried out in response to a single user command. The invention prevents a user from forgetting to extend the stabilizer leg for safely using the liftgate, and also prevents a user from forgetting to retract the stabilizer leg before towing the trailer.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to liftgate mechanisms mounted on truck trailers for loading and unloading cargo. More specifically, the present invention relates to a safer side-loading liftgate. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the trucking industry, it is known to equip a truck trailer with one or more liftgates for cargo handling. In one type of arrangement, the liftgate may be mounted to a subframe on the underside of the trailer at a rear or side door location of the trailer. The liftgate includes a platform for supporting cargo and an actuated linkage for moving the platform through various positions relative to the trailer, including (i) a storage position under the trailer, (ii) a raised position outside the trailer adjacent the trailer door, wherein the platform is approximately coplanar with a floor of the trailer, and (iii) a lowered position outside the trailer at ground level below the raised position. The actuated linkage may be a hydraulically-powered linkage capable of lifting heavy loads, for example loads on the order of 4,000 pounds. 
         [0003]    In the case of a liftgate mounted at a side door of a trailer, commonly referred to as a “sideloader,” imbalance during loading and unloading of heavy cargo loads poses a safety issue. The trailer will tilt toward the side of the load, which may cause cargo in the trailer and cargo on the liftgate platform to slide in a manner that may endanger nearby personnel. Because of this, it is known to provide an extendable stabilizer leg on the underside of the truck trailer adjacent the side-loading liftgate. The stabilizer leg, which is normally retracted when not in use, may be selectively extended downward to engage the ground near the side-loading liftgate to prevent the trailer from tilting when the liftgate is in use. 
         [0004]    Despite the availability of stabilizer legs, safety challenges remain. For example, an operator may forget to deploy the stabilizer leg prior to moving cargo onto the liftgate platform from the ground during loading, or moving cargo out of the trailer onto the liftgate during unloading. Failure to extend the stabilizer leg is more likely to happen when the operator is in a hurry to load and/or unload the trailer. 
         [0005]    Another problem associate with stabilizer legs is that the operator may forget to retract the stabilizer leg after using the liftgate. While the liftgate itself may be properly stored, the operator may not notice that the stabilizer leg remains deployed, and the operator may start driving while the stabilizer leg is still extended. This can cause expensive damage to the trailer, and may pose safety risks to vehicles and persons behind the trailer. 
         [0006]    What is needed is a stabilizer leg that is always extended when the liftgate is placed into service, and that is always retracted when the liftgate is returned to storage. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a sideloader liftgate system for a trailer that automatically extends a stabilizer leg of the liftgate system when a liftgate of the liftgate system is deployed, and automatically retracts the stabilizer leg when the liftgate is stored. 
         [0008]    In addition to the liftgate and the stabilizer leg, the liftgate system generally comprises a deployment mechanism connecting the liftgate to the trailer, an actuation system, and a user control interface. The deployment mechanism is adjustable to move the liftgate relative to the trailer between a storage position and a usage position, and the stabilizer leg is adjustable between a retracted state and an a ground-engaging extended state. The actuation system is operable to adjust both the deployment mechanism and the stabilizer leg. The control interface allows a user to issue user-selectable commands to operate the actuation system. One selectable command is a deployment command causing the actuation system to adjust the deployment mechanism to move the liftgate from the storage position to the usage position and to adjust the stabilizer leg from the retracted state to the extended state. Another selectable command is a storage command causing the actuation system to adjust the deployment mechanism to move the liftgate from the usage position to the storage position and to adjust the stabilizer leg from the extended state to the retracted state. 
         [0009]    The present invention encompasses a method of operating a liftgate system for a trailer. The method generally comprises the steps of inputting a deployment command to an actuation system, and operating the actuation system in response to the deployment command to (i) deploy a liftgate of the liftgate system relative to the trailer from a storage position to a usage position and (ii) actuate a stabilizer leg of the liftgate system from a retracted state to an extended state. The method may further comprise the steps of inputting a storage command to the actuation system, and operating the actuation system in response to the storage command to (i) move the liftgate relative to the trailer from the usage position to the storage position and (ii) actuate the stabilizer leg from the extended state to the retracted state. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing figures, in which: 
           [0011]      FIG. 1  is a perspective view of a side-loading liftgate system formed in accordance with an embodiment of the present invention; 
           [0012]      FIG. 2  is a perspective view showing a liftgate of the liftgate system in greater detail; 
           [0013]      FIG. 3A  is a rear elevational view of a truck trailer incorporating the side-loading liftgate system shown in  FIG. 1 , wherein a liftgate and a stabilizer leg of the liftgate system are shown in a storage position and a retracted state, respectively; 
           [0014]      FIG. 3B  is a view similar to that of  FIG. 3A , wherein the liftgate and the stabilizer leg are shown in a usage position and an extended state, respectively; 
           [0015]      FIG. 3C  is a view similar to that of  FIG. 3B , wherein the liftgate is shown in a lowered usage position receiving a cargo load; 
           [0016]      FIG. 4  is a schematic diagram of the liftgate system shown in  FIG. 1 ; 
           [0017]      FIG. 5  is a plan view showing a user interface of the liftgate system; 
           [0018]      FIG. 6  is a schematic diagram of a hydraulic actuation system thereof, illustrating hydraulic flow to deploy the liftgate and extend the stabilizer leg; 
           [0019]      FIG. 7  is a schematic diagram similar to that of  FIG. 6 , however illustrating hydraulic flow to store the liftgate and retract the stabilizer leg; 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]      FIG. 1  shows a sideloader liftgate system  10  formed in accordance with an embodiment of the present invention, wherein the liftgate system  10  is installed on a trailer  2 . Liftgate system  10  generally comprises a liftgate  12  and a stabilizer leg  20 . Liftgate  12  includes a linkage  14  adjustably supporting a cargo platform  16 . Stabilizer leg  20  may be, for example, a hydraulic jack. 
         [0021]      FIG. 2  shows liftgate  12  of liftgate system  10  in greater detail. Liftgate  12  is connected to subframe members  4  of trailer  2  by a deployment mechanism  18  that is adjustable to move liftgate  12  sidewise relative to trailer  2  between a storage position and a usage position. In the illustrated embodiment, deployment mechanism  18  includes a push-pull hydraulic cylinder pair  36  and laterally extending tracks  37  on which liftgate  12  is slidably mounted. For example, linkage  14  of liftgate  12  may include a mounting member  28  slidably coupled to tracks  37 , and hydraulic cylinder pair  36  may have a first hydraulic linear actuator  36 A and a second hydraulic linear actuator  36 B arranged to operate in tandem with one another to push liftgate  12  laterally outward from under trailer  2  for deployment, and to pull liftgate  12  laterally inward under trailer  2  for storage. 
         [0022]    In the embodiment of  FIG. 2 , linkage  14  includes a lift arm  24  and a parallel arm  26  adjustably linked to each end of mounting member  28  to provide a pair of parallelogram linkages for adjusting the position of platform  16  relative to mounting member  28 . Height adjustment of platform  16  may be powered by a hydraulic lift actuator  30  associated with each lift arm  24 . Tilt adjustment of platform  16  may also be provided, and may be powered by another pair of hydraulic actuators  32  not shown in  FIG. 2 , but represented schematically in  FIGS. 4, 6 and 7 . Platform  16  may be a folding platform having a primary portion  16 A coupled to arms  24  and  26 , and a folding portion  16 B pivotally coupled to primary portion  16 A by hinges  34 . 
         [0023]      FIG. 2  also shows constituents of an actuation system  22  operable to adjust both the deployment mechanism  18  and the stabilizer leg  20 . In the exemplary embodiment, actuation system  22  is a hydraulic system having a hydraulic pump box  50  enclosing a motorized hydraulic pump, and a battery box  52  enclosing a power sources therefor. Details of hydraulic system  22  will be described below with reference to  FIGS. 4, 6, and 7 . 
         [0024]      FIGS. 3A through 3C  provide an operational overview of liftgate system  10 .  FIG. 3A  shows liftgate system  10  when liftgate  12  is in a storage position under trailer  2 . As may be seen, stabilizer leg  20  is in a retracted state off of ground G.  FIG. 3B  shows liftgate  12  deployed laterally outward to a usage position. When liftgate  12  is moved outward to the usage position by deployment mechanism  18 , stabilizer leg  20  is automatically extended downward to meet ground G. Extension of stabilizer leg  20  may take place simultaneously with the deployment motion of liftgate  12 , or may be performed sequentially before or after the deployment motion of liftgate  12 . As will be explained below, deployment of liftgate  12  and extension of stabilizer leg  20  are caused by a single user input command; a separate command to extend stabilizer leg  20  is not necessary. As may be understood, a reverse process is followed for storing liftgate  12  after use. A single command entered by a user adjusts deployment mechanism  18  to bring liftgate  12  laterally inward underneath trailer  2 , and retracts stabilizer leg  20  out of engagement with ground G. 
         [0025]      FIG. 4  schematically represents liftgate system  10 . As may be seen, a user interface  80  is provided allowing a user to input commands to a controller  70  which controls a pump and directional valves of hydraulic actuation system  22  to operate deployment mechanism  18 , stabilizer leg  20 , lift actuators  30 , and tilt actuators  32 .  FIG. 5  shows one form of user interface  80 , wherein the user interface includes three rotary knobs, each having a neutral position and two opposite operating positions. A top knob  82  is manually rotatable to tilt platform  16  up or down by way of hydraulic tilt actuators  32 . A bottom knob  86  is manually rotatable to raise or lower the height of platform  16  by way of hydraulic lift actuators  30 . In accordance with the present invention, a third knob  84  is manually rotatable in one direction to deploy liftgate  12  by way of deployment mechanism  18  and extend stabilizer leg  20  downward, and is manually rotatable in an opposite direction to store liftgate  12  by way of deployment mechanism  18  and retract stabilizer leg  20  upward. Thus, stabilizer leg  20  is automatically extended and retracted in coordination with deployment and storage of liftgate  12 . 
         [0026]      FIGS. 6 and 7  are schematic diagrams of hydraulic actuation system  22 .  FIG. 6  illustrates hydraulic flow associated with deployment of liftgate  12  to a usage position and corresponding extension of stabilizer leg  20 , whereas  FIG. 7  illustrates hydraulic flow associated with movement of liftgate  12  to a storage position and corresponding retraction of stabilizer leg  20 . 
         [0027]    Looking first at  FIG. 6 , a motor  58  is signaled to drive a pump  56  to pump fluid from reservoir  54 , and a directional valve  62  is opened to allow hydraulic fluid to travel to hydraulic actuator s  36 A,  36 B. As may be understood, actuators  36 A and  36 B are oppositely arranged and hydraulic fluid is delivered such that the fluid causes both actuators to extend in opposite directions. As a result, liftgate  12  is deployed laterally outward. Pressurized hydraulic fluid is also delivered through valve  64  to stabilizer leg  20 , causing a piston  40  of stabilizer leg  20  to extend downward relative to a cylinder  38  of the stabilizer leg. Valve  64  may be a one-way check valve arranged such that when the valve is in its non-actuated state, the valve allows flow to extend stabilizer leg  20 , and prevents opposite flow in order to maintain pressure in cylinder  38 . Fluid on an opposite side of piston  40  is forced out of cylinder  38 . Similarly, fluid is forced out of actuators  36 A and  36 B. This discharged fluid from cylinder  38  and actuators  36 A and  36 B is circulated through directional valve  62 . 
         [0028]    Turning now to  FIG. 7 , directional valve  62  is closed and directional valve  60  is opened. Valve  64  is also actuated to permit reverse flow. Consequently, pumped hydraulic fluid is directed to the counter side of the pistons of hydraulic actuators  36 A,  36 B and the counter side of piston  40  of stabilizer leg  20 . As may be understood, this causes actuators  36 A,  36 B to retract and pull liftgate  12  back to its storage position, and further causes stabilizer leg  20  to retract. Retraction causes fluid to exit actuators  36 A,  36 B and stabilizer leg  20 . Actuation of valve  64  allows flow out of the top portion of cylinder  38 . The discharged fluid is routed back through directional valve  60  to reservoir  54 . 
         [0029]    As will be appreciated from the foregoing description, the present invention enhances safety by ensuring that stabilizer leg  20  is extended when liftgate  12  is deployed for use, and by also ensuring that the stabilizer leg is retracted when liftgate  12  is stored. Consequently, human error is eliminated. 
         [0030]    While the invention has been described in connection with an exemplary embodiment, the detailed description is not intended to limit the scope of the invention to the particular forms set forth. The invention is intended to cover such alternatives, modifications and equivalents of the described embodiment as may be included within the scope of the invention.