Abstract:
A pneumatic cylinder assembly and a method for lifting a hand truck frame generally vertically away from a ground surface exploits a cylinder housing including a longitudinal axis and first and second ends. The cylinder housing defines a cylinder cavity at the first end and a port generally at the second end in operative communication with the cylinder cavity and has at least one frame attachment point for attachment of the housing to the hand truck frame. A piston in the cylinder cavity is moveable in a first direction. A fluid space is defined between the actuation surface within the cylinder housing. An inlet valve is configured to admit a working fluid into the fluid space through the port at a pressure greater than an ambient pressure, thereby urging the piston in the first direction thereby to cause the movement of the piston in the first direction lifting the truck.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates generally to hand trucks and, more specifically, to pneumatically energized hand trucks. 
       BACKGROUND OF THE INVENTION 
       [0002]    A hand truck is an L-shaped payload-moving dolly having a frame including one or two handles located generally at an uppermost end. The frame is configured to rotate about an axle connecting wheels at a frame base. Extending from the base in opposed relation to the handle or handles is a tongue configured to support a payload. The tongue generally rests flat against a ground surface when the hand-truck is upright. 
         [0003]    The payload to be moved is placed upon the tongue. The frame is tilted away from the tongue lifting the payload allowing gravity to urge the payload into engagement with the frame. The payload is tilted back about the axle until the payload weight is balanced over the wheels. Used in such a fashion, the hand truck is used to transport bulky and heavy objects, making them easier to move, based upon the simple lever. The hand truck will not, however, significantly elevate a payload to lift that payload onto a sill of a delivery van or onto a loading dock. 
         [0004]    A number of solutions have been taught. In U.S. Pat. No. 2,875,852 (Mar. 3, 1959), Morrell taught the use of a power driven handling truck, having a very significant overall weight and an elaborate pulley mechanism to elevate the payload on the tongue. Likewise, Gibson in U.S. Pat. No. 2,925,887 (Feb. 23, 1960) taught a hand truck having both a significant base element and a fork elevating hydraulic ram. The Gibson solution is both heavy and unwieldy. 
         [0005]    In U.S. Pat. No. 3,055,523 (Sep. 25, 1962), Wurn taught the use of a manually telescoping hand truck gaining mechanical advantage through the use of cranks spooling cables through pulleys. The telescoping hand truck proved to offer too little a mechanical advantage to be useful. Vermett, et al. taught a refinement of the telescoping hand truck in U.S. Pat. No. 4,421,209 dated Dec. 20, 1983. 
         [0006]    The foregoing solutions bear similar earmarks of failure. The trucks have heavy bases supporting elaborate lifting structures. The hand trucks are heavy, large and unwieldy. What is needed in the art is a light, simple, elevating means that is neither overly complicated nor unduly heavy. 
       SUMMARY OF THE INVENTION 
       [0007]    A pneumatic cylinder assembly and a method for lifting a hand truck frame generally vertically away from a ground surface exploits a cylinder housing including a longitudinal axis and first and second ends. The cylinder housing defines a cylinder cavity at the first end and a port generally at the second end in operative communication with the cylinder cavity and has at least one frame attachment point for attachment of the housing to the hand truck frame. A piston in the cylinder cavity is moveable in a first direction. A fluid space is defined between the actuation surface within the cylinder housing. An inlet valve is configured to admit a working fluid into the fluid space through the port at a pressure greater than an ambient pressure, thereby urging the piston in the first direction to cause the movement of the piston in the first direction lifting the truck. 
         [0008]    An embodiment of the present invention comprises a pneumatically elevating hand truck. AS hand truck frame assembly includes a frame and two wheels spaced apart on an axle. The axle is attached to the frame to allow ready movement of the hand truck frame assembly along a ground surface. A tongue extends from the frame and configured for bearing a load. A fluid cylinder assembly includes a cylinder tube attached to the frame at frame attachment points. The cylinder has a port and encloses a piston having an actuating surface. The piston is fitted into the cylinder tube to be slidable in the cylinder tube. A piston rod is integrally fitted to the piston at a first rod end and extends away from the piston to a second rod end. A portion of the rod including the second end protrudes outside the cylinder tube by a protrusion amount. The protrusion amount is of the rod is changed according to entrance and exit of fluid into and out of a chamber the cylinder defines in conjunction with the activation surface. A control valve is configured to selectively allow entrance and exit of the working fluid into and out of the chamber. 
         [0009]    In accordance with some non-limiting examples of the invention, elevating and lowering a hand truck relative to a ground surface includes attaching a cylinder assembly having a longitudinal axis at frame attachment points to a hand truck. The longitudinal axis is oriented as generally vertical. The hand truck has a frame and an axle attached to the frame. The axle has two wheels spaced apart and configured for movement of the hand truck over a ground surface. A fluid is admitted into the cylinder assembly. The cylinder assembly includes at least one port, and first and second ends situated in first and second directions respectively along the longitudinal axis and defining a cylinder cavity at the first end. A piston is situated in the cylinder cavity, has an actuation surface and is moveable along the longitudinal axis. A fluid space exists between the actuation surface and the cylinder cavity and will receive the admitted fluid. A piston rod is connected to the piston at a first rod end. The piston rod has a first rod end attached to a piston and spaced apart from the actuation surface in the first direction along the longitudinal axis. A second rod end is further spaced apart in the first direction from the actuation surface and is configured to engage the ground surface. Expanding the fluid spaces exploits a differential pressure force in the first direction caused by the presence of the admitted fluid which drives the piston and piston rod in the first direction. The hand truck is lifted by movement of the piston rod in the first direction bearing against the ground surface at the second rod end. 
         [0010]    These and other examples of the invention will be described in further detail below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Preferred and alternative examples of the present invention are described in detail below with reference to the following drawings: 
           [0012]      FIG. 1  is a perspective view of an embodiment of a hand truck with a piston rod extended; 
           [0013]      FIG. 2  is a reverse perspective view of an embodiment of the hand truck with the piston rod retracted; 
           [0014]      FIG. 3  is front view of an embodiment of the hand truck with the piston rod retracted; 
           [0015]      FIG. 4  is a side view of an embodiment of the hand truck with the piston rod retracted; 
           [0016]      FIG. 5  is a rear view of an embodiment of the hand truck with the piston rod retracted; 
           [0017]      FIG. 6  is a front view of an alternate embodiment of the hand truck with the piston rod retracted and an auxiliary reservoir; 
           [0018]      FIG. 7  is a rear view of an embodiment of the hand truck with the piston retracted showing a sill; 
           [0019]      FIG. 8  is a rear view of an embodiment of the hand truck with the piston extended; 
           [0020]      FIG. 9  is a side view of an embodiment of the hand truck with the piston extended demonstrating the rotational movement about the piston; 
           [0021]      FIG. 10  is a side view of an embodiment of the hand truck with the piston extended demonstrating the removal of the payload; 
           [0022]      FIG. 11  is a side view of an embodiment of the hand truck with the piston partially extended demonstrating the retraction of the piston rod; 
           [0023]      FIG. 12  is a rear view of an embodiment of the hand truck with the piston partially extended demonstrating the rotation of the hand truck about the piston rod; 
           [0024]      FIG. 13  is a rear view of an embodiment of the hand truck with the piston retracted demonstrating the self centering rotation of the hand truck about the piston rod caused by engagement with cradles on a foot; 
           [0025]      FIG. 14  is a cross-sectional view of the cylinder assembly showing the piston rod retracted; and 
           [0026]      FIG. 15  is a cross-sectional view of the cylinder assembly showing the piston rod extended. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0027]    The addition of a pneumatic cylinder assembly to a hand truck provides a light, simple, hand truck elevating means that is neither overly complicated nor unduly heavy. Referring to  FIG. 1 , a perspective view of an embodiment of a hand truck assembly with a piston rod  39 ′ extended, demonstrates the easy and natural use of the inventive hand truck assembly  10 . The hand truck assembly  10  includes a hand truck frame  12  which, in one non-limiting embodiment, is hollow to receive a charge of compressed working fluid (generally, compressed air is used as a working fluid, however, there is no reason that any compressed gas, such as carbon dioxide, could not serve with equal facility). Affixed to the hand truck frame  12 , are an axle  15 , about which two wheels  18  rotate in contact with a ground surface, a tongue  27  for supporting a payload (not shown) and generally one or more handles  24  used to tilt the hand truck frame  12  about the axle  15  to lift a payload (not shown) residing on the tongue  27 . Generally, the rigidity of the frame is enhanced by the inclusion of a support assembly  21  including stringers used to buttress the axle  15  where it joins the frame  12 . 
         [0028]    In addition to those above-listed elements, the hand truck assembly  10  shares with a conventional hand truck, additionally, an actuator valve assembly  33  which selectably communicates the working fluid from the reservoir the frame  12  contains through the cylinder feed conduit  48 , to a cylinder assembly  39  enveloping the piston rod  39 ′. A charging nipple  51  and charging hose assembly  54  also communicate with the reservoir in the frame  12  to allow charging of the reservoir with the working fluid. By selectably actuating the actuator valve assembly  33 , the operator can elevate the hand truck assembly  10  by allowing the fluid to flow from the frame  12  to the cylinder assembly  39  where it urges the piston (not shown) and the attached piston rod  39 ′ to extend from the cylinder assembly. A foot  42  attached to the piston rod  39 ′ in opposed relation to the piston (not shown) contacts the ground surface to support and, by further extension of the piston rod  39 ′ from the cylinder assembly  39 , to elevate the hand truck assembly  10  relative to the ground surface. Shown on the upper surface of the foot  43  are optional cradles  43  that tend to align the foot  42  with the axle  15 . 
         [0029]      FIG. 2  depicts a reverse perspective view of the embodiment of the hand truck  10  with the piston rod  39 ′ retracted into the cylinder assembly  39 . A payload  30  is shown in phantom resting on the tongue  27 . As above, the axle  15  is affixed to the frame  12  by means of the support assembly  21 . In turn, the wheels  18  are spaced apart and rotatably attached to the axle  15  allowing easy movement on the ground surface. To selectably extend and retract the piston rod  39 ′ and the attached foot  42 , the actuator valve assembly  33  is shown along with an air exhaust horn  45  to facilitate the release of working fluid from the cylinder assembly  39  upon suitable activation of the actuator valve assembly  33 , thereby allowing the piston rod  39 ′ to retract into the cylinder assembly  39 . By means of alternate activation, the actuator valve assembly allows working fluid to pass under pressure (relative to the ambient) through the cylinder feed conduit  48 , to pressurize the cylinder assembly  39  to elevate the hand truck assembly  10 . 
         [0030]      FIG. 3  is a front view,  FIG. 4  a side view, and  FIG. 5  a rear view of the embodiment of the hand truck assembly  10  with the piston rod  39 ′ retracted into the cylinder assembly  39 .  FIG. 6  is a front view of an alternate embodiment of the hand truck with the piston rod  39 ′ retracted and an auxiliary reservoir  57 . These views show placement of the various components relative to the frame  12 . To further clarify the elevating and lowering functions of the hand truck assembly  10 , the fluid circuit will be described with reference to these  FIGS. 3 ,  4 ,  5 , and  6 . 
         [0031]    The working fluid is admitted to reside in the reservoir (depending upon the embodiment) contained either in the frame  12  or the auxiliary reservoir  57  through the charging hose assembly  54  into the charging nipple  51  which communicates with the reservoir. The working fluid resides in the reservoir under pressure until activation of the actuator valve assembly  33 . When suitably activated, a valve within the actuator valve assembly allows the fluid to communicate with the cylinder assembly  39  by passing through the cylinder feed conduit  48  as it runs from the actuator valve assembly  33  to the cylinder assembly  39 . Admitting the working fluid into the cylinder assembly  39  urges the piston rod  39 ′ to extend from the cylinder assembly  39 ′. In turn, the extension of the cylinder rod  39 ′ urges the foot  45  against the ground surface to elevate the hand truck assembly  10 . 
         [0032]    When the actuator valve assembly  33  is otherwise activated, the fluid returns through the cylinder feed conduit  48  from the cylinder assembly  39  through a valve in the actuator valve assembly  33  and is released to the ambient through the air exhaust horn  45 . As a consequence of the release of fluid to the ambient, the pressure the fluid exerts on the piston, and in turn on the piston rod  39 ′, decreases, allowing the ambient pressure and gravity to urge the piston rod  39 ′ back into the cylinder assembly  39 ′, thereby lowering the hand truck. Because of the relationship which the pressure within the cylinder assembly has to the lifting force the foot exerts on the ground surface, selective actuation of the actuator valve assembly  33  allows controlled elevation and lowering of the hand truck assembly  10 . 
         [0033]      FIG. 7  is a rear view of an embodiment of the hand truck with the piston retracted showing a sill;  FIG. 8  is a rear view of an embodiment of the hand truck with the piston partially extended;  FIG. 9  is a side view of an embodiment of the hand truck with the piston more fully extended;  FIG. 10  is a side view of an embodiment of the hand truck with the piston extended;  FIG. 11  is a side view of an embodiment of the hand truck with the piston partially extended;  FIG. 12  is a rear view of an embodiment of the hand truck with the piston partially extended; and  FIG. 13  is a rear view of an embodiment of the hand truck with the piston retracted. Together, these  FIGS. 9-13  demonstrate, in sequence, a maneuver made possible by one non-limiting embodiment of the hand truck assembly  10 . The cylinder assembly  39  and the piston and piston rod  39 ′ cooperate to form a fluid bearing which facilitates the maneuver shown in the sequence. 
         [0034]    Fluid bearings are those which solely support the bearing&#39;s loads on a thin layer of liquid or gas. Fluid bearings generally have very low friction—far better than mechanical bearings. Since no rigid mechanical element supports load, it may seem that fluid bearings can give only low precision. In practice, fluid bearings have clearances that change less under load (are ‘stiffer’) than mechanical bearings. It might seem that bearing stiffness, as with maximum design load, would be a simple function of average fluid pressure and the bearing surface area. In practice, when bearing surfaces are pressed together, the fluid outflow is greatly constricted. This significantly increases the pressure of the fluid between the bearing faces. As fluid bearings&#39; faces are comparatively large areas, even small fluid pressure differences cause large restoring forces, maintaining the gap. For that reason, the cylinder assembly  39  will readily pivot about the piston rod  39 ′, thereby allowing the hand truck assembly  10 , when elevated, to pivot a payload onto a sill. 
         [0035]    Initiating the sequence at  FIG. 7 , the payload  30  (shown in phantom) rests upon the tongue  27  and the hand truck assembly  10  stands adjacent to a sill selected as the desired location of the payload. By activating the actuator valve assembly, the fluid is allowed to escape the reservoir contained in the frame  12  (in the illustrated non-limiting embodiment), through the cylinder feed conduit  48  to the cylinder assembly. 
         [0036]      FIG. 8  is a rear view of the embodiment of the hand truck with the piston rod  39 ′ partially extended as a result of the fluid entering the cylinder assembly  39 . The payload  30  has been elevated on the tongue  27  of the hand truck assembly  10 , as the hand truck assembly  10  elevates in response to the fluid entering the cylinder assembly  39 . 
         [0037]      FIG. 9  is a side view of the embodiment of the hand truck assembly  10  with the piston rod  39  more fully extended. As explained above, the piston rod  39 ′ in cooperation with the cylinder assembly  39  forms a fluid bearing that supports the weight of the hand truck assembly  10  with the payload  30  resting on the tongue  27 . The hand truck assembly  10  is readily pivoted about the piston rod  39  to place the payload  30  on the sill. 
         [0038]      FIG. 10  is a side view of the embodiment of the hand truck assembly  10  with the piston rod  39 ′ extended. In the illustrated position, the payload is readily moved from the tongue  27  to the sill, now being oriented to allow this movement. Upon the translational movement from the tongue  27  to the sill, the hand truck assembly  10  is unladen. 
         [0039]      FIG. 11  is a side view of an embodiment of the hand truck assembly  10  with the piston rod  39 ′ partially extended as the actuator valve assembly  33  is activated to allow the working fluid to escape through the air exhaust horn  45 . As a consequence of the air escaping the cylinder assembly  39 , the piston rod  39 ′ retracts into the cylinder assembly  39 . In this manner, the hand truck assembly  10  moves downward. 
         [0040]      FIG. 12  is a rear view of an embodiment of the hand truck assembly  10  with the piston rod  39 ′ partially extended from the cylinder assembly  39 . Once again, the piston rod  39 ′ and the cylinder assembly  39  cooperate to form a fluid bearing. The hand truck assembly  10  readily pivots about the piston rod  39 ′ to return to its original orientation. 
         [0041]    In  FIG. 13 , an optional feature of the hand truck assembly  10  is demonstrated as the piston rod  39 ′ further retracts into the cylinder assembly  39 ′ to a point of repose. Cradles  43  located on an upper surface of the foot  45  engage the axle  15  in generally v-shaped cavities. Where the foot  45  is not in perfect alignment with the axle  15 , the retraction of the piston rod  39 ′ into the cylinder assembly  39  urges the axle  15  into deeper engagement with the cradles  43 , providing a rotational force to the foot  45 , causing the foot  45  to draw into alignment with the axle  15 . 
         [0042]      FIG. 14  is a cross-sectional view of the cylinder assembly showing the piston rod retracted; and  FIG. 15  is a cross-sectional view of the cylinder assembly showing the piston rod extended. Together,  FIGS. 14 and 15  demonstrate an additional non-limiting embodiment of the invention. As earlier explained, the piston rod  39 ′ is nestingly engaged in the cylinder assembly  39 . The piston rod  39 ′ comprises a piston with an actuating surface configured to contain the fluid within a cylindrical cavity that the cylinder assembly  39  defines. When working fluid enters the cylinder cavity through the cylinder feed conduit nipple  48 ′, the fluid presses against the actuation surface driving the piston and piston rod  39 ′ downward. 
         [0043]    In the non-limiting embodiment, a resilient member or spring  60  connects the cylinder assembly  39  to the piston rod  39 ′ biasing and, thus, urging the piston rod  39 ′ back into the position illustrated in  FIG. 14 . When fluid is admitted through the cylinder feed conduit nipple  48 ′ the pressure of the fluid overmasters the bias allowing the piston rod  39 ′ to extend relative to the cylinder assembly  39 , thereby allowing the elevation of the hand truck assembly  10  as described above. 
         [0044]    While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. For example, the hand truck assembly  10  may readily be configured to mate with a charging hanger on a van, thereby to recharge the fluid in the reservoir by the above-described means with each replacement of the hand truck assembly into the charging hanger. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.