Abstract:
In one embodiment, a vehicle comprises a body, a steerable drive wheel attached to the body, and a load platform connected to the body that is movable between a lowered position and a lifted position. A load wheel is connected to the load platform and an intermediate load wheel is connected to the vehicle and positioned between the drive wheel and the load wheel. The load wheel is configured to facilitate moving the load platform between the lowered position and the lifted position and the intermediate load wheel is configured to cooperate with the load wheel to facilitate moving the load platform between the lowered position and the lifted position. The intermediate load wheel is also configured to form a pivot about which the vehicle turns throughout a range of motion of the load platform between and including the lowered position and the lifted position.

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. provisional application No. 61/612,519 under 35 U.S.C. §119(e), titled “Delivery Pallet Jack” and filed on Mar. 19, 2012; the entirety of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Wheeled vehicles commonly rotate one or more steered wheels about a vertical axis to turn the vehicle in a turn circle. When a steered wheel is at its rotational limit, the vehicle turns in its smallest turn circle. Factors influencing the size of a vehicle&#39;s smallest turn circle are the length of the wheelbase, that is, how far the steered wheel is located from other wheels supporting the vehicle, and the extent of rotation of the steered wheel about the vertical axis. An exemplary vehicle, such as a pallet jack  5  ( FIG. 1 ), may have a steered wheel  10  capable of rotating 90° from a straight position to cause the pallet jack  5  to turn about a pivot  15  created by and located between the rear wheels  20  during turning maneuvers. Rotating the steered wheel  10  by 90° can result in a smallest turn circle  25  for the pallet jack  5  having a diameter that is roughly twice the vehicle wheelbase ( FIG. 2 ), that is, the distance between steered wheel  10  and the rear wheels  20 . 
     Some devices attempt to decrease the size of the minimum turn circle of a vehicle, such as the pallet jack  5 , by providing a structure located between steered wheels and rear wheels that contacts the ground when the forks  30  are at a lowered position. For example, see the devices described in U.S. Pat. Nos. 2,598,151; 4,615,533; 5,354,080; 7,226,060; and 8,336,913. 
     SUMMARY 
     In one embodiment, a vehicle comprises a body, a steerable drive wheel attached to the body, and a load platform connected to the body that is movable between a lowered position and a lifted position. A load wheel is connected to the load platform and an intermediate load wheel is connected to the vehicle and positioned between the drive wheel and the load wheel. The load wheel is configured to facilitate moving the load platform between the lowered position and the lifted position and the intermediate load wheel is configured to cooperate with the load wheel to facilitate moving the load platform between the lowered position and the lifted position. The intermediate load wheel is also configured to form a pivot about which the vehicle turns throughout a range of motion of the load platform between and including the lowered position and the lifted position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a bottom orthogonal view of a prior art pallet truck. 
         FIG. 2  illustrates a top view of the prior art pallet truck of  FIG. 1 . 
         FIG. 3  illustrates a right-side view of a pallet truck equipped with a first embodiment of a steering system. 
         FIG. 4  illustrates a bottom orthogonal view of the pallet truck of  FIG. 3  with the forks at a lowered position. 
         FIG. 5  illustrates a bottom orthogonal view of the pallet truck of  FIG. 3  with the forks at a raised position. 
         FIG. 6  illustrates a top view of the pallet truck of  FIG. 3 . 
         FIG. 7  illustrates a bottom orthogonal view of a pallet truck equipped with another embodiment of a steering system. 
         FIG. 8  illustrates a bottom orthogonal partial view of a pallet truck equipped with another embodiment of a steering system 
     
    
    
     DETAILED DESCRIPTION 
     The present inventor recognized that in cases of restricted clearance, such as inside a cargo truck, it may be desirable to have a more maneuverable vehicle capable of a smaller turn circle than typical vehicles have, and that it may be desirable to have a vehicle with such a smaller turn circle when a load platform is at its lowered position, its raised position, or anywhere in between. The present inventor also recognized that previous attempts to create a smaller turn circle for a vehicle have a common disadvantage of being restricted to having such a smaller turn circle when a load platform, such as a pair of forks, is at a lowered position. 
     The following description provides details for certain embodiments, but is not meant to be limiting in scope. The invention is described by the claims that follow the detailed description. 
     A vehicle, such as pallet truck  100 , includes a supporting structure, such as body  105 , with a drive wheel  110  attached thereto. The drive wheel  110  is configured to steer pallet truck  100 , for example, by linkage to tiller arm  115  via mechanical, hydraulic, electronic, or other suitable linking device, such that rotation of tiller arm  115  causes rotation of drive wheel  110 . Drive wheel  110  is optionally operatively connected to a motor or other suitable motive device for moving the pallet truck  100 , but the drive wheel  110  may be powered via force applied to the tiller arm  115 . 
     Pallet truck  110  includes a load platform, such as forks  120 , that is operatively connected to the body  105  for movement between a lowered position ( FIG. 4 ) and a raised position ( FIG. 5 ). The load platform lifts objects, for example, a pallet laden with goods, and may include one or more forks, a substantially flat surface, or other suitable structure for lifting objects. Rear load wheels  125  are connected to the forks  120 , and are configured to facilitate moving the forks  120  between the lowered position, where the forks  120  are proximate to the ground, and the raised position, where the forks  120  are distal from the ground. Rear load wheels  125  bear at least some of the weight of pallet truck  110  and of any load carried by the forks  120 . 
     At least one intermediate load wheel  130 , or center load wheel in some embodiments, is included between the drive wheel  110  and the rear load wheels  125 . Optionally, the intermediate load wheel  130  is located approximately halfway between the drive wheel  110  and the rear load wheels  125 , but the intermediate load wheel  130  may be located anywhere between the drive wheel  110  and the rear load wheels  125 . In the illustrated embodiment, two intermediate load wheels  130  are included and are attached to and underneath the forks  120 . However, one intermediate load wheel may be attached to a vehicle support structure, to a load platform, such as between forks  120 , or to any other suitable location of a vehicle. 
     The intermediate load wheels  130  and the rear load wheels  125  may be linked together so that they raise and lower in unison. Such linkage may occur via coordinated hydraulics, electronics, or mechanical apparatuses. In some examples, the intermediate load wheel  130  is not retracted within the fork  120  to the extent where the intermediate load wheel  130  loses contact with the ground while the rear load wheels  125  are retracted to a position where they lose contact with the ground when the forks  120  are at the lowered position. Optionally, the intermediate load wheel  130  is configured to continuously contact the surface of travel (ground). In some embodiments, the intermediate load wheel  130  supports a portion of the vehicle weight, a portion of the load on forks  120 , or both, with the forks  120  at a lowered position, at a raised position, or at any position in between. Preferably, the intermediate load wheel  130  is provided with a raising and lowering mechanism, such as mechanical linkage  135 , such that at least some, and preferably a majority, of the portion of the vehicle weight and load weight carried by the rear load wheels  125  and the intermediate load wheel  130  is borne by the intermediate load wheel  130 . 
     In some embodiments, the intermediate load wheels  130  may be located at a position between the drive wheel  110  and the rear load wheels  125  such that a first portion of the total vehicle weight and load weight is carried by the rear load wheels  125  and the intermediate load wheels  130  and a second portion of such weight is carried by the drive wheel  110 , wherein a majority of the first portion of such weight is borne by the intermediate load wheels  130 . Preferably, intermediate load wheels  130  bear a majority of the first portion of such weight with the forks  120  at the raised position ( FIG. 5 ), at the lowered position ( FIG. 4 ), and at all positions in between. For example, for a combined vehicle weight and load weight of 4,000 kilograms (kg), 3,000 kg may be carried by the rear load wheels  125  and the intermediate load wheels  130  and 1,000 kg may be carried by the drive wheel  110 . Preferably, of the 3,000 kg carried by the rear load wheels  125  and the intermediate load wheels  130 , the intermediate load wheels may bear 1,501 kg or more. Or, 1,900 kg may be carried by the rear load wheels  125  and the intermediate load wheels  130  and 2,100 kg may be carried by the drive wheel  110 . Preferably, of the 1,900 kg carried by the rear load wheels  125  and the intermediate load wheels  130 , the intermediate load wheels may bear 951 kg or more. Other suitable load weight distributions may be used. 
     Optionally, the rear load wheels  125  are provided with a castering, or swiveling, capability to facilitate the vehicle turning about a pivot  140  ( FIG. 6 ) defined by the intermediate load wheels  130 . Preferably, the rear load wheels  125  and the drive wheel  110  follow turn circles, or circular paths  126 ,  127 , respectively, about the pivot  140 . The circular paths followed by the drive wheel  110  and the rear load wheels  125  may be the same circular path, or may be different circular paths as illustrated in  FIG. 6 . The arrangement of an intermediate load wheel  130  located between a drive wheel  110  and rear load wheels  125  facilitates reducing the vehicle turn circle, for example, by creating a shortened effective wheelbase, thereby increasing maneuverability, compared to a vehicle having only a drive wheel and rear wheels. 
     In some embodiments, the intermediate load wheels  130  are mounted to the forks  120  via mechanical linkage  135 , which includes a crank arm assembly  136 . A mechanism, such as a hydraulic system (not illustrated), is operatively connected to the mechanical linkage  135  to move the crank arm assembly  136  between two positions to cause the rear load wheels  125  and the intermediate load wheels  130  to move away from and towards the forks  120 , which facilitates raising and lowering the forks  120 , respectively. Preferably, the weight of pallet truck  100  and of any load borne on the fork  120  is distributed between the drive wheel  110 , the intermediate load wheels  130  and the rear load wheels  125  throughout the range of motion of the forks  120 . Intermediate load wheels  130  define the pivot  140  which includes a vertical axis about which the pallet truck  100  may rotate, in other words, a turning point for maneuvering when the forks  120  are in the raised or lowered positions, or anywhere in between. 
     In some embodiments, the rear load wheels  125  are configured with an optional caster function, that is, each of the rear load wheels  125  may swivel to facilitate moving the rear end  145  of pallet truck  100  through its turn circle  126  ( FIG. 6 ). With the intermediate load wheels  130  contacting the ground, for example, when the forks  120  are raised (intermediate load wheels  130  and rear load wheels  125  lowered, or distal from the forks  120 ), lowered (intermediate load wheels  130  and rear load wheels  125  raised, or proximate to the forks  120 ), or anywhere in between, each rear load wheel  125  is able to rotate about a local vertical axis, making each of them essentially a caster wheel, and able to track about the pivot  140 , which may be defined by intermediate load wheels  130 , or may coincide with an intermediate load wheel, such as an intermediate load wheel that is positioned midway between rear load wheels, but longitudinally offset from such rear load wheels. 
     Optionally, a positioning caster  150  is located slightly ahead of the each rear load wheel  125 A ( FIG. 7 ). The positioning caster  150  may be held in a fixed position with respect to the fork  120 A so that the positioning caster  150  moves up and down with the fork  120 A. The positioning caster  150  may carry a portion of the load when forks  120 A are in the lowered position to assist with maneuverability, for example, when rear load wheels  125 A are not configured to swivel, or have a limited swiveling ability, or are not configured to bear load weight when the forks  120 A are lowered. 
     When a positioning caster  150  is included, an optional alignment feature may be provided on the underside of each fork  120 A to cause the rear load wheels  125 A to move into a pre-defined positional relationship with respect to the forks  120   a . A caster-alignment feature may engage the rear load wheel  125 A when the forks  120 A are lowered such that a longitudinal, or rolling, axis of the rear load wheel  125 A is substantially perpendicular to the longitudinal direction of forks  120 A and may be substantially parallel to the top surface of forks  120 A. For example, the rear load wheels  125 A may swivel or rotate to the proper storage orientation as a result of engaging a caster-alignment feature formed from a portion of the forks  120 A, such as fork cavity  155  as the mechanical linkage  135 A retracts the rear load wheels  125 A into the forks  120 A. In some embodiments, the rear load wheels  125 A may not support any weight when the forks  120 A are at their lowered position. 
     Optionally, a vehicle control system, such as a vehicle management system or an electronic controller (not illustrated) may receive input from one or more sensors that provide information relating to the vertical position of the tiller arm  115 , the horizontal position of the tiller arm  115 , the weight of a load on a load platform, or other suitable variable, singularly or in any combination. Based on the inputs, the vehicle control system may limit a maximum speed of the drive wheel  110 , for example, when tight maneuvers (turns) are executed, when maneuvers with a heavy load are executed, or under other suitable circumstances. In one example, when the tiller arm  115  is at or near a vertical position, the maximum allowable vehicle speed may be reduced or limited to enhance control during maneuvers, which may include pivoting the vehicle about the pivot  140 . When the tiller arm  115  is lowered, i.e., no longer at or near the vertical position, and the forks  120  are raised, a high travel speed may be enabled. 
     Another optional feature that may be included is a hinged or articulating fork  120 B ( FIG. 8 ) that accommodates a three-point load distribution between the drive wheel  110 B, intermediate load wheel  130 B, and rear load wheel  125 B. Providing a pivot joint  160  interposed between portions of the forks  120 B, or between the forks  120 B and the body  105 B, may facilitate having a relatively constant load at the drive wheel  110 A to maintain drive traction, for example, when traversing uneven ground. Rotation of the forks  120 B such that the ends  145 B of the forks  120 B move above and below the pivot joint  160  may permit the rear load wheels  125 B to elevate slightly with respect to the intermediate load wheels  130 B, so that the rear load wheels  125 B may raise over bumps, such as the entry of a pallet, and may permit the rear load wheels  125 B to descend slightly with respect to the intermediate load wheels  130 B, so that the rear load wheels  120 B may travel through divots, such as a pit in a floor, for operation without substantially tilting the pallet truck. In some embodiments, forks  120 B may rotate about pivot joint  160  approximately plus 5° and minus 5° (up and down) to facilitate moving a loaded or unloaded pallet truck up and down a handicap ramp. Forks  120 B, pivot joint  160 , or both, optionally include one or more hard stops that limit rotation of forks  120 B about pivot joint  160 , for example, to hinder a pallet truck from tipping over. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the systems and methods of the disclosure. Other embodiments of the methods and systems will be apparent to those skilled in the art from consideration of the specification and practice of the methods and systems disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the claims and their equivalents.