Abstract:
A hoist for elevating cargo onto the bed of a truck includes a frame ( 11 ) which may be mounted to the truck bed, a platform or container ( 12 ) which is connected to the frame by a pivoting arm ( 9 ), and an arrangement of linkages for rotating the arm ( 9 ) to position the platform either on the truck bed or on a loading and unloading position resting on the ground behind the truck. A hydraulic ram ( 24 ) is connected to the arm ( 9 ) via the linkages, with the linkages being arranged to increase the effective “flow” of the arm to provide a long travel distance of the arm.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to hoists and more particularly to a hoist for elevating a load-bearing platform from the ground to an open bed of a pickup truck and for returning the platform to the ground.  
         BACKGROUND OF THE INVENTION  
         [0002]    Pickup trucks and other vehicles having a cargo-carrying bed are commonly used to transport loads which are too heavy to be manually hoisted, for example, a user might wish to load a small and light vehicle such as a snowmobile, all terrain vehicles (“A.T.V.”) or riding lawn mowers. Such loads are usually loaded onto the truck by pushing or driving them up a ramp and onto the open bed of the truck. Loading of the truck bed in this manner can result in damage to the vehicles or other objects being loaded and injury to persons loading them. An example is the case of loading a vehicle onto a truck bed, using a ramp. The upper edge of the ramp must typically rest solidly on the rear bumper of the truck while the vehicle is being driven up the ramp. If the upper edge overhangs the bumper somewhat, the ramp will become unstable when the weight of the front wheels of the vehicle being loaded is on the overhang. At this point, the ramp will rock and become unstable and the driver may lose control of the vehicle.  
           [0003]    On the other hand, if the upper edge of the ramp overhangs the bumper insufficiently, vibration of the vehicle on the ramp may cause the upper edge to fall off the bumper with resulting damage to the vehicle and Injury to the driver.  
           [0004]    Similarly, a heavy load such as a large hay bale is manually loaded onto a truck bed only with great difficulty.  
           [0005]    It Is known to provide a hoist to assist in the loading or unloading of a truck, consisting generally of a cargo-carrying platform or container for resting on a truck bed and an arm for moving the platform between its travelling position on the truck bed and a loading position where it rests on the ground directly behind the truck. Thus, a heavy load can be readily pushed or driven onto the platform while the platform Is resting flat on the ground. The load is then secured and the platform hoisted onto the truck bed. An actuator such as a hydraulic ram, linked to an arm, moves a platform between the travel position supported on the truck bed and loading/unloading position resting on the ground. For example, U.S. Pat. No. 4,175,904 to Airaksinen discloses a container and associated hoist mechanism, whereby the container is moved by an arm between a position on a truck bed and resting on the ground directly behind a truck bed, with the hoist arranged for moving the container between the two positions. Similar arrangements are disclosed in U.S. Pat. No. 5,601,393 to Waldschmitt and U.S. Pat. No. 6,152,674 to Ogrodnick.  
           [0006]    It is desirable to provide a hoist, including an associated container or platform, suitable for use with a relatively light vehicle such as a light truck or pickup truck, which is also capable of bearing and hoisting a relatively heavy load such as a pair of snowmobiles.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention relates to an improved hoist which includes a moveable load-bearing platform which is moveable between a truck bed and a position resting at ground level, and further to a linkage arrangement for moving the platform.  
           [0008]    I have invented an improved hoist that will elevate a platform from the ground to an open bed of a truck such as a pickup truck. A vehicle such as a snowmobile, an A.T.V. and a riding mower can be driven onto the platform while the platform is resting solidly on the ground. The driver can then get off the vehicle and the platform. The hoist will then safely elevate the platform, bearing the vehicle resting on the platform and place these onto the open bed of the pickup. The vehicle is then In position to be transported on the pickup. Reversing the action of the hoist allows the vehicle to be unloaded from the pickup.  
           [0009]    Briefly the hoist of my Invention includes a moveable load-bearing platform, a framework adapted to be mounted on the open bed of a truck and having a longitudinally extending stringer; a cantilever arm pivotal relative to the stringer and being pivotally interconnected to the platform; and an actuator which is pivotal relative to the stringer and which, when retracting, causes the cantilever to pivot toward the actuator with resulting raising of the platform. The actuator comprises a longitudinally extending member such as a hydraulic ram. An arrangement of linkages connects the actuator with the cantilever arm to increase the leverage and “reach” of the actuator thereby permitting the actuator to be relatively short in comparison with the travel distance required of the cantilever arm. For example, it is desirable to provide a sufficient movement of the cantilever arm to lower the platform significantly below the truck wheels. This permits loading of watercraft, or of the platform on an irregular surface. The linkage arrangement comprises a first connecting link member interposed between the actuator and the cantilever arm, this first link member being pivotally joined at a first end to the actuator. The second end of the link member is pivotally engaged to the cantilever arm, at a point close to the pivot mount of the cantilever arm to the stringer. A second, generally upstanding anchoring link is pivotally mounted at its lower end to the stringer, at a point between the actuator and the cantilever arm. At its upper end the upstanding link is pivotally joined to the pivot mount joining the actuator and the first link. The actuator and first link form a scissors-like arrangement which unfolds as the actuator extends, thus increasing the “reach” and lifting force of the actuator. The second link serves to maintain longitudinal rigidity of the link system, i.e. to permit the horizontal thrust of the actuator to be transmitted to the cantilever arm.  
           [0010]    In one preferable version, the links are arranged such that they meet at an elbow junction at approximately a 90 degree angle when the actuator and cantilever arm are extended for depositing the platform at ground level. In this position, a retractive force of the actuator may be translated into an upward lifting action of the second link arm acting on the main cantilever arm. The second link arm joins with the cantilever arm at an angle of between 45 and 90 degrees when in this extended position, thereby enhancing the upward lifting and Inertial action of the actuator. This shallow angle is desirable to permit the first link to transfer the weight of the cantilever arm against the frame when the actuator retracts or extends.  
           [0011]    Preferably, the platform includes a at least one roller or wheel mounted at its distal end, to facilitate fore and aft movement of platform as the same as loaded and unloaded. A further desirable feature is fore and aft upstanding members at the respective fore and aft ends of the frame, for elevating and supporting the platform above the truck bed, thus permitting space between the truck bed and the platform for the various linkages and actuator. The rearward (aft) member desirably includes one or more rollers to ease the sliding of the platform over the rearward supporting member.  
           [0012]    Directional references such as “horizontal” and “vertical” are used for convenience of description. It will be understood that such references are used in relation to the device on a substantially horizontally-disposed truck, and that such terms also include a reasonable and mechanicallyeffective range of angles or positions.  
           [0013]    Expressions herein such as “substantially” or “approximately” in reference to dimensions and angles of the invention, cover a range of plus or minus 20% of any expressed length or 15° from any expressed angle. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0014]    The hoist of the invention is described with reference to the accompanying drawings and photographs. In the drawings:  
         [0015]    [0015]FIG. 1 is an elevation of the hoist in combination with a platform;  
         [0016]    [0016]FIG. 2 is a plan view of the lower framework of the hoist;  
         [0017]    [0017]FIG. 3 is an elevation of the hoist and the platform in position to be loaded;  
         [0018]    [0018]FIG. 4 is an elevation of the hoist and the platform in position to be transported;  
         [0019]    [0019]FIG. 5 is an elevation of the lower framework from the side;  
         [0020]    [0020]FIG. 6 is a plan view of a roller illustrated in FIG. 2, In enlarged scale;  
         [0021]    [0021]FIG. 7 is a perceptive view of the hoist position of the device, with the platform not shown, in perceptive, mounted to the bed of a pickup truck.  
         [0022]    [0022]FIG. 8 is a perceptive view of the device mounted in a bed of a pickup truck, showing in particular the platform portion.  
         [0023]    [0023]FIG. 9 is a plan view of a second embodiment of the hoist. 
     
    
       [0024]    Like reference characters refer to like parts through-out the description of the drawings.  
       DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0025]    With reference to FIGS. 1, 2 and  8  the hoist of the invention, generally  10 , is shown in conjunction with a platform, generally  12 . The hoist has a lower framework  11  which includes a pair of stringers  14 ,  16 , which are fastened to the open bed of a pickup  2  and extend longitudinally from the forward wall of the box adjacent to the cab of the vehicle to the rear edge of the bed. The lower framework is sized to conveniently fit within the bed of a pickup truck. It will be seen that the frame can be scaled up or down in size to permit mounting on a desired vehicle size. The frame is preferably removably mounted by the truck bed, for example by bolting to the truck bed. The invention is illustrated and described herein in association with a conventional pickup truck. It will be understood that any vehicle having a suitable bed will accommodate the invention.  
         [0026]    As illustrated in FIGS. 7 and 8, the rear gate of the pickup  2  is removed to accommodate the hoist and platform of the invention.  
         [0027]    A rod  18  extends between the two stringers. A cantilever arm  19  is pivotally mounted to the rod between the two stringers at first pivot mount  17 . The cantilever is a rigid unitary member comprising of three Interconnected segments, an inner segment  19   a , an intermediate segment  19   b  and an outer segment  19   c . The first angle, between the intermediate and outer segments is about 90 degrees while the second angle, between the Inner and intermediate segments is about 160 degrees. While the preferred first angle Is about 90 degrees, It Is contemplated that a range of angles would be suitable, for example, between 60 degrees and 120 degrees. An angle of substantially 90 degrees Is preferable to permit the cantilever to fit snugly against front wall of the platform  12  when the platform is in the “travel” position on the truck bed (e.g. FIG. 4). It will be seen that the platform may include a front wall which is canted away from the vertical, and this would lead to a preference that the angle of the cantilever arm between the intermediate and outer segments is correspondingly changed. The second angle, between the intermediate and inner segments of the cantilever, may range between 180 and 140 degrees. The provision of an angle at this position is desirable for permitting the arrangement of linkage, described below, to effectively operate. However, If the first angle is adjusted suitably to other than 90 degrees, it is contemplated that the second angle may be about 180 degrees. The cantilever arm may comprise a rigid metal beam, having a box-like or I-beam cross-sectional configuration.  
         [0028]    An actuator  22  is pivotally mounted to the stringers adjacent to their forward ends. As is conventional, the actuator is preferably a hydraulic cylinder  24  with a piston  26  which slides in the cylinder. The free end of the piston  26  is pivotally connected at  39  to first and second links  30 ,  32 . The first link is pivotally connected to rod  34  which extends between the stringers. The second link is pivotally connected to the cantilever at  36 .  
         [0029]    The links  30  and  32  are arranged to increase the lifting power of the actuator  22  for rotating the cantilever arm  19 . In particular, the purpose of the links is to convert a generally horizontal force of the actuator, into a substantially vertical force for retracting the cantilever arm, particularly when the arm  19  is in the fully extended position. For this purpose, the links are arranged such that the first link  30  is mounted to the frame at a position between the actuator and the cantilever arm pivot mount, and the second link  32  is mounted to the cantilever arm  19  at a position removed from its base  17 . As will be seen in FIG. 3, when the arm  19  is generally fully extended, the first and second links meet at a substantially right angle at pivotal interconnection  39 . The first link  30  is about the same length as the second link  32 , thereby permitting the links to be disposed at about the same angle (i.e. about 45 degrees from the horizontal), when the arm is in the extended position as seen in FIG. 3. This reasonably shallow angle permits the first link to transfer a forward thrust in an efficient manner to the frame, when the actuator is retracted. This permits the links to provide lift and inertia to the arm  19  as the actuator  22  is retracted (and similarly as the actuator  22  is extended to lower the arm  19 ). The linkage arrangement also makes it easier for the actuator  22  to be stopped at any position between the extended and retracted positions. It will be seen that a preferred system provides for the links  30  and  32 , and their respective contact points to be arranged such that the second link meets the segment  19 ( a ) at an angle of between about 350 and 90° from the vertical, when the inner segment  19 A of the arm  19  is horizontal. As suitable arrangement provides an angle of about 45°. It will however be seen that the right angle is not critical and the links may meet at a range of angles when the segment  19 A is horizontal and still serve their desired function. Further, the arm  19  may extend further downwardly from the position shown at FIG. 3, with the links  30  and  32  and actuator  22  rotating downwardly in a corresponding fashion. In effect, the first and second links define a folding arm with a pivotal elbow. The elbow is defined by pivot joint  39 , with the free end of the piston  26  being pivotally joined to the arm at the elbow joint. The elbow joint  39  may comprise a single pivot connecting the actuator arm and the two links, or alternatively it may comprise two spaced apart pivots.  
         [0030]    In one example, the extended actuator length is 47⅞ inches, the first link has a pivot-to-pivot length of 11.5 inches and the second link has a pivot-to-pivot length of 12 Inches.  
         [0031]    With reference to FIGS. 2, 5 and  6 , a transverse bar  40  extends upwardly from the forward ends of each stringer and a second transverse bar  42  extends upwardly from the rear ends of each stringer. The bars are mounted to upstanding supports  43 . Rollers  44 ,  46  are mounted at the upper ends of the latter bars. The bars  40  and  42  provide a support for the platform. The rollers are preferably journalled in a conventional roller bearing mount, on axles  49 . Axle mounts  47  support the rollers on the bar  42 . The rollers have a generally hourglass shape to permit the platform rails  61  to “track” on the rollers as the platform slides on or off the truck bed.  
         [0032]    The hoist illustrated in figures has a single cantilever. In a second embodiment, at FIG. 9, the hoist  90  has two cantilever arms  19  and associated actuators  22  and links  30 ,  32  In a paired side-by-side arrangement. The number of cantilevers is a matter of choice and will depend upon such factors as the proposed maximum loaded weight of the platform, the distribution of the weight and so on.  
         [0033]    With reference to FIGS. 3 and 8, the platform  12  includes side walls  52 ,  54 , a front wall  56 , a rear gate  58  and rollers or wheels  60 ,  62  which extend from the rear of the platform. A pair of side rails  59  forms part of the lower framework of the platform. The outer end of cantilever  19  is pivotally connected to the front wall of the platform by way of pivot mount  20 . The platform bed may include apertures to receive vehicle wheel blocks to prevent the carried vehicle from rolling. The platform may also include anchors to hold tie-downs to stabilize a load on the platform. The rear gate  58  swings open about either side or bottom-mounted hinges to permit a vehicle to be driven onto the platform or a load to be rolled or slid thereon. Alternatively, the rear gate  58  may be lifted out of side brackets  63  for complete removal.  
         [0034]    The elevated front and rear transverse bars  40 ,  42  to support the platform  12 , elevated above the linkages and hydraulic ram of the hoist.  
         [0035]    The operation of the hoist is as follows: The platform  12  is positioned to rest on the ground directly behind the truck. As seen in FIG. 3. For this purpose, the actuator  22  is extended, thereby rotating the arm  19  into its extended position. The load to be carried by the truck is then placed on the platform. If, for example, the load is a snowmobile or an A.T.V., the vehicle is driven onto the platform. The rear gate  58  of the platform is then closed. The vehicle, or other load, is secured to the platform by means of wheel blocks, tie downs or other suitable securing means.  
         [0036]    The actuator is then activated to retract the piston. As the piston retracts, the first and second links fold together and the cantilever arm is rotated forwardly. As the actuator  22  is retracted, the thrusting retractive force of the piston  26 , which is disposed in a near horizontal position, is converted by means of the links  30  and  32  into a generally upward retractive force in the manner explained above. The leading edge of the platform is drawn forwardly and upwardly, with the rails  61  of the platform sliding over the rollers  44 ,  46 , as illustrated In FIG. 1. The rear edge of the platform is supported by wheels  60 ,  62 . When the platform reaches the position illustrated in FIG. 1, the rails of the platform contacts rollers  44 ,  46  and the platform then rolls forward in the box of the pickup, with continued forward movement of the platform causing the wheels  60  and  62  to leave the ground until the platform is fully supported in a generally horizontal position on the transverse bars  40  and  42 .  
         [0037]    Preferably, a control unit  80  (see FIG. 1) is provided which controls the operation of the actuator. The control unit includes conventional controls from controlling a hydraulic ram, including a remote unit  82  (seen in FIG. 1 as connect4ed by a dotted line to the control unit  80 ) for actuation by a user standing a long side or behind the truck. The control unit may include an emergency shut-off switch which is triggered by e.g. a sudden increase in load indicative of a jam. The remote unit may include a “dead man” switch. The control unit and hydraulic ram are powered from the truck electric power supply, either by way of a cigarette lighter attachment or a dedicated electrical connection.  
         [0038]    When the outer segment  19   c  of the cantilever is vertical as illustrated in FIG. 4, the platform will be horizontal and fully supported by the bars  40 ,  42 . Preferably, the platform then will be retained within the confines of the truck bed and not overhang the truck edges.  
         [0039]    It will be seen that any suitable vehicle may be used in association with this invention for carrying the hoist, such as a flat-bed truck, a farm or construction vehicle, a towed vehicle such as a flat-bed trailer, and any other suitable vehicle.  
         [0040]    It will be understood that modifications can be made in the embodiments of the hoist illustrated and described herein without departing from the scope and purview of the invention.