Hoist for loading and unloading objects on a truck bed

1. A pickup truck and a bolt-on removably mounted hoist unit for loading and unloading objects to said pickup truck bed from positions significantly lower than ground level;

said hoist comprising: a frame, a platform and a moving structure system;

said frame comprising two or more stringers for mounting adjacent to and overlying said pickup truck bed in a generally horizontal orientation when mounted and defining a substantially horizontal plane;

said platform being suitable for carrying an object, said platform being displaceable between a first position supported on said pickup truck bed and a second position rearwardly and downwardly displaced from said pickup truck bed;

said second position may be near or well below ground level to load or unload said object thereon;

said moving structure comprises a rigid L-shaped dog-legged cantilever arm, an extendible ram and a linkage system;

said rigid L-shaped dog-legged cantilever arm for moving said platform between said first and second positions having a first end pivotally mounted to said platform adjacent said upper first end of said platform and having a second end pivotally mounted to a rod extending between two said stringers at a point where said cantilever arm will not engage said pickup truck bed as said cantilever arm moves through a range of motion;

a single longitudinally extendible ram having first and second ends, said first end being pivotally mounted to a forward region of said frame, said second end indirectly connected to said cantilever arm for rotating said cantilever arm;

said cantilever arm having a 90 degree bend spaced from said first end thereof so that when said platform is in said first position, said cantilever arm extends generally vertically from said pivotal connection to said platform to a point below said platform and above said stringers where said cantilever arm extends generally horizontally below said platform; and,

said cantilever arm has a second bend spaced from said second end to position said second end of said cantilever arm at said pivotal attachment on said stringers;

a linkage system for indirectly connecting said second end of said ram to said cantilever arm, said linkage system comprising first and second elongate rigid links, a first pivot mount joining together said first and second links of said ram about a single axis of rotation, and second and third pivot mounts joining said first and second elongate rigid links to said stringers and said cantilever arm respectively, wherein said first and second links, a portion of said cantilever arm and said horizontal plane of said stringers respectively define four sides of a tetragon all four sides of which are pivotal relative to each other, said ram being positioned fully forward of said rigid links when folded, said first link being pivotally mounted to said stringers between said ram and said cantilever arm for rotating between a rearwardly leaning position when said ram is fully extended, an intermediate vertical position and a forwardly leaning position when said ram is fully retracted, and said second link directly joining the second end of said ram and said cantilever arm for transmitting force therebetween, said first link being positioned and configured such that in said rearwardly leaning position the angle between said first and second links is about 90 degrees; and

wherein extension and retraction of said ram actuates said linkage system and said cantilever arm to move said platform between said first and second positions.

2. The pickup truck and said bolt-on removably mounted hoist as defined in claim 1 , wherein said cantilever arm is generally L-shaped dog-legged comprising a longest central portion, a medium length first end portion of said cantilever arm being engaged to said platform, and a shortest length second end portion of said cantilever arm engaged to said stringers.

3. The pickup truck and said bolt-on removably mounted hoist as defined in claim 1 , wherein said links are arranged such that said angle between said second link and said arm is about 45 degrees when said arm is horizontal and extended rearwardly towards said second position.

4. The pickup truck and said bolt-on removably mounted hoist as defined in claim 1 , wherein said first and second rigid links are substantially equal in length.

5. The pickup truck and said bolt-on removably mounted hoist as defined in claim 1 , wherein said second rigid link is pivotally mounted to said arm at a position which is close to said second end of said arm relative to said first end.

6. The pickup truck and said bolt-on removably mounted hoist as defined in claim 1 , wherein said ram comprises a base with an extendible ramrod extending therefrom, said base being mounted to a forward end of said frame and said extendible ramrod opening to the rear of said frame.

7. The pickup truck and said bolt-on removably mounted hoist as defined in claim 1 , wherein said first and second rigid links form substantially a right angle when said arm is in said second position.

8. The pickup truck and said bolt-on removably mounted hoist as defined in claim 1 , wherein opposing sides of said tetragon are non-parallel.

9. The pickup truck and said bolt-on removably mounted hoist as defined in claim 1 , wherein said ram is exterior to said tetragon and extends forwardly therefrom.

10. The pickup truck and said bolt-on removably mounted hoist as defined in claim 1 having two or more extendible rams, each operatively attached to said cantilever arm and said linkage system.

11. A bolt-on hoist unit sized to operatively fit in the bed of a standard pickup truck for loading and unloading objects to and from said pickup truck bed and to and from positions at and significantly lower than ground level;

said hoist unit comprising: a frame, a moving structure system attached to said frame, and a platform movable by said moving structure system;

said frame comprising at least two stringers for mounting adjacent to and overlying said pickup truck bed and presenting a generally flat surface to said pickup truck bed when mounted and defining a substantially horizontal plane;

said frame is removably secured to said pickup truck bed by at least two bolts;

said platform being suitable for carrying one or more objects;

said platform being displaceable between a first position supported on said pickup truck bed and a second position rearwardly and downwardly displaced from said pickup truck bed;

said second position may be near or well below ground level to load or unload said at least one object thereon;

said moving structure comprising a rigid L-shaped dog-legged cantilever arm, an extendable ram, a control unit, hydraulic cylinder, actuator, and a linkage system powered from an electic power supply from said pickup truck; said rigid L-shaped dog-legged cantilever arm moves said platform between said first and second positions and has a first end pivotally mounted to said platform adjacent said upper first end of said platform and has a second end pivotally mounted to a rod extending between two said stringers at a point where said cantelever arm will not engage said pickup truck bed as said cantelever arm moves from said first position to said second position through a range of motion;

a single longitudinally extendible ram having first and second ends;

said first end being pivotally mounted to a forward region of said frame;

said second end indirectly connected to said cantilever arm for rotating said cantilever arm;

said cantilever arm having an approximately 90 degree bend spaced from said first end thereof so that when said platform is in said first position, said cantilever arm extends generally vertically from said pivotal connection to said platform to a point below said platform and above said stringers where said cantilever arm extends generally horizontally below said platform;

said cantilever arm has a second bend spaced from said second end of said cantilever arm to said position of said second end of said cantilever arm at said pivotal attachment at said stringers;

a linkage system for indirectly connecting said second end of said ram to said cantilever arm;

said linkage system comprising first and second elongate rigid links, a first pivot mount joining together said first and second links of said ram about a single axis of rotation, and second and third pivot mounts joining said first and second elongate rigid links to said stringers and said cantilever arm respectively wherein said first and second links, a portion of said cantilever arm and said horizontal plane of said stringers respectively define four sides of a tetragon all four sides of which are pivotal relative to each other;

said ram being positioned fully forward of said rigid links when folded;

said first link being pivotally mounted to said stringers between said ram and said cantilever arm for rotating between a rearwardly leaning position when said ram is fully extended, an intermediate vertical position and a forwardly leaning position when said ram is fully retracted, and said second link directly joining the second end of said ram and said cantilever arm for transmitting force therebetween, said first link being positioned and configured such that in said rearwardly leaning position the angle between said first and second links is about 90 degrees;

said extension and retraction of said ram by said actuator and said control unit actuates said linkage system and said cantilever arm to move said platform between said first and second positions;

an electric control unit controls a hydraulic cylinder of said actuator; and,

an electricly operated remote control is housed in a pendant unit which can be operated from plugs placed in a pickup truck cab and at safe positions outside said cab.