Power apparatus for truck loading elevator

Abstract

A dock lift has a platform connected at each side to a frame by a scissors apparatus. At one end, a pair of crossed hydraulic cylinders connect the platform and the frame. The hydraulic connections to the cylinders are made so that a load imposed on one side of the platform imposes a load on one cylinder which cylinder in turn causes fluid pressure to be applied to the other cylinder in the sense such that the other side of the platform is drawn downwardly to aid in maintaining the platform approximately level.

I claim:  .[.1. In an apparatus such as a dock lift or the like and for use with a source of hydraulic fluid under pressure, said apparatus comprising a frame having two sides and two ends, a vertically movable platform device above the frame and also having two corresponding sides and two corresponding ends, two pair of scissors means respectively connecting opposite sides of the frame and platform device, and power means at one end of the frame and connecting the frame and platform device for vertically moving the platform device with respect to the frame, the improvement comprising:.]. 
     
        on the other side of the platform..]. 2.  In an apparatus as set forth in claim .[.1.]. .Iadd.8.Iaddend., wherein the members attached to the piston rods are secured to the platform device, and said hydraulic cylinders each 
     
     
        are a single stage 3. In an apparatus as set forth in claim .[.1.]. .Iadd.8.Iaddend.. wherein said platform device includes a deck with an enclosure at said one end of the device and extending above the level of the deck, said enclosure extending between said sides and having a top and an open bottom, said hydraulic cylinders extending into said enclosure through said open bottom, the piston rod members being attached adjacent 
     
     
        said top immediately adjacent the respective  4.  In an apparatus as set forth in claim .[.1.]. .Iadd.8.Iaddend., wherein said power means includes a fluid supply line, a fluid discharge line, and four check valves, one check valve being between the supply line and the first conduit to permit flow only in the direction toward the first conduit, the second check valve being between the supply line and the second conduit to permit flow only in the direction toward the second conduit, the third check valve being between the first conduit and the discharge line to permit flow only in the direction toward the discharge line, the fourth check valve being between the second conduit and the discharge line to permit flow only in the direction toward the discharge line, and a manually operable valve 
     
     
        means in said discharge line to control the fluid flow therethrough 5.  In an apparatus as set forth in claim .[.1.]. .Iadd.4.Iaddend., wherein the source of hydraulic fluid is a fluid pump driven by an electric motor, said pump supplying fluid to said first and second check valves without the presence of an accumulator therebetween; and including control means connected to said motor to energize and deenergize the same;   whereby said platform is raised only by operating said control means to energize said motor.  .[.6. In an apparatus such as a dock lift or the like comprising a frame having two sides and two ends, a vertically movable platform device above the frame and also having two corresponding sides and two corresponding ends, two pair of scissors means respectively connecting opposite sides of the frame and platform device, and power means at one end of the frame and connecting the frame and platform device for vertically moving the platform device with respect to the frame, and for use with a source of hydraulic fluid under pressure, the improvement wherein said power means comprises:.].   .[.two hydraulic cylinders each having a closed end, a piston rod extending from the other end, a first hydraulic connection adjacent the closed end thereof, and a second hydraulic connection adjacent the other end thereof;.].   .[.two hydraulic fluid conduits, one of said conduits communicating with the first connection of one cylinder and the second connection of the other cylinder to provide fluid communication therebetween, the other of said conduits communicating with the second connection of said one cylinder and the first connection of said other cylinder to provide fluid communication therebetween;.].   .[.whereby a load imposed on said platform at a first side thereof will push down on the hydraulic cylinder connected to said first side of the platform which hydraulic cylinder will in turn act through the respective communication to energize the other hydraulic cylinder to apply a downward   
     
     
        pulling force on the other side of the platform..].  7.  In an apparatus as set forth in claim .[.6.]. .Iadd.9.Iaddend., wherein said power means includes a fluid supply line and a fluid discharge line, and four check valves, one check valve being between the supply line and the first conduit to permit flow only in the direction toward the first conduit, the second check valve being between the supply line and the second conduit to permit flow only in the direction toward the second conduit, the third check valve being between the first conduit and the discharge line to permit flow only in the direction toward the discharge line, the fourth check valve being between the second conduit and the discharge line to permit flow only in the direction toward the discharge line, and a manually operable valve means in said discharge line to control the fluid flow therethrough. .Iadd. 8. In an apparatus such as a dock lift or the like and for use with a source of hydraulic fluid under pressure, said apparatus comprising a frame having two sides and two ends, a vertically movable platform device above the frame and also having two corresponding sides and two corresponding ends, two pair of scissors means respectively connecting opposite sides of the frame and platform device, and power means at one end of the frame and connecting the frame and platform device for vertically moving the platform device with respect to the frame, the improvement comprising: said power means comprising two hydraulic cylinders each cylinder having a closed end, a piston rod extending from the other end of the cylinder and connecting members on the closed end and the distal end of the piston rod, one of said cylinders having one member thereof pivotally secured to the frame at one side and the second member thereof pivotally secured to the platform device at the other side, the other of said cylinders having one member thereof pivotally secured to the frame at said other side and the second member thereof pivotally secured to the platform device at said one side, each cylinder having a first hydraulic connection adjacent the closed end thereof and a second hydraulic connection adjacent the other end thereof, said power means including two hydraulic fluid conduits, one of said conduits communicating with the first connection of one cylinder and the second connection of the other cylinder to provide fluid communication therebetween, the other of said conduits communicating with the second connection of said one cylinder and the first connection of said other cylinder to provide fluid communication therebetween, fluid supply line means through which hydraulic fluid flows from said source when said platform device is to be raised and through which hydraulic fluid returns from said cylinders when said platform device is to be lowered, and means connecting the fluid supply line means and said conduits for preventing hydraulic fluid from flowing from said one of said conduits to said other of said conduits when the platform device is not being raised or lowered, whereby a load imposed on said platform at a first side thereof will push down on the hydraulic cylinder connected to said first side of the platform which hydraulic cylinder will in turn act through the respective communication to energize the other hydraulic cylinder to apply a downward pulling force on the other side of the platform. .Iaddend. .Iadd. 9. In an apparatus such as a dock lift or the like comprising a frame having two sides and two ends, a vertically movable platform device above the frame and also having two corresponding sides and two corresponding ends, two pair of scissors means respectively connecting opposite sides of the frame and platform device, and power means at one end of the frame and connecting the frame and platform device for vertically moving the platform device with respect to the frame, and for use with a source of hydraulic fluid under pressure, the improvement wherein said power means comprises:   two hydraulic cylinders each having a closed end, a piston rod extending from the other end, a first hydraulic connection adjacent the closed end thereof, and a second hydraulic connection adjacent the other end thereof;   two hydraulic fluid conduits, one of said conduits communicating with the first connection of one cylinder and the second connection of the other cylinder to provide fluid communication therebetween, the other of said conduits communicating with the second connection of said one cylinder and the first connection of said other cylinder to provide fluid communication therebetween;   fluid supply line means through which hydraulic fluid flows from said source when said platform device is to be raised and through which hydraulic fluid returns from said cylinders when said platform device is to be lowered; and   means connecting the fluid supply line means and said conduits for preventing hydraulic fluid from flowing from said one of said conduits to said other of said conduits when the platform device is not being raised or lowered;   whereby a load imposed on said platform at a first side thereof will push down on the hydraulic cylinder connected to said first side of the platform which hydraulic cylinder will in turn act through the respective communication to energize the other hydraulic cylinder to apply a downward pulling force on the other side of the platform..Iaddend.