Device to control a lifting cylinder

Claim 1

In a system for pivotally lifting and lowering a load along a path such that the load moves through a point at which the center of gravity of the load is above the axis of pivotal movement thereof; said system being of the type including a double-acting lifting cylinder connectable to a load, a fluid pump, first and second fluid conduits leading from said pump to first and second chambers of said lifting cylinder for selectively pumping fluid under pressure through one of said fluid conduits into one of said chambers to selectively move said load and for returning fluid from the other of said chambers through the other of said fluid conduits to said pump, and a control device communicating with said first and second fluid conduits for controlling the quantity of fluid returned to said pump; the improvement wherein said control device comprises: a housing; a control piston slidably positioned within said housing and defining therewithin a pair of primary chambers; means for connecting each of said primary chambers to said pump; means defining a pair of auxiliary chambers within said housing, one each of said auxiliary chambers being connected to one of said first and second fluid conduits; a pair of restricted orifices respectively connecting one of said primary chambers with a corresponding one of said auxiliary chambers; a pair of valve means, one each in one of said auxiliary chambers, and means for biasing said valve means to normally close said restricted orifices when said pump is not operated; a pair of valve actuator means, separate from said valve means and said control piston, one each mounted within one of said restricted orifices, alternately contactable by said control piston upon movement thereof, for opening a respective of said valve means; whereby, when said pump supplies fluid under pressure into a first of said primary chambers, said fluid opens a corresponding first said valve means and passes through the corresponding first auxiliary chamber into a corresponding first chamber of said lifting cylinder, and said fluid simultaneously moves said control piston toward a second of said primary chambers, thus contacting the respective second valve actuator means and opening the respective second valve means, thereby allowing fluid from the second chamber of said lifting cylinder to pass through the second auxiliary chamber, said second restricted orifice and said second primary chamber and be returned to said pump; a pair of compression means, one each positioned in one of said primary chambers, for restricting movement of said control piston proportional to the pressure of fluid supplied by said pump to said first primary chamber; and each said valve actuator means having a first end portion of uniformly enlarged diameter slidably mounted in said housing adjacent said orifice and abutting said valve means, a second end portion, adjacent said control piston, of a uniformly reduced diameter, and an intermediate portion having a tapering cross-section of a tapered diameter increasing toward said valve means and positioned within said restricted orifice, thus forming means for controlling the amount of returned fluid proportional to the amount of movement of said control piston.