Patent ID: 6481202
Filing Date: 2002-11-19
Classification: B66C,F15B

Abstract:
A hydraulic circuit comprising:a) a first double-acting hydraulic cylinder having a bore, a piston mounted in said bore and forming a piston end of said cylinder, and a rod connected to said piston opposite said piston end and extending out of an exit end of the bore but being sealed at the exit end of the bore, thus forming a rod end of said cylinder, the cylinder having a first passageway in communication with said piston end and a second passageway in communication with the said rod end; b) a closed loop hydraulic pump having, during operation, a low pressure port in fluid communication with a low pressure side of the hydraulic circuit and a high pressure port in fluid communication with a high pressure side of the hydraulic circuit; c) a directional flow controller and hydraulic lines connecting the closed loop pump and the double-acting cylinder such that fluid from the pump can be directed to either said first or second passageways and fluid from the other of said first or second passageways is directed to return to the pump; d) a second hydraulic pump in fluid communication with the closed loop hydraulic pump so as to supply make-up hydraulic fluid to the low pressure side of the hydraulic circuit when said rod is being extended; e) a valve in fluid communication with the first passageway when the rod is being retracted to allow excess hydraulic fluid to flow out of the circuit; f) first and second pilot operated valves, the first pilot operated valve controlling flow of hydraulic fluid out of the first passageway and the second pilot operated valve controlling flow of hydraulic fluid out of the second passageway; and g) a cylinder directional control valve assembly connected to a charge pump which provides pressurized hydraulic fluid to operate the first and second pilot operated valves.