Patent ID: 6581379
Filing Date: 2003-06-24
Classification: B22D,F15B

Abstract:
A pressure intensifying apparatus for a hydraulic cylinder comprising:a working cylinder; a pressure intensifying cylinder for allowing a pressure intensifying chamber to communicate with a head-side cylinder chamber of said working cylinder; a switching valve for controlling supply and discharge of a hydraulic fluid with respect to a head-side port and a rod-side port of said working cylinder; a first pilot check valve which is disposed in a head-side supply and discharge circuit for connecting said head-side port of said working cylinder to said switching valve and whose pilot pressure is a pressure of a rod-side supply and discharge circuit for connecting said rod-side port of said working cylinder to said switching valve; a check-valve equipped sequence valve which is disposed in a connection circuit for connecting a drive chamber side of said pressure intensifying cylinder to a portion of said head-side supply and discharge circuit closer to said switching valve than said first pilot check valve, and switches from a closed state to an open state with a rated pressure of a hydraulic pump for supplying said hydraulic fluid to said head-side supply and discharge circuit via said switching valve; and a second pilot check valve whose pilot pressure is said pressure of said rod-side supply and discharge circuit, said working cylinder, said pressure intensifying cylinder, said switching valve, said first pilot check valve, said check-valve equipped sequence valve and said second pilot check valve being connected in series in such a way as to satisfy K>PLa/Pp where K is a pressure intensifying ratio of said pressure intensifying cylinder, Pp is said rated pressure of said hydraulic pump and PLa is a pressure in said head-side cylinder chamber when a maximum load occurring after Pp is balanced with a load acting on a piston rod of said working cylinder in a piston-rod advancing step of said working cylinder is applied, and &Dgr;V=(PLaâˆ’Pp)Ã—VaÃ—&bgr; where &Dgr;V is a maximum discharge volume of said pressure intensifying chamber of said pressure intensifying cylinder, Va is a volume of said head-side cylinder chamber when balance is held and &bgr; is a compressibility of said hydraulic fluid.