Power plants – Pressure fluid source and motor – With control means for structure storing work driving energy
Patent
1997-11-18
1999-01-05
Nguyen, Hoang
Power plants
Pressure fluid source and motor
With control means for structure storing work driving energy
F16D 3102
Patent
active
058551140
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an arrangement in a pressing tool for sheet metal forming in order to shut off or retard an oil flow in a hydraulic system in coordination with the closing and opening movements of the said tool.
In sheet metal forming operations, for example, it is usual to arrange a passive hydraulic system in the pressing tool. This is done in order to be able to shift some of the pressing force to another position and another direction, for example in order to be able to perform yet another operation in the same tool. Such a system can be achieved by arranging a primary hydraulic cylinder/piston unit in a lower tool half in such a way that the piston is pressed into the cylinder when the tool is closed. The oil flow from the primary hydraulic cylinder/piston unit can thus be used in order to produce a stroke in a secondary hydraulic cylinder/piston unit. The timing of the said stroke coincides with the closing of the tool.
In certain cases it is desirable to be able to freely determine the point in time at which the secondary force/movement is to act. Where a passive system of the above-mentioned type is used it is therefore desirable to be able to retard the oil flow between the primary and the secondary hydraulic cylinder/piston unit. Such a retardation is already known. This retardation is achieved by allowing a primary hydraulic cylinder/piston unit arranged in a lower tool half of a pressing tool to act in opposition to a gas-filled spring arranged in an upper tool half. A valve is arranged and designed to selectively permit a flow between the primary and the secondary hydraulic cylinder/piston unit. By keeping the valve closed when the tool is closing, the gas-filled spring in the upper part of the sheet metal forming tool is compressed against the piston rod of the hydraulic cylinder/piston unit. The said piston rod is not pressed into the cylinder when the tool is being closed, but only when the valve is opened after predetermined delay. The gas-filled spring then presses the piston rod into the cylinder so that the oil flows from the latter to the secondary hydraulic cylinder/piston unit, which can then supply force and movement. One limitation to the solution described is that the pressing tool must be in the fully closed position in order to be able to supply a satisfactory oil flow. This means that the time at which the secondary force/movement will act cannot be determined with complete freedom.
The object of the present invention is to produce an arrangement which can shut off or retard an oil flow in a hydraulic system in a pressing tool for sheet metal forming for an arbitrarily chosen period. This object is achieved according to the invention in that it comprises: a non-return return valve designed, when the tool is being closed, to permit a flow in one direction from a primary hydraulic cylinder/piston unit, which is thereby compressed, to a pressurised accumulator; a first valve designed to selectively permit a flow between the accumulator and a secondary hydraulic cylinder/piston unit, which is designed as a consequence of such a flow to move from a compressed basic position to an expanded position; and parallel with the non-return valve a second valve, designed so that when the primary hydraulic cylinder/piston unit has been relieved by opening of the tool, it will selectively permit a return flow to the primary hydraulic cylinder/piston unit from the accumulator or, if the first valve is also made to open, from the secondary hydraulic cylinder/piston unit, which is designed to be then returned to the compressed basic position, and wherein the accumulator is of dimensions sufficient to accommodate the oil which is in the system when both the hydraulic cylinder/piston units are compressed.
According to a special characteristic of the invention, the pressure in the accumulator is always equal to or greater than the working pressure in the hydraulic system.
According to a further special characteristic of the invention, a piston which separates the oil from pressure ge
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Nguyen Hoang
Stromsholmen AB
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