Metal deforming – With means to drive tool – Including pneumatic- or fluid-actuated tool support
Patent
1994-05-20
1996-03-19
Jones, David
Metal deforming
With means to drive tool
Including pneumatic- or fluid-actuated tool support
72407, 7245313, 100259, 267119, B21J 918
Patent
active
054995256
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a hydraulic drive for a press, in particular for a sheet metal forming press, said press comprising a press ram adapted to be moved up and down, and a hydraulically displaceable counter support, said counter support being adapted to be moved in a forward stroke in the direction towards the press ram via a hydraulic cylinder by means of a first hydrostatic machine, and said counter support being adapted to be moved by said press ram in a return or rearward stroke.
For example, DE-AS 20 43 967 discloses a sheet metal forming press having a press ram and a counter support and a hydraulic drive with the features mentioned above. In said known press a pump pumps oil into the hydraulic cylinder during the forward stroke of the counter support. As soon as the counter support has reached its end position, the supply of pressure medium from the pump driven by an electric motor to the cylinder is interrupted by means of control valves. When the counter support is displaced during the return stroke by means of the press ram, a certain pressure has to be maintained in the cylinder. It is generally known that for this purpose the pressure medium is drained into the pressure medium container or tank by means of a relief (or pressure limiting) valve, a flow control (or throttle) valve or a proportional valve. See for instance, EP 0 173 755 B1. When draining the pressure medium via the relief valve or via the flow control valve a large amount of heat is generated which gets lost without being used. Possibly even cooling has to be provided. This means additional cost for structural components.
SUMMARY OF THE INVENTION
It is an object of the present invention to create a hydraulic drive for a press, in particular for a sheet metal forming press, such that the energy balance sheet is improved with respect to prior art drives, i.e. the losses of unused energy are reduced.
This object is achieved for a hydraulic drive for a press, in particular for a sheet metal forming press by providing that the hydrostatic machine is designed as a pressure controlled machine, in particular, as a pressure controlled axial piston machine which is, in particular, adapted to be swivelled in both directions, and that at least during a part of the return stroke of the counter support pressure medium from the hydraulic cylinder flows across a second hydrostatic machine. Due to the pressure control of the first hydrostatic machine it is achieved that said machine supplies only the oil which is necessary to balance the leakage losses when the counter support has moved against an abutment at the end of the forward stroke, and that during the return stroke of the counter support the necessary pressure is maintained in the hydraulic cylinder. At the same time the energy which has been transferred by the press ram to the hydraulic cylinder can be retreaved by the second hydrostatic machine and can be used for driving the press ram or it can be fed into the electric power supply system.
Preferred embodiments of the hydraulic drive for a press are disclosed in the dependent claims.
Naturally, while the pressure medium flows from the hydraulic cylinder across the second hydrostatic machine, said machine is connected with a first port to the hydraulic cylinder. Depending on whether the pressure at the second port of the second machine is higher or lower than the counter support pressure in the hydraulic cylinder, the second machine operates as a hydraulic motor or as a hydraulic pump, wherein in both cases the balance sheet of the energy is improved. When operating as a hydraulic motor, the second machine supplies power. When operating as a hydraulic pump, less energy has to be supplied, inasmuch as the volume of the pressure medium coming from the hydraulic cylinder needs to be elevated to the higher pressure level at the second port of the second machine, i.e. starting already from the counter support pressure.
Preferably, the hydrostatic machine for the counter support is also provided with
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Kordak Rolf
Maxeiner Thassilo
Reinert Michael
Jones David
Mannesmann Rexroth GmbH
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