Power plants – Pressure fluid source and motor – With control means for structure storing work driving energy
Patent
1997-07-07
1998-12-29
Richter, Sheldon J.
Power plants
Pressure fluid source and motor
With control means for structure storing work driving energy
60421, 60484, 1002694, B30B 1516, F15B 100, F15B 1100
Patent
active
058529330
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a hydraulic drive system for a press, comprising a hydrostatic machine operating to maintain a substantially constant pressure in a fluid system and a hydraulic transformer.
BACKGROUND OF THE INVENTION
A system of this type is disclosed in German patent 32 02 015 owned by applicants. The system refers to a so-called secondary controlled drive system comprising a hydraulic transformer which is hydraulically connected to the fluid system in which a substantially constant pressure is being impressed. The transformer is defined by a pair of mechanically coupled hydrostatic machines each having an adjustable flow rate capacity. While the first hydrostatic machine is hydraulically connected to the fluid system, the second hydrostatic machine is hydraulically connected to a working cylinder. Accordingly, a secondary controlled drive system may be utilized for operating a working cylinder, resulting in a substantial saving of energy since the first hydrostatic machine connected to the fluid system of constant pressure only draws the amount of hydraulic energy from the fluid system which is required to satisfy the energy demand of the load, whereas in reverse the hydraulic energy being produced when the first hydraulic machine is operating as a pump, is returned to the fluid system to load an accumulator.
Generally, it is an aim of the present invention to operate a press cylinder of a hydraulic press in using a secondary controlled drive system of the type referred to. Principally it is known to subject both cylinder chambers of a press cylinder to a predetermined biasing pressure which is delivered by a separate biasing pump. For a press cylinder of the synchronizing type, i.e. a piston having equal annular piston area, identical biasing pressures readily result in both cylinder chambers. However, considering a differential cylinder, identical biasing pressures in the piston sided cylinder chamber as well as in the piston-rod-sided cylinder chamber may be produced by additional by providing at least a supplemental cylinder, i.e. the annular piston area of all cylinders should be substantially identical to the piston area of the press cylinder. This principle is known in fluid systems of different types.
SUMMARY AND OBJECT OF THE INVENTION
Accordingly, it is an object of the present invention to provide a drive system of the type referred to such that the biasing pressure may be produced in a simple and effective manner and that the losses in operating a press may be substantially reduced and, furthermore controlling press is simplified.
According to the invention, the press cylinder is hydraulically connected to the fluid system of the primary hydraulic machine, i.e. the fluid system in which an impressed pressure of substantially constant value is maintained, thus delivering the biasing pressure required for the press cylinder. According to the invention, the biasing of the press cylinder thus is provided free of any losses in tapping the constant pressure system which in combination supplies fluid to the first hydraulic machine of the hydraulic transformer. It is thus an advantage of the present invention to eliminate a separate biasing pump. Neither, the biasing pressure is produced by lowering a higher hydraulic pressure, for example by reducing a maximum operating pressure to the biasing pressure, nor by providing a special means as required in prior art systems. Furthermore, the supplemental cylinders required for a pressure balance of the press are also hydraulically connected to the fluid system of substantially constant pressure, i.e. the cylinder chambers of said supplemental cylinders are subjected to the biasing pressure. The supplemental cylinders are provided for acting in parallel to the press cylinder and the total sum of all annular areas of the cylinder pistons is equal or somewhat higher than the piston area in the piston sided chamber of the press cylinder.
The fluid system of substantially constant pressure is connected to the press cylinder through a ch
REFERENCES:
patent: 4235088 (1980-11-01), Kreiskorte
patent: 4707988 (1987-11-01), Palmers
patent: 4819429 (1989-04-01), Kordak
patent: 5460084 (1995-10-01), Ortremba et al.
patent: 5499525 (1996-03-01), Kordak et al.
patent: 5568766 (1996-10-01), Otremba et al.
Mannesmann Rexroth GmbH
Richter Sheldon J.
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