Power plants – Pressure fluid source and motor – With control means for structure storing work driving energy
Reexamination Certificate
1998-09-29
2001-07-31
Ryznic, John E. (Department: 3745)
Power plants
Pressure fluid source and motor
With control means for structure storing work driving energy
C060S415000
Reexamination Certificate
active
06266959
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device for saving energy, while using hydraulically operated active working assemblies or tool shanks having a piston accumulator.
BACKGROUND OF THE INVENTION
Such energy-saving and energy -recovery devices, as disclosed in PCT/WO 93/11363 and DE 44 38 899 C1, use traditional hydraulic-pneumatic accumulators as energy reservoirs. In the energy recovery device disclosed in the PCT specification, the piston chamber of a hydraulically operable working cylinder is connected with the hydraulic accumulator through a cartridge valve. The cartridge valve cooperates with a control manifold connected to a pressure relay as part of a fluid control system. This fluid control system arrangement is in turn connected at its control input to a low-pressure branch of the hydraulic circuit, which cooperates with the displaceable parts of the working machinery in the form of active working assemblies or the like. With lowering of the active working assembly or the like, the fluid volume on the piston side of the working cylinder is integrated with the relevant available potential energy. The fluid is then discharged under pressure to the hydraulic reservoir/accumulator, and can be recycled from there precisely quantifiably for the subsequent lifting or raising process concerning the active working assembly to recover the energy introduced into the hydraulic accumulator. A good energy recovery ratio is attained with this arrangement, insofar as three or more working cylinders are used as hydraulically working active working assemblies. For all practical purposes three or more working cylinders are not used, especially with hydraulically operable machinery such as steam shovels or excavators or the like. Also, while holding the active working assemblies, the cartridge valves are inclined to be lowered under the effect of the load until they oscillate or flutter. The oscillating or fluttering leads to an undesired rocking of the active working assembly arrangement, usually in the form of a steam shovel, excavator or crane jib.
In DE 44 38 899 C1 such cartridge valves are abandoned in favor of hydraulic lockable check valves in a connecting conduit extending between the hydraulic accumulator and the hydraulic machinery to be operated. This arrangement is also of reasonable cost and functionally reliable. However, it has been shown in practice that with hydraulic operable working cylinders, upon discharge of the recovered energy with the associated volume of fluid, these cylinders are strongly influenced in a negative sense, which can lead to stoppages in the train of movement.
An operating device for a hydraulically operable working cylinder is disclosed in U.S. Pat. No. 2,721,446. Continuous operation maintenance for hydraulically operated cylinder is obtained through a hydraulic pump protected by a check valve. When interference and interruption occur in the sense of need for emergency/temporary supply, the piston accumulator using two longitudinally displaced pistons and working through the preloaded internal gas pressure in the preloaded chamber secures further hydraulic supply for the working cylinder and causes displacement of the same. The ambient atmosphere chamber of the known piston accumulator arranged at the opposite end of the preloaded chamber extends through a ventilation opening into the ambient atmosphere. A supply line is guided in the branch between the piston accumulator and the working cylinder, protected by means of the check valve in relation to the hydraulic pump, and allows for the resulting emergency/temporary supply to the working cylinder. The supply line does not allow for an erroneous hydraulic connection, such as would be possible with this known device, for a continuous energy savings during operation of the working cylinder. Thus, an undesirable temperature rise caused by compression in the air-filled ambient atmosphere chamber results and the fluid volumes to be controlled for emergency/temporary operation turn out to be correspondingly large, which is unfavorable from the point of view of savings of energy.
SUMMARY OF THE INVENTION
Objects of the present invention are to provide a device for energy savings in hydraulically operable active working assemblies, with expanded range of use, which does not include the aforementioned drawbacks.
The foregoing objects are basically obtained by a device for saving energy, comprising a hydraulically operable working assembly, a hydraulic pump and a piston accumulator. The piston accumulator includes a housing in which first and second longitudinally displaceable pistons are arranged and are connected facing one another by a coupling part. The coupling part is guided for longitudinal displacement in a partition wall of the housing. The housing and the pistons define first and second fluid chambers therebetween. The first piston at least partially limits a preloaded chamber with a predeterminable internal gas pressure on one side of the first piston, with the first fluid chamber being on an opposite side of said first piston. The first fluid chamber is being provided with a filter medium and is connected to said working assembly. The second piston at least partially limits an ambient atmosphere chamber of the piston accumulator. The ambient atmosphere chamber is connected in fluid communication to the working assembly and to the first fluid chamber. A reversible fluid control unit connects the second fluid chamber to the hydraulic pump.
By forming the device in this manner, the forcefully coupled pistons of the piston accumulator can be moved so as to cause the preloaded chamber to become smaller and to allow an increase of the internal gas pressure. The internal gas pressure decreases, in the sense of the release of tension, as soon as the pistons are moved in the other direction with a resulting increase of the volume in the preloaded chamber. The volume of gas enclosed in the preloaded chamber then forms a sort of force accumulator comparable to a mechanical spring. The movement energy introduced by the displacement movement in the accumulator can be recaptured by suitable operation of the reversible fluid control unit. Since the ambient atmosphere chamber of the piston accumulator additionally is fluid-carrying, undesirable heating occurring as a result of compression processes is thus avoided, and the required fluid volumes to be controlled for execution of a lifting process can be minimized, which is favorable in terms of saving energy.
Piston accumulators being used in the energy saving device belong to the family of hydraulic accumulators to which also belong bubble accumulators and diaphragm/membrane accumulators or reservoirs. One of the main purposes of these hydraulic accumulators, dependent upon the volumes of compressed fluid of a hydraulic system, is to receive and to feed this back, needed, into the system. The known piston accumulators thus include a liquid part and a gas part with a piston serving as gas-tight partition element, in which the gas side is filled with nitrogen. The liquid side of the piston accumulator remains in connection with the hydraulic circuit, so that with a rise of the pressure in the piston accumulator more liquid is received, and the gas is compressed on the gas side. With dropping pressure the compressed gas expands and thereby forces the stored compressed liquid into the hydraulic circuit. Piston accumulators can then basically be used at any site where a perpendicular arrangement is preferred with the gas side upward, so that deposition of contaminants out of the liquid onto the piston gaskets is avoided. As opposed to the diaphragm/membrane and bubble accumulators, the piston accumulator has no flexible partition element in the form of a rubber diaphragm or rubber bubble, but rather has a rigid piston, which hardly undergoes any wear and as with the device according to the present invention can work without breakdown even over very long time periods.
With use of the piston accumulator according to the present invention, as
Hydac Technology GmbH
Roylance,Abrams,Berdo & Goodman, L.L.P.
Ryznic John E.
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