Abstract:
A device to save energy for hydraulically-operated tool shanks uses a piston-type accumulator having a housing in which at least two longitudinally displaceable pistons are arranged and are connected to by a coupling part. The coupling part is guided to be longitudinally displaceable in a partition wall of the housing which bounds two fluid chambers with the two pistons. At least one of the pistons bounds at least partially, a fluid chamber and a pre-loaded chamber with presettable internal gas pressure on the opposite sides. A wider range of possible applications is achieved for hydraulically-operated tool shanks using this energy saving device.

Description:
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 part of the energy saving device, it has been shown that in terms of energy and for saving of energy, it is especially favorable to associate a high internal gas pressure in the preloaded chamber with a middle piston or arm setting of the hydraulically operable active working assembly. The working assembly is slackened out of this middle position with discharge of energy, insofar as the arms is to be raised while under load. The energy saving device need not be limited to machinery, but rather can likewise be used in hydraulic braking assemblies, in cabin elevators and also with hydraulic engines or the like. In these cases, for the production of a small force constant or elasticity constant, it is a good idea to provide a large volume in the preloaded chamber. To attain this, an arrangement can be provided to connect the preloaded chamber to another gas supply arrangement, especially in the form of a nitrogen reservoir serving as a cushion. 
     Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, disclose preferred embodiments of the present invention. 
    
    
     BRIEF DESCRIPTIONS OF THE DRAWINGS 
     Referring to the drawings which form a part of this disclosure: 
     FIG. 1 is a schematic diagram showing the use of a piston accumulator in an energy saving arrangement for hydraulically operable active working assemblies or the like in the form of working cylinders according to the present invention; 
     FIG. 2 a side elevational view in a section of a first embodiment of the piston accumulator as shown in FIG. 1; and 
     FIG. 3 is a side elevational view in a section of a second embodiment of a piston accumulator which can be used in the circuit of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The piston accumulator shown in FIG. 2 has a housing, indicated in its entirety as  10 . Housing  10  is in the form of a cylindrical tube, but can also be configured of other cross sections (quadratic, elliptical). In housing  10 , two longitudinally displaceable pistons  12  and  14  are arranged and are connected with one another through a coupling part in the form of a solidly constructed coupling rod  16 . Coupling rod  16  is longitudinally displaceably guided on a partition wall  18  of housing  10 . Partition wall  18  is formed in the cylindrical middle segment of housing  10  and which, with two adjacent facing pistons  12  and  14 , defines two fluid chambers  20  and  22 . To seal off the two fluid chambers  20  and  22  from one another, the surrounding partition wall  18  incorporates corresponding round sealing gaskets  24 . Housing  10  is limited on the ends by two sealing walls  26  and  28 , which from the closing cover over the piston accumulator. Between left sealing wall  26  shown all the way to the left in FIG.  2  and the adjacent facing piston  12 , a preloaded chamber  30  is located. Chamber  30  is limited by these parts, and is set with the presettable internal gas pressure therein. 
     Fluid chambers  20  and  22  expand in diameter from partition wall  18  to the respective pistons  12  and  14  about a stage in which the coupling is constructed between pistons  12  and  14 . When one fluid chamber  20  has a small volume, the other fluid chamber  22  is proportionally enlarged to contain a correspondingly greater volume. Coupling rod  16  is configured to be solid, and is in tight contact or fixed engagement at the ends by means of screws  32  on the walls the respective pistons  12  and  14 . Pistons  12  and  14 , in conventional configuration, have exterior, suitably shaped, sliding gasket rings around their peripheries. Partition wall  18  is part of a tubular central support  34 . The ends of the central support are attached to the housing tube parts  36  of housing  10 , which serve for the longitudinal guiding of pistons  12  and  14 . In a radial or transverse direction relative to the longitudinal axis  38  and diametrically opposite and facing one another as well as limited by partition wall  18 , two connector plugs  40  and  42  extend through central support  34 , and open into the associated fluid chamber  20  or  22 . The H-shaped central support, as seen in FIG. 1, has a transverse section in the alignment of longitudinal axis  38 , and is inserted in turn in a sealed manner at both ends by gasket rings  44  into the two housing tubes  36  and fluid chambers  20  and  22 , sealed off from the surrounding atmosphere. Likewise, each of the two sealing walls  26  and  28  has a gasket ring  46  on the exterior periphery. 
     Sealing sheathings  50  serve for the setting of the sealing walls  26  and  28 . The sheathings, in turn are screwed into the free ends of the two housing tubes  36  to securely hold the sealing walls  26  and  28  in their positions shown in FIG.  2 . The respective connector plugs  40  and  42  open in turn in a cylindrical transverse passage  52 , with the coupling rod  16  passing therethrough, whatever the setting of pistons  12  and  14 . Passages  52  extend parallel to longitudinal axis  38  of the piston accumulator. For receiving screws  32 , as well as to adapt to the enlargement of preloaded chamber  30  and an opposing ambient atmosphere chamber  54 , each of the two pistons  12  and  14  has a hollow cylindrical middle cutout  56 . 
     Stationary sealing wall  26  of housing  10 , limiting the outside limits of the preloaded chamber  30 , has a connector plug  58 , which can be sealed off by a sealing plug (now shown). Following removal of the closing and sealing plug, the preloaded chamber  30  can be connected through the connector  58  to a gas supply device (cf. FIG.  1 ), especially in the form of a nitrogen reservoir  62 . The ambient atmosphere chamber  54 , which is limited by the other sealing wall  28  as well as by piston  14 , can be connected through a passage  64  to a supply line  66 . Housing  10 , with its two housing tubes  36 , defines and limits fluid chambers  20  and  22  around their exterior peripheries. 
     Preloaded chamber  30  is filled with a working gas, usually in the form of nitrogen, and is allowed a certain interior gas pressure. For the filling of preloaded chamber  30 , the closing plug need not be described in any more detail, and can be provided with a valve device  68  (FIG.  1 ). Valve device  68  allows gas passage in the direction of preloaded chamber  30 , but acting in the sense of a check valve blocks gas discharge. The gas in preloaded chamber  30  with presettable interior gas pressure consequently forms a gas or pressure cushion with a predetermined spring rigidity or elasticity constant, insofar as comparison to a mechanical model is made. The pressure cushion in this case, as compared with the mechanical model, forms a sort compression of pressure spring. If the two pistons  12  and  14  are displaced to their furthermost right positions in FIG. 2, piston  12  impacts on the facing end of the central support  34  and piston  14  contacts sealing wall  28 . Since ambient atmosphere chamber  54  is attached to supply line  66 , the fluid volume being stored in ambient atmosphere chamber  54  is forced out into supply line  66 . In the end setting which is reached in this moment, the preloaded chamber  30  then takes on its greatest volume as does also fluid chamber  22 , which can be filled with fluid through connector plug  42 . Fluid chamber  20 , preferably filled with air, and connector plug  40  which opens into the surrounding atmosphere, then takes in its smallest volume and the interior gas pressure in preloaded chamber  30  is diminished by the volume expansion taking place in preloaded chamber  30 , which is comparable in the mechanical model with slackening of the pressure spring. 
     In the reverse direction of movement, the volumes of preloaded chamber  30  as well as fluid chamber  22  decrease, and fluid chamber  20 , increases to its maximum possible volume. The gas in preloaded chamber  30  is correspondingly compressed and initially preloaded, so that it equals the tension of a mechanical spring. The gas or spring energy thus generated can then mandate the reaction, which is to be more clearly explained hereinafter, to assist in the operation of a hydraulic active working assembly or the like. In additional to the shown two-piston arrangement, still more pistons (not shown) can be used if necessary for further control procedures, which if necessary also increases the number of fluid chambers as well as preloaded chambers and other gas chambers. Also a plurality of piston accumulators could be connected in series either one after the other or in parallel. 
     FIG. 1 shows the use of the piston accumulator of FIG. 2 with a device for energy saving using a hydraulically operable active working assembly in the form of two hydraulic cylinders  70 . The two hydraulic cylinders  70  are working simultaneously in connection with one extended arm  74 , for example in the form of a crane or steam shovel or excavator arm, by means of their piston rods  72 . Arm  74  can also represent a lifting platform such as is used with freight elevators and personnel elevators as well as elevating platforms, insofar as these assemblies are displaceable by means of hydraulic cylinders. Instead of the two hydraulic cylinders  70  however a correspondingly constructed hydraulic engine can also be used to operate active working assembly. Furthermore, instead of the two hydraulically working cylinders  70 , one single working cylinder can be provided for the movements of extended arm  74 , which however is then moved back and forth with slightly lesser savings of volume. 
     On the rod side, the two hydraulic cylinders  70  are connected through a connection line  76  to each other and to a fluid-carrying to a fluid control unit  78 , which for example can be a controllable valve unit in the form of multi-way valves or the like. A motor-powered hydraulic pump  80  is connected to fluid control unit  78  as well as a tank conduit  82  leading to the tank  84 . On the discharge side, fluid control unit  78  has another fluid-carrying connection line  86 , which opens into the second connector plug  42 . The first connector plug  40  of fluid chamber  20 , in the embodiment shown in FIG. 1, is connected to the supply line  66 , and through this supply line  66  with ambient atmosphere chamber  54 . In such case, fluid chamber  20  is filled not with air, but rather with hydraulic fluid; supply line  66  is also filled with hydraulic fluid, and is connected through branch  66   a  with the hydraulic active working assembly in the form of the two hydraulic fluid-carrying cylinders  70 . With the movements of pistons  12  and  14  in the direction of fluid-filled ambient atmosphere chamber  54 , chamber  20  cannot then come under the pressure present in the air, and consequently cannot reach an undesired state of heating. Also, in the latter case, the fluid volumes to be controlled can be reduced or minimized for the execution of a power stroke. Supply line  66 , as well as a branch  66   a , open according to the representation of FIG. 1, into another fluid-carrying connection line  88 , which is bifurcated in the direction of hydraulic cylinders  70  and is connected to hydraulic cylinders  70  on piston ends  90 . 
     The energy saving arrangement is now set in such a manner that an average load setting or extended arm positioning of extended arm  74  in preloaded chamber  30  generates an interior gas pressure increase to the maximum possible pressure, which corresponds to a pre-biased mechanical compression spring. If extended arm  74  should now be lifted, in other words raised upward as shown in FIG. 1, hydraulic pump  80  is connected and through fluid-control unit  78  conveys pressurized fluid through connection line  86  and second connector plug  42  into fluid chamber  22 , whereby pistons  12  and  14  are moved to the right in FIG.  1 . The fluid stored in fluid chamber  20  of the piston accumulator, together with the fluid out of ambient atmosphere chamber  54 , is discharged through branch  66   a  or connection line  66  as well as the other connection line  88  on piston sides  90  of hydraulic cylinders  70 , whereby the pressure cushion in preloaded chamber  30  supports this movement process; and the energy stored in preloaded chamber  30  is discharged through whatever fluid-carrying arrangement leads to extended arm  74 . On piston rod sides  72  of working cylinders  70 , the fluid volumes expelled in such a manner are relieved of pressure through connection line  76  to fluid control unit  78  and then to tank  84  through connection line  82 , without pressure. 
     An accumulating process to accumulate hydraulic energy in preloaded chamber  30  then occurs with lowering of arm  74 , whereby the fluid stored on each piston side  90  is fed back again into fluid chamber  20  and also ambient atmosphere chamber  54 , with the result that pistons  12  and  14  move to the left in FIG.  1  and the preloading in preloaded chamber  30  increases. An especially favorable lift process can be further supported with movement of extended arm  74  around a midpoint. Insofar as extended arm  74  is to move with working machines, the gas supply arrangement  62  in the form of the nitrogen accumulator can be deleted. If, however, because it has to do with extended arm  74  moving around a lifting platform, the force constants or elasticity constants are lowered, in order to attain a uniform energy discharge over longer movement paths, the chamber volume of preloaded chamber  30  is increased through the connection of accumulator  62 . Furthermore, by switching fluid control unit  78 , the rod-side of each hydraulic cylinder  70  is filled under pressure through hydraulic pump  80 , which simplifies the lowering procedure as well as the increase of gas pressure in preloaded chamber  30 . 
     Another piston accumulator is shown in FIG. 3, which, similar to the piston accumulator embodiment of FIG. 2, is suitable for this energy-saving purpose, in which an energy saving device as shown in the diagram of FIG. 1 can be used the same structural parts of the piston accumulator as in FIG. 2 are indicated with the same references but increased by 100, when they are arranged according the representation of FIG.  2 . The statements made in reference to the embodiment of FIG. 2 consequently correspond to the embodiment of the piston accumulator of FIG.  3 . In the following, only features of the FIG. 3 embodiment which differ essentially from the embodiment as described in FIG. 2 are described. 
     In the embodiment of FIG. 3, the sealing walls  126  and  128  are constructed of one piece and are screwed together on the interior of the housing tube  136 . Connector plugs  140  and  142  open in one direction, in other words in the downward direction, as shown in FIG. 3 out of the interior of housing  110 . The two-part partition wall  118  in turn can adapt to a hollow cylindrical central member  134  and they engage mutually one into the other, whereby the tight connection is realized by a screw connection  192 , engaging through flange-like extensions of the central member of the two-part partition wall. Moreover, the cylindrical middle cutouts  156  in pistons  112  and  114  are arranged in coaxial alignment with the longitudinal axis  138 , as well as facing toward one another. Consequently, an expansion of the volume of fluid found in chambers  120  and  122  takes place. 
     The two embodiments of a piston accumulator as shown both in FIG.  2  and FIG. 3 show a partial arrangement arranged essentially symmetrical to a middle axis and to its longitudinal axis  38  or  138 . This allows for cost savings in the use of a plurality of piston accumulators using lower and cost standard structural parts in their manufacture. 
     While various embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.