Patent Publication Number: US-7591284-B2

Title: Hydraulic accumulator

Description:
FIELD OF THE INVENTION 
   The present invention relates to a hydraulic accumulator, in particular a piston accumulator, having an accumulator housing, and a separator piston movable in the longitudinal direction in the accumulator housing. The piston separates two working chambers from one another within the accumulator housing. The housing is closed on each end side by a cover part, at least one cover part on its one side being fixed by one free longitudinal edge of the accumulator housing, which edge is advanced onto this cover part for this purpose. 
   BACKGROUND OF THE INVENTION 
   Piston accumulators are in the broadest sense hydraulic accumulators used among other things to hold certain volumes of a pressurized liquid (hydraulic medium) of a hydraulic system and to return it if necessary to the system. Since the hydraulic medium is under pressure, hydraulic accumulators are treated like pressure vessels and must be designed for the maximum operating overpressure with consideration of the acceptance standards of diverse delivery countries. In most hydraulic systems at present hydropneumatic (gas-pressurized) accumulators with separating elements are used. For piston accumulators, the separating element is a piston within the piston accumulator housing, and separates a liquid chamber as the working chamber from the gas chamber as another working chamber. The working gas is generally nitrogen. The gas-tight piston largely permits decoupling from the gas chamber to the liquid chamber. 
   The liquid part is connected to the hydraulic circuit of the system so that when the pressure rises, the piston accumulator holds the hydraulic medium and the gas is compressed. When the pressure drops, the compressed gas expands and displaces the stored pressurized liquid back into the hydraulic circuit of the system. One advantage of a piston accumulator is that it can “work” in any position. A vertical configuration with the gas side up is preferred so that settling of dirt particles from the liquid on the seals of the piston part is avoided. 
   The important components of a piston accumulator are accordingly an external cylinder pipe as the accumulator housing, the piston as the separating element with its sealing system and the end-side sealing covers as cover parts containing a liquid port and a gas port, respectively. Generally the accumulator housing has two functions, first, storing the internal pressure, and second, guiding the piston within the accumulator housing. The cover parts close off the interior of the accumulator housing relative to the exterior on the end side are provided with an external thread on the outer peripheral side which can be screwed into a corresponding internal thread along the free longitudinal edge of the accumulator housing over a definable distance. Producing this threaded connection is time-consuming, making the production costs for a piston accumulator accordingly higher. Furthermore, safety measures must be taken to lock the added cover part in its position in the accumulator housing. 
   DE 103 03 988 A1 (corresponding to U.S. Patent Application Publication No. US 2006/0016074 A1) discloses avoiding the otherwise conventional threaded connections, and ensuring a reliable and secure connection of the cover part in the housing of the piston accumulator. For this purpose, in the disclosed solution on one side of the cover part it is fixed over the free longitudinal edge of the accumulator housing, which free longitudinal edge for this purpose undergoes a feed motion onto the cover part during the production process of the hydraulic accumulator. While avoiding the otherwise conventional screw connection solution for the respective cover part, a type of clamp seat on the respective free end of the accumulator housing is achieved. The cover part is clamped fast at least over the free longitudinal edge of the accumulator housing after its feed motion during production onto the cover part. In this connection, it is sufficient if part of the free longitudinal edge implements this clamping seat. 
   Although for the above-described hydraulic accumulator solution the cover part is provided with sealing means, especially in the form of gaskets, it cannot be precluded that especially at high pressures in the working chambers and/or for correspondingly long service lives the medium stored in the working chamber unintentionally travels to the exterior. Especially when using a working gas for the working chamber of the accumulator, it must be expected that portions of gas will travel to the exterior via the sealing means of the cover part. Viewed over the long-term, this gas escape degrades the operating reliability of the hydraulic accumulator. The degrading of the operating reliability occurs especially when the hydraulic accumulator with its sealing means is exposed to major temperature fluctuations of the magnitude of −40° C. to 130° C. This range of values causes the elastomer material of the sealing means generally to yield. 
   In the known hydraulic accumulator solutions, generally the possibility exists of adding working gas to the pertinent working chamber of the accumulator. This adding of has, however, is accompanied by the corresponding maintenance cost which is especially undesirable if the designed hydraulic accumulators are to be used in the form of a disposable solution on site within the hydraulic system only for a predetermined time. For the correspondingly designed hydraulic accumulator and depending on its application, it can be more economical to replace it terms of a disposable solution by a new one rather than maintain it on site. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide improved hydraulic accumulators that are largely media-tight on their gas sides so that they can also be designed as so-called disposables. 
   This object is basically achieved by a hydraulic accumulator with a gas-tight and/or fluid-tight sealing of at least one working chamber relative to the exterior. The associatable, advanced free longitudinal edge of the accumulator housing is connected to the respective cover part by a peripheral weld. Reliable sealing is obtained by the weld. Moreover, the weld provides a reliable connection between the free longitudinal edge and the respective cover part so that failure is reliably prevented, even when correspondingly high pressure peaks are experienced. On the whole, the connection stability for the accumulator solution can be increased by the peripheral weld. 
   The placement of the cover part in the accumulator housing, the preparation of a clamping seat between the free longitudinal end of the accumulator housing and the cover part, and the formation of the peripheral weld in the described region can be easily and economically accomplished. The described solution can then be implemented as a disposable concept without having to maintain these cheap accumulator solutions, especially not to refill them on the gas side with the working gas, but to dispose of them in case of maintenance or failure and replace them by a new cheap accumulator. 
   In one preferred embodiment of the hydraulic accumulator of the present invention, at least one of the two cover parts is provided on its one side with a conically extending fixing bevel against which the free longitudinal edge of the accumulator housing is advanced. Preferably, between the end of the free longitudinal edge of the accumulator housing and the fixing bevel of the cover part, a preferably V-shaped fillet groove is formed which holds the weld. This fillet groove dictates a guide path for the peripheral weld to be formed, and facilitates the weld production process accordingly. 
   In another preferred embodiment, V-shaped fillet groove is not provided with a welding filler. For example, with an electron beam welding process or other welding process suitable for this purpose, the facing edges, especially of the free longitudinal edge of the accumulator housing in addition to adjacent parts of the cover part, are welded on. These welded-on material parts then are able to fill the fillet groove accordingly. Generally, projection of the weld beyond the fillet groove should not then be expected. Depending on the materials used, welding on only the free longitudinal edge of the accumulator housing can be performed, leaving the material of the cover part essentially untouched. 
   In another especially preferred embodiment of the hydraulic accumulator of the present invention, the respective cover part which seals the working chamber with the working gas in the accumulator housing has a through opening at least for introducing the working gas. The trough opening can be sealed gas-tight by a terminating device. This terminating device can include a plug driven into the through opening. This terminating device leads to an especially economical solution. Alternatively, the terminating device can be formed from a detachable sealing cover allowing refilling processes for the hydraulic accumulator, especially on its side with the working gas. Regardless, hydraulic accumulators can be designed to be disposable at the site of their production or at central maintenance sites for re-use, and to refit them if failed parts can be replaced by new ones. 
   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, discloses preferred embodiments of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings which form a part of this disclosure and which are schematic and not to scale: 
       FIG. 1  is a partial, side elevational view in section of the top part of a piston accumulator according to a first exemplary embodiment of the present invention; 
       FIG. 2  are partial, side elevational views in section of cover parts of the piston accumulator used in  FIG. 1 , with a plug to be inserted; 
       FIG. 3  is an enlarged, side elevational view of the plug shown in  FIGS. 1 and 2 ; and 
       FIG. 4  is a side elevational view partially in section of the top and bottom part of a piston accumulator according to a second embodiment of the present invention, with an altered cover part, in addition to the attached closing cover. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The piston accumulator  10  shown in  FIG. 1  has an accumulator housing  10  formed as an outer cylinder pipe. The separating element is a piston (not detailed) with its sealing system on the outer peripheral side inserted into and movable longitudinally in housing  10 . These piston accumulators with pistons as the separating element are known in a host of designs, and are described for example in the state of the art in DE 103 03 988 A1. The piston within the accumulator housing  10  separates two working chambers  12 ,  14  ( FIG. 4 ) from one another, one or a first working chamber  12  being used to hold the working gas, especially in the form of nitrogen, and the other, second working chamber  14  forming the so-called liquid chamber for the piston accumulator. Depending on the operating situation of the accumulator, the movement positions of the piston and the volumetric portions of gas and fluid in the working chambers  12  and  14  vary. 
   On each front end of the accumulator housing  10 , there is one cover part  16 ,  18 . First cover part  16  has a gas port  20  in the form of a through opening  22  extending along the longitudinal axis  24  of the hydraulic accumulator and penetrating the first cover part  16 , and is the upper cover part, as viewed in  FIGS. 1 and 4 . The second cover part  16  has a liquid port  26  also extending coaxially to the longitudinal axis  24  for connecting the piston accumulator to a total hydraulic system. This gas port  20  in the form of a through opening  22  is used in turn to fill the accumulator with the working gas. The embodiment shown in  FIG. 1  fundamentally relates to a piston accumulator solution which, when the working gas is lost, is generally not refilled. The embodiment shown in  FIG. 4  relates to an accumulator which can be refilled with working gas. 
   To refit the hydraulic accumulator shown in  FIG. 1  or  4 , the cover parts  16  and  18 , with their sides  28  facing the inside are inserted into the accumulator housing against stops  30  in the form of offset, obliquely extending annular surfaces within the accumulator housing  10 . The outer side  32  of each cover part  16 ,  18  conversely is fixed via the free longitudinal edge  34  of the accumulator housing  10 . For this purpose, each longitudinal edge  34  undergoes a feed motion onto the respective cover part  16 ,  18 , as described below and in DE 103 03 988 A1. 
   For feed of each longitudinal edge  34  of the accumulator housing  10 , a shaping tool (not detailed) is used. The shaping tool is provided with a corresponding feed bevel which places or forces the longitudinal edge  34  on the respective cover part  16 ,  18  such that it is fixed as a clamp seat in the accumulator housing  10  between the respective stop  30  and longitudinal edge  34 . To prepare this clamp seat, one respective outer side  32  of the respective cover part  16 ,  18  is provided with a fixing bevel  36  tilted and tapering to the outside conically towards the longitudinal axis  24  of the accumulator housing  10 . The tilt or angle of this fixing bevel  36  corresponds generally to the feed bevel of the forming tool. Other tilts or bevels are also useable. 
   To achieve better deflection of the respective free longitudinal edge  34  around an articulation  38 , this longitudinal edge  34  has a reduced in wall thickness relative to the other wall parts of the accumulator housing  10  forming a main body portion between the free longitudinal edges. The transition site or articulation  38  between the different wall thicknesses forms the stop  30  for the respective cover part  16 ,  18 . The longitudinal edge  34  on its side facing the respective cover part  16 ,  18  and oriented to the exterior can be provided with an insertion bevel (not shown) extending especially conically to facilitate insertion of the respective cover part  16 ,  18  into the interior of the accumulator housing  10 . 
   In order not to endanger the secure position of the respective cover part  16 ,  18  in the accumulator housing  10 , and in order to prevent damaging application of forces, the end  40  of the respective free longitudinal edge  34  is guided such that it ends with its outermost exterior end essentially in one plane with the exterior  32  of the cover part  16 ,  18  extending transversely to the longitudinal axis  24  of the hydraulic accumulator. The indicated forming processes for the respective free longitudinal edge  34  can however proceed cold, as well as in a hot forming process. Conversely the material for the accumulator housing  10  can have correspondingly good workability, for example in the form of a conventional steel material. 
   To apply the respective clamping forces optimally to the associatable cover part  16 ,  18 , and to ensure good support in the accumulator housing  10 , on the edge side for the cover parts  16 ,  18 , the height of the respective cover part  16 ,  18  is matched to the conditions of use dictated by accumulator operation. Viewed in the direction of  FIGS. 1 ,  2 , and  4 , in one embodiment the height of the respective left half of the cover part  16 ,  18  is such that it is at least twice as great as the length of the longitudinal edge  34  between its free end  40  and the deflection site or articulation  38 . As shown in the respective right half of each figure, the height of the cover part  16 ,  18  can be reduced. This reduction applies especially when no engagement groove  42  for engaging a peripheral sealing means in the form of at least one gasket  44  is provided. When short service lives of the accumulator or low pressures are involved, the sealing means in the form of a gasket  44  located on the peripheral side in the respective cover part  16 ,  18  is not absolutely necessary. If the accumulator housing is made correspondingly large in diameter, the height of the cover part  16 ,  18  can be reduced accordingly relative to the length of the longitudinal edge  34 . 
   In all cases, a gas-tight and/or fluid-tight sealing of at least one working chamber  12 ,  14  is provided relative to the exterior. The respective advanced free longitudinal edge  34  of the accumulator housing  10  is connected to the respective cover part  16 ,  18  by a peripheral weld  46 . For positioning of the indicated weld  46 , a V-shaped fillet groove  58  is provided that between the end  40  of the free longitudinal edge  34  of the accumulator housing  10  and the fixing bevel  36  of the cover part  16 ,  18 . The weld  46  fills the fillet groove  48  with a projection, which viewed in cross section forms a convexly extending top  50  projecting over the top  32  of the respective cover part  16 ,  18  and the top of the free end  40  of the longitudinal edge  34 . The top  50  of the weld  46  protects beyond the respective end regions of the accumulator housing  10  and cover part  16 ,  19 , and visually enables checking to ensure a complete hermetic seal for a cleanly configured weld  46  in the fillet groove  48 . In another embodiment of the hydraulic accumulator of the present invention (not detailed), the weld  46  need not protrude over or beyond the groove  48  with a projection, but can end flush vertically with the top  32  of the cover part or can even be set back to the inside toward the accumulator housing  10 . A weld filling material can be placed in the V-shaped fillet groove  58 . Via a suitable welding process, such as an electron beam welding process, filling material can also melt-on the free end of the longitudinal edge  34  of the accumulator housing  10  to form the weld  46  via the melt addition of this material portion in the fillet groove  48 . Depending on the material selection, the respective cover part  16 ,  18  with its material portions can also contribute to formation of the weld. 
   With respect to the high volatility of the working gas in the working chamber  12 , this hermetic cover seal acquires special importance, relative to the gas side of the hydraulic accumulator. For the purpose of an economical solution shown in  FIG. 4 , on both sides of the accumulator housing  10 , the feed bevels over the longitudinal edge  34  are prepared at the same time by a shaping tool (not detailed). Since an especially gas-tight configuration in the region of the working chamber  12  is important, the fluid side of the accumulator with the working chamber  14  could have a different cover solution. Besides the additional sealing via the gasket  44 , simplified installation for the respective cover part  16 ,  18  is allowed since the gasket  44 , due to its elastic expansion, is able to keep the respective cover part on the inner periphery of the accumulator housing  10  in its installation position. In other configurations of the hydraulic accumulator, the sealing means in the form of a gasket  44  can be omitted, with sealing solely effected by the weld  46 . The gasket  44  can also perform the important sealing function, with the weld  46  serving as a holding means ensuring at high pressures that the free longitudinal edge  36  is not lifted off the respective cover part  16 ,  18 . 
   The cover part  16  sealing the working chamber with the working gas in the accumulator housing  10  is provided with a through opening  22  which can be sealed essentially gas-tight by a terminating means or terminator  52 . As shown in  FIG. 4 , on the opposing side of the accumulator housing  10 , the through opening  22  into the cover part  18  is a corresponding fluid passage site for connection of the accumulator to a conventional hydraulic system (not shown). In the embodiment shown in  FIG. 1 , the terminating means  52  includes a plug  54  shown enlarged in  FIG. 3 . The plug  54  is preferably formed of a ductile material, and in this way can be driven into the through opening  22  of the cover part  16  via a driving device (not shown). As a result of the completed deformation, the plug  54  remains adherent or fixed in the passage opening  22 , even if a corresponding high gas pressure is prevailing in the working chamber  12 . Preferably, the plug  54  be joined to the cover part  16  via a welding process, for example, a fiction welding process. For this purpose, which is not detailed, nitrogen filling of the working chamber  12  by a detachable means or connection is induced onto the top of the hydraulic accumulator, and sealed with the accumulator. The fixed connection is then produced via a friction welding means within the detachable means. 
   As seen in  FIG. 3 , the plug  54  has a stop head  56  larger in diameter than the cylindrical insertion part  58  projecting downward for engaging the through opening  22 . Between the stop head  56  and the insertion part  58  are conically tapering, bridge-like groove surfaces  60 . Each groove surface  60  partially widens on the bridge used for improved insertion into the through opening  22  and ensuring good adhesion to the respective interior wall of the through opening  22  so that unintentional disengagement, for example due to the gas pressure in the working chamber  12 , is precluded. Preferably, gas feed is ensured into the working chamber  12  via the recessed groove surface  60  with the plug  54  seated on the cover part  16 . In one step, the hydraulic accumulator is then filled with the active gas and the working chamber  12  is sealed via the plug  54  by the described friction welding process. With this sealing configuration by the plug  54  a reliable, cheap solution is achieved allowing the user to regard this hydraulic accumulator also as a disposable product, i.e., after one-time use to replace it by a new, comparable hydraulic accumulator and to accordingly dispose of the used one or return it to the manufacturer for recycling or to a maintenance shop. 
   The terminating means shown in  FIG. 4  differs from that of  FIGS. 1-3  in having a sealing cover  62  with a sealing means  64  in the form of a flat ring seal. The seal is guided on the end side on the inside of the sealing cover  62  on a corresponding offset receiver. This sealing cover  62  can be screwed onto a connecting part  66  penetrated by the through opening  22  and located as a cylindrical extension projecting from and beyond the cover part  16 . Preferably, for this configuration includes an engagement screw  68 , preferably in the form of an Allen screw, inserted into the through opening  22 . In addition to a media-tight termination, for example via an additional sealing element between the screw head and the engagement thread of the engagement screw  68 , the terminating means  52  by unscrewing the sealing cover  62  in addition to the engagement screw  68  allows a gas refilling process from the exterior to make the accumulator ready to operate again on site. 
   In  FIG. 2 , the cover part  16 ,  18  has between the engagement groove  42  for the sealing means  44  and the conically tapering fixing bevel  36 , an annular contact shoulder  70  projecting in the manner of a step over or beyond the remaining cover part  16 ,  18  with a small protrusion. This protrusion facilitates the folding-over process for the respective longitudinal edge  34  of the accumulator housing  10  in the manner of a flanging process. The conical surface parts extending toward one another in the form of a fixing bevel  36  with the longitudinal edge  34  and in the form of an articulation  38  form a reliable clamping seat for the respective cover part  16 ,  18 . 
   With the overall configuration in the region of the respective cover part  16 ,  18  including the end-side welds  46  and the sealing terminating means  52 , the hydraulic accumulator can be economically produced and satisfy the highest requirements with respect to its tightness. 
   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.