EP2126368B1 - Pressure tank, in particular hydraulic accumulator - Google Patents

Abstract

A pressure tank, in particular hydraulic accumulator (3, 5), has a parting element (1) separating a space (11) for a first gaseous working medium from a space for a second fluid working medium in the tank. The parting element is flexible, can move under deformation and defines a domed main parting plane extending from an annular edge (13). The parting element (1) is produced from a substance having a fluoroplastic material, preferably a substance composed entirely of fluoroplastic material.

Description

The invention relates to a pressure vessel, in particular to a hydraulic accumulator, with a space in the container for a first, in particular gaseous, working fluid from a space for a second working medium, in particular a fluid, separating, resilient and deformable under deformation separating element, the one Defined by an annular edge, curved main-separating surface defined, wherein the separating element defines a curved main-separating surface, on whose relative to the curvature on the inner side annular bead-like elevations are formed protruding. By using such a curved membrane is in the pressure vessel, a relatively large partition available, which can cause a relatively large volume change of the adjacent working spaces in the pressure vessel with ease of deformability.

A generic pressure vessel is from the WO 02/075161 A1 known. The known hydropneumatic accumulator has a storage housing and a therein, a movable partition between a first space, in particular a gas space, and a second space, in particular a liquid space, forming membrane. The membrane has a plurality of annular areas, the annular, in the Type of joints acting weak points are connected to each other, wherein the ring areas on the side facing away from the wall of the storage enclosure inside of the membrane surveys, which in the central region between adjacent weak points the largest, the wall thickness of the membrane increasing height and one of these weak points towards each falling gently and at least have a convex shape in some areas. These weak points extend on the inside of the membrane along the circumferential line concentric circular lines. In the ring areas between the weak points are flat, bead-like elevations.

Out US 5,217,797 A is a suitable for a pressure vessel membrane has become known. The membrane is composed of a series of layers, a solid polytetrafluoroethylene (PTFE) layer and a layer of flexible plastic. Additionally, the composite membrane may comprise an elastomeric layer having concentrically disposed ribs. Alternatively, the elastomeric layer may be bonded directly to the PTFE solid layer which is bent using the membrane.

WO 98/55781 A relates to a membrane of a stiff, non-stretchable material having an outer chucking edge and a center movable transversely to its edge and having a profile which is incorporated in the surface of the membrane and which has wave, pleat or groove-shaped structures. Characterized in that the structure in the region lying between the edge and the center at an angle to both the circumferential direction and to the radial direction of the membrane and that the membrane delimits a three-dimensional cavity, act on the operation of the membrane laterally and transversely to running each other Compression forces each at the same time obliquely on the profile that is thereby compressed from different directions and compensates for both compressions, the volumetric cavity arrangement in particular makes the use of the membrane for hydraulic accumulators seem suitable.

WO 98/55782 A relates to a membrane with reusable compensation of compression for better operation. This is provided with a profile, which is aligned in particular in a central region in neither radial nor in the circumferential direction. The diaphragm also compensates for the compression, as in the past, but additionally the compression occurring at an angle. For example, grooves from the direction of the membrane edge extend spirally in an arc in the approximate direction to the membrane center. When the diaphragm is actuated, the compression forces acting laterally and transversely to one another act obliquely on the profile at the same time, thereby compressing them from different directions and compensating for both compressions.

A pressure vessel in the form of a hydraulic accumulator is in the DE 28 52 912 A1 disclosed. The resilient separating element, which in the known hydraulic accumulator consists of a rubber-like material (synthetic rubber, such as acrylonitrile-butadiene rubber) forms a deformable by deformation membrane which separates a gas side in the storage housing from a liquid side. There are two main requirements for the performance of hydraulic accumulators with such deformable membranes. On the one hand impermeability of the membrane must be ensured in order to avoid gas diffusion. On the other hand, corresponding mechanical properties of the membrane are required, in particular easy mobility and high bending fatigue strength, which are maintained even under the influence of aggressive media.

In the mentioned, known hydraulic accumulator these demands are only partially fulfilled. In order to improve the impermeability of the rubber-like membrane, in the known accumulator annular bead-like elevations projecting from the main separation surface, provided in close succession. Although the elevations increase the average wall density, although an improvement in the diffusion-tightness results, the substantial increase in the wall thickness leads to a considerable stiffening and consequently to a deterioration of the mobility.

In view of this prior art, the invention has the object to provide a pressure vessel, in particular hydraulic accumulator available, which in contrast is characterized by a significantly improved performance.

According to the invention this object is achieved by a pressure vessel having the features of claim 1 in its entirety.

Due to the fact that according to the invention a separating element is provided in the pressure vessel, which is made of a fluoroplastic material or preferably consists entirely of fluorine plastic material, on the one hand excellent diffusion tightness is ensured, while on the other hand a fuel element is available, the which has optimum mechanical properties such as extreme fatigue strength for use as a membrane in hydraulic accumulators. It can therefore be used very small wall thicknesses, resulting in the desired easy mobility of the membrane leads. Due to the resulting good response of the pressure vessel is therefore particularly suitable for use as a pulsation damper. A particularly suitable material is polytretafluoroethylene.

Polytetrafluoroethylene (PTFE) is not plastically moldable because of its very high melt viscosity, and the particular desired shaped body of this material is cold pressed from powdered raw material with 200 to 400 bar and sintered at 370 ° to 380 ° without pressure. If you want to receive films, they are regularly peeled off from cylindrical solid blocks. Accordingly, polytetrafluoroethylene is regularly marketed in the form of rigid solids in the trade such as plates, rods, tubes, etc. It is surprising to one of ordinary skill in the membrane art that he can still obtain wholly or partially made of polytetrafluoroethylene material separator elements which have a have such high mobility that they can even take over the function of a flexible rolling membrane.

Since PTFE materials also have a particularly good chemical resistance, the pressure vessel according to the invention is also suitable for use in the presence of chemically aggressive media.

According to the invention, the annular bead-like elevations are formed by folding, which are open on the outer side and here form annular groove-like recesses in the main separating surface. Corresponding to the height of the folds, in the case of a membrane formed in this way, as is the case with a bellows, a particularly large length of the material web is available, which can be moved in order to roll or extend the membrane.

In preferred embodiments, successive elevations are separated from each other by flat wall sections extending along the main parting surface. Therefore, there is a free space between adjacent ridges, which is available for relative movements of adjacent ridges, so that, without adjacent annular ridges would support each other and stiffen the structure, the separator may deform in the manner of a rolling diaphragm.

Preferably, the vertexes of the annular bead-like elevations have a circular curvature, so that notch effects are avoided.

Preferably, the arrangement here is such that the height measured from the open end to the apex of the folds along their vertical axis is different from at least one fold with respect to the height of other folds.

As has been shown, particularly good mechanical properties result when the first fold closest to the annular edge has a lower height than the subsequent further folds.

In this regard, it is also advantageous if the wall section extending from the annular edge to the nearest first fold has a wall thickness which has the largest value at the annular edge and drops to the first fold towards the value of the wall thickness of the wall sections between the folds. The edge thickening thus formed favors, without impairing the flexibility of the remaining membrane, the clamping of the membrane on the associated housing element of the pressure vessel and the formation of a sealing connection at the clamping point.

• Fig. 1 einen abgebrochen und leicht schematisch vereinfacht gezeichneten Längsschnitt eines Ausführungsbeispieles des erfindungsgemäßen Druckbehälters in Form eines Hydrospeichers, wobei lediglich der Bereich des Gehäuseunterteiles und ein angrenzender Teil des Gehäuseoberteiles zu sehen sind;
• Fig. 2 einen gegenüber Fig. 1 vergrößert und halbseitig gezeichneten Längsschnitt nur des als Rollmembran ausgebildeten Trennelementes des Ausführungsbeispieles von Fig. 1 und
• Fig. 3 eine gegenüber Fig. 2 weiter vergrößerte Teilansicht des in Fig. 2 mit III gekennzeichneten Bereiches.

The invention is explained in detail below with reference to the drawing. Show it:

• Fig. 1 a broken and slightly schematically drawn longitudinal section of an embodiment of the pressure vessel according to the invention in the form of a hydraulic accumulator, wherein only the region of the lower housing part and an adjacent part of the upper housing part can be seen;
• Fig. 2 one opposite Fig. 1 enlarged and half-lined longitudinal section only formed as a rolling diaphragm separating element of the embodiment of Fig. 1 and
• Fig. 3 one opposite Fig. 2 further enlarged partial view of the in Fig. 2 area marked III.

Of an embodiment of the pressure vessel according to the invention in the form of a hydraulic accumulator are in Fig. 1 only one lower housing part 3 with a concentric to Gehäuselärigsachse 7, bottom-side fluid port 9 and a part of the lower housing part 3 adjacent to the housing upper part 5 is shown. At the junction between the lower housing part 3 and the upper housing part 5 is the open, annular edge 13 clamped a separating element in the form of a designated as a whole with 1 rolling diaphragm. In this case, an edge thickening 21 of the rolling diaphragm 1 is supported, on the one hand, on an annular surface 22 of the lower housing part 3 and, on the other hand, abuts an O-ring 15, which in turn sits in an annular groove 20 on an axially projecting annular body 14 of the upper housing part 5.

Fig. 1 and 2 show the rolling diaphragm 1 in a fully unrolled or extended condition in which the in Fig. 1 located above the diaphragm 1 space 11, the gas side of the hydraulic accumulator, the largest volume and the fluid port 9, there is no fluid pressure, so that the membrane 1 rests against the inner wall of the housing part 3, wherein a central reinforcing bead 29 of the membrane 1, the edge of the Fluid terminal 9 overlaps and thus forms a mechanical safeguard against a depression of the membrane 1 in the fluid port 9 in the absence of fluid pressure.

FIGS. 2 and 3 clarify details of the rolling diaphragm produced from a PTFE material 1. Because of the very good diffusion-tightness of the PTFE material and the particularly good strength properties for the rolling diaphragm 1 only a small wall thickness of the membrane in their emanating from the annular edge 13 course is required, which domed main interface defined. From this main separation surface successive ring-bead-like elevations project inwards, which are not formed by beads in the form of solid body in the example shown, but are formed by folding, of which a first, the edge 13 nearest fold is denoted by 17 and the subsequent folds are each denoted by 19. How out Fig. 1 can be seen changes, starting from the wall thickening 21 at the annular Edge 13, the wall thickness in such a way that the wall thickness decreases to the first fold 17, namely to the thickness value of flat wall portions 23, which are respectively between the folds 17 and 19. In a practical embodiment, the wall thickness drops from the thickening 21 to the first fold 17 from a value of 1.2 mm down to the value of 0.5 mm, which is given at the successive wall sections 23 between the folds 17 and 19 respectively is. As Fig. 2 also shows, forms the edge thickening 21 on the inside of a kind of shell shape, a Teilumfassung of in Fig. 2 not shown O-ring 15 forms.

How out Fig. 2 It can also be seen that the wrinkle height measured along the vertical axis 25 is less in the first fold 17 than in the subsequent folds 19, which each have the same height, with all the folds 17 and 19 being circular at their apex. The folds 17 and 19 are open at the outer side with respect to the curvature, so that annular groove-like recesses 27 (see in particular FIG Fig. 3 ) are formed, each forming interruptions in the curvature of the main separation surface between the wall sections 23. How special Fig. 3 it can be seen, the clear width of the annular groove-like recesses 27 at the open end of the folds 17, 19 each substantially less than the measured along the vertical axis 25 pleat height, and indeed in the example shown, the height of the folds 19 about a factor of 4 larger.

Like also out Fig. 3 As can be seen clearly, the inner sides of the depressions 27 of the folds 17, 19 run slightly diverging towards the open end, so that the open end of the depressions 27 has a greater width than the bottom of the depressions 27 at the vertex area of the folds. As Fig. 2 shows, the vertical axes 25 of the folds 19 each extend approximately perpendicular to the tangential plane to the adjacent wall portions 23, while the vertical axis 25 of the first fold 17 is slightly inclined to this tangential plane, wherein the vertical axis 25 of the first fold 17 with the plane of the annular edge 13 forms an angle of about 10 °. In the subsequent folds 19, the vertical axes 25 are increasingly inclined from fold to fold to the plane of the edge 13.

In the present example, on the inside of the membrane 1 projecting annular bead-like elevations are formed by folding 17 and 19, resulting in a particularly easy mobility for curling the membrane. However, trained as a solid body, ring-bead-like elevations could be provided. It is possible to use unfilled PTFE materials or those with filler and / or filler combinations, as may be provided in a manner known per se with PTFE materials, for example when extreme temperature resistance or other special properties are desired. Glass fiber materials, carbon or metallic fillers may be considered among others.

From PTFE materials are semi-finished in many forms available, for example, blocks peeled from slabs, rods, rounds and the like. Due to the mechanical properties of finished products, such as the rolling membrane used in the pressure vessel according to the invention, can be prepared by machining of moldings, which in turn are pressed from powdered raw material and sintered. In particular, in the case of thin-walled products, shaping by blow-molding of a PTFE dispersion before sintering is also possible. Unless the in Fig. 1 obtained membrane ball mold is obtained from a polytetrafluoroethylene full body, this is then by machining of the green body into the separation membrane shape shown. In order to minimize the polytetrafluoroethylene waste produced during the cutting process, it is preferable to produce a preform body as a blank in a half-shell mold as a press mold.

The said polytetrafluoroethylene material as the fluoroplastic material may comprise both pure PTFE and modified PTFE and include both unfilled PTFE and PTFE compounds. For a modified PTFE material fillers, such as bronze, carbon dust, MoS ₂ and glass fiber and carbon fiber materials come into question. In addition to PTFE, other fluoroplastic materials include ethylene tetrafluoroethylene (ETFE), ethylene chlorotrifluoroethylene copolymer (ECTFE), polychlorotrifluoroethylene copolymer (PCTFE), perfluoroalkoxy copolymer (PFA), polyvinylidene fluoride (PVDF) and tetrafluoroethylene-perfluoropropylene (FEP).

Claims (9)

1. A pressure tank, in particular to a hydraulic accumulator (3, 5) comprising a resilient separating element (1) which can be moved with deformation and which separates a space (11) in the tank for a first, in particular gaseous working medium from a space for a second working medium, in particular a fluid, and which defines a domed main separating surface which extends from an annular edge (13) on the inner side of which in relation to the dome projecting annular bead-like elevations (17, 19) are formed, characterised in that the separating element (1) is made of a substance which has a fluoroplastic material, preferably consists entirely of fluoroplastic material, and that the annular bead-like elevations are formed by folds (17, 19) which are open on the outer side and form annular groove-like depressions (27) here in the main separating surface (27).
2. The pressure tank according to Claim 1, characterised in that succeeding elevations (17, 19) are separated from one another respectively by flat wall sections (23) which extend along the main separating surface.
3. The pressure tank according to Claim 1 or 2, characterised in that the peaks of the folds (17, 19) have a round dome.
4. The pressure tank according to any of Claims 1 to 3, characterised in that the height of at least one fold (17) measured from the open end to the peak of the folds (17, 19) along its vertical axis (25) is different relative to the height of other folds (19).
5. The pressure tank according to Claim 4, characterised in that the first fold (17) nearest the annular edge (13) has a smaller height than the adjoining other folds (19).
6. The pressure tank according to Claim 4 or 5, characterised in that the height of the folds (17, 19) is larger at least by a factor of two than the width of the annular groove-like depressions (27) formed, which width is measured on the open end of the folds (17, 19).
7. The pressure tank according to any of Claims 4 to 6, characterised in that the vertical axes (25) of succeeding folds (17, 19) run tilted by a small angle to one another.
8. The pressure tank according to any of Claims 1 to 7, characterised in that the flat wall sections (23) which extend between successive folds (17, 19) respectively have the same wall thickness.
9. The pressure tank according to Claim 7, characterised in that the wall section which runs from the annular edge (13) to the nearest first fold (17) has a wall thickness which on the annular edge (13) has the largest value and decreases toward the first fold (17) to the value of the wall thickness of the wall sections (23) between the folds (17, 19).

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