Separation element and hydraulic accumulator comprising said separation element

Abstract

A separation element, in particular for bellows-type accumulators, manufactured by a 3D printing method, which, when viewed in cross section, consists of a single membrane that is turned in an arc at turning points 30 to form a number of bellows folds 28, which turning points 30 limit the bellows folds 28 on the outside and on the inside, and in which the imaginary extensions 32 of adjacent membrane surfaces 34 that border each turning point 30 form an acute angle α with each other, at least in the initial state, in order to obtain an isotensoidal or substantially isotensoidal stress profile in the membrane.

Description

[Technical field]

[0001] The invention relates in particular to a separating element for a bellows-type accumulator, which, when viewed in cross section, consists of a single membrane which is turned in an arc at turning points to form a number of bellows pleats, these turning points defining each bellows pleat on the outside and on the inside. [Background technology]

[0002] From DE 100 09 865 A1 a hydropneumatic accumulator, in particular a pulsation damper, designed in the form of a bellows-type accumulator is known, which has at least an accumulator housing including a fluid chamber for containing a gas charge that generates a preload pressure and another fluid chamber for containing a hydraulic medium; a metal bellows separating the two fluid chambers from each other, one end of which is closed by an end plate and the other end of which is connected to an accumulator housing, the interior of which forms a separate fluid chamber for the hydraulic medium; a passageway formed in a wall of the accumulator housing and opening into another fluid chamber; and a stop device for limiting the movement of the end plate of the metal bellows.

[0003] The stop device, which has one stopper each on the inside and outside of the end plate of the metal bellows, provides mechanical stroke limits for both the contraction and extension of the isolation bellows, effectively protecting the metal bellows from excessive loads and allowing it to maintain its functionality even after long-term use.

[0004] To obtain a one-piece metal bellows, a thin-walled tube is first manufactured as the starting material for the membrane, which can be produced by longitudinal seam welding in an endless manner. This tube cylinder must then be formed into a bellows, in which case annular corrugations must be formed as bellows pleats. This is mainly done by hydroforming. It is also possible to obtain corrugated bellows by mechanical roll forming.

[0005] However, both manufacturing methods have in common that the bellows pleats are manufactured individually, one after the other, from a solid material, with each pleat having a circular, in particular semicircular, cross-section at the respective turning point. The known bellows manufacturing method essentially prevents a reduction in wall thickness, which would affect the service life of the bellows, for example in the region of turning points with a circular pattern. However, it has the disadvantage that for each size of the separating bellows, which is a continuous individual membrane, a tube of the corresponding size must first be manufactured, which increases the manufacturing costs. Furthermore, since in the initial state before the membrane extension movement, the membrane surfaces associated with the bellows pleats run parallel to one another, during the operation of the separating bellows, the numerous expansion and contraction processes introduce unfavorable stresses into the membrane material, which, at least in the long term, are likely to lead to material failures, especially in the region of the turning points.

[0006] Furthermore, from DE 10 2006 014 456 A1 a hydraulic accumulator is known which has an accumulator housing in which a metal bellows with a number of individual membrane discs is arranged, the edges of which are interconnected by welded seams, so that the metal bellows forms a movable separating element between the gas side and the fluid side, the volume of which is variable by axially expanding or compressing the metal bellows in the accumulator housing. At least in part of the membrane disc, the weld seam is dimensioned in such a way that the thickness of the weld seam measured in the thickness direction of the membrane disc is at most equal to the total thickness of the membrane disc to be welded, resulting in a much more favorable loading state for the membrane disc than if the metal bellows were completely compressed by a pressure difference created by a high external pressure, as shown in other prior art.

[0007] In known solutions, circular membrane disks can also be welded together to form hollow cylindrical metal bellows, which have a corrugated profile between the pointed weld seams, each extending concentrically with the longitudinal axis of the metal bellows. When such a corrugated membrane disk is "blocked" with an adjacent membrane disk that is similarly constructed and welded, the metal bellows are fully compressed and the corrugated membrane disks bear against each other in a particularly advantageous manner, so that lateral forces that may then occur do not unintentionally cause the membrane disks to slide against each other, which could lead to failures in the region of the weld seams. Of course, despite the additional safety provided by such corrugations, failures cannot essentially be excluded, taking into account the large number of weld seams, even if they are produced by modern laser welding equipment. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] German Patent No. 10009865 [Patent Document 2] DE 102006014456 Summary of the Invention [Problem to be solved by the invention]

[0009] The object of the present invention is to proceed from the prior art and to provide a separating element, in particular for use in hydraulic accumulators, which can be manufactured simply and inexpensively and which operates without faults for a long period of time. [Means for solving the problem]

[0010] The above problem is solved by a separating element having the features of patent claim 1 in its entirety as well as by a hydraulic accumulator having the features of patent claim 10.

[0011] According to the invention, the separation elements consisting of integral individual membranes are produced together with the individual bellows pleats by 3D printing or additive manufacturing. In this case, the so-called electron beam melting method has proven to be particularly suitable as a 3D printing method. In electron beam melting, a metal powder is melted layer by layer and transferred together with the bellows pleats as a separation element. Selective laser melting, in which the metal powder is melted only locally, is also suitable. It is likewise possible to use selective laser sintering, in which the metal powder is briefly heated by a laser to melt it and then solidifies again to form the metallic separation element. All the above-mentioned 3D printing methods belong to the genres of sintering and powder printing in the broadest sense.

[0012] Each separation element can be obtained individually as a three-dimensional object by layer-by-layer shaping of the membrane material, allowing mass production in large numbers. In this way, the separation elements are obtained simply and cheaply, without the need for hydroforming, roll forming and / or welding processes.

[0013] Furthermore, it has been shown that the combination of the 3D printing method with the special geometric shape of the separating element, in which the turning points of the bellows pleats are formed in the shape of a circular arc in cross section and the virtual extensions of the adjacent membrane surfaces that respectively border at each turning point form an acute angle with respect to each other at least in the initial state, allows an isotensoid or substantially isotensoid stress profile to be achieved in the membrane in each operating state of the separating element, as a result of which material-damaging overloads are avoided even in dynamic operation, for example within the scope of conventional hydraulic accumulator applications. Designing the individual bellows pleats with circular or rounded turning points leads to a uniform stress introduction and stress distribution in the entire membrane, even in dynamic operation.

[0014] For a favorable stress profile in the membrane-like separation element, it has proven to be advantageous if the turning points each have a circular arc shape in cross section, at least partially formed from a semicircular arc, whereby it is furthermore advantageously provided that the acute angle between the two initially adjoining membrane surfaces is less than or equal to 30°, preferably less than or equal to 20°.

[0015] In a particularly preferred embodiment of the separation element according to the invention, the membrane material is adapted to have a reduced thickness between two adjacent turning points located on a common side of the membrane, preferably in the middle. It is surprising for the average person skilled in the art that, despite this reduced thickness, a uniform and improved stress introduction into the membrane is achieved, which contributes to a longer membrane life.

[0016] In another preferred embodiment of the separation element according to the invention, each membrane surface between two adjacent turning points located on opposite sides of the membrane has a corrugated pattern, in which case, in the context of self-stabilization, the individual corrugated membrane surfaces can be folded at least partially flush with one another when stacked together into a block, thus increasing the overall stability.

[0017] Advantageously, in the corrugation of the membrane, the membrane surface, viewed in the stacking order, has a steeper inclination toward the arcuate turning point than the adjacent membrane surface bordering this turning point, so that the membrane surface located above in the stacking order is correspondingly supported by the flatter membrane surface located below it, which overall favors the bellows expansion and contraction behavior during dynamic operation.

[0018] Materials preferably used for the separation elements obtained by 3D printing are titanium, stainless steel or aluminium.

[0019] Particularly preferably, the separating element or membrane forms a kind of hollow cylinder in the completed printing state, so that the separating element can also be used without problem as a compensation device within the framework of a compensation element for fluid-conveying pipes.

[0020] However, it is particularly preferred to use a bellows-like separating element in the context of a hydraulic accumulator in the form of a bellows-type accumulator, which separating element is used in an accumulator housing to separate two medium or fluid chambers from one another, the separating element preferably being designed as described above.

[0021] In the following, the separating element and hydraulic accumulator according to the invention are explained in more detail on the basis of various exemplary embodiments and on the basis of the drawings, which are principle views and are not drawn to scale. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a highly schematic, simplified longitudinal section of a hydraulic accumulator with a movable separating element inside the accumulator housing, the metal bellows being shown in an extended state. [Diagram 2] FIG. 2 is a highly simplified longitudinal section of a hydraulic accumulator with a movable separating element inside the accumulator housing, the metal bellows being shown collapsed into a block. [Diagram 3]FIG. 3 is a partial view of a pleat arrangement of a separation element in which the pleats extend linearly. [Figure 4] FIG. 4 shows a hollow cylindrical metal bellows resulting from the pleat pattern according to FIG. [Diagram 5] FIG. 5 shows another embodiment of a bellows-like separation element having a corrugated pleat pattern. [Figure 6] FIG. 6 further illustrates on both sides the pleat pattern resulting from the representation of FIG. [Figure 7] FIG. 7 is a perspective view, half cut away, of a hollow cylindrical bellows resulting from the pleat arrangement according to the representation of FIGS. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The hydraulic accumulator designed as a bellows-type accumulator according to Figures 1 and 2 comprises, by way of example, a cylindrical accumulator housing 10, inside which a metal bellows 12 is provided and which serves as a movable separating element 14 separating a gas side 16 from a fluid side 18 inside the accumulator housing 10. As is usual for such hydraulic accumulators, the accumulator housing 10 is provided with a connection 20 to the gas side 16 for a working gas, preferably nitrogen gas, and a fluid connection 22 to the fluid or liquid side 18.

[0024] 1 and 2, the metal bellows 12 or separating element 14 is welded at its lower open end to a fixing ring 24 secured to the inner wall of the accumulator housing 10. The other end of the metal bellows 12 is closed in a fluid-tight manner by a preferably welded end plate 26. Between the end plate 26 and the fixing ring 24, the metal bellows 12 has a number (a plurality) of individual continuous bellows folds 28, the configuration of which will be described in more detail with reference to the following figures.

[0025] FIG. 1 shows the hydraulic accumulator in an operating state with low or no gas pressure on the gas side 16, and correspondingly the metal bellows 12 is depicted in an expanded state, with the free volume of the gas side 16 located on the outside of the bellows reduced and the volume of the fluid side 18 adjacent the inside of the metal bellows 12 increased.

[0026] 2 shows an operating condition with low or no fluid pressure on the fluid or liquid side 18, in which the metal bellows 12 or separating element 14 is fully compressed and the individual bellows pleats 28 are pressed against each other and support each other, which is technically called the "blocked position" or "blocked". In this respect the metal bellows 12 forms an extremely pressure-resistant structure, so that the hydraulic accumulator maintains operational safety both at very high gas pressure levels and with low or no fluid pressure.

[0027] Fig. 3 shows a possible embodiment of the annular metal bellows 12 with individual bellows folds 28 arranged one above the other, the upper and lower bellows folds 28 not being fully represented, but it is self-evident that a number of such bellows folds 28 arranged one above the other depending on the application form the separating element 14. Each bellows fold 28 forms individual turning points 30, seen from the outside and the inside, which turn in a cross section in the shape of a circular arc, and in particular in the outer region at least partially has a semicircular arc. Each bellows fold 28 passes through a section going from a wave crest to a wave trough and then again to the following wave crest, and is formed by each semicircular turning point 30. As is further evident from Fig. 3, the imaginary extensions 32 of the adjacent membrane surfaces, which respectively border at each turning point 30, form an acute angle a of less than 30° with respect to each other in the fully extended initial state shown in Figs. 1 and 3. In contrast, when the metal bellows 12 enters the blocking position shown in FIG. 2, the pairs of adjacent membrane surfaces 34 move toward each other while simultaneously increasing the angle a.

[0028] The separation element shown in FIG. 3 consists of a single monolithic membrane produced by 3D printing. Powder printing is used in particular to produce the separation membrane. The metal powder for 3D printing can be a steel material such as stainless steel, or a material such as titanium or aluminum. It goes without saying that the materials mentioned here are merely exemplary and other suitable metals can also be used in 3D printing.

[0029] Due to the fact that the turning points 30 of the respective bellows folds 28 are formed in a circular arc shape in cross section and that the bordering membrane surfaces 34 in the initial state of the metal bellows 12 according to FIG. 3 form an acute angle a with respect to one another, a separation element 14 is obtained which has an isotensoid or substantially isotensoid stress curve over its entire surface. This means that a uniform stress introduction and stress distribution in the separation element 14 is achieved over the entire three-dimensional structure, so that stress peaks in the membrane material are avoided even in dynamic operation. This is advantageous for long-lasting operation and allows a fast reaction behavior of the separation element 14 even under high dynamic loads. There is no equivalent in the prior art.

[0030] The metal bellows 12, which is only partially shown in Figure 3, is shown in its entirety in Figure 4 and forms the separation element 14, which is shown in the form of a block in Figure 2. In this case, the upper side 36 is connected to the end plate 26, and the lower side 38 of the metal bellows 12 is connected, according to the representation in Figures 1 and 2, to the fastening ring 24 for fastening the separation element 14 inside the accumulator housing 10. It is self-evident that within the scope of 3D printing methods, the end plate 26 and possibly also the fastening ring 24 can also be formed integrally with the metal bellows 12 from a suitable metallic material.

[0031] Figure 5 shows another solution of the separating element, modified with respect to the solutions of Figures 3 and 4, the previous description also applies to this modified embodiment, so that the same reference numbers are used for the same components. Figure 5 shows a section of a corrugated membrane, in which the turning points 30 are again provided with a semicircular pattern on the end side. Here again, the mutually mating membrane surfaces 34 form an acute angle a of less than 20°, in particular an angle of 15°, with the imaginary extension 32 at each turning point 30. In this way, a kind of wedge is formed in the respective peripheral end region of the separating element when viewed in cross section, which is particularly effective in terms of absorbing forces when the metal bellows 12 is compressed.

[0032] As can further be seen in Fig. 5, the membrane surface 34 lying on top of each of the bellows pleats 28 in the stacking order has a greater curvature than the membrane surface 34 lying below it, which leads to an increased bending strength value. Furthermore, when each bellows pleat 28 resiliently contracts, an improved support effect with a correspondingly higher force input is achieved due to the flatter extending bottom formed by the membrane surface 34. Fig. 5 again relates to the initial state in which the bellows pleats 28 according to the representation of Fig. 1 are stretched against one another. Moreover, the individual bellows pleats 28 remain at a substantially constant distance from one another both in the extended and in the contracted state.

[0033] FIG. 6 shows the pleat pattern according to FIG. 5 for an entire corrugated separator membrane with turning points 30 located in the outer wall region and in the inner wall region.

[0034] The representation according to Fig. 7 shows a half section and, like the representation according to Fig. 4, shows the separation element as a hollow cylinder, which can again be connected at its upper side 36 to the end plate 26 and at its lower side 38 to the fixing ring 24. Moreover, as can be seen from Fig. 5 and Fig. 6, when the individual bellows pleats 28 are made into a block according to the representation of Fig. 2, the membrane surfaces 34, in their corrugated configuration, are at least partially folded against each other with their surfaces, which results in an improved stiffness against possible lateral forces.

[0035] Moreover, as can be seen from figure 3, the membrane material of the membrane can be reduced in thickness, preferably in the middle between two adjacent turning points 30 of the bellows pleats 28, such an area of ​​reduced thickness being indicated with 40 in figure 3. Such a reduction in thickness is also basically possible in membranes according to figures 5 to 7. For an average person skilled in the art of designing such separation elements, it is surprising that an improvement in the bending properties is obtained despite the aforementioned reduction in thickness 40.

Claims

1. In a separating element for an accumulator, manufactured by a 3D printing method, the separating element consists of a single membrane which, when viewed in cross-section, is turned in an arc at turning points (30) to form a number of bellows folds (28), the turning points (30) delimiting the bellows folds (28) on the outside and inside, and the virtual extensions (32) of adjacent membrane surfaces (34) which are adjacent to each other at each turning point (30) and delimit the boundary form an acute angle (α) with each other, at least in the initial state, in order to obtain an isotenoid or substantially isotenoid stress profile within the membrane.

2. The separating element according to claim 1, characterized in that the arc-shaped turning points (30) are each at least partially formed from a semi-circular arc, when viewed in cross-section.

3. The separating element according to claim 1, characterized in that the acute angle (α) is 30° or less, preferably 20° or less.

4. The separating element according to claim 1, characterized in that the membrane material of the membrane has a reduced wall thickness (40), preferably in the middle, between two adjacent turning points (30) located on the common side of the membrane.

5. The separating element according to claim 1, characterized in that each membrane surface (34) between two adjacent turning points (30) located on opposite sides of the membrane has a corrugated pattern.

6. The separating element according to claim 1, characterized in that the corrugated patterns of the individual membrane surfaces (34) are formed identically such that when the membrane surfaces (34) overlap each other to form blocks, the membrane surfaces (34) are folded flush with each other.

7. The separating element according to claim 1, characterized in that in the corrugation of the membrane, the membrane surface (34) has a stronger inclination with respect to the arc-shaped turning point (30) than the adjacent membrane surface (34) which delimits the boundary at the turning point (30), in the stacking order.

8. The separating element according to claim 1, characterized in that the material constituting the membrane is titanium, stainless steel, or aluminum.

9. The separating element according to claim 1, characterized in that the membrane forms a kind of hollow cylinder in the state after printing is completed.

10. A hydraulic accumulator having an accumulator housing (10) and a bellows-shaped separating element (14) arranged therein, the separating element (14) separating two medium chambers (16, 18) from each other within the accumulator housing (10). A hydraulic accumulator, characterized in that the separating element (14) is formed according to any one of claims 1 to 9.

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