Hydraulic accumulator

Abstract

1. Hydraulic accumulator 2. The invention relates to a hydraulic accumulator, at least consisting of two accumulator housing parts (24, 26) which are securely connected to one another along a peripheral weld seam (28) introduced from the outside of the accumulator housing (10), and having a covering ring (34) which covers the peripheral weld seam (28) on the inside (36) of the accumulator housing (10) in the manner of a weld pool backing in such a way that an introduction of foreign material, as occurs during the welding process, onto the inside (36) of the accumulator housing (10) is prevented, characterised in that, in order to increase the fatigue strength at the peripheral weld seam (28), individual parameters of the weld pool backing, in the form of the covering ring (34), can be changed, such as - position on the inside (36) of the accumulator housing (10), - constructional design, and / or - material selection relating thereto.

Description

[0001] 40cdh / 131975AVO

[0002] HYDAC TECHNOLOGY GMBH Industriestraße, 66280 Sulzbach / Saar, Germany

[0003] hydraulic accumulator

[0004] The invention relates to a hydraulic accumulator, comprising at least two accumulator housing parts which are firmly connected to each other along a circumferential weld seam introduced from the outside of the accumulator housing and with a cover ring which, in the manner of a weld pool seal, covers the weld seam on the inside of the accumulator housing in such a way that the introduction of foreign material, as occurs during the welding process, onto the inside of the accumulator housing is avoided.

[0005] EP 0 604 445 B1 discloses a hydraulic accumulator with a partition arranged in a housing. This partition separates a liquid chamber from a gas chamber within the housing and is held in place by a retaining element. This retaining element is connected to an annular connecting element, which serves as a weld pool retainer and is welded to the housing. To establish the connection, the retaining element at least partially surrounds the connecting element. Both the retaining element and the connecting element are annular in shape. The connecting element, or cover ring, covers a seam inside the housing between two shells that essentially form the housing. These shells are firmly joined along the seam by means of a welding process, particularly an electron beam welding process. The connecting element is simultaneously firmly connected to the housing along the seam.

[0006] DE 10 2009 049 547 B3 discloses a hydropneumatic pressure accumulator with a movable separating element arranged in an accumulator housing, which separates a first working chamber, preferably filled with a working gas, from a fluid chamber as a second working chamber and is formed by a membrane made of a flexible material, in particular an elastomer, wherein the accumulator housing has a housing opening providing access to the fluid chamber, the passage of which can be controlled by a valve arrangement that can be moved into a release position or a closed position, which has a valve body located on a surface section of the membrane, which moves the valve arrangement into the closed position when approaching a valve seat located at the housing opening, wherein the valve arrangement has a bypass arrangement that allows a limited flow through the housing opening in the closed position.and wherein the valve body, for forming the bypass arrangement, has at least one projection on its surface facing the valve seat, which forms a spacer relative to the valve seat, thus enabling flow through. In this known solution as well, a circumferential weld seam introduced from the outside between the two storage housing halves is covered on its inner circumference by a weld pool protection element in the form of a centering or cover ring, which prevents weld spatter from unintentionally reaching the inside of the storage housing and damaging the elastomeric membrane separating element. Furthermore, the cover ring serves to define a guide and retaining device for the separating membrane on the inside of the storage housing.

[0007] Based on this prior art, the invention aims to further improve known solutions while retaining their advantages. A hydraulic accumulator with all the features of claim 1 achieves this objective in its entirety.

[0008] By virtue of the fact that, according to the characterizing part of claim 1, individual parameters of the weld pool protection in the form of the cover ring can be changed to increase the fatigue strength at the circumferential weld seam, as described in its

[0009] Position on the inside of the storage enclosure,

[0010] - Through the design and / or material selection, a permanently high-strength storage housing connection is achieved. Hydraulic storage devices, such as hydraulic accumulators and pressure vessels, whose storage housing components are firmly joined by a circumferential weld, are subject to increasingly stringent requirements regarding weight reduction. For this reason, there is a trend towards the use of higher-strength materials while simultaneously reducing component wall thicknesses. However, higher-strength materials inherently exhibit increased susceptibility to fatigue cracking and tend to become more brittle due to heat. Despite their increased mechanical strength, these properties lead to fatigue failures under alternating or fluctuating loads, typically in the form of fatigue cracks and subsequent fatigue fractures.

[0011] The aforementioned solutions according to the invention for optimizing the position, design, and material of the weld pool protection in the form of the cover ring counteract the susceptibility to cracking of high-strength, weldable steel materials in every case. Furthermore, this results in a general increase in the fatigue strength of circumferential welds on pressure vessels, particularly as components of hydraulic accumulators. In a preferred embodiment of the hydraulic accumulator according to the invention, the cover ring is positioned on the inside of the accumulator housing such that the circumferential weld engages the cover ring in a central plane, transverse to its longitudinal orientation.Centering or cover rings pressed in off-center to the weld seam, a previously standard design for weld pool protection, have proven to be a crack initiator in the circumferential weld area during practical internal pressure surge tests. By contrast, pressing the centering or cover ring in at a central depth reduces bending stress components in this joint area, significantly improving fatigue strength. For the preferred insertion or pressing of the centering or cover ring into at least one storage housing part, this ring can be slotted and appropriately expanded so that, in its inserted state and with a reduced free diameter, it rests against the inside of the joined storage housing parts with a predefinable preload, before they are firmly joined together by means of the circumferential weld seam along their butt joint or weld point.Instead of a slotted ring, a closed ring can also be used.

[0012] In a further preferred embodiment of the hydraulic accumulator according to the invention, the cover ring is made of a molten material that has a lower modulus of elasticity than the material of the welded accumulator housing parts, which are made of a steel alloy. Molten materials, which have a lower modulus of elasticity than steel and thus also reduced stiffness, represent a further improvement in fatigue strength, since the differences in elongation between the cover ring and the adjacent wall of the accumulator housing parts can be reduced. In a further preferred embodiment of the hydraulic accumulator according to the invention, means are provided that prevent a bond between the cover ring, which acts as a weld pool retainer, and the corresponding wall sections of the welded accumulator housing parts.

[0013] This is preferably achieved by the cover ring having an annular chamber, located adjacent to the circumferential weld, which serves to prevent bonding with the circumferential weld. This chamber collects any foreign material that may occur during welding and is enclosed by wall sections of the cover ring. Preferably, the annular chamber is further arranged offset from the circumferential weld such that a smaller chamber volume faces the weld and a correspondingly larger chamber volume faces away from it. This spatial decoupling of the centering and cover rings from the circumferential weld prevents any connection in this area that could allow fatigue cracks to penetrate the accumulator housing material via the ring. In this way, reliable, long-lasting operation of the modified hydraulic accumulator is achieved.

[0014] An improvement in fatigue strength is also achieved by using a non-melting material, such as tungsten or ceramic, as a further means of preventing the circumferential weld from bonding to the cover ring. The circumferential weld then terminates flush with the inside of the storage housing. Since no material bond occurs in this design, the induction of fatigue or stress cracks is prevented.

[0015] A particularly space-saving and inherently stable design is achieved when, preferably, the cross-sectional shape of the cover ring forms a rectangle. One of its longitudinal sides extends along the inside of the storage housing, overlapping the circumferential weld seam. The other, opposite longitudinal side engages in a circumferential groove of a guide and / or retaining element of a separating element. Along its two transverse sides, the ring overlaps the wall sections of the circumferential groove, particularly its clamping areas. Preferably, the guide and / or retaining element serves to secure a membrane-shaped separating device that divides the storage housing into two media compartments, in particular a fluid compartment for a hydraulic medium and another fluid compartment for a gaseous medium, such as nitrogen gas.

[0016] The solution according to the invention is not limited to classic hydraulic accumulators or hydraulic accumulators with media separation, but also includes pressure vessels, such as air tanks without a separation device, which are still considered hydraulic accumulators within the scope of the present invention, as well as diaphragm accumulators, bladder accumulators, piston accumulators, metal bellows accumulators and spring accumulators, which use a spring arrangement, such as a compression spring, instead of a compressible working gas.

[0017] The centering or cover ring, which is at least partially additionally fixed to the accumulator housing via the circumferential weld, serves to position a locking device with the elastomeric separating membrane. Furthermore, the centering ring centers both housing parts relative to each other. However, it is still within the scope of the invention to use this centering or cover ring as a guide band for a separating piston that is movably guided within a hollow cylindrical accumulator housing of a piston accumulator.In such a design, the cover ring or the guide band of the piston should be in a starting position at the level of the circumferential weld to be applied, without being welded to it, so that the free movement of the (separating) piston is subsequently ensured and the circumferential weld can only be applied in the starting position while simultaneously increasing the fatigue strength, since there is again no connection between the ring and the weld.

[0018] The hydraulic accumulator according to the invention will now be explained in more detail with reference to exemplary embodiments shown in the drawing. The drawings are shown in a general and not to-scale representation.

[0019] Figure 1 shows a longitudinal section through the essential components of a hydraulic accumulator as a whole;

[0020] Figure 2 shows an enlarged view of a section of the image labeled X in Figure 1;

[0021] Figures 3, 4 and 5 show further alternative embodiments of a connection solution in the form of a placeholder, as can be used in the image section X according to Figure 1, whereby the same scale is not always maintained.

[0022] The hydraulic accumulator shown in Figure 1 is a so-called diaphragm accumulator with a separating device 12 in the form of an elastic, flexible diaphragm 14 arranged in an accumulator housing 10. The diaphragm-shaped separating device 12 divides the accumulator housing 10 internally into two media chambers 16, 18, in particular a fluid chamber 16 for a hydraulic medium and a further fluid chamber 18 for a gaseous medium, such as nitrogen gas. Both the first media chamber 16 and the second media chamber 18 each have a hollow cylindrical connection 20 or 22, respectively, by means of which the hydraulic accumulator can be connected in the usual manner to fluid- or media-carrying pipelines of a hydraulic system (not shown).

[0023] The storage housing 10 itself, viewed from the perspective of Figure 1, consists of a lower 24 and an upper storage housing part 26, which abut each other along a seam. Along this seam, the two storage housing parts 24, 26 are firmly joined to form the storage housing 10 by means of a suitable welding process, such as electron beam welding. The resulting annular, closed weld seam is represented as a circumferential weld seam with reference numeral 28. The two storage housing parts 24, 26 each essentially comprise half of the storage housing 10 as a whole and are designed to be pressure-resistant in the form of shells.The hydraulic fluid connection 20 is an integral part of the lower reservoir housing section 24; likewise, the upper second connection 22 is an integral part of the upper reservoir housing section 26, the through-opening of the upper second connection 22 being closed with a sealing screw 30, which seals the interior of the second media chamber 18 against the environment. Furthermore, the second connection 22 is sealed externally by a cap-like plastic cover 32. To fill the second media chamber 18 with a working gas, such as nitrogen gas, a standard refilling device (not shown) can be connected to the second connection 22 after removing the cover 32 and the sealing screw 30. Such filling procedures are commonplace and will not be described in detail here.

[0024] As can be seen particularly in Figure 2, which shows an approximately fivefold magnification of section X from Figure 1, a centering or cover ring 34 is provided. This ring, acting as a weld pool seal, covers the circumferential weld 28 on the inner surface 36 of the storage housing 10 in such a way that foreign material, such as weld spatter, which is inherent in the welding process, cannot reach the inner surface 36 of the storage housing 10. The centering or cover ring 34 can be inserted into the lower storage housing part 24 with a predetermined pressing or contact tension and thus rests against the corresponding inner wall section below the circumferential weld 28, which is yet to be applied. To maintain the desired preload, the cover ring 34 can be slotted and widened, allowing the two free ends of the slot to come into contact with each other again after clamping.However, a precisely fitting closed ring can also be used. The corresponding slot can also be completely closed, for example during a welding process, after the ring 34 has been fixed in place, so that no weld spatter can unintentionally reach the inside 36 of the storage housing 10 in this area. The centering or cover ring 34 shown in Figures 1 and 2 has a different design than the rings made of flat material, which, as the respective connecting part, are defined by means of the circumferential weld seam to be applied and are an integral part of the storage housing with its two storage housing parts. Such embodiments are shown by way of example in EP 0 604 445 B1 and in DE 10 2009 049 547 B3.

[0025] According to the present invention, however, in contrast to this, means are provided which prevent a firm connection between the cover ring 34, which forms the weld pool retainer, and the corresponding adjacent wall sections of the welded storage housing parts 24, 26. It has been shown that by avoiding such a connection, the fatigue strength of the surrounding weld seam 28 can be significantly increased. As a means of preventing this, the cover ring 34 has a circumferential annular chamber 38 which, in the fixed state, is adjacent to the circumferential weld seam 28 and which can collect any foreign material, such as weld spatter.The continuous annular chamber 38, with a constant rectangular cross-section, is enclosed on the inside by wall sections 40 of the cover ring 34 and on the outside by the adjacent inner wall sections of the storage housing parts 24, 26, as well as by the circumferential weld 28, which runs continuously around the storage housing 10 from the outside to the inside through the wall of the storage housing 10. Accordingly, the circumferential weld 28 opens into the surroundings at one free end and into the cavity formed by the annular chamber 38 in the cover ring 34 at the other free end. Due to the welding process, the circumferential weld 28, viewed in the direction shown in Figure 2, has a conical cross-section that tapers to a point in the direction of the annular chamber 38.

[0026] As can be further seen from Figures 1 and 2, the annular chamber 38 is arranged offset from the circumferential weld 28 within the storage housing 10 such that a smaller chamber volume 42 faces the weld 28 and a larger chamber volume 44 faces away from it. In this way, the smaller chamber volume 42 forms a kind of impact protection against the ingress of foreign material, as it lies horizontally opposite the exit of the weld 28 towards the interior of the storage housing 10 when viewed in the direction of Figures 1 and 2. The larger chamber volume 44 can thus be used as a central collection space for all the foreign material that accumulates.In cross-section, the centering or cover ring 34 forms a kind of C-shaped clamp which, together with the rigid longitudinal and transverse wall parts 40, delimits the annular chamber 38 and the free end faces of the transverse, delimiting wall parts 40 abut with preload along the adjacent wall sides of the lower and upper storage housing part 24 and 26 respectively.

[0027] A guide and retaining element 46 for receiving the membrane 14 at its foot along its head side, like the cover ring 44, is ring-shaped and has a circumferential groove 48 on its side facing the cover ring 34. This groove is essentially rectangular in cross-section and has two semicircular recesses 50 at the corners of its base to increase the elasticity of the retaining element 52 of the guide and retaining element 46. These recesses, with their clamp-like wall projections 54, engage the ring 34 with the annular chamber 38 from above and below under preload and are thus loosely fixed to the cover ring 34. The rear wall of the cover ring 34 has a narrow engagement gap in the radial direction to the base of the circumferential groove 48. Furthermore, the recesses 50 reduce the occurrence of stress concentrations.

[0028] Furthermore, one half of the ring 45 of the guide and retaining element 46 has a ring shape with a multitude of indentations 56, not all of which are shown, but which extend at equidistant intervals along the upper surface of the guide and retaining element 46 shown. The depth of the indentations 56, which run parallel to the longitudinal axis 58 of the storage housing, is dimensioned such that it is approximately half the height of the ring-shaped guide and retaining element 46. Due to these indentations 56, the guide and retaining element 46 can be more securely mounted on the cover ring 34, which engages in the circumferential groove 48 of the guide part of the guide and retaining element 46, with the guide part 46 being placed on the cover ring 34. The corresponding guide and retaining part 46 preferably consists in a known manner of a glass fiber reinforced plastic, for example of a polyamide with 40 to 50% glass fiber content.Other, partially elastically flexible plastic materials can also be used for part 46.

[0029] The other, lower ring half 59 of the guide and retaining part 46 then receives a rim bead 60 of the membrane 14, which is thickened compared to the wall of the membrane 14 and whose essentially square cross-section rests with one underside or contact surface against a wall recess 62 in the lower storage housing part 24 on its inner side. Furthermore, for clarity, a parting line 64 and a projecting sealing lug 66 are shown on the rim or ring bead 60, with both components 64 and 66 being pressed together over their entire surface in the installed state of the separating membrane 14, towards the inner wall side of the lower storage housing part 24, which is not shown.The other ring half 59 of the guide and retaining element 46 has a chamber-like, circumferential surround 68, which, in the usual manner, defines and receives the edge bead 60 of the diaphragm 14 and presses this edge bead 60 against the inner wall of the lower storage housing part 24 with a predefinable clamping force. The diaphragm 14 itself is shown in a fictitious intermediate position, in which it has a kind of W-shape, with a sealing element 70 vulcanized into the bottom of the diaphragm 14 in the usual manner, which, when the diaphragm 14 is fully unrolled, closes the through-opening in the lower liquid connection 20 as required. As soon as the diaphragm 14 is fixed to the ring 34 via the guide and retaining element 46, the upper storage housing part 26 is placed on top and the circumferential weld 28 is made to produce the storage housing 10 as a pressure vessel. Thus, the [assembly] shown in the Fig.The hydraulic accumulators shown in 1 and 2 are essentially complete.

[0030] The following embodiments according to Figures 3 to 5 will only be explained insofar as they differ substantially from the preceding embodiment according to Figures 1 and 2, whereby the same components are numbered with the same reference numerals and the explanations given in this respect also apply to the further embodiments according to Figures 3 to 5. In the embodiment according to Figure 3, the cover ring 34 is arranged off-center to the circumferential weld 28, as shown in the prior art, i.e., if the circumferential weld 28 forms a fictitious horizontal plane, the upper third of the cover ring 34 is welded to the circumferential weld 28 and the two lower thirds of the same extend vertically below this fictitious horizontal plane.Unlike the embodiment described above according to Figures 1 and 2, the cover ring is firmly connected to the two storage housing parts 24, 26 along their seam by means of the circumferential weld seam 28. Otherwise, as shown in Figure 3, the guide and retaining element 46 is clipped onto the cover ring 34 from the inside. To nevertheless achieve an increase in fatigue strength in the embodiment according to Figure 3, the cover ring 34 is made of a meltable material that has a lower modulus of elasticity than the material of the welded storage housing parts, which are made of a steel alloy. In this way, differences in expansion between the centering and cover rings 34 and the inner wall of the storage housing 10 are reduced, effectively preventing the occurrence of stress or fatigue cracks.

[0031] In the embodiment shown in Figure 4, the cover ring 34 is now positioned on the inside 36 of the storage housing 10 such that the circumferential weld 28 engages centrally in a horizontal central plane transverse to the longitudinal orientation of the cover ring 34, forming a welded connection. The central press-fit depth of the centering and cover ring 34 shown here results in improved fatigue strength because any bending stresses that may occur during operation between the connected components can be distributed evenly and thus reduced. 40cdh / 131975AVO

[0032] 14

[0033] In the embodiment shown in Figure 5, as in the embodiment shown in Figures 1 and 2, there is no connection whatsoever between the circumferential weld 28 and the cover ring 34. In particular, no weld connection is formed because the cover ring 34 in this configuration is made of materials such as tungsten or ceramic, whose melting point is significantly higher than that of steel, the material from which the storage housing parts 24 and 26 are usually made. In this way, a non-melting weld pool seal is achieved over the cover ring 34, and this approach also counteracts the susceptibility to cracking of the desired high-strength, weldable steel materials for the storage housing 10. In this respect as well, a general increase in the fatigue strength of the circumferential weld 28 of pressure vessels in general is achieved, such as the storage housing 10 described here.

Claims

Patent claims 1. Hydraulic accumulator, comprising at least two accumulator housing parts (24, 26) which are firmly connected to each other along a circumferential weld (28) applied from the outside of the accumulator housing (10) and with a cover ring (34) which, in the manner of a weld pool seal, covers the circumferential weld (28) on the inside (36) of the accumulator housing (10) in such a way that the introduction of foreign material, as occurs during the welding process, onto the inside (36) of the accumulator housing is prevented, characterized in that, in order to increase the fatigue strength at the circumferential weld (28), individual parameters of the weld pool seal in the form of the cover ring (34) are modifiable, such as its Position on the inside (36) of the storage housing (10), - constructive design and / or material selection relating to it.

2. Hydraulic accumulator according to claim 1, characterized in that the cover ring (34) is positioned on the inside (36) of the accumulator housing (10) such that the circumferential weld seam (28) engages in the cover ring (34) in a central plane, transverse to the longitudinal orientation of the cover ring (34).

3. Hydraulic accumulator according to claim 1 or 2, characterized in that the cover ring (34) is made of a meltable material which has a lower modulus of elasticity than the material of the accumulator housing parts (24, 26) welded together, which in particular consist of a steel material.

4. Hydraulic accumulator according to one of the preceding claims, characterized in that means are provided which a Prevent connection between the cover ring (34) as the weld pool protection and the associated wall parts of the welded storage housing parts (24, 26) including the circumferential weld seam (28).

5. Hydraulic accumulator according to one of the preceding claims, characterized in that the cover ring (34) has an annular chamber (38) as a means of preventing connection with the circumferential weld (28), which is adjacent to the circumferential weld (28), which receives any foreign material that occurs during welding, and which is enclosed by wall parts (40) of the cover ring (34).

6. Hydraulic accumulator according to one of the preceding claims, characterized in that the annular chamber (38) is arranged offset to the circumferential weld seam (28) such that a smaller chamber volume (42) faces the weld seam (28) and a larger chamber volume (44) faces away from it.

7. Hydraulic accumulator according to one of the preceding claims, characterized in that, as a further means of preventing the connection of the cover ring (34) with circumferential weld (28), the cover ring (34) is formed from a non-melting material, such as tungsten or ceramic, on which the circumferential weld (28) terminates flush along the inside (36) of the accumulator housing (10).

8. Hydraulic accumulator according to one of the preceding claims, characterized in that the cross-sectional shape of the cover ring (34) forms a rectangle, which extends with one longitudinal side overlapping the circumferential weld seam (28) at a predetermined distance along the inside (36) of the accumulator housing (10). 1 7 of the same extends, which engages with its other opposite longitudinal side in a circumferential groove (48) of a guide and / or holding part (46) of a separating device (12), and which is overlapping along its two transverse sides with contact with wall parts (54) of the circumferential groove (48), in particular with clamping areas thereof.

9. Hydraulic accumulator according to one of the preceding claims, characterized in that the guide and / or retaining part (46) serves to fix the diaphragm-shaped separating device (12) which divides the accumulator housing (10) into two media spaces (16, 18), in particular into a fluid space (16) for a hydraulic medium and into a further fluid space (18) for a gaseous medium, such as nitrogen gas.

10. Hydraulic accumulator according to one of the preceding claims, characterized in that it consists of a pressure vessel without A separation device exists.

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