Pressure accumulator having a piston and a bellows

Abstract

2. The invention relates to a device, at least consisting of a piston (12) and a bellows (14), which are accommodated in a common housing (10) and separate three different fluid chambers (16, 18, 20) from one another, characterised in that the piston (12) and the bellows (14) are accommodated in the housing (10) completely and without protrusion, the ends of the housing being limited by housing covers (22, 24) between which the piston (12) and the bellows (14) move.

Description

[0001] PRESSURE STORAGE TANK WITH ONE PISTON AND ONE BELLOWS

[0002] The invention relates to a device, at least consisting of a piston and a bellows, which are housed in a common casing and separate three different fluid spaces from each other.

[0003] In addition to air chambers, weight and spring accumulators, and diaphragm, bladder, or piston accumulators, there are designs in which a bellows with individual, interconnected folds, such as a corrugated or pleated bellows made of metal or plastic, is used as a separating element in a separation device. The advantage of bellows made of special plastics, such as PTFE, lies in their superior media and temperature resistance compared to conventional elastomer materials. Metal bellows generally offer the advantage of exceptional media and temperature resistance, and their potential applications are further enhanced by extremely high tightness for media, including gases; that is, absolute tightness with liquids and technical gas tightness are achieved.The last-mentioned advantage makes the metal bellows accumulator unique compared to all other accumulator designs and is particularly relevant when gas loss from a hydraulic accumulator is to be virtually eliminated and / or its operating fluids must not be contaminated even with trace amounts of nitrogen gas. The optimal media tightness for liquids and gases also makes metal bellows accumulators ideally suited for use as media separators.

[0004] When using corrugated and diaphragm bellows made of metal or plastic, hereinafter referred to simply as bellows, each with a separating element of bellows folds between the gas and liquid sides, for example in hydropneumatic accumulators, their extended and compressed lengths must be given special consideration in conjunction with the prevailing operating pressures and temperatures. Additionally, depending on their design, bellows can only withstand very specific differential pressures between the inside and outside of the bellows. If the permissible differential pressures are exceeded, a failure of the bellows wall, for example due to a tear, can lead to a loss of bellows function, including in the case of a hydraulic supply circuit to which such bellows are regularly connected. In the case of a nitrogen-filled accumulator, a bellows rupture would cause it to lose its gas pre-charge pressure and thus its accumulator function.If the system were to function as a media separator, the media to be separated would unintentionally mix in the event of failure. Even if a bellows is not immediately destroyed by an impermissibly high differential pressure, but merely damaged, meaning the separating function is initially retained, the bellows wall will nevertheless fail sooner or later, depending on the operating mode. Therefore, when designing bellows accumulators as one of the possible separation devices, it is of the highest priority to ensure that impermissible bellows lengths and differential pressures cannot occur at the bellows structure under any of the possible operating conditions (pressure and temperature). However, when it is stated below that no differential pressures exist at the bellows, this excludes those differential pressures that arise from the spring properties of the bellows structure in conjunction with compression or other factors.Stretching of the bellows folds is caused by this. These bellows-specific differential pressures are usually so small that they can be easily tolerated by the bellows.

[0005] With regard to the aforementioned problem, according to the doctrine of

[0006] DE 100 09 865 B4 already proposes, in the case of a hydropneumatic pressure accumulator, particularly in the form of a pulsation dampener, to provide an accumulator housing containing a gas chamber for receiving a gas filling that generates a pre-charge pressure, as well as an oil chamber, wherein a bellows or metal bellows is provided separating the gas chamber and the oil chamber, which is closed at one end by an end plate and connected at its other end to the accumulator housing in such a way that its interior forms the oil chamber. Furthermore, an oil channel formed in the wall of the accumulator housing is provided as a connection point, which opens into the oil chamber.A mechanical stroke limiting device for the movement of the bellows' end plate, comprising a first stop formed by a tubular body extending inside the metal bellows along its inner surface from the opening of the oil channel to near the inner surface of the end plate, and a second stop formed by a second tubular body extending concentrically to the tubular body from the wall of the storage housing in the gas space to near the outer surface of the metal bellows' end plate, provides mechanical stroke limitation for the bellows on both sides, ensuring that predefinable minimum and maximum bellows lengths are not exceeded for either contraction or extension.Nevertheless, the separating device, designed as a bellows, is subject to additional mechanical stress due to mechanical contact with the respective stroke limit, which can reduce the bellows' service life. US Patent 3,336,948 discloses a hydro-pneumatic accumulator that has a retractable bellows within its accumulator housing, enclosing a fluid chamber containing a working gas.Between the bellows and an end-mounted cover section of the accumulator housing, a longitudinally movable piston is guided within the housing. This piston separates two fluid chambers, particularly for the storage of hydraulic fluids such as hydraulic oil. A rod assembly, integrally connected to the piston, extends out of the accumulator housing via the cover section. At its end, this rod assembly connects to fixed wall sections of the housing cover, forming a housing that provides a stop for the rod assembly and meets increased safety requirements. Furthermore, individual fluid guides in the form of longitudinal channels are incorporated into the rod assembly. These channels open on the free side of the rod assembly towards the housing to dissipate any leakage that may occur during piston movement.Due to the rod assembly attached to the piston, the piston area between the piston and the adjacent cover section is reduced and is smaller than the opposite piston area located in the wider fluid chamber between the bellows accumulator and the piston. Consequently, the two fluid chambers, each containing hydraulic fluid, have different pressures, thus achieving a conventional pressure intensification.

[0007] Based on this state of the art, the invention aims to further improve the known devices in such a way that excessively high compression and stretching stresses as well as pressure differences affecting the bellows as a fluid separation device are largely avoided during operation.

[0008] A device with the features of claim 1 in its entirety solves such a problem. According to the characterizing part of claim 1, both the piston and the bellows are completely and without protrusion enclosed in the housing, which is bounded at its ends by housing covers between which both the piston and the bellows move, thus forming two separate separating devices within the device, one of which comprises the bellows and the other the piston.

[0009] Since the device according to the invention is designed as a media separator, only one of the two separating devices is pressurized from its connection side up to a predefinable nominal pressure, which is also referred to in technical terms as the design pressure, while the other separating device is simultaneously kept pressureless on its connection side, the device, in its particular embodiment with a bellows and a piston, can be pressurized from each side up to the nominal or design pressure while the opposite side remains pressureless, so that the bellows does not experience any relevant differential pressure. Applying the nominal pressure and restoring the pressureless state are carried out alternately as needed.Under all other operating conditions, where the piston is located between the opposing possible stop or travel positions in the associated housing, the same pressure prevails in all three fluid or media spaces or chambers within the device, and consequently there is no significant pressure difference at the bellows.

[0010] In contrast to conventional metal bellows accumulators with energy storage through a compressible working gas (US 3,336,948), the device according to the invention provides a media separator with a pressure transfer function, while largely relieving the pressure on the bellows during operation. The maximum differential pressure across the bellows is intended to be approximately 1 bar, which corresponds roughly to ambient pressure and can be generated by a vacuum on the connection side of the bellows when the piston, due to an operating pressure greater than the vacuum, reaches one of its travel positions adjacent to the bellows during operation. Furthermore, the device can also be used as a type of hydraulic accumulator if one of the connection sides of the bellows or piston is closed and a compressible working gas is enclosed in the housing.

[0011] In a preferred embodiment of the device according to the invention, a rigid coupling exists between the bellows and the piston, preferably formed by an incompressible fluid, such as a water-glycol mixture, which is enclosed in the housing. By using a liquid coupling medium as the rigid coupling, which completely fills the volume between one side of the bellows and the opposite side of the downstream piston, it is possible to limit the maximum and minimum bellows length during extension and compression, while simultaneously reliably preventing an undesirable or impermissible pressure differential. In this way, the piston, in addition to separating, also functions as a compensator.

[0012] In a further preferred embodiment of the device according to the invention, a trough-like recess in the piston, which opens towards an adjacent housing cover, receives a further fluid, preferably in the form of a working gas, such as nitrogen gas. In this way, the working gas creates an energy storage medium, and the piston side of the device can be considered part of a hydropneumatic storage system, provided the working gas is enclosed in the (storage) housing.

[0013] In a further preferred embodiment of the device according to the invention, the bellows inside the housing receives a third fluid, preferably a liquid that can be continuously introduced into and removed from the bellows via a connection in the adjacent housing cover. The interior of the bellows is thus in permanent fluid or media contact with a corresponding system circuit that interacts with the device.

[0014] In a further preferred embodiment of the device according to the invention, the bellows with its individual bellows folds is circumferentially encompassed by a sleeve-like support, at least in a starting position where the bellows folds are in an extended state. Preferably, the bellows has a closing part, preferably in the form of a closing plate, towards the piston. This closing part, provided with a guide ring on its circumference, comes into contact with an end region on the free end face of the support in the bellows' starting position. It is particularly preferred that the support is fixed to the adjacent housing cover by means of a fixing element comprising at least one screw. The housing cover engages partially into the interior of the bellows in a stepped manner with a central section, while maintaining a radial distance.In this way, the support can be attached simply, securely, and cost-effectively, thus reliably supporting the bellows folds outwards during operation. When the bellows moves within its support, the incompressible fluid between the bellows and piston reaches the outer side of the bellows folds facing the support, so that, in both the extended and retracted states, the fluid provides additional support for the bellows.

[0015] A particularly space-saving design with a high energy input rate is achieved when the free edge of the piston's trough rests flush against the inside of the adjacent housing cover at maximum piston deflection. The trough-like recess in the piston also allows for a space-saving design for the overall device, resulting in a short installation length. In a further particularly preferred embodiment of the device according to the invention, the piston's position within the housing is monitored by a monitoring device, preferably in the form of a displacement measuring system, and most preferably by means of a cable-extension sensor. This displacement measuring system can be connected to a central monitoring unit with evaluation electronics, enabling reliable monitoring of the device during operation and reliable control from the fluid side leading into the interior of the bellows.

[0016] The device according to the invention will now be explained in more detail using an exemplary embodiment. The only embodiment shown is...

[0017] The figure, in the form of a longitudinal section, shows the essential structure of the device with its individual components.

[0018] The figure shows a longitudinal section of a device comprising a hollow cylindrical housing 10. A piston 12 and a bellows 14 are housed together within the housing 10. The piston 12 and the bellows 14 define three distinct fluid chambers 16, 18, and 20 within the housing 10. Both the piston 12 and the bellows 14 are fully and flush within the housing 10, which is bounded at each end by a housing cover 22, 24. Both the piston 12 and the bellows 14 can move between the two housing covers 22, 24. The two essentially cylindrical housing covers 22, 24 are each recessed into the housing 10 from their free end faces and then held in position by a retaining ring 26, which is fixed along a threaded section 28 on the inner circumference of the housing 10.The respective retaining ring 26 is flush with the free end faces of the hollow cylindrical housing 10, and the respective housing cover 22, 24 is fixed to the adjacent retaining ring 26 by means of individual connecting screws 30 of a screw connection, in that the respective connecting screw 30 engages with one free end in the associated housing cover 22, 24. As can further be seen from the figure, the respective housing cover 22, 24 is enclosed at a central point in the usual manner by a sealing ring 32.

[0019] The piston 12 has a trough-like recess 34, which, with its hollow cylindrical outer wall 36, forms an integral part of a flat piston plate 38 extending transversely to the longitudinal axis LA of the device and, in a circular cylindrical shape, passing through the interior of the housing 10. The piston 12 as a whole is guided longitudinally on the inner circumferential side of the housing 10 and has, for this purpose, conventional sealing and guide bands 40 on its outer side. Viewed in the direction of the figure, the piston 12 is shown in its upper stop position, in which the free end edge of the outer wall 36 for the trough-like recess 34 is flush with the adjacent wall of the upper housing cover 22.The upper housing cover 22 contains two channel-like fluid passages 42 for introducing a working gas, particularly nitrogen gas, from the outside onto the fluid side 16 of the piston 12, with the right-hand channel 42 (as viewed in the figure) being fitted with a sealing plug 44. When the device is operated as a hydraulic accumulator, a corresponding sealing plug 44 is also provided for the left-hand channel 42 and any further channels of this type. When used as a media separator, however, the channel(s) 42 are kept clear to allow flow through the housing cover 22.Furthermore, the piston and bellows position shown in the figure is only an example and does not correspond to the actual operating position, in which the bellows 14 is at least partially extended and the piston 12 maintains a predetermined distance from the housing cover 22, so that the bellows 14 and piston 12 can position themselves independently relative to each other depending on the established force equilibrium. In particular, the axial length of the housing 10 can also be significantly greater.

[0020] Furthermore, the piston plate 38 has, by way of example, two filling valves 46 extending through this plate, which allow the introduction of another fluid, in particular in the form of an incompressible fluid, from the first fluid chamber 16 into the second fluid chamber 18. The incompressible fluid, forming a rigid coupling between the upper surface of the bellows 14 and the lower surface of the piston 12, can consist of a water-glycol mixture, which is thus fluid-tightly enclosed in the space between the piston 12 and the bellows 14 in the housing 10. To increase the storage capacity on the piston side with the working gas in the first fluid chamber 16, the trough-like recess 34, which is surrounded at its edges by the outer wall 36 of the piston 12, is preferably provided.

[0021] The bellows 14 inside the housing 10 receives a third fluid in the third fluid chamber 20, which is partially enclosed by the inner circumferential surface of the bellows 14. The third fluid is typically a liquid that can be continuously supplied to and discharged from the inside of the bellows 14 via a fluid-carrying connection 48 in the adjacent housing cover 24. The channel-like connection 48, which extends centrally through the lower housing cover 24, can be connected to a supply circuit (not shown) for the third fluid. The bellows 14, which can be made of stainless steel, for example, has individual, superimposed bellows folds 50. In the initial position of the bellows 14 shown in the figure, these folds are circumferentially enclosed at a predetermined radial distance by a sleeve-shaped support 52, which also ensures longitudinal guidance for the bellows 14 as a whole when it is retracted.The bellows 14 has an end section towards the piston 12, preferably in the form of a flat end plate 54, which is circumferentially enclosed by a guide ring 56. In the extended starting position of the bellows 14 shown, the guide ring 56 is in contact with the upper end region of the free end face of the support 52. When the bellows 14 moves from its maximally extended starting position, as shown in the figure, to a (maximally) retracted position, the guide ring 56 remains in contact with the inside of the support 52. The guide ring 52 has gaps on its outer circumference between individual guide ribs, which facilitate fluid exchange between the fluid chamber 18 and a fluid chamber between the support 52 and the outside of the bellows folds 50. Thus, the guide ring 56, with its outer circumference in the form of the guide ribs, slides along the inside of the support 52 during the movement of the bellows 14.The end plate 54 with the circumferential guide ring 56 can extend beyond the free end region of the sleeve-like support 52, but only if the fluid volume in chamber 18 is set too low. With the correct fluid volume in the fluid chamber 18, the plate 54 with the ring 56 can retract back into the free end region of the sleeve 52. To assist this retraction, an insertion ramp for the guide ring 56 can be provided at the upper free end of the sleeve 52. However, with the correct fluid volume setting in chamber 18, the position of the bellows 14 shown in the figure represents the maximum possible extension position.

[0022] The ring-shaped or sleeve-shaped support 52 is permanently fixed at its base to a stepped, projecting central portion of the lower housing cover 24 by means of a fixing element in the form of pin-shaped fixing screws 58, also in the form of set screws. As soon as the fixing screws 58 assume their fixed position, they are secured at least to the outside by the housing 10, which in this respect encompasses the fixing element at its edge. The central portion 60 engages at its base as a cylindrical block into the interior of the bellows 14 and supports its bellows folds 50 on the inside and opposite to the support 52, at least along a lower region.

[0023] To monitor the respective travel position of the piston 12 within the housing 10, a monitoring device is provided, preferably in the form of a displacement measuring system. In the illustrated embodiment of the device according to the invention, a cable-extension sensor 62 is used, which determines the unwound length of a cable 64, one free end of which is articulated to the piston plate 38 of the piston 12. The cable-extension sensor 62 is connected via a measuring cable connection 66 to measuring electronics (not shown) by means of which the operation of the device can be continuously monitored.

[0024] The device according to the invention makes it possible to limit the maximum and minimum bellows length for the bellows 14 during stretching and compression, while simultaneously reliably preventing an impermissible pressure differential. This is achieved by using the liquid coupling medium in the second fluid chamber 18, which is located between the bellows 14 and the adjacent piston 12 and completely fills the corresponding fluid chamber 18. On the opposite side of the piston 12, a working gas, preferably in the form of nitrogen gas, is located in the associated first fluid chamber 16. Alternatively, a spring assembly (not shown) could also be present in the first fluid chamber. In this way, the piston 12, with a working gas enclosed in the housing in the first fluid chamber 16 or with the spring assembly, fulfills a function similar to that of a hydraulic accumulator.If the device is intended to function as a media separator, it would contain a medium or fluid that needs to be separated from the medium on the connection side of the bellows 14 with the third fluid chamber 20. In this respect, in one embodiment as a media separator, a fluid connection to a supply circuit (not shown), for example in the form of a hydraulic circuit, could also be established via the channel-like fluid passages 42 in the upper housing cover 22.

[0025] To limit the movement of the bellows 14 to a minimum compressed and maximum extended length, the piston 12 is positioned between the upper piston stop with the upper housing cover 22 and a piston position located below it, which is determined by the rigid coupling via the second fluid chamber 18. This creates a displacement volume corresponding to the volume that the bellows 14 displaces between its minimum and maximum permissible lengths. If the entire system, consisting of the two separating devices bellows 14 and piston 12, is pressurized to the maximum design pressure on the connection side of the piston 12 and depressurized on the connection side of the bellows 14 thanks to the fluid-carrying connection 48, then the bellows 14 is held in one of its permissible folded extreme positions by the enclosed coupling medium or by the incompressible fluid in the second fluid chamber 18.If, however, the system consisting of bellows 14 and piston 12 is subjected to the maximum design pressure on the connection side of the bellows 14 via the fluid-carrying connection 48, and the piston 12 is held pressureless on its connection side by means of the channel-like fluid passages 42, then the enclosed incompressible fluid in chamber 18 acts as a rigid coupling, pressing the piston 12 into its stop position against the upper housing cover 22. In this position, the bellows 14 is then at its maximum extended length, as shown in the figure.

[0026] The pressure in the coupling medium, or the pressure of the incompressible fluid in chamber 18, then corresponds to the pressure on the connection side of the bellows 14 and the fluid-carrying connection 48. In this respect, there is no differential pressure between the inside and outside of the bellows 14 with its bellows folds 50. The maximum possible differential pressure at the bellows 14 can be approximately 1 bar and is generated by a vacuum on the connection side of the bellows 14 via the connection 48 in the lower housing cover 24 when the piston 12 is forced into one of its lower travel positions by a pressure greater than the vacuum. Accordingly, a special feature of the device is that the system, as a media separator consisting of the separating elements bellows 14 and piston 12, can be pressurized from either fluid side up to the design pressure while the opposite side remains pressureless, without the bellows 14 experiencing any significant differential pressure.Under all other operating conditions, where the piston 12 is located between its maximum deflection positions within the housing 10, the same pressure prevails in all three fluid spaces 16, 18 and 20 and consequently there is no harmful pressure difference at the bellows 14.

[0027] It should also be noted that, depending on the operating conditions and the friction pairing between the seals 40 on the outer circumference of the piston 12 and the wall of the housing 10, a certain differential pressure can occur between the incompressible fluid and the connection side of the piston 12 with the channel-like fluid passages 42. This pressure difference is easily tolerated by a conventionally constructed piston 12, and no pressure difference exists at the bellows 14, since the pressures inside and outside the bellows 14 can always equalize via axial movement of the bellows 14. This has no equivalent in the prior art.

Claims

Patent claims 1. Device, at least comprising a piston (12) and a bellows (14) which are housed in a common housing (10) and separate three different fluid spaces (16, 18, 20) from each other, characterized in that both the piston (12) and the bellows (14) are fully and without protrusion received in the housing (10), which is bounded at its ends by housing covers (22, 24) between which both the piston (12) and the bellows (14) move.

2. Device according to claim 1, characterized in that a rigid coupling exists between bellows (14) and piston (12), preferably formed from an incompressible fluid, such as a water-glycol mixture, which is enclosed in the housing (10).

3. Device according to claim 1 or 2, characterized in that a trough-like recess (34) in the piston (12), which opens towards an adjacent housing cover (22), receives a further fluid, preferably in the form of a working gas, such as nitrogen gas, which is received in the housing (10).

4. Device according to one of the preceding claims, characterized in that the bellows (14) inside the housing (10) receives a third fluid, which is preferably a liquid that can be continuously introduced into and removed from the bellows (14) via a connection (48) in the adjacent housing cover (24).

5. Device according to one of the preceding claims, characterized in that the bellows (14) with its individual bellows folds (50) is supported circumferentially at least in a sleeve-like support (52). a starting position is included in which the bellows folds (50) are in an extended state.

6. Device according to one of the preceding claims, characterized in that the bellows (14) has a closing part, preferably in the form of a closing plate (54), in the direction of the piston (12), which is provided with a guide ring (56) on its circumferential side and comes into sliding contact with an end area on the free end face of the support (52) in the initial position of the bellows (14).

7. Device according to one of the preceding claims, characterized in that the support (52) is fixed to the adjacent housing cover (24) via a fixing means having at least one screw (58), which engages partially in a stepped manner with a central part (60) while maintaining a radial distance into the interior of the bellows (14).

8. Device according to one of the preceding claims, characterized in that, during the movement of the bellows (14) within its support (52), the incompressible fluid between bellows (14) and piston (12) reaches the outside of the bellows folds (50) facing the support (52).

9. Device according to one of the preceding claims, characterized in that a free edge of the piston (10) is flush against the inside of the adjacent housing cover (22) when the piston is in its maximum deflected position.

10. Device according to one of the preceding claims, characterized in that the travel position of the piston (12) within the housing (10) is monitored by means of a monitoring device, preferably in the form of a displacement measuring system, particularly preferably by means of a cable pull sensor (62).

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