Piston accumulator

Abstract

The invention relates to a piston accumulator comprising an accumulator housing (10) and a separator piston (12) which is longitudinally moveably guided therein and separates two media chambers (14, 16) from one another inside the accumulator housing (10), in particular separating a media chamber (14) with a working gas from another media chamber (16) with a fluid, such as hydraulic oil, wherein the separator piston (12) has two piston parts (13, 15) which are formed as discs with the same outer diameter and which are securely connected to one another and held at a distance from one another via an elastically flexible piston rod (17), which, with the influence of at least one external force, allows for a curvature as a whole, starting from a starting state, and returns to the starting state with the removal of the respective force.

Description

[0001] HYDAC TECHNOLOGY GMBH

[0002] Piston accumulator

[0003] The invention relates to a piston accumulator with an accumulator housing and a separating piston which is guided longitudinally therein and which separates two media spaces from each other within the accumulator housing, in particular a media space with a working gas from another media space with a liquid, such as hydraulic oil.

[0004] Piston accumulators of this type are commercially available. They find widespread applications in hydraulic systems, for example, for energy storage, for emergency actuation to dampen mechanical shocks or pressure surges, for vehicle suspensions, and the like. DE 197 01 303 A1 discloses a piston accumulator with a first separating piston that can be moved longitudinally within an accumulator housing and separates a liquid side of the accumulator from its gas side. A second separating piston is arranged on the liquid side of the accumulator. A space between the two separating pistons is filled with a sealing medium that is preloaded under the action of the two separating pistons, which can be moved toward each other regularly via a force accumulator in the form of a compression spring.For this purpose, a connecting rod passes through the two separating pistons, and the compression spring rests at one end on the first separating piston and at the other end on the connecting rod. Thus, the first, block-shaped separating piston is guided longitudinally and stably over a relatively long distance using several sealing and guide bands arranged on the outer circumference on the inside of a rigidly designed accumulator housing; however, it is held on the connecting rod so that it can move axially against the preload of the compression spring. In contrast, the second, disc-shaped separating piston is guided with only one sealing ring along the inside of the accumulator housing and is firmly connected to the connecting rod.In this way, the two separating pistons, one designed as a solid block and the other as a disc-shaped body, are preloaded against each other under the effect of the compression spring acting on the connecting rod, so that a type of variable two-part separating piston is created with a gas barrier located in the space between the separating pistons, which prevents the small gas molecules from creeping through the otherwise tight sealing system in the form of the sealing rings arranged on the outer circumference of the separating pistons when the oil side is relaxed, which would impair the functional reliability of the known piston accumulator in the long term.

[0005] Due to the rigid construction of the accumulator housing and the separating piston arrangement, despite the ability of the separating pistons to move relative to each other, the known piston accumulator arrangement is only inadequately suitable for use where these are subject to relevant bending stresses from both the accumulator housing side and the separating piston arrangement. For example, DE 10 2016 003 345 B4 shows a bending stress for piston accumulators in the context of a balancing device for compensating the imbalance of wind turbine rotors, consisting of at least one rotor blade with two piston accumulators extending along its longitudinal axis, the separating pistons of which are each subject to prestressing via a compressible medium and which are connected to each other via a fluid line carrying an incompressible medium.

[0006] Control valve, which is connected to the respective fluid line and establishes the media connection between the two piston accumulators of a pair or separates them from each other,

[0007] acceleration sensor,

[0008] Rotor position sensor, and

[0009] Control system for evaluating sensor data and actuating at least one pair of piston accumulators by controlling the control valve. This balancing device makes it possible to balance the respective rotor of a wind turbine during operation. This is regularly necessary because imbalances can develop, particularly during operation, for example due to dirt deposits on the rotor blades or uneven wind flow, for example, when turbulence occurs during wind turbine operation.

[0010] The rotor blades are also regularly subject to deformations during operation of the wind turbine. Kinematic models are used to describe these deformations. These models are capable of describing the deformations of a rotor blade, for example, based on the assumptions of an Euler-Bernoulli bending beam. The theoretically deformations on the respective rotor blade correspond to practical measured values, which are preferably based on a combination of photogrammetric and laser scanner measurements. In any case, in practice, rotor blade deformations regularly occur in the form of reversible deflections along the rotor's longitudinal axis, and the piston accumulators hinged to the rotor blades according to the teaching of DE 10 2016 003 345 B4 must be able to follow these deformations, which result from a constantly changing bending pattern caused by the changing wind flow and the turbulence that occurs during operation.The piston accumulator solutions, which are usually made of solid steel materials, are then no longer able to follow the changing bending curve of the rotor blade, which often leads to a failure of the connection point between the piston accumulator and the rotor blade and thus to the unusability of the unbalance compensation device as a whole.

[0011] Irrespective of the initial situation described above for wind turbines, piston accumulators can also be exposed to other changing alternating bending stresses, for example if the piston accumulator is exposed to strong vibrations during the operation of a hydraulic system, such as when used in aircraft, rockets, military vehicles, agricultural machinery, etc.

[0012] Based on this prior art, the invention is therefore based on the object of further improving a piston accumulator of the type mentioned in such a way that even in the event of strong bending stresses, safe operation is guaranteed, even in conjunction with third-party components.

[0013] A piston accumulator having the features of patent claim 1 in its entirety solves this problem.

[0014] Because, according to the characterising part of patent claim 1, the separating piston has two piston parts which are designed as discs with the same outer diameter and which are held at a distance from one another and firmly connected to one another via an elastically flexible piston rod which, under the action of at least one external force, allows a curvature as a whole from an initial state and returns to the initial state when the respective force is removed, a piston accumulator is created which ensures that even in the event of large deflections of the accumulator housing, the separating piston with its two piston parts can follow the corresponding deflection without hindrance and, when the load is removed, returns to its initial state without deformation, and remains fully functional even in the event of the aforementioned deflection of the accumulator housing.A key factor in this is the rigid coupling of the two piston parts via the elastically flexible piston rod, which enables linear-elastic behavior (Hooke's law) for the multi-part separating piston. Furthermore, the elastically flexible coupling via the piston rod prevents the disc-shaped piston parts from tilting against each other within the accumulator housing to such an extent that smooth operation would no longer be guaranteed.

[0015] Further advantageous embodiments of the piston accumulator according to the invention are the subject of the dependent claims. In particular, the flexibility of the separating piston with its two piston parts, via the elastically flexible piston rod arranged between them, allows the piston rod to seamlessly follow the resulting bending line with its longitudinal axis in the event of any curvature of the accumulator housing along a central curvature axis. This also applies to the case of resetting, when the curved line again transitions into a straight central axis line. This has no equivalent in the prior art.

[0016] In the following, the piston accumulator according to the invention is explained in more detail using an embodiment according to the drawing.

[0017] In a schematic and not to scale representation, Figure 1 shows, in the form of a longitudinal section, the edge-side end areas of the storage housing constructed in a sandwich construction as a liner composite;

[0018] Figure 2 shows the front view of a housing cover for the storage housing according to Figure 1;

[0019] Figure 3 shows an enlarged section of the end section of the storage housing designated by X in Figure 1;

[0020] Figure 4 shows a schematic representation of the possible curvature of the storage housing according to Figure 1 when a bending force is applied in the direction of the arrow;

[0021] Figures 5 and 6 show a side view and a front view of a separating piston for the storage housing according to Figure 1;

[0022] Figure 7 shows the separating piston shown in Figure 5, inserted into a storage housing according to Figure 1; and

[0023] Figure 8 shows the use of a piston accumulator according to a

[0024] Design according to Figure 7 for a wind turbine with three rotating rotor blades.

[0025] Figure 1 shows a longitudinal section through an accumulator housing 10 of a piston accumulator, and Figure 7 shows the accumulator housing 10 with a longitudinally movable separating piston 12 arranged therein, which separates two media chambers 14, 16 from one another within the accumulator housing 10 and is shown in more detail in Figures 5 and 6. The media chamber 14 can serve to hold a working gas, such as nitrogen gas, and the further media chamber 16 serves to hold an operating fluid, such as hydraulic oil. Since the accumulator housing 10 can have a correspondingly large overall length, for example on the order of 2 meters, the accumulator housing 10 is only shown in the region of its end areas in Figures 1 and 7; in the central area, however, the accumulator housing 10 also corresponds to the edge-side end area design as far as the liner structure of the accumulator housing 10 is concerned.Accordingly, the storage housing 10 is constructed in a sandwich design from individual, partially different layers 18, 20, 22, and 24 in such an elastic manner that, under the action of at least one external force F, starting from an initial state as indicated in Figures 1 and 7, it permits a curvature as a whole, according to the simplified representation in Figure 4. When the respective force F is removed, the storage housing 10 elastically returns to its initial state. In this respect, the sandwich design allows for a linear-elastic behavior for the storage housing 10.

[0026] Within the framework of the aforementioned sandwich construction, the innermost layer 18 of the housing 10 is gas-impermeable, and the respective outwardly following layers 20, 22, and 24 are formed from a fiber winding. The corresponding layer composite is shown in particular in Figure 3, which shows an enlarged representation of the section designated X in Figure 1. The innermost layer 18 is designed, in terms of its wall thickness, as a thin steel tube, which is preferably produced from a single piece by means of flow forming and which, on the inner circumference, forms the smooth running surface 26 for the separating piston 12, as shown in Figure 7. The steel liner 18 extends over the entire length of the storage housing 10 up to the free front end thereof. The respective fiber winding for the storage housing 10 has a different winding direction than the fiber winding preceding it in the winding sequence.The respective fiber winding preferably consists of carbon fiber material, and the fiber winding of layer 20 is wound circumferentially onto the steel layer 18, thus having a winding direction of less than 90° to the longitudinal direction 28 of the storage housing 10. The subsequent layer 22, in contrast, can deviate by 0° to 45° from the aforementioned 90° winding direction; however, it is also possible to apply the respective layer 22 to the winding 20 largely parallel to the longitudinal direction 28 of the storage housing 10. Other winding directions are possible here, as is the application of additional layers depending on the respective application and the required rigidity for the overall storage housing 10. The outermost layer 24, in turn, consists of a fiber winding in the same direction as the wound layer 20, thus with a radial winding direction at 90° to the longitudinal direction 28.

[0027] As Figure 3 further shows in particular, an annular connecting part 30 is provided at each end of the storage housing 10, which are designed as identical parts. The annular or cylindrical connecting part 30 is penetrated by the steel liner 18 on its inner circumference and opens out at the free end of the connecting part 30. On the outer circumference, each connecting part 30 has an annular receiving groove 32 for receiving fiber layers of the two outermost windings 22 and 24. The receiving groove 32 is delimited on one side by a connecting flange 34 and on its inner side by a fixing ramp 36. Both the connecting flange 34 and the fixing ramp 36 have obliquely extending contact surfaces 38, 40 on their adjacent sides, which together form a cone in a fictitious extension towards a groove base 42.The fixing ramp 36 is thereby overlapped by the third layer 22, which in this way comes into direct contact with the groove base 42 of the receiving groove 32. The third layer 22 tapers to a point at its free front end and ends at the base of the inclined contact surface 38. The tapered end of the third layer 22 delimits a diagonal wall section 44 of this third layer 22, which, together with the inclined contact surface 38 of the connecting part 30, forms a further V-shaped engagement groove 46, which, likewise designed as an annular groove, serves for the engagement of the free end of the outer layer 24. The second layer 20, which follows the steel layer 18 in the winding assembly, nestles against a ramp section 48 of the fixing ramp 36, which in this area borders the innermost layer 18 at the base with a slight angle of inclination.In this way, within the framework of the sandwich construction, a secure layer or liner bond of the individual layers 18, 20, 22 and 24 is achieved in their free front area via the respective connecting part 30 with connecting flange 34 and fixing ramp 36.

[0028] At the point of transition between the steeply running contact surface 40 and the flatly running ramp rise surface in contrast, including the ramp part 48, the fixing ramp 36 has, as shown in Figure 3, a substantially horizontally running circumferential or engagement surface 50, which serves for the penetration of individual, preferably metallic, retaining pins 52, which are evenly distributed in the radial direction at discrete distances from one another around the storage housing 10 and firmly connect the layer assembly of the individual layers 18, 20, 22 and 24 to the connecting part 30 and thus ensure a secure layer assembly.

[0029] On the free end faces of the respective connecting flange 34 of the connecting part 30 there are pin recesses 54, which are evenly distributed around the outer circumference of the connecting flange 34. The respective cover part 56 can be pinned to the associated connecting part 30 via the corresponding pin recesses 54, with such a cover part 56 being present at each free end of the storage housing 10. The corresponding pins, not shown in detail, are to be attached to the cover part 56 along an annular surface 58 provided for this purpose, the fictitious inner course of which is represented by a dash-dotted line 60. In addition, the corresponding annular surface 58 serves to apply an adhesive to its inner side facing the storage housing 10 in order to create a media-tight connection between the two media chambers 14, 16 and the environment.Furthermore, in an embodiment not shown in detail, it is possible to connect the respective cover part 56 to the storage housing 10 in a media-tight and pressure-tight manner via a fiber winding. In the center region of each cover part 56 there is a connection opening 62 which can be tightly closed with the media chamber 14 on the gas side of the storage housing 10 and remains open on the liquid side in order to connect the further media chamber 16 to a conventional hydraulic circuit (not shown). In order to separate the two media chambers 14, 16, i.e. a gas side from a liquid side, in a media-tight manner, a separating piston 12 is inserted into the storage housing 10 in a longitudinally movable manner as shown in Figure 7. This separating piston 12 is shown in more detail in Figures 5 and 6, with Figure 6 showing a front view from the right of the separating piston 12 according to Figure 5.Accordingly, the separating piston 12 has two piston parts 13, 15, which are designed as disks with the same outer diameter and which are firmly connected to one another via an elastically flexible piston rod 17, held at a distance from one another. The piston rod 17, under the action of at least one external force F, allows a curvature as a whole, starting from an initial state, and returns to the initial state when the respective force F is removed. In this way, the double-disk piston arrangement of the separating piston 12 is suitable for following a curvature of the storage housing 10, as shown by way of example in Figure 4. Like the two piston parts 13, 15, the piston rod 17 is made of a suitable metal material, with the piston rod 17 preferably being designed to be more flexurally elastic than the disks 13, 15.In particular, the piston rod 17 prevents the relatively thin discs for the two piston parts 13, 15 from tilting along the running surface 26 in the accumulator housing 10 as part of the guide and thus inhibiting the movement of the separating piston 12.

[0030] One piston part 13, which faces one media chamber 14, has a guide band 19 on its outer circumference, and the other piston part 15, which faces the further media chamber 16, has a further guide band 21 and an annular seal 23 made of a conventional elastomer material. The two annular guide bands 19, 21 are designed as identical parts and consist of a material with good sliding properties, which is preferably correspondingly temperature-resistant, such as PTFE material. Both the guide bands 19, 21 and the annular seal 23 are inserted into annular receiving grooves in the associated piston parts 13, 15 and slide along the inner circumference of the storage housing 10 in the form of the running surface 26. In this respect, according to the illustration in Figure 5, the annular seal 23 is arranged between the two guide bands 19, 21 on the other piston part 15.Due to the disc-shaped arrangement of the two piston parts 13, 15, an annular space 25 is formed between them, which contains the medium of one media chamber 14, in particular in the form of the working gas. In order to avoid the aforementioned tilting of the disc-shaped piston parts 13, 15 and yet ensure that the separating piston 12 as a whole can follow the curved path of a storage housing 10 subject to bending stress, the distance between the two disc-shaped piston parts 13, 15 is greater than 1 / 3 of the diameter of the respective piston part 13, 15 and in any case smaller than the diameter. Furthermore, to ensure reliable displacement, the disc thickness of the piston part 13 with the guide band 19 is selected to be smaller than the disc thickness of the other piston part 15 with the further guide band 21 and the sealing ring 23.For unobstructed operation, it is further provided that the piston rod 17, with its two opposing shoulders 27, merges flush into the mutually facing free end faces 29, 31 of the two piston parts 13 and 15, respectively. Accordingly, the piston rod 17, with its opposite end regions, passes through the respective piston part 13, 15, and the piston rod 17 is secured to the associated piston part 13, 15 along this end region via a threaded section 33 by means of a conventional lock nut 35, only shown in the illustration according to Figure 6.

[0031] As can be further seen from Figures 5, 6, and 7, the discs of the two piston parts 13, 15 are provided with annular recesses 37, which serve to save weight and also increase the elasticity of the discs 13, 15. The recesses 37 are essentially identical on the opposite end faces of the two piston parts 13, 15 and are arranged concentrically with a central recess 39, which accommodates the respective associated threaded portion 33 of the piston rod 17 and the lock nut 35. Furthermore, an annular recess 37, widened on both the outer and inner circumferences, is provided on the inner end wall of the piston part 15, concentrically arranged with these recesses 37. The separating piston 12, designed to be elastic in this way, can also be used for "normal" storage housings 10; Likewise, storage housings 10 of the type presented can be used with "conventional" separating pistons.Instead of the lock nut 35, any other suitable connection can be used, such as bolting, gluing or using a locking pin.

[0032] Figure 4 now shows the elevated storage housing 10 on two bearing blocks 64 and a compressive force F is applied from above at an inlet point 66 in the center such that the storage housing 10 deflects as shown in Figure 4. The storage housing 10 is shown in Figure 4 in idealized form, in particular without the two end cover parts 56. If the force F is removed, the accumulator or the storage housing 10 returns to its original position as shown in Figures 1 and 7. It is understood that if the storage housing 10 is held at the inlet point 66 and the force is applied from below via the bearing blocks 64, a deflection comparable to that shown in Figure 4 occurs.

[0033] If the piston accumulator is installed as part of a balancing device for compensating the imbalance of wind turbine rotors, as shown by way of example in Figure 8, it is secured along the two bearing blocks 64 on one of the two blade sides of the respective rotor blade 68. In Figure 8, the partially illustrated tower of a wind turbine is designated 70. As is usual for wind turbines, a nacelle 72, also known in technical terms as a "gondola," is arranged at the upper end of the tower 70, which can be rotated forwards and backwards by two to three revolutions, and is rotatable about the tower's vertical axis. A rotor hub for three rotor blades 68 of a three-blade rotor, rotatably mounted on the nacelle 72, is not visible in the simplified illustration in Figure 8. Within each rotor blade 68 is a pair of piston accumulators, comprising an inner piston accumulator 74 and an outer piston accumulator 76.The respective piston accumulator 74, 76 is basically constructed as shown in Figure 7 with corresponding end-side closure parts, such as the respective cover part 56. The respective piston accumulator 74, 76 is attached to the associated rotor blade 68 via the associated bearing blocks 64.

[0034] The respective inner piston accumulator 74 is arranged in the area of ​​the blade root adjacent to the rotor hub, and the outer piston accumulator 76, in contrast, is offset toward the respective blade tip by a distance that extends along the longitudinal alignment of the respective rotor blade 68. Preferably, the outer piston accumulator 76 is dimensioned more slenderly than the inner piston accumulator 74 of the pair, corresponding to the smaller installation space available within the respective rotor blade 68 near the blade tip.

[0035] In the inner piston accumulators 74, the media or working chamber 14, which carries the compressible pressure medium such as the working gas, preferably in the form of nitrogen gas, faces the blade root, whereas in the outer piston accumulators 76, the working chamber 14, which carries the compressible medium, faces the blade tips. If necessary, the media chamber 14 of the inner piston accumulator 74 can also carry ambient air and be kept depressurized. In the other media chambers 16 of the piston accumulators 74 and 76, which face each other within the rotor blade 68, the incompressible medium, such as hydraulic fluid, is located as a mass that can be displaced within a respective rotor blade 68 to compensate for imbalance. These mutually facing fluid-carrying media chambers 16 are connected to one another via a fluid line 78, for example in the form of a pipe or hoses.In the respective fluid line 78, adjacent to the respective inner piston accumulator 74, a control valve 80 is arranged, for example in the form of an electromagnetically actuated switching valve, which can be centrally controlled by a control system 82. In order to transmit the values ​​of the transverse accelerations acting on the support structure of the wind turbine transversely to the rotor shaft to the control system 82, an acceleration sensor 84 is arranged in the tower head or the nacelle 72 and is connected to the control system 82 via corresponding measuring signal lines. Furthermore, a rotor position sensor 86 is provided, which, in the form of a rotor speed sensor or a rotor rotation position sensor on the rotor shaft, determines the position of the rotor blades 68 and transmits this data to the control system 82 via another measuring signal line.To perform an imbalance compensation process using the balancing device, the wind turbine is brought to an initial state by increasing the rotor speed to a speed at which the hydraulic fluid located in the fluid-carrying media chambers 16 of the piston accumulators 74, 76 and in the fluid line 78 between them is displaced outward toward the blade tips under the influence of centrifugal force when the control valves 80 are open, thereby compressing the working gas in the respective media chamber 14 of the outer piston accumulators 76, so that they are in a charged state. To detect the presence of an imbalance, the wind turbine must be operated at a critical speed. If an imbalance is present, operation at these speeds leads to transverse tower vibrations and thus to the occurrence of acceleration signals from the acceleration sensor 84.The determination of which of the rotor blades 68 has a different mass moment of inertia is carried out using the rotor rotation position sensor on the rotor shaft, which determines the precise position of the rotor blades 68 at any given time. From the instantaneous value of the lateral acceleration of the rotor position, the control system 82 determines which rotor blade 68 has the different mass moment of inertia and provides a control signal to the control valves 80, which partially discharge the relevant charged piston accumulators 76 to shift the mass of the incompressible hydraulic fluid such that no more lateral acceleration is measured. The rotor is then completely balanced.

[0036] It is understood that during operation of the rotor blades 68, the influence of wind force, including in the context of turbulence, leads to deformations due to bending forces, in particular to bending of the respective rotor blade 68 in its longitudinal orientation. Thanks to the piston accumulator solution described above, using a flexurally elastic accumulator housing 10 and / or a flexurally elastic separating piston 12, the respective bending deformations of the rotor blade 68 can be absorbed in all directions, whereby the piston accumulator pairs 74, 76 can reliably provide mass compensation to compensate for the imbalance of the rotor blades 68, even in the case of the described deflection.

Claims

Patent claims 1. Piston accumulator with an accumulator housing (10) and a separating piston (12) guided longitudinally therein, which separates two media spaces (14, 16) from each other within the accumulator housing (10), in particular a media space (14) with a working gas from a further media space (16) with a liquid, such as hydraulic oil, characterized in that the separating piston (12) has two piston parts (13, 15) which are designed as disks with the same outer diameter and which are held at a distance from each other by an elastically compliant piston rod (1 7), which allow a curvature as a whole from an initial state under the influence of at least one external force (F) and return to the initial state when the respective force (F) is removed.

2. Piston accumulator according to claim 1, characterized in that one piston part (13), which faces one media space (14), has a guide band (19) on its outer circumference and that the other piston part (15), which faces the further media space (16), has a further guide band (21) and a ring seal (25), which are arranged adjacent to one guide band (19) of one piston part (13) on the outer circumference of the other piston part (15).

3. Piston accumulator according to claim 1 or 2, characterized in that an intermediate annular space (25) is defined by the two piston parts (13, 15), which contains the medium of one media space (14), in particular in the form of the working gas.

4. Piston accumulator according to one of the preceding claims, characterized in that the distance between the two disc-shaped piston parts (13, 15) or the distance between the two guide bands (19, 21) is greater than 1 / 3 and less than the diameter of the respective piston part (13, 15).

5. Piston accumulator according to one of the preceding claims, characterized in that the disk thickness of the piston part (13) with the guide band (19) is smaller than the disk thickness of the other piston part with the further guide band (21) and the sealing ring (23).

6. Piston accumulator according to one of the preceding claims, characterized in that the piston rod (17) with two opposing shoulders (27) transitions planarly into the mutually facing free end faces (29, 31) of the two piston parts (13, 15).

7. Piston accumulator according to one of the preceding claims, characterized in that the piston rod (17) with its mutually opposing end regions extends through the respective piston part (13, 15) and is fixed to this associated piston part (13, 15) along this end region by means of a threaded section (33) by means of a lock nut (35).

8. Piston accumulator according to one of the preceding claims, characterized in that the disks of the two piston parts (13, 15) are provided with annular recesses (37).

9. Piston accumulator according to one of the preceding claims, characterized in that the annular recesses (37) extend concentrically to a central recess (39) which is the respective end region of the piston rod (17) is engaged with the lock nut (35). Piston accumulator according to one of the preceding claims, characterized in that the two guide bands (19, 21) are identical and, viewed in the axial direction, have a greater extent than the sealing ring (23), which is preferably made of an elastomer.

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