Hydraulic Accumulator

Abstract

1. A hydraulic accumulator, in particular in the form of a piston accumulator, comprising a separating element 10 which separates in a fluid-tight manner two fluid spaces 16, 18 arranged in an accumulator housing 14 from each other, in particular a closed accumulator space 20 containing a working gas from a liquid space 22 containing a hydraulic fluid, such as hydraulic oil, and a fluid connection 24 which is in a fluid-guiding connection with one of the fluid spaces 18, characterized in that in the part of the accumulator housing 14 which has the fluid connection 24, a magnetic field generating device 42 is accommodated, in order that magnetizable particles can be separated in a purifying manner in the direction of the magnetic field generating device 42 from the fluid respectively located between said part of the accumulator housing 14 and the separating element 10 and can be deposited therein.

Description

[Technical field]

[0001] The invention relates to a hydraulic accumulator, in particular in the form of a piston accumulator, which comprises a separating element fluid-tightly separating two fluid spaces arranged in an accumulator housing from each other, in particular a closed accumulator space containing a working gas from a liquid space containing a hydraulic fluid, such as hydraulic oil, and which fluid connection is in a fluid-guiding connection with one of the fluid spaces. [Background technology]

[0002] Hydraulic accumulators, for example (hydropneumatic) piston accumulators, are used in hydraulic systems to store a defined volume of liquid under pressure, for example hydraulic oil, and to return it to the system when required. In the case of commonly used hydropneumatic piston accumulators, in which a piston separates an oil-side liquid space from an accumulator space enclosed in said accumulator housing, which contains a working gas, such as nitrogen, the position of the piston changes during operation of the hydraulic accumulator, so that the hydraulic accumulator stores hydraulic oil when the pressure increases, and at the same time the working gas is compressed in the other fluid space or accumulator space. When the pressure drops, the gas thus compressed expands again and displaces the accumulated hydraulic oil, which is returned to the hydraulic circuit. The change in the volume of the working space during operation thus leads to a corresponding axial movement of the piston inside the accumulator housing in each case.

[0003] In this connection, such hydraulic accumulators are connected to a hydraulic working circuit within the framework of the operation of a hydraulic device, for example a working cylinder. The hydraulic working circuit basically has a filter arrangement with a filter element for cleaning and removing particle contamination from the working fluid, for example hydraulic oil. The filter element can be replaced with a new element if necessary. Despite such a filter arrangement, if contamination particles reach the clean side of the fluid and then arrive in the hydraulic accumulator, it is inevitable that this will cause damage to such accumulator and its components. Furthermore, since the filter element is limited in terms of its through-flow capacity, it is not always possible to use the filter element at very high volumetric flows and therefore high fluid pressures. In particular, when using piston accumulators, particle contamination can undesirably reach the sealing system of the separating piston. This can lead to failures of the accumulator and the hydraulic device connected to it. Since the particulate contamination generated is often caused by wear of hydraulic equipment, which is usually metallic in nature, and particularly during mechanical failure, such particles generated may be of such a size that the elastomeric material of the sealing device provided on the separating piston becomes non-dense or even destroyed.

[0004] From DE 10 2016 007 798 A1 a hydropneumatic piston accumulator is known, which has an accumulator housing with a cylinder tube defining a longitudinal axis, which is hermetically closed at both ends by a housing cover in each case, in which a piston is guided as a separating element in such a way that it can be moved in the longitudinal direction, which separates a fluid space for a compressible fluid, such as a working gas, in the housing from a further fluid space for an incompressible fluid, such as hydraulic oil, and furthermore a distance measuring device for contactlessly detecting the position of the piston in the housing, which has a non-magnetic measuring tube that runs along the longitudinal axis through a through-hole formed in the piston from one housing cover to the other and is sealed with respect to the interior space of the housing. A position sensor is guided in such a way that it can be moved in the tube itself, which follows the piston movement in the measuring tube by means of magnetic forces acting between the position sensor and the piston. A permanent magnet is provided on the piston to generate a magnetic force for forcing a tracking movement of the position sensor in the measuring tube. Such a permanent magnet, which moves continuously together with the separating piston during operation of the accumulator, is accommodated in the fluid space with the compressible working gas.

[0005] DE 41 16 482 A1 discloses a method and a device for measuring the pressure of a working gas in a pneumatic accumulator, which can be connected to a hydraulic working circuit and in which the working gas is separated from the operating or working liquid via a separating element in the form of an elastomeric accumulator bladder. When the accumulator bladder is in a definable position, the gas pressure which can be assigned to the accumulator bladder at this position is measured by a pressure value sensor arranged on the fluid side, and for this purpose the position of the disk valve of the accumulator is monitored by a monitoring device. For this purpose, the disk valve has a switching element with a permanent magnet in the fluid connection of the accumulator, the associated sensor consisting of a switch which can be actuated by a magnet or making use of the so-called Hall effect as soon as the switching element passes by such a sensor depending on the operating position of the disk valve and activates it.

[0006] Such a cube-shaped magnet, which is constantly reciprocating during operation of the accumulator, is not well suited to effectively prevent particulate contamination from occurring on the liquid side of the accumulator, as is a ring magnet located on the gas side of the accumulator housing. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] DE 102016007798 A1 [Patent Document 2] DE 4116482 A1 Summary of the Invention [Problem to be solved by the invention]

[0008] Starting from this prior art, the object underlying the present invention is therefore to further improve the known hydraulic accumulator solutions in such a way that failure cases can also be eliminated in the event of metal particle contamination. [Means for solving the problem]

[0009] This problem is solved by a hydraulic accumulator having the features of claim 1.

[0010] According to the characterizing feature of claim 1, a magnetic field generating device is accommodated in the part of the accumulator housing having the fluid connection, which is adapted to separate magnetizable particles from the fluid respectively located between the part of the accumulator housing and the separating element in a clean manner towards the magnetic field generating device and to deposit them on the magnetic field generating device, so that a strong, stationary magnetic field can be generated in the fluid region of the accumulator housing, so that magnetizable, in particular metallic, particles are collected in a central location and thus removed from the fluid without causing damage, in particular damage to a separating element such as a separating piston, as long as they reach the liquid side of the accumulator, in particular without causing damage to the separating element such as a separating piston with a sealing ring and a guide band of a hydropneumatic piston accumulator. Otherwise, in addition to sealing problems, the separating piston may also be "fressen" due to friction inside the accumulator housing, so that it can no longer move, thereby rendering the hydraulic accumulator totally useless. In particular, when a fluid flow is formed in which the filter device finds its limits, metallic magnetizable particles are reliably removed from the fluid flow by the magnetic separation of the hydraulic accumulator.

[0011] In an advantageous embodiment of the hydraulic accumulator of the invention, the part of the accumulator housing carrying the magnetic field generating device is a housing cover, which closes the end of the tubular wall part of the accumulator housing facing the liquid side of the hydraulic accumulator, so that in a first working step the housing cover can be inserted inexpensively into the cylindrical wall part of the accumulator housing, and then in a second working step the magnetic field generating device is introduced into the housing cover.

[0012] In a further advantageous embodiment of the hydraulic accumulator of the invention, the fluid connection on the liquid side passes through the housing cover centrally and coaxially to the longitudinal axis of the accumulator housing, and the magnetic field generator is arranged off-center in the housing cover. In this way, both the fluid connection and the magnetic field generator can be accommodated in the housing cover in a space-saving manner. In a further advantageous embodiment, it is also conceivable that several magnetic field generators are introduced into the housing cover. In any case, however, the magnetic field generator is accommodated close to the fluid connection and thus in the inlet region of the fluid, so that a direct and immediate removal of particles from the fluid is possible.

[0013] In a further advantageous embodiment of the hydraulic accumulator according to the invention, the housing cover has a flat upper surface in the direction of the separating element and the magnetic field generating device is arranged in the housing cover in a recessed state relative to the upper surface in a receiving part. The magnetic field generating device is arranged in a recessed state in the housing cover as part of the accumulator housing, so that a collection space is formed in which any particles that are generated can accumulate without remaining on the upper surface of the housing cover, which would otherwise cause damage, insofar as the piston-like separating element is subjected to impact-like impact against the upper surface of the housing cover within the framework of normal operation.

[0014] In a further advantageous embodiment of the hydraulic accumulator according to the invention, the magnetic field generating device consists of a permanent magnet, however, such a device can also be formed from an energizable magnet, this presupposing that the hydraulic accumulator is supplied with an appropriate amount of energy.

[0015] In a further advantageous embodiment of the hydraulic accumulator according to the invention, the permanent magnet is configured as a magnetic screw, which can be fixed, in particular screwed, into a non-magnetic insert and, preferably together with the insert, can be inserted, in particular screwed, into an associated receiving space in the housing cover. In this way, in an advantageous mounting configuration, the insert together with the magnetic screw can be inserted into the receiving space from the underside of the housing cover facing away from the separating element. In this way, it is possible to replace the magnetic screw and / or release magnetizable particle contaminants within the framework of maintenance.

[0016] In a further advantageous embodiment of the hydraulic accumulator according to the invention, a stepped receiving space is formed by a first recess between the insert and the flat underside of the housing cover and by a second recess between the magnetic screw and the free end face of the insert facing the magnetic screw, the free diameter of which increases in a step towards the flat underside of the housing cover. Both recesses result in an increased introduction space, which facilitates the assembly of the insert and the magnetic screw in the lower housing cover and the subsequent removal of the magnetic screw for cleaning purposes.

[0017] In a further advantageous embodiment of the hydraulic accumulator according to the invention, the magnetic screw has a detection device which responds when a predeterminable amount of magnetizable particle contamination is exceeded. For this purpose, the detection device preferably has a voltage source which is connected to a magnet part of the magnetic screw formed as a pole, and which transmits a signal to an evaluation unit as soon as an electrical connection is formed between the magnet part of the magnetic screw and a conductor by the magnetizable particle contamination, while the magnet part is spaced apart from the conductor as a further pole. A signal threshold can be defined, and only when the threshold is exceeded is the particle contamination signaled as disruptive, in which case cleaning of the magnetic screw is carried out as necessary within the framework of a maintenance operation.

[0018] In normally closed hydraulic circuits, metal particles can damage sensitive components, such as valves, piston accumulator seals, etc. Indeed, in hydraulic systems of construction machines, metal wear particles can be generated due to failure or friction of active elements, such as valves, cylinders, actuators, etc. The metal wear particles are then "flushed" through the circuit to the hydraulic accumulator. Since corresponding hydraulic accumulators, in particular piston accumulators, are often used in brake systems, the function of the brakes is limited or even completely stopped due to the destruction of the piston seals due to particle contamination. By using magnetic elements, such as commercially available magnetic screws, such particles can be drawn out of the hydraulic fluid and the life of the components of the hydraulic circuit can thus be significantly extended. The advantage of using magnetic screws in each case is that the respective screws can be unscrewed by hand, replaced or cleaned within the framework of maintenance work in order to dispose of the particles. With the above-mentioned contamination switch as detection device, contamination can be indicated by magnetizable metal particles emitting a signal and closing the associated current or switching circuit.

[0019] The hydraulic accumulator according to the invention is explained in more detail below on the basis of an embodiment shown in the drawing, in which a principle and not to scale drawing is shown. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 shows a longitudinal section of a hydraulic accumulator. [Diagram 2] FIG. 2 shows an end view from below of the hydraulic accumulator according to FIG. [Diagram 3] FIG. 3 shows the use of a contamination switch to indicate contamination in a magnetic screw as used in a hydraulic accumulator solution according to FIGS. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The hydraulic accumulator according to the invention, shown in FIG. 1 in the form of a so-called piston accumulator, has a separating piston 12 as a separating element 10. The separating piston 12 is arranged in an accumulator housing 14 and separates two fluid spaces 16, 18 from one another. The upper fluid space 16 as viewed in FIG. 1 forms a closed accumulator space 20 for receiving a working gas, such as nitrogen gas. The lower fluid space 18 forms a liquid space 22 for receiving a hydraulic fluid, such as hydraulic oil. Such a fluid space 18 or liquid space 22 is provided with a fluid connection 24 via which the accumulator can be connected to a hydraulic working circuit of the usual type, not shown in detail.

[0022] The accumulator housing 14 is formed in the form of a circular hollow cylinder or cylinder tube, the two free ends of which are tightly closed by a respective screwed housing cover 26, 28. Between these housing covers the separating piston 12 is guided coaxially along the housing longitudinal axis 30 so as to be freely movable.

[0023] The upper housing cover 26 has a through-flow fluid passage 32, which according to FIG. 1 is closed by a closing screw 34. Via such an arrangement 32, 34, the working gas in the accumulator space 16 can be emptied, for example for maintenance purposes, if necessary, but also the space 16 can be filled with working gas if it is depleted. The separating piston 12 itself is designed as a so-called hollow piston, in order to increase the effective gas volume on the side of the fluid space 16. On the outer periphery side, the separating piston 12 is guided along the inner surface 40 of the cylindrical accumulator housing 14 via at least one sealing ring 36 and at least one guide band 38. Within the framework of the realization of a practical embodiment, a number of such sealing rings and guide bands may be attached to the outer periphery of the separating piston 12 in combination with one another.

[0024] The conventional construction of such hydraulic accumulators, here in the form of piston accumulators, is typical and therefore will not be described in further detail, but only as necessary for the understanding of the invention. Thus, in the lower housing cover 28 as part of the accumulator housing 14, which has the fluid or liquid connection 24, a magnetic field generator 42 is accommodated. The magnetic field generator is adapted to separate magnetizable, in particular metallic, particles in a purifying manner from the fluid respectively located between the lower housing cover 28 as part of the accumulator housing 14 and the separating element 10 in the form of the separating piston 12, in the direction of said magnetic field generator 42 and to deposit them there. The fluid located in the fluid space 18 or in the liquid space 22 occupies different volumes depending on the operating state of the piston accumulator. 1, when the separating element 10 or the separating piston 12 moves downwards towards the lower housing cover 28, the fluid flows back through the fluid connection 24 into the liquid circuit and the magnetizable particles possibly present in the spaces 18, 22 are directed towards the magnetic field generating device 42 at the bottom of the housing cover 28 and collected there. However, already when the fluid flows into the spaces 18, 22 via the fluid connection 24, the magnetic force of the magnetic field generating device 42 is so strong that it can effectively attract the magnetizable particles possibly present and collect them at the device 42.

[0025] 1 and 2, the fluid connection 24 belonging to the liquid side of the hydraulic accumulator, to which the piping of the hydraulic circuit (not shown) is assigned, runs centrally and coaxially in the lower housing cover 28 with respect to the longitudinal axis 30 of the accumulator housing 14 and is integrated completely through the lower housing cover 28. In contrast, the magnetic field generating device 42 is arranged off-center in the housing cover 28. In this way, the fluid can flow unhindered via the fluid connection 24 into the spaces 18, 22 and out of the spaces 18, 22 again in the direction of the liquid circuit, with this free flow not being hindered by the off-center device 42 which generates a magnetic field. The magnetic field generating device 42 thus serves only to separate magnetic particles from the associated fluid flow. If necessary, several devices 42 of the above-mentioned type can be accommodated in the housing cover 28 in a group around the housing longitudinal axis 30.

[0026] As can be seen further from FIG. 1, the housing cover 28 has a flat upper surface 44 in the direction of the separating element 10, against which the magnetic field generator 42 is arranged in the housing cover 28, recessed in a cylindrical recess 46. The magnetic field generator 42 preferably consists of a permanent magnet. Alternatively, however, it is also possible to use an electromagnet that can be energized on the liquid side in the housing cover 28. In this case, however, the permanent magnet is formed as a so-called magnetic screw 48, i.e. a conventional screw with an external thread 50 and a screw head 52. This screw consists entirely of a magnetic material or has such material as a material component. The external thread 50 of the magnetic screw 48 is fixed in the corresponding internal thread 54 of an insert 56. The insert 56 can be fixed in the corresponding internal thread 60 of the lower housing cover 28 by means of the external thread 58 formed in the head extension. As FIG. 1 further shows, the free end face end region of the insert 56 has a seal in the form of a sealing ring 62 in the direction of the fluid space 18. The insert 56 with the magnetic screw 48 is inserted into said receiving space 46 from a flat-extending underside 64 of the lower housing cover 28 facing away from the separating element 10. A first recess 66 is formed between the insert 56 and the flat underside 64 of the housing cover 28, and a further second recess 68 is provided between the magnetic screw 48 and the free end face of the insert 56 facing away from the magnetic screw 48. A stepped receiving space 70 is thus formed. The free diameter of the receiving space widens in a step towards the flat underside 64 of the housing cover 28, and in this way the magnetic screw 48 can be screwed into and unscrewed from the insert 56 in a particularly assembly-friendly manner. In this way, when the hydraulic accumulator is emptied of liquid, the magnetic screw 48 can be removed from the housing cover 28 together with the trapped magnetic particles and, after the particles have been removed, brought back into position to attract and trap the particles from the liquid.

[0027] In particular, as shown in FIG. 3, in a modified embodiment of the magnetic screw 48, the magnetic screw 48 can be equipped with a detection device, generally designated 72, which responds when a predeterminable amount 74 of magnetizable particle contamination is exceeded. The detection device 72 thus has a common voltage source 76, which is current-guidedly connected to a magnetic part 78 of the magnetic screw 48, which is formed as a pole. The magnetic part 78 is formed from a cylindrical permanent magnet, which is inserted at its end side into a recess in the magnetic screw 48. In a coaxial arrangement, a hollow cylindrical electrical conductor 80 surrounds the inner magnetic part 78. In order to avoid short circuits between the two components 78, 80, a non-conductive sleeve piece is introduced as a separating sleeve 82, so that the two components 78, 80 are electrically decoupled from one another. Otherwise, the magnetic screw 48 can be screwed generally via its external thread 50 into the associated internal thread 54 of the insert 56 in the cover part 28.

[0028] In the current path between the voltage source 76 and the inner magnet part 78, a relay 84 is connected, which serves as a display. As soon as a quantity of magnetizable particles 74 gathers on the magnet part 78 of the magnet screw 48, such that the separating sleeve 82 bridges the particle contamination in the direction of the conductor 80, an electrical connection is made between the magnet part 78 and the conductor 80, as a result of which the relay 84 responds. The relay switches and transmits an indication of the thus achieved degree of particle contamination in the magnet screw 48 to the operator. The operator then removes the magnet screw 48 from the insert 56 in the housing cover 28 within the framework of maintenance and for cleaning the free end face of the magnet screw 48, and inserts it again after cleaning. In this way, a kind of contamination switch for indicating contamination in the magnet screw 48 is realized via the device shown in FIG. 3. With the exception of the permanent magnet 78 and the conductor 80, the other parts of the magnet screw 48 are in this case advantageously made of non-metallic material, for example of a suitable plastic material.

[0029] Precisely in the case of construction machines, the failure or friction of active elements, such as valves, working cylinders or actuators, can result in metallic wear particles which are then "flushed" through the circuit to the hydraulic accumulator. Such hydraulic accumulators are also usually used in the brake systems of such working machines, such as agricultural or construction machines. This causes the seal of the separating piston 12 to be destroyed by metal particles, limiting or even completely preventing its function.

[0030] By using a magnetic element, here in the form of a magnetic screw 48, which according to the embodiment shown in Fig. 3 may only have a permanent magnet 78 in the frontmost free end surface area, such magnetizable metal particles can be drawn out of the hydraulic fluid and thus the life of the components can be increased. By "picking out" such particles by the magnetic field generator 42 in the variable chamber volume between the separating element 10 and the lower housing cover 28, such metal particles are prevented in the closed hydraulic circuit from leaving the hydraulic accumulator and damaging sensitive components, such as valves, piston accumulators, seals, etc., so that all components of the hydraulic circuit are protected from such damage. There is no equivalent in the prior art.

[0031] The separation device according to the invention for magnetizable particles does not have to be limited to the piston accumulator solution as shown above, but can also be used in other accumulator solutions with separation elements, such as bladder accumulators, membrane accumulators and bellows accumulators. Furthermore, if necessary, a valve can be inserted into the fluid connection 24, for example a disk valve as is used for bladder accumulators of the usual construction type, without impairing the action of the magnetic field generating device 42 integrated in the housing cover 28.

Claims

1. A hydraulic accumulator, in particular in the form of a piston accumulator, comprising a separating element (10) which separates in a fluid-tight manner two fluid spaces (16, 18) arranged in an accumulator housing (14) from each other, in particular a closed accumulator space (20) containing a working gas from a liquid space (22) containing a hydraulic fluid, such as hydraulic oil, said fluid connection (24) being in fluid-guiding connection with one of the fluid spaces (18), 1. A hydraulic accumulator, characterized in that in the part of the accumulator housing (14) having the fluid connection (24) a magnetic field generating device (42) is accommodated, which is adapted to separate magnetizable particles in a purifying manner in the direction of the magnetic field generating device (42) from the fluid respectively located between the part of the accumulator housing (14) and the separating element (10) and to deposit them on the magnetic field generating device.

2. 2. The hydraulic accumulator according to claim 1, characterized in that the part of the accumulator housing (14) having the magnetic field generating device (42) is a housing cover (28), said housing cover closing an end of a tubular wall portion of the accumulator housing (14) facing the liquid side.

3. 3. A hydraulic accumulator according to claim 1 or 2, characterized in that the liquid-side fluid connection (24) passes through the housing cover (28) centrally and coaxially with respect to the longitudinal axis (30) of the accumulator housing (14), and that a magnetic field generating device (42) is arranged off-center in relation thereto within the housing cover (28).

4. 4. The hydraulic accumulator according to claim 1, wherein the housing cover (28) has a flat upper surface (44) extending in the direction of the separation element (10) and the magnetic field generating device (42) is arranged in the housing cover (28) in a recessed state (46) relative to said upper surface.

5. 5. A hydraulic accumulator according to claim 1, wherein the magnetic field generating device (42) consists of a permanent magnet.

6. 6. The hydraulic accumulator according to claim 1, wherein the permanent magnet is configured as a magnetic screw (48) and is fixable, in particular screwable, in a non-magnetic insert (56) and preferably insertable, in particular screwable, together with the insert (56) into an associated receiving space (46) in the housing cover (28).

7. 7. The hydraulic accumulator according to claim 1, wherein the insert (56) is inserted into the receiving portion (46) from an underside (64) of the housing cover (28) facing away from the separation element (10).

8. 8. The hydraulic accumulator according to claim 1, characterized in that a stepped accommodation space (70) is formed by a first recess (66) between the insert (56) and the flat underside (64) of the housing cover (28) and by a second recess (68) between the magnetic screw (48) and a free end face of the insert (56) facing the magnetic screw (48), the free diameter of the accommodation space increasing in a step towards the flat underside (64) of the housing cover (28).

9. 9. A hydraulic accumulator according to any one of claims 1 to 8, characterized in that the magnetic screw (48) includes a detection device (72) which responds when a predefinable amount (74) of magnetizable particle contaminants is exceeded.

10. 10. The hydraulic accumulator according to claim 1, characterized in that the detection device (72) has a voltage source (76) connected to magnet parts (78) formed as poles of the magnetic screw (48), the magnet parts (78) transmitting a signal to an evaluation unit (84) while being spaced apart from a conductor (80) as a further pole as soon as an electrical connection is formed between the two poles (78) and (80) of the magnetic screw (48) by the magnetizable particle contamination.

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