Patent Application
20150176654
This application claims priority to German patent application no. 10 2013 226 555.7 filed on Dec. 19, 2013, the contents of which are fully incorporated herein by reference.
The present disclosure is directed to the field rolling-element bearing seals.
Known bearing seals can protect a rolling-element bearing against dirt and contamination. However, these seals are generally configured for use with a bearing of a particular type or size and can only be adapted with difficulty for use with other bearings. This limits the number of each seal made and requires manufacturing seals of many different sizes and shapes. In addition, it can be difficult to replace an installed seal because a complex and cost-intensive disassembly effort is often needed to remove parts to allow the seal to be replaced. This is a particular problem in the field of large bearings having a diameter of approximately 400 millimeters or larger, bearings used, for example, in wind turbines.
Large bearings can also be protected by contacting sealing rings. These may comprise radial shaft seal rings, possibly including upstream dust lips, which are held in position using, e.g., cast support parts. These support parts likewise constitute a large mass and thus a large weight to be moved during assembly. This makes it impossible or at the very least difficult and expensive, to exchange the seal ring.
The two above-mentioned sealing concepts have the segregation from the rolling-element bearing in common. Therefore, the bearings can only be filled with lubricant in the assembled state. Such seals can only be installed after the assembly of the bearing, and only thereafter can the bearing be filled with lubricant.
In addition, integrated sealing concepts are known which are embodied purely from elastomer, and may be, e.g. bellows-shaped (see German patent document DE 10 2007 036 891 A1). Bearings with such seals scan be prelubricated—at a factory before delivery, for example. However, it may be difficult to achieve (or adequately achieve) the required seal system stiffness for large bearing diameters. Moreover, due to the closed geometry of the seal ring, it may be difficult or impossible to exchange the seal without disassembling the rolling-element bearing.
The existing sealing concepts discussed herein also accommodate only a limited bearing misalignment or tilt and fail to provide adequate sealing when a maximum tilt is exceeded. Especially in the case of self-aligning bearings, such as spherical roller bearings or compact aligning roller bearing (CARB) toroidal roller bearings, the maximum possible tilting of a bearing inner ring with respect to a bearing outer ring can be severely limited by conventional seals. This can lead, during installation of the bearing or in actual operation, to a rolling-element bearing roller bumping against the seal element. This in turn may damage the roller set, the seal element, or even the attachment mechanism on the respective bearing ring and lead to significant repair costs or an impairment of the service life of the bearing.
In addition, the support parts of the contacting sealing rings can also be manufactured from welded metal-plate structures and integrated in the rolling-element bearing so that no components extend beyond the external dimensions of the rolling-element bearing. In this case an exact aligning/centering of the seal lips to the associated seal countersurface (opposite seal contact surface) should occur via a defined reference position on the component (e.g. outer ring) supporting the seal lip. In these cases the reference position is realized by circulating reference grooves, reference surfaces, reference bores, reference edges, or the like. Due to the precision required in positioning these reference indicia, they must be produced by expensive and high-precision processes, such as, for example, hard turning. The methods mentioned are associated with high manufacturing costs. Furthermore, if components are disposed between the reference position on the supporting component and the seal lip to be centered, these must also be precisely positioned in order to maintain the necessary precision in view of the tolerance chain. These alignment requirements of the components are also associated with effort and cost.
In all seal concepts with contacting seal rings there can be significant friction losses depending on the quality of the paired surfaces (seal lip to countersurface). These energy losses could far exceed the actual power dissipation of the rolling-element bearing. Furthermore, signs of wear are also associated with the friction losses mentioned. In addition, the seal (seal lip) and the associated countersurface wear over their service lives, and after reaching a certain wear condition the seal ring should be replaced. A repair is much more difficult with worn countersurfaces. With external sealing concepts in the field, any scratches/scoring/markings/physical wear can be eliminated by so-called wear sleeves; however the installation of wear sleeves is complex and expensive. On the other hand, with integrated seal concepts, repair methods can be difficult or even impossible.
There is therefore a need to provide an improved concept for sealing rolling-element bearings.
Exemplary embodiments provide a rolling-element bearing including a seal unit. The rolling-element bearing comprises at least one bearing ring, and the seal unit comprises an at least part-ring shaped element attached to the bearing ring. The at least part-ring shaped element delimits a labyrinthine seal gap.
The rolling-element bearing can be, for example, a ball bearing, a barrel roller bearing, a tapered roller bearing, or a bearing including a single-row or multi-row arrangement of rolling elements. The first bearing ring may be attached to a stator. The second bearing ring may be attached to a rotor. Both the first bearing ring and the second bearing ring could respectively be an inner bearing ring or an outer bearing ring.
In some exemplary embodiments the seal unit is manufactured at least partially from a flexible, elastic material. For this purpose elastomers, for example, certain types of plastic or rubber-type materials, can be used. The term “seal unit” indicates that a penetration of certain substances from one side of the seal unit to the other is to be prevented. These substances can include dirt particles (e.g. soot, fine dust, sand, or mud), gases or vapors (e.g. oxygen, vapors of fuels or solvents, or also vapors of toxic or corrosive substances) or liquids (e.g. water, acids, lyes, oil), or also materials such as, greases. Moreover, the seal unit could be manufactured at least partially from metal, metal alloys, particularly low-friction plastics such as polytetrafluoroethylene (PTFE), or plastics having a high stiffness. Plastics having high stiffness could be so-called thermosets (thermosetting materials). Furthermore, the materials used could make possible a mass production by methods such as injection molding, vulcanization, etc. Production costs and material costs as well as weight can thus be reduced.
An at least part-ring shaped element can be formed by a complete ring, or also by parts of a ring, for example by segments. In addition to ring segments, however, embodiments are also possible in which a ring can be assembled from parts having irregular shapes. An embodiment in which the ring is formed from a plurality of parts could significantly facilitate maintenance since the installation and removal can occur without requiring a complete removal of the entire rolling-element bearing. If the element is segmented, a connection of the individual segments can be formed by using connecting plates, screws, adhesion, or welding.
In exemplary embodiments the attaching can occur in an interference-fit, friction-fit, or materially-bonded manner. Possible attachment means could comprise, for example, a screw, an adhesive surface, a welded surface, a soldered joint, a rivet, a bore, a thread, or a system including a groove and spring.
Moreover, in some exemplary embodiments the seal unit can be integrated into an already-existing rolling-element bearing. Due to its simple construction, this concept could be used on any rolling-element bearing, independent of design, bearing series, or diameter. The seal unit could thus be used flexibly. Compared to the conventional solution of the labyrinth seal, such as is used, for example, in wind turbines, the space to be filled by a lubricant could be substantially reduced and thus allow for the use of a smaller amount of lubricant. Moreover, in some exemplary embodiments the seal unit can be made from lightweight material. This could lead to a reduction of material costs and a weight reduction and thus allow a simplified, time-efficient installation. A factory prelubrication could make more difficult, or even prevent, a contamination during installation of the otherwise unsealed, open bearing.
A labyrinth or a labyrinthine seal gap refers to a structure that makes it difficult or impossible for contaminants to penetrate. This is because every possible path for penetration of substances through such a seal gap requires at least one change of direction. Such a change of direction of the path can be a change of direction from an axial direction to a radial direction. In general a change of direction can refer to a point at which two partial sections of a path meet such that they inevitably form an angle different from 180°. In other words, if a structure is sealed using a labyrinthine seal gap, there is no straight path from an exterior of the structure to an interior of the structure. A straight path between two points A and B could be represented as a direct line-of-sight from A to B. In addition, in some exemplary embodiments the labyrinthine seal gap can be filled with lubricant in order to increase the sealing effect. A labyrinthine gap could be contactless, i.e. the components which delimit the labyrinthine gap could be configured such that they generally do not come into contact under normal operating conditions. Wear occurring on the rolling-element bearing or the seal unit could thus be reduced or even minimized.
In some exemplary embodiments the seal unit can be mounted on the rolling-element bearing even before the rolling-element bearing is supplied to its actual intended purpose, i.e. for example mounted on a rotor or on a stator. A rolling-element bearing could also be filled with lubricant before it is mounted.
Optionally at least part of the seal gap does not extend beyond the bearing ring in the axial direction. In other words, dimensions of the bearing relevant to an installation (width, inner diameter, outer diameter) are not changed by providing the labyrinthine seal gap. Or in other words, the seal gap can lie completely between two bearing rings. The bearing rings can be an inner and an outer bearing ring, and can at least partially delimit the seal gap.
In exemplary embodiments the element is optionally formed in the shape of a plate. A plate-shaped element can also be understood to be a thin element; in other words, one of the three spatial dimensions (thickness) could be very small with respect to the other two spatial dimensions (length, width). In exemplary embodiments the thickness could respectively be up to 1%, 2%, 5%, 10%, etc. of the length or width. Using the plate-shaped form of the element, weight and material can be saved, as well as costs and effort associated therewith, for example in production or maintenance. Furthermore, the volume of the seal unit could be reduced so much that large amounts of installation space are saved. In some exemplary embodiments the element could even end flush with the bearing ring, i.e. not extend beyond the bearing ring in the axial direction. It could thereby be possible, for example, to maintain an installation space specified by the International Organization for Standardization (ISO).
Additionally or alternatively the seal gap may also be delimited by a recess in the bearing ring. Such a recess can be a groove. The groove or the recess can also have an extension in the axial direction which is greater than the thickness (axial extension) of the plate-shaped element. In the case of a spherical roller bearing, wherein two bearing rings can be tilted with respect to each other, a known clearance could be maintained for the element during tilting. The clearance could be maintained even during the tilting of a spherical roller bearing, and thus the sealing effect of the seal gap would also be maintained.
Additionally or alternatively, in exemplary embodiments the bearing ring includes a seal lip in abutment with the element. In some exemplary embodiments, the seal lip can be manufactured at least partially from a seal material. A seal material can be, for example, a plastic, e.g. polyurethane, nitrile rubber (nitrile butadiene rubber (NBR), hydrated nitrile butadiene rubber (HNBR)), depending on the type of material that is to be prevented from penetrating or escaping.
In some exemplary embodiments the seal lip can completely close the seal gap and thus further increase the sealing effect. The seal lip can also contact the element or the bearing ring at an acute angle (smaller than 90°) open towards a direction of the seal gap which points towards a rolling element of the rolling-element bearing. In this way the penetration of substances (i.e., for example, dirt particles or moisture) could be made more difficult, and an escape of excess lubricant could be facilitated. Furthermore, friction and associated wear occurring during operation of the rolling-element bearing could occur on the seal lip instead of on the bearing ring, so that the wear on the bearing ring could be substantially lower. The expense for replacing (and thus the maintenance effort and the maintenance costs) for the seal lip would also not be as great as the expense for replacing the bearing ring.
Additionally or alternatively, in some exemplary embodiments the element has a change of direction along its course of at least 45°. In other exemplary embodiments a change of direction could occur in any desired angle. A course of the labyrinthine passage which is delimited by the element can thus be extended by additional changes of direction, and a penetration of contaminants could thus be made more difficult. The change of direction takes place in a cross-sectional plane which comprises an axis of rotation of the bearing. In other words, the cross-sectional area of the element includes the change of direction.
Additionally or alternatively, the element corresponds to a first delimiting element, and the rolling-element bearing further comprises a second delimiting element, wherein the seal gap extends at least partially between the first and the second delimiting element. However, in further exemplary embodiments the element could equally correspond to the second delimiting element. Both delimiting elements can be plate-shaped, part-ring shaped, ring-shaped, and/or be manufactured from the same or from different materials. The seal gap could even extend completely between the two delimiting elements. Due to the presence of two delimiting elements, the seal gap could be additionally extended and its sealing effect could thereby be increased. The second delimiting element could also be attached to a bearing ring.
In such an exemplary embodiment, wherein the seal gap extends at least partially between the first and the second delimiting elements, the rolling-element bearing can additionally or alternatively include a third delimiting element attached to a bearing cage. The seal gap extends at least partially between the first delimiting element, the second delimiting element, and the third delimiting element. Moreover, the third delimiting element can have the same features as the first and second delimiting element (i.e. it can be plate-shaped, part-ring shaped, ring-shaped, and manufactured from the same materials as the first and the second delimiting element, or from other materials).
In some exemplary embodiments the two or three delimiting elements can also differ in particular with respect to these features. For example, the first and the second delimiting elements may be attached to different bearing rings. An unwanted escape of lubricant can thereby be prevented. This could additionally be improved or optimized by the part of the gap extending between the first delimiting element and the second delimiting element being disposed as centrally as possible (i.e. as far as possible from both bearing rings).
Additionally or alternatively, in exemplary embodiments the seal gap additionally includes a flocking and/or a seal lip. A flocking could serve as an additional filter which makes it more difficult for dirt particles to enter the bearing. As described above, a seal lip can make it harder for contaminants to enter the bearing and simultaneously also facilitate an escape of excess lubricant. The seal lip could in turn be manufactured from an elastomer, or generally from high-flexibility materials. The flocking could be manufactured from textile fibers whose desired strength or length is selectable depending on the application.
In some exemplary embodiments, at least the element is additionally or alternatively exchangeably attached to the bearing ring. In further exemplary embodiments this can accordingly also be the case for the first delimiting element or the second delimiting element. The third delimiting element can also be exchangeably connected to the bearing cage. Furthermore, in some exemplary embodiments the seal lip connected to the bearing ring or located in the seal gap can be exchangeably connected to the element or the bearing ring. “Exchangeably connected” as used herein means that a low-effort removal is possible (for example without using a tool), that a damage-free removal is possible, that a connection is releasable and restorable, that the element or the seal lip is repeatedly connectable or exchangeable, or that the element or the seal lip is reversibly connectable. Due to the exchangeable connectability, installation and maintenance processes can be accelerated and simplified. In addition damage to the seal elements or bearing elements during a removal of the element or of the seal lip can be prevented.
In exemplary embodiments the rolling-element bearing additionally or alternatively comprises a further bearing ring which is tiltable with respect to the bearing ring by a limited angle. This occurs, for example, in a spherical roller bearing. The maximum possible tilting of two bearing rings with respect to each other can be a fraction of a degree, but also a plurality of degrees, for example 2 or 3 degrees. In an exemplary embodiment the seal unit can be attached on an inner bearing ring so that a collision with the rolling elements during a tilting of the two bearing rings with respect to each other can be avoided. The use of a seal lip, which can be manufactured, for example, from elastomer, could provide so much clearance during tilting that the sealing function of the seal lip is maintained even with a tilting of one or two degrees. If the seal unit is attached to the outer bearing ring, manufacturing the seal unit from plastic could significantly reduce damage during severe tilting of both bearing rings with respect to each other, which damage could result from a collision of the seal unit with the rolling elements.
Additionally or alternatively the rolling-element bearing has an external radius or an external diameter of at least 400 mm. The diameter or the radius can be measured radially to an axis of rotation of the bearing. Bearings having an outer diameter or outer radius of 400 mm or more are often referred to as “large bearings.” Large bearings can be used, for example, in the field of energy generation (e.g. wind turbines, underwater turbines, turbines in general). Maintenance, installation, or replacement of a conventional seal in a large bearing can be expensive. The embodiment of the element as a plurality of disk-parts or ring-parts could significantly reduce this expense. A sealing of large bearings using the described seal unit could save significant amounts of material and also reduce weight. Manufacturing costs and manufacturing effort could also be reduced to a considerable degree. Mounting the seal unit on the bearing could also occur before as well as after the installation of the bearing itself.
Furthermore, in exemplary embodiments the seal unit additionally or alternatively has at least one liquid-permeable bore or grease outlet. If such grease outlet bores are incorporated in the seal unit, used lubricant could be discharged or pumped in an efficient and directed manner using, e.g., hoses/tubes or collecting tanks attached directly to the bores, and the metering of the lubricant escape could additionally be regulated via the gap formed. The contamination of surrounding components and of the surrounding space could thus be avoided.
Exemplary embodiments are described and explained in more detail below with reference to the accompanying Figures:
In the following description of the accompanying Figures, which show exemplary embodiments of the present disclosure, identical reference numerals indicate identical or comparable components. Furthermore, summarizing reference numerals may be used for components and objects that appear multiple times in an exemplary embodiment or in an illustration, but that are described together in terms of one or more common features. Components or objects that are described with the same or summarizing reference numerals can be embodied identically, but also optionally differently, in terms of individual, multiple, or all features, their dimensions, for example, as long as the description does not explicitly or implicitly indicate otherwise.
In the following, lower-case letters “a,” “b,” “c,” “d,” and “e” appended to a reference number respectively refer to different exemplary embodiments. Thus, for example, the reference numbers “10a” and “10b” can indicate two counterparts/instances of the same component in respective different embodiments.
In the following five exemplary embodiments (see
In description that follows, a first exemplary embodiment is described with reference to
Exemplary embodiments relate to a rolling-element bearing 10a; 10b; 10c; 10d; 10e including a seal unit 12a; 12b; 12c; 12d; 12e. The rolling-element bearing 10a; 10b; 10c; 10d; 10e comprises at least one bearing ring 14a; 14b; 14c; 14d; 14e; 15a; 15b; 15c; 15d; 15e, and the seal unit 12a; 12b; 12c; 12d; 12e comprises an at least part-ring shaped element 16a; 16b; 16c; 16d; 16e attached to the bearing ring 14a; 14b; 14c; 14d; 14e; 15a; 15b; 15c; 15d; 15e. Here the at least part-ring shaped element 16a; 16b; 16c; 16d; 16e delimits a labyrinthine seal gap 18a; 18b; 18c; 18d; 18e.
In further exemplary embodiments, however, a multi-part embodiment could also be possible, for example, an embodiment formed from a plurality of segments which can be assembled into a complete ring. In such a segmented embodiment, the connection of the individual elements or segments could be accomplished by adhering, welding, screwing, clamping, etc. In
In all five exemplary embodiments, the seal gap 18a; 18b; 18c; 18d; 18e can at least partially extend such that the seal gap 18a; 18b; 18c; 18d; 18e does not extend beyond the bearing ring 14a; 14b; 14c; 14d; 14e; 15a; 15b; 15c; 15d; 15e in the axial direction. In other words, the seal gap can thus be completely located in the “bearing interior,” as can be seen, for example, in
In the first to fifth exemplary embodiment the element 16a; 16b; 16c; 16d; 16e can be plate-shaped. In
In the first and third exemplary embodiments (
In the variant of
In the second to fourth exemplary embodiments, the element 16b; 16c; 16d can have a change of direction 40b; 40c; 40d (an angle or bend) along its course of at least 45°. In addition, in some of these embodiments the element 16b; 16d; 16e can correspond to a first delimiting element 24b; 24d; 24e, and the rolling-element bearing 10b; 10d; 10e can further comprise a second delimiting element 26b; 26d; 26e. In this case, the seal gap 18b; 18d; 18e extends at least partially between the first delimiting element 24b; 24d; 24e and the second delimiting element 26b; 26d; 26e.
In some exemplary embodiments the rolling-element bearing 10b includes a third delimiting element 28b attached to a bearing cage 32b. In these embodiments, part of the seal gap 18b extends between the first delimiting element 24b and the second delimiting element 26b, and part extends between the second delimiting element 26b and the third delimiting element 28b. In
In self-centering bearings, for example, spherical roller bearings, or compact aligning roller bearing (CARB) toroidal roller bearings, or axially displaceable rolling-element bearings such as cylindrical roller bearings, the penetration of contaminants could also be made more difficult by the bending (i.e. the change of direction 40b) of the delimiting elements 24b and 26b (second exemplary embodiment) towards the seal gap 18b. The degree of slanting is selectable based on the expected tilting or displacing of the inner ring 14b with respect to the outer ring 15b.
Selecting an appropriate configuration of the seal gap 18a; 18b in the first and second exemplary embodiment helps ensure the required angular mobility with CARB toroidal or spherical roller bearings. In non-self-centering rolling-element bearings 10a; 10b a narrow seal gap 18a; 18b can be used in order to achieve an increased sealing function.
The third exemplary embodiment shown in
As
Referring now to
In the first and third exemplary embodiment, the bearing ring 14a; 14c; 15a; 15c can include a seal lip 22a; 22c in abutment with the element 16a; 16c. Possible embodiments are shown in the third exemplary embodiment, in different variants, in
In addition, it can be seen in
Due to the integration of the seal unit 12c in the bearing 10c, the ISO installation space could be maintained. The seal unit 12c further allows a high angular and axial mobility of the bearing 10c. With wear and associated exchange (replacement) of the seal unit 12c, removal of the bearing 10c may not be necessary, which, for example, could be relevant in wind power applications. In addition, the releasable connection of the seal unit 12c could allow for a relubrication of the bearing 10c.
The fourth exemplary embodiment shown in
As depicted in
The delimiting elements 24d and 26d can be folded for installation and positioning purposes.
Both delimiting elements 24d and 26d can be centered in the recesses and attached by screwing, adhering, clamping or the like. According to the geometry chosen, a narrower seal gap 18d can be formed between the delimiting elements 24d and 26d near the outer ring such that a tilting between inner ring 14d and outer ring 15d is possible in spherical roller bearings such as the ones illustrated herein. In addition, the position of the seal gap 18d could be variable—closer to the outer ring 15d or inner ring 14d—depending on the geometry, environmental conditions, required tilting, etc.
In the exemplary embodiment of
A fifth exemplary embodiment shown in
In the five exemplary embodiments presented, the seal gap 18a; 18b; 18c; 18d; 18e can additionally include a flocking 34e and/or a seal lip 22e; 38e. As illustrated in
In
Since in the variant shown in
Depending on the choice of the seal gap 18e between the delimiting elements 24e and 26e, the required angular and axial mobility, e.g. in CARB toroidal or spherical roller bearings could be ensured while maintaining the ISO installation space. In non-self-aligning rolling-element bearings a narrow seal gap 18e can be provided in order to achieve an increased sealing function.
Further, different view perspectives of the seal unit 12e in the rolling-element bearing 10e are shown in
Some exemplary embodiments presented here, as shown in the Figures, make possible a simple integration of a wear-resistant seal unit 12a; 12b; 12c; 12d; 12e into an existing rolling-element bearing 10a; 10b; 10c; 10d; 10e. Due to the simple structure, the concept can be used on any rolling-element bearing, independent of design, bearing series, and diameter. Exemplary embodiments could thus be usable flexibly.
In contrast to variants for sealing rolling-element bearings including cover plates, wherein no recess is incorporated, with the seal variants presented here a metering or throttling function for defined lubricant escape could be formed by appropriate dimensioning of the gap. Lubricant could thus not simply escape unhindered but will be subjected to a significantly increased flow resistance due to the labyrinthine structure.
In comparison to the conventional solution of the external labyrinth seal, e.g. in wind turbines, further advantages could result. The space to be filled with lubricant could be significantly reduced, resulting in the need for less lubricant. In some exemplary embodiments the seal unit 12a; 12b; 12c; 12d; 12e is also made from a light material. This could lead to a reduction of material costs, a weight reduction, and thus to a simplified, time-efficient installation. A factory pre-fitting could reduce the risk of a contamination during installation of the otherwise unsealed, open bearing.
Using the economical seal designed proposed in some exemplary embodiments, a mass production of the seal unit 12a; 12b; 12c; 12d; 12e, e.g. by stamping, could be made possible. Even in low quantities the seal unit 12a; 12b; 12c; 12d; 12e could be economically manufactured, for example by laser-cutting.
In the exemplary embodiments discussed above, the design could additionally allow for a rudimentary centering of the seal unit 12a; 12b; 12c; 12d; 12e. A high-precision positioning of the seal unit 12a; 12b; 12c; 12d; 12e relative to the inner ring 14a; 14b; 14c; 14d; 14e could be avoided. Consequently cost-intensive processing steps could be omitted on the rolling-element bearing inner ring and outer ring. The required recess could be produced using machining manufacturing process, such as for example soft-turning prior to hardening.
Representative, non-limiting examples of the present invention were described above in detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Furthermore, each of the additional features and teachings disclosed above may be utilized separately or in conjunction with other features and teachings to provide improved seals for bearings.
Moreover, combinations of features and steps disclosed in the above detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the invention. Furthermore, various features of the above-described representative examples, as well as the various independent and dependent claims below, may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings.
All features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter, independent of the compositions of the features in the embodiments and/or the claims. In addition, all value ranges or indications of groups of entities are intended to disclose every possible intermediate value or intermediate entity for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2013 226 555.7 | Dec 2013 | DE | national |
