Anti-friction bearing having integrated current removal

Abstract

An anti-friction bearing having integrated current removal comprises two bearing rings (2, 3), a number of rolling bodies (4) arranged between the bearing rings (2, 3), and a removal element (11) which is provided in the form of an un-closed ring for producing an electrically conductive connection between the bearing rings (2, 3). The removal element (11) is in the form of a wire and has an electrically conductive coating (17) contacting the bearing rings (2, 3) and comprising at least two components (18, 19, 20, 21).

Description

[0001] Rolling bearings with integrated current discharge

[0002] The invention relates to a rolling bearing designed according to the preamble of claim 1 with integrated current discharge.

[0003] A rolling bearing of this type is known, for example, from EP 3228 890 B1. The known rolling bearing has a dissipation device for dissipating electrostatic charges, which comprises a flexible conductor. Various sections of the conductor are designed to engage a first bearing ring or a second bearing ring of the rolling bearing. The conductor of the device according to EP 3 228 890 B1 is formed from a carbon fiber arrangement, which can be a fiber braid or a fiber fleece. The carbon fiber arrangement is provided with a coating of pyrolytically deposited carbon.

[0004] EP 1 523 086 B1 relates to a grounding brush for reducing the electrical current in a motor shaft. Several electrically conductive threads are electrically connected to an annular frame. The annular frame defines an annular channel in which the end sections of the threads are located. Furthermore, the channel can contain a conductive powder mixed with an oil to form a paste.

[0005] Further rolling bearings with an integrated current-dissipation function are disclosed, for example, in documents DE 102017 106 695 B3 and DE 102019 112 825 A1. In both cases, the rolling bearing, which has an electrical connection between the bearing rings, is a deep groove ball bearing. The invention is based on the object of specifying a rolling bearing with integrated current dissipation that is further developed compared to the prior art, while striving for a particularly compact and production-friendly design with unrestricted functionality.

[0006] This object is achieved according to the invention by a rolling bearing having the features of claim 1. The rolling bearing, which has a current-conducting function, comprises, in a basic concept known per se, two bearing rings, a number of rolling elements arranged between the bearing rings, and a discharge element, which is provided in the form of a non-closed ring for establishing an electrically conductive connection between the bearing rings. According to claim 1, the discharge element is designed as a wire, wherein it has an electrically conductive coating comprising at least two components that contacts the bearing rings.

[0007] The manufacture of the discharge element from a metallic precursor, namely wire, especially steel wire, allows for very efficient production. At the same time, the required long-term electrical function is supported by the wire coating, or at least not significantly negatively impacted. Depending on the application, the coating may also have a wear-protection function. In all cases, the wire discharge element can be integrated into the rolling bearing with minimal space requirements.

[0008] According to a first group of embodiments, the mutually distinguishable components of the coating of the discharge element are formed by a plurality of layers of the electrically conductive coating. The total thickness of the coating is, for example, in the range of 100 nm to 200 nm.

[0009] The multilayer coating can, for example, comprise a first layer located on a metallic base body of the discharge element, as well as a second, outer layer formed as a PVD layer. The PVD layer contains carbon and can also contain hydrogen as well as metallic or non-metallic doping elements. For the technical background, reference is made to DE 10 2006 057 484 B4, which also relates to a rolling bearing.

[0010] The first layer deposited on the base body of the conductive element can contain titanium, particularly in the form of titanium carbide. Other materials that can be included in the multilayer coating include copper and nickel, particularly as components of the first, inner layer. Possible coating components, which can be included particularly in the second, outer layer of the coating, include the elements tin, copper, nickel, silver, zinc, bismuth, antimony, cobalt, manganese, and tungsten.

[0011] A second group of embodiments provides for various components to be present in one and the same layer of the electrically conductive coating of the wire-shaped discharge element. The total thickness of the electrically conductive coating is, for example, in the range of 5 μm to 10 μm. In this case, the coating can be designed, in particular, as a tin-nickel layer with incorporated particles. The tin-nickel alloy, which represents the main component of this layer, has, for example, a nickel content of 20 to 40 percent by weight. Instead of a tin-nickel alloy, a copper-tin alloy, a tin-silver alloy, a tin-zinc alloy, a tin-bismuth alloy, a tin-antimony alloy, a tin-cobalt alloy, a nickel-tungsten alloy, or a tin-manganese alloy can also be used.

[0012] The particles distributed in the coating are, for example, carbon-containing particles, in particular graphite particles. Other usable materials containing carbon include carbon nanotubes, carbon fibers, soot, graphene, and graphene oxide. Examples of carbon-free materials that can also be considered as particulate components of the coating of the discharge element are metal nitrides and metal carbides. Other non-metallic, electrically conductive or non-electrically conductive particles can also be distributed in the coating. These can be, for example, particles of metal sulfide, diamond, metal oxide, mica, or PTFE. The individual particles can, for example, have a granular shape, for example approximately spherical or cubic, or, as in the case of carbon nanotubes, be in the form of rods.

[0013] The particle-containing coating can be constructed in a single layer. Multilayer structures are also possible, with at least one of the superimposed layers, i.e., plies, being in the form of a carrier material representing a first component, in which particles are distributed as a further component. Such a multicomponent layer can be combined with at least one layer formed from a single component.

[0014] All coating variants described in DE patent application No. 10 2023 124 200.8, which was still unpublished on the filing date of the present application, represent conceivable variants of the coating of the discharge element, which is designed as a wire, of the rolling bearing according to the application.

[0015] The discharge element, in the form of a wire, represents a bypass conductor for transmitting electrical currents between two machine elements rotating relative to one another. The layer system comprising a plurality of components located on the bypass conductor can be produced partially or completely by electrolytic deposition from an aqueous electrolyte.

[0016] The rolling bearing according to the application can be designed as a sealed bearing or as an unsealed bearing. If seals are present, the conductive element made of coated wire for potential equalization is placed, in particular, between the outer side of a seal and a frontal plane tangent to both bearing rings. In principle, it is also possible to integrate multiple conductive elements into the rolling bearing.

[0017] In all embodiments, the EMC (electromagnetic compatibility) properties are drastically improved by the coated wire-formed discharge element compared to conventional rolling bearings that do not have such a bypass conductor. This also applies to applications with high discharge currents (EDM, Electrostatic Discharge Machining). In particular, the rolling bearing is suitable for discharging rotor earth currents in an electrical machine, i.e., an electric motor or generator, while protecting the bearing components, especially the rolling elements and bearing rings, which positively influences the service life of the rolling bearing and the entire electrical machine.

[0018] Two exemplary embodiments of the invention are explained in more detail below with reference to a drawing. In the drawings:

[0019] Fig. 1 a rolling bearing with integrated current discharge in a sectional view,

[0020] Fig. 2 the rolling bearing according to Figure 1 in a further sectional view,

[0021] Fig. 3 shows a discharge element of the rolling bearing according to Figure 1 intended for current discharge,

[0022] Fig. 4 shows the structure of a coating of the discharge element according to Figure 3, Fig. 5 shows, in a representation analogous to Figure 4, features of another discharge element provided with a coating and suitable for installation in the rolling bearing according to Figure 1.

[0023] Unless otherwise stated, the following explanations refer to both embodiments. Corresponding or essentially equivalent parts are identified by the same reference numerals in all figures.

[0024] A rolling bearing, designated overall by the reference numeral 1, is designed in the present case as a deep groove ball bearing and comprises two bearing rings 2, 3, namely an inner ring 2 and an outer ring 3, as well as rolling elements 4, i.e., balls, rolling between the bearing rings 2, 3. The rolling elements 4 are guided in a cage 5. Seals 6, 7 are provided to seal the rolling bearing 1. Each seal 6, 7 comprises a metallic support element 8 and a casing 9 made of an elastomer, through which sealing lips 10 are formed. The seals 6, 7 are thus designed as contact seals. Alternatively, non-contact seals, i.e., seals with a defined sealing gap, could be used. A design of the rolling bearing 1 as an unsealed bearing, in particular with oil lubrication, is also possible.

[0025] As can be seen from Figures 1 and 2, the rolling elements 4, as well as the seals 6, 7, are arranged asymmetrically between end planes E1, E2 of the rolling bearing 1. The left plane E1 in the arrangements according to Figures 1 and 2 is only slightly spaced from the seal 6. In contrast, the right seal 7 is at a greater distance from the nearest plane E2, which is tangent to the two bearing rings 2, 3 at the end face.

[0026] Between the latter seal 7 and the plane E2, a potential equalization conductor element 11 is arranged. This conductor element is made of wire, in this case with a circular cross-section. The conductor element 11 is also referred to as a metal clamp.

[0027] The outer ring 3 has a groove 12 for receiving a section of the deflection element 11, which groove has an approximately semicircular cross-section adapted to the deflection element 11. A further groove 13 is formed through the inner ring 2, which has a flatter, more angular, trough-like cross-sectional shape compared to the groove 12, so that the section of the deflection element 11 located in the groove 13 can be displaced at least slightly in the axial direction of the rolling bearing 1. Overall, the deflection element 11 is preloaded such that it is in contact with both bearing rings 2, 3 in every operating state of the rolling bearing 1.

[0028] The shape of the deflection element 11, viewed in the axial direction of the rolling bearing 1, is shown in Figure 3. A linear section 14 is clearly visible, which, in the state visible in Figure 3, lies in a plane parallel to the center axis of the rolling bearing 1 and transitions into an arcuate section 15 that extends over approximately 270° around the circumference of the bearing rings 2, 3. Overall, the deflection element 11, which has resilient properties, thus describes an incomplete, open ring shape.

[0029] The discharge element 11 comprises a metallic base body 16 and an electrically conductive coating 17 located thereon, intended for contacting both bearing rings 2, 3. In all exemplary embodiments, the coating 17 comprises a plurality of components 18, 19, 20, 21, which will be discussed in more detail below.

[0030] In the exemplary embodiment according to Figures 1 to 4, the coating 17 is composed of a first layer 18, which contains titanium, in this case in the form of titanium carbide, and a second, outer layer 19. The outer layer 19 is applied using the PVD (Physical Vapor Deposition) process and, in addition to sufficient electrical conductivity for this case, is characterized by excellent wear resistance. The total thickness of the coating 17 is designated dtotal and, in this case, is 150 nm.

[0031] The discharge element 11 constructed according to Figure 5 is also suitable for use in the rolling bearing 1 according to Figure 1 and has the external shape visible in Figure 3. In the case of Figure 5, a coating 17 is applied to the base component 16, which is designed as a tin-nickel layer 20 with incorporated particles 21. In this case, the coating 17 has a thickness d gesin the range of 5 to 10 pm. The tin-nickel layer 20, as the carrier material, represents the main component of the coating 17. The particles 21 are graphite particles. Overall, the coating 17 in the case of Figure 5 is produced by electrolytic deposition from an aqueous electrolyte.

[0032] List of reference symbols

[0033] 1 rolling bearing

[0034] 2 inner ring

[0035] 3 Outer ring

[0036] 4 rolling elements

[0037] 5 cage

[0038] 6 Seal

[0039] 7 Seal

[0040] 8 metallic support element

[0041] 9 Sheathing

[0042] 10 Sealing lip

[0043] 11 Discharge element

[0044] 12 Groove in the outer ring

[0045] 13 Groove in the inner ring

[0046] 14 Linear section

[0047] 15 arch sections

[0048] 16 basic bodies

[0049] 17 Coating

[0050] 18 first, inner layer

[0051] 19 second, outer layer

[0052] 20 tin-nickel layer carrier material

[0053] 21 particles da Thickness of the outer layer of the coating di Thickness of the inner layer of the coating dges Total thickness of the coating

[0054] E1 level

[0055] E2 level

[0056] MA central axis

Claims

Patent claims 1 . Rolling bearing with integrated current discharge, comprising two bearing rings (2, 3), a number of rolling elements (4) arranged between the bearing rings (2, 3), and a discharge element (11) which is provided in the form of a non-closed ring for producing an electrically conductive connection between the bearing rings (2, 3), characterized in that the discharge element (11) is designed as a wire and has an electrically conductive coating (17) which contacts the bearing rings (2, 3) and comprises at least two components (18, 19, 20, 21).

2. Rolling bearing according to claim 1, characterized in that said components (18, 19, 20, 21) are formed by a plurality of layers of the electrically conductive coating (17).

3. Rolling bearing according to claim 2, characterized in that the total thickness of the multilayer coating (17) is 150 nm ± 50 nm.

4. Rolling bearing according to claim 2 or 3, characterized in that the multi-layer coating (17) comprises a first layer (18) located on a base body (16) of the discharge element (11), which contains titanium, and a second, outer layer (19) which is designed as a PVD layer.

5. Rolling bearing according to claim 4, characterized in that titanium is present in the first layer (19) in the form of titanium carbide.

6. Rolling bearing according to claim 1, characterized in that said components (18, 19, 20, 21) are present in one and the same layer of the electrically conductive coating (17).

7. Rolling bearing according to claim 6, characterized in that the total thickness of the electrically conductive coating (17) is at least 5 pm and at most 10 pm.

8. Rolling bearing according to claim 7, characterized in that the electrically conductive coating (17) is designed as a tin-nickel layer (20) with incorporated particles (21).

9. Rolling bearing according to claim 8, characterized in that the electrically conductive coating (17) contains graphite particles.

10. Rolling bearing according to one of claims 1 to 9, characterized in that it is designed as a sealed bearing, wherein the diverting element (11) is placed between an outer side of a seal (7) and an end plane (E2) tangent to both bearing rings (2, 3).

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