Potential equalization device and mechanical arrangement

Abstract

Potential equalization device (7) for a mechanical arrangement (1) comprising at least two electrically conductive components (2, 3) movable relative to each other, in particular a bearing, wherein at least one of the components (2, 3) is movably mounted relative to the other and the potential equalization device (7) has an electrically conductive base body (8) to be inserted into a space (6) between the components (2, 3) with a fixed fit in the outer ring, wherein the electrically conductive base body has retaining areas (11) distributed over the inner circumference and in the radially inner area, a conductive thread (9) is stretched over the retaining areas (11), which tangentially contacts the inner component (2) between the retaining areas (11), characterized in that the conductive yarn surrounds the inner component (2).

Description

Field of the invention

[0001] The invention relates to a potential equalization device for a mechanical assembly, in particular a bearing, comprising at least two mutually movable, electrically conductive components, wherein at least one of the components is mounted so as to be movable relative to the other. The invention also relates to a mechanical assembly, in particular a bearing. Background of the invention

[0002] Difficulties can arise with opposing, moving components of a mechanical assembly, such as the inner and outer rings of a rolling bearing, if the two components have different electrical potentials. This can occur, for example, due to induction in a motor, where currents can be induced in the shaft, for example. It has been shown that this can lead to high surface charges and thus high voltages in the mechanical assembly, particularly the bearing, which can cause a sudden discharge through the bearing. This discharge can cause damage to the bearing material (EDM - Electric Discharge Machining), for example to so-called EDM pitting, a matte bearing raceway, and / or serrations on the outer bearing raceway. This shortens the service life of the bearing or, in general, the mechanical assembly.

[0003] To overcome this problem, a first approach in the prior art proposed the use of bearing protection rings, for example the shaft grounding rings known under the brand name "Aegis." Such rings can, for example, be screwed in front of a bearing and have rubbing carbon fiber brushes or nanofibers on the circumference of a component, such as a shaft, in order to transfer the current from the shaft as the first component via the shaft grounding ring to, for example, a housing as the second component, which is preferably grounded. One such concept is described, for example, in US 2004 / 0233592 A1. However, this approach carries the risk of contamination of the carbon fiber brushes, thereby limiting the conductivity and thus the functionality of the shaft grounding ring. Furthermore, the radially mounted carbon fiber brushes do not have an actively adjusting function to compensate for wear.

[0004] Another state-of-the-art solution involves the use of conductive fleeces, which can be attached or bonded to radial shaft seals and enable current to flow through a rolling bearing. The disadvantage of this concept is the axial space required and the severely limited adjustment of the conductive component.

[0005] Furthermore, DE 10 2015 206 520 A1 discloses a dissipation device for dissipating electrostatic charge from a shaft, comprising an annular holder and a conductor arrangement. The conductor arrangement comprises at least one flexurally elastic conductor arranged on the holder. The conductor is formed from a carbon fiber arrangement, with ends of the conductor each received in the holder. The conductor arrangement has at least two conductor sections extending transversely to a shaft longitudinal axis. The conductor sections each have a shaft contact section. The shaft contact sections together form a contact arrangement for contacting two circumferential contact regions of a shaft circumference arranged in a shaft contact plane W, such that the shaft contact sections are arranged tangentially to the shaft circumference when in contact with the shaft circumference. (cf. DE 10 2015 206 520 A1, abstract)

[0006] Furthermore, DE 10 2017 115 353 A1 discloses a rolling bearing arrangement with a rolling bearing and a potential equalization element, wherein the rolling bearing for supporting a shaft has at least one bearing outer ring and rolling elements rolling on this. According to the invention, a circular arc-shaped receiving groove open radially outwards is formed on the bearing outer ring, that the potential equalization element is elastic and loop-like, that the potential equalization element has an elastomer section and an electrically conductive yarn section, that the elastomer section and a first region of the yarn section are fixedly received in the receiving groove, and that a second region of the yarn section bears at least partially against the shaft or a bearing inner ring.The loop-like and flexible potential equalization element ensures low-maintenance and low-friction electrical potential equalization within the rolling bearing arrangement, reliably preventing damage due to induced voltages." (see DE 10 2017 115 353 A1, summary).

[0007] These solutions are also cost-intensive and require additional components. Object of the invention

[0008] The invention is therefore based on the object of providing an improved, in particular adjustable and reliable solution for current transport between two components of a mechanical arrangement, in particular a bearing, which are mounted against one another. Description of the invention

[0009] To achieve this object, in a potential equalization device of the type mentioned at the outset, the invention provides that the potential equalization device has an electrically conductive metallic base body which is to be introduced into a space between the components and which is firmly seated in the outer ring, and the electrically conductive base body has holding areas distributed over the inner circumference, and in the radially inner area of ​​the potential equalization device, a conductive thread is stretched over the holding areas, which tangentially contacts the inner bearing ring between the holding areas.

[0010] Furthermore, it is therefore proposed to provide a functional element as a potential equalization device, which ensures the passage of current between two components, in particular the inner and outer bearing ring of a rolling bearing or a housing and a shaft, which establishes the electrical contact by means of a conductive thread.

[0011] The thread is stretched over two or more holding areas of the base body, whereby the pre-tension of the thread is guaranteed in a particularly low-friction manner over the service life of the equipotential bonding device.

[0012] The conductive thread can expediently be a stretch-torn carbon fiber yarn, in particular a stretch-torn carbon fiber yarn, or a polymer yarn filled with conductive material. Carbon fiber yarn, in particular stretch-torn carbon fiber yarn, has the advantage of high tensile strength primarily in the fiber direction, which is advantageously utilized within the scope of the present invention, in conjunction with high conductivity and thus low resistance to current transport from one component to another. As already mentioned, the tangential contact of the carbon fibers with the component results in an extremely low coefficient of friction. To further reduce friction and further increase conductivity, it is also possible to use a filled polymer yarn, in particular a yarn made of a polymer whose matrix contains conductive components to bring about general conductivity of the polymer.Polymers generally exhibit very low friction and, through appropriate techniques, also offer the possibility of providing high conductivity. A generally advantageous embodiment of the present invention can, for example, provide that the specific electrical resistance is less than 50 microohmmeters, preferably less than 20 microohmmeters. If a stretch-torn carbon fiber yarn is to be used, SGL Carbon SE, for example, provides a yarn that has a tensile strength of 4.0 GPa, a tensile modulus of elasticity of 240 GPa, an elongation at break of 1.7%, and a specific electrical resistance of 14 microohmmeters.

[0013] A preferred embodiment of the potential equalization device provides that the electrically conductive base body is formed by a metal disc. Thus, various embodiments, such as cover or covering discs made of metal, can be developed for the electrically conductive base body.

[0014] According to the invention, the conductive thread of the equipotential bonding device completely surrounds the inner bearing ring, i.e., by at least 360°. This has the advantage that the thread is permanently ideally pre-tensioned and rests against the second component, usually the shaft.

[0015] The elasticity, or the resulting pre-tension, is not caused by the elasticity of the base body, but in this case by the thread stretched across the holding areas. This thread is designed so that the contact of the thread with the second component ensures a permanent and virtually frictionless conductive connection. It should be noted that if the conductive yarn itself has no or only minimal elastic properties, it is entirely conceivable to achieve the pre-tension solely through mechanical tensioning across the holding areas.

[0016] The equipotential bonding device is particularly suitable for use in a bearing arrangement to implement electrical conduction and grounding between the components. This represents a particular advantage, as it allows the existing sealing solutions, so-called cover plates, to be replaced with the equipotential bonding device without requiring any additional installation space. The equipotential bonding device can also be used for any application that performs rotating, pivoting, or sliding movements relative to one another. Applications for linear guides, grippers / robots in the food and medical sectors, and rollers in medical devices are also conceivable. Overall, a simple, safe, and cost-effective method for conducting power between components has been implemented.

[0017] This design offers a number of advantages. By designing the base body with holding areas, automated adjustment is ultimately achieved, thus compensating for effects such as shaft out-of-roundness, particularly eccentricities, and bearing play. Contamination does not impair functionality. The tangential contact of the inner component allows for minimal friction. The equipotential bonding device also proves to be extremely temperature-resistant, as the limiting factor is the material used for the conductive thread. The equipotential bonding device is maintenance-free and, by reliably establishing an electrically conductive connection, prevents damage to the components due to sparking / scoring or general EDM effects.

[0018] The equipotential bonding device is particularly suitable for electrical conduction and grounding between components that rotate, pivot, or slide relative to each other. Typical applications include electric motors and gears, linear guides, grippers / robots in the food and medical industries, and rollers in medical devices. Overall, a simple, safe, and cost-effective method for conducting power between components is realized.

[0019] In an advantageous embodiment of the present invention, it can be provided that, in the case of an inner component mounted in the bearing area in a rotationally symmetrical receptacle of an outer component, the base body is designed as a ring or a disk. Rotationally symmetrical bearings, for example for shafts or in rolling bearings with an inner ring as the inner component and an outer ring as the outer component, thus offer the possibility of partially filling the usually also rotationally symmetrical intermediate space by means of a prestressed base body in the form of a disk or a ring, with a ring representing a preferred embodiment. In particular, as will be discussed in more detail below, the equipotential bonding device can additionally act as a sealing element for sealing the intermediate space to the outside, thus offering the additional advantage of keeping dirt, dust and moisture out of the intermediate space.For example, a metallic cover plate can be further developed into an equipotential bonding device according to the invention by adding the holding area and the conductive yarn. Furthermore, the base body can be constructed from any conductive material. Examples include plastics filled with conductive elements. Constructing the equipotential bonding device as a sealing element thus provides sufficient additional protection against the ingress of dirt and moisture.

[0020] The conductive thread can expediently be a stretch-torn carbon fiber yarn, in particular a stretch-torn carbon fiber yarn, or a polymer yarn filled with conductive material. Carbon fiber yarn, in particular stretch-torn carbon fiber yarn, can be advantageously used within the scope of the present invention by providing high conductivity and thus low resistance to current transport from one component to another. The tangential contact of the carbon fibers with the component results in a low coefficient of friction. To further reduce friction and further increase conductivity, it can also be provided to use a filled polymer yarn, in particular a yarn made of a polymer whose matrix contains conductive components in order to bring about general conductivity of the polymer. Polymers generally have very low friction and, through appropriate techniques, also offer the possibility of providing high conductivity.A generally advantageous embodiment of the present invention can, for example, provide for the specific electrical resistance to be less than 50 microohmmeters, preferably less than 20 microohmmeters. If a stretch-torn carbon fiber yarn is to be used, SGL Carbon SE, for example, provides a yarn that has a tensile strength of 4.0 GPa, a tensile modulus of elasticity of 240 GPa, an elongation at break of 1.7%, and a specific electrical resistance of 14 microohmmeters.

[0021] It should be noted at this point that the present invention can be implemented in different sizes, which means that it can be applied to both small-sized components and larger machine components.

[0022] In addition to the potential equalization device, the invention also relates to a mechanical arrangement comprising a potential equalization device according to the invention and the two components. All statements regarding the potential equalization device according to the invention can be applied analogously to the mechanical arrangement according to the invention, so that the aforementioned advantages can be achieved with it.

[0023] In particular, it can be provided that the mechanical arrangement is designed as a rolling bearing, wherein the inner component is an inner ring and the outer component is an outer ring. In this context, it is particularly suitable to design the base body in a ring shape. The equipotential bonding device can be arranged on at least one side adjacent to a cage containing rolling elements in the space between the components. If the equipotential bonding device is then also used as a sealing element, a conventional sealing element can be provided on one side of the cage with the rolling elements, and the equipotential bonding device according to the invention on the other side. Care must be taken to ensure that the gap dimensions between the inner component and the base body of the equipotential bonding device are selected to be very small in order to ensure the best possible seal.

[0024] As already mentioned, it is particularly preferred according to the invention if the potential equalization device is also designed as a sealing element for one side of the gap. In particular, it can be provided that the potential equalization device almost completely fills the gap in the radial and circumferential directions in at least one plane. In this way, as already explained, the penetration of dirt and moisture into the gap, in particular into a cage with rolling elements in a rolling bearing, is additionally prevented.

[0025] It should be noted at this point that conductive threads of the type mentioned, in particular carbon fiber yarns, are available in extremely thin form, for example about the thickness of a hair, so that they enable the potential equalization device to be designed with only a minimal gap, and thus an ideal sealing effect with the inner component.

[0026] It should also be noted that within a single mechanical arrangement, several potential equalization elements can of course also be provided, for example in the case of a rolling bearing on both sides of the cage with the rolling elements. Short description of the drawings

[0027] The invention is explained below using exemplary embodiments with reference to the accompanying drawings. The drawings are schematic representations and show: Fig. 1 a perspective view of a cut-away mechanical arrangement according to the invention in the form of a rolling bearing, and Fig. 2a the rolling bearing according to Fig. 1 potential equalization device used, as well as Fig. 2b a side view of a mechanical arrangement according to the invention in the form of a rolling bearing. Detailed description of the drawings

[0028] Fig. 1 shows a cutaway perspective view of a mechanical assembly 1 according to the invention, which in this case is designed as a rolling bearing with an inner ring as the inner component 2 and an outer ring as the outer component 3. Rolling elements 4 can be guided within a cage 5, as is generally known. The inner component 2 and the outer component 3 are rotatably movable relative to one another, as is generally known, with the rolling elements 4 and the cage 5 being located within a gap 6 between the components 2, 3. The components 2, 3 are each made of metal and are therefore electrically conductive. If a potential difference were to exist between the inner component 2 and the outer component 3, there would be a risk of a discharge at the point of least electrical resistance, for example via the raceway and the rolling elements, which could lead to damage.To avoid this, an equipotential bonding element 7, which can also have a sealing effect, i.e. act as a sealing element, is arranged on one side of the cage 5 in the space 6 between the inner component 2 and the outer component 3. Said equipotential bonding element has an electrically conductive base body 8 in the form of a ring or a disk and an electrically conductive thread 9 stretched onto holding sections 11. The electrically conductive thread 9 is pressed tangentially onto the respective component 2, 3 via the electrically conductive base body 8 by the pre-tensioning, so that a low-resistance conductive connection is created between the inner component 2 and the outer component 3 after the thread has been stretched onto the holding area of ​​the base body. In one embodiment, this is the case evenly over the entire circumference of the base body 8, as can be seen from the top view in . Fig. As can be seen in Figure 2b, a current flow from the inner component 2 to the outer component 3 and thus a potential equalization can occur locally at different locations. Fig. 2a represents the Fig. 1 represents the potential equalization device used. Fig. 2 b further shows a side view of a mechanical arrangement according to the invention in the form of a rolling bearing.

[0029] A stretch-torn carbon fiber yarn or a filled polymer yarn with conductive materials incorporated into its matrix can be used as the conductive thread. These threads or yarns can be manufactured extremely thin, for example, with diameters of < 100 µm, and therefore barely protrude from the base body 8 toward the center of the equipotential bonding device 7, which is advantageous when used as a sealing element. A conventional sealing element 10 or another equipotential bonding device 7 can also be provided on the opposite side of the equipotential bonding device 7.

[0030] It should also be noted that the base body 8 can be designed differently, even deviating from the Fig.1. Furthermore, the present invention can be used in other areas beyond the illustrated rolling bearing, for example, in a shaft and a housing as components or in a linear guide with components that move linearly relative to one another. List of reference symbols 1 Mechanical arrangement 2 inner component 3 outer component 4 rolling elements 5 cage 6 gap 7 Equipotential bonding element 8 basic bodies 9 Conductive thread 10 Sealing element 11 Holding area

Claims

[1] Potential equalization device (7) for a mechanical arrangement (1), in particular a bearing, comprising at least two electrically conductive components (2, 3) which are movable relative to one another, wherein at least one of the components (2, 3) is mounted so as to be movable relative to the other, and the potential equalization device (7) comprises an electrically conductive base body (8) which is to be introduced into a space (6) between the components (2, 3) and which is firmly seated in the outer ring, wherein the electrically conductive base body has holding regions (11) distributed over the inner circumference, and in the radially inner region, a conductive thread (9) is stretched over the holding regions (11) and makes tangential contact with the inner component (2) between the holding regions (11), characterized by that the conductive yarn encloses the inner component (2). [2] Potential equalization device (7) according to claim 1, characterized bythat the electrically conductive base body is formed by a metal disc. [3] Potential equalization device (7) according to one of the preceding claims, characterized by that the conductive thread (9) is a particularly stretch-torn carbon fiber yarn or a polymer yarn filled with conductive material. [4] Mechanical arrangement (1) with a potential equalization device (7) according to one of the preceding claims and the two components (2, 3). [5] Mechanical arrangement (1) according to claim 4, characterized by that it is designed as a rolling bearing, wherein the inner component (2, 3) is an inner ring and the outer component (2, 3) is an outer ring. [6] Mechanical arrangement (1) according to claim 5, characterized by that the potential equalization device (7) is arranged on at least one side adjacent to a cage (5) containing rolling elements (4) in the intermediate space (6) between the components (2, 3). [7] Mechanical arrangement (1) according to one of claims 4 to 6, characterized by that the potential equalization device (7) is further designed as a sealing element against dust or liquid for one side of the intermediate space (6). [8] Mechanical arrangement (1) according to one of claims 4 to 7, characterized by that the potential equalization device (7) is fastened to the outer component (3) in a form-fitting and / or force-fitting manner.

Images