Grounding unit for components that can be rotated relative to each other about a common central axis

Abstract

The invention relates to an earthing unit (1) for components rotatable relative to each other about a common central axis (2), comprising at least the following components: - an outer ring (3); - a central element (4) which is rotatable relative to the outer ring (3) about the central axis (2); and - at least one planetary body (5) which, as a result of a rotation of the central element (4) relative to the outer ring (3), is arranged rolling between the outer ring (3) and the central element (4), wherein the outer ring (3), the central element (4) and the at least one planetary body (5) with their respective contact surfaces (6, 7, 8) are radially prestressed relative to each other forming a surface contact, and an electrical conductor is provided between the outer ring (3) and the central element (4) via at least one of the planetary bodies (5) by means of the surface contact, wherein at least one of the planetary bodies (5) is designed as a radially prestressed ring band element (9). The earthing unit proposed here enables safe earthing of a rotor shaft for the highest speeds and virtually wear-free over the entire lifespan of the motor.

Description

[0001] The invention relates to a grounding unit for components rotatable relative to one another about a common central axis, a bearing device with such a grounding unit with a rotational axis for a rotor shaft of an electric motor, an electric motor with such a grounding unit and / or bearing device with a rotational axis, a drive train with such an electric motor, and a motor vehicle with such a drive train.

[0002] From another field of expertise, for example disclosed in CN 2 20 797 364 U, an electrical discharge ring with rolling planetary bodies for space applications is known.

[0003] For electric motors, particularly in automotive applications, it is often necessary for the rotor shaft, which can build up a voltage deviating from the earthing level due to inductive charging during the electromagnetic generation of torque, to be earthed to the environment. Particularly when used in wet environments (i.e., with an oil sump or splash lubrication), the introduction of excessively high electrical voltage is often harmful to the gap between the stator and rotor or to the lubricating oil. At the same time, very high speeds are often required, for example, 10,000 or even 20,000 rpm [twenty thousand revolutions per minute]. So-called earthing rings or shunt elements exist for this purpose, which are usually integrated into a bearing concept. Some concepts for earthing components that rotate relative to one another are not suitable for such speeds.Others exhibit excessive electrical resistance. Known designs feature an electrical sliding contact. Over a specified lifetime, this leads to abrasion and deterioration of the electrical contact, resulting in sparks and ferromagnetic chips that can be drawn into the gap between the stator and rotor.

[0004] Based on this, the present invention is based on the object of at least partially overcoming the disadvantages known from the prior art. The features of the invention are derived from the independent claims, for which advantageous embodiments are presented in the dependent claims. The features of the claims can be combined in any technically reasonable manner, whereby the explanations from the following description as well as features from the figures, which comprise additional embodiments of the invention, can also be consulted for this purpose.

[0005] The invention relates to a grounding unit for components that can be rotated relative to one another about a common central axis, comprising at least the following components: - an outer ring; - a central element which is rotatable relative to the outer ring about the central axis; and - at least one planetary body which is arranged between the outer ring and the central element as a result of a rotation of the central element relative to the outer ring, wherein the outer ring, the central element and the at least one planetary body are radially clamped relative to one another with their respective contact surfaces forming a surface contact, and an electrical line is established between the outer ring and the central element via at least one of the planetary bodies by means of the surface contact and the planetary body is designed as a radially prestressed ring band element, preferably with a spring steel band providing the radial force.

[0006] In the following, reference is made to the central axis or rotational axis when, without explicit indication to the contrary, the axial direction, radial direction, or the direction of rotation and corresponding terms are used. Ordinal numbers used in the preceding and following descriptions serve only to clearly distinguish them and do not reflect an order or ranking of the designated components. An ordinal number greater than one does not necessarily imply that another such component must be present.

[0007] This proposes a completely new concept for a grounding unit for components that can be rotated relative to one another about a common central axis, such as a rotor shaft and a bearing mount (e.g., the motor housing or an external shaft mount). There is no sliding contact, yet the electrical contact between the components that can be rotated relative to one another is extremely reliable. A desired service life can be reliably achieved by, on the one hand, ensuring that abrasion is (at least almost) negligible, and, on the other hand, compensating for other wear phenomena, such as settlement. Since (at least virtually no) abrasion occurs over the service life, the penetration of electrically conductive or magnetically active chips into the gap between the stator and rotor is not a relevant issue for the design.Therefore, no maintenance requirements or a shortening of the service life of such an electric motor are to be expected.

[0008] The design of the outer ring is comparable to a ring gear of a planetary gear, as is the central element with a sun gear, and the at least one planetary body with a planetary gear. It should be noted that, although toothing is preferably used, as described below, it is not mandatory. Furthermore, it should be noted in advance that, in a preferred embodiment, the planetary body does not require guidance by a planet carrier. Alternatively or additionally, a cage is provided for guiding a plurality of planetary bodies, wherein preferably (unlike a bearing cage for the rolling elements of a rolling bearing), frictional contact between the contact surface of the respective planetary body and the cage is prevented, so that the contact surface is not impaired over its lifetime.At the same time, however, it should also be noted that (at least for most applications) neither a supporting function nor torque transmission is achieved here. For particularly low wear, it is advantageous if these components of the grounding unit move against each other in a purely rolling manner (e.g., ensured by a toothing), i.e., without slippage. In a preferred embodiment, this is ensured or supported by sufficient radial preload of these components against each other.

[0009] The central element is, for example, a shaft or a shaft connection, or alternatively, a sleeve for slipping or pressing on. The central element is preferably secured against rotation or integrally connected to one of the components that can rotate relative to one another about the common central axis. It should be noted that in one application, the outer ring is connected to the rotatable component or is a component of the rotatable component, with the central element preferably being rotationally fixed (i.e., stationary). In most applications, the central element is a component of the rotatable component (e.g., a shaft) or is connected to it so that it rotates with it.

[0010] The electrically conductive bridge between the outer ring and the central element is established by means of at least one planetary body (preferably two, three, or more). Because a mechanical load-bearing force (radial and / or axial) is not appropriate for most applications due to the required forces, in one corresponding embodiment, such a planetary body is designed as an annular element, i.e., one with a hollow center. It is thus lightweight (low mass) and can thus be constructed with negligible inertial mass. The electrical line runs through the planetary body itself or across its surface or through a surface layer of the planetary body. Preferably (even with a low mass), the planetary bodies are balanced relative to the central axis, preferably (for cost reasons) by means of symmetry regarding shape, material, mass (distribution), and arrangement.

[0011] The radial preload due to a radial force serves to ensure electrically conductive contact between the contact surfaces of the components of the grounding unit, preferably also for high acceleration loads and / or vibrations, such as those that occur in a mobile application in a motor vehicle. In one embodiment, the radial preload also creates a reserve for wear (for example caused by abrasion, spark erosion and / or settlement) over a desired service life and / or an assembly tolerance. In one embodiment, the radial preload is adjustable by means of a maintained undersize (for example, joinable by means of a temperature difference) and / or an elastic deformation. In one embodiment, the outer ring and / or the central element or the component with the respective contact surface is formed from a (spring steel) ring, which is elastically deformed by rolling as it rotates.In one embodiment, at least one planetary body (alone or additionally) is configured for elastic deformation, while the at least one other planetary body (preferably alone) is configured for electrical conduction and is in secure (and therefore highly conductive) electrical contact with the other components by means of the elastic deformation.

[0012] For the grounding function, very good electrical conductivity between the central element and the outer ring (specifically, between the sides or surfaces adjacent to the respective components) and a low electrical resistance of, for example, 10 Ω [ten ohms] or less must be ensured. This is facilitated by a macroscopic (elastic) deformation of at least one of the components of a respective contact pairing of the grounding unit, whereby an electrical contact area is enlarged compared to a smaller deformation (for example, an approximately ideally stiff contact pairing with a line contact or point contact). Above all, the contact pairing is significantly larger (by one or more orders of magnitude) than the total area of ​​the contact pairings in a rolling bearing between the bearing rings and the rolling elements.

[0013] Here, it is provided that at least one of the planetary bodies is elastically deformable. Preferably, a mechanical resistance is generated (as a result of an undersize), which generates a sufficient radial counterforce so that this (elastically deformable) planetary body itself forms a contact pairing via the respective contact surfaces with an electrically conductive area that is larger (compared to an undeformed state). Alternatively or additionally, an electrically conductive area of ​​the respective contact pairings is (correspondingly) larger in the other planetary bodies. Alternatively or additionally, a radial force is generated that is sufficiently large to ensure sufficiently electrically conductive contact between the central element and the outer ring over a desired service life (with expected wear under design load).

[0014] In a preferred embodiment, the radial force is maintained by forming the respective planetary body (preferably all of the planetary bodies) by means of a spring steel strip or by encompassing a spring steel strip. Preferably, the contact surface (of the respective planetary body) is formed by the spring steel strip, wherein the contact surface of the spring steel strip particularly preferably has a coating made of and / or doping with a highly electrically conductive material (for example, copper or silver or an alloy thereof). In one embodiment, such a coating is applied only in certain regions.

[0015] It is further proposed in an advantageous embodiment of the grounding unit that the outer ring, the central element and the at least one planetary body have a toothing corresponding to one another.

[0016] The corresponding toothing is designed to allow the respective components to roll against each other (or against each other). Alternatively or additionally, the toothing is designed to enlarge the (electrically conductive) area of ​​the contact pairing of the respective contact surfaces.

[0017] In an advantageous embodiment, the gearing ensures that, when a plurality of planetary bodies are present, they are always securely positioned at a distance from one another in the direction of rotation, specifically to avoid contact and preferably to maintain a desired balance. Preferably, this eliminates the need for a component comparable to a planetary carrier, i.e., such a component is not provided. This results in very high mechanical efficiency and very low construction effort (and thus costs). The individual planetary bodies thus rotate freely (i.e., without a separate guide element) at a constant distance from one another.

[0018] It is further proposed in an advantageous embodiment of the earthing unit that the respective contact surface of the outer ring, the central element and / or at least one of the planetary bodies is formed from a separate material, preferred as: - Strip material, preferably form-fitting and secured against rotation; - Press-on ring, preferably secured against rotation by stamping; or - Coating, preferably applied electrolytically.

[0019] Strip material is connected to a carrier body, for example, by means of coating and / or material-to-material joining (e.g., gluing, soft soldering, brazing, or welding). The strip material is preferably plastically deformed (preferably molded) and connected to the carrier body. Alternatively, the component in question is formed from a ring strip element.

[0020] A press-fit ring is applied to a support body by means of a press fit (i.e., an undersize). The press-fit ring is preferably rigid and (at least approximately) non-deformable under the design forces during operation of the grounding unit. For example, the central element is formed as a press-fit ring and pressed onto a shaft (e.g., a rotor shaft). Alternatively or additionally, the outer ring is designed as a press-fit ring and inserted (pressed) into a complementary opening.

[0021] A coating is preferably made of a highly electrically conductive material, for example, copper and / or silver or an alloy. Due to the low current intensities, a coating is extremely thin for many applications, for example, 10 µm [ten micrometers] or less, preferably 2 µm to 3 µm. In one embodiment, the coating is applied by electrolysis, for example, to a carrier body made of a plastic (sufficiently electrically conductive for electrolysis), preferably fiber-reinforced.

[0022] It is further proposed in an advantageous embodiment of the earthing unit that the outer ring has at least one lateral rim, preferably two lateral rims, for axially guiding the at least one planetary body, wherein the outer ring is preferably designed as a deep-drawn sleeve.

[0023] In one embodiment, no (separate) axial guide element is provided for the at least one planetary body. Instead, it is advantageous if a stop is formed at least axially on one side. Here, it is proposed that such an axial stop is formed by the outer ring, specifically by a rim (with a corresponding radial inward extension). In one embodiment, in an installation situation, a directly adjacent component is provided on one side, for example an outer bearing ring of a rolling bearing. In this case, no rim is preferably provided on the corresponding (axial) side of the outer ring. At the same time, preferably no axial stop is provided on the central element. Alternatively or additionally, a rim (preferably one rim on each side) is provided on the respective planetary body. It should be noted that in one embodiment, the rim is formed to be circumferentially closed or alternatively to be interrupted.

[0024] In an advantageous embodiment, the outer ring (or the carrier body) is formed cost-effectively from a sheet metal material, preferably by cold forming, particularly preferably by deep drawing. In one embodiment, the contact surface is formed by a separate element, for example, by a strip material that is inserted, pressed in, and / or integrally bonded to the inside of the (formed) outer ring (or the carrier body). Preferably, the at least one rim of the outer ring (or carrier body) is used as an assembly aid and / or for axial securing during operation.

[0025] It is further proposed in an advantageous embodiment of the earthing unit that the at least one planetary body and the central element are designed to be axially displaceable relative to each other, wherein preferably the central element has a contact surface with a first axial length and the at least one planetary body has a contact surface with a second axial length, wherein the first length is greater than the second length.

[0026] This embodiment takes into account the fact that an axial relative movement can occur between the components to be electrically connected by means of the grounding unit. For example, in the case of rotor shafts (of electric motors), it is known that a resulting (magnetic) axial force and / or settlement can lead to a permanent or dynamic axial displacement relative to the environment. Here, therefore, the central element and the at least one planetary body are preferably axially displaceable relative to one another. For example, no axial stop is provided. For example, only an axial lock (for example by means of a retaining ring, for example designed as a Seeger® ring) is provided, which serves to prevent loss, although axial play is provided so that unnecessary friction during normal operation is excluded.

[0027] In a preferred embodiment, the central element is designed such that an area with (electrically conductive) contact (i.e., the overlap of the contact pair) is determined by the length of the contact surface of the (respective) planetary body, regardless of the relative axial position of the central element and the at least one planetary body. For this purpose, the (first axial) length of the contact surface of the central element is greater than the (second axial) length of the contact surface of the (respective) planetary body, preferably by the amount of a possible axial displacement during operation over a desired service life and, if applicable, an assembly tolerance and / or a safety factor.Alternatively, these two lengths are designed in such a way that an undersize (at least for an extreme case of axial misalignment) is possible, i.e. the area of ​​the electrically conductive contact pairing is then actually reduced compared to an optimal axial overlap.

[0028] According to a further aspect, a bearing device with a rotational axis for a rotor shaft of an electric motor is proposed, comprising at least the following components: - a bearing inner ring for receiving a rotor shaft; - a bearing outer ring for fixing in a motor housing; - rolling elements which are arranged between the bearing inner ring and the bearing outer ring so that they can rotate around the axis of rotation and support each other with low friction; and - an earthing unit according to an embodiment as described above, wherein preferably at least one of the following pairs is formed in one piece or joined together in a materially bonded and / or form-fitting manner: - the outer ring and the bearing outer ring; and - the central element and the bearing inner ring.

[0029] In one embodiment, a bearing device is partially a conventional rolling bearing, for example, a ball bearing or cylindrical roller bearing. The bearing device is designed to radially and / or axially support a shaft (for example, the rotor shaft of an electric motor) in an environment (for example, in a motor housing) with low friction.

[0030] The bearing device features a bearing inner ring, which may be a separate component or formed integrally with a component to be supported (e.g., a shaft). The bearing inner ring is located in the center of the bearing device and, in a separate embodiment, is designed as a ring with a (usually circular and / or radially inner) mount for a component. A raceway for rolling elements is formed on the radially outer side, often with a rim (such as in a tapered roller bearing) and / or a recessed mount (such as in a deep groove ball bearing) for axial support.

[0031] The bearing assembly also includes an outer bearing ring, which may be a separate component or formed integrally with a component to be supported (e.g., a housing). The outer bearing ring is the radially outermost component of the bearing assembly and, in a separate embodiment, is designed as a ring with a (usually circular and / or radially outer) mount for a component. The outer bearing ring also has a raceway for rolling elements, which in this case is arranged on the radial inside. This raceway is often mirrored to the raceway of the inner bearing ring.

[0032] The rolling elements are usually provided in large numbers and roll between the bearing inner ring and the bearing outer ring on their running surfaces when these are rotated relative to each other. In one embodiment, the rolling elements are free; alternatively, they are guided by a so-called bearing cage (and fixedly spaced from each other). In most cases, a lubricant is provided, for example, a (viscous) grease or a (low-viscosity) oil. However, there are also (so-called dry) bearing systems in which at least one of the running surfaces and / or the rolling elements are, for example, ceramically formed or coated.

[0033] Here, it is proposed that a grounding unit is also provided, which in one embodiment according to the preceding description can be connected to, is connected to, or is integrated into the bearing device. The grounding unit is preferably arranged axially next to the rolling elements. Preferably, no additional radial installation space is required for the grounding unit compared to a bearing device without a grounding ring. Thus, the bearing device proposed here can be made radially smaller than a rolling bearing with a grounding ring. In addition, the electrical conduction path (via the grounding unit) is clearly separated from the bearing rings and rolling elements, and a comparatively large axial distance is formed. This reliably prevents spark erosion in the bearing device (especially on the running surfaces and the rolling elements).

[0034] In one embodiment, the outer ring of the grounding unit and the bearing outer ring are formed as a single piece, for example, a type of sleeve is formed in which a (compared to a conventional rolling bearing) additionally axially extending rim is provided as the outer ring of the grounding unit. Alternatively or additionally, such an rim is connected in a materially bonded manner (for example by gluing, soft soldering, brazing, or welding), which encloses part or the entire outer ring of the grounding unit. Alternatively or additionally, such an rim is positively connected, for example by plugging or caulking, to the bearing outer ring, which here too encloses part or the entire outer ring of the grounding unit, for example for easy assembly.

[0035] In one embodiment (additionally or exclusively), the central element of the grounding unit and the bearing inner ring are formed as a single piece, for example, a type of sleeve is formed in which a (compared to a conventional rolling bearing) additionally axially extending edge is provided as the central element of the grounding unit. Alternatively or additionally, such an edge is connected to the bearing inner ring in a materially bonded and / or form-fitting manner, for example as described above with reference to the outer ring, wherein the latter also comprises part or all of the central element of the grounding unit, for example for ease of assembly. It should be noted that in one embodiment, the central element is formed (for example, as a single piece) from the component to be grounded and supported.

[0036] The bearing device proposed here comprises a grounding unit by means of which an electrical grounding can be realized, at which abrasion-induced formation of ferromagnetic particles and a high rotational speed (for example up to 20 thousand rpm or more), as well as a sufficiently long (maintenance-free) operating time for a desired lifetime in an application, for example in an electric motor, can be achieved.

[0037] According to a further aspect, an electric motor with a rotation axis is proposed, comprising at least the following components: - an engine housing; - a stator fixed in the motor housing; - a rotor which can be electromagnetically rotated by the stator about the rotation axis and which has a rotor shaft; - a bearing arrangement, preferably comprising a bearing device according to an embodiment as described above, for low-friction, relatively rotatable support of the rotor relative to the stator; and - a grounding unit according to an embodiment as described above, wherein the rotor shaft is grounded relative to the motor housing and / or the environment by means of the grounding unit, wherein the central element and the rotor shaft are preferably formed in one piece or are joined to one another in a materially bonded and / or form-fitting manner.

[0038] The electric motor, for example, is designed at least functionally conventionally, for example, as a permanent magnet synchronous motor for a motor vehicle drivetrain. Such an electric motor is usually designed as a finished unit encased in a motor housing. Such a motor housing is configured, for example, for torque support (for example, in a motor vehicle chassis), for heat dissipation (for example, by means of fins), and / or for mechanical connection to a transmission housing.

[0039] A stator is fixed in the motor housing, thus supporting it against torque. It should be noted that the motor housing is electrically insulated from the power current in the stator (and / or, if applicable, the rotor). The motor housing is often suitable as a grounding sink (i.e., as the earth), preferably electrically connected to the chassis or a chassis component that is electrically insulated from a transport cell.

[0040] At the center of the stator is a rotor with a winding (or a magnetic core) complementary to the stator winding. By appropriately wiring the stator (or alternatively or additionally the rotor), a torque is generated at the rotor around the rotational axis of the electric motor by means of magnetic induction and transmitted via the rotor shaft.

[0041] The rotor or rotor shaft is supported with low friction by a bearing arrangement (e.g., with two bearings in a fixed-loose bearing arrangement or axially clamped in an X-arrangement or an O-arrangement), usually directly on the motor housing (preferably in the electric motor assembly). The bearing arrangement preferably does not include a (conventional) grounding ring.

[0042] A grounding unit (integrated into or formed separately from a bearing device) is provided for grounding the rotor shaft. The central element is applied to the rotor shaft (electrically conductive) or formed integrally with it, for example as a toothing and / or coating with a highly electrically conductive material (e.g. copper or silver). The outer ring is electrically conductively connected to a component in the surrounding area (e.g. the chassis of a motor vehicle) or to the motor housing or is integrated into it, for example as a toothing and / or coating with a highly electrically conductive material. In one embodiment, a highly electrically conductive paste is provided between the central element and the rotor shaft and / or between the outer ring and the surrounding area or the motor housing.

[0043] In one embodiment, the central element is pressed and / or plugged onto the rotor shaft (preferably with splines). Alternatively or additionally, the central element is caulked to the rotor shaft.

[0044] The electric motor proposed here comprises at least one grounding unit, by means of which an electrical grounding can be provided, in which abrasion-induced formation of ferromagnetic particles (dangerous or at least disturbing for the annular gap between stator and rotor) and a high speed (for example up to 20 thousand rpm or more), as well as a sufficiently long (maintenance-free) operating time for a desired lifetime of an electric motor can be achieved.

[0045] According to a further aspect, a drive train is proposed, comprising at least one electric motor according to an embodiment according to the above description, at least one consumer and at least one transmission by means of which the at least one consumer is connected to the electric motor in a torque-transmitting manner.

[0046] The drive train proposed here comprises at least one electric motor, for example connected to a rechargeable high-voltage battery for a battery-electric power supply, which forms the torque source of a torque flow at least in one main state. Furthermore, at least one consumer is included, for example drive wheels of a motor vehicle, which forms the torque sink of the torque flow at least in one main state. A transmission is interposed, via which the (preferably entire wheel-side) torque flow is conducted. At least one grounding unit is provided in and / or near the electric motor and / or in the transmission, so that the buildup of an electrical voltage with the risk of a voltage surge or electrical interference with other components of the drive train or its surroundings is reliably prevented.

[0047] The drive train proposed here comprises an electric motor or at least one grounding unit, by means of which an electrical grounding can be provided, in which abrasion-induced formation of ferromagnetic particles (dangerous or at least disruptive for the annular gap between stator and rotor) and a high speed (for example up to 20 thousand rpm or more), as well as a sufficiently long (maintenance-free) operating time for a desired lifetime of an electric motor can be achieved.

[0048] According to a further aspect, a motor vehicle is proposed, comprising a chassis, a drive train according to an embodiment as described above and at least one drive wheel, wherein the drive train is attached to the chassis and the at least one drive wheel is suspended, and wherein the at least one drive wheel is connected to the electric motor in a torque-transmitting manner, wherein preferably the rotor shaft of the electric motor is earthed to the chassis.

[0049] The motor vehicle is, for example, a passenger car, a truck, or a motorized two-wheeler. The motor vehicle has a drive train according to an embodiment as described above and a chassis, wherein the drive train is fastened in the chassis (for example, the electric motor is torque-supported) and is preferably electrically connected to it for grounding. The chassis is thus a grounding sink and is preferably electrically insulated from a transport cell (for example, for accommodating people or goods) and other contact areas (for example, a fuel tank filler neck and / or electrical charging connection for a high-voltage battery). The torque output by the at least one electric motor is transmitted via the transmission to the at least one drive wheel (consumer). The transmission referred to here is or comprises a (preferably switchable) transmission.Alternatively, the transmission is or includes, for example, a fixed transmission (i.e. with an unchangeable transmission ratio), a differential and / or a slip clutch.

[0050] The motor vehicle proposed here comprises a drive train or at least one grounding unit, by means of which an electrical grounding can be provided, in which abrasion-induced formation of ferromagnetic particles (dangerous or at least disruptive for the annular gap between stator and rotor) and a high speed (for example up to 20 thousand rpm or more), as well as a sufficiently long (maintenance-free) operating time for a desired service life of a motor vehicle can be achieved.

[0051] The invention described above is explained in detail below against the relevant technical background with reference to the accompanying drawings, which show preferred embodiments. The invention is in no way limited by the purely schematic drawings, whereby it should be noted that the drawings are not to scale and are not suitable for defining proportions. It is shown in Fig. 1: a grounding unit in a frontal view; Fig. 2: a grounding unit in a perspective sectional view; Fig. 3: the earthing unit according to Fig. 2 in a sectional view; Fig. 4: an electric motor with an earthing unit as part of a bearing device; and Fig. 5: a drive train in a motor vehicle.

[0052] In Fig. 1 shows a grounding unit 1 in a frontal view with a central axis 2. The grounding unit 1 comprises a central element 4, which here is arranged coaxially to the central axis 2. In this exemplary embodiment, the (purely optionally three) planetary bodies 5 and the outer ring 3 arranged around the planetary bodies 5 are arranged radially enclosing the central element 4. Each of these components comprises a contact surface 6, 7, 8, by means of which the components are in mechanical or electrical contact with one another. The design of the outer ring 3 with its contact surface 6 is comparable to a ring gear of a planetary gear, as is the central element 4 (with its contact surface 7) with a sun gear, and the planetary bodies 5 each with a planetary gear, whereby the planetary bodies 5 are designed here (purely optionally) without a planet carrier.

[0053] Here, a corresponding toothing is provided for the rolling movement of the respective components with one another (or on one another, preferably without slippage). The toothing is preferably designed to enlarge the (electrically conductive) area of ​​the contact pairing of the respective contact surfaces 6, 7, 8. Furthermore, the toothing ensures that the planetary bodies 5 are always securely positioned at a distance from one another in the direction of rotation, specifically to avoid contact and preferably to maintain a desired balancing. In this exemplary embodiment, the central element 4 is designed (purely optionally) as a press-on ring 12 on a (rotor 27) shaft.

[0054] The electrically conductive bridge between the outer ring 3 and the central element 4 is established by the planetary bodies 5. Here, the planetary bodies 5 are ring-shaped, i.e., hollow in their center, and (purely optionally) designed as ring-band elements 9. They are thus lightweight (low mass) and can be constructed with negligible inertial mass. The electrical conduction runs through the respective planetary body 5 itself or across its surface, or through a surface layer of the planetary body 5.

[0055] The planetary bodies 5 are preferably arranged between the outer ring 3 and the central element 4 in such a way that they form the surface contact between the components by means of a radial preload. In this exemplary embodiment, the radial force 10 is maintained by forming the respective planetary bodies 5 using a spring steel strip or by enclosing a spring steel strip. In one embodiment, the contact surface 8 of the spring steel strip is formed by a coating 13 and / or doping with a highly electrically conductive material.

[0056] As a result of the radial preload, an electrical contact area is enlarged by means of a macroscopic (elastic) deformation of at least one of the components of a respective contact pair of the grounding unit 1. It can be clearly seen here that the areas of the contact pairs are significantly larger (by one or more orders of magnitude) than the total area of ​​the contact pairs in a rolling bearing between the bearing rings and the rolling elements 25.

[0057] In Fig. 2 shows a perspective sectional view of an earthing unit 1. The earthing unit 1 is, without exclusion of generality, largely identical to the earthing unit 1 in Fig. 1, and in this respect, reference is made to the description therein. Here, the toothing of the planetary bodies 5 on the contact surface 8 and a corresponding toothing of the outer ring 3 and the central element 4 on their contact surfaces 6, 7 are clearly shown. In this embodiment, the central element 4 is formed integrally with a shaft (e.g., rotor shaft 20). The shaft is arranged coaxially with the central axis 2 of the grounding unit 1.

[0058] An (unacceptably large) axial displacement on the side of the outer ring 3 is excluded due to a left rim 14 and a right rim 15, which here serve as axial stops for the planetary bodies 5. In the embodiment shown, strip material 11 is arranged between the rims 14, 15, from which the contact surface 6 of the outer ring 3 is formed with a toothing corresponding to that of the planetary bodies 5. For this purpose, the outer ring 3 is formed, for example, cost-effectively from a sheet material, for example by cold forming or deep drawing. The strip material 11 is inserted, pressed in, and / or firmly bonded to the inside of the (formed) outer ring 3, with the rims 14, 15 of the outer ring 3 preferably being used as an assembly aid and / or for axial securing during operation.

[0059] In this exemplary embodiment, the planetary bodies 5 are preferably also arranged between the central element 4 and the outer ring 3 by means of a radial preload due to an oversize on their own diameter of, for example, 0.1 mm to 0.3 mm [one-tenth of a millimeter to three-tenths of a millimeter]. Thus, due to the axial stop by the rims 14, 15 and the radial preload, contact is ensured over the required service life.

[0060] In this exemplary embodiment, the grounding unit 1 is designed such that an axial displacement on the central element 4 is possible. Thus, even in the event of an axial offset of the rotor shaft 20 and / or an assembly tolerance, a large-area contact by means of the grounding unit 1 is ensured, as designed.

[0061] In Fig. 3 is the earthing unit 1 according to Fig. 2 in a sectional view. The shaft (for example rotor shaft 20) is arranged coaxially to the central axis 2 of the grounding unit 1 and comprises a toothing over a predetermined first length 16 of the contact surface 7. The toothing of the contact surface 7 of the central element 4 is designed to correspond to the toothing of the contact surface 8 of the planetary body 5, wherein the contact surface 8 of the planetary body 5 is formed over a predetermined second length 17. Here, the first length 16 is longer than the second length 17, preferably by the amount of a possible axial displacement during operation over a desired service life and, if applicable, an assembly tolerance and / or a safety factor, so that an axial offset on the side of the central element 4 can be represented without loss of contact.

[0062] In Fig. 4 shows a schematic sectional view of an electric motor 21 with a grounding unit 1 as part of a bearing device 18. The electric motor 21 comprises a stator 26 and a rotor 27, which are arranged rotatably about a rotational axis 19 within a motor housing 24. The rotor 27 is held by a rotor shaft 20, which is supported by a bearing arrangement 28 (here two bearing devices 18). By appropriately wiring the stator 26 (alternatively or additionally the rotor 27), a torque about the rotational axis 19 of the electric motor 21 is generated at the rotor 27 by means of magnetic induction and can be delivered via the rotor shaft 20. The motor housing 24 is configured, for example, for torque support (for example in a chassis 29 of a motor vehicle 34), for heat dissipation (for example by means of fins), and / or for mechanical connection to a transmission housing.The rotor shaft 20 is supported on the motor housing 24 by a bearing arrangement 28, wherein the bearing arrangement 28 here comprises the two bearing devices 18.

[0063] Each of the bearing devices 18 is provided with a bearing inner ring 22, which is shown here (purely optionally) as a separate component. The bearing inner ring 22 is arranged in the center of the bearing device 18. A running surface for rolling elements 25 is formed on the radial outside, shown here as an example in a deep groove ball bearing for (purely optional) axial support. In addition, a bearing outer ring 23 is provided in each case, which is shown here (purely optionally) as a separate component. The bearing outer ring 23 is the radially outermost component of the bearing device 18. The bearing outer ring 23 also has a running surface for rolling elements 25, which is then arranged on the radial inside here. This is shown here corresponding to the inner running surface as in a deep groove ball bearing.The rolling elements 25 are usually provided in large numbers and roll on the running surfaces between the bearing inner ring 22 and the bearing outer ring 23 when these are rotated relative to each other. Whether the bearing arrangement 28 is a fixed-loose arrangement or a clamped arrangement is not shown here.

[0064] In this embodiment, the bearing device 18 shown on the left is of conventional design, while the bearing device 18 shown on the right contains the earthing unit 1 according to Fig. 2. The grounding unit 1 is arranged such that the central axis 2 of the grounding unit 1 is congruent with the rotational axis 19 of the electric motor 21. The grounding unit 1 is arranged axially next to the rolling elements 25 and comprises an outer ring 3, a central element 4, and a plurality of planetary bodies 5. Preferably, no additional radial installation space is required for the grounding unit 1 compared to a bearing device 18 without a grounding ring (e.g., as shown on the left). Thus, the bearing device 18 proposed here can be made radially smaller than a rolling bearing with a grounding ring. In addition, the electrical conduction path (via the grounding unit 1) is clearly separated from the components of the bearing rings and rolling elements 25, and a comparatively large axial distance is formed. This reliably prevents spark erosion in the bearing device 18 (especially on the running surfaces and the rolling elements 25).

[0065] The outer ring 3 is here electrically connected to the motor housing 24. As an alternative to the illustrated embodiment, the outer ring 3 of the grounding unit 1 and the bearing outer ring 23 are formed as a single piece (here, an inserted additional sleeve with the rims 14, 15), for example, a type of sleeve in which a (compared to a conventional rolling bearing) additionally axially extending edge is provided as the outer ring 3 of the grounding unit 1. Furthermore, the central element 4 of the grounding unit 1 and the bearing inner ring 22 are formed as a single piece with the rotor shaft 20 of the electric motor 21 and are designed to be electrically conductive. For example, by means of a toothing and / or coating 13 with a highly electrically conductive material.

[0066] In Fig. 5 shows a drive train 30 in a motor vehicle 34. The motor vehicle 34 has a transport cell 36 (for example, for human occupants) which is aligned along the longitudinal axis 35 (along the main direction of travel of the motor vehicle 34), and the electric motor 21 of the drive train 30 is aligned in front of the transport cell 36 and its rotation axis 19 is aligned transversely to the longitudinal axis 35. The motor vehicle 34 has a chassis 29, which here forms a grounding sink (i.e., the environment). The transport cell 36 is preferably electrically insulated from the chassis 29 with respect to the occupants of the motor vehicle 34. The electric motor 21 is connected to a transmission 33 via its rotor shaft 20 in a torque-transmitting manner. Thus, a torque for the drive train 30 is output by means of the electric motor 21. However, a torque can also be absorbed, for example, by recuperating braking energy.On the output side, the gearbox 33 is connected to a purely schematically illustrated output, so that a left drive gear 31 and a right drive gear 32 can be supplied with torque from the electric motor 21 with a variable transmission ratio. The rotor shaft 20 is electrically connected by means of a grounding unit 1 in a simple, secure, and mechanically unrelated manner to a grounding sink, for example, the motor housing 24 and, above it, to the chassis 29 or directly to the chassis 29. For this purpose, the electric motor 21 is connected, for example, to a bearing device 18 as shown in FIG. Fig. 4 shown.

[0067] With the earthing unit proposed here, a safe earthing of a rotor shaft can be achieved for highest speeds and with virtually no wear over the lifetime of the motor. List of reference symbols 1 earthing unit 2 Central axis 3 Outer ring 4 Central element 5 planetary bodies 6 Contact surface (outer ring) 7 Contact surface (central element) 8 Contact surface (planetary body) 9 Ring band element 10 Radial force 11 Tape material 12 Press-on ring 13 Coating 14 left board 15 right board 16 first length 17 second length 18 Storage facility 19 Rotation axis 20 (Rotor) shaft 21 Electric motor 22 Bearing inner ring 23 Bearing outer ring 24 engine housing 25 rolling elements 26 Stator 27 Rotor 28 Bearing arrangement 29 Surroundings 30 Drivetrain 31 left drive wheel 32 right drive wheel 33 gearboxes 34 Motor vehicle 35 Longitudinal axis 36 Transport cell

Claims

[1] Earthing unit (1) for components rotatable relative to one another about a common central axis (2), comprising at least the following components: - an outer ring (3); - a central element (4) which is rotatable relative to the outer ring (3) about the central axis (2); and - at least one planetary body (5) which, as a result of a rotation of the central element (4) relative to the outer ring (3), is arranged in a rolling manner between the outer ring (3) and the central element (4), wherein the outer ring (3), the central element (4) and the at least one planetary body (5) are radially clamped relative to one another with their respective contact surfaces (6, 7, 8) forming a surface contact, and an electrical line is established between the outer ring (3) and the central element (4) via at least one of the planetary bodies (5) by means of the surface contact, wherein at least one of the planetary bodies (5) is designed as a radially prestressed annular band element (9). [2] Grounding unit (1) according to claim 1, wherein the outer ring (3), the central element (4) and the at least one planetary body (5) have a toothing corresponding to one another. [3] Grounding unit (1) according to one of the preceding claims, wherein the respective contact surface (6, 7, 8) of the outer ring (3), the central element (4) and / or at least one of the planetary bodies (5) is formed from a separate material, preferably as: - strip material (11), preferably positively secured against rotation; - press-on ring (12), preferably secured against rotation by stamping; or - Coating (13), preferably applied electrolytically. [4] Grounding unit (1) according to one of the preceding claims, wherein the outer ring (3) has at least one lateral rim (14, 15), preferably two lateral rims (14, 15), for axially guiding the at least one planetary body (5), wherein the outer ring (3) is preferably designed as a deep-drawn sleeve. [5] Grounding unit (1) according to one of the preceding claims, wherein the at least one planetary body (5) and the central element (4) are designed to be axially displaceable relative to one another, wherein preferably the central element (4) has a contact surface (7) with a first axial length (16) and the at least one planetary body (5) has a contact surface (8) with a second axial length (17), wherein the first length (16) is greater than the second length (17). [6] Bearing device (18) with a rotation axis (19) for a rotor shaft (20) of an electric motor (21), comprising at least the following components: - a bearing inner ring (22) for receiving a rotor shaft (20); - a bearing outer ring (23) for fixing in a motor housing (24); - rolling elements (25) which are arranged between the bearing inner ring (22) and the bearing outer ring (23) so as to be rotatable about the rotation axis (19) and support each other with low friction; and - an earthing unit (1) according to one of the preceding claims, wherein preferably at least one of the following pairs is formed in one piece or joined together in a materially bonded and / or form-fitting manner: - the outer ring (3) and the bearing outer ring (23); and - the central element (4) and the bearing inner ring (22). [7] Electric motor (21) with a rotation axis (19), comprising at least the following components: - a motor housing (24); - a stator (26) fixed in the motor housing (24); - a rotor (27) which is electromagnetically rotatable by the stator (26) about the rotation axis (19) and has a rotor shaft (20); - a bearing arrangement (28), preferably comprising a bearing device (18) according to claim 6, for low-friction, relatively rotatable support of the rotor (27) relative to the stator (26); and - a grounding unit (1) according to one of Claim 1 to Claim 5, wherein by means of the grounding unit (1) the rotor shaft (20) is grounded relative to the motor housing (24) and / or the environment (29), wherein preferably the central element (4) and the rotor shaft (20) are formed in one piece or are joined to one another in a materially bonded and / or form-fitting manner. [8] Drive train (30) comprising at least one electric motor (21) according to claim 7, at least one consumer (31, 32) and at least one transmission (33) by means of which the at least one consumer (31, 32) is connected to the electric motor (21) in a torque-transmitting manner. [9] Motor vehicle (34), comprising a chassis (29), a drive train (30) according to claim 8 and at least one drive wheel (31, 32), wherein the drive train (30) is attached to the chassis (29) and the at least one drive wheel (31, 32) is suspended, and wherein the at least one drive wheel (31, 32) is connected to the electric motor (21) in a torque-transmitting manner, wherein preferably the rotor shaft (20) of the electric motor (21) is earthed to the chassis (29).

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