Grounding unit for components that can be rotated relative to each other about a common central axis, electric motor with this grounding unit, drive train with this electric motor and motor vehicle with this drive train

Abstract

Earthing unit (1) for components rotatable relative to each other about a common central axis (2), comprising at least the following components: - a wave element (3) which is rotatable about the central axis (2); - an earthing terminal (4) which is arranged coaxially to the shaft element (3), wherein a sliding electrically conductive contact is formed between a contact surface (5) associated with the shaft element (3) and a counter-contact surface (6) associated with the earthing terminal (4), characterized by the fact that the electrically conductive contact between the contact surface (5) and the corresponding counter-contact surface (6) is formed by at least one diameter projection (7) and wherein which is formed by at least one diameter projection (7) of at least one of the following shapes, forming a line contact (8) of the contact surface (5): - Bridge shape (9) with axial main extension; - Thread form (10); and - Corrugation (11) with wave crest (12) with axial or inclined main extent.

Description

[0001] The invention relates to an earthing unit for components that are rotatable relative to each other about a common central axis, an electric motor with such an earthing unit having a central axis, a drive train with such an electric motor, and a motor vehicle with such a drive train.

[0002] Electric motors, especially electric traction motors, become electrically charged during operation due to induced shaft voltages. Additionally, circulating high-frequency currents can occur in high-power electric motors. Such electric motors have a rotor and a rotor shaft, which are mounted in a motor housing to allow for low-friction rotation via (e.g., rolling) bearings. Electrical discharges or the circulating high-frequency currents can damage the bearings. To prevent this, it is necessary to dissipate this electrical potential. Solutions for this purpose, such as those using lamellar discs, as shown in DE 10 2018 208 823 A1, grounding brushes according to DE 10 2018 218 530 A1, or radially acting grinding elements (carbon brushes), as disclosed, for example, in DE 10 2018 119 288 A1, are known for grounding the rotor shaft.The solutions known so far do not take into account the influence of (electrically insulating) coolant in the area of ​​the rotor shaft, which impairs its grounding.

[0003] Based on this, the present invention aims to overcome, at least partially, the disadvantages known from the prior art. The features of the invention are defined in the independent claims, for which advantageous embodiments are shown in the dependent claims. The features of the claims can be combined in any technically meaningful way, whereby the explanations in the following description and features from the figures, which comprise supplementary embodiments of the invention, can also be used.

[0004] The invention relates to an earthing unit for components that are rotatable relative to each other about a common central axis, comprising at least the following components: - a wave element which can be rotated around the central axis; - an earthing terminal which is arranged coaxially to the shaft element, wherein a sliding electrically conductive contact is formed between a contact surface associated with the shaft element and a counter-contact surface associated with the earthing terminal.

[0005] The grounding unit is characterized primarily by the fact that the electrically conductive contact between the contact surface and the corresponding counter-contact surface is formed by at least one diameter projection.

[0006] The following text refers to the aforementioned central axis whenever the axial direction, radial direction, or direction of rotation and corresponding terms are used, unless explicitly stated otherwise. Ordinal numbers used in the preceding and subsequent descriptions serve solely for unambiguous identification and do not indicate any order or ranking of the components referred to. An ordinal number greater than one does not necessarily imply the presence of another such component.

[0007] Here, a grounding unit is proposed, designed to dissipate an electrical charge or ground a shaft element. The shaft element is configured to rotate about a central axis. In one embodiment, the shaft element is the rotor shaft of an electric motor or is torque-resistant to it.

[0008] The grounding unit also includes a grounding connection through which the shaft element is electrically contacted. The grounding unit is arranged coaxially to the shaft element, i.e., to its central axis.

[0009] The reliable electrical contact to the shaft element (or its contact surface for electrical contacting) necessary for reliable grounding is established by means of a counter-contact surface which is assigned to the grounding connection, for example formed integrally with it (as with the antagonistic contact surface) or electrically connected to it.

[0010] The contact surface and / or the counter-contact surface are made of a material with high electrical conductivity, such as copper, steel or aluminum or an alloy thereof, or a plastic reinforced with electrically conductive additive material.

[0011] The electrical contact on the side of the wave element is thus achieved by means of a contact surface associated with the wave element. A sliding electrical contact is formed between these two antagonistic surfaces, which remains undisturbed by relative rotation.

[0012] In one embodiment, the contact surface and the counter-contact surface for a sliding electrical contact in a so-called dry environment, i.e. without, for example, circulating lubricants and / or coolant, are designed to be low-abrasion, i.e., wear-resistant, towards each other.

[0013] In a preferred embodiment, the contact surface and the mating contact surface are configured for a sliding electrical contact in a wet environment. In a wet chamber within an electric motor, a poorly electrically conductive oil or a so-called dielectric fluid is used. This can lead to the formation of a film between the two opposing surfaces, resulting in electrical insulation or an unacceptably severe impairment of electrical conductivity. Reliable grounding cannot therefore be guaranteed.

[0014] It is proposed here that the sliding electrical contact is not formed across the entire surface, nor by the (soft, floating) bristles of a contact brush. Rather, an electrical contact is formed between the two antagonistic surfaces of the shaft element and the grounding connection by means of a diaphragm projection. This ensures that any film of electrically insulating liquid that may form (in a wet application) or a deposit of electrically insulating abrasive material (especially in a dry application) cannot interfere with the mechanical contact.Rather, a sufficiently high contact pressure is created between the two opposing surfaces to reliably displace the film or abrasive material, and this contact pressure is effective only over a small area, so that only a low (generally negligible in the respective application) frictional resistance is generated. In a preferred embodiment, the frictional resistance is no greater than that of a conventional solution with a contact brush.

[0015] Preferably two diameter projections, particularly preferably three or more diameter projections, are arranged circumferentially (preferably equidistantly) on the contact surface of the shaft element or on the counter-contact surface of the grounding connection.

[0016] Such a diaphragmatic protrusion is designed in such a way that, by means of the sliding contact with the grounding terminal or its mating contact surface, it displaces any liquid or abrasive material in the direction of rotation. Due to this displacement, there is little to no (by design negligible) amount of insulating material between the contact surface and the mating contact surface, and thus the electrical contact between the contact surface and the mating contact surface remains (at least almost) undisturbed. An electrically insulating liquid or deposit therefore has no or only a negligible electrical insulating effect on the electrical contact.

[0017] It should be noted that in one embodiment, the shaft element is rotationally fixed, i.e., stationary during operation, and the grounding connection is configured for rotation around the central axis, i.e., it rotates coaxially around the shaft element during operation. Alternatively, this is reversed. Furthermore, it should be noted that in one embodiment, the mating contact surface, and alternatively the contact surface, is formed by the diaphragmatic projection.

[0018] The at least one diameter projection is formed by at least one of the following shapes, which form a line contact of the contact surface: - Bridge shape with axial main extension; - Thread form; and - Corrugation with a wave crest and axial or inclined main extent.

[0019] To ensure the displacement of insulating fluids in a wet environment, such as lubricants, and thus electrical contact between the contact surface and the mating contact surface, it is proposed here that the diaphragm projection have one of the aforementioned and subsequently detailed and / or supplemented list of shapes. It should be noted that the shapes listed here can be combined. The contact surface or the mating contact surface must have at least one diaphragm projection with the following shapes.

[0020] In one embodiment, the diameter projection is designed as a ridge shape with an axial main extent. The contact surface of the shaft element or the mating contact surface of the grounding connection is formed as a circumferential projection on this ridge shape. This reduces the total area of ​​such a contact surface or mating contact surface, i.e., the contact pair. As a result of the reduced area, the displacement of the liquid onto or wetting of the antagonistic surface of the contact pair is simplified, thus ensuring (sufficient) electrical contact, preferably permanently.

[0021] In an alternative or additional embodiment, the diameter projection is designed as a threaded form, i.e., as a ridge winding around the central axis with a thread pitch in the axial direction. Besides the electrical contact, the threaded form offers the additional advantage that, due to the thread pitch, a liquid on or wetting of the antagonistic surface of the contact pair is not displaced in the circumferential direction, but rather, in an embodiment of the projection that is (at least approximately) completely closed along the thread, is conveyed out in the axial direction.

[0022] The latter is advantageous in cases of sporadic wetting and / or when facilitating fluid transport. It should be noted that in one embodiment, the raised section along the thread is interrupted, for example, to minimize fluid transport and thus rotational resistance.

[0023] In one embodiment, both a web form with axial main extension and a thread form are provided, wherein preferably the thread form is interrupted in the web form, preferably with a gap or space.

[0024] In an alternative or additional embodiment, the diameter projection is designed as a corrugation with a crest having an axial or inclined main extent. A corrugation is, for example, a sinusoidal shape of the contact surface or the counter-contact surface, such as with an axial main extent along the direction of rotation. A crest with an axial main extent is a special rib shape with an axial main extent, wherein the elevation (i.e., the crest) slopes continuously towards the sides in the direction of rotation (at least approximately), and the crest has a corresponding rounding or plateau at its radial ends. This may result in a smoother introduction of the displacement forces.

[0025] A corrugation with a wave crest running in an inclined main extension is a correspondingly special thread form, analogous to the web form described. In this respect, reference is made to the preceding description concerning the (at least technically approximate) continuous pitch to the sides (here to the tangent of the thread).

[0026] In all embodiments, the respective shape creates a line contact between the contact surface and the mating contact surface. A line contact is a contact with a small area, which technically approximates a line. This line has a main extent and a small transverse extent, preferably a technically negligible transverse extent. The direction of the main extent is oriented as required. Due to the line contact, the pressure required to overcome surface tension or the viscosity of the liquid is low, and thus the frictional resistance is also low, taking into account manufacturing and assembly tolerances.

[0027] In an advantageous embodiment of the grounding unit, it is further proposed that at least the contact surface of the shaft element and / or the counter-contact surface of the grounding connection is formed from a sliding bearing material.

[0028] To ensure an electrical contact with a low coefficient of friction and simultaneously good frictional resistance against abrasion in the sliding contact, it is proposed here that the contact surface of the shaft element and / or the mating contact surface of the grounding terminal be formed from a sliding bearing material. A sliding bearing material can be designed to be highly electrically conductive. For example, the sliding bearing material is made of or comprises brass or a plastic with good sliding properties (e.g., polyamide), which is made sufficiently electrically conductive by incorporating an additive material (e.g., metal particles and / or carbon fibers). The sliding bearing material is applied to the shaft element and / or the grounding terminal, for example, by an additive manufacturing process (preferably weld overlay). Alternatively, the sliding bearing material is formed by a separate component, such as a sleeve.

[0029] In a further advantageous embodiment of the grounding unit, it is proposed that the contact surface is formed by a contact ring designed as a separate component. wherein the contact ring is preferably made of a sliding bearing material.

[0030] It should be noted that in one embodiment, the contact ring proposed here is not designed as a simple sleeve (as previously mentioned), but fulfills further structural functions, such as bridging a radial and / or axial gap, providing rotational fixation, and / or receiving a bearing element. Preferably, the contact ring is designed to compensate for tolerances.

[0031] The contact surface is designed as a separate contact ring, which is arranged on the shaft element. In one embodiment, this allows for easy replacement of the contact surface after a predetermined service life. In an alternative embodiment, the design as a separate component enables different material pairings between the shaft element and the contact ring. For example, the shaft element can be made less friction-resistant than the contact ring, making it more cost-effective and / or mechanically advantageous for the specific application. Alternatively or additionally, during maintenance, the (potentially worn) contact surface can be cost-effectively refurbished by replacing the separate component, thus restoring a sufficiently electrically conductive contact.

[0032] In a preferred embodiment, the contact ring is formed from a sliding bearing material. For example, the contact ring is made of or comprising brass, copper, or an alloy, or a plastic with good sliding properties, such as polyamide.

[0033] Alternatively or additionally, the mating contact surface of the grounding terminal is also manufactured as a separate component, so that the mating contact surface is also replaceable and / or different materials can be used between the grounding terminal and the mating contact surface. For example, in this embodiment, the mating contact surface of the grounding terminal is made of a sliding bearing material. In this respect, reference is made to the description of the contact surface analogously. Alternatively, the mating contact surface is made of a different material, but for a particularly advantageous material pairing, namely advantageous with regard to electrical conductivity and / or abrasion resistance and a low coefficient of friction.

[0034] In a further advantageous embodiment of the grounding unit, it is proposed that the contact ring be rotationally secured, preferably by frictional connection, to the shaft element or to the grounding connection.

[0035] To prevent relative rotation of the contact ring on the partner (i.e., shaft element or grounding connection) around its central axis, the contact ring is rotationally secured (preferably rotationally fixed) to the respective partner. The connection is preferably force-fit and / or form-fit. For example, the contact ring is rotationally secured to the shaft element or grounding connection by means of crimping, pressing, clamping, or clipping. Alternatively, such a rotationally fixed connection is created by means of, for example, a toothed joint, a keyway, or a tongue-and-groove connection. Alternatively or additionally, the contact ring is rotationally secured to the respective partner by means of a material-bonded connection such as gluing, soldering, or welding.

[0036] In a further advantageous embodiment of the grounding unit, it is proposed that a through-hole be provided in the shaft element and / or in the grounding connection.

[0037] Due to the need to establish a reliable electrically conductive contact, any liquid or wetting present on the opposing surface is displaced by the diameter projection (similar to a windshield wiper on a motor vehicle). Because liquid can be supplied, for example in an electric motor via a supply lance for a temperature control fluid, the proposed embodiment reliably prevents liquid accumulation within the grounding unit by providing at least one passage opening. Such a passage opening is, for example, designed with the geometric shape of a slot or a through-hole.

[0038] According to another aspect, an electric motor with a central axis is proposed, comprising at least the following components: - a stator with a stator winding; - a motor housing for fixing the electric motor in an installation situation and / or for holding the stator; - a rotor with a rotor package and a rotor shaft, which can be rotated around the central axis for torque transmission by means of a magnetic field of the stator; - a temperature control system for supplying a liquid temperature control medium for temperature control of the rotor and / or the stator, wherein an earthing unit according to an embodiment as described above is arranged between the rotor shaft and the motor housing and / or the environment.

[0039] The electric motor, for example, is functionally conventional, such as a permanent magnet or separately excited synchronous machine for a motor vehicle's drivetrain. Such an electric motor is usually manufactured as a complete unit, fixed in a motor housing within a specific installation. This motor housing is designed, for example, to support torque (e.g., in a vehicle chassis), to dissipate heat (e.g., by means of fins), and / or to be mechanically connected to a gearbox housing. Furthermore, the motor housing, either alone or in addition to the functions described above, is designed to accommodate a stator.

[0040] The stator is located within the motor housing, thus being supported against torque. It should be noted that the motor housing is electrically insulated from the power current in the stator (and / or, if applicable, in the rotor). The motor housing is often suitable as a ground (i.e., as the earth), preferably electrically connected to the chassis or to a component of the chassis that is electrically insulated from a transport cell. The stator comprises at least one stator winding. The stator winding is, for example, a hairpin winding, needle winding, or conventional coil winding, with the stator winding being arranged at externally slotted, internally slotted, or closed poles of the stator.

[0041] At the center of the stator is a rotor, which, together with a rotor core, has a winding (or magnetic core) complementary to the stator winding. The rotor core is mounted on a rotor shaft for rotation around the central axis. By means of appropriate wiring of the stator (alternatively or additionally of the rotor), a magnetic field is generated within the stator via magnetic induction, transmitting torque around the central axis of the electric motor to the rotor and then via the rotor shaft.

[0042] Furthermore, a temperature control system is proposed here, designed for the supply of liquid temperature control fluid. Due to the high currents, a significant amount of waste heat is generated within the motor housing, which must be dissipated. The rotor and / or stator can be temperature-controlled using the temperature control fluid, allowing the waste heat to be removed from the motor housing. The fluid is designed to absorb this waste heat and thus acts as a heat sink. It should be noted that heating an electric motor is advantageous in certain operating conditions. In such cases, the temperature control fluid can be used to transfer heat to the electric motor.

[0043] In one embodiment, the temperature control fluid is thermally connected to the environment or a larger heat sink (e.g., the chassis) via a heat exchanger in a heating circuit within the temperature control system, thus preventing the temperature control fluid from overheating within the engine housing during continuous operation. Alternatively or additionally, the temperature control fluid is present in sufficient quantity, for example, in a reservoir.

[0044] The temperature control fluid, being a good electrical insulator, is often designed as a dielectric oil with low electrical conductivity, thus preventing short circuits due to abrasion-related loss of insulating coatings on current-carrying elements of the electric motor.

[0045] In one embodiment, a liquid lubricant, usually a poorly conductive oil, is provided or circulated for the rotor bearings. The motor housing is designed as a wet chamber, at least in this area. Within the wet chamber, the lubricant is distributed across several or all components.

[0046] It is proposed here that the grounding unit described above be arranged between the rotor shaft and the motor housing and / or the surrounding environment. This grounding unit allows the lubricant or temperature control fluid within the motor housing to be displaced from the intended contact pair, thus ensuring a (slipping) electrical contact.

[0047] For grounding the rotor shaft, a grounding unit (integrated into or separate from a bearing assembly) is provided. The shaft element is electrically connected to the rotor shaft or formed integrally with it, for example, as webs and / or corrugations, optionally with a coating of a highly electrically conductive material (e.g., copper or silver). The shaft element and the grounding connection are electrically connected to or integrated into a component in the surrounding area (e.g., the chassis of a motor vehicle) or into the motor housing.

[0048] In an advantageous embodiment of the electric motor, it is further proposed that the grounding connection is formed by a, preferably vertical, supply lance for the temperature control medium of the temperature control system, and / or that the shaft element is formed by the rotor shaft.

[0049] It is proposed here that a supply lance be provided for feeding the lubricant or temperature control fluid into the motor housing, and that this lance also serves as the grounding connection. In one embodiment, the supply lance is conventionally designed as a rigid supply line and, for example, integrated into the temperature control system. The temperature control fluid can be fed via the supply lance to a predetermined position within the motor housing in the grounding unit. Within the grounding unit, the supply lance provides the electrical connection of the shaft element to a grounding ground. For example, the supply lance, via its mating contact surface, connects the shaft element to the environment, thus enabling grounding of the shaft element.

[0050] In a preferred embodiment, the feed lance is designed to be stationary, i.e., not rotating with the rotor shaft. For example, the feed lance is fixed in place, coaxial with the shaft element, which is also stationary and either free to rotate or rotates with the opposite side.

[0051] Alternatively or additionally, it is proposed here that the shaft element is formed by the rotor shaft. For example, the shaft element is electrically connected to the rotor shaft by means of a toothed connection or is formed integrally with the rotor shaft. For example, an axial end of the rotor shaft is designed as the shaft element. This ensures that, despite the rotor shaft being wetted (e.g., with a dielectric cooling fluid), grounding of the rotor shaft is guaranteed via the grounding unit on the shaft element.

[0052] According to another aspect, a drive train is proposed comprising at least one electric motor according to an embodiment as described above, at least one consumer and at least one gearbox by means of which the at least one consumer is connected to the electric motor in a torque-transmitting manner.

[0053] The proposed powertrain comprises at least one electric motor as described above, connected, for example, to a rechargeable high-voltage battery for battery-electric power supply, which, at least in one primary state, forms the torque source of a torque flow. It also includes at least one load, such as the drive wheels of a motor vehicle, which, at least in one primary state, forms the torque sink of the torque flow. A gearbox is interposed, through which the (preferably entire wheel-side) torque flow is routed. At least one grounding unit is provided in and / or at the electric motor and / or in the gearbox, thus reliably preventing the buildup of an electrical voltage that could lead to a voltage flashover or electrical interference with other components of the powertrain or its surrounding environment.

[0054] The proposed drive train comprises an electric motor or at least a grounding unit, by means of which electrical grounding is ensured even in a wet environment, and by means of which a high speed (for example up to 20 thousand rpm or more) and a sufficiently long (maintenance-free) operating time for a desired service life of an electric motor can still be achieved.

[0055] 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 from it, and where at least one drive wheel is connected to the electric motor in a torque-transmitting manner, preferably the rotor shaft of the electric motor is grounded to the chassis.

[0056] The motor vehicle is, for example, a passenger car, a truck, or a motorized two-wheeler. The motor vehicle comprises a drivetrain according to an embodiment as described above and a chassis, wherein the drivetrain is mounted in the chassis (for example, the electric motor is torque-supported) and preferably electrically connected to it for grounding. The chassis thus serves as a grounding mass and is preferably electrically insulated from a transport compartment (for example, for carrying persons or goods) and other contact areas (for example, fuel filler neck and / or electrical charging port for a high-voltage battery). The torque available from the at least one electric motor is transmitted via the transmission to the at least one drive wheel (consumer). The transmission described herein is, or comprises, a (preferably switchable) reduction gear.Alternatively, the transmission may include, for example, a fixed transmission (i.e., with an unchangeable gear ratio), a differential and / or a slip clutch.

[0057] The proposed motor vehicle includes a drive train or at least a grounding unit, by means of which electrical grounding is ensured even in a wet environment, and by means of which a high speed (for example up to 20 thousand rpm or more) and a sufficiently long (maintenance-free) operating time for a desired service life of an electric motor can still be achieved.

[0058] 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, although it should be noted that the drawings are not dimensionally accurate and are not suitable for defining size relationships. It is illustrated in Fig. 1: an electric motor with a grounding unit; Fig. 2: a schematic sectional view of an earthing unit in a first embodiment; Fig. 3: in a cross-sectional view of the grounding unit in a first embodiment; Fig. 4: in a cross-sectional view, earthing unit in a second embodiment; Fig. 5: in a schematic sectional view, an earthing unit in a third embodiment; and Fig. 6: A schematic top view of a drive train in a motor vehicle.

[0059] In Fig. Figure 1 shows a schematic sectional view of an electric motor 15 with a grounding unit 1. The electric motor 15 comprises a stator 16 and a rotor 19, which are rotatably arranged about a central axis 2 within a motor housing 18. The rotor 19 comprises a magnetically active rotor assembly 20, which is held by a rotor shaft 21. The rotor shaft is rotatably supported by a bearing arrangement (with two bearing devices 34, shown here purely as examples of ball bearings). By means of appropriate wiring of the stator 16 or its stator winding 17 (alternatively or additionally of the rotor 19 with its rotor assembly 20), a magnetic field and thus a torque about the central axis 2 of the electric motor 15 is generated at the rotor 19 by means of magnetic induction, which can be transmitted via the rotor shaft 21.The motor housing 18 is designed, for example, for torque support (e.g., in a chassis 35 of a motor vehicle 29), for heat dissipation (e.g., by means of fins), and / or for mechanical connection to a gearbox housing. The rotor shaft 21 is supported on the motor housing 18 by a bearing arrangement, here by means of the two bearing assemblies 34 shown. A feed lance 24 is also arranged inside the rotor shaft 21, the feed lance 24 serving both as a supply for a temperature control medium and as a grounding connection 4.

[0060] In this embodiment, an earthing unit 1 is provided at the left-hand bearing assembly 34 as shown, for example as in Fig. 2 to Fig. Figure 5 shows the earthing unit 1. It is arranged such that its central axis 2 is congruent with the central axis 2 of the electric motor 15. The earthing unit 1 is positioned between a feed lance 24 and the rotor shaft 21 and comprises a rotor-side shaft element 3 (with an optional contact ring 13) and an earthing connection 4. The electrical conductor path through the earthing unit 1 is clearly separated from the components of the bearing assembly 34. This reliably prevents spark erosion in the bearing assembly 34 (especially on running surfaces and rolling elements).

[0061] In Fig. Figure 2 shows a schematic sectional view of a grounding unit 1 in a first embodiment. The grounding unit 1 comprises a shaft element 3 arranged coaxially around the central axis 2 and a radially inner contact surface 5 (here, optionally, completely circumferential) (here, optionally, formed on a separately formed contact ring 13 that is rotatably fixed to the shaft element 3). The shaft element 3 is configured for rotation around the central axis 2, for example (as in Fig. (1 shown) is rotatably connected to a rotor shaft 21. A grounding connection 4 is arranged coaxially radially inside the shaft element 3. The grounding connection 4 comprises a counter-contact surface 6 antagonistic to the contact surface 5, which in this embodiment is, for example, designed as a circular surface coaxial with the central axis 2. The contact surface 5, on the other hand, has a diametrical projection 7 (preferably a plurality of diametrical projections 7). For example, the diametrical projection 7 shown is designed in a web shape 9. Due to the reduced area of ​​the contact pair 30 consisting of the contact surface 5 and the counter-contact surface 6, permanent sliding electrically conductive contact between the shaft element 3 and the grounding connection 4 is ensured even when the contact pair 30 is wetted or when (poorly electrically conductive) liquid flows through it, thus ensuring low electrical resistance.Thus, reliable grounding via this contact pair 30 is ensured.

[0062] The contact surface 5 and the mating contact surface 6 are, for example, made of a sliding bearing material. In this embodiment, the mating contact surface 6 is designed as a contact ring 13, preferably replaceable. The diameter projections 7 are designed such that, during operation, they form the contact pair 30 with the contact surface 5 of the shaft element 3, preferably with a line contact 8 (compare Fig. 3).

[0063] In this embodiment, the grounding connection 4 (purely optional) includes a through-opening 14, which is designed to drain a liquid (for example, a temperature control fluid) from the grounding unit 1 (compare this to...) Fig. 3) In this illustration, a section axis 33 through the passage opening 14 is shown. The section view through the section axis 33 is described below with reference to Fig. 3 described.

[0064] In Fig. 3 is earthing unit 1 in a cross-sectional view, for example according to Fig. 2, shown in a first embodiment. Reference is made to the description therein for purely exemplary purposes. Here and in the other examples, for the sake of clarity, the outer ring is always referred to as shaft element 3 and the inner component as grounding connection 4. However, it should be noted that the designation of the outer ring as shaft element 3 and the inner (here circular) component as grounding connection 4 is also reversible, for example with the rotor shaft 21 as the (radially inner) shaft element 3 and the grounding connection 4 as the housing-side (stationary) component, for example in the bore in a motor housing 18 for a bearing assembly 34 (compare Fig. 1) It should also be noted that in both cases there is a diameter projection 7 from the radially outer (compare Fig. 2 and here) or a radial-inward (compare Fig. 4 and Fig. 5) component is formed and / or from a (purely optional) contact ring 13 or from the solid material of the respective component.

[0065] Here, the formation of the contact pair 30 via a line contact 8 between the (here purely optional) diaphragmatic projections 7 on the contact surface 5 and the antagonistic counter-contact surface 6 is clearly visible. The (purely optional) through-hole 14 can be seen at the bottom of the illustration, preferably located at the bottom in operation (and possibly in a main state in a mobile application, such as in a motor vehicle 29) in the Earth's gravitational field for the passively assisted drainage of a liquid.

[0066] In Fig. 4 is earthing unit 1 in a cross-sectional view, for example according to Fig. 2, shown in a second embodiment. Reference is made here, purely by way of example, to the description therein. The earthing unit 1 is, without exclusion of the general principles, largely equivalent to the earthing unit 1 according to Fig. 3 identical and in that respect reference is made to the description there and only the differences are discussed below.

[0067] A plurality of diameter projections 7 are provided here, formed on the opposing contact surface 6, whereby the antagonistic contact surface 5 is circular with respect to the central axis 2 for a permanently sliding, reliably electrically conductive contact pairing 30. Furthermore, the diameter projections 7 are designed as corrugations 11, i.e., a special ridge shape 9, preferably with a line contact 8 also formed from the corrugation crest 12 to the antagonistic contact surface 5. Independently of this, two through-openings 14 are provided here (optionally diametrically opposed, and arranged above and below).

[0068] In Fig. 5 is shown in a schematic sectional view (as in Fig. 2) An earthing unit 1 is shown in a first embodiment. For example, the embodiment shown is similar to the embodiment according to Fig. 4 (for example, according to the indicated section axis 33) and in this respect reference is made to the description there. Here, the diameter projections 7 are not necessarily designed as corrugations 11. Here, the diameter projections 7 are designed similarly to or identical with a thread form 10.

[0069] In Fig. Figure 6 shows a schematic top view of a powertrain 25 in a motor vehicle 29. The motor vehicle 29 has a passenger compartment 31 (for example, for human occupants) which is oriented along the longitudinal axis 32 (along the main direction of travel of the motor vehicle 29). An electric motor 15 of the powertrain 25 is located in front of the passenger compartment 31, with its central axis 2 oriented transversely to the longitudinal axis 32. The motor vehicle 29 has a chassis 35, which forms a grounding point (i.e., surroundings 23). The passenger compartment 31 is preferably electrically insulated from the chassis 35 in relation to the occupants of the motor vehicle 29. The electric motor 15 is connected to a gearbox 28 via its rotor shaft 21 to transmit torque. The electric motor 15 thus delivers torque to the powertrain 25. It can also receive torque, for example, by recuperating braking energy.On the output side, the gearbox 28 is connected to a purely schematically represented output, so that a left drive wheel 36 and a right drive wheel 37 can be supplied with torque from the electric motor 15 with variable gear ratio. The rotor shaft 21 is electrically connected by means of a grounding unit 1 simply and safely to a grounding point, for example the motor housing 18 and via that to the chassis 35 or directly to the chassis 35. The electric motor 15 is, for example, as shown in . Fig. 1 shown equipped with an earthing unit 1.

[0070] The electric motor 15 is directly cooled by means of a temperature control system 22, so that the temperature control system 22 is fluidically connected to the electric motor 15. The motor housing 18 forms a wet cell, so that a temperature control fluid of the temperature control system 22 cools the electric motor 15 from the inside. By means of the grounding unit 1 according to one of the previously described embodiments, a reliable electrical contact is formed between the electric motor 15 and the rotor shaft 21 for grounding, thus providing reliable protection against spark erosion at the bearing assembly of the electric motor 15.

[0071] The earthing unit proposed here ensures reliable electrical earthing even in wet environments. Reference symbol list 1 earthing unit 2 Central axis 3 wave element 4 Earthing connection 5 Contact area 6 Counter contact area 7 diameter advantage 8 line contacts 9 Bridge shape 10 Thread form 11. Wave 12 wave crest 13 Contact ring 14 Passage opening 15 Electric motor 16 Stator 17 Stator winding 18 Motor housings 19 Rotor 20 Rotor package 21 Rotor shaft 22 Temperature control system 23 Surroundings 24 Feed lance 25 Powertrain 26 consumers 27 consumers 28 gearboxes 29 Motor vehicle 30 contact pairing 31 Transport cell 32 Longitudinal axis 33 Cutting axis 34 Storage facility 35 chassis 36 Drive wheel 37 Drive wheel

Claims

[1] Earthing unit (1) for components rotatable relative to each other about a common central axis (2), comprising at least the following components: - a wave element (3) which is rotatable about the central axis (2); - an earthing terminal (4) which is arranged coaxially to the shaft element (3), wherein a sliding electrically conductive contact is formed between a contact surface (5) associated with the shaft element (3) and a counter-contact surface (6) associated with the earthing terminal (4), characterized by , that the electrically conductive contact between the contact surface (5) and the corresponding counter-contact surface (6) is formed by at least one diameter projection (7) and wherein which is formed by at least one diameter projection (7) of at least one of the following shapes, forming a line contact (8) of the contact surface (5): - Bridge shape (9) with axial main extension; - Thread form (10); and - Corrugation (11) with wave crest (12) with axial or inclined main extent. [2] Earthing unit (1) according to claim 1, wherein at least the contact surface (5) of the shaft element (3) and / or the counter-contact surface (6) of the earthing connection (4) is formed from a sliding bearing material. [3] Earthing unit (1) according to one of the preceding claims, wherein the contact surface (5) is formed by a contact ring (13) designed as a separate component, wherein preferably the contact ring (13) is made of a sliding bearing material. [4] Earthing unit (1) according to claim 3, wherein the contact ring (13) is rotationally secured, preferably by frictional connection, to the shaft element (3) or to the earthing connection (4). [5] Earthing unit (1) according to one of the preceding claims, wherein a passage opening (14) is provided in the shaft element (3) and / or in the earthing connection (4). [6] Electric motor (15) with a central axis (2), comprising at least the following components: - a stator (16) with a stator winding (17); - a motor housing (18) for fixing the electric motor (15) in an installation situation and / or for receiving the stator (16); - a rotor (19) with a rotor package (20) and a rotor shaft (21), which is rotatable around the central axis (2) for torque transmission by means of a magnetic field of the stator (16); - a temperature control system (22) for supplying a liquid temperature control medium for temperature control of the rotor (19) and / or the stator (16), wherein an earthing unit (1) according to one of the preceding claims is arranged between the rotor shaft (21) and the motor housing (18) and / or the environment (23). [7] Electric motor (15) according to claim 6, wherein the grounding connection (4) is formed by a, preferably vertical, supply lance (24) for the temperature control medium of the temperature control system (22), and / or the shaft element (3) is formed by the rotor shaft (21). [8] Drive train (25) comprising at least one electric motor (15) according to claim 6 or claim 7, at least one consumer (26, 27) and at least one transmission (28) by means of which the at least one consumer (26, 27) is connected to the electric motor (15) in a torque-transmitting manner. [9] motor vehicle (29), comprising a chassis (35), a drive train (25) according to claim 8 and at least one drive wheel (36, 37), wherein the drive train (25) is attached to the chassis (35) and at least one drive wheel (36, 37) is suspended, and wherein at least one drive wheel (36,37) is connected to the electric motor (15) in a torque-transmitting manner, wherein preferably the rotor shaft (21) of the electric motor (15) is grounded to the chassis (35).

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