Shaft grounding, electric machine and electrically operated axle drive train

Abstract

The invention relates to a shaft grounding device (1) for dissipating an electrical charge and / or voltage from a shaft (4), in particular for a drive train of an electrically operated motor vehicle (3), comprising a retaining ring (5) that can be positioned coaxially to the shaft (4) and a discharge element (7) fixed to the retaining ring (5), which can be electrically contacted with an outer circumferential surface (8) of the shaft (4), wherein the discharge element (7) is designed in an annular disk shape and is arranged coaxially to the shaft (4) on the retaining ring (5), wherein a plurality of contact tabs (9) extend radially towards the shaft (4) from the discharge element (7) such that, in the assembled state of the shaft grounding device (1), they bear against the shaft (4) in a spring-like manner in the radial direction.

Description

[0001] The present invention relates to a shaft grounding system for discharging an electrical charge and / or voltage from a shaft, in particular for a drive train of an electrically operated motor vehicle, comprising a retaining ring that can be positioned coaxially to the shaft and a discharge element secured to the retaining ring, which can be electrically conductively contacted with an outer surface of the shaft. The invention further relates to an electric machine and an electrically operated axle drive train.

[0002] Electrical machines, especially electric traction machines, are electrically charged during operation by induced shaft voltages. In addition, circulating high-frequency currents can arise in high-power motors. Such electrical machines typically comprise a rotor and a rotor shaft, which are mounted in a housing via rolling bearings. Electrical discharges or circulating high-frequency currents can damage the rolling bearings. To prevent this, this electrical energy must be dissipated. For example, grounding brushes or radially acting sliding elements (carbon brushes) are known for grounding the rotor shaft. Axial-acting shaft grounding systems are also known.

[0003] The document DE 10 2020 119 719 A1, for example, discloses a discharge device for a motor for discharging an electrical charge and / or voltage from a rotor via a shaft to a housing, with a first contact module for electrical and mechanical connection to the shaft, with a second contact module for electrical and mechanical connection to the housing, wherein the first and the second contact module are rotatable relative to one another and are electrically connected to one another in an interior space sealed off from a housing space, wherein the interior space is filled with an electrically conductive liquid, wherein the first and the second contact module are electrically conductively connected to one another via the electrically conductive liquid.

[0004] In addition to mechanical wear caused by shaft rotation, another cause of wear in the bearings of an electric motor is electrical currents flowing from the rotor shaft to ground. Voltages of a certain magnitude can overcome the insulating properties of the bearing lubrication, generating sparks that can lead to pitting, ridged surfaces, fusion craters, and ultimately premature failure of the bearings and motor. Bearing voltage—the voltage between the two bearing shells—usually correlates with shaft voltage—the voltage between the shaft and ground.

[0005] Due to capacitive coupling between the stator winding and the rotor and the high-frequency control of the stator phases, a voltage potential builds up at the rotor bearings, which can damage the bearings through so-called discharge currents. Countermeasures include insulating the bearings (e.g., using ceramic balls) or grounding the shaft using a sliding ground contact (electrically parallel to the bearings).

[0006] Furthermore, a device and method for compensating a shaft voltage on a shaft are already known from DE 10 2017 109 049 A1. A compensation circuit for generating a compensation voltage couples the compensation voltage directly or indirectly to the rotor shaft via a coupling element. The shaft voltage is detected directly or indirectly on the rotor shaft via a tapping element.

[0007] EP 1 455 434 A1 discloses an electric motor with a stator and a rotor rotatably mounted in or on the stator by means of a bearing arrangement. For electrical insulation, at least one sleeve and / or plastic layer is provided that electrically insulates the bearing arrangement from the stator or rotor and / or the rotor shaft from the rotor. This prevents capacitive displacement currents through the bearings, which primarily arise at high pulse or switching frequencies. These can lead to a reduction in the service life of the bearings.

[0008] DE 20 2017 107 755 U1 describes a device for reducing harmful bearing voltages in an electrical machine fed by an intermediate circuit voltage of an intermediate circuit, comprising a stator having windings and insulated from earth, a rotor and a motor shaft, wherein furthermore a rotor-side bearing and a stator-side bearing are each insulated from earth, and wherein the rotor and the stator are electrically connected to one another via a bypass capacitor with a predetermined capacitance.

[0009] DE 10 2017 122 466 A1 relates to a drive device comprising a rotatable rotary shaft, a rotor connected in a rotationally fixed manner to the rotary shaft, and at least one balancing disc. To enable the drive device to be manufactured without external alignment devices, it is proposed that the balancing disc be in direct contact with the rotary shaft and be connected in a rotationally fixed manner to it, with at least a partial region of the balancing disc and the rotor being located adjacent to one another in a fixing plane orthogonal to the rotary shaft.

[0010] In the field of electromobility, such electric motors are also often integrated into an axle drive train, which forms a structural unit consisting of the power electronics (inverter), electric motor, and transmission. This structural unit must be connected to the vehicle's ground for potential equalization. This is usually done via a conductor located between the body and the housing of the structural unit.

[0011] In such axle drive trains, a grounding element is usually located in the gear set of the transmission and / or directly on the rotor shaft of the electric motor, in order to be able to protect the bearings located there particularly well from harmful currents or discharges thanks to the structural proximity. These grounding elements are usually electrically connected to the housing of the axle drive train.

[0012] Generally, such grounding elements have the problem that dry-running grounding elements generate electrically conductive abrasion, which can lead to short circuits in the electrical machine. Wet-running grounding elements, on the other hand, often have the problem that they do not function efficiently at all operating points when immersed in oil.

[0013] The object of the invention is therefore to reduce or completely avoid the disadvantages known from the prior art and to provide a shaft grounding system that is simple in design and offers high operational reliability and durability. Furthermore, the object of the invention is to realize an improved electric machine and an improved electrically operated axle drive train.

[0014] This object is achieved by a shaft earthing system for discharging an electrical charge and / or voltage from a shaft, in particular for a drive train of an electrically operated motor vehicle, comprising a retaining ring which can be positioned coaxially to the shaft and a discharge element which is fixed to the retaining ring and which can be contacted in an electrically conductive manner with an outer circumferential surface of the shaft, wherein the discharge element is designed in the shape of an annular disk and is arranged coaxially to the shaft on the retaining ring, wherein a plurality of contacting tabs extend from the discharge element in the radial direction towards the shaft in such a way that, in the assembled state of the shaft earthing system, they rest resiliently against the shaft in the radial direction.

[0015] This has the advantage that the voltage (or voltage potential) across the bearing is reduced, so that the probability of spark discharges is reduced and the energy / power of the discharges that still occur is limited, with the result that bearing damage due to electrical discharges is reduced.

[0016] This provides a radially acting shaft grounding system that functions efficiently in dry and wet electrical machines and at all operating points. Existing installation space, for example, in an electrical machine or gear arrangement, can be utilized without increasing the axial or radial dimensions of the electrical machine. Furthermore, shaft grounding can also be easily integrated into existing applications at a later date. This prevents bearing damage on the rotatably mounted shaft and improves electromagnetic compatibility (EMC), reducing or preventing interference with other devices.

[0017] A further advantage of the shaft earthing according to the invention is that the shaft earthing can be constructed as an independent system and thus offered as a pre-assembled unit.

[0018] The discharge element also compensates for the radial tolerance chain between the shaft and a connection structure of the shaft earthing.

[0019] The shaft earthing according to the invention can be used as a dry-running and / or wet-running shaft earthing.

[0020] A further advantage of the shaft grounding according to the invention is that the individual components of the shaft grounding are easy to manufacture and do not have any geometries that are challenging to manufacture, which also has a positive effect on the manufacturing price of the shaft grounding.

[0021] The retaining ring and / or the annular disc-shaped discharge element can be designed to be closed or open around its circumference. The retaining ring and / or the annular disc-shaped discharge element can also be designed in multiple parts, for example, as ring segments.

[0022] Further advantageous embodiments of the invention are specified in the dependent claims. The features listed individually in the dependent claims can be combined with one another in a technologically expedient manner and can define further embodiments of the invention. Furthermore, the features specified in the claims are further specified and explained in the description, where further preferred embodiments of the invention are presented.

[0023] According to an advantageous embodiment of the invention, the retaining ring can be provided with a plurality of retaining tabs that extend axially out of the retaining ring and that clamp the annular disc-shaped discharge element to the retaining ring. By using multiple retaining tabs, the holding force is evenly distributed across the discharge element, thereby achieving a firm and reliable hold. This is particularly important when the discharge element is subjected to heavy loads, such as vibrations, shock loads, or high speeds. Furthermore, the use of multiple retaining tabs enables easier assembly and disassembly of the discharge element. It may not be necessary to use special tools or fasteners, as the discharge element can simply be positioned and clamped between the retaining tabs.The retaining tabs can also be punched out of the retaining ring using a particularly simple manufacturing process, for example, by stamping. This also has the advantage that the retaining tabs are integrally connected to the retaining ring and thus cannot be removed, which also contributes to increased assembly security.

[0024] In the simplest embodiment, the contacting tabs can be essentially cuboid-shaped. It is also conceivable for the free ends of the contacting tabs to have a surface treatment and / or shape that can improve the electrical conductivity of the contacting tabs. For example, it is conceivable for the contacting tabs to have a bend at their free end that deviates from the cuboid shape, or to be hardened and / or provided with a particularly electrically conductive coating.

[0025] According to a further preferred development of the invention, it can also be provided that at least two of the contact tabs, preferably all of the contact tabs, have a different longitudinal extension from one another, so that the contact points of the contact tabs are arranged axially offset from one another on the outer surface of the shaft. This can ensure that the outer surface is not locally overstressed and worn by contact points located on a common circular ring.

[0026] Furthermore, according to a similarly advantageous embodiment of the invention, it can be provided that the contacting lugs, in the assembled state of the shaft grounding, are arranged axially offset relative to the discharge element at their free end contacting the outer surface. This makes it particularly easy to generate radial spring elasticity, which enables sufficiently good contact between the shaft and the contacting lugs and can also provide tolerance compensation in the radial direction.

[0027] The number of contacting tabs is preferably equal to the number of retaining tabs. According to a further particularly preferred embodiment of the invention, it can be provided that one contacting tab is positioned in the circumferential direction of the discharge element between two retaining tabs. Placing the contacting tab between two retaining tabs ensures that the contact surface of the respective contacting tab is pressed tightly against the surface of the retaining ring. This enables an optimal electrical connection between the retaining ring and the discharge element, thereby minimizing resistance and effectively dissipating electrical currents. Placing the contacting tab between the retaining tabs also contributes to the stability and security of the connection. The tab is held in position by the adjacent retaining tabs and protected from unwanted movement or loosening.This is especially important in environments where vibration, shock, or other mechanical stress may occur. Furthermore, positioning the contact tab between the retaining tabs allows for better distribution of the contact load. Because the contact tab is supported on both sides by the retaining tabs, the pressure on the contact surface is evenly distributed, ensuring greater resilience and durability.

[0028] Furthermore, the invention can also be further developed in such a way that the retaining tabs are arranged equidistantly over the circumference of the retaining ring, which can also contribute to an improved holding of the discharge element by a clamping effect that is evenly distributed over the circumference.

[0029] In a likewise preferred embodiment of the invention, it can also be provided that the retaining ring is produced from sheet metal by means of a forming process. The use of sheet metal material and forming processes enables cost-efficient production compared to other manufacturing methods. Sheet metal is also a comparatively lightweight material, which can contribute to a weight reduction of the retaining ring. This can be particularly advantageous in applications where low weight plays a role, for example in vehicles, in order to reduce the overall weight and optimize energy consumption. Furthermore, forming processes offer great flexibility with regard to the shape of the retaining ring. The sheet metal can be formed into various shapes and configurations in order to meet the specific requirements and geometric properties of the retaining ring.This also enables customized manufacturing for different applications. Additional functions or features can be integrated into the retaining ring during the forming process. For example, mounting holes, fasteners, or other specific design features can be machined directly into the retaining ring, facilitating assembly and integration into the overall system, such as an electric machine or an electrically operated axle drive train of a motor vehicle.

[0030] For the same reasons, it may also be advantageous to further develop the invention in such a way that the discharge element is produced from a sheet metal by means of a forming process.

[0031] It is understood that the retaining ring and the discharge element are made of an electrically conductive material. It can be provided that the retaining ring and the discharge element are made of different materials. By using different materials for the retaining ring and the discharge element, their material properties can be tailored to their specific requirements and functions. For example, the retaining ring can be made of a material with high strength and rigidity to ensure robust fastening, while the discharge element can be made of a material with high conductivity for the efficient discharge of electrical currents. The use of different materials can also make it possible to optimize the weight of the shaft grounding system.For example, if the discharge element is made of a lighter material than the retaining ring, this can lead to a weight reduction of the shaft earthing, which is particularly advantageous in applications where weight is a factor.

[0032] The retaining ring can preferably have an L-shaped contour in cross-section, wherein the axially extending leg of the retaining ring can then be coupled to a connecting structure, for example in an electrical machine or in an axle drive train, and the radially extending leg of the retaining ring can then be coupled to the discharge element. The L-shaped contour can contribute to the efficient use of the available installation space for shaft grounding. The combination of the axial and radial legs also creates a stable structure that can effectively absorb the loads and forces acting on the retaining ring. This is particularly important in applications where vibrations, shock loads, or other mechanical stresses may occur.By connecting the axial leg to the connecting structure and the radial leg to the discharge element, particularly reliable earthing and discharge of electrical currents is achieved by providing correspondingly large contact surfaces.

[0033] The object of the invention can further be achieved by an electric machine, in particular for a drive train of an electrically operated motor vehicle, comprising a stator and a rotor which is rotatably mounted relative to the stator and has a rotor shaft, wherein the electric machine has a shaft earthing according to one of the preceding claims 1-8, the retaining ring of which is connected in a rotationally fixed manner to a connection structure of the electric machine and the contacting tabs of which rest on the outer circumferential surface of the rotor shaft.

[0034] Finally, the object of the invention can also be achieved by an electrically operable axle drive train comprising an electric machine comprising a stator and a rotor rotatably mounted relative to the stator with a rotor shaft, as well as a gear arrangement coupled to the rotor of the electric machine in a torque-transmitting manner, wherein a shaft earthing according to one of the preceding claims 1-8 is arranged on a shaft lying in the torque flow of the axle drive train.

[0035] The invention will be explained in more detail below with reference to figures without limiting the general inventive concept.

[0036] It shows: Fig. 1 a shaft earthing in a perspective view, Fig. 2 a shaft earthing in a perspective axial section view, Fig. 3 an electrically operated axle drive train in a schematic block diagram.

[0037] The Fig. 1-2 show a shaft earthing 1 for discharging an electrical charge and / or voltage from a shaft 4, in particular for a drive train of an electrically operated motor vehicle 3, as is also shown in the Fig. 3 is outlined.

[0038] The shaft earthing comprises a retaining ring 5 that can be positioned coaxially to the shaft 4 and a discharge element 7 that is fixed to the retaining ring 5 and that makes electrically conductive contact with an outer surface 8 of the shaft 4.

[0039] The discharge element 7 is designed in the shape of an annular disk and arranged coaxially with the shaft 4 on the retaining ring 5. A plurality of contact tabs 9 extend from the discharge element 7 in the radial direction toward the shaft 4 such that, when the shaft grounding 1 is mounted, they rest resiliently against the shaft 4 in the radial direction.

[0040] The retaining ring 5 has a plurality of retaining tabs 10 that extend axially out of the retaining ring 5 and clamp the annular disc-shaped discharge element 7 to the retaining ring 5. The discharge element 7 is centered on the retaining ring 5 via the retaining tabs 10 and clamped in place by folding the retaining tabs 10. During assembly, the retaining tabs 10 can initially extend axially out of the retaining ring and are then pivoted radially inward after the discharge element 7 has been inserted in order to center and clamp the discharge element 7 relative to the retaining ring 5. In the exemplary embodiment shown, the retaining tabs 10 are essentially identical, and their pivot points with the retaining ring 5 lie on a common pitch circle, which can facilitate the centering of the discharge element 7.The clamping force of the retaining tabs 10 is adjusted in such a way that a rotation of the discharge element 7 against the retaining ring 5 is prevented by the driving torque on the respective retaining tabs 10 that occurs during operation of the shaft earthing 1.

[0041] The retaining ring 5 has a contour which is L-shaped in cross section, wherein the leg of the retaining ring 5 extending in the axial direction can then be coupled to a connecting structure, for example in an electrical machine 30 or in an axle drive train 40, and the leg of the retaining ring 5 extending in the radial direction can be coupled to the discharge element 7.

[0042] To ensure that the grazing marks of the contacting tabs 9 do not overlap on the outer surface 8 of the shaft 4, the contacting tabs 9 have a different longitudinal extent, so that the contact points of the contacting tabs 9 are arranged axially offset from one another on the outer surface 8 of the shaft 4. The enveloping circle of the respective contacting tabs 9 is less than the outer diameter of the shaft 4, so that when the shaft earthing 1 is placed on or the shaft 4 is pushed into the shaft earthing 1, the contacting tabs 9 are pivoted out in the axial direction from the diverting element 7 and then exert a radial force that acts against the outer surface 8 of the shaft 4. This radial spring force ensures permanent mechanical and electrical contact between the guide element 7 and the shaft 4, and thus ensures current conduction both when the shaft 4 is at a standstill and when the shaft 4 is rotating.

[0043] In the assembled state of the shaft earthing system 1, the contacting tabs 9 are arranged axially offset relative to the discharge element 7 at their free end 11 contacting the lateral surface 8. In the illustrated embodiment, a contacting tab 9 is positioned in the circumferential direction of the discharge element 7 between two retaining tabs 10, wherein the retaining tabs 10 are in turn arranged equidistantly over the circumference of the retaining ring 5.

[0044] The retaining ring 5 and the discharge element 7 are each made from a sheet metal by means of a forming process.

[0045] Fig. 3 shows an electric machine 30 in a drive train of an electrically operated motor vehicle 3, comprising a stator 31 and a rotor 32 rotatably mounted relative to the stator 31 and having a rotor shaft 33, wherein the electric machine 30 has a shaft earthing 1, the retaining ring 5 of which is connected in a rotationally fixed manner to the rotor shaft 33 and the sleeve 8 of which is connected to a connecting structure 34 of the electric machine 30.

[0046] Finally, the Fig.3 also shows an electrically operable axle drive train 40 comprising the electric machine 3 with a stator 31 and a rotor 32 rotatably mounted relative to the stator 31, having a rotor shaft 33, as well as a gear arrangement 41 coupled to the rotor 32 of the electric machine 3 in a torque-transmitting manner, wherein a shaft ground 1 is arranged on a shaft 42 located in the torque flow of the axle drive train 40. In the example shown, the gear arrangement 41 is designed as a planetary gear.

[0047] The invention is not limited to the embodiments illustrated in the figures. The above description is therefore not to be considered restrictive, but rather explanatory. The following claims are to be understood in such a way that a stated feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. Where the claims and the above description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing a priority. List of reference symbols 1 shaft grounding 3 Motor vehicle 4th wave 5 retaining ring 7 Discharge element 8 Shell surface 9 contact tabs 10 retaining tabs 11 End 30 electric machine 31 Stator 32 rotors 33 Rotor shaft 34 Connection structure 40 axle drive train 41 Gear arrangement 42 Wave QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2020 119 719 A1

[0003] DE 10 2017 109 049 A1

[0006] EP 1 455 434 A1

[0007] DE 20 2017 107 755 U1

[0008] DE 10 2017 122 466 A1

[0009]

Claims

[1] Shaft earthing (1) for discharging an electrical charge and / or voltage from a shaft (4), in particular for a drive train of an electrically operated motor vehicle (3), comprising a retaining ring (5) which can be positioned coaxially to the shaft (4) and a discharge element (7) which is fixed to the retaining ring (5) and which can be electrically conductively contacted with an outer surface (8) of the shaft (4), characterized by that the discharge element (7) is designed in the shape of an annular disk and is arranged coaxially to the shaft (4) on the retaining ring (5), wherein a plurality of contacting tabs (9) extend from the discharge element (7) in the radial direction towards the shaft (4) in such a way that, in the assembled state of the shaft earthing (1), they rest resiliently against the shaft (4) in the radial direction. [2] Shaft earthing (1) according to claim 1, characterized bythat the retaining ring (5) has a plurality of retaining tabs (10) which extend in the axial direction from the retaining ring (5) and which clamp the annular disc-shaped discharge element (7) to the retaining ring (5). [3] Shaft earthing according to claim 1 or 2, characterized by that at least two of the contacting tabs (9), preferably all of the contacting tabs (9), have a different longitudinal extent from one another, so that the contact points of the contacting tabs (9) on the lateral surface (8) of the shaft (4) are arranged axially offset from one another. [4] Shaft earthing (1) according to one of the preceding claims, characterized by that the contacting tabs (9) in the assembled state of the shaft earthing (1) are arranged axially offset with respect to the discharge element (7) at their free end (11) contacting the lateral surface (8). [5] Shaft earthing (1) according to one of the preceding claims, characterized bythat a contacting tab (9) is positioned in the circumferential direction of the discharge element (7) between two holding tabs (10). [6] Shaft earthing (1) according to one of the preceding claims, characterized by that the retaining tabs (10) are arranged equidistantly over the circumference of the retaining ring (5). [7] Shaft earthing (1) according to one of the preceding claims, characterized by that the retaining ring (5) is made from a sheet metal by means of a forming process. [8] Shaft earthing (1) according to one of the preceding claims, characterized by that the discharge element (7) is made from a sheet metal by means of a forming process. [9] Electrical machine (30), in particular for a drive train of an electrically operated motor vehicle (3), comprising a stator (31) and a rotor (32) which is rotatably mounted relative to the stator (31) and has a rotor shaft (33), wherein the electrical machine (30) has a shaft earthing (1) according to one of the preceding claims 1-8, the retaining ring (5) of which is connected in a rotationally fixed manner to a connecting structure (34) of the electrical machine (30) and the contacting tabs (9) of which bear against the outer circumferential surface (8) of the rotor shaft (33). [10] Electrically operable axle drive train (40) comprising an electric machine (3) comprising a stator (31) and a rotor (32) rotatably mounted relative to the stator (31) and having a rotor shaft (33), as well as a gear arrangement (41) coupled to the rotor (32) of the electric machine (3) in a torque-transmitting manner, wherein a shaft earthing (1) according to one of the preceding claims 1-8 is arranged on a shaft (42) lying in the torque flow of the axle drive train (40).

Images