Shaft grounding, electric machine and kit-of-parts

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 (2) of an electrically powered motor vehicle (3), comprising a rotatably mounted shaft (4) into which a cavity (7) extends axially from an end face (6) having a shaft opening (5), and a first, rotationally fixed and electrically conductive sleeve (8) extends through the shaft opening (5) and axially into the cavity (7) of the shaft (4), wherein an electrically conductive retaining element (9) is rotationally fixed to the shaft (4) in the cavity (7), from which an electrically conductive centering means (10) extends coaxially into the sleeve (8) in the axial direction or surrounds the sleeve (8) from the outside, and an electrically conductive bearing is located in the axial overlap area (11) of the centering means (10) and the sleeve (8). (12) is ordered,so that in the operation of the shaft grounding (1) an electrical contact is established between the sleeve (8) and the centering means (10) and wherein the retaining element (9) and the centering means (10) are formed in one piece.

Description

The present invention relates to a shaft ground for discharging an electrical charge and / or voltage from a shaft, in particular for a drive train of an electrically operable motor vehicle, comprising a rotatably mounted shaft, into which a cavity extends axially into the shaft proceeding from an end face having a shaft opening, and a first sleeve, which is rotationally fixed and electrically conductive with respect to the shaft, extends through the shaft opening and extends axially into the cavity of the shaft. The invention further relates to an electric machine and a kit-of-parts.Electric machines, in particular electric traction machines, are electrically charged during operation by induced wave voltages. In addition, circulating high-frequency currents can arise in motors of high power classes. Such electric machines generally have a rotor and a rotor shaft, which are mounted in a housing via rolling bearings. Owing to electrical discharges or the circulating high-frequency currents, damage to the rolling bearings can occur. In order to avoid this, dissipation of this electrical energy is necessary. For this purpose, for example, grounding brushes or radially acting grinding elements (carbon brushes) are known, which serve for grounding the rotor shaft. Furthermore, axially acting systems for shaft grounding are known.The publication 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, having a first contact module for electrical and mechanical connection to the shaft, having a second contact module for electrical and mechanical connection to the housing, wherein the first and the second contact modules are rotatable relative to one another and are electrically connected to one another in an interior space sealed with respect to 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.For the bearings of an electric motor, in addition to the mechanical wear due to shaft rotation, electric currents flowing from the rotor shaft to ground via the bearings are therefore a further cause of wear. Stresses of some magnitude can overcome the isolation properties of bearing lubrication, creating sparks which can lead to pitting, corrugated surface, fusion craters and eventually to premature failure of the bearings and motor. A bearing voltage, i.e. the voltage between the two bearing shells, usually correlates with a shaft voltage, i.e. the voltage between the shaft and ground.Due to capacitive coupling between the stator winding and the rotor and the high-frequency actuation of the stator phases, a voltage potential is formed on the rotor bearings, which voltage potential can damage the bearings by means of so-called discharge currents via the bearings. As countermeasures, for example, the bearings are insulated (for example by means of ceramic balls) or the shaft is grounded by means of a sliding ground contact (electrically parallel to the bearings).DE 10 2021 213 384 A1 discloses an arrangement for grounding a shaft, in particular a rotor shaft of an electric machine, comprising an at least sectionally tubular grounding hub which is electrically conductively connected to an electrical ground, preferably a housing. The ground hub is also electrically conductively connected to the shaft to be grounded via a sliding contact which is formed on a contact element, wherein the contact element is guided in a holder which is fastened on the end face of the ground hub to the ground hub.DE 10 2019 133 889 A1 discloses an electric machine having a discharge device for discharging an electrical charge and / or voltage from the rotor via the shaft to the housing section, wherein the discharge device has a first contact device for electrical and mechanical connection to the shaft and a second contact device for electrical and mechanical connection to the housing section, wherein the first and the second contact device are rotatable relative to one another.Furthermore, DE 10 2017 109 049 A1 already discloses a device and a method for compensating a wave voltage on a wave. In this case, by means of a compensation circuit for generating a compensation voltage, the compensation voltage is coupled directly or indirectly to the rotor shaft via a coupling element. A detection of the shaft voltage takes place directly or indirectly on the rotor shaft via a tapping element.EP 1 455 434 A1 discloses an electric motor having a stator and a rotor which is rotatably mounted in or on the stator by means of a bearing arrangement. For electrical insulation, at least one sleeve and / or plastic layer electrically insulating the bearing arrangement with respect to the stator or rotor and / or the rotor shaft with respect to the rotor is provided. As a result, capacitive displacement currents through the bearings are prevented, which primarily arise at high pulse or switching frequencies. These can lead to a reduction in the service life of the bearingsDE 20 2017 107 755 U1 describes a device for reducing harmful bearing voltages in an electric machine fed by an intermediate circuit voltage of an intermediate circuit, comprising a stator having windings and insulated from earth and a rotor and a motor shaft, wherein furthermore a rotor-side bearing and a stator-side bearing are each designed insulated from earth and wherein the rotor and the stator are electrically connected to one another via a bypass capacitance with a predetermined capacitance.DE 10 2017 122 466 A1 relates to a drive device which has a rotatable rotary shaft, a rotor which is connected to the rotary shaft in a rotationally fixed manner, and at least one balancing disk. In order to make it possible to produce the drive device without external alignment devices, it is proposed that the balancing disk has direct contact with the rotary shaft and is connected thereto in a rotationally fixed manner, wherein the balancing disk and the rotor lie next to one another with at least one partial region in a fixing plane orthogonal to the rotary shaft.In the field of electric mobility, such electric machines are also frequently integrated into an axle drive train, which forms a structural unit consisting of power electronics (inverter), electric machine and transmission. This structural unit must be connected to the vehicle ground for potential compensation. This is generally effected via a conductor which is located between the body and the housing of the structural unit.In such final drive trains, usually also a grounding element is located in the gear set of the transmission and / or directly on the rotor shaft of the electric machine, in order to be able to secure the bearings located there particularly well against harmful currents or discharges with the structural proximity. These grounding elements are usually electrically conductively connected to the housing of the axle drive train.In principle, such grounding elements have the problem that dry running grounding elements generate electrically conductive abrasion, which can thus lead to short circuits in the electric machine. Wet running grounding elements, on the other hand, often have the problem that they do not function efficiently under oil at all operating points.It is therefore the object of the invention to reduce or completely avoid the disadvantages known from the prior art and to provide a shaft grounding which is of simple construction and has a high operational reliability and also durability. It is also the object of the invention to realize an improved electric machine and an improved electrically operable axle drive train.This object is achieved by a shaft grounding for discharging an electrical charge and / or voltage from a shaft, in particular for a drive train of an electrically operable motor vehicle, comprising a rotatably mounted shaft, into which a cavity extends axially into the shaft starting from an end face having a shaft opening, and a first sleeve, which is rotationally fixed and electrically conductive with respect to the shaft, extends through the shaft opening and extends axially into the cavity of the shaft, wherein an electrically conductive retaining element is connected in the cavity in a rotationally fixed manner to the shaft, from which a electrically conductive centering means extends coaxially into the sleeve in the axial direction or engages around the sleeve from the radially outside, and an electrically conductive mounting is arranged in the axial overlap region of the centering means and sleeve, so that during operation of the wave grounding an electrical contact is established between the sleeve and the centering means.This achieves the advantage that the voltage (or voltage potential) present via the bearing is reduced, so that the probability of spark discharges is reduced and the energy / power of the discharges still occurring is limited, with the result that the bearing damage due to electrical discharges is reduced.As a result, a radially acting system for shaft grounding can be provided, which functions efficiently in dry and wet electric machines and at all operating points. In this case, an existing installation space, for example in an electric machine or a transmission arrangement, can be used without enlarging the electric machine axially or radially. The wave grounding can also be integrated later in existing applications in a simple manner. In this way, on the one hand, bearing damage to the rotatably mounted shaft can be prevented and, on the other hand, electromagnetic compatibility (EMC) can be improved in order to reduce or prevent the interference with other devices.The holding element and the centering means are formed in one piece, in particular monolithically. The one-piece, preferably also monolithic, shaping of the holding element and of the centering means produces a strong and stable structure. There are thus no joints or weak joints that could represent potential weak spots. This ensures high strength and stability of the holding element and of the centering means, even under load or under vibrations. The integral monolithic formation thus reduces the risk of component failure or loosening due to vibrations, fatigue or mechanical loads. The one-piece embodiment also enables a precise alignment of the holding element and the centering means. By being manufactured as a continuous piece, the components can be accurately positioned and aligned. The one-piece embodiment of course also facilitates the mounting of the holding element and the centering means, since they do not have to be mounted separately or connected to one another.A further advantage of the wave grounding according to the invention is that the wave grounding can be constructed as an independent system and thus be offered as a prefabricated unit.By means of the bearing, the first sleeve, which is designed, for example, as an oil lance, can be supported and guided in the cavity of the shaft and at the same time the streams can be safely discharged. As a result, the first sleeve can also be supported in the shaft by the centering means and the holding element.The bearing can be designed as a slide bearing or roller bearing. In connection with the invention, the configuration of the bearing as a plain bearing is preferred.The fact that the first electrically conductive sleeve is arranged rotationally fixed with respect to the shaft means that the sleeve is fixedly positioned in the circumferential direction, while the shaft is rotatable relative to the rotationally fixed sleeve.First, the individual elements of the claimed subject matter of the invention are explained in the sequence of their relevance or their denomination in the set of claims and particularly preferred embodiments of the subject matter of the invention are described below.A rotor is the rotating (rotating) part of an electric machine. The rotor comprises in particular a rotor shaft. The rotor shaft can be designed to be hollow in sections or completely, which on the one hand results in a saving in weight and which on the other hand allows the supply of lubricant or coolant to the rotor body.A rotor body is accordingly understood in the sense of the invention to mean the rotor without a rotor shaft.A rotor laminated core can in particular form a rotor body. A laminated rotor core is understood to mean a plurality of laminated individual laminations or rotor laminations which are generally produced from electric sheet and are laminated and laminated one above the other to form a stack, the so-called laminated rotor core. The individual sheets can then be joined together in the laminated core by adhesion, welding or screwing. A laminated rotor core can in particular also have magnetic elements introduced into the pockets of the laminated rotor core or fixed circumferentially on the laminated rotor core and axial cover parts, if present, for closing the pockets and the like.The electric machine can be designed in particular as a rotary machine. The rotary machine can be configured in particular as a radial flow machine. A radial flux machine is characterized in that the magnetic field lines extend in the radial direction in the air gap formed between the rotor and the stator. The air gap is the gap existing between the rotor and the stator. In a radial flux machine, this is a gap having an annular cross section and a radial width corresponding to the distance between the rotor body and the stator body.The electric machine is provided in particular for use within a drive train of a hybrid or fully electrically driven motor vehicle. In particular, the electric machine is dimensioned such that vehicle speeds greater than 50 km / h, preferably greater than 80 km / h and in particular greater than 100 km / h can be achieved. Particularly preferably, the electric motor has a power greater than 50 kW, preferably greater than 80 kW and in particular greater than 150 kW. It is furthermore preferred that the electric machine provides rotational speeds greater than 8,000 U / min, particularly preferably greater than 12,000 U / min, very particularly preferably greater than 15,000 U / min.Motor vehicles in the sense of this application are land vehicles which are moved by machine power without being bound to railway tracks. A motor vehicle can be selected, for example, from the group of passenger cars (passenger cars), trucks (trucks), small-size trucks, light-weight trucks, bicycles, buses (COM) or tractorsAccording to an advantageous embodiment of the invention, it can be provided that the first sleeve has at least one passage opening on a lateral surface, via which a fluid can be guided from the sleeve into the cavity. The advantage of this embodiment is that the sleeve can thus provide cooling and / or lubrication of the shaft or of components in the vicinity of the shaft. The first sleeve can therefore also be referred to as an oil lance.Preferably, the holding element also has passage openings through which the fluid can flow, for example, in the axial direction.A further advantage of the wave grounding is thus that it can be used in wet electric machines without additional installation space having to be provided. The small dimensions of the second sleeve that can be realized also do not, for example, prevent the supply of oil to the rotor.The holding element is preferably of ring-like configuration. The holding element is preferably designed as a ring closed in the circumferential direction, wherein the holding element is designed as a single piece. Preferably, the holding element is formed from a sheet metal.According to a further preferred development of the invention, it can also be provided that the shaft, starting from the cavity, has at least one through-channel which extends through the shaft in the radial direction and via which the fluid can be led out of the cavity, as a result of which a hydraulic connection for cooling the rotor and / or stator of an electric machine can be provided.Furthermore, according to a likewise advantageous embodiment of the invention, it can be provided that the retaining element is fixed in the cavity of the shaft by means of a press fit. The advantageous effect of this embodiment is due to the fact that the press fit ensures a firm and stable connection between the retaining element and the shaft. When using a press fit, it is usually not necessary to use additional fastening elements such as screws or bolts. This simplifies assembly and reduces the number of components required and assembly time.According to an advantageous embodiment of the invention, it can be provided that the bearing is designed as a sliding bearing. The advantage of this embodiment is that slide bearings provide a certain protection against dirt and contaminants, since the lubricating layer of the slide bearing can form a barrier between the slide surfaces and external influences such as dust, dirt or moisture. Due to the low friction and the effective damping of vibrations, sliding bearings are often also particularly low in noise and vibration. This is particularly advantageous in applications in which a smooth and quiet functioning is required, for example in electric motors.In a likewise preferred embodiment variant of the invention, it can also be provided that the bearing has a bearing sleeve, the outer lateral surface of which bears against the inner lateral surface of the sleeve and a sliding ring is arranged on the inner lateral surface of which sliding ring has an annular gap with the centring means, wherein the annular gap is filled by an electrically conductive fluid during operation of the shaft grounding. This can achieve the effect that an effective electrical grounding can be achieved by the presence of the electrically conductive fluid in the annular gap between the slide ring and the centering means. In this case, the conductive fluid then forms an electrical path between the centering means and the bearing sleeve, as a result of which electrical charges or faults can be discharged and safely discharged.It may also be advantageous to further develop the invention to the effect that the annular gap has a gap height of 40-80 μm. The annular gap with a gap height of 40-80 μm enables optimum lubrication between the sliding surfaces while at the same time providing a low electrical resistance through the annular gap. The annular gap also makes it possible to compensate for thermal expansions of the surrounding components. This is especially important in variable temperature applications to ensure the integrity and reliability of the storage as well as grounding.Furthermore, according to a likewise advantageous embodiment of the invention, it can be provided that the centering means has over its axial extent a first cylinder ring section with a substantially constant first diameter, which extends coaxially into the sleeve and has a second ring section with a second diameter, wherein the second diameter is larger than the first diameter, so that an axial stop for the sleeve is formed between the centering means and the holding element. By means of the first cylinder ring section with a constant diameter, a precise centering of the sleeve is achieved, wherein they move axially along the centering means and can be guided securely centered by the first ring section, so that the shaft grounding makes possible an axial tolerance compensation. The second ring section with a larger diameter forms an axial stop for the sleeve, so that the sleeve is not axially displaceable beyond the region of the second ring section. This allows only limited axial movement of the sleeve in one direction, which increases assembly reliability. The combination of a first cylinder ring section and a second ring section with different diameters moreover offers an increased stability and rigidity of the structure, whereby the resistance to mechanical loads, vibrations or other external influences can be improved.According to a further particularly preferred embodiment of the invention, it can be provided that a third ring section with a third diameter is formed on the holding element, wherein the third diameter is greater than the second diameter of the second ring section and / or is greater than the first diameter of the first cylinder ring section of the centering means. The stability of the holding element is further improved by the third ring section with a larger diameter, since the larger diameter can increase the contact surface with the shaft, which can contribute to an improved mechanical connection and rigidity of the holding element. Furthermore, the enlarged contact surface of the holding element can also have a positive effect on its electrical conductivity.Furthermore, the invention can also be further developed to the effect that the second ring section has a second diameter which is constant over its axial extent and / or the third ring section has a third diameter which is constant over its axial extent, and / or the second ring section has a second diameter which increases over its axial extent and / or the third ring section has a third diameter which increases over its axial extent.The constant diameters of the second and third ring sections enable simple and efficient production of the retaining element. The use of a constant diameter eliminates the need for complex shaping or variations along the axial extent. This facilitates the production of the holding element and can lead to cost savings. Furthermore, the constant diameters enable a comparatively simple and reliable formation of press fits for connecting the corresponding sections to the sleeve or the shaft.The use of increasing diameters allows the retainer to achieve a more accurate fit. As the diameters increase along the axial extent, the retainer can more closely abut the adjacent components and provide an improved fit. By means of an increasing diameter, a more precise alignment and centering of the holding element can thus be made possible. An increasing diameter may also contribute to a greater contact area between the retaining element and other components or surfaces and thus improve the electrical conductivity.In a likewise preferred embodiment variant of the invention, it can also be provided that the second ring section and / or the third ring section bears with its outer lateral surface against an inner lateral surface of the cavity and / or the second ring section and / or the third ring section bears with its inner lateral surface against an outer lateral surface of a bearing bolt extending axially from the shaft into the cavity.The bearing bolt can preferably be formed monolithically with the shaft and coaxially with the sleeve.It can also be advantageous to further develop the invention to the effect that spring tabs are formed on the second ring section and / or third ring section distributed over its circumference, which spring tabs provide a spring force in the radial direction, so that the holding element bears, under spring force loading, against the inner lateral surface of the cavity and / or, under spring force loading, against the outer lateral surface of the bearing bolt and / or, on the second ring section and / or third ring section, form-fitting means are formed distributed over its circumference, which form-fitting means protrude in the radial direction from the second ring section and / or third ring section, so that the holding element bears, under form-fitting, against the inner lateral surface of the cavity and / or, under form-fitting, against the outer lateral surface of the bearing boltBy using spring tabs which enable a spring-loaded contact on the inner lateral surface of the cavity and / or on the outer lateral surface of the bearing bolt, the holding element can be fastened securely and stably. The spring force ensures a constant contact pressure which holds the holding element firmly on the corresponding surfaces. The spring tabs also offer the possibility of compensating tolerances in the dimensions or positions of the components involved and of ensuring uniform contact of the retaining element. This is particularly advantageous if minor deviations or assembly inaccuracies can occur, since the spring tabs can compensate tolerances to a certain extent in the radial direction. Furthermore, vibrations and shocks can be absorbed and damped by the elastic deformation of the spring tabs, which can contribute to reducing vibrations, noises and mechanical loads. Finally, the use of spring tabs can also promote simple assembly of the holding element, since the holding element can be fastened to the shaft without special tools or additional fastening elements.The object of the invention is furthermore achieved by an electric machine, in particular for a drive train of an electrically operable motor vehicle, comprising a stator and a rotor rotatable relative to the stator, wherein the rotor is coupled in a torque-transmitting manner to a shaft having a shaft grounding, wherein the shaft grounding is formed according to one of claims 1-8.Finally, the object of the invention can also be achieved by a kit-of-parts for producing a wave grounding, in particular for a wave grounding of an electric machine• A shaft into which, starting from an end face having a shaft opening, a cavity extends axially into the shaft,• a first electrically conductive sleeve which can be inserted into the cavity,• an electrically conductive holding element, which can be inserted into the cavity and coupled to the shaft in a rotationally fixed manner, and from which an electrically conductive centering means extends coaxially into the sleeve or engages around the sleeve from the radially outer side, in the axial direction, and• an electrically conductive bearing which can be positioned in the axial overlap region of the centering means and sleeve, so that electrical contact is established between the sleeve and the centering means during operation of the shaft grounding.As a result, the components necessary for producing the wave ground can be made available in a particularly conventional manner. The kit-of-parts can be, for example, a packaging unit. It is also possible to configure the kit-of-parts as a collection of separate storage containers for storing the individual components or the respective component groups of the kit-of-parts.The invention will be explained in more detail below with reference to figures without limiting the general concept of the invention.It shows: FIG. 1 shows a first embodiment of a shaft grounding in an axial sectional view, FIG. 2 shows a second embodiment of a shaft grounding in an axial sectional view, FIG. 3 shows a third embodiment of a shaft grounding in an axial sectional view, FIG. 4 shows a fourth embodiment of a shaft grounding in an axial sectional view, FIG. 5 shows a detail illustration of the bearing in an axial sectional view, FIG. 6 shows a kit of parts for producing a wave ground in a schematic illustration, FIG. 7 shows a motor vehicle with an electric drive train in a schematic illustration.FIG. 1 shows a first embodiment of a shaft grounding 1 for the dissipation of an electrical charge and / or voltage from a shaft 4, in particular for a drive train 2 of an electrically operable motor vehicle 3, as is also outlined in FIG. 7.The shaft ground 1 comprises a rotatably mounted shaft 4, into which a cavity 7 extends axially into the shaft 4 starting from an end face 6 having a shaft opening 5, and a first sleeve 8, which is rotationally fixed and electrically conductive with respect to the shaft 4, extends through the shaft opening 5 and extends axially into the cavity 7 of the shaft 4. Thus, the shaft 4 rotates about the fixed sleeve 8.In the cavity 7, an electrically conductive holding element 9 is connected to the shaft 4 in a rotationally fixed manner, from which an electrically conductive centering means 10 is arranged coaxially in the sleeve 8 in the axial direction and an electrically conductive bearing 12 is arranged in the axial overlap region 11 of the centering means 10 and sleeve 8, so that an electrical contact is established between the sleeve 8 and the centering means 10 during operation of the shaft grounding 1. The bearing 12 is designed as a slide bearing.In the embodiments shown, the bearing 12 is designed as a plain bearing. The centering means 10 has an axial stop 34 against which the bearing 12 can abut axially. The bearing 12 has a sliding ring 18 with a flange 44 which has an annular gap 20 with the centering means 10 or the sleeve 8, wherein the annular gap 20 is filled by an electrically conductive fluid 19 during operation of the shaft ground 1. The annular gap 20 has a gap height 21 of 40-80 μm. This can be easily understood from the detailed illustration of FIG. 5. It can also be seen well that the slide bearing 12 is not encapsulated, so that, for example, the electrically conductive fluid 19 can pass into the annular gap 20 during operation of the shaft grounding 1, so that the slide bearing 12 represents an open system with respect to the fluid 19.The holding element 9 and the centering means 10 are formed monolithically with one another and are formed from a metal sheet by means of forming methods. The centering means 10 has over its axial extension a first cylinder ring portion 31 with a substantially constant first diameter 14, which extends coaxially into the sleeve 8. The centering means 10 also has a second ring section 32 with a second diameter 33, the second diameter 33 being greater than the first diameter 14, so that an axial stop 34 for the sleeve 8 is formed between the centering means 10 and the holding element 9.In the embodiment of FIG. 1, a third ring section 35 having a third diameter 36 is formed on the holding element 9, which third ring section is larger than the second diameter 33 of the second ring section 32 and larger than the first diameter 14 of the first cylinder ring section 31 of the centering means 10.The second ring section 32 has a constant second diameter 33 over its axial extension, and the third ring section 35 has a constant third diameter 36 over its axial extension. The third ring section 35 abuts with its outer lateral surface 37 against an inner lateral surface 38 of the cavity 7. In this case, a cylindrical opening, which is aligned coaxially with the sleeve 8, is formed in the shaft 4, the third ring section 35 of the holding element 9 being inserted into said opening axially. This also enables, among other things, a defined axial stop of the holding element 9 with respect to the shaft 4.The sleeve is designed as a fixed fluid-conducting oil lance, wherein the corresponding fluid can flow through the sleeve 8 and the centering means 10 or the holding element 9 and can pass via the openings 27 in the cavity 7 of the shaft 4.FIG. 2 shows a modification of the shaft grounding already known from FIG. 1, in which the second ring section 32 has been omitted.FIGS. 3-4 show embodiments of the shaft grounding 1 in which the second ring section 32 and / or the third ring section 35 each rest with its inner lateral surface 39 against an outer lateral surface 40 of a bearing bolt 41 extending axially from the shaft 4 into the cavity 7.In the embodiment of FIG. 3, both a second ring section 32 and a third ring section 35 are present. The second ring section 32 radially widens in the axial direction and then merges into the cylindrical third ring section 35 of the holding element 9, which then engages around the cylindrical bearing bolt 41 and secures the holding element 9 axially and radially there in a force-fit and / or form-fit manner.In the embodiment of FIG. 4, the second ring section 32 has been dispensed with and the third ring section 35 has a third diameter 36 which increases over its axial extent, with the result that the third ring section 35 bears against the conical bearing bolt 41.In the embodiments of FIGS. 1-4, spring tabs 42 are respectively formed on the second ring section 32 and / or third ring section 35 distributed over the circumference thereof, said spring tabs providing a spring force in the radial direction, such that the holding element 9 bears, under spring force loading, against the inner circumferential surface 38 of the cavity 7 and / or under spring force loading, against the outer circumferential surface 40 of the bearing bolt 41. positive locking means 43 are additionally formed on the second ring section 32 and / or third ring section 35 distributed over the circumference thereof, protruding, under radial direction, from the second ring section 32 and / or third ring section 35, such that the holding element 9 bears, under positive locking, against the inner circumferential surface 38 of the cavity 7 and / or, under positive locking, against the outer circumferential surface 40 of the bearing bolt 41.FIG. 7 shows a drive train 2 of an electrically operable motor vehicle 3 having an electric machine 23, comprising a stator 24 and a rotor 22 rotatable relative to the stator 24, wherein the rotor 22 is coupled in a torque-transmitting manner to a shaft 4 having a shaft ground 1, which is known from FIGS. 1-4.Finally, FIG. 6 shows a kit of parts 30 for producing a wave grounding 1, in particular for a wave grounding 1 of an electric machine 23• A shaft 4 into which, starting from an end face 6 having a shaft opening 5, a cavity 7 extends axially into the shaft 4,• A first electrically conductive sleeve 8 which can be inserted into the cavity 7,• an electrically conductive holding element 9, which can be inserted into the cavity 7 and coupled to the shaft 4 in a rotationally fixed manner, and from which an electrically conductive centering means 10 extends coaxially into the sleeve 8 in the axial direction or engages around the sleeve 8 from the radially outer side, and• an electrically conductive bearing 12, which can be positioned in the axial overlap region 11 of the centering means 10 and sleeve 8, so that electrical contact is established between the sleeve 8 and the centering means 10 during operation of the shaft grounding 1.The invention is not limited to the embodiments shown in the figures. The foregoing description is, therefore, not to be considered as limiting, but illustrative. The following claims should be understood to mean that a said feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. If the patent claims and the above description define "first" and "second" features, this designation serves to distinguish two features of the same type without specifying a ranking.List of reference characters1 Shaft grounding 2 Drive train 3 Motor vehicle 4 Shaft 5 Shaft opening 6 End side 7 Cavity 8 Sleeve 9 Holding element 10 Centering means 11 Overlap region 12 Bearing 14 First diameter 18 Sliding ring 19 Fluid 20 Annular gap 21 Gap height 22 Rotor 23 Electric machine 24 Stator 27 Openings 30 Kit-of-parts 31 Cylinder ring section (first ring section) 32 Second ring section 33 Second diameter 34 Stop 35 Third ring section 36 Third diameter 37 Outer jacket surface (of 35) 38 Inner jacket surface (of 7) 39 Inner jacket surface (of 35) 40 Outer jacket surface (of 41) 41 Bearing bolt 42 Spring tabs 43 Form-fitting means 44 Flange

Claims

A shaft grounding (1) for discharging an electric charge and / or voltage from a shaft (4), in particular for a drive train (2) of an electrically operable motor vehicle (3), comprising a rotatably mounted shaft (4) into which, starting from an end face (6) having a shaft opening (5), a cavity (7) extends axially into the shaft (4) and a first sleeve (8) which is rotationally fixed and electrically conductive relative to the shaft (4) extends through the shaft opening (5) and extends axially into the cavity (7) of the shaft (4), characterized in that in the cavity (7) an electrically conductive retaining element (9) is rotationally fixed to the shaft (4), The centering element (9) and the centering element (10) are formed in one piece from the outside of the sleeve, and an electrically conductive mounting (12) extends coaxially into the sleeve (8) in the axial direction from which an electrically conductive centering element (10) extends coaxially into the sleeve (8) in the axial overlap region (11) of the centering element (10) and the sleeve (8), so that electrical contacting is produced between the sleeve (8) and the centering element (10) during operation of the shaft grounding element (1).Shaft grounding (1) according to claim 1, characterised in that the bearing (12) is formed as a sliding bearing.The shaft grounding (1) according to any one of the preceding claims, characterized in that the centering means (10) has over its axial extension a first cylinder ring section (31) with a substantially constant first diameter (14), which extends coaxially into the sleeve (8) and has a second ring section (32) with a second diameter (33), wherein the second diameter (33) is larger than the first diameter (14), so that an axial stop (34) for the sleeve (8) is formed between the centering means (10) and the holding element (9).Shaft grounding (1) according to one of the preceding claims, characterized in that a third ring section (35) with a third diameter (36) is formed on the holding element (9), wherein the third diameter (36) is larger than the second diameter (33) of the second ring section (32) and / or larger than the first diameter (14) of the first cylinder ring section (31) of the centering means (10).Shaft grounding (1) according to one of the preceding claims, characterized in that the second ring section (32) has a second diameter (33) which is constant over its axial extension and / or the third ring section (35) has a third diameter (36) which is constant over its axial extension, or the second ring section (32) has a second diameter (33) which increases over its axial extension and / or the third ring section (35) has a third diameter (36) which increases over its axial extension.Shaft grounding (1) according to one of the preceding claims, characterized in that the second ring section (32) or the third ring section (35) bears with its outer lateral surface (37) against an inner lateral surface (38) of the cavity (7) or the second ring section (32) and / or the third ring section (35) bears with its inner lateral surface (39) against an outer lateral surface (40) of a bearing bolt (41) extending axially from the shaft (4) into the cavity (7).Shaft grounding (1) according to one of the preceding claims, characterized in that spring tabs (42) are formed on the second ring section (32) and / or third ring section (35) distributed over its circumference, which spring tabs provide a spring force in the radial direction, so that the holding element (9) bears under spring force load against the inner lateral surface (38) of the cavity (7) and / or positively engage means (43) are formed distributed over its circumference on the outer lateral surface (40) of the bearing bolt (41) or on the second ring section (32) and / or third ring section (35), which engage means protrude in the radial direction from the second ring section (32) and / or third ring section (35), so that the holding element (9) bears positively engage against the inner lateral surface (38) of the cavity (7) and / or positively engage against the outer lateral surface (40) of the bearing bolt (41).Electric machine (23), in particular for a drive train (2) of an electrically operable motor vehicle (3), comprising a stator (24) and a rotor (22) rotatable relative to the stator (24), wherein the rotor (22) is coupled to a shaft (4) having a shaft ground (1) in a torque-transmitting manner, characterized in that the shaft ground (1) is formed according to one of claims 1 - 7.Kit-of-parts (30) for producing a shaft grounding (1) according to Claim 1, in particular for a shaft grounding (1) of an electrical machine (23), comprising • a shaft (4) into which, starting from an end face (6) having a shaft opening (5), a cavity (7) extends axially into the shaft (4), • a first electrically conductive sleeve (8) which can be inserted into the cavity (7), • an electrically conductive retaining element (9) which can be inserted into the cavity (7) and can be coupled to the shaft (4) in a rotationally fixed manner, and from which an electrically conductive centring means (10) extends coaxially into the sleeve (8) in the axial direction or engages around the sleeve (8) from the radially outside, and • an electrically conductive mounting (12), which can be positioned in the axial overlap region (11) of the centering means (10) and the sleeve (8), so that during operation of the shaft grounding (1) an electrical contact is established between the sleeve (8) and the centering means (10).

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