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 operated 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), which is designed as a separate component, extends in the axial direction.extends coaxially into the sleeve (8) or surrounds the sleeve (8) radially from the outside and an electrically conductive bearing (12) is arranged in the axial overlap area (11) of 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).

Description

[0001] The present invention relates to a shaft grounding system for dissipating an electrical charge and / or voltage from a shaft, particularly for a drive train of an electrically powered motor vehicle, comprising a rotatably mounted shaft into which a cavity extends axially from an end face having a shaft opening, and a first sleeve, which is rotationally fixed relative to the shaft and is electrically conductive, extends through the shaft opening and axially into the cavity of the shaft. The invention further relates to an electric machine and a kit of parts.

[0002] Electric machines, especially electric traction machines, become electrically charged during operation due to induced shaft voltages. Additionally, circulating high-frequency currents can occur in high-power motors. Such electric machines typically have a rotor and a rotor shaft, which are supported in a housing by rolling bearings. Electrical discharges and / or the circulating high-frequency currents can damage the rolling bearings. To prevent this, it is necessary to dissipate this electrical energy. Grounding brushes or radially acting grinding elements (carbon brushes) are known for this purpose, serving to ground the rotor shaft. Furthermore, axially acting shaft grounding systems are also known.

[0003] Document DE 10 2020 119 719 A1, which represents the closest prior art, discloses a discharge device for a motor for discharging an electrical charge and / or voltage from a rotor via a shaft to a housing, comprising a first contact module for electrical and mechanical connection with the shaft, and a second contact module for electrical and mechanical connection with the housing, wherein the first and second contact modules are rotatable relative to each other and are electrically connected to each other in an interior sealed from a housing space, wherein the interior space is filled with an electrically conductive liquid, and wherein the first and second contact modules are electrically connected to each other via the electrically conductive liquid.

[0004] DE 10 2021 213 384 A1 discloses an arrangement for grounding a shaft, in particular a rotor shaft of an electric machine, comprising a grounding hub that is at least partially tubular and electrically connected to an electrical ground, preferably a housing. The grounding hub is also electrically connected to the shaft to be grounded via a sliding contact formed on a contact element, wherein the contact element is guided in a holder that is attached to the grounding hub at its end face.

[0005] DE 10 2019 133 889 A1 discloses an electric machine with a discharge device for discharging an electric 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 with the shaft and a second contact device for electrical and mechanical connection with the housing section, wherein the first and the second contact device are rotatable relative to each other.

[0006] The invention aims to create a shaft grounding system characterized by ease of assembly, improved conductivity, and wear-free operation. Furthermore, the invention aims to provide a correspondingly improved electrical machine. Finally, it also aims to provide a kit of parts that enables simplified and convenient assembly of the shaft grounding system.

[0007] This problem is solved by a shaft grounding system for dissipating an electrical charge and / or voltage from a shaft, in particular for a drive train of an electrically operated motor vehicle, comprising a rotatably mounted shaft, into which a cavity extends axially from an end face having a shaft opening, and a first, rotationally fixed and electrically conductive sleeve extends through the shaft opening and axially into the cavity of the shaft, wherein an electrically conductive retaining element is rotationally fixed to the shaft in the cavity, from which an electrically conductive centering means extends coaxially into the sleeve in the axial direction or surrounds the sleeve from the radial outside, and an electrically conductive bearing is arranged in the axial overlap area of ​​the centering means and the sleeve.so that during operation of the shaft grounding, an electrical contact is established between the sleeve and the centering device.

[0008] This enables the provision of a radially acting shaft grounding system that functions efficiently in both dry and wet electrical machines and at all operating points. It utilizes existing installation space without increasing the axial or radial dimensions of the electrical machine. Furthermore, the shaft grounding can be easily integrated into existing applications. This prevents bearing damage to the rotatably mounted shaft and improves electromagnetic compatibility (EMC) to reduce or prevent interference with other devices.

[0009] The centering element is designed as a separate component, which is received in a receptacle of the retaining element arranged coaxially with the sleeve. The advantage lies in the fact that the use of a separate centering element, which is received in a receptacle of the retaining element, enables a modular design of the shaft grounding system. The centering element can be manufactured and replaced independently of the retaining element, offering flexibility with regard to design changes, repairs, or maintenance. This also facilitates adaptation to different requirements or specific applications of the shaft grounding system.

[0010] By manufacturing the centering element separately, different materials or specific properties can be selected for the centering element. For example, the centering element can be made from a material with special properties such as high strength or wear resistance, while the retaining element is made of a different material.

[0011] Another advantage of the shaft grounding according to the invention is that the shaft grounding can be built as an independent system and thus offered as a pre-assembled unit.

[0012] The bearing allows the first sleeve, designed for example as an oil lance, to be supported and guided within the shaft cavity, while simultaneously ensuring the safe conduction of any currents. This also allows the first sleeve to be supported within the shaft by the centering device and the retaining element.

[0013] The bearing arrangement can be designed as a sliding bearing or a rolling bearing. In connection with the invention, the design of the bearing as a sliding bearing is preferred.

[0014] The fact that the first electrically conductive sleeve is arranged in a rotationally fixed manner relative to the shaft means that the sleeve is fixed in the circumferential direction, while the shaft is rotatable relative to the rotationally fixed sleeve.

[0015] First, the individual elements of the claimed subject matter of the invention are explained in the order of their relevance or their mention in the claim set, and subsequently, particularly preferred embodiments of the subject matter of the invention are described.

[0016] A rotor is the rotating part of an electric machine. The rotor includes, in particular, a rotor shaft. The rotor shaft can be partially or completely hollow, which reduces weight and allows lubricant or coolant to reach the rotor body.

[0017] For the purposes of the invention, a rotor body is therefore understood to be the rotor without a rotor shaft.

[0018] A rotor lamination stack can, in particular, form a rotor body. A rotor lamination stack is understood to be a plurality of laminated individual sheets, usually made of electrical steel, which are stacked and packaged on top of each other to form a stack, the so-called rotor lamination stack. The individual sheets can then be joined together in the stack by gluing, welding, or bolting. A rotor lamination stack can also include, in particular, magnetic elements inserted into the pockets of the rotor lamination stack or fixed around its circumference, as well as any axial cover parts for closing the pockets, and the like.

[0019] The electric machine can be designed, in particular, as a rotary machine. The rotary machine can be configured, in particular, as a radial flux machine. A radial flux machine is characterized by the fact that the magnetic field lines in the air gap formed between the rotor and the stator extend in a radial direction. The air gap is the gap existing between the rotor and the stator. In a radial flux machine, this is an annular gap with a radial width corresponding to the distance between the rotor body and the stator body.

[0020] The electric machine is intended for use within the powertrain of a hybrid or fully electric motor vehicle. In particular, the electric machine is dimensioned to enable vehicle speeds greater than 50 km / h, preferably greater than 80 km / h, and especially greater than 100 km / h. The electric motor preferably has a power output greater than 50 kW, preferably greater than 80 kW, and especially greater than 150 kW. It is further preferred that the electric machine provides rotational speeds greater than 8,000 rpm, particularly preferably greater than 12,000 rpm, and most preferably greater than 15,000 rpm.

[0021] For the purposes of this application, motor vehicles are defined as land vehicles that are moved by mechanical power and are not bound to railway tracks. A motor vehicle may be selected, for example, from the groups of passenger cars, trucks, mopeds, light vehicles, motorcycles, buses, or tractors.

[0022] According to an advantageous embodiment of the invention, the first sleeve can have at least one through-hole on a lateral surface through 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 components in the vicinity of the shaft. The first sleeve can therefore also be referred to as an oil lance.

[0023] Preferably, the retaining element also has openings through which the fluid can flow, for example, in an axial direction.

[0024] Another advantage of shaft grounding is that it can be used in wet electrical machines without requiring additional installation space. The small dimensions of the second sleeve also ensure that, for example, the rotor's oil supply is not obstructed.

[0025] The retaining element is preferably ring-shaped. Preferably, the retaining element is designed as a circumferentially closed ring. Preferably, the retaining element has a substantially C-shaped contour in cross-section, with a radially outer, axially extending section of the contour bearing against the inner surface of the shaft cavity. Preferably, the retaining element is formed from a sheet metal part.

[0026] According to a further preferred embodiment of the invention, it can also be provided that the shaft has at least one radially extending through the shaft, starting from the cavity, through which the fluid can be guided out of the cavity, thereby providing a hydraulic connection for cooling the rotor and / or stator of an electric machine.

[0027] Furthermore, according to another advantageous embodiment of the invention, the retaining element can be fixed in the shaft cavity by means of an interference fit. The advantage of this embodiment lies in the fact that the interference fit ensures a firm and stable connection between the retaining element and the shaft. When using an interference fit, it is generally not necessary to use additional fasteners such as screws or bolts. This simplifies assembly and reduces the number of components required and the assembly time.

[0028] According to an advantageous embodiment of the invention, the bearing can be designed as a sliding bearing. The advantage of this embodiment is that sliding bearings offer a certain degree of protection against dirt and contaminants, since the lubricating layer of the sliding bearing can form a barrier between the sliding surfaces and external influences such as dust, dirt, or moisture. Due to the low friction and effective damping of vibrations, sliding bearings are often also particularly quiet and vibration-free. This is especially advantageous in applications where quiet and low-noise operation is required, e.g., in electric motors.

[0029] According to a further particularly preferred embodiment of the invention, the sleeve may have a shoulder on its inner surface against which the bearing axially abuts. This makes it possible, in particular, to achieve precise axial positioning of the bearing by pressing and fixing the bearing against the shoulder, thus ensuring accurate alignment and positioning.

[0030] Furthermore, the invention can also be further developed such that the centering means has a substantially constant diameter over its axial extent. The advantage of this embodiment is that a particularly simple and cost-effective manufacturing of the centering means can be achieved.

[0031] In a further preferred embodiment of the invention, the bearing may also include a bearing sleeve whose outer surface rests against the inner surface of the sleeve, and on whose inner surface a sliding ring is arranged the sliding ring having an annular gap with the centering means. During shaft grounding operation, this annular gap is filled with an electrically conductive fluid. This ensures that effective electrical grounding is achieved through the presence of the electrically conductive fluid in the annular gap between the sliding ring and the centering means. The conductive fluid then forms an electrical path between the centering means and the bearing sleeve, thereby dissipating and reliably dissipating electrical charges or disturbances.

[0032] It can also be advantageous to further develop the invention such that the annular gap has a gap height of 40–80 µm. An annular gap with a gap height of 40–80 µm enables optimal lubrication between the sliding surfaces while simultaneously creating low electrical resistance. The annular gap also allows for the compensation of thermal expansion of the surrounding components. This is particularly important in applications with variable temperatures to ensure the integrity and reliability of the bearing and grounding.

[0033] The object of the invention is further solved by an electric machine, in particular for a drive train of an electrically operated motor vehicle, comprising a stator and a rotor rotatable relative to the stator, wherein the rotor is coupled to a shaft having a shaft grounding in a torque-transmitting manner, wherein the shaft grounding is designed according to one of claims 1-8.

[0034] Finally, the object of the invention can also be solved by a kit-of-parts for producing a shaft grounding, in particular for a shaft grounding of an electrical machine, comprising • A shaft into which a cavity extends axially into the shaft from an end face having a shaft opening, • A first electrically conductive sleeve that can be inserted into the cavity, • an electrically conductive retaining element that 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 in the axial direction or surrounds the sleeve from the radial outside and • an electrically conductive bearing that can be positioned in the axial overlap area of ​​the centering means and the sleeve, so that during shaft grounding operation an electrical contact is established between the sleeve and the centering means.

[0035] This allows the components necessary for manufacturing the shaft grounding system to be provided in a particularly convenient manner. The kit-of-parts can, for example, be a single packaging unit. Furthermore, it is possible to design the kit-of-parts as a collection of separate storage containers for the individual components or the respective component groups within the kit.

[0036] The invention will now be explained in more detail with reference to figures, without limiting the general concept of the invention.

[0037] It shows: Fig. 1 a wave grounding in an axial section view, Fig. 2. A detailed representation of the bearing in an axial section view. Fig. 3 a kit-of-parts for the production of a shaft grounding in a schematic representation, Fig. 4 A motor vehicle with an electric powertrain in a schematic representation.

[0038] The Fig. Figure 1 shows a shaft grounding system 1 for dissipating an electric charge and / or voltage from a shaft 4, in particular for a drive train 2 of an electrically powered motor vehicle 3, as is also the case in the Fig. 4 is shown.

[0039] The shaft grounding 1 comprises a rotatably mounted shaft 4, into which a cylindrical cavity 7 extends axially from an end face 6 having a shaft opening 5. A first, electrically conductive, annular, cylindrical sleeve 8, which is rotationally fixed relative to the shaft 4, passes through the shaft opening 5 and extends axially into the cavity 7 of the shaft 4. The sleeve 8 therefore does not rotate. The sleeve 8 can, in particular, be configured as an oil lance through which a fluid, for example, oil, is introduced into and / or discharged from the cavity 7. For this purpose, openings 27 are provided on the centering means 10, connecting the cavity 7 to the interior of the sleeve 8.

[0040] In the cavity 7, the electrically conductive retaining element 9 is rotationally fixed to the shaft 4, from which the electrically conductive centering means 10 extends coaxially into the sleeve 8. An electrically conductive bearing 12 is arranged in the axial overlap area 11 between the centering means 10 and the sleeve 8, so that during operation of the shaft grounding 1, electrical contact is established between the sleeve 8 and the centering means 10. Because the shaft grounding 1 is telescopically designed, any axial misalignment occurring during operation can be compensated for by the corresponding length provided in the first sleeve 8 or the centering means 10. The retaining element 9 and the centering means 10 have a cylindrical ring shape.

[0041] To ensure the current flow from the rotating shaft 4 via the first sleeve 8 to a stationary housing, the annular retaining element 9 is pressed into the cavity 7 of the shaft 4 using at least three retaining tabs. These three flexible retaining tabs compensate for vibrations and angular misalignment during operation. The transmission of rotation is achieved by means of a positive fit through three projections on the outer diameter of the retaining element 9 and three recesses in the shaft 4.

[0042] In the illustrated embodiment, the bearing 12 is designed as a sliding bearing. The sleeve 8 has a shoulder 13 on its inner surface 26 against which the bearing 12 axially abuts. The bearing 12 has a bearing sleeve 15, the outer surface 16 of which rests against the inner surface 26 of the sleeve 8, and a sliding ring 18 is arranged on the inner surface 17 of which a sliding ring 18 has an annular gap 20 with the centering means 10, wherein the annular gap 20 is filled with an electrically conductive fluid 19 during operation of the shaft grounding 1. The annular gap 20 has a gap height 21 of 40–80 µm. This can be clearly seen from the detailed illustration of the Fig. 4. It is also clearly evident that the sliding bearing 12 is not encapsulated, so that, for example, the electrically conductive fluid 19 can enter the annular gap 20 during operation of the shaft grounding 1, meaning that the sliding bearing 12 is an open system with respect to the fluid 19.

[0043] As in Fig. As shown in Figure 1, the centering means 10 of the shaft grounding 1 is designed as a separate component, which is received in a receptacle 25 of the retaining element 9 arranged coaxially to the sleeve 8 by means of an interference fit. The centering means 10 has a substantially constant diameter 14 over its axial extent. Fig. 1 The centering means 10 is designed as a cylindrical bolt. The bolt can also be formed from a bearing roller of a rolling bearing, in particular a needle roller.

[0044] A receptacle 25 of the retaining element 9, designed as a sleeve collar, is pressed onto the rotating centering means 10 during operation of the shaft grounding 1. Alternatively, the centering means 10 could be connected to the receptacle 25 by pinning, embossing, welding, or similar methods. The retaining element 9 can also be connected to the shaft 4 by means of a positive fit, for example, by axial and radial clips.

[0045] Fig. Figure 4 shows a drive train 2 of an electrically powered motor vehicle 3 with an electric machine 23, comprising a stator 24 and a rotor 22 rotatable relative to the stator 24, wherein the rotor 22 is torque-transmittingly coupled to a shaft 4 having a shaft ground 1, which consists of the Fig. 1 and Fig. 2 is known.

[0046] Finally, the Fig.3 a kit-of-parts 30 for the manufacture of a shaft grounding 1, in particular for a shaft grounding 1 of an electrical machine 23, comprising • A shaft 4 into which a cavity 7 extends axially into the shaft 4 from an end face 6 having a shaft opening 5, • A first electrically conductive sleeve 8, which can be inserted into the cavity 7, • an electrically conductive retaining element 9 that 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 an axial direction or surrounds the sleeve 8 from the radial outside and • an electrically conductive bearing 12 which can be positioned in the axial overlap area 11 of centering means 10 and 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.

[0047] The invention is not limited to the embodiment shown in the figures. The foregoing description is therefore not to be considered limiting, but rather explanatory. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not preclude the presence of further features. Insofar as the claims and the foregoing description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing any hierarchy. Reference symbol list 1 Wave grounding 2 Powertrain 3 Motor vehicle 4 wave 5 wave opening 6 Front 7 Cavity 8 Sleeve 9 retaining element 10 Centering devices 11 Overlap area 12 Storage Paragraph 13 14 diameter 15 Bearing sleeve 16 outer surface area (out of 15) 17 inner surface area (out of 15) 18 sliding ring 19 Fluid 20 annular gap 21 Gap height 22 Rotor 23 Electric Machine 24 Stator 25 recording 26 inner surface area (out of 8) 27 openings 30 Kit-of-parts

Claims

[1] Shaft earthing (1) for discharging an electrical 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 a cavity (7) extends axially from an end face (6) having a shaft opening (5) into the shaft (4), and a first sleeve (8) which is non-rotatable relative to the shaft (4) and electrically conductive passes through the shaft opening (5) and extends axially into the cavity (7) of the shaft (4), characterized byin that 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), which is designed as a separate component, extends coaxially into the sleeve (8) in the axial direction or surrounds the sleeve (8) from the radial outside and an electrically conductive bearing (12) is arranged in the axial overlap region (11) of the centering means (10) and the sleeve (8), so that during operation of the shaft earthing (1) an electrical contact is established between the sleeve (8) and the centering means (10). [2] Shaft earthing (1) according to claim 1, characterized by that the bearing (12) is designed as a plain bearing. [3] Shaft earthing (1) according to claim 1 or 2, characterized by that the centering means (10) is accommodated in a receptacle (25) of the holding element (9) arranged coaxially to the sleeve (8). [4] Shaft earthing (1) according to one of the preceding claims, characterized by that the sleeve (8) has a shoulder (13) on its inner circumferential surface (26) against which the bearing (12) abuts axially. [5] Shaft earthing (1) according to one of the preceding claims, characterized by that the centering means (10) has a substantially constant diameter (14) over its axial extent [6] Shaft earthing (1) according to one of the preceding claims, characterized by that the bearing (12) has a bearing sleeve (15), the outer surface (16) of which bears against the inner surface (26) of the sleeve (8) and on the inner surface (17) of which a sliding ring (18) is arranged, which has an annular gap (20) with the centering means (10), wherein the annular gap (20) is filled with an electrically conductive fluid (19) during operation of the shaft earthing (1). [7] Shaft earthing (1) according to claim 6, characterized by that the annular gap (20) has a gap height (21) of 40-80µm. [8] Electric machine (23), in particular for a drive train (2) of an electrically operated 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 earthing (1) in a torque-transmitting manner, characterized by that the shaft earthing (1) is designed according to one of claims 1-7. [9] Kit-of-parts (30) for producing a shaft earthing (1) according to claim 1, in particular for a shaft earthing (1) of an electrical machine (23), comprising • A shaft (4) into which a cavity (7) extends axially into the shaft (4) from an end face (6) having a shaft opening (5), • 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 can be 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 surrounds the sleeve (8) from the outside radially and • an electrically conductive bearing (12) which can be positioned in the axial overlap region (11) of the centering means (10) and the sleeve (8) so that an electrical contact is established between the sleeve (8) and the centering means (10) during operation of the shaft earthing (1).

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