ELECTRIC MACHINE WITH GROUNDED SHELL ARRANGEMENT

Description

[0001] The invention relates to an electrical machine comprising a stator, a rotor rotatable about a rotational axis and a bearing arrangement for supporting the rotor.

[0002] The electrical machine is in particular an electrical machine that can be operated with alternating current and preferably with three-phase alternating current, for example a synchronous machine or asynchronous machine.

[0003] In motor operation, the electric machine operates with an electromagnetic rotating field that is generated via a stator winding and serves to move the rotor. The rotor can, for example, carry permanent magnets. The electric machine is not operated directly via one or more phases of the power supply network, but rather a converter, such as a frequency converter, is connected between the power supply network and the electric machine. If the electric machine is connected to a converter that has a DC link, a time-varying common-mode voltage can arise between the stator winding and a reference potential (e.g. ground or earth). Due to this common-mode voltage, parasitic capacitances can become active in the electric machine, which can then be responsible for increased wear or damage.For example, due to parasitic capacitance and depending on the magnitude of the common mode voltage, breakdowns or arcs may occur in the area of ​​the bearing assembly, which may damage both the bearing and the lubricant present in the bearing or cause increased wear.

[0004] WO 2019 / 030181 A1 describes an electrical machine in which a shield arrangement is present between the stator winding and the outer bearing rings of the bearing assembly. The shield arrangement and the stator are each electrically connected to an electrical potential. For example, both the stator and the shield arrangement can be connected to a ground potential of the electrical circuit. Alternatively, it is also possible to ground the shield arrangement, while the stator is then connected to the ground potential. In another embodiment, the stator has no potential connection, while the shield arrangement is grounded via an impedance.

[0005] From K. Vostrov et al. "Shielding the end windings to reduce bearing currents", 2020 International Conference on Electrical Machines (ICEM), Gothenburg, 2020, pp. 1431-1437, doi: 10.1109 / ICEM49940.2020.9270673, it is known to use electrostatic shields to cover the end windings of the stator as a countermeasure against parasitic effects. The electrostatic shield can comprise one or more conductor loops that can be grounded. The conductor loops are arranged coaxially to the axis of rotation, adjacent to the air gap around the axial ends of the stator winding.

[0006] Furthermore, FJTE Ferreira et al., "Evaluation of Slot-Embedded Partial Electrostatic Shield for High-Frequency Bearing Current Mitigation in Inverter-Fed Induction Motors" in IEEE Transactions on Energy Conversion, vol. 27, no. 2, pp. 382-390, June 2012, doi: 10.1109 / TEC.2012.2187452, describes arranging a shield in the slotted stator windings that are connected to ground.

[0007] US 7,113,365 B1 describes a disk drive with an electric motor. The electric motor has an annular stator with a cylindrical central body. A hub is arranged on the cylindrical central body, which is arranged in an axial direction parallel to the axis of rotation next to a stator winding. The hub carries magnets arranged radially outward from the stator winding. The hub and the magnets thus form the rotor. In the axial direction, the stator winding and the rotor magnets are arranged outside the axial region defined by the two bearings.

[0008] An electric motor with a stator comprising a sleeve-shaped central body and a shaft rotatably mounted in the sleeve-shaped central body for arranging the rotor is described in US 2018 / 0298908 A1. The shaft protrudes from the central body and has a rotor support plate extending radially to the rotational axis. Permanent magnets of the rotor are arranged at the outer end of the support plate and coaxially surround the stator winding.

[0009] In both US 7 113 365 B1 and US 2018 / 0298908 A1, a shield extending substantially radially to the axis of rotation is arranged axially adjacent to the stator winding.

[0010] WO 2019 / 030181 A1 shows an electric motor with a shield that surrounds the axial end regions of a stator winding in a cap-like manner. The shield has two shield units, each of which is arranged at the level of a bearing of a bearing arrangement by means of which the rotor is rotatably mounted on a central body.

[0011] JP 2008-263698 A describes the possibility of electrically isolating the bearings of an electric motor from the stator.

[0012] However, it has been shown that the known principles are not applicable to all machine types and, depending on the machine type, do not provide sufficient protection for the bearing arrangement.

[0013] It can therefore be considered an object of the present invention to achieve an improvement in the protection of the bearing arrangement against common mode voltage effects in electrical machines.

[0014] This object is achieved by an electrical machine having the features of patent claim 1.

[0015] The electrical machine according to the present invention is, in particular, motor-operated and thus forms an electric motor. The electric motor is preferably operated with alternating current, in particular multiphase alternating current. The electrical machine can be an asynchronous machine or a synchronous machine. A converter, such as a frequency converter, which may have a DC link, can be used to control or operate the electrical machine or the electric motor.

[0016] The electric machine has a stator with a stator winding. Depending on the number of phases of the electric machine or electric motor, the stator winding can have several separate winding groups. An electromagnetic rotating field is generated around a rotational axis via the stator winding to drive a rotor rotating around the rotational axis. The rotor is mounted for rotation about the rotational axis by means of a bearing arrangement. The rotor is preferably arranged radially inward of the stator, so that the electric machine is designed as an external rotor machine.

[0017] The stator has a winding support made of electrically conductive material, on which the stator winding is arranged. The stator winding is electrically insulated from the winding support. The winding support is electrically grounded or the winding support is electrically connected to a reference potential. The winding support includes a central body. The central body defines the axis of rotation and extends along the axis of rotation. The central body can have a cylindrical outer surface and can be designed as a pin or sleeve.

[0018] The bearing assembly includes a first bearing and a second bearing. The first bearing and the second bearing are arranged on the central body and thus support the rotor on the central body. The first bearing and the second bearing are arranged at a distance from each other in an axial direction, parallel to the axis of rotation. The winding support of the stator is arranged axially between the first bearing and the second bearing. In the preferred embodiment, the bearings are rolling bearings, for example, ball bearings or roller bearings.

[0019] The electric machine also has a first shield unit and a second shield unit, which are electrically conductive. The shield units can be made of any electrically conductive material, for example, a metallic material or a metallic alloy or a composite material containing electrically conductive components.

[0020] The first shielding unit and the second shielding unit are grounded or connected to a reference potential, preferably by means of an impedance. The impedance can have an ohmic component and / or an inductive component and / or a capacitive component. The impedance can be formed by at least one component and / or by parasitic properties, for example, a contact or supply line. A potential of a DC link of the converter, for example, a ground potential, can be used as the reference potential.

[0021] The first shielding unit can be formed by an integral or monolithic first shielding element. Alternatively or additionally, the second shielding unit can be formed by an integral or monolithic second shielding element.

[0022] The first shield unit has an annular portion that extends in a circumferential direction around the rotation axis. The first annular portion extends from a radially inner end to a radially outer end obliquely and / or perpendicularly to the rotation axis. The radially inner end is arranged axially between the first bearing and the winding support and is mechanically connected to the central body. Preferably, this mechanical connection also establishes an electrical connection between the first shield unit and the central body.

[0023] The second shield unit also has a second ring portion extending circumferentially around the rotation axis. The second ring portion extends from a radially inner end outward to a radially outer end obliquely and / or perpendicular to the rotation axis. The radially inner end is arranged axially between the second bearing and the winding support and is mechanically connected to the central body. Preferably, this mechanical connection also establishes an electrical connection between the second shield unit and the central body.

[0024] This makes it possible to electrically connect the first shielding arrangement and / or the second shielding arrangement to the reference potential or earth via the central body.

[0025] The shield units are part of the stator and are not arranged to rotate relative to the central body.

[0026] The shielding units create a shielded space in which the stator winding and the winding support are located. The electrical connection of the shielding units to ground or a reference potential influences the parasitic capacitances between the bearings and the stator winding, as well as between the stator winding and the rotor. The capacitive coupling between the stator winding and the rotor is reduced and / or the capacitive coupling between the rotor and the stator is increased. Harmful electrical currents and / or voltages at the bearings of the bearing arrangement can be avoided or at least reduced. The risk of flashover at the bearings is significantly reduced.

[0027] According to the invention, the first ring part and / or the second ring part has openings arranged at a distance from one another in the circumferential direction, the respective edges of which have a first edge section arranged on an air guide part. The air guide part protrudes obliquely over the opening. A second edge section of the edge of the respective opening, opposite in the circumferential direction, is arranged offset in the axial direction from the first edge section. This can improve the transport of cooling air to the stator winding.

[0028] It is advantageous if the first shielding unit has an annular first circumferential part that extends in an axial direction parallel to the axis of rotation and in the circumferential direction around the axis of rotation. The first circumferential part can form a closed ring in the circumferential direction or, preferably, have openings arranged at a distance from one another in the circumferential direction. The circumferential part is preferably connected to the first ring part at the radially outer end of the first shielding unit.

[0029] Analogously, the second shielding unit can have an annular second circumferential part that extends in the axial direction and in the circumferential direction around the axis of rotation and can form a closed ring in the circumferential direction or, preferably, can have openings arranged at a distance from one another in the circumferential direction. Preferably, the second circumferential part is connected to the second ring part at the radially outer end of the second shielding unit.

[0030] The two circumferential parts can be arranged between the stator winding and the rotor. The two circumferential parts can be arranged on the same cylindrical surface around the axis of rotation and thus have the same distance from the axis of rotation.

[0031] The optional openings in the first circumferential part and / or the second circumferential part are provided in the circumferential direction at the locations where a high air flow is preferably to be generated, for example, in the radial direction approximately aligned with a groove of the winding support located between two immediately adjacent teeth. The two teeth, or at least a portion of at least one adjacent tooth, can be covered by a web of the respective circumferential part extending substantially in the axial direction.

[0032] The optional openings in the first peripheral part and / or the second peripheral part can be defined by an edge that does not extend within a single plane. For example, at least one portion of the edge can protrude from a plane in which the at least one other portion of the edge extends.

[0033] The first circumferential part and the first ring part can be formed integrally or monolithically. Alternatively or additionally, the second circumferential part and the second ring part can be formed integrally or monolithically. Optionally, it is possible for the two shield units and in particular the two circumferential parts to be connected to one another by axial webs extending in the axial direction. The axial webs can extend, for example, along the teeth of the winding support of the stator. The axial webs can also be present on each circumferential part without establishing a connection to the other circumferential part. In the circumferential direction, the axial webs of one circumferential part can be arranged offset from the axial webs of the other circumferential part. If the axial webs of the different circumferential parts are assigned to a common tooth, they can extend sectionally in the axial direction along the tooth.

[0034] It is advantageous if the two shield units are arranged in a space that is completely enclosed by the central body, the two bearings and the rotor.

[0035] The first circumferential part and the second circumferential part can be arranged at a distance from one another in the axial direction. Preferably, the two circumferential parts are mechanically connected to one another exclusively indirectly via the ring parts and the stator, for example, the central body of the stator. In the region of the air gap or in a region of the stator winding adjacent to the air gap, the two circumferential parts have no direct mechanical or electrical connection. In this embodiment, the shield arrangement has no component that extends in the axial direction from one circumferential part to the other circumferential part. This simplifies the structure of the shield arrangement. The two shield units can be handled and assembled independently of one another.

[0036] The first ring part and / or the second ring part each have a plurality of openings. The openings are arranged at a distance from one another in the circumferential direction in the respective ring part, preferably at regular intervals. The openings are, for example, delimited by a continuous edge of the ring part and are thus completely enclosed by the edge. Viewed radially to the axis of rotation, the openings are preferably arranged along the stator winding or in the region of the stator winding. Each opening can have a width that increases with increasing distance from the axis of rotation in the circumferential direction and, when viewed in the axial direction, can have a trapezoidal shape, for example. Two openings that are immediately adjacent in the circumferential direction are separated from one another by a web of the first ring part or the second ring part. The optionally present circumferential parts preferably also have openings.

[0037] The first ring part and / or the second ring part can each have an inner ring section and / or an outer ring section. The outer ring section can, for example, directly adjoin the optionally present first circumferential part or the optionally present second circumferential part. The outer ring section extends substantially parallel to a plane oriented perpendicular to the rotation axis. The inner ring section can, for example, extend at an angle other than 90° to the rotation axis.

[0038] The two shielding units or the two shielding elements are preferably not directly connected to one another mechanically and / or electrically, but are designed as separate shielding elements. The shielding elements or the shielding units are, for example, indirectly connected to one another mechanically and / or electrically, e.g., via the central body.

[0039] In a preferred embodiment, the first bearing and the second bearing are electrically insulated from the stator. The first bearing and the second bearing can be supported on the central body and each electrically insulated from the central body by means of an internal insulator.

[0040] Additionally or alternatively, it is possible to electrically insulate the first bearing and the second bearing from the rotor. For example, an external insulator can be arranged between the first bearing and the rotor, and between the second bearing and the rotor.

[0041] Advantageous embodiments of the invention will become apparent from the dependent claims, the description, and the drawings. Preferred embodiments of the invention are explained in detail below with reference to the accompanying drawings. In the drawings: Figure 1an embodiment of an electrical machine in a schematic, partially sectioned, basic representation, Figure 2 another embodiment of the electrical machine in a representation according to Figure 1 , Figure 3 an embodiment of the electrical machine with a structure according to Figure 1 or Figure 2 in a perspective sectional view in a sectional plane along a rotation axis, Figure 4 a partial representation of the embodiment according to Figure 3 in the area of ​​an air gap between a stator and a rotor, Figure 5 a partial representation of the embodiment according to Figure 3 in the region of a radially inner end of a first shield unit of the electrical machine, Figure 6 a partial representation of the embodiment according to Figure 3 in the area of ​​a second shielding unit of the electrical machine, Figure 7an electrical equivalent circuit diagram of a network of parasitic capacitances of the electrical machine with a structure corresponding to Figure 1 , Figure 8 an electrical equivalent circuit diagram of a network of parasitic capacitances of the electrical machine with a structure of the electrical machine according to Figure 2, Figure 9 a block diagram of an electrical circuit for controlling an electrical machine according to the invention and Figure 10 a partial perspective view of a modified embodiment for forming an opening in a shielding unit.

[0042] In the Figures 1 and 2Each of the following illustrates an embodiment of an electrical machine 10 that can be operated as a motor and thus can form an electric motor. The electrical machine 10 is, for example, an electrical machine that can be operated with alternating voltage, preferably multi-phase and, for example, three-phase alternating voltage. The operation of an electrical machine 10 by means of three-phase alternating voltage is schematically shown in Figure 9illustrated. The electrical machine 10 is connected via a converter circuit 11 to phase voltages U 1 , U 2 , U 3 of a three-phase AC voltage supply network. In the exemplary embodiment, the converter circuit 11 has a rectifier 12, which rectifies the three-phase AC voltage and provides a DC voltage in a DC voltage intermediate circuit 13, which is converted by an inverter 14 of the converter circuit 11 into a multi-phase and, for example, three-phase AC voltage for generating a rotating field in the electrical machine 10. Other converter topologies can also be used.

[0043] The multi-phase alternating voltage provided for the electrical machine 10 to generate the rotating field by the converter circuit 11 is not always equal to zero and this results in a common mode voltage U CM , which is also known as common modeThis common-mode voltage can cause a network of parasitic capacitances to form on components of the electrical machine that are not completely short-circuited and are separated from each other, for example, by a lubricant, air or the like, as shown schematically in the Figures 7 and 8 for different embodiments according to the Figures 1 and 2 If the common-mode voltage exceeds a certain value, breakdown can occur between the components of the electrical machine that form the parasitic capacitance, which can cause damage or increased wear. These effects are to be reduced and, ideally, eliminated by means of the present invention.

[0044] The electric machine 10 has a stator 17, an electrically conductive winding support 18, and a stator winding 19. In the exemplary embodiment, the stator winding 19 has several electrically separated winding groups, for example, three winding groups. The winding support 18 is arranged, for example, on a central body 24 of the stator 17, which extends along a rotational axis D. The central body 24 can be pin-shaped or sleeve-shaped. The radially outward-facing outer surface of the central body 24 is preferably continuous and, for example, formed by a cylindrical surface.

[0045] The winding support 18 and optionally also the central body 24 is / are electrically conductive and electrically connected to earth PE, which is Figures 7 and 8 can be seen in the electrical equivalent circuit diagram. The stator winding 19 is electrically insulated from the winding support 18.

[0046] The electric machine 10 also has a rotor 20, which is mounted for rotation about the axis of rotation D and can be driven in rotation about the axis of rotation D by means of a rotating field generated by the stator winding 19. For this purpose, the rotor 20 can have permanent magnets 21. In a radial direction radial to the axis of rotation D, an air gap 22 is formed between the permanent magnets 21 of the rotor 20 and teeth 23 of the winding support 18. The teeth 23 are separated from one another in the circumferential direction U by grooves (not shown), with conductor sections of the stator winding 19 running in the grooves.

[0047] The rotor 20 is rotatably mounted about the rotational axis D by means of a bearing assembly, wherein the bearing assembly 27 can be supported, for example, on the central body 24 or on another part of the stator 17. In the exemplary embodiment, the bearing assembly 27 has a first bearing 28 and a second bearing 29, which are arranged at a distance from one another in an axial direction A, parallel to the rotational axis D. The winding support 18 is arranged in the axial direction A between the first bearing 28 and the second bearing 29.

[0048] Each bearing 28, 29 has an outer ring 28a, 29a and an inner ring 28i, 29i. The outer rings 28a, 29a are mechanically connected to the rotor 20, while the inner rings 28i, 29i are arranged on a stationary part, for example, on the central body 24. In the exemplary embodiment, the bearings 28, 29 are designed as rolling bearings, so that rolling elements 30, for example balls, are arranged between the respective outer ring 28a, 29a and the associated inner ring 28i, 29i.

[0049] The electric machine 10 also has a first shield unit 34 adjacent to the first bearing 28 and a second shield unit 35 adjacent to the second bearing 29. In the exemplary embodiment, the two shield units 34, 35 are each formed by an integral component, namely a first shield element 36 and a second shield element 37, respectively. In a modification of the exemplary embodiment, the shield units 34, 35 could each also be designed in several parts.

[0050] As it is in the Figures 3-5 As can be seen, the first shielding element 36 has a first ring part 38 which extends from a radially inner end 39 of the first shielding unit 34 or the first shielding element 36 to a radially outer end 40 of the first shielding unit 34 or the first shielding element 36. At the radially outer end, the first shielding unit 34 or the first shielding element 36 has a first circumferential part 41 extending coaxially to the axis of rotation D. The first circumferential part 41 extends, for example, along a cylindrical jacket surface arranged coaxially to the axis of rotation D. Starting from the first ring part 38, the first circumferential part 41 extends in the axial direction A towards the second shielding unit 35. The first circumferential part 41 projects in the axial direction A beyond the adjacent axial end of the stator winding 19, which is also referred to as the winding head. The axial end of the stator winding 19 and the first circumferential part 41 are arranged overlapping in the axial direction A.

[0051] The second shielding unit 35 and the second shielding element 37 are constructed analogously to the first shielding unit 34 and the first shielding element 36. The second shielding element 37 has a second ring part 42 which extends from a radially inner end 43 of the second shielding unit 35 and the second shielding element 37 to a radially outer end 44 of the second shielding unit 35 and the second shielding element 37. At the radially outer end 44, the second shielding unit 35 and the second shielding element 37 has a second circumferential part 45 extending coaxially to the axis of rotation D. The second circumferential part 45 extends, for example, along a cylindrical surface arranged coaxially to the axis of rotation D. Starting from the second ring part 42, the second circumferential part 45 extends in the axial direction A towards the first shielding unit 34. The second circumferential part 45 projects in the axial direction A over the adjacent axial end of the stator winding 19, which is also referred to as the winding head.The axial end of the stator winding 19 and the second circumferential part 45 are arranged overlapping in the axial direction A.

[0052] The radially inner ends 39, 43 are, for example, directly mechanically connected to the central body 24 and preferably establish an electrical connection between the central body 24 and the respective shielding unit 34 or 35. The shielding units 34, 35 are thus electrically connected via the central body 24 to a reference potential (here: ground potential GND) or earth PE.

[0053] The electric machine defines a space, consisting of the central body 24, the two bearings 28, 29, and the rotor 20, in which the shield units 34, 35 are arranged. No component of the shield units 34, 35 protrudes from this space.

[0054] The first ring part 38 and the second ring part 42 can, as shown in the Figures 1 and 2schematically illustrated, extend parallel to a plane that is oriented perpendicular to the rotation axis D. Each ring part 38, 42 can have an outer ring section 46 and an inner ring section 47. The outer ring part 46 extends substantially parallel to a plane that is oriented perpendicular to the rotation axis D. In a modified embodiment, the inner ring part 47 extends obliquely inclined relative to the rotation axis D and thereby has a conical shape that widens towards the outer ring section 46. This is shown in Figure 6 illustrated as an example for the second ring part 42.

[0055] The ring parts 38, 42 have openings 48 arranged at regular intervals in the circumferential direction U. The openings 48 extend, for example, adjacent to the respective radially outer end 40, 44 in the radial direction radially to the axis of rotation D and preferably end at a distance from the respective radially inner end 39, 43. The openings 48 are present in the ring part 38, 42 where the ring part 38, 42 extends along the stator winding 19. Two openings 48 directly adjacent in the circumferential direction U are each separated from one another by a web 49 of the ring part 38 or 42.

[0056] If a rotating field is generated via the stator winding 19, electromagnetic stray fields also arise in the axial direction A, which can generate eddy currents in the shielding units 34, 35 and thus cause losses. The openings 48 adjacent to the axial ends of the stator winding 19 at least reduce such eddy current losses. Furthermore, the openings 48 can be used to cool the winding support 18 or the stator winding 19. If necessary, a fan impeller can be arranged on the rotor 20 to transport the cooling air.

[0057] As shown schematically in Figure 10 As illustrated, the edge that defines the respective opening 48 has a profile that does not extend entirely within a single plane. Viewed in the circumferential direction, at least one portion of the edge has an axial position that deviates from the axial position of the opposite portion of the edge. As shown in Figure 10As can be seen, the edge sections of the opening 48, which extend at least substantially in the radial direction, are arranged offset relative to one another in the axial direction A. A first edge section 51 is arranged on an air guide part 50, which projects obliquely over the opening 48. A second edge section 52, opposite in the circumferential direction, is arranged offset in the axial direction A from the first edge section 51.

[0058] The air guide part 50 can be integrally or monolithically connected to the immediately adjacent web 49. The air guide part 50 can be produced, for example, during the production of the opening 48 by forming a separating groove along the second edge section 52 of the opening 48 and bending the area delimited by the separating groove. This can improve the cooling air transport to the stator winding 19. The air guide part 50 is preferably arranged on the side of the opening 48 facing away from the air flow direction. For example, the air guide part 50 projects from the respective shield unit 34, 35 to the axially immediately adjacent part of the stator 17. However, other shapes and configurations of an edge of the opening 48 that does not extend within a single plane are also possible in order to improve the cooling air transport. Figure 10The first shielding unit 34 is shown merely as an example. The openings 48 of the second shielding unit 35 can be designed analogously.

[0059] In the exemplary embodiments, the circumferential parts 41, 45 have openings, similar to the ring parts 38, 42, but can alternatively be without openings. The circumferential parts 41, 45 extend in the circumferential direction U around the rotation axis D, whereby the openings can be evenly distributed in the circumferential direction U.

[0060] In the Figures 7 and 8 In each case, an electrical equivalent circuit diagram is illustrated, which represents the network of parasitic capacitances of the electrical machine 10, wherein the equivalent circuit diagram according to Figure 7 the embodiment according to Figure 1 and the equivalent circuit according to Figure 8 the embodiment according to Figure 2 corresponds.

[0061] According to the invention, the winding support 18 and optionally also the central body 24 are grounded (with ground PE). Due to a common-mode voltage U CM formed in the converter circuit 11, which is applied between the stator winding 19 and the ground potential GND of the converter circuit 11, parasitic capacitances become effective between the components of the electrical machine 10, as described in the Figures 7 and 8 illustrated are: C WS : parasitic capacitance between the stator winding 19 and the winding support 18 or earth PE; C WAs : parasitic capacitance between the stator winding 19 and the outer rings 28a, 29a to the stator 17 or winding support 18; C WAr : parasitic capacitance between the stator winding 19 and the outer rings 28a, 29a to the rotor 20; C WR : parasitic capacitance between the stator winding 19 and the rotor 20; C Ls : capacitance of the bearing arrangement 27 to the stator 17 or winding support 18; C Lr : parasitic capacitance of the bearing arrangement 27 to the rotor 20; C RE : parasitic capacitance between the rotor 20 and earth PE; C RS : parasitic capacitance between the rotor 20 and the stator 17 or winding support 18; CY : optional capacitance resulting from coupling with an optional EMC filter and / or Y capacitors built into the converter.

[0062] The parasitic capacitance CY can be omitted, e.g. if there is no EMC filter and / or if no Y capacitors are installed in the converter.

[0063] The above-mentioned parasitic capacitances are in both embodiments according to the Figures 1 and 2 The difference between the two embodiments of the Figures 1 and 2 is that in the embodiment according to Figure 2 Additionally, an inner insulator 53 is arranged between the central body 24 and the bearing inner rings 28i, 29i and / or an outer insulator 54 is arranged between the bearing outer rings 28a, 29a and the rotor 20. In this way, the bearing arrangement 27 can be electrically insulated from the central body 24 and thus from the stator 17 and / or from the rotor 20. The optional insulators 53, 54 create further parasitic capacitances, which in Figure 8 illustrated are: CIs: parasitic capacitance of the at least one inner insulator 53; CIr: parasitic capacitance of the at least one outer insulator 54.

[0064] The shielding units 34, 35 are either grounded (short-circuited to earth PE) or connected to the ground potential GND or another fixed reference potential via an impedance Z. The impedance Z can have a resistive component and / or a capacitive component and / or an inductive component.

[0065] The shielding units 34, 35 are electrically conductive, but preferably not ferromagnetic. They at least partially shield the stray electrical fields of the stator winding 19 and therefore influence the parasitic capacitances of the electrical machine, as shown schematically in the Figures 7 and 8is illustrated. In particular, the following parasitic capacitances C WAs , C WAr , and C WR between the stator winding 19 and the rotor 20 are reduced and the capacitive coupling between the stator winding 19 and the rotor 20 is reduced and ideally eliminated. In addition, the parasitic capacitance C RS between the rotor 20 and the stator 17 or winding support 18 and / or central body 24 is reduced or eliminated. In addition, the parasitic capacitance and thus the capacitive coupling between the rotor 20 and the stator 17 can also be reduced and ideally eliminated. Because of the grounded shield units 34, 35, the capacitive coupling between the rotor 20 and earth PE increases.

[0066] In this way, the bearings 28, 29 of the bearing assembly 27 will be better protected against damaging voltage breakdowns or currents.

[0067] The invention relates to an electrical machine 10 comprising a stator 17, a rotor 20, a bearing arrangement 27 with a first bearing 28 and a second bearing 29 on opposite sides of the stator 17, and a shield arrangement comprising a first shield unit 34 and a second shield unit 35. The rotor 20 is rotatably mounted about an axis of rotation D via the bearings 28, 29. The shield units 34, 35 are electrically conductive and each have an annular part 38, 42 which extends from a radially inner end 39, 43 to a radially outer end 40, 44 away from the axis of rotation D. Preferably, each shield unit 34, 35 has a circumferential part 41, 45 at the radially outer end 40, 44, which extends continuously in a ring shape around the axis of rotation D and is arranged in the axial direction A overlapping with the adjacent axial end of the stator winding 19 of the stator 17.The circumferential parts 41, 45 are preferably completely closed, whereas the ring parts 28, 42 can have openings 48. The first ring part 38 and / or the second ring part 42 has openings 48 arranged at a distance from one another in the circumferential direction U, the respective edge of which has a first edge section 51 arranged on an air guide part 50, wherein the air guide part 50 projects obliquely over the opening 48 and a second edge section 52 of the edge of the respective opening 48, opposite in the circumferential direction U, is arranged offset in the axial direction A from the first edge section 51. List of reference symbols:

[0068] 10electric machine 11converter circuit 12rectifier 13DC link 14inverter 17Stator 18Winding support 19Stator winding 20Rotor 21Permanent magnets 22Air gap 23Tooth 24Central body 27Bearing arrangement 28First bearing 28aOuter ring of the first bearing 28iInner ring of the first bearing 29Second bearing 29aOuter ring of the second bearing 29iInner ring of the second bearing 30Rolling elements 34First shielding unit 35Second shielding unit 36First shielding element 37Second shielding element 38First ring part 39Radial inner end of the first shielding unit 40Radial outer end of the first shielding unit 41First circumferential part 42Second ring part 43Radial inner end of the second shielding unit 44Radial outer end of the second shielding unit 45Second circumferential part 46Outer ring section 47Inner ring section 48Perforation 49Web 50Air guide part 51First edge section 52Second edge section 53Inner insulator 54Outer insulator AAxial direction C Ir Capacitance, insulation, rotor side C Is Capacitance, insulation, stator side C Lr Capacitance, bearing, rotor side C Ls Capacitance, bearing, stator side C WAs Capacitance, stator winding - outer ring, stator side C WS Capacitance, stator winding - stator C WAr Capacitance, stator winding - outer ring, rotor side C WR Capacitance, stator winding - rotor C RE Capacitance, rotor - earth C RS Capacitance, rotor - stator CY Coupling capacitance to EMC filter DRotational axis GNDGround potential PEEarth UCircumferential direction U 1 Phase voltage, first phase U 2 Phase voltage, second phase U 3 Phase voltage, third phase U CM Common mode voltage ZImpedance

Claims

1. Electrical machine (10) comprising: - a stator (17) comprising an electrically conductive winding support (18) electrically connected with earth (PE) or a reference potential (GND) and a central body (24) defining a rotation axis (D) and a stator winding (19), - a bearing arrangement (27) comprising a first bearing (28) arranged on the central body (24) and a second bearing (29) arranged on the central body (24), wherein the winding support (18) of the stator (17) is arranged in an axial direction (A) parallel to the rotation axis (D) between the first bearing (28) and the second bearing (29), - a rotor (20) rotatably supported around the rotation axis (D) by means of the bearing arrangement (27), - an electrically conductive first shielding unit (34) electrically connected with earth (PE) or a reference potential (GND) that comprises a first ring part (38) extending in a ring-shaped manner in a circumferential direction (U) around the rotation axis (D) and extending starting from a radial inner end (39) radially outward to a radial outer end (40), wherein the radial inner end (39) is arranged between the first bearing (28) and the winding support (18) and is connected with the central body (24), - an electrically conductive second shielding unit (35) that is electrically connected with earth (PE) or a reference potential (GND) that comprises a second ring part (42) extending in a ring-shaped manner in circumferential direction (U) around the rotation axis (D) and extending starting from a radial inner end (43) radially outward to a radial outer end (44), wherein the radial inner end (43) is arranged between the second bearing (29) and the winding support (18) and is connected with the central body (24), characterized in that the first ring part (38) and / or the second ring part (42) comprise through-holes (48) arranged with distance to one another in circumferential direction, the respective edge of which has a first edge section (51) arranged at an air guide part (50), wherein the air guide part (50) extends obliquely over the through-hole (48) and a second edge section (52) of the edge of the respective through-hole (48) oppositely arranged in circumferential direction (U), is offset in axial direction (A) relative to the first edge section (51).

2. Electrical machine according to claim 1, wherein the two shielding units (34, 35) are arranged in a space that is completely surrounded by the central body (24), the two bearings (28, 29) and the rotor (20).

3. Electrical machine according to any of the preceding claims, wherein the shielding units (34, 35) are electrically connected with the central body (24) via their respective ring part (38, 42) and with earth (PE) or the reference potential (GND) via the central body (24).

4. Electrical machine according to any of the preceding claims, wherein the central body (24) is a cylindrical sleeve or a cylindrical pin.

5. Electrical machine according to any of the preceding claims, wherein the first shielding unit (34) comprises a ring-shaped first circumferential part (41) that extends in axial direction (A) and in circumferential direction (U) around the rotation axis (D) and is arranged between the stator winding (19) and the rotor (20).

6. Electrical machine according to any of the preceding claims, wherein the second shielding unit (35) comprises a ring-shaped second circumferential part (45) that extends in an axial direction (A) and in circumferential direction (U) and is arranged between the stator winding (19) and the rotor (20).

7. Electrical machine according to any of the preceding claims, wherein the first shielding unit (34) consists of an integrally configured first shielding element (36) and / or wherein the second shielding unit (35) consists of an integrally configured second shielding element (37).

8. Electrical machine according to any of the preceding claims, wherein the air guide part (50) is arranged on the downstream side of the through hole (48) in air flow direction.

9. Electrical machine according to any of the preceding claims, wherein the air guide part (50) extends from the respective shielding unit (34, 35) toward the axially directly adjacent part of the stator (17).

10. Electrical machine according to any of the preceding claims, wherein two through holes (48) that are directly adjacent in circumferential direction (U) are separated from one another by means of a web of the first ring part (38) or the second ring part (42), and wherein the air guide part (50) is monolithically connected with the directly adjacent web (49).

11. Electrical machine according to any of the preceding claims, wherein the through holes (48) are arranged approximately aligned in a radial direction radial to the rotation axis (D) relative to a respectively assigned groove, wherein each groove is arranged between two directly adjacent teeth (23) of the winding support (18).

12. Electrical machine according to any of the preceding claims, wherein the first ring part (38) and / or the second ring part (42) comprise an outer ring section (46) that extends parallel to a plane orientated orthogonal to the rotation axis (D).

13. Electrical machine according to any of the preceding claims, wherein at least one of the two ring parts (38, 42) comprises an inner ring section (47) that extends obliquely relative to the rotation axis (D).

14. Electrical machine according to any of the preceding claims, wherein one inner insulator (53) is arranged between the first bearing (28) and the stator (17) and the second bearing (29) and the stator (17) respectively.

15. Electrical machine according to any of the preceding claims, wherein an outer insulator (54) is arranged between the first bearing (28) and the rotor (20) and the second bearing (29) and the rotor (20) respectively.