Electric machine having a shielding structure arranged in an air gap

Abstract

The invention relates to an electric machine (1) having a stator (2), a rotor (3) and an electric shielding structure (5) applied to at least one side (4a, 4b, 4c) of the stator (2) axially or radially facing the rotor (3) for capacitively decoupling the stator (2) from the rotor (3) by discharging capacitive electric currents in the direction of an electric mass in the form of a housing (6) which receives the stator (2).

Description

[0001] P241140

[0002] - 1 -

[0003] Electric machine with a shielding structure arranged in an air gap

[0004] The invention relates to an electric machine, in particular for a motor vehicle drive or aircraft drive, that is, a machine which is preferably used as an electric drive machine in a motor vehicle, such as a car, truck, bus or other commercial vehicle.

[0005] It is already well known to operate variable-speed electric motors using frequency converters. In this process, high-frequency voltages often induce bearing currents, meaning currents that are conducted through the bearings (e.g., rolling bearings) of the electric motor. This can directly lead to bearing damage and a significant reduction in the bearing's service life. Furthermore, it is known that voltage spikes can be so large that other conductive components, such as gears connected to the shaft / rotor shaft of the electric motor via low-resistance connections, can be damaged. Moreover, the currents transmitted in this way also create disadvantages with regard to electromagnetic interference (EMI) emissions from the electric motor.

[0006] The aim of the invention is to prevent the aforementioned disadvantages without adversely affecting the efficiency.

[0007] This is solved according to the invention by the subject matter of claim 1. Accordingly, an electric machine for a motor vehicle drive is claimed, comprising a stator, a rotor and an electrical shielding structure applied to at least one side of the stator facing axially or radially towards the rotor, for capacitive decoupling of the stator from the rotor by diverting capacitive electrical currents towards an electrical ground in the form of a housing connected to the stator (preferably accommodating / enclosing the stator).

[0008] CONFIDENTIAL P241140

[0009] - 2 -

[0010] This shielding structure reliably dissipates parasitic capacitive currents during operation. This results in a robust machine protected from damage caused by parasitic currents. The special design of the shielding structure does not impair the machine's performance.

[0011] Further advantageous embodiments are claimed in the dependent claims and are explained in more detail below.

[0012] Accordingly, it remains advantageous if the shielding structure has a disk area arranged on an axial end face of the stator. The disk area preferably extends over the entire end face of the stator, meaning it completely covers the stator at its end face. Preferably, the stator is covered by a disk area on each of its two opposite end faces.

[0013] Alternatively or additionally to providing at least one disk area, it is also advantageous if the shielding structure includes a sleeve area arranged on a radial inner side of the stator. This further optimizes the shielding.

[0014] For effective dissipation of parasitic capacitive currents, it is also advantageous if the shielding structure has a multitude of circumferentially distributed conductor tracks extending radially and / or axially, which are (at least partially) interconnected radially on the outside of the shielding structure via an arc-shaped or annular connection area. These conductor tracks preferably extend circumferentially, at least in sections, for example, branching, looping, meandering, etc. Preferably, the conductor tracks have a constant width. The conductor tracks are preferably spaced apart from each other circumferentially (especially in the section located within the connection area). Due to the very fine structure,

[0015] CONFIDENTIAL P241140

[0016] - 3 -

[0017] In this design, the influence on the magnetic field between the stator and rotor is so minimal that there is no significant reduction in the machine's power output or heating of the shield structure.

[0018] It is further advantageous if the shielding structure has several circumferentially distributed grounding connection areas on its radial outer surface, with each grounding connection area having a conductor cross-section many times larger than several conductor tracks extending radially inwards from this grounding connection area. This ensures efficient dissipation of the interference currents generated during operation. Due to the arrangement outside the gap between the stator and rotor, the conductor cross-section can be larger without any significant reduction in machine performance or heating of the shielding structure.

[0019] In this context, it is advantageous for further connection of the shielding structure to an electrical ground if the grounding connection areas are designed as tabs projecting radially outwards.

[0020] The grounding connections can then be directly or indirectly connected to / in contact with the housing that accommodates the stator.

[0021] In this respect, it is particularly advantageous if eyelet elements receive the grounding connection areas in a form-fitting and / or force-fitting manner and these eyelet elements are further connected to the housing via fastening means.

[0022] It is also advantageous if a stator housing attached to the housing is made of plastic and the shielding structure is electrically coupled to the housing by means of a fastening element that anchors the stator housing to the housing. The fastening element can, for example, consist of a screw element made of metal and a spacer sleeve, preferably also made of metal.

[0023] CONFIDENTIAL P241140

[0024] - 4 -

[0025] In a preferred embodiment, the shielding structure can be applied directly to at least one side of the stator made of a plastic material, for example by printing or chemical process. This allows the shielding structure to be implemented as thinly as possible.

[0026] Alternatively, it is also advantageous if the shielding structure is applied to a foil-like support structure, which in turn is applied to at least one side of the stator, for example, by gluing it on. This allows the shielding structure to be manufactured as simply as possible.

[0027] In this regard, it has also proven advantageous if the shielding structure has a maximum thickness of 50 pm, more preferably less than 10 pm. If the shielding structure is formed on a foil-like support structure, it is expedient if the assembly consisting of this support structure of the shielding structure has a maximum thickness of 0.3 mm, more preferably less than 0.05 mm.

[0028] This only slightly affects the air gap between the stator and the rotor. Therefore, existing electrical machines can be used largely unchanged.

[0029] It has proven particularly advantageous for the electric machine to be designed as an axial flux machine. Specifically, it has been found to be beneficial if a disk-shaped stator is surrounded on both its axial sides by disk-shaped rotors / rotor parts, and if a shielding structure is present on each axial side / end face.

[0030] The invention will now be explained in more detail below with reference to figures, in which context various embodiments are also indicated.

[0031] They show:

[0032] CONFIDENTIAL P241140

[0033] - 5 -

[0034] Fig. 1 shows a longitudinal section of an electrical machine according to a first embodiment of the invention, showing the position of a shielding structure attached to a stator and its further connection to a central housing.

[0035] Fig. 2 is a perspective exploded view of the electric machine according to Fig. 1, illustrating its essential components.

[0036] Fig. 3 shows a perspective exploded view of the stator used in Figs. 1 and 2, illustrating a shielding structure according to a first embodiment.

[0037] Fig. 4 shows a perspective exploded view of a stator designed as an alternative to Fig. 3, with an additional shielding structure having a sleeve area.

[0038] Fig. 5 shows a front view of a disk area belonging to the shielding structure of Figs. 1 to 4.

[0039] Fig. 6 shows two detailed views of the disc area of ​​Fig. 5, with the left part showing a circumferential area of ​​the shielding disc and the right part showing this circumferential area in detail from the perspective of a grounding connection area.

[0040] Fig. 7 shows a detailed top view of a connection area between the shielding structure and the housing of the electric machine.

[0041] Fig. 8 shows two detailed views of an eyelet element designed to receive / couple the grounding connection area, with the left part illustrating the open state of the eyelet element before the grounding connection area is inserted and the right part illustrating the folded state of the eyelet element in which the grounding connection area is held.

[0042] CONFIDENTIAL P241140

[0043] - 6 -

[0044] Fig. 9 shows a perspective detail view of the electric machine in the area of ​​an eyelet element in the assembled state, where its rotationally fixed support relative to the housing is clearly visible, and

[0045] Fig. 10 shows a longitudinal section view of the electrical machine similar to Fig. 1, illustrating the currents drawn during operation.

[0046] The figures are purely schematic and serve solely to illustrate the invention. The same elements are identified by the same reference symbols.

[0047] Figures 1 and 2 clearly show the basic structure of an electric machine 1 according to a first embodiment. The electric machine 1 is designed here as an axial flux machine.

[0048] The electric machine 1 therefore has a substantially disk-shaped stator 2. The stator 2 has a stator housing 16, which is preferably made of a plastic material. The stator 2 is attached to a housing 6 via its stator housing 16. The stator 2 / the stator housing 16 is attached to the housing 6 at its radial outer edge / at its radially outer edge region. The stator housing 16 is thus attached to the housing 6 of the electric machine 1 by several fastening means 17 distributed in the circumferential direction.

[0049] Furthermore, the electric machine 1 has a rotor 3. The rotor 3 is also disk-shaped, at least in sections. The rotor 3 even has two disk-shaped rotor sections 23a and 23b. The rotor sections 23a and 23b can also be referred to as independent rotors 3. In this embodiment, the two rotor sections 23a and 23b are connected radially along their inner surfaces and radially within the stator 2 to a central rotor shaft 24, which in turn forms the torque output of the electric machine 1.

[0050] CONFIDENTIAL P241140

[0051] - 7 -

[0052] In the usual way, the rotor shaft 24 is rotatably mounted in the housing 6 in the area of ​​at least one rolling bearing 25.

[0053] Rotor sections 23a and 23b are axially offset from each other and from the stator 2. Rotor sections 23a and 23b are arranged on opposite sides 4a and 4b of the stator 2 in the form of end faces 7a and 7b. An axial gap / air gap is formed between each rotor section 23a and 23b and the stator 2. The stator 2 is radially overlapped with rotor sections 23a and 23b for the majority of its length.

[0054] The rotor 3 has several circumferentially distributed magnetic elements 26 in its rotor sections 23a, 23b, which are arranged radially overlapping with the stator 2. The stator 2 has several coils 27 in the usual manner, which are energized during operation to drive the rotor shaft 24.

[0055] It is further known that this current supply can lead to the occurrence of capacitive interference currents, which adversely affect the function of the electric machine 1. According to the invention, a shielding structure 5 is provided on the stator 2 to dissipate these interference currents generated during operation. The shielding structure 5 generally serves to conduct these interference currents towards the housing 6 / via the housing 6, which in turn is designed as an electrical ground (Fig. 10). The housing 6 is therefore preferably made directly of a conductive material, such as a metal.

[0056] In the illustrated embodiment, the shielding structure 5 surrounds the stator 2 on both its axial (first and second) sides 4a, 4b and on its radial inner side 9 (third side 4c). Thus, the shielding structure 5 surrounds the stator 2 in three spatial directions / sides 4a, 4b, 4c. As can be seen in conjunction with Figures 3 and 4, it is also possible, in principle, to provide the shielding structure 5 (Figure 3) exclusively on the axial end faces 7a, 7b. Furthermore, it is alternatively possible to provide the shielding structure 5 only on one side 4a, 4b, 4c.

[0057] CONFIDENTIAL P241140

[0058] - 8 -

[0059] The shielding structure 5, in the embodiment shown in Fig. 1, therefore has two disk areas 8. The disk areas 8 are directly formed as individual shielding disks 22a, 22b. Each disk area 8 is arranged towards one of the end faces 7a, 7b and is in contact with the end faces 7a, 7b of the stator 2.

[0060] The sleeve area 10 (alternatively referred to as sleeve) of the shielding structure 5, which can still be used optionally according to Fig. 4, is attached / arranged / in alignment with the radial inner side 9 of the stator 2 / of a through hole centrally penetrating the stator 2.

[0061] With regard to the respective area of ​​the shielding structure 5, Figures 5 and 6 clearly show that it is formed by an electrically conductive conductor structure. The shielding structure 5 thus has a multitude of circumferentially adjacent, but spaced-apart, conductor tracks 11. The conductor tracks 11 therefore run radially in the longitudinal direction from the inside to the outside. The conductor tracks 11 have regular branches that project circumferentially. These branches can, however, also be shaped in other ways, for example as loops or wave-like sections. A very finely structured design is preferable here in order to achieve the lowest possible feedback effect on the magnetic field of the electric machine 1.

[0062] The conductor tracks 11 are connected to each other on a radial outer surface 12 of the shielding structure 5 via a common, at least arc-shaped, and in this case even ring-shaped, connection area 13. The connection area 13 is in turn connected to several circumferentially distributed grounding connection areas 14. The shielding structure 5 is manufactured as a single-material conductor structure, for example, from a copper material. A silver material is also possible as an alternative to copper. Due to its even better conductivity compared to copper, the layer can be made even thinner.

[0063] CONFIDENTIAL P241140

[0064] - 9 - With regard to the earthing connection areas 14, it can also be seen that each earthing connection area 14 has a conductor cross-section that is many times larger than the radially inner adjacent areas of the shielding structure 5 in the form of the conductor tracks 11 and the connection area 13. On closer inspection, the earthing connection areas 14 are implemented in particular in the form of tabs 15.

[0065] Furthermore, in connection with Figures 5 and 6, as well as the preceding Figures 3 and 4, it should be noted that the shielding structure 5 is preferably applied to a foil-like, i.e., foil-shaped, support structure 18. The support structure 18 is in turn directly attached to the end face 7a, 7b of the stator 2, for example, by gluing it. The shielding structure 5 is thus preferably part of a composite with the support structure 18, which composite can also be referred to as a shielding foil.

[0066] Alternatively, the shielding structure 5 can also be applied directly to sides 4a, 4b, 4c of the stator 2. For example, the shielding structure 5 can be applied to a plastic material of the stator housing 16, which directly forms the respective sides 4a, 4b, 4c, using a chemical process.

[0067] In the embodiment shown in Fig. 1, an eyelet element 19, as shown in Fig. 8, is attached to each grounding connection area 14. This essentially clamp-like eyelet element 19 receives the grounding connection area 14 in a form-fitting and force-fit manner. The eyelet element 19 projects radially outwards beyond the grounding connection area 14 and has a hole area 28 on its radial outer side, which is directly connected to the fastening means 17. As can again be seen in Fig. 1, the respective eyelet element 19 is penetrated by a screw element 20 of the fastening means 17 and thereby fixed to the housing 6.

[0068] CONFIDENTIAL P241140

[0069] - 10 -

[0070] In this regard, it should be noted that the fastening element 17 preferably also includes a spacer sleeve 21, which penetrates the stator 2 / the stator housing 16 along its entire length and serves as a support sleeve for the screw elements 20. Each spacer sleeve 21 is preferably also electrically conductive, for example made of a metal. The spacer sleeve 21 therefore also serves to dissipate interference currents. The spacer sleeve 21 thus preferably rests at one end against a screw head of the screw element 20 or is in contact with the eyelet element 19. At the opposite end, the spacer sleeve 21 rests against the eyelet element 19 of the other disk area 8, which in turn rests axially against the housing 6.

[0071] Figures 7 and 9 further show that the eyelet elements 19 are positively supported in the circumferential direction / direction of rotation by support lugs 29 attached to the stator housing 16 and / or the housing 6.

[0072] For the sake of completeness, it should be noted that the directional terms used here refer to the central axis of rotation 30 of the rotor 3. Axial direction thus refers to a direction along this axis of rotation 30, radial direction to a direction perpendicular to this axis of rotation 30, and circumferential direction to a direction along a circle running concentrically around the axis of rotation 30.

[0073] In other words, according to the invention, a shielding structure (shielding structure 5) is provided which is applied (e.g., by bonding) to both sides 4a, 4b of the stator assembly within the entire effective air gap of an axial flux machine and effectively prevents capacitive coupling between the winding and the stator iron core in the direction of the rotor 3 and dissipates capacitive parasitic currents to the electrical ground of the system. The physically "effective air gap" can essentially be understood as the volume of air and non-magnetic materials located between the iron materials in the stator 2 (stator iron core or pole shoes) and the rotor magnets. This results in, in particular, from a

[0074] CONFIDENTIAL P241140

[0075] - 11 -

[0076] Projection of the magnet's outer and inner diameters onto the pole shoe plane and the immediate edge areas.

[0077] The shielding structure is preferably designed to be so thin that the effective air gap of the electric machine 1 does not need to be changed in width, for example in the form of a plastic film as a non-conductive carrier material (carrier structure 18) with printed conductive traces 11 and a protective coating. Due to the thin design of the film, it can be curved at the edges. This allows height differences between the shielding structure in the air gap and the screw connection points to be compensated for.

[0078] Preferred thicknesses for substrate materials are a maximum of 0.3 mm and ideally less than 0.05 mm. Conductive layers applied to the substrate material (shielding structure 5 with the conductor tracks 11 themselves) preferably have a maximum thickness of 50 pm. Layer thicknesses of less than 10 pm are even more preferred.

[0079] Furthermore, the shield structure in the air gap consists of a multitude of very thin, branching, radially outward-extending conductor tracks 11, which do not exceed a technically feasible narrow width b across the entire air gap and are not interconnected (circumferentially), thus preventing conductor loops. This is important to avoid eddy current losses in the strong alternating magnetic field of the air gap, and consequently, a noticeable influence on the magnetic field and local overheating of the shield structure. In particular, closed conductor loops and planar conductor structures of greater width, which would lead to eddy currents and high losses, are avoided. At the same time, the conductor track fill factor (ratio of conductor track area to total area in the air gap) is targeted to be as high as possible to achieve maximum shielding effectiveness.Consequently, only the electric field, but not the magnetic field, is shielded by the shielding, and thus the magnetic air gap torque and the motor characteristics are not changed within the limits of usual measurement tolerances.

[0080] CONFIDENTIAL P241140

[0081] - 12 -

[0082] The individual radial conductors 11 are routed segment by segment via a significantly wider busbar (connection area 13) radially outside the effective air gap to a grounding connection point (grounding connection area 14). Since they must carry the current of numerous conductors 11, they are significantly wider to minimize electrical resistance and are positioned outside the effective air gap, and thus outside the main magnetic field, to prevent eddy current losses. The individual busbars are separated by breaks to prevent the formation of closed loops tangentially and thus avoid eddy current losses.

[0083] The shield structure is connected to the mounting points of the stator assembly via grounding contacts with the largest possible contact area. These grounding contacts establish electrical contact with the shield structure through a clamping or crimp connection. The connection to the central grounding points can be made via a shaped contact disc, such as a lug, which makes contact with the metal sleeves or the outer housing at the mounting points.

[0084] Furthermore, alignment features (e.g. small noses or recesses; here support noses 29) are provided on the stator side surface or on the grounding contacts, which ensure precise positioning of the shield structure and the grounding contacts and also provide anti-rotation protection for the grounding contacts during the screwing process.

[0085] Metallic grounding sleeves (spacer sleeves 21) in the area of ​​the mounting screws (screw elements 20) ensure the further grounding path through the outer plastic housing (stator housing 16) of the stator 2. These in turn are in surface contact with the metallic outer housing (housing 6) of the motor, which is connected to the central electrical ground.

[0086] CONFIDENTIAL P241140

[0087] - 13 -

[0088] The shielding structure and other components in the heat dissipation path are also made of a highly thermally conductive material (preferably metal). This allows them to also conduct heat and support heat dissipation from the air gap.

[0089] In another embodiment, the shielding structure is not only attached to the stator side faces (end faces 7a, 7b) but also extends into the area of ​​the stator's inner diameter (inner face 9) (wave shielding). This reduces the capacitive coupling of the windings to the shaft (rotor shaft 24). For this embodiment, the shielding foil (shielding structure 5) can be appropriately shaped or radially cut or segmented at the inner diameter.

[0090] In an alternative design, the shielding structure is integrated into the stator's sidewalls, which are made of non-conductive material (e.g., a polymer) and form integral components with the applied shielding structure. The sidewalls with the integrated shielding structure can be prefabricated as complete components and, due to the applied shielding structure, are only a few micrometers wider than the sidewalls without the shielding structure.

[0091] The shield structure can alternatively be made of a thin printed circuit board material with a copper layer into which the conductor tracks 11 are introduced by means of etching.

[0092] Alternatively, the grounding contacts can be attached to the shield structure by means of a soldered connection.

[0093] CONFIDENTIAL P241140 DE

[0094] - 14 -

[0095] List of reference signs

[0096] 1 electric machine

[0097] 2 Stator

[0098] 3 Rotor

[0099] 4a first page

[0100] 4b second page

[0101] 4c third page

[0102] 5 Shielding structure

[0103] 6 cases

[0104] 7a first front

[0105] 7b second front

[0106] 8 disc area

[0107] 9 Inside

[0108] 10 sleeve area

[0109] 11 conductor track

[0110] 12 Outside

[0111] 13 Connection area

[0112] 14 Earthing connection area

[0113] 15 tab

[0114] 16 Stator housings

[0115] 17 Fasteners

[0116] 18 Support structure

[0117] 19 eyelet elements

[0118] 20 screw element

[0119] 21 Spacer sleeve

[0120] 22a first shielding disc

[0121] 22b second shielding disc

[0122] 23a first rotor section

[0123] 23b second rotor section

[0124] 24 Rotor shaft

[0125] 25 rolling bearings

[0126] 26 magnetic element

[0127] 27 coil

[0128] 28-hole area

[0129] 29 Support nose

[0130] 30 Rotary axis

[0131] CONFIDENTIAL

Claims

P241140 DE - 15 - Patent claims 1. Electric machine (1) with a stator (2), a rotor (3) and an electrical shielding structure (5) applied to at least one side (4a, 4b, 4c) of the stator (2) facing axially or radially towards the rotor (3) for capacitive decoupling of the stator (2) from the rotor (3) by diverting capacitive electrical currents towards an electrical ground in the form of a housing (6) connected to the stator (2).

2. Machine (1) according to claim 1 , characterized in that the shielding structure (5) has a disk area (8) arranged on an axial end face (7a, 7b) of the stator (2) and / or a sleeve area (10) arranged on a radial inner side (9) or radial outer side of the stator (2).

3. Machine (1) according to claim 1 or 2, characterized in that the shielding structure (5) has a plurality of circumferentially distributed conductor tracks (11) extending in the radial direction and / or axial direction, which conductor tracks (11) are connected to each other via an arc-shaped or annular connection area (13) towards a radial outside (12) or radial inside of the shielding structure (5).

4. Machine (1) according to one of claims 1 to 3, characterized in that the shielding structure (5) has several circumferentially distributed grounding connection areas (14) towards its radial outer side (12), wherein each grounding connection area (14) has a conductor cross-section many times larger than several conductor tracks (11) adjoining this grounding connection area (14) in a radial direction inwards.

5. Machine (1) according to claim 4, characterized in that the earthing connection areas (14) are designed as radially outwardly projecting tabs (15). CONFIDENTIAL P241140 DE - 16 - 6. Machine (1) according to claim 4 or 5, characterized in that the earthing connection areas (14) are connected directly or indirectly to the housing (6) accommodating the stator (2).

7. Machine (1) according to one of claims 1 to 6, characterized in that a stator housing (16) attached to the housing (6) is made of a plastic and the shielding structure (5) is electrically coupled to the housing (6) by means of a fastening means (17) anchoring the stator housing (16) to the housing (6).

8. Machine (1 ) according to one of claims 1 to 7, characterized in that the shielding structure (5) is applied directly to the at least one side (4a, 4b, 4c) of the stator (2) formed from a plastic material.

9. Machine (1 ) according to one of claims 1 to 7, characterized in that the shielding structure (5) is applied to a foil-like support structure (18), which support structure (18) is in turn applied to at least one side (4a, 4b, 4c) of the stator (2).

10. Machine (1 ) according to one of claims 1 to 9, characterized in that the electrical machine (1 ) is designed as an axial flux machine. CONFIDENTIAL

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