Electric motor

Abstract

electric motor (1) comprising: - a rotor body (2) to which a plurality of permanent magnets (3) or a rotor winding can be attached, and - a shaft (4) for receiving the rotor base body (2), - wherein an insulating body (5) is attached between shaft (4) and rotor base body (2) to electrically insulate the rotor base body (2) from the shaft (4), - wherein the insulating body (5) engages at least partially in the shaft (4) and in the rotor base body (2) in order to connect the shaft (4) and the rotor base body (2) in a rotationally fixed manner, and - wherein the insulating body (5) is made of a composite of ceramic and plastic, characterized in that the insulating body (5) has a ceramic core (6) with at least a partial plastic sheathing (7).

Description

State of the art

[0001] The present invention relates to an electric motor. In particular, the invention relates to the design of the shaft-hub connection of the rotor of the electric motor.

[0002] Electric motors, particularly three-phase permanent magnet motors, are known from the prior art and offer high power density and high torque. Machine components of electric motors that guide a concentrated magnetic flux are constructed from stacked electrical steel sheets. One such component is a rotor assembly to which the permanent magnets are attached. The rotor assembly is mounted on a shaft. The shaft, typically made of steel, transmits the rotary motion of the rotor body outwards from the three-phase motor. For torque transmission, the rotor assembly is connected to a shaft or hub in a rotationally fixed manner, with the connection being made by an interference fit that simultaneously establishes a connection point for eddy currents.

[0003] DE 10 2011 000 438 A1 discloses an electric motor comprising a rotor body to which a plurality of permanent magnets or a rotor winding can be attached, and a shaft for receiving the rotor body. An insulating element is provided between the shaft and the rotor body to electrically isolate the rotor body from the shaft. The insulating element engages at least partially with the shaft and the rotor body to connect the shaft and rotor body in a rotationally fixed manner. The insulating element is made of a fiber-reinforced, high-performance plastic.

[0004] From DE 10 2014 226 047 A1 and DE 10 2010 061 778 A1, it is known that the insulating body is made of plastic. From US 2014 / 0 285 042 A1, it is known that the insulating body can be made of various materials.

[0005] WO 2009 / 000 599 A1 discloses an approach for creating a connection between a rotor shaft and a rotor base body. Disclosure of the invention

[0006] The electric motor according to the invention avoids so-called electropitting, which can occur in ball bearings used to support the shaft. Electropitting occurs when eddy currents from the rotor body are conducted via the shaft to the ball bearings, leading to electrical discharges. According to the invention, this is prevented by electrical insulation between the shaft and the rotor body.

[0007] The electric motor according to the invention comprises a rotor body to which either a plurality of permanent magnets or a rotor winding can be attached. If the rotor body has a rotor winding, slip rings are particularly necessary to transfer electrical energy to the winding. Therefore, the use of permanent magnets is preferred. The electric motor also has a shaft for receiving the rotor body. An insulating element is provided between the shaft and the rotor body. This electrically isolates the rotor body from the shaft. Furthermore, the insulating element provides a rotationally fixed connection between the shaft and the rotor body. This is achieved by the insulating element engaging at least partially with the shaft and the rotor body, thereby establishing the rotationally fixed connection between the rotor body and the shaft.The insulating body thus serves two purposes: Firstly, it provides electrical insulation between the shaft and rotor base, and secondly, it creates a rotationally fixed connection between the rotor base and shaft, primarily through positive locking. This eliminates the need for the press fit known from the prior art, which would not provide electrical insulation. The insulating body is made of a composite of ceramic and plastic. The ceramic component increases the mechanical strength of the insulating body, while the plastic advantageously provides electrical insulation. Furthermore, the use of ceramic increases the service life of the rotationally fixed connection, as the use of plastic alone would lead to a loss of strength over time due to temperature fluctuations. This would cause the shaft-hub connection to fail, a problem compensated for by the strength-enhancing ceramic component.

[0008] According to the invention, the insulating body comprises a ceramic core with at least a partial plastic sheath. The ceramic core thus advantageously serves to bear loads, while the plastic sheath provides electrical insulation. In particular, the volume of the ceramic core is larger than the volume of the plastic sheath. Therefore, the insulating body exhibits high strength and can thus transmit high torques between the shaft and the rotor body.

[0009] The dependent claims contain preferred further developments of the invention.

[0010] The ceramic core is particularly advantageous when designed as a press ring. This means that the ceramic core is ring-shaped and connected to the shaft via a press fit. Thus, in addition to the previously described positive-locking connection, at least a partially effective friction-locking connection can also be established.

[0011] The rotor body and / or the shaft preferably have at least one groove, the groove extending along a central axis of the shaft. The insulating body engages in this at least one groove. It is particularly advantageous for both the shaft and the rotor body to each have at least one groove, with the insulating body engaging in both grooves. This results in the aforementioned rotationally fixed connection. It is particularly advantageous for both the rotor body and the shaft to have several such grooves.

[0012] In a particularly advantageous embodiment, the at least one groove has a cross-section that is either constant or variable along its central axis. The cross-section can change either continuously or abruptly. It can also be initially reduced and then subsequently increased along the central axis. This variable change in the cross-section along the central axis axially fixes the rotor body relative to the insulation body and / or the shaft relative to the insulation body. Thus, either the insulation body can be fixed axially, i.e., along a direction of the shaft's central axis, or the entire rotor body can be fixed axially relative to the shaft.

[0013] In a further preferred embodiment, the insulating body extends into the rotor base body in a star-shaped configuration. "Star-shaped" here refers specifically to the insulating body extending in a ring shape, with projections extending radially outwards from this ring shape. It is also possible for the projections to extend radially inwards. This arrangement provides a rotationally fixed connection between the insulating body and the rotor base body. Furthermore, it allows for the direction of magnetic flux within the rotor base body. This direction of magnetic flux is achieved primarily due to the properties of the ceramic component of the insulating body. Since ceramics typically exhibit low permeability, i.e., low magnetic conductivity, the insulating body can provide not only electrical but also magnetic insulation.

[0014] The insulating body advantageously has at least one extreme point with a maximum radial extent. Radial extent is defined as a dimension perpendicular, i.e., radial, to the central axis of the shaft. The extreme point is located at an angular range around the central axis where a permanent magnet is also located on the rotor body. In particular, the permanent magnet is positioned at the point within said angular range where it has the smallest distance to the shaft. If the permanent magnet has a varying distance to the central axis of the shaft along its length, then the angular range corresponds specifically to the range where the permanent magnet has the smallest distance to the shaft and thus to the central axis of the shaft.

[0015] The insulating body advantageously has a concave surface between two extreme points. This concave surface preferably has a round or oval shape. This allows for optimal guidance of the magnetic flux within the rotor body. This means that the magnetic flux can extend from a permanent magnet, i.e., from one extreme point of the insulating body, along the concave surface to another permanent magnet, i.e., to another extreme point of the insulating body. Thus, the magnetic flux can be optimized.

[0016] In a preferred embodiment, the magnetic flux within the rotor body is guided along a predefined path. This is achieved in particular by the measures described above.

[0017] In particular, the magnetic conductivity of the rotor body is impaired by the insulating body. The insulating body preferably exhibits a magnetic insulating effect, as it is magnetically non-conductive or only poorly conductive. This prevents the magnetic flux from flowing through the insulating body, thus allowing the magnetic flux within the rotor body to be adjusted. By appropriately shaping the insulating body, the magnetic flux within the rotor body can be directed along a predefined path.

[0018] The plastic component of the insulating body can be, in particular, a thermoset or a thermoplastic. Specifically, the plastic is designed to be electrically insulating and thus serves to insulate the rotor body from the shaft. Brief description of the drawings

[0019] Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawing. The drawing shows: Fig. 1 a schematic view of an electric motor according to an embodiment of the invention, Fig. 2 a schematic view of a rotor of the electric motor according to the embodiment in a first alternative, Fig. 3 a schematic view of a rotor of the electric motor according to the embodiment in a second alternative, Fig. 4 a schematic view of a rotor of the electric motor according to the embodiment in a third alternative, Fig. 5 a schematic view of a rotor of the electric motor according to the embodiment in a fourth alternative, and Fig. 6 a schematic view of a rotor of the electric motor according to the embodiment in a fifth alternative. Embodiments of the invention

[0020] Fig. Figure 1 schematically shows an electric motor 1. The electric motor 1 comprises a rotor with a rotor body 2 and a shaft 4. The electric motor 1 also includes a stator 11 for driving the rotor.

[0021] The rotor body 2 is made of stacked electrical steel. The rotor body 2 serves to hold permanent magnets 3. Alternatively, the rotor body 2 can also be designed to hold a rotor winding. The shaft 4 is made of steel. To achieve electrical insulation between the rotor body 2 and the shaft 4, an insulating element 5 is arranged between the rotor body 2 and the shaft 4, thus preventing contact between the rotor body 2 and the shaft 4.

[0022] The insulating body 5 establishes a rotationally fixed connection between shaft 4 and rotor body 2, as the insulating body 5 engages at least partially with both shaft 4 and rotor body 2. In particular, this creates a positive connection between the insulating body 5 and shaft 4, as well as between the insulating body 5 and rotor body 2. The rotationally fixed connection between rotor body 2 and shaft 4 serves to transmit torque between the rotor body 2 and shaft 4. This allows the rotation of the rotor body 2, initiated by the stator 11, to be transferred from the electric motor 1.

[0023] To achieve the connection between shaft 4 and rotor base 2 via the insulating body 5, individual grooves 8 are provided in both shaft 4 and rotor base 2. The insulating body 5 engages in these grooves 8.

[0024] The insulating body 5 is made of a composite of ceramic and plastic. Specifically, the insulating body 5 comprises a ceramic core 6 surrounded by a plastic sheath 7. The ceramic core 6 serves primarily to transmit torque from the rotor body 2 to the shaft 4, as it exhibits higher strength than the plastic sheath 7. The plastic sheath 7 primarily serves as electrical insulation between the shaft 4 and the rotor body 2.

[0025] The ceramic core 6 also exhibits low magnetic conductivity, which enables the steering of magnetic flux within the rotor body 2. This is described below in the Fig. Shown 2 to 6.

[0026] The Fig. Figures 2 to 4 show different configurations of the arrangement of the permanent magnets 3 in the rotor body 2. In each case, the rotor body is provided with permanent magnets 3 that have a minimum radial distance to a central axis 100 of the shaft 4, or that have a minimum distance to the central axis 100 within a certain angular range. The ceramic core 6, and thus the insulating body 5, is advantageously star-shaped and therefore has extreme points 9 where the insulating body 5 extends radially the greatest. The same applies to the ceramic core 6, which also extends radially the greatest at the extreme points 9. The grooves 8 in the rotor body 2 are thus designed accordingly to accommodate these extreme points 9.

[0027] The extreme points 9 are located in particular at an angular range where the rotor body 2 has a permanent magnet 3 with the smallest radial distance to the central axis 100. Fig. 2. A single permanent magnet 3 is present, which has the aforementioned minimum distance to the central axis 100. Thus, the extreme point 9 extends along the angular range of this permanent magnet 3. In Fig. All permanent magnets 3 have the same distance from the central axis 100. Thus, each extreme point 9 extends along each permanent magnet 3. Fig. Figure 4 shows that one point on each pair of permanent magnets has the smallest distance to the central axis 100. Again, the extreme points 9 extend over the same angular range at these points of minimum distance.

[0028] To optimize the magnetic flux 200, the insulating body 5 preferably has a concave surface 10 extending between two extreme points 9. The concave surface 10 has either a round or an oval shape. In this way, magnetic fluxes can be optimally guided through the rotor body so that the magnetic flux 200 follows a predefined path between two permanent magnets 3. This optimization of the magnetic flux results in an increase in efficiency.

[0029] These measures aid in guiding the magnetic flux through the rotor body. Thus, the slots 8 in the rotor body 2, in addition to providing a rotationally fixed connection, also serve to optimize and direct the magnetic flux 200. Such a function is not required for the slots 8 of the shaft 4. Therefore, the slots 8 in the shaft 4 can be designed as desired and, in particular, optimized to facilitate simple and cost-effective assembly and manufacturing of the components of the electric motor 1.

[0030] The Fig. 5 and Fig. Figure 6 shows further embodiments of how the rotor base body 2 can be attached to the shaft 4. Fig. Figure 5 shows an example in which each groove 8 with a constant cross-section extends along the central axis 100 of the shaft 4. In contrast, Figure 5 shows Fig.Figure 6 shows an example where the cross-section of the grooves 8 changes around the central axis 100. This results in the axial fixation of the insulation body 5 to the rotor base body 2. Thus, slippage of the insulation body 5 is prevented.

Claims

[1] Electric motor (1) comprising: - a rotor body (2) to which a plurality of permanent magnets (3) or a rotor winding can be attached, and - a shaft (4) for receiving the rotor base body (2), - wherein an insulating body (5) is attached between shaft (4) and rotor base body (2) to electrically insulate the rotor base body (2) from the shaft (4), - wherein the insulating body (5) engages at least partially in the shaft (4) and in the rotor base body (2) in order to connect the shaft (4) and the rotor base body (2) in a rotationally fixed manner, and - wherein the insulating body (5) is made of a composite of ceramic and plastic, characterized by , that the insulating body (5) has a ceramic core (6) with at least a partial plastic coating (7). [2] Electric motor (1) according to claim 1, characterized by, that the ceramic core (6) is designed as a ring to create a press fit between shaft (4) and ceramic core (6). [3] Electric motor (1) according to one of the preceding claims, characterized by , that the rotor body (2) and / or the shaft (4) have at least one groove (8) extending along a central axis (100) of the shaft (4), wherein the insulating body (5) engages in the at least one groove (8). [4] .Electric motor (1) according to claim 3, characterized by , that at least one groove (8) has a cross-section that is constant or variable along the central axis (100). [5] Electric motor (1) according to any one of the preceding claims, characterized by , that the insulating body (5) extends in a star shape in the rotor base body (2). [6] Electric motor (1) according to any one of the preceding claims, characterized by, that the insulating body (5) has at least one extremum (9) with a maximum radial extent, wherein the extremum (9) is located at an angular range where a permanent magnet (3) inserted into the rotor body (2) has a minimum distance to the shaft (4). [7] Electric motor (1) according to claim 6, characterized by , that the insulating body (5) has a concave surface (10) between two extreme points (9), wherein the concave surface has a round or oval shape. [8] Electric motor (1) according to any one of the preceding claims, characterized by , that through the insulating body (5) a magnetic flux (200) is aligned within the rotor body (2) along a predefined path. [9] Electric motor (1) according to any one of the preceding claims, characterized by that the plastic includes a thermoplastic and / or a thermoset.

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