Electric machine

Abstract

Electric machine (2) with a housing (4) and with a stator (12) within the housing surrounding a rotor (6) fixedly arranged on a motor shaft (8) and having a rotating field winding which forms a winding head (16) on each of the end faces of the stator (12), - wherein the winding heads (16) are embedded in a thermally conductive potting material (20), - wherein the potting material (20) is in thermal contact with the housing (4) along the outer circumference of the winding head (16), and - wherein a segmented, comb-like cooling plate (24) is arranged on the inner circumference of the potted winding head (16), which has a number of lamellar sheet teeth (26) extending axially towards the opposite end face, which are freed by slot-like recesses (28) of the cooling plate (24).

Description

[0001] The invention relates to an electric machine with a housing and an internally mounted stator, which surrounds a rotor fixed to a motor shaft and has a rotating field winding that forms a winding head at each end face of the stator. It further relates to a motor vehicle equipped with such an electric machine.

[0002] Electric machines can serve as motors or generators in various technical applications, for example as compressor or starter drives. Nowadays, high-performance electric machines are particularly common as electric drive motors in hybrid or electric vehicles.

[0003] Such an electric motor, particularly a brushless one, typically has a stator core on the stator side. This core has a number of stator teeth and slots into which an electric rotating field winding is inserted, consisting of individual stator coils. These coils are wound from an insulating wire, i.e., a wire (copper wire) coated with an insulating layer, such as an insulating varnish.

[0004] The coil windings are often arranged such that they run longitudinally (axially) along the stator core between two opposing end faces and are deflected in a loop-like fashion at the end faces of the stator core, perpendicular to this longitudinal direction. The stator may, for example, have coil formers mounted on the stator teeth exposed by the stator slots, around which the coil wire is wound in turns. This area, where the coil windings extend axially beyond the stator core and are deflected, is commonly referred to as the (stator end) winding head.

[0005] To mechanically fix the coil windings relative to each other and to the respective coil former, it is common practice to encapsulate the stator components, at least in the area of ​​the winding ends, with a potting material such as epoxy resin or plastic. After the potting material has cured, the winding ends are mechanically and electrically protected by the resulting encapsulation.

[0006] In the case of a brushless electric motor as a multi-phase three-phase machine, the stator has several (motor) phases and thus at least a corresponding number of phase conductors or coil wires as phase or coil windings. The coil windings are each supplied with an electric current out of phase to generate a rotating magnetic field in which a rotor, usually equipped with permanent magnets, rotates.

[0007] During operation, the current generates power loss in the form of heat, which occurs, among other things, due to ohmic losses within the insulating wires. This heat loss unfortunately leads to power losses in the electric motor and can sometimes cause the insulating varnish and / or potting compound to melt, thus damaging the electric motor. Therefore, to reduce and dissipate the generated heat loss, it is necessary to adequately cool or dissipate the heat generated by the electric motor during operation.

[0008] The potting compound thermally insulates the stator coils in the area of ​​the winding heads, resulting in the highest coil temperature in this area. This "hot spot" reduces the continuous load capacity of the electric motor. To cool the winding heads, it is common practice to connect the potting compound to the motor housing, thus dissipating the heat loss to the housing's thermal mass. For example, water and / or air cooling systems are commonly used to cool the housing.

[0009] The connection to the housing is typically made radially on the outside of the stator lamination stack, and sometimes additionally via axial thermal contact between the potting material and a housing end face. To improve cooling, it is also common to achieve heat dissipation by thermally connecting the radially inner surface of the winding head, particularly by means of cooling structures in the housing or annular or hollow cylindrical cooling plates. The cooling plates act as an additional heat dissipation surface and are, for example, arranged within grooves in the potting compound or at least partially embedded in it. Advantageously, the cooling plates are made of a metallic material with high thermal conductivity, especially aluminum.

[0010] On the one hand, the effectiveness of heat dissipation from the winding head potting increases with decreasing distance between the winding head and the cooled housing or heat sink. On the other hand, the rotating magnetic field of the rotating field winding generates eddy currents in the electrically conductive surfaces of the heat sink and the housing, which in turn act as additional heat sources and thus impede the cooling of the potting. In other words, heat dissipation from the rotating field winding is reduced, thereby limiting the continuous load on the electric motor.

[0011] DE 12 04 316 A describes a cooling device for electric machines with a stator chamber enclosed by a slotted tube from the rotor chamber and ring-shaped heat conductors arranged between the winding heads and the housing shell, the heat conductors being in thermally conductive contact with a heat exchanger around their circumference. The winding heads are surrounded by an embedding compound in which finger-like, flexible extensions of the heat conductors are arranged, encompassing the winding heads at close intervals and extending to near the air gap.

[0012] US Patent 2014 / 0292116A1 discloses a cooling device for the stator of an electric machine. The cooling unit comprises a generally cylindrical heat sink with opposing longitudinal ends and at least one head cooling element attached to one of the longitudinal ends of the body; the head cooling element is configured to enclose the winding heads of the stator and incorporates thermally conductive material.

[0013] DE 102 01 012 A1 describes an electrical machine comprising a stator core with a first end and a second end and windings located therein, wherein the winding heads of the windings project from the first end and the second end of the stator core. The machine further comprises a first arrangement and a second arrangement of laminated aluminum rings, and a thermally conductive potting compound arranged between the winding heads and the respective first and second ring arrangements at the first end and the second end of the stator core, such that heat dissipation paths are created from the winding heads through the potting compound and the ring arrangements to the housing.

[0014] The laminated aluminium rings are positioned at the first end and the second end of the stator core and are in contact with the housing, with each lamella of the aluminium rings being insulated in each ring arrangement to reduce further losses due to eddy currents.

[0015] From DE 101 14 321 A1, an electric machine with a stator assembly, rotor, and encapsulated winding heads is known. The encapsulation of the winding heads is designed with surface-enhancing structures, which are in thermally conductive contact with a cooling jacket or with a cooling medium in cooling channels, and / or the encapsulation is at least partially enclosed by a thermally conductive covering that dissipates the heat.

[0016] DE 101 22 425 A1 discloses an electric machine comprising winding heads, a water-cooled stator, an air-cooled rotor with rotor through-holes, and bearing shields. The rotor and the electric machine are ventilated by means of an air inlet and an air outlet in the respective bearing shields, with the electric machine having its own fan.

[0017] The invention is based on the objective of providing an electric machine which is improved with regard to heat dissipation of the winding heads. Furthermore, a motor vehicle equipped with such an electric machine is to be provided.

[0018] With regard to the electric machine, the aforementioned problem is solved according to the invention with the features of claim 1, and with regard to the motor vehicle with the features of claim 5. Advantageous embodiments and further developments are the subject of the respective dependent claims.

[0019] The electrical machine according to the invention is, for example, designed as a permanent magnet machine or as an asynchronous machine of a motor vehicle, in particular as a drive motor of an electric or hybrid vehicle. For this purpose, the machine comprises a housing with an internally mounted stator that surrounds a rotor fixed to a motor shaft. The stator has a stator body onto which a rotating field winding is applied to generate a rotating magnetic field that sets the rotor in rotation. The rotating field winding is, for example, applied to the stator body as a distributed (coil) winding.

[0020] The coils of the rotating field winding extend axially beyond the stator at its end faces, forming a winding head on each side. In other words, the winding head is the part of the rotating field winding that extends axially beyond the stator core, i.e., the stator core or stator lamination stack, on both end faces. The winding heads are embedded in a thermally conductive potting material, which allows for the dissipation of heat generated in the winding heads during motor operation.

[0021] The potting compound is in thermal contact with the housing along the outer circumference of each winding head, i.e., radially on the outside, so that the heat loss for cooling the electric machine is dissipated via the thermal mass of the housing. In the following, thermal contact refers specifically to a thermally conductive contact between two or more materials, in which heat transfer from one material to another occurs via convection.

[0022] On its radial inner surface, the potted winding head is in thermal contact with a segmented cooling plate along its inner circumference. This cooling plate, preferably strip- or plate-shaped, is made of a metallic material and acts as a heat conductor. The cooling plate dissipates the heat absorbed by the potting material to a surrounding cooling medium, such as air, thus cooling the cooling plate and consequently the potting material and the winding head. Due to its position on the inner circumference of the potting material, the cooling plate advantageously has a substantially annular or hollow cylindrical geometry. The segmentation reduces or completely prevents the induction of eddy currents in the electrically conductive area of ​​the cooling plate, caused by the rotating magnetic field during motor operation.

[0023] In other words, the segmentation of the heat sink interrupts the extensive heat dissipation surface in such a way that the paths of the induced eddy currents are broken. As a result, no significant eddy currents occur within the heat sink during motor operation. Consequently, the heat sink generates considerably less heat during motor operation, allowing the potting material and thus the winding heads to dissipate heat more effectively towards the heat sink. This improved heat dissipation from the winding heads translates into a reduction in power loss and an increase in the continuous operating temperature of the electric motor.

[0024] Segmentation reduces the cooling surface area of ​​the cooling plate, which allows the potting material to dissipate heat. Experience has shown, however, that preventing eddy currents, and thus avoiding additional heat generation within the cooling plate, significantly improves the cooling of the winding head during motor operation. This enables particularly effective heat dissipation from the hot spots of the winding heads, which has a particularly beneficial effect on the performance potential and service life of the electric motor. As a result, an electric motor with a comparatively higher drive power can be achieved with the same overall volume.

[0025] The potting material is, for example, an epoxy resin or a curable plastic material, which is applied to the two opposing end faces of the stator for the long-term fixation of the winding heads. The cured potting material forms a substantially annular casting with a rectangular cross-section on each end face, in which the wire path of the winding heads is essentially completely enclosed. In addition to the circumferential connection to the housing, the respective potting is preferably in axial thermal contact with the corresponding housing end face. This further improves the cooling of the winding heads.

[0026] According to the invention, the segmentation of the cooling plate is formed by a number of recesses. These recesses can be filled, for example, with insulating material, i.e., an electrically non-conductive material. According to the invention, the recesses are preferably designed as axial slots in the cooling plate. By inserting or introducing slots or other types of insulating layers into the cooling plate, eddy current losses and the resulting waste heat are significantly reduced.

[0027] Another aspect of the invention provides that a comb-like cooling plate is provided with a number of sheet metal teeth extending axially towards the opposite end face. The lamellar sheet metal teeth are specifically defined by slot-like recesses resulting from the segmentation process.

[0028] Segmentation and the resulting reduction in eddy current losses make it possible to position the cooling plate closer to the winding head, thus further improving the cooling effect. For this purpose, in an advantageous embodiment, the cooling plate is at least partially embedded within the potting material. In other words, the cooling plate is, for example, potted together with the winding head in the potting material.

[0029] In a suitable design, the housing is cooled by means of a cooling system, in particular water cooling. This improves the cooling of the potting material on the housing side, thereby further improving the continuous load capacity of the electric machine.

[0030] In a suitable design, the cooling plate is made of aluminum. This makes the cooling plate particularly lightweight and cost-effective to manufacture, while simultaneously ensuring the highest possible thermal conductivity.

[0031] In the preferred application, the electric machine is used in a motor vehicle. Here, the electric machine is preferably designed as an asynchronous machine and, for example, installed as an electric motor drive in an electric or hybrid vehicle. The electric machine is preferably designed and suitable for generating torque for vehicle propulsion and for recuperating kinetic energy from the vehicle during operation and converting it into electrical energy for an energy storage device (generator operation).

[0032] The improved continuous load capacity of the electric motor translates advantageously into longer operating times for the drive system and any connected energy storage device. This, in turn, improves the driving range of the equipped vehicle.

[0033] Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. The drawing shows: Fig. 1 in a schematic sectional view an electric machine with a housing and with inside the housing a stator and a rotor arranged fixed to a motor shaft, Fig. 2 in a perspective view, a section of the winding head area of ​​the stator with a cooling plate and with a potting compound, Fig. 3 the winding head area in a sectional view, and Fig. 4 the cooling plate in a perspective view.

[0034] Corresponding parts and sizes are always marked with the same reference symbols in all figures.

[0035] At the in Fig. The electric machine 2 shown in Figure 1 is an electric motor drive for an electric or hybrid vehicle. For this purpose, the electric machine 2 is advantageously designed as an asynchronous machine and integrated within the drive train of the electric or hybrid vehicle. The electric machine 2 comprises a (motor) housing 4 in which a rotor 6 is mounted so as to rotate about an axis of rotation D.

[0036] The rotor 6 is fixedly mounted on a rotor or motor shaft 8, which is supported relative to the housing 4 by means of two bearings 10 at opposite end faces. The rotor 6 is enclosed within the housing by a stator 12. The stator 12 comprises a stator core or stator lamination stack (not described in detail) with a number of axially extending stator slots 14 on its inner circumference. The stator slots 14 extend, in particular, along an axial direction A that is oriented substantially parallel to the axis of rotation D.

[0037] In the stator slots 14, a distributed rotating field winding is inserted in the assembled state, which is only shown schematically by means of the winding heads 16. The rotating field winding protrudes from the two opposite end faces of the stator 12 as a loop-shaped winding, which forms the respective winding head 16 in this area.

[0038] During operation of the electric machine 2, the rotating field winding is supplied with three-phase electric current. This causes the rotating field winding to generate a rotating magnetic field in which the rotor 6, usually equipped with permanent magnets, rotates around the axis of rotation D. The current generates, among other things, power loss in the form of heat during operation.

[0039] The winding heads 16 are embedded in a potting compound 18 for the purpose of dissipating the heat loss from the rotating field winding generated during motor operation. This potting compound 18 consists of a cured potting material 20, in particular an epoxy resin or a plastic material. The potting compound 18 mechanically and electrically protects the winding heads 16 by fixing them to the stator 12. The potting compound 18 is approximately annular and, as shown in particular in Fig. 2 and Fig. 3 shows an approximately rectangular cross-section in which the respective winding head 16 is essentially completely enclosed.

[0040] The potting compound 18 is directly connected to the housing end faces 22 of the housing 4 along the axial direction A, so that heat is dissipated from the potting compound 18 to the outside of the housing 4. The housing end faces 22 are formed, in particular, by a housing base 4a of a cup-shaped housing body on the one hand, and by a housing cover 4b that closes this base on the other. The housing 4 is cooled by means of a cooling system, for example, by integrated coolant lines. Preferably, water is used as the coolant.

[0041] A comb-like cooling plate 24 is arranged along the inner circumference of the potting compound 18. During motor operation, a cooling fluid, for example in the form of an air or liquid flow, is guided past the cooling plate 24, so that the potting compound 18 is cooled via the cooling plate 24 to the interior of the stator 12.

[0042] The in Fig. The four individually depicted annular cooling plates 24 are made, in particular, of an aluminum material, for example, by means of a stamping-bending process. The cooling plate 24 is at least partially integrated or embedded in the potting compound 18, so that the distance between the winding heads 16 and the cooling plate 24 is as small as possible. This ensures particularly effective heat transfer from the winding heads 16 to the respective cooling plate 24, which advantageously affects the cooling of the winding heads 16.

[0043] The cooling plate 24 has a number of sheet metal teeth 26 extending axially towards the opposite housing end face 22. The lamellar sheet metal teeth 26 are exposed by slot-like recesses 28 in the cooling plate 24. Examples are shown in the Fig. 2 only three stator slots 14, sheet metal teeth 26 and recesses 28 are provided with a reference numeral.

[0044] The recesses 28 segment the cooling plate 24, reducing or preventing the formation of induced eddy currents due to the rotating magnetic field during operation. This reduces heat generation in the cooling plates 16, resulting in improved cooling of the winding heads 16. During the integration or embedding of the cooling plate 24 in the potting 18, the clear width of the recesses 28 is filled, for example, with potting material 20, so that essentially electrically insulating material is arranged between the plate teeth 26.

[0045] In a suitable dimensioned configuration, the cooling plate 24, for example, has a radial sheet thickness of 3 mm and an axial sheet height of approximately 30 mm. In such a configuration, the segmentation is dimensioned, for example, to approximately 6 mm, meaning that the width of the sheet teeth 26 and / or the clear width of the slot-like recesses 28 between the sheet teeth 26 is dimensioned to 6 mm. Reference symbol list 2 Electric Machine 4 cases 4a Case base 4b Housing cover 6 Rotor 8 Motor shaft 10 warehouses 12 Stator 14 Stator slot 16 winding head 18 potting 20 potting material 22 Front of housing 24 Cooling tray 26 sheet metal teeth 28 recess D axis of rotation A Axial direction

Claims

[1] Electric machine (2) with a housing (4) and with a stator (12) within the housing surrounding a rotor (6) fixedly arranged on a motor shaft (8) and having a rotating field winding which forms a winding head (16) on each of the end faces of the stator (12), - wherein the winding heads (16) are embedded in a thermally conductive potting material (20), - wherein the potting material (20) is in thermal contact with the housing (4) along the outer circumference of the winding head (16), and - wherein a segmented, comb-like cooling plate (24) is arranged on the inner circumference of the potted winding head (16), which has a number of lamellar sheet teeth (26) extending axially towards the opposite end face, which are freed by slot-like recesses (28) of the cooling plate (24). [2] Electric machine (2) according to claim 1, wherein the cooling plate (24) is arranged at least partially within the potting material (20). [3] Electric machine (2) according to claim 1 or 2, wherein the housing (4) is cooled by means of a cooling, in particular water or oil cooling. [4] Electric machine (2) according to one of claims 1 to 3, wherein the cooling plate (24) is made of an aluminium material. [5] Motor vehicle, in particular electric or hybrid vehicle, with an electric machine (2) according to any one of claims 1 to 4.

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