Stator lamination stack for an electric machine with a circumferential slot

Abstract

A stator lamination stack (7, 7a, 7b) for an electric machine (1) is described, comprising several axially stacked first and second stator laminations (8, 9, 9a, 9b) and having a circumferential groove (15) extending along its circumference. The circumferential groove (15) is formed by one or more first stator laminations (8) which have a smaller radial extent in the region of the circumferential groove (15) than the second stator laminations (9, 9a, 9b) adjacent on both sides. The circumferential groove (15) extends over a circumferential angle (α) of at least 270°. Furthermore, a stator (6) with such a stator lamination stack (7, 7a, 7b), an electric machine (1) with such a stator (6), a vehicle (22) with such an electric machine (1), and a method for operating such an electric machine (1) are described.

Description

TECHNICAL AREA

[0001] The invention relates to a stator lamination stack for an electric machine, comprising several axially stacked first and second stator laminations. Furthermore, the invention relates to a stator for an electric machine comprising a stator housing, a stator lamination stack of the aforementioned type arranged in the stator housing, and stator windings arranged on the stator lamination stack. The invention further relates to an electric machine with such a stator, a rotor rotatably arranged relative to the stator, and a cooling system configured to supply coolant to the circumferential slots. The invention also relates to a vehicle with such an electric machine and a method for operating such an electric machine. STATE OF THE ART

[0002] Such a stator lamination stack, such a stator, such an electric machine, such a vehicle, and such a method are all known in principle from the prior art. A general problem is the heat generation in the stator during operation of the electric machine. Especially at high power densities, special design measures are necessary to prevent excessive heating of the stator. For example, channels can be provided in the stator housing or in the stator lamination stack, through which a coolant flows. The cooling performance is directly related to the surface area of ​​these cooling channels; however, their use in the stator lamination stack is limited insofar as the cooling channels can negatively affect the guidance of the magnetic flux within the stator lamination stack. REVELATION OF THE INVENTION

[0003] One object of the invention is therefore to provide an improved stator lamination stack, an improved stator, an improved electric machine, an improved vehicle, and an improved method for operating an electric machine. In particular, the cooling capacity achievable in a stator lamination stack is to be increased compared to the prior art without any significant impairment of the magnetic flux within the stator lamination stack.

[0004] The object of the invention is achieved with a stator lamination stack of the type mentioned at the outset, which has a circumferential groove extending along the circumference of the stator lamination stack and formed with one or more first stator laminations which have a smaller radial extent in the region of the circumferential groove than adjacent second stator laminations on both sides, wherein the circumferential groove extends over a circumferential angle of at least 270° (in particular continuously).In other words, the stator lamination stack comprises several first and second stator laminations stacked axially in the direction of a stator axis, wherein the first stator laminations form radially recessed areas with respect to the stator axis and the second stator laminations each form adjacent areas radially raised with respect to the stator axis, wherein one radially recessed area and two adjacent radially raised areas form a circumferential groove extending around the stator axis over a circumferential angle of at least 270° (in particular continuously) with respect to the stator axis.

[0005] Furthermore, the object of the invention is solved with a stator for an electric machine comprising a stator housing, a stator lamination stack of the type mentioned arranged in the stator housing and stator windings arranged on the stator lamination stack.

[0006] Furthermore, the object of the invention is solved with an electric machine comprising a stator of the type mentioned, a rotor rotatably arranged relative to the stator, and a cooling system designed to supply coolant into the circumferential grooves.

[0007] Furthermore, the problem of the invention is solved with a vehicle equipped with such an electric machine which is intended to propel the vehicle.

[0008] Finally, the object of the invention is solved by a method for operating an electric machine of the type mentioned, in which the coolant is supplied to the circumferential grooves via the cooling system.

[0009] The circumferential groove substantially increases the surface area of ​​the stator core compared to a smooth, cylindrical surface, thus significantly improving cooling. Because the circumferential groove is located far to the outside of the stator core, it does not significantly impair the magnetic flux within the core. While a coolant can flow through the circumferential groove, the improved cooling effect may also be solely due to the increased surface area of ​​the stator core. In other words, a coolant flow through the circumferential groove is not strictly necessary. For example, the coolant - are fed into the circumferential grooves from above and flow downwards in the circumferential grooves following the force of gravity, - are fed into the circumferential grooves from below and flow upwards under overpressure in the circumferential grooves or - be sprayed into the circumferential grooves.

[0010] In the first embodiment, the flow can only be caused by gravity. However, it is also conceivable that the coolant flowing from top to bottom is pressurized by a pump. Preferably, the coolant inflow is adapted to an outflow via the circumferential grooves, so that all circumferential grooves are subjected to a substantially uniform flow of coolant.

[0011] The second design variant advantageously achieves a particularly uniform flow through the circumferential grooves, since gravity-induced drainage cannot lead to uneven flow through the grooves. A further advantage is that the coolant drain can be positioned almost arbitrarily.

[0012] In the third design variant, the coolant can, for example, be sprayed radially into the circumferential grooves, especially at several positions, which allows for a particularly high cooling performance.

[0013] Furthermore, the coolant can completely fill the circumferential grooves or the space between the stator and stator housing, with a drain for the coolant being positioned almost arbitrarily. Through this drain, the coolant can be directed, among other things, to a nozzle, through which it is sprayed onto a winding head of a stator winding. With the space between the stator and stator housing completely filled, the inner surface of the space is fully contacted by the coolant, thus ensuring optimal heat transfer.

[0014] In particular, the circumferential groove can extend over a circumferential angle of 360°. The circumferential groove is then annular in shape. It is also conceivable that the stator lamination stack has several circumferential grooves corresponding to the circumferential groove. Accordingly, when the singular form is used for circumferential groove in the following, it also refers to multiple circumferential grooves, and vice versa, unless otherwise specified.

[0015] It is also conceivable that - several first stator laminations are stacked on top of each other to form a continuous radially recessed area (i.e., the groove base of a circumferential groove) and / or - several second stator laminations are stacked on top of each other to form a continuous radially raised area.

[0016] In general, the first stator laminations and the second stator laminations can be made of electrical steel or a magnetically conductive material, respectively.

[0017] Further advantageous embodiments and developments of the invention will become apparent from the dependent claims and from the description in conjunction with the figures.

[0018] It is advantageous if the ratio of the groove width to the groove depth of the circumferential groove is in the range of 0.8 to 1.2, or in other words, if the cross-section of the circumferential groove has a ratio of groove width to groove depth in the range of 0.8 to 1.2. The groove cross-section is then approximately square. This allows the circumferential surface area of ​​the stator lamination stack to be essentially doubled compared to an arrangement where the stator lamination stack has a smooth, cylindrical surface, thereby further improving the cooling effect for the stator lamination stack. Furthermore, with such a groove width to groove depth ratio, favorable flow conditions exist for the flow of coolant through the circumferential grooves. In particular, a groove width and / or a groove depth can be in the range of 2 to 3 mm.A typical thickness of a stator lamination is in the range of 0.2 to 0.3 mm, so that a number of ten second stator laminations then results in the specified slot width.

[0019] Alternatively, the ratio of the groove width to the groove depth of the circumferential groove can be in a range of 0.4 to 0.6.

[0020] For example, the circumferential groove can have a rectangular and, in particular, a square profile. However, other profiles are also conceivable. For instance, the circumferential groove could have a V-shaped or U-shaped cross-section, namely if first stator laminations with different radial dimensions are provided in the area of ​​the circumferential groove.

[0021] The stator lamination stack can have several circumferential slots of the type mentioned, extending along its entire axial length. This results in a particularly effective cooling effect. However, it is also conceivable that the circumferential slots are arranged (only) in a central region of the stator lamination stack, extending axially from a first circumferential slot to a last circumferential slot, with the adjacent end regions of the stator lamination stack being free of circumferential slots on both sides. The axial length of the central region can be, in particular, at most 50%, 60%, or 80% of the axial length of the stator lamination stack. This allows the cooling effect to be limited or concentrated in the central region. In this context, it is also possible for the two end regions to differ in length by at most 10%. This allows for a (largely) symmetrical cooling effect.

[0022] In an advantageous embodiment of the stator, the circumferential slots can be radially closed, at least in some areas, by the stator housing. The circumferential slots and the stator housing then form circumferential channels extending around the stator axis. These channels can be arc-shaped (for a circumferential angle α < 360°) or annular (for a circumferential angle α = 360°).

[0023] If the circumferential slots are closed off by the stator housing, then the circumferential slots can be conceptually replaced by the term "circumferential channels". In other words, the term "circumferential slot" is synonymous with a circumferential channel in such a case, even if this is not explicitly stated everywhere.

[0024] In a preferred embodiment of the stator, the stator housing and / or the stator lamination stack can have an axial longitudinal channel connecting several circumferential slots. In the second case, the second stator laminations, in particular, can have recesses that form the axial longitudinal channel. The longitudinal channel can extend in the axial direction, or its path can have at least one axial component. The coolant can be easily supplied to the circumferential slots via the longitudinal channel. The longitudinal channel then acts as a distributor. The coolant exiting the circumferential slots can also be discharged via the longitudinal channel. The longitudinal channel then acts as a collector. In particular, several such longitudinal channels can be provided, distributed around the circumference of the stator lamination stack, specifically evenly distributed. One or more of these longitudinal channels can then each function as a distributor or each as a collector.

[0025] In one embodiment of the stator, a coolant distribution rail can be provided above the stator lamination stack. With such a coolant distribution rail, the coolant can be introduced into the circumferential groove(s) and then flow downwards in the circumferential grooves, particularly without pressure and under the influence of gravity (or solely based on gravity). BRIEF DESCRIPTION OF THE FIGURES

[0026] Exemplary embodiments of the invention are shown in the accompanying schematic figures. These show: Fig. 1 An exemplary and schematically depicted electrical machine in half-section with several circumferential grooves or channels; Fig. 2 a detailed view of the stator lamination stack in the area of ​​a circumferential groove which runs along the circumference of the stator lamination stack; Fig. 3 an embodiment with a coolant distribution rail arranged above the stator lamination stack; Fig. 4 an embodiment in which the second stator laminations have recesses which form several longitudinal channels, and Fig. 5 an exemplary vehicle with an electric machine of the proposed type. DETAILED DESCRIPTION OF THE INVENTION

[0027] It is stated in the introduction that identical parts in the different embodiments are provided with the same reference numerals or component designations, possibly with different indices. The disclosure of a component contained in the description can be applied analogously to another component with the same reference numeral or component designation. Furthermore, the positional indications chosen in the description, such as "top," "bottom," "back," "front," "side," and so on, refer to the figure directly described and illustrated and must be applied analogously to the new position if the position changes.

[0028] Fig. Figure 1 shows a half-section through a schematically represented electric machine 1 with a multi-part machine housing 2, comprising a stator housing 3, a front end shield 4, and a rear end shield 5. The electric machine 1 also has a stator 6, which has a stator lamination stack 7 with several axially stacked stator laminations 8, 9 and stator windings 10 arranged within the stator lamination stack 7. Furthermore, the electric machine 1 includes a rotor 11 with a rotor shaft 12 and a rotor lamination stack 13, which is mounted on the rotor shaft 12 and is not shown in detail. Rotor magnets, rotor windings, or a squirrel cage (not shown) can be arranged within the rotor lamination stack 13. The rotor shaft 12 is rotatably mounted about a rotor axis or stator axis A relative to the stator 6 by means of (rolling) bearings 14a, 14b. Specifically, the first bearing 14a is located in the front bearing shield 4 and the second bearing 14b is located in the rear bearing shield 5.

[0029] Fig. Figure 2 shows a detailed view of the stator lamination stack 7 in the area of ​​a circumferential groove 15 extending along the circumference of the stator lamination stack 7. In this example, the circumferential groove 15 is formed by several first stator laminations 8, which have a smaller radial extent in the area of ​​the circumferential groove 15 than the second stator laminations 9 adjacent on both sides. The circumferential groove 15 extends over a circumferential angle α of at least 270°, in particular continuously over a circumferential angle α of at least 270°, and specifically over a circumferential angle α of 360° (see also the Fig. 3 and Fig. 4) In other words, the first stator laminations 8 form a radially recessed area B with respect to the stator axis A, and the second stator laminations 9 form radially raised areas C1, C2 adjacent to the radially recessed area B with respect to the stator axis A.

[0030] The radially recessed area B forms the circumferential groove 15 extending around the stator axis A. Specifically, the radially recessed area B forms the groove base of the circumferential groove 15, and the two adjacent radially raised areas C1 and C2 form the flanks of the circumferential groove 15. The proposed measures substantially increase the circumferential surface area of ​​the stator lamination stack 7 compared to an arrangement where the stator lamination stack 7 has a smooth, cylindrical surface, thereby significantly improving the cooling effect of the stator lamination stack 7. Since the circumferential grooves 15 are located far to the outside of the stator lamination stack 7, there is no significant impairment of the magnetic flux within the stator lamination stack 7.

[0031] The first stator laminations 8 and the second stator laminations 9 can be made of electrical steel or of a magnetically conductive material, respectively.

[0032] In the Fig. In the detailed view shown in Figure 2, several first stator laminations 8 are stacked on top of each other to form a continuous radially recessed area B, and several second stator laminations 9 are stacked to form continuous radially raised areas C1, C2. However, it would also be conceivable that a radially recessed area B is formed by exactly one first stator lamination 8 and / or a radially raised area C1, C2 by exactly one second stator lamination 9.

[0033] In particular, the ratio of slot width b to slot depth t can be in the range of 0.8 to 1.2. This means the slot cross-section can be approximately square. This allows the circumferential surface area of ​​the stator lamination stack 7 to be essentially doubled compared to an arrangement where the stator lamination stack 7 has a smooth, cylindrical surface, thereby further improving the cooling effect of the stator lamination stack 7. Furthermore, with such a ratio of slot width b to slot depth t, favorable flow conditions exist for the flow of coolant through the circumferential slots 15. For example, a slot width b and / or a slot depth t can be in the range of 2 to 3 mm. A typical thickness of a stator lamination 8, 9 is in the range of 0.2 to 0.3 mm, so that a first set of ten stator laminations 8 then yields the slot width b.Alternatively, the same number of second stator laminations 9 can be stacked on top of each other to form a radially raised area C1, C2.

[0034] In the Fig. In the example shown in Figure 2, the circumferential groove 15 has a rectangular and, in particular, a square profile. However, other profiles would also be conceivable. For example, the circumferential groove 15 could have a V-shaped or U-shaped cross-section, namely by providing first stator laminations 8 with different radial dimensions in the region of the circumferential groove 15.

[0035] Naturally, several circumferential slots 15 corresponding to the circumferential slot 15 can be provided in the stator lamination stack 7, as is shown by way of example in the Fig. 1 is shown.

[0036] In the Fig. In the example shown in Figure 1, the circumferential slots 15 are at least partially closed radially or circumferentially by the stator housing 3. The circumferential slots 15 and the stator housing 3 thus form circumferential channels 16 extending around the stator axis A. Depending on the circumferential angle α over which the circumferential slot 15 extends, the circumferential channels 16 are arc-shaped (for circumferential angles α < 360°) or annular (for circumferential angles α = 360°). If the circumferential slots 15 are closed by the stator housing 3, then the term "circumferential slot 15" is used synonymously with a circumferential channel 16 in the following, even if this is not always explicitly stated. Furthermore, when the singular is used for a circumferential groove 15 or a circumferential channel 16, the plural of circumferential grooves 15 or circumferential channels 16 is also meant below, and vice versa unless otherwise stated.

[0037] Furthermore, the stator housing 3 includes an optional longitudinal channel 17, which extends in the axial direction or has at least one axial component and connects several of the circumferential slots 15 or several of the circumferential channels 16. In the given example, the longitudinal channel 17 connects all circumferential slots 15 or circumferential channels 16. An optional nozzle 18 is also provided in the stator housing 3, which is connected to the longitudinal channel 17.

[0038] In this example, the longitudinal channel 17 and the nozzle 18 are part of a cooling system designed to supply coolant to the circumferential grooves 15. During operation of the electric machine 1, coolant is supplied to the circumferential grooves 15 via this cooling system. Fig. Figure 1 symbolizes the flow direction D. The coolant is supplied via the nozzle 18 and distributed into the circumferential grooves 15 via the longitudinal channel 17. In the specific example shown, the coolant is supplied from above and flows downwards in the circumferential grooves 15. The coolant can be pressurized (i.e., a pressure line of a cooling system can be connected to the nozzle 18), but the coolant can also flow downwards in the circumferential grooves 15 by gravity, or (only) due to gravity. Preferably, the coolant inflow is matched to an outflow via the circumferential grooves 15, so that all circumferential grooves 15 are supplied with coolant in a substantially uniform manner. In the given example, the longitudinal channel 17 acts as a distributor.

[0039] The coolant can exit from the circumferential grooves 15 or from the circumferential channels 16 at the bottom and be collected in the stator housing 3, from where it can be discharged via a further nozzle connected to the suction side of the cooling system. It would also be conceivable, however, that several longitudinal channels 17 are provided in the stator housing, and in particular opposite the one in the Fig. In addition to the longitudinal channel 17 shown in Figure 1, a further longitudinal channel 17 is provided, which connects the circumferential slots 15 and circumferential channels 16, respectively, and then functions as a collector. The aforementioned suction-side nozzle is then connected to the further longitudinal channel 17. It would also be conceivable that more than two longitudinal channels 17 are provided, which can be distributed evenly around the circumference of the stator lamination stack 7 (see also Figure 1 in this context). Fig. 4) Several of the longitudinal channels 17 can each function as distributors or as collectors.

[0040] It would also be conceivable that the coolant is supplied to the circumferential grooves 15 or circumferential channels 16 from below and flows upwards through them under overpressure. In such a case, the pressure port 18 can be located at the bottom and the suction port at the top. The roles of distributors and collectors are then also reversed. An advantage of reversing the flow direction D is that, unlike with a top-down flow, gravity-induced outflow cannot lead to an uneven flow through the circumferential grooves 15. Optionally, the coolant can completely fill the circumferential grooves 15 or the space between the stator and the stator housing.

[0041] In the Fig. In the example shown in Figure 1, the circumferential grooves 15 extend over the entire axial length of the stator lamination stack 7, resulting in a particularly high cooling effect. In particular, it can be provided that the area in which circumferential grooves 15 are provided comprises at least 90% of the axial length of the stator lamination stack 7, so that the circumferential grooves 15 extend substantially over the entire axial length of the stator lamination stack 7.

[0042] It would also be conceivable that the circumferential slots 15 are concentrated in a central region E of the stator lamination stack 7, which extends axially from a first circumferential slot 15 to a last circumferential slot 15, with the adjacent end regions F1, F2 of the stator lamination stack 7 being free of circumferential slots 15 on both sides. In particular, the axial length of the central region E can be at most 50%, at most 60%, or at most 80% of the axial length of the stator lamination stack 7. This allows the cooling effect to be limited or concentrated on the central region E. Furthermore, it can be provided that the two end regions F1, F2 are of the same length, as shown in the Fig. 1. In particular, it can be provided that the two end regions F1, F2 differ in length by a maximum of 10%. This allows for a (largely) symmetrical cooling effect.

[0043] Fig. Figure 3 shows a schematic representation of an embodiment in which the stator slots 19 are visible in the stator lamination stack 7a and a coolant distribution rail 20 is arranged above the stator lamination stack 7a. In this embodiment, the coolant is supplied to the circumferential slots 15 from above and flows downwards under the influence of gravity, without pressure, in the circumferential slots 15. The coolant exits the circumferential slots 15 in the lower region of the stator lamination stack 7a and can then be collected, for example, in the stator housing 3. In this example, the circumferential slots 15 extend over a circumferential angle α < 360°, but they could also extend over a circumferential angle α = 360°. It would also be conceivable to provide several coolant distribution rails 20, which are distributed around the circumference of the stator lamination stack 7a and by means of which the coolant is sprayed into the circumferential slots 15. This allows for particularly high cooling performance.In the presentation of the . Fig. 3 only some of the stator slots 19 are occupied with stator windings 10, but in reality, unlike this, all stator slots 19 are occupied with stator windings 10.

[0044] Fig. Figure 4 shows a schematic representation of a stator lamination stack 7b, in which the second stator laminations 9b have recesses 21 distributed around the circumference of the stator lamination stack 7b, forming several longitudinal channels 17 that connect several of the circumferential channels 16. The function of the longitudinal channels 17 formed by the recesses 21 corresponds to the function of the longitudinal channels 17 arranged in the stator housing 3. In this example, the circumferential grooves 15 extend over a circumferential angle α = 360° and are therefore annular in shape; however, they could also extend over a circumferential angle α < 360° and consequently be arc-shaped.

[0045] The Fig.Figure 5 shows the electric machine 1 installed in a vehicle 22. The vehicle 22 has two axles, one of which is driven. Optionally, both axles can be driven. Specifically, the electric machine 1 is connected to the half-axles 24 of the rear axle via an optional transmission 23. The driven wheels 25 are mounted on the half-axles 24. The vehicle 22 is driven at least partially or temporarily by the electric machine 1. That is, the electric machine 1 can serve as the sole drive for the vehicle 22 or, for example, be used in conjunction with an internal combustion engine (hybrid drive).

[0046] In conclusion, it is noted that the scope of protection is defined by the patent claims. However, the description and drawings are to be used to interpret the claims. The features depicted in the figures can be freely exchanged and combined. In particular, it is also noted that the devices shown may, in reality, comprise more or fewer components than depicted. In some cases, the devices shown, or their components, may also be depicted not to scale and / or enlarged and / or reduced in size. Reference symbol list 1 electric machine 2 machine housings 3 Stator housings 4 first warehouse sign 5 second warehouse sign 6 Stator 7, 7a, 7b Stator lamination stack 8 first stator lamination 9, 9a, 9b second stator lamination 10 Stator winding 11 Rotor 12 Rotor shaft 13 Rotor lamination package 14a, 14b (rolling) bearings 15 circumferential groove 16 circumferential channel 17 Longitudinal channel 18 stubs 19 Stator nut 20 Coolant distribution rail 21 Recess in stator lamination 22 vehicles 23 gearboxes 24 Half-axis 25 wheel α circumscribed angle b Groove width t groove depth A Rotor axis / Stator axis B radially recessed area C1, C2 radially increased area D Flow direction E axial center area F1, F2 axial end range

Claims

Stator lamination stack (7, 7a, 7b) for an electric machine (1), comprising several axially stacked first and second stator laminations (8, 9, 9a, 9b), characterized in that the stator lamination stack (7, 7a, 7b) has a circumferential groove (15) extending along its circumference, which is formed with one or more first stator laminations (8) which have a smaller radial extent in the region of the circumferential groove (15) than the second stator laminations (9, 9a, 9b) adjacent on both sides, wherein the circumferential groove (15) extends over a circumferential angle (α) of at least 270°. Stator lamination stack (7, 7a, 7b) according to claim 1 , characterized in that the circumferential groove (15) extends over a circumferential angle (α) of 360°. Stator lamination stack (7, 7a, 7b) according to claim 1 or 2, characterized in that the ratio of a slot width (b) to a slot depth (t) of the circumferential slot (15) is in a range of 0.8 to 1.

2. Stator lamination stack (7, 7a, 7b) according to one of the preceding claims, characterized in that the circumferential groove (15) has a rectangular, V-shaped or U-shaped cross-section. Stator lamination stack (7, 7a, 7b) according to one of the preceding claims, characterized by several circumferential grooves (15) corresponding to the circumferential groove (15). Stator lamination stack (7, 7a, 7b) according to claim 5, characterized in that the circumferential slots (15) are arranged in a central region (E) of the stator lamination stack (7, 7a, 7b) which extends axially from a first circumferential slot (15) to a last circumferential slot (15), wherein end regions (E) of the stator lamination stack (7, 7a, 7b) adjacent on both sides are free of circumferential slots (15) and wherein the axial length of the central region (E) is at most 50%, at most 60% or at most 80% of the axial length of the stator lamination stack (7, 7a, 7b). Stator lamination stack (7, 7a, 7b) according to claim 6, characterized in that the two end regions (E) differ in length by a maximum of 10%. Stator (6) for an electric machine (1), comprising a stator housing (3), a stator lamination stack (7, 7a, 7b) arranged in the stator housing (3) according to one of the preceding claims and stator windings (10) arranged on the stator lamination stack (7, 7a, 7b). Stator (6) according to claim 8, characterized in that the circumferential grooves (15) are at least partially radially closed with the stator housing (3). Stator (6) according to claim 8 or 9, characterized in that the stator housing (3) and / or the stator lamination stack (7, 7a, 7b) have an axial longitudinal channel (17) which connects several circumferential grooves (15). Electric machine (1) comprising a stator (6) according to one of claims 8 to 10, a rotor (11) rotatably arranged relative to the stator (6) and a cooling system configured to supply coolant into the circumferential grooves (15). Vehicle (22) with an electric machine (1) according to claim 11, which is provided for driving the vehicle (22). Method for operating an electric machine (1) according to claim 11, characterized in that the coolant is supplied to the circumferential grooves (15) via the cooling system. Method according to claim 13, characterized in that the coolant is supplied to the circumferential grooves (15) from above and flows downwards in the circumferential grooves (15) following the force of gravity. Method according to claim 13, characterized in that the coolant is supplied to the circumferential grooves (15) from below and flows upwards under overpressure in the circumferential grooves (15).

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