WO2026005693A1 - Electric machine and vehicle - Google Patents

Abstract

The disclosure concerns an electric machine (4) comprising a stator (20) and a rotor (22). The stator (20) comprises a stator core (26) arranged around the rotor (22) and is provided with teeth (27) and slots (28), windings (56) arranged in the slots (28), and a slot sealing element (32) arranged at a radially inner portion of each slot (28). The stator (20) is provided with a system (37) of cooling fluid channels, which are arranged in fluid communication with each other. The system (37) comprises radial cooling fluid channels (40) extending substantially radially and being arranged at the teeth (27), and axial cooling fluid channels (42) being arranged at the radially inner portion of at least some of the slots (28).

Description

Electric Machine and Vehicle

TECHNICAL FIELD

The invention relates to an electric machine and to a vehicle.

BACKGROUND

The electric machine industry has been undergoing significant transformations in recent years, driven by the growing demand for environmentally friendly transportation options. Electrically propelled vehicles have emerged as a viable alternative to traditional fossil-fuel- based modes of transport, with electric machines playing a crucial role in their operation.

In general, an electric machine comprises a stator and a rotor rotatable about a rotational axis in relation to the stator. The stator is provided with one or more windings comprising electrical conductors. An airgap is provided between the rotor and the stator. The windings within the stator are typically arranged in slots, which are provided between so-called teeth in a core of the stator. Outside the slots, the windings form so-called winding heads, located at the extreme ends of the stator core.

One of the key challenges facing electric machine designers is the need for effective cooling of electric machines. As power densities increase and operating temperatures rise, the risk of overheating and reduced performance becomes more pronounced. In addition, high- temperature operation of electric machines can lead to material degradation and decreased lifespan, making reliable cooling essential for maintaining optimal electric machine efficiency. Moreover, effective cooling enables the use of less costly materials in the electric machine.

The electrical conductors of the windings are heated by electric current flowing therethrough. Accordingly, the windings heat the stator.

The windings arranged in the slots in the stator core comprise insulation materials such as papers and sleeves to provide electric insulation between the electrical conductors of the windings and the stator core. Additionally, resins or glues may be used to fixate the windings and the insulation materials, providing extra electric insulation and resistance to vibration and mechanical loads that could otherwise affect the windings. Slot sealing elements, also known as slot wedges, are arranged at radially inner portions of the slots in the stator core. Each slot sealing element delimits a relevant slot from the airgap between the stator and the rotor.

The windings including the insulation materials within the slots presents an obstacle to effective cooling. The packed nature of the insulation materials and the resins or glues can impede the flow of coolant fluids along the windings, making it difficult to achieve adequate cooling of the windings in the slots.

The prior art has attempted to address this issue by incorporating features that enable indirect cooling of the windings by cooling the stator core and its teeth.

US 2019/0334413 discloses a system for cooling the teeth of a stator of an electric machine. The stator includes a stator core that may be formed of a plurality of laminations. Each lamination has a plurality of back iron apertures, a plurality of tooth tip apertures, and a plurality of elongated apertures. When the laminations are assembled to form the stator core, the back iron apertures align to form back iron inlet channels and back iron outlet channels, and the tooth tip apertures align to form tooth tip cooling channels. The elongated apertures are L-shaped and connect the back iron inlet channels and back iron outlet channels to the tooth tip channels. Cooling fluid may flow, for example, axially through a back iron inlet channel, azimuthally and radially inward through an elongated aperture to a tooth tip, axially along a tooth tip channel, and to a back iron outlet channel through another elongated aperture.

Magnetic fields are utilised in electric machines to drive the rotor when operated as an electric motor and to generate electric current in the windings when operated as a generator. In the electric machine of US 2019/0334413, magnetic flux in the teeth is negatively affected by the tooth tip cooling channels. Namely, at the axially extending tooth tip cooling channel, in a tooth, local increases of magnetic flux occur. Such local increases of magnetic flux can lead to saturation in the magnetic material of the tooth i.e., a state when an increase in applied external magnetic field cannot increase the magnetisation of the material further, so the total magnetic flux does not increase. Saturation in the magnetic material of the stator core is an undesired physical restriction of the electric machine, which leads to a less efficient electric machine.

SUMMARY As discussed above, the electric machine of US 2019/0334413 is provided with axial cooling channels in the respective teeth. This has either the disadvantage of disturbing the magnetic flux to cause local saturation if the cooling channels have a respective large cross-sectional area, i.e. is devised for efficient cooling of the teeth of the stator core, or the disadvantage of compromising efficient cooling of the teeth of the stator core if the teeth are optimised for even magnetic flux distribution, which entails small respective cross-sectional areas of the cooling channels that cause high pressure drop in the cooling fluid.

It would be advantageous to achieve an electric machine overcoming, or at least alleviating, at least some of the above-mentioned drawbacks of the US 2019/0334413 electric machine. In particular, it would be desirable to enable a cooling of the teeth of a stator core in an electric machine without causing local saturation in the magnetic material of the teeth. To better address one or more of these concerns, one or more of an electric machine and a vehicle having the features defined in one or more of the independent claims is provided.

According to an aspect, there is provided an electric machine comprising a stator and a rotor configured to rotate around a rotational axis in relation to the stator. The stator comprises a stator core arranged around the rotor and is provided with teeth and slots that extend in parallel with the rotational axis, windings arranged in the slots, and a slot sealing element arranged at a radially inner portion of each slot. The stator is provided with a system of cooling fluid channels, the cooling fluid channels of the system being arranged in fluid communication with each other. The system of cooling fluid channels comprises radial cooling fluid channels extending substantially radially to the rotational axis and being arranged at the teeth, and axial cooling fluid channels extending substantially in parallel with the rotational axis and being arranged at the radially inner portion of at least some of the slots.

Since the axial cooling fluid channels are arranged at the radially inner portion of at least some of the slots, the teeth of the stator core lack cooling fluid channels extending axially therethrough. Thus, the electric machine is configured for efficient cooling of the stator core and particularly its teeth via the radial cooling fluid channels. This is achieved without causing high local magnetic flux in the teeth, which would risk causing saturation of a magnetic material of the teeth.

It may be noted that the magnetic field in the teeth has a substantially radial direction, which means that the radial cooling fluid channels, even if arranged at least partially in the teeth causing some portions of the teeth to be narrower in a circumferential direction than other portions of the teeth, affect the performance of the electric machine to a significantly lower extent than the axial cooling fluid channels in the teeth of the electric machine of US 2019/0334413.

Namely, any local saturation of the magnetic material of the teeth at the present radial cooling fluid channels only affects the magnetic field in the teeth at portions where the radial cooling fluid channels are positioned. On the other hand, any local saturation of the magnetic material of the teeth at axially extending channels in the teeth, such as in the electric machine of US 2019/0334413, limits the magnetic flux in the entire tooth.

According to a further aspect there is provided a vehicle comprising a powertrain including an electric machine according to any one of aspects and/or examples discussed herein.

In line with the reasoning above, in use in the vehicle, within the electric machine conditions for efficient cooling of the stator core and its teeth without causing saturation in the magnetic material of the teeth are provided.

The electric machine may form part of a propulsive system of a vehicle. The electric machine may be operated as an electric motor to drive the vehicle and/or the electric machine may form a generator for transforming kinetic energy of the vehicle into electric power to be utilised for charging one or more batteries aboard the vehicle.

Electric energy may be provided to the electric machine from a battery aboard the vehicle or from a power source external of the vehicle, such as an overhead power line or a rail arranged in or at a surface, such as a road surface, travelled by the vehicle.

The stator and its stator core are stationary, e.g. in relation to a chassis of a vehicle wherein the electric machine is arranged. An airgap is provided between the stator and the rotor.

The teeth of the stator may form part of the stator core.

The teeth and the slots are arranged alternatingly, seen along a circumferential direction.

The rotor of the electric machine is directly or indirectly connected to an output shaft of the electric machine. For instance, the rotor of the electric machine may be connected to the output shaft via a transmission. During use of the electric machine, electric current flows through the windings arranged in the slots of the stator core. Portions of the windings extending in the slots are connected to each other via winding heads, which are portions of the windings that extend axially outside the stator core.

The windings comprise electrical conductors and may comprise insulation materials such as papers and sleeves to provide electric insulation between the electrical conductors of the windings and the stator core. Additionally, resins or glues may be used to fixate the windings and the insulation materials, providing extra electric insulation and resistance to vibration and mechanical loads that could otherwise affect the windings.

At least part of the stator core including its teeth is comprised of a magnetic material, such as a ferromagnetic material. The magnetic material has high magnetic permeability, i.e. it can easily become magnetised and support the formation and conduction of magnetic fields.

The system of cooling fluid channels may comprise further cooling fluid channels, such as cooling fluid channels arranged in the stator core outside the teeth and/or the slots. Alternatively, or additionally, the radial cooling fluid channels may extend radially through the stator cores to an outside of the stator core, wherein they are connectable to a supply of cooling fluid.

A cooling system may be arranged to provide a cooling fluid, such as oil, to the electric machine. The cooling system provides cooling fluid to the system of cooling fluid channels. The cooling system may comprise conduits, passages, paths, and the like for conducting the cooling fluid to, and optionally, from the system of cooling fluid channels.

During use of the electric machine, when the cooling system provides cooling fluid to the system of cooling fluid channels, the stator core is cooled by heat exchange with the cooling fluid.

The cooling system may be configured for cooling further portions of the electric machine.

Herein, the rotational axis of the rotor defines an axial extension, unless otherwise defined, axial, radial and circumferential directions/extensions mentioned herein relate to this axial extension. For instance, a radially inner portion of a slot is closer to the rotational axis than a radially outer portion of the slot. Any axial cooling fluid channels mentioned herein that extend substantially in parallel with the rotational axis means that the axial cooling fluid channels extend at an angle within a range of +/- 15 degrees to the rotational axis. The radial cooling fluid channels extending substantially radially to the rotational axis means that the radial cooling fluid channels extend at an angle within a range of +/- 15 degrees to a radial direction extending perpendicularly from the rotational axis.

Since the slot sealing elements are arranged at the radially inner portions of the slots, the axial cooling fluid channels may be at least partially enclosed or at least partially delimited by the slot sealing elements.

The slot sealing elements may be comprises of a non-magnetic material, such as aluminium. Thus, the slot sealing elements do not affect the magnetic field to any particular extent.

According to some examples, at least one of the axial cooling fluid channels may at least partially be delimited by at least a portion of one of the slot sealing elements. In this manner, the axial cooling fluid channels may be provided in conjunction with the slot sealing elements.

Thus, cooling fluid that during use of the electric machine is distributed through the radial cooling fluid channels in the teeth, may flow to and/or from the axial cooling fluid channels in/at the slot sealing elements to enable the distribution through the radial cooling fluid channels without the axial cooling fluid channels disturbing the magnetic field in the teeth.

According to some examples, the radial cooling fluid channels may be arranged to at least contribute to fluid communication to/from the axial cooling fluid channels. In this manner, the system of cooling fluid channels may be configured such that cooling fluid may flow between the axial cooling fluid channels and the radial cooling fluid channels.

Accordingly, the teeth of the stator core may be cooled by cooling fluid flowing to/from the axial cooling fluid channels during use of the electric machine.

According to some examples, at least one of the radial cooling fluid channels is at least partially delimited by at least a portion of one of the teeth. In this manner, the teeth of the stator core may be directly cooled by cooling fluid flowing through the radial cooling fluid channels during use of the electric machine. According to some examples, the system of cooling fluid channels may comprise further axial cooling fluid channels extending substantially in parallel with the rotational axis and/or circumferential cooling fluid channels, the further axial cooling fluid channels and/or the circumferential cooling fluid channels being arranged in the stator core at positions radially outside the teeth and/or the slots. In this manner, during use of the electric machine, cooling fluid may be conducted also through stator core outside the teeth and/or the slots in order to cool the stator core.

A further alternative of cooling the stator core may be to direct cooling fluid along a radially outer portion of the stator core. Such cooling fluid flowing along the radially outer portion of the stator core may flow into/out of radial cooling fluid channels arranged in the stator core radially outside the teeth and/or the slots.

Further features of, and advantages with, the invention will become apparent when studying the appended claims and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects and/or examples of the invention, including its particular features and advantages, will be readily understood from the examples discussed in the following detailed description and the accompanying drawings, in which:

Fig. 1 illustrates examples of a vehicle configured for land-based propulsion,

Figs. 2a - 2e schematically illustrate portions of electric machines according to examples, Fig. 3 schematically illustrates a cooling system according to some examples,

Fig. 4 schematically illustrates a portion of a system of cooling fluid channels of an electric machine and a cooling system, and

Figs. 5a - 5d schematically illustrate cross-sections of slots and teeth of example electric machines.

DETAILED DESCRIPTION

Aspects and/or examples of the invention will now be described more fully. Like numbers refer to like elements throughout. Well-known functions or constructions will not necessarily be described in detail for brevity and/or clarity.

Fig. 1 illustrates examples of a vehicle 2 configured for land-based propulsion. Fig. 1 represents a schematic sectional top view of the vehicle 2. The vehicle 2 comprises one or more electric machines 4 according to aspects and/or examples discussed herein, such as the electric machine 4 discussed below with reference to Figs. 2a - 5.

In these examples, the vehicle 2 is a heavy load vehicle in the form of a truck. However, the invention is not limited to any particular type of vehicle configured for land-based propulsion. The vehicle 2 may be e.g., a bus, a truck, a heavy truck, a car, or a train. The vehicle may also be of another type. The vehicle 2 may be an electric vehicle, EV, for example a hybrid vehicle or a hybrid electric vehicle, HEV, or a battery electric vehicle, BEV. It is to be noted that the herein discussed electric machine may be utilised in further means of transportation, such as in boats or other marine vessels.

The one or more electric machines 4 may be configured for propelling the vehicle 2. The one or more electric machines 4 may be configured for charging one or more electric battery cells 8 and/or one or more electrical battery packs 12.

The vehicle 2 may comprise a powertrain 10, for example configured for one of an EV, HEV and BEV. The vehicle 2 may comprise one or more electrical battery packs 12 including two or more electric battery cells 8. The electrical battery pack 12 may be attachable to a chassis of the vehicle 2. The vehicle 2 may include further electrical and/or mechanical components e.g., a combustion engine 14, as transmission, and other devices required for a vehicle 2, such as for an EV, HEV, or BEV.

The powertrain 10 and/or the one or more electric machines 4 is/are configured to propel, or drive, the vehicle 2. The powertrain 10 may include the electrical battery pack 12. The one or more electric machines 4 may be arranged in other positions of the vehicle 2 than shown in Fig. 1. For example, in connection with one or more wheels 16 of the vehicle 2, or in connection with the combustion engine 14 to operate as an electric generator.

According to a further example, the electric machine 4 may form part of a compact powertrain provided directly in connection with an axle beam 19 of the vehicle 2, via inter alia a transmission, a differential, and drive shafts, all provided in connection with the axle beam 19, the electric machine 4 provides propulsive power to drive wheels 16 of the vehicle 2.

The vehicle 2 may comprise an electrical system 18. The electrical system 18 may be configured for direct current. The electrical system 18 may be a low voltage system such as a 24 Volt system. The electrical system 18 may be a higher voltage system configured for a high voltage such as 48 V or a voltage of 60 V or above for example, above 400 V, or above 450 V, such as above 650 V. For example, the high voltage system may be configured for a voltage up to 1500 V and/or for a voltage above 1500 V. The electric power, or the electric current, for example the direct current, of the electrical system 18 may be transferred for example, at one or more of the voltage levels mentioned above.

The electrical system 18 may be electrically connected, or connectable, to one or more electrical battery packs 12. The electrical battery packs 12 may be configured for one or more of the voltage levels mentioned above.

The electrical system 18 may be configured to electrically connect the electrical battery pack 12 to the powertrain 10 of the vehicle 2. The electrical system 18 may be configured to electrically connect the electrical battery pack 12 to the one or more electric machines 4 of the vehicle 2. The electrical system 18 may be configured to transfer electric power, or electric current, e.g., between the one or more electric machines 4 and/or the powertrain 10 and/or the electrical battery pack 12.

Alternatively, the electrical system 18 may be configured for alternating current. A further option may be for the electrical system 18 to be configured in part for direct current and in part for alternating current.

According to some examples, the electrical system 18 may be fed from an electrical power source external of the vehicle 2, such as an overhead power line or a powered rail arranged in, or at, a road surface.

Figs. 2a - 2e schematically illustrate portions of electric machines 4 according to examples. Fig. 2a shows an isometric view of a stator 20 and a rotor 22 of an electric machine 4. Fig. 2b illustrates a perspective view of a portion of an electric machine 4. Figs. 2c - 2e show close-up cross-sectional views of inter alia the stator 20 of respective electric machines 4 according to different examples. The cross sections of Figs. 2c - 2e extend perpendicularly to a rotational axis of the electric machine 4.

More specifically, what is shown in Figs. 2a and 2b applies to all examples of the electric machine 4. What is shown in Figs. 2c - 2e applies to all examples of the electric machine 4 with the exception of a system 37 of cooling fluid channels, of which system 37 various examples are discussed with reference to respective of Figs. 2c - 2e, see further below. The electric machine 4 may be comprised in a vehicle, such as a vehicle 2 discussed above with reference to Fig. 1. Accordingly, in the following reference is also made to Fig. 1.

The electric machine 4 may be operated as an electric motor e.g., for propelling the vehicle 2 and/or as an electric generator e.g., for charging one or more electric battery cells 8 and/or one or more electrical battery packs 12.

The electric machine 4 comprises a stator 20 and a rotor 22 arranged to rotate about a rotational axis 24 in relation to the stator 20.

The stator 20 comprises a stator core 26 arranged around the rotor 22. The stator core 26 is provided with axially extending teeth 27 and slots 28. Each slot 28 extends in parallel with the rotational axis 24 of the electric machine 4, i.e., the rotational axis 24 of the rotor 22 of the electric machine 4. Each tooth 27 extends in parallel with the rotational axis 24. The teeth 27 and the slots 28 are alternatingly arranged along a circumferential extension at a radially inner portion of the stator core 26.

Stator windings (not shown) are arranged in the slots 28, see further with reference to Figs. 5a - 5d. The stator windings, or herein also referred to as the windings, include winding heads (not shown) at axial ends of the stator core 26.

In a known manner, during use of the electric machine 4, an electric current flows through the windings to rotate the rotor 22 when the electric machine 4 is operated as an electric motor, or generated by the electric machine 4 when the electric machine 4 is operated as a generator and the rotor 22 is rotated e.g., by a forward momentum of the vehicle 2.

When the electric machine 4 is operated as an electric machine, electric current is fed from the one or more electric battery packs 12 to the windings. When the electric machine 4 is operated as a generator, electric current is fed from the windings to the one or more electric battery packs 12.

The rotor 22 may include one or more permanent magnets. Thus, the electric machine 4 may be a permanent magnet, PM, machine. According to alternative examples, the electric machine 4 may be configured to operate according to other electrical operation schemes for electric machines. For example, the rotor 22 may include one or more rotor windings. Conventional electrical operation schemes for electric machines are known to the skilled person and thus, are not discussed herein in further detail. A slot sealing element 32 is arranged at a radially inner portion of each slot 28. The slot sealing elements 32 form a barrier between the slots 28 and an airgap 34 provided between the stator 20 and the rotor 22, see Fig. 2c.

The slot sealing elements 32 are directly or indirectly mounted to the stator care 26. In the illustrated examples, the slot sealing elements 32 are mounted in axially extending recesses

36 provided in the stator core 26 on circumferentially opposed sides of each slot 28 i.e. , recesses 36 provided in the teeth 27 of the stator core 26.

The stator 20 is provided with a system 37 of cooling fluid channels. The cooling fluid channels of the system 37 are arranged in fluid communication with each other. The system

37 of cooling fluid channels extends through parts of the stator core 26 and through at least some of the slot sealing elements 32.

During use of the electric machine 4, a cooling fluid flows through the system 37 of cooling fluid channels to cool the stator 20 and also to cool the windings, directly or indirectly.

The system 37 of cooling fluid channels comprises radial cooling fluid channels 40 extending substantially radially to the rotational axis 24. The radial cooling fluid channels 40 are arranged at the teeth 27. In the examples of Figs. 2c - 2d, the radial cooling fluid channels 40 are shown to extend through the teeth 27. Alternative ways of arranging the radial cooling fluid channels 40 at the teeth 27 are discussed below with reference to Figs. 5a - 5d.

In Fig. 2c, examples of different arrangements of the radial cooling fluid channels 40 at the teeth 27 are shown. In two of the teeth 27 one radial cooling fluid channel 40 is arranged in a particular cross-section, perpendicularly to the rotational axis 24, of the relevant tooth 27. In one of the teeth 27 two radial cooling fluid channels 40 are arranged in a particular crosssection of the relevant tooth 27. The radial cooling fluid channels 40 may have any suitable cross-sectional shapes such square, rectangular, round, or oval.

In practice, one or more of such arrangements of the radial cooling fluid channels 40 exemplified in Fig. 2c may be provided for the radial cooling fluid channels 40 of the electric machine 4.

Furthermore, according to some examples, not all of the teeth 27 of the stator core 26 are provided with radial cooling fluid channels 40, see further below. The system 37 of cooling fluid channels comprises axial cooling fluid channels 42 extending substantially in parallel with the rotational axis 24. The axial cooling fluid channels 42 are arranged at the radially inner portion of at least some of the slots 28. For instance, the axial cooling fluid channels 42 may be arranged at the radially inner portion of every slot 28 or of every second slot 28 or of every third slot 28 or even farther in between e.g., depending on whether the radial cooling fluid channels 40 are arranged in each tooth 27 or in only some of the teeth 27 and/or whether the electric machine 4 is provided with further cooling arrangements.

In the illustrated example of Fig. 2c, the axial cooling fluid channels 42 are arranged at every slot 28. However, as realised from the discussion below, in order to supply cooling fluid to the radial cooling fluid channels 40 in each of the teeth 27, providing axial cooling fluid channels 42 at every second slot 28 suffices.

To further elaborate on examples of radial and axil cooling fluid channels 40, 42 - cooling of the windings in the slots 28 may be achieved from only one of the two teeth 27 adjacent to a relevant slot 28. In such case, every third tooth 27 may not be provided with any radial cooling fluid channel 40 and accordingly, the axial cooling fluid channels 42 may be arranged at the radially inner portion of every third slot 28.

The axial cooling fluid channels 42 are provided in connection with the slot sealing elements 32. Further, examples of this are discussed below with reference to Figs. 5a - 5d.

In addition to the radial and axial cooling fluid channels 40, 42 the system 37 of cooling fluid channels may comprise further cooling fluid channels arranged in the stator core 26 at positions radially outside the teeth 27 and/or the slots 28. Two such examples are shown in Figs. 2c and 2d. A further alternative is for the radial cooling fluid channels 40 to extend to a radially outer side 39 of the stator core 26, as in the example of Fig. 2e.

In the example of Fig. 2c, the system 37 of cooling fluid channels comprises further axial cooling fluid channels 38 extending substantially in parallel with the rotational axis 24. The further axial cooling fluid channels 38 are arranged in the stator core 26 at positions radially outside the teeth 27 and/or the slots 28. In the cross-sectional view of Fig. 2c, perpendicularly to the rotational axis 24, examples of cross-sections of the further axial cooling fluid channels 38 are shown, square and rectangular cross-sections. The further axial cooling fluid channels 38 may have other cross-sectional shapes than shown, such as round or oval cross-sections.

In the example of Fig. 2d, the system 37 of cooling fluid channels comprises circumferential cooling fluid channels 41 extending in the stator core 26, at least partially around the rotational axis 24. The circumferential cooling fluid channels 41 are arranged in the stator core 26 at positions radially outside the teeth 27 and/or the slots 28. The circumferential cooling fluid channels 41 are arranged at least partially in parallel with each other at an axial distance from each other. The circumferential cooling fluid channels 41 may have any suitable cross-sectional shapes such as square, rectangular, round, or oval.

In the example of Fig. 2e, the radial cooling fluid channels 40 extend to the radially outer side 39 of the stator core 26. For instance, in such examples, during use of the electric machine 4, at least a portion of the radially outer side 39 of the stator core 26 may be arranged in direct contact with cooling fluid. Accordingly, cooling fluid may be supplied from the radially outer side 39 to the radial cooling fluid channels 40 and/or from the radial cooling fluid channels 40 to the radially outer side 39 of the stator core 26.

In Fig. 2c, various examples of the fluid communication between the cooling fluid channels of the system 37 of cooling fluid channels including further axial cooling fluid channels 38 are schematically shown in one cross section of the electric machine 4 perpendicularly to the rotational axis 24. For a particular cross-section perpendicularly to the rotational axis 24, the axial cooling fluid channels 42 and the furth axial cooling fluid channels 38 may communicate via one radial cooling fluid channel 40. For a particular cross-section of the electric machine 4 perpendicularly to the rotational axis 24, the axial cooling fluid channels 42 arranged at two neighbouring slots 28 may communicate with a further axial cooling fluid channel 38 via one radial cooling fluid channel 40 in the tooth 27 arranged between the two neighbouring slots 28. For a particular cross-section of the electric machine 4 perpendicularly to the rotational axis 24, the axial cooling fluid channels 42 arranged at two neighbouring slots 28 may communicate with a further axial cooling fluid channel 38 via two separate radial cooling fluid channels 40 in the tooth 27 arranged between the two neighbouring slots 28. A further nonshown example may be for at a particular cross-section of the electric machine 4 perpendicularly to the rotational axis 24, the axial cooling fluid channels 42 arranged at two neighbouring slots 28 to communicate with two further axial cooling fluid channels 38 via two separate radial cooling fluid channels 40 in the tooth 27 arranged between the two neighbouring slots 28. In Fig. 2d, one example of the fluid communication between the cooling fluid channels of the system 37 of cooling fluid channels including circumferential cooling fluid channels 41 is shown in one cross section of the electric machine 4 perpendicularly to the rotational axis 24. For a particular cross-section perpendicularly to the rotational axis 24, the axial cooling fluid channels 42 and the circumferential cooling fluid channels 41 communicate via one radial cooling fluid channel 40 in each tooth 27. According to further non-shown examples, for a particular cross-section perpendicularly to the rotational axis 24, the axial cooling fluid channels 42 and each of the circumferential cooling fluid channels 41 communicates via radial cooling fluid channel 40 in only some of the teeth 27.

Various alternative ways of arranging the axial cooling fluid channels 42 at the slot sealing elements 32 are discussed below with reference to Figs. 5a - 5d.

Fig. 3 schematically illustrates a cooling system 44 according to some examples. The cooling system 44 is configured for cooling at least a portion of an electric machine 4 such as the electric machine 4 discussed herein, e.g. with reference to Figs. 2a- 2e and 4 - 5d.

Accordingly, in the following reference is also made to Figs. 2a - 2e and 4 - 5d.

The cooling system 44 is presented as an example of a cooling system configured for supplying cooling fluid to the system 37 of cooling fluid channels of the electric machine 4 discussed herein.

The cooling system 44 comprises conduits 46. During operation of the cooling system 44, a pump 48 is configured to pump coolant from a reservoir 50 via a heat exchanger 52 to the electric rotating machine 4 and back to the reservoir 50 via the conduits 46. The reservoir 50 forms a reservoir for cooling fluid. In the heat exchanger 52, the cooling fluid is cooled by a further fluid, such as ambient air or a water-based coolant.

The cooling system 44 may be configured for cooling at least a portion of the stator 20 of the electric machine 4 but may be configured for general cooling of the stator 20. A cooling fluid, such as oil or an oil mixture, is directed to the system 37 of cooling fluid channels in order to cool at least a portion of the stator core 26 of the electric machine and at least indirectly, its windings.

Fig. 4 schematically illustrates a portion of a system 37 of cooling fluid channels of an electric machine and a cooling system 44. The electric machine may be an electric machine 4 as discussed with reference to Figs. 1 - 2c and 5a - 5d. The cooling system 44 may be a cooling system 44 as discussed with reference to Fig. 3. Accordingly, in the following reference is also made to the discussions of Figs. 1 - x.

Again, the system 37 of cooling fluid channels comprises radial cooling fluid channels 40 arranged at the teeth 27, and axial cooling fluid channels 42 arranged at the radially inner portion of at least every second slot 28.

In Fig. 4, the system 37 of cooling fluid channels is shown including further axial cooling fluid channels 38. However, the system 37 may alternatively, or additionally, include circumferential cooling fluid channels 41, as discussed above. A further alternative may be for at least some of the radial cooling fluid channels 37 to extend to the radially outer side 41 of the stator core 26, as discussed above.

Within the system 37 of cooling fluid channels , the radial cooling fluid channels 40 are arranged to at least contribute to fluid communication between the axial cooling fluid channels 42 and the further axial cooling fluid channels 38 and/or between the axial cooling fluid channels 42 and the circumferential cooling fluid channels 41 and/or between the axial cooling fluid channels 42 and the outer side of the stator core 26.

The cooling system 44 is arranged in fluid communication with the system 37 of cooling fluid channels . For instance, as shown in Fig. 4, the cooling fluid is supplied from the cooling system 44 to the further axial cooling fluid channels 38 and cooling fluid is returned to the cooling system 44 via the axial cooling fluid channels 42. Alternatively, the cooling fluid may be supplied from the cooling system 44 to the axial cooling fluid channels 42 and cooling fluid may be returned to the cooling system 44 via the further axial cooling fluid channels 38. Other way of supplying and returning the cooling fluid to/from the system 37 of cooling fluid channels may be utilised.

The radial cooling fluid channels 40 may be fluidly connected to the axial cooling fluid channels 42 via at least partially circumferentially extending channels 54. See further below with reference to Figs. 5a - 5d.

Figs. 5a - 5d schematically illustrate cross-sections of slots 28 and teeth 27 of example electric machines. The electric machines may be electric machines 4 as discussed herein. Accordingly, in the following reference is also made to the discussions of Figs. 1 - 4. The cross-sections of Figs. 5a - 5d extend perpendicularly to the rotational axes 24 of the electric machines 4. Figs. 5a - 5d are shown as examples of the radial cooling fluid channels 40 and the axial cooling fluid channels 42 of the system 37 of cooling fluid channels and as examples of the extension at the teeth 28 and the radial inner portions of the slots 28.

Again, windings 56 are arranged in the slots 28. In a known manner, the windings 56 include electrical conductors and electrical insulation material. Also, within the slots 28, resins or glues are used to fixate the windings 56, providing extra electric insulation and resistance to vibration.

During use of the electric machine 4, cooling fluid flowing through the radial cooling fluid channels 40 cool the teeth 27 of the stator core 26. Moreover, the cooling fluid in the radial cooling fluid channels 40 cools portions of the windings 56 either indirectly via the teeth 27 as in the examples of Figs. 5a - 5c or directly as in the example of Fig. 5d. Further, the windings 56 may be cooled by cooling fluid flowing along the axial cooling fluid channels 42. Either indirectly as in the examples of Figs. 5a, 5b, and 5d or portions of the windings 56 being directly cooled such as in the example of Fig. 5c.

In the following discussions of Figs. 5a - 5d, mention is made of one, or at least one, axial cooling fluid channel 42 and/or one, or at least one, radial cooling fluid channel 40. However, more than one, such as all, axial cooling fluid channels 42 and/or more than one, such as all, radial cooling fluid channels 40 of the electric machine may be of the exemplified kind.

According to some examples, at least one of the axial cooling fluid channels 42 may be at least partially delimited by at least a portion of one of the slot sealing elements 32. In this manner, the axial cooling fluid channels 42 may be provided in conjunction with the slot sealing elements 32 at e.g., at least some of the slots 28.

Such examples are shown in each of Figs. 5a - 5d.

According to some examples, at least one of the axial cooling fluid channels 42 may be partially delimited by a portion of the windings 56. In this manner, the axial cooling fluid channel 42 may be delimited while also direct cooling of a portion of the windings 56, such as a portion of the radially innermost windings 56 is provided.

In such examples, the slot sealing element 32 may have a generally U-shaped cross-section with an open end of the U-shaped cross-section facing the windings 56. One such example is shown in Fig. 5c.

According to some examples, at least one of the axial cooling fluid channels 42 may be partially delimited by surface portions 58 of two of the teeth 27. In this manner, surface portions 58 of each of two teeth 27, forming therebetween a slot 28, may partially delimit axial cooling fluid channels 42.

In Fig. 5b, one of the surface portions 58 of the two teeth is shown at a righthand side of the axial cooling fluid channel 42. The surface portion 58 at a lefthand side in Fig. 5b is not visible in the shown cross-section but is simply indicated.

According to such examples, at least one of the slot sealing elements 32 may comprise a first member 60 and a second member 62, the first and second members 60, 62 being separate from each other and being arranged at a radial distance from each other in one of the slots 28. One of the axial cooling fluid channel 42 may be formed between the first and second members 60, 62. In this manner, the axial cooling fluid channel 42 may be provided in an uncomplicated manner between the teeth 27 and the first and second member 60, 62.

One such example is shown in Fig. 5b.

According to some examples, at least one of the axial cooling fluid channels may be delimited by one of the slot sealing elements 32, only. In this manner, one or more of the slot sealing elements 32 may each delimit one axial cooling fluid channel 42 in its entirety.

Such examples are shown in each of Figs. 5a and 5d.

According to some examples, at least one of the radial cooling fluid channels 40 may be at least partially delimited by at least a portion of one of the teeth 27.

Such examples are shown in each of Figs. 5a - 5d.

According to some examples, at least one of the radial cooling fluid channels 40 may be partially delimited by a portion of the windings 56. In this manner, cooling fluid may flow in direct heat exchange along portions of the windings 56.

One such example is shown in Fig. 5d. According to some examples, at least one of the radial cooling fluid channels 40 may be delimited by one of the teeth 27, only. In this manner, one or more of the teeth 27 may each delimit one or more radial cooling fluid channel 40 in its/their entirety/ies.

Such examples are shown in each of Figs. 5a - 5c.

According to some examples, at least one of the teeth 27 may be provided with a radially extending recess 64, and one of the radial cooling fluid channels 40 may extend along the recess 64. In this manner, at least one of the radial cooling fluid channels 40 may be provided between the recess 64 in the tooth 27 and a portion of the windings 56 in an adjacent slot 28.

One such example is shown in Fig. 5d.

The recess 64 extends in radial and circumferential directions from the adjacent slot 28 into the tooth 27.

According to some examples, the radial cooling fluid channels 40 may be arranged in fluid communication with the axial cooling fluid channels 42 via at least partially circumferentially extending channels 54. The at least partially circumferentially extending channels 54 may extend through the slot sealing elements 32 and/or through the teeth 27. In this manner, the radial cooling fluid channels 40 may be arranged in fluid communication with the axial cooling fluid channels 42.

Such examples are shown in each of Figs. 5a - 5d.

The at least partially circumferentially extending channels 54 may extend at a tangent to a circumferential direction, such as in the examples of Figs. 5a, 5c, and 5d, or at an angle to a tangent to a circumferential direction, such as in the example of Fig. 5b.

Alternatively, the radial cooling fluid channels 40 may directly connect to the axial cooling fluid channels 42. Mentioned purely as an example this may be provided in a non-shown example combining the recesses 64 of the Fig. 5d example with the slot sealing element 32 of the Fig. 5b example, which comprises the first and second members 60, 62. Even further combinations of the exemplified radial cooling fluid channels 40 and the axial cooling fluid channels 42 than shown in the respective of Figs. 5a - 5d may be provided in an electric machine 4.

The terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms "comprises," "comprising," "includes," and/or "including" when used herein specify the presence of stated features, integers, actions, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, actions, steps, operations, elements, components, and/or groups thereof.

It will be understood that, although the terms first, second, etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the scope of the present disclosure.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

It is to be understood that the foregoing is illustrative of various examples and that the invention is defined only by the appended claims. A person skilled in the art will realize that the examples may be modified, and that different features of the examples may be combined to create examples other than those described herein, without departing from the scope of the invention, as defined by the appended claims.

Claims

1. An electric machine (4) comprising a stator (20) and a rotor (22) configured to rotate around a rotational axis (24) in relation to the stator (20), wherein the stator (20) comprises a stator core (26) arranged around the rotor (22) and is provided with teeth (27) and slots (28) that extend in parallel with the rotational axis (24), windings (56) arranged in the slots (28), and a slot sealing element (32) arranged at a radially inner portion of each slot (28), wherein the stator (20) is provided with a system (37) of cooling fluid channels, the cooling fluid channels of the system (37) being arranged in fluid communication with each other, and wherein the system (37) of cooling fluid channels comprises radial cooling fluid channels (40) extending substantially radially to the rotational axis (24) and being arranged at the teeth (27), and axial cooling fluid channels (42) extending substantially in parallel with the rotational axis (24) and being arranged at the radially inner portion of at least some of the slots (28).

2. The electric machine (4) according to claim 1, wherein at least one of the axial cooling fluid channels (42) is at least partially delimited by at least a portion of one of the slot sealing elements (32).

3. The electric machine (4) according to claim 1 or 2, wherein at least one of the axial cooling fluid channels (42) is partially delimited by a portion of the windings (56).

4. The electric machine (4) according to any one of the preceding claims, wherein at least one of the axial cooling fluid channels (42) is partially delimited by surface portions of two of the teeth (27).

5. The electric machine (4) according to claim 4, wherein at least one of the slot sealing elements (32) comprises a first member (60) and a second member (62), the first and second members (60, 62) being separate from each other and being arranged at a radial distance from each other in one of the slots (28), and wherein one of the axial cooling fluid channels 42 is formed between the first and second members (60, 62).

6. The electric machine (4) according to claim 1 or 2, wherein at least one of the axial cooling fluid channels (42) is delimited by one of the slot sealing elements (32), only.

7. The electric machine (4) according to any one of the preceding claims, wherein the radial cooling fluid channels (40) are arranged to at least contribute to fluid communication to/from the axial cooling fluid channels (42).

8. The electric machine (4) according to any one of the preceding claims, wherein at least one of the radial cooling fluid channels (40) is at least partially delimited by at least a portion of one of the teeth (27).

9. The electric machine (4) according to any one of the preceding claims, wherein at least one of the radial cooling fluid channels (40) is partially delimited by a portion of the windings (56).

10. The electric machine (4) according to claim 8, wherein at least one of the radial cooling fluid channels (40) is delimited by one of the teeth (27), only.

11. The electric machine (4) according to claim 9, wherein at least one of the teeth (27) is provided with a radially extending recess (64), and wherein one of the radial cooling fluid channels (40) extends along the recess (64).

12. The electric machine (4) according to any one of the preceding claims, wherein the radial cooling fluid channels (40) are arranged in fluid communication with the axial cooling fluid channels (42) via at least partially circumferentially extending channels (54), and wherein the at least partially circumferentially extending channels (54) extend through the slot sealing elements (32) and/or through the teeth (27).

13. The electric machine (4) according to any one of the preceding claims, wherein the system (37) of cooling fluid channels comprises further axial cooling fluid channels (38) extending substantially in parallel with the rotational axis (24) and/or circumferential cooling fluid channels (41), the further axial cooling fluid channels (38) and/or the circumferential cooling fluid channels (41) being arranged in the stator core (26) at positions radially outside the teeth (27) and/or the slots (28).

14. A vehicle (2) comprising a powertrain (10) including an electric machine (4) according to any one of the preceding claims.