Assembly comprising a rotating electrical machine and a machine casing having axial channels

Abstract

Assembly comprising a rotating electrical machine extending along a longitudinal axis X and a machine casing (10) intended to house the rotating electrical machine, the rotating electrical machine comprising at least one stator. The machine casing (10) comprises a zone intended to receive the stator, comprising an inner surface (14) having a plurality of axial channels (16) extending along the longitudinal axis X, distributed around the stator and intended for the circulation of a cooling fluid. At least two channels of the plurality of axial channels (16) have different cross-sectional areas in a cross-section perpendicular to the longitudinal axis X.

Description

[0001] Description

[0002] Title: Assembly comprising a rotating electrical machine and a machine housing having axial channels

[0003] The present invention claims priority from French application 2503239 filed on March 28, 2025, the content of which (text, drawings and claims) is incorporated herein by reference.

[0004] technical field

[0005] The present invention relates to the field of cooling systems for rotating electrical machines. A cooling fluid is generally used to limit heat losses due to friction, particularly in the stator of the electrical machine and in the gearbox.

[0006] The machines can be synchronous or asynchronous, and alternating current. They can be traction or propulsion machines for electric (Battery Electric Vehicle) and / or hybrid (Hybrid Electric Vehicle - Plug-in Hybrid Electric Vehicle) motor vehicles, such as passenger cars, vans, trucks, or buses. The invention also applies to rotating electrical machines for industrial and / or power generation applications, particularly in the marine, aeronautical, or wind power sectors.

[0007] Previous technique

[0008] The cooling of the stator of an electrical machine by a cooling fluid is generally divided into two parts: the cooling of the active part of the stator consisting of the stator lamination packs and the cooling of the coil heads.

[0009] In most current configurations, the cooling of the active part relies on a gravity flow of the cooling fluid, which runs over the stator laminations before being discharged.

[0010] However, this approach has its limitations, because the cooling fluid generally fails to completely cover the surface of the active part.

[0011] Among the known solutions for coolant circuits used to cool the stator, the most common method involves injecting coolant onto the top of the stator laminations, allowing the fluid to trickle down onto the active part. However, this method has the drawback that some of the laminations do not come into contact with the coolant, thus reducing the cooling efficiency of the active part. It also potentially necessitates the addition of a component to distribute the coolant evenly over the laminations.

[0012] Another commonly used method involves cooling the active part using channels cut into the stator laminations. However, this solution has several drawbacks. To maintain the performance of the electric machine and the mechanical strength of the stator, the channels must remain very narrow, which results in significant pressure losses in the system and reduces the heat exchange surface area between the laminations and the cooling fluid. Furthermore, achieving precise alignment of the channels, cut directly into each lamination, can be complex.

[0013] Document WO 2024 / 105210 A1 describes a housing with internal grooves that allow the coolant to circulate in a zigzag pattern around the circumference of the stator. The presence of only one inlet and one outlet for the coolant does not allow for optimal stator cooling.

[0014] Documents EP 4254744 Al, EP 3 944463 Al and WO 2022 / 052848 Al disclose a machine housing having axial cooling fluid flow channels all having the same cross-section and therefore not taking into account the different volumes of cooling fluid that may flow in the different channels.

[0015] US patent 2025 / 0007338 Al discloses a circular part separate from the housing and containing a fluid passage. The part supplies a distributor having axial channels along the stator. As in the three previous patents, the axial channels all have the same cross-section.

[0016] Document EP 3 913 769 Al discloses a machine housing with internal circumferential grooves that cooperate with spaced grooves on the circumference of the stator. The housing does not have axial grooves of different cross-sections that are self-sufficient, i.e., do not need to be combined with grooves on the stator.

[0017] US patent 2022 / 0140697 Al discloses a cylindrical housing enclosing the stator and featuring a plurality of studs and grooves. A cooling fluid enters through a central opening on the top of the housing and circulates circumferentially between the housing and the stator laminations. Such a configuration is expensive and significantly increases pressure losses. There is a need for a simple and economical solution to optimize heat exchange between the cooling fluid and the stator laminations of an electrical machine, by substantially increasing the contact area between the cooling fluid and the active part of the stator to prevent localized overheating, and by accelerating the axial flow of the cooling fluid to improve the homogeneity of its distribution around the stator laminations, thus ensuring better cooling efficiency.

[0018] Summary of the invention

[0019] The invention aims to meet all or part of this need and achieves this, according to one of its aspects, through an assembly comprising a rotating electrical machine extending along a longitudinal axis X and a machine housing intended to house the rotating electrical machine, the rotating electrical machine comprising at least one stator, the machine housing comprising an area intended to receive the stator having an internal surface,

[0020] the inner surface of the machine casing comprising a plurality of axial channels extending along the longitudinal axis X, distributed around the stator and intended for the circulation of a cooling fluid,

[0021] at least two channels from the plurality of axial channels having different surfaces in a cross-section perpendicular to the longitudinal axis X.

[0022] By "different surfaces in a cross-section", we mean that the surfaces of the sections of the cooling fluid passage taken in a cross-section are different.

[0023] The rotating electrical machine may further comprise at least one rotor. The longitudinal axis X is the axis of rotation of the rotor.

[0024] Advantageously, the height or thickness of the axial channels, that is, their radial dimension, is varied, but their circumferential dimension is not modified. This avoids affecting the extent of the contact areas between the cooling fluid and the stator.

[0025] The invention has many advantages.

[0026] Thanks to the fact that the surfaces of the axial channel sections differ from each other, because they are chosen to take into account the pressure of the cooling fluid as well as the positions of the inlet and outlet of the cooling fluid, the invention makes it possible to obtain a homogeneous distribution of the cooling fluid around the stator laminations and in contact with them, thus promoting homogeneous and efficient cooling of the active part of the stator.

[0027] In addition, it optimizes heat exchange between the cooling fluid and the stator laminations by substantially increasing the contact area between the fluid and the laminations and accelerating the axial flow of the fluid, thus ensuring better cooling efficiency.

[0028] Furthermore, pressure losses are reduced because axial channels in the casing can have a larger cross-sectional area than channels integrated into the stator laminations, thus allowing a higher flow rate of cooling fluid to pass through.

[0029] Moreover, the solution proposed by the invention is inexpensive, in particular because it does not require the addition of any parts and can be implemented directly in the foundry.

[0030] Description of the invention

[0031] The coolant can be a liquid, including oil.

[0032] The plurality of axial channels can be adapted to guide the cooling fluid in a single direction parallel to the longitudinal X axis. This helps to avoid pressure losses.

[0033] The separation between the axial channels occurs between the machine housing and the stator, which is simply guided and not shrink-fitted onto the channels. The axial channels are in fact delimited by the stator laminations and by the shape of the machine housing.

[0034] The machine housing may also include, at one end of the area intended to receive the stator, a feed ring located at the inlet of the axial channels, adapted to distribute the cooling fluid, cooled by a heat exchanger, to the plurality of axial channels. When the electric machine also includes a gearbox, the feed ring is also adapted to distribute the cooled fluid to supply outlets for gearbox lubrication.

[0035] The feed ring can be formed between the inner diameter of the machine housing and the outer diameter of the stator.

[0036] The machine casing may also include, at a second end of the area intended to receive the stator, a recovery ring arranged at the outlet of the axial channels, adapted to collect and evacuate the cooling fluid heated by the thermal losses of the active part of the stator to an evacuation outlet equipped with a pump.

[0037] The feed ring and the retrieval ring interconnect the plurality of axial channels.

[0038] Alternatively, the output of the axial channels can be configured differently, without a recovery ring.

[0039] The plurality of axial channels can have as many inputs at the feed ring as outputs at the recovery ring. This helps to avoid pressure losses.

[0040] In a particular embodiment where the machine housing comprises a main housing and a closing housing, the recovery ring can be formed between the main housing and the closing housing.

[0041] The recovery ring can be formed between the inner diameter of the main housing and the outer diameter of the closing housing.

[0042] The feed ring and the recovery ring can be formed in the machine housing.

[0043] The plurality of axial channels can be formed within the thickness of the machine housing. They can thus be directly integrated into the casting of the machine housing, without the need to provide additional channels in the stator sheets.

[0044] In a particular embodiment where the machine housing is intended to also house a reducer, the axial channels positioned in the lower part of the machine housing when the rotating electrical machine is in its normal operating position may have a surface area in a cross-section perpendicular to the longitudinal axis X smaller than the axial channels positioned at the level of at least one supply outlet of the reducer for cooling fluid.

[0045] In a particular embodiment where the machine housing is intended to also house a reducer, the axial channels adjacent to a cooling fluid inlet may have a surface area in a cross-section perpendicular to the longitudinal axis X smaller than the axial channels positioned at the level of at least one cooling fluid supply outlet of the reducer.

[0046] The cooling fluid inlet is advantageously unique. Due to gravity, the cooling fluid has the highest flow rate at the bottom of the machine housing. Reducing the cross-sectional area of ​​the axial channels located at the bottom of the machine housing reduces this flow rate. Similarly, the cooling fluid has a particularly high flow rate at the fluid inlet or outlet, so reducing the cross-sectional area of ​​the axial channels there also reduces the flow rate. Larger cross-sectional areas are positioned at the gearbox feed outlets because the fluid is split between a low and a high outlet, which reduces the amount of fluid in the axial channels. These larger cross-sectional areas compensate for the lower flow rate in the axial channels.

[0047] The feed ring can be adapted to distribute the cooling fluid into at least one supply outlet of the cooling fluid reducer.

[0048] All channels of the plurality of axial channels can have a different surface in a cross section perpendicular to longitudinal X tax.

[0049] Alternatively, when the plurality of axial channels comprises at least three channels, two channels of the plurality of axial channels, possibly but not necessarily adjacent, may have an identical surface in a cross-section perpendicular to Longitudinal Tax X and when the plurality of axial channels comprises at least four channels, two or three channels of the plurality of axial channels, possibly but not necessarily adjacent, may have an identical surface in a cross-section perpendicular to Longitudinal Tax X.

[0050] The cross-section of the channels in the plurality of axial channels may widen slightly, for example by approximately 1 mm, towards their exit. This can indeed be caused by the draft angle of the casting.

[0051] The invention also relates to a propulsion device for a motor vehicle, comprising an assembly as defined above, a reducer and an inverter.

[0052] The propulsion system for a motor vehicle may include one or two rotating electrical machines.

[0053] The gearbox may have a single transmission stage. Alternatively, it may have several transmission stages, for example, two or three transmission stages. The rotating electrical machine(s) may be arranged on either side of the gearbox. Each rotating electrical machine may have a shaft connected to a primary shaft of the gearbox.

[0054] The invention also relates to a motor vehicle comprising a propulsion device as described above. The vehicle may have at least two drive wheels, each of the drive wheels being driven in rotation by the reduction gear, in particular by an output shaft thereof.

[0055] The drive wheels can be arranged on either side of the gearbox. Each drive wheel can have a shaft connected to an output shaft of the gearbox. The device can include a first drive wheel fixed in rotation to a first output shaft of the gearbox. The device can include a second drive wheel fixed in rotation to a second output shaft of the gearbox.

[0056] Brief description of the drawings

[0057] The invention will be better understood upon reading the detailed description that follows, a non-limiting example of its embodiment, and an examination of the attached drawings.

[0058] [Fig 1] Figure 1 is a schematic and partial perspective view of a machine housing included in an assembly according to the invention, in a particular embodiment.

[0059] [Fig 2] Figure 2 is a partial enlarged schematic cross-sectional view of the machine housing of Figure 1 and of a stator housed in the machine housing, showing a detail of an embodiment of the invention.

[0060] [Fig 3] Figure 3 is a simplified and partial schematic cross-sectional view of the machine housing of Figure 1 at the axial channels.

[0061] [Fig 4] Figure 4 is a schematic and partial cross-sectional view of the machine housing of Figure 1 and of the stator, at the level of the feed ring.

[0062] [Fig 5] Figure 5 is a schematic and partial cross-sectional view of the machine housing of Figure 1 and of the stator, at the level of the axial channels.

[0063] [Fig 6] Figure 6 is a schematic and partial longitudinal sectional view of the machine housing of Figure 1 and the stator. [Fig 7] Figure 7 is a schematic and partial longitudinal sectional view of the machine housing of Figure 1.

[0064] Detailed description

[0065] Figures 1 to 7 illustrate a machine housing 10 of an assembly according to the invention, in a particular embodiment of the invention. The assembly comprises a rotating electrical machine and the machine housing 10, which is designed to house the rotating electrical machine. As shown in Figures 1, 6, and 7, the rotating electrical machine extends along a longitudinal axis X and includes at least one stator 12 (visible in Figures 2 and 4 to 6).

[0066] The machine housing 10 includes an area intended to receive the stator 12, this area having an internal surface 14 (visible in figures 1 to 3).

[0067] According to the invention, the inner surface 14 of the machine housing 10 comprises a plurality of axial channels 16 extending along the longitudinal axis X. The axial channels 16 are distributed around the stator 12 and are intended for the circulation of a cooling fluid.

[0068] The plurality of axial channels 16 is adapted to guide the cooling fluid in a single direction parallel to the longitudinal axis X.

[0069] According to the invention, at least two channels of the plurality of axial channels 16 have different surfaces in a cross-section perpendicular to the longitudinal axis X.

[0070] The enlarged view of Figure 2 thus shows two axial channels 16 having different surfaces in the cross-section of the machine housing 10 which is shown.

[0071] As shown in Figure 1, the machine housing 10 also includes, at one end of the area intended to receive the stator 12, a supply ring 18 located at the inlet of the axial channels 16. This ring is adapted to distribute the cooling fluid to the plurality of axial channels 16 and also to two gearbox supply outlets 22, upper and lower (visible in Figures 3 and 4), which supply the gearbox lubrication system. The upper outlet 22 supplying the gearbox with cooling fluid allows any air bubbles that might form during the filling of the cooling fluid circuit to escape. This prevents the creation of hot spots if there is no purge solution. In the example described here, the supply ring 18 is formed between the inner diameter of the machine housing 10 and the outer diameter of the stator 12.

[0072] In the example described here, as shown in Figure 1, the machine housing 10 further includes, at a second end of the area intended to receive the stator 12, a recovery ring 20 disposed at the outlet of the axial channels 16, adapted to collect and evacuate the cooling fluid.

[0073] The plurality of axial channels 16 advantageously includes as many inputs at the level of the supply ring 18 as outputs at the level of the recovery ring 20.

[0074] In the example described here, the machine housing 10 comprises a main housing and a closing housing (not shown), which closes the main housing and the recovery ring 20 is formed between the main housing and the closing housing.

[0075] More specifically, the recovery ring 20 is formed between the inner diameter of the main housing and the outer diameter of the closing housing.

[0076] As shown in Figures 1 to 3 and 5, the plurality of axial channels 16 are formed in the thickness of the machine housing 10.

[0077] In the example described here, the machine housing 10 is intended to also house a reducer.

[0078] As shown in Figure 3, the axial channels 16 positioned in the lower part of the machine housing 10 when the rotating electrical machine is in its normal operating position, such as channel Cl, have a surface area in a cross-section perpendicular to the longitudinal axis X smaller than the axial channels 16 positioned at the two outlets 22 supplying the reducer with cooling fluid, such as channels C2 and C3, respectively located at the upper supply outlet of the reducer and the lower supply outlet of the reducer.

[0079] The axial channels 16 positioned in the lower part of the machine housing 10 when the rotating electrical machine is in its normal operating position, such as channel Cl, may have a surface area in a cross-section perpendicular to the longitudinal axis X smaller than all the other axial channels 16.

[0080] The axial channels 16 positioned at the level of the two outlets 22 supplying the reducer with cooling fluid, such as channels C2 and C3, may present a surface in a cross section perpendicular to the longitudinal axis X larger than all other axial channels 16.

[0081] As also shown in Figure 3, the axial channels 16 adjacent to a cooling fluid inlet 24, i.e., those closest to a cooling fluid inlet 24, such as channel CO, have a smaller cross-sectional area perpendicular to the longitudinal axis X than the axial channels 16 positioned at the two cooling fluid supply outlets 22 to the reducer, such as channels C2 and C3. The cooling fluid inlet 24 and the two cooling fluid supply outlets 22 to the reducer are also shown in Figure 4.

[0082] Axial channels 16 adjacent to a cooling fluid inlet 24, such as the CO channel, may have a surface area in a cross-section perpendicular to the longitudinal axis X smaller than all other axial channels 16.

[0083] In the example in Figure 3, the areas of the axial channels 16 in the cross-section perpendicular to the longitudinal axis X shown are larger in the areas outlined by dashed lines Z1 and Z3 and smaller in the area outlined by dashed lines Z2. Between the three areas Z1, Z2, and Z3, the areas of the axial channels 16 in the cross-section shown are different and transition, increasing or decreasing depending on the direction, towards the areas Z1, Z2, and Z3.

[0084] As a non-limiting example, the respective surface area, in mm 2 , of the eighteen axial channels 16 represented in Figure 3 in a cross-section perpendicular to the longitudinal axis X can be the following, starting from channel CO and going through the adjacent channels in a clockwise direction: 52.7; 52.7; 58.7; 61.7; 64.7; 67.8; 67.8; 70.8; 70.9; 67.8; 64.7; 64.7; 64.8; 80.5; 70.8; 67.8; 64.7; 61.7.

[0085] All the channels in the plurality of axial channels 16 can have a different surface area in a cross-section perpendicular to the longitudinal axis X. However, in the example described here, as shown in the numerical example above, two adjacent channels can have an identical surface area in a cross-section perpendicular to the longitudinal axis X. More generally, two non-adjacent channels can have an identical surface area in a cross-section perpendicular to the longitudinal axis X. The number of axial channels 16 can be between 9 and 30, preferably between 12 and 24, preferably between 15 and 20. For example, it is on the order of 18, as in the example described here.

[0086] The axial channels 16 distributed around the outer diameter of the stator 12 allow for the homogeneous distribution of the cooling fluid, thus ensuring a cool inlet temperature across the entire circumference of the stator laminations 12. Having a large number of independent axial channels 16 allows for better distribution of the cooling fluid and a cool inlet temperature in all axial channels 16. Advantageously, a compromise must be found between too many axial channels 16, which reduces the cross-sectional area of ​​each channel, thereby increasing pressure losses and reducing the heat exchange surface between the stator laminations 12 and the cooling fluid, and too few axial channels 16, which reduces the guiding span of the stator 12.

[0087] The minimum surface area of ​​an inlet cross-section of an axial channel 16 can be between 30 mm 2 and 70 mm 2, ideally between 40 mm 2 and 60 mm 2 , ideally between 50 mm 2 and 58 mm 2 For example, it is around 55 mm 2 .

[0088] The maximum surface area of ​​an inlet cross-section of an axial channel 16 can be between 60 mm 2 and 100 mm 2 , ideally between 70 mm 2 and 90 mm 2 , ideally between 75 mm 2 and 85 mm 2 For example, it is around 80 mm 2 .

[0089] The ratio between the maximum and minimum area of ​​an inlet cross-section of an axial channel 16 can be between 0.5 and 4, better between 1 and 2. For example, it is on the order of 1.5.

[0090] The minimum thickness, i.e. the radial height, of an axial channel 16 can be between 0.5 mm and 3 mm, preferably between 0.6 mm and 2 mm, preferably between 0.7 mm and 1 mm. It is for example on the order of 0.75 mm.

[0091] The maximum thickness (or radial height) of an axial channel 16 can be between 1 mm and 4 mm, preferably between 1.2 mm and 3 mm, preferably between 1.5 mm and 2.5 mm. For example, it is on the order of 1.8 mm.

[0092] The ratio between the maximum thickness (or radial height) and the minimum thickness (or radial height) of an axial canal 16 can be between 1 and 4, preferably between 1.5 and 3.5, preferably between 2 and 3. For example, it is on the order of 2.5. The length of an axial canal 16 can be between 80 mm and 150 mm, preferably between 90 mm and 140 mm, preferably between 100 mm and 130 mm. For example, it is on the order of 125 mm.

[0093] The volume of cooling fluid in the supply ring 18 can be between 15 cm 3 and 45 cm 3 , ideally between 20 cm 3 and 40 cm 3 , ideally between 25 cm 3 and 35 cm 3 For example, it is approximately 30 cm 3 .

[0094] The volume of coolant in the recovery ring 20 can be between 100 cm³ 3 and 160 cm 3 , ideally between 110 cm 3 and 150 cm 3 , ideally between 115 cm 3 and 135 cm 3 For example, it is approximately 125 cm 3 .

[0095] The ratio between the volume of coolant in the recovery ring 20 and the volume of coolant in the supply ring 18 can be between 2 and 6, better between 3 and 5. It is for example on the order of 4.

[0096] The propulsion system comprises an assembly as described above, a gearbox arranged in the machine housing 10, and an inverter. The gearbox may include a primary shaft, a secondary shaft in a transmission stage, and an output shaft.

[0097] In the non-limiting example described here, the electric machine comprises a stator and a rotor.

Claims

Demands 1. Assembly comprising a rotating electrical machine extending along a longitudinal axis X and a machine housing (10) intended to house the rotating electrical machine, the rotating electrical machine comprising at least one stator (12), the machine casing (10) comprising an area intended to receive the stator (12) having an internal surface (14), the inner surface (14) of the machine casing (10) comprising a plurality of axial channels (16) extending along the longitudinal axis X, distributed around the stator (12) and intended for the circulation of a cooling fluid, at least two channels of the plurality of axial channels (16) having different surfaces in a cross-section perpendicular to the longitudinal axis X, the machine casing (10) comprising, at a second end of the area intended to receive the stator (12), a recovery ring (20) disposed at the outlet of the axial channels (16), adapted to collect and evacuate the cooling fluid.

2. Assembly comprising a rotating electrical machine extending along a longitudinal axis X and a machine housing (10) intended to house the rotating electrical machine, the rotating electrical machine comprising at least one stator (12), the machine casing (10) comprising an area intended to receive the stator (12) having an internal surface (14), the inner surface (14) of the machine casing (10) comprising a plurality of axial channels (16) extending along the longitudinal axis X, distributed around the stator (12) and intended for the circulation of a cooling fluid, at least two channels of the plurality of axial channels (16) having different surfaces in a cross-section perpendicular to the longitudinal axis X, the machine housing (10) being intended to further house a gearbox, the axial channels (16) positioned in the lower part of the machine housing (10) when the rotating electrical machine is in its normal operating position having a surface in a cross-section perpendicular to the longitudinal axis X smaller than the axial channels (16) positioned at the level of at least one outlet (22) supplying the gearbox with cooling fluid.

3. Assembly according to claim 1 or 2, h plurality of axial channels (16) being adapted to guide the cooling fluid in a single direction parallel to the longitudinal axis X.

4. Together according to any one of the preceding claims, the machine housing (10) further comprising, at a first end of the area intended to receive the stator (12), a supply ring (18) disposed at the inlet of the axial channels (16), adapted to distribute the cooling fluid to the plurality of axial channels (16).

5. Assembly according to claim 4, the feed ring (18) being formed between the inner diameter of the machine housing (10) and the outer diameter of the stator (12).

6. Assembly according to claim 2, the machine housing (10) comprising, at a second end of the area intended to receive the stator (12), a recovery ring (20) disposed at the outlet of the axial channels (16), adapted to collect and evacuate the cooling fluid.

7. Together according to claim 4 or 5 and claim 6, the plurality of axial channels (16) having as many inputs at the level of the supply ring (18) as outputs at the level of the recovery ring (20).

8. Assembled according to any one of claims 1 to 5 and claim 6, the machine housing (10) comprising a main housing and a closing housing, the recovery ring (20) being formed between the main housing and the closing housing.

9. Assembly according to claim 8, the recovery ring (20) being formed between the inner diameter of the main housing and the outer diameter of the closing housing.

10. Assembled according to any one of the preceding claims, the plurality of axial channels (16) being formed in the thickness of the machine housing (10).

11. Assembly according to claim 1, the machine housing (10) being intended to further house a reducer, the axial channels (16) positioned in the lower part of the machine housing (10) when the rotating electrical machine is in its normal operating position having a surface in a cross section perpendicular to the longitudinal axis X smaller than the axial channels (16) positioned at the level of at least one outlet (22) supplying the reducer with cooling fluid.

12. Together according to any one of claims 1 to 10 and claim 11, the axial channels (16) adjacent to a cooling fluid inlet (24) having a surface in a cross section perpendicular to the longitudinal axis X smaller than the axial channels (16) positioned at the level of at least one cooling fluid supply outlet (22) of the reducer.

13. Assembly according to claim 4 or 5 and claim 11 or 12, the supply ring (18) being adapted to distribute the cooling fluid into at least one outlet (22) supplying the reducer with cooling fluid.

14. Together according to any one of the preceding claims, all the channels of the plurality of axial channels (16) having a different surface in a cross-section perpendicular to the longitudinal axis X.

15. Together according to any one of claims 1 to 13, the plurality of axial channels (16) comprising at least four channels, two or three channels of the plurality of axial channels (16) having an identical surface in a cross-section perpendicular to the longitudinal axis X.

16. Propulsion device for motor vehicle, comprising an assembly according to any one of the preceding claims, a reducer and an inverter.

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