Electric propulsion unit comprising a heat exchanger

Abstract

The invention relates to an aircraft propulsion system (1) comprising an electric propulsion unit (100) and a propeller (50) actuated by the electric propulsion unit (100) via a transmission shaft (52) able to be rotated about a main axis (X) of rotation defining an axial direction (DA) and a radial direction (DR) orthogonal to the axial direction (DA), the electric propulsion unit (100) comprising: - an electric motor (30), - a power electronics component (12, 13, 14, 15), - an electrical power source configured to supply power to the electric motor (30) via the power electronics component (12, 13, 14, 15), and - a heat exchanger (26) configured to cool the electric motor (30), the heat exchanger (26) being arranged radially around the electric motor (30).

Description

Description Title of the invention: Electric propulsion unit comprising a heat exchanger Technical Field

[0001] The present invention relates to the field of aircraft propulsion systems and, more particularly, to the cooling systems of these systems. Previous technique

[0002] Climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by different countries. In particular, an ambitious standard applies to both new types of aircraft and those already in operation, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively contributing to the fight against climate change for several years now.

[0003] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. The Applicant takes into account the factors impacting all phases of design and development in order to obtain aeronautical components and products that are less energy-intensive, more environmentally friendly, and whose integration and use in civil aviation have moderate environmental impacts, with the aim of improving the energy efficiency of aircraft.

[0004] The Applicant is working in research and development on new generations of engines, including materials used and lighter on-board equipment, electrical technologies to provide propulsion, and electric biofuels.

[0005] In this context, the Applicant is working on aircraft weight reduction.

[0006] A thermal propulsion system is traditionally lubricated, particularly the turbomachine bearings and gearboxes, by a lubrication circuit that includes an oil circuit. Once the oil has lubricated the various components of the propulsion system, it is cooled by a cooling system comprising a plurality of heat exchangers, and then reintroduced into the lubrication circuit.

[0007] The cooling requirements of thermal propulsion systems range from a few kW to several tens of kW, primarily for cooling the lubricating oil. Furthermore, these propulsion systems may include two main heat exchangers: an oil-kerosene intermediate heat exchanger and an air-oil heat exchanger. The oil-kerosene intermediate heat exchanger preheats the fuel before it enters the combustion chamber and cools the oil before it passes through the air-oil heat exchanger. With at least two heat exchangers in the thermal propulsion system, the system's size and mass are inevitably increased. In some cases, a second oil-kerosene intermediate heat exchanger may be added. The presence of this second oil-kerosene intermediate heat exchanger allows for a reduction in the size of the air-oil heat exchanger that cools the engine.

[0008] An electric propulsion system is traditionally cooled by a cooling system comprising a plurality of valves, pumps, and filters, as well as a circuit through which a heat transfer fluid circulates and a heat exchanger. The heat exchanger used in this configuration is generally an air-liquid exchanger.

[0009] The cooling requirements of electric propulsion systems are on the order of 70 to 80 kW for a 1 MW class motor. To meet these increased requirements, it is known to use a heat exchanger with greater mass and dimensions than for an equivalent internal combustion engine. This results in increased aerodynamic pressure losses and therefore increased aircraft drag.

[0010] In thermal propulsion systems and in electric propulsion systems, the air-liquid heat exchanger is generally installed in the airflow of the type scoop. And, it is generally necessary to increase the dimensions of the air-liquid heat exchanger in order to operate at high pressure and with high airflow. Indeed, if the dimensions of the air-liquid heat exchanger are not increased, in operation at high pressure and with high flow, the pressure in the circuit connecting the air-liquid heat exchanger to the airflow would be too high. This increase in the dimensions of the air-liquid heat exchanger impacts the sizing of the cooling circuit, resulting in increased aerodynamic and hydraulic pressure losses, oversizing of the pumps, and an increase in the aircraft's mass. Description of the invention

[0011] The invention aims to provide a propulsion system with a small footprint, reduced mass and enabling the reduction of aerodynamic and hydraulic pressure losses.

[0012] To this end, the invention proposes an aircraft propulsion system comprising an electric propulsion unit and a propeller driven by the propulsion unit via a drive shaft capable of being rotated about a principal axis (X) of rotation defining an axial direction and a radial direction orthogonal to the axial direction, the electric propulsion unit comprising: - an electric motor, - a power electronic component, - a power supply configured to power the electric motor (30) via the power electronics component, and - a heat exchanger configured to cool the electric motor.

[0013] According to a general characteristic of the propulsion system, the heat exchanger is arranged radially around the electric motor.

[0014] This configuration reduces the size and mass of the propulsion system by integrating the heat exchanger into the electric propulsion unit, while also ensuring improved cooling efficiency. Cooling efficiency is enhanced because this configuration of the electric propulsion unit increases heat transfer from the motor to the engine. In the heat exchanger, part of the heat exchange now occurs through thermal conduction. This leads to a rise in the heat exchanger's temperature, increasing its efficiency and allowing for optimized sizing. By increasing the heat exchanger's temperature, heat exchange with the air is enhanced. Indeed, the thermal output of a heat exchanger is proportional to the difference between the inlet temperature of the heat transfer fluid and the outlet temperature of the heat transfer fluid.

[0015] According to a particular characteristic, the heat exchanger can be configured to further cool said at least one power electronic component and / or said at least one power supply.

[0016] Depending on a particular feature, the propulsion system may further include a plurality of fastening elements connecting the heat exchanger to the electric motor.

[0017] Thus, it is possible to guarantee optimal fixing maximizing heat exchange by conduction between the heat exchanger and the electric motor.

[0018] According to a particular feature, the propulsion system may further include at least four circumferentially equidistant fastening elements around the electric motor.

[0019] This allows for the even distribution of the mounting forces exerted on the electric motor. Furthermore, the presence of the mounting elements provides support for the heat exchanger.

[0020] According to a particular characteristic, at least one of the fastening elements includes a hydraulic fitting.

[0021] This configuration allows for heat exchange via conduction between the electric motor and the heat exchanger. Furthermore, the mounting element can serve as a direct passage for the hydraulic connection, eliminating the need for an external fitting to install the hydraulic connection within the electric drive unit.

[0022] According to another particular feature, the electric motor may include an external casing, with each fastening element being attached to the electric motor via the external casing.

[0023] This feature significantly simplifies the manufacturing of the electric motor and its external housing. Each mounting element can be a separate component, facilitating its attachment to the motor. Each mounting element provides a mechanical interface between the motor's external housing and the heat exchanger.

[0024] Depending on a particular characteristic, the heat exchanger may include an air-liquid exchanger.

[0025] The presence of an air-liquid heat exchanger significantly improves cooling efficiency. Indeed, the higher the rated power of the propulsion system, the greater the heat losses within it. The liquid therefore allows for more efficient heat extraction from the propulsion system. Furthermore, this feature allows for optimal weight reduction of the propulsion system.

[0026] Depending on a particular characteristic, the heat exchanger may have an annular shape.

[0027] This facilitates the integration of the heat exchanger between the nacelle and the electric motor, particularly when the nacelle has an annular shape.

[0028] Depending on a particular characteristic, the heat exchanger may include a plurality of secondary exchangers.

[0029] This makes it possible to improve the operational reliability of the propulsion system. For example, if one of the secondary heat exchangers is blocked or malfunctions, cooling can continue to be provided by the other secondary heat exchangers that are not affected by the blockage or malfunction.

[0030] According to another aspect, the invention proposes a propulsion assembly comprising a nacelle, characterized in that it comprises a propulsion system according to the invention, the nacelle being arranged radially on the outside of the electric propulsion unit of the propulsion system and the heat exchanger being arranged radially between the electric motor and the nacelle.

[0031] Depending on a particular characteristic, the propulsion assembly may include a plurality of fastening elements, each fastening element connecting the heat exchanger to the nacelle.

[0032] In particular, the nacelle may include a plurality of fastening elements, each fastening element connecting the heat exchanger to the nacelle.

[0033] This allows for a reduction in vibrations experienced by the heat exchanger. The nacelle is only minimally affected by these vibrations. These vibrations originate from the propeller and are transmitted to the heat exchanger via the electric motor. The propulsion system's mountings dampen these vibrations. Furthermore, this ensures optimal attachment between the heat exchanger and the nacelle.

[0034] Depending on a particular characteristic, each fastening element may include at least one shock absorber.

[0035] This characteristic makes it advantageous to reduce, and do so optimally, the vibrations experienced by the heat exchanger.

[0036] According to yet another aspect, the invention proposes an aircraft characterized in that it comprises a propulsion system according to the invention.

[0037] Such an aircraft has a smaller footprint, lower mass, and better cooling efficiency. Brief description of the drawings

[0038] [Fig. 1] Figure 1 illustrates a first example of a propulsion assembly according to the invention,

[0039] [Fig. 2] Figure 2 illustrates a first example of a heat exchanger attached to the engine according to the invention,

[0040] [Fig. 3] Figure 3 illustrates a second example of a heat exchanger attached to the engine according to the invention,

[0041] [Fig. 4] Figure 4 illustrates a second example of a propulsion assembly according to the invention,

[0042] [Fig. 5] Figure 5 illustrates a third example of a propulsion assembly according to the invention,

[0043] [Fig. 6] Figure 6 illustrates a fourth example of a propulsion assembly according to the invention. Description of the implementation methods

[0044] The invention applies generally to aircraft propulsion systems and, more particularly, to propulsion systems comprising one or more electric motors.

[0045] Figure 1 illustrates a first example of a propulsion assembly according to the invention.

[0046] In the example illustrated in Figure 1, the propulsion assembly P comprises a nacelle 60 and a propulsion system 1 with a propeller 50 and an electric propulsion unit 100. The electric propulsion unit 100 comprises an electric motor 30, a drive shaft 52, a first power electronic component 12 and a second power electronic component 14.

[0047] The first power electronics component 12 and the second power electronics component 14 may each include an inverter, for example three-phase.

[0048] The number of power electronics components is not limiting to the invention and may be equal to one, two or even greater than two.

[0049] The drive shaft 52 extends between the propeller 50 and the electric motor 30 along a principal axis X, thus defining an axial direction DA extending along the principal axis X and a radial direction DR orthogonal to the axial direction DA. The drive shaft 52 is driven by the electric motor 30 to rotate the propeller 50 around the principal axis X.

[0050] The electric motor 30 comprises a rotor 34, a stator 32 and an outer casing 36. The stator 32 is mounted radially between the rotor 34 and the outer casing 36.

[0051] The outer casing 36 extends along a radial direction DR between an inner casing surface 360b and an outer casing surface 360a.

[0052] The number of electric motors 30 is not limiting to the invention, the electric propulsion unit 100 being able to comprise a plurality of electric motors 30.

[0053] The electric propulsion unit 100 further includes an electrical power supply (not shown) which supplies electric current to the electric motor 30 via the first power electronic component 12 and via the second power electronic component 14. The number of power supplies is not limiting to the invention; the electric propulsion unit 100 may include a plurality of electrical power supplies.

[0054] The first and second power electronic components 12, 14 can be inverters to convert direct current delivered by a direct current source, such as a battery, turbogenerator or fuel cell, into alternating current to control an alternating current electric motor.

[0055] The electric propulsion unit 100 also includes a cooling circuit 20. The cooling circuit 20 comprises channels 211 to 219, a first pump 22, a second pump 24 and a heat exchanger 26.

[0056] The first and second pumps 22 and 24 can be mechanically or electrically operated hydraulic pumps.

[0057] The heat exchanger 26 is connected to the cooling circuit via at least one hydraulic connection (not shown).

[0058] To facilitate understanding of the drawings, the representation of the cooling circuit 20 has been simplified. Thus, Figure 1 shows the elements of the cooling circuit 20 that require cooling, namely the first pump 22, the second pump 24, and, even more importantly, the The electronic power components and the stator 32 of the electric motor 30 are also included. The cooling circuit 20 comprises a heat transfer fluid that circulates through channels 211 to 219, pumps 22 and 24, and the heat exchanger 26. This fluid can be a liquid such as oil, glycol water, or another heat transfer fluid. Cooling the pumps reduces their operating temperature and thus improves their reliability.

[0059] A first channel 211 of the cooling circuit 20 is connected to an inlet of the first power electronic component 12 and supplies a cooled heat transfer fluid to the first power electronic component 12 to cool it.

[0060] A second channel 212 of the cooling circuit 20 is connected to an inlet of the second power electronic component 14 and supplies a cooled heat transfer fluid to the second power electronic component 14 to cool it.

[0061] A third channel 213 of the cooling circuit 20 is connected to an output of the first power electronic component 12 to recover the heat transfer fluid slightly heated by its passage through the first power electronic component 12. The third channel 213 carries the heated heat transfer fluid from the output of the first power electronic component 12 to the stator 32 of the electric motor 30 to cool the electric motor 30 and more particularly its stator 32.

[0062] A fourth channel 214 of the cooling circuit 20 is connected to an output of the second power electronic component 14 to recover the heat transfer fluid heated by the cooling of the second power electronic component 14. The fourth channel 214 carries the heat transfer fluid thus heated from the output of the second power electronic component 14 to the stator 32 of the electric motor 30 to cool the electric motor 30 and more particularly its stator 32.

[0063] A fifth channel 215 of the cooling circuit 20 is connected to an outlet of the stator 32 and carries the heat transfer fluid heated by the Cooling of the stator 32 extends to the heat exchanger 26. The heat transfer fluid passes through the heat exchanger 26 to remove the absorbed heat and thus be cooled. The fifth channel 215 then carries the cooled heat transfer fluid to the first pump 22 to cool the first pump 22.

[0064] A sixth channel 216 of the cooling circuit 20 is connected to an outlet of the stator 32 and carries the heat transfer fluid, heated by the stator 32 cooling, to the heat exchanger 26. The heat transfer fluid passes through the heat exchanger 26 to be cooled. The sixth channel 216 then carries the cooled heat transfer fluid to the second pump 24 to cool the second pump 24.

[0065] A seventh channel 217 of the cooling circuit 20 is connected to an outlet of the first pump 22 and carries the heat transfer fluid that cooled the first pump 22 to a ninth channel 219 of the cooling circuit 20.

[0066] An eighth channel 218 of the cooling circuit 20 is connected to an outlet of the second pump 24 and carries the heat transfer fluid which has cooled the second pump 24 to the ninth channel 219 of the cooling circuit 20.

[0067] The ninth channel 219 of the cooling circuit 20 in turn transmits the heat transfer fluid to the first channel 211 and the second channel 212.

[0068] The number and arrangement of the cooling circuit channels are not limiting to the invention.

[0069] The electric propulsion unit 100 is mounted radially inside the nacelle 60. In other words, the nacelle 60 and the electric propulsion unit 100 are arranged coaxially around the main X axis, with the electric propulsion unit being radially closer to the main X axis than the nacelle 60.

[0070] The nacelle 60 extends radially between an internal surface of the nacelle 61 and an external surface of the nacelle 62. The heat exchanger 26 is mounted in the radial direction DR between the electric motor 30 and the nacelle 60. That is to say, between the external surface 360a of the external housing 36 of the electric motor 30 and the internal surface of the nacelle 61 of the nacelle 60.

[0071] Figure 2 illustrates a first example of a heat exchanger 26 mounted on the external casing 36 of the electric motor 30 according to the invention.

[0072] Mounting the heat exchanger 26 on the electric motor 30, and more specifically on the external housing 36 of the electric motor 30, optimizes the cooling circuit 20 by reducing the amount of piping within it. This further reduces pressure losses and the aircraft's mass. Pressure losses correspond to drops in pressure within the cooling circuit. The greater the pressure drops, the more powerful the pumps supplying the cooling circuit with heat transfer fluid must be to compensate for these pressure drops. The length and arrangement of the piping can significantly influence pressure losses. For example, the longer the piping, the greater the pressure losses.

[0073] In the example illustrated in Figure 2, the electric motor 30 and the heat exchanger 26 each have an annular shape. The shape of the heat exchanger 26 and the electric motor 30 is not limiting to the invention.

[0074] As illustrated in Figure 2, the electric propulsion unit comprises four mounting elements 70. Each of the mounting elements 70 is fixed on one side to the external housing 36 of the electric motor 30 and on the other side to the heat exchanger 26.

[0075] In one variant, the fastening elements 70 are permanently assembled to the outer housing 36, for example by welding or brazing. In this case, the outer housing 36 is pre-machined or forged.

[0076] In another variant, the outer casing 36 and the fastening elements 70 are formed as a single unit. "Formed as a single unit" means formed from a single piece without the need for assembly. In other words, "formed as a single unit" means formed from a single, monolithic part. In this case, the single part can, for example, be manufactured by additive manufacturing.

[0077] In the example illustrated in Figure 2, each of the fastening elements 70 includes a hydraulic fitting 72.

[0078] The presence of the fixing elements, each containing a hydraulic system, allows for the creation of additional direct thermal conduction between the electric motor 30 and the heat exchanger 26. Thus, it is possible to obtain optimal cooling of the electric motor 30.

[0079] The number of fastening elements is not a limitation of the invention. Thus, the number of fastening elements 70 may be different from four, and preferably greater than or equal to four.

[0080] The presence of hydraulic fittings 72 in each of the fastening elements 70 is not a limitation of the invention. Fastening elements 70 may therefore be without hydraulic fittings 72.

[0081] Figure 3 illustrates a second example of a heat exchanger 26 mounted on the electric motor 30 according to the invention. In Figure 3, the elements bearing numerical references identical to those in Figures 1 and 2 are identical to the elements of the embodiments of Figures 1 and 2.

[0082] In the example illustrated in Figure 3, the heat exchanger 26 comprises a plurality of sub-heat exchangers 260, and the electric propulsion unit 100 comprises eight fastening elements 70.

[0083] The sub-heat exchangers 260 and the fixing elements 70 are equally distributed in a circumferential direction around the electric motor 30. In other words, the distance separating a pair of fixing elements 70 or a pair of sub-heat exchangers 260 is the same regardless of the pair of fixing elements 70 or the pair of sub-heat exchangers 260.

[0084] Some fasteners 70 include a hydraulic fitting 72. In the example shown, four of the eight fasteners 70 include a hydraulic fitting 72.

[0085] The external housing 36 of the electric motor 30 and the heat exchanger 26 can be produced by additive manufacturing as a single piece. Thus, it It is possible to obtain a single-piece unit that maximizes thermal conduction between the electric motor 30 and the heat exchanger 26.

[0086] Figure 4 illustrates a second example of a propulsion assembly P according to the invention.

[0087] In figures 4, 5 and 6 the elements bearing numerical references identical to those of figures 1, 2, 3 are identical to the elements of the embodiments of figures 1, 2 and 3.

[0088] In the example illustrated in Figure 4, the external surface 360a of the external housing 36 of the electric motor 30 has a plurality of fins 38, which increase the surface area for heat exchange with the air. When the aircraft is operating, the external housing 36 is at a first temperature T1, and the air around the external housing 36 is at a second temperature T2. The thermal performance of the cooling system depends on the heat exchange surface area between the external housing 36 of the electric motor 30 and the air, as well as on the difference between the first temperature T1 and the second temperature T2. The heat exchange surface area is increased by the fins because they circulate cool air when in operation. Furthermore, when the cooling system malfunctions, the presence of the fins ensures continued cooling of the electric motor housing 36.

[0089] In this case, the heat exchanger 26 is mounted on the internal surface 61 of the nacelle 60.

[0090] Figure 5 illustrates a third example of a propulsion assembly P according to the invention.

[0091] In the example illustrated in Figure 5, the electric propulsion unit 100 includes an air inlet 80 delimited by a hub 51 of the propeller 50 and by the internal surface 61 of the nacelle 60.

[0092] The air intake 80 of the electric propulsion unit 100 supplies the heat exchanger 26 with a flow of cold air, thus limiting aerodynamic pressure losses while maintaining a slim and therefore aerodynamic nacelle and having a direct airflow which cools the heat exchanger 26, the first pump 22 and the second pump 24.

[0093] In one embodiment, the heat exchanger 26 can be an air-liquid exchanger and the heat transfer fluid can be a liquid, such as oil, glycol water.

[0094] The cold airflow is divided into a first portion 92 and a second portion 94. The first portion 92 of cold air passes through the air-liquid heat exchanger and thus cools the liquid as it flows through the exchanger. This configuration allows for simple and efficient cooling of the liquid in the cooling circuit 20 as it passes through the heat exchanger 26, namely the air-liquid heat exchanger. The first portion 92 of cold air is warmed during the cooling of the heat exchanger 26.

[0095] The first pump 22 and the second pump 24 are arranged adjacently and downstream of an outlet of the heat exchanger 26, as illustrated in Figure 5. This reduces the pressure at the inlet of the heat exchanger and thus its mass. Positioning the first pump 22 and the second pump 24 near the heat exchanger 26, and therefore near the electric motor 30, allows for a reduction in the dimensions of the piping in the cooling circuit 20, particularly between the first pump 22 and the heat exchanger 26, and between the second pump 24 and the heat exchanger 26. This significantly reduces pressure drops and the risk of failures in the cooling circuit 20.

[0096] When the electric propulsion unit 100 includes an air inlet 80, the second portion 94 of cold air cools the first pump 22 and the second pump 24. The second portion 94 of cold air is heated during the cooling of the first pump 22 and the second pump 24.

[0097] Such a configuration allows for even more efficient cooling of the first pump 22 and the second pump 24.

[0098] The presence of the air inlet 80 is not limiting to the invention.

[0099] The nacelle 60 further includes an opening 64 which extends radially between the internal surface 61 of the nacelle 60 and an internal surface 260a of the heat exchanger 26, as illustrated in Figure 5. The opening 64 of the nacelle 60 extends circumferentially around the nacelle 60. The opening 64 of the nacelle 60 is arranged radially on the outside of the first pump 22 and the second pump 24.

[0100] Such a configuration facilitates the evacuation of the second portion of air 94 which was heated during the cooling of the first pump 22 and the second pump 24. This configuration also facilitates the evacuation of the first portion of air 92 which was heated during the cooling of the heat exchanger 26.

[0101] The presence and arrangement of the opening 64 of the nacelle 60 are not limiting to the invention.

[0102] Figure 6 illustrates a fourth example of a propulsion assembly P according to the invention.

[0103] In Figure 6, the elements bearing numerical references identical to those in Figures 1, 2, 3, 4 and 5 are identical to the elements of the embodiments in Figures 1, 2, 3, 4 and 5.

[0104] The propulsion system 1 further includes a scoop-type air intake 82 receiving a flow of cold air 83.

[0105] In one variant, the nacelle 60 of the propulsion system 1 includes the scoop-type air intake 82, as illustrated in Figure 6.

[0106] The scoop-type air inlet 82 extends radially between an internal air inlet surface 84 and an external air inlet surface 86. The scoop-type air inlet 82 is mounted, along the radial direction DR adjacent to an external exchanger surface 260b of the heat exchanger 26 and radially outside the propeller 50.

[0107] The scoop-type air inlet 82 allows for even more efficient cooling of the elements of the electric propulsion unit 100 which are located behind or downstream of the electric motor 30, namely the power electronics components 12 to 15, the first pump 22 and the second pump 24.

[0108] In the example illustrated in Figure 6, the electric propulsion unit 100 includes, in addition to the first power electronic component 12 and the second power electronic component 14, a third power electronic component 13 and a fourth power electronic component 15.

[0109] The number of power electronic components is not limiting to the invention, the number of power electronic components being able to be less than or greater than four.

[0110] The cooling circuit 20 includes, in addition to the nine channels 211 to 219, a tenth channel 220 and an eleventh channel. [YES] The scoop-type air inlet 82 is configured to cool the first power electronic component 12, the second power electronic component 14, the third power electronic component 13 and the fourth power electronic component 15.

[0112] Indeed, the cold air entering through the scoop-type air inlet 82 is guided downstream of the electric motor 30 to cool it and then cool the first power electronic component 12, the second power electronic component 14, the third power electronic component 13, and the fourth power electronic component 15. Next, a first portion 96 of the air that has cooled the power electronic components 12 to 15 passes through the first pump 22 and then through the heat exchanger 26, and a second portion 98 of the air that has cooled the power electronic components 12 to 15 passes through the second pump 24 and then through the heat exchanger 26, as illustrated in Figure 6. Thus, it is possible to further cool the motor, all the power electronic components, and the fluid in the heat exchanger 26.It should be noted that the maximum operating temperature of the power electronic components is lower than the maximum operating temperature of the electric motor 30.

[0113] Then the first portion 96 of the air and the second portion 98 of the air are evacuated through an air outlet 99.

Claims

Demands [Claim 1] Aircraft propulsion system (1) comprising an electric propulsion unit (100) and a propeller (50) driven by the electric propulsion unit (100) via a drive shaft (52) capable of being rotated about a principal axis (X) of rotation defining an axial direction (DA) and a radial direction (DR) orthogonal to the axial direction (DA), the electric propulsion unit (100) comprising: - an electric motor (30), - a power electronic component (12, 13, 14, 15), - a power supply configured to power the electric motor (30) via the power electronic component (12, 13, 14, 15), and - a heat exchanger (26) configured to cool the electric motor (30), characterized in that the heat exchanger (26) is arranged radially around the electric motor (30) and is mounted on the external casing 36 of the electric motor 30 to optimize the cooling circuit 20 by reducing the piping present in it. [Claim 2] Propulsion system (1) according to claim 1, further comprising a plurality of fastening elements (70) connecting the heat exchanger (26) to the electric motor (30). [Claim 3] Propulsion system (1) according to claim 2, comprising at least four fastening elements (70) circumferentially equidistant around the electric motor (30). [Claim 4] Propulsion system (1) according to any one of claims 2 or 3, wherein the electric motor comprises an outer casing (36), each fastening element (70) being fixed to the electric motor (30) via the outer casing (36). [Claim 5] Propulsion system (1) according to any one of claims 1 to 4, wherein the heat exchanger (26) comprises an air-liquid exchanger. [Claim 6] Propulsion system (1) according to any one of claims 1 to 5, wherein the heat exchanger (26) has an annular shape. [Claim 7] Propulsion system (1) according to any one of claims 1 to 6, wherein the heat exchanger (26) comprises a plurality of secondary exchangers (260). [Claim 8] Propulsion assembly (P) comprising a nacelle (60), characterized in that it comprises a propulsion system (1) according to any one of claims 1 to 7, the nacelle (60) being arranged radially on the outside of the electric propulsion unit (100) of the propulsion system (1) and the heat exchanger (26) being arranged radially between the electric motor (30) and the gondola (60). [Claim 9] Propulsion assembly (P) according to claim 8, wherein the nacelle (60) comprises a plurality of attachment elements (70), each attachment element (70) connecting the heat exchanger (26) to the nacelle (60). [Claim 10] Aircraft characterized in that it comprises a propulsion assembly (P) according to any one of claims 8 or 9.

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