Axial flux electric motor including closed-loop air cooling

Abstract

Axial flux electric motor comprising closed-circuit air cooling. Axial flux electric motor (1) comprising a stator (3), a rotor (2), at least one axial air gap (7A, 7B), and a first closed air cooling circuit, the air being circulated in said first circuit by rotation of the rotor, the first circuit comprising a first portion (P1) defined in at least one air gap, the air in the first portion being intended to flow from a central zone (Z1) of the stator to a peripheral zone (Z2) of the stator, said first circuit further comprising a second portion (P2), the air in the second portion being intended to flow from the peripheral zone of the stator to the central zone of the stator, the second portion being configured to guide the air along a spiral path. Figure for abbreviation: Figure 2

Description

Title of the invention: Axial flux electric motor comprising closed-circuit air cooling. Technical field of the invention

[0001] The invention relates to an axial flux electric motor comprising a closed-loop air cooling circuit. The invention also relates to a motor vehicle comprising such an electric motor. Prior art

[0002] So-called "electric" or "hybrid" motor vehicles include an electric motor configured to drive the vehicle's drive wheels. Among the various electric motor architectures, axial flux electric motors are known. In such motors, one or more air gaps between a stator and a rotor extend perpendicularly to an axis of rotation of the rotor. The rotor generally comprises a ring equipped with magnets and is fixed rigidly to a rotating shaft of the electric motor. The stator comprises windings of electrical wire through which a high-power electric current can flow.

[0003] The flow of electric current in the stator's wire windings causes significant heating, which can damage certain parts of the electric motor and / or disrupt its proper operation. It is therefore important to cool the electric motor during operation. For this purpose, axial flux electric motors with a closed oil cooling circuit are known. The oil is circulated by a pump and flows through oil channels within the motor housing. The cooling circuit is connected to a heat exchanger configured to cool the oil and thus dissipate the heat generated by the stator. However, an oil cooling system is bulky and does not cool the stator sufficiently effectively. Furthermore, some parts of an axial flux electric motor may be incompatible with contact with oil.These parts therefore cannot be directly cooled by the oil cooling system. For example, the air gap cannot be immersed in oil because this would severely penalize the efficiency of the electric motor.

[0004] Cooling systems for electric motors using forced air are also known. In this case, the electric motors are equipped with an electric blower powered by a vehicle battery. Such systems are also bulky and consume valuable electrical energy. Presentation of the invention

[0005] The object of the invention is to provide an axial flux electric motor that remedies the above disadvantages and improves upon known axial flux electric motors of the prior art.

[0006] More specifically, a first object of the invention is an axial flux electric motor equipped with an efficient, compact, and easy-to-manufacture cooling system. Summary of the invention

[0007] The invention relates to an axial flux electric motor comprising a stator, a rotor, and at least one axial air gap defined between the stator and the rotor, the electric motor comprising a first closed air-cooling circuit, the air being intended to be circulated in said first circuit by rotation of the rotor, the first circuit comprising a first portion defined in the at least one air gap, the air present in the first portion being intended to circulate from a central zone of the stator to a peripheral zone of the stator, said first circuit further comprising a second portion, the air present in the second portion being intended to circulate from the peripheral zone of the stator to the central zone of the stator, the second portion being configured to guide the air along a spiral path from the peripheral zone of the stator to the central zone of the stator.

[0008] The electric motor may include a housing attached to the stator, the housing enclosing the stator and the rotor, the second portion of the first circuit extending outside the housing.

[0009] The housing may include a wall having at least one first hole opposite the peripheral area, the air present in the first circuit being intended to circulate through the first hole, and the electric motor may include a cover fixed to the housing, the cover covering said first hole and at least partially said wall, the second portion extending between said wall and the cover, in particular said housing wall may include at least one second hole opposite the central area, the air present in the first circuit being intended to circulate through the second hole.

[0010] The cover may include an inner face turned towards an outer face of said housing wall, the cover including partitions extending projecting from its inner face, said partitions being configured to guide the air present in the second portion along a spiral path from the peripheral area of ​​the stator to the central area of ​​the stator.

[0011] The cover can be an element manufactured by plastic injection.

[0012] Said spiral-shaped path may comprise at least one complete turn.

[0013] The electric motor may further include a second closed oil cooling circuit, in particular at least one oil line, the second circuit being configured to cool the air present in the second portion of the first circuit.

[0014] The electric motor may include a rotating shaft integral with the rotor, the rotating shaft including at least one air circulation channel from said second portion to the central area.

[0015] The stator may include a front part and a rear part, a first air gap defined between the rotor and the front part of the stator, and a second air gap defined between the rotor and the rear part of the stator, the rotating shaft including at least a first opening configured to guide a first part of the air from the first circuit to the first air gap, the rotating shaft including at least a second opening configured to guide a second part of the air from the first circuit to the second air gap.

[0016] The invention also relates to a motor vehicle comprising an electric motor as defined above. Presentation of the figures

[0017] These objects, features and advantages of the present invention will be described in detail in the following description of various particular embodiments, given by way of non-limiting example, in connection with the accompanying figures, among which:

[0018] Fig. 1 is a perspective and cross-sectional view of an axial flux electric motor according to an embodiment of the invention, the cross-section being made in a plane passing through an axis of rotation of the rotor of the electric motor.

[0019] Fig. 2 is a perspective view of the electric motor of Fig. 1.

[0020] Fig. 3 is a cross-sectional view of the electric motor of Fig. 1, the section being carried out in a plane perpendicular to the axis of rotation of the rotor.

[0021] Fig. 4 is a cross-sectional view of an axial flux electric motor according to a first embodiment of the invention, the cross-section being made in a plane perpendicular to the axis of rotation of the electric motor rotor.

[0022] Fig. 5 is a cross-sectional view of an axial flux electric motor according to a second embodiment of the invention, the cross-section being made in a plane perpendicular to the axis of rotation of the electric motor rotor. Detailed description

[0023] Figure 1 schematically illustrates an axial flux electric motor 1 according to an embodiment of the invention. The electric motor 1 is a motor intended to drive the drive wheels of a motor vehicle. The motor vehicle may be, for example, a passenger car, a commercial vehicle, a truck, or even a bus. The electric motor 1 comprises a rotor 2 and a stator 3. The rotor 2 is free to rotate relative to the stator 3 about an axis of rotation X. The electric motor 1 further includes a rotating shaft 4 extending parallel to the axis of rotation X. The rotating shaft 4 is integral with the rotor 2 and is intended to be mechanically connected to the vehicle's drive wheels via a transmission system. The rotating shaft 4 includes a flange 5 against which the rotor 2 is fixed, notably by fixing screws 6. The rotating shaft also includes splines to provide a mechanical connection with the transmission system.

[0024] The stator 3 comprises two parts 3A, 3B, arbitrarily designated as the front part 3A and the rear part 3B. The two parts 3A, 3B of the rotor are separated from each other along the axis of rotation X. The rotor 2 is interposed between the two parts 3A and 3B of the rotor. The electric motor 1 thus comprises a first air gap 7A defined between the rotor 2 and the front part 3A of the stator, and a second air gap 7B defined between the rotor 2 and the rear part 3B of the stator. The air gaps 7A and 7B are free spaces formed between the rotor and the stator, each extending in planes perpendicular to the axis of rotation X. The air gaps can have dimensions on the order of a millimeter along the axis of rotation X. The electric motor 1 is said to be "axial flux" because a magnetic flux passing through the air gaps 7A and 7B between the rotor 2 and the stator 3 extends generally parallel to the axis of rotation X.

[0025] The electric motor 1 also includes a housing 8, preferably metallic, within which the rotor 2 and stator 3 are arranged. The housing 8 forms a sealed or nearly sealed enclosure around the rotor 2 and stator 3 to protect these components. The electric motor 1 can be attached to a vehicle structure via its housing 8. In particular, the housing 8 comprises two half-shells 8A, 8B fastened to each other by fixing screws 9. A parting line between the two half-shells 8A, 8B extends substantially perpendicularly to the axis of rotation X. The overall shape of the housing 8 can be generally cylindrical with an axis of revolution centered on the axis of rotation X. A front wall 10A and a rear wall 10B of the housing can thus be identified. As can be seen in [Fig.2], the walls 10A and 10B of the housing are roughly in the shape of a disc.

[0026] The electric motor 1 further comprises two platters 11A, 1IB arranged inside the housing 8. A front platter 11A extends against an inner face of the front wall 10A and a rear platter 1IB extends against an inner face of the rear wall 10B. The platters 11A and 1IB are fixed rigidly to the housing 8. Bearing housings 12A, 12B are arranged respectively at the interface between the platters 11A and 1IB and the rotating shaft 4. The platters 11A and 1IB thus support and guide the rotation of the rotating shaft 4.

[0027] In addition, oil lines 13 are provided between each plate 1 IA, 1 IB and the corresponding walls 10, 10B. The oil lines 13 belong to an oil cooling circuit for the electric motor 1. The electric motor 1 can It can thus be associated with an oil cooling system comprising said oil circuit, an oil pump configured to circulate the oil in the oil circuit, and a heat exchanger configured to dissipate the heat stored by the oil. This oil circuit is configured to circulate oil around the stators but not at the air gaps.

[0028] The rotor 2 comprises a set of magnets 14 arranged opposite the stator 3. The magnets 14 can be held by a ring 29, in particular made of composite material. The rotor 2 has a disc shape and a circular circumference.

[0029] Each part 3A, 3B of the stator comprises windings of electrical wire 15 and, optionally, ferromagnetic cores 16 arranged inside said windings. The stator 3 has a general ring shape centered on the axis of rotation X. The wire windings 15 and the magnetic cores 16 are positioned opposite the rotor magnets 14. The outer diameter of the stator 3 is at least roughly equal to the outer diameter of the rotor 2. As can be seen in [Fig. 1], a central zone Z1 extending inside the stator and a peripheral zone Z2 extending around the periphery of the stator can be defined. Zones Z1 and Z2 are free zones, i.e., filled with air, and they extend inside the housing 8. Zones Z1 and Z2 communicate with each other via air gaps 7A and 7B.

[0030] In addition to the oil cooling system, the electric motor 1 also includes an air cooling system. The air cooling system comprises a closed air circuit, illustrated by a set of arrows F in [Fig. 1]. By "closed" air circuit, it is understood that the air circuit does not communicate with the ambient air outside the electric motor 1. The air is therefore completely recycled within the air circuit. This prevents the introduction of particles and moisture into the housing 8, which could damage the electric motor.

[0031] The air circuit can be divided into several portions. A first portion PI of the air circuit is formed at the air gaps 7A and 7B. The air in this first portion PI is drawn in a centrifugal direction by the rotation of the rotor. Indeed, the rotor is designed to rotate at very high speeds, up to approximately 12,000 revolutions per minute, which generates a centrifugal force on the air masses in contact with it. It is therefore understood that, thanks to the rotation of the rotor 2, a centrifugal airflow is established in the air gaps 7A and 7B. When the engine is running, the air in the first portion is thus drawn from the central zone Z1 towards the peripheral zone Z2.

[0032] The air circuit also includes a second portion P2, further from the rotor, in which the air is intended to follow a centripetal direction. The air present in the The second section is therefore intended to circulate from the peripheral zone Z2 to the central zone Z1. Between the first section PI and the second section P2, the air in the air circuit can follow a direction at least roughly parallel to the axis of rotation X, or at least a direction with a non-zero component along the axis of rotation X, particularly in the zones Z1 and Z2. The air in the air circuit is thus intended to circulate in a loop, passing successively through the first section PI, then the peripheral zone Z2, then the second section P2, then the central zone Z1, before returning to the first section PL

[0033] The air in the air circuit is circulated solely by the rotation of the rotor 2, without the use of a blower or any other means of air circulation requiring an electrical power supply. Notably, the rotor 2 does not necessarily include blades or any other surface features to more effectively move the air. The rotor 2 may, in particular, have generally smooth surfaces. Indeed, the simple rotation of the rotor 2 at a sufficiently high speed is enough to establish airflow in the air circuit. Alternatively, such features could nevertheless be integrated into the rotor; however, such an arrangement would require increasing the complexity of the rotor and could also increase the overall size of the electric motor 1.

[0034] The second portion P2 extends outside the housing 8. In particular, the second portion P2 extends along the outer face of the rear wall 10B of the housing 8. Thus, the second portion P2 extends to a point distant from the rotor 2 and the stator 3. The air contained in the air circuit can be efficiently cooled as it passes through the second portion P2. Advantageously, the oil cooling circuit is configured to cool the air present in the second portion P2. In particular, at least one oil line 13 can separate the second portion P2 from the stator 3. As can be seen in [Fig. 1], at least one portion 17 of a wall of the housing 8 can comprise a first face in contact with the oil contained in the oil circuit and a second face in contact with the air contained in the second portion P2 of the air circuit.

[0035] The housing 8 includes a first hole 18 formed in the rear wall 10B, opposite the peripheral zone Z2. The air contained in the air circuit passes from the peripheral zone Z2 to the second portion P2 via the first hole 18. According to the embodiment illustrated in the figures, the housing 8 includes a single first hole communicating with the second portion P2. Alternatively, the housing 8 could include more first holes, for example two, three, or four first holes, or even any number greater than or equal to five.

[0036] The electric motor further comprises a cover 19 fixed to the housing 8. The cover 19 covers the first hole 18 and at least partially the outer face of the Rear wall 10B. The cover 19 is securely fixed to the housing 8 to prevent air exchange between the ambient air around the electric motor and the air in the air circuit. The second portion P2 extends between the outer face of the rear wall 10B of the housing and the cover 19. The rear wall 10B also includes a second hole 20 through which the rotating shaft 4 extends. The second hole 20 is located approximately in the center of the rear wall 10B, opposite the rotating shaft 4. The second hole 20 is also covered by the cover 19. Air is intended to flow in the second portion P2 of the air circuit between the first hole 18 and the second hole 20. The air in the air circuit exits the housing 8 through the first hole 18 and returns to the housing 8 through the second hole 20.

[0037] Advantageously, the rotating shaft 4 includes a circulation channel 21 for circulating air from the second portion P2 to the central zone ZI. The circulation channel 21 advantageously includes a central section 22, in particular a bore, extending parallel to the axis of rotation X and radial openings 23A, 23B, communicating with the central section 22. The rotating shaft 4 is thus configured to guide the air from the air circuit from the downstream end of the second portion P2 to the central zone ZI.

[0038] The rotating shaft 4 comprises at least one first opening 23A configured to guide a first portion of the air contained in the air circuit towards the first air gap 7A and at least one second opening 23B configured to guide a second portion of the air contained in the air circuit towards the second air gap 7B. Advantageously, the orientation, cross-section, and length of the openings 23A and 23B are adapted so that an equal amount of airflow passes through the air gaps 7A and 7B. Advantageously, the rotating shaft 4 comprises a plurality of first openings 23A and a plurality of second openings 23B distributed around the central section 22 to diffuse the air homogeneously throughout the volume of the central zone ZI.

[0039] According to one embodiment, a third hole 24 could be arranged directly between the central zone ZI and the outside of the housing 8. In such a case, the rotating shaft 4 might not include a circulation channel. In such a case, the rotor 2 could optionally include holes parallel to the axis of rotation X to allow the airflow to pass through the two air gaps 7A and 7B.

[0040] According to another original aspect of the invention, the second portion P2 is configured to guide the air along a spiral-shaped path from the peripheral zone Z2 to the central zone Z1. In other words, the second portion P2 does not follow the shortest possible path (i.e., a radial path) between the peripheral zone Z2 and the central zone Z1, but a path deviated in a spiral shape. This This design increases the airflow time in the second section P2, thereby enhancing heat exchange between the air in P2 and the surrounding environment. Preferably, the spiral path has at least one turn, meaning at least one complete revolution between the first hole 18 and the second hole 20. This maximizes the heat exchange surface area in the second section P2 and effectively cools the air within it. The crankcase surface area is maximized by separating the air circuit on one side and the oil circuit on the other. The proximity of these two circuits and the large surface area of ​​the crankcase separating them effectively cools the air in the second section P2.

[0041] With reference to [Fig. 3], it can be seen that the cover 19 comprises partitions 26 projecting from an inner face of the cover. The partitions 26 are configured to guide the air present in the second portion P2 along the spiral path from the peripheral zone Z2 of the stator to the central zone of the stator Z1. Preferably, the partitions extend parallel to the axis of rotation X. Preferably, the partitions 26 are in contact with the outer face of the rear wall 10B of the housing. Thus, the partitions form sealed channels to guide the air within the second portion P2.

[0042] Alternatively, the partitions 26 might not be in contact with the outer face of the rear wall 10B of the housing, or at least not along their entire length. In such a case, the free end of the partitions 26 could extend a short distance from the outer face of the rear wall 10B of the housing. Indeed, if there are some air leaks causing a portion of the air volume present between the rear wall 10B and the cover 19 to flow directly (i.e., radially) from the first hole 18 to the second hole 20 without following the spiral path formed by the partitions 26, this only slightly degrades the cooling of the air within the second portion.

[0043] The cover 19 comprises a main plate 25 extending substantially perpendicularly to the axis of rotation X and said partitions 26. The cover 19 is preferably an element manufactured by plastic injection molding. The plate 25 and the partitions 26 thus form a monolithic assembly. The cover 19 is therefore particularly simple to manufacture. The cover 19 is fixed to the housing by means of fixing screws 27. In particular, the cover may include a set of fixing tabs 28 extending radially from the plate 25, each fixing tab 28 comprising a hole cooperating with a fixing screw 27. One or more fixing screws 27 may also be provided through the plate 25. This ensures that the free end of the partitions 26 remains in contact with, or close to, the outer face of the rear wall 10B of the housing.Plate 25 is generally in the shape of a disc with an outgrowth 30 extending opposite the first hole 18.

[0044] According to the embodiment illustrated in [Fig. 3], the spiral-shaped path is delimited by two partitions 261, 262 substantially parallel to each other. The width L of the second portion of the air circuit may first narrow at the outlet of the first hole 18, then become substantially constant up to the second hole 20.

[0045] Figure 4 illustrates a first embodiment comprising a different arrangement of the partitions 26. According to this first embodiment, the cover is provided with a set of partitions 263, 264, 265, 266, distinct from one another. These partitions 263, 264, 265, 266 are connected to the plate 25 but without contact with each other. There are therefore spaces 31 between these different partitions through which the air present in the second portion may enter. According to this first embodiment, a major part of the airflow present in the second portion follows a more natural spiral path, while a small part of the airflow follows a more direct path between the first hole 18 and the second hole 20 via the spaces 31.

[0046] Figure 5 illustrates a second embodiment in which the cover 19 comprises a single external partition 267 and a single internal partition 268. The external partition 267 extends around the entire circumference of the cover 19 and bears against the external face of the rear wall 10B of the housing 8 to isolate the air circuit from the external environment. The internal partition 268 extends from one edge of the external partition 267 along a spiral path. The air in the air circuit is likely to come into contact with two opposite faces of the internal partition 268.

[0047] Alternatively, other partition arrangements 26 may be proposed, in particular to adapt to a configuration where the housing would include at least two first holes 18, and / or to adapt to a configuration where the air would return to the central zone ZI by passing through the third hole 24 as defined previously.

[0048] When the electric motor 1 is running, the rotor 2 rotates around the axis of rotation X at a high speed, generating a centrifugal airflow in the first section PI at the air gaps 7A, 7B. The air in the first section is heated by contact with the stator 3. The hot air exiting the first section PI passes through the peripheral zone Z2 and exits the housing 8 through the first opening 18. The air then enters the second section P2, where it follows a centripetal spiral path and is efficiently cooled, particularly by contact with walls that are themselves cooled by an oil circuit. The cooled air then returns to the inside of the housing through the second opening 20, notably via the circulation channel 21 provided in the rotating shaft 4. The air thus reaches the central zone ZI again and begins a new cycle in the air circuit.

[0049] Thanks to the invention, the temperature of the stator 3 can be lowered by a few more degrees. The electric motor 1 thus operates at a lower temperature and is therefore more reliable. The invention is particularly simple to implement because it does not require any pump or air blower to move the air in the air circuit.

Claims

Demands

1. An axial flux electric motor (1) comprising a stator (3), a rotor (2), and at least one axial air gap (7A, 7B) defined between the stator and the rotor, the electric motor comprising a first closed air-cooling circuit, the air being intended to be circulated in said first circuit by rotation of the rotor, the first circuit comprising a first portion (PI) defined in the at least one air gap, the air present in the first portion being intended to flow from a central zone (Z1) of the stator to a peripheral zone (Z2) of the stator, said first circuit further comprising a second portion (P2), the air present in the second portion being intended to flow from the peripheral zone of the stator to the central zone of the stator, the second portion being configured to guide the air along a spiral path from the peripheral zone of the stator to the central zone of the stator.

2. Electric motor (1) according to the preceding claim, characterized in that it comprises a housing (8) integral with the stator, the housing enveloping the stator (3) and the rotor (2), the second portion (P2) of the first circuit extending outside the housing.

3. Electric motor (1) according to the preceding claim, characterized in that the housing (8) comprises a wall (10B) having at least one first hole (18) opposite the peripheral zone (Z2), the air present in the first circuit being intended to circulate through the first hole, and in that the electric motor comprises a cover (19) fixed to the housing, the cover covering said first hole and at least partially said wall, the second portion (P2) extending between said wall and the cover, in particular in that said wall of the housing comprises at least one second hole (20) opposite the central zone (Z1), the air present in the first circuit being intended to circulate through the second hole.

4. Electric motor (1) according to the preceding claim, characterized in that the cover (19) comprises an inner face facing an outer face of said wall (10B) of the housing, the cover comprising partitions (26) projecting from its inner face, said partitions being configured to guide the air present in the second portion (P2) along a path in the shape of spiral from the peripheral zone (Z2) of the stator towards the central zone (Zl) of the stator.

5. Electric motor (1) according to claim 3 or 4, characterized in that the cover is an element manufactured by plastic injection.

6. Electric motor (1) according to any one of the preceding claims, characterized in that said spiral path comprises at least one complete turn.

7. Electric motor (1) according to any one of the preceding claims, characterized in that it further comprises a second closed oil cooling circuit, in particular at least one oil line (13), the second circuit being configured to cool the air present in the second portion (P2) of the first circuit.

8. Electric motor (1) according to any one of the preceding claims, characterized in that it comprises a rotating shaft (4) integral with the rotor (2), the rotating shaft comprising at least one air circulation channel (21) from said second portion (P2) to the central zone (Z1).

9. Electric motor (1) according to the preceding claim, characterized in that the stator (3) comprises a front part (3A) and a rear part (3B), a first air gap (7A) defined between the rotor (2) and the front part (3A) of the stator, and a second air gap (7B) defined between the rotor (2) and the rear part (3B) of the stator, the rotating shaft (4) comprising at least a first opening (23A) configured to guide a first part of the air from the first circuit to the first air gap, the rotating shaft (4) comprising at least a second opening (23B) configured to guide a second part of the air from the first circuit to the second air gap.

10. Motor vehicle, characterized in that it comprises an electric motor (1) according to any one of the preceding claims.

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