Axial flux electric motor including closed-circuit air cooling

Abstract

Axial flux electric motor comprising closed-circuit air cooling An 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 intended to be circulated in said first circuit by rotation of the rotor, the first circuit comprising a first portion (P1) defined in the at least one air gap, the air present in the first portion being intended to circulate 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 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-shaped path. Figure for abstract: 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-circuit air cooling circuit. The invention also relates to a motor vehicle comprising such an electric motor. State of the prior art

[0002] So-called "electric" or "hybrid" motor vehicles comprise 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 perpendicular to an axis of rotation of the rotor. The rotor generally comprises a crown provided with magnets and is securely attached to a rotating shaft of the electric motor. The stator comprises windings of electrical wires through which a high-power electric current can flow.

[0003] The circulation of electric current in the windings of electric wires of the stator causes significant heating, which may damage certain parts of the electric motor and / or disrupt its proper operation. It is therefore important to cool the electric motor during its operation. For this purpose, axial flux electric motors are known comprising a closed oil cooling circuit. The oil is circulated by a pump and circulates in oil pipes arranged in a casing of the electric motor. The cooling circuit is connected to a heat exchanger configured to cool the oil and thus dissipate the heat generated by the stator. An oil cooling system is nevertheless bulky and does not cool the stator sufficiently effectively. In addition, certain parts of an axial flux electric motor may be incompatible with contact with oil.These parts cannot therefore be directly cooled by the oil cooling system. For example, the air gap cannot be immersed in oil because this would significantly penalize the efficiency of the electric motor.

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

[0005] The aim of the invention is to provide an axial flux electric motor which overcomes the above disadvantages and improving the axial flux electric motors known from the prior art.

[0006] More specifically, a first object of the invention is an axial flux electric motor provided with an efficient, compact and simple 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-shaped path from the peripheral zone of the stator to the central zone of the stator.

[0008] The electric motor according to the preceding claim may comprise a casing secured to the stator, the casing enclosing the stator and the rotor, the second portion of the first circuit extending outside the casing.

[0009] The casing may comprise a wall provided with at least a first hole facing the peripheral zone, the air present in the first circuit being intended to circulate through the first hole, and the electric motor may comprise a cover fixed to the casing, 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 wall of the casing may comprise at least a second hole facing the central zone, the air present in the first circuit being intended to circulate through the second hole.

[0010] The cover may comprise an internal face facing an external face of said wall of the casing, the cover comprising partitions extending in projection from its internal face, said partitions being configured to guide the air present in the second portion following a spiral-shaped path from the peripheral zone of the stator towards the central zone of the stator.

[0011] The cover may 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 comprise a second closed oil cooling circuit, in particular at least one oil pipe, the second circuit being configured to cool the air present in the second portion of the first circuit.

[0014] The electric motor may comprise a rotating shaft secured to the rotor, the rotating shaft comprising at least one air circulation channel from said second portion to the central zone.

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

[0017] These objects, characteristics and advantages of the present invention will be explained in detail in the following description of various particular embodiments made without limitation in relation to the attached figures among which:

[0018] [Fig. 1] is a perspective and sectional view of an axial flux electric motor according to one embodiment of the invention, the 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.l].

[0020] [Fig.3] is a sectional view of the electric motor of [Fig.l], the section being made in a plane perpendicular to the axis of rotation of the rotor.

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

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

[0023] [Fig.l] schematically illustrates an axial flux electric motor 1 according to one 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 private vehicle, a utility vehicle, a truck or even a bus. The electric motor 1 comprises a rotor 2 and a stator 3. The rotor 2 is rotatable relative to the stator 3 about an axis of rotation X. The electric motor 1 further comprises a rotary shaft 4 extending parallel to the axis of rotation X. The rotary shaft 4 is integral with the rotor 2 and is intended to be mechanically connected to the drive wheels of the vehicle via a transmission system. The rotating shaft 4 comprises a flange 5 against which the rotor 2 is fixed, in particular by fixing screws 6. The rotating shaft also comprises splines to ensure a mechanical connection with the transmission system.

[0024] The stator 3 comprises two parts 3A, 3B, arbitrarily called front part 3A and rear part 3B. The two parts 3A, 3B of the rotor are distant 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 a dimension of 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 comprises a casing 8, preferably metallic, inside which the rotor 2 and the stator 3 are arranged. The casing 8 forms a sealed or almost sealed envelope around the rotor 2 and the stator 3, in order to protect these components. The electric motor 1 can be fixed to a structure of the vehicle by means of its casing 8. In particular, the casing 8 comprises two half-shells 8A, 8B fixed to each other by fixing screws 9. A joint plane between the two half-shells 8A, 8B extends substantially perpendicular to the axis of rotation X. The general shape of the casing 8 can be a generally cylindrical shape with an axis of revolution centered on the axis of rotation X. It is thus possible to identify a front wall 10A and a rear wall 10B of the casing. As can be seen in [Fig.2], the walls 10A and 10B of the casing are roughly disc-shaped.

[0026] The electric motor 1 further comprises two plates 11A, 11B arranged inside the casing 8. A front plate 11A extends against an inner face of the front wall 10A and a rear plate 11B extends against an inner face of the rear wall 10B. The plates 11A and 11B are fixedly attached to the casing 8. Rolling bearings 12A, 12B are arranged respectively at the interface between the plates 11A and 11B and the rotary shaft 4. The plates 11A and 11B thus make it possible to support and guide the rotary shaft 4 in rotation.

[0027] In addition, oil pipes 13 are provided between each plate 11A, 11B and the corresponding walls 10, 10B. The oil pipes 13 belong to an oil cooling circuit of the electric motor 1. The electric motor 1 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 may be held by a ring 29, in particular made of composite material. The rotor 2 comprises a disc shape and has a circular periphery.

[0029] Each part 3A, 3B of the stator comprises windings of electric wires 15 and, possibly, ferromagnetic cores 16 arranged inside said windings. The stator 3 has a general crown shape centered on the axis of rotation X. The electric wire windings 15 and the magnetic cores 16 are positioned opposite the magnets 14 of the rotor. 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.l], it is possible to define a central zone ZI extending inside the stator, and a peripheral zone Z2 extending to the periphery of the stator. The zones ZI and Z2 are free zones, that is to say filled with air and they extend inside the casing 8. The zones ZI and Z2 communicate with each other via the air gaps 7A and 7B.

[0030] In addition to the oil cooling system, the electric motor 1 also comprises an air cooling system. The air cooling system comprises a closed air circuit, illustrated by a set of arrows F in [Fig.l]. 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 in the air circuit. This avoids introducing particles and moisture inside the casing 8, which could damage the electric motor.

[0031] The air circuit can be broken down into several portions. A first portion PI of the air circuit is formed at the air gaps 7A and 7B. The air present in the first portion PI is driven in a centrifugal direction by the rotation of the rotor. Indeed, the rotor is intended to rotate at very high speed, in particular 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 air flow is established in the air gaps 7A and 7B. When the engine is running, the air present in the first portion is therefore driven from the central zone Z1 to the peripheral zone Z2.

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

[0033] The air present in the air circuit is circulated solely by the rotation of the rotor 2, without the use of an air blower or any other means of circulating the air requiring an electrical power supply. As a note, the rotor 2 does not necessarily include a blade or any other form of relief on its surface to drive the air more efficiently. The rotor may 2 may in particular include generally smooth surfaces. Indeed, the simple rotation of the rotor 2 at a sufficiently high speed is sufficient to establish circulation of an air flow in the air circuit. Alternatively, such reliefs could nevertheless be integrated into the rotor, however such an arrangement would require making the rotor more complex and could also penalize the general size of the electric motor 1.

[0034] The second portion P2 extends outside the casing 8. In particular, the second portion P2 extends along the external face of the rear wall 10B of the casing 8. Thus, the second portion P2 extends to a location distant from the rotor 2 and the stator 3. The air contained in the air circuit can be effectively cooled when 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 pipe 13 can separate the second portion P2 from the stator 3. As can be seen in [Fig.l], at least one part 17 of a wall of the casing 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 casing 8 comprises 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 casing 8 comprises a single first hole communicating with the second portion P2. Alternatively, the casing 8 could comprise 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 casing 8. The cover 19 covers the first hole 18 and at least partially the external face of the rear wall 10B. The cover 19 is fixed in a sealed manner to the casing 8 so as to prevent air exchanges between the ambient air around the electric motor and the air contained in the air circuit. The second portion P2 extends between the external face of the rear wall 10B of the casing and the cover 19. The rear wall 10B also comprises a second hole 20 through which the rotary shaft 4 extends. The second hole 20 is arranged substantially in the center of the rear wall 10B, opposite the rotary shaft 4. The second hole 20 is also covered by the cover 19. The air is intended to circulate in the second portion P2 of the air circuit between the first hole 18 and the second hole 20. The air contained in the air circuit leaves the casing 8 via the first hole 18 and returns to the casing 8 via the second hole 20.

[0037] Advantageously, the rotary shaft 4 comprises a circulation channel 21 for circulating the air from the second portion P2 to the central zone ZI. The circulation channel 21 advantageously comprises 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 rotary shaft 4 is thus configured to guide the air of the air circuit from the downstream end of the second portion P2 to the central zone ZI.

[0038] The rotary 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, the section and the length of the openings 23A and 23B are adapted so that an equal quantity of air flow circulates through the air gaps 7A and 7B. Advantageously, the rotary 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 an alternative embodiment, a third hole 24 could be arranged directly between the central zone ZI and the exterior of the casing 8. In such a hypothesis, the rotating shaft 4 could not comprise a circulation channel. In such a hypothesis, the rotor 2 could possibly comprise holes parallel to the axis of rotation X to allow the air flow 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 according to a spiral shape. This makes it possible to increase the time taken for the air to pass through the second portion P2, and therefore to increase the heat exchanges between the air present in the second portion P2 and the environment around the second portion. Preferably the spiral-shaped path spiral has at least one turn, that is to say at least one complete turn between the first hole 18 and the second hole 20. Thus the heat exchange surface at the level of the second portion P2 is large and the air contained in the second portion P2 is well cooled. The surfaces of the casing are maximized with the air circuit on one side and the oil circuit on the other. The proximity between these two circuits and the large surface area of ​​the casing separating these two circuits makes it possible to cool the air present in the second portion P2.

[0041] With reference to [Fig. 3], it is observed that the cover 19 comprises partitions 26 extending projecting from an internal face of the cover. The partitions 26 are configured to guide the air present in the second portion P2 along said spiral-shaped path from the peripheral zone Z2 of the stator to the central zone Z1 of the stator. Preferably, the partitions extend parallel to the axis of rotation X. Preferably, the partitions 26 are in contact against the external face of the rear wall 10B of the casing. Thus, the partitions form sealed channels to guide the air within the second portion P2.

[0042] Alternatively, the partitions 26 could not be in contact with the external face of the rear wall 10B of the casing, or at least not over their entire length. In such a hypothesis, the free end of the partitions 26 could extend a short distance from the external face of the rear wall 10B of the casing. Indeed, if there are some air leaks leading a portion of the volume of air 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 perpendicular to the axis of rotation X and said partitions 26. The cover 19 is preferably an element manufactured by plastic injection. The plate 25 and the partitions 26 thus form a monolithic assembly. The cover 19 is therefore particularly simple to produce. The cover 19 is fixed to the casing by means of fixing screws 27. In particular, the cover may comprise a set of fixing lugs 28 extending radially from the plate 25, each fixing lug 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 makes it possible to ensure that the free end of the partitions 26 remain in contact or at a short distance from the external face of the rear wall 10B of the casing.The plate 25 generally has the shape of a disc provided with a protrusion 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 until the second hole 20.

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

[0046] [Fig. 5] illustrates a second alternative 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 casing 8 to isolate the air circuit from the external environment. The internal partition 268 extends from an edge of the external partition 267 along a spiral-shaped path. The air present in the air circuit is likely to come into contact against two opposite faces of the internal partition 268.

[0047] As a variant, still other arrangements of partitions 26 could be proposed, in particular to adapt to a configuration where the casing would comprise 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 operating, the rotor 2 rotates around the rotation axis X at a high speed, which generates a centrifugal air flow in the first portion PI at the air gaps 7A, 7B. The air present in the first portion heats up on contact with the stator 3. The hot air leaving the first portion PI passes through the peripheral zone Z2 and leaves the casing 8 through the first opening 18. The air then enters the second portion P2 in which it follows a centripetal path in the form of a spiral and cools efficiently, in particular on contact with walls which are themselves cooled by an oil circuit. Then, the cooled air returns to the inside of the casing via the second opening 20, in particular via the circulation channel 21 provided in the rotary shaft 4. The air thus reaches the central zone Z1 again and begins a new cycle in the air circuit.

[0049] Thanks to the invention, it is thus possible to lower the temperature of the stator 3 by a few additional 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 set the air in motion in the air circuit.

Claims

Claims

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 circulate from a central zone (Zl) 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 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-shaped 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 casing (8) integral with the stator, the casing enclosing the stator (3) and the rotor (2), the second portion (P2) of the first circuit extending outside the casing.

3. Electric motor (1) according to the preceding claim, characterized in that the casing (8) comprises a wall (10B) provided with at least a first hole (18) facing 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 casing, 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 casing comprises at least a second hole (20) facing the central zone (Zl), 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 internal face facing an external face of said wall (10B) of the casing, the cover comprising partitions (26) extending projecting from its internal face, said partitions being configured to guide the air present in the second portion (P2) following a spiral-shaped path 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 one of the preceding claims, characterized in that said spiral-shaped path comprises at least one complete turn.

7. Electric motor (1) according to one of the preceding claims, characterized in that it further comprises a second closed oil cooling circuit, in particular at least one oil pipe (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 one of the preceding claims, characterized in that it comprises a rotary shaft (4) integral with the rotor (2), the rotary shaft comprising at least one air circulation channel (21) from said second portion (P2) to the central zone (Zl).

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 rotary shaft (4) comprising at least one first opening (23A) configured to guide a first portion of the air from the first circuit to the first air gap, the rotary shaft (4) comprising at least one second opening (23B) configured to guide a second portion 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 one of the preceding claims.

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