Axial flux electric machine including an air cooling circuit

Abstract

Axial flux electric machine comprising an air-cooling circuit. Axial magnetic flux electric machine (1) for a motor vehicle, the electric machine comprising a stator (3), a rotor (2) and at least one air gap (9A, 9B) defined between the stator and the rotor, the electric machine comprising an air-cooling circuit comprising an airflow guide chute (16), the chute comprising a circumferential collector (17) configured to collect a centrifugal airflow in the at least one air gap, and an air duct (18) downstream of the collector, the air duct being configured to guide an airflow in a direction substantially parallel to an axis of rotation (X) of the rotor relative to the stator. Figure for the abstract: Figure 1

Description

Title of the invention: Axial flux electric machine comprising an air cooling circuit. Technical field of the invention

[0001] The invention relates to an axial flux electric machine comprising an air-cooling circuit. The invention also relates to a motor vehicle comprising such an electric machine. 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. Furthermore, the small air gaps and the high rotor speed also contribute to heating of the rotor and stator area. 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 circuit does not effectively cool the air gaps.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 reduce 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 machine remedying the above disadvantages and improving upon known electrical machines of the prior art.

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

[0007] The invention relates to an axial magnetic flux electric machine for a motor vehicle, the electric machine comprising a stator, a rotor and at least one air gap defined between the stator and the rotor, the electric machine comprising an air cooling circuit comprising an air flow guide chute, the chute comprising a circumferential collector configured to collect a centrifugal air flow in the at least one air gap, and an air duct downstream of the collector, the air duct being configured to guide an air flow in a direction substantially parallel to an axis of rotation of the rotor relative to the stator.

[0008] The stator may include a first stator ring and a second stator ring, and the rotor may be positioned between the first stator ring and the second stator ring, the at least one air gap comprising a first air gap extending between the first stator ring and the rotor and a second air gap extending between the second stator ring and the rotor, the collector being configured to collect a centrifugal airflow in the first air gap and in the second air gap.

[0009] The manifold may include an air passage section of increasing surface area towards the air duct.

[0010] The collector may include a bottom wall, a first side wall and a second side wall, the bottom wall extending parallel to the axis of rotation of the rotor and all around the rotor, the first side wall extending perpendicularly to the axis of rotation of the rotor from a first edge of the bottom wall, the second side wall extending perpendicularly to the axis of rotation of the rotor from a second edge of the bottom wall.

[0011] The air duct may include a first portion extending parallel to the manifold, a quarter-turn bend, and a second portion extending parallel to the axis of rotation of the rotor.

[0012] The electric machine may include a casing inside which the stator, rotor and chute are arranged, the casing including an opening oriented parallel to the axis of rotation of the rotor, the air duct extending at least to the opening of the casing.

[0013] The electric machine may include a housing inside which are arranged the stator, the rotor and the chute, the chute including positioning means cooperating with the housing to position the chute within the housing.

[0014] Positioning means may include: - a set of ribs extending radially from an outer wall of the chute collector and bearing against a first wall of the housing to center the chute relative to the housing, and / or - a stop bearing against a second wall of the housing to prevent rotation of the chute relative to the housing around the axis of rotation of the rotor, and / or - at least one elastic element bearing against at least a third wall of the housing to position the chute relative to the housing along the axis of rotation of the rotor.

[0015] The chute can be made of plastic or aluminum.

[0016] The invention also relates to a motor vehicle comprising a electrical machine as defined previously. Presentation of the figures

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

[0018] The [Fig. 1] is a perspective and partial cross-sectional view of an electrical machine according to an embodiment of the invention.

[0019] Fig. 2 is a cross-sectional view of the electric machine along a plane perpendicular to an axis of rotation of a rotor of the electric machine.

[0020] Fig. 3 is a cross-sectional view of a part of the electric machine along a plane parallel to the axis of rotation of the rotor of the electric machine.

[0021] Fig. 4 is a first perspective view of a chute of an air cooling circuit of the electric machine.

[0022] Fig. 5 is a second perspective view of a chute of an air cooling circuit of the electric machine. Detailed description

[0023] Figure 1 schematically illustrates an axial flux electric machine 1 according to an embodiment of the invention. The electric machine 1 is capable of operating as an electric motor to drive the drive wheels of a motor vehicle. The electric machine 1 can also be capable of operating as an electric current generator using the kinetic energy of the vehicle. The motor vehicle can be, for example, a passenger car, a commercial vehicle, a truck, or even a bus. The electric machine 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 machine 1 further comprises 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 drive wheels of the vehicle via a transmission system.

[0024] The rotor 2, clearly visible in [Fig. 2], comprises a set of magnets 5 fixed to a support 6 (in this case twelve magnets, but alternatively this number could be different). The support 6 is itself fixed to the rotating shaft 4, notably by means of fixing screws 7. The support 6 has a star shape. The magnets 5 are housed in spaces, in particular of roughly trapezoidal shape, formed between the arms of the star. The magnets 5 are held by a circumferential ring 8, shrink-fitted around the magnets 5 and / or the support 6. The ring 8 can, for example, be a cylindrical element, for example made of a composite material. The ring 8 is intended to counteract the centrifugal force that may be exerted on the magnets 5 and thus keeps the magnets 5 in place within their respective spaces.The rotor 2 generally has the shape of a cylindrical cylinder of revolution with two bases extending perpendicularly to the axis of rotation X and a circular circumference.

[0025] As can be clearly seen in [Fig. 3], the stator 3 comprises two parts 3A, 3B, also referred to as the first stator ring 3A and the second stator ring 3B. Each stator ring 3A, 3B preferably comprises a set of electrical coils 10 arranged around a ferromagnetic core 11. The two stator rings 3A, 3B are separated from each other along the axis of rotation X. The rotor 2 is interposed between the two stator rings 3A and 3B. The electrical machine 1 thus comprises a first axial air gap 9A, defined between the rotor 2 and the first stator ring 3A, and a second axial air gap 9B, defined between the rotor 2 and the second stator ring 3B. The air gaps 9A and 9B are free spaces which each extend in planes perpendicular to the axis of rotation X. The air gaps 9A, 9B can have a dimension on the order of a millimeter along the axis of rotation X.The electric machine 1 is said to be "axial flux" because a magnetic flux passing through the air gaps 9A and 9B between the rotor 2 and the stator 3 extends globally parallel to the axis of rotation X.

[0026] The electric machine 1 also includes a housing 12, preferably metallic, particularly aluminum, inside which the rotor 2 and stator 3 are arranged. The housing 12 forms a sealed or nearly sealed enclosure around the rotor 2 and stator 3 to protect these components. The electric machine 1 can be attached to a vehicle structure via its housing 12. In particular, the housing 12 comprises two half-shells 12A, 12B fastened to each other by fixing screws 13. A parting line between the two half-shells 12A, 12B extends substantially perpendicular to the axis of rotation X. The general shape of the housing 12 can be a generally cylindrical shape with an axis of revolution centered on the axis of rotation X.

[0027] 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. 2], a central zone ZI extending inside the stator (between the rotating shaft 4 and the electrical coils 10) and a peripheral zone Z2 extending around the periphery of the stator can be defined. Zones ZI and Z2 are free zones, i.e., filled with air, and they extend inside the housing 12. Zones ZI and Z2 communicate with each other via air gaps 9A and 9B. The central zone ZI comprises a first part extending inside the first stator ring 3A and a second part extending inside the second stator ring 3B.The two parts of the central zone ZI communicate with each other through holes 15 provided in the support 6.

[0028] Furthermore, the electric machine 1 can be equipped with an oil cooling circuit. The oil cooling circuit includes, in particular, oil lines 14 extending along the internal walls of the casing 12. The electric machine 1 can thus be associated with an oil cooling system comprising said oil cooling circuit, an oil pump configured to circulate oil in the oil circuit, and a heat exchanger configured to dissipate the heat stored by the oil. The oil cooling circuit is configured to circulate oil around the stators but not at the air gaps 9A or 9B.

[0029] In addition to the oil cooling system, the electric machine 1 also includes an air cooling system. Preferably, the air cooling system comprises a closed air circuit. 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 / or moisture into the housing 12, which could damage the electric machine. Alternatively, the air circuit could be an open air circuit, that is, an air circuit that draws in free air from the environment around the electric machine and then discharges the air heated by contact with the electric machine back into this environment.

[0030] When the electric machine 1 is operating, the air present in the air gaps 9A and 9B 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 to 15,000 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 9A and 9B.

[0031] 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 have blades or any other surface features to more effectively move the air. The rotor 2 may, in particular, have generally smooth surfaces. Indeed, simply rotating the rotor 2 at a sufficiently high speed is enough to establish airflow in the air circuit. Alternatively, such features could 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.

[0032] It is therefore understood that the air circuit comprises a first portion in which the air flows in a centrifugal direction. Assuming that the air circuit is a closed circuit, it also comprises a second portion, further from the rotor, in which the air is intended to flow in a centripetal direction. The second portion may extend outside the housing 12. The air contained in the air circuit may be cooled as it passes through the second portion.

[0033] Advantageously, the rotating shaft 4 may include a circulation channel for conveying air from the second portion to the central zone. The circulation channel may include a central section, in particular a bore, extending parallel to the axis of rotation X at the center of the rotating shaft 4, and radial openings connecting the central section to the central zone ZI. The rotating shaft 4 can thus be configured to guide air from the air circuit from downstream of the second portion to the central zone ZI.

[0034] According to the invention, the air-cooling circuit includes an airflow guide duct 16. The duct 16 is designed to collect the centrifugal airflow in the air gaps 9A and 9B and to guide this airflow in a direction substantially parallel to the axis of rotation X. The duct 16, which is illustrated in Figures 4 and 5, includes a circumferential manifold 17 configured to collect a centrifugal airflow in the air gaps 9A and 9B. By "circumferential," it is understood that the manifold 17 extends all around the air gaps 9A and 9B, that is, 360° around the axis of rotation 360°. Thus, the manifold 17 collects, or in other words, receives all or at least most of the airflow passing through the air gaps 9A and 9B. The manifold 17 concentrates the airflow passing through the air gaps. The manifold 17 has an annular shape. It is positioned around the rotor 2 in the peripheral zone Z2.When the rotor rotates around the axis of rotation X, the airflow in the manifold 17 has a tangential direction. The tangential direction of the airflow is represented by a set of arrows in [Fig. 4].

[0035] The chute 16 further includes an air conduit 18 downstream of the manifold 17 following the direction of airflow. The air duct 18 is configured to guide an airflow in a direction substantially parallel to an axis of rotation of the rotor relative to the stator. By "substantially parallel to the axis of rotation X," we mean a direction forming an angle with the axis of rotation X of less than or equal to 45°, or even less than or equal to 30°, or preferably less than or equal to 15°, or even less than or equal to 5°. The air duct is therefore configured to deflect the airflow oriented tangentially in the manifold 17 towards a direction substantially parallel to the axis of rotation X. This direction is represented by an arrow in [Fig. 5]. Redirecting the airflow in a direction substantially parallel to the axis of rotation X minimizes the radial space occupied by the air circuit.The radial space available for the electric machine 1 can thus be used to increase the diameters of the rotor and stator, thereby providing a more powerful electric machine for the same radial footprint.

[0036] The air duct 18 thus comprises a first portion 19 extending parallel to the manifold, that is, parallel to a tangential direction, a bend 20 forming approximately a quarter turn, and a second portion 21 extending parallel to the axis of rotation of the rotor relative to the stator. As can be seen in [Fig. 3], the first portion 19 has a substantially square cross-section and the second portion 21 has an oval cross-section. The change in shape of the cross-section of the air duct 18 is gradual between the inlet and outlet of the air duct.

[0037] The housing 12 includes an opening 27, or window 27, oriented parallel to the axis of rotation X, through which the second portion 21 of the air duct 18 opens. The air duct 18 thus extends at least as far as the opening 27 of the housing. The air duct 18 may, however, be extended beyond the opening 27. In particular, the air duct 18 may be connected to a secondary air duct (not shown) configured to redirect the airflow towards the rotating shaft 4. The secondary air duct and the air duct 18 may be fixed to each other, or even form a single unit. Advantageously, a space formed between the outer wall of the air duct 18 and the inner wall of the opening 27 can be sealed to prevent particles from entering the housing 12. The housing 12 also includes a protrusion 28 to house the air duct 18. This protrusion 28 is formed at the cylindrical wall of the housing.

[0038] As a note, according to the embodiment presented, the first portion 19 extends in a tangential direction oriented in the direction of rotation of the rotor when the vehicle moves forward. When the vehicle moves backward, which corresponds to relatively rare use cases compared to forward operation, the first portion 19 extends in a direction tangential in the opposite direction to the rotor's rotation. In this case, the airflow enters the air duct less easily, and the motor's air cooling is less efficient. However, this is not a problem since reverse operation is quite rare and does not correspond to situations where the electric machine 1 is operating at full power.

[0039] The same manifold 17 is configured to collect the centrifugal airflow in the two air gaps 9A and 9B. The manifold 17 comprises a U-shaped cross-section, the two arms of which each point towards an air gap 9A or 9B. More specifically, the manifold 17 comprises a bottom wall 22, a first side wall 23, and a second side wall 24. The bottom wall 22 extends parallel to the axis of rotation X and all around the rotor. The first side wall 23 extends perpendicularly to the axis of rotation X from a first edge of the bottom wall 22. The second side wall 24 extends perpendicularly to the axis of rotation of the rotor from a second edge of the bottom wall 22. The side walls 23 and 24 thus form the arms of the U, and the bottom wall 22 forms the base of the U. The air passage section 25 of the manifold can be defined as the area between the side walls 23 and 24 and the bottom wall 22.In this particular case, the air passage section 25 has a roughly rectangular shape.

[0040] According to another advantageous aspect of the invention, the air passage section 25 has an increasing surface area towards the air duct 18. In this particular case, the progressive increase in the air passage section 25 is achieved by progressively moving the bottom wall 22 away from the axis of rotation X as one follows the path of the airflow in the manifold 17. This allows an increasing quantity of air to accumulate as one approaches the air duct 18. A stable airflow velocity is thus obtained in the manifold 17, and therefore more efficient operation of the manifold 17. In other words, the manifold 17 has a spiral shape with a coil, or in other words, a snail-like shape. In the cross-sectional view of [Fig. 3], the air passage section 25 is minimal: the bottom wall 22 is very close to the outer surface of the ring 8.The bottom wall 22 gradually moves away from the outer surface 8 of the ring until it reaches a position corresponding to the outer wall 26 of the first portion 19 at the point of entry into the air duct 18. .

[0041] The chute 16 also includes positioning means cooperating with the housing 12 to position the chute within the housing. In particular, the positioning means allow the precise definition of the position of the chute 16 within the housing 12, which makes it possible to efficiently collect the airflow while avoiding unwanted contact between the rotor and the chute.

[0042] In particular, the chute 16 comprises a set of ribs 29 extending radially from an outer wall of the chute collector and bearing against a first wall 30 of the housing to center the chute relative to the housing. Preferably, the chute comprises at least three ribs 29 distributed around the circumference of the chute 16. The ribs may extend radially from the bottom wall 22 in the centrifugal direction. The housing wall 30 against which the ribs 29 bear is preferably a cylindrical wall.

[0043] The chute 16 also includes a stop 31 bearing against a second wall of the housing (not shown) to prevent rotation of the chute relative to the housing about the axis of rotation X. The stop 31 may, for example, include a clamp, in particular an elastic clamp, cooperating with a rib of the housing projecting towards the clamp. Such a clamp prevents rotation of the chute relative to the housing in both directions. The stop 31 not only prevents rotation of the chute 16 but also allows its position to be indexed. During assembly of the chute in the housing, the cooperation of the stop 31 with the second wall of the housing allows the orientation of the chute about the axis of rotation X to be defined.

[0044] The chute 16 also includes at least one elastic element 32, for example at least one elastic tab, bearing against at least one third wall of the housing (not shown) to position the chute relative to the housing along the axis of rotation X. The at least one elastic element thus makes it possible to center the chute 16 in the housing 12, which makes it possible to efficiently collect the airflow generated by the rotation of the rotor 2. In this particular case, the chute 16 includes three elastic tabs distributed around its periphery.

[0045] Advantageously, these various positioning means are integral with the chute 16 and even formed directly onto the chute. This avoids the use of add-on parts to correctly position and / or orient the chute within the housing.

[0046] According to one embodiment, the chute 16 can be made of plastic, for example by molding. The chute 16 is thus particularly lightweight and easy to manufacture. Moreover, the use of plastic allows for a fairly wide variety of shapes. According to another embodiment, the chute 16 can be made of metal, in particular aluminum. Aluminum remains relatively lightweight and has the advantage of conducting heat well. The air circulating in the chute can thus be cooled more easily.

[0047] According to one embodiment, the chute 16 could include several air ducts downstream of the manifold. The chute could include, for example, two air ducts similar to the air duct 18 described above. The two Air ducts could be diametrically opposed on the manifold 17. According to another embodiment, the air duct 18 could include a branch, for example formed in the first portion 19. The chute would then include two bends analogous to the bend 20 previously described, and two second portions, each connected to a bend, each second portion extending parallel to the axis of rotation X but in opposite directions.

[0048] When the electric machine 1 is operating, an electric current flows through the stator's electrical coils 10, causing them to heat up. The air in contact with the stator also heats up. As the rotor 2 rotates around the axis of rotation X, a centrifugal airflow is generated at the air gaps 9A, 9B. The air heated by the stator is collected by the collector 17 of the chute 16 and guided into the air duct 18. The air then exits the housing 12 in a direction substantially parallel to the rotor's axis of rotation, and may follow a centripetal path while cooling. The cooled air can then return to the inside of the housing, notably by passing through the circulation channel 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 magnetic flux electric machine (1) for a motor vehicle, the electric machine comprising a stator (3), a rotor (2) and at least one air gap (9A, 9B) defined between the stator and the rotor, the electric machine comprising an air cooling circuit comprising an airflow guide chute (16), the chute comprising a circumferential collector (17) configured to collect a centrifugal airflow in the at least one air gap, and an air duct (18) downstream of the collector, the air duct being configured to guide an airflow in a direction substantially parallel to an axis of rotation (X) of the rotor relative to the stator.

2. An electric machine (1) according to the preceding claim, characterized in that the stator (3) comprises a first stator ring (3A) and a second stator ring (3B), and in that the rotor (2) is positioned between the first stator ring and the second stator ring, the at least one air gap comprising a first air gap (9A) extending between the first stator ring and the rotor and a second air gap (9B) extending between the second stator ring and the rotor, the collector (17) being configured to collect a centrifugal airflow in the first air gap and in the second air gap.

3. Electric machine (1) according to any one of the preceding claims, characterized in that the manifold (17) comprises an air passage section (25) of increasing surface area towards the air duct (18).

4. Electric machine (1) according to any one of the preceding claims, characterized in that the commutator (17) comprises a bottom wall (22), a first side wall (23) and a second side wall (24), the bottom wall extending parallel to the axis of rotation (X) of the rotor and all around the rotor (2), the first side wall extending perpendicularly to the axis of rotation of the rotor from a first edge of the bottom wall, the second side wall extending perpendicularly to the axis of rotation of the rotor from a second edge of the bottom wall.

5. An electric machine (1) according to any one of the preceding claims, characterized in that the air duct (18) comprises a first portion (19) extending parallel to the manifold (17), a bend (20) forming a quarter turn, and a second portion (21) extending parallel to the axis of rotation (X) of the rotor.

6. Electric machine (1) according to any one of the preceding claims, characterized in that it comprises a casing (12) within which are arranged the stator (3), the rotor (2) and the chute (16), the casing comprising an opening (27) oriented parallel to the axis of rotation (X) of the rotor, the air duct (18) extending at least to the opening of the casing.

7. Electric machine (1) according to any one of the preceding claims characterized in that it comprises a housing (12) within which are arranged the stator (3), the rotor (2) and the chute (16), the chute comprising positioning means cooperating with the housing to position the chute within the housing.

8. Electric machine (1) according to the preceding claim, characterized in that the positioning means comprise: - a set of ribs (29) extending radially from an external wall of the collector (17) of the chute (16) and bearing against a first wall (30) of the housing to center the chute relative to the housing, and / or - a stop (31) bearing against a second wall of the housing to prevent rotation of the chute relative to the housing around the axis of rotation of the rotor, and / or - at least one elastic element (32) bearing against at least a third wall of the housing to position the chute relative to the housing along the axis of rotation of the rotor.

9. Electric machine (1) according to any one of the preceding claims, characterized in that the chute (16) is made of plastic or aluminum.

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

Images