FR3133281A1 - Electromagnetic motor with surface magnets - Google Patents

Abstract

The invention relates to an electromagnetic motor (1) comprising an internal rotor (2) and an external rotor (2a) concentric with respect to a central axis of rotation (3), the rotors (2, 2a) interposing between them a stator ( 10) with an air gap (14, 14a) between the stator (10) and each rotor (2, 2a). Each rotor (2, 2a) is provided with a magnetic circuit (8) for circulating magnetic flux facing a respective air gap (14, 14a) and carries magnets (6). For the internal and external rotors (2, 2a), the magnets are surface magnets (6) positioned in or on the associated magnetic circuit (8) flush with the magnetic circuit (8) towards the respective air gap (14, 14a). . Abstract figure: FIGURE 1

Description

Electromagnetic motor with surface magnets

The invention relates to an electromagnetic motor for driving an organ enveloping it at least partially, in particular by integrating it into its interior, or by being attached to the motor, this motor being with surface magnets.

In a non-limiting embodiment of the present invention, the motor can be housed in a wheel of a vehicle for the propulsion of said vehicle, thus forming what is called a wheel motor. In the case of a vehicle equipped with several wheels, such a motor can be installed in each wheel of the vehicle.

Such a motor for driving a component is intended in particular for low speed and high torque applications in a small footprint with a substantially discoid shape.

To do this, it is known to use an electromagnetic motor comprising a rotor carrying permanent magnets and a stator carrying windings, the stator and the rotor defining an air gap between them.

Such a motor with a single air gap, although of reduced size which is favorable for its installation in a member to be driven, has the great disadvantage of not delivering a strong torque.

Document FR-A-2 881 290 describes an electric wheel or wheel motor comprising a motor incorporated in a wheel for its drive. The motor includes a stator and a rotor connected to a torque transmission system to transmit torque to the wheel.

In one embodiment, the rotor has two rotors or field generators each delimiting with the stator an air gap, each rotor comprising magnets with poles magnetized in a radial direction relative to an axis of rotation of the motor and magnetized yoke magnets each of which is placed between two adjacent pole magnets to reinforce the magnetic field formed by the pole magnets.

The presence of cylinder head magnets, however, reduces the space allocated to pole magnets in the necessarily reduced dimensions of the engine.

The problem underlying the present invention is to design an electromagnetic motor intended for driving a member delivering an increased power density while remaining as compact as possible by a significant increase in the magnetic exchange surfaces compared to a motor according to the state of the art.

For this purpose the present invention relates to an electromagnetic motor comprising an internal rotor and an external rotor concentric with respect to a central axis of rotation, the rotors interposing between them a stator with an air gap between the stator and each rotor, each rotor being provided with 'a magnetic circuit for circulating magnetic flux facing a respective air gap and carrying magnets, characterized in that, for the internal and external rotors, the magnets are surface magnets positioned in or on the magnetic circuit associated flush with the magnetic circuit towards the respective air gap.

By surface magnet is meant magnets protruding at least partially from the magnetic circuit. These surface magnets can be secured to the magnetic circuit by any means, in particular by bonding without penetrating the magnetic circuit. Alternatively, these surface magnets can be semi-buried in the magnetic circuit until they protrude only slightly from the magnetic circuit, therefore not completely buried on all sides by the magnetic circuit.

Such a motor makes it possible to achieve high volume torque in a reduced footprint, through better use of the allocated volume, resulting in better power density. The fact of using surface magnets makes it possible to increase the volume of useful magnet necessary for the creation of torque.

In order to obtain a high volume torque, current densities of between 15 and 20 A/mm ² can be achieved. Such a motor also makes it possible to achieve a low air gap value, around 0.8 millimeters or less.

When a motor has a high number of pole pairs, its architecture generally has a high internal bore diameter, a consequence of a high air gap diameter conducive to torque creation. This observation is valid whether the motor has an internal or external rotor.

A solution to be able to further gain torque is to use this internal volume by switching to a double air gap architecture with a stator and two rotors, which is recommended by the present invention, this with rotors equipped with surface magnets.

By making it possible to increase the electromagnetic exchange surface by positioning, for example, both an internal rotor around an internal axis and an external rotor on the periphery, we have the equivalent of “two motors in one”. This makes it possible to increase the torque of the motor within the given dimensions.

Surface magnets deliver a stronger magnetic field than buried magnets.

Advantageously, the magnets are segmented or pixelated.

By segmented, it is understood that the magnets are cut into relatively long strips or bars compared to smaller geometric surfaces obtained by pixelation, for example cubes, cylinders or polygonal shapes. Pixelated unit magnets are therefore in the form of small section pads compared to segmented magnets.

Advantageously, the unit magnets are in the form of parallelepiped bars or pads with circular, cylindrical or polygonal section.

A large magnet is subject to greater eddy current losses than its equivalent in small or micromagnets. The use of small magnets or micromagnets therefore makes it possible to reduce these losses which are detrimental to the operation of the rotor.

As a result, in each rotor, the eddy current losses in the magnets have been considerably reduced by offering rotors without iron or by offering magnet poles made up of a plurality of small unit magnets.

Advantageously, a number of magnet poles on the internal rotor is equal to a number of magnet poles on the external rotor.

This represents a simplification of the architecture of the motor, in order to seek the maximization of the volume torque but also of the mass torque by greatly simplifying in particular the architecture of the stator winding and by extension the compactness of the stator.

This can also make it possible to operate the two rotors together in a manner dependent on each other, which has the advantage, at a given torque, of reducing the difference in diameter between the external and internal diameter.

Advantageously, each surface magnet carried by the internal rotor is directly opposite a surface magnet of the same polarity carried by the external rotor. This allows synchronous operation of the motor and maximizes the magnetic flux.

Advantageously, each surface magnet carried by the internal rotor is offset in electrical degree from 1 to 30° relative to a surface magnet of the same polarity carried by the external rotor.

In the case of the presence of a so-called reluctant couple, for example for surface magnets of the type semi-buried in the magnetic circuit while flush with the magnetic circuit towards the air gap, a slight offset between the rotors can make it possible to maximize the couple.

Advantageously, the stator comprises an armature core carrying teeth having flanges at each of their longitudinal ends oriented towards a respective rotor, two adjacent teeth leaving between them a notch for a winding, the notch being narrowed by the flanges of the two teeth adjacent to each of their longitudinal ends.

Advantageously, the motor comprises at least one hoop circumferentially covering the magnets of the internal rotor.

Advantageously, masses of the magnets of the internal and external rotors are respectively selected with respect to each other so that the internal and external rotors reach an equivalent induction level.

An equivalent induction level is a necessary condition for the correct sizing of the magnetic circuit of a motor in general.

Advantageously, the motor has radial flow, the external and internal rotors being respectively in the form of a crown perpendicular to the axis of rotation, each crown being extended by a cylindrical portion connected to the external edge of the crown and extending to distance along the axis of rotation.

Advantageously, the rotors are mechanically linked to each other by a connecting part relative to the plane orthogonal to the axis of rotation.

From a theoretical point of view, a mechanical connection by connecting piece is not necessary but in practice this greatly simplifies the stability of the motor by making it impossible for a rotor to unhook.

The invention also relates to a member driven by such a motor, the member being arranged externally to the motor by enveloping it at least partially or by being attached to the motor.

Advantageously, the member is a wheel driven in rotation by said motor, the wheel housing the motor inside it.

The invention finally relates to a means of transport comprising at least one such member in the form of a wheel driven in rotation by said motor, the means of transport having a means of suspending the wheel while leaving the wheel free to rotate.

The accompanying drawings illustrate the invention:

represents a radial sectional view of a portion of an electromagnetic motor with a stator inserted between two rotors carrying surface magnets according to one embodiment of the present invention,

represents a perspective view of the internal and external rotors carrying surface magnets according to one embodiment of the present invention,

represents a total magnetic torque curve delivered by an electromagnetic motor according to the present invention,

represents a surface magnet segmented into several longitudinal bars each forming a unit magnet, such surface magnets being able to be carried by each rotor of an electromagnetic motor according to the present invention,

represents a surface magnet segmented into several lateral bars each forming a unit magnet, such surface magnets being able to be carried by each rotor of an electromagnetic motor according to the present invention,

represents a surface magnet pixelated into several small unit magnets in the form of pads of square section, such surface magnets being able to be carried by each rotor of an electromagnetic motor according to the present invention,

represents a surface magnet pixelated into several small unit magnets in the form of pads of hexagonal section, such surface magnets being able to be carried by each rotor of an electromagnetic motor according to the present invention,

represents a sectional view of a wheel rim comprising an electromagnetic motor according to the present invention,

represents a bottom view of a means of transport comprising four wheels, each of the wheels being equipped with an electromagnetic motor according to the present invention.

In what follows, reference is made to all the figures taken in combination. When reference is made to a specific figure, this figure must be taken in combination with the other figures for the recognition of the designated numerical references.

In the figures, when present, only a magnet or magnet pole and only a small unit magnet forming part of a magnet forming a magnet pole are referenced but what is stated respectively for the pole magnet and the unit magnet is valid for all pole magnets and all unit magnets respectively.

The same goes for the for stator elements that are only referenced for a single element of the same type.

Referring to all the figures and in particular in a first place to Figures 1, 2 and 8, the invention relates to a drive motor 1 which is intended to be associated with a member 15 to be driven by being housed at least partially in organ 15 or while leaning against organ 15.

The motor 1 comprises an internal rotor 2 and an external rotor 2a concentric with respect to a central axis of rotation 3, the rotors 2, 2a interposing between them a stator 10 with an air gap 14, 14a between the stator 10 and each rotor 2, 2a. Each rotor 2, 2a is provided with a magnetic circuit 8 for circulating magnetic flux facing a respective air gap 14, 14a and carrying magnets 6.

According to the invention, for the internal and external rotors 2, 2a, the magnets 6 are surface magnets positioned in or on the associated magnetic circuit 8 flush with the magnetic circuit 8 towards the respective air gap 14, 14a.

For a first type of surface magnet 6, the magnet 6 is positioned on the magnetic circuit 8 of the associated rotor without the presence of a housing to receive it, therefore stuck on the magnetic circuit 8.

A second type of surface magnet brings together magnets 6 partially inserted in a housing but extending at least slightly from their housing, these magnets being qualified as semi-buried magnets.

These 6 semi-buried or recessed magnets have the advantage of adding a reluctant torque which can be used to limit the magnet volume or the intensity of the current at a given torque. The theoretical gains must however be put into perspective because of the potential leaks between the magnets which are then greater.

The advantages of a surface magnet 6 of the first or second type are optimal use of the magnet 6 for the creation of torque at the internal and external rotors 2, 2a and a limitation of the inter-magnet leakage flux.

As can be seen in particular in Figures 1 and 2, in an optional embodiment of the present invention, the magnets 6 of the same polarity can be positioned face to face.

A number of magnet poles 6 on the inner rotor 2 may be equal to a number of magnet poles 6 on the outer rotor 2a. In this configuration, the field lines therefore cross the two rotors 2, 2a.

The advantage of this solution is to avoid the addition of looping of the field lines in notches 12 of the stator 10 containing the winding, which would reduce the space available for the windings. However, in this case, the internal and external rotors 2, 2a of the motor 1 operate in a dependent manner on one another, which reduces the degrees of freedom during the design.

In another optional embodiment, the addition of an angle between the two rotors 2, 2a may be of interest in reducing the torque ripple or in using a resulting torque.

Thus, each surface magnet 6 carried by the internal rotor 2 can be offset in electrical degree from 1 to 30° relative to a surface magnet 6 of the same polarity carried by the external rotor 2a.

Likewise, an architectural asymmetry between the two rotors 2, 2a can be advantageous.

Masses of the magnets 6 of the internal and external rotors 2, 2a can be respectively selected relative to each other so that the internal and external rotors 2, 2a reach an equivalent induction level.

With regard to the stator 10, the stator 10 may have no yoke and be made up of teeth 11 which may have flanges 13, also called isthmus, at each of the longitudinal ends of the teeth 11. The teeth 11 may be carried by a core armature, a notch 12 being inserted between two adjacent teeth 11 to receive a winding.

The looping of the flow then takes place in a magnetic circuit 8 present in each of the rotors 2, 2a. In order not to penalize the creation of torque between the two rotors 2, 2a, the depth of notch 12 can be significantly increased compared to a single air gap structure, in order to increase the number of turns.

Each notch 12 left between two adjacent teeth 11 can be narrowed laterally by the flanges 13 of the two teeth 11 adjacent to each of their longitudinal ends.

Without this being limiting, for purely illustrative purposes, motor 1 can have 28 pairs of poles and 84 notches.

It can be estimated that the external rotor 2a participates in the creation of the total torque in a proportion of approximately two thirds when the internal rotor 2 only participates in one third.

The difference in radius between the two rotors 2, 2a has a direct impact on the torque but also on the quantity of magnets if we want to keep a similar thickness. From a magnetic point of view, inductions of the order of 2.1 Tesla are achieved in a tooth 11, which is at the limit. A close induction level between the internal and external rotors 2, 2a may be desired to have optimal power density.

There presents the total electromagnetic torque referenced C mag t and measured in Newton. meter or N/m as a function of time. In this figure, a high torque ripple of around 25% can be observed.

The current density can reach 18 A/mm ² . While it is possible to achieve this peak current density with water cooling, continuous operation may require the implementation of oil cooling. The rationale for cooling will also depend on the thermal time constant of motor 1 and the actual temperature rise in the windings during operation.

Such a motor 1 can have a mass of the active parts estimated at almost 70 kg, which implies a relatively low specific power despite the high torque.

The double rotor architecture of the motor 1 according to the present invention made it possible, with the help of an increase in current density, to increase the torque value.

Referring in particular to Figures 4 to 6, the magnets 6 can be segmented or pixelated.

Indeed, it turned out that, for a motor 1 according to the present invention with the previously mentioned characteristics seeking the highest possible volume torque and/or mass torque for rotational speeds of the order of 1,500 rotations per minute, losses could remain high.

In addition, the high compactness of motors 1 means that extracting losses represents a real challenge, beyond performance considerations. Among all the losses, the most difficult to evacuate are those present at each rotor 2, 2a, linked to the rotary movement thereof.

It is thus optionally sought to reduce one of the main loss positions in motor 1 linked to magnets 6.

Due to the non-zero electrical conductivity of the ferromagnetic materials constituting the magnets 6, they are subject to the presence of eddy currents, sources of losses that are all the greater as the field passing through them is important.

To reduce the presence of these circulating currents, the objective was set to reduce the average conductivity of the medium without having too strong an impact on the magnetic properties of the material.

A first solution amounts to segmenting the magnets 6 into multiple strips 7. These strips 7 are spaced from each other by the presence of an electrically insulating material, for example a non-conductive varnish. This process makes it possible to drastically reduce the formation of circulating currents without significantly deteriorating magnetic performance.

Bars 7 extending longitudinally in the magnet 6 forming unit magnets 7 are shown in the while the shows bars 7 extending in the lateral direction of the magnet. These bars 7 can advantageously be of parallelepiped shape.

In Figures 4 and 5, it is visible that a large magnet intended to become a surface magnet 6 can be cut into more than five unit magnets 7 for longitudinal bars and more than twenty unit magnets 7 for lateral bars.

If this solution is not sufficient, it is possible to go further with pixelization. According to this technique, the magnets 6 will be segmented in two directions following rules similar to that of the tiling of the regular plane in the plane orthogonal to the direction of the flow or to the direction of polarization of the magnets 6.

The classic patterns used for pixelization can be square, rectangular, cylindrical or polygonal, in particular hexagonal. The unit magnets 7 in this configuration can be in the form of pads.

Thus, a large magnet intended to become a surface magnet 6 can be cut into a multitude of unit magnets 7 much smaller than bars. In Figures 6 and 7, more than fifty unit magnets 7 are shown forming part of the same surface magnet 6.

The 6 surface magnets can be cut by Laser. A layer of insulating and adhesive varnish or an insulating composite resin can be inserted between the unit magnets 7.

However, to maintain the unit magnets 7 in relation to each other before bonding, it may be advantageous to leave in the cut surface magnet 6 a heel which joins all the unit magnets 7 together. Such a heel can have a zig-zag shape, that is to say be non-planar by extending over several successive planes, which has proven to reduce the eddy currents created by a similar but flat heel.

Particularly in the case of segmented or pixelated surface magnets 6, as the internal and external rotors 2, 2a can rotate at high speed and be subjected to a high centrifugal force, the motor 1 can comprise at least one hoop circumferentially covering the magnets 6 of the internal rotor 2. For the external rotor 2a, it is the casing of the motor 1 which can serve as a hoop but it is also possible to provide a hoop for the external rotor 2a.

As shown in , the electromagnetic motor 1 according to the present invention can be radial flux. However, the present invention is not limited to a radial flux motor.

In this case, the external and internal rotors 2, 2a can respectively be in the form of a crown 9 perpendicular to the axis of rotation 3, each crown 9 being extended by a cylindrical portion 9a connected to the external edge of the crown 9 and extending at a distance along the axis of rotation 3. The references concern the crown 9 and the cylindrical portion 9a of the external rotor 2a but the internal rotor 2 has the same configuration.

The rotors 2, 2a can be mechanically linked to each other by a connecting part. This part can be offset from the plane orthogonal to the axis of rotation 3.

As shown in , the invention also relates to a member 15 driven by an electromagnetic motor 1 as previously described. A connecting part ensures torque transmission between the electromagnetic motor 1 and the driven member 15. The driven organ 15 is at this a wheel rim 15.

The member 15 can be arranged externally to the motor 1 by enveloping it at least partially, which is the case for a wheel motor for which the motor 1 is entirely or mainly integrated into the wheel. Alternatively, the member 15 can be attached to the electromagnetic motor 1 by being secured to one of the sides of the motor 1.

In the non-limiting case of a wheel motor, a common name for a wheel comprising within its interior an electromagnetic motor 1 for its drive, the wheel motor can form part of a means of transport 17 by being associated with one or more other wheel motors, the means of transport 17 having a means of suspending the wheel motor while leaving it free to rotate.

As shown in , the means of transport 17 may comprise a battery 21, advantageously high voltage, powering the wheel motor(s), the wheel motor also being able to serve as a generator for recharging the battery 21. This is valid for an electromagnetic motor 1 according to the present invention which can also be used as a generator.

The electromagnetic motor(s) 1 present in the wheel(s) 16 can be controlled by an electronic unit 18 for controlling the means of transport.

Claims (14)

Electromagnetic motor (1) comprising an internal rotor (2) and an external rotor (2a) concentric with respect to a central axis of rotation (3), the rotors (2, 2a) interposing between them a stator (10) with an air gap (14, 14a) between the stator (10) and each rotor (2, 2a), each rotor (2, 2a) being provided with a magnetic circuit (8) for circulating magnetic flux facing a respective air gap (14, 14a) carrying magnets (6), characterized in that, for the internal and external rotors (2, 2a), the magnets (6) are surface magnets (6) positioned in or on the magnetic circuit (8) associated flush with the magnetic circuit (8) towards the respective air gap (14, 14a). Motor (1) according to the preceding claim, in which the magnets (6) are segmented or pixelated. Motor (1) according to the preceding claim, in which the unit magnets (7) are in the form of parallelepiped bars (7) or studs with circular, cylindrical or polygonal section. Motor (1) according to any one of the preceding claims, wherein a number of magnet poles (6) on the inner rotor (2) is equal to a number of magnet poles (6) on the outer rotor ( 2a). Motor (1) according to claim 4, in which each surface magnet (6) carried by the internal rotor (2) is directly opposite a surface magnet (6) of the same polarity carried by the external rotor ( 2a). Motor (1) according to claim 4, in which each surface magnet (6) carried by the internal rotor (2) is offset in electrical degree from 1 to 30° relative to a surface magnet (6) of the same polarity carried by the external rotor (2a). Motor (1) according to any one of the preceding claims, in which the stator (10) comprises an armature core carrying teeth (11) having flanges (13) at each of their longitudinal ends oriented towards a rotor (2 , 2a) respectively, two adjacent teeth (11) leaving between them a notch (12) for a winding, the notch (12) being narrowed by the flanges (13) of the two teeth (11) adjacent to each of their longitudinal ends . Motor (1) according to any one of the preceding claims, in which the motor (1) comprises at least one hoop circumferentially covering the magnets (6) of the internal rotor (2). Motor (1) according to any one of the preceding claims, in which masses of the magnets (6) of the internal and external rotors (2, 2a) are respectively selected with respect to each other so that the rotors (2 , 2a) internal and external reach an equivalent level of induction. Motor (1) according to any one of the preceding claims, in which the motor (1) is radial flux, the external and internal rotors (2, 2a) being respectively in the form of a crown (9) perpendicular to the axis of rotation (3), each crown (9) being extended by a cylindrical portion (9a) connected to the external edge of the crown (9) and extending at a distance along the axis of rotation (3). Motor (1) according to any one of the preceding claims, in which the rotors (2, 2a) are mechanically linked to each other by a connecting part relative to the plane orthogonal to the axis of rotation (3). Member (15) characterized in that it is driven by a motor (1) according to any one of the preceding claims, the member (15) being arranged externally to the motor (1) enveloping it at least partially or in being leaned against the engine (1). Body (15) according to the preceding claim, which is a wheel (16) driven in rotation by said motor (1), the wheel (16) housing the motor (1) inside it. Means of transport (17), characterized in that it comprises at least one member (15) in the form of a wheel (16) driven in rotation by said motor (1) according to the preceding claim, the means of transport having means for suspending the wheel (16) while leaving the wheel (16) free to rotate.