FR3158842A1 - Overmolded rotor for axial flux electric motor with permanent magnets - Google Patents

Description

Overmolded rotor for axial flux electric motor with permanent magnets

The present invention relates to the field of electric motors, in particular torque motors, and more specifically axial flux torque motors with permanent magnets. In particular, the present invention relates to an overmolded rotor, in particular for an axial flux torque motor with permanent magnets, in particular intended to be implemented in an electric vehicle.

STATE OF THE ART

Permanent magnet axial flux electric motors are known for their use in electric vehicles. This type of axial flux torque motor is particularly popular for its compact, slim design that can be integrated into a wheel rim.

Axial flux torque motors are generally lightweight motors, not rotating quickly, so as to limit the gyroscopic effect which would be detrimental, in particular, to the steering of a motorcycle.

The present invention relates to a lightweight and thin rotor suitable for this type of axial flux torque motor. This type of axial flux torque motor is equipped with permanent magnets.

A known problem is that the large number of magnets requires optimization in terms of mass and size.

Another problem concerns the need to absorb the axial forces acting on them.

Another problem is the heat generated by these magnets during the operation of the axial flux torque motor. This problem is exacerbated when the magnets are small, particularly thin, which prevents the first problem addressed, i.e., size. The same applies to the problem of axial forces to be absorbed.

There is therefore a need for an axial flux torque motor in which the permanent magnets are cooled and magnetically isolated, while providing the rigidity and torque necessary to move an electric vehicle.

The skilled person would be tempted to resort to a change of material, by producing a stainless steel rotor, but this would lead to a significant increase in costs.

According to the invention, a resin-molded rotor is thus provided, in particular capable of diffusing heat to avoid any excessive heating of the magnets.

The resin-molded rotor according to the invention comprises cavities that have undergone bores to receive the permanent magnets. In addition, the overmolded rotor according to the invention allows mechanical retention of the magnets in their bore. Indeed, a magnet detaching during operation could have a catastrophic consequence.

However, if the magnets are simply glued into the bores, the shear forces induced on the rotor, during operation of the torque motor integrated into a wheel, can cause the magnets to detach.

It is further noted that an incidental advantage of the invention is that, given that the thermal problem linked to the magnets is better controlled, it is possible to make do with cheaper magnets.

PRESENTATION OF THE INVENTION

More specifically, the invention relates to a rotor for an axial flux torque motor, comprising 1 to N angular sectors, N being a natural integer, forming a body of section having a substantially annular shape, the body comprising a plurality of cavities distributed regularly over at least one annular portion of the body, each cavity comprising a magnet, the rotor being formed from a resin overmolding coating the body and integrating the magnets arranged in the cavities, the resin having a thermal conduction coefficient greater than 0.6 W/m.K.

The invention provides a lightweight and mechanically strong overmolded rotor that can be used in a permanent magnet axial flux motor. In particular, due to the high thermal conductivity of the resin, the heat produced by the magnets is easily dissipated.

According to one embodiment, the body has a thickness of between 10 mm and 20 mm and a diameter of between 150 mm and 400 mm, in particular equal to 305 mm.

For example, the cavities include a first set of cavities configured to receive magnets 18 mm in diameter and 12 mm in thickness and a second set of cavities configured to receive magnets 16 mm in diameter and 12 mm in thickness.

In particular, the first set of cavities and the second set of cavities are distributed uniformly, respectively along a first concentric annular portion and a second concentric annular portion, the first annular portion having an inner radius greater than an outer radius of the second annular portion.

In particular, the cavities are formed in the body and are cylindrical holes machined by boring.

According to one embodiment, the body consists of a single sector.

According to another embodiment, the body is made up of 2 to 8 identical angular sectors. In practice, according to the invention, the sectors making up the body are not necessarily identical but, when they are identical, the manufacturing process is simplified.

The invention also relates to an axial flux torque motor comprising a rotor as briefly described above.

The invention also relates to an electric vehicle comprising such an axial flux torque motor.

According to another aspect of the invention, it relates to a method of manufacturing a rotor as briefly described above, in which the angular sector(s) forming the body of the rotor are assembled in a mold, in particular made of aluminum; the magnets are placed in the corresponding cavities of the body; the resin is injected so as to fill the mold.

In particular, the mold includes an injection port located in a lower region of the mold, the resin injected into the mold being drawn through the mold, from the bottom to the top, until it is filled.

PRESENTATION OF FIGURES

The invention will be better understood on reading the following description, given solely by way of example, and referring to the appended drawings given as non-limiting examples, in which identical references are given to similar objects and in which:

there FIG. 1 is a schematic representation of an overmolded rotor body according to the invention;

there FIG. 2 is a schematic representation of an angular sector of the body of an overmolded rotor according to the invention;

there FIG. 3 is a schematic representation of a rotor body into which magnets are inserted, the whole being arranged in a half-mold;

there FIG. 4 is a schematic representation of a mold for manufacturing an overmolded rotor according to the invention;

there FIG. 5 shows an open half-mold, after resin injection and baking;

there FIG. 6 is a representation of a method of manufacturing a rotor according to the invention.

It should be noted that the figures set out the invention in detail to enable the invention to be implemented; although not limiting, said figures serve in particular to better define the invention where appropriate.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates firstly to an overmolded rotor for a permanent magnet axial flux torque motor, as well as a method for manufacturing such a rotor. The invention also relates to a permanent magnet axial flux torque motor comprising such an overmolded rotor, as well as a vehicle, such as a motorcycle, equipped with such a permanent magnet axial flux torque motor.

There FIG. 1 shows an example of an overmolded rotor body 20 according to the invention. The body 20 forms a skeleton intended to accommodate magnets in the cavities 231 and 232.

In particular, the body is made of injected plastic. For example, the body 20 is made of PA6 (also called nylon 6 or polyamide-6). According to one embodiment, said skeleton is composed of several angular sectors 21, as shown in the FIG. 2 , to be assembled in the mold 10 shown in the FIG. 4 .

The body 20 forms a ring, where appropriate composed by the juxtaposition of angular sectors 21. For example, the body 20 is composed of eight angular sectors 21, as in the FIG. 1 . The body 20 may however be in one piece or be composed of a number of angular sectors 21 other than eight.

The body 20 comprises cavities 231, 232 intended to receive magnets. In particular, the cavities, like the magnets, are cylindrical. According to one embodiment, first cavities 231 are regularly distributed in a first annular portion of the body 20 and second cavities 232 are regularly distributed in a second annular portion of the body 20, the first annular portion and the second annular portion being without intersection. In particular, the first annular portion has an inner radius greater than an outer radius of the second annular portion, as in the FIG. 1 .

According to this embodiment, the first annular portion comprises the first cavities 231 which have a radius greater than that of the second cavities 232 which are distributed in the second annular portion. Thus, the first cavities 231 are intended to house magnets of larger diameter than the magnets intended to be housed in the second cavities 232.

The body 20 also comprises, on its inner periphery and on its outer periphery, respectively, orifices 24, 25 allowing the passage of means for fixing the body of the overmolded rotor according to the invention, in particular in an axial flux motor with permanent magnets for an electric vehicle.

The rotor 20 is annular in shape, naturally including a central through passage for rotation around a hub. Material is preferably omitted or otherwise removed, particularly to lighten the overmolded rotor.

In reference to the FIG. 3 , the body 20 is shown with magnets 31, 32 housed in the respective cavities 231, 232. On the FIG. 3 , the body 20 comprising the magnets 31, 32 is arranged in a first cylindrical half-mold 11.

There FIG. 4 shows the closed mold 10, once the second half-mold 12 is placed over the first half-mold 11. The closed mold 10 houses the body 20 and the magnets 31, 32 placed in the corresponding cavities 231, 232 of the body 20.

There FIG. 5 represents the half-mold 11, filled with resin, at the end of step E7 of the manufacturing method described below, once the mold 10 has been opened.

In reference to the FIG. 6 , the invention also relates to a method comprising successive steps allowing the manufacture of an overmolded rotor according to the invention.

In step E1, the body 20 is produced from injected plastic. According to one embodiment, the body 20 is made of a single piece. According to another embodiment, the body is composed of N angular sectors 21, N being a natural integer, in particular greater than or equal to 2, for example equal to 8. For the manufacture of the body 20, a conventional plastic injection process is implemented.

The body 20 is notably made of a plastic material having good mechanical strength, for example PA6 (also called nylon 6 or polyamide-6).

According to one embodiment, the cavities 231, 232 are produced in step E2, for example by removing material, in particular by drilling, followed by boring.

In step E3, the body 20 is housed, if necessary by arranging side by side and assembling the different angular sectors 21, so as to form a ring corresponding to the skeleton already mentioned, in the first cylindrical half-mold 11, the half-mold 11, as well as the second half-mold 12, being in particular made of aluminum.

In step E4, the magnets 31, 32 are placed in the respective cavities 231, 232.

The magnets 31, 32 are thus regularly distributed, respectively in two distinct annular portions. In particular, the two annular portions are concentric, without intersection. For example, the first, outer, annular portion receives magnets 31 of larger diameter compared to the magnets 32, which are received in the second, inner, annular portion.

Once the body 20 and the magnets 31, 32 are arranged in the first half-mold 11, the mold 10 is closed, in step E5, by means of the second half-mold 12. The closed mold 10 is visible in the FIG. 5 . According to one embodiment, in a lower region of the mold 10, there is a resin injection hole and, in an upper region of the mold 10, there is a suction port.

According to a preferred embodiment, in step E6, the resin is sucked through the mold 10 so as to fill it from bottom to top, until it is filled. The resin is thus injected into the mold 10 via the injection hole located in the lower region of the mold, and is sucked, via the suction orifice located in the upper region of the mold, so as to fill the mold 10.

The suction allows the vacuum to be created at the same time as the mold 10 is filled. This is advantageous compared to a process in which the resin would be pushed into the mold, because it would then be necessary to create a vacuum beforehand.

Preferably, the resin is sucked in from the top of the mold 10, in particular, but not necessarily, under vacuum. Once the mold is filled with resin, the steaming step E7 is carried out.

After baking, in step E8, the mold 10 is opened and an overmolded rotor according to the invention is extracted, intended for an axial flux torque motor with permanent magnets.

The resin is chosen as having a high thermal conductivity, notably greater than 0.6 W/m.K. This makes it possible to effectively combat any excessive heating of the magnets 31, 32.

Indeed, if the thermal conductivity of the resin is reduced, the magnets 31, 32 will have to withstand more heating, which is not prohibitive but will involve the choice of more expensive magnets. We will therefore prefer a resin with very good thermal conductivity, in particular greater than 0.6 W/m.K, which allows us to “make do” with cheaper magnets. The resin is, for example, a two-component epoxy-based resin, including an additive to increase thermal conductivity.

Furthermore, the resin preferably has high mechanical strength, in particular a tensile stress greater than 45 MPa.

The body 20 has, for example, a thickness of between 10 mm and 15 mm.

The outer diameter of the rotor according to the invention is, for example, of the order of 305 mm. More generally, particularly for use as a rotor of an axial flux torque motor for an electric vehicle, the outer diameter of the rotor may be between 150 and 400 mm.

For example, there may be 64 magnets, including 32 first magnets with a diameter of approximately 18 mm and a thickness of approximately 12 mm, and 32 second magnets with a diameter of approximately 16 mm and a thickness of approximately 12 mm.

According to the invention, such an overmolded rotor is notably implemented in an axial flux torque motor with permanent magnets. Still according to the invention, such an axial flux torque motor with permanent magnets is used, for example, in a vehicle such as a motorcycle.

It will also be noted that the invention is not limited to the embodiments described above. It will indeed appear to those skilled in the art that various modifications can be made to the embodiment described above, in light of the teaching which has just been disclosed to them.

For example, it may be possible to manufacture an overmolded rotor without using a skeleton for positioning the magnets. In this case, the magnets would be held in position directly in the mold, until the execution of step E6 of overmolding by injection and suction of resin into the mold.

In the detailed presentation of the invention given above, the terms used should not be interpreted as limiting the invention to the embodiment set out in the present description, but should be interpreted to include all equivalents whose prediction is within the reach of a person skilled in the art by applying his general knowledge to the implementation of the teaching which has just been disclosed to him.

Claims (11)

Rotor for an axial flux torque motor, comprising 1 to N angular sectors (21), N being a natural number, forming a body (20) of section having a substantially annular shape, the body (20) comprising a plurality of cavities (231, 232) distributed regularly over at least one annular portion of the body (20), each cavity (231, 232) comprising a magnet (31, 32), the rotor being formed from a resin overmolding (40) coating the body (20) and integrating the magnets (31, 32) arranged in the cavities (231, 232), the resin (40) having a thermal conduction coefficient greater than 0.6 W/m.K. Rotor according to claim 1, in which the body (20) has a thickness of between 10 mm and 20 mm and a diameter of between 150 mm and 400 mm, in particular equal to 305 mm. Rotor according to claim 1 or 2, wherein the cavities (231, 232) comprise a first set of cavities (231) configured to receive magnets (31) of 18 mm diameter and 12 mm thickness and a second set of cavities (232) configured to receive magnets (32) of 16 mm diameter and 12 mm thickness. Rotor according to claim 3, wherein the first set of cavities (231) and the second set of cavities (232) are distributed uniformly, respectively along a first concentric annular portion and a second concentric annular portion, the first annular portion having an inner radius greater than an outer radius of the second annular portion. Rotor according to one of the preceding claims, in which the cavities (231, 232) are formed in the body (20) and are cylindrical holes machined by boring. Rotor according to claim 1, the body (20) being made up of a single sector. Rotor according to claim 1, the body (20) being made up of 2 to 8 identical angular sectors (21). Axial flux torque motor comprising a rotor according to one of the preceding claims. Electric vehicle comprising an axial flux torque motor according to the preceding claim. Method for manufacturing a rotor according to one of claims 1 to 7, in which the angular sector(s) (21) forming the body (20) of the rotor are assembled (E3) in a mold (10), in particular made of aluminum; the magnets (31, 32) are placed (E4) in the corresponding cavities (231, 232) of the body (20); the resin (40) is injected (E6) so as to fill the mold (10). A method according to claim 10, wherein the mold (10) comprises an injection orifice located in a lower region of the mold (10), the injected resin (E6) into the mold (10) being drawn through the mold (10), from bottom to top, until it is filled.