Encapsulated rotor of a rotating electric machine

Description

[0001] The present invention relates to a rotor for a synchronous rotating electrical machine with permanent magnets. These synchronous machines generally consist of a stator with at least one winding energized to produce a rotating magnetic field at the frequency of the supply signal, and a rotor whose permanent magnets, distributed around its periphery, also produce a magnetic field.

[0002] Permanent magnets are typically in the form of bars placed as regularly as possible around the periphery of the rotor. These bars are generally attached to a magnetic support using methods or techniques that do not always allow for precise final positioning of the components relative to one another. For example, the magnets may be glued to the support or placed in a dovetail-like recess, with the support then riveted in place. The problems associated with this type of assembly are numerous, stemming primarily from the lack of precision in the assembly, which does not guarantee a homogeneous peripheral distribution of the magnets, nor, individually, correct positioning. These deficiencies are primarily due to manufacturing tolerances in the magnet bars, and even in the support components, leading to dimensional variations that are difficult to manage.Furthermore, the use of glue, and more specifically the lack of uniformity in its application, can also generate inaccuracies.

[0003] However, imperfections in magnet positioning, whether radial, axial, or tangential, degrade the quality of rotation and lead to increased noise during rotation. A mass imbalance arises from inaccuracies in magnet placement, and potentially from defects related to manufacturing tolerances, ultimately shifting the axis of inertia of the rotating solid and generating an undesirable moment of inertia. In some applications, the outer diameter of the support / magnet assembly must be very precise (on the order of + / - 0.1 mm), which is very difficult to achieve given the manufacturing and assembly tolerances of the components used in these assemblies.

[0004] This is especially true since, to optimize the magnetic performance of the assembly, the aim is to cover as much of the rotor's peripheral surface as possible with magnets. This leads to the use of somewhat more complex shapes, more likely to deviate from the intended theoretical dimensions during manufacturing, such as tiles. In such cases of less basic magnet shapes, the problems of proper positioning and precise dimensioning also arise with regard to the rotor support that must house them, with essentially the same drawbacks and limitations as those mentioned previously.

[0005] For all these reasons, traditional assembly techniques are in fact quite uneconomical, because they are not easy to implement and therefore take time.

[0006] One of the aims of the present invention is to overcome these shortcomings and limitations by proposing a rotor whose technology largely eliminates the aforementioned drawbacks. The resulting rotor is particularly robust, allows for optimized and low-noise operation, with simplified manufacturing and lower cost relative to the performance achieved.

[0007] To this end, and in accordance with the invention, a rotating electric machine rotor with peripheral permanent magnets is proposed. These magnets consist of bars positioned parallel to the rotor axis, made of a single piece or several axially joined sections. The permanent magnets are attached to a shaft and positioned relative to said shaft via a connecting piece obtained by overmolding with at least one thermoplastic material loaded with magnetized material. The rotor is such that the connecting piece forms a cylindrical-shaped casing for the rotor, with the outer face of the permanent magnets flush with the surface of said casing.

[0008] Overmolding to join the various rotor components is not a necessary solution in this context, because the plastics commonly used for overmolding require thicknesses of around 0.8 mm for most commonly used materials (polyamide, polyoxymethylene, polyester, etc.) to control the molding process. These thicknesses can sometimes be as low as 0.3 mm for high-end materials such as liquid crystal polymers. However, these thicknesses are hardly compatible with the proper operation of rotating electrical machines, as they create air gaps that are detrimental to their magnetic performance.The contribution of the invention therefore consists in using magnetically charged thermoplastic materials to contribute positively to the magnetic performance of the machine by filling in particular the gaps between magnets with magnetic flux conductive materials instead of generating parasitic air gaps.

[0009] The use of overmolding offers many other advantages, particularly in terms of mechanics, because it generally allows for greater control over positioning and shape. This technique significantly increases the accuracy of the final rotor shape, ensures a reduction in overall mass, and improves concentricity (resulting in particular from better control of the external shape), which in turn helps minimize potential parasitic moments of inertia and ultimately reduce noise levels. The rotor's outer diameter is also much more precisely controlled, leading to a consistent air gap. The positioning of the magnets within the rotor is also more precise, thanks to the appropriate arrangements in the mold, contributing to improved mechanical behavior, in addition to enhancing the magnetic operation itself.The use of overmolding in rotors is already known, for example, disclosed in documents EP 2 667 482 A1 and WO96 / 25785 A1. In the first case, however, there are no permanent magnets in the form of bars, but only an overmolded layer of magnetized material. In the second case, the overmolding encases the pole face of the magnets opposite an armature, and consequently regulates the air gap, unlike the configuration of the present invention.

[0010] All types of magnetic and / or ferromagnetic materials combined with polymers can be used, within the scope of the invention, to produce the overmolded connecting part. They are generally used in powder form. According to one possibility, the thermoplastic material of the connecting part can be filled with ferrite. This is therefore a plastoferrite that rigidly binds the peripheral magnets to the metal core of the rotor. This is an economically attractive solution, as the production of plastoferrites uses common and reasonably inexpensive components. A possible alternative consists of a thermoplastic material filled with a magnetic material containing rare earth elements. These can, for example, be of the type containing neodymium. The neodymium is then used in alloys, notably with iron in a generic form NdFeB (including boron), creating very powerful permanent magnets known as NdFeB magnets.The resulting magnetic thermoplastic material is sometimes called plastoneodymium. Alternatively, a magnetic material containing a mixture of ferrite and / or rare earth elements, such as neodymium-containing rare earth elements, can also be used.

[0011] In practice, as mentioned previously, the connecting piece forms a cylindrical housing for the rotor, with the outer face of the permanent magnets flush with the surface of this housing. The ferrite of the permanent magnets is thus surrounded on several sides by plastoferrite or plastoneodymium. Thanks to overmolding, the outer diameter of the rotor is very precisely controlled. The magnetized thermoplastic material fills the space between the magnetic core or the central axis of the rotor and the magnets, regardless of their respective shapes, and therefore independently of any dimensional variation resulting from component manufacturing. In terms of magnetic operation, the fluxes can close onto a potential internal magnetic core of the rotor via the plastoferrite or plastoneodymium of the connecting piece.

[0012] Typically, permanent magnets consist of magnetized bars positioned parallel to the rotor axis, made either as a single piece or of several axially joined sections. These magnetized bars may, for example, have a tile-shaped cross-section to cover the largest possible peripheral surface area, with plastoferrite or plastoneodymium then filling axial grooves located between adjacent magnets.

[0013] However, according to one of the interesting advantages of the invention, the magnet bars can also be made in very simple shapes, for example, with a rectangular or even trapezoidal cross-section. These bars are then preferably surrounded on five sides by a magnetized thermoplastic material, with only the face facing the stator being free and flush with the peripheral surface of the rotor. The simpler and more compact permanent magnets are less fragile, resulting in a much more robust rotor subassembly. These examples of permanent magnet shapes are, of course, not limiting to the invention, but are illustrative of it.

[0014] The magnetic bars constituting the magnets can, in certain contexts (sensor control), extend axially beyond the overmolded connecting piece at at least one end of the rotor. In a configuration where the magnets are embedded on five sides in the thermoplastic connecting piece, if it is necessary to magnetize the polarizations of these magnets to the end of the rotor, the thermoplastic connecting piece can have an axial end portion, covering the axial ends of the magnetic bars, which is itself axially magnetized according to angular sectors of alternating polarization that correspond to the cross-sections of the permanent magnets they extend.

[0015] Among the key advantages of the invention, the existence of the overmolded, magnetized connecting piece allows for a simplification of the rotor structure, as the shaft can take the form of a simple central axis with peripheral transverse grooves for anchoring. This solution is highly economical, since the production cost of a simple axis is significantly lower than that of a central support with a magnetic core, whether laminated or not.

[0016] However, the invention also applies to a configuration in which the shaft has an axis to which a cylindrical magnetic core is attached, the thermoplastic material then simply filling less space between the magnets and the core.

[0017] The rotor configuration according to the present invention is advantageous in that it overcomes limitations, such as parasitic air gaps, resulting from prior manufacturing methods, particularly bonding. The invention also allows for improved bonding of the peripheral permanent magnets to the inner shaft, regardless of its configuration, and the use of simple, easy-to-manufacture, and economically produced magnets.

[0018] Other advantages and characteristics will become clearer from the following description of several embodiments, given as non-limiting examples of the rotor of a rotating electrical machine according to the invention, with reference to the attached figures: there figure 1 represents, in perspective view, a first rotor configuration according to the invention, with tile-shaped permanent magnets; the figure 2 shows the variant of the figure 1in partially exploded perspective view; the figure 3 schematically illustrates its magnetic operation; the figure 4 shows a second variant of the rotor according to the present invention, with magnets in the shape of prismatic bars; the figure 5 represents this variant in partial cross-section; and the figure 6 shows the variant of Figures 4 and 5 in partially exploded perspective view.

[0019] In the following sections, for the sake of simplicity and clarity for better understanding, the same numerical references will refer to the same elements. With reference to the figure 1The rotor (1) conventionally comprises a central shaft (2) and peripheral magnets (3). An intermediate piece (4), obtained by overmolding, fills the volumes between the ring of peripheral magnets (3) and a central magnetic core (5) on the one hand, and peripherally between the magnets (3) themselves on the other. The magnets (3) are in this case tile-shaped or ring-shaped. This overmolded connecting piece (4), filled as previously mentioned with ferrite or NdFeB magnetic material, or any other magnetic or ferromagnetic material or a mixture of these materials, comprises a central hub (6) in the portion between the magnets (3) and the core (5), and radially oriented wings (7) that flare at their ends to fit into the axial grooves between adjacent magnets (3) (see in particular in figures 2 and 3 ). Correct magnetic functioning results from the fact that the magnetic flux F, which appears in figure 3 , can close onto the magnetic core (5) via the connecting piece (4).

[0020] In this configuration, the central shaft consists of a shaft (2) and a core (5), and the hub (6) of the overmolded connecting piece (4) is therefore relatively thin, as are the radial wings (7). The axial ends of the hub (6) partially close around the core (5), forming a transverse annular wall that locks the connecting piece (4) relative to the shaft (2) / magnetic core (5) assembly.

[0021] Overmolding allows the molten thermoplastic material to fill all the available space in the mold under the pressure of the injection. The external peripheral surface of the rotor is perfectly cylindrical, as the tile-like magnetic bars (3) are positioned and distributed evenly around the periphery thanks to their proper preliminary placement in the mold. Dimensional variations related to the manufacturing of the magnets (3) are no longer a factor, nor is the method of attaching the magnets to the rotor (1), as could be the case, for example, in prior art bonding processes (excessive glue thickness). These limitations are completely eliminated, resulting in a rotor optimized for both mechanical and magnetic performance.

[0022] With reference to figures 4 to 6The possibilities arising from the existence of the overmolded connecting piece (4) are optimally exploited, insofar as the magnetic core (5) is eliminated and the magnet bars (3') are simplified. The closure of the internal magnetic fluxes within the rotor (1) is thus ensured by said piece (4) loaded with ferrite or NdFeB. The central mechanical element of the rotor (1) now consists of a simple shaft (2), easy and inexpensive to manufacture, with peripheral grooves (8), which can take other forms (knurling, notching), being machined into said shaft (2) for the purpose of anchoring the overmolded intermediate piece (4).

[0023] The permanent magnets become simple parallelepiped bars (3') embedded in the part (4), only the outer surface (9) of which is flush with the cylindrical peripheral surface of the envelope created by the overmolded part (4). These bars (3') are also very economical to manufacture. One of the advantages of this second configuration is that it offers good protection to the magnetic bars (3'), which can be somewhat fragile, and which are now protected on five of their six faces, embedded in the thermoplastic envelope.

[0024] For reasons of motor control using external sensors (not shown), it may be advantageous for the housing formed by the connecting piece (4) to extend axially at one end of the rotor (1), typically in the direction of the sensor(s), to ensure correct detection by the sensor(s). In this case, the axially protruding end portion (10) is axially magnetized in accordance with the angular distribution of the magnets (3') it extends from. This axial extension of the magnets (3) also appears in the version illustrated in the figures 1 to 3 , extension which then falls directly under the magnetic bars (3). The resulting overhang can constitute a factor weakening the rotor (1), which no longer exists in the version of the figures 4 to 6. There is therefore an alternating polarization at the axial end, necessary for detection, which further implies that the angular separation of the end magnetized sectors corresponds to that of the permanent magnets.

[0025] The invention is not limited, of course, to the examples described and explained with reference to the figures, which are merely specific illustrations thereof. On the contrary, the invention encompasses the variants and versions that fall within the scope of the claims.

Claims

1. Rotor for a rotating electric machine with peripheral permanent magnets (3, 3') consisting of magnetised bars positioned parallel to the axis of the rotor, made in one-piece or of a plurality of axially joined sections, the permanent magnets (3, 3') being secured to a shaft (2, 5) and positioned relative to said shaft (2, 5) via a connecting part (4) obtained by overmoulding using at least one thermoplastic material filled with magnetised material, characterised in that the connecting part (4) forms a cylindrical-looking envelope for the rotor (2, 5), the external face of the permanent magnets (3, 3') being flush with the surface of said envelope.

2. Rotor (1) for a rotating electric machine according to the preceding claim, characterised in that the magnetised material consists of any magnetic and / or ferromagnetic compound.

3. Rotor (1) for a rotating electric machine according to one of the preceding claims, characterised in that the thermoplastic material of the connecting part (4) is filled with ferrite.

4. Rotor (1) for a rotating electric machine according to one of Claims 1 or 2, characterised in that the thermoplastic material of the connecting part (4) is filled with a magnetic material containing rare earths.

5. Rotor (1) for a rotating electric machine according to one of Claims 3 or 4, characterised in that the thermoplastic material of the connecting part (4) is filled with a magnetic material containing a mixture of ferrite and rare earths.

6. Rotor (1) for a rotating electric machine according to one of Claims 4 or 5, characterised in that the magnetic material contains rare earths of the type comprising neodymium.

7. Rotor (1) for a rotating electric machine according to one of the preceding claims, characterised in that the magnetised bars (3) have a tile-shaped cross-section.

8. Rotor (1) for a rotating electric machine according to one of Claims 1 to 6, characterised in that the magnetised bars (3') have a rectangular or trapezoidal cross-section.

9. Rotor (1) for a rotating electric machine according to one of Claims 7 or 8, characterised in that the magnetised bars (3) project axially from the connecting part (4) to the central shaft (2, 5) at least at one end of the rotor (1).

10. Rotor (1) for a rotating electric machine according to one of Claims 7 or 8, characterised in that the thermoplastic connecting part (4) has an axial end part (10) covering the axial ends of the magnetised bars (3') and magnetised axially according to alternating polarisation angular sectors which correspond to the sections of the permanent magnetsthey extend.

11. Rotor for a rotating electric machine according to one of the preceding claims, characterised in that the shaft is a simple central shaft member (2), provided with peripheral transverse grooves (8).

12. Rotor for a rotating electric machine according to one of Claims 1 to 10, characterised in that the shaft has a shaft member (2) to which a magnetic core (5) of cylindrical appearance is secured.