EP3586425A1

EP3586425A1 - Rotating electric machine comprising a stator with sealed slots, and more particularly permanent magnet-assisted reluctant synchronous electric machine

Info

Publication number: EP3586425A1
Application number: EP18704988.7A
Authority: EP
Inventors: Benjamin GAUSSENS; Julien BOISSON; Luca FAVRE; Davide Bettoni; Wissam DIB
Original assignee: IFP Energies Nouvelles IFPEN; Mavel SRL
Current assignee: Mavel EDT SpA
Priority date: 2017-02-24
Filing date: 2018-02-16
Publication date: 2020-01-01
Also published as: US20200059125A1; CN110582925A; JP2020509728A; WO2018153783A1; FR3063398A1

Abstract

The invention relates to an electric machine comprising a rotor (1) and a stator (2) which has a wall (3) facing the rotor, the stator having a plurality of radial slots that are arranged circumferentially along the stator. The slots have openings (6) which extend into the inner wall and which are closed by sealing means (7, 8) in such a way as to form a plurality of closed slots (5).

Description

The present invention relates to a rotating electrical machine with a closed-slot stator and more particularly to a synchronous-electric machine assisted by a rotating electric machine with a stator with closed notches and more particularly a reluctant electric synchronous machine assisted by permanent magnets. permanent magnets.

More specifically, the electric machine comprises an open-slot stator which is closed by suitable means so that the gap between the outer surface of the rotor and the inner surface of the stator is substantially constant.

Generally, such an electric machine comprises a stator and a rotor arranged along the same axis one in the other.

The rotor is formed of a rotor body with a stack of sheets placed on a rotor shaft. These sheets include housings for permanent magnets and perforations to create flux barriers for radially directing the magnetic flux of the magnets to the stator.

This rotor is generally housed inside a stator which carries electrical windings to generate a magnetic field for rotating the rotor. As best described in EP 1 057 242, the stator is annular in shape and includes a plurality of radial notches open towards the rotor and extending all the way around the stator.

These notches are provided to receive armature coils which are introduced into the stator by the open face of the notches and are fixed thereto by any known means.

In general, torque ripple is important in this type of reluctant synchro machine assisted by permanent magnets. This can cause jerks and vibrations in the rotor causing discomfort in use of this machine.

WO201 6/188764 discloses an electric machine with a closed slot stator which reduces torque ripple and acoustic noise. However, this solution imposes in particular an implementation of unconventional manufacturing due to the notches closed.

For this purpose, the present invention relates to an electric machine comprising a rotor and a stator having an inner wall facing the rotor, said stator carrying a multiplicity of radial notches arranged circumferentially along said stator, said notches having openings opening into said internal wall.

According to the invention, said openings are closed by closure means so as to form a multiplicity of closed notches.

The notches of the electric machine may extend longitudinally along the axis of the stator.

Said closure means may comprise a wedge of magnetic material of dimensions corresponding to said openings so as to close the notches.

The spacers may have a thickness such that they are flush with the surface of the inner wall of the stator.

Wedges can be crimped, welded, or glued into openings.

The sealing means may comprise a cylinder of magnetic material disposed on the inner wall of the stator so as to close the notches.

Said cylinder can be fixed by shrinking in the inner wall of the stator.

The internal diameter of the cylinder can be adapted to receive the rotor. The other features and advantages of the invention will now appear on reading the following description, given solely by way of illustration and not limitation, and to which are appended:

FIGS. 1a and 1b, which are a schematic cross-sectional view of electrical machines according to the prior art,

FIGS. 1c and 1d, which are a schematic view in cross section of the stator of the machine according to the invention,

FIG. 2a which is a graph illustrating the evolution of the constant current torque as a function of the electric position of the rotor for electrical machines of the prior art and for two electrical machines according to the invention and

FIG. 2b which is a graph giving the amplitude of the harmonic torque (N.m) for the four embodiments described in FIGS. 1a, 1b, 1c and 1d.

FIGS. 1a, 1b, 1c and 1d show in partial section a rotating electrical machine, here a synchronous-reluctant electric machine assisted by permanent magnets, comprising a rotor 1 and a stator 2 nested one in the other by being coaxial.

The construction of the rotor comprises, in a known manner and in particular described in WO201 6/188764, a preferably magnetic shaft, on which is placed a stack of identical flat ferromagnetic sheets, which are assembled to each other by any known means. Figures 1 to 1 d show at least partially this type of rotor.

The circular-shaped sheets comprise a central bore through which the rotor shaft passes and a plurality of axial recesses 20 which pass through the sheets from one side to the other.

A series of rectangular axial recesses 20, arranged radially one above the other and at a distance from one another, form housings for magnetic flux generators, here permanent magnets in the form of a bar which is also rectangular and of substantially equal length. at the length of the stack of sheets. Preferably, the rotor comprises at least two series of rectangular axial recesses 20, radially arranged one above the other, the rectangular axial recesses 20 being distributed circumferentially on the rotor 1. Another series of recesses 40 consists of inclined radial direction perforations, which extend said housing to the vicinity of the edge of the sheets.

This creates flow barriers formed by the perforations. The magnetic flux from the magnets can then only pass through the solid parts between said perforations.

The use of series of rectangular axial recesses 20, arranged radially one above the other and at a distance from each other, forming housings for magnetic flux generators, and inclined radial perforations 40, extending the housings up to the voicinage of the edge of the sheets, improves the direction of the magnetic flux and thus improve the performance of the electric machine, the magnetic flux is then better channeled on the walls of the rotor, both more numerous and more thin.

A stator 2 according to the prior art, partially shown in FIGS. 1a, 1b, comprises an annular ring with an internal wall 3 whose inside diameter is designed to receive the rotor 1 with a space necessary to make a gap 4.

This ring comprises a multiplicity of holes 5, here of oblong section, which form notches for receiving the armature coils.

More precisely, these bores extend axially all along the stator by being arranged radially on the ring while being placed circumferentially at a distance from each other by a distance D.

Figure 1 depicts a closed volume that forms a closed notch for receiving the armature coil.

Thus, the wall 3 is a continuous wall and the gap 4 is almost constant between the rotor and the stator and that over the entire circumference.

In addition, since the outside of the rotor and the inside of the stator are smooth, this allows for reduced aerodynamic noise.

WO201 6/188764 describes in particular the advantages of closed notches. FIG. 1b describes the conventional configuration of a stator with open notches at the bottom of said notches by openings 6. These openings allow the winding of the armatures, in particular mechanically, whereas in the case of closed notches the windings of induced must be made manually.

The object of the present invention is to combine both the benefit of the closed notches with a stator with open notches that reduce the cost of production by the possibility of automated winding and obtain a better winding coefficient of the order of 0.6.

For this, after winding, the openings 6 of the stator are closed by suitable means, such as plates or wedges of magnetic material of the width of the openings 6 and the length corresponding to the length of the stator. Figure 1c illustrates this embodiment by showing in section the closure means 7 shaped wedge, or plate. These sealing means may be crimped, glued, welded, or maintained by any means available to the skilled person.

These wedges advantageously have a thickness such that they are flush with the surface of the inner wall of the stator.

Thus, the gap is substantially constant over the entire circumference, and the inner surface 3 of the stator is substantially smooth.

FIG. 1 d describes another embodiment of said means for closing the open notches 5. A cylinder 8 of diameter and length respectively corresponding to the internal surface and to the length of the stator is placed on the inner surface 3 of the open stator.

Thus, the inner surface of the stator is completely covered by the wall of the cylinder 8, or fret, and all the openings of the notches are thus closed. The gap 4 is constituted by the outer surface of the rotor and the inner surface of the hoop 8. The cylinder 8, or hoop, is made of a magnetic material. The cylinder may be fixed on the internal surface 3 of the stator by any means known to those skilled in the art, in particular by shrinking, gluing, welding. The cylinder 8 being of small thickness relative to its diameter, the hooping is a means of well fitting, hence the name "fret" for said means for closing the openings of the stator slots.

On a synchronous-reluctant structure assisted by permanent magnets, closing the open slots of a stator has three advantages:

• Reduced torque ripple (as well as harmonics of torque ripples);

• Reduced losses iron rotor and stator (fewer harmonics on the magnetic induction in iron);

· Noise reduction due to aerodynamic phenomena of the machine since the gap is constant.

When the rotor 1 of the permanent magnet assisted synchronizing machine comprises series of rectangular axial recesses 20, arranged radially one above the other, at a distance from each other, and forming housings for generators of magnetic flux, and that the rotor also has recesses 40 of the inclined radial perforation type, extending the housing to voicinage the edge of the sheets (as shown in Figures 1 a to 1 d), in combination with the use shutter means (7, 8) for the stator slots, the synchro-reluctant machine has significantly improved performance.

FIG. 2a is a graph with curves illustrating the torque of the electric machine (in Nm) relative to the electrical position of the rotor (in °) for a constant current, for the four embodiments of the stator: closed notches E, notches open O, notches closed by wedges C, notches closed by fretting F.

It can be noted that in the case of the open notches O, the torque ripples are much higher (9.0%), whereas they are respectively 5.1%, 6.4%, 5.4% for the configurations with closed notches E, notches closed. by magnetic wedges C, and notches closed by magnetic fretting.

Moreover, FIG. 2b gives the level of the harmonic content of the instantaneous torque. Note that in the case of the stator with notches open, the rank 36, corresponding to the number of teeth of the stator, predominates. In the other configurations, the amplitude of the harmonics tends to decrease while increasing in frequency. This is interesting, especially in terms of losses iron, because it does not come to excite harmonics of high rank that could generate more losses (the losses in the iron being proportional to /, f ² and ' ² ).

It is clear that the closure of the notches a posteriori the armature windings, in particular with magnetic shims or magnetic band, makes it possible to reduce the torque ripples compared to the stator structure with open notches, as well as the harmonics of torque.

In addition, the posterior closure does not introduce significant changes in the electromagnetic performance compared to the closed slot structure.

Claims

1) Electrical machine comprising a rotor (1) and a stator (2) having an inner wall (3) opposite the rotor, said stator carrying a multiplicity of radial notches (5) arranged circumferentially along said stator, said notches comprising openings (6) opening into said inner wall, characterized in that said openings are closed by closure means (7, 8) so as to form a multiplicity of notches (5) closed.

2) Electrical machine according to claim 1, wherein the notches extend longitudinally along the axis of the stator.

3) Electrical machine according to one of claims 1 or 2, wherein said closure means comprise a shim (7) of magnetic material of dimensions corresponding to said openings so as to close the notches.

4) Electrical machine according to claim 3, wherein the shims have a thickness such that they are flush with the surface of the inner wall of the stator.

5) Electrical machine according to one of claims 3 or 4, wherein the wedges are crimped, welded, or glued into the openings.

Electric machine according to one of claims 1 or 2, wherein the sealing means comprise a cylinder (8) of magnetic material disposed on the inner wall of the stator so as to close the notches.

An electric machine according to claim 6, wherein said cylinder is shrink-fitted in the inner wall of the stator.

8) Electrical machine according to one of claims 6 or 7, wherein the internal diameter of the cylinder is adapted to receive the rotor.