FR3069728A1 - CAGE ROTOR INJECTED - Google Patents

Abstract

Rotary electric machine rotor, comprising: - a bundle of magnetic sheets, the magnetic sheets having perforations forming notches (4) within the bundle, - bars (10) of a first electrically conductive material inserted into at least one part of the notches (4), at least a portion of these bars (10) being hollow, - a second material (20) electrically conductive, injected into the notches (4) at least inside the bars (10).

Description

INJECTED CAGE ROTOR

The present invention relates to rotary electrical machines and more particularly the rotors of such machines.

Background

Asynchronous electric motors conventionally comprise a bundle of magnetic sheets crossed by notches. Aluminum is injected under pressure to form bars which are connected to the outside of the sheet pack by short-circuit rings.

To improve electrical performance, it may be advantageous to further reduce the electrical resistivity of the bars by replacing aluminum with copper. However, since the melting temperature of copper is much higher than that of aluminum, it becomes difficult to inject copper into the notches.

A known solution thus consists in introducing copper conductive bars into the notches and in injecting aluminum under pressure to fill the space left free inside the notches by the bars.

Applications WO2011015494, W02010100007, W02009038678,

US2011291516, WO2014067792, WO2011020788, W02015071156, WO2012041943, JPH10234166, CN1925280, JPH11206080, JP2005278373, JPH1028360 describe rotors in which the sheet pack contains notches receiving copper bars and in which aluminum is pressurized.

summary

One of the difficulties which arise during the injection of aluminum is the filling of the rear ring, the aluminum being injected from the front and having to gain the rear ring by circulating through the notches, the cross section of which is reduced by the presence of copper bars.

However, a faulty filling of the rear ring causes the rotor to be scrapped or requires costly rework.

Furthermore, the presence of copper bars in the notches leads to an additional cost which makes the machine too expensive for certain applications. However, it might be desirable to improve the performance of the machine while keeping an acceptable cost for the application concerned.

There is a need to remedy some or all of the above drawbacks.

The subject of the invention is, according to a first of its aspects, a rotor of a rotating electric machine, comprising:

a pack of magnetic sheets, the magnetic sheets having openings forming notches within the pack,

- bars of a first electrically conductive material inserted in at least part of the notches, at least part of these bars being hollow,

- a second electrically conductive material, injected into the notches at least inside the bars.

The fact that the bars are hollow makes it easier to fill the cavity used to mold the rear short-circuit ring. Aluminum can flow inside a hollow bar along its entire length, between its front and rear axial ends.

The amount of copper used may be less.

The aluminum that is injected into the bars is protected from contact with oxygen by the material of the bars, except at the axial ends of the bars. This limits corrosion phenomena at the interface between aluminum and copper.

The bars have in section a closed contour, in particular non-circular.

Preferably, the second material fills the notches also outside the bars, especially when the bars do not occupy the entire section of the notches.

The bars, hollow or not, can extend over the entire radial dimension of the notches. In particular, the bars may have a cross section which is substantially the same shape as the notches.

As a variant, the bars, hollow or not, have a radial dimension which is less than that of the notches.

The bars, hollow or not, can extend over at least the length of the sheet bundle.

All the notches in the rotor can have hollow bars with the second material injected inside. As a variant, certain notches may not have a bar, being in this case entirely filled with the second conductive material. For example, the rotor has more notches with bars than not without bars, or vice versa.

Preferably, the first material, which is a better conductor than the second material, is copper, the second material being aluminum.

The bars can extend at least over the length of the sheet pack, and the rotor comprising, at each of the axial ends of the sheet pack, a guard sheet, the latter coming to bear by its internal face against the axial ends of the bars.

The invention also relates to a rotary machine comprising a rotor as defined above.

Description of the figures

The invention will be better understood on reading the detailed description which follows, examples of non-limiting implementation thereof, and on examining the appended drawing, in which:

FIG. 1 schematically represents, in axial section, an example of a rotor according to the invention,

FIGS. 2 to 6 schematically represent portions of the rotor according to the invention,

FIGS. 7A and 7B schematically represent alternative embodiments of the notches,

FIG. 8 represents a variant of the rotor according to the invention, and

- Figures 9A and 9B show, schematically, alternative embodiments of notch.

Rotor

FIG. 1 shows a rotor 1 according to the invention. This rotor 1 comprises a packet of magnetic sheets 2, mounted on a shaft 9, for example of steel, of axis X.

The package 2 is formed by the superposition of magnetic sheets 113 in which are cut openings 3.

The superposition of the openings 3 of the sheets 113 forms, within the package 2, notches 4 which extend longitudinally from one axial end of the package 2 to the other. The notches 4 can be straight, that is to say that all the sheets 2 are exactly superimposed without angular offset from one sheet 113 to the next. However, preferably, the sheets 113 are superimposed by being slightly angularly offset from one sheet to the next so that the longitudinal axes of the notches 4 follow a helical path around the axis of rotation of the rotor, in a manner known in itself.

In the example illustrated, all of the sheets 113 are identical and the openings 3 are also identical, so that the package 2 has identical notches 4. In variants, the package 2 is formed by assembling sheets 113 which are not strictly identical in front view, from the front of the package 2, so that the section of a notch 4 can have a shape which varies when moving from the front end of the notch 4 to the rear end. In particular, the sheets 113 may be identical when they are cut, but be assembled by turning certain sheets over others, so that they generate an evolution in the section of the notch 4, when the we move along the axis of rotation.

The rotor 1 includes copper bars 10, introduced into the notches 4, and a material 20 such as aluminum injected into the notches 4 in the space left free by the bars 10.

Short-circuit rings 120 and 130 are molded from aluminum at the ends of the sheet metal package 2. These rings 120 and 130 are in one piece with the aluminum cast in the notches 4.

Hollow bars

In the examples of FIGS. 2 to 6, the bars 10 are hollow and have an interior cavity 17, preferably longitudinal, which is filled with the second material 20, which is, in the examples considered, injected aluminum. The section of the cavity 17 is sufficient to allow the aluminum which is injected to flow through the bar 10, from its front end to its rear end.

In the example of FIG. 3, the copper bars 10 which are inserted in the notches 4 occupy substantially the whole section of the notches, the bars 10 having an external section which corresponds substantially to that of the notches.

In the variant illustrated in FIG. 4, the bars 10 each have an external dimension which is less than that of the associated notch, so that there remain spaces 7 and 8 therein, inside which aluminum can be injected. In this case, the aluminum can fill the inside of the bar 10 as well as the spaces 7 and 8 close to the bottom of the notch and the top of the notch respectively.

Also shown in this figure is the possibility for the rotor 1 to include, as in the example of FIG. 3, notches 4 which are devoid of bars and which in this case are completely filled with the second material.

Notches with friction reliefs

Certain notches may have friction reliefs 5 arranged to retain the bars by friction.

As illustrated in FIGS. 7A and 7B, at least part of the openings may have, on at least part of their periphery, reliefs 5, the electrically conductive bars 10 received in the notches 4 bearing by at least one main face 11 against said reliefs 5.

These reliefs 5 can effectively maintain the bars 10 inside the package 2 of sheets 113. The reliefs 5 can be produced very precisely when cutting the sheets 113, and allow greater cross-section tolerance of the bars.

In particular, when a material is injected into the notches 4 around the bars, the latter can remain stationary within the package. The reliefs 5 can also reduce the force to be exerted on the bars 10 to insert them into the pack 2 of sheets, by reducing the contact surface between the bars and the sheets.

The reliefs 5 can also, by reducing the contact surface between the bars and the sheets, reduce the inter-bar currents flowing in the sheets and the corresponding loss of energy by the Joule effect.

The reliefs 5 are preferably present on long opposite sides 4a of the notches 4, these long sides extending substantially radially and the conductive bars 10 come to bear against these reliefs 5 by two opposite main faces 4a.

The reliefs can be in the form of bosses 5, preferably extending over substantially the entire radial dimension of a bar 10.

The bosses can have an amplitude h of between 0.2 and 0.4 mm, for example 0.3 mm, as illustrated in FIG. 7A. These bosses are preferably of rounded shape and the radius of curvature R at the top is for example between 0.4 and 0.6mm, for example 0.5mm.

All the sheets in the package can be identical.

Notches with blocking reliefs

As illustrated in FIG. 7A, at least one sheet of the package may have at least one blocking relief 30 coming to bear against a radially outer end face 14 of a corresponding bar 10, better still two such opposite reliefs 30 each coming in support against the same end face.

At least one sheet of the package may also have at least one blocking relief 31 coming to bear against a radially inner end face 13 of a corresponding bar as illustrated in FIG. 7B, this blocking relief 31 preferably being centered on the median plane of symmetry of the corresponding aperture.

Notches with separation reliefs

As illustrated in FIG. 7B, separation reliefs 15 can extend within the openings and separate the notches into first 6 and second 8 separate compartments, the first compartments 6 being radially interior relative to the second compartments 8.

The conductive bars 10 of the first material can be placed in the first or second compartments of at least part of the notches 4. The second electrically conductive material 20, different from the first, can then be placed in the second or the first compartments of these notches 4, the separation reliefs 15 which extend within the openings preventing the first and second materials from coming into contact.

The bars 10 which are introduced into the pack of sheets can be held within the corresponding compartments by the separation reliefs 15. The latter are arranged so as to prevent the first and second materials from coming into contact. Thus, potential corrosion phenomena are eliminated.

The separation reliefs 15 can be of different shapes, being produced by cutting with the material of the magnetic sheets.

For example, as illustrated in FIG. 7B, the separation reliefs 15 are bridges of material which separate each notch into first and second non-communicating compartments.

In the variant illustrated in FIG. 9B, the separation reliefs are constituted by projections 15a arranged opposite one another and which provide between them a channel 16 sufficiently narrow to prevent contact between the first and second materials. For example, when the first compartments are filled by injection of molten aluminum, channels 16 having a width less than 0.6 mm and a height less than 2 mm can prevent aluminum from entering the second compartments through channels 16, and vice versa.

The conductive bars 10 of the first material can be inserted into the first compartments 6, the first material preferably being copper, the second material 20 being injected into the second compartments 8, this second material preferably being aluminum. Such an embodiment is particularly suitable for a machine intended to be driven with a current of fixed frequency. When the motor is connected to the network, starting the motor requires a high current compared to the nominal point. The ratio between the starting current and the nominal current being limited by the standards in force, the aim is to reduce it. At start-up, the part of the notch that generates the electrical resistance is above all the top of the notch, near the air gap due to the skin effect. In order to limit this starting current, the resistance of the cage must increase. Thus, having the material with the highest electrical resistivity closer to the air gap makes it possible to reduce the starting current.

In an alternative embodiment, the conductive bars of the first material are inserted into the second compartments, this first material preferably being copper, the second material being injected into the first compartments, this second material preferably being aluminum. Such an embodiment is more particularly suitable for a motor connected to a variator, for a variable speed drive. In this case, the starting current is not a constraint. Positioning the material of lower electrical resistivity in the compartment closer to the air gap and if necessary introducing an opening, in particular in the form of a slot, on the side of the air gap which is devoid of electrically conductive material, allows reduce electrical losses. In addition, the presence of a bar in the upper part of the notch prevents the second material from flowing into the possible opening of the notch on the side of the air gap during injection.

Number of bars lower than the number of notches

In the variants illustrated in FIGS. 3 and 4, the bars are present in only part of the notches 4.

The absence of bars in certain notches makes it possible to keep a larger total section for the passage of the injected aluminum, and thus to facilitate the filling of the rear ring when the injection is made from the front.

The presence of bars made of a material of lower electrical resistance such as copper in certain notches improves the electrical performance. It is possible, by choosing the number of bars added, to optimize the increase in performance with regard to the cost of the machine, copper being more expensive than aluminum.

The rotor may have more notches with bars than notches without bars. In other variants, it is the opposite and the rotor has more notches without bars than with bars.

Multiple arrangements of the bars within the notches are possible. For example, it is possible to alternate in the circumferential direction a notch without bar and a notch with bar. We can also alternate more generally neither notches without bar with n ₂ notches with bar, nor and n ₂ being integers strictly greater than 1.

In the variant of FIG. 3, the sheet pack has a notch out of three which does not have a bar 10 and which is entirely filled with the injected aluminum.

In the variant of FIG. 4, there is alternation in the circumferential direction between the notches which receive a copper bar 10 and those which do not have one and which are filled with injected aluminum only.

Secondary notches

In FIGS. 5 and 6, the possibility has been illustrated for the sheet pack to include, in addition to the notches 4 previously described, secondary notches 40, close to the radially inner edge 41 of the sheet pack, these secondary notches 40 being filled with the second material 20.

The magnetic sheets preferably comprise within the package n main notches 4 and m secondary notches 40, radially inner with respect to the main notches 4, with n and m integers not damaged and ri> m.

The secondary notches 40 are for example disjoint from the main notches.

In a variant, each secondary notch communicates with a main notch.

Each secondary notch 40 can be centered on the median plane of symmetry of a main notch.

The ratio n / m between the number of main notches 4 and the number of secondary notches 40 is for example equal to 2 or 3.

The secondary notches 40 preferably have an angular extent greater than that of a main notch 4, the angular extent of a notch being measured from the center of the rotor.

Guard plates

As illustrated in FIG. 8, the package 2 may include at least one guard plate 110 at at least one of its axial ends, preferably at each of the axial ends. Bars 10, better all the bars, come to bear at an axial end against this guard plate 110.

The presence of the guard plate (s) 110 makes it possible to hold at least one end of the bars 10, by pressing against the guard plate (s).

At least one guard sheet 110, and preferably each guard sheet, is produced with openings 220 which allow the injection, through the guard sheet 110, of the second material 20 into the pack of sheets. Thus, the presence of the guard plates 110 does not hinder unduly the injection of the second material 20, while contributing to the effective maintenance of the bars introduced into the notches until the injection operation.

The guard plate (s) 110 may include at least one relief 221 which is at least partially superimposed on the bars 10 to retain them axially. This relief 221 can be produced in various ways.

In exemplary embodiments, the or each relief 221 is formed by two opposite projections, by notch receiving a bar. These advances are superimposed on the bars. In alternative embodiments, the or each relief 221 comprises a material bridge by notch receiving a bar.

Blocking elements

The machine may include pins or rivets 70 inserted in the notches in contact with the bars.

As illustrated in FIGS. 9A and 9B, these pins or rivets 70 are arranged in the bottom of the notches 4, to come to bear against the radially inner end face 13 of the bars 10.

The pins or rivets 70 can be of conical shape.

Rotor manufacturing

To manufacture the rotor, the sheets 113 can be cut with a press equipped with a punch and form, during cutting, openings 3 corresponding to the notches 4 and, if necessary, to the secondary notches and the bosses 5.

Then, the sheets 113 are superimposed to form the package 2 then the bars 10 are inserted into the notches 4 by force. During insertion, the presence of the bosses 5 facilitates the advancement of the bars 10 within the packet 2 of sheets 113, and where appropriate, pins or rivets 70 are inserted into the bottom of the notches to block the bars 10 before injection. Once the bars 10 are in place, the second material 20, namely aluminum, can be injected into a press. The short-circuit rings can be made during injection by molding.

The bar cavities can be produced by extending the material which constitutes them within a die, or by rolling a strip of said material.

Of course, the invention is not limited to the examples which have just been described.

For example, the notches can have other shapes, as can the bars.

Other materials than copper and aluminum can be used.

Claims (11)

1. Rotor of a rotating electric machine, comprising: - a package (2) of magnetic sheets (13), the magnetic sheets (13) comprising openings (3) forming notches (4) within the package (2), - bars (10) of a first electrically conductive material inserted into at least part of the notches (4), at least part of these bars (10) being hollow, - a second electrically conductive material (20), injected into the notches (4) at least inside the bars (10). 2. Rotor according to claim 1, the second material (20) filling the notches (4) outside the bars (10). 3. Rotor according to one of claims 1 and 2, the bars (10) extending over the entire radial dimension of the notches (4). 4. Rotor according to the preceding claim, the bars (10) having a cross section which is substantially the same shape as the notches (4). 5. Rotor according to one of claims 1 and 2, the bars (10) having a radial dimension less than that of the notches (4). 6. Rotor according to any one of claims 1 to 5, the bars (10) extending at least along the length of the package (2) of sheets (13), the rotor comprising, at each of the axial ends of the package ( 2) of sheets (13), a guard sheet (110), the latter coming to bear by its internal face against the axial ends of the bars (10). 7. Rotor according to any one of the preceding claims, comprising notches (4) without bars inserted inside. 8. Rotor according to the preceding claim, comprising more notches (4) with bars (10) than notches without bars. 9. Rotor according to any one of the preceding claims, the first material being copper. 10. Rotor according to any one of the preceding claims, the second material (20) being aluminum. 11. Rotating electric machine, comprising a rotor according to any one of the preceding claims.