EP2457312A1

EP2457312A1 - Method for manufacturing an inner rotor for a rotary electric machine

Info

Publication number: EP2457312A1
Application number: EP10737020A
Authority: EP
Inventors: Maeick Blanc; Bertrand Vedy
Original assignee: Michelin Recherche et Technique SA Switzerland; Michelin Recherche et Technique SA France; Societe de Technologie Michelin SAS
Current assignee: Compagnie Generale des Etablissements Michelin SCA; Michelin Recherche et Technique SA France
Priority date: 2009-07-22
Filing date: 2010-07-21
Publication date: 2012-05-30
Also published as: JP2012533982A; US8935845B2; CN102474167A; FR2948508A1; WO2011009886A1; FR2948508B1; US20120206008A1

Abstract

The invention relates in particular to a method for manufacturing an inner rotor for a rotary electric machine, the rotor including a plurality of polar parts surrounding a shaft, each polar part being made of a stack of metal sheets (3) made of a magnetic material, the polar parts delimiting recesses for permanent magnets therebetween, said method including the consecutive steps of: cutting blanks (33), each grouping n metal sheets (3) together, "n" being the pole number of the rotor, the n metal sheets in a blank being kept rigidly connected by temporary bridges (35) straddling the recesses, each of at least two bridges comprising an outer lug (36); stacking the blanks while keeping the same aligned using the outer lugs; immobilizing the stack of blanks; and excising all the temporary bridges in order to enable the radial access to the recesses.

Description

Process for the manufacture of an inner rotor for a rotary electric machine

The invention relates to rotating electrical machines whose inner rotor comprises permanent magnets. More specifically, the invention relates to machines in which the magnets are disposed in recesses of the rotor. The electrical machines in question are commonly referred to by the term "buried magnets". This principle of rotor arrangement is widely applied for autopiloted synchronous machines with flux concentration.

The sizing of a rotating electrical machine depends on its nominal torque.

The higher the torque that a motor is capable of delivering, the larger the electric motor, all other things being equal. However, there are applications for which it is desirable to achieve both significant power and great compactness of the engine. To give just a concrete example, when it is desired to install electric traction motors in the wheels of motor vehicles, it is desirable to be able to develop powers of at least 10 kW per motor, and even for the most part at least 25 kW. or 30 kW per motor, for as little weight as possible to limit unsprung masses as much as possible. It is also desirable that the size is also very small, exceeding as little as possible the interior volume of the wheel so as not to interfere with the vehicle elements during suspension travel and other types of movement of the wheel relative at the vehicle's cash desk.

These two requirements (high power, space and low masses) make it very difficult to install electric traction motors in the wheels of passenger vehicles, except to radically improve the weight / power ratio of electrical machines currently available on the market. walk.

The choice of a high speed for an electric motor during the design of the engine is a solution allowing, at given power, to reduce the torque, therefore the size. In other words, for a nominal power of the given motor, the greater its nominal rotational speed, the lower its size.

A specific design to achieve high speeds of rotation has already been proposed in the patent application EP 1001507. The speeds referred to in this patent application are of the order of 12000 rpm, proposing for this purpose an arrangement particular of the assembly consisting of a polygonal non-magnetic one-piece shaft and judiciously polar parts arranged around this tree. An improvement to target speeds of about 20000 rpm has been proposed in the patent application EP 1359657, proposing for this purpose an arrangement using wedges to radially block the magnets in their housings between the pole pieces. The pole pieces consist of a stack of sheets, each sheet being cut in the form of a disk sector. The method of manufacturing these pole pieces and assembling the rotor is particularly long and complex, in particular to ensure the best alignment of the sheets in the stack.

An object of the invention is to improve the method of manufacturing rotors for rotating electric machine.

The invention thus proposes a method for the manufacture of an inner rotor for rotating electrical machine, the rotor comprising a plurality of pole pieces surrounding a shaft, each pole piece being made based on a stack of sheets of material. magnetic, the pole pieces delimiting between them housing for permanent magnets, said method comprising successively the steps of:

• Cut blanks grouping each n sheets, "n" being the number of pole of the rotor, the n sheets of a blank being held together by temporary bridges spanning the housing, at least two bridges each having an external lug (36). ,

• Stack the blanks by keeping them aligned through the outer pins, • Stabilize the stack of blanks,

• Remove all temporary bypasses to free radial access to dwellings.

Preferably, it immobilizes the stack of blanks between side flanges by means of tie rods, side flanges and tie rods then forming an integral part of the rotor. More preferably, the temporary bridging is removed by machining.

According to a first variant, the cutting of the blanks has the further effect of defining longitudinal grooves in the housing walls near the outer edge of the pole pieces. Preferably, the method further comprises a subsequent step of inserting the magnets radially into the housings and then placing radial holding wedges of the magnets in the longitudinal grooves.

[0013] Preferably, the blanks are obtained by cutting a strip, in particular by stamping.

According to a first variant of the method, a blank is returned to two after cutting and before stacking.

According to a second variant of the method, each blank is indexed at an angle OC with respect to the preceding blank during stacking, OC being a multiple of 360 ° / n. The invention finally relates to a rotating electrical machine comprising an inner rotor obtained by said method.

The invention will be better understood thanks to the following description, which is based on the following figures:

• Figure 1 is a sectional view along the axis of a rotor according to the invention along a broken line A-A visible in Figures 2 and 3.

FIG. 2 is a partial sectional view perpendicular to the axis of the rotor of FIG. 1 along a line B-B visible in FIG.

FIG. 3 is a sectional view perpendicular to the axis of the rotor of FIG. 1 along a line C-C visible in FIG.

FIG. 4 is a perspective view of a blank used in the manufacturing method according to the invention;

FIG. 5 is a perspective view illustrating the step of the method according to the invention of stacking a large number of blanks according to FIG. 4;

FIG. 6 is a perspective view illustrating the step of the method according to the invention of separating the stack into a plurality of pole pieces;

FIG. 7 is a sectional view perpendicular to the axis of the rotor along a line C-C visible in FIG. 1 but corresponding to the example of obtaining method illustrated in FIGS. 4 to 6.

FIG. 8 illustrates another example of a production method according to the invention. - AT -

FIG. 9 schematically shows another example of a tool that can be used in the method according to the invention.

FIGS. 10 and 11 illustrate a first preferred embodiment of the method of the invention in which the stacking operation of the blanks is combined with a reversal of the blanks;

FIGS. 12 to 14 illustrate a second preferred embodiment of the method of the invention in which the stacking operation of the blanks is combined with a rotation between each blank; In Figure 1, there is shown a rotor 1 for a hexa-polar machine further comprising a not shown stator. The rotor 1 comprises a shaft 2 resting on bearings 20. Six pole pieces 30 are seen, preferably formed by a stack of ferro-magnetic sheets 3. Each sheet 3 is substantially perpendicular to the axis of the shaft. The sheets have a very small thickness, for example of the order of a few tenths of a millimeter, for example 0.2 mm. Axially on either side of the shaft 2, we see a side flange 5, 5 '(preferably non-magnetic material), located on each side of the pole pieces 30. In Figure 1, we also see two optional intermediate flanges 7 (preferably also of non-magnetic material). Each lateral flange and optionally each intermediate flange 7 has a central opening. In the nonlimiting example described in FIG. 1, the shape of the central opening of the lateral flanges is circular whereas that of the central opening of the intermediate flanges is fitted to the grooved section of the shaft 2.

For each of the pole pieces 30, a tie rod 6 passes through the stack of sheets 3, where appropriate or the intermediate flanges 7, and allows to enclose the whole between the side flanges 5 and 5 '. We see parallelepiped permanent magnets 4 arranged in the housing 40 between the pole pieces 30. The housing is interrupted by the intermediate flanges 7. In the example of Figure 1, there are 3 magnets per pole . Each of the magnet housings is closed by a magnet spacer 51.

Furthermore, as shown in Figure 2, the longitudinal faces 300 of the pole pieces 30 each comprise a groove 31 parallel to the axis of the rotor, hollowed at a near radial level the outer edge 32 of each pole piece 30 (and therefore each sheet 3), said pole pieces also having a height (or more exactly a radial dimension) slightly greater than the height of the magnets 4. Each wedge 51 thus bears on two grooves 31 disposed on each of the adjacent pole pieces. The magnets 4 are thus made mechanically integral with the pole pieces 30. The essential function of each case 31 is to form a shoulder or a dovetail to oppose the centrifugation of the wedges and magnets. The pole pieces are interdependent with the tie rods and side flanges and possibly intermediate (s).

The pole pieces are themselves integral with the rotating shaft via a rib 34 cooperating with a groove 21 of the shaft and immobilized axially through the tie rods and side flanges. A rod 63 placed in a groove at one end of the tie stops it relative to one of the flanges (on the right in this figure) while a screw 62 is screwed to the other end of the same tie rod (to left in the figure). Such a rotor thus supports, without damage, very high speeds of rotation, much greater than 10000 rpm, namely speeds of the order of 20000 rpm at least.

Figures 4 to 13 illustrate essential aspects of the method according to the invention for the manufacture of such a rotor.

In Figure 4, we see a blank 33 grouping six sheets 3, each plate being intended to belong to one of the six pole pieces of the rotor. The six sheets are temporarily held together by temporary bridging 35. At least two of the bridges have outer pins 36 whose role will be described below.

The blank 33 is preferably obtained by cutting a strip, for example by stamping. The shape of the housings 40 for the magnets and the passages 61 for the tie rods are recognized. The blanks are then stacked and clamped between the side flanges by the tie rods.

In FIG. 5, only the stack of blanks is shown. The other elements (trees, side and intermediate flanges, tie rods) are omitted to facilitate the reading of the drawing. The reader is invited to consult Figures 1 to 3 where these elements are visible.

According to the invention, the stack of blanks is aligned by means of the outer lugs 36 formed on at least two temporary bridges 35, preferably on bypasses. diametrically opposed as shown here. Guides having a suitable groove receive these lugs and keep the blanks aligned with each other before they are secured by the tie rods. It is thus possible to guarantee excellent alignment of the sheets in the stack. The high accuracy of the alignment in turn reduces the air gap and thus improve the efficiency of the electric machine.

Once the stack immobilized by the tie rods, it is possible to remove the temporary bridges 35, for example by milling as shown schematically in FIG. 6. The removal of the bridges frees the radial access to the housings 40 and eliminates the external pins. 36 at the same time. It is understood that this essential feature of the method according to the invention accelerates the manufacture of rotors by reducing the number of parts and greatly facilitating the handling of the sheets.

In a particular embodiment, the operation of eliminating temporary bridging allows at the same time to achieve the foliage 31 for receiving the wedges 51 holding the magnets. This is represented by the example of FIG. 6 in which a conical cutter simultaneously makes it possible to machine the two grooves 31 and to eliminate the bridges.

In Figure 7, we see in section the rotor thus obtained. Around the groove shaft 2, we can see the magnets 4 held in their housings 40 by the wedges 51, as well as the tie rods 6 which compress the stack of the plates 3. The section of the wedges is here substantially trapezoidal (at the tail end). donde) but one can in fact adopt a completely different section only if it can cooperate with the grooves 31 of the pole pieces to close the housing and provide a radial locking of the magnets.

FIG. 8 illustrates another example of a production method according to the invention. This embodiment makes it possible to accommodate shims 51 of shouldered section in the form of a "T" as shown in FIG. 2. The corresponding grooves 31 are precut in the blank 33 and the operation to eliminate the bridges 35 then has no other function than that of releasing the radial access to the housing 40 of the magnets. This operation can be performed by cutting the two ends of the bridges as shown schematically here or by milling radial axis (according to the diagram of Figure 6 but using a cylindrical bur). Depending on the shape of the housing, the branches and shims, we understand that we can choose different methods and tools to achieve this operation. For example, the profile of the grooves of FIG. 6 can not be obtained by cutting or milling along a tangential axis as described in FIG. 8. On the other hand, the profile of the grooves of FIG. 8 could be obtained by milling according to FIG. radial axis provided to use a specific cutter, "T", for example according to the diagram of Figure 9.

Figures 10 and 11 illustrate a preferred characteristic of the rotor manufacturing method according to which the blanks are stacked upside down and preferably comprise a marking 63 for identifying the two faces of the blank. The marking 63 may be as here a particular cutout of the passage 61 arranged so that it is clear if we deal with one face or the other. Indeed, if we compare Figures 10 and 11 which each shows a different face of the same blank, we see that the cutout 63 appears offset on one side or the other of the passage 61.

The fact of stacking the blanks by systematically returning a blank out of two makes it possible to compensate for any variation in thickness from one edge to the other of the blank. The origin of this variation can result from a variation of the thickness of the strip or the method of cutting blanks or any other cause.

In order not to induce imbalance, the marking is preferably present on each of the six passages of the blank. In addition, the multiplication of markings further facilitates the identification of faces.

Figures 12 to 14 illustrate an alternative to the stacking upside down described in FIGS.

10 and 11. The blanks 33 are this time stacked by indexing each blank by a certain angle and preferably comprise a single marking 63 to identify a pulling passage among the six passages of the blank. It is seen by comparing Figures 12, 13 and 14 that, from one figure to the next, the blank is indexed a sixth of a turn (60 °) to the right. The indexing angle may correspond in fact to any multiple of 60 °, for example 120 °, 180 °, 240 °, etc. A 180 ° indexing can be quite satisfactory to compensate for any variations. thickness and at the same time allow a relatively simple process in which one sheet is indexed in two at a single angle (180 °). The indexing is preferred to the reversal described above, especially when the cutting process blanks tends to deform the edges of the parts. This is the case of stamping which tends to form burrs which then prevent the sheets to stack well in case of rollover. Naturally, one can perform at the same time an indexing and a flipping or alternating the two movements. Similarly, there is shown a hexapolar rotor and an indexing of 60 °, that is to say the angle between two adjacent poles. An equivalent effect is obtained with an indexation of oc = +/- 360 ° / n, where "n" is the number of rotor poles.

The markings 63 visible in the figures are easily obtained during the cutting of the blanks. Alternatively, these markings can be made on the temporary bypasses 35, including the outer pins 36. They are then doomed to disappear when the bypass are removed, which eliminates at the same time any unbalance possibly caused by markings.

Of course, other marking means may be used for the same purpose of locating a face or orientation of the blank for its reversal or indexing during stacking. The markings are especially useful in case of manual handling of the sheets. In the case of automated manipulations, we can usually do without it.

The method according to the invention makes it possible to obtain rotors of very good geometric quality under conditions of improved productivities.

However, once the rotor assembled permanently, weights 100 can be attached to the flanges to further perfect the static and dynamic balancing of the rotor (see figure).

2).

The balancing weights here have the form of grub screw 101 that is positioned in threaded holes 102 formed in the flanges. Each flange thus comprises six threaded holes 102 in addition to the six passages 61 for the six tie rods 6. It is understood that by adjusting the position, the length and / or the material chosen for each balancing weight, it is possible to finely adjust the balance of the rotor.

The method therefore preferably also comprises the subsequent steps consisting successively of: • Rotate the assembled rotor on a balancing machine;

• Determine positions and masses of weights necessary for balancing;

• Fix the necessary flyweights on the flanges. Alternatively, the flyweights can also be fixed on the tie rods.

Preferably, the assembly / balancing process further comprises a subsequent step of controlling the correct balancing of the rotor on the same machine.

More preferably, the assembly / balancing process further comprises a preliminary step of rotating the rotor while the tightening of the tie is reduced and then to perform the final tightening of the tie rods. In this way, it is ensured that all the constituent elements of the rotor (in particular ferro-magnetic sheets and permanent magnets) are well centrifuged before their final immobilization. Centrifugation can be carried out at a rotation speed of the order of 50% of the maximum speed envisaged in service.

Alternatively, the centrifugation can be performed after the final tightening by applying this time a rotation speed at least equal to the maximum speed envisaged in service (for example of the order of 120% of the maximum speed).

As we have seen, the figures show a hexa-polar rotor, that is to say comprising

3 pairs of poles but the person skilled in the art knows how to transpose the technical teachings of the present application to rotors comprising for example 2, 4 or 5 pairs of poles instead of 3.

Claims

Process for the manufacture of an inner rotor (1) for a rotating electrical machine, the rotor comprising a plurality of pole pieces (30) surrounding a shaft, each pole piece being made based on a stack of sheets (3) in magnetic material, the pole pieces delimiting between them housings (40) for permanent magnets (4), said method comprising successively the steps of:

• Cut blanks (33) each containing n sheets, "n" being the pole number of the rotor, the n sheets of a blank being held together by temporary bridges (35) spanning the housing, at least two bridges each comprising an external lug (36),

• Stack the blanks by keeping them aligned through the outer pins,

• immobilize the stack of blanks,

• Remove the set of provisional bypasses (35) to free the radial access to the dwellings (40).

2. Method according to claim 1 wherein the stack of blanks is immobilized between lateral flanges (5, 5 ') by means of tie rods (6), the side flanges and tie rods then forming an integral part of the rotor.

3. Method according to one of the preceding claims wherein the temporary bridges (32) are removed by machining.

4. Method according to one of claims 1 or 2 wherein the cutting of the blanks has the further effect of defining longitudinal grooves (31) in the walls of the housing near the outer edge (32) of the pole pieces (30). .

5. The method of claim 3 wherein the machining further has the effect of producing longitudinal grooves (31) in the housing walls near the outer edge (32) of the pole pieces (30).

6. The method of claim 4 or 5 further comprising a subsequent step of inserting the magnets (4) radially into the housings (40) and then placing shims (51) for maintaining radial magnets in the longitudinal grooves (31). .

7. Method according to one of the preceding claims wherein the blanks are obtained by cutting a strip, in particular by stamping.

8. Method according to one of the preceding claims wherein we return a blank of two after cutting and before stacking.

9. Method according to one of claims 1 to 7 wherein is indexed each blank by an angle α relative to the previous blank during stacking, OC being a multiple of 360 ° / n.

10. Rotating electric machine comprising an inner rotor (1) obtained by the method according to one of the preceding claims.