WO2018229098A1 - Twisted stator and manufacturing method - Google Patents

Abstract

The present invention relates to a caseless, in particular synchronous, electric motor including: - a rotor; - a stator (1) including a set (10) of laminations (11) exhibiting slots (14) accepting windings, the laminations exhibiting, at their radially outer periphery, radial extensions (20) through which housings (21) of oblong section pass, in which housings are engaged through-bolts (30), the laminations being angularly offset with respect to one another such that the slots (14) each lie along a helical path; - front and rear bearings, the through-bolts (30) coming into abutment against the bearings and imposing a geometry on the motor independently of that of the set of laminations.

Description

 The present invention relates to rotating electrical machines and more particularly but not exclusively to the stators of synchronous motors.

 Among the operating characteristics of electric motors, the torque pulsation (or torque ripple) is that which determines the flexibility of use, comfort, criteria that are fundamental in certain types of applications ( elevators, automobile traction, handling, ...).

 To obtain a low level of torque pulsations, it is necessary to have an inclination with respect to the axis of rotation:

 · At the rotor, with rotor notches following a helical path,

 • either at the stator, by twisting it.

 In the case of asynchronous motors with squirrel cage rotor, the simplest solution, widely used, is to mount before aluminum injection helical rotor plates, for example with the aid of a keyway helical or specific positioning tool, and then to inject the aluminum. A rotor such as that illustrated in FIG. 1 is obtained.

 For DC or synchronous wound rotor motors, the rotor laminations are mounted on the helical shaft, for example by means of a helical key groove or positioning tool as above, then the rotor is wound, by manual or mechanical insertion of the rotor windings in the notches.

 On synchronous motors with magnet rotor, these techniques can not be used because the magnets are rigid parallelepipedic or tile-shaped parts.

 There are then three possible solutions to obtain an inclination between the rotor and the stator:

 a) split the rotor as shown in Figure 2, in several rows (also called "slabs"), which amounts to having several magnets in the length of the rotor. An angular shift ("step skew") is created between the successive rows, which creates a kind of helix and thus makes it possible to reduce the torque pulsations;

b) twist the stator: the stator, of cylindrical outer shape, is twisted either before winding (in the case of manual winding) or after winding (in the case of automatic winding); c) a third solution is to use twisted magnets, but it has the disadvantage of requiring a type of magnet per machine length, which is only applicable for large series or very special cases, and the technique to develop and control helicoidal magnets is complex.

 The step skew of synchronous magnet rotors has the following drawbacks:

 a) It proves less effective: The effect of reducing the torque pulsations is less important than what can be obtained with an inclined stator or a helical rotor;

 b) in the case of short engines, it is necessary to split the rotor into rows of magnets (slabs) very short, which increases the number of magnets, their cost and complicates the implementation;

 c) the fact of having a significant angular difference between the rows of consecutive magnets locally creates a disturbance of the magnetic flux, detrimental to the efficiency of the motor: it is then desirable to set up a means to avoid contact between the magnets, for example by introducing an insulator between the rows of magnets, such as an insulating washer, which increases the length of the rotor and its price, or to position the magnets so that they can not touch each other, so to have magnets shorter than their axial housing, which complicates the manufacturing process.

 Moreover, traditionally, the stators of the electric motors are of round shape, being for the most part inserted in a housing after winding.

 Square-shaped stators, assembled by tie rods, first appeared for DC motors: this design eliminates the need for crankcases, costly parts, and optimizes the use of sheet metal even in angles, taking advantage of these angles to accommodate a fastening system or to make auxiliary poles. It causes a significant drop in the cost price, and tends to be widely used by most manufacturers of DC motors.

 Certain types of asynchronous or synchronous motors also use this square structure, as illustrated in FIG. 3, because of its economic interest. In Figure 3, we see that the magnetic laminations of the stator package is assembled using tie rods in the four corners, introduced into corresponding recesses of circular section.

US Pat. No. 2,650,316 discloses an electric motor having on the stator a bunch of corrugated sheets received in a housing. The sheets have at their periphery extensions radial in which are formed oblong holes for the passage of axial compression tie rods of the package. The method of assembling the sheets is not described in detail. Such a motor has the drawbacks associated with the presence of an outer casing, namely the bulk and the manufacturing cost in particular. In addition, the sheet package has a poorly controlled geometry. Given the presence of a housing, the bearings can nevertheless be maintained precisely by the latter, regardless of the geometry defects of the sheet package. However, for a crankcaseless engine, this inaccuracy would be problematic because the bearings are then directly maintained by the tie rods.

 Application US 2007/0096585 A1 discloses a twisted stator formed of square shaped contour sheets.

 US Pat. No. 7,531,936 gives other examples of twisted stators. There remains a need to further improve the electric motors without housings, including synchronous, in order to reduce the torque pulses, in an economical and efficient manner.

 There is also an interest in benefiting from a method of manufacturing a twisted stator of such an engine, which is simple to implement.

 The invention responds to these needs by means of an electric motor, in particular a synchronous motor, comprising:

 a rotor,

 a stator comprising a bundle of sheets having notches receiving coils, the sheets having at their radially outer periphery radial extensions traversed by slots of oblong section in which tie rods are engaged,

 the plates being angularly offset relative to each other so that the notches each extend in a helical path,

 front and rear bearings, the tie rods coming into abutment against the bearings and imposing a geometry to the motor independently of that of the sheet package.

Thanks to the invention, it eliminates possible defects in the geometry of the sheet package, since the bearings are positioned relative to each other thanks to the tie rods, so that the geometry of the assembly does not depend on the packet of sheets, including its thickness. The tie rods can come to bear at their ends against countersinks made in the bearings, in this case in particular having a length greater than that of the package of sheets. The invention makes it possible to retain the advantages of the square stator, in particular a low cost price, to conserve their bulk, and thus to respond to dimensional constraints, while obtaining a low level of torque pulsations.

 The invention can make it possible for synchronous rotors with permanent magnets to rationalize the lengths of magnets. The invention also makes it possible, to a certain extent, to optimize the filling of the notches by the winding and to make the best use of the length of the coil heads.

 According to a preferred embodiment, the stator comprises secondary slots extending on one side of the housings within said extensions, curvilinear around the axis of rotation of the motor.

 The presence of such slots facilitates the manufacture of the stator, allowing to introduce therein elements holding the sheets assembled before the winding operation or impregnation of the wound coil of sheets.

 The rotor used can be a straight rotor, which simplifies its manufacture and reduces its cost.

 When the rotor is permanent magnets, they may be of conventional shape, including parallelepiped or tile-shaped.

 The tie rods are preferably of circular section, and may be four in number, the invention is not limited to this number, which may be greater or smaller than four.

 The slots of oblong section may be of curvilinear section, and extend angularly on an angle allowing a rotation of the sheets of at least 5 ° around the axis of rotation of the rotor.

The sheets may have holes to align them angularly prior to the twisting operation of the package. These holes are preferably made in solid portions extending in the gap between one side of a square in which each sheet fits and an annular portion of the sheet, the latter being tangent to the middle of the square side. Such an arrangement makes it possible to cut the sheet in a strip, thus to reduce the losses of material. The holes receive during the alignment operation of the plates elements such as pins. These can be provided at at least one end of a circlip. These elements are removed for twisting. Prior to their removal, the holding elements can be engaged in the peripheral slots. These can still be housed, once the stator manufactured, the elements used to maintain the plate of the package. These elements may comprise pins, which can receive at at least one end a circlip, or be constituted by rivets, among other fasteners that can be used.

 Seals, especially of elastomer, can be interposed between the sheet package and the bearings. This can dampen the magnetic circuit vibrations and seal the bond between the sheet package and the bearings at the outer surface of the machine.

 Another subject of the invention, according to another of its aspects, is a method for manufacturing a stator, in particular the stator of an engine according to the invention as defined above, comprising the following steps:

 assembling a bundle of sheets without giving the bundle an inclination by angularly shifting the sheets together,

 provisional fixing of the sheets by means of elements engaged in holes corresponding to the sheet bundle or in curvilinear peripheral slots, centered on the axis of the stator, these elements being such as pins or rivets for example,

 winding the package of sheets,

 twisting the wound coil package,

 impregnation of the wound coil package,

 - Mounting the sheet package between bearings with tie rods engaged in oblong section housing present at the periphery of the package, the sheet package being positioned by the tie rods between the bearings.

 The initial assembly can be carried out by means of elements introduced into the holes corresponding to the pack of sheets, the latter preferably being holes of circular section.

 In such a manufacturing process, the elements engaged in the peripheral slots can be left in place after the impregnation.

 Twisting can occur after the winding operation, especially when it is automated. Alternatively, twisting takes place before the winding operation, especially when it is manual.

Preferably, the tie rods are put in place after the impregnation, which avoids having to clean them. The invention further relates, independently or in combination with the foregoing, to a synchronous electric motor, comprising:

 - a rotor,

 a stator comprising a bundle of plates having notches receiving coils, the plates having at their radially outer periphery radial extensions traversed by main housings of oblong section in which tie rods are engaged, the plates being angularly offset relative to each other; to others so that the notches each extend in a helical path, and secondary slots extending on one side of the housing within said extensions, these slots being curvilinear around the axis of rotation of the motor.

 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, previously described, shows a rotor inclined according to the state of the art,

 FIG. 2, previously described, represents a so-called "step skew" stator, according to the state of the art,

 FIG. 3, previously described, a square stator according to the state of the art, before the winding operation,

 FIG. 4 schematically and partially shows, in perspective, a stator according to the invention,

 FIGS. 5A and 5B illustrate steps in the manufacture of the stator, FIG. 6 represents an embodiment detail of a stator plate, FIG. 7 represents the complete motor,

 FIG. 8 is a longitudinal section of the motor,

 FIG. 9 represents, in isolation, the rotor, and

 Figure 10 shows a detail of the assembly of the package of sheets and bearings.

 FIGS. 7 and 8 show an engine according to the invention, comprising a stator 1 without a housing, and a rotor 2 rotating inside the stator.

The stator comprises front and rear bearings 4 bearing bearings 5 and 6 for the shaft 7 of the rotor, and a stator magnetic circuit disposed between the bearings. This magnetic circuit is represented in FIG. 4 and comprises a packet 10 of magnetic sheets 11.

 The plates 11 have notches 14, open on the air gap, which host phase windings 12, the motor being for example three-phase.

 The envelope surface of these coils has been schematically represented in FIG.

4. It can be seen that the coil heads 13 protrude axially from the package 10 of laminations 11, on each side thereof.

 According to the invention, the package 10 is twisted, that is to say that the notches 14 each extend in a helical path around the axis of rotation of the rotor.

 The teeth 16 of the plates which define the notches are connected by an annular portion 15.

 Peripheral extensions 20, four in number in the example shown, project on the annular portion 15 outwards.

 Each extension 20 is traversed, as can be seen in FIG. 6 in particular, by a main hole 21, with a long curvilinear section around the axis of rotation, by a secondary slot 22, which presents on one side of the main hole. 21, and an auxiliary hole 23, present on the opposite side. The slot 22 is curvilinear around the axis of rotation of the motor. The auxiliary hole 23 is of circular section.

 The holes 21 form, when the sheets 11 are superimposed, housings in which are engaged respective tie rods 30.

 These tie rods 30 are for example tapped at their ends, as shown in Figure 10, and are used for mounting the motor. The tie rods 30 are each of longitudinal axis parallel to the axis of rotation and abut at their ends 30a and 30b against the bearings 3 and 4 in countersinks 33 made therein, so that the spacing between them the last is imposed by the length of the tie rods and not by the thickness of the sheet package. The length of the tie rods 30 is greater than the thickness of the sheet package. The bearings 3 and 4 are fixed on the tie rods 30 with screws 32 engaged therein. Seals 34 preferably of elastomer are interposed between the guard plates of the package 10 and the bearings.

The bearings 3 and 4 are in continuity with the outer surface of the sheet package. The twisting of the stator corresponds, for example, to an angular offset between the guard plates of the package by about 10 °.

 The main holes 21 are of an angular extent, around the axis of rotation, which is such that each tie 30 bears against one end of the corresponding hole of the guard plate before and against the opposite end of the corresponding hole. the rear guard plate.

 Elements 40 are present in the slots 22 on the finished stator, as illustrated. These elements 40 are for example pins or rivets which allow the temporary fixing of the sheets of the package before its impregnation, as detailed below.

 The rotor is preferably a straight rotor with permanent magnets, as shown in FIG. 9, the motor being synchronous.

 To manufacture the stator 1, it is possible to cut the plates 11 so as to make the extensions 20 in the corners of a square, as illustrated in FIG. 5A. This minimizes material losses during the cutting operation.

 Note in FIG. 5A that the dimension in the radial direction of the solid portion 28 in which the auxiliary hole 23 is made is less than that in which the main hole 21 is made, which makes it possible to house the solid portion 28 in the gap between the annular portion 15 and the side of the square. The latter is tangent in the middle to the annular portion 15.

 After cutting, the sheets 11 are superimposed exactly and thus pre-assembled, for example by means of elements such as pins 45, inserted into the auxiliary holes 23.

 The elements 40 are introduced into the slots 22.

 We can then proceed to the winding operation, automatically, the notches being straight. In a variant, the winding takes place before the elements 40 are introduced into the slots 22.

 Once the winding operation is completed, it is possible to proceed with the twisting operation of the stator. The elements 45 are then removed to allow the inclination of the package.

Once twisting is performed, the notches in which are engaged the conductors of the coils each extend in a helical path. During the twisting operation, the elements are kept parallel to the axis of rotation. Once the desired kinking has been obtained, the impregnation of the magnetic circuit thus produced is carried out.

 Then, the tie rods 30 are placed in the housing 21 and the bearings are mounted thereon. The geometry of the motor is imposed by the axial and radial position of the tie rods in the bearings. Thus, the geometry defects of the sheet package, particularly in terms of thickness, do not negatively affect the accuracy of the mounting of the bearings.

 Of course, the invention is not limited to the example just described. In particular, the stator may be made with at its periphery reliefs intended to create cooling air guiding channels. The main holes may be of closed or open contour, with for example an opening opening radially outwards. Similarly, the peripheral slots may be open contour.

 In the illustrated example, each slot 22 is made in a solid portion adjacent to that which is traversed by the corresponding hole 21. In a variant, the portion in which the slit 22 is made is distinct from that through which the hole 21 passes, for example, between the two, a groove open towards the outside, the bottom of which is defined by the annular portion 15.

 The package of sheets can be covered by a cowling formed for example of a light sheet, formed by folding or stamping. Such a sheet is in no way comparable to a casing supporting bearings.

Claims

1. Electric motor without crankcase, in particular synchronous, comprising:  a rotor (9),  - a stator (1) comprising a bundle (10) of sheets (11) having notches (14) receiving coils, the sheets having at their radially outer periphery radial extensions (20) traversed by housings (21) of section ob long in which are engaged tie rods (30), the plates being offset angularly relative to each other so that the notches (14) each extend in a helical path,  front (3) and rear (4) bearings, the tie rods (30) abutting against the bearings and imposing a geometry to the motor independently of that of the sheet package.  2. Motor according to claim 1, the bundle of sheets having secondary slots (22) extending on one side of the housings (21) within said extensions (20), these slots being curvilinear about the axis of rotation. of the motor.  3. Motor according to claim 1, the rotor being straight.  4. Motor according to one of claims 1 and 2, the rotor (9) being permanent magnets.  5. Motor according to any one of the preceding claims, the housings (21) of oblong section being of curvilinear shape, and extending angularly at an angle allowing rotation of the sheets of at least 5 °.  6. Motor according to any one of the preceding claims, the plates (11) having holes (23) for angularly aligning them prior to the twisting operation of the package.  7. Motor according to claim 6, the holes (23) being made in solid portions (28) extending in the gap between one side of a square in which each sheet fits and an annular portion (25). of the sheet, the latter being tangent to the middle of the square. 8. Motor according to any one of the preceding claims, wherein claim 2, elements (40) for assembling the sheets of the packet being engaged in the slots (22), preferably pins each provided with at least one end of 'a circlip or rivets. 9. Motor according to any one of the preceding claims, seals (34), in particular elastomer, being interposed between the sheet package and the bearings (3; 4).  10. Motor according to any one of the preceding claims, the tie rods bearing at their ends (30a, 30b) against countersinks (33) made in the bearings.  11. A method of manufacturing a stator of an engine according to any one of claims 1 to 10, comprising the following steps:  assembling a bundle of sheets without giving the bundle an inclination by angularly shifting the sheets together,  temporary fixing of the sheets by means of elements engaged in holes (23) corresponding to the sheet bundle or in curvilinear peripheral slots (22), centered on the axis of the stator, these elements being such as pins or rivets for example,  winding the package of sheets,  twisting the wound coil package,  impregnation of the wound coil package,  mounting the plate package between bearings with tie rods (30) engaged in housings (21) of long section present at the periphery of the package, the plate package being positioned by the tie rods between the bearings (3, 4).  12. The method of claim 11, the initial assembly being effected by means of elements (45) introduced into the holes (23), the latter being preferably holes of circular section.  13. Method according to one of claims 11 or 12, the kinking taking place after the winding operation.  14. Method according to one of claims 11 or 12, the kinking taking place before the winding operation.  15. Method according to any one of claims 11 to 14, the tie rods being put in place after the impregnation.