IES990241A2

IES990241A2 - Grooved part of an electric motor and method for producing this part

Info

Publication number: IES990241A2
Application number: IE990241A
Authority: IE
Inventors: Antonio Benito Jose Izquierdo
Original assignee: Malivor Systemes Sa
Priority date: 1998-03-27
Filing date: 1999-03-26
Publication date: 1999-10-20
Also published as: ES1042942U; ITMI990173U1; IT246607Y1; AT3545U1; PT9528U; ITMI990173V0; DK199900139U1; FR2776856B3; PT9528T; CH692647A5; IES81074B2; RU13522U1; ES1042942Y; JP3062555U; GR990200050U; FR2776856A3; GR2002267Y

Abstract

In an e.g. permanent magnet electric motor, slots (3) are stamped in the sheet steel laminations forming the stator or rotor iron circuit to accommodate the winding (10). The magnetic flux is channelled to the air-gap through the teeth (2) thus formed. Each tooth is notched (8) near the tip, on either side, to receive the ends of the bridge-pieces (4), themselves stamped from the same sheet as the main laminations, which close the slot mouth over the whole length of the stator or rotor core. The correct assembly of these laminations is aided by holes stamped near each end whose rough edges, on one side, tend to bed into the slightly chamfered hole on the other face of the adjoining lamination. Bridging greatly reduces the variation in flux as each permanent magnet pole passes over the teeth. Corresponding reductions in eddy current loss allow the motor current to be increased, more than offsetting the loss of torque due to slot enclosure. Similar arrangements are described for motors with axial air-gaps. [FR2776856A3]

Description

The invention relates to a grooved part of an electric motor with permanent magnets, forming the rotor or stator of the motor, and to the method for producing this part.

The electric motors with permanent magnets to which the invention relates are, in particular, brushless motors, the grooved part forming the stator.

In electric motors, the advantage of the grooves in a magnetic sense is that the paths of the magnetic field through the air are reduced because they can enter from the pole pieces through a relatively small gap directly into the teeth of the stator, and the advantage in a mechanical sense is that the windings placed in the grooves are prevented from moving laterally because of the sides of the teeth defining the grooves.

However, grooved stators, in contrast to smooth stators, have a disadvantage caused by the interaction of the permanent magnets with the teeth of the stator. In fact, when the poles of the permanent magnets pass in front of the grooves a rapid fluctuation of the magnetic flux is produced, which causes a fluctuation in torque, vibrations, noise and heating of the magnets by the creation of eddy currents.

The aim of the invention is to propose a means of avoiding the variation in flux depending on the rotational angle of the rotor, such that the fluctuations caused by the presence of the grooves are reduced.

To this end the invention is characterised in that the grooves are covered, at least over a portion of their length, by bridge-like pieces of magnetic material·, these bridge-like pieces being fixed to the teeth which define each groove and providing partial magnetic closure between two teeth.

The said bridge-like pieces preferably cover the whole length of the grooves, at least approximately and in particular completely cover them. ________ OPEN TO SECTION .-. i!JU=23 IE 990241 The method for producing this grooved part is characterised in that a part provided with grooves is produced and that the winding is disposed in the grooves and that finally the bridge-like pieces are fixed on the said part so as to cover the grooves at least over a portion of their length.

The grooved part can be the stator or the rotor of a motor with a long rotor surrounded by the stator with a radial gap. This part can also be the stator of a motor with a flat rotor, thus with the rotor in the form of a disc disposed at the side of the stator and with an axial gap, or in particular with a stator of two pieces which are disposed on both sides of the rotor, thus forming two axial gaps.

Preferred embodiments of the invention are given by the dependent claims.

The attached drawings show embodiments of the invention by way of example.

Figure 1 illustrates a developed portion of a grooved part, in this case, of a stator with grooves, a groove being covered by a bridge-like piece, the coils being cut to show the teeth of the stator.

Figure 2 is an enlarged view of the bridge-like piece separated from the stator.

Figure 3 shows, on an enlarged scale, a detail of the zone for fixing one end of the bridge-like piece on the end of a tooth of the stator.

Figure 4 is an enlarged cross-sectional view along IV-IV of Figure 2 showing the bridge-like piece formed by assembly of cut-out metal sheets thus forming a block of laminations.

Figure 5 is a partial developed view of the periphery of the stator in accordance with the arrow F of Figure 1, the bridge-like pieces completely covering the grooves. • 30 Figure 6 is a view similar to Figure 5 but with the bridge-like pieces partially covering the IE 990241 grooves.

Figure 7 shows the stator of a flat motor with an axial gap and with bridge-like pieces completely covering the grooves.

Figure 8 is a view similar to Figure 7 but with the bridge-like pieces partially covering the grooves.

Figure 1 is a partial developed view of a stator 1 surrounding a rotor with permanent magnets, not shown in the drawing, the example in question thus relates to the stator of a motor with a radial gap. This Figure 1 shows three teeth 2 of the stator which define grooves 3. Windings 10 surrounding each tooth 2 are inserted in a conventional manner into the grooves 3. The openings of the grooves 3 are each covered over their whole length in the axial direction of the stator by a bridge-like piece 4 (Figure 5). The front faces of the teeth and the surfaces of the bridge-like pieces 4 thus define the gap.

By this means a certain partial magnetic short circuit is created between two adjacent teeth, which largely reduces the fluctuation in the magnetic flux in the permanent magnets as the permanent magnets of the rotor pass in front of the grooves. A certain reduction in the torque/current ratio is of course produced by reason of the magnetic circuit created between two consecutive teeth of the stator. However, because the losses caused by eddy currents are reduced it is possible to increase the current and consequently it is possible to increase the total useful torque of the motor.

The stator 1 is formed by a block of cut-out laminations and the bridge-like pieces 4 are themselves formed by a block of laminations 5 of magnetic material (Figure 2). The planes of each lamination 5 forming the bridge-like pieces 4 are parallel to the planes of the laminations of the stator 1, they are thus orientated perpendicular to the axis of the stator. The height H of the laminations 5, viewed in the longitudinal direction of the teeth, is between two and five times the thickness of the said laminations 5, which permits them to have a certain elasticity to aid their assembly as will be explained hereinunder.

IE 990241 Figures 2 and 3 show that the bridge-like pieces 4 are slightly arcuate h the outward radial direction. At each end they are provided with profiled projections 6 provided to fit precisely ' into recesses 8 of a mating shape and formed on the ends of the sides of the teeth 2 of the laminations of the stator defining the grooves 3.

The laminations 5 of the bridge-like pieces 4 have stamped holes 7 close to their ends, the stamping having formed burrs 7a on one side of the laminations, as illustrated in Figure 4, and the assembly of the laminations 5 with each other being effected by forcing the stamping burrs 7a into the hole 7 of the adjacent lamination 5 so that the block of laminations forming the bridge-like pieces is a compact assembly.

The method of producing a grooved part for a motor in accordance with the invention consists of making this part, assuming that the said part is the stator 1 of a motor, by means of a block of laminations cut out in such a way that the edges of the ends of the teeth 2 defining the grooves 3 have profiled recesses 8. Then, by means of cutting out and stamping, the bridgelike pieces 4 are made using laminations of the same magnetic material as the said part, in particular soft iron, so that these laminations 5 have, at their ends, on the one hand projections 6 of a shape mating with that of the recesses 8 at the ends of the teeth 2 of the stator 1, and on the other hand, holes 7 with burrs 7a which assist assembly of the laminations 5 with each other. The windings 10 of the stator are disposed in the grooves 3, then the bridge-like pieces 4 are introduced laterally into the grooves 3 of the stator 1 by threading their ends 6 into the recesses 8 in the ends of the teeth. The arrangement of the recesses 8 and of the bridge-like pieces 4 with their projections 6 is such that when the bridge-like pieces 4 are mounted they must be forced to bend slightly for their ends to slide into the recesses 8 in such a way that it is the elastic force which fixes them tightly in the recesses 8.

The bridge-like pieces 4 can cover the grooves 3 over their whole length (Figure 5) or over only a portion of their length (Figure 6) when a number of shorter pieces 4 are positioned, in the illustrated example there are, for example, three pieces 4 spaced apart from each other. Moreover, in this Figure 6 the coils disposed in the grooves 3 have not been drawn in so that the said grooves can be seen.

IE 990241 In the case of a long rotor the grooved part hi accordance with the invention may be either the stator or the rotor, defining a radial gap. The Figures I, 5, 6 can also be considered as a developed illustration of a rotor.

The grooved part in accordance with the invention can also be the stator of a motor with a flat, disc-shaped rotor (Figures 7 and 8), the rotor and the stator being disposed side by side and thus defining an axial gap. In this latter case of a motor with an axial gap, the length of the grooves covered by the bridge-like pieces is, of course, orientated radially. In the embodiment illustrated in Figure 7, the bridge-like pieces 4 completely cover the grooves between the teeth 2 of the stator, while in the embodiment illustrated in Figure 8 the bridgelike pieces 4 partially cover the grooves, the coil being left out of the illustration by choice in order to show the said grooves, as in the embodiment of Figure 6.

The invention is not limited to the embodiments described but can have diverse variations.

Claims

1. Grooved part of an electric motor with permanent magnets, forming the rotor or stator of the motor, characterised in that the grooves (3) are covered, at least over a portion of their 5 length, by bridge-like pieces (4) of magnetic material, these bridge-like pieces being fixed to the teeth ( 2. ) which define each groove and providing partial magnetic closure between two teeth.

• 2. Grooved part according to claim 1, characterised in that the grooves (3) are covered at 10 least approximately, preferably completely, over the whole length by the said pieces (4).

3. Grooved part according to claim 1, characterised in that it is formed by a block of laminations, and in that the bridge-like pieces (4) are also formed from a block of laminations (5), the planes of each of the laminations forming the bridge-like pieces being parallel to the 15 planes of the laminations of the grooved part.

4. Grooved part according to claim 3, characterised in that the bridge-like pieces (4), viewed in the longitudinal direction of the teeth, ie. the height (H) of the blocks of laminations (5) forming these pieces, extend over a distance between two and five times the thickness of the 20 laminations (5).

5. Grooved part according to one of claims 3 or 4, characterised in that the laminations (5) of the bridge-like pieces (4) are slightly arcuate in the outwards direction and are provided with profiled projections (6) at their ends and in that, at the ends of the sides of the teeth (2) of the 25 laminations of the said part defining the grooves (3), recesses (8) are provided of a shape mating with the shape of the projections (6) of the bridge-like pieces and into which these bridge-like pieces (4) are fixed.

6. Grooved part according to one of claims 3 to 5, characterised in that the laminations (5) of 30 the bridge-like pieces (4) have stamped holes (7) close to their ends, these holes having stamping burrs (7a) on one side, and in that these stamping burrs are engaged by force into the IE 990241 holes of an adjacent lamination so that the block of laminations ct'the bridge-like pieces forms a compact assembly.

7. Method for producing a grooved part of an electric motor according to one of the 5 preceding claims, characterised in that a part provided with grooves is made, that the winding is disposed in the grooves and that finally the bridge-like pieces are fixed on the grooved part so as to cover the grooves at least over a portion of their length.

8. Method according to claim 7, characterised in that the grooved part is made by using cut10 out laminations such that the ends of the sides of teeth of the laminations defining the grooves have profiled recesses, that the bridge-like pieces are made from laminations cut-out and stamped in the same material as the grooved part, these laminations having projections of a shape mating with the shape of the recesses in the laminations of the grooved part, and in that after having placed the winding in the grooves, the bridge-like pieces are introduced laterally 15 into the grooves by threading their ends into the recesses in the teeth of the grooved part.

9. Me±od according to claim 8, characterised in that the arrangement of the recesses (8) and of the bridge-like pieces (4) with their ends (6) is chosen to be such that the said bridge-like pieces (4) are bent in order to be introduced into the recesses (8).