DE102012218993A1 - Cylindrical rotor for permanent magnet-excited electric machine, has permanent magnet comprising partial magnets and arranged between pole shoes, where one of partial magnets has higher coercive force than another partial magnet - Google Patents

Abstract

The rotor has a permanent magnet comprising two partial magnets (71, 72) and arranged between two pole shoes (42) such that a magnetization direction of the permanent magnet is aligned in a tangential direction. One of the partial magnets has a higher coercive force than another partial magnet. The partial magnets are designed as sintered ferrite magnets with a block or cuboid-shape. A pocket for accommodating the permanent magnet is arranged between the pole shoes and extended in a radial direction from outer circumference of the rotor to an inference area of the rotor. An independent claim is also included for an electrical machine.

Description

Technical area

The present invention relates to permanent magnet excited electrical machines, in particular a rotor assembly for such an electrical machine.

State of the art

Rotor arrangements are known from the state of the art, which have pole pieces which provide a field magnet field generated by permanent magnets in the direction of an air gap to a stator arrangement. In a variant of the arrangement of the permanent magnets in the rotor arrangement, the permanent magnets are arranged with their polar direction parallel to the direction of movement of the rotor, so that the pole pieces of the rotor arrangement are located between the permanent magnets. In the pole shoes, the magnetic field emitted by the permanent magnets is deflected in the direction of the air gap.

Such types of rotor assemblies are nowadays used in many permanent magnet-excited electric machines, for example in steering assistance and in cooling devices. In this case, substantially parallelepiped-shaped permanent magnets are used, which are simple and can be produced with little effort, with a magnetization anisotropy and a magnetization direction rectified in the direction of movement of the rotor being aligned.

In rotary electric machines, such an arrangement of the permanent magnets is referred to as a spoke arrangement. The polar direction of the permanent magnets runs in the tangential direction.

An advantage of such rotor arrangements is that, by suitable dimensioning, an air gap flux density which is greater than the remanent flux density of the permanent magnets used can be achieved. Since the air gap flux density decisively determines the torque density of the electric machine, powerful electric machines with relatively high torque densities can be built thereby.

This is achieved in that the number of permanent magnets in the rotor is chosen such that its radial length is greater than the tangential width of the pole shoes between the permanent magnets. This arrangement concentrates the magnetic flux into the air gap to produce an air gap flux density that is higher than the remanent flux density of the permanent magnets.

The above rotor arrangements are often constructed in combination with permanent magnets of simple, inexpensive magnetic material, in particular magnetic material without rare earth compounds and with relatively low remanence flux density, such as, for example, permanent magnets of sintered ferrite materials of the sixth generation.

In addition, permanent magnets made of sintered ferrite materials have a relatively low coercive force, so that there is a risk of demagnetization in the case of an opposing magnetic field of sufficiently high field strength. To compensate for this relatively low coercivity, the permanent magnets are made relatively thick in the direction of their material anisotropy and their magnetization to make them more resistant to demagnetization by the stator field of the electric machine.

Furthermore, in the rotor arrangement described above, two air gaps are provided in the flow path of a permanent magnet. In order nevertheless to achieve a high air gap flux density as well as a high resistance to demagnetization, the permanent magnets thus arranged are often twice as thick (in the poling direction) as permanent magnets made of ferrite material with their polar direction parallel to the air gap magnetic field, the design only an air gap in their respective flow path exhibit.

In particular, in rotary electric machines with a certain rotor diameter and a predetermined number of poles in a spoke arrangement, any increase in the thickness of the permanent magnets in the tangential direction (poling direction) leads to a reduction in their maximum possible radial length. This limitation of the radial length of the permanent magnets limits the flux that can be provided by the permanent magnets and thereby reduces the air gap flux density and the torque density of the electric machine.

Moreover, any increase in the thickness of the permanent magnets results in a reduction in the angular coverage of the individual pole pieces at the air gap of the electrical machine and may also result in this angle being less than its optimum.

It is an object of the present invention to improve the demagnetization resistance in the demagnetization region of the permanent magnets.

Disclosure of the invention

This object is achieved by the rotor assembly for an electric machine according to claim 1 and by the electric machine according to the independent claim.

Further advantageous embodiments of the present invention are specified in the dependent claims.

• – einen Permanentmagneten, der aus mindestens zwei Teilmagneten zusammengesetzt ist; und
• – mindestens zwei Polschuhe, zwischen denen der Permanentmagnet angeordnet ist, so dass dessen Magnetisierungsrichtung in Anordnungsrichtung der Polschuhe ausgerichtet ist;

wobei der zweite Teilmagnet eine höhere Koerzitivfeldstärke als der erste Teilmagnet aufweist. According to a first aspect, there is provided a rotor assembly for an electrical machine comprising:

• - A permanent magnet, which is composed of at least two partial magnets; and
• - At least two pole pieces, between which the permanent magnet is arranged, so that its magnetization direction is aligned in the arrangement direction of the pole pieces;

wherein the second partial magnet has a higher coercive force than the first partial magnet.

Furthermore, the first partial magnet can have a higher remanence than the second partial magnet.

One idea of the above rotor arrangement is to design the permanent magnets in two or more parts, wherein a first air gap remote partial magnet has a lower coercive field strength than a second air gap near part magnet and wherein the second air gap near part magnet has a lower remanence than the first air gap remote part magnet. In this way, it is possible to improve the demagnetization resistance in the demagnetization region in which demagnetization may occur due to the stator magnetic field but at the same time to ensure that a sufficiently high flux density is provided by the composite permanent magnet.

Furthermore, thereby the air gap flux density and thus the torque density of the electric machine is increased because the air gap distant first partial magnet has a high remanence, so that only a relatively small part of the radial length of the permanent magnet must be used to the webs that hold the pole pieces in bring the saturation. The increased torque density makes it possible to reduce the axial length of the electric machine at a same nominal torque and so the weight of the electric machine, its size and their manufacturing costs can also be reduced.

It can be provided that the first partial magnet and / or the second partial magnet are block-shaped.

According to one embodiment, a pocket for receiving the permanent magnet is provided so that its pole faces abut against side surfaces of the adjacent pole shoes.

The rotor arrangement may be formed with pole contours at an air gap facing ends of the pole pieces, wherein the first partial magnet air gap remover is arranged as the second partial magnet.

Advantageously, the permanent magnet is formed anisotropic, wherein the magnetization direction extends in the tangential direction through the entire magnet geradlienig. For example, the coercive field strength of the second partial magnet is higher by up to 50% than that of the first partial magnet, with the coercive field strength of the second partial magnet in particular being in the range between 330 and 360 kA / m. For example, the remanence of the second partial magnet is up to 20% lower than that of the first partial magnet, with the remanence of the second partial magnet in particular being in the range between 380 to 460 mT.

According to a further aspect, an electrical machine with a stator arrangement for providing a stator magnetic field and the above rotor arrangement is provided, wherein the pole pieces of the rotor arrangement are separated from the stator arrangement by an air gap.

Brief description of the drawings

Preferred embodiments of the present invention will be explained in more detail with reference to the accompanying drawings. Show it:

1 a schematic cross-sectional view through an electric machine with a rotor assembly with multi-part permanent magnet;

2 a more detailed representation of a section of the cross section through the electric machine with illustrated magnetic field lines; and

3 a diagram illustrating the characteristics of the partial magnets for the construction of the permanent magnet for the rotor assembly of 1 ,

Description of embodiments

1 shows a schematic cross-sectional view of a conventional rotary, permanent magnet excited internal rotor machine 1 , The electric machine 1 has a cylindrical stator 2 on. The stator 2 includes a cylindrical stator yoke region 21 of which equidistantly arranged in the circumferential direction stator teeth 22 projecting radially inwardly and with their inwardly directed ends a likewise cylindrical inner recess 3 define. The stator teeth 22 are at their radially inner ends with tooth heads 23 provided, which have an approximately circular segment-shaped, concave outer contour. The stator teeth 22 are provided with (not shown) stator coils through which a stator magnetic field can be generated when energized.

In the interior recess 3 is a rotor assembly also a cylindrical rotor 4 (Rotor of the electric machine) rotatably on a shaft 5 arranged. The rotor 4 has a rotor body 41 on that with pole shoes 42 is provided, which over webs 43 with one on the shaft 5 arranged inference region 44 are connected.

The bridges 43 are preferably dimensioned so that they have sufficient mechanical stability to the pole pieces 42 against radially acting centrifugal forces as well as during acceleration or deceleration of the engine to hold in the tangential direction acting transverse forces and still have a cross-section which is sufficiently small to that by the permanent magnets 7 caused magnetic flux through the inference region 44 keep as low as possible. In particular, it is necessary that the through the webs 43 flowing part of the magnetic flux of the permanent magnets 7 sufficient to the magnetic flux density in the webs 43 to keep in saturation.

Between the pole shoes 42 are bags 6 arranged in which permanent magnets 7 are included. The bags 6 extend substantially oblong in the radial direction of approximately the outer circumference of the rotor 4 to the inference area 44 of the rotor 4 ,

To the bags 6 to limit in the radial direction to the outside, have the pole pieces 42 supernatants 45 on, those in the pockets 6 arranged permanent magnets 7 overlap and this reliable, even against the action of centrifugal forces upon rotation of the rotor 4 , in the pockets 6 to keep.

Such an electrical machine 1 is operated by an electric motor, for example, in that the stator coils are energized in such a way that a circulating stator magnetic field is generated, which is identical to that of the permanent magnets 7 over the pole shoes 42 caused exciter magnetic field interacts and thereby a torque on the rotor 4 exercises.

The permanent magnets 7 are usually prepared by pressing ferrite powder material and then sintered, wherein magnetization anisotropy is imparted to the ferrite material during pressing by application of a magnetic field, followed by magnetization of the sintered material in the direction of anisotropy. The permanent magnets 7 are preferably block or cuboid provided for reasons of ease of manufacture. The magnetic pole direction or magnetization of the permanent magnets 7 is in the tangential direction, ie perpendicular to the interfaces between the pole pieces 42 and the bags 6 aligned.

The permanent magnets 7 are formed in two or more parts. A first part magnet 71 is in the bag 6 Air gap far, ie adjacent to the yoke 44 , arranged and a second partial magnet 72 closes in the radial direction to the first part of the magnet 71 on and is arranged close to the air gap.

Preferably, as the first and second partial magnet 71 . 72 block-shaped, ie cuboid, permanent magnets 7 used, since these can be easily produced. The partial magnets used 71 . 72 preferably have a in the tangential direction (or arrangement direction of the pole pieces extending) rectilinear magnetization, so that their pole faces to the pole pieces 42 adjacent to the same poles.

The first part magnet 71 has the highest possible remanence. Depending on the manufacturing process and materials used for the first permanent magnets 71 these are selected to optimize their remanence. The first part magnet 71 is shaped so that he has the bag 6 fills in the air gap remote area and a magnetization in the tangential direction, ie in the direction of arrangement of the pole pieces 42 , provides.

At the first part magnet 71 closes in the radial direction of the second partial magnet 72 on, and as directly as possible. The second part magnet 72 is designed for high coercivity. In other words, in the production of the second partial magnet 72 selected the magnetic material used to achieve a high coercive force. As often as in 3 , the coercive field strength and the remanence of a magnetic material behave in opposite directions, this leads to the fact that the remanence of the second partial magnet 72 less than that of the first partial magnet 71 and the coercive force of the first partial magnet 71 less than that of the second partial magnet 72 ,

In 3 In each case the curve K1 show the course of the remanence with respect to the magnetic field strength for the first partial magnet 71 and the curve K2 the course of the remanence over the field strength for the second partial magnet 72 ,

The aspect ratio of the radial lengths of the second partial magnet 72 to the length of the first part magnet 71 is preferably between 0.1: 0.9 and 0.5: 0.5, preferably between 0.2: 0.8 and 0.4: 0.6.

2 shows a section of the sectional view of the electric machine 1 of the 1 with marked flow lines at full load. The flux density in the two air gap remote first partial magnets 71 near the inference area 44 is higher than that in the second partial magnet 72 near the air gap, which is represented by the distance between the field lines. The very low flux density in the demagnetization area in the upper right corner of the second partial magnet 72 is clearly visible, but can by the two-part design with the second partial magnet 72 an irreversible demagnetization of the second partial magnet 72 be prevented.

Claims (10)

Runner arrangement ( 4 ) for an electric machine ( 1 ), comprising: - a permanent magnet ( 7 ), which consists of at least two partial magnets ( 71 . 72 ) is composed; and - at least two pole shoes ( 42 ), between which the permanent magnet ( 7 ) is arranged so that its magnetization direction is aligned in the tangential direction; wherein the second partial magnet ( 72 ) has a higher coercive field strength than the first partial magnet ( 71 ) having. Runner arrangement ( 4 ) according to claim 1, wherein the first partial magnet ( 71 ) a higher remanence than the second partial magnet ( 72 ) having. Runner arrangement ( 4 ) according to claim 1 or 2, wherein the first partial magnet ( 71 ) and / or the second partial magnet ( 72 ) block-shaped or cuboid, and preferably both partial magnets ( 71 . 72 ) are formed as sintered ferrite magnets. Runner arrangement ( 4 ) according to one of claims 1 to 3, wherein a bag ( 6 ) for receiving the permanent magnet ( 7 ) is provided so that their pole faces on side surfaces of the adjacent pole pieces ( 42 ) issue. Runner arrangement ( 4 ) according to one of claims 1 to 4, wherein the rotor arrangement ( 4 ) with pole contours at an air gap ( 3 ) facing ends of the pole pieces ( 42 ), wherein the first partial magnet ( 71 ) air gap remover is arranged as the second partial magnet ( 72 ). Runner arrangement ( 4 ) according to one of claims 1 to 5, wherein the two partial magnets ( 71 . 72 ) abut each other directly in the radial direction, and in particular the permanent magnet 7 is formed longer in the radial direction than in the tangential direction. Runner arrangement ( 4 ) according to one of claims 1 to 6, wherein the permanent magnet ( 7 ) is anisotropic and in particular the direction of magnetization in the tangential direction extends through the entire magnet geradlienig. Runner arrangement ( 4 ) according to one of claims 1 to 3, wherein the coercive field strength of the second partial magnet ( 72 ) is up to 50% higher than that of the first part magnet ( 71 ), and in particular the coercive field strength of the second partial magnet ( 72 ) is in the range between 330 and 360 kA / m. Runner arrangement ( 4 ) according to one of claims 1 to 7, wherein the remanence of the second partial magnet ( 72 ) is up to 20% smaller than that of the first part magnet ( 71 ), and in particular the remanence of the second partial magnet ( 72 ) is in the range between 380 to 460 mT. Electric machine ( 1 ) with a stator arrangement ( 2 ) for providing a stator magnetic field and a rotor arrangement ( 4 ) according to one of claims 1 to 5, wherein the pole shoes ( 42 ) of the rotor arrangement ( 4 ) through an air gap ( 3 ) of the stator assembly ( 2 ) are separated.

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