WO1989002668A1

WO1989002668A1 - Electric machine energized by permanent magnets

Info

Publication number: WO1989002668A1
Application number: PCT/EP1988/000810
Authority: WO
Inventors: Marlene Marinescu; Nicolae Marinescu
Original assignee: Marlene Marinescu; Nicolae Marinescu
Priority date: 1987-09-11
Filing date: 1988-09-07
Publication date: 1989-03-23
Also published as: DE3730615A1

Abstract

In an electric machine, magnets are arranged in circle or in line, with their magnetization directions at an angle with respect to each other, in such a way that a polygonal field is created inside the magnet arrangement and stray fields on the sides opposite the polar faces are reduced. The angles of the magnetization vectors (4), i.e. the magnetization direction of each magnet, are arranged with a certain regularity, but very advantageous results can still be obtained even in the case of certain deviations from this regularity.

Description

Electrical machine with permanent magnet excitation

The invention relates to an electrical machine of the type specified in the preamble of claim 1. In particular, the invention relates to an electric motor, namely a direct current motor or a synchronous motor. However, the principles of the invention can advantageously also be used for other rotating or non-rotating electrical machines which serve to transmit forces, perform technically usable work or convert them into other forms of energy. The invention can thus also be used for electrical generators, for converters and magnetic couplings and for electromagnets. In addition, the invention can also be used for linear motors or for electrical measuring instruments. ^■

In classic permanent magnet-excited electric motors, regardless of whether they are DC motors or synchronous motors, the bowl-shaped permanent magnets with their magnetic north-south axis are arranged radially in the stator or in the rotor.

An electric motor has also already become known in which the magnetization does not run radially but parallel to the polar axis.

Both types of magnetization cause an idle induction in the air gap of the motor, which is approximately rectangular (see FIG. 9). This induction can be increased to a certain limit by increasing the radial height of the permanent magnet poles. From a certain magnet height, however, practically nothing is gained in air gap induction

(and therefore excitation flow in the motor). This limit value of the induction is always below the remanent induction of the permanent magnetic material used (see Fig. 9 for a 6-pole motor: the air gap induction is about 70% of the remanence). Both the shape and the value of the air gap induction that can be achieved with radially (or axially parallel) magnetized magnets are not always advantageous. One way to slightly improve the induction curve - in the direction of a sinusoidal curve over the pole angle - is to design the magnets in an expensive way: they are no longer radially uniformly high, but have a greater height in the center of the pole than at the pole edges. One way to increase the air gap induction beyond remanence is the so-called "collector construction", which "collects" the permanent magnetic flux via iron poles and leads to the air gap (the principle of a known "collector motor" is shown in Fig.I). The disadvantages of the collector design are known: in addition to the much higher manufacturing costs, the much stronger disadvantageous armature reaction (which must be suppressed with expensive measures) and the higher reluctance torques when idling are to be mentioned. In addition, such a motor only "collects" with relatively small pole positions, i.e. with large number of poles (under 6 poles, hardly a collector design is worthwhile). However, in a (ideal) limit case, air gap induction up to the saturation induction of soft iron and thus higher torques are achieved with a collector motor than with the shell construction. The shape of the air gap induction can also be influenced very elegantly by a special design Q of the iron poles between the permanent magnets.

All known permanent magnet excitations for motors require a magnetic yoke between the oppositely magnetized ~ adjacent permanent magnets (the collector effect is even based on the effect of these soft iron parts).

The shell motor can also work without inference, but then the air induction drops drastically (Fig. 9) and of all things Q in the polar axis, where it should be high. Such a course is no longer interesting at all. This reduced air gap induction to increase, the permanent magnets must be designed extremely high, which is certainly disadvantageous.

That: the presence of a strong iron yoke is not desirable for several reasons: firstly, this requires a higher weight and (. With external excitation) larger overall dimensions of the motor., Secondly, the yoke reinforces the negative effect of the armature reaction, i.e. the distortion of the air gap induction with all its undesirable consequences. Especially with flat shell magnets - like

101 (which are always made of the high-energy materials SmCo and NdFeB - the inference reinforces the armature reaction very disadvantageously. In addition, an iron yoke causes a higher inductance of the armature winding, which can also have a negative effect on the dynamic processes in the system. 5

The invention is therefore based on the object of improving a generic electrical machine in such a way that the field distribution is optimized.

0:

The problem is solved by the features specified in the characterizing part of claim 1. The position of the magnetization vectors, which coincide in direction with the magnetic preferred direction of the respective individual magnets, is achieved because the. Flux between the two pole faces of an associated pair of poles - is essentially closed via the permanent magnets, so that a magnetic conclusion about additional iron parts is not or only to a much lesser extent than previously required. An optimal field distribution could be achieved if an infinite number of permanent magnets were strung together. For practical reasons, however, it is necessary to limit the number of individual magnets, and it has been found that three individual magnets per pole pair already ensure a substantial improvement in several respects.

Through the invention, the advantages of the shell magnet design (very simple manufacture, low armature reaction, low raster moments) and the advantages of the collector design (high, flexibly designed air gap field) are combined in one construction. In addition, the permanent magnet excitation according to the invention can be used to implement electrical machines which do not require iron yoke for the permanent magnets, which has hitherto not been practicable in all known constructions.

The invention thus ensures a reduction in iron losses, because mostly no magnetic iron yoke is required. The anchor reaction becomes much smaller for the same reason. Furthermore, an almost sinusoidal field can be achieved and the risk of irreversible demagnetization of the permanent magnets can be reduced.

Ring magnets have already been developed for nuclear medicine (nuclear magnetic resonance tomography) which have a homogeneous magnetic field inside. Also for electron focusing and other physical devices, "inner" magnetic fields were magnetized with different types

Magnetic segments already developed. In all of these cases, however, there are no electrical conductors that are moved relative to and interact with this magnetic field to generate a force or a voltage. All known ring magnets (recently called "magic rings") generated (almost) homogeneous magnetic fields. Completely different results in the invention Field structures, namely those that arise when soft iron is attached in the immediate vicinity of such a ring magnet (this is not the conclusion of the magnets, but the iron present in the armature, via which the excitation flow closes). Or an air gap field is created with two ring systems - the inner one for an outer field and the outer one for an inner field.

While in the known "magic rings" a homogeneous magnetic field is to be generated, a much more complicated phenomenon occurs in the electrical machine according to the invention: the multipolar magnetic field generated by the ring is "reflected" on the iron surface and the superposition of the original appears in the air gap of the machine and the reflected field. If the ring also has its own magnetic yoke, its surface also acts as a reflection surface for the fields, so that the air gap field appears as the superposition of multipolar fields of different strengths. The course of the field strength over the pole width looks completely different in the electrical machine according to the invention than in the "magic ring".

The invention is primarily intended for the creation of electric motors, in particular also those of high power with diameters of several meters, in which a reduced armature reaction and the absence of iron yoke are particularly advantageous.

Appropriate embodiments of the invention result from the subclaims.

Exemplary embodiments of the invention are described below with reference to the drawing. These exemplary embodiments all represent rotating electrical machines. However, it is clear that the invention can also be used for linear arrangements, ie for unwound stator-rotor arrangements or magnetic lifting devices or the like. The drawing shows:

Fig.I is a schematic view of a "collector magnet" motor representing the prior art;

1 to 3 are schematic representations of a ring magnet arrangement with an external field;

4 shows a ring magnet arrangement with a field restricted to the interior;

5 shows a schematic representation of a rotating electrical machine with an internal armature;

Fig. 6 to 8 embodiments of electrical machines with an external armature.

9 shows a diagram of the comparison between the air gap induction in a known six-pole motor with radial magnetization and an excitation system according to the invention (in each case with a smooth armature);

10 shows in a diagram the air gap induction in a six-pole motor according to the invention (with a smooth armature) with a different number of segments (2, 3, 10);

In all the figures, the sector-shaped individual magnets (10), which add up to form a ring, are provided with arrows. These arrows indicate the magnetization vector of the individual magnets, the direction of which coincides with the respective preferred direction of the magnets if they are isotropic. The individual magnets adjoin one another in the circumferential direction or there are, as in the exemplary embodiment according to FIG. 2, between leave different gaps in different groups. The ring (12) arranged inside the ring magnet in FIGS. 1 to 3 or the ring (14) lying outside in FIG. 4 form a conclusion which leads to the permanent magnetic flux. In many cases this conclusion can be dropped. In any case, the conclusion can be made with smaller dimensions than at

_5 conventional machines.

1, 3 and 4, the polar axis lies

10 each between two individual magnets, the magnetization vectors of which are arranged symmetrically obliquely. In the exemplary embodiment according to FIG. 2, the magnetization vector of the individual magnet lying in each case in the pole axis lies in the radial direction.

Specifically, the direction of the magnetization vectors _._ in the i-th magnet segment results from the following relationship:

^• Tfc * - ^■ ^. if a magnetic field is to be generated outside of the ring and by

• γi = v? fi

20 if a magnetic field is to be generated within the ring. Here is for the outer field: n = 0,1,2, ... for the inner field: n = 2,3,4, ... "c- ^'~ - angle, which by connecting the center of gravity of the i -th

Magnetic sector with the axis of the motor is given with any but fixed radius vector. - = Angle that is to be counted in the same direction of rotation and from the same angular zero position as Lf.

30th 5 shows a ring magnet arrangement corresponding to FIG. 4 in connection with an internally arranged armature (16) with twelve grooves and with four instead of eight poles. These grooves are provided with coils in the usual way. However, the windings can also lie directly in the air gap on a smooth armature.

FIGS. 6 to 8 show a ring-magnet arrangement corresponding to FIGS. 1 to 3 (but only with four poles) with an external armature (18), the grooves of which are also provided with coils in the usual way. FIG. 7 shows how the same 4-pole excitation as in FIG. 6 can be generated with only twelve instead of 24 magnetic segments, namely with three segments per pole. In Fig. 7, the polar axis coincides with the axis of a magnetic segment, in the embodiment according to Fig. 8, however, with the boundary between two segments. The generated field distributions are different, which shows the flexibility of the field design »

9 shows the difference between the induction curve in the air gap in the known radial magnetization and in the excitation system according to the invention. A practically sinusoidal curve can be achieved with the system according to the invention, the maximum value being above the remanence. This value can be increased even further with stronger magnets. In contrast, the maximum value (70% of the remanence) has already been calibrated for radial magnetization. The system according to the invention without iron yoke is cheaper for many applications than known systems with iron yoke since no field is desired in the lateral areas anyway.

10 shows how the induction curve approaches the sinus shape with increasing number of segments. But even with three or two segments per pole, there are extensive advantages in terms of induction » In addition to these few exemplary embodiments shown here, a large variation of further exemplary embodiments is conceivable within the scope of the invention. For example, it is possible to arrange the ring magnet arrangements according to FIGS. 3 and 4 coaxially to one another such that an inner magnetic field (FIG. 4) interacts with an outer magnetic field (FIG. 3), ie the magnet arrangement according to FIG. 3 is of the 4 enclosed magnet arrangement. In this case, an effective magnetic coupling is obtained.

With such a concentric arrangement of two ring magnet arrangements, it is also possible to have a coil structure circulate between them. Such arrangements can also be nested concentrically several times.

As can be seen from the drawing, the individual magnetic modules are constructed essentially symmetrically with respect to their magnetization vectors in such a way that a relatively small number of differently magnetized modules can be used. Thus, only three differently magnetized segments are required in FIGS. 1, 3 and 4, and in the embodiment according to FIG. 2 four differently magnetized segments. By reversing the symmetrical parts can be installed in the manner shown.

In the schematically illustrated exemplary embodiments, only individual magnet segments can be seen in each case. However, a plurality of magnets or magnet segments can be arranged one behind the other in the axial direction, the magnetization vectors of which, in addition to their radial component and the component running in the circumferential direction, also have an axial component. The invention is not restricted to the mathematically exact angular position of the magnetization vectors, and it also includes certain deviations from these angles. The specified formulas provide guidelines, but corrections are possible for flexible design of the field.

Claims

1. Electrical machine with permanent magnet excitation, with a wound armature and with a relative to this movable arrangement of permanent magnets that successively define poles of different polarity and their magnetic field via the armature and 5 via the air gap between the armature and the pole faces of the poles assigned pole pair is closed, characterized in that between the pole faces of a pole pair along the air gap, several individual magnets are arranged side by side, the magnetization vectors of which are positioned at an angle to one another such that the field on the side of the individual magnets facing away from the pole surfaces displaces and essentially is closed directly via adjacent individual magnets.

2. Electrical machine according to claim 1,

15 characterized in that each pole is assigned a group of adjacent individual magnets and that at least some of the individual magnets have a magnetization vector with a component running in the direction of the pole axis.

3 "-" Electrical machine according to claims 1 and 2,

that the egg magnets lie directly on one another in groups and a space is provided between the groups.

4 .-- Electrical machine according to claims 1 and 2, dad ur ehr. G; ekennzeichne that -between the two adjacent poles associated groups of a single magnet is arranged at least its magnetization vector in substantial ^• JO perpendicular to the pole axes.

5. Electrical machine according to one of claims 1-4, characterized in that a plurality of individual magnets are arranged one above the other in the direction of the pole axes and / or 'perpendicular to the plane spanned by the pole axes - and that the magnetization vectors of at least some magnets in three are perpendicular to one another have standing level components;

20 6 .. Electrical machine according to one of claims 1-5, d a d u r c h g e k e n n z e i c h n e t that the magnetization vectors of the individual magnets between adjacent poles are arranged to run on symmetrical polygon courses.

"7. Electrical machine according to one of the preceding claims with a stator and with a rotor arranged concentrically therewith, so that the individual magnets form a closed ring in segments, with which a concentrically inner or concentrically outer armature is connected.

3 "has a collective effect.

8. Rotating electrical machine according to claim 7, so that the permanent magnet segment ring is provided on its side facing away from the pole faces with an iron yoke ring.

9. Rotating electrical machine according to claim 7, d a d u r c h g e k e n n z e i c h n t that several concentric permanent magnet segment rings are provided with an intermediate anchor ring.

10. Electrical machine according to claim 1, d a d u r c h g e k e n n z e i c h n e t that the individual magnets are arranged in a ring shape with respect to the magnet axis and the i-th magnet segment in the direction

is magnetized when a magnetic field is to be generated outside the ring u in the direction

? ^■ - i-ψ

is magnetized if a magnetic field is to arise within the ring, where n = 0, 1, 2, .... for the outer field and n = 2,3,4, .... for the inner field f = angle, which is given by the connection of the center of gravity of the i-th Magn sector with the axis of the motor and an arbitrary but fixed radius vector; i, = angle to be counted in the same direction of rotation and from the same zero angle position as y.

11. Electrical machine according to claim 10, characterized in that the width of a single magnet expressed as a sector angle is less than ^" / 2 (n + l) for external fields and less than // / 2 (nl) for internal fields.

12. Electrical machine, according to one of claims 1-11, d 'a ~ d u r c h g e k e n n z e i c h n e t that the width of the individual magnets with each other is the same or different

, 10th

13. Rotating electrical machine according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e that each magnetic pole (N, S) has two magnet segments with symmetrically at an angle 15 to the pole axis magnetization vectors.

14. A rotating electrical machine according to claim 13, so that at least 20 a magnet segment with a magnetization vector running essentially in the tangential direction is arranged in the central section between two magnetic poles of a pole pair.

15. Rotating electrical machine according to one of claims 7-11, d a d u r c h g e k e n n z e i c h n e t,

25 that each magnetic pole has at least one magnetic sector with a radially extending magnetization vector.

16. Rotating electrical machine according to claims 14 and 15, d a d u r c h g e k e n n z e i c h n e t,

30 that at each pole several, in particular three magnet segments are combined to form a group, which is arranged with a gap to the next group

17. Rotating electrical machine according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that. the armature (16) is arranged concentrically within the ring magnet structure.

5 ^:

18 .. Rotating electrical machine according to one of the preceding claims d ^* a ", that the armature (18) is arranged concentrically outside the ring magnet assembly.

10

19. Electrical machine, according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that when designed as a magnetic central rotary coupling an outer and a

_* Inner permanent magnet segment ring with the same number of magnetic poles 15 are provided, the number of segments corresponding to each pole being either the same or different.

20. Rotating electrical machine according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t,

20. dass.- it has two permanent magnet excitation systems and a winding between the two rings, the outer and the _' inner ring system being designed with or without iron yoke and the number of segments corresponding to each pole being either the same or different.

251 21. Electrical machine according to one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that in the case of training as a linear motor with permanent magnets a linear arrangement of individual magnets is provided, the magnetizations of which are arranged in such a way that they either follow the magnetic field

30 at the top or at the bottom, with an iron yoke optionally attached to the side facing away from the pole faces.