JP4870340B2 - Electric motor - Google Patents

Description

  The present invention relates to an electric motor using both a magnet torque and a reluctance torque, and more particularly to a structure relating to a magnetic path of a rotor of the electric motor.

  As a background technology of the present invention, there is a flux barrier type reluctance motor as shown in Patent Document 1 as a first example. An example of the cross-sectional structure of this electric motor is shown in FIG. This electric motor forms a plurality of divided magnetic paths 3 by providing a plurality of slits 2 in a rotor 1 made by laminating electromagnetic steel plates. These divided magnetic paths 3 constitute a magnetic flux path so that the magnetic resistance is reduced with respect to the magnetic flux flowing from the magnetic pole P1 to the magnetic pole P2 in the figure, for example. Further, the slit 2 constitutes a magnetic flux barrier so that the magnetic resistance becomes higher with respect to the magnetic flux flowing to the magnetic pole midpoint N1 and the magnetic pole midpoint N2, for example. The reason for having a plurality of divided magnetic paths 3 and slits 2 in this way is to subdivide the torque ripples by subdividing the magnetic poles by the respective divided magnetic paths and to keep the torque ripples of the entire rotor small.

  In the electric motor shown in FIG. 5, the stator 4 is provided with a plurality of slots 5, and an electric wire is inserted into the slot 5 to constitute a stator winding. This stator winding is the same as a general AC motor.

  In FIG. 5, a hollow shaft 6 is inserted in the center of the rotor 1. For example, in the case of an electric motor used for a main shaft of a lathe, a round bar-shaped workpiece (workpiece) penetrates the hollow portion of the shaft 6. Moreover, when using for the spindle of a machining center, the link mechanism (drawbar) required for holding | maintaining a tool penetrates. For this reason, the hollow portion is required to be as large as possible.

  As a second example of the background of the present invention, there is an embedded magnet motor as shown in Patent Document 2 below. In this case, as shown in FIG. 6, a permanent magnet is embedded in the entire slit provided in the rotor. The purpose of embedding the permanent magnet in this way is to suppress the leakage flux and increase the reluctance torque by generating a magnetic flux in the opposite direction to the leakage flux that passes through the slit. Further, since Lorentz force is generated between the magnetic flux generated by the permanent magnet and the current flowing through the stator winding, the output torque can be further increased.

  As a third example of the background of the present invention, there is an embedded magnet motor as shown in Patent Document 3 below. The rotor structure in this example is shown in FIG. In the slit 2 in the figure, a permanent magnet 7 is embedded only in the central portion. The purpose of using a magnet is to increase the output torque, as in the second case, but in this case, the use of a flat magnet simplifies the machining of the magnet and keeps the cost low. Can do.

  As a fourth example as the background of the present invention, there is an embedded magnet motor as shown in the following Non-Patent Document 1. The rotor structure in this example is shown in FIG. 7 is the same as the example shown in FIG. 7 in that the permanent magnet 7 is embedded in the center portion of the slit 2, but only one slit is provided between the magnetic poles, and no divided magnetic path is provided. For this reason, torque ripple is large, and it cannot be applied to applications that require rotational accuracy such as the spindle of a machine tool.

JP 11-206082 A JP 2002-78259 A JP 2002-272031 A Morimoto, Ueno, Takeda: “Wide-range variable speed control of PM motor with embedded magnet structure”, IEEJ Transactions, Vol.114-D, No.6, p668 (1994)

  A problem in the above-described conventional electric motor will be described. First, in the first case, in order to generate a sufficient reluctance torque, it is necessary to make the leakage magnetic flux passing through the slit 2 in FIG. 5 as small as possible. Therefore, it is necessary to make the slit 2 as wide as possible, and there is a problem that the diameter of the shaft 6 cannot be increased as a result of increasing the slit width particularly in a portion close to the center of the rotor.

  Next, in the second case, the above-described leakage magnetic flux can be suppressed by embedding a permanent magnet in the entire slit 2 as shown in FIG. For this reason, the width of the slit 2 can be reduced, and the diameter of the shaft 6 can be increased. However, in order to ensure the performance of the electric motor, it is necessary to use an expensive rare earth magnet, and there is a problem that the cost is high because the amount of permanent magnets used is large.

  Next, in the third example, the magnet is embedded only in the central portion of the slit 2 in FIG. 7, but the leakage magnetic flux is large in the portion where the magnets at both ends of the slit 2 are not embedded. For this reason, it is necessary to increase the width of the slit 2 as a whole, and there is a problem that the diameter of the shaft 6 cannot be increased.

  Next, in the fourth case, there is a problem that torque ripple is large because a plurality of slits and divided magnetic paths are not provided as shown in FIG.

  As described above, an object of the present invention is to provide an electric motor that can be provided with a large through hole in the center of the rotor so as to pass the shaft of the electric motor, reduce the amount of magnets used, reduce the cost, and reduce the torque ripple. It is to provide.

  An electric motor according to the present invention includes a stator that generates a rotating magnetic field by energizing a winding with a current, and a substantially cylindrical rotor that rotates in synchronization with the rotating magnetic field, and has opposite polarities on the circumference thereof. In order to alternately arrange the magnetic poles, a rotor having a plurality of divided magnetic paths formed by a plurality of slits and connecting adjacent magnetic poles, and a permanent magnet disposed in the slits are provided. ing. The plurality of slits include a radial slit portion formed substantially along the radial direction from the rotor surface toward the center in the vicinity of the surface of the magnetic pole, and a circumferential direction between adjacent magnetic poles in the rotor. Alternatively, it is formed by combining circumferential slit portions formed substantially along the chord direction. Furthermore, the slit width of the circumferential slit portion is smaller than the slit width of the radial slit portion, the permanent magnet is disposed only in the circumferential slit portion, and at least one slit in which the permanent magnet is disposed. And it arrange | positions in the at least edge part vicinity of the said circumferential direction slit part.

  By making the width of the circumferential slit portion smaller than the width of the radial slit portion, it is possible to increase the diameter of the through hole provided in the rotor in order to pass the shaft of the electric motor. Further, in the circumferential slit portion having a small slit width, a permanent magnet is arranged to suppress leakage magnetic flux. In particular, magnetic flux leakage is likely to occur near the end of the circumferential slit, and it is preferable to dispose a permanent magnet here.

  Moreover, a permanent magnet can be divided | segmented into both the edge parts of a circumferential direction slit part, and it can be made to open a space | interval. According to this, the usage-amount of a permanent magnet can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional structure diagram of the electric motor according to the present embodiment. The electric motor 10 of the present embodiment includes a stator 12 that generates a rotating magnetic field, and a rotor 14 that rotates by interaction with the rotating magnetic field. The stator 12 has teeth 16 arranged in the circumferential direction, and a predetermined current is passed through coil conductors (windings) inserted and disposed so as to wind the teeth 16 in slots 18 between the teeth. A rotating magnetic field is generated. The rotor 14 is formed in a generally cylindrical shape by laminating electromagnetic steel plates punched into a predetermined shape. The laminated electrical steel sheets have a cross-sectional shape as shown in FIG. Specifically, a plurality of side-by-side extending slits 20 are punched out, and a part between the slits 20 is formed as a divided magnetic path 22. A plurality of the divided magnetic paths 22 are arranged side by side, and these constitute a magnetic path connecting the magnetic poles Pn-1 and Pn + 1 adjacent to the magnetic pole Pn on the rotor surface, and the magnetic field of the magnetic pole P portion on the rotor 14 is formed. The resistance is reduced. Further, the multilayer slit 20 forms a magnetic barrier against the magnetic flux that attempts to pass from N1 to N2, for example, so that the magnetic resistance at the magnetic pole midpoint N is increased. In this way, by making a difference in the magnetic resistance of the rotor depending on the location, when a current is passed through the stator winding, a reluctance force is generated and a rotational force is generated.

  A shaft 24 is inserted in the center of the rotor 14. This shaft 24 is hollow, and when this hollow part is used for a main spindle of a lathe, for example, a round bar-shaped workpiece (workpiece) penetrates, or when used for a main spindle of a machining center. The link mechanism (drawbar) necessary for holding the tool penetrates.

  FIG. 2 shows the detailed shapes of the slit 20 and the divided magnetic path 22 of the rotor 14. One slit 20 has a radial slit portion 26 extending substantially along the radial direction of the rotor in the vicinity of the magnetic pole P, and a circumferential direction extending along the circumferential direction of the rotor or the chord direction connecting the magnetic poles at a portion between the magnetic poles P. And a slit portion 28. It can also be said that the circumferential slit 28 extends in a direction crossing the radial direction. The width of the slit 20 is such that the width b of the circumferential slit 28 is narrower than the width a of the radial slit 26. By forming the circumferential slit portion 26 to connect the magnetic poles substantially linearly and reducing the slit width here, the diameter of the through hole through which the shaft 24 passes can be increased. In the prior art shown in FIG. 6, the slit projects greatly toward the inner side of the rotor, and in the present embodiment, since this projecting is not present, a large through hole can be taken. Further, in the prior art shown in FIG. 7, the width of the slit is not narrowed in the radial slit portion, and this is an obstacle that protrudes inward and enlarges the through hole. In the present embodiment, the circumferential slit portion 28 is formed in a substantially linear shape, but it may be formed in an arc shape, that is, a shape slightly protruding outward in the center portion.

  As described above, the width of the slit 20 is reduced in the radial slit portion 26. As a result, the effect of the magnetic barrier by the slit is reduced, and the leakage of magnetic flux is increased. As a result, the difference in magnetic resistance is reduced and the reluctance force is reduced. In the present embodiment, in order to realize a rotor structure having a large hollow diameter, the magnetic flux leakage that reduces the reluctance force generated by narrowing the slit width is suppressed. Specifically, a configuration is adopted in which permanent magnets are arranged at both ends of the radial slot 26, and the principle is based on the analysis of individual leakage flux paths described below. Here, paths A, B, and C through which magnetic flux leaks are shown in FIG.

  Regarding the path A, the slit (radial slit portion) in this portion has a sufficiently large magnetic resistance because the width is not narrowed. For this reason, the leakage magnetic flux is sufficiently small.

For the path B, the slit width is narrow and the leakage magnetic flux is large. So part of the permanent magnet 30 the width of the slit is narrow, placed Sunawa Chi circumferential slit portion 28. The permanent magnet 30 (shown by hatching in the figure) is arranged so as to generate a magnetic flux that is in the opposite direction to the magnetic flux that attempts to pass through the slit, thereby canceling the leakage magnetic flux and canceling it out. is there. As a result, the leakage magnetic flux can be kept small. In addition, the path C has a larger magnetic resistance because the distance is longer than the path B. Further, since the magnetic flux tends to pass through the shortest distance, the magnetic flux passing through the path C is smaller than that of the path B. Therefore, even if the permanent magnet is omitted from the central portion of the circumferential slit portion, the leakage magnetic flux passing through the path C is sufficiently small. As a result, it is possible to realize a good electric motor with a small leakage flux for all of the paths A, B, and C.

  FIG. 3 shows a modification of the rotor. The rotor 32 has substantially the same configuration as that of the rotor 14, and the same components are denoted by the same reference numerals and description thereof is omitted. What is characteristic of the rotor 32 is that the permanent magnet 34 is disposed over almost the entire length of the circumferential slit 28. In the figure, the hatched portion is the permanent magnet 34. In the rotor 32, the amount of magnet used is slightly larger than that of the rotor 14, but permanent magnets are embedded in the entire circumferential slit 28 so that the leakage magnetic flux shown in the path C is minimized. As a result, the amount of magnets used is greater than that in the embodiment of FIG. 2, but the leakage flux can be minimized, so that the output torque per motor volume can be increased. Therefore, the electric motor can be reduced in size.

  The arrangement of the permanent magnets can be variously changed in consideration of performance, cost, and the like. As described above, the effect of arranging the permanent magnets near the end of the circumferential slit portion 28 is great, but it is necessary to arrange the permanent magnets only at both ends with respect to all the slits so as to leave a gap. Absent. In the rotor 14 shown in FIG. 1, the outermost circumferential slit of the rotor has a short overall length, and permanent magnets are arranged over the entire length. Schematically speaking, in the circumferential slit portion on the outer side of the rotor, it is preferable that the permanent magnet is arranged over the entire length, and the inner side is arranged separately at both ends thereof. Moreover, although this embodiment forms the division | segmentation magnetic path by four slits, the number of slits is not restricted to this example.

  The effect with respect to a prior art is demonstrated about the above embodiment. FIG. 4 shows a graph comparing the magnitude of the output torque with respect to the volume of the magnet used in the electric motor of this embodiment and the conventional electric motor while changing the value of the current density. Here, the conventional motor has a magnet embedded in the entire slit as shown in FIG. 6, and the motor of this embodiment has a graph of the motor using the rotor 14 and the motor using the rotor 16. It is. As can be seen from FIG. 4, in the electric motor according to the present invention, the output torque per magnet volume can be increased by a factor of 2 to 2.5 times compared to the prior art in which magnets are arranged inside the slit. In other words, it is possible to reduce the volume of the magnet to about 1/2 to 1 / 2.5 in an electric motor that generates the same output torque, and the amount of expensive magnets used can be reduced, thus reducing the material cost of the electric motor. be able to.

  According to this embodiment, a sufficient output torque can be obtained even if the amount of magnet used is small in an application having a hollow shaft with a large diameter, resulting in a reduction in material cost of the motor and a reduction in the size of the motor. can do. Further, the magnetic flux can be appropriately controlled by the function of the multilayer slit provided in the rotor, and as a result, good output characteristics with small torque ripple can be obtained.

It is a schematic diagram showing an axis orthogonal section of an electric motor of an embodiment concerning the present invention. It is a figure which shows the detail of the cross section of the rotor of the electric motor of FIG. It is the schematic which shows the axial orthogonal cross section of the rotor of the motor of a reference form. It is a graph which shows the relationship between the volume of a magnet, and a torque of the electric motor which has a rotor shown to FIG. 2 and FIG. It is rotor sectional drawing of the electric motor of a prior art. It is a rotor sectional view of other conventional electric motors. It is a rotor and stator sectional view of a multilayer slit type reluctance motor by a prior art. FIG. 6 is a cross-sectional view of a rotor of another conventional electric motor. FIG. 6 is a cross-sectional view of a rotor of another conventional electric motor.

Explanation of symbols

  10 motor, 14, 32 rotor, 20 slit, 22 split magnetic path, 26 radial slit, 28 circumferential slit, P magnetic pole, N magnetic pole midpoint.

Claims (2)

A stator that generates a rotating magnetic field by passing a current through the winding;
A substantially cylindrical rotor that rotates in synchronization with the rotating magnetic field, and connects adjacent magnetic poles divided by a plurality of slits to alternately arrange magnetic poles having opposite polarities on the circumference thereof. A rotor formed with a plurality of divided magnetic paths;
A permanent magnet disposed inside the slit;
In an electric motor with
The plurality of slits include a radial slit portion formed substantially along the radial direction from the rotor surface toward the center in the vicinity of the surface of the magnetic pole, and a circumferential direction or string between adjacent magnetic poles in the rotor. Formed by combining circumferential slit portions formed substantially along the direction,
The slit width of the circumferential slit portion is smaller than the slit width of the radial slit portion,
The permanent magnet is disposed only in the circumferential slit portion,
Wherein among the plurality of slits in which a permanent magnet is disposed, the outermost slit of the rotor radial direction is in contact with the boundary in the vicinity of the boundary between the radial slit portion at the end of both of the circumferential slit portion The permanent magnet is disposed;
The outermost of said plurality of slits permanent magnets other than the slits are arranged, wherein each is in contact with the boundary only in the vicinity of the boundary between the radial slit portion at the end of both of the circumferential slit portion permanently A magnet is disposed, and at least one of the circumferential slit portions is not disposed between the permanent magnets disposed in contact with the boundary only in the vicinity of the boundary with the radial slit portion. An electric motor characterized by being a part . 2. The electric motor according to claim 1, wherein a circumferential length of a circumferential slit portion in each of the plurality of slits is longer toward a circumferential slit portion on an inner side in a rotor radial direction, and is permanently attached to the circumferential slit portion . has a plurality of said slits having a portion where the magnet is not arranged, the circumferential length of the permanent portion of the magnet is not arranged in the circumferential slit portion is longer as the inner circumferential slit portion ,Electric motor.

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