JP2007151233A - Permanent magnet motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively reduce a cogging torque, a vibration and a noise in a permanent magnet motor. <P>SOLUTION: The permanent magnet motor (1) comprises: a stator (2) having a stator iron core (10) provided with a plurality of magnetic pole teeth (12) and slots (16) for a stator winding; and a rotor (3) having a plurality of fixed permanent magnets (5) and rotatably supported within the stator. A plurality of the permanent magnets are divided in the direction of the center of a rotating shaft. Each permanent magnet is circumferentially shifted so as to cancel the cogging torque. A stator iron core piece (20a) is disposed in a region of the stator iron core facing a boundary (9) of the divided permanent magnet and having the closed slots. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a permanent magnet type motor having a permanent magnet attached to a rotor, and more particularly to a technique for reducing noise and vibration by reducing the cogging torque.

  FIG. 11 is a cross-sectional view of a general configuration of a permanent magnet motor 50 in which a field permanent magnet is attached to a rotor. The motor 50 includes a stator 51 and a rotor 52. The stator 51 includes a cylindrical stator core 53 and a stator winding 54. A plurality of magnetic pole teeth 56 are formed inward from the peripheral yoke portion 55 of the stator core 53, and a slot 57 for winding the stator winding 54 is formed between the adjacent magnetic pole teeth 56. A gap 58 is formed between the tip protruding portions of adjacent magnetic pole teeth 56, and the slot 57 is an open slot opened to the rotor 52 side by the gap 58. The stator core 53 having such a shape is manufactured by, for example, stacking a plurality of stator core pieces obtained by punching magnetic steel sheets into a shape as shown in the cross section of the figure.

  The rotor 52 is obtained by attaching a plurality of permanent magnets 61 to a cylindrical rotor core 60 and is rotatably supported inside the stator 51. The illustrated rotor 52 has a surface magnet structure in which the permanent magnet 61 is attached to the surface of the rotor core 60. The plurality of permanent magnets 61 are alternately arranged with N poles and S poles. When the stator winding 54 is energized to form a rotating magnetic field, the rotor 52 rotates around the rotation axis.

  In such a permanent magnet type motor 50, when an attempt is made to rotate the rotor 52 at a constant speed by applying a rotational torque from the outside in a non-energized state, uneven rotation occurs in the required torque. This torque unevenness is due to the fact that the static magnetic attractive force acting between the rotor 52 and the stator 51 varies depending on the rotational position, and is called cogging torque. The magnitude of the cogging torque is considered to be a value obtained by differentiating the total magnetic energy of the magnetic path of the magnetic flux created by the permanent magnet 61 with the rotation angle. When the opening (gap) 58 exists in the slot 57 of the rotor core 60 as in the motor 50 shown in FIG. 11, the magnetic resistance of the magnetic path changes with the rotation of the rotor 52, and the total magnetism of the magnetic path. Energy also changes. As a result, cogging torque is generated.

  If the cogging torque is large, not only vibration and noise are generated, but also the motor efficiency may be lowered. For these reasons, reducing the cogging torque is a major issue for permanent magnet motors.

  As a conventional technique for reducing the cogging torque, for example, as shown in FIG. 12, the permanent magnet 61 attached to the rotor 52 is divided into a plurality of stages in the axial direction, and the circumferential direction is increased as the divided permanent magnet 61 advances in the axial direction. There is a proposal of forming a so-called step skew, which is attached by changing gradually in steps (see Patent Document 1). This is to try to cancel the cogging torque generated at each stage mutually. However, when the step skew is formed, portions where the permanent magnets having different polarities are close to each other in the axial direction are generated, and a leakage magnetic flux as indicated by an arrow 62 in the drawing is generated at these close portions. When such a leakage magnetic flux is generated, the effective rotational torque is reduced, and the magnetic flux distribution created by the permanent magnet 61 deviates from the sine wave, and the effect of canceling the cogging torque is reduced.

  In order to reduce the leakage magnetic flux when the step skew is formed, a gap 63 is provided between adjacent steps as shown in FIG. 13 (see Patent Document 2), or a nonmagnetic material is interposed in the gap 63. There is a proposal (see Patent Document 3).

Furthermore, there is also a proposal (see Patent Document 4) in which a magnetic insulating layer made of a nonmagnetic material is provided on the stator core portion facing the boundary between adjacent steps in the step skew. However, the stator core is generally manufactured in one production line while being “automatically caulked” by pressing. In order to laminate two kinds of materials, a magnetic material and a non-magnetic material, separate production lines are required, and a caulking process is also required separately. For this reason, the use of a non-magnetic material for a part of the stator core leads to an increase in manufacturing man-hours and causes problems such as an increase in parts procurement and mixing of materials.
Japanese Utility Model Publication No. 61-17876 JP-A-8-251847 JP 2000-308287 A JP 2003-284276 A

  The present invention has been made to solve such problems of the prior art, and the problem is that a permanent magnet that effectively reduces cogging torque and reduces vibration and noise without increasing the number of manufacturing steps. It is to provide a shaped motor.

  According to a first aspect of the present invention, there is provided a stator having a stator iron core provided with a plurality of magnetic pole teeth and a stator winding slot, and a plurality of permanent magnets fixed to the inside of the stator. In the permanent magnet type motor provided with a rotor rotatably supported by each other, the plurality of permanent magnets are divided into a plurality in the direction of the rotation axis, and the divided permanent magnets are arranged with their circumferential positions shifted from each other, The permanent magnet motor is characterized in that a stator core piece with all slots closed is disposed at a portion of the stator core facing the boundary between the divided permanent magnets.

  In this way, if the permanent magnet attached to the rotor is divided into a plurality of parts in the axial direction and shifted in the circumferential direction, so-called step skew is formed, the cogging torque generated in each divided part cancels each other and is synthesized. The cogging torque is reduced. Further, in this configuration, a stator core piece having a closed slot is disposed at a position of the stator core facing the boundary between the divided permanent magnets (step skew boundary). For this reason, it is possible to prevent the magnetic energy of the magnetic path due to the leakage magnetic flux newly generated in the portion adjacent to the axial direction of the heteropolar magnet generated by the step skew formation from being changed by the rotation of the rotor. As a result, there is an effect that generation of new cogging torque due to the formation of the step skew is prevented.

  According to a second aspect of the present invention, in the permanent magnet type motor according to the first aspect, the stator core portion which is a closed slot is in close contact with the circumferential end surfaces of the tip overhang portions of adjacent magnetic pole teeth. It is a permanent magnet type motor characterized by being constituted.

  With such a configuration, the slot can be closed after winding the stator winding around the magnetic pole teeth, and the effect of facilitating the winding operation of the stator winding is achieved.

  According to a third aspect of the present invention, in the permanent magnet type motor according to the first aspect of the present invention, the circumferential direction of the tip overhanging portion of the adjacent magnetic pole teeth is located on the portion of the stator core facing the boundary of the permanent magnet. The permanent magnet motor is characterized in that two stator core pieces, which are closed slots with their end faces in close contact with each other, are arranged with their close contact positions shifted in the circumferential direction.

  With such a configuration, it is possible to more reliably prevent the magnetic energy of the magnetic path from changing due to the leakage magnetic flux newly generated in the axially adjacent portion of the heteropolar magnet generated by the step skew formation. Therefore, the generation of new cogging torque due to the step skew formation can be more effectively prevented.

  According to a fourth aspect of the present invention, in the permanent magnet type motor according to the second or third aspect, the closed slot has a V-shaped protrusion on one of the circumferential ends of the tip overhang portions of the magnetic pole teeth. A permanent magnet comprising a groove (32) formed on the other side with an inverted V-shaped protrusion (33) fitted into the protrusion, and the protrusion and the protrusion are fitted together. Type motor.

  With such a fitting configuration, there is an effect that the inner peripheral surface of the stator core piece in which the closed slot is formed can be accurately aligned in a cylindrical surface shape.

  Hereinafter, an embodiment of a permanent magnet type motor according to the present invention will be described with reference to the drawings. The permanent magnet type motor 1 of the present embodiment is characterized by the configuration of a stator core constituting the stator and the arrangement of permanent magnets attached to the rotor. FIG. 1 is a perspective view showing the configuration of the stator 2 and the rotor 3 and the arrangement relationship thereof, and the stator 2 shows a one-side portion divided into two on the surface including the rotation axis of the motor 1. . The rotating shaft necessary for the motor, its support mechanism, the stator winding, and the motor case are omitted.

  The rotor 3 has a surface magnet structure in which a permanent magnet 5 is attached to the outer surface of a cylindrical rotor core 4, and is supported rotatably around its axis by a rotation shaft (not shown) attached to the center hole 6. ing. The permanent magnet 5 is divided into two in the axial direction and arranged in two stages. The permanent magnet 5 is formed in a substantially arc shape in cross section, and N poles and S poles are alternately arranged in the circumferential direction with a predetermined circumferential gap 7 therebetween. Each of the permanent magnets 5 divided into two is arranged at a divided portion (a step-to-step boundary) 9 with a circumferential position shifted from each other, and a so-called step skew is formed.

  FIG. 2 is a top view of the rotor 3 and the stator 2 shown in FIG. As the stator 2, only the stator core 10 is shown. The stator core 10 includes an outer cylindrical yoke 11 and a plurality of magnetic pole teeth 12 projecting radially from the inside toward the center. The yoke 11 and the magnetic pole teeth 12 are manufactured by laminating a required number of magnetic steel plates such as silicon steel plates, each of which is punched into the shape shown in 2, and caulking in the axial direction. The magnetic pole teeth 12 are fixed inside the yoke 11 by a dovetail structure.

  At the tip of the magnetic pole tooth 12, an overhanging portion 14 that protrudes on both sides in the circumferential direction is provided. The body portion 15 and the overhanging portion 14 of the adjacent magnetic pole teeth 12 and the portion surrounded by the yoke 11 constitute a slot 16 for passing the stator winding. A gap 17 is formed between the tip projecting portions 14 of the adjacent magnetic pole teeth 12, and the slot 16 is opened to the rotor 3 side by the gap 17. That is, the slot 16 in this case is an open slot.

  As shown in FIG. 1, the stator core 10 of the present embodiment is formed by stacking a required number of stator core pieces (one stator core layer) 20 having an open slot except for one in the axial center. It is. Only the single stator core piece 20a in the center is configured such that the slot 16 becomes a closed slot without the gap between the tip overhanging portions 14 of the magnetic pole teeth 12 as shown in FIG. Such a closed slot is formed by extending the protruding length of the tip protruding portion 14 of the magnetic pole tooth 12 and bringing the circumferential end faces into close contact with each other.

  The rotor 3 is attached by adjusting the axial position so that the boundary 9 of the permanent magnet 5 having a two-stage skew is positioned at the center of the thickness of the stator core piece 20a having the closed slot. is there. An air gap 22 is secured between the rotor 3 and the stator 2.

  As described in “Background Art”, the cogging torque is due to a difference in static magnetic attractive force between the stator 2 and the rotor 3 depending on the rotor position. The magnitude is considered to be a change (differential value depending on the rotation angle) of the total magnetic energy of the magnetic path of the magnetic flux created by the permanent magnet 5 with respect to the rotor rotation angle. The change in the total magnetic energy is caused by the change in the magnetic resistance of the magnetic path due to the rotation of the rotor 3.

  When the rotor 3 is rotated inside the stator core 10 having the open slots as shown in FIG. 2, the gaps 17 of the open slots are scattered in the circumferential direction, so that the magnetic force depends on the rotation angle of the rotor 3. The resistance changes and the total magnetic energy of the magnetic path changes. The open slot gaps 17 exist at equal intervals, and the permanent magnets 5 of the rotor 3 are also mounted at equal intervals. Therefore, the cogging torque is repeatedly generated by the least common multiple of the number of poles of the rotor 3 and the number of slots of the stator 2 while the rotor 3 makes one rotation. One cycle of the cogging torque is equal to the time for which the rotor 3 rotates by dividing the mechanical angle obtained by dividing 360 ° by the least common multiple. In the case of the 8-pole 12-slot configuration as shown in FIG. The time for 15 ° rotation is one cycle of cogging torque.

  The magnitude of the cogging torque changes with a waveform that is almost similar to a sine wave during one period. Curve (1) in FIG. 4 is a waveform example of cogging torque generated in the upper half portion (upper portion) of the rotor 3 in the permanent magnet type motor 1 in FIG. Since the cogging torque changes in such a waveform, it can be expected that if the waveforms are shifted by a half period and added together, the two cogging torques cancel each other and the combined cogging torque can be reduced.

  Curve (2) in FIG. 4 indicates that the permanent magnet 5 in the lower half (lower part) of the rotor 3 in the permanent magnet type motor 1 in FIG. This is the magnitude of the cogging torque generated at the lower part of the rotor 3 when it is mounted shifted in the circumferential direction by an amount corresponding to 1/2 of the rotation angle of 15 ° of the rotor 3 corresponding to one period waveform of the cogging torque. . The combined cogging torque obtained by synthesizing the upper curve (1) and the lower curve (2) is ideally very small because the waveforms cancel each other as shown by the curve (3) in FIG. Value. The slightly remaining synthetic cogging torque is due to waveform distortion.

  By the way, the cogging torque can be canceled out by forming the step skew as described above, among the magnetic flux components produced by the permanent magnet 5, the change in magnetic energy due to the component on the plane perpendicular to the rotation axis. Only. Magnetic energy changes due to axial components do not cancel each other.

  When the step skew is formed by dividing the permanent magnet 5 into two parts and shifting it in the circumferential direction, as shown in FIG. 1, the number of poles 24 in which the different polarity magnets are adjacent in the axial direction is formed in the axial direction. . In that portion, a leakage magnetic flux that does not contribute to torque generation as shown by an arrow in the figure is generated. FIG. 5 schematically shows a magnetic path through which leakage magnetic flux passes by enlarging a portion 24 where the different pole magnets are adjacent in the axial direction (a portion of the portion where the different pole magnet faces the portion 24 adjacent in the axial direction). The stator core 10 is shown in a longitudinal sectional view). As shown in the drawing, the magnetic path of the leakage magnetic flux includes a magnetic path 26 that directly connects the different pole magnets, a magnetic path 27 that passes through the air gap 22 between the rotor 3 and the stator 2, and an air gap 22. There is a magnetic path 28 that passes through the stator core 10 and again passes through the air gap 22 and enters the different pole magnet.

  Among these, the magnetic path 28 of the leakage magnetic flux that also passes through the stator core 10 is obtained when the tip 30 of the magnetic pole teeth 12 of the stator core 10 is present in a portion where the heteropolar magnet faces the portion 24 adjacent in the axial direction. It is a magnetic path to be formed. When the stator core 10 is formed in the open slot, when the adjacent portion 24 of the different-polarity magnet comes to a position facing the open slot, only the portion corresponding to the open slot has the tip end portion (tip extension) 30 is not present). Therefore, the magnetic path of the leakage magnetic flux (magnetic path 28 in FIG. 5) that also passes through the stator core 10 is not formed at that position, and the magnetic path 27 that passes through the air gap 22 and the heteropolar magnet as shown in FIG. Only the magnetic path 26 that directly connects is formed.

  When the stator core piece 20 having the open slot is disposed at a position facing the step skew boundary 9 as described above, the magnetic path is changed by the rotation of the rotor 3 so that adjacent portions of the heteropolar magnets are adjacent to each other. The magnetic energy due to the axial magnetic flux component of the air gap 22 adjacent to 24 changes. This change causes cogging torque. That is, when the step skew is formed, a new factor for generating the cogging torque is generated near the boundary 9.

  In order to prevent the occurrence of cogging torque due to this new factor, the state of the air gap 22 and the stator core 10 at which the different-polar magnets face the axially adjacent portions 24 is always the same regardless of the rotational position. It should just become. Then, even if the rotor 3 rotates, the magnetic energy does not change, so that cogging torque is not generated.

  Therefore, in the permanent magnet type motor 1 of the present embodiment, as shown in the overall view of FIG. 1 and the enlarged enlarged view of the boundary portion in FIG. 7, a closed slot is formed in the stator core 10 portion at a position facing the step skew boundary 9. The formed stator core pieces 20a are arranged. Since the leakage magnetic flux generated in the adjacent portions 24 of the different-polar magnet passes only in the vicinity of the adjacent portions 24, only one stator core piece 20a having a closed slot is required. The axial direction position of the rotor 3 is adjusted so that the step skew boundary 9 is positioned at the center of the thickness of the stator core piece 20a in which the closed slot is formed.

  Since the leakage magnetic flux entering the stator core 10 passes through the surface layer portion of the stator core 10, the magnetic path of the leakage magnetic flux becomes as shown in FIG. The shape of the magnetic path is almost the same as the magnetic path shown in FIG. 5 and does not change even when the rotor 3 rotates. Accordingly, it is possible to prevent the generation of new cogging torque due to the leakage magnetic flux newly generated in the adjacent portion 24 of the heteropolar magnet.

  FIG. 8 compares the magnitude of the cogging torque with and without the measure for reducing the cogging torque by the measured value. The curve of (1) is the measured value when no countermeasure is taken, and the curve of (2) is the stator in which a closed slot is formed at a position opposite to the countermeasure for forming the step skew and the step skew boundary 9 as described above. This is the cogging torque of the permanent magnet type motor 1 of the present embodiment in which both measures for arranging the core pieces 20a are taken. The permanent magnet type motor 1 of this embodiment in which measures are taken shows that the cogging torque is greatly reduced.

  In the permanent magnet type motor 1 of this embodiment, the stator core 10 is entirely made of only a magnetic material, and no nonmagnetic material as described in Patent Document 4 is used. Therefore, the stator core 10 can be manufactured on the same production line, and since there is only one kind of material, there is an effect that there is no increase in parts procurement and no mixing of materials occurs.

  In the above embodiment, a permanent magnet type motor having 8 poles and 12 slots and permanent magnets attached to the surface of the rotor core is described as an example. However, the same idea applies to motors having different numbers of poles and slots. It can be applied and has the same effect. Furthermore, a magnet-embedded motor in which a permanent magnet is embedded in the stator core, an abduction type (outer rotor type) motor in which a cylindrical rotor with a permanent magnet is rotated outside the stator, and on the stator side The present invention can be similarly applied to a commutator motor in which a rotor core having a permanent magnet and a winding is rotated.

(Modified embodiment)
The permanent magnet motor 1 may be modified as follows.
(1) In the above-described embodiment, the configuration has been described in which the permanent magnet attached to the rotor is divided into two in the direction of the rotation axis and the two-stage skew is provided, but the number of stages may be further increased. In this case, the circumferential shift angle of the permanent magnet between the stages is an angle obtained by dividing the rotation angle (mechanical angle) corresponding to one cycle of the cogging torque generated at each stage by the number of stages. In this way, the combined cogging torque obtained by synthesizing the cogging torque generated at each stage can be canceled more effectively.

(2) The planar shape of the stator core piece 20a in which the closed slot is formed in the embodiment is as shown in FIG. 3, and the circumferential direction of the tip overhanging portion 14 of each magnetic pole tooth 12 forming the closed slot The end face was formed into a flat surface and was in close contact with the adjacent end face. As shown in the plan view of FIG. 9, the contact end face is provided with a V-shaped convex groove 32 in the axial direction on one side and an inverted V-shaped convex projection 33 in the axial direction to be fitted on the other side. Alternatively, the surfaces may be brought into close contact with each other by fitting. With such a fitting configuration, there is an advantage that the inner peripheral surface of the stator core piece 20a in which the closed slot is formed can be accurately aligned in a cylindrical surface shape.

(3) In the permanent magnet type motor 1 described above, one stator core piece 20a having a closed slot is disposed in the stator core 10 at a position facing the boundary 9 of the step skew. Instead, two stator core pieces 20a each having a closed slot are used, and they are shifted and overlapped so that the positions 35 where the end faces 14 of the adjacent magnetic pole teeth 12 are in close contact with each other do not coincide with each other. You may make it arrange a thing. As such a configuration, a configuration example of the stator core 10 is shown in FIG. The two stator core pieces 20a formed with closed slots in the figure have two types of extension lengths of the tip extension portions 14 of the magnetic pole teeth 12 in the stator core pieces 20a shown in FIG. The ones arranged alternately are shifted and overlapped in the circumferential direction by one pole of the magnetic pole teeth.
With such a configuration, it is possible to more reliably prevent the generation of cogging torque due to the leakage magnetic flux in the adjacent portion 24 of the heteropolar magnet.

It is a lineblock diagram of permanent magnet type motor 1 concerning one embodiment of the present invention. FIG. 2 is a top view of a rotor 3 and a stator 2 of the permanent magnet type motor 1 shown in FIG. 1. It is a top view of the stator core piece 20a which formed the closed slot. It is a figure explaining the reduction of cogging torque by formation of a stage skew. It is a figure explaining the magnetic path of the leakage magnetic flux in case the stator core 10 exists in the position facing the adjacent part 24 of a different pole magnet. It is a figure explaining the magnetic path of the leakage magnetic flux in case there exists an open slot in the position facing the adjacent part 24 of a different pole magnet. It is a figure explaining the magnetic path of the leakage magnetic flux at the time of arrange | positioning the stator core piece 20a which formed the closed slot in the position facing the adjacent part 24 of a different pole magnet. It is a figure explaining the cogging torque reduction effect of the permanent magnet type motor 1 which took the countermeasure which reduces cogging torque. It is other embodiment of the stator core piece 20a which formed the closed slot. It is a structural example of the stator core 10 using two stator core pieces 20a. It is sectional drawing of one structure of the permanent magnet type motor which concerns on a prior art. It is a structural example of the rotor which concerns on the prior art which formed the step skew. It is another structural example of the rotor which concerns on the prior art which formed the step skew.

Explanation of symbols

  In the drawings, 1 is a permanent magnet type motor, 2 is a stator, 3 is a rotor, 4 is a rotor core, 5 is a permanent magnet, 9 is a permanent magnet boundary (step skew boundary), 10 is a stator core, 12 is a magnetic pole tooth, 14 is an overhang, 16 is a slot, 20 is a stator core piece having an open slot, 20a is a stator core piece having a closed slot, 32 is a V-shaped convex groove, 33 is An inverted V-shaped convex protrusion is shown.

Claims (4)

A stator (2) having a stator core (10) provided with a plurality of magnetic pole teeth (12) and a stator winding slot (16), and a plurality of permanent magnets (5) are fixed to the inside of the stator A permanent magnet motor comprising a rotor (3) rotatably supported by
The plurality of permanent magnets are divided into a plurality of parts in the direction of the rotation axis, and the divided permanent magnets are arranged with their circumferential positions shifted from each other,
A permanent magnet type motor, wherein a stator core piece (20a) having all the slots as closed slots is disposed at a portion of the stator core facing the boundary (9) of the divided permanent magnet.   2. The permanent magnet motor according to claim 1, wherein the closed slot is formed by closely contacting the circumferential end surfaces of the tip overhanging portions (14) of adjacent magnetic pole teeth.   2. The permanent magnet type motor according to claim 1, wherein a circumferential slot end surface of the adjacent magnetic pole teeth is closely attached to a portion of the stator core facing the boundary of the permanent magnet to close the slot. A permanent magnet type motor characterized in that the two stator core pieces are arranged with their close contact positions shifted in the circumferential direction. The permanent magnet type motor according to claim 2 or 3, wherein the closed slot has a V-shaped convex groove (32) at one of circumferential ends of a tip projecting portion of each magnetic pole tooth and the convex at the other. A permanent magnet type motor characterized in that an inverted V-shaped convex protrusion (33) that fits into a groove is formed and the convex groove and the convex protrusion are fitted together.

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