JP2004007868A - Brushless dc motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain high efficiency and less vibration by increasing the effective interlinking flux of a small fan blower brushless DC motor. <P>SOLUTION: In this DC motor, main poles/pole pieces of two sets of stator yokes are arranged so as to shift by 180 degrees of an electrical angle from each other. A notch is provided to reduce a pole area toward the front-end direction of the pole piece. The area of the pole piece is increased and a boundary between the main pole and the pole piece is set large as much as possible. As a material of a center yoke in the center of the stator yoke, a soft magnetic stainless steel sheet is employed to increase the effective interlinkage flux of the motor, and such a structure as to reduce the vibration of the magnetic piece is created. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a radial air gap type brushless DC motor which is used in a small fan blower and uses a magnet which is multipolarly magnetized in a circumferential direction. More specifically, the present invention relates to a radial air gap type brushless DC motor having a structure in which a center yoke for magnetically short-circuiting each other is provided between the center portions of two sets of stator yokes and an annular coil is arranged between the two sets of stator yokes. It is.
[0002]
[Prior art]
The structure of this type of conventional radial air gap type brushless DC motor is disclosed in Japanese Utility Model Laid-Open Publication No. Sho 61-153486, Japanese Patent Laid-Open Publication No. Sho 58-63065, Japanese Patent Laid-Open Publication No. Sho 61-214759, Japanese Patent Publication No. Hei 7-46894, and Japanese Patent Laid-Open Publication No. Hei 6-68494. No. 303750 and others. FIG. 6 is an exploded perspective view of a motor proposed in Japanese Patent Publication No. 7-46894.
[0003]
In FIG. 6, a rotor 1 is constituted by a cylindrical rotor yoke 2 made of a magnetic material, a magnet 3 fitted into the rotor yoke 2 and multipole magnetized in a circumferential direction, and a motor shaft 4. Reference numeral 5 denotes a first stator yoke having a plurality of main magnetic poles 13 and pole pieces 21; 23, a bobbin for winding; 24, an annular coil wound on the bobbin 23; The lead wire of the coil 24 is connected to the terminal 25 and soldered. Reference numeral 6 denotes a second stator yoke having a plurality of main magnetic poles 14 and magnetic pole pieces 22. The second and first stator yokes 5 and 6 are telescopically fitted to the center portions of the first and second stator yokes 5 and 6 in order to magnetically short-circuit them. A cylindrical center yoke 7 is formed, respectively. An axial slit 12 is provided in the center yoke. Reference numeral 9 denotes a Hall element which is a magnetoelectric conversion element for detecting a magnetic pole of a magnet, and reference numeral 11 denotes a printed wiring board for electrically wiring the Hall element 9 and the terminal 25 to a drive circuit.
[0004]
FIG. 7 shows a two-phase half-wave drive circuit that alternately energizes two coils 24a and 24b having a phase difference of 180 degrees in electrical angle. In the drawing, 60 is a motor unit, 61 and 62 are transistors operated by the signals of the motor drive IC, 63 is a motor drive IC, 64 is a DC power supply, and 65 is an electric component mounted and wired on a printed circuit board. Is shown.
[0005]
Also, the shape and arrangement of the pole pieces of the first stator yoke and the second stator yoke are described in lines 30 to 38 of page 4 (2) of JP-B-7-46894, and FIG. It is shown. The motor of this structure has a positional relationship between a magnet and a pole piece that cannot be activated in principle, and is arranged in consideration of avoiding the dead point and reducing torque ripple during rotation. FIG. 4 is a positional relationship diagram for explaining the contents, and shows the positional relationship among the magnet 3, the first stator yoke, and the second stator yoke. The opening angle a of the magnetic pole piece is 1/5 to 4/5 of one magnetic pole of the magnet, and the smaller space angle b between the magnetic pole piece of the first stator yoke and the magnetic pole piece of the second stator yoke is an electrical angle. It is said that it is desirable to be within the range of π / 4 to 3π / 4.
It is also proposed that the center yoke 7 is provided with a slit 12 in the axial direction to reduce eddy current generated by magnetic flux flowing in the axial direction, reduce eddy current loss, and be suitable for a brushless DC motor compatible with high-speed rotation.
[0006]
In addition, the sum of the energizing torque and the cogging torque is the motor torque in "0006" of page (3) of JP-A-6-303750, and points out the problem of the ripple and the negative torque of the motor torque. As described above, it is proposed that the opening angles a and c of the pole pieces of the first stator yoke and the second stator yoke have different values.
[0007]
FIG. 5 shows a first stator yoke and a second stator yoke which illustrate a method proposed in Japanese Patent Application Laid-Open No. 58-63065. It is proposed to extend the protruding portion 20 on one side in a direction opposite to the rotation direction of the magnet.
[0008]
[Problems to be solved by the invention]
However, such a structure has the following disadvantages. Japanese Patent Publication No. 7-46894 describes that the space angle between the first stator yoke and the second stator yoke is large and small, and consequently the opening angle a of the pole piece becomes small with respect to the angle of one magnetic pole of the magnet. Magnetic flux cannot be used effectively. In the positional relationship shown in FIG. 4, the magnetic flux generated from the magnet north pole goes axially from the first stator yoke through the center yoke 7 and returns to the magnet south pole through the magnetic pole piece of the second stator yoke. However, a part of the magnetic pole piece of the second stator yoke is located at the boundary of the magnet NS pole, so that the entire amount of magnetic flux coming out of the N pole cannot be returned to the S pole and is limited. Since the magnetic flux passing through the center yoke 7 interlinks the toroidal coil, the effective interlinkage magnetic flux of the motor decreases, and the motor efficiency decreases.
[0009]
FIG. 8 shows the back electromotive force of the motor and the interlinkage magnetic flux characteristics of the motor coil with respect to the motor speed when the material and the shape of the center yoke are changed. When a general electromagnetic soft iron is used, the back electromotive force is (1) and the linkage magnetic flux is (4). As the rotation speed increases, the frequency of the alternating magnetic flux flowing through the center yoke increases, and the magnetic flux linked by the eddy current is suppressed. As a result, the back electromotive force shows a saturation phenomenon. When one slit is inserted in the center yoke in the axial direction, the back electromotive force is (2) and the linkage flux is (5). The effect of the eddy current cutoff appears, and both the back electromotive force and the interlinkage magnetic flux are improved in a high speed region, but the interlinkage magnetic flux is reduced in a low speed region.
Furthermore, providing a slit in the center yoke affects the accuracy of the outer dimensions of the center yoke.
[0010]
Also in Japanese Patent Application Laid-Open No. 6-303750, in order to make the opening angles a and c of the pole pieces of the first and second stator yokes different from each other, it is necessary to reduce one of the opening angles. Yes, the width of the pole piece is reduced, and as a result, the motor effective linkage flux is reduced as in the above example, and the motor efficiency is reduced.
[0011]
FIG. 5 illustrates a method proposed in Japanese Patent Application Laid-Open No. 58-63065. In FIG. 5, the protrusion 20 is extended on the pole piece, but the area of the pole piece is reduced. Decrease. Further, in the motor of the present system, there is often no allowance for the thickness of the magnetic steel sheets of the two sets of stator yokes, and there is a concern about magnetic saturation of the magnetic steel sheets. The magnetic flux from the magnet 3 flows from the tip of the pole piece to the main magnetic pole, and the magnetic flux density increases accordingly, so that narrowing of the magnetic flux path on the way may cause magnetic saturation.
[0012]
In addition, when the annular coil is energized, not only a rotational force but also a suction / repulsion force in the direction of the center of the stator yoke is generated between the magnet 3 and the projections 20 of the magnetic pole pieces 21 and 22, and the magnetic pole piece is accompanied by vibration. When the width of the boundary between the magnetic pole pieces 21 and 22 and the main magnetic poles 13 and 14 is small, the vibration increases, and as a result, the motor vibration and noise are adversely affected.
[0013]
Furthermore, although a magnetic steel sheet is used as a material for the stator yoke, a problem of processing distortion of the magnetic steel sheet occurs at the boundary between the main magnetic pole and the pole piece in the bent portion 40, which is common to the above-described conventional method. This processing distortion appears as a remarkable decrease in the magnetic permeability of the magnetic steel sheet, and as a result, the effective interlinkage magnetic flux of the motor decreases as in the above-described example, and the motor efficiency remarkably decreases. To cope with this, a heat treatment called annealing is required after the bending, which causes an increase in cost.
[0014]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a motor structure that solves the above-mentioned problems and reduces the effective interlinkage magnetic flux and prevents the pole piece from vibrating without increasing the cost.
[0015]
[Means for Solving the Problems]
A radial air gap type brushless DC motor according to the present invention includes a rotor having a rotor yoke attached to a motor shaft, a ring-shaped magnet attached to the rotor yoke and being multipolarly magnetized in a circumferential direction, each having a diameter from the center. A magnetic pole piece extending in the axial direction from the tip end to the inner peripheral surface of the magnet so as to face the inner peripheral surface of the magnet. Half of the number of the main magnetic poles of the magnetic pole pieces are opposed to each other, and each main magnetic pole faces the electrical angle. And a stator yoke arranged at equal intervals with respect to the rotation center so as to be displaced by approximately 180 degrees with a motor shaft via a bearing, and the center portions of the two sets of stator yokes are communicated and magnetically short-circuited. A center yoke, an annular coil sandwiched between the main magnetic poles of two sets of stator yokes, and provided so that the outer circumference thereof is covered with a magnetic pole piece; A magnetic pole comprising a stator yoke having a conversion element and configured to face the inner peripheral surface of the magnet via a gap, and a printed wiring board on which a drive circuit is mounted, and forming two sets of stator yokes It is characterized in that at least one of the pieces is provided with a notch for reducing the pole area toward the tip of the pole piece.
[0016]
Further, as a separate structure, a rotor having a rotor yoke attached to a motor shaft, a ring-shaped magnet held by the rotor yoke, and multipolarly magnetized in a circumferential direction, and a magnet from the outer peripheral edge of the disk-shaped electromagnetic steel sheet. 2 has pole pieces extending in the axial direction opposite to the inner peripheral surface of the magnetic pole piece, and is arranged at equal intervals with respect to the center of rotation so that the pole pieces face each other and are shifted by about 180 degrees in electrical angle. A set of stator yokes, a center yoke that fits to the motor shaft via a bearing, and communicates the center of the two sets of stator yokes to magnetically short-circuit, and a disk-shaped part of the two sets of stator yokes An annular coil provided so that the outer periphery thereof is covered with the magnetic pole piece, and a magnetoelectric conversion element, and is configured to face the inner peripheral surface of the magnet via a gap. And a printed circuit board on which a drive circuit is mounted, wherein the ratio of the thickness of the ring-shaped magnet to the distance between the inner surfaces of the two sets of stay yoke constricted portions arranged opposite to each other is 0.7 to 0.9. It is characterized by being formed so as to be in a range.
[0017]
Alternatively, it is characterized in that the center yoke is formed of a soft magnetic stainless steel plate comprising 10 to 15% of chromium and 85 to 90% of iron.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an exploded perspective view showing a first embodiment applied to a four-pole radial air gap type brushless DC motor according to claim 1 of the present invention, and FIG. 2 is a positional relationship diagram of the present invention. In FIG. 1, the magnetic pole pieces 21 and 22 of the two sets of stator yokes 5 and 6 have notches in the direction of rotation of the magnet 3 from the end face of the magnetic pole piece 21 toward the main magnetic pole 13. In FIG. 2, the two sets of stator yokes 5 and 6 are arranged such that their magnetic pole pieces are shifted by 180 degrees in electrical angle. The opening angle a of the pole piece is 7/10 to 9/10 of one magnetic pole of the magnet, which is the same for both sets of stator yokes.
[0019]
From the positional relationship shown in FIG. 2, the magnetic flux generated from the magnet north pole returns in the axial direction from the first stator yoke through the center yoke 7 and returns to the magnet south pole through the magnetic pole piece of the second stator yoke. Unlike the conventional example, the opening angle of the pole piece 21 can be made large, and each pole piece is also arranged at the same angle as the magnetic pole of the magnet 3, so that the element limiting the magnetic flux pointed out in the problem of the prior art is reduced, It is possible to increase the motor effective linkage magnetic flux.
[0020]
The positional relationship between the magnetic poles of the magnet 3 and the stator yokes 5 and 6 in FIG. 2 is a position where the motor of this structure cannot be started, but the positional relationship where cogging torque occurs due to the notch 27 provided in the magnetic pole piece is shifted. 2, the motor does not stop and the motor cannot be started.
[0021]
Further, the notch 27 of the pole pieces 21 and 22 of the present invention is located at a position that does not reach the bent portion 40 with the main magnetic poles 13 and 14, so that the stator yoke supports the attracting / repelling force in the center direction. The force is large and the vibration is small.
[0022]
FIG. 3 is an exploded perspective view showing a second embodiment according to claims 2 and 3 of the present invention. In the figure, 5 ° and 6 ° are a plurality of magnetic pole pieces extending in the axial direction so as to shorten the outer periphery of a disk-shaped electromagnetic steel plate, and to extend from its tip end 42 so as to face the inner peripheral surface of the magnet via a gap. Two sets of stator yokes 21 and 22 respectively. The ratio of the length h1 of the distance 42 between the inner surfaces of the two stay yoke constricted portions and the thickness h2 of the magnet 3 is set so that h2 / h1 = 0.7 to 0.9.
[0023]
The second embodiment is characterized in that the main magnetic pole portion of the conventional embodiment is eliminated, the outer periphery of the disk-shaped electromagnetic steel plate is shortened, and the magnetic pole piece is formed directly from the tip. It is possible to compensate for the decrease in magnetic permeability due to the processing distortion of the magnetic steel sheet, which has been a problem in the related art, and to suppress the vibration of the pole pieces.
[0024]
The magnetic flux from the magnet 3 passes through the pole pieces 21 and 22, passes through the throttle section 41, and flows to the stator yoke 5 {6}. Although the magnetic permeability of the narrowed portion 41 where processing distortion occurs is reduced, the narrowed portion 41 is located on the entire circumference of the disk shape, and the decrease in the magnetic permeability can be compensated for by increasing the cross-sectional area of the magnetic flux passage. It can be used without annealing. Also, the support of the pole piece is strengthened, so that motor vibration can be reduced.
[0025]
In addition, the ratio of the length h1 of the distance 42 between the inner surfaces of the two stay yoke constricted portions and the thickness h2 of the magnet 3 limits the leakage magnetic flux from the magnet 3 and maximizes the effective interlinkage magnetic flux of the motor. H2 / h1 = 0.7 to 0.9 can be said to be optimal.
[0026]
FIG. 8 shows the back electromotive force (6) and linkage magnetic flux (7) characteristics when a soft magnetic stainless steel sheet comprising 10 to 15% of chromium and 85 to 90% of iron is used as the material of the center yoke. Show. The electrical resistivity of a soft magnetic stainless steel plate is as high as 6300 (μΩ · m), while the electrical resistivity of general electromagnetic soft iron is 1400 (μΩ · m). As a result, as shown in the figure, it can be confirmed that the characteristics of both the back electromotive force and the interlinkage magnetic flux are improved in the entire rotational speed range from low speed to high speed.
[0027]
【The invention's effect】
The effects of the brushless DC motor of the present invention will be listed below.
(1) The opening angle of the pole pieces can be increased to increase the effective interlinkage magnetic flux of the motor.
(2) The pole piece of the first stator yoke and the second stator yoke can be arranged at 180 degrees, so that the effective interlinkage magnetic flux of the motor can be increased.
(3) The decrease in the area of the pole piece and the magnetic saturation can be minimized, and the effective interlinkage magnetic flux of the motor can be increased.
(4) The effective interlinkage magnetic flux of the motor can be increased without reducing the magnetic flux path.
(5) The decrease in magnetic permeability due to bending of the magnetic steel sheet is compensated for, and the effective interlinkage magnetic flux of the motor can be increased.
(6) The vibration of the motor can be suppressed by increasing the number of support portions of the pole pieces.
(7) By using a soft magnetic stainless steel plate for the center yoke, the effective interlinkage magnetic flux in the high-speed rotation region can be increased.
[0028]
As described above, according to the present invention, it is possible to manufacture a small, high-efficiency, low-vibration brushless DC motor while minimizing the cost. When the present invention is used for a small fan blower, the effect is large.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of a first embodiment according to the present invention.
FIG. 2 is a positional relationship diagram of the example of FIG.
FIG. 3 is an exploded perspective view relating to a second embodiment according to the present invention.
FIG. 4 is a positional relationship diagram of an example according to the related art.
FIG. 5 is an explanatory diagram of an example of a stator yoke corresponding to FIG.
FIG. 6 is an exploded perspective view of the example of FIG.
FIG. 7 is an explanatory diagram of a driving circuit according to a conventional technique.
FIG. 8 is an explanatory diagram showing an example of motor back electromotive force and linkage magnetic flux characteristics according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Rotor 2 Rotor yoke 3 Magnet 4 Motor shaft 5 First stator yoke 6 Second stator yoke 5 First stator yoke 6 Second stator yoke 7 Center yoke 8 Coil 9 Hall element 10 Electrical component 11 Printed wiring board 12 Slit 13 Main magnetic pole 14 Main magnetic pole 21 Magnetic pole piece 22 Magnetic pole piece 23 Bobbin 24 Coil 25 Terminal 31 Bearing 40 Bending part 41 Throttle part 42 Throttle end face 60 Motor part 61 Transistor 62 Transistor 63 Motor drive IC
64 DC power supply 65 Electrical related parts

Claims (3)

A rotor having a rotor yoke attached to the motor shaft, and a ring-shaped magnet attached to the rotor yoke and being multipolarly magnetized in a circumferential direction; each extending radially outward from the center, and A magnetic pole piece extending in the axial direction opposite to the inner peripheral surface of the main pole, and having half of the number of main magnetic poles of the magnetic pole pieces, the magnetic pole pieces facing each other and rotating so that the main magnetic poles are shifted by about 180 degrees in electrical angle. A stator yoke arranged at equal intervals with respect to the center, a center yoke fitted to the motor shaft via a bearing, and communicating the center of the two sets of stator yokes to magnetically short-circuit; An annular coil sandwiched between the main magnetic poles of two sets of stator yokes and provided so as to cover the outer circumference with the magnetic pole pieces, and a magnetoelectric conversion element; The two sets of stator yokes are formed in a radial air gap type brushless DC motor including the stator yoke configured to oppose an inner peripheral surface via a gap and a printed wiring board on which a drive circuit is mounted. A radial air gap type brushless DC motor, characterized in that at least one of the pole pieces is provided with a notch for reducing a pole area toward a tip end of the pole piece. A rotor having a rotor yoke attached to a motor shaft, a ring-shaped magnet held by the rotor yoke and being multipolarly magnetized in a circumferential direction, and an inner periphery of the magnet formed from an outer peripheral edge of the disk-shaped electromagnetic steel plate. Two sets of magnetic pole pieces extending in the axial direction facing the surface and having half the number of magnet magnetic poles, the magnetic pole pieces facing each other and being equidistant from the center of rotation so as to be shifted by about 180 degrees in electrical angle. A stator yoke, a center yoke fitted to the motor shaft via a bearing, and communicating the center of the two sets of stator yokes for magnetically short-circuiting; An annular coil provided so that the outer periphery thereof is covered with the magnetic pole piece, and a magnetoelectric conversion element, and is configured to face the inner peripheral surface of the magnet via a gap. And a printed wiring board on which a drive circuit is mounted, and wherein the ratio of the thickness of the ring-shaped magnet to the distance between the inner surfaces of the two sets of stay yoke constricted portions arranged opposite to each other is 0.7 to 0.9. A radial air gap type brushless DC motor, wherein the brushless DC motor is formed to have a range. The radial air gap type according to any one of claims 1 to 2, wherein the center yoke is formed of a soft magnetic stainless steel plate including 10 to 15% of chromium and 85 to 90% of iron. Brushless DC motor.

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