JPH02142333A - Rotor for brushless motor - Google Patents

Abstract

PURPOSE:To suppress vibration of a motor by tapering the circumference of magnet section outwardly and arching the surface of the magnet section facing with the stator around the rotary axis. CONSTITUTION:A rotary magnet 9 comprises four magnet sections 22-25. Inner circumferential faces 22a-25a of the magnet sections 22-25 facing with a stator 3 are arched with radius R around a rotary shaft 6. Furthermore, radial width of each magnet section 22-25 decreases gradually from the central section toward the opposite longitudinal end sections. By such arrangement, the dimension of a gap formed between the facing surface and the stator 3 does not vary and the torque ripple can be suppressed through sinusoidal approximation of the variation of gap density during rotation of the rotor 5, and thereby vibration of motor is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rotor used in a radial gap type DC brushless motor.

[Conventional technology]

FIG. 8 shows a conventional thin DC brushless motor used, for example, in a magnetic disk drive device. In the figure, 1 is the motor housing, which includes a printed wiring board 2.
is attached, and a stator 3 is also attached. The stator 3 is formed by winding wires 3c around a plurality of radially arranged salient poles 3b, each of which has a stator core 3a made of laminated steel plates. Further, a rotor 5 is rotatably supported by the motor housing 1 via a bearing 4. The rotor 5 includes a rotating shaft 6 that penetrates the motor housing 1 in the thickness direction and is supported by a bearing 4, a rotor yoke 8 that is connected to the rotating shaft 6 via a rotor bush 7, and a rotor yoke 8 that is attached to the rotor yoke 8. It is formed from a rotor magnet 9 and a hub 10 connected to the other end of the rotating shaft 6.

The rotor magnet 9 is made up of a plurality of (for example, four as shown in FIG. 9) approximately arch-shaped magnet portions 9a to 9d arranged in a ring shape to form magnetic poles. Moreover, the inner peripheral surface and the outer peripheral surface of each of the magnet parts 9a to 9d are both formed of circular arc surfaces with radii r1 and r2 centered on the rotating shaft 6, and the radial direction of each part of each of the magnet parts 9a to 9d is The width dimension W along is the same.

Further, a position sensor 11 such as a Hall element is attached to the printed wiring board 2, as well as a driving IC, a control IC, and other circuit components (not shown). The position sensor 11 is arranged between adjacent salient poles 3b of the stator 3, and is arranged between the rotor magnets 9
are opposed to each other in close proximity to the inner circumferential surface of. This position sensor 1
1 detects the rotational position of the rotor 5, the excitation of the winding 3c of the stator 3 is sequentially switched. As a result, the magnetic flux generated in the stator 3 and the magnetic flux generated in each of the rotor magnet sections 9a to 9d of the rotor magnet 9 are attracted to each other, and the rotor 5 is rotated.

[Problem to be solved by the invention]

However, in the rotor 5 having the above configuration, since the width dimension W along the radial direction of each of the magnet parts 9a to 9d of the rotor magnet 9 is the same, there is no change in the distribution of magnetic flux density. Therefore, the magnitude of the magnetic flux coming out from the inner circumferential surface of each part of the rotor magnet 9 and heading toward the salient pole 3b is equal, and the magnitude of the magnetic flux is equal to that of the adjacent magnet parts 9a to 9d.
The direction of the magnetic force suddenly switches at the boundary.

Therefore, as the rotor 5 rotates, the magnetic flux density in the air gap g between the magnet parts 9a to 9d and the salient poles 3b is such that the direction of the approximately rectangular waveform changes alternately as shown in FIG. It shows repeated changes.

Conventionally, as the air gap magnetic flux density changes each time the rotor 5 rotates by a predetermined angle (90° in the case of the four poles), the torque ripple increases accordingly, and the vibration of the motor increases. The problem was that it was big.

An object of the present invention is to obtain a rotor for a brushless motor that can reduce vibration.

[Means to solve the problem]

In order to achieve the above object, in the rotor for a brushless motor of the present invention, a plurality of substantially arch-shaped magnet sections disposed in a ring shape are arranged in a radial direction of the magnet sections toward both longitudinal ends thereof. The magnet part has a tapered shape with a smaller width along the axis, and the surface of each of these magnet parts facing the stator is formed into an arcuate surface having a radius centered on the rotation axis.

[Effect]

In the above configuration, since the surface of each magnet part facing the stator is formed by an arcuate surface with a radius centered on the rotation axis, the size of the gap formed between this facing surface and the stator changes. There is no.

Under these conditions, each magnet part is
Since the magnet part has a tapered shape in which the width dimension along the radial direction of the magnet part decreases toward both ends in the length direction, the magnetic flux density of each magnet is large at the center and becomes smaller toward both ends. Such magnetic flux density allows the change in air gap density when the rotor rotates to approximate a sine wave.

〔Example〕

A first embodiment of the present invention will be described with reference to FIGS. 1 to 3. Note that the structure of the rotor magnet of the present invention is different from the conventional example, and the structure of other parts is the same as that of the conventional example. Therefore, the same reference numerals are given to the parts, and the explanation thereof will be omitted, and the following description of the rotor will be made. The configuration will be explained with reference to FIG. 8 as necessary.

The rotor magnet 9 attached to the inner peripheral surface of the rotor yoke 8 shown in FIGS. 1 and 8 is formed of, for example, four magnet parts 22 to 25, as shown in FIG. Although the magnet parts 22 to 25 in this embodiment are segment-shaped, when such segment-shaped magnet parts 22 to 25 are used, adjacent magnet parts do not need to be in contact with each other. Each magnet part 22-2
The rotor magnets 5 each have a substantially arch shape, and the ends thereof are arranged in a ring shape to form a rotor magnet 9 and also form the magnetic poles of the magnet 9.

Then, the stator 3 (
8), that is, the inner circumferential surfaces 22a to 25a in this embodiment are the rotating shaft 6 of the rotor 5 (see FIG. 8).
It is formed of a circular arc surface with radius R centered at . Moreover, each of the magnet parts 22 to 25 has a width dimension along its radial direction (as shown in FIG. ) is formed in a tapered shape that gradually becomes smaller from the center toward both ends in the length direction (a>b>c). In order to achieve such a configuration, in the case of this embodiment, the outer circumferential surface of each of the magnet parts 22 to 25 is centered at a position q that is a distance p from the rotating shaft 6 toward the inner circumferential surfaces 22a to 25a. The case is shown in which a circular arc surface with a radius r is formed.

According to the rotor 5 equipped with the rotor magnet 9 consisting of the magnet parts 22 to 25 as described above, the magnet part 2
2 to 25 have a tapered shape in which the width dimension along the radial direction gradually decreases from the center of the length direction to both ends,
Each magnet portion 22
The magnetic flux density of ~25 is highest at the center and decreases toward both ends.

Therefore, due to the magnetic flux density of such distribution, the rotor 5
When rotated, the magnetic flux from the center of each magnet part 22 to 25 to the salient pole 3c passes through the gap g (see Fig. 8), and from the end of each magnet 22 to 25 to the salient pole 3C. Since the magnetic flux can be reduced, the air gap magnetic flux density change is the third
As shown in the figure, it approximates a sine wave.

Therefore, each time the rotor 5 rotates 90 degrees, the air gap magnetic flux density no longer changes abruptly, but instead changes gently, and accordingly, the torque ripple of the motor becomes smaller. Therefore, by using the rotor 5 having the above configuration, vibration of the motor can be reduced, and high quality of magnetic disk drive devices and the like can be realized. Note that the surfaces 22a to 25a of each of the magnet parts 22 to 25 facing the stator 3 are as follows.
Since both are formed of circular arc surfaces with a radius R centered on the rotating shaft 6, the opposing surfaces 22a to 25a and the stator 3
The dimensions of the gap g formed between the two do not change. Therefore, the above configuration does not become a new cause of torque fluctuation.

In the second embodiment of the present invention shown in FIG. 4, the outer periphery of each magnet portion 26 having a substantially arcuate shape is formed with a plane that slopes from the center toward both ends. The width dimension along the radial direction is the magnet part 2
This example has a tapered shape that gradually becomes smaller from the center in the lengthwise direction of 6 toward both ends, and has the same configuration as the first embodiment described above except for this point. Even if such a magnet section 26 is used, the intended purpose of the present invention can be achieved.

The third embodiment of the present invention shown in FIG.
The structure is the same as that of the first embodiment except that it is formed of an arcuate surface in contact with the inner circumferential surface of the rotor yoke 8. Further, in the fourth embodiment of the present invention shown in FIG. 6, the outer surface 26b of the central portion of each magnet portion 26 (the range indicated by the symbol E in FIG. 6) is formed by an arcuate surface in contact with the inner peripheral surface of the rotor yoke 8. This embodiment has the same configuration as the second embodiment except for the following points.

The magnet portion 2 shown in these third and fourth embodiments
2.26, it is of course possible to achieve the intended purpose of the present invention, but these central outer surfaces 22b, 26
The engagement with the inner circumferential surface of the rotor yoke 8 in b facilitates positioning on the rotor yoke 8, and therefore each magnet portion 22, 26 can be easily attached to the rotor yoke 8.

Further, the present invention can be applied not only to the outer rotor type DC brushless morph shown in each of the above embodiments, but also to the rotor in the inner rotor type brushless morph as shown in FIG. In this fifth embodiment, the surfaces of the magnet parts 22 to 25 that face the stator 3 are of course the outer peripheral surfaces 22a to 25a of the magnetic solenoid parts 22 to 25, and the surfaces shown in FIG. 27 is a molded resin that integrally connects the rotating shaft 6 and the magnet parts 22 to 25.

Moreover, in the present invention, the rotor magnet is not limited to the segment shape, but the rotor magnet is made of plastic magnet, and after molding, the outer periphery is magnetized to have the above-mentioned magnetic flux density distribution. It may be an integral ring-shaped rotor magnet in which the magnet portion is integrally formed. Furthermore, it goes without saying that the present invention is applicable not only to DC brushless motors used in magnetic disk drives, but also to DC brushless motors used as scanner motors in laser printers, and to the rotors of DC brushless motors for other uses.

〔Effect of the invention〕

According to the present invention configured as described above, the plurality of bow-shaped magnet parts arranged in a ring shape have a tapered shape in which the width dimension along the radial direction of the magnet parts becomes smaller toward both ends in the length direction. In addition, since the surface of each of these magnet parts facing the stator is formed as a circular arc surface with a radius centered on the rotation axis, the change in air gap density when the rotor is rotated is approximated to a sine wave, thereby reducing torque ripple. Can be made small,
This allows the vibration of the motor to be reduced.

[Brief explanation of the drawing]

1 to 3 show a first embodiment of the present invention, FIG. 1 is a plan view showing the rotor magnet attached to the rotor yoke, FIG. 2 is a plan view of the magnet part, and FIG. 3 is the air gap magnetic flux. FIG. 3 is a waveform chart showing changes in density. FIG. 4 is a plan view of a magnet section showing a second embodiment of the invention, FIG. 5 is a plan view of a magnet section showing a third embodiment of the invention, and FIG. 6 is a plan view of a magnet section showing a fourth embodiment of the invention. It is a top view of the magnet part shown. FIG. 7 is a cross-sectional plan view showing a rotor together with a stator according to a fifth embodiment of the present invention. Figures 8 to 10 show conventional examples, Figure 8 is a vertical cross-sectional side view showing the entire DC brushless motor, Figure 9 is a plan view of the rotor magnet attached to the rotor yoke, and Figure 10 is the air gap magnetic flux density. FIG. 3... Stator, 5... Rotor, 6... Rotating shaft,
9... Rotor magnet, 21... Rotor magnet, 22-26... Magnet part, 22a-25a1
22c to 25c... Surfaces facing the stator. Applicant's agent Patent attorney Takehiko Suzue 22a-25a-・Suda Hinoko Ku Vu1 Figure 1 22-25 -s Figure 2 Figure 7 Figure 8 Figure 9 Figure 10

Claims (1)

[Scope of Claims] A rotor that is used in a radial gap type brushless motor and is equipped with a rotor magnet in which a plurality of substantially arch-shaped magnet parts are arranged in a ring shape, each of the above-mentioned magnet parts being The magnet portion has a tapered shape in which the width dimension along the radial direction becomes smaller toward both ends in the length direction, and the surface of each of these magnet portions facing the stator of the motor is formed into an arc of a radius centered on the rotation axis. A rotor for a brushless motor characterized by being formed with a flat surface.