JPH0210781Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention includes a field magnet in which an S-pole region and an N-pole region are successively formed, and a three-phase stator coil facing the field magnet. The present invention relates to a three-phase, bidirectional 120° current-carrying type brushless motor in which the stator coils are sequentially shifted by 120° in electrical angle and current is supplied in both directions.

In recent years, ultra-compact precision equipment such as portable VTRs and tape recorders have become widely available on the market, and these types of equipment are attracting significant attention as luxury products in ordinary households. When developing such precision equipment, it is essential to improve the motor, which is the tape drive source, in terms of reduced rotational speed unevenness, high precision rotation, high reliability, and miniaturization.

By the way, DC brushless motors are widely used as tape drive sources in small VTRs, etc.
As is well known, the rotation system of this brushless motor includes a three-phase unidirectional 120° energization system and a three-phase bidirectional 120° energization system. FIG. 1 shows the positional relationship between stator coils 1a to 1c and a ring-shaped field magnet (rotor magnet) 2 in this type of brushless motor 1. Stator coil 1a of each phase
1c are energized as shown in FIG. 2A in the case of three-phase unidirectional 120° current, and are energized as shown in FIG. 3A in the three-phase bidirectional 120° current.
In these cases, the field magnet 2 is usually
As shown in FIG. 4, since the north and south poles are magnetized almost trigonometrically, the torque characteristics of the brushless motor are as shown in FIGS. 2B and 3B. In a brushless motor with a 3-phase unidirectional 120° energization system, the torque ripple is extremely large, as is clear from the torque curve T ₁ in Figure 2B, and the degree of torque ripple is α ₁ − β ₁ / α ₁ + β ₁ × 100≒33 %.

Furthermore, in a three-phase bidirectional 120° current-carrying brushless motor, as is clear from the torque curve T ₂ in FIG. 3B, the torque ripple is reduced compared to the torque curve T ₁ , but the degree of torque _ripple is −β ₂ /α ₂ +β ₂ ×100≒7.2%, which is quite large.

In small VTRs, etc., when the motor shaft of the brushless motor is directly connected to the capstan, supply and take-up reels, etc., and these are directly driven at low speed (direct drive), extremely high precision rotation can be obtained. At the same time, it is required that rotational speed unevenness be extremely small. For this reason, a brushless motor with extremely low torque ripple is required, and conventional three-phase unidirectional 120° current-carrying type and three-phase bidirectional 120° current-carrying type brushless motors can be used in direct drive type VTRs, tape recorders, etc. as mentioned above. There are performance problems in its application.

Therefore, in order to obtain a brushless motor with small torque ripple, the following method can be considered. That is, the brushless motor is constructed in a three-phase bidirectional 120° energizing system, and the field magnet 2 is magnetized in a triangular shape as shown in FIG. 5A, or in a trapezoidal shape as shown in FIG. 6A. In this method, the torque ripple is ideally reduced to 0% as shown in FIG. 5B or FIG. 6B. However, in reality, it is very difficult to perform triangular magnetization. It is also possible to perform trapezoidal magnetization, but in this case, the average value of the generated torque will drop significantly and the efficiency will deteriorate, which is not preferable.

The present invention was devised in view of the above-mentioned circumstances, and aims to provide a three-phase bidirectional 120° current-carrying brushless motor that greatly reduces torque ripple without reducing the generated torque. That is.

Embodiments of the present invention will be described below with reference to FIGS. 7 to 14.

7 to 9 show a first embodiment of the present invention. In the three-phase, bidirectional, 120° energizing type brushless motor 3 of this embodiment, six stator coils 4, for example, are arranged and fixed in an annular shape on a substrate 5 made of an iron plate or the like via a printed circuit board 5a. On the other hand, a ring-shaped field magnet 7 is fitted and fixed to the rotor yoke 6 concentrically with the motor shaft 8. The field magnet 7 is disposed close to and facing the stator coil 4 described above, and the motor shaft 8 is rotatably supported by a bearing (not shown). Therefore, this brushless motor 3 is configured as a so-called plane facing type.

Further, in this embodiment, the ring-shaped field magnet 7 has, for example, eight magnetized regions 9a to 9h successively formed at equal angular intervals so as to have alternately different polarities in the circumferential direction. As shown in FIG. 8, each of the magnetized regions 9a to 9
The angular width of h is 45° (180° in electrical angle),
A pair of magnetized regions adjacent to each other, for example, a south pole region 9a and a north pole region 9b, form an electrical angle of 360°.

Further, in this embodiment, each magnetized region 9a
-9h are provided with recesses 10a-10h at predetermined locations, respectively. That is, as is clear from FIGS. 7 and 8, in a part of the surface of the field magnet 7 facing the stator coil 4, and in the S pole regions 9a, 9c, 9e, and 9g, the electrical angle is At points corresponding to approximately 60° and 120°,
Concave portions 10a, 10c, 10e, and 10g are formed to extend longitudinally in the radial direction of the field magnet 7. Similarly, it is a part of the surface of the field magnet 7 facing the stator coil 4, and corresponds to approximately 240° and 300° in electrical angle in the N-pole regions 9b, 9d, 9f, and 9h. In the place,
Concave portions 10b, 10d, 10f, and 10h are formed to extend longitudinally in the radial direction of the field magnet 7. Note that the recesses 10a to 10h are provided at positions equidistant from the center of the field magnet 7, and these recesses 10a to 10h are configured to correspond to part of the outward path 4a and return path 4b of the stator coil 4. .

According to the brushless motor 3 configured as described above, the recesses 10a to 10a are formed at predetermined locations of the field magnet 7.
10h, the magnetized state of the field magnet 7 in the curve l portion of FIG. 8 is as shown in FIG. 9A.
It will look like this. That is, due to the presence of the recesses 10a to 17h, electrical angles of approximately 60°, 120°, 240° and
The interlinkage magnetic flux in the vicinity of 300° is reduced, and the magnetic field strength is locally weakened in the areas where these recesses 10a to 10h are provided. Furthermore, the magnetic flux linkage in the case where the recesses 10a to 10h are not provided is as shown by the dashed line in FIG. 9A.
In the case of this embodiment, the peak value is slightly lowered due to the influence of the recesses 10a to 10h. Note that the degree of this decrease varies depending on the dimensions and shapes of the recesses 10a to 10h, but these recesses 10a to 10h
~10h is provided locally, so the amount of decrease is relatively small. Therefore, the brushless motor 3
This does not cause any inconvenience such as a significant decrease in the generated torque.

Therefore, when a field magnet 7 having a magnetization pattern as shown in FIGS. 8 and 9A is used and three-phase bidirectional current is applied, the generated torque T ₃ of the brushless motor 3 is as shown in FIG. 9B. It comes to show. In this case, because the interlinkage magnetic flux at electrical angles of approximately 60°, 120°, 240°, and 300° is depressed, the generated torque T ₃ is equal to the generated torque T ₂ of a conventional three-phase bidirectional 120° current-carrying brushless motor. (See the dashed line in FIG. 9B) As is clear from the comparison, the generated torque at electrical angles of approximately 60°, 120°, 240°, and 300° is reduced. As a result, the ripple in the torque T ₃ generated by the brushless motor 3 becomes extremely small. In the case of this embodiment, it is possible to significantly reduce the torque ripple without causing any inconvenience such as the average value of the generated torque being significantly reduced.

Therefore, the above-mentioned brushless motor 3 can be applied to direct drive compact VTRs, compact tape recorders, etc. that require high performance. When this brushless motor 3 is applied to a direct drive type VTR or tape recorder, wow and flutter can be greatly reduced.

FIG. 10 shows a second embodiment of the present invention. In this embodiment, each of the magnetized regions 9a to 9h of the ring-shaped field magnet 7 has an electrical angle of approximately 60° and 120°. Through holes 1 penetrating the field magnet 7 in the thickness direction at locations corresponding to 240° and 300°
2a to 12h are provided, respectively. Note that the other configurations may be the same as those of the first embodiment described above.

When configured in this way, the through holes 12a to 12
Due to the existence of h, as in the case of the first embodiment, the magnetic flux linkage decreases at locations corresponding to approximately 60°, 120°, 240°, and 300° in electrical angle, and the magnetic field strength at these portions decreases locally. It will be weakened by As a result,
The magnetic flux linkage characteristic becomes a pattern as shown in FIG. 9A, and the torque ripple can be significantly reduced without reducing the generated torque.

FIG. 11 shows a third embodiment of the present invention, in which the present invention is applied to a cylindrical surface facing brushless motor using a cylindrical field magnet 15. It is. That is,
For example, eight magnetized regions are formed at equal angular intervals in the cylindrical field magnet 15 so as to have alternately different polarities in the circumferential direction. The angular width is 90° (360° electrical angle). and S
Longitudinal recesses 18 extending along the axial direction are formed in the polar region 16 at locations corresponding to approximately 60° and 120° in electrical angle, and in the N-pole region 17, approximately 240° in electrical angle are formed. and 300°,
A longitudinal recess 19 extending along the axial direction is provided. Note that in the areas where these recesses 19 are provided, there are through holes 20 that penetrate in the thickness direction of the field magnet 15, as shown in FIG.
may be provided.

Even in this configuration, the recesses 18 and 19
Or, due to the presence of the through hole 20, the field magnet 1
Since the magnetic field strength due to the magnetic field 5 is locally weakened, torque ripple can be significantly reduced.

In each of the above-mentioned embodiments, it is easily possible to provide a recess or a through hole in a field magnet made of ferrite, but for example, it is possible to use a field magnet made of ferrite and provide a recess or a through hole in the magnet. When a so-called plastic magnet made by sintering in a mixed state is used as a field magnet, it is advantageous because the field magnet having recesses or through holes can be manufactured very easily.

Although the present invention has been described above with reference to embodiments, the present invention is not limited to these embodiments, and various modifications and changes can be made based on the technical idea of the present invention.

For example, the recess 1 provided in the field magnet 7
The through holes 0a to 10h (or the through holes 12a to 12h) may be formed in a groove shape over the entire radial direction of the field magnet 7, as shown in FIG. Further, the recess 1 provided in the field magnet 15
8 and 19 may be formed in a groove shape over the entire axial direction of the field magnet 15, as shown in FIG.

As mentioned above, the present invention provides a recess or a through hole partially in the surface of the field magnet facing the stator coil in a three-phase bidirectional 120° current-carrying brushless motor. The location where the recess or through hole will be provided is measured using an electrical angle
The locations were selected to correspond to electrical angles of approximately 60°, 120°, 240°, and 300° in the pair of south and north pole regions that make up 360°. Therefore, the magnetic field strength at the corresponding locations mentioned above is locally weakened, so that the torque obtained by superimposing the torques from the three-phase stator coils is as shown in the conventional case shown in FIG. The torque characteristics are flat as a whole without extreme peaks in the portions corresponding to the corresponding locations, and therefore the torque ripple can be significantly reduced without substantially reducing the generated torque. Therefore, when the brushless motor according to the present invention is used as a drive source for a VTR or tape recorder, it is extremely advantageous because highly accurate rotation with extremely little rotational unevenness can be guaranteed.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing the positional relationship between the stator coil and field magnet in a conventional brushless motor, Fig. 2A is a diagram showing the energization period of each stator coil in the case of 120° energization in one direction of three phases, Figure B is a characteristic diagram showing the generated torque characteristics in the case of 120° current conduction in three phases in one direction, and Figure 3 A is a characteristic diagram showing the generated torque characteristics in the case of energization in three phases in both directions.
Figure 3B is a diagram showing the energization period of each stator coil in the case of 120° energization. Figure 3B is a characteristic diagram showing the generated torque characteristics in the case of 120° energization in both three-phase directions.
The figure is a characteristic diagram showing the flux linkage characteristics of a field magnet, Figures 5A and 6A are diagrams showing examples of flux linkage characteristics different from those in Figure 4, and Figures 5B and 6 are diagrams showing examples of flux linkage characteristics different from those in Figure 4. FIG. B is a characteristic diagram showing the generated torque characteristics. 7 to 9 show a first embodiment of the present invention, in which FIG. 7 is an exploded perspective view of a planar opposed brushless motor, and FIG. 8 shows a magnetization pattern of a field magnet. 9A is a characteristic diagram showing the interlinkage magnetic flux characteristics of the field magnet on curve l in FIG. 8, FIG. 9B is a characteristic diagram showing the generated torque characteristics of the brushless motor, and FIG. 10 is a plan view. 11 shows a fourth embodiment of the present invention, in which a perspective view of a field magnet is shown, and FIG. A partially cutaway perspective view of a field magnet, FIG. 12 is a perspective view similar to FIG. 11 showing a fourth embodiment of the present invention, and FIGS. 13 and 14 show modified examples of the present invention, respectively. FIG. 3 is a perspective view of the field magnet shown in FIG. In addition, in the symbols used in the drawings, 3...
…3-phase bidirectional 120° current-carrying brushless motor, 4
...Stator coil, 7...Ring-shaped field magnet, 9a to 9h...Magnetized region, 10a to 10h
...Recess, 12a to 12h...Through hole, 15...
Cylindrical field magnet, 16...S pole region, 17
... N pole region, 18, 19 ... recess, 20 ... through hole.

Claims (1)

[Claims for Utility Model Registration] A field magnet having a continuous S-pole region and a N-pole region, and a three-phase stator coil facing the field magnet, and these stator coils In a three-phase bidirectional 120° current-carrying brushless motor in which the electric current is supplied in both directions with a sequential shift of 120° in electrical angle, the field magnet has a partially recessed or A through hole is provided, and at this time, the recess of the opposing surface or the location where the through hole is provided is approximately 60 degrees in electrical angle between a pair of south and north pole regions that make up 360 degrees in electrical angle.
A brushless motor characterized by being selected for locations that correspond to 120°, 240°, and 300°.