JPS63167657A - Dc brushless motor - Google Patents

Abstract

PURPOSE:To suppress a torque ripple by forming a thin part or a slot radially in a rotor yoke to reduce an air gap magnetic flux density, and varying a torque waveform. CONSTITUTION:A rotor yoke 11 to which a permanent magnet 1 is attached and an armature yoke 12 in which a flat coil 2 is disposed are all composed of a soft magnetic material. A radial thin part or a cutout slot 13 is disposed on the yoke 11. The thin part or slot 13 is formed at a part corresponding to the pole of the magnet 1, and two slots are provided at an interval of 15 deg. at 3-equally divided positions of the respective poles.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to DC brushless motors, and more particularly to a small, ironless DC brushless motor that suppresses the occurrence of torque ripple.

[Conventional technology]

Conventionally, small DC brushless motors have a high torque! l11
It has been widely used in AV equipment, 0^ equipment, etc. because it is easy to control speed flJm, has a long life, and is highly reliable.

However, for applications such as drum motors and capstan motors for videotape recorders that require both highly constant speed and rotational speed fluctuation characteristics, motors in principle have The problem is that it is extremely difficult to technically solve this problem because rotational unevenness occurs due to fluctuations in torque.

3A and 3B show an example of the configuration of a conventional three-phase, bidirectional current-carrying brushless motor. Figure 3A shows the form of the permanent magnets constituting the rotor, where 1^,
1B, IC, . . . , IH are eight 6B poles of permanent magnets that are alternately magnetized to N and S poles in the circumferential direction. Also, FIG. 3B shows the armature, where 2-1
and 2-1°, 2-2 and 2-2°, and 2-3 and 2-3° are flat coils each having one phase arranged at centrally symmetrical positions.

However, although the eight magnetic poles 1^ to IH are uniformly saturated magnetized in the direction perpendicular to the plane of the paper, when the rotor having the above-mentioned permanent magnet 1 rotates and intersects the coil 2, It is known that the density of the magnetic flux generated in the gap between the two changes almost sinusoidally under the influence of the adjacent magnetic poles. Therefore, in the case of constant current drive, the electromagnetic torque generated between the coils 2 of each phase is as shown in Fig. 4 (^
) changes in a sinusoidal manner.

That is, FIG. 4 shows the state of the torque generated in the rotor when the above-mentioned motor coil 2 is driven by supplying a constant current with a phase angle of 120° in both directions, and here,
The horizontal axis represents the rotation angle of the rotor expressed in electrical angle, and the vertical axis represents the state of change in the generated torque. Note that U, V, and W each represent electromagnetic torque generated between the three-phase coils 2 whose phases are shifted by 60 degrees in electrical angle.

Therefore, assuming that the amplitude of torque fluctuation in each phase is 1, for example, from 90'' to 150 degrees electrical angle, the combined torque curve of torques U and V will be as shown in Fig. 4 (B). For example, it reaches its maximum at an electrical angle of 120°, and its maximum value is theoretically 1.732.It also reaches its minimum at an electrical angle of 9G' and 150°, and its minimum value is 1.5 ( As shown in B), a ripple waveform that looks like a continuous part of a sine wave is generated.This situation is also the same when the torques V and W and W and U are combined.

As a result, as shown in Figure 4, the resultant torque is approximately 1
Torque ripples with an amplitude of 4% will occur, and such torque ripples may impede the functionality of some equipment.

Therefore, various proposals have been made to suppress the occurrence of torque ripple as described above. Figure 5 is JP-A-58
This example shows an example disclosed in Japanese Patent No. 22574, in which a non-magnetized portion, a non-saturated magnetized portion, or a different polarity portion is provided in each magnetic pole of the main permanent magnet, and by forming such compensation magnetic poles, the composite torque ripple is reduced. This is an attempt to reduce the amount of water used.

In FIG. 5, 3^, 3B, . 60° in electrical angle for each individual magnetic pole of 1.

By forming compensating magnetic poles at positions maintaining angles of 120°, 240°, and 300°, a rotor with poles as shown in FIG. 5 can be obtained. It is possible to reduce the torque ripple by changing the electromagnetic torque at the compensating magnetic pole 3.

[Problem that the invention seeks to solve]

However, as in the above example, forming a compensating magnetic pole by a non-magnetized part, a non-saturated magnetized part, or a magnetized part of opposite polarity in the main pole region of a field permanent magnet is difficult from a design point of view, and furthermore, It is difficult to maintain the delicate relationship between the main pole magnetizing current and the compensation electrode magnetizing current.
In addition to requiring a complicated magnetization process, it is also difficult to achieve a stable magnetization distribution, and even if it could be achieved, a large torque loss would occur.

The purpose of the present invention is to suppress torque ripple by changing the distribution of magnetic resistance in the magnetic circuit in which the main magnetic flux is formed by conventionally used field permanent magnets without requiring any special magnetization process. The object of the present invention is to provide a small DC brushless motor that can perform the following functions.

[Means for solving problems]

In order to achieve such an object, the present invention provides a rotor yoke with a plurality of magnetic poles of a multi-pole magnetized permanent magnet, and each of the coils constituting the three phases disposed on the armature facing the permanent magnet. In a DC brushless motor in which both sides are energized, a thin-walled part or slotted part is arranged in relation to the electrical angle in which the coil is arranged at a position on the rotor yoke corresponding to a plurality of magnetic poles, and the thin-walled part or slotted part The present invention is characterized in that the torque waveform is changed by reducing the air gap magnetic flux density.

[For production]

According to the DC brushless motor of the present invention, the magnetic flux density can be lowered in the thin walled part or the slotted part provided in the radial direction of the rotor yoke than in other parts, thereby making it possible to reduce the amplitude of the composite torque ripple. Furthermore, by making the frequency of the ripple twice as high as the fundamental wave of the original ripple, the rotation unevenness can be halved by the inertia of the rotor itself.

〔Example〕

Embodiments of the present invention will be described in detail and specifically below based on the drawings.

FIG. 1A and FIG. 1B show an embodiment of the present invention, and this embodiment is also of the three-phase, bidirectional current-carrying type. Here, 11 is a rotor yoke to which the permanent magnet 1 is attached, 12 is an armature yoke to which the flat coil 2 is arranged, and both yokes 11 and 12 are made of a soft magnetic material.

In this example, as shown in FIG.
13 (hereinafter referred to as a compensation hole) is provided.

In this case, the compensation hole 13A is located at the magnetic pole I of the permanent magnet 1.
Below, in the part corresponding to A, 13B, 13C,...
, 13H are magnetic poles IB, IC,..., I, respectively.
They are formed in the portion corresponding to H, and two of them are provided at 15° intervals at three equal positions on each magnetic pole.

Therefore, in the DC brushless motor configured in this way, as shown in FIG.
, 120°, . . . due to the compensation hole 13, the air gap magnetic flux density is reduced by the air gap l! at other electrical angle positions. ! Even if the permanent magnet 1 is uniformly magnetized, the electromagnetic torques u', v' and W are lower than the magnetic flux density in each phase.
As a result, as shown in (B) in Figure 2, the height of the peak of the composite torque is halved compared to the ripple shown in (B) in Figure 4, and its frequency is reduced. It is possible to double the amount and change it into a fine ripple. In other words, in (B) of Figure 4, the height of the ripple peak was (1,732-1,5) = 0.232, but it has been reduced to about the same level, and the frequency has been finely tuned. By doing so, it is possible to significantly suppress torque ripple.

In order to suppress the torque ripple as described above, when setting the compensation hole 13 described above, the magnetic flux density at that position may be reduced by about 14%.

[Effects of the Invention] As described above, according to the present invention, the rotor yoke is provided with a thin walled portion or a slotted hole, and the air gap magnetic flux density is adjusted by the thin walled portion or slotted hole at a predetermined electrical angle. Since the waveform of the electromagnetic torque is modified by lowering the torque ripple, it is possible to suppress the torque ripple by increasing the frequency at which the torque ripple occurs and reducing its amplitude.

[Brief explanation of the drawing]

FIGS. 1A and 1B are a sectional view and a plan view of the rotor yoke, respectively, showing an example of the structure of the DC brushless motor of the present invention, and FIG. 2 illustrates the torque ripple suppression effect that can be achieved by the DC brushless motor of the present invention. Electromagnetic torque waveform curve diagrams, Figures 3A and 3B for
The figure is a schematic diagram showing the configuration of the permanent magnet on the rotor yoke side and the flat coil on the armature side in a conventional DC brushless motor, and Figure 4 is an electromagnetic diagram to explain the torque ripple that occurs in a conventional DC brushless motor. The torque waveform curve diagram in FIG. 5 is a schematic diagram showing an example of means for suppressing torque ripple in a conventional DC brushless motor. 1... Permanent magnet, l^~18... Magnetic pole, 2... Flat coil, 11... Rotor yoke, 13A~13) 1... Thin wall part or slotted hole (compensation hole)
, u', v', w'...electromagnetic torque. IA 2;j! Pole 1 Hi Figure 1B Figure 3A Figure 3B.

Claims (1)

[Scope of Claims] A rotor yoke is provided with a plurality of magnetic poles of a multi-pole magnetized permanent magnet, and each of the coils constituting three phases arranged on the armature facing the permanent magnet is energized. In the DC brushless motor, a thin wall portion or a slotted portion is provided in relation to an electrical angle at which the coil is arranged at a position on the rotor yoke corresponding to the plurality of magnetic poles, and a thin wall portion or a slotted portion is provided in the thin wall portion or the slotted portion. A DC brushless motor characterized in that the torque waveform is changed by reducing the air gap magnetic flux density.