JP4042279B2 - Brushless motor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a brushless motor for a magnetic disk apparatus that is mounted with at least one magnetic disk of the magnetic disk apparatus and is driven to rotate. Further, the motor has a small torque ripple, cogging, and iron loss and a good torque constant. The present invention relates to a brushless motor that obtains characteristics, and particularly relates to a shape structure of a stator core.
[0002]
[Prior art]
Conventionally, brushless motors are often used in OA equipment and AV equipment. However, in recent years, polygon scanner motors for laser copiers and spindle motors for magnetic disks have advanced to higher speeds. The polygon scanner motor exceeds 20000 rpm, and the spindle motor for the magnetic disk requires high speed and high rotation for increasing the memory capacity and increasing the transfer speed. In recent years, 12000 rpm has become normal. As rotation speed increases, vibrations caused by coil energization and vibrations caused by cogging are amplified, and problems related to vibration have occurred. In addition, with respect to noise, the vibration sources due to motor unbalance and the like have increased due to high rotation, which has become a problem. Further, the loss increases and the power consumption tends to increase. Current consumption is dominated by losses such as windage loss, shaft loss, and iron loss. Iron loss is divided into hysteresis loss and eddy current loss. Hysteresis loss is proportional to the number of rotations (more precisely, the coil energization frequency). It is generally known that the eddy current loss is proportional to the square of the rotation speed (more precisely, the coil energization frequency). As the motor speed increases, that is, when the motor speed increases, eddy current loss increases, and the ratio of iron loss to the loss increases.
[0003]
Smooth rotation is required to reduce vibration. It is necessary to reduce the cogging and eliminate the torque ripple, which is usually dealt with by the rotor magnet skew magnetization and the stator core skew lamination, but conversely, there is a problem that the torque constant decreases. It is out.
[0004]
Furthermore, in order to reduce the iron loss, the method of reducing the iron loss of the stator core itself and the number of magnetic poles are usually changed by changing the silicon steel sheet for laminating the stator core to a material with small iron loss or annealing. This is handled by reducing the coil energization frequency.
[0005]
[Problems to be solved by the invention]
However, providing a skew between the rotor magnet and the stator core leads to a reduction in torque ripple and cogging, but reduces motor efficiency and torque constant. Particularly in recent years, there has been a demand for low vibration and low noise without lowering the torque constant and motor efficiency due to downsizing of devices, and it has been desired to reduce torque ripple and cogging as a motor.
[0006]
Japanese Patent No. 2636108 discloses a method for reducing cogging due to skew magnetization of a rotor magnet. An example thereof is cited in FIG. When the number of magnetic poles of the rotor magnet is 2n and the number of slots of the stator core is 3n, in the figure, (76 ° / n) × 0.8 ≦ θ2 ≦ (76 ° / n) × 1.2 Yes.
[0007]
This states that the skew angle of the skew magnetization of the rotor magnet is set to a skew angle with reduced cogging and torque ripple without deteriorating the motor efficiency.
[0008]
However, this is an effective technique when there is a margin in the motor dimensions, and it is difficult to configure when the motor is reduced in size and thickness. In particular, when the motor is thin and the number of stacked stator cores is very small, when the height of the rotor magnet cannot be taken, this skew magnetization is ineffective, and cogging reduction and torque ripple reduction cannot be expected. In addition, the motor characteristics and Kt are deteriorated.
[0009]
Next, a method of reducing the iron loss by changing the material of the silicon steel plate to a material with reduced iron loss or annealing is treated as a general method, but the cost tends to increase. Moreover, the annealed material has problems such as corrosion, and the surface treatment must be sufficiently performed.
[0010]
Japanese Unexamined Patent Publication No. 7-31085 discloses a method of integrally forming a core without stacking and reducing iron loss. A practical example is cited in FIG.
[0011]
6A is a sectional view of a conventional motor, FIG. 6B is a plan view of a stator core of the conventional motor, and FIG. 6C is a side view of the stator core of the conventional motor.
[0012]
In FIG. 6, reference numeral 25 denotes a stator core around which a coil 26 is wound. The rotor magnet 28 is fixed to the inner peripheral surface of the projecting portion 27d so as to face the stator core 25. The stator core 25 has a hole 25a to be fixed, an annular base 25b provided on the outer periphery of the hole 25a, and a tooth 25c projecting radially from the outer periphery of the base 25b and around which the coil 26 is wound. ing. A convex pole 25d protruding in the axial direction is formed at the tip of each tooth 25c. Components such as the base 25b and the teeth 25c are integrally formed by pressing or cutting, and an annealing process is performed.
[0013]
In this way, the stator core is not laminated, but is integrally formed and annealed to reduce the loss.
[0014]
However, this has many press processes, cutting processes and processing steps, is unstable in quality, and has no cost merit. Further, the saturation magnetic flux density of the stator core is improved, but the effect of reducing the iron loss is small. When the motor height is high, it cannot be configured, and the motor characteristics and Kt are deteriorated.
[0015]
The present invention solves such a conventional problem, and can be easily configured in any size motor, thereby reducing torque ripple, cogging, and iron loss, and obtaining motor characteristics with a good torque constant. The purpose is to realize a motor.
[0016]
[Means for Solving the Problems]
In order to solve the above problems, the brushless motor of the present invention has a plurality of magnetic poles, is disposed at a position facing the rotor magnet via a rotor magnet and an air gap for rotating the rotor, has a plurality of convex poles, The brushless motor has a stator core around which windings are wound, and the ratio of the outer diameter of the stator core to the teeth width around which the windings of the stator core are wound is 8-12 .
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0018]
(Embodiment 1)
FIG. 1 shows an enlarged plan view of the main part of the motor according to the present invention, which has 6 magnetic poles and 9 slots.
[0019]
The basic configuration of the motor is the same as that of the prior art, and description thereof is omitted. The rotor magnet and stator core will be described. In FIG. 1, 1 is a stator core and 2 is a rotor magnet. The rotor magnet 2 is a neodymium bond magnet and has six magnetic poles in the circumferential direction. The stator core 1 has nine convex poles 3 radially integrated on the outer peripheral portion, and faces the rotor magnet 2 via an air gap. The convex pole 3 has a tooth portion 4, and a coil (not shown) is wound around the tooth portion 4. The outer diameter of the stator core 1 is D1, and the width of the tooth portion 4 is a teeth width, which is indicated by t1.
[0020]
FIG. 2 shows an embodiment of a motor according to the present invention, in which the number of magnetic poles of the rotor magnet is 6, the number of slots of the stator core is 9, and the brushless motor in-hub type for 3.5 inch magnetic disks (outer diameter of the stator core is 20 mm or less) It is a characteristic curve of Kt, torque ripple, cogging, and iron loss (at 10000 rpm) when the teeth width t1 is changed. As shown in FIG. 3, the torque ripple is obtained by synthesizing each phase of the coil and represented by (Tmax−Tmin) / Tmax × 100. From the results of FIG. 2, Kt, torque ripple, and cogging tend to improve as the tooth width increases, but iron loss tends to increase. The teeth width t1 that satisfies the characteristics within a range where the iron loss is allowed is set to 1.7 mm to 2.2 mm, or the outer diameter D1 / tooth width t1 of the stator core 1 is set to 8 to 12.
[0021]
Thus, by setting the outer diameter D1 / tooth width t1 of the stator core 1 to 8 to 12, optimum design of Kt, torque ripple, cogging, and iron loss becomes possible.
[0022]
When the outer diameter D1 / tooth width t1 of the stator core 1 is larger than 12, the magnetic flux is saturated in the tooth portion 4 of the stator core 1, and the induced voltage of the coil is distorted from the sine waveform. Kt, torque ripple, and cogging are best when the coil induced voltage is a sinusoidal waveform. When the coil induced voltage is distorted, Kt deteriorates, torque ripple deteriorates, and cogging deteriorates.
[0023]
Conversely, if the outer diameter D1 / tooth width t1 of the stator core 1 is smaller than 8, the winding space is eliminated and the required Kt cannot be satisfied. Further, the eddy current loss increases at the tip of the tooth portion 4 and the convex pole 3 on the surface of each layer of the laminated stator core, and the iron loss becomes very large.
[0024]
The maximum energy product of the neodibond magnet is BHmax8 to 11 MGOe, which is more effective in the case of the maximum energy product equivalent to the neodibond magnet. The material of the rotor magnet is widely used from rare earth magnets to plastic magnets, but the maximum energy product varies. When a neodymium bond magnet is used and the air gap is 0.2 to 0.35 mm, the air gap magnetic flux density between the rotor magnet and the stator core is 4500 to 5000 gauss. Rare earth magnets and plastics have the same effect by setting the air gap between the rotor magnet and the stator core so that the gap magnetic flux density is 4500 to 5000 gauss. Further, when the number of magnetic poles of the rotor magnet and the number of slots of the stator core are changed, the same effect can be obtained by setting the gap magnetic flux density to 4500-5000.
[0025]
Further, it is more effective if the motor has a rotational speed of 7200 rpm or more. The iron loss is because the ratio of the iron loss to the loss increases as the rotational speed (more accurately, the coil energization frequency) increases.
[0026]
A motor having a stator core of 50 mm or less, which can be used for all sizes of the stator core, but can be constructed with a neodymium bond magnet. Furthermore, the brushless motor for a magnetic disk of 3.5 inches or less that requires a reduction in size and thickness and a high output is very effective.
[0027]
It does not require any special processing method and can be easily and accurately performed by pressing. In addition, no special construction method is required for assembly, and the apparatus can reduce vibration, noise, and current consumption.
[0028]
(Embodiment 2)
It is also effective when the number of magnetic poles is 8 and the number of slots is 9. This will be described with reference to FIG. In the figure, 11 is a stator core and 12 is a rotor magnet. The rotor magnet 12 is made of a neodymium bond magnet and has eight magnetic poles in the circumferential direction. The stator core 11 has nine convex poles 13 radially integrated on the outer peripheral portion, and faces the rotor magnet 12 through an air gap. The convex pole 13 has a tooth portion 14, and a coil (not shown) is wound around the tooth portion 14. The outer diameter of the stator core 11 is D2, and the width of the teeth portion 14 is a teeth width, which is indicated by t2. This configuration also has the same effect as that of the first embodiment, and a detailed description thereof is omitted.
[0029]
【The invention's effect】
As described above, in the brushless motor according to the present invention, the ratio of the outer diameter of the stator core to the teeth width of the stator core is configured to be 8 to 12, so no special processing method is required, and press processing is performed with high accuracy. It is easy to configure, and it is possible to reduce cogging and torque ripple as vibration sources, and to obtain low vibration and low noise. In noise, switching noise can be reduced, and there is an effect of 3 dB or more.
[0030]
In addition, iron loss can be reduced and stabilized, and current consumption can be reduced.
[0031]
In particular, a neodymium bond magnet is used, and there is a remarkable effect at a rotational speed of 7200 rpm or more.
[0032]
Because of such a stator core shape, an excellent brushless motor with low vibration, low noise, low current consumption, and low cost can be realized.
[Brief description of the drawings]
FIG. 1 is an enlarged plan view of an essential part of a motor having six magnetic poles and nine slots, showing an embodiment of a motor according to the present invention. FIG. 2 is a variation in teeth width t1 in the motor according to the present invention. Kt, torque ripple, cogging, iron loss characteristic curve diagram of the motor [Fig. 3] Torque ripple composite waveform diagram of the motor according to the present invention [Fig. 9 is an enlarged plan view of the main part of the 9 slots. FIG. 5 is an explanatory diagram of skew magnetization of a conventional motor. FIG. 6 is a sectional view of another conventional motor. FIG. 5B is a stator core plan view of the motor. Side view of stator core of the motor 【Explanation of symbols】
1, 11, 25 Stator core 2, 12, 28 Rotor magnet 3, 13, 25d Convex pole 4, 14, 25c Teeth D1, D2 Outer diameter of stator core t1, t2 Teeth width

Claims (4)

  A stator core having a plurality of magnetic poles, disposed at a position facing the rotor magnet via a rotor magnet and an air gap for rotating the rotor, having a plurality of convex poles and having a winding wound thereon A brushless motor in which the ratio of the outer diameter of the stator core to the teeth width around which the winding of the stator core is wound is 8 or more and 12 or less.   The brushless motor according to claim 1, wherein the number of magnetic poles of the rotor magnet is 8 and the number of slots of the stator core is 9 slots. The brushless motor according to claim 1, wherein the number of magnetic poles of the rotor magnet is 6 and the number of slots of the stator core is 9 slots. The brushless motor according to claim 1, wherein the rotor magnet is a neodymium bond magnet.

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