JP2003009440A - Brushless dc motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a brushless DC motor which hardly impairs an output characteristic and surely reduces cogging torque. SOLUTION: A magnetic pole center line J1 is diviated from an effective magnetic pole opening angle center line K1 by an angle of θ4, at the magnetic pole of a permanent magnet 3(S). A magnetic pole center line J2 corresponds to an effective magnetic pole opening angle center line K2 at the magnetic pole of the permanent magnet 3(N). The timing when the end of the permanent magnet 3(S) crosses stator teeth 2 is not synchronized with the timing when the permanent magnet 3(N) crosses the stator teeth 3. The individual cogging torque generated by both magnetic poles cancels each other. The whole cogging torque is reduced. An influence on the rotating balance of a rotor is suppressed by adjacently arranging the magnetic poles with different diviation angles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brushless DC motor having a rotor with a permanent magnet. More specifically, the present invention relates to a brushless DC motor in which the output characteristics are not sacrificed as much as possible to reduce the cogging torque.

[0002]

2. Description of the Related Art Brushless DC motors have a VT because they do not generate mechanical or electrical noise, have high rotational performance, have a long life, and so on.
It is widely used in R cylinders, capstans for cassette decks, and drives such as flexible disks and compact disks. In recent years, it has come to be used as a drive motor for an electric power steering device of a vehicle. In a brushless DC motor, a slot for winding is present in the stator and a permanent magnet is present in the rotor, so that torque pulsation, that is, cogging torque is inevitably generated.

As a conventional countermeasure against this cogging torque, there is one as shown in FIG. 14, for example. In FIG. 14, the permanent magnet 103 has a shape in which the outer peripheral curvature is stronger than the outer peripheral curvature of the rotor core 104. This is because the gap between the permanent magnet 103 and the stator tooth 102 is
It is designed to be gradually larger from the center to both ends in the circumferential direction. As a result, the rotor core 1
When 04 rotates, the magnetic flux interlinking with each stator tooth 102 changes smoothly instead of being stepped. Thus, the cogging torque is reduced. Instead of devising the shape of the permanent magnet 103, the outer circumferential shape of the rotor core 104 may be devised to provide the same effect.

Another example of the conventional measures is shown in FIG. In FIG. 15, the arrangement of the magnetic poles in the axial direction of the rotor 114 has a skew angle θS. As a result, when the rotor 114 rotates, the timing at which the boundary between the magnetic poles crosses the stator teeth varies depending on the axial position of the rotor 114. Thus, stator teeth 1
The change in the magnetic flux interlinking with 02 is alleviated and the cogging torque is reduced.

[0005]

However, all of the above-mentioned conventional techniques have problems such as poor magnetic efficiency.

First, the problems of the structure shown in FIG. 14 will be described. In the case of FIG. 14, the permanent magnet 103 and the stator tooth 1 are
The average gap between the two is large. Therefore, the magnetic efficiency is poor, and the rotation output cannot be earned as compared with the magnetic force of the permanent magnet 103. Further, determination of the outer peripheral shape of the permanent magnet 103 or the rotor core 104 requires various analyzes and trial production, which increases the development cost. Further, since it is necessary to machine a small shape with high precision, the machining itself is difficult. Nevertheless, the goal of reducing cogging torque is not fully achieved. In particular, the original cogging torque itself is considerably large when a strong rare-earth permanent magnet is used due to the recent demand for miniaturization. For this reason, measures such as this were not sufficient.

Next, the problem of FIG. 15 will be described. Also in the case of FIG. 15, the magnetic efficiency is poor and the rotation output cannot be earned. This is because the arrangement of the magnetic poles has the skew angle θS, so that the effective magnetic flux of the magnetic poles is small accordingly. In the case of FIG. 15, on the side surface of the rotor 114,
One magnetic pole occupies a region of a substantially parallelogram. Near the apex of the acute angle, the magnetic flux at that portion does not act effectively as motor performance. For this reason, the rotation output cannot be earned as in the previous case.

The present invention has been made to solve the above-mentioned problems of the conventional technique. That is, an object of the invention is to provide a brushless DC motor in which output characteristics are hardly sacrificed and cogging torque is reliably reduced.

[0009]

The brushless DC motor of the present invention, which has been made for the purpose of solving this problem, has a plurality of magnetic poles having permanent magnets mounted in magnet mounting holes at equal pitches in the circumferential direction. A rotor and a stator in which a plurality of slots are arranged at equal pitches in the circumferential direction, and the magnetic pole of the rotor is formed by the center line of the effective magnetic pole opening angle and the center line of the magnet mounting hole. The magnet displacement angle has a first angle and a second angle. Naturally, the first angle and the second angle are different angles.

In this brushless DC motor, the magnetic pole of the rotor has a magnet deviation angle of a first angle (hereinafter,
There is a magnetic pole having a second angle (hereinafter referred to as a "magnetic pole having a second angle") and a magnetic pole having a second magnetic deviation angle. Therefore, the cogging torque generated by the magnetic poles at the first angle and the cogging torque generated by the magnetic poles at the second angle do not match in phase. That is, these cogging torques never peak at the same time. This is because, with these magnetic poles, there is a deviation in the timing at which the end of the magnet crosses the end of the slot of the stator due to rotation. Therefore, the cogging torque of the brushless DC motor as a whole is reduced as compared with the case where the magnet deviation angles of all the magnetic poles are the same.

Here, the difference θ between the second angle and the first angle θ
It is more preferable that 4 is within the range defined by the following equation: 0.2 × θ5 ≦ θ4 ≦ θ3- (0.2 × θ5). In this case, the first
With reference to the angled magnetic pole, the angle θ
Permanent magnets are attached at positions that precede (or follow) in the rotational direction by 4. Here, if the first angle is 0, the second angle is θ4. In this case, in the magnetic pole of the first angle, the center line of the effective magnetic pole opening angle and the center line of the magnet mounting hole coincide with each other. On the other hand, in the second angle magnetic pole, the center line of the effective magnetic pole opening angle is deviated from the center line of the magnet mounting hole by θ4.

Therefore, there is a difference in the timing at which the cogging torque peaks between these magnetic poles.
If this deviation is too small, the effect of reducing the cogging torque of the brushless DC motor as a whole cannot be sufficiently obtained. On the other hand, if the deviation is too large, the timing at which the cogging torque reaches its peak will eventually approach due to the relationship with the adjacent slot in the stator.
That is, the magnet offset angle is the stator slot pitch angle θ
If it is large enough to agree with 3, this will happen. If the difference between the first angle and the second angle is within the above range,
Without such a situation, the cogging torque of the brushless DC motor as a whole is reliably suppressed.

In the brushless DC motor of the present invention, it is desirable that the rotor has the same number of magnetic poles of the first angle and magnetic poles of the second angle. This is because the suppression of the waveform of the cogging torque between the magnetic poles of the first angle and the magnetic pole of the second angle cancels the entire cogging torque more reliably. Further, in the brushless DC motor of the present invention, it is desirable that the rotor be provided with the magnetic pole of the first angle and the magnetic pole of the second angle side by side. Since the rotor is a rotating object, the balance of rotation must be taken into consideration. It is undeniable that changing the magnet deviation angle by using the magnetic poles may shift the center of gravity of the rotor from its axial center, thus impairing the rotational balance. However, by disposing the magnetic poles of the first angle and the magnetic poles of the second angle side by side, it is possible to minimize the loss of the rotational balance.

In the brushless DC motor,
The rotor may have a configuration in which it is divided into a plurality of blocks in the axial direction. When the present invention is applied to such a structure, it is preferable that the magnetic poles of the first angle and the magnetic poles of the second angle are present at positions corresponding to the axial direction in different blocks. The position corresponding to the axial direction is a position having the same angular coordinate around the axis. In this way, the waveform of the cogging torque is canceled within one magnetic pole of the rotor as a whole. Therefore, it is possible to obtain an effect as if the cogging torque generated by one magnetic pole is reduced. As a result, the cogging torque of the brushless DC motor as a whole is effectively suppressed.

Further, in the brushless DC motor of the present invention, the rotor further has a magnetic pole having a magnet deviation angle of a third angle (hereinafter, referred to as a "third angle magnetic pole"), and the second angle and the second angle The difference θ4 from the first angle is within the range determined by the above equation, and the difference between the third angle and the first angle is θ
It is better that the size is the same as 4 and the sign is opposite, that is, -θ4. In this case, if the magnetic pole of the first angle is used as the reference,
In the magnetic pole of the second angle, the permanent magnet is attached at a position leading in the rotation direction by the angle θ4, and in the magnetic pole of the third angle, the permanent magnet is attached at a position trailing in the rotation direction by the angle θ4. Will be. The leading and trailing lines may be interchanged. In this way, the cogging torque is canceled by the three waveforms that are offset from each other at equal intervals. Therefore, the cogging torque of the brushless DC motor as a whole can be suppressed more reliably.

In this case, it is further desirable that the rotor has magnetic poles of the first angle, magnetic poles of the second angle, and magnetic poles of the third angle in the same number. As a result, the suppression of the entire cogging torque by canceling the waveforms of the cogging torque of the magnetic pole of the first angle, the magnetic pole of the second angle, and the magnetic pole of the third angle,
It will be more certain. In this case,
It is more preferable that the total number of magnetic poles of the rotor is an integral multiple of 6, and that all of the magnetic poles are any of the magnetic poles at the first angle, the magnetic poles at the second angle, and the magnetic poles at the third angle. By doing so, since there is no extra waveform component, the cogging torque is suppressed more reliably. The total number of magnetic poles is the product of the number of blocks and the number of magnetic poles in each block when the rotor is divided into a plurality of blocks in the axial direction.

In the brushless DC motor of the present invention, alternatively, the rotor has a convex portion corresponding to the magnetic pole at the edge thereof, and the magnetic pole of the rotor has a convex portion formed by the center line of the convex portion and the center line of the magnet mounting hole. The misalignment angle may have a first angle and a second angle.

In this brushless DC motor, the magnetic poles of the rotor are classified into those having a convex deviation angle of a first angle and those having a convex deviation angle of a second angle. The phases of the cogging torques generated by these magnetic poles do not match each other. That is, these cogging torques never peak at the same time. This is because, in these magnetic poles, the timing at which the end of the convex portion crosses the end of the slot of the stator is deviated due to rotation. Therefore, the cogging torque of the brushless DC motor as a whole is reduced as compared with the case where the protrusion deviation angles of all the magnetic poles are the same. In addition, since the protrusion of the rotor is very small in weight, it has almost no influence on the position of the center of gravity of the rotor.

Further, in the brushless DC motor of the present invention, the magnet deviation angle and the convex deviation angle of the magnetic pole of the rotor are both the first angle and the second angle. It may have a certain configuration. In the magnetic pole of this brushless DC motor, in which the magnet deviation angle and the convex deviation angle are both the first angle, the center line of the effective magnetic pole opening angle and the center line of the convex portion coincide with each other. The same applies to the magnetic pole in which both the magnet deviation angle and the protrusion deviation angle are the second angle. Therefore, the magnetic force is efficiently used. Of course, the effect of reducing the cogging torque due to the difference in the magnet deviation angle and the convex deviation angle for each magnetic pole can also be obtained.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments embodying the present invention will be described in detail below with reference to the accompanying drawings.

(First Embodiment) In this embodiment, as shown in FIG. 1, the present invention is applied to a brushless DC motor having a magnet-embedded rotor 4 having four magnetic poles. That is, the rotor 4 of this brushless DC motor is provided with magnet mounting holes 5 at four locations along the outer circumference, and the permanent magnets 3 are mounted in the respective magnet mounting holes 5. Each permanent magnet is located near the outer circumference of the rotor 4. Therefore, the open angle of each permanent magnet viewed from the rotation center axis O may be regarded as the effective magnetic pole open angle. The permanent magnets 3 are arranged so that adjacent ones have opposite polarities. The stator 1 has 12 stator teeth 2. In FIG. 1, only the upper half is shown for simplicity, but the lower half has the same structure. Although not shown in FIG. 1, a winding is attached to each stator tooth 2 in an actual use state.

In FIG. 1, J1 and J2 indicate the center line of each magnet mounting hole 5, that is, the magnetic pole center line. These are structurally related to the core of the rotor 4. K1 and K2 indicate the center lines of the permanent magnets 3 (S) and 3 (N), that is, the center lines of the effective magnetic pole opening angles of the respective magnetic poles. These are the actual center positions of the magnetic force.
θ1 indicates a structural pitch angle of the rotor 4 viewed from the rotation center axis O. θ2 indicates the effective magnetic pole opening angle of the permanent magnet 3 (S). θ3 indicates the slot pitch angle of the stator 1. θ4 represents a deviation angle between the magnetic pole center line J1 and the effective magnetic pole opening angle center line K1 in the magnetic pole of the permanent magnet 3 (S). θ5 indicates a slot opening angle which is an opening angle between adjacent stator teeth 2. Here, it is merely a coincidence that one of the lines that divides both ends of the slot pitch angle θ3 coincides with the center line K1 of the effective magnetic pole opening angle, and it has no particular meaning. Similarly, it is a mere coincidence that the other of the lines defining both ends of the slot pitch angle θ3 coincides with one of the lines defining both ends of the effective magnetic pole opening angle θ2. Furthermore, it is a mere coincidence that one of the lines defining both ends of the slot opening angle θ5 coincides with one of the lines defining both ends of the effective magnetic pole opening angle θ2.

From the above, in the brushless DC motor of FIG. 1, the magnetic pole center line J1 is used for the magnetic pole of the permanent magnet 3 (S).
There is an angle deviation between the effective magnetic pole opening angle center line K1 and the value is θ4. On the other hand, in the magnetic pole of the permanent magnet 3 (N), the magnetic pole center line J2 and the effective magnetic pole opening angle center line K2 coincide. That is, the value of the deviation angle between them is zero. Therefore, there is a difference of θ4 between the magnetic poles between the magnetic pole center line and the effective magnetic pole opening angle center line.

The condition of the cogging torque in the brushless DC motor having the above structure will be described with reference to FIGS. 2 and 3. In FIG. 2, the stator teeth 2 (2-1, 2-2, ..., 2-) in the brushless DC motor of FIG.
n, 2- (n + 1)), magnet mounting hole 5, and permanent magnet 3
(N) and 3 (S) are linearly expanded and shown. FIG. 3 shows the waveform of the cogging torque generated by the brushless DC motor. The upper part is a graph when the deviation angle θ4 is equal to the slot opening angle θ5 in the brushless DC motor of FIG. The lower part is shown for comparison and is a graph when the deviation angle θ4 is zero.
Since θ4 = θ5, it is necessary that θ5 ≦ (5/6) θ3 in order to satisfy 0.2 × θ5 ≦ θ4 ≦ θ3- (0.2 × θ5). However, since θ5 is usually about half or less than θ3, it can be considered that the above equation holds.

From the state of FIG. 2, consider the situation where the rotor rotates and the permanent magnets 3 (N), 3 (S) move to the right in the figure. At this time, the left end of the permanent magnet 3 (N) has a stator tooth 2-
Receives suction power from 1. This attractive force is generated by the permanent magnet 3 (N)
Acts as an obstacle to the rightward movement of. And
Due to the movement, the left end of the permanent magnet 3 (N) is the stator tooth 2.
When it reaches a position closer to the stator teeth 2-2 rather than -1, the left end of the permanent magnet 3 (N) receives a force in a direction to assist the movement. Stator teeth 2-
This is because the suction force from 2 becomes dominant. In this way, the left end of the permanent magnet 3 (N) generates a cogging torque that periodically repeats obstruction and auxiliary movement.

Similarly, the left end of the permanent magnet 3 (S) also produces a cogging torque. However, when the left end of the permanent magnet 3 (S) receives a force in the blocking direction in relation to the stator teeth 2-n, and when the left end of the permanent magnet 3 (N) receives the force in the blocking direction in relation to the stator teeth 2-1. There is a time lag between when the force is applied. The time difference is the deviation angle θ
It is a delay equivalent to four. There is a similar time difference in the timing of receiving the force in the assisting direction. Therefore, the cogging torque generated at the left end of the permanent magnet 3 (N) and the permanent magnet 3
There is a phase difference corresponding to the shift angle θ4 with the cogging torque generated at the left end of (S).

The upper graph of FIG. 3 shows this situation when the deviation angle θ4 is equal to the slot opening angle θ5. That is, in this graph, the thin solid line indicates the cogging torque TC1 generated at the left end of the permanent magnet 3 (N). The broken line indicates the cogging torque TC2 generated at the left end of the permanent magnet 3 (S). Further, the thick solid line shows the cogging torque TC0 of the combination thereof. The amplitude of the cogging torque TC0 is considerably smaller than the sum of the amplitudes of the cogging torques TC1 and TC2. This is because the cogging torques TC1 and TC2 have a time difference between their peaks due to the phase difference between them, and most of the torques cancel each other out.

This is shown in the lower graph of FIG. 3 (deviation angle θ4
When it is 0), the effect can be clearly understood. That is, in the lower graph, the amplitude of the cogging torque TC0 is the cogging torque TC1,
It is equal to the sum of the amplitudes of TC2 (which matches in the lower part of FIG. 3). This is because there is no phase difference between the cogging torques TC1 and TC2, both peak at the same time, and the torque is added as it is. That is, the effect of the present invention is that the amplitude of the cogging torque TC0 in the upper graph is significantly smaller than the amplitude of the cogging torque TC0 in the lower graph.

Incidentally, this kind of brushless DC motor is generally designed to make the slot opening angle θ5 as small as possible. This is because the magnetic resistance between the permanent magnets and the stator teeth is made as small as possible to secure a large interlinkage magnetic flux. On the other hand, this is a factor that makes the rate of change (the maximum gradient of the curve in the graph of FIG. 3) of the individual cogging torque (corresponding to TC1 and TC2) generated by each permanent magnet steep. Where the permanent magnet 3
If the shift angle θ4 between (N) and 3 (S) is equal to the slot opening angle θ5, the sudden change in individual cogging torque is effectively canceled. Therefore, the combined cogging torque (T
(Corresponding to C0) is small. Θ4 in the upper part of FIG.
This is the reason why the example in the case of = θ5 is shown. Further, the slot opening angle θ5 is 1 / of the slot pitch angle θ3.
If it is equal to 2, the cogging torques TC1 and TC2 have an antiphase relationship. In this case, both cogging torques cancel each other very well.

FIG. 4 shows a graph of the relationship between the deviation angle θ4 and the peak value of the combined cogging torque. In this graph, the horizontal axis represents the shift angle θ4. The range is from 0 to the slot pitch angle θ3. This is because when the shift angle θ4 is equal to the slot pitch angle θ3, the permanent magnet is shifted by one slot, which is the same as no shift. The vertical axis represents the peak value of the combined cogging torque. The scale of the vertical axis is a ratio based on the value when the deviation angle θ4 is 0. Further, in FIG. 4, two curves of TC0-1 (solid line) and TC0-2 (dotted line) are drawn. These two are due to the difference in the waveforms of the individual cogging torques (corresponding to TC1 and TC2). The curve TC0-1 is a case where the waveform is different at the time of rising and at the time of falling, that is, when the even harmonic components are included. The one in the graph of Fig. 3 belongs to here though it is not so remarkable. This is often the case in practice. The curve TC0-2 is when the waveform is symmetrical at the time of rising and at the time of falling, that is, when the even harmonic components are not included.

The following can be seen from the graph of FIG. As for the curve TC0-1, both ends (θ4 = 0, θ
4 = θ3), the value on the vertical axis is 1. This is because there is no gap. The value on the vertical axis decreases sharply if the point is slightly inward in the horizontal axis direction. This is due to the effect of offsetting the cogging torque due to the shift. The distance from both ends is 0.2 times the slot opening angle θ5 (θ4 = 0.2 ×
When θ5, θ4 = θ3− (0.2 × θ5)) is reached, the change in the value on the vertical axis is moderate inside. This is because the waveforms at the time of rising and at the time of falling are not completely offset. The minimum value of the vertical axis within this range is the center in the horizontal axis direction (θ4 = 0.5 × θ3), which is approximately half of both ends. From this, it is understood that the range of the deviation angle θ4 in which the effect of reducing the cogging torque is effectively obtained is 0.2 × θ5 ≦ θ4 ≦ θ3- (0.2 × θ5).

The curve TC0-2 in the graph of FIG.
Looking at, there is not much difference from the curve TC0-1 near both ends.
However, even within the range of 0.2 × θ5 ≤ θ4 ≤ θ3- (0.2 × θ5), the value on the vertical axis further decreases significantly. In the center (θ4 = 0.5 × θ3), the value on the vertical axis is almost 0.
Has become. This is because the cogging torque is more reliably canceled out because the waveform is symmetrical at the time of rising and at the time of falling.

As described above, the brushless DC shown in FIG.
In the motor, the deviation angle θ4 reduces the cogging torque as a whole. Further, in the brushless DC motor of FIG. 1, the magnetic pole having a deviation angle of 0 (permanent magnet 3 (N)) and the magnetic pole having a deviation angle of θ4 (permanent magnet 3 (S)) are arranged side by side. ing. For this reason, the center of gravity of the rotor 4 does not deviate much from the axis even though the permanent magnet 3 (S) has the deviation angle θ4. Therefore, the rotational balance of the rotating object is not so affected. Therefore, the rotation is smooth.

Although only the upper half of the rotor 4 is shown in FIG. 1, similarly in the lower half, one magnetic pole having a deviation angle of 0 and one magnetic pole having a deviation angle of θ4 are arranged as shown in FIG. It is better to set. By doing so, the rotor 4 as a whole has the same number of magnetic poles with a deviation angle of 0 and two magnetic poles with a deviation angle of θ4. Therefore, the cogging torque of the brushless DC motor as a whole can be reduced more effectively. Further, in the structure shown in FIG. 5, the magnetic poles having a deviation angle of 0 and the magnetic poles having a deviation angle of θ4 are arranged so as to exist at symmetrical positions. For this reason, when viewed in the circumferential direction, magnetic poles with a deviation angle of 0 and magnetic poles with a deviation angle of θ4 are present alternately. Therefore, the influence of the deviation angle on the position of the center of gravity of the rotor 4 is offset. Therefore, the center of gravity coincides with the axis, and the rotational balance is very good.

(Second Mode) Next, the second mode will be described. This embodiment employs a block configuration in which the rotor is divided in the axial direction. Here, an example of two divisions will be described. The rotor of the present embodiment includes the block shown in FIG.
It is composed of the block shown in FIG. The number of magnetic poles in each block is 4, which is the same as that shown in FIG. Since the stator is similar to that shown in FIG. 1, it is omitted in FIG.

In the block of FIG. 6 (a), the deviation angle at each magnetic pole is as follows. In the upper left magnetic pole (permanent magnet 311 (N)) in the figure, there is a deviation of an angle θ4 between the magnetic pole center line J1-1 and the effective magnetic pole opening angle center line K1-1. In the upper right magnetic pole (permanent magnet 312 (S)) in the figure, the magnetic pole center line J2-1 and the effective magnetic pole opening angle center line K2-1 coincide. In the lower right magnetic pole (permanent magnet 313 (N)) in the figure, there is a deviation of an angle θ4 between the magnetic pole center line J3-1 and the effective magnetic pole opening angle center line K3-1 as in the upper left magnetic pole. In the lower left magnetic pole (permanent magnet 314 (S)) in the figure, the magnetic pole center line J4-1 and the effective magnetic pole opening angle center line K4-1 are similar to the upper right magnetic pole.
Are consistent with. That is, there are two magnetic poles with a deviation angle of 0 and two magnetic poles with a deviation angle of θ4, which are alternately arranged in the circumferential direction.

In the block of FIG. 6 (b), the deviation angle at each magnetic pole is as follows. In the upper left magnetic pole (permanent magnet 321 (N)) in the figure, the magnetic pole center line J1-2 and the effective magnetic pole opening angle center line K1-2 coincide. In the upper right magnetic pole (permanent magnet 322 (S)) in the figure, there is a deviation of an angle θ4 between the magnetic pole center line J2-2 and the effective magnetic pole opening angle center line K2-2. In the lower right magnetic pole (permanent magnet 323 (N)) in the figure, the magnetic pole center line J3-2 and the effective magnetic pole opening angle center line K3-2 coincide with each other as in the upper left magnetic pole. In the lower left magnetic pole (permanent magnet 324 (S)) in the figure, between the magnetic pole center line J4-2 and the effective magnetic pole opening angle center line K4-2, the angle θ is the same as in the upper right magnetic pole.
There is a gap of 4. That is, the magnetic pole having a deviation angle of 0 and the deviation angle θ
There are two magnetic poles and two magnetic poles, which are arranged alternately in the circumferential direction. This is the same as that shown in FIG. 5 above.

When the two blocks are compared with each other, the presence or absence of the deviation angle is exchanged between the magnetic poles corresponding to the axial direction. Therefore, the brushless DC motor of this embodiment has the following effects. That is, in both blocks, as described above with reference to FIG. 5, the cogging torque is satisfactorily reduced and the rotation balance is also good. In addition, the presence or absence of the deviation angle is different between the magnetic poles corresponding to the axial direction, which has the following effect.
That is, when viewed as the whole rotor, the cogging torque is canceled in one magnetic pole (for example, the permanent magnet 311 (N) and the permanent magnet 321 (N)). Therefore, when viewed as a brushless DC motor as a whole, the individual cogging torque itself is reduced. Therefore, the cogging torque as a whole is very small.

Further, also in the rotational balance, the influence of the deviation is locally reduced in various parts of the rotor. Therefore, it is also suitable for applications where sudden acceleration or deceleration is required, and applications where high speed rotation is used. Also,
The magnetic poles corresponding to the axial direction have the same polarities of the permanent magnets, and some of them have a deviation and some do not. Therefore, when viewed as the entire brushless DC motor, the effective magnetic pole opening angle is substantially widened. The magnetic pole pitch of the rotor itself is evenly spaced. Further, in the gap between the rotor and the stator, the change in magnetic flux density in the circumferential direction is smooth.

(Third Mode) Next, a third mode will be described. In this embodiment, the rotor has six magnetic poles in the circumferential direction. The rotor of this embodiment has a structure shown in FIG. That is, the rotor 41 has 6
Magnet mounting holes 51 to 56 are provided at the locations, and the permanent magnets 31 to 56 are respectively provided in the magnet mounting holes 51 to 56.
36 is attached. Each permanent magnet 31-36
Adjacent ones are arranged so that their polarities are opposite to each other. The stator is not shown in FIG. 7 because it has no particular difference from that shown in FIG.

In the rotor 41, the deviation angle at each magnetic pole is as follows. Magnetic pole on the left side of the figure (permanent magnet 31
(N)), magnetic pole center line J11 and effective magnetic pole opening angle center line K
11 matches. The upper left magnetic pole (permanent magnet 32
(S)), magnetic pole center line J12 and effective magnetic pole opening angle center line K
There is a deviation of an angle θ4 with respect to 12. If the rotor 41 is rotated clockwise in the rotation direction, the K12 line is ahead of the J12 line by an angle θ4. Even in the magnetic pole (permanent magnet 33 (N)) in the upper right of the figure, there is a deviation of an angle θ4 between the magnetic pole center line J13 and the effective magnetic pole opening angle center line K13. However, the direction of the deviation is opposite to that of the upper left magnetic pole, and the K13 line is at a position behind the J13 line by the angle θ4. In the magnetic pole on the right side of the figure (permanent magnet 34 (S)), the magnetic pole center line J14 and the effective magnetic pole opening angle center line K14 coincide with each other like the magnetic pole on the left side. In the lower right magnetic pole (permanent magnet 35 (N)) in the figure, between the magnetic pole center line J15 and the effective magnetic pole opening angle center line K15,
Similar to the upper left magnetic pole, there is a deviation of an angle θ4 in the advancing direction.
In the lower left magnetic pole (permanent magnet 36 (S)) in the figure, there is a deviation of an angle θ4 between the magnetic pole center line J16 and the effective magnetic pole opening angle center line K16 in the delay direction as in the upper right magnetic pole.

That is, there are the same number of magnetic poles having a deviation angle of 0, a magnetic pole having a deviation angle θ4 in the advance direction, and three magnetic poles having a deviation angle θ4 in the delay direction. And, there is no magnetic pole having a deviation angle other than these three types. Also,
Magnetic poles having a deviation angle of 0 are arranged on both sides of the magnetic pole having a deviation angle of 0 (left side and right side).

In the brushless DC motor having the rotor 41 having the above structure, the cogging torque is canceled out as shown in the graph of FIG. In the graph of FIG. 8, thin solid lines indicate the cogging torque TC11 generated by the left and right magnetic poles in FIG. The broken lines indicate the cogging torque TC12 generated by the upper right and lower left magnetic poles in FIG. The alternate long and short dash line shows the cogging torque TC13 generated by the upper left and lower right magnetic poles in FIG. Further, the thick solid line shows the cogging torque TC10 obtained by combining these. Note that FIG. 7 shows the case where the size of the deviation angle θ4 is equal to 1/3 of the slot pitch angle θ3. As described above, in the present embodiment, the cogging torque is canceled in a three-phase synthetic manner. Therefore, the cogging torque TC10 in FIG. 7 is almost zero. Even if the individual cogging torque has an asymmetric waveform including even harmonic components, the cogging torque as a whole can be reduced very well. In addition, the effect is stable even if there is a slight distortion in the waveform or there is some variation in the size of the individual cogging torques.

Here, looking closely at the rotor 41 of FIG. 7,
The three magnetic poles adjacent to each other in the circumferential direction do not include those having the same deviation angle (including the direction). This holds for any three adjacent magnetic poles. Therefore, in the rotor 41, the influence on the rotational balance due to the misalignment is locally eliminated at various places. Therefore, it has excellent rotational performance.

(Fourth Mode) The fourth mode shown in FIG.
This is a combination of the second form and the third form.
That is, the number of magnetic poles is set to 6 and a block division structure is adopted. The rotor of this embodiment is composed of the block shown in FIG. 9A and the block shown in FIG. The stator will be omitted in this embodiment as well.

In the block of FIG. 9 (a), the deviation angle at each magnetic pole is as follows. In the magnetic pole (permanent magnet 31-1 (N)) on the left side of the drawing, the magnetic pole center line J11-1 and the effective magnetic pole opening angle center line K11-1 coincide. In the upper left magnetic pole (permanent magnet 32-1 (S)) in the figure, the magnetic pole center line J1
There is a deviation of an angle θ4 in the advancing direction between 2-1 and the effective magnetic pole opening angle center line K12-1. In the upper right magnetic pole (permanent magnet 33-1 (N)) in the figure, an angle θ4 is formed in the delay direction between the magnetic pole center line J13-1 and the effective magnetic pole opening angle center line K13-1.
There is a gap. Magnetic pole on the right side of the figure (permanent magnet 34-1
(S)), like the left magnetic pole, the magnetic pole center line J14-1
And the effective magnetic pole opening angle center line K14-1 are coincident with each other. In the lower right magnetic pole (permanent magnet 35-1 (N)) in the figure, between the magnetic pole center line J15-1 and the effective magnetic pole opening angle center line K15-1, the angle θ4 in the advancing direction is the same as in the upper left magnetic pole. There is a gap. In the lower left magnetic pole (permanent magnet 36-1 (S)) in the figure, between the magnetic pole center line J16-1 and the effective magnetic pole opening angle center line K16-1, an angle θ4 is formed in the delay direction in the same manner as the upper right magnetic pole. There is a gap. This is the same as that shown in FIG.

In the block of FIG. 9 (b), the deviation angle at each magnetic pole is as follows. In the magnetic pole on the left side of the figure (permanent magnet 31-2 (S)), an angle θ is formed in the delay direction between the magnetic pole center line J11-2 and the effective magnetic pole opening angle center line K11-2.
There is a gap of 4. The upper left magnetic pole (permanent magnet 32-2)
In (N), the magnetic pole center line J12-2 and the effective magnetic pole opening angle center line K12-2 coincide. In the upper right magnetic pole (permanent magnet 33-2 (S)) in the figure, between the magnetic pole center line J13-2 and the effective magnetic pole opening angle center line K13-2, the angle θ4 in the advancing direction is formed.
There is a gap. Magnetic pole on the right side of the figure (permanent magnet 34-2
(N)), the magnetic pole center line J14-
2 and the effective magnetic pole opening angle center line K14-2, there is a deviation of an angle θ4 in the delay direction as in the case of the left magnetic pole. In the lower right magnetic pole (permanent magnet 35-2 (S)) in the figure, like the upper left magnetic pole, the magnetic pole center line J15-2 and the effective magnetic pole opening angle center line K1.
5-2 matches. Magnetic pole in the lower left of the figure (permanent magnet 3
6-2 (N)), the magnetic pole center line J16-2 and the effective magnetic pole opening angle center line K16-2 have a deviation of an angle θ4 in the advancing direction as in the case of the upper right magnetic pole.

When the two blocks are compared with each other, the magnetic poles corresponding to the axial direction always have different deviation angles. Therefore, the brushless DC motor of this embodiment has the following effects. That is, in each of the blocks, as described above with reference to FIG. 7, the cogging torque is satisfactorily reduced and the rotation balance is also good.
In addition, since the deviation angle is different between the magnetic poles corresponding to the axial direction, the effect described in FIG. 6 is also obtained.
That is, when viewed as the entire rotor, the cogging torque and the rotational imbalance cancel each other out even within one magnetic pole. Therefore, the cogging torque as a whole is very small and the rotation balance is good.

(Fifth Embodiment) In this embodiment, instead of disposing the position of the permanent magnet, another means is used to cancel the cogging torque between the magnetic poles. Another means is
This is to provide convex portions corresponding to the magnetic poles on the outer edge of the rotor core, and to shift the position of each convex portion for each magnetic pole. The rotor 42 of this embodiment has a structure shown in FIG. Rotor 42
Has 4 magnetic poles, but unlike the previous ones,
Each permanent magnet is mounted in the center of each magnet mounting hole. That is, in all the magnetic poles, the magnetic pole center line (J21 etc.) and the effective magnetic pole opening angle center line (K21 etc.) coincide.

However, the rotor 42 has convex portions 61 to 64 corresponding to the respective magnetic poles on its outer circumference. Figure 10
Inside, L1-L4 have shown the centerline of each convex part seen from the rotation center axis O. In the upper left convex portion 61 in the figure, the convex center line L1 coincides with the magnetic pole center line J21 and the effective magnetic pole opening angle center line K21. In the convex portion 62 at the upper right of the figure, the convex center line L2 is at a position displaced from the magnetic pole center line J22 and the effective magnetic pole opening angle center line K22. The deviation angle is θ4. In the lower right convex portion 63 in the figure, the convex portion 61
Similarly, the convex center line L3 coincides with the magnetic pole center line J23 and the effective magnetic pole opening angle center line K23. In the convex portion 64 at the lower left of the figure, as in the convex portion 62, the convex center line L4 is
It is at a position deviated from the magnetic pole center line J24 and the effective magnetic pole opening angle center line K24 by an angle θ4. The convex portions 61 to 64 in FIG. 10 are exaggerated for ease of viewing. In reality, the step is very slight.

In the brushless DC motor using the rotor 42, in each magnetic pole, the gap between the rotor and the stator is smaller and the magnetic resistance is smaller at the convex portion than at the outside thereof. Therefore, since the magnetic flux concentrates on this portion, the convex portion also contributes dominantly to the generation of cogging torque. Therefore, the presence of the convex portion with the deviation angle and the convex portion without the deviation angle has the same effect of reducing the cogging torque as described in the first embodiment and the like.

Further, in this embodiment, since the permanent magnet is not provided with a gap, the following effects are also obtained.
That is, the deviation of the convex portion has a much smaller effect on the position of the center of gravity of the rotor than the deviation of the permanent magnet. Therefore, it has excellent rotational balance. In addition, since the permanent magnet is not provided with a gap, it is possible to use a permanent magnet as large as possible within the range of the magnet mounting hole.
Furthermore, it is possible to make the permanent magnet occupy the entire magnetic pole pitch. By doing so, a stronger rotational force can be obtained. Even if not so much, there is an advantage that there is a large degree of freedom in designing the brushless DC motor. Also, the cogging torque itself generated by one magnetic pole is smaller than that without a convex portion. This is because the end of the permanent magnet and the end of the convex portion each generate cogging torque, and there is a phase difference between them.

(Sixth Mode) In the sixth mode, both the permanent magnet and the convex portion are provided with a shift. Rotor 4 of this embodiment
3 is configured as shown in FIG. Rotor 43
Then, the deviation angle at each magnetic pole is as follows.
In the upper left magnetic pole (projection 611) in the figure, the magnetic pole center line J3
1, effective magnetic pole opening angle center line K31, and convex portion center line L1
All of 1 are in agreement. Magnetic pole (convex part 61)
In 2), the effective magnetic pole opening angle center line K32 and the convex portion center line L12 are both displaced from the magnetic pole center line J32 by the angle θ4. The magnetic pole center line J33, the effective magnetic pole opening angle center line K33, and the convex portion center line L13 all match in the lower right magnetic pole (projection 613) in the figure, as in the upper left magnetic pole. In the lower left magnetic pole (convex portion 614) in the figure, the effective magnetic pole opening angle center line K34 and the convex portion center line L14 are both displaced from the magnetic pole center line J34 by the angle θ4, similarly to the upper right magnetic pole. With the magnetic poles with deviation (upper right and lower left),
The deviation angle of the convex portion and the deviation angle of the permanent magnet are both θ4. Therefore, in any magnetic pole, the convex portion is located at the center with respect to the permanent magnet.

In the rotor 43, the cogging torque is reduced by the magnetic poles with deviation and the magnetic poles without deviation in both the permanent magnet and the convex portion. Further, since the centers of the permanent magnets and the convex portions of each magnetic pole are aligned, the following effects are obtained. First, the magnetic force of the permanent magnet can be used more effectively. This is because there is a convex portion in the center of the permanent magnet. Further, depending on the relationship between the angular difference between the end of the permanent magnet and the end of the convex portion and the slot pitch angle of the stator, it can be mentioned that the cogging torque can be canceled here as well.

(Modification) Next, a modification of the shapes of the rotor core and the permanent magnet will be described. FIG. 12 shows an application example in the case where there is a relatively large distance between the outer circumference of the rotor core and the permanent magnet. The rotor of FIG. 12 uses linear permanent magnets. Then, between the permanent magnets and the outer circumference of the rotor, there are substantially arcuate magnetic body regions 71 to 74. The outer edges of the magnetic material regions 71 to 74 are the effective magnetic pole opening angle M1.
Make ~ 4. In this rotor, the arrangement of the permanent magnets themselves is at the same pitch, and no offset is provided. However, the shapes of the magnetic regions 71 to 74 are different. That is, the upper right and lower left magnetic regions 72,
At 74, the magnetic pole center line J is symmetrical. Therefore, the magnetic pole center line J and the effective magnetic pole opening angle center line K coincide with each other. However, the upper left and lower right magnetic regions 71, 7
In No. 3, it is left-right asymmetric. Therefore, there is a deviation angle θ4 between the magnetic pole center line J and the effective magnetic pole opening angle center line K. Therefore, the cogging torque is reduced depending on the presence or absence of the deviation angle for each magnetic pole.

In FIG. 13, the permanent magnet in FIG. 12 is replaced with a curved type. Also in this rotor, there is a deviation angle for each magnetic pole due to the difference in the shape of the magnetic body region between the permanent magnet and the outer circumference of the rotor. This reduces the cogging torque. 12 or 1
The modification shown in FIG. 3 can be applied to any of the first to sixth embodiments. Further, the permanent magnet is not limited to that shown in FIG. 12 or FIG. 13, and may be replaced by a permanent magnet having any known shape or arrangement such as a V-shape, a V-shape (concave) with a bottom, a bow (inverted kamaboko) shape, and the like. . Further, it is also possible to arrange two (or more) permanent magnets inside and outside one magnetic pole.

As described above in detail, in the present embodiment, the deviation angle between the magnetic pole center line and the effective magnetic pole opening angle center line differs depending on the magnetic pole. This prevents the phases of the individual cogging torques generated by the magnetic poles from being aligned. Therefore, by canceling the individual cogging torques, a brushless DC motor in which the cogging torque as a whole is reduced is realized. Especially, by setting the difference θ4 of the deviation angle within the range of 0.2 × θ5 ≦ θ4 ≦ θ3− (0.2 × θ5) with respect to the slot pitch angle θ3 and the slot opening angle θ5, the cogging is effectively performed. The torque can be reduced.

Further, by considering the direction of the deviation angle, by providing a reference magnetic pole and three kinds of magnetic poles having the deviation angle in the advance direction and the delay direction with respect to the reference magnetic pole, the cogging torque is canceled out by three-phase synthesis. It is also possible to do so. In this case, in particular, even when the individual cogging torque has an asymmetric waveform or the like, the cogging torque can be significantly reduced. Further, in both cases of two-phase and three-phase, by providing the same number of magnetic poles at each deviation angle, a better effect can be obtained. Especially in the case of three-phase, all magnetic poles have one of three types of deviation angles,
Moreover, if the number of magnetic poles at each deviation angle is the same, the cogging torque as a whole can be practically reduced to nearly zero.

Further, if the magnetic poles adjacent in the circumferential direction do not have the same deviation angle, the influence of the deviation angle on the center of gravity of the rotor is reduced. This makes it possible to minimize the loss of rotational balance. In particular, in the case of three phases, the rotation balance can be maintained almost completely by including all three kinds of deviation angles in any three adjacent magnetic poles in the circumferential direction.

When the rotor has a block structure divided in the axial direction, the magnetic poles corresponding to the axial direction are arranged so that the deviation angles are different from each other, so that the cogging torque is reduced and the rotation balance is improved. There are merits in both maintenance.

Further, in order to reduce the cogging torque due to the difference in deviation angle, in addition to providing a deviation angle on the effective magnetic pole opening angle center line, a convex portion corresponding to the magnetic pole is provided on the outer circumference of the rotor, and the position of the convex portion It is also possible to provide a shift angle in the. In this case, shifting the position of the convex portion also has an advantage that the influence on the rotational balance is very small as compared with shifting the position of the permanent magnet.

The present embodiment is merely an example and does not limit the present invention. Therefore, naturally, the present invention can be variously improved and modified without departing from the gist thereof.

For example, in the first embodiment, a magnetic pole having no deviation between the magnetic pole center line and the effective magnetic pole opening angle center line and a magnetic pole having a deviation angle θ4 were considered. Is not mandatory. The point is that the relative difference in the deviation angle between the magnetic poles is a problem. Therefore, a magnetic pole having a deviation angle θ0 between the magnetic pole center line and the effective magnetic pole opening angle center line is used as a reference, and a magnetic pole having a deviation angle obtained by adding or subtracting θ4 to or from the deviation angle θ0 is provided. Good. The same applies to the convex part deviation angle as in the fifth or sixth embodiment. The convex deviation angle as in the fifth or sixth embodiment can of course be combined with the block division configuration.

[0064]

As is apparent from the above description, according to the present invention, the brushless D is capable of reducing the cogging torque without sacrificing the output characteristics.
A C motor is provided.

[Brief description of drawings]

FIG. 1 is a sectional view partially showing a structure of a brushless DC motor according to a first embodiment.

FIG. 2 is a diagram showing a relationship between magnetic poles of a rotor and stator teeth in the brushless DC motor of FIG.

FIG. 3 is a graph showing how cogging torque is combined in a brushless DC motor in comparison with that of FIG. 1 and the conventional one.

FIG. 4 is a graph showing a relationship between a deviation angle θ4 and cogging torque.

5 is a diagram showing an example of the overall structure of a rotor in the brushless DC motor of FIG.

FIG. 6 is a sectional view showing a structure of a rotor of a brushless DC motor according to a second embodiment.

FIG. 7 is a sectional view showing a structure of a rotor of a brushless DC motor according to a third embodiment.

FIG. 8 is a graph showing how cogging torque is combined in the brushless DC motor of FIG.

FIG. 9 is a sectional view showing a structure of a rotor of a brushless DC motor according to a fourth mode.

FIG. 10 is a sectional view showing a structure of a rotor of a brushless DC motor according to a fifth embodiment.

FIG. 11 is a sectional view showing the structure of a rotor of a brushless DC motor according to a sixth mode.

FIG. 12 is a sectional view showing a modified example of the structure of the rotor in the brushless DC motor of the present invention.

FIG. 13 is a sectional view showing another modification of the structure of the rotor in the brushless DC motor of the present invention.

FIG. 14 is a diagram showing an example of measures against cogging torque in a conventional brushless DC motor.

FIG. 15 is a diagram showing another example of measures against cogging torque in a conventional brushless DC motor.

[Explanation of symbols]

1 stator 2 stator teeth 3,31 etc. Permanent magnet 4, 41 etc. rotor 5, 51 etc. Magnet mounting holes 61-64 etc. Convex part J1 etc. Magnetic pole center line K1 etc. Effective magnetic pole opening angle center line L1 etc. Convex center line θ3 Stator slot pitch angle θ4 deviation angle θ5 Stator slot opening angle

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Minoru Kitabayashi             Aichi-cho, 2 Aichi-cho, Kasugai-shi, Aichi             Mason Electric Co., Ltd. (72) Inventor Tetsuo Horie             Aichi-cho, 2 Aichi-cho, Kasugai-shi, Aichi             Mason Electric Co., Ltd. (72) Inventor Hirohide Inayama             3-5-8 Minamisenba, Chuo-ku, Osaka-shi, Osaka               Koyo Seiko Co., Ltd. (72) Inventor Sadaaki Mori             3-5-8 Minamisenba, Chuo-ku, Osaka-shi, Osaka               Koyo Seiko Co., Ltd. (72) Inventor Atsushi Ishihara             3-5-8 Minamisenba, Chuo-ku, Osaka-shi, Osaka               Koyo Seiko Co., Ltd. F-term (reference) 5H019 AA03 CC03 CC08                 5H622 AA02 CA02 CA07 CA13 CB01

Claims (10)

[Claims] 1. A rotor in which a plurality of magnetic poles having permanent magnets mounted in magnet mounting holes are provided at equal pitches in the circumferential direction, and a stator in which a plurality of slots are arranged at equal pitches in the circumferential direction. In the brushless DC motor having the above, in the magnetic pole of the rotor, the angle formed by the center line of the effective magnetic pole opening angle and the center line of the magnet mounting hole (hereinafter, referred to as "magnet displacement angle") is the first angle. And a second angle, a brushless DC motor. 2. The brushless DC motor according to claim 1, wherein a difference θ between the second angle and the first angle.
4 is within the range defined by the following equation: 0.2 × θ5 ≦ θ4 ≦ θ3- (0.2 × θ5). θ3: Stator slot pitch angle θ5: Stator slot opening angle 3. The brushless DC motor according to claim 1 or 2, wherein the rotor has a magnetic pole having a magnet deviation angle of a first angle and a magnetic pole having a magnet deviation angle of a second angle. There are the same number of brushless DC motors. 4. Any one of claims 1 to 3
In the brushless DC motor according to the third aspect, the rotor is provided with a magnetic pole having a magnet deviation angle of a first angle and a magnetic pole having a magnet deviation angle of a second angle side by side. Brushless DC motor. 5. Any one of claims 1 to 3
In the brushless DC motor according to the third aspect, the rotor is configured to be divided into a plurality of blocks in an axial direction, and the magnetic pole has a magnet deviation angle of a first angle and the magnet deviation angle has a second angle. A brushless DC motor, wherein the magnetic poles are present at positions corresponding to the axial direction in different blocks. 6. The brushless DC motor according to claim 2, wherein the magnetic pole of the rotor has a third magnet deviation angle.
The angle between the third angle and the first angle is the same as the difference between the second angle and the first angle, and the signs are opposite. Brushless DC motor characterized by. 7. The brushless DC motor according to claim 6, wherein the rotor has a magnetic pole having a magnet deviation angle of a first angle and a magnetic pole having a magnet deviation angle of a second angle.
A brushless DC motor having the same number of magnetic poles each having a magnet deviation angle of a third angle. 8. The brushless DC motor according to claim 7, wherein the total number of magnetic poles of the rotor is an integral multiple of 6, and all the magnetic poles of the rotor are magnetic poles having a magnet deviation angle of a first angle. A brushless DC motor, characterized in that it is either a magnetic pole having a magnet deviation angle of a second angle or a magnetic pole having a magnet deviation angle of a third angle. 9. A rotor in which a plurality of magnetic poles having permanent magnets mounted in magnet mounting holes are provided at equal pitches in the circumferential direction, and a stator in which a plurality of slots are arranged at equal pitches in the circumferential direction. In the brushless DC motor having the above, the rotor has a protrusion corresponding to a magnetic pole on an edge thereof, and the magnetic pole of the rotor has an angle (hereinafter, referred to as an angle between a center line of the protrusion and a center line of the magnet mounting hole). A brushless DC motor characterized in that there are one having a first angle and one having a second angle. 10. A rotor in which a plurality of magnetic poles having permanent magnets mounted in magnet mounting holes are provided at equal pitches in the circumferential direction, and a stator in which a plurality of slots are arranged at equal pitches in the circumferential direction. In the brushless DC motor having, the rotor has a convex portion corresponding to a magnetic pole on an edge thereof, and the magnetic pole of the rotor has a magnet deviation angle and a convex deviation angle both being a first angle. , A brushless DC motor characterized in that both are at a second angle.