JP2003088078A - Brushless dc motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce torque pulsation due to cogging without decreasing efficiency or the maximum torque of a brushless DC motor. SOLUTION: The brushless DC motor comprises a large tooth section 10 having a large tooth width (θr) and a small tooth section 11 having a small tooth width (θs<θr) alternatively formed inside a stator core 1. When a surface permanent magnet type rotor arranged in the core 1 is rotated, positional relationships between poles of the rotor, tooth parts 10, 11 of the core 1 and a slot opening 13 are different between the poles, and hence the torque pulsation due to the cogging is dispersed. Accordingly, a change in composite torque is reduced. Further, a stator winding is wound at substantially the same pitch as a pole pitch (in a full-pitch winding), generated torque is increased to improve its efficiency.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a brushless DC.
The present invention relates to a motor, and more particularly to a motor used for home appliances, FA, in-vehicle equipment, and other applications requiring low torque fluctuation.

[0002]

2. Description of the Related Art In recent years, brushless DC motors have been widely used as small motors for home appliances, industrial equipment, and in-vehicle equipment. Most stator cores of such motors have slots. Because the winding is easy to wind in the slot, the manufacturing cost is low, and the generated torque acts on the tooth part of the core, and the winding is mechanically strong because no electromagnetic force acts on it. This is because it can be structured.

In a motor having a stator core with slots, as the rotor rotates, the magnets of the rotor alternately pass through the teeth of the stator core and the vicinity of the slot openings. Based on this, torque pulsation (cogging) occurs. Since this cogging impairs the smooth rotation of the rotor and causes noise and vibration, various measures for reducing cogging have been proposed as compared with the related art.

For example, there is a method in which the frequency of torque pulsation due to cogging is increased by increasing the number of slots, and a pulsation component is reduced by a low-pass filter formed by a mechanical time constant of the rotor.

As another method, the shape of the magnet and the magnetizing pattern are devised to gradually change the distribution of the magnetic resistance or the magnetic flux density in the circumferential direction in the gap, and the motor having such a structure is subjected to a sine wave. By driving, the effect of cogging accompanying a sudden change in magnetic resistance is reduced.

[0006]

However, although the above-mentioned method reduces cogging, it has the following problems.

That is, in the method of increasing the number of slots,
Since the opening of the stator core increases as the number of slots increases, the magnetic resistance of the gap between the stator core and the rotor poles becomes equivalently large, and as a result, the effective magnetic flux density decreases and the motor It causes the deterioration of the characteristics and efficiency.

Further, in a motor having a magnet shape and a magnetizing pattern devised, smooth rotation can be obtained when driven by a sine wave. A relatively expensive sensor is required, and control is complicated, resulting in high cost. On the other hand, when such a motor is driven by a rectangular wave energization method which is widely used because of its low cost and easy control, a large torque pulsation may occur due to the following reasons.

That is, in the rectangular wave energization method, it is desirable that the back electromotive force waveform generated in each winding is also a rectangular wave. At this time, the torque waveform generated as the product of the back electromotive force generated in the winding and the current also becomes a rectangular wave, the generated torque becomes maximum, and the rotational torque obtained by combining the torques of each phase is obtained. Is constant regardless of the rotation angle of the rotor. In order to generate such a back electromotive force by energizing a rectangular wave, it is necessary that the magnetic flux density distribution in the gap part by the magnet also has a rectangular wave shape, but in order to reduce cogging, the magnetic flux density distribution by the magnet Since the change is made gradual, the counter electromotive force waveform approaches a trapezoidal wave or a sine wave from a rectangular wave, and as a result, the generated torque is not constant and pulsates.

The present invention has been made in view of the above problems, and an object of the present invention is to reduce cogging without reducing the efficiency of a brushless DC motor and to reduce torque fluctuations during rectangular wave energization drive.

[0011]

According to a first aspect of the present invention, a ring having a plurality of teeth protruding inward and a plurality of slots formed between two adjacent teeth. A stator core formed in a circular shape, a multi-phase stator winding provided in the slot by a distributed winding method, and a permanent magnet having a plurality of magnetic poles arranged in the circumferential direction on the outer circumference, In order to achieve the above object, a brushless DC motor including a rotor disposed therein is characterized in that the tooth widths of the plurality of tooth portions are set to at least two types.

In the invention thus constructed, the tooth widths of the tooth portions provided on the stator core are not all the same, but tooth portions having two or more different tooth widths are mixed. Therefore, the relative positional relationship between the plurality of magnetic poles provided on the rotor and the tooth portions and the slot openings of the stator core is not the same for all the magnetic poles. Therefore, the timings at which the magnetic poles pass in the vicinity of the tooth portions and the slot openings are not coincident with each other, but are slightly shifted.

As described above, the cogging phenomenon is caused by the tooth portions and the slot opening portions having different magnetic resistances being alternately arranged in the gap portion, and the magnetic poles of the rotor passing in the vicinity thereof. Therefore, in the conventional motor in which the tooth widths of all the tooth portions are all equal, the timing at which each magnetic pole of the rotor passes in the vicinity of each tooth portion of the stator core and each slot opening is the same for all magnetic poles. A large torque pulsation is generated by adding all the cogging torques generated in each magnetic pole.

On the other hand, as in the present invention, the timing at which each magnetic pole passes through each tooth and each slot opening is deviated, so that the cogging torque generated at each magnetic pole is dispersed and the torque pulsation is reduced. . Moreover, since the frequency component of the torque pulsation due to cogging becomes high, the torque pulsation can be further reduced by the low-pass filter effect due to the mechanical time constant of the rotor.

According to a second aspect of the present invention, the stator core has a large tooth portion having a first tooth width and a small tooth portion having a second tooth width smaller than the first tooth width. The feature is that they are arranged alternately.

In the invention thus constructed, the tooth widths of the adjacent tooth portions are different, and the magnetic poles of the rotor alternately pass near the tooth portions having different tooth widths, so that the pulsating torque has a high frequency. It will contain many ingredients. Therefore, torque pulsation can be reduced by the low-pass filter effect due to the mechanical time constant of the rotor.

Further, since the tooth widths of the tooth portions are of two sizes, large and small, and they are arranged alternately, it is easy to arrange all the tooth portions at an equal pitch. The pitch of the wires can be made constant, winding of the winding becomes easy, and an increase in manufacturing cost can be suppressed.

The invention according to claim 3 is characterized in that the winding pitch of the stator winding is substantially equal to the pitch per magnetic pole of the rotor. In the invention thus constituted, the winding pitch of the stator winding and the magnetic pole pitch of the rotor are made substantially equal, that is, so-called full-pitch winding, so that the magnetic flux from each magnetic pole interlinking with each stator winding is maximized. Therefore, the counter electromotive force induced in each stator winding along with the rotation of the rotor becomes maximum, and the generated torque can also be maximized at this time.

The invention according to claim 4 is characterized in that the stator winding has three-phase windings and is driven by a 120 ° rectangular wave energization method.

In the invention thus constituted, rectangular wave-shaped currents flow in the respective stator windings by performing rectangular wave energization in which the phases of the three phases are shifted by 120 °. In addition, since the ring-shaped permanent magnets provided on the outer peripheral surface of the rotor also make the magnetic flux density distribution in the gap part rectangular, the counter electromotive force induced in each stator winding as the rotor rotates also becomes rectangular. . for that reason,
The torque that appears in proportion to the product of the current and the counter electromotive force also has a rectangular wave shape, the magnitude of which is maximum and is constant throughout the energization period per phase. By energizing the windings of each of the three phases by shifting the phase by 120 °, the combined torque obtained by adding the torques of the respective phases becomes constant regardless of the rotational position of the rotor, so that a rotational torque without pulsation can be obtained. You can

Further, such an energization method can be realized by a simple combination of on / off operations of a plurality of switching elements based on predetermined timing,
Moreover, since an inexpensive Hall IC can be used as the position sensor, the control and drive circuit can be configured easily and at low cost.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Brushless DC according to the present invention
As one embodiment of the motor, a brushless DC motor for electric power steering (hereinafter, simply referred to as “motor”) mounted on an automobile will be described below. Since the motors for such applications have severe requirements for low cogging torque and cost reduction, they are suitable for application of the present invention. FIG. 1 is a sectional view showing the structure of the brushless DC motor of this embodiment. 2 is a connection diagram showing the connection of the stator winding of this motor, and FIG. 3 is a diagram showing an example of the drive voltage waveform applied to this winding.

The motor of this embodiment is a three-phase brushless DC motor having three-phase stator windings, and as shown in FIG. 1, a stator core 1 having twelve teeth protruding inward, Four sets of stator windings U1 to U4, V1 to V4, W1 per phase wound by a distributed winding method in slots 12 formed between two adjacent tooth portions
It is composed of W4 and the rotor 2 arranged inside the stator core 1. Details of the structure of the stator core 1 will be described later.

As shown in FIG. 1, the rotor 2 is composed of a cylindrical rotor core 20 and four divided ring-shaped permanent magnets 21 to 24 attached to the outer peripheral surface of the rotor core 20. It is configured to rotate by a rotating magnetic field generated inside the stator core 1 by energizing a stator winding described later. Here, the permanent magnets 21 to
Instead of 24, a single ring-shaped permanent magnet having a plurality of magnetic poles arranged in the circumferential direction may be used.

The permanent magnets 21 and 23 are magnetized so that the outer side in the radial direction (the side facing the teeth of the stator core 1) becomes the N pole, while the other permanent magnets 22 and 2 are magnetized.
No. 4 is magnetized so that the S pole is on the outer side, and is attached to the outer peripheral surface of the rotor 2 so that the adjacent magnets have opposite polarities. Therefore, on the outer circumference of the rotor 2, a rectangular wave-shaped magnetic flux that changes over two cycles of N → S → N → S per rotation is distributed. That is, this motor is a surface permanent magnet (SPM) type motor having a four-pole rotor 2 having four magnetic poles, and an angle (magnetic pole pitch) ψ per magnetic pole is 90 °. And in this motor, the mechanical angle of 180 ° is 3 electrical angle.
It corresponds to 60 °.

Further, each stator winding U1 to U4, V1 to
As shown in FIG. 1, each of V4 and W1 to W4 is wound so as to straddle three tooth portions, and the winding pitch thereof is approximately 90 °, which substantially matches the magnetic pole pitch ψ of the rotor 2. Is configured to. These windings are shown in Figure 2.
As shown in FIG. 4, four pieces are connected in parallel for each phase and star-connected between each phase. For example, U
The four windings U1 to U4 forming the phase are connected in parallel with each other as shown in FIG.
One end of 4 is connected to the U-phase drive terminal U, while the other end is connected to the neutral point N. The same applies to the V phase and the W phase. Four windings for each phase are connected in parallel, one end of which is connected to each phase drive terminal V or W, and the other end is connected to the neutral point N. There is.

As shown in FIG. 1, the four stator windings of each phase are arranged at positions deviated from each other by 90 ° with respect to the central axis of the stator core 1.

The rotor 2 is rotated by energizing such a stator winding by a three-phase inverter drive device (not shown) by a 120 ° (electrical angle) rectangular wave energization method. For example, when a drive voltage having the waveform shown in FIG. 3 is applied from the inverter drive device to each phase drive terminal U, V, W, the direction of the input current due to this drive voltage is sequentially changed, and the stator core A rotating magnetic field rotating clockwise in FIG. 1 is generated in the gap G between the rotor 1 and the rotor 2, and a rotating torque acts on the rotor 2 by this rotating magnetic field, causing the rotor 2 to rotate clockwise in FIG. As described above, this motor has the rotor 2 with four poles, and the rotor 2 has a half rotation (180 in mechanical angle) for one cycle of three-phase energization (360 ° in electrical angle). °) will be done.

Next, the stator core 1 in this motor
The structure will be described in more detail with reference to FIGS. 4 and 5. FIG. 4 is a view showing a sectional structure of the stator core 1 in the motor of this embodiment. Further, FIG. 5 is a sectional structural view of a conventional stator core shown for comparison with this embodiment.

In this stator core 1, as shown in FIG. 4, the tooth widths of 12 tooth portions are not uniform. That is, the large tooth portion 10 having an angle θr at which the tip portion 10a is seen from the central axis of the stator core 1 and the angle at which the tip portion 11a is seen is θs.
Small tooth portions 11 of (θs <θr) are arranged alternately.
Corresponding to the width of the tip portion 10a of the large tooth portion 10 being larger than the width of the tip portion 11a of the small tooth portion 11, the widths of the respective base portions 10b and 11b are also equal to the tip portions 10a and 1b.
It is formed to have the same ratio as the tooth width of 1a.

The tooth portions 10 and 11 have different tooth widths as described above, but are arranged so that their center lines are arranged at equal pitches in the circumferential direction of the stator core 1. That is, one tooth 10 and the adjacent tooth 1
The angle formed by the respective center lines of 1 is constant at 30 ° for all the tooth portions.

A slot 12 is formed between these tooth portions 10 and 11, and each of the stator windings U1, U2,
, Are accommodated in the slots 12, but for the above reason, the pitch of the adjacent slots 12 is also constant at 30 °, so that the stator windings U1, U2, ... Can all have the same pitch. It is advantageous in terms of cost.
A slot opening 13 having an opening angle θo is provided between the tip ends 10a and 11a of the teeth.

Incidentally, the stator core 1 and the rotor core 2
Is formed of a high magnetic permeability material such as iron or silicon steel. In order to reduce the eddy current loss inside the core and improve the efficiency, a thin plate formed in the shape shown in FIG. 1 or 4 is used. It is desirable that the layers are stacked in the axial direction (direction perpendicular to the paper surface).

Hereinafter, in this embodiment, θr = 3
An example in which 0 ° (mechanical angle, the same applies hereinafter), θs = 22 °, and θo = 4 ° will be described, but these angles are not limited to this combination and do not depart from the scope of the present invention. It goes without saying that it may be modified appropriately.

Due to the combination of the above angles, in the stator core 1 of this embodiment, two large tooth portions 10 and
The angle θ1 = 90 ° = ψ formed by one small tooth portion 11 with respect to the center of the stator core 1, while the angle θ2 = 82 ° <ψ formed by two small tooth portions 11 and one large tooth portion 10. Has become.

In the motor having the stator core 1 having such a structure, the relative positional relationship between each magnetic pole of the rotor 2 and each tooth of the stator core 1 in the gap G is 4
Not the same for all two poles. For example,
In the rotor position shown in FIG. 1, the permanent magnets 21 and 23 attached to the rotor 2 and generating the N pole face one large tooth portion and two small tooth portions of the stator core 1. , S-pole generating permanent magnets 22 and 24
Faces two large tooth portions and one small tooth portion. Similarly, even when the rotor 2 is in another position, the permanent magnets 21 and 23 that generate the north pole and the magnet 22 that generates the south pole are generated.
And 24 are different in relative positional relationship with respect to each tooth portion of the stator core 1.

Therefore, the tooth portions 10, 1 of the stator core 1 are
1 between the torque pulsation acting on the permanent magnets 21 and 23 due to the cogging phenomenon accompanying the change in the positional relationship between the slot opening 13 and the magnetic poles of the rotor 2, and the torque pulsation acting on the permanent magnets 22 and 24, There will be a deviation in the timing of occurrence.

As described above, the generation timing of the torque pulsation is deviated, so that the pulsation in the combined torque obtained by adding the torques generated from the respective magnetic poles is dispersed, and the spectrum thereof contains a lot of high frequency components. Further, the rotor 2 and the motor load connected thereto have a mechanical time constant due to inertia, and the high-frequency component is attenuated by the filter effect due to this time constant, so the torque pulsation is further reduced and smooth rotation is achieved. Can be obtained.

On the other hand, in the prior art, as shown in FIG. 5, all the tooth widths of the tooth portions are equal. That is, the angle θc looking into the tip 101a of each tooth 101 from the central axis of the stator core 100 is the same for every tooth. Therefore, this stator core 100
The relative positions of the teeth of the stator core 100 and the slot openings with respect to the magnetic poles of the rotor disposed inside are
It is always the same among the four magnetic poles. Therefore, the torque pulsation acting on each permanent magnet due to the cogging phenomenon always occurs at the same timing, and the pulsation in the combined torque also becomes large by adding them.

Next, the torque generated when the motor of this embodiment is driven by the rectangular wave energization method will be described with reference to FIG. FIG. 6 is a schematic diagram in which the gap G in the vicinity of the stator winding U1 is linearly expanded along the circumferential direction.

In the motor of this embodiment, as shown in FIG. 6A, the winding pitch of the stator winding U1 (tooth portion 10
And effective winding pitch considering the tooth width of 11) θ1
Is selected to be 90 °, which is the same as the magnetic pole pitch ψ of the rotor 2. At this time, the magnetic flux from the permanent magnet 31 interlinking with the winding U1 becomes maximum, and the counter electromotive force induced in the stator winding U1 with the rotation of the rotor 2 is as shown by the solid line in FIG. 6 (c). The waveform is close to a rectangular wave. Therefore, the torque acting on the rotor 2 as the product of the counter electromotive force and the input current is maximum and is constant regardless of the position of the rotor 2.

On the other hand, in the conventional motor in which the tooth widths of all the tooth portions are constant, the effective winding pitch θ3 is smaller than the magnetic pole pitch ψ, as shown in FIGS. 5 and 6 (b). Therefore, the counter electromotive force has a waveform in which the shoulder portion is reduced as shown by the dotted line in FIG. 6C, and the torque acting on the rotor is reduced.

Here, an example of the result of an experiment conducted to verify the effect of reducing the cogging torque according to the present invention is shown in FIG.
And shown in FIG. In this experiment, the torque pulsation and the stator winding under the same driving condition were compared between the motor having the stator core having the shape shown in FIG. 4 and the conventional motor having the stator core having the shape shown in FIG. The back electromotive force waveform induced in the is actually measured. Here, FIG. 7 is a diagram showing a state of torque pulsation in both, and FIG. 8 is a diagram showing a counter electromotive force waveform induced in a one-phase winding in both.

As shown in FIG. 7, in the conventional core-shaped motor (FIG. 7A), the torque pulsation due to cogging has a large peak, whereas in the motor to which the present invention is applied (FIG. In b)), the torque pulsation due to cogging is dispersed and the large peak disappears, and the cogging reduction effect according to the present invention appears.

Further, as shown in FIG. 8 (a), in the conventional motor, the counter electromotive force waveform has a decrease in a flat portion and a swell near the zero cross, whereas the present invention is applied. In the motor, as shown in FIG. 8B, the counter electromotive force has a waveform closer to a rectangular wave, and it has been found that a larger torque can be generated.

As a result of actual measurement, the total torque fluctuation including fluctuations due to causes other than cogging was about 5.0% in the conventional motor, whereas it was about 4% in the motor to which the present invention was applied. As small as 0.3%, it was confirmed that the present invention has an effect of suppressing torque fluctuation.

Thus, in the motor of this embodiment,
The tooth widths of the tooth portions 10 and 11 formed on the stator core 1 are not all the same, and the large tooth portions 10 having a large tooth width and the small tooth portions 11 having a small tooth width are alternately arranged. As a result, the timing of the cogging torque generated in each magnetic pole due to the rotation of the rotor 2 is dispersed, and the high frequency component in the pulsation increases, so the torque pulsation is further reduced by the filter effect due to the inertia of the rotor 2. There is. Therefore, it is not necessary to increase the number of slots and to complicate the shape of the permanent magnet or the magnetizing pattern, which is a cause of a decrease in efficiency in the conventional technique, so that torque pulsation is reduced while maintaining high efficiency. It is possible to do.

Further, since the tooth widths of the tooth portions 10 and 11 are two kinds, large and small, and are alternately arranged at equal pitches, the structure of the stator core 1 is simple, and all the stator windings are arranged at the same pitch. Since it can be wound, the manufacturing cost can be kept low.

Further, the generated torque is maximized by making the winding pitch of the stator winding equal to the magnetic pole pitch, and the motor efficiency is further improved.

The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, the tooth widths of the large tooth portion 10 and the small tooth portion 11 and the opening angle θo of the slot opening portion 13 may be combinations other than the above numerical values.

In the motor of the above embodiment, the stator winding has three phases, the number of stator windings per phase is 4, the number of slots of the stator core 1 is 12, and the number of poles of the rotor 2 is 4. However, the combination of the number of winding phases, the number of windings per phase, the number of slots, and the number of rotor poles is not limited to this, and other combinations may be used. However, the number of slots is preferably an integer multiple of the number of phases and the number of windings per phase from the viewpoint of winding symmetry, and as described above, in order to increase the generated torque, the winding pitch Since it is preferable that the magnetic pole pitch be equal to the magnetic pole pitch, a combination satisfying these relationships is desirable.

[0052]

As described above, according to the first aspect of the present invention, since the tooth width of each tooth portion formed on the stator core is not uniform, each magnetic pole provided on the rotor has each tooth portion The timing of passing near each slot opening is deviated. Therefore, the cogging torque is dispersedly generated, and the pulsation includes a large amount of high-frequency components, so that the mechanical time constant of the rotor further attenuates the components, and the cogging torque can be reduced. it can.

Further, according to the invention described in claim 2, since the tooth widths of the adjacent tooth portions are different and the magnetic poles of the rotor alternately pass near the tooth portions having different tooth widths,
The pulsating torque contains many high frequency components. Therefore, torque pulsation can be reduced by the low-pass filter effect due to the mechanical time constant of the rotor. Further, by arranging all the tooth portions at an equal pitch and keeping the pitch of each stator winding constant, winding of the winding becomes easy, and an increase in manufacturing cost can be suppressed.

Further, according to the third aspect of the present invention, the stator winding and the rotor magnetic pole pitch are made substantially equal to each other, so-called full-pitch winding, so that the stator windings are interlinked. Since the magnetic flux from each magnetic pole is maximized, the counter electromotive force induced in each stator winding along with the rotation of the rotor is maximized, and the generated torque can also be maximized at this time.

According to the invention described in claim 4, the current flowing through each stator winding and the counter electromotive force induced in the winding both have a rectangular wave shape, and the torque generated as a product of these is generated. Maximum, and no pulsation due to rotor position occurs. Further, since the control can be performed using an inexpensive position sensor, the cost of the entire system can be reduced.

[Brief description of drawings]

FIG. 1 is a brushless DC according to an embodiment of the present invention.
It is sectional drawing which shows the structure of a motor.

FIG. 2 is a connection diagram showing a connection of stator windings of this motor.

FIG. 3 is a diagram showing an example of a drive voltage waveform applied to a stator winding of this motor.

FIG. 4 is a stator core 1 in the motor of this embodiment.
It is a cross-sectional view showing the structure of.

FIG. 5 is a sectional view showing a structure of a stator core in a conventional motor.

FIG. 6 is a schematic diagram in which a gap in the vicinity of a stator winding is linearly developed along the circumferential direction.

FIG. 7 is a diagram showing a state of torque pulsation in the conventional motor and the motor of the present invention.

FIG. 8: 1 in the conventional motor and the motor of the present invention
It is a figure which shows the back electromotive force waveform induced in the winding of a phase.

[Explanation of symbols]

1 Stator core 2 rotor 10 teeth (large teeth) 11 Teeth (small teeth) 12 slots 20 rotor core 21-24 Permanent magnet G gap U1-U4, V1-V4, W1-W4 Stator winding ψ Magnetic pole pitch

Claims (4)

[Claims] 1. A stator core formed in a ring shape having a plurality of teeth protruding inward and a plurality of slots formed between two adjacent teeth, and distributed winding in the slots. A brushless DC motor including a plurality of phases of stator windings provided in a wire system, and a rotor having a permanent magnet formed by arranging a plurality of magnetic poles in a circumferential direction on an outer periphery thereof and arranged inside the stator core, A brushless DC motor, wherein the tooth widths of the plurality of tooth portions are set to at least two types. 2. The stator core is configured by alternately arranging large tooth portions having a first tooth width and small tooth portions having a second tooth width smaller than the first tooth width. 1. The brushless DC motor according to 1. 3. The brushless DC motor according to claim 1, wherein a winding pitch of the stator winding is substantially equal to a pitch of each magnetic pole of the rotor. 4. The stator winding has a three-phase winding,
The brushless DC motor according to claim 3, wherein the brushless DC motor is driven by a 120 ° rectangular wave energization method.