JPH08126279A - Brushless dc motor - Google Patents

Abstract

PURPOSE: To increase the output torque constant of a brushless DC motor and decrease its torque ripple constant, by making the ratio of its magnetic-pole number to its salient-pole number specific in its permanent magnet, and by so forming the skew angle of its magnetic pole as to be represented as a specific electrical angle. CONSTITUTION: In a permanent magnet 9 of a brushless DC motor, the ratio of its magnetic-pole number to its salient-pole number is so formed as to be 1:3n (n is a natural number). For example, when the skew angle of its magnetic pole is represented as an electrical angle of 40 deg.-60 deg., a salient pole 31 is moved relatively from the position covered completely with one-pole (N pole) to the position covered completely with the neighboring one-pole (S pole), by the fact that a rotor 6 of the motor is rotated during the applying of a rectangular wave current to a coil 51. On the other hand, salient poles 32, 33 are moved relatively from the respective positions covered completely with respective one-poles to the respective positions covered completely with respective neighboring one-poles, by the fact that the rotor 6 is rotated during the applyings of respective rectangular wave currents to the coils 52. 53. Thereby, the motor is so controlled that three-phase rectangular wave currents each of which has the electrical angle of 120 deg. are applied in succession to the coils 51-53.

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 provided with a permanent magnet as a constituent element, and has a large output torque constant and a small torque ripple constant. Brushless DC configured
It concerns a motor.

[0002]

2. Description of the Related Art Conventionally, there are many kinds of motors as a drive source, but among them, a DC motor is small and has a large drive torque, and it is easy to control speed and positioning by using an electronic circuit. It has the excellent property of being able to However, since the brush for power feeding and the commutator slide, the brush is worn and sparks are generated. For this reason, it is impossible to operate for a long time of several thousand hours, and complicated maintenance work is required such that the brush must be replaced and the commutator surface must be machined every time a certain period of time elapses. In recent years, brushless DC motors that have solved such drawbacks have been widely used.

7 and 8 show a conventional brushless D
FIG. 3 is a longitudinal sectional view and an explanatory transverse sectional view of an essential part showing an example of a C motor, where 8 magnetic poles, 12 salient poles, (number of magnetic poles): (number of salient poles)
Is formed at 1: 1.5. 7 and 8, reference numeral 1 denotes a stator, for example, a stator formed by arranging, for example, twelve salient poles 3 in the circumferential direction at equal intervals in a case 2 formed in the shape of a hollow cylinder with a bottom. The core 4 is provided, and this salient pole 3
The coil 5 is wound around each.

Next, 6 is a rotor, and eight permanent magnets 9 formed in, for example, an arc segment are provided on the outer periphery of a holder 8 which penetrates the shaft 7, and magnetic poles having different polarities alternately in the circumferential direction. It is fixed so that it can be seen. Reference numeral 10 denotes a lid plate, which is fitted in the opening of the case 2 and rotatably supports the rotor 6 by the bottom portion of the case 2, the bearings 11 and 12 provided on the lid plate 10, and the shaft 7. Reference numeral 13 denotes a permanent magnet for position detection, which is formed, for example, in the shape of a disk and is fixed to one end face of the rotor 6, and the permanent magnet 9 is attached to the end face.
It is formed so that a magnetic pole having the same polarity as the above appears. Reference numeral 14 denotes a substrate, which is provided in the lid plate 10 and has a Hall element 15 and a drive circuit 16 mounted thereon, facing the permanent magnet 13. The three Hall elements 15 are mounted at intervals of 60 °, for example.

With the above structure, the hall element 15 detects the magnetic pole of the permanent magnet 9 constituting the rotor 6 by the position detecting permanent magnet 13 and outputs a signal, and the drive circuit 16 causes the stator 1 to generate a signal. Since the coils 5 are sequentially energized and energized, the rotor 6 rotates and the shaft 7 can drive an external device (not shown).

However, in the brushless DC motor having the above-described structure, the boundary line between the permanent magnets 9, 9 forming the rotor 6 is formed in a straight line parallel to the axis line in the axial direction, so that a so-called torque ripple is generated. However, there is a problem that the rotation of the rotor 6 is not smooth. Further, this torque ripple is generated irrespective of the rotation speed of the rotor 6 and causes vibration of the motor, and this vibration resonates with other components to induce noise. The effect becomes noticeable when the vehicle rotates at low speed.

As a means for eliminating the above torque ripple, there is a proposal in which the boundary line between the magnetic pole yokes 90, 90 constituting the rotor 6 is skewed as shown in FIG. 9 (for example, Japanese Utility Model Laid-Open No. 2-37553). (See gazette). By forming the magnetic pole yoke 90 of the rotor 6 in this way, it is possible to reduce torque ripple and prevent generation of undesired vibration or noise. In addition to the above-mentioned (number of magnetic poles) :( number of salient poles) of 1: 1.5, brushless DC motors of 1: 3 are widely put into practical use.

[0008]

As described above, in the conventional brushless DC motor, the ratio between the number of magnetic poles and the number of salient poles is 1: 1.5 or 1: 3, and the permanent magnet or the magnetic pole yoke is used. Those skewed are known. And the purpose of forming this skew is the conventional brushless D
The purpose was to reduce the torque ripple generated by the magnetic attractive force acting between the magnetic poles and the salient poles of the C motor.

However, although the torque ripple constant is reduced by forming the skew as described above, there is a problem that the output torque constant is reduced at the same time. In the present situation, no effective technical means has been found to suppress the decrease of the output torque constant due to the skew formation.

FIG. 10 is a diagram showing a relationship between a skew angle and a torque constant in a conventional motor. In FIG. 10, the skew angle on the horizontal axis is represented by an electrical angle, the curve a shows the torque ripple constant, and the curve b shows the output torque constant. FIG. 10 shows that the torque ripple constant gradually decreases as the skew angle increases. However, on the one hand it can be seen that the output torque constant also decreases.

Considering the cause of the decrease in the output torque constant as described above, for example, in FIG.
Observing any one salient pole 3a of the salient pole 3 around which any one coil 5a is wound, when no skew is added, the The entire pole 3a is completely covered by one arbitrary magnetic pole (for example, N pole 9a) of the permanent magnet 9 (closest to face) and is completely covered by an adjacent magnetic pole (for example, S pole 9b). The rotor 6 is relatively moved by the rotation of the rotor 6 until it comes into contact with each other. Then, by continuing this movement, a predetermined output torque constant can be obtained.

However, when the permanent magnet 9 is skewed, the boundary line between the permanent magnets 9 and 9 is displaced in the circumferential direction as in the case of the magnetic pole yoke 90 in FIG. At the time of
Any salient pole 3 will not be completely covered by any one magnetic pole with opposing permanent magnets 9. Therefore, the output torque constant gradually decreases as the skew angle increases, and the result shown by the curve a in FIG. 10 is obtained.

An object of the present invention is to solve the problems existing in the above-mentioned prior art and to provide a brushless DC motor having a small torque ripple constant and a large output torque constant.

[0014]

In order to achieve the above object, in the first aspect of the present invention, a coil is wound around a plurality of salient poles arranged in the circumferential direction by concentrated winding of salient poles. A rotor, which is formed by using permanent magnets so that magnetic poles having different polarities alternately appear in the circumferential direction, is rotatably interposed inside or outside the child, and the coil is arranged at an electrical angle of 3
In a brushless DC motor including a drive circuit for sequentially energizing with a rectangular phase-wave current, a ratio between the number of magnetic poles and the number of salient poles is set to 1: 3n (n is a natural number), and a skew angle of the magnetic poles is formed. Is formed at an electrical angle of 40 to 80 °,
I adopted the technical means.

Next, in the second invention, a permanent magnet is used inside or outside a stator formed by winding a coil around a plurality of salient poles arranged in a circumferential direction by concentrated salient pole winding. A rotor formed so that magnetic poles having different polarities alternately appear in the circumferential direction is rotatably interposed, and a drive circuit for sequentially energizing the coils with a three-phase rectangular wave current having an electrical angle of 120 ° is provided. In the brushless DC motor, the ratio between the number of magnetic poles and the number of salient poles is set to 1: 3n (n is a natural number), and the skew angle of the salient poles is 40 to 80 ° in electrical angle.
The technical means of forming it was adopted.

In the above invention, it is most preferable to form the skew angle at an electrical angle of 60 ° or 1/3 of the center angle of the arc of the magnetic pole because the torque ripple constant can be zero. The torque ripple constant in terms of motor characteristics is
In general, it is preferably 20% or less of the output torque constant, and therefore it is preferable to form the skew angle to an electrical angle of 40 to 80 °.

In the above invention, the cross-sectional shape of the permanent magnet can be formed into an arc segment shape or a ring shape. Further, in the above invention, the salient pole is formed so as to be completely covered by any one of the magnetic poles at the start and end of energization of the coil, and the skew angle is 40 to 40 in electrical angle. 60
Preferably, it is formed at a temperature of 90 degrees.

In the above invention, a known manufacturing method,
For example, by the sintering method, casting method, ultra-quenching method, bonded magnet method, etc.
A permanent magnet manufactured according to the above method can be used. Forever like this
As a magnet, a general formula expressing its basic composition is R-Fe-
B system and R-Co_FiveSystem, R ₂-Co₁₇System (R includes Y
One or more of the rare earth elements, necessary
Depending on Co, Al, Nb, Ca, Fe, Cu, Zr,
Known additives effective for magnetic properties of Ti, Hf, Ni, Si, etc.
One or more additional elements and O, C, H, N, etc.
Can contain one or more unavoidable impurity elements)
Rare earth magnets, ferrite magnets,
Of known permanent magnets such as Lunico magnets and Mn-Al-C magnets
One kind or two or more kinds can be used. these
Of these, it is particularly preferable to use an R-Fe-B system sintered magnet.
New

[0019]

With the above structure, any salient pole around which the coil is wound at the start and end of energization is covered with the one magnetic pole having the opposing permanent magnet, which is most closely opposed to the magnetic pole. In addition to the effect of drastically reducing the torque ripple constant due to, the magnetic attraction force between the salient poles and the permanent magnets can be secured to a predetermined value, and as a result, a predetermined output torque constant that is almost the same as when no skew is applied is obtained. It is possible.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a structural explanatory view showing an embodiment of the present invention. (A) shows a cross section of a main part, (b) shows a side surface of a main part of a rotor in (a), and the same parts are the same as the above. The same reference numerals as in FIGS. 7 and 8 are used. In FIG. 1A, the stator 1 has 24 salient poles 3 arranged at equal intervals in the circumferential direction, and the coils 5 are concentratedly wound on each salient pole 3. The magnetic pole pattern on the end surface 9e of the permanent magnet 9 in FIG. 1 (b) is shown by a broken line in the permanent magnet 9 in FIG. 1 (a).

Next, the permanent magnet 9 constituting the rotor 6 has N
d-Fe-B system sintered magnet (HS-3 manufactured by Hitachi Metals, Ltd.)
7BH), the cross section is formed into an arc segment shape, and at the central angle of the cross section, for example, θ in electrical angle.
= 55 ° skewed, NS on the outer surface in the circumferential direction
Eight pieces are fixed to the outer peripheral surface of the holder 8 so that the magnetic poles appear alternately. Note that 360 ° in FIG. 1 (a) is represented by an electrical angle.

With the above structure, the rotor 5 is rotated by sequentially energizing the coil 5 with a three-phase rectangular wave current having an electrical angle of 120 ° via a drive circuit (not shown) additionally provided. Can be done.

2A and 2B are development views of a permanent magnet in a brushless DC motor, where FIG. 2A shows a non-skewed one and FIG. 2B shows a skewed electrical angle θ. In FIG. 2, for example, if the coil (see reference numeral 5 in FIG. 1A) is concentrated salient pole winding, and three salient poles cover the same central angle as one magnetic pole, the solid line hatching on the magnetic pole The magnetic flux in the area A is linked to the salient poles. The output torque constant is generated at the relative position between the magnetic pole and the salient pole where the flux linkage changes.

Generally, a brushless DC motor aiming at high output torque is driven by a three-phase rectangular wave current having an electrical angle of 120 °, and a one-phase energization pattern is shown by an arrow. That is, the ON arrow indicates the coil 5 wound around any one of the salient poles 3 when the center of any one of the salient poles 3 shown in FIG. 1 (a) is in this range.
It means that electricity is being supplied to. In this case, if the magnetic poles are ideally switched at the relative positions of the salient poles 3 and the permanent magnets 9, there is no change in the interlinkage magnetic flux at the position of the region B shown by the hatching in broken lines, and the regions B and C are not changed.
In between, the coil 5 is energized, but there is a so-called ineffective portion where the output torque is not obtained.
However, in reality, the interlinkage magnetic flux waveform cannot be a perfect rectangular wave, so that some output torque is generated.

In the present invention, by utilizing the above-mentioned ineffective portion, the electrical angle θ (θ
= 40 to 80 °), and by forming in this way, the arbitrary salient pole 3 around which the coil 5 is wound at the start of energization and the end of energization is completely formed by any one magnetic pole. Will be covered by.

FIG. 3 is an explanatory view showing the relative positions of the permanent magnet and the salient pole in the embodiment of the present invention. In FIG.
Reference numerals 3A and 3B respectively indicate a start position and a end position of energization of the coil 5 of the arbitrary salient pole 3 in FIG. 1 (a).
It should be noted that 3C indicates an intermediate position of energization. That is, during energization of the coil 5, the arbitrary salient pole 3 around which the coil 5 is wound is between positions 3A and 3B in FIG.
At the start of energization and the end of energization, it can be completely covered by any one magnetic pole of the permanent magnet 9, for example, N pole or S pole.

FIG. 4 is a diagram showing the relationship between the skew angle and the torque constant in the embodiment of the present invention and corresponds to FIG. In FIG. 4, the skew angle is represented by an electrical angle. Further, in FIG. 4, the curve a represents the torque ripple constant, and the curve b represents the output torque constant. As is clear from FIG. 4, when the skew angle is increased, the torque ripple constant gradually decreases, becomes 0 at the skew angle of 60 °, and thereafter gradually increases. On the other hand, even if the skew angle is increased, the output torque constant can be maintained substantially constant (0.240 when the skew angle is 60 ° or less and 0.235 when the skew angle is 80 °).

As described above, the arbitrary salient pole 3 shown in FIG. 1 (a) is completely driven by one magnetic pole of the permanent magnet 9 at the start and end of the energization of the wound coil 5. Because it is covered. For example, the salient pole 31 of FIG.
When the skew angle is 40 to 60 degrees in electrical angle,
By rotating the rotor 6 while the rectangular wave current is being applied to the coil 51, the rotor 6 is relatively covered from a position completely covered by one magnetic pole (N pole) to a position completely covered by an adjacent one magnetic pole (S pole). Move to. On the other hand, the salient poles 32 and 33 are completely covered with one magnetic pole like the salient pole 31 as the rotor 6 rotates while the rectangular wave current is being applied to the wound coils 52 and 53, respectively. To the position where it is completely covered by one adjacent magnetic pole. The coils 51 to 53 are controlled so that a three-phase rectangular wave current having an electrical angle of 120 ° is sequentially applied.

In the above description, one magnetic pole and three salient poles 31 to 33 in FIG. 1 (a) were described, but all magnetic poles and all salient poles 3 shown in FIG. 1 (a) are described. Since the relative movement relationship in the above description is established over the above range, the torque ripple constant can be reduced and the output torque constant can be maintained substantially constant due to the increase in the skew angle as described above.

On the other hand, when the skew angle is in the range of more than 60 ° and less than 80 ° in terms of electrical angle, this arbitrary value is set at the start of energization of the coil 5 wound around an arbitrary salient pole 3 in FIG. 1 (a). The salient pole 3 may not be completely covered by one magnetic pole. However, since the torque ripple constant in this case is 20% or less of the output torque constant, and the decrease in the output torque constant is negligible and negligible, there is no practical problem.

FIG. 5 is a longitudinal sectional view of a main part showing another embodiment of the present invention. The one shown in FIGS. 1, 7 and 8 is called an inner rotor type, while the one shown in FIG. 5 is called an outer rotor type. In FIG. 5, reference numeral 21 denotes a stator, and, for example, 24 salient poles 23 are provided at equal intervals in the circumferential direction on the outer periphery of a holder 22 formed in a hollow cylindrical shape, and the coil 24 is concentrated on the salient pole 23. Roll and configure. Next, 25 is a rotor, and eight magnetic poles having different polarities appear alternately on the inner peripheral surface of the holder 26 formed in the shape of a hollow cylinder with a bottom, for example, in the form of a ring-shaped permanent magnet 27 in the circumferential direction. After being magnetized, it is fixed and configured.

A shaft 28 is fixed to the holder 26, and is fitted and inserted through a bearing 29 provided on the holder 22, so that the rotor 25 is attached to the stator 21 so that the permanent magnet 27 faces the salient pole 23. It is rotatably installed. Reference numeral 30 denotes a substrate, which is fixed to the holder 22 so as to face the open side of the rotor 25, and the substrate 30 is provided with the Hall element 34 and the drive circuit 32.

With the above structure, the Hall element 34 detects the magnetic pole of the permanent magnet 27 of the rotor 25 and outputs a signal, and the drive circuit 32 sequentially energizes the coil 24 of the stator 21 by this signal, The rotor 25 rotates and the shaft 28 drives an external device (not shown).

The salient poles 23 forming the stator 21 in FIG. 5 have a skew (for example, a skew angle of electrical angle θ = 6).
0 °) is attached. In this case, since the salient poles 23 are usually formed by stacking silicon steel plates, the salient poles 23 can be skewed by sequentially shifting and assembling them in the circumferential direction during stacking. When the skew angle is 40 to 80 in electrical angle, the magnetic pole of the permanent magnet 27 and the salient pole 23 are
The relationship with is similar to that in the above-mentioned embodiment.

FIG. 6 shows the permanent magnet 27 and the salient pole 2 in FIG.
It is explanatory drawing which shows the relative position with respect to 3, and corresponds to said FIG. In FIG. 6, 23A and 23B are the positions at which the salient pole 23 in FIG. 5 starts and ends the energization of the coil 24, and 23C indicates the intermediate position. That is, at the start of energization and the end of energization, any salient pole 23 around which the coil 24 is wound can be completely covered by, for example, one N pole of the permanent magnet 27. Therefore, the torque ripple constant can be reduced as in the above-described embodiment, and the output torque constant can be maintained at a predetermined value even if the skew angle is increased. The relationship between the skew angle and the torque constant is the same as that shown in FIG.

In the above-mentioned embodiment, an example was described in which the cross-sectional shape of the permanent magnet constituting the rotor was formed into an arc segment shape and a ring shape. However, for example, it was formed into an arc segment shape or a rod shape (block shape). A permanent magnet and a yoke material (non-magnetic material or magnetic material) may be combined to form a rotor, and a plurality of magnetic poles having different polarities may appear alternately in the circumferential direction of the rotor.

The skew angle may be provided on either the permanent magnet or the salient pole. The number of magnetic poles and the number of salient poles of the permanent magnet depends on the characteristics required for the brushless DC motor, and the ratio of the number of magnetic poles to the number of salient poles is 1: 3n (n is a natural number).
It can be arbitrarily set within the range. However,
From the viewpoint of magnetic characteristics, the number of magnetic poles is preferably 2 to 100,
4-36 poles are more preferable.

[0038]

EFFECTS OF THE INVENTION Since the present invention has the structure and operation as described above, the following effects can be obtained.

(1) Since the permanent magnet and the salient pole around which the coil is wound are skewed, the rotor rotates smoothly and the torque ripple constant can be greatly reduced.

(2) By keeping the skew angle within a predetermined range, it is possible to secure an output torque constant that is substantially the same as that when no skew is applied.

[Brief description of drawings]

FIG. 1 is a configuration explanatory view showing an embodiment of the present invention, (a)
Shows the cross section of the main part and (b) shows the side surface of the main part of the rotor in (a).

2A and 2B are development views of a permanent magnet in a brushless DC motor, where FIG. 2A is a diagram without a skew, and FIG. 2B is a diagram with a skew of an electrical angle θ.

FIG. 3 is an explanatory diagram showing relative positions of a permanent magnet and a salient pole in the embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between a skew angle and a torque constant in the example of the present invention.

FIG. 5 is a longitudinal sectional view of a main part showing another embodiment of the present invention.

6 is an explanatory diagram showing relative positions of a permanent magnet 27 and a salient pole 23 in FIG.

FIG. 7 is a longitudinal sectional view of an essential part showing an example of a conventional brushless DC motor.

FIG. 8 is a cross-sectional explanatory view of a main part showing an example of a conventional brushless DC motor.

FIG. 9 is an explanatory diagram showing an example of a conventional rotor in which a magnet yoke is skewed.

FIG. 10 is a diagram showing a relationship between a skew angle and a torque constant in a conventional motor.

[Explanation of symbols] 3,23 salient poles 9,27 permanent magnets

Claims (5)

[Claims] 1. A permanent magnet is used to alternately polarize in a circumferential direction inside or outside a stator formed by winding coils by salient pole concentrated winding around a plurality of salient poles arranged in a circumferential direction. In a brushless DC motor, the rotor formed so that different magnetic poles appear is rotatably interposed, and a drive circuit for sequentially energizing the coils with a three-phase rectangular wave current with an electrical angle of 120 ° is provided. The brushless DC motor is characterized in that the ratio between the number of the poles and the number of the salient poles is formed to be 1: 3n (n is a natural number), and the skew angle of the magnetic poles is formed to an electrical angle of 40 to 80 °. 2. A permanent magnet is used to alternately polarize in a circumferential direction inside or outside a stator formed by winding a coil around a plurality of salient poles arranged in a circumferential direction by concentrated winding of salient poles. In a brushless DC motor, the rotor formed so that different magnetic poles appear is rotatably interposed, and a drive circuit for sequentially energizing the coils with a three-phase rectangular wave current with an electrical angle of 120 ° is provided. The brushless DC motor is characterized in that the ratio between the number of the salient poles and the number of the salient poles is set to 1: 3n (n is a natural number), and the skew angle of the salient poles is set to an electrical angle of 40 to 80 °. 3. The brushless DC motor according to claim 1, wherein the permanent magnet is formed in an arc segment shape in cross section. 4. The brushless DC motor according to claim 1, wherein the permanent magnet has a ring-shaped cross section. 5. The salient pole is formed so as to be completely covered by any one of the magnetic poles at the start and end of energization of the coil, and the skew angle is 40 to 60 in electrical angle. The brushless DC motor according to any one of claims 1 to 4, wherein the brushless DC motor is formed at a temperature of 5 °.