JPH07108084B2 - Abduction type brushless DC motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention uses a stator yoke having a salient pole structure in which a plurality of plate-shaped ferromagnetic bodies are laminated, and the number of magnetic poles of a rotor magnet and the stator winding are applied. The present invention relates to a brushless DC motor that satisfies a certain ratio with the number of salient poles. Here, the stator yoke is set so that the cross-sectional area A of one salient pole portion around which the stator coil is wound and the circumferential length L thereof maintain a specific relationship, whereby an iron core is used even in a small motor. The effect (that is, improvement in magnetic circuit efficiency) can be sufficiently obtained.

Since this brushless DC motor can secure a space for incorporating a rotor magnetic pole position detector and attached electronic circuit parts, it is suitable for miniaturization and thinning (for example, about several W or less and about 10 mm or less in thickness). It is useful for spindle motors.

[Conventional technology]

It is well known that the magnetic circuit efficiency of a motor is improved by using a ferromagnetic material such as an iron plate as a winding core of a stator coil (of course, the iron plate and the coil are electrically insulated). An example of a motor utilizing this principle is an outer rotor / radial gap type brushless DC motor. The stator yoke is formed, for example, by stacking a plurality of plate-shaped ferromagnetic bodies in which a large number of salient pole portions are formed radially outward from a ring-shaped portion in the axial direction of the motor, and subjecting the salient pole portions to insulation treatment to form a stator coil. It has a wound structure.

In recent years, demand for smaller, thinner, and lighter motors of this type has been increasing with the progress of electronics. In this case, the cross-sectional area of the salient pole portion around which the stator coil is wound is determined by the magnetic flux density in relation to the material of the ferromagnetic material used, but no special consideration is given to the cross-sectional shape. .

[Problems to be Solved by the Invention]

In order to make the brushless DC motor smaller (output less than several W) and thinner (thickness less than 10 mm), a rotor magnetic pole position detector (Hall element etc.) and a plurality of small motor drive motors must be installed inside the motor. It is necessary to secure a space for housing electronic components. Further, it is desirable to reduce the number of salient stator poles in order to shorten the winding work time as much as possible. For these reasons, it has become difficult to construct an efficient magnetic circuit with a motor having a conventional structure.

An object of the present invention is to solve such a problem, and to reduce the excitation loss accompanying the coil excitation as much as possible and to reduce the magnetic resistance of the coil winding portion in the iron core type small and thin motor, thereby reducing the magnetic flux in the air gap. It is an object of the present invention to provide a brushless DC motor and a stator yoke thereof in which a yoke shape that maximizes the density is devised so that the effect of using an iron core can be sufficiently brought out and the weight thereof can be reduced.

[Means for Solving the Problems]

In order to solve such a technical problem, in the present invention, a factor called a cross-sectional shape characteristic coefficient was introduced, and an examination was conducted to find an optimum structure by simulation and experiment.

First, the base motor structure is the number of magnetic poles P of the rotor magnet.
(P is an even number) and the number of salient poles N to which the stator winding is applied (N is an integer multiple of the number of phases) is a brushless DC motor satisfying a relationship of N / P <1. A particularly preferred structure is such that the N / P is about 0.75. The stator yoke is formed by laminating a plurality of plate-shaped ferromagnetic bodies and winding a stator coil around the salient pole portions. Here, when the cross-sectional area of the coil winding portion of the salient pole portion is A and the peripheral length surrounding the cross-section is L, the factor of the cross-sectional shape characteristic coefficient R (R = L ² / A) is introduced in the present invention. And that is 4π ≦ R ≦ 16.3
Is configured to satisfy the relationship.

There are various possible cross-sectional shapes of the coil winding portion of the salient pole portion, but the circular shape is the most preferable in consideration of only the characteristics. The shape may be a square shape or a rectangular shape, but in that case, it is preferable to form chamfers or cutouts at four corners.

[Action]

In a magnetic circuit having a constant average magnetic path length and a constant length for winding a coil, it is preferable to make the cross-sectional area of the coil winding portion as large as possible. This is because the magnetic resistance decreases. However, generally, there is a limit to increase the cross-sectional area due to the convenience of winding the coil, and if it is excessively increased, the weight becomes large, which is not preferable. Therefore, it can be inferred that the cross-sectional shape is an important factor in obtaining the necessary minimum cross-sectional area.

In the present invention, the ratio P / N between the number P of poles of the rotor magnet and the number N of salient poles on which the stator winding is applied is set to be smaller than 1. When the required cross-sectional area of the stator yoke iron core is determined, the coil length per turn is shortened by setting the iron core cross-sectional shape so that the circumference surrounding the cross section is as short as possible. Is smaller and the voltage drop inside the motor is smaller. This improves motor efficiency.

In the present invention, in order to numerically capture the cross-sectional shape, a factor called a cross-sectional shape characteristic coefficient R is used, which is defined as R = L ² / A by the cross-sectional area A and the peripheral length L, which is 4π. ≤ R
The relation ≦ 16.3 is satisfied. From the above description, in the brushless DC motor having the same size and the same structure, the smaller the sectional shape characteristic coefficient R, the higher the motor efficiency. The minimum value of this coefficient is 4π ≈ 12.6 (in the case of a circle),
From the simulation and experiment, the maximum value is 1 in the present invention.
Up to 6.3. When the sectional shape characteristic coefficient R is set within this range, the motor efficiency is sufficiently high. In particular, when the cross section is rectangular, it is preferable to chamfer or cut off the four corner portions to reduce the cross-sectional shape characteristic coefficient R as much as possible.

To configure a smaller and thinner motor, the maximum value of the central angle θ formed by the coil winding part of the salient pole part can be set within the range of 0 <θ ≦ (1 / 2.5) × (360 ° / N). For example, the space between the salient poles in the stator and the salient poles can be widened in combination with the limitation of the N / P, and the rotor position magnetic pole detector and the attached electronic circuit can be efficiently accommodated in the space,
A highly efficient, compact, thin, and lightweight motor can be obtained.

〔Example〕

FIG. 1 is an exploded perspective view showing an embodiment of a brushless DC motor according to the present invention. This motor has a rotor pole number P
16, Outer rotor / radial gap type three-phase brushless DC with 16 stator salient poles N, N / P = 0.75, θ = 10.8 °
It is a spindle motor.

The motor is mainly composed of a housing 1, a drive circuit board 2, a stator 3, a rotor 4 and the like. The housing 1 houses a bearing 5 that rotatably supports the rotor 4, and the stator 3
It is a frame body made of aluminum that fixes the drive circuit board 2 and the drive circuit board 2 with screws. The drive circuit board 2 has an electric circuit necessary for driving a three-phase brushless DC motor, and has electronic components such as an integrated circuit, a hall sensor, a resistor, and a capacitor mounted thereon. It should be noted that these electronic components are preferably housed in the motor as much as possible in order to meet the demands for smaller and lighter motors. The stator 3 is obtained by insulating each salient pole portion of a stator yoke 6 having a plurality of salient pole portions radially formed from a ring-shaped portion and winding a stator coil 7 around the salient pole portion. The drive circuit board 2 and the stator 3 are fixed to the housing 1 with set screws 8. In the rotor 4, a ring-shaped magnet 10 is bonded to the inner circumference of a rotor yoke 9 made of a ferromagnetic material, and a shaft 11 is fixed to the central portion. Rotor 4
Are rotatably supported by bearings 5 mounted on the housing 1.

The present invention is characterized by the cross-sectional shape of the coil winding portion of the stator 3, particularly the salient pole portion of the stator yoke 6. The details of the stator yoke 6 are shown in FIG. A plurality of stator yokes 6 (12 in this embodiment) are provided outward from the central ring-shaped portion 15.
The present invention has a structure in which the salient pole portion 16 of this) extends radially, and a plurality of silicon steel plates (four in this embodiment) are laminated and fixed in the axial direction by press-punching silicon steel plates. As described above, at least the coil winding portion of each salient pole portion 16 is subjected to insulation treatment, and the stator coil having the required winding specifications is wound thereon.

The salient pole portion 16 of the stator yoke 6 generally has a smaller cross-sectional area than other magnetic circuit portions due to the winding of the coil.
The magnetic flux density is the highest in the magnetic circuit, and its value is a problem. Therefore, particularly in the case of a brushless DC motor with a small size (about several W of output) and a thin type (thickness of about 10 mm or less), a space for incorporating a rotor magnetic pole detector (Hall element, etc.) is required. It is difficult to secure a sufficient iron core cross-sectional area due to the restriction of.

However, in the present invention, attention is paid to the cross-sectional shape of the salient pole portion 16 of the stator yoke 6, and the cross-sectional shape characteristic coefficient R is defined by the following equation using the cross-sectional area A and the peripheral length L surrounding it. We adopted a method to evaluate the size.

R = L ² / A According to this expression, the smaller the cross-sectional shape characteristic coefficient R, the larger the surrounding cross-sectional area at the same circumference. This means that if the conditions on the coil side are the same, the magnetic flux density in the ferromagnetic material can be suppressed low. As a result, the magnetic potential drop at the salient pole portion 16 of the stator yoke is reduced, and the magnetic flux density in the air gap can be correspondingly increased. On the other hand, if the conditions on the magnetic circuit side are the same (the cross-sectional area of the salient pole portion is constant), the coil magnetomotive force can be increased. Therefore, in any case, the smaller the cross-sectional shape characteristic coefficient R, the higher the torque constant and the lower the current are expected, and the motor efficiency is consequently improved.

3 to 7 show examples of the sectional shape of a salient pole portion having a total thickness of 2.0 mm obtained by laminating four silicon steel plates having a thickness of 0.5 mm.

It can be easily mathematically proved that the minimum value of the sectional shape characteristic coefficient R is finite and the sectional shape is a circle as shown in FIG. At this time, the value of the cross-sectional shape characteristic coefficient R is 4π≈12.6
Is.

Although the cross-sectional shape of the salient pole portion 16 for winding the coil is arbitrary, it is a small and thin three-phase brushless as described in FIG.
DC motors are often rectangular because they are used by stacking pressed silicon steel plates. If the cross-sectional shape is a quadrangle, the minimum value of the cross-sectional shape characteristic coefficient R is a square as shown in FIG. 4, and the value is 16. Therefore, it is about 27% larger than the circular case.

Fig. 5 shows a rectangle with a short side of 2.0 mm and a long side of 2.5 mm. In this case, the cross-sectional shape characteristic coefficient R is about 16.2, which is a slight increase of 1.25% as compared with the case of the square shown in FIG.

Fig. 6 shows a shape in which four corners of a rectangular cross section are chamfered with 0.5R. In this case, the cross-sectional shape characteristic coefficient R is about 13.8, which is smaller than that of the square cross-section. 7th
The figure shows four corners of a rectangular cross section cut off linearly. The cross-sectional shape factor R in this case is approximately 14.4.
Becomes smaller than that of the square cross section. It can be seen that even in the case of a rectangular cross section as described above, the sectional shape characteristic coefficient R can be reduced by chamfering or cutting off the corner portion.

The effect of such a cross-sectional shape characteristic coefficient R on the motor characteristics will be described by the results obtained by simulation and experiment. The motor is the outer rotor three-phase brushless DC motor shown in FIG. 1, and the rotor magnet magnetic pole number P = 16, salient pole number N = 12, and θ = 10.8 °. Salient pole portion of stator yoke 6
The cross-sectional shape of 16 is a quadrangle, and the ratio of the short side to the long side x
FIG. 8 shows simulation results of the rate of change Dr of the cross-sectional shape characteristic coefficient R and the motor braking constant D with respect to the change of (= short side / long side) in 0 <x ≦ 1. In the DC motor, the braking constant D is expressed by the following equation by the torque constant k _T , the induced voltage constant k _E and the winding resistance r.

D = k _T · k _E / r Here, the braking constant D is used as the motor characteristic value because the torque constant k _T , the induced voltage constant k _E, and the winding resistance r change due to the change of the sectional shape characteristic coefficient R. Therefore, the braking constant D
It is because it was considered optimal to evaluate by. A large braking constant D means that the ratio of speed fluctuations to torque fluctuations is small, and motors of the same size and structure are excellent.

In the brushless DC motor having the same size and the same structure, the rate of change of the braking constant Dr shown in FIG. If only aspect ratio is changed, Dr is set when x = 1
= 1 (expressed as a so-called rate of change), and was simply calculated based on the following two conditions in the range of 0 <x ≦ 1.

The conditions on the magnetic circuit side are the same even if the ratio of the short side / the long side changes. That is, the cross-sectional area A of the salient pole portion is constant.

Use motors with the same winding resistance. That is, when the circumference per turn is short, the number of turns is increased until the resistance value becomes the same.

From FIG. 8, the cross-sectional shape characteristic coefficient R increases sharply as the ratio x of short sides / long sides decreases, but gradually decreases as x approaches 1, and approaches the minimum value 16. On the other hand, the braking constant change rate Dr, contrary to the sectional shape characteristic coefficient R, sharply decreases as x decreases, but gradually increases as x approaches 1, and approaches the maximum value 1. As much as possible as Dr (1 (10
0%, that is, square) is desirable, but practically 1
This is the limit because there is no noticeable difference until 0% down. The braking constant D at this time is R = 16.3 or less,
It can be seen that the value rapidly approaches a fixed value.

FIG. 9 shows the result of a trial experiment. 8 from the same figure
It can be seen that the tendency is almost the same as that shown in the figure.

From FIG. 8 and FIG. 9, the cross-sectional shape characteristic coefficient R is substantially
It can be seen that the braking constant D decreases little as a motor up to 16.3 or less (especially in the case of a quadrangle, the short side / long side is 0.75). As described above, when the value of the cross-sectional shape characteristic coefficient R is set to 16.3 based on the simulation and experiment, the motor braking efficiency is reduced because the decrease in the motor braking constant is small.

The present invention is not limited to the above embodiment. In particular, the reduction of the cross-sectional shape characteristic coefficient by cutting off the chamfer at the corner is effective regardless of the shape and size of the embodiment. The present invention can be applied to the case where there are holes, grooves, etc. parallel to the direction in which the magnetic flux passes, and the same effect can be obtained by reducing the sectional shape characteristic coefficient R. The structure of the stator yoke, that is, the shape corresponding to the type of motor and the number of salient poles are not limited to the structure of the above-described embodiment.

〔The invention's effect〕

According to the present invention, as described above, N / P (the number of salient poles on which the stator winding is applied / the number of magnetic poles of the rotor magnetic pole) is smaller than 1, and the cross-sectional area of the coil winding portion of the salient pole portion is A. When the surrounding length is L, the cross-sectional shape characteristic coefficient R = L ² / A
Is a brushless DC motor that satisfies the relationship of 4π ≦ R ≦ 16.3, so that the excitation loss accompanying the coil excitation of the motor is reduced, and the Tokle constant and the induced voltage constant can be increased. Further, if the maximum value θ of the angles formed by the coil winding part of the salient pole part is set to (1 / 2.5) × (360 ° / N) or less, a space is created between the salient poles in the stator, The rotor magnetic pole position detector and attached electronic circuit parts can be effectively accommodated in the space, which is highly effective in miniaturization and thinning.

Further, in the present invention, when the same magnetomotive force is generated, the coil length per turn can be shortened, so that the total length of the coil can be shortened, resulting in cost reduction.

Furthermore, when the salient pole portion has a quadrangular cross-sectional shape, the difference in length between the short side and the long side is small, the number of coil breakages during winding work is reduced, and efficient winding is possible.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a schematic configuration of an embodiment of a brushless DC motor according to the present invention, and FIG. 2 is a partially cutaway perspective view showing a stator yoke used therein. 3 and 4
FIG. 5, FIG. 6, FIG. 6 and FIG. 7 are explanatory views showing examples of the sectional shape of the salient pole portion. Further, FIG. 8 is a graph showing the relationship between the ratio x of the short side / long side of the salient pole portion, the section shape characteristic coefficient R, and the motor braking constant change rate Dr, and FIG. 9 is the short side of the salient pole portion /
6 is a graph showing a relationship between a ratio x of long sides and a motor braking constant D. 1 ... Housing, 2 ... Drive circuit board, 3 ... Stator, 4 ... Rotor, 6 ... Stator yoke, 7 ... Stator coil, 9 ... Rotor yoke, 10 ... Rotor magnet,
11 …… Shaft, 15 …… Ring-shaped part, 16 …… Salient pole part.

Claims (4)

[Claims] 1. An outer rotation brushless DC motor having a rotor (4) and a stator (3), wherein a rotor magnet (10) is attached to an inner peripheral surface of a rotor yoke (9). , The shaft (11) is fixed to the central part, and the stator (3) has a plurality of plate-shaped ferromagnetic bodies provided with a central ring-shaped part (15) and a plurality of salient pole parts (16) radially. The stator yoke (6) is laminated, and the stator coil (7) wound around each salient pole portion (16) is provided between the tip of the salient pole portion (16) and the rotor magnet (10). And has an air gap in the radial direction, and the number N of salient poles of the stator yoke (6) (N is an integer multiple of the number of drive phases) is N / with respect to the number P of magnetic poles of the rotor magnet (10) (P is an even number). The relation of P <1 is satisfied, the cross-sectional area of the coil winding portion of the salient pole portion (16) is A, and the peripheral length surrounding the cross-section is L. At this time, the cross-section shape factor R = L ² / A satisfies the relationship of 4π ≦ R ≦ 16.3, and is an outer rotation type brushless DC motor. 2. The stator (3) has a central angle formed by a coil winding portion of a salient pole portion (16), where θ is a maximum value, θ ≦ (1 / 2.5) × (360 ° / N) The outer rotation type brushless DC motor according to claim 1, which satisfies the relation. 3. The abduction-type brushless DC motor according to claim 1, wherein the stator (3) has a coil winding portion of the salient pole portion (16) having a substantially circular cross section. 4. The stator (3) according to claim 1, wherein the coil winding portion of the salient pole portion (16) has a square or rectangular cross section and four corners are chamfered or cut off. Abduction type brushless DC motor.