JPH09266646A - Brushless dc motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To utilize the reluctance torque of a rotor effectively, by a method wherein permanent magnets of which respective rotor poles are composed are arranged with spacings at least larger than the opening widths of the slots of a stator. SOLUTION: In a rotor core 1a made of high permeability magnetic material, one pole is composed of 3 permanent magnets 2a, 2b and 2c. 4 groups of such permanent magnets are arranged in quadrants to constitute a 4-pole rotor. Stator coils are wound in a plurality of slots 5 in a stator core 4. If the widths of the rotor core parts 10a and 10b between the permanent magnets 2a, 2b and 2c are larger than the widths of the slot openings of the stator, the parts 10a and 10b face some of the tooth parts of the stator with shortest air gap distances without fail, so that a reluctance torque can be utilized effectively, flux Ψ can pass easily, and stable magnetic paths can be formed.

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 permanent magnet embedded in a rotor.

[0002]

2. Description of the Related Art An interior permanent magnet motor (hereinafter abbreviated as IPM) constructed by embedding a permanent magnet inside a rotor has conventionally been constructed as shown in FIGS. That is, the permanent magnets 2p, 2q, 2r, 2s or 2t, 2 are arranged so as to have the same number of magnetic poles as the number of poles of the IPM.
u, 2v, and 2w are arranged in the rotor substantially evenly. The embedded permanent magnet is usually formed sufficiently thick so as to have sufficient proof stress so that demagnetization or demagnetization does not occur with respect to the magnetomotive force from the stator side when the IPM is operating. On the other hand, the rotor housing 1d or 1e in which the permanent magnet is to be embedded is usually made of a high magnetic permeability material, and the magnetic flux of the embedded permanent magnet forms a magnetic path through the air gap between the stator and the rotor. In this case, in order to minimize the leakage flux between adjacent permanent magnets of different poles of the rotor and secure a large amount of magnetic flux effective for the torque of the motor, the inter-pole widths δt1 and δt2, and The magnetic path widths δs1 and δs2 between the end of the permanent magnet and the air gap are made as narrow as possible.

Since the IPM has a magnetic material having a high magnetic permeability such as a silicon steel plate on the outer peripheral portion of the rotor, a surface type permanent magnet rotor (excluding a member for preventing scattering of the permanent magnets) is used for a motor of the same capacity. The inductance of the stator winding is larger than that of a motor having a structure in which a permanent magnet is arranged on the outer peripheral portion), and the phase delay of the current with respect to the applied voltage phase when driving the motor becomes significant. In order to avoid this, generally, advance angle energization control for advancing energization of a predetermined phase to the regular rotor position is performed. Also, IP
Focusing on the magnetic material that is present between the permanent magnet and the air gap generated in the structure of the M rotor, the advancing angle energization control is positively performed, and the d-axis (center of the rotor magnetic pole and the center of the rotor rotation axis) is formed by the original permanent magnet. In addition to the torque of the phase current corresponding to the direction connecting O), the reluctance torque generated by the phase current corresponding to the q-axis in the direction orthogonal thereto is used.

[0004]

The above-mentioned conventional IPM structure.
In the rotor of No. 2, the q-axis direction magnetic flux path for effectively utilizing the reluctance torque is not sufficiently secured between the adjacent magnetic poles. That is, in FIGS. 11 and 12, in order to reduce the leakage flux of the permanent magnet as much as possible, the inter-electrode widths δt1 and δt2 are narrowed at the end outer peripheral magnetic path widths δs1 and δs2. Therefore, θd1 in FIG. 11 and θd2 in FIG.
Therefore, the outer peripheral portion of the rotor corresponding to the above angle does not act effectively as the magnetic path for reluctance torque. Moreover,
This portion occurs between all magnetic poles of the rotor. The ineffective angle θd1 or θd2 of the magnetic path for reluctance torque
In the case of increasing the proof stress against demagnetization or demagnetization of the permanent magnet due to the stator magnetomotive force, it is inevitably geometrically larger.

As another problem, the above-mentioned ineffective angles θd1 and θd2 are portions that do not effectively act as a path for the magnetic flux from the permanent magnets to pass through to the stator, if they are regarded as rotor magnetic poles, and the IPM is used as the stator. The distribution of the air gap magnetic flux Φ in the case where the rotors are combined has a distribution with a large amount of distortion as shown in FIG. 13, and the induced voltage v generated between the lines includes many third harmonics. In such a motor, sound and vibration are increased.

[0006]

DISCLOSURE OF THE INVENTION The present invention makes it possible to effectively utilize the reluctance torque of a rotor as an IPM to reduce noise and vibration. A permanent magnet is arranged in a radial direction per pole in a rotor core. In a brushless DC motor that is divided into a plurality of parts and incorporated, a permanent magnet (hereinafter referred to as an inner magnet) arranged on the rotor shaft side that forms the same magnetic pole and a permanent magnet (hereinafter referred to as an inner magnet) that is arranged on the outer peripheral side of the rotor Outer magnet) and at least a slot opening width of the stator facing the rotor.

A second aspect of the invention is characterized in that a magnetic material other than the rotor core is interposed between the inner magnet and the outer magnet. A third aspect of the invention is characterized in that the distance between the inner magnet and the outer magnet is constant.

As a fourth invention, in any one of the first to third inventions, all the permanent magnets forming the same magnetic pole are in a direction parallel to a line connecting a rotor shaft center and the magnetic pole center in a radial direction. It is characterized in that it is magnetically oriented. As a fifth invention, in any one of the first to third inventions, all the permanent magnets forming the same magnetic pole are on an extension line connecting a rotor shaft center and a magnetic pole center in a radial direction, and at least the focal point. Is magnetically oriented in a direction outside the outer peripheral surface of the rotor. A sixth invention is characterized in that, in the fifth invention, the focal points of the magnetic orientation of the plurality of permanent magnets forming the same magnetic pole are different from each other.

[0009]

In the first aspect of the present invention, the change in the inductance of the stator coil due to the rotation of the rotor reduces the ripple caused by the slot opening, and
Since the maximum and minimum widths are large, the reluctance torque due to the q-axis current can be increased.

In the second aspect of the present invention, the permanent magnet can be mounted without causing large play between the rotor core and the rotor core, and the magnetic material has characteristics such as high permeability, high frequency characteristics, and high saturation magnetic flux density. Can be selected and adopted. Further, the third aspect of the invention has an effect of effectively ensuring the magnetic flux path by the current of the q-axis component.

Further, in the fourth to sixth inventions, the design operation for making the magnetic flux distribution in the air gap suitable for the purpose of use of the IPM becomes easy.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 1a is a rotor core made of a magnetic material having high magnetic permeability, which forms a housing for permanent magnets 2a, 2b, 2c, and a shaft 3 is fitted in the central portion thereof. The three permanent magnets 2a, 2b, 2c form one pole, and the three permanent magnet groups are arranged in an equal arrangement to form a four-pole rotor. Reference numeral 4 is a stator core having a plurality of slots 5, and a stator coil 6 is mounted in the slots 5. FIG. 2 is an enlarged view of a main part of the motor shown in FIG. 1. Dr1 is permanent magnets 2a and 2
b shows the width of the rotor core 1a interposed therebetween, and similarly Dr2 shows the width of the rotor core 1a interposed between the permanent magnets 2b and 2c. Further, Ds indicates the slot opening width of the stator core 4. In the present invention, the values of Dr1 and Dr2 are both set to be larger than Ds, and it is preferable that the value is equal to or larger than the facing width of the rotor outer circumference corresponding to the slot pitch angle of the stator core 4.

FIG. 3 is an enlarged view of FIG. 2, where 8a, 8b and 8c are the teeth of the stator core 4,
ψ indicates the magnetic flux due to the magnetomotive force of the stator coil.
If the width of the rotor core portions 10a, 10b interposed between the permanent magnets 2a, 2b, 2c is wider than the width of the slot opening 9 of the stator, the portions 10a, 10b will always have the shortest air gap distance with any of the teeth portions. Thus, the magnetic flux ψ can easily pass through and a stable magnetic path can be formed. As a result, the magnetic flux ψ becomes large and stable. This can be easily confirmed by the winding inductance measured from the stator coil side.

FIG. 4 shows an inductance L between arbitrary stator coil terminals with respect to the rotation angle θ of the rotor. In this figure, when the widths of the rotor core portions 10a and 10b between the permanent magnets on the stator facing surface, ie, Dr1 and Dr2, are such that the curve La is approximately equal to the slot pitch angle of the stator, the curve Lb is approximately the slot opening width. In the case of equality, the curve Lc shows the case where it is narrower than the slot opening width. As is clear from FIG. 4, the change in the La inductance has few ripples due to the status lot opening, and the maximum and minimum widths are large, whereas in the case of Lc, the ripples are large and the average maximum and average inductances are large. The minimum width is getting smaller. Further, Lb is between La and Lc. As a factor for determining the generation of reluctance torque, when the change of the inductance L is almost a sine wave, a coefficient α obtained from the average maximum Lmax and the average minimum Lmin of the inductance is well known in the analysis of the reluctance motor.

[0015]

[Equation 1]

It is said that the larger the coefficient α, the larger the reluctance torque. Therefore, as in the embodiment of FIGS. 1 to 3, a plurality of permanent magnets are arranged so that the width of the magnetic material interposed between the inner magnet and the outer magnet forming the same magnetic pole is at least the slot opening width of the stator. As a result, the reluctance torque due to the q-axis current can be increased.

In the above description of the present invention, the width of the magnetic material interposed between the adjacent permanent magnets of the same magnetic pole is considered based on the width of the rotor outer periphery facing the stator, but the IPM depends on the current of the q-axis component. In order to effectively secure the magnetic flux path, it is preferable that this width in the rotor, that is, the widths indicated by Dr1 and Dr2 in FIG. 2 be constant. However, in the actual design process, the width may be widened or narrowed within the rotor within a geometrically possible range due to design considerations that require mechanical changes. As a result, in the change of the inductance L with respect to the rotor rotation angle θ in FIG. 4, it is possible to increase or decrease the amplitude of the change of the inductance L while keeping the influence of the ripple caused by the status lot opening small. The ingredients can be adjusted arbitrarily.

In the embodiment shown in FIGS. 1 to 3, the permanent magnets 2a, 2b and 2c are embedded in the rotor core 1a, so that a rotor core material is provided between adjacent permanent magnets of the same magnetic pole. Although a magnetic material such as a silicon steel plate is interposed, another magnetic material may be interposed between the inner magnet and the outer magnet adjacent to each other, and an example is shown in FIG. In FIG. 5, 7 is a permanent magnet 2
a non-directional magnetic material inserted between a and 2b,
Other configurations are similar to those of the embodiment shown in FIGS. FIG.
In the case of the rotor core 1b shown in (1), a large accommodating hole for inserting the permanent magnets 2a, 2b and the magnetic material 7 together is provided. It can be absorbed by adjusting the dimensions, and the permanent magnets 2a and 2b can be mounted without causing a large play with the rotor core 1b. Also, with the structure shown in FIG. 5, a magnetic material having a relatively high strength is used for the main rotor core material 1b to cope with the deformation due to the centrifugal force due to the rotation of the rotor, and the permanent magnets 2a and 2b have a higher permeability. Using magnetic materials with magnetic susceptibility to reduce the magnetic resistance of the magnetic path, using magnetic materials with good high frequency characteristics, magnetic materials with high saturation magnetic flux density, etc.
It can be selected and adopted without much concern for mechanical strength. Further, the magnetic material 7 is not limited to the example shown in FIG. 5, and it goes without saying that the magnetic material 7 may be arranged between the permanent magnets 2a and 2b, between 2b and 2c, or both of them at the same time.

Further, although the number of permanent magnets forming the same magnetic pole is three in the embodiment of the present invention, the number of permanent magnets is not limited to this, and the constitution of the present invention can be obtained if the number is two or more. it is obvious. By forming a plurality of permanent magnets that form the same magnetic pole in this way, it is possible to employ permanent magnets having different characteristics. In the conventional IPM rotor, one permanent magnet is used for one magnetic pole, and the orientation direction of the magnet material is only selected either radial or parallel.
When the permanent magnet is determined, the amount and distribution of the magnetic flux between the stator and the rotor are determined by the size, the characteristic, and the permeance of the motor structure. As a result, the magnetic flux distribution in the air gap was as described above with reference to FIG.

6 to 8 each show another embodiment of the present invention, which shows an example of magnetic orientation of a permanent magnet. FIG.
Is the permanent magnets 2d, 2e, 2f forming the same magnetic pole,
A line P- connecting the rotor shaft center and the magnetic pole center in the radial direction
An example of magnetic orientation in a direction parallel to P is shown. The magnetic poles other than the magnetic poles having the permanent magnets 2d, 2e, 2f also have the same structure, have the magnetic orientation shown by the arrow in the figure, and are alternately magnetized in the circumferential direction in the NS direction to form a total of 4 equally distributed 4 poles Constitutes the magnetic pole of.

FIG. 7 shows a permanent magnet 2 forming the same magnetic pole.
An example in which g, 2h, and 2i are magnetically oriented on an extension line Q-Q connecting the rotor shaft center and the magnetic pole center in the radial direction, and at least at a point Q1 where the focal point is outside the rotor outer peripheral surface. Is shown. Permanent magnets 2g, 2h, 2i
Magnetic poles other than the magnetic poles having the same structure have the same magnetic orientation as shown by the arrow in the drawing, and are alternately magnetized in the circumferential direction in the NS direction to form a magnetic pole having four equally distributed four poles. . FIG. 8 shows a modification of the embodiment shown in FIG. 7, in which the magnetic orientations of the permanent magnets 2j, 2k and 2l forming the same magnetic pole are R1 and R2, respectively. An example is shown in which the focus of the magnet 2j is R3, and the focus is in the direction away from the rotor axis in order from the outer magnet 21 to the inner magnet 2j.

In any of these FIGS. 6 to 8, the magnetic flux of the permanent magnets arranged in the rotor passes through the magnetic material of the rotor arranged in the radial direction and faces the outer peripheral surface of the rotor. Flow to. At this time, as described above, since the magnetic material between the inner magnet and the outer magnet forming the same magnetic pole has a gap equal to or larger than the slot opening width of the stator, they face each other with at least the shortest air gap distance. Since there is a region to obtain, the magnetic flux of the permanent magnet can be effectively guided. As a result, the conventional rotor shown in FIGS. 11 and 12 locally has a rectangular wave-shaped air gap magnetic flux distribution as shown in FIG. 13, whereas the rotors shown in FIGS. In the case of FIG. 6, the distribution is Ba, the case of FIG. 7 is Bb, and the case of FIG. 8 is Bc. In FIG. 9, the horizontal axis Lg is the circumferential distance at the center of the air gap.

In the embodiment of FIG. 6, since the magnetic orientations of the permanent magnets are parallel, the magnetic flux passing directly through the magnetic material on the radially outer side of each permanent magnet toward the stator teeth is 90 ° or with respect to the magnetic orientation. It will turn at an angle less than that. In the embodiment of FIG. 7, since the magnetic orientation of the permanent magnet is in the direction toward the focus Q1, for example, the magnetic flux directly passing through the magnetic material on the outer side in the radial direction of the permanent magnet to the stator teeth has the parallel orientation of FIG. You have to make a relatively large turn as compared to. Therefore, the amount of magnetic flux from each permanent magnet directly to the stator via the magnetic material decreases, and the magnetic flux distribution in the air gap appears as the difference between Ba and Bb shown in FIG. In the case of the embodiment shown in FIG. 8, as is apparent from the description of FIGS. 6 and 7, the inner magnet operates in a tendency similar to that in FIG. 6, and the outer magnet operates in a tendency similar to that in FIG. It will be easily understood that the resulting magnetic flux distribution in the air gap is as shown by Bc in FIG.

In the case of the embodiment shown in FIG. 8, the magnetic orientation of the permanent magnets forming the same magnetic pole is not set so that the inner magnet has its focal point farther than the outer magnet, but rather an arbitrary magnetic pole centerline. By making the points different from each other, it becomes easier to change the magnetic flux distribution in the air gap according to the purpose of use of the IPM. As shown in FIGS.
As shown in the embodiment of the present invention, by performing various design operations of the magnetic orientation of the permanent magnet, it becomes possible to change the magnetic flux distribution in the air gap, for example, by reducing the noise and vibration by making the magnetic flux distribution close to a sine wave, or In a motor that conducts electricity at 120 °, it is easy to improve the motor efficiency by providing a magnetic flux distribution in which the induced voltage is increased only in the conduction region.

FIG. 10 shows another embodiment of the present invention. Instead of the arc-shaped permanent magnets 2a, 2b, 2c forming one pole shown in FIG. 1, a U-shaped permanent magnet is used. Magnet 2
It is constituted by m, 2n and 2o, and the constitution of the present invention can be applied without any difference from that shown in FIG. Further, not limited to these shapes, in an extreme case, the application effect of the present invention can be greatly expected even in a case where flat permanent magnets are arranged in parallel and combined.

[0026]

According to the present invention, one permanent magnet is provided in the rotor core.
In a brushless DC motor which is divided into a plurality of parts in the radial direction for each pole and is built in, the inner magnet and the outer magnet forming the same magnetic pole are spaced at least by a slot opening width of a stator facing the rotor. As a result, the change in the stator coil inductance due to the rotation of the rotor has less ripple due to slot opening, and the maximum and minimum widths are large, and the reluctance torque due to the q-axis current is reduced. It is possible to increase the value, and it is possible to arbitrarily adjust the reluctance torque component.

Further, by interposing a magnetic material other than the rotor core between the inner magnet and the outer magnet, the permanent magnet can be mounted without causing a large play with the rotor core, and high magnetic permeability and high frequency can be achieved. A magnetic material having characteristics such as characteristics and high saturation magnetic flux density can be selectively adopted. Further, the magnetic orientation of all permanent magnets forming the same magnetic pole is set in a direction parallel to a line connecting the rotor shaft center and the magnetic pole center in the radial direction, or an extension connecting the rotor shaft center and the magnetic pole center in the radial direction. The magnetic flux distribution in the air gap is set to I on the line by making at least the focal point outside the rotor outer peripheral surface, and by making the focal point different for each permanent magnet.
It becomes easy to operate the distribution so as to be suitable for the purpose of use of PM, and it is possible to reduce noise and vibration and improve motor efficiency.

[Brief description of drawings]

FIG. 1 is a plan sectional view of a brushless DC motor showing a first embodiment of the present invention.

FIG. 2 is an enlarged view of a main part of FIG.

FIG. 3 is an enlarged explanatory view of an essential part showing the action in the brushless DC motor of FIG. 1.

FIG. 4 is a diagram showing the relationship between the rotation angle θ of the rotor and the inductance L between the stator coil terminals.

FIG. 5 is a cross-sectional plan view of the essential parts of the rotor of the brushless DC motor according to the second embodiment of the present invention.

FIG. 6 is a plan sectional view of a rotor of a brushless DC motor showing a third embodiment of the present invention.

FIG. 7 is a plan sectional view of a rotor of a brushless DC motor showing a fourth embodiment of the present invention.

FIG. 8 is a plan sectional view of a rotor of a brushless DC motor showing a fifth embodiment of the present invention.

FIG. 9 is a diagram showing the relationship of the distribution of the air gap magnetic flux density B with respect to the circumferential distance Lg in the IPM.

FIG. 10 is a plan sectional view of a brushless DC motor showing a sixth embodiment of the present invention.

FIG. 11 is a plan sectional view of a rotor of a brushless DC motor showing a conventional example.

FIG. 12 is a plan sectional view of a rotor of a brushless DC motor showing another conventional example.

FIG. 13 is a diagram showing the relationship between the amount of magnetic flux Φ interlinking with the stator coil and the induced voltage v with respect to time t in the IPM.

[Explanation of symbols]

 1a-1e Rotor core 2a-2w Permanent magnet 3 Shaft 4 Stator core 5 Status lot 6 Stator coil 7 Magnetic material 9 Slot opening

Claims (6)

[Claims] 1. A brushless DC motor having a rotor core in which a plurality of permanent magnets are incorporated for each pole, and a permanent magnet (hereinafter referred to as an inner magnet) arranged on the rotor shaft center side forming the same magnetic pole. A brushless DC motor, characterized in that permanent magnets (hereinafter referred to as outer magnets) arranged on the outer peripheral side of the rotor are arranged with a gap of at least the slot opening width of the stator facing the rotor. 2. The brushless DC motor according to claim 1, wherein a magnetic material other than the rotor core is interposed between the inner magnet and the outer magnet. 3. The brushless DC motor according to claim 1, wherein the inner magnet and the outer magnet are arranged so that a distance between them is constant. 4. All permanent magnets forming the same magnetic pole are
4. The brushless DC motor according to claim 1, wherein the brushless DC motor is magnetically oriented in a direction parallel to a line connecting the rotor shaft center and the magnetic pole center in the radial direction. 5. All permanent magnets forming the same magnetic pole are
The magnetic orientation is on an extension line connecting the rotor shaft center and the magnetic pole center in the radial direction, and at least the focal point is magnetically oriented in a direction outside the rotor outer peripheral surface. Brushless DC motor. 6. The brushless DC motor according to claim 5, wherein the magnetic orientations of the plurality of permanent magnets forming the same magnetic pole have different focal points.