JP4463947B2 - Structure of brushless DC motor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a brushless DC motor, and particularly provides a structure that easily reduces cogging torque.
[0002]
[Prior art]
Conventional brushless DC motors (hereinafter abbreviated as motors) generate torque fluctuations, that is, cogging torque, which occurs due to the presence of slots for winding. That is, the magnetic flux of the field magnetic flux generated from the magnetic pole of the rotor during relative movement between the rotor and the stator changes periodically every time the magnetic pole of the rotor crosses the slot opening of the stator, resulting in a magnetic flux distribution in the gap. Due to changes. Therefore, the period and size of this cogging depend on the number of slots provided in the stator core and the number of magnetic poles of the rotor, and the waveform with respect to the rotation angle varies greatly depending on the shape and dimensions of the stator slot opening and rotor magnetic poles. To do.
[0003]
Conventionally, various methods have been proposed for cogging countermeasures. However, as a general practice, the magnetic spatial distance (gap) between the rotor and the stator is increased at both ends of the rotor magnetic poles to cause inequality. It is constituted so that the change of magnetic flux interlinking with an arbitrary stator tooth is made smooth. Further, the magnetic poles of the rotor are skewed with respect to the direction of the rotation axis, thereby mitigating the change in the magnetic flux linkage to the stator when the magnetic pole pole portion of the rotor crosses the stator teeth.
[0004]
[Problems to be solved by the invention]
In order to prevent cogging due to unequal gaps, the shape of the permanent magnet is usually handled by machining, and the shape needs to be changed according to the shape of the teeth of the stator and the size of the slot opening. At present, many prototypes and various types of analysis are performed. Although such a measure improves the cogging torque of the motor considerably, it cannot be said to be sufficient. In addition, the more the cogging torque is reduced by applying such measures, the more the gap between the rotor poles needs to be greatly widened, and the interlinkage magnetic flux from the rotor to the stator decreases. .
[0005]
As another method, when skew is applied to the rotor magnetic poles, an effect can be expected by increasing the skew angle. However, the effective magnetic flux of the magnetic poles decreases in proportion to the skew angle, thereby deteriorating motor characteristics. That is, from the viewpoint of the electrical characteristics of the motor, it can be said that the permanent magnet at the portion where the skew exists does not act as an effective magnetic flux as the motor performance and uses a useless permanent magnet.
[0006]
Furthermore, in recent years, many motors have attempted to reduce the size of rare earth permanent magnets with high magnetic flux density, and the cogging torque itself has increased. In this case, the structure of the conventional cogging torque reduction method is sufficient. It has become impossible to take. In addition, it is difficult to process a permanent magnet with a small shape with high accuracy. In addition, in the case of applying a skew, a combination of the permanent magnets must skew the permanent magnets themselves in the segment, which makes the mass production impossible.
[0007]
FIG. 9 shows a perspective view of a rotor in which the skewed permanent magnet 2 is combined. In the figure, four permanent magnets 2 having a skew angle θS in the direction of the rotation axis are arranged on the surface of the rotor core 3 in the circumferential direction to constitute a four-pole rotor. As a method of not skewing the permanent magnet in shape, there is a case where a ring-shaped permanent magnet is used. However, there is a problem that there is a useless area corresponding to the skew portion in terms of electrical characteristics as the motor described above. Still remains.
[0008]
In addition, in this type of motor, a motor in which a permanent magnet is embedded in the core of the rotor has been proposed, and the electrical characteristics have been improved. There is no proposal for a configuration or manufacturing method for reducing effective and simple cogging torque.
[0009]
[Means for solving problems]
The present invention has been made in view of the above problems, and the effective magnetic pole opening angle of the rotor is set to a value obtained by adding an angle corresponding to one slot opening angle to an integral multiple of the slot pitch of the stator, and the rotor is divided into three in the axial direction. The divided rotors are configured by shifting the mechanical angle corresponding to 1/2 cycle with respect to each cogging torque around the axis ,
The rotor located at the central portion in the axial direction has a cogging torque waveform twice as large as that of the rotor located at both ends, and the rotor located at both ends has the same cogging torque phase and magnitude. The present invention provides a brushless DC motor structure characterized by being assembled in the following manner.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on examples. The same components in the rotor configuration or those having the same meaning in practical use are designated by the same reference numerals as those in FIG. FIG. 1 shows a four-pole motor having distributed winding with 24 stator slots. However, the windings are omitted for the sake of clarity. 2 is a permanent magnet, 3 is a rotor core, 4 is a stator core, and the permanent magnet 2 is attached to the surface of the rotor core 3. In the configuration of the motor, the magnetic pole pitch related to the excitation on the stator side is expressed by 24 slots / 4 poles, and is every 6 slot pitch. Normally, in a general winding method, one coil is housed in one slot at a time, so the effective excitation magnetic pole angle of the stator is an angle that spans five teeth in a 6-slot pitch so as to face the rotor. .
[0011]
Similarly, FIG. 2 shows an example of so-called concentrated winding in which winding is concentrated on one tooth with six slots. In this case, the magnetic pole pitch related to the excitation on the stator side is every slot pitch, and it is obvious that the effective magnetic pole angle of the stator is the angle of one tooth facing the rotor.
[0012]
The cogging torque is generated independently of the stator windings. Therefore, when the rotor with a permanent magnet magnetized in the stator without excitation is rotated counterclockwise from an arbitrary angular position, An example in which the cogging torque is calculated by magnetic field analysis is shown in FIG. In the figure, the present invention does not consider the relative positional relationship between the rotor and the stator of the cogging torque, but the cogging torque waveform is a problem. The positional relationship between the stator and the rotor showing the positive value is used as a base point.
[0013]
As for the effective magnetic pole opening angle on the rotor side, when at least one end is within the opening angle of the stator teeth at any rotational position of the rotor, that is, in the effective magnetic pole opening angle such as θ1 in FIGS. The waveform has a steep rise and a gentle fall as indicated by Tθ1 in FIG.
[0014]
Conversely, when the rotational position of the effective magnetic pole opening angle on the rotor side is such that there is a state where both ends of the rotor magnetic pole are within the opening angle of the slot opening, that is, the effective magnetic pole as indicated by θ2 in FIGS. At the open angle, the cogging torque waveform has a gentle rise and a steep fall as shown in FIG.
[0015]
Here, the effective magnetic pole opening angle on the rotor side is set to a value obtained by adding an angle corresponding to the opening angle of one slot to an integral multiple of the slot pitch of the stator. That is, if the effective magnetic pole opening angle of the rotor is set so as to match the angle over the inner side of the opposing stator teeth as indicated by θk in FIGS. 1 and 2, the cogging torque waveform is a half cycle as indicated by Tθk in FIG. The waveform is symmetrical and has the same positive and negative amplitude. In the present invention, θk is selected to be the closest angle to the geometrical stator excitation magnetic pole angle in order to secure a field magnetic flux as a motor.
[0016]
FIGS. 1 and 2 show a structure in which the permanent magnet is attached to the surface of the rotor. FIGS. 4A and 4B show a case where the permanent magnet is embedded in the rotor core. In the case of (1) in FIG. 4, since the permanent magnet and the rotor surface are close, the effective magnetic pole opening angle is substantially equal to the opening angle of the permanent magnet. Therefore, the purpose of the present invention can be satisfied by setting the opening angle of the permanent magnet to θk. In the case of (2) in FIG. 4, since the magnetic magnet rotor core has a wide portion in the rotor radial direction on the surface of the permanent magnet and the rotor, the opening angle of the portion becomes the effective magnetic pole opening angle. Therefore, the gist of the present invention is satisfied by setting the opening angle to θk.
[0017]
Cogging torque can be canceled by combining rotors having an effective magnetic pole opening angle with mechanical angles corresponding to half the amplitude period of the cogging torque so as to be relatively different. FIG. 5 is a perspective view of a rotor formed of the structure described in FIGS. 1 and 2 of the present invention. FIG. 6 is a waveform showing a state of cogging torque cancellation in the rotor structure of FIG. RC1 and RC2 in FIG. 5 are divided in the axial direction and are in a state in which the mechanical angle corresponding to the half cycle of the amplitude cycle θe shown in FIG. 6 is relatively different. The rotor divided into two in the axial direction in the rotor structure of the present invention has the same rotor structure. Note that the rotor structure described in FIGS. 4A and 4B is the same as that in FIGS.
[0018]
The cogging torques of the respective divided rotors RC1 and RC2 are represented by TC1 and TC2 in FIG. 6, and the divided rotors are combined at an angle θm in FIG. The cogging torque synthesized by setting the θm to a mechanical angle corresponding to θe which is a half cycle of the cogging torque shown in FIG. 6 is theoretically zero as shown by TC0 shown in FIG. The cogging of the split rotor cancels each other out.
[0019]
Further, when the effective magnetic pole opening angle of the rotor divided in the axial direction is θ1 in FIG. 1 or θ2 in FIG. 2, the positive / negative change of the cogging torque is point-symmetric, and therefore the machine corresponds to a half cycle of the cogging torque. Although the cogging torque cannot be canceled even when combined in a state where the angles are relatively different, Tθ1 having an effective magnetic pole opening angle of θ1 in FIG. 1 and θ2 in FIG. 2 is shown in FIG. And a rotor having a waveform and a magnitude that follow each other's cogging torque waveform in the opposite direction, such as the waveform of Tθ2, each rotor can be set to a relative mechanical angle corresponding to a half cycle of the cogging torque. It is possible to cancel the cogging torque by combining them in different states.
[0020]
Therefore, if Tθk is selected as the effective magnetic pole opening angle of the rotor, the cogging torque theoretically becomes zero as in TC0 shown in FIG. 6 only by combining the rotors having the same structure. FIG. 5 shows the rotor structure divided in two in the axial direction, but a better effect can be obtained by dividing each component in the axial direction into a plurality of parts without departing from the present invention. .
[0021]
However, depending on the motor specifications, when the cogging torque of each divided rotor is large in the simplest combination of divided rotors shown in FIG. This gives a twisting force to the shaft. Since this force is physically separated from the position of the split rotor, the point of action differs with respect to the shaft. As a result, a bending moment is generated on the shaft to give a complicated vibration mode. The vibration is generated from the motor as a sound synchronized with a higher-order cogging frequency with respect to the rotational speed of the motor.
[0022]
In view of this problem, in the present invention, the rotor is divided into three in the axial direction, and the divided rotor arranged in the center with respect to the three divided rotors is set to have a cogging torque twice that of the divided rotor arranged on both sides thereof. In addition, the divided rotors arranged on both sides have the same magnitude and phase relationship with respect to the cogging torque. This configuration is shown in the perspective view of FIG. Split rotors RC3 and RC5 are arranged on both sides so as to sandwich central split rotor RC4. The divided rotors RC3 and RC5 are arranged so that the cogging torque is exactly the same with respect to the rotation of the rotor, and the central divided rotor RC4 has a mechanical angle corresponding to a half of the cogging cycle with respect to the divided rotor RC3 or RC5. Arranged at different positions.
[0023]
Therefore, the cogging torque of each divided rotor has a waveform shown in FIG. TC3 is a cogging torque waveform of the divided rotor RC3, TC5 is a cogging torque waveform of the divided rotor RC5, and a combination of these two cogging torque waveforms is TC3 + TC5 and TC4 is a cogging torque waveform of the central divided rotor RC4. The divided rotor RC4 is set to have twice the cogging torque of the divided rotors at both ends, and is assembled at different positions by a mechanical angle corresponding to a half cycle of the cogging torque cycle. The combined cogging torques cancel each other as described with reference to FIGS. 5 and 6, resulting in the waveform of TC0 in FIG. That is, it becomes zero, which is the same as TC0 in FIG. Furthermore, there exists a twisting force on the shaft due to the cogging torque, but the bending moment acting on the shaft is not canceled out. Although FIG. 7 shows the rotor structure divided into three in the axial direction, the components of each of the divided rotors RC3, RC4, and RC5 are further divided into a plurality of parts without departing from the present invention. , Better effect can be obtained.
[0024]
【The invention's effect】
In the motor according to the first aspect, by setting the effective magnetic pole opening angle of the rotor to a value obtained by adding one slot opening angle to an integer multiple of the status lot pitch, the waveform of the cogging torque becomes positive and negative, and the cogging torque half Since it is symmetrical with respect to the cycle, it is possible to cancel each other's cogging torque as much as possible by assembling the divided rotors having the cogging torque in different states by the mechanical angle corresponding to the half cycle of the cycle. .
[0025]
Regarding the bending moment of each divided rotor acting in the axial direction of the rotating shaft when canceling the cogging torque, the rotor divided into three in the axial direction is twice as large as the rotor located at both ends. The rotors located at both ends have the same cogging torque phase and magnitude so that the combined moment can be canceled out, and the motor vibration caused by the cogging torque and the noise caused by this can be reduced. It is possible to prevent.
[0026]
In addition, a special shape is not requested | required so that it may not mention at all about the shape of the permanent magnet required for this invention in the said description. Accordingly, the cogging torque is drastically reduced only by satisfying the effective magnetic pole opening angle of the rotor in accordance with the gist of the present invention.
[0027]
The effective magnetic pole opening angle of the rotor can be arbitrarily selected as long as the conditions of the present invention are satisfied. However, the effective magnetic pole opening angle of the rotor is selected to be the closest angle to the geometric excitation magnetic pole angle of the stator. As a result, the magnetic flux from the rotor can almost ensure the magnetic flux required for the motor, and there is no need to skew the permanent magnet as in the prior art, so the motor characteristics are not sacrificed. In addition, since the number of cogging torques during one rotation is equal to or greater than the number of slots in the stator, the mechanical shift angle amount when combining the divided rotors in the configuration of the rotor of the present invention is at most ½ slot. Therefore, even if assembled at this mechanical angle, the effective magnetic pole opening angle of the rotor does not exceed the physically possible maximum magnetic pole opening angle. Therefore, the magnetic fluxes of the permanent magnets constituting the magnetic poles of the divided rotors do not cancel each other, and the motor can be used effectively without leaving any excess.
[0028]
With regard to the arrangement of the permanent magnets in the rotor structure of the present invention, those attached to the surface of the rotor core and those embedded in the interior can be applied. Also, the stator structure can be applied to distributed winding and concentrated winding. Yes, it can be used with any motor .
[0029]
In particular, when the rotor of a motor, which is often used when incorporated in a compressor used in a refrigeration air conditioner or the like, rotates in a cantilever manner, the effect is great because it is easily affected by the bending moment.
[0030]
In the present invention, the cogging torque of each divided rotor varies depending on the shape and size of the permanent magnet, the amount of magnetic flux, the type, and the gap width as a conventionally used motor. Therefore, the present invention can be realized without being affected at all, and can be applied even if high performance is required according to the equipment and application to which the motor is applied. Therefore, it is particularly effective for servo motors that require high-accuracy positioning and high output density, as well as motors that require low vibration and low noise.
[0031]
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a distributed winding motor showing an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a concentrated winding motor showing an embodiment of the present invention.
FIG. 3 is a diagram showing a state of cogging torque in FIGS. 1 and 2;
FIG. 4 is a cross-sectional view of a rotor showing another embodiment of the present invention.
FIG. 5 is a perspective view of a rotor structure showing an embodiment of the present invention.
FIG. 6 is a diagram showing cancellation of cogging torque of the rotor in FIG. 5;
FIG. 7 is a perspective view of a rotor structure showing an embodiment of the present invention.
FIG. 8 is a diagram showing a state of cogging torque cancellation in FIG. 7;
FIG. 9 is a cross-sectional view of a rotor showing a conventional example.
[Explanation of symbols]
θ1, θ2, θk, θm: mechanical angle, θe: electrical angle, 2: magnet, 3: rotor core, 4: stator core, RC1 leading to RC5: split rotor, TC0 leading TC5: cogging torque wave, θs: skew angle.

Claims (1)

In a brushless DC motor composed of a rotor on which a permanent magnet is mounted and a stator having a plurality of slots, the effective magnetic pole opening angle of the rotor is an integral multiple of the slot pitch of the stator plus an angle corresponding to one slot opening angle. Set to
The rotor is divided into three parts in the axial direction, and the divided rotors are configured to be shifted around the axis corresponding to ½ period with respect to each cogging torque ,
The rotor located at the center divided into three in the axial direction has a cogging torque waveform twice as large as the rotor located at both ends, and the rotor located at both ends has the same cogging torque phase. Brushless DC motor characterized by its size.

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