JP4308378B2 - Brushless DC motor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a brushless DC motor, and more particularly to improvement in characteristics, low noise, and low vibration of a brushless DC motor having a structure in which a permanent magnet is disposed in a rotor.
[0002]
[Prior art]
A structure in which a slit is provided in a rotor and a permanent magnet is disposed on the rotor is usually called a permanent magnet embedded rotor and is used in many fields. An example of a rotor structure in a conventional brushless DC motor is shown in FIGS.
[0003]
FIG. 4 shows a permanent magnet arranged in a slit formed along the outer periphery of the rotor. FIG. 5 shows a case in which permanent magnets are arranged in slits formed so as to form strings on the outer periphery of the rotor. 4 and 5, 1 and 4 are slits, 2 and 5 are permanent magnets, and 3 and 6 are cores of the rotor. In FIG. 4, the permanent magnet 2 is magnetically oriented in the radial direction of the rotor, and the outer peripheral surface magnetic flux is almost uniform for each pole of the rotor.
[0004]
In FIG. 5, the permanent magnet 5 is generally a flat plate magnetically oriented in the radial direction for each pole. In this type, the core, which is a magnetic material thicker in the rotor radial direction than the permanent magnet and the rotor surface, is used to apply a reluctance torque in addition to the normal permanent magnet torque to improve the motor torque. As in the case of FIG. 4, the magnetic flux of the permanent magnet is distributed by the core, which is a magnetic material in which the magnetic flux generated by the permanent magnet is interposed between the permanent magnet and the rotor surface. It is almost uniform.
[0005]
The diameter of the core, which is a magnetic material interposed between the permanent magnet and the rotor surface, the more the position where the permanent magnet is arranged is on the inner diameter side of the rotor, that is, the more effectively the reluctance torque is used as a motor. Since the direction becomes wider, the magnetic flux is easily dispersed, and the magnetic flux distribution on the rotor surface is more likely to be uniform. 6 and 7 show how the magnetic flux generated by the permanent magnet is dispersed. The same symbol in each figure represents the same part as FIG.4 and FIG.5.
[0006]
Here, FIG. 8 shows a facing portion between the stator and the rotor of the motor configured in combination with such a rotor. This figure is developed in the circumferential direction on the surface of the stator facing the rotor. In FIG. 8, a rotor part is shown by the type of FIG. 6, and the same symbol shows the same part. Reference numeral 7 denotes a stator having a 12-slot which is normally used. S1 to S12 indicate the slot numbers of the stator 7. In this example, since there are 12 slots, they are arranged in sequence up to S12 and return to S1. The slot is provided with a U / V / W phase winding with an omission and a 4-pole configuration. In this figure, if the rotor rotates clockwise, the magnetic flux of the permanent magnet flowing from the rotor core 3 to the stator 7 moves from left to right.
[0007]
Now, in a state where the rotor is rotating at a constant speed, the magnetic flux flowing from the rotor to the stator is uniform. Therefore, the change in the amount of magnetic flux Φ interlinked with each phase winding changes the state of FIG. ), For example, when looking at the U-phase winding, the waveform shown in the upper part of FIG. 9 is obtained. The induced voltage Vs generated in the U-phase winding at this time is theoretically the waveform shown in the lower part of FIG. It becomes.
[0008]
Therefore, as can be easily determined from this figure, the induced voltage waveform includes harmonic components up to the very high order. Such motors must be energized by changing the direction of the current sharply according to the phase of the induced voltage of the phase, and a large reverse torque is generated even with a slight timing shift. There is a risk that vibrations will occur or that the worst case will be out of use as a motor.
This requires an extremely delicate and high-speed controllability for the device that controls and drives the motor, and is not practical.
[0009]
[Problems to be solved by the invention]
In this type of conventional motor, when it is intended to maintain controllability without using a complicated method for controlling an external control device that drives the motor because of low vibration, It is a well-known fact that it is desirable to make the induced voltage generated in the winding of the sine wave as sinusoidal as possible.
[0010]
However, if the surface magnetic flux of the rotor is almost uniform in the pole as in the above-mentioned conventional example, the change in the magnetic flux linked to the stator winding by the rotation of the rotor becomes constant, so that the induction for each phase winding is induced. In order to make the voltage sinusoidal, it is necessary to make the distribution of the phase windings sinusoidal, and the stator winding configuration for this purpose has to be complicated. In order to cope with the stator structure itself, it is necessary to increase the number of slots so as to enable the distribution of the sine wave of the phase winding. Distribution cannot be achieved.
[0011]
In particular, when trying to improve the motor performance using reluctance torque with a magnetic material interposed between the outer periphery of the rotor and the permanent magnet, in the case of the rotor structure shown in FIG. It is dispersed by the intervening magnetic material core and becomes almost uniform on the outer circumferential surface of the rotor. As described above, if the magnetic flux distribution on the outer peripheral surface of the rotor is made sinusoidal, the distribution of the phase windings can be designed with concentrated winding of one coil, for example, without making it sinusoidal.
[0012]
The present invention has been made in view of the above, and makes the magnetic flux distribution on the outer peripheral surface of the rotor sinusoidal so that the stator winding has a simple configuration and improves the performance of the motor.
[0013]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, in the present invention, a slit for arranging a permanent magnet of a rotor core is curved in an arc shape from the outer periphery of the rotor to the inside as it goes from between the field poles to the center of the field pole. The magnetic flux distribution on the outer peripheral surface of the rotor is made sinusoidal while effectively utilizing the magnetic flux of the permanent magnet.
[0014]
In addition, the crossing angle between the tangent line at the arc end of the field pole center line side of the average arc center line of the outer circumference and the inner circumference of the slit and the field pole center is set in the range of 0 to 90 degrees, and is arranged in the slit. The angle is decreased as the magnetic flux density of the permanent magnet increases. Furthermore, the above-described problem can be solved more effectively by assuming that the permanent magnets arranged in the slits thus arranged are oriented radially in the center of the arc of the slit and having an orientation focal point.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment according to the present invention will be described with reference to the drawings. FIG. 1 shows a rotor structure having four field poles according to an embodiment of the present invention. In the rotor 10, a slit 8 for disposing a permanent magnet 9 between the field poles and the center of the field pole in the rotor core 10 is set near the outer periphery of the rotor between the field poles. The center is set to be closer to the inner periphery of the rotor, and the slit shape from the field poles to the center of the field pole is curved into an arc shape with an arbitrary curvature so as to form an arc in the same direction as the outer periphery of the rotor. is there.
[0016]
The slit 8 is similarly provided between the field poles at the other end of the same field pole. The slit 8 extending from between the field poles to the pole center of the field pole is in contact with the field pole center line at an angle θ1 (hereinafter referred to as a crossing angle θ1) at the field pole center of the rotor.
[0017]
In this way, permanent magnets 9 having the same shape as the slits 8 are arranged in the slits formed in the core 10 of the rotor. In the following, in order to facilitate the explanation of the flow, strength and direction of the magnetic flux, the slit of the present invention is treated as a permanent magnet having the same shape and the same dimension as the slit, unless otherwise specified, Permanent magnets and slits are synonymous in the description regarding dimensions and arrangement.
[0018]
FIG. 2 shows the flow of the rotor magnetic flux when the permanent magnet is oriented in the radial direction to form a motor. In this figure, only one pole is shown, and the other poles are the same. If the curved permanent magnet 9 is radially oriented with a focal point inside the curve, the direction of the magnetic flux from the permanent magnet 9 will be smoothly along the curve and substantially perpendicular at each point. Become. Therefore, the magnetic flux flowing out from the permanent magnet 9 inserted into the slit 8 is almost directed in the radial direction of the rotor in the vicinity of the left and right field poles, and gradually toward the field pole center of the rotor as it approaches the pole center.
[0019]
In this way, if the permanent magnets arranged on the left and right with reference to the field pole center line have the same ability, the field pole is formed in such a manner that a large amount of magnetic flux is concentrated near the pole center line. The concentration of the magnetic flux depends on the angle formed by the permanent magnets 9 on both sides of the field pole central axis.
[0020]
The crossing angle θ1 between the center of the field pole in FIG. 2 and the tangent at the location closest to the center of the field pole in the arc of the average diameter of the permanent magnet 9 arranged in the slit 8 is set to 0 ° or more and 90 ° or less. This is a possible range. If the crossing angle θ1 is 90 ° or more, the direction of the magnetic flux from the permanent magnets 9 on both sides across the field center line becomes a spreading direction, which is different from the gist of the present invention. Further, the fact that the crossing angle θ1 intersects at 0 ° or less, that is, at a negative angle means that the direction of the magnetic flux from the permanent magnet 9 is directed toward the inner circumferential direction rather than the outer circumferential direction of the rotor with respect to the portion of 0 ° or smaller. It deviates from the purpose. Now, assuming that the magnetic flux density of each permanent magnet 9 is Brp, the effective magnetic flux density component as the field pole is the radial direction of the field pole. Therefore, if the function of the magnitude is F1, F1∝2 × Brp × cos (θ1) (1)
F2 関 数 2 × Brp × sin (θ1) (2) where F2 is a function of the concentration degree of magnetic flux intended by the present invention.
Fp∝F1 × F2∝cos (θ1) × sin () where the magnitude of the magnetic flux density as the field pole and the ability of the magnetic flux concentration at the center of the field pole are defined as Fp using the formulas (1) and (2). θ1) (3)
Can be derived.
[0021]
As apparent from the equation (3), the crossing angle θ1 has a maximum value when the angle is 45 °, and can be said to be an angle that successfully balances the magnitude of the resultant magnetic flux density and the concentration.
If the crossing angle θ1 is less than 45 degrees, the resultant magnetic flux density decreases, but the concentration of the resultant magnetic flux density on the center of the rotor field magnetic pole increases, and conversely if it exceeds 45 degrees, the concentration becomes weaker. Therefore, by appropriately setting the crossing angle θ1, it is possible to deal with the intended sinusoidal magnetic flux distribution on the rotor surface. Normally, the crossing angle is reduced when the magnetic flux concentration is important, and the crossing angle is increased when the magnetic flux amount is important. Further, when the magnetic flux density of the permanent magnet 9 inserted into the slit 8 is high, the dispersion becomes stronger in an attempt to make the magnetic flux density uniform in the rotor magnetic material. Therefore, the effect is obtained by relatively reducing the crossing angle θ1. Can be lowered.
[0022]
Here, the flow of magnetic flux and the magnetic flux density distribution when the field pole shown in FIG. 2 is developed in the circumferential direction with reference to the rotor surface are as shown in FIG. The lower part of FIG. 3 shows how the magnetic flux φ flows from the permanent magnet, and the upper part shows the distribution of the magnetic flux density Br on the surface of the lower rotor.
[0023]
The average combined magnetic flux of the permanent magnet 9 as a single unit is represented by an angle θ2 (hereinafter abbreviated as an inclination angle θ2) formed with the field pole centerline of the string connecting both ends of the permanent magnet 9 at the average arc centerline. When the individual parts are viewed locally, the permanent magnets 9 are curved from both ends of the field poles toward the rotor center side to form arbitrary rotor field poles. The direction of the magnetic flux intersects with the center of the field pole gradually at a larger angle as it approaches the center of the field pole. However, if the permanent magnets 9 are configured symmetrically with respect to the field magnetic pole center line, the magnetic fluxes are combined and, as a result, are orthogonal to the outer periphery of the rotor, and the magnitudes thereof are vector combined at each part. Value. As is clear from the figure, a relatively large amount of magnetic flux is synthesized at the center of the field pole, and the magnetic flux between both poles is directed toward the center of the field pole. The magnetic flux that is present in the vicinity acts in a direction that prevents the magnetic flux from dispersing.
[0024]
Therefore, even if a magnetic material is present on the outer peripheral side of the permanent magnet 9, the dispersion of the magnetic flux is suppressed, and a sinusoidal magnetic flux distribution as shown in the upper part of FIG. 3 can be obtained. The action of maintaining the magnetic flux can be arbitrarily changed by appropriately setting the angle formed by the field pole center line and the permanent magnets 9 on both sides thereof, that is, the crossing angle θ1 and the inclination angle θ2. Assuming that the effective magnetic flux density component as the field magnetic pole when the inclination angle of the permanent magnet 9 is θ2 and the ability of the magnetic flux concentration are Fs, it can be considered as in the case of the crossing angle.
Fs∝cos (θ2) × sin (θ2) (4)
It is expressed. Here, it is not a matter of course that the expression (4) becomes the largest under the condition of the inclination angle θ2 = 45 degrees. If the tilt angle θ2 is smaller than 45 degrees, the combined magnetic flux amount decreases, but the concentration of the combined magnetic flux amount on the rotor field magnetic pole center increases. On the contrary, if it is larger than 45 degrees, the concentration power is weakened.
[0025]
Therefore, a sinusoidal magnetic flux distribution on the target rotor surface can be obtained by appropriately setting the tilt angle θ2. Now, if the opening angle of one field pole is θk and the number of poles of the motor is P,
θk = 360 / P (5)
When one field pole is formed by two permanent magnets 9, the inclination angle θ 2 of one permanent magnet 9 that is to form the same pole is the half open angle of the field pole and the rotor outer circumference arc of the 1/2 field pole. Is the maximum θmax that can be set as a complementary angle with respect to the inner angle of the rotor outer circumference on the common side with the field pole center line of the isosceles triangle composed of the chords at
θmax = 90 ° + θk / 4 (6)
It can be expressed by the following formula.
[0026]
FIG. 10 is a schematic diagram showing the relationship in the case of a 4-pole rotor. In FIG. 10, 11 indicates a field pole center line, and 12 indicates a line between the field poles. As is apparent from FIG. 10, the inclination angle satisfying the gist of the present invention is θmax>θ2> θk / 2 (7)
The range is valid.
[0027]
Among these, the particularly effective range of the inclination angle θ2 is around 45 ° as can be inferred from the equation (4). Normally, the inclination angle θ2 is decreased when importance is attached to the concentration of magnetic flux, and the inclination angle θ2 is increased when importance is attached to the amount of magnetic flux. In the same way as described above, when the magnetic flux density of the permanent magnet inserted into the slit is high, the dispersion becomes stronger in an attempt to make the magnetic flux density uniform in the magnetic material of the rotor, so the inclination angle θ2 should be relatively small. The effect can be lowered. In the above description, the curvature is not particularly mentioned with respect to the curvature of the slit. However, if the curvature is increased, the crossing angle θ1 is decreased even if the inclination angle θ2 of the permanent magnet is increased, and the magnetic flux concentration near the field pole center line is reduced. The condition can be increased. Therefore, by changing the curvature according to the purpose, the magnetic flux in the vicinity of the field pole center line can be strengthened while manipulating the total magnetic flux amount as the field pole. 11 and 12 show the second and third embodiments of the present invention, and the same or corresponding parts in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted. FIG. 11 shows an example in which the inclination angle θ2 and the crossing angle θ1 of the permanent magnet are both relatively large, and shows a case where the securing of the magnetic flux amount as the entire field pole is more important than the concentration of magnetic flux, and the securing of the magnetic flux amount. The configuration in the case where the arc end of the permanent magnet on the center side of the field pole is relatively away from the center of the field pole is shown. FIG. 12 shows a configuration in which both the inclination angle θ2 and the crossing angle θ1 of the permanent magnet are relatively small, and the concentration of the magnetic flux near the center of the field pole is more important than securing the amount of magnetic flux.
[0028]
FIG. 13 shows a fourth embodiment. The curvature does not need to be unitary, and the same effect can be obtained by making the curvature large between the poles of the field pole and small on the pole center line side. It is easily inferred that it may be partially straight within a range that satisfies the gist of the present invention. Furthermore, the same effect can also be obtained by dividing the curvature of the target slit into a plurality of portions and lining up the straight slits at a predetermined angle and bending them in an equivalent manner. In this case, the permanent magnet into which the slit is inserted may be a flat plate arranged in parallel in the thickness direction, instead of the radial orientation described above. The permanent magnets on both sides of the field pole center line constituting the same field pole are not necessarily divided, and may be constituted as a single unit as long as the slits are continuous. In addition, if the permanent magnet placed in the slit has a high magnetic flux density, the center of the normal field pole may be used depending on the application in which the motor is used. It is possible to divide by the magnetic material of the rotor without merging the slits that merge at. That is, it is possible to bridge with a magnetic material that connects the outer periphery and the inner periphery of the rotor with the permanent magnet sandwiched between the poles of the field pole. This prevents a part of the magnetic flux concentrated at the center of the field pole from saturating the bridge and prevents further magnetic flux from passing therethrough, so that the rotor of the present invention can be obtained without losing the magnetic flux concentration so much.
[0029]
【The invention's effect】
In the present invention, the magnetic material of the rotor is provided with an arc-shaped slit across the field pole center line so as to form the same field pole, and the slit is located between the field poles on the outer periphery side of the rotor and the field pole center. Since it is applied to the inner peripheral side on the line side, the magnetic flux inevitably tends to gather at the center of the field pole by arranging a permanent magnet having the same shape and the same polarity as the slit in the slit. Therefore, the magnetic flux distribution on the rotor surface as the field pole is sinusoidal even if the magnetic material is interposed between the permanent magnet and the outer periphery of the rotor, and the dispersion of the magnetic flux is suppressed. In particular, if the permanent magnets arranged in the slit are oriented radially with the arc center side of the permanent magnet as the focal point, the magnetic flux is directed toward the field pole center line as it approaches the field pole center. Is more strongly suppressed.
[0030]
Since the rotor surface magnetic flux has a smooth sine wave shape, the winding structure of the stator that forms the motor in combination with the rotor can generate an induced voltage with a sine wave shape even if it is a simple structure such as concentrated winding of one coil. It can be. This is an extremely effective effect when the number of slots of the stator is small. For example, a winding such as a 3-slot or 6-slot stator is wound around one stator tooth in a concentrated manner, and an excitation pole of an arbitrary phase is obtained. This is particularly effective when trying to generate the above.
[0031]
In addition, the 12 slots and 24 slots taken up in the embodiments of the present invention can be said to be suitable methods for simplifying the winding and making the motor easy to manufacture. As a result, a low vibration motor can be easily obtained. Further, in the rotor of the conventional example, the surface magnetic flux of the rotor is almost uniform, so that when it is configured as a motor, the center position of the field magnetic pole is likely to change due to the armature reaction at the time of load. Therefore, for the control to detect the rotor position and flow the current to the stator winding, the optimum energization timing and the position will vary depending on the load, making the control extremely difficult, and making the motor stable and efficient. Not only can it not be driven well, but the generated torque of the motor pulsates, which is the cause of the generation of noise and vibration.
[0032]
In the present invention, as described above, the slit of the rotor is provided so that the magnetic flux of the permanent magnet is concentrated on the central axis of the field magnetic pole, and the permanent magnet is arranged in the slit. There is little fluctuation with respect to the load at the center of the field pole due to the armature reaction pointed out in the above, and stable driving can be performed without special control, and also from this aspect, stable efficiency, low vibration, and low noise are realized. be able to.
[0033]
Further, in the rotor represented by the structure shown in FIG. 5 in the conventional example, the torque is improved by utilizing the reluctance torque generated by the excitation magnetic flux from the stator orthogonal to the magnetic flux direction of the permanent magnet in addition to the torque generated by the permanent magnet of the rotor. However, if the corresponding field pole reaches the excitation area of the winding, the magnetic flux path cross section suddenly expands due to the presence of the magnetic material between the permanent magnet and the outer periphery of the rotor. The exciting magnetic flux generated by the winding increases to generate a considerably large reluctance torque. Although this is effective in terms of average torque, it becomes a problem with respect to sound and vibration. In the present invention, as is clear from the structure of FIG. 1, the excitation magnetic flux passage cross section involved in the reluctance torque with respect to the excitation of the corresponding excitation winding is configured to gradually widen. Does not change. Therefore, there is a great effect on sound and vibration in this aspect.
[0034]
As described above, by implementing the present invention, a low vibration, low noise motor can be configured without any special operation or contrivance regarding the stator structure and its windings, and at the same time, a control for driving the motor. With respect to the motor system, it is possible to construct a motor system with low sound and vibration without performing a high-speed and complicated control method and configuration that can suppress the pulsation torque of the motor.
[0035]
As described above, the present invention is extremely useful for a brushless DC motor and an apparatus for driving and controlling the same. Furthermore, in some cases, it is possible to bridge with a magnetic material that connects the outer periphery and inner periphery of the rotor with a permanent magnet at the center of the rotor field magnetic pole, so the strength against centrifugal force due to the rotation of the rotor is greatly improved. In addition, the deformation of the outer periphery of the rotor can be suppressed. In terms of manufacturing, there is no thin and long rotor outer peripheral bridge as in the conventional example of FIG. 4, so that the structure and process of a press die for punching this out can be simplified and the rotor can be manufactured at low cost.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a rotor showing a first embodiment of the present invention.
2 is an explanatory diagram showing a flow of magnetic flux of an arbitrary field magnetic pole in the rotor of FIG. 1; FIG.
FIG. 3 is an explanatory diagram showing a magnetic flux flow and a magnetic flux distribution when the field pole shown in FIG. 2 is developed in the circumferential direction with respect to the rotor surface.
FIG. 4 is a transverse sectional view of a rotor showing a conventional example.
FIG. 5 is a cross-sectional view of a rotor showing another conventional example.
6 is an explanatory diagram showing a flow of magnetic flux in the rotor of FIG. 4;
7 is an explanatory diagram showing a flow of magnetic flux in the rotor of FIG. 5; FIG.
8 is a development explanatory view showing a configuration example of a brushless DC motor using the rotor of FIG. 4; FIG.
9 shows a change in flux linkage in an arbitrary phase of the motor shown in FIG. 8 and an induced voltage waveform generated in the phase.
FIG. 10 is a schematic diagram for explaining an inclination angle θmax.
FIG. 11 is a cross-sectional view of a rotor showing a second embodiment of the present invention.
FIG. 12 is a cross-sectional view of a rotor showing a third embodiment of the present invention.
FIG. 13 is a cross-sectional view of a rotor showing a fourth embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, 4, 8 ... Slit, 2, 5, 9 ... Magnet, 3, 6, 10 ... Magnetic material, 7 ... Stator, U, V, W ... Stator winding, S1-S12 ... Stator slot, [theta] 1 , Θ2, θmax: angle, 11: field magnetic pole center line, 12: line between the field magnetic poles, 13: average arc center line, φ: magnetic flux, Φ: magnetic flux amount, Br: magnetic flux density.

Claims (6)

In a brushless motor in which a slit is formed in the rotor core and a permanent magnet is arranged in the slit to form a field pole, the slit shape has a larger curvature than the outer periphery of the rotor and is curved along the outer periphery of the rotor. In addition, the brushless DC is characterized in that the arrangement is performed such that the inter-magnetic pole side of the rotor is closer to the outer periphery of the rotor and the central side of the magnetic pole is closer to the inner periphery of the rotor, and a permanent magnet is disposed in the slit. motor. In the slit, the tangent at the arc end of the field pole center line side of the average arc center line of the outer circumference and the inner circumference, or the intersection angle θ1 between the extension line and the field pole center line is set in the range of 0 to 90 degrees. The brushless DC motor according to claim 1. When the angle between the field pole center line of the string connecting the field poles of the arbitrary poles on the outer periphery of the rotor and the field pole center line is θmax, and the opening angle of the field pole is θk, the outer periphery and the inner periphery of the slit The inclination angle θ2 formed by the string connecting the arc ends of the average arc center line or its extension line and the field pole center line is θmax>θ2> θk / 2.
The brushless DC motor according to claim 1 or 2, wherein the brushless DC motor is within the range. 4. The brushless DC motor according to claim 1, wherein the crossing angle θ <b> 1 is made smaller as the magnetic flux density of the permanent magnet disposed in the slit is higher. 5. 4. The brushless DC motor according to claim 1, wherein the inclination angle θ <b> 2 is reduced as the magnetic flux density of the permanent magnet disposed in the slit increases. 5. 6. The brushless DC motor according to claim 1, wherein the permanent magnet disposed in the slit has a focal point on the center side of the arc and is oriented in the radial direction.

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