JP2010130724A - Magnet for electric motors, and dc motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide such structure that prevents the drop of starting torque of a motor due to cogging torque while reducing it. <P>SOLUTION: The change to the radial angle in the direction of a magnetic vector between the magnetic poles of a field magnet is made small, that is, the rate of change in the angle of the magnetic vector in the range of &plusmn;10&deg; from the center between the magnetic poles of the field magnet is made 1.5 or under. Hereby, it reduces the cogging torque while suppressing the drop of starting torque. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a motor magnet and a DC motor.

  In motors, it is important to reduce cogging torque. As a technique for reducing the cogging torque in a DC motor, for example, a technique described in Patent Document 1 is known. Patent Document 1 describes a configuration in which a surface magnetic flux waveform in a field magnet is set to 0 at a portion where the polarity is reversed, and a sinusoidal waveform in which the surface magnetic flux density is thinned so as to be a small value in the vicinity thereof. .

JP 2003-111360 A

  The configuration described in the cited document 1 is one method for reducing the cogging torque. However, since the magnetic flux density in the vicinity where the polarity of the field magnet is switched decreases, the starting torque of the motor decreases.

  Accordingly, an object of the present invention is to provide a configuration that can reduce the cogging torque while preventing the decrease in the starting torque of the motor as much as possible.

  The invention according to claim 1 is a field magnet having a plurality of magnetic poles fixed along the inner peripheral surface of the annular yoke, at the center of the magnetic pole of the field magnet as viewed from the center of rotation. The magnetic vector in the field magnet is parallel or substantially parallel to the radial direction, and the magnetic vector in the field magnet is perpendicular or substantially perpendicular to the radial direction at the boundary between adjacent magnetic poles of the field magnet, The motor magnet is characterized in that the rate of change of the angle of the magnetic vector in the range of ± 10 ° from the boundary of the magnetic pole of the field magnet is greater than 0 and 1.5 or less.

  The angle of the magnetic vector is the angle in the direction of the magnetic vector in the field magnet, and the rate of change of the angle of the magnetic vector is the rate of change of the angle. In the present invention, the ratio of the change in the direction of the magnetic vector in the field magnet with respect to the change in the angle in the radial direction as viewed from the center of rotation (the portion corresponding to the rotation axis of the motor when assembled as a motor) is represented by the magnetic vector in the field magnet. Is defined as the rate of change in angle (change rate of magnetic vector angle).

  For example, when the change in the direction of the magnetic vector with respect to the change in the radial direction viewed from the center of the rotation axis is abrupt, the rate of change in the angle of the magnetic vector increases. Further, when the change in the direction of the magnetic vector with respect to the change in the radial direction as viewed from the center of the rotation axis is moderate, the change rate of the angle of the magnetic vector becomes small. Note that the rate of change in the angle of the magnetic vector is a dimensionless number because it is a change in the direction of the magnetic vector (change in angle) with respect to a change in angle in the radial direction as viewed from the center of the rotation axis.

  Next, the meaning of setting the rate of change of the magnetic vector angle in the field magnet in the range of ± 10 ° from the boundary of the magnetic pole of the field magnet to be greater than 0 and 1.5 or less will be described. The rate of change in the angle of the magnetic vector under this condition is 0 when there is no change in the angle of the magnetic vector in the field magnet in the range of ± 10 ° from the boundary of the magnetic pole of the field magnet. At the boundary of the magnetic pole of the field magnet, the polarity of the magnetic pole is switched, and the switched portion does not contribute to the generation of the starting torque. Therefore, the fact that there is no change in the angle of the magnetic vector in the field magnet in the range of ± 10 ° from the boundary of the magnetic pole of the field magnet means that the range does not contribute to the starting torque. Therefore, in the present invention, a condition is adopted in which the change rate of the angle of the magnetic vector in the field magnet in the range of ± 10 ° from the boundary of the magnetic pole of the field magnet is larger than zero.

  According to the measured data, when the rate of change of the angle of the magnetic vector in the field magnet in the range of ± 10 ° from the boundary of the magnetic pole of the field magnet is 1.5 or less, compared to the rate of decrease in cogging torque, The rate of decrease in the effective portion of the magnetic flux generated by the magnet magnet is reduced, and a difference between the two begins to occur. That is, it is possible to relatively suppress a decrease in the utilization efficiency of the magnetic flux generated by the field magnet while reducing the cogging torque.

  Since the utilization efficiency of the magnetic flux generated by the field magnet is proportional to the starting torque, this means that the reduction of the starting torque can be relatively suppressed while the cogging torque is reduced. Based on this, the above numerical range is selected.

  As a method of controlling the rate of change of the angle of the magnetic vector in the field magnet in a range of ± 10 ° from the boundary of the magnetic pole of the field magnet when viewed from the rotation center, a method of adjusting the composition of the raw material of the field magnet, There are a method of adjusting the molding conditions (pressure, etc.) when molding the field magnet, a method of adjusting the magnetizing conditions, and a method of combining a plurality of these factors.

  The direction of the magnetic vector can be accurately measured three-dimensionally with a dedicated measuring device. By setting the measuring conditions of this device, the direction of the magnetic vector is within ± 10 ° from the boundary of the magnetic pole of the field magnet as viewed from the center of rotation. Data on the change rate of the angle of the magnetic vector in the field magnet can be obtained accurately.

  Hereinafter, an outline of a method for setting the change rate of the angle of the magnetic vector in the field magnet in the range of ± 10 ° from the boundary of the magnetic pole of the field magnet when viewed from the center of rotation will be described. First, a parameter (for example, magnetization condition) for controlling the rate of change of the angle of the magnetic vector in the present invention is determined. And the data regarding the correlation between this parameter and the change rate of the angle of the magnetic vector in the present invention is acquired. Next, by using the acquired correlation, the value of the above-mentioned parameter for obtaining a field magnet having a target magnetic vector angle change rate is selected, and the field magnet is manufactured. In this way, a field magnet having a desired change rate of the angle of the magnetic vector is obtained.

  According to a second aspect of the present invention, in the first aspect of the present invention, the rate of change of the angle of the magnetic vector is 1.3 or less. In the data obtained by the inventors, when the rate of change of the angle of the magnetic vector defined in claim 1 is 1.3 or less, the rate of decrease in the starting torque is further smaller than the rate of decrease in the cogging torque. As a result, the difference in the degree of reduction between the two increases more remarkably. That is, the decrease in cogging torque becomes more prominent, and on the other hand, the degree of decrease in the start-up torque becomes more gradual. Therefore, by adopting the limitation of claim 2, it is possible to obtain a field magnet for obtaining a motor having a lower cogging torque and a small decrease in starting torque.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein the change rate of the angle of the magnetic vector is 0.8 or more. As described above, when the rate of change of the angle of the magnetic vector is 1.5 (more remarkably 1.3) or less, the effective portion of the magnetic flux generated by the field magnet is compared with the rate of decrease of the cogging torque. The rate of decrease in the ratio decreases, and a difference between the two begins to occur. However, this tendency shows a saturation tendency when the change rate of the angle of the magnetic vector is about 1.0, and shows a clear saturation tendency at about 0.8.

  An object of the present invention is to reduce the cogging torque while suppressing a decrease in the starting torque. On the other hand, from FIG. 3, when the rate of change of the angle of the magnetic vector in the range of ± 10 ° from the boundary of the magnetic pole of the field magnet decreases, the effective portion of the magnetic flux generated by the field magnet that becomes the source of the starting torque decreases. The tendency to do can be seen. Therefore, it is preferable that the value of the change rate of the angle of the magnetic vector is not made as small as possible.

  When the data shown in FIG. 3 is analyzed, the rate of decrease in the effective portion of the magnetic flux generated by the field magnet is smaller than the rate of decrease in cogging torque, and the range in which the difference between the two gradually increases is as follows: The rate of change of the angle of the magnetic vector in the field magnet in the range of ± 10 ° from the boundary of the magnetic pole of the field magnet starts from about 1.5 (more noticeably about 1.3), and about 1.0 (margin) In the range of about 0.8).

  In a range outside this range, there is no tendency for a significant difference between the starting torque reduction rate and the cogging torque reduction rate corresponding to the decrease in the change rate of the angle of the magnetic vector. From the above consideration, in order to suppress the decrease in the starting torque and reduce the value of the cogging torque, the lower limit of the change rate of the angle of the magnetic vector is set to 1.0 and the margin is set to 0.8. It is concluded that this is desirable.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the shape of the field magnet viewed from the axial direction has a polygonal outer shape with rounded corners. And According to invention of Claim 4, the field magnet for motors which has a square cylinder shape with a rounded corner is provided.

  The invention according to claim 5 is characterized in that, in the invention according to any one of claims 1 to 3, the shape of the field magnet viewed from the axial direction has an annular shape. To do. According to invention of Claim 5, the field magnet for cylindrical motors is provided.

  The invention according to claim 6 includes a field magnet using the motor magnet according to any one of claims 1 to 5, and a plurality of salient poles arranged inside the field magnet. A direct current motor comprising a rotor. According to the sixth aspect of the present invention, there is provided a DC motor that can reduce the cogging torque and suppress the decrease in the starting torque of the motor as much as possible.

  ADVANTAGE OF THE INVENTION According to this invention, the structure which can prevent the fall of the starting torque of a motor by it can be reduced as much as possible while reducing a cogging torque.

(1) First embodiment (overall outline)
FIG. 1 is a conceptual diagram of a cross section viewed from the axial direction of a DC motor using the invention. A DC motor 100 is shown in FIG. The DC motor 100 has a cylindrical structure having a square cross section with rounded corners made of a magnetic material, and includes a yoke 101 that also serves as a motor frame. Inside the yoke 101 is housed a field magnet 102 having an outer shape that fits within the yoke 101, the outer shape being a quadrangle with rounded corners, and the inner shape having a circular cross-sectional shape.

  In the space inside the field magnet 102, a rotor 103 made of a magnetic material is housed. The rotor 103 rotates with respect to the field magnet 102 around the rotation shaft 104. In this example, the rotor 103 includes six salient poles. Coils (not shown) are wound around these salient poles, and these coils receive power from a brush power supply mechanism (not shown). Since these structures are the same as those of a normal motor, illustration and description are omitted.

(Field magnet structure)
The field magnet 102 has four corners as magnetic poles. In this example, each corner is magnetized in the order of N pole → S pole → N pole → S pole. The centers of these magnetic poles are configured to coincide with the portion where the radial thickness is maximum. In addition, the thickness of the field magnet 102 in the radial direction has a cross-sectional shape that is minimized at the center portion between the magnetic poles, that is, at the portion where the magnetic poles are switched.

  The field magnet 102 is made of anisotropic Sm—Fe—N magnet powder. An arrow (105 as an example) in the field magnet 102 in FIG. 1 conceptually shows the state of magnetic vector distribution in the field magnet.

  Hereinafter, the definition of the angle will be described. First, the basic angle is called a mechanical angle. The definition of the mechanical angle is described in the lower part of FIG. The mechanical angle is set to 0 ° in the 9 o'clock direction (left direction) in FIG. 1, and from there, the clockwise 12 o'clock direction (upward) is 90 °, the 3 o'clock direction (right direction) is 180 °, 6 ° The hour direction (downward) is defined as 270 °. According to this definition, the portion indicated by A in FIG. 1 is a portion having an angle of 0 °. A portion indicated by B is a portion having an angle of 180 °.

  In the field magnet 102, the portion where the magnetic pole is switched is the portion where the thickness in the radial direction is the smallest, and the position is an angle position of 0 ° (360 °), 90 °, 180 °, 270 ° when viewed in mechanical angle. Become. In these portions, the direction of the magnetic vector in the field magnet is perpendicular (or substantially perpendicular) to the radial direction. In other words, in these portions, the direction of the magnetic vector coincides with or substantially coincides with the direction of the tangent to the circumferential direction of the inner circumference of the field magnet 102. On the other hand, in the portions of angles 45 °, 135 °, 225 °, and 315 ° that are the central portions of the magnetic poles in the field magnet, the direction of the magnetic vector is parallel to the radial direction (that is, the same direction or the opposite direction) or substantially parallel. Become.

  Considering the angle of the magnetic vector with respect to the tangential direction of the inner peripheral surface of the field magnet, the angle of the magnetic vector with respect to the tangential direction at the mechanical angle of 0 ° is 0 ° (that is, parallel), and the mechanical angle is 45 °. 90 ° (right angle) in the part, 0 ° (parallel) in the part with the mechanical angle of 90 °, 90 ° (right angle) in the part with the mechanical angle of 135 °, and 0 ° (part with the mechanical angle of 180 °) Parallel), 90 ° (right angle) at the mechanical angle of 225 °, 0 ° (parallel) at the mechanical angle of 270 °, and 90 ° (right angle) at the mechanical angle of 315 ° .

  FIG. 2 shows a summary of this relationship. In FIG. 2, the horizontal axis is the mechanical angle, and the vertical axis is the angle of the magnetic vector with respect to the tangential direction of the inner peripheral surface of the field magnet.

  As shown in FIG. 1, the direction of the magnetic vector in the field magnet is gradually 45 between the central part of the magnetic pole (for example, 45 ° part) and the part where the magnetic pole is switched (for example, 90 ° part). It varies in the range of °. This is realized by performing magnetization so as to have such a distribution.

  The rate of change in the direction of the magnetic vector is the rate of change in the angle of the magnetic vector. In the present specification, the change rate of the angle of the magnetic vector is represented by Δθ / Δφ. Here, θ is the angle of the magnetic vector, φ is the mechanical angle, and these minute changes are Δθ and Δφ. The definition of the magnetic vector angle θ is the same as the mechanical angle. Intuitively, the slope of the graph of FIG. 2 corresponds to the change rate of the magnetic vector angle.

  According to this definition, the rate of change in the angle of the magnetic vector is relatively large, which means that the rate of change in the radial direction of the magnetic vector is relatively large (i.e. The direction changes significantly). Conversely, the rate of change in the angle of the magnetic vector is relatively small, which means that the rate of change in the direction of the magnetic vector in the radial direction is relatively small (that is, the change in the direction of the magnetic vector depending on the location is small). Means.

(Explanation of experimental data)
A motor provided with the field magnet shown in FIG. 1 was produced. At this time, the magnetic vector in a range of ± 10 ° centering on the four portions where the central polarity between adjacent magnetic poles is switched, that is, the mechanical angles 0 °, 90 °, 180 °, and 270 ° in FIG. A sample with a different angle change rate was prepared, and a cogging torque value of a motor using this sample was obtained. Further, the rate of change of the total magnetic flux generated from the field magnet 102 in a state where the field magnet 102 is mounted on the yoke 101 was obtained. The starting torque of the motor is almost proportional to the total amount of magnetic flux. The obtained data is shown in Table 1.

  A summary of the above data is shown in FIG. The horizontal axis of the graph shown in FIG. 3 is the rate of change in the angle of the magnetic vector described above (average value of four locations), and is calculated based on the value measured using a device that can measure the magnetization state three-dimensionally. Data. The vertical axis on the right side shows the amount of magnetic flux generated by the field magnet 102 and the value indicating the percentage of the magnetic vector angle change rate with respect to the value when the change rate of the magnetic vector angle is 2 as a reference (100%). is there. The value on the right vertical axis indicates the amount of decrease in the amount of magnetic flux that contributes to the starting torque, and indicates that the starting torque decreases as the value decreases. The vertical axis on the left side of FIG. 3 is the cogging torque of a DC motor using the field magnet measured by a dedicated measuring device.

  In FIG. 3, when the rate of change of the angle of the magnetic vector in the range of ± 10 ° in the mechanical angle 0 °, 90 °, 180 °, and 270 ° portions of FIG. 1 decreases, the cogging torque decreases linearly, On the other hand, the decrease in starting torque tends to be gentler than the decrease in cogging torque. This tendency starts to become remarkable when the change rate of the magnetic vector angle becomes 1.5 or less, and becomes more remarkable when it becomes 1.3 or less.

  From this, when the rate of change of the angle of the magnetic vector in the range of ± 10 ° in the mechanical angle 0 °, 90 °, 180 °, and 270 ° portions of FIG. 1 is set to a value of 1.5 or less (more preferably If the value is 1.3 or less), the reduction in the starting torque can be reduced compared to the reduction in the cogging torque, and the reduction in the starting torque of the motor can be prevented as much as possible while reducing the cogging torque. It is concluded that it is obtained.

  The rate of change in the angle of the magnetic vector under this condition is zero when there is no change in the angle of the magnetic vector in the field magnet in a range of ± 10 ° from the boundary of the magnetic pole of the field magnet. At the boundary of the magnetic pole of the field magnet, the polarity of the magnetic pole is switched, and the switched portion does not contribute to the generation of the starting torque. Therefore, when there is no change in the angle of the magnetic vector in the range of ± 10 ° from the boundary of the magnetic pole of the field magnet, the range does not contribute to the starting torque. Therefore, the lower limit of the change rate of the angle of the magnetic vector is a value larger than zero.

  The following limitation is also effective for the lower limit of the change rate of the angle of the magnetic vector. Referring to FIG. 3, the rate of decrease in the effective portion of the magnetic flux generated by the field magnet is smaller than the rate of decrease in cogging torque, and the difference between the two increases. When the rate of change is about 1.0, a saturation tendency is shown, and when the rate of change is about 0.8, saturation occurs.

  That is, when the rate of change of the angle of the magnetic vector in the field magnet in the range of ± 10 ° from the boundary of the magnetic pole of the field magnet becomes a value of 1.0 (more notably 0.8) or less, the magnetic vector There is no significant increase in the difference between the decrease rate of the starting torque and the decrease rate of the cogging torque corresponding to the decrease in the angle change rate. Therefore, it is desirable to set the lower limit of the rate of change of the angle of the magnetic vector to 1.0 and 0.8 to allow for a reduction in the value of the cogging torque while suppressing a decrease in the starting torque. Become.

(Field magnet manufacturing method)
Hereinafter, an example of a manufacturing method of the field magnet 102 of FIG. 1 will be described. First, an injection molding apparatus having a magnetizing function for manufacturing a field magnet will be described. FIG. 4 is a conceptual diagram showing an example of an injection molding apparatus having a magnetizing function. FIG. 4 shows an injection molding apparatus 400. The injection molding apparatus 400 includes a mold 402 having a cavity space 401. The cavity space 401 is a space serving as a mold for generating the field magnet 102 of FIG.

  The mold 402 has a separable structure and is pressed by a support structure 403. Reference numeral 404 denotes an exciting coil for controlling the crystal axis of the magnetic material in the raw material filled in the cavity space 400 and having the shape of the field magnet 102.

  The injection molding apparatus 400 includes an extrusion member 405 for injecting a raw material into the cavity space 401. The pushing member 405 slides in the injection cylinder 406. The pushing member 405 is driven by a piston 407 that slides in the cylinder 408. The piston 407 is driven by hydraulic pressure. This hydraulic pressure is adjusted by the control valve 409. The control valve 409 is controlled by the control computer 410. In addition, the control computer 410 controls the excitation coil control device 411 that supplies an excitation current to the excitation coil 404.

  The field magnet 102 in FIG. 1 is made of a material obtained by mixing anisotropic Sm—Fe—N magnet powder and resin powder as a material. In molding, the raw material is first heated to melt the resin component and filled in the injection cylinder 406. Next, in a state where an exciting magnetic flux is applied from the exciting coil to the cavity space, the raw material in which the resin component is melted is injected into the cavity space 400 by hydraulic pressure. In the course of solidification of the molten resin component, the crystal axis of the magnet powder is controlled by the excitation magnetic flux.

  At this time, the magnetic vector distribution state shown in FIG. 1 is obtained by the magnetic field applied from the exciting coil 404. The distribution state of the magnetic vector includes the distribution state and strength of the magnetic flux for excitation from the excitation coil 404, the composition of the raw material filled in the cavity, the type and composition of the resin, the injection molding conditions, the resin temperature, and the mold temperature. Etc. In other words, by controlling these parameters, the magnetic vector distribution state shown in FIG. 1 can be controlled. The content of this control may be determined experimentally. In this example, first, the condition for obtaining the state of the magnetic vector shown in FIG. 1 is experimentally found, and further, the magnetic vector in the range of ± 10 ° of the mechanical angles 0 °, 90 °, 180 °, and 270 ° of FIG. The adjustment of the rate of change of the angle is controlled by the value of the exciting current flowing through the exciting coil.

(2) Second Embodiment Next, a DC motor including an annular field magnet fixed along the inner peripheral surface of an annular yoke will be described. FIG. 5 is a cross-sectional view showing a cross-sectional structure of a DC motor using the present invention. FIG. 5 shows a DC motor 500. The DC motor 500 has a structure in which a cylindrical field magnet 502 is housed in a cylindrical yoke 501. The field magnet 502 is magnetized in the state indicated by the magnetic vector 505.

  In this example, the magnetic poles of the field magnet 502 are angle portions of the illustrated mechanical angles of 45 °, 135 °, 225 °, and 315 °. The boundaries between the magnetic poles in the field magnet 502 are angle portions of 0 ° (360 °), 90 °, 180 °, and 270 °.

  A rotor 503 having six salient poles is arranged inside the field magnet 502. The rotor 503 can rotate around the rotation shaft 504, and a coil (not shown) is wound around each salient pole. When a current flows from the brush mechanism (not shown) to the coils of the salient poles, the rotor 503 rotates around the rotation shaft 504. These mechanisms are the same as those of a normal DC motor.

(Other)
In the first and second embodiments, the number of magnetic poles of the field magnet is not limited to four. The number of magnetic poles of the rotor is not limited to 6 shown in the figure.

  The present invention can be used for a DC motor.

It is a conceptual diagram which shows the cross-section of the DC motor using this invention. It is a graph which shows the change of the direction of the magnetic vector of a field magnet with respect to the contact direction of a field magnet inner peripheral surface. This is data showing the relationship between the change rate of the magnetic vector angle between the poles and the magnetic flux generated by the field magnet, and the change rate of the magnetic vector angle between the poles and the cogging torque. It is a conceptual diagram which shows an example of the injection molding apparatus for making a field magnet. It is a conceptual diagram which shows the cross-section of the DC motor using this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... DC motor, 101 ... Yoke, 102 ... Field magnet, 103 ... Rotor, 104 ... Rotating shaft, 105 ... Magnetic vector, 400 ... Injection molding apparatus, 401 ... Cavity space, 402 ... Mold, 403 ... Support Structure 404: Excitation coil 405 ... Extruding member 406 ... Cylinder for injection 407 ... Piston 408 ... Cylinder 409 ... Control valve 410 ... Control computer 411 ... Excitation coil controller

Claims (6)

A field magnet having a plurality of magnetic poles fixed along the inner peripheral surface of the annular yoke,
Seen from the center of rotation,
At the center of the magnetic pole of the field magnet, the magnetic vector in the field magnet is parallel or substantially parallel to the radial direction,
At the boundary between adjacent magnetic poles of the field magnet, the magnetic vector in the field magnet is perpendicular or substantially perpendicular to the radial direction,
A motor magnet, wherein a rate of change of an angle of the magnetic vector in a range of ± 10 ° from a boundary between magnetic poles of the field magnet is greater than 0 and 1.5 or less.   The motor magnet according to claim 1, wherein a rate of change of an angle of the magnetic vector is 1.3 or less.   The motor magnet according to claim 1 or 2, wherein a rate of change of an angle of the magnetic vector is 0.8 or more.   4. The motor magnet according to claim 1, wherein a shape of the field magnet viewed from the axial direction has a polygonal outer shape with rounded corners. 5.   4. The motor magnet according to claim 1, wherein the shape of the field magnet viewed from the axial direction has an annular shape. 5. A field magnet using the motor magnet according to any one of claims 1 to 5,
A DC motor comprising: a rotor having a plurality of salient poles arranged inside the field magnet.

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