JP2010141985A - Direct current motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for suppressing the occurrence of cogging torque. <P>SOLUTION: Field magnets of two types different in thickness are arranged in an axial direction. A phase of an output waveform of cogging torque which occurs when the field magnet different in thickness exists in a single body makes opposite by using that the phase of the waveform of cogging torque changes if thickness of the field magnet is changed. When the magnets of the two types are adjacently disposed in the axial direction, the waveforms of two cogging torque negate each other by synthesizing them. A value of a peak of the waveform of cogging torque can be suppressed. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a DC motor.

  As a technique for suppressing the cogging torque, Patent Document 1 describes a configuration in which the thickness of the field magnet is increased at the center in the axial direction.

JP 2003-111361 A

  The technique described in Patent Document 1 describes a configuration in which the thickness of the central portion of the field magnet is increased in the axial direction and is decreased toward the front and rear. If the thickness of the field magnet is changed, the cogging torque can be reduced. However, the cogging torque reducing action is not sufficient.

  An object of the present invention is to provide a DC motor that can effectively suppress the generation of cogging torque.

  The invention according to claim 1 includes an annular yoke, and a first field magnet and a second field magnet fixed adjacent to the inner peripheral surface of the yoke in the axial direction, The field magnet and the second field magnet have different thickness dimensions, and the period of the cogging torque obtained when only the first field magnet is provided and the second field magnet is not provided. The phase of the waveform and the phase of the periodic waveform of the cogging torque obtained when only the second field magnet is provided and the first field magnet is not provided are opposite or substantially opposite in phase. DC motor.

  The present inventors performed computer simulation of cogging torque when the thickness of the field magnet was changed. As a result, it was found that the phase of the periodic waveform of the cogging torque changes when the thickness dimension of the field magnet is changed. Here, the periodic waveform of the cogging torque is a graph of the fluctuation of the cogging torque when the rotor makes one rotation (360 degrees).

  On the other hand, a principle is known in which cancellation is performed by superimposing two waveforms having the same period and a phase difference of 180 ° (π), and the amplitude of the waveform after superposition can be reduced. The present invention is based on this principle and the result of the above simulation. Two field magnets are arranged side by side in the axial direction, the waveform of cogging torque generated by the influence of one field magnet, and the other field. The thickness dimensions of the two field magnets are set to values different from each other so that the waveform of the cogging torque generated by the influence of the magnetic magnet is in an opposite phase.

  That is, the field magnet is divided into two in the axial direction, and the thickness dimension of each of the field magnets is basically set to the first thickness and the second thickness that satisfy the anti-phase condition of the cogging torque. The basic principle is to suppress the occurrence of cogging torque itself.

  According to a second aspect of the present invention, in the first aspect of the present invention, the first rotor housed inside the first field magnet, and the first rotor share a rotating shaft. A second rotor housed inside the second field magnet, the outer diameter of the first rotor and the outer diameter of the second rotor having different dimensions, A gap between an inner circumferential surface of the first field magnet and an outer circumferential surface of the first rotor, an inner circumferential surface of the second field magnet, and an outer circumferential surface of the second rotor. The gaps between are the same or substantially the same.

  According to the invention of claim 2, even if the thickness dimension of the first field magnet and the thickness dimension of the second field magnet are different, the outer diameter of the rotor is made to correspond to the difference. By setting it as a different dimension, the clearance gap dimension between a field magnet and a rotor can be made the same. Although it is not essential to make the gap dimensions the same, by minimizing the gap dimension as much as possible, the amount of magnetic flux flowing into the rotor is maximized. By increasing the amount of magnetic flux flowing into the rotor, the motor torque is increased, and as a result, energy consumption can be reduced. The minimum gap size here is generally determined by component processing accuracy, assembly reliability, cost, and the like.

  According to a third aspect of the present invention, in the first aspect of the present invention, the first rotor housed inside the first field magnet, and the first rotor share a rotating shaft. A second rotor housed inside the second field magnet, and the outer diameter of the first rotor and the outer diameter of the second rotor are the same or substantially the same size. A gap between the inner peripheral surface of the first field magnet and the outer peripheral surface of the first rotor, the inner peripheral surface of the second field magnet, and the second rotor. The annular yoke includes a first inner diameter portion and a second inner diameter portion so that a gap between the outer circumferential surface and the outer circumferential surface is the same or substantially the same.

  According to invention of Claim 3, even if the thickness dimension of a 1st field magnet differs from the thickness dimension of a 2nd field magnet by making the internal diameter of a yoke into a 2 step | paragraph structure, The gap size between the field magnet and the rotor can be made the same. Although it is not essential to make the gap dimensions the same, by minimizing the gap dimension as much as possible, the amount of magnetic flux flowing into the rotor is maximized. By increasing the amount of magnetic flux flowing into the rotor, the motor torque is increased, and as a result, energy consumption can be reduced. The minimum gap size here is generally determined by component processing accuracy, assembly reliability, cost, and the like.

  According to a fourth aspect of the present invention, there is provided an annular yoke, a first field magnet and a second field magnet fixed in the axial direction adjacent to the inner peripheral surface of the yoke, and the first field. A first rotor housed inside a magnet magnet, and a second rotor sharing a rotating shaft with the first rotor and housed inside the second field magnet, The first field magnet and the second field magnet have different thickness dimensions, and the outer diameter of the first rotor and the outer diameter of the second rotor are different. , A gap between the inner peripheral surface of the first field magnet and the outer peripheral surface of the first rotor, the inner peripheral surface of the second field magnet, and the outer peripheral surface of the second rotor. The direct current motor is characterized in that the gap between the two is the same or substantially the same.

  According to the fourth aspect of the present invention, by changing the thickness dimension of the two field magnets arranged adjacent to each other in the axial direction, the effect of reducing the cogging torque due to the canceling effect of the antiphase waveform described above can be obtained. .

  The invention according to claim 5 is the invention according to claim 4, comprising only the first field magnet and the first rotor, the second field magnet and the second rotor. A phase of a cogging torque periodic waveform obtained when not provided, and only the second field magnet and the second rotor, and the first field magnet and the first rotor. It is characterized in that the phase of the periodic waveform of the cogging torque obtained when there is no phase is opposite or substantially opposite.

  According to a sixth aspect of the present invention, in the first to fifth aspects of the present invention, the first field magnet and the second field magnet are integrally formed.

  The invention according to claim 7 is the invention according to any one of claims 1 to 5, wherein the first field magnet and the second field magnet have an annular structure.

  ADVANTAGE OF THE INVENTION According to this invention, the direct current motor which can suppress generation | occurrence | production of cogging torque effectively is provided.

(1) First embodiment (overall outline)
FIG. 1 is a conceptual diagram showing a cross section of a DC motor using the invention cut by a plane parallel to an axis. FIG. 1 shows a DC motor 1. The DC motor 1 includes a yoke (motor frame) 2 having a round cylindrical shape and made of a magnetic material. Inside the yoke 2, a first field magnet 3 and a second field magnet 4 are housed.

  FIG. 2 is a perspective view showing the field magnet. FIG. 2A is a perspective view showing the whole, and FIG. 2B is a perspective view showing a state in which the field magnet is divided into two planes parallel to the axis. FIG. 2 shows a first field magnet 3 and a second field magnet 4.

  The first field magnet 3 and the second field magnet 4 have a circular shape when the inner circumference is seen in a cross section perpendicular to the axial direction, and the outer circumference is a rounded corner when seen in a cross section perpendicular to the axial direction. It has a quadrangular rectangular tube shape. Both field magnets differ only in the thickness dimension in the radial direction. In this example, the second field magnet 4 is obtained by enlarging (increasing) the inner diameter from the inner peripheral side of the first field magnet 3. Therefore, the first field magnet 3 and the second field magnet 4 have the same axial length and outer diameter, but different inner diameters. In addition, both materials are the same and magnetization is performed on the same conditions.

  FIG. 1 shows a rotor (rotating iron core) 5. The shaft 6 is fixed to the rotation center of the rotor 5 so as to penetrate therethrough. The shaft 6 is supported on the yoke 2 by bearings 7 and 8 so as to be rotatable. The rotor 5 has a 6-slot structure including six salient poles, and windings (not shown) are wound around the salient poles. Reference numeral 9 denotes a power feeding mechanism using a brush for supplying an exciting current to the windings wound around the salient poles of the rotor 5. Since the structure of the salient poles, windings, and brush feeding mechanism is the same as that of a normal DC motor, detailed description thereof is omitted.

  FIG. 3 is a perspective view showing the shape of the rotor. The rotor 5 has a structure in which a plurality of iron plates having six salient poles having the shape shown in the figure are stacked. The outer periphery of the rotor 5 is shaped along a circumferential line. The rotor 5 has a structure in which a first rotor portion 5a and a second rotor portion 5b having different outer diameters are arranged adjacent to each other in the axial direction with the shaft 6 in common. Here, the second rotor portion 5b has a structure in which the outer diameter of the first rotor portion 5a is reduced.

  The outer diameters of the first rotor portion 5a and the second rotor portion 5b are determined as follows. First, the dimension of the gap between the first rotor portion 5a and the first field magnet 3 is defined as d1. Further, the dimension of the gap between the second rotor portion 5b and the second field magnet 4 is d2. Here, the outer diameter of the first rotor portion 5a and the outer diameter of the second rotor portion 5b are determined so that d1 = d2.

  According to this configuration, even if there is a difference in the inner diameter of the field magnet in the axial direction, the difference is provided in the outer diameter of the rotor in the axial direction so as to fill the difference. The size of the gap can be the same in the axial direction. Although it is not essential to make the gap dimensions the same, by minimizing the gap dimension as much as possible, the amount of magnetic flux flowing into the rotor is maximized. By increasing the amount of magnetic flux flowing into the rotor, the motor torque is increased, and as a result, energy consumption can be reduced. The minimum gap size here is generally determined by component processing accuracy, assembly reliability, cost, and the like.

(How to determine thickness of field magnet)
An example of how to determine the thickness dimensions of the first field magnet 3 and the second field magnet 4 will be described. First, assuming a structure including the first field magnet 3 and not including the second field magnet 4, a waveform of cogging torque is calculated by computer simulation. At this time, the thickness of the first field magnet is selected from values appropriate for the field magnet of the DC motor. Further, the rotor 5 has a structure including the first rotor portion 5a and not including the second rotor portion 5b.

  Next, assuming a structure including the second field magnet 4 and not including the first field magnet 3, the waveform of the cogging torque is calculated by computer simulation. At this time, the thickness dimension of the second field magnet 4 is set to a value smaller than the thickness dimension of the first field magnet 3, and the cogging torque waveform is only the first field magnet 3. Then, the value is adjusted so that the phase is shifted by 180 ° (the phase is opposite). Here, the 2nd field magnet 4 is made into the shape which expanded the internal diameter of the 1st field magnet 3 (shape which was sharpened so that an internal diameter may expand from an inner periphery). The rotor 5 has a structure that includes the second rotor portion 5b and does not include the first rotor portion 5a.

  A waveform of the cogging torque in the case of only the first field magnet 3 and the first rotor portion 5a obtained as described above, and a case of only the second field magnet 4 and the second rotor portion 5b. Calculate the cogging torque waveform. FIG. 4 shows this result. The horizontal axis in FIG. 4 is the phase angle of the waveform, and the vertical axis is the relative value of the cogging torque value.

  The cogging torque is a change in resistance force that appears when the rotor is forcibly rotated from the outside. This fluctuation fluctuates periodically as shown in FIG. In this example, when the rotor is rotated once, a periodic variation of 18 cogging torques is measured.

  FIG. 4 shows a waveform A of cogging torque in the case of only the first field magnet 3 and the first rotor portion 5a, and in the case of only the second field magnet 4 and the second rotor portion 5b. The state where the waveform B of the cogging torque has a phase difference (antiphase) of 180 ° is shown. In FIG. 4, a waveform obtained by combining both waveforms is shown as a combined waveform. As shown in FIG. 4, by combining both waveforms, a cogging torque waveform canceling effect is obtained, and the cogging torque value is suppressed.

  That is, since the waveform of the cogging torque caused by the first field magnet 3 and the waveform of the cogging torque caused by the second field magnet 4 are in opposite phases, when both field magnets are used simultaneously, The anti-phase waveforms are not perfect but cancel each other, thereby suppressing the peak value of the cogging torque.

(Verification)
Based on the results of the simulation, the following three samples were prototyped.
(First sample)
A DC motor that includes the first field magnet 3 and the first rotor portion 5a, but does not include the second field magnet 4 and the second rotor portion 5b.
(Second sample)
A DC motor that includes the second field magnet 4 and the second rotor portion 5b, but does not include the first field magnet 3 and the first rotor portion 5a.
(3rd sample)
A DC motor including a first field magnet 3 and a first rotor portion 5a, and a second field magnet 4 and a second rotor portion 5b.

  Each sample had the same structure except for the portion described. The magnet material was a Nd—Fe—B rare earth bonded magnet. Here, the bond magnet refers to a magnet formed by an injection molding method using raw material pellets obtained by kneading resin powder and magnet powder. In this manufacturing method, the raw material pellets are heated to melt the resin component, and injection molding is performed. At this time, a field magnet is obtained by performing magnetization after injection molding.

  And the cogging torque of each sample was measured. Since the measurement apparatus used cannot measure the angle dependency of the cogging torque (average value is measured), the average value calculated from the simulation result of FIG. 4 was compared with the measured average value. As a result, in each sample, it was confirmed that the cogging torque values (average values) matched within a range of ± 20%. Thereby, the cogging torque reduction effect by the canceling action using the cogging torque waveform showing the opposite phase was confirmed.

  As described above, in this embodiment, two types of field magnets having different thicknesses are arranged in the axial direction. Here, changing the thickness of the field magnet makes use of the fact that the phase of the cogging torque waveform changes, and the waveforms of the cogging torque output when each of the two types of field magnets are used alone are reversed. Try to be in phase. Thereby, when these two types of magnets are arranged adjacent to each other in the axial direction, the two cogging torque waveforms are combined to cancel each other, and the peak value of the cogging torque waveform can be suppressed.

  Further, the rotor is arranged so that the difference in the thickness of the gap between the rotor and the field magnet does not occur due to the difference in thickness (difference in inner diameter) between the two field magnets arranged adjacent to each other in the axial direction. The outer diameter is a two-stage structure. Thereby, the loss by the said clearance gap becoming large is suppressed, and high efficiency can be pursued.

(2) Second Embodiment In the configuration in which the field magnets are arranged in two stages, the thicknesses of the two field magnets are changed by matching the inner diameters of the adjacent field magnets in the axial direction and changing the outer diameter. You can also have it. Hereinafter, this example will be described. FIG. 5 is a conceptual diagram showing another example of a DC motor using the invention. FIG. 5 conceptually shows a cross-sectional structure of the DC motor 50.

  A DC motor 50 shown in FIG. 5 includes a yoke 51 that also serves as a motor frame. The yoke 51 has a rectangular tube structure having a substantially quadrangular shape with rounded corners. Inside the yoke 51, a first field magnet 52 having a relatively large thickness dimension and a second field magnet 53 having a relatively small thickness dimension are accommodated. The first field magnet 52 corresponds to the field magnet 3 of FIGS. 1 and 2, and the second field magnet 53 corresponds to the field magnet 4 of FIGS. 1 and 2.

  Both the first field magnet 52 and the second field magnet 53 have a ring shape, and the outer periphery is a substantially quadrangular shape with rounded corners in contact with the inner periphery of the yoke 51, and the inner periphery is circular. The cross-sectional shape is as follows. Here, the second field magnet 53 is obtained by reducing the outer diameter of the first field magnet 52. Therefore, when the first field magnet 52 and the second field magnet 53 are arranged in the axial direction, the inner diameters match and the outer diameters do not match.

  The inner circumference of the yoke 51 has a stepped structure in the axial direction having a first inner diameter and a second inner diameter. 5 is a first inner diameter portion, and 55 is a second inner diameter portion. The inner diameter dimensions of the first inner diameter portion 54 and the second inner diameter portion 55 are such that the first field magnet 52 and the second field magnet 53 are aligned with each other in the axial direction. When the magnets are arranged side by side in the yoke 51, the outer circumference of each field magnet is in contact with the inner circumference of the yoke 51, and the inner circumference (inner diameter portion) is aligned in the axial direction.

  A rotor 56 is disposed inside the first field magnet 52 and the second field magnet 53. The rotor 56 can be divided into a first rotor portion 56a and a second rotor portion 56b for convenience, but in this example, the outer diameter is a constant structure in the axial direction.

  The rotor 56 has a 6-slot structure with 6 salient poles, and the details thereof are the same as those of a normal DC motor. A shaft 57 is fixed to the rotation center of the rotor 56 so as to penetrate therethrough. The shaft 57 is rotatably supported by the yoke 51 by bearings 58 and 59. Reference numeral 60 denotes a brush feeding mechanism. The brush power supply mechanism 60 supplies drive power to a winding (not shown) wound around the salient pole of the rotor 56. The configuration of this part is the same as that of a normal DC motor.

  In this example, the waveform of the cogging torque in the case where the first field magnet 52 and the first rotor portion 56a are provided and the second field magnet 53 and the second rotor portion 56b are not provided, The cogging torque waveform when the first field magnet 52 and the first rotor portion 56a are not provided is in an opposite phase so as to have the opposite phase magnet 53 and the second rotor portion 56b. The relationship between the thickness dimension of the first field magnet 52 and the thickness dimension of the second field magnet is selected.

  According to this configuration, the cogging torque can be reduced by the effect of canceling the waveform of the antiphase waveform shown in FIG. Moreover, the dimension of the clearance gap between the rotor 56 and the field magnets 52 and 53 can be made the same value.

(3) Third Embodiment The field magnet is not limited to an annular shape. That is, the field magnet may be separated for each magnetic pole. An example of this will be described below. FIG. 6 is a perspective view showing an example of a field magnet in a DC motor using the invention.

  In the example shown in FIG. 6, the field magnet shown in FIG. 2 is separated for each magnetic pole (in this case, four magnetic poles). That is, the first field magnet is divided into first field magnets 3a to 3d arranged at the four corners inside the yoke, and the second field magnet is arranged at the four corners inside the yoke. It is divided into two field magnets 4a to 4d. The field magnets 3a and 4a, the field magnets 3b and 4b, the field magnets 3c and 4c, and the field magnets 3d and 4d have an integral structure. Since the structure of the rotor is the same as that in the first embodiment, the description thereof is omitted. Here, an example in which the field magnet is divided for each magnetic pole in the first embodiment has been described. However, in the second embodiment, the field magnet may be divided for each magnetic pole.

(4) Fourth Embodiment In FIG. 1, an example in which the yoke is a square tube having a square cross section with rounded corners has been described. However, the present invention is applied to a DC motor having a circular outer shape of the yoke. It can also be applied. In this case, the field magnet has a cylindrical shape. Further, if the field magnet is separated for each magnetic pole, the field magnet portion having an arcuate outer periphery is arranged at each magnetic pole portion.

(Other)
The number of magnetic poles of the field magnet is not limited to four. The rotor is not limited to the 6 slots shown. The material constituting the field magnet may be an Sm—Fe—N rare earth magnet or a ferrite magnet. These magnets may be bonded magnets or sintered magnets.

  Two field magnets may be formed as a single body. In this case, the field magnet portion constituting the magnetic pole has a structure including portions corresponding to the first field magnet and the second field magnet. In addition, the rotor may have a structure separated in the axial direction as long as the rotor does not have an integral structure but has a common shaft.

  The present invention can be used for a DC motor.

It is a conceptual diagram which shows the cross section which cut the DC motor using invention by the surface parallel to an axis | shaft. It is a perspective view which shows the shape of a field magnet. It is a perspective view which shows the shape of a rotor. It is a graph which shows the periodic waveform of cogging torque. It is a conceptual diagram which shows the cross section which cut the DC motor using invention by the surface parallel to an axis | shaft. It is a perspective view which shows the shape of a field magnet.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... DC motor, 2 ... Yoke (motor frame), 3 ... 1st field magnet, 4 ... 2nd field magnet, 5 ... Rotor, 5a ... 1st rotor part, 5b ... 2nd Rotor portion, 6 ... shaft, 7 ... bearing, 8 ... bearing, 9 ... brush feeding mechanism, 50 ... DC motor, 51 ... yoke (motor frame), 52 ... first field magnet, 53 ... second field Magnet magnet 56... Rotor 56 a First rotor part 56 b Second rotor part 57 Shaft 58 Bearing 59 59 Bearing 60 Brush feeding mechanism

Claims (8)

An annular yoke,
A first field magnet and a second field magnet fixed adjacent to the inner peripheral surface of the yoke in the axial direction;
The first field magnet and the second field magnet have different thickness dimensions,
A phase of a cogging torque periodic waveform obtained when only the first field magnet is provided and the second field magnet is not provided; and only the second field magnet is provided, and the first field magnet is provided. A DC motor characterized in that a phase of a cogging torque periodic waveform obtained when a magnet is not provided is opposite or substantially opposite in phase. A first rotor housed inside the first field magnet;
A second rotor that shares a rotation axis with the first rotor and is housed inside the second field magnet;
The outer diameter of the first rotor and the outer diameter of the second rotor have different dimensions,
A gap between an inner circumferential surface of the first field magnet and an outer circumferential surface of the first rotor, an inner circumferential surface of the second field magnet, and an outer circumferential surface of the second rotor. The DC motor according to claim 1, wherein a gap between the two is the same or substantially the same. A first rotor housed inside the first field magnet;
A second rotor that shares a rotation axis with the first rotor and is housed inside the second field magnet;
The outer diameter of the first rotor and the outer diameter of the second rotor have the same or substantially the same dimensions,
A gap between an inner circumferential surface of the first field magnet and an outer circumferential surface of the first rotor, an inner circumferential surface of the second field magnet, and an outer circumferential surface of the second rotor. The DC motor according to claim 1, wherein the annular yoke includes a first inner diameter portion and a second inner diameter portion so that a gap therebetween is the same or substantially the same. An annular yoke,
A first field magnet and a second field magnet fixed adjacent to the inner peripheral surface of the yoke in the axial direction;
A first rotor housed inside the first field magnet;
A second rotor that shares a rotation axis with the first rotor and is housed inside the second field magnet;
The first field magnet and the second field magnet have different thickness dimensions,
The outer diameter of the first rotor and the outer diameter of the second rotor have different dimensions,
A gap between an inner circumferential surface of the first field magnet and an outer circumferential surface of the first rotor, an inner circumferential surface of the second field magnet, and an outer circumferential surface of the second rotor. A direct current motor characterized by having the same or substantially the same gap.   A phase of a periodic waveform of cogging torque obtained when only the first field magnet and the first rotor are provided and the second field magnet and the second rotor are not provided; The phase of the periodic waveform of the cogging torque obtained when only the second field magnet and the second rotor are provided and the first field magnet and the first rotor are not provided is antiphase or substantially The direct current motor according to claim 4, wherein the direct current motor has a reverse phase.   The DC motor according to any one of claims 1 to 5, wherein the first field magnet and the second field magnet are integrally formed.   The DC motor according to claim 1, wherein the first field magnet and the second field magnet have an annular structure.   The DC motor according to any one of claims 1 to 6, wherein the first field magnet and the second field magnet are separated for each magnetic pole.

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