JP5513265B2 - DC motor - Google Patents

Description

  The present invention relates to a DC motor.

  In a small DC motor, the thickness of the frame (yoke) and the thickness of the magnet are limited. For this reason, it is necessary to obtain good characteristics in a limited dimension. In general, increasing the thickness of the frame is effective for eliminating magnetic saturation. However, increasing the thickness of the frame creates significant constraints on other dimensions. In addition, increasing the thickness of the magnet increases the magnetic force, but also causes magnetic saturation. Also, the frame thickness and magnet thickness all have a large effect on the amateur diameter. When priority is given to the frame thickness or the magnet thickness, the armature diameter decreases in inverse proportion to it, and the torque decreases. About the optimal combination of the dimension of these each part, it describes in the patent document 1 and the patent document 2, for example.

JP 2003-244870 A JP 2009-1000056 A

  Japanese Patent Application Laid-Open No. H10-228667 describes the relationship between the dimensions of each part in a cylindrical brush motor. However, the cylindrical motor is disadvantageous for fixing, and the use efficiency of the magnetic force of the magnet arranged on the frame side is not high. In this regard, a DC motor using a cylindrical magnet having an outer cross-sectional shape that is substantially a square when viewed from the axial direction and a circular inner cross-sectional shape has a flat surface on the side of the frame. Easy to do. Further, since the thickness in the radial direction of the magnetic pole portion can be relatively increased considering the same magnet volume, the magnetic force of the magnet is effectively used, and high efficiency can be obtained as compared with a DC motor using a cylindrical magnet.

  Therefore, as for the DC motor using a cylindrical magnet whose outer cross-sectional shape is a substantially square when viewed from the axial direction and whose inner cross-sectional shape is a circular shape, there is knowledge about the optimal relationship of the dimensional relationship of each part. Although required, the contents described in Patent Document 1 are based on the assumption of a cylindrical magnet, and thus cannot meet this requirement.

  On the other hand, Patent Document 2 discloses an optimum relationship of dimensions of each part of a DC motor using a magnet whose outer cross-sectional shape is a substantially square when viewed from the axial direction and whose inner cross-sectional shape is a circular shape. The knowledge about is described. However, Patent Document 2 mentions the dimensional relationship regarding the frame and the magnet, but does not mention the dimension regarding the amateur (rotor). As will be described later, according to the knowledge obtained by the present inventors, when the motor is downsized, the dimensions of the frame, magnet, and amateur are closely related to the motor characteristics, and the dimensions related to the amateur are also taken into consideration. Otherwise, it has been found that the performance of the motor cannot be pursued. Therefore, the technique disclosed in Patent Document 2 is not sufficient in this respect.

  In such a background, the present invention provides a small DC motor using a cylindrical magnet having an outer cross-sectional shape that is substantially a quadrangle when viewed from the axial direction and a circular inner cross-sectional shape. An object of the present invention is to provide a configuration in which the relationship between the frame thickness, the magnet thickness, and the armature outer diameter is optimized so that the characteristics of torque and low cogging torque can be obtained.

According to the first aspect of the present invention, a cylindrical frame made of an iron material whose outer and inner corners are round when viewed from the axial direction and having a substantially square shape in cross-section, and an axial direction disposed inside the frame. A cylindrical magnet whose outer cross-sectional shape is a substantially quadrangular shape when viewed from above , a circular magnet whose inner cross-sectional shape is a thick portion, and six pole teeth extending in the radial direction An outer periphery of the pole teeth is disposed inside the cylindrical magnet with a gap, and an armature that is rotatable relative to the cylindrical magnet, and the thickness of the frame is a, The diameter of the armature as seen from the axial direction , where b is the thickness of the thinnest part of the cylindrical magnet, c is the length of one side of the frame, and d is the length of the flat part on one side of the frame. Where x is d / c ≧ 0.25, 0. A 1 ≦ (a + b) /X≦0.2 , the one side length c of the frame than 2mm square, a small DC motor which is characterized in that not more than 5mm square.

  According to the first aspect of the present invention, high torque characteristics and low cogging torque characteristics can be obtained in a well-balanced manner as backed up by the data of FIG. As shown in FIG. 2, when (a + b) / X is smaller than 0.04, the torque rapidly decreases and the cogging torque rapidly increases. Further, when (a + b) / X exceeds 0.24, the torque rapidly decreases and the cogging torque increases rapidly.

  According to the first aspect of the present invention, in a small DC motor using a cylindrical magnet whose outer cross-sectional shape is substantially a square when viewed from the axial direction and whose inner cross-sectional shape is a circular shape, There is provided a configuration in which the relationship between the frame thickness, the magnet thickness, and the armature outer diameter is optimized so as to obtain the characteristics of high torque and low cogging torque.

It is a figure which shows the cross-sectional structure seen from the axial direction of the DC motor of embodiment. It is a graph which shows the relationship between the dimensional relationship of each part, and a motor characteristic.

(Construction)
FIG. 1 shows an internal structure of the DC motor 1 according to the embodiment as viewed from the axial direction. The DC motor 1 includes a frame 2. The frame 2 is made of a magnetic material (in this example, iron material) and functions as a back yoke. The frame 2 has a cylindrical structure in which the shape of the outer periphery and the inner periphery viewed from the axial direction is a substantially square shape with rounded corners. In the figure, the thickness of the frame 2 is indicated by a, and the outer diameter dimension viewed from the axial direction is c. The outer diameter dimension c is grasped as a dimension of a portion corresponding to the length of a substantially rectangular side viewed from the axial direction. Note that both end portions of the frame 2 in the axial direction (the end portion on the near side in FIG. 1 and the end portion on the back side in FIG. 1) are covered, but at least part of the portion is integrated with the frame 2. It may be.

  A field magnet 3 (permanent magnet) is disposed inside the frame 2 in contact with the inner periphery thereof. Although the material of the field magnet 3 is not specifically limited, For example, a rare earth magnet, a ferrite magnet, etc. can be used. The field magnet 3 has a cylindrical structure in which the outer periphery viewed from the axial direction has a substantially square shape with rounded corners, and the inner periphery has a circular shape. According to this structure, when viewed from the axial direction, the field magnet 3 is formed with four thick portions 4 having relatively thick corners and four thin portions 5 having relatively small thickness. Yes. Here, the thick portions 4 at the four corners serve as magnetic poles. The four thick portions 4 are magnetized so that adjacent portions in the circumferential direction have different polarities. Further, the thickness dimension of the thin portion 3 which is the thinnest portion when viewed from the axial direction is denoted by b. In this example, the frame 2 and the field magnet 3 constitute a stator.

  When viewed from the axial direction, the field magnet 3 has four flat portions that are not rounded corner portions. The width d of these four flat portions is 33% of c (d / c = 0.33). In order to obtain the advantage of a square magnet having an outer cross-sectional shape that can effectively use the volume of the magnet as compared with a field magnet having a round cross section, it is desirable that d / c ≧ 0.25.

  Inside the field magnet 3, an armature 6 around which a coil for generating a torque with a gap is wound is disposed. The amateur 6 is an iron core that functions as an armature (in this example, a rotor (rotor)), and includes six pole teeth 8 extending in the radial direction. The tip of the pole tooth 8 is opened in an umbrella shape, and the outer periphery thereof is opposed to the inner periphery of the field magnet 3 with a gap. A coil 9 is wound around each of the pole teeth 8. In this example, the diameter of the armature 6 is indicated by the symbol X.

  A rotation shaft 7 is fixed to the rotation center of the amateur 6. The rotating shaft 7 extends in a direction perpendicular to the paper surface of the drawing, and is held in a rotatable state by bearings (not shown) at two locations sandwiching the armature 6. The outer rings of the two bearings are fixed to the frame 2, and the armature 6 is structured to be rotatable relative to a stator constituted by the frame 2 and the field magnet 3.

  Although not shown, a brush power supply mechanism is arranged on the stator side, and a drive current is supplied to the electrode (not shown) of the receiving commutator provided on the rotating shaft 7 via the brush power supply mechanism described above. Is supplied. This drive current is supplied to the coil 9 and the polarity is switched as the armature 6 rotates, so that a torque for rotating the armature 6 with respect to the field magnet 3 is generated. The configuration related to this brush power supply mechanism is the same as that of a normal DC brush motor.

(Dimensional relations of each part)
Hereinafter, a preferable relationship among a, b, c, and X in FIG. 1 will be described. FIG. 2 shows a graph in which the horizontal axis represents the dimensional ratio (a + b) / X, and the vertical axis represents the relative ratio between the torque constant and the cogging torque. FIG. 2 shows data when the outer diameter dimension c is 3 mm square, 4 mm square, 5 mm square, and 6 mm square. Here, the torque constant is a ratio when the maximum value of torque in the four types of DC motors having different outer diameter dimensions is 100. Similarly, the cogging torque is a ratio when the minimum value of the cogging torque in four types of DC motors is set to 1. Here, the torque constant indicates that the motor has a larger torque as it approaches 100. Further, it is shown that the smaller the cogging torque is, the more smoothly and smoothly rotate the characteristic is.

  As can be seen from FIG. 2, when the following formula 1 is satisfied, a characteristic in which a large torque constant and a small cogging torque are balanced can be obtained.

  Note that the data of c = 6 mm shows a tendency different from the data of other groups. Therefore, it is considered that it is appropriate that the effect obtained by setting the range of the above formula 1 is not obtained when c = 6 mm. From this, it is considered that the limitation of the number 1 is limited to the case where c = 5 mm or less.

  In addition, as a manufacturable size, the lower limit is about c = 2 mm for a DC motor having a structure in which the data of FIG. 2 can be obtained. Also, from FIG. 2, it can be seen that the data tends to shift to the right of the graph as the value of c decreases. That is, when the value of c becomes smaller than the value shown in FIG. 2, the tendency of gradually deviating from the characteristics of the data shown in FIG. 2 is suggested in FIG. From this, it is concluded that the lower limit of the value of c is about c = 2 mm.

  In addition, it can be seen from FIG. 2 that if better characteristics (high torque characteristics, low cogging torque characteristics) are obtained, the range of the following formula 2 is preferable, and the range of the following formula 3 is more preferable.

  In the following, the factors for obtaining the data of FIG. 2 will be considered. First, when (a + b) / X is less than 0.04, the torque constant decreases and the cogging torque increases. First, in this case, since the diameter of the armature 6 can be increased in a limited dimension, a margin is generated in the line product, and many thick wires can be wound, so that the torque constant increases. However, since the sum of the thickness a of the frame 2 and the thickness b of the thin portion 5 of the field magnet 3 becomes thin, the tendency for magnetic saturation to occur increases. Further, when the field magnet 3 is made thin, the magnetic force of the field magnet 3 is insufficient. For this reason, magnetism does not efficiently flow into the amateur, and the torque constant decreases. For the same reason, the tendency that the polarity of the pole teeth 8 is not smoothly switched with respect to the magnetic poles (four corners) of the field magnet 3 increases, and the cogging torque increases. In FIG. 2, it is considered that these phenomena tend to become prominent with (a + b) /X=0.04 as a boundary.

  On the other hand, when (a + b) / X exceeds 0.24, the magnet 3 can be thickened in a limited dimension, so that the magnetic force can be improved. Moreover, since the thickness of the frame 2 can be increased, it is advantageous in that the occurrence of magnetic saturation on the stator side is suppressed. However, in the condition where the value of c is limited, when a + b is increased, the value of X must be decreased, and the diameter of the armature 6 is decreased. In this case, the line product becomes small and the winding of the coil 9 becomes poor. Therefore, the torque constant tends to decrease. Further, since the balance between the magnetic force of the field magnet 3 and the magnetic force of the coil 9 is deteriorated, the polarity of the pole teeth 8 with respect to the magnetic poles (four corners) of the field magnet 3 is not smoothly switched, and the cogging torque The tendency to become higher increases. In FIG. 2, it is considered that these phenomena tend to become prominent at the boundary of (a + b) /X=0.24.

  For the above reasons, the region where the balance between the improvement in torque by the magnetic force of the field magnet 3 and the improvement in torque by securing the diameter of the armature 6 is the best is the range of the above formula 1. Conceivable. As a result, in the range of Equation 1, since the magnetic circuit on the stator side and the magnetic circuit on the amateur side are balanced, the interaction of the magnetic force is performed smoothly and the occurrence of magnetostriction is suppressed. Therefore, it is considered that the cogging torque is also suppressed.

  As described above, the value of (a + b) / X is not preferable even if it is too small, and is not preferable if it is too large. In order to obtain high torque and low cogging torque characteristics, there is an appropriate range for the value of (a + b) / X. However, as is clear from FIG. 2, this relationship has an overall dimensional dependency. When the outer diameter is 6 mm or more, it cannot be discussed in the same row.

(Other)
In FIG. 1, the outer portion where the field magnet 3 is arranged becomes a stator and the armature 5 in the inner portion rotates. However, the opposite form, that is, the field magnet 3 side rotates, and the armature 5 is rotated. The present invention can also be applied to a structure (outer rotor type) in which the side becomes a stator.

  The aspect of the present invention is not limited to the individual embodiments described above, and includes various modifications that can be conceived by those skilled in the art, and the effects of the present invention are not limited to the contents described above. That is, various additions, modifications, and partial deletions can be made without departing from the concept and spirit of the present invention derived from the contents defined in the claims and equivalents thereof.

  The present invention can be used for a DC motor.

DESCRIPTION OF SYMBOLS 1 ... DC motor 2 ... Frame 3 ... Field magnet 4 ... Thick part 5 ... Thin part 6 ... Amateur 7 ... Rotary shaft 8 ... Polar tooth 9 ... Coil

Claims (1)

A cylindrical frame made of an iron material having a substantially quadrangular cross-sectional shape with rounded outer and inner corners when viewed from the axial direction;
A cylindrical magnet disposed inside the frame and having an outer cross-sectional shape that is substantially a square when viewed in the axial direction, and a circular inner cross-sectional shape in which the corner portion is a thick portion ;
An armature comprising six pole teeth extending in the radial direction, the outer circumference of the pole teeth being arranged inside the cylindrical magnet with a gap, and being rotatable relative to the cylindrical magnet And
The thickness of the frame is a, the thickness of the thinnest portion of the cylindrical magnet is b, the length of one side of the frame is c, and the length of the flat portion on one side of the frame is d,
When the diameter of the amateur seen from the axial direction is X,
d / c ≧ 0.25,
0.1 ≦ (a + b) /X≦0.2 ,
A small DC motor, wherein a length c of one side of the frame is 2 mm square or more and 5 mm square or less.

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