JP2010148209A - Dc motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC motor reduced in weight and inhibited in deterioration of motor performance and for obtaining low cogging torque. <P>SOLUTION: Openings 11a, 11b are formed at corners of the motor frame 10 opposite to the magnetic poles of a field magnet. The corners have lower magnetic flux and have little adverse effects on the motor performance when the corners are opened. Furthermore, the opening angle seen from the shaft of the openings 11a, 11b is set within a range of 2° to 14°. Thus, the DC motor of less cogging torque, is provided while being reduced in weight and in the deterioration of the motor performance. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a DC motor.

  The motor frame of the DC motor also functions as a magnetic path of magnetic force created by the field magnet. For this reason, the motor frame is usually made of magnetic metal. Magnetic metal has a high density, which is disadvantageous when it is necessary to reduce the weight of the DC motor. On the other hand, DC motors are required to be further reduced in weight in response to the reduction in weight of electronic devices. Against this background, a technique for reducing the weight by forming notches and holes in a motor frame of a DC motor is known. This technique is described in, for example, Patent Documents 1 to 3.

Japanese Utility Model Publication No. 50-75006 JP-A-4-67757 Japanese Patent Laid-Open No. 4-190646

  In the above-described patent document, it is described that if it is a portion facing the central portion of the magnetic pole of the field magnet, even if a notch or a hole is formed in the motor frame, the influence on the operation is small.

  In order to reduce the weight, it is desirable to increase the above-described notches and holes formed in the motor frame so that the proportion of the motor frame material in the entire DC motor is as small as possible. However, since the motor frame also functions as a magnetic path, if the notches and holes described above are enlarged, the magnetic path is limited and the performance as a motor is reduced.

  Therefore, the problem is to determine the balance between the weight reduction and performance degradation of the motor frame. The cited documents 1 to 3 described above do not describe this point. Further, although it is important for the motor to reduce the cogging torque, the cited documents 1 to 3 do not describe a technique for reducing the cogging torque. Therefore, an object of the present invention is to provide a direct current motor that can be reduced in weight, suppressed in performance degradation, and has low cogging torque.

  The invention according to claim 1 is an annular motor frame made of a magnetic material, a field magnet having a plurality of magnetic poles and disposed inside the motor frame, and disposed inside the field magnet. A portion facing the center of the magnetic pole of the field magnet in the motor frame is an opening forming region in which one or a plurality of openings are formed, and the portion of the opening forming region The direct current motor is characterized in that the opening angle as viewed from the rotating shaft of the rotor is in the range of 2 ° to 14 °.

  In the present invention, the portion of the motor frame facing the magnetic pole center of the field magnet is not used as a magnetic path. Therefore, even if this portion is removed, there is little influence on the performance degradation of the motor, and the above portion is reduced. When the motor frame structure is removed, the opening angle value seen from the rotation axis of this part is within a predetermined range, and the balance of the force attracted by the rotor due to the surface magnetic flux density between the magnetic pole center of the field magnet and the magnetic pole. This is based on the phenomenon that the cogging torque is lower than that of a normal motor frame structure.

  That is, according to the first aspect of the present invention, the width of the opening forming region defined by the opening angle as viewed from the rotation axis is limited to a range of 2 ° to 14 °, thereby opening the motor frame. It is possible to simultaneously obtain a weight reduction by providing an opening, a suppression of a decrease in starting torque by forming an opening in a range that does not disturb the magnetic path, and a low cogging torque characteristic.

  When there is one opening, the entire opening formation region becomes one opening. When there are a plurality of openings, a plurality of openings are formed in the opening formation region. When there are a plurality of openings, the effect of reducing the weight is reduced as compared with the case where there is a single opening, but it is advantageous in terms of securing strength.

  The opening angle seen from the rotation axis of the rotor means an angle range from one boundary portion to the other boundary portion in the radial direction when the opening forming region is seen from the rotation shaft. The larger the opening angle, the larger the circumferential dimension of the opening forming region.

  The opening formation region is ideally formed in all the portions facing the center of the magnetic pole of the field magnet, but may be a part thereof. However, if the opening formation area is arranged at an asymmetrical position when viewed from the axial direction, the radial balance of the force acting on the rotor tends to be lost, so the opening formation area is arranged at a symmetrical position when viewed from the axial direction. The structure is preferred.

  According to a second aspect of the present invention, there is provided an annular motor frame made of a magnetic material, a field magnet having a plurality of magnetic poles and disposed inside the motor frame, and disposed inside the field magnet. A portion facing the center of the magnetic pole of the field magnet in the motor frame is a thinned region with a reduced thickness, and is from a rotating shaft of the rotor in the thinned region. The DC motor is characterized in that the opening angle seen is in the range of 2 ° to 14 °.

  According to the second aspect of the present invention, the motor frame can be reduced in weight by reducing the thickness of the motor frame instead of providing an opening. Since the thinned region is a portion that is not used as a magnetic path as described in relation to claim 1, there is no problem in operation even if the thinned region is used. According to the invention described in claim 2, since the material constituting the motor frame remains in the thinned portion, it is advantageous in securing the strength of the motor frame.

  The invention according to claim 3 is characterized in that the motor frame has a substantially square shape, and the opening angle is in a range of 2 ° to 10 °. According to the third aspect of the present invention, it is possible to obtain a direct current motor with particularly reduced cogging torque.

  According to a fourth aspect of the present invention, in the first or second aspect of the present invention, the motor frame has a substantially square shape, and the opening angle is in a range of 2 ° to 6 °. According to the fourth aspect of the present invention, it is possible to obtain a DC motor having a starting torque higher than that of a normal motor frame structure and a small cogging torque.

  When the motor frame has a polygonal shape, the corner portion is formed by bending. For this reason, stress is concentrated, and the influence of this stress extends to other parts of the motor frame functioning as a magnetic path. On the other hand, when the motor frame has a square shape, the portion of the motor frame facing the center of the field magnet is the corner portion. Therefore, the opening forming region and the thin region of the present invention are formed in the portion where the stress is concentrated. When the opening formation region and the thin region are formed, the influence of the concentrated stress is alleviated, so that the residual stress in the entire motor frame is alleviated. If there is residual stress, the magnetic material tends to decrease in permeability. However, the structure according to claim 4 reduces the residual stress of the motor frame. As a result, the magnetic permeability increases. For this reason, the utilization efficiency of magnetic force becomes high and starting torque becomes large. Further, since the range of the opening angle defined in claim 4 is a range in which the cogging torque is reduced, a low cogging torque characteristic can be obtained at the same time.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the field magnet is annular.

  According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the motor frame has a substantially quadrangular shape, a corner portion has an arc shape, and the field magnet is The center of the magnetic pole is made to coincide with the corner portion, and the thickness gradually decreases from the center of the magnetic pole toward both end portions of the magnetic pole.

  A seventh aspect of the invention is characterized in that, in the first to sixth aspects of the invention, the axial dimension of the opening is equal to or greater than the axial dimension of the field magnet. According to the seventh aspect of the present invention, the motor frame portion that does not function as a magnetic path can be used to provide an opening forming region or a thin-walled region, and the DC motor can be reduced in weight while suppressing a decrease in the performance of the DC motor. Can be realized.

  ADVANTAGE OF THE INVENTION According to this invention, the direct current | flow motor from which weight reduction, suppression of a performance fall, and a low cogging torque are obtained is provided.

(1) First embodiment (configuration)
(Configuration of motor frame)
FIG. 1 is an example of a motor frame constituting a DC motor utilizing the present invention. A motor frame 10 is shown in FIG. The motor frame 10 includes an annular structure (a rectangular tube structure) having a substantially square outer peripheral shape and an inner peripheral shape with rounded corners when viewed from the axial direction. Here, the motor frame 10 is made of a steel material having ferromagnetic properties. An opening is formed in each of the four corners of the motor frame 10. FIG. 1 shows the openings 11a and 11b.

  FIG. 2 is a cross-sectional view of the motor frame 10 as viewed from the axial direction. In FIG. 2, four openings 11 a to 11 d formed in the motor frame 10 are shown. The openings 11a to 11d are formed at four corners of the motor frame 10 and have an elongated shape extending in the axial direction (see FIG. 1). Here, the openings 11a to 11d have the same shape and dimensions. FIG. 2 shows the opening angle α viewed from the rotation axis of the opening 11a. Here, the center of the angle α coincides with the center of the radius of curvature of the corner portion and coincides with the center of the motor.

  As shown in the figure, the opening angle α is an angle formed between one edge and the other edge of the opening 11a in the radial direction. In addition, when providing several opening in the part of opening 11a-11d, the area | region in which opening 11a-11d is provided becomes an opening formation area. The axial lengths of the openings 11a to 11d are the same as or longer than the axial length of salient poles of a rotor, which will be described later.

(Configuration of DC motor)
FIG. 3 is a cross-sectional view of the DC motor of the embodiment from the same viewpoint as FIG. FIG. 3 shows the DC motor 1. The DC motor 1 includes a motor frame 10 shown in FIGS. 1 and 2. Openings 11 a to 11 d are formed at four corners of the motor frame 10. A field magnet 12 is fixed inside the motor frame 10. The field magnet 12 has a cylindrical structure in which the outer periphery has a substantially quadrangular shape, the corner portion has an arc shape, and the inner periphery has a circular cross section. The field magnet 12 includes four magnetic poles 13a to 13d. In FIG. 3, the positions of the centers of the magnetic poles 13 a to 13 d are 45 °, 135 °, 225 °, and 315 ° angular positions. Further, the centers of the magnetic poles 13 a to 13 d are positions facing the four corners of the motor frame 10.

  In the angular position shown in FIG. 3, portions of 0 ° (360 °), 90 °, 180 °, and 270 ° serve as boundaries (ends) with the adjacent magnetic poles of the magnetic poles 13a to 13d. For example, the magnetic pole 13a Both end portions of the are positioned at an angular position of 0 ° and an angular position of 90 °. The field magnet 12 has a cross-sectional structure in which the thickness gradually decreases from the center of the magnetic pole toward the boundary portion of the magnetic pole, and the thickness becomes the smallest at the boundary portion.

  A rotor 14 is disposed inside the field magnet 12. The rotor 14 has a 6-slot structure with 6 salient poles as shown. A rotation shaft 15 is fixed to the rotation center of the rotor 14.

  FIG. 4 is a cross-sectional view of the DC motor whose cross-sectional shape is shown in FIG. 3 cut along a plane parallel to the axial direction. FIG. 4 shows a state in which the rotating shaft 15 of the rotor 14 is supported on the motor frame 10 by bearings 17 and 18 so as to be rotatable. Reference numeral 16 denotes a brush power supply mechanism, through which drive current is supplied to windings (not shown) wound around the salient poles of the rotor 14. These mechanisms are the same as those of a normal DC motor.

(Magnetic flux distribution of motor frame)
The present inventors investigated the state of magnetic flux in the motor frame during operation of the DC motor using computer simulation. The results will be described below. FIG. 5 is a sectional view showing an outline of a sectional shape of a general DC motor.

  FIG. 5 shows an annular motor frame 51 having a substantially rectangular outer periphery and an inner periphery with rounded corners, an outer periphery accommodated inside the motor frame 51 having a substantially square shape with rounded corners, and an inner periphery being circular. A field magnet 52 and a six-slot rotor 53 are shown.

  As a result of examining the magnetic flux distribution when the DC motor 50 shown in FIG. 5 was operated, it was found that the reference numeral 54 in the motor frame 51 has a high magnetic flux density and the reference numeral 55 has a low magnetic flux density. In particular, it has been found that the magnetic flux density of the central portion of the portion 55 of the motor frame 51 (the portion facing the center of the magnetic pole of the field magnet 52) is nearly zero. From this, it was confirmed that the portion of the motor frame facing the center of the magnetic pole of the field magnet (the central portion of the reference numeral 55) is not used as a magnetic path. On the other hand, the portion of the motor frame (portion 54) facing the vicinity of the boundary between the adjacent magnetic poles of the field magnet has been confirmed to have a high magnetic flux density and function as a magnetic path.

(About the opening angle of the opening)
FIG. 6 is a graph showing the results of measuring the relationship between the opening angle of the opening formed with the motor frame and the starting torque, and the relationship between the opening angle and the cogging torque. The values of the starting torque and the cogging torque on the vertical axis in FIG. 6 are relative values. The data shown in FIG. 6 shows the starting torque and cogging torque when the opening angles of the openings 11a to 11d (see FIG. 2) are changed from 0 ° every 2 ° in the DC motor 1 shown in FIGS. It is the data which measured the value. In addition, in each of the openings 11a to 11d, the angular positions of the centers in the radial direction are the angular positions 45 °, 135 °, 225 °, and 315 ° of FIG. As was done by changing the opening angle.

  The following can be recognized from FIG. That is, when the opening angle of the openings 11a to 11d is set to 2 ° to 14 °, an inferior value is obtained as compared with the case without the opening, and when the opening angle exceeds 14 °, To drop. Further, when the opening angle is 2 to 6 °, a larger starting torque can be obtained than when there is no opening.

  It can be inferred that this tendency was observed for the following reason. That is, when the opening angle is 14 ° or less, the decrease in the starting torque is moderate because the openings 11a to 11d are formed in the portion of the motor frame that does not function as a magnetic path during operation. It is presumed that the impact on the environment does not manifest.

  In addition, when the opening angle exceeds 14 °, the starting torque is suddenly reduced because the openings 11a to 11d are extended to the magnetic path portion and the motor frame portion functioning as the magnetic path is reduced. This is presumed to be because the tendency for the utilization efficiency of magnetic flux to decrease becomes large.

  In addition, when the opening angle is 2 to 6 °, it is surmised that the larger starting torque can be obtained than when there is no opening 11a to 11d for the following reason. That is, a large residual strain remains in the corner portion of the motor frame formed by bending. This residual strain extends to a portion that has not been bent. On the other hand, generally, when a large strain is applied to a ferromagnetic material, a phenomenon in which the magnetic permeability decreases is observed. Here, since the openings 11a to 11d are formed, the portion of the motor frame where the residual distortion exists is removed, so that the influence of the distortion is reduced and the magnetic permeability of the entire motor frame 10 is increased. Therefore, it is presumed that the magnetic resistance of the magnetic path formed in the motor frame 10 is reduced, and an effect of increasing the starting torque can be obtained by increasing the amount of magnetic flux contributing to the starting torque.

  In addition, the following is recognized from FIG. That is, when focusing on the cogging torque, if the opening angle of the openings 11a to 11d is 2 ° to 10 °, the value is reduced by about 20% compared to the case of no opening. If the opening angle exceeds 10 °, the value of the cogging torque gradually increases, and if it exceeds 18 °, the effect of reducing the cogging torque is not seen.

  What is important for the motor is that it has a large starting torque (which means high efficiency) and a small cogging torque. Therefore, in view of the balance between the two, when the opening angles of the openings 11a to 11d are 2 ° to 14, high starting torque and low cogging torque can be obtained. It is also concluded that the opening angle of the openings 11a to 11d is preferably 2 ° to 6 ° if higher starting torque is to be obtained. It is also concluded that the opening angle of the openings 11a to 11d is preferably 2 ° to 10 ° if low cogging torque is to be pursued.

(2) Second Embodiment FIG. 7 is a perspective view showing an example when two openings are formed in the opening formation region. FIG. 7 shows a state in which two openings are formed at four corners of a frame 71 having the same shape as that shown in FIG. That is, when attention is paid to one corner, openings 72 a and 72 b are provided in the opening formation region 72. This structure is the same in the other three corners.

  Although FIG. 7 shows an example in which two openings are formed in the opening formation region, the number of openings may be three or more. A structure in which a plurality of openings are arranged in the circumferential direction is also possible. Further, the shape of the opening is not limited to the shape shown in the figure, and may be a polygonal shape other than a round shape or a square shape.

(3) Third Embodiment FIG. 8 is a cross-sectional view showing an example of the embodiment. FIG. 8 shows an example in which, in the structure shown in FIG. 3, the openings 11 a to 11 d are not recessed from the front and back, but are recessed from the outer peripheral side. In this case, as shown in FIG. 8, the portions of the openings 11 a to 11 d are thinned from the outer peripheral surface, and the motor frame 10 has a structure having thin portions 10 a to 10 d at four corner portions. In the case of this structure, weight can be reduced while ensuring strength.

(4) Fourth Embodiment FIG. 9 is a cross-sectional view showing an example of the embodiment. FIG. 9 shows an example in which the field magnet is divided into magnetic poles in the structure shown in FIG. In the example shown in FIG. 9, the field magnet has a structure including field magnets 21, 22, 23, and 24 separated for each magnetic pole.

(5) Fifth Embodiment FIG. 10 is a cross-sectional view showing an example of the embodiment. In the example shown in FIG. 10, the structure of the motor frame 10 is modified in the structure shown in FIG. In this example, the thickness between the magnetic poles of the motor frame 10 (between adjacent magnetic poles of the field magnet 12) is increased. In FIG. 10, the thickened portion between the magnetic poles is indicated by reference numerals 31 to 34. A portion between the magnetic poles of the motor frame 10 provided with the thick portions 31 to 34 is a portion used as a magnetic path. By providing the thick portions 31 to 34, the cross-sectional area of the magnetic path increases, and the magnetic resistance of that portion becomes lower than that in the case where the structure is not. Thereby, magnetic loss can be reduced and the efficiency of the motor can be increased.

  According to the structure shown in FIG. 10, in addition to the above-described advantages, the weight reduction by the openings 11 a to 11 d is distributed to the thick portions 31 to 34, thereby suppressing an increase in the weight of the entire motor. The advantage of high efficiency is also obtained. The thick portions 31 to 34 can also be obtained by a structure (external structure) in which the magnetic material is adhered and fixed to the outside in the structure of the motor frame 10 shown in FIGS.

(6) Examples The following three patterns of samples were manufactured. Table 1 below summarizes the normal product, the product 1 and the product 2 using the invention. Here, the prototype DC motor was based on the structure shown in FIGS. 3 and 4 and the structure other than that described in the remarks column was the same. Thickening the gap between the frames in the working product 2 refers to the cross-sectional structure of the motor frame shown in FIG. In the implementation product 2, the weight corresponding to the weight reduction achieved by the opening formation in the implementation product 1 is directed to the thickening of the gap portion, and the overall weight is the same as that of the comparative example. The opening angle of the opening is 10 °.

  As shown in Table 1, the motor can be reduced in weight by forming openings as shown in FIG. 1 at the four corners of the motor frame facing the magnetic pole center of the field magnet. In the working product 2, the starting torque was increased and the amount of magnetic flux leakage could be greatly reduced by increasing the thickness of the inter-electrode portion of the motor frame while maintaining the same weight as the comparative example. The amount of magnetic flux leakage is a value obtained by measuring the amount of magnetic flux leaking from the motor frame by bringing the probe close to the outer portion between the magnetic poles of the motor frame.

  It is considered that the starting torque increased because the cross-sectional area of the magnetic path of the motor frame increased, the magnetic resistance in that portion decreased, and the loss of magnetic flux decreased. Further, it is considered that the amount of magnetic flux leaking from the motor frame without passing through the magnetic path portion of the motor frame is reduced for the same reason.

(7) Others In order to reinforce the openings 11a to 11d and prevent dust from entering, resin filling may be used. In the embodiment, 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 Nd—Fe—B magnet or a ferrite magnet. These magnets may be bonded magnets or sintered magnets.

  The present invention can be used for a DC motor.

It is a perspective view which shows the external appearance of the motor frame utilized for the direct-current motor of embodiment. It is sectional drawing which shows the cross-section of the motor frame of FIG. It is sectional drawing which shows the cross-section of the direct-current motor of embodiment. It is sectional drawing which shows the cross-section of the direct-current motor of embodiment. It is sectional drawing which shows the cross-section of a general DC motor. It is a graph which shows the relationship between the opening angle of the opening formed in the motor frame, and starting torque. It is a perspective view which shows the external appearance of the motor frame of embodiment. It is sectional drawing which shows the cross-section of the motor frame of embodiment. It is sectional drawing which shows the cross-section of the motor frame of embodiment. It is sectional drawing which shows the cross-section of the motor frame of embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... DC motor, 10 ... Motor frame, 11a ... Opening, 11b ... Opening, 11c ... Opening, 11d ... Opening, 12 ... Field magnet, 13a-13d ... Magnetic pole of field magnet, 14 ... Rotor, 15 ... Rotation Shaft, 16 ... brush feeding mechanism, 17 ... bearing, 18 ... bearing.

Claims (7)

An annular motor frame made of magnetic material;
A field magnet having a plurality of magnetic poles and disposed inside the motor frame;
A rotor disposed inside the field magnet,
A portion of the motor frame facing the center of the magnetic pole of the field magnet is an opening forming region in which one or a plurality of openings are formed, as viewed from the rotation axis of the rotor in the opening forming region. A direct current motor having an opening angle in a range of 2 ° to 14 °. An annular motor frame made of magnetic material;
A field magnet having a plurality of magnetic poles and disposed inside the motor frame;
A rotor disposed inside the field magnet,
A portion of the motor frame facing the center of the magnetic pole of the field magnet is a thin region with a reduced thickness, and an opening angle of the thin region as viewed from the rotation axis of the rotor is 2 °. A direct current motor characterized by being in a range of ˜14 °.   The DC motor according to claim 1, wherein the motor frame has a substantially square shape, and the opening angle is in a range of 2 ° to 10 °.   The DC motor according to claim 1, wherein the motor frame has a substantially square shape, and the opening angle is in a range of 2 ° to 6 °.   The DC motor according to claim 1, wherein the field magnet is annular. The motor frame has a substantially quadrangular shape, and a corner portion has an arc shape,
6. The field magnet according to claim 1, wherein a thickness of the field magnet gradually decreases from the center of the magnetic pole toward both ends of the magnetic pole while the center of the magnetic pole is opposed to the corner. The DC motor according to one item.   6. The DC motor according to claim 1, wherein the dimension of the opening in the axial direction is equal to or greater than the dimension of the field magnet in the axial direction.

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