JP2004297969A - Electric motor with brush - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce fluctuation in output torque of an electric motor with brushes, and to suppress occurrence of cogging torque in the motor. <P>SOLUTION: Segmented auxiliary magnets 18, arranged to face a magnetic pole different from each other, are mounted on the inside circumferential surface side of a yoke 3, and on the axial directional end portion, or an overhanging portion 5a, of a main magnet 5 so as to form a magnetic field inside the yoke 3. Also, the mounting positions of these auxiliary magnets 18 are displaced by a prescribed angle in the circumferential direction to the center position of the circumferential direction of the main magnet 5. The fluctuation of the output torque of a shaft is reduced by offsetting the fluctuation of electromagnetic torque that is generated to the shaft with synthetic cogging torque produced by synthesizing main cogging torque by the main magnet 5 and auxiliary cogging torque by the auxiliary magnets 18. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a brushed electric motor, and more particularly to a technique for reducing torque ripple.
[0002]
[Prior art]
An electric motor with a brush is a device that converts a current supplied from a power supply into a mechanical rotating motion and outputs the same, and is widely used from automobile parts such as wipers to consumer devices such as OA and AV devices. I have.
[0003]
Such an electric motor with a brush has a yoke formed in a cylindrical shape with a bottom, and an armature having a plurality of armature coils is rotatably housed inside the yoke. An amateur core formed with a plurality of teeth protruding toward the inner peripheral surface of the yoke is fixed to the armature shaft, and an armature coil is wound around each of the teeth. A commutator having a plurality of commutator pieces arranged radially is axially mounted on the shaft, and the armature coils are electrically connected to the corresponding commutator pieces. A plurality of brushes connected to the positive electrode and the negative electrode of the power supply are in sliding contact with the commutator, respectively, and the current rectified by the brush and the commutator is supplied to the armature coil. .
[0004]
On the other hand, a plurality of permanent magnets are fixed to the inner peripheral surface of the yoke, for example, as shown in Patent Document 1, so that a magnetic field is formed inside the yoke. These permanent magnets are formed in an arc shape that curves along the inner peripheral surface of the yoke, are arranged to face different polarities, and are shifted from each other in the circumferential center position by an electrical angle of 180 °.
[0005]
When a current rectified by the commutator flows in the armature coil, an electromagnetic force is generated in the armature coil located in the magnetic field, and the electromagnetic force generates an electromagnetic force torque on the shaft and the armature rotates. I have.
[0006]
[Patent Document 1]
Japanese Utility Model Laid-Open No. 5-50954 (page 4-5, FIG. 1-2)
[0007]
[Problems to be solved by the invention]
Recent brushed electric motors are becoming smaller and lighter, and are structurally more prone to vibration.
[0008]
However, in the conventional brushed electric motor, the number of armature coils that generate electromagnetic force due to the rectifying action, that is, the number of effective conductors fluctuates sequentially, and the torque taken out as the rotational force of the armature fluctuates. Further, a magnetic attraction force acts between the permanent magnet and the teeth, which causes a variation in magnetic resistance with respect to the rotation of the armature, and generates a cogging torque on the shaft. In addition, the output torque taken out of the motor shaft is a combination of the electromagnetic force torque and the cogging torque by the armature coil, but in general, the electromagnetic force torque and the cogging torque are generated as waveforms having the same phase. Tends to be large. This is a factor that promotes vibration and noise of the brushed electric motor, and reducing the fluctuation of the output torque is an important issue in reducing the vibration and noise of the motor. I have.
[0009]
An object of the present invention is to reduce fluctuations in output torque in an electric motor with a brush.
[0010]
Another object of the present invention is to suppress generation of cogging torque in an electric motor with a brush.
[0011]
[Means for Solving the Problems]
An electric motor with a brush according to the present invention is an electric motor with a brush in which an armature in which a commutator slidingly in contact with a brush and an armature core provided with a plurality of teeth are fixed to a shaft is rotatably housed in a yoke. A main magnet fixed to an inner peripheral surface of the yoke and forming a magnetic field in the yoke; and a magnetic field applied to the shaft by the magnetic field of the main magnet, the main magnet being connected to the commutator and wound around the teeth. A plurality of armature coils for generating torque, and auxiliary cogging torque generating means for generating auxiliary cogging torque to be added to the main cogging torque generated by the main magnet, and applying a combined cogging torque to the shaft to offset fluctuations in the electromagnetic force torque And reduces fluctuations in the output torque of the shaft. And characterized in that.
[0012]
An electric motor with a brush according to the present invention is an electric motor with a brush in which an armature in which a commutator slidingly in contact with a brush and an armature core provided with a plurality of teeth are fixed to a shaft is rotatably housed in a yoke. A main magnet fixed to an inner peripheral surface of the yoke and forming a magnetic field in the yoke; and a magnetic field applied to the shaft by the magnetic field of the main magnet, the main magnet being connected to the commutator and wound around the teeth. A plurality of armature coils for generating torque, and auxiliary cogging torque generating means for applying auxiliary cogging torque to the shaft for canceling main cogging torque generated by the main magnet, and reducing cogging torque generated on the shaft. Features.
[0013]
The electric motor with a brush according to the present invention is characterized in that the auxiliary cogging torque generating means is an auxiliary magnet fixed to the yoke at a predetermined angle in the circumferential direction with respect to a circumferential center position of the main magnet. .
[0014]
In the electric motor with a brush according to the present invention, the auxiliary magnet has a higher magnetic flux density than the main magnet.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0016]
FIG. 1 is a cross-sectional view showing an electric motor with a brush according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the electric motor with a brush shown in FIG. FIG. 3 is a cross-sectional view showing a mounting state of an auxiliary magnet shown in FIG.
[0017]
The brushed electric motor 1 shown in FIG. 1 has a bottomed yoke 3 formed by pressing a deep drawn steel plate with a press, and the open end of the yoke 3 has a bottomed cylindrical shape formed by aluminum die casting. Is closed by the front bracket 4 formed at the bottom.
[0018]
A pair of segment-shaped main magnets 5 and 6 having different magnetic poles facing each other are fixed to the inner peripheral surface of the yoke 3 so as to form a magnetic field inside the yoke 3.
[0019]
An armature 7 is housed inside the yoke 3 in the magnetic field. The amateur 7 is rotatable inside the yoke 3 by the shaft 8 being supported by the self-aligning bearings 9 and 10 provided in the bottom 3a of the yoke 3 and the through hole 4a formed in the front bracket 4. Has become. Further, the tip of the shaft 8 protrudes to the outside from the through hole 4a, and by connecting a driven member (not shown) to this tip, the output torque of the shaft 8 can be transmitted to the driven member.
[0020]
The armature 7 has an armature core 11 fixed to a shaft 8. The amateur core 11 is formed by stacking a large number of amateur punched sheets, and is provided with twelve teeth 12 protruding radially toward the main magnets 5 and 6 on the outer peripheral side thereof. A plurality of amateur coils 13 each formed of a copper wire whose surface is insulated are wound around these teeth 12. In the present embodiment, the number of teeth 12 is set to 12, but the number is not limited to this and may be any number.
[0021]
The armature 7 has a commutator 14 fixed to the shaft 8 adjacent to the left side of the armature 11 in the drawing. The commutator 14 includes a body 14a fixed to the shaft 8 and commutator pieces 14b radially arranged on the outer periphery of the body 14a. Each of the amateur coils 13 electrically connects the corresponding commutator piece 14b. Connected.
[0022]
The front bracket 4 is provided with a pair of brush holders 15. The brush holder 15 incorporates a pair of brushes 17 which are slidably contacted with the commutator pieces 14b of the commutator 14 by springs 16, respectively. ing. These brushes 17 are electrically connected to connection terminals (not shown). When a current is supplied to the connection terminals, rectified currents flow through the armature coil 13 via the respective brushes 17 and the commutator 14. ing.
[0023]
The brushed electric motor 1 is provided with two auxiliary magnets 18 and 19 as auxiliary cogging torque generating means in addition to the main magnets 5 and 6. These auxiliary magnets 18 and 19 are supported by holders 20 and are fixed to the inner peripheral surface of the yoke 3 at axial ends of the main magnets 5 and 6, that is, at the overhang portions 5a. The different magnetic poles face each other, and are arranged to be shifted by 10 ° in the circumferential direction with respect to the circumferential center positions of the corresponding main magnets 5 and 6. These auxiliary magnets 18 and 19 form a magnetic field inside the yoke 3 similarly to the main magnets 5 and 6. In the illustrated case, the auxiliary magnets 18 and 19 are fixed using the holder 20, but are not limited to this. The auxiliary magnets 18 and 19 are directly fixed to the yoke 3 by bonding or the like, or are integrated with the main magnets 5 and 6. It may be formed. When the auxiliary magnets 18 and 19 are formed integrally with the main magnets 5 and 6, a magnetized core having a portion forming the main magnets 5 and 6 and a portion forming the auxiliary magnets 18 and 19 may be used. good.
[0024]
FIG. 4A is a characteristic diagram showing waveforms of the electromagnetic force torque and the combined cogging torque when the auxiliary magnet is mounted at a position shifted from the center position of the main magnet in the circumferential direction by 10 ° in the circumferential direction. () Is a characteristic diagram showing waveforms of the electromagnetic force torque and the main cogging torque when only the main magnet is mounted. FIG. 5 is a characteristic diagram showing the relationship between the mounting angle of the auxiliary magnet with respect to the main magnet and the torque ripple reduction effect.
[0025]
In the electric motor 1 with a brush configured as described above, when a current is supplied to the brush 17, a rectified current flows through the brush 17 and the commutator 14 to the armature coil 13 located in the magnetic field, and An electromagnetic force is generated in the armature 7 by the magnetic fields formed by the magnets 5 and 6 and the auxiliary magnets 18 and 19 according to Fleming's left-hand rule. Then, an electromagnetic force torque is generated on the shaft 8 by the electromagnetic force, and the shaft 8 rotatably supported by the bearings 9 and 10 starts rotating.
[0026]
At this time, the number of the armature coils 13 that generate an electromagnetic force, that is, the number of effective conductors changes in accordance with the rotation of the shaft 8, so that the electromagnetic force torque generated on the shaft 8 is as shown by a solid line in FIG. , The rotation angle of the shaft 8 fluctuates at a cycle of about 30 °. Further, a combined cogging torque as shown by a broken line in FIG. 4A is generated on the shaft 8 by magnetic attraction generated between the teeth 12 and the main magnets 5 and 6 and the auxiliary magnets 18 and 19. Since the output torque of the shaft 8 is obtained by combining the electromagnetic force torque and the cogging torque, this output torque is not shown, but the waveform of the electromagnetic force torque shown in FIG. The so-called torque ripple is generated by fluctuating with the combined waveform.
[0027]
Here, as a comparative example, looking at the electromagnetic force torque generated on the shaft when only the main magnets 5 and 6 are mounted, the electromagnetic force torque in this case is also shown in FIG. As in the case shown in FIG. 4A, the number of the armature coils 13 that generate the electromagnetic force varies according to the rotation of the shaft 8, so that the rotation angle of the shaft 8 varies at a cycle of about 30 °. Further, the cogging torque in this case is composed of only the main cogging torque generated between the main magnets 5 and 6 and the teeth 12, and as shown by a broken line in FIG. It has a phase difference of about 10 ° with respect to the electromagnetic force torque while varying at a cycle of °. In this case, since the phase difference between the peak of the electromagnetic force torque and the peak of the main cogging torque is small, the torque ripple of the output torque increases as shown in FIG. I have.
[0028]
On the other hand, in the brushed electric motor 1 of the present embodiment, the auxiliary magnets 18 and 19 are provided as auxiliary cogging torque generating means, so that the shaft 8 has the auxiliary magnets 18 and 19 and the teeth in addition to the main cogging torque. 12, an auxiliary cogging torque is generated by the magnetic attraction force. In this case, the auxiliary magnets 18 and 19 are located at a position where the auxiliary cogging torque generated by the auxiliary magnets 18 and 19 has a 180 ° out of phase relationship with the electromagnetic torque generated by the armature coil 13, that is, the auxiliary cogging torque and the electromagnetic torque Are arranged in such a position as to cancel out the fluctuations. This substantially coincides with the position where the fluctuation of the output torque, which is the combined torque of the electromagnetic force torque and the main cogging torque, is offset. Therefore, the combined cogging torque shown in FIG. 4A, which is the combined torque of the main cogging torque by the main magnets 5 and 6 and the auxiliary cogging torque by the auxiliary magnets 18 and 19, is a new cogging at the position shown by the arrow in the figure. Due to the creation of the peak of the torque, the phase of the peak position is shifted from the case where substantially only the main magnets 5 and 6 are mounted. The peak position of the resultant cogging torque has a relationship of 180 ° out of phase with the fluctuation of the electromagnetic force torque, thereby canceling out the electromagnetic force torque and the resultant cogging torque, as shown in FIG. Therefore, the fluctuation of the output torque of the shaft 8, that is, the torque ripple is reduced.
[0029]
As described above, in the electric motor with brushes 1 of the present invention, the fluctuation of the output torque of the shaft 8 is offset by the auxiliary cogging torque due to the magnetic attraction between the auxiliary magnets 18 and 19 and the teeth 12. 1 can reduce the fluctuation of the output torque.
[0030]
FIG. 6A is a characteristic diagram showing a waveform of the electromagnetic force torque per tooth when only the main magnet is mounted, and FIG. FIG. 6C is a characteristic diagram showing a waveform of a magnetic flux distribution per tooth when the auxiliary magnet is mounted shifted by 10 °, and FIG. 6C is a characteristic diagram showing a waveform of the electromagnetic force torque before and after mounting the auxiliary magnet. is there.
[0031]
In the case where only the main magnets 5 and 6 are mounted, if the same brush 17 simultaneously contacts two adjacent commutator pieces 14b, the corresponding armature coil 13 has both coil ends short-circuited and no current flows. As shown in FIG. 6 (A), a state in which the electromagnetic force torque is not generated partially in a predetermined cycle. Therefore, the number of the armature coils 13 through which the current flows, that is, the number of effective conductors varies according to the rotation of the shaft 8, and the electromagnetic force torque varies.
[0032]
On the other hand, in the electric motor 1 with brushes, by providing the auxiliary magnets 18 and 19 in addition to the main magnets 5 and 6, the magnetic flux distribution flowing into each tooth 12 by the magnetic field formed inside the yoke 3 is improved. Is partially increased by the magnetic field formed in the auxiliary magnets 18 and 19, as shown in FIG. Since the auxiliary magnets 18 and 19 are arranged in the circumferential direction with respect to the main magnets 5 and 6, the increase in the magnetic flux distribution increases in a portion where the electromagnetic force torque decreases. Therefore, as shown in FIG. 6 (C), the electromagnetic force torque generated on the shaft 8 as the sum of the electromagnetic forces of the respective teeth 12 is compensated for a drop as compared with the case where the auxiliary magnets 18 and 19 are not provided. Thereby, the fluctuation of the output torque is reduced. Also, by compensating for the drop in the electromagnetic force torque, the average torque output by the shaft 8 increases.
[0033]
As described above, in the brushed electric motor 1 of the present invention, since the auxiliary magnets 18 and 19 are provided in addition to the main magnets 5 and 6, the drop in the electromagnetic force torque is compensated, and the brushed electric motor 1 is compensated for. Can be reduced.
[0034]
By the way, the mounting positions of the auxiliary magnets 18 and 19 are set to 10 ° so as to cancel out the fluctuation of the combined cogging torque and the electromagnetic force torque, but the mounting positions of the auxiliary magnets 18 and 19 are not limited to this. . For example, when the mounting positions of the auxiliary magnets 18 and 19 are set to positions shifted by 15 ° in the circumferential direction from the circumferential center position of the main magnets, the main cogging torque by the main magnets 5 and 6 and the auxiliary magnets 18 and 19 As shown in FIG. 5, the cogging torque is canceled and the output torque when the current is not supplied to the armature coil 13, that is, the combined cogging torque generated on the shaft 8, is compared with the case where only the main magnets 5 and 6 are mounted. Almost halved. Therefore, in this case, even when the current supplied to the armature coil 13 is small and the shaft 8 is rotating at a low speed, the fluctuation of the output torque of the shaft 8 is reduced by reducing the combined cogging torque. Thus, the shaft 8 can be smoothly rotated. In this case, since the combined cogging torque is reduced, the starting torque of the electric motor with brush 1 can be reduced.
[0035]
The present invention is not limited to the above embodiment, and can be variously modified without departing from the gist thereof. For example, in the above-described embodiment, the auxiliary magnets 18 and 19 are attached to one end of the main magnets 5 and 6, but the present invention is not limited to this. It may be attached to only one or both sides. The shapes of the auxiliary magnets 18 and 19 are not limited to the segment shape as shown in FIG. 3, and various shapes, arrangements, and numbers can be selected. FIG. 7 is a perspective view showing a modification of the auxiliary cogging torque generating means. In the case shown in the figure, a plurality of protrusions 22 are integrally formed as auxiliary cogging torque generating means on a main magnet portion 21 for generating main cogging torque, and have an H-shaped shape as a whole.
[0036]
In short, the auxiliary cogging torque generating means only needs to be housed inside the yoke 3 and change the magnetic field generated only from the main magnets 5, 6, and the auxiliary magnets 18, 19 as in the above-described embodiment are used. Attachment to the main magnets 5 and 6 separately is only one embodiment of the auxiliary cogging torque generating means. Further, it is not always necessary to arrange the main magnets 5, 6 and the auxiliary magnets 18, 19 in contact with each other.
[0037]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the fluctuation | variation of the output torque which is the synthesis | combination of an electromagnetic force torque and a synthetic | combination cogging torque is reduced by mounting an auxiliary magnet at a predetermined angle in the circumferential direction from the circumferential center of the main magnet. Can be. This makes it possible to reduce the vibration and the noise of the electric motor with brush.
[0038]
Further, by mounting the auxiliary magnet at a further predetermined angle from the predetermined position, the generation of the combined cogging torque can be suppressed. Thus, even when the brushed electric motor is rotated at a low speed, the vibration can be reduced, and the starting torque can be reduced.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an electric motor with a brush according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of the electric motor with brush shown in FIG. 1, taken along line AA.
FIG. 3 is a sectional view showing a mounting state of the auxiliary magnet shown in FIG. 2;
FIG. 4A is a characteristic diagram showing waveforms of an electromagnetic force torque and a combined cogging torque when an auxiliary magnet is mounted at a position shifted by 10 ° in a circumferential direction from a circumferential center position of a main magnet, and FIG. () Is a characteristic diagram showing waveforms of the electromagnetic force torque and the main cogging torque when only the main magnet is mounted.
FIG. 5 is a characteristic diagram showing a relationship between an attachment angle of an auxiliary magnet with respect to a main magnet and a torque ripple reduction effect.
FIG. 6A is a characteristic diagram showing a waveform of an electromagnetic force torque per tooth when only the main magnet is mounted, and FIG. 6B is a diagram illustrating a waveform from a circumferential center position of the main magnet in a circumferential direction. It is a characteristic diagram which shows the waveform of the magnetic flux distribution per tooth at the time of attaching an auxiliary magnet by shifting by 10 degrees, and (C) is a characteristic diagram which shows the waveform of the electromagnetic force torque before and after the auxiliary magnet is mounted. .
FIG. 7 is a perspective view showing a modification of the auxiliary cogging torque generating means.
[Explanation of symbols]
Reference Signs List 1 electric motor with brush 3 yoke 4 front bracket 5, 6 main magnet 5a, 6a overhang portion 7 amateur 8 shaft 9, 10 bearing 11 amateur core 12 teeth 13 amateur coil 14 commutator 15 brush holder 16 spring 17 brush 18, 19 auxiliary Magnet 20 Holder 21 Main magnet part 22 Projecting part

Claims (4)

An electric motor with a brush in which an armature in which a commutator slidingly contacting a brush and an armature core provided with a plurality of teeth are fixed to a shaft is rotatably housed in a yoke,
A main magnet fixed to the inner peripheral surface of the yoke and forming a magnetic field in the yoke;
A plurality of armature coils connected to the commutator and wound around the teeth, and generating an electromagnetic force torque on the shaft by a magnetic field of the main magnet;
Auxiliary cogging torque generating means for generating an auxiliary cogging torque to be added to the main cogging torque generated by the main magnet, and applying a combined cogging torque to the shaft to cancel the fluctuation of the electromagnetic force torque,
An electric motor with a brush, wherein the fluctuation of the output torque of the shaft is reduced. An electric motor with a brush in which an armature in which a commutator slidingly contacting a brush and an armature core provided with a plurality of teeth are fixed to a shaft is rotatably housed in a yoke,
A main magnet fixed to the inner peripheral surface of the yoke and forming a magnetic field in the yoke;
A plurality of armature coils connected to the commutator and wound around the teeth, and generating an electromagnetic force torque on the shaft by a magnetic field of the main magnet;
Auxiliary cogging torque generating means for applying to the shaft an auxiliary cogging torque for canceling a main cogging torque generated by the main magnet,
An electric motor with a brush, wherein cogging torque generated in the shaft is reduced. 3. The brushed electric motor according to claim 1, wherein the auxiliary cogging torque generating means is an auxiliary magnet fixed to the yoke at a predetermined angle in a circumferential direction with respect to a circumferential center position of the main magnet. An electric motor with a brush. The electric motor with a brush according to claim 3, wherein the auxiliary magnet has a higher magnetic flux density than the main magnet.

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