JP2002078252A - Dc machine and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve rectification of a d-c motor with low cost. SOLUTION: A rotor 4 is provided with a plurality of teeth 8a and a coil 9 is wound around the teeth 8a. A motor housing 7 is formed in a bottomed and generally cylindrical shape and the rotor 4 is contained in the motor housing 7. Ferrite magnets 2, 3 formed in arcuately shaped cross section are arranged along the circumferential direction on the inner surface of the motor housing 7. By providing protrusions 7a, 7b on the motor housing 7, air gap parts 11a, 11b are formed in the part of contact surface with the ferrite magnets 2, 3 in the direction of rotation of the rotor 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a DC machine and a method for manufacturing the same.

[0002]

2. Description of the Related Art As shown in FIG. 6, a DC motor (DC motor) 20 includes ferrite magnets 21 and 22 and a rotor 2.
3, a brush 24 and the like. Core 26 of rotor 23
Are formed with a plurality of teeth 26a, and a coil 27 is wound around five of the teeth 26a. Although not shown, another coil is similarly wound around each of the five teeth 26a. That is, the winding system of the DC motor 20 is a distributed winding. Further, a commutator 28 is provided on the rotor 23. The commutator 28 includes a plurality of segments 2
8a, and 2 so as to slide on the segment 28a.
Three brushes 24 are provided.

In the DC motor 20, when a DC current flows into the coil 27 via the brush 24 and the segment 28a of the commutator 28, the direction of the current flowing through the coil 27 is changed, and the rotor 23 rotates. Has become.

Here, the change in current flowing from the brush 24 to the coil 27 will be described with reference to FIG. First, FIG.
7A, the rotor 23 rotates and the commutator 28 moves rightward with respect to the brush 24 as shown in FIG. 7B from the state in which the current I flows through the coil 27 from right to left. . Then, the two segments 28 a are short-circuited by the brush 24, and a short-circuit current i flows through the coil 27. Further, when the rotor 23 rotates, the current I flows through the coil 27 from left to right as shown in FIG. That is, when the rotor 23 rotates in the order of FIGS. 7A, 7B, and 7C, the direction of the current I flowing through the coil 27 at that time is reversed. At this time, from + I to -I
A current for making a change of 2I is supplied from the brush 24. Thus, the direction of the current I flowing through the coil 27 is changed, and the direction of the magnetic field in the core 26 wound around the coil 27 is reversed. The electromagnetic force of this coil 27,
Rotational force is generated by the magnetic force from the ferrite magnets 21 and 22, and the motor 20 is driven to rotate.

[0005] As described above, the reversal of the current I flowing through the coil 27 short-circuited by the brush 24 during the short-circuit period is called "rectification".

[0006]

When the motor 20 is driven, the coil 27 short-circuited by the brush 24 is used.
A voltage is induced in a direction that delays the rectification of the current, and a phenomenon (insufficient rectification) occurs in which the direction of the current I suddenly switches at the end of the rectification. As a result, spark discharge occurs at the rear end of the brush, causing noise and brush wear.

As a countermeasure, a method has been adopted in which the installation position of the brush 24 is moved in a direction opposite to the rotation direction of the rotor 23 to improve commutation. Since the proper position of the brush 24 changes depending on the rotation speed of the motor 20 and the current of the coil 27, it is difficult to maintain good rectification when the motor load fluctuates and the rotation speed and the current of the coil 27 change. Had become.

Accordingly, the applicant of the present application has filed Japanese Patent Application No.
No. 0566 proposes a technique capable of always performing good rectification without being affected by a load.
According to the technique, in a magnet of a motor, a magnetic flux distribution in a rotation direction of the magnet is devised so that good commutation can be maintained even when a load fluctuates. In particular,
By changing the magnetic flux density in the rotation direction of the magnet as shown in FIG. 8, it is possible to exhibit an excellent effect of improving rectification. That is, in the magnet of the motor, a part of the magnet has a magnetic flux change having a minimum point, and the magnetic flux passing through the rectifying coil 27 is increased. The change in magnetic flux generates an induced voltage that cancels a voltage (reactance voltage) generated in a direction that delays rectification, thereby improving rectification. There is a demand for a technique capable of realizing such a magnetic flux distribution excellent in rectification improvement at low cost.

An object of the present invention is to provide a DC machine capable of improving rectification at low cost and a method of manufacturing the same.

[0010]

Means for Solving the Problems To achieve the above object, an invention according to claim 1 is provided with a rotor having a plurality of teeth wound by windings, a rotor having a substantially cylindrical shape,
A yoke including the rotor, and a plurality of magnets formed in an arc-shaped cross section and disposed along a circumferential direction on an inner surface of the yoke, and at a contact surface between the yoke and the magnet, The gist is that a gap is formed in a part of the rotor on the rotation direction side.

According to a second aspect of the present invention, there is provided the DC machine according to the first aspect, further comprising a brush for short-circuiting the winding so as to reverse the direction of the current of the winding during rectification. The gist of the present invention is that when the commutation of the winding is started, the tip in the rotation direction of the tooth wound by the winding is positioned in the gap.

[0012] The invention according to claim 3 is the invention according to claim 1 or 2.
The gist of the direct current machine described in (1) is that a gap portion is formed on a contact surface with the magnet by providing a protruding portion projecting outward with the yoke.

According to a fourth aspect of the present invention, in the DC machine according to any one of the first to third aspects, the magnet is magnetized so that a magnetic flux density becomes a minimum value at a portion corresponding to the gap. The gist is that it has been done.

According to a fifth aspect of the present invention, in the method of manufacturing a DC machine according to the fourth aspect, a step of attaching an unmagnetized magnet to a predetermined position on an inner surface of the yoke, and the yoke to which the magnet is attached The gist comprises a step of inserting the rotor into the magnet and a step of magnetizing the magnet to apply a strong magnetic field in a certain direction from outside the yoke.

(Operation) According to the first aspect of the present invention,
Since a gap is formed in a part of the contact surface between the yoke and the magnet on the side of the rotor in the rotation direction, the gap serves as a magnetic resistance, and the magnetic flux in a portion of the magnet corresponding to the gap is weakened. In other words, in the magnetic flux density distribution with respect to the rotation direction of the magnet, it is possible to have a magnetic flux change having a minimum point in a part thereof, and it is possible to improve the rectification by generating an induced voltage that cancels the reactance voltage by the magnetic flux change. Become. As described above, by forming the gap on the contact surface between the yoke and the magnet, rectification can be improved at low cost.

According to the second aspect of the present invention, at the start of commutation, the tip of the tooth wound around the winding in the rotation direction is located at a position where the magnetic flux in the magnet is weakened. When the rotor rotates, the magnetic flux passing through the winding increases with the rotation. Due to this change in magnetic flux, an induced voltage that cancels out the reactance voltage is generated, and rectification can be improved.

According to the third aspect of the present invention, a void is formed on the contact surface with the magnet by providing the projection projecting outward at the yoke. According to the fourth aspect of the present invention, since the magnetic flux density is minimized at a portion corresponding to the gap, the magnetic flux density is minimized. The magnetic flux density at the portion where the light is applied can be further reduced. In this case, the change in magnetic flux can be increased, and the induced voltage associated with the change can be increased. Therefore, it becomes suitable for a DC machine in which the reactance voltage at the time of rectification becomes large.

According to the fifth aspect of the invention, when a strong magnetic field in a certain direction is applied to the magnet from outside the yoke in the magnetizing step, the gap formed on the joint surface between the yoke and the magnet becomes a magnetic resistance. And the magnetic flux at the time of magnetization passes avoiding this portion. Therefore, in the magnet, the intensity of magnetization at a portion corresponding to the gap is reduced. With this configuration, the magnet having the minimum magnetic flux density at the portion corresponding to the gap, that is, the magnet in the DC machine according to claim 4 can be easily magnetized.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a blower motor of an air conditioner unit for a vehicle will be described below with reference to the drawings. In the air conditioner unit, the magnitude of the current flowing through the blower motor changes depending on the position of the operation switch. Specifically, when the operation switch is operated to the Hi position (high output position), a current of 18 A flows to the motor, and when the operation switch is operated to the Lo position (low output position), a current of 4 A flows to the motor. It is configured as follows. Due to this change in the current, the number of rotations of the motor is changed and the amount of air sent to the air conditioner unit is adjusted.

FIG. 1 is a partial sectional view showing a schematic structure of a blower motor 1 as a DC machine. As shown in FIG.
The blower motor 1 includes ferrite magnets 2 and 3, a rotor 4,
A brush 5, a rotating shaft 6, a motor housing 7, and the like are provided.

More specifically, in the blower motor 1, a motor housing 7 as a yoke is formed in a substantially cylindrical shape with a bottom and includes the rotor 4 therein. A ferrite magnet 2 having an arc-shaped cross section is provided on the inner side of the motor housing 7.
3 are arranged along the circumferential direction. That is, the two magnets 2 and 3 are arranged to face each other across the rotor 4 in the motor housing 7. The motor housing 7 is made of a ferromagnetic material (soft iron). An N pole and an S pole are formed by the ferrite magnets 2 and 3.

The rotor 4 includes a core 8, a coil (winding) 9 wound around the core 8, and a commutator 1.
0. A plurality of teeth 8a are formed in the core 8, and a coil 9 is wound around five of the teeth 8a. In the present embodiment,
The number of the teeth 8a is 12, and the number of the teeth 8a
Are formed every 30 ° in the circumferential direction of the rotor 4. That is, the adjacent teeth 8a are formed such that the angle between the center lines thereof is 30 ° (= 360 ° / 12). Although not shown, a plurality of other coils are similarly wound around the five teeth 8a. That is, the winding method of the winding is distributed winding.

The commutator 10 is disposed at one end of the rotor 4 and has a plurality of segments (commutator pieces) 10a. Further, the two brushes 5 are disposed in a state of being urged so as to slide on the commutator 10. The DC current supplied from a DC power supply (not shown) is applied to the brush 5 and the segment 10 a of the commutator 10.
Through the coil 9. Thereby, the coil 9
The direction of the current flowing through the rotor 4 is changed, and the rotor 4 rotates in the clockwise direction (the X arrow direction in the figure), and its rotational force is transmitted via the rotating shaft 6 extending from the center of the rotor 4. It is transmitted to the outside. In the present embodiment, twelve segments 10a are provided every 30 ° in the circumferential direction, and when the rotor 4 rotates 30 ° with respect to the brush 5,
The direction of the current of the coil 9 is changed. That is, FIG.
This shows a state in which commutation of the coil 9 is started. When the rotor 4 rotates from this state, the coil 9 is short-circuited by the brush 5 and a short-circuit current flows. The rectification of the coil 9 is performed by rotating the rotor 4 by 30 ° from the state of FIG.

As shown in FIGS. 1 and 2, in the motor housing 7, protrusions 7a, 7 protruding outward are provided at positions corresponding to the ends of the ferrite magnets 2, 3 on the rotation direction side.
b is formed along the axial direction of the motor 1. FIG. 2 is a sectional view taken along the line AOA of FIG. Void portions 11a and 11b extending in the axial direction are formed by the inner surfaces of the protrusions 7a and 7b and the outer surfaces of the ferrite magnets 2 and 3. Also, at the bottom of the motor housing 7,
A mark hole 7c is formed on the center line of the ferrite magnets 2, 3. The gaps 11a and 11b are formed as shown in FIG.
As shown in the figure, the width corresponding to the angle θ2 from the position of the angle θ1 in the rotation direction of the rotor 4 is provided with reference to the line (the center line of the ferrite magnets 2 and 3) connecting the mark hole 7c and the center point O. It is formed. Here, the angle θ1 is set based on the width of the core 8 wound by the coil 9 (the width corresponding to the angle 150 ° formed by the five teeth 8a). The angle θ2 is set based on the commutation period (width corresponding to 30 °), and specifically, is set within a range of about 25 ° to 35 °.

When manufacturing the blower motor 1, first,
Unmagnetized ferrite magnets 2, 3, rotor 4, brush 5,
Parts such as the rotating shaft 6 are assembled in the motor housing 7. At this time, with reference to the mark hole 7c at the bottom of the motor housing 7, the mark hole 7c and the ferrite magnets 2, 3
The ferrite magnets 2 and 3 are fixed to the inner surface of the motor housing 7 so that the center lines coincide with each other. After that, the rotor 4 is inserted into the motor housing 7 and fixed. The brush 5 is also fixed at a predetermined position based on the mark hole 7c. At the time of this assembling, as shown in FIG. 1, when commutation of the coil 9 is started due to the short-circuit of the brush 5, the tip 8b on the rotation direction side of the tooth 8a wound by the coil 9 that commences the commutation. But the gap 11
a and 11b.

The motor 1 in which the components have been assembled as described above is installed in the magnetizing device 12 shown in FIG. 3 to magnetize the ferrite magnets 2 and 3. Hereinafter, a method of magnetizing ferrite magnets 2 and 3 in the present embodiment will be described in detail.

As shown in FIG. 3, the magnetizing device 12 includes magnetizing yokes 13 and 14, and the magnetizing yokes 13 and 14
The distal end surface is formed in an arc shape having an arc radius slightly larger than the arc surface radius of the outer peripheral surface of the motor housing 7. In addition, the motor housing 7 of the tip surface
The recesses 13a and 14a extending in the axial direction (perpendicular to the paper surface) are formed in portions corresponding to the protruding portions 7a and 7b. The magnetized yoke 13 and the magnetized yoke 14 are opposed to each other so as to cover (internally) the ferrite magnets 2 and 3 from outside the motor housing 7 in correspondence with the positions of the opposed ferrite magnets 2 and 3. Have been. In this state, the space 13 is formed between the protrusions 7a, 7b of the motor housing 7 and the magnetized yokes 13, 14 by the concave portions 13a, 14a formed at the tips of the magnetized yokes 13, 14.
a and 15b are formed. A coil 16 is wound around the magnetized yoke 13, and a coil 17 is wound around the magnetized yoke 14.

An electric current is applied to the coils 16 and 17 in the directions (+,-) shown in FIG. However, (+) indicates the direction from the near side to the back side of the paper, and (-) indicates the direction from the back side to the near side. When the current flows in this manner, a magnetic flux is generated in the direction shown by the broken line in FIG. 3 (from left to right in the figure). At this time, since the spaces 15a and 15b and the gaps 11a and 11b provide magnetic resistance, the magnetized yoke 1
The magnetic flux generated between 3 and 14 passes avoiding the spaces 15a and 15b and the gaps 11a and 11b. As a result, FIG.
As shown in (2), in the ferrite magnets 2, 3, the magnetic flux density at the portions corresponding to the protruding portions 7a, 7b is weakened, and the weak magnetic flux portions 2a, 3a are formed. Motor 1
When the motor housing 7 is driven, the protrusions 7a, 7b
Gap 11 formed between the ferrite magnets 2 and 3
Since a and 11b are magnetic resistances, the gaps 11a and 11b
The magnetic flux generated from the portion (weak magnetic flux portions 2a, 3a) corresponding to 11b is further reduced. Therefore, the magnetic flux density in the rotation direction (X arrow direction) by the ferrite magnets 2 and 3 is different from the angular position (weak magnetic flux portion 2) corresponding to the gaps 11a and 11b.
The minimum value is obtained at a, 3a).

As described above, according to the present embodiment, in the magnetic flux distribution of the ferrite magnets 2 and 3, it is possible to have a magnetic flux change having a local minimum in a part, and to approach the ideal magnetic flux density change shown in FIG. And, due to this change in magnetic flux,
An induced voltage is generated so as to cancel the reactance voltage. More specifically, as shown in FIG. 1, when commutation of the coil 9 is started, the tips 8 b of the teeth 8 a wound by the coil 9 are separated from the gaps 11 a and 11 b (weak magnetic flux portions 2).
a, 3a). Therefore, when the rotor 4 rotates from the state shown in FIG. 1, the magnetic flux passing through the rectifying coil 9 increases, and an induced voltage is generated so as to cancel the reactance voltage by the change in the magnetic flux.

In the blower motor 1, when the load is changed to adjust the air volume of the air conditioner unit, the reactance voltage changes according to the current of the coil 9, but the induced voltage also changes according to the rotation of the rotor 4. I do. For example, when the operation switch is operated from the Lo position to the Hi position, the current of the coil 9 is increased from 4A to 18A. In this case, the reactance voltage increases according to the current of the coil 9, but the motor rotation speed increases and the induced voltage also increases.
That is, even if the load fluctuates, an induced voltage that always cancels the reactance voltage is generated, and rectification is performed satisfactorily.

As described above, this embodiment has the following features. (1) By providing the projecting portions 7a and 7b protruding outward in the motor housing 7, an air gap is formed in a part of the contact surface between the motor housing 7 and the ferrite magnets 2 and 3 on the rotation direction side of the rotor 4. Parts 11a and 11b were formed.
In this case, the gaps 11a and 11b become magnetic resistance, and the magnetic flux in the ferrite magnets 2 and 3 corresponding to the gaps 11a and 11b becomes weak. Further, in the present embodiment, the ferrite magnet is magnetized so that the magnetic flux density becomes a minimum value at the portions corresponding to the gaps 11a and 11b. As a result, in the magnetic flux density distribution in the rotation direction of the ferrite magnets 2 and 3, it is possible to have a magnetic flux change having a local minimum at a part thereof. Due to this change in magnetic flux, it is possible to generate an induced voltage that cancels out the reactance voltage, thereby improving rectification. By forming the gaps 11a and 11b on the contact surfaces between the motor housing 7 and the ferrite magnets 2 and 3, rectification can be improved at low cost.

(2) At the time when commutation of the coil 9 is started by the brush 5, the tip 8b of the tooth 8a wound by the coil 9 on the rotation direction side is replaced with the gap 11a, 1
1b. In this case, the magnetic flux passing through the rectifying coil 9 increases with the rotation of the rotor 4. Due to this change in magnetic flux, an induced voltage that cancels out the reactance voltage is generated, and rectification can be improved.

(3) In the present embodiment, the ferrite magnets 2, 3 are magnetized so that the magnetic flux density becomes a minimum value at the portions corresponding to the air gaps 11a, 11b, and therefore have a large change in magnetic flux. This is suitable for a motor in which the reactance voltage at the time of commutation increases.

(4) In the step of magnetizing the ferrite magnets 2, 3, after the motor 1 is assembled, the motor housing 7
A strong magnetic field in a certain direction is applied to the ferrite magnet from outside. Further, in the present embodiment, the magnetized yoke 1
At the ends of 3, 14 there are provided recesses 13a, 14a at positions corresponding to the gaps 11a, 11b.
Spaces 15a and 15b are formed by 14a. In this case, the gaps 11a, 11b and the spaces 15a,
15b is a magnetic resistance, and the magnetic flux generated at the time of magnetization passes avoiding this portion. Therefore, in the ferrite magnets 2 and 3, the strength of magnetization of the portions corresponding to the gaps 11a and 11b is weakened. This makes it possible to easily magnetize the ferrite magnets 2 and 3 whose magnetic flux density has a minimum value at the portions corresponding to the gaps 11a and 11b.

(5) Mark holes 7c are formed in the bottom of the motor housing 7, and the positions of the ferrite magnets 2, 3 and the brush 5 are set with reference to the mark holes 7c. The positioning of the brush 5 can be performed accurately.

(6) Since the rectification is improved by configuring the blower motor 1 as described above, spark discharge can always be suppressed, and the life of the blower motor 1 can be improved. In addition, since spark discharge is suppressed, noise countermeasures (countermeasures against noise and electric noise) become unnecessary, and the manufacturing cost of the blower motor 1 can be reduced.

The above embodiment may be implemented in the following manner. In the above embodiment, the ferrite magnets 18 and 19 shown in FIG. 5 may be used instead of the ferrite magnets 2 and 3 having the weak magnetic flux portions 2a and 3a as shown in FIG. In other words, the outer shapes of the ferrite magnets 18 and 19 are the same as those of the ferrite magnets 2 and 3, but the ferrite magnets 18 and 19 have the same appearance.
The magnetic flux distribution at 19 is substantially uniform as a whole. When the ferrite magnets 18 and 19 are applied to the blower motor 1 shown in FIG. 1, the gaps 11a and 1 formed between the ferrite magnets 18 and 19 and the motor housing 7 are formed.
1b is a magnetic resistance, so that the gaps 11a, 11b
The magnetic flux generated from the portion corresponding to the above is weakened. That is,
Even when the ferrite magnets 18 and 19 are mounted on the motor 1, the magnetic flux distribution by the ferrite magnets 18 and 19 can have a magnetic flux change in which a part has a minimum point. Therefore, the induced voltage due to the change in the magnetic flux is generated so as to cancel the reactance voltage, and the rectification can be improved. However, when the ferrite magnets 18 and 19 are used, the change in magnetic flux is smaller than when the ferrite magnets 2 and 3 are used as in the above-described embodiment. Therefore, the present invention is preferably applied to a motor having a small reactance voltage.

In the above-described embodiment, the protrusions 7a and 7b are provided on the motor housing 7 so that the gaps 11a and 11b are formed on the contact surfaces between the motor housing 7 and the ferrite magnets 2, 3, 18, and 19. However, a void may be formed by providing a recess or a hole in the motor housing 7. Even in this case, since the magnetic flux distribution can have a magnetic flux change having a minimum point in a part, the commutation of the motor can be improved at low cost.

In the above embodiment, the present invention is applied to the two-pole motor 1 having two ferrite magnets.
Alternatively, the present invention may be applied to a multi-pole DC motor such as a 4-pole DC motor. Also, ferrite magnets 2, 3, 18, 19
It may be embodied by a magnet other than the above, for example, a magnet mixed with resin or the like.

In the above embodiment, the DC motor is embodied in the blower motor 1, but may be embodied in another motor. Further, the above configuration may be applied to a DC generator. Also in this case, rectification is performed well, so that noise in the generator can be reduced.

The technical ideas other than those described in the claims which can be grasped from the above embodiment will be described below together with their effects. (A) The DC machine according to any one of claims 1 to 4, wherein a mark is formed on the yoke, and the positions of the magnet and the brush are set based on the mark. . In this case, the magnet and the brush can be accurately positioned, which is practically preferable.

[0042]

As described in detail above, according to the present invention,
By forming a gap on the contact surface between the yoke and the magnet, rectification can be improved at low cost.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a blower motor according to the present embodiment.

FIG. 2 is a sectional view taken along line AOA of FIG. 1;

FIG. 3 is a schematic configuration diagram of a magnetizing device.

FIG. 4 is a diagram showing a magnetic flux distribution of a magnetized ferrite magnet.

FIG. 5 is a diagram showing a magnetic flux distribution of another ferrite magnet.

FIG. 6 is a schematic configuration diagram of a conventional DC motor.

FIG. 7 is a diagram illustrating rectification.

FIG. 8 is a diagram showing a magnetic flux distribution in a rotation direction of a ferrite magnet.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Blower motor as DC machine, 2, 3 ... Ferrite magnet, 4 ... Rotor, 7 ... Motor housing as yoke, 7a, 7b ... Projection, 8a ... Teeth, 8b ... Tip, 9 ... As winding Coil, 11a, 11b: void, 18: ferrite magnet, 19: ferrite magnet.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H02K 15/03 H02K 15/03 G 23/04 23/04 F term (reference) 5H002 AA09 5H605 AA00 BB05 BB09 CC01 CC07 DD03 5H613 AA07 BB04 BB14 GA03 GA09 PP02 PP04 PP05 SS07 TT01 5H622 CA02 CB01 PP10 PP17 QB01 5H623 AA05 AA07 BB07 GG13 GG16 JJ06 JJ08

Claims (5)

[Claims] A rotor having a plurality of teeth wound by windings; a yoke formed in a substantially cylindrical shape and including the rotor; and a yoke formed in an arcuate cross-section and provided on an inner surface of the yoke. A plurality of magnets disposed along a circumferential direction of the rotor, and a gap is formed in a part of the contact surface between the yoke and the magnet on a part of the rotor in a rotation direction side. Machine. 2. The DC machine according to claim 1, further comprising: a brush for short-circuiting the winding so as to reverse the direction of the current of the winding during rectification, and commutation of the winding is started by the brush. A DC machine characterized in that, at a point in time, the tip of the tooth wound around the winding in the rotation direction is positioned in the gap. 3. The DC machine according to claim 1, wherein a gap is formed on a contact surface with the magnet by providing a protrusion protruding outward at the yoke. Machine. 4. The DC machine according to claim 1, wherein the magnet is magnetized so that a magnetic flux density becomes a minimum value at a portion corresponding to the gap. DC machine. 5. The method for manufacturing a DC machine according to claim 4, wherein an unmagnetized magnet is mounted at a predetermined position on an inner surface of the yoke, and the rotor is inserted into the yoke to which the magnet is mounted. And a magnetizing step of applying a strong magnetic field in a certain direction to the magnet from outside the yoke.