JPH0333176Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a DC brushless motor, and in particular to a DC brushless motor that can be used as a motor for driving a cooling fan, has a simple structure, is manufactured at low cost, and has a long life. It is.

Conventionally, electric motors for driving cooling fans are
Generally, AC induction motors were used. The reason for this is that induction motors have a simple structure, can be manufactured at low cost, and have a long lifespan as they have no parts that wear out. However, induction motors have the inconvenience of being able to be used only in places with AC power.On the other hand, in the process of miniaturizing electronic devices and promoting their widespread use over a wide area, the power supplies in electronic devices are being standardized to low voltage DC. In order to meet this demand, motors for driving cooling fans that can be operated at low DC voltage have become necessary.

In response to this request, using a normal DC motor with a commutator and brushes as a drive motor would result in abrasion particles generated from the brushes contaminating electronic equipment, and the life of the motor would be shorter than that of an induction motor. Because of these disadvantages, it has been proposed to use a DC brushless motor that does not have brushes.

A conventional example of a DC brushless motor will be explained with reference to FIG. Figure 1a is a sectional view showing the main part configuration;
FIG. b is an energization control circuit diagram for flowing direct current through the stator windings. In Fig. 1, 1 is a rotor shaft, 2 is a rotor hub, and 3 is a permanent magnet.
3 constitutes the rotor of the electric motor. Half the circumference of the cylindrical permanent magnet 3 is magnetized to the north pole, and the remaining half circumference is magnetized to the south pole. 5-1 to 5-4 are stator iron core pole shoes, 6-1 to 6-4 are stator magnetic poles, and 7-1 to 6-4 are stator magnetic poles.
7-4 is a stator winding wound around each stator magnetic pole 6-1 to 6-4, 8 is a stator yoke, and 9-
1 and 9-2 are magnetic detectors that detect the magnetic pole position of the permanent magnet 3, Q-1 to Q-4 are each stator winding 7-
Transistor R- for controlling energization of 1 to 7-4
1 to R-8 are resistors, respectively. 4 is the outer peripheral surface of the permanent magnet 3 and the pole shoe 5-1 of the stator iron core.
This is the gap between the inner circumferential surface of 5-4. In the example shown in FIG. 1, magnetic detectors 9-1 and 9-2 are fixedly mounted at positions on the center lines of stator magnetic poles 6-1 and 6-2, respectively.

This DC brushless motor is driven as follows. When a predetermined DC voltage is applied to the power supply terminal shown in Fig. b, the magnetic detector 9-1 shown in Fig. Therefore, there is no output from the magnetic detector 9-1, and therefore the transistors Q-2 and Q
No current flows through the base of stator winding 7-4.
2 and 7-4, and on the other hand, since the magnetic detector 9-2 faces the S pole of the permanent magnet 3, it detects this S pole and applies a positive voltage to the base of the transistor Q-1. , a negative voltage is applied to the base of the transistor Q-3, which makes the transistor Q-1 conductive and causes a current to flow through the stator winding 7-1, and the magnetic field generated by this current causes the S pole of the permanent magnet 3 to A counterclockwise rotational force is generated, and the rotor starts rotating counterclockwise. Considering a state in which the rotor is slightly rotated counterclockwise, the permanent magnet facing the magnetic detector 9-1 becomes the south pole, and the magnetic detector 9-1 detects the magnetic field of the south pole and turns on the transistor Q-. A positive voltage is output to the base of transistor Q-2 and a negative voltage is output to the base of transistor Q-4.
A current is applied to the winding 7-1 to generate a rotational force that rotates the rotor counterclockwise, thereby rotating the rotor together with the winding 7-1 in the counterclockwise direction. The rotational force generated by the current flowing through the winding 7-1 continues until the rotor rotates 90 degrees counterclockwise from the position shown in the figure, and the rotation stops.
When the angle exceeds 90 degrees, the permanent magnet facing the magnetic detector 9-2 becomes N-pole, and the output of the magnetic detector 9-2 applies a negative voltage to the base of the transistor Q-1, and a negative voltage to the base of the transistor Q-3.
Applying a positive voltage to the base of transistor Q-1
Q-3 becomes non-conductive, and Q-3 becomes conductive, and a current flows through the winding 7-3, generating a torque that rotates the rotor counterclockwise, thereby rotating the rotor together with the winding 7-2. Thereafter, it operates in the same way, constantly passing current to two adjacent windings, and each time the rotor rotates 90 degrees, the energized winding is replaced with the unenergized winding located in the opposite direction of rotation. The rotational force is continuously generated in a fixed direction (counterclockwise in the above example) by switching. According to this configuration, no matter what position the rotor is in, the rotor is immediately generated when energized, and there is no rotor position where the rotational force is zero, so it exhibits excellent characteristics as an electric motor, and can be used in many applications. It is prized for its purpose.

However, the brushless motor with the configuration shown in FIG. 1 has four stator windings, four transistors that control the energization of each winding, and two magnetic detectors.
It requires many related circuit parts such as resistors R-1 to R-8 and a complicated assembly process, making it expensive, so conventionally it has been used only for high-end applications such as measuring instruments and information processing equipment. It had been. Therefore, adopting a brushless motor with the configuration shown in Figure 1 for the fan drive motor, which used to use an inexpensive induction motor, would be fully satisfactory in terms of performance, but would be inappropriate in terms of price. It was hot.

The present invention aims to solve the above-mentioned problems and provide a brushless electric motor with a simple structure and low cost, which is suitable for specific uses such as driving a fan. First, let's compare and examine the characteristics required for fan drive and the characteristics of the brushless motor shown in FIG. The rotational force characteristics required for a fan drive electric motor are such that the nature of the fan power is approximately proportional to the square of the fan's rotational speed, so the starting rotational force required at startup is small enough to overcome the frictional rotational force of the bearing. It is sufficient if there is rotational force, and it is desirable that the generated rotational force increases during acceleration after startup and the maximum rotational force can be obtained near the rated speed.The characteristics of conventionally used induction motors are It can be said that it is well suited as a drive motor. On the other hand, brushless motors have a drooping characteristic in which they generate maximum rotational force at startup under a constant supply voltage, and as they accelerate, the current decreases and the rotational force decreases, so a fan is required when rotating at high speeds. In order to generate that much rotational force, it is necessary to use an electric motor that generates much greater rotational force at startup. Therefore, in the present invention, by reducing the number of components of the brushless motor of the configuration shown in Figure 1, which has excessive characteristics for fan drive use, and finding an equilibrium point between performance and price, we have created an inexpensive structure suitable for fan drive motors. The purpose is to provide a simple DC brushless motor.

First, considering reducing the number of components in Figure 1 by half, as shown in Figure 2, the rotor is one piece, so leave it as it is, and the stator magnetic poles and stator windings. halved from 4 to 2, and halved the number of magnetic detectors from 2 to 1.
By halving the number of energization control transistors from four to two, the number of circuit components including resistors has been halved, simplifying the configuration and potentially achieving a significant price reduction. The configuration shown in Figure 2 has a major disadvantage. In FIG. 2a, the rotor is placed on the outside and the stator is placed on the inside, which is the opposite arrangement to that in FIG. 1, but this is not a particularly essential problem. 3 is a hollow cylindrical permanent magnet magnetized to N and S poles and rotatably supported; 8 is a stator yoke; 6a and 6;
b is a stator magnetic pole, 7a and 7b are stator windings, 5
a and 5b are pole shoes provided on the stator magnetic poles;
9 is a magnetic detector; 4 is a gap between the outer peripheral surface of the pole shoes 5a and 5b and the inner peripheral surface of the permanent magnet 3; 10
is a gap in the circumferential direction at each tip of the two pole shoes 5a and 5b, and 31 and 32 are neutral lines where the magnetic poles of the permanent magnet 3 are reversed. In the brushless motor having the configuration shown in Fig. 2a, the change in magnetic resistance between the permanent magnet 3 and the stator iron core when the rotor is rotated once with no current applied to the stator windings 7a and 7b is as follows. Second
The position shown in the curve 1 of FIG. c is the same as that of the state shown in FIG.
The line connecting them is the center line A- of the stator magnetic poles 6a and 6b.
The minimum value is reached at a position orthogonal to A', the maximum value is reached when the permanent magnet 3 is rotated 90 degrees from the current position, and thereafter, the minimum and maximum values are repeated every time the rotor rotates 90 degrees. The reason for this is that due to the arrangement shape of the pole shoes 5a and 5b, the magnetic resistance within the stator core is minimum in the direction of the center line A-A' of the magnetic poles 6a and 6b.
This is because it is maximum in the direction perpendicular to this.

Therefore, if the stator windings 7a and 7b are left unenergized, the rotor will move to the position where the magnetic resistance between the permanent magnets 3 and the pole shoes 5a and 5b is minimized by the action of the magnetic attraction between the permanent magnets 3 and the pole shoes 5a and 5b. The state of the magnetic flux of the permanent magnet 3 at that time is as shown in the curve 2 of Fig. 2c. If the magnetic detector 9 is arranged in a direction perpendicular to the center line A-A' of the magnetic poles 6a and 6b as shown in FIG.
is located on the neutral line 31-32 of the permanent magnet 3, there is no output from the magnetic detector 9, the energization control device does not operate, and therefore the terminal of the control circuit of FIG. Even if a voltage is applied, no current flows through the stator windings 7a and 7b, and they cannot be started automatically from a stationary point.

Therefore, the following methods have been conventionally employed to provide self-starting performance in the configuration shown in FIG. 2a. That is, a small piece made of magnetic material is moved from the center line of the stator magnetic poles 6a, 6b by a certain angle in the rotor rotation direction to the pole shoe 5.
By disposing them on the outer peripheral surfaces of the small pieces a and 5b, the static position of the rotor is moved in the rotational direction by the attractive force between the small pieces and the permanent magnets 3. Moreover, as another means, the outer circumferential shape of the pole shoes 5a, 5b is made non-concentric, and the radial dimension of the air gap 4 is increased on one hand between a certain angle around the center line of the stator magnetic poles 6a, 6b. On the other hand, a method has been proposed in which the static position of the rotor is moved by changing the value of magnetic resistance between the rotor and stator by reducing the dimensions.

However, the former method of attaching small pieces made of magnetic material has the inconvenience of generating vibration noise due to the action of the alternating magnetic field of the permanent magnet, and the latter method of changing the gap size makes the outer circumferential shape of the pole shoe complicated and mass production. There were inconveniences that worsened the quality and did not solve the problem of lower prices.

In order to create a structure that eliminates the above disadvantages, the present inventor first developed (a) a permanent magnet made into a hollow cylindrical shape, with half the circumference magnetized to the N pole and the remaining half circumference to the S pole, and this permanent magnet. A rotor formed by a rotating hub that is rotatably supported; (b) a cylindrical stator yoke; A stator magnetic pole, a pole shoe fixed to the tip of each stator magnetic pole so that the outermost peripheral surface faces the inner peripheral surface of the permanent magnet through a small gap, and between these pole shoes. The length of the magnetic flux gap is determined to be approximately equal to the length of the magnetic flux gap between the outer circumferential surface radially planted on the outer circumferential part of the stator yoke and the inner circumferential surface of the permanent magnet, so that the pole shoe tip and the intermediate One piece that is fixedly placed in the magnetic flux gap at a position slightly moved toward the pole shoe side from the center line connecting the center of the circumferential gap between the tip of the magnetic pole and the center of the stator yoke to detect the rotational position of the permanent magnet. a magnetic detector, and (d) an energization control circuit that receives the output of the magnetic detector and controls the current flowing through each stator winding to drive the rotor in a fixed direction. (Refer to Japanese Patent Application No. 15613/1983).

Below, we will discuss the above proposal in more detail in the third section.
This will be explained with reference to FIG. In the cross-sectional view of Fig. 3, 3 is a permanent magnet made into a hollow cylindrical shape, half of its circumference is magnetized to N pole, and the remaining half circumference is magnetized to S pole, and is rotatably supported by a rotating hub (not shown). This forms the rotor of the electric motor. 31,3
2 is a neutral wire of the permanent magnet 3. Reference numeral 8 denotes a cylindrical stator yoke, and the outer periphery of the stator yoke 8 is divided into two parts (in the illustrated example, there is a cylindrical stator yoke in the Y-axis direction and the Y'-axis direction of the XY orthogonal coordinate axis passing through the center of the stator yoke). ) Two stator magnetic poles 6a and 6b are installed radially, and pole shoes 5a and 5b are installed at the tips of these stator magnetic poles 6a and 6b, respectively, so that the outer circumferential surface of the outermost tip thereof is the inner circumferential surface of the permanent magnet 3. They are fixed so as to face each other with a small gap 4 interposed therebetween, and furthermore, on the outer circumferential portion of the stator yoke 8, there are provided holes protruding in the X-axis direction and the X'-axis direction, and between the pole shoe 5a and the pole shoe 5b. The stator yoke 8, the stator magnetic poles 6a, 6b, the pole shoes 5a, 5b, and the intermediate magnetic poles 11, 11' are all made of magnetic material. It is made to form the stator of an electric motor. 7a and 7b are stator magnetic poles 6a and 7b, respectively.
This is the stator winding wound around 6b. intermediate magnetic pole 1
1 and 11' are not wound with windings. intermediate magnetic pole 11,
The length of the magnetic flux gap between the outer circumferential surface of pole shoe 11' and the inner circumferential surface of permanent magnet 3 is equal to the magnetic flux gap length (4 in FIG. 3) between the outer circumferential surface of pole shoes 5a, 5b and the inner circumferential surface of permanent magnet 3. In addition, there are four air gaps 12(1), 12(2), 12 between the tip of the pole shoe and the tip of the intermediate magnetic pole in the circumferential direction.
(3) and 12(4) are also made to have approximately the same gap length. B-B' is the center line connecting the center of gap 12(1) and the center of gap 12(3), and therefore passes through the center of the stator yoke; similarly, C-C' is the center line connecting the center of gap 12(1) and the center of gap 12(3);
2(2) and the center of the void 12(4). β is the angle between the centerline B-B' and the X-X' axis, as well as the angle between the centerline C-C' and the X-X' axis. Reference numeral 9 denotes a magnetic detector, such as a Hall element, for detecting the rotational position of the permanent magnet 3, and in the embodiment shown in FIG. installed in a shape. γ is the angle between the center line passing through the center of the magnetic detector 9 and the center line C-C'.
Although the magnetic detector 9 is installed at the position shown in the embodiment shown in FIG. 3, the present invention operates in the same way even if it is installed at any one of the three positions indicated by the circle in the same relationship. do.

In the above configuration, the change in magnetic resistance of the stator when no current is applied to the stator windings 7a, 7b is as shown by curve 1 in FIG. 4. The position where the magnetic resistance is minimum is influenced by the intermediate magnetic poles 11 and 11',
It is not in the Y-axis and Y'-axis directions, but is at a position separated by an angle β from the Y-axis and Y'-axis. Therefore, if the permanent magnet 3 is left freely without energizing the stator windings 7a and 7b, the line connecting the center lines 31 and 32 of the permanent magnet 3 will coincide with the center line B-B' or C-C'. At that time, the maximum magnetic pole positions of the N and S poles are at angle β away from the Y axis and Y' axis, and the state of change in magnetic flux is as shown by curve 2 or 2' in Figure 4. Become. Curve 2 stopped at a position where the line connecting the neutral wires 31 and 32 of permanent magnet 3 coincided with center line B-B', and curve 2' also stopped at a position where it coincided with center line C-C'. It shows the change in magnetic flux at each time. For example, the maximum magnetic pole position of the S pole of the permanent magnet 3 at this stop position is shifted from the Y axis by an angle β.

Next, the operation as a DC brushless motor will be explained. If the static position of the permanent magnet 3 when the stator windings 7a and 7b are not energized is the position of curve 2 in Figure 4 (the static position where the neutral line of the permanent magnet coincides with the center line B-B'). The magnetic detector 9 detects the north pole of the permanent magnet 3 and causes current to flow through the stator winding 7b via the energization control circuit (the circuit configuration is the same as in FIG. 2b), thereby generating a north pole in the pole shoe 5b. , On the other hand, the maximum magnetic pole position of the N pole is at a position shifted to the right by the angle β from the Y' axis, so the N generated in the pole shoe 5b
The repulsive force between the poles and the north pole of the permanent magnet 3 rotates the rotor counterclockwise. When the rotor rotates counterclockwise from the illustrated position by an angle of π-(2β+γ), the output of the magnetic detector 9 becomes zero and the current flowing through the stator winding 7b also becomes zero, but the rotor is rotated due to inertia. Continue rotating. As a result, the magnetic detector 9 detects the S pole, current flows through the stator winding 7a, generates an N pole in the pole shoe 5a, and is repelled by the N pole of the opposing rotor, generating rotational force in the same direction. It rotates continuously and operates as an electric motor. Therefore, although the torque generated by this electric motor is of a pulsating type that becomes zero approximately every 180 degree rotation, there is no problem in practical use for driving a fan.

When the initial stationary position of the permanent magnet 3 is curve 2' in FIG. 4, that is, the neutral line of the permanent magnet 3 is the center line C.
- When it is stationary in agreement with C', the magnetic detector 9
detects the north pole of the permanent magnet 3 and causes current to flow through the stator winding 7b to generate a north pole at the pole shoe 5b. On the other hand, since the maximum magnetic pole position of the N pole is on the left side of the Y' axis by the angle β, the repulsive force acting between the pole shoe 5b and the N pole of the permanent magnet rotates the rotor clockwise. When the rotor moves clockwise by an angle γ, the position of the rotor facing the magnetic detector 9 becomes the neutral wire 32, the output of the magnetic detector 9 becomes zero, and the current flowing through the stator winding 7b also becomes zero. ,
Although the rotational torque disappears, the rotor continues to rotate clockwise due to inertia, and the neutral wire 32 slightly touches the magnetic detector 9.
If you go too far in the clockwise direction, the magnetic detector 9
detects the S pole and sends a current to the stator winding 7a,
Generate a N pole on the pole shoe 5a, and
The rotor is rotated counterclockwise by the attractive force between the poles, and when the neutral line 32 crosses the center line C-C' and reaches the center line B-B' due to the inertia of the rotor, from then on, continues to rotate counterclockwise in accordance with the counterclockwise motion described above.

In addition to the above-mentioned curves 2 and 2', the rest position of the rotor when the stator windings 7a and 7b are not energized is as follows:
There is a position where the N and S poles of the permanent magnet 3 are opposite, but in this case, the polarity of the magnet detected by the magnetic detector 9 in a stationary state is the S pole, so the first winding to be energized is 77a. The only difference is that the rotor rotates counterclockwise, with the other effects being exactly the same.

It can be easily inferred from the above operation explanation that the magnetic detector 9 can be installed at any one of the positions marked with a circle in addition to the position shown in the figure, and similarly operates as an electric motor. However, when installing near the pole shoe near the center line C-C', and when installing near the center line B-C',
The prescribed rotation direction of the rotor is opposite to that when the rotor is installed near the pole shoe near B'. Also,
Up to now, we have explained that the pole shoes 5a and 5b are magnetized to the north pole when the stator windings 7a and 7b are energized, but even if they are magnetized to the south pole, the direction of rotation is simply reversed. The rotational operation as an electric motor is the same.

As described above, the proposed configuration has the advantage of reducing the number of major parts by almost half compared to conventional electric motors, making it a highly productive and inexpensive product. It is uncertain whether the rotor's resting position when the child winding is not energized will be at the position of curve 2 or 2', and depending on the resting position, the rotor may be slightly However, there remains a problem in that the robot may rotate in the normal direction after moving in the opposite direction.
The above-mentioned problem that the direction of rotation of the rotor is uncertain immediately after energization does not pose any practical problem when this electric motor is used to drive a fan, but it is preferable when used for general purposes. is not a problem.

An object of the present invention is to provide a direct current brushless motor that can solve the above-mentioned problems in the previously proposed configuration and ensure that the rotor rotates in the normal direction immediately after energization.

The features of this invention are, in order to achieve the above objectives,
A of the above proposed configurations A, B, C, D, and H,
Leave B, C, and E as they are, and change the configuration of D to G1, G2, and G in the four circumferential gaps that occur between the pole shoe tip and the intermediate magnetic pole tip in the circumferential direction.
3. G4 is the circumferential gap length of G1 and G3.
2, make it larger than that of G4, and make G2,
Fixedly placed in the magnetic flux gap at a position slightly moved toward the pole shoe side from the center line connecting the centers of G4 to detect the rotational position of the permanent magnet 1
The present invention has a configuration in which two magnetic detectors are provided.

An embodiment of the present invention will be explained with reference to FIGS. 5 and 6. FIG. 5 is a sectional view of the embodiment, and FIG. 6 is a diagram showing changes in magnetic resistance and magnetic flux for the embodiment of FIG.
In FIG. 5, G1, G2, G3, G4 are the tips of the pole shoes 5a, 5b and the intermediate magnetic poles 11, 1.
There are four circumferential gaps created between the tip of 1' and 12(1), 12(2), 12 in the case of
(3), corresponds to 12(4). In the present invention, the circumferential gap lengths of G1 and G3 are set to G2 and G4.
The length of the gap in the circumferential direction is determined to be larger than the length of the gap in the circumferential direction. With this determination, the magnetic resistance between the permanent magnet 3 and the stator changes as shown by curve 1 in FIG. 6, and the magnetic flux changes as shown by curve 2 or 2'. Curve 2 is the neutral line 31 of the permanent magnet 3,
The line connecting 32 is the center line B- of the gaps G1 and G3
Curve 2' is the change in magnetic flux when stopped at a position coincident with B', and curve 2' is also a change in magnetic flux when stopped at a position coincident with center line C-C' of gaps G2 and G4. At this stop position, the maximum magnetic pole position of the S pole of the permanent magnet 3 is shifted from the Y axis by an angle β (for curve 2) and an angle β' (for curve 2').

With the above configuration, the stator winding 7
If the permanent magnet 3 is left with no current flowing through a and 7b, the probability that the neutral wires 31 and 32 of the permanent magnet 3 will stop on the line that coincides with the center line B-B' of the gaps G1 and G3 is This is much larger than the probability of stopping on the line that coincides with C-C', and the third
Problems with the diagram proposed configuration are resolved. According to the experimental results, the gap lengths of the gaps G1 and G3 are changed to the gap lengths of the gaps G2 and G4.
It was confirmed that the above problem can be reliably solved by making the gap length 1.5 times the void length of

FIG. 5 is a sectional view showing an example of an electric fan using the DC brushless motor of the present invention as a drive source.
1 is a rotor shaft, 52 is a rotor boss, 53 is a permanent magnet, 54 is a rotor hub that also serves as a magnetic yoke, 5
5 is a stator iron core, 57 is a stator winding, 59 is a magnetic detector, 60 is a circuit support plate on which an energization control circuit is mounted, 61 is a bearing, 62 is a hub to which a fan blade is attached, 63 is a fan blade, 64 is a bench lily, 65 is a column supporting the fan motor, 66
is the motor cover.

As explained above, according to the present invention, the number of main parts is reduced by almost half compared to conventional DC brushless motors,
A small piece of magnetic material for starting is not required, and the magnetic flux gap length is made uniform, making it possible to create a highly productive and inexpensive product.Furthermore, the rotation direction of the rotor immediately after energization can be changed. This solves the problem with the conventional configuration that it is fixed, and has the effect of always being able to start rotation in the normal direction.

[Brief explanation of the drawing]

Figure 1 is a sectional view and energization control circuit diagram of a conventional example, Figure 2 is a sectional view of a conventional example with two stator magnetic poles, an energization control circuit diagram, and a diagram of changes in magnetic resistance and magnetic flux. is a sectional view of yet another conventional example, FIG. 4 is a diagram of changes in magnetic resistance and magnetic flux with respect to FIG. 3, FIG. 5 is a sectional view of an embodiment of the present invention, and FIG.
FIG. 7 is a cross-sectional view of an electric fan using the present invention. Explanation of symbols, 3...Permanent magnet, 5a, 5b...
Pole shoe, 6a, 6b...Stator magnetic pole, 7
a, 7b...Stator winding, 8...Stator yoke,
9...Magnetic detector, 10, 12(1) to 12(4), G1
~G4... air gap, 11, 11'... intermediate magnetic pole, 3
1, 32...neutral wire, 51...rotor shaft, 52...
... Rotor boss, 53 ... Permanent magnet, 54 ... Rotor hub, 55 ... Stator core, 57 ... Stator winding, 59 ... Magnetic detector, 61 ... Bearing, 62
...Hub for attaching fan blade, 63...Fan blade, 64...Bench lily.

Claims (1)

[Scope of Claim for Utility Model Registration] (a) A permanent magnet made into a hollow cylindrical shape with half its circumference magnetized as N pole and the remaining half circumference as S pole, and a rotating hub that rotatably supports this permanent magnet. (b) A cylindrical stator yoke, two stator magnetic poles installed radially on the outer periphery of the stator yoke so as to bisect the outer periphery, and (b) a cylindrical stator yoke; a pole shoe fixed to the tip of each stator magnetic pole so that its surface faces the inner circumferential surface of the permanent magnet through a small gap; a stator made of a magnetic material and formed of intermediate magnetic poles installed radially around the outer periphery of the child yoke; (c) a stator winding is wound around each of the stator magnetic poles; The length of the magnetic flux gap between the outer circumferential surface of the magnetic pole and the inner circumferential surface of the permanent magnet is determined to be equal to the magnetic flux gap length between the outer circumferential surface of the pole shoe and the inner circumferential surface of the permanent magnet. G the four circumferential gaps created between the magnetic pole tip and the magnetic pole in order in the circumferential direction.
1, G2, G3, G4, the circumferential gap length of G1, G3 is made larger than that of G2, G4, and in the magnetic flux gap at a position moved to the pole shoe side from the center line connecting the centers of G2, G4. One magnetic detector is fixedly arranged and detects the rotational position of the permanent magnet; (e) The rotor is driven in a fixed direction by controlling the current flowing through each stator winding in response to the output of this magnetic detector. A direct current brushless motor characterized by comprising an energization control circuit for controlling the current flow.