JPH11215749A - Outer rotor type motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further reduce the noise of an outer rotor type motor. SOLUTION: In this motor, an outer rotor 3 is a monolithic molding and has N magnetic poles and S magnetic poles, alternately formed over the entire inner surface. At the boundaries between each N magnetic poles 3a and the adjacent S magnetic poles 3a, circular arc-shaped recessed sections 3b are formed, and the width of each recessed section 3b is made smaller than the width in the circumferential direction of each magnetic pole 3a, and a specified range at the center of each magnetic pole 3a separated from the stator is made equal in distance. Due to this structure, a cogging torque waveform becomes nearly a sine waveform, and noise reduction can be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric motor having an integrally formed outer rotor, and more particularly, to an outer rotor type in which a magnetic pole shape of the outer rotor is devised so that a cogging torque waveform becomes a sine wave to reduce noise. Related to electric motors.

[0002]

2. Description of the Related Art An outer rotor type electric motor used in an electric fan or a washing machine is provided with a ring around a stator as described in, for example, JP-A-9-266657 and JP-A-9-163650. An outer rotor in a shape of a circle is arranged, and the outer rotor is rotated by a rotating magnetic field generated by a stator, so as to generate wind and agitate water with blades formed on the outer periphery of the outer rotor.

[0003] As shown in FIG. 3, the stator of the conventional outer rotor type electric motor includes a plurality of electromagnets 30 arranged radially, and a rotating magnetic field generated by these electromagnets 30 generates a rotating magnetic field inside the outer rotor 31. The outer rotor 31 rotates by acting on the permanent magnet 32 magnetized on the peripheral surface. This outer rotor 31 is, for example, a mixture of a magnetic powder and a semi-liquid synthetic resin material, which is put into a mold and solidified.
In this case, a plurality of N poles and S poles are alternately formed along the entire circumference of the inner peripheral surface of the outer rotor.

[0004]

As shown in FIG. 4A, the inner peripheral surface of the conventional outer rotor 31 is formed so that the distance from the stator is uniform over the entire circumference. ,
Each magnetic pole is formed using a magnetized yoke. When the width of the magnetized yoke is large, as shown in FIG.
The waveform of the cogging torque becomes trapezoidal. The trapezoidal waveform of the cogging torque means that the cogging torque has a harmonic component. As a result, the outer rotor 31 cannot rotate smoothly, and a sound is generated due to vibration and the like accompanying the rotation. This causes a problem of generating noise to the surroundings.

[0005] For this reason, conventionally, the width of the stator is reduced to reduce the noise, but if the width of the stator is reduced, another problem occurs in that the torque decreases. Furthermore, at the boundary between the N pole and the S pole, the N pole magnetic field and the S pole magnetic field are disturbed, and the cogging torque waveform does not become an ideal waveform, which is an obstacle to noise reduction. In order to prevent the magnetic field from being disturbed, there is a problem that the control of the current flowing through the magnetized yoke when magnetizing becomes strict, and the quality is varied.

SUMMARY OF THE INVENTION An object of the present invention is to provide an outer rotor type electric motor having a uniform quality and capable of achieving further noise reduction without lowering the torque.

[0007]

The object of the present invention is to provide an electric motor having an outer rotor in which N-poles and S-poles are formed integrally and alternately magnetized along the entire inner peripheral surface. An arc-shaped recess is formed at the boundary between each of the N-pole magnetic poles and the S-pole magnetic pole adjacent thereto, and the width of each of the recesses is made smaller than the circumferential width of the magnetic poles. The predetermined range is to make the distance with the stator uniform,
Achieved.

The above object is also achieved by an electric motor having an outer rotor in which N-poles and S-poles are alternately formed along the entire inner peripheral surface of the outer rotor. This is achieved by forming a concave portion having a sinusoidal waveform of the cogging torque at the boundary between the magnetic pole and the adjacent south magnetic pole.

Instead of making the inner peripheral surface of the outer rotor uniform as in the present invention, a concave portion is formed at the boundary between the adjacent magnetic poles to increase the distance from the stator at the boundary and to reduce the shape of the concave portion. By devising, the cogging torque waveform becomes a sine wave, the rotation of the outer rotor becomes smooth, the vibration becomes extremely small, and the noise can be further reduced. In addition, since a concave portion is formed to weaken the magnetic field at the boundary, magnetization is facilitated, and variation in quality can be suppressed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a schematic view of a stator and an outer rotor of an outer rotor type electric motor according to one embodiment of the present invention as viewed from a center axis direction. In the stator of the outer rotor type electric motor according to the present embodiment, a plurality of, for example, 12-pole electromagnets 2 are radially arranged around the central axis 1, and the outer diameter D <b> 1 of the stator connecting the core ends of the electromagnets 2 is larger than the outer diameter D <b> 1. A ring-shaped outer rotor 3 having a slightly larger inner diameter D2 is arranged on the outer periphery of the stator.

The outer rotor 3 is integrally formed in a ring shape by pouring a magnetic powder mixed with a binder, for example, a semi-liquid synthetic resin material into a mold and solidifying the same, as is known in the above-mentioned known examples. At this time, a plurality of N-pole magnetic poles and S-pole magnetic poles are alternately adjacently arranged at regular intervals by a magnetized yoke provided in the mold. For example, in the illustrated example, seven N-pole magnetic poles and seven S-pole magnetic poles are formed. They are formed on the inner peripheral surface at equal intervals adjacent to each other.

The width of each of the 14 magnetic poles 3a of the outer rotor 3 is formed to have the same width x, and about x at both ends of each magnetic pole 3a.
Is retracted to the side opposite to the stator, and a recess 3b having a width of about 2 × / 3 is formed at the boundary between adjacent magnetic poles 3a. In the present embodiment, the concave portion 3b is formed in a flat arc shape, and the central portion of each magnetic pole 3a keeps a uniform distance from the stator over a width of about x / 3. Such a concave portion 3b may be formed after integrally forming the outer rotor 3 with a mold, but it is better to integrally form the outer rotor 3 with the die including the concave portion 3b so that a convex portion for forming the concave portion 3b is formed in a mold. It is possible to manufacture a large number of outer rotors having a uniform quality.

As shown in FIG. 2A, when the outer rotor and the stator of the present embodiment relatively move, cogging occurs in the present embodiment due to the effect of the shape of the recess 3b provided between the magnetic poles 3a. It is possible to make the torque waveform an arbitrary waveform. In the present embodiment, a cogging torque waveform close to a sine wave is obtained as shown in FIG. 2B by forming the flat circular concave portion 3b as shown. As described above, since the recess 3b is provided and the distance between the stator and the rotor is adjusted at the boundary to control the magnitude of the magnetic field, it is not necessary to strictly control the current flowing through the magnetizing yoke when magnetizing. In addition, it is possible to manufacture an outer rotor in which the disturbance of the magnetic field at the boundary between the magnetic poles 3a is extremely small, smooth rotation of the outer rotor 3 is guaranteed, and further noise reduction can be achieved. In addition, since it is not necessary to reduce the width of each electromagnet on the stator side, a large torque can be generated.

[0014]

According to the present invention, since a concave portion for making the cogging torque close to a sine wave is provided at the boundary between the magnetic poles of the integrally formed outer rotor, the rotation of the outer rotor becomes smooth and the noise is reduced. It has the effect that it can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic view of an outer rotor type electric motor according to one embodiment of the present invention.

FIG. 2 is a diagram showing a waveform of a cogging torque of the outer rotor type electric motor shown in FIG.

FIG. 3 is a schematic view of a conventional outer rotor type electric motor.

FIG. 4 is a diagram showing a waveform of a cogging torque of a conventional outer rotor type electric motor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Stator center axis, 2 ... Stator side electromagnet, 3 ... Outer rotor, 3a ... Magnetic pole, 3b ... Depression.

Claims (2)

[Claims] 1. An electric motor having an outer rotor in which N-poles and S-poles are alternately magnetized and formed along an entire circumference of an inner peripheral surface of an N-pole magnetic pole. A circular arc-shaped concave portion is formed at the boundary with the S pole magnetic pole adjacent to the magnetic pole, and the width of each concave portion is smaller than the circumferential width of the magnetic pole. An outer rotor type electric motor having a uniform distance. 2. An electric motor having an outer rotor in which N magnetic poles and S magnetic poles are alternately magnetized and formed along the entire circumference of an inner peripheral surface, wherein each of the N magnetic poles is An outer rotor type electric motor characterized in that a concave portion having a sinusoidal cogging torque waveform is formed at a boundary portion between an S pole magnetic pole adjacent to the S pole magnetic pole.