JPH0811043Y2 - Rotation noise reduction structure of magnet rotor type DC motor - Google Patents

Description

[Detailed description of the device]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure for reducing the rotating sound of a magnet rotor type DC motor.

[0002]

2. Description of the Related Art FIG. 5 is a half cross-sectional view of an example of a conventional magnet rotor type brushless DC motor. Reference numeral 1 is a fixed frame, in which a stator core 3 is press-fitted and fixed to the outside of a cylindrical central boss portion 2 of the fixed frame. 2, the cup-shaped rotor frame 6 is press-fitted and fixed to the rotating shaft 5 supported by the bearing 4 inside,
It has a structure in which a rotor magnet 8 facing the stator core 3 with a gap 7 is fixed inside the rotor frame 6. In the structure described above, the electromagnetic attraction force between the core 3 and the magnet 8 that generates torque varies depending on the rotational position of the magnet 8. Therefore, in order to minimize the axial vibration caused by this variation, the core 3 is generally It is necessary to match the axial center planes X and X ′ with the magnet 8.

[0003]

However, in the case of such a brushless motor, since the hall element 9 and the speed detecting element 10 are provided to detect the position of the rotor magnet 8, the center planes X, X are conventionally provided. 'Cannot always be matched, and in that case, there is a problem that axial vibration is generated by the electromagnetic attraction force and rotational noise is generated.

An object of the present invention is to improve the present situation and propose a rotation noise reducing structure for a magnet rotor type DC motor.

[0005]

In order to achieve the above object, the present invention provides a magnet rotor type DC motor having a stator core and a rotor magnet, wherein the stator core is disposed not in the geometric center plane direction of the rotor magnet but in the rotor magnet. The rotor whose magnetic flux density is maximized by making a certain axial portion of the rotor magnet different in degree of radial anisotropy from other portions so as to attract toward the magnetic center plane direction The magnetic center plane of the magnet is distant from the geometric center plane of the rotor magnet and axially coincides with the geometric center plane of the stator core, thus
A rotation noise reduction structure of a magnet rotor type DC motor is characterized in that the rotation noise of the motor is reduced.

[0006]

When the geometric center plane of the stator core and the magnetic center plane of the rotor magnet are made to coincide with each other, the component force of the magnetic attraction force in the rotation axis direction is reduced as compared with the case where they do not coincide with each other, and vibration due to the component force is generated. Will be reduced.

[0007]

In the embodiment of the present invention shown in FIG. 1, the magnetic center plane having the maximum air gap magnetic flux density in the rotation axis direction of the rotor magnet 8 with respect to the geometric center plane X in the rotation axis direction of the stator core 3 in FIG. Match Xm. Magnetization center plane X
When m is deviated in this way, the air gap magnetic flux density in the axial direction is distributed asymmetrically with respect to the plane Xm, and the center of the electromagnetic attractive force with the core 3 is the geometric center plane X ′ of the magnet 8.
Since it is biased toward Xm, the component force of the electromagnetic attraction force in the direction of the rotation axis is reduced, and the rotation sound is also reduced accordingly.

FIG. 2 shows the geometrical center plane X of the stator core 3.
Of the magnetic center plane Xm of the magnet rotor 8 from the
Is a measured diagram of the relationship between the rotation sound level L and δ = 0.8 mm
It was confirmed that the rotation sound level of 45.4db was reduced to 40db when δ = 0 according to the present invention.

3 and 4 show a molding device for shifting the magnetic center plane Xm of the outer rotor type magnet 8 made of magnetic powder to a required axial position, and the magnet 8 has a ring shape. Briefly explaining this molding device,
The cylindrical base 11 and the annular base 12 are fixed concentrically and with their upper surfaces flush with each other on a fixed base (not shown), and the bush 13 having the outer peripheral surface flush with the cylindrical base 11 is attached to the upper end of the cylindrical base 11. The bush 14 is fitted in the center hole of the annular base 12, and the bush 14 facing the bush 13 is fitted therein. The lower punch 15 moves up and down along the outer circumference of the cylindrical base 11, and the upper punch 16 hits the upper end surfaces of the bushes 13 and 14. Both bushes 1 which are mold materials using as a pressure material
Magnetic powder 17 such as ferrite charged between 3 and 14 is pressure-molded.

An exciting coil 20 is held between an annular base 12 and a support ring 19 fixed to the lower part thereof with a bolt 18, and the coil 20 is energized at the same time as the pressure forming so that the magnetic powder 17 is directed in the direction of the magnetic path a. Magnetize to.

The bushes 13 and 14 have upper and lower intermediate portions 13a and 14a, which correspond to the magnetic center plane Xm, made of a steel material having a higher magnetic permeability than the upper and lower portions 13b and 14b. For example, the parts 13a and 14a are hot-molded alloy tool steel SKD (saturation magnetic flux density 13,000 to 15,000 gauss).
The alloy tool steel SKS for impact resistant tools (saturation magnetic flux density 8,000 to 10,000 gauss)
To form.

At this time, the portion of the magnetic powder 17 in contact with the intermediate portions 13a and 14a is magnetized in the radial direction more strongly than the portion in contact with the other portions by the energization, and the degree of anisotropy in the radial direction is axially increased. It becomes a different magnetic material. After demagnetizing the magnetization of the annular magnetic body once, it is magnetized again by the conventional magnetizing method so that the N and S magnetic poles appear on the inner surface thereof to obtain the desired rotor magnet 8.

The present invention described for the outer rotor type motor can be applied to the inner rotor type motor.

[0014]

The present invention reduces the axial dimension of the rotor magnet required to generate a desired torque by changing the distribution of the air gap magnetic flux density of the rotor magnet to move the magnetic center in the axial direction. There is an effect that the rotation noise can be reduced without doing so, and the axial movement amount of the magnetic center can be easily adjusted by only partially changing the dimension and the material of the material used for the magnetic path. This has the effect of facilitating the design of a magnet rotor type DC motor with low power consumption. In addition, since the magnetic center plane and the geometric center plane of the rotor magnet are offset from each other, it is possible to secure a space in which elements such as Hall elements and speed detecting elements are provided without impairing the rotation of the rotor magnet. It has the effect of being able to.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a main structure of a magnet rotor type DC motor to which the present invention is applied.

FIG. 2 is an actual measurement diagram of a relationship between a displacement size of a stator core center plane of a magnet rotor type DC motor and a magnetic center plane of a rotor magnet and a rotation sound level.

FIG. 3 is a sectional view of an essential part of a rotor magnet molding apparatus used in the present invention.

FIG. 4 is a partially enlarged sectional view of FIG.

FIG. 5 is a half sectional view of a conventional magnet rotor type DC motor.

[Explanation of symbols]

 3 Stator core 5 Rotating shaft 8 Rotor magnet X Geometric center plane of stator core Xm Magnetic center plane

Claims (1)

[Scope of utility model registration request] 1. A magnet rotor type DC motor having a stator core and a rotor magnet, wherein the rotor core is attracted toward the magnetic center plane of the rotor magnet, not toward the geometric center plane of the rotor magnet. The magnetic center plane of the rotor magnet is made to have a maximum magnetic flux density by making a certain portion in the axial direction of the magnet different in degree of anisotropy in the radial direction from other portions. Rotation noise reduction of a magnet rotor type DC motor, characterized in that it is remote from the center plane and axially coincides with the geometric center plane of the stator core, thus reducing the rotation noise of the motor. Construction.