JPS63213441A - Manufacture of magnet material for dc motor rotor - Google Patents

Abstract

PURPOSE:To reduce a rotational noise without decreasing a motor torque by varying a part of magnetic reluctance of a molding apparatus to be a magnetic path when magnetizing a magnet material for the purpose of giving said material a radial anisotropy. CONSTITUTION:An exciting coil 20 is retained between an annular stand 12 and a backing ring 19 fixed by a bolt 18 to the lower part of said stand, and power is applied to the coil 20 simultaneously with pressure molding so that magnetic powder 17 is magnetized in the direction of a magnetic path (a). The vertical intermediate parts 13a, 14a of bushes 13, 14 corresponding to a magnetic center plane are formed of steel with magnetic permeability more than that of parts 13b, 14b respectively higher and lower than said intermediate parts. In this manner, portions of the magnetic powder 17 contacting the intermediate parts 13a, 14a by said power application are radially magnetized more than those contacting other parts to form a magnetic material axially differing in the degree of a radial anisotropy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a DC motor in which a magnetic powder type magnet rotor of the DC motor can be magnetized with the magnetic center plane in the rotational axis direction being shifted from the geometric center plane. The present invention relates to a method of manufacturing a magnet material for a rotor.

Prior art and its problems FIG. 5 is a half-sectional view of an example of a conventional magnetic rotor type brushless DC motor. Reference numeral 1 denotes a fixed frame, and a stator core 3 is press-fitted and fixed on the outside of a tubular boss portion 2 of the fixed frame. A cup-shaped rotor frame 6 is press-fitted and fixed to a rotating shaft 5 supported by a bearing 4 inside the rotor frame 6.
It has a structure in which a rotor magnet 8 is fixed inside the stator core 3 and faces the stator core 3 with a gap 7 between them.

In the above structure, the electromagnetic attractive force between the core 3 and the magnet 8 that generates torque fluctuates as the magnetic resistance between them changes according to the rotational position, so the axial vibration caused by this fluctuation is minimized. For this purpose, it is necessary to align the axial center planes x and x' of the core 3 and the magnet 8. However, in the case of a brushless morph, because a Hall element 9 is provided to detect the position of the rotor magnet 8 and a speed detection element 10 is provided, conventionally, the center planes x and x' cannot necessarily be aligned. In this case, there is a problem in that vibrations in the axial direction occur due to the electromagnetic attraction force, resulting in rotational noise.

As a means of solving this problem, the present inventor focused on the fact that it is effective to align the magnetic center plane of the rotor magnet with the maximum air gap magnetic flux density of 4 degrees to the center plane of the stator core in the direction of the rotation axis. Anisotropy with strength and weakness in the axial direction is provided in advance so that the magnetic center plane is shifted by a desired amount from the geometrical center plane in the axial direction by magnetization, so that the axial position of the rotor magnet is biased. Another object of the present invention is to provide a method of manufacturing a magnet material for a rotor of a DC motor in which the magnetic center plane coincides with the center plane of the stator core.

Means for Solving the Problems In order to achieve the above object, the present invention provides an intermediate part in the direction of the motor rotation axis of a mold material that is in contact with a side surface facing the gap of a rotor magnet of a DC motor and a side surface opposite to the side surface. Pressure is applied in parallel to both mold materials and the side surfaces so that the magnetic resistance per unit cross-sectional area in the radial direction of the required portion is smaller than the magnetic resistance per unit cross-sectional area in the radial direction of the portion other than the intermediate required portion. Magnetic powder is embedded in the space surrounded by the pressure material, and the magnetic powder is pressure-molded by the pressure material, and is passed through both mold materials and magnetized in the radial direction to give it anisotropy. It is characterized by removing magnetization caused by the magnetization.

If a required intermediate portion in the direction of the rotation axis of the working mold material is formed of a material with higher magnetic permeability than the other portions, and this is magnetized in the radial direction during pressure molding of magnetic powder, the intermediate required portion will have a surface. The part of the magnetic powder that is magnetized is more strongly magnetized than the other parts of the magnetic powder, and anisotropy in the radial direction, which is stronger or weaker in the axial direction, is obtained.

Therefore, once the magnetization caused by the magnetization is demagnetized, the rotor magnet material of the present invention can be obtained.

If the mold material is formed into an annular shape, an annular magnet material can be obtained, and if a magnetized element is magnetized using a normal magnetization method so that a predetermined number of N and S magnetic poles appear inside this material, the strength and weakness in the axial direction can be changed. According to a certain anisotropy, the intermediate required portion is magnetized more strongly than other portions, resulting in a rotor magnet whose magnetic center plane is offset from the geometrical axial center plane.

If the material and axial position of the intermediate required portion are made variable, the amount of deviation of the magnetic center plane can be changed.

Embodiment FIGS. 1 and 2 show a forming device for shifting the magnetic center plane Xta (FIG. 4) of the outer rotor type magnet 8 of the magnetic powder part to a required axial position. shall be in the form of To briefly explain this molding device, a cylindrical table 11 is placed on a fixed table (not shown), and an annular table 12 is placed on a fixed table (not shown).
are fixed concentrically and with the top surfaces flush with each other, and the cylindrical base 11
A bush 1 whose outer peripheral surface is flush with the cylindrical base 11 at the upper end.
3 is fitted onto the outside, and the bushing 14 facing the bushing 13 is fitted into the center hole of the annular stand 12, and the lower punch 15 that moves up and down along the outer periphery of the cylindrical stand 11 hits the upper end surface of the pusher 13°14. Magnetic powder 1, such as ferrite, is charged between the two bushings 13 and 14, which are mold materials, using the upper punch 16 as a pressurizing material.
7 is pressure molded.

An annular stand 12 and a support ring 1 fixed at the bottom with a pole) 18
An excitation coil 20 is held between the magnetic powder 17 and the magnetic powder 17, and the coil 20 is energized at the same time as the pressure molding is performed to magnetize the magnetic powder 17 in the direction of the magnetic path a.

The bushes 13 and 14 are arranged such that upper and lower middle parts 13a and 14a corresponding to the magnetic center plane Xm are connected to upper and lower middle parts 13b and 14a thereof.
It is made of a steel material with higher magnetic permeability than b. For example, 1
3a and 14a are made of hot die alloy tool steel SKD (
The portions 13b and 14b are made of alloy tool steel SKS for impact-resistant tools (glass with a saturation magnetic flux density of 8,000 to 10.000).

At this time, due to the energization, the portions of the magnetic powder 17 that are in contact with the intermediate portions 13a and 14a are more strongly magnetized in the radial direction than the portions that are in contact with other portions, and the degree of radial anisotropy is different in the axial direction. Becomes a magnetic material. After the annular magnetic body is once demagnetized, the desired rotor magnet 8 is obtained by magnetizing it again using a conventional magnetization method so that N and S magnetic poles appear on its inner surface.

FIG. 3 shows an embodiment of a molding device for an inner rotor type magnet. Since the inner rotor type magnet has a small center hole into which the rotating shaft is press-fitted, an excitation coil 20a is also provided in the upper punch 16a in FIG. do. A high permeability material 14a is provided in the bushing 14, and the bushing 13 is omitted.

In the above embodiment, instead of forming the intermediate desired portions 13a, 14a of the bushings 13, 14 with a material having a higher magnetic permeability than the upper and lower portions 13b, 14b, the portions 13b, 14b are formed with a thin layer made of a non-magnetic material or a thin layer made of a non-magnetic material. A layer of magnetically permeable material may also be provided.

FIG. 4 shows the distribution of the air gap magnetic flux density of a rotor magnet in which the material of the present invention is remagnetized to provide N and S magnetic poles on the side facing the air gap. In this case, even if a uniform magnetizing force is applied in the axial direction, the anisotropy of the portions in contact with the intermediate required portions 13a and I4a is particularly stronger than other portions, so that the portions 13a and 14
The magnetic flux density is high in the portion in contact with a, and the entire magnetic center plane is biased to the position Xl11.

Effects of the Invention The present invention provides a method for reducing the magnetic resistance of a part of the molding device that becomes a magnetic path when pressurizing magnetic powder to form a rotor magnet material and magnetizing the magnet material to impart radial anisotropy. It is possible to change the distribution of air gap magnetic flux density in the direction of the rotational axis of the magnet without increasing the number of steps by changing the relatively simple method of changing the number of steps. Therefore, the magnetic center plane of the rotor magnet can be shifted in the axial direction to match the center plane of the stator core. This has the effect of making it easier to design a design that reduces rotational noise without reducing the motor torque.Furthermore, if the parts of the molding device with different magnetic resistances are made interchangeable, it is possible to use the same molding device. This has the effect of making it possible to obtain various rotor magnet materials with different magnetic centers.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a main part of a molding device which is an embodiment of the present invention, FIG. 2 is a partially enlarged cross-sectional view of FIG. 1, and FIG. 3 is a main part of a molding device which is another embodiment of the present invention. 4 is an air gap magnetic flux density distribution diagram of a rotor magnet whose magnetic center plane is offset according to the present invention, and FIG. 5 is a half sectional view of a conventional magnet rotor type DC motor. 7... Gap 8... Rotor magnet 13.14... Mold material 13a, 14a... Intermediate required portion 13b, 14b... Portion other than the intermediate required portion 15.1
6...Pressure material 17...Magnetic powder agent Patent attorney Yujou - 2 other famous paintings 1 Figure 2 Figure 3 Figure 5

Claims (2)

[Claims] (1) The magnetic resistance per unit cross-sectional area in the radial direction of the intermediate required portion in the direction of the motor rotation axis of the mold material that is in contact with the side surface facing the gap of the rotor magnet of the DC motor and the side surface opposite to the side surface, respectively, is calculated as follows. Magnetic powder is filled into a space surrounded by both of the mold materials and a pressurizing material that presses parallel to the side surface, the magnetic resistance of which is smaller than the magnetic resistance per unit cross-sectional area in the radial direction of the portion other than the intermediate required portion. A rotor for a DC motor, characterized in that the magnetic powder is pressure-molded by a pressurizing material, passes through both mold materials and is magnetized in the radial direction to impart anisotropy, and then the magnetization due to the magnetization is removed. manufacturing method of magnetic material for (2) The DC motor according to claim 1, wherein the magnetic permeability of the material of the intermediate required portion of the mold material in the direction of the motor rotation axis is made greater than the magnetic permeability of the material of the portion other than the intermediate required portion. A method for manufacturing rotor magnet material.