JPH0737715A - Plastic magnet and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve magnetic flux density in each signal band by introducing anisotropic orientation for the interior thereof in the plastic magnet in the direction that the signal bands which require generation of magnetic flux are coupled. CONSTITUTION:An almost ring type plastic magnet 18 having the hollow portion at the center thereof has different signal bands at the internal circumferencial surface 14 and end face 13. The interior of this plastic magnet 18 introduces the anisotropic orientation in such a direction that the axis of easy magnetization of magnetic particles links the internal circumferencial surface 14 and end face 13. The anisotropic internal circumferencial surface 14 of the plastic magnet 18 is magnetized with eight magnetic poles so that the the pole N and pole S are alternately located in the circumferencial direction to form a magnetic field for driving a brushless motor. Moreover, the end face 13 is magnetized with 16 magnetic poles to form the magnetic field for frequency generation for detecting the number of rotations of a rotor of the brushless motor. Magnetic flux is almost not generated from the external circumference 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic magnet having improved magnetic characteristics, which is suitable for use in a rotor such as a brushless motor, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, when a plastic magnet is used as a rotor of a brushless motor, for example, the plastic magnet provides a field magnetic field for rotating the brushless motor and also detects the rotational speed of the rotor. Some also have the function of providing a magnetic field for frequency power generation. As shown in FIG. 7, these have a magnetic field for driving on the inner peripheral surface (1) of the plastic magnet (3) and a magnetic field for frequency power generation on the end surface (2) thereof.

In order for the plastic magnet (3) to be provided with these magnetic fields, an anisotropic magnetic field is generally applied in the radial direction or the axial direction at the time of molding and manufacturing the plastic magnet (3). .

Further, as disclosed in Japanese Patent Publication No. 2-20129, the plastic magnet (3) is molded by applying an anisotropic magnetic field simultaneously in two directions, a radial direction and an axial direction. A technique for obtaining a high-performance plastic magnet (3) has also been proposed.

[0005]

However, the above-mentioned plastic magnet (3) is, as schematically shown in FIG. 7, an inner peripheral surface (1) or an end surface of the plastic magnet (3) which requires generation of magnetic flux. (2) The magnetic flux (7) is also generated in the outer peripheral portion (5) other than the (signal band), and this magnetic flux (7) may adversely affect other electronic components and devices around the motor.

Further, since there is the magnetic flux (7) emitted to the outer peripheral portion (5), there is a drawback that the magnetic flux on the necessary inner peripheral surface (1) and end surface (2) is reduced.

If a shield plate (6) made of a magnetic material that covers the outer peripheral portion (5) of the plastic magnet (3) is used to solve these problems, the number of parts and the number of assembling steps increase. Further, since the two parts are combined, the balance is poor, and there is a problem in that it is necessary to maintain a dynamic balance after assembling.

Further, in order to compensate for the decrease in the magnetic flux in the required signal bands (1) and (2), if the mixing ratio of the magnetic powder mixed in the plastic magnet (3) is increased to 90% or more, voids will be generated. Or the plastic magnet (3) may be cracked or cracked.

The present invention has been made under such a circumstance, in which magnetic flux is generated only from the required signal band (magnetic pole row), and the magnetic field can be obtained without a member such as the shield plate (6). , A plastic magnet with good mechanical properties,
It is an object of the present invention to provide a manufacturing method capable of easily mass-producing this.

[0010]

In order to solve such a problem, the plastic magnet of the present invention is a plastic magnet having a plurality of signal bands composed of a plurality of magnetic poles, and the inside of the plastic magnet is The plurality of signal bands are anisotropically oriented in a direction in which the signal bands are connected to each other, and magnetic flux is not generated from other than the plurality of signal bands.

According to the method of manufacturing a plastic magnet of the present invention, in a molding die provided with an exciting device, an exciting device is formed so as to form a magnetic path interconnecting a plurality of signal bands inside the molded plastic magnet. A molding step of molding the plastic magnet in a magnetic field generated from

After the molding step, a demagnetizing step of demagnetizing the molded plastic magnet, and a magnetizing step of magnetizing a plurality of magnetic poles in each signal band of the demagnetized plastic magnet. Is equipped with.

Further, the exciter comprises a first exciter which generates a magnetic flux forming a main magnetic path for anisotropic orientation, and a second exciter which is arranged in the main magnetic path. The second exciter can be configured to generate a magnetic flux in a direction that strengthens or weakens the magnetic flux generated from the first exciter.

Further, a magnetic flux adjusting member may be arranged in a magnetic path formed by the magnetic flux generated by the exciter so that the amount of magnetic flux in the magnetic path can be adjusted.

[0015]

In the plastic magnet of the present invention constructed as described above, the inside thereof is anisotropically oriented only in the direction in which a plurality of signal bands are interconnected, that is, the easy axis of magnetization of the magnetic particles in the plastic magnet. Are arranged along the path connecting the signal bands, the magnetic flux from the plastic magnet is generated only from the magnetic poles of the signal bands.

Further, with this structure, since magnetic flux is not generated from unnecessary portions of the plastic magnet, a high magnetic flux density can be obtained in a necessary signal band, so that the content ratio of magnetic powder is increased more than necessary. You don't have to.

In the method of manufacturing a plastic magnet according to the present invention, when the plastic magnet is molded, a magnetic field that forms a magnetic path connecting the signal bands of the plastic magnet is applied by the exciter arranged in the molding die. Therefore, it is easy to anisotropy the direction of connecting the signal bands of the plastic magnet.

[0018]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 and 2 are a sectional view and a perspective view, respectively, showing one embodiment of the plastic magnet of the present invention.

In FIG. 1, a substantially annular plastic magnet (18) having a hollow portion in the center is used, for example, in a rotor of a brushless motor, and has an inner peripheral surface (14) and an end surface (13) respectively. It has different signal bands (pole arrays). Inside the plastic magnet (18), the axis of easy magnetization of the magnetic particles in the plastic magnet (18) connects the inner peripheral surface (14) and the end surface (13) as shown by the broken line (15) in the figure. Is anisotropically oriented in such a direction.

On the inner peripheral surface (14) of the plastic magnet (18) thus anisotropic, as shown in FIG. 2, for example, N poles and S poles alternate in the circumferential direction. Eight magnetic poles are magnetized to form a field magnetic field for driving the brushless motor. The end surface (13) of the plastic magnet (18) is magnetized to have, for example, 16 poles so that N poles and S poles are alternately arranged in the circumferential direction, and the rotation speed of the rotor of the brushless motor is A magnetic field for frequency power generation for detection is formed.

The magnetic flux generated from the plastic magnet (18) is a signal band in which the magnetic flux needs to be generated, that is, the inner peripheral surface (14), as schematically shown by the reference numeral (17) in part in FIG. The plastic magnet (1) that is generated from the portion and the end face (13) and does not require the generation of magnetic flux.
It is hardly generated from the outer peripheral portion (16) of 8).

Further, since the magnetic flux does not leak to unnecessary portions,
The magnetic flux density in the required signal bands (13) and (14) is correspondingly high, and there is no need to increase the mixing ratio of the magnetic powder in particular, so there is little fear of occurrence of voids (cavities) and cracking of the plastic magnet.

Furthermore, since the rotor of the brushless motor can be constituted by the plastic magnet (18) alone without the need for the conventional shield plate (6) and the like, the number of parts is small and the dynamic balance is remarkably improved.

Next, an embodiment of the method for manufacturing a plastic magnet of the present invention will be described with reference to FIGS.

FIG. 3 is a sectional view of a molding die (28) of a plastic magnet (18) for explaining one embodiment of the present invention. In the figure, an exciting device (11) made of a permanent magnet has a flat cylindrical shape, and its end faces are
That is, the upper surface and the lower surface are magnetized in the thickness direction so as to have monopoles having different polarities. This exciting device (11) is arranged on a center core (22) made of a magnetic material, and a magnetic material part (23 ') is provided around the exciting device (11).
And a non-magnetic material portion (23 ″)
3) is arranged. A magnetic material portion (2) for extruding a molded product is provided on the outer peripheral portion of the taper core (23).
1 ') and a non-magnetic material part (21 ") are arranged, and the stripper bush (21) is provided with a buckling core (2) made of a magnetic material.
0) is fixed with screws (24). Reference numeral (32) is a gate for injecting a liquid pellet of a plastic magnet into the molding die (28).

Liquid pellets are poured into and filled in such a molding die (28) and the plastic magnet (18) is filled.
Is molded. At this time, in the molding die (28),
From the exciter (11) to the magnetic material part (23 ') of the taper core (23), the inner peripheral surface (14) of the plastic magnet (18), its end surface (13), and the magnetic material part (21' of the stripper bush (21). ), A buckling core (20) made of a magnetic material, and a center core (2) made of a magnetic material.
A magnetic path (12) is formed which passes through 2) and returns to the exciter (11). Inside the plastic magnet (18), the magnetic path (1
During the molding of the plastic magnet (18), a magnetic path (15) is formed so as to connect the inner peripheral surface (14) and the end surface (13) of the plastic magnet (18), which is a part of 2). The plastic magnet (1
The easy axis of magnetization of the magnetic particles that composes 8) is the magnetic path (1
5) Aligned with each other and anisotropically oriented.

The plastic magnet (18) thus formed is magnetized to form a predetermined number of magnetic poles in each signal band (13) (14) by a known magnetizing power supply device and a magnetizer connected thereto. It is used for various purposes.

In the molded product after the above-mentioned molding process, since each signal band (13) (14) is magnetized to a single pole of N pole or S pole, it is directly magnetized as described above. If applied, a difference may occur in the magnetization intensity between the N pole and the S pole in one signal band. If this is not preferable for some applications, after the molding step described above, the demagnetized step of demagnetizing the molded plastic magnet (18) to erase the magnetism of the molded article is performed. By magnetizing a predetermined number of magnetic poles in (), it is possible to eliminate the intensity difference between the magnetic poles in one signal band.

Next, another embodiment of the present invention will be described with reference to FIGS. The same components as those in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 4 is a sectional view of a molding die (28) for explaining an example of another embodiment of the present invention. In this embodiment, the permanent magnet (11) has a main magnetic path (not shown, but not shown in FIG. 3) for anisotropically orienting the inside of the plastic magnet (18) in the molding die (28).
Functioning as a first exciter forming the same as 2),
In this magnetic path, a second exciter (2) embedded in the non-magnetic material portion (21 ″) of the stripper bush (21).
5) is provided.

The second exciting device (25) is composed of a ring-shaped permanent magnet, and both end faces thereof are magnetized in the thickness direction so as to have monopoles of different polarities, and the first exciting device (25) Make sure that the polarity of the device (11) is opposite to the polarity of
That is, the magnetic flux of the second exciter (25) is added to the magnetic flux of the first exciter (11) to be strengthened.

By molding the plastic magnet (18) using such a molding die (28), an anisotropic orientation force inside the plastic magnet (18) is obtained as compared with the embodiment of FIG. Can be strengthened.

FIG. 5 is similar to FIG. 4 in that the first excitation device (1
1) and a molding die (2) provided with a second excitation device (25 ')
8) is a sectional view of FIG. 8), but in this embodiment, the second exciter device (25 ′) is in the opposite direction to the embodiment of FIG. 4, that is, in the direction in which the magnetic flux of the first exciter device (11) is weakened. It is located in. By using such a molding die (28), the anisotropic orientation force of the plastic magnet (18) can be weakened.

FIG. 6 is a sectional view of a molding die (28) for explaining still another embodiment of the present invention. Also in this figure, the same components as those in FIG. 3 are denoted by the same reference numerals.

In the molding die (28) used in this embodiment, the magnetic path (not shown in the figure, the magnetic path (12) in FIG. 3) formed in the molding die (28) by the exciting device (11). The same as the above), adjustment members (26) and (27) for adjusting the magnetic resistance of this magnetic path are provided.

These adjusting members are composed of the magnetic material part (2
1 ') a stripper bush (21) provided with a magnetic material buckling core (20) and a thin plate ring-shaped non-magnetic material adjusting plate (26) and magnetic material adjusting plate (27). Consists of. The magnetic flux amount in the magnetic path can be adjusted by adjusting the thickness and the number of laminated layers of the non-magnetic material adjusting plate (26) and the magnetic material adjusting plate (27), and the anisotropic orientation of the plastic magnet (18). The force can be adjusted to the desired level and molded.

In the above-mentioned embodiment, an example of adjusting the magnetic flux amount of the magnetic path in the molding die (28) using the non-magnetic material adjusting plate (26) and the magnetic material adjusting plate (27) has been shown. However, in order to achieve the object of the present invention, it suffices that an adjustable magnetic resistance is interposed in the magnetic path formed by the exciting device (11).
It is also possible to provide an air gap between the stripper bushing (0) and the stripper bush (21) whose distance can be adjusted.

[0038]

As described above, in the plastic magnet of the present invention, the inside thereof is anisotropically oriented in the direction in which the signal bands that require the generation of magnetic flux are interconnected. Since there is almost no generation of magnetic flux from, it is difficult to adversely affect other peripheral devices and electronic parts,
The magnetic flux density in each signal band is improved. Moreover, since a shield plate or the like is not required, the number of parts is reduced, and the dynamic balance is improved when used in a rotating body.

In the method of manufacturing a plastic magnet of the present invention, when a plastic magnet is molded, a magnetic field that forms a magnetic path connecting the signal bands of the plastic magnet is applied by an exciting device provided in the molding die. Therefore, the inside of the plastic magnet is easily anisotropy in the direction of connecting the signal bands. Further, the anisotropic orientation force of the plastic magnet is easily adjusted by disposing the second exciter or the member capable of adjusting the amount of magnetic flux in the magnetic path formed by the exciter. It is possible to obtain a plastic magnet suitable for desired characteristics.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of a plastic magnet of the present invention.

FIG. 2 is a perspective view of the plastic magnet shown in FIG.

FIG. 3 is a vertical cross-sectional view of a molding die for explaining an embodiment of the method for manufacturing a plastic magnet of the present invention.

FIG. 4 is a vertical sectional view of a molding die for explaining another embodiment of the method for manufacturing a plastic magnet of the present invention.

FIG. 5 is a vertical cross-sectional view of a molding die for explaining still another embodiment of the method for manufacturing a plastic magnet of the present invention.

FIG. 6 is a vertical cross-sectional view of a molding die for explaining still another embodiment of the method for manufacturing a plastic magnet of the present invention.

FIG. 7 is a vertical sectional view showing an example of a conventional plastic magnet.

[Explanation of symbols]

 (1) (14) Inner peripheral surface (signal band) (2) (13) End surface (signal band) (3) (18) Plastic magnet (5) (16) Outer peripheral part (6) Shield plate (7) (17) ) Magnetic flux (11) Exciter (first exciter) (12) Magnetic path (20) Buckling core (21) Stripper bush (21 ') Magnetic material part (21 ") Non-magnetic material part (22) Center core (22) 23) Tapered core (23 ') Magnetic material part (23 ") Nonmagnetic material part (24) Screw (25) (25') Second exciter (26) Nonmagnetic material adjusting plate (adjusting member) (27) Magnetic material adjustment plate (adjustment member) (28) Mold (32) Gate

Claims (7)

[Claims] 1. A plastic magnet having a plurality of signal bands composed of a plurality of magnetic poles, wherein the interior of the plastic magnet is anisotropically oriented in a direction connecting the plurality of signal bands to each other, and other than the plurality of signal bands. A plastic magnet characterized by the absence of magnetic flux. 2. A method of manufacturing a plastic magnet having a plurality of signal bands composed of a plurality of magnetic poles, wherein the plurality of signal bands are connected to each other inside the plastic magnet in a molding die provided with an exciting device. A method of manufacturing a plastic magnet, comprising a molding step of molding the plastic magnet in a magnetic field generated from the exciting device so as to form a magnetic path. 3. A demagnetizing step of demagnetizing the molded plastic magnet after the molding step, and a plurality of demagnetizing steps for the plurality of signal bands of the demagnetized plastic magnet after the demagnetizing step. The method of manufacturing a plastic magnet according to claim 2, further comprising: a magnetizing step of magnetizing the magnetic poles. 4. A first exciting device, wherein the exciting device generates a magnetic flux which is disposed substantially in the center of the molding die and forms a main magnetic path for anisotropic orientation, and the first exciting device. A second exciter located in the main magnetic path outside of the
4. The method according to claim 2 or claim 3, characterized in that
A method for manufacturing the described plastic magnet. 5. The method of manufacturing a plastic magnet according to claim 4, wherein the second excitation device generates a magnetic flux in a direction in which the magnetic flux generated from the first excitation device is strengthened. 6. The method of manufacturing a plastic magnet according to claim 4, wherein the second exciter device generates a magnetic flux in a direction that weakens the magnetic flux generated from the first exciter device. 7. A magnetic flux adjusting member is arranged in a magnetic path formed by magnetic flux generated by the exciter, and the amount of magnetic flux in the magnetic path is adjusted by adjusting the magnetic flux adjusting member. The method for manufacturing a plastic magnet according to any one of claims 2 to 6.