JP2000333428A - Dc brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a motor small and to reduce its cost. SOLUTION: This motor 1 is made up of a stator 9, a rotor 7 that is arranged to face the stator 9 and rotates, a circular position detecting magnet 11 that comprises N, S with magnetic poles arranged alternately in the circumferential direction and is integrated with the rotor 7, and a position detecting element 12 arranged to face the position detecting magnet 11 to detect its rotational position by the magnetic field. In this motor, the position detecting magnet 11 has a plurality of slits 11b arrayed in the circumferential direction and magnetic poles aligned radially outside these slits 11b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC brushless motor, and more particularly to an improvement in a position detecting magnet for detecting a rotational position of a rotor.

[0002]

2. Description of the Related Art A conventional DC brushless motor is disclosed in Japanese Patent Application Laid-Open No. Hei 7-322588. As shown in FIG. 6, the DC brushless motor 1 is covered with a motor case 2, and a stator 9 made of a magnetic material provided with an exciting coil 8 is fixed to an inner wall of the motor case 2.

[0003] A rotor 7 mounted on a rotating shaft 6 supported by a bearing 5 faces a stator 9 arranged outside the rotor 7. The detailed configuration of the rotor 7 is disclosed in Japanese Patent Laid-Open No. 9-200.
No. 982, etc., as shown in FIG. A plurality of permanent magnets 22 are buried in a through hole 21a provided in a core 21 made of a cylindrical magnetic material. Both ends of the core 21 are closed by end plates 23 and 24 to prevent the permanent magnet 22 from dropping off in the axial direction.
The bolt 25 is screwed into the female screw portion 24a of the end plate 24 through the insertion holes 23a and 21b, and fastens the core 21 and the end plates 23 and 24.

A rotating shaft 6 is provided with a position detecting magnet 11.
Are integrated. As shown in FIG. 7, the position detecting magnet 11 has an annular shape having N and S magnetic poles alternately arranged on an outer peripheral surface thereof and having a through hole 11a at the center.
As shown in FIG. 8, the position detecting magnet 11 includes an upper mold 31 and a lower mold 32 made of a non-magnetic material, an outer mold 33 made of a magnetic material,
The magnet material surrounded by the inner mold 34 is pressed by the upper mold 31 and formed. At this time, a magnetic field is applied in the direction of the arrow, and the film is formed to have anisotropy in the radial direction (hereinafter, referred to as “radial orientation”).

A position detecting element 12 composed of a hall element or the like is integrated with the motor case 2 and is arranged to face the position detecting magnet 11. When the position detecting magnet 11 rotates together with the rotor 7, the position detecting element 12 detects the rotational position of the rotating shaft 6 by detecting a change in magnetic flux due to the rotation of the position detecting magnet 11.

[0006]

In the conventional DC brushless motor 1 described above, one of the end plates 23 and 24 is also used as the position detecting magnet 11 to reduce the number of parts and to provide the DC brushless motor 1. The size can be reduced. At this time, an insertion hole or a female screw portion through which the bolt 25 is inserted into the position detecting magnet 11 is required.

When the annular position detecting magnet 11 having an insertion hole or a female screw portion is radially oriented as shown in FIG. 8, it becomes difficult to form a magnetic pole on the outer peripheral portion with high accuracy. As a result, the magnetic field generated from the position detecting magnet 11 is partially weakened, and the position detecting accuracy is reduced.

For this reason, if the position detecting magnet 11 having an insertion hole or a female screw portion is isotropically formed without radial orientation and then magnetized, the generated magnetic field is weakened as a whole. Therefore, it is necessary to use an expensive magnet such as a neodymium-iron-boron-based rare earth magnet having a large coercive force to generate a strong magnetic field. Therefore, there is a problem that the material cost is increased.

SUMMARY OF THE INVENTION An object of the present invention is to provide a DC brushless motor that can be reduced in size and cost.

[0010]

Means for Solving the Problems In order to achieve the above object, the invention described in claim 1 comprises a stator, a rotor arranged opposite to the stator and rotating, and N, N in the circumferential direction.
A circular position detecting magnet in which the magnetic poles of S are alternately arranged and integrated with the rotor, and position detection that is disposed opposite to the position detecting magnet and detects the rotational position of the position detecting magnet by a magnetic field. In the DC brushless motor provided with the element, the position detecting magnet has a plurality of openings arranged in a circumferential direction, and the magnetic poles are radially oriented outside the openings.

According to this configuration, when the stator is energized, the rotor rotates together with the position detecting magnet. The position detecting magnet is radially oriented between the opening and the outer peripheral surface, and the rotational position of the position detecting magnet is detected by a magnetic field generated from magnetic poles arranged outside the opening.

According to a second aspect of the present invention, in the DC brushless motor according to the first aspect, the opening is an arc-shaped slit.

According to a third aspect of the present invention, in the DC brushless motor according to the second aspect, the slits are provided in a plurality of rows in the radial direction, and the slits in adjacent rows are arranged at different positions in the circumferential direction. It is characterized by doing.

According to a fourth aspect of the present invention, in the DC brushless motor according to the first aspect, the opening is a hole.

According to a fifth aspect of the present invention, in the DC brushless motor according to any one of the first to third aspects, the center of the position detecting magnet is closed. And

According to a sixth aspect of the present invention, in the DC brushless motor according to any one of the first to fifth aspects, the position detecting magnet is connected to the rotor by a mounting member inserted through the opening. It is characterized by being attached to.

According to a seventh aspect of the present invention, in the DC brushless motor according to any one of the first to sixth aspects, a magnetic body is fitted into the opening.

According to an eighth aspect of the present invention, in the DC brushless motor according to any one of the first to seventh aspects, the position detecting magnet is a plastic magnet.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. For convenience of explanation, the same parts as those of the conventional example shown in FIGS. 1 and 2
1 is a front sectional view and a bottom view showing a DC brushless motor according to one embodiment.

The DC brushless motor 1 is covered with a motor case 2, an upper plate 3 and a bottom plate 4, and a stator 9 having a stator core provided with an exciting coil 8 is fixed to an inner wall of the motor case 2. The rotor 7 integrated with the rotating shaft 6 supported by the bearing 5 is disposed to face the stator 9. A disc-shaped position detecting magnet 11 is integrated with the rotating shaft 6. The position detecting magnet 11 is provided with a plurality of arc-shaped slits 11b (openings) on the same circumference.

As shown in FIG. 3, the position detecting magnet 11 is made of a magnetic material surrounded by an upper mold 31 and a lower mold 32 made of a non-magnetic material, and an outer mold 33 and an inner mold 35 made of a magnetic material. 3
It is pressed by 1 and formed. At this time, a magnetic field is applied in the direction of the arrow, and N, S
Are radially oriented so that the magnetic poles are alternately arranged.

A position detecting element 12 composed of a Hall element, a Hall IC, a magnetoresistive element or the like is integrated with the motor case 2 and is arranged to face the outer peripheral surface of the position detecting magnet 11. The position detecting element 12 detects the rotational position of the rotating shaft 6 by detecting a change in magnetic flux due to the rotation of the position detecting magnet 11.

The rotor 7 has a plurality of permanent magnets 22 embedded in a core 21 made of a columnar non-magnetic material. Both ends of the core 21 are closed by the end plate 24 and the position detecting magnet 11 to prevent the permanent magnet 22 from falling off. Bolt 2
5 (attachment member) is screwed into a female screw portion (not shown) of the end plate 24 through a slit 11b and an insertion hole (not shown) provided in the core 21, and the core 21, the end plate 24 and the position detection The magnet 11 is fastened.

In the DC brushless motor 1 having the above configuration, when the plurality of exciting coils 8 of the stator 9 are energized at a predetermined timing, the permanent magnet 22 attracts and repels the stator 9 to rotate the rotor 7. The position detecting magnet 11 rotates with the rotation of the rotor 7, and the magnetic field generated from the N and S magnetic poles on the outer peripheral surface of the position detecting magnet 11 is used as the position detecting element 1.
2 detects the position detecting magnet 11, that is, the rotational position of the rotating shaft 6.

According to the DC spindle motor 1 of the present embodiment, a plurality of slits 11
By providing b, the magnetic pole can be easily radially oriented outside the slit 11b. Therefore, the position detecting magnet 1 is fixed by the bolt 25 passing through the slit 11b.
1 can be attached to the rotor 7 to prevent the permanent magnet 22 from falling off.

Even if an inexpensive plastic magnet having a low holding force is used, a strong magnetic field can be generated by the magnetic poles arranged in the radial direction around the position detecting magnet 11. As a result, the number of parts is reduced and D
The size and cost of the C spindle motor 1 can be reduced.

Further, even when the through hole 11a (see FIG. 7) is not provided at the center of the position detecting magnet 11, the magnetic pole can be radially oriented outside the slit 11b. Therefore, a sufficient magnetic field can be generated even when the through-hole 11a cannot be provided due to the design of the DC spindle motor 1 and the central portion is closed. Furthermore, when a magnetic material is fitted into the slit 11b,
This is desirable because a stronger magnetic field can be generated.

The slit 11b of the position detecting magnet 11 is
It is not always necessary to arrange them on the same circumference. As shown in FIG. 4, a plurality of slits are provided and slits 1 in adjacent rows are provided.
1b and 11b 'may not be overlapped in the circumferential direction. In addition, as shown in FIG.
1c may be provided on the circumference, and the magnetic pole may be radially oriented outside the hole 11c.

[0029]

According to the present invention, by providing a plurality of openings such as slits and holes on the periphery of the position detecting magnet, the magnetic pole can be easily radially oriented outside the openings. Therefore, it is possible to prevent the permanent magnet embedded in the rotor from falling off by attaching the position detecting magnet to the rotor by the mounting member inserted through the opening.

Further, even if an inexpensive plastic magnet having a low holding force is used, a strong magnetic field can be generated by the magnetic poles arranged on the outer periphery of the position detecting magnet. As a result, it is possible to reduce the number of parts, reduce the size of the DC spindle motor, and reduce the cost.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing a DC brushless motor according to an embodiment of the present invention.

FIG. 2 is a bottom view showing a position detecting magnet of the DC brushless motor.

FIG. 3 is a front sectional view showing a forming state of a position detecting magnet of the DC brushless motor.

FIG. 4 is a bottom view showing a position detecting magnet of another shape of the DC brushless motor.

FIG. 5 is a bottom view showing still another shape detecting magnet of the DC brushless motor.

FIG. 6 is a front sectional view showing a conventional DC brushless motor.

FIG. 7 is a bottom view showing a position detecting magnet of a conventional DC brushless motor.

FIG. 8 is a front sectional view showing a state of forming a position detecting magnet of a conventional DC brushless motor.

FIG. 9 is a perspective view showing a rotor of a conventional DC brushless motor.

[Explanation of symbols]

 Reference Signs List 1 DC brushless motor 2 Motor case 3 Top plate 4 Bottom plate 5 Bearing 6 Rotating shaft 7 Rotor 8 Exciting coil 9 Stator 11 Magnet for position detection 11b Slit 11c Hole 12 Position detection element 22 Permanent magnet 24 End plate 25 Bolt

Claims (8)

[Claims] 1. A stator, a rotor arranged opposite to the stator and rotating, a circular position detecting magnet in which N and S magnetic poles are alternately arranged in a circumferential direction and integrated with the rotor, A DC brushless motor comprising: a position detecting element disposed opposite to the position detecting magnet to detect a rotational position of the position detecting magnet by a magnetic field, wherein the position detecting magnet has a plurality of openings arranged in a circumferential direction. And a magnetic pole radially oriented outside the opening. 2. The DC brushless motor according to claim 1, wherein the opening is an arc-shaped slit. 3. The DC brushless motor according to claim 2, wherein the plurality of slits are radially arranged in rows, and slits in adjacent rows are arranged at different positions in a circumferential direction. 4. The DC brushless motor according to claim 1, wherein the opening is a hole. 5. The DC brushless motor according to claim 1, wherein a center of the position detecting magnet is closed. 6. The DC brushless motor according to claim 1, wherein the position detecting magnet is mounted on the rotor by a mounting member inserted through the opening. 7. The DC according to claim 1, wherein a magnetic body is fitted into the opening.
Brushless motor. 8. The DC brushless motor according to claim 1, wherein the position detecting magnet is a plastic magnet.