JP2000358339A - Small-size motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve cogging characteristic by reducing air gaps and stabilize quality. SOLUTION: A magnet 24 and a bearing 25 are integrally molded through the insertion molding by injecting a magnet material to a small size motor case molded with a curling mold. A size accuracy of the relative positions of the bearing surface 25a and inner circumferential surface 24a of the magnet 24 is determined uniquely within the same metal die and the work accuracy of the motor case 20 will not intervene for such a dimensional accuracy. An air gap G2 can be shortened sufficiently and the motor can increase its power. Cogging can also be controlled by adequately controlling a thickness T2 and a radius R2 of curvature of a magnet 14. Moreover, it is easily to cope with the requirements for a narrower motor having a large aspect ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small motor having a magnet on an inner peripheral surface of a motor case, and more particularly, to a structure of a magnet and a bearing.

[0002]

2. Description of the Related Art FIG. 5 is a partial sectional view of a conventional small motor 100. A magnet 101 is fixed to an inner peripheral surface 103 of a cylindrical motor case 102 by an adhesive. When the motor case is of an oval type, it is fixed by a dedicated fixing part or the like, or is fixed by an adhesive after press-fitting.

[0003]

However, when the magnet is fixed with an adhesive, the gap between the inner peripheral surface 103 of the motor case 102 and the outer surface 105 of the magnet 101 is about 0.02 to 0.1 mm. Is required. Therefore, the inner peripheral surface 1 of the magnet 101 with respect to the rotating shaft 110
The relationship of 07 is that the eccentricity of the inner peripheral surface 103 with respect to the press-fit portion of the bearing 108 of the motor case 102 and the magnet outer peripheral surface 1
Accuracy is limited by the total stacking dimension including the deviation caused by the bonding operation between the inner surface 05 and the inner peripheral surface 103 of the motor case and the eccentricity of the outer diameter with respect to the inner diameter of the magnet 101.

For this reason, the inner peripheral surface 10 of the magnet 101
The air gap 106 between the motor case 102 and the outer peripheral surface 109 of the rotor 104 cannot be reduced by ignoring the bonding margin and the stacking dimension relating to the eccentricity of the inner and outer diameters of the motor case 102 and the magnet 101, and the output characteristics cannot be reduced. Has prevented the improvement. In addition, it is difficult to accurately match the curvature of the arc of the motor case inner peripheral surface 103 with the curvature of the arc of the magnet outer surface 105, and a gap is generated due to the curvature mismatch, which causes unstable cogging characteristics. In addition, the use of the adhesive not only takes time and effort in the management of the coating process, but also is affected by the environment such as temperature and humidity, and aging is inevitable.

Accordingly, an object of the present invention is to reduce the air gap between the rotor and the magnet, improve the motor output characteristics and improve the cogging characteristics, and stabilize the product quality without using an adhesive for mounting the magnet. It is to make.

[0006]

In order to achieve the above object, in a small motor according to the present invention, when a magnet for driving a rotor is mounted on a motor case, the magnet and the motor case are formed by insert molding. did. Further, the magnet and a bearing that rotatably supports the rotor are integrally formed of the same magnet material by the insert molding. The motor case has openings on upper and lower surfaces that are orthogonal to the rotation axis and opposed to each other. Preferably, the motor case is an oval type in which a plane portion and an arc portion are respectively symmetrical, and the magnet is insert-molded in the arc portion, and the motor case is formed by curling a thin plate-shaped magnetic body in a circumferential direction. And mold.

Further, both the center of the arc forming the inner peripheral surface of the arc portion of the motor case and the center of the arc forming the inner peripheral surface of the magnet coincide with the axis of rotation of the rotor, so that the magnet is made uniform. It was formed with a thickness. Further, while the center of the arc forming the inner peripheral surface of the motor case arc portion faces the rotor rotation axis, the center of the magnet forming the inner peripheral surface of the magnet faces the outer side of the rotor rotation axis. The magnet may be biased so that the thickness of the magnet is gradually reduced toward both edges of the arc portion. Preferably, the center where the arc forming the inner peripheral surface of the motor case arc portion faces and the center where the arc forming the inner peripheral surface of the magnet faces both coincide with the position deviated outward from the rotor rotation axis. Then, the magnet is formed with a uniform thickness.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a motor case 10 according to a first embodiment of a small motor according to the present invention, wherein (a) is a cross-sectional view of a side surface, and (b) is a plan view taken along line bb of (a). . The motor case 10 is formed by deep drawing, and a magnet material is injected and the magnet 14 and the bearing 15 are integrally formed by insert molding. One end face 10a of the motor case 10 is opened, and a spoke 18 is formed on the other end face 10b, being bent inward from the cylindrical surface and connected to the bearing 15, and the remainder is an opening 16.

A mold (not shown) that surrounds the motor case 10 by moving it from both sides in the axial direction includes an upper mold and a lower mold, and forms a cavity in which the magnet 14 and the bearing 15 communicate with each other through the opening 16. The dimensional accuracy of the relative position between the bearing surface 15a and the magnet inner peripheral surface 14a is uniquely and accurately determined in the same mold, and there is no room for the machining accuracy of the motor case 10 to intervene during this. A positioning hole 17 for determining the position of the motor case 10 with respect to the mold is formed in the spoke 18.
It engages with a positioning pin of a mold (not shown).

The opening 16 is filled with a magnet material to form an end face 16a. Rotating shaft 19b indicated by a two-dot chain line
Is supported on the bearing 15 and the outer peripheral surface 1 of the rotor 19 which rotates.
Since only the mold error interferes with the accuracy of the air gap G1 between the magnet 9a and the magnet inner peripheral surface 14a, this gap can be sufficiently reduced and the motor output can be increased. The insert-molded magnetic polymer magnet 14 is removed from the mold after curing, and is magnetized from the outside to form a permanent magnet.

FIG. 2 shows a second embodiment in which a magnet 24 and a bearing 25 are insert-molded in a motor case 20 formed by curling. (A) is a rear view of the motor case 20 viewed from one end face A, (b) is a cross-sectional view of the motor case 20 along line bb in (a), and (c) is (b)
FIG. 10 is a plan view seen from an end face C on a side opposite to the view of FIG.

The motor case 20 curls a thin plate-shaped magnetic body in the circumferential direction, joins the front edge and the rear edge in the curling direction at a seam 21, and connects the arc portion 22 and the flat portion 23 at symmetric positions. Each has a formed oval cross section. One end surface A of the motor case 20 is open, and the other end surface C forms a spoke 28 connected to the bearing 25 by bending a part of the arc portion 22 inward, and the remaining portion becomes the opening 26.

As in the first embodiment, a mold (not shown) is composed of an upper mold and a lower mold which move around the motor case 20 from both sides in the axial direction and surround the motor case 20.
To form a communicating cavity. The magnet 24, the bearing 25, and the opening 26 are filled with the same magnet material and integrally formed by insert molding, and the filled opening 26 is formed.
Forms an end face 26a. Reference numeral 27 denotes a positioning hole for accurately positioning the motor case 20 with respect to a mold (not shown).
The uneven thickness of the two opposing magnets 24 is prevented.

The inner circumferential surface 2 of the magnet with respect to the bearing surface 25a
The position of 4a is automatically determined by the mold. Therefore, the outer peripheral surface 29a of the rotor 29 indicated by a two-dot chain line that rotates while the rotating shaft 29b is supported by the bearing 25 can be dimensioned sufficiently close to the inner peripheral surface 24a of the magnet within a mold error range. It is possible to increase the output of the motor by reducing the air gap G2.

R1 is a radius of curvature of an arc forming the inner peripheral surface 22a of the motor case arc portion, and R2 is a magnet inner peripheral surface 24a.
The radius of curvature of the arc forming a. The center of the radius of curvature R1 facing the inner peripheral surface 22a of the motor case arc portion and the center of the radius of curvature R2 facing the inner peripheral surface 24a of the magnet coincide with the rotor rotation axis C1.

The outer peripheral surface of the magnet 24 is the motor case 2
Since the gap is filled with no gap in contact with the inner peripheral surface 22a of the 0 arc portion 22, troubles caused by a mismatch between the curvature of the magnet 24 and the arc portion 22 and a change in the adhesive layer are eliminated, and the cogging characteristics are stabilized. Even if the motor case 20 is slightly deformed, the difference between R1 and R2 hardly fluctuates over the entire arc, and the thickness T2 (= R1−R2) of the magnet 24 becomes substantially uniform. Therefore, since the air gap G2 between the magnet inner peripheral surface 24a and the rotor outer peripheral surface 29a is constant over the entire arc portion 22, the motor can secure a strong and stable starting torque.

FIG. 3 shows a third embodiment in which a magnet 34 and a bearing 35 are insert-molded in a motor case 30 formed by curling. (A) shows the motor case 30 in FIG.
It is a rear view seen from the same direction as (a). Similarly to the motor case 20 of the second embodiment, the motor case 30 is formed by curling a thin plate-shaped magnetic body in the circumferential direction, and joining the front edge and the rear edge in the curling direction at the seam 31 so as to be in a symmetrical position. It has an oval cross section in which an arc portion 32 and a plane portion 33 are respectively formed.

As in the second embodiment, one end face of the motor case 30 is open, and the other end face is formed by bending a part of the circular arc portion 32 inward to be connected to the bearing 35. A spoke 38 for forming a positioning hole 37 cooperating with a positioning pin and an opening 36 are formed. The same mold as that of the second embodiment is used for insert molding of the magnet material, and the magnet 34 and the bearing 35 are simultaneously molded integrally with the insert. At this time, the communicating opening 36 is also filled with the same material, and the end face 36a is filled. Form.

The inner circumferential surface 3 of the magnet with respect to the bearing surface 35a
As in the second embodiment, the position of the rotor 4a is automatically determined by the mold, as in the second embodiment. The outer peripheral surface 39a of the rotor 39 indicated by a two-dot chain line rotates while the rotating shaft 39b is supported by the bearing 35.
Since the size can be set sufficiently close to the magnet inner peripheral surface 34a within a mold error range, the motor output can be increased by minimizing the air gap G3.

In the third embodiment, the radius of curvature R3 of the arc forming the inner peripheral surface 32a of the arc portion 32 of the motor case 30 is centered on the rotor rotation axis C1 as in R1 of the second embodiment. The center C2 of the radius of curvature R4 facing the magnet inner peripheral surface 34a is located at a position deviated outward by a distance S1 from the rotor rotation axis C1. In this case, it can be seen that the thickness T3 (= R3-R4) of the magnet 34 becomes maximum at the center of the arc portion 32 and gradually decreases as approaching both edges of the arc portion 32.

In the third embodiment, as in the second embodiment, the outer peripheral surface of the magnet 34 is in contact with the inner peripheral surface 32a of the arc portion 32 of the motor case 30 and is filled without gaps.
Trouble caused by the curvature mismatch between the fourth and arc portions 32 and the fluctuation of the adhesive layer is eliminated, and the cogging characteristics are stabilized. Moreover, the air gap G3 between the inner peripheral surface 34a of the magnet and the outer peripheral surface 39a of the rotor 39 expands at both ends of the magnet 34, and the magnetic field becomes non-uniform. Therefore, play of the rotating shaft is suppressed, cogging is reduced, the rotating torque is stabilized, and smooth rotation is achieved.

FIG. 4 shows a fourth embodiment, similar to the second embodiment, and is a rear view of the end face of the motor case 40 viewed from the same direction as FIG. 2A. Motor case 40 is also motor case 2
As in the case of 0, the thin plate-shaped magnetic body is curled in the circumferential direction, the front edge and the rear edge in the curling direction are joined at the seam 41, and the arc portion 42 and the plane portion 43 are formed at symmetrical positions. It has an oval cross section.

The structure of the motor case 40 is the second and third motor cases.
As in the embodiment, one end face is opened, and a positioning hole 47 cooperating with a positioning pin of a mold is formed in the opposite end face to form a spoke 48 and an opening 46 which are connected to the bearing 45.
And the bearing 45 is opened simultaneously with the magnet 44 in the same insert molding die as in the second and third embodiments.
6 and the end surface 46a which is filled with the same magnet material.

In the fourth embodiment, as in the second and third embodiments, the position of the magnet inner peripheral surface 44a with respect to the bearing surface 45a is automatically determined by the mold.
The outer peripheral surface 49a of the rotor 49 indicated by a two-dot chain line that rotates while the rotating shaft 49b is supported can be dimensioned sufficiently close to the magnet inner peripheral surface 34a within a mold error range, and the air gap G4 is reduced as much as possible. Thus, the motor output can be increased.

In the fourth embodiment, the center of the radius of curvature R5 facing the arc forming the arc portion inner peripheral surface 42a of the motor case 40 and the center of the radius of curvature R6 facing the arc forming the magnet inner peripheral surface 44a are the rotor rotation. Distance S from axis C1
It is located at a position C3 offset outward by two. In this case, the second
Similarly to the third embodiment, since the outer peripheral surface of the magnet 44 is in contact with the inner peripheral surface 42a of the arc portion 42 of the motor case 40 and is filled without a gap, the curvature mismatch between the magnet 44 and the arc portion 42 and the fluctuation of the adhesive layer are caused. And the cogging characteristics are stabilized.

Even if the motor case 40 is slightly deformed, the thickness T4 of the magnet 44 is
(R5−R6) becomes substantially uniform, and a strong and stable starting torque of the motor can be secured. Moreover, the air gap G4 gradually widens toward both ends of the magnet 44, and the overall balance is improved. Accordingly, it is possible to improve the starting characteristics, the rotation accuracy, and the cogging while securing the starting torque.

As described above, all of the motor cases 20, 30, and 40 of the second to fourth embodiments are formed by progressive curling in the circumferential direction, and the front edge and the rear edge are jointed to each other.
It has an oval cross section joined by 1, 31, 41, and has arc portions 22, 32, 42 and plane portions 23, 33, 43 at symmetrical positions, respectively. Molded motor cases 20, 30, 4
0 is open at one end, and the other end is
The spokes 28, 3 are formed by bending a part of the spokes 32, 42 inward.
8, 48, and the rest are openings 26, 36, 46.

As described above, the motor cases 20, 30, 40
Has openings at both ends, so it is possible to fit an upper mold and a lower mold divided by a plane perpendicular to the axis by a mold (not shown) that moves from both sides in the axial direction and surrounds it. No type is required. The dimensional accuracy of the relative position between the bearing surfaces 25a, 35a, 45a and the magnet inner peripheral surfaces 24a, 34a, 44 is uniquely and accurately determined in the same mold, and the machining accuracy of the motor cases 20, 30, and 40 intervenes. Never.

The magnets 24, 34, 44 and the bearing 25,
The molds forming 35, 45 communicate with the openings 26, 36, 46 and cooperate to form a cavity. Spoke 2
8, 38, and 48 have motor cases 20,
Positioning holes 27, 37, 4 for determining the positions of 30, 40
7, and a positioning pin of a mold (not shown) is engaged.

The openings 26, 36, 46 are filled with a magnet material to form end faces 26a, 36a, 46a. The outer circumferential surfaces 29a, 39a, 49a of the rotors 29, 39, 49 and the inner circumferential surfaces 24a, 3 of the magnets shown by two-dot chain lines.
Since the air gaps G2, G3, and G4 with the air gaps 4a and 44a can be sufficiently compressed to the mold error range, the motor output can be increased. After hardening, the magnetic polymer magnets 24, 34, and 44 formed by insert molding are removed from the mold and magnetized from the outside to form permanent magnets.

[0031]

As described above, according to the small motor according to the present invention, since the magnet and the bearing are integrally insert-molded into the motor case at the same time, all the operations and members required for inserting, bonding and fixing the magnet are completely eliminated. In addition to being unnecessary, since no adhesive is used, it is hardly affected by the use environment such as temperature and humidity, and there is no aging. The accuracy of the eccentricity of the inner surface of the magnet with respect to the inner diameter of the bearing press-fit part is determined only by the accuracy of the insert mold, ensuring the accuracy of the magnet molding and ensuring no gap between the joint between the motor case and the magnet. I do.

In particular, a motor case formed by curling molding has an upper mold and a lower mold in which the injection mold is a combined mold, so that the dimensional accuracy can be easily obtained, the mold can be easily manufactured, and it is possible to cope with a demand for an elongated motor having a large aspect ratio. . Furthermore, by setting the radius of curvature of the arc portion of the motor case and the radius of curvature of the inner circumferential surface and / or the outer circumferential surface of the magnet freely, it is possible to improve the starting characteristics and cogging without reducing the motor output characteristics.

[Brief description of the drawings]

FIG. 1 is a first embodiment of a small motor according to the present invention,
(A) is sectional drawing of a side surface, (b) is a front view along the bb line of (a).

FIG. 2 is a second embodiment of the small motor according to the present invention,
(A) is a back view of the motor case, and (b) is b-
(a) is a sectional view of the motor case taken along line b, and (c) is a motor case shown along line cc in (b).
It is the front view seen from the end face of the opposite side.

FIG. 3 is a back view of a motor case in a third embodiment of the small motor according to the present invention.

FIG. 4 is a rear view of a motor case according to a fourth embodiment of the small motor according to the present invention.

FIG. 5 is a side view showing a cross section of a part of a conventional small motor.

[Explanation of symbols]

 10, 20, 30, 40 Motor case 22, 32, 42 Arc part 23, 33, 43 Plane part 14, 24, 34, 44 Magnet 14a, 24a, 34a, 44a Magnet inner peripheral surface 15, 25, 35, 45 Bearing 19a, 29a, 39a, 49a Rotor outer peripheral surface 17, 27, 37, 47 Positioning hole G1, G2, G3, G4 Air gap

Claims (8)

[Claims] 1. A small motor in which a magnet for driving a rotor is mounted on a motor case, wherein the magnet and the motor case are formed by insert molding. 2. The small motor according to claim 1, wherein the magnet and a bearing rotatably supporting the rotor are integrally formed of the same magnet material by the insert molding. 3. The motor case according to claim 1, wherein the motor case has openings on upper and lower surfaces orthogonal to and opposed to a rotation axis.
Or the small motor according to 2. 4. The motor case according to claim 1, wherein the motor case is an oval type in which a flat portion and an arc portion are respectively provided at symmetrical positions, and the magnet is insert-molded in the arc portion. Small motor according to crab. 5. The small motor according to claim 4, wherein the motor case is formed by curling a thin plate-shaped magnetic body in a circumferential direction. 6. A center where an arc forming the inner peripheral surface of the arc portion of the motor case faces and a center where an arc forming the inner peripheral surface of the magnet faces coincide with the rotor rotation axis, and the magnet is made uniform. The small motor according to claim 4, wherein the small motor is formed with a thickness. 7. A center where an arc forming the inner peripheral surface of the motor case arc portion faces the rotor rotation axis, and a center where the arc forming the inner peripheral surface of the magnet faces the rotor rotation axis. The small motor according to claim 4 or 5, wherein the magnet is biased further outward so that the thickness of the magnet is gradually reduced toward both edges of the arc portion. 8. A center where an arc forming the inner peripheral surface of the motor case arc portion faces and a center where an arc forming the inner peripheral surface of the magnet faces both are located at positions deviated outward from the rotor rotation axis. The small motor according to claim 4, wherein the magnets are formed to have a uniform thickness.