JPH0744809B2 - Field device for small electric motors - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field device for a small electric motor, and more particularly to a field device for a small electric motor suitable for an electric motor for starting an internal combustion engine.

[Background of the Invention]

A permanent magnet field type DC machine using a permanent magnet as a field,
For example, it is known from Japanese Examined Patent Publication No. Sho 48-35721 and is widely used in general.

In this field pole, a permanent magnet and an auxiliary pole made of a magnetic material such as mild steel that acts to increase the armature reaction magnetomotive force are juxtaposed with the permanent magnet in the circumferential direction.

In these permanent magnet field type DC machines, the armature reaction magnetic flux flows through the permanent magnets and the auxiliary poles due to the current supplied to the armature coil of the rotor.

Particularly in a permanent magnet arranged on the demagnetization side, this magnetic flux exerts a demagnetization action. Therefore, in order to secure the demagnetization resistance of the permanent magnet, it has been proposed to use a composite permanent magnet, which is a high coercive force member and a high residual magnetic flux density member, as a field magnet, as in JP-A-58-29358. There is.

However, in this case, since the shape of the high coercive force member is rectangular, the area occupied by the high residual magnetic flux density member is small. Therefore, a large magnetic flux cannot be obtained from the permanent magnet,
As a result, only a rotating machine with a small rotating torque could be obtained.

[Object of the Invention]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a field device for a small rotating machine, which has a simple structure and generates a large amount of magnetic flux while securing the proof strength against the demagnetizing field of a permanent magnet.

[Outline of Invention]

The present invention, as a structure of a composite permanent magnet that obtains a large amount of magnetic flux, increases the axial dimension of the most demagnetized end of the high coercive force portion of the permanent magnet, and increases the axial dimension of the high coercive force portion toward the demagnetization side. Is to reduce. By doing so, the demagnetization resistance of the permanent magnet due to the armature reaction magnetic flux is ensured, and the field device for a small electric motor that generates a large amount of magnetic flux can be obtained.

Example of Invention

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an axial sectional view of a permanent magnet field type electric motor with an auxiliary pole of a two-pole machine, and FIG. 2 is a radial sectional view.

In the figure, a rotor 1 includes a shaft 2, a commutator 3,
An armature core 5 around which a winding 4 is wound, and both ends of the shaft 1 are supported by fixed end brackets 7a and 7b via bearings 6a and 6b.

The end brackets 7a, 7b are fixed to a cylindrical yoke 8, and on the inner circumference of the yoke 8, a composite permanent magnet 9 and a magnetic material that acts to increase the armature reaction as shown in FIG. And (for example, mild steel) auxiliary electrode 10 are arranged side by side in an arc shape in close contact with each other.

The composite permanent magnet 9 that is the main part of the present invention is obtained by filling a high residual magnetic flux density member having the same basic composition and a raw material for a high coercive force member into a molding die and sintering the same at a high temperature. It is formed by integrally molding a magnet member having a high residual magnetic flux density portion and a high coercive force portion into an arc shape and magnetizing it.

As shown in the plan view of FIG. 3 and the sectional view of FIG. 4, the composite permanent magnet 9 has a high residual magnetic flux density member at 9a and 9b.
Is a high coercive force member. The shape of the high coercive force member 9b is surrounded by the high residual magnetic flux density member 9a, and the shape thereof is in the axial direction toward the center point P direction of the boundary line OO 'of the field magnetizing and demagnetizing. Has a trapezoidal shape whose width L ₂ gradually decreases.

Width L ₂ axial end 11 of the high coercive force member 9b of the trapezoidal shape is the length of 1.2 L _a with respect to the lamination thickness L _a of the armature core 5 as shown in Figure 3. The width L _{2 in the} axial direction is determined by the distribution of the demagnetizing field of the armature reaction acting on the composite permanent magnet. That is, the current flowing through the armature winding 4 causes the armature reaction magnetic flux to demagnetize the composite permanent magnet 9, and as shown in FIG. 6, the product thickness L of the composite permanent magnet 9 and the armature core 5 is reduced. looking at the air-gap flux density distribution in the axial direction with _a, the magnetic flux density is small over the range of up to approximately 1.2 L _a product thickness of the armature core.

This is an abbreviation for permanent magnets placed on the demagnetization side of the field pole.
This means that the 1.2L _a part is receiving a demagnetizing field. Therefore, in the composite permanent magnet 9 of the present invention, the axial width L ₂ of the end portion 11 of the high coercive force member 9b is set to 1.2L _a so that the permanent magnet is not demagnetized.
It is composed of dimensions.

On the other hand, the width L _{2 in} the axial direction of the high coercive force member 9b of the composite permanent magnet 9
Decreases as the direction from the end 11 to the center line 0-0 'field pole, the width L ₃ of the interface 12, there as 0.4 L _a of lamination thickness of the armature core 5.

The length of the 0.4 L _a is determined by the armature reaction magnetomotive force distribution shown in Figure 5. That is, although the armature reaction magnetomotive force at the end 11 of the composite permanent magnet 9 is as large as H _a1 , the boundary surface 11
In the portion of, the peripheral angle θ ₁ from the magnetic pole center 0-0 ′ is the end
Since the armature reaction magnetomotive force H _a2 is approximately 1/3 of the peripheral angle θ _{2 of} 11, the magnitude is approximately 1/3 of H _a1 .

Therefore, even if the demagnetizing field due to the armature reaction acts on the boundary surface 12 up to 1.2L _{a in} the axial direction, the thickness of the composite permanent magnet 9 does not change, so that the axial width L ₂ is 0.4l _a. Then, the composite permanent magnet 9 will not be demagnetized. In the permanent magnet field-type motor with auxiliary poles that employs the composite permanent magnet 9 of the present invention thus configured, the area of the high residual magnetic flux density member is 8b, 8c while ensuring the demagnetization resistance that acts on the permanent magnet. The amount of magnetic flux generated from the field pole increases because of the increase in the portion of. For this reason, the torque of the electric motor is increased, and an electric motor with high efficiency can be obtained.

In the present invention, the axial width L ₃ of the boundary surface 12 is 0 at the magnetic pole center.
It is determined by the product of the peripheral angle ratio θ ₁ / θ ₂ from −0 ′ and the width L ₂ of the end portion 11 of the high coercive force member 9b, as long as the shape of the high coercive force member 9b is trapezoidal, You may allow a margin in the dimension. Therefore, it is obvious that the length may be less than the dimension width L ₃ obtained by the product and less than the axial dimension width L _{2 of the} end portion.

Further, the axial width dimension of the end portion 11 is not particularly limited to 1.2 L _a, demagnetizing field of an armature reaction at various dc machine is determined respectively by the scope on the permanent magnet. In general, the range of 1.1L _a to 1.3L _a with respect to the laminated thickness L _{a of the} armature core is sufficient.

Further, as shown in FIG. 7, the high holding force member 8b may be trapezoidal from both corners of the end 11.

Further, as shown in FIG. 8, as a field device for a small electric motor of a forward / reverse rotating machine, a high coercive force member 9b is provided on the left and right sides and each has a trapezoidal shape, and the same effect as the present invention can be obtained. .

Further, as shown in FIG. 9, it is obvious that the high coercive force member may have a triangular shape toward the magnetic pole center 0-0 '.

Further, as shown in FIG. 10, the essence does not change even if the high holding force member 9b has a substantially convex shape.

The composite permanent magnet 9 may be formed by separately molding the high coercive force member 9b and the high residual magnetic flux density member, and then joining and sintering the members instead of the above-mentioned integrally molded product.

A high residual magnetic flux density member 9a in the composite permanent magnet 9;
If the boundary surface 12 of the high coercive force member 9b is not a straight line but has a corrugated shape or an uneven shape, it is possible to prevent an abrupt change in the magnetic flux of the high residual magnetic flux density member and the high coercive force portion, and further increase the surface area. The binding force can be improved. The axial width L ₁ of the high residual magnetic flux density member 9b shown in FIG.
The length may exceed 1.2L _a .

According to the above-described embodiment, the area of the high residual magnetic flux density member is increased by making the high coercive force of the field device for a small electric motor into a trapezoidal shape or a triangular shape.

Therefore, when the composite permanent magnet is used as a field pole of a permanent magnet field type electric motor with an auxiliary pole or a permanent magnet field type electric motor, a large amount of magnetic flux can be obtained with the permanent magnet. Therefore, a large motor torque is obtained and the motor characteristics are improved.

Further, since the high holding force member can prevent the demagnetizing action of the permanent magnet due to the armature reaction magnetic flux, the reliability of the device is improved.

〔The invention's effect〕

As described above, according to the present invention, it is possible to provide a field device for a small rotating machine with a simple structure, which secures the proof stress against the demagnetizing field of the permanent magnet, and which generates a large amount of magnetic flux.

[Brief description of drawings]

FIG. 1 is an axial sectional view of a permanent magnet field type electric motor with an auxiliary pole adopting an embodiment of the present invention, FIG. 2 is a radial sectional view of FIG. 1, and FIG. 3 is a composite permanent magnet of the present invention. Plan view of magnet, 4th
Fig. 5 is a sectional view taken along the line aa 'in Fig. 3, Fig. 5 is an electric machine reaction magnetomotive force distribution map, Fig. 6 is a void magnetic flux density distribution map depending on the axial distance under a permanent magnet, and Figs. 7 and 8. , Fig. 9, Fig.
FIG. 10 is a plan view of a composite permanent magnet showing each application example of the present invention. 9 ... composite permanent magnet, 9a ... high residual magnetic flux density member, 9b ... high retention member, 11 ... end of the composite permanent magnet, 12 ... interface high residual magnetic flux density member and a high retention member, L _a ... Electric Laminate thickness of the child core, θ ₁ ... Peripheral angle of high residual magnetic flux density member, θ ₂ ... Peripheral angle of high coercive force member.

Claims (2)

[Claims] 1. A field device for a small electric motor having a field composite permanent magnet (9), wherein the field composite permanent magnet (9) comprises a plurality of arc-shaped yokes (8). ) Is arranged and fixed in an annular shape on the inner peripheral surface of the magnetic head and has a high residual magnetic flux density member (9a) and a high coercive force member (9b), and the high coercive force member (9b) is the center line (0-0 of the field pole). ′) Is formed into a flat trapezoidal shape or a triangular shape in which the axial width (L ₂ ) is gradually reduced toward the center point (P) direction, and the high residual magnetic flux density member (9a) is a high coercive force member (9b). ) Is integrally formed in an arc shape or integrally joined and is magnetized, and is a magnetic field device for a small electric motor. 2. The composite permanent magnet for field according to claim 1, wherein the high coercive force member (9b) has an axial width (L ₂ ) of the circumferential end portion (11). The field device for small electric motors whose width is 1.1 to 1.3 times the width (La) of the armature core.