JP2006230142A - Small motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To constitute a small motor in which eddy current loss can be suppressed and prescribed starting torque and mechanical strength of the motor can be secured without enlarging the outside diameter of the motor. <P>SOLUTION: This is the small motor in which an inner rotor provided with a rotating shaft in the center of a magnet is arranged so as to be rotatable inside a housing of roughly a cylindrical shape that forms a part of a magnetic circuit and a field coil is arranged on the inner wall of the housing so as to face the magnet via a gap. The housing is structured with an inner layer of a magnetic material configured to have an electrically insulated portion at least in the axial direction and an outer casing of the magnetic material that encircles the surrounding of the inner layer to hold the inner layer integrally. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention mainly relates to a small motor used for mechatronics products such as industrial small robots, medical equipment, precision equipment, and the like.

  As an example of a small motor used in the field, there is a small DC brushless motor. As an example of the form, a rotor having a rotating shaft at the center of a magnet is rotatably arranged in a cylinder of a substantially cylindrical housing, and a field coil is arranged on the inner wall of the housing so as to face the magnet with a gap. There is an inner rotor type that is arranged and configured, and in such a configuration, the housing becomes a part of the magnetic circuit.

  As described above, in the inner rotor type motor having the housing as a part of the magnetic circuit, the magnetic flux generated from the magnet passes through the housing, so that the distribution of the magnetic flux in the housing changes during operation, that is, when the inner rotor rotates. .

  Due to the distribution of the magnetic flux in the housing, that is, the change in the magnetic flux density, an eddy current is generated in the housing, resulting in an eddy current loss. This eddy current loss causes an increase in internal loss torque of the motor and heat generation.

  In general, the number of rotations of motors tends to increase with downsizing. Further, in order to improve the generated torque per unit volume of the motor, a magnet having a high energy product is often used as the magnet used for the inner rotor. On the other hand, eddy current loss occurs in proportion to the square of the number of revolutions and the square of the maximum flux linkage density at the portion where eddy current is generated. Therefore, such a small motor tends to increase eddy current loss. is there.

For this reason, as a means for reducing eddy current loss, there has been proposed a method of making it difficult for eddy currents to flow by using a laminated steel plate in which thin ring-shaped steel plates made of a magnetic material are laminated in the housing in the axial direction.

Laminated steel sheets are constructed by laminating thin ring-shaped steel sheets that are electrically insulated from each other, so that it is difficult for current to flow in the laminating direction. Compared with the case where a housing made of a steel ingot is used, eddy current loss can be reduced.

  However, since it is difficult to ensure the mechanical strength as a motor only with laminated steel sheets, the housing needs a case for holding the laminated steel sheets.

  Conventionally, this exterior case is made of a non-magnetic material, and in order to obtain a starting torque equivalent to the case where a housing made of a magnetic material of a single steel in such a configuration is used, a single steel ingot is used. It is necessary to use a laminated steel sheet having a radial thickness equivalent to that of the housing, and a non-magnetic outer case is disposed on the outer periphery. Therefore, the motor outer diameter is equal to the thickness of the non-magnetic outer case. The size increased and hindered the reduction in diameter.

  As a means to solve the problem as in the above example, a groove is provided in a part of each steel plate constituting the laminated steel plate, the groove portions of each steel plate are aligned and laminated, and the continuous groove portions are filled with resin or the like and integrated. Thus, there has been proposed a method of configuring a small motor without using a nonmagnetic exterior case (Patent Document 1).

However, the laminated steel sheet housing integrated by the method disclosed in Patent Document 1 has lower mechanical strength than the case where a single steel ingot or an outer case is used, There are problems such as cogging due to the provision of grooves in the part, reduction of magnetic flux due to reduction of the magnetic path cross-sectional area, increase in the number of processing steps of individual steel plates and reduction in mechanical strength.
Japanese Patent Laid-Open No. 2002-136034

  An object of the present invention is to configure a small motor that can suppress eddy current loss and can ensure a predetermined starting torque and mechanical strength of the motor without increasing the outer diameter of the motor.

  According to a first aspect of the present invention, an inner rotor having a rotation shaft at the center of a magnet is rotatably disposed in a cylinder of a substantially cylindrical housing forming a part of a magnetic circuit, and the magnet is disposed on an inner wall of the housing. A small motor that has a magnetic field coil disposed opposite to each other with a gap between the inner layer and the inner layer formed of a magnetic material and having an electrically insulating portion in the axial direction. And a magnetic outer case for integrally holding the inner layer.

  A second aspect of the present invention is characterized in that the outer case is magnetic free-cutting steel.

  A third aspect of the present invention is characterized in that the inner layer is constituted by a laminated steel plate in which a plurality of substantially ring-shaped magnetic steel plates electrically insulated from each other are laminated in the axial direction.

  A fourth aspect of the present invention is characterized in that the inner layer is formed of a compact of a magnetic powder having an insulating coating on each surface.

  According to a fifth aspect of the present invention, an inner rotor having a rotating shaft at the center of a magnet is rotatably disposed in a cylinder of a substantially cylindrical housing forming a part of a magnetic circuit, and the magnet is disposed on an inner wall of the housing. A small motor in which a field coil is arranged to face each other through a gap, and an outer diameter of the housing is φ12 mm or less.

  In the small motor of the present invention, the inner layer and the outer case that surrounds and integrally holds the inner layer are made of a magnetic material, and the inner layer and the outer case integrally form the housing. The effective magnetic flux required to generate the starting torque equivalent to the case where the housing is formed of a steel ingot can be ensured.

  In addition, since the inner layer portion is configured so that the eddy current does not easily flow during rotation, generation of eddy current can be suppressed as compared with the case where the housing is configured with a single steel ingot.

  Furthermore, it is difficult to ensure the mechanical strength with only the inner layer composed of a magnetic material and having an electrically insulating portion at least in the axial direction, but the outer periphery of the inner layer is surrounded and integrally held by the outer case. Therefore, it is possible to improve the mechanical strength as compared with the case where the housing is constituted by a member other than a single steel ingot such as a laminated steel plate, and sufficient mechanical strength as a motor can be ensured. For this reason, it is not necessary to secure mechanical strength by using another member on the outer periphery of the housing thickness that needs to be made of a magnetic material in order to ensure a predetermined starting torque, which is advantageous for miniaturization of the motor.

  Further, as shown in Patent Document 1, it is not necessary to provide a groove in a part of the laminated steel sheet, and therefore problems such as the occurrence of cogging do not occur.

  Therefore, by using the configuration of the present invention, it is possible to suppress the eddy current loss, and to configure a small motor capable of ensuring a predetermined starting torque and motor mechanical strength without increasing the motor outer diameter. Is possible.

[Embodiment 1]
FIG. 1 is a sectional view of a small DC brushless motor using the configuration of the present invention. This small DC brushless motor is used for mechatronics products, medical equipment, precision equipment, or the like, and has an outer diameter of φ12 mm or less.

  The small DC brushless motor 1 has a substantially cylindrical shape, and is housed inside a housing 2 having a specific structure described later, a cylindrical stator field coil 3 fixed inside the housing 2, and the housing 2. In addition, the inner rotor 4 is arranged coaxially with the housing 2 and arranged inside.

  The inner rotor 4 includes a cylindrical magnet 5 and a rotation shaft 6 that is fixed through and protruding at the center of the magnet 5, and is disposed in the cylinder of the stator field coil 3 with a gap. .

A flange 7a and an end flange 7b in which bearings 8a and 8b are fitted and fixed are respectively fitted and fixed at the end of the housing 2, and the rotary shaft 6 is rotatably supported by the bearings 8a and 8b. Yes.

  Between the cylindrical magnet 5 and the end flange 7b, a cylindrical spacer 9 is mounted on the axis of the rotary shaft 6 so as to keep an interval between them. Further, liners 10a and 10b for smooth sliding during rotation of the inner rotor 4 are mounted between the cylindrical magnet 5 and the bearing 8a and between the cylindrical spacer 9 and the bearing 8b. .

The substrate 11 is fixed to the step portion of the housing, and the lead wire 12 connected to the external driver (not shown) is connected to the tap wire 13 drawn from the stator field coil 3 through the circuit pattern of the substrate 11. A power feeding mechanism is formed.

  The housing 2 is composed of an inner layer 14 made of a laminated steel plate of a plurality of magnetic rings 14a, 14b... Electrically insulated from each other, and an outer case 15 made of a substantially cylindrical magnetic body surrounding the outer periphery of the inner layer 14. ing. Here, it is preferable to use an easily processable material such as magnetic free-cutting steel for the exterior case 15.

  Since the inner layer 14 is composed of a laminated steel plate in which a plurality of magnetic rings 14a, 14b,... Are laminated in the axial direction of the rotating shaft 6 of the inner rotor 4, the laminated steel plates are laminated in the housing when the inner rotor 4 rotates. Eddy currents generated in the direction can be suppressed. As an example, for a small DC brushless motor having an outer diameter of 12 mm, a rotational speed of 14700 rpm, and the same configuration except for the housing, eddy current loss is compared using electromagnetic field analysis by the finite element method. As a result, it was possible to reduce the eddy current loss by about 60% as compared with the case where the housing is formed of a steel ingot.

In the embodiment of the present invention, since the magnet is a magnetic flux generation source, the magnetic flux density in the housing increases near the inner wall of the housing where the distance from the inner rotor is small, that is, on the inner layer side of the housing. Since eddy current loss occurs in proportion to the square of the maximum flux linkage density and the square of the rotational speed of the portion where the eddy current is generated, a large amount of eddy current loss occurs in a portion where the magnetic flux density is large. Therefore, by configuring the inner layer portion having a high magnetic flux density with a structure that can suppress the generation of eddy current, it is possible to significantly reduce the eddy current loss generated in the housing.

Moreover, in the small DC brushless motor 1 configured by including the housing 2 having such a specific structure, since the housing 2 is composed of a magnetic material in both the inner layer and the exterior case, both are effective as a magnetic circuit. It is possible to ensure a starting torque equivalent to the case where the housing is constituted by a single steel ingot having the same thickness.

Furthermore, since the inner layer 14 is integrally held by the outer case 15, only a housing thickness that needs to be made of a magnetic material to generate a predetermined starting torque ensures a sufficient mechanical strength as a motor. It becomes possible.

[Embodiment 2]
FIG. 2 shows a small DC brushless motor 1 ′ according to the second embodiment. In this small DC brushless motor, instead of having an inner layer 14 made of a laminated steel plate in which magnetic rings 14a, 14b,... Electrically insulated from each other are laminated, magnetic powder with an insulating film applied to each surface is used. An inner layer 14 ′ is formed of a powder-molded magnetic body that is a molded body. The rest of the configuration is the same as that of the first embodiment.

Since the powder-molded magnetic body has an insulating film on each surface of the magnetic powder, it has a low electrical conductivity even when it becomes a molded body, but it is a magnetic body. Has the same magnetic properties as other magnetic materials. By using this powder-molded magnetic body as an inner layer, it is possible to reduce eddy current loss in the inner layer portion and to secure an effective magnetic flux necessary for generating a predetermined starting torque. Even if it is DC brushless motor 1 ', the effect similar to Embodiment 1 can be acquired. As an example, for a small DC brushless motor having an outer diameter of 12 mm, a rotational speed of 14700 rpm, and the same configuration except for the housing, eddy current loss is compared using electromagnetic field analysis by the finite element method. As a result, it was possible to reduce the eddy current loss by about 40% as compared with the case where the housing is formed of a steel ingot.

Here, FIG. 3 schematically shows the arrangement of the magnet and the housing of the small DC brushless motor according to the comparative products (a), (b) and the product (c) of the present invention. These use a magnetic material having the same radial thickness for the housing or a part of the housing, so that the magnetic flux that can be secured in the housing is the same, and a structure that can generate an equivalent starting torque. It has become. Also, the alternate long and short dash line in the figure shows a comparison of the housing outer diameter.

  The comparative product (a) is a small DC brushless motor having a housing 19 made of a single steel ingot. Further, the comparative product (b) includes a laminated steel plate 21 in which a housing 20 is laminated with a plurality of magnetic rings electrically insulated from each other, and an exterior case 22 made of a non-magnetic material that holds the laminated steel plate from the outside. It is a small DC brushless motor comprised from these. The product (c) of the present invention is a small DC brushless motor having the configuration shown in FIGS.

  In the comparative product (a), since the effective magnetic flux can be secured by the housing 19 made of a single steel ingot of magnetic material, a predetermined starting torque can be generated, but the housing 19 is a single steel ingot. Since the electric resistance is low and eddy current flows easily, eddy current loss often occurs when the inner rotor rotates.

  In the comparative product (b), since the inner layer side of the housing is composed of the laminated steel plates 21, eddy currents hardly flow in the lamination direction of the laminated steel plates, and generation of eddy currents during rotation of the inner rotor is suppressed. However, in order to obtain a starting torque equivalent to that of the comparative product (a), the laminated steel sheet 21 needs to have a thickness equivalent to that of the housing 19 of the comparative product (a). The outer case 22 is disposed, and the outer diameter is increased by the thickness of the outer case 22.

  In contrast to these comparative products (a) and (b), in the product (c) of the present invention, the housing 16 is composed of a laminated steel plate 17 and an outer case 18 made of a magnetic material that holds the laminated steel plate 17. The generation of eddy current can be suppressed, and the same starting torque can be obtained with the same outer diameter as that of the small DC brushless motor of the comparative product (a).

  As described above, in the configuration of the present invention, the eddy current loss is suppressed, and the sufficient mechanical strength as a motor is ensured without increasing the outer diameter, and the internal loss torque and heat generation are small. A highly efficient small motor can be realized.

It is sectional drawing of the small DC brushless motor which concerns on Embodiment 1 of this invention. It is sectional drawing of the small DC brushless motor which concerns on Embodiment 2 of this invention. It is a schematic diagram which shows the structure of comparative product (a), (b) and this invention product.

Explanation of symbols

2, 16, 19, 20 Housing 3 Stator field coil 4 Inner rotor 5 Magnet 6 Rotating shaft 14a, 14b ... Magnetic body ring 14, 14 'Inner layer 15, 18, 22 Exterior case

Claims (5)

An inner rotor having a rotation shaft at the center of the magnet is rotatably arranged in a cylinder of a substantially cylindrical housing that forms a part of the magnetic circuit, and the inner wall of the housing is opposed to the magnet via a gap. A small motor in which a field coil is arranged,
The housing is composed of an inner layer made of a magnetic material and having a structure having an electrically insulating portion at least in the axial direction, and an outer case made of a magnetic material that surrounds the inner layer and integrally holds the inner layer. A small motor.   The small motor according to claim 1, wherein the outer case is magnetic free-cutting steel.   The small size according to claim 1 or 2, wherein the inner layer is constituted by a laminated steel plate in which a plurality of substantially ring-shaped magnetic steel plates electrically insulated from each other are laminated in the axial direction. motor.   3. The small motor according to claim 1, wherein the inner layer is formed of a compact of magnetic powder having an insulating coating applied to each surface. An inner rotor having a rotation shaft at the center of the magnet is rotatably arranged in a cylinder of a substantially cylindrical housing that forms a part of the magnetic circuit, and the inner wall of the housing is opposed to the magnet via a gap. A small motor in which a field coil is arranged,
The small motor according to any one of claims 1 to 4, wherein an outer diameter of the housing is 12 mm or less.

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