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Method of manufacturing a stator core

Inactive Publication Date: 2005-09-22
KOSHIISHI HIROMICHI +3
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

[0022] It is an object of the present invention to ascertain the relationship of material properties and annealing conditions to the magnetizing feature of motor stator cores annealed when magnetic annealing is performed on the stator cores which are fabricated out of conventional Si-rich non-oriented electrical steel sheets as well as Al-rich non-oriented electrical steel sheets having more favorable magnetizing feature or, in particular, the stator cores for use in electric vehicle motors to be driven in lower magnetic fields, and to provide a motor stator core for achieving improved magnetizing feature and reduced iron loss in lower magnetic fields and a method of manufacturing the same.
[0025] In annealing the stator core fabricated out of the non-oriented electrical steel sheets, the magnetic field is applied to the heated stator core at least in the temperature range from the temperature immediately above the Curie point to 300° C. in the process of cooling the stator core. A stator core of reduced iron loss can thus be manufactured as one for use in a high-speed high-efficiency motor typified by an electric vehicle motor to be driven in lower magnetic fields. In particular, if the direction of the magnetic field applied to the stator core in the cooling process is rendered along the direction of excitation of the stator when used to drive a motor, it follows that the directions of magnetization of the domains in the crystals of the stator core approach the direction of excitation of the stator for motor driving. Consequently, the domains of the stator core are easily oriented in the direction of excitation when the stator is excited. This increases the magnetic induction and decreases the hysteresis loss, allowing a reduction in the total iron loss of the stator. Since the directions of magnetization of the domains in the crystals of the stator core approach the direction of excitation of the stator for motor driving, the stator core is prevented from dropping in magnetic induction when under high-frequency exciting currents of 400 to 600 Hz which are used in electric vehicle motors. Besides, the saturation induction is increased. It is therefore possible to achieve a further power improvement or miniaturization of the motor that uses this stator.
[0026] Moreover, since the stator core is given a grain size of 100 μm or greater at the time of application of the magnetic field, the domains in the crystals annealed in the magnetic field become easier to orient in the same direction of magnetization with a further improvement to the effect of improving the magnetizing feature.

Problems solved by technology

Even with Fe—Si alloys, however, it has been concluded in the 1960s that “heat treatment in a magnetic field has been developed for the purpose of improving Fe—Si alloys' permeability and produced excellent outcomes in laboratories, but of little practical value since it requires a lot of work and cost.” No practical use has thus been attempted so far.
The inventors have also filed a patent application for a method and apparatus for annealing a motor stator core in a magnetic field as Japanese Patent Application No. 2002-156136, whereas this prior application has not provided sufficient resolution in this regard.

Method used

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  • Method of manufacturing a stator core
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  • Method of manufacturing a stator core

Examples

Experimental program
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Effect test

embodiment 1

[0045]FIGS. 2A to 3B are schematic diagrams showing the steps for annealing a stator core according to the embodiment of the present invention. The shown steps are of processing prior to the start of annealing.

[0046]FIG. 2A shows a seat 1, an axial rod 2, and a pipe member 3 for stacking stator cores (hereinafter, referred to as cores) C to be annealed. The pipe member 3 is a heat-resistant silica tube. FIG. 2B shows five cores (C1 to C5). In the present embodiment, each of the cores C is a lamination of non-oriented electrical steel sheet layers as material which have been punched in a ring shape. Each core has an outer diameter of 300 mm, an inner diameter of 200 mm, and a thickness of 200 mm. The height of the five cores stacked is 1000 mm.

[0047]FIG. 2C shows the five cores C stacked. In the diagram, the reference numeral 4 represents a core mount, and 5 a heat insulator of alumina wool which is wound around the pipe member 3. The five cores C are stacked on the core mount 4 wh...

experimental example 1

Experimental Condition

[0058] Used material: non-oriented electrical steel sheets (sample symbol: HTH1500) 0.20 mm in thickness, no skin passed rolling, 60 μm in grain size [0059] Sample dimensions: 80 mm in outer diameter, 60 mm in inner diameter [0060] Heating temperature: 850° C., 750° C. [0061] Field application: in the process of cooling from 750° C. to 300° C. [0062] Field intensity: 0 (nonmagnetic annealing), 800, 6000 (A / m)

Experimental Results

[0063] Table 1 shows the experimental results.

TABLE 1AnnealingField intensityB0.5W7 / 50Grain sizecondition(A / m)(T)(W / kg)(μm)Heating60000.7260.46970temperature8000.6290.49770850° C.00.5870.50970Heating60000.5530.51360temperature8000.5280.52860750° C.00.4340.55460Non-annealed—0.3420.63360steel sheets

NOTE:

B0.5 and W7 / 50 were measured in accordance with ASTM A596-69 (revised in 1979).

[0064] As can be seen from Table 1, the application of magnetic fields of 800 A / m or above in the process of cooling from immediately above the Curie poin...

experimental example 2

Experimental Condition

[0065] Used material: non-oriented electrical steel sheets (sample symbol: 35H230) 0.35 mm in thickness, no skin passed rolling, 100 μm in grain size [0066] Sample dimensions: 80 mm in outer diameter, 60 mm in inner diameter [0067] Heating temperature: 750° C. [0068] Field application: in the process of cooling from 750° C. to 300° C. [0069] Field intensity: 0 (nonmagnetic annealing), 6000, 12000 (A / m)

Experimental Results

[0070] Table 2 shows the experimental results.

TABLE 2AnnealingField intensityB0.5W7 / 50Grain sizecondition(A / m)(T)(W / kg)(μm)Heating120000.7490.522100temperature60000.6830.531100750° C.00.4600.606100Nonannealed—0.3430.676100steel sheets

NOTE:

B0.5 and W7 / 50 were measured in accordance with ASTM A596-69 (revised in 1979).

[0071] As can be seen from Table 2, the use of the material having a greater grain size enhanced the effect of improving the magnetizing feature. The application of the 6000-A / m magnetic field and that of the 12000-A / m magnet...

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Abstract

A motor stator core for achieving improved magnetizing feature in lower magnetic fields and reduced iron loss, and improving motor power. The stator core fabriated out of non-oriented electrical steel sheets is annealed by applying a magnetic field to the heated stator core at least in the temperature range from a temperature immediately above a Curie point thereof to 300° C. in the process of cooling the stator core. The magnetic field has the same direction as the direction of exitation of a stator in the motor when used to drive a motor. This increases the magnetic induction in lower magnetic fields in particular and reduces the hysteresis loss, with a reduction in the total iron loss of the stator. A motor using this stator core increases in saturation induction under exciting currents of higher frequncies, allowing enhanced motor power.

Description

[0001] This application is a divisional of U.S. application Ser. No. 10 / 688,929, filed Oct. 21, 2003.BACKGROUND OF THE INVENTION [0002] This application claims the benefit of Japanese Patent Application No. 2003-005840, filed on Jan. 14, 2003; Japanese Patent Application No. 2003-106674, filed on Apr. 10, 2003; and Japanese Patent Application No. 2003-309297, filed on Sep. 1, 2003. [0003] 1. Field of the Invention [0004] The present invention relates to a motor stator core made of non-oriented electrical steel sheets. In particular, the invention relates to a motor stator core of improved magnetizing feature in lower magnetic fields and a method of manufacturing the same. [0005] 2. Description of the Related Art [0006] Recently, in view of environmental and resources problems, energy savings and improved efficiency have been increasingly demanded of electric equipment. The biggest request for motors is also an efficiency improvement, which in turn requires reductions of iron loss, c...

Claims

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Application Information

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IPC IPC(8): C21D9/46H01F41/02H02K1/00H02K1/02H02K15/02
CPCH01F41/0233H02K1/02Y10T29/49009Y10T29/4902Y10T29/49078H02K15/02H02K1/12
Inventor KOSHIISHI, HIROMICHIOGATA, TOMIYAEGUCHI, SHIGEKIHASEGAWA, HIDEO
Owner KOSHIISHI HIROMICHI