JP2005311196A - Dust core for vehicle-mounted motor, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dust core for a vehicle-mounted motor which has high density and low iron loss, and to provide a manufacturing method thereof. <P>SOLUTION: The dust core for the vehicle-mounted motor is a compressed compact of soft magnetic powder, substantially having a composition of 1.0 to 7.0 mass% Si and Fe for the rest and also having its surface coated with an insulating film, the relative density of ≥95% and the electric resistivity of ≥200×10<SP>-8</SP>Ωm. This is manufactured by compressing and compacting the soft magnetic powder coated with the insulating film under the conditions of pressure of ≥200 MPa and temperature of 400 to 900°C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a dust core for a motor mounted on a vehicle and a manufacturing method thereof. More specifically, the present invention relates to a high-density and low iron loss, and enables high-efficiency, high output density / high-speed by enabling three-dimensional motor magnetic circuit An object of the present invention is to provide a dust core suitable for being incorporated in a motor for driving an automobile, and a method for manufacturing the same, which can realize a motor having a torque density.

A magnetic core constituting a general motor is formed by stacking a plurality of thin electromagnetic steel sheets into a bulk body. This magnetic core exhibits excellent soft magnetic properties in the in-plane direction perpendicular to the laminating direction of the electromagnetic steel sheets, but has a problem that the magnetic properties are extremely lowered in the laminating direction.
On the other hand, since the dust core exhibits substantially three-dimensional isotropic magnetic characteristics, the magnetic circuit of the motor can be configured three-dimensionally using this. Therefore, by using the dust core, it is possible to realize a motor having a structure different from that of a conventional motor constituted by a two-dimensional magnetic circuit using an electromagnetic steel plate.

By the way, this powder magnetic core is normally manufactured as follows.
First, a soft magnetic powder having a predetermined particle size and particle size distribution is manufactured by applying a mechanical grinding method or an atomizing method to a soft magnetic alloy having a predetermined composition.
Next, the surface of the soft magnetic powder is separated from the insulating binder by mixing a predetermined amount of an insulating binder such as water glass which is an insulating material and a binder component having a binding ability at the same time. Cover with an insulating film.

Next, after filling the above-mentioned mixture into a mold together with a lubricant such as zinc stearate, compression molding is usually performed by applying a predetermined pressure at room temperature.
Finally, the obtained compression-molded body is subjected to a heat treatment to remove distortion accumulated during the compression molding.
The dust core produced as described above has a structure in which the particles of the soft magnetic powder coated with the insulating film are bound to each other through the insulating film.

At present, the mainstream of powder magnetic cores is that using Fe-based alloy powder as soft magnetic powder. However, when this is applied to motor applications, there are the following problems.
First, motor driving is generally performed in a low frequency region (approximately 10 kHz or less). In this case, the iron core of the dust core is larger than that of the magnetic steel sheet. Therefore, it is difficult to apply to a motor that requires high efficiency.

Therefore, when considering application of the dust core to a highly efficient motor, it is necessary to further reduce the iron loss of the dust core.
In addition, since the packing density of the soft magnetic powder is not so high in the conventional dust core, for example, when considering improving the torque of the motor, the magnetic flux density level of the conventional dust core is not always satisfactory. There is a problem that you can not.

Therefore, when considering the application of a dust core to a motor having a high torque density, it is necessary to further increase the magnetic flux density by increasing the packing density of the soft magnetic powder in the dust core to increase the density. .
The present invention is a dust core developed by considering the above-mentioned problems when applying the dust core to a motor application, and has a low iron loss and high density, so that it is highly efficient and large. An object of the present invention is to provide a dust core that can be used for, for example, a vehicle drive motor that operates at an output density / a large torque density, and a method for manufacturing the same.

In the research process for achieving the above object, the present inventors set a target value for densification of the powder magnetic core to be developed to 95% or more in terms of relative density.
This is because if the relative density is 95% or higher, the occupation ratio of the soft magnetic powder in the powder magnetic core is high, and therefore the magnetic flux density is high, and it can be determined that the application to motor use is possible.
In view of the fact that the iron loss is the sum of the hysteresis loss peculiar to the soft magnetic powder to be used and the eddy current loss in the dust core, the Fe-Si based powder described later is used for the former. Addressed by.

The latter was dealt with by defining the insulation state between the powders. Specifically, the target value for reducing the iron loss of the dust core was set to 200 × 10 ⁻⁸ Ω · m or more in terms of electrical resistivity.
If the electric resistivity of the dust core is 200 × 10 ⁻⁸ Ω · m or more, the eddy current loss in the low frequency region of the dust core can be virtually ignored, and it is incorporated into a high-efficiency motor. This is because it is determined that it is possible.

In order to realize the above target value, the present inventors have studied the conditions in the manufacturing process, particularly the conditions at the time of compression molding, and as a result, the target value described above can be realized under the conditions described later. The facts were found and the present invention was developed.
That is, the dust core for a vehicle-mounted motor of the present invention has a composition of Si: 1.0 to 7.0% by mass, the balance being substantially composed of Fe, and the surface is covered with an insulating film. A compression molded body of magnetic powder,
The relative density is 95% or more, and the electrical resistivity is 200 × 10 ⁻⁸ Ω · m or more.

  Further, in the present invention, Si: 1.0 to 7.0% by mass, and the balance of the soft magnetic powder substantially consisting of Fe and an insulating binder are mixed to coat the surface of the soft magnetic powder with an insulating film. Then, the powder obtained is compression-molded under the conditions of a pressure of 200 MPa or more and a temperature of 400 to 900 ° C., preferably a method for producing a dust core for a vehicle-mounted motor, preferably after compression molding, A method of manufacturing a dust core for a vehicle-mounted motor that performs heat treatment at 500 ° C. or higher is provided.

In the dust core of the present invention, Fe-Si soft magnetic powder having an insulating binder insulating film formed on the surface thereof is compression-molded under conditions of a pressure of 200 MPa or more and a temperature of 400 to 900 ° C. The density is as high as 95% or more, and the electrical resistivity is also 200 × 10 ⁻⁸ Ω · m or more, and the insulation is high.
Therefore, the dust core has a high magnetic flux density and low iron loss, and can be incorporated in a vehicle-mounted motor that requires high efficiency.

The dust core of the present invention has a relative density of 95% or higher, an electric resistivity of 200 × 10 ⁻⁸ Ω · m or higher, and high insulation.
The relative density referred to here is a value obtained by multiplying the value obtained by dividing the weight of a certain volume of the dust core by the weight of the same volume of the melted material made of the soft magnetic alloy used for the dust core. Yes, in%.

The electrical resistivity is a value measured by a direct current four-terminal method.
This dust core is manufactured as follows.
First, as a soft magnetic powder to be used, an Fe-Si alloy powder is prepared. The reason for using it is that this Fe—Si-based alloy has a smaller magnetocrystalline anisotropy and magnetostriction than Fe, and a small hysteresis loss in the low frequency region. That is, it is a material that contributes to a reduction in iron loss of the dust core to be produced.

Here, the Fe—Si based alloy powder to be used is limited to those having a Si content of 1.0 to 7.0 mass%.
When an alloy powder having a Si content of less than 1.0% by mass is used, the above-described effects are not exhibited, and conversely, an increase in iron loss starts to occur in the dust core. Further, when an alloy powder having a Si content of more than 7.0% by mass is used, the saturation magnetic flux density of the obtained dust core is abruptly reduced, and the suitability as a magnetic core for motor use is lost.

As the alloy powder, it is preferable to use an alloy powder having an average particle diameter of 5 to 500 μm.
This is because a powder having an average particle size of less than 5 μm has poor moldability at the time of compression molding, which will be described later, so that the productivity of the dust core is reduced. Moreover, when a powder having an average particle size larger than 500 μm is used, the electrical resistivity in the obtained powder magnetic core is lowered, the eddy current loss is increased and the electrical resistivity is lowered, and as a result, low iron loss is realized. I can't do that.

In addition, this Fe-Si type alloy powder can be manufactured by the mechanical grinding | pulverization of a casting ingot or the atomization method of a molten alloy.
Next, the above-described Fe—Si based alloy powder and an insulating binder are mixed, and the surface of the alloy powder is coated to form an insulating film.
This insulating film functions to maintain the insulating state between the alloy powders in the manufactured powder magnetic core, to ensure the electrical resistivity of the powder magnetic core, and to suppress the occurrence of eddy current loss.

The insulating binder to be used is required to have heat resistance to this temperature because compression molding described later is performed at a temperature of 400 to 900 ° C.
For example, water glass, phosphoric acid, phosphoric acid such as phosphate containing phosphoric acid, Al ₂ O ₃ powder, SiO ₂ powder, BN powder, and the like can be used.
In addition, organic materials such as phenol resin, silicone resin, amide resin, and imide resin can also be used. However, in that case, since thermal decomposition is not allowed during compression molding, an organic insulating binder is used when a relatively low temperature range is employed in the above temperature range.

The thickness of the insulating film to be formed is preferably 10 nm to 1 μm.
When this thickness is less than 10 nm, the surface of the alloy powder may not be substantially covered with an insulating film, so that the alloy powder is in direct contact with each other, and the eddy current loss of the manufactured dust core is reduced. The occurrence cannot be suppressed. Further, when the thickness is thicker than 1 μm, the volume ratio of the nonmagnetic component in the powder magnetic core increases, so that the saturation magnetic flux density cannot be ignored.

The adjustment of the thickness of the insulating film can be realized by adjusting the amount of the insulating binder mixed with the alloy powder.
The alloy powder having the insulating film formed on the surface in this manner is then compression-molded to obtain a dust core having a desired shape.
In that case, since the Fe—Si-based alloy has high hardness, there is a problem that even if the powder is press-molded at room temperature, for example, a dense and high-density molded body cannot be obtained.

Therefore, in the present invention, compression molding is performed in which pressurization and heating are simultaneously applied to the alloy powder. For example, a hot press method or a discharge plasma sintering method is applied.
In that case, the pressure is set to 200 MPa or more, and the temperature is set to 400 to 900 ° C.
Here, when the pressure is lower than 200 MPa or the temperature is lower than 400 ° C., a high-density powder magnetic core having a relative density of 95% or more is manufactured even if compression molding is performed under such conditions. I can't.

If compression molding is performed at a high pressure, the obtained compression molded body is densified and its relative density is also increased. However, on the other hand, since the breakdown of the insulating film proceeds, the electrical resistivity of the compression molded body is reduced, causing an increase in eddy current loss. For this reason, the upper limit of the pressure is preferably set to about 1500 MPa.
In addition, if compression molding is performed at a temperature higher than 900 ° C., it is true that the alloy powder is softened and contributes to higher density. Increases current loss.

When the powder magnetic core obtained by compression molding under the above-mentioned conditions is further heat-treated at a temperature of 500 ° C. or higher, the distortion accumulated in the powder magnetic core during compression molding is released and the magnetic properties are further improved. Since it becomes a dust core, it is suitable.
The above-described compression molding may be performed by lightly compressing the powder once at room temperature to form a preform, and then applying the above-described conditions to the preform.

A soft magnetic powder having a composition of Fe-3 mass% Si was produced by a water atomization method. Classification was performed to prepare a powder having an average particle size of 60 μm under 100 mesh.
To 100 parts by mass of the powder, 0.5 part by mass of a silicone resin (insulating binder) was uniformly mixed to form an insulating film covering the powder surface. When the thickness of the insulating film was measured by an Auger analysis method, the average value was 0.1 μm.

The powder was filled into a mold and hot pressed to form a dust core. At this time, the heating temperature and the applied pressure were changed.
About the obtained powder magnetic core, the relative density and the electrical resistivity were measured. The results are shown in FIGS. 1 and 2, respectively.
In FIG. 1, the numbers in the circles represent the relative density (unit%), and in FIG. 2, the numbers in the circles represent the electrical resistivity (unit: × 10 ⁻⁸ Ω · m).

As is apparent from FIG. 1, in order to increase the density to a relative density of 95% or more, it is necessary to perform compression molding under conditions of a pressure of 200 MPa or more and a temperature of 400 to 900 ° C.
Further, as is apparent from FIG. 2, in order to achieve an electric resistivity of 200 × 10 ⁻⁸ Ω · m or higher, it should be compression molded under the conditions of a pressure of 200 MPa or higher and a temperature of 400 to 900 ° C.

The powder used in Example 1 was filled in a mold, and preformed at a pressure of 500 MPa at room temperature using a hydraulic press. The relative density of the obtained preform was 82%.
Next, the preform was packed into a can made of mild steel, Ar gas was sealed therein, and the can was forged and pressed. At this time, the heating temperature and the applied pressure were changed.
After compression molding, the dust core was taken out of the can and its relative density and electrical resistivity were measured. The results are shown in FIGS. 3 and 4, respectively.

Also in this case, as in Example 1, an electric resistivity of 200 × 10 ⁻⁸ Ω · m or more was obtained by compression molding under the conditions of a pressure of 200 MPa or more and a temperature of 400 to 900 ° C.

  The dust core of the present invention has a high density (high magnetic flux density), low iron loss, and isotropic magnetic characteristics. By using this dust core, the motor magnetic circuit can be made three-dimensional. Can be realized. In that case, a motor with high efficiency and large output density / large torque density can be realized, and can be used as a magnetic core for a vehicle-mounted motor.

In Example 1, it is a graph which shows the relative density of the manufactured powder magnetic core when changing heating temperature and applied pressure. In Example 1, it is a graph which shows the electrical resistivity of the manufactured powder magnetic core when changing heating temperature and applied pressure. In Example 2, it is a graph which shows the relative density of the dust core manufactured when changing heating temperature and applied pressure. In Example 2, it is a graph which shows the electrical resistivity of the dust core manufactured when changing heating temperature and applied pressure.

Claims (5)

Si: 1.0 to 7.0% by mass, the balance is a compression molded body of soft magnetic powder having a composition substantially consisting of Fe and having a surface coated with an insulating film,
A dust core for a vehicle-mounted motor, having a relative density of 95% or more and an electric resistivity of 200 × 10 ⁻⁸ Ω · m or more.   The dust core for a vehicle-mounted motor according to claim 1, wherein the soft magnetic powder has an average particle diameter of 5 to 500 μm.   The dust core for a vehicle-mounted motor according to claim 1 or 2, wherein the insulating film has a thickness of 10 nm to 1 µm.   Si: 1.0 to 7.0% by mass, with the balance being substantially Fe, soft magnetic powder and an insulating binder are mixed to coat the surface of the soft magnetic powder with an insulating film. A method for producing a powder magnetic core for a motor mounted on a vehicle, comprising compression molding under conditions of a pressure of 200 MPa or more and a temperature of 400 to 900 ° C.   The method for producing a dust core for a vehicle-mounted motor according to claim 4, wherein the heat treatment is performed at a temperature of 500 ° C or higher after the compression molding.

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