JP2005228830A - Permanent magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide, in a permanent magnet consisting of a plurality of permanent magnet element pieces integrated via an insulating film, a means with little reduction in magnet characteristics due to the insulating film for suppressing failures in heat generation, due to leakage current. <P>SOLUTION: The permanent magnet consists of the plurality of permanent magnet element pieces, integrated via the insulation film for electrically insulating the pieces from each other. In the permanent magnet, the coating resistance H(=d×ρ<SB>r</SB>÷ρ<SB>m</SB>), defined as a value that the product of the thickness d (m) of the insulation film and volume resistivity ρ<SB>r</SB>(Ωm) of the insulation film, is divided by the volume resistivity ρ<SB>m</SB>(Ωm) of the permanent magnet element piece, and the thickness t (mm) of the magnet element piece, satisfy the expression of H≥23,000×t<SP>-1</SP>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a permanent magnet used for rotating equipment, electronic components, electronic equipment, motors, and the like.

  Permanent magnet rotating machines have mainly used ferrite permanent magnets with high electrical resistance. However, with the recent increase in performance of rotating machines, the use frequency of higher performance rare earth permanent magnets has increased. Yes.

  However, since the rare earth permanent magnet is a metal magnet, its electric resistance is low. For this reason, when incorporated in a rotating device or the like, there arises a problem that eddy current loss increases and motor efficiency decreases. In addition, there is a problem that the magnet performance decreases due to the temperature rise.

  In view of the above points, in order to reduce the eddy current loss of rare earth magnet materials, some attempts have been made to increase the electric resistance by configuring the permanent magnet to be composed of a plurality of magnet segments and insulating each magnet segment. Proposed. Patent Document 1 discloses a permanent magnet in which thin plates of a plurality of permanent magnets insulated from each other are stacked. Patent Document 2 and Patent Document 3 disclose a permanent magnet in which a plurality of magnet pieces are arranged in parallel with a magnetic field so as to be insulated from each other.

However, in the case of producing a permanent magnet in which a plurality of magnet pieces are bonded via an insulating material, if the insulating material is too thick, the magnet component decreases, and the magnetic force of the magnet decreases. On the other hand, if the insulating material is too thin, insulation may be incomplete and leakage current may occur. Since heat generation is proportional to (current) ² × (volume resistivity), even a slight leakage current may cause abnormal heat generation of the insulating material. Such heat generation defects due to insulation failure are likely to occur during mass production of magnets, and need to be improved from the viewpoint of quality stability.
Japanese Patent Laid-Open No. 4-79741 JP-A-6-70520 JP 2001-25189 A

  Therefore, an object of the present invention is a means for suppressing a heat generation failure due to a leakage current in a permanent magnet in which a plurality of permanent magnet pieces are integrated via an insulating film, with little reduction in magnet characteristics due to the insulating film Is to provide.

The present invention is a permanent magnet in which a plurality of permanent magnet pieces are integrated through an insulating film for electrically insulating the permanent magnet pieces from each other, and the film thickness d ( m) and the volume resistivity ρ _r (Ωm) of the insulating film divided by the volume resistivity ρ _m (Ωm) of the permanent magnet element, the covering resistance H (= d × ρ _r ÷ ρ _m ) and the plate thickness t (mm) of the permanent magnet element satisfy H ≧ 23000 × t ⁻¹ .

  In the permanent magnet of the present invention, there is little deterioration in magnet characteristics due to the insulating film, high magnet characteristics are maintained, and generation of heat generation failure due to leakage current is effectively suppressed.

  The law of electromagnetism shows that the eddy current induced in a magnet placed in a periodic magnetic field increases as the cross-sectional area perpendicular to the magnetic field direction of the magnet increases. Therefore, when the magnet is divided by the insulating film to suppress the eddy current, it is expected that the insulating film that insulates the magnet has different insulating properties to be satisfied depending on the cross-sectional area of the magnet. That is, it is considered that an insulating film having suitable insulating properties should be formed according to the cross-sectional area of the magnet.

In order to investigate the relationship between the cross-sectional area of the magnet and the insulating property of the insulating film, the inventors have prepared magnets with various plate thicknesses insulated with an insulating film made of a polymer compound, and have a constant periodic magnetic field. The calorific value in the inside was compared. As a result, the inventors have found the relationship between the cross-sectional area of the magnet and the insulating property of the insulating film with respect to the suppression of eddy current, and have completed the present invention. Specifically, the thickness of the insulating film that insulates adjacent permanent magnet pieces is d (m), the volume resistivity of the insulating film is ρ _r (Ωm), and the volume resistivity of the permanent magnet pieces is ρ _m ( Ωm), the covering resistance H represented by H = d × ρ _r ÷ ρ _m and the plate thickness t (mm) of the permanent magnet element satisfy H ≧ 23000 × t ⁻¹ . Design permanent magnets. Preferably, the permanent magnet is designed to satisfy H ≧ 61500 × t ^−1.1 . By designing the permanent magnet so as to satisfy the above relationship, the eddy current loss in the permanent magnet made of the permanent magnet piece insulated by the insulating film is effectively suppressed.

  The film thickness d (m) of the insulating film and the plate thickness t (mm) of the permanent magnet element are preferably d ≦ 0.10 t, more preferably d ≦ 0.05 t, and further preferably d ≦ 0. .02t is satisfied. By designing the permanent magnet so that the film thickness d of the insulating film and the plate thickness t of the permanent magnet element satisfy such a relationship, it is possible to minimize a decrease in magnet characteristics.

  Hereinafter, the permanent magnet of the present invention will be described in detail.

  The permanent magnet of the present invention comprises a plurality of permanent magnet pieces. The permanent magnet segment is a plurality of magnets constituting the permanent magnet, and the plurality of permanent magnet segments are integrated through an insulating film for electrically insulating the permanent magnet segments from each other. Is configured.

  The shape of the permanent magnet and the permanent magnet piece is not particularly limited. The shape of the permanent magnet may be determined according to the part to which the permanent magnet is applied. For example, when applied to a motor of an automobile, the size and shape of the permanent magnet may be determined in accordance with the size and shape of the motor.

  The kind of the permanent magnet is not particularly limited and can be applied to various metal magnets. Preferably, the permanent magnet piece of the present invention is a rare earth magnet. Since the magnetic force of the magnet is somewhat reduced by the insulating film, the use of a magnet having a strong magnetic force such as a rare earth magnet can suppress the deterioration of the magnet characteristics due to the insulating film to the minimum. However, a magnet other than the rare earth magnet may be used as long as there is a special reason such as a case where the magnetic force is not required so much, and such an embodiment is also included in the technical scope of the present invention. sell.

  Examples of rare earth magnets include Nd—Fe—B magnets and Sm—Co magnets. The main elements constituting the rare earth magnet may be replaced with other elements as necessary. For example, a part of Nd may be substituted with Pr, Dy, Tb, etc., and a part of Fe may be substituted with Co.

The shape of the permanent magnet is not particularly limited as described above, but in the present invention, the plate thickness t (mm) of the permanent magnet piece and the volume resistivity ρ _m (Ωm) of the permanent magnet piece are defined as described above. Designed to meet.

  The plate thickness t (mm) of the permanent magnet element means the length of the short side of the permanent magnet element in the magnet cross section in the direction perpendicular to the periodic magnetic field applied to the permanent magnet from the outside. As in the permanent magnet disclosed in FIG. 2 of Patent Document 2, when the short side of the permanent magnet piece is different between the central axis side and the external side of the permanent magnet, the average value is meant. Moreover, when the cross section of a permanent magnet piece is changing in the direction of a periodic magnetic field, the average value is meant. The plate thickness t of the permanent magnet element may be measured by a normal measuring means. With respect to the assembled permanent magnet, the plate thickness t may be measured, or the assembled magnet may be disassembled and the plate thickness t may be measured.

  If the plate thickness t is too thick, the effect produced by cutting may be poor, and if it is too thin, the cutting cost may increase. For this reason, the plate thickness t is preferably 0.5 mm to 50 mm, more preferably 1.0 mm to 20 mm.

The volume resistivity ρ _m (Ωm) of the permanent magnet segment is an index indicating the difficulty of current flow in the permanent magnet segment, and is defined as an electric resistance value of a material having a unit cross-sectional area. The higher the volume resistivity, the higher the insulation. The volume resistivity can be measured according to a known measurement method such as JIS K6911. Although not particularly limited, the volume resistivity ρ _m of the permanent magnet element is usually about 0.5 × 10 ^{−4 to} 2.5 × 10 ⁻⁴ μΩm.

  As the insulating film disposed between the permanent magnet pieces, ceramics having a low electrical conductivity, polymer resin such as epoxy resin or vinyl resin, inorganic film, or the like can be used. However, the present invention is not limited to these, and other materials may be used as long as they can insulate the permanent magnet pieces and satisfy the conditions defined in the present invention.

Although the shape of the insulating film is not particularly limited, an insulating film exists at least between adjacent permanent magnet pieces, and the permanent magnet pieces are insulated by the insulating film. In the present invention, the film thickness d (m) of the insulating film and the volume resistivity ρ _r (Ωm) of the insulating film are designed to satisfy the above-mentioned definition.

  The film thickness d (m) of the insulating film means the thickness of the insulating film existing between adjacent permanent magnet pieces. The thickness of the insulating film can be controlled by adjusting the mass of the insulating material used. If possible, an insulating film having a predetermined thickness may be attached to the surface of the permanent magnet piece. The film thickness d of the insulating film can be measured by observing the insulating film with a microscope such as an electron microscope. The thickness d of the insulating film is preferably uniform in order to exhibit stable insulating performance, but may be slightly changed as long as the insulating performance is not affected. When the film thickness d is not uniform, an average value is adopted as the film thickness d of the insulating film. The average value may be obtained, for example, by measuring each of the nine in-plane planes and calculating the average thereof, or the average film thickness may be calculated from the mass of the insulating film to be used. Although not particularly limited, the thickness d of the insulating film is usually about 0.01 to 0.1 mm.

The volume resistivity ρ _r (Ωm) of the insulating film is an index indicating the difficulty of current flow in the insulating film, like the volume resistivity ρ _m (Ωm) of the permanent magnet piece. Defined as electrical resistance value. The volume resistivity can be measured according to a known measurement method such as JIS K6911. Although not particularly limited, the volume resistivity ρ _m of the insulating film is usually about 10 ⁵ to 10 ¹⁵ Ωm.

  The use of the permanent magnet of the present invention is not particularly limited, but can be applied to a motor. In the permanent magnet of the present invention, generation of eddy current is suppressed, and in addition, it has high magnet performance. For this reason, if the motor manufactured using the permanent magnet of the present invention is used, the continuous output of the motor can be easily increased, and it can be said that it is suitable as a medium to large output motor. Moreover, since the motor using the permanent magnet of the present invention has excellent magnet characteristics, the product can be reduced in size and weight. For example, when applied to automotive parts, fuel efficiency can be improved as the vehicle body becomes lighter. Furthermore, it is particularly effective as a drive motor for electric vehicles and hybrid electric vehicles. Drive motors can be installed in places where it was difficult to secure space so far, which will contribute to the generalization of electric vehicles and hybrid vehicles.

  Hereinafter, a correlation between each parameter and battery characteristics is shown for a permanent magnet formed by bonding a Nd—Fe—B rare earth sintered magnet as a permanent magnet piece with a polymer resin film as an insulating film. .

<Experimental example 1>
A 20 × 20 × 5 mm Nd—Fe—B rare earth sintered magnet (Br: 13.5 kG, iHc: 16.5 kOe, volume resistivity ρ _m : 0.000002 Ωm) in a direction perpendicular to a 20 × 20 mm surface It was divided into two. By bonding the divided permanent magnet pieces using an epoxy resin (volume resistivity ρ _m : 1.0 × 10 ¹³ Ωm) acting as an insulating film, two permanent magnet elements of 10 × 20 × 5 mm A permanent magnet in which the pieces were integrated through an insulating film was obtained. The thickness of the insulating film was controlled to 0.01 μm by adjusting the mass of the epoxy resin used. The thickness of the insulating film was measured by observing the structure with an electron microscope.

  The produced permanent magnet was allowed to stand for 10 minutes in a periodic magnetic field having a magnetic field strength of 0.1 T and a frequency of 1000 Hz, and the temperature change and heat generation at that time were observed. The calorific value was evaluated as a relative calorific value with respect to this calorific value, assuming that the calorific value of a permanent magnet of the same size with no insulating film disposed. The magnetic field was applied in a direction perpendicular to the 20 × 20 mm surface. Therefore, the plate thickness t of the permanent magnet element is 10 mm. The conditions and evaluation results are shown in Table 1.

  Further, the residual magnetization Br and the coercive force iHc of the obtained permanent magnet were measured using a BH tracer. Table 2 shows values obtained by dividing the thickness d of the insulating film by the thickness t of the permanent magnet piece. Further, the residual magnetization Br indicates the amount of Br remaining in percent based on the Br of the non-divided Nd—Fe—B rare earth sintered magnet.

<Experimental Examples 2-38>
The number of divisions (2, 4, 5, or 10 divisions) of the Nd—Fe—B rare earth sintered magnet, the type of polymer resin (polyvinyl resin or epoxy resin) used as the insulation film, and the thickness of the insulation film Various permanent magnets were obtained by the same procedure as in Experimental Example 1, with changes as shown in Tables 1 and 2.

FIG. 1 is a graph in which data of a part of a produced permanent magnet is plotted, with the horizontal axis representing the coating resistance H represented by H = d × ρ _r ÷ ρ _m and the vertical axis representing the relative heat value. As shown in FIG. 1, when the covering resistance H is increased, the heat generation amount converges to a value determined by the magnet thickness t. That is, in order to suppress the heat generation due to the generation of eddy current, it is sufficient that the covering resistance H is equal to or greater than a predetermined value determined by the plate thickness t. For example, when the plate thickness t = 2 mm, it is sufficient that the covering resistance H is about 10 ⁴ (m), and the permanent magnet may be designed so that the covering resistance H is equal to or greater than this value.

FIG. 2 is a graph in which data of a part of the produced permanent magnet is plotted with the thickness t on the horizontal axis and the covering resistance H on the vertical axis. In FIG. 2, “◎” indicates a sample where “relative calorific value of sample <lower limit value of relative calorific value at the plate thickness + 0.01”, and ◯ indicates “lower limit value of relative calorific value at the plate thickness + 0.01 < Samples where the relative calorific value of the sample <the lower limit value of the relative calorific value at the plate thickness + 0.02 ”are shown, and x is“ the lower limit value of the relative calorific value at the plate thickness + 0.02 <the relative calorific value of the sample ”. A sample is shown. As shown in FIG. 2, in order to converge the relative calorific value, it is sufficient to satisfy “H ≧ 23000 × t ⁻¹ ”, and preferably “H ≧ 61500 × t ^−1.1 ”. I know it ’s good.

  Further, from the viewpoint of improving the magnet characteristics, as shown in Table 2, it is preferable that the film thickness d and the plate thickness t satisfy d ≦ 0.10t, that is, d / t is 0.1 or less. . As shown in Table 2, the permanent magnet satisfying d ≦ 0.10t maintains a high magnetic characteristic with a residual magnetization of 90% or more. In addition, the permanent magnet satisfying d ≦ 0.05t has a residual magnetization of 95% or more, and the permanent magnet satisfying d ≦ 0.02t has a residual magnetization of 98% or more.

<Mass production suitability evaluation>
In order to evaluate the suitability for mass production of the permanent magnet of the present invention, a 20 × 20 × 5 mm Nd—Fe—B rare earth permanent magnet (Br: 13.5 kG, iHc: 16.5 kOe) It was divided into 5 in the direction perpendicular to The divided permanent magnet pieces were bonded together via an insulating film so as to meet the definition (H ≧ 23000 × t ⁻¹ ) defined in the present invention, and 100 permanent magnets were produced. Further, in accordance with a conventionally used method, a permanent magnet in which generation of eddy currents was prevented by 100 insulating films was produced.

  About the manufactured permanent magnet, it was left to stand in a periodic magnetic field, and the emitted-heat amount in that case was observed. FIG. 3 is a graph showing the distribution of relative heat generation when the permanent magnet of the present invention is manufactured, and the distribution of relative heat generation when the conventional permanent magnet is manufactured. A permanent magnet having a relative calorific value of 0.02 or less was accepted, and a permanent magnet that exhibited a relative calorific value exceeding 0.02 was determined to be defective. As is apparent from FIG. 3, the permanent magnet of the present invention has a low incidence of defective products and is suitable for mass production.

It is the graph which plotted some data of the produced permanent magnet, with the horizontal axis representing the coating resistance H represented by H = d × ρ _r ÷ ρ _m and the vertical axis representing the relative calorific value. It is the graph which plotted some data of the produced permanent magnet, with the plate thickness t on the horizontal axis and the covering resistance H on the vertical axis. It is a graph which shows the distribution of the relative calorific value when the permanent magnet of the present invention is manufactured, and the distribution of the relative calorific value when the conventional permanent magnet is manufactured.

Claims (4)

A plurality of permanent magnet pieces are permanent magnets integrated through an insulating film for electrically insulating the permanent magnet pieces from each other,
It is defined as a value obtained by dividing the product of the film thickness d (m) of the insulating film and the volume resistivity ρ _r (Ωm) of the insulating film by the volume resistivity ρ _m (Ωm) of the permanent magnet element. A permanent magnet, wherein the covering resistance H (= d × ρ _r ÷ ρ _m ) and the plate thickness t (mm) of the permanent magnet element satisfy H ≧ 23000 × t ⁻¹ .   The permanent magnet according to claim 1, wherein a thickness d of the insulating film and a plate thickness t of the permanent magnet element satisfy d ≦ 0.10 t.   The permanent magnet according to claim 1, wherein the permanent magnet element is a rare earth magnet.   The motor using the permanent magnet of any one of Claims 1-3.

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