JP2012161139A - Motor core having small deterioration in iron loss under compressive stress and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor core having small deterioration in the iron loss characteristics at high frequencies even under presence of a compressive stress, and to provide a method of manufacturing the same.SOLUTION: An electromagnetic steel sheet applied with an insulation coating, preferably, containing Si:7 mass% or less, Al:3 mass% or less, Mn:5 mass% or less, S:0.01 mass% or less, N:0.005 mass% or less, and O:0.01 mass% or less is punched using a die having multiple micro protrusions formed entirely or partially on the surface of a motor core in contact with the back yoke. A core material where micro recesses having a depth of 10-50 μm and a diameter of 0.05-2 mm are formed entirely or partially in the back yoke on the surface of the punched electromagnetic steel sheet at such intervals as the closest distance becomes 0.2-5 mm is thereby obtained. The core materials are then laminated and a compressive stress of 10 MPa or more is imparted in the circumferential direction thus obtaining a motor core.

Description

  The present invention relates to a motor core used for a compressor motor of a home air conditioner, a drive motor or a generator (hereinafter simply referred to as “motor”) of a hybrid electric vehicle (EV), and a manufacturing method thereof. The present invention relates to a motor core having a small iron loss deterioration (small increase in iron loss) even in the presence of compressive stress and a method for manufacturing the same.

  Compressor motors for home air conditioners are generally operated at variable speeds with a maximum frequency of about 200 to 400 Hz, and are further controlled by PWM (Pulse Width Modulation) type inverter control. Are superimposed and used. Recently, drive motors and generators of hybrid electric vehicles that are rapidly spreading are also driven at a frequency of about several kHz from the viewpoint of achieving high output and miniaturization.

  A material (core material) used for a core such as a stator (stator) or a rotor (rotor) of the motor as described above is required to have low iron loss from the viewpoint of improving energy efficiency. Therefore, high-grade non-oriented electrical steel sheets to which Si and Al are added in a total amount of about 3 to 4 mass% are used for the motor core material in order to reduce iron loss in the high frequency range to be used.

  By the way, in a compressor motor of an air conditioner or a motor of a hybrid electric vehicle, a shrink fitting method or a press-fitting method is adopted as a method for fixing the stator to the housing (motor case). , A compressive stress of about several tens to 100 MPa is generated. Moreover, since the resin motor is generally applied to the drive motor of the hybrid electric vehicle, a compression stress is also applied to the motor core. In the presence of such compressive stress, it is known that the magnetic properties of the electrical steel sheet constituting the core are greatly deteriorated (iron loss increases).

Therefore, it is desired to develop an electromagnetic steel sheet with small iron loss degradation due to compressive stress. As such a material, for example, Si: 2.6 to 4 mass% is added to Patent Document 1 and the specific resistance is 50. A non-oriented electrical steel sheet having a grain size of ˜75 × 10 ⁻⁸ Ωm and an average crystal grain size of more than 60 μm and 165 μm or less is disclosed.

Japanese Patent No. 4023183

  However, the non-oriented electrical steel sheet of Patent Document 1 has only a specific resistance and a crystal grain size equivalent to those of a currently available high-grade electrical steel sheet. Therefore, even if a motor core is manufactured using this material, the degree of iron loss deterioration due to compressive stress is not significantly different from that of conventional materials. Therefore, development of a technique that can further reduce the stress dependence of iron loss is required.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a motor core in which deterioration of iron loss characteristics at high frequencies is small even in the presence of compressive stress, and to propose an advantageous manufacturing method thereof.

  The inventors diligently studied to solve the above problems. As a result, it was found that deterioration of iron loss characteristics due to compressive stress can be suppressed by imparting processing strain to the back yoke portion of the electromagnetic steel sheets (hereinafter also referred to as “stator core material”) that are stacked to constitute the stator core. The present invention has been completed.

  That is, according to the present invention, in a motor core in which electromagnetic steel sheets are laminated and a compressive stress of 10 MPa or more is applied in the circumferential direction, a large number of minute recesses are formed on the entire surface or part of the back yoke portion surface of the electromagnetic steel sheets constituting the motor core. It is a motor core characterized by being formed.

  The minute recesses in the motor core of the present invention have a depth of 10 to 50 μm, a diameter of 0.05 to 2 mm, and a distance between nearest neighbors of 0.2 to 5 mm.

  The minute recesses in the motor core of the present invention are characterized in that they are press-molded with projections formed on the surface of a die that is punched into a core shape.

  In the motor core of the present invention, Si: 7 mass% or less, Al: 3 mass% or less, Mn: 5 mass% or less, S: 0.01 mass% or less, N: 0.005 mass% or less, O: 0.00. It is characterized in that it contains not more than 01 mass% and the remainder has a component composition consisting of Fe and inevitable impurities.

  The present invention also relates to a method of manufacturing a motor core in which a compressive stress of 10 MPa or more is applied in the circumferential direction by laminating core materials obtained by punching electromagnetic steel sheets into a motor core shape. A manufacturing method of a motor core is proposed, which is performed using a punching die in which a large number of minute convex portions are formed on the entire surface or a part of the surface in contact with the back yoke portion.

  According to the present invention, it is possible to provide a motor core with a small increase in iron loss at high frequencies even in the presence of compressive stress. Accordingly, the motor core of the present invention is a compressor motor for an air conditioner used in a state where compressive stress is applied by shrink fitting, press fitting, resin molding, or the like, a drive motor for a hybrid vehicle (HV) or an electric vehicle (EV), It can be suitably used for a generator, a drive motor of a fuel cell vehicle (FCEV), a high-frequency rotating machine of a high-speed generator, and the like.

It is a schematic diagram explaining the motor core of this invention. It is a figure explaining the method to measure the high frequency iron loss of a stator core. It is a graph which shows the influence which the compressive stress has on the iron loss of a motor core. It is a schematic diagram explaining the other example of the motor core of this invention.

First, the basic technical idea of the present invention will be described.
In drive motors such as compressor motors for home appliance air conditioners and hybrid electric vehicles, shrink fitting or press-fitting methods are generally employed as means for fixing the core to the motor case. It is said that the compressive stress applied in the circumferential direction of the motor core by this shrink-fitting method or press-fitting method is about 20 to 150 MPa. This compressive stress degrades the iron loss characteristics of the electrical steel sheet that constitutes the motor core, and consequently greatly reduces the motor efficiency. Therefore, there is a demand for a motor core with little deterioration in iron loss characteristics even under compressive stress.

  The inventors investigated the high-frequency iron loss characteristics under the compressive stress of the magnetic steel sheet constituting the stator of the motor, and found that not only the hysteresis loss but also the eddy current loss increased in the presence of the compressive stress. It became clear. In general, motors such as compressor motors for air conditioners and hybrid vehicles are driven with harmonics of several kHz superimposed on them in order to control the inverter in addition to the high fundamental frequency. . Therefore, in order to improve the high frequency iron loss characteristic, it is an important issue to suppress an increase in eddy current loss.

  Therefore, when the cause of the increase in eddy current loss in the presence of compressive stress was investigated, when compressive stress was applied to the material, the magnetization vector in the steel plate relaxed within the plate surface of the steel plate to relieve the compressive stress. It changes to face the direction perpendicular to the compressive stress. Therefore, when trying to magnetize this steel plate, it is necessary to change the direction of the magnetization vector greatly compared to the case where there is no compressive stress, and the eddy current for that flow flows in the steel plate surface. As a result, eddy current loss increased.

  Furthermore, the inventors have studied a motor core (stator) in which eddy current loss does not increase even when compressive stress is applied. As a result, if the magnetic domain width of the back yoke portion of the laminated electromagnetic steel sheets (stator core material) constituting the stator can be reduced, it is possible to suppress the deterioration of the iron loss characteristics due to the compressive stress generated by shrink fitting. I thought. Then, as means for reducing the magnetic domain width, the following experiment was conducted by conceiving that processing distortion is imparted to the back yoke portion by applying special processing to the surface of the die used for punching.

Thickness: 0 consisting of component composition of Si: 3.3 mass%, Al: 0.5 mass%, Mn: 0.5 mass%, S: 0.002 mass%, N: 0.0015 mass%, O: 0.0012 mass%: 0 Using a non-oriented electrical steel sheet coated with an organic resin-inorganic mixed coating (aluminum dichromate-acrylic resin emulsion-ethylene glycol) as an insulating coating on the surface of a 35 mm steel plate, outer diameter: 100 mmφ, back yoke width : 20-mm, 12-slot stator core material was punched.
At this time, in the die used for the punching process, hemispherical projections having a height of 30 μm and a diameter of 0.3 mm are arranged in a square lattice pattern at intervals of 3 mm on the surface of the die in contact with the core back. Two types were used: a special mold in which convex portions were formed at the intersections of the above and a conventional mold having no convex portions.

  Next, the stator core material is laminated to a stack thickness of 30 mm, and a stator core is manufactured. The stator core material is fixed to a non-magnetic stainless steel ring imitating a motor case by changing the shrinkage, and the circumferential direction generated in the back yoke portion is fixed. The compressive stress was changed in the range of 0 to 100 MPa. The circumferential compressive stress was measured by attaching a strain gauge to the center of the back yoke. Here, the shrinkage allowance of 0 μm means a free state in which the stator core is not fixed to the ring at all.

Next, an excitation coil and a pickup coil are wound around the back yoke portion including the stainless steel ring on the stator core fixed to the stainless steel ring, as shown in FIG. _{10 / 3k} ). FIG. 3 shows the result of the above measurement as a relationship between the compressive stress in the circumferential direction of the stator generated by shrink fitting and the high-frequency iron loss.

  From FIG. 3, in the motor core having a compressive stress of 0 PMa without shrink fitting, the iron loss increases by applying the strain. However, in the motor core not applying the strain, the iron loss increases as the compressive stress increases. Increases rapidly, but in a motor core with strain, the increase in iron loss due to compressive stress is small. As a result, in a mocore in which compressive stress due to shrink fitting is generated at 10 MPa or more, strain is applied to the back yoke. By doing, it turns out that the increase in the iron loss by a compressive stress can be suppressed rather than the case where distortion is not provided.

  Therefore, when investigating the cause of the decrease in iron loss due to strain application, when the core loss of the shrink-fit core was separated, the hysteresis loss increased slightly due to strain application, but the eddy current loss decreased greatly due to strain application. It became clear that The reason why the eddy current loss is reduced by applying the strain is considered to be because the magnetic domain of the back yoke portion is subdivided by applying the strain.

Moreover, the reason why the iron loss increased by applying strain in the core that does not shrink fit (compression stress 0) is considered to be that the hysteresis loss increased by applying strain. Therefore, imparting strain to the teeth portion where no shrink-fit stress has occurred causes an increase in iron loss. Therefore, in the present invention, strain is imparted only to the core back portion to which compressive stress is imparted. I decided to do it.
The present invention has been developed based on the above findings.

Next, the electromagnetic steel sheet used for the motor core of the present invention will be described. First, the electrical steel sheet used for the motor core of the present invention preferably has the following component composition.
Si: 7 mass% or less Si is an element effective for increasing the specific resistance of steel. However, when added in excess of 7 mass%, the magnetic flux density of the motor core also decreases as the saturation magnetic flux density decreases. Further, when rolling to the final plate thickness, there is a possibility that the plate breaks even if it is warm-rolled, so the upper limit is preferably 7 mass%. In addition, although a minimum in particular is not restrict | limited, From a viewpoint of raising specific resistance, it is preferable that it is 0.1 mass% or more. More preferably, it is the range of 0.5-6.5 mass%.

Al: 3 mass% or less Al is an element effective for increasing the specific resistance. However, if it exceeds 3 mass%, the magnetic flux density of the motor core decreases as the saturation magnetic flux density decreases. Therefore, the upper limit is set to 3 mass%. Is preferred. More preferably, it is 2 mass% or less.

Mn: 5 mass% or less Mn is an element necessary for increasing specific resistance and preventing red heat embrittlement due to S, and it is preferably added in an amount of 0.05 mass% or more. On the other hand, if the addition exceeds 5 mass%, the saturation magnetic flux density decreases, so the upper limit is preferably 5 mass%. More preferably, it is the range of 0.1-4 mass%.

S: 0.01 mass% or less S is an impurity that is inevitably mixed. When the content of S is increased, a large amount of sulfide inclusions such as MnS are formed, which causes an increase in iron loss. . Therefore, in the present invention, the upper limit is preferably set to 0.01 mass%. More preferably, it is 0.005 mass% or less.

N: 0.005 mass% or less N is an impurity that is inevitably mixed in as in S, and if the content is large, a large amount of AlN is formed and iron loss increases, so the upper limit is It is preferable to set it as 0.005 mass%.

O: 0.01 mass% or less O, like S and N, is an impurity that is inevitably mixed in. If the content is large, a large amount of oxide inclusions are formed, and the iron loss increases. Therefore, the upper limit is preferably set to 0.01 mass%.

  In the electrical steel sheet used for the motor core of the present invention, the balance other than the above components is Fe and inevitable impurities. However, as long as the effects of the present invention are not impaired, the inclusion of components other than those described above is not rejected.

  Moreover, the electrical steel sheet used for the motor core of the present invention is preferably one in which an insulating coating is applied to the steel sheet surface having the above component composition. As the insulating film, only an organic component, an inorganic component, an organic / inorganic composite, or the like can be used. Specifically, the organic component includes acrylic, acrylic silicon, polyester, epoxy, and fluorine resins, and the inorganic component includes chromate, dichromate, and borate. , Phosphate-based, silicate-based, and the like, and examples of the organic / inorganic composite (semi-organic) include the composite of the organic component and the inorganic component described above.

  In addition, the motor core of the present invention needs to be provided with a processing strain for magnetic domain subdivision in the back yoke portion when a magnetic steel sheet as a material is punched into a predetermined motor core (stator core). Here, the processing strain is preferably a minute recess having a depth of 5 to 50 μm and a diameter of 0.05 to 2 mm. When the depth of the minute recess is less than 5 μm or the diameter is less than 0.05 mm, sufficient strain necessary for magnetic domain subdivision cannot be imparted. On the other hand, when the depth exceeds 50 μm or the diameter exceeds 2 mm, the strain is large. This is because the hysteresis loss increases. The shape of the concave portion may be any of a hemispherical shape, a cylindrical shape, a conical shape, a triangular pyramid shape, a quadrangular pyramid shape, and the like. However, the diameter in cases other than the hemispherical shape and the cylindrical shape is a diameter of a circle corresponding to the area of the recess.

  Moreover, it is preferable to form the space | interval of a micro recessed part so that the distance between nearest neighbors may be 0.2-5 mm. If the distance is less than 0.2 mm, a large strain is introduced into the surface of the steel sheet, so that the punched core may be deformed. On the other hand, if the thickness exceeds 5 mm, the effect of magnetic domain fragmentation cannot be obtained sufficiently. However, the minute recesses may be arranged at random, or may be regularly arranged in a square lattice shape, a rectangular lattice shape, a triangular lattice shape, a hexagonal lattice shape, or the like.

  In addition, the minute recesses are formed in the back yoke portion of the motor core by forming the protrusions for forming the recesses on the surface of the die used for the punching process in contact with the die. It can be performed by using and punching. However, in this case, it is preferable to determine the dimension of the convex portion in consideration of the transfer rate.

  In addition, the motor core of the present invention is obtained by laminating the core material stamped as described above. Before the core material is laminated, the insulating film is reapplied on the surface of the steel plate to which strain is applied. As a result, the iron loss can be more reliably reduced. This is to prevent the insulating film from being locally broken by the application of strain and causing a short circuit to reduce the interlayer resistance between the stacked layers. The insulating film after the application of strain may be applied to the entire surface or only the strained portion. The insulating film to be overcoated may be any of the above-described organic resin or organic resin-inorganic mixed insulating film as long as the interlayer resistance can be increased.

  Further, in the present invention, the reason why the value of the compressive stress generated in the motor core is limited to 10 MPa or more is that the motor core cannot be sufficiently fixed if it is less than 10 MPa, and as shown in FIG. This is because the iron loss reduction effect cannot be obtained.

  The motor to which the motor core of the present invention can be applied may be of any type as long as compressive stress is applied to the motor core. For example, a concentrated winding type permanent magnet motor or a distributed winding type permanent magnet motor. It can be applied to a split core type permanent magnet motor, an induction motor, a reluctance motor, and the like.

  Steel having the composition shown in Table 1 was melted and continuously cast into a steel slab by a generally known refining process such as converter-degassing. Next, this steel slab was reheated at 1120 ° C. × 1 hr, and hot rolled to a finish rolling finish temperature of 850 ° C. to obtain a hot rolled sheet having a thickness of 2.0 mm. After hot-rolling sheet annealing at 1000 ° C. × 30 sec, pickling, cold rolling to form cold-rolled sheets with thicknesses of 0.30 mm and 0.20 mm, and finishing annealing at 1000 ° C. × 10 sec A non-oriented electrical steel sheet was manufactured by applying an insulating film of aluminum dichromate-acrylic resin emulsion-ethylene glycol organic resin-inorganic mixture.

The following evaluation was performed on the electromagnetic steel sheet.
<Measurement of magnetic flux density B ₅₀ >
From the magnetic steel sheet, an Epstein test piece having a width of 30 mm and a length of 280 mm was taken from the rolling direction and the direction perpendicular to the rolling direction, and the magnetic flux density B ₅₀ when magnetized at 5000 A / m was measured according to JIS C2550.
<Motor core iron loss measurement>
When the non-oriented electrical steel sheet is stamped into a stator core material having the same 12 slots as in FIG. 1 and having an outer diameter of 100 mmφ and a back yoke width of 20 mm, the die surface portion in contact with the back yoke portion of the stator core material is By using a mold in which hemispherical convex portions are arranged in a square lattice shape, a regular triangular lattice shape, or a random shape at intervals of 0.1 to 6.0 mm, the core back portion has a height of 4 to 70 μm. A hemispherical recess having a diameter of 0.03 to 3.0 mm was formed, and then the same insulating coating as described above was applied again. In some cases, recoating was omitted.
Next, the punched core material is laminated to a stacking thickness of 30 mm to produce a stator core, and this stator core is shrink-fitted to a non-magnetic stainless steel ring having an inner diameter of about 100 mmφ by changing the shrink-fitting allowance. A compressive stress of 0 to 100 MPa was generated in the circumferential direction. The compressive stress was measured using a strain gauge attached to the center of the back yoke of the stator. Next, as shown in FIG. 2, an excitation coil and a pickup coil including the stainless steel ring are wound around the back yoke portion, and the iron loss W _{10 / in the} circumferential direction of the motor core at a frequency of 1 kHz and a maximum magnetic flux density of 1T. _3k was measured.

  Table 1 also shows the results of the above measurements. From this result, it was confirmed that the stator core in which the working strain was imparted to the back yoke portion under the conditions suitable for the present invention can suppress the deterioration of the iron loss characteristic under the compressive stress.

  The motor core technology of the present invention can be applied to high-speed motors that are fixed by shrinkage fitting, such as drive motors and generators for hybrid electric vehicles, compressor motors for air conditioners, and spindle motors for machine tools.

1: Stator core 2: Strain imparted portion 3: Rotor 4: Permanent magnet 5: Stainless steel ring (non-magnetic)
6: Winding

Claims (5)

In a motor core in which electromagnetic steel sheets are laminated in which a compressive stress of 10 MPa or more is applied in the circumferential direction, a number of minute recesses are formed on the entire or part of the surface of the back yoke portion of the electromagnetic steel sheets constituting the motor core. Motor core. 2. The motor core according to claim 1, wherein the minute recesses have a depth of 5 to 50 μm, a diameter of 0.05 to 2 mm, and a closest distance of 0.2 to 5 mm. . 3. The motor core according to claim 1, wherein the minute recess is press-molded by a protrusion formed on a die surface that is punched into a core shape. 4. The electromagnetic steel sheet contains Si: 7 mass% or less, Al: 3 mass% or less, Mn: 5 mass% or less, S: 0.01 mass% or less, N: 0.005 mass% or less, O: 0.01 mass% or less, The motor core according to any one of claims 1 to 3, wherein the balance has a component composition composed of Fe and inevitable impurities. In a method of manufacturing a motor core in which a compressive stress of 10 MPa or more is applied in the circumferential direction by stacking electromagnetic steel sheets punched into a motor core shape, when the electromagnetic steel sheet is punched, it comes into contact with the back yoke portion of the moor core A method for manufacturing a motor core, which is performed using a punching die in which a large number of minute protrusions are formed on the entire surface or part of the surface.

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