JP5609057B2 - Motor core - Google Patents

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 specifically, compressive stress. The present invention relates to a motor core in which the increase in iron loss is small even in the presence of.

  Compressor motors for home air conditioners operate at a variable speed with a fundamental frequency of about 50 to 300 Hz, and recently, a carrier frequency of several kHz for PWM (Pulse Width Modulation) type inverter control, etc. Is used in a superimposed state. Recently, a drive motor of a hybrid electric vehicle that has been rapidly spread is also driven at a frequency of several kHz from the viewpoint of achieving high output and miniaturization.

  The core material (electromagnetic steel sheet) used for the stator (stator) and rotor (rotor) of the motor is required to have low iron loss from the viewpoint of improving energy efficiency. Therefore, a high grade non-oriented electrical steel sheet to which about 3 to 4 mass% in total of Si and Al are added is used for the core material of the motor 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 of the motor core to the housing, and as a result, in the circumferential direction of the stator A compressive stress of about 30 to 150 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). It is desired.

As a material with improved iron loss characteristics under compressive stress, for example, Patent Document 1 contains Si: 2.6 to 4 mass%, specific resistance is 50 to 75 × 10 ⁻⁸ Ωm, average crystal grain A non-oriented electrical steel sheet having a diameter of more than 60 μm and not more than 165 μm and an average _iron loss value W _15/200 of 16 W / kg is disclosed.

Japanese Patent No. 4023183

  However, since the non-oriented electrical steel sheet of Patent Document 1 has only the same specific resistance and crystal grain size as the high-grade electrical steel sheet currently on the market, even if a motor core is manufactured using this material, the compressive stress The degree of iron loss deterioration due to slag is not significantly different from that of conventional materials, and there is a need for the development of a technology that further reduces stress dependency.

  Accordingly, an object of the present invention is to provide a motor core in which the deterioration of high-frequency iron loss characteristics is small even in the presence of compressive stress.

  As described above, in a compressor motor of an air conditioner for home appliances, a motor of a hybrid electric vehicle, and the like, the stator core is fixed to the housing by a shrink-fitting method or a press-fitting method. Therefore, a compressive stress of about 30 to 150 MPa in the circumferential direction of the core Occurs, which increases iron loss and reduces motor efficiency.

  Therefore, the inventors examined the stress dependence of the iron loss of the electromagnetic steel sheet, and found that not only the hysteresis loss of the steel sheet increases but also the eddy current loss increases under compressive stress. As described above, a compressor motor, a motor of a hybrid electric vehicle, and the like are not only driven in a high frequency range but also used in a state where a harmonic of several kHz is superimposed for inverter control or the like. Therefore, it is extremely important to suppress an increase in eddy current loss in the high frequency region of such a motor.

Furthermore, the inventors examined the cause of the increase in eddy current loss under compressive stress. When compressive stress is applied to the material, the magnetization vector is directed in the direction of the steel plate in order to relax the compressive stress. However, when the motor was in operation, it was found that eddy currents flow in the plate surface to correct it. And in order to suppress the orientation of the magnetization vector due to the compressive stress in the direction of the steel plate and reduce the increase in eddy current loss, the magnetostriction constant of the core material in the direction of receiving the compressive stress is reduced, and -0.1 Realizing a motor with low iron loss deterioration even under compressive stress due to shrink fitting, etc., by effectively using a value in the range of 10 × 10 ⁻⁷ and appropriately using the core material having the magnetostrictive characteristics described above The present invention was developed by finding out what can be done.

That is, according to the present invention, in a motor core having a compressive stress in the circumferential direction of the stator of 10 MPa or more, the steel plate used for the stator has a magnetostriction constant in a range corresponding to the circumferential direction of the stator in the range of −0.1 to 10 × 10 ⁻⁷ . And Si: 4.5 to 6.6 mass%, Al: 1 mass% or less, Mn: 0.05 to 2 mass%, S: 0.005 mass% or less, N: 0.005 mass% or less In addition , the motor core is characterized in that the remainder has a composition composed of Fe and inevitable impurities, and is composed of a split core having a direction perpendicular to the rolling direction of the steel sheet as a circumferential direction of the core .

  According to the present invention, it is possible to provide a motor core having a small high-frequency iron loss even under compressive stress. Therefore, the motor core of the present invention includes a compressor motor for an air conditioner, a drive motor for a hybrid electric vehicle, a drive motor for a fuel cell vehicle (FCEV), which is used in a state where compression force is applied by shrink fitting, press-fitting or resin molding, It can be suitably used as a material for a high-frequency rotating machine of a high-speed generator.

It is a graph which shows the influence which magnetostriction has on the iron loss characteristic and motor efficiency of a steel plate.

First, the magnetostriction characteristics that the steel sheet used for the motor core of the present invention should have will be described.
Magnetostriction λ _10/400 : −0.1 to 10 × 10 ⁻⁷
The magnetostriction constant λ _{10/400 in the} direction corresponding to the circumferential direction of the stator of the steel sheet used for the motor core of the present invention needs to be a value in the range of −0.1 to 10 × 10 ⁻⁷ . Here, the magnetostriction constant λ _10/400 is a width of 30 mm × length so that the direction corresponding to the circumferential direction of the stator, for example, the direction perpendicular to the rolling direction of the steel plate is the length direction from the core material (magnetic steel plate). A test piece having a thickness of 280 mm × thickness was cut out, and a strain of 1.0 T when a butterfly curve was drawn by measuring a strain in a direction perpendicular to the rolling direction when excited at 400 Hz and 1.0 T with a laser displacement meter. This is a value obtained by subtracting the strain amount of 0T from the amount.

  The reason why the magnetostriction measurement direction is a direction perpendicular to the rolling direction is that the split core (stator) is usually cut from the core material (electromagnetic steel sheet) when the direction perpendicular to the rolling direction of the steel sheet is the back yoke. This is because the direction of the compressive stress generated by shrink fitting or the like is a direction perpendicular to the rolling direction of the steel sheet.

FIG. 1 shows a magnetostriction value in a direction perpendicular to the rolling direction and a compressive stress of 50 MPa in a direction perpendicular to the rolling direction of the steel sheet having various Si contents (thickness 0.25 mm). This shows the relationship with the motor efficiency when an actual motor is manufactured using the iron loss value W _{10 / 3k} and the steel plate and rotated at 6000 rpm with a torque of 5 Nm.

  Here, the motor is an 8-pole, 12-slot IPM motor (internal magnet embedded motor) having a stator outer shape: 110 mmφ, a rotor outer shape: 75 mmφ, and a stacking thickness: 80 mm. The core is used in such a manner that the direction perpendicular to the rolling direction of the steel sheet is the circumferential direction of the stator (the length direction of the teeth is the rolling direction). The core (stator) was fixed to the housing with a shrinkage allowance of 55 μm, and a compressive stress of about 50 MPa was generated in the circumferential direction of the central portion of the core back.

From FIG. 1, if the magnetostriction constant _{10/400 in the} direction perpendicular to the rolling direction (the circumferential direction of the stator) is a value in the range of −0.1 to 10 × 10 ⁻⁷ , the high-frequency iron loss W ₁₀ under compressive stress. _{/ 3k} is low, and it can be seen that the motor efficiency is also improved. The reason why the iron loss was evaluated by W _{10 / 3k} in the above measurement is that the use frequency of the high-frequency motor is about 3 kHz. The reason why the value at 400 Hz is used as the magnetostriction constant λ should be measured at 3 kHz, but it is extremely difficult to measure magnetostriction at 3 kHz, and the highest frequency that can be accurately measured is about 400 Hz. Because.

As shown in FIG. 1, the inventors consider the reason why the magnetostriction constant affects the iron loss characteristic and the motor efficiency as follows.
In the case of a steel plate with a large positive value of magnetostriction constant like a normal electromagnetic steel plate, when compressive stress is applied in a direction perpendicular to the rolling direction, the magnetization vector changes to face the steel plate surface direction. To do. And when this is magnetized, the eddy current for directing the said magnetization vector to a magnetization direction flows in a steel plate surface, and an eddy current loss increases compared with a no-stress state. On the other hand, in the case of a steel sheet having a small magnetostriction constant, the eddy current is mainly a plate thickness cross section because the magnetization vector directed in the steel sheet surface direction decreases due to the application of compressive stress in the direction perpendicular to the rolling direction. The increase in eddy current loss due to compressive stress is suppressed.

Next, a method for setting the magnetostriction constant in the direction perpendicular to the rolling direction of the motor core material (magnetic steel sheet) to a value in the range of −0.1 to 10 × 10 ⁻⁷ as described above will be described.
Any method may be used to set the magnetostriction constant in the direction perpendicular to the rolling direction of the steel sheet to a small value. For example, there is a method of manufacturing an electromagnetic steel sheet using steel added with 4.5 mass% or more of Si as a raw material. However, as will be described later, the addition of Si exceeding 6.6 mass% not only decreases the magnetic flux density as the saturation magnetic flux density decreases, but also makes it difficult to produce a steel sheet by rolling, so the upper limit is 6 .6 mass% is necessary.

  Moreover, in the manufacture of electromagnetic steel sheets, when finish annealing is performed in a continuous annealing line or the like, generally, from the viewpoint of preventing meandering of the steel sheet, the sheet is passed while applying tension in the longitudinal direction (rolling direction) of the steel sheet. However, the tension at this time generates a compressive stress in the sheet width direction of the steel sheet (the direction perpendicular to the rolling direction).

The inventors investigated in detail about the influence which the tensile tension | tensile_strength provided to the said steel plate has on the magnetostriction characteristic of a steel plate. As a result, when finish annealing is performed in a state where compressive stress is applied in the sheet width direction of the steel sheet, the magnetic domain form of the steel sheet after annealing becomes different from that without tension, and the magnetostriction constant in the direction perpendicular to the rolling direction In order to prevent negative effects due to the application of tension and to set the magnetostriction constant in the direction perpendicular to the rolling direction to a value in the range of −0.1 to 10 × 10 ⁻⁷ , the finish annealing is performed. It was newly found that it is necessary to reduce the steel plate tension at the time to 2.94 MPa or less.

  Note that the effect of Si on magnetostrictive properties and the effect of tension during finish annealing on magnetostrictive properties are independent, and even if the Si content is controlled within an appropriate range, the tension during finish annealing is inadequate. If appropriate, the magnetostriction constant in the direction perpendicular to the rolling direction of the steel sheet cannot be in the above range. Therefore, it is necessary to control the component composition of the raw material within an appropriate range and to control the steel plate tension during finish annealing within the appropriate range.

Next, the component composition that the steel plate (motor core material) used for the motor core of the present invention should have will be described.
The motor core material (electromagnetic steel sheet) of the present invention has any component system as long as the magnetostriction constant λ _{10/400 in the} direction perpendicular to the rolling direction exhibits a value in the range of −0.1 to 10 × 10 ^−7. For example, when the steel material is Si-added steel, it is preferable to have the following component composition.

Si: 4.5 to 6.6 mass%
Si is an element effective in increasing the specific resistance of steel and realizing low iron loss. However, if added over 6.6 mass%, not only does the magnetic flux density decrease as the saturation magnetic flux density decreases, but it also becomes difficult to roll and produce a steel sheet. On the other hand, when Si is less than 4.5 mass%, the magnetostriction constant increases and exceeds 10 × 10 ⁻⁷ . Therefore, Si is preferably in the range of 4.5 to 6.6 mass%. More preferably, it is in the range of 5.0 to 6.5 mass%.

Al: 1 mass% or less Al, like Si, is an element that is effective in increasing the specific resistance of steel, but if added over 1 mass%, the amount of Si added to reduce the magnetostriction constant increases, and the core It causes embrittlement of the material. Therefore, the upper limit is preferably set to 1 mass%. More preferably, it is 0.8 mass% or less.

Mn: 0.05-2 mass%
Mn is an element necessary for preventing red heat brittleness due to S or the like, and it is preferable to add 0.05 mass% or more. On the other hand, if added over 2 mass%, the amount of Si added increases to reduce the magnetostriction constant, leading to embrittlement of the core material. Therefore, the upper limit is preferably set to 2 mass%. More preferably, it is the range of 0.1-0.5 mass%.

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

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 nitride is formed, causing iron loss to increase. Is preferably 0.005 mass%.

  When Si-added steel is used as the steel material, the balance other than the above components is Fe and inevitable impurities. However, addition of components other than those described above is not rejected as long as the effects of the present invention are not impaired.

Next, the manufacturing method of the motor core material used for the motor core of this invention is demonstrated.
The manufacturing method of the core material (electromagnetic steel sheet) used for the motor core of the present invention is such that the magnetostriction λ _{10/400 in the} direction perpendicular to the rolling direction of the steel sheet has a value in the range of −0.1 to 10 × 10 ^−7. Any method may be used. For example, steel is melted in a converter or an electric furnace, or further subjected to secondary refining such as degassing to adjust to the above-mentioned predetermined composition, and cast into a steel slab. Then, the steel slab is hot-rolled to a predetermined sheet thickness by one or more cold and / or warm rolling, or two or more cold and / or warm rolling sandwiching the intermediate annealing, and then It can be manufactured by performing finish annealing. In addition, the rolling temperature and winding temperature in the said hot rolling should just be normally well-known conditions, and there is no restriction | limiting in particular. Moreover, the hot-rolled sheet annealing after hot rolling can be performed as needed.

However, since steel containing a large amount of Si is hard and brittle, it is difficult to roll it into a steel plate having a predetermined thickness. Therefore, when using Si-added steel as a steel material, in order to improve manufacturability, for example, an upstream process until cold rolling to the final sheet thickness is manufactured as a low Si material of, for example, Si ≦ 4 mass%, It is heated to 1000 to 1250 ° C., is contacted with an atmospheric gas containing silicon tetrachloride (SiCl ₄ ), is subjected to a siliconization treatment, and is further subjected to a Si diffusion treatment at 1000 to 1400 ° C. as necessary to obtain a predetermined amount of Si. You may employ | adopt the method of containing.

Moreover, in the case of performing finish annealing in a continuous line such as a continuous annealing line, in order to set the magnetostriction constant in the direction perpendicular to the rolling direction of the steel sheet to a value in the range of −0.1 to 10 × 10 ⁻⁷ or less, 800 ° C. It is preferable to anneal the steel sheet in the above temperature range with a tension of 2.94 MPa or less. Here, the above-mentioned finish annealing means the final annealing that is heated to 600 ° C. or higher after cold or warm rolling to the final plate thickness. When processing is performed, it means diffusion processing.

  The core material used for the motor core of the present invention is not particularly limited with respect to the plate thickness, but is preferably 0.35 mm or less and more preferably 0.2 mm or less for the purpose of the present invention to reduce high-frequency iron loss. On the other hand, the lower limit of the plate thickness is preferably 0.05 mm or more from the viewpoint of ensuring productivity.

Next, the motor core of the present invention will be described.
Since the core material used for the motor core of the present invention exhibits low iron loss even in a high frequency region of 1 kHz or higher in the presence of compressive stress, it can be suitably used for the core of a high frequency motor. Here, the high frequency of 1 kHz or higher includes not only the case where the fundamental frequency is 1 kHz or higher but also the case where the carrier frequency is 1 kHz or higher.

However, when using the above core material for the motor core of the present invention, it is necessary to align the direction of the low magnetostriction constant of the steel sheet and the direction of the compressive stress received during use, for example, the direction of the low magnetostriction constant (for example, It is necessary to align the direction perpendicular to the rolling direction of the steel plate with the circumferential direction of the stator. Therefore, in the present invention, it is preferable to use a split core so that the circumferential direction of the stator is a direction perpendicular to the rolling over the entire circumference (the length direction of the teeth is parallel to the rolling direction). However, if the magnetostriction constant other than the direction perpendicular to the rolling is also in the range of −0.1 to 10 × 10 ⁻⁷ , the motor core to which compressive stress such as shrink fitting is applied as an integrated motor core other than the split core. Of course, it may be used.

  Further, when the motor core is fixed to the housing, it is necessary to generate a compressive stress of 10 MPa or more in the circumferential direction of the stator by a shrink fitting method or a press fitting method. This is because if the pressure is less than 10 MPa, sufficient fixing force cannot be obtained. For example, when fixing by shrink fitting, if the shrinkage allowance is about 50 μm, a compressive stress of about 50 MPa can be generated in the circumferential direction of the central portion of the core back of the stator. However, as the compressive stress increases, not only shrink fitting or press fitting becomes difficult, but also iron loss increases and motor efficiency also decreases greatly. Therefore, the upper limit is preferably set to about 200 MPa.

A steel having the composition shown in Table 1 is melted and cast into a small slab using a vacuum melting furnace, and the small slab is heated to 1140 ° C. × 1 hr, and then the finish rolling finish temperature is 800 ° C. And it rolled up at 500 degreeC, it was set as the hot-rolled sheet of 2.0 mm in thickness, and 1000 degreeC * 30 second hot-rolled sheet annealing was performed. Next, after pickling the hot-rolled sheet, it was warm-rolled at a temperature of 400 ° C. to obtain a cold-rolled sheet having the thickness shown in Table 1, and subjected to finish annealing at 1000 ° C. × 10 sec to obtain an electromagnetic steel sheet.
Note that the steel plate tension at 800 ° C. or higher in the above finish annealing is varied between 0.98 and 4.90 MPa as shown in Table 1, and the magnetostriction constant in the direction perpendicular to the rolling direction of the steel plate is changed. It was.

Next, the various electrical steel sheets shown in Table 1 were subjected to the following measurements.
<Magnetic strain measurement>
A test piece having a width of 30 mm, a length of 280 mm, and a plate thickness was cut out from the electromagnetic steel sheet so that the direction perpendicular to the rolling direction was the length direction, and in a no-stress state, the frequency was 400 Hz and the maximum magnetic flux density was 1.0 T. The magnetostriction λ _10/400 was obtained by measuring the strain in the direction perpendicular to the rolling direction when excited with a laser displacement meter to draw a butterfly curve and subtracting the strain amount of 0T from the strain amount of _1.0T . .
<Motor efficiency>
Using the above magnetic steel sheet as a stator material, a stator outer shape: 110 mm, a rotor outer shape: 75 mm, a stacking thickness: 80 mm, and an 8-pole, 12-slot embedded internal magnet motor (IPM motor) with a torque of 5 Nm The motor efficiency when rotating at 6000 rpm was measured. The stator is a 12-part split core used so that the direction perpendicular to the rolling direction of the steel sheet is the circumferential direction of the stator (the rolling direction is the length direction of the teeth), and when the stator core is fixed to the housing The shrinkage allowance was adjusted so that the compressive stress in the circumferential direction of the stator was 50 MPa. The compressive stress was measured using a strain gauge.
<Magnetic properties>
A test piece having a width of 30 mm, a length of 280 mm, and a plate thickness was cut out from the electromagnetic steel sheet so that the direction perpendicular to the rolling direction was the length direction, and the same magnitude as the compression stress in the stator circumferential direction of the motor (50 MPa) ) Of iron loss W _{10 / 3k} (iron loss at a frequency of 3000 Hz and a maximum magnetic flux density of 1.0 T) and B ₅₀ (magnetic flux density at a magnetic field strength of 5000 A / m). ) Was measured.

  The results of the above measurements are shown together in Table 1. From this result, a high-frequency motor with low iron loss and high efficiency is realized by producing a motor core using an electromagnetic steel sheet (core material) having magnetostriction characteristics suitable for the present invention under conditions suitable for the present invention. I understand that I can do it.

No. shown in Table 1 above. The same IPM motor as in Example 1 was produced using the electrical steel sheets 1 and 2, and the motor efficiency was measured in the same manner as in Example 1. In manufacturing the motor, the compressive stress in the stator circumferential direction was changed in the range of 0 to 120 MPa as shown in Table 2 by changing the shrinkage allowance when the stator core was fixed to the housing. Further, the magnetic properties of the steel sheet were such that the iron loss W _{10 / 3k} in the compressive stress applying direction was applied in the same manner as in Example 1 while applying the same compressive stress as the compressive stress generated in the circumferential direction of the stator of the motor. (Iron loss at a frequency of 3000 Hz and maximum magnetic flux density of 1.0 T) and B ₅₀ (magnetic flux density at a magnetic field strength of 5000 A / m) were measured.

  The results of the above measurements are also shown in Table 2. From this result, it can be seen that a high-efficiency high-frequency motor can be realized by using a core material suitable for the present invention for the stator and firmly fixing the circumferential compressive stress in the range of 10 to 200 MPa to the housing.

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

Claims (1)

In the motor core where the compressive stress in the stator circumferential direction is 10 MPa or more,
The steel sheet used for the stator has a magnetostriction constant in a direction corresponding to the circumferential direction of the stator in a range of −0.1 to 10 × 10 ⁻⁷ , Si: 4.5 to 6.6 mass%, Al: 1 mass% or less, Mn: 0.05 to 2 mass%, S: 0.005 mass% or less, N: 0.005 mass% or less, with the balance being composed of Fe and inevitable impurities ,
A motor core comprising a split core having a direction perpendicular to the rolling direction of the steel sheet as a circumferential direction of the core.

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