JP6373788B2 - Rotating electrical machine and method for manufacturing the rotor - Google Patents

Description

  The present invention relates to a rotating electrical machine (motor) such as a three-phase squirrel-cage induction motor using a rotor (rotor) in which an iron core (core) is formed of a soft magnetic thin plate laminate such as an electromagnetic steel plate.

Rotating electric machine (motor) is the maximum power consuming device that uses 40% of the electric energy, from the viewpoint of preventing global warming by reducing the CO ₂ gas discharged in the power generation, the loss reduction in the motor, the electric energy consumption by high efficiency There is a need to reduce the amount.

  Motor loss includes iron loss that occurs in the stator (stator) core, primary copper loss of the stator winding, secondary copper loss of the conductor in the rotor, friction loss of the bearing, mechanical loss due to wind loss in the cooling fan, and It is roughly divided into stray load loss.

  Among these losses, iron loss and copper loss are the main loss components. For the purpose of reducing these main losses, technological improvements such as advanced motor design and improved material characteristics have been actively carried out. Loss reduction is approaching its limit.

  Among the remaining losses, stray load loss has a relatively high ratio to the total loss, and has an effect on efficiency. As for the stray load loss, there are many unexplained parts regarding the generation mechanism, and there is much room for reduction. The stray load loss is mainly caused by the harmonic magnetic flux inevitably generated in the motor. For example, as described in Patent Document 1, a three-phase squirrel-cage induction motor has a slit in the outer periphery of the rotor slot. A method of providing a stray load loss reduction method has been proposed.

JP-A-9-224358

Yasuhiro Ohsane and 7 others, “Cogging torque analysis of permanent magnet motors considering the effect of stress distribution in the iron core”, IEEJ Transactions D, Vol.126, No.1, pp.74-83 (2006) Fuminori Ishibashi, two others, "High-frequency electromagnetic force of induction motor gap", IEEJ Transactions D, Vol.129, No.4, pp.376-381 (2009)

  In Patent Document 1, it is necessary to form a bridge portion between the slit on the outer periphery of the slot and the slot so that the secondary conductor (rotor bar) formed by die casting is not pushed into the slit. In this case, since the width of the bridge portion becomes as narrow as 0.3 to 0.5 mm, there is a problem that die damage is likely to occur when the rotor core is punched, resulting in an increase in die cost and high motor manufacturing cost. .

  An object of the present invention is to provide a high-efficiency motor having no problem as in the prior art and having reduced stray load loss.

  The present invention has been obtained as a result of diligent research regarding stray load loss reduction, and heat treatment is performed on the surface of the rotor whose outer periphery is subjected to machining such as cutting in the final rotor manufacturing process, thereby controlling the rotor core surface stress. As a result, it was found that stray load loss can be reduced, leading to the present invention.

  It is qualitatively explained that stray load loss is caused by eddy current flowing on the core surface as a result of the harmonic magnetic flux acting on the core surface of the motor. Therefore, stray load loss can be reduced by making it difficult for the harmonic magnetic flux to flow to the core. As a means for this, in the present invention, the surface of the rotor core is subjected to heat treatment after machining and the rotor core surface stress is controlled to make it difficult for harmonic flux to flow in the radial direction of the rotor core. Low stray load loss can be achieved by reducing eddy current loss due to infiltration.

  To give an example of a typical “rotary electric machine” of the present invention, a rotor in which a rotor core is formed of a laminate of soft magnetic thin plates, its outer peripheral surface is machined, and surface heat treatment is used is used. The rotating electrical machine is characterized in that the circumferential surface stress of the outer peripheral surface of the rotor is in the range of 0 to 700 MPa, and the axial surface stress is in the range of 0 to 200 MPa.

  Further, as an example of a representative “method for manufacturing a rotor of a rotating electric machine” of the present invention, a step of machining an outer peripheral surface of a rotor core formed of a laminate of soft magnetic thin plates, and the rotation Heat treating the outer peripheral surface of the core and setting the circumferential surface stress of the rotor outer peripheral surface within a range of 0 to 700 MPa and an axial surface stress within a range of 0 to 200 MPa. Is.

  According to the present invention, by controlling the circumferential stress on the rotor core surface within the range of 0 to 700 MPa and the axial stress within the range of 0 to 200 MPa by heat treatment of the surface after machining of the outer periphery of the rotor core. A high-efficiency motor with reduced stray load loss can be provided.

It is a figure which defines the surface stress of the rotor core surface in this invention. It is a schematic diagram of the induction heating used in the Example of this invention. It is a microscope picture which shows the metal structure of the rotor core surface in a comparative example. It is a figure which shows the relationship between the magnetic permeability of an electromagnetic steel plate, and stress. It is a figure which shows the surface stress area | region of this invention. It is a figure which shows the relationship between stray load loss and axial surface stress.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
An example and a comparative example for a rotor of an output 2.2 kW, four-pole three-phase squirrel-cage induction motor are used. As the rotor, a laminated core having an outer thickness of 109 mm and an electromagnetic steel plate core having a thickness of 0.5 mm and a stack thickness of 81 mm was used. The rotor core is provided with 28 slots, and an aluminum rotor bar is formed in the slot by die casting. After die casting of the rotor bar, the shaft is shrink-fitted into the shaft hole at the center of the rotor core, and as a final step, outer periphery processing is performed to provide a predetermined gap between the stator / rotor. The rotor core is a closed slot and is skewed by one slot.

  A plurality of rotors manufactured in the same process and under the same conditions are manufactured, arbitrary rotors are heat-treated under the respective conditions, stray load loss and surface stress (residual stress) are measured, and the difference between stray load loss and surface stress is measured. Correlation was evaluated.

  The stray load loss was measured by fixing the stator and replacing the heat-treated rotor under each condition to eliminate the effect of variations in stator characteristics. The number of slots in the stator is 36. The stray load loss measurement was performed in accordance with Japanese Industrial Standard JIS C4034-2-1.

  The surface stress was measured by an X-ray stress measurement method. The measurement area was a rectangular area of 4 mm × 4 mm in the center of the rotor core, and the surface stress in the circumferential direction and the axial direction of the rotor core was determined by the sin ψ2 method.

  FIG. 1 illustrates the direction of the measured surface stress with respect to the rotor 1 used in Examples and Comparative Examples. In the figure, reference numeral 5 corresponding to the axial direction of the rotor 1 represents axial surface stress, and reference numeral 6 corresponding to the circumferential direction of the rotor 1 represents circumferential surface stress. In the rotor 1, slots (not shown) in the rotor core 2, end rings 3 and cooling fins (not shown) at both ends are collectively formed by die casting, and then the shaft 4 is shrink-fitted. After measuring the stray load loss, the rotor 1 was removed from the stator, the central portion of the rotor core 2 was irradiated with CrKα characteristic X-rays having a wavelength of 0.2291 nm, and the axial surface stress 5 and the circumferential surface stress 6 were measured. The diffraction surface was the (211) plane.

  Table 1 shows the measurement results of stray load loss and surface stress in Examples and Comparative Examples of the present invention. The stray load loss is a value at 200 V / 50 Hz. When the surface stress value is positive, tensile stress is applied, and when it is negative, compressive stress is applied.

[Table 1]

  Examples 1 to 5 and Comparative Example 2 are measurement results when surface heating is performed using a high-frequency induction heating power source with a frequency of 23 kHz and 10 kW. From induction heating A of Example 1 to induction heating of Comparative Example 2 It is the result of testing by increasing the heating time in the order of F. Specifically, the heating time was increased to 75, 100, 150, 200, 250, and 300 seconds in the order of induction heating A to F, and the influence of the heating time was evaluated.

  FIG. 2 is a schematic diagram of induction heating used for heating the rotors of Examples 1 to 5 and Comparative Example 2. A solenoid coil-shaped induction coil 7 was arranged around the rotor 1 and heated by flowing a high-frequency current. The induction coil 7 is made of a copper tube and is water-cooled when energized.

Example 6 and Comparative Example 3 are the results of applying the flame heating method to the surface heating of the rotor. As the flame, an acetylene and oxygen mixed burner flame was used. In the flame heating A of Example 6, the oxygen pressure was 2.5 kg / cm ^2, and in the flame heating B of Comparative Example 3, the oxygen pressure was 5.0 kg / cm 2. ² . The flow rate of the acetylene gas was adjusted so that the flame state shows the optimum shape at the oxygen pressure.

  Example 7 is the result of heating the surface of the rotor by fluidized bed heating in which high temperature gas was blown into the alumina powder and heat treated. The temperature of the alumina fluidized bed was 600 ° C., and the immersion time of the rotor was 1 minute.

  Comparative Example 1 is a general rotor in which the outer periphery of the rotor core is machined but not heat-treated thereafter. In the present invention, the presence / absence of the effect was determined by the increase / decrease from the stray load loss based on Comparative Example 1. And the quality of the rotor heating effect was determined by the difference in stray load loss with this rotor.

  As can be seen from Table 1, the surface of the rotor is heat-treated, so that the surface stress is relaxed from the machining state of the outer periphery of the rotor core of Comparative Example 1, the stress level is lowered, and accordingly, the stray load loss is lowered. .

  FIG. 3 is a photomicrograph showing the metal structure of the outer periphery of the machined rotor core of Comparative Example 1 that has not been heat-treated. The figure shows the structure in the vicinity of the machined outer peripheral surface 11. The cutting tool cutting edge in machining moves from the left to the right in FIG. 3 to cut the rotor core surface. In FIG. 3, the presence of recrystallized grains 12, which is the initial structure of the electromagnetic steel sheet of the core material, is clearly observed in a region that is about 100 μm in the radial direction from the outer peripheral surface of machining, and the influence of machining on the outer periphery of the core is affected. It turns out that it does not reach. On the other hand, the shear band generated by the cutting process is clearly observed just below the outer peripheral machined surface in the radial direction, and the residual plastic strain can be easily understood.

  On the other hand, considering that the penetration depth of X-rays in the X-ray stress measurement used in the present invention is several μm, it can be understood that the surface stress in Table 1 is a stress value corresponding to plastic strain ( In X-ray stress measurement, strain is basically measured.)

Here, assuming that plastic strains in the circumferential direction, the axial direction, and the radial direction are ε _θ , ε _Z , and ε _r , the relationship of the following expression 1 is approximately established between the plastic strains.

ε _θ + ε _z + ε _r = 0 (1)
From this equation, if the plastic strain in the circumferential direction and the plastic strain in the axial direction are large with positive values, the plastic strain in the radial direction is large with negative values. As described above, since the presence of surface stress is synonymous with the presence of strain, the plastic strain ε _r in the core radial direction in the region immediately below the core outer peripheral machining surface due to axial stress or circumferential stress on the core surface. The level is reduced by the heat treatment of the embodiment from the machined initial state. Here, if the stress on the core surface is a positive value, the strain in the core radial direction is a negative value, and the plastic strain in the core radial direction is a strain in the compression direction.

  By the way, it is known that the magnetic steel sheet of the core material has a significant decrease in magnetic permeability due to the action of compressive strain (stress) (see Non-Patent Document 1). Further, under the influence of a slot or the like provided in the stator core, harmonic magnetic flux is generated in the gap between the stator and rotor of the motor (see Non-Patent Document 2). This eddy current loss due to the harmonic magnetic flux contributes to stray load loss, and the results obtained in the examples and comparative examples of the present invention are explained mainly from the relationship between the magnetic permeability of the rotor core and the eddy current due to the harmonic magnetic flux. obtain.

  FIG. 4 shows the relationship between the relative magnetic permeability and stress of the electromagnetic steel sheet cited from Non-Patent Document 1. The horizontal axis represents applied stress, a positive value indicates tensile stress, and a negative value indicates compressive stress. It can be seen that the magnetic permeability rapidly decreases due to the action of the compressive stress. In the figure, graphs of magnetic flux density B of 0.5T, 1.0T, and 1.5T are shown.

  The penetration depth δ of the harmonic magnetic flux is expressed by the following formula 2, where the frequency of the harmonic magnetic flux is f, the specific resistance of the core material is ρ, and the magnetic permeability is μ.

δ = (ρ / πfμ) ^1/2 (2)
From this equation, as the magnetic permeability μ increases, the penetration depth δ of the harmonic magnetic flux decreases.

  The magnetic permeability in the radial direction is restored with a reduction in the radial compressive strain on the outer periphery of the rotor core. Accordingly, the harmonic magnetic flux in the radial direction is less likely to penetrate into the rotor core. The rotor core of the induction motor used in the examples and comparative examples of the present invention has a closed slot shape as described above, and a core material is interposed between the rotor outermost peripheral surface and the rotor bar. When the radial compressive strain on the outer periphery of the rotor core is large and the permeability in the radial direction of the rotor core is low, the harmonic magnetic flux in the radial direction is likely to permeate and pass through the core interposed between the outermost peripheral surface of the rotor and the rotor bar and reach the rotor bar. It is fully conceivable. In this case, an eddy current due to the harmonic magnetic flux flows in the rotor bar having a low electric resistance, and the loss increases.

  If the radial harmonic magnetic flux becomes difficult to penetrate into the rotor core along with the reduction of the radial compressive strain on the outer periphery of the rotor core, the eddy current due to the harmonic magnetic flux only flows in the core interposed between the rotor outermost peripheral surface and the rotor bar. Loss is reduced.

As the plastic strain is released by the surface heating, the axial surface stress turns into a compressive stress state as in Comparative Examples 2 and 3. Although this phenomenon is presumed to be caused by a complex stress state in the radial direction that exists during machining, the axial permeability decreases with the compression stress (compression strain) in the axial direction.
As described above, the rotor core of the induction motor used in the examples and comparative examples of the present invention is skewed. By being skewed, a fundamental magnetic flux distribution is generated in the rotor axial direction, and a fundamental iron loss included in the stray load loss is generated. When the axial compressive stress acts, the magnetic permeability decreases, the degree of axial magnetic flux distribution due to skew increases, and the fundamental wave iron loss increases. Therefore, it is preferable that the axial surface stress takes a positive value.

  Regarding the circumferential surface stress, if a compressive stress acts in the circumferential direction and the circumferential permeability of the rotor core surface decreases, the circumferential harmonic magnetic flux passes through the rotor bar. As in the case of the magnetic flux, an eddy current is generated in the aluminum rotor bar and the loss increases, which is not preferable. Therefore, it is preferable that the circumferential surface stress has a positive value.

  FIG. 5 shows the surface stress state at each point in the examples and comparative examples in the present invention. From each example, it can be seen that the stress range 21 shown in FIG. 5 is a surface stress state effective for reducing stray load loss. That is, it is an effective range for reducing the free play load loss when the circumferential surface stress of the rotor outer circumferential surface is in the range of 0 to 700 MPa and the axial surface stress is in the range of 0 to 200 MPa. .

  FIG. 6 shows the relationship between the axial surface stress and the stray load loss measurement value of the examples and comparative examples of the present invention. FIG. 6 shows the existence of the axial surface stress condition that provides the minimum stray load loss. This is considered to be due to the influence of the axial fundamental wave magnetic flux distribution due to the skew. From FIG. 6, the axial surface stress on the outer peripheral surface of the rotor is more preferably in the range of 15 to 170 MPa where the stray load loss is 55 W or less. From the data in Table 1, the circumferential surface stress on the outer circumferential surface of the rotor is more preferably in the range of 80 to 630 MPa where the stray load loss is 55 W or less.

A method for manufacturing the rotor (rotor) of the present invention will be described below.
A rotor core (rotor core) is formed by laminating soft magnetic thin plates such as electromagnetic steel plates, and a rotor bar and a shaft are attached.
Next, in order to provide a predetermined gap between the rotor and the stator, machining such as cutting is performed on the outer periphery of the rotor core.
Next, the surface of the rotor core is heat-treated, and the surface stress on the outer peripheral surface of the rotor is in a predetermined range (circumferential surface stress is in the range of 0 to 700 MPa and axial surface stress is in the range of 0 to 200 MPa). The surface is heated so that As a method for heating the surface of the rotor, induction heating, flame heating, fluidized bed heating, or the like described in the above embodiments can be used. By adjusting the heating intensity and the heating time, the surface stress can be controlled within the predetermined range.

  In the embodiment of the present invention, as a method for heating the rotor surface. Although the effect was verified using three methods of induction heating, flame heating, and fluidized bed heating, molten salt heating, laser heating, and plasma heating methods can be applied in addition to these heat treatment methods.

  In the present embodiment, the induction motor (IM motor) has been described as an example. However, the present invention can be used for other types of motors such as a permanent magnet motor (PM motor).

  According to this embodiment, in the rotor of a rotating electrical machine in which the rotor iron core is formed of a laminate of soft magnetic thin plates and the outer peripheral surface thereof is machined, the circumferential surface stress of the rotor outer peripheral surface is subjected to surface heat treatment. Is within the range of 0 to 700 MPa and the axial surface stress is within the range of 0 to 200 MPa, a high-efficiency motor with reduced stray load loss can be provided.

DESCRIPTION OF SYMBOLS 1 Rotor 2 Rotor core 3 End ring 4 Shaft 5 Axial surface stress 6 Circumferential surface stress 7 Induction heating coil 11 Outer peripheral machined surface 12 Crystal grain 21 Effective surface stress region

Claims (10)

The rotor iron core is a rotating electrical machine using a rotor formed of a laminate of soft magnetic thin plates, the outer peripheral surface of which is machined, and subjected to surface heat treatment,
A rotating electrical machine wherein a circumferential surface stress of a rotor outer peripheral surface is in a range of 0 to 700 MPa and an axial surface stress is in a range of 0 to 200 MPa. In the rotating electrical machine according to claim 1,
A rotating electric machine using an induction heating-treated rotor as the rotor subjected to the surface heat treatment. In the rotating electrical machine according to claim 1,
A rotating electric machine using a rotor subjected to flame heating treatment as the rotor subjected to the surface heat treatment. In the rotating electrical machine according to claim 1,
A rotating electrical machine using a fluidized bed heat-treated rotor as the rotor subjected to the surface heat treatment.   The rotating electrical machine according to any one of claims 1 to 4, wherein the rotating electrical machine is an induction motor or a permanent magnet motor. Machining the outer peripheral surface of the rotor core formed of a laminate of soft magnetic thin plates;
Heat treating the surface of the outer peripheral surface of the rotor core so that the circumferential surface stress of the rotor outer peripheral surface is in the range of 0 to 700 MPa and the axial surface stress is in the range of 0 to 200 MPa;
The manufacturing method of the rotor of a rotary electric machine provided with. In the manufacturing method of the rotor of the rotating electrical machine according to claim 6,
A method of manufacturing a rotor of a rotating electrical machine, wherein induction heating is used as a heat treatment method of the outer peripheral surface of the rotor core. In the manufacturing method of the rotor of the rotating electrical machine according to claim 6,
A method of manufacturing a rotor of a rotating electrical machine, wherein flame heating is used as a heat treatment method of the outer peripheral surface of the rotor core. In the manufacturing method of the rotor of the rotating electrical machine according to claim 6,
A method for manufacturing a rotor of a rotating electrical machine, wherein fluidized bed heating is used as a heat treatment method for the outer peripheral surface of the rotor core. In the manufacturing method of the rotor of the rotating electrical machine according to any one of claims 6 to 9,
A method of manufacturing a rotor of a rotating electrical machine, wherein the rotating electrical machine is an induction motor or a permanent magnet motor.

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