JP2011114950A - Motor core - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor core capable of effectively reducing deterioration in iron loss, even when used while a compressive stress is applied from the outer periphery of the core. <P>SOLUTION: The motor core has a stator comprising a laminate of electromagnetic steel plates, which has teeth and a back yoke, and is imparted with a compressive stress of ≥10 MPa to the circumferential direction of the stator. In the motor core, the compressive stress of ≥0.3 MPa is imparted in the laminate direction of the back yoke, and the thickness of an insulation coating of the electromagnetic steel plates is set at ≥0.4 μm and ≤10 μm per one surface when the insulation coating is applied on both surfaces of the steel plate, and at ≥0.8 μm and ≤20 μm per one surface when the insulation coating is applied on only one surface of the steel plate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a motor core, and particularly intends to effectively reduce deterioration of core iron loss, which is a concern when a compressive force is applied from the outer periphery of the core.

The compressor motor of a home air conditioner is operated at variable speed, the maximum frequency is about 200-400Hz, and it is used with a carrier frequency of several kHz superimposed by PWM (Pulse Width Modulation) control etc. Yes.
In addition, drive motors and generators of hybrid electric vehicles that have been rapidly spreading recently are also driven at a frequency of several kHz from the viewpoint of high output and miniaturization.

  Non-oriented electrical steel sheets used as the core material of such motors are required to have low high-frequency iron loss, and high-grade electrical steel sheets with a (Si + Al) content of about 3 to 4% by mass are used. Has been.

By the way, in compressor motors, shrink fitting is applied for core fastening, so the motor core is used in a state where a compression force of about 100 MPa is applied from the outer periphery thereof. Moreover, since the resin mold etc. are given also to the drive motor of hybrid EV (Electric Vehicle), compression force will be added to the motor core from the outer periphery.
However, it is known that the magnetic properties of the electrical steel sheet are greatly deteriorated under such compressive stress.

For example, Patent Document 1 discloses that Si: 2.6 to 4%, specific resistance: 50 to 75 × 10 ⁻⁸ Ωm, and crystal grain size: 60 to 165 μm are provided to improve the iron loss characteristics under compressive stress. A grain-oriented electrical steel sheet is disclosed.

Japanese Patent No. 4023183

  However, even if the material disclosed in Patent Document 1 is used, the amount of improvement in the iron loss deterioration allowance due to the application of compressive force from the outer periphery of the core is not significantly greater than that of the conventional material. There is a need for a technique for suppressing the deterioration of loss.

  The present invention advantageously responds to the above-described demand, and an object of the present invention is to propose a motor core that can effectively reduce the deterioration of iron loss even when used in a state where a compression force is applied from the outer periphery of the core. And

Now, the inventors have intensively studied to solve the above problems, and by applying a compressive force in the motor core laminating direction, compression in the circumferential direction of the stator added during shrink fitting or the like. The present inventors have obtained knowledge that the deterioration of iron loss due to stress can be effectively reduced, and that the thickness of the insulating coating of the magnetic steel sheet to be used is effective for further suppressing the deterioration of iron loss.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
In a motor core having a stator composed of a laminate of electromagnetic steel sheets having a tooth portion and a back yoke portion, and applying a compressive stress of 10 MPa or more in the circumferential direction of the stator, 0.3 MPa in the lamination direction of the back yoke In addition to applying the above compressive stress, the thickness of the insulating coating of the electrical steel sheet is 0.4 μm or more and 10 μm or less per side when the insulating coating is applied to both sides of the steel plate, and the insulating coating is applied only to one side of the steel plate. If it is, a motor core characterized by being 0.8 μm or more and 20 μm or less per side.

According to the present invention, a motor core having a low iron loss can be obtained even in a use state in which a compressive stress is applied in the circumferential direction of the stator.
Accordingly, by using the motor core of the present invention, an air conditioner compressor motor in which a compression force is applied to the core material by shrink fitting, resin molding, etc., a hybrid EV drive motor, an EV drive motor, an FCEV drive motor, a high speed In a generator or the like, the iron loss can be reduced.

It is the figure which showed the point which gives the compressive stress to the lamination direction of a back yoke and the state where the compression force was added to the motor core from the outer periphery. It is the figure which showed the relationship between the compressive stress of the circumferential direction of a stator core, and an iron loss. It is the figure which showed the relationship between the compressive stress of a lamination direction, and an iron loss. It is the figure which showed the relationship between the insulation film thickness of an electromagnetic steel plate surface, and an iron loss.

The elucidation process of the present invention will be described below.
In an air conditioner compressor motor for home appliances or a motor for a hybrid electric vehicle, a shrink fit of the housing or press-fitting into the housing is performed to fix the core. The compressive stress applied to the motor core by shrink fitting or press fitting is said to be about 20 to 150 MPa, and a technique for suppressing iron loss deterioration under such compressive stress has been desired.

  First, the inventors conducted a detailed study on the iron loss characteristics under such compressive stress, and found that not only hysteresis loss but also eddy current loss increases due to the compressive stress. Hybrid EV motors and air-conditioner compressor motors are not only driven in the high frequency range, but are also controlled by the inverter, so harmonics of several kHz are added, so iron loss deterioration due to eddy current loss can be suppressed. It becomes important.

  Thus, the inventors examined the cause of this eddy current loss degradation. When compression stress is applied to the stator core (motor core), the magnetism is magnetized in the direction of the surface of the electrical steel sheet constituting the core in order to mitigate it. When the vector is oriented and magnetized in this state, an eddy current flows in the plate surface, and it has become clear that this is the cause of iron loss deterioration.

  Therefore, the inventors further consider that it is important from the viewpoint of suppressing eddy current loss that the magnetization vector is directed in the direction of the plate surface of the electromagnetic steel sheet. I came up with the idea of applying stress in the direction.

In order to verify the above idea, a 12-slot stator core was manufactured by punching using a 3 mass% Si steel plate having a thickness of 0.35 mm. Here, the stator outer diameter was 100 mm, and the stacking thickness was 60 mm.
Subsequently, the core was shrink-fitted with a shrinkage allowance of 5 to 50 μm. At that time, when the compressive stress in the circumferential direction of the central portion of the core back was measured using a strain gauge, the compressive stress in the circumferential direction (shrink fit stress) was 5 to 50 MPa.
Next, in order to apply a compressive stress in the stacking direction, as shown in FIG. 1, a ring 2 made of nonmagnetic stainless steel is attached to the back yoke portion 1, and this ring 2 is tightened in the core stacking direction with a hydraulic press. Various compressive forces were applied. The compression force at that time was measured by sandwiching a pressure sensitive paper between the ring and the stator core. In FIG. 1, reference numeral 3 denotes a tooth portion and 4 denotes a shrink-fitting ring (housing).

FIG. 2 shows the result of examining the influence of the circumferential compressive stress of the stator core on the core iron loss. The iron loss of the stator core was measured by measuring the iron loss in the circumferential direction of the stator core by winding an excitation coil and a pickup coil from above the nonmagnetic material of the back yoke portion.
As shown in the figure, it was confirmed that when the compressive stress from the outer periphery of the core is 10 MPa or more, the deterioration of the iron loss becomes remarkable.

FIG. 3 shows a motor core having a shrink fit stress (circumferential compressive stress) of 30 MPa and a motor core not subjected to such shrink fit when compressive force is applied in the stacking direction (plate thickness direction). The result of investigating the relationship between applied stress and core iron loss is shown.
As is clear from the figure, there was almost no change in iron loss even when compressive force was applied in the stacking direction when shrink fitting was not performed, but in the stacking direction when shrink fitting was performed. It can be seen that the iron loss is greatly improved by applying the compressive force. In particular, it was found that the improvement allowance was large when the applied stress was 0.3 MPa or more.
Therefore, in the present invention, the compressive stress in the stacking direction is set to 0.3 MPa or more, more preferably 0.5 MPa or more, and further preferably 3 MPa or more. However, if the compressive stress applied in the stacking direction is too large, there is a risk of adverse effects such as core deformation. Therefore, the applied stress is preferably 100 MPa or less.

Here, the compressive stress in the plate thickness direction is an average stress of the back yoke to which shrink fit stress is applied, and is preferably applied uniformly over the entire back yoke.
And, any method may be used as a method of applying the compressive force in the plate thickness direction. For example, as described above, a ring-shaped contact plate is applied to both ends of the motor core, and the contact plate is tightened with a bolt or the like. And a method of welding the end face of the core in a state in which a compressive force in the stacking direction is applied to the core with a press or the like.

Even in the conventional motor core, a compressive force may be applied in the stacking direction by caulking or the like, but the compressive stress in that case is as small as about 0.2 MPa or less, and this technique is a shrink fit stress. It is not intended to suppress the iron loss deterioration caused by the above, but simply intended to fix the core.
Also, there are motor cores that are fixed by bolting, and compression force may be applied in the stacking direction, but the compression force by bolting is only in the vicinity of the bolt, and the back yoke where the magnetic flux mainly flows The compressive force is hardly acting. In addition, it has not been conventionally performed to shrink fit the motor core fixed by bolt tightening, and the purpose of the bolt tightening is not to suppress characteristic deterioration caused by shrink fit stress.

Next, the influence of the insulating coating on the surface of the electromagnetic steel sheet on the iron loss of the motor core was investigated.
As shown in Fig. 1, a semi-organic film with a coating thickness of 0.2 to 1.2 µm was applied to both sides of a 3 mass% Si steel plate with a thickness of 0.35 mm to produce a stator core with an outer diameter of 100 mm. FIG. 4 shows the result of investigating the relationship between the thickness of the insulating coating on the steel sheet surface and the iron loss after manufacturing the motor core. The compressive stress in the circumferential direction was 30 MPa, and the applied stress in the stacking direction was 3 MPa.
As shown in the figure, the effect of the insulation film thickness on the iron loss was not observed when no compressive force was applied in the stacking direction, but when the compressive stress of 3 MPa was applied, the insulation film thickness It can be seen that the iron loss increases when is less than 0.4 μm. This is considered that the end face is easily short-circuited when a compressive force is applied. Therefore, the insulating film thickness is 0.4 μm or more per side, preferably 0.8 μm or more. On the other hand, when the insulation film thickness exceeds 10 μm, the space factor is remarkably lowered and the motor efficiency is lowered.
Therefore, the insulation film thickness on the surface of the electromagnetic steel sheet is 0.4 μm or more and 10 μm or less per side (0.8 μm or more and 20 μm or less in total on both sides).

  Any method can be used to adjust the insulation film thickness of the steel sheet, but the film thickness can be controlled by controlling the rotational speed of the roll coater and changing the amount of the liquid film to be scraped. Is advantageous. Moreover, although it is preferable to provide an insulating film on both surfaces, according to the objective, you may form a film only in one side. In that case, for the same reason as that applied to both sides, the insulating film thickness on the surface of the electromagnetic steel sheet is set to 0.8 μm or more and 20 μm or less per side.

A 12-slot stator core was punched with a 5% clearance mold from a material containing 3% by mass of Si and having an insulating coating on both sides of a non-oriented electrical steel sheet having a thickness of 0.35 mm. Here, the stator outer diameter was 100 mm, and the stacking thickness was 60 mm. The stator core thus obtained was shrink-fitted at a shrinkage allowance of 0 to 50 μm. At that time, the compressive stress in the circumferential direction at the center of the core back was measured using a strain gauge. Next, to apply compressive force in the stacking direction, as shown in FIG. 1, a ring made of nonmagnetic stainless steel is attached to the back yoke, and the compressive force is changed by tightening the ring in the core stacking direction with a hydraulic press. I let you. The compressive stress at that time was measured by sandwiching a pressure sensitive paper between the ring and the stator core.
Table 1 shows the results of examining the iron loss W _{10 / 1k} (W / kg) of the stator core thus obtained.

  Also, using this stator core, a stator outer diameter: 100 mm, rotor outer diameter: 70 mm, stacking thickness: 60 mm, an 8-pole, 12-slot embedded internal magnet motor (IPM motor), and torque and rotation speed Table 1 also shows the results of measurement of the maximum motor efficiency when various changes are made. Table 1 also shows the insulation film thickness (per one surface) on the steel sheet surface, shrink fit stress (circumferential compressive stress), and compressive stress applied in the stacking direction.

  As apparent from the table, according to the present invention, a compressive stress of 0.3 MPa or more is applied in the stacking direction of the back yoke (the steel plate thickness direction), and the insulation film thickness on the steel plate surface is in the range of 0.4 to 10 μm ( It can be seen that the iron loss deterioration due to shrink-fit stress can be reduced by setting the total of both surfaces to a range of 0.8 μm to 20 μm.

1 Back yoke part 2 Ring 3 Teeth part 4 Shrink fit ring (housing)

Claims (1)

  In a motor core having a stator composed of a laminate of electromagnetic steel sheets having a tooth portion and a back yoke portion, and applying a compressive stress of 10 MPa or more in the circumferential direction of the stator, 0.3 MPa in the lamination direction of the back yoke In addition to applying the above compressive stress, the thickness of the insulating coating of the electrical steel sheet is 0.4 μm or more and 10 μm or less per side when the insulating coating is applied to both sides of the steel plate, and the insulating coating is applied only to one side of the steel plate If it is, a motor core characterized by being 0.8 μm or more and 20 μm or less per side.

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