Stator, electric motor, compressor, refrigerating and air conditioning apparatus, and method for manufacturing stator

A stator includes a yoke portion, and a tooth portion located inside the yoke portion in a radial direction. A fracture surface ratio of an inner surface of the tooth portion in the radial direction is lower than a fracture surface ratio of a side surface of the yoke portion.

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. national stage application of International Patent Application No. PCT/JP2017/017652 filed on May 10, 2017, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a stator for an electric motor.

BACKGROUND

An electric motor such as an interior permanent magnet motor including a rotor and a stator is generally used. In the interior permanent magnet motor, magnetic flux from the rotor flows into the distal end of a tooth portion in the radial direction to form a magnetic circuit. Accordingly, the tooth portion contributes to the efficiency of the electric motor more than a yoke portion. The stator is formed of a plurality of sheets such as electrical steel sheets stacked in the axial direction of the axis of rotation of the rotor. It is a common practice to form the sheet such as an electrical steel sheet using press working (more specifically, blanking) from the viewpoint of cost and ease of machining (see, for example, patent reference 1).

PATENT REFERENCE

Patent Reference 1: Japanese Patent Application Publication No. 2008-228442

When, however, the sheet is formed by press working, the contour of the sheet exhibits a fracture surface. In this case, since a shear stress has occurred on the fracture surface due to factors associated with press working, the magnetic characteristics of the sheet have degraded. In the stator, especially the tooth portion contributes to the efficiency of the electric motor more than the yoke portion. To enhance the efficiency of the electric motor, therefore, it is desired to improve the magnetic characteristics of the tooth portion.

SUMMARY

It is an object of the present invention to enhance efficiency of an electric motor.

In accordance with an aspect of the present invention, a stator includes a yoke portion, and a tooth portion located inside the yoke portion in a radial direction, wherein at least a part of an inner surface of the tooth portion in the radial direction is a surface formed by etching, and a fracture surface ratio of the inner surface is lower than a fracture surface ratio of a side surface of the yoke portion.

In accordance with another aspect of the present invention, a stator includes a yoke portion, and a tooth portion located inside the yoke portion in a radial direction, wherein a fracture surface ratio of an inner surface of the tooth portion in the radial direction is lower than a fracture surface ratio of side surfaces of the yoke portion, the fracture surface ratio of the inner surface is a ratio of an area of a fracture surface formed on the inner surface to a total area of a distal end of the tooth part, and the fracture surface ratio of the side surfaces of the yoke portion is a ratio of an area of a fracture surface formed on the side surfaces to a total area of the side surfaces.

According to the present invention, efficiency of an electric motor can be enhanced.

DETAILED DESCRIPTION

FIG. 1is a sectional view schematically illustrating the internal structure of an electric motor1including a stator2according to Embodiment 1 of the present invention.

An arrow D1indicates the direction (to be referred to as the “circumferential direction” hereinafter) along the outer circumference of each of the stator2, a stator core2a, and a rotor3. In an x-y-z orthogonal coordinate system illustrated in each drawing, the z-direction (z-axis) indicates a direction (to be referred to as the “axial direction” hereinafter) parallel to an axis A1(that is, the center of rotation of the rotor3) of a shaft (a shaft32; to be described later) of the electric motor1, the x-direction (x-axis) indicates a direction perpendicular to the z-direction, and the y-direction (y-axis) indicates a direction perpendicular to both the z- and x-directions.

The electric motor1includes the stator2and the rotor3. In the example illustrated inFIG. 1, the electric motor1further includes a frame4(also called a housing, a shell, or a motor frame). The electric motor1is designed as, for example, an interior permanent magnet motor.

The stator2includes a stator core2aformed in an annular shape, and windings27wound around the stator core2a. The stator2is formed in an annular shape in the circumferential direction about the axis A1(that is, the center of rotation of the rotor3). The rotor3is rotatably provided inside the stator2. A 0.3- to 1-mm air gap is formed between the inner surface of the stator2and the outer surface of the rotor3. When a current is supplied from an inverter to the windings27of the stator2, the rotor3rotates. The current supplied to the windings27has its frequency synchronized with a commanded rotation speed.

The stator2(more specifically, the stator core2a) is held by the frame4. For example, the stator2(more specifically, the stator core2a) is fixed to the frame4by press fitting or shrinkage fitting.

The stator2includes a plurality of divided core portions25a. In the example illustrated inFIG. 1, the plurality of divided core portions25aare arranged in an annular shape in the circumferential direction about the axis A1to form the stator2.

FIG. 2is a plan view schematically illustrating the structure of the stator core2a.

The stator core2aincludes at least one yoke portion21aand at least one tooth portion22a. The stator core2ais formed of a plurality of stator cores20adivided (to be also referred to as the “divided stator cores20a” hereinafter). Therefore, each divided stator core20aincludes the yoke portion21aand the tooth portion22a.

Note, however, that the stator2need not always be formed of the plurality of divided stator cores20a. The stator core2amay be formed by, for example, stacking a plurality of annular materials (for example, electrical steel sheets or amorphous materials such as amorphous metals).

In the stator core2a, the yoke portion21aof one divided stator core20ais connected to the yoke portion21aof another divided stator core20aadjacent to the former, as illustrated inFIG. 2. A region surrounded by the two yoke portions21aand the two tooth portions22aserves as a slot portion26.

A plurality of slot portions26are equidistantly formed in the circumferential direction. In the example illustrated inFIG. 2, nine slot portions26are formed in the stator core2a.

The stator core2aincludes a plurality of tooth portions22a, which are adjacent to each other with the slot portions26in between, as illustrated inFIG. 2. Therefore, the plurality of tooth portions22aand the plurality of slot portions26are alternately arranged in the circumferential direction. The arrangement pitches of the plurality of tooth portions22ain the circumferential direction (that is, the widths of the slot portions26in the circumferential direction) are equal.

FIG. 3is a sectional view schematically illustrating the structure of the divided core portion25a.

Each divided core portion25aincludes a yoke portion21a, a tooth portion22alocated inside the yoke portion21ain the radial direction, a winding27, and insulators24aand24binsulating the stator core2a. In this Embodiment, the yoke portion21aand the tooth portion22aare formed integrally, but a tooth portion22aformed separately from the yoke portion21amay be mounted on the yoke portion21a.

The winding27is wound around the stator core2awith the insulators24aand24bin between to form a coil for generating a rotating magnetic field. More specifically, the winding27is wound around the outer periphery of the tooth portion22a.

The winding27is, for example, a magnet wire. For example, the stator2has three phases, and the winding27(that is, the coil) is connected in Y-connection (also called star connection). The number of turns and the wire diameter of the winding27are determined in accordance with, for example, the rotation speed, the torque, and the voltage specification of the electric motor1, and the cross-sectional area of the slot portion26. The wire diameter of the winding27is, for example, 1.0 mm. The winding27is wound around each tooth portion22aof the stator core2aby, for example, 80 turns. However, the wire diameter and the number of turns of the winding27are not limited to these examples.

As the winding scheme of the windings27, concentrated winding is used. In, for example, a state before the divided stator cores20aare arranged in an annular shape (for example, the state in which the divided stator cores20aare arranged linearly), the windings27can be wound around the divided stator cores20a. The divided stator cores20a(that is, the divided core portions25a) having the windings27wound around them are folded in an annular shape and fixed together by welding or the like.

FIG. 4is a plan view schematically illustrating the structure of the divided stator core20a.

FIG. 5is a perspective view schematically illustrating the structure of the divided stator core20a.

The yoke portion21aextends in the circumferential direction, and the tooth portion22aextends inwards (in the −y-direction inFIG. 3) in the radial direction of the stator core2a. In other words, the tooth portion22aprojects from the yoke portion21atoward the axis A1. The tooth portion22aincludes a main body portion221aand a tooth top portion222a, as illustrated inFIGS. 4 and 5. The tooth top portion222ais formed at the distal end of the tooth portion22a(more specifically, the end of the main body portion221a) in the radial direction. In the example illustrated inFIGS. 4 and 5, the main body portion221ahas a uniform width along the radial direction. The tooth top portion222aextends in the circumferential direction, and is formed to stretch in the circumferential direction.

A fixing hole24cto fix the insulator24ais formed in the divided stator core20a(for example, the yoke portion21a), as illustrated inFIGS. 3 to 5.

The divided stator core20ais formed of at least one sheet28(also called a plate). In this Embodiment, the divided stator core20ais formed of a plurality of sheets28stacked in the axial direction (that is, the z-direction).

The sheets28are formed into a predetermined shape by press working (more specifically, blanking) first. The sheets28are, for example, electrical steel sheets. When electrical steel sheets are used as the sheets28, the thickness of the sheet28is, for example, 0.01 mm to 0.7 mm. In this Embodiment, the thickness of the sheet28is 0.35 mm. One sheet28is fastened by caulking24dto another sheet28adjacent to the former.

Generally, iron losses (that is, energy losses) such as a hysteresis loss and an eddy current loss occur in the stator core. The hysteresis loss is an energy loss caused when the magnetic domain of the stator core changes in magnetic field direction by an alternating magnetic field, and is theoretically proportional to the frequency of a change in magnetic flux occurring in the stator core. The eddy current loss is an energy loss caused by an eddy current generated in the stator core (for example, electrical steel sheets). Generally, an electric motor (for example, a brushless DC motor) controlled by an inverter is driven by high frequencies. Accordingly, the ratio of the eddy current loss to the iron loss occurring in the electric motor is higher than that of the hysteresis loss. The eddy current loss is theoretically proportional to the square of the frequency of a change in magnetic flux occurring in the stator core, and also proportional to the square of the thickness of each sheet (for example, each electrical steel sheet) of the stator core. To prevent an increase in iron loss, especially an increase in eddy current loss, therefore, it is effective to set the thicknesses of the sheets small.

The sheet28may be made of a material other than an electrical steel sheet and, for example, made of a nanocrystal material or an amorphous material such as an amorphous metal. When an amorphous material is used as the material of the sheet28, the thickness of the amorphous material is about 3% to 15% of an electrical steel sheet. For example, an electrical steel sheet having a thickness of about 0.2 mm to 0.5 mm is used as the material of the sheet28, while an amorphous material can be formed at a thickness of about 15 μm to 30 μm. Generally, since the eddy current loss gets lower in proportion to the square of the thickness of the sheet, the use of an amorphous material as the material of the sheet28makes it possible to prevent an increase in iron loss even if the electric motor1is operated at high frequencies.

When an amorphous material is used as the material of the sheet28, the iron loss density in the stator core2acan be kept low. In other words, the iron loss in the stator core2acan be kept from increasing. For example, the iron loss density of an electrical steel sheet is 1.2 W/kg (for a magnetic flux density of 1.0 T at 50 Hz), while the iron loss density of an amorphous material is 0.05 W/kg (for a magnetic flux density of 1.0 T at 50 Hz). Accordingly, the iron loss density of the amorphous material is far lower than that of the electrical steel sheet.

Generally, an amorphous material such as an amorphous metal has hardness (for example, Vickers hardness) three to six times that of an electrical steel sheet, and therefore exhibits poor workability. For example, the Vickers hardness of an electrical steel sheet is about 187 GN/m3, while the Vickers hardness of an amorphous material is about 900 GN/m3. Thus, since the hardness of the amorphous material is high, when the amorphous material is machined by press working, a high shear stress occurs in the amorphous material. When a high shear stress occurs in the amorphous material, the magnetic characteristics of the amorphous material significantly degrade. Again, since the hardness of the amorphous material is high, when the amorphous material is machined by press working, a working tool severely wears, and this increases the maintenance frequency (time) and the maintenance cost. For this reason, as a high hardness material such as an amorphous material, etching is more suitable than press working in terms of both magnetic characteristics and manufacture.

A broken line B1illustrated inFIG. 4represents the boundary between the yoke portion21aand the tooth portion22a. In this case, the fracture surface ratio of a tooth end surface222, that is, the inner surface of the tooth portion22ain the radial direction is lower than the fracture surface ratio of side surfaces211of the yoke portion21a.

The tooth end surface222is the distal end of the tooth portion22aand, more specifically, a portion, facing the rotor3, of the tooth portion22a. The fracture surface ratio of the tooth end surface222means the ratio of the area of a fracture surface formed on the tooth end surface222to the total area of the tooth end surface222, in the divided stator core20a.

The side surfaces211of the yoke portion21aare portions, other than the two end surfaces in the axial direction, of the outer surfaces of the yoke portion21a. The fracture surface ratio of the side surfaces211of the yoke portion21ameans the ratio of the area of fracture surfaces formed on the side surfaces211of the yoke portion21ato the total area of the side surfaces211, in the divided stator core20a.

The fracture surface means a surface formed by brittle fracture. In this Embodiment, the fracture surface is formed when the sheets28are machined using press working (more specifically, blanking).

In the stator2, since magnetic flux concentrates more on the tooth portion22athan on the yoke portion21a, the tooth portion22ais desirably etched. Accordingly, the magnetic characteristics of the etched portion is improved. In other words, the iron loss of the etched portion is reduced. Magnetic flux from the rotor3flows from the tooth end surface222and the tooth top portion222ainto the tooth portion22a(that is, the main body portion221a). Therefore, since the magnetic flux concentrates on the tooth top portion222a, especially on the tooth end surface222, the tooth top portion222aand the tooth end surface222are desirably etched.

In this Embodiment, at least a part of the tooth end surface222is a surface formed by etching. The entire tooth end surface222is desirably formed by etching. For example, after the sheets28are machined by blanking into a shape illustrated inFIG. 4, the tooth end surface222is formed by etching. A corrosion surface is formed by etching. More specifically, portions, other than the tooth end surface222, of the sheets28are formed by blanking, and the etched tooth end surface222is formed of a corrosion surface. Accordingly, the fracture surface ratio of the tooth end surface222is lower than the fracture surface ratio of the side surfaces211of the yoke portion21a. This improves the magnetic characteristics of the tooth end surface222.

During rotation of the rotor3, a magnetic field is formed so that magnetic flux concentrates on the upstream side of the tooth portion22ain the rotation direction of the rotor3. Therefore, etching is desirably performed on the upstream side of the tooth portion22ain the rotation direction of the rotor3. In this case, the side surface of the tooth portion22a(for example, the side surface of the main body portion221aand the side surface of the tooth top portion222a) on the upstream side in the rotation direction of the rotor3is desirably etched.

Upon etching, the dislocation density of the etched portion lowers. Accordingly, the dislocation density of the tooth end surface222of the tooth portion22ais lower than the dislocation density of the side surfaces211of the yoke portion21a. This improves the magnetic characteristics of the etched portion.

The yoke portion21amay even be formed by press working. The magnetic characteristics of the side surfaces211of the yoke portion21adegrade due to press working, but the yoke portion21acontributes to the efficiency of the electric motor1less than the tooth portion22a. Therefore, the use of press working makes it possible to machine the yoke portion21amore easily and to keep the manufacturing cost less than when the sheets28are machined using only etching.

FIG. 6is a view illustrating another example of the divided stator core20a.

The divided stator core20amay partially vary in composition. For example, in the divided stator core20a, the silicon concentration of the tooth portion22amay be higher than that of the yoke portion21a. In this case, the tooth portion22acontains more silicon than the yoke portion21a. In addition, in the tooth portion22a, desirably, the more the position lies to the inside in the radial direction, the higher the silicon concentration, as illustrated inFIG. 6. In the divided stator core20a, increasing the silicon concentration makes it possible to reduce the iron loss. In a portion having a highest silicon concentration, this concentration is 6%. In the example illustrated inFIG. 6, the silicon concentrations of the tooth top portion222aand the tooth end surface222are 6%. A high silicon concentration portion has high hardness, and is therefore more suited to etching than to press working.

The Vickers hardness of the tooth portion22ais higher than that of the yoke portion21a. For example, a high silicon concentration portion has high Vickers hardness, as described above. Increasing the Vickers hardness makes it possible to reduce the iron loss and, in turn, to enhance the efficiency of the electric motor1.

The structure of the rotor3will be described below.

FIG. 7is a sectional view schematically illustrating the structure of the rotor3.

The rotor3includes a rotor core31, a shaft32, at least one permanent magnet33, at least one magnet insertion hole34, at least one flux barrier35, at least one air hole36, and at least one slit38. The rotor3is rotatable about the axis A1. The rotor3is rotatably placed inside the stator2with the air gap in between. The axis A1serves as the center of rotation of the rotor3and as the axis of the shaft32.

In this Embodiment, the rotor3is designed as an interior permanent magnet rotor. A plurality of magnet insertion holes34are formed in the rotor core31in the circumferential direction of the rotor3. The magnet insertion holes34serve as voids in which the permanent magnets33are inserted. One permanent magnet33is inserted in each magnet insertion hole34. However, a plurality of permanent magnets33may be arranged in each magnet insertion hole34. The permanent magnets33inserted in the magnet insertion holes34are magnetized in the radial direction of the rotor3(that is, a direction perpendicular to the axis A1). The number of magnet insertion holes34corresponds to the number of magnetic poles on the rotor3. The positional relationships of the individual magnetic poles are uniform. In this Embodiment, the number of magnetic poles on the rotor3is 6. However, the number of magnetic poles on the rotor3need only be 2 or more.

The permanent magnet33uses, for example, a rare-earth magnet (to be referred to as an “Nd—Fe—B permanent magnet” hereinafter) containing neodymium (Nd), iron (Fe), and boron (B) as main ingredients.

The coercive force or coercivity of the Nd—Fe—B permanent magnet has the property of lowering depending on the temperature. When, for example, an electric motor using an Nd rare-earth magnet is used at high temperatures of 100° C. or more, as in a compressor, since the coercivity of the magnet deteriorates by about −0.5 to −0.6%/AK depending on the temperature, it is necessary to enhance the coercivity by adding Dy (dysprosium). The coercivity improves nearly in proportion to the Dy content. In a general compressor, since the upper limit of the ambient temperature of an electric motor is about 150° C., the electric motor is used in the range of temperature rise of about 130° C. with respect to 20° C. At, for example, a temperature coefficient of −0.5%/AK, the coercivity lowers by 65%.

Keeping demagnetization from occurring at the maximum load of the compressor requires a coercivity of about 1,100 to 1,500 A/m. To ensure the coercivity at an ambient temperature of 150° C., it is necessary to set the room temperature coercivity to about 1,800 to 2,300 A/m.

With no Dy being added to the Nd—Fe—B permanent magnet, the room temperature coercivity is about 1,800 A/m. To obtain a coercivity of about 2,300 kA/m, it is necessary to add about 2 wt % of Dy. Unfortunately, although adding Dy improves the coercivity characteristics, it degrades the residual magnetic flux density or remanence characteristics. When the remanence degrades, the magnet torque of the electric motor lowers, the supplied current increases, and the copper loss thus increases. It is, therefore, desired to keep the amount of added Dy less, in consideration of the efficiency of the electric motor.

The rotor core31is formed by stacking a plurality of electrical steel sheets. The thickness of each electrical steel sheet constituting the rotor core31is, for example, 0.1 mm to 0.7 mm. In this Embodiment, the thickness of each electrical steel sheet constituting the rotor core31is 0.35 mm. One electrical steel sheet of the rotor core31is fastened by caulking to another electrical steel sheet adjacent to the former.

At least one slit38is formed outside the magnet insertion hole34in the radial direction of the rotor3. In this Embodiment, a plurality of slits38are formed outside the magnet insertion hole34in the radial direction of the rotor3. Each slit38is elongated in the radial direction.

The shaft32is connected to the rotor core31. The shaft32is fixed by, for example, shrinkage fitting or press fitting to a shaft hole37formed in the rotor core31. With this arrangement, rotational energy generated by rotation of the rotor core31is transmitted to the shaft32.

The flux barriers35are formed at positions adjacent to the magnet insertion holes34in the circumferential direction of the rotor3. The flux barriers35reduce leakage magnetic flux. To prevent a short-circuit of the magnetic flux between adjacent magnetic poles, the distance between the flux barrier35and the outer surface (outer edge) of the rotor3is desirably small. The distance between the flux barrier35and the outer surface of the rotor3is, for example, 0.35 mm. The air holes36are designed as through holes. When, for example, the electric motor1is used for a compressor, a refrigerant can pass through the air holes36.

A method for manufacturing a stator2according to Embodiment 1 will be described below.

FIG. 8is a flowchart illustrating an exemplary process of manufacturing a stator2.

In step S1, the plurality of sheets28having a predetermined structure are formed. For example, the plurality of sheets28are formed into the shapes of the yoke portion21aand the tooth portion22aby press working (more specifically, blanking). However, the tooth portion22aneed not always be formed by press working. For, for example, the tooth portion22a, etching may be used to form the plurality of sheets28into the shape of the tooth portion22a. In this case, the yoke portion21aand the tooth portion22amay be formed in independent steps.

In step S2, the divided stator core20ais assembled. More specifically, the divided stator core20ais assembled by stacking the plurality of sheets28in the axial direction. The plurality of sheets28are stacked in the axial direction while, for example, being fastened together by caulking24d. The plurality of sheets28may be fixed by a method (for example, an adhesive) other than the caulking24d. When the electric motor1is used for a compressor, it is desired to use an adhesive resistant to heat and to a compressor refrigerant.

In step S3, etching is performed. More specifically, at least a part of the tooth end surface222of the tooth portion22ais formed by etching so that the fracture surface ratio of the tooth end surface222of the tooth portion22ais lower than the fracture surface ratio of the side surfaces211of the yoke portion21a. The entire tooth end surface222is desirably formed by etching. Not only the tooth end surface222, but also a portion including at least a part of the tooth top portion222amay be etched. In this case, etching is desirably performed on the upstream side of the tooth portion22ain the rotation direction of the rotor3. The processes in steps S2and S3may be performed in reverse order.

In etching, a resist is applied onto the sheets28, exposed to light, and developed to leave the resist in the shape of the sheets28. Any unnecessary resist is removed. A fracture surface is removed by corroding only a portion (that is, the tooth end surface222), which is not coated with the resist, using a corrosive chemical (more specifically, an etching solution). Etching is advantageous in terms of achieving a machining accuracy higher than that of press working, and generating no shear stress on a machined surface. Etching can prevent any shear stress, and, in turn, prevent degradation in magnetic characteristic, that is, deterioration in iron loss.

In step S4, the winding27is wound around the divided stator core20a. The winding27can be wound by, for example, the flyer scheme using a winding machine. The process in step S4is repeated to form the plurality of divided core portions25a. When insulators24aand24bare used, they are combined with the divided stator core20abefore the winding27is wound. The winding27is wound around the divided stator core20aequipped with the insulators24aand24b.

In step S5, the plurality of divided core portions25aare folded in an annular shape and fixed together by welding or the like.

With the above-mentioned processes, the stator2can be manufactured. The above-mentioned method for manufacturing the stator2may be applied to the manufacture of stators according to other embodiments (to be described later).

The effects of the stator2according to Embodiment 1 will be described below.

In the electric motor1, magnetic flux from the rotor3flows from the tooth end surface222and the tooth top portion222ainto the tooth portion22a(that is, the main body portion221a). Therefore, the magnetic characteristics of the tooth portion22a, especially those of the tooth end surface222and the tooth top portion222a, are directly relevant to the characteristics of the electric motor1, and thus contribute to the characteristics of the electric motor1more than the magnetic characteristics of other portions in the electric motor1. When the sheets28are formed by press working, a shear stress occurs in the sheets28. When a shear stress occurs in the sheets28, the magnetic characteristics of the sheets28degrade. In this Embodiment, the fracture surface ratio of the tooth end surface222is lower than the fracture surface ratio of the side surfaces211of the yoke portion21a. This improves the magnetic characteristics of the tooth end surface222. In other words, the iron loss of the tooth end surface222is reduced. As a result, the efficiency of the electric motor1can be enhanced.

In the divided stator core20a, when the silicon concentration of the tooth portion22ais higher than that of the yoke portion21a, the iron loss can be kept less. As described above, the magnetic characteristics of the tooth end surface222and the tooth top portion222aare directly relevant to the characteristics of the electric motor1, and thus contribute to the characteristics of the electric motor1more than the magnetic characteristics of other portions in the electric motor1. Accordingly, increasing the silicon concentrations of the tooth end surface222and the tooth top portion222amakes it possible to reduce the iron loss and, in turn, to enhance the efficiency of the electric motor1.

The electric motor1including the stator2according to Embodiment 1 has the above-mentioned effects. In the electric motor1, furthermore, since the permanent magnets33are magnetized in the radial direction of the rotor3(that is, a direction perpendicular to the axis A1), magnetic flux from the rotor3readily concentrates on the tooth top portion222aand the tooth end surface222. This makes it possible to enhance the efficiency of the electric motor1.

In the electric motor1, at least one slit38is formed outside the magnet insertion hole34in the radial direction of the rotor3. When the tooth end surface222is formed by etching, the portion formed by etching has fewer defects in its crystal structure than that formed by press working. Because of the fewer defects in the crystal structure, good magnetic characteristics are obtained, and especially the inductance (that is, the ease of passage of magnetic flux) thus improves. Generally, however, the higher the inductance, the stronger the magnetic attraction force produced by magnetic flux from the stator. This attraction force vibrates the rotor and therefore increases noise. In this Embodiment, since at least one slit38is formed outside the magnet insertion hole34in the radial direction of the rotor3, the inductance in the circumferential direction (also called the q-axis) lowers. This weakens the above-mentioned attraction force, so that the vibration of the rotor3and the noise in the electric motor1can be dampened.

With the method for manufacturing a stator2according to Embodiment 1, the stator2having the above-mentioned effects can be manufactured.

In this Embodiment, furthermore, the use of etching in the process of manufacturing a stator2allows the fracture surface ratio of the tooth end surface222to be lower than the fracture surface ratio of the side surfaces211of the yoke portion21a. This makes it possible to improve the magnetic characteristics of the tooth end surface222.

FIG. 9is a plan view schematically illustrating the structure of a divided stator core20bof a stator according to Modification 1.

FIG. 10is a perspective view schematically illustrating the structure of the divided stator core20bof the stator according to Modification 1.

The divided stator core20bof the stator according to Modification 1 includes a tooth portion22bhaving a structure different from that of the tooth portion22aof the divided stator core20aof the stator2according to Embodiment 1, and is the same as in Embodiment 1 in other respects. The divided stator core20bis applicable to the stator2according to Embodiment 1 in place of the divided stator core20a.

In the divided stator core20b, a yoke portion21aincludes at least one first sheet28a, and the tooth portion22bincludes at least one second sheet28b. In the example illustrated inFIG. 10, a plurality of first sheets28aare stacked in the axial direction, and a plurality of second sheets28bare also stacked in the axial direction. A broken line B1illustrated inFIG. 9represents the boundary between the yoke portion21aand the tooth portion22b. Therefore, the tooth portion22b(more specifically, a main body portion221a) includes parts of the first sheets28a, and the second sheets28b. A tooth top portion222ais formed of the second sheets28b.

The divided stator core20bis separated into a first portion231and a second portion232. In the divided stator core20b, a portion formed of the first sheets28ais defined as the first portion231. In the divided stator core20b, a portion formed of the second sheets28bis defined as the second portion232. The first portion231includes the yoke portion21a, and a part of the tooth portion22b. The second portion232is a part of the tooth portion22b.

The second sheets28b(that is, the second portion232) are mounted at the inner ends of the first sheets28a(that is, the first portion231) in the radial direction. For example, the second sheets28bare fixed to the first sheets28aby an adhesive.

The materials of the first sheet28aand the second sheet28bare different from each other. For example, the first sheet28ais made of an electrical steel sheet, and the second sheet28bis made of a nanocrystal material or an amorphous material such as an amorphous metal.

The second sheet28bis thinner than the first sheet28a. When an electrical steel sheet is used as the first sheet28a, the thickness of the first sheet28ais 0.20 mm to 0.50 mm. When an amorphous material is used as the second sheet28b, the thickness of the second sheet28bis 10 μm to 100 μm. A material as thin as the 10- to 100-μm-thick second sheet28bproduces a considerable effect of reducing the iron loss.

The stator according to Modification 1 can be manufactured in the same processes as the processes (FIG. 8) in the method for manufacturing a stator2according to Embodiment 1. For example, in step S1illustrated inFIG. 8, a plurality of first sheets28aand a plurality of second sheets28bare formed to have predetermined structures by blanking. When an amorphous material is used as the second sheet28b, a plurality of second sheets28bmay be formed to have a predetermined structure by etching instead of press working, in consideration of the ease of machining.

In step S2, a divided stator core20bis assembled. More specifically, a first portion231is assembled by stacking the plurality of first sheets28ain the axial direction. The plurality of first sheets28aare stacked in the axial direction while, for example, being fastened together by caulking24d. A second portion232is further assembled by stacking the second sheets28bin the axial direction. The plurality of second sheets28bare, for example, bonded together by an adhesive and stacked in the axial direction. The second portion232is attached to the first portion231. The second portion232is fixed to the first portion231by, for example, an adhesive. The processes subsequent to step S2are the same as the above-mentioned processes in steps S3to S5.

The stator according to Modification 1 has the same effects as those of the stator2according to Embodiment 1.

In Modification 1, furthermore, the tooth end surface222and the tooth top portion222aare formed of the second sheets28b(that is, the second portion232). Therefore, a material (for example, an amorphous material) excellent in magnetic characteristic can be used for a portion (for example, the second portion232) greatly affecting the characteristics of the electric motor1(for example, the efficiency of the electric motor). In particular, a material as thin as the 10- to 100-μm-thick second sheet28bproduces a considerable effect of reducing the iron loss. This makes it possible to reduce the iron loss in the second portion232. An electrical steel sheet that is an inexpensive material can be used for a portion (for example, the first portion231) having a small effect on the characteristics of the electric motor1(for example, the efficiency of the electric motor). As a result, the efficiency of the electric motor1can be enhanced, and the rise in cost of the electric motor1(more specifically, the stator) can be curbed.

FIG. 11is a plan view schematically illustrating the structure of a divided stator core20cof a stator according to Modification 2.

The divided stator core20cof the stator according to Modification 2 includes a tooth portion22chaving a structure different from those of the tooth portion22aof the divided stator core20aof the stator2according to Embodiment 1 and the tooth portion22bin Modification 1.

In the divided stator core20c, a first portion231includes a flat portion in contact with a second portion232, and the second portion232includes a flat portion in contact with the first portion231.

Other structures in the divided stator core20care the same as those in the divided stator core20bdescribed in Modification 1. The divided stator core20cis applicable to the stator2according to Embodiment 1 in place of the divided stator core20a.

The stator according to Modification 2 has the same effects as those of the stator according to Modification 1.

FIG. 12is a plan view schematically illustrating the structure of a divided stator core20dof a stator according to Modification 3.

The divided stator core20dof the stator according to Modification 3 includes a tooth portion22dhaving a structure different from those of the tooth portion22aof the divided stator core20aof the stator2according to Embodiment 1 and the tooth portion22bin Modification 1.

In the divided stator core20d, a first portion231includes a yoke portion21a, and a main body portion221aof the tooth portion22d, and a second portion232is a tooth top portion222aof the tooth portion22d.

Other structures in the divided stator core20dare the same as those in the divided stator core20bdescribed in Modification 1. The divided stator core20dis applicable to the stator2according to Embodiment 1 in place of the divided stator core20a.

The stator according to Modification 3 has the same effects as those of the stator according to Modification 1.

FIG. 13is a plan view schematically illustrating the structure of a divided stator core20eof a stator according to Modification 4.

The divided stator core20eof the stator according to Modification 4 includes a tooth portion22ehaving a structure different from those of the tooth portion22aof the divided stator core20aof the stator2according to Embodiment 1 and the tooth portion22bin Modification 1.

In the divided stator core20e, a first portion231includes a yoke portion21a, a main body portion221aof the tooth portion22e, and a part of a tooth top portion222aof the tooth portion22e, and a second portion232includes a part of the tooth top portion222aof the tooth portion22e. Therefore, the first portion231includes a part of a tooth end surface222, and the second portion232includes a part of the tooth end surface222. The second portion232may include the main body portion221aof the tooth portion22e.

Other structures in the divided stator core20eare the same as those in the divided stator core20bdescribed in Modification 1. The divided stator core20eis applicable to the stator2according to Embodiment 1 in place of the divided stator core20a.

The stator according to Modification 4 has the same effects as those of the stator according to Modification 1.

FIG. 14is a plan view schematically illustrating the structure of a divided stator core20fof a stator according to Modification 5.

The divided stator core20fof the stator according to Modification 5 includes a tooth portion22fhaving a structure different from those of the tooth portion22aof the divided stator core20aof the stator2according to Embodiment 1 and the tooth portion22bin Modification 1.

In the divided stator core20f, a second portion232is longer in the radial direction than the second portion232in Modification 4. A first portion231includes a yoke portion21a, a part of a main body portion221aof the tooth portion22f, and a part of a tooth top portion222aof the tooth portion22f, and the second portion232includes a part of the main body portion221aof the tooth portion22f, and a part of the tooth top portion222aof the tooth portion22f. Therefore, the first portion231includes a part of a tooth end surface222, and the second portion232includes a part of the tooth end surface222.

Other structures in the divided stator core20fare the same as those in the divided stator core20bdescribed in Modification 1. The divided stator core20fis applicable to the stator2according to Embodiment 1 in place of the divided stator core20a.

The stator according to Modification 5 has the same effects as those of the stator according to Modification 1.

FIG. 15is a plan view schematically illustrating the structure of a divided stator core20gof a stator according to Modification 6.

The divided stator core20gof the stator according to Modification 6 includes a tooth portion22ghaving a structure different from those of the tooth portion22aof the divided stator core20aof the stator2according to Embodiment 1 and the tooth portion22bin Modification 1.

In the divided stator core20g, a second portion232is located on the upstream side in the rotation direction of a rotor3. A first portion231includes a yoke portion21a, a part of a main body portion221aof the tooth portion22g, and a part of a tooth top portion222aof the tooth portion22g, and the second portion232includes a part of the main body portion221aof the tooth portion22g, and a part of the tooth top portion222aof the tooth portion22g. Therefore, the first portion231includes a part of a tooth end surface222, and the second portion232includes a part of the tooth end surface222.

Other structures in the divided stator core20gare the same as those in the divided stator core20bdescribed in Modification 1. The divided stator core20gis applicable to the stator2according to Embodiment 1 in place of the divided stator core20a.

The stator according to Modification 6 has the same effects as those of the stator according to Modification 1.

During rotation of the rotor3, magnetic flux concentrates on the upstream side of the tooth portion22ain the rotation direction of the rotor3. Therefore, in the stator according to Modification 6, since the second portion232is located on the upstream side in the rotation direction of the rotor3, the iron loss can be more effectively kept from increasing, and the efficiency of the electric motor1can thus be enhanced.

A compressor6according to Embodiment 2 of the present invention will be described below.

FIG. 16is a sectional view schematically illustrating the structure of the compressor6according to Embodiment 2.

The compressor6includes an electric motor60as an electric power element, a sealed or closed container61as a housing, and a compression mechanism62as a compression element. In this Embodiment, the compressor6is implemented as a rotary compressor. However, the compressor6is not limited to the rotary compressor.

The electric motor60is identical to the electric motor1equipped with the stator2according to Embodiment 1 (including the stator according to each Modification). In this Embodiment, the electric motor60is designed as an interior permanent magnet motor, but it is not limited to this.

The closed container61covers the electric motor60and the compression mechanism62. Freezer oil to lubricate the sliding portions of the compression mechanism62is stored at the bottom of the closed container61.

The compressor6further includes a glass terminal63fixed to the closed container61, an accumulator64, a suction pipe65, and a discharge pipe66.

The compression mechanism62includes a cylinder62a, a piston62b, an upper frame62c(first frame), a lower frame62d(second frame), and a plurality of mufflers62erespectively mounted on the upper frame62cand the lower frame62d. The compression mechanism62further includes a vane to separate the cylinder62ainto the suction and compression sides. The compression mechanism62is driven by the electric motor60.

The electric motor60does not include the frame4illustrated inFIG. 1. The stator2of the electric motor60is fixed in the closed container61by press fitting or shrinkage fitting, in place of the frame4. The stator2may be directly installed in the closed container61by welding instead of press fitting and shrinkage fitting.

Power is supplied to coils (for example, the windings27illustrated inFIG. 1) of the stator of the electric motor60via the glass terminal63.

A rotor (more specifically, a shaft32of a rotor3) of the electric motor60is rotatably held by the upper frame62cand the lower frame62dthrough bearing portions respectively provided on the upper frame62cand the lower frame62d.

The shaft32is inserted in the piston62b. The shaft32is rotatably inserted in the upper frame62cand the lower frame62d. The upper frame62cand the lower frame62dclose the end faces of the cylinder62a. The accumulator64supplies a refrigerant (for example, a refrigerant gas) to the cylinder62avia the suction pipe65.

The operation of the compressor6will be described below. The refrigerant supplied from the accumulator64is drawn by suction into the cylinder62afrom the suction pipe65fixed to the closed container61. As the electric motor60rotates by inverter power supply, the piston62bfitted to the shaft32rotates in the cylinder62a. With this operation, the refrigerant is compressed in the cylinder62a.

The refrigerant ascends in the closed container61through the mufflers62e. The compressed refrigerant is mixed with the freezer oil. As for the mixture of the refrigerant and the freezer oil, separation between the refrigerant and the freezer oil is accelerated in passing through the air holes36formed in the rotor core31, so that the freezer oil can be prevented from flowing into the discharge pipe66. In this way, the compressed refrigerant is supplied to the high-pressure side of a refrigeration cycle through the discharge pipe66.

As the refrigerant of the compressor6, R410A, R407C, or R22, for example, can be used. However, the refrigerant of the compressor6is not limited to these examples. As the refrigerant of the compressor6, a low-GWP (Global Warming Potential) refrigerant, for example, can be used.

As typical examples of the low-GWP refrigerant, the following refrigerants are available.

(1) An exemplary halogenated hydrocarbon having a carbon-carbon double bond in its composition is HFO-1234yf (CF3CF=CH2). HFO is an abbreviation of Hydro-Fluoro-Olefin. Olefin is an unsaturated hydrocarbon having only one double bond. The GWP of HFO-1234yf is 4.
(2) An exemplary hydrocarbon having a carbon-carbon double bond in its composition is R1270 (propylene). R1270 has a GWP of 3, which is lower than the GWP of HFO-1234yf, but R1270 is more flammable than HFO-1234yf.
(3) An exemplary mixture containing at least one of a halogenated hydrocarbon having a carbon-carbon double bond in its composition or a hydrocarbon having a carbon-carbon double bond in its composition is a mixture of HFO-1234yf and R32. Since HFO-1234yf is a low-pressure refrigerant and therefore causes a considerable pressure loss, it readily degrades the performance of the refrigeration cycle (especially in an evaporator). It is, therefore, desired to use a mixture with, for example, R32 or R41, which is a high-pressure refrigerant.

The compressor6according to Embodiment 2 has not only the effects described in Embodiment 1 (including each Modification), but also the following effects.

With the stator2being fixed in the closed container61by press fitting or shrinkage fitting, a stress occurs in the yoke portion21aof the stator2. In this case, the magnetic characteristics in the yoke portion21areadily degrade. However, the yoke portion21acontributes to the efficiency of the electric motor60less than the tooth portion22a. Therefore, as described in Embodiment 1, in the electric motor60, since the magnetic characteristics of the tooth portion22a(including each Modification) highly contributing to the efficiency of the electric motor60, especially those of the tooth end surface222, are improved, the efficiency of the electric motor60can also be improved, and a compressor6exhibiting high compression efficiency can thus be provided.

A refrigerating and air conditioning apparatus7including the compressor6according to Embodiment 2 will be described below.

FIG. 17is a diagram schematically illustrating the configuration of the refrigerating and air conditioning apparatus7according to Embodiment 3 of the present invention.

The refrigerating and air conditioning apparatus7serves as, for example, an air conditioner capable of cooling and heating operations. The refrigerant circuit diagram illustrated inFIG. 17is an exemplary refrigerant circuit diagram of an air conditioner capable of a cooling operation.

The refrigerating and air conditioning apparatus7according to Embodiment 3 includes an outdoor unit71, an indoor unit72, and refrigerant piping73connecting the outdoor unit71to the indoor unit72to form a refrigerant circuit (refrigeration circuit).

The outdoor unit71includes the compressor6, a condenser74, a throttling device or expansion valve75, and an outdoor fan76(first fan). The condenser74condenses a refrigerant compressed by the compressor6. The expansion valve75controls the flow rate of the refrigerant by decompressing the refrigerant condensed by the condenser74.

The indoor unit72includes an evaporator77and an indoor fan78(second fan). The evaporator77cools indoor air by evaporating the refrigerant decompressed by the expansion valve75.

The basic operation in the cooling mode of the refrigerating and air conditioning apparatus7will be described below. In the cooling operation, the refrigerant is compressed by the compressor6and flows into the condenser74. The refrigerant is condensed by the condenser74, and the condensed refrigerant flows into the expansion valve75. The refrigerant is decompressed by the expansion valve75, and the decompressed refrigerant flows into the evaporator77. The refrigerant evaporates in the evaporator77into a refrigerant gas, which flows into the compressor6of the outdoor unit71again. The outdoor fan76delivers outdoor air to the condenser74, and the indoor fan78delivers indoor air to the evaporator77, to exchange heat between the refrigerant and the air.

The above-mentioned configuration and operation of the refrigerating and air conditioning apparatus7are merely examples, and are not limited to the above-mentioned examples.

The refrigerating and air conditioning apparatus7according to Embodiment 3 has not only the effects described in Embodiments 1 and 2, but also the following effect.

Since the refrigerating and air conditioning apparatus7according to Embodiment 3 includes a compressor6exhibiting high compression efficiency, a highly efficient refrigerating and air conditioning apparatus7can be provided.

While preferred embodiments have been described in detail above, it would be apparent to those skilled in the art that various changes may be made based on the basic technical concept and teaching of the present invention.

The features in each Embodiment and the features in each Modification, described above, can be combined together as appropriate.