Permanent magnet embedded electric motor, compressor, and a refrigerating and air conditioning device

A permanent magnet embedded electric motor includes a stator core disposed inside the frame and having a back yoke and a plurality of magnetic pole teeth; a rotor disposed on an inner diameter side of the plurality of magnetic pole teeth; and compression sections in which compression stress higher than compression stress occurring in the back yoke due to pressing force generated between the frame and the back yoke occurs. A compression section group having a set of two or more compression sections and of the plurality of compression sections is disposed on an outer circumferential section of the stator core. A sum of the rotating direction widths of the plurality of compression sections constituting the compression section group is smaller than a radial direction thickness of the frame.

CROSS REFERENCE TO RELATED APPLICATION

This application is a U.S. national stage application of International Patent Application No. PCT/JP2014/072962 filed on Sep. 1, 2014, which claims priority to International Patent Application No. PCT/JP2013/079317 filed on Oct. 29, 2013, the disclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a permanent magnet embedded electric motor that includes a frame, a stator core disposed inside the frame, and a rotor disposed on an inner diameter side of the stator core; to a compressor; and to a refrigerating and air conditioning device.

BACKGROUND

In a compressor that uses a permanent magnet embedded electric motor as a drive source, a stator core of an electric motor is often fixed to an inner circumferential section of a cylindrical frame by using a shrink-fit or press-fit. The stator core of a conventional electric motor as described in Patent Literature 1 has a back yoke and a plurality of magnetic pole teeth extending from the back yoke in a direction toward the center of the electric motor. The stator core is fixed inside the outer circumferential section of the back yoke by the shrink-fit, in a state in which the outer circumferential section of the back yoke corresponding to each of the magnetic pole teeth is not in contact with the inner circumferential section of the frame and in a state in which the outer circumferential section of the back yoke other than the position corresponding to the magnetic pole teeth is in contact with the inner circumferential section of the frame. Because a part of the outer circumferential section of the back yoke is in a state of not being in contact with the inner circumferential section of the frame in this way, a gap between the stator core and the rotor is prevented from becoming uneven due to the deformation of the stator core. In the conventional technique described in Patent Literature 2, a plurality of stress relaxation slits are formed on an outer circumferential section of a split yoke portion corresponding to a split stator core, and when a stress-receiving section provided in each of the stress relaxation slits is deformed, the compression stress occurring in a magnetic flux region in the split yoke is reduced, thereby improving the iron loss characteristics in the split stator cores.

PATENT LITERATURE

However, in the related art illustrated in Patent Literature 1, because most of the outer circumferential section of the back yoke is fixed in a state of being in contact with the inner circumferential section of the frame, any magnetic flux that is incapable of passing through the inner circumferential side of the back yoke leaks to the frame via a contact portion between the outer circumferential section of the back yoke and the inner circumferential section of the frame. Because a large iron loss occurs in the frame due to the magnetic flux leakage to the frame, there is a risk of performance degradation of the electric motor due to the magnetic flux leakage. In particular, because the magnetic flux leakage to the frame increases in an electric motor using a magnet with a high magnetic flux density, such as a rare earth magnet, an efficiency drop of the electric motor becomes a problem. Meanwhile, in the related art illustrated in Patent Literature 2, the sum of rotating direction widths of radially outer tip surfaces of a plurality of stress-receiving sections is greater than the thickness of the core case. Therefore, when the split stator core is housed in the core case by using a shrink-fit, the force that presses the stress-receiving section group is absorbed by the core case, and the core case is more easily deformed than the stress-receiving section group. In this case, high compression stress does not act on the stress-receiving section group, and the magnetic permeability in the stress-receiving section group remains a high value. Thus, there are problems in that the magnetic flux leaks along a path from the split stator core, via the stress-receiving section group, to the core case. This leads to an increase in the iron loss due to the magnetic flux leakage in the core case and a decrease in the efficiency of the electric motor.

SUMMARY

The present invention has been achieved in view of the above and an objective of the present invention is to provide a permanent magnet embedded electric motor, a compressor, and a refrigerating and air conditioning device capable of improving the electric motor efficiency.

In order to solve the problem and achieve the objective mentioned above, the present invention relates to a permanent magnet embedded electric motor that includes: a stator core disposed inside a frame and having a back yoke and a plurality of magnetic pole teeth extending from the back yoke in a direction toward a center of the back yoke; a rotor disposed on an inner diameter side of the plurality of magnetic pole teeth; and a plurality of compression sections which are formed between an outer circumferential section of the back yoke and an inner circumferential section of the frame, and in which, by being deformed by the pressing force generated between the frame and the back yoke, compression stress occurs that is higher than compression stress generated due to the pressing force in the back yoke. A compression section group having a set of two or more compression sections of the plurality of compression sections is disposed on the outer circumferential section of the back yoke corresponding to each of the plurality of magnetic pole teeth. A sum of rotating direction widths in the plurality of compression sections constituting the compression section group is smaller than a radial direction thickness of the frame.

The present invention achieves an effect whereby it is possible to improve the efficiency of an electric motor.

DETAILED DESCRIPTION

Exemplary embodiments of a permanent magnet embedded electric motor, a compressor, and a refrigerating and air conditioning device according to the present invention will be described in detail below with reference to the drawings. The present invention is not limited to these embodiments.

Embodiment

FIG. 1is a vertical cross-sectional view of a rotary compressor1provided with a permanent magnet embedded electric motor7according to an embodiment of the present invention.FIG. 2is a cross-sectional view taken along the arrow A-A illustrated inFIG. 1.FIG. 3is a detailed view of the major parts of the permanent magnet embedded electric motor7illustrated inFIG. 2.FIG. 4is a diagram illustrating the distribution of compression stress in the permanent magnet embedded electric motor7after shrink-fitting.FIG. 5is a diagram illustrating the flow of magnetic flux in the permanent magnet embedded electric motor7according to the embodiment.FIG. 6is a diagram illustrating the flow of magnetic flux in a conventional electric motor7A.FIG. 7is a diagram illustrating a back yoke8cin which the caulking position8ghas been changed.FIG. 8is a diagram illustrating a back yoke8cprovided with a gap8g2instead of caulking8g.FIG. 9is a diagram illustrating a BH curve of the magnetic body used in a compression section group180.FIG. 10is a diagram illustrating ratios of magnetic flux leakages.FIG. 11is a diagram illustrating ratios of iron losses.

A permanent magnet embedded electric motor7and a compression element14are provided in a frame6of a rotary compressor1illustrated inFIG. 1. Hereinafter, the permanent magnet embedded electric motor7is simply referred to as an “electric motor7”. The electric motor7is a brushless DC motor that includes a stator30, a rotor22and a rotary shaft10. The stator30includes a stator core8and a winding29, with the rotary shaft10disposed near the center of the stator core8. In the embodiment, although the electric motor7as an electric element of the closed type rotary compressor1is used, the electric motor7can be also used as the electric elements of all devices other than the rotary compressor1.

The compression element14is configured to include a cylinder12provided in a vertically laminated state; the rotary shaft10, which is rotated by an electric motor7; a piston13into which the rotary shaft10is inserted; a vane not illustrated that divides the interior of the cylinder12into a suction side and a compression side; an upper frame17and a lower frame16as a pair of upper and lower frames to which the rotary shaft10is inserted to close an axial end surface of the cylinder12; an upper discharge muffler11mounted on the upper frame17; and a lower discharge muffler15mounted on the lower frame16.

The frame6is formed in a cylindrical shape by drawing a steel sheet having a thickness of about 3 mm; and refrigerator oil (not illustrated) is accumulated at the bottom of the frame6to lubricate each of the sliding sections of the compression element14. The rotor22is provided via a gap26of an inner diameter side of the stator core8. The rotary shaft10is held in a rotatable state by a bearing unit provided in the lower part of the rotary compressor1, i.e., the upper frame17and the lower frame16. The stator core8is held in an inner circumferential section6aof the frame by a shrink-fit. The winding29wound around the stator core8is supplied with power from a glass terminal4fixed to the frame6.

The shrink-fit is a technique in which the stator core8with its outer diameter slightly larger than an inner diameter of the frame6is heated to a high temperature, e.g., 300° C., to expand the frame6so that the stator core8fits into the expanded frame6. Thereafter, since the frame6shrinks when the temperature of the frame6drops, the stator core8becomes fixed into the frame6.

FIG. 2illustrates the stator core8that is disposed inside the frame6, the rotor22that is disposed on the inner diameter side of the stator core8, and a compression section group180that has a set of two magnetic compression sections18-1and18-2formed by a magnetic body. Eighteen compression sections18-1and18-2are formed in total in the stator core8of the illustrated example. Six magnet insertion holes20are formed on the outer circumferential section of a rotor core23in a hexagonal shape, and six flat plate-like permanent magnets24in which an N-pole and a S-pole are alternately magnetized and rare earth permanent magnets mainly containing neodymium, iron, and boron are inserted into each of the magnet insertion holes20. A shaft hole21is formed on the center side of the rotor core23, and the rotary shaft10for transmitting rotational energy is connected to the shaft hole21by a shrink-fit or a press-fit. A plurality of air holes25serving as flow paths for the refrigerant are provided between each of the magnet insertion holes20and the shaft holes21.

The gap26is formed between the outer circumferential surface of the rotor core23and the inner circumferential surface of the stator core8. The width of the gap26is 0.3 mm to 1.0 mm. A rotary magnetic field is generated by supplying the current of the frequency synchronized with the command rotation speed to the stator core8so that the rotor core23rotates. The stator core8is obtained by punching an electromagnetic steel sheet with a thickness of 0.30 mm or less into a particular shape, by laminating a plurality of punched electromagnetic steel sheets, and by crimping the steel sheets. Further, by performing an annealing treatment on the stator core8integrally provided with the compression section group180, it is possible to lessen the distortion made when being punched, and an oxide film layer is formed on the compression section group180and an outer circumferential section8aof the stator core. Because the magnetic resistance of the compression section group180increases due to the oxide film layer, it is possible to enhance the effect of reducing the magnetic flux leakage in the compression section group180. Details of the structure and effect of the compression section group180will be described later.

The stator core8is configured to have a back yoke8c; a plurality of magnetic pole teeth8dextending from the back yoke8cin a direction toward the center of the back yoke8c; and teeth tip portions8eformed on the inner diameter side of each magnetic pole teeth8dof the plurality of magnetic pole teeth8d. In the illustrated example, nine magnetic pole teeth8dare formed in the back yoke8c. Further, the stator core8is provided with a slot8fserving at a space that is defined by the back yoke8c, the magnetic pole teeth8d, and the teeth tip portion8e. Nine slots8fdisposed in the rotational direction are formed in the stator core8of the illustrated example.

The width in the rotational direction of the magnetic pole teeth8dis formed so as to be the same width as the distance from the back yoke8ctoward the teeth tip portion8e. The winding29that generates the rotary magnetic field is wound around the magnetic pole teeth8d. The teeth tip portions8eare formed in an umbrella shape in which both sides spread in the rotational direction.

The winding29is formed by directly winding a magnet wire (not illustrated) around the magnetic pole teeth8dvia an insulating section9. This winding type is called a concentrated winding. Further, the winding29is connected to a three-phase Y-connection. The number of turns and the wire diameter of the winding29are defined by the rotational speed, the torque, the voltage specification, and the cross-sectional area of the slots, which are required characteristics.

Grooves8bare intended to hold the stator core8when the stator core8is manufactured and are provided on the outer diameter side of the back yoke8con a central axis19that passes through a center position G of the stator core8and the center of the magnetic pole teeth8d. The grooves8bof the illustrated example are formed in a trapezoidal shape.

In the outer circumferential section8aof the stator core, which is the outer circumferential section of the back yoke8ccorresponding to each of the nine magnetic pole teeth8d, a compression section group180including a set of two compression sections18-1and18-2of the plurality of compression sections as illustrated inFIG. 3is provided. The compression sections18-1and18-2have a configuration in which, by being deformed by a pressing force toward the stator core8from the frame6when the frame6shrinks due to the shrink-fit, compression stress higher than the compression stress occurring in the stator core8due to the pressing force occurs. In the illustrated example, the two compression sections18-1and18-2are provided at symmetrical positions in the rotational direction with respect to the central axis19so as to span the groove8b. By disposing the two compression sections18-1and18-2at symmetrical positions in the rotational direction with respect to the central axis19, when the frame6shrinks under the shrink-fit, the pressing force applied to the two compression sections18-1and18-2is equalized, and thus, it is possible to equalize the value of the compression stress generated in the two compression sections18-1and18-2. Further, the two compression sections18-1and18-2may be continuously formed from one axial end to the other axial end of the stator core8, or they may be provided by being divided into several places from the one axial end to the other axial end of the stator core8.

When the sum of the respective rotating direction widths A1and A2of the two compression sections18-1and18-2, which constitute the compression section group180, is set as A, a radial direction thickness of the frame6is set as B, and a radial direction thickness of each of the compression sections18-1and18-2is set as C, then the compression section group180of the illustrated example has a shape that satisfies a relation following B>A>C. Because the dimension of the radial direction thickness B is greater than the dimension of the sum A, rigidity of the compression section group180, i.e., the degree of resistance to dimensionally change, is lower than the rigidity of the frame6. Thus, the compression section group180of the illustrated example is more easily deformed than the frame6. The compression stress which occurs, when the compression section group180is deformed, follows a relation B≤A. That is, the compression stress is greater than the compression stress that occurs when the compression section group180is deformed, where B is formed to be A or less. The reason is that, in the compression section group180having the shape that follows B≤A, the frame6is more easily deformed than the compression section group180, and the force for pressing the compression section group180is absorbed by the frame6.

In the related art illustrated in Patent Literature 2, the sum of the rotating direction width on the tip surface of the radially outer side of the plurality of stress-receiving sections is greater than the thickness of the core case. That is, in a case where the sum of the rotating direction width on the tip surface of the radially outer side of the plurality of stress-receiving sections is set as A and the radial direction thickness of the core case is set as B, there is a relation that follows B≤A. Therefore, when the split stator core is housed in the core case with a shrink-fit, the force that presses on the stress-receiving section group is absorbed by the core case, and the core case is more easily deformed than the stress-receiving section group. In this case, great compression stress does not operate on the stress-receiving section group, and magnetic permeability remains at a high value in the stress-receiving section group. Thus, there are problems such as leakage of the magnetic flux in a path along such as the split stator core, the stress-receiving section group and the core case; an increase in iron loss due to the magnetic flux leakage in the core case; and a decrease in the efficiency of the electric motor.

In the embodiment, the outer diameter of the stator core8including the compression section group180is formed to be greater than the inner diameter of the frame6by about 100 μm at room temperature; and the rotating direction widths A1and A2are formed to be approximately half of the radial direction thickness B. When the stator core8is fixed to the frame6by a shrink-fit, the pressing force of the frame6is applied to the compression section group180; great compression stress exceeding 100 MPa occurs locally in the respective compression sections18-1and18-2; and a compression stress of approximately 50 MPa occurs on the outer circumferential side of the back yoke8c.

FIG. 9illustrates a BH curve corresponding to the compression stress that occurs in the compression section group180, in which a horizontal axis thereof represents the magnetic field intensity H, and a vertical axis thereof represents the magnetic flux density B. Three BH curves are obtained for when the compression stress is 0 MPa, 50 MPa and 100 MPa. The magnetic flux density B can be represented by the product of the magnetic permeability μ and the magnetic field intensity H. Therefore, when the intensity H of the magnetic field is set at a constant value, because the compression stress in the compression section group180becomes higher, the magnetic permeability of the compression section group180, i.e., the magnetic flux density B, becomes lower. Therefore, in the compression section group180in which the compression stress occurs, it is higher than the compression stress occurring on the outer circumferential side of the back yoke8c, and therefore, the magnetic flux leakage from the stator core8to the frame6is reduced. Here, the compression stress occurring on the outer circumferential side of the back yoke8cis 50 MPa for example, and compression stress higher than the compression stress is 100 MPa. As a result, the iron loss that occurs in the frame6caused by the magnetic flux leakage is reduced.

FIG. 4illustrates, in the electric motor7according to the embodiment, the distribution of the compression stress that occurs in the stator core8and the compression section group180during shrink-fit. Numbers in parentheses indicate the magnitude of the compression stress, and as the value of the number is large, the region with the number is a region on which higher compression stress acts. In the electric motor7according to the embodiment, large compression stress represented by (7), 100 MPa as an example, acts on the compression section group180along with the shrink-fit. Although compression stress represented by (5) and (6) also act on the back yoke8c, the compression stress occurring on the outer circumferential side of the back yoke8cis a value lower than the compression stress occurring in the compression section group180. Further, large compression stress also acts around the V caulking. Hereinafter, the V caulking is referred to as a “caulking8g”.

FIG. 5illustrates the magnetic flux31flowing in the stator core8in which the compression stress is distributed as illustrated inFIG. 4. The electric motor7being driven constitutes a magnetic circuit in which the rotary magnetic field flows through a part with small magnetic resistance, and since the magnetic resistance of the back yoke8cis lower on its inner diameter side than on its outer diameter side, the magnetic flux density on the inner diameter side is high. At this time, most of the magnetic flux31aof the magnetic flux31passing through the magnetic pole teeth8dpasses through the inner circumferential side of the back yoke8c. Meanwhile, some magnetic flux31bincapable of passing through the inner circumferential side of the back yoke8cpasses through the outer circumferential side of the back yoke8c. Specifically, between the caulking8gprovided on the back yoke8cand the compression section group180, there is a region of the compression stress lower than the compression stress occurring in the compression section group180. Thus, the magnetic flux31bpasses through this region. The region of compression stress lower than the compression stress occurring in the compression section group180is a region represented by (5) inFIG. 4.

FIG. 6illustrates the magnetic flux31flowing through the back yoke8cof the conventional electric motor7A. When the conventional electric motor7A is shrink-fitted, the most outer circumferential section8aof the stator core is fixed in a state being in contact with the inner circumferential section6aof the frame. When the magnetic flux density of the back yoke8cincreases by driving the conventional electric motor7A at high load, the magnetic flux31bincapable of passing through the inner circumferential side of the back yoke8cleaks out to the frame6via the contact portion between the outer circumferential section8aof the stator core and the inner circumferential section6aof the frame. Since great iron loss occurs in the frame6due to the magnetic flux leakage to the frame6in this way, there is a risk of performance degradation of the conventional electric motor7A caused by the magnetic flux leakage. In contrast, in the electric motor7according to the embodiment, since the compression section group180is deformed, the compression stress of the compression section group180is higher than the compression stress occurring on the outer circumferential side of the back yoke8c, and magnetic permeability of the compression section group180decreases. As a result, the magnetic flux leakage flowing through the frame6is reduced, and a decrease in efficiency of the electric motor7caused by the magnetic flux leakage is reduced.

FIG. 10illustrates a ratio of the magnetic flux leakage in the electric motor7according to the embodiment to the magnetic flux leakage of the conventional electric motor7A. As can be seen fromFIG. 10, in the electric motor7according to the embodiment, the magnetic flux leakage to the frame6is reduced by 69% than the conventional electric motor7A. Further,FIG. 11illustrates a ratio of the iron loss occurring in the frame6of the electric motor7according to the embodiment to the iron loss occurring in the frame6of the conventional electric motor7A. As can be seen fromFIG. 11, in the electric motor7according to the embodiment, the iron loss occurring in the frame6is reduced by 82% than the conventional electric motor7A.

Further, since the outer circumferential side portion near the central axis19of the back yoke8cis a part in which magnetic flux is hard to flow, the compression section18-1and the compression section18-2are preferably provided at a position close to the central axis19. Furthermore, since the compression section18-1and the compression section18-2cannot be effectively utilized as a magnetic path of the stator core8, the radial direction thickness C of the compression section18-1and the compression section18-2is preferably thin, and is 1 mm or less.

Further, when a narrowest width in the radial direction width of the back yoke8cis set as D, and a radial direction width from a portion in which the compression section18-1or the compression section18-2is in contact with the back yoke8cto an inner diameter surface8c1of the back yoke8cis set as D1inFIG. 3, the back yoke8chas a shape that satisfies a relation that follows D1>D. Because the outer circumferential section8aof the stator core is curved, in the back yoke8c, the width of the outer circumferential section8aof the stator core to the inner diameter surface8c1is not uniform. In a region of the outer diameter side of a line32located at a constant distance D of the outer diameter side from the inner diameter surface8c1, the magnetic flux is hard to flow than the region of the inner diameter side of the line32. Thus, by forming a back yoke8cso as to satisfy a relation that follows D1>D, the magnetic flux is hard to flow through the compression section18-1and the compression section18-2, and it is possible to further reduce the magnetic flux leakage.

Furthermore, the caulking8gof the back yoke8cillustrated inFIG. 3is preferably provided on the outer circumferential side of the back yoke8c. In a case where the distance between the compression section18-1or the compression section18-2and the caulking8gis set as E, and the distance from the caulking8gto the inner diameter surface8c1is set as F, the caulking8gof the back yoke8chas a shape that satisfies a relation that follows F>E.FIG. 7illustrates an example of a caulking8g1in which the distance E is formed to be narrower than the configuration example ofFIG. 3. By providing the caulking8g1near the compression section18-1or the compression section18-2in this way, a region with high compression stress is formed on the outer circumferential side of the back yoke8c, and the magnetic permeability of this region decreases. Therefore, the magnetic flux31billustrated inFIG. 5is hard to flow in this region, and it is possible to enhance the effect of reducing the magnetic flux leakage to the frame6.

Moreover, in the caulking8g1ofFIG. 7, a lengthwise width of the caulking8g1is formed to be wider than the rotating direction widths A1and A2of the compression sections18-1and18-2, and the lengthwise surface of the caulking8g1is formed in parallel to the lengthwise widths of the compression sections18-1and18-2. With this configuration, it is possible to further enhance the effect of reducing the magnetic flux leakage to the frame6. Further, it is possible to obtain the same effect even when using a gap8g2as illustrated inFIG. 8, instead of the caulking8gand8g1that is a V caulking of the illustrated example.

Further, when the annealing treatment is applied to the frame6, an oxide film layer is formed on the inner circumferential section6aof the frame, and the magnetic resistance of the frame6increases by the oxide film layer. Therefore, it is possible to enhance the effect of reducing the magnetic flux that enters the frame6from the stator core8.

Further, it is preferable to use a rare earth magnet as the permanent magnet24of the rotor22according to the embodiment. Since the residual magnetic flux density of the rare earth magnet is high, the magnetic flux density of the stator core8is high in the electric motor7using a rare earth magnet, and the magnetic flux is liable to leak to the frame6. However, it is possible to effectively reduce the magnetic flux leakage by providing the compression section group180, and the effect of efficiency improvement is great. Moreover, the performance improvement can also lead to a reduction of the magnet usage.

Further, it is desirable to use the winding29of a concentrated winding in the stator30according to the embodiment. The magnetic flux is distributed so that the magnetic flux is locally concentrated in the electric motor7of the concentrated winding as compared to the case of distributed winding, and thus the magnetic flux density of the stator core8increases and the magnetic flux is liable to leak to the frame6. However, it is possible to effectively reduce the magnetic flux leakage by providing the compression section group180, and the effect of efficiency improvement is great.

Next, the operation of the rotary compressor1will be described. The refrigerant gas supplied from the accumulator2is sucked into the cylinder12from a suction pipe3fixed to the frame6. When the electric motor7rotates by the electric conduction of the inverter, the piston13fitted to the rotary shaft10rotates inside the cylinder12. Thus, the compression of the refrigerant is performed inside the cylinder12. After passing through the muffler, the refrigerant rises in the frame6through the air hole25and the gap26of the electric motor7. At this time, the refrigerator oil is mixed with the compressed refrigerant. When the mixture of the refrigerant and the refrigerator oil passes through the air hole25provided in a rotor iron core, the separation of the refrigerant and the refrigerator oil is promoted, and thus, it possible to prevent the refrigerator oil from flowing into a discharge pipe5. In this way, the compressed refrigerant is supplied to the high pressure side of the refrigeration cycle through the discharge pipe5provided in the frame6.

Further, although R410A, R407C and R22 are conventionally used as the refrigerant of the rotary compressor1, it is also possible to apply any refrigerant of a low GWP, that is, a low global warming potential. A low GWP refrigerant is desired from the viewpoint of preventing the global warming. As a representative example of the low GWP refrigerant, there are following refrigerants.

(1) HFO-1234yf (CF3CF═CH2) that is an example of halogenated hydrocarbon having a double bond of carbon in the composition. HFO is an abbreviation of Hydro-Fluoro-Olefin, and Olefin is unsaturated hydrocarbon with one double bond. In addition, GWP of HFO-1234yf is 4.
(2) R1270 (propylene) that is an example of hydrocarbon having a double bond of carbon in the composition. Further, although GWP is 3 smaller than HFO-1234yf, flammability is greater than HFO-1234yf.
(3) A mixture of HFO-1234yf and R32 is an example of a mixture containing any of halogenated hydrocarbon having a double bond of carbon in the composition or hydrocarbon having a double bond of carbon in the composition. Since HFO-1234yf is a low-pressure refrigerant, the pressure loss increases, and the refrigeration cycle, in particular, the performance in an evaporator is liable to decrease. Therefore, a mixture of R32 or R41 as a high-pressure refrigerant compared to HFO-1234yf is practically influential.

It is possible to obtain a highly reliable compressor with high efficiency, by using the electric motor7in the rotary compressor1configured as described above. Moreover, by using the rotary compressor1in the refrigerating and air conditioning device, it is possible to obtain a highly reliable refrigerating and air conditioning device with high efficiency and low noise.

Further, although an example of fixing the stator core8to the frame6by using a shrink-fit has been described in the embodiment, freeze-fitting as a method of cooling the stator core8or press-fit may be applied. Further, although a brushless DC motor has been described as an example of the electric motor7in the embodiment, the fixing method of the stator core8of the embodiment is also applicable to an electric motor other than the brushless DC motors and is also applicable to a motor that does not use a permanent magnet of an induction electric motor as an example, and it is also possible to obtain the same effect in these motors.

Further, although the number of magnetic poles of the rotor22may be two or more poles, in the embodiment, an electric motor7in which the number of magnetic poles of the rotor22is six is used as an example. Also, although an Nd—Fe—B (neodymium-iron-boron)-series rare earth magnet is used as a permanent magnet in the embodiment, the kind of the permanent magnets is not limited thereto. The rare earth magnet used for the rotor22of the compressor electric motor7is added with Dy (dysprosium) that is a heavy rare earth element amount to reduce a decrease in demagnetization due to a decrease in a coercive force at high temperatures. The rare earth magnet has characteristics in which, when Dy is added, the coercive force is improved, and meanwhile, the residual magnetic flux density decreases. Thus, the rare earth magnet with Dy content of 2% is used here. Further, the electric motor7using the rotor22of the embodiment performs a high-efficiency operation according to the required product load conditions, by performing the variable speed driving through a PWM control using an inverter of a driving circuit (not illustrated). Further, the electric motor7using the rotor22of the embodiment is mounted on a compressor of an air conditioner as an example to ensure the use in 100° C. or more high-temperature atmosphere.

Further, although the compression section group180of the embodiment is formed in a protruding shape toward the inner circumferential section6aof the frame from the outer circumferential section8aof the stator core, integrally with the stator core8, the configuration of the compression section group180is not limited thereto. The compression section group180may be formed in a protruding shape toward the outer circumferential section8aof the stator core from the inner circumferential section6aof the frame, integrally with the frame6. Also, the compression section group180produced separately from the stator core8and the frame6may be provided between the stator core8and the frame6. It is also possible to reduce the magnetic flux leakage flowing through the frame6by such a configuration.

Also, when the compression section group180is integrally formed with the stator core8, the thickness of the electromagnetic steel sheet constituting the stator core8is desirably set as 0.30 mm or less. The thinner the sheet thickness of the electromagnetic steel sheet is, the larger the amount of deformation of electromagnetic steel sheet is, and the compression stress occurring in the electromagnetic steel sheets increases accordingly. The compression stress occurring in the compression section group180formed integrally with the stator core8formed by laminating the magnetic steel sheets having a thickness of 0.30 mm represents a value higher than the compression stress occurring in the compression section group180formed integrally with the stator core8formed by laminating the electromagnetic steel sheets having the thickness of 0.35 mm. Therefore, it is possible to further increase the effect of reducing the magnetic flux that enters the frame6.

Moreover, in the embodiment, although the compression section group180includes two compression sections18-1and18-2, the number of compression sections constituting the compression section group180is not limited to two. As long as a sum A of rotating direction widths of the plurality of compression sections constituting the compression section group180and a radial direction thickness B of the frame6are in a relation that follows B>A, the number of compression sections constituting the compression section group180may be three or more. Further, in the embodiment, the two compression sections18-1and18-2constituting the compression section group180span the groove8band are disposed at symmetrical positions with respect to the central axis19in the rotational direction. However, the position of arranging the plurality of compression sections constituting the compression section group180is not limited thereto. As long as the sum A and the radial direction thickness B are in the relation that follows B>A, the two compression sections span the groove8band may be provided at asymmetrical positions with respect to the central axis19in the rotational direction. Also, the electric motor7according to the embodiment is not limited to the brushless DC motor, which, however, may be a motor other than the brushless DC motor.

As described above, the electric motor7according to the embodiment is equipped with the stator core8that is disposed inside the frame6and has the back yoke8cand a plurality of magnetic pole teeth8d, the rotor22disposed on the inner diameter side of the plurality of magnetic pole teeth8d, and a plurality of compression sections in which compression stress higher than the compression stress occurring in the back yoke8cdue to the pressing force generated between the frame6and the back yoke8coccur. In the outer circumferential section8aof the stator core that is an outer circumferential section of the back yoke8ccorresponding to each of the plurality of magnetic pole teeth8d, the compression section group180having a set of two or more compression sections18-1and18-2of the plurality of compression sections is disposed. The sum A of the rotating direction widths A1and A2of the plurality of compression sections18-1and18-2constituting the compression section group180is smaller than the radial direction thickness B of the frame6. With this configuration, the magnetic permeability of the deformed compression sections18-1and18-2decreases, and the magnetic flux leaking from the stator core8to the frame6is reduced. Therefore, because the iron loss occurring in the frame6caused by the magnetic flux leakage is reduced, it is possible to obtain an electric motor7with efficiency higher than that of the related art. There is an effect of improving the efficiency of the saving rare earth motor with a high magnetic flux density, and it is possible to apply the performance improvement to a reduction of the magnet usage.

Further, the embodiments of the present invention illustrate an example of the contents of the present invention and may be combined with another known techniques, and it is a matter of course that the embodiments may also be configured with a partial omission and change within the scope that does not depart from the scope of the present invention.