Electric motor, compressor, and refrigeration cycle device

Abstract

An electric motor according to the present invention is installed in a compressor, the electric motor comprising a rotor that has a permanent magnet, and a stator. The refrigerant used in the compressor is: a single refrigerant selected from R1234yf, R1234ze (E), R290, and R1123; a mixed refrigerant containing at least one of R1234yf, R1234ze (E), R290, R1123, and R32; or a mixed refrigerant containing at least one of R447A, R447B, R454A, R454B, R454C, and R455A. The permanent magnet is a rare earth magnet containing neodymium, iron, and boron, and the amount of dysprosium contained in the permanent magnet is 4 wt% or less.

Description

Electric motor, compressor and refrigeration cycle device

[0001] The present disclosure relates to an electric motor, a compressor, and a refrigeration cycle device.

[0002] In electric motors used in compressors, rare earth magnets are generally used as permanent magnets. Because rare earth magnets are prone to demagnetization at high temperatures such as those inside compressors, heavy rare earth elements such as dysprosium are added to improve coercivity.

[0003] Increasing the amount of heavy rare earth elements added to rare earth magnets increases manufacturing costs and reduces remanence, so Patent Document 1 discloses limiting the dysprosium content in rare earth magnets to 4 wt % or less.

[0004] Patent No. 5661955 (see claim 1)

[0005] However, the compressors equipped with the above-mentioned electric motors use a single refrigerant, R32, which has a high discharge temperature, so the temperature inside the compressor tends to be high. As the temperature inside the compressor increases, the coercive force of the rare earth magnet decreases, and therefore the amount of heavy rare earth elements that needs to be added to the rare earth magnet increases.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to reduce the content of heavy rare earth elements in permanent magnets.

[0007] The electric motor of the present disclosure is mounted on a compressor and includes a rotor having permanent magnets and a stator. The refrigerant used in the compressor is any one of R1234yf, R1234ze(E), R290, and R1123, a mixed refrigerant containing at least one of R1234yf, R1234ze(E), R290, R1123, and R32, or a mixed refrigerant containing at least one of R447A, R447B, R454A, R454B, R454C, and R455A. The permanent magnet is a rare earth magnet containing neodymium, iron, and boron, and the dysprosium content in the permanent magnet is 4 wt% or less.

[0008] According to the present disclosure, the refrigerant discharge temperature is lower than that of a single refrigerant, so the temperature rise inside the compressor is suppressed, and demagnetization of the permanent magnet can be suppressed while keeping the content of dysprosium, a heavy rare earth element, low in the permanent magnet.

[0009] 1 is a cross-sectional view showing an electric motor of embodiment 1. FIG. 2 is a cross-sectional view showing a rotor of embodiment 1. FIG. 3 is a top view showing a stator of embodiment 1. FIG. 4 is a cross-sectional view showing a compressor of embodiment 1. FIG. 5 is a diagram showing a refrigeration cycle device of embodiment 1. FIG. 6 is a graph showing the relationship between the Dy content in a permanent magnet and the coercive force and residual magnetic flux density. FIG. 7 is a table showing the characteristics of a refrigerant used in embodiment 1. FIG. 8 is a graph showing the relationship between the phase magnetomotive force of an electric motor and the demagnetization factor of a permanent magnet. FIG. 9 is a graph showing the relationship between the Dy content required to keep the demagnetization factor of a permanent magnet within a specified range and the number of poles of the electric motor. FIG. 10 is a graph showing the relationship between the number of poles of an electric motor and motor efficiency. FIG. 11 is a diagram showing an example of a 4-pole, 24-slot electric motor (A) and a diagram showing an example of an 8-pole, 24-slot electric motor (B). FIG. 12 is a diagram showing protrusions and their surroundings provided in magnet insertion holes of the rotor of embodiment 1, and a diagram for explaining stator magnetic flux flowing through the protrusions. FIG. 13 is a cross-sectional view showing an electric motor of embodiment 2. 10A is a diagram showing a part of a rotor of embodiment 2, and FIG. 10B is a diagram for explaining the concentration of magnetic flux between a slit and a magnet insertion hole.

[0010] Embodiment 1. <Motor Configuration> Fig. 1 is a cross-sectional view showing an electric motor 5 according to embodiment 1. The electric motor 5 according to embodiment 1 has a rotatable rotor 3 and a stator 1 surrounding the rotor 3. An air gap of 0.3 to 1.0 mm is provided between the stator 1 and the rotor 3.

[0011] Hereinafter, the direction of the axis Ax, which is the center of rotation of the rotor 3, will be referred to as the "axial direction." The circumferential direction centered on the axis Ax will be referred to as the "circumferential direction." The radial direction centered on the axis Ax will be referred to as the "radial direction." Note that FIG. 1 is a cross section perpendicular to the axial direction.

[0012] <Configuration of Rotor> Fig. 2 is a cross-sectional view showing the rotor 3. The rotor 3 has a rotor core 30 and permanent magnets 40 attached to the rotor core 30. The rotor core 30 has a cylindrical shape centered on the axis Ax. The rotor core 30 is made by laminating multiple electromagnetic steel plates in the axial direction and fixing them together by caulking, rivets, or the like. The thickness of each electromagnetic steel plate is, for example, 0.1 to 1.0 mm, and is 0.35 mm as an example.

[0013] The rotor core 30 has an outer periphery 30a and a central hole 30b. A shaft 45 is press-fitted and fixed into the central hole 30b of the rotor core 30. The central axis of the shaft 45 defines the axis Ax described above.

[0014] The rotor core 30 has a plurality of magnet insertion holes 31 along the outer periphery 30a. Here, six magnet insertion holes 31 are arranged at equal intervals in the circumferential direction. One permanent magnet 40 is arranged in each magnet insertion hole 31.

[0015] One permanent magnet 40 constitutes one magnetic pole. Since there are six permanent magnets 40, the rotor 3 has six poles. However, the number of poles of the rotor 3 is not limited to six, as long as it is two or more. Furthermore, two or more permanent magnets 40 may be arranged in one magnet insertion hole 31, and one magnetic pole may be constituted by the two or more permanent magnets 40.

[0016] The circumferential center of each magnet insertion hole 31 is the pole center. A radial line passing through the pole center is defined as the pole center line C. The pole center line C is the d-axis of the rotor 3. An inter-pole portion N is formed between adjacent magnet insertion holes 31.

[0017] The magnet insertion hole 31 extends linearly in a direction perpendicular to the pole center line C, but may also extend in a V-shape, for example. A protrusion 33 is formed in the magnet insertion hole 31 to position the permanent magnet 40 in the circumferential direction. This protrusion 33 will be described later.

[0018] The permanent magnets 40 are flat plate-shaped members that have a width in the circumferential direction and a thickness in the radial direction. The permanent magnets 40 are magnetized in the thickness direction, i.e., the radial direction. The magnetization directions of adjacent permanent magnets 40 in the circumferential direction are opposite to each other.

[0019] The permanent magnet 40 is a rare earth magnet. More specifically, the permanent magnet 40 is a rare earth magnet containing neodymium (Nd), iron (Fe), and boron (B), i.e., a neodymium rare earth magnet. The neodymium rare earth magnet may contain dysprosium (Dy), a heavy rare earth element. The Dy content is 0% by weight or more and 4% by weight or less.

[0020] Flux barriers 32 are formed at both circumferential ends of the magnet insertion holes 31. The flux barriers 32 are holes that extend radially from the circumferential ends of the magnet insertion holes 31 toward the outer periphery 30a of the rotor core 30. The flux barriers 32 act to suppress leakage flux between adjacent magnetic poles.

[0021] A circumferentially long side slit 34 is formed on the pole center line C side of the flux barrier 32. The side slit 34 reduces magnetic flux leakage between adjacent magnetic poles and also functions to collect magnetic flux emitted from the permanent magnet 40 toward the pole center line C side.

[0022] The crimped portions 39 that integrally fasten the electromagnetic steel sheets that make up the rotor core 30 are formed on a radial straight line that passes through the inter-pole portion N. However, the arrangement of the crimped portions 39 is not limited to this position.

[0023] The rotor core 30 also has through holes 36, 37, and 38 located radially between the magnet insertion holes 31 and the center hole 30b. The through hole 36 is formed on the pole center line C. The through hole 37 is formed radially inside the crimped portion 39. The through holes 38 are formed on both circumferential sides of the crimped portion 39.

[0024] The through holes 36, 37, and 38 all pass through the rotor core 30 in the axial direction and are used as refrigerant passages. Any of the through holes 36, 37, and 38 may also be used as rivet holes. The positions of the through holes 36, 37, and 38 are not limited to those described above and can be changed as appropriate. The rotor core 30 only needs to have at least one through hole that passes through the rotor core 30 in the axial direction between the magnet insertion holes 31 and the center hole 30b in the radial direction.

[0025] 1, the stator 1 has an annular stator core 10 centered on the axis Ax, and a winding 20 wound around the stator core 10. The stator core 10 is made by stacking a plurality of electromagnetic steel plates in the axial direction and fixing them by caulking or the like. The thickness of each electromagnetic steel plate is, for example, 0.1 to 1.0 mm, and is 0.35 mm as an example.

[0026] The stator core 10 has an annular core back 11 and a plurality of teeth 12 extending radially inward from the core back 11. The core back 11 has an outer peripheral surface 14 that is a cylindrical surface centered on the axis Ax. The outer peripheral surface 14 of the core back 11 is fixed to the inside of a shell 111 of a compressor 100 (FIG. 4) described below, for example.

[0027] The teeth 12 are formed at equal intervals in the circumferential direction. Each tooth 12 has an extending portion 12b extending in the radial direction and a tooth tip portion 12a formed at the tip of the extending portion 12b. The tooth tip portion 12a is wider in the circumferential direction than the extending portion 12b and faces the rotor 3. A winding 20 is wound around the teeth 12 in a distributed winding manner. The number of teeth 12 is 18 in this example, but it may be two or more.

[0028] A slot 13 is formed between adjacent teeth 12. The number of slots 13 is the same as the number of teeth 12, which is 18 in this example. A winding 20 is housed in the slot 13.

[0029] A notch 15 is formed in the outer peripheral surface 14 of the core back 11. The notch 15 extends linearly in a plane perpendicular to the axial direction and from one end to the other end of the stator core 10 in the axial direction.

[0030] Here, the notches 15 are formed at four locations at 90-degree intervals around the axis Ax. A refrigerant passage is formed between the notches 15 and the inner circumferential surface of the shell 111 (FIG. 4) of the compressor 100.

[0031] Of the four notches 15, two notches 15 that face each other across the axis Ax are formed with convex portions 15a that protrude radially outward, and groove portions 15b are formed at the circumferential centers of the convex portions 15a. However, the convex portions 15a and the groove portions 15b do not necessarily have to be formed. Furthermore, the number and arrangement of the notches 15 are not limited to the example described here.

[0032] As described above, the windings 20 are wound around the teeth 12 in a distributed winding manner. The windings 20 are three-phase windings having winding sections for U-phase, V-phase, and W-phase. The windings 20 are made of aluminum wire, copper wire, or clad wire having a copper layer and an aluminum layer. It is particularly desirable that the windings 20 be made of aluminum wire. The windings 20 and the stator core 10 are insulated from each other by an insulating material (not shown) made of resin.

[0033] 3 is a top view showing the stator 1. The winding 20 is wound around the stator core 10 in a distributed winding manner. The winding 20 is, for example, a three-phase coil. A U-phase winding 20U serving as a first-phase coil, a V-phase winding 20V serving as a second-phase coil, and a W-phase winding 20W serving as a third-phase coil are wound around the stator core 10. The windings 20U, 20V, and 20W will be referred to as windings 20 unless there is a need to distinguish them.

[0034] 3, three windings 20U, 20V, and 20W are provided. The three windings 20U are arranged at 120-degree intervals around the axis Ax, and each winding 20U is wound across three teeth 12. Each winding 20U has two coil sides 21 inserted into the slots 13 and two coil ends 22 extending along both axial end surfaces of the stator core 10.

[0035] Similarly, the three windings 20V are arranged at 120-degree intervals around the axis Ax, and each winding 20V is wound across three teeth 12. Each winding 20V has two coil sides 21 inserted into the slots 13 and two coil ends 22 extending along both axial end faces of the stator core 10.

[0036] The three windings 20W are arranged at 120-degree intervals around the axis Ax, and each winding 20W is wound across three teeth 12. Each winding 20W has two coil sides 21 inserted into the slots 13 and two coil ends 22 extending along both axial end surfaces of the stator core 10.

[0037] The windings 20U, 20V, and 20W are arranged such that the winding 20U is located at the innermost position in the radial direction, the winding 20V is located at the outermost position in the radial direction, and the winding 20W is routed from the outer side of the winding 20U to the inner side of the winding 20V in the radial direction. One coil side 21 is inserted into each of all the slots 13 of the stator core 10.

[0038] However, the arrangement of the windings 20U, 20V, and 20W described here is merely an example, and other arrangements are also possible.

[0039] 4 is a cross-sectional view showing a compressor 100 including the electric motor 5 according to the first embodiment. The compressor 100 is a scroll compressor in this example, but may be another type of compressor, such as a rotary compressor.

[0040] The compressor 300 includes a compression mechanism 105, an electric motor 5 that drives the compression mechanism 105, a subframe 106 that supports the lower end of a shaft 45 of the electric motor 5, and a sealed container 110 that houses these components. The sealed container 110 includes a cylindrical shell 111, a container upper part 112 that covers the upper part of the shell 111, and a container bottom part 113 that covers the lower part of the shell 111.

[0041] The compression mechanism 105 includes a fixed scroll 101, an orbiting scroll 102, a compliant frame 103, and a guide frame 104. The fixed scroll 101 and the orbiting scroll 102 each have plate-shaped spiral teeth and are combined to form a compression chamber therebetween. The compliant frame 103 holds the upper end of the shaft 45. The guide frame 104 is fixed to the shell 111 and holds the compliant frame 103.

[0042] The fixed scroll 101 has a discharge port 101a that discharges the refrigerant compressed in the compression chamber. A suction pipe 107 that penetrates the shell 111 is press-fitted into the fixed scroll 101. A discharge pipe 108 that penetrates the sealed container 110 and discharges the high-pressure refrigerant gas discharged from the discharge port 101a of the fixed scroll 101 to the outside is also provided.

[0043] The stator 1 of the electric motor 5 is fitted and fixed inside the shell 111. The configuration of the electric motor 5 is as described above. The glass terminal 109 that supplies power to the electric motor 5 is fixed to the shell 111 by welding.

[0044] The compressor 100 operates as follows: When the electric motor 5 is driven, the shaft 45 rotates together with the rotor 3. When the shaft 45 rotates, the orbiting scroll 102 orbits, changing the volume of the compression chamber between the fixed scroll 101 and the orbiting scroll 102. As a result, refrigerant gas is drawn into the compression chamber from the suction pipe 107 and compressed.

[0045] High-pressure refrigerant gas compressed in the compression chamber between the scrolls 101 and 102 is discharged from the discharge port 101 a of the fixed scroll 101 into the sealed container 110 and then to the outside through the discharge pipe 108. In addition, a portion of the refrigerant gas discharged from the compression chamber into the sealed container 110 flows through the gap between the notch 15 ( FIG. 1 ) of the stator core 10 and the shell 111, or through the through holes 36, 37, and 38 ( FIG. 2 ) of the rotor core 30, and cools the electric motor 5.

[0046] <Refrigeration cycle device> Fig. 5 is a diagram showing a refrigeration cycle device 80 having the compressor 100 shown in Fig. 4. The refrigeration cycle device 80 is, for example, an air conditioner, but is not limited to this and may be, for example, a refrigerator.

[0047] 5 has an outdoor unit 81 and an indoor unit 82, which are connected by a refrigerant pipe 83. The refrigeration cycle system 80 also includes a compressor 100, a condenser 84 that condenses the refrigerant, a pressure reducing device 85 that reduces the pressure of the refrigerant, and an evaporator 87 that evaporates the refrigerant. The compressor 100, the condenser 84, and the pressure reducing device 85 are provided in the outdoor unit 81, and the evaporator 87 is provided in the indoor unit 82.

[0048] The compressor 100, the condenser 84, the pressure reducing device 85, and the evaporator 87 are connected by a refrigerant pipe 83 to form a refrigerant circuit. The refrigeration cycle device 80 also includes an outdoor fan 86 that blows air to the condenser 84, and an indoor fan 88 that blows air to the evaporator 87.

[0049] The refrigeration cycle apparatus 80 operates as follows: The compressor 100 compresses the refrigerant it draws in and sends it out as high-temperature, high-pressure refrigerant gas. The condenser 84 exchanges heat between the refrigerant sent out from the compressor 100 and outdoor air sent by the outdoor air blower 86, condenses the refrigerant, and sends it out as liquid refrigerant. The pressure reducing device 85 expands the liquid refrigerant sent out from the condenser 84 and sends it out as low-temperature, low-pressure liquid refrigerant.

[0050] The evaporator 87 exchanges heat between the low-temperature, low-pressure liquid refrigerant delivered from the pressure reducing device 85 and the indoor air, evaporating the refrigerant and delivering it as refrigerant gas. The air from which heat has been removed in the evaporator 87 is supplied by an indoor fan 88 to the room, which is the space to be air-conditioned.

[0051] <Coercive Force of Permanent Magnet> As described above, the permanent magnet 40 is a neodymium rare earth magnet containing Nd, Fe, and B. Here, the coercive force of the neodymium rare earth magnet will be described.

[0052] 6 is a graph showing the relationship between the Dy content of a neodymium rare earth magnet and the coercive force and residual magnetic flux density, where the horizontal axis represents the Dy content (wt %) and the vertical axis represents the coercive force (kA / m) and residual magnetic flux density (T).

[0053] As shown in Figure 6, the coercive force of a neodymium rare earth magnet increases in proportion to the Dy content, while the remanence decreases in proportion to the Dy content.

[0054] In a typical compressor, the upper limit of the temperature inside the compressor, i.e., the ambient temperature of the motor 5, is set to 150° C. That is, the motor of a typical compressor is used between the normal temperature of 20° C. and the upper limit temperature of 150° C.

[0055] Neodymium rare earth magnets have the property that their coercivity decreases as the temperature rises, with the rate of decrease being 0.5 to 0.6% / K. If the rate of decrease in coercivity is assumed to be 0.5% / K, the coercivity at 150°C will decrease by approximately 65% ​​compared to the coercivity at 20°C.

[0056] A coercive force of 1100 to 1500 kA / m is required to prevent demagnetization of the rare earth magnets when the maximum load expected for compressor 100 is generated. To ensure this coercive force at an ambient temperature of 150°C, the coercive force at room temperature (20°C) must be 1800 to 2300 kA / m.

[0057] When no Dy is added to a neodymium rare earth magnet, its coercive force at room temperature (20°C) is 1000 kA / m. Therefore, in order to obtain a coercive force of 1100 to 1500 kA / m at maximum load, it is common to add 6 to 8 weight percent Dy to the neodymium rare earth magnet. However, the higher the Dy content, the higher the manufacturing cost of the electric motor 5, so it is desirable to reduce the Dy content.

[0058] Furthermore, an increase in the Dy content leads to a decrease in the residual magnetic flux density, as shown in Figure 6, and to a decrease in the magnet torque of the electric motor 5. In this case, the current flowing through the winding 20 must be increased to maintain the output of the electric motor 5, which results in an increase in copper loss. Therefore, from the viewpoint of motor efficiency as well, it is desirable to reduce the Dy content.

[0059] <Refrigerant> Next, a description will be given of the refrigerant used in the compressor 100 of the first embodiment. In order to prevent global warming, the compressor 100 uses a refrigerant with a GWP (global warming potential) of 1500 or less. Hereinafter, the types of refrigerant will be described using refrigerant numbers beginning with "R" defined in the international standard ISO 817.

[0060] The compressor 100 of the first embodiment uses the following refrigerants. These refrigerants are called low GWP refrigerants.

[0061] (1) First, R1234yf, R1234ze(E), R290, or R1123 can be used as a single refrigerant. R1234yf is a fluoroolefin. R1234ze(E) is trans-1,3,3,3-tetrafluoropropene. R290 is propane. R1123 is 1,1,2-trifluoroethylene.

[0062] (2) It is also possible to use a mixed refrigerant containing at least one of R1234yf, R1234ze(E), R290, R1123, and R32 with another refrigerant. R32 is difluoromethane.

[0063] (3) It is also possible to use a mixed refrigerant of any one of R447A, R447B, R454A, R454B, R454C, and R455A, or a mixed refrigerant containing at least one of these. R447A, R447B, R454A, R454B, R454C, and R455A are all mixed refrigerants, and their composition ratios are as shown in Figure 7 (described below).

[0064] The refrigerants (1) to (3) have lower discharge temperatures and GWPs than the R32 single refrigerant used in general compressors. In the compressor 100 using such a refrigerant with a low discharge temperature, the temperature inside the compressor 100 (i.e., the ambient temperature of the motor 5) is set lower than in a compressor using R32.

[0065] Furthermore, the refrigerants (1) to (3) have lower operating pressures than R32 alone. The operating pressure of the refrigerant is the same as the saturation pressure of the refrigerant. In order to obtain the same motor output as when R32 alone is used using such refrigerants with low operating pressures, it is necessary to increase the rotation speed of the electric motor 5. Increasing the rotation speed of the electric motor 5 increases the flow rate of the refrigerant and refrigeration oil due to the swirling flow caused by the rotation of the rotor 3, thereby improving the cooling performance of the electric motor 5.

[0066] Fig. 7 is a table showing the characteristics of the refrigerant used in compressor 100 of embodiment 1. As shown in Fig. 7, the discharge temperatures of R1234yf, R1234ze(E), R290, R1123, R447A, R447B, R454A, R454B, R454C, and R455A are in the range of 48 to 71°C, which is lower than the discharge temperature of R32, which is 77°C.

[0067] As described above, in a compressor using only R32 refrigerant, the ambient temperature of the motor ranges from room temperature, 20° C., to an upper limit of 150° C. In contrast, in compressor 100 using any of refrigerants (1) to (3), the upper limit of the ambient temperature of motor 5 can be set lower (i.e., below 150° C.) than in a compressor using only R32 refrigerant.

[0068] The coercive force of the permanent magnets 40, which are neodymium rare earth magnets, decreases as the temperature increases and increases as the temperature decreases. Therefore, by lowering the upper limit of the ambient temperature of the electric motor 5 as described above, it is possible to suppress the decrease in coercive force of the permanent magnets 40 and reduce the amount of Dy required to maintain coercive force. Reducing the Dy content leads to an improvement in the residual magnetic flux density of the permanent magnets 40 (see FIG. 6), which increases the amount of effective magnetic flux of the permanent magnets 40 and leads to improved motor efficiency.

[0069] 8 is a graph showing the relationship between the demagnetization factor and the phase magnetomotive force when the thickness and Dy content of the permanent magnet 40 are constant and the number of poles of the motor 5 is changed. The horizontal axis of FIG. 8 represents the phase magnetomotive force (AT), and the vertical axis represents the demagnetization factor (%).

[0070] The demagnetization factor is calculated as follows. The stator 1 and rotor 3 are fixed in a relative rotational position such that magnetic flux flows from the stator 1 in the direction opposite to the magnetization direction of the permanent magnet 40. In this state, a current is passed through the winding 20, causing demagnetization (more specifically, irreversible demagnetization) of the permanent magnet 40. The induced voltage V of the motor 5 before demagnetization occurs is ０ and the induced voltage V of the motor 5 after demagnetization occurs. １ and these induced voltages V ０ , V １ From {(V １ / V ０ )-1} x 100 to calculate the demagnetization rate (%).

[0071] The phase magnetomotive force (AT) is the product of the current value (A) of the current flowing through the winding 20 and the number of turns of the winding 20 around one tooth 12 (i.e., the number of turns).

[0072] The magnitude of the phase magnetomotive force when the demagnetization factor is −1.5% is one of the performance guarantee values ​​of the compressor 100. As the number of poles of the motor 5 increases, the phase magnetomotive force when the demagnetization factor is −1.5% increases.

[0073] For example, when the number of poles is four, the phase magnetomotive force when the demagnetization factor is -1.5% is 1.5 times that when the number of poles is six compared to when the number of poles is four, twice that when the number of poles is eight, and 2.5 times that when the number of poles is ten.

[0074] From this result, it can be seen that the greater the number of poles of the motor 5, the less likely demagnetization occurs in the permanent magnets 40. This is because the greater the number of poles, the more dispersed the magnetic field acting on each permanent magnet 40 from the stator 1, reducing the effect of causing demagnetization of the permanent magnets 40.

[0075] In other words, assuming that the ambient temperature of the motor 5 and the torque generated by the motor 5 are constant, the greater the number of poles in the motor 5, the smaller the coercive force, i.e., the smaller the Dy content, of the neodymium rare earth magnet that can be used.

[0076] 9 is a graph showing the relationship between the Dy content required to suppress the absolute value of the demagnetization factor to 1.5% or less when using a single refrigerant, R32, and the number of poles of the motor 5. The horizontal axis of FIG. 9 represents the number of poles of the motor 5, and the vertical axis represents the Dy content (wt %) of the permanent magnet 40.

[0077] 9 shows that increasing the number of poles of the electric motor 5 allows for improved demagnetization resistance while reducing the Dy content. When the number of poles is six, the Dy content of the permanent magnet 40 can be reduced to 3.8% by weight or less. Similarly, when the number of poles is eight, the Dy content of the permanent magnet 40 can be reduced to 2.7% by weight or less, and when the number of poles is ten, the Dy content of the permanent magnet 40 can be reduced to 1.9% by weight or less.

[0078] Fig. 10 is a graph showing the analysis results of motor efficiency when the number of poles of the electric motor 5 is changed. The horizontal axis of Fig. 10 represents the number of poles of the electric motor 5, and the vertical axis represents motor efficiency. Motor efficiency is the ratio of output to input to the electric motor 5. The input to the electric motor 5 is the power supplied to the windings 20, and the output of the electric motor 5 is the product of torque and rotational speed.

[0079] Assuming that the rotation speed of the electric motor 5 remains the same, an increase in the number of poles of the electric motor 5 increases the frequency of the current supplied from the inverter to the windings 20. When the frequency increases, the fluctuation of the magnetic flux becomes larger, which increases iron loss and, as a result, reduces the motor efficiency.

[0080] For example, when R32 is used as the refrigerant and the Dy content of the permanent magnet 40 is kept constant at 4 wt %, as shown by curve D1 in Figure 10, the motor efficiency is maximized when the number of poles is four, and the motor efficiency decreases as the number of poles increases.

[0081] In contrast, if the Dy content of the permanent magnets 40 is reduced in accordance with an increase in the number of poles of the electric motor 5 (see FIG. 9), the residual magnetic flux density of the permanent magnets 40 is improved (see FIG. 6), and copper loss can be reduced. As a result, even if iron loss increases due to the increase in the number of poles described above, motor efficiency can be improved by reducing copper loss.

[0082] For example, when R32 is used as the refrigerant and the Dy content is reduced in accordance with the increase in the number of poles, such as by setting the Dy content to 7.0 wt % for 4 poles, 3.8 wt % for 6 poles, and 2.7 wt % for 8 poles, as shown in Figure 9, the motor efficiency can be improved as shown by curve D2 in Figure 10. Furthermore, the improvement in motor efficiency also makes it possible to reduce the size of the electric motor 5.

[0083] Furthermore, as described above, in the compressor 100 using any one of the refrigerants (1) to (3), the ambient temperature of the electric motor 5 is lower than in a compressor using only R32 refrigerant. Since the permanent magnet 40 is a neodymium rare earth magnet whose coercive force decreases with increasing temperature, a decrease in the ambient temperature of the electric motor 5 suppresses a decrease in the coercive force of the permanent magnet 40 even if the Dy content is low.

[0084] By reducing the Dy content, the residual magnetic flux density of the permanent magnet 40 is improved, which increases the amount of effective magnetic flux of the permanent magnet 40 and further improves motor efficiency.

[0085] Therefore, when one of the above refrigerants (1) to (3) is used instead of R32 and the Dy content is reduced in accordance with the increase in the number of poles as shown in FIG. 9, the motor efficiency is improved as shown by curve D3 in FIG. 10.

[0086] Furthermore, the operating pressure of the above-mentioned refrigerants (1) to (3) is lower than that of R32 alone, so in order to obtain the same output as when R32 is used without changing the configuration of the compressor 100, it is necessary to increase the rotation speed of the motor 5.

[0087] As the rotation speed of the electric motor 5 increases, a swirling flow of the refrigerant and refrigeration oil is generated by the rotation of the rotor 3, and the refrigerant and refrigeration oil flow at high speed through the through holes 36, 37, 38 of the rotor 3 and between the notch 15 of the stator 1 and the shell 111. The electric motor 5 is cooled by the refrigerant and refrigeration oil, which further suppresses the decrease in the coercive force of the permanent magnets 40.

[0088] In particular, since the rotor core 30 has through holes 36, 37, and 38 between the magnet insertion hole 31 and the center hole 30b, the permanent magnets 40 are efficiently cooled by the refrigerant flowing through the through holes 36, 37, and 38, further suppressing the decrease in the coercive force of the permanent magnets 40.

[0089] In the above (2), the "other refrigerants" to be mixed with at least one of R1234yf, R1234ze(E), R290, R1123, and R32 are not limited to those shown in Fig. 7. However, it is desirable that the discharge temperature and GWP of the mixed refrigerant be lower than those of R32 alone. That is, it is desirable that the discharge temperature of the mixed refrigerant be lower than 77°C and the GWP be lower than 675.

[0090] For example, in (2) above, it is desirable that the other refrigerant mixed with R32 has a lower discharge temperature and a lower GWP than the R32 refrigerant alone.

[0091] Similarly, in (3) above, the "other refrigerants" to be mixed with at least one of R447A, R447B, R454A, R454B, R454C, and R455A are not limited to the refrigerants shown in Figure 7. However, it is desirable that the discharge temperature and GWP of the mixed refrigerant be lower than those of R32 alone. That is, it is desirable that the discharge temperature of the mixed refrigerant be less than 77°C and that the GWP be less than 675.

[0092] <Examples of Motor Configuration> While the configuration of a six-pole motor 5 is shown in Fig. 1 above, configurations of motors with other numbers of poles will be described below. Fig. 11(A) is a cross-sectional view showing a four-pole motor 5A, and Fig. 11(B) is a cross-sectional view showing an eight-pole motor 5B.

[0093] The electric motor 5A shown in Fig. 11A corresponds to an electric motor with four poles on the curve D3 in Fig. 10. The electric motor 5A has a stator 1A and a rotor 3A. The stator 1A has a stator core 10 and a winding 20. The stator core 10 has a core back 11 and 24 teeth 12, with slots 13 formed between adjacent teeth 12.

[0094] The rotor 3A has a rotor core 30 and permanent magnets 41, 42. The rotor core 30 has four magnet insertion holes 31 in the circumferential direction. A permanent magnet 41, 42 is arranged in each magnet insertion hole 31. The permanent magnets 41, 42 arranged in each magnet insertion hole 31 form one magnetic pole. In other words, the rotor 3A has four poles. An inter-pole portion is formed between adjacent magnet insertion holes 31. Note that each magnet insertion hole 31 may have only one permanent magnet arranged therein.

[0095] The rotor core 30 has through holes 301 and 302 radially between the magnet insertion hole 31 and the center hole 30b. The through hole 301 is formed radially inward of the circumferential center of the magnet insertion hole 31. The through hole 302 is formed radially inward of the inter-pole portion. The cross-sectional area of ​​the through hole 302 is larger than the cross-sectional area of ​​the through hole 301.

[0096] Both through holes 301 and 302 axially pass through rotor core 30 and are used as refrigerant passages. Either through hole 301 or 302 may be used as a rivet hole. The positions of through holes 301 and 302 are not limited to those described above. The cross-sectional area of ​​through hole 302 may be smaller than or the same as the cross-sectional area of ​​through hole 301.

[0097] Furthermore, a crimped portion 303 is formed between adjacent through holes 301, 302 in the circumferential direction. The crimped portion 303 is a portion for fixing the electromagnetic steel sheets that make up the rotor core 30. However, the position of the crimped portion 303 is not limited to the position described above. Furthermore, the electromagnetic steel sheets may be fixed with rivets or the like without providing the crimped portion 303.

[0098] Electric motor 5B shown in Fig. 11(B) corresponds to an electric motor with eight poles on curve D3 in Fig. 10. Electric motor 5B has a stator 1B and a rotor 3B. Stator 1B has a stator core 10 and windings 20. Stator core 10 has a core back 11 and 24 teeth 12, with slots 13 formed between adjacent teeth 12.

[0099] The rotor 3B has a rotor core 30 and permanent magnets 40. The rotor core 30 has eight magnet insertion holes 31 in the circumferential direction. A permanent magnet 40 is arranged in each magnet insertion hole 31. The permanent magnet 40 arranged in each magnet insertion hole 31 constitutes one magnetic pole. In other words, the rotor 3B has eight poles. An inter-pole portion is formed between adjacent magnet insertion holes 31. Note that two or more permanent magnets may be arranged in each magnet insertion hole 31.

[0100] The rotor core 30 has through holes 301 and 302 between the magnet insertion hole 31 and the center hole 30b. The through hole 301 is formed radially inward from the circumferential center of the magnet insertion hole 31. The through hole 302 is formed radially inward from the inter-pole portion. The cross-sectional area of ​​the through hole 302 is the same as the cross-sectional area of ​​the through hole 301.

[0101] Both through holes 301 and 302 pass through rotor core 30 in the axial direction and are used as refrigerant passages. Either through hole 301 or 302 may be used as a rivet hole. The positions of through holes 301 and 302 are not limited to those described above. The cross-sectional areas of through holes 301 and 302 may be different. A crimped portion may be provided on rotor core 30, or the electromagnetic steel plates may be fixed with rivets or the like without providing crimped portion 303.

[0102] 11A and 11B show motors with four and eight poles on the curve D3 of FIG. 10, but the motor with six poles on the curve D3 of FIG. 10 is motor 5 shown in FIG. 1.

[0103] <Protrusion in Magnet Insertion Hole> Figure 12(A) is an enlarged view of the protrusion 33 and its surroundings provided in the magnet insertion hole 31. The protrusion 33 is formed on the radially inner edge of the magnet insertion hole 31 in a position where it abuts against the end face 40a of the permanent magnet 40 in the width direction. The protrusion 33 serves to position the permanent magnet 40 in the circumferential direction.

[0104] Because the protrusions 33 are made of the same magnetic material as the rotor core 30, magnetic flux generated by the current flowing through the windings 20 of the stator 1 easily flows to the protrusions 33 as shown by arrow F in Figure 12(B) . Therefore, the end faces 40a of the permanent magnets 40 that contact the protrusions 33 are easily demagnetized by the magnetic flux from the stator 1.

[0105] However, in the compressor 100 using any of the above-described refrigerants (1) to (3), the ambient temperature of the motor 5 is lower than in a compressor using only R32 refrigerant, and therefore, the decrease in the coercive force of the neodymium rare earth magnet 40 is suppressed. Therefore, even if the protrusion 33 is provided in the magnet insertion hole 31, demagnetization of the permanent magnet 40 can be suppressed.

[0106] Although the case where a protrusion 33 is provided in the magnet insertion hole 31 has been described here, if there is another means for positioning the permanent magnet 40 within the magnet insertion hole 31, it is possible not to provide the protrusion 33.

[0107] Effect of the Embodiment As described above, the electric motor 5 according to the first embodiment is an electric motor 5 mounted on the compressor 100, and includes the rotor 3 having the permanent magnet 40, and the stator 1. The refrigerant used in the compressor 100 is any one of R1234yf, R1234ze(E), R290, and R1123, a mixed refrigerant containing at least one of R1234yf, R1234ze(E), R290, R1123, and R32, or a mixed refrigerant containing at least one of R447A, R447B, R454A, R454B, R454C, and R455A. The permanent magnet 40 is a rare earth magnet containing Nd, Fe, and B, with a Dy content of 4 wt % or less.

[0108] By using the above refrigerant, the temperature inside the compressor 100 can be lowered compared to when a single refrigerant, R32, is used, and a decrease in the coercivity of the permanent magnets 40, which are neodymium rare earth magnets, can be suppressed. As a result, even with a small Dy content, demagnetization of the permanent magnets 40 can be suppressed. Furthermore, by reducing the Dy content, the residual magnetic flux density of the permanent magnets 40 can be improved, thereby improving motor efficiency.

[0109] In particular, when a protrusion 33 for positioning the permanent magnet 40 is provided within the magnet insertion hole 31, magnetic flux from the stator 1 is likely to flow into the permanent magnet 40 via the protrusion 33. However, by lowering the temperature within the compressor 100 as described above, the decrease in the coercive force of the permanent magnet 40 is suppressed, and therefore demagnetization of the permanent magnet 40 can be suppressed.

[0110] Furthermore, by lowering the temperature inside the compressor 100 as described above, it is possible to use aluminum wire, which has a higher electrical resistance (and therefore a larger amount of heat generation) than copper wire, for the windings 20 .

[0111] Furthermore, when the windings 20 are wound around the stator core 10 in a distributed winding manner, the coil ends 22 are larger than when the windings are wound in a concentrated winding manner, and therefore, a refrigerant with a low discharge temperature flows through the coil ends 22, allowing the heat of the windings 20 to be dissipated from the coil ends 22. This suppresses an increase in the resistance of the windings 20 due to a rise in temperature, and improves motor efficiency.

[0112] In addition, since the rotor core 30 has through holes 36, 37, and 38 radially between the magnet insertion hole 31 and the center hole 30b, the temperature rise of the permanent magnets 40 caused by refrigerant with a low discharge temperature passing through the through holes 36, 37, and 38 can be suppressed.

[0113] Furthermore, since the GWP of the above-mentioned refrigerant is lower than the GWP of a single refrigerant such as R32 (in other words, less than 675), the environmental impact can be reduced and the need to prevent global warming can be met.

[0114] 13 is a cross-sectional view showing an electric motor 5C of embodiment 2. The electric motor 5C of embodiment 2 differs from the electric motor 5 of embodiment 1 in that it has at least one slit 35 between the outer periphery 30a of the rotor core 30 of the rotor 3C and the magnet insertion hole 31.

[0115] 14 is a diagram showing the slits 35 and their surroundings in a rotor 3C according to embodiment 2. As in embodiment 1, flux barriers 32 are formed at both circumferential ends of the magnet insertion holes 31. Furthermore, circumferentially long side slits 34 are formed on the pole center line C side of the flux barrier 32.

[0116] The rotor core 30 has eight slits 35 formed symmetrically around the pole center line C between each magnet insertion hole 31 and the outer periphery 30a of the rotor core 30. More specifically, a first slit 35a, a second slit 35b, a third slit 35c, and a fourth slit 35d are formed in this order from the side closest to the pole center line C. All of the slits 35a, 35b, 35c, and 35d are long in the radial direction.

[0117] The slits 35a, 35b, 35c, and 35d rectify the magnetic flux emitted from the permanent magnet 40, and make the magnetic flux distribution on the outer periphery 30a of the rotor 3 closer to a sinusoidal waveform, thereby suppressing the generation of vibration and noise.

[0118] As in the first embodiment, the following refrigerants can be used as the refrigerant for compressor 100 in the second embodiment: (1) any one of R1234yf, R1234ze(E), R290, and R1123, (2) a mixed refrigerant containing at least one of R1234yf, R1234ze(E), R290, R1123, and R32, or (3) a mixed refrigerant containing at least one of R447A, R447B, R454A, R454B, R454C, and R455A.

[0119] When slits 35a to 35d are provided between the magnet insertion hole 31 and the outer periphery 30a of the rotor core 30, the magnetic flux flowing from the stator 1 into the rotor core 30 tends to concentrate in the thin-walled portion between the magnet insertion hole 31 and the slits 35a to 35d, as shown by arrow f in Figure 14 (B), and the surface of the permanent magnet 40 on the outer periphery 30a side tends to be demagnetized.

[0120] However, in the compressor 100 using any of the refrigerants (1) to (3), the ambient temperature of the motor 5 is lower than in a compressor using only R32 refrigerant, so the decrease in coercivity of the neodymium rare earth magnets 40 is suppressed. Therefore, even if the slits 35a to 35d are provided between the magnet insertion holes 31 and the outer periphery 30a of the rotor core 30, demagnetization of the permanent magnets 40 can be suppressed.

[0121] The number of slits 35 formed between each magnet insertion hole 31 and the outer periphery 30a of the rotor core 30 is not limited to eight, but may be one or more. Also, although side slits 34 are formed adjacent to the flux barrier 32 here, the side slits 34 do not necessarily have to be formed.

[0122] As described above, in embodiment 2, at least one slit 35 is formed between the outer periphery 30a of the rotor core 30 and each magnet insertion hole 31, and magnetic flux tends to concentrate between the slit 35 and the magnet insertion hole 31. However, by using any of the refrigerants (1) to (3), the temperature inside the compressor 100 can be lowered and a decrease in the coercive force of the permanent magnets 40, which are neodymium rare earth magnets, can be suppressed. Therefore, even if the slits 35 are provided, demagnetization of the permanent magnets 40 can be suppressed.

[0123] Although the preferred embodiments have been specifically described above, various improvements and modifications can be made to these embodiments.

[0124] DESCRIPTION OF SYMBOLS 1, 1A, 1B stator, 3, 3A, 3B rotor, 5, 5A, 5B, 5C electric motor, 10 stator core, 11 core back, 12 teeth, 13 slot, 14 outer periphery, 15 notch, 20, 20U, 20V, 20W winding, 21 coil side, 22 coil end, 30 rotor core, 30a outer periphery, 30b center hole, 31 magnet insertion hole, 33 protrusion, 35 slit, 36, 37, 38 through hole, 40, 41, 42 permanent magnet, 45 shaft, 80 refrigeration cycle device, 81 indoor unit, 82 outdoor unit, 84 condenser, 85 pressure reducing device, 87 evaporator, 100 compressor, 105 Compression mechanism, 110: sealed container, 111: shell, 301: through hole, 302: through hole, 303: crimped portion.

Claims

1. An electric motor mounted on a compressor, comprising a rotor having a permanent magnet and a stator surrounding the rotor, wherein the refrigerant used in the compressor is any one of single refrigerants of R1234yf, R1234ze(E), R290 and R1123, a mixed refrigerant containing at least one of R1234yf, R1234ze(E), R290, R1123 and R32, or a mixed refrigerant containing at least one of R447A, R447B, R454A, R454B, R454C and R455A, and the permanent magnet is a rare earth magnet containing neodymium, iron and boron, and the dysprosium content in the permanent magnet is 4% by weight or less.

2. The electric motor according to claim 1, wherein the rotor has a rotor core having a magnet insertion hole in which the permanent magnet is disposed, and the rotor core has a protrusion for positioning the permanent magnet inside the magnet insertion hole.

3. The electric motor according to claim 1 or 2, wherein the rotor has a rotor core having a magnet insertion hole in which the permanent magnet is disposed, and the rotor core has a slit between the magnet insertion hole and the outer periphery of the rotor core.

4. The electric motor according to any one of claims 1 to 3, wherein the rotor has a rotor core having a magnet insertion hole in which the permanent magnet is disposed and a central hole to which a shaft is fixed, and the rotor core has a through hole penetrating the rotor core in the axial direction of the shaft between the central hole and the magnet insertion hole.

5. The electric motor according to any one of claims 1 to 4, wherein the stator has a stator core and a winding wound around the stator core, and the winding is composed of aluminum wire.

6. The electric motor according to any one of claims 1 to 5, wherein the stator has a stator core and a winding wound around the stator core, and the winding is wound in a distributed winding.

7. The electric motor according to any one of claims 1 to 6, wherein the discharge temperature of the refrigerant is less than 77°C and the GWP of the refrigerant is less than 675.

8. A compressor comprising the electric motor according to any one of claims 1 to 7, a compression mechanism driven by the electric motor, and a sealed container housing the electric motor and the compression mechanism.

9. The compressor according to claim 8, wherein the ambient temperature of the electric motor in the compressor is less than 150°C.

10. A refrigeration cycle device comprising the compressor according to claim 9, a condenser, a decompression device, and an evaporator.

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