KR20210016901A - Permanent magnet synchronous motor and hermetic compressor using the same - Google Patents

Abstract

Disclosed is a permanent magnet synchronous motor for a hermetic compressor which can reduce noise. The permanent magnet synchronous motor comprises: a stator having a plurality of teeth on which a coil is wound to form an electromagnetic field; and a rotor having a rotor yoke rotatable from the outside of the stator in a cylindrical shape, and a plurality of permanent magnets provided along a circumferential direction on an inner surface of the rotor yoke. The thickness of the rotor yoke is equal to or less than the thickness of the permanent magnet and is greater than the minimum thickness corresponding to a saturated counter electromotive force.

Description

Permanent magnet synchronous motor and hermetic compressor using the same

The present invention relates to a hermetic compressor, and more particularly, to a high-efficiency and low-noise permanent magnet synchronous motor used in a hermetic compressor.

The hermetic compressor is an electric compressor in which the compressor and the driving motor are integrated into a closed container. Compared to an open compressor, a permanent magnet synchronous motor is required that is smaller in size, has less noise, and does not have a shaft sealing device.

Permanent magnet synchronous motor (PMSM) is composed of a stator having a plurality of teeth and a rotor that can rotate by maintaining an air-gap from the teeth of the stator. The stator is composed of a plurality of teeth and a yoke connecting the teeth, and a plurality of coils are wound around the plurality of teeth, and the rotor is a permanent magnet that is concentric with the outer diameter of the stator and has different poles. They are assembled in turn.

Synchronous motors can be classified into internal and external types according to the assembly structure of the stator and rotor. The number of poles and slots of a synchronous motor may be determined in consideration of the required output, required operation speed (RPM RANGE) characteristics, and the outer dimension limit of the motor. Therefore, a small synchronous motor used in a hermetic compressor is required to be designed to show the maximum output efficiency in consideration of the limited outer dimension.

In addition, the synchronous motor generates cogging torque in a no-load state due to the permanent magnet assembled in the rotor, the teeth of the stator, and the slot structure. Reluctance depends on the location of the permanent magnet and the spatial location of the stator core. Cogging torque is a phenomenon in which the permanent magnet is about to move to the point where the magnetic resistance is minimized, and it can adversely affect the noise of the motor and the product. Therefore, the synchronous motor used in the hermetic compressor needs a design capable of reducing cogging torque.

Accordingly, an object of the present invention is to solve the above-described conventional problem, to provide a permanent magnet coin operated motor capable of reducing noise by improving the output efficiency of the motor in a limited outer dimension and reducing cogging torque, and a hermetic compressor using the same. In having to.

To achieve the above object, a permanent magnet synchronous motor according to an embodiment of the present invention is disclosed. The permanent magnet synchronous motor includes a stator having a plurality of stator teeth in which coils are wound to form an electromagnetic field, a rotor yoke that is rotatable outside the stator in a cylindrical shape, and is provided along the circumferential direction on the inner surface of the rotor yoke. It includes a rotor having a plurality of permanent magnets, the thickness of the rotor yoke is less than or equal to the thickness of the permanent magnet, and is greater than a minimum thickness corresponding to the saturated back EMF.

The number of slots on each pole may be 1/3 or less.

The permanent magnet is made of ferrite, and the thickness of the rotor yoke may be at least 0.375 times the thickness of the permanent magnet.

The shoe of the stator tooth may include a first arc surface portion facing the rotor at a center and having a surface curved outward, and a first flat surface portion having flat surfaces on both sides of the first arc surface portion.

The permanent magnet may include a second arc surface portion facing the stator at a center and having an inwardly curved surface, and a second flat surface portion having flat surfaces on both sides of the second arc surface portion.

The first arc surface portion and the first flat portion may face each other in correspondence with the second arc surface portion and the second flat surface portion at a position in which the tooth and the permanent magnet are aligned with each other.

The angle θs of the first arc surface portion may be greater than or equal to the angle θr of the second arc surface portion.

The angle θs of the first arc surface portion may be less than or equal to the polar arc angle θm of the permanent magnet.

The polar arc angle (θm) of the permanent magnet may satisfy the following equation.

288°/number of poles ≤ θm ≤ 360°/number of poles

The angle θmc between the extension line of the second plane part and the rotation center line may satisfy the following equation.

80°≤ θmc ≤ 90°

A hermetic compressor according to an embodiment of the present invention is provided. The hermetic compressor includes a compression unit for compressing a gas, a stator having a plurality of stator teeth in which coils are wound to form an electromagnetic field, and a rotor yoke and the rotor yoke rotatable outside the stator in a cylindrical shape. It includes a permanent magnet synchronous motor having a rotor having a plurality of permanent magnets provided along the circumferential direction on the inner surface, the thickness of the rotor yoke is less than or equal to the thickness of the permanent magnet, and is greater than the minimum thickness corresponding to the saturated back EMF .

The permanent magnet synchronous motor according to the present invention can improve the output efficiency by making the thickness of the rotor yoke larger than the minimum thickness representing the saturation back EMF in a limited outer dimension. In addition, the synchronous motor can improve mass production and reduce noise by reducing the number of slots of each pole to 1/3.

1 is a perspective view showing a compressor according to a first embodiment of the present invention.
2 is a perspective view of the compressor with the container removed from FIG. 1.
3 is a cross-sectional view taken along line AA of FIG. 2.
4 is an exploded perspective view of the electric motor of FIG. 2.
5 is a view showing a stator and a rotor of a permanent magnet synchronous motor according to an embodiment of the present invention.
6 is a plan view showing the rotor of FIG. 5.
7 is a graph showing the relationship of back EMF according to the thickness ratio of the permanent magnet and the rotor yoke.
8 is a view showing the structure of the teeth of FIG. 7.
9 is a diagram showing the structure of the stator yoke of FIG. 7.
10 is a diagram showing a permanent magnet.
11 is a view showing the rotor of FIG. 7.
12 is a graph showing a comparison of the cogging torque of the present invention and a conventional electric motor.
13 is an enlarged view showing a part of the stator and the rotor.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present invention. The present invention may be implemented in various different forms and is not limited to the embodiments described herein. In order to clearly describe the present invention, the same reference numerals are attached to the same or similar components throughout the specification.

Hereinafter, a structure of the compressor 1 according to an embodiment of the present invention will be described with reference to the drawings.

1 is a perspective view showing a compressor 1 according to a first embodiment of the present invention.

Referring to FIG. 1, the hermetic compressor 1 includes a compression unit 10 that is sealed in the inner space of the container 2, an electric motor 20 and a compression unit 10 that provide power to the compression unit 10. ) And a support frame 30 for supporting the electric motor 20. The container 2 is constructed by combining the upper container 2-1 and the lower container 2-2 in a state in which the compressor 1 is accommodated.

2 is a perspective view of the compressor 1 with the container 2 removed from FIG. 1, and FIG. 3 is a cross-sectional view taken along line A-A of FIG.

2 and 3, the compression unit 10 is a cylinder 12 having a cylindrical compression space (PS) for compressing a gas, for example, a refrigerant, and operates to reciprocate within the compression space (PS). It may include a piston 14 and a connecting rod 16 provided between the piston 14 and the electric motor 20 and converting the rotational motion of the electric motor 20 into a linear reciprocating motion of the piston 14.

The electric motor 20 may transmit power to the piston 14 of the compression unit 10 to cause the piston 14 to suck and compress gas. The electric motor 20 is connected to the center of the stator 22 in which a plurality of winding coils are provided in the circumferential direction, the cylindrical rotor 24 rotating around the stator 22, and the rotor 24 It may include a rotation shaft 26 for transmitting the rotational force of the former 24. In addition, although not shown in FIGS. 1 and 2, the electric motor 20 may include one or more bearings supporting the rotating shaft 26.

The electric motor 20 may include a power supply unit and a switching unit receiving power from the power supply unit and applying it to the winding coil.

In order to supply DC power by rectifying and smoothing the input AC power, the power supply unit can convert the rectified DC power into a three-phase AC power in the form of a pulse with a variable frequency through a rectifier circuit composed of a rectifier and a smoothing capacitor. have.

The switching unit may be formed of a plurality of switching elements. The switching unit may apply power supplied from the power supply unit to the stator 22 as the switching device operates on or off.

The electric motor 20 may further include a controller for driving control as a system.

4 is an exploded perspective view of the electric motor 20 of FIG. 2.

Referring to FIG. 4, the electric motor 20 is a surface-attached three-phase permanent magnet synchronous motor, for example, a stator 22 fixedly supported, and a rotor that rotates provided with a certain air gap on the outer circumferential surface of the stator 22 ( 24) may be included. Hereinafter, the electric motor 20 will be described with an example of an unrestricted 8-pole 6-slot structure. In Fig. 4, the winding coil wound around the stator 22 is omitted.

The stator 22 may include a stator yoke 222, an insulator 224, a stator support 226 and a stator cover 228.

The stator yoke 222 is, for example, an iron core made of silicon steel and extends radially equally spaced apart from the outer peripheral surface of the shaft hole 2222 and the shaft hole 2222 having a through hole through which the rotating shaft 26 passes. For example, it may include six stator teeth 2224.

A shoe 2226 extending in the circumferential direction is provided at an end of the stator tooth 2224. The shoe 2226 prevents the winding coil wound around the stator tooth 2224 from being pulled out.

Six slots 2228 may be formed between the six stator teeth 2224, for example. Each slot 2228 is a space for winding the winding coil around the stator teeth 2224 and a space in which the winding coil is located. Here, the winding coil is wound around the stator teeth 2224 a plurality of times, and an electromagnetic field may be generated by an induced current applied from the power supply.

The insulator 224 may include six insulating slots 2242 fitted into each slot 2228 for insulation between winding coils wound around each stator tooth 2224.

The stator support part 226 may support the stator yoke 222 in which the winding coil is wound. The stator support part 2262 may include six insulating separation walls 2262 for insulating and separating the stator cover 228 in each slot 2228.

The stator cover 228 may accommodate and support the stator yoke 222 in which the winding coil is wound together with the stator support 226.

The rotor 24 includes, for example, eight permanent magnets 244 and permanent magnets 244 provided to be spaced apart in a circumferential direction on the inner circumferential surface of the cylindrical rotor yoke 242 and the rotor yoke 242. It may include a rotor support 246 for receiving and supporting the mounted rotor yoke 242.

The rotor yoke 242 may be formed in a cylindrical shape made of, for example, silicon steel.

The permanent magnet 244 may be formed of at least one of an alico magnet, a ferrite magnet, a neodym magnet, or a samarium cobalt magnet. The permanent magnet 244 has an arcuate cross-sectional shape, and a concave central portion is disposed toward the rotation center of the rotor yoke 242 and may be mounted on the inner peripheral surface of the rotor yoke 242.

The rotor support 246 may include a rotor accommodating unit 2462 for receiving and supporting the rotor yoke 242 provided with permanent magnets 244 in a cylindrical shape with one side open. The rotor accommodating portion 2462 is provided with a plurality of openings 2464 along the outer circumferential surface. The rotor accommodating part 2462 is provided with a rotation shaft 26 at the center of the other side.

The electromagnetic field generated by the stator 22 and the magnetic field of the permanent magnet 244 of the rotor 24 interact to generate a repulsive force or a suction force, and as a result, the rotor 24 may rotate.

Hereinafter, a design method for improving the output efficiency and reducing noise of the electric motor 20 for the hermetic compressor 1 will be described.

The reluctance (RELUCTANCE) varies depending on the location of the permanent magnet 244 and the spatial location of the stator yoke 222. The cogging torque is a phenomenon in which the permanent magnet 244 of the rotor 24 attempts to move to a point at which magnetic resistance is minimized. Therefore, in order to reduce the noise of the motor 20 and the vibration and noise of the compressor 1, a design for reducing cogging torque that affects the vibration and noise is required. The cogging coefficient (K) can be determined by the following equation.

Cogging coefficient (K) = (number of poles x number of slots)/(Last common multiple of number of poles and number of slots)

For example, the cogging coefficient (K) of each of 4 poles 6 slots, 6 poles 9 slots, and 8 poles 12 slots may be 2, 3, or 4. Accordingly, the cogging torque is inversely proportional to the least common multiple of the number of slots and the number of poles when considering the alignment relationship between the pole axis of the permanent magnet and the stator axis, and the cogging torque increases as the number of repetitions of the same arrangement increases. As a result, it is possible to grasp the effect of cogging torque according to the pole-slot combination of the same type motor through the cogging coefficient before design.

The pole-slot combination needs to consider mass production, e.g., winding process, terminal portion and wiring, improvement in power density (compactization, high output), and maximization of winding coefficient.

Table 1 shows the winding coefficient for each pole-slot structure. In Table 1, when considering the mass production of the small electric motor 20 used in the hermetic compressor 1, the number of slots is 6 slots, the minimum number of slots, and the number of poles is the 4 poles of the rotor 24 when considering the winding coefficient. You can select 8 poles. Here, 9 slots-8,10 poles/12 slots-10, 14 poles/15 slots-14,16 poles/18 slots-14,16 poles have magnetic inequality, so they can be excluded in consideration of noise and vibration.

4 pole 6 pole 8 pole 10 poles 12 poles 14 poles 16 poles 6 slots 0.866 0.866 0.5 0.5 0.866 9 slots 0.866 0.9452 0.9452 0.866 12 slots 0.866 0.966 0.966 0.866 15 slots 0.866 0.9514 0.951 18 slots 0.866 0.902 0.945 21 slots 0.866 0.773 24 slots 0.866

The eight poles of the rotor 24 represent a back EMF of 11.3 (Vrms), and the four poles represent a back EMF of 10.1 (Vrms). Therefore, the 8 poles show 12.3% better back electromotive force than the 4 poles. In addition, the 8-pole back EMF of 11.3 (Vrms) satisfies the limit value of 11.79Vrms or less. Therefore, among the 4 poles and the 8 poles, 8 poles can be selected when considering the power density.

Table 2 is a value showing the cogging coefficient (K) according to the number of slots on each pole. The number of slots sold by the motor 20 may be determined by the following equation.

Selling number of slots = number of slots/(number of poles x number of phases)

Therefore, in a three-phase motor, when the number of slots is smaller than that of the number of poles, the number of slots sold per pole is less than 1/3. In Table 2, 4 poles -6 slots and 8 poles -6 slots have a cogging coefficient (K) of 2.0, which is superior to other pole-slot combinations. At this time, since the power density is superior to 8 poles than 4 poles, 6 slots of 8 poles can be determined.

Number of poles Number of slots Selling slots Cogging coefficient (K) 4 6 0.50 2.0 6 9 0.50 3.0 8 12 0.50 4.0 8 6 0.25 2.0

Table 3 shows the cogging torque when the 8-pole 6-slot structure selected as described above is applied to the withstand and abduction type motors, respectively. Here, the internal electric motor has a structure in which the rotor 24 is provided inside and the stator 22 surrounds the rotor 24, and the abduction type electric motor has a stator 22 inside and the rotor 24 ) Is a structure provided to surround the stator 22. In Table 3, the 8-pole 6-slot abduction motor exhibits about 16.2% of the cogging torque compared to that of the 8-pole 6-slot withstand motor. Therefore, it can be seen that the 8-pole 6-slot abduction motor can significantly reduce noise compared to the 8-pole 6-slot withstand motor.

rescue Prototype 8-pole 6 slots External 8-pole 6 slots Cogging torque [Nm] 0.01140 0.00185

5 is a view showing the structure of an 8-pole 6-slot abduction type permanent magnet synchronous motor 20 according to an embodiment of the present invention. The abduction type permanent magnet synchronous motor 20 may include a stator 22 and a rotor 24 that rotates provided with a predetermined air gap on the outer circumferential surface of the stator 22.

The stator 22 may include a stator yoke 222. The stator yoke 222 is an iron core of silicon steel, for example, a shaft hole portion 2222 having a through hole through which the rotating shaft passes, and six pieces extending radially and spaced apart from the outer peripheral surface of the shaft hole portion 2222 at equal intervals. It may include a stator tooth 2224.

A shoe 2226 extending in the circumferential direction is provided at an end of the stator tooth 2224. The shoe 2226 prevents the winding coil wound around the stator tooth 2224 from being pulled out. In FIG. 5, the winding coil is omitted for convenience of description.

Six slots 2228 may be formed between the six stator teeth 2224. Each slot 2228 is a space for winding the winding coil around the stator teeth 2224 and a space in which the winding coil is located.

The rotor 24 may include a cylindrical rotor yoke 242, and, for example, eight permanent magnets 244 provided to be spaced apart in a circumferential direction on an inner peripheral surface of the rotor yoke 242.

The rotor yoke 242 may be formed in a cylindrical shape made of, for example, silicon steel. The rotor yoke 242 may include eight magnet mounting portions 2422 for mounting eight permanent magnets 244 on the inner circumferential surface.

6 is a plan view showing the rotor 24 of FIG. 5.

Referring to FIG. 6, the rotor 24 may include a cylindrical rotor yoke 242 having a thickness Tb and a permanent magnet 244 having a thickness Tm made of ferrite and mounted on the inner circumferential surface of the rotor yoke 242.

FIG. 7 is a graph showing a relationship between the back electromotive force according to the ratio of the thickness Tb of the rotor yoke 242 and the thickness Tm of the permanent magnet 244 in FIG. 6. The vertical axis represents the back electromotive force (Vrms), and the horizontal axis represents the thickness ratio (Tb/Tm) of the rotor yoke 242 and the permanent magnet 244. The thickness (Tm) of the ferrite permanent magnet 244 was fixed to 4 mm, and the back electromotive force (Vrms) was measured while increasing the thickness (Tb) of the rotor yoke 242 in 0.5 mm increments.

Referring to FIG. 7, the back electromotive force Vrms linearly increases until the thickness Tb of the rotor yoke 242 is 1.5 mm, and then reaches saturation. That is, the minimum thickness Tb of the rotor yoke 242 corresponding to the saturated back EMF is 0.375 times the thickness Tm of the permanent magnet 244. Therefore, in order to obtain the maximum output of the motor 20, the thickness (Tb) of the rotor yoke 242 is equal to or greater than the minimum thickness (0.375Tm) corresponding to the saturated back EMF, and is less than the thickness (Tm) of the permanent magnet 244. Can be equal to or equal to.

The permanent magnet 244 uses a ferrite magnet, but when a neodymium magnet having a higher magnetic force is used instead of ferrite, the minimum thickness corresponding to the saturation back EMF of the rotor yoke 242 is a minimum thickness other than 0.375Tm. Will display the value.

In addition, the counter electromotive force was measured while changing the minimum thickness (Tb) of the rotor yoke 242 while the thickness (Tm) of the permanent magnet 244 was set to 4 mm, but the thickness (Tm) of the permanent magnet 244 was 3 mm or Even when measuring the back electromotive force while changing the thickness (Tb) of the rotor yoke 242 in a state of 5 mm, the minimum thickness (Tb) of the rotor yoke 242 corresponding to the saturated back electromotive force is a minimum thickness other than 0.375Tm Will represent the value.

As described above, the minimum thickness Tb of the rotor yoke 242 corresponding to the saturation back EMF may be different depending on the number of poles or dimensions of the rotor yoke 242 in addition to the material or thickness of the permanent magnet 244. Accordingly, in consideration of this difference, the thickness Tb of the rotor yoke 242 may be less than or equal to the thickness Tm of the permanent magnet 244 and may be greater than the minimum thickness corresponding to the saturated back EMF.

FIG. 8 is a view showing the structure of the stator teeth 2224 of FIG. 7, and FIG. 9 is a view showing the structure of the stator yoke 222 of FIG. 7.

8 and 9, a shoe 2226 extending in the circumferential direction is provided at an end of the stator tooth 2224. The angle α between the stator teeth 2224 and the shoe 2226 may have an acute angle to obtain a uniform magnetic flux density. The shoe 2226 includes a first inner arc surface portion (s1) facing the inner stator yoke 222, a first outer arc surface portion (s2) facing the rotor 24 in the center and having a surface curved outward, and a first A first flat surface portion s3 having a flat surface may be included on both sides of the outer arc surface portion s2. The first outer arc surface portion s2 has a predetermined outer arc angle θs with respect to the center O.

10 is a view showing the permanent magnet 244 of FIG. 7, and FIG. 11 is a view showing the rotor 24 of FIG. 7.

10 and 11, the permanent magnet 244 is a second outer arc surface portion (r1) corresponding to the curvature of the inner circumferential surface of the rotor yoke 242, a second inner arc surface portion facing the stator 22 and having a surface curved inward. It may include (r2) and a second inner planar portion (r3) having a flat surface on both sides of the second inner surface portion (r2). The permanent magnet 244 has a predetermined extreme arc angle θm with respect to the center O, and the second inner arc surface portion r2 has a predetermined inner arc angle θr with respect to the center O. The second inner planar portion r3 has a predetermined extension angle θmc with respect to the center line.

9 and 11, the outer arc angle θs of the shoe 2226 is less than or equal to the extreme arc angle θm of the permanent magnet 244 and greater than or equal to the inner arc angle θr of the permanent magnet 244.

The angle θmc formed between the second inner plane portion r3 and the center line may be formed by the following equation.

80°≤θmc ≤ 90°

12 is a graph showing cogging torque for the structure of the shoe 2226 and the permanent magnet 244 according to the present invention and in the related art. Here, in the present invention, the outer arc angle (θs) of the shoe 2226 is smaller than or equal to the extreme arc angle (θm) of the permanent magnet 244 and greater than or equal to the inner arc angle (θr) of the permanent magnet 244, and conventionally The shoe and permanent magnet have a single curved surface.

Referring to FIG. 12, the present invention has a cogging torque of 1.29 [mNm], and a conventional cogging torque of 3.93 [mNm]. As such, the structure of the present invention has an effect of reducing cogging torque by 67.2% compared to the conventional structure, and as a result, noise and vibration can be reduced.

13 is an enlarged view of a part of the stator 22 and the rotor 24.

Referring to FIG. 1 3, a slot opening portion 2229 may be included between the shoe 2226 and the shoe 2226 adjacent to the stator 22. The slot opening 2229 is a space through which the nozzle of the winding machine passes when the winding coil is wound around the stator teeth 2224. The slot opening dimension (s/o) of the slot opening portion 2229 may be 1.8 to 2.2 mm in consideration of dimensional tolerances.

The extreme arc angle (θm) of the permanent magnet 244 may be determined by the following equation when considering the counter electromotive force THD [%] and the cogging torque [kgf-cm].

(288°/number of poles) <θm <(360°/number of poles)

As described above, the present invention has been described in detail through preferred embodiments, but the present invention is not limited thereto and may be variously implemented within the scope of the claims.

1: compressor
10: compression unit
20: electric motor
22: stator
222: stator yoke
2224: stator tooth
2226: Shu
2228: slot
2229: slot opening
224: insulator
24: rotor
242: Rotor York
244: permanent magnet

Claims (11)

In a permanent magnet synchronous motor,
A stator having a plurality of stator teeth on which coils are wound to form an electromagnetic field;
A rotor yoke rotatable outside the stator in a cylindrical shape, and a rotor having a plurality of permanent magnets provided along a circumferential direction on an inner surface of the rotor yoke,
The thickness of the rotor yoke is less than or equal to the thickness of the permanent magnet, and is greater than the minimum thickness corresponding to the saturated back electromotive force. The method of claim 1,
Permanent magnet synchronous motor with less than 1/3 of the number of slots on every pole. The method of claim 1,
The permanent magnet is made of ferrite,
A permanent magnet synchronous motor having a thickness of the rotor yoke at least 0.375 times the thickness of the permanent magnet. The method of claim 1,
The shoe of the stator teeth is a permanent magnet synchronous motor comprising a first arc surface portion facing the rotor at a center and having a surface curved outward, and a first flat surface portion having flat surfaces on both sides of the first arc surface portion. The method of claim 4,
The permanent magnet is a permanent magnet synchronous motor comprising a second arc surface portion having a surface curved inward and facing the stator in a center, and a second flat surface portion having flat surfaces on both sides of the second arc surface portion. The method of claim 5,
The first arc surface portion and the first plane portion, at a position in which the tooth and the permanent magnet are aligned with each other, the permanent magnet synchronous motor facing each other in correspondence with the second arc surface portion and the second flat portion, respectively. The method of claim 6,
An angle (θs) of the first arc surface portion is greater than or equal to the angle (θr) of the second arc surface portion. The method of claim 6,
The first arc surface portion angle (θs) is less than or equal to the polar arc angle (θm) of the permanent magnet permanent magnet synchronous motor. The method of claim 4,
The pole arc angle (θm) of the permanent magnet is a permanent magnet synchronous motor that satisfies the following equation.
(288°/number of poles) ≤ θm ≤ (360°/number of poles) The method of claim 5,
An angle (θmc) between the extension line of the second plane portion and the rotation center line satisfies the following equation.
80°≤ θmc ≤ 90° In the hermetic compressor,
A compression unit for compressing air;
A stator having a plurality of stator teeth in which coils are wound to form an electromagnetic field, a rotor yoke rotatable outside the stator in a cylindrical shape, and a rotor having a plurality of permanent magnets provided along the circumferential direction on the inner surface of the rotor yoke It includes a permanent magnet synchronous motor with electrons,
A hermetic compressor, characterized in that the thickness of the rotor yoke is less than or equal to the thickness of the permanent magnet, and is greater than a minimum thickness corresponding to the saturated back electromotive force.

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