WO2001039355A1

WO2001039355A1 - Permanent magnet type ac low-velocity synchronous motor

Info

Publication number: WO2001039355A1
Application number: PCT/KR2000/001137
Authority: WO
Inventors: Seok-Joo Lee
Original assignee: Lee Seok Joo
Priority date: 1999-11-27
Filing date: 2000-10-11
Publication date: 2001-05-31
Also published as: AU7692100A; KR20000012340A

Abstract

A permanent magnet type AC low-velocity synchronous motor comprises a stator having a first small-toothed unit plate which is formed on an inner surface thereof with radial teeth, a unit AC coil, and a second small-toothed unit plate which is formed on an inner surface thereof with radial teeth, the first small-toothed unit plate, the unit AC coil, the second small-toothed unit plate defining one phase and being sequentially inserted into a case to be coupled one with another; and a rotor having a first pair of core plates which are mounted around a rotating shaft, have the same length as the first and second small-toothed unit plates and are formed on outer surfaces thereof with radial teeth such that the radial teeth of the first pair of core plates correspond to the radial teeth of the first and second small-toothed unit plates, respectively, and a first permanent magnet which is positioned between the first pair of core plates thereby to correspond to the unit AC coil and has the same length as the unit AC coil, the first pair of core plates and the first permanent magnet defining another phase, the rotor further having a second pair of core plates and a second permanent magnet which are disposed adjacent to the first pair of core plates and the first permanent magnet so as to afford starting power, the first and second pair of core plates having a phase difference therebetween.

Description

PERMANENT MAGNET TYPE AC LOW-VELOCITY SYNCHRONOUS MOTOR

Technical Field

The present invention relates to a permanent magnet type AC low-velocity synchronous motor, and more particularly, the present invention relates to a permanent magnet type AC low-velocity synchronous motor which includes a stator wherein an AC coil having an annular configuration and a pa r of small -toothed plates each having also an annular configuration and being respectively arranged at both sides of the AC coil are sequentially fitted into a motor case m a lengthwise direction of the motor case thereby to define one phase, and a rotor wherein a pair of core plates and a permanent magnet are disposed m such a way as to respectively correspond to the pair of small -toothed plates and the AC coil of the stator.

Also, the present invention relates to a general AC motor which includes a stator having slots each defined between two adjoining large teeth and AC coils wound m the slots, and a rotor, and more particularly, the present invention relates to an axially assembled type AC motor which includes a stator structured m a manner such that a first small -toothed unit plate not having slots, an AC coil having an annular configuration and a second small- toothed unit plate are sequentially fitted into a motor case m an axial direction of the motor case thereby to define one phase.

Background Art Motors are necessarily composed of rotors and stators, regardless of their kinds, and are divided into DC motors and AC motors depending upon driving power .

AC motors are divided by a structure into non- synchronous motors and synchronous motors, and the synchronous motors are divided by driving power into reluctance motors, permanent magnet type motors and hysteresis motors.

In these days, step motors which receive DC power but are rotated within a predetermined angle by separate control circuits, have been widely used throughout the world.

A reluctance synchronous motor has a salient -poled rotor. In the reluctance synchronous motor, a number of salient poles is the same as a number of poles of the motor and corresponds to a number of magnetic poles which are created by a stator. The reluctance synchronous motor can have a constant velocity in synchronism with a power frequency without experiencing slip.

Step motors are divided by a structure of a rotor into variable reluctance (VR) type step motors, permanent magnet (PM) type step motors and hybrid type step motors . In a step motor, DC power is selectively supplied by phases to afford desired rotation of a rotor. In other words, as shown in FIG. 1, DC power is supplied from a DC power supply V through a diode D and a resistor R to stator coils L1~L . The respective coils L1~L4 are configured in a manner such that DC power is selectively supplied thereto through switching transistors Q1~Q4 each of which is turned on for a predetermined period depending upon pulses from control terminals B1~B4 which in turn are controlled by a control section. The drawing reference symbols Cl, C2 and C3 represent condensers .

FIG. 2 is a block diagram illustrating a controlling procedure of the conventional step motor shown in FIG. 1. An input pulse is fed into an input circuit 1 and then, is provided to a distributing circuit 2. The distributing circuit 2 is configured in a manner such that it distributes the input pulse and transfers the distributed input pulse through a switching circuit 3 to a desired coil of a step motor 4 thereby to selectively drive the desired coil. A hybrid type step motor is a representative type of step motors and comprises a rotor which is structured by combining a permanent magnet and a salient -poled rotor. A typical example of the hybrid type step motor is illustrated in FIGs. 3 and 4. That is to say, the hybrid type step motor is composed of a rotor 5 and a stator 6. In the rotor 5, a permanent magnet 5-1 is securely fitted around a rotation shaft 5-3. Laminated steel plates 5-2 are securely fitted around the rotation shaft 5-3 at both ends of the permanent magnet 5-1 and are also securely fitted around the permanent magnet 5-1 adjacent both ends of the permanent magnet 5-1. The laminated steel plates 5-2 are formed, at their circumferential outer surfaces, with small teeth 5-4. The stator 6 is formed with large teeth 6-1 a number of which corresponds to a number of phases and small teeth 6-2 which face the small teeth 5-4 of the rotor 5. In the stator 6, a slot 6-4 is defined between two adjoining large teeth 6-1, and coils 6-3 are wound m the slot 6-4.

In the windings, the coils 6-3 each defining a phase are wound on the four pole-defining large teeth 6- 1. These four coils are connected m series. A pair of coils are wound on a large tooth serving as one of the pole-defining large teeth. An inner coil of the pair of coils defines a pole which is opposite to that defined by an outer coil of the pair of coils. The pair of coils comprise bifilar windings.

To be more detailed, describing operations with reference to FIGs . 5(A) and 5(B) which are respectively taken along the lines A-A being a cross-section of an N pole and B-B being a cross-section of an S pole, m four-phase coils, if optional large teeth 6-1 (on the basis of a I-phase and a Ill-phase m FIG. 4) are magnetized to have an S polarity by the coils 6-3, the I-phase of corresponding large tooth 6-1 defines an N pole and the Ill-phase of the corresponding large tooth 6-1 defines an S pole. By this, since the small teeth 6-2 of the I-phase portion define an S pole, a magnetic path is produced from the small teeth 5-4 of an N pole side of the rotor 5. The N-pole which is induced m the small teeth 6-2 of the Ill-phase portion, produces a magnetic path toward the permanent magnet (the S pole) of the rotor 5 to define a magnetic path of the rotor 5. Thereafter, as a phase shift toward a II -phase occurs, the rotor 5 is deviated by a 1/4 pitch. By this principle, every time current is applied to each of the phases m the order of I , II, III and IV, the rotor 5 is rotated in a state wherein it is deviated rightward by the 1/4 pitch.

In this case, when assuming, for example, that the I-phase is the coil LI of FIG. 1, the I-phase is realized in a manner such that the distributing circuit 2 and the switching circuit 3 shown in FIG. 2 turn on the control terminal Bl and thereby the corresponding transistor Ql is driven. The II-phase is realized by turning on the coil L2 and the transistor Q2 , the III- phase by turning on the coil L3 and the transistor Q3 , and the IV-phase by turning on the coil L4 and the transistor Q4. Therefore, the respective phases can be distributedly realized depending upon an input pulse from the input circuit 1. As a consequence, relying upon the input pulse shown in FIG. 2, the step motor is rotated by a predetermined angle (a step angle) . By continuously and distributedly providing pulses, a velocity of the motor is proportional to a pulse frequency. In the above- exemplified type of step motor, it is the norm that the step angle is 1.8° or 0.9° . This step angle is substantially a large angle when considering the fact that an angle corresponding to the step angle upon driving an inverter of a synchronous motor is 60° in the case of a two-pole three-phase motor and 30° in the case of a four-pole three-phase motor.

In the step motor, when a pulse is not fed, the rotor is continuously maintained at a fixed position and resists to external force for rotating the rotor. Accordingly, as the step motor has peculiar starting and stopping characteristics, a ratio between a torque and a moment of inertia is enlarged, and only a pulse train which falls within a predetermined frequency range, must be provided to start and synchronously drive the step motor. In the step motor, if the pulse train is stopped, the rotor can be abruptly stopped.

However, the step motor constructed as mentioned above suffers from defects m that, since it is driven by the rotation through the step angle, a costly control circuit for providing the step angle is separately needed.

On the other hand, m a reluctance motor which is representative of a synchronous motor, as shown m FIG. 6, salient poles 7-1 are formed on a circumferential outer surface of a rotor 7 m such a way as to project m a lengthwise direction and bar-shaped conductors 7-2 are fitted around the salient poles 7-1. At this time, a number of the salient poles 7-1 must correspond to a number of phases and be equal to a number of magnetic poles which are created by a stator. In the reluctance motor, the reason why the rotor

7 is formed with the salient poles 7-1, is m that a self -starting capability cannot be accomplished m the absence of the salient poles. Namely, even though a switch is turned on and thereby a rotating magnetic field abruptly starts to be rotated, because the rotor 7 is not abruptly actuated due to a moment of inertia, the salient poles 7-1 are used so as to accomplish the self- starting capability m this situation.

The reluctance motor is driven at a synchronous velocity as denoted by 120f/p (rpm) , which is proportional to a frequency f of AC power and is inversely proportional to a number of poles p. Hence, the reluctance motor is rotated at several hundreds or thousands of rpm.

Thus, in realizing a low-velocity using the reluctance motor, inconvenience is induced in that a reduction device must be employed or a geared motor with which a reduction gear is integrated, must be employed.

To cope with this problem, a low-velocity synchronous motor (a reluctance AC low-velocity synchronous motor) had been developed. A basic construction of the reluctance AC low-velocity synchronous motor which is representative of the low- velocity synchronous motor, is illustrated in FIGs . 7 through 11. A rotor 12 is securely fitted around a rotation shaft 11, and in this state, the rotation shaft 11 is fitted through front and rear covers 15 and 16 via bearings 13 and 14. A stator 17 is close-fitted into a motor case 18.

Coils 19 are wound on the stator 17. The stator 17 is made of silicon steel plates. The stator 17 is formed, on a circumferential inner surface thereof, with large teeth 17-1 which are to be poles (that is, poles which are to be created by current flowing through the coils) and on inner surfaces of the large teeth 17-1, with small teeth 17-2 (numbers of the large teeth and the small teeth can vary depending upon design options. The large teeth 17-1 and the small teeth 17-2 which are formed on the silicon steel plates, are arranged in an axial direction. A slot 10 is defined between two adjoining large teeth 17-1 of the stator 17, and one- phase or three-phase coils 19 can be accommodated in the slot 10 m obedience to a principle and a design. At this time, m the case that the coils 19 which are embodied m the present invention, are the three-phase coils, they can be configured as shown m FIG. 16. In FIG. 16, the drawing reference symbols S1~S12 represent positions of slots 10. An arrangement of windings of U, V and W phases is, for example, effected m a manner such that U-phase windings m the slots SI and S4 constituting a first unit loop and U-phase windings m the slots S4 and S7 constituting a second unit loop define a wavelike contour m which they are oppositely, sequentially and repeatedly wound m the slots, and remaining V-phase and W-phase windings define the same wavelike contour. A number of the respective positions S1-S12 of the slots 10 are not specifically limited, and instead, varies depending upon a number of the large teeth. Therefore, the slots 10 can be broadly designated by Sl~Sn. The rotor 12 is made by laminating silicon steel plates each having an annular configuration or is made of soft magnetic steel. A figure, a separation and a number of small teeth which are formed on a circumferential outer surface of the rotor 12, can vary depending upon design options m a diversity of ways. A remarkably complicated magnetic field is produced m a gap between the stator 17 and the rotor 12 of the reluctance AC low-velocity synchronous motor. In order to theoretically analyze this magnetic field, when first assuming a situation wherein only the stator 17 is formed with the teeth, the circumferential outer surface of the rotor 12 is not formed with the teeth, and single-phase current is applied to the coils 19, the magnetic field is created m an equivalent gap between the rotor 12 and the stator 17, as expressed below: BZs(chι) = F(chι) lambda zs(chι) =

Yf , Cos—v -λn Cosn(πz, - a) l τ ? pτ where is a magnetic intensity of the magneti

h is created m the equivalent gap by the coils, and λn c )) is a

magnetization degree of a magnetic orce layer of the stator, Fm represents a widthwise dimension of a magnetic intensity of a vth magnetic wave, λn represents a widthwise dimension of an nth magnetization degree due to the teeth, P is a number of pairs of magnetic poles which are constituted by the coils, r is a pitch of the small teeth, Z, is a number of the slots which are defined on the circumferential inner surface of the stator, and a is a degree of a phase angle which is related with a magnetic pole center and a position of a tooth.

If only the rotor 12 is formed with the teeth and the circumferential inner surface of the stator 17 is not formed with the teeth, a similar magnetic field is created, as given below: < PSTYLE > ∑ Fm_x - Cos — v ^■J λk ■ Cosk(^x - z₂ω₂t + a) v=l ^τ n=l P ^τ where λk is a widthwise dimension of a & th magnetization degree due to the teeth of the rotor, Z, is a number of the small teeth which are formed on the circumferential outer surface of the rotor, ω₂ is an angular velocity when the rotor is rotated, and is a position angle which reveals a first position of the rotor.

If the circumferential inner surface of the stator 17 and the circumferential outer surface of the rotor 12 are respectively formed with the small teeth 17-2 and 12-1, a magnetic wave length m the equivalent gap between the rotor 12 and the stator 17 is more

where μ is a magnetization percentage of air, and δ is the gap .

An order (of an wave type) and a rotating velocity of each of the numerous magnetic fields are represented as given below: δ' = δ Kδ s - Kδ

By solving an external term of the above equation with respect to Bz(X) , from an equality ω₂ = ± (1 - Svz) , co + KZ co KZ₂ an equation Svz = —- can be obtained. ω From this equation, it is to be readily understood that, if ω_η = + , Sz = 0. In other words, a multitude

KZ₂ of corresponding waves which are determined by a K th wave of a magnetization degree and are generated m the rotor, are not moved relative to the stator. That is to say, the motor is rotated at a synchronous velocity.

This condition indicates when an order of a magnetic field wave of the small teeth 12-1 of the rotor

12 is equal to an order of a magnetic field wave of the small teeth 17-2 of the stator 17. In order to satisfy this condition, relational expressions given below are established among a number Zs of the small teeth 17-2 of the stator 17, a number Zr of the small teeth 12-1 of the rotor 12 and a number of phases of the coils : 1. Zr-Zs = ±2

2. Zr - 2Zs = ± 2 3 . Zr = 2

From the above expressions, it is to be readily understood that, from an equality 2P = 2r which is a relational equation of a general reluctance synchronous motor, a number of salient poles of the rotor equals a number of phases of the coils. Also, m an equation Zr - 2Zs = ± 2ι , a torque is small due to the fact that the result of the equation is a high frequency. As a result, the expression Zr - Zs = ± 2 is directly applied to the reluctance AC low-velocity synchronous motor.

FIG. 8 is a view for explaining a rotation principle of the reluctance AC low-velocity synchronous motor shown m FIG. 7. In FIG. 8, if an axis of a rotating magnetic field of the stator 17 is on a point A, it can be seen that small teeth Nos . 1 and 9 of the stator 17 are on the same line as small teeth Nos. 1 and 10 of the rotor 12, and small teeth Nos. 2 and 10 of the stator 17 are angularly deviated from small teeth Nos. 2 and 11 of the rotor 12 by an angle of a . If a center of a magnetic flux of the rotating magnetic field is moved to a point B by action of AC current flowing through the coils 19 of the stator 17, the rotor 12 is moved by an angle of a , whereby the small teeth Nos. 2 and 10 of the stator 17 are respectively opposite to the small teeth Nos. 2 and 11 of the rotor 12. Namely, while the rotating magnetic field is rotated by an angle of 2π I Zs , the rotor 12 is rotated by the angle of a (at this time, Zs represents the number of the small teeth 17-2 of the stator 17 and Zr represents the number of the small teeth of the rotor) .

Therefore, it is found that, by denoting a ratio between rotational velocities of the rotating magnetic field and the rotor 12 as a reduction ratio Kp , a following expression is established:

rdinarily complicated magnetic field is created m the gap between the stator

17 and the rotor 12 of the reluctance AC low-velocity synchronous motor, by summarizing the magnetic field based on the above-described theoretical analysis, the magnetic field can be expressed m the following elements :

First, a magnetic field Bδ which is created m the equivalent gap by the current flowing through tne coils. Second, a magnetic field Bzs which is created by the small teeth 17-1, that is, prominence and depressions, formed on the circumferential inner surface of the stator 17.

Third, a magnetic field Bzr which is created by the small teeth 12-1, that is, prominence and depressions, formed on the circumferential outer surface of the rotor 12.

Fourth, a new magnetic field and the like, which can be created by mixing of the second and third magnetic fields with each other. As aforementioned above, by giving external terms to the above-described magnetic fields, the following relational equations can be obtained:

Zr - Zs = ± 2p (2) where p is a number of pairs of the magnetic poles (m the case of two poles, p = 1 , and m the case of four poles, p = 2 ) , that is, a number of poles of the coils, and Zr and Zs respectively represent the number of small teeth 12-1 of the rotor 12 and the number of small teeth

17-2 of the stator 17.

Hence, a number of revolution of the rotating magnetic field can be expressed as Ns =

(rpm) where f indicates a power frequency. As a consequence, a number of revolution of the reluctance AC low-velocity synchronous motor (see FIG. 8) can be denoted as given below:

_N __ H __ ∞L_IKp Zr

60/ - Kp = 60// p = 120// Zr (rpm)

Kp p Zr - Zs

By combining the above three equations (1), (2) and (3), the reduction ratio Kp of the reluctance AC low-velocity (reaction type) synchronous motor is directly proportional to the number Zr of the small teeth of the rotor 12 and is inversely proportional to a difference Zr - Zs between the number of the small teeth of the rotor 12 and the number of the small teeth of the stator 17. Also, the difference between the number of small teeth of the rotor 12 and the number of small teeth of the stator 17 is equal to the number ±2P of poles which are formed by the coils 19. Specifically, as can be readily seen from the above expression (3), the number N of revolution of the reluctance AC low- velocity synchronous motor is directly proportional to the power frequency and is inversely proportional to the number of small teeth of the rotor. The number of revolution is not related with the number of poles of the stator 17, which are formed by the coils 19. From these statements, it is to be noted that the reluctance AC low-velocity synchronous motor is a kind of motor which is different from the conventional AC motor.

A most important factor which must be considered m designing the AC low-velocity motor, is that a specification capable of accomplishing a low-velocity of a desire level by directly connecting power having a frequency of 50HZ or 60HZ to the motor is as described below:

1. Power frequency: 50Hz or 60Hz 2. The number of phases of the power: m=2 (see

FIG. 9), realizing two-phase by phase-shifting to single-phase power, m=3 (see FIG. 11)

3. The number of revolution of motor: m the case of 50Hz, n=120rpm (m the case of 60Hz, n=144rpm) By solving the above-described conditions by a simultaneous equation of the above expressions (1), (2) and (3), values are obtained as given below: Zs = 48 , Zr = 50 and Zp = 25 By using these values, it is possible to respectively manufacture a single-phase motor and a three-phase motor. FIG. 9 is a partial enlarged view illustrating a core of the stator 17 of a single-phase reluctance AC low-velocity synchronous motor, taken along a diametrical direction (that is, a partial cross- sectional view of a single-phase motor, which of course can be applied to a three-phase motor), and FIG. 11 is a cross-sectional view taken along the diametrical direction, illustrating a core of the stator 17 of a reluctance AC low-velocity synchronous motor according to the present invention. FIG. 10 is a cross-sectional view of the rotor 12, and structures of rotors of single-phase motor and three-phase motor are the same with each other. By comparing FIGs . 9 and 11 with each other, while the numbers of large teeth 17-1 are not the same with each other, the numbers of small teeth 17-2 are the same with each other, and the numbers of poles of coils must be same with each other so as to satisfy the above expressions (1) through (3) .

And, m the case of the single-phase as shown m FIG. 3, while a pitch of the small teeth 17-2 which are formed on the large teeth 17-1, is the same as a pitch

(angle) of the rotor 12, a difference of 0.5 pitch exists between two adjoining large teeth. However, referring to FIG. 11, m the case of a three-phase, while pitches of the small teeth 17-2 which are formed on the large teeth 17-1, are the same one with another, a difference of 1/3 pitch exists between two adjoining large teeth. Here, it can also be found that two adjoining large teeth 17-1 have a difference of 0.5 pitch angle (of the small teeth 17-2) m the case of the single-phase and have a difference of 1/3 pitch angle (of the small teeth 17-2) m the case of the three- phase .

A motor which can be rotated at a low-velocity, can be realized m the form of a magnet type motor m addition to the reluctance motor. Magnet type AC low- velocity synchronous motors are divided into permanent magnet type motors and electronic type motors . Herembelow, the permanent magnet type motors will be described m detail . In a permanent magnet type AC low-velocity synchronous motor, as shown m FIGs. 12 through 14, cores 22-1 and 22-2 and a permanent magnet 21 of a rotor 22 are securely fitted around a rotation shaft 23. The drawing reference numeral 27 designates a stator. Each of large teeth 27-2 which serve as magnetic poles due to current flowing through coils 24, is regularly formed with small teeth 27-1 having a number of n (n=l, 2, 3..) which varies depending upon design options. Also, the cores 22-1 and 22-2 of the rotor 22 are formed on circumferential outer surfaces thereof with prominence and depressions, that is, small teeth 22-3. The drawing reference numeral 23 represents an annular permanent magnet which is magnetized m an axial direction. An important factor m a basic structure of the permanent magnet type AC low-velocity synchronous motor is m the fact that, while a basic structure of the stator 27 is similar to that of the stator of the reluctance AC low- velocity synchronous motor, m this permanent magnet type AC low-velocity synchronous motor, the cores 22-1 and 22-2 of the rotor 22 are respectively disposed on both ends of the permanent magnet 21 and the prominence and depressions which are formed on the circumferential outer surfaces of the cores 22-1 and 22-2, are deviated from each other by a 1/2 pitch (In this connection, since a winding pattern of the coils 24 is the same as that m the case of the reluctance type shown m FIG. 16, detailed descriptions therefor will be omitted herein.) . In other words, a center of a prominence of the core 22-2 is m line with a center of a depression of the core 22-1. If all of the small teeth 22-3 and the depressions of the core 22-2 which is disposed on one end of the permanent magnet 21, have an N polarity, all of the small teeth 22-3 and the depressions of the core 22-1 which is disposed on the other end of the permanent magnet 21, have an S polarity.

Equations which are derived m the permanent magnet type AC low-velocity synchronous motor, are similar to those which are derived m the reluctance type AC low-velocity synchronous motor, and from this point of view, a rotating angular velocity of the rotor 22 can be expressed as denoted below:

ω ω, = ± - z where ω-, is a rotating angular velocity of the rotor 22, Z, is a number of small teeth of the rotor 22, and ω is a rotating angular velocity of a magnetic field.

At this time, because magnetic field waves by the small teeth 22-3 of the' rotor 22 are not moved relative to the stator 27, the rotor can be synchronously rotated. Further, a magnetic field must be present m a gap

(a gap between the stator and the rotor) of the motor.

If single-phase coils 24 having a number . of poles are arranged in slots defined m the stator 27, magnetic field basic waves v - — by the coils 24 create a magnetic field, and this magnetic field is expressed m the form of mixed waves of the stator 27 and the rotor 22. From the above statements, the following relationships are obtained.

1. When a basic wave of the magnetic field satisfies an equality v , = — P--> , the rotor 22 is not moved

*\ m a space . 2. When a mixed wave of the small teeth by the

Z, P, stator satisfies an equality vzs = — - ± — , the rotor 22 is

P P also not moved in the space.

3. When a mixed wave o e rotor satisfies equalities v'zr =

the rotor 22 can be rotated m the space by equalities co,., = ± and β> =± .

VZ ^■ V VZ,

For synchronized rotation of the rotor 22, an order of the mixed magnetic waves into the small teeth of the rotor 22 must be the same as that of the mixed magnetic waves into the small teeth of the stator. In other words, the following equations must be satisfied with:

- Z,? ± Z,L + ι ₌ _ P^, _and ^Z,. + ,1 = ^Z, + .^ P, (_a)

P P P_x P_x P,

Also, from the above descriptions, a number of revolution which is caused as the mixed waves which are induced by an optional coil E2 , are provided to the rotor, is the same as that which is caused as the mixed waves which are induced by another coil El , are provided to the stator. The number of revolution can be expressed as given below:

ived by the above expressions (a) and (b) :

Z₂ ± Z_] = ± (Pχ P₂) Z₂ = Z_l = ± (P_] ± P₂) where Z, is a number of small teeth of the stator and Z₂ is a number of small teeth of the rotor.

Also, when a motor is designed as the permanent magnet type AC low-velocity synchronous motor, when assuming that AC coils are El and DC coils are P2 , a voltage transformation phenomenon can occur between the coils El and E2.

If a resistance of the coil E2 is very small, the coil P2 is short-circuited. In order to avoid this situation, it is preferred that a number of pairs of the poles of the coils be a multiple of 2 as designated below:

P P — = 2K or - = 2K P_x P₂

where K is a positive integer.

While, under an individual situation, the voltage transformation phenomenon can be advantageously used, as DC current momentarily flows through a coil circuit, the rotor is synchronously rotated.

Energy for obtaining this DC current is provided from an AC power supply, and m this status, a ratio between the numbers of pairs of poles of the coils El and E2 is an odd number. That is, — P=-,- = n or — Pi = « , where

E, P, n = X, 3, 5

When comparing the permanent magnet type synchronous motor and the reluctance synchronous motor with each other, if the numbers of the small teeth of the rotors of the two motors are the same with each other, it is to be readily understood that the number of revolution of the permanent magnet type low-velocity synchronous motor becomes a half of the number of revolution of the reluctance synchronous motor.

Also, by magnetizing the rotor by the permanent magnet, it is possible to obtain a characteristic of a motor to which the coil P2 is mounted. Moreover, a construction of the motor is simplified, efficiency is elevated, and a moment of inertia of the rotor itself is increased. Furthermore, FIG. 13 is of views for explaining a rotating principle of the permanent magnet type AC low- velocity synchronous motor, wherein FIG. 13 (A) is a cross-sectional view taken along the line A' -A' of FIG. 12, and FIG. 13(B) is a cross-sectional view taken along the line B'-B' of FIG. 12.

As can be readily seen from FIG. 13, windings of the stator 27 have four poles. In FIG. 13(A), a status wherein an axis of a rotating magnetic field is m direct accord with centers of corresponding Nos. 1, 5, 9 and 13 of small teeth 27-1 of a core 26 of a stator 27, is illustrated, and m this status, the small teeth Nos. 1 and 9 of the stator 27 are arranged m direct opposition to the small teeth Nos. 1 and 10 of a rotor 22. In FIG. 13(B), the small teeth Nos. 1 and 10 of the rotor 22 are located on a center of the rotor 22. If a rotating magnetic field moves the small teeth of the stator 27 by one unit angle m a clockwise direction, that is, the axis of the rotating magnetic field is m accord with the small teeth Nos. 2 and 10 m FIG. 13(A), the rotor 22 is also rotated and thereby the small teeth Nos. 2 and 11 of the rotor 22 are arranged m direct opposition to the small teeth Nos. 2 and 10 of the stator 27. If the rotating magnetic field is rotated by 2π I ZS , the rotor 22 is rotated by an angle of a - (1/ Zs - 1/ Zr)2π . Therefore, a ratio between a rotational velocity of the rotating magnetic field and a rotational velocity of the rotor is expressed as given below:

2π ., X X .. Zr ,

Kp = —/( )2π = (1')

Zs Zs Zr Zr - Zs

where Zs is a number of small teeth of the stator, Zr is a number of small teeth of the rotor and Kp is a reduction ratio.

And, when assuming that a number of poles of the coils 24 is 2p , an equality Zr - Zs = ± P (2') is established, and a rotational velocity of the motor is

_Λr Ns 60/ Zr - Zs 60 f (rpm) , . expressed as N = = — = —^y (3 ' ) .

Kp p Zr Zr

From the above equations (l¹), (2') and (3'), following results can be obtained.

That is to say, from the above equation (l^τ) , it is to be recognized that the reduction ratio Kp is directly proportional to the number of small teeth 22-3 of the motor rotor 22 and is inversely proportional to a difference between the numbers of the small teeth of the rotor and the stator 27. Also, from the equation (2'), it is to be recognized that the difference between the numbers of the small teeth of the rotor 22 and the stator 27 corresponds to a half of the number of poles of the coils.

Also, from the equation (3 ' ) , it is to be recognized that the number of revolution of the motor is directly proportional to a power frequency and is inversely proportional to the number of small teeth of the rotor. Further, when comparing the permanent magnet type AC low-velocity motor and the reluctance AC low- velocity motor with each other, the numbers of these motors are not related with the numbers of poles of the windings on the contrary to the conventional AC motor, but related with the numbers of small teeth of the rotors. When the numbers of small teeth of the rotors are the same with each other, as aforementioned above, the permanent magnet type motor is rotated at a number of revolution which corresponds to a half of that of the reluctance type (reaction type) motor.

In the meanwhile, as shown in FIGs. 14 and 15, a rotation principle can be qualitatively explained. For example, in the poles of the permanent magnet 22, when assuming that a left side forms an N pole, a right side forms an S pole, a magnetic pole which is induced in the large tooth 27-2 at a position No. 1 by the coil 24, is an S pole and a magnetic pole of the large tooth 27-2 which is placed in two phase separation at a position No. 2 where corresponding three-phase coil 24 is wound on the large teeth 27-2, is an N pole, a magnetic pole leftward of the rotor 22 (for example, N pole) defines a magnetic path toward the S pole of the large tooth 27-2 on the position No. 1.

However, because a right portion of the rotor 22 has an S polarity, the magnetic path through the large tooth 27-2 at the position No. 1 can be moved rightward, and, because the large tooth 27-2 at the position No. 2 has an N polarity, the S pole at the position No. 1 defines a magnetic path toward the position No. 2. (Referring to FIG. 16, this is caused from the fact that, for example, a slot SI and a slot S4 define a loop and thereby create an instantaneous magnetic pole. This principle can also be applied to the above-described reluctance type motor m the same manner.)

Thus, the S pole on the right side of the rotor 22 and the S polarity which is induced to the large tooth 27-2 of the stator 27 at the position No. 2, act as repulsive forces to each other. Also, the N pole on the left side of the rotor 22 and the N polarity which is induced to the large tooth 27-2 of the stator 27 at the position No. 2 act as repulsive forces to each other. By this, the rotor 22 is rotated m the clockwise direction. While, m the above descriptions, the stator 27 is illustrated and explained with respect to three- phase motor, the same phase must be obtained m the status of coils 24 which satisfies a sequential wave form winding pattern by the respective U, V and W phases as shown in FIG. 16 for accomplishing S-N-S-N (its reverse order is also possible) m the stator 20.

A person skilled m the art will readily recognize from the Lenz ' s law that the coils 24 have polarities at the large teeth 22. More concretely speaking, as shown m FIG. 15, when assuming that an S pole is induced to the large tooth 27-2 at the position No. 1 (m FIG. 15, a position No. Al) of the stator 27 by the coil 24, the small teeth 22-3 of the rotor 23 become an N pole. When viewing from a point TI of FIG. 15(B), since the coils 24 of Bl and Cl phases become an N pole, repulsive forces are generated by the Bl and Cl phases, and thereby, force for rotating the rotor 22 rightward is appl ied .

That is to say, while, m the conventional step motor, as DC power is selectively applied, depending upon a pulse, to the coils wound on the large teeth, a torque is flimsy, as shown m FIGs. 15(A) and 15(B), if magnetic paths are systematically formed by the respective phases, the respective magnetic paths form harmonic waves to be added or subtracted, and a low- velocity rotation of a large torque is enabled. On the other hand, values with respect to a number of revolution of the motor can be calculated using the equations (1'), (2 ' ) and (3') and the given conditions, as described herembelow.

When assuming that a power frequency f=60Hz, a power phase number m=3 and a number of revolution of a motor n=72rpm, a rotor synchronous velocity Ns=60f/p =60x60/2=3600/2=1800 where p=2 and 2p=4 , a number of small teeth of the rotor Zr=60f/n=60x60/72=52 , a number of small teeth to be formed on the large teeth Zs=Zr+p=50±2=52 or 48, a number of slots m which coils are wound S=m 2p=3x4=12 , a number of small teeth co be formed on each large tooth Z ' =Zs/s=48/l2=4 , a reduction ratio Kp=Zr/ (Zr-Zs) =50/ (50-48) =25, and a rotational velocity of the motor n=Ns/Kp=1800/25=72rpm. However, the reluctance AC low-velocity synchronous motor and the permanent magnet type AC low- velocity synchronous motor suffer from defects m that, since the AC coils which are coupled to the stators, are exposed forward and rearward of the cores of the rotors, lengths of the motors are increased, and, since a probability of exposed portions of the AC coils to be damaged is elevated, durability of the entire motors are deteriorated. Moreover, due to the presence of the exposed portions, power efficiency of the motors is impaired and a manufacturing cost is raised.

Disclosure of the Invention

Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and an object of the present invention is to provide a permanent magnet type AC low-velocity synchronous motor wherein a stator has an annular configuration and is coupled to a motor case in a manner such that it is fitted into the motor case in an axial direction without causing exposure of an AC coil, thereby to shorten a length of the motor. In order to achieve the above object, in the present invention, a guide groove is defined in a motor case. A stator includes small-toothed plates each of which has an annular configuration and which are sequentially fitted into the motor case. AC coils each having an annular configuration are repeatedly intervened between two small -toothed plates to define an axial connection pattern. A rotor includes core plates and permanent magnets which are arranged in a manner such that the core plates and the magnets correspond to the small-toothed plates and the AC coils of the stator, respectively.

That is, according to one aspect of the present invention, there is provided a permanent magnet type AC low-velocity synchronous motor in which a permanent magnet is fastened to a center portion of a rotor and a pair of cores are fastened to both ends of the permanent magnet thereby to define one phase, a stator has coils which are wound around large teeth with a slot defined between two adjoining large teeth and to which AC power is supplied, a circumferential outer surface of the rotor and inner surfaces of the large teeth of the stator being formed with small teeth while having a phase difference therebetween to afford starting force, the motor comprising: a stator having a first annular small -toothed unit plate which is formed on a circumferential inner surface thereof with radial teeth while not having lengthwise slots, an annular unit AC coil, and a second annular small-toothed unit plate which is uniformly formed on a circumferential inner surface thereof with radial teeth while not having lengthwise slots, the first annular small -toothed unit plate, the annular unit AC coil and the second annular small -toothed unit plate defining one phase and being sequentially inserted into a motor case along a guide groove which is defined on a circumferential inner surface of the motor case and extends m the lengthwise direction, thereby to be coupled thereto; and a rotor having a pair of first core plates which are fastened to a rotating shaft, have the same length as the first and second annular small -toothed unit plates and are formed on circumferential outer surfaces thereof with radial teeth extending in the lengthwise direction m a manner such that the radial teeth of the first pair of core plates correspond to the radial teeth of the first and second annular small -toothed unit plates, respectively, and a first permanent magnet which is positioned between the first pair of core plates m such a way as to correspond to the annular unit AC coil and has the same length as the annular unit AC coil, the first pair of core plates and the first permanent magnet defining one phase, the rotor further having at least one second pair of core plates and at least one second permanent magnet which are disposed, m consideration of a number of phases, adjacent to the first pair of core plates and the first permanent magnet so as to afford starting power, the first and second pairs of core plates having a phase difference therebetween.

Also, according to another aspect of the present invention, there is provided an AC motor m which slots and teeth are formed on a circumferential inner surface of a stator in a lengthwise direction of the motor, AC coils are wound on the teeth, and a rotor is rotated by a variation m magnetic fields generated upon current application, the AC motor comprising: a stator having a first annular small-toothed unit plate which is formed on a circumferential inner surface thereof with radial teeth while not having lengthwise slots, an annular unit AC coil, and a second annular small -toothed unit plate which is uniformly formed on a circumferential inner surface thereof with radial teeth while not having lengthwise slots, the first annular small-toothed unit plate, the annular unit AC coil and the second annular small-toothed unit plate defining one phase and being sequentially inserted into a motor case along a guide groove which is defined on a circumferential inner surface of the motor case and extends m the lengthwise direction, thereby to be coupled thereto; and a rotor rotated m synchronism with magnetization of the phase which is defined by the first and second annular small - toothed unit plates and the annular unit AC coil .

Brief Description of the Drawings The above objects, and other features and advantages of the present invention will become more apparent after a reading of the following detailed description when taken m conjunction with the drawings, m which: FIG. 1 is a circuit diagram illustrating a construction of a conventional step motor;

FIG. 2 is a block diagram illustrating a controlling procedure of the conventional step motor;

FIG. 3 is a cross-sectional view illustrating a conventional hybrid type step motor;

FIG. 4 is a longitudinal cross-sectional view of the conventional hybrid type step motor shown m FIG. 3 ;

FIG. 5(A) is a diagrammatic view taken along the line A-A of FIG. 3, for explaining magnetic paths; FIG. 5(B) is a diagrammatic view taken along the line B-B of FIG. 3, for explaining magnetic paths;

FIG. 6 is a schematic view illustrating a construction of a rotor of a conventional reluctance AC low-velocity synchronous motor; FIG. 7 is a cross-sectional view illustrating another reluctance AC low-velocity synchronous motor;

FIG. 8 is a view for explaining a rotating principle of the motor shown m FIG. 7 ;

FIG. 9 is a partial enlarged view illustrating an example of a single-phase stator core shown m FIG. 8; FIG. 10 is a partial enlarged view illustrating an example of a two-phase stator core shown m FIG. 9 ;

FIG. 11 is a partial enlarged view illustrating an example of a three-phase stator core shown m FIG. 9; FIG. 12 is a half cross-sectional view illustrating another magnet type AC low-velocity synchronous motor;

FIG. 13(A) is a cross-sectional view taken along the line A' -A' of FIG. 12; FIG. 13(B) is a cross-sectional view taken along the line B'-B* of FIG. 12;

FIG. 14 is a partially broken-away perspective view for explaining operations of the motor shown m FIG. 12; FIG. 15(A) is a diagrammatic view illustrating a developed status of a stator and a rotor shown m FIG. 14, for exemplifying a magnetic pole characteristic;

FIG. 15(B) is a waveform diagram of electric power which is supplied to the stator and the rotor shown m FIG. 15(A) at an arbitrary time;

FIG. 16 is an exploded coil wiring diagram of a low-velocity synchronous motor;

FIG. 17 is a cross-sectional view illustrating small- toothed unit plates and an AC coil which are fitted into a motor case m accordance with an embodiment of the present invention;

FIG. 18 is a cross-sectional view taken along the line A-A of FIG. 17;

FIG. 19 is a front view illustrating a rotor according to the present invention;

FIG. 20 is a cross-sectional view taken along the

FIG. 21 is a cross-sectional view taken along the

FIG. 22 is a half cross-sectioned side view illustrating an assembled status of the motor according to the present invention.

Best Mode for Carrying Out the Invention Reference will now be made m greater detail to a preferred embodiment of the invention, an example of which is illustrated m the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts.

FIG. 17 is a cross-sectional view illustrating small -toothed unit plates and an AC coil which are fitted into a motor case m accordance with an embodiment of the present invention. A guide groove 141 is defined on a circumferential inner surface of the motor case to which a stator is to be coupled, m such a way as to extend m a lengthwise direction. A stepped portion 142 is formed at an end of the guide groove 141. A rear cover 143 is coupled to an end of the motor case 140, and a bearing 144 for rotatably supporting a rotation shaft of a rotor which will be described later, is mounted to the rear cover 143. First and second annular small-toothed unit plates 110 and 130 are fitted into the motor case 140 along the guide groove 141. An AC coil 120 is positioned between the first and second annular small -toothed unit plates 110 and 130. The first and second annular small-toothed unit plates 110 and 130 are formed on circumferential inner surfaces thereof with radial teeth 111 and 131, respectively.

FIG. 18 is a cross-sectional view taken along the line A-A of FIG. 17. The first annular small-toothed unit plate 110 which is formed, on the circumferential inner surface thereof, with the radial teeth 111 and, on a circumferential outer surface thereof and at least one place, w th a projection 112, is fitted into the motor case 140. To this end, the motor case 140 is formed with the guide groove 141 m a manner such that the projection 112 is engaged m the guide groove 141.

FIG. 19 is a front view illustrating a rotor according to the present invention; FIG. 20 is a cross- sectional view taken along the line B-B of FIG. 19; FIG. 21 is a cross-sectional view taken along the line C-C of FIG. 19; and FIG. 22 is a half cross-sectioned side view illustrating an assembled status of the motor according to the present invention. A first permanent magnet 170 is mounted around a rotation shaft 151, and a first pair of core plates 160 and 180 are mounted around the rotation shaft 151 at both sides of the first permanent magnet 170. The first pair of core plates 160 and 180 are formed on circumferential outer surfaces thereof with small teeth 161 and 181, respectively. The first pair of core plates 160 and 180 and the first permanent magnet 170 are coupled one with another to define one phase of the motor. A second permanent magnet 170' and a second pair of core plates 160' and 180' which are formed on circumferential outer surfaces thereof with small teeth 161' and 181', define another phase. Also, a third permanent magnet 170' ' and a third pair of core plates 160' ' and 180' ' which are formed on circumferential outer surfaces thereof with small teeth 161' ' and 181' ', define still another phase. The small teeth are configured m a manner such that the small teeth 181 and 161' have therebetween a difference of 1/3 pitch, and the small teeth 181' and 161' ' have therebetween a difference of 1/3 pitch. Further, the core plates 160 and 180' ' are supported by fixing rings 152, respectively. In FIG. 22, it is illustrated that an input power supplying wire 145 is exposed to the outside out of the motor case 140.

In the permanent magnet type AC low-velocity synchronous motor according to the present invention, constructed as mentioned above, the first small -toothed unit plate 110 which has an annular configuration, is inserted into the motor case 140 along the guide groove 141 as shown in FIG. 17 thereby to be coupled thereto. Then, the AC coil 120 and the second small-toothed unit plate 130 are also fitted into the motor case 140 m a manner such that the first and second small-toothed unit plates 110 and 130 and the AC coil 120 define the one phase. This procedure is repeated to result m a status as shown m FIG. 22. Thereafter, the first through third core plates 160, 180; 160', 180'; and 160'', 180'' and the first through third permanent magnets 170, 170' and 170' ' are mounted around the rotation shaft 151. Then, one end of the rotation shaft 151 is fitted into the bearing 144 of FIG. 17 to be rotatably supported thereby. Hence, m the permanent magnet type AC low- velocity synchronous motor according to the present invention, driving force is provided to the small teeth 111 and 131 which are formed on the first and second annular small-toothed unit plates 110 and 130 and the small teeth 161 and 181 which are formed on the first pair of core plates 160 and 180 constituting the rotor 150, m such a way as to define a phase one with another. Of course, m this case, because a number of revolution of the permanent magnet type AC low-velocity synchronous motor is obtained by an equation Ns=60f/z where f is a power frequency and Z is a number of small teeth, and a principle for driving the motor is the same as m the conventional art, detailed descriptions therefor will be omitted herein. But, m the present invention, due to the fact that the coil which is to be installed on the stator, is structured to have the annular configuration, the coil can be easily coupled to the motor case. Also, since no portion of the coil is exposed to the outside, it is possible to reduce a length of the motor by the un-exposed portion of the coil. In addition, because efficiency of the coil can be maximized, efficiency of the motor is also raised and a manufacturing cost of the motor can be significantly reduced. And, by the fact that the pair of core plates 160 and 180 are coupled with each other and only the small teeth 161 and 181 are formed on the circumferential outer surfaces of the core plates 160 and 180, it is not necessary to form large teeth as m the conventional art, whereby the core plates can be manufactured m an easier manner. Although the above descriptions were made for a three-phase structure wherein the first pair of core plates 160 and 180 define one phase, the second pair of core plates 160' and 180' define another phase and the third core plates 160' ' and 180' ' define still another phase, a person skilled m the art will readily appreciate that a number of pairs of core plates can be adjusted m obedience to a number of phases.

Also, while the above descriptions were made with respect to the permanent magnet type AC low-velocity synchronous motor, the present invention can be applied to a conventional AC motor m which a coil is wound m slots defined between large teeth formed on a circumferential inner surface of a stator and rotating force for rotating a rotor is generated upon application of AC power. In the case that the present invention is applied to the conventional AC motor, the rotor is constructed m the same manner as the conventional art, and the stator which has the structure of the stator of the present invention (as shown m FIGs. 17 and 18) , is used. By magnetic force for rotating the rotor, as shown m FIG. 22, for example, (In this case, while a rotor structure of the AC low-velocity synchronous motor is illustrated m the drawing, the drawing implies the case m which the stator of the present invention is applied to the conventional AC motor. Since the rotor of the AC motor can have a variety of structures, the rotor of the AC motor is not particularly illustrated herein. Therefore, m the case that the rotor of FIG. 22 is applied to the conventional AC motor, the rotor is replaced with another rotor having a structure of the conventional AC motor.) the right small-toothed plates 110 and 130 and the right AC coil 120 which constitute one group and define one phase (for the sake of convenience, an A phase) , are driven to rotate the rotor by a phase angle. Then, for example, the center small - toothed plates 110 and 130 and the center AC coil 120 which constitute another group and define another phase (for the sake of convenience, a B phase) , are driven to additionally rotate the rotor by a phase angle. Thereafter, the left small-toothed plates 110 and 130 and the left AC coil 120 which constitute still another group and define still another phase (for the sake of convenience, a C phase) , are driven to rotate the rotor by a phase angle in such a way as to continue the rotation of the rotor.

In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.

Industrial Applicability

As a result, by the permanent magnet type AC low- velocity synchronous motor according to the present invention, constructed as mentioned above, advantages are provided in that, since a stator is fitted into a motor case to be coupled thereto, assemblability of the motor is improved, and, since the stator does not have slots, workability of the stator can be enhanced. Also, because an AC coil has an annular configuration and is fitted into the motor case, assembling operations can be implemented in a faster and simpler way when compared to the case m which an AC coil is wound in slots, and a labor cost is reduced. Moreover, due to the fact that the AC coil is not exposed to the outside, efficiency of the AC coil can be elevated by an un-exposed portion of the AC coil, and a cost of the AC coil can be saved by 50% or more. Further, by the fact a length of the motor can be decreased, it is possible to accomplish a compact size of the motor while maintaining the same capacity. Accordingly, as the stator is fabricated in such a way as to be assembled, since disassembling operations can also be easily implemented, cost induced in assembling and disassembling the motor can be significantly reduced.

Furthermore, in the case that a conventional AC motor is used in a state wherein a stator is fitted into a motor case in an axial direction, a size and a wound amount of a coil can be reduced, whereby a manufacturing cost can be decreased and efficiency of the coil can be enhanced.

Claims

1. A permanent magnet type AC low-velocity synchronous motor m which a permanent magnet is fastened to a center portion of a rotor and a pair of cores are fastened to both ends of the permanent magnet thereby to define one phase, a stator has coils which are wound around large teeth with a slot defined between two adjoining large teeth and to which AC power is supplied, a circumferential outer surface of the rotor and inner surfaces of the large teeth of the stator being formed with small teeth while having a phase difference therebetween to afford starting force, the motor comprising: a stator having a first annular small -toothed unit plate which is formed on a circumferential inner surface thereof with radial teeth while not having lengthwise slots, an annular unit AC coil, and a second annular small -toothed unit plate which is uniformly formed on a circumferential inner surface thereof with radial teeth while not having lengthwise slots, the first annular small -toothed unit plate, the annular unit AC coil and the second annular small -toothed unit plate defining one phase and being sequentially inserted into a motor case along a guide groove which is defined on a circumferential inner surface of the motor case and extends m the lengthwise direction, thereby to be coupled thereto; and a rotor having a pair of first core plates which are fastened to a rotating shaft, have the same length as the first and second annular small -toothed unit plates and are formed on circumferential outer surfaces thereof with radial teeth extending m the lengthwise direction m a manner such that the radial teeth of the first pair of core plates correspond to the radial teeth of the first and second annular small-toothed unit plates, respectively, and a first permanent magnet which is positioned between the first pair of core plates m such a way as to correspond to the annular unit AC coil and has the same length as the annular unit AC coil, the first pair of core plates and the first permanent magnet defining one phase, the rotor further having at least one second pair of core plates and at least one second permanent magnet which are disposed, m consideration of a number of phases, adjacent to the first pair of core plates and the first permanent magnet so as to afford starting power, the first and second pairs of core plates having a phase difference therebetween.

2. The motor as claimed m claim 1, wherein a stepped portion is formed at an end of the guide groove m such a way as to limit insertion of the first annular small-toothed unit plate.

3. The motor as claimed m claim 1, wherein each of the first and second annular small -toothed unit plates is formed on at least one place along a circumferential outer surface thereof with a projection which is engaged m the guide groove of the motor case.

4. An AC motor m which slots and teeth are formed on a circumferential inner surface of a stator m a lengthwise direction of the motor, AC coils are wound on the teeth, and a rotor is rotated by a variation in magnetic fields generated upon current application, the AC motor comprising: a stator having a first annular small -toothed unit plate which is formed on a circumferential inner surface thereof with radial teeth while not having lengthwise slots, an annular unit AC coil, and a second annular small-toothed unit plate which is uniformly formed on a circumferential inner surface thereof with radial teeth while not having lengthwise slots, the first annular small-toothed unit plate, the annular unit AC coil and the second annular small -toothed unit plate defining one phase and being sequentially inserted into a motor case along a guide groove which is defined on a circumferential inner surface of the motor case and extends in the lengthwise direction, thereby to be coupled thereto; and a rotor rotated in synchronism with magnetization of the phase which is defined by the first and second annular small-toothed unit plates and the annular unit AC coil .