GB2266196A

GB2266196A - A reversable switched reluctance motor

Info

Publication number: GB2266196A
Application number: GB9305937A
Authority: GB
Inventors: Cheol Baik; Jun Young Lim; Doo Jin Shin
Original assignee: Gold Star Co Ltd
Current assignee: LG Electronics Inc
Priority date: 1992-03-25
Filing date: 1993-03-23
Publication date: 1993-10-20
Anticipated expiration: 2013-03-23
Also published as: JPH0614508A; JP3350567B2; GB2266196B; KR930020813A; GB9305937D0; KR960001954B1

Abstract

The switched reluctance motor comprises a stator (11) and rotor (12) each of which includes a plurality of poles (13; 14) with the stator to rotor pole ratio of 8:6, excitation coils (15) wound around poles of the stator, respectively, a position detection device (20) for detecting a position of the rotor, and a control unit for generating a signal for exciting each phase, based on a position detection signal from the position detection device. The position detection device comprises a sensing disc (20) provided with alternating circumferential outer and inner opening and closing portions (21, 22) (23, 24), and two sensors (S1, S2) adapted to detect each of the outer opening and closing portions and each of the inner opening and closing portions passing them, respectively. The outer and inner opening portions overlap by a predetermined circumferential angle. An alternative embodiment has stator/rotor pole ratios of 6:4. <IMAGE>

Description

SWITCHED RELUCTANCE MOTOR BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a reluctance motor, and more particularly to a switched reluctance motor capable of reducing the number of poles of each of its stator and rotor and yet obtaining a low speed and a high torque required in a direct drive type laundry machine, as well as of controlling normal/reverse rotations only by using two sensors and a control unit with a simple construction.

Description of the Prior Art Generally, switched reluctance motors are mainly used as motion power sources for direct drive type laundry machines and vacuum cleaners, since they adapt a relatively simple control system which makes their manufacture easy and the cost inexpensive.

Referring to FIGS. 1 and 2, there is illustrated such general switched reluctance motors. As shown in the drawings, each of the switched reluctance motors comprises a stator 1 fixedly mounted to a motor housing and provided with a plurality of inwardly protruded poles 3 uniformly spaced from one another and a rotor 2 stunted rotatably about a rotation shaft 2a inwardly of the poles 3 of stator 1 and provided with a plurality of outwardly protruded poles 4 uniformly spaced from one another. Coils 5 are individually wound around pairs of opposed poles 3 of the stator 1. FIGS. 1 and 2 show only two coils wound around the pole pair a-a', by way of example.

The switched reluctance motor also comprises a position detection device for detecting a position of the rotor 2 and a control unit for generating a signal for exciting each phase, based on a position detection signal from the position detection device, so as to supply an electric power to the corresponding coil 5. FIG. 1 shows a three-phase motor having the stator/rotor pole ratio of 6:4, whereas FIG. 2 shows a four-phase motor having the stator/rotor pole ratio of 8:6.

Operation of such a conventional switched reluctance motor with the above-mentioned construction will be now described.

As one of coils 5 wound around the stator 1 is excited, a rotation force is generated in a direction of minimizing a reluctance, namely, a magnetic resistance between each pole 3 of stator 1 and each pole 4 of rotor 2. As all of coils 5 are then sequentially excited, the rotation force is continuously generated, thereby causing the motor to be driven, The sequential excitation of coils corresponding respective phases is achieved by detecting sequential positions of rotor 2 by the position detection device and logically combining position detection signals sequentially generated from the position detection device, so as to excite the phases sequentially.

As mentioned above, the stator/rotor pole ratio is 6:4 in the case of the three-phase motor shown in FIG. 1 and 8:6 in the case of the four-phase motor shown in FIG. 2. Each of practical stators and rotors in reluctance motors used as motion power sources of machines requiring a low speed and a high torque such as laundry machines has poles which correspond in number to a multiple of proper times the number of poles corresponding to the above-mentioned basic stator/rotor pole ratio of 6:4 or 8:6. Coils are wound around the poles, so as to establish at least three phases. This is for the purpose of increasing the numbers of poles of stator and rotor and thus obtaining a high torque at a low speed.

For example, U.S. Patent No. 4,998,052 disclosed a reluctance motor used as a motion power source of a laundry machine, wherein each of its stator and rotor has poles corresponding in number to a multiple of three or more times (for example, five times) the number of poles corresponding to the stator/rotor pole ratio selected from the ratio consisting of 6:4 and 8:6.

In a three-phase case, the stator includes poles with the number of 18 to 30 and the rotor includes poles with the number of 12 to 20 based on the stator/rotator pole ratio of 6:4, so as to obtain a high torque at a low speed. In a fourphase case, the stator includes poles with the number of 24 to 40 and the rotor includes poles with the number of 13 to 30 based on the stator/rotator pole ratio of 8:6, so as to achieve the same purpose as the three-phase case.

The position detection device of the conventional switched reluctance motor comprises a plurality of optical sensors fixedly mounted to the motor housing1 that is, three optical sensors Sl to S3 in the three-phase case and four optical sensors St to S. In FIG. 3, only three sensors S, to SX are shown. The position detection device also comprises an interrupting type sensing disc 6 fixedly mounted to the rotation shaft 2a to rotate with the rotor 2 and having the same shape as the rotor 2. The sensors output position detection signals indicative of the sequential positions of rotor 2. By the control unit (not shown), the position detection signals from the sensors are logically combined together, so as to sequentially drive the phases of rotor 2.

The sensing disc 6 has protrusions 7 with the same number as the poles of rotor 2. The sensors serve to detect the protrusions 7 passing them. FIGS. 3 and 5 illustrates cases having the stator/rotor pole ratios of 6:4 and 8:6, respectively.

In the position detection device of the conventional three-phase reluctance motor, each protrusion 7 of the sensing disc 6 is spaced 90 apart from adjacent protrusions 7 and has a circumferential angle of 30 , as shown in FIG. 3. On the other hand, each recess 8 of the sensing disc 6 defined between adjacent protrusions 7 has a circumferential angle of 60 . Adjacent ones of the sensors S1 to S3 are spaced 1204 apart from each other. With this construction, the sensors S to S1 detect the protrusions 7 of sensing disc 6 sequentially.

The position detection signals from the sensors S, to S3 shown by S,, S2 and S3 in FIG. 4 are sent to the control unit constituted by a TTL device. Based on the position detection signals S, S2 and S3, the control unit generates not only a current command signal and an angle command signal, but also an a-phase excitation signal SI S2, a b-phase excitation signal S! S2 and and a c-phase excitation signal S1 . S2, so as to drive the motor in counter-clockwise.

The phase excitation signals are used as signals for activating bases or gates of switching elements adapted to excite the phases of a drive unit (not shown) of the reluctance motor, so as to drive the motor. As these phase excitation signals are sequentially applied for exciting the phases in the order of a # b - c, the rotor 2 rotates in counter-clockwise. On the other hand, where the sequential phase excitation is carried out in the order of a - b, the rotor 2 rotates in clockwise. In the three-phase motor, te phase excitation signals can be obtained only by two sensors.

However, three sensors are practically needed, since a phase advance angle varies in direction, depending on the direction of rotation. Accordingly, the phase advance angle should be considered when the motor is desired to rotate in both directions. That is, where the rotor rotates in counterclockwise, the phase excitation signals are obtained by the position signals from the sensors S and S,. When the rotor rotates in clockwise, the position detection signals from the sensors S and S3 are combined together to generate the phase excitation signals, since the phase advance angle is reversely generated, as compared with the case when the rotor rotates in counter-clockwise.

In the position detection device of the conventional four-phase reluctance motor, each protrusion 7 of the sensing disc 6 is spaced 60 apart from adjacent protrusions 7 and has a circumferential angle of 18', as shown in FIG. 5. On the other hand, each recess 8 of the sensing disc 6 defined between adjacent protrusions 7 has a circumferential angle of 42. Adjacent ones of the sensors Sl to S are spaced 45 apart from each other. With this construction, the sensors S to S4 detect the protrusions 7 of sensing disc 6 sequentially.

As shown in FIG. 6, the position detection signals from the sensors S. to Sl are signals S, S:, S:.l,nd S, having a low level fcr 18 corresponding to the angle through which each protrusion 7 passes and having a high level for '2 corresponding to the angle through which each recess 8 passes.

These position detection signals are sent to the control unit constituted by a TTL device. Based on the position detection signals Sl, S2, S3 and So, the control unit generates not only a current command signal and an angle command signal, but also an a-phase excitation signal i 54, a b-phase excitation signal S3. S1, a c-phase excitation signal S2.S3 and a d-phase excitation signal S1 S2 so as to drive the motor in counterclockwise.

As these phase excitation signals are sequentially applied for exciting the phases in the order of a - b - c the rotor 2 rotates in counter-clockwise. On the other hand, where the sequential phase excitation is carried out in the order of a - d - c - b, the rotor 2 rotates in clockwise.

Even where simple normal/reverse direction drives are required as in direct drive type laundry machines, the motor must have three sensors for three phases and four sensors for four phases. Furthermore, normal/reverse advance angles, which are determined by the signals detected by the sensors, the rotation direction and the rotation speed, should be considered in generating the phase excitation signals. As a result, the control unit becomes complex. This results in the unnecessarily complicated overall construction unsuitable as a motion power source for home asoliances and an increase in manufacture cost.

The relative position between adjacent sensors is also limited by a certain angle, for example, 1200 for three phases and 450 for four phases. Such a limitation may result in a poor workability in assembling sensors. Moreover, if the relative position between adjacent sensors is incorrect, erroneous position detection signals may be generated.

For example, where phase excitation signals are generated only by position detection signals from two sensors in the three-phase motor, if the positional relation between the two sensors is not incorrect, the position detection signals are not varied simultaneously at points (for example, the 30 point and the 60 point) where they are to be normally varied.

This results in an erroneous interval such as a no signal interval or a signal overlap interval. In this case, the motor can not started when it has been stopped at the erroneous interval. Also, there is a problem that undesirable phase excitation signals may be generated during the driving of motor, even for a short time.

The conventional reluctance motors have so many poles, since the number of poles is a multiple of three times or five times the number of poles corresponding to the stator/rotor pole ratio of 8:6 or 6:4, so as to obtain a low speed and a high torque. As a result, the motors have a complicated construction which makes the compactness impossible. These HrW31ems affects adversely the constructive characteris~ c of reluctance motors making the manufacture relatively easy.

SUMMARY OF THE INVENTION The present invention has been made in view of the abovementioned problems encountered in the prior arts and an object of the invention is to provide a switched reluctance motor capable of controlling normal/reverse rotations by detecting sequential positions of its rotor by only two sensors.

Another object of the invention is to provide a switched reluctance motor capable of detecting sequential positions of its rotor by two sensors aligned with each other, so as to improve a workability in assembling the motor and prevent an error due to a positional relation between the sensors.

Another object of the invention is to provide a switched reluctance motor capable of providing a simple control unit, by making advance angles symmetrical to each other with respect to a conduction angle and thus giving the same advance angles upon both normal and reverse rotations.

Still another object of the invention is to provide a switched reluctance motor capable of not only achieving an easy manufacture which is an advantage of reluctance motors and a compactness, but also obtaining a low speed and a high torque sufficient to apply ehe motor to laundry machines, by making the stator/rotor pole ratio correspond to 12:8 or 16:12 which is a multiple of two times the ratio of 6:4 or 8:6 and constructing coils for three phases or four phases.

In accordance with the present invention1 this object can be accomplished by providing a switched reluctance motor comprising: a stator fixedly mounted to a housing of said switched reluctance motor and having a plurality of poles; a rotor rotatably disposed inwardly of said stator and having a plurality of outwardly extending poles; excitation coils wound around said poles of the stator, respectively, and connected with one another to form at least three phases for the energization of the switched reluctance motor; position detection means for detecting a position of said rotor; control means for generating a signal for exciting each phase, based on a position detection signal from said position detection means, so as to supply an electric power to the corresponding coil; said stator and rotor having the stator to rotor pole ratio selected from the ratios consisting of 6:4 and 8:6 with the actual number of poles being a multiple of 2 times those numbers; and said position detection means comprising: a sensing disc fixedly mounted to a rotation shaft of the rotor and provided at its peripheral portion with a plurality of alternating outer opening and closing portions arranged on a circle thereon and having predetermined circumferential angles and a plurality of alternating inner opening and closing portions arranged on a circle concentrically to and inwardly of the circle of said outer opening and closing portions and having predetermined angles; and two sensors adapted to detect each of said outer opening and closing portions and each of said inner opening and closing portions passing them, respectively.

Each of outer opening and closing portions of the sensing disc is offset from each corresponding one of inner opening and closing portions by a predetermined circumferential angle such that they are overlapped with each other by 1/2 of their circumferential angle.

The sensors, the sensing disc and the rotor have a positional relationship thereamong determined such that advance angles each corresponding to 1/2 of a conduction angle are given at opposite sides of the conduction angle. That is, each of the sensors is aligned with a center line of an optional pole of said stator and a phantom center i line extending along the middle of each overlapped portion between each outer opening portion and each corresponding opening portion of the sensing disc is aligned with a center line of an optional pole of the rotor, so as to give the same advance angle upon normal/reverse rotations.

As the rotor rotates, the sensing disc fixed to the rotation shaft of rotor rotates together with the rotor.

During this rotation of sensing disc, the sensors detect the outer opening and closing portions and the inner opening and closing portions passing them in an alternating and sequential manner and generate position detection signals. The position detection signals from the sensors are logically combined into phase excitation signals for driving respective phases according to the rotation direction.

During the operations, there is no point at which the two sensor signals are simultaneously varied, that is, edges of the two sensor signals are overlapped with each other. As a result, correct phase excitation signals can be generated1 without any errors.

In accordance with the present invention, advance angles each corresponding to 1/2 of a conduction angle are present at opposite sides of the conduction angle. As a result, it is possible to drive the motor in normal/reverse directions, without any errors in operation.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and aspects of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings in which: FIG. 1 is a schematic sectional view of a general threephase switched reluctance motor, showing its stator and rotor; FIG. 2 is a schematic sectional view of a general fourphase switched reluctance motor, showing its stator and rotor; FIG. 3 is a schematic view illustrating arrangements of a sensing dise and sensors equipped in a conventional three- phase switched reluctance motor;; FIG. 4 is a timing diagram of position detection signals arid phase excitation signals generated from the conventional three-phase switched reluctance Inotor; FIG. 5 is a schematic view illustrating arangements of a sellsing disc are sensors equipped in a conventional fourphase switched re 1 uctance motor; FIG. 6 is a t i ming diagram of position detection signals and phase excitation signals generated from the conventional four-phase switched reluctance motor;; FIG. 7 is a schematic sectional view of a four-phase switched reluctance motor according to title present invention, showing its stator and rotor; FIG . 8 i S a schematic view illustrating arrangements of a sensing disc and sensors equipped in the four-phase switched reluctance motor according to the present invention; FIG. 9 is a sectional view illustrating a a mounting construction of the sensing disc and sensors of the switched reluctance motor according to the present invention; ; FIG. 10 is a logic table of position detection signals and phase excitation signals generated from tiie four-phase switched reluctance motor according to the present invention; FIG. 11 is an inductance profile curve explaining a conduction angle and advance angles of the four-phase switched reluctance motor according to the present invention; FIG. 12 is a table illustrating the conduction angle and advance angle according to the stator/rotor pole ratio employed in the switched reluctance motor according to the present invention; FIG. 13 is a schematic view illustrating arrangements of a sensing disc and sensors equipped in a three-phase switched reluctance motor according to the present invention; and FIG. 14 is a timing diagram of position detection signals and phase excitation signals generated from the three-phase switched reluctance motor according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 7 and 8, there is illustrated a fourphase switched reluctance motor in accordance with an embodiment of the present invention.

As shown in FIGS. 7 and 8, the reluctance motor comprises a stator 11 having a plurality of poles 13 and a rotor 12 having a plurality of poles 14. The ratio of poles 13 and 14 is 8:6. Coils 15 are individually wound around pairs of opposed poles 13 of the stator 11. FIGS. 7 and 8 show only one coil wound around one pole of one (a-a') of the pole pairs a-a', b-b', c-c' and d-d', by way of example. The reluctance motor also comprises a position detection device for detecting a position of the rotor 12 and a control unit (not shown) for generating a signal for exciting each phase, based on a position detection signal from the position detection device, so as to supply an electric power to the corresponding coil 5.

In this embodiment, the number of poles 13 of the stator 11 and the number of poles 14 of the rotor 12 are 16 and 12, respectively, so as to satisfy the stator/rotor pole ratio of 8:6. That is, respective numbers of poles 13 and 14 are a multiple of two times those numbers corresponding to the ratio of 8:6.

As shown in FIG. 8, the position detection device comprises a sensing disc 20 fixedly mounted to a rotation shaft of the rotor 12. The sensing disc 20 has at its center portion a shaft hole 20a for receiving the rotation shaft and at its peripheral portion a plurality of alternating outer opening and closing portions 21 and 22 arranged on a circle thereon and a plurality of alternating inner opening and closing portions 23 and 24 arranged on a circle concentrically to and inwardly of the circle of the opening and closing portions 21 and 22. The sensing disc 20 also has two sensors Sl and adapted to detect each outer opening portion 21 and each inner opening portion 23 of sensing disc 20 passing them, respectively.

In the illustrated case, each of the numbers of outer opening and closing portions 21 and 22 is 12 identical to the number of poles of the rotor 12. Also, the numbers of inner opening and closing portions 23 and 24 are the same as the numbers of outer opening and closing portions 21 and 22. Each inner opening portion 23 and each inner closing portion 24 are offset from each corresponding outer opening portion 21 and each corresponding outer closing portion 22 by a predetermined circumferential offset angle, respectively. In the illustrated case, the circumferential offset angle is 1/2 of the circumferential angle of each outer opening portion 21.

Each of the outer and inner opening portions 21 and 23 has a shape of an arc slot perforated throughout the thickness of the sensing disc 20. Each of the outer and inner closing portions 22 and 24 is provided by each sensing disc portion defined between adjacent opening portions. The shapes of opening and closing portions of the sensing disc 20 are not limited to those mentioned above. For example, the outer opening and closing portions of sensing disc may have recess and protrusion shapes, whereas the inner opening portions have an arc slot shape in the same manner as mentioned above.

Each of alternating outer opening and closing portions 21 and 22 has a circumferential angle of 15'. Also, each of alternating inner opening and closing portions 23 and 24 has a circumferential angle of 15 and is offset 7.5 from each corresponding one of the outer opening and closing portions 21 and 22 so that it is overlapped with each half, namely, each 7.5 circumferential angle of adjacent outer opening and closing portions 21 and 22.

Two sensors S1 and S2 are optical sensors for detecting each of outer opening and closing portion 21 and 22 and each of inner opening and closing portions 23 and 24 of sensing disc 20 passing them, respectively. In the illustrated case, they are arranged adjacent to each other on the sensing disc 20. However, the arrangement of sensors is not limited to the illustrated arrangement. For example, the sensors may be arranged oppositely to each other (with respect'to the center of rotor).

In order to give the same advance angles upon both normal reverse rotations, the relative positions among the sensing disc 20, the sensors Sl and S2 and the poles of rotor 12 are adjusted for making left and right advance angles symmetrical to each other with respect to a conduction angle, that is, making each conduction angle equal to 1/2 of the conduction angle.

To this end, the sensors S and S2 are fixedly mounted to proper positions of the motor housing such that they are arranged on center lines of optional poles of the stator 11, respectively. Also, the sensing disc 20 is fixedly mounted to the rotation shaft such that a phantom center line of overlapping portions of each outer opening portion 21 and each corresponding inner opening portion 23 is aligned with a center line of an optional pole of the rotor 12. That is, the assembling of motor elements is achieved so that the phantom center line spaced apart from both the leading edge of the outer opening portion 21 and the trailing edge of the inner opening portion 23 by an angle of 3.75 , taking the normal/reverse advance angles into consideration.Otherwise, the sensors may be positioned so that they are offset rightward from a center line of an optional pole of the stator 11 by an angle of 3.754. Here, the word "center line" means a phantom vertical plane extending between the center portion of pole and the rotation center.

As shown in FIG. 9, the sensing disc 20 is fixedly mounted to the rear portion of the rotation shaft 31 protruded into an end bracket 30. Each of the sensors Sl and comprises a light emitting element and a light receiving element which are supported by a sensor bracket 34. The sensor bracket 34 includes one end having spaced opposed portions defining a beam hole 35 and supporting the light emitting element and the light receiving element of each sensor, respectively. At the other end, the sensor bracket 34 is fixedly mounted to the end bracket 30 of motor housing, by means of screws 36 and nuts 36a.

The mounting of the sensing disc 20 to the rotation shaft 31 is achieved by fitting a spacer 32 and the sensing disc 20 around the rear end of rotation shaft 31 and then threadedly coupling a nut 33 to a threaded portion 31b formed on the rear end of rotation shaft 31, so as to rotate the sensor disc 20 together with the rotation shaft 31.

The rotation shaft 31 has a flat portion 31a at its outer surface. Also, the shaft hole 20a of sensing disc 20 has a flat portion engaged with the flat portion 31a of rotation shaft 31, as shown in FIG. 8. With such a construction, the sensing disc 20 can be always coupled in position to the rotation shaft 31. For the same purpose, other means such as a key and key groove construction may be used.

Although the illustrated sensing disc of position detection device has the stator/rotor pole ratio of 8:6 with respective actual numbers of stator and rotor poles being 16 and 12, it is limited thereto and other ratios and actual pole numbers may be employed. For example, the actual number of poles can be a multiple of three or more times the number corresponding to the stator/rotor pole ratio of 8:6. In this case, the c circumferential angle of each of the opening and closing portions are reduced at a rate corresponding to the rate of increasing the number of poles.

In FIG. 9, the reference numeral "37" denotes a bearing for supporting the rotation shaft 31 to the end bracket 30.

Operation of the four-phase reluctance motor with the above-mentioned construction according to the present invention will now be described.

As the rotor 12 rotates, the sensing disc 20 fixed to the rotation shaft 31 of rotor 12 rotates together with the rotor 12. During this rotation of sensing disc 20, the sensors and S2 detect the outer opening and closing portions 21 and 22 and the inner opening and closing portions 23 and 24 passing them in an alternating and sequential manner and generate position detection signals.

Where the sensing disc 20 rotates in counter-clockwise, as shown in FIG. 10, the detection signals [S1,S2] from the sensors Sl and S2 take the repetitive form of [1,0] - t0,0] [0,1] - [1,1]. These signals are logically combined by the control unit (not shown), so as to generate phase excitation signals for driving the phases in the order of b - a - d - c.

On the contrary, when the sensing disc 20 rotates in clockwise, the detection signals CSI,S21 from the sensors Si and S2 take the repetitive form of t1,0] - [1,1] - [0,13 [0,0]. These signals are logically combined by the control unit, so as to generate phase excitation signals for driving the phases in the order of d - a - b - c.

During the above-mentioned operations, there is no point at which the two sensor signals are simultaneously varied, that is, edges of the two sensor signals are overlapped with each other. As a result, correct phase excitation signals can be generated, without any errors.

As shown in FIG. 11, the intervals in which the gradient dL/dO is "+" have the mechanical angle of 15.. The conduction angle Be which is an angle for exciting one phase is 7.5o.

The advance angel Ga is 3.75'. Accordingly, the motor can be driven in normal/reverse directions only by rotor position detection signals from the sensors S1 and S2, under a control of the control unit.

FIG. 12 shows a conduction angle and an advance angle based on the stator/rotor pole ratio in the switched reluctance motor according to the present invention. As shown in FIG. 12, the advance angle Ga corresponds to 1/2 of the conduction angle Go. The advance angles Ga present at opposite sides of the conduction angle 8e are symmetrical to each other. As a result, it is possible to drive the motor in normal/reverse directions, without any errors in operation.

Where the stator/rotor pole ratio is 16:12, it is also possible to obtain a low speed and high torque required in direct drive type laundry machines.

On the other hand, FIG. 13 illustrates a position detection device of a three-phase reluctance motor according to the present invention. This three-phase reluctance motor has the same constructions as those of the above-mentioned four-phase reluctance motor, except for the position detection. Although not shown, the constructions with the same reference numerals will be incorporated in the following description for the three-phase reluctance motor.As shown in FIG. 13, the position detection device comprises a sensing disc 40 having at its peripheral portion a plurality of alternating outer opening and closing portions 41 and 42 (in the illustrated case, four opening portions and four closing portions) arranged on a circle thereon and a plurality of alternating inner opening and closing portions 43 and 44 (in the illustrated case, four opening portions and four closing portions) arranged on a circle concentrically to and inwardly of the circle of the opening and closing portions 41 and 42.

Each of inner opening and closing portions 43 and 44 is offset from each corresponding on of outer opening and closing portions 41 and 42, by a predetermined angle. The sensing disc 40 also has two sensors Sl and S2 adapted to detect each of outer opening and closing portions 41 and 42 and each of inner opening and closing portions 43 and 44 of sensing disc 40 passing them, respectively.

The outer opening and closing portions 41 and 42 have recess and protrusion shapes, respectively. On the other hand, each inner opening portion 43 has a shape of an arc slot perforated throughout the thickness of the sensing disc 40.

Each inner closing portion 44 is provided by each sensing disc portion defined between adjacent opening portions 43. The shapes of opening and closing portions of the sensing disc 20 are not limited to those mentioned above. For example, all outer and inner opening portions of the sensing disc may have the arc slot shape, whereas all outer and inner closing portions are provided by the disc portions not perforated.

Each of alternating outer opening and closing portions 41 and 42 has a circumferential angle of 454. Also, the alternating inner opening and closing portions 43 and 44 have circumferential angles of 60 and 30 , respectively. Each of the inner opening portions 43 is offset 30 from each corresponding one of the outer opening and closing portions 41 and 42 so that it is overlapped with each half, namely, each 30 circumferential angle of adjacent outer opening and closing portions 41 and 42. Each of the inner closing portions 44 is offset 15 from each corresponding one of the outer opening and closing portions 41 and 42 so that it is overlapped with each half, namely, each 15 circumferential angle of adjacent outer opening and closing portions 41 and 42.

Two sensors Sl and S2 are arranged adjacent to each other on the sensing disc 20. However, the arrangement of sensors is not limited to the illustrated arrangement. For example, the sensors may be arranged oppositely to each other.

The position detection device of the three-phase reluctance motor has the same construction as the position detection device of the four-phase reluctance motor, except that each number of opening and closing portions 41, 42, 43 and 44 is four corresponding to the number of poles of the rotor and that each circumferential angle of opening and closing portions 41, 42, 43 and 44 is different from that of the four-phase reluctance motor.

The sensing disc 40 is fixedly mounted to the rotation shaft such that a phantom center line of overlapping portions of each outer opening portion 41 and each corresponding inner opening portion 43 is aligned with a center line of an optional pole of the rotor 12. The sensors S1 and S2 are fixedly mounted to proper positions of the motor housing such that they are arranged on center lines of optional poles of the stator 11, respectively. Constructions for mounting the sensing disc and sensors are the same as those of the embodiment relating to the four-phase reluctance motor described in conjunction with FIG. 9.

Although the illustrated sensing disc of position detection device has the stator/rotor pole ratio of 6:4 with respective actual numbers of stator and rotor poles being 6 and 4, it is limited thereto and other ratios and actual pole numbers may be employed. For example, the actual number of poles can be a multiple of two or more times the number corresponding to the stator/rotor pole ratio of 6:4. In this case, the circumferential angle of each of the opening and closing portions are reduced at a rate corresponding to the rate of increasing the number of poles.

Operation of the three-phase reluctance motor with the above-mentioned construction according to the present invention will now be described.

As the rotor 12 rotates, the sensing disc 40 fixed to the rotation shaft of rotor 12 rotates together with the rotor 12.

During this rotation of sensing disc 40, the sensors Sl and detect the outer opening and closing portions 41 and 42 and the inner opening and closing portions 43 and 44 passing them in an alternating and sequential manner and generate position detection signals.

The position detection signals from the sensors S1 and are signals Sl and S2, as shown in FIG. 14. These position detection signals are sent to the control unit (not shown) constituted by a TTL device. Based on the position detection signals S1 and S2, the control unit generates phase excitation signals 5i'52' S1 S2, and so S2 or Sl S2. -These phase excitation signals are applied as activating signals to bases or gates of switching elements for exciting the phases. Accordingly, the phases are excited in a sequential manner, so as to drive the motor.

In this case, the intervals in which the gradient dL/dO is "+" have the mechanical angle of 454. The conduction angle #c which is an angle for exciting one phase is 30 . The advance angel 0a is 15o. Accordingly, the motor can be driven in normal/reverse directions only by two position detection signals from the sensors Sl and S2, under a control of the control unit, namely, the TTL device.

The advance angle ea corresponds to 1/2 of the conduction angle Oc. As a result, it is possible to drive the motor in normal/reverse directions, without any errors in operation.

As apparent from the above description, the present invention makes it possible to drive in normal/reverse directions,by detecting the sequential positions of the rotor by only two sensors. Accordingly, there are effects of a reduced manufacture cost and a good workability in assembling.

In accordance with the present invention, the advance angles are symmetrical to each other with respect to the conduction angle. Accordingly, it is possible to obtain automatically the same advance angles upon the normal/reverse rotations and thus to provide a control unit with a simple construction.

During the operation of motor, there is no point at which the two sensor signals are simultaneously varied, that is, edges of the two sensor signals are overlapped with each other, in accordance with the present invention. Accordingly, it is possible to avoid a generation of an erroneous interval such as a no signal interval or a signal overlap interval and a generation of undesirable phase excitation signals during the driving of motor, even for a short time.

In accordance with the present invention, it is also possible to obtain a high torque at a low speed required in laundry machines and yet maintain the advantage of reluctance motors, that is, a easy manufacture, in that the numbers of stator poles and rotor poles are 16 and 12, respectively.

Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

WHAT IS CLAIMED IS:

1. A switched reluctance motor comprising: a stator fixedly mounted to a housing of said switched reluctance motor and having a plurality of poles; a rotor rotatably disposed inwardly of said stator and having a plurality of outwardly extending poles; excitation coils wound around said poles of the stator, respectively, and connected with one another to form at least three phases for the energization of the switched reluctance motor; position detection means for detecting a position of said rotor; control means for generating a signal for exciting each phase, based on a position detection signal from said position detection means, so as to supply an electric power to the corresponding coil; said stator and rotor having the stator to rotor pole ratio selected from the ratios consisting of 6:4 and 8:6 with the actual number of poles being a multiple of 2 times those numbers; and said position detection means comprising: a sensing disc fixedly mounted to a rotation shaft of the rotor and provided at its peripheral portion with a plurality of alternating outer opening and closing portions arranged on a circle thereon and having predetermined circumferential angles through which they extend circumferentially and a plurality of alternating inner opening and closing portions arranged on a circle concentrically to and inwardly of the circle of said outer opening and closing portions and having predetermined circumferential angles through which they extend circumferentially; and two sensors adapted to detect each of said outer opening and closing portions and each of said inner opening and closing portions passing them, respectively.

2. A switched reluctance motor in accordance with claim 1 , wherein each of said inner opening and closing portions of said sensing disc is overlapped with each corresponding one of said outer opening and closing portions, by a predetermined circumferential angle.

3. A switched reluctance motor in accordance with claim 2, wherein each of said outer and inner opening potions has a shape of an arc slot perforated throughout the thickness of said sensing disc and each of said outer and inner closing portions is provided by each sensing disc portion defined between adjacent perforated sensing disc portions.

4. A switched reluctance motor in accordance with claim 2, wherein each of said outer opening portion has a shape of a recess and each of said outer closing portion has a shape of a protrusion, whereas each of said inner opening potions has a shape of an arc slot perforated throughout the thickness of said sensing disc and each of said inner closing portions is provided by each sensing disc portion defined between adjacent perforated sensing disc portions.

5. A switched reluctance motor in accordance with claim 2, wherein said sensors, said sensing disc and said rotor have a positional relationship thereamong determined such that each of the sensors is aligned with a center line of an optional pole of said stator and that a phantom center line extending along the middle of each overlapped portion between each outer opening portion and each corresponding opening portion of the sensing disc is aligned with a center line of an optional pole of the rotor, so as to give advance angles at opposite sides of a conduction angle and corresponding to 1/2 of said conduction angle.

6. A switched reluctance motor in accordance with claim 5, wherein each of said sensors comprises a light emitting element and a light receiving element which are supported by a sensor bracket including one end having spaced opposed portions defining a beam hole and supporting said light emitting element and said light receiving element, respectively, said sensor bracket being at the other end thereof fixedly mounted to said motor housing.

7. A switched reluctance motor in accordance with claim 5, wherein said sensing disc has a shaft hole fitted to one end of said rotation shaft having a flat portion at its outer surface, said shaft hole having a flat portion engaged with said flat portion of the rotation shaft so that the sensing disc can be always coupled in position to the rotation shaft.

8. A switched reluctance motor in accordance with claim 2, wherein said stator and rotor have 16 poles and 12 poles, respectively, each of alternating outer opening and closing portions has a circumferential angle .of 15", and each of alternating inner opening and closing portions has a circumferential angle of 15 and is offset 7.5 from each corresponding one of the outer opening and closing portions so that it is overlapped with each half, namely, each 7.5 circumferential angle of adjacent outer opening and closing portions.

9. A switched reluctance motor in accordance with claim 8, wherein said sensing disc is fixedly mounted to said rotation shaft such that a center line of each overlapped portion between each outer opening portion and each corresponding inner opening portion is aligned with a center line of an optional pole of said rotor, os as to give an advance angle of 3.75 upon normal/reverse rotations.

10. A switched reluctance motor in accordance with claim 2, wherein said stator and rotor have 6 poles and 4 poles, respectively, each of alternating outer opening and closing portions has a circumferential angle of 45, and the alternating inner opening and closing portions have circumferential angles of 60 and 306, respectively, each of the inner opening portions is offset 30 from each corresponding one of the outer opening and closing portions so that it is overlapped with each half, namely, each 30" circumferential angle of adjacent outer opening and closing portions, and each of the inner closing portions is offset 15 from each corresponding one of the outer opening and closing portions so that it is overlapped with each half, namely, each 15 circumferential angle of adjacent outer opening and closing portions.

11. A switched reluctance motor in accordance with claim 10, wherein said sensing disc is fixedly mounted to said rotation shaft such that a center line of each overlapped portion between each outer opening portion and each corresponding inner opening portion is aligned with a center line of an optional pole of said rotor, os as to give an advance angle of 15. upon normal/reverse rotations.

12. A switched reluctance motor substantially as hereinbefore described with reference to and as shown in Figs. 7 to 14 of the accompanying drawings.