GB2310322A

GB2310322A - Winding structure for operating a two phase motor from a three phase source

Info

Publication number: GB2310322A
Application number: GB9602972A
Authority: GB
Inventors: Jr Peter Senak
Original assignee: Dana Inc
Current assignee: Dana Inc
Priority date: 1996-02-13
Filing date: 1996-02-13
Publication date: 1997-08-20
Also published as: FR2745125B1; DE19605662A1; JPH09233789A; FR2745125A1; CA2169515A1; GB9602972D0

Description

0 2310322 TITLE WINDING STRUCTURE FOR OPERATING A TWO PHASE MOTOR FROM A

THREE PHASE SOURCE

BACKGROUND OF THE INVENTION

This invention relates in general to windings for electric motors. More specifically, this invention relates to a winding structure which permits a two phase electric motor to be operated from a three phase source of electrical energy.

Electric motors are well known devices which convert electrical energy to rotary mechanical energy. To accomplish this, electric motors establish and control electromagnetic fields so as to cause the desired rotary mechanical motion. The two basic components of an electric motor are (1) a stationary member which typically generates a rotating electromagnetic field, generally referred to as the stator, and (2) a rotatable member driven by the rotating magnetic field, generally referred to as the rotor. Usually, a set of windings of an electrical conductor are provided on the stator for generating the electromagnetic fields.

Most electric motors are constructed to operate from a source of electrical energy which provides an alternating electrical current to the set of windings within the motor. Such a source of electrical energy generates a flow of electrical current through the windings which changes in direction as a function of time. The simplest form of an alternating current source of electrical energy is a singl phase system. In a single phase system, a single flow of electrical current is provided through a single electrical conductor to a single set of windings within the motor. Most households are wired for single phase alternating 1 2 current, and most electrically driven devices found in such households are constructed with single phase motors.

However, many electric motors are constructed to operate from a multiple phase source of alternating electrical current. A two phase system of alternating current can be thought of as two electrically distinct single phase systems having separate electrical conductors which are connected to separate sets of windings within the motor. Each of the electrical currents passed through the respective electrical conductors alternate in direction of flow, but not simultaneously. Rather, the flow of electrical current in the second phase of the motor is electrically offset from the flow of electrical current in the first phase of the motor by a predetermined amount. Usually, the two phases from the source of electrical energy are offset by one-quarter of a cycle, or 9V. In a three phase system, the three phases from the source of electrical energy are equally offset from each other by one-third of a cycle, or 1201. Single phase, two phase, and three phase sources of electrical energy are well known in the art, as are single phase, two phase, and three phase electric motors adapted to be driven thereby.

Two phase motors are in common use for constant speed applications, and sources of electrical energy which generate the two phases of electrical current at a constant frequency are well known and readily available. In some applications, it is desirable that two phase motors be operated at variable speeds. Unfortunately, sources of electrical energy which generate the two phases of electrical current at variable frequencies are not readily available. However, sources of electrical energy which generate three phases of electrical current at variable frequencies are well known and readily available. Thus, it is known to adapt a three phase, variable frequency source of electrical energy for use by a two phase motor by means 3 of external circuitry, such as a Scott "T" transformer circuit. While effective, it has been found that such external circuitry increases the cost, size, and complexity of the overall motor. Accordingly, it would be desirable to provide a structure which permits a two phase electric motor to be operated directly from a three phase source of electrical energy, without the use of any external or additional circuitry.

SUMMARY OF THE INVENTION

This invention relates to a winding structure for an electric motor which permits a two phase electric motor to be operated from a three phase source of electrical energy. The motor includes a stator which is generally hollow and cylindrical in shape, having a plurality of radially inwardly extending stator poles. A cylindrical rotor assembly is coaxially supported within the stator for relative rotational movement. The first phase of the motor includes a first set of windings which are provided on a first set of stator poles and which are connected to a first electrical current generating circuit. Thus, the first phase of the motor is energized solely by the output electrical current from the first electrical current generating circuit. The second phase of the motor includes a second set of windings which are provided on a second set of stator poles and which are connected to a second electrical current generating circuit. The second phase of the motor further includes a third set of windings which are provided on the same second set of stator poles with the second set of windings. The third set of windings are connected to a third electrical current generating circuit and are wound in opposite directions from the second set of windings. Thus, the second phase of the motor is energized by the output electrical current from the second electrical current generating circuit less the output electrical 4 current from the third electrical current generating circuit. Thus, the input current signals for the two phases exhibit a 900 phase differential, which make them well suited for use in operating a two phase motor from a three phase source of electrical energy.

Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a sectional side view of a basic mechanical structure for a synchronous inductor electric motor, excluding the windings.

Fig. 2 is a sectional end view taken along line 2-2 of Fig. 1 which schematically illustrates a conventional winding structure for the basic synchronous inductor electric motor, permitting it to be operated as a two phase 20 motor by a two phase source of electrical energy.

Fig. 3 is a sectional end view similar to Fig. 2 which schematically illustrates a winding structure in accordance with this invention for the same basic synchronous inductor electric motor, permitting it to be operated as a two phase electric motor by a three phase source of electrical energy.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, there is illustrated in Fig. 1 the basic mechanical structure of a synchronous inductor motor, indicated generally at 10. The motor 10 includes a stator 11 which is generally hollow and cylindrical in shape. A plurality of radially inwardly extending stator poles, indicated generally at 12, are formed on the stator 11 and extend longitudinally throughout the length thereof. The stator poles 12 are preferably provided in opposed pairs, such as shown at Al and A2, Bl and B2, Cl and C2, and D1 and D2. Thus, eight stator poles 12 are provided on the illustrated stator 11. The eight illustrated stator poles 12 are evenly spaced apart from one another by 451. However, a greater or lesser number of stator poles 12 may be provided.

Each of the stator poles 12 is generally rectangular in cross sectional shape. A plurality of teeth 13 (five in the illustrated embodiment) is provided on the radially innermost surface of each of the stator poles 12. The stator teeth 13 extend longitudinally throughout the associated stator poles 12. The stator 11 and the stator poles 12 are formed from a magnetically permeable material, such as iron. As will be explained below, the stator pole pairs Al, A2, and Cl, C2 represent a first phase for energizing the synchronous inductor motor for operation, while the stator pole pairs Bl, B2, and D1, D2 represent a second phase for energizing the synchronous inductor motor for operation.

A cylindrical rotor assembly, indicated generally at 15, is co-axially supported within the stator 11 for relative rotational movement. The rotor assembly 15 includes a shaft 16 having a first rotor pole section 17 secured for rotation therewith. The first rotor pole section 17 has a plurality of radially outwardly extending teeth 17a (fifty in the illustrated embodiment) formed on the outer surface thereof. Similarly, the rotor assembly also includes a second rotor pole section 18 secured for rotation therewith. The second rotor pole section 18 has a plurality of radially outwardly extending teeth 18a (also fifty in the illustrated embodiment) formed on the outer surface thereof. The first and second rotor pole sections 17 and 18 are both formed from a magnetically permeable material, such as iron.

6 Preferably, the teeth 17a provided on the first rotor pole section 17 and the teeth 18a provided on the second rotor pole section 18 are formed having the same size and pitch. The teeth 13 provided on the stator 11, however, are usually formed having a different pitch from the teeth 17a and 18a. The teeth 17a provided on the first rotor pole section 17 are not axially aligned with the teeth 18a provided on the second rotor pole section 18. Rather, the teeth 17a provided on the first rotor pole section 17 are offset from the teeth 18a provided on the second rotor pole section 18 by one-half tooth pitch. Thus, when the teeth 17a provided on the first rotor pole section 17 are aligned with the teeth 13 provided on the stator 11, the teeth 18a provided on the second rotor pole section 18 are aligned with the valleys between the teeth 13 provided on the stator 11, as shown in Fig. 1.

A permanent magnet 19 is mounted on the rotor shaft 16 between the first rotor pole section 17 and the second rotor pole section 18. As can be readily appreciated from Fig. 1, the permanent magnet 19 causes the entire first rotor pole section 17 to exhibit a north polar magnetization. The magnet 19 further causes the entire second rotor pole section 18 to exhibit a south polar magnetization.

Fig. 2 schematically illustrates a conventional winding structure for the basic synchronous inductor electric motor 10 described above which permits it to be operated as a two phase motor by a two phase source of electrical energy. As shown therein, the first phase of the two phase motor includes first pairs of windings 20 and 21, which are provided on the opposed stator pole pairs Al, A2 and Cl, C2, respectively. The first pairs of windings and 21 are connected to a first electrical current generating circuit 22, either in series (as illustrated) or in parallel. The first pairs of windings 20 and 21 are 7 wound in opposite directions such that when they are energized, the teeth 13 of the stator poles Al, A2 (upon which the windings 20 are disposed) and the teeth 13 of the stator poles Cl, C2 (upon which the windings 21 are disposed) exhibit opposite polar magnetizations.

Similarly, the second phase of the two phase motor includes second pairs of windings 23 and 24, which are provided on the opposed stator pole pairs Bl, B2 and D1, D2, respectively. The second pairs of windings 23 and 24 are connected to a second electrical current generating circuit 25, either in series (as illustrated) or in parallel. The second pairs of windings 23 and 24 are wound in opposite directions such that when they are energized, the teeth 13 of the stator poles Bl, B2 (upon which the windings 23 are disposed) and the teeth 13 of the stator poles D1, D2 (upon which the windings 24 are disposed) exhibit opposite polar magnetizations.

The current generating circuits 22 and 25 represent the two phases of a two phase source of electrical energy for operating the motor 10. The current generating circuits 22 and 25 are both conventional in the art and are adapted to selectively cause electrical currents to flow respectively through the windings 20 and 21 of the first phase of the motor and through the windings 23 and 24 of the second phase of the motor. The electrical currents which are generated by the current generating circuits 22 and 25 may take any conventional form. For example, the electrical currents may be continuously time varying in nature (such as sinusoidal input signals) for synchronous free-running operation of the motor 10. Alternatively, the electrical currents may be discretely time varying in nature (such as square wave input signals) for synchronous stepping operation of the motor 10. Also, the electrical currents may be non-time varying in nature (such as a direct current input signals) for causing the motor 10 to 8 provide a stationary holding torque. The timing, magnitude, and polarity of the electrical currents generated by the two current generating circuits may, if desired, be determined by a conventional rotor position sensor (not shown), as is well known in the art.

When electrical current is supplied to the first pairs of windings 20 and 21 by the current generating circuit 22, the stator 11 becomes magnetized. As mentioned above, the first pairs of windings 20 and 21 are wound in opposite directions such that when they are energized, the teeth 13 of the stator poles Al, A2 (upon which the windings 20 are disposed) and the teeth 13 of the stator poles Cl, C2 (upon which the windings 21 are disposed) exhibit opposite polar magnetizations. The second pairs of windings on the other stator pole pairs Bl, B2, and D1, D2 are similarly wound in opposite directions and, therefore, also exhibit opposite polar magnetizations when energized.

In operation, assume that electrical current is supplied to the first pair of windings 20 provided on the stator poles Al and A2 so as to energize the teeth 13 thereon to become magnetic south poles. As a result, the teeth 17a of the first rotor pole section 17 (which, because of the permanent magnet 19, are magnetic north poles) are attracted toward the adjacent stator teeth 13 provided on the stator poles Al and A2. Thus, the rotor assembly 15 is attracted to rotate toward the rotational position illustrated in Fig. 1. The teeth 18a of the second rotor pole section 18 (which, because of the permanent magnet 19 are magnetic south poles) are repelled from the adjacent stator teeth 13 provided on the stator poles Al and A2. However, as described above, the teeth 18a of the second rotor pole section 18 are offset from the teeth 17a of the first rotor pole section 17. Thus, the rotor assembly 15 is simultaneously repelled to rotate 9 toward the rotational position illustrated in Fig. 1 by the second rotor pole section 18.

At the same time, electrical current is supplied to the second pair of windings 21 provided on the stator poles Cl and C2 so as to energize them to become magnetic north poles. As a result, the teeth 17a of the first rotor pole section 17 (which, because of the permanent magnet 19, are magnetic north poles) are repelled from the adjacent stator teeth 13 provided on the stator poles Cl and C2.

Similarly, the teeth 18a of the second rotor pole section 18 (which, because of the permanent magnet 19, are magnetic south poles) are attracted to the adjacent stator teeth 13 provided on the stator poles Cl and C2. Thus, the first and second rotor pole sections 17 and 18 are respectively repelled from and attracted toward the stator poles Cl and C2 in the same manner as described above with respect to the stator poles Al and A2. Thus, the rotor assembly 15 is moved to the rotational position illustrated in Fig. 1. Throughout this initial energization, no electrical current is supplied to the stator poles pairs Bl, B2 and D1, D2.

Subsequently, the stator pole pairs Al, A2 and Cl, C2 are de-energized, the stator pole pair Bl, B2 is energized to become magnetic south poles, and the stator pole pair D1, D2 is energized to become magnetic north poles.

Because of the same magnetic attractions and repulsions described above, the rotor assembly 15 is rotated one-quarter of a rotor tooth pitch from the position illustrated in Fig. 1. Similarly, in the next step, the stator pole pair Al, A2 is energized to become magnetic north poles, the stator pole pair Bl, B2 is de-energized, the stator pole pair Cl, C2 is energized to become magnetic south poles, and the stator pole pair D1, D2 is de-energized. In this manner, rotation of the electromagnetic field generated by the stator 11 causes rotation of the rotor assembly 15.

Fig. 3 schematically illustrates a winding structure in accordance with this invention for the basic synchronous inductor electric motor 10 described above which permits it to be operated as a two phase motor by a three phase source of electrical energy. As shown therein, the first phase of the two phase motor includes first pairs of windings 30 and 31, which are provided on the opposed stator pole pairs Al, A2 and Cl, C2, respectively. The first pairs of windings and 31 are connected to a first electrical current generating circuit 32, either in series (as illustrated) or in parallel. The first pairs of windings 30 and 31 are wound in opposite directions such that when they are energized, the teeth 13 of the stator poles Al, A2 (upon which the windings 30 are disposed) and the teeth 13 of the stator poles Cl, C2 (upon which the windings 31 are disposed) exhibit the opposite polar magnetization.

The second phase of the two phase motor includes second pairs of windings 33 and 34, which are provided on the opposed stator pole pairs Bl, B2 and D1, D2, respectively. The second pairs of windings 33 and 34 are connected to a second electrical current generating circuit 35, either in series (as illustrated) or in parallel. The second pairs of windings 33 and 34 are wound in opposite directions. The second phase of the two phase motor further includes third pairs of windings 36 and 37, which are also provided on the opposed stator pole pairs Bl, B2 and D1, D2, respectively with the second pairs of windings 33 and 34. The third pairs of windings 36 and 37 are connected to a third electrical current generating circuit 38, either in series (as illustrated) or in parallel. The third pairs of windings 36 and 37 are also wound in opposite directions.

As shown in Fig. 3, the stator pole Bl has both a winding 33 and a winding 36 provided thereon. The winding 33 and the winding 36 are wound upon the stator pole Bl in 11 opposite directions. Likewise, the stator pole B2 has both a winding 33 and a winding 36 provided thereon which are wound in opposite directions. Similarly, the stator pole D1 has both a winding 34 and a winding 37 provided thereon which are wound in opposite directions, and the stator pole D2 has both a winding 34 and a winding 37 provided thereon which are wound in opposite directions. The purpose for providing dual, oppositely wound windings 33, 36 and 34, 37 on the stator poles Bl, B2 and D1, D2 will be explained below.

The three electrical current generating circuits 32, 35, and 38 represent the three phases of a three phase source of electrical energy for operating the motor 10.

The three electrical current generating circuits 32, 35, and 38 are conventional in the art and are adapted to selectively cause electrical currents to flow respectively through their associated windings 30 and 31, 33 and 34, and 36 and 37. As with the electrical current generating circuits 22 and 25 described above, the electrical currents which are gene rated by the electrical current generating circuits 32, 35, and 38 may take any conventional form.

As will be explained below, the first pairs of windings 30 and 31 and the first electrical current generating circuit 33 represent the first phase of the two phase motor. The second pairs of windings 33 and 34 and the second electrical current generating circuit 35, together with the third pairs of windings 36 and 37 and the third electrical current generating circuit 38 represent the second phase of the two phase motor.

For the purpose of illustration, let it be assumed that the three phase source of electrical energy provided by the three electrical current generating circuits 32, 35, and 38 generate sinusoidal electrical currents which are electrically offset in phase at 01, 120, and 240'.Thus, 12 the output electrical currents from the three phase energy source can be expressed as follows:

i a = A sin (wt) i b = A sin (wt + 120) ic = A sin (wt + 240') For the two phase electric motor, the input electrical currents can be expressed as follows:

ia = ia ib = i b - ic Thus, the first phase of the motor is energized solely by the output electrical current from the first electrical current generating circuit 32. However, the second phase of the motor is energized by the output electrical current from the second electrical current generating circuit 35 less the output electrical current from the third electrical current generating circuit 38. This difference occurs because the second pairs of windings 33 and 34 are wound upon the stator poles Bl, B2 and D1, D2 in opposite directions from the third pairs of windings 36 and 37. By substituting the values for the output electrical current signals, the input current signals can be expressed as follows:

I a = A sin (wt) I b = A sin (wt + 1200) - A sin (wt + 240) Using easily derivable trigonometric functions, the input electrical current signals can be re-written as follows:

I a = A sin (wt) I b = -J-3 A sin (wt - 90) 13 Thus, it can be seen that the input current signals exhibit a 900 phase differential, which make them well suited for use in operating the motor 10 as a two phase operation from a three phase source. The operation of the motor 10 from this point on is conventional in the art.

In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been described and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope. For example, although the invention has been described and illustrated in the context of a synchronous inductor electric motor, it will be appreciated that the invention may be use in other types of electric motors.

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Claims

What is claimed is:

1. A component for use in an electric motor comprising:

a stator having first and second stator poles; a first winding provided on said first stator pole and adapted to be connected to a first electrical current generating circuit; a second winding pro-ided on said second stator pole and adapted to be connected to a second electrical current generating circuit; and a third winding provided on said second stator pole and adapted to be connected to a third electrical current generating circuit, said third winding being wound on said second stator pole in an opposite direction from said second winding.

2. The component for use in an electric motor defined in Claim 1 wherein said stator further includes first and second pairs of stator poles.

3. The component for use in an electric motor defined in Claim 2 wherein said first winding is provided on each of said first pair of stator poles, each of said first windings adapted to be connected to said first electrical current generating circuit.

4. The component for use in an electric motor defined in Claim 3 wherein said first windings are wound in opposite directions.

5. The component for use in an electric motor defined in Claim 3 wherein said second winding is provided on each of said second pair of stator poles, each of said second windings adapted to be connected to said second electrical current generating circuit.

6. The component for use in an electric motor defined in Claim 5 wherein said third winding is provided on each of said second stator poles, each of said third windings adapted to be connected to said third electrical current generating circuit, each of said third winding being wound on said second stator poles in opposite directions from each of said second windings.

7. An electric motor comprising:

stator having a plurality of stator poles; first winding provided on a first one of said plurality of stator poles and adapted to be connected to a first electrical current generating circuit; a second winding provided on a second one of said plurality of second stator poles and adapted to be connected to a second electrical current generating circuit; a third winding provided on said second one of said plurality of stator poles and adapted to be connected to a third electrical current generating circuit, said third winding being wound on said second -)ne of said plurality of stator poles in an opposite direction from said second winding; and a rotor assembly supported within said stator for relative rotational movement.

8. The electric motor defined in Claim 7 wherein said first winding is provided on each of a first pair of stator poles, each of said first windings adapted to be connected to said first electrical current generating circuit.

9. The electric motor defined in Claim 8 wherein said first windings are wound in opposite directions.

16

10. The electric motor defined in Claim 8 wherein said second winding is provided on each of a second pair of stator poles, each of said second windings adapted to be connected to said second electrical current generating circuit.

11. The electric motor defined in Claim 10 wherein said third winding is pro,-ided on each of said second pair of stator poles, each of said third windings adapted to be connected to said third electrical current generating circuit, each of said third windings being wound on said second stator poles in opposite directions from each of said second windings.

12. A synchronous inductor electric motor comprising: a stator formed from a magnetically permeable material, said stator including a plurality of radially inwardly extending stator poles, each of said stator poles having a plurality of radially inwardly extending teeth formed thereon; a first winding provided on a first one of said plurality of stator poles and adapted to be connected to a first electrical current generating circuit; a second winding provided on a second one of said plurality of second stator poles and adapted to be connected to a second electrical current generating circuit; a third winding provided on said second one of said plurality of stator poles and adapted to be connected to a third electrical current generating circuit, said third winding being wound on said second one of said plurality of stator poles in an opposite direction from said second winding; and a rotor assembly supported within said stator for relative rotational movement, said rotor assembly including 17 a shaft having a first and second rotor pole sections secured for rotation therewith, each of said first and second rotor pole sections being formed from a magnetically permeable material and having a plurality of radially outwardly extending teeth formed thereon, said rotor shaft assembly further including a permanent magnet being disposed between said first and second rotor pole sections.

13. The synchronous inductor electric motor defined n Claim 12 wherein said first winding is provided on each of a first pair of stator poles, each of said first windings adapted to be connected to said first electrical current generating circuit.

14. The synchronous inductor electric motor defined in Claim 13 wherein said first windings are wound in opposite directions.

15. The synchronous inductor electric motor defined in Claim 13 wherein said second winding is provided on each of a second pair of stator poles, each of said second windings adapted to be connected to said second electrical current generating circuit.

16. The synchronous inductor electric motor defined in Claim 15 wherein said third winding is provided on each of said second pair of stator poles, each of said third windings adapted to be connected to said third electrical current generating circuit, each of said third windings being wound on said second stator poles in opposite directions from each of said second windings.

17. An electric motor including the component defined in Claim 1 and further including a rotor supported within said stator for relative rotational movement.

18. A synchronous inductor motor including the component defined in claim 1 wherein said stator is formed from a magnetically permeable material and further including a rotor assembly supported within said stator for relative rotational movement, said rotor assembly including a shaft having a first and second rotor pole sections secured for rotation therewith, each of said first and second rotor pole sections being formed from a magnetically permeable material and having a plurality of radially outwardly extending teeth formed thereon, said rotor shaft assembly further including a permanent magnet being disposed between said first and second rotor pole sections.

19. A component for use in an electric motor substantially as described herein, with reference to, and as shown in Figures 1 and 3 of the accompanying drawings.

20. An electric motor substantially as described herein, with reference to, and as shown in Figures 1 and 3 of the accompanying drawings.