Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.


  1. Advanced Patent Search
Publication numberUS1050444 A
Publication typeGrant
Publication dateJan 14, 1913
Filing dateFeb 11, 1908
Priority dateFeb 11, 1908
Publication numberUS 1050444 A, US 1050444A, US-A-1050444, US1050444 A, US1050444A
InventorsValere Alfred Fynn
Original AssigneeValere Alfred Fynn
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Alternate-current motor.
US 1050444 A
Previous page
Next page
Description  (OCR text may contain errors)



1,050,444. Patented Jan.14, 1913.


Fig j V. A. FYNN.



1,050,444. Patented Jan. 14,1913.


j IHHH E 5 4:

Impedance N VE/VTOR I WITNESSES: MA$w iii m VQA. FYNN.



1,050,444, Patented Jan. 14, 1913.





Patented Jan. 14, 1913.


INVENTOR By Atzofneys,





To all whom "it may concern Be itltnown that l. Vanimn Awash FYNN, of 18 lllessington road, Blackheath, London, England. electrical engineer. have invented certain new and useful Improvements in or Relating to AltG-TI]ittB-QIIKIEDt Motors, of which the following is a specification.

My invention relates to alternate current motors, being in some cases used for starting in others'for starting and operating. these purposes being accomplished in an improved manner withoutmaking use of a commutator for the said purposes and without. the help of moving machinery such as rotary phase converters and the like.

This invention is applicable to alternate current induction motors which have an induced member capable of being short circuited along one or more axes and which are connected to one phase of an alternate current supply 5. c. to a single phase supply or to one phase only of a polyphase supply.

The object of this invention is to provide improved means for starting such motors or for operating them or tor both purposes. This object is achieved by producing in the motor by means of inducing windings two or more transformer fields differing in phase by a. suitable amount. the invention consisting in the improved means for securing the required number of E. M. Fs (littering in phase by the required amount. This is achieved by providing a phase displacing circuit comprising; two or more elements of differing impedance, that is containing at least. one positive and one negative reactance or one positive and one neutral reactance (2'. e. ohmic resistance) or one negative and one neutral reactance said reactances being; conductively or inductively or both eonductively and inductively related to the phase displacing-circuit of which they form a part. It is to be noted that one or more of the said elements may form an integral part of the motor or apparatus to which the invention is to be applied. Further by do riving from at least one of these elements an E. M. F. preferably differing in phase from the E. M. F. of the'supply and applying this E. M. F. either alone or with one or more other E. M. Fs to the winding at the ter minals of which an E. M. F. difiering in tpecification of Letters Patent.

Application. filed Februatytl, 1908.

Patented Jan. fl-ll. tSr'il Serial Ho. 415,442.

phase from the phase of the supply E. F. is required.

The induced member oi-r the motors herein referred to may be the rotor in which case it can be permanently short-circuited. one known rotor construction of this type is the squirrel cage. Or this induced member can be adapted to be gradually or suddenly short-circnited through slip rings and over capacities, resistances or the like. Conversely and as is well known. the induced member can be the stator instead of the rotor. For the sake of simplicity the construction of the induced member is not hereinafter again referred to and it is to be understood that it may be of any of the above mentioned types or other equivalent constructions which will allow of the application of the invention. In all the examples given the induced member will be indicated by the letter A.

I have pointed, out in a number ot publications and patents that motorsconstituted in the manner described may operate in two distinctways. lit the inducing member carries one winding only or its equivalent and it this winding is supplied with a single phase E. M. F. then the motor will operate as a single phase self-excited. partly compensated, shunt. induction motor with one armature and one field axis per pole pair. If the inducing member carries two or more windings displaced in space with regard to each other and fed by E. M. F.s difiering in phase (whether derived from a single or polyphase supply), then the motor will operate as a two or more phase separately excited, partly compensated. shunt induction motor with two or more armature and two or more field axes per pole pair. although, and as will be more clearly understood from what follows. all axes may not be contributing an equal or even a useful torque. Motors which are started or operated with two or more axes per pole pair while the necessary E. M. F.s of (littering phase are derived from a'single phase supply are generally termed split-phase motors. It is well understood that a motor started as a split-phase motor can be operated as a single phase, self-excited, partly compensated, shunt induction motor.

The present invention allows, among' other things, of motors operated from one phase of the supply only to be started or started and operated as split-phase motors with a more powerful torque and under more favorable conditions than has hitherto been possible; it also allows of motors started in the improved manner here described to be operated as ordinary single phase self excited. partly or totally compensated, shunt induction motors.

In describing this invention, reference will be had to the drawings filed herewith, and where Figures land 2 represent known phase splitting devices in conjunction with singlephase motors. Fig. 3 shows one way of carrying out the invention and Figs. 4 to 12 inclusive are explanatory diagrams referring to Fig. 3. In Fig. 13 is shown a more elaborate connection diagram of Fig. 3, together with slight modifications of Fig. 3. Fig. 1 1- shows a modification of Fig. 3. In Fig. 15 the E. M. F. impressed on one of the inducing windings, is derived partly from the mains and partly from the capacity in circuit with the other inducing winding. Figs. 15 and 15 show modifications of Fig. 15. Iu Fig. 16 the E. M. F. impressed on one inducing winding is derived from two elements forming part ,of the phase displacing circuit which includes the other inducing winding. In Fig. 17 both inducing windings form part of phase displacing circuits. In Fig. 18 an arrangement similar to that shown in Fig. 17 is combined with an auto transformer interposed between line and motor. Fig. 19 shows an arrangement similar to that of Fig. 3. In Fig. 20 the invention is shown as applied to a motor with three inducing windings. In Fig. 21 one inducing winding forms part of a phase displacing circuit, whereas the other has three F. M. F.s impressed on it.

A number of devices have already been proposed for starting such motors; they generally comprise in the first place at least two windings disposed on the inducing part of the motor. If two inducing motor wind ings only are used their they are as a rule displaced by degrees and so forth. For the case of two windings it is generally stated that the condition aimed at is to secure a phase difference as near 90 as possible between the currents flowing through the two windings. For the case of three windings that phase angle is generally given as 120. It will be seen from what follows that such statements are by no means always correct or sufficient, what is of at least equal importance inmost of the methods heretofore proposed is that the E. M. F .s acting at the terminals of the windings in question shall differ by 90 or 120 degrees as the case may be so that the transformer fields due to those inducing motor windings shall differ in phase by 90, 120, or any other angle corresponding to the number of inducing motor windings chosen and to their displacement in space if the motor is to start under polyphase conditions the establishing of these polyphase conditions has generally been aimed at. In order to create as nearly as possible the necessary phase difference between the E.M. F.s acting at the terminals of the various inducing motor windings it has been usual to either insert the latter into parallel circuits containing elements of differing impedance, all circuits being connected to the same phase of the supply, or to connect the inducing motor windings in series, and shunt at least one of them by means of an element of differing impedance. The two most usual types of arrangements are diagrammatically indicated in Figs. 1 and 2 for the case of 9-pole motors provided with two inducing motor windings S and S displaced by 90 in space. In Fig. 1 there are two parallel circuits, 5. c. 123 and 1-i3. In the first there are two elements R and S of differing impedance, It is a noninductive resistance and S is one of the inducing motor windings and has a certain amount of positive reactance, 2'. self-induction. In the second there are also two elements I1 and S of differing impedance. L is a high positive reactance, and S is the other inducing motor winding and has a smaller positive reactance than L. In Fig. 2 the two inducing windings are connected in series and one of them, here S is shunted by means of 'a negative reactance, i. e. a 'capacity C. It will be understood that the impedance 2 is expressed by z=ajr +mfi where r stands'for the ohmic resistance and 00 for the reactance of the circuit also can pressed in ohms; 00 has a. positive value in the case of self-induction and a negative value in the case of capacity. Hereinafter L will always designate an element having a positive, C a negative, and It a neutral reactance. It will then be understood that L, C and it stand respectively for a selfinduction, a capacity and an ohmic resistance. When it is intended to convey that the element in question may have either of these three reactances then it will be designated by Y. Every current consuming device such for instance as the inducing winding of a motor and at the terminals of which an E. M. F. is to be produced which differs from the E. M.- F. of the supply or from that of any other'chosen current consuming device will hereinafter be designated by S. The above mentioned letters will be used as required with or without indexes. It is known that it is possible to so choose the relative impedance of the various elements forming part of a circuit as to obtain at the terminals of any one of them an E. M. F. either leading or lagging behind that E. M. F. which is impressed onthe whole of the circuit. It is also known however that the range of phase differences to be obtain'edin this manner between the E. M. F.s at the terminals of elements havin r -a nearly equal impedance (as is gen erally the case with inducing motor windings such as S and S is more limited than is required. Theoretically a suflicient range should be available, practically it falls short of requirements, for I believe that the known methods can only yield a. sufiicient phase difference if a perfect negative reactance is available and it is well known that such is not the case. Now according to my invention I obtain at the terminals of any current consuming device or at the terminals of at least one inducing motor winding an E. M. F. difiering in phase from that of the supply and of any required or predetermined phase by impressing on the circuit containing that current consuming device or said winding one or more E. M. Fs at least one of which is derived from an element forming art of a circuit containing elements of diflering impedance such as hereinbefore specified and connected to the single phase supply, 2'. e. forming part of what may be termed a phase displacing circuit. If it be assumedthat all inducing windings are alike and that the reactance oi the induced member is the same along any axis the following all important conditions prevail: If the phase difference between the E. M. F. induced in the induced member and the current due to it is a for all the transformer axes, and there are say two such ares, then three cases may arise according to the phase difference a which exists the moment of starting between the two transformer fields due to the inducing windings. (1) It a is smaller than ,8 then two torques will bepresent in the motor but they will oppose each other although they may not be of the same magnitude. (2) is equal to (5 there will be only one torque in the motor, if in this particular case 6:45" then this one torque will be directly proportional to the product of the transformer flux into the rotor current to which this torque is due for these two will be practically ot same phase although they may be of opposite sign. The other transformer flux and the other current will under these conditions be practically in quadrature and will not yield any torque. (3) If 51 is greater than {5 there will be two torques in the motor both of which will be of same direction although they may not be of same magnitude. A special case arises where a=90 for then both torques will not only be of same sign but also of same magnitude and will be the greater the smaller (5 both becoming zero for 6:90". Itwill be seen that in all cases it is advantageous to make (5 as small as possible, to this end the time constant of the induced member should be,made as small as possible and when required an ohmic resistance or a negative reactance may be introduced in some known manner. It will further be seen that in order to obtain a good starting torque per ampere it is necessary that a should at least equal 5. \Vhether the best results are obtained for 0::{5 or for a fi principally depends on the magnitude of [5. It is thought that the conditions just stated have not so far been fully understood and that as a rule it has not been possible with the same means hitherto employed to obtain an a of suflicient magnitude.

'1 will now proceed to describe in some detail with reference to my theory one way of applying my invention for the purpose of starting a split phase motor having an induced member capable of being shortcircuited. Following this description I will indicate without going into such detail as in the first example, other ways of carrying out my invention when used for starting or starting and operating split phase motors.

As it is obviously impossible to indicate in connection with every example every possible modification to which the particular example lends itself, it is to be understood that even if not specially mentioned a modification described in connection with one example is to be taken as transferable or applicable to any of the other examples shown or to which the invention is applicable as long as the use of that particular modification is not obviously precluded. It is further to be understood that two or more of the modifications can in some cases be combined for use with the one or other example or applications of the invention. The theory herein set forth together with the examples given should enable those skilled in the art not only to fully recognize all other possible combinations but also their peculiar advantages proportions which should preferably be given to the various elements in order to secure the best results in every case.

lwo pole machines will be referred to throughout the specification for the sake of together with those j llilll Err simplicity but it will be understood that the invention is equally applicable to motors with any number of pole pairs.

The first example referred to will be described with reference to Fig. 3 which shows the invention as applied to an alternate current motor for the purpose of starting or starting and operating it from a single phase supply. The motor has an induced member A. capable of being short circuited, and. by way of example, two inducing motor windings S and S disposed on the stator and displaced by degrees with respect to each other. The object is to impress on S and S two F. M. Fs (F and F differing in phase by an angle z 6. The proportions are, by way of example, to he so chosen that at starting or shall be equal to 90. For this purpose, and according to this invention, I provide a phase displacing circuit 12-3 containing two elements of differing impedance and preferably including one of the motor inducing windings. say S, as one of the elements of that circuit. By the nature of things S will have a positive reactance. The other element in this circuit I choose by way of example so as to have a negative reactance and as indicated by C. It will he understoodthat this or any such phase displacing circuit may contain more than two elements of differing impedance. I then obtain at the terminals of S an IQ. M. F. differing from that of the supply (1C) and differing from that at the terminals of S by impressing in this instance on the circuit 4 56. and which contains S an F. M. F. (0") derived from the elements a forming part of the phase displacing circuit 1-2--3 together with the E. M. F. (E) taken directly from the supply an m. Let E be the E. M. F at the terminals of S FF that at the terminals of S and 15 that at the terininals. of G. Then E will lag behind E and R will lead F. In this case the transformer T situated outside the motor is made use of for deriving e -from S T can have a variable ratio as shown at K. The supply E. M. F. is applied to the circuit -l 56 directly, it will be understood that a transformer may be interposed. It will be seen from the corresponding diagrams, Figs. at to 8 that almost any phase displacement between E and E can be obtained, in any case it is an easy matter to make a larger than 5 or equalto 90; the latter case is shown in the diagrams. Fig. t shows the phase relations between the principal quantities ('2'. e. currents and E. M. Ffs) of the transformer (S a t) when an E. M. F. (Ff) in quadrature with F is applied to S Fig. 5 shows the same for the transformer (S -A) with E at its terminals. The same E is also applied to the transformer T, the secondary E. M. F. of T is e see Fig. 6, and this secondary must carry the same current as S 2'. 6., the current I for the two windings are in series. If

is the magnetizing current of T then P in Fig. 6 must flow through T in parallel with T which flows through S The current taken from the mains by circuit- (S -C) is therefore I as shown in Fig. 7 and the whole of I must flow through C. Now itis seen that if C can produce a phase differ ence between the current I passing through C and the E. M. F. E required at its terminals then F Will lead E by to. But if E does lead E by c) then we can bring about a phase diflerence a 90 between E and E by impressing on S the resultant of E and of the secondary E. M. F. (6) of T as shown in Fig. 8. It will be noted in this lastdiagram that e is greater than E, T must therefore transform up, the ratio necessary in this particular example being about 11.48. This ratio has been taken into account when preparing Fig. 6. It should be noted that a is only about 26 degrees and such a phase difference can easily be brought about by a commercial negative reactance. The phase displacement to be brought about by C can be reduced by choosing the magnetizing current of T large as has been done in Fig. 6. This can, for instance, be achieved by using a hedgehog transformer at T or by making the magnetic density in an ordinary transformer high or by introducing an air-gap into such a transformer or the like. Fig. 8 further shows the phase relation between the supply E. M. F. (E) and the currents T and 1 taken by the two parallel circuits respectively, also the phase difference (p between E and the total current I taken from the mains. The torque conditions for this particular cmodiment of the invention are illustrated by Figs. 9, 10, 11 and 12, and show that both torques are in the same direction, there is consequently no loss and the motor will always reach it full speed. lit is also easy to see that the magnitude of a is little altered if at all with increasing speed. Any alteration that does take place can be counteracted for instance by varying C or by inserting resistance .or a positive reactanee into the circuit containing S The diagrams given indicate all such possibilities very clearly. In order to reverse the direction oi rotation it is only necessary to reverse E or E or S or S In order to reverse lE it is necessary to reverse E and e Switches for this purpose are shown at M M M in Fig. 13, which also shows E dein phase and magnitude. At no load I rived from the mains for the circuit of S through a transformer T The mains are shown, byway of example, as directly connected to the circuit of S in order to indicate that the higher the E. M. F. across a capacity the easler it is to achieve a large phase displacement with its help.

Another modification shown in Fig. 13 consists of a positive reactance L connected in parallel with-- a secondary of T for the purpose of obtaining in Fig. 6 a greater lag of I behind E thereby reducing the amount of displacement which C is required to provide. Regulating devices are in every case designated by the letter K to which an index is attached when required. As the speed increases I will approach the phase of E and will as a rule decrease so that I will remain of nearly constant phase but will decrease if the load on the motor is normal. At no load and normal speed I will be nearly equal to will be practically equal to so that the resultant I will lag far behind E and either the capacity effect should be reduced or the values of either E or 6* or of both (in the circuit of S should be readjusted if E is to be kept in quadrature with E and made equalto E If T i is made equal to the value of I at full load then at full load I will be nil or nearly so; and since at full load I is nearly cophasal with E the capacity effect should be increased in order to maintain a constant, or all should be increased. Means for varying may therefore be useful in some cases, such means are known. These considerations show how the various possible cases can be met and what provisions are necessary 1 when the motor is only to be started or when it is not only to be started but also to be operated when connected as shown in Figs.

understood from what has been already said. Such a resistance'is shown by way of example in Fig. 1a which also shows a modification consisting in that the transformer T of Fig. 3 is here embodied in the motor itself. In this figure are also shown further means of regulation and adjustment which may be employed in all cases and Which consist in varying the number of turns of the windings S or S Reversing switches are omitted for the sake of clearness. In a further modification a positive reactance L ma be used in parallel with S and as is indicated in Fig. 14.

Instead of deriving 6* from S it can be derived from the resistance R which is connected in series with S or from the negative reactance C in series with S and a transformer such as T of Fig. 3 canagain be used for the purpose, this last manner of carrying the invention into practice is illustrated in Fig. 15. All the modifications previously described apply here as well and it will also be clear from the theory given how adjustments can be made in order to compensate for the variations introduced by increasing or varying speed and the like.

A study of the diagrams Figs. 4 and 8 will, for instance, show that in this case it is preferable that 9 the magnetizing current of T, should be small so that I may lead E by as much as possible. With the same object a negative reactance C may be connected as shown in the modifications indicated in Figs. 15 and 15*, either in parallel with S or with T. No regulating, adjusting or reversing de- 'vices have been shown in Fig. 15 as it is felt that these have been sufficiently described for instance in connection with Figs. 13 and 14. Y

Another way of carryinlg this invention into practice is shown in ig. 16 where S is connected across the mains in series with Y which represents any desired impedance diflering in value from that of S In this case two E. M. Fs are impressed on S both being derived from an element of the phase displacing circuit 12-3, the two E. M. Fs e and are connected in series. The modifications already described or to be described can be used in this case as far as they apply.

In another way of carryin out the,invention, a third E. M. Fabesi es e and of Fig. 16 could be impressed on S and it itself is made use of as a transformer.

could be derived from the mains, either directly or through a transformer, as shown in Fig. 21. 1

So far it has always been S which was included in the'phase displacing circuit connected to the supply and from which an E. M. F. or E. M. Fs were derived and impressed on the circuit containing S It will be understood that S can or will serve the purpose just as well.

In that manner of carrying this invention into practice which is shown in Fig. 17 both S and S form part of phase displacing circuits. An E. M. F. derived from one element in the circuit containing S is impressed on thecircuit containing S and vice versa. In this figure the auxiliary E. M. Fs

GT and 0 are by way of example derived from S and S by transformation. Instead of making use of separate transformers for the purpose, as was for instance done in the case of Fig. 3, that modification has been shown.

by way of example which has already been illustrated in Fig. 14 and in which the mt itkor e stator windings t and t act. in this case as secondaries to S and S Y and Y represent any kind of impedance the only condition being that the impedance Y should differ in value from that of S and that of Y from that of S A further example is shown in Fig. 18. The phase displacing circuit 123 is connected to the mains by way of example through the autotransformer T and regulator K The transformer T may as shown also be used for boosting the voltage if required. There are in this case three E. M. Fs impressed on S one of them is derived from the transformer T forming part of the phase displacing circuit. T may have a largemagnetizing current and provision may be made to vary the latter. Another is derived from S by way of t and regulator K while the third is taken from the supply by way of T and regulator K The proportions may be so chosen that the current passing through S and t leads the E. M. F.

due to t thereby acting as a capacity in parallel with S In the example shown in Fig. 19 the phase displacing circuit is 123. By connectinga capacity such as C in parallel with S the phase of'E is made to differ more considerably from that of E and from that of E An E. M. F. such as e of same or opposite phase to E is derived from S by transformation and with the help of the winding 25 disposed on the stator coaxially with S TheE. M. F. impressed on S is the resultant of (2 and E, the latter being depair.

known manner.

the motor has three inducing windings S 5 S displaced in space by 120 degrees.

The object in this case is, by way of example, to impress on these windings three E. M. F.s (E E E',) differing in phase by 120 degrees or thereabout in which case.

the machine will start as a motor having three armature and three field axes per pole In the figure is shown one way of achieving this object. The circuit 123 is the phase displacing circuit comprising by Way of example a negative reactance C in series with the positive reactance S The derived from S through the transformer T 15 lmpressed in series with E on S and derived from S through T is impressed on S in series with E.

1 ply in which case T may be dispensed with.

There are certain known devices which are often resorted to in order to improve the starting performance of single or polyphase motors 0f the shunt induction type, and in which each motor inducing winding is connected in parallel to the mains and with or without the interposition of other elements in series with said winding. I have already enumerated some of them and will now name some others for it is to be understood that the present invention may be used in connection or in combination with any such devices.

Both members of the motor are sometimes provided with two complete sets of windings, each set being wound for a different number of poles, the winding on the induced member corresponding to the one number of poles having a high ohmic resistance, the other winding on the induced member having a low ohmic resistance. Two stators with one common rotor are sometimes used for instance in the manner shown in British patent specification No. 4170 of 1894. Then again the magnetic system of each phase is sometimes arranged on independent inducing -members of the motor whereas the induced member is common to all. It will also be understood that when applying this invention the supply voltage may when required be boosted in some Also that the inducing windi need not necessarily be all alike, as has een assumed in most cases for the sake of simplicity, they may difler in various ways; Thus their ohmic resistance, number of turns, style or type of winding or the mutual induction between these inducing windings and the rotor in the corresponding axis may differ, this mutual induction may be made to diifer in some lmown manner, for instance by making the axial or the peripheral span, or both axial and peripheral spans of one motor inducing winding different from the corresponding spans of another motor inducin winding. The changes brought about'in tfiis manner will be understood without difliculty for such devices have often been used in split phase motors and the theory here given will show their effect when used in connection with this in-' vention.

This invention may of course also be used in connection with any of the methods proposed for varying the number of poles of the motors for the purpose of varying their speed; It is further to be understood that although it is generally recommended I to choose a at least equal to 5 whenstarting the motorwith more than one armature and more than one field axis the invention is in no way bound to any particular value of a.

What I claim and desire to secure ters Patent is:

1.- In an alternating current motor, the combination with an induced member, of an inducing1 member having an inducing winding, a p ase displacing circuit containing a plurality of elements one of which is a second inducing winding, said elements being conductively independent from the circuit containing the inducing winding, and means for impressing on said first in ucing winding two E. M. Fs difiering in base, one of said E. M. Fs being deriv inductively from an element of the phase displacing circuit.

2. In an alternating current motor, the combination with an induced member, of an inducin member having an inducing winding, a p ase displacing circuit containing a plurality of elements of difiering reactance connected in series acrom the mains, a transformer hiwing its primary winding connectby Leta,

ed in parallel with one of said elements and its secondary winding connected across the mains in series with the inducing winding.

3. In an alternating current motor, the combination with an induced member, of an inducing member having an inducing winding, a phase displacing circuit containing a plurality of elements one of which is a second inducing winding, a transformer having its primary winding connected in parallel with one of said elements and its secondary winding connected across the mains in series with the first inducing winding.

4. In an alternating current motor, the combination with an induced member, of an inducing member provided with an inducing winding, a phase displacing circuit contaming an inductance and a capacity connected in series across the mains, a transformer having its primary winding connected in parallel with said inductance and its secondary winding connected across the mains in series with the inducing winding.

5. In an alternating current motor, the

combination with an induced member, of

an inducing memberhaving an inducing winding, a phase displacing circuit containing a second inducing winding and a capacity, a transformer having its primary winding connected in parallel to one of said inducing windings and its secondary winding connected across the mains in series with the other inducing winding.

6. In an alternating current motor, the combination with an induced member,v of an inducin member provided with an inducing win ing, a phase displacing circuit contaming an inductance and a capacity connected. in series across the mains, a trans former havin its primary winding connected in ara el with said inductance and its secon mains in series with the inducing winding, and an inductancecconnected in parallel to said transformer.

In witness whereof, I have hereunto signed my name in the presence of'two subscribing witnesses;




winding connected across the y

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2489637 *Jun 28, 1946Nov 29, 1949Raytheon Mfg CoSplit-phase induction motor control
US2606311 *Jun 30, 1949Aug 5, 1952G M Lab IncSingle phase induction motor
US2661452 *Jan 29, 1948Dec 1, 1953Sperry CorpServomotor and control system therefor
US2880388 *Feb 27, 1956Mar 31, 1959Bosch Arma CorpElectro-mechanical resolvers
US3201673 *Aug 28, 1961Aug 17, 1965WillifordInduction motor starting circuits
US4808868 *Aug 12, 1987Feb 28, 1989S.P.C. Holding Co., Inc.Single and polyphase electromagnetic induction machines having regulated polar magnetic symmetry
US4959573 *Feb 27, 1989Sep 25, 1990S.P.C. Holding, Co., Ltd.Electromagnetic induction machines having regulated polar magnetic symmetry
U.S. Classification318/816
Cooperative ClassificationH02K17/04