US2713646A - Self-starting alternating current motors - Google Patents

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2,713,646 ELF-STARTKNG Are ERNA it o CURRENT Morons Henry H. Hammerstrorn and Lee E. Woodruit, Los Angeles, Calif.

Application April 15, 1954-, Serial No. 423,411 19 Claims. (Cl. Slit-172) This invention relates to improved nating current electric motors.

One of the most diificult problems in designing a single phase alternating current motor is the problem of providing for a substantial starting torque, without at the same time rendering the motor very inetficient. ous arrangements have been devised for imparting starting torque to such a motor, all of these with which we are acquainted have either introduced excessive electrical losses into the device, usually resulting in overheating; or have involved special starting contacts, switches, or other extra parts which both complicate the motor and greatly increase the possibility of operational ditficulties.

The general object of the present invention is to provide an improved type of electric motor which may function on single phase alternating current, if desired, and which has a very substantial starting torque. Particularly contemplated is a motor in which the self starting effect is accomplished without brushes or any special starting contacts or switches. At the same time, motors constructed in accordance with the invention are considerably more efiicient electrically than prior similar devices, and as a result can be built in larger sizes than has been possible with most prior self starting single phase alternating current motors.

A device embodying the invention is conventional to the extent of including stator and rotor sections, one of which, usually the stator, has electrically energized magnetic poles which act to produce rotation of the rotor. The starting torque of the present device is attained in large part by the provision on the pole carrying section (i. e. ordinarily on the stator) of means acting to direct or divert the lines of force from one or more of its poles in a manner producing, in effect, a rotating magnetic field, Which is capable by virtue of its rotary motion of inducing movement in an initially stationary rotor. More specifically, the magnetic material of the pole carrying section may form, adjacent one of the poles, a magnetic along which some of the lines of force from a portion of the pole may return to the body of the pole passage through the other section of the device. It is found that the provision of such a shunt path, particularly where the path is unsymmetrical circularly with respect to the associated pole, results in the development of a rotating field, giving starting torque to the motor. The apparent reason for this effect will be described at a later point.

The material forming the shunt path desirably extends self-starting alterto of the device, and may include a plug of magnetic material forming a magnetic bridge between the main pole and the stator body. This plug is desirably unlaminated, Whereas the rest of that section of the device may be laminated. A layer of nonconductive material may be located between the plug and the adjacent laminated magnetic parts, to prevent the plug from forming electrical short circuits between the laminations. The shunt path should be so designed as to become saturated magnetical- Though varily considerably before the main flux through the rotor has reached its peak.

The above and other features and objects of the present invention will be better understood from the following detailed description of the typical embodiments illustrated in the accompanying drawing in which:

Fig. 1 is a side view of the rotor and stator of an alternating current electric motor built in accordance with the invention;

Fig. 2 is a fragmentary perspective view of the stator of Fig. 1;

Fig. 3 is a fragmentary perspective view of the Fig. 1 rotor;

Fig. 4 is a view corresponding to Fig. 1; but showing a variational form of the invention; and

Fig. 5 is a fragmentary perspective view of the stator of the Fig. 4 device.

Referring first to Figs. 1 to 3, the motor there shown includes a rotor section ill and a stator section 11. The rotor section includes the usual central shaft 112, and is are attached to ends of the roof copper, form together the conventional squirrel cage rotor winding. Radially outwardly of conductors 15, slots 14 may have circular portions containing transversely extending plugs or pins 115', these plugs being formed of iron or other suitable magnetic metal, and desirably extending from one of the rings 16 to the other.

The stator section 11 of the device includes a stationary magnetic metal stator body 17, which may be externally square, as shown, and is shaped to form two inwardly projecting diametrically opposed circularly intermediate and smaller starting poles 19. Between the outer ends of base portions 20 and 21 of poles 18 and 19, the magnetic material of stator body 17 has portions 22 for conducting magnetic lines of force between the outer ends of the poles. The inner ends of the poles form inwardly directed cylindrical pole faces 23 and 24 which are reto the outer cylindrical Both the rotor body 13 and the stator body 17 may be formed of a number of identically shaped laminations, as seen in Figs. 2 and 3. These laminations, and therefore the rotor and stator bodies, may be shaped substantially the same as shown in Fig. 1, which is a full size representation of substantially the exact configuration of a rotor and stator combination which has actually been built and very successfully operated.

The two primary poles 18 of the stator are energized by a pair of coils 25 extending thereabout and connected in series and reversely to an alternating current power supply, typically 120 volts 60 cycles. As an example, each of these coils may comprise 275 turns of No. 26 B & S insulated copper wire. The intermediate starting poles 19 of the device do not have thereabout any energizing coil connected to a power supply, but instead are energized only indirectly by the coils 25 about poles 18.

Each of the poles 18 has, at its circularly leading side,

a reduced dimension portion 26 extending circularly toing means energizing said poles and setting up a magnetic field extending therebetween through the magnetic material of the other section, said other section having winding means coactive with said magnetic field to cause relative rotation of the sections, said first gized by alternating current and to create alternating whose magnetic strengths rise and fall in phase, said one section includterial interposed between and forming a magnetic shunt bridge between said one pole and said body of said one section.

4. An electric motor comprising a stator and a relatively rotatable rotor both having bodies formed of magnetic material, said stator including a plurality of gized by alternating current and to create alternating magnetic polarities in strengths rise and fall in phase, said stator includlng shunt bridge betweenone side of one of said poles and the stator body, and means forming a thin electrically non-conductive layer of material between said plug and the adjacent surfaces between which it forms a magnetic bridge.

7. An electric motor as recited in claim 6, in which said plug is substantially cylindrical and unlaminated, the major portion of the stator and rotor bodies being laminated.

tween one of said first mentioned poles and the stator body.

9. An electric motor as recited in claim 8, in which there are two of said first mentioned poles and two of said starting p'oles each adjacent and circularly offset from an associated one of said first mentioned poles and associated pole, there being no magnetic material forming a shunt path at the opposite circularly offset side of said associated pole.

10. An electric motor as recited in claim 9, in'which the shunt paths through said starting poles become subtending between each of said first mentioned poles and the rotor when the motor is in operation.

ll. An electric motor as recited in claim 10, in Which said shunt path means include two magnetic metal plugs each inserted between and substantially engaging one of said first mentioned poles and a corresponding one of said starting poles, there being a thin layer of electrically non-conductive material inserted between the plugs and said first mentioned and starting poles.

12. An electric motor as recited in claim 4, in which said shunt p'ath becomes substantially saturated with lines of force at a flux value which is far below the maximum fiux flowing between said one pole and the rotor in operation.

13. An electric motor as recited in claim 4, in which said rotor is a squirrel cage type rotor.

14. An electric motor as recited in claim 4, in which said magnetic shunt path means include an auxiliary starting pole circularly between said two first mentioned poles presenting a pole face closely proximate to the rotor, and magnetic material forming a magnetic bridge between one of said first mentioned poles and said starting pole, said last mentioned magnetic material including a reduced dimension projection extending circularly from one of the poles between which the bridge extends, and a magnetic metal plug interposed between and substantially engaging said projection and the other of the bridged poles.

15. An electric motor as recited in claim 4, in which said winding means on the rotor includes a plurality of generally axially extending circularly spaced conductors carried by the rotor body at circularly spaced locations and interconnected to form a series of endless conductive loops.

16. An electric motor as recited in claim 4, in which said magnetic shunt path means include an auxiliary starting pole circularly between said two first mentioned poles presenting a pole face closely proximate to the rotor and forming a portion of said shunt path between one of said first mentioned poles and the stator body, said rotor winding means including a plurality of generally axially extending circularly spaced conductors interconnected to form a series of endless conductive loops, and the magnetic metal of said rotor having pole faces with circular extends corresponding approximately to the circular extent of said pole face of said starting pole.

17. An electric motor as recited in claim 8, in which said shunt path means include a portion of one of said first mentioned poles and a portion of said starting pole extending into closely proximate relation, one of said pole portions being of smaller cross section than the main portion of the same pole.

18. An electric motor comprising two relatively rotatable sections having bodies formed of magnetic material, one of said sections including a plurality of poles of magnetic material having first ends adjacent the magnetic material of the other section and having base ends connected to the body of said one section, and winding means energizing said poles and setting up a magnetic field extending therebetween through the magnetic material of the other section, said other section having winding means coactive with said magnetic field to cause relative rotation of the sections, said first mentioned Winding means being adapted to be energized by alternating current and to create alternating magnetic polarities in said poles, said one section including magnetic shunt path means through which some of the magnetic field of at least one of said poles is shunted therefrom back to the body of said one section along a path other than through said other section or through said base end of that pole, said shunt path means being magnetically unsymmetrical circularly with respect to each pole from which a shunt path is formed and being adapted to become saturated with flux during each current cycle at a point such that the flux shift resulting solely from such saturation of the unsymmetrical shunt path means is sufficient by itself to start rotation of one of said sections from a standstill.

19. An electric motor comprising a stator and a relatively rotatable rotor both having bodies formed of magnetic material, said stator including a plurality of poles of magnetic material having first ends adjacent the magnetic material of the rotor and having base ends connected to the stator body, and winding means energizing said poles and setting up a magnetic field extending therebetween through the magnetic material of the rotor, said rotor having winding means coactive with said magnetic field to turn the rotor, said first mentioned winding means being adapted to be energized by alternating current and to create alternating magnetic polarities in said poles, said stator including magnetic shunt path means through which some of the magnetic field of at least one of said poles is shunted from a portion thereof back to the stator body along a path other than through the rotor or through said base end of that pole, said shunt path means being magnetically unsymmetrical circularly with respect to each pole from which a shunt path is formed and being adapted to become saturated with flux during each current cycle at a point such that the flux shift resulting solely from such saturation of the unsymmetrical shunt path means is sufificient by itself to start rotation of the rotor from a standstill.

References Cited in the file of this patent UNITED STATES PATENTS 1,508,152 Alger Sept. 9, 1924 1,590,025 Hall June 22, 1926 2,100,809 Larocca Nov. 30, 1937 2,567,976 Spinasse et al Sept. 18, 1951 y 19, 1955 T. FRANKEL SIGNALING SYSTEMS Filed Jan. 5, 1952 EOX MUSE u INVENTOR. THE 000/? F RAN/(E L BY A TTOR/VE V

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