Synchronous motor for clocks and the like

Claim 2

A synchronous AC motor for driving a clock or the like comprising, in combination, an annular coil, a magnetic pole structure including a cup and a central post receiving the coil and extending axially beyond it, a pair of magnetic discs secured to the end of the post and defining an airgap with respect to the rim portion of the cup, a shading ring in the form of a disc of conducting material interposed between the magnetic discs, the rim of the cup being notched to form a circular array of parallel pole pieces, the magnetic discs being notched at the edge to form corresponding rings of shaded and unshaded poles respectively offset from one another, a rotor having a rim interposed in the annular gap between the poles and pole pieces, the rim having two loops of retentive magnetic material of substantially different coercive magnetic intensity arranged side-by-side thereon to provide starting and running torque.

Claim 3

The combination as claimed in claim 1, the rotor being in the shape of a shallow cup of nonmagnetic material having a peripheral rim formed with a shallow internal annular recess and with the loops being discontinuous and presprung for expansion outwardly into side-by-side seated position in the recess.

Claim 4

The combination as claimed in claim 1 in which one of the loops is formed of magnetic material heat treated to have a coercive magnetic intensity of approximately 250 oersted with the other of said loops being heat Treated to have a coercive magnetic intensity for approximately 140 oersted.

Claim 5

The combination as claimed in claim 2 in which each of the loops is in the shape of a shallow helix of less than a complete turn and in which the internal recess in the rotor has an axial length of approximately double the diameter of the loop material so that upon insertion of the loops into the rotor the ends become contiguous and the loops are deformed into final planar configuration.

Claim 6

The combination as claimed in claim 1 in which at least one of the magnetic discs is of stepped cross section centrally dished to provide substantial spacing between the discs in the region of the axis, the shading ring being formed to occupy substantially all of the space between the discs extending to the vicinity of the periphery thereof.

Claim 7

The combination as claimed in claim 1 in which the shading ring is of composite construction, having an axially thin portion which extends substantially out to the airgap and a separate axially thick portion which extends only a portion of the way to the airgap, the innermost one of the magnetic discs being dished to accommodate the thick portion of the ring.

Claim 8

The combination as claimed in claim 1 in which the rotor has sufficient end play so that the soft ring may occupy the position of maximum flux during starting and so that the two rings share the position of maximum flux during synchronous running conditions.

Claim 9

A synchronous AC motor for driving a clock or the like comprising, in combination, an annular coil, a magnetic pole structure receiving the coil including a cup and central post, the cup having a series of pole pieces formed about the edge thereof and the post having a cooperating pole member presenting a series of poles and defining with the pole pieces an annular airgap in which the flux is concentrated within a short axial distance, means including a shading ring for shading a portion of the flux thereby to provide a rotating field in the airgap, a rotor having a shaft journaled in the post and having a shallow cup-shaped body of thin nonmagnetic material including a narrow rim mounted for rotation in the airgap, the rim having a shallow internal annular recess, a pair of loops mounted side-by-side in the recess, said loops being discontinuous and presprung for expansion outwardly into side-by-side seated position in the recess, said loops being formed of retentive magnetic material of substantially different coercive magnetic intensity, the coercive magnetic intensity of one of the loops being sufficiently low so as to provide torque for breakaway and acceleration under the influence of the field flux and the coercive magnetic intensity of the second loop being sufficiently high as to create induced durable spots of permanent magnetism to provide torque when the rotor comes up to a speed approaching synchronism for locking in of the rotor to the synchronous field.

Claim 10

A synchronous AC motor for driving a clock or the like comprising, in combination, an annular coil, a magnetic pole structure receiving the coil including a cup and central post, the cup having a series of pole pieces formed about the edge thereof and the post having a cooperating pole member presenting a series of poles and defining with the pole pieces an annular airgap in which the flux is concentrated within a short axial distance, means including a shading ring for shading a portion of the flux thereby to provide a rotating field in the airgap, a rotor having a shaft journaled in the post and having a shallow cup-shaped body of thin nonmagnetic material including a narrow rim mounted for rotation in the airgap, the rim having a shallow internal annular recess, a pair of loops mounted side-by-side in the recess, said loops being discontinuous and presprung for expansion outwardly into side-by-side seated position in the recess, said loops being formed of retentive magnetic material of substantially different coercive magnetic intensity, the coercive magnetic intensity of one of the loops being sufficiently low so as to provide torque for breakaway and acceleration under the influence of the field flux and the coercive magnetic intensity of the second loop being sufficiently high as to create induced durable spots of permanent magnetism to provide torque when the rotor comes up to a speed approaching synchronism for locking in of the rotor to the synchronous field.