1. A rotor-stator device for cooperation with an external source of magnetic flux to form an electric-rotating machine, said device comprising a permanent magnet cylindrical rotor and a stator structure of generally cylindrical configuration in coaxial relationship with said rotor and forming a housing for said rotor, said stator structure including a pair of pole pieces each having a flat portion and salient poles projecting from the periphery of said flat portion in spaced relationship with said rotor to define an airgap therebetween, said stator structure also including shading means at least partially disposed in the airgap between selected ones of said poles and said rotor, to provide said rotor with a unidirectional self-starting characteristic upon the application of magnetic flux to the stator structure from a flux source external to said housing.

5. A rotor-stator device comprising a cylindrical permanent magnet rotor having a greater length than diameter, a stator structure of generally cylindrical configuration in coaxial relationship with said rotor, said stator structure including a pair of pole pieces, each of said pole pieces having a flat portion and a plurality of salient poles projecting from the periphery of said flat portion, said pole pieces being disposed adjacent opposite ends of said rotor with said salient poles arranged in an arcuate array around said rotor in spaced relationship therewith to define a gap between said rotor and said stator structure, and means disposed within said gap for shading selected ones of said stator poles.

6. A rotor-stator device comprising a permanent magnet rotor having at least one pair of rotor poles, and a cylindrical stator structure in coaxial relationship with said rotor, said stator structure including a plurality of pole pieces each having a flat portion and a pair of salient poles protruding from the periphery of said flat portion and including a generally tubular shading member coextensive with and surrounding said rotor for shading selected ones of saiD salient poles.

7. A rotor-stator device comprising a permanent magnet rotor having at least one pair of nonsalient rotor poles, and a stator structure of generally cylindrical configuration disposed about said rotor, said stator structure including a plurality of ferromagnetic pole pieces each having a flat portion and a pair of salient poles projecting perpendicularly from the periphery of said flat portion, and including a shading member for shading one of the salient poles on each pole piece, the shading member being interwoven with said salient poles and surrounding said rotor to form a dust cover therefor.

8. A rotor-stator device comprising a permanent magnet rotor having at least one pair of rotor poles, and a stator structure of generally cylindrical configuration disposed about said rotor, said stator structure including a plurality of pole pieces each having a flat portion and a pair of salient poles projecting perpendicularly from said portion in spaced relationship with said rotor to define an airgap therebetween, said stator structure also including a shading member for shading one of the salient poles on each pole piece, the shading member being at least partially disposed in the airgap between the shaded salient poles and said rotor, said shading member interconnecting said pole pieces and surrounding said rotor to form a dust cover therefor.

9. A rotor-stator device comprising a cylindrical permanent magnet rotor having an axial length greater than its diameter and including at least one pair of nonsalient rotor poles, and a cylindrical stator structure disposed about said rotor, said stator structure including a plurality of ferromagnetic pole pieces each having a flat portion and a pair of salient poles projecting perpendicularly from the periphery of said flat portion, said salient poles extending in an arcuate array around said rotor in spaced relationship therewith to define a cylindrical airgap between the rotor and the stator structure, and a generally tubular member having a first sleeve portion located in said airgap and a second portion interwoven with said salient poles for shading one of the salient poles of each pole piece, said sleeve portion surrounding said rotor to form a dust cover therefor.

10. A rotor-stator device for cooperation with an external field coil to form an electric rotating machine, said device comprising a cylindrical rotor having a pair of permanently magnetized rotor poles, a pair of stator pole pieces including flat portions respectively disposed adjacent opposite ends of said rotor, each of said stator pole pieces having two salient stator poles projecting from the periphery of the flat portion thereof in directions parallel to the axis of said rotor and in spaced relationship with the cylindrical surface of the rotor, means carried by the flat portions of the pole pieces for rotatably supporting said rotor, and shading means including at least one tubular member surrounding said rotor between said flat portions, said tubular member being interwoven with said stator poles such that portions of the tubular member are externally disposed with respect to certain of said stator poles and alternate portions of the tubular member are positioned between the remaining stator poles and said rotor, said shading means forming an enclosure for said rotor, said stator poles and said shading means providing said rotor with a unidirectional self-starting characteristic upon the energization of a field coil surround said shading means.

11. A rotor-stator device for cooperation with an external field coil to form an electric rotating machine, said device comprising a cylindrical rotor having a length greater than its diameter and only a single pair of nonsalient permanently magnetized rotor poles, a pair of stator pole pieces including flat portions respectively disposed adjacent opposite ends of said rotor, each of said stator pole pieces having only two salient stator poles projecting from the flat portion thereof in directionS parallel to the axis of said rotor and in spaced relationship with the cylindrical surface of the rotor, one of the salient stator poles on each pole piece being closer to said cylindrical surface than the other salient stator pole and the pole pieces being arranged with the closer stator poles alternating with the remaining stator poles to form a substantially cylindrical array of stator poles around the periphery of the rotor, means carried by the flat portions of the pole pieces for rotatably supporting said rotor, and shading means including an elongated sleeve surrounding said rotor between said flat portions, said sleeve being interwoven with said stator poles such that portions of the sleeve are externally disposed with respect to said closer stator poles and alternate portions of the sleeve are positioned between the remaining stator poles and said rotor, said shading means forming an enclosure for said rotor and maintaining said stator poles in fixed relationship with each other, said stator poles and said shading means providing said rotor with a unidirectional self-starting characteristic upon the energization of a field coil surround said shading means.

12. A rotor-stator device for cooperation with an external field coil to form an electric rotating machine, said device comprising a cylindrical rotor having a length greater than its diameter and only a single pair of nonsalient permanently magnetized rotor poles, a pair of stator pole pieces including flat portions respectively disposed adjacent opposite ends of said rotor, each of said stator pole pieces having only two salient stator poles projecting from the periphery of the flat portion thereof in directions parallel to the axis of said rotor and in spaced relationship with the cylindrical surface of the rotor, one of the salient stator poles on each pole piece being closer to said cylindrical surface than the other salient stator pole and the pole pieces being arranged with the closer stator poles alternating with the remaining stator poles to form a substantially cylindrical array of stator poles around the periphery of the rotor, means carried by the flat portions of the pole pieces for rotatably supporting said rotor, and shading means including first and second tubular members surrounding said rotor between said flat portions, said first tubular member being interposed between said rotor and said arcuate array of stator poles with portions of the first tubular member in contact with the closer poles, said second tubular member being interwoven with said stator poles such that portions of the second tubular member are externally disposed with respect to said closer stator poles and alternate portions of the second tubular member are positioned between the first tubular member and the remaining stator poles, said shading means forming an enclosure for said rotor and maintaining said stator poles in fixed relationship with each other, said stator poles and said shading means providing said rotor with a unidirectional self-starting characteristic upon the energization of a field coil surround said shading means.

13. A rotor-stator device for cooperation with an external source of magnetic flux to form an electric-rotating machine, said device comprising a permanent magnet cylindrical rotor and a stator structure of generally cylindrical configuration in coaxial relationship with said rotor and forming a housing for said rotor, said stator structure including a pair of pole pieces each having a flat portion and salient poles projecting from the periphery of said flat portion and means for shading selected ones of said poles, to provide said rotor with a unidirectional self-starting characteristic upon the application of magnetic flux to the stator structure from a flux source external to said housing, a magnetic structure having two arms between which said rotor-stator device is mounted, and a field coil for generating magnetic flux in said arms of said magnetic structure.

14. A rotor-stator device for cOoperation with an external source of magnetic flux to form an electric-rotating machine, said device comprising a permanent magnet cylindrical rotor and a stator structure of generally cylindrical configuration in coaxial relationship with said rotor and forming a housing for said rotor, said stator structure including a pair of pole pieces each having a flat portion and salient poles projecting from the periphery of said flat portion and means for shading selected ones of said poles, to provide said rotor with a unidirectional self-starting characteristic upon the application of magnetic flux to the stator structure from a flux source external to said housing, two magnetic members disposed adjacent opposite ends of said rotor-stator device, a field coil for generating a magnetic flux in said members when said field coil is energized, and permanent magnet means in magnetic circuit relationship with said members for generating a magnetic biasing flux passing through said rotor-stator device with a strength and direction which is respectively less than and opposed to the flux generated by said field coil.