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A simplified fan and brushless DC motor employs an annular permanent magnet magnetized in segments about its circumference. Each segment is oppositely radially magnetized with respect to its adjacent segments. Fan blades are located within the annular magnet. A coil comprising two electrically indep

A simplified fan and brushless DC motor employs an annular permanent magnet magnetized in segments about its circumference. Each segment is oppositely radially magnetized with respect to its adjacent segments. Fan blades are located within the annular magnet. A coil comprising two electrically independent and bifilar wound windings, connected to be oppositely energized, and an electromagnet structure defining two pole pieces reside outside the permanent magnet annulus. A Hall effect device alternately energizes the separate coil windings in response to passage of the segments of the rotor magnet to alternately produce opposite magnetic fields in the pole pieces. Thus commutated, the double coil arrangement affects rotation of the rotor and the fan blades.

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1. A DC motor comprising: a rotor with an annular permanent magnet defining magnetic segments oppositely polarized in the radial outward direction, wherein said segments are arranged circumferentially to comprise the magnet, and wherein the rotor is free of encircling stator iron; a stator havin

1. A DC motor comprising: a rotor with an annular permanent magnet defining magnetic segments oppositely polarized in the radial outward direction, wherein said segments are arranged circumferentially to comprise the magnet, and wherein the rotor is free of encircling stator iron; a stator having an electromagnet structure outside said annular magnet, proximate the periphery thereof, said electromagnet structure including coil means comprising a core having two electrically independent coil windings wound thereon, said electromagnetic structure further including electromagnetic flux conducting means in flux conducting relation to the coils and core and located for establishing magnetic fields of opposite polarities to attract the oppositely polarized segments of, and for applying continuous rotational torque to, the annular magnet; and position detecting means located outside said annular magnet for detecting the position of the rotor relative to the stator and for commutating electrical current to the coil means to repeatedly produce said opposite polarity fields and attract said segments in dependence on said relative positioning. 2. The motor according to claim 1, wherein the rotor is free of encircling stator windings and wherein the electromagnetic flux conducting means defines at least one pole piece of flux conducting material terminating adjacent the exterior of the annular magnet. 3. The motor according to claim 1, further including commutation circuit means connected to said position detecting means and to said coil means for reversing the field polarity at the approach of each oppositely polarized magnet segment to the position detecting means, whereby said coil means is energized to produce the alternating field throughout substantially all of the 360° of rotor movement. 4. The motor according to claim 1, wherein the electromagnet structure includes a flux path having a pair of arms in magnetic flux conducting relation with the coil means and extending to two pole pieces spaced apart along the circumference of the annular magnet. 5. The motor according to claim 4, wherein the pole pieces are spaced apart by such a distance as to each attract a separate magnetized segment of the annular magnet when the coil means is energized. 6. The motor according to claim 5, wherein adjacent segments of the annular magnet are oppositely polarized, and wherein the pole pieces are located to attract the adjacent, oppositely polarized segments when the coil means is energized. 7. The motor according to claim 1, wherein the coil means comprises two electrically independent coil windings which produce magnetic fields of opposite polarities when energized, the detecting means comprises means for commutating electrical current to a different coil winding to produce said opposite polarity fields and attract said segments in dependence on said relative positioning. 8. The motor according to claim 1, wherein the two coil windings are concentrically wound on said core. 9. A fan having a motor according to claim 1, the fan having blades located within the annular magnet. 10. A fan according to claim 9, wherein the fan blades extend from proximate the inside surface of the annular magnet to a central hub, said stator having a central member supporting, for rotation, the hub, the blades, and the rotor members, including the annular magnet, the stator further including struts extending outwardly from the central stator member to a housing encircling the fan blades, said housing supporting the coil proximate the annular rotor magnet and adjacent the outer surface thereon. 11. A fan having a motor according to claim 1, including a central rotatable hub and fan blades radiating outwardly from the hub, said permanent magnet encircling the blades of the fan and secured to the blades, a housing encircling the annular permanent magnet, and wherein the stator coil and electromagnet structure is supported by the housing outside the annular magnet commutation means responsive to the position of the permanent magnet to repeatedly and alternately energize the coil windings to apply a rotary force to segments of the annular. 12. A DC motor comprising: a rotor with an annular permanent magnet defining magnetic segments oppositely polarized in the radial outward direction, wherein said segments are arranged circumferentially to comprise the magnet; a stator having an electromagnet structure outside said annular magnet, proximate the periphery thereof, said electromagnet structure including two electrically independent coil windings and electromagnetic flux conducting means in flux conducting relation to the coil windings and located for establishing magnetic fields of opposite polarities to attract the oppositely polarized segments of, and for applying rotational torque to, the annular magnet when the coil windings are energized; position detecting means located outside said annular magnet for detecting the position of the rotor relative to the stator and for commutating electrical current to a different coil winding to repeatedly produce said opposite polarity fields and attract said segments in dependence on said relative positioning; and wherein the means for commutating current includes at least a first transistor means connected in current conducting relation to a first of said windings, and at least a second transistor means in current conducting relation to the second of said windings, resistance means for establishing biases to the first and second transistor means and said position detecting means comprising a Hall device responsive to a magnetic field of the magnetic segments of one polarity for providing bias from the resistance means to the first transistor means to cause conduction therein while depriving the second transistor means of bias to prevent conduction therein, and responsive to the absence of said field for providing bias from the resistance means to the second transistor means to cause conduction therein while depriving the first transistor means of bias to prevent conduction thereof. 13. The motor according to claim 12, wherein each transistor means connected in series with its associated winding across motor input voltage connections, the resistance means comprises resistors in series and connected with at least one of the motor input voltage connections, and connected with terminals of the transistors to bias the first or second transistor means into conduction upon establishment of appropriate bias voltage across the resistors, and the Hall device comprises a Hall switch connected between a junction of the resistors and one of the motor input voltage connections, said Hall switch being connected with the resistors to bypass at least one resistor in the presence of said field of magnetic segments of one polarity and to thereby alter the bias provided by the resistors to the transistor means. 14. A motor according to claim 13, wherein the first transistor means is a PNP transistor connected between a high side of the motor input connections and the first winding, and the second transistor means is an NPN Darlington transistor pair connected between a low side of the motor input connections and the second winding, both of said transistor means having their bases connected to the resistance means for control by the Hall switch. 15. A motor according to claim 13, wherein the first transistor means is a power transistor means requiring a relatively high drive to cause conduction therein and the second transistor means is a high gain transistor means requiring a relative low drive to cause conduction therein, said resistor in series providing the relatively low drive to the second transistor means when the Hall switch is open and the Hall switch being connected to place a relatively large voltage drop across at least a portion of the resistors in series when closed, thereby to substantially short the bias to the high gain transistor means and supply the relatively high bias to the power transistor means. 16. A DC motor comprising: a rotor with an annular permanent magnet defining magnetic segments oppositely polarized in the radial outward direction, wherein said segments are arranged circumferentially to comprise the magnet; a stator having an electromagnet structure outside said annular magnet, proximate the periphery thereof, said electromagnet structure including two electrically independent and concentrically wound coil windings, and wherein the electromagnetic structure defines at least one pole piece and wherein the coil windings are wound on a core in electromagnetic flux conducting relationship to the pole piece and located for establishing magnetic fields of opposite polarities to attract the oppositely polarized segments of, and for applying rotational torque to, the annular magnet; and position detecting means located outside said annular magnet for detecting the position of the rotor relative to the stator and for commutating electrical current to the coil means to repeatedly produce said opposite polarity fields and attract said segments in dependence on said relative positioning. 17. A DC motor comprising: a rotor with an annular permanent magnet defining magnetic segments oppositely polarized in the radial outward direction, wherein said segments are arranged circumferentially to comprise the magnet; a stator having an electromagnet structure outside said annular magnet, proximate the periphery thereof, said electromagnet structure including coil means comprising a core having two electrically independent coil windings wound thereon, said electromagnetic structure further including electromagnetic flux conducting means in flux conducting relation to the coils and core and located for establishing magnetic fields of opposite polarities to attract the oppositely polarized segments of, and for applying rotational torque to, the annular magnet, wherein the stator includes a housing defining a compartment at one location on the periphery of the path of rotation of the annular magnet, and wherein said coil means is located in said compartment; and position detecting means located outside said annular magnet for detecting the position of the rotor relative to the stator and for commutating electrical current to the coil means to repeatedly produce said opposite polarity fields and attract said segments in dependence on said relative positioning. 18. The motor according to claim 17, wherein said coil means has two windings, wherein said compartment houses the position detecting means for detecting and commutating, and wherein the position detecting and commutating means includes a Hall effect device located proximate the annular magnet, and switching circuit means for energizing one coil winding when magnetized segments of a first polarity are adjacent the Hall effect device, and for energizing the other coil winding when magnetized segments having a second polarity opposite said first polarity are adjacent the Hall effect device. 19. The motor according to claim 17, wherein the stator housing encircles the annular magnet. 20. A DC motor comprising: a rotor with an annular permanent magnet defining magnetic segments oppositely polarized in the radial outward direction, wherein said segments are arranged circumferentially to comprise the magnet; a stator having an electromagnet structure outside said annular magnet and proximate the periphery thereof, and wherein the stator electromagnet structure is located in a location to one side of the annular magnet and extends less than 180° around the magnet, said electromagnet structure including coil means comprising a core having two electrically independent coil windings wound thereon, said electromagnetic structure further including electromagnetic flux conducting means in flux conducting relation to the coils and core and located for establishing magnetic fields of opposite polarities to attract the oppositely polarized segments of, and for applying rotational torque to, the annular magnet; and position detecting means located outside said annular magnet for detecting the position of the rotor relative to the stator and for commutating electrical current to the coil means to repeatedly produce said opposite polarity fields and attract said segments in dependence on said relative positioning. 21. A DC motor comprising: a rotor with an annular permanent magnet defining magnetic segments oppositely polarized in the radial outward direction, wherein said segments are arranged circumferentially to comprise the magnet; a stator having an electromagnet structure outside said annular magnet and proximate the periphery thereof, and wherein the stator electromagnet structure is located in a location to one side of the annular magnet and extends less than 90° around the magnet, said electromagnet structure including coil means and electromagnetic flux conducting means in flux conducting relation to the coil and located for establishing magnetic fields of opposite polarities to attract the oppositely polarized segments of, and for applying rotational torque to, the annular magnet; and position detecting means located outside said annular magnet for detecting the position of the rotor relative to the stator and for commutating electrical current to the coil means to repeatedly produce said opposite polarity fields and attract said segments in dependence on said relative positioning.