Brushless machine with tapered poles

Abstract

A method and apparatus in which a rotor ( 11 ) and a stator ( 17 ) define a radial air gap ( 20 ) for receiving AC flux and at least one DC excitation coil ( 23, 24 ) positioned near the stator end turn to produce DC flux in axial air gaps ( 21, 22 ) additive to the AC flux. Side magnets ( 16 ) and flux-guiding magnets ( 14 ) are provided as boundaries separating the side poles ( 12 a, 12 b ) of opposite polarity from other portions of the rotor ( 11 ) and from each other to define PM poles ( 12 a, 12 b ) for conveying the DC flux to or from the primary air gap ( 20 ) and for inhibiting flux from leaking from said pole portions prior to reaching the primary air gap ( 20 ). Side magnets ( 16 ), side poles ( 12 a and 12 b ), flux-guiding magnets ( 14 ), ferromagnetic end plates ( 11 c ), non-magnetic end plates ( 12 c ), and ring bands ( 37 ) are optionally provided for performance improvement.

1 .- 4 . (canceled) 
     
     
         5 . A brushless electric machine comprising:
 a cylindrical stator;   a rotor having an axis of rotation, the rotor being spaced from the stator to define an annular primary air gap that receives an AC flux from the stator, the rotor having longitudinal pole portions running parallel to the axis of rotation and alternating in polarity around a circumference of the rotor;   wherein portions of permanent magnet (PM) material are positioned to form boundaries separating the rotor pole portions of opposite polarity from an interior of the rotor and from each other to define PM poles for conveying the DC flux to or from the primary air gap and for inhibiting flux from leaking from said pole portions prior to reaching the primary air gap when said direct current is of the first polarity;   wherein at least one pole portion in each pair of rotor pole portions is provided by ferromagnetic pole material and extends longitudinally from the axial air gap towards a middle of the rotor;   wherein the pole material has a relative greater cross section at the axial air gap and tapers to a relatively narrower cross section proximate the middle of the rotor to conduct flux that turns ninety degrees from the secondary air gap to reach the primary air gap; and   at least one device selected from the group consisting of side magnets, side poles, flux-guiding magnets, ferromagnetic end plates, non-magnetic end plates, and ring bands.   
     
     
         6 . The brushless machine of  claim 5  further comprising at least one stationary excitation coil and at least one stationary flux collector for receiving direct current from an external source and being positioned across an axial air gap from one end face of the rotor so as to induce a DC flux in the rotor which increases a resulting flux in the primary air gap when said direct current is of a first polarity and which reduces the resulting flux in the primary air gap when said direct current is of a second polarity opposite said first polarity. 
     
     
         7 . The brushless machine of  claim 6 , wherein a return path for the DC flux to the excitation coil is provided by the magnetic stator frame and stator core. 
     
     
         9 . (canceled) 
     
     
         10 . The brushless machine of  claim 5  further comprising side magnets in place of said side poles. 
     
     
         11 - 22 . (canceled) 
     
     
         23 . A brushless electric machine comprising:
 a cylindrical stator;   a rotor having an axis of rotation, the rotor being spaced from the stator to define an annular primary air gap that receives an AC flux from the stator, the rotor having a plurality of longitudinal pole portions disposed parallel to the axis of rotation and alternating in polarity around a circumference of the rotor;   wherein each longitudinal pole portion comprises portions of permanent magnet (PM) material positioned to form boundaries separating the longitudinal pole portions of opposite polarity from an interior of the rotor and from each other to define PM poles and wherein at least one of the longitudinal pole portions has a first end and a side magnet is disposed adjacent the first end; and   a ferromagnetic end plate disposed adjacent the side magnet wherein the side magnet is disposed between the ferromagnetic side plate and the first end of the at least one longitudinal pole portion.