Patent ID: 6972504
Filing Date: 2005-12-06
Classification: H02K

Abstract:
1. 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; at least a first stationary excitation coil assembly for receiving direct current from an external source and being positioned across a secondary 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; and 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; and reluctance poles of ferromagnetic material positioned between the PM poles to produce reluctance torque in the rotor in response to AC flux in the primary air gap, wherein said reluctance poles have a cross section that varies in an axial direction relative to the rotor.