Patent ID: 7795830

Claim:
An electric motor comprising: an armature having at least two armature windings arranged to form two respective armature phases; a salient pole rotor arrangement within the armature which rotor is separated from the armature by an air gap, said rotor being shaped and configured so that the salient pole arrangement defines a higher and a lower magnetic reluctance path through said gap between the rotor and armature, and which rotor further includes field windings about the salient poles of the rotor which windings are configured to form at least one pole pair, said field windings terminating in a selective electrical switch which determines the electrical continuity of said field windings so that a reverse voltage bias imposed across the switch results in the field winding being open circuit; and control means which is configured to regulate the magnetizing of the field winding by applying a voltage to the armature phase linked to the field winding via the lower reluctance path so that the energized armature phase in turn imposes a reverse voltage bias across the switch through induction, this reverse bias preventing the flow of current in the field winding but the applied voltage to the armature phase increasing magnetic flux density in the rotor, the control means thereafter removing said applied voltage once a predetermined flux density in the rotor is reached so that the removal of applied voltage induces a reversal of voltage to a forward voltage bias across the switch allowing current to flow in the field winding which current prevents the decay of the flux density in said rotor, and which control means is further configured to regulate the production of torque in the motor by applying a voltage to the other respective armature phase not responsible for energizing the field winding, so that, at any given moment, one armature phase is usable for magnetizing the field winding whilst the other phase is responsible for torque production.