Patent ID: 7939982

Claim:
An electric motor rotor comprising, a core adapted to be received within a cylindrical opening defined by an interior surface of a stator for rotation of the core within the cylindrical opening about a central longitudinal axis of the core, said core having an outer surface contour as viewed in a cross section of the core taken in a plane perpendicular to said central longitudinal axis, said outer surface contour consisting of: a number of first outer surface segments defined by first arcs centered on said central longitudinal axis and configured to provide uniform air gaps between said first outer surface segments and said interior surface of the stator, a number of second outer surface segments defined by second arcs not centered on said central longitudinal axis and configured to provide non-uniform air gaps between the second outer surface segments and said interior surface of the stator, each uniform air gap having a gap width which remains substantially constant along an entire length of the air gap, and each non-uniform air gap having a gap width which varies along the length of the air gap, wherein each second arc has a radius less than the radius of each first arc, slots in the core spaced radially outward from said central longitudinal axis, and magnets in the slots.