Patent ID: 8405273

Claim:
A universal motor comprising a wound stator, and a wound rotor, the stator comprising a stator core and a stator winding, wherein the stator core comprises a U-shaped yoke having a base and two arms extending from the base, each arm has a distal end remote from the base and forming a non-salient stator pole, each stator pole is formed with an inner concave surface forming a pole face which faces the rotor; each stator pole is formed with a plurality of separate magnetic flux barriers adjacent the pole face and arranged in the circumferential direction of the rotor, the spacing between adjacent magnetic flux barriers remote from the stator winding are greater than that between adjacent magnetic flux barriers closer to the stator winding, measured in the circumferential direction of the rotor, the magnetic flux barriers are void holes extending through the poles in a direction parallel to the axis of the rotor, and in each stator pole, the edges of each of the void holes, at the point closest to the pole face, are spaced equidistant from the pole face.