Patent ID: 7116030

Claim:
An electric motor comprising a ferromagnetic stator ( 11 ) having a plurality of teeth ( 11 A) spaced apart along a circumferentially extending line, a ferromagnetic rotor ( 13 ) having a rotor core ( 16 ) with a plurality of reluctance poles ( 17 ) which are spaced apart along a circumferentially extending line in confronting relation with the stator teeth and spaced from the stator teeth by an air gap (G), a rotor shaft ( 14 ) supporting the rotor for rotation in the stator, and a winding ( 12 ) on the stator for producing a multipolar magnetic field continuously travelling along the air gap and linking the stator teeth with the reluctance poles ( 17 ) of the rotor core ( 16 ), the magnetic field having an even number of poles equal to the number of reluctance poles of the rotor; characterised by the combination of the following features: at least a part of the outer portion of each reluctance pole ( 17 ) of the rotor core ( 16 ) forms a magnetically saturable surface layer having a saturation flux density which is lower than the flux density in the air gap (G) which saturates the teeth ( 11 A) of the stator ( 11 ), and the rotor core ( 16 ), including the reluctance poles ( 17 ) with the associated magnetically saturable surface layer of each pole, and the rotor shaft ( 14 ) are formed from a single solid piece of ferromagnetic material.