Patent ID: 7230359

Claim:
An electric motor, comprising: a stator ( 28 ) having a lamination stack formed with slots ( 126 ), said slots having a predetermined slot pitch (τ s ); a multi-phase stator winding (U, V, W) arranged in these slots ( 126 ); a rotor ( 36 ) separated by an air gap ( 39 ) from said stator ( 28 ), said rotor having, on its air-gap-adjacent side, a plurality of salient poles with pole shoes ( 136 ) facing said air gap ( 39 ) and on its air-gap-remote side, a magnetic core ( 130 ), connected mechanically by connecting parts ( 134 a , 134 b ) to the poles shoes ( 136 ), said pole shoes serving for generation of at least one sinusoidal induced voltage in the stator winding (U, V, W); a recess ( 138 , 140 ) provided between the magnetic core ( 130 ) and a pole shoe ( 136 ) and at least one permanent magnet ( 38 ), arranged in said recess, to generate a magnetic flux in said pole shoe ( 136 ) so that, at an interface between said permanent magnet to the associated pole shoe, a magnet/pole shoe boundary is defined, and adjacent said recess, on each side of said at least one permanent magnet ( 38 ), there extends a magnetically poorly conductive region ( 146 a , 146 b ), said region being bounded, on its air-gap-adjacent side, by one of said connecting parts ( 134 a , 134 b ); a circumferentially measured breadth (β) of each pole shoe ( 136 ) diminishing, at least partially, in a direction from the magnet/pole shoe boundary ( 138 ) toward said air gap ( 39 ) and, at a position of least breadth ( 142 ), having an angular extent (β c ) which has the following relationship to the slot pitch: β c =n *(τ s) (1−0.02) . . . n *(τ s )(1−0.2) wherein n=1, 2, 3 . . . and the angles β c * and τ s are specified in mechanical degrees; and wherein a circumferentially extending magnet/pole shoe boundary ( 138 A) is defined; and a first magnetic breadth (βM) of said pole shoe ( 136 ), at said magnet/pole shoe boundary, is greater than a second magnetic breadth (βC) of said pole shoe at a point ( 142 ), located radially farther than said boundary from the central axis of said rotor, at which the magnetic breadth of said pole shoe is smallest, and a transition from the first magnetic breadth to the second magnetic breadth is provided on both sides of said pole shoes, so that the magnetically poorly conductive regions, provided on both circumferential sides of the respective permanent magnets, further extend in a radial direction and are of similar shape.