Patent ID: 6853105

Claim:
An electric power steering system comprising a permanent magnet motor including: a rotor having M magnetic poles disposed at an interval in a peripheral direction of the rotor; a stator having P magnetic pole pieces arranged at a spacing in the peripheral direction, the P magnetic pale pieces being opposed to the M magnetic pales of the rotor; respective slots between adjacent magnetic pole pieces of the stator, wherein 0.040<c/W<0.125, c is a dimension, measured along the peripheral direction, at the faces of the P magnetic pole pieces, that is (i) distance between nearest pairs of magnetic pole pieces and (ii) width of each auxiliary groove, and W is distance, measured along the peripheral direction, at the faces of the P magnetic pole pieces, between centers of nearest pairs of the slots; and n auxiliary grooves in a face of each of the magnetic pole pieces of the stator opposed to the magnetic poles of the rotor, wherein the smallest integer of which M and (n+1)·P are factors is X, m satisfies 61<(180 mM)/X<84, M, P, m, and n are integers, and a skew having an electrical angle in a range of 61° to 84° is provided relatively between the rotor and the stator.