Patent ID: 7298064

Claim:
An electric motor having a laminated core structure formed by stacking a plurality of core plates made of rolled electromagnetic sheet steel, wherein: the same number of core plates are stacked with respective rolling directions of the electromagnetic sheet steel angularly displaced by machine angles with respect to a reference angle so as to produce a phase difference of cogging torques by magnetic anisotropy of the core plates, each phase α of the cogging torque is represented by (360 n/s) mod {360/(m·s)} ×m·s, which is a value obtained by multiplying a remainder of division of an angle (360 n/s) of each of slots or poles by an angle 360/(m·s) of one cycle of the cogging torque, by m·s which is the number of cycles of the cogging torque per rotation, where s is the number of slots or poles provided in the laminated core structure, and m and n are natural numbers, and said machine angles are determined such that the phase difference of the cogging torques is substantially 180° in an approximately rectilinear relation between the phase of the cogging torque and the machine angle of the rolling direction obtained by connecting the phases at respective angles of the slots or poles.