Patent ID: 7839045

Claim:
A permanent magnet motor, comprising: a stator, comprising: a stator shaft having an outer surface; K salient teeth formed upon the outer surface; and K winding slots formed among the K salient teeth; and a rotor, comprising: a first inner surface facing the outer surface; and P pairs of permanent magnets formed on the first inner surface, each of which has a second inner surface facing the outer surface, two boundaries and at least a groove formed on the second inner surface between the two boundaries, the groove causing a reduction in cogging torque, wherein K is a natural number larger than 1 and K≦54, P is a natural number and P≦100, the groove on the second inner surface has a specific angular position chosen from n electrical angular positions, 180 Mod((2P/K)i−P/f,1) degrees, wherein i=1, 2, . . . , n, and the groove has a width of w ps , 0.2D≦w ps ≦1.1D degrees, n=M/(2P), M is a lowest common multiple of 2P and K, Mod( ) is a remainder operator, f is a wave-cyclic number of the cogging torque per rotation in the absence of the groove, and D=180 Mod(2P/K,1) degrees; and wherein the groove further comprises an optimized depth value being a highest one of depth values satisfying a condition that a predetermined structural strength of the motor is maintained, and a waveform and a value of a counter electromotive force of the motor are both kept unchanged so as to reduce the cogging torque.