Patent ID: 7119507

Claim:
A brushless DC motor comprising: a stator; and a rotor comprising a plurality of permanent magnets each having a predetermined thickness and being mounted in an interior of the rotor, a plurality of flux bafflers made of non-magnetic sections, each of flux bafflers beginning from an edge section in circumferential direction of one of the permanent magnets, extending up to vicinity in a surface of the rotor, and having a length in a circumferential direction which is greater than a thickness of the permanent magnets, and a rib which is disposed between magnetic poles, the flux bafflers are configured and arranged such that an angle θ 0 between an edge section of the flux baffler on a magnetic pole center side and an edge section on a side for coming in contact with the rib of an adjacent one of the flux bafflers, with respect to a rotor center, is determined to be equal to or greater than an angle satisfying a following relationship θ 0 =180 ° *m /( Pn *( f/f 0 )), where 2θ 0 −θ r <90°, wherein, a frequency of vibration which is to be reduced is represented with f, a pole pair number is represented with Pn, an electrical frequency is represented with f 0 =Pn*N, a motor revolution is represented with N, m is equal to an odd number and an angle of the rib with respect to the rotor center is represented with θr.