Patent ID: 7408279

Claim:
A permanent magnet synchronous motor comprising: a rotor including: a rotor core; a permanent magnet mounted on an outer wall of said rotor core, said permanent magnet having an outer wall with respect to a radial direction of said rotor, and having an inwardly-tapered section at each end of said outer wall of said permanent magnet for preventing demagnetization of said permanent magnet; and a hollow cylinder wrapped around said permanent magnet such that an open space is formed between said inwardly-tapered section of said permanent magnet and said hollow cylinder, said hollow cylinder being formed of non-magnetic material; and a stator including teeth and concentrated windings such that adjacent teeth have different polarities; wherein said rotor and said stator are arranged to satisfy the relationship: 0.10 As<Am<0.25 As, wherein: Am is an angle of an arc length of said inwardly-tapered section at each end of said outer wall of said permanent magnet measured with respect to a central axis of said rotor; and As is an angle of an arc length of each tooth of said stator measured with respect to said central axis of said rotor.