Permanent magnet synchronous motor including permanent magnet with tapered outer edges

An apparatus comprising:

• a compressor in one of an air-conditioner and an electric refrigerator;
• and
• a permanent magnet synchronous motor for driving said compressor, said 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.