Patent ID: 8063529

Claim:
An electric motor comprising a stator and a rotor disposed within the stator and having an outer surface confronting the stator, wherein the stator comprises a shell, the shell comprising at least four flat sidewalls and arcuate connection parts connecting adjacent neighboring sidewalls, the cross section of the shell being a polygon with rounded corners formed by the connection parts; the stator further comprising a plurality of magnets disposed inside the arcuate connection parts, each magnet having an outer surface contacting inner surfaces of two adjacent sidewalls with a gap being formed between each magnet and the corresponding arcuate connection part such that the magnets do not contact the arcuate connection part, and air gaps being formed between an inner surface of the magnets and the outer surface of the rotor, and wherein the width of the air gap measured in the radial direction between the rotor and the inner surface of each magnet is not constant, the air gap being narrower at the circumferential middle of the inner surface than at the circumferential edges, and the inner surfaces of the magnets are arcuate in the circumferential direction and the air gap is narrowest corresponding to the thickest part of magnets and is widest corresponding to the thinnest parts of the magnets.