| 摘要 |
A brushless DC motor includes a permanent field magnet secured to a rotor and having a radially directed annular surface, and two phase coil elements in the form of a sectorial loop secured to a stationary stator and disposed in a plane parallel to the annular magnet surface, the loop having circumferentially extending portions which are in inner and outer relation in respect to the center of the annular magnet surface, with the magnet and each coil element being relatively rotatable about the axis of the rotor. The mean radial distance f between the inner and outer circumferentially extending portions of each coil element and the radial width b of the annular surface of the magnet are selected as that the ratio b/f is within the range of 0.8 to 1.2 for maximizing the viscosity factor mu of the motor. In addition to providing the above ratio within the stated range or as an alternative thereto, the mechanical viscosity factor mu can be maximized by providing a reduced air gap d'= 2ROOT 2d/ 2ROOT ab, in which a is the mean radius of the magnet, d is the size of the air gap between the annular magnet surface and the stator, and d' has a value within the range of 0.15 to 0.30. |
