| 摘要 |
An electric motor comprises a stator 12 having plural permanent magnets 13 and plural electro-magnets 14 and a rotor having a rotation axis 15 with respect to the stator. A circumferentially extending stator cover 20 comprises plural magnetic portions 21 and is movable relative to the stator. The stator cover can be adjacent the outer surface of the stator or the end surface of the stator (fig 9) and move circumferentially, radially or axially with respect to the stator. Each magnetic portion of the cover can be associated with a permanent magnet 13, move between positions that are remote and proximate from the magnet where it can overlap an adjacent electro-magnet. Magnetic portions can be uniform in cross section, or non-uniform having a radially increasing thickness (fig 7B, 7C) or be stepped (fig 7D). Magnetic portions 21 can: be coupled together by a frame comprising non-magnetic portions 22; be formed of iron; have a length equal to that of the permanent magnets; and have a thickness between 2 and 30 mm. The cover thickness can be adapted to minimise the iron loss of the motor. Movement of the circumferentially extending stator cover with respect to the stator allows for the control of the efficiency of the electric motor which can be a flux-switching permanent magnet electric motor, and be applied to a vehicle drive train or an industrial machine such as a pump. |
