MULTISTAGE AXIAL-FLUX PM MACHINE FOR WHEEL DIRECT-DRIVE

The design of direct-drive wheel motors must comply with diameter rest riction due to housing the motor in a wheel rim and allow the achievem ent of very high torque density and overload capability. Slotless axia l-flux permanent magnet machines (AFPM's) prove to be the best candida te for application in electric vehicles as direct-drive wheel motors, as in comparison with conventional machines they allow designs with hi gher compactness, lightness and efficiency, The paper presents a newly conceived AFPM which has a multistage structure and a water-cooled ir onless stator, In the proposed new topology of the machine the space f ormerly occupied by the toroidal core becomes a water duct, which remo ves heat directly from the interior surface of the stator winding, The high efficiency of the machine cooling arrangement allows long-term 1 00% overload operation and great reduction of the machine weight. The multistage structure of the machine is suited to overcome the restrict ion on the machine diameter and meet the torque required at the wheel shaft, The paper gives guidelines for the design of a multistage AFPM with water-cooled ironless stator, and describes characteristics of a two-stage prototype machine rated 215 N . m, 1100 r/min.