Performance improvement in PM machine using two-piece stator design

Miniature permanent magnet (PM) brushless motors used in Industrial power tool application require high torque and efficiency. Further, the size constraints imposed by the hand-held tool requires the use of high torque density motor. Therefore, by utilizing the stator slot area to achieve the required number of amperes turns is important while considering the low-cost motor solution. Existing single-piece stator lamination design has poor conductor fill factor in the slots due to manual insertion of the coils in the narrow slot opening. Hence to solve the poor slot fill factor (SFF) and to simplify the winding process, the stator lamination is split into two-parts and the pre-wound coils are placed outwards in the open slots. This results in increased SFF and result into 22% improvement on motor regulation. The FEA based the simulation is carried out and simulated motor performance is validated with experimental results. In addition, the challenges during the prototype motor build is discussed.