Influence of the permanent magnet overhang on the performance of the brushless dc motor

Axial overhang of the permanent magnets has been used to enhance the performance of radial flux brushless de motors, but its precise contribution to performance is not well known. This article aims at the investigation of the overhang effects by finite element and lumped parameter modeling. An empirical formula which allows two-dimensional analysis to account for overhang effects is proposed. A three-dimensional equivalent magnetic circuit model is developed and its ability to accurately predict overhang effects is assessed. Results of finite element and lumped parameter models are compared and a design methodology is forwarded. (C) 1998 American Institute of Physics. [S0021-8979(98)46911-1].