Coreless Axial Flux Permanent Magnet Synchronous Machine With Modular Ceramic Substrate Windings for E-Bike Applications

Coreless axial flux motors are an attractive choice for light transportation applications such as electric bicycles due to their lower mass, low frequency-dependent losses and superior efficiency at high speed. To further improve the power density of coreless motors, the volume of the windings and the effective electromagnetic airgap are reduced by using ceramic substrate active metal brazed (AMB) copper windings instead of conventional stranded wire conductors. The high thermal conductivity of the Aluminum Nitride (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">AlN</i>) substrate allows higher current densities, which enables minimization of conductor cross-sectional area. This reduces the eddy current losses in the stator windings, which are significant in coreless motors. The presence of copper conductors on both surfaces of the planar ceramic substrate mitigates the thermal stress caused by the mismatch of coefficient of thermal expansion of the conductor and the substrate.