YASA, a UK-based company, is developing yokeless and segmented armature (YASA) axial-flux electric motors. The company announced in February that it has signed an agreement with a global automotive manufacturer to innovate and develop hybrid and electric vehicle (HEV & EV) drivetrains with the mandate to “improve performance whilst reducing vehicle weight”.
There are several electric motor technologies that utilise the force between two magnetic fields as the method of generating torque from battery-stored energy. The efficiency of different motors is determined by the amount of energy that is lost between the battery and the motor output. The highest efficiency motors, therefore, allow EV manufacturer to optimise range for a given battery capacity. In current magnet technologies, neodymium-iron-boron (NdFeB) magnets lead the way in efficiency for motor applications, especially at low-revolution speeds.
Axial-flux motors, such as those developed by YASA and Magnax, utilise available empty space on the rotor face (and either side of the stator) of typical radial-flux motor designs. This increases the magnet volume for a given motor size and allows for a significant increase in power density. Some motor/generator applications can utilise lower quality magnets in axial-flux designs to compete with typical NdFeB radial-flux performance, but ultimately, where weight and performance need to be optimised and to reduce battery cost, NdFeB magnets currently take first prize.
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