Generally, the YASA configuration demonstrates higher efficiencies at higher speeds, while the single-stator, single-rotor is more efficient in high-torque duty cycles. Two axial-flux permanent-magnet motors are being widely studied: a double-rotor single-stator yokeless and segmented armature structure, and a single-stator single-rotor configuration. Different TopologiesĪxial-flux machines appear in research literature in different topological forms due to a number of different flux path options, together with different winding and magnet configurations. Furthermore, this type of motor typically has suitable dimensions for packaging in, or close to, each of the vehicle wheels. Axial-flux motors can generate more torque, have fewer thermal-management issues, and use fewer materials, reducing overall weight and cost. The energy density per kilogram of the motor is higher. The iron in the stator of the YASA motor is dramatically lower when compared to other axial-flux motors, typically by 50%, leading to an overall increase in torque density of around 20%. The motor uses powdered iron materials that enable complex magnetic parts to be manufactured easily (Fig. The YASA topology is based around a series of magnetically separated segments that form the stator of the machine. In addition, to overcome processing difficulties, the stator and rotors of the motor can be fabricated using soft magnetic composites. This makes it more efficient and provides a higher power density. The core advantage of an axial-flux motor is that the spinning rotor has a larger diameter, because it turns alongside the stator rather than inside it. In comparison, the axial-flux PMSM, especially the yokeless and segmented armature axial-flux variety, exhibits advantages such as high torque density, short axial length, and higher efficiency. However, with the increase of motor speed, the problems of bearing life and motor noise become more prominent. Two main ways to increase the power density of the radial-flux PMSM are to improve the speed and reluctance torque (the torque experienced by a ferromagnetic object placed in an external magnetic field, which causes the object to line up with the external magnetic field). EV makers such as Tesla rely on these radial electric motors, which can trace their history back 40 years or so. At present, radial-flux PMSMs have mostly been used on EVs with power densities in the range of 2.0 to 3.6 kW/kg.įor motors used in EV drive systems, the requirements are a large torque output in the low-speed area and a wide constant-power speed range in the high-speed area. The main difference is that the magnetic flux travels parallel to the motor rotation axis in an axial motor, rather than perpendicularly in radial-flux motor designs. According to the direction of flux, PMSMs can be divided into categories: radial-flux motors and axial-flux motors. Permanent-magnet synchronous-motor (PMSM) design has been widely applied to date in electric vehicles due to its high power density and high efficiency. It was developed for Mercedes by the company’s subsidiary YASA. This harbinger of exciting things to come is powered by a new type of motor, a yokeless (it has no stator yoke) and segmented armature (YASA) topology that promises increased torque density, a shorter axial length, and high efficiency. The four-door electric coupe show car is currently being developed for the carmaker’s performance models, providing a preview of AMG’s all-electric future.Īccording to Philipp Schiemer, Chairman of the Management Board of Mercedes-AMG GmbH, “With this study, we are now offering a first glimpse of how we are transferring the AMG DNA into the all-electric future, starting in 2025.” No Yoke Mercedes-Benz and others believe it’s the axial-flux motor, revealed in M-B’s new Vision AMG (Fig. The better question, the one automakers are asking themselves, is “What’s next?” If you find yourself wondering about an EV’s practicality, or bang-for-the-buck equation, or why more Americans should abandon internal combustion vehicles, stop. Details of the YASA axial-flux motor topology.Advantages of the "yokeless" axial-flux motor.Comparing the axial-flux motor with the radial-flux motor for EVs.
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