Reduced Dysprosium Permanent Magnets and Their Applications in Electric Vehicle Traction Motors

Abstract

Permanent magnet (PM) machines employing rare-earth magnets are receiving increasing interest in electrical vehicle (EV) traction applications. However, a significant drawback of PM machine-based EV tractions is the extremely high cost and volatile supply of rare-earth materials, especially for dysprosium (Dy), whose price is almost 6 times higher than neodymium. This paper describes a new Dy grain boundary-diffusion process for sintered Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B magnets to maximize its effect on coercivity enhancement. The new process gains an 81% reduction in Dy consumption normally required by the conventional Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B magnets for the equivalent performance and 17% higher remanence. The investigation into the application in an interior PM (IPM) machine for a small-sized EV traction shows that compared with the conventional Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B magnets, despite the relatively low coercivity, the low-Dy-content magnets still withstand the thermal and demagnetization challenge over various driving operations. In addition, with the magnet’s high remanence and energy product, the machine gains significant torque and energy efficiency improvements. The analysis results are validated by a series of tests carried out on a prototype IPM machine with the new magnets.