Rare earth magnets still optimum choice, says motor design expert

April 16, 2015 // By Graham Prophet
Promoting a workshop to be held at the forthcoming CWIEME Berlin event, by Motorsolver president and IEEE life fellow Jim Hendershot, the organisers have released a preview of some of his findings regarding current industry practice in the selection of traction motors.

At the conference, Hendershot will explore the pros and cons of hybrid and electric vehicle motor designs, encompassing performance, manufacturing methods and cost.

Amid concerns over the price, supply and hazardous extraction of rare earth metals used in permanent magnet motors, many members of the motor manufacturing community, especially those in the automotive sector, are carrying out extensive research into eliminating or reducing their use. Visitors to the 2015 CWIEME Berlin exhibition, taking place 5-7th May, can hear about several initiatives in this area, such as the EU-funded MotorBrain project and work of the Karlsruhe Institute of Technology’s Helmholz Center for hybrid and electric vehicles, in the seminar programme.

Practically speaking, however, rare earth permanent magnets still remain the number one choice in hybrid and electric vehicle motors, according to leading design expert Jim Hendershot, who will be running the workshop at the exhibition. Mr. Hendershot, based in Kentucky, USA, has over 40 years’ experience in the design of permanent magnet and brushless switch-reluctant motors for computer disc drives, servo systems, traction drives, and hybrid vehicles, as well as micro-turbine and diesel generators. He has co-authored two of the leading design books on permanent magnet motors and generator design and has worked for some of the world’s most influential manufacturers, including General Motors.

“There are several types of electric motors for engineers to choose from for hybrid and electric vehicle traction drives: induction (or asynchronous), permanent magnet synchronous, switched-reluctance synchronous or reluctant synchronous. A couple of large front-end loaders [earth-moving machines] use switched-reluctance wheel motors and some large dump trucks and [bull]dozers use AC induction motors for traction, as well as newer forklift trucks. But all major hybrid electric vehicles currently in production use rare earth permanent magnet synchronous traction motors,” he says.

“When BMW were beta testing their new i3 model, they ran them around for a few years with induction motors in them. But when it came to