Configuration and Material Selection
High Performance Electric Motors
Permanent magnet synchronous motors (PMSMs) provide excellent performance in torque density, energy efficiency, and controllability. Mounting permanent magnets to the rotor of a brushless DC (BLDC) motor reduces rotor inertia and allows higher acceleration. This topology is well suited for high speed applications but is limited by how well the magnets can be kept secured in place on the rotor.
Rare Earth Magnets
Rare earth magnets, first developed in the 1960s, have a misleading name. The elements used, such as neodymium, samarium, and cobalt, are relatively common around the world. But their distribution is diffuse; no large deposits offer easy access. That makes mining time-consuming and labor-intensive, and therefore expensive.
Because materials lose their magnetic properties at extremely high temperatures, rare earth magnets are formed by sintering—applying moderate heat and pressure to force materials into a shape. The results have stronger magnetic properties than alnico alloys, ceramic ferrites, or magnetite, but are relatively brittle. This creates additional challenges for keeping the magnets intact and in place at high rotational speeds.
Motors used in energy recovery systems and electric turbochargers can reach top rotational speeds in excess of 100,000 rpm. Any permanent magnet rotor with a rated top speed of more than 10,000 rpm should incorporate a secondary, redundant magnet retention system.
- Retention Methods and Materials
- Material Properties and Priorities
- Metal Alloy Sleeves
- Synthetic Fiber Roving