How an EV motor makes its magnetic field without magnets

Описание: BMW's new iX3 has a rear motor with no magnets in it, while most electric cars do use them (about 90%, according to Renault). So where does a motor get its magnetic field without a magnet, and what does it cost?

Every electric motor needs two magnetic fields. The question is where the rotor's field comes from. This video walks through the three answers: a permanent magnet (a free field, but rare earths and heat sensitivity), an induction motor (current in rotor bars, paid for in rotor losses), and the wound-rotor motor BMW and Renault chose (an electromagnet fed through brushes and slip rings, paid for in field power and a bit of size). Then the company numbers, what each one is measured against, and how to read the motor line on a spec sheet.

The efficiency comparison (about 98% vs 95.5% peak) comes from a single computer-modelling study of two same-size motor designs, not a test of real motors. BMW's 40% loss reduction is against its own previous generation (which already used a wound rotor) and covers the whole drive technology. Tesla's and MAHLE's statements are company claims.

CHAPTERS
0:00 A rear motor with no magnets
0:24 Two magnetic fields
1:25 Answer 1: the permanent magnet
2:59 Answer 2: the induction motor
4:37 Answer 3: an electromagnet in the rotor
6:54 What the company numbers measure
8:23 Reading the spec sheet
9:47 Next: solid-state batteries

SOURCES
[1] IEA Policies Database, "Export controls on certain medium and heavy rare earth items" (updated 2025-05-05) – https://www.iea.org/policies/26796
[2] BMW Group PressClub UK (2025-09-05), "The start of a new era: the new BMW iX3" – https://www.press.bmwgroup.com/united...
[3] Renault Group Magazine (2025-10-16), "All about electric motors with no rare earths" – https://renaultgroup.com/en/magazine/...
[4] Quoc et al. (2023), "Performance Comparison of Permanent Magnet and Electrically Excited Motors for Electric Vehicles", Journal Européen des Systèmes Automatisés 56(3), DOI 10.18280/jesa.560318 – https://www.iieta.org/node/14924
[5] Charged EVs (2022), "A closer look at brushed AC motors in EVs" – https://chargedevs.com/features/a-clo...
[6] Arnold Magnetic Technologies (2015), "The Important Role of Dysprosium in Modern Permanent Magnets" – https://www.arnoldmagnetics.com/wp-co...
[7] Electrek (2023-03-01), "Tesla is going (back) to EV motors with no rare earth elements" – https://electrek.co/2023/03/01/tesla-...
[8] MAHLE Newsroom (2021-05-05), "MAHLE develops highly efficient magnet-free electric motor" – https://newsroom.mahle.com/press/pl/p...
[9] Gundogdu, Zhu, Chan (2022), "Comparative Study of Permanent Magnet, Conventional, and Advanced Induction Machines for Traction Applications", World Electric Vehicle Journal 13(8):137 (CC BY) – https://doi.org/10.3390/wevj13080137

Export rules can change; the April 2025 licensing requirement is described as of the IEA entry's last update.