When it comes to the usual way electric vehicles are run, rare-earth permanent magnets are king. The interaction between the positive and negative poles of these magnets are exploited to produce the power that drives nearly every electric vehicle on the market today. The use of these superpowered magnets helps to make sure that these EVs can drive longer distances with less of a battery charge. Though these are wholly effective means of powering electric vehicles—as anyone who has been overtaken in traffic by the nearly silent streak of an EV knows—the truth is that it takes very specific materials to make these permanent magnets. And these rare earth metals required are becoming harder to source (China produces roughly 90%), so BMW decided that it was time to try something different.
A Modern EV Motor Without the Rare-Earth Magnets
BMW has taken a page out of the past to produce something that will run the motors in their most modern of engines. The brushed electric motor in its most basic form has been around for well over a century. Instead of using the frictionless interactions between many rare-earth magnets, this type of motor—as you may have guessed—uses conductive brushes to transmit the electricity to the rotor.
The brushed electric motor is composed of a stator (the fixed outer part of the motor), the spinning wire wrapped iron core rotor in the center, and the commutator that contains the brushes and the electrical connections. These brushes are made of a conductive material and are in constant contact with the commutator, producing and transmitting electrical energy. The main problem with these brushed motors is that the brushes wear out. Unsurprisingly, these metal brushes (which are usually made of a composite material similar to the type that forms brake pads) both wear down and produce a fine metal dust that can be harmful to engines. Many brushed motors also often do contain magnets around the interior of the stator which use the iron core to help to fuel the brushes, but the new BMW engine is different, boasting a net total of exactly zero magnets.
Brushed Electric With Zero Magnets: The Engine of the Future?
Here’s where things get interesting. With BMW’s new 5th generation motor, the magnets have all been removed to completely focus on the seemingly retro brushed motor technology. Instead it is a three-phase AC synchronous motor which only uses the combination of the brushes and the commutator to power the rotor.
It is amazing that this sort of technology can be used to produce the new BMW iX M60 that MotorTrend reports has (with the combined output of the front and rear electric motors) 532 horsepower and 749 lb-ft of torque, with jumps to 610 hp in sport mode, and is upped further in launch mode to a whopping 811 lb-ft of torque. It does make us beg the question, however, “What happens when the brushes wear down?”
At this point in time BMW makes no claims as to the longevity of the components of these brushed engines. They do claim that the modern materials used in their production will allow the ever-eroding brushes to have, in MotorTrend’s vague words, “a reasonable service interval.” BMW also claims that brushes themselves are fully sealed and will not allow the inevitable dust that is produced to contaminate the stator or the rotor.
Though there is definitely a reason that the engines that rely on rare-earth magnets became standard in EV, it is never a good idea to put all of your EV engine options into a single type that relies entirely on something that is increasingly difficult to source. It will be interesting to see these BMW brushed electric motors put to the test.
