The article claims the opposite. I haven't looked at BMW's press release, so I don't know where the claim comes from.
"It's a big advance in terms of the efficiency of the electric motor, while getting away from the use of rare earth minerals."
Their reasoning:
"Permanent magnet machines typically rank as the most power-dense electric motors, but there's no turning permanent magnets "off." Their magnetic fields never change, so when they're not being powered by energy in the stator winding, they're generating energy in those windings, which creates drag."
Yeah, but only by adding a clutch or something to prevent the drag when the motor is coasting. I'm a little confused by this, I thought the motor would turn into a generator in that situation.
Motor regen is good to recover energy when you want to slow down. But apparently the most efficient way to drive is to coast as much as possible, rather than always trying to regen when off the gas. These motors let you do that without needing a clutch.
I think BMW's implementation of one pedal driving uses front radar and map info to adapt between coasting and regen as needed to get the most efficiency.
Their existing ICE cars also have a coast mode where they disconnect the engine from the transmission when you're not giving it gas (to eliminate engine braking). That function is only active when you put the car in eco mode. It's surprisingly smooth and responsive, you can't really feel the engine disconnect and reconnect as you're driving.
So, in the magnet-less design, are they saying that you are more efficient because your motor won't pull away energy/speed when not powered? As opposed to a permanent-magnet design, where you have to constantly add energy to maintain speed?
That's one quick explanation for how a magnet-less design would be more efficient...
After driving an EV for a while now, coasting is the number one thing that drives me crazy when driving an ICE car. It just isn't something that my mind thinks about anymore, so when it happens, it's a bit jarring at first. My wife's profile in my car is set to "coast" mode because she is the opposite. Her primary car is an ICE, so when she is driving my EV, it is jarring for her too!
I guess, for me, this would really have an impact on highway driving. And with non-highway driving (changing speeds frequently), I'd rather have the better one-pedal control. But what I didn't see what how much of an impact this would really have for energy efficiency.
Maybe the end game here is a magnet-less design that has a longer highway range. So you'll have two different range numbers: city vs highway ranges. Which would be very similar to the city vs highway MPG ratings we currently have for ICE cars. But those are the numbers I'd really like to see.
> So, in the magnet-less design, are they saying that you are more efficient because your motor won't pull away energy/speed when not powered? As opposed to a permanent-magnet design, where you have to constantly add energy to maintain speed?
Yes. And the magnetless motors are still able to regen when you want to slow down.
It would be theoretically possible to have a magnetic 'switch' which turned the permanent magnets off when not needed. Sounds impossible but it's possible[1].
Yes, and.... the time constant of an LR circuit = L/R -- it takes finite time to 'turn off' the electromagnets. And, the collapsing magnetic field's energy has to go 'somewhere'; and it's of opposite polarity to the current that created it.
In other words, yes, possible, but more complicated than one might think. For example, we could build a circuit that "sucks out" the field by jamming very high currents in the opposite direction through the coils. To do this needs even higher voltages that the motor normally uses.
So, yes, it's possible. Not especially easy for optimal efficiency.
"It's a big advance in terms of the efficiency of the electric motor, while getting away from the use of rare earth minerals."
Their reasoning:
"Permanent magnet machines typically rank as the most power-dense electric motors, but there's no turning permanent magnets "off." Their magnetic fields never change, so when they're not being powered by energy in the stator winding, they're generating energy in those windings, which creates drag."