Recently we read an interesting paragraph on the InsideEVs Blog. They compare the significant difference in range between the Jaguar I-Pace and the Tesla Model 3.
In the article we can read:
"Tesla Model 3 all-wheel drive raises the bar even higher to 4.1 miles of range per kWh.
In the case of the competition, current and upcoming all-wheel drive electric cars (think Jaguar I-Pace, for example) vary between 2.4 to 2.8 miles of range per kWh according to EPA. That’s not even on the level of the Model X"
Now, why does the Tesla Model 3 deliver a much higher range (or efficiency) compared to the Jaguar I-Pace while the aerodynamics of the car are not that much different?
The Jaguar I-Pace has two PM motors, one radial flux (RF) Permanent Magnet (PM) motor in the front and one RF PM motor in the rear. When little torque is needed, one of the motors is switched off, so the other can work at higher efficiency.
However, without a clutch, the freewheeling / spinning (front) PM motor also uses energy, mainly due to eddy current and hysteresis losses in the motor’s stator iron. This is a consequence of the ‘always-on’ magnetic flux of the permanent magnets. The iron mass in a traditional EV motor (RF motors), is quite high because these motors have a stator yoke to carry the magnetic flux around the stator.
So the yoke in the RF PM machine greatly contributes to the no-load losses.
Let's go a bit more in detail:
Jaguar originally claimed 292 miles of range, while the reality is more like 234 miles. (source)
Other sources compare the 44 kWh/100 miles for the Jag I-Pace with the Tesla Model X 75D which consumes only 36 kWh/100 miles). And the Model 3 delivers even better results than the X.
Jaguar I-Pace uses 2 PM motors while Tesla uses one PM motor and one induction motor. So why did Tesla choose for at least one induction motor while everybody knows that PM motors deliver higher overall efficiency?
The reason is that induction motors are not affected by the ‘no-load loss' problem. We guess that this is the reason why Tesla chose an induction motor for the front and a PM RF motor at the back axis in the Model 3. Of course, induction motors suffer from other drawbacks (such as low efficiency at partial loads but it seems that the no-load losses problem was prioritized over this.
Removing the Yoke
Using a Yokeless PM motor solves the problem. PM motors without a yoke (only possible with axial flux PM motors) have lower stator losses because there simply is no yoke and as such, much less iron. No yoke means very few iron losses, which results in more range for a given battery capacity (or a smaller battery for the same range).
This clearly benefits the business case for Magnax Yokeless Axial Flux PM motors, which are not only delivering significant benefits in terms of power density, but also benefits the battery requirements.
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