Prius Power Split Device (2007)
eahart.com
eahart.com
This is a detailed simulation of what the Prius's computer system is thinking about, trying to balance the three motors (1x ICE + 2x Electric) to achieve the wheel-speeds across different driving conditions.
For those unaware: the PSD (Power-split device) is a glorified and inverted differential. Instead of allowing 2x wheels to be driven at different speeds, the PSD allows multiple power-inputs (MG2 Electric motor + ICE) to combine together to drive the axle (which ultimately goes into a differential to power the two wheels later in the car's powertrain).
In any case, this is all possible because the two motors, MG1 and MG2, carefully are controlled to allow the ICE engine to shift up or down through "virtual gears", so to speak. The ICE engine at 1000-RPM can (depending on MG1 vs MG2 settings), travel as low as 0mph to 65mph despite never changing its RPM (albeit requiring different amounts of power to be given to MG1 and MG2 electric motors).
What the computer chooses depends on the battery pack's power. In particular, the ICE engine also charges up the battery pack, so loading the ICE more for more battery charging could be chosen. Or the computer could choose to run more EV power (draining the battery, "making room" for more power from regenerative braking later). There's a lot of decisions the computer could make, and it all comes down to the speed of MG1 and MG2.
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Modern Prius from 2024 has a beefier system with far more power for the ICE, MG1 and MG2 motors. The RAV4 Hybrid and RAV4 Prime systems are even bigger (as appropriate for a larger SUV). So the specific RPMs may not be true anymore for a modern system, but its still a good demo to give an idea of what the computer is thinking about.
Despite the changes in motor size and ICE engine size, and a few gear ratios... a modern Prius, Prius Prime, Rav4 and RAV4 prime still uses this 2x electric motor (MG1 + MG2) plus ICE system today in 2024 as its hybrid drive train.