Is the maximum speed obtained also with the electric motor ?

Motor/Generator 2 propels the wheels. The internal combustion engine can assist M/G 2, by pushing against M/G 1, but M/G 2 is directly connected to the wheels.

As I recall, 79% of engine torque can mechanically assist M/G 2, while 21% becomes electrical power in M/G 1 to assist M/G 2.

The engine never powers the car down the road alone, in fact, neutral is emulated by just not powering M/G 1 & 2 so the engine has nothing to push against.

 

It can't achieve top speed in EV mode. This is determined by the maximum speed of MG1. It is set around 10.000rpm. Above that the ICE needs to run to prevent an overspeed condition of MG1.
There are actually a lot of situations where MG2 isn't contributing any torque to the wheels. If you look at the Hybrid Assistant app for example you can easily check the speeds and torque of the ICE, MG1 and MG2.
When driving at low loads at constant speeds you can see the so called heretical mode. In this mode MG2 is actually generating power to spin MG1. In this mode all the propulsion torque is coming from the ICE (when looking at the OBD datastream you see negative torque for MG2).

 

That's true for the cordless Prius but the Prime model has an extra clutch to allow high speeds while operating on electric only.

I don't know if the electric-only top speed matches the hybrid top speed.

 

From my experience the EV assist does not kick in post 70(ish) MPH (UK).
Why don't you…
Find a safe and legal place to attempt a max speed test
Display the animation which shows where the power comes from
Have a passenger
Boot it to max speed whilst your passenger records the output of the animation.

 

That doesn't make sense.
MG1 has to draw power to maintain the 'gear ratio' between the engine and the wheels.
And that power has to come from MG2 when just cruising steady state down the road.
It's called an eCVT for that reason. It always has to consume some of the power to control the gear ratio.

It was an amazing invention.
But now there is a new Fuel Economy champ!
Probably because its transaxle does not need power once the gear ration is selected from actual gears. All the engine power goes to the wheels with none consumed in the 'transmission' of that power.

 

The main thing the transmission does with electrical power is move it around between MG1 and MG2, as a second path for power from the engine to the wheels (the first path being the mechanical one).

In ordinary (non-overdrive) driving modes, the electrical power is generated by MG1 and sent to MG2, where it produces a torque that appears at the wheels in addition to what was passed along mechanically from the engine. The generation of power in MG1 is what resists the engine rotation so the mechanical path also carries power. If you have ever turned a hand-crank or bicycle generator and increased the electrical load on it, you physically felt how that works.

In low-power cruising (overdrive conditions) the electrical flow is the reverse of that: MG2 is generating some power (thus subtracting from the torque at the wheels) which is returned to MG1, which acts as a motor and allows the wheel speed to be higher for a lower engine speed, i.e., nothing different from any other transmission's overdrive gearing, only we obtain it in a kind of brain-teasing way. Early commenters didn't call it "heretical mode" for nothing.

The only power "consumed" in the transmission as it controls the gear ratio would be the unavoidable losses as heat because the motors and inverter switches are not perfect ideal motors and switches, and gears and bearings that aren't perfectly frictionless. But ORNL's teardown and study showed those losses to be really low.

Other than that, the transmission is just a machine for getting power from the input shaft to the output shaft, like any other transmission, and the power going in one end comes out the other, possibly with speed lower and torque higher, or speed higher and torque lower.

For limited periods, it is able to run a surplus or a deficit, using the battery. But that entails additional losses, both into the battery and back out again, so it prefers to stay out of that business when conditions permit, and just act as an ordinary transmission with the power flowing internally. ("Internally" is here understood to include the short orange cables and the MG1 and MG2 transistors inside the inverter, even though they aren't packaged inside the transmission.)

As far as the actual original question, I'm not sure it matters how you attain the maximum speed. In some road and wind conditions it might take everything the car has got, and in some other conditions it might not. But either way, I believe you get the maximum speed by taking the maximum RPM allowed for MG2 (13,500) and the MG2 reduction gearing and final drive ratios and doing the math. And MG2 always spins in that same ratio to the wheels no matter what. Because of that, it would seem like a bad idea to exceed that speed, no matter how you attain it.

 

Agreed. MG1 is always using power to hold the gear ratio the brains select at the moment.
That is the question. How much power? A teardown wouldn't answer that. Clamp-on ammeters on the wires to both MG's would and then calculate the losses in the inverter.
MG1 is handling/manipulating all the HP the engine is producing. That has to be something, even if it's 'really low'.

And I wonder if this is why the Prius wasnot the king of the hill for fuel economy.
Actually it is back on top with the 2023 version!

 

If that's what you believe, then "agreed" is the wrong word, 'cause we don't.

But I see how it happened. Notice that in the part of my post that you did quote:

you were reusing only my description of the "heretical mode" overdrive cruise operation (above, I restored the start of my sentence that you ...'ed out). You entirely left out the preceding paragraph, describing normal driving:

If you did that by mistake, it was unfortunate; if you did it on purpose, it was dishonest. I'm not clairvoyant so I don't know which it was. The former, I hope.

In the normal driving mode, your notion that "MG1 is always using power" is clearly not supported, as MG1 is producing electrical power then.

The case in overdrive is more complicated. Yes, electrical power is going into MG1 in that case. But that in itself is not a source of transmission inefficiency. The transmission is simply using the power path from MG2 to MG1 as part of an arrangement that delivers the same output power as was input, but at higher speed and lower torque. If MG1 and MG2 were perfect motors and the inverter transistors were perfect switches, there would be no loss on that path at all.

In reality, of course, there are the losses you expect because real motor windings and transistors get warm, and that happens both when the power flow is MG1 to MG2 and when it's the other way. But that's a far cry from thinking all the power "used" by MG1 is being somehow lost. It isn't; only the fraction going to incidental electrical losses along the path. All the rest gets put right back into the mechanical output.

(There are also incidental losses along the mechanical path, in bearings and gear teeth and stirring of oil. No transmission is free of those.)