Question on how engine starts

The second electric motor (generator/starter) revs it to around 1,000 rpm before igniting. Revving it higher than a traditional starter is possible due to more powerful electric motor.

 

To elaborate on USB's answer, there are two motor generators in the Prius, MG1 and MG2. MG2 is the one you would be using in your above scenario, it will propel the car. MG1 is the one used to start the ICE (engine). It spins up the engine then once ready the fuel is injected. Both spin when the car is moving, at various RPMs depending on engine RPM, and vehicle speed. So there is no "Bendix gear" or other mechanical engagement device. Both can also be used to generate power, for example in regenerative braking, though usually it's MG1 that does that.

 

You should look at: Toyota Prius - Power Split Device

From this it can easily be shown how the starting occurs. Set the MG2 RPMs to 1495, since the MG2 is directly connected to the ring gear, and that is connected to the wheels, this means that the car is traveling at 25 MPH. The engine is turning at 0 RPMs and the MG1 is turning 'backwards' at 3887 RPMs.

Now, the Prius wants to start the engine, since the speed of the car shouldn't change, MG2 needs to remain at 1495 RPMs, which means that the MG1 needs to slow to about 250 RPM (still backwards) to bring the engine up to 1000 RPM.

Then the engine ignition occurs, and the car brings it up to an efficient RPM, let's say 1500 RPM, in order to keep a constant speed, the MG2 needs to change speed along with it, to about 1500 RPMs in a 'forward' direction now. Interestingly, the PSD is at this point running in lock step, none of the gears are moving relative to each other.

Play around some more with the flash animation, it is very educational.

 

This link has a great explanation and animations.

Understanding Contents