Video: Toyota demonstrates "Safely Stopping Your Toyota Hybrid Vehicle"

Pressing P while moving is effectively the same as shifting into N. The only difference is that the car will beep at you because it couldn't shift into P. Be aware that pressing P at low speed (3 mph or so) *will* shift into Park and you will stop right now.

Under normal operation, the Prius uses MG1 to position the ICE when it shuts off. This is why you will sometimes feel a little gallop when a cold ICE shuts off. If it misses the proper stopping position, MG1 will spin it around and try again.

The ICE is directly attached to the ring planet gear carrier on the PSD. It can be spun by MG1, MG2, the car's momentum, or by it's own power. To remain stationary while MG2 and car go forward, MG1 must spin backward. Removing all power to MG1 will allow it to freewheel, which will keep the ICE from spinning.

Tom

 

OK bear with me, when the ICE is free wheeling (no fuel provided), what physically prevents the MG1 from overspinning if any ? Or the equivalent questio is what keeps the ICE turning ?

 

To prevent MG1 from over-spinning, all it has to do is act as a generator to slow itself down.

If we take an example at 94 mph and the gear is shifted to N, ICE has to be spinning at least 1,050 RPM in order to prevent MG1 from over-spinning (above max 10,000 RPM). To keep the ICE RPM from going lower, all MG1 has to do is create resistance (generate electricity). We are talking about less than 1 hp.

 

The problem occurs when the ICE is *not* turning but the car is going fast. To prevent this situation, MG1 acts as a generator to keep its speed under control. The force from MG1 forces the ICE to spin, although no spark or fuel is applied.

Tom