Forgive me if this is a stupid question, my Prius is on order. I've read about how the Hybrid Synergy drive works, and the PSD, and don't understand the suggestion to put the Prius into Neutral to stop SUA (Sudden Unintended Acceleration). My understanding is that the Prius transmission has no clutch, and there is just one always engaged gear (a planetary set). So how can you put that into Neutral? I understand on the Prius Neutral is just a command to the ECU to run MG1 in a contrary manner to prevent the ICE from making the car move. Is there actually a Neutral?
The HSD system goes into neutral by "programming" the motor/generators to rotate COUNTER to the ICE, if the ICE is running. The HSD drive system, ICE, MG1, MG2, is NEVER mechanically "uncoupled" from the drive wheels.
The ICE is not directly pushing the wheels, resistance from MG1 forces Engine power to the wheels. (In heretical mode, MG1 is pushing through the engine) If MG1 and MG2 are not producing or consuming power, the ICE has nothing to push against, so it turns freely. I use this visual aid when text is not enough A simulation of Prius's Planetary Gear You can push up the red lever alone and the wheels never turn. There is no Neutral in the sense of the Engine rotation not rotating the PSD, only in the sense of not rotating the wheels.
In the simplest case, if you remove all power from the motor-generators (MG1 & MG2), all the engine (ICE) can do is spin MG1 as a freewheel. Shut off the electricity to the MGs, and everything stops. Tom
