Quote:
Originally Posted by Daox
I was under the impression that mechanically, drive and neutral are identical. Is that incorrect, or is there some other advantage I don't know about to coasting in neutral?
|
Mechanically, you are correct. The magic happens with MG1 and the planetary gear. It is so different from ordinary transmissions.
In the Toyota hybrid transmissions, MG1 combines the function of clutch as well as variable gear ratios. The way it works is:
- no current flow - MG1 spins without resistance so the engine driven gears have nothing to 'push' against. This is the equivalent of neutral.
- generator mode - by allowing MG1 to work as a generator, it causes a reactive torque against the engine driven gears. With something to push against on the MG1 side, the engine gears can apply torque to the other side, the ring gear, that drives the wheels. The torque ratio is 28% to MG1 and 72% to the ring gear.
- generator mode normal - the power from MG1 races through the inverter and then feeds into MG2 that is on the ring gear side. So 72% of the ICE power flows through the ring gear and 28% slides around via the electrical circuit. Thus no power is lost except for some ohmic heating and normal gear losses.
- energy recirculate mode - at speeds around 25 mph, 40 km/h, MG1 slows down (check the earlier software model) and can no longer generate power and the resistance torque needed. At this point, power is taken from MG2 that is spinning and is fed to MG1 to work as a motor and make the torque needed by the ICE gears. But because of the gearing, this mechanical power combines with the ICE power on the way to MG2 where some is converted to electrical power to drive MG1.
- variable gear ratio - the MG1 torque is computer controlled by the current. By driving more current, the reactive torque looks like a 'taller gear' and the engine can deliver more power. Less MG1 torque looks like a 'smaller gear' so the engine can deliver less power.
Seriously, it takes an entirely different way of thinking to understand this transaxle. But the more I've studied, more I've come to appreciate what an engineering marvel it is.
Bob Wilson