salimshah

I had a strange experience today on my FWD.

I was stopped at an sharp inline 18 degrees and I almost sure that the gas engine shutoff (normal). I wanted to back up, so I put the RX in reverse. As I lifted my foot off the brake the RX started rolling forward ... [expected behavior]. So I did the two pedal action ,,, left foot on the brake and the right on the gas pedal. I did not floor it but with gentle pressure on gas pedal, as I lifted my foot off the brake the RX rolled forward. Gasoline engine did not kick in.

I was in a hurry and I simply put the gear in drive and with the roll I drove forward. Once on a flat area, I out the RX in reverse and with the momentum (and this time gas engine running) I had no problem backing up the same incline.

Any one else experienced this in their 450H?

Salim

Droid13

Reverse is powered electrically only. In Drive the engine can participate in forward motion directly, but in reverse it's all electric motors, which can of course be assisted indirectly by the engine through the generator. While this hasn't happened to me directly, I suspect that on an incline requires quite a bit of power and that a substantial amount of gas pedal pressure would have been required and quickly.

salimshah

Setup the same conditions today. As advised, I pushed the gas pedal more and the electric motor complied.

Salim

vlad_a

That's what the old Priuses did. Newer generations will run the gas engine to assist with reverse movement when needed. MG1 will have to compensate by rotating faster.

Droid13

I'm aware that later gens had higher RPM MG1s which physically allows an engine start while moving backwards, but I don't think that changed the fact that reverse is still 100% electrically driven directly. In forward speeds, MG2 and engine spin in the same direction and resistance of MG1 (acting as generator) will cause some transfer of mechanical power from the engine to MG2 (ie the wheels), typically of course, lots of different forward speed modes, the miracle of Toyota's hybrid drive system.

Reverse is not so miraculous I think...

In reverse the engine and MG2 are spinning in the opposite direction.To cause mechanical power from engine to MG2 in reverse, MG1 would have to act as a motor, spin up high and consume electric power, rather than generate electrical power, to force the mechanical energy of the engine to reverse back through to MG2. With MG1 acting as motor, where would this extra electricity come from? Can't be the engine, MG2 is likely not spinning fast enough to generate electricity (unless going quickly in reverse) so if the battery, then why bother with all the shenanigans, just power MG2 directly from the battery (as the 1st gens did). Alternatively when using MG1 as generator only (creating resistance) this will cause the engine to resist reverse motion. Seems counter-productive, but I believe this is what happens and why I think this is why you'll never hear the engine rev high while in reverse, start yes, maybe idle high, enough to produce some extra power but never produce a lot of torque. This extra electricity along with battery push in reverse while engine pushes forward a little. This works because MG2 has gobs of torque at very low rpms and the engine doesn't.

NateJG

IIRC, In reverse, the ICE spins MG1 generating power to add to that which is already available from the traction battery to MG2/MGR. The MG1's ability to generate is vehicle-speed dependent due to the difference in direction between the carrier, ICE, and MG2 (the faster the vehicle goes in reverse, the less MG1 can contribute).

ukrkoz

You will get nowhere holding brake pedal and pressing gas pedal. Been there, done that. Plenty of very steep inclines here. You got to trust the antiroll feature, release brakes and immediately press accelerator pedal. I know it's counterintuitive but that's how it works.
Also, should not be really rolling. It should roll a skosh and stop. Thing about antiroll is, if you were on the brakes just for a moment, it sort of does not kick in. You have to stop stop. Hold brake for few seconds, so antiroll figures you actually want to stay in place.