Lexi450

Thanks for the info!!

riredale

I suspect the traction battery was too full, and the computer had MG1 spin the V6 engine (with the fuel off) to burn off the excess charge. But it probably didn't spin the engine long enough, and as soon as it shut things down and measured the battery voltage again, it was still too high.

I'd always wondered where the system put the excess electrical energy (big resistor bank, perhaps?) for those conditions where there was TOO MUCH, until someone mentioned the computer had the option of spinning the engine without turning on the fuel. After all, an ICE with a closed throttle is essentially just a great big vacuum pump, and as such it requires a lot of energy to spin it.

I've read that the battery indicator F and E conditions actually correspond to 80% and 40% of theoretical capacity. They set the parameters after doing lots of research into battery longevity. So if a long downhill with lots of brake regeneration would result in overtopping the 80% mark the computer bleeds off the surplus by spinning the engine. Pretty clever.

vlad_a

You are correct, it stops charging battery and initiates engine-braking. It could also waste excess energy by having MG1 fight against MG2 and, of course, having ICE stuck right in the middle.
It is really cool how they set it up. On our road trips through mountains, RX goes into engine-braking mode when going downhill automatically and you can hear ICE spinning at higher RPMs.
Should I even tap the accelerator, it disengages it immediately.

MellonC00

I can confirm that this is the case. when I top off the battery even after the indicator is full by, say, mildly breaking on a downhill for a bit, my acceleration times for 0 to 60 is better.

vlad_a

I never noticed any acceleration variation based on battery levels in both Prius and the RXh, unless the battery was depleted.