Downhill behavior

my guess would be your car would be in overcharge mode.

the battery has reached its maximum SOC and the regenerator is still trying to send power to it. so the battery attempts to "burn off" some charge by spinning up the engine (w/o) fuel.

 

You might want to try using the battery prior to reaching the top of that hill in order to make room for the downhill charge. If you can coax a little EV time out of the car before the downhill, you might give a small boost to your mileage. If that isn't practical then, of course, it's nothing to worry about.

 

Hmmm. If I'm understanding this....

I'm planning on ascending Mt Washington in early May. On the descent (5000') it doesn't matter if I use "B" or not? As soon as I fully charge the battery I'll be in "B" anyway? A fully charged battery should happen pretty quickly on the descent, certainly in no more than 1/2 mile no matter what state the battery is in at the peak.

I won't be descending at high mph; figure 15-25 mph absolutely tops, it's pretty steep. Would it be better to use "B" as needed (or continually)before fully charging the battery? My understanding tells me that "B" uses regenerative braking under a certain mph anyway.

I guess I'm asking what is the best way to descend a steep 5000'.

TIA

 

Pretty much, yep. That's a good way to describe it.

When you reach maximum SOC and are still heading downhill, the Prius enters a sort of "super B" mode - the engine is louder and (presumably) spinning at higher RPM. This is absolutely normal, if a bit unsettling to the Prius neophyte.

 

It's simple: if you find yourself riding the brake on the way down, put it in "B". Remember to put it back in "D" when you get to the bottom or your fuel economy may suffer.

 

The cruise control will not work if you leave it in B mode.

 

It seems logical that in B mode, since the engine now is "engaged," more fuel would be consumed than when riding the brake downhill.

 

No, the engine can turn without fuel, that's the point of engine braking vs engine accelerating. When a conventional car is engine braking, it is idling, but also being pushed to turn faster by the momentum of the car through the gears. You could also turn the conventional car engine off, but then you lose power brakes and power steering that need the engine power, unless the engine braking turns the engine fast enough to run the power steering pump and provide vacuume for the brake booster.