Automatic B-mode at 84% SOC

I have Scan.... and not CAN... I can tell you that most of the time while I'm desending a pretty steep hill with my foot off the accelerator, the RPM's increase just as if I was in "B" mode but the indicator still shows "D". This appears to be a self induced engine breaking (or what ever you call it) which keeps my MPH down. I don't know if this is what you are refering to but as soon as touch the accelerator pedal, the RPM's decrease. I hope this is a normal function.

 

Yep, I've seen it several times descending the Appalachians, the most recent just yesterday on a drive on the Blue Ridge Parkway. The highest I've seen SOC is 82%, but CV shows full-fledged "B" mode with an ICE RPM close to 3000 at times.

Another thing you'll probably find if you check for it is a hot hybrid battery. Last year on the way to Hybridfest it got up to 120F at the bottom of a descent; yesterday it peaked at 116F. Another interesting piece to that is how slowly it cools. I estimate that 15-20 minutes (maybe longer) later yesterday, long after the terrain had flattened out, it was still at 111F -- with the AC running. I had my data capture going, so hopefully within the next two or three days I'll have time to pull some charts together and post them in my charts thread.

 

I just remembered another interesting observation. I had a passenger during my mountain drive Sunday, and I was explaining to him what all the CV numbers meant. I pointed out the battery temperature and explained to him that EV mode (previously described to him) would not activate. I tried to demonstrate it -- and EV mode activated! So apparently high battery temperature is not an absolute criterion for "EV deny," and instead the car's desire to reduce SOC is a greater priority at 80+%.

 

Interesting to know... I wonder one thing though: Does the CAN-bus send out a specific signal that says "hey, the car's in B-mode" or does CAN-View interpret the various data to mean that it's most likely in B-mode? I know it's a subtle difference, and probably not even a meaningful one if the car is behaving exactly as if it were in B-mode, but I'm still curious.

 

I drive down a long, downhill section every day and I routinely get all green bars. I read somewhere on this forum that the regen
Braking cuts out at that
point and the regular brakes kick in. The advice was to go downhill in B to avoid this. Is this true? Based on this thread maybe the Prius automatically goes into B saving me from having to manually do this?

 

That's somewhat true Eurosteve, but your reading is missing one thing: The recommendation is to put your car into B-mode intentionally early on a long hill that you know will max out the SoC. That way you'll regen more slowly the whole time and maybe not max out SoC at the same time. You probably don't heat up the battery quite so much either when you do it that way (speculation).

If you don't do B-mode early then your SoC will max out, and the car will do various things (including spin the engine) to waste energy, and will also avoid regen braking.

 

So it's true... I've been wearing out my brakes all these months during the last mile of my ride home when I have all green bars. Is there
any downside to running in B for 3+ miles each day?

 

interesting on the B mode. refresh my memory, exactly what changes happen when B mode is enabled. i know about higher regen, but the engine changes sound as well so something has to be going on as well...

i wonder, if car conditions can be manually duplicated by the driver with slight braking in certain conditions that might make CANVIEW think the car was in B mode?

 

oic... the negative flow would be hard to reproduce... what causes the engine to change pitch?? its sounds like downshifting?

 

OK, here's a question I've been pondering recently. Is there any fuel flow? I thought I heard someone say there wasn't, but I don't have time to search for that now. Hobbit's article on B mode describes the engine as "spinning," implying (to me anyway) that there is no fuel flow. I didn't think to look at fuel flow or injector timing during my descent Sunday, though I'll have that in my data capture, assuming it is reliable.

 

on fuel flow, i seem to remember that there was some but what you would see when idling...like .1 gph...or something small like that

 

I saw this any number of times in the process of coming from
the west coast to Denver, where I am now, up and down significant
rises and falls. "D" mode starts behaving like normal "B" after
SOC reaches 80+, and when you're at that level then "B" thrashes
the engine much harder than when at a more normal SOC. I generally
quit using "B" after topping out the pack, and stay in "D" to
let the engine still bleed off some energy but not quite as
fast, as I carefully modulate the brakes to take up the rest
of it. Oh, and no fuel is injected during any of this, at least
until you start pressing the go-pedal again whereupon you'll
get into a killer 40-amps-pushing-the-car warp-stealth mode for
a while until the SOC gets back down.
.
Being able to manage this and cut your losses is key to maintaining
good MPG in the mountains.
.
_H*

 

A lot of Japanese Prius drivers experienced such "automatic B-mode" at 80+ SOC.

When I saw 82.5% SOC, the battery temperature was 50C and I could not activate the EV switch.
The "EV denied mode" was continued even the SOC down to 60's.
I tried many times to activate the EV switch, then I finally could do it when the battery temperature became 45C.

We see no fuel usage during any B-mode.

Ken@Japan