Automatic B-mode at 84% SOC

[efusco]

Last week while driving the family in hot weather I descended a hill in northern Arkansas that always drives my SOC up...usually into the upper 70% range.

Well, this time the SOC at the top of the hill was quite high already (~63%) and I hit 84% (per CAN-View) before reaching the bottom of the hill....at that point (84%) CAN-View's little status indicator (showing ICE Run, ICE spin, Stealth, EV mode, etc) switched itself to show "B-mode"!

I'd never seen that before and I certainly hadn't hit the B-mode on the shifter...the LCD showed I was still in Drive. The ICE spun and amperage showed -10 amps just as if I were in B-mode. Once I got back down to 83% SOC.

Now, I've certainly seen the ICE spin up before to bleed off excess SOC. And I've seen regeneration decrease or drop out, but I've never seen this all out forced b-mode before.

Just wondering if Ken in Japan or anyone else with advanced monitoring stuff has noted this before.

[ThePackage]

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.

[JimboK]

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.

[efusco]

The battery is a pretty huge thermal mass...and it takes a while to both heat up and cool down. I didn't happen to notice battery temp (though I have it on the same screen as the RPM and stuff I routinely watch).

[JimboK]

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+%.

[efusco]

Yea, there must be multiple factors required to prevent EV...I've had it refuse to engage at times I couldn't understand and other times it worked when many factors seemed against it. SOC may be the only absolute.

[Ichabod]

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.

[efusco]

Originally Posted by Ichabod

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'm not sure, guess we'd have to ask atilla or norm... I suspect it's some specific CAN code that triggers that signal.

[eurosteve]

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?

[Ichabod]

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.