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Driving in "B" Mode Regularly

Discussion in 'Prime Main Forum (2017-2022)' started by stevepea, May 25, 2017.

  1. stevepea

    stevepea Senior Member

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    To some in the "just drive the car" camp, this may be a waste of time, but since a lot of Prime drivers try their hardest to get the most from their battery, this is for those who wish to do so...

    Took the Prime out for a long rush-hour freeway commute today, and had a chance to test driving in the "B" mode. Here's what I found, your thoughts and comments welcome. NOTE: this post concerns FLAT area driving, not hilly or mountainous roads (where you'd normally use "B" for a steep downhill grade). I was trying to figure out if "B" could be advantageous for driving in flat areas like a lot of Southern California.

    In a nutshell: "B" can be very advantageous in EV MODE (at any speed), but probably not in HV mode.

    WHEN DRIVING IN EV MODE: (Stop-and-Start as well as Fast)

    (1) Stop-and-Start in EV Mode: Especially with slow traffic and lots of starts and stops, I think "B" mode is by far the best. It really does recharge the battery so much more than "D" (without having to use and wear out the brakes). And while in EV mode, you're very much trying to keep the battery charged as long as possible before it's depleted and HV mode kicks in. "B" seems to be win-win -- it really kept recharging the battery, didn't wear out the brakes, and didn't seem to cause any loss of efficiency no matter how many different screens I looked at comparing B and D. Once you get used to the feel, I'm confident this is the best mode for stop-and-go rush hour traffic when in EV Mode.

    (2) Faster Driving in EV Mode: Because rush-hour commutes often go back and forth between "stop-and-start" areas and faster driving areas (and often back to stop-and-start again), I wanted to see if faster driving in EV "B" mode would cause a loss of efficiency (so the driver doesn't have to go back and forth between "D" and "B"). As long as the car was in EV mode, I wasn't able to see any downside of keeping the car in "B" mode, even when driving faster. That said, if you're driving late at night where you know you're not going to be stopping much, I would just keep it in "D". But if your drive goes back and forth between stop-and-start and faster sections, I think it's okay to just keep it in "B" until the EV range is depleted. I looked at all the monitor screens I could, and switched back and forth between D and B at different speeds and such, and could find no indication that "B" was less efficient in EV MODE even when driving faster (like an old car's "low gear" might be) -- and it had the plus of strong regen when one needed to slow down, without pressing the brake (and if one is in D, you really do have to brake quite a bit to match the regen of B).

    WHEN DRIVING IN HV MODE:
    "B" may not be as good an idea in HV mode. In stop-and-start driving, one would think it's still a great idea (the same way it is in EV mode) but I noticed a problem using "B" in HV mode.

    You know when you're driving in HV mode normally (in D), how, if you look at the graphic showing where the power is coming from and going to, the car will keep alternating back and forth between Gas and EV (even if the battery is depleted, there's still a buffer used for HV driving). So normal HV driving with "D" will alternate back and forth between Gas and EV (like 20 seconds in EV, 20 seconds in gas/recharge, 20 seconds in EV, 20 seconds in gas/recharge, etc).

    That didn't seem to work the same way if you were in "B" instead of "D" (in HV mode). The car only occasionally alternated to EV (in HV-mode-"B"), and stayed a whole lot longer in "gas" mode. As soon as I moved it back to "D" then it would go back to alternating between Gas and EV, but not so much in "B". This would make it a lot less efficient (since the Prime gets its good HV MPG by alternating back and forth between gas and EV). Not to mention that trying to keep the EV battery recharged as much as possible isn't so important in HV mode anyway.

    I should do some more research and see if this was just a fluke today or not, but it did seem that if you were in HV-mode "B" it mostly wanted to stay in gas mode and rarely alternated to EV.

    So my initial findings are: When in EV MODE, I think "B" is better than D for stop-and-go traffic, and the same as D in fast moving traffic (so you don't need to constantly switch back and forth). However in HV MODE it seems that "B" might adversely affect efficiency by keeping the car in "gas" more than alternating between gas/ev.

    I think when I'm doing a rush-hour commute, I'm going to drive regularly in "B" now, until the EV charge depletes.. and when the EV is depleted and the car goes to HV, I'll switch it back to D...

    Would anyone care to test my observations and report back? :)
     
    #1 stevepea, May 25, 2017
    Last edited: May 25, 2017
  2. Insirt

    Insirt Junior Member

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    Screenshot_20170525-233809.png

    I thought "B" was exclusively engine breaking but based on wording from the manual it may be that while in EV mode it just ups the Regen. "...or strong breaking..."

    I'll have to see and maybe compare the noise and feel in EV vs. HV modes to see if it seems like the engine is turning in both or just the MG in EV mode.

    Posted via the PriusChat mobile app.
     
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  3. Mendel Leisk

    Mendel Leisk Senior Member

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    I've heard B is somewhat different in plug-in version??

    Other'n that, I would reserve B for mountain descents.
     
  4. I'mJp

    I'mJp Senior Member

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    cruise control works even better on descents. If the result is no speed change, the brake lights do not turn on in cruise, and you get all the re-gen.
     
  5. stevepea

    stevepea Senior Member

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    I don't know about other Prius models, but on the Prime, as it says in the manual, the "B" pretty much is just strong regen braking when you release the accelerator pedal. It uses the example of a downhill grade because that's a good example of when it would be good to use -- but my point is that it doesn't just have to be on downhill grades. The only "negatives" (as mentioned in the manual) are a tiny bit more noise (caused by the regenerative braking -- though it's less noise than what you get by applying the brakes!) and "loss of MPG" -- which according to my observations occur only when in HV Mode (because it keeps the gas on longer), NOT in EV mode, where I observed NO loss of efficiency at all.

    So what I've been able to observe is NO negatives when using "B" in EV Mode (if driving fast, no difference one way or the other, if doing start-and-stop rush hour driving, it really kept the battery charged and extended the EV range more than braking in "D" did, and didn't wear out the brakes).

    So unless it's an all-freeway trip where there's no traffic, I'm going to start driving in "B" when in EV Mode -- and when the battery depletes and goes into HV Mode, will then switch to "D" for HV Mode.

    It could just be my imagination, but in stop-and-go traffic, "B" really did seem to constantly extend the miles left on the EV charge more than "D-with-braking" did, with the added plus of not wearing out the brakes as much over time.

    As I don't do a daily rush-hour commute, I'd love if others could test my observations and report back! :)
     
  6. Prius from Dad

    Prius from Dad Senior Member

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    Ill try it next week, my AM commute is mostly, if not all, EV. I have a good idea of what range I should expect in EV only, so I can compare it to B mode EV. I'll let you know on Friday. (y):)
     
    #6 Prius from Dad, May 26, 2017
    Last edited: May 26, 2017
  7. CharlesH

    CharlesH CA HOV Decal #5 on former PiP

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    Taking your foot off the brake pedal in D mode and gently applying the brakes is exactly equivalent to B mode, at least in EV mode. No friction braking at all. In HV mode, B can trigger engine braking, which is just tossing the energy out the window. And I cannot see how B mode would be so great in city driving, since there are losses when doing regeneration, so taking your foot off the throttle would result in more losses over the lighter regeneration in D mode; it would be like lightly applying the brake every time you took your foot off the throttle, whether you needed to slow down or not. Yes, there is energy being put into the battery by regeneration, but you don't get out as much as you put it.
     
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  8. Prius from Dad

    Prius from Dad Senior Member

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    Experiments never (almost never) hurt anyone, besides they're fun. ;)
     
    #8 Prius from Dad, May 26, 2017
    Last edited: May 26, 2017
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  9. Trollbait

    Trollbait It's a D&D thing

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    Most plug ins have a way of increasing the amount of regen braking. Some have deceleration rates high enough that the brake lights are triggered, and may even bring the car to a complete stop.

    The advantage is in not having to move your from the accelerator to the brake pedal in order to start bringing the car to a stop. In city conditions, the time saved could be the difference between being in a crash or not. Some people just prefer one pedal driving too.

    Personally, I'd have to see if B mode effected the ability of getting into a glide, and if its regen braking came on too fast before deciding on using it normally.
     
  10. Krzysiek_KTA

    Krzysiek_KTA Active Member

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    My driving using "B" in EV mode does not prevent me from gliding (coasting) to eliminate/minimize re-gen. It works exactly same as in "D" mode. Actually the only inconvenience of "B" mode is that DRCC is disabled.
    I found DRCC very convenient in Stop&go traffic with prolonged stops. If there is a stopped vehicle in front engaging DRCC ( lever up = resume) will allow me to take my foot off the brake which is very comfortable (at least for me)

    just my 5 cents

    cheers

    Kris
     
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  11. Mendel Leisk

    Mendel Leisk Senior Member

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    I downloaded a pdf of the Prius Prime Owner's Manual, and I'm not seeing any of your points. Again, I would just leave it in D, reserve B mode for mountain descents.

    upload_2017-5-27_7-37-16.png
     
    #11 Mendel Leisk, May 27, 2017
    Last edited: May 27, 2017
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  12. Trollbait

    Trollbait It's a D&D thing

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    That chart was likely just cut & pasted from the Prius manual.
    While in a Prime's EV mode, nobody has reported the system spinning up the ICE when B is engaged. Without that spinning, increased regen becomes the only possible option for the car to increase the selected gear's braking ability.
     
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  13. Mendel Leisk

    Mendel Leisk Senior Member

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    Ok I gotcha: B might behave differently in the Prime, that I have heard here. And my snapshot from the Prime manual, may well just be what Toyota cut-and-paste from the regular Prius manual when creating the Prime manual.

    A lot of the uncertainty and debate can be laid on Toyo's doorstop, their instruction is extremely terse. Maybe they don't know how and when to use it either? Or at least at the manual writing level.
     
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  14. giora

    giora Senior Member

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    In EV mode, B position is same as lightly pressing the brake pedal in D position - same regeneration for the required deceleration (and no friction brake).
    I think that with the Prime - B position does not activate brake lights (worth checking) and if so it is a hazard in stop-and-go driving.
    Using B position constantly in stop-and-go may develop to "less efficient" driving habit of late letting off the throttle pedal.
    I am using B (with my PiP) only when going down a mountain where B suppresses acceleration.
    I don't think so, AFAIK the liftback manual does not have the statement "...or strong braking..." which is unique to the plug-ins being in EV mode.
     
    #14 giora, May 27, 2017
    Last edited: May 27, 2017
  15. alexcue

    alexcue Active Member

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    My scenario is such. Normal D mode but downhill after a cold start and full recharge. I've had the ICE spin up several times now. The EV mode WILL turn off automatically, full battery mind you. ( the indicator shifts from EV to empty car symbol) To burn off the excess charge coming in from braking down the long hill. Have no choice as car will just pickup too much speed.

    I'll experiment with B next time but it makes no sense that it won't spin up anyway.
     
  16. giora

    giora Senior Member

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    Is it practical for you to partial charge and letting the long downhill do the rest?
     
  17. CharlesH

    CharlesH CA HOV Decal #5 on former PiP

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    If the battery is full, then engine braking is the only choice. And when the engine is spun for any purpose, it has to go through its warmup cycle.
     
  18. alexcue

    alexcue Active Member

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    Not really...

    That's been my fear, waste of energy. I guess my ECO score is gonna get even worse I'm better off just stepping on gas more to start to lower the battery a bit more.

    But anyway, back to topic, I'll let others test the B mode in EV city (flats). I suspect though that there will be less glide taking place.
     
  19. Trollbait

    Trollbait It's a D&D thing

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    No brake lights being a hazard determination requires knowing the current deceleration rate. Other plug ins that regen braking rate disconnected from the brake pedal, have the brake lights activate based upon what that rate is. The rate at which the brake light goes from off to on could be dictated by regulation.

    The braking of B 'gear' is mild. It is not strong enough that drivers behind the car need additional warning of its slowing.
     
  20. giora

    giora Senior Member

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    What about the other points raised in the post you elected to quote in its entirety?