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Driving in "B" Mode Regularly

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

  1. Lee Jay

    Lee Jay Senior Member

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    If you are regenerating (from going down a hill) and the battery is full, there's no place to put the energy except into engine losses. So it fires up the engine and spins it for engine braking.
     
  2. Krzysiek_KTA

    Krzysiek_KTA Active Member

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    I use "B" quite often in EV mode, but decided also to try to find out how it behaves in HV mode and... if the Traction baterry is not full "B" mode behaves exactly same as in EV mode - just applies much stronger re-gen. :)

    So it looks like the Prime manual is missing that. The description looks like copy paste from Gen4(?)
    just my 5 cents to contribute to this knowledgeable forum :)
     
  3. alexcue

    alexcue Active Member

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    You are missing the part about potentially over charging the battery beyond its safe zone. The ICE kicks on to burn off excess electricity being generated.
     
  4. Krzysiek_KTA

    Krzysiek_KTA Active Member

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    You are right. That's why I noted "if the traction battery is not full".
    But I suspect the full in that case might mean 80% - same limit as for CHG mode. Haven't checked it out though.
     
    #184 Krzysiek_KTA, Aug 5, 2017
    Last edited: Aug 5, 2017
  5. Lee Jay

    Lee Jay Senior Member

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    My experience is exactly the opposite. In Hv mode it cranks up engine braking no matter how much room is left in the battery. In Ev mode it will charge to just a little beyond 100%.
     
  6. stevepea

    stevepea Senior Member

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    Sorry I haven't read all of the previous posts, just the last couple, so let me comment on those. I continue to use "B" mode when in EV rush hour traffic (slow, start/stop) with very good results, but the one thing you have to watch for, is to remember to switch back to "D" once your EV range runs out. A couple times I've forgotten for a bit, and did see the MPG suffer until I remembered to switch it back to "D" after the EV has run out.

    As far as "over charging" the traction battery: won't happen, unless one has an unusual very downhill drive right from the beginning (a possibility of course, but not the norm for most people -- can't remember Alex, if you're the person who does have such a drive -- but that's not normally the case for most people), for unless you have such a big downhill grade right near the beginning, you'll always still use more battery than you replenish, so no need to worry about overcharging. There will always be exceptions (good to bring it up just in case), but most people's rush hour drives are usually pretty flat, or only slightly hilly at most. Unless there's a large downhill grade right at the beginning and your battery is fully charged, you'll never have this problem (and if so, that's a different problem in its own right that you need to think about even when you're in "D", for even though "D" won't do it as fast, "D" can still present a problem in such an unusual situation).

    As far as doing "B" in HV mode, I've personally found it not to be as efficient -- the "ICE then temporary EV" cycle hardly wants to go to "temporary EV" (especially if you don't lift your foot up off the pedal) worsening MPG, and the engine does feel draggy. While I find it beneficial (and use it all the time now) in start-stop/city/rush-hour EV Mode driving, I found the opposite when in HV Mode. (Not to mention that if you do it while in EV Mode, that little bit of extra is helping extend the EV Battery's range before it runs out, but when in HV Mode, if the EV mode is depleted, it won't give enough extra to let you turn on EV Mode again and the MPG gets worse because it doesn't want to switch to "temporary EV" mode in HV like it would if you were in "D"). Just my observations..
     
    #186 stevepea, Aug 5, 2017
    Last edited: Aug 5, 2017
  7. Lee Jay

    Lee Jay Senior Member

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    Every time I leave the house to go to work I have a small down-hill. Interestingly, getting out of my neighborhood and getting to the bottom of the hill often results is more reported range than I had when I left. For example, if it says 28.4 miles when I get into the car, it often says 28.6 miles when I get to the bottom of the hill.

    At work, I have a really large hill (1.4 miles at 7%) only 2 miles after I leave if I go a certain direction. That hill has caused the engine to trip on several times, and not only when the battery was full (it's tripped on at 90% too). I have a suspicion that B-mode does this. The last time I took that hill, I used D-mode and pedal braking instead and the engine didn't trip on the entire way despite being right at 100% full on the battery.
     
  8. Krzysiek_KTA

    Krzysiek_KTA Active Member

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    I think my experience is not as extensive. I just tested B mode while HV driving and observed the energy monitor while taking foot of the acceleration pedal and noticed higher re-gen flow into the battery. I might have missed the rev up of the ICE since those were only short tests on flat Houston roads, not the long downhills.
     
  9. stevepea

    stevepea Senior Member

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    That's the worst scenario for a plug-in (starting going downhill, and ending going uphill). You could always move from Colorado to Death Valley, CA (which is below sea level) so you have the opposite commute. Your EV Range should improve, if the battery (and rest of the car) doesn't melt first...
     
  10. Lee Jay

    Lee Jay Senior Member

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    It's not for me since my downhill is short and the engine never starts rolling down even when I start at 100% charge.
     
  11. alexcue

    alexcue Active Member

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    Yeah it's me.... I still suffer from it when going the back roads to my daughter's. Even if I don't turn on B mode it'll still turn on the ICE. What's worse is there's no avoiding having to hit the brakes because this car just picks up so much speed on its own. I've just learned to live with it.
    When I'm coming home from work before the uphills start I do use B mode in the afternoon traffic. I do seem to regenerate more quickly. Once the hills start and the speed picks up I have to remember to move it back to D and into HV.
     
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  12. CharlesH

    CharlesH CA HOV Decal #5 on former PiP

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    Hitting the brake pedal does not necessarily result in using the friction brakes; it will use regeneration if possible to slow you down. On big downhills, I just use the cruise control to hold the speed, and let the system apply the exact needed amount of regeneration. That is one of the nice thing about cruise control and hybrids: it can keep you from going to fast as well as keep you from going to slow.
     
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  13. GT4Prius

    GT4Prius Active Member

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    ICE comes on if traction battery is full when braking on long descents whether using B mode or not.

    What would you expect the car to do on a descent?

    It either speeds up or otherwise has to do something with the energy of the car's motion in order to slow it down. That energy has to go somewhere.

    That means either regen braking if there's space in the battery, engine braking if not, or friction braking creating heat which risks brake fade.

    Even Priuses are subject to the laws of physics.

    Posted via the PriusChat mobile app.
     
  14. Trollbait

    Trollbait It's a D&D thing

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    I only clicked once
     
  15. Trollbait

    Trollbait It's a D&D thing

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    ugh
    My post was posted four times. I start cleaning up the extras, and the two that still have my intended content vanish.
     
  16. Joel Berman

    Joel Berman Junior Member

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    Steve
    I think you’re right. I tried B mode in highway traffic yesterday while in EV mode and the battery range stayed the same over a mile or two. I also didn’t feel any drag while driving like you would in low on a regular car.

    I still don’t see any real difference between EV and EV Auto mode and wondering why they devoted a whole button for EV Auto? I’ll keep testing B mode but I think it’s a great tip so far. Thanks.
     
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  17. priuscatprimeguy

    priuscatprimeguy Senior Member

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    In EV Auto ICE will kick in when you accelerate briskly weareas when in just EV ( the default setting when car is put in READY) ICE will not kick in
     
  18. stevepea

    stevepea Senior Member

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    I continue to use "B" all the time when in EV mode -- but if you do so, you just have to remember to switch it back to "D" as soon as you go back to HV mode (like when the EV range runs out, or you put it to HV manually).

    Note that you can't go from "P" to "B", you have to first go to "D" for a second, then put it to "B"... and cruise control won't engage if in "B". But unless I want to use cruise control in EV mode, I always put it in "B" when in EV mode... and just remember to put it back in "D" when the car goes back to HV mode. A little bit of extra work (remembering) but I find it worth it from what I see (and like the feel of B better than using more brake pedal), otherwise I wouldn't bother. Everyone's different though :)
     
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  19. rsl360

    rsl360 Junior Member

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    Is it just me, or is anyone else petrified of accidently putting the car in reverse when trying to get it out of B mode? I do not find that shifter intuitive, and it seems "backwards" to me. Has anyone found out if reverse is locked out over a certain speed?
     
  20. Lee Jay

    Lee Jay Senior Member

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    You can't put it into reverse at any significant speed.
     
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  21. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Ahhh! The forbidden experiment.

    April 1st, take the biggest Prius skeptic you can find for a test drive. Then at say 30+ mph say "Watch this!" and shift in "R".

    Bob Wilson
     
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