B drive

Discussion in 'Prime Main Forum (2017-Current)' started by Northerner, Aug 11, 2020.

  1. Northerner

    Northerner Member

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    I tested the B drive going down a hill and posted in another thread that after I shifted into it (on the fly) that the car slowed to a near stop before I shifted back out of it to roll down hill faster. The response received was that it needs to be a pretty steep grade to leave your foot off the gas and keep rolling and recharging the battery at the same time. However, for hills with lesser slopes, pressing the gas pedal does not, at first, burn any gas but just slows the rate at which the battery gets recharged. This is a paraphrased interpretation.
    This possibly incorrect understanding led me to trying to go down a hill in B drive again, this time ready to put my foot on the gas and also (importantly) watching the HUD display.
    I was overwhelmed by what came up (TMI!). What I think I saw was that when I put my foot on the gas pedal I could exceed the neutral energy-use position fairly quickly. However, when I did (in B drive) it appeared I was burning battery power rather than burning actual gas.
    Did I read it correvctly?
    In other words, when going down a steep hill, does B-drive have a default that requires it to use up the battery’s energy first - and then use gas only when the battery is depleted?
     
    #1 Northerner, Aug 11, 2020
    Last edited: Aug 11, 2020
  2. bisco

    bisco cookie crumbler

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    i think you need a scan gauge or the like
     
  3. fuzzy1

    fuzzy1 Senior Member

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    If the hill really is steep, it shouldn't use any battery power or gas at all. It should be feeding electric energy back into the battery.

    Just in case we have different definitions of steep, try another test the next time you are on that hill. Going downhill at normal travel speed, shift into Neutral for a bit, then watch your speed.

    If it is steep, then gravity will pull it to go faster. Switching back to B mode, with just the right gas pedal touch to maintain speed (or D mode with cruise control), it should be charging the battery, not depleting it.

    If it is not steep, then the car will gradually slow down. In this case, it will require a shift back to D (or B) and some gasoline or battery power to maintain constant speed. And you'll need to adjust your definition of "steep".
     
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  4. Tideland Prius

    Tideland Prius Moderator of the North
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    If the accelerator is twitchy, then try a ECO mode. Lightly pressing the accelerator pedal in B has the same effect as in D - it reduces regeneration for gliding and of course as you continue to depress, it’ll propel the car forward.

    Note that on steeper hills, the engine will eventually come on in B mode to vacuum pump, especially if you’re gaining speed - the computer thinks there’s not enough to slow you down so it turns on the engine to provide more braking power.
     
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  5. jerrymildred

    jerrymildred Senior Member

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    Exactly! If D will maintain the speed, B will slow you too much. I haven't used B since May last year when we were in Colorado. And then, not very much. At the risk of over-simplifying things, you basically use B anywhere that would necessitate downshifting a manual transmission.
     
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  6. sam spade 2

    sam spade 2 Senior Member

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    Why did you NOT put this at the end of the other thread ????
    Scattering discussions like this all over the place in fragmented threads just creates a mess.
     
  7. Northerner

    Northerner Member

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    I had two thoughts when I started a new thread. One was that a title like Prime vs CRV wasn’t giving the B drive discussion its due credit and part was because of my confusion over what the HUD display is telling me when I go down a hill in B drive - or in any other mode, for that matter.
    It appears we can watch that display while coasting down a hill and know instantly what is happening with the battery (quantitatively?) as we press the brake and accelerator.
    I have long since decided to drive the Prime and not the CRV so the other title no longer had a connection to this subject.
     
    #7 Northerner, Aug 16, 2020
    Last edited: Aug 16, 2020
  8. Austin Longenecker

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    You don't have to listen to that guy, he trys his absolute hardest to be wrong. Posting a new thread for a new topic was the right choice.

    I use B occasionally when going down steeper hills, but here in Minnesota, only a few locations in the bluffs has steep enough hills for it to be very beneficial. In town I use it to slow down. Never had the chance to test it in the mountains.
     
  9. jerrymildred

    jerrymildred Senior Member

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    You must be referring to the only person I've ever ignored on any forum. He does get things right sometimes, but he seems to make everything an attack. The less he knows, the more belligerent he becomes. The phrase "Hmmm. I didn't know that." isn't in his vocabulary.
     
  10. sam spade 2

    sam spade 2 Senior Member

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    It is not nice to tell lies, Jerry.
     
  11. fuzzy1

    fuzzy1 Senior Member

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    Q.E.D.
     
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  12. Austin Longenecker

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  13. alexcue

    alexcue Active Member

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    I used B in my last regular Prius, but to be honest, I've never even used it (forgot it was there) on my Prime.
     
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