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Transaxel braking

Discussion in 'Gen 2 Prius Main Forum' started by PatapscoPete, Jul 13, 2006.

  1. PatapscoPete

    PatapscoPete New Member

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    Here's just the type of question you might expect from a new owner (purchased July 4, 2006, White Package #6 ... maybe I should change my moniker to PatriotPete).

    Does it make sense to use the Transaxel Brake whenever possible to increase regenerative braking? Is the best usage just to slow the vehicle, or does the increased ICE revolutions increase regeneration? If it increases regeneration, does the increase in power recorvery outweigh the wear and tear that increased revs cause to the ICE and trans?
     
    #1 PatapscoPete, Jul 13, 2006
  2. john1701a

    john1701a Prius Guru

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    <div class='quotetop'>QUOTE(PatapscoPete @ Jul 13 2006, 01:03 PM) [snapback]285748[/snapback]</div>
    No, it does exactly the opposite. Having the engine absorb some of the kinetic energy takes away from the potential available for the electric motors. This has been proven too, numerically with a scanner.

    By the way, the "transaxel" is almost always referred to as the PSD (Power Split Device). All motion is directed through that, whether it is engine or motors. But I knew what you meant.
     
    #2 john1701a, Jul 13, 2006
  3. efusco

    efusco Moderator Emeritus
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    It's best to not use it at all. It serves very little useful purpose and will not maximize regeneration, you can do better with your foot on the brake. Plus, it forces the ICE to spin to create drag and that's wasteful.

    It is convenient to use it on very long grades to reduce the amount you have to use the brake, but that's about it.
     
    #3 efusco, Jul 13, 2006
  4. john1701a

    john1701a Prius Guru

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    I've found "B" mode very effective for graceful deceleration on unexpectedly slippery curves. It reduces the risk of putting too much reliance on the brakes.
     
    #4 john1701a, Jul 13, 2006
  5. barbaram

    barbaram Active Member

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    It is also helpful if you discover you need to stop much more quickly than you first anticipated! Use both! :blink:
     
    #5 barbaram, Jul 14, 2006
  6. hobbit

    hobbit Senior Member

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    Possibly too overwhelming for a new owner and probably makes
    reference to many other concepts you have yet to run across, but
    http://techno-fandom.org/~hobbit/cars/b-mode.html is my best effort
    at a FULL rundown on what B mode is, does, doesn't do, etc.
    If you can get through it without falling asleep and then go look
    up every term therein that you don't understand yet, you'll get a
    good prius-education-by-storm out of it!
    .
    _H*
     
    #6 hobbit, Jul 14, 2006
  7. PatapscoPete

    PatapscoPete New Member

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    <div class='quotetop'>QUOTE(hobbit @ Jul 14 2006, 12:07 AM) [snapback]286091[/snapback]</div>
    An excellent discourse. This clears up several issues I had.

    Thanks,
    PPete
     
    #7 PatapscoPete, Jul 14, 2006
  8. kimgh

    kimgh Member

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    <div class='quotetop'>QUOTE(PatapscoPete @ Jul 14 2006, 09:34 AM) [snapback]286240[/snapback]</div>
    I'd like to know how to tell when to shift into "B" on a long downgrade. Immediately? After SOC is all green? Somewhere before that?

    The article hints at an answer, but I don't think it is that clear. I'd be interested in other's experiences, because I'm about to embark on a long trip that will include several mountain passes (Siskyous, Snoqualmie, Owyhee, Donner, Altamont). Any experienced folks? Donner is by far the biggest challenge I would think, so who has taken his Prius over Donner?
     
    #8 kimgh, Jul 14, 2006
  9. hobbit

    hobbit Senior Member

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    Last time I was juggling mountain descents I tried to balance the
    process and use enough "B" early in the game to control speed, and
    basically would bounce back and forth between "D" and "B" as terrain
    demanded. Oh, and I tried to remember to go into EV mode and *empty*
    the SOC before cresting, but that's hard to predict sometimes.
    .
    Basically the battery will hold only so much section of a big hill,
    and where along the path you capture that [and waste the rest]
    really doesn't matter that much. If you can maximize it by starting
    from as low as possible, that's good, but may not be feasible if
    you've got someone screaming up behind you at > 33 mph.
    .
    _H*
     
    #9 hobbit, Jul 14, 2006
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