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I rarely see this happen

Discussion in 'Gen 2 Prius Main Forum' started by Brian K, Apr 17, 2006.

  1. Brian K

    Brian K New Member

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    I've deliberately tried to have this happen after first hearing of it a year ago on this forum. It has happened one other time w/o descending a mountain. My deliberate efforts to force it to happen in "normal" driving all failed. Sure, I could have feathered the brake to achieve green bars before a long downhill grade, but that wasn't how I wanted to do it.

    When we "go into town", we go down a long gradual hill and the speed limit reduces from 55 to 25 and a light (a series of lights actually) is at the bottom of the hill. It's common to see a full SOC after this, but tonight the car went into auto "B" mode. I just happened to catch the lights all green and was able to maximize the charge rate to achieve it. I heard the engine braking and wondered if the sound was coming from the radio, then realized what it was.

    Neat.
     
    #1 Brian K, Apr 17, 2006
  2. Bill Merchant

    Bill Merchant absit invidia

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    What you observed was charge dumping, not "auto 'B' mode".

    B mode is using the ICE to reduce kinetic energy (speed) so you don't go to mechanical braking any faster than necessary. When the battery is fully charged, regen slowing stops and all braking is mechanical.

    When you completely charge your battery (for purists, I mean when the battery icon is green, not the battery at 100% charge) the Prius uses the electric motors to spin up the ICE without fuel to reduce electrical energy and get the battery to an optimum charge level. It will frequently cycle the ICE up and down when you get close to optimal charge since the spin-up may take charge down enough, but chemical hysteresis pushes it back too high.

    It really is the smartest car on the road.
     
    #2 Bill Merchant, Apr 17, 2006
  3. Brian K

    Brian K New Member

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    <div class='quotetop'>QUOTE(Bill Merchant @ Apr 17 2006, 01:54 AM) [snapback]240780[/snapback]</div>
    Bill, I understand what you wrote, but would the motor hold the ICE spinning for maybe 10 seconds? It sure sounded like the compression braking "Jake brake" sound of B mode. Previously I've noticed what you write of, the spinning up of the ICE and back down again multiple times (same location on the road too), but this wasn't that.
     
    #3 Brian K, Apr 21, 2006
  4. efusco

    efusco Moderator Emeritus
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    <div class='quotetop'>QUOTE(Brian K @ Apr 21 2006, 05:02 PM) [snapback]243369[/snapback]</div>


    Yes, it keeps it spinning. Bill's description/explaination is dead on. As long as you keep moving MG1 keeps the ICE spinning to charge dump. I've only seen it a handful of times...and it annoys the hell out of me that there isn't somewhere 'useful' for that charge to go. :angry:
     
    #4 efusco, Apr 21, 2006
  5. hyo silver

    hyo silver Awaaaaay

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    <div class='quotetop'>QUOTE(efusco @ Apr 21 2006, 05:14 PM) [snapback]243377[/snapback]</div>
    Think of it as "free" power. Crank up the heat, or the air conditioning, or the stereo... :)
     
    #5 hyo silver, Apr 21, 2006
  6. Betelgeuse

    Betelgeuse Active Member

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    <div class='quotetop'>QUOTE(Bill Merchant @ Apr 17 2006, 01:54 AM) [snapback]240780[/snapback]</div>
    I don't understand the difference between the two states that you've listed. In "B mode" you say that you're "using the ICE to reduce kinetic energy." How is this working, if not by using the electric motor to spin up the ICE?
     
    #6 Betelgeuse, Apr 21, 2006
  7. Brian K

    Brian K New Member

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    <div class='quotetop'>QUOTE(efusco @ Apr 21 2006, 06:14 PM) [snapback]243377[/snapback]</div>
    Well, OK. You guys know more about the Prius than I do, so I defer. But dang if it doesn't sound like a mild sounding jake brake.

    What makes the compression braking noise?
     
    #7 Brian K, Apr 21, 2006
  8. Bill Merchant

    Bill Merchant absit invidia

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    <div class='quotetop'>QUOTE(Betelgeuse @ Apr 21 2006, 03:48 PM) [snapback]243392[/snapback]</div>
    The ICE being spun makes the compression braking noise. It's braking of you are moving, it's charge dumping if the ICE is spinning and you aren't moving, or moving slowly.
     
    #8 Bill Merchant, Apr 22, 2006
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