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Stealth at higher speed

Discussion in 'Gen 2 Prius Technical Discussion' started by ScottY, Jun 21, 2006.

  1. ScottY

    ScottY New Member

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    I've noticed this for a while now. When the speed is between ~35 to 41mph, lift my feet off the gas pedal, the car will go into stealth mode almost all the time. But when my speed is lower than 30mph, this won't happen. If my speed starts out below 30mph, ICE running. ICE won’t stop till couple of seconds after the car completely stop. From CAN-View, I know the ICE is warmed up already at that time (around 190 degrees F).

    Anybody know why it is easier to get in stealth mode at higher speeds?
     
    #1 ScottY, Jun 21, 2006
  2. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    I always assumed that it's due to inertia. At slower speeds, you have to work to move the weight. At higher speeds, however, since the weight is already moving, it's easier to just keep it moving. I always figured that around 35mph was the tipping-point.
     
    #2 TonyPSchaefer, Jun 21, 2006
  3. efusco

    efusco Moderator Emeritus
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    The algorythm clearly prefers to allow immediate ICE off stealth b/w 35-41, it can be very difficult b/w 30&35, but will under some conditions. The next cut-off seems to be speeds below 20mph where it usually will go into stealth, but again, not always.

    I intentionally keep my speed at 35mph or even intentionally accelerate to 35 when normally i'd have only gone to 33 or so just to make the transition to stealth easier. The advantage of doing that over using the EV button is that it will stay in stealth at speeds over 34mph whereas with EV the ICE will spin up briefly until you exceed 35 again.
     
    #3 efusco, Jun 21, 2006
  4. ScottY

    ScottY New Member

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    <div class='quotetop'>QUOTE(efusco @ Jun 21 2006, 01:57 PM) [snapback]274747[/snapback]</div>
    yeah, that's what I do sometimes. Accelerate over 35mph then stealth~ B)
     
    #4 ScottY, Jun 21, 2006
  5. sub3marathonman

    sub3marathonman Active Member

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    <div class='quotetop'>QUOTE(efusco @ Jun 21 2006, 01:57 PM) [snapback]274747[/snapback]</div>
    I guess it could be too that the people programming figured if you wanted electric mode under 35 mph you would be using the EV switch.
     
    #5 sub3marathonman, Jun 21, 2006
  6. efusco

    efusco Moderator Emeritus
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    <div class='quotetop'>QUOTE(sub3marathonman @ Jun 21 2006, 02:14 PM) [snapback]274788[/snapback]</div>
    Maybe, my thought was that that was considered more of an 'in between' speed where they expect you'll be accelerating to a higher speed and by keeping the ICE spinning it's 'ready to go' when you touch the accelerator.



    But that's purely a guess....it may have something to do with the physics of the system or ideal MG1 RPM rate or something like that...I just can't say with certainty.
     
    #6 efusco, Jun 21, 2006
  7. ScottY

    ScottY New Member

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    Seems like everything is guessing at this point. Anybody has something solid on this topic? :unsure: Where are the Prius gurus?
     
    #7 ScottY, Jun 21, 2006
  8. efusco

    efusco Moderator Emeritus
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    <div class='quotetop'>QUOTE(ScottY @ Jun 21 2006, 03:14 PM) [snapback]274819[/snapback]</div>
    the Prius "gurus" (which I'm typically considered one of) have nothing but guesses. There's no way to know/test without asking a programmer...this is the kind of information that is secret and can only be infered by observation.
     
    #8 efusco, Jun 21, 2006
  9. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    MMMmmmm Prius gyros
    [​IMG]
     
    #9 TonyPSchaefer, Jun 21, 2006
  10. donee

    donee New Member

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    Hi All,

    Yes, the 35 to 41 mph stealth ease was also observed here. I learned to do it in 25 F weather, and at that temp, at the end of my commute, this was the only time I could get the car to drop into stealth! With warmer weather the ease and range has expanded.

    I think it might have something to do with tire friction. I have yet to find any reference on this. I remember from casual reading in the 70's that rolling resistance fell linearly with speed, as aerodynamic drag increased with the square of speed. If this is so, depending on the max rolling resistance and min rolling resistance over the speed range of the vehicle, and the aerodynamic force curve, there would be a speed where there is a propulsion force minima.

    The rolling resistance of tires might be related to the centrifugal lift that the heavy tire circumference would exert. Ever see drag racers go full throttle? The large diameter wheels lift the car. I think the same thing might be happening with road cars. The more round the tire (at the higher speed) is the higher the car will be, and the less side-wall flex occurs in the tire. And this results in less rolling resistance.

    Does anybody have any real references on tire rolling resistance?
     
    #10 donee, Jun 21, 2006
  11. hobbit

    hobbit Senior Member

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    It's called "stage 3b". Go read the "five stages" document, with
    the caveat that none of the "gurus" necessarily know *why* the system
    was designed that way. Having to find a long enough stop to reach
    stage 4 is annoying, but if you know how to play the "over 34" game
    in the meantime [or force EV mode if you have to], you can work
    around it.
    .
    _H*
     
    #11 hobbit, Jun 21, 2006
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