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Cruise control is an under-damped control system and is annoying

Discussion in 'Gen 4 Prius Main Forum' started by nategold, Apr 3, 2016.

  1. nategold

    nategold Member

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    An under-damped system means that if there is a stimulus (like you have set the cruise control to 65 and at speed 55 you turn on cruise control) it approaches its final value (65) and does not overshoot. You would not want it to go to 67, back to 64, then up to 65. That would be an over-damped system.

    But the Prius is way under-damped so that if you come down a hill, at the bottom it will go to 64 and then on an uphill will either never get back to 65 or else it takes a long time. This is totally annoying. The only solution I have found it to set it to 66. Most of the time it will be at 65 and occasionally at 66. If the terrain was totally flat I might be able to set it to 65, but here in Massachusetts it is hilly.
     
    #1 nategold, Apr 3, 2016
  2. bisco

    bisco cookie crumbler

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    agreed. i don't know if it's a symptom of the hsd, but i've found that none of the toyota hybrids hold the speed well in hilly terrain.
     
    #2 bisco, Apr 3, 2016
  3. David Beale

    David Beale Senior Member

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    Uh, I think you have have it backwards. It's overdamped. Underdamped systems oscillate over and under the set speed, like my FJ Cruiser. "Damping" prevents fast responses to input.

    Standard feedback system, depending on gain and delay (or damping). You have to balance the two together.

    For a car, overdamped is good. You won't get a ticket. ;)
     
    #3 David Beale, Apr 3, 2016
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  4. I'mJp

    I'mJp Senior Member

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    Use your foot on the accelerator. The good news is that when you take your foot off, it does not use dynamic braking to slow back down.
     
    #4 I'mJp, Apr 3, 2016
  5. WilDavis

    WilDavis Senior Member

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    My heart bleeds for you. The cruise control on my 2009 Gen 2 works exactly as it supposed to, and if I ever get fed up with its quirks (none found as of yet) those crafty Japanese have provided the perfect solution - the one in my car is fitted with an "OFF" switch - hope this helps - (actually DGD ;):))
     
    #5 WilDavis, Apr 3, 2016
  6. JohnF

    JohnF Active Member

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    Keeping myself from speeding is one of the two reasons I use cruise control. The other is if I am on dead flat roadway. Very little of that around here, mostly gently rolling. Constant speed does not mean optimum fuel economy; I find I can do better if I let the speed vary in response to the terrain or traffic ahead (less variation if there is traffic behind me of course).
     
    #6 JohnF, Apr 3, 2016
  7. I'mJp

    I'mJp Senior Member

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    Having different filters for the cruise control would be very cool.You could have one super loose, that is optimized for evanother one that will not let the ice go out othe eco rangea normal range like we havea tight range that keeps speed no matter what.
    But we a dealing with a company that won't let us set the backup beeps.
    So it's all fantasy...
     
    #7 I'mJp, Apr 3, 2016
  8. nategold

    nategold Member

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    David Beale, you are correct - I got it backwards.
     
    #8 nategold, Apr 4, 2016
  9. bwilson4web

    bwilson4web BMW i3 and Model 3

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    You might consider editing the first post to make it correct:
    Still, I agree with the goal of having a smarter cruise control:
    • under Normal or Power - work as it does today, relatively strict speed control.
    • under ECO - slack off the speed when the engine enters inefficient power mode but strict on the high-side. This would have the effect of slowing down when going up a steep grade at high velocities. For example, slacking off to not exceed 3,200 rpm (maximum EGR valve setting Gen-3) when under cruise control and Eco mode.
    Bob Wilson
     
    #9 bwilson4web, Apr 4, 2016
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  10. nategold

    nategold Member

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    I tried all 3 drive modes and the cruise control works the same in all modes.
     
    #10 nategold, Apr 4, 2016
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