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Inconsistent cruise control speed

Discussion in 'Gen 3 Prius Main Forum' started by 7th_paramita, Jun 23, 2009.

  1. 7th_paramita

    7th_paramita Junior Member

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    I have been using the cruise control to make sure that my speed does not drop too much on highway driving. Several times though I noticed that the speed dropped 5-10 miles below the set speed, and the engine would kick on and go into the power area to regain the speed ruining my mpg. What's up, anyone else had similar experiences?
     
    #1 7th_paramita, Jun 23, 2009
  2. Busaholic

    Busaholic New Member

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    Thats normal. Only the power of a V8 can keep the car pretty much within a 1 to 2 mph range with cruise control engaged going up hill.
     
    #2 Busaholic, Jun 23, 2009
  3. Tideland Prius

    Tideland Prius Moderator of the North
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    huh?? I've had plenty of 4 cylinder Toyotas that have no problems on the hill.
     
    #3 Tideland Prius, Jun 23, 2009
  4. firepa63

    firepa63 Former Prius Owner

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    My 09 might drop a couple of mph going up a hill, but nowhere near 5-10. What speed are you setting the CC to?
     
    #4 firepa63, Jun 23, 2009
  5. qbee42

    qbee42 My other car is a boat

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    +1. My 2006 Prius will give it all it has to hold speed on a hill. Short of mountain driving, I've never had it stray from the speed setpoint, and in the mountains I would never use cruise control. Is it possible that this comes from using Econ mode?

    Tom
     
    #5 qbee42, Jun 23, 2009
  6. 7th_paramita

    7th_paramita Junior Member

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    I set my cruise control at the speed limit, 55, 65, or 70 and then increase the speed and play with the pulse-glide technique going up and down hill. These are rather gentle inclines. It seems that when my speed drops while gliding, usually on a gentle uphill slope, it can drop past the set speed limit set on the CC up to ten ten miles. Suddenly the engine comes to life and tries to correct the speed difference, pushing the engine in the power range. Other times, perhaps when the engine is running, the CC responds correctly and adjusts the speed when the set speed limit is reached. I have it in normal mode.
     
    #6 7th_paramita, Jun 23, 2009
  7. qbee42

    qbee42 My other car is a boat

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    Do I understand correctly that you engage CC, but then press on the accelerator pedal to override the speed? In that case, yes, you will introduce control oscillations. Any feedback system will do this when you introduce noise, unless the system is seriously over-damped.

    Tom
     
    #7 qbee42, Jun 23, 2009
  8. yardman 49

    yardman 49 Active Member

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    That's incorrect. I've had V6 powered GM minivans for several years. They are very stable with cruise on when going up hills.
     
    #8 yardman 49, Jun 23, 2009
  9. yardman 49

    yardman 49 Active Member

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    I have never used pulse and glide with cruise control on.

    I have found that on the highway, whether in a moderately hilly or flat area, the Prius GII cruise control does a very good job of maintaining a stable speed.

    The only problem that I've had is on winding secondary roads, with speed limits of 35 to 45 mph. Where my Uplander minivan will hold speed nicely on such roads, the Prius will oscillate a few mph above and beneath. So although I'm a cruise control fan, I've stopped using it on some secondary roads with the Prius.

    I thought that I'd read somewhere on the forums that the Prius uses some adaptive learning technology, where it slightly adapts to your driving style. I really have no idea if this is true or not. But if so, maybe the cruise control can be adversely affected by trying to pulse and glide when it is activated? Just a thought.
     
    #9 yardman 49, Jun 23, 2009
  10. firepa63

    firepa63 Former Prius Owner

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    How the heck can you use pulse & glide with the cruise control on? Never heard of that. P&G results in mph oscillations, where CC is designed to hold steady speeds.
     
    #10 firepa63, Jun 23, 2009
  11. Blauer Glimmer

    Blauer Glimmer Active Member

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    That explains the fluctuation. The purpose of cruise control is to maintain a steady speed. Why would you even attempt pulse and glide while using cruise at highway speeds?
     
    #11 Blauer Glimmer, Jun 23, 2009
  12. 7th_paramita

    7th_paramita Junior Member

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    I thought that I made it clear that I don't want to go too slow and hold up the traffic so I set the cruise control at the lowest speed I'm comfortable with, usually the speed limit. Then I increase the speed between 5-10 miles and fluctuate the speed depending on the terrain and try to take advantage of improved FE as I go down hill or able to glide. It's easy to get distracted and have the speed drop too much and end up a nuisance for coal or heavy trucks. I don't like to have a rear collision if I can help it. The interesting observation was that at times the CC responds accurately and kicks in when the speed drops to the set speed and other times it does not.
     
    #12 7th_paramita, Jun 23, 2009
  13. qbee42

    qbee42 My other car is a boat

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    As stated above, it depends on the control inputs that preceded hitting the target speed. The variation is operator induced.

    Tom
     
    #13 qbee42, Jun 23, 2009
  14. Paradox

    Paradox Prius Enthusiast / Moderator
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    Just got back from a 600+ mile trip and used the DRCC almost the whole time. I went to upstate NY from the city and even with all the mountains etc the car maybe flucuated 1mph. The DRCC and LKA is phenominal on long trips, it really reduces driver fatigue...
     
    #14 Paradox, Jun 23, 2009
  15. Busaholic

    Busaholic New Member

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    I guess it's just me. Everything I drove that wasn't a V8, losing speed going up a hill was always my one complaint. Some of them couldn't even pull their own weight. My Prius on some hills loses 5mph but mostly 3mph before kicking into power mode.
     
    #15 Busaholic, Jun 23, 2009
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