Cruise Control Helps MPG?

Discussion in 'Prius c Fuel Economy' started by kindlewood, May 1, 2012.

  1. kindlewood

    kindlewood New Member

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    Okay, so I've only had my Prius C for about two weeks now and have been loving every minute of it! It's really become a game for me to squeeze ever mile I can out it.

    Anyways, one of the biggest problems I've had so far has been maintaining, or gaining mpg on flat roads. Whenever I get to these, I find it very hard to maintain the speed limit and still gain, or at least hold my current mpg. This has lead to countless times of losing as much as 2, or 3 miles per gallon, depending on the length of the flat road, even while maintaining a steady foot and steady speed.

    Well, yesterday, I was sick of stressing out about it, so I decided to put on the cruise control for the flat road I was traversing, figuring that if I lost mileage, I could at least blame it on the cruise control. To my surprise, for the first time since getting the car, I actually gained mpg!?!? I've since used it on every flat road I've been on and it either holds my current mpg, or actually increases my mpg.

    For the life of me, I can't figure out what it's doing that I'm not. I've even watched the Energy Monitoring screen, to see how it's distributing the energy and it doesn't seem to add up to increased mpg. I'm happy that it's helping me, but I'm baffled as to how and why.

    Has anyone else noticed this too? I don't have a lot of flat roads where I live (although I don't have many steep hills either). The flat roads last, at the most, a few miles before the roads turn hilly again. However, until now, flat roads have been my bane.

    I drive in Eco mode and 90% of the time on back roads, avoiding the highway at all costs. I drive a total of about 60 to 80 miles a day, broken up into two commutes each day of about 15 to 20 miles each way (I work a split shift), depending on the route I take, or any out of the way stops I need to make along the way. Speeds tend to run from mid-teens, to a max speed of 45mph.

    Any thoughts as to how the cruise control is increasing my mpg on flat roads, while all my previous attempts have failed?
     
  2. vinnie97

    vinnie97 Whatever Works

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    I have become dependent on cruise control. I use it as a crux, lol. It manages energy well enough. I imagine we could gain, at best, 1-2 mpg if we implemented pulse & glide with precision compared to cruise? Who knows, as you can see, I'm doing pretty well in MPG with CC usage.
     
  3. donny612

    donny612 "Captain Jack Sparrow"

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    As long as the roads are flat I've found that the cruise can help but if there are ups and downs to deal with the CC seems to hurt mileage. CC speed adjustments for hills seem to be more severe/extreme than when I'm controling the acceleration. I used to use CC everywhere...in town or on the highway just to keep from speeding. Since I've had the PC I've seen where the cruise in town hurts mpg. I still use it on the highway as long as the road is reasonably flat.
     
  4. SquallLHeart

    SquallLHeart The Techie Guy

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    cruise control would only really help if you're on completely flat roads.

    the car cannot predict road situations or can it see what's up ahead in the road such as hills and such....

    therefore.. on uphills, the car will waste more gas trying to maintain that set speed... and on downhills, the car will regen trying to maintain speed.

    if the road is completely flat.. well.. it'll find the most efficient way to maintain speed.. and with no road conditions that would cause changes in fuel use... it could potentially help your mileage vs you driving yourself..

    however.. a well experienced or trained driver can always beat cruise control with regards to mileage.
     
  5. dig4dirt

    dig4dirt MoonGlow

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    Somehow the CC knows how much gas to apply to the situation.

    I was using CC today and noticed that even when going downhills, it does not
    go under the eco line. I thought what? How and why would it do this, since
    bringing it below would relatively think it would save going down a hill.
    But then when going up a hill (slight grade) it doesnt bring it even close to the
    power line. How can it maintain speed without getting close?

    I figured that it does not need the boost that we typically would give it.
    (now if going up a steeper grade, of course the CC will race the engine)

    Since getting the C and 3G, I actually pulse and release, and glide.

    From a stop, if there is traffic, I give just enough gas to stay with the flow.
    Then I will release the pedal PART way, and stay with traffic.
    If conditions allow, and you can gain distance from the leading car...
    you can then pulse/glide. But you can also PART release the gas to allow
    for less consumption but still maintain speed and flow of traffic.

    For each their own, but this will always depend on conditions.

    Just keep in mind that when accelerating you can always still gain speed and
    stay with the flow of traffic by PARTLY releasing gas pedal.
    You dont need to gas to the power line just to get up to speed then glide.
     
  6. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    When you read that CC is not as good as a human, it is always with respect to hills and stops. If you are on level ground (60 foot elevation change in 154 miles, for me) at a constant speed, then CC is fine. And yes, the computers 'trust' the CC more than they trust your right foot.
     
  7. F8L

    F8L Protecting Habitat & AG Lands

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    I think Part of the reason CC works better for some people is foot control.

    Some people drive in a pulsing manner. They tend to speed up the slow down, speed up then slow down. This is not efficient and CC fixes the problemby maintaining a constant throttle input that varies much less.

    Some people have a hard time judging their speed so that as they are accelerating to reacha desired speed, they maintain too much throttle input and overshoot the desired speed or once they have achieved that speed they reduce throttle input but not enough so as to discontinue accelerating and over the course of the next 15sec or so they are accelerating to the next higher mph. Atthat point they notice they are going 66mph instead of 65mph and they wasted 15sec or so accelerating at a terribly inefficient rate. CC would have reduced throttle input much sooner.
     
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  8. El Dobro

    El Dobro A Member

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    I always use CC. It keeps me from speeding up with the rest of the highway when I want to stick with the speed limit.
     
  9. kindlewood

    kindlewood New Member

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    Thanks everyone for responding.

    I got some interesting answers and I agree with many of them.

    Just some quick info. that I forgot to mention before. When I mention that I can't seem to maintain and often lost mpg on flat roads, it's only when I'm at fairly high mpg already (over 58mpg, usually mid-60s). When I'm still in the high 40s to mid 50s, I have no problem maintaining mpg on flat roads. I'm also usually driving between 40 to 45mph on these flat roads, so I'm not going highway speeds.

    It just surprised me that even at 60+mpgs, cruise control was actually helping me to maintain, or even gain mpgs on flat roads.
     
  10. Corwyn

    Corwyn Energy Curmudgeon

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    A prius with all the options has a GPS, so it knows what road it is actually on, and the GPS has a map with elevations, so it knows about upcoming elevation changes. It has a radar, so it knows a little something about immediate preceding traffic. It could even be getting traffic updates for external sources. Cruise control could be a lot smarter. I can't be the only engineer who has thought of this. I suspect that we are seeing a lawyer problem not an engineer problem. Driving at a set speed is accepted, and no liability accrues to Toyota for automating it. Speeding up and slowing down, on purpose, even a little, might.
     
  11. frugaldriver

    frugaldriver Ceterum censeo Carthaginem delendam esse - Cato

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    What kind of mpg numbers are you guys getting using CC at 65 mph or 70mph on flat roads? And, has anyone done this long enough (like a long road trip) to see an accurate number for this mpg?
     
  12. kindlewood

    kindlewood New Member

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    I, personally, have yet to drive over 60mph. And then only for, at most, 10 miles. I'm sure someone else on the forum can answer this better than I can.

    I will say that the highway I drive on is fairly flat and in that 10 miles I can get upwards of 54 to 55mpg, while using cruise control...on nice days anyways...48 to 52ish on rainy and/or cold days.

    I'm sure this summer and definitely in the Fall I'll be taking it on longer, higher speed trips, but I'm avoiding them for as long as I can right now and enjoying the higher mpgs I'm getting while it lasts. :)
     
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  13. actiondonkey

    actiondonkey Member

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    This.

    I never use cruise because there are no appreciable flat stretches around here. However when I take the drive through Texas and Oklahoma I'd expect to use it for a while.
     
  14. XRinger

    XRinger Member

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    We are trying to get a C2 for my wife. I need CC because of an old injury. (right ankle shattered)
    I find it almost impossible to drive very long without using CC.
    (She would have been happy with a C1).

    I also find that using CC on flat roads gives me better mpg than normal.
    My Ford Escape (plain old 2.5L 6sp AT) at 30-40 mph does 40 mpg.
    But only on fairly flat roads. It's the hills that kills the mpg.

    I sometimes use CC on hills. I watch my SG2 mpg and click the CC down a notch
    (1 mph) as I see the mpg falling off. I use a series of down-clicks and try to space them,
    so that I'm still going at a safe speed when I hit the top. (Be it somewhat slow).
    Then I'll click-up slowly on the down side (still watching the mpg). Works pretty well.

    I'm hoping the CC with be as useable on the new C2. (If my wife lets me drive it). :eek:

    Cheers,
    Rich
     
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