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Any special tips for driving uphill?

Discussion in 'Gen 2 Prius Fuel Economy' started by ystasino, Jun 15, 2007.

  1. ystasino

    ystasino Active Member

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    Understandably I'm seeing huge discrepancies in FE going downhill to work and uphill back home. Part of it is traffic and the easy to time favorable traffic lights at the time I go to work, but it's mostly the terrain.

    I average about 64 mpg to work and 44 mpg from work to home. Any tips that would help me deal with the terrain? I could choose to take the highway at around 55-60mph, but it's still uphill and probably gives me the same FE as through the city.

    Thanks
     
    #1 ystasino, Jun 15, 2007
  2. JimboK

    JimboK One owner, low mileage

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    One thing that would help you, but that the Prius is not equipped with, is a tachometer. The research of Hobbit and others suggests a "sweet spot" of efficiency below about 2300-2400 RPM. My observations suggest you're probably there when instantaneous MPG > MPH x 0.5. If you can do some simple math on the fly, then maybe this rule of thumb will help.

    Of course your hills and traffic volume may not allow this. Steep uphills will require more pedal than this to maintain speed. But if traffic allows, you can give it less pedal on the uphill, bleeding off speed until you crest. Any downhills you have can be used to gain momentum for the next uphill using either glide or, at 42+ MPH, "warp stealth".

    Finally, be careful not to run the ICE at too low an RPM on those downhills or level terrain. Below 1400 or so it "loafs" (as Hobbit describes it) inefficiently, where you might as well use glide or warp stealth. Keeping instantaneous MPG less than MPH x 1.2 will probably keep you above 1400 RPM.
     
    #2 JimboK, Jun 15, 2007
  3. ystasino

    ystasino Active Member

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    <div class='quotetop'>QUOTE(JimboK @ Jun 15 2007, 01:38 PM) [snapback]462409[/snapback]</div>
    I will try this for a while and report back. I think I have it figured pretty well going downhill, mostly because I'm really lucky with the traffic at the time, the traffic lights and the terrain.

    I'm not sure how much better than 54 mpg I can really do though when my tank is about 70% between 55-65mph.

    But every little mpg I can do it would be helpful. If I found someone with a tachometer I would probably pick up the sound at the sweet spot you describe fairly well...
     
    #3 ystasino, Jun 15, 2007
  4. efusco

    efusco Moderator Emeritus
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    Some hills will just kill you and that's just the way it is. I, too, subscribe to the 1700-2300rpm "sweet spot" philosophy. To achive that it means that I sometimes begin accelerating well before I hit a hill so that I have momentum to carry me up the hill while keeping within my preferred rpm range.

    If traffic allows you can let the speed fall off as you approach the crest. If you have rolling hills try to allow your momentum to build by gliding down one hill and then using that momentum with judicious use of the accelerator as your start up the next hill.
     
    #4 efusco, Jun 15, 2007
  5. ystasino

    ystasino Active Member

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    <div class='quotetop'>QUOTE(efusco @ Jun 15 2007, 02:27 PM) [snapback]462454[/snapback]</div>
    I have been following what you mentioned Evan. However from a brief drive it seems that I was accelerating way too fast according to Jim's formula that my MPH must never be more than double my mpg.

    Evan (and everyone else who wants to help), I remember from an earlier post you have Can-view so I had a couple of questions on related to this topic and one slightly OT.

    1) I assume that slowly accelerating with the battery only is very inefficient because the battery will eventually need to be recharged? And is there any way one can accelerate (the braking regen I understand) on any surface to keep the battery as charged up as possible without added instrumentation? In my unscientific experience low battery levels are a drag on mpg. Sometimes the inverter charges the battery sometimes the other way around. I'm trying to find out how the direction of that arrow varies.

    2) If your instrumentation tells you exactly how many gallons of fuel you have left even with the bladder, one could assume that for low levels of gas this would not vary by much from bladder to bladder. So what would an indication of 1 pip (just turned from two to one) mean?

    Thanks
     
    #5 ystasino, Jun 15, 2007
  6. efusco

    efusco Moderator Emeritus
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    <div class='quotetop'>QUOTE(ystasino @ Jun 15 2007, 03:36 PM) [snapback]462545[/snapback]</div>
    1a) your assumption is correct. 1b)The way I do it in our Highlander Hybrid is to look at the energy screen...I want to accelerate at a rate where there are arrows from the ICE to BOTH the wheels and to the battery...this seems to be what's usually occuring during sweet-spot acceleration. This is tough to do early after starting from a stop and takes some 'foot play'...but can usually be achieved.

    2)My instrumentation tells me the % of the fuel tank left. With one pip that's usually 15% and the last pip flashes at around 10-12%. That said, that percentage can vary...I've parked the car with it showing 12% and the last bar flashing then started up a few hours later and it showing 15%--once you get to a lower level on the fuel guage it won't go back up though. Sometimes I'll go up a steep hill and the fuel tank will show a drop from 20% to 15%...I'll drop from 2 pips to just 1, and once things flatten back out the tank % goes back up to 20...but the guage stays at 1 pip.
     
    #6 efusco, Jun 15, 2007
  7. ystasino

    ystasino Active Member

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    There must be a way of making out an average range of what two, one or one flashing pips mean if only from experience given that we can measure the exact mpg from two to one pip and one pip to one flashing pip.

    Since we know the miles driven per pip there must be a way of averaging the empirical changes and making a figure with the standard deviations from means medians etc.

    I wonder if anyone in the community would like to participate?
     
    #7 ystasino, Jun 15, 2007
  8. ystasino

    ystasino Active Member

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    <div class='quotetop'>QUOTE(JimboK @ Jun 15 2007, 01:38 PM) [snapback]462409[/snapback]</div>
    I tried this MPH<MPGx2 formula. But that is such a huge range. Is there some formula such as MPG*1.5<MPH<MPG*2 because if we are talking 2300-2400 RPM that's probably some range of values rather than MPH<MPGx2

    I know I should get a tachometer, but I really can't spend money on scangauge etc

    MPG to work today: 66.67mpg
    MPG from work today (using the MPH<MPGx2 formula): 40.99 mpg

    Since this is my first time measuring MPG that precisely I'll experiment further. In case anyone is interested in finding out how I get these precise mpgs/trip it is explained here

    http://priuschat.com/Calculating-mileage-o...rip-t34761.html

    Thanks anyway
     
    #8 ystasino, Jun 15, 2007
  9. hobbit

    hobbit Senior Member

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    A Scangauge II might be a good and possibly more accurate second-guess
    on MPG. The Chi-town squad relies heavily on them.
    .
    Some hills, no matter what you do, just demand quite a bit more than
    2300 rpm. I try to let it go not much over 3000 in such cases and
    just crawl up a little more slowly than most people would be happy
    with; much above that and you start getting into some different and
    MPG-horrendous run modes as well as pulling hard on the battery.
    .
    _H*
     
    #9 hobbit, Jun 15, 2007
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