Some MPG/hypermiling questions

Discussion in 'Gen 2 Prius Fuel Economy' started by Tekdeus, Jan 20, 2011.

  1. Tekdeus

    Tekdeus Shifted to Green

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    Hi Folks, I've been getting into some light hypermiling in my recently purchased '04, and had some small detail questions not found by searching:

    1. When accelerating from a dead stop, is it more efficient to start out somewhat slowly, using only EV power, then roll into approx 40% throttle to engage the ICE to start the pulse & glide process? Or is it better to immediately engage the ICE from a dead stop with a more brisk acceleration?

    2. Is it worth trying to pulse and glide at highway speeds by alternating between pulsing and warp stealth? Or is just using cruise control close enough?

    3. Heater usage: Is it best to try to leave it on MAX COLD with the A/C off to maximize efficiency? If I leave it set to room temp, approx 72 degrees while it is 38 to 50 degrees outside, will this engage the ICE more often and hurt economy?

    4. Regarding the initial 5 minute hit of brutal warm-up MPG, is there any way to lessen this? Does leaving the car outside vs in a garage or using a block heater make a significant impact?

    5. Is long, slow, super soft braking best for regen/efficiency, or is more moderate mild braking better?

    6. What is the most efficient cruising sweet spot for the Prius II? 31, 37, or 44mph?
     
  2. donee

    donee New Member

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    Hi Tekdeus,

    I usually engage the engine at about 5 mph. Extreme hypermilers on empty roads tend to stretch this out to 15 mph.

    Pulse and Glide effectiveness is very sensative to the accelleration RPM. I used between 1800 and 2200 RPM on my Gen II. I imagine its lower on the Gen III

    At highway speeds, Super Highway Mode (SHM) is best on level terrain. One can do a power-on/power-off mode in hilly terrain as you just cannot hold SHM operating parameters on any kind of hill at all.

    I run 65 F on the heater, which is enough to keep the windows clear, usually, and in winter outdoor clothing, its plenty warm.

    Yes, the block heater effects the first five minute mileage dramatically. Also, park the car indoors or in a wind-shadowed location if you can. This avoids wind conduction cooling.

    Best braking efficiency occurs with moderate braking power. Not supper slow braking. Shoot for about a 200 to 300 yard 40 mph to 0 mph braking.

    The best crusing sweet spot is 50 to 53 mph (depending on tires and aero mods), in the summer , in sunshine, doing SHM at 70 to 75 mpg in the Gen II. Below 40 mph, its best to pulse and glide in the Gen II, so there is no constant speed sweet spot there. This is because the required engine power is just too low for good efficiency.
     
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  3. BAllanJ

    BAllanJ Active Member

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    I try not to use the battery at all to avoid conversion losses, so I get onto the ice right away.

    I do a pulse (2000 rpm) and super highway mode when I can on secondary roads, and pulse and glide in the city. On the big motorways I try to find a big truck going my way... they're governed at about 105 km/hr here so I get a couple seconds behind and turn on the cruise.

    I grill block and use a block heater in the winter, then I try not to use the heater any more than necessary until the engine gets up over 70 C so I can get into stage 4.

    Braking to keep regenerative braking , which means moderate at city speeds and light at highway speeds, although it's best to try to avoid as possible.
     
  4. msirach

    msirach Member

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    Try not to brake at all. Time your lights to where you won't come to a stop. Remember Newton's Law!
     
  5. bisco

    bisco cookie crumbler

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    well said all!
     
  6. mikewithaprius

    mikewithaprius New Member

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    I've wondered about this idea of trying not to use the battery, because it seems in some routes it's beneficial to do so - but hypermilers let me know what you think.

    There's one bridge near me where it's a huge trek to the top, sapping almost 10mpg from the trip total, but then on the way down I can do a combo of regen braking/gliding to get to a full green (if not, close) SOC just by the time I get to the bottom. There's a toll at the bottom where you essentially stop completely (possible to roll at about 5mph, which I try to do), so then my next segment of the trip benefits enormously from a fully green SOC. Common sense tells me that's much more efficient than anything else I could be doing, since otherwise the part of my trip after the toll would simply not use the battery at all, and I'd be accelerating from 0 to 50mph. Am I wrong here?
     
  7. ItsNotAboutTheMoney

    ItsNotAboutTheMoney EditProfOptInfoCustomUser Title

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    What you have is a "regen opportunity". When you have an upcoming regen opportunity you can make use of charge before it, because otherwise you'll be missing out on some charge. But after your regen opportunity you're better to "save" the charge until the Prius best needs it. If you just drive normally after the toll you should find the Prius will make use of the "extra" charge as an opportunity arises.
     
  8. Rae Vynn

    Rae Vynn Artist In Residence

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    Accelerate briskly - then ease off and do your "dead band" gliding (no arrows to/from engine/battery/wheels on MFD) as you are able to. Generally, it takes a feather touch on the accelerator to overcome the "drag" that has arrows going to the battery from the wheels, and which slows you faster, but not so much pressure that you kick in either the ICE or the battery for power.

    If you are in traffic that will be less tolerant of speed changes, just drive the car conservatively.
     
  9. mainerinexile

    mainerinexile No longer in exile!

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    Cruise control in a Prius is not a good thing for gas mileage, which is true for all automatic transmissions. The car will inevitably try to accelerate hard just before the crest of the hill, for example. But CC is a necessary evil on a trip, so go with it. CC supposedly works slightly more efficiently in ECO mode, but I'm not sure I've actually seen it help.
     
  10. uart

    uart Senior Member

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    You want to avoid trying to run too much on electric when there are no regen opportunities. It's a mistake for example to try to coax it to stay in all electric mode too long on flat terrain and start dropping SOC, since the battery charge needs to be made up with more power from the engine once it eventually does start.

    When you've got natural regen opportunities then you're basically getting battery charge for free (not really free, but it would otherwise have been wasted). A good strategy is then to try to run electric and perhaps get the SOC to drop a bar or so just prior to getting the large regen. If possible for example you could try and make it drop to electric mode just as you're "cresting" the bridge. This both saves fuel and drops the SOC a little to give more capacity to accept regeneration.
     
  11. mikewithaprius

    mikewithaprius New Member

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    Thank you all, that makes sense to use more electric prior to the regen opportunity. I'll try perhaps on the straightaway before the huge hill (the bridge is two miles long altogether, it's a doozy!), since up the hill it's around 25mpg whether I like it or not.
     
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