Max MPG driving uphill

Discussion in 'Gen 3 Prius Fuel Economy' started by white2011, Oct 12, 2011.

  1. white2011

    white2011 Junior Member

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    What are the specific tips for saving gas while driving uphill?

    On my commute I have a long uphill grade on the freeway. Does it matter to MPG if I use ECO, normal or PWR? Holding 65 mph really seems to suck it down, but dropping to 55 doesn't seem to help much either, and I really don't want to go slower. Is it best to hold a steady speed on a steady gradient, or is it better to speed up and slow down?

    Suggestions/tips?
     
  2. F8L

    F8L Protecting Habitat & AG Lands

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    It is best to maintain your speed until you start climbing the hill then let your speed drop until you crest the hill then glide down the other side. Most of the time this is not safe on a busy road and frankly, it is nerve wracking.

    Your other option is to pick up speed while on the flat such that as you climb the hill you can let your speed drop like in the above scenario but by the time you crest the hill you are at your normal driving speed. This is the second best approach and a lot safer. In either case, do your best to glide on the downhill section without using fuel.

    On a hypothetical hill that has equal uphill and downhill lengths: Says you get 30mpg going uphill and you get infinite mpg downhill then you have averaged 60mpg over the entire length of the hill. This is a perfect condition scenario and doesn't account for other factors.
     
  3. dhanson865

    dhanson865 Expert and Devil's advocate

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    I've found on a highway where I can safely go 65 MPH I get better mileage going faster than slower but I don't do fixed speed. Look up the term "driving with load" for discussion.

    As an example of what I do on an interstate with large hills I watch the display and try to coast on the downhill, above a certain speed you can't truly coast so when it hits that point I either go for electric only acceleration or slight regen depending on how much speed I've gained.

    On the bottom of the hill I hit the gas even though I'm going the limit or slightly above until I see the display show gas engine going and energy going into the battery (Gen II display, I guess that is just barely past half way accross your power section on Gen III), Whatever gas pedal position it takes to hold speed at the bottom of the hill or slightly gain speed I hold that going up the hill.

    Now if I do that with 55 - 60 on the down hill I get to 55 - 45 depending on how steep & long the uphill is.

    What surprised me was when I did the same route and tried doing it all 10 mph faster I got better MPG.

    You'll have to experiment to find the correct balance but in short you want to go as fast as you safely legally can before you start the hill and avoid putting more gas pedal when you are going up. Eventually if you slow down to much you'll just have to bite the bullet and stomp the gas.

    When I do stomp the gas up a long hill in a Gen II it's very slow to respond. With a Gen III if you know you'll be driving hilly terrain you might want to try Power mode so the gas pedal will be more responsive. Save Eco mode for more flat terrain.
     
  4. sipnfuel

    sipnfuel New Member

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    The best strategy is to give it as much as it needs to get up the hill. If you are at freeway speeds, just pick a speed and climb the hill.

    The reason that your MPG appears low is because MPG doesn't take into account the fact that you are gaining height or potential energy. In fact the slower you go, the lower the apparent "MPG" but in reality you are driving more efficiently. When you are going slower, proportionally more gasoline is used to climb the hill than is used to move forward, but that gasoline is converted into potential energy and not wasted at all.

    There is no reason to game the uphill because you have to use energy to climb the hill. If you employ pulse and glide or any other method it will not work. Every foot of height you gain must use the same amount of energy no matter what. It's not the same as every foot of distance you gain; in that case less energy can be used to gain the same distance and thus we can employ technique to reduce fuel usage.

    In reality going uphill will sometimes keep the ICE in its highest efficiency zone.

    In short, keep your foot down as necessary to get up the hill. Reserve fuel saving techniques downhill, flat or sometimes very mild uphill sections.
     
  5. F8L

    F8L Protecting Habitat & AG Lands

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    Sipnfuel, are you trying to say that climbing the hill uses the same amount of fuel regardless of speed?
     
  6. sipnfuel

    sipnfuel New Member

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    Well not entirely, because the ICE will have a different thermal efficiency depending on how much power is being produce, and what RPM it is running at. In the Prius, vehicle speed is somewhat decoupled from engine RPM, but there certain constraints on what range of RPM the ICE can spin at, depending on how fast the vehicle is moving.
     
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  7. sipnfuel

    sipnfuel New Member

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    Just to clarify, I think F8L's technique as outlined in post # 2 is the appropriate one to use when you have a series of short uphill and downhill sections where you can gain and lose speed.

    In what the OP described, a very long sustained uphill climb, basically it is not very useful to pulse and glide, or use SHM. To climb you will be pulsing. So it's just best to pulse at the speed you are comfortable at.

    Then, when appropriate and the grade is not so steep, or you need to slow down a bit, or the terrain is flat, or you are going downhill, you can glide or go into SHM.

    But in a long sustained uphill climb, gliding will make you lose speed so fast that it is ineffective. This is why I say to just pulse uphill at your desired speed until you are out of that section.
     
  8. mtngal

    mtngal New Member

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    What "long uphill grade on a freeway" are you talking about? I've only had my Prius for a little less than 2 weeks, but my commute includes the Sepulveda and Newhall passes, along with half the Grapevine. I tried several different ways of driving the long uphill grades of the Grapevine - letting the speed drop some and gliding where I can, pushing the downhill parts to 70, then letting the speed drop more on the uphill parts. There's just some grades that require a lot of power to get up and over no matter what. I do try to start off faster and not let my speed drop too much in the beginning of the grade, because that lets me glide more downhill and if I lose too much speed initially I feel like I'm playing catch-up too much). And I've definitely given up trying to maintain 65 - letting my speed drop some might add 5 minutes or so (which isn't much with a normal commute of an hour and a half more or less). I haven't tried using eco or power mode, just keep it in normal. Perhaps I'll figure out how to get more mpg but I'm not too concerned - I'm averaging 47-50 mpg so far (just over 2,000 miles and have a cumulative calculated mpg of 51). I more than make up on the long downhill grades what I expend going up the grades. Haven't tried using eco or power modes, just leaving it in normal. As time goes on I'll probably try a couple of tanks with the other modes, just to see how they differ.
     
  9. fuzzy1

    fuzzy1 Senior Member

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    While I wouldn't word my detailed response the same, the summary would match sipnfuel's piece here.

    Basic physics requires energy to climb a hill. In the Gen3 Prius, this costs about 1 gallon per 10,000 vertical feet (+/- 20%) of extra fuel, in addition to the fuel needed to travel a flat but otherwise identical route. While you can game the start and end a bit (see F8L's reply), especially when the uphill is next to a downhill, there is not much that can be gained in between, compared to simply climbing the hill steadily at the minimum speed you can tolerate. And if you care about fuel efficiency, you probably are already driving at this minimum speed on the flats too, set either by traffic conditions or the value of your time.

    On a steady climb on most hills, the Prius engine will remain at, or very close to, its peak efficiency. (Non-hybrids often are more efficient while climbing, but Prius's Atkinson-cycle engine already gets that improvement all the time.) On the real steep ones that knock it away from this peak, you don't really have any alternatives.

    Downhills are another matter, as this is where a typical untrained driver will lose the most. It is easy to get excited and settle for 99.9 mpg when a ScanGauge could be reading far higher. Focus most of your mountain-related fuel conserving attention on the down side.
     
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  10. F8L

    F8L Protecting Habitat & AG Lands

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    I guess I should have described a scenario that uses a long uphill climb like portions of the grapevine in LA or I-80 in Norcal while climbing up the Sierra Nevada range in those conditions I totally agree. Just drive at the slowest speed that is safe and you can tolerate. :)

    My morning commute is mostly a rolling climb from 50ft. to 1,200 ft. with one section where I cannot do anything but maintain a steady speed.
     
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  11. white2011

    white2011 Junior Member

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    For those of us without ScanGuage, what can we do to maximize mpg on the downhill?
     
  12. sipnfuel

    sipnfuel New Member

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    The basic strategy is to avoid using your brakes, and to avoid using the battery.

    This will involve "Glide" or "Super Highway Mode". Typically even on a downhill, you will need to provide some throttle, unless you are slowing down.

    So several strategies, in order of increasing power requirement:
    Glide - basically coasting downhill without using battery power
    Stealth or Warp Stealth - this is not ideal but can be used occasionally
    Glide & SHM
    Glide & Pulse (or Pulse & Glide)
    SHM
    SHM & Pulse

    If the above is too confusing, just remember at highway speeds, using the engine is good. Using the battery is bad. Gliding is OK.
     
  13. F8L

    F8L Protecting Habitat & AG Lands

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    In my situation, the minimum speed I can realistically travel is 60mph. On the downhill section my only option is to have the engine off and allow regen or to very lightly apply pedal pressure to disengage regen and use the battery until it reaches 47.5% SOC at which point the engine turns on and drops mpg from infinite to around 330mpg. Because I have 2 smaller hills to tackle after the big hill I choose to keep my speed up by letting the engine turn back on as I approach the bottom of the big hill as opposed to allowing regen to slow me down. This keeps me from having to try and accelerate up the next hill. Instead I apply light throttle to maintain speed which seems to be better for FE and keep me from angering other motorists. This is a very busy 3 lane interstate freeway (I-80).
     
  14. Roadburner440

    Roadburner440 Member

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    I think you are just going to have to come to terms with you are going to burn a substantial amount of fuel (compared to normal) for climbing sustained steep grades. As mentioned before it is just basic physics at work. It is something that I even notice in the Volt. If I climb up the bridge on my normal morning commute I will start with X amount of miles, but by the time I hit the top I have lost 1 or 2.. Usually regain them on the back side though. You just have to remember that when you do the return journey you will be going downhill, and you will be recouping at least some of the mileage you have lost on the way up. The only suggestions I have for you to increase your fuel economy going uphill is a.) increase your tire pressures to reduce rolling resistance (will also reduce traction) b.) start removing stuff that you do not use from the interior of the vehicle (back seats, passenger seat, insulation)... Other than that I really do not know of much. The car is pretty optimized for fuel economy already, so those are really the only things that can be done to make it better.

    As far as going downhill goes don't know why you would need a scan gauge to make it better.. Once I crest the hill, I take my foot off the gas, and the engine shuts off and I coast to the bottom. Sometimes need to utilize some battery power to maintain speed (providing you are at 45mph or less). I really would not want to use a Scangauge to mess with timing or anything like that while I was driving in attempts to optimize fuel economy.. If you want to play with that stuff it is best to take it to a dyno where they can monitor how lean/rich the mix is out of the exhaust, and make the appropriate adjustments to your computer. Trying to do it on the road (like I used to do with my SRT-8 in the search of power) is asking for disaster.
     
  15. Zanrok

    Zanrok Casual Prius Lover

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    I travel the same road as f8 at times... But moreover, my work commute takes me up and down some pretty bad hills. I was wondering if its beneficial to ever use the "B" setting on the shifter when going down the hills? On one of my test drives the dealer mentioned that is what it is for.
     
  16. F8L

    F8L Protecting Habitat & AG Lands

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    Roadburner, the Scangauge II doesn't allow you to manage ECU parameters. It simply displays them. It really helps you understand what is going on with the vehicle.

    Zanrock, B use is generally limited to long steep grades where it can't help to slow you down much like downshifting in a manual equipped vehicle. Otherwise it generally doesn't help much.
     
  17. our1vue

    our1vue Member

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    The top of a hill is the beginning/ending points of my daily commute. The hills are long and steep and I can't get a run at them. These are
    country roads, so no one is going to care if I go up them at 45 or 30. I'm pretty much the only car on the road. If I go up them fast, I can
    see the electric motors driving the wheels along with the ICE, but the engine is revving like crazy. If I go slow, the engine is at a much
    lower rpm, but the electric motors are not contributing because I'm not giving the car that much gas. It would be nice if the electric motors would contribute more at a slower speed. I know what I take out of the battery I have to put back, but that is what the down hill run does when I start the trip. The hills are long enough to fully charge the battery within the first mile.
    Most of the ideas in this thread deal with hills at highway speeds. Any hints, suggestions, ideas on how to get better mileage going up a hill
    at non highway speeds ? Thanks
     
  18. walter Lee

    walter Lee Hypermiling Padawan

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    IF driving is on the multi lane freeway at +50 mph,
    THEN
    PWR mode=ON.
    windows are closed/rolled up
    Tire pressure +7 ps overinflated
    IF (driving temperature > +90 F degrees for over 30 minutes && speed >= 60 mph ) OR
    the windshield is fogging up inside from humidity
    THEN AC=on
    call freeway procedure
    end-IF

    Freeway procedure
    =============
    While driving in a freeway Do
    If there is a long uphill grade THEN

    Begin Case A

    Case A.1 light or no traffic

    Begin Case A.1.B

    Case A.1.B.1 - driver is not tired - hypermile
    Do-- Driving with Load
    before going up hill
    increase speed by about 5 to 12 mph above the speed at the bottom of the hill
    acceleration should be synchronize with going downhill if possible
    slow down gradually by 5 or 12 mph as the Prius reaches the top of the hill
    avoid using the regenerative brakes is possible
    At top of hill - coast/glide Prius
    end- Driving with Load
    end Case A.1.B.1

    Case A.1.B.2 - driver is tired - computer autopilot on
    at bottom of hill turn on cruise control (cc)
    set cc to something close to the psl (like 58 mph)
    let cc drive the Prius uphill
    at top of hill turn off cc
    end case A.1.B.2

    End case A.1.B

    Case A.2 heavy traffic- donot hypermile

    Begin Case A.2.B

    Case A.2.B,1 - travel time short
    get into the fastest lane,
    pace your car behind another vehicle from a safe distance.
    end case A.2.b.1

    Case A.2.B.2 - travel time long
    get into the slowest lane
    pace your car behind another vehicle from a safe distance.
    end case A.2.B.2

    end Case A.2.B

    end while driving on freeway loop
    return
     
    #18 walter Lee, Jun 27, 2014
    Last edited: Jun 27, 2014
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  19. zebekias

    zebekias Member

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    I've only had my 2010 toyota auris hybrid (3rd gen HSD) for one month, so I'm definitely not an authority on strategies; I'm still learning. I regularly climb a 10 mile, 1500 ft gain road up a mountain, which is atrocious to mpg on the way up. I tried both constant speed of 80 kph, which is my normal cruising speed, and constant load--ICE at peak efficiency by keeping the HSI needle around the 3/4 area of Eco (above the centerline, credit to hobbit). I got better overall mpg using the second method (with which you end up climbing slower, at around 55-60 kph, so there is less aero drag too). Last time I did it, I started the trip with an indication of 3.9 l/100km, and when I returned home it was at 4.0 l/100km. Near the peak I went all EV and emptied the battery since I knew I'll fully charge it via regen on the way down.
     
  20. walter Lee

    walter Lee Hypermiling Padawan

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    Yes. For those without a ScangaugeII - for the most part the ICE is between 60% to 90% Load (which equates to the most efficient RPM speed for the ICE) when the HSI power display/ meter is under the "ECO" pill label. Which is where the Prius should be when going uphill most of the time. It's more efficient to gain some extra speed momentum a few seconds before climbing up a hill - whether it be a long uphill or short one- and lose that extra speed/momentum gradually pushing the ICE to maintain most your speed until the Prius gets to the top of the hill. Experience tells one how much extra speed one needs to start off at the bottom of the hill... it is pretty much a situational thingy. you need to have the stereo off so you can hear the ICE running - going up hill you need the ICE running. Going downhill you can do a Pulse and Glide to keep the Prius at an acceptable highway speed - going downhill you want to avoid recharging the batteries if you don't need it ( above 5 bars) because recharging the batteries is a lossy energy conversion and its more efficient just to go faster and loss a bit of energy via aerodynamic drag... by and large - its better to go under 55 mph when going downhill but that might be problematically or impossible on today's superhighway so just find the slowest moving lane on the superhighway (that is not a jammed up and a temporary parking lot) and cruise along in that lane.... maybe its 60 mph maybe its 65 mph but at least your Prius is not speeding along at a less fuel efficient speed of 70 to 80 mph...

    white2011 is correct in observing that experienced hypermilers compensate for the loss of fuel efficiency of going up hill by optimizing their fuel efficiency while going downhill which is why they use things like the ScangaugeII -- this is done by keeping the Prius speed lower while going downhill to avoid losing momentum/speed from aerodynamic drag -- and waiting to speeding up when the Prius needs to go uphill again.

    Walter
     
    #20 walter Lee, Aug 18, 2014
    Last edited: Aug 18, 2014
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