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Updated MPG vs MPH chart

Discussion in 'Gen 3 Prius Fuel Economy' started by bwilson4web, Jun 27, 2009.

  1. Former Member 68813

    Former Member 68813 Senior Member

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  2. fuzzy1

    fuzzy1 Senior Member

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    Apples vs. Oranges.

    I'd say they were testing under very different conditions. Bob tested at steady speeds with a fully warmed engine and little or no accessory loads. His results were consistent with several others, including results by the serious American hypermilers, separate finding by the serious Japanese hypermilers, and previous government tests of previous Prii.

    The DOE report you link covers data from instrumented cars driven by typical drivers in typical traffic, including acceleration, stop and go at varying speeds, and the engine still warming up. I.e. it includes many conditions that Bob and the others deliberately tried to exclude, and these penalties are weighted far more strongly to the low speed portion of the curve.
     
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  3. F8L

    F8L Protecting Habitat & AG Lands

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    I concur with the fuzzy one. My experiences match Bob's graph assuming similar conditions. :)
     
  4. bwilson4web

    bwilson4web BMW i3 and Model 3

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    As others pointed out, their data includes the least efficient driving modes and in particular the first two miles. These short trips are likely to include the engine warm-up overhead and really hit the mileage hard. It may also include times when the car was left "ON" but "parked."

    To really understand their data, we need the raw data file. But my own testing suggests:
    • 0->~45 seconds - during the catalytic converter light-off, the car will draw heavily from the traction battery. By shifting between "D" and "N" one can reach ~40 mph and coast with excellent fuel efficiency.
    • ~45 -> ~300 seconds - during this time the engine is warming up the coolant and burning fuel heavily.
    • ~300 seconds+ - fully warmed up, the engine and hybrid rules apply. Now the car will be efficient like mine and other graphs show.
    I have long felt there is 'low hanging fruit' in our Prius:
    1. More EV in the 45->300 second warm-up - Toyota already turns off the ICE soon but only when stopped. During this warm-up phase, the Prius control laws should continue to more heavily tap traction battery power. Then handle charge replacement when the car is cruising or regeneration. IMHO, there is 5% potentially lurking with this change.
      • Several times I've asked PIP and Volt owners if they have the option of switching to some sort of 'engine in idle' mode while using stored traction battery for motive power (i.e., in ordinary EV mode.)
    I see this potential fuel-saving pattern in the recorded data. It is simply an extension of EV mode into the second, engine warm-up period. But pending a change in the control-laws, there is an approach that works:
    • First, cold-soak, start - drive 1.5-2 miles, neighborhood, 25 mph speed, flipping from "D" to "N" and coasting as much as possible. Let the engine continue to warm-up at 'idle' during coasts, no use of heater. Once the coolant reaches 70C, let the car go into normal hybrid mode (some changes with the ZVW30), and drive normally. Don't worry about the traction battery charge as normal intra-urban speeds, 40-50 mph, will easily supply the missing charge efficiently.
    I do applaud their improved metrics BUT they need to share the raw data for a 'Bob' look. <grins>

    Bob Wilson
     
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  5. Former Member 68813

    Former Member 68813 Senior Member

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    Thanks for the explanation. Makes sense. How did you measure MPG under 40 MPH? At those low speeds car shuts down ICE on flat surface. Did you do longer stretches with multiple battery discharge/recharge cycle?
     
  6. VABeachPrius

    VABeachPrius Member

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    I am back after a five year hiatus. I got rid of the wife. She took my gen 2 Prius. Tomorrow I pick up a CPO 2010 Prius hatchback, package V. I feel like the lost child back after straying. Yes I drove a 20 mpg premium gas guzzler for a few years. It was nice and horrible at the same time. The nerd and cheapskate is back. Blizzard pearl, tinted windows; you know the rest. I'll have to shoot for another 1,000 mile tank :). The gen 3 appears to be such an improvement over the gen 2. Thanks for all your work bob, I am sure I will have a few questions. I hope I don't get too much abuse here; i still want a F430 Scuderia.
     
  7. F8L

    F8L Protecting Habitat & AG Lands

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  8. bwilson4web

    bwilson4web BMW i3 and Model 3

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    I still remember a day shortly after getting our first Prius nearly eight years ago when I realized I had become a Prius gear-head. I started reading SAE papers (yippie April, new SAE papers!), subscribe to AutoWeek, and the only people at work whom I could even discuss car technology using the right terms were the Corvette and Ford enthusiasts.
    You are in for a treat as somethings have gotten way better. Warm-up is much improved but there is room for improvement. The cooling drag is still higher than it needs to be and once the transaxle reaches operating temperature, it is a low-drag rolling beast with good, high-pressure tires. Handing is improved over the NHW11 although this means 'Prius handling'.
    My 'boy toy':
    [​IMG]
    I had just towed ~1,700 lbs of trailer and airplane, 600 miles, ~53-54 mph, ~28 MPG, through a NorEasterner. Yes that is my tow vehicle (need to get air-bags for the rear springs next time.) But around town:
    [​IMG]

    There is one other airplane owner at work and two flyers. Everyone else has learned not to mention either 'Prius' or 'airplane' around me unless they have time for a Bob-talk on my latest work. <GRINS> . . .

    I had just gotten up from a nap to work on a CAD program designing the next engine mount. I've already shipped off the original carbed, VW engine, 60hp @3200 rpm, 172.3 lbs. I am replacing it with a fuel injection, oil injection, liquid cooled Hirth 3502, 60hp @2400 rpm (prop), 112 lbs. Instead of a fixed pitch, wooden prop, it will use an electrically controlled, variable pitch, 3-blade composite prop . . . required by the slower turning prop.

    The plane is going through a major refit that should reduces the empty weight, improve the electronics, and speed-brakes to steepen the final approach. I am also looking at (testing required) a tri-gear design of my own making to improve landing. I'm not expecting faster as much as quicker takeoff, faster climb, similar range, higher reliability, quieter, and lower maintenance.

    Oh did I mention, don't use the word 'airplane' around me? <GRINS>

    Welcome back to the world of efficient cars!

    Bob Wilson
     
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  9. DumbMike

    DumbMike Active Member

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    Bob,

    I still think your graph is the best thing to happen on these boards. I think the numbers are accurate, but even assuming they are off a bit, people can still get the idea of what MPH they will be getting at the approximate speeds.

    Plus, you can't (and we can't) duplicate driving conditions. So, with a variance of 2-3 MPH either way, we still get a real good idea of the expected MPG.

    Thanks!

    Mike
     
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  10. VABeachPrius

    VABeachPrius Member

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    F8L,

    Thanks. I saw the leaders several months ago while cruising the forums. As Bob and others have proven, it is just a matter of driving slow enough, time, route, and patience. I have to do it at least once once I learn the car. The delivery trip home was 800 miles from Indianapolis to Virginia Beach. I had to be back and had little time which meant 75 mph 50 mpg. I am still on a partial tank from freeway driving. I pumped the 17 tires up and await a fresh tank to try for a good tank.

    Bob,

    I agree. I really like the gen 3 vs. the gen 2. The seat adjustment, layout, and warm up cycle is great. I don't know if it is good to coast in neutral during initial warmup? I don't know why the pips flash so early. I think I should be able to use what I understand to be 1-2 gallons after it flashes. It seems to agree with fuel used on the scan gage that I have 1-2 gallons left. Does the gen 3 stop when out if fuel or will it still move like when a gen 2 is out of gas?

    In limited screwing around, I can pretty easily see mid sixties for mpg, and mid 70's if I slow down and concentrate; I am rusty though. I have been using the brakes too often and I'm not anticipating traffic. Damn regular gas car brought back bad habits.

    Chris
     
  11. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Comments inserted.

    * * *
    . . . I don't know if it is good to coast in neutral during initial warmup?

    Run your Scangauge II showing 'GPH' and you soon find that there is about a 2x difference in the first 2-3 minutes between "D" and "N". Although warm-up is much improved, it still accounts for the bulk of the fuel burn in the first 5-10 minutes. These are not 'hard rules' as I just got a data recording OBD scanner, call these anecdotal observations:
    • ~45-55 sec catalytic converter warm-up - running open loop, the car will accelerate nicely using the ICE to speeds above 40 mph. Shifting into "N" puts the engine in minimum fuel burn rate and the instant MPG goes through the roof.
    • ~50-~120 sec coolant warm-up - thankfully the engine shuts down when the car is stopped. However, at a constant speed, shifting into "N" cuts the gallons per hour significantly. Sorry, I don't have hard numbers but it looks like once the coolant reaches a little over 50C, fuel consumption becomes closed loop, very efficient, and shifting to "N" is no longer helpful.

    I don't know why the pips flash so early. I think I should be able to use what I understand to be 1-2 gallons after it flashes. It seems to agree with fuel used on the scan gage that I have 1-2 gallons left. Does the gen 3 stop when out if fuel or will it still move like when a gen 2 is out of gas?

    I have only found one indication with our ZVW30 that it has finally burned the last of the gas . . . the arrows in the 'power flow' display disappear. It silently goes into traction battery mode and you can easily discharge it low enough until it suddenly shows a power steering fault, "PS", and becomes an inertial mass. When driving on 'flash', I switch to 'power flow' and monitor the power flow arrows. When they go away, I use the remaining traction battery power to find a safe place to park and add the spare gallon.

    My six fuel exhaustion experiments found from "flash" to "out of gas" there was 2.1 gallons with our car. I recommend checking your own car's "flash" to "out of gas" (carry a spare 1 gallon container.) In our case, I reset "B" trip meter when "flash" begins and use the MPG and miles to calculate how much fuel is burned. Since I'm running over 50 MPG, our 2.1 gallons is good for 100-130 miles to schedule a fuel stop when it works for me . . . the owner.
    * * *

    GOOD LUCK!
    Bob Wilson
     
  12. GasperG

    GasperG Senior Member

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    There is one more thing to think about when coasting in N when warming up. In D mode the battery is charging, not much, but it is charging, in N there is no charging to the battery. And if you are doing a long coast in N and engine is warm enough to shut down it wont shut down in N, so maybe you are still burning gas where in D enginu would already shut down.

    Maybe it is better to coast in N than D, but tell me how do you do a pulse in warm up and not drain your battery, I would let the engine run for 10 sec or so moving out the driveway, but then if I need to accelerate more quickly I must go into power region, just a little to hear the engine is driving the wheels, I think no more than 3.000 rpm.
     
  13. VABeachPrius

    VABeachPrius Member

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    GasperG,

    In my experience with my 2006, I saw a drastic increase in iMPG when I coasted in N during that period after the engine first starts. It is the same time period where acceleration does not change the engine RPM, but relies on HV battery. After that 30-45 seconds or so, I drove like normal until the car warmed up. So for example, when I would roll out of my driveway I would accelerate to the first turn, put the car in N, roll the corner (yield sign), go back to D, accelerate and coast in N to my first stop sign. Coasting in N during this period would result in iMPG of between 70-99.9 mpg vs. 25-35 iMPG.
     
  14. F8L

    F8L Protecting Habitat & AG Lands

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    I've observed something similar during long downhill runs when the engine had turned back on to recharge the ICE. Trying to warp stealth while the engine was on recharging the ICE the best I could manage was 130-150 iMPG but with the car in neutral I could do 300+ iMPG.
     
  15. GasperG

    GasperG Senior Member

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    I agree that instant MPG will be greater in N during warm up, I just wanted to say that in D fuel doesn't just go to waste but it does charge the battery, but obviously with all energy transformation loses, and you hypermilers want to use battery as little as possible.
    What is bugging me is how you accelerate during first seconds of warm up, luckily I have a slow downhill driving in the morning and don't need much power. But if I would have an up hill drive or higher speed from the start I would drain the battery during a warm up, so the question is what is better:

    a. wait couple of sec with car in N and foot on the brake, and get a fixed low fuel usage in gal/h.
    b. wait couple of sec with the car in P and then drive off, and get a little charge to the battery, that you can later use
    c. drive off and use as little throttle as possible, but draining the battery almost completely
    d. drive off and just touch the power region of HSD to activate the ICE directly drive the wheels, in trying to do this you would still loose a bar of the battery and put more strain on the cold ICE.

    As I don't like to sit in a car before driving off I usually end up with option c. and sometimes I use d. but let the engine couple of sec before doing that.
     
  16. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Excellent!
    This is how we should approach experimentation. Now about "c", this happens during the catalytic converter warm-up. Once you reach speed, shift into "N" and you'll turn off the traction battery drain. This reduces the battery drain until the catalytic converter begins operating in about 45-50 seconds. Thereafter, using "N" doesn't really buy much and the traction battery needs the replacement charge.

    Bob Wilson