Best practice, accelerating from red to green light

Discussion in 'Gen 3 Prius Fuel Economy' started by karma, Jun 12, 2013.

  1. karma

    karma Junior Member

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    I just bought a 2010 Prius, so newbie and learning everyday new stuff.


    To get good mpg, what is the best practice in accelerating from complete stop? Say the speed limit is 35, should I press gas paddle hard and quickly bring car to speed limit and then cost, or bring car to speed limit gradually by driving under ECO bar?
     
  2. Rupert B Puppenstein

    Rupert B Puppenstein Active Member

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    It depends. If there is traffic, then you can usually accelerate gradually and not sacrifice gas mileage. I am not one to make the drivers around me mad, so I tend to follow the speed of the traffic around me. If there are hills around, I tend to accelerate less conservatively knowing that I have a hill ahead that I can coast down and make up any lost mpg. It is all trial and error. But, I will say that I have learned to love traffic. ;)

    Don't focus too much on that bar when accelerating from a stop. You should focus on that more when your car is actually moving.
     
  3. macman408

    macman408 Electron Guidance Counselor

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    Don't keep it under the halfway mark, unless you absolutely have to; keep it on the right half of the HSI. The left half of the HSI generally correlates with electric-only propulsion, which is a bad idea when you're accelerating from 0 to 35 (but it's OK for going from 0 to 10 in a parking lot). Going a little way into the PWR bar won't kill your efficiency if you need to.
     
  4. bwilson4web

    bwilson4web BMW i3 and Model 3

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    You need instrumentation that includes the engine RPM. You can then accelerate at peak engine efficiency ranges and soon discover you keep up with traffic, nicely. Our 2010 has a Scangauge but there are many choices available today.

    Bob Wilson
     
  5. css28

    css28 Senior Member

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    In normal traffic I'm generally close to or into the PWR bar until I'm within 10 mph of the goal, then I gradually back off to about 5/8 of the entire scale to reach the speed.
     
  6. eliteconcept

    eliteconcept 700 mile club, top tank mpg 69.5

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    why would he want to keep it on the right of the bar? I believe he is curious about maximizing efficiency. If that is the case I'd think he would want to stay to the left of the bar and in the electric mode as long as possible. I do this on the 3 miles i travel home each day off the interstate, though several stop signs, I typically make it the whole way and only have to use gas for about 1/2 a mile. The trick is not having others behind you. However even in the city though stop lights you should be able to stay on all electric and then charge back up while breaking and slowing down for the next stop light.
     
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  7. Sfcyclist

    Sfcyclist Senior Member

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    Isn't this about accelerating from a stop? so to do so in a reasonable manner, you have to right of the bar? key word being reasonable. you can accelerate left of but that is what I call unreasonable manner.
     
  8. karma

    karma Junior Member

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    Thanks all for your response.
    Awesome car, awesome forum!!

    Macman408, why it is a bad idea to run it only in electric-only propulsion (left side of the bar) when you're accelerating from 0 to 35?
    Because I am in the same understanding as eliteconcept statement.
     
  9. macman408

    macman408 Electron Guidance Counselor

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    In general, it's a bad idea to use electric power; unless you have a plug-in hybrid, all power is coming from the gas engine, which necessarily means that there is some lost efficiency in the electrical path: It is more efficient to run the engine to power the wheels directly than it is to run the engine to power the motor-generator to charge the battery, and then later discharge the battery to power the motor-generator to power the wheels. All those extra steps in the EV path mean that you have to burn more gasoline for the same amount of power to the wheels.

    There are some exceptions to this rule; for example, if you are about to go down a very long hill that will fully charge the battery, you can certainly discharge the battery at the top and charge it back up for "free" on the way down (otherwise the extra energy would be dissipated in your brakes once the battery was full). Or, if you're doing something that would require running the engine at a very inefficient range - such as a very brief acceleration, very low speeds, etc; much like you would get from driving around a parking lot - then you can benefit from "borrowing" electric power, which will be replaced when you run the engine in a more efficient range.

    So for a normal acceleration, you probably want to use EV just a tiny bit as you get moving (I hear that the engine is inefficient at low speeds), which the car will mostly do naturally since the engine is already stopped. Then you want to keep it at a medium RPM (~1900-2100 or so) for most of the acceleration, since that is the most efficient range for the engine.

    Related to this, if you have used a lot of electric power before and the battery is below about 58% SoC, then you will reach 2000 RPMs earlier on the HSI, as the car is putting extra power into charging the battery. Likewise, if the battery is over about 62% SoC, then you can accelerate faster and sometimes go well into the PWR bar before hitting 2000 RPMs, as the car is trying to rid itself of extra stored energy - it always wants to be at 60% SoC. Unhelpfully, the 6th bar on the battery icon encompasses about 55% to 66.5% SoC, so without external instrumentation, you'll have no idea whether you're above or below that magic 60% mark (nor what the RPMs are, for that matter).

    All of this generally adds up to many experts' recommendations for the Prius: Just drive it. It'll figure out what to do, and it'll do a darn good job of it 95% of the time. You'll get far more benefits from anticipating stops and coasting to them from as far away as possible than you will from accelerating at exactly the "correct" rate.
     
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  10. jhinsc

    jhinsc Senior Member

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    Yesterday was a hot one and I was shuttling customers to see several homes. With the a/c running full blast, it doesn't take long for the SOC to get low. When I left work to go home, temps were still 96-99, so with the a/c running full blast, set at 75, making my way at 55 mph, I barely was getting in the 40's on my instant mpg's, and unfortunately I have no hill's to take advantage of free charging. I think I lost 1 mpg on this tank just during my 22 mile drive home. Point of this story is when you let the SOC get down low, it really affects your mileage because the ICE is now accomplishing dual tasks of moving you down the road and charging up the battery. And with me running the a/c full blast, the poor battery was struggling at lights to maintain it's charge. I did turn off the a/c for about 90 seconds at a light. I was amazed how quickly the temp's inside started soaring!
     
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  11. css28

    css28 Senior Member

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    The point of the story was that you had a lot of air conditioning to do. The AC is much more efficient when you're in motion, with the extra air flow through the condensor in front. The SOC got low because you managed to spend some time with the engine off while the air conditioning was running.
    The consolation is in thinking what your mileage would have been in similar circumstances with you previous, conventional car.
     
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