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Hypermilage questions

Discussion in 'Gen 2 Prius Technical Discussion' started by Viscor, Jul 24, 2008.

  1. Viscor

    Viscor New Member

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    I've seen a great many articles/posts on people getting mileage in excess of 60 MPG and sometimes in excess of 80 MPG. I haven’t seen that kind of mileage. I typically get about 45 MPG in the city and around 55 MPG on the highway (Yes, I’m complaining about amazingly high MPG numbers. Go figure. ::)). I follow most of the basic “rules†that people have posted about keeping your MPG high. The techniques I used are:

    Note: all of the below is ONLY when it does not inconvenience drivers around me.
    1. I use cruise control.
    2. I try and time lights.
    3. I try, when possible, to accelerate with battery power only.
    4. I glide down hills.
    5. I keep to the speed limit.
    6. When I know I’m going to hit a red light I coast from as far back as practical.
    7. I keep my tires at the maximum rated pressure.

    So, my long winded question is “How are people getting these amazingly high mileage numbers?†The best I’ve ever done is 62 MPG on a run from Reno, CA to Stockton, CA (basically all down hill). I’ve NEVER seen MPG numbers higher than 65 MPG over more than a couple of miles.
     
  2. JimboK

    JimboK One owner, low mileage

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    First, to respond to your list items one-by-one:

    1. CC is good for average fuel economy, but better FE can be obtained in most cases by actively working the pedal to keep the ICE in efficient ranges. CC keeps speed constant at the expense of RPM.
    2. Good -- keep practicing.
    3. Don't! To force battery-only propulsion is less efficient than staying out of the battery when possible.
    4. Good. Make sure your glides truly are glides and not coasting.
    5. Good. Even better is to go lower, if safe.
    6. Good. Even better is to glide.
    7. Good.
    Then for a detailed analysis of how I routinely get 70-85 MPG on my commutes, see this thread.
     
  3. Austin50mpg

    Austin50mpg Prius Driving Right Winger

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    I can get 75 to 100 MPG while going between 18 and 30 MPH. I sometimes have all max 100 MPG yellow bars across my MFD in the last 30 minutes of my commute to work. However, while driving over 31 MPH I start loosing MPG's and end up with an average in the low 50's MPG per tank of gas. I suppose if you are in an area where you can go slower without people shooting the finger or bullets in your direction, you should be able to get the magical high MPG numbers.
     
  4. Viscor

    Viscor New Member

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    Ok, my newbieness is showing, but I'm not sure I'm clear on the difference between gliding and coasting.
    Coasting: Foot off the pedal
    Gliding: Foot on the pedal but electric only?
     
  5. Viscor

    Viscor New Member

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    Oh and while I'm at it. Is the EV switch mod worth the bother? I have a degree in Electrical Engineering so I'm quite capable of making the mod but it's unclear to me whether or not I need bother with it.
     
  6. nerfer

    nerfer A young senior member

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    Correct. On the energy screen, with coasting there is slight regen (green arrows from wheels to battery). This is to simulate how a normal car's engine and transmission causes drag with the foot off the pedal. For gliding, you have the pedal lightly depressed (or pressed, if you prefer), and there are no arrows (this only happens at speeds under 41 mph, except for warp stealth which is another topic).

    Earlier, when you said you keep your tires at maximum rated pressure, is that rating from the tire sidewalls (typically 44 psi) or the recommended pressure on the door frame sticker (35/33)? The door sticker is a recommendation based on a compromise of handling, life, fuel economy, ride comfort etc. Going above 35/33 PSI is probably step #1 for improving your fuel economy. I recommend at least 10% above Toyota's standard recommended pressure. (It's not a maximum pressure, as in vehicles that are rated for heavy loads they tell you to increase the pressure above that number when a load is present).

    And as mentioned, don't try to use the battery when accelerating. That borrows energy that must be replenished from the gas engine. The battery allows a smaller engine with the Atkinson cycle to be used instead of a larger engine with the standard Otto cycle, by delivering extra energy when really needed (passing, heavy acceleration), but it's actually not that efficient itself when you include the regen and storage steps.
    Bottom line, it's much more important to stop slowly than to start slowly (within reason, obviously don't try to chirp the tires on a green light).

    Probably not, unless you often move your vehicle a short distance and don't want to turn it on (if my understanding is correct). You have to be knowledgeable about when to use it, and somebody who has installed it can correct me on that. If you have winters where you're at, an Engine Block Heater (EBH) is probably more useful. That and a scangauge - if you're an engineer, read up on that little toy.
     
  7. JimboK

    JimboK One owner, low mileage

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    Nerfer's answer is on target.

    On the subject of the block heater, even if your winters aren't terribly cold, I would recommend it over the EV switch, especially for short drives. The greatest value of the EV switch to me is forcing ICE shutdown during warmup when the ICE is not needed for propulsion. After full warmup the ICE will shut down on its own. The EBH shortens the time to warmup and largely obviates the need for an EV switch for this purpose. And it doesn't carry the risks of the EV switch: worsening fuel economy by misuse and potential warranty issues.

    At the risk of overwhelming you (though I figure an EE can handle it ;)), here are two more links to long-winded discussions: one on gliding (in particular a comparison of two methods) and the other on the EV switch.
     
  8. FireEngineer

    FireEngineer Active Member

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    Did I hear engine block heater in northern California?

    Wayne
     
  9. JimboK

    JimboK One owner, low mileage

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    Uh-oh. Itching for another road trip again, huh? :eek:
     
  10. Viscor

    Viscor New Member

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    I think I'm getting the engine block heater confused with the ones I used when I lived in -40 deg zones. You either had one or had no hope of starting your car in the morning.

    I live just east of San Francisco and it gets a couple of degrees below zero maybe 2-5 days out of the year. If we're talking about a similar kind of beastie then I would hardly require one of those. The only reason I can think of having one in my climate is to help reduce the 2-3 minute VERY low MPG warm-up time. I therefore assume that's what you're getting at. Right?

    Oh, I should also mention that I gave the pulse-glide technique a go on the way home from work (about 4 miles) and was pleasantly surprised to get just over 60 mpg when I would normally have been lucky to get 48 or so mpg. I have to admit, however, that I am having great difficultly achieving the glide state. More often than not the car wants to go into the mode where it is drawing all power from the battery, back into pulse mode or into a state where the wheels are charging the batteries. I can only briefly (1 or 2 seconds) get into the glide mode (no arrows).

    Can anyone give me some tips on getting into the glide mode? (E.g. When I'm getting all power from the battery should I press down more on the gas? This would seem counter intuitive.).
     
  11. Genoz World

    Genoz World ZEN-style living

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    HOW about the EV switch mod? i'm eager to hear the census on that!
     
  12. F8L

    F8L Protecting Habitat & AG Lands

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    That is correct. Even with our normal 34-40deg winter mornings an EBH can help boost the MPG in that crucial first 2-4 minutes of your commute. I have not purchased one yet as I don't garage my car and don't want to have an extension cord hanging out in the driveway. I did start grille blocking though.

    I practice this sometimes to "artificially" boost my MPG # when I've had to deal with traffic and lowered my #s more than I would like.

    I think the first step would be to remove your shoe so you can get a better feel for the pedal. :)

    There are various explainations on how you should pulse (accelerate) so I'll let the experts go over that. As for the glide part. Once you have pulsed up to the desired speed simply lift off the gas pedal completely then very lightly press back down on it again. If you are under 39mph then you will see the green (battery) arrows appear for a brief moment then they will disappear and you will be gliding. If the green arrows remain then reduce gas pedal pressure slightly till they go away or lift off completely and try again. If you continue to have trouble then you could have a number of other issues that are inhibitig your ability to glide and they include but are not limited to:

    • Battery SOC is low and is keeping the ICE on to charge it
    • Battery is hot (you will still appear to glide but the scangauge tells it differently)
    • Engine is not up to operating temperate
    • You are on an incline (you can generally still glide but it's not effective)
    • You are over the 39mph limit for full no arrows glide (that's how it works on my '05)