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HELP on Arrows (or a Primer for the Arrow Challenged)

Discussion in 'Gen 2 Prius Fuel Economy' started by aknee87, May 7, 2004.

  1. aknee87

    aknee87 Junior Member

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    I've had my #9 for 3 weeks and am on 2nd tank of gas. After 400 miles on this tank at 45-46 mpg I, too, am jonesing for a bit higher mile. I know, I know...that's great mileage and I'm grateful for it, but when I see what some others are getting I know there's room for improvement. I'm sure the newness of my car is a factor as are the length of my commute and the hills in town, but I'm still hopeful that I can influence my overall mpg. In an effort to do so, I've been reading some of the previous posts and I must say that I'm not getting it on "the arrows". I assumed the best mode to be in was the one where the green arrows were heading back to the battery, like when I'm coasting downhill. Evidently not. Seems like I hardly ever have NO arrows. Part of my commute home is a low-speed (18-25 mph) meander along the ocean with very little uphill resistance. Seems to me that I should be operating on electric only at this time, but I don't think I am.

    Could somebody *pretty please* provide a non-technical neophite with a brief description of what's going on with the various colored arrows and their relationship to attaining higher mpg? Can you tell by the arrows that you are in stealth mode vs. ICE? Is, indeed, the optimum place to be no arrows? If so, what are the best conditions to achieve that "sweet spot"? I'd be eternally grateful to be straightened out.

    Thanks,
    Dazed and Confused by the Arrows
     
  2. seasalsa

    seasalsa Active Member

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    The only use I have found for the energy screen is for explaining how the Prius works.

    I drive by the consumption screen, it shows instantaneous MPG and is a great stealth indicator as well as showing how you have been doing in 5 minute intervals.

    I find that when the desired speed is reached it is possible to let up slightly and maintain the same speed. If the car is warm and you are moving less than 40 mph it will usually force it into stealth.

    Try it and see if it is not easier to drive with the consumption screen rather than the energy screen.
     
  3. rdverb

    rdverb New Member

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    I've found I only go into pure stealth mode reliably under 15 mph when the engine is warm, there's no call for more power, and the batteries are charged over ~60%. Faster than that, the ICE is used for power plus intermittantly to keep the battery charge up & keep warm, etc., depending on hills, wind, and acceleration. I think the arcade game display is only an approximation of what the car is actually doing because the engine runs more than is indicated anywhere. (A tachometer would be a good addition to see what the engine is doing.)

    I'm on the coast, too, and I think the engine cools off rapidly and needs to run frequently to keep up its efficiency and keep emissions down.

    To go into freewheeling coast, let up on the throttle until you feel the drag of regeneration (green arrows from wheels to battery), then just barely touch the throttle and the arrows should go off. You'll feel the drag let up when you get it.
     
  4. efusco

    efusco Moderator Emeritus
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    Dazed:
    First of all, you shouldn't worry too much about this right now, much will come with time and experience.

    But, since you asked, I'll do what I can to clarify some of the theory and practice of optimizing.

    Over on the 2G-Yahoo Group there's been some pretty extensive discussion of the ways to optimize mileage. One of the key things the Japanese drivers have found to be effective (though I'm a tad doubtful) is what's being called "Dead Banding". The theory with this technique is that any transfer of energy to the battery and then back to the electric motor from the battery has inherent loss of energy and thus is less efficient than using power exclusively from the ICE to the wheels. Of course there's no way to completely prevent battery and motor use, but minimizing it supposedly improves overall performance. My belief on this is that although it's probably true that you can improve mileage significantly with this technique, that it is more due to the fact that you're using a relatively small ICE for power at very low rates of acceleration and, in the long run, you're going to become very frustrated (as will other cars on the road) with the slow acceleration and low power mode. IMO, that is not how the Prius was designed to work and essentially defeats much of the purpose of a hybrid--they could have just built an underpowered ICE driven car if that was the goal.

    What I tend to do is this. I try to maximize "no arrow" driving. Think about it, when feasable coasting is the time where you are getting maximum fuel efficiency. You mentioned thinking that green arrows to the battery was what you thought would be most efficient. It isn't. The reason is that with green arrows to the battery (foot off pedal) the electric motor (MG1) is creating drag and recharging the battery. Although this is MUCH better than what happens with a traditional--non-hybrid--vehicle, there is still energy loss--you can't recapture all the kinetic energy during the transfer process. Also, you will slow down much faster than in a 'no-arrows' condition so you'll either have to wait longer to start coasting or you'll have to use power to maintain speed sooner.

    Now, what really happens with the 'no arrows'. It's hard to maintain a no-arrows condition for extended periods. But what you can do is accelerate up to your desired speed (this all assumes relatively flat terrain--hills make it much tougher) then 'Feather' the pedal. To feather I lift my foot quickly but very briefly off of the accelerator then very slightly depress it. If you're on the Energy screen (and you should as you're learning to 'feel' this technique) you will see the arrows showing the usual power from ICE and HV battery to the motors and wheels, then when you feather the pedal you might briefly see green arrows from wheel to battery. But you're shooting for no visible arrows at all. Depending on the Battery SOC (state-of-charge) and your speed of travel you may or may not be able to attain and sustain that 'no-arrows' state. It doesn't really matter, as long as you're close. Often, at higher speeds and lower SOC what I'll achieve is a frequent back and forth and maybe even brief periods of arrows from the ICE (by brief I mean 1-2 seconds max.) You'll have a definite seat-of-pants feel of 'free-wheeling' rather than the usual slowing felt in the foot-off-pedal coasting. You can then very gingerly depress the pedal to sustain 'stealth or hyper-stealth (stealth above 41mph--the ICE will be on even if you can't see it on the Energy screen) on level terrain with minimal use of power from the battery for very long periods of time and little power drain.

    You probably need to print that out and read it a million or so times then practice and practice to really get a feel for what I mean. It seems difficult and cumbersome initially, but it becomes second nature after a few thousand miles (I drove my Ford Expedition yesterday to pick up some furniture and found myself subconsciously using the feathering technique with it--didn't work so well!! :wink: .)

    If you have a long hill near you I think that's a good place to practice and get a feel for the difference b/w coasting (foot off pedal) and gliding (feathering then foot on pedal to achieve no arrows). I have one particular long hill on my commute. It is in a 60mph speed zone and I'm usually right at 60 when I start the downhill part. If I'm coasting I'll usually slowly gain speed and at the bottom I'll be going about 64mph (give or take 1-2mph). If I glide on that hill I'm almost always at 69-70mph and can then continue the glide for another 1/2 mile or more before I'm back down to 60mph--I'll usually nurse in a little battery use to make the glide longer while trying to avoid the ICE. There's an uphill section shortly after and I replace any used battery charge going up that.

    As you noted in your post, mileage will improve with experience and with time as the car breaks in. Be sure you've checked the oil level and that it is below the MAX level on the dip stick. Consider pushing tire pressures up to as close to the 44f/42r level as you're comfortable with. Turn off the AC when practical and keep the settings conservative when you do use it. Don't haul a bunch of junk around that you don't need. Really anticipate stop lights and glide/coast to them when you can--if you can avoid actually stopping that helps greatly too.

    I think you'll start seeing better mileage soon with that.

    Just for your own sense of reassurance, take a look at my mileage chart I have over at Jason's GreenHybrid.com site:

    http://www.greenhybrid.com/compare/mileage...ils.php?cid=129

    You'll see how my mileage has improved since I got to the 5000 mile mark. Warmer temps had a lot to do with it, decreasing or not using AC at all had a lot to do with it, but I think technique had the most to do with it.

    Sorry to be long winded, let me know if there are any details I can clarify, and if you're unfortunate enough to be in SW Missouri any time soon give me a hollar and I'll take you out for a driving 'lesson' in my Prius!
     
  5. aknee87

    aknee87 Junior Member

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    Thanks to you all, for your responses. I suspect that the coastal cooling may be a factor, too. A special thanks to you, Evan, for your detailed and encouraging response. I did some focused driving this weekend, and I am starting to *feel* what's going on a lot better, and I'm beginning to *see* on the screen what I'm feeling. I actually had quite a bit of no arrow time...very rewarding. I just filled up for the second time this morning and will see if what I'm learning affects this tank's average mpg. Unfortunately, my morning commute is a killer...short (8 miles), cold engine and uphill. I can't really do anything about that, but I will certainly work on the mpg the rest of the time. Again, many thanks.
     
  6. V8Cobrakid

    V8Cobrakid Green Handyman

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    I live in San Jose, CA... over here the roads are up and down.. it's not very noticable when i get more towards the city.. but out here where i live you have a raise of a couple feet.. and a drop.. then a raise.. then a drop.. i feel like i am on a kiddy roller coaster. On the way out, it's not too bad because it's technically down hill and i can average around 60 to 70mpg with a lot of effort. i've tried several things. One i find pretty effective (but i am abandoning it with this tank to test other theories) is to get up to speed.. well.. about 5 over.. then let off the gas.. slowly press the gas pedal till you are propelling the care with the ICE and charging the battery. If you are just barely maintaining speed, you should be getting around 50+ ( i get 55+ using this ) till the battery starts to get a little fuller... once it's charged to a higher level.. the motor likes to kick in and assist.. a this time my mpg can be as high as mid 80's.. but is usually around 70. as a constant speed driving condition.. i find this works well.. speed limit around here is mainly 45.. everyone usually goes 60.. i try to keep it around low 50's

    Learning the "better driving" techniques is hard for me. It is kindof fun to keep an eye on the screen to see what mpg your getting... but seeing that the radio is blasting and i keep the ac at 72, it's a bit more of a challenge to keep that battery full.... and i'm still a bit used to my 87 Lincoln Mark VII LSC with it's High Output 5.0L gas guzzler. I loved speeding around in that car... which.. i have a lead foot... I try to not use the lead foot and use the "enviromentaly friendly" foot... it's a lot of work ( like i've said) on my last two tanks.. yeah.. last two tanks.. i am averaging 42-43mpg. With lots of practice.. but unfortunetly lots of driving/zooming around on this tank, i might be able to pull 45+mpg average. Currently i am reading about 45mpg.. but i raised it from 43 today.. i almost have 200 miles on this tank. and 7/10th of a tank left

    btw.. when i fill up. i have 1 left.. and i put in 9.5 gallons
     
  7. jchu

    jchu New Member

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    Check out this link http://john1701a.com. He has the title of "Prius Guru" on PriusChat, very knowledgeable and has a lot of info on his web page. You will find your arrow questions answered here as well as answers to many other questions that you haven't even thought of yet.