Short trips? Here's a trick!

Discussion in 'Gen 2 Prius Fuel Economy' started by nooaah, Sep 19, 2008.

  1. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    i forced EV mode on startup one morning when it was 20º F. was simply moving car from front of house around to alley to park in garage. about 2 blocks of travel. did this because we were loading up for trip that would not start for another few hours so havent seen this inability to force EV in colder temps.

    as far as engine shutting down even when not warm, ya, it happens to me all the time and at the same light which is just over a mile from my house. water temp is usually only around 120 or so.

    *edit*

    ooops... just saw you said 90º... well, it happens to me every cold morning i drive the Pri, never paid much attention to the lower end of the temp range. problem is, the winters are usually mild, so i dont see temps in the 90's that often for more than a min or so after startup.
     
  2. efusco

    efusco Moderator Emeritus
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    It absolutely is possible to never get into S4...at some point you MUST come to a stop (or at least be below 5mph) with the ICE running until it shuts itself down. I've gone several hundred miles in S3.
     
  3. nooaah

    nooaah New Member

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    I experienced that today driving in downtown Philadelphia in 25 degree/F weather. Absolutely horrendous mid-30's mileage until I got on the highway. Then I was in the 50mpg range again. For some reason I always get mid-50's on the highway and 40's-low 50's on "city". I'd imagine it's due to the short blocks and hills. The roads in this area are designed so poorly it's almost criminal. They literally time the lights so if you hit one red light on a given length of road, you'll hit every single red for that stretch unless you REALLY speed.
     
  4. ken1784

    ken1784 SuperMID designer

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    http://priuschat.com/forums/knowled...le-mode-european-instructions.html#post163662

    The UK owner's manual says as follows;
    [email protected]
     
  5. ZooPrius

    ZooPrius New Member

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    I'm a newbie here but prius chat looks pretty useful. I bought a 2004 on e-bay a few weeks ago and live in the frozen north. So I know what you are talking about. I drove it home from Boston to Michigan and averaged about 50. The next few days the weather was unseasonably warm sso I was getting 62 mpg. Now I am hovering around 40. I am mostly driving 6 miles each way to work with some hills and some lights and speeds up to 45 mph. I see lots of great advice here. What is grill blocking? Is it safe? How about engine block heating? I have heard about it from people who live even further north but I have never needed one. Is this something you just place under the car or to you actually have to put it under the hood?
     
  6. dedes08prius

    dedes08prius Wifey's Prius

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    Sorry to ask but can you explain S2, S3, S4?
     
  7. dedes08prius

    dedes08prius Wifey's Prius

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    I'm only trying to improve my gas mileage. It always seems that the gas mileage is always low on the starting up no matter if you have left the car for 8 hours or 15 minutes. If we go on a short trip, I usually loose .2 to .4 mpg on starting and going a short distance such as a mile or two. I was going to look up Coastal but I don't have there e-mail address to check out their EV Switch. That sounds interesting.
     
  8. JimboK

    JimboK One owner, low mileage

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    http://priuschat.com/forums/prius-technical-discussion/25456-five-stages-document-back.html

    You are correct that fuel economy (FE) is low on startup, in large part due to the nuances of the warmup sequence described in the link I just provided. And you are correct that short trips hurt FE, though that is true in any vehicle. The effect is probably a little more exaggerated in the Prius, however, given that its ICE (internal combustion engine) will shut down if not needed for propulsion after warmup, but won't before.

    Two notes of caution regarding Coastal and the EV switch: First, Coastal has a very spotty customer service record in these parts. I wouldn't do business with them. I suggest doing a thorough search of this forum to get a good sense of their record before buying anything. At least then your decision is an informed (or one might say, forewarned) one. Second, the EV switch itself has drawbacks. I also suggest a good search to thoroughly educate yourself on its pros and cons. BTW, there are other options for the switch besides Coastal.

    Many of us use an engine block heater, with good results, to accelerate the warmup process and improve FE in the first few minutes. That's generally what I recommend to folks before an EV switch.
     
  9. Rokeby

    Rokeby Member

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    +1. In my experience, getting the most -- which isn't all that much -- out
    of the EV switch/mode in 20 degF and lower temps is not a simple matter.

    Jimbo,

    It is frequently stated that the EV mode is not accessable if the defroster is
    in use. And I've found that to be true. Lately temps here in Ballamer have
    been below freezing, and even with the defroster off I couldn't access EV
    mode.

    FWIW, I have found that even as low as 14 degF, EV mode is sometimes
    accessible with a stone cold ICE/HV battery if the AC is off. There seems
    to be an unknown to me condition that is relevant, perhaps HV battery
    temp. But, I would think that the difference in battery temps after sitting
    all night in 14F or 20F would be inconsequential.

    To make sure AC is off when I go to READY in the morning, I turn the AC
    off just before I shut down the night before.
     
  10. JimboK

    JimboK One owner, low mileage

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    Indeed, HV battery temp appears to be an issue. See this for another recent discussion. It certainly seems intuitive that when ambient temps are that low, six degrees wouldn't matter. I can't fully explain that; I can only speculate that it's actually more complicated and HV battery temp is only one criterion in the "deep-freeze battery management algorithm." Or maybe when EV works on a cold morning the HV battery temp was higher (e.g., from a lot of EV and regen) when the car was put to bed. It loses and gains radiant heat pretty slowly.
     
  11. Rokeby

    Rokeby Member

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    Jimbo,

    The HSD integrates two power sources the primary being the ICE, the
    secondary being the HV battery. Most discussions of maintaining high
    FE/MPGs in cold temps invariably include a recommendation to install
    an EBH to "preheat" the ICE. All well and good as far as that goes.

    But what about warming up the HV battery? I can't remember it being
    recommended too. It would seem like a logical next step. And on first
    consideration, relatively easily done with some sort of electrical warming
    pad, foot warmer, etc.

    Or have I missed something... really long warm up time... fire danger... ?
     
  12. JimboK

    JimboK One owner, low mileage

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    I seem to recall someone suggesting it. If so, I didn't pay much attention to it because "EV deny" from a cold battery has been so rare in my climate. And of course, as opposed to the designed-in capability for an EBH, the car isn't made for it. Many unanswered questions: What would one use for a heater? How to plug it in? How much of a pain to install and use? How to keep it safe? Any unanticipated side effects on battery chemistry or function? Would the fuel savings offset the cost to run it? Would the fuel savings offset the hassle of installing it and using it on the few occasions it's really needed? Etc.

    On the other hand, if someone wants to experiment on their own car and then can document safety and effectiveness, I'll consider anything that boosts my fuel economy by 0.002783 MPG. :D
     
  13. Fred_H

    Fred_H Misoversimplifier

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  14. Rokeby

    Rokeby Member

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    Fred_H,

    Thank you very much for the cite.

    So, the answer is yes, preheating HEV batteries to room temperatures can
    make a significant contribution to efficient charge/discharge at very cold
    ambient temps. The most efficient method to preheat is direct application of
    high frequency AC to the battery terminals. No way I'm doing that!

    But there is the suggestion that by preheating with hot air through the
    cooling duct will work, although with major inefficiencies. I guess preheat
    could be done with a hair dryer... probably a significant fire hazard.

    But there is still the possibility of contact heating with a heat pad, etc.

    I've got some reading to do. Here's the result of a preliminary Google
    search:

    hev battery preheat - Yahoo! Search Results
     
  15. Fred_H

    Fred_H Misoversimplifier

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    Good morning Rokeby,
    I think the most important thing to keep in mind is that it's important to keep the temperatures even within the Battery. Uneven temperatures are bad for the battery.

    I would say that we can rule out attaching heat pads to every single battery module, for most do-it-yourselfers. Using a heat pad on the outside of the battery pack would probably result in uneven temperatures unless special measures are taken. For example surrounding the battery completely with heat pads and heating it very slowly for many hours, or circulating air to distribute the heat more evenly.

    Which brings us to the air heating method. Of course, the Prius already has a good air circulation system for the battery, so we could just push some hot air through it. But simply hooking up a forced air heater to one end would be very inefficient, because most of the heat would be exhausted into the atmosphere at the other end.
    If you could figure out a practical way to recirculate the air without danger of overheating, then I think you could build a halfway efficient battery preheater. You have to make sure that air can not bypass the battery through the heater or recirculate to the battery when the battery needs to be cooled.

    I have thought a little bit about this before, but soon realized that on my wife’s daily commute, the benefit would be minimal, because the first part of her route requires no significant battery power, and by the time she gets to the part that does, the battery is sufficiently warm from the cabin heat.

    But for people who start their commute with a long city drive in very cold temperatures, I can imagine that a preheated battery could make a significant difference.

    If there’s not already an old thread about this somewhere, maybe you could start a new battery preheat thread in the technical discussion section?

    For HEVs battery preheat is not really necessary, but for the upcoming PHEVs, it will be important, and for BEVs battery preheat will be crucial in cold weather.

    Fred
     
  16. Rokeby

    Rokeby Member

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    Fred_H.

    Thank you for your thoughts. Your input has been very helpful as I think
    through this matter.

    I now believe that a recirculating warm air system would be most practical.
    Most likely, the system would use a 120V AC fan and heating element.
    It would require tapping into both the supply and exhaust sides of the HV
    battery ducting, and perhap using the cabin as part of the circuit -- some
    synergy there; preheating the cabin would tend to cut down on the interior
    windshield icing issues some folks experience. All this is not impossible, but
    daunting nonetheless.

    I think you're right. This topic should be given stand-alone visibility. I'm
    gathering data from various threads, and hopefuly a picture or two of the HV
    battery ducting. Hopefully I'll be able to post the new thread later today.
     
  17. LeoLucid

    LeoLucid New Member

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    You guys are nuts, gotta drive a little aggressively, get the juices flowing. Trying to max your EV on a cold engine and sitting on the curb to tease out 0.1% better fuel economy is what sucks the joy out of owning a Prius.
     
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