1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Do Hypemilers Really Need the electric engine?

Discussion in 'Gen 2 Prius Fuel Economy' started by driveprius, Jan 28, 2006.

  1. driveprius

    driveprius New Member

    Joined:
    Oct 30, 2005
    112
    0
    0
    Location:
    Delaware
    Some time ago a group of hypermilers were able to average 100 mpg or higher in a Toyota Prius. This was done in warm weather on a well chosen coarse. The technique they used was pulse and glide. The general technique was to accelerate in "deadband" mode and coast in with no arrows on the energy display.

    So if you able to follow this technique well then the electic motor would never get involved and the battery would stay at constant charge. The battery would never get charged or discharged. The overriding theory to avoid electric power is that while it's true that inefficiencies in power conversion to and from electric outweigh the benefits of being able to use the electric power to save on gas.

    So I pose this question. For those same hypermilers wouldn't they have been able to get the same performance in a non-hybrid Prius?

    So then I bring up the more interesting question. What truly is at the core of being able to achieve stellar gas mileage. Is it the electric motor or maybe it's really just the atkinson engine and transmission that allows you to coast without engine braking. Yes, I know it's kind of true that it's the electric engine that allows the atkinson engine to start up optimally, but I kind of pose the idea of eliminating the electric engine because of a more serious day-to-day driving question.

    So far in moderately cold weather (30 to 40 deg F), I've now started to master getting 50 mpg or higher gas mileage. I used to attempt pulse-and-glide and would generally only get in the 40's. In real world driving with cars closely in front and behind you there is little room to pulse and glide. You are generally forced to keep the same speed all the time. So now I tend to do a pulse and electric assisted glide, except now my glide stays at constant speed. The argument against doing this is that I will drain my battery. But you can generally only do this electric glide on level roads with light accelerator pressure so the battery drain is quite slow. It's actually difficult to drain our battery this way, because in real life driving you will eventually be forced to stop and accelerate again. Once you accelerate you'll be in pulse mode and will use gas and the gas will tend to charge up the battery.

    So now my general strategy is to be aggressive on draining the battery as much as I can, because when I do use just the battery I'm making a big dent in increasing my average mileage, and the opportunities to stay in this mode of driving tend to be rare. For me a good driving run is when I park my car and have only 4 bars left. This leaves me enough battery to start up initially in EV mode in the morning. A bad run is when my battery is showing green because it means there was plenty of wasted opportunity to have used pure electric. Although I'll have the fully charged battery available the next morning it won't mean very much because when the Prius is starting to warm up it tends to use the gas engine which tends to charge up the battery. So if your battery is already charged then the excess power of the gas engine generates during the warm up phase just gets thrown away.

    I've driven only 2500 miles in my Prius and so far this is my take on how to achieve 50 mpg or higher in normal city and suburban driving. I open the floor for comments from more experienced Prius drivers.
     
    #1 driveprius, Jan 28, 2006
  2. Tempus

    Tempus Senior Member

    Joined:
    Feb 17, 2004
    1,690
    6
    0
    Location:
    Washington DC
    Vehicle:
    2004 Prius
    I think your summary is essentially correct.

    True "Pulse and Glide" is clearly best when you can have a fairly siginificant variation in speed.

    When you need to keep up with traffic as in urban/suburban "Stop and Slow" traffic, you have to modify the technique, and periods spent on battery only to maintain constant speed can be very useful. The technique of feathering the pedal to get the ICE to shut off and allow you to use gentle battery power for long stretches is key.

    If you find yourself in what I think of as "Accordian" traffic, you can mix the two techniques. In an accordian situation, traffic breaks loose for a hundred yards or so, and everyone floors it to rush up to the next stop. You can anticipate the breakout when the cars a few lengths ahead of you release, and 'pulse' up to speed, then 'glide' as you see the brake lights flare up a hundred feet down the road. If you time it perfectly, you never have to touch the brakes and are ready for the next pulse when all those people who rushed to the next road block are ready to go again :)

    I get to practice that every day.
     
    #2 Tempus, Jan 28, 2006
  3. hdrygas

    hdrygas New Member

    Joined:
    May 22, 2004
    3,650
    6
    0
    Location:
    Olympia Wa
    Vehicle:
    2004 Prius
    My obeservations using the CAN-View suggest that "gliding" represents a steady drain of the battery at twice the rate of the at rest discharge. Dead banding at its best is rapid occelation between low level charging and discharging. When I am gliding on the MFD at my best I am getting a steady discharge of the battery. I think that gliding is just a lower level of electric mode. Dead Banding on the MFD does not recharge the battery at the same rate it dischages during "gliding". At no time are you near no discharge or recharge. At best you pass through that state. MG1 and MG2 appear to be intergral to the success of the hypermilers allowing the ICE to stop.
     
    #3 hdrygas, Jan 29, 2006
  4. tomdeimos

    tomdeimos New Member

    Joined:
    Feb 16, 2004
    995
    2
    0
    Location:
    Lexington, MA
    I use battery as much as possible but I also try to keep it as charged as possible. The battery is most efficient at the higher charge levels.

    I can never discharge much anyway, due to hills or traffic.

    So otherwise my technique is similar. I do make a point to run on engine power up virtually every hill, when weather is cool, because otherwise I am likely to be at a traffic light with a cold engine running just to warm up.

    In summer I may try to hold engine off for the smaller hills.

    So my general technique is battery on flat and downhill runs (which are normally not step enough to just coast on.) and engine going up hills with a good charge going to the battery.

    Beyond the points above, I try to stay engine off as long as I can.

    This can give me mpgs in the mid 70's in summer when traffic is light, but normally traffic causes too many stops and I may only get around 65 mpg. This is on routes going 35 to 40 mph.

    Most of my driving is on highways going 55 to 65 and then I am quite happy to beat the epa with anything over 51 mpg.

    Someone on Yahoo once calculated using engine and battery that 80 mpg could be doable. So far my trip record is 78.

    Some day I'd like to find some country roads with no traffic and try more pulse and glide, but so far I can't get away from the other cars enough.
     
    #4 tomdeimos, Jan 30, 2006
  5. hobbit

    hobbit Senior Member

    Joined:
    Mar 23, 2005
    4,089
    468
    0
    Location:
    Bahstahn
    Vehicle:
    2004 Prius
    Model:
    N/A
    The advantage of the Prius system is the ability to run the engine
    efficiently, or not at all. And move smoothly between those two
    states. You could try similar techniques in a conventional car,
    but how would you restart the engine? Bump-start it with a clutch?
    It's that or leave it idling.
    .
    "Glide" does send a little trickle of current from the battery into
    MG2, it seems. It's certainly a little more "push" than just
    popping into "N" -- and then asking for a little more push than
    that brings on the orange arrows on the MFD. I think someone
    found that the threshold is like 5 amps.
    .
    _H*
     
    #5 hobbit, Jan 30, 2006
  6. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

    Joined:
    Apr 13, 2004
    15,140
    611
    0
    Location:
    South Puget Sound, WA
    Vehicle:
    2013 Nissan LEAF
    Model:
    Persona
    yep max efficiency is the name of the game. the battery efficiency is pretty flat over a wide range of charge states. no so the ICE, its best efficiency has to have a certain RPM level. low RPM's are a killer and hurt a regular car. that also includes low torque situations at relatively high speeds. the hypermilers were able to do well because of the minor elevation changes that alternately increase EV time while also forcing the ICE to run at a better efficieny rating. coasting down the hill with the ICE running as in a regular car would be enough to put a large dent in the overall mileage because of the low torque, low RPM, inefficient engine range.
     
    #6 DaveinOlyWA, Jan 30, 2006
  7. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

    Joined:
    Apr 13, 2004
    15,140
    611
    0
    Location:
    South Puget Sound, WA
    Vehicle:
    2013 Nissan LEAF
    Model:
    Persona
    yep max efficiency is the name of the game. the battery efficiency is pretty flat over a wide range of charge states. no so the ICE, its best efficiency has to have a certain RPM level. low RPM's are a killer and hurt a regular car. that also includes low torque situations at relatively high speeds. the hypermilers were able to do well because of the minor elevation changes that alternately increase EV time while also forcing the ICE to run at a better efficieny rating. coasting down the hill with the ICE running as in a regular car would be enough to put a large dent in the overall mileage because of the low torque, low RPM, inefficient engine range.
     
    #7 DaveinOlyWA, Jan 30, 2006
(You must log in or sign up to post here.)