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Driving in bumper-to-bumper crawling traffic

Discussion in 'Gen III 2010+ Prius Fuel Economy' started by Misty fog, Feb 14, 2012.

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  1. Misty fog

    Misty fog Junior Member

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    Would like to discuss a technique that I've tried, i.e "Reverse Drive without Brake".

    During severe bumper-to-bumper, crawling traffic, I find that crawling along (effectively on EV-mode) is ineffective since any engine recharge (to bring up the SOC) usually will result in a *huge* FC hit. The SOC will only rise by one bar, which allows you to move on EV-mode for a few more meters before it recharges again. The FC hit is horrendous!

    It may be better to drive with a very heavy-footed pulse (not wide open, but well into the right hand region of the HSD gauge and perhaps into the PWR region), and holding that pulse until you are near enough to the next car that you need to brake (safely, and without triggering emergency friction braking). This is to ensure that the car moves mostly on gasoline (aided by some regenerative braking), which allowed me to hold off engine recharge for a lot longer, with moderate impact on FC (rather good as compared to engine recharge!). From several observations so far, this seems like an effective way to combat crawling traffic. However, it is also rather counter-intuitive and violates the "driving without brakes" principles.

    What do you guys think?
  2. qbee42

    qbee42 My other car is a boat

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    What you describe is a low speed form of pulse and glide, which is well documented on PC. The only difference is your use of the brake, which hurts mileage. You want to glide as much as possible, avoiding the use of the brake.

    Tom
  3. GrumpyCabbie

    GrumpyCabbie Senior Member

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    And despite the engine coming on to charge the battery, you're still using much less fuel than if you were driving a traditional car.
    1 person likes this.
  4. Misty fog

    Misty fog Junior Member

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    Hi Tom,

    To clarify, the traffic condition is such that any gap that opens up is probably the distance of about 1-3 cars, before it stops again. Initially, I have attempted P&G with gentle gliding (i.e. limited braking), but due to the small accelerating distance, the car never reaches sufficient speed to allow regenerative braking, and despite the heavy pedal, it still led to significant drain in battery SOC. I could not get this to work effectively. Therefore I tried a modified method which allows me to reach a higher speed, and although I will need to apply the brakes more forcefully, at least I could recapture some energy. I found that this worked better.
  5. Misty fog

    Misty fog Junior Member

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    GrumpyCabbie, agreed. Despite driving a lot in crawling traffic (i.e. move the distance of 2-3 cars, stop, move again), I'm still getting less than 6L/100km which is a lot better than the 10L/100km which I was getting in my previous car! But I'm still trying to figure out ways that I can optimize this. From my limited observation I might be able to squeeze another 10% mileage by unconventional means to avoid the engine recharge.
  6. bisco

    bisco cookie crumbler

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    what does 'reverse drive without brake' mean?

    what speeds are you getting upto before braking? i do this all the time and can usually avoid the brake until i'm creeping the last few feet to avoid hitting the car in front of me. btw, this always drives the person behind you banana's, and many times, people shoot into the space i leave before i hit the gas.
  7. Misty fog

    Misty fog Junior Member

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    What I meant was deliberate braking during extremely heavy traffic conditions. Since the gap is usually only the length of 1-3 cars, and the car in front of me is stationary, I had to accelerate pretty hard up to 20-30 kmph, with braking distance of 1-2 metres. With this method I found that I could hold off on engine recharge for quite sometime, and therefore avoid the big MPG hit. Of course the MPG was gradually falling as well with this method, but not as much as when the engine recharges the battery. FYI, my typical commute takes about 30 minutes over 8km, or average speed about 16kmph.
  8. qbee42

    qbee42 My other car is a boat

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    You don't want to do that. Regenerative braking is the least efficient method of recharging your battery. Instead, just use enough power to creep forward, and let the Prius worry about keeping the battery charged. You will get better mileage that way, and you won't have to fuss.

    Tom
  9. Codyroo

    Codyroo Senior Member

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    This is the type of traffic I hate, because I can't keep my SOC up on the battery, and like the OP, it drains quickly and my overall fuel mileage goes down when the engine tries to recharge the battery.

    I agree with Grumpy Cabbie, at least with the Prius, you are still getting better mileage that the other cars who are all idling in this situation. At least your engine is occasionally off.

    Of course, this would be a much better situation for an all electric car.
  10. Robsquatch

    Robsquatch Junior Member

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    Which one has a prius?
  11. jerrydelrey

    jerrydelrey Junior Member

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    I was surprised to realize that in crawling traffic the prius battery drains really fast.
    When I first test drove the prius, I was pleasantly surprised at being able to go all electric for a mile or so in 10-20 mph traffic. I had a 2006 civic hybrid, it has an engine off mode that can do the same, but not as graceful as the Prius.
    But in crawling traffic, the Civic’s mpg would drastically go down. Because the engine needs to be on to move a couple of feet. (In my commute I have a morning jam entering Pearl Harbor, So this is every weekday). One of the reasons I got the Prius, is I thought I can go all electric at least a mile in crawling in this traffic.
    But it wasn’t much different from the civic, The engine would come on with in a 2-3 minute wait, and I haven’t even come close to 1 mile. I don’t understand why the battery drains so much even when your not moving far. I say 1/8 a mile of stop and go, waiting for the car in the front to get checked. It should easily be able to go all electric. I have the A/C off too??? But the ICE goes on in about 5 feet of waiting. The civic would be completely off, and turn on when moving. The Prius would still be on, when I’m not moving. The mpg in crawling ended up not being much better than the Civics.
    I think when not at a crawl, just off the brake, not completely off, the electric motor is using a lot of battery power to overcome the brake, and crawl.
    So I think it’s more of a drain issue, vs a charge issue in crawling traffic.
    Maybe going to neutral when at a stop will make the electric motor completely shut off, till you need it to move. Making the battery drain less.
    Btw, my overall difference in mpg between the civic and prius ends up 41 mpg civic vs 45 mpg prius. (using fill up and milage data, not the computer). So the prius is still better overall, and it’s bigger.
  12. jerrydelrey

    jerrydelrey Junior Member

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    deleted because my computer reposted the same stuff.
  13. 32kcolors

    32kcolors Senior Member

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    Drive it like a bumper car. You know what I mean if you've been in one.
  14. Slugdoc

    Slugdoc New Member

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    THis is all odd.
    I've only had my prius 1.5 months, but I commute in heavy traffic in NYC. I can usually get from 132nd st (with a relatively full battery, getting off the Deegan) and Eco mode EV it nearly all the way to 98th St without having too much engine turn on. The only time I get the engine on is when I've got a rare clear block that lets me accelerate, and when that happens, I guess I give the battery some extra charge.
    But I never see the battery draining down enough that the engine ICE goes on unless I am purposely turning it on to accelerate...
  15. jerrydelrey

    jerrydelrey Junior Member

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    In heavy traffic, yeah mine does not turn on. But In the situation I was in, the car never got past 1-2 mph. When your foot is on the brake all the time, to move you just release the brake without pushing the gas. Like getting out of a parking garage crawl, or busy pay booth on a toll way.

    In heavy stop and go traffic, i can cruise along on electric for a long time.

    Everybody's commute is different, and you might not get in to this situation.
  16. El Dobro

    El Dobro A Member

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    I'm in stop and go traffic every day and the Prius is doing quite well with fuel mileage and the SOC. No complaints here.
  17. citybug

    citybug Junior Member

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  18. qbee42

    qbee42 My other car is a boat

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    A further reason for the frequent charge cycles during stop and go is the need to keep the ICE and catalytic converter hot. The Prius could cycle the battery through a larger range, but it would need to run the engine periodically to make heat, so it makes more sense to charge the battery.

    Tom
  19. bisco

    bisco cookie crumbler

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    distance matters too, how far is 34 blocks?
  20. puckdrop

    puckdrop Junior Member

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    I have a Gen2, and I think the following applies to your situation...

    In "constantly creeping" rather than stop-go traffic, I have noticed that the 8mph is not just the friction brake zone, its also the point where regen stops and the motor starts powering the car.

    This is effectively the "auto creep simulation" feature. Anything below 8mph for braking during creeping, and you're braking against the motor - watch it on the screen ( not sure if you get it on the G3 ).. the power flow never actually goes off until you stop.. and sometimes you have to really push the pedal down to cut the power flow..

    So, if you can, get it up to 8mph or more, and glide as much as possible, then stop quickly but gently from 8mph to zero to minimize the time you're braking against the motor ( wasted electricity ).
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