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(B) braking.

Discussion in 'Gen III 2010+ Prius Technical Discussion' started by Caug1, Jun 12, 2011.

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  1. Caug1

    Caug1 Member

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    I ve been using B for braking. it works fine for me, but should i use it all the time?
    Would it heart the car in any way?
    Please let me know.
    Thanks,
    C
  2. firepa63

    firepa63 Former Prius Owner

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    It won't hurt your car, but it will hurt your MPGs. Use the 'B' only when going down long hills. Otherwise, use your regenerative braking to slow the car. The friction brakes don't come into play until about 7 mph.
  3. jdcollins5

    jdcollins5 Senior Member

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    The B-mode (engine braking) runs the ICE without fuel to act as an air pump to slow the car. It will never hurt the engine to do this.

    As stated above, the main purpose for this is for going down long downgrades. After the battery gets fully charged in regen, it will stop taking a charge and kick out regen. You will have to use either the friction brakes or B-mode. This is when B-mode is most effective.

    Having said that, I like to use B-mode every now and then when going around corners. It reminds me of downshifting in a manual.
  4. bisco

    bisco cookie crumbler

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    i have never used B in 8 years. what would posess you to do that?
  5. JGC61

    JGC61 Junior Member

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    I have been using the B mode to slow down at highway speeds.
    Most times I can slow down without using the brakes and charge the battery at the same time.
    Just remember to shift back to Drive or your economy will be suffer.
    Have been getting at least 50 MPG and many times more.:D
  6. Teakwood

    Teakwood Member

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    Well, just maybe, when one is following a long downgrade, it makes sense, just like down-shifting.:attention:
    Huh? Maybe? Ya think?:eek:
    Sheesh!:eek:hwell:
  7. bisco

    bisco cookie crumbler

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    not in this part o the country. never downshifted in any automatic i've owned around here. havn't been out to the rockies.
  8. qbee42

    qbee42 My other car is a boat

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    If you want to slow down and charge the battery, press the brake pedal. Using B mode throws away energy that would otherwise go into the battery.

    Tom
  9. JimboPalmer

    JimboPalmer Nadir of Wrongness

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    And again, B mode is less fuel efficient than normal braking, it is poor at recharging the HV Battery. Just think what your mileage could have been if you did not use B mode.
  10. Teakwood

    Teakwood Member

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    More flat-lander jibberish.
    In the mountains, "B" recharges the battery just fine.
  11. bisco

    bisco cookie crumbler

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    maybe, but caug is from boston.
  12. Caug1

    Caug1 Member

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    I thought, by using ( B ) it will charge the big battery more, which i use for pulse & glide, more juice it gets more gliding i can get out of it, right?
    why my mpg will go down by using it?
    The last tank of gas @51.50 corculated vs. 52.50 on display. once drove with 6 people all night from bar to bar. Also had a couple of 100mph runs. Basically drove it like i stole it. didn't in really baby the car on last fill up.
    Thanks,
    C
  13. bisco

    bisco cookie crumbler

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    i am speechless.
    1 person likes this.
  14. Prius-it

    Prius-it Junior Member

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    One thing I found useful is using ( B ) braking when I need to brake hard. Engine braking like characteristic helps the car stop much faster/shorter distance.

    Caug, just think of B braking as engine braking. If you put a Prius on a B mode and drive, the car will put RESISTANCE against the car going forward.

    Another example would be....Prius's drag coefficient being lower, allowing less wind RESISTANCE against the car, thus assisting in the car's fuel efficiency (the car doesn't have to work harder to move).

    I don't have any technical background/document to back this up. This is solely based on my assumption using my common sense. So...I could be wrong. :)
  15. JimboPalmer

    JimboPalmer Nadir of Wrongness

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    He lives on Long Island. You point out the mountains on Long Island and I will retract everything I said.

    I have consistently praised B mode on hills with more than a 600 foot drop.

    http://www.oregon.gov/ODOT/MCT/docs/EmigrantHill.pdf?ga=t
  16. ksstathead

    ksstathead Active Member

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    B mode substitutes engine braking for a portion of regen braking. Better to use the brake pedal for greater regen EXCEPT where the slope is long enough to fill the battery before reaching bottom.
  17. Caug1

    Caug1 Member

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    Cool thanks to all, but still dont understand ,why it should hurt mpg.
  18. ksstathead

    ksstathead Active Member

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    It hurts mpg when you spin the engine instead of putting more of that energy back in the pack. Spinning the engine requires energy. Recharging the pack requires energy. The kinetic energy of the moving car is fixed at a point in time, so it is a zero sum game. That which goes to spinning the engine cannot go to the pack. The brake pedal does not spin the engine unless the pack is full.

    B on long descent is not a problem since the pack gets full by the bottom anyway.
  19. Caug1

    Caug1 Member

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    So to get better mpg i should not use it at all, right?
    Then why bother with long down hills in B mode, if i could use brakes and it will not hurt the mpg?
    I think we should use it Only in the snow storm going down hill, right?
    The only useful/safety place to use b mode.
    c
  20. qbee42

    qbee42 My other car is a boat

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    Think of it like this: If you tie an anchor onto the bumper of your Prius and drag it around, will it help or hurt mileage? B mode is like tying an anchor to your car. It deliberately wastes energy. That is its one and only use, to toss away excess energy.

    Your Prius recaptures energy during standard braking, which is why it is called regenerative braking. In B mode it recaptures *less* energy.

    Tom
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