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"D" vs. "B" ?

Discussion in 'Gen 3 Prius Fuel Economy' started by Telkwa, Jul 18, 2011.

  1. Telkwa

    Telkwa Junior Member

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    I see plenty of posts regarding Eco Mode vs. other modes.

    Can anyone explain the deal with the "B" position on the shifter? The salesman said it makes the regen system act more aggressively. You could use it for long downhills, he said. I've tried flicking our 2010 into "B" when leaving the freeway via offramp. I could hear the car rev up fairly high. Not sure that's a good thing to do...

    If anyone can point out some posts or articles that explain the appropriate use of the "B" position that would be great!

    EDIT: Never mind, I found some good articles. I had the wrong impression of "B"; thought it put more energy into the battery.
     
    #1 Telkwa, Jul 18, 2011
  2. cproaudio

    cproaudio Speedlock Overrider

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    don't use B. When HV battery is full, B is activated in the background. You don't even have to shift to B for it to work.
     
    #2 cproaudio, Jul 18, 2011
  3. GrumpyCabbie

    GrumpyCabbie Senior Member

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    I use it BUT only when going down really long hills. It is an engine braking mode similar to that found on traditional automatic transmissions. It will rev the engine after a while but that is normal and is a way of the car 'running off' excess charge in the battery.

    In other words if you're going down a long steep hill use it as it gives you more control.
     
    #3 GrumpyCabbie, Jul 18, 2011
  4. Tchou

    Tchou Member

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    this is NOT TRUE, whereas the engine will rev when not into B Mode to avoid over-charing the traction battery, it will also stop the regen and allow the car to accelerate as if you were in N mode,
    the B mode allow the car to keep the regen while reving the engine so a part of the braking power is coming from the regen and not only from the brakes, allowing the brakes to not overheat…
     
    #4 Tchou, Jul 18, 2011
  5. cproaudio

    cproaudio Speedlock Overrider

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    When you're going really long down hill, use cruise control. The cruise control will activate regen to keep the speed match to the set speed. Once the HV pack is full, engine brake kicks in and maintain the set speed (automatic B mode). At the bottom of the hill, you'll have full battery pack. You can enjoy the rare occasion of driving in EV mode at freeway speed until it has depleted the pack to the normal 6 bars. The fastest EV/stealth I've driven is 76mph. BTW cruise control doesnt work in B mode,
     
    #5 cproaudio, Jul 18, 2011
  6. Teakwood

    Teakwood Member

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    "B" slows the downhill acceleration in much the same way as "L" on a regular automatic transmission, and is useful for some downhill stretches. However, one can also use the cruise control, in other cases.
    Personally, I use both methods and find that "B" is most useful on steep curvy hills which may require sudden changes in forward speed around curves.
    The cruise control method works well on long straighter downhill stretches in which the forward speed is expected to be steady.

    As to the comments above that suggest not ever using "B," that is just a lot of ignorant flatulence.
     
    #6 Teakwood, Jul 18, 2011
    1 person likes this.
  7. fuzzy1

    fuzzy1 Senior Member

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    You haven't yet driven your Prius down enough different hills, especially steep hills, and winding hills.
     
    #7 fuzzy1, Jul 19, 2011
  8. cproaudio

    cproaudio Speedlock Overrider

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    No, I haven't taken my Prius down Lombard Street yet.
     
    #8 cproaudio, Jul 19, 2011
  9. situationalawareness

    situationalawareness Member

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    I can attest that the "B" is very helpful in mountainous terrain. My last trip from Phoenix to Flagstaff & back hits some decent sized ones, and once my battery was full I had to use "B" to engine brake to have a better deceleration than the generator when you lightly press the pedal. It's a long run downhill at points, so it's not something you want your brake riding the whole time.
     
    #9 situationalawareness, Jul 19, 2011
  10. fuzzy1

    fuzzy1 Senior Member

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    I haven't taken anything larger than shoe leather down Lombard Street, but don't expect B mode to be useful there. The 5 mph speed limit is too slow to engage engine compression (~20 mph) or even regeneration (7 mph). And the 110 foot elevation change is not enough to fill a traction battery from its normal 6 bars, or to overheat the brakes.

    Try something a bit more challenging. Hills that come immediately to mind are many-thousand-foot-class descents such as Pikes Peak Road and Trail Ridge Road in Colorado, and Powder River Pass in Wyoming.
     
    #10 fuzzy1, Jul 19, 2011
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