B mode: What is the advantage to use B mode when driving, more regeneration? more economy?

Discussion in 'Prime Technical Discussion' started by Gaëtan Lafrance, Jul 5, 2018.

  1. Gaëtan Lafrance

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    Bonjour,

    Hi

    What is the advantage to use B mode when driving, more regeneration? more economy?


    Is it good for the mechanic of the car to use always B mode?

    Est-ce que mode B est bon pour l'économie de carburant et pour la regénération?
     
  2. schja01

    schja01 One of very few in Chicagoland

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    More regenerative braking for sure.
    I never used it a lot on my Gen 2 but when coasting up to a stop sign
    or stop and go light I used B mode as long as there was no one close
    behind (as the brake lights do not come on) to throw some extra juice
    in the battery and save the brake pads (if there were going to be used
    at all to make the stop).
     
  3. sam spade 2

    sam spade 2 Senior Member

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    Read your owners manual.
    It is intended to be used only for additional engine braking on downhill grades.

    All things considered, using it in "normal" driving won't really gain you anything.
    And it might cause you to suddenly decelerate WITHOUT ANY BRAKE LIGHTS......and that could be dangerous.
     
  4. jerrymildred

    jerrymildred Senior Member

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    What @sam spade 2 said. The owners manual spells it out clearly. At least the one for my version of Prius does.
     
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  5. FuelMiser

    FuelMiser Senior Member

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    As far as I'm concerned, you can use B mode all you want without worry of damaging any drivetrain components, but the intended purpose of B mode is when coasting down long grades, just like using lower gears in traditional vehicles. During long grades, the traction battery can become "full" and regen braking will be stopped in order to protect the battery from over-charging. All subsequent braking is then via the friction brakes. To help keep the friction brakes from over-heating, B mode uses the resistance of spinning the ICE to help with additional braking.
     
  6. jerrymildred

    jerrymildred Senior Member

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    And unless the battery is already full, it would take a humdinger of a hill to fill a Prime's battery.
     
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  7. Gaëtan Lafrance

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    Thanks,

    Merci

    Thanks

    Merci.
     
    #7 Gaëtan Lafrance, Jul 5, 2018
    Last edited by a moderator: Jul 6, 2018
  8. Mendel Leisk

    Mendel Leisk Senior Member

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    B mode might be a bit different on the Plug-Ins, considering the larger battery. All things considered, I would just put it in D, mostly leave it there. Personally, with a non-plug-in, I reserve B for long descents; even local hills I don't bother with it, it's a bit of a pain with the high revving. The only time I use it around here is for descent of Mount Seymour.
     
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  9. Gaëtan Lafrance

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    Thanks

    Merci.
     
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  10. FuelMiser

    FuelMiser Senior Member

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    In fact, the easiest way to descend a long grade is to set the cruise control and let the computer decide how to keep the speed under control. It will use a combination of regen braking, friction braking and engine braking (B mode) that it determines best suits the situation!
     
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  11. Old Bear

    Old Bear Senior Member

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    It is the equivalent of shifting to a lower gear when going down a steep hill. It uses regeneration to absorb some of the downhill kinetic energy into the battery, thus slowing the car with less wear on the brakes. (If the battery is fully charged, I believe that the internal combustion engine will be used in a non-running mode to assist slowing the car.)

    B mode can be used any time you want without damaging anything, but it will reduce the fuel efficiency of the car.

    I have found it useful at times when in stop-and-go traffic when I want the car to slow when I remove my foot from the accelerator pedal. One still needs to step on the brake to come to a full start, but in city traffic when you're 3 meters from the car in front of you and going from 30 km/hr to 8 km/hr and back, it can save you from having to move your foot from the accelerator to the brake pedal as often.
     
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  12. Tideland Prius

    Tideland Prius Moderator of the North
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    The B mode is there to simulate a lower gear on a regular transmission vehicle. (I think it's a law that a vehicle requires to have a transmission that can engine brake in case of brake pad or brake system failure)

    The transmission is electronically controlled so there's no harm in leaving it in B. However, if you are in hybrid mode, B will kick the engine on to provide engine braking and when you come to a stop, the engine will not shut off until you shift back into D.
     
  13. Gaëtan Lafrance

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    Merci Thanks for the explanation
     
  14. stevepea

    stevepea Senior Member

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    In EV Mode (all electric): "B" all the time can be very good (see below).
    In HV Mode (using gas): use "B" only for downhill, otherwise fuel economy will suffer.
    In "regular" Prius (NON-Prime): use "B" only for downhill, otherwise fuel economy will suffer.

    I have written lots of posts about this subject, please try to see if you can find them for more detail.
    I can tell you from 1.5 years of using my Prime that I use "B" ALL THE TIME (again, ONLY in EV Mode on the PRIME) and it works great.

    If you are doing slow driving (city driving, rush hour, start-stop, etc) in EV Mode the additional regeneration can help extend the EV range without having to use the brake pedal. If you are ONLY driving fast on the freeway, there is NO difference either way (in EV MODE) between B or D... so for myself, while I am driving in EV MODE, I just keep it in B all the time, and when my EV range runs out and the car switches to HV Mode, I then move it to D.

    It's also preference, some people like the "1-pedal driving" feel, others don't. After 1.5 years I can tell you, it has helped extend the range of EV for me at least (maybe because it's immediate regen, whereas there's a short time delay if you were to have to move your foot to the brake pedal... whatever it is, I see the difference in the numbers).

    But the trick is learing how to drive smartly in B. A lot of times you'll want that fast stop... but there might be times where you want to coast instead (more like "D") so you just keep your foot barely on the pedal. But you can do EITHER if you're in B (whereas in D you only have one choice: coast & brake).

    I've had my car 1.5 years and believe me, I wouldn't go through the extra effort if I didn't see the difference in the numbers, or like the feel of B. But it's only for EV mode -- NOT HV mode, or "normal" Prius (in HV or "normal" Prius, it's for going downhill only, otherwise it will eat more gas).

    But in all-EV mode, it can make driving easier and improve the range once you get used to it. Know that the one downside is that the brake lights will not come on (for the person behind you) in "B" --- the same as if you were in a stickshift car, and decided to downshift to brake.
     
    #14 stevepea, Jul 8, 2018
    Last edited: Jul 8, 2018
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  15. padroo

    padroo Senior Member

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    I like it in stop and go traffic to keep from tapping my brakes. Kind of like driving a standard transmission in traffic. Try it sometime.
     
  16. Pdog808

    Pdog808 Active Member

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    Remember as @stevepea mentioned it is only for EV mode.

    Because "B" mode increases the regen rate of the electric motors, your car will decelerate a lot more quickly when letting off the gas pedal in EV.

    Also, keep in mind that "B" also helps keep your regen bar from going all the way to the left which indicates you are using actual brake pads instead of the electric motor to decelerate.

    Brake pad usage = heat generated = lost regen energy = lower battery range.
     
  17. jerrymildred

    jerrymildred Senior Member

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    I've never heard that before. Is it actually in the manual or otherwise documented? If so, that would be a game changer, but there's nothing like that in the PiP manual. There's a maximum amount of regeneration available whether its from B mode or the brake pedal.
     
  18. Starship16

    Starship16 Senior Member

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    I ALWAYS want my brake lights to work. They don't come on if you're using the B mode? That's crazy! That should be illegal. It's clearly a safety hazard. Why would Toyota deactivate the BRAKE LIGHTS!

    What if I have to make a sudden stop while going down that hill? The idiot following too close behind me will probably rear-end me, because he doesn't see any brake lights. The brake lights should work in ALL driving modes.
     
  19. Mendel Leisk

    Mendel Leisk Senior Member

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    They're not deactivated. Basically, it's just that in B if you take your foot off the gas you tend slow faster (due to engine braking), compared to if you were in D. But still whenever you apply the brakes the brake lights come on, per usual.

    My 2 cents: fugedabout B, unless you're coming down a serious mountain.
     
    #19 Mendel Leisk, Jul 9, 2018
    Last edited: Jul 9, 2018
  20. Starship16

    Starship16 Senior Member

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    Thank you! I can calm down now. :ROFLMAO: Having no brake lights would be nuts! Back to my Pizza.
     
    #20 Starship16, Jul 9, 2018
    Last edited: Jul 9, 2018
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