B mode and regeneration

Discussion in 'Prime Fuel Economy & EV Range' started by Gaëtan Lafrance, Nov 15, 2018.

  1. Gaëtan Lafrance

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    Bonjour,



    Now, in city road in Montréal, I always use B mode on EV . In Montréal, there is a lot of stop sign and red light.

    Is B mode good to get the best regeneration with my Prius?

    Merci.
     
  2. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Yes, though it may come at the expense of coasting.

    Regeneration is a good way to save some of your kinetic energy for later. Coasting is a great way to use all of it in the moment.
     
  3. jerrymildred

    jerrymildred Senior Member

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    That's a good, succinct way to express the physics involved. When you use friction brakes, all the energy you spent getting up to speed is thrown away as heat, minus what little is lost to wind and rolling resistance. When you use regeneration, part of it is still thrown away because the current in the wires and windings generates heat, and the loss to wind and rolling resistance. When you coast, the only loss is to rolling and wind resistance.
     
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  4. sam spade 2

    sam spade 2 Senior Member

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    NO. It wasn't designed to be used like that.

    It will result in a large amount of regen braking every time you let off the gas.......even if you only need to slow down a little.
    In that case, it might actually cost you fuel in the long run.

    And......a personal opinion.....if you have to concentrate while attempting to eek out that last ounce of fuel use, you are not paying enough attention to driving SAFELY. Eyes on the road, not the display.
     
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  5. Usle

    Usle Member

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    If you watch the regen meter, using the B mode gives less regeneration than using the brakes.
    Below 12 mph the brakes are friction brakes, above 12 mph the brakes regenerate electricty.
     
  6. stevepea

    stevepea Senior Member

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    Short answer is Yes, but maybe I don't understand the question. Were you talking about just regen, or efficiency, or range?

    In either B or D, just lifting up your foot causes regen (B much more than D, though of course you slow down more).
    Pressing down the brake: doing so a little bit (in either D or B) will add more regen, but as you press more, it then becomes a mix of regen and brake pads.

    If you're talking about efficiency, there are many other threads covering this with caveats and explanations, but the short answer is yes, it's fine in B for stop-start city driving (it's what I do all the time, as long as it's in EV mode not HV). It doesn't hurt the car at all to use. It's just you'll get less efficiency when in HV (unless going down a hill, which it was designed for), but no harm or loss of efficiency if it's in EV if you know how to brake and drive using it -- brake differently depending on the distance. If you have a smaller distance to coast to a stop, just lifting up your foot is great (or obviously using the brake too if you need to). If you have a longer distance, then (even in B) you can keep your foot barely on the gas pedal to still longer-coast to stop (to simulate as if it were in D). But in city driving one usually winds up with shorter distances, needing to short-coast more than long-coast... thus B works out good. In the back of your head be aware that the brake lights don't turn on unless you step on the brake. I experimented both ways (D vs B) in city-driving EV mode, and while on paper it should be the same (or B no better) in the real world I find B extends my range (I get further along before EV runs out and ICE turns on when doing the same daily start-and-stop rush hour freeway drive, and get my best city driving numbers using B), maybe because of the time lapse putting your foot on the brake? I don't know. At any rate, what I tell people is, try it, if it works for you great, if not, don't do it. I've tried it both ways, and use B myself as the default for city, or start-and-stop rush hour driving (in EV) and have for well over a year now. Just also keep in mind, as soon as your EV range runs out and the ICE comes on, you have to remember to put it back to D, otherwise you'll start losing efficiency once the gas engine comes on if you're still in B.
     
    #6 stevepea, Nov 15, 2018
    Last edited: Nov 15, 2018
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  7. Gaëtan Lafrance

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    I did not know that. Thanks.
     
  8. PushingSquares

    PushingSquares New Member

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    Re: the brake lights not coming on when decelerating in B mode - Interesting point to know. I'm curious is this is also the case when using adaptive cruise control? Or is there a deceleration-rate threshold where the brake lights come on?
     
  9. sam spade 2

    sam spade 2 Senior Member

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    Yes and no. In that order.

    I suspect that vehicles equipped to actually do emergency braking automatically would also light the brake lights.......but I don't know that for sure.
     
  10. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    AFAIK cruise control (all forms) is unavailable when in B mode. When in D mode any use of brakes (regen or friction) whether triggered by human or automatic system will trigger the brake lights.

    The last 70 years worth of cars sold in the USA did not light up their brake lights when shifted into lower gear for safer grade descent; no reason for a Prius to do it either.
     
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