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Using "B" to slow

Discussion in 'Gen 3 Prius Main Forum' started by Angel And The wolf, Mar 28, 2024.

  1. Angel And The wolf

    Angel And The wolf Junior Member

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    In an effort to save my brake pads, and regenerate electricity, I have been pulling the joystick into B when approaching a stop. I worry that the brake lights don't light up until I depress the brake pedal, and that inattentive drivers behind will not notice that my car is slowing. Does an easy fix exist that would light the brake lights in B mode? I have a US model 2011 Prius. I also would like electric mode to work for acceleration without kicking out due to excessive speed, or excessive acceleration. My car has the NiMH battery pack. My ideal system would kick the car into B mode with a touch of the brake pedal, with lit brake lights, and back into electric mode when the accelerator is depressed, until Cruse Control is reactivated. The IC engine would only maintain speed.
     
  2. Mendel Leisk

    Mendel Leisk Senior Member

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    B gear supposedly reduces charging, substituting engine braking. I would reserve it for long downhill stretches only, and just keep an eye on the rear view mirror, say do a few light brake taps if someone behind is inattentive.

    For acceleration: the third gen’s battery will allow gentle, low speed acceleration without kicking in the engine, but anything more it’ll use the engine. Overriding this, either by tactics or mods, you don’t gain anything, and will run the battery down to 2 bars, which will force the engine on to recoup charge.
     
    #2 Mendel Leisk, Mar 28, 2024
    Last edited: Mar 28, 2024
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  3. ChapmanF

    ChapmanF Senior Member

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    Yes, the car automagically regenerates electricity to save the brake pads when you use the brake pedal normally.

    It does the same things in B mode, but only changing some parameters a little. You'll feel a slightly stronger slowing when your foot's off the go pedal (this is to make it feel like downshifting in some other car), while at the same time the car will be slightly less eager to regenerate into the battery, and faster to burn off the energy by twirling the engine. That's because B is specifically there for uncommon situations like long downhills, where you want to both protect the brake pads from overheating, and the battery from excessive charging.

    For other situations, you'll get better results just letting the car do what it's programmed to do normally.

    As a final note, regenerating energy into the battery is the second worst thing you can do with it. The worst, of course, is to burn it off as heat in the brakes or engine twirling and lose it forever. but stuffing it back into the battery is second worst. It costs you conversion loss on the way into the battery and again when you use it later.

    To the extent you can drive so that you keep your momentum and don't have to slow and then accelerate again often, that will be better.
     
  4. PriusCamper

    PriusCamper Senior Member

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    Just wrapped up a maximum lifespan experiment on original brake pads in a Prius at 288K miles. Could of got 300K miles out of the pads, but one of them had premature wear and turned into metal on metal before the others.

    In the weeks leading up to finally have time to replace the pads and rotors I was that guy with really noisy brakes and learned a great deal about how to use B-mode to slow the car down to limit brake pad noise. Main lesson is B-mode is a great way to slow down from your max speed without using brake pads, but not so useful at 15mph or slower.

    The worst part of the experience was any sudden unexpected hard braking even at super slow speeds, which would take miles of driving afterward to get the bad brake pad to stop making noise.

    I'm so grateful to have a quiet braking car again... It was so stressful to not have time to get the job done, but still needing to drive everyday.
     
  5. Tombukt2

    Tombukt2 Senior Member

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    How much saving of your brakes are you trying to do brake pads on a generation 3 take like 30 minutes and Axle to change if you're just slapping in pads and not fooling with the rotors I usually put in new rotors with pads personally they're that inexpensive now yeah I know cheap ones might not be flat and so on and so forth but we get around that pretty well just don't bother the cheapest junk you can purchase. Like I stated above we make $200,000 just about on regular brake pads in these cars generation 2's and threes so most owners don't actually get to change the pads because most owners are out long before that happened that's just the laws of nature generally speaking people are always trying to get a newer nicer or something so they don't generally make it long enough to change the pads they may wind up doing it just because they feel that something they need to do and then they take them off and see they're like half Worn . Woops
     
  6. PriusCamper

    PriusCamper Senior Member

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    Yep... When I didn't have a spare hour to do my front pads, I found these drilled and slotted front rotors for $48 and it gave me an excuse to procrastinate more soon as that first pad was metal on metal: Front Drilled Slotted Brake Rotors Pair 2 for 2004-2008 2009 Toyota Prius 1.5L | eBay
     
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  7. fuzzy1

    fuzzy1 Senior Member

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    This is all the more reason to use the foot brake pedal instead of "B" for flat-land stopping: the foot brake lights up the brake light, AND is more 'energy efficient' than B mode for similar braking effect, as others have explained. And under normal circumstances, when foot braking to the same effect as B can provide, the friction pads are only barely engaged, regeneration is doing almost all the work. If you aren't using the HSI display, bring that up and watch the CHG side of the display during braking. When it isn't pegged to the left, you should be within the regen-only braking range, absent certain temperature and other limits.

    Note also that B mode doesn't 'brake' any harder than downshifting in most non-hybrid transmissions -- or even as hard -- which also does not illuminate the brake light. So you aren't giving anyone a special surprise that they aren't already getting from non-hybrids.
     
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  8. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Yeah, just get better at soft-pedaling the brake earlier. You get more regen, more control, more safety, less workload (because it's just foot modulation instead of mode-switching) and the stop-lamp warning is built in.
     
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  9. Tombukt2

    Tombukt2 Senior Member

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    I believe mine are those are similar mine were coated with some black stuff and they're still black except for the contact area so the coating is done pretty well and I've had these on about 4 years now.
     
  10. ASRDogman

    ASRDogman Senior Member

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    It's very easy to just touch the brake pedal while in "B" mode.
    I use it ALL the time. If I notice someone behind me not paying attention,
    I'll touch the brake pedal just a little, which turns on the brake lights.
    And also aids the generators to charge the battery.

    It would require reprograming the computer(s) to notice that the transmission is
    in the B mode and to turn on the brake lights. Easier to touch the brake pedal...

     
    #10 ASRDogman, Mar 28, 2024
    Last edited: Mar 28, 2024
  11. fuzzy1

    fuzzy1 Senior Member

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    If he is is already using B early enough, then he doesn't even need to start soft-pedaling the brake any earlier. It should already be early enough.
     
  12. rjparker

    rjparker Tu Humilde Sirviente

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    305,000 on original rotors and front pads. Always quiet. Rear pads changed at 250k just because one rear hub was making noise. Never use B even though I live up a steep hill.

    IMG_4596.jpeg
    IMG_4595.jpeg

    Neutral causes more trouble
    IMG_4597.jpeg
     
  13. PriusCamper

    PriusCamper Senior Member

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    Did you break them in with 5-8 rounds of hard braking from 60mph to 10mph like the instructions said? I never found a road for that amid the current busy chaos in my life and given Prius wear on brake pads, I'm ok with a shorter lifespan because I'm about to hit 300K.
     
  14. Angel And The wolf

    Angel And The wolf Junior Member

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    Thank you guys. I didn't know the engine was connected in B. I thought all the drag down was due to the electric motors acting as generators. I learned a lot here. Guess I'll look into some of those motorcycle inertial deceleration lights. Suppose I'll wait 'til the traction battery goes, and convert to plug in. At 75, I can't afford to buy new, and we love our 2011.
     
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  15. Mendel Leisk

    Mendel Leisk Senior Member

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    Gotta ask: what’s the miles on it?
     
  16. ChapmanF

    ChapmanF Senior Member

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    Everything is connected all the time; this powertrain has no mechanical things capable of disengaging or shifting. Keeps it simple.

    The car can control the speed and torque of the different things, and blend those in different proportions. It knows all the same tricks in D that it knows in B, just as it knows all the same tricks in normal, ECO, or PWR modes. Essentially, these are all game-controller inputs that merely make small tweaks to the numbers in a recipe.
     
  17. PriusCamper

    PriusCamper Senior Member

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    Most vehicles on the road slow down at the same rate as Prius in B-mode, so people behind you are used to following someone who takes their foot off the gas like that. If you add additional lights to indicate that you're breaking when in B-Mode, the good is that you might have less chance of getting rear-ended at some point, but on the day to day, the bad is that you're going to increase traffic behind you because people will over-react to that after-market light indication.
     
  18. rjparker

    rjparker Tu Humilde Sirviente

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    One thing a Prius can do is apply a lot of braking power when you really need it by combining power hydraulic brakes with regenerative braking which can be very strong.
     
  19. fuzzy1

    fuzzy1 Senior Member

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    I'm betting that trading for a used Prime will be cheaper and better than doing a conversion.
     
  20. JimLudden

    JimLudden Junior Member

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    "B" mode does not use engine braking when plug-in hybrid is in EV mode -- the engine is not rotating.
    That chart (from rjparker) does not apply to Prius Prime.
    We use "B" mode all the time.