Bmode and better regen

Discussion in 'Prime Main Forum (2017-Current)' started by isakprius, Dec 28, 2019.

  1. fuzzy1

    fuzzy1 Senior Member

    Joined:
    Feb 26, 2009
    13,852
    7,409
    90
    Location:
    Western Washington
    Vehicle:
    2012 Prius
    Model:
    Three
    This shouldn't happen, unless there is some change that I missed. MG2 has a fixed ratio to the wheels, and simply can't overspeed without exceeding the electronic speed limiter set (for flat roads) at something over 100 mph.

    MG1 will overspeed only when the ICE is off, not spinning, and the safe threshold speed for the Prime has been boosted quite high (to 80 mph???), well above Gens 1-3. With ICE spinning, MG2 is safe in all Prii generations, at least while under the electronic speed limiter.
     
    #21 fuzzy1, Dec 29, 2019
    Last edited by a moderator: Jun 11, 2020
    vvillovv likes this.
  2. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

    Joined:
    May 12, 2018
    3,721
    3,652
    1
    Location:
    Pennsylvania
    Vehicle:
    2018 Prius c
    Model:
    Two
    If you step on the brake pedal while in any drive mode with a full battery, you'll be getting friction brakes because there's no way to store the energy that would be recovered by regen braking.

    If you use B during a long hill descent, you get the gentle charge rate that you've documented. The car has no idea how long the descent will continue, so they've programmed it to make that drag effect last as long as possible. The reduced charge rate also causes less heating in the battery, which is better for long-term health. Lower temps also leave the battery more ready for a heavy draw to climb the next hill.

    By leaving it in B mode during the descent, the car is less likely to require brake pedal input in the first place. Also the computer is primed to divert torque into the gas engine for compression braking, which provides drag but does not depend on battery status. If the battery fills up, overheats or fails while you are halfway down the hill in B mode, the gas engine will still provide enough drag to prevent a runaway. If that happens in D mode, it's on you to figure out the situation and react to the problem, hopefully without burning your pads & rotors into ash.

    If you find that your use of B mode is not recovering as much energy as D + some pedal action per descent, then you are probably using it on flatter or lower hills than the situation it was designed for.
     
    #22 Leadfoot J. McCoalroller, Dec 29, 2019
    Last edited: Dec 29, 2019
    Mendel Leisk likes this.
  3. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    40,404
    28,942
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Maybe that should be printed out and tucked into the Owner's Manual, to supplant the cryptic explanation Toyota came up with.
     
  4. Dael

    Dael Junior Member

    Joined:
    Jul 6, 2019
    91
    19
    1
    Location:
    Ohio
    Vehicle:
    2020 Prius Prime
    Model:
    Limited
    Seems like MG1 has RPM limit so it has to drop out?
     
  5. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    8,163
    9,928
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    The Prime's transaxle is way different than a Gen 2. It's even different from a regular Gen 4 thanks to the sprague clutch. That's what enable MG1 to help power the car at speeds up to 84 mph. See Dr. Kelly's videos on the Gen 4 & Prime transaxles.
     
    Dael likes this.
  6. Dael

    Dael Junior Member

    Joined:
    Jul 6, 2019
    91
    19
    1
    Location:
    Ohio
    Vehicle:
    2020 Prius Prime
    Model:
    Limited
    The MG1 is limited to 6500 rpms? Need specs on new transaxle?
     
  7. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    8,163
    9,928
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    The Gen 4/Prius has a max rotation speed for both rotors of 17,000 RPM. It's a whole nuther animal.
     
    Dael likes this.
  8. Dael

    Dael Junior Member

    Joined:
    Jul 6, 2019
    91
    19
    1
    Location:
    Ohio
    Vehicle:
    2020 Prius Prime
    Model:
    Limited
    Thank you @jerrymildred !

    RPM starts here, sorry same video but starts at exact location.
     
    #28 Dael, Jun 11, 2020
    Last edited: Jun 11, 2020
  9. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    40,404
    28,942
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    I have a problem with those videos, not sure if it's John Kelly's voice or just all those fascinating gears, but I keep nodding off.
     
  10. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    8,163
    9,928
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    He does tend to drone. :LOL: But it's better now than that old Gen 2 transaxle video. :sleep:
     
  11. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    40,404
    28,942
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Yeah I could NOT stay awake through those. New Yankee Workshop the same problem; I'd typically konk out during the safety talk at the beginning, wake up when the finished piece was being varnished.
     
    jerrymildred likes this.
Loading...