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Interesting Reddit Discussion from r/Prius

Discussion in 'Gen 5 Prius Main Forum' started by Paul Gregory, Sep 19, 2024.

  1. Paul Gregory

    Paul Gregory Active Member

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  2. ChapmanF

    ChapmanF Senior Member

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    This may be a more usable link to the same content, for anyone using cautious browser settings:

    /r/prius/comments/mhz3bd/

    Interesting that one commenter named Sam_Buck over there seems to believe that if the battery fills outside of B mode, regen braking will cease and nothing will take its place and the car will be "freewheeling down the hill like a runaway truck with failed brakes".

    A similar claim has been made once or twice here on PriusChat, but is at odds with what many Prius drivers, with and without datalogging instruments, have observed happening in that situation.
     
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  3. hill

    hill High Fiber Member

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    These are old reads & I'm not finding what is supposed to be so interesting. Perhaps the OP can elaborate by saying, "this is interesting because ......"
     
    #3 hill, Sep 19, 2024
    Last edited: Sep 19, 2024
  4. bisco

    bisco cookie crumbler

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    what would cause a driver to suddenly start using b mode in all slowing situations without reading the o/m?
     
  5. soft_r

    soft_r Junior Member

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    NOT THIS SHIT AGAIN

    WE DO NOT NEED ANOTHER B MODE THREAD
     
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  6. CooCooCaChoo

    CooCooCaChoo Senior Member

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    Especially one based on a reddit thread that is like 3 years old.

    OP, you do you. You wanna drive in B Mode, you go right on ahead. It's your car and nobody's gonna tell you how to drive.
     
  7. Paul Gregory

    Paul Gregory Active Member

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    It's obvious to anyone with eyes and half a brain, that the only kind of braking that happens when you let off the accelerator is regen braking. All you have to do is look at the regen gauge. It would make zero sense for the designers to waste energy on engine braking when regen works better and more efficiently.

    Those who think that engine braking works when the engine is off, don't have much of a clue. And it's true that the engine is off when you are coasting with the accelerator pedal off.
     
  8. ChapmanF

    ChapmanF Senior Member

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    When the battery has capacity to accept it, sure.

    So naturally they don't, when regen works better and more efficiently, which means when the battery has capacity to accept it.

    The designers did have a decision to make for what to do when the battery reaches full charge and can accept no more regen.

    At that point, as Sam_Buck over in that reddit thread seemed to think, the designers could have chosen for regen to cease, with nothing else replacing it, and the car "freewheeling down the hill like a runaway truck with failed brakes". You have made similar claims in other threads here.

    That could be called an odd choice for the designers to make, of course, because it could be kind of astonishing to a driver who isn't obsessively watching the battery state of charge and isn't expecting a sudden change in the car's deceleration rate.

    If the designers put a priority on not astonishing a driver like that, they could have made a different design choice, such as handing off from regen to engine braking as the battery reaches full charge, to keep the car's deceleration rate consistent.

    It is not hard to drive a Prius for a while and find out which choice the designers, in fact, made.

    On the other hand, those who think that engine braking is happening when their ears and/or OBD instruments tell them it is are simply paying attention to the clues right in front of them.

    "When the engine is off" is kind of a tricky phrase, as the engine certainly isn't 'on' (with fuel and spark) when engine braking. It only happens to be turning, which is easy to see on a tachometer and, at higher RPMs, easy to hear.
     
  9. Paul Gregory

    Paul Gregory Active Member

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    How "tricky" is it to see that the engine is not running when you are coasting? Your indicator panel shows it, and if you listen, you can hear it. How did the myth get started in this forum that engine braking engages automatically when you let off the accelerator? How can a stopped engine do any engine braking? Can anyone who has said that the engine is braking, provide any evidence whatsoever?
     
  10. fuzzy1

    fuzzy1 Senior Member

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    How could someone so seriously misrepresent what most other participants have stated or claimed in the other threads?
     
  11. rjparker

    rjparker Tu Humilde Sirviente

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    Paul has trust issues
     
  12. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Well if you've already rejected "readings on a tachometer" and "the sound of an engine being spun at high RPM" as evidence, then what would you accept as evidence?
     
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  13. bisco

    bisco cookie crumbler

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    a post on reddit
     
  14. Paul Gregory

    Paul Gregory Active Member

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    What tachometer?
     
  15. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    It's true that the car does not come with a readout, but that doesn't mean you can't add one- and many people have.

    It's literally plug-and-play, with regards to the popular ScanGauge II product.
     
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  16. fuzzy1

    fuzzy1 Senior Member

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    The aftermarket add-on tachometers that we have previously described multiple times.

    Though my '24 RAV4 Prime has it built-in from the factory, in one of the option packages.
     
  17. Paul Gregory

    Paul Gregory Active Member

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    Are you sure you're actually reading engine speed, and not rotor speed? Since there's no sort of clutch, the motor/generator must turn when the engine is off.
     
  18. fuzzy1

    fuzzy1 Senior Member

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    Both MG RPMs are also available. On a ScanGauge-II, and probably numerous other OBDII-port monitors as well, you can display Engine, MG1, and MG2 RPMs simultaneously.
     
  19. Paul Gregory

    Paul Gregory Active Member

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    So, you rejected my practical experiment, where I tried to prove myself wrong on a long slope, so you now move the goalposts and want me to buy an OBD to prove you right?
     
  20. fuzzy1

    fuzzy1 Senior Member

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    You rejected our practical experiments, instead changing the test procedures in ways that prevented the needed conditions from occurring.

    We didn't move the goalposts. You refused to look in the direction of the goalposts, instead running in various other directions away from the goalposts.
     
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