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The most misunderstood aspect of the Toyota hybrid synergy drive system

Discussion in 'Gen 5 Prius Technical Discussion' started by Paul Gregory, Jun 30, 2024.

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  1. ChapmanF

    ChapmanF Senior Member

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    Well, I found my cruise control applying about 13 kW of regen, as I went down a particular hill in Indiana.

    I'm pretty sure if I had canceled cruise and pressed the brake pedal, more than 13 kW of regen would have happened, up to whatever the power management control ECU was reporting for the charge control value at that time. The gen 3 repair manual gives a normal value for that as "−33 kW or more" (where they're saying "more" because it's a negative number, so, for example, −27 is 'more" than −33). The ECU can adjust the charge control value to "more" (i.e., gentler regen) if it finds the battery to be hot or tired.
     
  2. Fred_H

    Fred_H Misoversimplifier

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    Here is another documented example of how automatic engine braking in shifter position D works:

    Yesterday, by chance, I happened to drive down a hill with my 2007 Gen 2 Prius in D mode, and when the battery reached max SOC, engine braking automatically kicked in. I did not shift to B mode.

    Here is what my realtime display setup looks like:

    Data logging was also enabled with ten second log intervals. Here is a graph of a portion of the logged data, from shortly before regenerative braking, through the transition to engine braking, to shortly after engine braking:
     
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  3. bisco

    bisco cookie crumbler

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    great documentation fred, thanks!
     
  4. ChapmanF

    ChapmanF Senior Member

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  5. Paul Gregory

    Paul Gregory Active Member

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    I posted the video by an expert so we could all learn.
    Not to ignore to make your own arguments easier.
     
  6. Paul Gregory

    Paul Gregory Active Member

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    Incredulity is not a basis for refuting a claim. Flat earthers use it all the time.
    It's a logical fallacy.
     
  7. NullDev

    NullDev Junior Member

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    Out of curiosity, what data logger software is that? I have a semi-long hill on my interstate commute that I'd like to try as a test. However, it's about 20 miles from home, so I'm hoping I can keep the battery full prior to getting there. I suppose I should look into the battery charge mode that I've never found a need for.
     
  8. Fred_H

    Fred_H Misoversimplifier

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    That is the OBDLink app that came with my OBDLink LX. You can make customized dashboards on it, like the one above that I put together.
     
  9. Paul Gregory

    Paul Gregory Active Member

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    Why would Toyota create an engine brake if it were not needed?
    It's just common sense.
     
  10. KMO

    KMO Senior Member

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    It appears it may have hit a limit on its ability to follow the conversation.
    So it's back to fortune cookie mode.

    Maybe it can't actually parse images?
     
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  11. Mendel Leisk

    Mendel Leisk Senior Member

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    One reason I've heard: they're legally obligated to provide a gear that'll help slow you down.

    As to whether it's needed or not;

    The car has no way of knowing how long a hill is in front of you, and in D will only commence engine braking when the hybrid battery is nearly full. When you've got something like a downhill on a ski mountain ahead, this allows you to start the engine braking sooner.
     
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  12. Paul Gregory

    Paul Gregory Active Member

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    Where's the proof that engine braking kicks in automatically? If it does, why would there be a B position on the shifter?
    Think about it: When descending a long hill, the engine is stopped. The regenerative braking will have no place to put the energy, once the battery is full. What's stopping the car from picking up speed?
    The burden of proof is not on me to justify common sense, it's on those who claim that engine braking happens automatically.
     
  13. KMO

    KMO Senior Member

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    Not only has it failed to read the current page, it's got so confused that it's lost lots of context and gone back to an earlier section of the routine already tried. Turing test fail. (Which is quite tragic if actually human.)
     
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  14. Mendel Leisk

    Mendel Leisk Senior Member

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    You can hear it happening, when in D, when the battery fills.
     
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  15. Paul Gregory

    Paul Gregory Active Member

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    As a 12 yr Prius owner, I can honestly say I've never heard that.
     
  16. Mendel Leisk

    Mendel Leisk Senior Member

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  17. ChapmanF

    ChapmanF Senior Member

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    You posted a video by Car Care Nut, who bills himself (and I have no reason to doubt it) as having been through Toyota's technician training courses (check out the course materials under the Technical Library tab on TIS) to the "master diagnostic technician" level.

    That's a solid credential—we can say 'expert' if you like—and his videos are generally fairly well respected around here. That doesn't mean there are never mistakes in them. The video you linked had been linked and discussed here before, and the things that were right in it then are still right, and the things that were mistakes are still mistakes.

    The mistakes are generally on non-essential points. Like, does B immediately apply "full" regen? Clearly it doesn't, as anyone can show in seconds by comparing to the regen you can get with the brake pedal. Seems more like he got that phrase in his head and repeated it a few times in the video. While it's technically not right, it's kind of a side point and doesn't undermine the video's main points: the mode is intended for use on long downhills, and engine braking is involved with how it works. He's right about those main points. He's not the first expert who ever got the main points right and grazed the side points a little.

    I haven't seen anyone "ignore" the video you linked. It got discussed, recognizing the hits and misses, and leading into the further discussion in the thread.

    His video, by the way, never makes your claim that no engine braking happens outside of B mode. He explains the basics of engine braking and says that it does happen in B mode, which is all true. He never says, though, that it isn't used in any other mode. That's your belief, but the video you linked doesn't support it, and therefore nobody has to "ignore" the video just to see that your belief is mistaken. All it takes is to look at a graph such as that posted by Fred_H in #102.
     
    #117 ChapmanF, Jul 7, 2024
    Last edited: Jul 7, 2024
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  18. Paul Gregory

    Paul Gregory Active Member

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    Meaning, either that the conditions were never right for me,
    or that it doesn't happen.
    Not calling anyone a liar, just looking for actual evidence.
     
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  19. ChapmanF

    ChapmanF Senior Member

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    It's hard to tell what you are calling anyone. Maybe there is some way you are not saying I fabricated the quantitative results here, or that Fred_H made this graph in Photoshop,

    [​IMG]

    or that everyone else who has reported the same behavior is in on the con.

    But if that's not what you're saying, then what are you saying, exactly?
     
  20. NullDev

    NullDev Junior Member

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    I just want to take this opportunity to thank all the mods for paying us so well for our role in keeping up the con. It really is a thankless job and we couldn't continue to do it without you...



    /s
     
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