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Is there a legitimate use for charge mode in the Prime?

Discussion in 'Gen 5 Prime Charging' started by Will B, Oct 27, 2023.

  1. dbstoo

    dbstoo Senior Member

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    I'll ask again... What are the GPS co-ordinates of that stretch of hill where the car continues to pick up speed forever without any braking" ? Again, I remind Paul G that the car in question is a 2024 Prius Prime, not some other car. It's being driven in the normal D mode. And the phrase used by Paul G was "pick up speed" forever.
     
  2. ChapmanF

    ChapmanF Senior Member

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    There are grades where you will pick up speed forever, even with all the engine braking the car can do—depending on your speed at the start.

    For any downgrade, there will be a speed where your energy gain from gravity just equals what the engine can twirl off (somewhere around 13 kW in a gen 3, anyway), and engine braking can just manage to hold that speed steady. Start off below that speed, and there's plenty of engine braking to hold it or slow you. Right at that speed, holding steady is possible, and above it, you'll be picking up speed.

    On a tame grade, not much to think about because whatever speed you're likely to drive will be below that critical speed.

    On a very steep grade, you may have to choose a speed a lot slower than you'd like to drive, if you want the engine braking to be able to maintain it.
     
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  3. Paul Gregory

    Paul Gregory Active Member

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    Maybe it never happened because someone was actually paying attention while driving. It happens. They likely applied the friction brakes, or is they were smarter, they engaged the engine brake. No one wants to overspeed down a hill.
    It is there for a reason.
     
  4. vvillovv

    vvillovv Senior Member

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    The first time I saw the Energy Monitor graph after going down a steep drop starting at different speeds I called it dynamic regen. That was a long time before I understood anything about how Prius decides which way and how much to use its breaking and / or regen. A lot of owners most likely ever notice those differences.

    One difference I think most all of us could agree on regarding B mode is that it doesn't ever use friction brakes. At least not that I've ever noticed B using friction brakes.
     
    #124 vvillovv, Jul 6, 2024
    Last edited: Jul 6, 2024
  5. dbstoo

    dbstoo Senior Member

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    This is quite sad. Paul Gregory (or his bot) typed 5 sentences without ever addressing the point that I made and that he quoted. I've traveled over 400,000 miles in 4 Toyota hybrid models throughout the west and have never experienced the "pick up speed" forever that he's complaining about.

    One thing that I found disconcerting about the 2010 Camry hybrid's cruise control was that it would go into free-wheeling mode when cruise was set and the car was driving down hill. This is in direct contrast to the 2002 Prius cruise that would keep the speed steady even when going down a long, steep (6%) downhill stretch.
     
  6. ChapmanF

    ChapmanF Senior Member

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    In my experience, gen 1's behavior was different. I drove a 2001, but I've never heard '02 or '03 were different.

    In my 2001, cruise control worked just the way it used to work in conventional cars, where it was only a servo that pulled on the throttle cable. It could give you more go as needed when heading uphill, but didn't have any way to give you less go when heading down. Of course it wasn't a servo pulling on anything, just some logic in the HV ECU, but it was as if they had just copied the cruise control logic from their other cars and pasted it into the new ECU.

    So in my gen 1, I did combine cruise with B mode, so it would do a better job of holding my speed on the downhills. In D mode in gen 1, it would tend to pick up speed.

    So when I replaced my gen 1 with gen 3, when I first discovered the gen 3 cancels cruise if shifted to B so you can't use them together, my reaction was unprintable.

    But as soon as I had observed the gen 3 cruise control using engine braking on its own in D mode to keep my speed on downhills, I stopped cussing and realized they'd made it more convenient. I no longer had to shift to B to get downhill speed holding with cruise, because they had just made it how the cruise control now normally behaves.
     
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  7. Trollbait

    Trollbait It's a D&D thing

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    I believe that the general evolution of cruise control in general. Now they might apply the brakes if need be.