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Living at the top of a hill... Disabling engine braking?

Discussion in 'Gen 1 Prius Plug-in 2012-2015' started by Nougatti, Aug 20, 2016.

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  1. Nougatti

    Nougatti Member

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    I've lately been experiencing even worse behavior.. Let me know if this is common:

    I've got some 60-80% charge in EV mode and no AC running. Start going down a hill at 70 kph, braking to keep the speed limit at 70 kph. Battery charges as it should. Not even utilizing full CHG-area on the HSI. The hill is about 1 km long or so. When nearing the bottom, I can feel the brake pedal not increasing the charge as I press harder. And boom, engine fires up and starts engine braking. Battery isn't close to full either.. After medium strength braking for less than a minute... Is it normal? I've still got warranty and wanna know what you guys have experienced.

    Posted via the PriusChat mobile app.
     
    #21 Nougatti, Oct 6, 2016
  2. Redpoint5

    Redpoint5 Senior Member

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    Seems normal based on your description, but a video would be better. I have the ICE turn on all the time when using medium regen, but only after a longer period of sustained braking. I've yet to explain the phenomenon because no monitored temperatures go outside of normal range, and the battery should have plenty of capacity to take the charge. My best guess is it's a safety precaution taken by Toyota to ensure the battery doesn't get too warm. Perhaps the temperature probes on the battery don't react quickly enough to be reliable at protecting them.
     
    #22 Redpoint5, Oct 6, 2016
  3. Nougatti

    Nougatti Member

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    I'll try to get a video soon.
     
    #23 Nougatti, Oct 13, 2016
  4. Nougatti

    Nougatti Member

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    All right, here's a video I took today. Outside temperature 4'C (39.2'F). ICE has been on a couple of minutes ago to heat the cabin, but now the AC system is completely off and the car is in EV mode.

    Braking starts at 0:20.
    I let off the brake and throttle partially at 1:00 before braking further
    ICE fires up at about 1:20, having regenerated 1.1 km (0.68 mi) of EV range.
    So more or less a full minute of braking, though only moderate braking.

    Btw, keep in mind that fuel economy here is measured by fuel volume per distance driven [L/100 km] and not distance driven per fuel volume [mpg] like you do in the US, so the lower the number (and horizontal bars in the MPG display), the better. When the ICE turns on, you can see the bars pop up.



    Does everything look normal to you?
     
    #24 Nougatti, Oct 15, 2016
    Redpoint5 likes this.
  5. Redpoint5

    Redpoint5 Senior Member

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    Completely normal. This is exactly the scenario I described in my thread when I attempted to explain why the engine turns on. So far nothing explains why the engine comes on.

    I have found that traveling at lower speeds and using less regen can sometimes avoid the engine coming on.

    I suggest beginning that downhill portion from a slower speed, and trying to maintain a constant but gentle regen. This should avoid the engine turning on.

    Here is my thread discussing the topic.
    PiP Regen Behavior? | PriusChat
     
    #25 Redpoint5, Oct 15, 2016
  6. bisco

    bisco cookie crumbler

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    could the battery be charging too quickly?
     
    #26 bisco, Oct 15, 2016
  7. Nougatti

    Nougatti Member

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    Thank you for the thread link! Glad to know I'm not the only one trying to figure out the trigger..
     
    #27 Nougatti, Oct 16, 2016
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