Engine Starts at 100% Charge in EV Mode?!

Discussion in 'Prime Main Forum (2017-Current)' started by HanS0lo, Apr 27, 2021.

  1. HanS0lo

    HanS0lo New Member

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    Here is what observed today, I was on EV mode the entire time:
    1. 100% charge level before I head out
    2. 99% charge level before the Prime starts to go downhill
    3. 100% charge level at the middle of the hill,
    4. 100% charge level, engine kicked in at the bottom of the hill, (elevation loss is 315ft, I just checked Google Map)
    5. 99% charge level after I get on the highway, the engine stopped.

    Did anyone experience something like this before? Why the engine kicks in at 100% charge level during EV mode?
     
  2. Tideland Prius

    Tideland Prius Moderator of the North
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    Because you’ve maxed out the charge in the battery so the engine comes on to spin and “burn” the excess charge that you’re regenerating.
     
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  3. fuzzy1

    fuzzy1 Senior Member

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    ... also known as engine braking.

    It wasn't burning any fuel for propulsion, though it may have burned some fuel for engine warmup. To prevent this in the future, try to begin the downhill with a slightly lower battery charge. Leave some room for the battery to accept the downhill regeneration.
     
  4. Salamander_King

    Salamander_King Senior Member

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    Yap, perfectly normal on a fully charged battery on the downhill. If you routinely drive this downhill on a full charge, you may want to stop the charge slightly before the traction battery is 100% to give it room to store the regenerative energy.
     
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  5. HanS0lo

    HanS0lo New Member

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    I understand the engine braking, but why it is needed? There are 4 other brakes.

    So, I guess the regen braking stop working when the battery is fully charged? Why not just turn the regen off when battery is 100% charged?
     
  6. Henrik Helmers

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    I imagine putting the car in natural would disable regenerative and engine braking, leaving you with only friction brakes only. But the system is designed to work with regeneration and engine braking enabled.
     
  7. jerrymildred

    jerrymildred Senior Member

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    It waits till the battery is to the point where it needs protection, which is slightly over 100%. That's because when it does turn off regen, that starts the engine braking. So if it did what you suggest, the engine braking would start even sooner.

    Actually, even though driving in neutral is not recommended, this should work. I'd give it a try in that situation for sure. Many of us coast in neutral anyway to stretch our m/kWh. The bonus would be getting the rust scrubbed off the rotors sooner. The drawback would be a little more wear on the pads.
     
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  8. PaulDM

    PaulDM Active Member

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    I really miss the colour change of the battery indicator that was on the Second Gen Prius
    Blue - Normal
    Purple - low charge (ev button disabled and charging by ice initiated)
    Green - I’m full mode ( initiates voltage shedding as above )
     
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  9. jerrymildred

    jerrymildred Senior Member

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    The Prime still has a little of that. The EV part is green and the HV part is blue. No green showing means no EV range. But that whole section is full. On my car, the blue never gets more than a couple pixels below those little dividers between green & blue.
    IMG_0164.jpg
     
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  10. PiPLosAngeles

    PiPLosAngeles Senior Member

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    The ICE will also come on when the current is too high or the battery gets too warm, even if there is plenty of battery capacity to accept the charge. A steep hill for more than a few minutes can easily do this.

    There's a hill I descend semi-regularly that is about 20 minutes of B mode with brakes too. It always triggers ICE even when the battery is not anywhere near full. The ICE will run at something like 4,000-5,000 RPM on this hill (it's really revving hard, but I don't have a tachometer so it's only a guess from the sound and decades of driving manual transmissions). I only recently noticed that it seems that the car was not able to bleed off enough energy to prevent the battery from being "force fed" anyway, but that will require additional investigation.

    I need to get an ODBII and app so I can see the real SOC, engine RPMs, and battery temp in real time.
     
    #10 PiPLosAngeles, Apr 28, 2021
    Last edited: Apr 28, 2021
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  11. HanS0lo

    HanS0lo New Member

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    That 27.3 EV range is amazing! The highest I observed so far is just 25.4.
     
  12. Salamander_King

    Salamander_King Senior Member

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    With warmer weather starting, as long as you drive conservatively, you should see a steady climb on the GOM (Guess-O-Meter) reading all the way up to 50.0miles. Yap, that is the upper limit of the GOM display.
     
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  13. Trollbait

    Trollbait It's a D&D thing

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    Brake fade.

    People go down descents far bigger than little hills. Having the car automatically apply the friction brakes could lead to them overheating. When hot, the effectiveness of the brakes drops. Brakes getting hot enough to melt the brake line and ignite the brake fluid isn't impossible.

    On declines that don't require the driver to apply the brake pedal, that would mean the car would suddenly go from keeping steady speed or slowing down to speeding up. The hybrid system is designed to behave like an automatic transmission. Foot off the accelerator, it applies enough regen to simulate the transmission drag and engine braking of an automatic car coasting. Turning off that regen would be like shifting the automatic into neutral without the driver knowing it will happen.
     
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  14. HanS0lo

    HanS0lo New Member

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    Thank for all the explanation, it was a bit un-intuitive when I first hear engine kicked on when car is 100% charged, but now I understood the concept.
     
  15. fuzzy1

    fuzzy1 Senior Member

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    Absent engine braking, those friction brakes can destructively overheat when descending mountain grades somewhere in the range of 3000 vertical feet or more. Or less if the car is heavily loaded. I regularly use full engine braking on 7% grades with 2000 foot descents.

    The availability of engine braking is a legal requirement. On pre-hybrids, the driver can downshift.
     
  16. HanS0lo

    HanS0lo New Member

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    How did other full EV deal with this situation?
     
  17. jerrymildred

    jerrymildred Senior Member

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    Sorry to kind of rub it in but that is 27.3 miles left after having driven 9.5 miles. :D But that's unusually high for me. I can usually get about 32 miles in my go-to-work commute. There's another road I often have to drive that only lets me get about 27 miles total. Local errands on the 35 mph streets would probably get me 40 miles if I drove that far at those speeds. The other day on an errand, I got over 6 miles/kWh. Sunday on the aforementioned road, I got 4.3 m/kWh.
     
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  18. Trollbait

    Trollbait It's a D&D thing

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    Generally by having a bigger battery with larger upper buffer. I guess they could put the A/C or heat on full blast to use extra energy, or put the motor into reverse to use the magnetic fields for braking.
     
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  19. fuzzy1

    fuzzy1 Senior Member

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    The Leafsters and Teslarati will have to chime in on this. Regular Prii had to address it with a small-battery hybrid architecture before those large-battery models existed.

    But my first guess is similar to the first sentence of Trollbait's reply. The full EVs have much larger batteries than regular Prii and even plug-in Prii, so can have a much larger uncharged reserve (never filled by plugging in) at the top end to temporarily store regenerated energy before completely filling up. If this capacity is large enough to handle North American mountain descents without overheating the mechanical brakes, then they could be covered.

    This may also presume that BEV drivers are not charging while parked atop Pikes Peak and Mt. Evans. The cars charging at the base before climbing won't have any problem, the climb releases more than enough regeneration capacity for the descent.
     
    #19 fuzzy1, Apr 28, 2021
    Last edited: Apr 28, 2021
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  20. PaulDM

    PaulDM Active Member

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    I saw an interesting video on YouTube recently. Comparing Tesla with Prius (non PHEV)
    They drove up a mountain then down again. Pretty even on the costs but the Tesla took 2 hours to “fill up” and the Prius 10 min.
     
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