Hybrid vs EV mode

Discussion in 'Prime Technical Discussion' started by Pizza Driver, Oct 17, 2016.

  1. Lee Jay

    Lee Jay Senior Member

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    Yes, the "target" in regular hybrid mode is something like 60% charge. But even once it's there, you'll see energy flowing to the battery in the display the entire time you are at a steady speed on level ground despite the fact that the battery state of charge never increases beyond the target.
     
  2. Prius Maximus

    Prius Maximus Senior Member

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    Oh so you're specifying beyond maximum (60%) charge. Prior to that point the ICE does charge the battery, and I think that was the question Pizza driver was asking.
     
  3. Lee Jay

    Lee Jay Senior Member

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    In the Prime, that point will be below where Ev mode will work. It will be at 15% or something - 15% of a far larger battery, but still once Ev mode is depleted. The only ways to get back into Ev mode will be CHG mode, descending a big hill or plugging in. Driving an unlimited distance in normal conditions in Hv mode won't get you back to Ev mode levels of charge.
     
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  4. giora

    giora Senior Member

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    The LB first priority (engine warm) is to stay in EV if conditions allow (stop and go is an example) but when Battery SOC drops to the minimum allowed the engine starts to charge it partially.
    The second priority (EV is not possible) is that the SOC will stay at ~60-65% any drop from this level (like in acceleration) will be followed by charging the battery back to this level. Any increase from this (like in driving downhill) will follow by using the extra charge by the motor back to this level.
    This is all for protecting the battery.
    PiP, in HV mode, once EV is depleted, behaves the same, only in a SOC window of about 16-26% of the bigger battery. You cannot go back to EV miles unless you have a very long regeneration opportunity.
     
    #24 giora, Oct 18, 2016
    Last edited: Oct 18, 2016
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  5. GasperG

    GasperG Senior Member

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    If CHG mode runs the engine even when decelerating when ICE should be at 0 rpm then IMO that's just stupid engineering.
     
  6. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    A couple people have asked why I don't use an exterior charger. I live in a condo townhouse. I am not going to pay to install anything here and the association would probably veto it anyway.

    I used an extension cord to power my engine block heater until the snow removers rip it out and broke the heater. No way in Hell I'm exterior-charging my car.

    I'm sure someone will try to argue with me but I am more knowledgeable in my situation and am firm in my plans.
     
  7. Jan Treur

    Jan Treur Active Member

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    Do you mean that you only have a 1-car garage currently? Or no garage at all? In the former case, why not give this car the highest priority?
     
  8. JamesBurke

    JamesBurke Senior Member

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  9. GasperG

    GasperG Senior Member

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    Maybe because he has a Leaf in the garage ;)
     
  10. john1701a

    john1701a Prius Guru

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    I have no doubt that high priority of best use for the gas engine continued. Prius isn't going to sacrifice overall efficiency simply for the sake of offering more EV... unlike what others have done.

    The approach is to seek out a balance, despite the wide variety of uses it must fulfill.

    The expectation is that we'll see outstanding performance from charge-mode in some cases (like highway cruising), where we'll promote the use. In others, we'll discourage. But even when it's not as good of a return, it will still be clearly better than what a traditional vehicle offers.

    It is interesting reading those old posts. That serves as a great remember of what market expectations were and how they've changed since.
     
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  11. Trollbait

    Trollbait It's a D&D thing

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    Fair enough. I've heard enough about HOAs to avoid them for any of my homes.

    Or just the wife's, whatever it maybe.
     
  12. Pizza Driver

    Pizza Driver Active Member

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    I read through that thread. Thank you for linking to it. Let me see if I understand something.

    Currently, my Prius C generates electricity when cruising at 65 mph. According to the energy monitor, this is sent to the battery most of time, with the battery occasionally sending some juice to the motor. So it seems to me in my current "hybrid mode" (my one and only mode) I am generating enough juice during hiway driving to charge a much larger battery than the one I have.

    So is it our understanding right now that if I were to use the "charge" function under these circumstances that I could regain EV miles without seeing a decrease in efficiency compared to the LB being driven under the same conditions?
     
  13. Lee Jay

    Lee Jay Senior Member

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    No, that would be getting something for nothing. If you are charging the Ev battery, that energy is coming from the engine and being ultimately converted from the thermal energy in the gasoline. As Danny said, switching to charge mode reduces current measured mileage obviously by increasing the power output of the engine (and thus its fuel consumption) with the extra power being converted to electricity by the generator (MG1) and sent to the battery.
     
  14. Trollbait

    Trollbait It's a D&D thing

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    Gave some more thought to this.

    There is 33.4kWh of energy in a gallon of gasoline. For 20 miles on EV, the Prime needs 5.01kWH. That's based from the 133mpge figure, which includes charging losses from the wall.

    At 40% thermal efficiency, the engine needs to burn 12.525kWh of gas, or 37.5% of a gallon, which means it is a little worse than just burning the gas in hybrid mode.

    This is a YMMV number since when Charge mode is entered may put the ICE at its most efficient, or knock it out of it. Then the charging loss is assumed to be the same as for charging from the wall, and MPGe does not account for production losses, so I think the chances that the loss between the ICE and battery is worse than wall charging is greater. Finally, this ignores the negative impact Charge mode has on hybrid efficiency.
    The energy monitor isn't showing you everything, and what it does show is an approximation.
    You don't see the energy taken to run accessories like the lights, radio, and air conditioner. The arrows from the MG1 don't show how much energy is coming from it; modulating that is how the system varies the gear ratios.

    Then the battery monitor is just a percent charge reading for an @1.5kWh amount. The Primes usable capacity is at least 5 times this. Some slow steady growth of the SOC seen on your display would barely budge the Prime's display.

    A portion of the ICE's torque is always going to MG1. Ideally, any electricity it makes will go directly to MG2. The power demand of highway cruising is too low for this, and losses of storing this electricity in the battery is acceptable. Up to a up point. When possible, the system takes energy out of the battery to run MG2, and cut fuel to the ICE. This is a counter to the gasoline energy lost charging the battery, and keeps overall efficiency high.

    To charge up a battery in the Prime while cruising requires skipping those ICE off, MG2 operation periods, and thus reduced overall efficiency.
     
  15. giora

    giora Senior Member

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    The arrows on the monitor are "binary icons" in the sense that they are either on or off, when an arrow is on - you cannot tell if it is 10mA that initiate it or 10A... you cannot make a magnitude decisions out of them.
     
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  16. Pizza Driver

    Pizza Driver Active Member

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    I watched a video discussing how the transaxle of a Prius works. (2nd gen) One of the things noted in that demonstration is that above a certain engine RPM the generator has to kick in because otherwise it would spin too fast. I don't remember the RPM number, but if this is still the case, and depending on the engine reaches the RPM then it will be throwing off electricity regardless.
     
  17. Lee Jay

    Lee Jay Senior Member

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    And that generated electricity is going to the other motor - MG2 - to help propel the car.
     
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  18. Pizza Driver

    Pizza Driver Active Member

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    That shows up occasionally in my energy monitor. On occasion, at hwy speed, I see a line from the motor to the wheels as well as the battery, but mostly the flow seems to be going to the battery.
     
  19. Lee Jay

    Lee Jay Senior Member

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    And in that "mostly" mode, once the battery is at the target level, that flow is only there as make-up current to cover the electricity being drawn by the accessories. If the battery state of charge isn't changing, then no net electricity is flowing to the battery.
     
  20. giora

    giora Senior Member

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    From memory:
    the route: MG1 - MG2 - Wheels (without occasional battery "help") is not shown on the monitor at all, correct me if I am wrong.
     
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