Battery fully charged (saturated) during a descent, but ICE stays on for long time after that

Discussion in 'Gen 4 Prius Technical Discussion' started by flic, Nov 13, 2017 at 5:19 PM.

  1. flic

    flic New Member

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    Hi buddies, I have a gen4 since July and I am a bit disappointed for a strange behaviour that happens right after long downhills. During the long descents (in B or D) the battery become fully charged and ICE switches on. Nothing strange here. What is strange is that even after the descent is finished and SoC starts to be restored to 7 bars or less ICE remains ON for long time (silently, at low revs), even if the power required should normally recall for an EV only. This Behavior seems to be evident for a time that seems to be in a ratio of the time for which battery was saturated during downhill. I wonder why with a full battery, ICE stays ON for so long time burning fuel even with no or low power request from the driver. Battery temperature? I don't know, it happened in summer and autumn. Not sure. However it seems not my Prius fault, I'm sharing this thoughts with other Prius owners in Italy that have observed a similar behaviour.
     
  2. 2k1Toaster

    2k1Toaster Brand New Prius Batteries

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    If the battery is hot or overcharged, it will do this as normal. Also if previously driving in EV and the engine kicks on, it must complete a full warm-up cycle.
     
  3. jdenenberg

    jdenenberg EE Professor

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    The ICE is indeed spinning at the times you mention, but it is not "on". Your Prius is using engine braking (Acting as a vacuum pump) to dissipate excess energy, no gasoline is being injected into the cylinders. Regenerative braking is not available at those times and you will be using friction braking to slow your car down.

    There is one more time that this happens. I have "Full range" dynamic cruise control in my 2016 Prius. When it needs to slow the car down it spins up the ICE to dissipate excess energy and slow the car faster than standard regeneration would allow.

    JeffD
     
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  4. flic

    flic New Member

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    As said, Battery temperature may be the reason. Even using Hybrid Assistant we are not yet able to read such values on Gen4. The only thing I noticed that happened in summer time as well as during coming days with 10/15 deg C.

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  5. flic

    flic New Member

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    Hi Jeff,
    That's what happens during the portion of downhill with full SoC. Engine switches on (in B spins only, now burns fuel).
    But I'm talking a bit of what happen after the descent. You believe that with a fully charged battery you can start to use EV with ICE off for a while, but it is not what happens. ICE stays on even if you are pushing gently to keep the power in the EV area. Ah, if you try to push EV button at a proper low speed a message comes on saying that is not available at the moment.

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  6. alanclarkeau

    alanclarkeau Senior Member

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    You said "silently, at low revs" - which means it's not engine braking, which is far from silently.

    If you display the ENERGY MONITOR it will give you a much better idea of what is going on - it's much more useful and accurate than the Hybrid System Indicator:
    upload_2017-11-14_8-45-11.png
     
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  7. wjtracy

    wjtracy Senior Member

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    Assuming Gen4 still works like a Gen2, you need to first be aware of the hybrid warm up Stages. Final Stage 5(?) only kicks in after a full stop. So if by chance in your commute, you may never get to the last stage, that is sometimes the complaint.
     
  8. flic

    flic New Member

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    Indeed.
    Engine breaking (B gear) is astonishingly noisy when the Battery get saturated.
    While I'm telling you that, after downhill, you drive smoothly at low power using mainly electricity, and you expect the EV light to be plain.... but it's not. So you start to think that something is wrong with that light (it's not a bulb, so can't fail!) And paying attention to the engine you can hear it running at low revs.
    Try a long downhill tomorrow. Try it and believe me.

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  9. alanclarkeau

    alanclarkeau Senior Member

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    The EV light is despicably inaccurate, I threw that screen into the "don't bother" class after a couple of weeks with my car, never used it since.

    Use the screen I suggested (Energy Monitor) and it shows what's really happening.

    But, that said - mine will sometimes, for reasons unbeknown to me, tell me that "EV Mode is Unavailable", and the ICE will run whenever the car is driving, but turns off at traffic lights - maybe for 5 minutes, then goes back to "normal". I haven't been able to determine why - just some secret the microprocessors are keeping to themselves.

    I just go with the flow. I'm not quite sure if there is something as definable as "normal" with a PRIUS.
     
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  10. Trollbait

    Trollbait It's a D&D thing

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    I'll go with overcharge in the OP's scenario.

    The system doesn't use the full range of the battery's capacity; there is buffer at the bottom and at the top of it. This is to maximize the battery's life. There are times when the system will allow the SOC to go beyond the high and low points. Slowing down and stopping is more important than battery life for instance.

    On a long descent, the car will activate engine braking when the SOC reaches its top limit. Engine braking doesn't completely stop the regen braking while coasting though. So the battery is being charged beyond that top limit. Once you reach flat ground, and the system sees that you no longer coasting and gaining speed, it wants to get the battery SOC back into its safe range. If using EV mode alone isn't doing so fast enough, the ICE will be spun by M/G1 to use up battery charge. Gas isn't being burned.
     
  11. RCO

    RCO Senior Member

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    Can't remember who said it recently, but it is necessary for the ICE to turn from time to time simply to keep the various pumps lubricated

    NB, don't overthink it!!!
     
  12. flic

    flic New Member

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    Thanks for this hint, however it seems not this the case.

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  13. flic

    flic New Member

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    So, ICE would be used once at flat ground to faster discharge of the battery at standard levels? Interesting. Is this idea double checked using apps like Torque or Hybrid Assistant that gives you the exact percentage of SoC. I did not check personally (I'll do!) But quite sure to have seen screenshots in an Italian discussion where the upper limit reached was not 100 but 80%.

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  14. Trollbait

    Trollbait It's a D&D thing

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    80% is the upper limit for the NiMH battery, but the Li-ion limit will be close to that. So the full battery SOC on the car display is that amount. It isn't a hard limit though, and the charge can go higher under certain conditions. If it does, the car will try to get it back under 80% as soon as possible.
     
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  15. laevus

    laevus Junior Member

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    I drive in Italy a 2016 Prius4, with NiMh battery and ~20,000mi done.

    I normally use a ScangaugeII OBD device, in which I look, among others, at the SOC and HV Current xGauges. These values appear to be consistent with Prius instrumentation and with the evolution of driving conditions.

    Few months after the car purchase, some oddities started appearing at the ends of SOC range in the hybrid system, for low values (2 bars and <~43%) and, specially, for high values (7 bars and >~70%). Previously I had no OBD equipments and it is possible that I had not recognized these behaviors before.

    I recently serviced the Prius. The Hybrid Check test has been regularly passed and the HV battery fan appeared clean.

    Next behaviors don't depend, as far as I can evaluate, on the temperature of ICE or of Battery. Engine finished the warming-up and the Idle Check was already performed. External temperature and battery fan status did not suggest any overheating issue.

    - Early Saturation -
    It can start immediately after the the switching on of seventh bar (SOC> 67%), or slightly over. In any case, much earlier than usual values of other HSDs (8 bars and SOC at 77-78%). Seeing all 8 bars activated is not common.

    - Engine spinning persistence -
    Once the Saturation is reached, the time to restore normal conditions is often unexpectedly long. As normal conditions it’s intended, below 110kph, the switching off of the ICE when gas is released and the possibility of moving in EV under 1/2 ECO. Sometimes I drove for tens of kilometers, with the SOC even dropping up to 50%, before the ICE switched off again.

    - Low SOC recharging hysteresys -
    When SOC level is low, at 2 Bars and below 43%, the transaction discharging -> recharging seems to be retarded and losing an appreciable amount of energy. You can see for some time ~ -20A flowing into the battery ( > 4kW of recharging power) but the SOC, instead increasing, get lower of some %. The amount of energy dissipated before an actual charge starts and the SOC regain the initial value is appreciable. The black hole where it is absorbed is unknown.
    At higher SOC values, the discharge -> recharge transition is, as usual, immediate.

    - Forced Decharging after a Saturation -
    In, luckily, rare cases a saturation can result in a not interruptible forced discharge, characterized by ICE rotation and by production of a large amount of electrical power, up to more than 100A. The SOC quickly comes under 40% and continues up to level that the system considers appropriate. At that point the SOC restarts increasing and the system returns in normal state once it reaches 47% (upper limit of forced recharging). The SOC lower level I've seen is 24%. Normally it remains over 30%. In any case, the instrumentation continues to display 2 Bar of charge level.
     
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