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To burn or not to burn

Discussion in 'Gen 2 Prius Technical Discussion' started by PoulStaugaard, Jun 22, 2008.

  1. PoulStaugaard

    PoulStaugaard Now a PriusOwner

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    The reasoning of the drive control computer still puzzles me :confused:. One minute, it will shut down the engine as soon as I lift off. The next minute, it will refuse to shut down until it has been sitting still for 4-5 seconds. It is not simply a matter of whether I run the A/C, nor is it seemingly related to the state of charge: Often it will happlily shut down the engine even though it has only 3 bars, at other times, it will run the engine until has charged itself (sometimes) up to green bars. The result of this behaviour is also apparent on the consumption bar graph, which will sometimes vary unpredictably between 35-40 km/l and 20 km/l. At other times, it will show a more steady 25-30 km/l.

    Is this normal behaviour or is it a sign of malfunction? The car is only 5 months & 4000 miles old.
     
    #1 PoulStaugaard, Jun 22, 2008
  2. qbee42

    qbee42 My other car is a boat

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    This is normal behavior. The control algorithm is complex. It factors in load, temperature, idle check, speed, SOC, and probably a few other factors. Until you spend a lot of time with it, it's hard to guess what it will do when, and under what circumstances.

    Tom
     
    #2 qbee42, Jun 22, 2008
  3. patsparks

    patsparks An Aussie perspective

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    I agree with Tom. Often the ICE will run to warm the coolant or cat converter, sometimes to charge the battery. When it runs until you stop then shuts down that isn't a bad thing, that is the HSD switching to it's best level of operation.
     
    #3 patsparks, Jun 22, 2008
  4. PoulStaugaard

    PoulStaugaard Now a PriusOwner

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    I'm sure it has it's reasons, I just wish it would explain them better. Sometimes when it seems it must have run the engine long enough and it still doesn't shut down as I'm slowing to a halt, I will hit the EV button. It will take my advice allright, but if I then switch out of EV mode while at a halt, it will start the engine, run it for 5 seconds, then shut it down. That seems to me like plain stubbornness. It can't be that the cat or the coolant needs heating, I shouldn't think, and the state of charge is reported as just right, so why...?
     
    #4 PoulStaugaard, Jun 22, 2008
  5. JimboK

    JimboK One owner, low mileage

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    This will describe the "what" and "when" of many of the behaviors you're seeing, though the "why" for some of them, like that 5+ second ICE-on idle routine, remains a mystery to all but (apparently) Toyota engineers.
     
    #5 JimboK, Jun 22, 2008
  6. Bob64

    Bob64 Sapphire of the Blue Sky

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    Answer: depends mainly on your engine coolant temp.

    If your below 70c, it'll shutoff readily. If your above 70c for the FIRST time and stopping, it will "wait" for 5 seconds before shutting off - which is the signal that you've entered stage 4 mode, which will enable the engine to shutoff while moving.
     
    #6 Bob64, Jun 22, 2008
  7. richard schumacher

    richard schumacher shortbus driver

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    Unless you want to get deep into the arcana of hypermiling theory it's probably best to let the car manage itself, and use the EV button only at low speed at either end of a given trip (e.g., while leaving and entering your garage).
     
    #7 richard schumacher, Jun 23, 2008
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