unnecessary engine restarts at max charge

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by tkil, Jan 26, 2006.

  1. tkil

    tkil New Member

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    My 2005 Prius has had this issue for at least a few months: at the end of a long highway drive, I coast the last half mile or so (downhill, then down a ramp) to a complete stop. At that point, the state-of-charge meter shows full, and the gas engine seems to cycle on and off continuously. Creeping forward even a little bit seems to stop it.

    Is this the "dieselling" that I've seen mentioned elsewhere? Is anyone else seeing this?

    Temperatures are generally moderate (inland north county San Diego, so from 90F down to 50F). My commute is 25mi each way, of which about 23 is highway; I'm coming off 25 minutes at 65mph (on cruise) when I drop the cruise and do the coast to a stop.

    My best guess is that the computer decides the battery is a bit overcharged, and cycling the motor is the best way to work off the extra charge (since the Prius doesn't have a resistor bank, at least so far as I know...) Thanks for any info!
     
  2. olends

    olends New Member

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    this is correct
     
  3. tideland_raj

    tideland_raj New Member

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    Since this is the case, if it's a mild descent, you may want to alternate between neutral and drive, I find this useful because neutral is faster (ie, HSD is disengaged), and the only reason you want HSD engaged is to gain battery charge thru HSD.

    Of course, being in neutral is bad if you *do* brake, since it will not use the regenerative brake and you'll be wasting brakepads. So I usually keep my hand on the silver knob whenever im in neutral just in case I need to throw it back into drive to hit the brake.
     
  4. john1701a

    john1701a Prius Guru

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    But it actually isn't.

    The engine never uses any gas during that cycling. What's really happening is the computer is utilizing the startup process (spin the engine up to the ignition point) to use up that excess electricity. Then it allows the engine to slow down. Then it repeats... and repeats.

    This is one of those cases where you'd what to take advantage of "B" mode, since that reduces the amount of recharging.

    By the way, I've only experienced that once. And it was intentional, to find out firsthand what the heck owners dealing with long decents with a stop at the bottom were talking about.
     
  5. hdrygas

    hdrygas New Member

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    As far as I know the Prius never "diesels". Yes there is a shutter on stop but this does not represent traditional "dieseling" as some of us remember in carbureted cars. See John1701a post, on the running of MG1 to use up excess charge. The shutter of stopping of the ICE is also confused with "dieseling" but it seems clear that the mechanism of the shutter and dieseling caused by compression combustion of fuel in older carbureted cars is different.
     
  6. Ken Cooper

    Ken Cooper New Member

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    Now that's interesting, and it makes sense, and it matches what I've experienced. I used to experience this daily as I'd wait at the light after the long down hill drive from my former home. The battery indicator would show all green bars, the engine would seem to cycle on and off, but the display showed no indication of the engine running/delivering power (via generator) to the battery.

    I mentioned this to my local Toyota Prius mechanic but all he could say was that the diagnostic tests showed everything within the hybrid system operating correctly. I'll share your comments with him.

    Thanks!
     
  7. hobbit

    hobbit Senior Member

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    If you don't have a hill handy and want to duplicate this behavior
    yourself, you can always force-charge the battery up to max-
    indicated-SOC and then watch it do the dance. [hold down brake,
    press accelerator till the ICE starts]
    .
    _H*
     
  8. tochatihu

    tochatihu Senior Member

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    Or if force charging is too slow, try hyper-force-charging!

    On, park gas gas, neutral gas gas, park gss gas, (HV flash), start.

    Now you are in inspection mode and have a ! on the mfd. Force-charge at 30 amps or better. But don't go driving in slippery places.

    Shut down cancels inspection mode. Hope I don't regret sending this.
     
  9. hobbit

    hobbit Senior Member

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    Erm ... I don't think force-charge current changes if you're in
    inspection mode or not. It does, however, change depending on how
    far you press the accelerator. Yes, ideally you need a battery-
    current meter to tell this, but without one you can sort of tell
    what's going on by listening carefully to the inverter whine.
    .
    When the ICE slows down by itself and goes back to idling despite
    how hard you've floored the accelerator, you're done.
    .
    Oh, right, I should clarify that all of this happens in Drive...
    .
    _H*
     
  10. tkil

    tkil New Member

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    Spiffy, thanks for the (insanely!) quick answer. Between your reassurance and john1701a's explanation, I feel much better about it. :)
     
  11. tkil

    tkil New Member

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    Interesting -- that sounds like a really nifty idea. I'll give it a shot tomorrow. (Although I need to read up on how to get into neutral from drive while moving -- I'll check the manual before I head out. If it's a well-known secret, a pointer would be great. Thanks!)
     
  12. tkil

    tkil New Member

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    Ok, that makes sense -- thanks for the detailed explanation! I didn't mean to imply that the engine was actually catching; I can't tell one way or another, just felt the start-up / shut-down shudders. (And usually my music is pretty loud at that point, so...)

    Thanks again for the detailed info. I browsed some of your docs earlier; do you happen to have one addressing this situation? More generally, it seems I have to choose between:
    1. normal D mode and possible overcharging (and possible unnecessary wear on the ICE);
    2. N mode and coasting (back to D/B for regen braking);
    3. B mode and maybe cost some gas?

    Or does B mode do the same as the spin-up/spin-down, not use any gas, just relies on vacuum braking (and the wear is reduced due to electronic oil pump and pre-warming?)

    Sorry for all the newbie questions, quick URL pointers are more than welcome. Thanks for all the info you've supplied us already!
     
  13. tkil

    tkil New Member

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    Apologies; I didn't realize that there was a specific phenomenon associated with the term. I thought people just used it to describe the torque-y shuddering that happens when the ICE engages/disengages. (The fact that I don't know that term probably also demonstrates my age. Eeep.)

    That's why I put it in quotes, to indicate that I wasn't sure I was using it properly (and sure enough...) Thanks for straightening me out. :)
     
  14. olends

    olends New Member

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    I would choose normal D. The discharge Spin, is 0 wear. Since the computer has no intention of allowing the engine to start, no fuel is supplied, and the valves are adjusted to a 0 compression state, (or as close as mechanical limits allow). And since the coolant and oil pump are both mechanical. this state ensures that the system stays sufficiently cool and well lubricated.

    B mode is similar to compression breaking on large trucks, the engine valves are configured opposite the above state. a Bit of fuel is supplied to ensure that a sudden loss of force on the engine will not cause it to stall out unexpectedly, causing an overspin on MG1.
     
  15. darelldd

    darelldd Prius is our Gas Guzzler

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    Wow. With such a large (relatively) overhead of battery capacity that is not normally used, you'd think this wouldn't be a problem. That a wee bit of extra charge could just be stored up without harm (seeing as how the chemical reaction has already taken place!) And when you consider that the car KNOWS when it is fully charged, you'd think it could manage to avoid what it considers "over charging" before it has to bleed it off later.

    There is NO doubt that the smart folks at Toyota have done the best they could with what they have to work with... yet I still wonder what they were thinking here!
     
  16. finman

    finman Senior Member

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    "There is NO doubt that the smart folks at Toyota have done the best they could with what they have to work with... yet I still wonder what they were thinking here!"

    It's called an 8-year/100,000 mile battery/hybrid component warranty. Longer (10 years/150,000 miles) in the CARB states (CA, NY, etc.)

    Yes, this is one smart, clean car.
     
  17. seasalsa

    seasalsa Active Member

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    I haven't had this problem since getting my EV mod. I have a spot on my commute where there is a stoplight at the bottom of a long downgrade. The car would shudder every time before the Mod, now when I stop I switch to EV and am ready to go when the light turns green without any shudder and can use the excess charge to my advantage.
     
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