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Scan Gauge Dispute: At What Speed does the ICE shut off ?

Discussion in 'Gen 2 Prius Main Forum' started by SageBrush, Dec 28, 2009.

  1. SageBrush

    SageBrush Senior Member

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    Common knowledge that the ICE stops spinning below ~ 42 mph if no gas pedal is applied. Or so I thought, until I started watching my scangauge these past few weeks. The rpm gauge stays around 1000 - 1280 until speed is about 35 mph. Instant mpg is less than 100 mpg, suggesting ICE spin from combustion.

    I wondered if I was just seeing the end effects of the ICE slowing down, but the cutoff from 1000 rpm to zero seems pretty quick, and did not happen in the high 30's mph when I glided for an extended distance.

    Is the cutoff temperature dependent ? Doesn't seem to be, since I am pretty sure I saw the same cutoff when the ICE fluid was 180F.

    Calibration problem ? The reported car speed on the scangauge is about 1 mph less than the MFD.

    SOC ? Same observation, even when the SOC is in the green range.

    First sign of early battery failure ? 12V is new and has good voltages. All I can say about the traction battery is that fuel economy seems about the same for the season.

    ok, I'm stumped ;-)
     
  2. usbseawolf2000

    usbseawolf2000 HSD PhD

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    You probably did not get to S4 due to low temps. ICE will shut down below 34 MPH only if you are in S4.
     
  3. ksstathead

    ksstathead Active Member

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  4. SageBrush

    SageBrush Senior Member

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    from my op:
    "Is the cutoff temperature dependent ? Doesn't seem to be, since I am pretty sure I saw the same cutoff when the ICE fluid was 180F."
     
  5. ken1784

    ken1784 SuperMID designer

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    I bet there is no single threshold, but there is a hysteresis.
    I don't remember the ICE stop speed, but I'm sure the ICE continues to spin at 40 mph when decreasing the speed.
    The scangauge has some limitation to display the instantaneous mpg on fuel-cut mode.

    Ken@Japan
     
  6. SageBrush

    SageBrush Senior Member

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    Thanks Ken.
    I'll check cutoffs when car speeds are going up just prior to letting off the gas pedal, instead of down like I had checked until now.
     
  7. David Beale

    David Beale Senior Member

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    There is a delay in ICE shutoff. If you are coasting down, that could easily account for your confusion. I've seen the ICE shut down at about 60 km/hr (scangauge goes to 0 RPM). I've also seen it go to no-fuel spin from about 65 km/hr all the way up to over 100 km/hr (scangauge indicates about 950 RPM, fuel drops to 0.02 l/hr, which is the scangauge holdover for "other technical reasons"). It does often take some time for the HSD to put the engine to sleep. At a light, for example, it usually takes around 4 sec. to shut down, yet sometimes it shuts down as I coast up to the light.

    So, as ken says, it's variable. I've even seen the car -not- go to S4 when it should have (based on the above guidelines). It did it to me on Sunday. Coolant up to +70C, speed had gone up to 75 km/hr, yet I was not in S4 when I slowed to a stop (engine started for cabin heat at coolant temp of 62C while waiting at a light).
     
  8. SageBrush

    SageBrush Senior Member

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    Hi David,
    I'm unsure that ICE or gauge delay is the answer, because I was able to to hold the car's speed at about 40 mph yesterday for at least a few seconds, perhaps over five, and the ICE rpm stayed constant. This was when the ICE was nicely warmed up.

    Maybe more than one variable is at play ?
     
  9. AussieOwner

    AussieOwner Active Member

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    Many thanks for this. It has helped explain why I cannot get into glide mode in certain situations. Here in Australia, all the local city councils have now brought the speed limit down to 50kph, which I now see is below the lower limit in Note A. Whilst I do not have a ScanGauge, I have noticed that the ICE will not shut down unless I quickly accellorate upt to 60kph, and then take to foot of the pedal and let the car slow back to the speed limit, then the ICE will shut down. Once I get to an actual stop and let the idle check kick in, I then get into stage 4 and all is well. The problem I have is that I do not get that idle check opportunity until some 3 km of potential glide travel.
     
  10. Oddest_raindrop

    Oddest_raindrop New Member

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    A few things I have noticed. The ice will run to 940 rpm and is dependent on the coolant temp some what. It is very unlikely to shut off under 112F. If the heater is operating it is unlikely for the ice to shut off under between unless the temp is above 155-164 range. It can be helped off be simply turning off the heat. Once it hits 164 is will tend to shut off on it's own and rather quickly until the heat is dissipated from the ICE. If a glide has been used or electric propulsion, once the ice starts up it does not want to shut off quickly again until the soc reaches a set point. I have also seen the car charge up the traction battery to all green on it's own and do a complete electric propulsion up through 50 MPH with the ice turning. It's not a long period of time but can get some great mpg average improvements. Another ICE temp factoid, 112F the fan will just start and at 128F you will have full fan on auto. 184F seems to be where the thermostat kicks in with cold outside temps can see a drop in engine temp the first time hitting this in a trip. Keep in mind I may be off a little on my values since this is from memory and observed while driving. Fun traction battery fact, there are at least 2 observed levels based on battery temperature for max current in and out. Less current is allowed to enter or leave the battery when it is cold.
    In short it's moody and has a mind of it's own. Between the engine temp, the state of charge and the previous running mode it decides what is wants to do.
     
  11. SageBrush

    SageBrush Senior Member

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    Ken was right,
    If you believe the SG, ICE shuts off around 36 mph if the prior condition was over 40ish. If however 40 mph is reached from a *lower* speed, ICE shuts off at 40 mph. Perhaps conditions exist wherein ICE shuts off at 41 or 42 mph, but I have not identified them yet.

    For me, the practical point to be gained from these numbers is that the pulse in P&G should not exceed 40, perhaps even 39 mph to avoid delayed ICE shutoff while 'gliding'. The MFD does not show the ICE running in the scenario being discussed. SG reports 200 - 250 mpg during this false glide state, in case anybody is curious how much fuel is being used :)

    All data obtained with MFD SOC in green, and water temp by SG over 160F
     
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  12. bestmapman

    bestmapman 04, 07 ,08, 09, 10, 16, 21 Prime

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    The scanguage is a great tool.

    However, you must also know how the car operates. You should learn the four stages of operation S-1 thru S-4 and that will help you realize what the car is doing. The stages are both temperature and time dependant.

    The ICE shut off is also dependent on other factors such as AC/heat settings and defrost settings.

    If all looks good and the ICE still fails to shut off, I always check the Defrost as I usually mistakingly have that on.
     
  13. SageBrush

    SageBrush Senior Member

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    bestmapman, I'm pretty sure all my tests have been during S4