1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Gliding/coasting from highway speed to a stop: ICE comes in between 43 and 41 MPH...?

Discussion in 'Gen 3 Prius Main Forum' started by Philosophe, Apr 14, 2010.

  1. Philosophe

    Philosophe 2010 Prius owner

    Joined:
    Jun 2, 2009
    437
    72
    1
    Location:
    Montréal, Québec (Canada)
    Vehicle:
    2010 Prius
    Model:
    N/A
    I haven't been able to find an answer on this on the existing forums:

    When I get off the highway, I usually glide (keeping the HSI into neutral by applying slight pressure on the accelerator), until I later go into regenerative breaking to come to a full stop at a red light.

    While I coast this way, consuming no fuel (instant fuel consumption gauge at 0 L/100km), the ICE kicks in at around 43 MPH, consuming fuel (instant gauge moving up to about 2.5 L/100km), and turning fully off at around 41 MPH (instant gauge going back down to 0). I can also feel the ICE having a slight impact on deceleration while doing so.

    So my question is: why does the ICE comes in between and 43 and 41 MPH, consuming fuel? Why can't it simply stop turning at around 42 MPH?

    Note: I understand that the ICE has to turn when the car goes at more ~42 MPH, to prevent MG1 from spinning over its design limits.
     
    #1 Philosophe, Apr 14, 2010
  2. tumbleweed

    tumbleweed Senior Member

    Joined:
    Oct 3, 2005
    4,067
    687
    0
    Location:
    Eastern Oregon
    Vehicle:
    2010 Prius
    Model:
    V
    If the car is fully warmed up and the battery is up to 5 or 6 bars I see the ICE shut down when I drop below 41 MPH, sometimes I need to come completely off the throttle for this to happen other times it will shut down when I am in glide. Going the other way I can creep up to 46 MPH before it restarts if I keep the HSI to the left of center. I consider this normal operation.

    Note: The "idling check ceremony" must be completed in stage 3 before the car will enter stage 4, prior to that it may not shut down while moving.

    http://priuschat.com/forums/gen-iii...-discussion/76501-gen3-warming-up-stages.html
     
    #2 tumbleweed, Apr 14, 2010
  3. Philosophe

    Philosophe 2010 Prius owner

    Joined:
    Jun 2, 2009
    437
    72
    1
    Location:
    Montréal, Québec (Canada)
    Vehicle:
    2010 Prius
    Model:
    N/A
    My description is with a fully heated engine (S4) and no heating requirement from the cabin heater.
     
    #3 Philosophe, Apr 14, 2010
  4. David Beale

    David Beale Senior Member

    Joined:
    Jul 24, 2006
    5,963
    1,981
    0
    Location:
    Edmonton Alberta
    Vehicle:
    2012 Prius
    You have slight pressure on the accelerator? That can cause the ICE to start. Keep your foot off the peddle and you will find the ICE will run at about 960 RPM with no fuel to 42 MPH then stop as you continue to slow.
     
    #4 David Beale, Apr 14, 2010
  5. Philosophe

    Philosophe 2010 Prius owner

    Joined:
    Jun 2, 2009
    437
    72
    1
    Location:
    Montréal, Québec (Canada)
    Vehicle:
    2010 Prius
    Model:
    N/A
    So you're saying that by using slight regenerative braking (foot off the gas pedal) instead of gliding, the ICE would not turn on temporarily at around 42 MPH?... I'll have to try this.
     
    #5 Philosophe, Apr 14, 2010
  6. eric1234

    eric1234 Active Member

    Joined:
    Jun 8, 2008
    390
    198
    0
    Location:
    Hamden, CT
    Vehicle:
    2016 Prius
    Model:
    Three
    Hi Tom,

    I've noticed the exact same thing at 46 MPH. But here's the funny thing: If I'm going downhill, with engine off (100 MPG indicated on instant mileage gauge) up to 46 - it stays at 100 MPG. When I hit 46, the instant mileage drops (indicating starting of engine), and within a few seconds stops - going back up to 100 MPG.

    I don't have a scan gauge, but what I imagine is going on here, is that when the ICE first starts moving (to prevent MG1 overspeed), fuel is consumed, but then it stops consuming fuel. (with MG1 now turning the ICE (?))

    So here's the question: Why does the ICE need to consume any fuel (presuming that my guess is correct) when it first begins to turn?? Isn't the power of MG1 (presumably) sufficient to begin turning the ICE without the need to burn any fuel? (I've noticed this repeated many times, since I have a long downhill run just near my house, and I see it everytime I hit 46 going down the hill).
     
    #6 eric1234, Apr 23, 2010
  7. Philosophe

    Philosophe 2010 Prius owner

    Joined:
    Jun 2, 2009
    437
    72
    1
    Location:
    Montréal, Québec (Canada)
    Vehicle:
    2010 Prius
    Model:
    N/A
    I confirm that by either maintaining the car into a glide (HSI in "neutral") or by leaving the foot off the pedals, this phenomenon does happen, each and every time.
     
    #7 Philosophe, Apr 23, 2010
  8. tumbleweed

    tumbleweed Senior Member

    Joined:
    Oct 3, 2005
    4,067
    687
    0
    Location:
    Eastern Oregon
    Vehicle:
    2010 Prius
    Model:
    V
    I guess I haven't seen it because I haven't looked for it. I'll try to remember to watch for it and see what the RPM and throttle position are doing when it happens. I'm not sure if the fuel flow xgauge works right or not but it may tell us something also.

    EDIT: I tried it several times this afternoon, it happens to me also. I see the MPG gauge go down and back up just as I feel the ICE shutdown. Scan Gauge isn't much help I'm afraid, it only updates every two seconds and this little bump in the MPG readout is to fast for the Scan Gauge to catch. I was able to confirm that the ICE is running up until the little bump then it shuts down, but I think you guys already knew that.

    Could it be some kind of software glitch? Maybe there isn't any fuel flow and it's something weird with the readout? Just a guess.
     
    #8 tumbleweed, Apr 23, 2010
(You must log in or sign up to post here.)