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ICE running when Prius is in reverse

Discussion in 'Gen 2 Prius Technical Discussion' started by yardman 49, Apr 18, 2009.

  1. yardman 49

    yardman 49 Active Member

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    Hello all:

    I thought that I had read in several places that the ICE doesn't run when the Prius is in reverse.

    I have a brand new 2009, and it seems that many times when I put it into reverse, the ICE runs. It doesn't start right away. But if the car is in reverse for more than a few seconds, the engine oftens starts.

    I haven't tried to really correlate it to something else, such as "is the climate control calling for heat", or "is the hybrid battery drained". But today, after a drive of about 5 miles, my SOC was at "green bars" (but not all the way full), it was 68 degrees out (and I think that I had the climate control either off or at 68 degrees, which is my usual setting), and yet the engine started as I was backing into the driveway.

    I usually notice it when the car has been shut off for some time, and I start the car and put it into reverse.

    Is this behavior typical?? Also, since the engine is running, what decouples it from the drive train so that it doesn't try to make the car go forward while the car is going in reverse??

    Thanks for your advice
     
    #1 yardman 49, Apr 18, 2009
  2. john1701a

    john1701a Prius Guru

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    The ICE doesn't contribute any thrust in reverse. It runs though... in a forward direction. The electric motor simply rotates more in the opposite direction.

    The PSD allows this, without disengaging anything. It's a feature of the flexibility the device offers.
    .
     
    #2 john1701a, Apr 18, 2009
  3. yardman 49

    yardman 49 Active Member

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    Thanks, John.

    Do you have any idea why it would run in reverse after a drive when it was fully warmed up and the SOC seemed to indicate that the traction battery had a sufficient charge?? Is the car possibly trying to run the water pump, or something else??

    Thanks.
     
    #3 yardman 49, Apr 18, 2009
  4. Starky

    Starky Prius fan

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    The SOC indication on MFD is not a full statesmen of the state of charge...but merely a general indication. HV Battery ECU commands the ICE when in reverse--of course with no contribution to the motion--based on its detailed reading of the SOC.

    Regards,
     
    #4 Starky, Apr 19, 2009
  5. qbee42

    qbee42 My other car is a boat

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    The ICE does not provide mechanical torque when reversing (actually it does, but in the wrong direction), but it does provide power. The ICE spins MG1, which makes electricity to charge the battery and power MG2. The ICE also warms itself and the emission control system.

    Why would you expect the ICE to not run?

    Tom
     
    #5 qbee42, Apr 19, 2009
  6. usbseawolf2000

    usbseawolf2000 HSD PhD

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    #1 priority for Prius is to bring up the emission system to the normal operating temp. Since saving gas is #2, the engine turns on even if you are in reverse.

    If you are curious how this is achieved mechanically, see this simulator.

    Slide up the ICE to 1,000 RPM and slide down the MG2 to 500 RPM. That's about 10 MPH in reverse.
     
    #6 usbseawolf2000, Apr 19, 2009
  7. Simtronic

    Simtronic Active Member

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    There are several reasons the engine will run apart from the emission control, AC and HV battery charging there is also the 12 volt auxilary battery to keep charged.
     
    #7 Simtronic, Apr 19, 2009
  8. timberwolf

    timberwolf New Member

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    The 12V Aux battery is charged at a pretty slow rate and is charged from the HV battery through a DC-DC converter, so I think indirectly the engine would need to run (sometimes) to charge the HV battery to charge the 12V battery and run all the 12V systems in the car.

    (I now await for the technically knowledgeable to rip my post to shreds :) )
     
    #8 timberwolf, Apr 19, 2009
  9. yardman 49

    yardman 49 Active Member

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    Many thanks to all who have responded! Your replies have been reassuring that nothing weird is going on.

    Tom: I guess I was confused. On at least a couple of threads here on the forum, I thought that I had read statements to the effect that the ICE does not run in reverse. That was an error on my part. I see now that it's just that the ICE does not contribute to the reverse torque, but it actually does run when needed for other functions.

    Thanks again to all.
     
    #9 yardman 49, Apr 19, 2009
  10. patsparks

    patsparks An Aussie perspective

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    Timberwolf, I'm not sure how many hours the HV battery (via the DC-DC converter) can run the radio for, but it's a long time when it's fully charged.
     
    #10 patsparks, Apr 19, 2009
  11. qbee42

    qbee42 My other car is a boat

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    I suspect the torque issue confuses a lot of people. When backing, torque from the ICE is fighting MG2. It's not an efficient setup, but fortunately you don't drive very far in reverse. If you do reverse for a distance, or go up a hill, the ICE is necessary for electrical power. The HV battery is relatively small, and if you start with a low SOC the Prius isn't going to let you back very far before it will want the ICE running to generate power. Once the ICE is running, backing distance is limited only to the amount of fuel in the tank.

    Also, as you have pointed out, the ICE needs to heat up to warm itself and the catalytic converter.

    Tom
     
    #11 qbee42, Apr 19, 2009
  12. Bob64

    Bob64 Sapphire of the Blue Sky

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    keep in mind folks: that the HV battery is NOT used unless your in ready mode!

    Accessory mode does NOT use the HV battery. If you leave the car on in acc mode for long periods of time, you may find that your 12v battery will be drained!
     
    #12 Bob64, Apr 19, 2009
  13. Bob64

    Bob64 Sapphire of the Blue Sky

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    If you've turned off the car, the engine will usually do its "warmup" cycle when you turn it back on.

    Try turning it on and waiting like 10 seconds without shifting. You will see that it isn't the reversing that turns one the engine.
     
    #13 Bob64, Apr 19, 2009
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