transmission slipping??

Discussion in 'Gen 2 Prius Main Forum' started by jbmitchell, Nov 9, 2009.

  1. jbmitchell

    jbmitchell New Member

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    In the last month, my 2008 Prius engine speeds up with no change in speed - as if the clutch was slipping in the old days. This happens about 2 minutes after I leave the house when I first start out, never after it warms up a few minutes, as I pull out onto a 2 lane street so not during a major acceleration effort...just a normal increase in speed. And not all the time, about once every 3 weeks so far.

    Any thoughts??
     
  2. MJFrog

    MJFrog Active Member

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    SOC on the HV pack is low and it's being recharged.
     
  3. firepa63

    firepa63 Former Prius Owner

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    It's also trying to get the ICE up to operating temperature...
     
  4. qbee42

    qbee42 My other car is a boat

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    First, just to get it out of the way, there is nothing to slip in the Prius transmission. It has no shiftable gears or clutches. Now you don't have to worry about transmission issues.

    Engine speed is related to the required power. If the car needs more, the engine runs faster. Figure out why the car needs power at that moment and you will have your answer. As the previous posters mentioned, it could be a low SOC, cold engine, uphill grade, or anything like that.

    Tom
     
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  5. jayman

    jayman Senior Member

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    With my '04, it would also do that if I parked in the hot sun. With the battery pack heat-soaked, the motor would really rev while driving, until the A/C got things under control. It also had a lot less power until the battery pack got to a more reasonable temp
     
  6. Bob64

    Bob64 Sapphire of the Blue Sky

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    Chances are your engine isn't warmed up when your trying to accelerate. That's why it feels like its slipping, but in actuality, its using like 90% battery power. This is normal.
     
  7. ystasino

    ystasino Active Member

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    One of the unexpected/peculiar realities of the prius is that accelerating hard for the first 30s after startup wastes battery charge.
     
  8. uart

    uart Senior Member

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    I sometimes get the *exactly* same experience as the OP. I have a small hill to climb just as I leave my street and when the engine's cold it tries to use electric only (with the ICE basically just on idle). If there's no traffic and I'm gentle on the accelerator then it goes up the hill entirely like that. Other times however when I push the accelerator just a tiny bit more it switches rather abruptly to a significantly higher RPM where the ICE can provide useful power. If I then back off by again just a tiny amount the ICE changes abruptly back to idle once more.

    If you've ever had old manual with a dodgy clutch then it really can feel quite similar. When going up a hill pulling a high gear then the engine RPM is low but the torque on the clutch is very high. You try for just a bit more power and the clutch cant hold it and the engine rev's out. Of course what's going on in the prius is completely different but I can understand why the OP noticed the similarity.
     
  9. Frayadjacent

    Frayadjacent Resident Conservative

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    The 'transmission' in the Prius can't 'slip'. If the ICE runs higher, it's for some reason that the computers determine - temperature or battery state of charge are most likely.
     
  10. patsparks

    patsparks An Aussie perspective

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    I believe the engine revs are allowed to go high to generate a required amount of electricity in MG1 to be fed to MG2 to provide the torque to accelerate and climb hills, but because the engine is cold the control algorythm prevents a high torque load being placed on a cold ICE.

    A given amount of power is torque times revs, so to get the same power with less torque loading on the crankshaft you need higher revs. That is why the engine seems to race.
     
  11. donee

    donee New Member

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    Hi Jb...,

    Most likely this is the S1/S2 transistion. The S#s are the warmup stages. In S1 the engine is limited in its torque it can provide to driving, and most of the propulsive torque comes from the battery. Thus the engine does not shoot up high in RPM.

    At one minute from startup (pretty closely) things change. And the engine changes over to its normal operation. Which is to run up high in RPM when high accelleration is commanded. Also, if you have run the battery to a low state of charge during this first minute, the engine will go up high in RPM to recharge it.

    If your first minute of driving is agressive, or uphill, you can expect the engine to start reving suddenly right after that first mintue ends. Remember the engine power does not neccassarily all go to pushing the car if you have run the battery down.

    To limit this, be conservative when driving the first minute, and if going uphill, try to avoid battery usage. This requires a very light gas pedal to accomplish. But it only last for the first minute.
     
  12. pekemo

    pekemo New Member

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    I experience a similar surge in my 06 and think it's normal.
     
  13. Soylent

    Soylent The v isn't a station wagon! It's just big boned

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    This also has started happening to me in the last year or so. I believe it's related to the battery somehow, cause it's usually very low when it happens...
     
  14. qbee42

    qbee42 My other car is a boat

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    When the HV battery is low, the Prius does not want to use MG2 for power, as this would further delete the low battery. That means that most of the power must come from the ICE, requiring the ICE to speed up. Furthermore, the HV battery needs to be charged in this situation, and the power for this comes from the ICE, so then ICE needs to run even faster to supply power to move the car and charge the battery.

    In a normal car, the engine speed is tied to the speed of the car. As the car speeds up, so does the engine. This means that the engine spends a lot of time running at inefficient speeds.

    With the Prius, the ICE speed is independent of the speed of the car. Because of this, the Prius can run the ICE only when needed, and at optimal speeds. This is the reason that the ICE speeds up so much in a low battery condition. The control system looks at the power requirement and battery state, and says to itself "If I need to run the engine to move the car, I might as well open it up to an optimal speed and charge the battery at the same time."

    Tom
     
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