Transmission Question. Is the the ICE still coupled to the planetry gear when ICE is off?

Discussion in 'Gen 2 Prius Technical Discussion' started by uart, Nov 8, 2009.

  1. uart

    uart Senior Member

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    I was just wondering if the Engine output shaft is still coupled to the planet carrier of the power split gears when the prius is in all electric mode.

    Does the planet carrier just stop (and mg1 freewheel) or is there a clutch or something that decouples the planet carrier and lets it freewheel in this mode?
     
    #1 uart, Nov 8, 2009
  2. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    No clutch.
    I found this simulator useful (Click on the green THS to get THSII for Gen II)
    A simulation of Prius's Planetary Gear

    The only mechanical 'change' in this transmission is that in Park a locking pawl is engaged. All else is software.
     
    #2 JimboPalmer, Nov 8, 2009
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  3. patsparks

    patsparks An Aussie perspective

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    Neutral is just achieved by allowing MG1 to freewheel. That is why it is important not to coast to a high speed down a hill in neutral, it might overspeed MG1. To prevent overspeeding the ICE (internal Combustion Engine) is spun when traveling at high speed on trailing throttle with no fuel injected and valve timing to minimise loss by applying an electrical load on MG1. Toyota often refer to MG1 as the generator.

    The gears in a manual car are always engaged too even in neutral. Each has a dog clutch allowing drive to not be transmitted through a gear set unless selected. Only reverse in actually disengaged at the gear teeth.
     
    #3 patsparks, Nov 8, 2009
  4. uart

    uart Senior Member

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    Thanks Jimbo and Pat for the info. :)

    Yeah that was exactly what I was wondering, if there was something like a "dog gear" or whatever that could engage/disengage the ICE from the planet gear. Now I know that there isn't, thanks.

    No wonder the prius power split device is considered a marvel of (mechanical) simplicity. I'm only really just starting to understand it and find it quite amazing. :)

    BTW. How fast do you have to be going in all electric mode before it starts spinning the ICE (without petrol) just to prevent MG1 from going too fast?
     
    #4 uart, Nov 8, 2009
  5. jpadc

    jpadc Type before I think too often

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    #5 jpadc, Nov 8, 2009
  6. patsparks

    patsparks An Aussie perspective

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    You're welcome.


    My observations from watching my scan gauge is 65km/h. Aparently with plug in conversions and a little trickery you can get it up to over 100km/h.
     
    #6 patsparks, Nov 8, 2009
  7. grand total

    grand total Member

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    Things must be different in the southern hemisphere, my car manages 67 or 68km/h depending on the phase of the moon, tides etc. But, seriously, why is that? At that speed MG1 is spinning at 6,500 RPM, why doesn't the Prius software allow MG1 to spin up to it's maximum speed of 10,000 RPM and so allow a maximum speed with ICE stopped of 103 km/h?
     
    #7 grand total, Nov 8, 2009
  8. BAllanJ

    BAllanJ Active Member

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    I think max rpm for MG1 is 6500 for the gen2 prius... only 10000 rpm for gen3.
     
    #8 BAllanJ, Nov 8, 2009
  9. uart

    uart Senior Member

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    On the eahart simulation site linked above they state the following :
    Perhaps they were just being a bit over conservative with the 6500 rpm limit? I'm pretty sure early transmission failures would have made seriously bad to press for the Prius so I wouldn't be surprised that they didn't want to take any risks.

    I have to agree though that it would be nice to be able to glide at up to 100km/hr (60 MPH) without spinning the ICE.
     
    #9 uart, Nov 8, 2009
  10. ken1784

    ken1784 SuperMID designer

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    #10 ken1784, Nov 8, 2009
  11. qbee42

    qbee42 My other car is a boat

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    If you think about designing the control algorithms for the HSD, there aren't many circumstances where a Prius runs all electric at speed, certainly not for any distance. I suspect the MG1 speed limit was set low to be conservative, knowing that it doesn't make a lot of practical difference whether it is 6500 RPM or 10000 RPM. Hypermilers and Prius nuts would like any extra they could get, but for an ordinary driver it is splitting hairs.

    Tom
     
    #11 qbee42, Nov 8, 2009
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