About that clutch

Discussion in 'Gen 3 Prius Technical Discussion' started by SagradaFamilia, Nov 26, 2011.

  1. SagradaFamilia

    SagradaFamilia Junior Member

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    Regularly comments are made regarding a lack of clutch in the HSD but a youtube video from Western State University shows a clutch and pressure plate attached to the shaft driving the planetary gear carrier.
    Although this is apparently a second generation HSD it prompts several questions.
    1) Does it still exist in the 2010 Prius HSD?
    2) Does it engage and dis-engage every time the ICE is started and stopped?
    3) What engages the mechanism? Electric or hydraulic?

    You see, I'm trying to figure out what happens to the ICE when it is OFF. Is it continuously turning and driving the pistons? If so are the valves fully opened? Maybe not necessary if this clutch is disengaging.

    Thanks for the insight.
     
  2. john1701a

    john1701a Prius Guru

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    With traction-control, there's always going to be some means of disrupting power sent to the wheels. So, keep that in mind when observing connections.

    When the ICE (engine) stops, the RPM really does go to zero. With the Classic & Iconic models, that threshold is 42 mph. With the 2010+ it's 46. With the plug-in (while charge is available) it's 62. The carriers in the PSD (power-split device) simply rotate around the stopped component. Above the speed threshold, the engine pumps without consuming any gas.

    That's the beauty of the PSD, the traction motor can go about its business independently of what the gas engine is doing.
    .
     
  3. jdcollins5

    jdcollins5 Senior Member

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  4. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    The 'clutch' you see is a last ditch shock absorber in the drive train. It has no actuators and no part of the system can try to operate it, but in scenarios where the engine can't stop as instantly as the PSD, it can give way. It seems to be called the dampner

    Prius 1st gen - Replacing Transaxle


    1.yes
    2. no
    3. neither.

    Below 41 (45 in Gen 3?) the engine need not rotate when off. Above that speed the electric motor 1 would over rev so the engine always rotates.

    Most simulations are of Gen 1, so do not get too worried about the exact RPMs and MPHs, and just study the principles.

    Toyota Prius - Power Split Device
     
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  5. jdenenberg

    jdenenberg EE Professor

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    The "clutch" is there as a torque limiter. It will slip in the unlikely occurrence of excessive toque stress in the drive train. There is no mechanism to disengage it, it is always engaged. I believe that it is still there in the current generation Prius.

    JeffD
     
  6. SagradaFamilia

    SagradaFamilia Junior Member

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    Thank you all for the explanations gentlemen. Obviously no need to worry about wear.
     
  7. spiderman

    spiderman wretched

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    Great question. I would have never guess there was a clutch/damper in there... but it does make sense.
     
  8. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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  9. Teakwood

    Teakwood Member

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    Cool video!
    Thanks, Jimbo.:thumb:
     
  10. ecoprius

    ecoprius Junior Member

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    Love the video! I'm trying to learn as much as possible about this car what a great video. I have never worked on a car so don't really even know the basics on car repair or how they work. I helped my dad with cars as a teen, but that info is long lost in my memory. Thanks so much for posting!
     
  11. Feri

    Feri Active Member

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    Fascinating Video. I've been wondering why the chain was designed out of the GenIII. As an apprentice I was taught that the chain transmitted energy more efficiently than gears do??
     
  12. xs650

    xs650 Senior Member

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    Their efficiency overlap, but the best gear meshes beat the best chain drives.
     
  13. Pinto Girl

    Pinto Girl New Member

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    Excellent video. Makes me wonder how a few folks got electric-only freeway speeds out of their GIIs, since it seems that would over-rev MG1.

    Great stuff!