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What Exactly does the Added Clutch Do?

Discussion in 'Prime Technical Discussion' started by mr88cet, Jan 18, 2017.

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  1. mr88cet

    mr88cet Senior Member

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    As you all probably know, Toyota says that they added clutch to the drive system on the P.Prime, to allow both MGs to drive in EV mode.

    What two things specifically does that clutch make a mechanical connection between?

    Conceptually, I can see two ways that the power-split device could be clutched to allow both MGs to drive the wheels:
    • The ring gear could be connected to the sun gear, so that the entire planetary-gear complex is frozen together into a single unit, and both MGs turn in the same direction at the same speed.
    • The engine and thus the planetary-gear carrier is frozen still, and the two MGs turn in opposite directions, the sun gear turning considerably faster than the ring gear.
    Since it can go up to 84MPH in EV, I'm guessing it's the former. If it were the latter, the sun gear would have to turn mighty fast! If it is the former, it's kinda unfortunate that the ICE keeps cranking over in EV mode, especially if the oil hasn't had a chance to warm up. Sure would be great if the engine were completely motionless!

    Any of you know how it works?
     
    #1 mr88cet, Jan 18, 2017
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  2. bhtooefr

    bhtooefr Senior Member

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    #2 bhtooefr, Jan 18, 2017
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  3. MikeDee

    MikeDee Senior Member

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    Seems like the term Sprag clutch is a misnomer; if the Prius uses clutches like that shown in the article. Sprag clutches use bearings; not ratcheting pawls like a bicycle freewheel.
     
    #3 MikeDee, Jan 18, 2017
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  4. mr88cet

    mr88cet Senior Member

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    So it looks like it's not as much a clutch as a ratchet.

    I was kinda hoping that the engine would for-sure not rotate (neither forward nor backward) in order to reduce wear and drag. No guarantee that it won't turn forward, it appears.
     
    #4 mr88cet, Jan 18, 2017
  5. bhtooefr

    bhtooefr Senior Member

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    However, what'll happen is that MG1 will apply torque to try to accelerate itself to higher negative RPMs, which would turn the engine in reverse. The one-way clutch prevents that, so MG1's torque instead spins the ring gear faster.

    Play with Toyota Prius - Power Split Device some... it doesn't show torques, only RPMs, but realize that MG1 increasing torque to increase vehicle speed would be in the direction of more negative RPMs.
     
    #5 bhtooefr, Jan 18, 2017
  6. Lee Jay

    Lee Jay Senior Member

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    It's a sprag clutch.

    "A sprag clutch is a one-way freewheel clutch."
     
    #6 Lee Jay, Jan 18, 2017
  7. Boomer 2298

    Boomer 2298 Junior Member

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    It’s a sprag clutch used in industrial power transmission for decades. Highly reliable.
     
    #7 Boomer 2298, Feb 22, 2021
  8. ChapmanF

    ChapmanF Senior Member

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    Can't believe we went four years without clearing that up.
     
    #8 ChapmanF, Feb 22, 2021
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  9. PiPLosAngeles

    PiPLosAngeles Senior Member

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    The press release says it's for 2.5L engines, which means it's not for the Prime?
     
    #9 PiPLosAngeles, Mar 18, 2021
  10. Tideland Prius

    Tideland Prius Moderator of the North
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    Not sure but there is a sprag clutch on the Prime to allow it to use both MG1 and MG2 for forward propulsion in EV Drive Mode.
     
    #10 Tideland Prius, Mar 18, 2021
  11. Gokhan

    Gokhan Senior Member

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    From my new-car features manual, the one-way clutch is connected to the planet-gear carrier, the latter of which is also connected to the ICE. MG1 is connected to the sun gear, and when the ICE is on, it turns in the same direction as the ICE, which charges the HV battery as well as providing power to MG2. When the ICE is off, MG1 functions as a motor and turns in the opposite direction as the ICE but with minimal torque to only keep the ICE from spinning, not really providing power to the wheels. However, in the EV mode under high acceleration, MG1 turns in the opposite direction with high torque and functions as a motor supplementing the larger MG2. The one-way clutch locks to the transmission case when that happens and applies a stationary torque on the planet-gear carrier, which holds the ICE stationary and prevents it from turning in the reverse direction, and it allows MG1 in this way to serve as a motor instead of a generator. In summary, the one-way clutch is free from the transmission case to rotate freely when MG1 is working as a generator, and it is locked into the transmission case and applies a stationary torque on the ICE and planet-gear carrier to keep them from rotating when MG1 is working as a motor.

    Post 1 | Regenerative Braking Details? | Page 3 | PriusChat

    and

    Post 2 | Regenerative Braking Details? | Page 3 | PriusChat
     
    #11 Gokhan, Oct 3, 2021
    Last edited: Oct 3, 2021
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