Power Split Device

Discussion in 'Gen 4 Prius Technical Discussion' started by dstahre, Jun 27, 2016.

  1. dstahre

    dstahre Member

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    Perhaps this belongs in the "Newbie" forum but I'm trying to understand the functioning of the PSD. I understand that initially MG2 may power the car with the ICE stopped. This means that MG1 is turning and because it is a permanent magnent device it should be generating power. I assume this is fed back to MG2, correct?

    When the ICE starts MG1 should slow, stop or reverse direction, correct? What I'm wondering is how this is accomplished? I assume that power is either fed back to MG1 or MG1 is loaded to control its speed, correct? This is where I get a little confused about the virtual gear ratio.

    Anybody help me clear the fog?

    Thanks!
     
  2. bisco

    bisco cookie crumbler

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    try the knowledge base articles forum.
     
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  3. bwilson4web

    bwilson4web i3 and Prime

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    • MG1 - starts the engine and there after, provides 'counter torque' to force the engine power to pass through the mechanical part of the Power Split Device. Without MG1, even if the engine is running, nothing happens.
    • MG2 - provides reverse and it also absorbs or generates power from MG1. At slow speeds, less than ~25 mph, the counter torque comes from MG1 working like a generator. That power is sent to MG2 which feeds it back into the drive gears to the wheels. At speeds over ~25 mph, MG2 generates power that it feeds to MG1 so it can provide counter torque for the engine. That power takes the mechanical path through the Power Split Device and on to the drive gears.
    Don't feel bad, it took a couple of years before I finally understood it:
    http://hiwaay.net/~bzwilson/prius/pri_PSD.html

    Bob Wilson
     
    #3 bwilson4web, Jun 27, 2016
    Last edited: Jun 27, 2016
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  4. CR94

    CR94 Senior Member

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    Whoa! I suspect you meant to say " At speeds over ~25 mph, MG2 generates power that it feeds to MG1 so it can provide counter torque ... ".

    Actually there's nothing magical or significant about the specific speed of 25 mph. Whether MG1 acts as a generator feeding power to MG2, or vice versa depends on the ratio of speeds of the engine and wheels. Generally the former tends to occur at low wheel speeds relative to the engine speed (i.e., simulating "low" gear ratios), and the latter at higher wheel speeds (simulating "high" gears). The PSD follows the same simple algebraic rules as every other single-stage planetary gear set.
     
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  5. bwilson4web

    bwilson4web i3 and Prime

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    [​IMG]
    I don't remember why I was thinking 25 mph. This data shows the power flow reversal.

    Bob Wilson
     
  6. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    As I understand the Gen4 version, M/G2 is now where you show it, although the chain is now gears.
     
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  7. bwilson4web

    bwilson4web i3 and Prime

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    Correct. The Gen-1 and Gen-2 have a 'silent chain' and the Gen-3 and Gen-4 have gears. I was trying to show the power flows through the power split device.

    Bob Wilson
     
  8. William Redoubt

    William Redoubt Senior Member

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    This is the clearest explanation I have seen, and you get a feel for the way Chevrolet handles the device in the Volt. I finally just gave up and built a planetary gear set on my 3D printer and then used it to simulate the various modes. It is quite ingenious.

    [​IMG]

    Study it, but realize that the power can move through more than just the single center shaft. The ring gear is MG2's rotation, the planet carrier rotating is the ICE's output, and the sun gear with the central shaft is the rotational force from MG1.
     
  9. bwilson4web

    bwilson4web i3 and Prime

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    Well done!
    I used a similar approach: PSD Model

    Having a mechanical model in hand, you can feel the torque which otherwise is not so easy to visualize.

    Bob Wilson
     
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  10. dstahre

    dstahre Member

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    I thank you kindly for your excellent explanation and for your patience with me. I find this car to be an extremely clever and elegant piece of engineering!
     
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  11. tzx4

    tzx4 Active Member

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    Toyota Prius - Power Split Device

    Play with this interactive website. It is very instructive. The fun thing about the 2016 Prius is that they have somehow tweaked it so the motor can be at 0 rpm up to 73 mph (in my 2016 in fact, and have not attained or heard of a higher speed) All previous ones had to engage the gas motor above mid 40's mph.
     
    #11 tzx4, Jun 29, 2016
    Last edited: Jun 29, 2016
  12. Jeff N

    Jeff N The answer is 0042

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    Note that the illustration shows how the 1st generation Volt (model years 2011-2015) works. The 2nd generation Volt has a completely different design.

    If you want to read more about the new Volt design (shared by the 2016 Malibu hybrid) see:

    Second-Generation Volt Transmission Operation Explained

    plus a video explainer based on the above article:



    and

    2016 Chevrolet Volt Powertrain: How It Works In Electric, Hybrid Modes
     
    #12 Jeff N, Jun 30, 2016
    Last edited: Jun 30, 2016
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  13. Priyzf

    Priyzf Junior Member

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    American Engineering vs. Japanese Engineering

    Always a good read
     
  14. pakitt

    pakitt Senior Member

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    I managed to have the Gen4 in EV mode at 80-90km/h but 117km/h (73mph) never... it sticks using the ICE - I think you need a full battery for that...
     
  15. tzx4

    tzx4 Active Member

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    I see 73 mph only on sustained downgrades which are plentiful here in central Colorado. I have to wonder if the Li Ion battery vs NiMH battery might be a factor. Also for some reason the EV icon is more prone to lighting up when cruise control is NOT engaged, even when the energy monitor indicates no output from the ICE.
     
    #15 tzx4, Jul 15, 2016
    Last edited: Jul 19, 2016
  16. Roger T

    Roger T Member

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    Awesome explanation. You should summarize how the battery comes to play during the process you talked about, like how the SOC of battery affects the process, and when the battery is low and the car is actively charging the battery.

    I have been always curious in what extend has the battery assisted in acceleration when the engine is on. I suppose it will assist in acceleration when the car is driving under 25mph by feeding power to MG2. But what about above 25mph.
     
    #16 Roger T, Jul 17, 2016
    Last edited: Jul 17, 2016
  17. bwilson4web

    bwilson4web i3 and Prime

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    Traction battery roles:
    1. Powers MG1 to start engine.
    2. Absorbs excess engine power when vehicle, drag-load, is low and SOC is low
    3. Provides power when engine is off and the vehicle needs power to move
    4. Absorbs vehicle kinetic energy during regenerative braking
    5. Powers 12V inverter for vehicle electronics and lights
    6. Additional power when demand exceeds ICE power (Thanks @ChapmanF )
    Bob Wilson
     
    #17 bwilson4web, Jul 17, 2016
    Last edited: Jul 17, 2016
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  18. ChapmanF

    ChapmanF Senior Member

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    6. Contributes power when engine is running and accelerator demand has momentarily exceeded engine output. You can see this on the MFD 'car' display; with a ScanGauge you can see how many amps are being contributed.

    Sometimes 'momentarily' means more than just momentarily, too ... a year ago I was in my Gen 1 as a passenger while my sister drove up through Rockfish Gap and she was maintaining about 80 mph all the way up. I was watching the scangauge and the battery was supplying 10 to 20 amps or more pretty much the whole way up the mountain. I was watching the state of charge count down through the 40s, expecting that the instant it reached 39.5 my sister would suddenly find herself driving a much slower car. Our exit came just before that happened. :)

    -Chap
     
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  19. Roger T

    Roger T Member

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    Interesting. I have never seen this behavior except when the SOC of traction battery is high and the ECU wants to get rid of excess battery charge to make room for regen.
     
  20. ChapmanF

    ChapmanF Senior Member

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    You've never let my sister drive your car.
     
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