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But how does it work, really? HSD mechanical question

Discussion in 'Gen 2 Prius Main Forum' started by KMO, Apr 26, 2004.

  1. KMO

    KMO Senior Member

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    I've read all the technical blurb I can find about the Hybrid Synergy Drive, but I still don't quite get it.

    I understand the planetary gear that keeps the linear relationship between the speed of MG1, the petrol engine and MG2, and all the different operating modes, but how is it regulated?

    If you put your foot down, and the ICE throttles up, what stops it from just sending MG1 spinning up rather than accelerating the car? Is it that MG1 is pushed electrically in the opposite direction to direct the rotation to the wheels? Or does it work because MG2 is always pushing at the same time?

    Are there any other functional units in the gear train other than the 3-way planetary gear to direct the power?
     
    #1 KMO, Apr 26, 2004
  2. bigbaldcuban

    bigbaldcuban New Member

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    You just made my brai hurt. I guess it's sort of like explaining how a megaton jumbo jet gets off the ground. I don't understantd how it works, but I trust it because others have done it without blowing up. :)
     
    #2 bigbaldcuban, Apr 26, 2004
  3. naterprius

    naterprius Senior Member

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    Short Answer: There is essentially a brake on whichever part you need "locked."

    Long answer: (with history) On an traditional automatic transmission, these are bands that wrap around the ring. On a newer trans, these are clutch packs that engage. Both are controlled by hydraulic pressure, with the valve for that pressure controlled by four factors: engine speed vehicle speed, throttle position, and current gear. Each one changes the pressure in a valve body until one of them wins, sending the pressure to a particular brake in the sets of planetaries. (Like pressure for vehicle speed > pressure from being in second gear causes shift to third).
    In newer cars, solenoids are added to a computer to make better decisions about when to shift. Most automatics can run in full mechanical mode, but less efficiently. Handy when the trans computer fails for whatever reason.

    I'm pretty sure the Prius planetary trans uses pure electronic control over the planetary, another break through in transmission technology.

    Nate
     
    #3 naterprius, Apr 26, 2004
  4. efusco

    efusco Moderator Emeritus
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    #4 efusco, Apr 26, 2004
  5. bookrats

    bookrats New Member

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    Also, this thread has some good pointers to "how the planetary gear works".

    I like Graham's site, but found that several of the other sites mentioned in this thread (particularly howitworks.com) eased me into the subject. After digesting these (and the animations, which I think are better), I felt up to tackling Graham's explanation.
     
    #5 bookrats, Apr 26, 2004
  6. KMO

    KMO Senior Member

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    Thanks for that link - I hadn't seen that one. And that thread was helpful.

    It confirms what I thought might be happening - it's a sort of balancing act where power from the ICE (in the middle) is directed by adjusting the loads on MG1 and MG2. I wasn't quite sure whether it really could be that "simple", and that no other parts were involved.

    It may be a simple solution in mechanical terms, especially compared to a conventional automatic gearbox, but it's the sort of stunt that can only be pulled off with really sophisticated computer control.

    Of course, Toyota have pulled off a real coup here. By refining their system first, and patenting it up to the eyeballs, they've made it very hard for everyone else to catch up without coughing up license fees.

    At the risk of thread drift, does anyone else know how this compares to the early days of ICE cars? Were the basic concepts of alternators and electric starter motors subject to patents?

    Thanks for your help, guys.
     
    #6 KMO, Apr 27, 2004
  7. bookrats

    bookrats New Member

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    Hey, all the fun around here comes from thread drift! :D

    Great question -- I have no idea about how tight patents were in the early days of motor car manufacturing.

    However, here's an interesting recent thread about the Woods Gas Electric hybrid -- from 1917!
     
    #7 bookrats, Apr 27, 2004
  8. tomdeimos

    tomdeimos New Member

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    If you want lots of technical detail on how it works, check out:

    www.engin.umd.umich.edu/vi/w4_workshops/Miller_W04.pdf

    Looks like our Prius started being designed in 1905 with a big further
    boost in 1971.

    Covers Ford GM and Renault systems as well as Prius.

    Note especially our "Negative Split Mode" which seems to be their
    name for the Heuretical or overdrive mode.
     
    #8 tomdeimos, Jun 8, 2005
  9. NuShrike

    NuShrike Active Member

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    There seems to be 3 break-points for the Ng(i), generator? on slide 43.

    At 20mph, 55?mph, and 75?mph. Are these different efficiency points and related to a previous thread of which speeds were the best to drive at?

    Hmm, and the Ford system is basically Toyota's except with gearing at the output...

    Thanks, very informative slides..
     
    #9 NuShrike, Jun 8, 2005
  10. vincent1449p

    vincent1449p Active Member

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    I don't see how it is related, sorry.

    I think the author is trying to show the relationship of the vehicle speed against the engine speed and generator speed. From the planetary gear speed equations, you can determine the RPM of one if given the other two:

    MG1 = 3.6 * Engine - 2.6 * MG2
    MG2 = (3.6 * Engine - MG1) / 2.6
    Engine = (MG1 + 2.6 * MG2) / 3.6

    Since the engine speed is decoupled from the vehicle speed, the Hybrid ECU can vary the generator speed to respond to the discountinuities of the engine speed to achieve a linear and smooth acceleration. Beside this speed control, torque control is also executed every 4 ms.

    If you want more details, I recommend the following US patents:

    Power output apparatus and method of controlling the same
    Power output apparatus and method of controlling the same
    Power output apparatus and method of controlling the same
    Power output apparatus and method of controlling the same
    Power output apparatus and method of controlling the same
    Power output apparatus and method of controlling the same

    Vincent
     
    #10 vincent1449p, Jun 9, 2005
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