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System of limited slip differentials with two power sources

  1. Jun 15, 2015 #1
    My first ever post here, so hello world!
    So I've attached an image of a conventional 4x4 system with one RIC engine and LSDs for all wheels so that all four wheels can be driven, or just one depending on conditions. the front/rear LSD may in fact be locked, but that isn't particularly important...
    RIC + LSDs.gif
    So if the front axle is at the bottom of the page, and the rear axle is at the top (the car is driving down your screen) and i added two electric motors where the rear brakes would usually go, then how would the system behave under acceleration? I know that removing the brakes isn't a great idea in real life, but for the purposes of this question its easier to describe it that way.
    RIC + LSDs + Motors.gif
    If you want numbers to play with then lets say the engine is 100kWm and the electric motors are 30kWm each and the LSDs can be whatever type you thing is best for this scenario
    All the tyres are the same tread and grip, and we are assuming that the vehicle is on a level homogeneous road surface to keep it to the problem in hand.
    My first conclusion on this problem is that the LSDs will sort themselves out (provided they have the right settings - which I can't define) and 1/4 of the overall 160kWm (that's 40kWm) would be applied to each wheel. I just can't decide if in reality the front/read LSD would think that the rear wheels were slipping and send all the power to the front initially, until the LSDs begin to limit the slip in the front/back...
    also, what effect would locking the front/rear diff have? would it be better?
    thanks to all for your help!
     
  2. jcsd
  3. Jun 15, 2015 #2

    Baluncore

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    There is a problem. The RIC will act as a fulcrum that may effectively reverse the drive from the electric motors to the front axle.
    Locking the middle diff will eliminate the problem.
     
  4. Jun 17, 2015 #3

    tech99

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    Suppose the RIC is stopped and the rear LH wheel is on solid ground. If the RH rear wheel is on ice, I think the motor will cause it to spin.
    By the way, I have drawn myself an electrical analogue of the set up, using transformers for the differentials. When a differential locks, it seems to be equivalent to grounding the transformer centre tap.
     
  5. Jun 17, 2015 #4

    Baluncore

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    Can you please attach a copy of your model to a post.
    I would have thought that pinion drive would be through the centre tap with a resistor between the opposite ends to simulate a LSD. A short between the opposite ends would emulate a locked diff.
     
  6. Jun 18, 2015 #5

    tech99

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    I have tried to attach my diagram of the electrical analogue. Sorry if it does not work.
     

    Attached Files:

  7. Jun 18, 2015 #6

    Baluncore

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    This is my transformer analogy. Torque for different motors is identified by different mutually prime frequencies.
    Change the value of R_lock to lock the centre diff.
     

    Attached Files:

    • AWD.png
      AWD.png
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