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How Does The Throttle Work?

Discussion in 'Roadster' started by Pantera Dude, Dec 21, 2012.

  1. Pantera Dude

    Pantera Dude Member

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    Someone asked me one of many questions I haven't been able to answer about the car; "How does the throttle work, is it a rheostat, if so, how does a rheostat work?"
     
  2. doug

    doug Administrator / Head Moderator

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    I would have thought they used an encoder, but I've heard they use a pair of potentiometers. As you depress the pedal, one goes up in resistance and the other goes down. Both are mapped to give a certain accelerator value and if they don't agree the system throws an error.


    Potentiometer - Wikipedia, the free encyclopedia
     
  3. Pantera Dude

    Pantera Dude Member

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    Thanks Doug!

    Art
     
  4. TEG

    TEG TMC Moderator

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    Same basic component used in all sorts of things that need variable low voltage control.
    Similar to the gain knobs in an electric guitar, volume control on an old transitor radio, etc.
    You are basically adjusting the imediance/resistance of current by varying the distance the current has to travel over a resistive material.
     
  5. Pantera Dude

    Pantera Dude Member

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    Thanks Teg.
    So was Doug's description correct, is what you have described a poteniometer?
     
  6. vfx

    vfx Well-Known Member

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    In my experience, very well thank you. :)
     
  7. TEG

    TEG TMC Moderator

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    #7 TEG, Dec 25, 2012
    Last edited by a moderator: Mar 13, 2016
    Yes, absolutely.

    - - - Updated - - -

    By the way, the old fashioned term "throttle" comes from the fact that the pedal used to control a cable that moved a valve in the carburetor (or intake manifold with fuel injection) that would "starve" the engine for air to keep it from trying to fully rev. You basically could prevent the engine from making full power. These days many/most gasoline cars use a "drive by wire" system where the pedal controls a potentiometer and a solenoid type device moves the air intake 'throttle'. I think they do this in part to manage emissions (such as closing the valve during shifts), help with fuel economy, and otherwise fine tune the driving experience (such as making the pedal more responsive on hills.)



    I think for EVs it is better to use the term "accelerator pedal", not "throttle" or "gas pedal".

    (In some old threads, some liked to call it the "torque pedal", since in cars like the Roadster you can also let off to cause negative torque / regen slowing. )
     
  8. Pantera Dude

    Pantera Dude Member

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    #8 Pantera Dude, Dec 25, 2012
    Last edited by a moderator: Mar 13, 2016
    Thank you!
     

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