Is there a way to control adjust the accelerator "curve"?

Discussion in 'E9 Projects and Restorations' started by Bmachine, May 8, 2019.

  1. Bmachine

    Bmachine Well-Known Member Site Donor $$

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    I have a stock B35 motor with Motronic 1.3. I find that the accelerator pedal activates most the fuel delivery in the first third of its travel. Is this something that can be adjusted so it is a bit more linear along the pedal travel?

    Thank you
     
  2. Markos

    Markos Parts Mule Staff Member Site Donor $$

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    This is how Volkswagen has been doing it for 32 years. The small butterfly opens first then at WOT on the little guy, the large butterfly opens. Very smooth!


    82897EE8-8440-4DF5-B7BE-1410AC8296AD.jpeg
     
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  3. Mike Goble

    Mike Goble Active Member

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    Air flow through a throttle blade is basically a square root function. 1/4 open gives you √.25 on the air flow, which is about 50% . 1/2 open is about 70%. We used to use characterizing cams on the air flow controllers we built for boiler controls. You could develop a gas pedal with an increasing throttle displacement per angle of depression. Something where the throttle lever starts out well up the pedal then as the pedal is depressed it the point of contact moves to the outer end of the pedal.
     
  4. sfdon

    sfdon Well-Known Member

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    Throttle by wire can be mapped for anything you want
     
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  5. Bmachine

    Bmachine Well-Known Member Site Donor $$

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    Yes, I have definitely been thinking about that, in theory at least. How hard is it, in reality, to make this happen on a coupe?
     
  6. sfdon

    sfdon Well-Known Member

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    Not going to happen....
     
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  7. Belgiumbarry

    Belgiumbarry Well-Known Member

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    we were lately testing different EML mappings on my SC 850i project.... with the "Wokke" chips.
    OEM is "lazy" , so we tested the Wokke V2 to found out is was to aggressive… now, with the V1 it is better .
    I assume OEM curve mapping is less than linear , V1 is about linear , V2 is more than linear.

    With the V2 , only a minor touch of the gas pedal jumps the rev's to much. So in shifting (manual six speed) i had sometimes revving up the engine needless before clutch was fully released … also at cruise the difference is to great between a bit pedal and no pedal.

    Most important thing was to get rid of the "bug" in some OEM EML's , with which the throttle blades under WOT pedal only open full after 4200 rpm.
     
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  8. sfdon

    sfdon Well-Known Member

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    Same results with my 850 last year - stock was lethargic, Canadian chip made it too aggressive in low speed traffic.
     
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  9. Stevehose

    Stevehose Well-Known Member Site Donor $

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    Could this be achieved by changing the geometry of the linkage? Specifically the bell crank lever to one with less gear effect?

     
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  10. Belgiumbarry

    Belgiumbarry Well-Known Member

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    one should found a system that the throttle opens less than linear with the pedal move.... as Mike wrote, 1/4 open throttle blade is already 1/2 air flow.... now all to the drawing board :D
     
  11. sfdon

    sfdon Well-Known Member

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    CD951125-0638-4C67-8FB0-D2E5005481C4.jpeg Looking at an injected bmw 3 liter engine throttle body you will see that there is a throttle lever that allows about 20% opening of the butterfly at 50% throttle and the other 80% at 100% throttle.
     
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  12. Bmachine

    Bmachine Well-Known Member Site Donor $$

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    Am I oversimplifying by thinking that one could 3D print one of those with a different curve for that "banana" opening?
     
  13. sfdon

    sfdon Well-Known Member

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    The point of that particular curve is to give the best drivability for a street car.
     
  14. Markos

    Markos Parts Mule Staff Member Site Donor $$

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  15. Cornishman

    Cornishman Active Member Site Donor

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    Fantastic model and video, well done Markos.

    Bo, no need to 3D print, with a drill and a file you could make one. Perhaps use CAD to get the correct shape.
    In this instance, CAD is Cardboard Aided Design
     
  16. Markos

    Markos Parts Mule Staff Member Site Donor $$

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    I would want the linkage to be captured so you don’t roll off the end at WOT. Replace that diamond plate
    with the piece from Don, which captures a ball or bearing.
     
  17. Bmachine

    Bmachine Well-Known Member Site Donor $$

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    Yes I was looking at how that piece (in Don's pic) works over the weekend. I think I'd rather find a solution in the linkage if at all possible. Messing with the curve of that piece would be a real science project.
     

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