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  • Belleville spring characteristics

    Discussion in 'Calculations' started by k.udhay, Jun 7, 2012.

    1. k.udhay

      k.udhay Member

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      Hi,

      I have been working on designing something for a clutch which is pressed by a bellivelle spring. When clutch pedal is pressed, a linkage uses a leverage and works against the bellivelle spring, thus releasing the cluch plates. At this point, I came across a graph that describes the characteristic of the mechanism:
      [​IMG]
      As you can see, the mechanism needs totally a different pattern of forces to displace the clutch between new and old. Especially when the clutch is new, the curve is flat at some place and climbs up again. For an old clutch condition there is no flat portion as such and there is a drop of force after a displacement of 12 mm.

      Can someone pl explain why this happens? Thanks.
       
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    3. MDR

      MDR Active Member

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      Bellville springs are nonlinear and follow force/displacement curves that often look much like your 'worn' curve. I suspect the difference has to do with the displacement vs. spring compression relationship changing as the plates wear and displace. I'd need more information about the mechanism in order to give a better answer, unfortunately
       
    4. MDR

      MDR Active Member

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      If you could sketch the mechanism that would definitely help.
      What material is the spring made of and how many cycles has it encountered between 'new' and 'worn' conditions? Any chance strain hardening is occurring?
      Is there more than one washer in this assembly?
      Also, is the spring washer simply round or does it have fancy cutouts in it? (most clutch springs do)
       
      Last edited: Jun 8, 2012
    5. k.udhay

      k.udhay Member

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      Hi MDR,

      First of all, thanks for your effort and eagerness to answer my question. But honestly, I don't have much information about the clutch mechanism. This was a graph given to me by the customer. He wanted me to make sure that the mechanism I design will work suitably for both new and worn conditions. Since the curves look different from each other, I thought I would post this question here.


      "I suspect the difference has to do with the displacement vs. spring compression relationship changing as the plates wear and displace" - In fact, I thought about this, too. But what surprised me in that case was the new can not require more force than the old in such a condition. Another point is the new clutch curve should have an offset instead showing a totally different shape...

      I believe there is only one belleville spring employed here.

      Thanks again.
       
    6. MDR

      MDR Active Member

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      It's a very interesting case! If you do find out why, I would love to know.
       
    7. MDR

      MDR Active Member

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      It depends on what force is being measured here. If the force is being measured at the spring, then yes I agree with you it is surprising. If the force of actuation, at the end of a mechanism, is being measured, then the linkage/mechanism could change its geometry as the clutch wears such that it has more mechanical advantage in the new condition and less in the worn condition.
       

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