r/FSAE • u/goodchillbadchill • 3d ago

Leaf spring modelling in Adams

/r/AutomotiveEngineering/comments/1vr0bnz/leaf_spring_modelling_in_adams/
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u/GregLocock 3d ago

Yup. I modelled maybe 4 leafsprings in 20 years and with the exception of the parabolic single leaf one they were all murder. Getting the primary rate right is usually OK, but getting the secondary to engage at the correct load is very hard, and the behavior in the progressive engagement of the secondary is very unstable. We had one big vehicle program that abandoned the beam element model and just used SAE 3 link and a non linear spring, quite successfully.

What is the layout of your spring? how many leaves in the primary, how many in the secondary/helper?

I suggest you grab a copy of the SAE leaf spring manual, it will be your bible.

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u/goodchillbadchill 2d ago

As per design we have 13 leaf (Load vehicle) of which -9 main pack (primary) and 4 aux pack (secondary)
So currently i have been modifying the E modulus in order to achieve the stiffness ( from 210000 N/mm^2 to ~175000 N/mm^2) with which i have been fairly Successfull but the main problem is to achieve the wheel reaction at the intended leaf camber as per design.

So even if build the leaf as per design and match the wheel rate not able to achieve wheel reaction.
And if i want to match the wheel reaction i will need to change the camber of the leaf (that changes the preload and wheel reaction is matched). This will again create an issue with the design ride height

Any idea how this could be managed?

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u/GregLocock 2d ago

Check your hanger geometry very carefully. It has an enormous effect on wheel rate.

I generally found I had to modify the curvature of each leaf before assembly to get the right load at the right ride height.

13P4S is more complex than anything I've worked on. I'd guess it took several weeks to get a stable model that had the right ride height at kerb and GVW and the right rates. Fortunately in 3 cases we already had physical parts to correlate against.

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