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I must simulate with simulink an air spring, connected to a device. In many book is present this non linear formula:

k(h)=-(n*P0*Ae*h0^n)/(h^(n+1))

Where:

P0 is the air pressure at the equilibrium condition

h0 is the spring heigth at the equilibrion condition

Ae=F/P0 is the effective area

n is the polytropic coefficient

So for checking the formula, I try to compare my result with the stiffness provided by the supplier and unfortunately I get a different value (40% less) .

In this link you can find an air spring catalogue:

http://213.164.133.30/catalog/ShowBalgPDF/SZ 50-11.pdf

For example, at 3bar=3*10^5 Pa I got an force of 1200N, h0=0.15m

K(h0)=1.4*1200/0.15=11200N/m, instead of 18500N/m. What is wrong in my calculation?

Thanks

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# Air spring stiffness calculation

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