Air spring stiffness calculation

[serbring]

Hi guys,

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

 

[kammieorama]

hi were you able to get an answer to this ...?

 

[serbring]

Unfortunately not

 

[kammieorama]

are you working on Air Spring simulation ? was it for some college project ?

 

[serbring]

I am working on air spring simulation for a multibody simulation project

 

[kammieorama]

Oh that's good. Even i am doing same. What all are you investigating ? Maybe we can converse over mails, if that is ok with you .

 

[JBA]

This is an obvious question; but, are you sure you are using the same value of "n" as the manufacturer is using in the equation for the type of gas in the cylinder?

 

[JBA]

After viewing the air spring design configuration (which I should have done before entering my above post) I don't think that my question in that post is of any value.

Alternatively, I suspect that a curve based upon actual load vs deflection test results are the only way to establish a truly accurate curve for the sleeve deflections on that type of air spring. If you need to simulate such a spring for a project I recommend that you select a specific manufacturer's spring that suits your application and based upon the actual travel range you require; then, try to establish a curve fit equation for F vs d for that section of the manufacturer's supplied F vs d curve to use to determine the effective k values in your calculations.

 

[kammieorama]

lets write to each other on mail. kamran.shd@gmail.com