Air spring stiffness calculation

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SUMMARY

The discussion focuses on the calculation of air spring stiffness using the non-linear formula k(h)=-(n*P0*Ae*h0^n)/(h^(n+1)). The user encountered a discrepancy of 40% between their calculated stiffness (11200 N/m) and the supplier's value (18500 N/m) at 3 bar pressure. Key parameters include the polytropic coefficient (n), effective area (Ae), and equilibrium conditions (P0 and h0). The conversation emphasizes the importance of using the correct value of n and suggests that empirical data from load vs. deflection tests may provide a more accurate stiffness curve.

PREREQUISITES
  • Understanding of air spring mechanics and non-linear stiffness calculations
  • Familiarity with Simulink for simulation of mechanical systems
  • Knowledge of polytropic processes and coefficients in gas behavior
  • Ability to interpret manufacturer specifications and performance curves
NEXT STEPS
  • Research the impact of the polytropic coefficient (n) on air spring performance
  • Learn how to conduct load vs. deflection tests for air springs
  • Explore curve fitting techniques for establishing effective stiffness equations
  • Investigate the use of Simulink for modeling non-linear mechanical systems
USEFUL FOR

Engineers and researchers involved in mechanical design, specifically those working with air springs in automotive or industrial applications, will benefit from this discussion.

serbring
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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
 
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hi were you able to get an answer to this ...?
 
Unfortunately not
 
are you working on Air Spring simulation ? was it for some college project ?
 
I am working on air spring simulation for a multibody simulation project
 
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 .
 
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?
 
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.
 

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