Calculation method of progessive stage/rate leaf springs.

[mitra1987]

Hi

This is Abhijeet Mitra. I am a designer of suspension systems in India.

Can somebody help me find the calculation method to find out stage stiffness of progressive/rate leaf spring ( Considering the length and camber of leaves in the spring system )

 

[israelkk]

Can you provide a picture/sketch/drawing of the setup?

 

[GregLocock]

use the sae leaf spring design manual

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[GregLocock]

http://books.sae.org/hs-788/

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[mitra1987]

Thanks Greg & israelKK

My basis of design calculations is SAE J 788. But in actual samples it is always observed that stage 1 stiffness is greater than calculated. For example if required stiffness values are 6 and 13 kgf/mm, then observation is 8.8 and 13 kgf/mm. Snapshot for concerned spring system is attached.

 

[israelkk]

As stated in SAE J 788 1982 page 53 2nd column regarding the load deflection diagram "It has been drawn without considering such details as the change in moment arm length when the spring is deflected from positive camber to flat to negative camber". Add to this friction in eyelets, friction between leaves, etc., You also have to put tolerances for the rate value it should be at least +/- 15% due to the complexity of multi leaf spring compared to single leaf horizontal beam spring.

 

[GregLocock]

If you really want to get the rates right then there is no substitute for a crude beam element model. This will account for the influence of shackle angle, and the camber effect.

I'd use matlab, but here's an examplf ro a single leaf I did in Smath

http://smath.info/wiki/Examples.ashx

http://smath.info/wiki/GetFile.aspx?File=Examples/finger4.pdf

You will also be able to model the effect of the second stage more accurately, although that gets very tricky.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?