coil over shock friction

[Pavsta]

Is it possible to quantify the amount of friction between a coil spring and shock as a result of the spring twisting during linear deflection?

I have been trying to mathematically define this but I am finding it a little difficult.

Cheers

 

[GregLocock]

You mean as a result of the line of action of the spring moving around as it is compressed?

However, establishing the axis is pretty hard as it depends on the shape and stiffness of the spring seat, and its alignment with the other spring seat. We measure it. You could build a non linear geometry and contact model to calculate it. I /think/ the spring manufacturers can do this. I expect the SAE spring design manual tells you how to do it by hand.

Once you know the location of the axis then it is possible to calculate the bending moment induced in the strut, so you can work out the sideload on the piston and rod. Turning that into a friction figure is a bit harder, you need a coefficient of friction for the two, which you'll probably have to measure.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[israelkk]

GregLocock

See Pavsta's post in the "Spring engineering" forum where his question is clearer. As I understand his question, he is looking for the relative rotation of the end coils as a result of the spring linear deflection. This pnenomena is coupled with the outside diameter growth when a compression spring is compressed to a shorter length.