Progressive springs

[Cris]

Hi,

Does anyone know about the maths behind progressive springs? There is nothing in Milliken and I was looking into doing the calculations.

Thank you

[Cris]

Hi,

Does anyone know about the maths behind progressive springs? There is nothing in Milliken and I was looking into doing the calculations.

Thank you

[ben]

Do you mean a coil spring that's progressive? Why not just use bump rubbers?

Ben

[Cris]

That is what I mean, because my project is programming a calculator to assist others in the design of suspension... And progressive springs are a nice feature!

[exFSAE]

The math isn't any different from a normal spring. You just have to replace a constant springrate term with a variable.

[Mikey Antonakakis]

You can use a linear spring and design your rockers (assuming you use them) to give you a progressive wheel rate if that's desired.

[Cris]

exFSAE, I explained myself unclearly. What I mean is once you know what range of spring stiffnesses you want and over what range of lengths. How do you go about calcuating the coil spacing, wire diameter, wire thickness... such as is done for a normal spring on the following link:
http://www.efunda.com/DesignSt...lc_comp_designer.cfm (http://www.efunda.com/DesignStandards/springs/calc_comp_designer.cfm)

[Cris]

exFSAE, I expressed myself unclearly. What I meant to ask is once you have the desired spring stiffness range and the range of displacements for which you desire these stiffnesses, how do you go about calculating the specs of the spring, such as the spring diameter, coil thickness, coil spacing...
such as is done with the following calculator on the site:
http://www.efunda.com/DesignSt...lc_comp_designer.cfm (http://www.efunda.com/DesignStandards/springs/calc_comp_designer.cfm)

[Cris]

exFSAE,
I asked my question wrongly. What I meant is once you know you want a spring that compresses by an amount (x1,x2,x3,x4) at forces (f1,f2,f3,f4) and you want to use a progressive spring to do so. How do you go about calculating the spring properties such as coil diameter, wire thickness, coil spacing... as is done on following link for a linear spring:
http://www.efunda.com/DesignSt...lc_comp_designer.cfm (http://www.efunda.com/DesignStandards/springs/calc_comp_designer.cfm)

[Cris]

exFSAE,
I asked my question wrongly. What I meant is once you know you want a spring that compresses by an amount (x1,x2,x3,x4) at forces (f1,f2,f3,f4) and you want to use a progressive spring to do so. How do you go about calculating the spring properties such as coil diameter, wire thickness, coil spacing... as is done for a linear spring on efunda's site..

[exFSAE]

Ahh, gotcha. Good question. Still.. are you winding the springs yourself?? If not, I'd say.. go to a spring manufacturer and tell them what you want in terms of force/deflection.

Or the much easier and cheaper method.. get your progression from rocker geometry and use a linear spring...

[Luniz]

The trick behind progressive springs is that after a certain amount of deflection, one part of the windings are in block. The other way round that means that the inclination angle of the windings is not constant.

That means that you actually have two (or even more) springs in series until a certain deflection, and after that just one, because the other one is blocked.

[Adambomb]

Yep, off-road folks use these a lot (including our baja team). Best way to think of it, as far as the math goes, is two separate springs in series mated at the end coil. Here's a pic:

http://motorcycleinfo.calsci.com/Images/SHOCKS3.gif

[Cris]

Hi,
well because I wish to help others calculate it, I do not have a specific situation for a manufacturer to solve. If you see what I am making it may help: www. suspensioncalculator .com
I plan on launching it soon and want it to be an open source project to help all students in future!

[The_Man]

Another type of progressive spring can be where you have 2 co-axial springs of different diameters and lengths, such that one of them is initially having no preload. As the first spring compresses beyond a certain length, the second spring kicks in making it 2 springs in parallel.

[ben]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by The_Man:
Another type of progressive spring can be where you have 2 co-axial springs of different diameters and lengths, such that one of them is initially having no preload. As the first spring compresses beyond a certain length, the second spring kicks in making it 2 springs in parallel. </div></BLOCKQUOTE>

Surely what's actually happening is both springs deflect up until the point one goes coil bound then only one continues to deflect giving a soft initial rate followed by a stiffer one.

Ben

[Cris]

Hi,

Well now I have released the first version of my suspension calculator, and it has 19 tools on it. Hope it helps some of you with your work and I'd be delighted to get some input http://fsae.com/groupee_common/emoticons/icon_smile.gif
The forums block me writing the domain in directly so here it is slightly differently:

suspensioncalculator
c
o
m

[DougMilliken]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Cris:
Does anyone know about the maths behind progressive springs? There is nothing in Milliken and I was looking into doing the calculations.
</div></BLOCKQUOTE>

Better late than never?

We cover this topic, but it's hidden under a more general title - see RCVD p766, as well as the short note on p771. For more detail, the SAE spring manuals are recommended, our Refs. 5-7 (may be published under different titles now).
-- Doug Milliken