How to design parabolic leaf spring?

[ksachanta]

hi,
can anyone please help me to design a parabolic leaf spring for vehicle suspension...
is there any software available?

 

[ksachanta]

hi,
can anyone please help me to design a parabolic leaf spring for vehicle suspension...
is there any software available?

Plz anyone can help me on this...?

 

[Travis_King]

It's not simple matter of saying "Make it like this"
You have to consider many variables:
(a) Is this a custom application? What is your req'd, if any, eye-to-eye dimension?
(b)What is the resultant ride height you are looking for?
(c) What load must the springs carry?
(d) How much flex is required?
(e) How far apart will they be situated?

These things all make a huge difference in designing leafs. Suspension systems (even leaf springs) are not cookie cutter.

 

[ksachanta]

Thanks for ur reply.
i want to design a parabolic spring for a heavy commercial vehicle.
the inputs are -
-- eye to eye length is ~ 1200mm to 1500 mm
-- width of leaf is taken as 70 mm or 90 mm
-- stifness required is 30 - 35 kgf/mm
-- load on each spring ranges from - 1300 kg to 1500 kg
-- flex required is about 60 - 100 mm (at laded condition)
-- camber ( free curvature of unloaded spring) is taken around 200mm
-- springs are situated at 850 mm apart.
-- Ride clearance(dist. from axle centre to chassis bottom to me maintained at 200mm

the spring to be checked for 2g load and 3.1g load (over load) conditions, where the flex will be maximum.

Here i have to decide on number of leaves required and Centre thickness & end thickness of leaves.
How could you design the parabolic profile of leaf once you got your center and end thicknesses.

Plz. help me on this .. I am unable to get exact formulas to design the spring .. suggest me some that know..

Thankyou very much .. waiting for ur reply...

Regards
Srikanth

 

[Travis_King]

https://www.modelica.org/events/modelica2006/Proceedings/sessions/Session2d1.pdf

That might give you some insight. I've never done this as the equations aren't anything simply like

(#leaves)*(eye-to-eye)=Spring_Dimensions

There is some calculus involved. You have your variables though, so you've got that going for you.

Take a look at how some existing springs are designed. Remember, the more accurate you want your calculations (that is, the more variables up there that you want to satisfy) the more difficult they will become. My experience with stuff like this: you have to trade some of your requirements for the ones that are more pressing. Like forfeiting some flex to support your load, or some ride height to allow your flex, etc.

 

[BadBrain]

I'm thinking that you might want to abandon your theoretical approach, and work by trial and error.

My favorite parabolic leaf springs are those aboard the US Army's J-118 Escort Wagon:

http://www.transchool.lee.army.mil/museum/transportation museum/wagons.htm

In particular, I like the scissor-spring shock absorbers of the driver's seat (a scissor-spring being, essentially, a double parabolic leaf spring with the open sides facing one another).

I would recommend experimentation with leaves as thin, and made of material as light, as possible. It might take a while, but it might make you rich!