Leaf Spring Calcs

[claver]

Hi

Can someone help me with what I believe is referred to as a 3 point formula for calculating the open and closed length of a leaf spring.

My problem is that I have a multi leaf spring and have to work out the geometry for arriving at the best shackle length and its position.

If I can describe the spring length as, from A to B – This is the length from centre of each eye of the spring when it is under no load – If I drew a line from each eye – centre to centre I can measure my camber length when the spring is under no load.

As I load up my spring – Assuming that point A is fixed to the chassis. B will move backwards. The camber length will reduce and the length from A to B will increase. Point B is attached to the shackle plates which will pivot on point C on the chassis. I have the length of the shackle plate – from centre to centre ….

I know the open length of the spring A to B

I know the fully loaded length of the spring which is the flat plate length plus the eye.

I know the camber length when the spring is under no load

I know the ratio – Weight to reduction in camber length (the spring rate)

I do not know how much the distance will increase from A to B as the spring is loaded…..

Can anyone help please …..

Jan

 

[GregLocock]

For a crude estimate just assume it is a segment of a circle, and assume that it remains constant in length.

Neither assumption is correct, probably, but I suspect that that will be good enough for all practical purposes.

Cheers

Greg Locock

 

[claver]

Thanks for the reply Greg..… Unfortunately this approximation is not accurate enough. The leaf spring is rated at 4000Kg and the movement is relatively large, 150mm or so ….

To optimise the shackle plates I was hoping someone would have a formula for working out the change in length against the change in camber …

 

[notnats]

How accurate do you need it?

If the spring is 1000mm between eyes with 150mm of set, the difference in offset between an arc and a parabola is only 2mm at a point 250mm from the eye.

Laying it out in cad, the difference in flat length is about 1.4mm. Someone who remembers more maths can probably calculate the difference.

I would be surprised if the leaves are formed that accurately.

Jeff

 

[claver]

Valid point. I was looking at same thing today and must admit that I was probably getting to bogged down in details ..

Jan