Air Suspension / McPherson Side Load Compensation

[Pneuride]

I am currently developing an air suspension system where the air bags act as "air over" bags on a McPherson strut in place of the coil spring. We think we can tackle side load compensation on the McPherson strut with the air bag. Not being experts in strut design I wanted to ask.

What are the main effects of not having side load compensation on a McPherson strut?

What is the best way to measue the effect?

 

[GregLocock]

Measure the force against deflection as you cycle the suspension up and down.

The 'width' of the loop is function of the friction in the system.

You might also get some interesting results trying to measure the stiction (breakaway friction) in the strut.

We found that air springs have more inherent friction in them than steel springs, but that might have been due to side load.

You can buy spring seats that have linear bearings in them, if you want to build a 'perfect' system with no preload to try out. (sorry no source)

Now let's see.. cars expensive enough to justify air springs, but with MacPherson struts. BM?X?



Cheers

Greg Locock

 

[Pneuride]

Cheers Greg,

The area in the loop is the hysterisis in the spring system With coil springs this is practically zero.

With air suspension the hysterisis is higher dependant on a number of factors, namely, moulded dia in relation to inflated dia. The angle of the cross ply - neutral angle relationship, the stretch of the cord (nylon or aramid), the temperature of test and the direction the wind blows on any given day.

Best results are found when the air bag is placed inside a steel can so the rubber flex is reduced and the dia is constant. Also allows the use of thinner materials.

The breakaway friction is higher, we're working on this by tapering the rolling lobe area to encourage the roll from ride height.

The Side load problem mainly lies in getting the spring to point towards the wheel centre and survive durability, there are compromises needed.

Thanks for the pointer on the linear spring seats, i'll look into it.