Air Spring 1

[nobog]

Is this a true statement: "Unlike a metal spring, and air spring actually absorbs energy as it cycles, making the job of controlling rebounding much more straightforward".

I understand metal springs store energy, my question is in the accuracy of the word "absorb". This is in reference to a Firestone Airide spring.

Thanks for any input, Jim, Minnesota

 

[MikeHalloran]

The air will heat up a little, but I think the rebound is less of a problem because the air spring's rate is nonlinear.



Mike Halloran
Pembroke Pines, FL, USA

 

[GregLocock]

You can also put in some valves and a reserve volume, to create a damper. Gates have been promoting this solution for many years.



Cheers

Greg Locock

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

 

[BioMax]

I work with air springs everyday, they do absorb a small amount of energy, but their aggressively rising rate and the amateur’s habit of installing too small of a part make the statement negligible. But, with the right size part and some time spent playing with expansion tanks of different volumes and hoses of varying length and size, you might be able to have a system that is tolerable at best.

 

[Fabrico]

Be prepared for your experiments to expand exponentially. If that air is doing anything beyond springing, its temperature will change rapidly along with the spring rate.

 

[nobog]

Thanks for the replies. The reason I ask is that the "press" sometimes makes some claims based on what sounds good for the moment, which is where I got the quote above.

http://www.teamfast.com/

you can see they just came out with a air bag spring for a snowmobile and I was wondering about the theory if the bag works significantly different from a metal spring when it comes to rebound. Jim@DeyCore (

http://www.deycore.com)

 

[MikeHalloran]

Air bag springs give a "rising rate", which is attainable with metal springs plus linkages, but the air bags are lighter. The rising rate means they are less likely to bottom out with extra load, so they make sense for vehicles that sometimes carry heavy loads. I.e., relative to steel spirngs, a given change in payload will have somewhat less of an affect on ride height, even if the vehicle doesn't have a compressor and automatic leveling system.

Conversely, the rate falls on rebound, so the air springs will give a gentler thump as the vehicle becomes airborne and the shocks reach full extension. That might be a virtue to a hard-core snowmobile racer; it wouldn't make a difference to me.

You still need shock absorbers; the air bags don't absorb enough energy to make them irrelevant, so the quotation is, if not fallacious, at least grossly overstated.



Mike Halloran
Pembroke Pines, FL, USA

 

[BioMax]

It can get a whole lot more complicated than that. The steel spring, at rest, has no stored energy, but the air spring, needing a certain volume of air to be a spring, will be constantly fighting the suspension to "get out," much like torsion bars. On lighter vehicles that will be seeing some "air time," a negative spring should be used to make droop travel feel more like a steel spring system. Some designs use a steel negative spring, but the tunability of an air spring being used as a negative is preferred.

The real advantages of the air spring are weight, ease of spring rate change and the last portion of travel being naturally progressive. The beginning and middle of the travel, on air systems, is still mediocre, for performance uses, air is still being mastered.

 

[patprimmer]

The biggest advantages I see in air springs are light weight and instant adjust ability to correct ride height changes due to load

Regards

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[nobog]

I don't see the airbag temp changing considerably as under a snowmobile suspension snow is constantly swirling. The main failures with regard to snowmobile suspensions are anything electronic (computer adjustable shocks) or any remote reservoirs where a hose connects to the shock body. Ice, sticks, flexing, and temperature all take a toll. The conditions under there are brutal, so it will be interesting to see how long an airbag will last. Thanks for all the input. Jim