Let's leave the leafs and coils aside , for awhile .
I want to use air bags like the Scorpion uses :

Now lets go to the technical side :
I want to inflate the bags - to get the highest clearance - BUT - i want that the 'spring rate' would be as low as possible - flexy .
When i deflate the bags - for speed drive - i want the 'spring rate' would be as high as possible - stiff .

I've been thinking about this for a long time , and i figured out that the only way that i can get this is - CHANGE THE VOLUME OF AIR NOT THE PRESSURE - if i'll change the pressure , let's say put it higher the bag will inflate more BUT the air inside will be dense , there for stiff and while deflate i'll lower the pressure and the bag will be soft , not suitable for the real need.

* Am i wrong ?
* How does it works in the real world ?
* How does the Scorpion perform with the bags ?

Thank's in advance

ummmm wrong. The bags volume it holds doesn't change. when deflated the ride will be low and stiff (no spring at all cuz no air to cushion it) when it s fully inflated it'll be stiff its only soft in the middle. Airzuk has an airbag setup his works good check em out at ottindustries.com its in the section about their rig. I think bc4x4.com has a story on it to in there feature vechiles section.

I've thought about doing something like this, although I am no where near actually doing it. IIRC, the Scorpion uses air bags AND 1/4 elliptic springs. The air bags are between the springs and the chassis. Seems like you could make a bump stop to keep from over collapsing the airbags. Then, when you let the air out, it would sit on the stops and be like any other 1/4 elliptic suspension but with the lowest possible stance based on chassis/tire config. Set the rate however you like it. Then, when you need clearance and/or flex, air em up. The springs still work and you get the added flex of the bags.

Baddog thats good way to go. best of all worlds and if the bags spring a leak you still got springs.

Originally posted by BadDog
IIRC, the Scorpion uses air bags AND 1/4 elliptic springs. The air bags are between the springs and the chassis.


try again the scorpion uses airbags only. but your theory would work.

There's no way to make an "adjustable spring rate" air bag.

Nor is there a way to do it with metal springs. The only way to change spring rate is to alter the design/size of the spring/bag itself.

Even with a limiter on the bag (such as a strap or a negative spring), you're still not changing the spring rate, you're just changing the preload.

You're best bet with an air bag suspension would probably be to run adjustable shocks, a la' Rancho 9k's. Set them soft off road and firm on road.

Or, you could just engineer a multi-stage pneumatic cylinder with multi pistons of varying diameter. SMC has something similar to that, but nothing on the scale that would support a vehicle. Call up Bimba, maybe they'll do a special for ya' ... BWAHAHAHA.

cm "the gears, they are a turnin' " k

Originally posted by cmk
There's no way to make an "adjustable spring rate" air bag.

How about get rid of the Bag, and use a air piston with a metal case. Then have the piston volume divided into to seperate chambers with a "floating piston" in between. The bottom would be filled with air, and the top with hydraulic fluid. Add more hydraulic fluid to the top, and you would have less air space, and therefore a higher spring rate. Take out hydraulic fluid, and increase the air, for a flexier soft spring rate.

Another thought I have had would be to use standard air bags with a large air chamber (say about the same volume as the bag)mounted to the frame (or anywhere) connected with a hose and seperated with a valve. Close the valve, and the air bag is seperated from the other chamber, and has a higher spring rate. Open the valve, and the air bag has more volume, and therefore a lower spring rate.

Please note I have no experience with air bag suspension, these are just ideas I've kicked around in my head while building my dream rig, and I'm sure they have many flaws that will be pointed out soon :)

chad

Originally posted by chadl

Please note I have no experience with air bag suspension, these are just ideas I've kicked around in my head while building my dream rig, and I'm sure they have many flaws that will be pointed out soon :)


Here we go ...


How about get rid of the Bag, and use a air piston with a metal case. Then have the piston volume divided into to seperate chambers with a "floating piston" in between. The bottom would be filled with air, and the top with hydraulic fluid. Add more hydraulic fluid to the top, and you would have less air space, and therefore a higher spring rate. Take out hydraulic fluid, and increase the air, for a flexier soft spring rate.


First off, how do you divide a "piston volume" ? I presume you are talking about the "cylinder volume." What you describe is a standard air/oil cylinder. This setup is commonly used to provide smooth, controllable motion to a pneumatic cylinder.

The proces you speak of does nothing for the spring rate. The only way to change the spring rate of a pneumatic cylinder, of any sort, is to change the cylinder's diameter. Changing the piston's position (volume) or pressure only changes the force output of the cylinder, not the rate at which it outputs force.


Another thought I have had would be to use standard air bags with a large air chamber (say about the same volume as the bag)mounted to the frame (or anywhere) connected with a hose and seperated with a valve. Close the valve, and the air bag is seperated from the other chamber, and has a higher spring rate. Open the valve, and the air bag has more volume, and therefore a lower spring rate.

chad

*shaking my head*

Once again, the volume of the cylinder/bag has no effect on the spring rate. You must change the cylinder's/bag's effective diameter to change the spring rate.

Due to the fact that air is a compressible fluid, adding a volume chamber will make the system more "spongy," but it still does nothing for the spring rate.

cm "there is a way to do it with standard bags ... but if I told ya', I'd have to kill ya' " k

air springs and bags.

www.firestoneindustrial.com


:usa:

Originally posted by BadDog
I've thought about doing something like this, although I am no where near actually doing it. IIRC, the Scorpion uses air bags AND 1/4 elliptic springs. The air bags are between the springs and the chassis. Seems like you could make a bump stop to keep from over collapsing the airbags. Then, when you let the air out, it would sit on the stops and be like any other 1/4 elliptic suspension but with the lowest possible stance based on chassis/tire config. Set the rate however you like it. Then, when you need clearance and/or flex, air em up. The springs still work and you get the added flex of the bags.

You have just discribed my suspension. It works great. The system gives 10" of ride height adjustment. Air down handles great on the road. Air up Handles great off-road.

Yes your right what I meant was the volume of air, or the volume the piston moves through. by dividing it I ment some type of floating piston that would seperate the air side from the hydraulic fluid side.

Okay, I'm sure there's holes in this, but I guess I don't see it yet.

Say I got a 4000 lb rig, I have perfect weight distrubution for 1000 lb per spring. I use a 4" cylinder with a piston area of 12 1/2 sq inchs. To balance the weight of the vehicle I would need 1000 lb divided by 12 1/2 sq in or 80 psi per clyinder. Now say my cylinder is 12" long, and assume the gas is ideal, and is sealed off from the air supply by a check vallve. So now I start with 150 in^3 (12 1/2 in sq X 12" long) of volume, full of air at 80 psi. Using the ideal gas equation, if I cut the volume in half, (to a 6" long) by compressing the spring, I will double the pressure too 160 psi assuming the temperature of the air changes little. That give me a spring rate of 1000 pounds per 6" or 166 lb/in Now if I fill half my cylinder with hydraulic fluid, or valve it off. then the pressure would increase to 2000 psi after only traveling 3" or 333 lb/in this seems to me to change the spring rate. So basically if you cut the volume in half, you double the spring rate.

Now lets say I got off my a$$ and built something like this, and I drive into an off camber situation, that puts nearly all the weight on two tires. In this situation I would have the springs set at "max air volume" and the spring would deflect half the volume 6" then I finish my trail ride, and get out on the highway, where I replace most of the air with hydraulic fluid leaving say 4" of air in the cylinder. Now when I dive into that tight turning, and put nearly all the weight on two wheels, the cylinder will deflect only 2" keeping the vehicle level. Regardless if this changes "spring rate" it does provide the type of suspension many would like, long travel for slow speed rock crawling, or relatively short travel for higher speed or on road applications.

The idea of a variable or changing piston diameter is very insteresting, but hard to picture right now, I need a chaulk board and a six pack to work on that one for a while.

Until then I'll stick to my guns that by changing volume does effectively change spring rate in air cylinders, and by all means let me know where I'm wrong... like I need to say that :)

chad

Originally posted by cmk
There's no way to make an "adjustable spring rate" air bag.

Nor is there a way to do it with metal springs. The only way to change spring rate is to alter the design/size of the spring/bag itself.

Even with a limiter on the bag (such as a strap or a negative spring), you're still not changing the spring rate, you're just changing the preload.




You best get on the phone to Firestone because you know way more than there engineers.:rolleyes:


Quote from Firestone Engineering & Design Guide. "Unlike most springs, the rate of an air spring is not constant. It is a function of the change in effective area, volume and PRESSURE."

better return my e-mail
laredo

the springrate can be adjustable. I just bought 2 Frieghtliner FL 50s and the ride was to stiff on large bumps. I took them back and they installed Ping tanks inbetween the bags and the valve. They ride much better because when the bags compress there is a larger volume of air so the pressure doesn't rise up as high. Thats what freightliner told me!

Check out this link too...

http://www.goodyearindustrialproducts.com/airsprings/index.html

As was mentioned earlier, air springs are one of the few springs that can offer variable rate. The rate is dictated by the contour of the piston...as the cross section goes up or down, F = P/A so you can change rate. This is mainly on rolling lobe springs. Bellows don't allow as much flexibility.

Also - if you do decide to go with them, get an internal bump stop type so you have some cushion in case you lose air and / or bottom out.