Quarter Elliptical Tech

I'm trying very hard to resist linking the rear of my junk, but since i have the front suspension torn out, and a rear crossmember already built, it's becoming har dot resist. I don't want CO's or air shocks, as my cargo area is currently being used. I'm interested in a quarter elliptical setup like Beez's old junk.

I'm thinking a setup that a hinged, bushed eye at the frame end, about 4-5 inches forward of the stock spring mount would work well. I would want to run either a jack plate and screw or a small air bag set-up so I could level the rig under heavy loads. That could be located right where the OEM spring bracket is. Of course, the QE setup would be outboard of the frame to keep it out of the rocks.

So, how do I figure spring rate for a QE setup? Obviously, everything behind the jack plate would be active spring, but I can't find a calculator that takes this into account, or even calculates spring rate for a eafs, period.

Here's one (gay): http://www.therangerstation.com/tech_library/leafspringrate.htm

Another here: http://www.thedirtforum.com/leafspringrate.htm

Some QE discussion: http://www.jeepaholics.com/tech/quarterellip/

Neither of those calculators seem accurate for my current National 10 leaf pack, but I may be giving the worng spring thickness number.

Anybody have any idea how to calculate the spring rate for a QE?

What you're describing is very close to what I have, except I run the quarter pack from aft of the axle and Beezil ran it fore.

As to spring rate??????
What I did was start with a total of 13 leaves and trial and error'd my way down to the 9 I currently run.
I also run a detatched quarter pack where the spring pack rests on a bronze roller on the axle. The spring rate varries greatly depending on where on the pack it is engaging the roller.

I also have the air bag over the pack like you described. The air bag brings a few advantages over jack screws. You can adjust it on the fly and get some forced articulation effect and it is also a suspension component where a jack screw is not.

9 leaves, stock XJ thickness? How much arch?

I wanted to run the bag closer to the pivot point, maybe 6 inches away. I wonder if a bag can be run at high enough pressures to even force articulation with such a short lever arm?

I'm thinking of running a captured shackle at the axle to help control droop a bit, but a single leaf probably won't do much anyway. An anti-sway bar is probably a must for roll-control.

C-ROK said:

What you're describing is very close to what I have, except I run the quarter pack from aft of the axle and Beezil ran it fore.

As to spring rate??????
What I did was start with a total of 13 leaves and trial and error'd my way down to the 9 I currently run.
I also run a detatched quarter pack where the spring pack rests on a bronze roller on the axle. The spring rate varries greatly depending on where on the pack it is engaging the roller.

I also have the air bag over the pack like you described. The air bag brings a few advantages over jack screws. You can adjust it on the fly and get some forced articulation effect and it is also a suspension component where a jack screw is not.

Click to expand...

My pack is a combination of XJ and YJ leaves (maybe some Cjs in there too - I don't recall). All 1/4" thickness with about 1" of difference in length as you ascend the pack.

I have the complete Firestone engineering design guide I can send you. It's got force curves (spring rates) for all the bags they manf. Most of the bags have burst pressures up near 200-250psi I think. The larger diameter the bag, the higher the forces (and travel range) you can get out of it. Getting a bag with high enough force curves to force articulation won't be a problem, fitting such a large (diameter) bag in place will be.

If you run the bag closer to the hinge point obviously the forces on it will be greater but the travel range will increase considerabley. Mine is just offset to the hinge side of center. I get about 6" of travel range out of it.

Capturing the end with a shackle will give you an additional benefit that you won't need the vertical member to locate the leave pack/arm like I do.
I also had a lot of complications with the leave getting behind the roller. The shackle will prevent that too.
Trying to get a bunch of travel range out of the air bag will get complicated with the shackle though. The arc travel of the leaf pack will change the Y axis engagement point of the leaves on the axle so much, the shackle may not be able to accomodate it. Even with mine 'nearly' centered over the axle my spring-axle engagement point varries over about 8"-10".

I run an anti-sway and it definitely was neccesary. Depending on how high you choose to make your roll axis though, you may not get much body roll. That's how Beezil handled it. He just got his roll axis up near the CG centerline. Good for anti-sway, not neccesarily good for other handling characterisitics.

I'm worried about fatiguing the spring pack with a captured shackle/spring at the axle due to the extreme twisting of the leaves under articulation. I would run a double triangulated link setup, so at least I won't have ot worry as much about shortening the axle to spring mount dimension. Arms look like they'll be about 39 inches, and I'd try to get roll center up towards CG, though likely not as high as the ellipsoid-mobile.

I hate not being able to calculate the spring rate. I know what I like, and what feels good, and it drives me nuts to guess at it. Throw in the added variable of the air bag, and I'm betting the calculation is a nightmare, though. Maybe it's analogous to a dual-rate coil spring set-up....have to think about it more.

CRASH said:

I'm worried about fatiguing the spring pack with a captured shackle/spring at the axle due to the extreme twisting of the leaves under articulation. I would run a double triangulated link setup, so at least I won't have ot worry as much about shortening the axle to spring mount dimension. Arms look like they'll be about 39 inches, and I'd try to get roll center up towards CG, though likely not as high as the ellipsoid-mobile.

I hate not being able to calculate the spring rate. I know what I like, and what feels good, and it drives me nuts to guess at it. Throw in the added variable of the air bag, and I'm betting the calculation is a nightmare, though. Maybe it's analogous to a dual-rate coil spring set-up....have to think about it more.

Click to expand...

Have the shackle connect to the axle with a pivot point. That's real common on quarter elip designs. The shackle accomodates the fore-aft movement and the pivot takes care of the changing engagement angle during articulation.

What I think you'll find once you get an airbag in there is that it will become the main suspension compont in compression. I ride so high up on my leaf pack with the bag even partially inflated that I have hardly any travel range on the quarter pack. Getting the spring rate for the bag will be easy and at least that will take of the compression side of the equation. Of course it will get a little more complicated if you run it off center, but it is just a linear math lever calc.

e-mail me at [email protected] and I'll dig up the Firestone design guide for you to start playing with.
Lots of other info in there too about the bag design parameters; misalignment limits, etc.

This begs the question, why have QE's at all if the bags are doing most of the work?

C-ROK said:

Have the shackle connect to the axle with a pivot point. That's real common on quarter elip designs. The shackle accomodates the fore-aft movement and the pivot takes care of the changing engagement angle during articulation.

What I think you'll find once you get an airbag in there is that it will become the main suspension compont in compression. I ride so high up on my leaf pack with the bag even partially inflated that I have hardly any travel range on the quarter pack. Getting the spring rate for the bag will be easy and at least that will take of the compression side of the equation. Of course it will get a little more complicated if you run it off center, but it is just a linear math lever calc.

e-mail me at [email protected] and I'll dig up the Firestone design guide for you to start playing with.
Lots of other info in there too about the bag design parameters; misalignment limits, etc.

Click to expand...

CRASH said:

This begs the question, why have QE's at all if the bags are doing most of the work?

Click to expand...

Ahhhh. There are some brain cells up there....

I would go with a solid pivot arm supported by an air bag. I don't see a reason to have 2 springs per side. The only downfall would be the travel offered by the airbag, but if you run it on a roller like C-Rok than droop is a mute point.

CRASH said:

This begs the question, why have QE's at all if the bags are doing most of the work?

Click to expand...

From static to full compression yes, but not through the entire travel range. On droop, I have still spring contact (and force) on the roller for about 12" or more below static.
Your air bag travel ranges are very limited. My front bags have a total of about 13" of travel but they're quite large.

For low speed crawling, I could see you getting away with a dettached arm and air bag only, but during high speed suspension travel when the arm separated from the axle, you would have zero suspension until the point it re..... collided with the bag/arm on the way up.
With my quarter pack and bag, I maintain suspension contact for almost all of my travel range.
As the suspension droops, the quarter pack relaxes to maintain contact.
While the spring may be very light at the extreme end of it, it does compound as it compresses.

Rather than go with any kind of a dettached arm and air bag, you'd be better off going with a design that locates the bag way up on the lower link so you get a 3:1 or so range mutliplier for bag travel to axle travel.
People have done that with some success. Your lower links obviously need to be extremely strong (and thus heavy) and the bag is much more exposed to trail damage too.
I toyed with idea but ultimately decided against it.

no coilovers because of cargo room? common, i'm sure you could come up with a cantilever setup to lay them flat

what's wrong with regular coils?

BrettM said:

no coilovers because of cargo room? common, i'm sure you could come up with a cantilever setup to lay them flat

what's wrong with regular coils?

Click to expand...

That would be way cool. Go with a 2:1 bell crank. You can get away with running some 8"-10" coil overs (way cheaper!!!). You'll get 16"-20" of wheel travel. I see a potential URF bolt on kit in the future...

BrettM said:

no coilovers because of cargo room? common, i'm sure you could come up with a cantilever setup to lay them flat

what's wrong with regular coils?

Click to expand...

I would guess no coils because of the single rate. With the varying degree of wieght. Also its effective range of travel is much shorter than most leafs. To get the effective travel out of a coil, it would have to be long with a low spring rate if i remember correctly.

Coilovers are a PIA. and they still don't have the effectiveness that leafs have with weight differences. A QE with a helper bag would be the way to go... if you can design it to handle the high speed and crawling.

I kinda recall that for the longest time, desert runners were using QE before coilovers. Long travel and essentially adjustable spring rate.

Andy, I may be blowing smoke... but I think you could do something similar to Greg's with a few twists. I would think rather than a roller, a teflon disc could be used. It may cut down on suspension noise and prevent the springs going under the roller. Also the detached spring would be ideal, but with very tuned limit straps.

Greg, i remember we discussed the pro/con of the pad versus the roller. Maybe you can reiterate that to me(us).

Matt

FarmerMatt said:

That would be way cool. Go with a 2:1 bell crank. You can get away with running some 8"-10" coil overs (way cheaper!!!). You'll get 16"-20" of wheel travel. I see a potential URF bolt on kit in the future...

Click to expand...

could you imagine maintaining that though matt? i know i sure as hell wouldnt want to help design that! :shocked:

Scrappy said:

could you imagine maintaining that though matt? i know i sure as hell wouldnt want to help design that! :shocked:

Click to expand...

the work is already done - Andy himself showed us the thread -
http://www.naxja.org/forum/showthread.php?t=70338



.... :stir: :stir:

Scrappy said:

Andy, I may be blowing smoke... but I think you could do something similar to Greg's with a few twists. I would think rather than a roller, a teflon disc could be used. It may cut down on suspension noise and prevent the springs going under the roller. Also the detached spring would be ideal, but with very tuned limit straps.

Greg, i remember we discussed the pro/con of the pad versus the roller. Maybe you can reiterate that to me(us).

Matt

Click to expand...

None of my noise comes (or came to speak of a "past" problem) from the roller to spring contact, or the roller motion itself. The roller is a sintered alumi-bronze alloy and the bolt is a greasable 5/8" Gr 8. The roller moves quite freely and quietly.
All my noise came from the metal to metal contact at the vertical spring arm retaining tube you can see in the picture.
That has since been sleeved with a piece of polypro pipe and it's nice and quiet now.

The Teflon pad idea was done by some guy in a Suzi a couple years back. It's just another idea of the same thing. My dislikes of the pad idea is that you are quite limited to the range of spring to axle engagment since the pad can only be so big. The roller or shackle allows for a lot more total travel.

I'm being ultra lazy tonight. If it's been covered I don't care.

OneTon made a bracket to capture the ends of the springs and I believe a heim on the axle end so the springs didn't get hit with as much twisting force.

Can barely see them in this pic.


If you went the coil route you could always use my setup and stuff some of those cheap bags on the inside. Mine are rated to 500 lbs each at 30 psi with 5 lb minimum. It does provide somewhat of a progressive rate though.

The problem I was having was finding room for everthing once the links were in. I've been looking at it again and thinking about 1/4's or even keeping my coils and making those work. Exhaust is going to be a bit** no matter what.

Lincoln said:

Exhaust is going to be a bit** no matter what.

Click to expand...

stacks out the hood

BrettM said:

stacks out the hood

Click to expand...

I still like my idea of just plumbing them into the cab and putting an RV vent for a sun roof. They call it an exhaust vent.

I was thinking about doing this a while back....a few years ago. Mounting the spring pack wouldn't be hard, and the links have the same challenge rehardless of the choice of springs. I wonder how you'll find the room for an airbag with the springs mounted outboard of the frame, seems it would be pretty tight. One thing is that the travel or capacity of the bag wouldn't need to be a lot since the spring would be carrying most of the weight.......the bag would simply be for excess load to maintain ride height. One of the smallest bellows type bags should do the job, more capacity and enough travel, if you could make it fit.

I assume you're not going to cut up your nice National pack. It shouldn't be that hard to get the springs right with some trial and error, even though I know that the URF style is to have everything calculated precisely before the fabbing begins. You'll just have to abandon the infamous URF quasi-CAD-calculator for this one.

XJ_ranger said:

the work is already done - Andy himself showed us the thread -
http://www.naxja.org/forum/showthread.php?t=70338

.... :stir: :stir:

Click to expand...

those are all for dampning, the spring rate comes from a torsion bar.

how bout that Andy? I haven't seen that in a rock-crawler... seems like the packaging would be really easy...