Front suspension geometry...lets get in depth...

[Beezil]

The steeper the angle of the lower arm, the more axle steer

You may one day, experience driving your rig home, with ONE rear axleshaft operating......

I can guarantee you won't worry about the effects of a little "axle steer" in a maladjusted 4-link after that!

 

[XJJPR]

Gee, I recognize that jeep, I knew he plowed fields but ROCKS?

hinkley

 

[Beezil]

Oh, I get it now...

no wonder he painted his rig "john deere green".....

 

[Willis]

You are gonna HANG like a horse theif with a 3" rock snagger on 35's....

Ya, that's why I plan on playing with it, to see if I can make it better. You are right, it makes my numbers look good, and will probably give me good road characteristics, but at the cost of offroad-ability. Guess the compromising begins.

 

[Beezil]

Guess the compromising begins.

isn't it a bitch???

have fun!

remember, its supposed to be fun!

best of luck.

don't forget to keep watering this thread.

 

[FarmerMatt]

One day goat herder... you will pay for that pic. I'll have you all know the mounts sit up flush with the cross member now. I haven't been hung on the cross member since raising the mounts. On road handleing was better with the mounts lower, but raising the mounts so as not to have anymore pics like this one is worth the compramise.

"remember, its supposed to be fun!"

I think you should have remembered this in the begining of this thread beaver butt.

Matt

 

[Goatman]

Ya, that's why I plan on playing with it, to see if I can make it better. You are right, it makes my numbers look good, and will probably give me good road characteristics, but at the cost of offroad-ability. Guess the compromising begins.

That's why you need good design priorities, at least to me it means that. What you are willing to compromise and what you aren't willing to compromise, and how much. Priorities.........

I do think you can make an XJ suspension do everything well, but it won't be the absolute best at anything, and you can always keep fine tuning it. I really do drive mine from CA to Moab and CO and wheel it hard, and it handles and rides reasonably well. Plus, it can be loaded up with people and camping gear. Many of us have rigs that work well in most situations, something that is really nice about a well built XJ.

 

[Goatman]

One day goat herder... you will pay for that pic. I'll have you all know the mounts sit up flush with the cross member now. I haven't been hung on the cross member since raising the mounts. On road handleing was better with the mounts lower, but raising the mounts so as not to have anymore pics like this one is worth the compramise.

Matt

Hey Matt, just think about that pic as a contribution to the education process. You have enlightened many people.

 

[Bob Sheaves]

For your viewing pleasure (along the discussion here).....an extreme design that could be used in certain conditions:

I go away for a day and the thread explodes!!! OK, hope I get everyone that asked in here...

Ed- I did not have to reverse engineer the XJ system- I had all that info, plus the testing, analysis, and issue reports available to work from. That makes the job a LOT easier.

As a sidebar, you must remember Walter Voss then from that time period-I was wroking for him at the time. I did all the simulation and dynamics approvals and rework when necessary. I also did "field support"...

Goatman- Thanks for the support! I agree that IFS (as well as IRS) can get the shakes as bad as a 4link overconstrained system.

Beezil- Nice work so far on your sketches. Please accept my apologies for my comments earlier.

Willis- I know there is a lot of info to be understood about these overconstrained systems, but hang in there-it just takes time (and a really BIG bottle of asprin).

XJguy-I am not familiar with the design you mentioned (it's heck being the newbie at times) so I cannot comment. I'd need to see it and get a few measurements to form an opinion. Sorry.

Grant- I could not agree more. When I got out of the military, I started as a liasiaon engineer for IH on the Scout Group (that ought to tell you how crotchity I can be...LOL). My supervisor was an old fart that made me spend the first 6 months of my work there working in the plant, learning how to build the vehicles, and their problems, from the bare frame, to body assembly, paint, building seats and engines, wiring (I STILL have nightmares about chasing down shorts)..etc. I do not understand how the "engineering schools" can turn out a "qualidied engineer" that doesn't know which end of a screwdriver to use....

Best regards to all,

Bob

 

[Beezil]

Bob, I can appreciate your education, your experience, and your presence on the board, but seriously, what *is* your purpose on this thread, except for maybe impressing some of us?

I'll admit, I'm impressed, but so far, you haven't really done anything except, list some credentials, post some cool looking CAD, and take part in some engineer-SPEAK.

If you could have done any of those things WHILE MAKING AN ATTEMPT to help willis design a suspension system that incorporates 35" tires with 7" of lift on a JEEP CHEROKEE, you would have impressed me even more.

 

[FarmerMatt]

Ok... Explain what we're looking at here. It seems like we're looking at a swing arm assembly with a built in IRS system suspended by a cross mounted leaf spring, driven by hyd. or electric motors on gear reduction boxes? Although the last pic seems to show a drive shaft. You can't drop a bomb like this & not splain what's going on to us common folk.

Matt

 

[Bob Sheaves]

Ok... Explain what we're looking at here. It seems like we're looking at a swing arm assembly with a built in IRS system suspended by a cross mounted leaf spring, driven by hyd. or electric motors on gear reduction boxes? Although the last pic seems to show a drive shaft. You can't drop a bomb like this & not splain what's going on to us common folk.

Matt

Hi Matt,

My intention was not to drop a bomb, but rather show by design how some of the problems in wheel travel and the control arm length can be corrected. I prefer to allow people to ask questions, as some of the ideas presented in this design are rather unorthodox and esoteric.

If you follow the pix url back to race-dezert.com, you will see that this design was in response to a question on how to design a high travel suspension for the desert, without going to a fully independent desigh, as is currently common in the truggys and trophy trucks. This thread is 10 pages long, but contains a LOT more detail on the hows and whys....

In the application of Willis', meaning the +7" height and 35" tall tires, the common approach in these trucks (which DO require a great deal of articulation, as well as vehicle speed) is the "Jeepspeed approach" (for the time being-I will assume you understand this approach). One of the changes made between this design and the OE suspension on the XJ is a lack of a track bar. The shown pix demonstrate how to delete this item and still maintain control over the motion of the axle. (BTW- do NOT be impressed-this is just the application of basic "book larnin' ".)

The overall design is an application of a DeDion type suspension. If you have never seen one-look under the rear of a Chrysler AWD minivan. The primary benifit of the DeDion is a lower unsprung weight of an independent syspension (good for high speed and reducing the "death wobble" mentioned earlier), with the grund contact patch control of a hotchkiss ( a leaf sprung live axle). Follow the explaination so far?

Best as always,

Bob

 

[Bob Sheaves]

I will continue....

The DeDion tube is supported by 2 inverted struts, rigidly mounted to the engine cage structure in the chassis (not shown for clarity). In a common XJ-these struts would be supported by bracketry on either wheelhouse on the Z axis and tied together across the top of the engine, and then tied back from each strut to the dash panel (common term is the firewall) and under dash cross car beam that should be installed in the front cage section.

The DeDion tube itself is no different in concept than the dead axle on the front of a 2WD XJ. This tube supports the knuckle yokes, Steering knuckles, brakes (altho this design uses, as you surmised, hydrostatic drive and braking), wheels, tire, beadlocks, and CTIS. At the outer ends of the tube, facing rear, are a pair of brackets not unlike the existing lower control arm brackets, that pick up the tringular, tubular construction, lower control arm and voided bushings. The reason for voided bushings is to control the deflection of the control arm arc by utilizing the elastomer in the bushing to allow deflection on one plane but not either of the 2 other pivot planes. In one of the pictures, you can see that the "top and bottom" of the bushing has no elastomer, but the fore and aft positions do have the rubber. This is what allows the pivot location to vary (increasing and decreasing the active length (as opposed to static length) of the lower control arms as the axle moves from full rebound (commonly called "droop") through design (static load height-where the truck sits at rest), up to the full jounce (commonly called "bump") position.

More in a bit....

Best as always,

Bob

 

[Willis]

The overall design is an application of a DeDion type suspension. If you have never seen one-look under the rear of a Chrysler AWD minivan. The primary benifit of the DeDion is a lower unsprung weight of an independent syspension (good for high speed and reducing the "death wobble" mentioned earlier), with the grund contact patch control of a hotchkiss ( a leaf sprung live axle). Follow the explaination so far?

I know the DeDion very well actually. The rear axle in my Alfa Romeo Milano is of the DeDion design with an IRS transaxle. It handles great! On my list is to change out the rubber bushing at the front mount to a factory race spherical bearing for additional axle control. Down side is it transfers more road noise and vibration to the chassis.


Damnit! I'm contributing to the hi-jacking of my own thread.
*edit* Not complete hi-jacking, but I don't see how a DeDion can be used in the front or rear of an XJ. If you know otherwise, please elaborate *edit*

 

[Bob Sheaves]

I know the DeDion very well actually. The rear axle in my Alfa Romeo Milano is of the DeDion design with an IRS transaxle. It handles great! On my list is to change out the rubber bushing at the front mount to a factory race spherical bearing for additional axle control. Down side is it transfers more road noise and vibration to the chassis.


Damnit! I'm contributing to the hi-jacking of my own thread.

Willis, if you bear with me for a bit-you will see how that applies (especially the comment you made about the axle). Actually, I do not think this constitutes hijacking, does it? It has direct applicability to your original application question.

Best as always,

Bob

 

[Beezil]

do any specs exist on this type of set-up in terms of articulation or suspension travel?

 

[Bob Sheaves]

do any specs exist on this type of set-up in terms of articulation or suspension travel?

Yes, and I will get to them shortly. If you are in a hurry-go tothe original thread on race-dezert.com.

Bob

 

[Willis]

Actually, I do not think this constitutes hijacking, does it? It has direct applicability to your original application question.

Hehe, you were posting while I was editing. No not really hi-jacking, I just don't quite understand how this all relates to the XJ, or how to make it relate. It may help us understand the geometry, but I don't know about the direct application of the design. I personally don't think the DeDion flexes well (articulation), and if it were usable, it would have to be mounted very high on the axle, or have a pretty extreme angle to work well. In that case, it would have similar characteristics to radius arms, where they have very high anti-dive percentages. Correct me if I am wrong.

 

[Bob Sheaves]

Hehe, you were posting while I was editing. No not really hi-jacking, I just don't quite understand how this all relates to the XJ, or how to make it relate. It may help us understand the geometry, but I don't know about the direct application of the design. I personally don't think the DeDion flexes well (articulation), and if it were usable, it would have to be mounted very high on the axle, or have a pretty extreme angle to work well. In that case, it would have similar characteristics to radius arms, where they have very high anti-dive percentages. Correct me if I am wrong.

This design has controls there in the form of motion design that compensates. I will get in more depth shortly. If you guys do not mind-it's 1:15am here and I have to be in the office at 6:30 for a 7am review meeting. I'd like to continue this tomorrow afternoon when I get home. OK????

Best as always,

Bob

PS: One final research "assignment" look up the Morgan "sliding pillar" front suspension design and compare it to the "struts" shown....

ADDENDUM: think what the primary purpose of a suspension and drive axle is-forget the "type" of suspension used for the time being...just concentrate on what it is you are trying to accomplish (NOT in terms of components, but in performance).

 

[Beezil]

willis, screw the 4-link.

just build one of these instead: