"Link-X" suspension 1

[Dave K]

I just heard about, and started looking into the "Link-X" suspension system. The concept is interesting, but I haven't had a chance to lay one out in the comptuter yet, to see how things work.

The setup requires crossing the A-arms, ie attaching the "upper" A-arm's inboard pickup points below the inboard pickup points of the "lower" A-arm. The concept is to work the cars natural roll against itself, to resist the roll, eliminating the need for an anti-roll bar.

I'm curious if anyone has looked into this type of setup, and any pro's, con's, or thoughts regarding it.

Some links:

The Link-X inventors webpage:

http://www.wageng.com/

Articles on it:

http://www.autofieldguide.com/articles/040203.html

http://www.autofieldguide.com/driven/0602dri05.html

http://www.caranddriver.com/article.asp?section_id=29&article_id=4816

-Dave

http://www.moslerauto.com

 

[GregLocock]

We did discuss this a while back but the thread has vanished. That's a shame since the inventor himself did participate.

He thinks he has solved the obvious problem with camber control, I don't know how and he wouldn't say.

Cheers

Greg Locock

 

[Dave K]

I had heard it was discussed, via a google search, but searching here didn't turn up the old thread, so I figured I'd ask again. I should be meeting the inventor tomorrow, so I've been trying to find out all I can on it. Hopefully I can get a demo of it too, since I can't find any good pictures online.

I'll post back, if I learn anything from him regarding it.


-Dave

http://www.moslerauto.com

 

[patprimmer]

I would anticipate sever camber change problems.

The only method I can think of to reduce this would be to have the top arm very long (like past the centreline of the chassis) and the bottom arm quite short and inclined in the same direction as the top arm, but not so steeply.

Say the top arm is 800 mm long, at 10 deg to horizontal, and the bottom arm is 400mm long at 5 deg to horizontal for example. I have no idea as to how these numbers would work out, and what the horizontal distance between the ball joints has to be, and if the inboard top arm pivot would end up below the bottom one, but with the concept in mind, and a drawing board, or better still a CAD program, it could be pretty easily roughed out to see the camber changes.

It might be a bit more difficult to work out the roll resistance and the effect on ride and bump steer, but I won't stick my neck out any further as I am no where near being a suspension guy.

Regards
pat

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[HDS]

Sorry I was sloppy and replied to the wrong thread.

The inventor is quite paranoid. He pulled posts from his own forum that mentioned his patent number. I bet he asked to have the old thread removed. If someone can find the text in a google cache or somewhere else we should repost it.

The original thread was Thread108-21170. There is another thread with the patent number here: Thread800-54517

The idea of having the roll center near the C.G. to reduce roll is very old. I doubt that the patent would hold up in court. There are probably huge issues with jacking because the C.G. of an SUV is very high. His videos look like that is a problem.

I also would like to know what happens when truck is full and the C.G. moves below the roll center. This will create roll moments in different directions at each end of the vehicle.

 

[HDS]

http://patft.uspto.gov/netacgi/nph-...d=PALL&S1=6,550,797&OS=6,550,797&RS=6,550,797

 

[Dave K]

Anyone able to get the images to show up for the patent?

I haven't seen an actual "link-x" yet, but I have seen what he refers to as being 75% as effective...which basically looks like a traditional SLA suspension, with some radical anti-dive goemetry, and a vary high rollcenter (near the CG), and very soft springs.

The drivers impression wasn't very good, but it was just assembled, and had no time to tweak it yet, so I'm not making any judgement yet.

-Dave

http://www.moslerauto.com

 

[mloew]

Sorry for the off topic commentary, but the following information might be useful:

To view the tiff images on the USPTO website, it is recommended that you use the one of the viewers referenced on this page:

http://www.uspto.gov/patft/help/images.htm

I copy the individual images to a Word document and save the entire patent electronically.

Best regards,

Matthew Ian Loew
"Luck is the residue of design."
Branch Rickey

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[HDS]

Matt
I'd say this not very off topic. Here is the same patent in PDF form off of the European patent office webpage.

http://v3.espacenet.com/origdoc?DB=EPODOC&IDX=US2003067135&QPN=US2003067135

He has also gotten a WIPO patent.

 

[patprimmer]

I'm not a suspension man, but from my observation of the drawings, there are some extreme angles re anti dive, anti squat, scrub radius and camber change, The camber change must be horrific, and I imagine would lead to problems re bump steer.

Regards
pat

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[shanba]

I think the toe curve could be controlled by the longitudinal angle of the upper and lower control arms. The biggest problem I see is the short and severely angled instantaneous center causing severe camber change and track width change through suspension travel. While the body roll is minimized by the high roll center, the wheels will camber out due to a larger roll moment on the unsprung mass and tire deflections. The large track width changes will wear tires out rapidly. For trucks without ride height control, the camber change with varying payload will wear tires out unevenly, similar to the twin i-beam suspension.

 

[RKPsyche]

The swing axle is simpler, probably safer and not under patent. Simply move the points of articulation outwards until the roll center is above the CG and you get the same effect. Porsche did the same thing when he stole Ledwinka ideas (Ledwinka’s designs placed the point of articulation at the center of the chassis), and produced the worst handling cars ever. There might be some geometric refinement to the Link-X that I am not taking into account, but it isn’t enough to make it viable.

 

[WagEng]

Hi All,

I'm the inventor of Link-X. I'm a mechanical engineer and have invented several manufacturing processes. When I invented this suspension for my solo car, I didn't know that much about suspensions in general. If I had, I probably wouldn't have pursued it!

You are right about the fact that known theory suggests that the camber change (there isn't any CL track change, but the camber change moves the contact patch) will make a vehicle with Link-X shift laterally over bumps and wear out the tires.

But...with some help from a generous venture capital firm (over 5 long years) we have solved all of the 'issues' via clever engineering and in some cases via other bad suspension characteristics that act in the opposite direction! For example, we use a lot of scrub radius to offset lateral disturbances. As a result, we have less steering wheel shake over bumps and driveway lips than most OEM vehicles.

We did a tire wear test with our '99 Expediton prototype (converted to all indep. suspension) against a '03 independent suspension Expedition. Over the 8500 mile test the Link-X machine got 16-31% LESS wear.

Camber gain is part of the solution, not the problem anymore. We have both tires leaning into the corner so we get optimal grip on both inner and outer tires. The tires wear more evenly as well.

The biggest remaining problem which someone pointed out is using Link-X on the rear of a truck. Load variations lead to high static camber. In moderation, this effect offsets load-induced transition to oversteer. SUVs seldom are loaded heavily, so the extra wear isn't that meaningful. Regardless, we are focusing on using Link-X only on the front.

We've found that this setup yields about 70% of the value of Link-X and has zero drawbacks.

Cheers!
Todd

 

[shanba]

Thanks Todd for your comments. If this system is used in a front suspension with a more conventional rear suspension, do you see adverse affects to having such a high front roll center with a lower rear roll center, opposite of conventional implementation. Does this create stability issues due to the phasing of the front and rear suspensions as lateral load is building? Usually the rear builds faster than the front for driver comfort/predictability. With your setup, the turn-in response must be much quicker, but wonder how the axle phasing is handled. With that much camber gain, is there straight ahead stability issues/wandering due to camber thrust? Or are toe curves used to compensate for this. Just curious, you've obviously been refining this.

 

[WagEng]

Good question. The only vehicle that we have applied Link-X to in this way was an ATV. It completely transformed it and actually made it easier to handle, you could just drive it like a car instead of leaning all over the place. It took most of the 'fear of death' factor out of riding an ATV.

We had Prodrive do an extensive (expensive) Adams analysis on a Link-X front and a stock live axle rear. It did show 31% faster yaw response - it got to the intended yaw 31% faster. This is good, but what is better is that there was negligible overshoot! The Prodrive guys rated the Link-X setup as 3 times more stable than the stock setup. Of course ours also had better ride quality and less roll.

A lot of people talked to us about camber thrust, but it doesn't really amount to much in the real world. In order to get a meaningful amount of camber you have to hit a 30mm or larger bump and the bump is only instantaneous...so it's 'easy' to use load-based toe changes to offset any camber thrust, tire-patch movement, etc.

I'm working on grip-phasing now with a vehicle, because the rear has significantly taller sidewalls than the front. We compensate for grip phasing on the Link-X setup by running a much lower-than-normal bump:rebound damping ratio. We don't have any 'jacking down' problems with it.

As I understand it, having a higher rear roll center improves driver comfort by pitching the car forward slightly in corners. We get this same effect by installing rebound springs in the front shocks that contact the shock piston immediately below ride height. We also have another method that is still trade secret.

People ask us about lift, but we actually have slight negative lift! Having this allows us to make both (inside and outside) tires camber into the corner, but with the outside cambering slightly more...no other suspension I've ever encountered can do that.

Todd

 

[GraviMan]

I must admit I am sceptical about the use of four bar mechanisms to push up the roll centre on off road vehicles from where a panhard rod would put it. The problem I usually face is that the majority of inputs are one wheeled. The lateral acceleration greatly reduces the driver comfort (I work with 60 tonne trucks).

I have looked at similar systems to lower roll centre to ground height, but decided in the end that independant is the way to go (ie vertical movement). Designing an active steering system into the axle does help, by allowing the wheels to move laterally without vehicle input, but it does begin to get complex (viscous couplings reacting against springs etc). In the end the thing always ends up active, so you may as well fit active roll control - an electric motor is so much cheaper! Seems to have helped Land Rover...

Mart

 

[WagEng]

The Prodrive guys are actually working with a firm that builds Dakar rally-type vehicles. The fact that Link-X makes sway bars obsolete is very appealing for the very reason you mention...most inputs are single-wheel.

If I remember correctly, they said the 'cross axis' stiffness is very low with Link-X. Thus it is perfect for off-road vehicles. One problem is that our suspension gets too much camber at extreme amounts of droop. I like to limit droop to about 3".

Bump doesn't seem to pose a problem. Our ATV prototype actually has more overall wheel travel than it's stock counterpart.

 

[patprimmer]

My experience with off road racing is that things like camber change and track change really don't matter so much, as the surface is loose and uneven, and traction low.

Maximum travel and rebound control are paramount.

I can see a great advantage with completely independent action on each wheel, so long as there was another method to control roll.

Regards
pat

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[GraviMan]

Interesting. Must admit I'm a fan of the Lotus floating subframe technique. The subrame held independant suspension to the wheels, but was then attached to the vehicle by a four bar link. The original purpose was to put subframe roll centre below ground height, so that wheel camber was always optimised - particularly on corners.

Modern design techniques (ADAMS) have rendered the technique obsolete, but I have wondered about a variation on the idea. The subframe is allowed to slide sideways in the vehicle, but two angled links connect to the stub axles, with top ends constrained to the vehicle by a DeDeon arrangement. Like X-link, the roll centre goes up (so you still need roll rate controlled passive steering), but track remains constant. Roll centre could even be put above mass centre. Dynamically it would be excellent, package wise it could prove a nightmare.

All sounds very complicated, when hydraulics and an electric motor can force the vehicle to lean into the corner. I was a great fan of Lotus's work on active suspension. It was a very sad day for motor sport when Williams were banned from using the technique...

Mart

 

[ProEpro]

wageng
Have presented any SAE papers or similar technical presentations with the info from the ADAMS analsis?

Thanks for continueing the join the conversation. It's too bad the orginal thread on your design is gone.



ProEpro

http://www.whitelightdesign.com

Pro/E FAQ

http://www.whitelightdesign.com/servicestips.htm