"Link-X" suspension
"Link-X" suspension
(OP)
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&a...
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&a...





RE: "Link-X" suspension
He thinks he has solved the obvious problem with camber control, I don't know how and he wouldn't say.
Cheers
Greg Locock
RE: "Link-X" suspension
I'll post back, if I learn anything from him regarding it.
-Dave
http://www.moslerauto.com
RE: "Link-X" suspension
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
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: "Link-X" suspension
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.
RE: "Link-X" suspension
RE: "Link-X" suspension
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
RE: "Link-X" suspension
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
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: "Link-X" suspension
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=US2003067...
He has also gotten a WIPO patent.
RE: "Link-X" suspension
Regards
pat
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: "Link-X" suspension
RE: "Link-X" suspension
RE: "Link-X" suspension
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
RE: "Link-X" suspension
RE: "Link-X" suspension
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
RE: "Link-X" suspension
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
RE: "Link-X" suspension
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.
RE: "Link-X" suspension
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
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: "Link-X" suspension
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
RE: "Link-X" suspension
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
www.whitelightdesign.com
Pro/E FAQ www.whitelightdesign.com/servicestips.htm
RE: "Link-X" suspension
About a year ago we looked at Graviman's idea of a floating subframe to give us more rebound travel. It seemed too complicated and the need for further droop wasn't compelling enough for us to try it.
We're working with the Military on the next-gen Hummer type machine (all indep susp). The Hummer rolls over a lot more than people know. Also, the 50mm machine gun is hard to control because of body roll...even when the vehicle is sitting still! Our moment-inversion principle can keep the platform stable.
The ADAMS model predicts a higher rollover threshold as well because of lower cg displacement & lower rolling momentum (less stored energy because the sway bars are gone).
RE: "Link-X" suspension
good luck,
ProEpro
www.whitelightdesign.com
Pro/E FAQ www.whitelightdesign.com/servicestips.htm
RE: "Link-X" suspension
Presumably this is what you mean by a load based toe changes? The system ends up looking like McPhearson strut, with an axle between, using the axle rotational inertia to control the wheel toe angle. The struts take the vehicle weight. Not sure how the steering input goes in yet, but I'll get there! Packaging wise this looks good too, since the wheel tops stay about the same position (in plane of mass center).
How big can these axles be made? I take it 20 tonne axle weight is out of the question!
Mart
RE: "Link-X" suspension
2004-01-1545 Link-X Suspension for Roll and Pitch Elimination
2003-32-0071 Link-X Stability System
Best regards,
Matthew Ian Loew
"Luck is the residue of design."
Branch Rickey
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: "Link-X" suspension
After further thought I am having doubts as to how well such a system might respond to the step input of say a curb strike. Steering would not allow the wheels to move sideways quickly enough. OK this is fairly extreme, but I know that active suspension and ground height roll centre will cope with this, and still eliminate roll. We are talkng about an off-road suspension system...
BTW is there any merit in designing a conventional beam axle to have bump steer? I'm thinking steering towards bump, to reduce centre of mass lateral movement. The trucks I'm involved with have very high cabs that would benefit greatly from reduced lateral movement (Articulated 6x6 tractor trailor combination), not to mention higher ground speed from reduced mass center disturbance.
Mart
RE: "Link-X" suspension
The lateral motion that you're talking about is not near as large as you're envisioning because the instant center of rotation moves up with the tire. Load-based toe change in the case of my suspension means that upon an impact on the front of the tire, the bushings are designed to generate a tiny bit of toe-out so the tire steers its way over the face of the bump. It works beautifully!
I would think that a lot of the lateral movement you're getting in the tall cab is from the roll of the vehicle coupled with the large distance between the roll axis and the position of the driver.
Link-X will reduce that distance and generate less overall roll, so lateral movement of the driver himself should be lower...I think.
RE: "Link-X" suspension
But roll centre is still above ground height!?!
I certainly agree with the idea of load based toe change. I'm trying something similar (albeit less sophisticated) with the truck system. This helps the truck to rotate about it's mass centre, rather than roll centre.
Trouble with bump steer avoidance is that it really needs to be linked to rate of change of wheel height. Load based toe change would approximate this due to the damper load, and I can certainly see how this would work with smaller bumps. When the bump contacts nearer tyre front, I can't see how steering would help. An example of this is curb strike - steering just ain't gonna help reduce the contact patch scrub.
"I would think that a lot of the lateral movement ... large distance between the roll axis and the position of the driver."
Yup!
"Link-X will reduce that distance and generate less overall roll, so lateral movement of the driver himself should be lower...I think."
Well, yes and no. Truck will need lower roll stiffness, true. Unless bump steer works perfectly, large lateral movement with high roll centre will cause high lateral accelerations. I can see how this sytem would cope very well with less rough ground, but in the extremes that out trucks have to deal with...
The final concern is cost. Don't forget the hidden costs of reliability, something I have to think about every day. There are hydraulic systems for active spring adjustment, which become more practical every day. I have read the paper sent to me, but it dealt more with the theory than application. Engineers love pictures of oily bits...
Mart
RE: "Link-X" suspension
I can understand the need to keep the driveline length constant, but having tyre roll centre outboard of centreline is asking for trouble. As a fan of the "handbrake technique", I would be worried about sudden and unforeseen roll above a certain cornering g. This is why I prefer, at least, the idea of a floating subframe (keeps contact patch distances across car the same).
It's good to think outside the box, as long as you see the big picture! Believe me I'm the first to get overenthusiastic.
Mart
RE: "Link-X" suspension
I think the Chevy you mean is the Corvair.
You forgot early Porsche and some old Mercedes Benz and Auto Union
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: "Link-X" suspension
We have less camber gain, ability to build-in a
The most important difference is that the Link-X roll center doesn't migrate. A swing arm's roll center moves up as the wheels droop - that is unstable.
RE: "Link-X" suspension
1. Ride comfort (lateral acceleration) in extreme off-road conditions - bearing in mind my point about bumps contacting near tyre front.
2. Structural stability. The need to have overlapping links reduces the ability to reinforce against lateral loads - bearing in mind we see at least 20 tonnes per axle.
This usually ends up requiring, at least, expensive (in small volume) ADI castings.
Don't get me wrong, I really like your concept. I just remain to be convinced that it can handle extreme loads and terrain without becoming prohibitively expensive. Admitedly the size of the tyres we use will help to keep contact patch at centre. We have, at this stage, even had to reject hydraulic suspension on cost grounds - although the view is still that this offers the best dynamics...
Mart
RE: "Link-X" suspension
I'm curious on locating the rollcenter of the Link-X setup. In a standard SLA setup the instant center is on the opposite side of the car centerline, so the 'instant center' to 'tire contact patch center' line crosses the car centerline. Thus diagraming the instant rollcenter is easy.
http://www.miracerros.com/mustang/t_roll_center.jpg
On the Link-X, the instant center looks to be between the wheel and the frame, where the link bars cross. Putting it on the same side of the car centerline as the wheel, thus the 'instant center' to 'tire contact patch center' line never crosses the car centerline...so how is the rollcenter height determined?
-Dave
http://www.moslerauto.com
"Everything should be designed as simple as possible, but not simplier"
RE: "Link-X" suspension
The geometric roll center determined by the intersection of lines through the each suspension's contact patch center and IC. This suspension, just as a swing arm suspension, indeed has the IC on the same side of the centerline as the CP as you noted, but this does not change the method to determine the roll center. Lines are infinite, line segments have a finite length.
Best regards,
Matthew Ian Loew
"Luck is the residue of design."
Branch Rickey
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: "Link-X" suspension
Thanks!
-Dave
http://www.moslerauto.com
"Everything should be designed as simple as possible, but not simplier"
RE: "Link-X" suspension
We use arms that are similar in length to a traditional SLA, but still exist on the same planes as would be the case with a 'long arm' Link-X setup. The IC is still in between the wheel and vehicle centerline so the rollcenter is still very high. The knuckles are very short, so unsprung weight is reduced.
The roll center can be designed to be absolutely motionless and as an auxilliary benefit total camber gain is reduced and droop camber gain is considerably less. High-droop, off-road setups are more reasonable in this configuration.
We have found that you still get about 85% of the roll reduction just from the high roll center without extending the arms all the way to get 'moment inversion' benefits. Crossing the arms is still better, but considering the cost/weight/footprint savings...
This is the setup we have on the supercar, and it works spectacularly well. The turn-in is almost magical.
t
RE: "Link-X" suspension
RE: "Link-X" suspension
RE: "Link-X" suspension
A high front RC will typically make the car feel like it's rolling onto it's rear. We've compensated for that and achieve slight forward pitch with roll. This has been proven to inspire the most confidence in drivers.
RE: "Link-X" suspension
As one wheel travels in more than the other, the wheelload is compensated by the anti swaybar.
I can imagine the x-link setup has no compensation for wheelloads when cornering.
Offcourse the vehicle stays horizontal with the x-link layout, but what happens to the wheelloads?
Don't you need a swaybar for this?