The heart of the Link-X suspension, as applied to a Ford Expedition. The upper and lower arms cross to keep the tires upright and reduce body roll. No anti-roll bars are fitted, and the coil-over spring/shock unit is responsible for no more than 35% of the vehicle's roll resistance.
During testing, the Link-X Expedition exhibited much less body roll, higher speed through the lane change, and less overshoot than its standard counterpart. This was possible, claims inventor Todd Wagner, without hurting ride quality.
Todd Wagner, CEO of Wagner Engineering (Wallingford, CT), has a long road ahead of him. First, he has to convince automakers and Tier 1 suppliers alike that new ideas can come from outside the automotive fraternity, never an easy job. Second, Wagner must prove his unusual suspension design–upper and lower control arms that cross top-to-bottom–is viable, and does what he claims. Third, the young looking 31-year old has to convince his OEM and supplier peers–most of whom are older veterans of the political jungle–that he's not some kid, but someone they should take seriously–especially when he tells them his design eliminates $20, five to 10 lbs., and 40 parts per vehicle. Then, and only then, will Wagner be able to determine whether his idea for a new suspension design will succeed.
In the Beginning
"The first time I thought of this was 1997," says Wagner when asked about the origins of his Link-X Stability System. "My kinematics professor at Virginia Tech said one of the strongest tools in engineering is inversion–looking at things from the outside-in. You have to imagine that you are the object and see what is happening to you," he says innocently, unaware that he sounds like Chevy Chase's character in Caddyshack ["There's a force in the Universe that makes things happen. And all you have to do is get in touch with it, stop thinking, let things happen and be the ball."]. "It took me most of a year running simulations to convince myself this design didn't have some fatal flaw I wasn't seeing," he says. "I did model after model, and eventually got to the point where I said, ‘I guess it does work.'" His next move was to find some capital.
"Connecticut Innovations is the venture capital arm of the State of Connecticut," says Andrew Brandyberry, the department's executive vice president and COO. "We make seed and early stage investments in emerging technologies, take a significant equity position, sit on the board, and participate in developing a business plan." Yet, before that could happen, it was necessary to get a patent on the design in order to protect Wagner's intellectual property. It wasn't at all certain this would happen.
Off to the Patent Office
"There were a lot of questions from the patent office regarding the simplicity of the design, whether it could work, and if it had been done before," says Brandyberry. "They scoured their database looking for prior art of a similar design." None was ever found. Eventually, a senior examiner in the Patent Office was asked to investigate, and finally walked the design through the patent process, convinced the design was unique and functional. A patent was granted in January 2001–25 months after the initial application.
"With the funding we built a couple of prototypes," says Wagner. The first had 0°º body roll. "I'll never do that again," says Wagner. Though the SUV was exceptionally agile–"It just pivoted left or right," he says–it inspired too much confidence in the driver, thus defeating the Link-X Stability System's safety goal. Plus, the kinematics program showed it had one interesting tendency. "If you have zero body roll or even a slight lean into a corner," Wagner explains, "and hit a curb while sliding across the road surface, the body will twist back in the opposite direction and pop the vehicle into the air!"
In practice, a slight amount of body roll acts as a signal to the driver of increasing cornering load and speed. Plus, it allows Wagner to use rebound springs to tune the front-to-rear handling balance. "The rebound springs sit inside the shock absorbers, and are compressed when the wheels droop," says Wagner. "We use them to set the balance–in most cases to moderate understeer–without having to resort to anti-roll bars." Ah, anti-roll bars. This is where the weight, cost, and assembly complexity argument comes in.
"Our analysis shows Link-X will save about $20 and 5 to 10 lbs. per vehicle," says Wagner. "The 40 parts of a typical anti-roll bar system–washers, nuts, bushings, mounts, bar, etc.–are eliminated, as is their approximate $30-per-unit cost." One advisor to the project also suggested the design could eliminate the need for a subassembly station within the assembly plant, and an analysis done by Dana Corp. for Wagner says the Link-X design costs about the same as a double wishbone or multi-link independent suspension, minus the cost of the anti-roll bars. This only serves to strengthen Wagner's resolve. "If automakers are willing to spend up to $1.80 for each pound eliminated by switching to aluminum," he says, "then I don't see why they wouldn't want to at least investigate this solution."
By retrofitting the Expedition (and Honda CRV, and Smart) with his suspension, Wagner proved it's possible to add Link-X to an existing platform. However, to garner the full effect, it's best to start from a clean sheet of paper. "If you're adding Link-X as part of a scheduled redesign," says Wagner, "it's fairly easy to design it in. It's not always easy to add it on."
Take the Ford Expedition Wagner chose as his proof-of-concept vehicle. It came with a live rear axle. Because full wheel articulation is essential to the Link-X concept, it was necessary to design a fully independent rear suspension that bolted into place. The differential housing was cut from the Expedition rear axle, modified to accept attachment to constant velocity joints, and mated to stub axles from the front drive unit of another Expedition. "It would have been much easier to do this if we could have used a 2003 Expedition," deadpans Wagner. "That model has an independent rear suspension straight from the factory."
Apples, Oranges, and Expeditions
Aware of the questions this change might raise, Wagner took an unmodified Expedition, a 2002 Ford Explorer, and the Link-X Expedition to the Transportation Research Center in Ohio for testing. Though he acknowledges this isn't the same as having an Expedition with an independent rear suspension, the lighter, smaller, lower center of gravity Explorer was one of the few SUVs in the world with this feature at the time the tests were performed, and should outperform the base Expedition. If the Link-X vehicle could better its marks, Wagner felt, it would be difficult for skeptics to question the ability of his suspension design.
For safety, each vehicle was fitted with metal outriggers front and rear to help keep the vehicles from overturning, and casters placed at the end of each beam to keep them from digging into the asphalt. Videotapes of the test–a high-speed double lane change–show a dramatic difference between the cornering attitude of the Link-X Expedition and its competitors. Each vehicle was tested both fully loaded and unloaded, and the speeds averaged to create a composite number. The standard Expedition went through the course at an average of 57.2 mph with a roll rate of 32º°/sec. The independently sprung Explorer ran the course at 58.35 mph with a roll rate of 27°/sec., a significantly better performance.
When the Link-X Expedition ran the course, the visual difference was noticeable. Unlike the base vehicle, the outriggers stayed steady and well above the track surface, plus the truck drifted slightly at the apogee of each directional change. It didn't lurch as undulations in the pavement fed vertical inputs into the suspension, or show the same degree of "overshoot" as the others when changing direction. According to Wagner, the Link-X Expedition averaged 62.05 mph at a roll rate of 22º°/sec. Unfortunately, we couldn't verify this or any other claim made for the design because the Link-X Expedition Wagner and his crew brought along on their visit had broken a suspension link the night before.
Undaunted, Wagner promises to rectify this situation, and hopes to get automakers to test his system. It will be interesting to see if he succeeds.