DETROIT (March 19, 2001)—Group Michelin wants to bring the cornering control of race cars to drivers everywhere.
The tire maker has developed a new axle system that uses mechanically induced tire camber to optimize vehicle cornering, tire performance and comfort.
"By optimizing the contact patch, you are able to more fully utilize the potential adherence characteristics of the tire," said Norman Frey, group leader for vehicle suspension analysis at Michelin Americas Research & Development Corp. in Greenville, S.C. "It´s always better to have more traction."
The new system, dubbed "Project Ecco," can work with any type of tire, Mr. Frey said. Although designing suspension systems is not traditionally an area of expertise for Michelin, the French tire maker developed the concept to optimize tire performance, premiering it during the Society of Automotive Engineers 2001 World Congress, March 5-8 in Detroit.
"It´s always a tire-vehicle system; you can´t separate one from the other," Mr. Frey said.
Because Michelin lacks metal production capabilities, it needs to tap the expertise of another automotive supplier for the structural components of the axle. "We´re wide open as far as how we´re going to work out the fabrication of this when it gets into mass production," Mr. Frey said.
The tire maker already has a relationship with French metal parts maker Groupe Vallourec. The two linked up in 1999 to work on a project-by-project basis in the development of suspension system products. Last year they introduced EVAX, a hollow tube axle that uses natural rubber bushings to take up the torsion forces and act as springs in the system.
Michelin wouldn´t say how much it has invested in the more recent Ecco project, but it dedicated plenty of engineering resources to it over the past year and a half. The new rear axle system is being tested on an unspecified European coupe. It also could be used in front-end applications, Mr. Frey said, but packaging would be more difficult.
Like standard suspensions, Ecco is a short-long control arm system. Unlike conventional assemblies, it uses kinematic linkages to allow the vehicle´s tires to roll off vertical center automatically in a turn, while retaining a position perpendicular to the road on straightaways.
The idea of using negative camber to increase cornering force is not a new one. Race cars have long used static negatively cambered rear tires, tilted in at the tops. "They do that to help compensate for the tread pattern that is developed when you´re in a corner," Mr. Frey said. "You want to have the ability to generate cornering force at the rear of the car for stability."
As a vehicle goes into a turn, centrifugal force pushes the vehicle´s weight to the shoulder of the tires on the outside of the turn. That force leans the cambered tire into the turn—much like a motorcycle does—making the tires perpendicular to the road once more and allowing them to attain maximum adherence or traction and an optimal, square-shaped contact patch.
Without proper camber, tire contact patches are distorted to a triangular shape. The areas absorbing contact stress are greatly decreased, which means wear and heat in those areas increase, Mr. Frey said.
Stress on the contact patch is more evenly distributed with the induced tire camber or tilt of the Ecco system. This increases potential grip and cornering force by as much as 10 to 15 percent, he said, depending on the profile of the tire, inflation pressure, and the change in loads because of suspension and vehicle design.
"Anything that you do to a suspension system that improves the durability of the tire—which is both treadwear and structural integrity—is very good for the buying public," said Jacques Bajer, president of Tire Systems Engineering Inc., a Grosse Pointe, Mich., consultancy.
With their static negative camber, race cars achieve optimal contact patch or tire performance when they are cornering. But on straightaways, that camber can degrade braking and accelerating performance because there is less available traction, Mr. Frey said.
Ecco utilizes kinematic linkages in the axle to camber the tires automatically into turns and keep them perpendicular to the road on straight paths, giving drivers of vehicles equipped with the systems the best of both worlds, according to Mr. Frey.
Ecco also enhances passenger comfort by enabling the tire to absorb shock better while encountering bumps during turns, he said.
"This (Ecco) system that we have is 100 percent passive. There´s no semi-active component to it," Mr. Frey said.
The system relies fully on mechanical components, he said. There´s no electronics or sensors to fail, and therefore no additional cost and no maintenance required for the system. "It´s like a conventional suspension, except it has a breakthrough concept," Mr. Frey said.
"The concept looks fundamentally sound, but its execution in production must be consistently precise," Mr. Bajer said.
"That´s commendable if they (Michelin) can do it," he said.