DETROIT—The next generation tire won´t be a tire at all if Michelin North America Inc. executives are correct. It will be a "Tweel," a non-pneumatic integrated tire/wheel unit.
Michelin officials tout the product as revolutionary, but the revolution is starting modestly, fitted on a Segway-inspired stair-climbing wheelchair.
"Major revolutions in mobility may come along only once in a hundred years," Terry Gettys, president of Michelin Americas Research and Development Center, said at a news conference at the recent North American International Auto Show in Detroit. "But a new century has dawned, and Tweel has proved its potential to transform mobility.
"Tweel enables us to reach levels of performance that quite simply aren´t possible with today´s conventional pneumatic technology."
Several industry executives from other companies said the Tweel concept isn´t new, although its execution appears to be novel.
The Tweel uses a network of elastomeric polyurethane spokes fused to a wheel hub and a circular outer flat rim to replace the casing, beads and sidewall structures as the load-bearing element. The outer surface of the Tweel rim is covered with a more conventional rubber tread and an underlying reinforcing belt.
Without the air needed by pneumatic tires, Tweel still delivers pneumatic-like performance in weight-carrying capacity, ride comfort and the ability to "envelop" road hazards, Michelin claims. The design is covered by at least two patents.
The first larger-scale commercial application could be for skid-steer and similar civilian and/or military vehicles. Gettys said a first-generation passenger car prototype has shown considerable potential, which prompted the firm to go public with it.
However, it could be at least 10 to 15 years before a commercially viable passenger Tweel debuts, he said.
The Tweel was designed and developed by engineers at the Michelin R&D center in Greenville, S.C., based on lessons learned from work on the firm´s Zero Pressure run-flat pneumatic tires, said Bart Thompson, Michelin´s lead engineer on the project.
New materials for old idea
Spring-type wheel designs date to the origins of the tire industry in the late 1800s, said Joseph Walter, adjunct professor of tire mechanics and vehicle dynamics at the University of Akron and a former Bridgestone/Firestone executive. What´s new, however, are advances in materials development and engineering computing power that allow today´s engineers to make the idea of the elastic wheel practical.
Walter said he believes another Michelin non-pneumatic tire concept—dubbed "Airless"—actually has more promise, at least for larger vehicles. The invention by Michelin engineers in Europe uses a series of polymeric rings arranged radially around a wheel hub, to which is attached a reinforcing belt/tread package.
Michelin executives said the Airless concept certainly is better suited to applications like motorcycles or off-road, where a more rounded tread and sidewall come into play for traction.
Joe Gingo, executive vice president for quality systems and chief technical officer at Goodyear, agreed the concept´s becoming a viable option to the pneumatic tire will depend on the evolution in materials. "Has the science (of urethane) evolved to the point where it can overcome the difficulties of making the concept work like a pneumatic?" he asked.
Gingo has not yet seen the Tweel in action, and he wondered about its ability to generate adequate lateral forces so critical to vehicle handling. He said the concept seemed well-suited to lower-speed applications like the skid-steer market.
The Tweel fitment unveiled in Detroit was for the iBOT mobility systems invented by Dean Kamen, the inventor of the motorized, gyroscopic-controlled, two-wheeled Segway scooter. The six-wheeled iBOT mobility device has the ability to climb stairs and navigate uneven terrain, offering mobility freedom impossible with traditional wheelchairs. Gettys said tire inflation is the No. 1 maintenance issue with wheelchairs.
The iBOT user even can operate the chair balancing on just two wheels, bringing the rider eye-to-eye with other standing pedestrians. Additionally, Segway L.L.C.´s Concept Centaur, a prototype that applies self-balancing technology to a four-wheel device, also has been equipped with Tweel.
The Tweel automotive concept, as demonstrated at the Michelin research center on an Audi A4, is a "stretch application with strong future potential," Gettys said. "Our concentration is to enter the market with lower-speed, lower-weight Tweel applications. What we learn from our early successes will be applied to Tweel fitments for passenger cars and beyond."
The Tweel prototype demonstrated on the Audi A4 is within 5 percent of the rolling resistance and mass levels of current pneumatic tires, Michelin said, translating to within 1 percent of the fuel economy of a conventional pneumatic original equipment fitment. The tire maker also has increased the lateral stiffness by a factor of five, making the prototype "unusually responsive in its handling."
The drawbacks now include noise—the open spokes generate considerable noise—weight and higher rolling resistance, Gettys said. But the company is confident it can overcome these.