Submitted as proof that not every invention at the 2001 Society of Automotive Engineers World Congress is some variation on a whiz-bang electronic device: Michelin SA's elegant and simple -- no power required -- rear suspension that allows the tires to work more efficiently.
Michelin's term for the new suspension isn't exactly simple, though: with no catchy moniker yet, the company calls it the "new axle system with optimized contact patch."
The advance of the new independent rear suspension, say Michelin engineers, is that it passively uncouples vehicle roll movement from wheel lean. What that means to you and me is that this is a suspension design that gets the most out of your tire's embrace with the road.
If you "got it" in geometry class, you might understand what's going on here: Norman Frey, Michelin's group leader of vehicle suspension analysis, says that the new rear suspension design "optimizes the contact patch in a corner," yet doesn't compromise that same contact patch when the wheel moves up and down to accomodate a bump. That's the traditional tradeoff in rear suspension setup; if you want the wheel to stay in maximum contact with the road when the vehicle hits bumps or ripply pavement, that type of suspension geometry can't also deliver maximum cornering grip.
"There's always a compromise with a short/long arm (SLA) independent suspension," says Mr. Frey. "If a system is optimized for roll control, it's compromised for vertical displacement."
The innovation, then, with the new suspension system, is the design that its chief engineer, Michel Blondelet, recently patented -- a design, he says, that "adds one degree of freedom to the suspension by decoupling roll camber from vertical displacement camber."
The crafty new design isn't exactly magic, but Mr. Blondelet obviously "got it" in geometry class. His idea delivers on the road by adding a "mobile cradle" -- along with its associated two link rods and various bushings -- that allows the wheels to work independent of body roll in corners while retaining the optimum design for maintaining tire contact when the wheels move up and down. Until Mr. Blondelet's unique design, a single independent suspension design couldn't do both.
Mr. Frey says the design permits the vehicle to develop an extra 10% to 15% of cornering force, because the wheel can now "lean" into the turn in a fashion similar to the way a motorcycle wheel leans into a corner.
Although higher cornering forces and maximized contact patch may be a little esoteric for everyday customers, Michelin adds that its new suspension improves safety by maximizing adhesion so that antilock brakes (ABS), traction control and stability control all can work more effectively.
And there's a final factor that's curiously at odds with the presumed goal of a tiremaker: the new suspension system actually will increase tire longevity.