For 2003, breakthrough suspension technology is the Chevy Corvette's Magnetic Selective Ride Control. It's not just our Bow-Tie bias that provokes that statement. We've driven several '03 Vettes with that system and it's effect on ride and handling is revolutionary.
We are not alone in this belief. Popular Science magazine announced Magnetic Selective Ride Control winner of its prestigious "Best of What's New in Automotive Technology" award for 2002. The Society of Automotive Engineers magazine, Automotive Engineering International, named it one of its "Top 10 Technologies" for 2002.
Magnetic Selective Ride Control (some call it "MagneRide" or just "MR") is a computer-controlled shock absorber system but that's not really news. Corvette has had computerized ride control systems since 1989 and some Chevy trucks have had them since the late '90s.
Previous systems used conventional hydraulic shocks. A servo-operated bypass or pressure control altered their valving, but the damping was still done by a piston forcing shock oil through small orifices.
MagneRide's breakthrough is that not only is the damping varied electrically, but some of the shock absorber hardware is replaced by electronics, too. Also, there's no oil in a MR shock. And, GM does this for 1,700 bucks-a hell of a bargain.
Secret SauceThe shock oil is replaced by magnetorheological (say "mag-knee-toe-ree-oh-lodge-i-kul") fluid. Manufactured by the Lord Corporation, "MRF" is a staggeringly complex, synthetic-hydrocarbon-based liquid having 20 to 40 percent "carbonyl iron" particles (CIP) in suspension.
CIP are microscopic, iron spheres of very high purity and have excellent electromagnetic properties. BASF is the only manufacturer of CIP we found selling a product intended for MRFs. BASF told us that one grade, "...'Carbonyl Iron Powder CR' is designed to meet the requirements of the magnetorheological fluid in shock absorbers."
When asked for more information on CR, BASF was not accommodating, however, it hinted it was similar to another product, "CM" which varies in diameter from four to 22 microns with at least 50 percent of it being about 7 microns in diameter. A micron is 39 millionths of an inch (.000039) so, we're talking way small particles. Lord Corporation also declined to provide specifics about its MRF citing proprietary concerns. Whatever the source of Lord's CIP, we believe it's similar to BASF CM.
Before the particles are added to the fluid carrier, they look and feel like black flour. Once MRF is formulated, it looks and feels like dirty engine oil. The key property of this high-tech witch's brew is its flow characteristics, or "rheology" changes, when subjected to a direct-current, magnetic field. CIP are attracted to each other and the magnet's poles forming a sort of fibrous matrix that changes the fluid's yield stress. The magnitude of this effect is proportional to the field strength. A little magnetism and MRF is like thick oil. A little more, it's like heavy gear lube. When the field is strongest, the fluid is like grease.
MRF reacts to changes in field strength in a couple of milliseconds. MagneRide's overall system response is slower but, still quicker than any other production, electronic ride control system. Other systems may have a potentially wide range of damping but, in practice, can't switch rapidly or accurately enough to make such a range effective.
Magnetorheological fluid was discovered more than a half-century ago but it wasn't until about 1990, once digital processors became fast enough and cheap enough, that MRF in automotive suspension dampers became practical. It took Lord and Delphi Corporation, which manufactures the shocks and controls for GM, over a decade to take MRF from a product around which scientists would stand and speculate, "Uh yeah, dude, this stuff is sweet. It could work in, like...a shock absorber on a car," to where they could put it in a production Chevrolet.