Magnetorheological Dampers 8
Magnetorheological damping is a badass technology. (Pronunciation tutorial: Lead villain in X-Men: The Last Stand…”Magneto.” Really old MP3 player…”Rio.” Spock’s favorite word…”logical.” Put ‘em together: “Magneto”…”Rio”…”logical”. Sweet.) There’s no coincidence that the pronunciation tutorial came up with three examples plucked from geekdom, these shock absorbers are science-fiction level cool. Though usually only found on high-end cars, it’s a technology worth understanding for the effect of appreciation. Perhaps a bit of a refresher on shock absorbers is needed.
Shock absorbers. It’s one of those pieces of technology we each depend on every time we drive our cars but their praise is never sung. And as long they are functioning properly the ride is smooth they don’t need a fleeting thought. Usually the only time they are ever mentioned is in a sentence spoken with extreme irritation or disappointment (i.g. “The mechanic had to replace my shocks”).
The wheels on a car are not mounted in a fixed position. (That would be a VERY bumpy ride.) Between the wheel and the car is a heavy duty spring. It allows the wheel to make two corrective movements.
1) If the car hits a bump in the road, the wheel will be forced up toward the car to lessen the upward movement for the car and its occupants.
2)If the car hits a pothole, the spring will force the wheel down (faster than gravity) into the void to catch the vehicle and control its “fall”.
The problem with a spring is that it oscillates. If a spring were attached to the ceiling with a weight, and someone pulled the weight down and released it, the spring would probably bob up and down (oscillate) for a minute or two. Various forms of friction (such as wind resistance) slow the weight down and eventually bring it to a standstill. The friction is damping the spring system to bring it a halt. This is exactly what shock absorbers do. Shocks absorbers damp energy from the spring to bring the entire system to a motionless equilibrium.
Usually mounted inside of the spring, shock absorbers look like a telescoping tube. Inside the tube is a combination of oil and gas separated by some pistons. The gas will expand and contract, but oil does not. As the piston moves inside the damper, oil rushes past it and produces friction proportional to the viscosity (thickness) of the oil. (The higher the viscosity the stronger the friction.) This friction is the fundamental damping force.
Now what if the viscosity of the oil in the damper could be changed on the fly? The suspension would no longer be passive and would be considered semi-active. Magnetorheological dampers contain oil with special particles suspended in the fluid. When these particles are excited by a magnetic field, they tend to clump together and this clumping greatly increases the experienced viscosity.
So when is it preferable to have greater viscosity in the dampers? In racing situations it’s preferred to sacrifice comfort for quicker response from the suspension. With just the flick of a finger, a sport mode can be activated which turns on electromagnets in the dampers and instantly delivers a stiffer and sportier ride. And it’s just as easy to switch back for the more comfortable ride.
What car do you pick up to experience magnetorheological dampers? I recommend the Cadillac XLR. This technology is on a number of different sports cars, but only the XLR looks like it deserves dampers from Geordi La Forge’s garage. Kudos Cadillac.
I wish I could say exactly how it feels to drive with magneto dampers, but I will admit I have never had the pleasure. I then appeal to any of my readers to entrust their XLR to me for one day to enable one of my car reviews. (I prefer “Radiant Silver” but would be willing to drive “Elektra Blue Tintcoat.”)
