How Do Magnetic Shocks Work?
Things in the automotive world usually move pretty slowly, and it’s rare that any one manufacturer will completely catch everyone else out on a particular technology. But when Skunkworks-silent engineering combines with excellent patent protection, the result can be either an industry-wide revolution, a comedy of errors as others attempt to catch up, or both.
Youngsters might take electronically adjustable dampers for granted today — but it wasn’t long ago when a set of Edelbrock IAS shocks represented the pinnacle of suspension control technology. Yes, back in that ancient era known as "the 1990s," the idea of electron-quick suspension response seemed the stuff of sci-fi pipe dreams. But somewhere between Sliders and X-Files, a little American company (previously known primarily for floaty, retiree-spec luxo barges) brought to the mass-market a revolution in handling equipment.
That left the public speechless; partly in shock, but mostly because nobody could figure out how to pronounce "magnetorheological dampers."
While discussing this article with my editor, I was explicitly forbidden from going into a 2,000-word history on the technology. Which, if you’ve read any tech article of mine, you’ve probably noticed is kind of a running theme. Fortunately for all involved, there isn’t much history to write. Sort of.
Short story: Megnetorheological (MR) dampers were developed by General Motors’ British subsidiary Delphi Automotive Systems between 1997 and 1999. In 1999, Delphi went public and became an independent entity, but GM and Delphi still maintained a close relationship, and GM maintained rights to the technology.
Corvette enthusiasts will tell you that magnetic suspension debuted on the 2003 ’Vette — but they’re wrong. Cadillac got "MagneRide" first, and offered it as an option (RPO F55) on Seville STS models built after January 14th, 2002.
Sorry, gold-chainers; the golfers edged you out on this one.
It’s true that some of those were Cadillacs sold as 2003 models, but the 2003 Corvette didn’t go into production until several months later. So, Caddy did beat Chevy to market with magnetic suspension. Sorry, gold-chainers; the golfers edged you out on this one.
Almost immediately afterward, Delphi came under investigation from the SEC for "irregular accounting practices" (embezzlement), and filed Chapter 11. After closing a bunch of plants and getting re-purchased by GM, Delphi eventually sold its suspension and brake holdings off to the Chinese in 2009 for the fire-sale price of $100 million.
Could they have been hiding in Howard Hughes' secret stash of inventions for decades? Probably not, but maybe.
Now that BeijingWest owns the patent, GM and everyo ne else pays China for use of a technology originally developed in Britain with American money. Great job, Wall Street.
But, on a less depressing, more interesting and more historical note: it’s rumored that the fluid that makes MR shocks work (or, more accurately the application for it) was first envisioned by none other than billionaire genius-turned-lunatic Howard Hughes. There’s actually some meat to that rumor: GM used to own Hughes Aircraft, which through a series of splits and mergers with AC Delco eventually went on to spawn Delphi in 1997.
It was the very next year that work began on MR dampers. Could they have been hiding in Howard Hughes’ secret stash of inventions for decades? Probably not, but maybe. Who knows how long it took to sort through all those used tissues and the insane ramblings scrawled on them?
Speaking of insane ramblings — history lesson over. On to the real article now.
Basic Shock Function
Before getting into how MR shocks work, it might help to know how regular shocks work.
A hydraulic shock starts out pretty much like any other hydraulic ram, which themselves work just like the hypodermic syringes you’d find in any doctor’s office. A syringe has three basic parts: the outer tube, a needle on the end, and a plunger to push fluid out of the tube and through the needle.
Imagine what would happen if you took the needle off, plugged the hole and pushed down on the plunger. At first, it wouldn’t move. The liquid inside, being liquid, doesn’t compress. So no matter how hard you push on the plunger, it’s never going to move because the fluid has nowhere to go. However, in the real world, if you push hard enough on the plunger, fluid pressure will build up, and the fluid will start squeezing out of the tiny gap between the rubber plunger and plastic tube.
Once that happens, the plunger will start moving, but will move very slowly. The fluid in the tube can only leak out so fast. The plunger will go down faster if the fluid is thin like water — but replace that water with cold maple syrup, and the higher viscosity syrup will come through the gap much slower. No matter how hard you press on it, the maple syrup will always leak slower than the water. Increasing fluid viscosity like this is one way to control the plunger’s "rate of compression."
Another way to do it is to poke a hole in the rubber plunger with a needle. Now, with a hole in the plunger, the fluid inside has somewhere to go when you press down. The plunger compresses a lot faster, and using a great deal less force than before. If you want it to go down even faster and easier, you can either make the needle-hole in the plunger bigger, or you can poke more holes in it. This is the second method of controlling the rate of compression — by putting more and bigger holes in the plunger.
That’s how almost all modern shock absorbers work. By forcing a thick-or-thin fluid to flow through many small-or-large holes, the shock "dampens" the up-and-down movement of the wheel. That keeps the car from endlessly bouncing like a rubber ball every time you hit a bump. Functionally, the only difference between our "plugged-off syringe" and a full-sized damper is that a damper has to work in both directions. That is, compression and "rebound." For that reason, the top of our "syringe" tube would be sealed off instead of open, and a seal on the plunger shaft would keep it air-tight.
That creates a second chamber in the tube for fluid to flow into (the back side of the plunger) after it goes through the plunger holes. Now, the damper works in both directions, because fluid has to fight to get from one chamber to the other, and fight to get back.
Generally, car dampers will use oil as a control fluid. Often very thin, equivalent to 0W-5 motor oil...but heavy-duty truck shocks might go up to something like a 90W chain oil.
A slower/firmer shock (smaller holes and/or thicker oil) provides a firm ride and better handling; a softer/faster shock (bigger holes and thinner oil) makes for a softer ride at the expense of more body bounce and roll. Ideally, what you want is a shock that’s soft and floaty on rough roads, but hard and firm when you want the car to handle on smooth roads.
Adjustable shocks have been around for quite a while now — but almost all of those older designs relied on controlling the size of the holes in the plunger to moderate fluid flow. Manually adjustable race coilovers use this approach, and so do older auto-adjusting systems like those used on the 1996 Ford Taurus SHO. The Taurus system was fairly advanced for its time, and at least allowed the car two different settings for comfort or handling. For hooligan fun, it also just happened to default to the small-orifice "hard" setting. Meaning, if you pulled the suspension control relay, the suspension would stay in full-sporty mode all the time. Speaking from experience.
What you want is a shock that's soft and floaty on rough roads, but hard and firm when you want the car to handle on smooth roads.
But even this system was only debatably better than the aforementioned Edelbrock Performer IAS. This shock used an inertia-sensitive valve that opened and closed the plunger orifice holes depending on the road surface. On rough roads, the intertia valve would keep the orifice holes big, and oil would flow through quickly. On smooth roads, the inertia valve would settle down and close, this closing off the oil holes and firming up the shock.
While this orifice-size control method works well, it does have two drawbacks. First, even auto-adjusting systems like the inertia valve can only react to changes in road condition so quickly. Hit a big pothole on an otherwise-smooth road, and you might actually wind up breaking something, because the shock is in full hard mode. Nevermind adjusting to tiny imperfections within 0.001 second; these mechanical-orifice designs did well to respond to speed bumps within 0.1 second. The design is just too slow and too blunt. Second, closing off the orifice too far to cope with fast, hard-handling cycles (like a slalom course) could easily overheat the oil, causing it to thin out and fail.
A better alternative, if it were possible, would be to use a fluid that could change its "thickness" on demand. That way, you could use an adjustable orifice hole to make big changes in handling settings, and vary the thickness of the fluid for smaller adjustments. But where might we find such a miraculous liquid — one that could be thin as water one second, and thick as maple syrup the next?
Better yet: What if you could also get rid of the orifice-size-changing mechanism completely, and go back to simple holes in the "plunger?" Turns out, this "miracle fluid" has an app for that, too.
Memorize this line: "Magnetorheological fluid is a composite of ferritic nano-dipoles suspended in a carrier fluid, which align themselves along lines of applied magnetic flux to vary the yield stress of the whole."
In other words: Iron filings mixed with 10W oil.
Yes, it’s a pretty simple recipe, but "ferromagnetic" fluids like this can pull off some pretty amazing tricks when magnets are nearby. Remember that grade-school experiment where the teacher had you dump iron filings on a piece of paper with a magnet under it? Same thing happens when you take those same filings and dump them into oil. It’s even capable of making some seriously creepy-beautiful "living" sculptures when you play with the magnetic field strength.
In other words:Iron filings mixed with 10W oil.
As you can see in the above video, the "ferrofluid" ("iron fluid") doesn’t just flow in one great lump. It follows the lines of magnetic force, resulting in interesting ripples and peaks in the fluid. Note how it goes from water thin to fairly thick and hard in the most magnetic areas.
Very simply, this is exactly how MR shocks work. Instead of pure oil, they contain ferrofluid. An electromagnetic coil either wraps around the shock body (on older designs) or it’s incorporated into the plunger head. Those electromagnets control the "thickness" of the fluid as it passes through the holes in the plunger. The particles in the fluid line up along the lines of magnetic force, and make for a kind of "plug" that fights fluid flow and cause the fluid to act more like 90W chain oil than 10W motor oil.
In designs with magnetic coils integrated into the plunger, you get a second benefit. Because more particles stick to the walls of the holes in the plunger, they basically work to "narrow" the orifices. In this way, you get the double-action effect of variable-viscosity fluid and adjustable orifice size. This design (which you’ll find on many modern systems) gives the shock a huge range of softness and stiffness. And because it’s just iron particles and magnets, this type of MR shock can make those enormous changes very quickly.
Pros and Cons
Aside from the fact that these systems are expensive, there aren’t any real drawbacks. They do everything traditional self-adjusting shocks do, but faster, better and preemptively.
They do everything traditional self-adjusting shocks do, but faster, better and preemptively.
As though millisecond response to changes in road condition and handling demands weren’t good enough, most electronic suspensions don’t even wait that long to react. With the right combination of sensors and computers, MR suspensions can detect road conditions, steering, brake and accelerator inputs, and harden or soften before mechanical force even gets to them.
That works very well for reducing squat and nose-dive under acceleration and braking, and body roll when you turn the steering wheel. For instance, when you turn the wheel to the right at high speed, the computer knows to firm up your left-side dampers in order to keep the body flat and level.
But it’s in the smaller motions where the control computer does its most impressive work.
For instance, say you’re on a smooth road, and hit an expansion joint. The front wheel sensors will detect motion, and the computer will soften the shocks before that expansion joint has even made it from one end of the tire contact patch to the other. After the crack is passed, the suspension will immediately harden again. That’s a neat trick, but not as neat as the one it pulls with the rear tires.
Engineers now have the freedom to design suspension systems without compromise between handling and ride.
Having seen the expansion joint coming, the suspension computer will automatically soften the rear shocks just before those tires hit the expansion joint. By the time the joint gets there, the rear tires are already prepared for it, and the computer knows exactly how long to leave their dampers in soft mode.
Pretty sweet — but it does always leave the front tires at a slight disadvantage. They have no way of knowing if that expansion joint, pothole or road reflector is coming before they hit them. Unless, that is, you install a sonar, radar or optical laser sensor under the front bumper, as some high-end manufacturers are wont to do these days. The sensor sees road imperfections coming before they even hit your tires, giving the front suspension a chance to calculate and execute the appropriate response.
These sensors can also serve double duty in assisting the stability control system, or in detecting rain, snow or loose dirt and gravel. Each of these require different suspension, ABS, stability- and traction-control system strategies — all of which the computer can alter at a moment’s notice using information from its road-surface sensors.
All of this has given engineers the freedom to design better suspension systems without relying on full-race geometry, rock-hard springs and super-stiff roll-bars to maintain handling. It’s also allowed 21st century luxury cars to deliver a cloud-like rides to rival the best of any Rolls Royce, while turning out handling numbers that would have been unthinkable for any 20th century sedan.
If you’re old enough to remember the 1990s — welcome to the future. No, we don’t have flying cars yet, but we do have cars capable of flying over any road, any time, while delivering safety, comfort and handling prowess in equal abundance.
This, brought to you by General Motors, a fluid nobody can pronounce, and Howard Hughes.