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.
The three most significant challenges in getting it there were making: 1) its rheological properties consistent over time, 2) its CIP not abrasive, and 3) its CIP not settle out of the fluid when the car was at rest. How Lord solved these problems, particularly the first, is a bit unclear. When asked specifics, Lord Corporation continued the company's policy of not commenting, then referred SUPER CHEVY to some public domain information.
The oil refining industry uses additives to make abrasive substances suspended in liquids nonabrasive. We believe similar additives are introduced into MRF which either coat or lubricate, or both, such that CIP becomes nonabrasive. The settling problem is also addressed with additives. Though we're not sure whether they form a buoyant coating on the CIP or whether the additive is a "thixotropic agent," which thickens the fluid while it's at rest so that it resists settling, but liquifies as soon as the fluid moves.
Changes in the fluid's rheology and abrasion are virtually nonexistent. MRF is resistant, but not totally immune, to the CIP settling. If a MR shock is at rest for six months or longer, there can be some settling, however, it takes only a few strokes of the shock for it to work as intended.
MR Shock HardwareThere are no valves in a Delphi MagneRide shock absorber. All are replaced by an electromagnet inside the piston assembly resulting in a 40 percent reduction in each shock's part count.
The rest of MR shock architecture is similar to that of a traditional, gas-charged, mono-tube unit. The shock tube bolts to the suspension. The piston rod bolts to the chassis. The rod ends in a piston, which moves in the tube. A piston seal prevents MRF from bypassing the piston and a piston rod seal keeps fluid from leaking out. At the bottom of the tube, a divider piston and seal separate the magnetorheological fluid from a gas chamber, which pressurizes the fluid to prevent foaming.
Each piston/electromagnet assembly has four annular channels. As the piston moves in the shock tube, magnetorheological fluid flows through these channels. When the magnetic field is weak, it flows freely. As the magnetic field gets stronger the yield stress of the fluid is altered.
This change in yield stress is localized inside the piston channels. As MRF flows into the channels, the CIP align in matrices and as the fluid exits, the matrices dissipate. The altered rheology fluid inside the channels restricts flow and dissipates the kinetic energy of the piston's motion thus absorbing the "shock" of suspension movement.
Control and the "Sky Hook" AlgorithmIt took scores of people, hundreds of millions of dollars and a decade of work to perfect Magnetic Selective Ride Control. The lion's share of that went into the last word: "control."
The heart of MR is a powerful, dual-processor controller capable of making 1,000 adjustments per second in each of the four shocks. At highway speeds that's a damping change about every inch the car moves.
MR's position sensors measure wheel movement. With that data, the controller determines three types of body motion: pitch, roll and heave. Pitch (front end moves up or down) and roll (the car leans), are terms we've heard before, but heave might be a new one. When the car heaves, both ends move the same way. If you drive over a rise, the body heaves up, then down. MR's controller also uses brake, throttle, steering angle, lateral acceleration, vehicle speed, and air temperature data in making its decisions
The controller processes sensor data with various software algorithms. When SUPER CHEVY talked with Mike Neal, Corvette's lead ride-and-handling engineer, we heard about "sky hook," an algorithm focused on isolation and body control. It gets its name from the idea that, if the car could be hooked to the sky, it would ride nice regardless of how nasty the road gets. Sky hook is not a literal term. As good as MR is, it cannot isolate the car completely.
"Sky Hook," Mike Neal told us, "is one of MR's main algorithms. Based on it, MR commands some force level at each shock, separate at each corner and specific to compression or rebound. This is done in an attempt to make the car not heave, pitch, nor roll. Sky hook is a body control algorithm. We have others for wheel control which give us different damping forces.
"Separate from those fundamental algorithms, we have a bunch of others. If you're getting to the end of the travel, we have algorithms which recognize that then do something to reduce impact on the bump stop. We have algorithms that compensate for temperature...algorithms which condition the signal to smooth transient spikes and things like that."
Once MagneRide's sensors gather data and its controller processes it with the proper algorithms, four electrical drivers adjust current flow to the electromagnets in the shocks, which vary the magnetorheological effect to provide the correct damping. This could be damping to improve ride, to improve handling, or to limit frontend lift during acceleration or dive during braking.
The driver has some input to the controller via a two-position switch. In the "tour" position, the MR controller emphasizes the sky hook algorithm when setting shocks and when switched to "sport", it emphasizes wheel control.
What's it Like Out There?"If you're on a smooth road," Mike Neal told us, "while you'll notice better isolation, MR's advantages to handling are minimal. It's on roads which cause large ride events and body motion where it has huge benefits.
"Go to a place like the Nrburgring (a famous race track) in Germany, where the track has lots of dips and undulations and you're takin' every turn at 100 mph or faster. At that speed, it doesn't take much of a ride event to really heave the car, pitch it and roll it around. In a place like that, MR is a huge advantage."
North of Los Angeles are the San Gabriel Mountains. About 8 miles into the San Gabriels on State Route 2, hang a left on LA County N3. After about 30 miles, you're in the desert town of Palmdale and you'll have been over some of the better roads for high-speed touring west of Nrburgring.
I drove an MR-equipped '03 Convertible, a perfect choice to see how MR works in the real world. N3 had lots of heaves and undulations of different depths, heights and lengths. There were a few Nrburgring-style, bumpy 100-mph turns, too.
It was easy to feel Magnetic Selective Ride Control doing its thing. Compared to a base Corvette, it was like night and day. Compared to the '97-02, Real Time Damping system, MR has improved wheel control over the higher frequency (10-15 Hz) ride movements because it can bring more damping authority to bear and it can switch damping levels more quickly. The system effectively damps the big heaves, pitches, and rolls that come from bumps and dips or low spots on the edge of the road. Thirty miles, running hard over N3 sold me on MagneRide.
Does MR have shortcomings? Really high frequency (17-20 Hz or more) stuff, little ripples on concrete highways or washboard/chatter-bump surfaces, are a slight problem. In a straight line, the ride is a little harsh over sufaces like that. At high speed and at high lateral acceleration over chatter bumps, the car wants to skate sideways.
MR seems to be less effective in damping this kind of harshness presumably because, even with a 10 millisecond response time, with the car moving fast, it can't react quickly enough to bring the most ideal damping to bear. While this harshness is a shortcoming, the types of surfaces that cause it are rare and it might not be entirely an MR issue. The stiff sidewalls of C5's run-flat tires amplify harshness to the suspension. C6 will arrive in 2005 with a new, Goodyear EMT having improved harshness qualities, which might solve this problem.
On relatively smooth roads near the car's limits in abrupt transitions and turns at high lateral acceleration, a MR car's small stabilizer bars show their limited roll stiffness. GM sources tell us DIY tuners can trade a little isolation to gain more roll stiffness by adding Z51 stabilizer bars to MR cars which, in the hands of a talented drivers, react well to the change.
Hard core racers, autocrossers, and very aggressive street drivers will still want either Z51s or Z06es, both of which have the bigger "stab" bars along with stiffer springs and fixed-valve shocks tuned specifically for motorsports.
MR on other Chevrolets?At this writing in early 2003, the only Chevrolets with MagneRide are the Corvette Coupe and Convertible. As time goes on, will MR be on other Chevys?
It's a possibility, but apparently, not a probability. Jeff Holland, communications representative for GM's Performance Division, the folks responsible for taking proof-of-concept vehicles, such as a straight-cab, six-speed version of the Silverado SS, a TrailBlazer SS, and a Tahoe SS shown at the 2002 SEMA Show, to production told Super Chevy, "MagneRide is certainly on the table for consideration in some of those products, but it's an expensive system. Its cost is not consistent with what many believe a Chevrolet SS-branded product should be."
Dave Caldwell, spokesperson for GM performance car engineering issues told us, "Currently slated to get MR [other than the Corvette & Cadillac STS, which already have it] are the Cadillac XLR [a luxury roadster] and SRX [launching this summer], which is notable as the first SUV to get this technology. It's body control benefits are particularly useful for an SUV. At this time, it's not slated for other trucks. Expect this technology to remain in up-market vehicles in the foreseeable future due to cost.
"As you know from your visit to the Milford Proving Ground, there's a ton of development work in putting this system on a production vehicle. There's no compelling case right now for replacing suspensions in other vehicles-TrailBlazers or Suburbans, which perform pretty darn well as is-with MR."
Those interesting comments seem to indicate MR's body control benefits are useful on SUVs but Chevy's current top selling utes, Tahoe and Suburban, are not going to benefit from the technology in the near future.
Frankly, if there's to be a Tahoe SS, we'd like to skip On-Star and other dumb telematics options to spend our money on MagneRide shocks...oh yeah, 6L, six-speed, too.
How cool would that be?
MR Retrofit?Interesting intel we developed in preparing this article is that it is possible to retrofit Magnetic Selective Ride Control to older C5 Corvettes originally optioned with RTD. Remove the RTD shocks and the RTD controller and replace those items with MR shocks and an MR controller. The wheel sensors are the same and RTD selector switch can be retained. The existing wiring harness can be used; however, jumpers or adapters must be fabricated to connect the RTD harness to the MR shocks and controller. This would be a time-consuming but not impossible task for a DIY experienced with electrical system modification and armed with the proper wiring diagrams. We also heard scuttlebutt that Delphi might consider developing these jumper/adapter units as an aftermarket product but, as yet, has no plans to do so.
Our search for ways to put MR on other Chevys led us to Carrera Racing Shocks, an Atlanta, Georgia, manufacturer of high-end racing and performance street shock absorbers. In the mid-'90s, Carrera chairman, Dick Anderson, after learning of the MRF technology Lord Corporation was developing for dampers used in heavy, on- and off-highway vehicle seat assemblies, decided the motorsports shock absorber industry would eventually incorporate electronics into its high-end products.
"I figured I'd better start lookin'." Anderson told SUPER CHEVY. "Everybody else was doing stuff where electronics controlled the valving in a hydraulic shock. They'd never be able to make that fast enough to do what a reactive suspension needed to do. The fastest we'd ever heard of was about 50-millisecond response time. We needed a couple of milliseconds. It was highly unlikely anyone could build something using mechanical servos that could respond that fast.
"When I saw the research being done on MR fluid, I decided we better get involved because that technology could make a shock that could respond quick enough. That led me to Lord. They have done more [with MRF for motion dampers] than the rest of the world put together."
In late 1999, Carrera introduced "MagnaShock 1", an oval-track shock absorber and the first commercially-viable application of MRF to an automotive suspension damper. The system has no computer controls and the shocks are "50/50", offering the same damping authority on both compression and rebound. That authority was varied by a control box that could operate one, two, or four shocks. The adjustment is accomplished by rotary switches. The shocks' range of authority is seven of the damping "units" on the scale that is industry standard in oval track racing. The controller can be programmed to use any five of those seven ranges.
A popular application of MagnaShock 1 in late model oval-track cars is a single pair on the right side. This is a cost effective because shocks on the outside of the turn are the most critical from a chassis set-up perspective. The advantage of MagnaShock is in quick shock-tuning changes, which significantly reduced test time and offered the driver the ability to change the car's chassis tuning during a race.
In late 2002, Carrera introduced a second, more refined and sophisticated "MagnaShock 2," which is adjustable on both compression and rebound. Each shock contains a sensor that sends piston position and velocity data to the MagnaShock 2 controller. With that information, a processor using Carrera's own software algorithms sends a signal to four shock drivers, which command the level of damping the user has selected.
MagnaShock 2 has developed a following in the road racing community because it can be programmed with different damping authority for both compression and rebound. Like MagnaShock 1, the shocks have a damping range of seven. A MagnaShock 2 controller is designed to run four shocks and can store up to five different set-ups each having five steps. A common use of this memory feature is a tiny switch on the steering wheel allowing the driver to select two or three different set-ups during a race or even on a per-lap basis.
"Almost every track has one turn-usually a real sharp one-which the person doing the set-up has to give away," Carrera's Dick Anderson said. "If you set-up to go fast there, you'll be terrible everywhere else. Usually, they give that one up in favor of having a better set-up for the rest of the track. If you were really fast in that turn, too, you could gain a half or even a full second per lap. With MagnaShock 2, you can change all four shocks just for that turn. Flip the switch and you're in that set-up. You'll come off that turn like a rocket."
The MRF Lord makes for Carrera is similar to what Delphi uses in production Corvette shocks. The Carrera hardware is also similar to Delphi's in that both are mono-tube, gas-filled dampers. Materials are where there are some differences. Carrera shock tubes are billet aluminum whereas Delphis are steel. Delphi uses a segmented, annular MRF passage whereas Carrera uses a full annulus. The pistons on both are composed of a magnetic coil and annular passages though which the MRF flows; however the Delpi passage is segmented but the Carrera is continous. Another difference is there is a Carrera piston has only one area where MRF forms fibrous matrices. In a Delphi MagneRide shock piston there are two.
MagnaShock 1 costs about $800 per wheel and MagnaShock 2 is $1500 a wheel. While that's in an acceptable price range for late model stock cars and SCCA GT-class road racers and is actually less expensive than some of the high-end, hydraulic shocks on the market; it's a bit pricey for a street application. Nevertheless, Anderson told us that, the week before we interviewed him, Carrera shipped a MagnaShock system to a customer in California who is building a street-driven, road-race-style, Fourth-Gen Camaro. Obviously, the advantage in MagnaShock to a car like that is the quick adjustability from damping for a nice ride to damping with aggressive wheel control. For more information on MagnaShock contact, Carrera Racing Shocks, 5412 New Peachtree Rd., Dept. SC, Atlanta, GA 30341, (770)451-8813, www.carrerashocks.com
Looking for more examples of potential street applications, we asked Anderson if it would be possible to install a MagnaShock system on the author's '65 Malibu. He said it could be done with some modification to the front, upper shock mounts. Adapting a MagnaShock system for street use on a musclecar-era Chevrolet is an interesting idea and perhaps something we'll pursue in the future.