Magnetic Fields Turn Liquids Solid


The U.S. Office of Naval Research hasselected Lord Corp.s Magnetorheological (MR) fluid technology, which uses a magnetic field to change the properties of fluid in a suspension damper from liquid to solid and back, as part of an advanced suspension system for a new family of tactical vehicles for U.S. armed forces.

Intended for the Variable Load and Ride Height Suspension System for existing and future military vehicles, the contract is for science and technology activities – to include trade studies, technology development and concepting – for the suspension system on the U.S. Armys and Marine Corps Joint Light Tactical vehicles. Its a next generation of vehicles that is expected to be fielded in 2010 to 2012, essentially to replace the Humvee fleet, Lord Corp. market manager Kristopher Burson told Lube Report.

Cary, N.C.-based Lord Corp.s MR technology provides damping in the suspension system. Instead of traditional hydraulic fluid, the suspensions dampers contain Lord’s MR fluid which is affected by an electromagnet in the dampers piston. The fluids are typically oil-based fluids which have micron-sized iron in it, Burson explained. So you have between 20 and 40 percent iron suspended in the fluid, along with a variety of different additives and lubricants. He said Lord Corp. developed a proprietary additive package that solves the issues of iron suspensions – including iron oxidation, wear on the particles and device, settling of particles and viscosity modifiers.

He explained that the magnetic field causes the formation of chains of iron within the fluid that resist flow. You can eventually have this stuff free flowing just like the base oil that its in – and then you put a magnetic field on it and it goes almost completely solid, Burson said. The process is instantaneous, variable and reversible, he added.

Burson said the technology is suited for harsh environments, such as those that military vehicles often face. The shock is protected as any other conventional shock – perhaps more so, as the seals on the MR damper have to be able to keep the iron filings inside, he said. The iron is suspended in the fluid, so you dont want it passing your seals because it can chew up seals and rods. So its very well sealed against the environment. He added that small amounts of contamination do not affect its performance.

The technology is based on proprietary and patented fluid, damper, mount, brake and clutch designs and computer control algorithms. The suspensions spring characteristics use variable-pressure air spring technology in a package that allows for variable ride height and improved transportability. The system enables engineers to design a wide range of devices and systems with greater flexibility than before possible. Benefits include improved performance, reduced part count and complexity, smaller package size and less weight.

Demonstrations have shown that replacing conventional shocks with MR dampers gives substantial improvements in maneuverability and safe driving speed, improved vehicle stability, a significant improvement in driver absorbed power, and a reduction in vehicle wear-and-tear due to up-armoring, Burson said.

Most typical shock absorbers are limited to one or two shock curves, he said, where the force output of the shock depends on the velocity when, for example, a vehicle hits a pothole. The extra control with MR technology allows customizing of the shocks characteristics, using sensors and electronics. That can be based on road conditions, driver input such as braking or steering wheel angle, or temperature effects, he said.

The magnetic field is electrically generated, working in conjunction with a control unit and sensors. In a typical MR system you have at least one control unit, one sensor and power going to the dampers, Burson said. The control unit needs to know at a minimum where each damper is in its stroke, and which direction its moving. So you do have to have sensors.

The MR technology has been in commercial use in a variety of vehicles, beginning with General Motors vehicles such as the Chevrolet Corvette and Cadillac Seville STS in 2002. Burson said that within the last one and a half years, other manufacturers such as Ferrari, Audi, Acura and Australian automobile manufacturer Holden have begun using the technology.

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