A magnetorheological damper or magnetorheological shock absorber is a damper filled with magnetorheological fluid, which is controlled by a magnetic field, usually using an electromagnet. This allows the damping characteristics of the shock absorber to be continuously controlled by varying the power of the electromagnet. This type of shock absorber has several applications, most notably in semi-active vehicle suspensions which may adapt to road conditions, as they are monitored through sensors in the vehicle, and in prosthetic limbs.
The technology was originally developed by General Motors for use in the Cadillac and Chevrolet Corvette in 1998.
These types of systems are available from OEMs for several vehicles, including the Acura MDX, Audi TT and R8, Buick Lucerne, Cadillac ATS, CTS-V, DTS, XLR, SRX, STS, Chevrolet Corvette, Camaro ZL1, Ferrari 458 Italia, 599GTB, F12 Berlinetta and Holden HSV E-Series. These systems were produced by the Delphi Corporation and now by BWI Group under the proprietary name MagneRide.
MillenWorks has also included them in several military vehicles including the MillenWorks Light Utility Vehicle, and in retrofits to the US Army Stryker and HMMWV for testing by TARDEC. 2012 Us Engine Production Inc
MRF-based dampers are excellent candidates for stability augmentation of the lead-lag (in-plane bending) mode of rotor blades in helicopters. MRF-based squeeze film dampers are being designed for use in the rotary wing industry to isolate vibrations from the aircraft structure and crew.
A magnetorheological damper is controlled by algorithms specifically designed for the purpose. There are plenty of alternatives, such as skyhook or groundhook algorithms. The idea of the algorithms is to control the yield point shear stress of the magnetorheological fluid with electric current. When the fluid is brought into a magnetic field, the metal particles of the fluid are aligned according to the field lines. This makes the fluid stiff. When this occurs at the right instant, the properties of the damper change, which helps in attenuating an undesired shock or vibration. The relative efficacy of magnetorheological dampers to active and passive control strategies is usually comparable.
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- http://www.millenworks.com/html/aboutus/news/Stryker_Test.pdf MillenWorks Active Damper Suspension System[dead link]
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- http://www.hindawi.com/journals/ijrm/2004/546845/abs/ A Magnetorheological Fluid Damper for Rotor Applications
- Magnetorheological Damper Laboratory
- ALY, Aly Mousaad; Richard Christenson (2008). "On the evaluation of the efficacy of a smart damper: a new equivalent energy-based probabilistic approach". Smart Materials and Structures.