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In the study of mechanical networks in control theory, an inerter is a two-terminal device in which the forces applied at the terminals are equal, opposite, and proportional to relative acceleration between the nodes. The generated strength satisfies the equation

$F=b({\dot {v}}_{2}-{\dot {v}}_{1})$,

for a suitable constant b.

Malcolm C. Smith, a control engineering professor at the University of Cambridge, first introduced inerters in a 2002 paper. However, a similar device was demonstrated in 1998 by Polish engineer Lucianus Lagiewka and used in an automobile bumper application. The principle and design are the same: a kinetic energy absorbing system that can be used as a bumper or vibration absorber. The device was in the public knowledge since 1998. Smith extended the analogy between electrical and mechanical networks (the mobility analogy). He observed that the analogy was incomplete, since it was missing a mechanical device playing the same role as an electrical capacitor. It was found that it is possible to construct such a device using gears.

Applications

Shortly after its discovery, the inerter principle was used under the name of J-damper in the suspension systems of Formula 1 racing cars. When tuned to the natural oscillation frequencies of the tires, the inerter reduced the mechanical load on the suspension. McLaren Mercedes began using a J-damper in early 2005, and Renault shortly thereafter.

J-dampers were at the center of the 2007 Formula One espionage controversy which arose when Phil Mackereth left McLaren for Renault.

Construction

A linear inerter can be constructed by meshing a flywheel with a rack gear. The pivot of the flywheel forms one terminal of the device, and the rack gear forms the other.

A rotational inerter can be constructed by meshing a flywheel with the ring gear of a differential. The side gears of the differential form the two terminals.

References

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External links

• The Inerter Concept and Its Applications, lecture notes
• J-dampers in Formula 1