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Success Stories
FOR CONTROL
Control for Formula One!
What Is an Inerter?
The standard analogy between mechanical and electrical networks relates force
to current and velocity to voltage. The following correspondences exist between
standard modeling elements:
•
spring
inductor
•
damper
resistor
•
mass
capacitor
The correspondence is perfect for the spring and damper, but the mass element is
analogous to a grounded electrical capacitor and not to a general two-terminal capacitor.
Without a two-terminal capacitor equivalent, mechanical systems are unable to provide
the same fl exibility in dynamic response that electrical systems can. The two-terminal
electrical model suite above can be used to produce any “passive impedance” device.
A ballscrew inerter (fl ywheel removed) made at
Cambridge University, Department of Engineering,
in 2003, designed by N.E. Houghton
The inerter overcomes this limitation of mechanical systems; this two-terminal element
has the property that the applied force at the terminals is proportional to the relative
acceleration between them.
In August 2008, the deployment of a novel
mechanical control device in Formula One
racing was announced. Developed at the
University of Cambridge by Malcolm Smith
and colleagues, the device, called an “inerter,”
was deployed by the McLaren team in 2005
in Barcelona.
Schematic of an inerter with
a fl ywheel driven by a rack,
pinion, and gears
The First Application: Vehicle Suspensions
Malcolm Smith’s group at Cambridge University, in attempting to build high-performance
mechanical impedances for car suspensions, realized that the lack of a true capacitor
equivalent was a fundamental limitation.
After several fruitless efforts to prove that such a device could not exist, they realized
it could be built, and in a relatively simple manner. They ultimately developed several
prototypes of the device they called the inerter.
Kimi Raikkonen crosses the i nish line to take victory for
McLaren in Barcelona 2005 in the i rst car to race the
inerter. Photo courtesy of LAT Photographic
Contributor: Malcolm Smith, Cambridge University, UK
From:
The Impact of Control Technology,
T. Samad and A.M. Annaswamy (eds.), 2011. Available at www.ieeecss.org.
From the Laboratory
Stolen Secrets . . . and the Truth Ultimately Comes Out
During development, McLaren invented a decoy name for the inerter (the “J-damper”)
to keep the technology secret from its competitors for as long as possible. The “J”
has no meaning and is just a ruse, and of course the device is not a damper. The idea
behind the decoy name was to make it dificult for personnel who might leave McLaren
to join another Formula One team to transfer information about the device and in
particular to make a connection with the technical literature on the inerter, which
Malcolm Smith and his group were continuing to publish.
to the Racetrack
Analyses of inerter-based
suspensions indicated
This strategy succeeded in spectacular fashion during the 2007 Formula One
“spy scandal,” when a drawing of the McLaren J-damper came into the hands of
the Renault engineering team. The FIA World Motor Sport Council considered this
matter at a hearing in December 2007. According to the Council inding, “[a drawing
of McLaren’s so-called J-damper] was used by Renault to try to have the system that
they thought McLaren was using declared illegal. This failed because Renault had
certain fundamental misunderstandings about the operation of the J-damper system.”
A full transcript of the decision is available on the FIA website: http://www.ia.com/
mediacentre/Press_Releases/FIA_Sport/2007/December/071207-01.html.
a potential performance
advantage for vehicle
suspensions that might be
large enough to interest a
Neither the World Motor Sport Council nor McLaren made public what the J-damper
was. Thereafter, speculation increased on Internet sites and blogs about the function and
purpose of the device. Finally, the truth was discovered by Craig Scarborough, a motor
sport correspondent from
Autosport
magazine.
Autosport
ran an article on May 29,
2008, which revealed the Cambridge connection and that the J-damper was an inerter.
Formula One team. Cambridge
University iled a patent on the
More Applications Anticipated
device and then approached
With the truth out, and McLaren’s exclusivity expired, Cambridge University decided
to enter a license agreement with Penske Racing Shocks, enabling Penske to supply
inerters to any team in Formula One. A more widespread use of inerters in Formula
One is now anticipated. The Cambridge University research group is working with
partners to develop other applications of the inerter.
McLaren in conidence.
McLaren signed an agreement
with the University for exclusive
rights in Formula One for a
limited period.
After a rapid development
process, the inerter was raced
for the irst time at the 2005
Spanish Grand Prix by Kimi
Raikkonen, who achieved a
Kimi Raikkonen leading the ield in the McLaren-Mercedes MP4-20 at the Spanish Grand Prix,
May 8, 2005, Circuit de Catalunya, Barcelona, Spain. Photo courtesy of LAT Photographic
victory for McLaren.
For further information: M.C. Smith, Synthesis of mechanical networks: The inerter, IEEE Transactions
on Automatic Control, vol. 47, no. 10, October 2002; http://www.admin.cam.ac.uk/news/dp/2008081906;
http://www.eng.cam.ac.uk/news/stories/2008/McLaren
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