The Inerter races to market

The adoption of the ‘Inerter’ – a component in vehicle suspension systems that helps cars take corners faster without losing control – has now expanded from Formula 1 to other types of motor sport, and could be used in railways in future. The Inerter, which was kept a closely guarded secret for many years, is now a standard component on most Formula 1 cars.

The device, a third component in passive suspension systems, allows drivers to take corners at higher speeds without coming off the track. The Inerter patent was filed by Cambridge Enterprise in 2001, and licensed exclusively to McLaren, who completed extensive testing on the device before first using it competitively in the 2005 Spanish Grand Prix. The race was won for McLaren by Kimi Raikkonen. Confidentiality restrictions associated with the original licence were lifted in 2008, and the device was then licensed to Penske Racing Shocks to provide Inerters to other Formula 1 teams. Penske have since begun supplying Inerters to other motor sports, including IndyCar, where they have been used since 2012.

The Inerter grew out of research on mechanical networks and suspension systems that began more than 20 years ago by Professor Malcolm Smith of the University’s Department of Engineering. In the 1990s, he worked with the Williams Formula 1 team on active suspension systems, which proved so successful that they were eventually banned.

Following the ban, Professor Smith started looking at the fundamentals of passive suspension. Building on electrical theory first devised in the 1930s, he set out to determine what the optimal impedance would be for a suspension system, without a separate power source inside the circuit.

Standard suspension systems are based around two components – springs and shock absorbers. Together, these components absorb and dissipate energy in order to improve a vehicle’s ride and handling. Even in Formula 1 cars, where passenger comfort is not as important as in domestic vehicles, standard suspensions are tuned in such a way that there is a constant trade-off between sensitive handling, which requires a harder suspension, and good mechanical grip, which requires a softer suspension.

Professor Smith realised that this poor trade-off between handling, comfort and grip could be resolved if a third type of component was added to the suspension system to make it more flexible: the Inerter.

At first glance, the Inerter looks like a conventional shock absorber, with an attachment point at each end – one end may be attached to the car body and the other to the wheel assembly. A plunger slides in and out of the main body of the Inerter as the car moves up and down. This causes the rotation of a flywheel inside the device, which is designed in such a way that the force between the attachment points is in proportion to their relative acceleration. In combination with the springs and shock absorbers, the Inerter reduces the effect of the oscillations, helping the car retain a better grip on the road.

Professor Smith’s group has also been developing Inerters which are of much lower cost than those used in motorsport. These devices show great potential for railway suspension systems, where they would reduce wear on the tracks and wheels, lowering costs for the carriers and providing a more comfortable ride for the passengers.

You can learn more about the Inerter in our film.

Photo credit: formula 1 (titl shift) by Jose Maria Miñarro Vivancos via Flickr

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