SUSPENSION SYSTEMS
Shock tactics
Technology that improves cars’ road grip may soon be available outside of the
highly secretive world of F1 racing. Siobhan Wagner reports
A FORMER ‘top secret’ McLaren
Formula One component will be available
to all race teams following a deal between
its UK developers and a US motorsport
technology group.
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The suspension device, code-named
the ‘J-Damper’ has been used by McLaren
since 2005 under a confidential
arrangement between the team and
Cambridge University. Called an inerter,
it is used to improve mechanical grip but
can offer greater flexibility in a vehicle’s
suspension system. Standard suspension
systems are based on two components—
springs and shock absorbers (dampers).
These systems are designed to keep
vehicle occupants from rolling around
when the car corners, springing back
when it speeds up or feeling discomfort
travelling down a bumpy road.
Yet, no matter how well a suspension
system is designed, there is usually a
compromise between handling, comfort
and grip. Even in F1 cars, where comfort
is less important, the suspension needs to
be set to allow sensitive handling and
good mechanical grip. But sensitive
handling usually requires harder
suspension, and good mechanical grip
usually needs a softer suspension. So
there is still some oscillation because the
load on the tyres varies and this impedes
the vehicle’s grip, slowing it down.
In 1997 Prof Malcolm Smith of
Cambridge University realised the
compromise between handling, comfort
and grip could be resolved if a third type
of component was added to a suspension
system to make it more flexible. Thus, the
concept of the inerter.
This looks to the average observer
like a conventional shock absorber
with an attachment point at each end.
For example, 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 a flywheel
inside the device to rotate in proportion
to the relative displacement between the
attachment points. The result is that the
The inerter
concept was given
the seal of
approval in 2005
when it was
used in the
McLaren that
won the Spanish
Grand Prix
flywheel stores rotational energy as it
spins. In combination with the springs
and dampers, the inerter reduces the
effect of the oscillations and helps the
car keep a better grip on the road.
Smith said he was nervous talking
about the idea of the inerter at first
because it seemed such an elementary
concept. He could not believe it
had not been done before. When he
realised it hadn’t, the next question
was, could it be done?
‘That step was very quick because I
realised what was required in
principle,’ he said, adding that the
embodiment he had in mind was a
simple rack-and-pinion device.
‘Finding the most convenient way to do
it in a car suspension evolved over a
period of time.’
The inerter concept was given the
seal of approval at the Spanish Grand
Prix in 2005 when it was used in
the winning car driven by Kimi
Raikkonen. Cambridge Enterprise, the
university’s commercialisation arm,
recently signed a licence agreement
with the US company Penske Racing
Shocks, to enable Penske to supply the
devices to any team in F1.
While they are being used only in
F1, Smith said his research group is
working on finding applications for
the inerter outside the realm of
motorsport — in passenger vehicles
and motorcycle steering systems.
However, it is not going to be a
simple case of just bolting on the same
device used in F1 cars to passenger
vehicles and motorcycles.
‘In translating this to road cars the
performance measures are very
different,’ he said. ‘The suspensions are
totally different. They’re much more
softly sprung.’
Smith said they still need to
determine if there would be a huge
advantage in having these in regular
road cars. ‘In Formula 1 the margins
are so tight that if you have a device
that gives you a small percentage gain,
then it’s of definite interest.’ he said.
‘If we can give Lewis Hamilton a
couple tenths of a second, then that is
very important.’
‘There could be an advantage for
road cars but we need to know how
much of an advantage. Whether the
gain is big enough for the amount
of money it costs to manufacture
these devices is something that
remains to be seen.’
the EnGIneeR 1–14 SEPTEMBER 2008
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