A strong
connection: the suspension of a Formula 1 car makes sure that the power of
the engine is transferred perfectly to the road. In passenger-car
production, on the other hand, the functions of the suspension are primarily
safety-related.
The days of high-speed marathons at Hockenheim are past. Last year, the
German Grand Prix was held on a new and improved track layout. The forest
straight has been omitted and now there are 17 corners of all types – from
the 1016-metrelong Parabolica, in which the cars reach over 300km/h, to the
Spitzkehre hairpin, where they have to brake to 70km/h. These constant
corner changes give the teams a difficult challenge in terms of setting up
the cars: the main factor is to adjust the suspension to suit the track
requirements. The
suspension consists of the upper and lower wishbones, and the compression
struts. These compression struts transfer the forces generated to a system
of shock absorbers and springs. The wishbones, which control the wheels, are
described as triangular because of their shape.
This complex system influences
the road-holding and the driving properties of the car, determining whether
it is balanced, easy to control and if it understeers or oversteers. On the
one hand, the suspension must be soft enough to absorb shocks or uneven
surfaces, such as driving over kerbs. On the other hand, a certain level of
rigidity is needed to stop the underbody from striking the ground.
The high cornering speeds at Hockenheim require a relatively soft setting,
which provides the necessary grip. Conversely, the best example of a hard
suspension set-up is that used at Monaco: the narrow city track without any
high cornering
speeds can only be mastered with the precise handling of a hard set-up. |
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Whether soft or
hard, the two alternatives for setting up the suspension cannot be
arbitrarily enhanced. If the tuning is too soft, the car becomes more
difficult to control, because it ‘begins to swim’, as the drivers say. Grip
or handling,
aerodynamics and ground clearance – it is not an easy task for the engineers
to find the perfect compromise to guarantee balance on the track.
“The suspension is one of the most sensitive areas of a race car,” says Sam
Michael, chief operations engineer at WilliamsF1. “It has to react extremely
sensitively. At the same time, it has to be extremely robust to be able to
withstand the forces generated. It is important to set the suspension so
that all
four wheels constantly have the same level of contact with the road, so that
the car is as balanced as possible in any situation. This guarantees the
manoeuvrability and ensures the ideal transfer of forces during braking and
acceleration.”
To maintain the balance the left and right sides of the suspension are
linked with elastic torsion bars. These stabilisers come into action when
the car is cornering. If the wheels are compressed differently, the torsion
rods – also
referred to as ‘anti-roll bars’ – twist and provide resistance on the
compressed side, so keeping the car rigid. A further refinement is the use
of so-called ‘bump rubbers’ to restrict the spring travel. The springs
strike against the ‘bump rubbers’ and so keep the underbody above the track
surface. As a result, the
engineers can choose a softer setting.
Nowadays, the suspension is made of carbon-fibre composite materials,
because they are lighter and more durable than the metal used in the past.
For instance, wishbones made of carbon fibre weigh approximately 400 grams
less than steel wishbones, which have not been used since the mid-1990s. The
suspension elements outside the chassis are also designed to cause as little
air resistance as possible.
The components are tested on test beds to optimise the aerodynamics and to
adapt the suspension to the loads it has to bear. Individual race tracks can
be computer-simulated on the test beds: the car is fitted into a system of
hydraulic drives which can apply a greater load to the suspension than
occurs during a race. For instance, the test bed can duplicate the corners
at the new Hockenheimring and any possible uneven surfaces at the track.
Tests with more compact systems, such as the revolutionary new rotary shock
absorber, show the excellent aerodynamic potential of a smaller, more
compact
suspension.
In spite of the elaborate preparations, a suspension failure is still one of
the most frequent faults in Formula 1. Although the struts, wishbones and
shock absorbers are perfectly tuned to the track, even these hi-tech
components sometimes reach their limits. Therefore, the driving style of the
driver often plays
an important role in deciding whether the suspension can complete the full
race without incurring any damage. In passenger-car production, the
suspension, together with the tyres and the brakes, is one of the most
important safety
elements on the car. As in Formula 1, the suspension in passenger cars
interacts with other running gear components to determine the driving
properties. It has to transfer all of the forces between the wheels and the
body, and keep the car safely on the road. It should keep full tyre contact
of the wheels
on the road, regardless of the driving conditions. This also guarantees
wheel control with low rolling resistance and low tyre wear.
“The suspension can only perform its tasks during driving if the axle
geometry is set correctly,” says Dr. Hartmuth Wolff of the Allianz Centre
for Technology. “Impacts against kerbs or when driving through potholes at
excessive speed can cause changes in the toe and camber. This will impair
the car’s handling,
increase the wear on the tyres, and the car looses its straight running
stability. If damage or wear does occur in the suspension joints, it often
causes a fluttering in the wheels.” The safety expert recommends having
checks at an authorised workshop on the first indication of these changes.
Complex single-wheel suspensions have also long since become established in
the development of passenger cars. Compared to the rigid axles used in the
past, a modern
suspension prevents the axles from shifting on uneven surfaces. Overall, it
provides better road-handling – and so more safety. In the future,
electronically-controlled suspensions should provide even more safety and
driving comfort. |
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