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Simulation output and interpretation 439
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Fig. 7.38 Yaw versus steer angle – note the circular quality of the data traces,
indicating a 90 degree phase difference between the two quantities
this instance the proposed ideal function is inadequate. Commercial proprieties
prevent the discussion of this particular topic in any further detail
but readers are assured there is indeed an appropriate ideal function.
7.10 Some consequences of using signal-to-noise ratio
Previously, vehicle dynamicists have sought to address a wide range of
phenomena – unintended yaw rate change following lift-off in a turn,
delays following turn-in, non-linearity with increasing lateral acceleration
and so on. It is eminently possible to attack each of these issues in turn,
although it is also likely that solutions to some may become problematic
for others.
The use of a single measure – signal-to-noise ratio – and an ideal function
allows experimentation to optimize the performance of the vehicle in its
entirety. Questions of balancing one attribute against another no longer
become subjective but can be expressed objectively, since an increase in
yaw damping will increase signal-to-noise ratio where it controls yaw overshoots
in response to disturbances but reduce signal-to-noise ratio where it
blunts turn-in. This is not to say that the endeavour of optimizing vehicle
dynamics will become trivial; defining the correct ‘handling sign-off’
usage over which to record signal-to-noise ratio remains difficult, instrumentation
challenges remain, and the difficulties of accurately simulating
vehicle and driver behaviour over a lengthy handling sign-off test are far
from trivial. Also non-trivial is the engineering of areas of vehicle behaviour
where the departure from the ideal function might be regarded as
‘character’ rather than a non-optimum. An example of such behaviour is