PRODUCT PROFILE 45
FIGURE 2A (FAR
LEFT): Response at
the axle level as a
function of lateral
acceleration
capturing nonlinearities
and
enhancing test
robustness, using
simulation and
testing
FIGURE 2B (LEFT):
Response at the
axle level as a
function of lateral
acceleration
capturing design
changes at low
response level for
base (red) and
modified (blue)
conditions
FIGURE 3A (FAR
LEFT): Modelled
cornering stiffness
characteristic with
parameters based
on default and
extended testing
protocol
FIGURE 3B (LEFT):
Modelled offset
of the lateral force
at zero slide with
parameters based
on default (green)
and extended (blue)
testing protocol
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November/December 2019 • VehicleDynamicsInternational.com
loads with high precision as well as high
robustness, even at low response levels;
or by applying simplified vehicle models
to drive the identification of the chassis
motions, as illustrated in Figure 2.
The result in Figure 2 demonstrates
that this approach allows testing with
high precision, even at low response
levels, as the measurement variation is
significantly lower compared to classic
test approaches. Next to that, the nonlinearity
in vehicle performance, clearly
present when moving to small steering
inputs, is objectively characterised in a
robust approach. This enables engineers
to accurately quantify the (changing)
vehicle performance and understand the
role of the axle or chassis component
in view of the full vehicle behaviour.
Model-driven test solutions provide
OEMs with a powerful testing process,
even with boundary conditions as
challenging as on-centre behaviour.
The acquired response quantities help
users to understand vehicle dynamics
performance changes caused by design
variations, at the full vehicle level as
well as on individual axles or chassis
components. This capability allows users
to define advanced metrics in support of
vehicle development, considering both
objective characterisation and subjective
assessments.
Tyre modelling in a full vehicle
simulation context
The Simcenter Tyre solution provides
an integral tyre modelling approach to
provide accurate and cost-efficient tyre
models for vehicle dynamic simulations.
The solution not only comprises the tyre
model development, but also tyre testing
services for model parameterisation
and knowledge-intensive engineering
projects. This approach provides
customers with a tyre modelling
methodology rather than just a tyre
modelling software tool.
In the field of tyre modelling, an
integrated test and simulation approach
is essential. On the one hand, tyre tests
are used for model parameterisation
and significantly influence the final
tyre model performance. On the other,
tyre models are used in vehicle dynamic
simulations which are often validated
by means of vehicle tests.
For tyre test and model
parameterisation, there are two
important requirements. Firstly, several
tyre conditions and states are not
modelled, but instead inherited from the
tyre measurements. During tyre testing,
conditions such as the road surface
properties, tyre thermal state, and tyre
wear need to be manually tuned to
mimic the desired full vehicle operating
conditions. To increase the applicability
of the Simcenter Tyre models, the 2020.2
product release will include the tyre
thermal and velocity dependency.
Secondly, for conditions such as sideslip
angle, inclination angle and vertical
load, the tyre testing protocol should
cover the complete operating envelope
of the final full vehicle application. By
adding tests for specific operating areas,
tyre model accuracy can be increased.
In our example, the on-centre
handling application is considered with
side-slip angles and camber angles
that remain very small. The baseline
Simcenter Tyre testing protocol includes
tyre tests that determine the tyre’s
lateral slip characteristics over a range
of +/- 12° of slide-slip angle. Due to the
significant tyre forces during this test,
tyre heat build-up is inevitable and will
alter tyre performance in the low-slip
region. To avoid an equal numerical
weight over the complete side-slip
angle range, adding dedicated low sideslip
angle measurements needs to be
considered. This keeps the tyre in the
representative operating condition and
adds more fidelity in the low-slip region,
which is of importance for on-centre
handling applications.
The example in Figure 3 demonstrates
the resulting tyre model characteristics
of one tyre variant, of which the
parameters were identified based on the
default tyre testing protocol and the
default tyre testing protocol, extended
with dedicated low-slip measurements.
Two key tyre characteristics are
compared; cornering stiffness as a
function of the vertical load, and offset
of the lateral force at zero slide-slip.
Both characteristics show a new level
of accuracy when deploying the testing
and parameterisation method. While at
OEMs, the cost for tyre testing increases
and the high-slip model accuracy slightly
deteriorates, the tyre test and model
parameterisation methodology showed
excellent results at a major passenger
car manufacturer, significantly improving
the correlation between simulations
and vehicle tests.
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