vehicle dynamics simulation challenges - TESIS … · SIMULATION AND CALCULATION VEHICLE DYNAMICS ....
Transcript of vehicle dynamics simulation challenges - TESIS … · SIMULATION AND CALCULATION VEHICLE DYNAMICS ....
AUTHOR
Dr. Cornlius Chucholowski General Manager of TESIS DYNAware
GmbH
Understanding Dynamic
Simulation
Dynamic simulation is the numerical
integration of differential equations
that describe system behavior.
Rapid progress in computer tech-
nology now makes it easier to apply
this demanding and time-consuming
computing process in small time
steps to increasingly complex
systems. The tools have also
fundamentally changed. Whereas
the differential equations used to be
created and programmed manually,
we now have special tools for multi-
body systems or generic modeling
programs that can be applied
without the need for mathematical
knowledge. What is more, there are
now ready-made libraries for
increasing numbers of sub-systems
that users can employ.
User-friendly complete solutions for
vehicle-dynamics simulation support
first-time users and quickly lead to
results. However, this simplicity of
use also has a disadvantage.
Users no longer need to deal with
the funda-mental principles and to
critically query the results. Experts
know that there is never one exact
solution, but only an approach to-
wards reality. The result can only be
as exact as the modeling process
and the numerical data permit.
Furthermore, even the best program
is useless if there are no valid data
available for parameterization.
Simulation is an indispensable tool
for the validation of vehicle dy-
namics and active control systems.
However, users must be aware of
the background conditions and must
select the properly adapted tools
and modeling depths. It also goes
without saying that simulation will
not achieve its full benefits unless it
is supported by road tests .
Demands on Vehicle Dynamics
Simulation
The experience of TESIS
DYNAware goes back to a time in
which there were no or only very
few tools for dynamic simulation
and every program had to be
created individually.
Simulation enables trustworthy
predictions to be made, provided
that the user is clear about its
limitations. One danger is to have
blind faith in numerical data.
The integration process and the
computing step size should be
selected in adaptation to the
problem. The computing step size
is oriented towards the dynamics of
the system and must be small
enough to resolve high-frequency
vibrations. A computing step size
that is too small will result in
"numerical noise" and will falsify the
result. TESIS DYNAware is
specialized in real-time-capable
simulation, as is required for testing
ECUs in HiL operation. In real-time
operation, events – for example for
a control mode changeover for the
transition from grip to skid – must
be given special treatment in order
to achieve precise results even with
a fixed step size. This is not covered
by standard libraries. Very large
libraries tempt users to make the
models more detailed than necessa-
ry. Detailed models require high
computing power and are more
complex to parameterize and
validate. An increase in the number
of parameters also increases the
susceptibility to errors.
For proof of concept tests, it is also
advisable to make use of very
simple models, such as a point
mass model for driving performance
and fuel consumption, a single-track
model for lateral dynamics or a
quarter-vehicle model for vertical
dynamics. These models make it
possible to perform an analytical
study that is well suited for
determining control structures and
testing control concepts, but is less
suitable for applying parameters.
Conventional chassis development
uses simulations based on generic
multi-body programs, such as
ADAMS/Car.
The high-fidelity applications can
also consider flexible structures.
The models are derived from
component and design data.
Dynamic truck tipping test: Comparison
of simualtion and test drive in the animation
TESIS DYNAware Suspension Analysis Toolbox enables the determination of axle
kinematic and axle compliance from virtual or real K&C test rig measurements.
Vehicle manufacturers go to great
lengths to parameterize the complex
models and to validate them to such
an extent that they can be used as
virtual reference vehicles. Suppliers
seldom have access to the data
required or cannot afford the effort
involved.
The high-fidelity models are focused
on new designs. For functional
development and the testing of
control systems, active systems, and
ECUs, specialized vehicle dynamics
programs are used that are easy to
parameterize and which can also
run in real time on HiL systems.
The depth of detail is reduced, but is
still fine enough to simulate the most
important vehicle-dynamics effects.
Up to 30 Hz, the results hardly differ
from those of high-fidelity programs.
The TESIS DYNAware programs
use Simulink as the runtime environ-
ment. Simulink is a preferred
platform for developing control
systems from their initial design to
their series production maturity. As an alternative to resolved axle
modeling, users can specify
kinematics maps with compliance,
which they calculate on the real ve-
hicle or by analyses on the complex
full vehicle model. The concept
developed by TESIS DYNAware has
proven itself extremely well and is
used by suppliers who do not have
any design data at their disposal
Full Vehicle Toolkit
3D vehicle dynamics includes
lateral, longitudinal, and vertical
dynamics. The three areas are
strongly interwoven.
The distribution of driving and
braking torque to the front and rear
axle changes the self-steering
behaviour. In an electric or hybrid
vehicle with selective drive to each
axle, this has an impact on energy
management. Roll stabilization
systems or active suspensions also
have an influence not only on
vertical dynamics but also on lateral
and longitudinal dynamics. The
same depth of detail is not required
for every aspect in every
development phase. However, it is
advisable to use the same basic full
vehicle toolbox in all areas, which
can then also be used in all phases
of the V model.
For that reason, the DYNA4
simulation framework from TESIS
DYNAware provides the possibility
to adapt and combine the simulation
models without difficulty.
The basic driver-vehicle-
environment architecture is always
the same for full-vehicle simulation.
There are also hardly any
differences in operation and control.
Steering maneuvers, fuel
consumption cycles, or general
driver control are selected from a
maneuver catalogue in a similar
manner. The route or the traffic
conditions can be specified in the
environment module.
The information used is dependent
on the maneuver.
The core of the simulation
environment is the vehicle module,
which can be configured
interactively and flexibly without
knowledge of modeling. One feature
of the model structure is its flexible
data buses. These make it possible
to exchange model components with
very different levels of detail by
check boxes, for example a simple
engine map can be replaced by a
complex engine model with real-
time-capable cyclic process
calculation .
DYNA4 manages Simulink modules.
Separate modules can be integrated
by using wizards that provide the
meta-data. Users with modeling
know-how can also make changes
in the Simulink model themselves
and can have the changes managed
in the model library.
For applications in automotive
technology, a large number of
Modelica-based libraries are
meanwhile available, for example for
powertrain components, electrics, or
hydraulics. If the system limits are
suitably chosen, the physical models
can be used to create functional
modules, which can be integrated
into the DYNA4 user interface as
"functional mockup units" (FMU) and
parameterized. On the other hand, it
is also possible in Simulink to create
very modular libraries and to
manage these in DYNA4 .
Continuous Model Usage of MiL,
SiL to HiL
In the TESIS DYNAware models,
the control system and the route are
strictly separated.
Only in this way is it possible to
ensure continuous usage in the V
process, i.e. to replace the software
ECU in HiL operation by a real ECU
at a later development phase.
Therefore, the simulation framework
is suitable for function-oriented tests.
On the first level same structure of complete vehicle simulation, in detail flexible models for the particular range of applications, e.g.engine models with different level of detail.
"Virtual reality" for vehicle-dynamics
programs for testing driver assistance systems.
Results Representation and
Reporting
Processing and revision-safe
reporting of the results are important
components of vehicle dynamics
simulation. Further support is
provided by animation running
parallel to the simulation, in both
Office and HiL operation. This option
is not included in every generic
simulation program, or the program
may require extensive and complex
configuration before it can offer it.
Driver Assistance Systems and
Vehicle Connectivity
The increasing use of driver
assistance systems and an increase
in vehicle connectivity also present a
challenge for vehicle dynamics
simulation. The focus is no longer on
vehicle dynamics alone, but on the
simulation of the environment, the
sensor systems, and communica-
tion. Apart from the effect of side
wind, the vehicle makes contact with
the environment only through its
tires. The "virtual driver" used in the
simulation program only needs to
get information on the route and will
then perform his task accordingly.
If driver assistance systems are
involved, the driver model must also
behave like an assisted driver. In
this case, the environ-ment must be
simulated much more precisely in
order, for example, to represent
visibility, road junctions, or traffic.
The key element is the quality and
content of the graphical
representation. However, the effort
required in creating the content must
not be under-estimated.
For this purpose, TESIS DYNAware
employs a chain of tools that use
navigation data and other generally
accessible information to generate a
virtual environment which simulates
a virtual reality for the assistance
systems .
Outlook
There are therefore tailor-made
solutions for every application.
Almost as important as correct and
fast vehicle-dynamics simulation is
support for cooperation in the com-
pany across various departments,
areas, and domains. Furthermore,
quality and acceptance specifica-
tions require reproducible simulation
and documentation.
This can be achieved only if the
simulation environment is flexibly
tailored to it. The top priority is that
all use the same basis and can
make use of a managed model
library .
A systematic storage system for
models and results ensures
reproducibility and transparency.
DYNA4 already supports these
requirements and will be further
developed in this direction.
Contact
TESIS DYNAware GmbH
www.tesis-dynaware.com
Phone: +49 89 7473 777 444
E-Mail: [email protected]
Collaborative engineering through cross-company management of simulation objects in a uniform environment
enDYNA library concept for Simulink-based engine simulation